Artículos de J.I. Ramos en el INSPEC (Ingeniería e Informática) - Papers by - "RAMOS JI"

Datos obtenidos el lunes 11 de febrero de 2002

Registro 1 de 100 en INSPEC 2002/02 Week 1

TI: Wave propagation and suppression in excitable media
with holes and external forcing

AU: Ramos-JI

SO: Chaos,-Solitons-and-Fractals. vol.13, no.6; May 2002;
p.1243-51.

PY: 2002

LA: English

AB: The propagation and suppression of spiral waves in
inhomogeneous excitable media is

studied numerically. The inhomogeneities correspond to
either holes whose size and location are

varied or constant external forcing on the activator's
reaction rate. For the case of a single hole and

localized external forcing, it is found that the spiral
wave is robust, although it may break up into

two branches which reconnect with each other after the
wave overcomes either the hole or the

region where the external forcing is applied. When five
holes are presented but there is no external

forcing or the external forcing is localized, the spiral
wave is robust and exhibits high

concentration of the activator between holes and corners
when it approaches and interacts with the

holes. In the presence of several holes and external forcing
across the excitable medium, the spiral

wave is suppressed and the activator exhibits a breathing
behaviour characterized by fronts that

propagate towards the boundaries of the excitable medium,
and complex patterns when the front

is located near the holes.

AN: 7166377

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Registro 2 de 100 en INSPEC 2002/02 Week 1

TI: Parallel simulation of spiral waves in reacting and
diffusing media

AU: Ortigosa-EM; Romero-LF; Ramos-JI

SO: Acta-Cybernetica. vol.15, no.2; 2001; p.173-84.

PY: 2001

LA: English

AB: The propagation of spiral waves in excitable media
is governed by non-linear

reaction-diffusion equations. In order to solve these
equations in three-dimensional space, two

methods have been implemented and parallelized on both
shared- and distributed-memory

computers. These implicit methods linearize the equations
in time, following alternate directions in

the first case (ADI), and using the Crank-Nicolson discretization
in the second. A linear system of

algebraic equations has been obtained and has been solved
using direct methods in the ADI

technique, while in the second case the conjugate gradient
(CG) method has been used. An

optimized version of the CG algorithm is presented, in
which the largest efficiency has been

obtained.

AN: 7165889

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Registro 3 de 100 en INSPEC 2001/09-2001/12

TI: Drawing of annular liquid jets at low Reynolds numbers

AU: Ramos-JI

SO: Computational-and-Theoretical-Polymer-Science. vol.11,
no.6; 2001; p.429-43.

PY: 2001

LA: English

AB: Asymptotic methods based on the slenderness ratio
are used to obtain the leading-order

equations that govern the fluid dynamics of axisymmetric,
isothermal, Newtonian, annular liquid

jets such as those employed in the manufacture of textile
fibres, annular membranes, composite

fibres and optical fibres, at low Reynolds numbers. It
is shown that the leading-order equations

are one-dimensional, and analytical solutions are obtained
for steady flows at zero Reynolds

numbers, zero gravitational pull, and inertialess jets.
A linear stability analysis of the viscous flow

regime indicates that the stability of annular jets is
governed by the same eigenvalue equation as

that for the spinning of round fibres. Numerical studies
of the time-dependent equations subject to

axial velocity perturbations at the nozzle exit and/or
the take-up point indicate that the annular jet

dynamics evolves from periodic to chaotic motions as the
extension or draw ratio is increased.

The power spectrum of the annular jet's radius at the
take-up point broadens and the phase

diagrams exhibit holes at large draw ratios. The number
of holes increases as the draw ratio is

increased, thus indicating the presence of strange attractors
and chaotic motions.

AN: 7083607

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Registro 4 de 100 en INSPEC 2001/09-2001/12

TI: Singularities and stability of inviscid, planar liquid
membranes

AU: Ramos-JI

SO: International-Journal-of-Engineering-Science. vol.39,
no.17; Nov. 2001; p.1935-48.

PY: 2001

LA: English

AB: The equations governing the fluid dynamics of inviscid,
planar liquid membranes subject to

pressure differences are first derived along and normal
to the membrane, and then written in

Cartesian coordinates. It is shown both algebraically
and differentially that the steady-state

equations may have removable singularities at or below
the nozzle exit if the Weber number is

equal to or less than one, and that these singularities
indicate that the liquid exits the nozzle at an

angle which is different from the nozzle exit. It is also
shown that vertically falling membranes are

stable and oscillate in both space and time. Finally,
some asymptotic solutions of the equations are

obtained.

AN: 7065317

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Registro 5 de 100 en INSPEC 2001/09-2001/12

TI: Interaction of spatial solitons with a localized spatially-modulated
medium

AU: Ramos-JI

SO: Mathematics-and-Computers-in-Simulation. vol.56, no.6;
9 July 2001; p.571-83.

PY: 2001

LA: English

AB: The propagation of solitons through spatially-modulated
media is studied numerically as a

function of the amplitude, frequency and length of the
spatial nonuniformities. It is shown that for

a fixed amplitude and length of modulation, an increase
in frequency may result in a soliton that

propagates in the opposite direction to the one encountering
the nonuniform medium because of

reflection, whereas, for a fixed frequency and length,
an increase in the amplitude of the spatial

modulation results in a surface wave and a soliton that
may propagate towards either the right or

left boundary. In either case, the radiation increases
as the amplitude of the spatial modulation is

increased. For fixed amplitude and frequency, an increase
in the length of nonuniformities results

in both surface waves whose amplitude decreases and right-traveling
solitons whose velocity

decreases as the length of these nonuniformities is increased.
A comparison between space and

time variations of the dispersion index is also presented.

AN: 7033618

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Registro 6 de 100 en INSPEC 2001/01-2001/08

TI: Tile patterns in excitable media subject to nonsolenoidal
flow fields

AU: Ramos-JI

SO: Chaos,-Solitons-and-Fractals. vol.12, no.12; Sept.
2001; p.2267-81.

PY: 2001

LA: English

AB: The propagation of spiral waves in excitable media
subject to a nonsolenoidal advective field

which satisfies the no-penetration condition on the boundaries
of the domain is studied

numerically, and it is shown that, depending on the amplitude
and spatial frequencies of the

velocity field, the spiral wave may be distorted highly,
break up into a number of smaller spiral

waves, or exhibit polygonal shapes or tile patterns. These
patterns reflect the symmetry/asymmetry

of the velocity field and are characterized by thick regions
of high concentration at stagnation

points where the velocity gradient is largest, and thin
ones which are parallel to the velocity vector.

It is also shown that the advective field distorts the
spiral wave by decreasing its thickness where

the velocity is largest due to the stretching of the wave,
and by increasing it at the stagnation points

where the curvature of the wave is largest.

AN: 7003819

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Registro 7 de 100 en INSPEC 2001/01-2001/08

TI: Nonlinear dynamics of hollow, compound jets at low
Reynolds numbers

AU: Ramos-JI

SO: International-Journal-of-Engineering-Science. vol.39,
no.12; Aug. 2001; p.1289-314.

PY: 2001

LA: English

AB: The leading-order fluid dynamics equations of isothermal,
axisymmetric, Newtonian, hollow,

compound fibers at low Reynolds numbers are derived by
means of asymptotic methods based on

the slenderness ratio. These fibers consist of an inner
material which is an annular jet surrounded

by another annular jet in contact with ambient air. The
leading-order equations are

one-dimensional, and analytical solutions are obtained
for steady flows at zero Reynolds numbers,

zero gravitational pull, and inertialess jets. A linear
stability analysis of the viscous flow regime

indicates that the stability of hollow, compound jets
is governed by the same eigenvalue equation

as that for the spinning of round fibers. Numerical studies
of the time-dependent equations subject

to axial velocity perturbations at the nozzle exit and/or
the take-up point indicate that the fiber

dynamics evolves from periodic to chaotic motions as the
extension or draw ratio is increased.

The power spectrum of the interface radius at the take-up
point broadens and the phase diagrams

exhibit holes at large draw ratios. The number of holes
increases as the draw ratio is increased,

thus indicating the presence of strange attractors and
chaotic motions.

AN: 7001888

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Registro 8 de 100 en INSPEC 2001/01-2001/08

TI: Convection-induced anisotropy in excitable media subject
to solenoidal advective flow fields

AU: Ramos-JI

SO: Chaos,-Solitons-and-Fractals. vol.12, no.10; Aug.
2001; p.1897-908.

PY: 2001

LA: English

AB: The effects of solenoidal velocity fields on the propagation
of spiral waves in excitable media

is studied numerically by means of a time-linearized method.
It is shown that the advective field

distorts the spiral wave at moderate frequencies, whereas,
at large frequencies, the average shape

of the spiral wave is nearly identical to that in the
absence of convection, although its inner and

outer parts exhibit spatial oscillations whose frequency
increases as that of the velocity field is

increased. At low frequencies and high amplitudes of the
velocity field, the concentration of the

activator and the wave propagation are controlled by the
symmetry of the velocity and the number

and location of the stagnation points, and the concentration
of the activator may exhibit either

counter-rotating regions or a layered structure.

AN: 6975974

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Registro 9 de 100 en INSPEC 2001/01-2001/08

TI: Solitons in nonlinear waveguides with sinusoidal Kerr-index

AU: Villatoro-FR; Ramos-JI

SO: ISRAMT'99. 1999 7th International Symposium on Recent
Advances in Microwave

Technology Proceedings. ISRAMT, Spain; 1999; iii+801 pp.
p.41-4.

PY: 1999

LA: English

AB: The effect of a nonlinear optical medium with a sinusoidal
variation of the Kerr refraction

index on the propagation of solitons is studied numerically
by means of a linearized theta -method.

Both the width and wavelength of the sinusoidal variation
and the width of the soliton determine

whether the soliton will be trapped in or pass through
the region where the sinusoidal variation

occurs. In both cases, the soliton radiates energy upstream
and downstream. The effect of linear

losses is small and does not alter the main characteristics
of the interaction of the soliton with the

periodically nonlinear medium.

AN: 6957075

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Registro 10 de 100 en INSPEC 2001/01-2001/08

TI: Spatio-temporal patterns in excitable media with non-solenoidal
flow straining

AU: Ramos-JI

SO: Mathematics-and-Computers-in-Simulation. vol.55, no.4-6;
15 March 2001; p.607-19.

PY: 2001

LA: English

AB: The propagation of spiral waves in excitable media
with the Belousov-Zhabotinsky reactions

in a non-solenoidal, time-independent velocity field is
studied numerically as a function of the

amplitude and frequency of the velocity. It is shown that
the spiral wave is slightly distorted for

small amplitudes and low frequencies, whereas it breaks-up
into new spiral waves which merge

and form periodic, cusped fronts at moderate amplitudes
and small frequencies. For larger

amplitudes but still small frequencies, the spiral wave
undergoes a second transition to thick fronts

characterized by small curvature, and the radius of curvature
increases as the amplitude of the

velocity field is increased. It is also shown that an
increase in the frequency of the velocity field

results in front distortion and corrugations which are
due to the increase in the number of

stagnation points as the frequency is increased, straining
of the front at stagnation points and the

non-solenoidal velocity field employed in the paper. An
explanation of these corrugations in terms

of the straining, gradient of the transverse velocity
along the normal to the front and

compressibility is provided.

AN: 6903907

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Registro 11 de 100 en INSPEC 2001/01-2001/08

TI: Domain decomposition techniques for reaction-diffusion
equations in two-dimensional

regions with re-entrant corners

AU: Ramos-JI; Soler-E

SO: Applied-Mathematics-and-Computation. vol.118, no.2-3;
9 March 2001; p.189-221.

PY: 2001

LA: English

AB: A system of two nonlinear reaction-diffusion equations
is solved numerically by means of

linearized B-methods and both overlapping and non-overlapping
domain decomposition

techniques in two-dimensional regions with re-entrant
corners. Two numerical methods based on

either approximate factorization (AF) or the bi-conjugate-gradient-stabilized
(BiCGstab) technique

are employed. A study of the effects of the number of
overlapping grid lines on both the accuracy

and numerical efficiency is presented, For non-overlapping
domain decomposition techniques, the

unknown values at the common interface between adjacent
subdomains have been updated by

means of Dirichlet, Neumann and Robin couplings, and combinations
thereof. It is shown that

non-overlapping domain techniques are less accurate than
overlapping ones for domains with

re-entrant corners because the interfaces between adjacent
subdomains are evaluated by imposing

continuity of the unknowns and their normal derivatives
there, and therefore, the partial

differential equations are not solved at the interfaces
between adjacent subdomains. Nevertheless,

the accuracy of these techniques increases as the grid
spacing is decreased, although they still

exhibit large errors near the re-entrant corners.

AN: 6888118

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Registro 12 de 100 en INSPEC 2001/01-2001/08

TI: Propagation of spiral waves in anisotropic media:
from waves to stripes

AU: Ramos-JI

SO: Chaos,-Solitons-and-Fractals. vol.12, no.6; May 2001;
p.1057-64.

PY: 2001

LA: English

AB: The effects of anisotropic diffusion on the propagation
of spiral waves in excitable media are

studied numerically by means of time-linearized methods
in very refined meshes and with very

small time steps. It is shown that the anisotropy of the
inhibitor's diffusivity tensor does not play

as important role on wave propagation as that of the activator.
It is also shown that the

off-diagonal components of the activator's diffusivity
tensor cause stretching of the activator's

concentration along the principal directions of this tensor,
and that a large difference between the

diffusion coefficients in the x- and y-directions may
result in the spiral wave annihilation and

stripe formation.

AN: 6885650

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Registro 13 de 100 en INSPEC 2001/01-2001/08

TI: Asymptotic analysis and stability of inviscid liquid
sheets

AU: Ramos-JI

SO: Journal-of-Mathematical-Analysis-and-Applications.
vol.250, no.2; 15 Oct. 2000; p.512-32.

PY: 2000

LA: English

AB: Asymptotic methods are employed to determine the leading-order
equations that govern the

fluid dynamics of slender, and thin and slender, inviscid,
irrotational, planar liquid sheets subject

to pressure differences and gravity. Two flow regimes
have been identified depending on the

Weber number, and analytical solutions to the steady state
equations are provided. Linear stability

studies indicate that the sinuous mode corresponds to
Weber numbers on the order of unity, while

the varicose mode is associated with small Weber numbers.
For small Weber numbers, the

nonlinear stability of liquid sheets is determined analytically
in terms of elliptic integrals of the

first and second kinds. It is also shown that the sinuous
mode of thin and slender liquid sheets is

identical to the same mode for slender sheets.

AN: 6816180

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Registro 14 de 100 en INSPEC 2000/07-2000/12

TI: Three-dimensional simulations of spiral waves in reacting
and diffusing media on DSM

computers

AU: Ortigosa-EM; Romero-LF; Ramos-JI

SO: Applications of High-Performance Computing in Engineering
VI. Sixth International

Conference. WIT Press, Southampton, UK; 2000; 491 pp.
p.11-20.

PY: 2000

LA: English

AB: Parallel ADI and conjugate gradient (CG) methods based
on the time-linearization of the

three-dimensional reaction-diffusion equations which govern
the propagation of spiral waves in

excitable media, have been implemented on both shared-
and distributed-memory computers. ADI

has been implemented by means of a dynamic block Cartesian
decomposition and its efficiency

tends to that of the CG technique as the mesh is refined.
The largest efficiency of CG was obtained

on an Origin-2000 with a message passing model, private
memory and 16 processors, and the

efficiency of CG is larger than that of ADI.

AN: 6690468

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Registro 15 de 100 en INSPEC 1999/11-2000/06

TI: Heat and mass transfer in annular liquid jets: III.
Combustion within the volume enclosed

AU: Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.110, no.2-3;
15 April 2000; p.185-204.

PY: 2000

LA: English

AB: For pt.III. see ibid., p. 165-183. The nonlinear dynamics
of and heat and mass transfer

processes in annular liquid jets are analyzed by means
of a nonlinear system of integrodifferential

equations which account for the liquid motion and the
gases enclosed by the jet. Both linear and

sinusoidal heat and mass addition sources are considered
to take place homogeneously within the

volume enclosed by the jet's inner interface in an attempt
to simulate the combustion of hazardous

wastes or materials within this volume. It is shown that
the liquid's temperature at the jet's inner

interface increases rapidly with linear heat addition,
but drops also quickly to its initial value once

heat addition is ended, whereas the pressure coefficient
and the volume enclosed by the jet

increase until they reach a maximum value and then decrease
in an oscillatory manner towards

their steady values. For the case of sinusoidal heat addition,
it is shown that the pressure

coefficient and interfacial concentration, temperature
and heat and mass fluxes oscillate in a

sinusoidal manner with the same frequency as that of the
sinusoidal heat source. It is also shown

that mass transfer phenomena are much slower than heat
transfer ones. For the case of linear mass

addition, it is shown that the temperature of the gases
enclosed by the jet first decreases because of

dilution and then it increases until it reaches a constant
value that corresponds to the same

temperature for the gases and the flowing liquid. The
pressure of the gases enclosed by the jet first

increases because of mass addition and then slowly decreases
because of mass absorption by the

jet.

AN: 6573145

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Registro 16 de 100 en INSPEC 1999/11-2000/06

TI: Heat and mass transfer in annular liquid jets. II.
g-jitter

AU: Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.110, no.2-3;
15 April 2000; p.165-84.

PY: 2000

LA: English

AB: For pt.I. see ibid., p. 133-64. The effects of g-jitter
on heat and mass transfer in

underpressurized, annular liquid jets are analyzed numerically
as a function of the amplitude and

frequency of the gravitational modulation by means of
a mapping technique that transforms the

time-dependent geometry of these jets into a unit square
and a conservative finite difference

method. It is shown that the pressure coefficient, gas
concentration at the jet's inner interface, heat

fluxes at the jet's inner and outer interfaces and interfacial
temperature are periodic functions of

time whose amplitudes increase as the amplitude of the
g-jitter is increased, but decrease as the

jitter frequency is increased. The pressure coefficient
is almost in phase with the heat flux at the

jet's outer interface, and out of phase with the mass
transfer rate at the jet's inner interface. It is

also shown that the temperature field adapts itself rapidly
to the imposed gravity modulation, and

thermal equilibrium is reached quickly. However, mass
transfer phenomena are very slow and

require a very long time to become periodic.

AN: 6573144

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Registro 17 de 100 en INSPEC 1999/11-2000/06

TI: Heat and mass transfer in annular liquid jets. I.
Formulation

AU: Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.110, no.2-3;
15 April 2000; p.133-64.

PY: 2000

LA: English

AB: Heat and mass transfer phenomena in annular liquid
jets are analyzed at high Reynolds

numbers by means of a model derived from the governing
equations that takes into account the

effects of surface tension and boundary conditions at
the gas-liquid interfaces and the large

differences between the thermal and mass diffusivities,
densities, dynamic viscosities, and thermal

conductivities between gases and liquids. The model clearly
illustrates the stiffness in both space

and time associated with the concentration, linear momentum
and energy boundary layers, and the

initial cooling of the gases enclosed by the jet when,
starting from a steady state where gases are

injected into the volume enclosed by the jet at a rate
equal to the heat and mass absorption rates by

the liquid, gas injection is stopped. It is shown that,
owing to the non-linear integro-differential

coupling between the fluid dynamics and heat and mass
transfer processes, the pressure of the

gases enclosed by the jet may vary in either a monotonic
or an oscillatory manner depending on

the large number of non-dimensional parameters that govern
the heat and mass transfer

phenomena. For the underpressurized jets considered here,
it is shown that thermal equilibrium is

achieved at a much faster rate than that associated with
mass transfer, double diffusive phenomena

in the liquid may occur, and the mass and volume of the
gases enclosed by the jet may increase or

decrease as functions of time until a steady equilibrium
condition is reached.

AN: 6573143

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Registro 18 de 100 en INSPEC 1999/11-2000/06

TI: Parallel computing of semiconductor laser equations

AU: Romero-LF; Zapata-EL; Ramos-JI

SO: Proceedings Eighth SIAM Conference on Parallel Processing
for Scientific Computing. Soc.

Ind. Appl. Math, Philadelphia, PA, USA; 1997; CD-ROM pp.
8 pp..

PY: 1997

LA: English

AB: Parallel Hopscotch's and implicit, linearized 0-methods
have been developed to solve the

two-dimensional equations of multi-striped semiconductor
lasers. For the latter, a BiCGSTAB

algorithm has been used and, in both methods, an efficient
technique which overlaps the

communications and the computations has been developed.
Such a technique also reduces the

number of messages to be communicated to other processors
and yields an almost perfect

speed-up for the Hopscotch method which is much more efficient
than implicit, linearized

techniques. It is also shown that the speed-up of the
latter increases almost linearly as the number

of processors increases.

AN: 6402087

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Registro 19 de 100 en INSPEC 1999/01-1999/10

TI: On the method of modified equations. VI. Asymptotic
analysis of and asymptotic

successive-corrections techniques for two-point, boundary-value
problems in ODE's

AU: Villatoro-FR; Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.105, no.2-3;
Nov. 1999; p.137-71.

PY: 1999

LA: English

AB: The modified equation technique is extended to two-point,
boundary-value problems, and a

second-order accurate, implicit, centered, finite difference
scheme for nonhomogeneous,

second-order, ordinary differential equations with linear
boundary conditions is analyzed. The

first, second and third modified equations, or equivalent,
second equivalent and (simply) modified

equations, respectively, for this scheme and its boundary
conditions are presented. It is shown that

the three kinds of modified equations are asymptotically
equivalent when the equivalent equation

is used for the boundary conditions, since an asymptotic
analysis of these equations with the grid

size as small parameter yields exactly the same results.
For a linear problem, multiple scales and

summed-up asymptotic techniques are used and the resulting
uniform asymptotic expansions are

shown to be equivalent to the solution of the original
finite difference scheme. Asymptotic

successive-corrections techniques are also applied to
the three kinds of modified equations to

obtain higher-order schemes. Higher-order boundary conditions
are easily treated in the

asymptotic successive-corrections technique, although
these boundary conditions must be

obtained by using the equivalent equation in order to
obtain a correct estimate of the global error

near the domain boundaries. The methods introduced in
this paper are applied to homogeneous

and non-homogeneous, second-order, linear and non-linear,
ordinary differential equations, and

yield very accurate results.

AN: 6392069

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Registro 20 de 100 en INSPEC 1999/01-1999/10

TI: Linearized methods for ordinary differential equations

AU: Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.104, no.2-3;
15 Sept. 1999; p.109-29.

PY: 1999

LA: English

AB: The conservation properties, singularities and nonlinear
dynamics of both time-linearized

methods which provide piecewise analytical solutions and
keep the independent variable

continuous, and implicit, linearized theta -techniques
which are based on discretization and

linearization, are analyzed in this paper. It is shown
that both methods are implicit and provide

explicit maps, but they do not preserve the energy in
conservative systems. It is also shown that

time-linearized methods preserve both the fixed points
and the linear stability of the original

ordinary differential equation, whereas linearized theta
-techniques do preserve the fixed points

and the linear stability of attractors, but the stability
of the repellers depends on the time step and

the implicitness parameter. The results clearly indicate
that the linearized theta -techniques which

more faithfully reproduce the nonlinear dynamics of the
original ordinary differential equation are

second-order accurate in time.

AN: 6353497

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Registro 21 de 100 en INSPEC 1999/01-1999/10

TI: On the method of modified equations. V. Asymptotic
analysis of and direct-correction and

asymptotic successive-correction techniques for the implicit
midpoint method

AU: Villatoro-FR; Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.103, no.2-3;
15 Aug. 1999; p.241-85.

PY: 1999

LA: English

AB: For pt.IV. see ibid., p. 213-40. The equivalent, second
equivalent and (simply) modified

equations for the implicit midpoint rule are shown to
be asymptotically equivalent in the sense that

an asymptotic analysis of these equations with the time
step size as small parameter yields exactly

the same results; for linear problems with constant coefficients,
they are also equivalent to the

original finite difference scheme. Straight forward (regular),
multiple scales and summed-up

asymptotic techniques are used for the analysis of the
implicit midpoint rule difference method,

and the accuracy of the resulting asymptotic expansion
is assessed for several first-order,

non-linear, autonomous ordinary differential equations.
It is shown that, when the resulting

asymptotic expansion is uniformly valid, the asymptotic
method yields very accurate results if the

solution of the leading order equation is smooth and does
not blow up. The modified equation is

also studied as a method for the development of new numerical
schemes based on both

direct-correction and asymptotic successive-correction
techniques applied to the three kinds of

modified equations, the linear stability of these techniques
is analyzed, and their results are

compared with those of Runge-Kutta schemes for several
autonomous and non-autonomous,

first-order, ordinary differential equations.

AN: 6296085

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Registro 22 de 100 en INSPEC 1999/01-1999/10

TI: On the method of modified equations. IV. Numerical
techniques based on the modified

equation for the Euler forward difference method

AU: Villatoro-FR; Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.103, no.2-3;
15 Aug. 1999; p.213-40.

PY: 1999

LA: English

AB: The modified equation method is studied as a technique
for the development of new

numerical techniques for ordinary differential schemes
based on the third modified or (simply)

modified equation of the explicit Euler forward method.
Both direct-correction and

successive-correction techniques based on the modified
equation are used to obtain higher-order

schemes. The resulting numerical techniques are completely
explicit, of order of accuracy as high

as desired, and self-starting since the truncation error
terms in the modified equation have no

derivatives. The methods introduced in this paper are
applied to autonomous and

non-autonomous, scalar and systems of ordinary differential
equations and compared with

second- and fourth-order accurate Runge-Kutta schemes.
It is shown that, for sufficiently small

step sizes, the fourth-order direct-correction and successive-correction
methods are as accurate as

the fourth-order Runge-Kutta scheme.

AN: 6296084

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Registro 23 de 100 en INSPEC 1999/01-1999/10

TI: On the method of modified equations. III. Numerical
techniques based on the second

equivalent equation for the Euler forward difference method

AU: Villatoro-FR; Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.103, no.2-3;
15 Aug. 1999; p.179-212.

PY: 1999

LA: English

AB: For pt.II. see ibid., p. 141-178. Direct-correction
and asymptotic successive-correction

methods based on the second equivalent equation are applied
to the Euler forward explicit

scheme. In direct-correction, the truncation error terms
of the second equivalent equation which

contain higher-order derivatives together with a starting
procedure, are discretized by means of

finite differences. Both explicit and implicit direct-correction
schemes are presented and their

stability regions are studied. The asymptotic successive-correction
numerical technique developed

in Part II of this series with a consistent starting procedure
is applied to the second equivalent

equation. Both all-backward and all-centered asymptotic
successive-correction methods are

presented. The numerical methods introduced in this paper
are applied to autonomous and

non-autonomous, scalar and systems of ordinary differential
equations and compared with the

results of second- and fourth-order accurate Runge-Kutta
methods. It is shown that the

fourth-order Runge-Kutta method is more accurate than
the successive-correction techniques for

large time steps due to the need for higher-order derivatives
of the Euler solution; however, for

sufficiently small time steps, but larger enough so that
round-off errors are negligible, both

methods have nearly the same accuracy.

AN: 6296083

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TI: On the method of modified equations. II: Numerical
techniques based on the equivalent

equation for the Euler forward difference method

AU: Villatoro-FR; Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.103, no.2-3;
15 Aug. 1999; p.141-77.

PY: 1999

LA: English

AB: For pt.I. see ibid., p. 111-39. New numerical successive-correction
techniques for ordinary

differential equations based on the Euler forward explicit
method and the first modified or

equivalent equation are presented. These techniques are
similar to iterative updating deferred

methods and are based on the application of asymptotic
methods to modified equations which do

not require initial conditions for the high order derivatives
in the truncation terms and which yield

stable numerical methods. It is shown that, depending
on the discretization of the high order

derivatives in the high order correction equations, different
methods of as high order of

consistency as required can be developed. In this paper,
backward and centered formulas are

used, but the resulting numerical methods are not self-starting.
It is shown that, if the starting

procedure is not adequate, the numerical order of the
method can be smaller than the theoretical

one. In order to avoid this loss of numerical order, a
method for consistently starting the

asymptotic successive-correction technique based on the
use of fictitious times is presented and

applied to autonomous and nonautonomous, ordinary differential
equations, and compared with

the results of second and fourth-order Runge-Kutta methods.
It is shown that the fourth-order

Runge-Kutta method is more accurate than the successive-correction
techniques for large time

steps due to the higher order derivatives in the successive-correction,
but, for sufficiently small

time steps, these techniques have almost the same accuracy
as the fourth-order Runge-Kutta

method.

AN: 6296082

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TI: On the method of modified equations. I. Asymptotic
analysis of the Euler forward difference

method

AU: Villatoro-FR; Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.103, no.2-3;
15 Aug. 1999; p.111-39.

PY: 1999

LA: English

AB: The method of modified equations is studied as a technique
for the analysis of finite

difference equations. The non-uniqueness of the modified
equation of a difference method is

stressed and three kinds of modified equations are introduced.
The first modified or equivalent

equation is the natural pseudo-differential operator associated
to the original numerical method.

Linear and nonlinear combinations of the equivalent equation
and their derivatives yield the

second modified or second equivalent equation and the
third modified or (simply) modified

equation, respectively. For linear problems with constant
coefficients, the three kinds of modified

equations are equivalent among them and to the original
difference scheme. For nonlinear

problems, the three kinds of modified equations are asymptotically
equivalent in the sense that an

asymptotic analysis of these equations with the time step
as small parameter yields exactly the

same results. In this paper, both regular and multiple
scales asymptotic techniques are used for the

analysis of the Euler forward difference method, and the
resulting asymptotic expansions are

verified for several nonlinear, autonomous, ordinary differential
equations. It is shown that, when

the resulting asymptotic expansion is uniformly valid,
the asymptotic method yields very accurate

results if the solution of the leading order equation
is smooth and does not blow up, even for large

step sizes.

AN: 6296081

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TI: Two-dimensional simulations of magma ascent in volcanic
conduits

AU: Ramos-JI

SO: International-Journal-for-Numerical-Methods-in-Fluids.
vol.29, no.7; 15 April 1999; p.765-89.

PY: 1999

LA: English

AB: A two-dimensional model for magma ascent in volcanic
conduits is presented. The model

accounts for the magma rheology, heat flux to the surrounding
country rock, planar and

axisymmetric geometries, and flow in the mushy region
by means of a continuum mixture

formulation that does not require keeping track of the
liquid-solid interfaces. Numerical

experiments for Newtonian and visco-plastic Bingham rheologies
of magmas are presented as

functions of the volumetric flow rate at the dyke's entrance
and wall heat fluxes for both round

conduits and fissures. It is shown that, depending on
the magma rheology, dyke geometry,

volumetric flow rate and wall heat flux, the magma may
solidify along the original dyke's walls,

thus reducing the available cross-sectional area to the
flow, or the original dyke's walls may melt.

It is also shown that the dyke's wall temperature may
first increase and then decrease, and that the

axial velocity profile exhibits a parabolic shape in the
core region and a plug zone near the dyke's

walls for Bingham rheologies.

AN: 6260384

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TI: Parallel simulation of semiconductor laser arrays

AU: Romero-LF; Zapata-EL; Ramos-JI

SO: Supercomputation in Nonlinear and Disordered Systems.
Algorithms, Applications and

Architectures. World Scientific, Singapore; 1997; xvii+400
pp. p.335-42.

PY: 1997

LA: English

AB: A parallel hopscotch algorithm for the simulation
of semiconductor laser arrays which

overlaps computations and communications is presented.
The method uses a Lax-Wendroff

scheme for the hyperbolic part of the operators and allows
to obtain near-to-perfect speed-ups on

MIMD computers. Numerical experiments indicate that semiconductor
laser arrays exhibit a rich

dynamic behavior ranging from uncoupled to coupled oscillations
and chaotic phenomena

depending on the width of and separation between the current
stripes.

AN: 6219505

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TI: Asymptotic analysis of compound liquid jets at low
Reynolds numbers

AU: Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.100, no.2-3;
May 1999; p.223-40.

PY: 1999

LA: English

AB: Asymptotic methods based on the slenderness ratio
are used to obtain the leading-order

equations which govern the fluid dynamics of both hollow
and solid, compound jets such as those

employed in the manufacture of textile fibers, composite
fibers and optical fibers. These fibers

consist of an inner material which may be a round jet
or an annular one and which, in turn, is

surrounded by an annular jet in contact with ambient air.
It is shown that the leading-order

equations are one-dimensional and that it is possible
to obtain analytical solutions for several flow

regimes for steady, compound jets. These analytical solutions
are presented here. The

one-dimensional leading-order equations for the fluid
dynamics of annular liquid jets at low

Reynolds numbers are also derived here.

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TI: Linearized factorization techniques for multidimensional
reaction-diffusion equations

AU: Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.100, no.2-3;
May 1999; p.201-22.

PY: 1999

LA: English

AB: An iterative predictor-corrector technique for the
elimination of the approximate factorization

errors which result from the factorization of linearized
theta -methods in multidimensional

reaction-diffusion equations is proposed, and its convergence
and linear stability are analyzed.

Four approximate factorization techniques which do not
account for the approximate factorization

errors are developed. The first technique uses the full
Jacobian matrix of the reaction terms,

requires the inversion of, in general, dense matrices,
and its approximate factorization errors are

second-order accurate in time. The second and third methods
approximate the Jacobian matrix by

diagonal or triangular ones which are easily inverted
but their approximate factorization errors are,

however, first-order accurate in time. The fourth approximately
factorized method has

approximate factorization errors which are second-order
accurate in time and requires the

inversion of lower and upper triangular matrices. The
techniques are applied to a nonlinear,

two-species, two-dimensional system of reaction-diffusion
equations in order to determine the

approximate factorization errors and those resulting from
the approximations to the Jacobian

matrix as functions of the allocation of the reaction
terms, space and time.

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TI: Leading-order equivalence of two formulations for
long, annular liquid membranes

AU: Ramos-JI

SO: Applied-Mathematical-Modelling. vol.22, no.6; June
1998; p.453-7.

PY: 1998

LA: English

AB: The author (1996) studied both analytically and numerically
the steady fluid dynamics of

annular liquid jets by means of the models developed by
Boussinesq (1869) and Ramos (1992). In

this short note, the formulation developed by Lee and
Wang (1986) for annular liquid membranes,

i.e., annular liquid jets of zero thickness, in the absence
of gravity is generalized to include the

gravitational acceleration and compared with the one developed
by Ramos (1992) for annular

liquid membranes and annular liquid jets.

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TI: Annular liquid jets and other axisymmetric free-surface
flows at high Reynolds numbers

AU: Ramos-JI

SO: Applied-Mathematical-Modelling. vol.22, no.6; June
1998; p.423-52.

PY: 1998

LA: English

AB: A perturbation method based on a long wavelength approximation
is used to obtain the

leading order equations governing the fluid dynamics of
laminar, annular, round and compound

liquid jets and liquid films on convex and concave cylindrical
surfaces. An approximate, integral

balance method is also used to determine the inviscid
core and the thickness of the boundary

layers of annular liquid jets near the nozzle exit. The
steady state equations are transformed into

parabolic ones by means of the von Mises transformation
and solved in an adaptive, staggered

grid to determine the axial velocity distribution and
the location of the free surfaces. It is shown

that, for free surface flows subject to inertial gravity
and surface tension, there is a contraction

near the nozzle which increases as the Reynolds and Froude
numbers are decreased, and is nearly

independent of the Weber number for Weber numbers larger
than about one hundred. It is also

shown that this contraction depends on the flow considered,
and is larger for films on convex

surfaces. It is also shown that, for round jets, the acceleration
of the jet's free surface is larger than

that of the jet's centerline, although, sufficiently far
from the nozzle exit, the axial velocity is

uniform across the jet.

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TI: Intermediate boundary conditions in operator-splitting
techniques and linearization methods

AU: Ramos-JI; Garcia-Lopez-CM

SO: Applied-Mathematics-and-Computation. vol.94, no.2-3;
15 Aug. 1998; p.113-36.

PY: 1998

LA: English

AB: The intermediate boundary conditions for the solution
of linear, one-dimensional

reaction-diffusion equations have been determined analytically
for the case that the reaction and

diffusion operators are solved once each in each time
step. These boundary conditions have been

used to solve systems of nonlinear, one-dimensional reaction-diffusion
equations by means of

linearized theta -methods and time-linearized techniques
which are based on the linearization of

the nonlinear algebraic and differential, respectively,
equations of the reaction operator; both

techniques provide analytical solutions to the reaction
operator although in discrete and

continuous forms, respectively. Since the linearization
of reaction operators may result in dense

Jacobian matrices, diagonally and triangularly linearized
techniques which uncouple or couple in a

sequential manner, respectively, the dependent variables
are proposed. It is shown that the

accuracy of time-linearized methods is higher than that
of linearized theta -techniques, whereas the

accuracy of both linearization methods deteriorates as
the coupling between dependent variables is

weakened.

AN: 5993200

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TI: Implicit, compact, linearized theta -methods with
factorization for multidimensional

reaction-diffusion equations

AU: Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.94, no.1;
1 Aug. 1998; p.17-43.

PY: 1998

LA: English

AB: An iterative predictor-corrector technique for the
elimination of the approximate factorization

errors which result from the factorization of implicit,
three-point compact, linearized theta

-methods in multidimensional reaction-diffusion equations
is proposed, and its convergence and

linear stability are analyzed. Four compact, approximate
factorization techniques which do not

account for the approximate factorization errors and which
involve three-point stencils for each

one-dimensional operator are developed. The first technique
uses the full Jacobian matrix of the

reaction terms, requires the inversion of, in general,
dense matrices, and its approximate

factorization errors are second-order accurate in time.
The second and third methods approximate

the Jacobian matrix by diagonal or triangular ones which
are easily inverted but their approximate

factorization errors are, however, first-order accurate
in time. The fourth approximately factorized,

compact, implicit method has approximate factorization
errors which are second-order accurate in

time and requires the inversion of lower and upper triangular
matrices. The techniques are applied

to a nonlinear, two-species, two-dimensional system of
reaction-diffusion equations in order to

determine the approximate factorization errors and those
resulting from the approximations to the

Jacobian matrix as functions of the allocation of the
reaction terms, space and time.

AN: 5986465

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TI: Maps of implicit, linearized theta -methods for the
logistic differential equation

AU: Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.94, no.1;
1 Aug. 1998; p.1-15.

PY: 1998

LA: English

AB: Implicit, linearized theta -methods for the logistic
differential equation which provide explicit

expressions for the value of the dependent variable at
one time level as function of that at the

previous time and the values of the time step and implicitness
parameter, are developed. The fixed

points of the maps of implicit, linearized theta -methods
and their linear stability are determined

analytically, together with their basins of attraction
and singularity sets. It is shown that the basin

of attraction of second-order accurate, implicit, linear
methods technique is the right-most fixed

point, whereas that of first-order accurate ones depends
on the time step. The monotonic or

oscillatory convergence to the fixed points is also determined
analytically and numerically.

AN: 5986464

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TI: Upstream boundary conditions for flows in porous channels

AU: Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.93, no.2-3;
15 July 1998; p.149-54.

PY: 1998

LA: English

AB: The upstream velocity profile for the Darcy-Forchheimer-Brinkman
and

Darcy-Lapwood-Forchheimer-Brinkman models of flow in porous
channels is determined

analytically as a function of the Reynolds number, permeability
of the medium, and drag

coefficient. It is shown that this profile is governed
by the Korteweg-de Vries equation in a frame

moving at constant speed and given as a Jacobi elliptic
function on account of the no-slip

boundary conditions at the solid walls.

AN: 5986453

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TI: A piecewise time-linearized method for the logistic
differential equation

AU: Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.93, no.2-3;
15 July 1998; p.139-48.

PY: 1998

LA: English

AB: A piecewise time-linearized technique is employed
to determine an approximate, analytical

solution to the logistic differential equation. This technique
yields a nonlinear map or difference

equation which preserves the fixed points and linear stability
of the logistic differential equation. It

is shown that this map is continuous and piecewise differentiable,
coincides with that of the Euler

forward method for small time steps, and differs from
the predictor-corrector method proposed

by Certaine and Adomian's decomposition technique.

AN: 5986452

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TI: Linearized finite difference methods: application
to nonlinear heat conduction problems

AU: Garcia-Lopez-CM; Ramos-JI

SO: Advanced Computational Methods in Heat Transfer IV.
Comput. Mech. Publications,

Southampton, UK; 1996; 647 pp. p.527-36.

PY: 1996

LA: English

AB: Partially-linearized, approximate factorization methods
for multidimensional, nonlinear

reaction-diffusion problems are presented. These methods
first discretize the time derivatives and

linearize the equations, and then factorize the multidimensional
operators into a sequence of

one-dimensional ones. Depending on how the Jacobian matrix
is approximated, fully coupled,

sequentially coupled or uncoupled, linear, one-dimensional
problems are obtained. It is shown

that the approximate errors of the linearized techniques
presented are nearly the same, whereas

their accuracy depends on the approximation to the Jacobian
matrix.

AN: 5899754

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TI: Comments on a recent paper dealing with the finite-analytic
method

AU: Ramos-JI; Garcia-Lopez-CM

SO: International-Journal-of-Numerical-Methods-for-Heat-&-Fluid-Flow.
vol.7, no.8; 1997;

p.794-800.

PY: 1997

LA: English

AB: The authors refers to Montgomery and Fleeter (see
ibid., vol.6, p.59-77 (1996)) who

employed the finite-analytic method of Chen et al. (1980)
to study steady, two-dimensional,

inviscid, compressible, subsonic flow in a nozzle. The
authors show that, contrary to the statement

made by Montgomery and Fleeter, their boundary conditions
at the computational cell's

boundaries are not constructed from the particular solution
to one of their equations. The authors

deduce from a simple non-linear second-order ordinary
differential equation that the finite or

locally analytic method of Chen et al. (1980) only yields
continuous but not differentiable

solutions. They suggest a finite-analytic method which
provides continuous and differentiable

solutions.

AN: 5865068

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Registro 39 de 100 en INSPEC 7/97-12/97

TI: Linearization methods for reaction-diffusion equations:
multidimensional problems

AU: Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.88, no.2-3;
30 Dec. 1997; p.225-54.

PY: 1997

LA: English

AB: Four types of linearization methods for the numerical
solution of multidimensional reaction

diffusion equations are presented. The first two types
are based on the discretization of the time

variable, time linearization and approximate factorization.
The first type also discretizes the spatial

coordinates, results in block tridiagonal matrices, and
provides discrete solutions in space and

time. The second type employs space linearization, yields
linear, ordinary differential equations in

space, and produces either piecewise continuous or piecewise
differentiable solutions. The third

type is based on the discretization of the spatial coordinates
and time linearization, and yields

continuous solutions in time. The fourth type uses time
and space linearization, and results in a

multidimensional, linear, elliptic equation whose solution
by means of separation of variables

provides continuous approximations in space and discrete
in time. The fourth type also yields nine

point finite difference expressions compared with the
five point ones of the first three types.

AN: 5775532

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TI: Linearization methods for reaction-diffusion equations:
1-D problems

AU: Ramos-JI

SO: Applied-Mathematics-and-Computation. vol.88, no.2-3;
30 Dec. 1997; p.199-224.

PY: 1997

LA: English

AB: Three types of linearized finite difference methods
are presented. The first type is based on a

theta formulation which provides discrete solutions in
both space and time. It is shown that this

type is a linearly implicit Rosenbrock's or a W method
depending on whether the full or an

appropriate Jacobian is employed. The second one requires
the solution of two point, linear,

ordinary differential equations and provides either piecewise
continuous or piecewise

differentiable solutions in space and discrete in time.
The third type is based on the discretization

of the spatial coordinate and provides a system of linear,
ordinary differential equations in time

which can be integrated analytically. Therefore, the third
type of linearized finite difference

methods provides continuous solutions in time and discrete
in space, and may be transformed into

one of the first type by discretizing the time variable.

AN: 5775531

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TI: Analysis of annular liquid membranes and their singularities

AU: Ramos-JI

SO: Meccanica. vol.32, no.4; Aug. 1997; p.279-93.

PY: 1997

LA: English

AB: The singularities of the equations governing the fluid
dynamics of steady, axisymmetric,

annular liquid membranes subject to gravity are analyzed
by means of two techniques based on

the membranes's slope and curvature, and the membrane's
mean radius, mass per unit length, and

axial and radial velocity components, respectively. It
is shown that no singularity is possible at or

downstream from the nozzle exit for Weber numbers greater
than unity because of the

gravitational pull. For a Weber number equal to one, a
singularity at the nozzle exit appears and

the flow slope there is undetermined; however, the slope
acquires a finite value if the liquid is

assumed to leave the nozzle at angle different from that
of the annular orifice. It is also shown

that, for Weber numbers smaller than one, a singularity
may occur downstream from the nozzle

exit which may also be removed, and that the shapes of
annular liquid membranes for Weber

numbers equal to or less than one take a rounded form
which is in agreement with experimental

observations. An asymptotic analysis shows that, to leading
order, the shapes of capillary, annular

liquid membranes are arcs of circumferences, and this
result is again in accord with available

experimental findings.

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TI: Nonstandard finite difference equations for ODEs and
1-D PDEs based on piecewise

linearization

AU: Ramos-JI; Garcia-Lopez-CM

SO: Applied-Mathematics-and-Computation. vol.86, no.1;
15 Sept. 1997; p.11-36.

PY: 1997

LA: English

AB: A method for the solution of initial and boundary
value problems in nonlinear, ordinary

differential equations, and for one-dimensional, partial
differential equations which provides

C/sup 1/ solutions is presented. The method is based on
the linearization of the differential

equation in intervals which contain only two grid points
and provides three-point, nonstandard

finite difference equations for the nodal amplitudes.
The method is applied to steady

reaction-diffusion equations, two-point, singularly perturbed
boundary value problems and the

steady Burgers equation, and compared with standard finite
difference and finite element

formulations. For one-dimensional, partial differential
equations, the temporal derivatives are first

discretized, and the resulting ordinary differential equation
accounts for both the temporal and

spatial stiffnesses and is solved by means of piecewise
linearization. Since the linearization

includes a Jacobian matrix, it may be easily employed
to refine the mesh where steep gradients

occur.

AN: 5705319

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TI: Lumped models of gas bubbles in thermal gradients

AU: Ramos-JI

SO: Applied-Mathematical-Modelling. vol.21, no.6; June
1997; p.371-86.

PY: 1997

LA: English

AB: The motion of spherical gas bubbles in isothermal
and nonisothermal glass melts is analyzed

both analytically and numerically by means of lumped models.
The analytical studies provide

expressions for the bubble radius and location as functions
of time in the absence of mass transfer

and have been obtained using a lineal temperature gradient,
a linear dependence of the surface

tension on the temperature, and average values for the
dynamic viscosity and/or surface tension.

Three flow regimes have been analyzed: buoyant, thermocapillary,
and mixed

buoyant-thermocapillary regimes. Numerical solutions to
both the bubble radius and location have

been obtained using the local values of both the dynamic
viscosity and surface tension in the

absence of mass transfer. These numerical results indicate
that the bubble radius at refining is

about 8% of the bubble's initial radius, while the bubble
velocity increases as the initial bubble

radius, mean temperature, and thermal gradient are increased
Bubbles in zero-gravity

environments and without mass transfer move slowly, and
the bubble radius and velocity increase

as the initial bubble radius and temperature gradient
are increased but they decrease as the glass

melt mean temperature is decreased. Numerical studies
of gas bubbles with mass transfer in

nonisothermal glass melts indicate that, for a bubble
containing only oxygen initially, nitrogen,

carbon dioxide, and water vapor diffuse from the glass
melt to the bubble, whereas the oxygen

diffuses from the bubble to the glass melt.

AN: 5699073

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TI: Mass transfer in annular liquid jets in the presence
of liquid flow rate fluctuations

AU: Ramos-JI

SO: Applied-Mathematical-Modelling. vol.21, no.6; June
1997; p.363-9.

PY: 1997

LA: English

AB: The effects of sinusoidal oscillations in the liquid's
mass flow rate at the nozzle exit on the

fluid dynamics of and mass transfer in annular liquid
jets have been analyzed numerically in the

absence of interfacial mass-transfer resistance. It is
shown that the pressure and volume of the

gases enclosed by the jet, the gas concentration at the
jet's inner interface, and the mass absorption

rates at the jet's inner and outer interfaces are sinusoidal
functions of time, which have the same

frequency as, but exhibit a phase lag with respect to,
the liquid's mass flow-rate oscillations. The

amplitude of these oscillations increases and decreases,
respectively as the amplitude and

frequency, respectively, of the mass flow rate oscillation
are increased. For the amplitudes and

frequencies considered in the paper, no mass enhancement
due to mass flow-rate oscillations is

observed despite the nonlinear, integrodifferential coupling
between the fluid dynamics and

mass-transfer phenomena.

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TI: Asymptotic and numerical analysis of vertical, planar
liquid sheets subject to London-van der

Waals forces

AU: Ramos-JI

SO: International-Journal-of-Numerical-Methods-for-Heat-&-Fluid-Flow.
vol.7, no.1; 1997;

p.42-62.

PY: 1997

LA: English

AB: Asymptotic methods are employed to derive the long
wave equations governing the fluid

dynamics of thin, time-dependent, incompressible, vertical,
planar liquid sheets at low Reynolds

numbers subjected to London-van der Waals body forces
and gravity. Analytical solutions for

steady, viscous sheets in gravitational and zero-gravity
environments are obtained for large surface

tension. Numerical studies of planar liquid sheets at
low Reynolds numbers with no surface

tension indicate that, for plane stagnation flows, the
deceleration of the sheet as it approaches the

solid wall decreases as the London-van der Waals forces
are increased, the effects of these body

forces decrease as the Froude number is increased. And,
for Reynolds-to-Froude numbers greater

than one, the thickening of the sheet as it approaches
the solid boundary increases as the Hamaker

constant is increased. Numerical experiments of film casting
processes with three different flow

approximations which account for or neglect inertia and/or
the gravitational full have also been

performed and indicate that: for high take-up speeds,
a boundary layer is formed at the

downstream boundary, the thickness of this layer decreases
as the London-van der Waals forces

are increased, and, for Reynold-to-Froude numbers larger
than one, the leading-order thickness

and axial velocity component are very sensitive to the
value of the Hamaker constant.

AN: 5604487

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TI: A parallel Theta -method for a semiconductor laser
array model

AU: Romero-LF; Zapata-EL; Ramos-JI

SO: Proceedings of the 8th Joint EPS-APS International
Conference on Physics Computing, PC

'96. Acad. Comput. Centre CYFRONET-KRAKOW, Krakow, Poland;
1996; xvi+603 pp. p.325-8.

PY: 1996

LA: English

AB: A time-dependent, two-dimensional model of a semiconductor
laser array is numerically

studied by means of Theta - and Newton-Raphson methods.
A parallel version of the BiCGSTAB

algorithm for the solution of the linear equations resulting
from the Newton-Raphson technique is

presented. It is shown that the proposed method reduces
by half the number of messages and, by

means of communications overlapping, allows to achieve
a near-to-perfect speedup in the

computations.

AN: 5596307

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Registro 47 de 100 en INSPEC 1/97-6/97

TI: Piecewise-linearized methods for initial-value problems

AU: Ramos-JI; Garcia-Lopez-CM

SO: Applied-Mathematics-and-Computation. vol.82, no.2-3;
15 March 1997; p.273-302.

PY: 1997

LA: English

AB: Piecewise-linearized methods for the solution of initial-value
problems in ordinary differential

equations are developed by approximating the right-hand-sides
of the equations by means of a

Taylor polynomial of degree one. The resulting approximation
can be integrated analytically to

obtain the solution in each interval and yields the exact
solution for linear problems. Three

adaptive methods based on the norm of the Jacobian matrix,
maintaining constant the value of the

approximation errors incurred by the linearization of
the right-hand sides of the ordinary

differential equations, and Richardson's extrapolation
are developed. Numerical experiments with

some nonstiff, first- and second-order, ordinary differential
equations, indicate that the accuracy

of piecewise-linearized methods is, in general, superior
to those of the explicit, modified,

second-order accurate Euler method and the implicit trapezoidal
rule, but lower than that of the

explicit, fourth-order accurate Runge-Kutta technique.
It is also shown that piecewise-linearized

methods do not exhibit computational (i.e., spurious)
modes for the relaxation oscillations of the

van der Pol oscillator, and, for those systems of equations
which satisfy certain conservation

principles, conserve more accurately the invariants than
the trapezoidal rule. An error bound for

piecewise-linearized methods is provided for ordinary
differential equations whose

right-hand-sides satisfy certain Lipschitz conditions.

AN: 5528135

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Registro 48 de 100 en INSPEC 1/97-6/97

TI: Linearized Theta -methods. II. Reaction-diffusion
equations

AU: Garcia-Lopez-CM; Ramos-JI

SO: Computer-Methods-in-Applied-Mechanics-and-Engineering.
vol.137, no.3-4; 15 Nov. 1996;

p.357-78.

PY: 1996

LA: English

AB: Second-order accurate in space, partially-linearized,
triangular and diagonal Theta -methods

for reaction-diffusion equations, which employ either
a standard or a delta formulation, are

developed and applied to both the study of a system of
one-dimensional, reaction-diffusion

equations with algebraic nonlinear reaction terms and
the propagation of a one-dimensional,

confined, laminar flame. These methods require the solution
of tridiagonal matrices for each

dependent variable, and either uncouple or sequentially
couple the dependent variables at each

time step depending on whether they are diagonally- or
triangularly-linearized techniques,

respectively. Partially-linearized, diagonal methods yield
larger errors than partially-linearized,

triangular techniques, and the accuracy of the latter
depends on the time step, standard or delta

formulation, implicitness parameter and the order in which
the equations are solved. Fully- and

partially-linearized, operator-splitting methods for reaction-diffusion
equations are also developed.

The latter provide explicit expressions for the solution
of the reaction operator.

AN: 5459588

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Registro 49 de 100 en INSPEC 1996

TI: Irrotational, annular liquid jets

AU: Ramos-JI

SO: Journal-of-Mathematical-Analysis-and-Applications.
vol.202, no.2; 1 Sept. 1996; p.538-54.

PY: 1996

LA: English

AB: Perturbation methods are used to derive the asymptotic
equations that govern the fluid

dynamics of steady and unsteady, incompressible, inviscid,
axisymmetric, irrotational annular

liquid jets employing as a small parameter the slenderness
ratio.

AN: 5388520

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TI: G-jitter effects on mass transfer in annular liquid
jets

AU: Ramos-JI

SO: International-Journal-of-Numerical-Methods-for-Heat-&-Fluid-Flow.
vol.6, no.5; Aug. 1996;

p.17-28.

PY: 1996

LA: English

AB: This paper analyses numerically the effects of sinusoidal
g-jitter on the fluid dynamics of, and

mass transfer in, annular liquid jets. It is shown that
the pressure and volume of the gases

enclosed by the jet, the gas concentration at the jet's
inner interface, and the mass absorption rates

at the jet's inner and outer interfaces are sinusoidal
functions of time which have the same

frequency as that of the g-jitter. The amplitude of these
oscillations increases and decreases,

respectively, as the amplitude and frequency, respectively,
of the g-jitter is increased. The pressure

coefficient and the gas concentration at the jet's inner
interface are in phase with the applied g-jitter

and the amplitude of their oscillations increases almost
linearly with the amplitude of the g-jitter.

The mass absorption rates at the jet's inner and outer
interfaces exhibit a phase lag with respect to

the g-jitter.

AN: 5381892

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Registro 51 de 100 en INSPEC 1996

TI: Force fields on inviscid, slender, annular liquid
jets

AU: Ramos-JI

SO: International-Journal-for-Numerical-Methods-in-Fluids.
vol.23, no.3; 15 Aug. 1996; p.221-39.

PY: 1996

LA: English

AB: Regular perturbation expansions are used to analyse
the fluid dynamics of unsteady, inviscid,

slender, thin, incompressible (constant density), axisymmetric,
upward and downward, annular

liquid jets subjected to non-homogeneous, conservative
body forces when both the annular jets

are very thin and the gases enclosed by and surrounding
the jet are dynamically passive. Both

inertia- and capillarity-dominated annular jets are considered.
It is shown that, for

inertia-dominated jets, closure of the leading-order equations
is achieved at second order in the

perturbation parameter, which is the slenderness ratio,
whereas closure is achieved at first order

for capillarity-dominated jets. The steady leading-order
equations are solved numerically by means

of both an adaptive finite difference method which maps
the curvilinear geometry of the jet onto a

unit square and a fourth-order-accurate Runge-Kutta technique.
It is shown that the fluid

dynamics of steady, annular liquid jets is very sensitive
to the Froude and Weber numbers and

nozzle exit angle in the presence of non-homogeneous,
conservative body forces. For upward jets

with inwardly or axially directed velocities at the nozzle
exit the effect of the non-homogeneous,

conservative body forces is to increase the leading-order
axial velocity component, decrease the

jet's mean radius and move the stagnation point downstream.
For downward jets with radially

outward velocity at the nozzle exit the axial velocity
component decreases monotonically as the

magnitude of the non-homogeneous, conservative body forces
is increased.

AN: 5364059

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Registro 52 de 100 en INSPEC 1996

TI: Efficient parallel solution of a semiconductor laser
array dynamics model

AU: Romero-LF; Zapata-EL; Ramos-JI

SO: High-Performance Computing and Networking. International
Conference and Exhibition

HPCN EUROPE 1996. Proceedings. Springer-Verlag, Berlin,
Germany; 1996; xxv+1040 pp.

p.938-9.

PY: 1996

LA: English

AB: A parallel algorithm for solving a system of time-dependent,
two-dimensional, partial

differential equations (pdes) modelling a semiconductor
array based on the Hopscotch method is

proposed. This method reduces by half the number of messages
and, by means of

communications overlapping, allows to achieve a near-to-perfect
speedup.

AN: 5347519

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Registro 53 de 100 en INSPEC 1996

TI: Upward and downward annular liquid jets: conservation
properties, singularities, and

numerical errors

AU: Ramos-JI

SO: Applied-Mathematical-Modelling. vol.20, no.6; June
1996; p.440-58.

PY: 1996

LA: English

AB: A one-dimensional hydraulic model for inviscid incompressible
axisymmetric annular liquid

jets is derived by assuming that the pressure is uniform
throughout the jet and that the velocity

components are uniform on each cross-section. This model
can be derived from that of

Boussinesq if the slope of the annular jet is small. Both
models indicate that the liquid jet's

acceleration and curvature may become singular for Weber
numbers less than or equal to one. The

singularity does not depend on the Froude number and pressure
difference between the gases

enclosed by and surrounding the annular liquid jet, and
it is in good accord with available

experimental data. Since jets are observed experimentally
for Weber numbers less than one, the

analysis presented indicates that annular jets leave the
nozzle exit with an angle that differs from

that of the nozzle. An asymptotic analysis of the governing
equations for small Weber numbers

indicates that the shape of annular liquid jets may be
a circular arc, and this is in accordance with

available experimental and theoretical data. Numerical
experiments and comparisons with

analytical solutions for long annular liquid jets indicate
that the convergence length is nearly

independent of the accuracy of the numerical method and
computer precision, while the local and

global energy errors increase as the computer precision
is decreased. It is also shown that upwind

finite difference methods which conserve linear momentum
do not conserve mechanical energy

and yield larger errors than explicit fourth-order accurate
Runge-Kutta techniques. The shape of

annular liquid jets exhibits a rounded form for Weber
numbers much less than unity; however, the

long wave approximation employed in the derivation of
the hydraulic model may not be valid for

small Weber numbers.

AN: 5317626

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Registro 54 de 100 en INSPEC 1996

TI: A piecewise-linearized method for ordinary differential
equations: two-point boundary value

problems

AU: Garcia-Lopez-CM; Ramos-JI

SO: International-Journal-for-Numerical-Methods-in-Fluids.
vol.22, no.11; 15 June 1996;

p.1089-102.

PY: 1996

LA: English

AB: Piecewise-linearized methods for the solution of two-point
boundary value problems in

ordinary differential equations are presented. These problems
are approximated by piecewise

linear ones which have analytical solutions and reduced
to finding the slope of the solution at the

left boundary so that the boundary conditions at the right
end of the interval are satisfied. This

results in a rather complex system of non-linear algebraic
equations which may be reduced to a

single non-linear equation whose unknown is the slope
of the solution at the left boundary of the

interval and whose solution may be obtained by means of
the Newton-Raphson method. This is

equivalent to solving the boundary value problem as an
initial value one using the

piecewise-linearized technique and a shooting method.
It is shown that for problems characterized

by a linear operator a technique based on the superposition
principle and the piecewise-linearized

method may be employed. For these problems the accuracy
of piecewise-linearized methods is of

second order. It is also shown that for linear problems
the accuracy of the piecewise-linearized

method is superior to that of fourth-order-accurate techniques.
For the linear singular perturbation

problems considered in this paper the accuracy of global
piecewise linearization is higher than that

of finite difference and finite element methods. For non-linear
problems the accuracy of

piecewise-linearized methods is in most cases lower than
that of fourth-order methods but

comparable with that of second-order techniques owing
to the linearization of the non-linear

terms.

AN: 5311432

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Registro 55 de 100 en INSPEC 1996

TI: Planar liquid sheets at low Reynolds numbers

AU: Ramos-JI

SO: International-Journal-for-Numerical-Methods-in-Fluids.
vol.22, no.10; 30 May 1996;

p.961-78.

PY: 1996

LA: English

AB: Asymptotic methods are employed to derive the leading-order
equations which govern the

fluid dynamics of time-dependent, incompressible, planar
liquid sheets at low Reynolds numbers

using as small parameter the slenderness ratio. Analytical
and numerical solutions of relevance to

both steady film casting processes and plane stagnation
flows are obtained with the leading-order

equations. It is shown that for steady film casting processes
the model which accounts for both

gravity and low-Reynolds-number effects predicts thicker
and slower planar liquid sheets than

those which neglect a surface curvature term or assume
that Reynolds number is zero, because the

neglect of the curvature term and the assumption of zero
Reynolds number are not justified at high

take-up velocities owing to the large velocity gradients
that occur at the take-up point. It is also

shown that for Reynolds number/Froude number ratios larger
than one, models which neglect the

surface curvature or assume a zero Reynolds number predict
velocity profiles which are either

concave or exhibit an inflection point, whereas the model
which accounts for both curvature and

low-Reynolds-number effects predicts convex velocity profiles.
For plane stagnation flows it is

shown that models which account for both low-Reynolds-number
and curvature effects predict

nearly identical results to those of models which assume
zero Reynolds number. These two

models also predict a faster thickening of the planar
liquid sheet than models which account for

low-Reynolds-number effects but neglect the surface curvature.
This curvature term is very large

near the stagnation point and cannot be neglected there.

AN: 5298403

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Registro 56 de 100 en INSPEC 1996

TI: Linearized Theta -methods. I. Ordinary differential
equations

AU: Ramos-JI; Garcia-Lopez-CM

SO: Computer-Methods-in-Applied-Mechanics-and-Engineering.
vol.129, no.3; 15 Jan. 1996;

p.255-69.

PY: 1996

LA: English

AB: Fully-linearized Theta -methods for autonomous and
non-autonomous, ordinary differential

equations are derived by approximating the non-linear
terms by means of the first-degree

polynomials which result from Taylor`s series expansions.
These methods are implicit but result in

explicit solutions, A-stable, consistent and convergent;
however, they may be very demanding in

terms of both computer time and storage because the matrix
to be inverted is, in general, dense.

The accuracy of fully-linearized Theta -methods is comparable
to that of the standard, implicit,

iterative Theta -methods, and deteriorates as the value
of Theta is decreased from Theta =0.5, for

which both Theta and fully-linearized Theta -methods are
second-order accurate.

Partially-linearized Theta -methods based on the partial
linearization of non-linear terms have also

been developed. These methods result in diagonal or triangular
matrices which may be easily

solved by substitution. Their accuracy, however, is lower
than that of fully-linearized Theta

-methods.

AN: 5233408

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TI: The effects of fluctuating body forces on annular
liquid jets

AU: Ramos-JI

SO: Archive-of-Applied-Mechanics. vol.65, no.8; Oct. 1995;
p.548-63.

PY: 1995

LA: English

AB: The nonlinear dynamics of axisymmetric, inviscid,
incompressible, thin, annular liquid jets

subjected to fluctuating body forces is studied numerically
by means of an adaptive finite

difference method which maps the time-dependent, curvilinear
geometry of the jet into a unit

square. The fluctuating body forces may arise from fluctuations
in the gravitational acceleration in

inertial frames or from the acceleration of a non-inertial
frame of reference which translates

parallelly to an inertial one. It is shown that both the
pressure coefficient and the axial location at

which the annular jet becomes a solid one are periodic
functions of time with a period equal to

that of the imposed body force fluctuations, and that
their magnitude increases as the amplitude of

the body force fluctuations is increased. It has also
been shown that, for both intermittent,

sinusoidal or rectangular excitations, increases in the
frequency of the excitation result in the

creation of superharmonics, broad, albeit peaked, spectra,
and closed phase planes with many

loops.

AN: 5151007

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Registro 58 de 100 en INSPEC 1995

TI: Fluid dynamics of slender, thin, annular liquid jets

AU: Ramos-JI

SO: International-Journal-for-Numerical-Methods-in-Fluids.
vol.21, no.9; 15 Nov. 1995; p.735-61.

PY: 1995

LA: English

AB: Perturbation methods are used to obtain the one-dimensional,
asymptotic equations that

govern the fluid dynamics of slender, thin, inviscid,
incompressible, axisymmetric, irrotational,

annular liquid jets from the Euler equations. It is shown
that, depending on the magnitude of the

Weber number, two flow regimes are possible: an inertia-dominated
one corresponding to large

Weber numbers, and a capillary regime for Weber numbers
of the order of unity. The steady

equations governing these two regimes have analytical
solutions for the liquid's axial velocity

component and require a numerical integration to determine
the jet's mean radius for

inertia-dominated jets. The one-dimensional equations
derived in this paper are shown to be

particular cases of a hydraulic model for annular liquid
jets, and this model is used to determine

the effects of gravity modulation on the unsteady fluid
dynamics of annular liquid jets in the

absence of mass injection into the volume enclosed by
the jet and mass absorption. It is shown

that both the convergence length and the pressure coefficient
are periodic functions of time which

have the same period as that of the gravity modulation,
but undergo large variations as the

amplitude, frequency and width of gravitational pulses
is varied.

AN: 5120859

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Registro 59 de 100 en INSPEC 1995

TI: One-dimensional, time-dependent, homogeneous, two-phase
flow in volcanic conduits

AU: Ramos-JI

SO: International-Journal-for-Numerical-Methods-in-Fluids.
vol.21, no.3; 15 Aug. 1995; p.253-78.

PY: 1995

LA: English

AB: A one-dimensional, time-dependent, isothermal, homogeneous,
two-phase flow model was

developed to study magma ascent in volcanic conduits.
The physical modeling equations were

numerically solved by means of a TVD (total variation
diminishing) predictor-corrector procedure

and by means of a predictor-corrector technique based
on the method of characteristics. The

results from the transient model were verified with an
analytical solution for wave propagation in

conduits without friction and gravitational effects. The
numerical solutions were also compared

with those of a steady-state, homogeneous, two-phase model
for basaltic and rhyolitic magma

ascents in the fissures and circular conduits of Vesuvius
and Mt. St. Helens. An application of the

model to magma decompression in conduits indicates very
short times for gas exsolution,

fragmentation, and shock wave propagation, implying that
the modelling of gas exsolution should

involve non-equilibrium kinetics effects. Future coupling
of the transient magma ascent model

with magma chamber and pyroclastic dispersion models should
allow for more realistic

simulations of the time-dependent behavior of real volcanic
eruptions.

AN: 5052536

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Registro 60 de 100 en INSPEC 1995

TI: Hopf bifurcation in annular liquid jets with mass
transfer

AU: Ramos-JI

SO: International-Journal-for-Numerical-Methods-in-Fluids.
vol.20, no.12; 30 June 1995;

p.1293-314.

PY: 1995

LA: English

AB: A numerical study of Hopf bifurcations in annular
liquid jets with mass transfer is presented.

The study is based on the asymptotic equations which govern
the dynamics of inviscid,

incompressible, thin, annular liquid jets and on equilibrium
conditions for mass transfer at the jet's

inner and outer interfaces. It is shown that the amplitude
of the time-periodic motion that results

from the Hopf bifurcation increases whereas its frequency
decreases as the solubility ratio is

increased.

AN: 5017239

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Registro 61 de 100 en INSPEC 1995

TI: On the growth of underpressurized annular liquid jets

AU: Ramos-JI

SO: Applied-Mathematical-Modelling. vol.19, no.1; Jan.
1995; p.13-25.

PY: 1995

LA: English

AB: A numerical study of annular liquid jets used for
burning toxic wastes within the volume

enclosed by these jets is presented. The study considers
the dynamic behavior of both the liquid

and the gases enclosed by the jet both under steady-state
conditions and when the chemical

reactions are extinguished and employs a grid generation
technique that maps the time-dependent

curvilinear geometry of thin, axisymmetric, incompressible,
inviscid annular jets into a unit

square. The governing equations are solved in strong-conservation
law by means of finite

differences. The results show that underpressurized liquid
jets grow once the chemical reactions

taking place in the volume enclosed by these jets are
extinguished and that this growth depends on

the Froude (gravity), Weber (surface tension), and Peclet
(mass diffusion) numbers, the pressure

at the jet's outer interface, the initial pressure of
the gases enclosed by the annular jet, the

concentration of the gases dissolved in the liquid at
the nozzle exit, the jet's thickness and exit

angle at the nozzle exit, the solubilities of the gases
enclosed by and surrounding the jet, and the

temperature of the gases enclosed by the jet. It is shown
that, for the cases considered in this

paper, there is no leakage of gaseous combustion products
through the jet's outer interface, and

that the amount of gases dissolved in the liquid at the
nozzle exit and the solubility ratio play a

paramount role in determining the mass fluxes of toxic
products at the annular jet's interfaces.

AN: 4929796

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Registro 62 de 100 en INSPEC 1995

TI: Asymptotic methods for the analysis of wave propagation
in nonlinear, lossless transmission

lines and equivalent circuits

AU: Ramos-JI

SO: Microwave-and-Optical-Technology-Letters. vol.8, no.4;
March 1995; p.186-93.

PY: 1995

LA: English

AB: Perturbation methods are employed to determine the
small-signal behavior of an LC-ladder

nonlinear, lossless transmission line. It is shown that
a straightforward regular perturbation

analysis results in nonuniformly valid expansions, which
can be rendered uniformly valid by

stretching the time variable. Perturbation methods are
also used to show that, when dispersion

effects are accounted for, solitons may propagate along
the nonlinear, lossless transmission line.

The dispersion characteristics of some equivalent circuits
derived from a lossless transmission line

are also analyzed.

AN: 4926534

Mostrar Registro Completo

Registro 63 de 100 en INSPEC 1993-1994

TI: Classical forces on solitons in finite and infinite
nonlinear planar waveguides

AU: Ramos-JI; Villatoro-FR

SO: Microwave-and-Optical-Technology-Letters. vol.7, no.13;
Sept. 1994; p.620-5.

PY: 1994

LA: English

AB: Conservation equations for the mass, linear momentum,
and energy densities of solitons

propagating in finite, infinite, and periodic nonlinear
planar waveguides and governed by the

nonlinear Schrodinger equation are derived. These conservation
equations are used to determine

classical force densities that are compared with those
derived by drawing a quantum mechanics

analogy between the propagation of solitons and the motion
of a quantum particle in a nonlinear

potential well.

AN: 4821659

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Registro 64 de 100 en INSPEC 1993-1994

TI: Application of the two-dimensional Fourier transform
to nonlinear wave propagation

phenomena

AU: Molina-Fernandez-I; Camacho-Penalosa-C; Ramos-JI

SO: IEEE-Transactions-on-Microwave-Theory-and-Techniques.
vol.42, no.6; June 1994;

p.1079-85.

PY: 1994

LA: English

AB: A new technique based on the two-dimensional Fourier
transform is presented and applied to

the study of nonlinear wave propagation phenomena in one-dimensional,
finite, nonlinear

transmission lines. The technique permits determining
the effects of nonlinearities and boundary

conditions on the Fourier transform and identifying incident
and reflected waves and solitons

which may propagate through the transmission line at constant
speed. The effects of windows on

the Fourier transform are also assessed in both linear
and nonlinear transmission line models.

AN: 4737643

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Registro 65 de 100 en INSPEC 1993-1994

TI: A quantum mechanics analogy for the nonlinear Schrodinger
equation in the finite line

AU: Ramos-JI; Villatoro-FR

SO: Computers-&-Mathematics-with-Applications. vol.28,
no.4; Aug. 1994; p.3-17.

PY: 1994

LA: English

AB: A quantum mechanics analogy is used to determine the
forces acting on and the energies of

solitons governed by the nonlinear Schrodinger equation
in finite intervals with periodic and with

homogeneous Dirichlet, Neumann and Robin boundary conditions.
It is shown that the energy

densities remain nearly constant for periodic, while they
undergo large variations for

homogeneous boundary conditions. The largest variations
in the force and energy densities occur

for the Neumann boundary conditions, but, for all the
boundary conditions considered, the

magnitudes of these forces and energies recover their
values prior to the interaction of the soliton

with the boundary, after the soliton rebound process is
completed. It is also shown that the

quantum momentum changes sign but recovers its original
value after the collision of the soliton

with the boundaries. The asymmetry of the Robin boundary
conditions shows different dynamic

behaviour at the left and right boundaries of the finite
interval.

AN: 4736811

Mostrar Registro Completo

Registro 66 de 100 en INSPEC 1993-1994

TI: Forces on solitons in finite, nonlinear, planar waveguides

AU: Ramos-JI; Villatoro-FR

SO: Microwave-and-Optical-Technology-Letters. vol.7, no.8;
5 June 1994; p.378-81.

PY: 1994

LA: English

AB: The forces acting on and the energies of solitons
governed by the nonlinear Schrodinger

equation in finite planar waveguides with periodic and
with homogeneous Dirichlet, Neumann,

and Robin boundary conditions are determined by means
of a quantum analogy. It is shown that

these densities have S-shaped profiles and increase as
the hardness of the boundary conditions

increases.

AN: 4693674

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Registro 67 de 100 en INSPEC 1993-1994

TI: Nonlinear wave propagation in transmission lines

AU: Molina-Fernandez-I; Camacho-Penalosa-C; Ramos-JI

SO: Proceedings of the 1992 URSI International Symposium
on Electromagnetic Theory. URSI,

Washington, DC, USA; 1992; xxiv+585 pp. p.287-9.

PY: 1992

LA: English

AB: A new technique, based on the application of the bidimensional
Fourier transform (BFT), is

used to study wave propagation in a one-dimensional, nonlinear
transmission line consisting of

lumped elements. It is shown that BFT provides a convenient
tool for separating the incident wave

from the one reflected by the load, even in the nonlinear
case in which, due to the fact that the

superposition principle is no longer valid, these waves
cannot be defined exactly.

AN: 4553091

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Registro 68 de 100 en INSPEC 1993-1994

TI: Adaptive methods of lines for one-dimensional reaction-diffusion
equations

AU: Ramos-JI

SO: International-Journal-for-Numerical-Methods-in-Fluids.
vol.16, no.8; 30 April 1993;

p.697-723.

PY: 1993

LA: English

AB: Adaptive and nonadaptive finite difference methods
are used to study one-dimensional

reaction-diffusion equations whose solutions are characterized
by the presence of steep,

fast-moving flame fronts. Three nonadaptive techniques
based on the methods of lines are

described. The first technique uses a finite volume method
and yields a system of nonlinear,

first-order, ordinary differential equations in time.
The second technique uses time linearization,

discretizes the time derivatives and yields a linear,
second-order, ordinary differential equation in

space, which is solved by means of three-point, fourth-order
accurate, compact differences. The

third technique takes advantage of the disparity in the
time scales of the reaction and diffusion

processes, splits the reaction-diffusion operator into
a sequence of reaction and diffusion

operators and solves the diffusion operator by means of
either a finite volume method or a

three-point, fourth-order accurate compact difference
expression.

AN: 4428130

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Registro 69 de 100 en INSPEC 1990-1992

TI: Analysis of the formation and interaction of solitons
in nonlinear transmission lines by means

of a harmonic balance technique

AU: Molina-Fernandez-I; Camacho-Penalosa-C; Ramos-JI

SO: 6th Mediterranean Electrotechnical Conference. Proceedings.
(Cat. No.91CH2964-5). IEEE,

New York, NY, USA; 1991; 2 vol. xxxii+1584 pp. p.672-5
vol.1.

PY: 1991

LA: English

AB: A harmonic balance technique is used to study the
formation and interaction of solitons in

discrete, lossless, nonlinear transmission lines as a
function of the number of harmonics, number

of LC-cells, and pulse height and width at the generator.
It is shown that the number of harmonics

required to accurately determine the soliton formation
and propagation increases as the generator's

fundamental frequency is decreased, and that about 500
LC-cells are needed to observe the

propagation and interaction of solitons. It is also shown
that, for the calculations presented, the

transmission line is almost perfectly adapted. A Taylor
series expansion was used to determine the

continuous analog of the discrete transmission line presented.

AN: 4198735

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TI: Oscillating annular liquid membranes

AU: Ramos-JI; Falgueras-J

SO: Archive-of-Applied-Mechanics. vol.62, no.1; 1992;
p.43-52.

PY: 1992

LA: English

AB: The response of annular liquid membranes to sinusoidal
mass flow rate fluctuations at the

nozzle exit is analyzed as a function of the amplitude
and frequency of the axial velocity

fluctuations of the nozzle exit and thermodynamic compression
of the gas enclosed by the

membrane. It is shown that both the pressure of the gases
enclosed by the annular membrane and

the axial distance at which the annular membrane merges
on the symmetry axis are periodic

functions of time which have the same period as that of
the mass flow rate fluctuations at the

nozzle exit. They are also nearly sinusoidal functions
of time for small amplitudes of the mass

flow rate fluctuations at the nozzle exit, and exhibit
delay and lag times with respect to the

sinusoidal axial velocity fluctuations at the nozzle exit.
Both the delay and the lag times are

functions of the amplitude and frequency of the mass flow
rate fluctuations at the nozzle exit and

the polytropic exponent. The amplitudes of both the pressure
of the gases enclosed by the annular

liquid membrane and the convergence length increase and
decrease, respectively, as the amplitude

and frequency of the mass flow rate fluctuations at the
nozzle exit, respectively, are increased.

AN: 4153749

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Registro 71 de 100 en INSPEC 1990-1992

TI: Dynamics of liquid membranes. II. Adaptive finite
difference methods

AU: Ramos-JI

SO: International-Journal-for-Numerical-Methods-in-Fluids.
vol.12, no.9; 20 May 1991; p.881-94.

PY: 1991

LA: English

AB: For pt.I, see ibid., vol.12, no.9, p.859 (1991). Two
domain-adaptive finite difference methods

are presented and applied to study the dynamic response
of incompressible, inviscid, axisymmetric

liquid membranes subject to imposed sinusoidal pressure
oscillations. Both finite difference

methods map the time-dependent physical domain whose downstream
boundary is unknown onto

a fixed computational domain. The location of the unknown
time-dependent downstream

boundary of the physical domain is determined from the
continuity equation and results in an

integrodifferential equation which is non-linearly coupled
with the partial differential equations

which govern the conservation of mass and linear momentum
and the radius of the liquid

membrane. One of the finite difference methods solves
the non-conservative form of the

governing equations by means of a block implicit iterative
method. This method possesses the

property that the Jacobian matrix of the convection fluxes
has an eigenvalue of algebraic

multiplicity equal to four and of geometric multiplicity
equal to one. The second finite difference

procedure also uses a block implicit iterative method,
but the governing equations are written in

conservation law form and contain an axial velocity which
is the difference between the physical

axial velocity and the grid speed. These methods yield
almost identical results and are more

accurate than the non-adaptive techniques. The actual
value of the pressure coefficient determined

from linear analyses can be exceeded without affecting
the stability and convergence of liquid

membranes if the liquid membranes are subjected to sinusoidal
pressure variations of sufficiently

high frequencies.

AN: 3918398

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Registro 72 de 100 en INSPEC 1990-1992

TI: Dynamics of liquid membranes. I. Non-adaptive finite
difference methods

AU: Ramos-JI; Pitchumani-R

SO: International-Journal-for-Numerical-Methods-in-Fluids.
vol.12, no.9; 20 May 1991; p.859-79.

PY: 1991

LA: English

AB: A non-adaptive method and a Lagrangian-Eulerian finite
difference technique are used to

analyse the dynamic response of liquid membranes to imposed
pressure variations. The

non-adaptive method employs a fixed grid and upwind differences
for the convection terms,

whereas the Lagrangian-Eulerian technique uses operator
splitting and decomposes the mixed

convection-diffusion system of equations into a sequence
of convection and diffusion operators.

The convection operator is solved exactly by means of
the method of characteristics, and its

results are interpolated onto the fixed (Eulerian) grid
used to solve the diffusion operator.

Although the method of characteristics eliminates the
numerical diffusion associated with

upwinding the convection terms in a fixed Eulerian grid,
the Lagrangian-Eulerian method may

yield overshoots and undershoots near steep flow gradients
or when rapid pressure gradients are

imposed, owing to the interpolation of the results of
the convection operator onto the fixed grid

used to solve the diffusion operator. This interpolation
should be monotonic and

positivity-preserving and should satisfy conservation
of mass and linear momentum.

AN: 3918397

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Registro 73 de 100 en INSPEC 1990-1992

TI: Computation of turbulence noise

AU: Berman-CH; Ramos-JI

SO: Computational Acoustics. Proceedings of the 2nd IMACS
Symposium. North-Holland,

Amsterdam, Netherlands; 1990; 3 vol. (x+276+x+322+x+343)
pp. p.241-51 vol.2.

PY: 1990

LA: English

AB: Methods for computing the noise generated by turbulent
jets are identified and their viability

for practical applications is assessed. Emphasis is placed
on both noise source and extrapolation

techniques. Recommendations are presented for the minimum
size of the computational domain

required for accurate far field noise results.

AN: 3875025

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Registro 74 de 100 en INSPEC 1990-1992

TI: Finite difference and finite element methods for MHD
channel flows

AU: Ramos-JI; Winowich-NS

SO: International-Journal-for-Numerical-Methods-in-Fluids.
vol.11, no.6; 20 Oct. 1990; p.907-34.

PY: 1990

LA: English

AB: A Galerkin finite element method and two finite difference
techniques of the control volume

variety have been used to study magnetohydrodynamic channel
flows as a function of the

Reynolds number, interaction parameter, electrode length
and wall conductivity. The finite

element and finite difference formulations use unequally
spaced grids to accurately resolve the

flow field near the channel wall and electrode edges where
steep flow gradients are expected. It is

shown that the axial velocity velocity profiles are distorted
into M-shapes by the applied

electromagnetic field and that the distortion increases
as the Reynolds number, interaction

parameter and electrode length are increased. It is also
shown that the finite element method

predicts larger electromagnetic pinch effects at the electrode
entrance and exit and larger pressure

rises along the electrodes than the primitive-variable
and streamfunction-vorticity finite difference

formulations. However, the primitive-variable formulation
predicts steeper axial velocity gradients

at the channel walls and lower axial velocities at the
channel centreline than the

streamfunction-vorticity finite difference and the finite
element methods.

AN: 3778566

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TI: Finite element methods for one-dimensional combustion
problems

AU: Ramos-JI

SO: International-Journal-for-Numerical-Methods-in-Fluids.
vol.11, no.6; 20 Oct. 1990;

p.893-906.

PY: 1990

LA: English

AB: Three adaptive finite element methods based on equidistribution,
elliptic grid generation and

hybrid techniques are used to study a system of reaction-diffusion
equations. It is shown that these

techniques must employ sub-equidistributing meshes in
order to avoid ill-conditioned matrices

and ensure the convergence of the Newton method. It is
also shown that elliptic grid generation

methods require much longer computer times than hybrid
and static rezoning procedures. The

paper also includes characteristic, Petrov-Galerkin and
flux-corrected transport algorithms which

are used to study a linear convection-reaction-diffusion
equation that has an analytical solution.

The flux-corrected transport technique yields monotonic
solutions in good agreement with the

analytical solution, whereas the Petrov-Galerkin method
with quadratic upstream-weighted

functions results in very diffused temperature profiles.

AN: 3778565

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Registro 76 de 100 en INSPEC 1985-1989

TI: An analysis of laminar boundary layers on liquid curtains

AU: Ramos-JI; Pitchumani-R

SO: Zeitschrift-fur-Angewandte-Mathematik-und-Physik.
vol.40, no.5; Sept. 1989; p.721-39.

PY: 1989

LA: English

AB: A simplified analysis of the laminar boundary layer
along an isothermal liquid curtain falling

under gravity is presented. The analysis uses a von Karman-Pohlhausen
integral method and

includes the effects of gravity, pressure differences,
surface tension and nozzle exit geometry on

the convergence length of liquid curtains which have applications
as chemical reactors and as

protection systems in laser fusion reactors. It is shown
that the effects of the surrounding gases on

the curtain shape and convergence length are small, and
that good approximation to the liquid

curtain shape can be obtained by using inviscid flow analyses.

AN: 3497009

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Registro 77 de 100 en INSPEC 1985-1989

TI: Multicomponent gas bubbles. II. Bubble dynamics

AU: Ramos-JI

SO: Journal-of-Non-Equilibrium-Thermodynamics. vol.13,
no.2; 1988; p.107-31.

PY: 1988

LA: English

AB: For pt.I. see ibid., vol.13, p.1-25 (1988). The growth
of rising gas bubbles in soda-lime glass

melts is analyzed by means of a lumped parameter model
which accounts for the surface tension.

It is shown that for glass melt temperatures higher than
1400 degrees C, the bubble radius

increases linearly with time and with the initial bubble
radius. Refining times are shown to

decrease with the initial bubble radius and glass melt
temperature and to be independent of mass

transfer. However, considering the bubble boundary motion
results in shorter refining times than

if this motion is disregarded. The bubble location is
shown to be a linear function of time and

controlled by buoyancy. For glass melt temperatures lower
than 1400 degrees C, the bubbles first

shrink and then grow. The amount of growth depends on
the initial bubble radius, initial bubble

composition, glass melt height and glass melt temperature.
Water vapor bubbles shrink more than

nitrogen, oxygen, carbon dioxide and sulfide bubbles in
agreement with the results shown in Part I

for isolated bubbles. The results of the calculations
here indicate that for glass melt temperatures

higher than 1400 degrees C, gas bubbles migrate to the
melt surface. However, for lower

temperatures mass transfer has an important effect on
determining the bubble dynamics and

refining agents may be necessary to cause bubble dissolution
or growth by chemical reaction.

AN: 3173716

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Registro 78 de 100 en INSPEC 1985-1989

TI: Multicomponent gas bubbles. I. Growth of stationary
bubbles

AU: Ramos-JI

SO: Journal-of-Non-Equilibrium-Thermodynamics. vol.13,
no.1; 1988; p.1-25.

PY: 1988

LA: English

AB: The growth of isolated, stationary gas bubbles which
initially consist of nitrogen, oxygen,

carbon dioxide, sulfide or water vapor is analyzed accounting
for the bubble surface motion. The

bubbles are submerged in an isothermal, soda-lime glass
melt. It is shown the bubbles may first

shrink and then grow depending on their initial composition.
The size of bubbles which initially

consist of nitrogen or carbon dioxide increases monotonically
with time until an equilibrium is

reached with the glass melt gaseous species. The bubble
radius is a linear function of time for

large times. It is also shown that, for the same glass
melt temperature, all bubbles reach the same

final composition. However, the time required to reach
the final composition depends on the

initial bubble composition and glass melt temperature.
For a carbon dioxide bubble, the final

concentration of sulfide increases with the glass melt
temperature, whereas those of nitrogen,

oxygen, carbon dioxide and water vapor decrease with the
glass melt temperature.

AN: 3154050

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Registro 79 de 100 en INSPEC 1985-1989

TI: Modified equation techniques for reaction-diffusive
systems. II. Time-linearization and

operator-splitting methods

AU: Ramos-JI

SO: Computer-Methods-in-Applied-Mechanics-and-Engineering.
vol.64, no.1-3; Oct. 1987;

p.221-36.

PY: 1987

LA: English

AB: For pt.I see ibid., vol.64, p.195-219 (1987). Modified
equation methods are applied with

time-linearization and operator-splitting techniques to
the study of a reaction-diffusion equation

which has an exact travelling wave solution. Comparisons
between the exact and computed

solutions have been made in terms of L/sup 2/-norm errors
and wave speeds. It is shown that

modified time-linearization methods are less accurate
than time-linearized techniques if the time

derivatives are evaluated by means of first-order accurate
approximations. However, if

second-order accurate discretizations are used to evaluate
the time derivatives, modified

time-linearization methods are more accurate than the
Beam-Warming (1978) and

Briley-McDonald (1977-80) schemes. Second-order accurate
(in time) modified time-linearization

methods yield L/sup 2/-norm errors which are almost independent
of time and of the time step

used in the calculations. The accuracy of modified time-linearization
techniques deteriorates as

both the step step and grid spacing are increased.

AN: 3041086

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Registro 80 de 100 en INSPEC 1985-1989

TI: Modified equation techniques for reactive-diffusive
systems. I. Explicit, implicit and

quasilinear methods

AU: Ramos-JI

SO: Computer-Methods-in-Applied-Mechanics-and-Engineering.
vol.64, no.1-3; Oct. 1987;

p.195-219.

PY: 1987

LA: English

AB: A family of modified equation techniques for one-dimensional
reaction-diffusion equations

has been developed and applied to the study of a single
reaction-diffusion equation which has an

exact travelling wave solution. Modified equation methods
have also been applied to study the

propagation of a laminar flame through an ozone-oxygen
mixture. It is shown that modified

implicit techniques are less accurate than the standard
implicit method if the time derivatives are

evaluated by means of a first-order accurate formula.
If the time derivatives are approximated by

second-order accurate expressions, modified equation methods
yield L/sup 2/-norm errors which

are almost independent of the time step used in the calculations;
they are also independent of time.

Large accuracy improvements can be obtained by using modified
equation methods. These

improvements are achieved at the expense of involving
five grid points and requiring iterations if

quasilinear techniques are used in the calculations. A
linear stability analysis of the modified

equation methods presented shows that the modified explicit
scheme requires smaller time steps

than the standard explicit method.

AN: 3041085

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Registro 81 de 100 en INSPEC 1985-1989

TI: Numerical solution of reaction-diffusion equations
by compact operators and modified

equation methods

AU: Ramos-JI; Shih-TI-P

SO: International-Journal-for-Numerical-Methods-in-Fluids.
vol.7, no.4; April 1987; p.337-51.

PY: 1987

LA: English

AB: A system of reaction-diffusion equations which governs
the propagation of an ozone

decomposition laminar flame in Lagrangian co-ordinates
is analysed by means of compact

operators and modified equation methods. It is shown that
the use of fourth-order accurate

compact operators yields very accurate solutions if sufficient
numbers of grid points are located at

the flame front, where very steep gradients of temperature
and species concentrations exist.

Modified equation methods are shown to impose a restriction
on the time step under certain

conditions. The solutions obtained by means of compact
operators and modified equation

methods are compared with solutions obtained by other
methods; good agreement is obtained.

AN: 2923295

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Registro 82 de 100 en INSPEC 1985-1989

TI: On the accuracy of block implicit and operator-splitting
algorithms in confined flame

propagation problems

AU: Ramos-JI

SO: International-Journal-of-Computer-Mathematics. vol.20,
no.3-4; 1986; p.299-324.

PY: 1986

LA: English

AB: The propagation of a one-dimensional, confined, laminar
flame is studied by means of two

operator-splitting methods, four linear block implicit
schemes and the standard implicit and

Crank-Nicolson techniques. The accuracy and stability
of the methods are compared.

AN: 2913683

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Registro 83 de 100 en INSPEC 1985-1989

TI: A numerical study of a swirl stabilized combustor

AU: Ramos-JI

SO: Journal-of-Non-Equilibrium-Thermodynamics. vol.10,
no.4; 1985; p.263-86.

PY: 1985

LA: English

AB: A mathematical model has been developed to study exhaust
gas emissions from a swirl

stabilized combustor. The combustor consists of two confined,
coaxial jets with premixed methane

and air in the inner jet, and air in the outer jet. A
two-equation model of turbulence, a quasi-global

kinetics mechanism for the oxidation of methane, and the
Zel'dovich mechanism for the nitric

oxide formation have been used to study the emissions
from a gas turbine under a variety of

operating conditions. The model predictions are compared
with available experimental data and

show that counter-swirls (jets rotating in opposite directions)
produces a larger recirculation zone

at the combustor centerline, lower nitric oxide emissions,
and relatively higher levels of carbon

dioxide and methane than co-swirls. The predictions are
in good agreement with experimental

data.

AN: 2732576

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Registro 84 de 100 en INSPEC 1985-1989

TI: Magnetohydrodynamic channel flow study

AU: Ramos-JI; Winowich-NS

SO: Physics-of-Fluids. vol.29, no.4; April 1986; p.992-7.

PY: 1986

LA: English

AB: A finite-difference study of a steady, incompressible,
viscous, magnetohydrodynamic (MHD)

channel flow which has direct application to DC electromagnetic
pumps is presented. The study

involves the numerical solution of the coupled Navier-Stokes
and Maxwell equations at low

magnetic Reynolds numbers. It is shown that the axial
velocity profiles have a characteristic M

shape as the fluid approaches and passes the electrode.
The electric potential varies almost linearly

from the channel centerline to the channel wall. The current
shows a steep gradient near the

electrodes. Comparison between the finite-difference solution
and a quasi-one-dimensional

approach are presented. The two-dimensional numerical
calculations predict a larger pressure rise,

a smaller net current, and a smaller pump efficiency than
the quasi-one-dimensional model.

AN: 2701499

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Registro 85 de 100 en INSPEC 1985-1989

TI: Probability density function calculations in turbulent
chemically reacting round jets, mixing

layers and one-dimensional reactors

AU: Givi-P; Ramos-JI; Sirignano-WA

SO: Journal-of-Non-Equilibrium-Thermodynamics. vol.10,
no.2; 1985; p.75-104.

PY: 1985

LA: English

AB: A single-point joint probability density function
equation for two scalars is solved by means

of a Monte Carlo method to study turbulent reacting, incompressible,
isothermal, round jets,

mixing layers and one-dimensional reactors. Calculations
have been performed by means of

two-equation models of turbulence and different molecular
mixing frequencies in gaseous and

liquid reacting flows employing ozone and nitric oxide,
and hydrochloric and sodium hydroxide,

respectively. The calculations have been compared with
available experimental data on reacting

turbulent round jets, mixing layers and one-dimensional
reactors. Good agreement between the

probability density function (PDF) calculations based
on a molecular mixing frequency

corresponding to the large scale eddies and experimental
data are obtained in the round jet for the

mean ozone concentrations. The numerical predictions overpredict
the product concentration in

the reacting mixing layers, but are in qualitative agreement
with the experimental data and show

the same trends in the PDF profile.

AN: 2700921

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Registro 86 de 100 en INSPEC 1985-1989

TI: Multicomponent gas bubble dynamics in glass melts

AU: Ramos-JI

SO: Numerical Methods in Laminar and Turbulent Flow. Proceedings
of the Fourth International

Conference. Pineridge Press, Swansea, UK; 1985; 2 vol.
1851 pp. p.1194-205 vol.2.

PY: 1985

LA: English

AB: The motion and growth of a gas bubble in a glass melt
containing several dissolved gases is

considered. The equations governing the bubble radius
and location as a function of time have

been formulated to account for the effects of forced convection
mass transport. The bubble

motion is assumed to be governed by Stokes drag law. It
is shown that small bubbles always grow

with time whereas larger ones may first shrink and then
grow. The bubble radius was found to

increase with the glass melt temperature and height, and
to decrease with the initial bubble radius.

The influence of the initial bubble composition was found
to be minor in determining the gas

bubble behavior.

AN: 2667545

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Registro 87 de 100 en INSPEC 1985-1989

TI: A heuristic control strategy for non-linear reaction-diffusion
equations

AU: Ramos-JI

SO: International-Journal-of-Control. vol.43, no.2; Feb.
1986; p.473-83.

PY: 1986

LA: English

AB: A heuristic control strategy is proposed to control
the speed of a wave front that is governed

by a one-dimensional advection-diffusion-reaction equation.
The strategy employs the

time-dependent temperatures measured by two sensors located
at different positions. These

temperatures are used to vary the wave speed in such a
manner that the wave front is located

between the two sensors. Results are presented for different
sensor locations and time constants

and show that the control strategy drives the wave front
to its analytic solution.

AN: 2640047

Mostrar Registro Completo

Registro 88 de 100 en INSPEC 1985-1989

TI: Numerical solution of reactive-diffusive systems.
III. Time linearization and operator-splitting

techniques

AU: Ramos-JI

SO: International-Journal-of-Computer-Mathematics. vol.18,
no.3-4; 1986; p.289-309.

PY: 1986

LA: English

AB: For pt.II see ibid., vol.18, p.141-61 (1985). Four
time linearization techniques and two

operator-splitting algorithms have been employed to study
the propagation of a non-dimensional

wave governed by a reaction-diffusion equation. Comparisons
amongst the methods are shown in

terms of the L/sup 2/-norm error and computed wave speeds.
The calculations have been

performed with different numerical grids in order to determine
the effects of the temporal and

spatial step sizes on the accuracy. It is shown that a
time linearization procedure with a

second-order accurate temporal approximation and a fourth-order
accurate spatial discretization

yields the most accurate results. The numerical calculations
are compared with those reported in

parts 1 and 2. It is concluded that the most accurate
time linearization method described in this

paper offers a great promise for the computation of multi-dimensional
reaction-diffusion

equations.

AN: 2630499

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Registro 89 de 100 en INSPEC 1985-1989

TI: Numerical solution of reactive-diffusive systems.
II. Methods of lines and implicit algorithms

AU: Ramos-JI

SO: International-Journal-of-Computer-Mathematics. vol.18,
no.2; 1985; p.141-61.

PY: 1985

LA: English

AB: For pt.I see ibid., vol.18, p.43-65 (1985). Two implicit
procedures, a finite element method,

an implicit predictor-corrector technique and three methods
of lines have been employed to study

the propagation of a one-dimensional wave governed by
a reaction-diffusion equation.

Comparisons amongst the methods are presented in terms
of the L/sup 2/-norm errors and

computed wave speeds. The calculations have been performed
with different numerical grids in

order to determine the effects of the temporal and spatial
step sizes on the accuracy. It is shown

that a fourth-order accurate, in both space and time,
method of lines yields the most accurate

results. The numerical calculations are also compared
with those reported in pt.I.

AN: 2591038

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Registro 90 de 100 en INSPEC 1985-1989

TI: Numerical solution of reactive-diffusive system. I.
Explicit methods

AU: Ramos-JI

SO: International-Journal-of-Computer-Mathematics. vol.18,
no.1; 1985; p.43-65.

PY: 1985

LA: English

AB: Seven explicity numerical procedures are employed
to calculate the propagation of a

one-dimensional wave which is governed by a reaction-diffusion
equation. Comparisons amongst

the method are presented in terms of the L/sup 2/-norm
error and computed wave speeds. The

calculations have been performed with different numerical
grids in order to determine the effects

of the temporal and spatial step sizes on the accuracy
and computed wave speed. It is shown that a

second-order accurate, in both space and time, explicit
predictor-corrector method produces the

least L/sup 2/-norm errors. It is also shown that a modified
Saul'yev average scheme yields the

most accurate and constant wave speed.

AN: 2582187

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Registro 91 de 100 en INSPEC 1985-1989

TI: Swirling flow in a research combustor

AU: Ramos-JI; Somer-HT

SO: AIAA-Journal. vol.23, no.2; Feb. 1985; p.241-8.

PY: 1985

LA: English

AB: Measurements of turbulent, confined, swirling flows
have been obtained by means of a

two-color laser Doppler velocimeter in a research combustor
and compared with other

experimental data and numerical results obtained by means
of two two-equation models of

turbulence. The combustor consists of two confined, concentric,
swirling jets whose mass flow

rates and swirl numbers can be controlled independently,
and which can be used to study cold

flow, premixed and non-premixed reactive flows, and two-phase
flows. Results are reported for

cold flow conditions under co- and counterswirl.

AN: 2503048

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Registro 92 de 100 en INSPEC 1985-1989

TI: On the calculation of heat, mass and momentum transport
in coaxial jets and mixing layers

AU: Givi-P; Ramos-JI

SO: International-Communications-in-Heat-and-Mass-Transfer.
vol.12, no.3; May-June 1985;

p.323-36.

PY: 1985

LA: English

AB: Deals with the determination of mass, momentum and
heat transport in turbulent mixing

layers and with the determination of momentum transport
in concentric round jets. Mixing length,

k/ epsilon and k/ omega models are employed in the calculations.
The constants appearing in these

models are evaluated to yield the correct spreading rate,
mean axial velocity, concentration and

temperature profiles. A single-point probability density
function (PDF) has been employed to

calculate heat and mass transport in mixing layers. It
is shown that the concentric jet mean velocity

profiles are accurately predicted if the constants multiplying
the production terms in the epsilon -

and omega -equation have values of 1.52 and 1.50. These
constants have to be taken equal to 1.44

and 3.80 for mixing layers. The calculated turbulent Schmidt/Prandtl
number is 0.70 for mixing

layers.

AN: 2499997

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Registro 93 de 100 en INSPEC 1985-1989

TI: Development and application of an adaptive finite
element method to reaction-diffusion

equations

AU: Ramos-JI

SO: International-Journal-for-Numerical-Methods-in-Fluids.
vol.5, no.1; Jan. 1985; p.13-23.

PY: 1985

LA: English

AB: An adaptive finite element method is developed and
applied to study the ozone

decomposition laminar flame. The method uses a semidiscrete,
linear Galerkin approximation in

which the size of the elements is controlled by an integral
which minimizes the changes in mesh

spacing. The sizes and locations of the elements are controlled
by the location and magnitude of

the largest temperature gradient. The numerical results
obtained with this adaptive finite element

method are compared with those obtained using fixed-node
finite-difference schemes and an

adaptive finite-difference method. It is shown that the
adaptive finite element method developed

using 36 elements can yield as accurate flame speeds as
fourth-order accurate, fixed-node,

finite-difference methods when 272 collocation points
are employed in the calculations.

AN: 2451868

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Registro 94 de 100 en INSPEC 1985-1989

TI: Torsional oscillations in symmetrical structures

AU: Ramos-JI

SO: Applied-Mathematical-Modelling. vol.8, no.6; Dec.
1984; p.433-41.

PY: 1984

LA: English

AB: A two-time perturbation technique is used to study
the lateral and torsional motions of a

nonlinear symmetrical structure subject to a lateral sinusoidal
ground motion. It is shown that

when the ground acceleration frequency is about one-third
of or three times the natural frequency

of the lateral motion, the symmetrical structure is particularly
susceptible to torsional oscillations

even when the natural frequency of torsion is not close
to the natural frequency of the lateral

motion. The implication of this type of nonlinear coupling
between the lateral and torsional

motions in real structures subject to earthquakes is also
discussed.

AN: 2414369

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Registro 95 de 100 en INSPEC 1985-1989

TI: On some accurate finite-difference methods for laminar
flame calculations

AU: Ramos-JI

SO: International-Journal-for-Numerical-Methods-in-Fluids.
vol.4, no.10; Oct. 1984; p.915-30.

PY: 1984

LA: English

AB: The ozone-decomposition flame has been studied by
means of fourth- and second-order

accurate schemes. The fourth-order methods include a method
of lines, a time-linearization

algorithm, and a majorant operator-splitting technique.
The second-order schemes include two

time-linearization methods which use different temporal
approximations. It is shown that the

fourth-order techniques yield comparable results to those
obtained with very accurate finite

element and adaptive grid finite-difference algorithms.
The results of the second-order methods

are in good agreement with second-order explicit predictor-corrector
methods but predict a lower

flame speed than that obtained by means of fourth-order
techniques. It is also shown that the

temporal approximations are not as important as the spatial
approximations in flame propagation

problems characterized by the presence of several small
time scales.

AN: 2397993

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Registro 96 de 100 en INSPEC 1985-1989

TI: Turbulent nonreacting swirling flows

AU: Ramos-JI

SO: AIAA-Journal. vol.22, no.6; June 1984; p.846-8.

PY: 1984

LA: English

AB: The author presents some numerical results for incompressible,
confined, swirling flows in a

model combustor. These results have been obtained by means
of the k- epsilon and k-l models of

turbulence and compared with the experimental data of
Vu and Gouldin (1980). The calculations

have been performed in a model combustor which consists
of a 3.43 cm diam inner pipe and a

14.5 cm diam outer pipe. The outside diameter of the inner
pipe is 3.86 cm. The turbulence

models used in the author's study use an isotropic eddy
diffusivity whose validity in swirling

flows has been seriously questioned. The models solve
the axisymmetric form of the conservation

equations of mass; axial, radial, and tangential momentum;
turbulent kinetic energy k; turbulent

length scale t; or dissipation rate of turbulent kinetic
energy epsilon . Similar calculations have

been performed by Srinivasan and Mongia (1980) who employed
the k- epsilon model and who

also compared their theoretical results with the experimental
data of Vu and Gouldin. Srinivasan

and Mongia concluded that the k- epsilon model had to
be modified to include the effects of the

curvature Richardson number in order to predict a recirculation
zone for both coswirl (jets

rotating in the same direction) and counterswirl (jets
rotating in opposite directions) conditions.

However, the k- epsilon model does predict a recirculation
zone for both co- and counterswirl

flow conditions if suitable inlet conditions are used.

AN: 2367273

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Registro 97 de 100 en INSPEC 1980-1984

TI: On the calculation of heat and momentum transport
in a round jet

AU: Givi-P; Ramos-JI

SO: International-Communications-in-Heat-and-Mass-Transfer.
vol.11, no.2; March-April 1984;

p.173-82.

PY: 1984

LA: English

AB: This communication deals with the determination of
the turbulent Prandtl number and some

constants which appear in the mixing length, k/ epsilon
and k/w turbulence models. The

determination is carried out in a heated round jet by
means of a finite-difference algorithm whose

results are compared with the available experimental data.
It is shown that in round jets the

constants that multiply the production terms in the epsilon
- and w- equations have values of 1.52

and 1.50, and the turbulent Prandtl number is 0.80.

AN: 2266221

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Registro 98 de 100 en INSPEC 1980-1984

TI: A numerical study of one-dimensional enclosed flames

AU: Ramos-JI

SO: Numerical Properties and Methodologies in Heat Transfer.
Proceedings of the Second

National Symposium. Hemisphere Publishing Corp, Washington,
DC, USA; 1983; ix+554 pp.

p.529-46.

PY: 1983

LA: English

AB: The propagation of a laminar flame in a closed container
has been analyzed by means of nine

finite-difference schemes. A lagrangian transformation
has been used to eliminate the convection

terms from the governing equations, giving rise to a system
of integrodifferential

reaction-diffusion equations. The chemistry has been modeled
by one-step Arrhenius-type

reaction. The numerical schemes evaluated include two
methods of lines where the reaction terms

are integrated point by point, an implicit predictor-corrector
algorithm, a quasilinearization

procedure, a linear block tridiagonal implicit algorithm,
an operator splitting technique and the

standard explicit, implicit and Crank-Nicolson schemes.
All of the numerical methods use second

order accurate spatial approximations and different temporal
approximations. The results show

that the explicit, implicit and Crank-Nicolson schemes
underpredict the location of the flame front

and the pressure, whereas the quasilinear, linear block
and implicit predictor-corrector techniques

overpredict them slightly. It is also shown that the explicit
method is by far the most efficient in

terms of computer time among the numerical algorithms
considered.

AN: 2210818

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Registro 99 de 100 en INSPEC 1980-1984

TI: Application of the finite-element method to one-dimensional
flame propagation problems

AU: Lee-DN; Ramos-JI

SO: AIAA-Journal. vol.21, no.2; Feb. 1983; p.262-9.

PY: 1983

LA: English

AB: A linear semidiscrete Galerkin method and an adaptive
finite-element method are first used to

compute the steady-state wave speed of a reaction-diffusion
equation which has an exact traveling

wave solution. The Galerkin method is then applied to
study the propagation of a laminar flame in

a closed combustor. The numerical results obtained with
the Galerkin and adaptive finite-element

methods are compared with those obtained with a finite-difference
Crank-Nicolson scheme. The

comparisons show that the finite-element methods overpredict
the wave speed, whereas the

Crank-Nicolson scheme underpredicts it. The Galerkin method
results are closer to the exact

solution than those of the Crank-Nicolson scheme for a
901 point grid. The adaptive finite element

requires about 171 points to obtain a wave speed equal
to that of the Galerkin method with 901

points. The application of the Galerkin method to the
propagation of one-dimensional enclosed

deflagrations shows that, in order to account properly
for the steep temperature gradients at the

flame front, at least 400 grid points are required. The
largest temperature difference between the

finite-difference and finite-element results is less than
2%. This difference is attributed to the

oscillations present in the finite-element method, the
linearization of the reaction terms and the use

of linear basis.

AN: 2055059

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TI: The calculation of the pressure in unsteady flows
using a control-volume approach

AU: Ramos-JI; Sirignano-WA

SO: Journal-of-Computational-Physics. vol.41, no.1; May
1981; p.211-16.

PY: 1981

LA: English

AB: A new method is proposed to calculate the pressure
correction in unsteady flows using the

finite-difference scheme of Gosman and Ideriah's TEACH-T
code (1976). The method was

originally developed by the authors (1979) to study the
flow field in axisymmetric internal

combustion engine configurations; however, its extension
to other geometries and three

dimensions is obvious. In many flow fields, pressure variations
are produced by the compression

and expansion of the gas, as in an internal combustion
engine; however, pressure variations are

also produced by the fluid motions. Since the pressure
drives the flow, one must accurately

predict the small-scale pressure variations in order to
resolve the flow field. To calculate the

pressure, the authors propose to correct the pressure
field after the solution of the momentum

equations has been obtained in two ways: by a uniform
global pressure correction, and by local

pressure corrections.

AN: 1726960

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