Datos obtenidos el lunes 11 de febrero de 2002
 

Registro 1 de 40 en EI COMPENDEX (2001/07-2002/01) TI: Dynamics of spiral waves in excitable media with local time-periodic modulation AU: Ramos-JI SO: Chaos,-Solitons-and-Fractals. v 13 n 7 June 2002, p 1383-1392. IS: 0960-0779 AB: The propagation of spiral waves in excitable media with locally inhomogeneous time-periodic modulations is studied numerically, and it is shown that the size of the local inhomogeneity and the amplitude and frequency of the periodic forcing play a major role in determining the spiral wave dynamics, suppression and breakup. It is also shown that, in the absence of breakup, spiral waves flatten and thicken as the size of the inhomogeneity is increased, and that spiral waves may penetrate into the modulation region if the forcing frequency is sufficiently small. At high frequencies, however, it is shown that the inhomogeneity behaves as an obstacle. It is also reported that, for sufficiently large modulation regions, the spiral wave may be annihilated and become an almost cylindrical wave with initially high concentration of the activator in the center of the inhomogeneity. copy 2002 Elsevier Science Ltd. All rights reserved. 18 Refs. PY: 2002 LA: English AN: E2001546795537 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 2 de 40 en EI COMPENDEX (2001/07-2002/01) TI: Wave propagation and suppression in excitable media with holes and external forcing AU: Ramos-JI SO: Chaos,-Solitons-and-Fractals. v 13 n 6 May 2002, p 1243-1251. IS: 0960-0779 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. copy 2002 Elsevier Science Ltd. All rights reserved. 15 Refs. PY: 2002 LA: English AN: E2001546792438 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 3 de 40 en EI COMPENDEX (2001/07-2002/01) TI: Propagation of spiral waves in anisotropic media: From waves to stripes AU: Ramos-JI SO: Chaos,-Solitons-and-Fractals. v 12 n 6 2001, p 1057-1064. IS: 0960-0779 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. (Author abstract) 6 Refs. PY: 2001 LA: English AN: E2001385594947 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 4 de 40 en EI COMPENDEX (2001/07-2002/01) TI: The sine-Gordon equation in the finite line AU: Ramos-JI SO: Applied-Mathematics-and-Computation-(New-York). v 124 n 1 Nov 10 2001, p 45-93. IS: 0096-3003 AB: A numerical study of the perturbed and nonperturbed sine Gordan equation in one-dimesional Cartesian coordinate and finite domain was presented. Linearity implicit finite difference methods of differential accuracy formed the basis of this analysis. The spatially homogenous solution of unperturbed sGE was analyzed for linearized stability and the methods of separation of variables was used to obtain the analytical solutions. The results depicted that the accurate computation of homoclinic orbits of the sGE were controlled by both spatial accuracy of numerical methods and energy preserving characterstics. (Edited abstract) 36 Refs. PY: 2001 LA: English AN: E2001416677353 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 5 de 40 en EI COMPENDEX (2001/07-2002/01) TI: Stability and nonlinear dynamics of planar film casting processes AU: Ramos-JI SO: International-Journal-of-Engineering-Science. v 39 n 17 November 2001, p 1949-1961. IS: 0020-7225 AB: A linear stability analysis of isothermal planar film casting processes at zero Reynolds numbers is performed, and shown to be governed by the same eigenvalue equation as that of the spinning of round jets. Numerical studies on the nonlinear dynamics of planar film casting processes are reported as functions of the nondimensional parameters that characterize the fluid dynamics equations and the amplitude and frequency of imposed axial velocity perturbations at either the upstream or downstream boundaries. It is shown that the power spectrum broadens and the phase diagram may present holes at low Reynolds numbers, thus indicating the presence of chaos and strange attractors. copy 2001 Elsevier Science Ltd. All rights reserved. 9 Refs. PY: 2001 LA: English AN: E2001366638944 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 6 de 40 en EI COMPENDEX (2001/07-2002/01) TI: Singularities and stability of inviscid, planar liquid membranes AU: Ramos-JI SO: International-Journal-of-Engineering-Science. v 39 n 17 November 2001, p 1935-1948. IS: 0020-7225 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. copy 2001 Elsevier Science Ltd. All rights reserved. 9 Refs. PY: 2001 LA: English AN: E2001366638943 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 7 de 40 en EI COMPENDEX (2001/07-2002/01) TI: Spatio-temporal patterns in excitable media with non-solenoidal flow straining AU: Ramos-JI SO: Mathematics-and-Computers-in-Simulation. v 55 n 4-6 2001, p 607-619. IS: 0378-4754 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 distorsion 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. copy 2001 IMACS. Published by Elsevier Science B.V. All rights reserved. 14 Refs. PY: 2001 LA: English AN: E2001356633282 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 8 de 40 en EI COMPENDEX (2001/07-2002/01) TI: Interaction of spatial solitons with a localized spatially-modulated medium AU: Ramos-JI SO: Mathematics-and-Computers-in-Simulation. v 56 n 6 2001, p 571-583. IS: 0378-4754 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. copy 2001 IMACS. Published by Elsevier Science B.V. All rights reserved. 8 Refs. PY: 2001 LA: English AN: E2001356632927 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 9 de 40 en EI COMPENDEX (2001/07-2002/01) TI: Tile patterns in excitable media subject to non-solenoidal flow fields AU: Ramos-JI SO: Chaos,-Solitons-and-Fractals. v 12 n 12 September 2001, p 2267-2281. IS: 0960-0779 AB: The propagation of spiral waves in excitable media subject to a non-solenoidal 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. copy 2001 Elsevier Science Ltd. 15 Refs. PY: 2001 LA: English AN: E2001346622236 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 10 de 40 en EI COMPENDEX (2001/07-2002/01) TI: Convection-induced anisotropy in excitable media subject to solenoidal advective flow fields AU: Ramos-JI SO: Chaos,-Solitons-and-Fractals. v 12 n 10 August 2001, p 1897-1908. IS: 0960-0779 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. copy 2001 Elsevier Science Ltd. 16 Refs. PY: 2001 LA: English AN: E2001316601411 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 11 de 40 en EI COMPENDEX (2001/07-2002/01) TI: Nonlinear dynamics of hollow, compound jets at low Reynolds numbers AU: Ramos-JI SO: International-Journal-of-Engineering-Science. v 39 n 12 August 2001, 2001 p 1289-1314. IS: 0020-7225 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. copy 2001 Elsevier Science Ltd. 15 Refs. PY: 2001 LA: English AN: E2001266557339 Mostrar Registro Completo

Registro 12 de 40 en EI COMPENDEX (1999-2001/06) TI: Heat and mass transfer in annular liquid jets: III. Combustion within the volume enclosed by the jet AU: Ramos-JI SO: Applied-Mathematics-and-Computation-(New-York). v 110 n 2 2000, p 185-204. IS: 0096-3003 AB: 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. (Author abstract) 11 Refs. PY: 2000 LA: English AN: E2000225144315 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 13 de 40 en EI COMPENDEX (1999-2001/06) TI: Heat and mass transfer in annular liquid jets: II. g-jitter AU: Ramos-JI SO: Applied-Mathematics-and-Computation-(New-York). v 110 n 2 2000, p 165-183. IS: 0096-3003 AB: 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. (Author abstract) 16 Refs. PY: 2000 LA: English AN: E2000225144314 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 14 de 40 en EI COMPENDEX (1999-2001/06) TI: Heat and mass transfer in annular liquid jets: I. Formulation AU: Ramos-JI SO: Applied-Mathematics-and-Computation-(New-York). v 110 n 2 2000, p 133-164. IS: 0096-3003 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 integrodifferential 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. (Author abstract) 20 Refs. PY: 2000 LA: English AN: E2000225144313 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 15 de 40 en EI COMPENDEX (1999-2001/06) TI: Two-dimensional simulations of magma ascent in volcanic conduits AU: Ramos-JI SO: International-Journal-for-Numerical-Methods-in-Fluids. v 29 n 7 1999, p 765-789. CF: Proceedings of the 1997 10th International Congress on Nmerical Methods in Laminar and Turbulent Flow. Swansea, UK IS: 0271-2091 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. (Author abstract) 15 Refs. PY: 1999 LA: English AN: EIX99374734170 Mostrar Registro Completo

Registro 16 de 40 en EI COMPENDEX (1999-2001/06) TI: Asymptotic analysis of compound liquid jets at low Reynolds numbers AU: Ramos-JI SO: Applied-Mathematics-and-Computation-(New-York). v 100 n 2-3 May 1999, p 223-240. IS: 0096-3003 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. (Author abstract) 13 Refs. PY: 1999 LA: English AN: EIX99254648886 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 17 de 40 en EI COMPENDEX (1997-1998/12) TI: Leading-order equivalence of two formulations for long, annular liquid membranes AU: Ramos-JI SO: Applied-Mathematical-Modelling. v 22 n 6 Jun 1998, p 453-457. IS: 0307-904X AB: A model, recently developed for annular liquid membranes, is generalized to account for the gravitational acceleration, and the governing equations are based on the axial and radial velocity components rather than on those along and normal to the membrane and the resulting equations are compared with those of the model of Ramos. A long-wave analysis of the equations is carried out for inertia and capillary, annular liquid membranes. It is shown that the models developed are governed by the same leading-order equations for long, annular liquid membranes. 5 Refs. PY: 1998 LA: English AN: EIX98434359235 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 18 de 40 en EI COMPENDEX (1997-1998/12) TI: Annular liquid jets and other axisymmetric free-surface flows at high Reynolds numbers AU: Ramos-JI SO: Applied-Mathematical-Modelling. v 22 n 6 Jun 1998, p 423-452. IS: 0307-904X 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 inertia, 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. (Author abstract) 18 Refs. PY: 1998 LA: English AN: EIX98434359234 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 19 de 40 en EI COMPENDEX (1997-1998/12) TI: Short communication 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-and-Fluid-Flow. v 7 n 8 1997, p 794-800. IS: 0961-5539 AB: In a study conducted recently by Montgomery and Fleeter, a finite-analytic method was used to analyze steady, two-dimensional, inviscid, compressible, subsonic flow in a nozzle. As a follow-up, the present study shows that the cell boundary conditions employed in the previous study are not exact. By means of a simple one-dimensional example, it is illustrated that the finite-analytic method is really a piecewise-parabolic approximation which involves only three consecutive grid points. A finite-analytic method is proposed which employs the exact boundary conditions at the cell boundaries and provides continuous and differentiable solutions. 6 Refs. PY: 1997 LA: English AN: EIX98144054234 Mostrar Registro Completo

Registro 20 de 40 en EI COMPENDEX (1997-1998/12) TI: Effect of surfactants on the growth of underpressurized, annular liquid jets AU: Ramos-JI SO: Chemical-Engineering-Communications. v 160 1997, p 157-174. IS: 0098-6445 AB: The effects of surfactants on the growth of isothermal, underpressurized, inviscid, annular liquid jets are studied under both steady state and transient conditions by means of an interfacial mass transfer law which depends on the equilibrium interfacial concentration and a mass resistance parameter. Equilibrium interfacial concentrations governed by both Henry's and Sievert's solubility laws are considered. It is shown that, for mass Biot numbers larger than unity, the underpressurized jet grows until the pressure of the gases enclosed by the annular liquid jet is equal to that of those surrounding the jet, while, for mass Biot numbers less than or equal to one, the pressure coefficient increases very little. It is also shown that, in some cases and contrary to the results observed in the absence of mass transfer resistance, the time required by the annular jet to reach a steady equilibrium configuration may be shorter when the equilibrium interfacial concentration is governed by Sievert's law than when it is governed by Henry's solubility law, particularly at low Peclet numbers and for high mass transfer resistances. (Author abstract) 17 Refs. PY: 1997 LA: English AN: EIX97433809183 Mostrar Registro Completo

Registro 21 de 40 en EI COMPENDEX (1997-1998/12) TI: Lumped models of gas bubbles in thermal gradients AU: Ramos-JI SO: Applied-Mathematical-Modelling. v 21 n 6 Jun 1997, p 371-386. IS: 0307-904X AB: The motion of spherical gas bubbles in isothermal and nonisothermal glassmelts 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 linear 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: the buoyant, the thermocapillary, and the 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 glassmelt mean temperature is decreased. Numerical studies of gas bubbles with mass transfer in nonisothermal glassmelts indicate that, for a bubble containing only oxygen initially, nitrogen, carbon dioxide, and water vapor diffuse from the glassmelt to the bubble, whereas the oxygen diffuses from the bubble to the glassmelt. The lime required by the bubble to be dissolved increases as the initial bubble radius, mean temperature, and thermal gradient are increased. (Author abstract) 16 Refs. PY: 1997 LA: English AN: EIX97423799360 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 22 de 40 en EI COMPENDEX (1997-1998/12) TI: Mass transfer in annular liquid jets in the presence of liquid flow rate fluctuations AU: Ramos-JI SO: Applied-Mathematical-Modelling. v 21 n 6 Jun 1997, p 363-369. IS: 0307-904X 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 this 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. (Author abstract) 11 Refs. PY: 1997 LA: English AN: EIX97423799359 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 23 de 40 en EI COMPENDEX (1997-1998/12) TI: Short note: a nonstandard finite difference method for the one-dimensional advection equation in cylindrical-polar coordinates AU: Ramos-JI SO: Applied-Mathematical-Modelling. v 21 n 6 Jun 1997, p 337-338. IS: 0307-904X AB: This article describes method for solving one-dimensional advection equation in cylindrical-polar coordinates. There exists a variety of finite difference methods for advection equation equations that are based on upwind or flux limiters, so that numerical solution satisfies certain monotonicity and entropy conditions and is free of unphysical oscillations. New analytical approximation is described which is used to obtain finite difference expressions for spherical wave equation based on piecewise linearization technique. This method does not require known analytical solution. It can be used to obtain finite expressions for other equations. If solution is continuous, piecewise linearization technique provides piecewise continuous solutions. (Edited author abstract) 2 Refs. PY: 1997 LA: English AN: EIX97423799356 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 24 de 40 en EI COMPENDEX (1997-1998/12) 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-and-Fluid-Flow. v 7 n 1 1997, p 42-62. IS: 0961-5539 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 pull 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. (Author abstract) 9 Refs. PY: 1997 LA: English AN: EIX97203579409 Mostrar Registro Completo

Registro 25 de 40 en EI COMPENDEX (1997-1998/12) TI: Linearized Theta -methods. Part II: reaction-diffusion equations AU: Garcia-Lopez-CM; Ramos-JI SO: Computer-Methods-in-Applied-Mechanics-and-Engineering. v 137 n 3-4 Nov 15 1996, p 357-378. IS: 0045-7825 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. (Author abstract) 11 Refs. PY: 1996 LA: English AN: EIX97093481678 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 26 de 40 en EI COMPENDEX (1995-1996) TI: G-jitter effects on mass transfer in annular liquid jets AU: Ramos-JI SO: International-Journal-of-Numerical-Methods-for-Heat-and-Fluid-Flow. v 6 n 5 Aug 1996, p 17-28. IS: 0961-5539 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. (Author abstract) 11 Refs. PY: 1996 LA: English AN: EIX96483355118 Mostrar Registro Completo

Registro 27 de 40 en EI COMPENDEX (1995-1996) TI: Force fields on inviscid, slender, annular liquid jets AU: Ramos-JI SO: International-Journal-for-Numerical-Methods-in-Fluids. v 23 n 3 Aug 15 1996, p 221-239. IS: 0271-2091 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. (Author abstract) 7 Refs. PY: 1996 LA: English AN: EIX96433304016 Mostrar Registro Completo

Registro 28 de 40 en EI COMPENDEX (1995-1996) TI: One-dimensional models of steady, inviscid, annular liquid jets AU: Ramos-JI SO: Applied-Mathematical-Modelling. v 20 n 8 Aug 1996, p 593-607. IS: 0307-904X AB: One-dimensional models for inviscid, incompressible, axisymmetric, annular liquid jets falling under gravity are obtained by means of methods of regular perturbations for slender or long jets, integral formulations, Taylor's series expansions, weighted residuals, and variational principles. It is shown that perturbation methods result in an axial velocity component which corresponds to Torricelli's free-fall law regardless of the value of the Weber number. It is also shown that the (integral) control-volume formulation yields a third-order ordinary differential equation for the radii of the jet's interfaces, whereas the hydraulic model presented in this paper and that of Boussinesq result in second-order ordinary differential equations. The hydraulic model presented in this paper is asymptotically equivalent to that of Boussinesq for slender and thin annular liquid jets. The models based on Taylor's series expansions, method of weighted residuals, and the Kantorovich-Galerkin technique also result in third-order ordinary differential equations. The control-volume formulation is identical to that of the hydraulic model if the pressure of the liquid is assumed to be uniform throughout the annular jet. (Author abstract) 24 Refs. PY: 1996 LA: English AN: EIX96413287220 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 29 de 40 en EI COMPENDEX (1995-1996) TI: Upward and downward annular liquid jets: Conservation properties, singularities, and numerical errors AU: Ramos-JI SO: Applied-Mathematical-Modelling. v 20 n 6 Jun 1996, p 440-458. 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 here 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. (Author abstract) 12 Refs. PY: 1996 LA: English AN: EIX96343229999 Mostrar Registro Completo

Registro 30 de 40 en EI COMPENDEX (1995-1996) TI: 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. v 22 n 11 Jun 15 1996, p 1089-1102. IS: 0271-2091 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 methods 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. (Author abstract) 7 Refs. PY: 1996 LA: English AN: EIX96333227844 Mostrar Registro Completo

Registro 31 de 40 en EI COMPENDEX (1995-1996) TI: Planar liquid sheets at low Reynolds numbers AU: Ramos-JI SO: International-Journal-for-Numerical-Methods-in-Fluids. v 22 n 10 May 30 1996, p 961-978. IS: 0271-2091 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. 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. 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. 9 Refs. PY: 1996 LA: English AN: EIX96313208652 Mostrar Registro Completo

Registro 32 de 40 en EI COMPENDEX (1995-1996) TI: Linearized Theta -methods. I. Ordinary differential equations AU: Ramos-JI; Garcia-Lopez-CM SO: Computer-Methods-in-Applied-Mechanics-and-Engineering. v 129 n 3 Jan 15 1996, p 255-269. IS: 0045-7825 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 equals 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. (Author abstract) 10 Refs. PY: 1996 LA: English AN: EIX96243142251 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 33 de 40 en EI COMPENDEX (1995-1996) TI: Inviscid, slender, annular liquid jets AU: Ramos-JI SO: Chemical-Engineering-Science. v 51 n 6 Mar 1996, p 981-994. IS: 0009-2509 AB: Regular perturbation expansions are used to analyse unsteady, inviscid, slender, incompressible (constant density), axisymmetric, annular liquid jets when 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 leading order equations are used to determine the fluid dynamics of steady annular jets. (Author abstract) 10 Refs. PY: 1996 LA: English AN: EIX96203107833 FTXT: ScienceDirect (tm) Mostrar Registro Completo

Registro 34 de 40 en EI COMPENDEX (1995-1996) TI: Effects of fluctuating body forces on annular liquid jets AU: Ramos-JI SO: Archive-of-Applied-Mechanics. v 65 n 8 Oct 1995, p 548-563. IS: 0939-1533 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. (Author abstract) 21 Refs. PY: 1995 LA: English AN: EIX96102946909 Mostrar Registro Completo

Registro 35 de 40 en EI COMPENDEX (1995-1996) TI: Isothermal mass transfer in annular liquid jets with Sievert's solubility law AU: Ramos-JI SO: Archive-of-Applied-Mechanics. v 65 n 4 Apr 1995, p 260-269. IS: 0939-1533 AB: A study of isothermal gas absorption by underpressurized, axisymmetric, thin, inviscid, incompressible, annular liquid jets which form enclosed volumes, where hazardous wastes may be burned, is presented. The study considers the nonlinear dynamical coupling between the fluid dynamics of, and the gases enclosed by, the annular liquid jet. It assumes equilibrium conditions at the interfaces, and employs Sievert's solubility law to determine the gas concentration at the gas-liquid interfaces. Both steady-state and transient conditions are considered. Under steady-state conditions, the fluid dynamics and mass transfer phenomena are uncoupled, and the rate of generation of combustion gases is equal to the mass absorption rate by the liquid. The transient behaviour of the annular jet is determined from initial conditions corresponding to steady-state operation, once there is no gas generation by the combustion of hazardous wastes. It is shown that, for most of the conditions 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 hazardous combustion products at the annular jet's interfaces. (Author abstract) 13 Refs. PY: 1995 LA: English AN: EIX95322745219 Mostrar Registro Completo

Registro 36 de 40 en EI COMPENDEX (1995-1996) 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. v 8 n 4 Mar 1995, p 186-193. IS: 0895-2477 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. (Author abstract) 17 Refs. PY: 1995 LA: English AN: EIX95192629187 Mostrar Registro Completo

Registro 37 de 40 en EI COMPENDEX (1995-1996) TI: On the growth of underpressurized annular liquid jets AU: Ramos-JI SO: Applied-Mathematical-Modelling. v 19 n 1 Jan 1995, p 13-25. IS: 0307-904X 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't interfaces. (Author abstract) 9 Refs. PY: 1995 LA: English AN: EIX95172606807 Mostrar Registro Completo

Registro 38 de 40 en EI COMPENDEX (1995-1996) TI: Classical forces on solitons in finite and infinite nonlinear planar waveguides AU: Ramos-JI; Villatoro-FR SO: Microwave-and-Optical-Technology-Letters. v 7 n 13 Sept 1994, p 620-625. IS: 0895-2477 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. (Author abstract) 10 Refs. PY: 1994 LA: English AN: EIX95012420910 Mostrar Registro Completo

Registro 39 de 40 en COMPENDEX*PLUS (1993/01-1994/12) TI: Forces on solitons in finite, nonlinear, planar waveguides AU: Ramos-JI; Villatoro-FR SO: Microwave-and-Optical-Technology-Letters. v 7 n 8 Jun 5 1994, p 378-381. IS: 0895-2477 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. (Author abstract) 9 Refs. PY: 1994 LA: English AN: EIX94361342719 Mostrar Registro Completo

Registro 40 de 40 en COMPENDEX*PLUS (1993/01-1994/12) TI: Adaptive methods of lines for one-dimensional reaction-diffusion equations AU: Ramos-JI SO: International-Journal-for-Numerical-Methods-in-Fluids. v 16 n 8 Apr 30 1993, p 697-723. IS: 0271-2091 AB: Adaptive and non-adaptive 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. The non-adaptive methods of lines presented in this paper may use equally or non-equally spaced fixed grids and require a large number of grid points to solve accurately one-dimensional problems charactrized by the presence of steep, fast-moving fronts. The three adaptive techniques presented in this paper use physical coordinates and may employ finite volume or three-point, compact methods. The adaptive and non-adaptive finite difference methods presented in the paper are used to study a decomposition chemical reaction characterized by a scalar, one-dimensional reaction-diffusion equation, the propagation of a one-dimensional, confined, laminar flame in Cartesian co-ordinates and the Dwyer-Sanders model of one-dimensional flame propagation. 14 Refs. PY: 1993 LA: English AN: EIX93300999387 Mostrar Registro Completo