Book Reviews by Luis Eduardo Aleman Reyna
Papers by Luis Eduardo Aleman Reyna
Physics of Fluids a Fluid Dynamics, 1992
Rarefied gas dynamics can be simulated numerically by Monte Carlo particle methods in which energ... more Rarefied gas dynamics can be simulated numerically by Monte Carlo particle methods in which energy and momentum are conserved in expectation, but not exactly, through each collision. The conservation of the expected values of these moments does not imply the conservation of other expected second moments. For example, in Nanbu's method (1980) (which was proven to converge), the expected value of the temperature decreases through each collision step, and the relaxation of a gas calculated by this scheme leads to the zero temperature state. The decrease in expected temperature is of order O(1/N), where N is the number of simulated particles.
Page 1. METASTABLE INTERNAL LAYER DYNAMICS FOR THE VISCOUS CAHN-HILLIARD EQUATION Luis G. Reyna M... more Page 1. METASTABLE INTERNAL LAYER DYNAMICS FOR THE VISCOUS CAHN-HILLIARD EQUATION Luis G. Reyna Mathematical Sciences IBM Thomas Watson Research Center Yorktown Heights, New York 10598 Michael J. Ward y Dept. of Mathematics Univ. ...
We analyzed the dynamics of confined ions driven by a quantized radiation field. The ions can abs... more We analyzed the dynamics of confined ions driven by a quantized radiation field. The ions can absorb photons from an incident laser beam and relax back to the ground state by either induced emissions or spontaneous emissions. Here we assume that the absorption of photons is immediately followed by spontaneous emissions, resulting in single-level ions perturbed by the exchange of momentum with the radiation field. The probability distribution of the ions is calculated using singular expansions in the low noise asymptotic limit. The present calculations reproduce the quantum results in the limit of heavy particles in static traps, and the classical results of ions in radio-frequency confining wells.
Gesellschaft Angewandte Mathematik Und Mechanik Jahrestagung Goettingen West Germany Zeitschrift Flugwissenschaften, 1987
Axially symmetric vortices with approximately cylindrical flow surfaces are investigated in the l... more Axially symmetric vortices with approximately cylindrical flow surfaces are investigated in the limiting case of unsteady initial conditions. The axial velocity profile has a discontinuity at the edge of the core but is otherwise uniform. The peripheral component is determined by the rotation of a solid body in the core and by potential vortex behavior outside it. The discontinuity conditions for mass and impulse flow can be formulated for inviscid flows and can in turn be used to determine the location of the discontinuity as well as the velocity and pressure distributions in the flow field. For certain initial and boundary conditions the flow surface gradients can increase arbitrarily, rendering the slender vortex approximation invalid.
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Journal of Tribology, 1991
Health Phys, 2003
In this work a study of the energy fluence of the photon beam produced by a commercial irradiator... more In this work a study of the energy fluence of the photon beam produced by a commercial irradiator that uses a single collimated 137Cs source is performed by employing the Monte Carlo code PENELOPE. A set of lead attenuators is placed at the exit window of the irradiator to vary the air kerma rate that is required to cover the instrument scales at a particular calibration distance. A possible variation in response due to this beam modification isalso investigated for LiF (TLD-100) dosimeters and for a secondary standard radiation protection level ionization chamber. The results show an important enhancement of beam mean energy from 633 to 642 keV as the lead attenuators increase in thicknesses. For this energy range, a maximum response change of 45% was found for LiF and 4.4% for the ionization chamber. These results reinforce the idea that a single source may very well be a practical solution for calibration laboratories without compromising the overall uncertainties acceptable for this application.
Methods and Applications of Analysis, 1995
Page 1. METASTABLE INTERNAL LAYER DYNAMICS FOR THE VISCOUS CAHN-HILLIARD EQUATION Luis G. Reyna M... more Page 1. METASTABLE INTERNAL LAYER DYNAMICS FOR THE VISCOUS CAHN-HILLIARD EQUATION Luis G. Reyna Mathematical Sciences IBM Thomas Watson Research Center Yorktown Heights, New York 10598 Michael J. Ward y Dept. of Mathematics Univ. ...
Journal of Applied Physics, 1994
We study the efficiency of using multilayer structures as an etch-stop mechanism in the ablation ... more We study the efficiency of using multilayer structures as an etch-stop mechanism in the ablation of polyimide films by ultraviolet lasers. The study is done using a photothermal model that includes the light absorption by the decomposed fragments, which shield the polymer from the laser beam, an intermediate zone in which the polymer is suffering a phase transition and the underlying unburned material. The layers are differentiated from each other through their optical properties. Variation in the optical properties of polyimide has been achieved by a proper selection of impurities. From our modeling work, we conclude that optically thin foils may be used as etch stop in the ablation process when the penetration depth of the middle layer is around three times larger than the penetration depth of the surrounding layers, this for fluences below 200 mJ/sq cm. We also present som experimental results.
Rheinisch Westfaelische Technische Hochschule Aerodynamisches Institut Abhandlungen, 1985
Crucial questions regarding vortex breakdown have not yet been answered. Thus, it is currently no... more Crucial questions regarding vortex breakdown have not yet been answered. Thus, it is currently not possible to conduct calculations regarding vortex breakdown for flows with large Reynolds numbers. The present investigation is concerned with a study of the flow upstream from the vortex breakdown. The study is based on the assumption that the vortex is slender. Frictionless and viscous flows are considered. The effect of compressive and frictional forces is represented separately. The two types of forces affect the initiation of the breakdown process in a different way. An approximation employed by Hall (1967) is used for slender, viscous vortices. Conditions of stationarity and axial symmetry are introduced, because of the conceptual and computational difficulties which arise in the absence of these restrictions. One objective of this investigation involves the study of slender vortices for large Reynolds numbers, taking into account also the frictional forces.
Physical Review Letters, Jul 1, 1988
Phase transitions of trapped particles and ions, observed initially in 1959 by collisional coolin... more Phase transitions of trapped particles and ions, observed initially in 1959 by collisional cooling and recently by laser cooling, are explained as order-chaos transitions. Here, two trapped Ba+ ions are examined experimentally and by computer solution of the equations of motion. The ordered state, quasiperiodic with two frequencies, becomes chaotic when a bifurcation introduces a third frequency at a critical value of a control parameter. This route evolves from the nonlinear Coulomb coupling of the ion pair's axial and radial motions, displaying frequency locking and hysteresis, which is observed.
Salud Sociedad, Apr 28, 2015
Introducción: El cine documental permite interiorizarse en algún fenómeno social, analizar sus pr... more Introducción: El cine documental permite interiorizarse en algún fenómeno social, analizar sus problemáticas y soluciones. La promoción de la salud continúa limitada a la visión clínica de tomadoras y tomadores de decisión de las instituciones oficiales de salud, siendo aplicada a través de modelos medicalizados unidireccionales en donde la comunidad toma un rol pasivo y la institución el rol de quien indica qué se debe hacer para incidir en la salud de las poblaciones, obviando acciones cotidianas que se dan desde la comunidad. Objetivo: Reflexionar sobre las representaciones culturales cotidianas y el cine, como herramientas conjuntas para la promoción de la salud, a través de un estudio de caso con jóvenes “B-boys” en Morelos (México). Resultados: Se obtuvo un cortometraje documental en donde los “B-boys” exponen cómo su cotidianidad en el mundo del “breakdance” puede ser un medio preventivo de problemáticas sociales con especial impacto en los jóvenes. Conclusiones: El cine es una herramienta valiosa como medio de apoderamiento comunitario en temáticas sociales, así como de difusión de acciones que suceden en la cotidianidad de las poblaciones, que puede ser una excelente estrategia de promoción de la salud, para ser considerada por las instituciones oficiales de salud.
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Siamam, 1991
... The equations are to be solved onOáyãL, where L represents the scaled length of the device. A... more ... The equations are to be solved onOáyãL, where L represents the scaled length of the device. At the endpoints we assume perfect ohmic contacts, for which the boundary conditions are np + \d(y) = 0 aty = 0,L, (1.2) np = \ aty = 0,L, ф(0) = фы(0) and ф(Ь) = фы(Ь)-У. ...
Physical Review a, 1994
The probability distribution of a two-level ion confined in a time-dependent nonlinear trapping f... more The probability distribution of a two-level ion confined in a time-dependent nonlinear trapping field and driven by a radiation field is calculated using an alternative treatment based on a singular asymptotic expansion. It is assumed that the ion is excited by electromagnetic radiation and relaxes back irreversibly by spontaneous emission. The present calculations reproduce the quantum results of the laser cooling of ions in static traps in the heavy-particle limit, and previous classical treatments for the confinement and cooling of ions in radio-frequency traps.
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Book Reviews by Luis Eduardo Aleman Reyna
Papers by Luis Eduardo Aleman Reyna