Vol. 51 No. 4 (2005): Revista Mexicana de Física.

Published: 2005-01-01

Articles

  • Métodos vibrónicos generalizados aplicaciones a sistemas del tipo elpasolitas estequiométricas Cs$_{2}$NaErCl$_{6}$

    R.Acevedo., A.Soto-Bubert., T.Meruane., G. Navarro
    330-0

  • Spontaneous imbibition in a porous medium under longitudinal temperature gradients

    M. Sánchez, A. Medina, A. Rojano
    349-0
    Abstract:
    In this work, the influence of a longitudinal temperature gradient on the spontaneous imbibition into a homogeneous porous medium has been analyzed. Theory and experiments done on a permeable rock (Berea sandstone) allow us to show how this gradient modifies the temporal evolution of the averaged imbibition front $h(t)$. Despite the existence of a thermal boundary layer outside the rock, experimental data are in good agreement with the theoretical profiles of $h(t)$.
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  • Materiales compuestos de matriz metálica rica en Zn con alto contenido de Al y componente estructural de ZnO

    J. A, J. R, a.
    356-0
    Abstract:
    The aims of this work were to elaborate composites of metallic matrix rich in Zn with high content of Al and different contents of particulate ZnO by the conventional technique of powders metallurgy; to establish initial times of theirs manufactures, structural changes, basic mechanical properties of integrants and microstructures, and basic phenomena happened during formation of this composites as a function of the process time and ZnO content. It was begun with preparation of Zn and Al powder mixes, in convenient proportions to form Zn -- 22%wt Al alloy, and powders quantities of ZnO that were 0.0%, 0.01%, 0.1%, 1% y 10% of the total weight of each mix. The mixes were after compacted with a load of 16 tons and acetone as lubricant. The sintering was made in steps of 15 minutes of duration at 357$^\circ$C. Before each sintering step, the samples were conventionally grinded, polished and etched. The obtained structures were photographed. Vickers micro-hardness and Rockwell G hardness were respectively measured in constituents and microstructures. The ZnO in proportions not higher than 0.1%wt causes that it is concentrated the compression on metallic powders. Which improves atomic species diffusion and, therefore, it accelerates the union among components, formation of solid solutions and the interest alloy, producing an initial reinforcement of the matrix that seems not to depend on the oxide quantity at short times of process. It is established an increase of integrants size and the formation of pearlite type substructure, which is characteristic of the homogenized Zn - 22% wt Al alloy, in a considerable proportion of the microstructures at longer process times. This causes a softening of the matrix and then it is evident the reinforcement caused by ZnO. The ZnO content above 0.1% wt. delays the alloy formation in matrix. The minimal time for elaboration of these materials is 75 minutes.
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  • Respuestas pupilares a estímulos cromáticos en el espectro de 400 nm a 650 nm, en el estado estable

    D. Rodríguez Guzmán, A. Zúñiga López, E. Suaste Gómez
    365-0
    Abstract:
    an instrumental methodology was implemented to analyze the pupillary responses in the dilation and contraction process elicited by chromatic stimulus. Chromatic stimuli were employed in the visible spectrum from 400 nm to 650 nm. Three different stimulation software was developed and used in order to obtain a contrasted pupillary response PG0, PG12 and PG20. This test was applied to 39 subjects (29 male, 9 female and 1 child, 22-52 years and 6 years), 10 of them were stimulated with PG0, 21 were stimulated with PG12 and 16 with PG20. 6 subjects participate at least in 2 tests. Ishihara plates were exhibited to the subjects before the stimulation, 37 of the present a normal vision color, 1 present deuteranopy.
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  • Propagation of a photoinduced surface wave along an ideal metal--photorefractive crystal interface

    Rafael Torres-Cordoba.
    371-0
    Abstract:
    A mathematical model is developed in order to study self-confinement of the square beam propagating along the boundary of the Ideal Metal-Photorefractive Crystal media. It is shown that the square beam is self-bending and can be balanced by internal reflection at the Photorefractive Crystal surface to result in surface wave formation. Theoretical evidence is given.
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  • A mean field model for brownian and turbulent coagulation of polydispersed aerosols

    A.T. Celada, A. Salcido
    379-0
    Abstract:
    A mean field model for Brownian and turbulent coagulation of polydispersed aerosols is proposed. This model is based on a discrete balance equation that gives the rate of change for the number density of particles with diameters within a given range in terms of the rates of formation and loss of particles in all other diameter ranges. A monomer structure for the particles is not considered in this model, differing in this sense from the Smoluchowsky theory. Instead, it uses a probabilistic estimate of formation or loss of particles which depends on the diameters ranges of the colliding particles. To test this model, five aerosol coagulation experiments, carried out by Kim et al. [1], Rooker and Davies~[2], and Okuyama et al. [3] were used to try to reproduce the results. The computer simulation results were found in good agreement with the experimental data.
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  • Bulk anisotropic excitons in type-II semiconductors built with 1D and 2D low-dimensional structures

    H.A. Co, otécatl., M. del Castillo-Mussot, J.A. Re, es., G.J. Vázquez, J.A. Montema, or-Aldrete., J.A. Re, es-Esqueda., G.H. Cocoletzi
    387-0
    Abstract:
    We used a simple variational approach to account for the difference in the electron and hole effective masses in Wannier-Mott excitons in type-II semiconducting heterostructures in which the electron is constrained in an one-dimensional quantum wire (1DQW) and the hole is in a two-dimensional quantum layer (2DQL) perpendicular to the wire or viceversa. The resulting Schrödinger equation is similar to that of a 3D bulk exciton because the number of free (nonconfined) variables is three; two coming from the 2DQL and one from the 1DQW. In this system the effective electron-hole interaction depends on the confinement potentials.
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  • Analytical approach for the design of cascaded raman fiber lasers

    A. Martínez Rios, I. Torres Gómez, R. Selvas Aguilar, G. Anzueto Sanchez, A.N. Starodumov
    391-0
    Abstract:
    An analytical approach for the design of cascaded Raman fiber lasers is presented. The model computes the values of the pump and Stokes powers at the fiber laser output based on the boundary conditions, the invariants resultanting from the analysis of the coupled differential equations, and assuming that the sum of the forward and backward Stokes waves resonated inside the cavity is constant. The model is applied to Raman fiber lasers based on five nested cavities and compared with published results based on numerical models obtaining a good correlation.
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  • Image restoration of blurring due to rectilinear motion: constant velocity and constant acceleration

    J.S. Pérez Huerta, G. Rodriguez Zurita
    398-0
    Abstract:
    If a relative motion exists between a given object's image and a recording medium (such as a photographic film) during exposure, the recorded image will be blurred. This effect can be expressed by an impulse response in irradiance function and the respective image restoration is made possible by a post-recording process. General one-dimension motion is considered here. Two cases are discussed: constant velocity motion and constant acceleration motion. Image simulations representing those degradation mechanisms are shown, as well as the corresponding restored images after using the method which is described in this work. This method is based on Dirac delta function propreties. We also show real digital images affected by those motions. It can be experimentally obtained by using an air-rail. The blurred images are processed digitally by spatial filters given by the proposed method. Numerical and experimental results are shown.
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  • Transient effects in two channel interactions and an application to the behavior of a time dependent shutter

    Tobias Kramer., Marcos Moshinsk., .
    407-0
    Abstract:
    The subject of transient effects in quantum mechanics has been of interest to one of the authors (MM) since long before it became possible to study them experimentally. In particular, the problem of opening a shutter instantaneously led him to the concept of diffraction in time\cite{1}. Physically, it is only possible to open a shutter as a function of time and this complicates the problem greatly, as it is then not invariant under time translations and thus, among other difficulties, the energy of the system is not a constant of the motion. Kleber and Scheitler\cite{2} analyzed the problem describing the shutter as a $\delta-$function potential at the origin $x=0$, but whose strength was an inverse function of time. In this paper, we follow another procedure by adding to our initial two particle channel another one, and make them interact through appropriate time independent boundary conditions at the point of coincidence. The full problem conserves the total energy, but this does not happen if we restrict ourselves to a description in the first channel only. Thus, we have a rough but analytically solvable problem using a Laplace transform, which mimics some aspects of a time-dependent shutter, and compare our results with some of those derived by the different procedure of reference\cite{2}.
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  • Third harmonic conversion efficiency from laser-dense plasma interactions

    R. Ondarza
    415-0
    Abstract:
    A perturbative nonlinear procedure is used to account for the conversion efficiency of the third harmonic reflected from a dense plasma illuminated by a short laser pulse. It is found that the power ratio of the third harmonic to that of the fundamental is given by $P_3/P_0 \sim a_0^4\, {\left( \omega_0/ \omega_p \right) }^2$, where $a_0$ is the amplitude of the incident wave, and $\omega_0$ and $\omega_p$ are the optical and plasma frequency, respectively. This power ratio was found to be in agreement with particle-in-cell (PIC) simulations. Furthermore, the model presented here predicts a resonant enhancement around a density four times critical. This effect is captured as well by numerical simulations, and proved to be a distinctive feature in the radiation spectra.
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  • Confocal profiling of grooves and ridges with circular section using the divided aperture technique

    J.F. Aguilar
    420-0
    Abstract:
    The divided-pupil technique for the simulation of confocal imaging is applied to remove those artifacts appearing due to the symmetry of the object. A rigorous treatment is used to model the imaging system which is a two-dimensional confocal microscope, working in reflection mode. Since the geometry of the associated electromagnetic problem is 2-D, the objects analyzed are highly symmetric and cylindrical. The advantages and limitations of this technique are discussed and shown by means of examples.
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  • Near-field microscopy of evanescent microwaves

    V. Coello, R. Villagómez, R. Cortés, R. López, C. Martínez
    426-0
    Abstract:
    Local control of evanescent microwaves is experimentally investigated using a scanning near-field microwave microscope. The capabilities of the microscope and the contribution, on the near field images, of propagating field components stemming from inelastic (out-of-plane) scattering were elucidated. A set of two-dimensional mirrors for a local control of evanescent modes are shown along with their corresponding near-field image, and their efficiency is discussed. We believe that the experimental approach used is reliable enough to be used as a check of potential (two-dimensional) micro-components and possibly for micro and nano-circuits.
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  • Técnicas ópticas para el contorneo de superficies tridimensionales

    A. Martínez, J.A. Ra, as., J.M. Flores M., R. Rodríguez-Vera, D. Donato Agua, o.
    431-0
    Abstract:
    We will present some non-contact systems for obtaining three-dimensional objects topography. The described systems are incoherent fringe projection technique, Talbot and speckle interferometry. In fringe projection technique, the digitalization is realized when black and white lines are projected over the object and this image is captured by the CCD. In Talbot interferometry, the object is collocated on one of the grating auto-image planes. The deformed grating image is captured by the CCD and superposed with a synthetic grating generated in the computer for obtaining a moiré pattern which gives information about the object topography. In the speckle interferometry technique, dual collimated illumination is used for contouring. The collimated beams illuminate symmetrically the object at an angle $\theta $ with the optical axis, and an image is recorded in the usual way. Now if the object is tilted by a small $\Delta \theta $, a system of equispaced interference planes intersects the object. A second recorded is taking in this object position. Both images are processed to get the object topography. The shape of the car part, a gasket, shoe mold and other examples of digitalized objects are shown. Advantages and disadvantages of the techniques are discussed.
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