Vol. 49 No. 5 (2003): Revista Mexicana de Física.

Published: 2003-01-01

Articles

  • The electric resistance in electrolytic solutions

    F. Fernández E., J.S. Meráz M., L.F. Magaña
    397-0
    Abstract:
    We present a new method to measure the electric resistance of electrolytic solutions contained in conductivity cells. The innovations are the use of a new type of conductivity cell, with variable longitude and to take into account the phenomenon of electric resonance in order to cancel the effects of the double layer capacity at electrode-solution interfaces. Analysis of error propagation on geometric parameters of the cell was performed and absolute measurements were done, without chemical patterns of calibration. The results obtained with this new method and new cell type suggest the possibility of covering a wider range of values for the conductivity of electrolytic solutions.
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  • Obtención de estados tipo gato de Schrödinger mediante transformaciones canónicas en el espacio fase cuántico*

    A. Zúñiga-Segundo
    401-0
    Abstract:
    Employing canonical transformations defined in the coherent-state representation of quantum mechanics, we introduce Schrödinger-Cat-Like-States. The squeezed displaced number states with real squeezing parameter are contained in these states.
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  • ``One-dimensional" coherent states and oscillation effects in metals in a magnetic field

    D.A. Contreras-Solorio, J.A.de la Cruz-Alcaz., S.T. Pavlov
    407-0
    Abstract:
    Using the ``one-dimensional" coherent electron states in a quantizing magnetic field the oscillating part of the electron density of states for a metal, which determines the physical nature for the oscillations of the thermodynamic and kinetic metal characteristic in magnetic field, is calculated. The physical reason of the significant simplification of the mathematical procedure is that the coherent states are most adequate to describe the quantum macroscopic phenomena such as the Shubnikov - de Haas and the de Haas - van Alphen effects in metals.
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  • Magnetism of the vanadium surfaces

    A. Rubio-Ponce, A.E. García, R. Baquero
    411-0
    Abstract:
    We investigate the magnetic activity of the (001), (110), and (111) vanadium surfaces. The (001) orientation is particularly interesting since some controversy persists about its magnetic activity between the theoretical studies and the experimental results. On the (110) surface there is no magnetic activity. The (111) surface is interesting in the sense that the atoms in this plane are the most distant from each other as compared to the other two planes. This, in principle, should give the largest magnetic moments as we, indeed, find. We used the surface Green's function matching method to calculate the local density of states and the Stoner model to obtain the magnetic moment.
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  • On the Hamilton-Jacobi formalism for fermionic systems

    C. Ramírez, P.A. Ritto\S
    415-0
    Abstract:
    The Hamilton-Jacobi formalism for fermionic systems is studied. We derive the HJ equations from the canonical transformation procedure, taking into account the second class constraints typical of these systems. It is shown that these constraints ensure the consistency of the solution, according to the characteristics of fermionic systems. The explicit solutions for simple examples are computed. Some aspects related to canonical transformations and to quantization are discussed.
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  • Spherical fused silica microlenses fabricated by the melting method

    S. Calixto, F.J. Sanchez-Marin
    421-0
    Abstract:
    Fiber ends are irradiated by a focused CO$_{2}$ beam causing material to melt. Surface tension shapes the melted material into a spherical micro-lens that remains joined to the fiber. Such lenses can be used to form images or to focus light. Back focal distances and other parameters of the lenses have been measured.
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  • Franck-Condon factors and r-centroids for certain band systems of gallium and indium mono-fluorides

    N. Prithivi Kumaran, V. Raja, N. Rajamanickam
    425-0
    Abstract:
    For the first time, the Franck-Condon factors and r-centroids, which are very closely related to vibrational transition probabilities, have been evaluated for the bands of $A^3\Pi_0^+ - X^1\Sigma^+, B^3\Pi_1^- X^1\Sigma^+,$ and $C^1\Pi - X^1\Sigma^+$ systems of GaF and InF molecules. A numerical integration procedure is followed to evaluate these transition probability parameters, using a suitable potential.
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  • Movimiento browniano activo mediante velocidades estocásticas

    A. Castellanos-Moreno
    429-0
    Abstract:
    A formalism based in one step stochastic processes to study active Brownian motion is developed in this paper. Stationary and equilibrium properties are treated by defining an extended entropy and by introducing an indicator function to know when stationary state is reached. Stochastic velocities are recovered as a theoretical tool to get insight about the difference between equilibrium and stationary states. An angular velocity is defined to show how its magnitude is different from zero when detailed balance is not accomplished. All the formalism is illustrated through an example.
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  • On the figure eight orbit of the three-body problem

    E. Piña, P. Lonngi
    439-0
    Abstract:
    A new solution to the three-body problem interacting through gravitational forces with equal masses and zero angular momentum, has been recently discovered. This is a periodic symmetric orbit where the particles follow a figure eight trajectory in the plane. They alternate between six isosceles-aligned positions and six isosceles triangle positions in a periodic orbit composed by twelve equivalent segments. The condition of zero angular momentum is considered assuming that the three masses can be equal or different, yielding in both cases the same final expression for the kinetic energy. We found that the property of this orbit of having isosceles configurations, is a general feature to be found in any orbit of the equal-mass case, associated with an increase of $\pi/6$ in one angle of our set of coordinates. The figure-eight solution is determined by expanding two of our coordinates in a Fourier series of that angle, by using the Jacobi-Maupertuis principle as opposed to the standard Lagrangian action. The time and the angle conjugated to the angular momentum are also expressed in terms of that same angle.
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  • Symplectic structures and Hamiltonians of a mechanical system

    G.F. Torres del Castillo, G. Mendoza Torres
    445-0
    Abstract:
    It is shown that in the case of a mechanical system with a finite number of degrees of freedom in classical mechanics, any constant of motion can be used as Hamiltonian by defining appropriately the symplectic structure of the phase space (or, equivalently, the Poisson bracket) and that for a given constant of motion, there are infinitely many symplectic structures that reproduce the equations of motion of the system.
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  • Nuevos dispositivos analógicos de cálculo

    L. Kawecki
    450-0
    Abstract:
    The paper presents the general structure and the method of synthesis of new types of analog converters, called the dynamic converters, which allow carry out the desired mathematical dependences between the signals of their input and output. They are also presented the results of the investigation of the static and dynamic exactitude of this converters comparing it with the exactitude of the static converters used nowadays more frequently in the industrial instrumentation, indirect measurements, automation, analog and hybrid computation etc.
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  • Calibration of diffusion barrier charcoal detectors and application to radon sampling in dwellings

    M.E. Montero Cabrera, L. Colmenero Sujo, L. Villalba, J. Sáenz Peinado, A. Cano Jiménez, A. Moreno Baca, S. de la Cruz G, ara., M. Rentería Villalobos, A. López Mir, a., E.F. Herrera Peraza
    457-0
    Abstract:
    Some calibration conditions of diffusion barrier charcoal canister (DBCC) detectors for measuring radon concentration in air were studied. A series of functional expressions and graphs were developed to describe relationship between radon concentration in air and the activity adsorbed in DBCC, when placed in small chambers. A semi-empirical expression for the DBCC calibration was obtained, based on the detector integration time and the adsorption coefficient of radon on activated charcoal. Both, the integration time for 10 % of DBCC of the same batch, and the adsorption coefficient of radon for the activated charcoal used in these detectors, were experimentally determined. Using these values as the calibration parameters, a semi-empirical calibration function was used for the interpretation of the radon activities in the detectors used for sampling more than 200 dwellings in the major cities of the state of Chihuahua, Mexico.
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  • Porqué y cómo exponenciamos matrices hamiltonianas

    Kurt Bernardo Wolf.
    465-0
    Abstract:
    Las trayectorias de puntos masa en la mecánica clásica de osciladores, y de rayos de luz en la óptica geométrica paraxial, se obtienen exponenciando matrices. Las matrices hamiltonianas representan y clasifican mediante equivalencia las dinámicas posibles de los sistemas lineales. En mecánica unidimensional y en guías de onda planas son posibles los sistemas armónico, repulsivo, o el libre; esto es bien conocido y sólo requiere de matrices de $2\times2$ con 3 parámetros independientes. Aquí abordamos el problema de sistemas mecánicos en dos dimensiones, que coincide con el de las guías de onda ópticas en tres dimensiones, donde se requiere de matrices de $4\times4$ con 10 parámetros. Conocida la estructura de los eigenvalores, reducimos la exponencial de una matriz hamiltoniana a una suma de sus cuatro primeras potencias, con coeficientes que calculamos analíticamente, resolvemos la degeneración presente en el plano de eigenvalores, y comentamos sobre los sistemas lineales ondulatorios a los que se aplican estos resultados. Ponemos énfasis en las referencias que han tratado los tópicos contenidos en este trabajo, las cuales se detallan en párrafos separados.
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  • Heat conduction and near-equilibrium linear regime

    B. Poznaniak, M. Kot{\l}owska, I. Danielewicz-Ferchmin, A.R. Ferchmin
    477-0
    Abstract:
    A comparison of experiment on heat conduction in a rod with a calculation shows that if the conditions for the near-equilibrium linear regime are fulfilled, the differences between the rigorous solution of the minimum entropy production problem and its linearized version are small. They usually fall within the limits of experimental error. Hence, it may well illustrate that the Prigogine's theorem of minimum entropy production, despite its well-known limits recalled in a recent discussion, may serve as a useful approximation to the problem in question.
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  • Nonlinear size effects of hot electrons in semiconductor thin films

    H. Lohvinov, Y. Gurevich, O. Titov
    482-0
    Abstract:
    Theory of nonlinear heat size effects is developed in semiconductor films in the presence of external d.c. electric field. It is supposed that this field is applied along the film surfaces. The electron temperature is introduced, and it is shown that it depends on the electric field and the film thickness. The main equations are obtained for calculation this temperature, and analysis is done for the case of the weak electron heating. The characteristic length of the problem is discussed. It is the electron cooling length measured on submicron scale. It is shown that the heat size effects arise in the case when this length is comparable or less of the film thickness.
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  • Complex functions as lumps of energy

    R.J. Cova, C. Uberoi
    485-0
    Abstract:
    We present an application of the basic mathematical concept of complex functions as topological solitons, a most interesting area of research in physics. Such application of complex theory is virtually unknow outside the community of soliton researchers.
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