Vol. 52 No. 1 (2006): Revista Mexicana de Física.

Published: 2006-01-01

Articles

  • Carbon nanotubes produced from hexane and ethanol

    D. Mendoza, P. Santiago, E. Re, es Pérez.
    1-0
    Abstract:
    The synthesis of multi-wall carbon nanotubes using hexane or ethanol as the carbon source, hydrogen as the carrier gas, and iron as the catalyst with a thermal chemical vapor deposition method, is reported. It was found that the use of ethanol as the carbon source under low temperature (700$^{\circ}$C) gives better results than other liquid precursors in obtaining long and clean carbon nanotubes on quartz substrates.
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  • A survey of embedded solitons

    J. Fujioka, A. Espinosa-Cerón, R.F. Rodríguez
    6-0
    Abstract:
    At the end of the nineties a brand-new type of soliton was discovered: the embedded solitons. Initially they were found in optical systems, and afterwards they were also found in hydrodynamic models, liquid crystal theory and discrete systems. These peculiar solitary waves are interesting because they exist under conditions in which, until recently, the propagation of solitons was thought to be impossible. At first these nonlinear waves were believed to be necessarily isolated and unstable, but later on it was found that they can be stable and may exist in families. This paper explains what these embedded solitons are, in which models they have been found, and what variants exist (stable, unstable, continuous, discrete, etc.).
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  • Annealing effects on the mass diffusion of the CdS/ITO interface deposited by chemical bath deposition

    A. Ordaz-Flores, P. Bartolo-Pérez, R. Castro-Rodríguez, A.I. Oliva
    15-0
    Abstract:
    Cadmium sulphide thin films prepared by chemical bath deposition (CBD) were deposited on indium tin oxide (ITO) substrates with different deposition times (i.e. thickness) and characterised by their morphology and band gap energy. Samples were analysed as deposited and after annealing at 90 and $150^{\circ}$C, in order to study the interface diffusion and its effects on the properties mentioned. Auger depth profiles were used to determine the mass diffusivity coefficient in the CdS/ITO interface. The initial surface rms-roughness measured with AFM, as well as the initial band gap energy, are reduced after the annealing process. We obtained very small diffusion coefficient values, around \mbox{$10^{-21}$ m$^{2}$/s,} for the different elements analysed in the interface.
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  • Induced nematic-like phase in dipolar and quadrupolar colloids

    O. Alarcón-Waess
    20-0
    Abstract:
    We compute the one-body probability density function of a dipolar and a quadrupolar colloid driven by an external ordering field. Colloids with low structure in the absence of the external field, and with axially symmetric coupling potential are assumed. To compute the one-body probability density function, it is assumed that the dynamics of the colloid are given by the Smoluchowski equation without hydrodynamic interactions. We use an appropiate homogeneous external field for each moment. The results for the one-body probability density function predict an axial nematic-like phase for the dipole moment, whereas a biaxial nematic-like phase is predicted for the quadrupole moment.
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  • Symmetric energy-momentum tensor in Maxwell, Yang-Mills, and Proca theories obtained using only Noether's theorem

    Merced Montesinos., Ernesto Flores.
    29-0
    Abstract:
    The symmetric and gauge-invariant energy-momentum tensors for source-free Maxwell and Yang-Mills theories are obtained by means of translations in spacetime via a systematic implementation of Noether's theorem. For the source-free neutral Proca field, the same procedure yields also the symmetric energy-momentum tensor. In all cases, the key point to get the right expressions for the energy-momentum tensors is the appropriate handling of their equations of motion and the Bianchi identities. It must be stressed that these results are obtained without using Belinfante's symmetrization techniques which are usually employed to this end.
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  • Ultrasonic determination of real contact area of randomly rough surfaces in elastoplastic contact

    A. Baltazar, J-Y. Kim, S.I. Rokhlin
    37-0
    Abstract:
    Micromechanical characterization of interfacial properties of non-conforming rough surfaces in contact was performed by a method based on ultrasonic waves. The method to estimate the interfacial properties is based on ultrasonic spectroscopy of signals reflected from the interface. Ultrasonic results are complemented with probabilistic contact mechanics to model the normal and tangential interfacial stiffness (K$_{N}$ and K$_{T})$ constants for different degrees of closure. The results show that a single set of stiffness constants K$_{N}$ and K$_{T}$ is sufficient to describe the dynamic response of the interface independently of the incident angle of the ultrasonic waves. Plastic deformation of the rough interface is studied using the same ultrasonic method. Experimental results indicate that the hysteretic effect observed by repetitive loading cycles is an indication of plastic deformation at the asperity summits with greater height values. The phenomenon is explained using micromechanical and probabilistic models. The results show the possibility of using the method to estimate the interfacial stiffness, presence of plastic deformation, and the real contact area, which in the past have been impossible to measure accurately.
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  • Crecimiento de películas de CdTe:Al

    M. González-Alcudia, M. Zapata-Torres, M. Meléndez-Lira, J.L. Peña
    48-0
    Abstract:
    CdTe:Al films were grown by the close space vapor transport technique combined with free evaporation (CSVT-FE). The Aluminum (Al) evaporation was made by two kinds of sources: one made of graphite and the other of tantalum. The films were deposited on glass substrates. The Al source temperatura was varied maintaining the CdTe source temperature fixed as well as the substrate temperature. The films were characterized by x-ray energy dispersive analysis (EDAX), x ray diffraction and optical transmission. The results showed for the films grown with the graphite source for Al evaporation, the Al did not incorporate in the CdTe matrix, at least to the level of EDAX sensitivity; they maintained the same crystal structure and band gap. For the samples grown with the tantalum source, we were able to incorporate the Al. The x ray diffraction patterns show that the films have a crystal structure that depends on Al concentration. They were cubic up to 2.16 at.% Al concentration; for 19.65 at.% we found a mixed phase; for Al concentration higher than 21 at.% the films were amorphous. For samples with cubic structure it was found that the lattice parameter decreasesand the band gap increases with Al concentration.
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  • Image encryption based on phase encoding by means of a fringe pattern and computational algorithms

    J.A. Muñoz Rodríguez, R. Rodríguez-Vera
    53-0
    Abstract:
    A computational technique for image encryption and decryption is presented. The technique is based on light reflection, intensity superposition and computational algorithms. The image to be encrypted is a reflectance map obtained by means of the light reflected by a scene. To perform the encryption procedure, the image is encoded in a computer-generated fringe pattern. The model of the fringe pattern is a cosine function, which adds to its argument the image to be encrypted as a phase. It generates a fringe pattern deformed according to the image. To complete the encryption, a random mask is superimposed on the fringe pattern. The decryption procedure is performed by subtracting the random mask from the encrypted image and applying a phase recovery method. To retrieve the phase from the fringe pattern, the heterodyne demodulation method is used. To describe the accuracy of results of the decrypted images and the robustness of the encryption, a root mean square of error is calculated. All steps of the encryption and decryption are performed in computational form. The results of encryption and decryption are thus improved. It represents a contribution to the field of encryption and decryption. This technique is tested with simulated images and real images, and its results are presented.
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  • Algebraic approach for the reconstruction of Rössler system from the $x_{3}-$ variable

    C. Aguilar Ibáñez
    64-0
    Abstract:
    In this paper we propose a simple method to identify the unknown parameters and to estimate the underlying variables from a given chaotic time series $\{x_{3}(t_{k})\}_{0}^{k=n}$ of the three-dimensional Rössler system (RS). The reconstruction of the RS from its $x_{3}-$ variable is known to be considerably more difficult than reconstruction from its two other variables. We show that the system is observable and algebraically identifiable with respect to the auxiliary output $\ln (x_{3})$, hence, a differential parameterization of the output and its time derivatives can be obtained. Based on these facts, we proceed to form an extended re-parameterized system (linear-in-the -parameters), which turns out to be invertible, allowing us to estimate the variables and missing parameters.
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  • Uniformly accelerated observers in special relativity

    G.F. Torres del Castillo, C.I. Pérez Sánchez
    70-0
    Abstract:
    The red shift for an electromagnetic wave measured by two observers in a uniformly accelerated frame, which, according to the equivalence principle, should correspond to a gravitational red shift, is calculated as well as the bending of light rays.
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  • Desarrollo de un campo de fuerzas de mecánica molecular para la interacción de Na$^{ + }$ con agua

    A. Deriabina, J.O. Ledesma, E. González, J.N. Herrera, V. Poltev
    74-0
    Abstract:
    Molecular Mechanics potential functions of 1-6-12 type have been proposed to describe sodium ion -- water interactions. The coefficients of the potential functions are adjusted to reproduce both ab-initio quantum mechanics data for Na$^{ + }$- (H$_{2}$O)$_{n}$ clusters (n varying from 1 to 6) and experimental data permitting evaluate differential enthalpies of these cluster formations at 0K. The 6-12 part of Na$^{ + }$\ldots O potential has the values of 2.569{\AA} and 1.8 kcal/mol for the equilibrium distance and depth of energy well respectively.
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  • Doughnut shape atom traps with arbitrary inclination

    R. Rodríguez, Masegosa., H. Mo, a-Cessa., S. Chávez-Cerda
    80-0
    Abstract:
    Since the invention of magneto-optical trap (MOT), there have been several experimental and theoretical studies of the density distribution in these devices. To the best of our knowledge, only horizontal orbital traps have been observed, perpendicular to the coil axis. In this work we report the observation of distributions of trapped atoms in pure circular orbits without a nucleus whose orbital plane is tilted up to $90^{\circ }$ with respect to the horizontal plane. We have used a stabilized time phase optical array in our experiments and conventional equipment used for~MOT.
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