Vol. 56 No. 4 (2010): Revista Mexicana de Física.

Published: 2010-01-01

Articles

  • Realization of multiscroll chaotic attractors by using current-feedback operational amplifiers

    R. Trejo-Guerra, E. Tlelo-Cuautle, C. Sánchez-López, J.M. Muñoz-Pacheco, C. Cruz-Hernández
    268-0
    Abstract:
    Multiscroll chaotic attractors are physically implemented by using commercially available current-feedback operational amplifiers (CFOAs). The values of the circuit elements are obtained systematically by a proposed technique based in the saturation of the CFOA to create Piece-Wise Linear (PWL) functions. Herein the technique is verified by Spice simulations and in experimental form by using CFOAs to generate $n$-scroll attractors in a systematic way. Lyapunov exponents are given to prove the chaotic behavior.
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  • Estudio experimental de un láser sintonizable en longitud de onda usando un filtro de Sagnac con selectividad espectral mediante cambios en la temperatura

    A. González-García, O. Pottiez, R. Grajales-Coutiño
    275-0
    Abstract:
    We demonstrated experimentally a simple configuration to perform wavelength-tuning and multi-wavelength operation in an Erbium-doped fiber ring laser that includes a fiber-optic Sagnac interferometer as spectral filter formed by 7 m of high birefringence fiber and a symmetric coupler. We analyzed the temperature effect on the Sagnac filter response. Through temperature control, we were able to perform wavelength-tuning and multi-wavelength operation in the laser.
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  • Analysis of the $\pi$ phase-shifts obtained in the Fourier spectra of phase gratings and grids by using two-window grating interferometry

    N.-I. Toto-Arellano, G. Rodríguez-Zurita, A. Martínez García, J.F. Vázquez-Castillo, J.A. Ra, as Álvarez.
    281-0
    Abstract:
    As it is very well known, the Fourier coefficients of only-phase gratings are Bessel functions of the first kind of integer order. Because the values of these real-valued functions oscillate around zero, they can adopt negative values, thereby producing phase shifts of $\pi$ between some diffraction orders. To better understand the practical implications of this effect, in this work the phase shifts in the Fourier spectra of several phase gratings and grids are numerically found in order to compare them with experimental phase shifts. These experimental shifts induce changes in the modulation of the interference fringes formed by grating (or grid) interferometers when placing two windows at object plane of the system. Measurements of the changes in the interferograms are presented.
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  • Finite-time exergy with a finite heat reservoir and generalized radiative heat transfer law

    Shaojun Xia., Lingen Chen., Fengrui Sun.
    287-0
    Abstract:
    The problem of the maximum work that can be extracted from a system consisting of one finite heat reservoir and one subsystem with the generalized radiative heat transfer law [$q \propto \Delta (T^n)$] is investigated in this paper. Finite-time exergy is derived for a fixed duration and a given initial state of the subsystem by applying optimal control theory. The optimal subsystem temperature configuration for the finite-time exergy consists of three segments, including the initial and final instantaneous adiabatic branches and the intermediate heat transfer branch. Analyses for special examples show that the optimal configuration of the heat transfer branch with Newton's heat transfer law [$q \propto \Delta (T)$] is that the temperatures of the reservoir and the subsystem change exponentially with time and the temperature ratio between them is a constant; The optimal configuration of the heat transfer branch with the linear phenomenological heat transfer law [$q \propto \Delta (T^{ - 1})$] is such that the temperatures of the reservoir and the subsystem change linearly and non-linearly with time, respectively, and the difference in reciprocal temperature between them is a constant. The optimal configuration of the heat transfer branch with the radiative heat transfer law [$q \propto \Delta (T^4)$] is significantly different from those with the former two different heat transfer laws. Numerical examples are given, effects of changes in the reservoir's heat capacity on the optimized results are analyzed, and the results for the cases with some special heat transfer laws are also compared with each other. The results show that heat transfer laws have significant effects on the finite-time exergy and the corresponding optimal thermodynamic process. The finite-time exergy tends to the classical thermodynamic exergy and the average power tends to zero when the process duration tends to infinitely large. Some modifications are also made to the results from recent literatures.
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  • Formation and characterization of ion beam assisted nanosystems in silicon

    P.R. Poudel, B. Rout, K.M. Hossain, M.S. Dhoubhadel, V.C. Kummari, A. Neogi, F.D. McDaniel
    297-0
    Abstract:
    Even though silicon is optically inactive, the nanoscale particle structures (e.g. SiC) in Si or silica matrices are potential candidates for light emitting solid state device applications with higher operation temperatures. The synthesis of these nanostructures involves ion implantation and subsequent thermal annealing. The film thicknesses and sizes of the nanostructures can be controlled by ion energy, fluence, and annealing conditions. Particle accelerator based characterization was used at different stages of formation and analysis of these nanosystems in Si. Results will be presented using infrared spectroscopy (IR), X-ray diffraction spectroscopy (XRD), and photoluminescence (PL) spectroscopy.
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  • Heating load, COP, exergy loss rate, exergy output rate and ecological optimizations for a class of generalized irreversible universal heat pump cycles

    Lingen Chen., Huijun Feng., Fengrui Sun.
    302-0
    Abstract:
    The optimal performance of a class of generalized irreversible universal steady flow heat pump cycle model, which consists of two heat-absorbing branches, two heat-releasing branches and two irreversible adiabatic branches with the losses of heat-resistance, heat leakage and internal irreversibility is analyzed by using finite time thermodynamics. The analytical formulae about heating load, coefficient of performance (COP), exergy loss rate, exergy output rate and ecological function of the universal heat pump cycle are derived. Moreover, performance comparisons among maximum COP condition, a given exergy output rate condition and maximum ecological function condition are carried out by using numerical examples. It is shown that the ecological function objective is an excellent candidate objective with the ideal of an ecological and long-term goal. The effects of heat leakage and internal irreversibility on the cycle performance are discussed. The universal cycle model gives a unified description of seven heat pump cycles, and the results obtained include the performance characteristics of Brayton, Otto, Diesel, Atkinson, Dual, Miller and Carnot heat pump cycles with the losses of heat-resistance, heat leakage and internal irreversibility.
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  • Femtosecond pulse source based on soliton filtering from a supercontinuum generated in a microstructured fiber

    J. Licea Rodríguez, K. Gara, Palmett., R. Rangel Rojo
    311-0
    Abstract:
    In this article we report the implementation of a tunable source of ultrashort pulses, based on the generation of a supercontinuum in a photonic crystal fiber, using sub-100 fs pulses from a Ti:sapphire oscillator, and filtering the soliton with the longest wavelength out of the continuum. Using a zero dispersion filtering system we were able to get a pulse duration close to the minimum possible for the soliton. The pulses obtained were continuously tunable in the 850-1100 nm range, and tuning was achieved by input pulse energy variation. We present a complete characterization of the filtered pulses and show that the experimental results have a qualitative agreement with theory.
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  • Universal testing machine for mechanical properties of thin materials

    E. Huerta, J.E. Corona, A.I. Oliva, F. Avilés, J. González-Hernández
    317-0
    Abstract:
    In this work, the design, construction, calibration and compliance measurement of a universal testing machine for tension tests of materials in film geometry are presented. A commercial load cell of 220 N and sensitivity of 1.2345 mV/V is used to measure the applied load. Material strain is measured by movement of the crosshead displacement of the machine with a digital indicator with 0.001 mm resolution and 25 mm maximum displacement, connected to a PC through an interface. Mechanical strain is achieved by an electric high precision stepper motor capable to obtain displacement velocities as low as 0.001 mm/s. The stress-strain data acquired with a GPIB interface are saved as a file with a home-made program developed in LabView 7.0. Measurements of the elastic modulus and yield point of a commercial polymer film (500~HN Kapton) were used to validate the performance of the testing machine. The obtained mechanical properties are in good agreement with the mean values reported by the supplier and with the values obtained from a commercial machine, taking into account the limitations of thin film testing and experimental conditions.
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  • Influence of the absorption grating on the diffraction efficiency in thick photovoltaic media in transmission geometry under non linear regimes

    L.M. Cervantes, A. Zúñiga, L.F. Magaña, J.G. Murillo
    323-0
    Abstract:
    With simultaneous phase and absorption gratings, we calculated the contribution of the absorption grating to the total diffraction efficiency in thick samples ($ \approx $ 1 cm) of iron doped LiNbO$_{3}$. We considered transmission geometry, with an applied field of 5 kV/cm. First we solved numerically the set of partial, non linear, material rate differential equations. These solutions were used to calculate the energy exchange in two wave mixing. We solved numerically the beam coupling equations along sample thickness, for different values of grating period. For the used value of iron doping, we found that the contribution of the absorption grating is less than 0.02% of the total value of the diffraction efficiency.
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  • Crecimiento de nanopartículas de cobre en matriz de erionita

    F. Chavez Rivas, V. Petranovskii, R. Zamorano Ulloa
    328-0
    Abstract:
    Unreduced and reduced in hydrogen flow copper exchanged synthetic erionite, with a SiO$_{2}$/Al$_{2}$O$_{3}$ molar ratio of 7.7, have been characterized by X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), and electron spin resonance spectroscopy (ESR). The XRD patterns show that the reduction process does not change the zeolite structure, besides the reduced form at 450$^{\circ}$C present diffraction lines assigned to copper metallic particles. The DRS measurements have detected isolated Cu$^{2 + }$ ions as well as plasma resonance peak of copper metallic nanoparticles. The ESR simulation analysis of the spectra measured at 20$^{\circ}$C indicates the presence of two different Cu$^{2 + }$ ions sites localized in the erionite matrix. Up to 450$^{\circ}$C only one type of sites take place in the reduction process, participating in Cu metal clusters and Cu metal nanoparticles formation, keeping the Cu$^{2 + }$ ions of the second site intact.
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  • Análisis de la sensibilidad a las vibraciones del método de medición de tensión superficial mediante gota suspendida

    M.A. Álvarez Valenzuela, J.A. Díaz García, J.L. Pérez Díaz
    334-0
    Abstract:
    The measurement of the surface tension is of a great importance for a number of industries. The method of the pendant drip or Axisymmetric Drop Shape Analysis is one of the most commonly used. It is assumed that an isolated environment with a small level of vibrations is required for a correct measurement. Indeed, there is not any systematic study on the acceptable level of vibrations. In this paper we have experimentally determined how vibrations affect to the measurement of the surface tension. It is demonstrated how the swinging and oscillating resonances of the drop are of a great importance and how the use of a double antivibration bank can reduce the standard deviation of the measurement of the surface tension in two orders of magnitude.
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  • Optical trapping of particles at the air/water interface for studies in Langmuir monolayers

    A. Gutiérrez-Campos, R. Castillo
    339-0
    Abstract:
    Optical experimental devices allow to observe and manipulate several micron-sized objects, for instance, condensed phase domains formed in Langmuir monolayers at the air/water interface. In this paper, an experimental instrument designed to trap and manipulate those domains is presented. This instrument consists of optical tweezers, colloidal beads as handles and Brewster angle microscopy (BAM) to observe the trapped domains. With this instrument it was possible to trap and observe small domains ($20-30 \; \mu$m) of nervonic acid monolayers.
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