Vol. 57 No. 3 (2011): Revista Mexicana de Física.

Published: 2011-01-01

Articles

  • Spurline structures and its application on microwave coupled line filter

    J.R. Loo-Yau, O.I. Gómez-Pichardo, F. S, oval-Ibarra., M.C. Ma, a-Sánchez., J.A. Re, noso-Hernández.
    184-0
    Abstract:
    We propose and demonstrate experimentally that spurline structures enhance the rejection bandwidth of microwave bandstop coupled line filters. We have investigated the influence of spurlines structures on the rejection bandwidth of a typical microwave coupled line filters (with a notch frequency at 3.0 GHz). Momentum simulations and experimental results show that using spurline structures (designed to present a notch frequency at 2.4 GHz and 3.2 GHz) enhance in high percentage the performance of microwave coupled line filters (CLF).
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  • Entrelazamiento cuántico espurio con matrices seudopuras extendidas 4 por 4

    J.D. Bulnes, L.A. Peche
    188-0
    Abstract:
    In this paper, we consider one mathematical extension for the concept NMR pseudo-pure matrix in the particular case of $4\times4$ matrices, from non-physical matrices. Examples of entangled density matrices are presented. Those entanglement, identified by the Peres-Horodecki criterion, is spurious because it is not possible to assign these matrices to any physical state of a system of NMR nuclear spins.
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  • Electrostatic models of charged hydrogenic chains in a strong magnetic field

    A. Escobar
    193-0
    Abstract:
    Simple one-dimensional electrostatic models of one-(two) electron molecular systems H$_2^{+}$, H$_3^{2+}$, H$_4^{3+}$ and H$_2$, H$_3^{+}$, H$_4^{2+}$ in a strong magnetic field are proposed to estimate the binding-(ionization) energy of the corresponding ground states. The study is carried out in the range of magnetic fieds $B=10^2-10^6\,$ a.u. The models are inspired (and based) on the quasi one-dimensional form of the ground state electronic distribution function which is obtained by precise variational calculations in the Born-Oppenheimer approximation in a non-relativistic framework. It is shown that the models give, for all magnetic fields considered, a very good description of the binding-(ionization) energy of the one-electron molecular systems H$_2^{+}$, H$_3^{2+}$, H$_4^{3+}$, being accurate in $2.5%$, $5%$ and $5%$ respectively, and $15%$ for the two-electron systems H$_3^{+}$, H$_4^{2+}$ ($30%$ for H$_2$) as compared with the corresponding variational calculations.
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  • Estimador estocástico para un sistema tipo caja negra

    J. de J, R.U. Parrazales, R.P. Orozco
    204-0
    Abstract:
    This paper considers a black box system with unknown internal dynamics. The estimator based on instrumental variable requires, the transition matrix used in the identifier which results in a simplified model. The recursive space state model allows an explicit internal gain which is unknown and undescribed. The recursive estimator allows knowing the internal dynamics of the black box system in an analytic manner and in the best cases, converges to a reference neighborhood, becoming a necessary identification tool solving the convergence filter problem. The convergence estimator and the identifier are seen from the recursive functional identification error. An example was developed to simulate the DC motor in a finite differences model that requires knowing the operation of internal dynamics. The instrumental variable estimator describes the different operating condition parameters and monitors the direct current signal in finite differences. The functional error to different gains in the stability discrete region converges, and approximates the distribution of the direct current model.
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  • Ferromagnetismo en manganitas sustituidas con plata de estructura perovskita

    N. Hernández, T. Hernández, I. Dzul, Y. Peña
    211-0
    Abstract:
    A series of mixed oxides of general formula Sm$_{1 - x}$Ag$_{x}$MnO$_{3}$ with perovskite structure were prepared by first time by conventional solid-state reaction processing. The structure, morphology and magnetism of the samples are investigated. The X-ray diffraction patterns show that the x = 0.1 sample is a single perovskite structure, while x $ \ge $ 0.2, samples consist of a ferromagnetic perovskite phase and two nonmagnetic phases, Ag and Ag$_{1.8}$Mn$_{8}$O$_{16}$. The ferromagnetic behavior of Sm$_{1 - x}$Ag$_{x}$MnO$_{3}$ decrease with increase of Ag composition. The SEM analysis when x = 0.1 revealed that the random distribution of morphology and size of particles result of preparation method. The samples of Sm$_{1 - x}$Ag$_{x}$MnO$_{3}$ by x between 0.1 and 0.5 show that applying 10 T fields these cannot reach a saturation value.
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  • Effects on the quantum not and controlled-not gates of a modular magnetic field in the z-direction in a chain of nuclear spin system

    G.V. López, M. Avila
    215-0
    Abstract:
    We study the simulation of a single qubit rotation and Controlled-Not gate in a solid state one-dimensional chain of nuclear spins system interacting weakly through an Ising type of interaction with a modular component of the magnetic field in the z-direction, characterized by $B_{z}(z,t)=Bo(z)\cos\delta t$. These qubits are subjected to electromagnetic pulses which determine the transition in the one or two qubits system. We use the fidelity parameter to determine the performance of the Not (N) gate and Controlled-Not (CNOT) gate as a function of the frequency parameter $\delta$. We found that for $|\delta|\le 10^{-3}$ MHz, these gates still have good fidelity.
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  • Spherical MoS$_{2}$ micro particles and their surface dispersion due to addition of cobalt promoters

    M.A. Ramos, V. Correa, B. Torres, S. Flores, J.R. Farias Mancilla, R.R. Chianelli
    220-0
    Abstract:
    We present here a hydrothermal synthesis on spherical shape molybdenum di-sulfide (MoS$_{2})$ micro-particles using thiomolybdate salts and sodium silicate as reducing agent. To understand the role of cobalt promoters on this particular MoS$_{2}$ spherical shape a second reaction was carried out using same precursors plus addition of Co following same pressure and temperature conditions. Both products (before and after Co promoter) were characterized using scanning electron and transmission electron microscopic analysis. From SEM measurements a spherical average size diameter of $\sim $ 2.855 $\mu $m on pure MoS$_{2}$ is observed and disperse surface once cobalt is incorporated into the reaction. From TEM observations an interlayer average distance of $\sim $ 0.63 nm is obtained for MoS$_{2}$-MoS$_{2}$ slabs on samples with Co content. X-ray diffraction indicated principal crystallographic planes to be (002), (100), (101), (102), (103), (006), (105), and (110) for both MoS$_{2}$ and MoS$_{2}$/Co samples.
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  • Estructura y morfología de películas de pm-Si:H crecidas por PECVD variando la dilución de diclorosilano con hidrógeno y la presión de trabajo

    C. Álvarez-Macías, J. Santo, o-Salazar., B.M. Monro, M.F. García-Sánchez, M. Picquart, A. Ponce, G. Contreras-Puente, G. Santana., .
    224-0
    Abstract:
    Hydrogenated polymorphous silicon (pm-Si:H) is an attractive material for applications in the photovoltaic industry as it has optoelectronic properties similar to amorphous silicon (a-Si:H), which is the material currently used, and better stability to prolonged exposure to solar radiation. In this work we report experimental results of structural and morphological characterization of pm-Si:H films in terms of grain size and crystalline fraction obtained by Raman spectroscopy studies and the analysis of surface roughness with atomic force microscopy. The films were obtained by PECVD under conditions of generation of nano-crystalline silicon inclusions embedded in an amorphous silicon matrix. Changes in pressure of the reactor chamber (250 and 500 mTorr) and variations in the dilution of the silicon precursor gas (SiH$_{2}$Cl$_{2}$) with hydrogen (H$_{2}$) (flow rates of 25, 50, 75 and 100 sccm) modified the nanocrystals size and the crystalline fraction. The morphological analysis showed that for 25 sccm of H$_{2}$ there is a difference of 8 nm in the RMS roughness between both pressures, while for the other flows of H$_{2}$ the same RMS roughness (2 to 3 nm) was obtained. These results are very important because the optoelectronic properties of materials depend on the size and density of nanocrystals and the roughness analysis helps determine the growth conditions to produce high quality interfaces for application of the material in photovoltaic devices.
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  • Single-electron Faraday generator

    G. González
    232-0
    Abstract:
    In this paper I study the posibility of inducing a single-electron current by rotating a non-magnetic conducting rod with a small tunnel junction immerse in a uniform magnetic field perpendicular to the plane of motion. I show first, by using a thermodynamic approach, the conditions needed to pump electrons around the mechanical device in the Coulomb blockade regime. I then use a density matrix approach to describe the dynamics of the single-charge transport including many-body effects. The theory shows that it is possible to have single-electron tunneling (SET) oscillations at low temperatures by satisfying conditions similar to the Coulomb blockade systems.
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  • $\gamma$-Fe$_{2}$O$_{3}$/ZnO composite particles prepared by a two step chemical soft method

    S. López-Romero, F. Morales Leal
    236-0
    Abstract:
    Composite iron oxide-Zinc oxide ($\gamma $- Fe$_{2}$O$_{3}$/ZnO) was synthesized by two step method: in the first one step $\gamma$-Fe$_{2}$O$_{3}$ particles were obtained by a cetyltrimethylammonium hydroxide (CTAOH) assisted hydrothermal method at low temperature (60$^{\circ}$C). In the second step, the $\gamma $-Fe$_{2}$O$_{3}$ particles were included in the ZnO particles synthesis, which were obtained by a hexamethylenetetramine (HMTA) assisted hydrothermal method at low temperature (90$^{\circ}$C). SEM study of the samples revealed that the $\gamma $-Fe$_{2}$O$_{3}$/ZnO composites present a compact morphology. The $\gamma $-Fe$_{2}$O$_{3}$ and ZnO phases were identified by XRD, energy dispersive X-ray analysis (EDX) and analysis of the IR spectrum. The composite exhibit the characteristic emissions of ZnO under UV radiation and ferromagnetic behavior of $\gamma $-Fe$_{2}$O$_{3}$ under an external magnetic field.
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  • Room temperature thermal properties of Pb(Fe$_{1 /2}$Nb$_{1 / 2}$)O$_{3}$ ferroelectromagnetic ceramics

    R. Font, E. Marín, A. Lara-Bernal, O. Ra, mond., A. Calderón, J. Portelles, J.M. Siqueiros
    241-0
    Abstract:
    The thermal properties of ferroelectromagnetic Pb(Fe$_{1 / 2}$Nb$_{1 / 2})$O$_{3}$ ceramics obtained using the conventional ceramic method at different sintering temperatures between 850$^{\circ}$C and 1000$^{\circ}$C by stoichiometric mixing of the corresponding oxides and using different kinds of precursors, have been investigated for the first time. In particular the thermal conductivity was calculated from the measured values of thermal diffusivity and specific (volume) heat capacity using the photoacoustic technique and the temperature relaxation method, respectively. Whereas no influence of the kind of precursor used for sample preparation on the thermal conductivity ($k$) was observed, we have found that the value of $k$ depends on sintering temperature and has a maximum for samples synthesized at 900$^{\circ}$C, regardless of the use of precursors or not. This paper shows that such feature is determined by the competition of the thermal conductivity mechanisms inside the grains and those at the grain boundaries in combination with the morphologic features.
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  • Applications and extensions of the Liouville theorem on constants of motion

    G.F. Torres del Castillo
    245-0
    Abstract:
    We give an elementary proof of the Liouville theorem, which allows us to obtain $n$ constants of motion in addition to $n$ given constants of motion in involution, for a mechanical system with $n$ degrees of freedom, and we give some examples of its application. For a given set of $n$ constants of motion that are not in involution with respect to the standard symplectic structure, there exist symplectic structures with respect to which these constants will be in involution and the Liouville theorem can then be applied. Using the fact that any second-order ordinary differential equation (not necessarily related to a mechanical problem) can be expressed in the form of the Hamilton equations, the knowledge of a first integral of the equation allows us to find its general solution.
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  • Controlling a laser output through an active saturable absorber

    M. Wilson, V. Aboites, A. Pisarchik, V. Pinto, Y. Barmenkov
    250-0
    Abstract:
    Using the modified Statz - De Mars equations to describe a two laser optical system, it is shown how a saturable absorber can be made into an active control device when an external Electro Optic Modulator modulated low-intensity laser pumps directly into a saturable absorber inside a dye laser cavity. The direct modulation enables to control when and how the pulse train coming from the saturable absorber is released. The results here presented show that the pulse characteristics such as width, intensity and pulse frequency coming from the dye laser cavity, depend on the absorber characteristics and the modulation frequency.
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  • Simultaneous phase-shifting cyclic interferometer for generation of lateral and radial shear

    D.I. Serrano-García, N.I. Toto-Arellano, A. Martínez García, J.A. Ra, as Álvarez., A. Téllez-Quiñones, G. Rodríguez-Zurita
    255-0
    Abstract:
    We present experimental results obtained by a phase-shifting interferometer employing polarization capable of retrieve directional derivatives in $x$-direction (lateral shear). The system was adapted to obtain radial derivative (radial shear) and implemented with a cyclic interferometer with phase grid to multiplex the interference patterns. Using phase shifting by polarization, the interferometer is capable of processing the optical phase data with n-interferograms captured in a single shot. Experimental results are presented.
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  • Sistema automatizado para la medición de la conductividad térmica de líquidos mediante el método del alambre caliente

    S. Alvarado, E. Marín, A.G. Juárez, A. Calderón, R. Ivanov
    259-0
    Abstract:
    We present the implementation of an automated system based on the hot-wire technique for measurement of the thermal conductivity of liquids using high precision equipment (current source and voltage meter) that allow to work without an array of resistances known as a Wheatstone bridge, commonly used in such equipments. We also use a criterion to verify that we are working on the correct linear region of the curve $\Delta T$ versus ln$ (t)$, which is used for experimental data processing. Finally we validate the functionality of the hot-wire experimental array by measuring the thermal conductivity in samples of liquids with well-known thermal properties.
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  • The shadowgraph imaging technique and its modern application to fluid jets and drops

    R. Castrejón-Garc{\'\i}a, J.R. Castrejón-Pita, G.D. Martin, I.M. Hutchings
    266-0
    Abstract:
    The shadowgraph technique is discussed in terms of some modern application to fluid visualization and the characterization of free-surface flows. A brief description of shadowgraph photography is presented which emphasizes the parameters which need to be controlled to obtain useful images for digital processing and analysis. Several examples of shadowgraph images are presented together with their analysis to exemplify the variety of quantitative measurements that are possible with modern imaging tools. Three experimental setups were developed for different novel applications at different length scales: centimeter-long jets, millimeter-size sprays and micrometer-size droplets. The components used for these shadowgraph imaging systems range from standard photographic flash sources to specialized spark flash lamps and from single lens reflex (SLR) camera lenses to purpose-built systems with research-grade optical elements. Image analysis was developed and used to derive various types of information from the different systems. For jets it was used to determine the dynamic surface tension of the jetted fluid, for sprays it was employed to determine the ligament-droplet size distribution along the jetting axis and in inkjet printing it was used to determine the angular deviation and terminal speed of the jets and droplets.
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