Vol. 55 No. 6 (2009): Revista Mexicana de Física.

Published: 2009-01-01

Articles

  • Adsorption of carbon monoxide on graphene with high titanium coverage

    I. Carrillo, L.F. Magaña
    409-0
    Abstract:
    Density functional theory and molecular dynamics were used to study the adsorption of CO on a graphene layer modified with high titanium coverage (C$_{2}$Ti) at atmospheric pressure and 300 K. We found that the CO molecule is adsorbed and dissociated.
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  • Decoherence from qubit-qubit dipolar interaction in an all silicon quantum computer

    M. Avila
    412-0
    Abstract:
    The qubit-qubit dipolar interaction arises with the very presence of the nuclear qubits in an all--silicon quantum computer (ASQC). Since such interaction depends on the qubit spatial separation noise is induced on entanglement through a damping contribution to the density matrix. A closed condition of ``robustness'' against decoherence is found. The term ``robustness'' is defined unambiguosly. The existence of at least two exceptional coherent states is infered. The preparation of such states is within the range of present technological capabilities. Thus, the harmful effects of decoherence coming from the dipolar interaction can be diminished considerably. An approximate condition against decoherence, to leading order in 1/(qubit separation)[3], is derived. By expanding the time evolution operator in a series of Chebyshev polynomials an approximated expression for the density matrix, whose precision is of order $10^{-4}$, is also found. From this expression, a next-to-leading order approximation for the condition of robustness against decoherence is derived.
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  • Density functional investigation of silver, palladium and silver-palladium small sized clusters

    E. Carvajal, O. Hahn-Herrera, E. Orgaz
    418-0
    Abstract:
    We have investigated the geometrical and electronic properties of small sized Ag and Pd as well as bimetallic Ag-Pd clusters. By means of a pseudopotential scheme within density functional theory, we found the ground-state geometries and the spin multiplicity state for this family of metallic clusters. We computed the binding energy and the atom addition energy change for these family of clusters with two different density functionals. Ag and Pd cluster series exhibit a clear different behavior as a consequence of the atomic electronic structure. In particular we discuss the high symmetry silver clusters and the trends in the small sized bimetallic Ag-Pd systems.
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  • Propiedades mecánicas de nitruros metálicos depositados con UBM: tecnología eficiente y ambientalmente limpia

    J.J. Ola, a., D.M. Marul, a., S.E. Rodil, B. Bhushan
    425-0
    Abstract:
    The aim of this research is to study the influence of the magnetic field configuration in a sputtering system on the mechanical properties of CrN, TaN, TiN, NbN and ZrN coatings. Different magnetic field configurations were quantified through the unbalance coefficient, $K_{G}$, which is proportional to the zero field point in the magnetron. In this work, films were deposited in two magnetic field configurations, $K_{G}$=1.3 and 0.825. The most important effect of the magnetic field configuration was observed on film hardness. When depositing on AISI M2 and 304 steels, mechanical properties and wear resistance were increased when increasing energy parameter; higher hardness was obtained for TaN, NbN and ZrN films. Another consequence of the change in the magnetic field was compressive residual stress variation. Higher variation was presented on TaN films while CrN films presented lower stress concentration.
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  • Impedancia longitudinal de un gas bidimensional de electrones en régimen de efecto Hall cuántico

    C. Hernández, C. Chaubet
    432-0
    Abstract:
    We have measured the longitudinal impedance of a two dimensional electron gas in the quantum Hall effect regime. We have found smooth resonances of impedance for the middle of quantized plateaus and large resonances at the beginning and the end of the plateaus. Those resonances can be partially described using a simplified electrical circuit model. The analysis of the different experimental results shows a great influence of the experimental setup on the experimental measurements.
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  • Monte carlo simulations of drop growth by coalescence and collision-induced breakup

    L. Alfonso, G.B. Raga, D. Baumgardner
    437-0
    Abstract:
    A Monte Carlo framework to simulate the evolution of drop spectra by coalescence and collision-induced breakup is presented. The stochastic algorithm of Gillespie [1] for chemical reactions in the formulation proposed by Laurenzi and Diamond [2] was used to simulate the kinetic behavior of the drop population. Within Gillespie's framework, the collision-induced breakup process is modeled as a new ``chemical reaction''. The results of the Monte Carlo simulations were compared with the analytical solution to the collection-breakup equation obtained by Feingold et al. [3], for an exponential distribution of satellite drops, and a constant collection and breakup kernels. A good correspondence between the analytical and the stochastic algorithm was found for this case.
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  • Quasi-static electromagnetic fields created by an electric dipole in the vicinity of a dielectric sphere: method of images

    Jorge R. Zurita-Sánchez
    443-0
    Abstract:
    We present a quasi-static description of the electromagnetic fields created by an oscillating electric dipole in the vicinity of a dielectric sphere. In this description: the fields are generated by image sources, a simple physical picture of the electromagnetic response of the dipole nearby a dielectric sphere is obtained, and the nearfields are calculated from the Green tensor of a bulk medium. This quasi-static description can be applied to study radiative properties of emitters (molecules, atoms, etc.) placed in the vicinity of a dielectric spherical nanoparticle.
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  • Some studies on safe maximum packing of live agents in crowds or containers

    O. Córdoba-Rodríguez, M. del Castillo-Mussot, J.A. Montema, or-Aldrete.
    450-0
    Abstract:
    We study the geometrical and physical conditions for maximizing the safe packing of live agents in crowds or in containers, like wagons or subways. In order to accommodate small children in interstitial spaces among adults, we first approximate standing-up people, as observed from above, as circles or ellipses. According to our results, in very crowded conditions babies are better protected only among ``athletic'' adults (in the sense that their shoulder-shoulder lateral distance is sufficiently larger than their lateral waist) by positioning them on the adults flank at kidney level. In several adults we applied sustained pectoral or thoracic pressure in order to find the applied force dependence of the chest compression, and the maximum chest compression before not being able to breathe. For every five people barely fitting in a container, we can barely accommodate one more person, due to the chest compression of all persons. Practical recommendations are given in very crowded situations.
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  • Information-theoretical analysis of gene expression data to infer transcriptional interactions

    K. Baca-López, E. Hernández-Lemus, M. Ma, orga.
    456-0
    Abstract:
    The majority of human diseases are related with the dynamic interaction of many genes and their products as well as environmental constraints. Cancer (and breast cancer in particular) is a paradigmatic example of such complex behavior. Since gene regulation is a non-equilibrium process, the inference and analysis of such phenomena could be done following the tenets of non-equilibrium physics. The traditional \emph{programme} in statistical mechanics consists in inferring the joint probability distribution for either microscopic states (equilibrium) or mesoscopic-states (non-equilibrium), given a model for the particle interactions (e.g. the potentials). An \emph{inverse problem} in statistical mechanics, in the other hand, is based on considering a \emph{realization} of the probability distribution of micro- or meso-states and used it to infer the interaction potentials between particles. This is the approach taken in what follows. We analyzed 261 whole-genome gene expression experiments in breast cancer patients, and by means of an information-theoretical analysis, we deconvolute the associated set of transcriptional interactions, i.e. we discover a set of fundamental biochemical reactions related to this pathology. By doing this, we showed how to apply the tools of non-linear statistical physics to generate hypothesis to be tested on clinical and biochemical settings in relation to cancer phenomenology.
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  • Capillary penetration in cells with periodical corrugations

    F.A. Sánchez, G.J. Gutiérrez, A. Medina
    467-0
    Abstract:
    In this work we present a theoretical study of the spontaneous capillary flow of a viscous liquid, developed in the gap between a couple of parallel corrugated plates (corrugated Hele-Shaw cell). The periodical corrugation of the interior walls of the plates is assumed as a sine-like pattern, transverse to the flow direction. Such a configuration may generate periodical gaps with a structure where zones of maximum and minimum closing occur. This is a simple idealization of typical micro and nano fabricated gaps used to mould polymers by capillarity. This model can also be useful to understand the capillary flow in naturally fractured reservoirs. By using lubrication theory we found that a very peculiar temporal flow is developed which could be of interest in improving our knowledge of this type of moulding.
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  • Procesamiento y caracterización de aceros microaleados calmados al aluminio

    M.A. Suarez, R. Herrera-Becerra, S. Valdez, B. Campillo, J.A. Juárez-Islas
    472-0
    Abstract:
    A series of microalloyed aluminium-killed steels stabilized with titanium, were made by means of the route of electrical arc furnace, vacuum degasser, secondary refinement and steel solidified into a continuous casting process. The resultant samples were hot rolling at 1100$^{\circ}$C, cooled in air down to 650$^{\circ}$C during 30 minutes, and cooled to room temperature. The resultant samples were cold rolled at room temperature and annealed at 700$^{\circ}$C. In their microstructural, texture and mechanical properties evaluation, the re-crystallized samples showed mechanical properties similar to those used in the automotive industry.
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  • Non-destructive measurement of the dielectric constant of solid samples

    A. Guadarrama-Santana, A. García-Valenzuela
    477-0
    Abstract:
    We discuss and analyze a practical methodology for the determination of the dielectric constant of a macroscopic solid sample in a non-destructive way. The technique consists in measuring the capacitance between a pointer electrode and the dielectric surface as a function of the separation distance in a scale comparable to the radius of curvature of the tip's apex. The changes in capacitance that must be measured will commonly be in the atto-farad scale and require specialized instrumentation which we also describe here. The technique requires two calibration standards and the sample needs to have a portion of its surface flat and some minimum dimensions, but otherwise it can have an arbitrary shape. We used a simple model based on the method of images to explain the methodology and present experimental results with the proposed methodology.
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