Vol. 55 No. 4 (2009): Revista Mexicana de Física.

Published: 2009-01-01

Articles

  • Momento electromagnético, efectos cuánticos y la masa del fotón

    G. Spavieri, J. Erazo, A. Sánchez, M. Rodriguez
    236-0
    Abstract:
    We review the role of the momentum of the electromagnetic (EM) fields $\mathbf{P}_{e}$ in several areas of modern physics, revising the most recent achievements and its relationship with $\mathbf{P}_{e}$. The moment $\mathbf{P}_{e}$ represents the EM interaction in equations for matter and light waves propagation. As an application of wave propagation properties, a first order optical experiment which tests the speed of light in moving rarefied gases is presented. Moreover, $\mathbf{P}_{e}$ is the link to the unitary vision of the quantum effects of the Aharonov-Bohm (AB) type and, for several of these effects, the explicit expression of $\mathbf{P}_{e}$ is evaluated. Finally, these effects provide a quantum approach to evaluate the limit of the photon mass~$m_{ph}$. A new effect of the AB type, together with the scalar AB effect, provides the basis for table-top experiments which yield the limit $m_{ph}\simeq9.4\times10^{-52}$g, a value that improves the results achieved with recent classical and quantum approaches.
    ⬇️ Scroll down to see the full summary

  • Ac response to humidity and propane of sprayed Fe-Zn oxide films

    A. Avila-García, M. García-Hipólito, Y. Matsumoto-Kuwabara.
    249-0
    Abstract:
    Iron-zinc oxide films with different Zn contents were ultrasonically sprayed on glass substrates and inter-digital gold electrodes were evaporated on them. Films were deposited from solutions containing 2, 10 and 30 at.% Zn. Hematite, amorphous and Franklinite structures resulted, respectively. They were assessed as humidity and propane detectors under alternating-current conditions for frequencies from 1 to 10$^{5}$ Hz and two temperatures: 30 and 250$^{\circ}$C. Their impedances in dry air, humid air and humid air plus propane were determined from voltage measurements with a Lock-In amplifier. Sensitivity values to both humidity (53% RH.) and 189, 500 and 786 ppm of propane from the response of the real and imaginary parts of the impedance and also the total impedance were determined as functions of frequency. Maximum sensitivity for each case and the corresponding frequency are reported. The maximum sensitivity to humidity ranges from 24% up to 308%. In the case of propane, the maximum sensitivity ranges from 45% up to 711%. The largest sensitivity values correspond in all cases to the imaginary part of the impedance. From the dynamical response, the response and recovery times are determined, along with the concentration-dependence of the sensitivity. The sensing mechanisms are also discussed.
    ⬇️ Scroll down to see the full summary

  • Relaxation of residual stresses induced by laser shock processing

    C. Rubio-González, A. Garnica-Guzmán, G. Gómez-Rosas
    256-0
    Abstract:
    The Laser shock processing (LSP) is a new surface treatment technique that induces a compressive residual stress field. This work examines the effect of cyclic loading and temperature on the stability of the stress field induced by LSP on 6061-T6 aluminum samples. Residual stress relaxation due to cyclic loading is reported for different stress amplitudes and temperatures. Due to the cyclic creep effect, the residual stress decreases linearly with the logarithm of the number of cycles, N.
    ⬇️ Scroll down to see the full summary

  • Issues of duality in abelian gauge theory and in linearized gravity

    J.A. Nieto, E.A. León, J.A. Nieto, E.A. León
    262-0
    Abstract:
    We start by describing two of the main proposals for duality in abelian gauge theories, namely $F$(ield strength)-duality approach and the $S$% -duality formalism. We then discuss how $F$-duality and $S$-duality can be applied to the case of linearized gravity. By emphasizing the similarities and differences between these two types of dualities we explore the possibility of combining them in just one duality formalism.
    ⬇️ Scroll down to see the full summary

  • A numerical analysis of the supersymmetric flavor problem and radiative fermion masses

    J.L. Díaz-Cruz, O.\., Félix-Beltrán., M. Gómez-Bock, R. Noriega-Papaqui, A. Rosado
    270-0
    Abstract:
    We perform a numerical study of the SUSY flavor problem in the MSSM, which allows us to estimate the size of the SUSY flavor problem and its dependence on the MSSM parameters. For that, we have made a numerical analysis, randomly generating the entries of the sfermion mass matrices and then determined what percentage of these points is consistent with current bounds on the flavor violating transitions on lepton flavor violating (LFV) decays $l_i \rightarrow l_j \, \gamma$. We applied two methods, the mass-insertion approximation method (MIAM) and the full diagonalization method (FDM). Furthermore, we determined which fermion masses could be radiatively generated (through gaugino-sfermion loops) in a natural way, using those random sfermion matrices. In general, the electron mass generation can be obtained for 30% of points for large $\tan\beta$, while in both schemes the muon mass can be generated by 40% of points only when the most precise sfermion splitting (from the FDM) is taken into account.
    ⬇️ Scroll down to see the full summary

  • Effect of heat transfer on the performance of a thermoelectric heat pump driven by a thermoelectric generator

    Lingen Chen., Fankai Meng., Fengrui Sun.
    282-0
    Abstract:
    A model of a thermoelectric heat pump driven by a thermoelectric generator with external heat transfer irreversibility is proposed. The performance of the combined thermoelectric heat pump device obeying Newton's heat transfer law is analyzed using the combination of finite time thermodynamics and non-equilibrium thermodynamics. Two analytical formulae for heating load versus working electrical current, and the coefficient of performance (COP) versus working electrical current, are derived. For a fixed total heat transfer surface area of four heat exchangers, the allocations of the heat transfer surface area among the four heat exchangers are optimized for maximizing the heating load and the COP of the combined thermoelectric heat pump device. For a fixed total number of thermoelectric elements, the ratio of the number of thermoelectric elements of the generator to the total number of thermoelectric elements is also optimized for maximizing both the heating load and the COP of the combined thermoelectric heat pump device. The influences of thermoelectric element allocation and heat transfer area allocation are analyzed by detailed numerical examples. The optimum working electrical currents for maximum heating load and maximum COP at different total numbers of thermoelectric elements and different total heat transfer areas are provided, respectively.
    ⬇️ Scroll down to see the full summary

  • Thermal and optical characterization of pigments attached to cellulose substrates by means of a self-normalized photoacoustic technique

    J.A. Balderas-López, I.S. Martínez-López, M. León-Martínez, Y.M. Gómez, Gómez., M.E. Bautista-Ramírez, A. Muñoz-Diosdado, G. Gálvez-Co, t.., J. Diaz-Re, es.
    292-0
    Abstract:
    A self-normalized photoacoustic (PA) methodology, involving the front and transmission configurations in the Beer-Lambert model for light absorption, is implemented for the measurement of optical and thermal properties of thin layers of substances in solid phase. To achieve this, the corresponding theoretical equations describing the PA effect in the Rosencwaig-Gersho model, were used. This new methodology was applied for the measurement of the optical absorption coefficient (at 658 nm) and thermal diffusivity of paper samples with different colors. This last physical property was also measured for all paper samples by using a self-normalized PA technique, already reported in the literature, involving the surface absorption model. In order to fulfill the theoretical assumptions in this last case, the paper samples were painted, on both sides, with a black marker. The thermal diffusivity values obtained in both cases were quite consistent among themselves and with the corresponding ones reported for similar materials.
    ⬇️ Scroll down to see the full summary

  • The geometrical characteristics of fcc, hcp, and polycrystalline nanowires: simulations of transmission electron microscopy images and diffraction patterns

    J.M. Montejano-Carrizales, R.A. Guirado-López, J.L. Rodríguez-López, J.L. Morán-López
    298-0
    Abstract:
    To theoretically study the physicochemical properties of nanowires, it is necessary to build the corresponding atomic geometrical models. Here we present the geometrical characteristics of nanowires with fcc, hcp, and polycrystalline structures. We consider fcc and hcp wires grown along the (111) and $z$ axis directions, respectively, with various diameters and lengths. In addition, since staking faults in these systems are very common, we analyze also the case of nanowires formed by stacked pieces having different crystalline structures and orientations, a fact that leads to the formation of several internal interfaces. By performing simulations of transmission electron microscopy (TEM) images and diffraction patterns of the nanowires considered here, we reveal how sensitive are the calculated images to the defocus condition as well as to the orientation of the wire with respect to the incident beam, a result that must be taken into account in order to better understand the measured data.
    ⬇️ Scroll down to see the full summary

  • Umbrales de percolación de sitios. Pequeñas celdas bidimensionales asimétricas

    W. Lebrecht, J.F. Valdés
    307-0
    Abstract:
    Site percolation thresholds $p_c$ and critical exponent $\nu$ associated to square lattices, triangular lattices and hexagonal lattices are obtained. We consider a methodology consisting in the growth in size of cells for each geometry, denoted for $M$. A site is occupied with probability $p$ and $1-p$ if it is not occupied. Two directions of the plane: horizontal and vertical, through asymmetrical cells are considered for studying site percolation phenomena, so, a percolation functions associated to horizontal or vertical direction, $f^H(M,p)$ or $f^V(M,p)$ are obtained respectively. Using finite scaling techniques, the critical points at the thermodynamic limit are obtained. Site percolation thresholds are compared through three different ways: first, using the maximum of the derivative of the function $f^{(H,V)}(M,p)$ denoted by $p_p^{(H,V)}(M)$, second, considering the solution of the equation $f^{(H,V)}(M,p)=p$, denoted by $p_g^{(H,V)}(M)$, and third, using the cross-point of the curves associated to percolation thresholds for horizontal and vertical directions, represented by $p_f(M)$. Critical exponent $\nu$ is obtained through two different ways: first, using the maximum of the derivative defined as $f'^{(H,V)}(M,p_p)$, and second, considering the cross point of both derivatives $f'(M,p_f)$. The values associated to site percolation thresholds and critical exponent $\nu$ are in good agreement with the similar ones informed in literature, validating the methodology proposed here.
    ⬇️ Scroll down to see the full summary

  • Two, three and four photon absorption of naphthalene

    J.C. Poveda, A. Guerrero., I. Álvarez, C. Cisneros
    312-0
    Abstract:
    The effects of the multiple-photon absorption on the ionization, MPI, and dissociation, MPD, of Naphthalene were investigated. Laser radiation of 266 nm at pulse widths of 4.5 ns and intensities of the order of 10$^{8}$-10$^{10}$ W$\cdot $cm$^{ - 2}$, and carrier gases, CGs, such as helium, neon, argon, krypton, and xenon were used. In order to identify the produced ions, the time of flight mass spectrometry technique, ToF-MS, was employed. From the experimental data the number of photons absorbed was calculated, being two at low energies per pulse, less than 1.0 mJ, where the parent ion, C$_{10}$H$_{8}^{ + }$, was detected, in agreement with the ionization energy of Naphthalene, 8.14 eV. Increasing the energy per pulse to more than 1.0 mJ, new ions were observed, and three and four photons processes were identified. The effect of the CG was also investigated: the ion yields change as a function of energy per pulse and the CG. A sequence of pathways for photoionization and photodissociation was proposed taking into account the energy per pulse, number of absorbed photons and normalized ion yields.
    ⬇️ Scroll down to see the full summary

  • The three dynamical fates of Boson Stars

    F.S. Guzmán
    321-0
    Abstract:
    In this manuscript the three types of late-time behavior of spherically symmetric Boson Stars are presented, namely: stable configurations, unstable bounded that collapse and form black holes and unstable unbounded that explode. These three possibilities have been predicted by perturbation theory and other analytical results, whereas the full non-linear evolution of Boson Star configurations has verified the stable and unstable bounded cases using numerical relativity. In this paper also the unbounded case is confirmed to happen. In order to do so, Boson Star solutions are used as initial data of the Einstein-Klein-Gordon system of equations formulated as a constrained initial value problem, which in turn is solved using the finite differences approximation.
    ⬇️ Scroll down to see the full summary

  • Empleo de detector semiconductor de c-Si del tipo microbandas en la obtención de imágenes radiográficas digitales de maniquíes y muestras biológicas de mamas

    A. Le, va., A. Cabal, I. Piñera, Y. Abreu, C.M. Cruz, L.M. Montaño, C.C. Díaz, M. Fontaine, C.M. Ortiz, F. Padilla, R. de la Mora
    327-0
    Abstract:
    The present work synthesizes the experimental results obtained in the characterization of 64 microstrips crystalline silicon detector designed for experiments in high energies physics, with the objective of studying its possible application in advanced medical radiography, specifically in digital mammography and angiography. The research includes the acquisition of two-dimensional radiography of a mammography phantom using the scanning method, and its comparison with similar images simulated mathematically for different X rays sources. The paper also shows the experimental radiography of two biological samples taken from biopsies of mammas, where it is possible to identify the presence of possible pathological lesions. The results reached in this work point positively toward the effective possibility of satisfactorily introducing those advanced detectors in medical digital imaging applications.
    ⬇️ Scroll down to see the full summary