Vol. 57 No. 6 (2011): Revista Mexicana de Física.

Published: 2011-01-01

Articles

  • Nano hydroxyapatite crystals obtained by colloidal solution

    D. Meza, I.A. Figueroa, C. Flores-Morales, M.C. Piña-Barba
    471-0
    Abstract:
    A process for synthesising nanocrystalline hydroxyapatite powders using calcium nitrate tetrahydrated [Ca(NO$_{3})_{2}$-4H$_{2}$O] and phosphorous pentoxide [P$_{2}$O$_{5}$] by colloidal solution, is presented and discussed. The powders were washed and calcinated at different temperatures and then characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The powder size was compared with the results obtained from TEM and the calculated with the Scherrer's formula.
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  • Refractive index of multiline nanosecond laser-induced periodic surface structures and porous silicon

    J.E. Alfonso-Orjuela, D.F. Andrade-Zambrano, J.M. Arro, o-Osorio.
    475-0
    Abstract:
    To study the effect of multiline laser processing in the optical response of silicon, a set of p-type single-crystalline silicon wafers with 0.01 to 0.02 $\Omega$m resistivity, 525 $\mu$m thickness, and [111] orientation, was irradiated with a multiline Nd:YAG pulsed laser (1064, 532 and 355 nm) applying energies from 310 to 3100 J. A group of those surfaces was produced using argon gas blowing, while other group was manufactured in free atmosphere. Using confocal microscopy, it was observed that the gas-protected samples shown surface periodic structures in the form of ripples with an average pitch of 547 nm. Trough diffuse reflectance tests it was determined that proportionally to the energy supplied in the laser processing, these surfaces reflect between 10% and 30% in the UV region and between 60% and 80% in the IR region. On the other hand, the free atmosphere-made surfaces presented structures and diffraction properties characteristic of porous silicon (PS). The refractive index of the surfaces with periodic structures was calculated based on the diffuse reflectance measures while that of PS surfaces was calculated using the surface voids fraction (pores) determined with the confocal microscope image analysis software.
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  • WKB quantization for completely bound quadratic dissipative systems

    G. González, H. Iván Piza
    481-0
    Abstract:
    We study the energy quantization for completely bound dissipative systems over a full cycle of motion. We approach the problem by means of an effective phenomenological Hamiltonian and the WKB quantization rule to obtain the energy levels in the system. An example of this approach is given for the quantum bouncer with quadratic dissipation.
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  • Propiedades termodinámicas de fluidos de hombro/pozo cuadrado

    M. Bárcenas, G. Odriozola, P. Orea
    485-0
    Abstract:
    Shoulder-square-well systems are studied by means of replica exchange Monte Carlos simulations. By fixing the depth and range of the square well, the influence of the shoulder height is analyzed on the phase diagrams, structure, and phase behavior. Results show that an increase of the shoulder height leads to a decrease of the critical point temperature and density. Furthermore, a larger shoulder height also favors crystallization by restricting the bonding length range.
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  • La abertura de una lente, su efecto en el espectro de difracción convolutivo, frecuencia espacial y viñeteado

    E. Andrés-Zárate, A. Cornejo-Rodríguez
    491-0
    Abstract:
    We present two diffraction models considering spatial frequencies, one paraxial and the other non-paraxial, to study the effect of the finite aperture of a lens used as transformer of the diffracted light. We use concepts of both geometrical and physical optics as the propagation of the angular spectrum as a convolved diffracted field of monochromatic waves. The analysis is based on the propagation of a diffracted monochromatic electric field produced by an object, located in a perpendicular plane to the propagation path, and placed at a finite distance of a transformer lens. We obtained a set of equations for the paraxial and maximum spatial frequencies accepted by the entrance pupil, associated to the lens, with respect to the size of the diffracting object, in order to reduced the vignetting.
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  • La morfogénesis como resultado de la transmisión e integración de información biológica

    L. de J, P. Padilla-Longoria
    499-0
    Abstract:
    In his original paper on the chemical basis of morphogenesis, A.M. Turing [1] proposes a mechanism based on the combined effect of diffusion and two reacting morphogens to explain the emergence of patterns. In the same paper he suggests that this framework can be applied to the case of genetic regulatory networks. This approach has been criticized since the so called morphogenes have been difficult to identify in many cases. In this paper we propose that the effect of diffusion and chemical reactions can be either replaced or complemented by intercellular communication mechanisms. Conceptually this is equivalent to saying that what is effectively diffusing is information. In other words, that information can be treated as the actual morphogene. We present a formalism based on stochastic $\Pi$-calculus that enables us to obtain patterns in a prototypical case, namely, the activator-inhibitor system.
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  • Anharmonic properties of raman modes in double wall carbon nanotubes

    J. Marquina, CH. Power, J.M. Broto, E. Flahaut, J. Gonzalez
    510-0
    Abstract:
    The temperature dependence of the radial breathing modes (RBMs) and the zone-center tangential optical phonons (G-bands) of double-walled carbon nanotubes (DWCNTs) has been investigated between 300 and 700 K using Raman scattering. As expected, with increasing temperature, the frequencies of the Raman peaks, including the RBMs and G-bands downshift simultaneously. We show here that the temperature dependence of the RBMs can be fitted by a simple linear dependence and different RBMs have different frequency shifts. We observe a noticeable nonlinearity in the temperature dependence of the G-band associated with the outer semiconducting tube $\text{G}_{\text{ext}}^ + \left( \text{s} \right)$. The deviation from the linear trend is due to the contribution of the third-order anharmonic term in the lattice potential energy with a pure temperature effect. An estimated value of 1.5 for the Grüneisen parameter of the $\text{G}_{\text{ext}}^ + \left( \text{s} \right)$ band was found.
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  • Comparative measurement of in plane strain by shearography and electronic speckle pattern interferometry

    A. Martínez, J.A. Ra, as., R. Cordero, F. Labbe
    518-0
    Abstract:
    In this work, an optical setup that gives the possibility of using either ESPI or ESPSI has been implemented to assess in-plane strains induced on a composite sample. First, in-plane ESPI was used to measure displacement fields, which later allowed us to evaluate the corresponding strain fields. Next, we applied ESPSI to measure the derivative of in-plane surface displacements (the strains). The experimental results obtained by applying both techniques (ESPI and ESPSI) were compared. We found that the difference between the strain fields obtained by ESPSI and ESPI was roughly a constant. This result was expected since, although ESPI allows computing absolute strain values, the strains measured by ESPSI are relative to a reference that must be measured using an additional method. Once calibrated the system ESPSI, the ESPI could no longer be used. The strain field obtained in ESPSI is corrected by the sum of constant value calculated.
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  • Enhancement backscattering of light: a direct visual-desktop experience

    R. Espinosa-Luna, G. Atondo-Rubio, S. Hinojosa-Ruiz
    524-0
    Abstract:
    Direct visual images of the angular distribution of light scattered by one-dimensional, quasi-one-dimensional and two-dimensional randomly rough surfaces, in both plane- and conical-geometries of incidence, are shown. By using a simple desktop arrangement, the images clearly show the enhancement backscattering of light effect for these samples under a 633 nm wavelength, un-polarized, He-Ne laser illumination. Of particular interest is a circularly symmetric enhanced backscattering pattern associated to the uniformly two-dimensional rough surface employed. The surface profiles of the well-characterized samples can be modeled as a Gaussian random process with Gaussian correlation functions too.
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  • Estudio experimental sobre la evolución de los efectos no lineales que generan un espectro supercontinuo en fibras de cristal fotónico usando pulsos con duración de ns

    J. C, J.M. Estudillo-A, ala., R. Rojas-Laguna, O. Pottiez, R.I. Mata-Chavez, J.M. Delgado-Negrete, E. Vargas-Rodríguez, J.A. Andrade-Lucio
    528-0
    Abstract:
    This paper presents the experimental study on the spectral evolution of a pump pulse spread into two different types of microstructures with solid core in photonic crystal fiber (PCF). We use as pumping source a laser Q-Switched Nd: YAG operating in the regime of nanosecond pulses (6 ns) with a central wavelength of 1064 nm, a repetition rate of 20 Hz and an energy of $\sim $ 180 mJ. Supercontinuum spectrum evolution is presented for a range of variation of input power between 0.05 mW to 1.86 mW at the input of the PCF. We analyze the pulse broadening explains the nonlinear phenomena involved in the process generation of new frequencies that appear in the input pulse. An important aspect is based on the development of an optical scheme which is capable of providing adequate control over the coupling of light at the input of the PCF and prevents the damage to the fibers used in this work. As it is known, the pulses generated by the laser Q-SWITCH Nd:YAG are very intense and can damage the PCF used, for this reason, the development of optical scheme was essential to obtain the spectra of supercontinuum generated in each of the PCF (spectra that have with a spectral width of $\sim $ 705 nm and $\sim $ 1100 nm). Finally, this paper describes the possible potential applications that can be implemented with the type of spectrum generated in each fiber.
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  • Medición de temperatura usando un VCO integrado en silicio

    E. Monto, a-Suárez., F. S, oval-Ibarra., S. Ortega-Cisneros
    535-0
    Abstract:
    The oscillation frequency $f_{0}$ of a VCO current-starved has been used for sensing temperature ranging from 20 to 99$^{\circ}$C. Since $f_{\text{0}}$ is directly proportional to the short-circuit current of the basic cell delay (NOT gate), and taking into account that this current, $I_{\text{SHORT}}$, is directly proportional to the carrier mobility, it is possible to explain how $f_{\text{0}}$ changes as temperature, $T$, changes too. This oscillator that was manufactured in a CMOS standard process, N-well, 0.5 $\mu $m, 5 V, facilitates the integration of circuitry conditioning, which means the feasibility of integrating the whole sensor system in a chip. Digital circuit measures the frequency $f_{\text{0}}$ each 53 ms because the measure step is deduced from the linear fitting applied to the $f_{\text{0}}$ vs. $T$ characteristic.
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  • Single-electron Faraday generator in a rotating electric field

    G. González
    541-0
    Abstract:
    Recently, it was shown in Ref. 1 that single-electron tunneling (SET) oscillations were possible by rotating a conducting rod with a small tunnel juntion immerse in a uniform magnetic field perpendicular to the plane of motion. The purpose of this letter is to show that SET oscillations can be enhanced by applying a rotating electric field in resonance with the rotational motion of the conducting rod.
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