Ensenada Center for Scientific Research and Higher Education

About: Ensenada Center for Scientific Research and Higher Education is a facility organization based out in Ensenada, Mexico. It is known for research contribution in the topics: Population & Nonlinear system. The organization has 1934 authors who have published 3733 publications receiving 63115 citations.

An improved method for the wave propagation constant ? estimation in broadband uniform millimeter-wave transmission line

Abstract: A new method is derived for computing the wave propagation constant γ of a uniform transmission line. The new method is based on the properties of a similar and unitary matrix, and allows us to minimize the errors due to connection repeatability. These matrices are obtained from the wave cascade matrices (computed from scattering parameter measurements) of two different length lines of identical but unknown characteristic impedance. The usefulness of the new method is demonstrated by assessing the dispersion of the dielectric constant eeff and the attenuation constant α of an ultra-low-loss transmission line in the frequency range of 0.040–65 GHz. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 22: 268–271, 1999.

Correlating the Arperos Basin from Guanajuato, central Mexico, to Santo Tomás, southern Mexico: Implications for the paleogeography and origin of the Guerrero terrane

Abstract: The Guerrero terrane has been interpreted either as a Mesozoic Pacific multi-arc system accreted to North America, or as a detached slice of the North American continental margin, which was rifted during backarc spreading and subsequently accreted back to the continental mainland. In order to test these two scenarios, we present here a petrologic study of metasandstones from the Santo Tomas area, southern Mexico. Our data document that the Guerrero terrane suture belt contains the remnants of the Tithonian–Cenomanian Arperos Basin. This basin displays a marked provenance asymmetry. Its eastern margin is composed of metasedimentary rocks derived from sources in the North American continental mainland, whereas its western margin consists of a metasedimentary succession derived from volcanic sources of the Guerrero terrane. Sedimentation in the Arperos Basin was coeval with the emplacement of Tithonian–Barremian felsic dikes and lava flows with volcanogenic massive sulfide deposits and Aptian–Cenomanian intraplate-like and mid-ocean ridge basalts. This suggests that the Arperos Basin evolved progressively from continentally to oceanic floored during the Early Cretaceous and that a mature oceanic crust was generated only ca. 15 Ma before the accretion of the Guerrero terrane, which took place in the late Cenomanian. On the basis of this evidence, we favor a North American origin for the Guerrero terrane, which is then considered to represent a west-facing North American arc that was rifted from the continental mainland during backarc spreading and subsequently accreted back to nuclear Mexico.

On the stability of elliptical vortex solutions of the shallow-water equations

Abstract: The one-layer reduced gravity (or ‘shallow water’) equations in the f-plane have solutions such that the active layer is horizontally bounded by an ellipse that rotates steadily. In a frame where the height contours are stationary, fluid particles move along similar ellipses with the same revolution period. Both motions (translation along an elliptical path and precession of that orbit) are anticyclonic and their frequencies are not independent; a Rossby number (R0) based on the combination of both of them is bounded by unity. These solutions may be taken, with some optimism, as a model of ocean warm eddies; their stability is studied here for all values of R0 and of the ellipse eccentricity (these two parameters determine uniquely the properties of the solution).Sufficient stability conditions are derived from the integrals of motion; f-plane flows that satisfy them must be either axisymmetric or parallel. For the model vortex, the circular case simply corresponds to a solid-body rotation, and is found to be stable to finite-amplitude perturbations for all values of R0. This includes R0 > ½, which implies an anticyclonic absolute vorticity.The stability of the truly elliptical cases are studied in the normal modes sense. The height perturbation is an n-order polynomial of the horizontal coordinates; the cases for 0 ≤ n ≤ 6 are analysed, for all possible values of the Rossby number and of the eccentricity. All eddies are stable to perturbations with n ≤ 2. (A property of the shallow-water equations, probably related to the last result, is that a general finite-amplitude n-order field is an exact nonlinear solution for n ≤ 2.) Many vortices - noticeably the more eccentric ones - are unstable to perturbations with n ≥ 3; growth rates are O(R02f) where f is the Coriolis parameter.

N-Doped carbon nanotubes enriched with graphitic nitrogen in a buckypaper configuration as efficient 3D electrodes for oxygen reduction to H2O2

Abstract: Herein, a series of N-doped carbon nanotube (CNx) samples were obtained by modifying the synthesis temperature. Consequently, the proportion of graphitic nitrogen (Ngraph) in the samples was systematically increased as a function of temperature. This allowed evaluation of the role of the CNx graphitic nitrogen in the oxygen reduction reaction (ORR). A correlation between the Ngraph content and the ORR onset potential was observed, which shifted to more positive potentials with an increase in kinetic current density (jk); this showed that Ngraph played a significant catalytic role in the ORR. The samples with high Ngraph content favored the two-electron pathway for the ORR not only in basic media (pH = 13) but also in neutral media (pH = 7), representing an attractive alternative for wastewater remediation through the on-site generation of H2O2. The energetic calculations showed that the formation of H2O2 must be favorable in the presence of graphitic nitrogen sites. Finally, the performance of the buckypaper arrangement was evaluated, and the CNx buckypaper showed a higher cathodic current peak as compared to CNx traditional ink dispersions. Overall, this study not only sheds light on the role of Ngraph in the ORR, but also demonstrates that CNx buckypaper is an efficient 3D electrode for electrocatalytic applications.