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Search Results: 1 - 10 of 274664 matches for " Carlos R. Cabrera "
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Presencia de Trachemys Agassiz, 1857 (Testudines, Emydidae) en el Pleistoceno tardío del centro de la Argentina
Cabrera,Mario R.; Luna,Carlos A.;
Cuadernos de herpetolog?-a , 2011,
Abstract: the first fossil record at central argentina of both the turtle genus trachemys agassiz, 1857 and the family emydidae rafinesque, 1815 is described. the fossil material, of late pleistocene - early holocene age, is composed of the proneural plate, the right pleurals iv and viii, and fragments of the left pleurals iii and iv, parts of the right epiplastron, hyoplastron and hypoplastron, and three indeterminate fragments. these shell elements were discovered at el silencio site (30°53'20" s, 62°49'29" w), southern coast of the saline mar chiquita lake, córdoba province, argentina, in a siltite level with calcium carbonate intercalations assigned to the tezanos pinto formation, whose deposition occurred between 36000 and 8000 years bp. the fossil record is related to a humid event between 16500 and 15500 years bp that, if marked and temporarily sustained enough, may have favoured the colonization by trachemys (as well as other vertebrate taxa) during the pleistocene into this area where the genus do not live today, 220 km far to the west of its present distribution.
Presencia de Trachemys Agassiz, 1857 (Testudines, Emydidae) en el Pleistoceno tardío del centro de la Argentina
Cabrera, Mario R.,Luna, Carlos A.
Cuadernos de Herpetología , 2011,
Abstract: En este trabajo se describen restos del caparazón de una tortuga que constituyen el primer registro del género dulceacuícola Trachemys Agassiz, 1857 y de la familia Emydidae Rafinesque, 1815 en la provincia de Córdoba, y el hallazgo más occidental de ambos en la Argentina. Los materiales recuperados consisten en la placa proneural, las placas pleurales IV y VIII derechas y fragmentos de las placas pleurales III y IV izquierdas, epiplastron, hioplastron e hipoplastron derechos, más tres fragmentos indeterminables. Los restos provienendel Sitio El Silencio (30°53’20" S, 62°49’29" W), un yacimiento paleontológico de edad Pleistoceno tardío - Holoceno temprano, expuesto en la costa de la actual laguna Mar Chiquita, en un nivel de limo con intercalaciones de carbonato de calcio asignado a la Formación Tezanos Pinto, cuya depositación se produjo entre los 36.000 y 8.000 AP. El registro esrelacionado con un evento húmedo acontecido entre los 16.500 y 15.500 a os AP, que pudo haber sido lo suficientemente marcado y sostenido como para posibilitar el ingreso deTrachemys (y otros taxones vertebrados) durante el Pleistoceno a cercanías de la laguna Mar Chiquita, unos 220 km hacia el oeste de su distribución actual.
Politerapia en Epilepsias "Polytherapy in Epilepsy"
Fernando Cabrera R,Carlos Acevedo Sch,Mario Mu?oz R
Revista chilena de pediatría , 1984,
Abstract:
On the classification of laminations associated to quadratic polynomials
Carlos Cabrera
Mathematics , 2007,
Abstract: Given any rational map $f$, there is a lamination by Riemann surfaces associated to $f$. Such laminations were constructed in general by Lyubich and Minsky. In this paper, we classify laminations associated to quadratic polynomials with periodic critical point. In particular, we prove that the topology of such laminations determines the combinatorics of the parameter. We also describe the topology of laminations associated to other types of quadratic polynomials.
Vulcan/Pt/Ce Catalysts Prepared by Impregnation Using EDTA for Direct Methanol Fuel Cell, Direct Ethanol Fuel Cell, and Polymer Electrolyte Membrane Fuel Cell  [PDF]
Rolando Guzmán-Blas, Christian L. Menéndez, Carlos A. Vélez, Estev?o Rosim Fachini, Aaron Johnston-Peck, Sanjaya D. Senanayake, Dario Stacchiola, Kotaro Sasaki, Carlos R. Cabrera
Smart Grid and Renewable Energy (SGRE) , 2013, DOI: 10.4236/sgre.2013.47A001
Abstract:

A wet chemistry synthesis of Pt-Ce doped catalysts on carbon Vulcan support using an impregnation method with EDTA is presented. The composite catalyst was characterized by XRD, XPS and TEM. The catalytic activity of the prepared material was tested in a direct fuel cell using methanol, ethanol and hydrogen as fuels. The polarization and power curves showed that the Vulcan/Pt/Ce(III) doped catalysts improved the performance of the fuel cells when compared with Vulcan-Pt anode materials.

Nanostructural Formation of Pd-Co Bimetallic Complex on HOPG Surfaces: XPS and AFM Studies
Lisandra Arroyo-Ramírez,Rubenier Montano-Serrano,Raphael G. Raptis,Carlos R. Cabrera
Journal of Nanotechnology , 2009, DOI: 10.1155/2009/971423
Abstract: A new single source approach was developed to synthesize Pd-Co nanoparticles using a bimetallic compound, [ E t 3 N H ] 2 [ C o P d 2 ( ?? - 4 - I - 3 , 5 - M e 2 p z ) 4 C l 4 ] ( C o P d 2 ) , as a molecular precursor to obtain dispersed catalyst on highly ordered pyrolytic graphite (HOPG) surface, in view of preparing oxygen reduction catalysts for low temperature fuel cells. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques were employed to characterize the nanostructure formations and to determine the composition and morphology of the complex on the HOPG. Results of high resolution XPS analysis (HR-XPS) revealed the binding energies corresponding to the atomic constituents of the precursor. When the precursor solution was placed on the surface of the HOPG, the bimetallic complex assumes a tubular structure and it appears that the surface of the HOPG offers a ground for the self-organization of nanostructural formations. 1. Introduction Nanoarchitecture is an emerging area that fuels the interests of scientists and engineers alike, largely due to the novel material properties that can be engineered and tuned at molecular levels. These nanomaterials are mainly used for heterogeneous catalysis. Platinum is used extensively as a catalyst in both anodes and cathodes of low-temperature polymer electrolyte fuel cells. Low-temperature fuel cells are considered alternate power sources for portable and transportation applications [1]. In spite of its excellent electrocatalytic activity, the use of monometallic platinum is disadvantageous due to its intermediate poisoning and high cost. Sophisticated bimetallic, cost-effective Pd-Co catalysts were recently proposed for oxygen reduction reaction in low-temperature fuel cells, especially for direct methanol fuel cell applications due to their methanol tolerance ability and appreciable oxygen reduction efficiency [2]. When bimetallic catalysts are prepared by using multiple precursors, it is difficult to attain homogeneous catalytic system characterized by a uniform particles size distribution. In order to achieve such objective, in this paper, a single organometallic precursor characterized by a well-defined Pd-Co ratio has been used. This approach would allow the formation of nanostructures and nanoparticles with defined size and composition distribution. This paper reports on the characterization of a CoPd2 precursor and deposition for the nanoarchitectural formation on highly ordered pyrolytic graphite surface through surfaces analysis techniques such as X-ray photoelectron
Sequential Electrodeposition of Platinum-Ruthenium at Boron-Doped Diamond Electrodes for Methanol Oxidation
Ileana González-González,Camille Lorenzo-Medrano,Carlos R. Cabrera
Advances in Physical Chemistry , 2011, DOI: 10.1155/2011/679246
Abstract: Sequential electrodeposition of Pt and Ru on boron-doped diamond (BDD) films, in 0.5?M H2SO4 by cyclic voltammetry, has been prepared. The potential cycling, in the aqueous solutions of the respective metals, was between 0.00 and 1.00?V versus Ag/AgCl. The catalyst composites, Pt and PtRu, deposited on BDD film substrates, were tested for methanol oxidation. The modified diamond surfaces were also characterized by scanning electron microscopy-X-ray fluorescence-energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and Auger electron spectroscopy. The scanning Auger electron spectroscopy mapping showed the ruthenium signal only in areas where platinum was electrodeposited. Ruthenium does not deposit on the oxidized diamond surface of the boron-doped diamond. Particles with 5–10% of ruthenium with respect to platinum exhibited better performance for methanol oxidation in terms of methanol oxidation peak current and chronoamperometric current stability. The electrogenerated ?OH radicals on BDD may interact with Pt surface, participating in the methanol oxidation as shown in oxidation current and the shift in the peak position. The conductive diamond surface is a good candidate as the support for the platinum electrocatalyst, because it ensures catalytic activity, which compares with the used carbon, and higher stability under severe anodic and cathodic conditions. 1. Introduction The direct methanol fuel cells (DMFC) are electrochemical cells that convert chemical energy in electrical energy that can be use to power all kind of appliances. Similar to polymer electrolyte membrane fuel cells (PEMFCs), in the DMFC the anode catalyst draws the hydrogen from the methanol, and both systems use a solid electrolyte, reducing the corrosion of the device and improving the power density. Various catalytic composite systems have been studied, including PtRuOsIr [1], PtRuOs [2], PtMo [3, 4], and PtRu [5, 6]. Electrodes with catalyst nanoparticles have been found to have highly catalytic performance, and the catalytic activity was found to depend on the particle size, the nature of the support, as well the preparation method [7]. One of the subjects of research on high-efficiency fuel cells is how to minimize the electrocatalytic noble metal loading without losing the high catalytic activity. This is achieved by dispersing nanoparticles of the catalytic materials (mainly Pt-based alloys) on high surface area materials used as supports. The supports need to, in addition to having high surface, be stable and conductive. The most commonly used particle support
Anisakiasis outbreak by Anisakis simplex larvae associated to Peruvian food in Spain Epidemia de Anisakiasis por larvas de Anisakis simplex en Espa a asociada a alimentos peruanos
R. Cabrera
Revista Espa?ola de Enfermedades Digestivas , 2010,
Abstract:
Preparación y evaluación de conjugados de polisacárido Vi de Salmonella typhi con toxoide tetánico
Cabrera,Osmir; Cuello,Maribel; Soto,Carmen R.; Pérez,Oliver; Taboada,Carlos M; Fari?as,Mildrey; Sierra,Gustavo;
Vaccimonitor , 2002,
Abstract: salmonella typhi vi polysaccharide is a t-independent antigen that has proven to be protective in young adults. in controlled clinical trials in areas with high rates of typhoid fever, the protective efficacy of the vi was approximately 70%. however, in high-risk populations, different methods have been used, to synthesize vi polysaccharide-protein conjugates in order to enhance the antibody response and to confer t-dependent properties to the polysaccharide. in this study a conjugate, vi polysaccharide -protein, was obtained and its immunogenicity was evaluated in mice. purified vi polysaccharide was linked to a carrier protein (tetanus toxoid (tt), via a carbodiimide-mediated reaction. the resultant conjugate was more immunogenic in mice than vi alone. in contrast to the t-independent properties of vi, the conjugates of this polysaccharide with tt induced secondary responses and an increase in the duration of igg anti vi antibodies, in mice. serum of animals inoculated with the conjugate showed high igg anti-tt antibody titers, similar to native tt.
Consentimiento informado traslativo: Caso clínico
Cabrera Lozada,Carlos;
Revista de Obstetricia y Ginecología de Venezuela , 2001,
Abstract: the doctor-patient relation is a fundamentally humane relationship which requires honesty and respect from its participants in cases of incapacity to exert the bioethical principle of autonomy, informed substitute consent is required. a case is presented where the patients is medically sterilized by surgery due to her mental incapacity, with informed substitute consent from her mother. five years later the patient issues a claim with her husband questioning the dilemma of her right to procreation combined to quality of life issues. the matter is analyzed and it is concluded to concede the informed substitutive consent to her husband so a tube recanalization is performed, allowing her to bear children. as a result, the term translative of inform substitutive consent is proposed, for cases where the informed consent is reassigned from one tutor to another
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