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Search Results: 1 - 10 of 146 matches for " Persi Schacht "
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Influence of Vanadium Oxidation States on the Performance of V-Mg-Al Mixed-Oxide Catalysts for the Oxidative Dehydrogenation of Propane
Leticia Schacht,Juan Navarrete,Persi Schacht,Marco A. Ramírez
Revista de la Sociedad Química de México , 2010,
Abstract: Se prepararon mezclas de óxidos de V-Mg-Al como catalizadores en la reacción de deshidrogenación oxidativa de propano. Los catalizadores se obtuvieron a partir de la descomposición térmica de hidróxidos Mg-Al de doble capa y modificados con vanadio en la intercapa. El comportamiento catalítico depende de la manera de incorporación del vanadio dentro de la estructura, la cual esta definida por la relación Mg/Al. Los resultados obtenidos muestran que la relación Mg/AL determina la forma de incorporación y el estado de oxidación del vanadio en la estructura. Las propiedades superficiales se estudiaron por medio de espectroscopia fotoelectrónica de rayos X, espectroscopia UV-visible y temperatura programada de reducción. La información obtenida de estos análisis permitió establecer los estados de oxidación del vanadio antes y después de la reacción química. De acuerdo con estos resultados, se sugiere que la selectividad hacia propeno depende del estado de oxidación del vanadio en el catalizador.
Effect of Support Acidity on n-heptane Reforming over Pt/Beta zeolite+γAlumina Catalysts
Sergio Ramírez,Persi Schacht,Jorge Ancheyta
Revista de la Sociedad Química de México , 2005,
Abstract: En el presente trabajo se prepararon muestras de catalizadores de platino soportadas en mezclas de zeolita beta+gama alúmina. Los catalizadores se sintetizaron utilizando diferentes contenidos de zeolita en el soporte final, así como empleando zeolita previamente intercambiada con cationes de litio y cesio, y mezclada con alúmina. Los soportes y los catalizadores se caracterizaron por absorción atómica, difracción de rayos X, adsorción de nitrógeno, FTIR de la adsorción de piridina y CO, quimisorción de hidrógeno y TPD de amoníaco. Los resultados de la caracterización de los soportes muestran propiedades con valores entre las de los materiales iniciales y revelan una composición uniforme sin destrucción de las estructuras cristalinas de la zeolita beta y la alúmina. La actividad catalítica de los catalizadores se evaluó en un reactor de vidrio a 663 K y presión atmosférica. Se utilizó la reformación de n-heptano como reacción de prueba. Las variaciones en la selectividad de los productos con la composición del soporte se correlacionaron con el grado de neutralización de la zeolita. Estas variaciones se atribuyeron a la modificación de las propiedades electrónicas del platino soportado que afectan la fuerza y la duración del enlace del hidrocarburo adsorbido. Los espectros FTIR de la adsorción de CO también sugieren la posibilidad de que las modificaciones en la morfología de las partículas de platino contribuyan a los cambios de selectividad observados
Effect of CoMo/HSO3-functionalized MCM-41 over Heavy Oil
Persi Schacht,Julia Aguilar-Pliego,Marco Ramírez-Garnica,Sergio Ramírez
Revista de la Sociedad Química de México , 2010,
Abstract: En el presente trabajo se explora el potencial del catalizador Co-Mo/MCM-41 funcionalizado en la reacción de hidroconversión de aceite crudo pesado. El material MCM-41 fue sintetizado conforme a métodos reportados en literatura. El Co y Mo se incorporaron al soporte empleando la técnica de impregnación simultánea. Así mismo, el catalizador sintetizado fue caracterizado determinando su área específica, difracción de rayos X; se confirmó su distribución de canales de poros por medio de microscopía electrónica de transmisión. También se estudiaron las propiedades ácidas por espectroscopia de infra-rojo así como también de la adsorción de piridina. Para medir la actividad catalítica, se empleó aceite crudo pesado del Golfo de México. La gravedad API se incrementó de 12.5 a 20.2, la viscosidad cinemática se redujo de 18700 a 110 cSt determinada a 298 K, el contenido de asfaltenos y azufre también se reducen notablemente.
Effect of CoMo/HSO3-functionalized MCM-41 over Heavy Oil
Schacht, Persi;Aguilar-Pliego, Julia;Ramírez-Garnica, Marco;Ramírez, Sergio;Abu, Ibrahim;Nore?a-Franco, Luis;
Journal of the Mexican Chemical Society , 2010,
Abstract: the potential of co-mo metals supported on functionalized mcm-41 as catalyst to hydrodesulfurization of heavy oil has been explored in this work. the mcm-41 functionalized sample was synthesized according to methods previously reported in the literature. co and mo metals were incorporated into the support by simultaneous impregnation. the catalyst was characterized by specific surface area and x-ray diffraction. the pore channel of mcm-41 was confirmed by transmission electronic microscopy and infra red spectroscopy. catalytic activity tests were carried out using heavy oil from gulf of mexico. the api gravity was increased from 12.5 to 20.2, the kinematics viscosity was decreased from 18,700 to 110 cst at 298 k, the contents of asphaltene and sulfur were also reduced.
Spin State Detection and Manipulation and Parity Violation in a Single Trapped Ion
M Schacht
Physics , 2013,
Abstract: Atomic Parity Violation provides the rare opportunity of a low energy window into possible new fundamental processes at very high mass scales normally investigated at large high energy accelerators. Precise measurements on atomic systems are currently the most sensitive probes of many kinds of new physics, and complement high energy experiments. Present atomic experiments are beginning to reach their limits of precision due to either sensitivity, systematics or atomic structure uncertainties. An experiment in a single trapped Barium ion can improve on all of these difficulties. This experiment uses methods to precisely manipulate and detect the spin state of a single ion in order to measure a parity induced splitting of the ground state magnetic sublevels in externally applied laser fields. The same methods can be used to provide precise measurements of more conventional atomic structure parameters.
Two Potential Mechanisms of Spatial Attention in Early Visual Areas
Erez Persi
Quantitative Biology , 2008,
Abstract: We investigate theoretically the effect of spatial attention on the contrast-response function (CRF) and orientation-tuning curves in early visual areas.We look at a model of a hypercolumn developed recently (Persi et al., 2008), that accounts for both the contrast response and tuning properties in the primary visual cortex, and extend it to two visual areas. The effect of spatial attention is studied in a model of two inter-connected visual areas, under two hypothesis that do not necessarily contradict. The first hypothesis is that attention alters inter-areal feedback synaptic strength, as has been proposed by many previous studies. A second new hypothesis is that attention effectively alters single neuron input-output properties. We show that with both mechanisms it is possible to achieve attentional effects similarly to those observed in experiments, namely contrast-gain and response-gain effects, while keeping the orientation-tuning curves width approximately contrast-invariant and attention-invariant. Nevertheless, some differences occur and are discussed. We propose a simple test on existing data based on the second hypothesis.
Some things we've learned (about Markov chain Monte Carlo)
Persi Diaconis
Statistics , 2013, DOI: 10.3150/12-BEJSP09
Abstract: This paper offers a personal review of some things we've learned about rates of convergence of Markov chains to their stationary distributions. The main topic is ways of speeding up diffusive behavior. It also points to open problems and how much more there is to do.
171Yb+ System Stability, 5D3/2 Hyperfine State Detection Efficiency and F=2 Lifetime
M. Schacht,M. Schauer
Physics , 2013,
Abstract: A data acquisition system is described that is designed to stabilize cooling and probe rates to maximize detection sensitivity and minimize possible systematic errors due to correlations between drifting experimental conditions and varying drive parameters. Experimental parameters that affect the Yb171 5D3/2 hyperfine state preparation and detection efficiency are characterized and optimized. A set of wait times for optimal sampling of the D3/2(F=2) lifetime is chosen and used to measure that lifetime with high statistical sensitivity. A systematic variation in this lifetime seems to be apparent. The source of the variation was not identified, but ion number and cooling rate appear to be ruled out. A net determination is made of tau=61.8ms+-(0.6)_stat+-(6.4)_sys which is significantly longer than other measurements of the same quantity. An alternate shelving scheme is proposed that would provide S-D state discrimination for Yb even isotopes as well as improved sensitivity for D state hyperfine discrimination in odd isotopes.
Standard Model Predictions and New Physics Sensitivity in B->DD Decays
Martin Jung,Stefan Schacht
Physics , 2014, DOI: 10.1103/PhysRevD.91.034027
Abstract: An extensive model-independent analysis of B->DD decays is carried out employing SU(3) flavour symmetry, including symmetry-breaking corrections. Several theoretically clean observables are identified which allow for testing the Standard Model. These include the known time-dependent CP asymmetries, the penguin pollution of which can be controlled in this framework, but notably also quasi-isospin relations which are experimentally well accessible and unaffected by symmetry-breaking corrections. Theoretical assumptions can be kept to a minimum and controlled by additional sum rules. Available data are used in global fits to predict the branching ratio for the B0->DsDs decay as well as several CP asymmetries which have not been measured so far, and future prospects are analyzed.
Note on bipartite graph tilings
Jan Hladky,Mathias Schacht
Mathematics , 2008,
Abstract: Let s
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