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Search Results: 1 - 10 of 456619 matches for " J. -C. Rojas-Sanchez "
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Velocity asymmetry of Dzyaloshinskii domain walls in the creep and flow regimes
M. Vanatka,J. -C. Rojas-Sanchez,J. Vogel,M. Bonfim,A. Thiaville,S. Pizzini
Physics , 2015, DOI: 10.1088/0953-8984/27/32/326002
Abstract: We have carried out measurements of domain wall dynamics in a Pt/Co/GdOx(t) wedge sample with perpendicular magnetic anisotropy. When driven by an easy-axis field Hz in the presence of an in-plane field Hx, the domain wall expansion along x is anisotropic, as expected for samples presenting Dzyaloshinskii-Moriya interaction. In the creep regime, the sign and the value of the domain wall velocity asymmetry changes along the wedge. We show that in our samples the domain wall speed vs. Hx curves in the creep regime cannot be explained simply in terms of the variation of the domain wall energy with Hx, as suggested by previous works. For this reason the strength and the sign of the Dzyaloshinskii-Moriya interaction (DMI) cannot be extracted from these measurements. To obtain reliable information on the DMI strength using magnetic field-induced domain wall dynamics, measurements have been performed with high fields, bringing the DW close to the flow regime of propagation. In this case, the large values of DMI are coherent with those obtained from current-driven domain wall dynamics.
Crossover from spin accumulation into interface states to spin injection in the germanium conduction band
A. Jain,J. -C. Rojas-Sanchez,M. Cubukcu,J. Peiro,J. C. Le Breton,E. Prestat,C. Vergnaud,L. Louahadj,C. Portemont,C. Ducruet,V. Baltz,A. Barski,P. Bayle-Guillemaud,L. Vila,J. -P. Attané,E. Augendre,G. Desfonds,S. Gambarelli,H. Jaffrès,J. -M. George,M. Jamet
Physics , 2012, DOI: 10.1103/PhysRevLett.109.106603
Abstract: Electrical spin injection into semiconductors paves the way for exploring new phenomena in the area of spin physics and new generations of spintronic devices. However the exact role of interface states in spin injection mechanism from a magnetic tunnel junction into a semiconductor is still under debate. In this letter, we demonstrate a clear transition from spin accumulation into interface states to spin injection in the conduction band of $n$-Ge. We observe spin signal amplification at low temperature due to spin accumulation into interface states followed by a clear transition towards spin injection in the conduction band from 200 K up to room temperature. In this regime, the spin signal is reduced down to a value compatible with spin diffusion model. More interestingly, we demonstrate in this regime a significant modulation of the spin signal by spin pumping generated by ferromagnetic resonance and also by applying a back-gate voltage which are clear manifestations of spin current and accumulation in the germanium conduction band.
Experiencia de caries y fluorosis dental en escolares que consumen agua con diferentes concentraciones de fluoruro en Maiquetía, Estado Vargas, Venezuela
Montero,Maglynert; Rojas-Sanchez,Fátima; Socorro,Mairobys; Torres,José; Acevedo,Ana María;
Investigación Clínica , 2007,
Abstract: the objective of this study was to determine the experience of fluorosis and dental caries in 8- 12 year old children that drink water with different fluoride concentrations, from maiquetía, vargas state. four hundred and twenty-one children were evaluated and divided in groups of 84 children each, according with their age (8-9-10-11) but 85 for the age 12. this evaluation was developed by a calibrated dentist using dean?s index for dental fluorosis examining only the six upper anterior teeth and dmft/dmft index to determine dental caries, following the criteria established by the who. in addition, a social status questionnaire was given to the subjects and samples of water and salt from the communities were collected. thirty-three per cent of the children in this study were males and 67% were females. results indicated that the mean dmft and dmft were 0.91 and 1.88, respectively, showing a total of 2.17 teeth with dental caries being the decayed component, the highest component observed in both dentitions. the mean prevalence of dental fluorosis for the studied population was 16.6%, where the very mild category (8.5%) predominated. maria may was the most affected school with dental fluorosis (41.5%) and the fluoride concentration in drinking water after analyses was 1.58%. the results of this study indicate the presence of an inverse relationship between fluoride concentrations in the water collected at the schools and the prevalence of dental fluorosis in the permanent dentition of school children, but not in the primary dentition.
Experiencia de caries y fluorosis dental en escolares que consumen agua con diferentes concentraciones de fluoruro en Maiquetía, Estado Vargas, Venezuela Dental caries and fluorosis in children consuming water with different fluoride concentrations in Maiquetía, Vargas State, Venezuela
Maglynert Montero,Fátima Rojas-Sanchez,Mairobys Socorro,José Torres
Investigación Clínica , 2007,
Abstract: El objetivo del estudio fue determinar la experiencia de caries y fluorosis dental en escolares que consumen agua con diferentes concentraciones de fluoruro en Maiquetía, Estado Vargas, Venezuela. Se examinaron 421 ni os distribuidos en grupos de 84 ni os para las edades de 8, 9, 10, 11 y 85 para la edad de 12 a os. El examen clínico fue realizado por un personal calibrado, se utilizó el índice de Dean para fluorosis dental para lo cual se examinaron los 6 dientes antero-superiores y el índice CPOD y ceod para caries dental, según los criterios propuesto por la OMS. Adicionalmente se realizó una encuesta socioeconómica y se tomaron muestras de agua y de sal en la localidad. De la muestra seleccionada el 33% fueron ni os y el 67% ni as. Los resultados revelaron un índice CPOD promedio de 0,91, un ceod de 1,88 y un promedio total de dientes afectados por caries de 2,17. De igual manera se identificó el componente cariado como el más elevado en ambas denticiones. La prevalencia promedio de fluorosis dental para toda la población evaluada fue de 16,6%, siendo más frecuente el grado de fluorosis muy leve (8,5%). La Unidad Educativa María May fue la más afectada por fluorosis dental (41,5%) y la concentración de fluoruro en el agua recolectada de esta unidad educativa fue de 1,58 ppm. De acuerdo a los resultados obtenidos en este estudio se concluye que existe una relación inversa entre la concentración de fluoruro presente en las aguas de los colegios y la prevalencia de fluorosis dental en la dentición permanente de los ni os evaluados, pero no en la dentición primaria. The objective of this study was to determine the experience of fluorosis and dental caries in 8- 12 year old children that drink water with different fluoride concentrations, from Maiquetía, Vargas State. Four hundred and twenty-one children were evaluated and divided in groups of 84 children each, according with their age (8-9-10-11) but 85 for the age 12. This evaluation was developed by a calibrated dentist using Dean’s Index for dental fluorosis examining only the six upper anterior teeth and DMFT/dmft index to determine dental caries, following the criteria established by the WHO. In addition, a social status questionnaire was given to the subjects and samples of water and salt from the communities were collected. Thirty-three per cent of the children in this study were males and 67% were females. Results indicated that the mean DMFT and dmft were 0.91 and 1.88, respectively, showing a total of 2.17 teeth with dental caries being the decayed component, the highest component observed in
Macroion correlation effects in electrostatic screening and thermodynamics of highly charged colloids
Ramon Castaneda-Priego,Luis F. Rojas-Ochoa,Vladimir Lobaskin,J. C. Mixteco-Sanchez
Physics , 2006, DOI: 10.1103/PhysRevE.74.051408
Abstract: We study macroion correlation effects on the thermodynamics of highly charged colloidal suspensions using a mean-field theory and primitive model computer simulations. We suggest a simple way to include the macroion correlations into the mean-field theory as an extension of the renormalized jellium model of Trizac and Levin [Phys. Rev. E {\bf 69}, 031403 (2004)]. The effective screening parameters extracted from our mean-field approach are then used in a one-component model with macroions interacting via Yukawa-like potential to predict macroion distributions. We find that inclusion of macroion correlations leads to a weaker screening and hence smaller effective macroion charge and lower osmotic pressure of the colloidal dispersion as compared to other mean-field models. This result is supported by a comparison to primitive model simulations and experiments for charged macroions in the low-salt regime, where the macroion correlations are expected to be significant.
Potential for Conversion of Agrosilvopastoral Systems of Dairy Cattle to the Organic Production Model in South Eastern Mexico
J. Nahed-Toral,B. Sanchez-Munoz,Y. Mena,J. Ruiz-Rojas,R. Aguilar-Jimenez,J. Ma. Castel,F. de Asis Ruiz,M. Orantes-Zebadua,A. Manzur-Cruz,J. Cruz-Lopez,C. Delgadillo-Puga
Journal of Animal and Veterinary Advances , 2012, DOI: 10.3923/javaa.2012.3081.3093
Abstract: In the municipality of Tecpatan, Chiapas, in Southeastern Mexico, traditional agrosilvopastoral systems of dairy production have great potential for conversion to the organic production model. The objective of this study was to characterize silvopastoral systems and evaluate the potential of converting traditional agrosilvopastoral systems to the organic model. Researchers studied 75 cattle farms belonging to three Rural Production Societies (RPS; rural cooperatives): RPS Grijalva (RPS-G: n = 35), RPS Pomarroza (RPS-P: n = 22) and RPS Malpaso (RPS-M: n = 18). For this, researchers used as a guide the multi-criteria methodology of the Organic Livestock Proximity Index (OLPI) proposed by Mena adapting it to suit the purposes. In the current study, researchers designed a new OLPI with 35 variables which integrate 10 indicators. Information was obtained through direct observation and a questionnaire applied to producers. Statistical analysis of the results of 10 indicators used did not show significant differences among rural production societies. The same was true for the organic conversion index (p>0.05: RPS-G = 62.5%; RPS-M = 63.4% and RPS-P = 64.6%). The data suggest that all cattle farms need to substantially improve veterinary care, safety of milking, quality of milk and dairy products, ecological management and sustainable grassland management. In general, producers of the three rural production societies should be trained in a variety of organic cattle production and management techniques so that cattle farms may achieve a closer approximation to the organic model of production and thus may be certified.
DETERMINACIóN DE LA INCIDENCIA DEL TIRO LIBRE EN EL RESULTADO FINAL A TRAVéS DEL ANáLISIS ESTADíSTICO 1
D. Cárdenas,J. Rojas
Motricidad : European Journal of Human Movement , 2010,
Abstract: RESUMEN Las reglas de juego del baloncesto determinan que el objetivo del mismo es conseguir un mayor número de encestes que el equipo rival. La utilización de todos los contenidos técnico-tácticos ya sean individuales como colectivos, van orientados a conseguir dicho objetivo. Dentro de los diferentes tipos de lanzamientos, el de tiros libres es el único que puede ser considerado como tarea cerrada, es decir, desarrollado en unas condiciones estables, a pesar de lo cual, los porcentajes de eficacia obtenidos en competición se alejan de lo ideal. Este estudio pretende analizar la verdadera incidencia del tiro libre sobre el resultado del encuentro como punto de partida para hacer una revisión profunda de la metodología de entrenamiento. PALABRAS CLAVE: Baloncesto y Tiro Libre ABSTRACT The basic rules of basketball determine the principal aim of this game, which is to get a bigger score than opposite team. The use of all the individual or collective technical-tactical contents are oriented to achieve this objective. Between the different kind of shots, the only one which can be considered as a close task is the free throw, which means that it is developed in a stable environment. Despite of that the accuracy percentage obtained in real competition are really far away from the ideal results. This work try to analyse the incidence of free throw in the final score of the official games as a start point to revise deepthly about the methodological process of training. KEY WORDS: Basketball, Free Throw
Variational Study of the Phase Transition at Finite T in the $λ φ^4 $-Theory
G. Palma,J. C. Rojas
Physics , 1995, DOI: 10.1016/0920-5632(96)00157-0
Abstract: Assuming triviality of the 4-dimensional $\lambda \phi ^4$-theory we compute the effective potential by means of a self consistent Feynman-Bogoliubov method. This potential $U_{eff}^{FB}$ depends on a UV-cutoff, which is fixed by a stability condition for the gap-equation for the plasma mass. It shows a second order phase transition at zero temperature, in agreement with a large amount of analytical and RG analysis as well as Monte Carlo numerical evidence. As the cutoff $\Lambda $ is removed the renormalized self coupling constant $\lambda _R$ goes to zero consistent with the claim of triviality. At finite temperature the phase transition becomes weakly first order.
Curvaton reheating allows TeV Hubble scale in NO inflation
Sanchez, J. C. Bueno;Dimopoulos, K.
High Energy Physics - Phenomenology , 2007, DOI: 10.1088/1475-7516/2007/11/007
Abstract: Curvaton reheating is studied in non-oscillatory (NO) models of inflation, with the aim to obtain bounds on the parameters of curvaton models and find out whether low scale inflation can be attained. Using a minimal curvaton model, it is found that the allowed parameter space is considerably larger than in the case of the usual oscillatory inflation models. In particular, inflation with Hubble scale as low as 1 TeV is comfortably allowed.
Some classical properties of the non-abelian Yang-Mills theories
Sanchez-Monroy, J. A.;Quimbay, C.
High Energy Physics - Phenomenology , 2007,
Abstract: We present some classical properties for non-abelian Yang-Mills theories that we extract directly from the Maxwell's equations of the theory. We write the equations of motion for the SU(3) Yang-Mills theory using the language of Maxwell's equations in both differential and integral forms. We show that vectorial gauge fields in this theory are non-fermionic sources for non-abelian electric and magnetic fields. These vectorial gauge fields are also responsible for the existence of magnetic monopoles. We build the continuity equation and the energy-momentum tensor for the non-abelian case.
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