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Search Results: 1 - 10 of 329704 matches for " Balbina Rojas-Sánchez "
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Bibliotecología puertorrique a un acercamiento a sus primeros representantes en la Universidad de Puerto Rico.
Balbina Rojas-Sánchez,Brenda Pérez-Martínez
Simbiosis : Revista Electrónica de Ciencias de la Información , 2011,
Abstract: La tesis explora y describe la labor y aportaciones de bibliotecarios profesionales pioneros de la bibliotecología puertorrique a. Este estudio surge con el propósito de dar a conocer las aportaciones significativas de los bibliotecarios profesionales de la Universidad de Puerto Rico en sus primeros a os 1903-1969 y es un resumen del proyecto “Pioneros de la bibliotecología puertorrique a 1903-1969” realizado por las mismas autoras. Se utilizó el enfoque cualitativo, para rescatar los datos biográficos y bibliográficos de estas personas. Dentro del dise o cualitativo se utilizó la investigación biográfica y la investigación histórica haciendo uso de las técnicas del análisis de documentos, historia oral y la síntesis de la información recopilada. El producto final del mencionado proyecto fue la presentación de un CD-ROM con la síntesis de la vida, obra y aportaciones de cada uno de los bibliotecarios que conformaron la muestra. En este artículo presentamos como resultados un resumen de los aportes de estos bibliotecarios. Abstract The dissertation presents a sample of professional librarians, pioneers of the Puerto Rican librarianship and a summary of their contributions to it. This study arises in order to publicize the significant contributions of professional librarians at the University of Puerto Rico in the early years 1903-1969 and is a summary of the project “Pioneers of Puerto Rican librarianship: University of Puerto Rico, 1903-1969” by the same authors. Qualitative approach was used to rescue biographical and bibliographical data of these people. Within the qualitative design was used the biographical research and historical research using the techniques of document analysis, oral history and synthesis of information gathered. The final product of this project was the presentation of a CD-ROM with the synthesis of the life, work and contributions of each of the librarians who formed the sample. In this article we present as results, a summary of the contributions of these librarians.
Algunas consideraciones sobre caries dental, fluoruros, su metabolismo y mecanismos de acción
Rojas-Sánchez,Fátima;
Acta Odontológica Venezolana , 2008,
Abstract: this article presents a review of the current vision about dental caries, and microorganisms associated to the development of dental caries. mechanisms of dental caries lesion, the role of fluoride through its mechanisms of action: demineralization, remineralization and antibacterial action. a scheme of the metabolism of fluorides, absorption, distribution and excretion is presented. some considerations about the initiation of the natural water fluoridation program in the world, and about the threshold dose of fluoride, and dental fluorosis.
Algunas consideraciones sobre caries dental, fluoruros, su metabolismo y mecanismos de acción
Fátima Rojas-Sánchez
Acta Odontológica Venezolana , 2008,
Abstract: El presente artículo esta dirigido a estudiantes y profesionales de la odontología interesados en profundizar sus conocimientos sobre caries dental y fluoruros. El objetivo primordial de la presente revisión es actualizar algunos conceptos sobre caries dental, su inicio y desarrollo, así como el papel principal que tienen los fluoruros como agente anticariogénico de primera elección para controlar o revertir la historia natural de la lesión cariosa. Se describe brevemente que son los fluoruros, origen, abundancia en la naturaleza y comportamiento químico, así como, los mecanismos de acción: inhibición de la desmineralización, remineralización y acción antibacteriana. De igual manera se mencionan aspectos relevantes sobre su metabolismo, absorción, distribución y excreción, así como su farmacocinética. This article presents a review of the current vision about dental caries, and microorganisms associated to the development of dental caries. Mechanisms of dental caries lesion, the role of fluoride through its mechanisms of action: demineralization, remineralization and antibacterial action. A scheme of the metabolism of fluorides, absorption, distribution and excretion is presented. Some considerations about the initiation of the natural water fluoridation program in the world, and about the threshold dose of fluoride, and dental fluorosis.
Efecto inhibitorio del nonanoato de potasio y el fluoruro de sodio en la acidogenicidad de la placa dental humana in vitro: Nonanoato de Potasio y Fluoruros como inhibidores de la placa dental
Rojas-Sánchez,Fátima; Lalaguna,Fernando; Infante,Yanira; Acevedo,Ana Maria;
Acta Odontológica Venezolana , 2000,
Abstract: nonanoic acid a saturated 9-carbon fatty acid, was earlier shown to reduce fissure caries in rats when included in their diet (hayes and berkovitz, 1979). griffiths in 1979 showed that potassium nonanoate added to sugar-rinses inhibits plaque bacteria in man. the aim of this study was to evaluate the effect of potassium nonanoate (nk), sodium fluoride (naf) and their combination on acid production, and this was assessed by back tritation using the method described by hayes and roberts, (1980). at ph 7.4 kn and naf added separately reduced acid production by 45.0% and 54.5%, respectively, compared to the control. the reduction in acid production when using the compounds in combination was 39%. at ph 5.5, both kn and naf alone showed 21.2% and 29.3% inhibition, respectively, and when combined this inhibition increased to 49.3%. at ph 5.5 a cumulative effect of kn and naf was observed. we conclude that at acid ph both compounds, kn+naf combined would be the best to be effective.
Efecto inhibitorio del nonanoato de potasio y el fluoruro de sodio en la acidogenicidad de la placa dental humana in vitro: Nonanoato de Potasio y Fluoruros como inhibidores de la placa dental
Fátima Rojas-Sánchez,Fernando Lalaguna,Yanira Infante,Ana Maria Acevedo
Acta Odontológica Venezolana , 2000,
Abstract: El ácido nonanoico es un ácido graso saturado de 9 carbonos el cual se ha demostrado reduce la aparición de caries de fisura en ratas cuando es incluido en la dieta (Hayes y Berkovitz, 1979). En 1979, Griffiths demostró que el nonanoato de potasio agregado en enjuagues con sacarosa inhibe la producción de ácidos por parte de las bacterias de la placa dental en humanos. El objetivo de esta investigación fue estudiar el efecto de ácidos grasos y fluoruros en la producción de cidos en placa dental de humanos in vitro. Para ello se recolectó placa dental en ayunas de 3 horas, en ni os con caries activa y con edades comprendidas entre los 5 y 12 a os. La producción de ácidos fue determinada por el método de titulación reportado por Hayes y Roberts (1980) luego de la adición de glucosa exógena. Los resultados demostraron que a pH 7,4 el NK (3mM) y el NaF (13 mM) produjeron una inhibición en la producción de ácidos en un 45,0% y 54,5% respectivamente, mientras que con la mezcla se observó una reducción de un 39%. A pH 5,5 el NK y el NaF a una concentración de 0,26 mM produjeron una inhibición de 21.2% y 29,3% respectivamente, y cuando se mezclaron esta inhibición se incrementó a 49,3%. Estos resultados sugieren que a pHs cercanos a la neutralidad (7,4) no hay efecto aditivo del NK y NaF, mientras que a pH ácido (5,5) la combinación de estos compuestos incrementó significativamente (p<0.01) su efectividad. Nonanoic acid a saturated 9-carbon fatty acid, was earlier shown to reduce fissure caries in rats when included in their diet (Hayes and Berkovitz, 1979). Griffiths in 1979 showed that potassium nonanoate added to sugar-rinses inhibits plaque bacteria in man. The aim of this study was to evaluate the effect of potassium nonanoate (NK), sodium fluoride (NAF) and their combination on acid production, and this was assessed by back tritation using the method described by Hayes and Roberts, (1980). At pH 7.4 KN and NaF added separately reduced acid production by 45.0% and 54.5%, respectively, compared to the control. The reduction in acid production when using the compounds in combination was 39%. At pH 5.5, both KN and NaF alone showed 21.2% and 29.3% inhibition, respectively, and when combined this inhibition increased to 49.3%. At pH 5.5 a cumulative effect of KN and NaF was observed. We conclude that at acid pH both compounds, KN+NaF combined would be the best to be effective.
Hábitos de higiene bucal y el nivel socio-económico de ni?os entre 15 y 20 meses de edad.
Mairobys,Socorro; Gómez,Dilia; Torres,José; Acevedo,Ana María; Rojas-Sánchez,Fátima;
Acta Odontológica Venezolana , 2007,
Abstract: tooth brushing and dentifrice use have been undoubtedly reported by several studies as the primary oral hygiene practices carried out to reduce and control caries development, observing differences among social levels. objective: the aim of this study was to associate oral hygiene habits with the social levels of children among 15 to 20 months. methods: one hundred and twelve children were selected from 10 different daycare centers. the criteria of selection included, children among 15 to 20 months, apparently healthy, with a consent form signed by the parent and attending the daycare. questionnaires assessed tooth-brushing patterns and fluoride dentifrice use considering other possible oral hygiene practices developed at the moment and reporting when these were initiated. a socioeconomic form was also completed for each child. results: according to graffar, only 39.3% belonged to the lower social class and the rest of the children (21.4%-39.3%) were classified within the middle and the higher social levels, respectively. the average age of introducing oral hygiene habits was 12.8 months. from the 112 children evaluated, 42 (37.5%) developed any oral hygiene routine, 19.0% of the children's teeth were brushed or cleaned only with water, 76.2% of them used fluoridated dentifrice, and 81.3% of the mothers placed the dentifrice on the toothbrush. conclusions: the results of this study showed the absence of a significant relationship between parents? socioeconomic status and dental hygiene habits observed in children between 15 to 20 months of age. an important finding was that a high percentage of the children at this age did not show any oral hygiene habit, as well as, mothers played the most important role.
Perpendicular magnetization reversal in Pt/[Co/Ni]$_3$/Al multilayers via the Spin Hall Effect of Pt
J. -C. Rojas-Sánchez,P. Laczkowski,J. Sampaio,S. Collin,K. Bouzehouane,N. Reyren,H. Jaffrès,A. Mougin,J. -M. George
Physics , 2015,
Abstract: We experimentally investigate the current-induced magnetization reversal in Pt/[Co/Ni]$_3$/Al multilayers combining the anomalous Hall effect and magneto-optical Kerr effect techniques in crossbar geometry. The magnetization reversal occurs through nucleation and propagation of a domain of opposite polarity for a current density of the order of 0.3 TA/m$^2$. In these experiments we demonstrate a full control of each stage: i)the {\O}rsted field controls the domain nucleation and ii) domain-wall propagation occurs by spin torque from the Pt spin Hall effect. This scenario requires an in-plane magnetic field to tune the domain wall center orientation along the current for efficient domain wall propagation. Indeed, as nucleated, domain walls are chiral and N\'eel like due to the interfacial Dzyaloshinskii-Moriya interaction.
Spin Pumping and Inverse Spin Hall Effect in Platinum: The Essential Role of Spin-Memory Loss at Metallic Interfaces
J. -C. Rojas-Sánchez,N. Reyren,P. Laczkowski,W. Savero,J. -P. Attané,C. Deranlot,M. Jamet,J. -M. George,L. Vila,H. Jaffrès
Physics , 2013, DOI: 10.1103/PhysRevLett.112.106602
Abstract: Through combined ferromagnetic resonance, spin-pumping and inverse spin Hall effect experiments in Co|Pt bilayers and Co|Cu|Pt trilayers, we demonstrate consistent values of spin diffusion length $\ell_{\rm sf}^{\rm Pt}=3.4\pm0.4$ nm and of spin Hall angle $\theta_{\rm SHE}^{\rm Pt}=0.051\pm0.004$ for Pt. Our data and model emphasize on the partial depolarization of the spin current at each interface due to spin-memory loss. Our model reconciles the previously published spin Hall angle values and explains the different scaling lengths for the ferromagnetic damping and the spin Hall effect induced voltage.
Conferencia y Asamblea Anual 2012 Sociedad de Bibliotecarios de Puerto Rico (SBPR) Investigación, Publicaciones y Proyectos Innovadores en Bibliotecología y Ciencias de la Información
Balbina J. Rojas Sánchez
Simbiosis : Revista Electrónica de Ciencias de la Información , 2012,
Abstract:
Spin Pumping and Inverse Spin Hall Effect in Germanium
J. -C. Rojas-Sánchez,M. Cubukcu,A. Jain,C. Vergnaud,C. Portemont,C. Ducruet,A. Barski,A. Marty,L. Vila,J. -P. Attané,E. Augendre,G. Desfonds,S. Gambarelli,H. Jaffrès,J. -M. George,M. Jamet
Physics , 2013, DOI: 10.1103/PhysRevB.88.064403
Abstract: We have measured the inverse spin Hall effect (ISHE) in \textit{n}-Ge at room temperature. The spin current in germanium was generated by spin pumping from a CoFeB/MgO magnetic tunnel junction in order to prevent the impedance mismatch issue. A clear electromotive force was measured in Ge at the ferromagnetic resonance of CoFeB. The same study was then carried out on several test samples, in particular we have investigated the influence of the MgO tunnel barrier and sample annealing on the ISHE signal. First, the reference CoFeB/MgO bilayer grown on SiO$_{2}$ exhibits a clear electromotive force due to anisotropic magnetoresistance and anomalous Hall effect which is dominated by an asymmetric contribution with respect to the resonance field. We also found that the MgO tunnel barrier is essential to observe ISHE in Ge and that sample annealing systematically lead to an increase of the signal. We propose a theoretical model based on the presence of localized states at the interface between the MgO tunnel barrier and Ge to account for these observations. Finally, all of our results are fully consistent with the observation of ISHE in heavily doped $n$-Ge and we could estimate the spin Hall angle at room temperature to be $\approx$0.001.
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