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Search Results: 1 - 10 of 523235 matches for " P.R.;Casta?eda-Guzmán "
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Sound speed resolved by photoacoustic technique
Pérez Ruíz, S.J.;Alcántara Iniesta, S;Hernández, P.R.;Castaeda-Guzmán, R;
Revista mexicana de física , 2007,
Abstract: in this work a new method for measuring the speed of sound in materials is reported. this method uses the photoacoustic effect, which is the generation of sound waves by pulsed optical radiation incident on a material sample. the sound waves generated on the surface of the sample travel through the material and are detected with two piezoelectric sensors separated by a known distance. an appropriate processing of the photoacoustic signal permits the separation of the information of the generated longitudinal waves, of their reflections, as well as of other types of waves generated (shear, surface, etc). the advantages and disadvantages, of this method are discussed in comparison with standard methods.
Sound speed resolved by photoacoustic technique
S.J. Pérez Ruíz,S. Alcántara Iniesta,P.R. Hernández,R. Castaeda-Guzmán
Revista mexicana de física , 2007,
Abstract: En el presente trabajo se reporta una técnica novedosa para medir la velocidad del sonido en materiales. Este método de medición utiliza el efecto fotoacústico, que consiste en irradiar una muestra de material con pulsos cortos de radiación láser, registrando la onda acústica generada con dos sensores piezoeléctricos separados por una distancia conocida. Un procesamiento adecuado de la se al fotoacústica permite separar la información de las ondas longitudinales generadas, de sus reflexiones, así como de los frentes de onda de otro tipo de ondas generadas (cortantes, de superficie, etc.). Se discuten sus ventajas y desventajas frente a los métodos usuales.
Photoacoustic Studies of Colloidal Silica Particles after MeV Ion-Induced Shape Deformation  [PDF]
Ulises Morales, Rosalba Castaeda-Guzmán, Santiago Jesús Pérez-Ruiz, Juan Carlos Cheang Wong
New Journal of Glass and Ceramics (NJGC) , 2011, DOI: 10.4236/njgc.2011.12011
Abstract: Ordered arrays of colloidal submicrometer-sized silica particles deposited onto silicon wafers were irradiated with MeV Si ions. The spherical silica particles turned into oblate particles as a result of the increase of the particle dimension perpendicular to the ion beam direction and the decrease in the parallel direction. Pulsed laser photoacoustic spectroscopy was used to study the structural changes of the silica particles after the ion-induced shape deformation. Our purpose is to correlate the mechanical vibrations generated by the pulsed laser as a function of the Si irradiation parameters: ion energy and fluence. Fast Fourier transform analysis of the photoacoustic signal was carried out in order to obtain the normal vibration modes of the system. The size, size distribution and shape of the silica particles were determined by scanning electron microscopy. Our results revealed significant structural differences between the spherical and the deformed silica particles.
Determinación de la temperatura de transición ferroeléctrica por efecto fotoacústico: La fenomenología involucrada
Huanosta-Gutiérrez,Areli; Castaeda-Guzmán,Rosalba; Pérez-Ruiz,Santiago J; Huanosta-Gutiérrez,Thalía; Huanosta-Tera,Alfonso;
Revista Latinoamericana de Metalurgia y Materiales , 2009,
Abstract: as far as we know, for the first time it is here stated the appropriate experimental conditions and offered an explanation to the mechanism for the determination of ferroelectric transition temperatures by photoacoustic effect. the explanation involves the analysis of the temperature dependence of an intrinsic parameter of the material: compressibility. at a constant temperature, δv/δp determines the compressibility of a material, but this last ratio is also involved in the fotoacoustic effect, these facts are used here to achieve the analysis of experimental results. the found relation explains the behavior of a correlation function constructed with the response of photoacoustic successive events. the photoacoustic effect is used here to obtain tc in batio3. ferroelectric transition temperatures determined by the permittivity behavior, investigated as a function of temperature, are perfectly compatible with the obtained via photoacoustic experiments, as shown in this work. however, there is an advantage when photoacoustic is used; results are not affected by the presence of high conductivity components, as happens with permittivity determinations. from our point of view, the interpretation given here can be applied to every phase transition that involves a change in compressibility.
Determinación de la temperatura de transición ferroeléctrica por efecto fotoacústico: La fenomenología involucrada
Areli Huanosta-Gutiérrez,Rosalba Castaeda-Guzmán,Santiago J Pérez-Ruiz,Thalía Huanosta-Gutiérrez
Revista Latinoamericana de Metalurgia y Materiales , 2009,
Abstract: Hasta donde sabemos, por primera vez se establecen las condiciones experimentales y se ofrece una explicación relativa al mecanismo utilizado para la determinación de temperaturas de transición ferroeléctrica por medio del efecto fotoacústico. La explicación involucra el análisis de la dependencia de la temperatura de un parámetro intrínseco del material; la compresibilidad. A temperatura constante, la razón de cambio ΔV/Δp determina la compresibilidad de un material, pero esta razón de cambio también está involucrada en el efecto fotoacústico, este hecho se utiliza aquí para analizar los resultados experimentales obtenidos. La relación encontrada permite explicar el comportamiento de una función de correlación construida con la respuesta fotoacústica de eventos sucesivos. El efecto fotoacústico se aplicó para obtener la Tc del BaTiO3. Como se muestra en este trabajo, la determinación de la temperatura de transición ferroeléctrica por medio del comportamiento de la permitividad, en función de T, es perfectamente compatible con la determinación de Tc obtenida utilizando el efecto fotoacústico. Sin embargo hay una ventaja, cuando se utiliza la fotoacústica, en la determinación de Tc, los resultados no se ven afectados por la presencia de componentes de conductividad elevados, como sucede con la permitividad. Desde nuestro punto de vista, la interpretación que se propone aquí puede ser aplicada a cualquier transición de fase que involucre un cambio en la compresibilidad. As far as we know, for the first time it is here stated the appropriate experimental conditions and offered an explanation to the mechanism for the determination of ferroelectric transition temperatures by photoacoustic effect. The explanation involves the analysis of the temperature dependence of an intrinsic parameter of the material: compressibility. At a constant temperature, ΔV/Δp determines the compressibility of a material, but this last ratio is also involved in the fotoacoustic effect, these facts are used here to achieve the analysis of experimental results. The found relation explains the behavior of a correlation function constructed with the response of photoacoustic successive events. The photoacoustic effect is used here to obtain Tc in BaTiO3. Ferroelectric transition temperatures determined by the permittivity behavior, investigated as a function of temperature, are perfectly compatible with the obtained via photoacoustic experiments, as shown in this work. However, there is an advantage when photoacoustic is used; results are not affected by the presence of high conductiv
Optical sensing technique for Young's modulus measurements in piezoelectric materials
Pérez Ruíz, S.J;Montero Díaz, J.A;Alcántara Iniesta, S;Hernández, P.R;Castaeda G, R;
Revista mexicana de física , 2008,
Abstract: in the design of microsensors using microelectromechanical system (mems) technology, it is necessary to know the elastic properties of the materials employed in their fabrication. reliable mechanical properties of the materials are critical to the safety and correct functioning of these microdevices. mechanical testing of microstructures that are only a few microns thick requires novel techniques and specialized procedures for preparation and handling. in this paper a simplified optic sensing is used to measure the young's modulus in piezoelectric cantilever. this optical technique was chosen because it is the most appropriate when working with small devices, besides being easily implemented and low cost.
Detención fotoacústica de transiciones de fase en cerámicas ferroeléctricas
Castaeda Guzmán, R.,Villagrán Muniz, M.,Saniger Blesa, J. M.
Boletín de la Sociedad Espa?ola de Cerámica y Vidrio , 1999,
Abstract: Phase transition on ferroelectric ceramics were detected by photoacoustic laser technique which allows the measurement of the Curie temperature and ferro-paraelectric transitions. The photoacoustic signal produced by low energy laser pulses using a piezoelectric transducer attached to the sample by a glass or quartz rod is shown. The developed technique requires nor signal amplification neither special preparation of the sample and have an excellent signal to noise ratio. In order to validate this technique it was applied to the measurement of Curie temperature of the PbSmTiO3 and Pb(MgNb)TiO3 ceramics. These results were compared with those obtained by DTA, DMA and dielectric permittivity. Se presenta una técnica fotoacústica de láser pulsado para detectar las transiciones de fase en cerámicas ferroeléctricas, determinando la temperatura de Curie y el cambio de estructura ferro-paraeléctrico. Se muestran los cambios producidos en las se ales fotoacústicas generadas por láser pulsado de baja energía (< 200 μJ), utilizando para la detección un sensor piezoeléctrico pegado a la muestra por medio de una varilla de vidrio o cuarzo. La técnica desarrollada no requiere amplificación de la se al, ni preparación especial de la muestra y presenta una relación se al a ruido excelente. Para demostrar la validez de la técnica se aplicó al estudio de la determinación de la temperatura de Curie de las cerámicas: PbSmTiO3 y Pb(MgNb)TiO3. Los resultados se comparan con los obtenidos por otras técnicas como son DTA, DMA y permitividad dieléctrica.
Estrogenic Effect of 70% Ethanol Turmeric (Curcuma domestica Val.) Extract on Ovariectomized Female Mice (Mus musculus L.)
Dadang Kusmana,R.R.R. Soraya,P.R. Ratri,A.N. Dewi
Makara Seri Sains , 2007,
Abstract: The influence of extract turmeric (Curcuma domestica Val.) on endometrium thickness, vaginal epithelium, mammary gland, and protein of estrogen receptor of ovariectomized mice was examined. Twenty five ovariectomized mice which were divided into five groups, were treated by ethynilestradiol (8,4 x 10-3 g), aquades (10 ml), and turmeric extract at doses 230 mg/kg b.w.; 310 mg/kg b.w.; and 390 mg/kg b.w. for eight days. At the end of experiments the mice were killed, then the uterus, vagina, and mammae were removed and the wet weight of uterus was recorded. Uterus, vagina, and mammae were examined histologically. Estrogen receptor protein from uterus were analized by using SDS-PAGE. One way anava test showed that turmeric extract at doses 310 mg/kg b.w. and 390 mg/kg b.w give estrogenic effect on vaginal ephitelium, endometrium thickness, and diametre of mammary glands. SDS-PAGE analysis showed there were differences in protein concentration between control and treatment groups which were seen in the thickness of the bands. Estrogen receptor band could be detected in sampel of treatment groups at molecular weight 45 kDa.
Algoritmos genéticos para la calibración del modelo climático de invernadero
Guzmán-Cruz, R.;Castaeda-Miranda, R.;García-Escalante, J. J.;Lara-Herrera, A.;Serroukh, I.;Solis-Sánchez, L. O;
Revista Chapingo. Serie horticultura , 2010,
Abstract: greenhouse crop production, compared with field production, yields greater quality and quantity and higher prices in any period of the year. these advantages are related to the climatic conditions in which crop grows and the specific climatic conditions of each region thus, it is important to have a system of control to maintain the values of climate variables within an optimum range for crop development. however, the design of these systems is based on mathematical models that describe a given process, but it is necessary to have a model to predict the behavior of internal greenhouse environment. the goal of this work was to fit a mathematical model for greenhouse environment under the climatic conditions of central méxico. furthermore, analyses of sensitivity, calibration and validation were performed and coefficient of correlation (r) of the model was obtained. data were obtained from universidad autónoma of querétaro's biotronic laboratory greenhouse. the model's input variables were outside temperature and relative humidity, wind velocity and solar radiation. results showed that estimated air temperature inside the greenhouse had a better fit to the measured air temperature (r = 0.86) and, the estimated relative humidity fit less well to the measured relative humidity (r = 0.78).
Antihyperlipidemic Activity of Gymenma sylvestre R. Br. Leaf Extract on Rats Fed with High Cholesterol Diet
P.R. Rachh,M.R. Rachh,N.R. Ghadiya,D.C. Modi
International Journal of Pharmacology , 2010,
Abstract: Effect of Gymnema sylvestre R. Br. Leaf extract on high cholesterol fed diet rats was investigated. Hyperlipidemia was induced in rats by giving high cholesterol diet (2% cholesterol, 1% sodium cholate and 2% coconut oil) for seven days in standard rat chow diet. The hydroalcoholic extract of Gymnema sylvestre R. Br. leaves (200 mg kg-1 b.wt.) was orally administered once a day to rats fed with a high cholesterol diet for seven days. High cholesterol fed diet rats exhibited significant increase in total serum cholesterol, triglycerides, low density lipoproteins, very low density lipoprotein and significant decrease in high density lipoproteins. Treatment with hydroalcoholic extract of Gymnema sylvestre R. Br. leaves significantly decreased total serum cholesterol, triglycerides, low density lipoproteins, very low density lipoprotein and increased the high density lipoproteins in hyperlipidemic rats and was comparable with that of standard atorvastatin. Hence, it was concluded that significant antihyperlipidemic activity of hydroalcholic extract of Gymnema sylvestre R. Br. leaves may be due to the presence of acidic compounds, flavonoids, phenols, saponins, tannis (Phenolic compounds) and triterpenoids found in the preliminary phytochemical screening.
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