968 resultados para ddc: 658.403
Resumo:
A colloid supported against gravitational settling by means of an imposed electric field behaves, on average, as if it is at equilibrium in a confining potential T. M. Squires, J. Fluid Mech. 443, 403 (2001)]. We show, however, that the effective Langevin equation for the colloid contains a nonequilibrium noise source, proportional to the field, arising from the thermal motion of dissolved ions. The position fluctuations of the colloid show strong, experimentally testable signatures of nonequilibrium behavior, including a highly anisotropic, frequency-dependent ``effective temperature'' obtained from the fluctuation-dissipation ratio.
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This work explores the preparation of nanocrystalline Cr3+ (1-5 mol%) doped CaSiO3 phosphors by solution combustion process and study of its photoluminescence (PL) behavior. The nanopowders are well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infra-red (FTIR) spectroscopy. PXRD results confirm monoclinic phase upon calcination at 950 degrees C for 3 h. SEM micrographs indicates that the powder is highly porous and agglomerated. The TEM images show the powder to consist of spherical shaped particles of size similar to 30-60 nm. Upon 323 nm excitation, the emission profile of CaSiO3:Cr3+ exhibits a narrow red emission peak at 641 nm due to E-2 -> (4)A(2) transition and broad band at 722 nm due to T-4(2g) -> (4)A(2g). It is observed that PL intensity increases with increase in Cr3+ concentration and highest PL intensity is observed for 3 mol% doped sample. The PL intensity decreases with further increase in Cr3+ doping. This decrease in PL intensity beyond 3 mol% is ascribed to concentration quenching. Racah parameters are calculated to describe the effects of electron-electron repulsion within the crystal lattice. The parameters show 21% reduction in the Racah parameter of free ion and the complex, indicating the moderate nephelauxetic effect in the lattice. (C) 2014 Elsevier B.V. All rights reserved.
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A new general route for the synthesis of novel beta-aryl-beta-(methylthio)acroleins, a class of stable potential 1,3-dielectrophilic synthons, has been reported. The overall protocol involves treatment of either beta-chloroacroleins or their precursor iminium salts (generated in situ from the corresponding active methylene ketones under Vilsmeier-Haack reaction conditions) with S,S-dimethyldithiocarbonates (DDC)/aqueous KOH in either a one-pot or two-step process. The dimethyldithiocarbonate (DDC)/30% aqueous KOH has been shown to be an excellent source of methylthiolate anion. (C) 2014 Elsevier Ltd. All rights reserved.
Resumo:
Background: We recently reported significant association of non-polio enteroviruses (NPEVs) with acute diarrhea in children. Persistent diarrhea (PD) remains a major cause of morbidity and mortality in infants below two years of age in developing countries. Understanding age-dependent frequency and duration of NPEV infections is important to determine their association with persistent diarrhea and disease burden. Objectives: A cohort of 140 infants was followed for 6 months to 2 years of age to determine the frequency, duration, and association with PD of NPEV infections in comparison with rotavirus and other agents. Study design: Stool samples were collected every 14 days, and diarrheal episodes and their duration were recorded. Enteroviruses were characterized by RT-PCR and VP1 gene sequence analysis, rotavirus by electropherotyping, and other agents by PCR. Results: Of 4545 samples, negative for oral polio vaccine strains, 3907 (85.96%) and 638 (14.04%) were NPEV-negative and NPEV-positive, respectively, representing 403 (8.87%) infection episodes. About 68% of NPEV infections occurred during the first year with every child having at least one episode lasting between four days and four months. Approximately 38% and 22% of total diarrheal episodes were positive for NPEV and RV, respectively. While about 18% of NPEV infection episodes were associated with diarrhea, 6% being persistent, 13% of total diarrheal episodes were persistent involving infections by monotype NPEV strains or sequential infections by multiple strains and other agents. Conclusions: This is the first report revealing NPEVs as the single most frequently and persistently detected viral pathogen in every PD episode. (C) 2014 Elsevier B.V. All rights reserved.
Resumo:
Surface texture influences friction during sliding contact conditions. In the present investigation, the effect of surface texture and roughness of softer and harder counter materials on friction during sliding was analyzed using an inclined scratch testing system. In the experiments, two test configurations, namely (a) steel balls against aluminum alloy flats of different surface textures and (b) aluminum alloy pins against steel flats of different surface textures, are utilized. The surface textures were classified into unidirectionally ground, 8-ground, and randomly polished. For a given texture, the roughness of the flat surfaces was varied using grinding or polishing methods. Optical profilometer and scanning electron microscope were used to characterize the contact surfaces before and after the experiments. Experimental results showed that the surface textures of both harder and softer materials are important in controlling the frictional behavior. The softer material surface textures showed larger variations in friction between ground and polished surfaces. However, the harder material surface textures demonstrated a better control over friction among the ground surfaces. Although the effect of roughness on friction was less significant when compared to textures, the harder material roughness showed better correlations when compared to the softer material roughness.
Resumo:
The transformation of flowing liquids into rigid glasses is thought to involve increasingly cooperative relaxation dynamics as the temperature approaches that of the glass transition. However, the precise nature of this motion is unclear, and a complete understanding of vitrification thus remains elusive. Of the numerous theoretical perspectives(1-4) devised to explain the process, random first-order theory (RFOT; refs 2,5) is a well-developed thermodynamic approach, which predicts a change in the shape of relaxing regions as the temperature is lowered. However, the existence of an underlying `ideal' glass transition predicted by RFOT remains debatable, largely because the key microscopic predictions concerning the growth of amorphous order and the nature of dynamic correlations lack experimental verification. Here, using holographic optical tweezers, we freeze a wall of particles in a two-dimensional colloidal glass-forming liquid and provide direct evidence for growing amorphous order in the form of a static point-to-set length. We uncover the non-monotonic dependence of dynamic correlations on area fraction and show that this non-monotonicity follows directly from the change in morphology and internal structure of cooperatively rearranging regions(6,7). Our findings support RFOT and thereby constitute a crucial step in distinguishing between competing theories of glass formation.
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Abrin obtained from the plant Abrus precatorius inhibits protein synthesis and also triggers apoptosis in cells. Previous studies from our laboratory suggested a link between these two events. Using an active site mutant of abrin A-chain which exhibits 225-fold lower protein synthesis inhibitory activity than the wild-type abrin A-chain, we demonstrate in this study that inhibition of protein synthesis induced by abrin is the major factor triggering unfolded protein response leading to apoptosis. Since abrin A-chain requires the B-chain for internalization into cells, the wild-type and mutant recombinant abrin A-chains were conjugated to native ricin B-chain to generate hybrid toxins, and the toxic effects of the two conjugates were compared. The rate of inhibition of protein synthesis mediated by the mutant ricin B-rABRA (R167L) conjugate was slower than that of the wild-type ricin B-rABRA conjugate as expected. The mutant conjugate activated p38MAPK and caspase-3 similar to its wild-type counterpart although at later time points. Overall, these results confirm that inhibition of protein synthesis is the major event contributing to abrin-mediated apoptosis.
Resumo:
This paper presents the stability analysis of functionally graded plate integrated with piezoelectric actuator and sensor at the top and bottom face, subjected to electrical and mechanical loading. The finite element formulation is based on first order and higher order shear deformation theory, degenerated shell element, von-Karman hypothesis and piezoelectric effect. The equation for static analysis is derived by using the minimum energy principle and solutions for critical buckling load is obtained by solving eigenvalue problem. The material properties of the functionally graded plate are assumed to be graded along the thickness direction according to simple power law function. Two types of boundary conditions are used, such as SSSS (simply supported) and CSCS (simply supported along two opposite side perpendicular to the direction of compression and clamped along the other two sides). Sensor voltage is calculated using present analysis for various power law indices and FG (functionally graded) material gradations. The stability analysis of piezoelectric FG plate is carried out to present the effects of power law index, material variations, applied mechanical pressure and piezo effect on buckling and stability characteristics of FG plate.
Resumo:
目前高速公路中央分隔带波形梁护栏立柱的实际设置中,普遍存在着由于分隔带地基强度低于压实路基,护栏立柱承载能力偏低,护栏的防护性能达不到设计要求的问题。对粘性土地基中立柱的受力情况进行了分析,并对地基为压实土与回填土两种情况进行了对比,给出了中央分隔带中立柱地基的加固方案。
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It is known that the press formability and the elongation of laser textured sheet are improved, and the service life of textured roll is longer than that of the un-textured roll due to hardening of the treated surface. One of the goals to develop high repetitive rate YAG laser-induced discharge texturing (LIDT) is to get deeper hardening zone. By observing and measuring cross-section of LIDT spots in different discharge conditions, it is found that the single-crater, which is formed by the discharge conditions of anode, which is covered by an oil film and with rectangular current waveform, has the most depth of heat affected zone (HAZ) comparing with other crater shapes when discharge energy is the same. The depth of HAZ is mainly depends on pulse duration when the discharge spot is single-crater. The results are analyzed.
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While the world is focused on controlling the spread of diseases such as HIV and malaria in the developing world, another approaching epidemic has been largely overlooked. The World Heath Organization predicts that there will be 16 million new cancer cases per year in 2020 and 70% of these will be in the developing world. Many of these cancers are preventable, or treatable when detected early enough. Establishing effective, affordable and workable cancer control plans in African countries is one step in the right direction toward limiting this epidemic.
Resumo:
El presente estudio se realizó en la granja cunícula de la Facultad de Ciencia Animal de la Universidad Nacional Agraria, ubicada en el Km. 12 1/2 de la carretera Norte, Managua, Nicaragua. El cual abarca una fase retrospectiva y una prospectiva, realizándose con ayuda de los registros productivos y reproductivos de cada animal. El objetivo del estudio fue establecer retrospectivamente las tasas de mortalidad del período de enero de 1994 a diciembre de 1998, e implementar un plan sanitario en forma prospectiva con el fin de disminuir la mortalidad encontrada en los años anteriores. Las fases del estudio realizado se enfocaron en el análisis de la mortalidad de los animales, teniendo como variables las diferentes categorías, raza, destino, mes y año. En la fase retrospectiva, la mortalidad de las hembras por raza dio como resultado, un porcentaje de muertos mayor en la raza Neozelandés Blanca con 27 hembras muertas representando el 48.2 % de la mortalidad entre 8 diferentes razas, presentándose las muertes en su mayoría en los meses de época seca, así como también 403 gazapos muertos lo que representa un porcentaje de 58 %. En la fase prospectiva, el total de conejos estudiados fue de 112, de los cuales se obtuvo un total de 4 hembras muertas para un porcentaje de 14.28% en lo que respecta a su categoría. El porcentaje de mortalidad de los gazapos al nacimiento fue de 25.8% dándose el número mayor de muertos en la época seca. En la categoría de engorde fue un total de 11 conejos muertos lo que representa el 13.9% de mortalidad en esa categoría. Los resultados demuestran que la implementación de un plan sanitario es indispensable para una alta producción de conejos, ya que sin este el índice de mortalidad e incidencia de enfermedades se aumentan, igualmente el factor económico haciendo gastos innecesarios en medicamentos para curar las enfermedades.
Resumo:
El presente estudio se realizó en la granja porcina de la Universidad Nacional Agraria (U.N.A), ubicada en el Km. 13 a los 86°. 09' 36" longitud oeste y los 12° 08'15" latitud norte de la comunidad de Sabana Grande, Municipio de Managua con un elevación de 56 m sobre el nivel del mar (INETER, 1987). La fase de campo fue realizada de Julio a Octubre de 1999, con el objetivo de evaluar el comportamiento productivo de cerdos en crecimiento, desarrollo y engorde alimentados con tres raciones diferentes: (T1) Desperdicio de Galleta 100%, (T2) Desperdicio de Galleta 75% + Desperdicio de cocina 25%, (T3) Desperdicio de cocina 100%. Se utilizaron 18 cerdos comerciales de ambos sexos, con peso promedio de inicio de 54.86 kg, que fueron distribuidos en tres tratamientos con seis repeticiones con los datos levantados de pesaje de los diferentes tratamientos, se efectúo el análisis estadístico correspondiente al diseño experimental completamente al Azar (DCA) y su correspondiente análisis para las variables en estudio, G.M D. y C.A. Los cerdos que presentaron una ganancia de peso más alta, fueron los que se alimentaron con la ración l00 % de desperdicio de cocina teniendo una ganancia media diaria de 0.758 kg. los cerdos alimentados 75 % DDG, + 25 % DDC, alcanzaron una ganancia de peso promedio de 0.578 kg. mientras que el tratamiento 100% DDG alcanzo una ganancia media de peso promedio de 0.17 kg. El análisis de la ganancia media diaria se demostró con una alfa de 5 %. El análisis estadístico mostró que las diferencias en conversión alimenticia fueron significativas entre tratamientos con un Alfa al 5 %. Al comparar las utilidades generadas entre el T t y T2, estos resultaron financieramente aceptables, de forma similar se comportaron el T1 y T3., no obstante, desde el punto de vista nutricional, estos no cumplieron los requerimientos de la categoría, por lo que el T2, se presentó finalmente como el más aceptable nutricionalmente.