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Search Results: 1 - 10 of 144581 matches for " F. Fiuza "
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High-brilliance synchrotron radiation induced by the plasma magnetostatic mode
F. Fiuza,L. O. Silva,C. Joshi
Physics , 2010, DOI: 10.1103/PhysRevSTAB.13.080701
Abstract: Using multi-dimensional PIC simulations we show that the magnetic undulator-type field of the plasma magnetostatic mode is indeed produced by the interaction of a laser pulse with a relativistic ionization front, as predicted by linear theory for a cold plasma. When the front with this magnetostatic mode is followed by a relativistic electron beam, the interaction of the beam with this magnetic field, produces FEL-type synchrotron radiation, providing a direct signature of the magnetostatic mode. The possibility of generating readily detectable ultrashort wavelength radiation using this mode, by employing state-of-the-art laser systems, is demonstrated, thus opening the way towards experimental observation of the hitherto unseen magnetostatic mode and the use of this plasma FEL mechanism to provide a source of high-brilliance ultrashort wavelength radiation.
Acceleration in perpendicular relativistic shocks for plasmas consisting of leptons and hadrons
A. Stockem,F. Fiuza,R. A. Fonseca,L. O. Silva
Physics , 2012, DOI: 10.1088/0004-637X/755/1/68
Abstract: We investigate the acceleration of light particles in perpendicular shocks for plasmas consisting of a mixture of leptonic and hadronic particles. Starting from the full set of conservation equations for the mixed plasma constituents, we generalize the magneto-hydrodynamical jump conditions for a multi-component plasma, including information about the specific adiabatic constants for the different species. The impact of deviations from the standard model of an ideal gas is compared in theory and particle-in-cell simulations, showing that the standard-MHD model is a good approximation. The simulations of shocks in electron-positron-ion plasmas are for the first time multi-dimensional, transverse effects are small in this configuration and 1D simulations are a good representation if the initial magnetization is chosen high. 1D runs with a mass ratio of 1836 are performed, which identify the Larmor frequency \omega_{ci} as the dominant frequency that determines the shock physics in mixed component plasmas. The maximum energy in the non-thermal tail of the particle spectra evolves in time according to a power-law proportional to t^\alpha with \alpha in the range 1/3 < \alpha < 1, depending on the initial parameters. A connection is made with transport theoretical models by Drury (1983) and Gargate & Spitkovsky (2011), which predict an acceleration time proportional to \gamma and the theory for small wavelength scattering by Kirk & Reville (2010), which predicts a behavior rather as proportional to \gamma^2. Furthermore, we compare different magnetic field orientations with B_0 inside and out of the plane, observing qualitatively different particle spectra than in pure electron-ion shocks.
Relativistic generalization of formation and ion reflection conditions in electrostatic shocks
A. Stockem,E. Boella,F. Fiuza,L. O. Silva
Physics , 2013, DOI: 10.1103/PhysRevE.87.043116
Abstract: The theoretical model by Sorasio et al. (2006) for the steady state Mach number of electrostatic shocks formed in the interaction of two plasma slabs of arbitrary density and temperature is generalized for relativistic electron and non-relativistic ion temperatures. We find that the relativistic correction leads to lower Mach numbers, and as a consequence, ions are reflected with lower energies. The steady state bulk velocity of the downstream population is introduced as an additional parameter to describe the transition between the minimum and maximum Mach numbers in dependence of the initial density and temperature ratios. In order to transform the soliton-like solution in the upstream region into a shock, a population of reflected ions is considered and differences to a zero-ion temperature model are discussed.
The impact of kinetic effects on the properties of relativistic electron-positron shocks
A. Stockem,F. Fiuza,R. A. Fonseca,L. O. Silva
Physics , 2012, DOI: 10.1088/0741-3335/54/12/125004
Abstract: We assess the impact of non-thermally shock-accelerated particles on the magnetohydrodynamic (MHD) jump conditions of relativistic shocks. The adiabatic constant is calculated directly from first principle particle-in-cell simulation data, enabling a semi-kinetic approach to improve the standard fluid model and allowing for an identification of the key parameters that define the shock structure. We find that the evolving upstream parameters have a stronger impact than the corrections due to non-thermal particles. We find that the decrease of the upstream bulk speed yields deviations from the standard MHD model up to 10%. Furthermore, we obtain a quantitative definition of the shock transition region from our analysis. For Weibel-mediated shocks the inclusion of a magnetic field in the MHD conservation equations is addressed for the first time.
Cytoskeletal Proteins of Actinobacteria
Michal Letek,María Fiuza,Almudena F. Villadangos,Luís M. Mateos,José A. Gil
International Journal of Cell Biology , 2012, DOI: 10.1155/2012/905832
Abstract: Although bacteria are considered the simplest life forms, we are now slowly unraveling their cellular complexity. Surprisingly, not only do bacterial cells have a cytoskeleton but also the building blocks are not very different from the cytoskeleton that our own cells use to grow and divide. Nonetheless, despite important advances in our understanding of the basic physiology of certain bacterial models, little is known about Actinobacteria, an ancient group of Eubacteria. Here we review current knowledge on the cytoskeletal elements required for bacterial cell growth and cell division, focusing on actinobacterial genera such as Mycobacterium, Corynebacterium, and Streptomyces. These include some of the deadliest pathogens on earth but also some of the most prolific producers of antibiotics and antitumorals. 1. Introduction All cells require cytoskeletal proteins for cell division and growth [1]. These structural components are essential for the maintenance of cell shape as well as for other dynamic processes critical for the cell, such as chromosomal segregation, the equal partitioning of cytosolic material, cell polarization, and motility [2]. The ubiquity of the cytoskeletal proteins reflects their early evolutionary acquisition and bacterial origin [3]. In fact, it is difficult to imagine an adaptable free-living cell without a versatile internal cytoskeleton. However, this notion is very recent since only just a decade ago it was thought that bacteria lacked a cytoskeleton. Instead, the required cell membrane support was assumed to be provided by the bacterial cell wall, which was thus considered to function as an “exoskeleton,” forming a physical barrier that contained the hydrostatic internal cell pressure and prevented the rupture of the cell membrane [4]. In fact, this exoskeleton does determine the characteristic shape of a bacterial cell, since in the absence of cell wall rod-shaped bacteria lose their morphology and become perfect spheres. But given that the chemical composition of the bacterial cell wall is essentially the same in the vast majority of Eubacteria (it is basically made of peptidoglycan or murein), it was also recognized that other factors must drive the determination of bacterial cell shape [5]. Osmotic pressure was thought to have some role in this process albeit a limited one, in view of the high morphological variability observed in different wild-type bacterial species and in strains carrying mutations in the different genes involved in cell morphology determination (morphogenes) [5]. In addition, and despite their
Intera??o entre Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), Campoletis flavicincta (Ashmead) (Hymenoptera: Ichneumonidae) e Bacillus thuringiensis aizawai, em laboratório
Dequech, S?nia T.B.;Silva, Rogério F.P. da;Fiuza, Lidia M.;
Neotropical Entomology , 2005, DOI: 10.1590/S1519-566X2005000600010
Abstract: larvae of healthy spodoptera frugiperda (j.e. smith), parasitized by campoletis flavicincta (ashmead), infected by bacillus thuringiensis aizawai, and both parasitized and infected, were obtained in the laboratory and fed with corn leaves. parasitized and infected larvae showed less leaf consumption (in average 2.3 cm2) than the others, but did not differ from only parasitized larvae. mean mortality of larvae both parasitized and infected was higher (96.5%) than the only parasitized (78.4%) and only infected ones (44.3%). the feeding period of the infected larvae (in average 29.6 days) did not differ from that of the healthy ones, in spite of having a longer larval period. offsprings from pairs of parasitoids that had emerged from infected larvae did not have the biological characteristics modified. therefore, the combined use of the parasitoid and the bacterium results in higher mortality and less foliar consumption and does not result in damage to the parasitoid.
Associa??es entre déficits cognitivos e qualidade de vida na esquizofrenia
Cruz, Breno Fiuza;Salgado, Jo?o Vinícius;Rocha, Fábio Lopes;
Revista de Psiquiatria Clínica , 2010, DOI: 10.1590/S0101-60832010000500009
Abstract: background: the quality of life (qol) is a valuable way of assessing the impact of diseases in daily life and favors more effective interventions under a biopsychosocial perspective. objectives: this article aimed to critically analyze the available data on the relationship between qol and cognitive function in schizophrenia. methods: we performed a search in pubmed and lilacs databases with the terms "schizophrenia" and "cognition disorder" or "cognition" and "quality of life" or "outcome assessment". results: from the 27 selected articles that studied the relationship between cognition and qol measured by scales, 20 articles showed associations. the association was more robust in studies using scales administered by a researcher, compared to self-report scales. discussion: the cognitive assessment is important not only as a parameter for determining qol of patients, but also as a factor to be taken into account when analyzing the data obtained by self-report qol scales.
The effect of crude ethanol extract and fractions of Hyptidendron canum (Pohl ex Benth.) Harley on the hepatopancreas of Oreochromis niloticus L
Biological Research , 2009,
Abstract: Hyptidendron canum (Pohl ex Benth.) Harley is a native tree of the Brazilian Savannah. The fish Oreochromis niloticus L. was used as an experimental model to determine the bioactivity of the crude ethanol extract as well as ethyl acetate, hexanic and chloroform fractions obtained from its leaves. The plant ethanol extract and fractions were administered to the fish orally with their feed. Twenty four hours later, the fish were sacrificed and their livers dissected, fixed in neutral formalin, embedded in paraffin and sectioned. Histological analyses were performed using Masson's trichrome and Haematoxylin-Eosin. Histochemical studies were performed using Feulgen, PAS (Periodic Acid Schiff) and PAS + salivary amylase and Sudan IV stain. The qualitative analysis of the material showed that both the crude ethanol extract and the fractions from H. canum induced vasoactive activity, causing vasodilation and vascular congestion, and the hexanic fraction also caused an apparent proliferation of capillaries. Hepatopancreas toxicity was evident through inflammatory processes. Pancreatic (chloroform fraction) and hepatic alterations, hemorrhagic spots and necroses were observed in fish treated with-ethanol extract and fractions. This study is the first description of the biologic action of the crude ethanol extract and the hexane, ethyl acetate and chloroform fractions in fish.
Bioactivity of crude ethanol extract and fractions of Eugenia uniflora (Myrtaceae) in the hepatopancreas of Oreochromis niloticus L
Biological Research , 2009,
Abstract: This study evaluates the bioactivity of the crude ethanol extract and ethyl acetate, hexane and chloroform fractions obtained from Eugenia uniflora leaves using the hepatopancreas of Oreochromis niloticus L. as an experimental model. The ethanol extract and fractions were administered to the fish orally with their feed. Twenty-four hours later, the fish were sacrificed and their livers dissected, fixed in neutral formalin, embedded in paraffin and sectioned. Histological analyses were performed using Masson's trichrome and Haematoxylin-Eosin. Histochemical studies were performed using Feulgen, PAS (Periodic Acid Schiff) and PAS + salivary amylase and Sudan IV stain. The qualitative analysis of the material showed that the crude extract and the ethyl, chloroform and hexane fractions induced vasodilation, vascular congestion and toxicity due to the presence of eosinophilic granular cells, rodlet cells, some leukocytic infiltrate and rare focal necroses. The Nile tilapia proved to be a satisfactory model for screening plant products.
Determina o de taninos e metilxantinas no guaraná em pó (Paullinia cupana Kunth, Sapindaceae) por cromatografia líquida de alta eficiência Determination of tannins and methylxanthines in powdered guarana (Paullinia cupana Kunth, Sapindaceae) by high performance liquid chromatography
Sandra A. Sousa,Suzana F. Alves,Joelma A. M de Paula,Tatiana S. Fiuza
Revista Brasileira de Farmacognosia , 2010,
Abstract: As sementes de guaraná (Paullinia cupana Kunth, Sapindaceae) s o utilizadas como estimulante e os principais constituintes químicos s o as metilxantinas e os taninos, tais como catequina e epicatequina. Este trabalho teve por objetivo investigar um método por cromatografia líquida de alta eficiência (CLAE) para quantificar, simultaneamente, cafeína, teofilina, teobromina, catequina e epicatequina em pó de guaraná. Os valores obtidos foram comparados com os resultados encontrados no método espectrofotométrico da Farmacopéia Brasileira IV ed. Pelo método cromatográfico, os teores de metilxantinas e taninos totais foram de 4,04% e 1,48%, respectivamente. Os teores de metilxantinas e taninos totais, obtidos pelo método espectrofotométrico, foram de 4,88% e 4,05%, respectivamente. Acredita-se que, nas condi es experimentais empregadas, o método espectrofotométrico n o foi específico, quantificando outras substancias fenólicas presentes no guaraná. Portanto, sugere-se o emprego desse método cromatográfico no controle de qualidade do guaraná em pó, por ser preciso, sensível, específico e rápido. The seeds of Paullinia cupana Kunth, Sapindaceae, are used as a stimulant and the main chemical constituents are the methylxanthines and tannins, as catechin and epicatechin. This study aimed to investigate a method by high performance liquid chromatography (HPLC) to quantify both caffeine, theophylline, theobromine, catechin and epicatechin in powdered of P. cupana. The values obtained were compared with the results of the spectrophotometric method of the Brazilian Pharmacopoeia IV ed. For the chromatographic method, the levels of methylxanthines and total tannins were 4.04% and 1.48%, respectively. The levels of methylxanthines and total tannins obtained by the spectrophotometric method, were 4.88% and 4.05%, respectively. It is believed that, under our experimental conditions, the spectrophotometric method was not specific and quantified others phenolic substances present in the P. cupana. Therefore we suggest the use of this chromatographic method in quality control of P. cupana powder, to be accurate, sensitive, specific and fast.
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