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Search Results: 1 - 10 of 235504 matches for " R;Ribeiro "
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Eimeria lepidosirenis n.sp. (Apicomplexa:Eimeriidae) of the South American lungfish Lepidosiren paradoxa (Osteichthyes:Dipnoi) from Amazonian Brazil
Lainson, R;Ribeiro, Lucia;
Memórias do Instituto Oswaldo Cruz , 2006, DOI: 10.1590/S0074-02762006000300018
Abstract: the mature oocysts of eimeria lepidosirenis n.sp. are described in faeces removed from the lower region of the intestine of a single specimen of the south american lungfish lepidosiren paradoxa, from belém, state of pará, amazonian brazil. oocysts with endogenous sporulation: spherical to slightly subspherical, 30.8 × 30.3 μm (28.1 × 25.9 -33.3 × 31.8), shape-index (ratio length/width) 1.0, n = 25. oocyst wall a very thin, single layer approximately 0.74 μm thick, smooth, colourless, with no micropyle and rapidly breaking down to release the sporocysts. oocyst residuum a bulky ovoid to spherical mass of approximately 20.0 × 15 μm, composed of fine granules and larger globules and enclosed by a very fine membrane: no polar bodies seen. sporocysts 15.5 × 9.0 μm (14.5 × 8.0 16.0 × 9.0), shape index 1.7 (1.6-1.8), n = 30, ovoid, with one extremity rather pointed and with a very delicate stieda body but no sub-stieda body: sporocyst wall a single extremely thin layer with no valves. sporocyst residuum a spherical to ovoid mass of approximately 5.0 × 4.0 μm, composed of fine granules and small globules and enclosed by a very fine membrane. sporozoites strongly recurved at their ends and apparently with only a single refractile body. site of development in the host uncertain: no evidence of endogenous stages was found in fresh scrapings and stained smears of the intestinal epithelium.
Adiabatic Computation - A Toy Model
P. Ribeiro,R. Mosseri
Physics , 2006, DOI: 10.1103/PhysRevA.74.042333
Abstract: We discuss a toy model for adiabatic quantum computation which displays some phenomenological properties expected in more realistic implementations. This model has two free parameters: the adiabatic evolution parameter $s$ and the $\alpha$ parameter which emulates many-variables constrains in the classical computational problem. The proposed model presents, in the $s-\alpha$ plane, a line of first order quantum phase transition that ends at a second order point. The relation between computation complexity and the occurrence of quantum phase transitions is discussed. We analyze the behavior of the ground and first excited states near the quantum phase transition, the gap and the entanglement content of the ground state.
Entanglement in the symmetric sector of $n$ qubits
P. Ribeiro,R. Mosseri
Physics , 2011, DOI: 10.1103/PhysRevLett.106.180502
Abstract: We discuss the entanglement properties of symmetric states of $n$ qubits. The Majorana representation maps a generic such state into a system of $n$ points on a sphere. Entanglement invariants, either under local unitaries (LU) or stochastic local operations and classical communication (SLOCC), can then be addressed in terms of the relative positions of the Majorana points. In the LU case, an over complete set of invariants can be built from the inner product of the radial vectors pointing to these points; this is detailed for the well documented three-qubits case. In the SLOCC case, cross ratio of related M^bius transformations are shown to play a central role, examplified here for four qubits. Finally, as a side result, we also analyze the manifold of maximally entangled 3 qubit state, both in the symmetric and generic case.
Anion exchange resin as support for invertase immobilization
Revista de Ciências Farmacêuticas Básica e Aplicada , 2009,
Abstract: The invertase (EC from Saccharomyces cerevisiae was employed as a model enzyme in the evaluation of the adsorption capacity of DOWEX-1X8-50 , a basic anion exchange resin, when used as support in enzyme immobilization. By mixing 100mg of resin with 27mg of invertase (pI = 4.0) in buffer solution (pH 4.6, 25°C), stirred at 100rpm, an adsorption of 93% was achieved. The activities (1U = amount of enzyme forming 1mg reducing sugars/min) of soluble and insoluble invertase were 0.084 U/mgE and 0.075 U/mgE, respectively, giving an immobilization coefficient of 90.4%. The immobilized invertase had a higher thermal stability than the soluble form. The highest activity was observed at pH 4.5 in both forms of the enzyme, whereas the pH stability ranges for soluble and insoluble invertase were 3.5-5.0 and 4.5-5.5, respectively. The kinetic constants for soluble invertase were KM = 18.3 mM and Vmax = 0.084 U/mgE, and for the insoluble form, KM = 29.1 mM and Vmax = 0.075 U/mgE. The resin tested adsorbed the invertase very well, provided the enzyme molecule had a net negative charge, i.e., the immobilization and reaction procedures had to be carried out at pH > pI. Keywords: Invertase, immobilization, adsorption, anionexchange resin.
SHRIMP U-Pb and U-Pb Laser Ablation Geochronological on Zircons from Monte Santo Alkaline Intrusive Suite, Westhern Araguaia Belt, Tocantins State, Brazil  [PDF]
Rúbia Ribeiro Viana, Gislaine Amorés Battilani
Journal of Geoscience and Environment Protection (GEP) , 2014, DOI: 10.4236/gep.2014.23022

The Monte Santo Alkaline Intrusive Suite (MSAIS) is an association syenite foid, nepheline syenite and syenite, which are intruded in metapelites of the Rio do Coco meta-volcanic-sedimentary Sequence, presenting abundant pegmathoid veins cutting all of them. The ages obtained by Shrimp (1051 ± 22 Ma, 1048 ± 11 Ma) are very close those younger age obtained by U-Pb laser ablation (1056 ± 21), beeing interpreted as crystallization age. These dating reveal also that MSAIS rocks were affected by common succession of younger events below 550 Ma ago, responsible by the later rocky bodies of varying composition occurring in the region, including the alkaline pegmatites hosted in the nepheline syenite of the MSAIS.

Geochemistry and Petrography of Alkaline rocks from Monte Santo Alkaline Intrusive Suite, Western Araguaia Belt, Tocantins State, Brazil  [PDF]
Rúbia Ribeiro Viana, Gislaine Amorés Battilani
Journal of Geoscience and Environment Protection (GEP) , 2014, DOI: 10.4236/gep.2014.23010

The Monte Santo Alkaline Intrusive Suite (MSAIS) is an association syenite foid, nepheline syenite and syenite. The MSAIS rocks are intruded in metapelites of the Rio do Coco meta-volcanic-sedi- mentary Sequence and are abundant pegmathoid veins cutting all of them. The mineral paragenesis is represented by aegirina, arfvedsonite, albite and nepheline, crystallized during the initial phase of crystallization. A late magmatic phase show nepheline, perthite, calcite and biotite, and a hydrothermal phase allowed for the formation of cancrinite, sodalite, analcime and natrolita associated with altered nepheline. The geochemical analyses showed metaluminous and medium to high potassium characteristics, being classified as miaskitic rocks, according to agpaicity and the Na + K > 1/6Si indexes. However, the mineralogical assemblage suggests a low to medium agpaitic composition, which can be related to a transition from miaskitic to agpaitic crystallization regime. The rare earth elements showed depletion in heavy rare earth and a strong negative Eu anomaly and enrichments in the some lithophile elements, suggesting a differentiated pattern later, which can be associated to metasomatic alterations.

Electrochemical Investigation of Corrosion on AISI 316 Stainless Steel and AISI 1010 Carbon Steel: Study of the Behaviour of Imidazole and Benzimidazole as Corrosion Inhibitors  [PDF]
Roberta R. Moreira, Thiago F. Soares, Josimar Ribeiro
Advances in Chemical Engineering and Science (ACES) , 2014, DOI: 10.4236/aces.2014.44052
Abstract: An electrochemical investigation of the corrosion on AISI 316 austenitic stainless steel and AISI 1010 carbon steel in sodium chloride solution (3.0 wt.%) was performed in the absence and presence of imidazole and benzimidazole corrosion inhibitors. The results showed that at any inhibitor concentration (25 ppm to 1000 ppm), there was an increase in the polarisation resistance of both steels. The highest efficiency of corrosion inhibition was obtained using imidazole at a concentration of 50 ppm for both steels, with values of 96% for the AISI 316 stainless steel and 73% for the AISI 1010 carbon steel.
Non-Markovian effects in electronic and spin transport
Pedro Ribeiro,Vitor R. Vieira
Physics , 2014, DOI: 10.1103/PhysRevB.92.100302
Abstract: We derive a non-Markovian master equation for the evolution of a class of open quantum systems consisting of quadratic fermionic models coupled to wide-band reservoirs. This is done by providing an explicit correspondence between master equations and non-equilibrium Green's functions approaches. Our findings permit to study non-Markovian regimes characterized by negative decoherence rates. We study the real-time dynamics and the steady-state solution of two illustrative models: a tight-binding and an XY-spin chains. The rich set of phases encountered for the non-equilibrium XY model extends previous studies to the non-Markovian regime.
Estratigrafía, facies y evolución depositacional de la Formación Sauce Grande (Carbonífero Superior): Cuenca Sauce Grande, Sierras Australes, Buenos Aires, Argentina Stratigraphy, facies and depositional evolution of the Sauce Grande Formation (Upper Carboniferous): Sauce Grande Basin, Sierras Australes, Buenos Aires, Argentina
R. R. Andreis,M. Torres Ribeiro
Revista de la Asociación Geológica Argentina , 2003,
Abstract: Se encara el examen detallado de las litofacies y su composición, así como el análisis de los procesos depositacionales que condujeron a la acumulación de materiales siliciclásticos de la Formación Sauce Grande y que representa la primera sedimentación acontecida en la cuenca Sauce Grande. Fueron analizados dos perfiles estratigráficos de la unidad: el perfil Norte (con 826 m) y el perfil Sur (con 1095 m). La unidad está compuesta por importantes volúmenes de diamictitas [Dmm1, Dmm2, Dmg, Dms, Dms(r)], así como de areniscas (Sma, Smw, Sh, Sr, Sp), pelitas (Fm, Fl, Fd) y escasos conglomerados (Dcm, Dcg). También fue analizada la ciclicidad de las sucesiones, reconociéndose tres megaciclos (inferior, medio y superior con sus respectivas asociaciones litofaciales). El megaciclo inferior permite visualizar el paleorrelieve devónico (Formación Lolén) y está constituido por abundantes diamictitas, areniscas y escasos conglomerados. El megaciclo medio contiene areniscas y conglomerados y en el megaciclo superior se advierte una disminución en la participación de diamictitas con una mayor frecuencia de cadilitos (guijarro a bloque), sustituida por areniscas y pelitas (en el perfil Norte). En los megaciclos inferior y superior las facies Dmm1, Dmm2 y Dms(r), con espesores decamétricos y extensiones de centenares de metros son los miembros más conspicuos y corresponden a deslizamientos de masas semiconsolidadas o fluidas (flujos de detritos cohesivos) generados en pendientes fuertes proximales. Es probable que en el megaciclo superior las diamictitas sean del tipo rain out. La facies Dms(r)incluye cuerpos arenosos contorsionados y/u orientados y frecuentes intraclastos pelíticos. Las facies conglomerádicas son flujos no cohesivos dejados atrás por flujos hiperconcentrados o como flujos de granos modificados en su densidad. Las areniscas Sma habrían sido depositadas por procesos suspensivos densos y escasamente compactados, mientras que las waques (Smw) representan flujos de detritos finos y densos transicionales a flujos licuefactos. Las demás areniscas representan acción de oleaje o corrientes (Sr) o por acreción frontal en barras transversales o dunas de arena por flujos traccionales (Sp). El comienzo de los procesos depositacionales de la Formación Sauce Grande fue caracterizado por una rápida transgresión en el Carbonífero tardío bajo condiciones de moderada subsidencia (procesos eustáticos). El megaciclo inferior se caracteriza por la sedimentación en un slope apron o debris apron localizado en las cercanías del talud continental, con fuerte agradación y rara
Stability of boron nitride bilayers: Ground state energies, interlayer distances, and tight-binding description
R. M. Ribeiro,N. M. R. Peres
Physics , 2011, DOI: 10.1103/PhysRevB.83.235312
Abstract: We have studied boron nitride monolayer and bilayer band structures. For bilayers, the ground state energies of the different five stackings are computed using DFT in order to determine the most stable configuration. Also, the interlayer distance for the five different types of stacking in which boron-nitride bilayers can be found is determined. Using a minimal tight binding model for the band structures of boron nitride bilayers, the hopping parameters and the onsite energies have been extracted by fitting a tight binding empirical model to the DFT results.
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