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Search Results: 1 - 10 of 683194 matches for " J. M. F. dos Santos "
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The Thick-COBRA: a New Gaseous Electron Multiplier for Radiation Detectors
F. D. Amaro,C. Santos,J. F. C. A. Veloso,A. Breskin,R. Chechik,J. M. F. dos Santos
Physics , 2010, DOI: 10.1088/1748-0221/5/10/P10002
Abstract: The operation principle and preliminary results of a novel gas-avalanche patterned hole electron multiplier, the Thick-COBRA (THCOBRA), are presented. This micro-hole structure is derived from the THGEM and MHSP. Sub-millimeter diameter holes are mechanically drilled in a thin G10 plate, Cu-clad on both faces; on one of the faces the Cu is etched to produce additional anode strips winding between circular cathode strips. Primary avalanches occurring within the holes are followed by additional ones at the anode-strips vicinity. Gains in excess of 5*104 were reached with 22.1 x-rays in Ar, Ne and Ar-10%CH4, with 12.2 % FWHM energy resolution in Ar-10%CH4. Higher gains were measured with single photoelectrons. This robust multiplier may have numerous potential applications.
High-gain DC-mode operated Gaseous Photomultipliers for the visible spectral range
A. Lyashenko,A. Breskin,R. Chechik,F. D. Amaro,J. Veloso,J. M. F. Dos Santos
Physics , 2008, DOI: 10.1016/j.nima.2009.05.112
Abstract: We shortly describe recent progress in photon detectors combining bi-alkali photocathodes and cascaded patterned gas-avalanche electron multipliers. It permitted the development and the first feasibility demonstration of high-gain gaseous photomultipliers sensitive in the visible spectral range, operated in DC mode with single-photon sensitivity.
Ontogenetic patterns and genetic variation in Anopheles (Anopheles) intermedius Chagas, 1908 and Anopheles (Anopheles) mattogrossensis Lutz & Neiva, 1911 (Diptera: Culicidae) in the Brazilian Amazon
RODRIGUEZ, G. A. D.;SANTOS, J. M. M. dos;MAIA, J. de F.;
Revista Brasileira de Biologia , 2000, DOI: 10.1590/S0034-71082000000200020
Abstract: changes in the expression of genes were observed during development in populations of anopheles (anopheles) intermedius and anopheles (anopheles) mattogrossensis. esterase showed seven zones of activity: est1 was present in all developmental stages of both species; est2 was observed only in larvae of a. intermedius and larvae and pupae of a. mattogrossensis, with greater activity in pupae; est3 and est5 were present in all developmental stages, with greater intensity in larvae; est4 and est6 showed weak activity in larvae of a. mattogrossensis and was not found in a. intermedius. leucine aminopeptidase showed four zones of activity, of which lap1 and lap2 were found in all stages of a. intermedius, with highest activity in larvae, and in larvae only of a. mattogrossensis. lap3 was detected in all stages of a. mattogrossensis and in larvae only of a. intermedius. lap4 was detected only in larvae and pupae of a. mattogrossensis, with greater intensity in pupae. a-glycerophosphate dehydrogenase showed a single zone of activity, detected in older fourth-instar larvae and becoming more intense from the pupal stage onwards.
Ontogenetic patterns and genetic variation in Anopheles (Anopheles) intermedius Chagas, 1908 and Anopheles (Anopheles) mattogrossensis Lutz & Neiva, 1911 (Diptera: Culicidae) in the Brazilian Amazon
RODRIGUEZ G. A. D.,SANTOS J. M. M. dos,MAIA J. de F.
Revista Brasileira de Biologia , 2000,
Abstract: Changes in the expression of genes were observed during development in populations of Anopheles (Anopheles) intermedius and Anopheles (Anopheles) mattogrossensis. Esterase showed seven zones of activity: EST1 was present in all developmental stages of both species; EST2 was observed only in larvae of A. intermedius and larvae and pupae of A. mattogrossensis, with greater activity in pupae; EST3 and EST5 were present in all developmental stages, with greater intensity in larvae; EST4 and EST6 showed weak activity in larvae of A. mattogrossensis and was not found in A. intermedius. Leucine aminopeptidase showed four zones of activity, of which LAP1 and LAP2 were found in all stages of A. intermedius, with highest activity in larvae, and in larvae only of A. mattogrossensis. LAP3 was detected in all stages of A. mattogrossensis and in larvae only of A. intermedius. LAP4 was detected only in larvae and pupae of A. mattogrossensis, with greater intensity in pupae. alpha-Glycerophosphate dehydrogenase showed a single zone of activity, detected in older fourth-instar larvae and becoming more intense from the pupal stage onwards.
Nonvanishing boundary conditions and dark solitons in the NLS model
L. F. dos Santos,H. Blas,M. J. B. F. da Silva
Physics , 2009,
Abstract: We consider non-vanishing boundary conditions (NVBC) for the NLS model [6,7,27] in the context of the hybrid dressing transformation and $\tau$-function approach. In order to write the NLS model in a suitable form to deal with non-vanishing boundary conditions it is introduced a new spectral parameter in such a way that the usual NLS parameter will depend on the affine parameter through the so-called Zukowsky function. In the context of the dressing transformation the introduction of the affine parameter avoids the construction of certain Riemann sheets for the usual NLS spectral parameter. In this way one introduces a Lax pair defined for the new spectral parameter and the relevant NVBC NLS $\tau$ functions are obtained by the dressing transformation method. We construct the one and two dark-soliton solutions explicitly.
Re-observing the EUV emission from Abell 2199: in-situ measurement of background distribution by offset pointing
R. Lieu,M. Bonamente,J. P. D. Mittaz,F. Durret,S. Dos Santos,J. Kaastra
Physics , 1999, DOI: 10.1086/312401
Abstract: The EUV excess emission from the clusters A2199 and A1795 remains an unexplained astrophysical phenomenon. There has been many unsuccessful attempts to `trivialize' the findings. In this Letter we present direct evidence to prove that the most recent of such attempts, which attributes the detected signals to a background non-uniformity effect, is likewise excluded. We address the issue by a re-observation of A2199 which features a new filter orientation, usage of a more sensitive part of the detector and, crucially, includes a background pointing at $\sim$ 2$^o$ offset - the first {\it in situ} measurement of its kind. We demonstrate quantitatively two facts: (a) the offset pointing provides an accurate background template for the cluster observation, while (b) data from other blank fields do not. We then performed point-to-point subtraction of the {\it in situ} background from the cluster field, with appropriate propagation of errors. The resulting cluster radial profile is consistent with that obtained by our original method of subtracting a flat asymptotic background. The emission now extends to a radius of 20 arcmin; it confirms the rising prominence of EUV excess beyond $\sim$ 5 arcmin as previously reported.
X-ray imaging with GEMs using $100\,μ$m thick foils
H. Natal da Luz,J. A. Mir,X. Carvalho,J. M. F. dos Santos
Physics , 2013, DOI: 10.1088/1748-0221/9/06/C06007
Abstract: A simple X-ray imaging system using off-the-shelf electronics and simple reconstruction algorithms aiming a spatial resolution of 1.7 mm ($\sim 3\,\%$ of the detector length) is described in this work. For this, two 100 cm$^2$ Gas Electron Multiplier (GEM) foils with a thickness of 100 \mu m (2-fold thicker than the standard ones) were immersed in a mixture of argon and carbon dioxide (70:30). The charge readout with 2D position determination was done with resistive charge division. Due to their higher thickness with respect to the standard GEMs, the 100 \mu m thick GEM foils were found to be less prone to damage caused by the electrical discharges. X-ray images are shown and some descriptions of the physical processes involved are presented. We describe the advantages of this method that allows counting each X-ray photon or particle entering the detector, its interaction position, as well as measuring of its energy. The results of our present work show a position resolution below 2 mm, being limited by the gas mixture used, and not the detecting system, with a very good cost effectiveness. Future work is being carried out to optimize the present system for a medical application as a proton beam monitor.
Efficient ion blocking in gaseous detectors and its application to gas-avalanche photomultipliers sensitive in the visible-light range
A. V. Lyashenko,A. Breskin,R. Chechik,J. M. F. Dos Santos,F. D. Amaro,J. F. C. A. Veloso
Physics , 2008, DOI: 10.1016/j.nima.2008.08.063
Abstract: A novel concept for ion blocking in gas-avalanche detectors was developed, comprising cascaded micro-hole electron multipliers with patterned electrodes for ion defocusing. This leads to ion blocking at the 10^{-4} level, in DC mode, in operation conditions adequate for TPCs and for gaseous photomultipliers. The concept was validated in a cascaded visible-sensitive gas avalanche photomultiplier operating at atmospheric pressure of Ar/CH_{4} (95/5) with a bi-alkali photocathode. While in previous works high gain, in excess of 10^{5}, was reached only in a pulse-gated cascaded-GEM gaseous photomultiplier, the present device yielded, for the first time, similar gain in DC mode. We describe shortly the physical processes involved in the charge transport within gaseous photomultipliers and the ion blocking method. We present results of ion backflow fraction and of electron multiplication in cascaded patterned-electrode gaseous photomultiplier with K-Cs-Sb, Na-K-Sb and Cs-Sb visible-sensitive photocathodes, operated in DC mode.
Development of high-gain gaseous photomultipliers for the visible spectral range
A. V. Lyashenko,A. Breskin,R. Chechik,J. M. F. Dos Santos,F. D. Amaro,J. F. C. A. Veloso
Physics , 2009, DOI: 10.1088/1748-0221/4/07/P07005
Abstract: We summarize the development of visible-sensitive gaseous photomultipliers, combining a semitransparent bi-alkali photocathode with a state-of-the-art cascaded electron multiplier. The latter has high photoelectron collection efficiency and a record ion blocking capability. We describe in details the system and methods of photocathode production and characterization, their coupling with the electron multiplier and the gaseous-photomultiplier operation and characterization in a continuous mode. We present results on the properties of laboratory-produced K$_2$CsSb, Cs$_3$Sb and Na$_2$KSb photocathodes and report on their stability and QE in gas; K$_2$CsSb photocathodes yielded QE values in Ar/CH$_4$(95/5) above 30% at wavelengths of 360-400 nm. The novel gaseous photomultiplier yielded stable operation at gains of 10$^5$, in continuous operation mode, in 700 Torr of this gas; its sensitivity to single photons was demonstrated. Other properties are described. The successful detection of visible light with this gas-photomultiplier pave ways towards further development of large-area sealed imaging detectors, of flat geometry, insensitive to magnetic fields, which might have significant impact on light detection in numerous fields.
High pressure operation of the Photon-Assisted Cascaded Electron Multiplier
F. D. Amaro,J. F. C. A. Veloso,J. M. F. dos Santos,A. Breskin,R. Chechik,A. Lyashenko
Physics , 2008, DOI: 10.1109/TNS.2008.2010396
Abstract: We present the operation of the recently introduced Photon Assisted Cascaded Electron Multiplier (PACEM) in xenon at high pressure. The PACEM is a multi step electron multiplier where the VUV scintillation produced in the electron avalanches is used for signal propagation: the VUV scintillation produced in the first element of the cascade induces the emission of photoelectrons from a CsI photocathode placed on the top-surface of the second element. These photoelectrons are further multiplied, via charge avalanche. A metallic mesh electrode placed between the first and the second elements of the cascade completely blocks the charge transfer between them. Optical gains of 103 were achieved in xenon at atmospheric pressure, dropping to 25 at 3.3 bar, for applied voltages of 700 and 1100 V, respectively. Taking into account the subsequent charge multiplication, total gains are higher than those obtained with a triple GEM and double THGEM.
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