Ion backflow studies with a triple-GEM stack with increasing hole pitch

Gas Electron Multipliers have undergone a very consistent development since their invention in 1997. Their production procedures have been tuned in such a way that nowadays it is possible to produce foils with areas of the order of the square meter that can operate at a reasonable gain, uniform over large areas and with a good stability in what concerns electrical discharges. For the third run of LHC, they will be included in the CMS and ALICE experiments after significant upgrades of the detectors, confirming that these structures are suitable for very large experiments. In the special case of Time Projection Chambers, the ion backflow and the energy resolution are sensitive issues that must be addressed and the GEM has shown to be able to deal with both of them. In this work, a stack of three GEMs with different pitches has been studied as a possible future approach for ion-backflow suppression to be used in TPCs and other detection concepts. With this approach, an ion backflow of 1 % with an energy resolution of 12 % at 5.9 keV has been achieved with the detector operating in an Ar/CO2 (90/10) mixture at a gain of ~ 2000.Comment: 15 pages, 11 figure

Super-poissonian photon statistics and correlations between pump and probe fields in Electromagnetically Induced Transparency

We have measured the photon statistics of pump and probe beams after interaction with Rb atoms in a situation of Electromagnetically Induced Transparency. Both fields present super-poissonian statistics and their intensities become correlated, in good qualitative agreement with theoretical predictions in which both fields are treated quantum-mechanically. The intensity correlations measured are a first step towards the observation of entanglement between the fields.Comment: 4 pages, two-column, 4 figures, first submitted to PRL on Aug. 6, 200

Geometrically induced singular behavior of entanglement

We show that the geometry of the set of quantum states plays a crucial role in the behavior of entanglement in different physical systems. More specifically it is shown that singular points at the border of the set of unentangled states appear as singularities in the dynamics of entanglement of smoothly varying quantum states. We illustrate this result by implementing a photonic parametric down conversion experiment. Moreover, this effect is connected to recently discovered singularities in condensed matter models.Comment: v2: 4 pags, 4 figs. A discussion before the proof of Proposition 1 and tomographic results were included, Propostion 2 was removed and the references were fixe

Universal and nonuniversal contributions to block-block entanglement in many-fermion systems

We calculate the entanglement entropy of blocks of size x embedded in a larger system of size L, by means of a combination of analytical and numerical techniques. The complete entanglement entropy in this case is a sum of three terms. One is a universal x and L-dependent term, first predicted by Calabrese and Cardy, the second is a nonuniversal term arising from the thermodynamic limit, and the third is a finite size correction. We give an explicit expression for the second, nonuniversal, term for the one-dimensional Hubbard model, and numerically assess the importance of all three contributions by comparing to the entropy obtained from fully numerical diagonalization of the many-body Hamiltonian. We find that finite-size corrections are very small. The universal Calabrese-Cardy term is equally small for small blocks, but becomes larger for x>1. In all investigated situations, however, the by far dominating contribution is the nonuniversal term steming from the thermodynamic limit.Comment: 6 pages, 3 figure

Segunda validação do CalcMadeira: estimativa de peças serradas de desdobros empíricos.

Na cadeia produtiva de madeira serrada, uma informação não usual, mas relevante para avaliação econômica e de aproveitamento da madeira, é a quantificação de peças serradas a priori. As poucas aplicações que oferecem solução para este problema abordam a tora individualmente e usam geralmente técnicas de otimização ao invés de modelos para padrões de corte. Além disso, muitas serrarias não adotam padrões de corte, usam a experiência e a intuição do operador, que executa cortes por um procedimento empírico. Com o objetivo de estimar resultados de desdobro empíricos, foi desenvolvido e testado um algoritmo que simula giros da tora. Os melhores resultados foram obtidos com ângulo médio da costaneira de 30º e proporção do raio de 0,60, com exatidões de 2,2 e -5,4% para número e volume de peças, respectivamente, e com rendimento de 53% comparado ao de 56% obtido no desdobro empírico de toras entre 20 e 40 cm de diâmetro.bitstream/item/217846/1/Bol-214.pd