44,891 research outputs found

    Adaptive meshless refinement schemes for RBF-PUM collocation

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    In this paper we present an adaptive discretization technique for solving elliptic partial differential equations via a collocation radial basis function partition of unity method. In particular, we propose a new adaptive scheme based on the construction of an error indicator and a refinement algorithm, which used together turn out to be ad-hoc strategies within this framework. The performance of the adaptive meshless refinement scheme is assessed by numerical tests

    Efficient computation of partition of unity interpolants through a block-based searching technique

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    In this paper we propose a new efficient interpolation tool, extremely suitable for large scattered data sets. The partition of unity method is used and performed by blending Radial Basis Functions (RBFs) as local approximants and using locally supported weight functions. In particular we present a new space-partitioning data structure based on a partition of the underlying generic domain in blocks. This approach allows us to examine only a reduced number of blocks in the search process of the nearest neighbour points, leading to an optimized searching routine. Complexity analysis and numerical experiments in two- and three-dimensional interpolation support our findings. Some applications to geometric modelling are also considered. Moreover, the associated software package written in \textsc{Matlab} is here discussed and made available to the scientific community

    Photon statistics without counting photons

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    We show how to obtain the photon distribution of a single-mode field using only avalanche photodetectors. The method is based on measuring the field at different quantum efficiencies and then inferring the photon distribution by maximum-likelihood estimation. The convergence of the method and its robustness against fluctuations are illustrated by means of numerically simulated experiments.Comment: references added, new figure

    Degradation of continuous variable entanglement in a phase-sensitive environment

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    We address the propagation of twin-beam of radiation through Gaussian phase-sensitive channels, i.e. noisy channels with squeezed fluctuations. We find that squeezing the environment always reduces the survival time of entanglement in comparison to the case of simple dissipation and thermal noise. We also show that the survival time is further reduced if the squeezing phase of the fluctuations is different from the twin-beam phase.Comment: to be published in the special issue of J. Mod. Opt. (April 2004) edited by R. Bonifacio, B.G. Englert and M.G.A. Paris, devoted to the 2003 Garda Lake Workshop on "Mysteries, Puzzles and Paradoxes in Quantum Mechanics

    THE INHIBITORY EFFECT OF PROPOLIS AND CAFFEIC ACID PHENETHYLESTER ON CYCLOOXYGENASE ACTIVITY IN J774 MACROPHAGES.

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    The effect of an ethanolic extract of propolis, with and without CAPE, and some of its components on cyclooxygenase (COX-1 and COX-2) activity in J774 macrophages has been investigated. COX-1 and COX-2 activity, measaured as prostaglandin E-2 (PGE(2)) production, were concentration-dependently inhibited by propolis (C x 10(-3)-3 x 10(2) mugml(-1)) with an IC50 of 2.7 mugml(-1) and 4.8 x 10(-2) mugml(-1), respectively. Among the compounds tested pinocembrin and caffeic, ferulic, cinnamic and chlorogenic acids did not affect the activity of COX isoforms. Conversely, CAPE (2.8 x 10(-4)-28 mugml(-1); 10(-9)-10(-4) M) and galangin (2.7 x 10(-4)-27 mugml(-1); 10(-9)-10(-4) M) were effective, the last being about ten-twenty times less potent. In fact the IC50 of CAPE for COX-1 and COX-2 were 4.4 x 10(-1) mugml(-1) (1.5 x 10(-6) M) and 2 x 10(-3) mugml(-1) (6.3 x 10(-9) M), respectively. The IC50 of galangin were 3.7 mugml(-1) (15 x 10(-6) M) and 3 x 10(-2) mugml(-1) (120 x 10(-1) M), for COX-1 and COX-2 respectively. To better investigate the role of CAPE, we tested the action of the ethanolic extract of propolis deprived of CAPE, which resulted about ten times less potent than the extract with CAPE in the inhibition of both COX-1 and COX-2, with an IC50 of 30 mugml(-1) and 5.3 x 10(-1) mugml(-1), respectively. Moreover the comparison of the inhibition curves showed a significant difference (p < 0.001). These results suggest that both CAPE and galangin contribute to the overall activity of propolis, CAPE being more effective

    Quantum erasure in the presence of a thermal bath: the effects of system-environment microscopic correlations

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    We investigate the role of the environment in a quantum erasure setup in the cavity quantum electrodynamics domain. Two slightly different schemes are analyzed. We show that the effects of the environment vary when a scheme is exchanged for another. This can be used to estimate the macroscopic parameters related to the system-environment microscopic correlations.Comment: 10 pages, 2 figure

    Numerical modeling of strain rate hardening effects on viscoplastic behavior of metallic materials

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    The main goal of the present work is to provide a finite strain elasticviscoplastic framework to numerically account for strain, strain rate hardening, and viscous effects in cold deformation of metallic materials. The aim is to provide a simple and robust numerical framework capable of modeling the main macroscopic behavior associated with high strain rate plastic deformation of metals. In order to account for strain rate hardening effects at finite strains, the hardening rule involves a rate dependent saturation hardening, and it accounts for linear hardening prevailing at latter deformation stages. The numerical formulation, finite element implementation, and constitutive modeling capabilities are assessed by means of decremental strain rate testing and constant strain rate loading followed by stress relaxation. The numerical results have demonstrated the overall framework can be an efficient numerical tool for simulation of plastic deformation processes where strain rate history effects have to be accounted for
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