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991.
The dynamics of the pairwise entanglement in a qubit lattice in the presence of static imperfections exhibits different regimes. We show that there is a transition from a perturbative region, where the entanglement is stable against imperfections, to the ergodic regime, in which a pair of qubits becomes entangled with the rest of the lattice and the pairwise entanglement drops to zero. The transition is almost independent of the size of the quantum computer. We consider both the case of an initial maximally entangled and separable state. In this last case there is a broad crossover region in which the computer imperfections can be used to create a significant amount of pairwise entanglement. 相似文献
992.
Discretization of phase space usually nullifies chaos in dynamical systems. We show that if randomness is associated with discretization dynamical chaos may survive and be indistinguishable from that of the original chaotic system, when an entropic, coarse-grained analysis is performed. Relevance of this phenomenon to the problem of quantum chaos is discussed. 相似文献
993.
Dissimilar material joining using laser (aluminum to steel using zinc-based filler wire) 总被引:9,自引:0,他引:9
Alexandre Mathieu Rajashekar Shabadi Alexis Deschamps Michel Suery Simone Matteï Dominique Grevey Eugen Cicala 《Optics & Laser Technology》2007,39(3):652-661
Joining steel with aluminum involving the fusion of one or both materials is possible by laser beam welding technique. This paper describes a method, called laser braze welding, which is a suitable process to realize this structure. The main problem with thermal joining of steel/aluminum assembly with processes such as TIG or MIG is the formation of fragile intermetallic phases, which are detrimental to the mechanical performances of such joints. Braze welding permits a localized fusion of the materials resulting in a limitation on the growth of fragile phases. This article presents the results of a statistical approach for an overlap assembly configuration using a filler wire composed of 85% Zn and 15% Al. Tensile tests carried on these assemblies demonstrate a good performance of the joints. The fracture mechanisms of the joints are analyzed by a detailed characterization of the seams. 相似文献
994.
The idea of treating quantum general relativistic theories in a perturbative expansion around a topological theory has recently
received attention, in the quantum gravity literature. We investigate the viability of this idea by applying it to conventional
Yang–Mills theory on flat spacetime. This theory admits indeed a formulation as a modified topological theory, like general
relativity. We find that the expansion around the topological theory coincides with the usual expansion around the free abelian
theory, though the equivalence is non-trivial. In this context, the technique appears therefore to be viable, but not to bring
particularly new insights. On the other hand, we point out that the relation of this expansion with the actual quantum BF
theory is far from being transparent. Some implications for gravity are discussed. 相似文献
995.
Simone Bugani Mara Camaiti Luciano Morselli Elke Van de Casteele Koen Janssens 《X射线光谱测定》2007,36(5):316-320
Cultural heritage materials are subject to continuous chemical and physical changes depending on the establishment of a dynamic equilibrium with the environment in which they are placed. In particular, different phenomena can take place, such as formation of black crusts, corrosion of the material, internal cracks. Lecce stone, a biocalcarenite mainly used for historical buildings in South Italy, has a high total porosity. In order to prevent its deterioration, different kinds of hydrophobic organic products are applied on the surface of the restored artefacts. Since the efficacy of the treatments depends mostly on the penetration depth and the distribution of the products in the pores, porosity and internal structure of the stone material were mainly investigated in this research. Micro x‐ray computed tomography (µ‐CT) has been used to study and characterize the internal structure of different samples, untreated and treated with protective products. The porosity and other parameters of the rock were then calculated and compared, before and after the conservation treatment, in order to highlight the changes due to the application of the product. On the other hand, small pieces of the untreated and treated samples were analysed by sub‐micron resolution x‐ray tomography where it was possible to see the distribution of the products inside the pores. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
996.
Umberto Russo Rodolfo Graziani Sandro Calogero Umberto Casellato 《Transition Metal Chemistry》1979,4(2):82-86
Summary Urea (ur), thiourea (tu) and diisopropylthiourea (diptu) form high-spin complexes with iron(II), for which57Fe Mössbauer quadrupole splitting and spectroscopic data suggest an octahedral distorted geometry. The x-ray diffraction study on Fe(tu)4Cl2 confirms this geometry. The crystals are tetragonal, space groupP42/n witha=13.71,c=8.94 Å andZ=4. The molecules are centrosymmetric with two axial chlorine atoms (Fe-Cl=2.46 Å) and four equatorial sulfur atoms (Fe-S=2.61 and 2.57 Å respectively). A similartrans-octahedral geometry is proposed for the new Fe(diptu)4Cl2 complex and an octahedral metal coordination in the new [Fe(ur)6]Br2, Fe(tu)3Br2 and Fe(ur)3Br2 complexes. 相似文献
997.
Novel nonlinear superposition formulae are given for solutions of the class of nonlinear evolution equations solvable via the spectral transform associated with the Zakharov-Shabat spectral problem, and an algebraic procedure is provided to construct solutions of these equations. 相似文献
998.
Derek H. R. Barton Jean-Clauude Beloeil Annick Billion Jean Boivin Jean-Yves Lallemand Patrick Lelandais Simone Mergui 《Helvetica chimica acta》1987,70(8):2187-2200
The oxidation of cedrol ( 1 ), β- and γ-eudesmol ( 6 and 7 , resp.), sclareol ( 14 ) manoyl oxide ( 15 ), 1,9-dideoxyforskolin ( 22 ) (±)-methyl trans-dihydrojasmonate ( 28 ), and tetrahydrolinalool ( 32 ) nearly all of natural terpenoid origin, by the ‘Gif system’ has afforded a number of novel products ( 3 , 11 , and 12 , 16/17 , 18/19 , 26 , 29–31 , and ketones corresponding to 34–35 , res.). The structures of these compounds were established by spectroscopic techniques including 2D-NMR and, where appropriate, by comparison with authentic samples. 相似文献
999.
This paper presents a study on the worsening caused by a random perturbation of the weighting window (modeling, in this way, the uncertainty on the channel sensitivity), or by an alteration of the shape of the transmitted pulse, for a wideband array. In the stability evaluation, main-lobe width and signal to noise ratio evaluated at different dB levels of the beam pattern play the role of quality parameters. Two different profiles of the weighting window have been used for this analysis: a typical raised cosine, and a window optimized by a Simulated Annealing procedure. Also for the pulse envelope, two distinct shapes have been chosen: perfectly Gaussian and experimentally measured. The analysis of the obtained results provides useful hints about the amount and the kind of the beam pattern worsening, when realistic fluctuations occur. Moreover, the results show that the weighting windows provided by the simulated annealing procedure are particularly robust to such fluctuations. 相似文献
1000.
Davies CT Follana E Gray A Lepage GP Mason Q Nobes M Shigemitsu J Trottier HD Wingate M Aubin C Bernard C Burch T DeTar C Gottlieb S Gregory EB Heller UM Hetrick JE Osborn J Sugar R Toussaint D Di Pierro M El-Khadra A Kronfeld AS Mackenzie PB Menscher D Simone J 《Physical review letters》2004,92(2):022001
The recently developed Symanzik-improved staggered-quark discretization allows unquenched lattice-QCD simulations with much smaller (and more realistic) quark masses than previously possible. To test this formalism, we compare experiment with a variety of nonperturbative calculations in QCD drawn from a restricted set of "gold-plated" quantities. We find agreement to within statistical and systematic errors of 3% or less. We discuss the implications for phenomenology and, in particular, for heavy-quark physics. 相似文献