Dynamics of entanglement in quantum computers with imperfections

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.     

Coarse-grained probabilistic automata mimicking chaotic systems

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.     

Dissimilar material joining using laser (aluminum to steel using zinc-based filler wire)

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.     

On the expansion of a quantum field theory around a topological sector

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.     

Investigation on porosity changes of Lecce stone due to conservation treatments by means of x‐ray nano‐ and improved micro‐computed tomography: preliminary results

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.     

Characterization of some high-spin iron(II) complexes with urea derivatives. The crystal structure of dichlorotetrakis(thiourea)iron(II)

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.     

Elementary bäcklund transformations,nonlinear superposition formulae and algebraic construction of solutions for the nonlinear evolution equations solvable by the Zakharov-Shabat spectral transform

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.     

Functionalisation of saturated hydrocarbons. Part XI. Oxidation of cedrol, β- and γ-eudesmol,sclareol, manoyl oxide, 1,9-dideoxyforskolin,methyl trans-dihydroiasmonate,and tetrahydrolinalool by the ‘Gif system’

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.     

On the stability of wideband beam patterns with respect to weighting and envelope fluctuations

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.