Gastrointestinal stenting: Current status and imaging features

AbstractThe use of stents in the gastrointestinal tract has been subjected to major changes. Initially, the use of stents was restricted to malignant strictures in patients with metastatic disease. But thanks to reduction of the morbidity and mortality rates, they are now used with curative intention and in patients with benign diseases after careful selection. However, for patients presenting with colon obstruction due to an advanced colon carcinoma, the mortality and morbidity are still high. The purpose of this review is to provide an overview of indications, techniques and further developments of the stents in the gastrointestinal tract and to highlight the predominant role of multidetector row computed tomography (MDCT) in the detection of potential complications

Weak localization competes with the quantum oscillations in a natural electronic superlattice: the case of Na1.5(PO2)4(WO3)20

We report an investigation of the combined structural and electronic properties of the bronze Na1.5 (PO2 )4 (WO3 )20 . Its low-dimensional structure and possible large reconstruction of the Fermi surface due to charge density wave instability make this bulk material a natural superlattice with a reduced number of carriers and Fermi energy. Signatures of multilayered two-dimensional (2D) electron weak localization are consequently reported, with an enhanced influence of quantum oscillations. A crossover between these two antagonistic entities, previously observed only in genuine low-dimensional materials and devices, is shown to occur in a bulk crystal due to its hidden 2D nature

Exact solution of Markovian master equations for quadratic fermi systems: thermal baths, open XY spin chains, and non-equilibrium phase transition

We generalize the method of third quantization to a unified exact treatment of Redfield and Lindblad master equations for open quadratic systems of n fermions in terms of diagonalization of 4n x 4n matrix. Non-equilibrium thermal driving in terms of the Redfield equation is analyzed in detail. We explain how to compute all physically relevant quantities, such as non-equilibrium expectation values of local observables, various entropies or information measures, or time evolution and properties of relaxation. We also discuss how to exactly treat explicitly time dependent problems. The general formalism is then applied to study a thermally driven open XY spin 1/2 chain. We find that recently proposed non-equilibrium quantum phase transition in the open XY chain survives the thermal driving within the Redfield model. In particular, the phase of long-range magnetic correlations can be characterized by hypersensitivity of the non-equilibrium-steady state to external (bath or bulk) parameters. Studying the heat transport we find negative thermal conductance for sufficiently strong thermal driving, as well as non-monotonic dependence of the heat current on the strength of the bath coupling.Comment: 24 pages, 12 figures, submitted to New Journal of Physics, Focus issue "Quantum Information and Many-Body Theory

Evidence for LineLike Vortex Liquid Phase in Tl2_2Ba2_2CaCu2_2O8_8 Probed by the Josephson Plasma Resonance

We measured the Josephson plasma resonance (JPR) in optimally doped Tl$_2$Ba$_2$CaCu$_2$O$_{8+\delta}$ thin films using terahertz time-domain spectroscopy in transmission. The temperature and magnetic field dependence of the JPR frequency shows that the c-axis correlations of pancake vortices remain intact at the transition from the vortex solid to the liquid phase. In this respect Tl$_2$Ba$_2$CaCu$_2$O$_{8+\delta}$ films, withanisotropy parameter $\gamma\approx 150$, are similar to the less anisotropic YBa$_2$Cu$_3$O$_{7-\delta}$ $(\gamma\approx 8)$ rather than to the most anisotropic Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ single crystals $\gamma\geq 500$).Comment: Submitted to Physical Review Letter

FACTEUR GYROMAGNÉTIQUE DE L'ÉTAT 12+ DES ISOTOPES DE PLOMB DE MASSE 198, 196 ET 194

Un état isomérique 12+, interprété comme un état à deux quasi-particules (νi 13/2)-2, a été mis en évidence dans les isotopes de plomb déficients en neutrons. Il possède une période de quelques centaines de ns, qui se prête à la mesure du moment magnétique par la méthode des distributions angulaires différentielles perturbées (TDPAD). Ces mesures ont été réalisées, afin de confirmer la configuration de l'état et d'étudier l'effet du nombre de nucléons sur les phénomènes de polarisation du coeur. Le tableau indique les valeurs expérimentales du facteur g et de la période du niveau 12+ des isotopes de masse A = 198, 196, 194. Une analyse multidimensionnelle des informations (Eγ, t) permet d'étudier simultanément ces trois noyaux, formés par la réaction naturelle W(16O, 4n)Pb. Les facteurs g sont reportés sur la figure, ainsi que les valeurs obtenues par ailleurs pour l'état 12+ du 206Pb [1], 200Pb [2] et l'état 13+/2 du 205Pb [3]. [MATH]. La constance de g en fonction de A suggère que les effets observés dans le 206Pb se retrouvent dans les isotopes plus légers, et notamment que la configuration (νi 13/2)-2 demeure largement dominante. L'écart notable à la valeur de Schmidt (g = - 0,294) peut s'expliquer par un important effet de polarisation du coeur. Un calcul, utilisant le formalisme de Arima et Horie, et une interaction résiduelle delta de surface (SDI) sont effectués pour rendre compte de ces résultats

Evolution in the split-peak structure across the Peak Effect region in single crystals of 2H2H-NbSe2_2

We have explored the presence of a two-peak feature spanning the peak effect (PE) region in the ac susceptibility data and the magnetization hysteresis measurements over a wide field-temperature regime in few weakly pinned single crystals of $2H$-NbSe$_2$, which display reentrant characteristic in the PE curve near $T_c$(0). We believe that the two-peak feature evolves into distinct second magnetization peak anomaly well separated from the PE with gradual enhancement in the quenched random pinning.Comment: 9 figure

Using an on-line image analysis technique to characterize sucrose crystal morphology during a crystallization run

The morphological forms and habits of crystals and agglomeration are important properties on crystallization processes. Online techniques for realtime measurement of these properties are mandatory for a better comprehension of crystal growth phenomenon. The present paper presents and describes a new online method to determine the complexity level of a crystal or a population of crystals during a crystallization process. An image analysis technique is combined with discriminant factorial analysis leading to results that allow the computation of the complexity of crystals through the parameter agglomeration degree of crystals. With this methodology, it has been possible to distinguish online and automatically among three different classes of crystals according to their complexity. It further describes the application of such methodology on the study of CaCl2, D-fructose, and D-glucose influence on the crystallization of sucrose, namely, on crystal size, morphology, and complexity. The effect of supersaturation, growth rate, and impurity concentration on the type, amount, and complexity level of the agglomerates was determined at different temperatures. The combination of image analysis and kinetic results allowed to understand better the crystallization phenomena in the presence and absence of impurities. The image analysis results suggest the possible application of this tool for process control, optimizing, by this way, laboratory and industrial crystallizers.This work was supported by Fundacao para a Ciencia e Tecnologia under program contract numbers SFRH/BD/11315/2002 and SFRH/BPD/45637/2008

Distribution of Transport Current in a Type II Superconductor Studied by Small Angle Neutron Scattering

We report Small-Angle Neutron Scattering (SANS) measurements on the vortex lattice in a PbIn polycrystal in the presence of an applied current. Using the rocking curves as a probe of the distribution of current in the sample, we observe that vortex pinning is due to the surface roughness. This leads to a surface current that persists in the flux flow region. We show the influence of surface treatments on the distribution of this current.Comment: 5 pages 5 figures. accepted for publication in Phys Rev Let