Pair correlations and the survival of superconductivity in and around a super-conducting impurity

The problem of the survival of superconductivity in a small super-conducting grain placed in a metal substrate is addressed. For this aim the pair correlations and super-conducting gap around and inside a negative-U impurity in one and two dimensions is calculated, in a discrete tight-binding model and a continuous model. Using the Hartree-Fock-Gorkov mean-field decomposition, it is found that pairing inside the gap occurs when the system has a degeneracy between successive number of electron pairs, and is highly sensitive to the chemical potential. For finite pairing in the island, pair correlations in the normal part may either decay exponentially or be long-ranged, depending on the strength of interaction. In addition, it is shown analytically that there is a minimal island size under-which pairing vanishes, and that it scales as a power-law, rather then exponentially as in isolated grains. These results are interpreted in terms of screening of the negative-U impurity by the electron gas.Comment: Accepted for publication in Phys.Rev.

Current in open quantum systems

We show that a dissipative current component is present in the dynamics generated by a Liouville-master equation, in addition to the usual component associated with Hamiltonian evolution. The dissipative component originates from coarse graining in time, implicit in a master equation, and needs to be included to preserve current continuity. We derive an explicit expression for the dissipative current in the context of the Markov approximation. Finally, we illustrate our approach with a simple numerical example, in which a quantum particle is coupled to a harmonic phonon bath and dissipation is described by the Pauli master equation.Comment: To appear in Phys. Rev. Let

Generic Finite Size Enhancement of Pairing in Mesoscopic Fermi Systems

The finite size dependent enhancement of pairing in mesoscopic Fermi systems is studied under the assumption that the BCS approach is valid and that the two body force is size independent. Different systems are investigated such as superconducting metallic grains and films as well atomic nuclei. It is shown that the finite size enhancement of pairing in these systems is in part due to the presence of a surface which accounts quite well for the data of nuclei and explains a good fraction of the enhancement in Al grains.Comment: Updated version 17/02/0

Sidescan Sonar Image, Surficial Geologic Interpretation, and Bathymetry of the Long Island Sound Sea Floor off Hammonasset Beach State Park, Connecticut

Ongoing research by the U.S. Geological Survey (USGS) in Long Island Sound, a major East Coast estuary surrounded by the most densely populated region of the United States, is building upon cooperative research with the State of Connecticut that was initiated in 1982. During the initial phase of this cooperative program, geologic framework studies in Long Island Sound were completed and results published (Lewis and Needell, 1987; Needell and others, 1987; Lewis and Stone, 1991). Emphasis of the present program in Long Island Sound is shifting from framework studies toward studies of the sediment distribution, processes that control this sediment distribution, nearshore environmental concerns, and the relation of benthic community structures to the sea-floor geology. Because of the enormous surrounding population, large inputs of anthropogenic wastes (e.g., fertilizer and sewage) and toxic chemicals have produced stresses on the environment of the Sound, causing degradation and potential loss of benthic habitats (Long Island Sound Study, 1994). To examine this problem, we are constructing sidescan sonar mosaics (complete-coverage acoustic images) of the sea floor within areas of special interest, such as in areas affected by seasonal hypoxia like the Norwalk survey or near major coastal resources like the Hammonasset Beach survey (fig.1). The mosaic that we have constructed off Hammonasset Beach State Park and which is presented herein allows insight into the geological variability of the sea floor, which is one of the primary controls of benthic habitat diversity. It also provides a detailed framework for future research, monitoring, and management activities, and it improves our understanding of the complex processes that control the distribution of bottom sediments, benthic habitats, and associated infaunal community structures off one of the most significant coastal recreational facilities within the State of Connecticut. Because precise information on environmental setting is important to the selection of sampling sites and to the accurate interpretation of point measurements, the sidescan sonar mosaics also act as base maps for subsequent sedimentological, geochemical, and infaunal sampling and bottom photography

New body scales reveal body dissatisfaction, thin-ideal, and muscularity-ideal in males

The aim of the current study was to develop, test, and re-test two new male body dissatisfaction scales: The Male Body Scale (MBS; consisting of emaciated to obese figures) and the Male Fit Body Scale (MFBS; consisting of emaciated to muscular figures). These scales were compared to the two most commonly used visually-based indices of body dissatisfaction (Stunkard Figure Rating Scale, SFRS; and Somatomorphic Matrix, SM). Male participants rated which body figure on each scale most represented their current figure, then their ideal figure, and then rated which one of the three scales (MBS, MFBS, and SFRS) best represented their current and ideal body overall. Finally, they completed the Drive for Muscularity Scale (DMS), the Eating Disorder Examination Questionnaire (EDE-Q 6.0), and their actual body composition was calculated. This was followed by a re-test and manipulation check two to six weeks later. Participants’ actual body mass index, fat- and muscularity-percentage were all highly related to their current body figure choice, and both new scales were consistently valid and more reliable between test and re-test than the SFRS and SM body dissatisfaction scores. Importantly, each scale was sensitive to different types of body dissatisfaction within males. Specifically, the MBS revealed that males’ desire for the thin-ideal significantly corresponded to higher eating disorder tendencies as identified by EDE-Q 6.0 scores, whilst the MFBS revealed much higher body dissatisfaction toward the larger, muscularity-ideal, predicting higher drive for muscularity as identified by DMS scores. Results validated the new scales, and inform male-focused eating disorder research

Multifactorial Patterns of Gene Expression in Colonic Epithelial Cells Predict Disease Phenotypes in Experimental Colitis

Background— The pathogenesis of inflammatory bowel disease (IBD) is complex and the need to identify molecular biomarkers is critical. Epithelial cells play a central role in maintaining intestinal homeostasis. We previously identified five “signature” biomarkers in colonic epithelial cells (CEC) that are predictive of disease phenotype in Crohn\u27s disease. Here we investigate the ability of CEC biomarkers to define the mechanism and severity of intestinal inflammation. Methods— We analyzed the expression of RelA, A20, pIgR, tumor necrosis factor (TNF), and macrophage inflammatory protein (MIP)-2 in CEC of mice with dextran sodium sulfate (DSS) acute colitis or T-cell-mediated chronic colitis. Factor analysis was used to combine the five biomarkers into two multifactorial principal components (PCs). PC scores for individual mice were correlated with disease severity. Results— For both colitis models, PC1 was strongly weighted toward RelA, A20, and pIgR, and PC2 was strongly weighted toward TNF and MIP-2, while the contributions of other biomarkers varied depending on the etiology of inflammation. Disease severity was correlated with elevated PC2 scores in DSS colitis and reduced PC1 scores in T-cell transfer colitis. Downregulation of pIgR was a common feature observed in both colitis models and was associated with altered cellular localization of pIgR and failure to transport IgA. Conclusions— A multifactorial analysis of epithelial gene expression may be more informative than examining single gene responses in IBD. These results provide insight into the homeostatic and proinflammatory functions of CEC in IBD pathogenesis and suggest that biomarker analysis could be useful for evaluating therapeutic options for IBD patients

Mesoscopic fluctuations of the ground state spin of a small metal particle

We study the statistical distribution of the ground state spin for an ensemble of small metallic grains, using a random-matrix toy model. Using the Hartree Fock approximation, we find that already for interaction strengths well below the Stoner criterion there is an appreciable probability that the ground state has a finite, nonzero spin. Possible relations to experiments are discussed.Comment: 4 pages, RevTeX; 1 figure included with eps

Quantum information with continuous variables

Quantum information is a rapidly advancing area of interdisciplinary research. It may lead to real-world applications for communication and computation unavailable without the exploitation of quantum properties such as nonorthogonality or entanglement. We review the progress in quantum information based on continuous quantum variables, with emphasis on quantum optical implementations in terms of the quadrature amplitudes of the electromagnetic field.Comment: accepted for publication in Reviews of Modern Physic

Optical properties of quantum wires: Disorder-scattering in the Lloyd-model

The Lloyd model is extended to the exciton problem in quasi one-dimensional structures to study the interplay between the Coulomb attraction and disorder scattering. Within this model the averaging and resummation of the locator series can be performed analytically. As an application, the optical absorption in quantum box wires is investigated. Without electron-hole interaction, fluctuations in the well-width lead to an asymmetric broadening of the minibands with respect to the lower and upper band-edges.Comment: 7 pages, 6 figure