658 research outputs found

    Current density inhomogeneity throughout the thickness of superconducting films and its effect on their irreversible magnetic properties

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    We calculate the distribution of the current density jj in superconducting films along the direction of an external field applied perpendicular to the film plane. Our analysis reveals that in the presence of bulk pinning jj is inhomogeneous on a length scale of order the inter vortex distance. This inhomogeneity is significantly enhanced in the presence of surface pinning. We introduce new critical state model, which takes into account the current density variations throughout the film thickness, and show how these variations give rise to the experimentally observed thickness dependence of % j and magnetic relaxation rate.Comment: RevTex, 9 PS figures. To appear in Phys. Rev.

    Strong Pinning in High Temperature Superconductors

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    Detailed measurements of the critical current density jc of YBa2Cu3O7 films grown by pulsed laser deposition reveal the increase of jc as function of the filmthickness. Both this thickness dependence and the field dependence of the critical current are consistently described using a generalization of the theory of strong pinning of Ovchinnikov and Ivlev [Phys. Rev. B 43, 8024 (1991)]. From the model, we deduce values of the defect density (10^21 m^-3) and the elementary pinning force, which are in good agreement with the generally accepted values for Y2O3-inclusions. In the absence of clear evidence that the critical current is determined by linear defects or modulations of the film thickness, our model provides an alternative explanation for the rather universal field dependence of the critical current density found in YBa2Cu3O7 films deposited by different methods.Comment: 11 pages; 8 Figures; Published Phys. Rev. B 66, 024523 (2002

    Temporal and between-site variation in helminth communities of bank voles (Myodes glareolus) from N.E. Poland. 1. Regional fauna and component community levels

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    Helminth infections were studied in bank voles (Myodes glareolus) from 3 woodland sites in N.E. Poland in the late summers of 1999 and 2002, to assess the temporal stability of derived statistics describing the regional helminth fauna and component community structure, and spatial influence on the latter. Regional helminth fauna changed dramatically between the two years, primarily due to a fall in the abundance of Syphacia petrusewiczi but was partially compensated for by an increase in Mesocestoides lineatus and Cladotaenia globifera. It was dominated by nematodes overall, but more so in 1999 than in 2002 when larval cestodes were more frequent. Most derived parameters for component community structure varied considerably between sites and the two surveys, the hierarchical order for sites not being maintained between surveys. They were susceptible to the disproportionate influence of three relatively rare, unpredictable species with the greatest overall aggregated distribution among hosts. Jaccard’s similarity index was less influenced by the rare species, showing greater stability between sites and across years. In conclusion, temporal variation confounded any site-specific characteristics of the summary measures quantified in this study and their usefulness is therefore restricted to the years in which the surveys were conducted

    Social pathways for Ebola Virus Disease in rural Sierra Leone, and some implications for containment

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    The current outbreak of Ebola Virus Disease in Upper West Africa is the largest ever recorded. Molecular evidence suggests spread has been almost exclusively through human-to-human contact. Social factors are thus clearly important to understand the epidemic and ways in which it might be stopped, but these factors have so far been little analyzed. The present paper focuses on Sierra Leone, and provides cross sectional data on the least understood part of the epidemic-the largely undocumented spread of Ebola in rural areas. Various forms of social networking in rural communities and their relevance for understanding pathways of transmission are described. Particular attention is paid to the relationship between marriage, funerals and land tenure. Funerals are known to be a high-risk factor for infection. It is suggested that more than a shift in awareness of risks will be needed to change local patterns of behavior, especially in regard to funerals, since these are central to the consolidation of community ties. A concluding discussion relates the information presented to plans for halting the disease. Local consultation and access are seen as major challenges to be addressed

    Temporal and between-site variation in helminth communities of bank voles (Myodes glareolus) from N.E. Poland: 2. The infracommunity level

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    The relative importance of temporal and spatial effects was assessed in helminth communities of bank voles (Myodes glareolus) in 3 woodland sites in N.E. Poland in the late summers of 1999 and 2002. Among common species the rank order of sites in relation to prevalence and abundance of infection was maintained between surveys. Site effects accounted for most of the deviance (in statistical models), and time was less important, so the exact location from which voles were sampled was of critical importance. The only exception was Syphacia petrusewiczi. In contrast, for derived measures such as species richness and diversity, most deviance was accounted for by host age, and the interaction between site and year was significant, implying that rank order of sites changed between years. Temporal effects on derived measures were generated primarily by a combination of relatively small changes in prevalence and abundance of the common, rather than the rare, species between the years of the study. In the medium-term, therefore, helminth communities of bank voles in N.E. Poland had a stable core, suggesting a substantial strong element of predictability

    Use of online cultural content for mental health and well-being during COVID-19 restrictions : cross-sectional survey

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    AIMS AND METHOD: To gain a deeper understanding of the use of online culture and its potential benefits to mental health and well-being, sociodemographic characteristics and self-reported data on usage, perceived mental health benefits and health status were collected in an online cross-sectional survey during COVID-19 restrictions in the UK in June-July 2020. RESULTS: In total, 1056 people completed the survey. A high proportion of participants reported finding online culture helpful for mental health; all but one of the benefits were associated with regular use and some with age. Reported benefits were wide-ranging and interconnected. Those aged under 25 years were less likely to be regular users of online culture or to have increased their use during lockdown. CLINICAL IMPLICATIONS: There may be benefits in targeting cultural resources for mental health to vulnerable groups such as young adults

    A Framework for Achieving KDM-CCA Secure Public-Key Encryption

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    We propose a framework for achieving a public-key encryption (PKE) scheme that satisfies key dependent message security against chosen ciphertext attacks (KDM-CCA security) based on projective hash function. Our framework can be instantiated under the decisional diffie-hellman (DDH), quadratic residuosity (QR), and decisional composite residuosity (DCR) assumptions. The constructed schemes are KDM-CCA secure with respect to affine functions and compatible with the amplification method shown by Applebaum (EUROCRYPT 2011). Thus, they lead to PKE schemes satisfying KDM-CCA security for all functions computable by a-priori bounded size circuits. They are the first PKE schemes satisfying such a security notion in the standard model using neither non-interactive zero knowledge proof nor bilinear pairing. The above framework based on projective hash function captures only KDM-CCA security in the single user setting. However, we can prove the KDM-CCA security in the multi user setting of our concrete instantiations by using their algebraic structures explicitly. Especially, we prove that our DDH based scheme satisfies KDM-CCA security in the multi user setting with the same parameter setting as in the single user setting

    Ribosome Display Selection of a Murine IgG1 Fab Binding Affibody Molecule Allowing Species Selective Recovery Of Monoclonal Antibodies

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    Affinity reagents recognizing constant parts of antibody molecules are invaluable tools in immunotechnology applications, including purification, immobilization, and detection of immunoglobulins. In this article, murine IgG1, the primary isotype of monoclonal antibodies (mAbs) was used as target for selection of novel binders from a combinatorial ribosome display (RD) library of 1011 affibody molecules. Four rounds of selection using three different mouse IgG1 mAbs as alternating targets resulted in the identification of binders with broad mIgG1 recognition and dissociation constants (KD) in the low nanomolar to low micromolar range. For one of the binders, denoted Zmab25, competition in binding to full length mIgG1 by a streptococcal protein G (SPG) fragment and selective affinity capture of mouse IgG1 Fab fragments after papain cleavage of a full mAb suggest that an epitope functionally overlapping with the SPG-binding site in the CH1 domain of mouse IgG1 had been addressed. Interestingly, biosensor-based binding experiments showed that neither human IgG1 nor bovine Ig, the latter present in fetal bovine serum (FBS) was recognized by Zmab25. This selective binding profile towards murine IgG1 was successfully exploited in species selective recovery of two different mouse mAbs from complex samples containing FBS, resembling a hybridoma culture supernatant
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