510 research outputs found

    Identifying Overlapping and Hierarchical Thematic Structures in Networks of Scholarly Papers: A Comparison of Three Approaches

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    We implemented three recently proposed approaches to the identification of overlapping and hierarchical substructures in graphs and applied the corresponding algorithms to a network of 492 information-science papers coupled via their cited sources. The thematic substructures obtained and overlaps produced by the three hierarchical cluster algorithms were compared to a content-based categorisation, which we based on the interpretation of titles and keywords. We defined sets of papers dealing with three topics located on different levels of aggregation: h-index, webometrics, and bibliometrics. We identified these topics with branches in the dendrograms produced by the three cluster algorithms and compared the overlapping topics they detected with one another and with the three pre-defined paper sets. We discuss the advantages and drawbacks of applying the three approaches to paper networks in research fields.Comment: 18 pages, 9 figure

    Measurement of the Transverse Beam Spin Asymmetry in Elastic Electron Proton Scattering and the Inelastic Contribution to the Imaginary Part of the Two-Photon Exchange Amplitude

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    We report on a measurement of the asymmetry in the scattering of transversely polarized electrons off unpolarized protons, A_\perp, at two Q2^2 values of \qsquaredaveragedlow (GeV/c)2^2 and \qsquaredaveragedhighII (GeV/c)2^2 and a scattering angle of 30<θe<4030^\circ < \theta_e < 40^\circ. The measured transverse asymmetries are A_{\perp}(Q2^2 = \qsquaredaveragedlow (GeV/c)2^2) = (\experimentalasymmetry alulowcorr ±\pm \statisticalerrorlowstat_{\rm stat} ±\pm \combinedsyspolerrorlowalucorsys_{\rm sys}) ×\times 106^{-6} and A_{\perp}(Q2^2 = \qsquaredaveragedhighII (GeV/c)2^2) = (\experimentalasymme tryaluhighcorr ±\pm \statisticalerrorhighstat_{\rm stat} ±\pm \combinedsyspolerrorhighalucorsys_{\rm sys}) ×\times 106^{-6}. The first errors denotes the statistical error and the second the systematic uncertainties. A_\perp arises from the imaginary part of the two-photon exchange amplitude and is zero in the one-photon exchange approximation. From comparison with theoretical estimates of A_\perp we conclude that π\piN-intermediate states give a substantial contribution to the imaginary part of the two-photon amplitude. The contribution from the ground state proton to the imaginary part of the two-photon exchange can be neglected. There is no obvious reason why this should be different for the real part of the two-photon amplitude, which enters into the radiative corrections for the Rosenbluth separation measurements of the electric form factor of the proton.Comment: 4 figures, submitted to PRL on Oct.

    Evidence for Strange Quark Contributions to the Nucleon's Form Factors at Q2Q^2 = 0.108 (GeV/c)2^2

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    We report on a measurement of the parity violating asymmetry in the elastic scattering of polarized electrons off unpolarized protons with the A4 apparatus at MAMI in Mainz at a four momentum transfer value of Q2Q^2 = \Qsquare (GeV/c)2^2 and at a forward electron scattering angle of 30<θe<40^\circ < \theta_e < 40^\circ. The measured asymmetry is ALR(ep)A_{LR}(\vec{e}p) = (\Aphys ±\pm \Deltastatstat_{stat} ±\pm \Deltasystsyst_{syst}) ×\times 106^{-6}. The expectation from the Standard Model assuming no strangeness contribution to the vector current is A0_0 = (\Azero ±\pm \DeltaAzero) ×\times 106^{-6}. We have improved the statistical accuracy by a factor of 3 as compared to our previous measurements at a higher Q2Q^2. We have extracted the strangeness contribution to the electromagnetic form factors from our data to be GEsG_E^s + \FakGMs GMsG_M^s = \GEsGMs ±\pm \DeltaGEsGMs at Q2Q^2 = \Qsquare (GeV/c)2^2. As in our previous measurement at higher momentum transfer for GEsG_E^s + 0.230 GMsG_M^s, we again find the value for GEsG_E^s + \FakGMs GMsG_M^s to be positive, this time at an improved significance level of 2 σ\sigma.Comment: 4 pages, 3 figure

    Hard Two-Photon Contribution to Elastic Lepton-Proton Scattering: Determined by the OLYMPUS Experiment

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    The OLYMPUS collaboration reports on a precision measurement of the positron-proton to electron-proton elastic cross section ratio, R2γR_{2\gamma}, a direct measure of the contribution of hard two-photon exchange to the elastic cross section. In the OLYMPUS measurement, 2.01~GeV electron and positron beams were directed through a hydrogen gas target internal to the DORIS storage ring at DESY. A toroidal magnetic spectrometer instrumented with drift chambers and time-of-flight scintillators detected elastically scattered leptons in coincidence with recoiling protons over a scattering angle range of 20°\approx 20\degree to 80°80\degree. The relative luminosity between the two beam species was monitored using tracking telescopes of interleaved GEM and MWPC detectors at 12°12\degree, as well as symmetric M{\o}ller/Bhabha calorimeters at 1.29°1.29\degree. A total integrated luminosity of 4.5~fb1^{-1} was collected. In the extraction of R2γR_{2\gamma}, radiative effects were taken into account using a Monte Carlo generator to simulate the convolutions of internal bremsstrahlung with experiment-specific conditions such as detector acceptance and reconstruction efficiency. The resulting values of R2γR_{2\gamma}, presented here for a wide range of virtual photon polarization 0.456<ϵ<0.9780.456<\epsilon<0.978, are smaller than some hadronic two-photon exchange calculations predict, but are in reasonable agreement with a subtracted dispersion model and a phenomenological fit to the form factor data.Comment: 5 pages, 3 figures, 2 table

    RNase 7 Contributes to the Cutaneous Defense against Enterococcus faecium

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    Background: Human skin is able to mount a fast response against invading microorganisms by the release of antimicrobial proteins such as the ribonuclease RNase 7. Because RNase 7 exhibits high activity against Enterococcus faecium the aim of this study was to further explore the role of RNase 7 in the cutaneous innate defense system against E. faecium. Methodology/Principal Findings: Absolute quantification using real-time PCR and ELISA revealed that primary keratinocytes expressed high levels of RNase 7. Immunohistochemistry showed RNase 7 expression in all epidermal layers of the skin with an intensification in the upper more differentiated layers. Furthermore, RNase 7 was secreted by keratinocytes in vitro and in vivo in a site-dependent way. RNase 7 was still active against E. faecium at low pH (5.5) or high NaCl (150 mM) concentration and the bactericidal activity of RNase 7 against E. faecium required no ribonuclease activity as shown by recombinant RNase 7 lacking enzymatic activity. To further explore the role of RNase 7 in cutaneous defense against E. faecium, we investigated whether RNase 7 contributes to the E. faecium killing activity of skin extracts derived from stratum corneum. Treatment of the skin extract with an RNase 7 specific antibody, which neutralizes the antimicrobial activity of RNase 7, diminished its E. faecium killing activity. Conclusions/Significance: Our data indicate that RNase 7 contributes to the E. faecium-killing activity of skin extracts an

    Microscopic dynamics in liquid metals: the experimental point of view

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    The experimental results relevant for the understanding of the microscopic dynamics in liquid metals are reviewed, with special regards to the ones achieved in the last two decades. Inelastic Neutron Scattering played a major role since the development of neutron facilities in the sixties. The last ten years, however, saw the development of third generation radiation sources, which opened the possibility of performing Inelastic Scattering with X rays, thus disclosing previously unaccessible energy-momentum regions. The purely coherent response of X rays, moreover, combined with the mixed coherent/incoherent response typical of neutron scattering, provides enormous potentialities to disentangle aspects related to the collectivity of motion from the single particle dynamics. If the last twenty years saw major experimental developments, on the theoretical side fresh ideas came up to the side of the most traditional and established theories. Beside the raw experimental results, therefore, we review models and theoretical approaches for the description of microscopic dynamics over different length-scales, from the hydrodynamic region down to the single particle regime, walking the perilous and sometimes uncharted path of the generalized hydrodynamics extension. Approaches peculiar of conductive systems, based on the ionic plasma theory, are also considered, as well as kinetic and mode coupling theory applied to hard sphere systems, which turn out to mimic with remarkable detail the atomic dynamics of liquid metals. Finally, cutting edges issues and open problems, such as the ultimate origin of the anomalous acoustic dispersion or the relevance of transport properties of a conductive systems in ruling the ionic dynamic structure factor are discussed.Comment: 53 pages, 41 figures, to appear in "The Review of Modern Physics". Tentatively scheduled for July issu

    Antimicrobial Peptides and Skin: A Paradigm of Translational Medicine

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    Antimicrobial peptides (AMPs) are small, cationic, amphiphilic peptides with broad-spectrum microbicidal activity against both bacteria and fungi. In mammals, AMPs form the first line of host defense against infections and generally play an important role as effector agents of the innate immune system. The AMP era was born more than 6 decades ago when the first cationic cyclic peptide antibiotics, namely polymyxins and tyrothricin, found their way into clinical use. Due to the good clinical experience in the treatment of, for example, infections of mucus membranes as well as the subsequent understanding of mode of action, AMPs are now considered for treatment of inflammatory skin diseases and for improving healing of infected wounds. Based on the preclinical findings, including pathobiochemistry and molecular medicine, targeted therapy strategies are developed and first results indicate that AMPs influence processes of diseased skin. Importantly, in contrast to other antibiotics, AMPs do not seem to propagate the development of antibiotic-resistant micro-organisms. Therefore, AMPs should be tested in clinical trials for their efficacy and tolerability in inflammatory skin diseases and chronic wounds. Apart from possible fields of application, these peptides appear suited as an example of the paradigm of translational medicine for skin diseases which is today seen as a `two-way road' - from bench to bedside and backwards from bedside to bench. Copyright (c) 2012 S. Karger AG, Base

    Measurement of the parity violating asymmetry in the quasielastic electron-deuteron scattering and improved determination of the magnetic strange form factor and the isovector anapole radiative correction

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    A new measurement of the parity-violating asymmetry in the electron-deuteron quasielastic scattering for backward angles at ⟨Q[superscript 2]⟩=0.224 (GeV/c)[superscript 2], obtained in the A4 experiment at the Mainz Microtron accelerator (MAMI) facility, is presented. The measured asymmetry is A[subscript PV][superscript d]=(-20.11±0.87[subscript stat]±1.03[subscript sys])×10[superscript -6]. A combination of these data with the proton measurements of the parity-violating asymmetry in the A4 experiment yields a value for the effective isovector axial-vector form factor of G[subscript A][superscript e,(T=1)]=-0.19±0.43 and R[subscript A][superscript e(T=1),anap] =-0.41±0.35 for the anapole radiative correction. When combined with a reanalysis of measurements obtained in the G0 experiment at the Thomas Jefferson National Accelerator Facility, the uncertainties are further reduced to G[subscript M][superscript s]=0.17±0.11 for the magnetic strange form factors, and R[subscript A][superscript (T=1),anap]=-0.54±0.26.Deutsche Forschungsgemeinschaf
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