282 research outputs found

    Ab initio Calculations of Multilayer Relaxations of Stepped Cu Surfaces

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    We present trends in the multilayer relaxations of several vicinals of Cu(100) and Cu(111) of varying terrace widths and geometry. The electronic structure calculations are based on density functional theory in the local density approximation with norm-conserving, non-local pseudopotentials in the mixed basis representation. While relaxations continue for several layers, the major effect concentrates near the step and corner atoms. On all surfaces the step atoms contract inwards, in agreement with experimental findings. Additionally, the corner atoms move outwards and the atoms in the adjacent chain undergo large inward relaxation. Correspondingly, the largest contraction (4%) is in the bond length between the step atom and its bulk nearest neighbor (BNN), while that between the corner atom and BNN is somewhat enlarged. The surface atoms also display changes in registry of upto 1.5%. Our results are in general in good agreement with LEED data including the controversial case of Cu(511). Subtle differences are found with results obtained from semi-empirical potentials.Comment: 21 pages and 3 figure

    Low Q^2 Jet Production at HERA and Virtual Photon Structure

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    The transition between photoproduction and deep-inelastic scattering is investigated in jet production at the HERA ep collider, using data collected by the H1 experiment. Measurements of the differential inclusive jet cross-sections dsigep/dEt* and dsigmep/deta*, where Et* and eta* are the transverse energy and the pseudorapidity of the jets in the virtual photon-proton centre of mass frame, are presented for 0 < Q2 < 49 GeV2 and 0.3 < y < 0.6. The interpretation of the results in terms of the structure of the virtual photon is discussed. The data are best described by QCD calculations which include a partonic structure of the virtual photon that evolves with Q2.Comment: 20 pages, 5 Figure

    Hadron Production in Diffractive Deep-Inelastic Scattering

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    Characteristics of hadron production in diffractive deep-inelastic positron-proton scattering are studied using data collected in 1994 by the H1 experiment at HERA. The following distributions are measured in the centre-of-mass frame of the photon dissociation system: the hadronic energy flow, the Feynman-x (x_F) variable for charged particles, the squared transverse momentum of charged particles (p_T^{*2}), and the mean p_T^{*2} as a function of x_F. These distributions are compared with results in the gamma^* p centre-of-mass frame from inclusive deep-inelastic scattering in the fixed-target experiment EMC, and also with the predictions of several Monte Carlo calculations. The data are consistent with a picture in which the partonic structure of the diffractive exchange is dominated at low Q^2 by hard gluons.Comment: 16 pages, 6 figures, submitted to Phys. Lett.

    Measurement of D* Meson Cross Sections at HERA and Determination of the Gluon Density in the Proton using NLO QCD

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    With the H1 detector at the ep collider HERA, D* meson production cross sections have been measured in deep inelastic scattering with four-momentum transfers Q^2>2 GeV2 and in photoproduction at energies around W(gamma p)~ 88 GeV and 194 GeV. Next-to-Leading Order QCD calculations are found to describe the differential cross sections within theoretical and experimental uncertainties. Using these calculations, the NLO gluon momentum distribution in the proton, x_g g(x_g), has been extracted in the momentum fraction range 7.5x10^{-4}< x_g <4x10^{-2} at average scales mu^2 =25 to 50 GeV2. The gluon momentum fraction x_g has been obtained from the measured kinematics of the scattered electron and the D* meson in the final state. The results compare well with the gluon distribution obtained from the analysis of scaling violations of the proton structure function F_2.Comment: 27 pages, 9 figures, 2 tables, submitted to Nucl. Phys.

    Measurement of Leading Proton and Neutron Production in Deep Inelastic Scattering at HERA

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    Deep--inelastic scattering events with a leading baryon have been detected by the H1 experiment at HERA using a forward proton spectrometer and a forward neutron calorimeter. Semi--inclusive cross sections have been measured in the kinematic region 2 <= Q^2 <= 50 GeV^2, 6.10^-5 <= x <= 6.10^-3 and baryon p_T <= MeV, for events with a final state proton with energy 580 <= E' <= 740 GeV, or a neutron with energy E' >= 160 GeV. The measurements are used to test production models and factorization hypotheses. A Regge model of leading baryon production which consists of pion, pomeron and secondary reggeon exchanges gives an acceptable description of both semi-inclusive cross sections in the region 0.7 <= E'/E_p <= 0.9, where E_p is the proton beam energy. The leading neutron data are used to estimate for the first time the structure function of the pion at small Bjorken--x.Comment: 30 pages, 9 figures, 2 tables, submitted to Eur. Phys.

    Re-evaluating currently available data and suggestions for planning randomised controlled studies regarding the use of hydroxyethyl starch in critically ill patients - a multidisciplinary statement

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    Introduction: Hydroxyethyl starch (HES) is a commonly used colloid in critically ill patients. However, its safety has been questioned in recent studies and meta-analyses. Methods: We re-evaluated prospective randomised controlled trials (RCT) from four meta-analyses published in 2013 that compared the effect of HES with crystalloids in critically ill patients, focusing on the adherence to 'presumably correct indication'. Regarding the definition of 'presumably correct indication', studies were checked for the following six criteria (maximum six points): short time interval from shock to randomisation (<6 h), restricted use for initial volume resuscitation, use of any consistent algorithm for haemodynamic stabilisation, reproducible indicators of hypovolaemia, maximum dose of HES, and exclusion of patients with pre-existing renal failure or renal replacement therapy. Results: Duration of fluid administration ranged from 90 min up to a maximum of 90 days. Four studies considered follow-up until 90-day mortality, three studies 28-/30-day mortality, whereas four studies reported only early mortality. Included studies showed a large heterogeneity of the indication score ranging between 1 and 4 points with a median (25%; 75% quartile) of 4 (2; 4). Conclusions: The most important question, whether or not HES may be harmful when it is limited to immediate haemodynamic stabilisation, cannot be answered yet in the absence of any study sufficiently addressing this question. In order to overcome the limitations of most of the previous studies, we now suggest an algorithm emphasising the strict indication of HES. Additionally, we give a list of suggestions that should be adequately considered in any prospective RCT in the field of acute volume resuscitation in critically ill patients

    Costs and health-related quality of life in patients with NMO spectrum disorders and MOG-antibody-associated disease: CHANCE(NMO) study

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    OBJECTIVE: To evaluate costs and health-related quality of life (HRQoL) of neuromyelitis optica spectrum disorders (NMOSD) and myelin oligodendrocyte glycoprotein-antibody associated disease (MOGAD).MethodsIn this multicenter cross-sectional study, data on consumption of medical and non-medical resources and work ability were assessed via patient questionnaires. Costs were analyzed in EUR for 2018 from the societal perspective. HRQoL was captured by the EuroQoL EQ-5D-5L questionnaire. Clinical data were retrieved from the Neuromyelitis Optica Study Group (NEMOS) database. RESULTS: Two hundred twelve patients (80% women; median age 50 [19-83] years; median disease duration 7 [0-43] years; median Expanded Disability Status Scale [EDSS] 3.5 [0-8.5]; 66% Aquaporin-4 IgG, 22% MOG IgG positive, 12% double seronegative) were analyzed. The mean total annual per capita cost of illness accounted for EUR (Euro) 59 574 (95% CI 51 225 to 68 293; USD [United States dollars] 70 297, 95% CI 60 445 to 80 586), and the mean index value of the EQ-5D-5L was 0.693 (95% CI 0.65 to 0.73). The most important cost drivers were informal care costs (28% of total costs), indirect costs (23%) and drugs (16%), especially immunotherapeutics. Costs showed a positive correlation with disease severity (ρ=0.56, 95% CI 0.45 to 0.65); in the EDSS 6.5-8.5 subgroup the mean annual costs were EUR 129 687 (95% CI 101 946 to 160 336; USD 153 031, 95% CI 120 296 to 189 196). The HRQoL revealed a negative correlation to disease severity (ρ=-0.69, 95% CI -0.76 to -0.61); in the EDSS 6.5-8.5 subgroup the EQ-5D-5L mean index value was 0.195 (95% CI 0.13 to 0.28). Neither antibody status nor disease duration influenced the total annual costs or HRQoL. CONCLUSION: These German data from the era without approved preventive immunotherapies show enormous effects of the diseases on costs and quality of life. An early and cost-effective therapy should be provided to prevent long-term disability and preserve quality of life
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