6,316 research outputs found
Natural linewidth analysis of d-band photoemission from Ag(110)
We report a high-resolution angle-resolved study of photoemission linewidths
observed for Ag(110). A careful data analysis yields kdd\tau_h \geq 22
d$-hole dynamics in Cu (I.\
Campillo et al., Phys. Rev. Lett., in press) we interpret the lifetime
enhancement by a small scattering cross-section of - and -states below
the Fermi level. With increasing distance to the -hole lifetimes get
shorter because of the rapidly increasing density of d-states and contributions
of intra--band scattering processes, but remain clearly above
free-electron-model predictions.Comment: 14 pages, 7 figure
Sparsest factor analysis for clustering variables: a matrix decomposition approach
We propose a new procedure for sparse factor analysis (FA) such that each variable loads only one common factor. Thus, the loading matrix has a single nonzero element in each row and zeros elsewhere. Such a loading matrix is the sparsest possible for certain number of variables and common factors. For this reason, the proposed method is named sparsest FA (SSFA). It may also be called FA-based variable clustering, since the variables loading the same common factor can be classified into a cluster. In SSFA, all model parts of FA (common factors, their correlations, loadings, unique factors, and unique variances) are treated as fixed unknown parameter matrices and their least squares function is minimized through specific data matrix decomposition. A useful feature of the algorithm is that the matrix of common factor scores is re-parameterized using QR decomposition in order to efficiently estimate factor correlations. A simulation study shows that the proposed procedure can exactly identify the true sparsest models. Real data examples demonstrate the usefulness of the variable clustering performed by SSFA
Using network-flow techniques to solve an optimization problem from surface-physics
The solid-on-solid model provides a commonly used framework for the
description of surfaces. In the last years it has been extended in order to
investigate the effect of defects in the bulk on the roughness of the surface.
The determination of the ground state of this model leads to a combinatorial
problem, which is reduced to an uncapacitated, convex minimum-circulation
problem. We will show that the successive shortest path algorithm solves the
problem in polynomial time.Comment: 8 Pages LaTeX, using Elsevier preprint style (macros included
Development of a rolling technology for twin-roll cast magnesium strips
With the best lightweight potential of all metallic construction materials, magnesium primarily helps to increase energy efficiency over the lifecycle of automotive and non-automotive industrial products. Yet to assess overall energy efficiency, the production process must also be taken into account. This paper provides an insight into the energy-efficient production of magnesium strips up to 0,8 mm in thickness based on twin-roll casting and strip rolling on an industrial scale, as developed at the Institute of Metal Forming at the Technical University Bergakademie Freiberg (Germany) in cooperation with MgF Magnesium Flachprodukte GmbH (Germ any). The technology of twin-roll casting and strip rolling on a four-high reversing mill is described
Belief-propagation algorithm and the Ising model on networks with arbitrary distributions of motifs
We generalize the belief-propagation algorithm to sparse random networks with
arbitrary distributions of motifs (triangles, loops, etc.). Each vertex in
these networks belongs to a given set of motifs (generalization of the
configuration model). These networks can be treated as sparse uncorrelated
hypergraphs in which hyperedges represent motifs. Here a hypergraph is a
generalization of a graph, where a hyperedge can connect any number of
vertices. These uncorrelated hypergraphs are tree-like (hypertrees), which
crucially simplify the problem and allow us to apply the belief-propagation
algorithm to these loopy networks with arbitrary motifs. As natural examples,
we consider motifs in the form of finite loops and cliques. We apply the
belief-propagation algorithm to the ferromagnetic Ising model on the resulting
random networks. We obtain an exact solution of this model on networks with
finite loops or cliques as motifs. We find an exact critical temperature of the
ferromagnetic phase transition and demonstrate that with increasing the
clustering coefficient and the loop size, the critical temperature increases
compared to ordinary tree-like complex networks. Our solution also gives the
birth point of the giant connected component in these loopy networks.Comment: 9 pages, 4 figure
Lifetime of d-holes at Cu surfaces: Theory and experiment
We have investigated the hole dynamics at copper surfaces by high-resolution
angle-resolved photoemission experiments and many-body quasiparticle GW
calculations. Large deviations from a free-electron-like picture are observed
both in the magnitude and the energy dependence of the lifetimes, with a clear
indication that holes exhibit longer lifetimes than electrons with the same
excitation energy. Our calculations show that the small overlap of d- and
sp-states below the Fermi level is responsible for the observed enhancement.
Although there is qualitative good agreement of our theoretical predictions and
the measured lifetimes, there still exist some discrepancies pointing to the
need of a better description of the actual band structure of the solid.Comment: 15 pages, 7 figures, 1 table, to appear in Phys. Rev.
Z decays into light gluinos: a calculation based on unitarity
The Z boson can decay to a pair of light gluinos through loop-mediated
processes. Based on unitarity of the S-matrix, the imaginary part of the decay
amplitude is computed in the presence of a light bottom squark. This imaginary
part can provide useful information on the full amplitude. Implications are
discussed for a recently proposed light gluino and light bottom squark
scenario.Comment: 19 pages, LaTeX, 3 figures, submitted to Phys. Rev.
A protocol for a randomised controlled trial investigating the effect of increasing Omega-3 index with krill oil supplementation on learning, cognition, behaviour and visual processing in typically developing adolescents
Introduction: The influence of n-3 long-chain polyunsaturated fatty acids (LCPUFA) supplementation on brain functioning is debated. Some studies have found positive effects on cognition in children with learning difficulties, elderly people with cognitive impairment and depression scores in depressed individuals. Other studies have found null or negative effects. Observational studies in adolescents have found positive associations between fish consumption (containing n-3 LCPUFAs) and academic achievement. However, intervention studies in typically developing adolescents are missing. Objective: The goal of this study is to determine the influence of increasing Omega-3 Index on cognitive functioning, academic achievement and mental wellbeing of typically developing adolescents. Methods and data analysis: Double-blind, randomised, placebo controlled intervention;264 adolescents (age 13-15 years) attending lower general secondary education started daily supplementation of 400 mg eicosapentaenoic acid and docosahexaenoic acid (EPA+DHA) in cohort I (n=130) and 800 mg EPA+DHA in cohort II (n=134) or a placebo for 52 weeks. Recruitment took place according to a low Omega-3 Index (<5%). The Omega-3 Index was monitored via a finger prick at baseline and after 3, 6 and 12 months. The supplement dose was adjusted after 3 months (placebo analogously) to reach an Omega-3 Index of 8-11%. At baseline, 6 and 12 months, a neuropsychological test battery, a number of questionnaires and a standardised math test (baseline and 12 months) were administered. School grades were collected. In a subsample, sleep quality and quantity data (n=64) and/or eye-tracking data (n=33) were collected. Ethics and dissemination: Food2Learn is performed according to Good Clinical Practice. All data collected are linked to participant number only. The results will be disseminated on group level to participants and schools. The results will be presented at conferences and published in peer-reviewed journals. The study is approved by the Medical Ethical Committee of Atrium-Orbis-Zuyd Hospital and is registered at the Netherlands Trial Register (NTR4082)
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