2,571 research outputs found

    Exhaustive generation of kk-critical H\mathcal H-free graphs

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    We describe an algorithm for generating all kk-critical H\mathcal H-free graphs, based on a method of Ho\`{a}ng et al. Using this algorithm, we prove that there are only finitely many 44-critical (P7,Ck)(P_7,C_k)-free graphs, for both k=4k=4 and k=5k=5. We also show that there are only finitely many 44-critical graphs (P8,C4)(P_8,C_4)-free graphs. For each case of these cases we also give the complete lists of critical graphs and vertex-critical graphs. These results generalize previous work by Hell and Huang, and yield certifying algorithms for the 33-colorability problem in the respective classes. Moreover, we prove that for every tt, the class of 4-critical planar PtP_t-free graphs is finite. We also determine all 27 4-critical planar (P7,C6)(P_7,C_6)-free graphs. We also prove that every P10P_{10}-free graph of girth at least five is 3-colorable, and determine the smallest 4-chromatic P12P_{12}-free graph of girth five. Moreover, we show that every P13P_{13}-free graph of girth at least six and every P16P_{16}-free graph of girth at least seven is 3-colorable. This strengthens results of Golovach et al.Comment: 17 pages, improved girth results. arXiv admin note: text overlap with arXiv:1504.0697

    Benchmarking common quantification strategies for large-scale phosphoproteomics

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    Quantitative phosphoproteomics has become a standard method in molecular and cell biology. Here, the authors compare performance and parameters of phosphoproteome quantification by LFQ, SILAC, and MS2-/MS3-based TMT and introduce a TMT-adapted algorithm for calculating phosphorylation site stoichiometry

    Isoflavones in Legumes as Functional Forages and Feeds in Ruminant Grazing Systems

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    Legumes are often utilized in livestock grazing systems to improve diet quality, diversity, and consequently animal performance. In addition to their nutritional utility, legumes contain phytoestrogenic isoflavones that have selective antimicrobial activity in the rumen and once absorbed can cause arterial vasodilation. These added bioactive functions of isoflavones suggest that legumes could be strategically utilized in grazing systems as functional forages to improve ruminant performance and health. The objective of this presentation will be to discuss past and current research on the application of isoflavones via legumes as an antimicrobial for growth promotion and as a mitigation strategy for fescue toxicosis in grazing ruminants

    Analysis of OPM potentials for multiplet states of 3d transition metal atoms

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    We apply the optimized effective potential method (OPM) to the multiplet energies of the 3dn^n transition metal atoms, where the orbital dependence of the energy functional with respect to orbital wave function is the single-configuration HF form. We find that the calculated OPM exchange potential can be represented by the following two forms. Firstly, the difference between OPM exchange potentials of the multiplet states can be approximated by the linear combination of the potentials derived from the Slater integrals F2(3d,3d)F^2({\rm 3d,3d}) and F4(3d,3d)F^4({\rm 3d,3d}) for the average energy of the configuration. Secondly, the OPM exchange potential can be expressed as the linear combination of the OPM exchange potentials of the single determinants.Comment: 15 pages, 6 figures, to be published in J. Phys.

    First-principles calculations of the self-trapped exciton in crystalline NaCl

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    The atomic and electronic structure of the lowest triplet state of the off-center (C2v symmetry) self-trapped exciton (STE) in crystalline NaCl is calculated using the local-spin-density (LSDA) approximation. In addition, the Franck-Condon broadening of the luminescence peak and the a1g -> b3u absorption peak are calculated and compared to experiment. LSDA accurately predicts transition energies if the initial and final states are both localized or delocalized, but 1 eV discrepancies with experiment occur if one state is localized and the other is delocalized.Comment: 4 pages with 4 embeddded figure

    Direct Minimization Generating Electronic States with Proper Occupation Numbers

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    We carry out the direct minimization of the energy functional proposed by Mauri, Galli and Car to derive the correct self-consistent ground state with fractional occupation numbers for a system degenerating at the Fermi level. As a consequence, this approach enables us to determine the electronic structure of metallic systems to a high degree of accuracy without the aid of level broadening of the Fermi-distribution function. The efficiency of the method is illustrated by calculating the ground-state energy of C2_2 and Si2_2 molecules and the W(110) surface to which a tungsten adatom is adsorbed.Comment: 4 pages, 4 figure

    Point defects, ferromagnetism and transport in calcium hexaboride

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    The formation energy and local magnetic moment of a series of point defects in CaB6_6 are computed using a supercell approach within the generalized gradient approximation to density functional theory. Based on these results, speculations are made as to the influence of these defects on electrical transport. It is found that the substitution of Ca by La does not lead to the formation of a local moment, while a neutral B6_6 vacancy carries a moment of 2.4 Bohr magnetons, mostly distributed over the six nearest-neighbour B atoms. A plausible mechanism for the ferromagnetic ordering of these moments is suggested. Since the same broken B-B bonds appear on the preferred (100) cleavage planes of the CaB6_6 structure, it is argued that internal surfaces in polycrystals as well as external surfaces in general will make a large contribution to the observed magnetization.Comment: Calculated defect formation energies had to be corrected, due to the use of a wrong reference energy for the perfect crystal in the original pape

    Surface relaxation and ferromagnetism of Rh(001)

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    The significant discrepancy between first-principles calculations and experimental analyses for the relaxation of the (001) surface of rhodium has been a puzzle for some years. In this paper we present density functional theory calculations using the local-density approximation and the generalized gradient approximation of the exchange-correlation functional. We investigate the thermal expansion of the surface and the possibility of surface magnetism. The results throw light on several, hitherto overlooked, aspects of metal surfaces. We find, that, when the free energy is considered, density-functional theory provides results in good agreement with experiments.Comment: 6 pages, 4 figures, submitted to Phys. Rev. Lett. (April 28, 1996
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