25,386,640 research outputs found

    Neutron star properties with relativistic equations of state

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    We study the properties of neutron stars adopting relativistic equations of state of neutron star matter, calculated in the framework of the relativistic Brueckner-Hartree-Fock approximation for electrically charge neutral neutron star matter in beta-equilibrium. For higher densities more baryons (hyperons etc.) are included by means of the relativistic Hartree- or Hartree-Fock approximation. The special features of the different approximations and compositions are discussed in detail. Besides standard neutron star properties special emphasis is put on the limiting periods of neutron stars, for which the Kepler criterion and gravitation-reaction instabilities are considered. Furthermore the cooling behaviour of neutron stars is investigated, too. For comparison we give also the outcome for some nonrelativistic equations of state.Comment: 43 pages, 22 ps-figures, to be published in the International Journal of Modern Physics

    The Rising Age Gap in Economic Well-Being

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    Compares changes in median net worth of households between 1984 and 2009 by age of head of household. Examines contributing factors, including the housing market bubble, the 2007-09 recession's effect on employment, and longer-term demographic trends

    The 1998 outburst of the X-ray transient XTE J2012+381 as observed with BeppoSAX

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    We report on the results of a series of X-ray observations of the transient black hole candidate XTE J2012+381 during the 1998 outburst performed with the BeppoSAX satellite. The observed broad-band energy spectrum can be described with the superposition of an absorbed disk black body, an iron line plus a high energy component, modelled with either a power law or a Comptonisation tail. The source showed pronounced spectral variability between our five observations. While the soft component in the spectrum remained almost unchanged throughout our campaign, we detected a hard spectral tail which extended to 200 keV in the first two observations, but became barely detectable up to 50 keV in the following two. A further re-hardening is observed in the final observation. The transition from a hard to a soft and then back to a hard state occurred around an unabsorbed 0.1-200 keV luminosity of 10^38 erg/s (at 10 kpc). This indicates that state transitions in XTE 2012+281 are probably not driven only by mass accretion rate, but additional physical parameters must play a role in the evolution of the outburst.Comment: Paper accepted for publication on A&A (macro included, 9 pages, 5 figures

    Ultrarelativistic limits of boosted dilaton black holes

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    We investigate the ultrarelativistic limits of dilaton black holes, black pp-branes (strings), multi-centered dilaton black hole solutions and black pp-brane (string) solutions when the boost velocity approaches the speed of light. For dilaton black holes and black pp-branes (boost is along the transverse directions), the resulting geometries are gravitational shock wave solutions generated by a single particle and membrane. For the multi-centered dilaton black hole solutions and black pp-brane solutions (boost is along the transverse directions), the limiting geometries are shock wave solutions generated by multiple particles and membranes. When the boost is along the membrane directions, for the black pp-brane and multi-centered black pp-brane solution, the resulting geometries describe general plane-fronted waves propagating along the membranes. The effect of the dilaton on the limit is considered.Comment: Revtex, 17 pages, no figure

    Who Moves? Who Stays Put? Where's Home?

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    Analyzes results of a Pew Social & Demographic Trends survey on Americans' geographic mobility, including perceptions of "home," reasons for moving or staying, and economic considerations, by race/ethnicity, education, region, and other demographics

    Measurement of the multi-TeV neutrino cross section with IceCube using Earth absorption

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    Neutrinos interact only very weakly, so they are extremely penetrating. However, the theoretical neutrino-nucleon interaction cross section rises with energy such that, at energies above 40 TeV, neutrinos are expected to be absorbed as they pass through the Earth. Experimentally, the cross section has been measured only at the relatively low energies (below 400 GeV) available at neutrino beams from accelerators \cite{Agashe:2014kda, Formaggio:2013kya}. Here we report the first measurement of neutrino absorption in the Earth, using a sample of 10,784 energetic upward-going neutrino-induced muons observed with the IceCube Neutrino Observatory. The flux of high-energy neutrinos transiting long paths through the Earth is attenuated compared to a reference sample that follows shorter trajectories through the Earth. Using a fit to the two-dimensional distribution of muon energy and zenith angle, we determine the cross section for neutrino energies between 6.3 TeV and 980 TeV, more than an order of magnitude higher in energy than previous measurements. The measured cross section is 1.30−0.19+0.211.30^{+0.21}_{-0.19} (stat.) −0.43+0.39^{+0.39}_{-0.43} (syst.) times the prediction of the Standard Model \cite{CooperSarkar:2011pa}, consistent with the expectation for charged and neutral current interactions. We do not observe a dramatic increase in the cross section, expected in some speculative models, including those invoking new compact dimensions \cite{AlvarezMuniz:2002ga} or the production of leptoquarks \cite{Romero:2009vu}.Comment: Preprint version of Nature paper 10.1038/nature2445

    On the Decomposition of Clifford Algebras of Arbitrary Bilinear Form

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    Clifford algebras are naturally associated with quadratic forms. These algebras are Z_2-graded by construction. However, only a Z_n-gradation induced by a choice of a basis, or even better, by a Chevalley vector space isomorphism Cl(V) \bigwedge V and an ordering, guarantees a multi-vector decomposition into scalars, vectors, tensors, and so on, mandatory in physics. We show that the Chevalley isomorphism theorem cannot be generalized to algebras if the Z_n-grading or other structures are added, e.g., a linear form. We work with pairs consisting of a Clifford algebra and a linear form or a Z_n-grading which we now call 'Clifford algebras of multi-vectors' or 'quantum Clifford algebras'. It turns out, that in this sense, all multi-vector Clifford algebras of the same quadratic but different bilinear forms are non-isomorphic. The usefulness of such algebras in quantum field theory and superconductivity was shown elsewhere. Allowing for arbitrary bilinear forms however spoils their diagonalizability which has a considerable effect on the tensor decomposition of the Clifford algebras governed by the periodicity theorems, including the Atiyah-Bott-Shapiro mod 8 periodicity. We consider real algebras Cl_{p,q} which can be decomposed in the symmetric case into a tensor product Cl_{p-1,q-1} \otimes Cl_{1,1}. The general case used in quantum field theory lacks this feature. Theories with non-symmetric bilinear forms are however needed in the analysis of multi-particle states in interacting theories. A connection to q-deformed structures through nontrivial vacuum states in quantum theories is outlined.Comment: 25 pages, 1 figure, LaTeX, {Paper presented at the 5th International Conference on Clifford Algebras and their Applications in Mathematical Physics, Ixtapa, Mexico, June 27 - July 4, 199

    Antimicrobials: a global alliance for optimizing their rational use in intra-abdominal infections (AGORA)

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    Intra-abdominal infections (IAI) are an important cause of morbidity and are frequently associated with poor prognosis, particularly in high-risk patients. The cornerstones in the management of complicated IAIs are timely effective source control with appropriate antimicrobial therapy. Empiric antimicrobial therapy is important in the management of intra-abdominal infections and must be broad enough to cover all likely organisms because inappropriate initial antimicrobial therapy is associated with poor patient outcomes and the development of bacterial resistance. The overuse of antimicrobials is widely accepted as a major driver of some emerging infections (such as C. difficile), the selection of resistant pathogens in individual patients, and for the continued development of antimicrobial resistance globally. The growing emergence of multi-drug resistant organisms and the limited development of new agents available to counteract them have caused an impending crisis with alarming implications, especially with regards to Gram-negative bacteria. An international task force from 79 different countries has joined this project by sharing a document on the rational use of antimicrobials for patients with IAIs. The project has been termed AGORA (Antimicrobials: A Global Alliance for Optimizing their Rational Use in Intra-Abdominal Infections). The authors hope that AGORA, involving many of the world's leading experts, can actively raise awareness in health workers and can improve prescribing behavior in treating IAIs

    Color suppressed contributions to the decay modes B_{d,s} -> D_{s,d} D_{s,d}, B_{d,s} -> D_{s,d} D^*_{s,d}, and B_{d,s} -> D^*_{s,d} D^*_{s,d}

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    The amplitudes for decays of the type Bd,s→Ds,dDs,dB_{d,s} \to D_{s,d} D_{s,d}, have no factorizable contributions, while Bd,s→Ds,dDs,d∗B_{d,s} \to D_{s,d} D^*_{s,d}, and Bd,s→Ds,d∗Ds,d∗B_{d,s} \to D^*_{s,d} D^*_{s,d} have relatively small factorizable contributions through the annihilation mechanism. The dominant contributions to the decay amplitudes arise from chiral loop contributions and tree level amplitudes which can be obtained in terms of soft gluon emissions forming a gluon condensate. We predict that the branching ratios for the processes Bˉd0→Ds+Ds−\bar B^0_d \to D_s^+ D_s^-, Bˉd0→Ds+∗Ds−\bar B^0_d \to D_s^{+*} D_s^- and Bˉd0→Ds+Ds−∗\bar B^0_d \to D_s^+ D_s^{-*} are all of order (2−3)×10−4(2- 3) \times 10^{-4}, while Bˉs0→Dd+Dd−\bar B^0_s \to D_d^+ D_d^-, Bˉs0→Dd+∗Dd−\bar B^0_s \to D_d^{+*} D_d^- and Bˉs0→Dd+Dd−∗\bar B^0_s \to D_d^+ D_d^{-*} are of order (4−7)×10−3(4- 7) \times 10^{-3}. We obtain branching ratios for two D∗D^*'s in the final state of order two times bigger.Comment: 15 pages, 4 figure
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