338 research outputs found
Tilt Grain-Boundary Effects in S- and D-Wave Superconductors
We calculate the s- and d-wave superconductor order parameter in the vicinity
of a tilt grain boundary. We do this self-consistently within the Bogoliubov de
Gennes equations, using a realistic microscopic model of the grain boundary. We
present the first self-consistent calculations of supercurrent flows in such
boundaries, obtaining the current-phase characteristics of grain boundaries in
both s-wave and d-wave superconductors
Dynamical renormalization group approach to transport in ultrarelativistic plasmas: the electrical conductivity in high temperature QED
The DC electrical conductivity of an ultrarelativistic QED plasma is studied
in real time by implementing the dynamical renormalization group. The
conductivity is obtained from the realtime dependence of a dissipative kernel
related to the retarded photon polarization. Pinch singularities in the
imaginary part of the polarization are manifest as growing secular terms that
in the perturbative expansion of this kernel. The leading secular terms are
studied explicitly and it is shown that they are insensitive to the anomalous
damping of hard fermions as a result of a cancellation between self-energy and
vertex corrections. The resummation of the secular terms via the dynamical
renormalization group leads directly to a renormalization group equation in
real time, which is the Boltzmann equation for the (gauge invariant) fermion
distribution function. A direct correspondence between the perturbative
expansion and the linearized Boltzmann equation is established, allowing a
direct identification of the self energy and vertex contributions to the
collision term.We obtain a Fokker-Planck equation in momentum space that
describes the dynamics of the departure from equilibrium to leading logarithmic
order in the coupling.This determines that the transport time scale is given by
t_{tr}=(24 pi)/[e^4 T \ln(1/e)}]. The solution of the Fokker-Planck equation
approaches asymptotically the steady- state solution as sim e^{-t/(4.038
t_{tr})}.The steady-state solution leads to the conductivity sigma = 15.698
T/[e^2 ln(1/e)] to leading logarithmic order. We discuss the contributions
beyond leading logarithms as well as beyond the Boltzmann equation. The
dynamical renormalization group provides a link between linear response in
quantum field theory and kinetic theory.Comment: LaTex, 48 pages, 14 .ps figures, final version to appear in Phys.
Rev.
First-order cosmological phase transitions in the radiation dominated era
We consider first-order phase transitions of the Universe in the
radiation-dominated era. We argue that in general the velocity of interfaces is
non-relativistic due to the interaction with the plasma and the release of
latent heat. We study the general evolution of such slow phase transitions,
which comprise essentially a short reheating stage and a longer phase
equilibrium stage. We perform a completely analytical description of both
stages. Some rough approximations are needed for the first stage, due to the
non-trivial relations between the quantities that determine the variation of
temperature with time. The second stage, instead, is considerably simplified by
the fact that it develops at a constant temperature, close to the critical one.
Indeed, in this case the equations can be solved exactly, including
back-reaction on the expansion of the Universe. This treatment also applies to
phase transitions mediated by impurities. We also investigate the relations
between the different parameters that govern the characteristics of the phase
transition and its cosmological consequences, and discuss the dependence of
these parameters with the particle content of the theory.Comment: 38 pages, 3 figures; v2: Minor changes, references added; v3: several
typos correcte
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
Measuring the metric: a parametrized post-Friedmanian approach to the cosmic dark energy problem
We argue for a ``parametrized post-Friedmanian'' approach to linear
cosmology, where the history of expansion and perturbation growth is measured
without assuming that the Einstein Field Equations hold. As an illustration, a
model-independent analysis of 92 type Ia supernovae demonstrates that the curve
giving the expansion history has the wrong shape to be explained without some
form of dark energy or modified gravity. We discuss how upcoming lensing,
galaxy clustering, cosmic microwave background and Lyman alpha forest
observations can be combined to pursue this program, which generalizes the
quest for a dark energy equation of state, and forecast the accuracy that the
proposed SNAP satellite can attain.Comment: Replaced to match accepted PRD version. References and another
example added, section III omitted since superceded by astro-ph/0207047. 11
PRD pages, 7 figs. Color figs and links at
http://www.hep.upenn.edu/~max/gravity.html or from [email protected]
An organizational impression management perspective on the formation of corporate reputations
Researchers have only recently turned their attention to the study of corporate reputation. As is characteristic of many early areas of management inquiry, the field is decidedly multidisciplinary and disconnected. This article selectively reviews reputation research conducted mainly during the past decade. A framework is proposed that views reputation from the perspective of organizational impression management. Corporations are viewed as social actors, intent on enhancing their respectability and impressiveness in the eyes of constituents
Recommendations for reporting ion mobility Mass Spectrometry measurements
Here we present a guide to ion mobility mass spectrometry experiments, which covers both linear and nonlinear methods: what is measured, how the measurements are done, and how to report the results, including the uncertainties of mobility and collision cross section values. The guide aims to clarify some possibly confusing concepts, and the reporting recommendations should help researchers, authors and reviewers to contribute comprehensive reports, so that the ion mobility data can be reused more confidently. Starting from the concept of the definition of the measurand, we emphasize that (i) mobility values (K0) depend intrinsically on ion structure, the nature of the bath gas, temperature, and E/N; (ii) ion mobility does not measure molecular surfaces directly, but collision cross section (CCS) values are derived from mobility values using a physical model; (iii) methods relying on calibration are empirical (and thus may provide methodâdependent results) only if the gas nature, temperature or E/N cannot match those of the primary method. Our analysis highlights the urgency of a community effort toward establishing primary standards and reference materials for ion mobility, and provides recommendations to do so. © 2019 The Authors. Mass Spectrometry Reviews Published by Wiley Periodicals, Inc
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