3,090 research outputs found
Inversion of stellar fundamental parameters from Espadons and Narval high-resolution spectra
The general context of this study is the inversion of stellar fundamental
parameters from high-resolution Echelle spectra. We aim indeed at developing a
fast and reliable tool for the post-processing of spectra produced by Espadons
and Narval spectropolarimeters. Our inversion tool relies on principal
component analysis. It allows reduction of dimensionality and the definition of
a specific metric for the search of nearest neighbours between an observed
spectrum and a set of observed spectra taken from the Elodie stellar library.
Effective temperature, surface gravity, total metallicity and projected
rotational velocity are derived. Various tests presented in this study, and
done from the sole information coming from a spectral band centered around the
Mg I b-triplet and with spectra from FGK stars are very promising.Comment: 13 pages, 8 figures (accepted A&A). arXiv admin note: text overlap
with arXiv:1401.108
Weak radiative corrections to the Drell-Yan process for large invariant mass of a dilepton pair
The weak radiative corrections to the Drell-Yan process above the Z-peak have
been studied. The compact asymptotic expression for the two heavy boson
exchange - one of the significant contributions to the investigated process -
has been obtained, the results expand in the powers of the Sudakov electroweak
logarithms. At the quark level we compare the weak radiative corrections to the
total cross section and forward-backward asymmetry with the existing results
and achieve a rather good coincidence at \sqrt{s}>= 0.5 TeV. The numerical
analysis has been performed in the high energy region corresponding to the
future experiments at the CERN Large Hadron Collider (LHC). To simulate the
detector acceptance we used the standard CMS detector cuts. It was shown that
double Sudakov logarithms of the WW boxes are the dominant contributions in
hadronic cross section. The considered radiative corrections are significant at
high dilepton mass M and change the dilepton mass distribution up to ~+3(-12)%
at the LHC energies and M=1(5) TeV.Comment: Changed content; 13 pp, 4 fig, 1 tabl
Hopf Categories
We introduce Hopf categories enriched over braided monoidal categories. The
notion is linked to several recently developed notions in Hopf algebra theory,
such as Hopf group (co)algebras, weak Hopf algebras and duoidal categories. We
generalize the fundamental theorem for Hopf modules and some of its
applications to Hopf categories.Comment: 47 pages; final version to appear in Algebras and Representation
Theor
Spin diffusion in the one-dimensional s = 1/2 XXZ model at infinite temperature
Time-dependent spin-autocorrelation functions at T = ∞ and (in particular) their spectral densities for the bulk spin and the boundary spin of the semi-infinite spin-1/2 XXZ model (with exchange parameters Jx = Jy = J, Jz) are investigated on the basis of (i) rigorous bounds in the time domain and (ii) a continued-fraction analysis in the frequency domain. We have found strong numerical evidence for spin diffusion in quantum spin models. For Jz/J increasing from zero, the results of the short-time expansion indicate a change of the bulk-spin xx-autocorrelation function from Gaussian decay to exponential decay. The continued-fraction analysis of the same dynamic quantity signals a change from exponential decay to power-law decay as Jz/J pproaches unity and back to a more rapid decay upon further increase of that parameter. By contrast, the change in symmetry at Jz/J = 1 has virtually no impact on the bulk-spin zz-autocorrelation function (as expected). Similar contrasting properties are observable in the boundary-spin autocorrelation functions
QED Radiative Corrections in Processes of Exclusive Pion Electroproduction
Formalism for radiative correction (RC) calculation in exclusive pion
electroproduction on the proton is presented. A FORTRAN code EXCLURAD is
developed for the RC procedure. The numerical analysis is done in the
kinematics of current Jefferson Lab experiments.Comment: 13 pages, 9 figures; requires RevTeX
Morita base change in Hopf-cyclic (co)homology
In this paper, we establish the invariance of cyclic (co)homology of left
Hopf algebroids under the change of Morita equivalent base algebras. The
classical result on Morita invariance for cyclic homology of associative
algebras appears as a special example of this theory. In our main application
we consider the Morita equivalence between the algebra of complex-valued smooth
functions on the classical 2-torus and the coordinate algebra of the
noncommutative 2-torus with rational parameter. We then construct a Morita base
change left Hopf algebroid over this noncommutative 2-torus and show that its
cyclic (co)homology can be computed by means of the homology of the Lie
algebroid of vector fields on the classical 2-torus.Comment: Final version to appear in Lett. Math. Phy
Организация и ведение поисково и аварийно-спасательных работ на водоемах
Проведение поисковых и аварийно-спасательных работ на воде с применением спасательных судов при возникновении чрезвычайных ситуаций является одной из основных задач Единой государственной системы предупреждения и ликвидации чрезвычайных ситуаций (РСЧС), позволяющих уменьшить жертвы и сохранить здоровье людей. Спасение терпящих бедствие на воде должно быть организовано своевременно, оперативно и комплексно, то есть в полном объеме по всём необходимым в конкретной обстановке видам работ по спасению пострадавших.Conducting search and rescue operations on the water with the use of rescue vessels in the event of emergencies is one of the main tasks of the Unified State System for the Prevention and Elimination of Emergencies (RSES), which makes it possible to reduce casualties and preserve people's health. Salvation of those in distress on the water must be organized in a timely manner, promptly and in a comprehensive manner, that is, in full volume for all kinds of rescue work for the victims
Pair Excitations and Vertex Corrections in Fermi Fluids
Based on an equations--of--motion approach for time--dependent pair
correlations in strongly interacting Fermi liquids, we have developed a theory
for describing the excitation spectrum of these systems. Compared to the known
``correlated'' random--phase approximation (CRPA), our approach has the
following properties: i) The CRPA is reproduced when pair fluctuations are
neglected. ii) The first two energy--weighted sumrules are fulfilled implying a
correct static structure. iii) No ad--hoc assumptions for the effective mass
are needed to reproduce the experimental dispersion of the roton in 3He. iv)
The density response function displays a novel form, arising from vertex
corrections in the proper polarisation. Our theory is presented here with
special emphasis on this latter point. We have also extended the approach to
the single particle self-energy and included pair fluctuations in the same way.
The theory provides a diagrammatic superset of the familiar GW approximation.
It aims at a consistent calculation of single particle excitations with an
accuracy that has previously only been achieved for impurities in Bose liquids.Comment: to be published in: JLTP (2007) Proc. Int. Symp. QFS2006, 1-6 Aug.
2006, Kyoto, Japa
Red- and blue-detuned magneto-optical trapping with liquid crystal variable retarders
We exploit red- and blue-detuned magneto-optical trapping (MOT) of 87Rb benefitting from a simplified setup and a novel approach based on liquid crystal variable retarders (LCVR). To maintain the trapping forces when switching from a red- to a blue-detuned MOT, the handedness of the circular polarization of the cooling beams needs to be reversed. LCVRs allow fast polarization control and represent compact, simple, and cost-efficient components, which can easily be implemented in existing laser systems. This way, we achieve a blue-detuned type-II MOT for 8.7 × 108 atoms of 87Rb with sub-Doppler temperatures of 44 μK well below the temperatures reached in a conventional 87Rb type-I MOT. The phase space density is increased by more than two orders of magnitude compared to the standard red-detuned type-I MOT. The setup can readily be transferred to any other systems working with 87Rb
Raman-Scattering Detection of Nearly Degenerate -Wave and -Wave Pairing Channels in Iron-Based BaKFeAs and RbFeSe Superconductors
We show that electronic Raman scattering affords a window into the essential
properties of the pairing potential of
iron-based superconductors. In BaKFeAs we observe band
dependent energy gaps along with excitonic Bardasis-Schrieffer modes
characterizing, respectively, the dominant and subdominant pairing channel. The
symmetry of all excitons allows us to identify the subdominant
channel to originate from the interaction between the electron bands.
Consequently, the dominant channel driving superconductivity results from the
interaction between the electron and hole bands and has the full lattice
symmetry. The results in RbFeSe along with earlier ones in
Ba(FeCo)As highlight the influence of the Fermi
surface topology on the pairing interactions.Comment: 5 pages, 4 figure
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