2,447 research outputs found
Fermionic statistics in the strongly correlated limit of Density Functional Theory
Exact pieces of information on the adiabatic connection integrand
, which allows to evaluate the exchange-correlation energy
of Kohn-Sham density functional theory, can be extracted from the leading terms
in the strong coupling limit (, where is the
strength of the electron-electron interaction). In this work, we first compare
the theoretical prediction for the two leading terms in the strong coupling
limit with data obtained via numerical implementation of the exact Levy
functional in the simple case of two electrons confined in one dimension,
confirming the asymptotic exactness of these two terms. We then carry out a
first study on the incorporation of the fermionic statistics at large coupling
, both numerical and theoretical, confirming that spin effects enter
at orders
A Lyman-alpha blob in the GOODS South field: evidence for cold accretion onto a dark matter halo
We report on the discovery of a z = 3.16 Lyman-alpha emitting blob in the
GOODS South field. The blob has a total Ly-alpha luminosity of ~ 10^(43) erg
s^(-1) and a diameter larger than 60 kpc. The available multi-wavelength data
in the GOODS field consists of 13 bands from X-rays (Chandra) to infrared
(Spitzer). Unlike other discovered Ly-alpha blobs, this blob shows no obvious
continuum counter-part in any of the broad-bands. In particular, no optical
counter-parts are found in the deep HST/ACS imaging available. For previously
published blobs, AGN (Active Galactic Nuclei) or 'superwind' models have been
found to provide the best match with the data. We here argue that the most
probable origin of the extended Ly-alpha emission from the blob in the GOODS
South field is cold accretion onto a dark matter halo.Comment: 4 pages, 2 tables, 2 figures, Accepted to A&A Letters, minor changes
to tex
Sliding charge density wave in manganites
The so-called stripe phase of the manganites is an important example of the
complex behaviour of metal oxides, and has long been interpreted as the
localisation of charge at atomic sites. Here, we demonstrate via resistance
measurements on La_{0.50}Ca_{0.50}MnO_3 that this state is in fact a
prototypical charge density wave (CDW) which undergoes collective transport.
Dramatic resistance hysteresis effects and broadband noise properties are
observed, both of which are typical of sliding CDW systems. Moreover, the high
levels of disorder typical of manganites result in behaviour similar to that of
well-known disordered CDW materials. Our discovery that the manganite
superstructure is a CDW shows that unusual transport and structural properties
do not require exotic physics, but can emerge when a well-understood phase (the
CDW) coexists with disorder.Comment: 13 pages; 4 figure
Compressibility and thermal expansion of cubic silicon nitride
The compressibility and thermal expansion of the cubic silicon nitride (c-Si3N4) phase have been investigated by performing in situ x-ray powder-diffraction measurements using synchrotron radiation, complemented with computer simulations by means of first-principles calculations. The bulk compressibility of the c-Si3N4 phase originates from the average of both Si-N tetrahedral and octahedral compressibilities where the octahedral polyhedra are less compressible than the tetrahedral ones. The origin of the unit cell expansion is revealed to be due to the increase of the octahedral Si-N and N-N bond lengths with temperature, while the lengths for the tetrahedral Si-N and N-N bonds remain almost unchanged in the temperature range 295-1075 K
Fermi LAT Observation of Diffuse Gamma-Rays Produced Through Interactions between Local Interstellar Matter and High Energy Cosmic Rays
Observations by the Large Area Telescope (LAT) on the \textit{Fermi} mission
of diffuse -rays in a mid-latitude region in the third quadrant
(Galactic longitude from 200\arcdeg to 260\arcdeg and latitude
from 22\arcdeg to 60\arcdeg) are reported. The region contains no known
large molecular cloud and most of the atomic hydrogen is within 1 kpc of the
solar system. The contributions of -ray point sources and inverse
Compton scattering are estimated and subtracted. The residual -ray
intensity exhibits a linear correlation with the atomic gas column density in
energy from 100 MeV to 10 GeV. The measured integrated -ray emissivity
is (1.63 \pm 0.05) \times 10^{-26} {\rm photons s^{-1} sr^{-1}
H\mathchar`-atom^{-1}} and (0.66 \pm 0.02) \times 10^{-26} {\rm photons
s^{-1} sr^{-1} H\mathchar`-atom^{-1}} above 100 MeV and above 300 MeV,
respectively, with additional systematic error of . The differential
emissivity in 100 MeV--10 GeV agrees with calculations based on cosmic ray
spectra consistent with those directly measured, at the 10% level. The results
obtained indicate that cosmic ray nuclei spectra within 1 kpc from the solar
system in regions studied are close to the local interstellar spectra inferred
from direct measurements at the Earth within .Comment: accepted for publication in the Astrophysical Journal. Revised
according to the author proof.(correction of typos and minor revisions
Technical Design Report for the PANDA Solenoid and Dipole Spectrometer Magnets
This document is the Technical Design Report covering the two large
spectrometer magnets of the PANDA detector set-up. It shows the conceptual
design of the magnets and their anticipated performance. It precedes the tender
and procurement of the magnets and, hence, is subject to possible modifications
arising during this process.Comment: 10 pages, 14MB, accepted by FAIR STI in May 2009, editors: Inti
Lehmann (chair), Andrea Bersani, Yuri Lobanov, Jost Luehning, Jerzy Smyrski,
Technical Coordiantor: Lars Schmitt, Bernd Lewandowski (deputy),
Spokespersons: Ulrich Wiedner, Paola Gianotti (deputy
Random-phase approximation and its applications in computational chemistry and materials science
The random-phase approximation (RPA) as an approach for computing the
electronic correlation energy is reviewed. After a brief account of its basic
concept and historical development, the paper is devoted to the theoretical
formulations of RPA, and its applications to realistic systems. With several
illustrating applications, we discuss the implications of RPA for computational
chemistry and materials science. The computational cost of RPA is also
addressed which is critical for its widespread use in future applications. In
addition, current correction schemes going beyond RPA and directions of further
development will be discussed.Comment: 25 pages, 11 figures, published online in J. Mater. Sci. (2012
Feasibility studies of time-like proton electromagnetic form factors at PANDA at FAIR
Simulation results for future measurements of electromagnetic proton form
factors at \PANDA (FAIR) within the PandaRoot software framework are reported.
The statistical precision with which the proton form factors can be determined
is estimated. The signal channel is studied on the basis
of two different but consistent procedures. The suppression of the main
background channel, , is studied.
Furthermore, the background versus signal efficiency, statistical and
systematical uncertainties on the extracted proton form factors are evaluated
using two different procedures. The results are consistent with those of a
previous simulation study using an older, simplified framework. However, a
slightly better precision is achieved in the PandaRoot study in a large range
of momentum transfer, assuming the nominal beam conditions and detector
performance
Measurement of the cross-section and charge asymmetry of bosons produced in proton-proton collisions at TeV with the ATLAS detector
This paper presents measurements of the and cross-sections and the associated charge asymmetry as a
function of the absolute pseudorapidity of the decay muon. The data were
collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with
the ATLAS experiment at the LHC and correspond to a total integrated luminosity
of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements
varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the
1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured
with an uncertainty between 0.002 and 0.003. The results are compared with
predictions based on next-to-next-to-leading-order calculations with various
parton distribution functions and have the sensitivity to discriminate between
them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables,
submitted to EPJC. All figures including auxiliary figures are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13
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