1,893 research outputs found
Correlation effects in total energy of transition metals and related properties
We present an accurate implementation of total energy calculations into the
local density approximation plus dynamical mean-field theory (LDA+DMFT) method.
The electronic structure problem is solved through the full potential linear
Muffin-Tin Orbital (FP-LMTO) and Korringa-Kohn-Rostoker (FP-KKR) methods with a
perturbative solver for the effective impurity suitable for moderately
correlated systems. We have tested the method in detail for the case of Ni and
investigated the sensitivity of the results to the computational scheme and to
the complete self-consistency. It is demonstrated that the LDA+DMFT method can
resolve a long-standing controversy between the LDA/GGA density functional
approach and experiment for equilibrium lattice constant and bulk modulus of
Mn.Comment: 14 pages, 5 figure
Neutrino production through hadronic cascades in AGN accretion disks
We consider the production of neutrinos in active galactic nuclei (AGN)
through hadronic cascades. The initial, high energy nucleons are accelerated in
a source above the accretion disk around the central black hole. From the
source, the particles diffuse back to the disk and initiate hadronic cascades.
The observable output from the cascade are electromagnetic radiation and
neutrinos. We use the observed diffuse background X-ray luminosity, which
presumably results {}from this process, to predict the diffuse neutrino flux
close to existing limits from the Frejus experiment. The resulting neutrino
spectrum is down to the \GeV region. We discuss modifications of
this scenario which reduce the predicted neutrino flux.Comment: 12 Pages, LaTeX, TK 92 0
Absolute calibration of the LOPES antenna system
Radio emission in extensive air showers arises from an interaction with the
geomagnetic field and is subject of theoretical studies. This radio emission
has advantages for the detection of high energy cosmic rays compared to
secondary particle or fluorescence measurement methods. Radio antennas like the
LOPES30 antenna system are suited to investigate this emission process by
detecting the radio pulses. The characteristic observable parameters like
electric field strength and pulse length require a calibration which was done
with a reference radio source resulting in an amplification factor representing
the system behavior in the environment of the KASCADE-Grande experiment.
Knowing the amplification factor and the gain of the LOPES antennas LOPES30 is
calibrated absolutely for systematic analyses of the radio emission.Comment: 5 pages, Proceedings of International Workshop on Acoustic and Radio
EeV Neutrino detection Activities: ARENA, May 17-19, 2005, DESY Zeuthe
Spinning compact binary inspiral II: Conservative angular dynamics
We establish the evolution equations of the set of independent variables
characterizing the 2PN rigorous conservative dynamics of a spinning compact
binary, with the inclusion of the leading order spin-orbit, spin-spin and mass
quadrupole - mass monopole effects, for generic (noncircular, nonspherical)
orbits. More specifically, we give a closed system of first order ordinary
differential equations for the orbital elements of the osculating ellipse and
for the angles characterizing the spin orientations with respect to the
osculating orbit. We also prove that (i) the relative angle of the spins stays
constant for equal mass black holes, irrespective of their orientation, and
(ii) the special configuration of equal mass black holes with equal, but
antialigned spins, both laying in the plane of motion (leading to the largest
recoil found in numerical simulations) is preserved at 2PN level of accuracy,
with leading order spin-orbit, spin-spin and mass quadrupolar contributions
included.Comment: v2: 19 pages, extended, improved, published versio
Self-consistency over the charge-density in dynamical mean-field theory: a linear muffin-tin implementation and some physical implications
We present a simple implementation of the dynamical mean-field theory
approach to the electronic structure of strongly correlated materials. This
implementation achieves full self-consistency over the charge density, taking
into account correlation-induced changes to the total charge density and
effective Kohn-Sham Hamiltonian. A linear muffin-tin orbital basis-set is used,
and the charge density is computed from moments of the many body
momentum-distribution matrix. The calculation of the total energy is also
considered, with a proper treatment of high-frequency tails of the Green's
function and self-energy. The method is illustrated on two materials with
well-localized 4f electrons, insulating cerium sesquioxide Ce2O3 and the
gamma-phase of metallic cerium, using the Hubbard-I approximation to the
dynamical mean-field self-energy. The momentum-integrated spectral function and
momentum-resolved dispersion of the Hubbard bands are calculated, as well as
the volume-dependence of the total energy. We show that full self-consistency
over the charge density, taking into account its modification by strong
correlations, can be important for the computation of both thermodynamical and
spectral properties, particularly in the case of the oxide material.Comment: 20 pages, 6 figures (submitted in The Physical Review B
Spectroscopic signatures of a bandwidth-controlled Mott transition at the surface of 1T-TaSe
High-resolution angle-resolved photoemission (ARPES) data show that a
metal-insulator Mott transition occurs at the surface of the quasi-two
dimensional compound TaSe. The transition is driven by the narrowing of the
Ta band induced by a temperature-dependent modulation of the atomic
positions. A dynamical mean-field theory calculation of the spectral function
of the half-filled Hubbard model captures the main qualitative feature of the
data, namely the rapid transfer of spectral weight from the observed
quasiparticle peak at the Fermi surface to the Hubbard bands, as the
correlation gap opens up.Comment: 4 pages, 4 figures; one modified figure, added referenc
Contact Discontinuities in Models of Contact Binaries Undergoing Thermal Relaxation Oscillations
In this paper we pursue the suggestion by Shu, Lubow & Anderson (1979) and
Wang (1995) that contact discontinuity (DSC) may exist in the secondary in the
expansion TRO (thermal relaxation oscillation) state. It is demonstrated that
there is a mass exchange instability in some range of mass ratio for the two
components. We show that the assumption of {\it constant} volume of the
secondary should be relaxed in DSC model. For {\it all} mass ratio the
secondary alway satisfies the condition that no mass flow returns to the
primary through the inner Lagrangian point. The secondary will expand in order
to equilibrate the interaction between the common convective envelope and the
secondary. The contact discontinuity in contact binary undergoing thermal
relaxation does not violate the second law of thermodynamics. The maintaining
condition of contact discontinuity is derived in the time-dependent model. It
is desired to improve the TRO model with the advanced contact discontinuity
layer in future detailed calculations.Comment: 5 pages in emulateapj, 1 figur
Detection and imaging of atmospheric radio flashes from cosmic ray air showers
The nature of ultrahigh-energy cosmic rays (UHECRs) at energies >10^20 eV
remains a mystery. They are likely to be of extragalactic origin, but should be
absorbed within ~50 Mpc through interactions with the cosmic microwave
background. As there are no sufficient powerful accelerators within this
distance from the Galaxy, explanations for UHECRs range from unusual
astrophysical sources to exotic string physics. Also unclear is whether UHECRs
consist of protons, heavy nuclei, neutrinos or gamma-rays. To resolve these
questions, larger detectors with higher duty cycles and which combine multiple
detection techniques are needed. Radio emission from UHECRs, on the other hand,
is unaffected by attenuation, has a high duty cycle, gives calorimetric
measurements and provides high directional accuracy. Here we report the
detection of radio flashes from cosmic-ray air showers using low-cost digital
radio receivers. We show that the radiation can be understood in terms of the
geosynchrotron effect. Our results show that it should be possible to determine
the nature and composition of UHECRs with combined radio and particle
detectors, and to detect the ultrahigh-energy neutrinos expected from flavour
mixing.Comment: Nature, May 19, 2005 issue (PDF, 14 pages),
http://www.astro.ru.nl/lopes/?loc=publication
Cosmic Ray Protons and Magnetic Fields in Clusters of Galaxies and their Cosmological Consequences
The masses of clusters of galaxies estimated by gravitational lensing exceed
in many cases the mass estimates based on hydrostatic equilibrium. This may
suggest the existence of nonthermal pressure. We ask if radio galaxies can heat
and support the cluster gas with injected cosmic ray protons and magnetic field
densities, which are permitted by Faraday rotation and gamma ray observations
of clusters of galaxies. We conclude that they are powerful enough to do this
within a cluster radius of roughly 1 Mpc. If present, nonthermal pressures
could lead to a revised estimate of the ratio of baryonic mass to total mass,
and the apparent baryonic overdensity in clusters would disappear. In
consequence, , the clumping part of the cosmological density
, would be larger than .Comment: Accepted by ApJ, 16 pages, LaTeX, 2 figures, epsfig.sty, aaspp4.st
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