1,335 research outputs found
Spectral modeling of type II supernovae. I. Dilution factors
We present substantial extensions to the Monte Carlo radiative transfer code
TARDIS to perform spectral synthesis for type II supernovae. By incorporating a
non-LTE ionization and excitation treatment for hydrogen, a full account of
free-free and bound-free processes, a self-consistent determination of the
thermal state and by improving the handling of relativistic effects, the
improved code version includes the necessary physics to perform spectral
synthesis for type II supernovae to high precision as required for the reliable
inference of supernova properties. We demonstrate the capabilities of the
extended version of TARDIS by calculating synthetic spectra for the
prototypical type II supernova SN1999em and by deriving a new and independent
set of dilution factors for the expanding photosphere method. We have
investigated in detail the dependence of the dilution factors on photospheric
properties and, for the first time, on changes in metallicity. We also compare
our results with two previously published sets of dilution factors by Eastman
et al. (1996) and by Dessart & Hillier (2005), and discuss the potential
sources of the discrepancies between studies.Comment: 16 pages, 12 figures, 2 tables, accepted for publication in A&
Spin-orientation-dependent spatial structure of a magnetic acceptor state in a zincblende semiconductor
The spin orientation of a magnetic dopant in a zincblende semiconductor
strongly influences the spatial structure of an acceptor state bound to the
dopant. The acceptor state has a roughly oblate shape with the short axis
aligned with the dopant's core spin. For a Mn dopant in GaAs the local density
of states at a site 8 angstrom away from the dopant can change by as much by
90% when the Mn spin orientation changes. These changes in the local density of
states could be probed by scanning tunneling microscopy to infer the magnetic
dopant's spin orientation.Comment: 5 pages, 4 figure
Triplet-singlet relaxation in semiconductor single and double quantum dots
We study the triplet-singlet relaxation in two-electron semiconductor quantum
dots. Both single dots and vertically coupled double dots are discussed. In our
work, the electron-electron Coulomb interaction, which plays an important role
in the electronic structure, is included. The spin mixing is caused by
spin-orbit coupling which is the key to the triplet-singlet relaxation. We show
that the selection rule widely used in the literature is incorrect unless near
the crossing/anticrossing point in single quantum dots. The triplet/singlet
relaxation in double quantum dots can be markedly changed by varying barrier
height, inter-dot distance, external magnetic field and dot size.Comment: 7 pages, 4 figures, PRB in pres
Theory of excitons in cubic III-V semiconductor GaAs, InAs and GaN quantum dots: fine structure and spin relaxation
Exciton fine structures in cubic III-V semiconductor GaAs, InAs and GaN
quantum dots are investigated systematically and the exciton spin relaxation in
GaN quantum dots is calculated by first setting up the effective exciton
Hamiltonian. The electron-hole exchange interaction Hamiltonian, which consists
of the long- and short-range parts, is derived within the effective-mass
approximation by taking into account the conduction, heavy- and light-hole
bands, and especially the split-off band. The scheme applied in this work
allows the description of excitons in both the strong and weak confinement
regimes. The importance of treating the direct electron-hole Coulomb
interaction unperturbatively is demonstrated. We show in our calculation that
the light-hole and split-off bands are negligible when considering the exciton
fine structure, even for GaN quantum dots, and the short-range exchange
interaction is irrelevant when considering the optically active doublet
splitting. We point out that the long-range exchange interaction, which is
neglected in many previous works, contributes to the energy splitting between
the bright and dark states, together with the short-range exchange interaction.
Strong dependence of the optically active doublet splitting on the anisotropy
of dot shape is reported. Large doublet splittings up to 600 eV, and even
up to several meV for small dot size with large anisotropy, is shown in GaN
quantum dots. The spin relaxation between the lowest two optically active
exciton states in GaN quantum dots is calculated, showing a strong dependence
on the dot anisotropy. Long exciton spin relaxation time is reported in GaN
quantum dots. These findings are in good agreement with the experimental
results.Comment: 22+ pages, 16 figures, several typos in the published paper are
corrected in re
SU(2)xSU(2) nonlocal quark model with confinement
The nonlocal version of the SU(2)xSU(2) symmetric four-quark interaction of
the NJL type is considered. Each of the quark lines contains the form factors.
These form factors remove the ultraviolet divergences in quark loops. The
additional condition on quark mass function m(p) ensures the absence of the
poles in the quark propagator(quark confinement). The constituent quark mass
m(0) is expressed thought the cut-off parameter Lambda, m(0)=Lambda=340 MeV in
the chiral limit. These parameters are fixed by the experimental value of the
weak pion decay and allow us to describe the mass of the light scalar meson,
strong decay rho -> pi pi and D/S ratio in the decay a_1 -> rho pi in
satisfactory agreement with experimental data.Comment: 8 pages, 1 figure
Topological susceptibility at zero and finite temperature in the Nambu-Jona-Lasinio model
We consider the three flavor Nambu-Jona-Lasinio model with the 't Hooft
interaction incorporating the U(1)_A anomaly. In order to set the coupling
strength of the 't Hooft term, we employ the topological susceptibility
instead of the eta' meson mass. The value for is taken from lattice
simulations. We also calculate at finite temperature within the model.
Comparing it with the lattice data, we extract information about the behavior
of the U(1)_A anomaly at finite temperature. We conclude that within the
present framework, the effective restoration of the U(1)_A symmetry does not
necessarily take place even at high temperature where the chiral symmetry is
restored.Comment: 9 pages, 14 figures, to be published in Phys.Rev.
Interactive Effects of Parentsâ Trait Verbal Aggressiveness and Situational Frustration on Parentsâ SelfâReported Anger
Examines the relationship between anger experienced by parents\u27 trait verbal aggressiveness and the frustrations, caused by the interaction with children. What was cited as an ordinary interaction between parents\u27 trait verbal aggressiveness and situational frustration; Process in which the examination was conducted; Exploration of a measure of trait verbal aggressiveness to parents; Discussion based on the results
Spatial structure of Mn-Mn acceptor pairs in GaAs
The local density of states of Mn-Mn pairs in GaAs is mapped with
cross-sectional scanning tunneling microscopy and compared with theoretical
calculations based on envelope-function and tight-binding models. These
measurements and calculations show that the crosslike shape of the Mn-acceptor
wavefunction in GaAs persists even at very short Mn-Mn spatial separations. The
resilience of the Mn-acceptor wave-function to high doping levels suggests that
ferromagnetism in GaMnAs is strongly influenced by impurity-band formation. The
envelope-function and tight-binding models predict similarly anisotropic
overlaps of the Mn wave-functions for Mn-Mn pairs. This anisotropy implies
differing Curie temperatures for Mn -doped layers grown on differently
oriented substrates.Comment: 4 pages, 4 figure
Interactive Effects of Parentsâ Trait Verbal Aggressiveness and Situational Frustration on Parentsâ SelfâReported Anger
Examines the relationship between anger experienced by parents\u27 trait verbal aggressiveness and the frustrations, caused by the interaction with children. What was cited as an ordinary interaction between parents\u27 trait verbal aggressiveness and situational frustration; Process in which the examination was conducted; Exploration of a measure of trait verbal aggressiveness to parents; Discussion based on the results
A Mean Field Approach To The Instanton-Induced Effect Close To The QCD Phase Transition
In the instanton models the chiral phase transition is driven by a transition
from random instanton-antiinstanton liquid and correlated
instanton-antiinstanton molecules. So far this phenomenon was studied by
numerical simulations, while we develop alternative semi-analytic approach. For
two massless quark flavors, both instantons and ``molecules" generate specific
4-fermion effective interactions. After those are derived, we determine the
temperature dependence of the thermodynamic quantities, the quark condensate
and the fraction of molecules using standard mean field method. Using
Bethe-Salpeter equation, we calculate T-dependence of mesonic correlation
functions.Comment: 26 pages, LaTeX, 6 postscript files of 6 figures in additio
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