1,029 research outputs found
Ab initio investigation of VOSeO3, a spin gap system with coupled spin dimers
Motivated by an early experimental study of VOSeO3, which suggested that it
is a quasi-2D system of weakly coupled spin dimers with a small spin gap, we
have investigated the electronic structure of this material via
density-functional calculations. These ab initio results indicate that the
system is better thought of as an alternating spin-1/2 chain with moderate
interchain interactions, an analog of (VO)2P2O7. The potential interest of this
system for studies in high magnetic field given the presumably small value of
the spin gap is emphasized.Comment: 4 pages, 5 figure
Bulk Viscous LRS Biachi-I Universe with variable and decaying
The present study deals with spatially homogeneous and totally anisotropic
locally rotationally symmetric (LRS) Bianchi type I cosmological model with
variable and in presence of imperfect fluid. To get the
deterministic model of Universe, we assume that the expansion in the
model is proportional to shear . This condition leads to , where ,\; are metric potential. The cosmological constant
is found to be decreasing function of time and it approaches a small
positive value at late time which is supported by recent Supernovae Ia (SN Ia)
observations. Also it is evident that the distance modulus curve of derived
model matches with observations perfectly.Comment: 11 pages, 4 figures and 1 table, Accepted for publication in
Astrophysics and Space Scienc
Experimental Investigation on the Deformation Response of Hybrid 3D Woven Composites
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97059/1/AIAA2012-1572.pd
Halogen-mediated exchange in the coupled-tetrahedra quantum spin systems Cu2Te2O5X2 (X=Br,Cl)
Motivated by recent discussion on possible quantum critical behavior in the
coupled Cu-tetrahedra system Cu2Te2O5Br2, we present a comparative ab initio
study of the electronic properties of Cu2Te2O5Br2 and the isostructural
Cu2Te2O5Cl2.
A detailed investigation of the copper-copper interaction pathes reveals that
the halogen-ions play an important role in the inter-tetrahedral couplings via
X_4-rings (X=Br, Cl).
We find that, contrary to initial indications, both systems show a similar
electronic behavior with long range exchange pathes mediated by the X_4-rings.Comment: 5 pages, 7 figure
Limits on the monopole magnetic field from measurements of the electric dipole moments of atoms, molecules and the neutron
A radial magnetic field can induce a time invariance violating electric
dipole moment (EDM) in quantum systems. The EDMs of the Tl, Cs, Xe and Hg atoms
and the neutron that are produced by such a field are estimated. The
contributions of such a field to the constants, of the T,P-odd
interactions and are also estimated for the TlF, HgF and YbF molecules (where
() is the electron (nuclear) spin and is the molecular
axis). The best limit on the contact monopole field can be obtained from the
measured value of the Tl EDM. The possibility of such a field being produced
from polarization of the vacuum of electrically charged magnetic monopoles
(dyons) by a Coulomb field is discussed, as well as the limit on these dyons.
An alternative mechanism involves chromomagnetic and chromoelectric fields in
QCD.Comment: Uses RevTex, 16 pages, 4 postscript figures. An explanation of why
there is no orbital contribution to the EDM has been added, and the
presentation has been improved in genera
The Planetary Nebula Luminosity Function at the Dawn of Gaia
The [O III] 5007 Planetary Nebula Luminosity Function (PNLF) is an excellent
extragalactic standard candle. In theory, the PNLF method should not work at
all, since the luminosities of the brightest planetary nebulae (PNe) should be
highly sensitive to the age of their host stellar population. Yet the method
appears robust, as it consistently produces < 10% distances to galaxies of all
Hubble types, from the earliest ellipticals to the latest-type spirals and
irregulars. It is therefore uniquely suited for cross-checking the results of
other techniques and finding small offsets between the Population I and
Population II distance ladders. We review the calibration of the method and
show that the zero points provided by Cepheids and the Tip of the Red Giant
Branch are in excellent agreement. We then compare the results of the PNLF with
those from Surface Brightness Fluctuation measurements, and show that, although
both techniques agree in a relative sense, the latter method yields distances
that are ~15% larger than those from the PNLF. We trace this discrepancy back
to the calibration galaxies and argue that, due to a small systematic error
associated with internal reddening, the true distance scale likely falls
between the extremes of the two methods. We also demonstrate how PNLF
measurements in the early-type galaxies that have hosted Type Ia supernovae can
help calibrate the SN Ia maximum magnitude-rate of decline relation. Finally,
we discuss how the results from space missions such as Kepler and Gaia can help
our understanding of the PNLF phenomenon and improve our knowledge of the
physics of local planetary nebulae.Comment: 12 pages, invited review at the conference "The Fundamental Cosmic
Distance Scale: State of the Art and Gaia Perspective", to appear in
Astrophysics and Space Scienc
G\"{o}del black hole, closed timelike horizon, and the study of particle emissions
We show that a particle, with positive orbital angular momentum, following an
outgoing null/timelike geodesic, shall never reach the closed timelike horizon
(CTH) present in the -dimensional rotating G\"{o}del black hole
space-time. Therefore a large part of this space-time remains inaccessible to a
large class of geodesic observers, depending on the conserved quantities
associated with them. We discuss how this fact and the existence of the closed
timelike curves present in the asymptotic region make the quantum field
theoretic study of the Hawking radiation, where the asymptotic observer states
are a pre-requisite, unclear. However, the semiclassical approach provides an
alternative to verify the Smarr formula derived recently for the rotating
G\"{o}del black hole. We present a systematic analysis of particle emissions,
specifically for scalars, charged Dirac spinors and vectors, from this black
hole via the semiclassical complex path method.Comment: 13 pages; minor changes, references adde
Resonant charge and spin transport in a t-stub coupled to a superconductor
We study transport through a single channel t-stub geometry strongly coupled
to a superconducting reservoir. In contrast to the standard stub geometry which
has both transmission resonances and anti-resonances in the coherent limit, we
find that due to the proximity effect, this geometry shows neither a T=1
resonance (T is the transmission probability for electrons incident on the
t-stub) nor a T=0 anti-resonance as we vary the energy of the incident
electron. Instead, we find that there is only one resonant value at T=1/4,
where charge transport vanishes while the spin transport is perfect.Comment: This is the published versio
Bianchi Type V Viscous Fluid Cosmological Models in Presence of Decaying Vacuum Energy
Bianchi type V viscous fluid cosmological model for barotropic fluid
distribution with varying cosmological term is investigated. We have
examined a cosmological scenario proposing a variation law for Hubble parameter
in the background of homogeneous, anisotropic Bianchi type V space-time.
The model isotropizes asymptotically and the presence of shear viscosity
accelerates the isotropization. The model describes a unified expansion history
of the universe indicating initial decelerating expansion and late time
accelerating phase. Cosmological consequences of the model are also discussed.Comment: 10 pages, 3 figure
Cross Section Measurements of Charged Pion Photoproduction in Hydrogen and Deuterium from 1.1 to 5.5 GeV
The differential cross section for the gamma +n --> pi- + p and the gamma + p
--> pi+ n processes were measured at Jefferson Lab. The photon energies ranged
from 1.1 to 5.5 GeV, corresponding to center-of-mass energies from 1.7 to 3.4
GeV. The pion center-of-mass angles varied from 50 degree to 110 degree. The
pi- and pi+ photoproduction data both exhibit a global scaling behavior at high
energies and high transverse momenta, consistent with the constituent counting
rule prediction and the existing pi+ data. The data suggest possible
substructure of the scaling behavior, which might be oscillations around the
scaling value. The data show an enhancement in the scaled cross section at
center-of-mass energy near 2.2 GeV. The differential cross section ratios at
high energies and high transverse momenta can be described by calculations
based on one-hard-gluon-exchange diagrams.Comment: 18 pages, 19 figure
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