19,810 research outputs found
Exact renormalization in quantum spin chains
We introduce a real-space exact renormalization group method to find exactly
solvable quantum spin chains and their ground states. This method allows us to
provide a complete list for exact solutions within SU(2) symmetric quantum spin
chains with and nearest-neighbor interactions, as well as examples
with S=5. We obtain two classes of solutions: One of them converges to the
fixed points of renormalization group and the ground states are matrix product
states. Another one does not have renormalization fixed points and the ground
states are partially ferromagnetic states.Comment: 8 pages, 5 figures, references added, published versio
Inclusive and Direct Photons in S + Au Central Collisions at 200A GeV/c
A hadron and string cascade model, JPCIAE, which is based on LUND string
model, PYTHIA event generator especially, is used to study both inclusive
photon production and direct photon production in 200A GeV S + Au central
collisions. The model takes into account the photon production from the
partonic QCD scattering process, the hadronic final-state interaction, and the
hadronic decay and deals with them consistently. The results of JPCIAE model
reproduce successfully both the WA93 data of low p_T inclusive photon
distribution and the WA80 data of transverse momentum dependent upper limit of
direct photon. The photon production from different decay channels is
investigated for both direct and inclusive photons. We have discussed the
effects of the partonic QCD scattering and the hadronic final-state interaction
on direct photon production as well.Comment: 6 pages with 5 figure
Density-functional theory for 1D harmonically trapped Bose-Fermi mixture
We present a density-functional theory for the one dimensional harmonically
trapped Bose-Fermi mixture with repulsive contact interactions. The ground
state density distribution of each component is obtained by solving the
Kohn-Sham equations numerically based on the Local Density Approximation and
the exact solution for the homogeneous system given by Bethe ansatz method. It
is shown that for strong enough interaction, a considerable amount of fermions
are repelled out of the central region of the trap, exhibiting partial phase
separation of Bose and Fermi components. Oscillations emerge in the Bose
density curves reflecting the strong correlation with Fermions. For infinite
strong interaction, the ground state energy of the mixture and the total
density are consistent with the scenario that all atoms in the mixture are
fully fermionized.Comment: 10 pages, 8 figure
The Measure-theoretic Identity Underlying Transient Fluctuation Theorems
We prove a measure-theoretic identity that underlies all transient
fluctuation theorems (TFTs) for entropy production and dissipated work in
inhomogeneous deterministic and stochastic processes, including those of Evans
and Searles, Crooks, and Seifert. The identity is used to deduce a tautological
physical interpretation of TFTs in terms of the arrow of time, and its
generality reveals that the self-inverse nature of the various trajectory and
process transformations historically relied upon to prove TFTs, while necessary
for these theorems from a physical standpoint, is not necessary from a
mathematical one. The moment generating functions of thermodynamic variables
appearing in the identity are shown to converge in general only in a vertical
strip in the complex plane, with the consequence that a TFT that holds over
arbitrary timescales may fail to give rise to an asymptotic fluctuation theorem
for any possible speed of the corresponding large deviation principle. The case
of strongly biased birth-death chains is presented to illustrate this
phenomenon. We also discuss insights obtained from our measure-theoretic
formalism into the results of Saha et. al. on the breakdown of TFTs for driven
Brownian particles
Numerical Simulation of Magnetic Interactions in Polycrystalline YFeO3
The magnetic behavior of polycrystalline yttrium orthoferrite was studied
from the experimental and theoretical points of view. Magnetization
measurements up to 170 kOe were carried out on a single-phase YFeO3 sample
synthesized from heterobimetallic alkoxides. The complex interplay between
weak-ferromagnetic and antiferromagnetic interactions, observed in the
experimental M(H) curves, was successfully simulated by locally minimizing the
magnetic energy of two interacting Fe sublattices. The resulting values of
exchange field (H_E = 5590 kOe), anisotropy field (H_A = 0.5 kOe) and
Dzyaloshinsky-Moriya antisymmetric field (H_D = 149 kOe) are in good agreement
with previous reports on this system.Comment: 26 pages, 9 figure
PPAK Wide-field Integral Field Spectroscopy of NGC 628: I. The largest spectroscopic mosaic on a single galaxy
We present a wide-field IFS survey on the nearby face-on Sbc galaxy NGC 628,
comprising 11094 individual spectra, covering a nearly circular field-of-view
of ~6 arcmin in diameter, with a sampling of ~2.7 arcsec per spectrum in the
optical wavelength range (3700--7000 AA). This galaxy is part of the PPAK IFS
Nearby Galaxies Survey, (PINGS, Rosales-Ortega et al. 2009). To our knowledge,
this is the widest spectroscopic survey ever made in a single nearby galaxy. A
detailed flux calibration was applied, granting a spectrophotometric accuracy
of \,0.2 mag.
The age of the stellar populations shows a negative gradient from the inner
(older) to the outer (younger) regions. We found an inversion of this gradient
in the central ~1 kpc region, where a somewhat younger stellar population is
present within a ring at this radius. This structure is associated with a
circumnuclear star-forming region at ~ 500 pc, also found in similar spiral
galaxies. From the study of the integrated and spatially resolved ionized gas
we found a moderate SFR of ~ 2.4 Msun yr. The oxygen abundance shows a a
clear gradient of higher metallicity values from the inner part to the outer
part of the galaxy, with a mean value of 12~+~log(O/H) ~ 8.7. At some specific
regions of the galaxy, the spatially resolved distribution of the physical
properties show some level of structure, suggesting real point-to-point
variations within an individual \hh region. Our results are consistent with an
inside-out growth scheme, with stronger star formation at the outer regions,
and with evolved stellar populations in the inner ones.Comment: 31 pages, 22 Figuras, Accepted for Publishing in MNRAS (corrected
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