52,043 research outputs found
Improving Stochastic Estimator Techniques for Disconnected Diagrams
Disconnected diagrams are expected to be sensitive to the inclusion of
dynamical fermions. We present a feasibility study for the observation of such
effects on the nucleonic matrix elements of the axial vector current, using
SESAM full QCD vacuum configurations with Wilson fermions on
lattices, at . Starting from the standard methods developed by the
Kentucky and Tsukuba groups, we investigate the improvement from various
refinements thereof.Comment: One author added. Contribution to Lattice 1997, 3 pages LaTex, to
appear in Nucl. Phys. B (Proc. Suppl.
Spin liquid close to a quantum critical point in NaIrO
NaIrO is a candidate material for a 3-dimensional quantum
spin-liquid on the hyperkagome lattice. We present thermodynamic measurements
of heat capacity and thermal conductivity on high quality
polycrystalline samples of NaIrO down to mK and mK,
respectively. Absence of long-range magnetic order down to mK strongly
supports claims of a spin-liquid ground state. The constant magnetic
susceptibility below K and the presence of a small but
finite linear- term in suggest the presence of gapless spin
excitations. Additionally, the magnetic Grneisen ratio shows a
divergence as K and a scaling behavior which clearly
demonstrates that NaIrO is situated close to a zero-field QCP.Comment: 5 pages, 4 figures, PRB rapid, in pres
The structure of parafermion vertex operator algebras
It is proved that the parafermion vertex operator algebra associated to the
irreducible highest weight module for the affine Kac-Moody algebra A_1^{(1)} of
level k coincides with a certain W-algebra. In particular, a set of generators
for the parafermion vertex operator algebra is determined.Comment: 12 page
Spatial structures in a simple model of population dynamics for parasite-host interactions
Spatial patterning can be crucially important for understanding the behavior
of interacting populations. Here we investigate a simple model of parasite and
host populations in which parasites are random walkers that must come into
contact with a host in order to reproduce. We focus on the spatial arrangement
of parasites around a single host, and we derive using analytics and numerical
simulations the necessary conditions placed on the parasite fecundity and
lifetime for the populations long-term survival. We also show that the parasite
population can be pushed to extinction by a large drift velocity, but,
counterintuitively, a small drift velocity generally increases the parasite
population.Comment: 6 pages, 6 figure
Bulk-fragment and tube-like structures of AuN (N=2-26)
Using the relativistic all-electron density-functional calculations on the
AuN (N=2-26) in the generalized gradient approximation, combined with the
guided simulated annealing, we have found that the two- to three-dimensional
structural transition for AuN occurs between N=13 and 15, and the AuN (16<= N
<=25) prefer also the pyramid-based bulk fragment structures in addition to the
Au20. More importantly, the tubelike structures are found to be the most stable
for Au24 and Au26, offering another powerful structure competitor with other
isomers, e.g., amorphous, bulk fragment, and gold fullerene. The mechanism to
cause these unusual AuN may be attributed to the stronger s-d hybridization and
the d-d interaction enhanced by the relativistic effects.Comment: 12 pages and 3 figure
Multipole polarizability of a graded spherical particle
We have studied the multipole polarizability of a graded spherical particle
in a nonuniform electric field, in which the conductivity can vary radially
inside the particle. The main objective of this work is to access the effects
of multipole interactions at small interparticle separations, which can be
important in non-dilute suspensions of functionally graded materials. The
nonuniform electric field arises either from that applied on the particle or
from the local field of all other particles. We developed a differential
effective multipole moment approximation (DEMMA) to compute the multipole
moment of a graded spherical particle in a nonuniform external field. Moreover,
we compare the DEMMA results with the exact results of the power-law graded
profile and the agreement is excellent. The extension to anisotropic DEMMA will
be studied in an Appendix.Comment: LaTeX format, 2 eps figures, submitted for publication
Oriented gap opening in the magnetically ordered state of Iron-pnicitides: an impact of intrinsic unit cell doubling on the square lattice by atoms
We show that the complicated band reconstruction near Fermi surfaces in the
magnetically ordered state of iron-pnictides observed by angle-resolved
photoemission spectroscopies (ARPES) can be understood in a meanfield level if
the \emph{intrinsic unit cell doubling} due to As atoms is properly considered
as shown in the recently constructed S microscopic effective model. The
(0,) or (,0) col-linear antiferromagnetic (C-AFM) order does not open
gaps between two points at Fermi surfaces linked by the ordered wave vector but
forces a band reconstruction involving four points in unfolded Brillouin zone
(BZ) and gives rise to small pockets or hot spots. The S symmetry naturally
chooses a staggered orbital order over a ferro-orbital order to coexist with
the C-AFM order. These results strongly suggest that the kinematics based on
the S symmetry captures the essential low energy physics of iron-based
superconductors.Comment: 5 figures, 5 page
The Third Law of Quantum Thermodynamics in the Presence of Anomalous Couplings
The quantum thermodynamic functions of a harmonic oscillator coupled to a
heat bath through velocity-dependent coupling are obtained analytically. It is
shown that both the free energy and the entropy decay fast with the temperature
in relation to that of the usual coupling from. This implies that the
velocity-dependent coupling helps to ensure the third law of thermodynamics.Comment: 4 pages, 3 figures, 22 conference
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