4,727 research outputs found
Integrability in Theories with Local U(1) Gauge Symmetry
Using a recently developed method, based on a generalization of the zero
curvature representation of Zakharov and Shabat, we study the integrability
structure in the Abelian Higgs model. It is shown that the model contains
integrable sectors, where integrability is understood as the existence of
infinitely many conserved currents. In particular, a gauge invariant
description of the weak and strong integrable sectors is provided. The
pertinent integrability conditions are given by a U(1) generalization of the
standard strong and weak constraints for models with two dimensional target
space. The Bogomolny sector is discussed, as well, and we find that each
Bogomolny configuration supports infinitely many conserved currents. Finally,
other models with U(1) gauge symmetry are investigated.Comment: corrected typos, version accepted in J. Phys.
VLTI/AMBER spectro-interferometry of the late-type supergiants V766 Cen (=HR 5171 A), sigma Oph, BM Sco, and HD 206859
We add four warmer late-type supergiants to our previous
spectro-interferometric studies of red giants and supergiants.
V766 Cen (=HR 5171 A) is found to be a high-luminosity log(L/L_sun)=5.8+-0.4
source of Teff 4290+-760 K and radius 1490+-540 Rsun located close to both the
Hayashi and Eddington limits; this source is consistent with a 40 Msun
evolutionary track without rotation and current mass 27-36 Msun. It exhibits
NaI in emission arising from a shell of radius 1.5 Rphot and a photocenter
displacement of about 0.1 Rphot. V766 Cen shows strong extended molecular (CO)
layers and a dusty circumstellar background component. This suggest an
optically thick pseudo-photosphere at about 1.5 Rphot at the onset of the wind.
V766 Cen is a red supergiant located close to the Hayashi limit instead of a
yellow hypergiant already evolving back toward warmer Teff as previously
discussed.
The stars sigma Oph, BM Sco, and HD 206859 are found to have lower
luminosities of about log(L/Lsun)=3.4-3.5 and Teff of 3900-5300 K,
corresponding to 5-9 Msun tracks. They do not show extended molecular layers as
observed for higher luminosity red supergiants of our sample. BM Sco shows an
unusually strong contribution by an over-resolved circumstellar dust component.
These stars are more likely high-mass red giants instead of red supergiants.
This leaves us with an unsampled locus in the HR diagram corresponding to
luminosities log(L/Lsun)~3.8-4.8 or masses 10-13 Msun, possibly corresponding
to the mass region where stars explode as type II-P supernovae during the RSG
stage.
Our previously found relation of increasing strength of extended molecular
layers with increasing luminosities is now confirmed to extend to double our
previous luminosities and up to the Eddington limit. This might further point
to steadily increasing radiative winds with increasing luminosity.
[Abridged]Comment: 16 pages, 14 figures, accepted for publication in Astronomy and
Astrophysics (A&A
Opening the Rome-Southampton window for operator mixing matrices
We show that the running of operators which mix under renormalization can be
computed fully non-perturbatively as a product of continuum step scaling
matrices. These step scaling matrices are obtained by taking the "ratio" of Z
matrices computed at different energies in an RI-MOM type scheme for which
twisted boundary conditions are an essential ingredient. Our method allows us
to relax the bounds of the Rome-Southampton window. We also explain why such a
method is important in view of the light quark physics program of the RBC-UKQCD
collaborations. To illustrate our method, using n_f=2+1 domain-wall fermions,
we compute the non-perturbative running matrix of four-quark operators needed
in K->pipi decay and neutral kaon mixing. Our results are then compared to
perturbation theory.Comment: 8 pages, 7 figures. v2: PRD version, minor changes and few references
adde
Expansion around half-integer values, binomial sums and inverse binomial sums
I consider the expansion of transcendental functions in a small parameter
around rational numbers. This includes in particular the expansion around
half-integer values. I present algorithms which are suitable for an
implementation within a symbolic computer algebra system. The method is an
extension of the technique of nested sums. The algorithms allow in addition the
evaluation of binomial sums, inverse binomial sums and generalizations thereof.Comment: 21 page
Low--Temperature Series for Renormalized Operators: the Ferromagnetic Square--Lattice Ising Model.
A method for computing low--temperature series for renormalized operators in
the two--dimensional Ising model is proposed. These series are applied to the
study of the properties of the truncated renormalized Hamiltonians when we
start at very low temperature and zero field. The truncated Hamiltonians for
majority rule, Kadanoff transformation and decimation for blocks
depend on the how we approach the first--order phase--transition line. These
Renormalization Group transformations are multi--valued and discontinuous at
this first--order transition line when restricted to some finite--dimensional
interaction space.Comment: 14 pages, uuencode tar-compressed ps file. Version accepted for
publication in J. Stat. Phys. Many changes with respect to the first version
A Rigourous Treatment of the Lattice Renormalization Problem of F_B
The -meson decay constant can be measured on the lattice using a
expansion. To relate the physical quantity to Monte Carlo data one has to know
the renormalization coefficient, , between the lattice operators and their
continuum counterparts. We come back to this computation to resolve
discrepancies found in previous calculations. We define and discuss in detail
the renormalization procedure that allows the (perturbative) computation of
. Comparing the one-loop calculations in the effective Lagrangian approach
with the direct two-loop calculation of the two-point -meson correlator in
the limit of large -quark mass, we prove that the two schemes give
consistent results to order . We show that there is, however, a
renormalization prescription ambiguity that can have sizeable numerical
consequences. This ambiguity can be resolved in the framework of an
improved calculation, and we describe the correct prescription in that case.
Finally we give the numerical values of that correspond to the different
types of lattice approximations discussed in the paper.Comment: 27 pages, 2 figures (Plain TeX, figures in an appended postscript
file
Biomimetic Ca-P coatings Incorporating bisphosphonates produced on starch-based degradable biomaterials
In this study, sodium clodronate, a well-known therapeutic agent from the family
of bisphosphonates (BPs), is incorporated in a biomimetic calcium phosphate (CaP) coating,
previously formed on the surface of a starch-based biomaterial by a sodium silicate
methodology, as a strategy to develop a site-specific drug delivery system for bone tissue
regeneration applications. The effects on the resulting CaP coatings were evaluated in terms of
morphology, chemistry, and structure. The dissolution of Ca and P from the coating and the
release profiles of sodium clodronate was also assessed. As a preliminary approach, this first
study also aimed at evaluating the effects of this BP on the viability of a human osteoblastic
cell line since there is still little information available on the interaction between BPs and this
type of cells. Sodium clodronate was successfully incorporated, at different doses, in the
structure of a biomimetic CaP layer previously formed by a sodium silicate process. This
type of BPs had a stimulatory effect on osteoblastic activity, particularly at the specific
concentration of 0.32 mg/mL. It is foreseen that these coatings can, for instances, be
produced on the surface of degradable polymers and then used for regulating the
equilibrium on osteoblastic/osteoclastic activity, leading to a controlled regenerative effect
at the interface between the biomaterial and bone
Anomalous dimension of the gluon operator in pure Yang-Mills theory
We present new one loop calculations that confirm the theorems of Joglekar
and Lee on the renormalization of composite operators. We do this by
considering physical matrix elements with the operators inserted at non-zero
momentum. The resulting IR singularities are regulated dimensionally. We show
that the physical matrix element of the BRST exact gauge variant operator which
appears in the energy- momentum tensor is zero. We then show that the physical
matrix elements of the classical energy-momentum tensor and the gauge invariant
twist two gluon operator are independent of the gauge fixing parameter. A
Sudakov factor appears in the latter cases. The universality of this factor and
the UV finiteness of the energy-momentum tensor provide another method of
finding the anomalous dimension of the gluon operator. We conjecture that this
method applies to higher loops and takes full advantage of the triangularity of
the mixing matrix.Comment: submitted to Phys. Rev. D, 18 pages LaTEX uses psfig and revtex
macros, figures appended as uuencoded Postscript file (complete Postsript
version including figures available via anonymous ftp from
ftp://max.physics.sunysb.edu/preprints/harris/paper.ps.Z), ITP-SB-94-3
Modelling Li+ Ion Battery Electrode Properties
We formulated two detailed models for an electrolytic cell with particulate electrodes based on a lithium atom concentration dependent Butler-Volmer condition at the interface between electrode particles and the electrolyte. The first was based on a dilute-ion assumption for the electrolyte, while the second assumed that Li ions are present in excess.
For the first, we used the method of multiple scales to homogenize this model over the microstructure, formed by the small lithium particles in the electrodes.
For the second, we gave rigorous bounds for the effective electrochemical conductivity for a linearized case.
We expect similar results and bounds for the "full nonlinear problem" because variational results are generally not adversely affected by a sinh term.
Finally we used the asymptotic methods, based on parameters estimated from the literature, to attain a greatly simplified one-dimensional version of the original homogenized model. This simplified model accounts for the fact that diffusion of lithium atoms within individual electrode particles is relatively much faster than that of lithium ions across the whole cell so that lithium ion diffusion is what limits the performance of the battery. However, since most of the potential drop occurs across the Debye layers surrounding each electrode particle, lithium ion diffusion only significantly affects cell performance if there is more or less complete depletion of lithium ions in some region of the electrolyte which causes a break in the current flowing across the cell. This causes catastrophic failure. Providing such failure does not occur the potential drop across the cell is determined by the concentration of lithium atoms in the electrode particles. Within each electrode lithium atom concentration is, to leading order, a function of time only and not of position within the electrode. The depletion of electrode lithium atom concentration is directly proportional to the current being drawn off the cell. This leads one to expect that the potential of the cell gradually drops as current is drawn of it.
We would like to emphasize that all the homogenization methods employed in this work give a systematic approach for investigating the effect that changes in the microstructure have on the behaviour of the battery. However, due to lack of time, we have not used this method to investigate particular particle geometries
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