3,005 research outputs found
Lattice results for the decay constant of heavy-light vector mesons
We compute the leptonic decay constants of heavy-light vector mesons in the
quenched approximation. The reliability of lattice computations for heavy
quarks is checked by comparing the ratio of vector to pseudoscalar decay
constant with the prediction of Heavy Quark Effective Theory in the limit of
infinitely heavy quark mass. Good agreement is found. We then calculate the
decay constant ratio for B mesons: .
We also quote quenched MeV.Comment: 11 pages, 3 postscript figs., revtex; two references adde
Granulocyte Macrophage Colony-Stimulating Factor: A New Putative Therapeutic Target in Multiple Sclerosis
Experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis, can be induced by immunization with a number of myelin antigens. In particular, myelin oligodendrocyte glycoprotein, a central nervous system (CNS)-specific antigen expressed on the myelin surface, is able to induce a paralytic MS-like disease with extensive CNS inflammation and demyelination in several strains of animals. Although not well understood, the egress of immune cells into the CNS in EAE is governed by a complex interplay between pro and antiinflammatory cytokines and chemokines. The hematopoietic growth factor, granulocyte macrophage colony-stimulating factor (GM-CSF), is considered to play a central role in maintaining chronic inflammation. The present study was designed to investigate the previously unexplored role of GM-CSF in autoimmune-mediated demyelination. GM-CSF−/− mice are resistant to EAE, display decreased antigen-specific proliferation of splenocytes, and fail to sustain immune cell infiltrates in the CNS, thus revealing key activities for GM-CSF in the development of inflammatory demyelinating lesions and control of migration and/or proliferation of leukocytes within the CNS. These results hold implications for the pathogenesis of inflammatory and demyelinating diseases and may provide the basis for more effective therapies for inflammatory diseases, and more specifically for multiple sclerosis
't Hooft vertices, partial quenching, and rooted staggered QCD
We discuss the properties of 't Hooft vertices in partially quenched and
rooted versions of QCD in the continuum. These theories have a physical
subspace, equivalent to ordinary QCD, that is contained within a larger space
that includes many unphysical correlation functions. We find that the 't Hooft
vertices in the physical subspace have the expected form, despite the presence
of unphysical 't Hooft vertices appearing in correlation functions that have an
excess of valence quarks (or ghost quarks). We resolve an apparent paradox that
arises when one uses rooted staggered fermions to study one-flavor QCD, by
showing how, in partially quenched theories, it is possible to have spontaneous
symmetry breaking of a non-anomalous symmetry in finite volume. Using these
results, we demonstrate that arguments recently given by Creutz--claiming to
disprove the validity of rooted staggered QCD--are incorrect. In particular,
the unphysical 't Hooft vertices do not present an obstacle to the recovery of
taste symmetry in the continuum limit.Comment: 19 pages, revtex, shortened version to appear in Phys. Rev.
Baryon Density Correlations in High Temperature Hadronic Matter
As part of an ongoing effort to characterize the high temperature phase of
QCD, in a numerical simulation using the staggered fermion scheme, we measure
the quark baryon density in the vicinity of a fixed test quark at high
temperature and compare it with similar measurements at low temperature and at
the crossover temperature. We find an extremely weak correlation at high
temperature, suggesting that small color singlet clusters are unimportant in
the thermal ensemble. We also find that at the total induced
quark number shows a surprisingly large component attributable to baryonic
screening. A companion simulation of a simple flux tube model produces similar
results and also suggests a plausible phenomenological scenario: As the
crossover temperature is approached from below, baryonic states proliferate.
Above the crossover temperature the mean size of color singlet clusters grows
explosively, resulting in an effective electrostatic deconfinement.Comment: 26 pp, RevTeX, 12 postscript figures, combined in a single shell
archive file. (Also available in 13 postscript files by anonymous ftp from
einstein.physics.utah.edu, /pub/milc/paper.sh.Z.
The QCD spectrum with three quark flavors
We present results from a lattice hadron spectrum calculation using three
flavors of dynamical quarks - two light and one strange, and quenched
simulations for comparison. These simulations were done using a one-loop
Symanzik improved gauge action and an improved Kogut-Susskind quark action. The
lattice spacings, and hence also the physical volumes, were tuned to be the
same in all the runs to better expose differences due to flavor number. Lattice
spacings were tuned using the static quark potential, so as a byproduct we
obtain updated results for the effect of sea quarks on the static quark
potential. We find indications that the full QCD meson spectrum is in better
agreement with experiment than the quenched spectrum. For the 0++ (a0) meson we
see a coupling to two pseudoscalar mesons, or a meson decay on the lattice.Comment: 38 pages, 20 figures, uses epsf. 5/29/01 revision responds to
referee's Comments, changes pion fits and tables, and corrects Fig. 10 and
some minor error
Scaling tests of the improved Kogut-Susskind quark action
Improved lattice actions for Kogut-Susskind quarks have been shown to improve
rotational symmetry and flavor symmetry. In this work we find improved scaling
behavior of the rho and nucleon masses expressed in units of a length scale
obtained from the static quark potential, and better behavior of the Dirac
operator in instanton backgrounds.Comment: 4 pages, 4 figures, Revte
One-Flavour Hybrid Monte Carlo with Wilson Fermions
The Wilson fermion determinant can be written as product of the determinants
of two hermitian positive definite matrices. This formulation allows to
simulate non-degenerate quark flavors by means of the hybrid Monte Carlo
algorithm. A major numerical difficulty is the occurrence of nested inversions.
We construct a Uzawa iteration scheme which treats the nested system within one
iterative process.Comment: 11 pages, to appear in proceedings of the workshop "Numerical
Challenges in Lattice QCD", Springer Verla
Topological susceptibility with the improved Asqtad action
As a test of the chiral properties of the improved Asqtad (staggered fermion)
action, we have been measuring the topological susceptibility as a function of
quark masses for 2 + 1 dynamical flavors. We report preliminary results, which
show reasonable agreement with leading order chiral perturbation theory for
lattice spacing less than 0.1 fm. The total topological charge, however, shows
strong persistence over Monte Carlo time.Comment: Lattice2002(algor
A calculation of the Lepage-Mackenzie scale for the lattice axial and vector currents
We calculate the perturbative scales (q*) for the axial and vector currents
for the Wilson action, with and without tadpole improvement, using Lepage and
Mackenzie's formalism. The scale for the pseudoscalar density (times the mass)
is computed as well. Contrary to naive expectation, tadpole improvement reduces
q* by only a small amount for the operators we consider. We also discuss the
use of a nonperturbative coupling to calculate the perturbative scale.Comment: 13 pages. One postscript figur
Optimizing interfacial features to regulate neural progenitor cells using polyelectrolyte multilayers and brain derived neurotrophic factor
The development of biomaterials with controllable interfacial features which have the capability to instruct cellular behavior are required to produce functional scaffolds for the treatment of spinal cord injury (SCI). Here, poly-ɛ-caprolactone surfaces were biofunctionalized via layer-by-layer (LbL) deposition. The polyelectrolytes employed in this LbL technique were heparin and poly-L-lysine (PLL), the latter being chosen to improve cell adhesion and the subsequent cellular function of in vitrocultured neural progenitor cells. Material characterization results confirmed the deposition of well structured multilayers. Cell culture studies revealed significant differences in the cellular response to these adhesive/nonadhesive (PLL/heparin) polyelectrolyte multilayer (PEM)surfaces, with neurite outgrowth being significantly promoted on the PLL terminating layers. In addition, brain derived neurotrophic factor (BDNF) was adsorbed onto the LbL surfaces. This combined chemical and biological effect was then characterized in terms of neurite length along with the full length/truncated isoform 1 tyrosine kinase receptor (TrkB-FL/TrkB-T1) and growth associated protein-43 mRNA levels. Here, the authors report the differential effect of adsorbed and soluble BDNF of different concentrations. Adsorbed BDNF promoted neurite outgrowth and led to elevated, sustained TrkB mRNA levels. These findings highlight the potential of PEM biofunctionalized surfaces with integrated chemical and neurotrophin supportive cues to overcome SCI inhibitory environments and to promote regeneration
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