16,724 research outputs found
Ground States for Exponential Random Graphs
We propose a perturbative method to estimate the normalization constant in
exponential random graph models as the weighting parameters approach infinity.
As an application, we give evidence of discontinuity in natural parametrization
along the critical directions of the edge-triangle model.Comment: 12 pages, 3 figures, 1 tabl
Spontaneous current generation in the gapless 2SC phase
It is found that, except chromomagnetic instability, the gapless 2SC phase
also exhibits a paramagnetic response to the perturbation of an external color
neutral baryon current. The spontaneously generated baryon current driven by
the mismatch is equivalent to the one-plane wave LOFF state. We describe the
2SC phase in the nonlinear realization framework, and show that each
instability indicates the spontaneous generation of the corresponding pseudo
Nambu-Golstone current. We show this Nambu-Goldstone currents generation state
covers the gluon phase as well as the one-plane wave LOFF state. We further
point out that, when charge neutrality condition is required, there exists a
narrow unstable LOFF (Us-LOFF) window, where not only off-diagonal gluons but
the diagonal 8-th gluon cannot avoid the magnetic instability. We discuss that
the diagonal magnetic instability in this Us-LOFF window cannot be cured by
off-diagonal gluon condensate in color superconducting phase, and it will also
show up in some constrained Abelian asymmetric superfluid/superconducting
system.Comment: 8 pages, no figure, final version to appear in PR
An Analytic Solution of Hydrodynamic Equations with Source Terms in Heavy Ion Collisions
The energy and baryon densities in heavy ion collisions are estimated by
analytically solving a 1+1 dimensional hydrodynamical model with source terms.
Particularly, a competition between the energy and baryon sources and the
expansion of the system is discussed in detail.Comment: LaTeX2e, 7 pages, 4 postscript figures, submitted to Int. J. Mod.
Phys.
Measurement of Photon Statistics with Live Photoreceptor Cells
We analyzed the electrophysiological response of an isolated rod
photoreceptor of Xenopus laevis under stimulation by coherent and
pseudo-thermal light sources. Using the suction electrode technique for single
cell recordings and a fiber optics setup for light delivery allowed
measurements of the major statistical characteristics of the rod response. The
results indicate differences in average responses of rod cells to coherent and
pseudo-thermal light of the same intensity and also differences in
signal-to-noise ratios and second order intensity correlation functions. These
findings should be relevant for interdisciplinary studies seeking applications
of quantum optics in biology.Comment: 6 pages, 7 figure
On Size and Shape of the Average Meson Fields in the Semibosonized Nambu & Jona-Lasinio Model
We consider a two-flavor Nambu \& Jona-Lasinio model in Hartree approximation
involving scalar-isoscalar and pseudoscalar-isovector quark-quark interactions.
Average meson fields are defined by minimizing the effective Euklidean action.
The fermionic part of the action, which contains the full Dirac sea, is
regularized within Schwinger's proper-time scheme. The meson fields are
restricted to the chiral circle and to hedgehog configurations. The only
parameter of the model is the constituent quark mass which simultaneously
controls the regularization. We evaluate meson and quark fields
self-consistently in dependence on the constituent quark mass. It is shown that
the self-consistent fields do practically not depend on the constituent quark
mass. This allows us to define a properly parameterized reference field which
for physically relevant constituent masses can be used as a good approximation
to the exactly calculated one. The reference field is chosen to have correct
behaviour for small and large radii. To test the agreement between
self-consistent and reference fields we calculate several observables like
nucleon energy, mean square radius, axial-vector constant and delta-nucleon
mass splitting in dependence on the constituent quark mass. The agreement is
found to be very well. Figures available on request.Comment: 12 pages (LATEX), 3 figures available on request, report FZR 93-1
Screening masses in neutral two-flavor color superconductor
The Debye and Meissner screening masses of the gluons and the photon in
neutral and beta-equilibrated dense two-flavor quark matter are calculated. The
results are presented in a general form that can be used in gapped as well as
gapless color superconducting phases. The results for the magnetic screening
masses indicate that the system develops a chromomagnetic instability. Possible
consequences of the instability are discussed.Comment: 29 pages, 2 figures. Minor corrections. References added. Version
accepted to Phys. Rev.
Regulation of Membrane Targeting of the G Protein-coupled Receptor Kinase 2 by Protein Kinase A and Its Anchoring Protein AKAP79
The beta 2 adrenergic receptor (beta 2AR) undergoes desensitization by a process involving its phosphorylation by both protein kinase A (PKA) and G protein-coupled receptor kinases (GRKs). The protein kinase A-anchoring protein AKAP79 influences beta 2AR phosphorylation by complexing PKA with the receptor at the membrane. Here we show that AKAP79 also regulates the ability of GRK2 to phosphorylate agonist-occupied receptors. In human embryonic kidney 293 cells, overexpression of AKAP79 enhances agonist-induced phosphorylation of both the beta 2AR and a mutant of the receptor that cannot be phosphorylated by PKA (beta 2AR/PKA-). Mutants of AKAP79 that do not bind PKA or target to the beta 2AR markedly inhibit phosphorylation of beta 2AR/PKA-. We show that PKA directly phosphorylates GRK2 on serine 685. This modification increases Gbeta gamma subunit binding to GRK2 and thus enhances the ability of the kinase to translocate to the membrane and phosphorylate the receptor. Abrogation of the phosphorylation of serine 685 on GRK2 by mutagenesis (S685A) or by expression of a dominant negative AKAP79 mutant reduces GRK2-mediated translocation to beta 2AR and phosphorylation of agonist-occupied beta 2AR, thus reducing subsequent receptor internalization. Agonist-stimulated PKA-mediated phosphorylation of GRK2 may represent a mechanism for enhancing receptor phosphorylation and desensitization
Walker Design for Kinetic Assessment of Upper Extremity Joint Demands in Children with Osteogenesis Imperfecta
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