28,285 research outputs found
Lax matrices for Yang-Baxter maps
It is shown that for a certain class of Yang-Baxter maps (or set-theoretical
solutions to the quantum Yang-Baxter equation) the Lax representation can be
derived straight from the map itself. A similar phenomenon for 3D consistent
equations on quad-graphs has been recently discovered by A. Bobenko and one of
the authors, and by F. Nijhoff
Cooperativity and Stability in a Langevin Model of Protein Folding
We present two simplified models of protein dynamics based on Langevin's
equation of motion in a viscous medium. We explore the effect of the potential
energy function's symmetry on the kinetics and thermodynamics of simulated
folding. We find that an isotropic potential energy function produces, at best,
a modest degree of cooperativity. In contrast, a suitable anisotropic potential
energy function delivers strong cooperativity.Comment: 45 pages, 16 figures, 2 tables. LaTeX. Submitted to the Journal of
Chemical Physic
On the Green-Functions of the classical offshell electrodynamics under the manifestly covariant relativistic dynamics of Stueckelberg
In previous paper derivations of the Green function have been given for 5D
off-shell electrodynamics in the framework of the manifestly covariant
relativistic dynamics of Stueckelberg (with invariant evolution parameter
). In this paper, we reconcile these derivations resulting in different
explicit forms, and relate our results to the conventional fundamental
solutions of linear 5D wave equations published in the mathematical literature.
We give physical arguments for the choice of the Green function retarded in the
fifth variable .Comment: 16 pages, 1 figur
Stationary state volume fluctuations in a granular medium
A statistical description of static granular material requires ergodic
sampling of the phase space spanned by the different configurations of the
particles. We periodically fluidize a column of glass beads and find that the
sequence of volume fractions phi of post-fluidized states is history
independent and Gaussian distributed about a stationary state. The standard
deviation of phi exhibits, as a function of phi, a minimum corresponding to a
maximum in the number of statistically independent regions. Measurements of the
fluctuations enable us to determine the compactivity X, a temperature-like
state variable introduced in the statistical theory of Edwards and Oakeshott
[Physica A {\bf 157}, 1080 (1989)].Comment: published with minor change
Integrating Multiple Analytical Datasets to Compare Metabolite Profiles of Mouse Colonic-Cecal Contents and Feces.
The pattern of metabolites produced by the gut microbiome comprises a phenotype indicative of the means by which that microbiome affects the gut. We characterized that phenotype in mice by conducting metabolomic analyses of the colonic-cecal contents, comparing that to the metabolite patterns of feces in order to determine the suitability of fecal specimens as proxies for assessing the metabolic impact of the gut microbiome. We detected a total of 270 low molecular weight metabolites in colonic-cecal contents and feces by gas chromatograph, time-of-flight mass spectrometry (GC-TOF) and ultra-high performance liquid chromatography, quadrapole time-of-flight mass spectrometry (UPLC-Q-TOF). Of that number, 251 (93%) were present in both types of specimen, representing almost all known biochemical pathways related to the amino acid, carbohydrate, energy, lipid, membrane transport, nucleotide, genetic information processing, and cancer-related metabolism. A total of 115 metabolites differed significantly in relative abundance between both colonic-cecal contents and feces. These data comprise the first characterization of relationships among metabolites present in the colonic-cecal contents and feces in a healthy mouse model, and shows that feces can be a useful proxy for assessing the pattern of metabolites to which the colonic mucosum is exposed
Constraints on short-range spin-dependent interactions from scalar spin-spin coupling in deuterated molecular hydrogen
A comparison between existing measurements and calculations of the scalar
spin-spin interaction (J-coupling) in deuterated molecular hydrogen (HD) yields
stringent constraints on anomalous spin-dependent potentials between nucleons
at the atomic scale (). The dimensionless coupling constant
associated with exchange of pseudoscalar (axion-like)
bosons between nucleons is constrained to be less than for
boson masses in the range of . This represents improvement by a
factor of about 100 over constraints placed by measurements of the
dipole-dipole interaction in molecular . The dimensionless coupling
constant associated with exchange of a heretofore
undiscovered axial-vector boson between nucleons is constrained to be
for bosons of mass , improving constraints at this distance scale by a factor of 100 for
proton-proton couplings and more than 8 orders of magnitude for neutron-proton
couplings. This limit is also a factor of 100 more stringent than recent
constraints obtained for axial-vector couplings between electrons and nucleons
obtained from comparison of measurements and calculations of hyperfine
structure.Comment: 4 pages 2 figure
Nonlinear double Compton scattering in the full quantum regime
A detailed analysis of the process of two photon emission by an electron
scattered from a high-intensity laser pulse is presented. The calculations are
performed in the framework of strong-field QED and include exactly the presence
of the laser field, described as a plane wave. We investigate the full quantum
regime of interaction, where photon recoil plays an essential role in the
emission process, and substantially alters the emitted photon spectra as
compared to those in previously-studied regimes. We provide a semiclassical
explanation for such differences, based on the possibility of assigning a
trajectory to the electron in the laser field before and after each quantum
photon emission. Our numerical results indicate the feasibility of
investigating experimentally the full quantum regime of nonlinear double
Compton scattering with already available plasma-based electron accelerator and
laser technology.Comment: 5 pages, 3 figure
A study of the angular size-redshift relation for models in which decays as the energy density
By modifying the Chen and Wu ansatz, we have investigated some Friedmann
models in which varies as . In order to test the consistency of
the models with observations, we study the angular size - redshift relation for
256 ultracompact radio sources selected by Jackson and Dodgson. The angular
sizes of these sources were determined by using very long-baseline
interferometry in order to avoid any evolutionary effects. The models fit the
data very well and require an accelerating universe with a positive
cosmological constant. Open, flat and closed models are almost equally
probable, though the open model provides a comparatively better fit to the
data. The models are found to have intermediate density and imply the existence
of dark matter, though not as much as in the canonical Einstein-de Sitter
model.Comment: LaTex, 15 pages including 2 figures (Revised version appeared in CQG
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