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 $\tau$). 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 $\tau$.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 (${\rm \sim 1 \AA}$). The dimensionless coupling constant $g_P^pg_P^{N}/4\pi$ associated with exchange of pseudoscalar (axion-like) bosons between nucleons is constrained to be less than $5\times 10^{-7}$ for boson masses in the range of $5 {\rm keV}$. This represents improvement by a factor of about 100 over constraints placed by measurements of the dipole-dipole interaction in molecular ${\rm H_2}$. The dimensionless coupling constant $g_A^pg_A^N/4 \pi$ associated with exchange of a heretofore undiscovered axial-vector boson between nucleons is constrained to be $g_A^pg_A^N/4 \pi < 2 \times 10^{-19}$ for bosons of mass $\lesssim 1000 {\rm eV}$, 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 Λ\Lambda decays as the energy density

By modifying the Chen and Wu ansatz, we have investigated some Friedmann models in which $\Lambda$ varies as $\rho$. 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