9,234 research outputs found

    Origin of entropy convergence in hydrophobic hydration and protein folding

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    An information theory model is used to construct a molecular explanation why hydrophobic solvation entropies measured in calorimetry of protein unfolding converge at a common temperature. The entropy convergence follows from the weak temperature dependence of occupancy fluctuations for molecular-scale volumes in water. The macroscopic expression of the contrasting entropic behavior between water and common organic solvents is the relative temperature insensitivity of the water isothermal compressibility. The information theory model provides a quantitative description of small molecule hydration and predicts a negative entropy at convergence. Interpretations of entropic contributions to protein folding should account for this result.Comment: Phys. Rev. Letts. (in press 1996), 3 pages, 3 figure

    Changes in intergenerational eating patterns and the impact on childhood obesity

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    The objective of this study was to examine intergenerational eating patterns within two sets of families, those with an obese child and those with a normal weight child, and to assess the impact of intergenerational influences on children's eating. A qualitative study design was used, incorporating focus groups and semi-structured interviews. Sixteen focus groups took place and 27 semi-structured interviews were held with different generations. Focus groups were conducted in the community with grandparents, parents and children from different families. This was followed by semi-structured interviews, involving individuals from three generations within families with an obese child and within families with a normal weight child. An examination of intergenerational eating has shown that eating patterns have changed regardless of whether or not families have children who are obese. The grandparent's eating patterns were more structured, whereas the children's eating patterns were less so. There have been more changes, and eating is less structured, within those families with an obese child than those families with a normal weight child. It is recommended that approaches to tackling childhood obesity concentrate on the family setting and the ways in which professionals can support families to change eating practices. Future research should formally test the relationship between the concept 'structured eating' and the 'what' of eating, in order to determine whether there is a link between intergenerational eating patterns and childhood obesity. © The Author(s) 2010

    The Quark-Gluon Plasma in a Finite Volume

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    The statistical mechanics of quarks and gluons are investigated within the context of the canonical ensemble. Recursive techniques are developed which enforce the exact conservation of baryon number, total isospin, electric charge, strangeness, and color. Bose and Fermi-Dirac statistics are also accounted for to all orders. The energy, entropy and particle number densities are shown to be significantly reduced for volumes less than 5 cubic fm.Comment: 8 pages, 3 figure

    A system of relational syllogistic incorporating full Boolean reasoning

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    We present a system of relational syllogistic, based on classical propositional logic, having primitives of the following form: Some A are R-related to some B; Some A are R-related to all B; All A are R-related to some B; All A are R-related to all B. Such primitives formalize sentences from natural language like `All students read some textbooks'. Here A and B denote arbitrary sets (of objects), and R denotes an arbitrary binary relation between objects. The language of the logic contains only variables denoting sets, determining the class of set terms, and variables denoting binary relations between objects, determining the class of relational terms. Both classes of terms are closed under the standard Boolean operations. The set of relational terms is also closed under taking the converse of a relation. The results of the paper are the completeness theorem with respect to the intended semantics and the computational complexity of the satisfiability problem.Comment: Available at http://link.springer.com/article/10.1007/s10849-012-9165-

    Spin freezing and dynamics in Ca_{3}Co_{2-x}Mn_{x}O_{6} (x ~ 0.95) investigated with implanted muons: disorder in the anisotropic next-nearest neighbor Ising model

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    We present a muon-spin relaxation investigation of the Ising chain magnet Ca_{3}Co_{2-x}Mn_{x}O_{6} (x~0.95). We find dynamic spin fluctuations persisting down to the lowest measured temperature of 1.6 K. The previously observed transition at around T ~18 K is interpreted as a subtle change in dynamics for a minority of the spins coupling to the muon that we interpret as spins locking into clusters. The dynamics of this fraction of spins freeze below a temperature T_{SF}~8 K, while a majority of spins continue to fluctuate. An explanation of the low temperature behavior is suggested in terms of the predictions of the anisotropic next-nearest-neighbor Ising model.Comment: 4 pages, 2 figure

    Muon-spin relaxation and heat capacity measurements on the magnetoelectric and multiferroic pyroxenes LiFeSi2O6 and NaFeSi2O6

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    The results of muon-spin relaxation and heat capacity measurements on two pyroxene compounds LiFeSi2O6 and NaFeSi2O6 demonstrate that despite their underlying structural similarity the magnetic ordering is considerably different. In LiFeSi2O6 a single muon precession frequency is observed below TN, consistent with a single peak at TN in the heat capacity and a commensurate magnetic structure. In applied magnetic fields the heat capacity peak splits in two. In contrast, for natural NaFeSi2O6, where multiferroicity has been observed in zero-magnetic-field, a rapid Gaussian depolarization is observed showing that the magnetic structure is more complex. Synthetic NaFeSi2O6 shows a single muon precession frequency but with a far larger damping rate than in the lithium compound. Heat capacity measurements reproduce the phase diagrams previously derived from other techniques and demonstrate that the magnetic entropy is mostly associated with the build up of correlations in the quasi-one-dimensional Fe3+ chains

    Superconducting Pairing Symmetries in Anisotropic Triangular Quantum Antiferromagnets

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    Motivated by the recent discovery of a low temperature spin liquid phase in layered organic compound κ\kappa-(ET)2_2Cu2_2(CN)3_3 which becomes a superconductor under pressure, we examine the phase transition of Mott insulating and superconducting (SC) states in a Hubbard-Heisenberg model on an anisotropic triangular lattice. We use a renormalized mean field theory to study the Gutzwiller projected BCS wavefucntions. The half filled electron system is a Mott insulator at large on-site repulsion UU, and is a superconductor at a moderate UU. The symmetry of the SC state depends on the anisotropy, and is gapful with dx2y2+idxyd_{x^2-y^2}+id_{xy} symmetry near the isotropic limit and is gapless with dx2y2d_{x^2-y^2} symmetry at small anisotropy ratio.Comment: 6 pages, 5 figure

    Brightest Cluster Galaxies and Core Gas Density in REXCESS Clusters

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    We investigate the relationship between brightest cluster galaxies (BCGs) and their host clusters using a sample of nearby galaxy clusters from the Representative XMM Cluster Structure Survey (REXCESS). The sample was imaged with the Southern Observatory for Astrophysical Research (SOAR) in R band to investigate the mass of the old stellar population. Using a metric radius of 12h^-1 kpc, we found that the BCG luminosity depends weakly on overall cluster mass as L_BCG \propto M_cl^0.18+-0.07, consistent with previous work. We found that 90% of the BCGs are located within 0.035 r_500 of the peak of the X-ray emission, including all of the cool core (CC) clusters. We also found an unexpected correlation between the BCG metric luminosity and the core gas density for non-cool core (non-CC) clusters, following a power law of n_e \propto L_BCG^2.7+-0.4 (where n_e is measured at 0.008 r_500). The correlation is not easily explained by star formation (which is weak in non-CC clusters) or overall cluster mass (which is not correlated with core gas density). The trend persists even when the BCG is not located near the peak of the X-ray emission, so proximity is not necessary. We suggest that, for non-CC clusters, this correlation implies that the same process that sets the central entropy of the cluster gas also determines the central stellar density of the BCG, and that this underlying physical process is likely to be mergers.Comment: 16 pages, 8 figures, accepted Astrophysical Journa

    Boundary and expansion effects on two-pion correlation functions in relativistic heavy-ion collisions

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    We examine the effects that a confining boundary together with hydrodynamical expansion play on two-pion distributions in relativistic heavy-ion collisions. We show that the effects arise from the introduction of further correlations due both to collective motion and the system's finite size. As is well known, the former leads to a reduction in the apparent source radius with increasing average pair momentum K. However, for small K, the presence of the boundary leads to a decrease of the apparent source radius with decreasing K. These two competing effects produce a maximum for the effective source radius as a function of K.Comment: 6 pages, 5 Eps figures, uses RevTeX and epsfi
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