Crystal structure, electronic, and magnetic properties of the bilayered rhodium oxide Sr3Rh2O7

The bilayered rhodium oxide Sr3Rh2O7 was synthesized by high-pressure and high-temperature heating techniques. The single-phase polycrystalline sample of Sr3Rh2O7 was characterized by measurements of magnetic susceptibility, electrical resistivity, specific heat, and thermopower. The structural characteristics were investigated by powder neutron diffraction study. The rhodium oxide Sr3Rh2O7 [Bbcb, a = 5.4744(8) A, b = 5.4716(9) A, c = 20.875(2) A] is isostructural to the metamagnetic metal Sr3Ru2O7, with five 4d electrons per Rh, which is electronically equivalent to the hypothetic bilayered ruthenium oxide, where one electron per Ru is doped into the Ru-327 unit. The present data show the rhodium oxide Sr3Rh2O7 to be metallic with enhanced paramagnetism, similar to Sr3Ru2O7. However, neither manifest contributions from spin fluctuations nor any traces of a metamagnetic transition were found within the studied range from 2 K to 390 K below 70 kOe.Comment: To be published in PR

Vortex dynamics and states of artificially layered superconducting films with correlated defects

Linear resistances and $IV$-characteristics have been measured over a wide range in the parameter space of the mixed phase of multilayered a-TaGe/Ge films. Three films with varying interlayer coupling and correlated defects oriented at an angle $\approx 25$ from the film normal were investigated. Experimental data were analyzed within vortex glass models and a second order phase transition from a resistive vortex liquid to a pinned glass phase. Various vortex phases including changes from three to two dimensional behavior depending on anisotropy have been identified. Careful analysis of $IV$-characteristics in the glass phases revealed a distinctive $T$ and $H$-dependence of the glass exponent $\mu$. The vortex dynamics in the Bose-glass phase does not follow the predicted behavior for excitations of vortex kinks or loops.Comment: 16 pages, 10 figures, 3 table

Black hole thermodynamical entropy

As early as 1902, Gibbs pointed out that systems whose partition function diverges, e.g. gravitation, lie outside the validity of the Boltzmann-Gibbs (BG) theory. Consistently, since the pioneering Bekenstein-Hawking results, physically meaningful evidence (e.g., the holographic principle) has accumulated that the BG entropy $S_{BG}$ of a $(3+1)$ black hole is proportional to its area $L^2$ ($L$ being a characteristic linear length), and not to its volume $L^3$. Similarly it exists the \emph{area law}, so named because, for a wide class of strongly quantum-entangled $d$-dimensional systems, $S_{BG}$ is proportional to $\ln L$ if $d=1$, and to $L^{d-1}$ if $d>1$, instead of being proportional to $L^d$ ($d \ge 1$). These results violate the extensivity of the thermodynamical entropy of a $d$-dimensional system. This thermodynamical inconsistency disappears if we realize that the thermodynamical entropy of such nonstandard systems is \emph{not} to be identified with the BG {\it additive} entropy but with appropriately generalized {\it nonadditive} entropies. Indeed, the celebrated usefulness of the BG entropy is founded on hypothesis such as relatively weak probabilistic correlations (and their connections to ergodicity, which by no means can be assumed as a general rule of nature). Here we introduce a generalized entropy which, for the Schwarzschild black hole and the area law, can solve the thermodynamic puzzle.Comment: 7 pages, 2 figures. Accepted for publication in EPJ

Classical molecular-dynamics simulation of the hydroxyl radical in water

We have studied the hydration and diffusion of the hydroxyl radical O H0 in water using classical molecular dynamics. We report the atomic radial distribution functions, hydrogen-bond distributions, angular distribution functions, and lifetimes of the hydration structures. The most frequent hydration structure in the O H0 has one water molecule bound to the O H0 oxygen (57% of the time), and one water molecule bound to the O H0 hydrogen (88% of the time). In the hydrogen bonds between the O H0 and the water that surrounds it the O H0 acts mainly as proton donor. These hydrogen bonds take place in a low percentage, indicating little adaptability of the molecule to the structure of the solvent. All hydration structures of the O H0 have shorter lifetimes than those corresponding to the hydration structures of the water molecule. The value of the diffusion coefficient of the O H0 obtained from the simulation was 7.1× 10-9 m2 s-1, which is higher than those of the water and the O H-. © 2005 American Institute of Physics

Humidity-dependent Structural Changes In Native Collagen Studied By X-ray Diffractometry.

1. X-ray diffractometry was used in this work to study structural modifications of powdered native collagen submitted to repeated cycles of gradual drying and hydration. 2. Hysteresis effects known to exist in water sorption isotherms of this fibrous protein were detected in the plots of relative humidity vs integrated intensity of the wide angle X-ray reflections which constitute the main features of the diffraction pattern. 3. A gradual loss of structured material was observed after each drying and rehydration process. An increase in the amorphous regions of the fibrils could also be inferred from the diffraction data. 4. Drying the samples up to a critical degree of hydration (0.12 g H2O per g protein) did not produce a hysteresis loop in the plots of the parameters studied. 5. One-step drying-rehydration cycles did not seem to affect the order of the samples since they repeatedly recovered their original structure. The difference between these results and those of the gradual hydration processes may be attributed to the kinetic properties of biopolymer hydration. The rate of water removal seems to be an important factor in the structural modifications produced by the hydration (dehydration) process.24111512

Conformation analysis of trehalose molecular dynamics simulation and molecular mechanics

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