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131.
Trempe JF Denisov A Gehring K 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,164(2):329-337
Measurement of dipolar couplings, chemical shift anisotropies, and quadrupole couplings in oriented media such as liquid crystals are of great importance for extraction of structural parameters in biological macromolecules. Here, we introduce a new technique, SAD-REDOR, that consists of recoupling heteronuclear dipolar couplings in molecules dissolved in a single-domain liquid crystal or other oriented medium through the combined use of magic-angle spinning and rotor-synchronized radiofrequency pulses. This application of the REDOR pulse sequence to oriented media offers several advantages such as selectivity over the type of coupling recovered and tunable scaling of the interaction. The effectiveness of the technique is demonstrated both theoretically and experimentally, using the recently developed polyacrylamide-stabilized Pf1 phage medium and 15N-labeled benzamide as the aligned molecule. 相似文献
132.
We study the Metropolis dynamics of a simple spin system without disorder, which exhibits glassy dynamics at low temperatures. We use an implementation of the algorithm of Bortz, Kalos and Lebowitz [1]. This method turns out to be very efficient for the study of glassy systems, which get trapped in local minima on many different time scales. We find strong evidence of aging effects at low temperatures. We relate these effects to the distribution function of the trapping times of single configurations. 相似文献
133.
V.G. Rostiashvili M. Rehkopf T.A. Vilgis 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(2):233-243
In this paper the Martin-Siggia-Rose (MSR) functional integral representation is used for the study of the Langevin dynamics
of a polymer melt in terms of collective variables: mass density and response field density. The resulting generating functional
(GF) takes into account fluctuations around the random phase approximation (RPA) up to an arbitrary order. The set of equations
for the correlation and response functions is derived. It is generally shown that for cases whenever the fluctuation-dissipation
theorem (FDT) holds we arrive at equations similar to those derived by Mori-Zwanzig. The case when FDT in the glassy phase
is violated is also qualitatively considered and it is shown that this results in a smearing out of the ideal glass transition.
The memory kernel is specified for the ideal glass transition as a sum of all “water-melon” diagrams. For the Gaussian chain
model the explicit expression for the memory kernel was obtained and discussed in a qualitative link to the mode-coupling
equation.
Received: 9 January 1998 / Revised: 24 April 1998 / Accepted: 2 July 1998 相似文献
134.
The mean field spin glass model is analyzed by a combination of exact methods and a powerful Ansatz. The method exploited is general, and can be applied to others disordered mean field models such as, e.g., neural networks.It is well known that the probability measure of overlaps among replicas carries the whole physical content of these models. A functional order parameter of Parisi type is introduced by rigorous methods, according to previous works by F. Guerra. By the Ansatz that the functional order parameter is the correct order parameter of the model, we explicitly find the full overlap distribution. The physical interpretation of the functional order parameter is obtained, and ultrametricity of overlaps is derived as a natural consequence of a branching diffusion process.It is shown by explicit construction that ultrametricity of the 3-replicas overlap distribution together with the Ghirlanda-Guerra relations determines the distribution of overlaps among s replicas, for any s, in terms of the one-overlap distribution. 相似文献
135.
136.
We consider an Ising competitive model defined over a triangular Husimi tree where loops, responsible for an explicit frustration, are even allowed. We first analyze the phase diagram of the model with fixed couplings in which a “gas of noninteracting dimers (or spin liquid) — ferro or antiferromagnetic ordered state” zero temperature transition is recognized in the frustrated regions. Then we introduce the disorder for studying the spin glass version of the model: the triangular ±J model. We find out that, for any finite value of the averaged couplings, the model exhibits always a finite temperature phase transition even in the frustrated regions, where the transition turns out to be a glassy transition. The analysis of the random model is done by applying a recently proposed method which allows us to derive the critical surface of a random model through a mapping with a corresponding nonrandom model. 相似文献
137.
Diego O. Russo Jesús Ma. Rincón L. Carlos J.R. González Oliver 《Journal of Non》2008,354(14):1541-1548
The thermal properties (expansion, Tg and TSOFT.) of glasses, having 56-66% P2O5, 14.8-34.2% Fe2O3 and 2-25 wt% additions of SiO2, Al2O3, Na2O and UO2, were comparatively estimated from dilatometric measurements in similar conditions. The Tg reversibility was clearly verified by varying the heating rates between 1 and 5 °C min−1. From linear equations fits of the various glass properties as functions of the six components it is suggested the iron, sodium and uranium oxides decrease the thermal expansion (for 50 < T ? 300 °C), Tg and TSOFT. From DTA/XRD analysis of three glasses it was confirmed the crystallization tendency decreased with increasing the UO2 level in the glasses. Leaching test data for two compositions containing Na2O suggest addition of UO2 increases the chemical durability of the related glass. The roles of UO2, Na2O and Fe-oxide species as structural components of the glass network are discussed. 相似文献