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1.
CV Tomy D Pal SS Banerjee S Ramakrishnan AK Grover S Bhattacharya MJ Higgins G Balakrishnan McK Paul 《Pramana》2002,58(5-6):925-935
The weakly pinned single crystals of the hexagonal 2H-NbSe2 compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder
transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of
the peak effect phenomenon in three crystals of 2H-NbSe2, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of
a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability
effects and pinning. 相似文献
2.
The historical Ehrenfest model dating back to 1907 describes the process of equilibration together with fluctuations around the thermal equilibrium. This approach represents a special case in the dynamics of N uncoupled two-state systems. In this article we present a generalization of the original model by introducing an additional parameter p which denotes the probability of a single state change. Analytical solutions for the probability distribution of the system's state as well as the fluctuation distribution are derived. Interestingly, close inspection of the fluctuation distribution reveals an intrinsic time scale. Sampling the system's state at much slower rates yields the familiar macroscopic exponential distribution for equilibrium processes. For faster measurements a power law extends roughly over log10 N orders of magnitude followed by an exponential tail. At some point, further increases of the sampling rate merely result in a shift of the fluctuation distribution towards higher values leaving plateau at small fluctuation sizes behind. Since the generic solution is rather unwieldy, we derive and discuss simple and intuitive analytical solutions in the limit of small p and large N. Furthermore, we relax the quantization of time by considering a complementary approach in continuous time. Finally we demonstrate that the fluctuation distributions resulting from the two different approaches bear identical characteristic features. 相似文献
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Alberti G Brunet E Dionigi C Juanes O de La Mata MJ Rodríguez-Ubis JC Vivani R 《Angewandte Chemie (International ed. in English)》1999,38(22):3351-3353
The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space. 相似文献
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Robert G. Nagler 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(4):763-802
Abstract Exploring the other planets of our solar system with atmospheric probes and landers places new requirements on polymeric systems. Because of a preoccupation with weight, designers of capsule components are switching over to plastics with increasing frequency. Ablative heat shields, aeroshell structures, antennas, insulators, electronics packaging, parachutes, and many specialty items could be made from plastics which are tailored to the specific environmental needs. In spite of generally poor practices which limit the reproducibility of commercial products, much is being done to delineate the problems set forth by these environments. This paper outlines the specific environments expected for Mars and Venus capsules and discusses some of the efforts in process, or prospective, within or for the National Aeronautics and Space Administration (NASA), to provide the understanding necessary to tailor new composites for these specific environments. Although much of the work is oriented toward ablative heat shield development, the application is generally similar for all of the other capsule components. Based on this work, an idealized polymer would be a reproducible high-temperature plastic with low volatile content, low-temperature flexibility, and a low number of reactive sites after cure. Though we are some distance from this ideal, progress is being made toward this objective. 相似文献
8.
Stone MB Tian W Lumsden MD Granroth GE Mandrus D Chung JH Harrison N Nagler SE 《Physical review letters》2007,99(8):087204
High resolution neutron scattering is used to study excitations in the organometallic magnet (CH3)2NH2CuCl3 (DMACuCl3). Combined with bulk magnetization and susceptibility studies, the new results imply that DMACuCl3 is a realization of the S=1/2 alternating antiferromagnetic-ferromagnetic (AFM-FM) chain. Coupled-cluster calculations indicate that the AFM and FM interactions have nearly the same strength, while analysis of scattering intensities shows evidence for interdimer spin correlations. Results are discussed in the context of recent ideas concerning quantum entanglement. 相似文献
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Brian C. Sales V. O. Garlea M.B. Stone M. D. Lumsden S. E. Nagler D. Mandrus 《哲学杂志》2020,100(10):1204-1210
ABSTRACTSingle crystals of the underscreened Kondo ferromagnet Yb14MnSb11 were investigated using polarised neutron diffraction and magnetisation measurements. The magnitude and direction of the magnetisation at each of the 9 distinct crystallographic sites was measured using polarised neutron diffraction. A large moment of close to 4.2?μB was found at the unique Mn site. A compensating antiferromagnetic moment of ≈?0.5?μB was found to be distributed uniformly among the remaining Yb and Sb sites, which was not expected from a previous theoretical calculation. The compensating magnetisation, however, is consistent both in size and magnitude with the expected Kondo screening cloud. 相似文献