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71.
Nicholas J. Curro Charles P. Slichter 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):186-194
Measurement ofT2G, the Gaussian component of the spin-echo envelope of planar Cu nuclei in high-temperature superconductors, gives important information about the real part of the Cu electron spin susceptibility. In the traditional picture of the planar Cu echo decay, the internuclear coupling is assumed to remain static with respect to spin–lattice relaxation and mutual exchange fluctuations. In some circumstances, however, this assumption breaks down. We calculate the internuclear corrections arising from spin–lattice relaxation to the conventional theory ofT2Gand show thatT2Gcan be easily corrected for these effects. We argue that mutual exchanges due to the perpendicular indirect couplings are suppressed in these materials. For YBa2Cu4O8, we find a correction on the order of 10% inT2Gand using the corrected values we find that the isotope ratio63T2G/65T2Gagrees with theory. 相似文献
72.
S.F. Lienin R. Brüschweiler R.R. Ernst 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,131(2):184-190
The viscosity-dependent retarding effect of a polymeric solvent on the rotation of small solute molecules is investigated by13C NMR relaxation measurements. It is found that the relaxation data of 1,3-dibromoadamantane in highly viscous polymeric chlorotrifluoroethene can be explained neither by isotropic nor by realistic anisotropic tumbling in a single environment. The experimental data are rationalized in terms of fast exchange between at least two environments with correlation times differing by up to two orders of magnitude. The study shows that a uniform retardation of molecular tumbling by a polymeric solvent, desirable for shifting the NMR observation window in studies of intramolecular mobility, is not always feasible. 相似文献
73.
74.
The dynamics of the one-dimensional spin glass with asymmetric interactions between neighboring spins is considered. We confine ourselves to discrete couplings with values ±J. We show that the algebraic decay of the remanent magnetization of the infinite ±J-spin chain at zero temperature is only valid for symmetric couplings. Our analytical investigations as well as computer simulations show stretched exponential decay for any finite concentration of antisymmetric bonds. Thus, the asymmetric ±J-spin chain shows an asymmetry-induced phase transition at zero temperature. 相似文献
75.
Soft matter, like colloidal suspensions and surfactant gels, exhibit strong response to modest external perturbations. This
paper reviews our recent experiments on the nonlinear flow behaviour of surfactant worm-like micellar gels. A rich dynamic
behaviour exhibiting regular, quasi-periodic, intermittency and chaos is observed. In particular, we have shown experimentally
that the route to chaos is via Type-II intermittency in shear thinning worm-like micellar solution of cetyltrimethylammonium
tosylate where the strength of flow-concentration coupling is tuned by the addition of sodium chloride. A Poincaré first return
map of the time series and the probability distribution of laminar length between burst events show that our data are consistent
with Type-II intermittency. The existence of a ‘Butterfly’ intensity pattern in small angle light scattering (SALS) measurements
performed simultaneously with the rheological measurements confirms the coupling of flow to concentration fluctuations in
the system under study. The scattered depolarised intensity in SALS, sensitive to orientational order fluctuations, shows
the same time-dependence (like intermittency) as that of shear stress. 相似文献
76.
提出了一种非刚性点匹配的算法并把其运用于医学图像配准.该算法采用信号滤波的方法来获得点集间的匹配信息,并运用松弛标记法将各点邻域关系对模糊的匹配信息进行迭代获得明确的匹配关系.在此基础上,利用高斯径向基函数来描述点模式间的弹性形变,在基本的迭代框架下实现问题的求解.实验结果显示在形变程度为5%、出格点比率50%和噪声标准差为5%的情况下该算法的匹配误差能控制在0.13以下,表明了该算法的鲁棒性和有效性,较好地解决了医学非刚性形变的点匹配问题. 相似文献
77.
akir Aydoan Mustafa Salam Abdulmecit Türüt 《Journal of Polymer Science.Polymer Physics》2006,44(11):1572-1579
The polypyrrole/p‐InP structure has been fabricated by the electrochemical polymerization of the organic polypyrrole onto the p‐InP substrate. The current–voltage (I–V), capacitance–voltage (C–V), and capacitance–frequency (C–f) characteristics of the PPy/p‐InP structure have been determined at room temperature. The structure showed nonideal I–V behavior with the ideality factor and the barrier height 1.48 and 0.69 eV respectively. C–f measurements of the structure have been carried out using the Schottky capacitance spectroscopy technique and it has been seen that there is a good agreement between the experimental and theoretical values. Also, it has been seen that capacitance almost show a plateau up to a certain value of frequency, after which, the capacitance decreases. The higher values of capacitance at low frequencies were attributed to the excess capacitance resulting from the interface states in equilibrium with the p‐InP that can follow the a.c. signal. The interface state density Nss and relaxation time τ of the structure were determined from C–f characteristics. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1572–1579, 2006 相似文献
78.
Lagrangian relaxation is commonly used in combinatorial optimization to generate lower bounds for a minimization problem.
We study a modified Lagrangian relaxation which generates an optimal integer solution. We call it semi-Lagrangian relaxation
and illustrate its practical value by solving large-scale instances of the p-median problem.
This work was partially supported by the Fonds National Suisse de la Recherche Scientifique, grant 12-57093.99 and the Spanish
government, MCYT subsidy dpi2002-03330. 相似文献
79.
The thermal properties of perfluorocarbonsulfonic acid ionomer films cast from solution and their temperature-dependent far infrared spectra have been investigated. In addition to the endotherms and spectral changes associated with the loss of solvent as the films were heated, a significant exotherm has been observed and assigned to the relaxation associated with rearrangements resulting in partially crystallized phases in insoluble thermally treated membranes. © 1993 John Wiley & Sons, Inc. 相似文献
80.
Spin-lattice relaxation mechanisms in kaolinite have been reinvestigated by magic-angle spinning (MAS) of the sample. MAS is useful to distinguish between relaxation mechanisms: the direct relaxation rate caused by the dipole-dipole interaction with electron spins is not affected by spinning while the spin diffusion-assisted relaxation rate is. Spin diffusion plays a dominant role in 1H relaxation. MAS causes only a slight change in the relaxation behavior, because the dipolar coupling between 1H spins is strong. 29Si relaxes directly through the dipole-dipole interaction with electron spins under spinning conditions higher than 2 kHz. A spin diffusion effect has been clearly observed in the 29Si relaxation of relatively pure samples under static and slow-spinning conditions. 27Al relaxes through three mechanisms: phonon-coupled quadrupole interaction, spin diffusion and dipole-dipole interaction with electron spins. The first mechanism is dominant, while the last is negligibly small. Spin diffusion between 27Al spins is suppressed completely at a spinning rate of 2.5 kHz. We have analyzed the relaxation behavior theoretically and discussed quantitatively. Concentrations of paramagnetic impurities, electron spin-lattice relaxation times and spin diffusion rates have been estimated. 相似文献