The spin dynamics of the random transverse Ising chain with a double-Gaussian disorder

The dynamical properties of one-dimensional random transverse Ising model （RTIM） with a double-Gaussian disorder is investigated by the recursion method. Based on the first twelve recurrences derived analytically, the spin autocorrelation function （SAF） and associated spectral density at high temperature were obtained numerically. Our results indicate that when the standard deviation σg （or OrB） of the exchange couplings Ji （or the random transverse fields Bi） is small, no long-time tail appears in the SAE The spin system undergoes a crossover from a central-peak behavior to a collectivemode behavior, which is the dynamical characteristics of RTIM with the bimodal disorder. However, when σJ （or σB） is large enough, the system exhibits similar dynamics behaviors to those of the RTIM with the Gaussian disorder, i.e., the system exhibits an enhanced central-peak behavior for large σJ or a disordered behavior for large σB. In this instance, SAFs exhibit a similar long-time tail, i.e., C（t） ~ t ^-2 for large t. Similar properties are obtained when Ji （or Bi） satisfy the double-exponential distribution or the double-uniform distribution. Besides, when both the standard deviations and the mean values of the exchange couplings are small, the effects of the Gaussian random bonds may drive the system undergo two crossovers from a triplet state to a doublet state, and then to a collective-mode state.     

Chain dynamics in partially cross-linked polyethylene by combined rheology and NMR-based molecular rheology

In recent years, ¹H double-quantum NMR (DQ NMR) was established as a suitable molecular-rheology technique to elucidate chain dynamics and to determine entanglement or crosslink densities in linear entangled polymer melts and permanent as well as transient networks. In this work, industrial grade high-density polyethylene, partially cross-linked via electron beam irradiation in the semicrystalline state, is probed in the melt state by low-field DQ NMR and shear rheology. The DQ NMR data is analyzed by two approaches, one assuming the presence of a permanent network and the other considering the potentially complex relaxation spectrum of the studied inhomogeneous systems. A correlation between the DQ NMR results and extent of cross-linking is found. By direct comparison of the rheological results and the NMR-based segmental orientation autocorrelation functions (OACF) via time–temperature superposition (TTS), qualitative consistency between the microscopic and macroscopic observables is established. In this way, the frequency range of shear rheology can be extended by about two decades into the 10 krad/s range. The NMR method is thus a valuable extension of the toolbox of characterization techniques, where gel content measurements by solvent extraction proved to be the least sensitive.     

一种基于β-warping变换算子的被动声源距离估计方法

基于浅海简正波水平波数差与波导不变量之间的关系, 本文提出了一种适用于水平不变浅海声波导中接收信号自相关函数的频域卷绕变换算子. 该算子可以将接收信号自相关函数中的简正波互相关成分变换为时域上可分离的脉冲序列, 且脉冲序列的相对延迟时间包含声源距离信息. 利用已知距离的引导声源, 由单水听器记录的脉冲信号即可实现被动声源距离估计. 对仿真和实验获得的脉冲信号数据处理结果验证了该变换算子用于被动声源距离估计的有效性.     

2-Adic complexity of binary sequences with interleaved structure

In this paper, 2-adic complexity of some binary sequences with interleaved structure is investigated. Firstly, 2-adic complexity of low correlation zone (LCZ) sequences constructed by Zhou et al. [23] is completely determined. We show that their 2-adic complexity could attain the maximum if suitable parameters are chosen. Secondly, we also determine 2-adic complexity of optimal autocorrelation sequences constructed by Tang and Ding [16]. Results show that they have the maximum 2-adic complexity.     

Electrons in cuprates: A consistent ARPES view

Angle resolved photoemission spectroscopy (ARPES) has been playing a crucial role in understanding of physics behind high-temperature superconductivity. Our ARPES investigation of superconducting cuprates, performed over a decade and accomplished by very recent results, suggests a consistent view of electronic interactions in cuprates which provides natural explanation of both the origin of the pseudogap state and the mechanism for high-temperature superconductivity. Within this scenario, the spin-fluctuations play a decisive role in formation of the fermionic excitation spectrum in the normal state and are sufficient to explain the high transition temperatures to the superconducting state while the pseudogap phenomenon is a consequence of a Peierls-type intrinsic instability of electronic system to formation of an incommensurate density wave. In view of these results and their projection to numerous other materials, two general questions are arising: is the normal state in 2D metals ever stable and how does this intrinsic instability interplay with superconductivity?     

Bulk vs. surface effects in ARPES experiment from La2/3Sr1/3MnO3 thin films

Experiments directly probing the electronic states using angle-resolved photoemission (ARPES) were carried out on La_2/3Sr_1/3MnO₃ in order to elucidate its electronic properties. ARPES is a surface sensitive technique where bulk and surface states are usually both present. We present high-resolution ARPES studies in the (1 0 0) and (1 1 0) mirror planes and compare them with simulated ARPES based on GGA + U band structure calculations. In the (1 1 0) mirror plane we identify surface umklapps accounted by surface reconstruction which couple to bulk electronic states. As predicted by the simulated spectra there is additional spectral intensity at the Fermi level detected in ARPES data due to k_⊥-broadening effects in the photoemission final states. We demonstrate that this additional spectral intensity is a convenient spectral marker for determination of the k_F Fermi momenta.     

截面数据插值的组合模型及其实证

采用Moran指标分析截面数据空间自相关性.针对具有空间自相关截面数据缺失插值问题,分别建立一阶空间自回归插值模型与克立格方法插值模型,在此基础上建立截面数据的组合插值模型,并用信息熵法确定组合插值模型的加权系数.用2003年福建部分市县城镇化水平的截面数据建立插值模型实证研究结果表明:组合插值模型的效果优于单项插值模型的效果.     

Multiplicative Difference Sets via Additive Characters

We use Fourier analysis on the additive group of to give an alternative proof of the recent theorem of Maschietti and to prove recent conjectures of No, Chung and Yun and No, Golomb, Gong, Lee and Gaal on difference sets in the multiplicative group of , m odd. Along the ay e prove a stronger form of a celebrated theorem of Welch on the 3-valued cross-correlation of maximal length sequences.     

Molecular dynamics calculations of shear viscosity time-correlation functions for hard spheres

The time-correlation function for shear viscosity is evaluated for hard spheres at volumes of 1.6 and 3 times the close-packed volume by a Monte Carlomolecular dynamics technique. At both densities, the kinetic part of the timecorrelation function is consistent, within its rather large statistical uncertainty, with the long-timet ^–3/2 tail predicted by the mode-coupling theory. However, at the higher density, the time-correlation function is dominated by the cross and potential terms out to 25 mean free times, whereas the mode-coupling theory predicts that these are asymptotically negligible compared to the kinetic part. The total time-correlation function decays roughly ast ^–3/2, with much larger than the mode-coupling value, similar to the recent observations by Evans in his nonequilibrium simulations of argon and methane. The exact value of the exponent is, however, not very precisely determined. By analogy with the case of the velocity autocorrelation function, for which results are also presented at these densities, it is argued that it is quite possible that at high density the asymptotic behavior is not established until times substantially longer than those attainable in the present work. At the lower density, the cross and potential terms are of the same magnitude as the kinetic part, and all are consistent with the mode-coupling predictions within the relatively large statistical uncertainties.Work performed under the auspices of U.S. Department of Energy.