穿越深海会聚区的声源定位方法研究

基于WKBZ近似深海会聚区预报模型和方位滤波方法建立了穿越会聚区声源运动参数的估计模型，模拟结果表明，方位误差较小时，在前三个会聚区内，目标运动参数估计结果与模拟设定参数符合较好。     

Structure of the sound field in convergence zones of the tropical Pacific

Experimental data are presented on the intensity and angular structures of the sound field in the first and second convergence zones for the tropical region of the Pacific Ocean, southwest of the Hawaian Islands. The experiment is carried out using continuous pseudonoise signals in one-third-octave bands around central frequencies of 1.25 and 3.15 kHz with both source and receiver positioned under the discontinuity layer at a depth of 250 m. The experimental data are compared with calculations based on the ray model. The discrepancies arising between the experimental and calculated data at the entry onto the first convergence zone are compared with the corresponding parameters obtained earlier in the tropical regions of the Atlantic and Indian oceans. The detailed intensity structure of the sound field is correlated with the parameters of internal waves observed during the acoustic measurements.     

Lorenz系统的可预报性

定义一个动态窗口，以Lorenz模型为预报方程，通过对落入动态窗口中的粒子数和平均预报X分量随积分时间演化规律的分析，从另一个角度初步研究了Lorenz系统的可预报性问题，并讨论了高斯白噪声对系统可预报性的影响.结果表明，落入动态窗口中的粒子数在一定程度上反映了系统的可预报性，处于不同区域的初值集合预报时限各不相同，且不同区域内的初值对于小扰动的敏感程度不一样；对于不同区域内的初值集合，高斯白噪声对系统的可预报时限的影响各不相同. 关键词： 可预报性 Lorenz 动态窗口     

地震原理新论——兼述地震预测的科学基础

地震是给人类造成巨大损失的自然灾害,地震预测是社会广泛关注的重大的科学问题。然而,地震机理还远未认识清楚,当前国际地震界的主流观点认为地震是不可预测的。本文以物理学的新观念为基础, 从新的视角研究地震孕育和发生过程, 提出了对地震原理的新认识, 剖析了地震不可预测论的错误。地震不可预测论产生的根源在于对地震原理的不正确认识以及对自组织临界性的误解。地震具有自组织临界性的特征, 表明不可能对地震作中长期预测, 但短期预测应是可能的。成功预测的前提包括：对地震原理的正确认识, 获得足够的特征前兆信息, 并且掌握相关的地质资料。传统地震学基于固体连续介质理论, 认为地震是地壳岩石的脆性破裂造成, 用所谓“弹性回跳”来表述地震发生机制。此观点与实际观测严重不符, 无法解释诸多地震现象, 自然也不能正确地获取和理解地震前兆信息, 因而得出地震不可预测的结论。作者根据地壳由岩石层块和其间断层泥组成这一基本事实, 将地壳作为离散态体系处理, 用颗粒物理原理认识地震孕育过程。获得的认识是：构造力以力链的方式传播, 岩块以滞滑移动的方式运动。另一方面, 在认真分析地壳岩石强度和构造作用力随深度分布规律基础上,提出地震发生的物理机制是岩石的塑性滑移和岩块运动的堵塞—解堵塞转变。对地震原理这些新认识, 可解释传统地震学无法理解的很多地震学现象, 例如, 消解了传统的“弹性回跳”原理所遭遇的“热流佯谬”, 解释了深源地震的成因等。基于对地震原理的新认识, 提出了如何正确获取地震前兆信息, 实现地震短期预测的途径。     

Regional variability of the phenomenon of sound penetration into shadow zones in the ocean with fine-structure stratification

The regional variability of the phenomenon of the shadow zone insonification in the ocean is manifested in the variability of the main parameters of the sound signals that penetrate into these zones because of the scattering by the fine-structure inhomogeneities of the refractive index. The intensity of the phenomenon is governed by a combination of the vertical distribution of intensity of the fine-structure inhomogeneities and the caustics that exist in the insonified domains, along with the caustic intensity and position, both of which depend on the mean sound speed profile and on the geometry of the experiment. For the chosen typical regions of the ocean, the characteristics of the fine structure are systematized, and the phenomenon under study is analyzed. The results obtained offer a justified approach to solving inverse problems and a way to perform practical-purpose studies aimed at improving the ultimate performance of underwater observation and monitoring systems.     

On the convergence of the Fitness-Complexity algorithm

We investigate the convergence properties of an algorithm which has been recently proposed to measure the competitiveness of countries and the quality of their exported products. These quantities are called respectively Fitness F and Complexity Q. The algorithm was originally based on the adjacency matrix M of the bipartite network connecting countries with the products they export, but can be applied to any bipartite network. The structure of the adjacency matrix turns to be essential to determine which countries and products converge to non zero values of F and Q. Also the speed of convergence to zero depends on the matrix structure. A major role is played by the shape of the ordered matrix and, in particular, only those matrices whose diagonal does not cross the empty part are guaranteed to have non zero values as outputs when the algorithm reaches the fixed point. We prove this result analytically for simplified structures of the matrix, and numerically for real cases. Finally, we propose some practical indications to take into account our results when the algorithm is applied.     

On the convergence of the Zassenhaus formula

The domain of convergence of the Zassenhaus formula in a Banach algebra is studied. This domain is shown to be strictly larger than the one which was already known.     

Newton's method as a dynamical system: Global convergence and predictability

Newton's method as an iterative scheme to compute both unstable and stable fixed points of a discrete dynamical system is considered. It is shown for Newton iteration that the basins of attraction are intertwinted in a complicated manner. This complex structure appears to fractal, and its dimension is estimated. Consequences for predictability for the final state are given in terms of imprecision in the initial data.     

On the convergence of planar diagram expansions

Renormalizable quantum field theories whose perturbation expansions are described by planar Feynman diagrams only, such as SU() gauge theory, are considered in 4 dimensional Euclidean space. For studying asymptotic properties of the perturbation series one might wish to isolate first all those planar diagrams that do not contain any ultraviolet divergent subgraphs. In this paper it is proved that this infinite set of diagrams, when summed, converges within a finite radius of convergence for the coupling constant.     

On the analytical convergence of the QPA procedure

We present an analytical proof of the convergence of the “quantum privacy amplification” procedure proposed by Deutsch et al. [Phys. Rev. Lett. 77 (1996) 2818]. The proof specifies the range of states which can be purified by this method.     

On the evidence of deterministic chaos in ECG: Surrogate and predictability analysis

The question whether the human cardiac system is chaotic or not has been an open one. Recent results in chaos theory have shown that the usual methods, such as saturation of correlation dimension D(2) or the existence of positive Lyapunov exponent, alone do not provide sufficient evidence to confirm the presence of deterministic chaos in an experimental system. The results of surrogate data analysis together with the short-term prediction analysis can be used to check whether a given time series is consistent with the hypothesis of deterministic chaos. In this work nonlinear dynamical tools such as surrogate data analysis, short-term prediction, saturation of D(2) and positive Lyapunov exponent have been applied to measured ECG data for several normal and pathological cases. The pathology presently studied are PVC (Premature Ventricular Contraction), VTA (Ventricular Tachy Arrhythmia), AV (Atrio-Ventricular) block and VF (Ventricular Fibrillation). While these results do not prove that ECG time series is definitely chaotic, they are found to be consistent with the hypothesis of chaotic dynamics. (c) 1998 American Institute of Physics.     

On the rate of convergence to equilibrium in one-dimensional systems

We determine the essential spectral radius of the Perron-Frobenius-operator for piecewise expanding transformations considered as an operator on the space of functions of bounded variation and relate the speed of convergence to equilibrium in such one-dimensional systems to the greatest eigenvalues of generalized Perron-Frobenius-operators of the transformations (operators which yield singular invariant measures).This work has been supported by the Deutsche Forschungsgemeinschaft     

On the configuration of Guinier-Preston zones in Al-Ag and Al-Zn alloys

An experimental investigation of the short-range ordering in the spatial distribution of isotropic G.-P. zones in supersaturated solid solutions of Ag or Zn in Al is presented. The intensity distribution of the small-angle diffuse scattering can be satisfactorily explained by inter-zone X-ray interferences when using the data on metastable miscibility gaps determined by Gerold for Al-Ag and by Hillert for Al-Zn. The investigation was carried out for a wide interval of annealing temperatures on Al-Ag (6 at. % Ag) and on Al-Zn (11 at. % Zn) samples.The authors wish to express their gratitude to their colleagues of the Institute of Solid State Physics: J. Laek, C.Sc, for valuable discussions and for chemical analyses, V. íma for alloy preparations, and Z. iký for his assistance in the measurements and computations.     

On the convergence of reflectionless approximations to confining potentials

The construction of reflectionless potentials supporting a prescribed spectrum of Schrödinger bound states is discussed and related to the inverse problem for confining potentials. A simple formula is derived for the Jost solution in a one-dimensional reflection-less potential with N bound states. This leads to compact expressions for the potential and the bound-state wavefunctions in terms of the bound-state energies. For symmetric potentials, N-fold product formulas are obtained for bound-state wavefunctions and their slopes at the origin. Corresponding quantities in a confining potential are given by infinite products. Comparison of the finite-product and infinite-product expressions allows a demonstration of the convergence of the reflectionless results to the confining potential results as N → ∞. Several sum rules satisfied by the reflectionless potential at the origin are applied to numerical studies of convergence.     

On phonetic convergence during conversational interaction

Following research that found imitation in single-word shadowing, this study examines the degree to which interacting talkers increase similarity in phonetic repertoire during conversational interaction. Between-talker repetitions of the same lexical items produced in a conversational task were examined for phonetic convergence by asking a separate set of listeners to detect similarity in pronunciation across items in a perceptual task. In general, a listener judged a repeated item spoken by one talker in the task to be more similar to a sample production spoken by the talker's partner than corresponding pre- and postinteraction utterances. Both the role of a participant in the task and the sex of the pair of talkers affected the degree of convergence. These results suggest that talkers in conversational settings are susceptible to phonetic convergence, which can mark nonlinguistic functions in social discourse and can form the basis for phenomena such as accent change and dialect formation.     

On the dynamics of a novel ocean wave energy converter

Buoy-type ocean wave energy converters are designed to exhibit resonant responses when subject to excitation by ocean waves. A novel excitation scheme is proposed which has the potential to improve the energy harvesting capabilities of these converters. The scheme uses the incident waves to modulate the mass of the device in a manner which amplifies its resonant response. To illustrate the novel excitation scheme, a simple one-degree of freedom model is developed for the wave energy converter. This model has the form of a switched linear system. After the stability regime of this system has been established, the model is then used to show that the excitation scheme improves the power harvesting capabilities by 25-65 percent even when amplitude restrictions are present. It is also demonstrated that the sensitivity of the device's power harvesting capabilities to changes in damping becomes much smaller when the novel excitation scheme is used.