Statistical analysis of synthetic earthquake catalogs generated by models with various levels of fault zone disorder

The stress release model, a stochastic version of the elastic rebound theory, is applied to the large events from four synthetic earthquake catalogs generated by models with various levels of disorder in distribution of fault zone strength (Ben-Zion, 1996) They include models with uniform properties (U), a Parkfield-type asperity (A), fractal brittle properties (F), and multi-size-scale heterogeneities (M). The results show that the degree of regularity or predictability in the assumed fault properties, based on both the Akaike information criterion and simulations, follows the order U, F, A, and M, which is in good agreement with that obtained by pattern recognition techniques applied to the full set of synthetic data. Data simulated from the best fitting stress release models reproduce, both visually and in distributional terms, the main features of the original catalogs. The differences in character and the quality of prediction between the four cases are shown to be dependent on two main aspects: the parameter controlling the sensitivity to departures from the mean stress level and the frequency-magnitude distribution, which differs substantially between the four cases. In particular, it is shown that the predictability of the data is strongly affected by the form of frequency-magnitude distribution, being greatly reduced if a pure Gutenburg-Richter form is assumed to hold out to high magnitudes.

The degree of predictability of earthquakes in several regions of China: statistical analysis of historical data

The stress release model, a stochastic version of the elastic-rebound theory, is applied to the historical earthquake data from three strong earthquake-prone regions of China, including North China, Southwest China, and the Taiwan seismic regions. The results show that the seismicity along a plate boundary (Taiwan) is more active than in intraplate regions (North and Southwest China). The degree of predictability or regularity of seismic events in these seismic regions, based on both the Akaike information criterion (AIC) and fitted sensitivity parameters, follows the order Taiwan, Southwest China, and North China, which is further identified by numerical simulations. (c) 2004 Elsevier Ltd. All rights reserved.

Statistical analysis of sequence features of introns with positive transcriptional regulation in yeast genes

A great deal of experimental studies have shown that many introns of eukaryotic genes function as regulators of transcription. However, comprehensive studies of this problem have not yet been conducted. After checking the transcription frequencies of some Saccharomyces cerevisiae (yeast), genes and their introns, a remarkable phenomenon was discovered that generally the introns of the genes with higher transcription frequencies are longer, and the introns of the genes with lower transcription frequencies are shorter. This suggests that the longer introns of genes with higher transcription frequencies may contain some characteristic sequence structures, which could enhance the transcription of genes. Therefore, two sets of introns of yeast genes were chosen for further study. The transcription frequencies of the first set of genes are higher (>30), and those of the second set of genes are lower (less than or equal to10). Some oligonucleotides are detected by statistically comparative analyses of the occurrence frequencies of oligonucleotides (mainly tetranucleotides and pentanucleotides), whose occurrence frequencies in the first set of introns; are significantly higher than those in the second set of introns, and are also significantly higher than those in the exons flanking the introns of the first set. Some of these extracted oligonucleotides are the same as the regulatory elements of transcription revealed by experimental analyses. Besides, the distributions of these extracted oligonucleotides in the two sets of introns and the exons show that the sequence structures of the first set of introns are favorable for transcription of genes.

Statistical analysis of microscale gas flows and stock price changes

First, recent studies on the information preservation (IP) method, a particle approach for low-speed micro-scale gas flows, are reviewed. The IP method was validated for benchmark issues such as Couette, Poiseuille and Rayleigh flows, compared well with measured data for typical internal flows through micro-channels and external flows past micro flat plates, and combined with the Navier-Stokes equations to be a hybrid scheme for subsonic, rarefied gas flows. Second, the focus is moved to the microscopic characteristic of China stock market, particularly the price correlation between stock deals. A very interesting phenomenon was found that showed a reverse transition behaviour between two neighbouring price changes. This behaviour significantly differs from the transition rules for atomic and molecular energy levels, and it is very helpful to understand the essential difference between stock markets and nature.

Avalanche behavior and statistical properties in a microcrack coalescence process

Fracture owing to the coalescence of numerous microcracks can be described by a simple statistical model, where a coalescence event stochastically occurs as the number density of nucleated microcracks increases. Both numerical simulation and statistical analysis reveal that a microcrack coalescence process may display avalanche behavior and that the final failure is catastrophic. The cumulative distribution of coalescence events in the vicinity of critical fracture follows a power law and the fracture profile has self-affine fractal characteristic. Some macromechanical quantities may be traced back and extracted from the mesoscopic process based on the statistical analysis of coalescence events.

Statistical formulation and experimental determination of growth rate of micrometre cracks under impact loading

A new statistical formulation and a relevant experimental approach to determine the growth rate of microcracks were proposed. The method consists of experimental measurements and a statistical analysis' on the basis of the conservation law of number density of microcracks in phase space. As a practical example of the method, the growth rate of microcracks appearing in an aluminium alloy subjected to planar impact loading was determined to be ca. 10 mu m/mu s under a tensile stress of 1470 MPa and load duration between 0.26 mu s and 0.80 mu s.

Detection of potential positive regulatory motifs of transcription in yeast introns by comparative analysis of oligonucleotide frequencies

We conducted a comparative statistical analysis of tetra- through hexanucleotide frequencies in two sets of introns of yeast genes. The first set consisted of introns of genes that have transcription rates higher than 30 mRNAs/h while the second set contained introns of genes whose transcription rates were lower than or equal to 10 mRNAs/h. Some oligonucleotides whose occurrence frequencies in the first set of introns are significantly higher than those in the second set of introns were detected. The frequencies of occurrence of most of these detected oligonucleotides are also significantly higher than those in the exons flanking the introns of the first set. Interestingly some of these detected oligonucleotides are the same as well known "signature" sequences of transcriptional regulatory elements. This could imply the existence of potential positive regulatory motifs of transcription in yeast introns. (C) 2003 Elsevier Ltd. All rights reserved.

Structural and Mechanical Properties of the Organic Matrix Layers of Nacre

The type of nanostructure referred to in biomineralization as a mineral bridge has been directly observed and measured in the organic matrix layers of nacre by transmission electron microscopy and scanning electron microscopy. Statistical analysis provides the geometric characteristics and a distribution law of the mineral bridges in the organic matrix layers. Experiments reveal that the nanostructures significantly influences the mechanical properties of the organic matrix layers. In addition, the mechanical analysis illustrates the effects of the nanostructures on the behaviors of the organic matrix layers, and the analytical results explain the corresponding experimental phenomena fairly well. The present study shows that the mineral bridges play a key role in the mechanical performances of the organic matrix layers of nacre. The results obtained provide a guide to the interfacial design of synthetic materials.

Microstructure and characteristics in the organic matrix layers of nacre

The direct observation of a type of microstructure in the organic matrix layers of nacre was obtained with a transmission electron microscope. The microstructure, which is referred to as mineral bridge in the biomineralization, is nanoscale and randomly distributed in the layers. Statistical analysis gives the distribution laws and characteristics of mineral bridges in the organic matrix layers. The existence of mineral bridges in nacre was confirmed, and it was shown that the microarchitecture of nacre should be described as a "brick-bridge-mortar" arrangement rather than traditional "brick and mortar" one.

The strength distribution of brittle materials with a high-concentration of cavities

The maximum stress concentration factor in brittle materials with a high concentration of cavities is obtained. The interaction between the nearest cavities, in addition to the far field interactions, is taken into account to evaluate the strength distribution based on the statistical analysis of the nearest distance distribution. Through this investigation, it is found that the interaction between the nearest neighbors is much more important than the far field interactions, and one has to consider it in calculating the strength of brittle materials even if the volume fraction of cavities it contains is small. The other important conclusion is that the maximum stress concentration factor has a wide scattered distribution.

植物种群小尺度空间结构的数量分析

采用位置指数、分异指数、结构复杂性指数、Shannon-Wiener多样性指数以及Ripley的K-方程，探讨了华南海岸英罗港红树植物木榄种群的分布格局、胸围和树高分异以及冠层结构方面的空间异质性。结果表明，多数木榄种群呈现随机分布，其个体胸围和树高的分异程度较低;而少数木榄种群呈现集群分布，其个体胸围和树高的分异程度明显。采用地理信息系统对木榄种群冠层和空隙斑块进行多种水平和垂直尺度的分析，冠层与空隙斑块之间的镶嵌格局因种群而异，这种格局可基于树冠投影用Shannon-Wiener多样性指数进行定量描述。冠层结构的空问异质性随空间尺度而变化，但这种变化在一定尺度范围内保持相对的稳定。这一尺度范围可作为木榄红树林更新或生态管理单位的参考尺度。 采用多重分形理论和方法对华南海岸北海红树林区红树植物白骨壤幼苗种群的分布格局进行了分析。结果表明，白骨壤幼苗种群的分布格局具有多标量和多重分形行为。随着q值由-2增加到4，Dq值介于1.078-1.997，f(a)值介于0.402-1.678，a(q)值介于0.909-2.480。多重分形的参数值与幼苗种群的集聚强度密切相关。差值（D。-D1）和[f(-1) –D]。是度量格局空间异质性程度的有效指数。海洋水文周期性规律、不同面积大小的裸地、树冠的阻拦作用等是制约白骨壤幼苗种群多重分形格局形成的主要因子。 采用地统计学理论和方法，对北京东灵山落叶松和胡桃楸针阔混交林下的克隆植物绢毛匍匐委陵菜分株种群的统计变量和土壤变量的空间格局进行了分析和比较。结果表明，绢毛匍匐委陵菜分株种群各器官生物量以及分株数和叶数的空间格局具有较高程度的异质性。总生物量以及茎、叶和根生物量的半方差函数曲线为指数模型，叶柄生物量、分株数和叶数的为球状模型，叶片生物量的为线性无基台值模型，而匍匐茎生物量的为纯块金效应模型。除叶片和匍匐茎的生物量外，其它器官生物量以及分株数和叶数由空间自相关引起的空间异质性．SHA主要表现在120-3 50cm的尺度范围内，SHA占总空间异质性的比例在50%以上。生境中，各种土壤变量的空间格局也具有较高程度的异质性。土壤含水量、NO3-、NH4+、有机质、全磷和PO4(3-)的半方差函数曲线为球状模型，而全氮、K+和pH的为指数模型。土壤变量由空间自相关引起的空间异质性SHA主要表现在8-lOOcm的尺度范围内，SHA占总空间异质性的比例在68%以上。绢毛匍匐委陵菜分株种群空间格局的自相关尺度显著大于其生境中土壤变量空间格局的自相关尺度，表明绢毛匍匐委陵菜通过匍匐茎相互联结的克隆分株种群对异质性土壤资源表现出较大的缓冲能力。绢毛匍匐委陵菜分株数的空间格局与土壤的含水量和全氮空间格局之间在几乎所有尺度上的相关性都不显著，但与其它土壤变量空间格局之间都存在不同程度的相关性，其中与NH4+、pH、PO4(3-)和全磷空间格局之间的相关性尺度范围较为明显和较大。通过分株数、叶数和生物量分配的可塑性变化，绢毛匍匐委陵菜分株种群的空间格局与土壤资源的空间格局之间产生相互联系，并随空间尺度的变化会发生改变。

Insight into human sex ratio imbalance: the more boys born, the more infertile men

This study investigated, through large-scale statistical analysis of the global population, whether the human sex ratio is skewing worldwide, and if so, why and how it shifts, and the impact of any shift on human reproduction. A significant imbalance of t