应用小波理论处理油(气)田长时压力监测数据

自90年代以来,越来越多的生产井和注入井安装了长时井底压力计.关于长时压力数据分析的主要障碍是数据中的噪音和奇异点、巨大的数据容量、不完备的信息以及缺少动态分析工具.本文以小波理论为基础,经过反复试验,寻找到了适合于处理长时压力数据的小波类型;在Chee kin(2001)的线性回归方法与小波分解的基础上,建立了剔除异常点的多重阀值法、剔除噪音的软阀值方法以及确定瞬变值的多步法;油(气)田实例说明了上述方法的有效性.     

Sufficient Dimension Folding for Regression Mean Function

In this article, we consider sufficient dimension folding for the regression mean function when predictors are matrix- or array-valued. We propose a new concept named central mean dimension folding subspace and its two local estimation methods: folded outer product of gradients estimation (folded-OPG) and folded minimum average variance estimation (folded-MAVE). We establish the asymptotic properties for folded-MAVE. A modified BIC criterion is used to determine the dimensions of the central mean dimension folding subspace. We evaluate the performances of the two local estimation methods by simulated examples and demonstrate the efficacy of folded-MAVE in finite samples. And in particular, we apply our methods to analyze a longitudinal study of primary biliary cirrhosis. Supplementary materials for this article are available online.     

A Serrin criterion for compressible nematic liquid crystal flows

This paper is concerned with a simplified system, proposed by Ericksen and Leslie, modeling the flow of nematic liquid crystals. We establish a blowup criterion for three‐dimensional compressible nematic liquid crystal flows, which is analogous to the well‐known Serrin's blowup criterion for three‐dimensional incompressible viscous flows. Copyright © 2012 John Wiley & Sons, Ltd.     

Strong solutions of 3D compressible Oldroyd‐B fluids

This paper is concerned with a compressible viscoelastic fluids of Oldroyd‐B type. We prove the existence of unique local strong solutions for all initial data satisfying some compatibility condition. Moreover, we establish a blow‐up criterion for the strong solution in terms of the norm of the density tensor ρ and the norm of the symmetric tensor of constraints τ. All the results hold for the initial density vanishing from below. Copyright © 2012 John Wiley & Sons, Ltd.     

强磁场中相互作用费米气体的相对论稳定性

由单粒子的弱相互作用能谱及泊松公式,导出了强磁场中相互作用费米气体的相对论热力学势函数,求解了系统力学稳定性的判别式,分析了相互作用、磁场及相对论效应对系统稳定性的影响机理.结果表明,强磁场中弱相互作用费米气体的力学稳定性会受到弱相互作用的影响,强磁场对这种影响具有调节作用,而相对论效应对相互作用的影响基本没有调节作用.     

Zero-sum stochastic games with average payoffs: New optimality conditions

In this paper we study zero-sum stochastic games. The optimality criterion is the long-run expected average criterion, and the payoff function may have neither upper nor lower bounds. We give a new set of conditions for the existence of a value and a pair of optimal stationary strategies. Our conditions are slightly weaker than those in the previous literature, and some new sufficient conditions for the existence of a pair of optimal stationary strategies are imposed on the primitive data of the model. Our results are illustrated with a queueing system, for which our conditions are satisfied but some of the conditions in some previous literatures fail to hold.     

双均值逼近屈服准则解析含腐蚀缺陷管道爆破压力

通过对Tresca和TSS屈服边长和边心距的均值同时进行逼近,建立了一个线性屈服准则,称为双均值逼近屈服准则.该准则在π平面上是一个等边非等角的十二边形,位于Mises圆内部.利用该准则对受内压作用的管道进行塑性极限分析,导出了含腐蚀缺陷管道爆破压力的解析解.该解析解是管材屈强比(σY/σT)、原始管道厚径比(t0/D0)、抗拉强度σT以及缺陷深度比(d0/t0)的函数.对比表明,该解析解所预测爆破压力与已有模拟和实验数据吻合较好.影响参数的定量分析表明,爆破压力随着屈强比或原始管道厚径比的增大而增大,随着缺陷深度比的增加而减小.所建立的爆破压力解析解对于管道的选材、设计以及安全评估具有重要意义.     

Theoretical analysis of crack front instability in mode I+III

This paper focusses on the theoretical prediction of the widely observed crack front instability in mode I+III, that causes both the crack surface and crack front to deviate from planar and straight shapes, respectively. This problem is addressed within the classical framework of fracture mechanics, where the crack front evolution is governed by conditions of constant energy-release-rate (Griffith criterion) and vanishing stress intensity factor of mode II (principle of local symmetry) along the front. The formulation of the linear stability problem for the evolution of small perturbations of the crack front exploits previous results of Movchan et al. (1998) (suitably extended) and Gao and Rice (1986), which are used to derive expressions for the variations of the stress intensity factors along the front resulting from both in-plane and out-of-plane perturbations. We find exact eigenmode solutions to this problem, which correspond to perturbations of the crack front that are shaped as elliptic helices with their axis coinciding with the unperturbed straight front and an amplitude exponentially growing or decaying along the propagation direction. Exponential growth corresponding to unstable propagation occurs when the ratio of the unperturbed mode III to mode I stress intensity factors exceeds some “threshold” depending on Poisson's ratio. Moreover, the growth rate of helical perturbations is inversely proportional to their wavelength along the front. This growth rate therefore diverges when this wavelength goes to zero, which emphasizes the need for some “regularization” of crack propagation laws at very short scales. This divergence also reveals an interesting similarity between crack front instability in mode I+III and well-known growth front instabilities of interfaces governed by a Laplacian or diffusion field.     

螺型位错偶极子与界面钝裂纹的干涉效应

研究了螺型位错偶极子与界面钝裂纹的干涉效应.应用保角变换技术,得到了复势函数与应力场的封闭解析解,讨论了位错偶极子方位、臂长及裂纹钝化程度对位错偶板子屏蔽效应和发射条件的影响.结果表明,与单个螺型位错不同,螺型位错偶极子与x轴夹角在一定范围内时才可以降低界面钝裂纹尖端的应力强度因子(屏蔽效应),屏蔽效应随偶板子臂长的增大而增强,随裂纹钝化程度的增大而增强,屏蔽区域也随裂纹钝化程度的增大而增大;位错偶极子发射所需的临界无穷远加载随偶极子臂长的增加而减小,随位错方位角及裂纹钝化程度的增加而增大;最可能的位错偶极子发射角度为0.螺型位错偶极子的发射比单个螺型位错的发射要困难.本文解答的特殊情况与相关文献给出的解答一致.