Propagation characteristics of the Pc3 frequency range pulsations in the cusp latitudes

Two induction magnetometers have been installed at Zhongshan Station and Davis Station, Antarctica respectively. We adopt with cross-spectral analysis technique to analyze the data of the two induction magnetometers, in June, September,December 1996 and March 1997. to investigate the Pc3 frequency range pulsation occurrence and propagation characteristics in the cusp latitudes. The results are summarized as following:At Zhongshan-Davis Stations, the Pc3 frequency range pulsations occur mainly around the local noon/ local magnetic noon and local magnetic midnight respectively. In daytime, the pulsations have a seasonal variation in amplitude, occurrence and temporal range, all of them are sma1lest in winter. But in nighttime, the pulsations have no such a variation. The pu1sation amplitude in nighttime is much larger than the one in daytime all oveI the year. The pulsation propagating direction is mainly western in daytime and irregularly in nighttime. It can be thought that the different sources of the pulsation and the ionospheric electric conductivity are mainly responsible for these characteristics.

Propagation and source of Pc5 frequency range pulsation at cusp latitude

Two induction magnetometers have been installed at Chinese Zhongshan Station and Australia Davis Station, Antarctica respectively. We adopt the cross spectral analysis technique to analyze the data of the two induction magnetometers, in June, September, December 1996 and March 1997, and to investigate Pc5 frequency range pulsation (150 600 s) occurrence and propagation in cusp latitude. The results are summarized as follows: At Zhongshan Davis Station, the magnetic pulsations in Pc5 frequency band can occurs over a wide time, but more frequently at pre local magnetic noon and pre local magnetic midnight. The Pc5 pulsations have no significant seasonal variation in the amplitude, occurrence and propagation. The amplitude has a small peak at pre local magnetic noon and large value sometimes at pre local magnetic midnight. In daytime, the Pc5 pulsations propagate westward in morning and eastward in afternoon, and reversal at local magnetic noon. In nighttime, the Pc5 pulsations propagate westward before 20:00 MLT and eastward after 20:00 MLT. Near dusk time, the Pc5 pulsations propagate irregularly. These characteristics indicate that the Pc5 pulsations have different source at different local magnetic time.

On Verification of the New Criterion of Adiabaticity by Numerical Simulation of Acoustic Propagation through the Polar Front

To assess the adiabaticity of acoustic propagation in the ocean is very important for acoustic field calculation(forward problem) and tomographic retrieving (inverse problem). A new criterion of adiabaticity is proposed recently (Shang et al., 2001). In this paper, numerical simulation has been conducted for acoustic propagation through the Polar Front to verify the new criterion. Numerical results on the f (frequency) -m (mode number) plan demonstrate that the new criterion works very well for this extremely non-gradual ocean structure.

Well-Posedness and Infinite Propagation Speed for the Fifth-Order Camassa-Holm Equation with Weakly Dissipative Term

In this paper, we study the fifth-order Camassa-Holm equation with weakly dissipative term. We first give the local well-posedness result and the blow up criterion. Then, we establish sufficient conditions to guarantee that the solution exists globally in time. Finally, the infinite propagation speed of this equation is also investigated.

1m级间隙正极性雷电冲击闪络判据海拔校正方法的适用性

绝缘子及空气间隙的雷电冲击闪络判据是评估输电线路耐雷性能的重要仿真模型之一,同一间隙的闪络判据在不同海拔地区应用需要进行海拔校正。绝缘子及空气间隙的雷电冲击U50%闪络判据可以采用g参数进行海拔校正,但是更加精确的闪络判据如伏秒特性及先导发展模型法尚缺乏有效的海拔校正方法。该文针对110kV线路用复合绝缘子及1m棒-板间隙,分别在平原和高海拔地区开展了正极性标准雷电冲击试验,对比了海拔对冲击闪络特性的影响,分析了现有海拔校正方法在U50%及伏秒特性散点校正中存在的问题。然后,拟合了适用于不同海拔的110 kV单支复合绝缘子及1 m棒-板间隙的正极性标准雷电波先导发展模型,并将该模型计算得到的U-t曲线与试验所得的伏秒特性散点进行对比分析,验证了先导发展模型通过改变相对空气密度开展闪络判据海拔校正的适用性。最后,通过对比分析不同先导发展模型对计算110kV输电线路耐雷水平的影响,证明了先导发展模型闪络判据海拔校正的精确性。

基于黏弹性近场动力学方法的素混凝土板冲击破坏形态分析

通过拉格朗日方程推导出一种基于单键双参数键型近场动力学的黏弹性模型,对冲击荷载下的素混凝土板的破坏过程进行模拟,采用单轴动态强度S准则得出物质点对间键的动态断裂准则。分别将低速落锤撞击下的素混凝土板的仿真结果与连续-不连续介质力学方法(CDEM)的模拟结果,高速子弹射击下的素混凝土板的仿真结果与试验结果进行对比。结果表明,黏弹性单键双参数近场动力学模型能合理地描述混凝土在冲击荷载下的破坏形态,且该模型能针对不同加载速率做出不同的反应,为冲击作用下的混凝土防护与混凝土的结构改造提供了一种有效的方法。

玻璃布增强PC复合材料分层裂纹的扩展行为

利用光学显微镜原位研究在Ⅰ型动态加载下玻璃布增强ＰＣ复合材料层板的分层断裂过程及其微观机理．结果表明，分层损伤微裂纹易萌生在平行于裂纹扩展方向的纱线束和交织面内．在层板边缘，主裂纹可沿经纱的方向穿过经纱和纬纱的交织面向前扩展，造成织物分隔．随裂纹张开位移的增大，纬纱才回到原织物平面内．

满足k阶PC(l)的密码函数的新构造

该文基于线性分组码和双射函数,给出了满足七阶PC(l)的均衡相关免疫布尔函数新的构造方法。并据此进一步给出满足七阶PC(l)的(n,m,t)弹性函数的一般构造方法。此外,该文还揭示了这些函数的其它良好的密码学性质,如较高的非线性度、良好的代数次数、良好的构造计数等。

考虑多种失效模式耦合的复合材料损伤分析

复合材料的损伤失效形式是多样的,其损伤失效形式包括层合板损伤、胶体裂纹扩展和界面脱黏。为了探讨层合板损伤、胶体裂纹扩展、界面脱黏3种损伤失效之间的内在联系,先利用ABAQUS/Explicit软件建立混合型弯曲(MMB)断裂有限元模型,通过数值仿真结果与实验结果的比较,从而证明MMB模型的准确性。然后结合Hashin失效准则、扩展有限元法(XFEM)和内聚力模型(CZM)来研究3种失效模式的内在联系。结果表明:层合板损伤不仅可以影响界面脱黏失效发生时间,同时也能影响胶体中裂纹扩展路径,为复合材料损伤问题数值分析提供了一定的参考。

快衰落Rayleigh信道下短LDPC码两类BP-Based译码的优化设计

该文基于最小均方误差(MMSE)准则,对快衰落瑞利(Rayleigh)信道下短码长低密度校验(LDPC)码的ScaledBP-Based和OffsetBP-Based两类改进译码算法进行了优化设计。利用该准则,得出了两类改进算法的最优校正因子,并给出了相应的数值计算。对码长为504和1008的1/2码率(3,6)规则LDPC码实验仿真显示,使用该准则设计的两类算法能够取得优于置信传播(BP)算法的译码性能。

Fracture initiation and propagation in intact rock—A review

The initiation and propagation of failure in intact rock are a matter of fundamental importance in rock engineering. At low confining pressures, tensile fracturing initiates in samples at 40%-60% of the uniaxial compressive strength and as loading continues, and these tensile fractures increase in density, ultimately coalescing and leading to strain localization and macro-scale shear failure of the samples. The Griffith theory of brittle failure provides a simplified model and a useful basis for discussion of this process. The Hoek-Brown failure criterion provides an acceptable estimate of the peak strength for shear failure but a cutoff has been added for tensile conditions. However, neither of these criteria adequately explains the progressive coalition of tensile cracks and the final shearing of the specimens at higher confining stresses. Grain-based numerical models, in which the grain size distributions as well as the physical properties of the component grains of the rock are incorporated, have proved to be very useful in studying these more complex fracture processes.

Stability of the formation interface under the impact of hydraulic fracture propagation in the vicinity of the formation interface

Unconventional hydrocarbon reservoirs in layered formations,such as tight sandstones and shales,are continually being developed.Hydraulic fracturing is a critical technology for the high-efficiency development of hydrocarbon reservoirs.Understanding the stress field and stability of the formation interface is vital to understanding stress propagation,preferably before the growing hydraulic fracture contacts the formation interface.In this study,models are developed for computing the stress field of hydraulic fracture propagation near the formation interface,and the stress fields within and at the two sides of the formation interface are analyzed.Four failure modes of the interface under the impact of hydraulic fracture propagation in its vicinity are identified,and the corresponding failure criteria are proposed.By simulating the magnitude and direction of peak stress at different parameters,the failure mode and stability of the formation interface are analyzed.Results reveal that when the interface strength is weak,the formation interface fails before the growing hydraulic fracture contacts it,and its stability is significantly related to a variety of factors,including the type of formation interface,rock mechanical properties,far-field stress,structural parameters,distance between the hydraulic fracture and formation interface,and fracturing execution parameters.

PC准则下错误指定模型中回归系数有约束LS估计的优良性

在错误指定的回归模型和线性约束条件下，于ＰＣ准则下，比较了回归系数的有约束的最小二乘估计（ＲＬＳＥ）相对于通常的最小二乘估计（ＬＳＥ）的优良性．也对预测情形类似的问题进行了讨论．

SPECTRAL CHARACTERIZATION OF BOOLEANFUNCTIONS SATISFYING k DEGREEPROPAGATION CRITERIA

This paper discusses spectral characterization of Boolean functions satisfying k degree propagation criteria and satisfying fc order strict avalanche criterion respectively. Meanwhile, introduces the generalized e-k degree propagation criteria and gives its spectral characterization.

NEW CONCEPT FOR DETERMINING THE ORDERS OF SAC AND PC

The autocorrelation of a Boolean function possesses the capability to reflect such characteristics as linear structure, Strict Avalanche Criterion(SAC) and Propagation Criterion(PC)of degree k. But it can do nothing in determining the order of SAC or PC. A calculating table for the autocorrelation is constructed in this paper so as to show what is beyond the autocorrelation and how the three cryptographic characteristics are exhibited. A deeper study on the calculating table in a similar way has helped us to develop a new concept, named as the general autocorrelation, to address efficiently the problem how to determine the orders of SAC and PC. The application on the Advanced Encryption Standard(AES) shows the SAC and PC characteristics of Boolean functions of AES S-box.

The mechanism and criterion of tectonic zone around karstic collapse column reactivation-induced water-conducting

In order to study the mechanism of tectonic zone around karstic collapse col-umn reacts to leak water and prevent water invasion in mine. According to the character of the surrounding cracks- penetrated water KCC, The fracture mechanics theory can be used to study the propagation and perforation process of cracks and hitches around the KCC. The criterion of crack start rupture and the length of secondary crack and criterion of crack propagation have been attained. The influencing factors of KCC reacts to water con-duction were analyzed.

Towards fully automatic modelling of the fracture process in quasi-brittle and ductile materials:a unified crack growth criterion

Fully automatic finite element(FE) modelling of the fracture process in quasi-brittle materials such as concrete and rocks and ductile materials such as metals and alloys,is of great significance in assessing structural integrity and presents tre-mendous challenges to the engineering community. One challenge lies in the adoption of an objective and effective crack propagation criterion. This paper proposes a crack propagation criterion based on the principle of energy conservation and the cohesive zone model(CZM) . The virtual crack extension technique is used to calculate the differential terms in the criterion. A fully-automatic discrete crack modelling methodology,integrating the developed criterion,the CZM to model the crack,a simple remeshing procedure to accommodate crack propagation,the J2 flow theory implemented within the incremental plasticity framework to model the ductile materials,and a local arc-length solver to the nonlinear equation system,is developed and im-plemented in an in-house program. Three examples,i.e.,a plain concrete beam with a single shear crack,a reinforced concrete(RC) beam with multiple cracks and a compact-tension steel specimen,are simulated. Good agreement between numerical predictions and experimental data is found,which demonstrates the applicability of the criterion to both quasi-brittle and ductile materials.

不同应力路径下岩石细观力学性能离散元研究

岩体工程中的应力状态对围岩的稳定性具有重要影响。为研究地下巷道中岩体应力状态对围岩稳定性的影响规律,基于离散元理论,对地下巷道开挖过程的应力状态进行分析,开展了围压卸载—轴压增加、围压卸载—轴压不变和围压卸载—轴压减少3种不同卸载路径下的三轴压缩数值模拟试验,并与常规三轴压缩试验进行对比,分析了不同应力路径下的岩石宏观强度特征及细观损伤过程差异性。结果表明:强度准则和应力张量状态不受卸载路径的影响,但不同应力路径下岩体的损伤过程不同,围压卸载—轴压不变应力路径下的微观裂纹发育最密集,而围压卸载—轴压增加应力路径下的裂纹丛集速度最快。研究结果可为地下巷道开挖过程中的围岩应力卸载破坏分析提供参考。

复杂水力裂缝网络延伸规律研究进展

随着天然裂缝性储层、煤层气、页岩气、致密砂岩气、致密油和复杂岩性低渗透油气藏勘探开发进程的加快,大规模体积压裂实践及微地震裂缝实时监测技术对水力裂缝延伸模拟提出了巨大挑战。复杂网络裂缝延伸受储层岩性、岩石力学性质、地质力学和天然裂缝特征等影响,文中综述了天然裂缝对水力诱导裂缝延伸影响的国内外研究进展。水力诱导裂缝与天然裂缝相交前、相交时和相交后的复杂力学行为决定了水力诱导裂缝的复杂延伸规律:水力裂缝尖端逼近时,诱导应力场会导致胶结天然裂缝张性或剪性脱粘;相交时,天然裂缝可能出现剪切破裂导致压裂液大量滤失、或水力裂缝穿过天然裂缝沿原方向延伸、或转向沿天然裂缝延伸并在其端部或弱结构点起裂;相交后,可能出现多个裂缝尖端同时延伸的情况,形成复杂网络裂缝。真三轴压裂测试系统结合工业CT扫描、声发射装置、X-衍射等是研究复杂网络裂缝形成机理的主要试验手段;而非常规裂缝模型和扩展有限元方法(XFEM)是模拟复杂网络裂缝延伸的主要数值手段。XFEM是处理含裂纹等不连续问题的最有效方法,并具有有限元方法的所有优点,考虑到裂缝内流体压力是水力裂缝延伸的驱动力,故基于XFEM的渗流-应力-裂缝延伸全耦合研究是未来体积压裂复杂网络裂缝延伸模拟的重要发展方向。

渗透压作用下压剪岩石裂纹损伤断裂机制

在研究渗透水压和远场应力共同作用下压剪滑移型岩石裂纹的起裂、扩展规律的基础上,考虑分支裂纹相互作用,建立压剪应力场和渗流场共同作用下岩石裂纹体的损伤断裂力学模型和考虑岩桥损伤所引起的附加应力强度因子演化方程,提出分支裂纹临界长度时裂纹尖端虚拟应力强度因子KI(LC)作为压剪岩石裂纹的损伤断裂贯通的破坏准则。研究结果表明:在既定裂纹分布下,分支裂纹尖端应力强度因子KI受侧压力系数λ、渗透压p、裂纹表面摩擦因数μ的制约;当轴向应力和裂纹面摩擦因数一定时,在低渗透压、侧向拉应力共同作用下,压剪岩石裂纹趋向于轴向贯穿破坏,而在高渗透压作用下会导致分支裂纹尖端岩桥剪切破坏。