扩展

Active attack cryptanalysis based and fully scalable FGS encryption algorithm Aimed to the weakness of the current selective encryption algorithms in the sense of cryptanalysis, we design a active spacial—temporal correlation attack scheme and propose a both encryption strategies on base-layer and enhancement-layer. Not only the general FGS stream encryption is dealt with but also the case of FGST (fine granularity sealable temporal) is also well addressed.

2基于主动攻击安全的充分可扩展FGS加密算法针对目前压缩视频流加密算法所经常采用的选择加密方法，通过进行主动时域、空域相关性攻击，指出该类算法存在的问题，包括对于FGS基本层单独加密的安全分析，然后设计实现了基本层和增强层同时加密的安全策略，为保证FGS充分可扩展功能，算法同时还支持细粒度时域可扩展编码FGST(fine granularity scalable temporal)的情况。

On the basis of previous approaches to query expansion, this paper proposes a new approach to query expansion based on set theory,which combines three traditional methods—thesauri,automatic relevance feedback and the related words of the question type.

通过分析已有的查询扩展方法，提出了基于集合论的查询扩展新方法。它结合了3种传统的查询扩展方法：语义词典法、自动相关反馈法和问题类型词。实验结果表明该方法在Web检索方面是有效并且优于传统的方法。

The damage and failure modes of brittle materials under tension and compression are different. The self-similar growth of open microcracks under tension, the frictional sliding, mode-n self-similar growth and kinking of closed microcracks under compression and their influences on the mechanical properties of materials are studied in detail.

在拉伸和压缩情况下微裂纹损伤机制和材料破坏模式都不相同，本文对张开微裂纹的自相似扩展和闭合微裂纹的摩擦滑移、自相似扩展、弯折扩展进行了详细的研究，分别给出了它们对材料的宏观力学性质的影响。

Even though at a very low temperature (-196℃), the cleavage cracking dominates the fracture process, it can not propagate straight forward through entire ligament and shows the pop-in extension in macroscopic tests and the quasi-cleavage mode in microscopic feature. It is found that the strong resistance which hinders the crack propagation is provided by three barriers: original austenite grain boundaries, bainite colony boundaries and inter-layers between bainite laths.

在－196℃的极限温度下，准解理开裂控制了整个断裂过程，但它仍然不能扩展通过整个韧带，在宏观曲线上出现POP-IN的扩展特征，微观上表现为准解理特征和韧性撕裂特征断口交替出现；同时发现阻止裂纹扩展的阻力来源于三个方面：原奥氏体晶粒边界，贝氏体团边界以及贝氏体片。

The mechanical mechanism of crack formation and crack growth based on partial concentration of stress of the roadbed are discussed. Crack growth is controlled by tensile stress and crack growth angle which is controlled by shear stress.

就路堤应力集中现象来讨论裂纹的形成和扩展力学机理，即裂纹扩展主要受拉应力作用，而裂纹的扩展角受剪应力的控制。

As a foundation of measuring the dynamic stress intensity factor, the influences of geometry and size of the caustics due to the crack propagation velocity are analyzed in detail.

特别分析了裂纹扩展速度对焦散斑和初始曲线的形状、大小的影响，为测量扩展裂纹尖端的动态应力强度因子K_1~d提供了依据，并通过拟合得到了以裂纹扩展速度为参量的修正因子表达式。

Thus, we may have to extend our view from one dimensional axis to multi-dimensional space, m -space, and to extend our research tools from scalars to multi-component vectors, m -vectors.

因而，我们可能要扩展我们的眼光，把我们的眼光从一维的&数轴&扩展到&多维空间&，把我们的分析工具从&标量&扩展到&多元向量&。

The conclusions are: The sonic velocity determined by the material's properties is the upper limit of the crack velocity; Bridging fibers plays a key role in increasing the composite's toughness and stopping the crack's propagation; The semi-infinite crack propagating in infinite region with the fiber bridging traction action is equal to the semi-infinite crack propagating in strip.

结论有：(1)由材料性能决定的音速是裂纹传播速度的上限；(2)桥联纤维在增韧复合材料和组织裂纹扩展中起了关键作用；(3)受桥联纤维力作用的半无限长裂纹在无限域中扩展等效于半无限长裂纹在带域中扩展。

It is clarified for the first time that the thermal fatigue failure of solder joint is actually a creep strain low cycle fatigue failure, and a physical model for creep fatigue crack propagation has been proposed. It was pointed out that creep strain increases in the high stress area ahead of the tip of thermal fatigue crack, results on one hand that the slide of crack tip increase, inactivation more serious and crack close length increases, the other hand, that intergranular crack exists, whose direction will affect the fatigue crack propagating.

本文首次阐明了焊点的热循环失效本质上是以焊点内循环蠕变为主要应变的低周疲劳失效，并在此基础上提出了蠕变疲劳裂纹扩展的物理模型，指出热循环裂纹前端的高应力区内，蠕变加剧，使裂纹前端滑移增加，裂纹钝化加剧，导致随后的裂纹闭合扩展长度增加；同时蠕变也使裂纹前端的高应力区出现晶间裂纹，蠕变沿晶裂纹对主裂纹扩展的影响取决于沿晶裂纹的连接方向。

The main research tasks and results are as follows:(1) Through comparing the stress intensity factor of compact tension specimen calculated by finite element software with the theoretical value, the feasibility of calculating fracture parameters of crack tip in ABAQUS software was verified.(2) The relationship between the elastic modulus of the material and research scale was studied based on deriving the cohesive stress theory and other relevant theories. And the elastic modulus of the material on meso-scale was determined.(3) Global model and sub-model of the finite element were built in th...e macro-scale, and stress-strain field nearby the crack tip was analyzed, and the results show that the detailed stress-strain in the crack tip could be obtained by using the sub-model technique.(4) In meso-scale, the crack growth model was also established by assuming the crack propagating along the grain boundary, and the detailed stress-strain field in the crack tip was obtained.(5) The effect of crack length on Von Mises stress, and maximum principal stress and strain was analyzed in meso-scale when equivalent KI equals 30MPa.m1/2. And the results show that except for crack tip area, the stress-strain distribution in whole specimen is not affected.

主要完成研究内容和取得成果如下：(1)利用有限元软件计算出紧凑拉伸试样的裂纹尖端应力强度因子KI值，其结果与理论值一致，从而验证了利用ABAQUS计算裂纹尖端相关断裂参量的可行性；(2)在研究内聚应力等相关理论的基础上，推导出了研究尺度与材料弹性模量的近似关系，并确定了介观尺度上的弹性模量；(3)在宏观尺度上建立了全局有限元计算模型和子模型，得到了裂纹尖端应力应变场分布，结果表明利用子模型技术获得比较准确的裂纹尖端应力应变场分布是可行的；(4)在介观尺度上利用平均晶粒尺度的方式建立了裂纹沿晶扩展模型，得到了裂纹尖端断裂过程区的微观应力应变场；(5)当应力强度因子为30MPa.m1/2时，分析了介观尺度上在裂纹沿晶扩展过程中裂纹长度对Mises应力、最大主应力和应变的影响，结果表明，裂纹扩展长度对试样整体应力应变分布影响不大，而对裂纹尖端区域有较大影响；(6)介。。。

Chrysanthemum of 10 thousand birthday is lax to edaphic requirement, with the arenaceous qualitative loam with fecund, good drainage had better.

万寿菊对土壤要求不严，以肥沃。排水良好的砂质壤土为好。

He unstepped the mast and furled the sail and tied it.

他拔下桅杆，把帆卷起，系住。