桂林市岩溶塌陷及防治

根据收集的大量钻探资料统计, 分析了桂林市岩溶地面塌陷的成因机制、分布规律及防治措施, 对桂林市的市政工程建设具有一定的参考价值。     

Electric-stress reliability and current collapse of different thickness SiNx passivated AlGaN/GaN high electron mobility transistors

This paper investigates the impact of electrical degradation and current collapse on different thickness SiNx passivated AlGaN/GaN high electron mobility transistors.It finds that higher thickness SiNx passivation can significantly improve the high-electric-field reliability of a device.The degradation mechanism of the SiNx passivation layer under ON-state stress has also been discussed in detail.Under the ON-state stress,the strong electric-field led to degradation of SiNx passivation located in the gate-drain region.As the thickness of SiNx passivation increases,the density of the surface state will be increased to some extent.Meanwhile,it is found that the high NH 3 flow in the plasma enhanced chemical vapour deposition process could reduce the surface state and suppress the current collapse.     

Effects of SiNx on two-dimensional electron gas and current collapse of AlGaN/GaN high electron mobility transistors

SiN_x is commonly used as a passivation material for AlGaN/GaN high electron mobility transistors (HEMTs). In this paper, the effects of SiN_x passivation film on both two-dimensional electron gas characteristics and current collapse of AlGaN/GaN HEMTs are investigated. The SiN_x films are deposited by high- and low-frequency plasma-enhanced chemical vapour deposition, and they display different strains on the AlGaN/GaN heterostructure, which can explain the experiment results.     

基于工业CT图像重构的网格模型的保特征简化方法

对基于工业CT图像重构的网格模型进行网格简化时,大多数现有网格模型简化算法会丢失特征,出现网格质量不好的问题。因此提出一种网格模型保特征简化方法,该方法用三角形折叠法对原始模型进行简化,当简化后模型的平均二面角角度误差达到允许误差后,再使用边折叠法对模型进行简化。在三角形折叠法中提出了利用被折叠三角形的法向量、各个顶点的高斯曲率及其在周边三角形上的投影确定该三角形的折叠点,利用局部体积误差与二面角角度误差的无因次化和确定折叠代价的方法;在边折叠法中提出了将二面角角度误差引入到二次误差测度（QEM）法的折叠代价中的改进QEM法。实验结果表明：与其他算法相比,该方法能够生成保特征、高质量、低几何误差的网格模型。     

基于数据重建的三角网格模型简化优化方法

由CT切片数据重建得到的三角网格模型常存在数据量大、狭长三角形多等问题,针对这些问题,研究了一种保持特征的高质量三角网格模型的简化优化方法。该方法分为网格简化和网格优化两个阶段。首先,采用基于曲面变化的二次误差度量计算边折叠代价,并按代价值的大小进行迭代的折叠简化,可较好地保持模型表面的特征;其次,通过二阶加权伞算子对简化模型中局部存在的狭长三角形进行优化处理,改善三角网格模型的质量。实验结果表明,该方法能够较好地保持特征区域的细节信息,并可靠地生成高质量、低几何误差的简化模型。     

伪火花放电开关电压跌落过程实验研究

设计了典型参数下的伪火花放电开关,进行了空气介质下的电压特性实验,给出了伪火花开关放电电压与气压变化的关系曲线;测量了产生伪火花放电的气压范围（1~29Pa）和单间隙伪火花放电开关耐受电压的最大值(40kV),测得了伪火花放电与辉光放电的转折点气压(29Pa),并对实验结果进行了理论分析。研究了伪火花放电开关电压跌落时间与放电电压的关系,首次将开关电压跌落过程分为暂态阶段和稳态阶段,讨论了放电电路参数,气体压力,开关结构和放电电压对电压跌落时间的影响。实验表明,在气压和开关结构不变的条件下,暂态过程时间由放电电压决定,电压越高,则所需时间就越短;稳态过程时间由放电电路参数决定,不受放电电压影响。     

索-桁预应力穹顶结构的动力性能研究

索－桁结构是一种有潜力的空间结构，但目前的研究尚不够深入，本文提出了一种圆形索－桁预应力结构，采用反应谱法和时程法分析，研究了其动力性质，结果表明，该种结构的频谱极为密集，振型较为复杂，这类结构采用反应谱法计算动内力将导致不可接受的误差，而应采用相应的时程分析法计算动内力，同时还得出了这种结构预应力的施加不可缺少，否则将有可能导致动力破坏的结论。     

Causality Implies Formal State Collapse

A physical theory of experiments carried out in a space-time region can accommodate a detector localized in another space-like separated region, in three, not necessarily exclusive, ways: (1) the detector formally collapses physical states across space-like separations, (2) the detector enables superluminal signals, and (3) the theory becomes logically inconsistent. If such a theory admits autonomous evolving states, the space-like collapse must be instantaneous. Time-like separation does not allow such conclusions. We also prove some simple results on structural stability: within the set of all possible theories, under a weak empirical topology, the set of all theories with superluminal signals and the set of all theories with retrograde signals are both open and dense.     

Letter: Self-Similar Collapse of Scalar Field with Plane Symmetry

Plane symmetric self-similar solutions to Einstein's four-dimensional theory of gravity are studied and all such solutions are given analytically in closed form. The local and global properties of these solutions are investigated and it is shown that some of the solutions can be interpreted as representing gravitational collapse of the scalar field. During the collapse, trapped surfaces are never developed. As a result, no black hole is formed. Although the collapse always ends with spacetime singularities, it is found that these singularities are spacelike and not naked.     

A renormalization group analysis of lattice models of two-dimensional membranes

We study lattice models of two-dimensional membranes of interest in statistical physics. The energy functional of a membrane is expressed as a sum of terms proportional to the surface area of the membrane, an extrinsic curvature and an intrinsic curvature quantity, respectively, but we neglect excluded volume effects. We introduce a renormalization transformation for these models which preserves the form of the energy functional, up to nonlocal terms. Our renormalization group construction is used to analyze the phase diagram and the different critical regimes of our models. We find evidence for a crumpling transition, separating a regime where surfaces are crystalline from one where the surfaces collapse to branched polymers, and we find a third genuine random-surface regime.