环焊缝强度匹配对长输管道性能的影响

环焊缝强度匹配是天然气管道研究与应用的热点问题.介绍了焊接接头匹配性的概念,阐述了不等强匹配对长输管道极限载荷、韧性、残余应力、缺陷容限等的影响,最后提出了在长输管道环焊缝强度匹配领域需要解决的技术问题.     

Syntactic mismatches in machine translation

This paper addresses one of the central problems arising at the transfer stage in machine translation: syntactic mismatches, that is, mismatches between a source-language sentence structure and its equivalent target-language sentence structure. The level at which we assume the transfer to be carried out is the Deep-Syntactic Structure (DSyntS) as proposed in the Meaning-Text Theory (MTT). DSyntS is abstract enough to avoid all types of divergences that result either from restricted lexical co-occurrence or from surface-syntactic discrepancies between languages. As for the remaining types of syntactic divergences, all of them occur not only interlinguistically, but also intralinguistically; this means that establishing correspondences between semantically equivalent expressions of the source and target languages that diverge with respect to their syntactic structure is nothing else than paraphrasing. This allows us to adapt the powerful intralinguistic paraphrasing mechanism developed in MTT for purposes of interlinguistic transfer.     

Robust Space Time Receiver for CDMA-based Antenna Arrays

In this paper, we propose a new robust code division multiple access (CDMA) receiver of which weight vector is obtained by projecting the effective spatio-temporal signature waveform onto the signal subspace of the data covariance matrix. We verified our proposed algorithm by the field measured data obtained with a custom-built wideband CDMA test-bed. It will be shown that the proposed algorithm is robust to the signal mismatch.     

Effects of crack size and weld metal mismatch on the has cleavage toughness of wide plates

The heat affect zone (HAZ) is in many cases considered to be the most critical part of a weldment. In this paper, the effect of crack size and weld metal mismatch on the HAZ cleavage toughness of wide plate specimens with X-groove has been investigated by the J-Q-M theories and a simple micromechanism for cleavage fracture. Two crack sizes have been studied (a/w = 0.1 and 0.3). In the analyses, the HAZ yield strength is assumed to be higher than the base metal. For each crack size, weld metal local overmatch and local evenmatch with respect to the HAZ are considered. For a given global strain, the results indicate that weld metal overmatch and evenmatch yield the same crack tip loading in terms of J-integral for a/w = 0.3. For a/w = 0.1, overmatch gives lower crack tip loading than evenmatch. For a given crack tip loading, weld metal local evenmatch in general results in less effective crack tip loading than the overmatch. Overmatch is detrimental to HAZ toughness, but this detrimental effect becomes less significant when the crack size decreases.     

Studies on nucleation kinetics of InxGa1−xN/GaN heterostructures

Nucleation kinetics during the growth of In_xGa_1−xN on a GaN substrate have been studied. The behavior of nonequilibrium between the In_xGa_1−xN and the GaN substrate has been analyzed, and hence, the expression derived for the stress-induced supercooling/superheating has been numerically evaluated. The maximum amount of stress-induced supercooling is found to be 1.017 K at x=0.12. These values are incorporated in the classical heterogeneous nucleation theory. Using the regular solution model, the interfacial tension between the nucleus and substrate and, hence, the interfacial tension between nucleus and mother phase and thermodynamical potential of the compounds have been calculated. The amount of driving force available for the nucleation has been determined for different compositions and degrees of supercooling. It has been shown that the value of the interaction parameter of InN-GaN plays a dominant role in nucleation and growth kinetics of In_xGa_1−xN on a GaN substrate. These values have been used to evaluate the nucleation parameters. It is shown that the nucleation barrier for the formation of a In_xGa_1−xN nucleus on a GaN substrate is minimum in the range of x=0.12 to x=0.17, and it has been qualitatively proved that good quality In_xGa_1−xN on GaN can be grown only in the range 0<x≤0.2.     

MOS晶体管的阈值电压不匹配特性

集成电路中器件的匹配性对于模拟电路和数字电路的设计有着很重要的影响,而现在重要的是还缺乏精确的器件匹配的模型。在模拟集成电路设计中,MOS管阈值电压的匹配特性对集成电路尤其是电流Ids的大小有着重要的影响。基于短沟道系列模型,MOS氧化层中的固定电荷和杂质原予服从泊松分布,分析了NMOS和PMOS器件不匹配的物理原因,并验证σVT/VT遵循与1/(?)成比例的结论。     

基于余弦相似度的改进ORB匹配算法

针对ORB(oriented FAST and rotated BRIEF)在匹配多相似区域图像时误匹配率高的问题,提出一种基于余弦相似度的改进ORB算法。该算法首先通过汉明距离(Hamming distance)最近邻匹配,计算匹配特征向量的余弦相似度;其次通过梯度计算法计算余弦相似度的最优阈值范围;然后将汉明距离高自由度最近次近邻粗匹配结果,利用余弦相似度不变性剔除不在最优阈值范围的匹配点;最后用RANSAC算法再次精确匹配。实验结果表明:该算法能在保证匹配特征点数以及实时性的基础上,高效降低误匹配率,尤其在匹配多相似区域图像时,可将原算法产生的误匹配率降低80%左右,同时该算法还超越了原算法在图像发生视角、旋转、尺度、模糊、光照变化时的适应性。     

NiTi形状记忆合金的相变温度滞后

用透射电镜、正电子湮没和电阻测量,研究了NiTi形状记忆合金的组织结构与相变滞后的关系结果表明,经不同制度时效处理的组织,其相变温度滞后大小的顺序是:片状马氏体>R相>束状马氏体。Ti_(11)Ni_(14)相质点周围的共格应力场对这些相的可逆转变起障碍作用。正电子湮没Doppler展宽能谱S参数值与试样的温度滞后值之间存在线性关系,从而确认Ti_(11)Ni_(14)相析出的错配位错密度及由此而建立的晶体中弹性应力场分布是决定NiTi合金相变温度滞后的主要因素。     

Creep-induced local lattice parameter changes in a monocrystalline nickel-base superalloy

The γ-γ lattice mismatch of specimens of the monocrystalline nickel-base superalloy SRR 99 has been measured by a high-resolution X-ray diffraction technique for the undeformed state and after high-tem-perature creep deformation. During creep deformation beyond the minimum creep rate (total strain =0.5%), the lattice mismatches, measured in and perpendicular to the [001] stress axis, respectively, un-dergo changes in opposite directions. This reflects the buildup of a complex deformation-induced triaxial state of internal stress in the phases y and γ. The overall resolved shear stresses that act in γ and y due to the combined action of the external and internal stresses are estimated, and the conditions under which cutting of the γ phase by dislocations should occur are discussed.