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1.
高速目标平动补偿是弹道目标微动特征信息提取中一个较难解决的问题.利用弹道导弹宽带回波信号,提出了一种基于散射中心极化散射特性的非相干宽带回波对齐方法,通过极化相似性参数实现散射点中心对齐,并利用目标散射中心的高分辨一维距离像走动提取瞬时微动参数,对目标的尺寸和微动参数进行估计.仿真结果表明,该方法可以有效地在较低信噪比下实现包络对齐与微动参数提取,为后续工程化应用奠定了理论基础.  相似文献   
2.
海上风机基础正常工作条件下要承受上部结构传递的水平荷载H、倾覆力矩M及竖向荷载V,单桩-摩擦盘复合基础(桩盘复合基础)结合了单桩基础和重力式基础的承载优势,是一种新型的海上风机基础形式。为研究桩盘复合基础在组合力下的承载特性,基于自行设计的V-H组合加载装置,完成一系列桩盘复合基础室内载荷模型实验,获得了上硬下软地层中V-H共同作用时桩盘复合基础的水平荷载-位移曲线及桩身弯矩分布。经无量纲化处理和拟合,得到组合力下桩盘复合基础承载力包络线及计算公式。之后在模型试验的基础上建立多组数值模型,并通过数值模拟对桩盘复合基础的组合受力特性进行参数分析。结果表明:桩盘复合基础在上硬下软地层中V-H荷载空间的承载特性明显优于单桩基础;V-H组合作用时,预先施加的V在达到(0.5~0.6)Vu时,其对基础的水平及弯矩承载力提高作用最明显。实际工程中,可根据海上风机受力特点与破坏包络线的关系进行基础设计,由本研究拟合得到的承载力计算公式可评估桩盘复合基础的承载能力。  相似文献   
3.
The original unified hardening (UH) model, in which a straight Hvorslev envelope was employed to determine the potential peak stress ratio of overconsolidated soils, is revised using a smoothed Hvorslev envelope (Hermite-Hvorslev envelope). The strength at the intersection between the straight Hvorslev envelope and the critical state surface (i.e. Mohr-Coulomb envelope) can be undefined due to the discontinuous change in the slope of the two linear strength envelopes mentioned above. A smoothed Hvorslev envelope is derived through Hermite interpolation to ensure a smooth change between the proposed Hvorslev envelope and the zero-tension surface as well as a smoothed transition between the proposed Hvorslev envelope and the critical state surface. The Hermite-Hvorslev envelope is then integrated into the original UH model, and then the UH models with four different functions of the Hvorslev envelope are compared with each other. The UH model revised by the Hermite-Hvorslev envelope can well predict the mechanical behaviors of normally consolidated and overconsolidated soils in drained and undrained conditions with the same parameters in the modified Cam-Clay model.  相似文献   
4.
In this study, a method has been proposed to obtain the failure envelope of brittle adhesives using the experimental failure loads of precracked single lap joints (SLJs). The proposed technique is based on the principles of linear elastic fracture mechanics (LEFM), on J-integral relations, and on results of a numerical analysis. Compared to the previous approaches, the introduced experimental method has some advantages such as low manufacturing costs and simpler test procedure. The proposed method can also provide a wide range of mode mix ratios without the need of an additional apparatus. The fracture envelope obtained from the proposed method was then verified by performing some fracture tests including double cantilever beam (DCB), end-notched flexure (ENF), and single leg bending (SLB) specimens. Good correlation was seen between the fracture envelopes of the proposed method and the ones obtained from the fracture mechanics experiments.  相似文献   
5.
地震动具有显著的时域和频域非平稳性,传统的均匀调制地震动模型不能充分表征时频两域的非平稳性,并影响结构随机振动分析的精准度。为了克服上述不足,建立由多峰平滑包络和非平稳噪声信号点乘而成的非均匀调制地震动模型,该模型能够在时域上充分反映地震动的波动和衰减特性,同时其频谱特征也与真实信号相接近。在此基础上,建立同时以时间和频率为变量的非平稳地震动演变谱随机模型。分析结果表明,以上两种模型在时域和频域的合成精度上均优于均匀调制模型。针对以上地震动随机模型的形式和特点,对传统结构随机振动响应求解方法进行改进。通过算例证明,按照均匀调制模型计算结构随机响应不能充分获得结构时频域的非平稳特性且结果偏于不安全,而利用两种改进模型可以获得更精确的结构响应概率特征和更细致的非平稳性演变过程。  相似文献   
6.
Laminopathies are a clinically heterogeneous group of disorders caused by mutations in the LMNA gene, which encodes the nuclear envelope proteins lamins A and C. The most frequent diseases associated with LMNA mutations are characterized by skeletal and cardiac involvement, and include autosomal dominant Emery–Dreifuss muscular dystrophy (EDMD), limb-girdle muscular dystrophy type 1B, and LMNA-related congenital muscular dystrophy (LMNA-CMD). Although the exact pathophysiological mechanisms responsible for LMNA-CMD are not yet understood, severe contracture and muscle atrophy suggest that mutations may impair skeletal muscle growth. Using human muscle stem cells (MuSCs) carrying LMNA-CMD mutations, we observe impaired myogenic fusion with disorganized cadherin/β catenin adhesion complexes. We show that skeletal muscle from Lmna-CMD mice is unable to hypertrophy in response to functional overload, due to defective fusion of activated MuSCs, defective protein synthesis and defective remodeling of the neuromuscular junction. Moreover, stretched myotubes and overloaded muscle fibers with LMNA-CMD mutations display aberrant mechanical regulation of the yes-associated protein (YAP). We also observe defects in MuSC activation and YAP signaling in muscle biopsies from LMNA-CMD patients. These phenotypes are not recapitulated in closely related but less severe EDMD models. In conclusion, combining studies in vitro, in vivo, and patient samples, we find that LMNA-CMD mutations interfere with mechanosignaling pathways in skeletal muscle, implicating A-type lamins in the regulation of skeletal muscle growth.  相似文献   
7.
Proteins displayed on the cell surface of lactic acid bacteria (LAB) perform diverse and important biochemical roles. Among these, the cell-envelope proteinases (CEPs) are one of the most widely studied and most exploited for biotechnological applications. CEPs are important players in the proteolytic system of LAB, because they are required by LAB to degrade proteins in the growth media into peptides and/or amino acids required for the nitrogen nutrition of LAB. The most important area of application of CEPs is therefore in protein hydrolysis, especially in dairy products. Also, the physical location of CEPs (i.e., being cell-envelope anchored) allows for relatively easy downstream processing (e.g., extraction) of CEPs. This review describes the biochemical features and organization of CEPs and how this fits them for the purpose of protein hydrolysis. It begins with a focus on the genetic organization and expression of CEPs. The catalytic behavior and cleavage specificities of CEPs from various LAB are also discussed. Following this, the extraction and purification of most CEPs reported to date is described. The industrial applications of CEPs in food technology, health promotion, as well as in the growing area of water purification are discussed. Techniques for improving the production and catalytic efficiency of CEPs are also given an important place in this review.  相似文献   
8.
随着油气田开发程度的深入,复合河道砂体尺度的研究难以满足生产需求,需要开展单河道砂体边界的识别。埕海一区明化镇组曲流河河道频繁地决口、改道和侧向迁移,复合河道砂体较为发育。依据单河道砂体接触部位地震波形及振幅发生变化的特点,首先利用边缘检测属性突出岩性变化引起的振幅响应,识别出单河道的边界;再利用倾角方位属性能够反映地震波形的细微变化,预测单河道的侧向迁移方向;借助上述方法识别研究区单河道的边界,并且精确预测了单河道点坝砂体的具体位置。预测结果与钻井吻合程度较高,有效地指导了井网关系调整及剩余油挖潜,也为类似地区的单河道识别与划分提供了一种新的方法。  相似文献   
9.
10.
为解决风电机组传动链易发生故障的问题,文章阐述了风电机组齿轮箱特征频率的计算方法和基于振动信号分析的故障特征提取方法。结合实际情况,以行星级齿轮磨损、中间轴小齿轮崩齿、高速轴齿轮崩齿和发电机轴承电腐蚀等典型故障为例,通过齿轮箱特征频率和传动链典型故障振动信号基本特征分析,可较好地完成故障识别。结果表明,采用经典信号处理方法能对上述典型故障进行特征提取,验证了经典方法对单一、明显故障特征提取的有效性,为深入开展传动链故障特征提取方法研究奠定了基础,为风电机组故障检修维护提供了技术支撑。  相似文献   
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