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针对薄宽带钢冷轧过程中易发多发的局部型中浪瓢曲缺陷,引入非均匀载荷宽度、弹性约束系数及平均张应力建立了屈曲变形的解析计算模型。应用能量最低原理对屈曲变形区域进行搜索求解,得到了局部型中浪屈曲临界条件(包括临界应力、屈曲波长和屈曲波宽),获得了其与非均匀载荷宽度、弹性约束系数、平均张应力的关系,并发现平均张应力是产生局部型中浪的重要影响因素。应用样条有限元方法对局部型中浪进行数值仿真分析,验证了屈曲解析计算方法的正确性。在实验轧机上进行了轧制研究,通过轧制获得了局部型中浪屈曲模态,对实验结果分析得到了相对应的屈曲临界条件,与解析法和样条有限元法结果基本吻合,证明了样条有限元计算方法与解析计算方法的正确性及其工程应用价值。 相似文献
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INFLUENCE OF DAMPING MODELS ON DYNAMIC ANALYSES OF A BASE-ISOLATED COMPOSITE STRUCTURE UNDER EARTHQUAKES AND ENVIRONMENTAL VIBRATIONS 下载免费PDF全文
Structural design simultaneously governed by earthquakes and environmental vibrations has received a lot of attention in recent years.Base-isolated composite structures are typically used in the above-mentioned structural design.The corresponding analysis involves validating structural safety under earthquakes and human comfort under environmental vibrations through a time-history analysis.Thus,a reasonable damping model is essential.In this work,the representatives of viscous damping model and rate-independent damping model,namely the Rayleigh damping model and uniform damping model,were adopted to investigate the influence of damping models on the time-history analysis of such structural designs.The energy dissipation characteristics of the above-mentioned damping models were illustrated via a dynamic test of recycled aggregate concrete specimens.A case study was performed on a base-isolated steelconcrete composite structure.The dynamic responses under the excitation of earthquakes and environmental vibrations were compared using different damping models.The uniform damping model was found to be more flexible than the Rayleigh damping model in dealing with excitations with different frequency components.The uniform damping model is both theoretically advantageous and easy to use,demonstrating its potential in dynamic analysis of structures designed simultaneously governed by earthquakes and environmental vibrations. 相似文献
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Effective vibration recognition can improve the performance of vibration control and structural damage detection and is in high demand for signal processing and advanced classification.Signal-processing methods can extract the potent time-frequency-domain characteristics of signals;however,the performance of conventional characteristics-based classification needs to be improved.Widely used deep learning algorithms(e.g.,convolutional neural networks(CNNs))can conduct classification by extracting high-dimensional data features,with outstanding performance.Hence,combining the advantages of signal processing and deep-learning algorithms can significantly enhance vibration recognition performance.A novel vibration recognition method based on signal processing and deep neural networks is proposed herein.First,environmental vibration signals are collected;then,signal processing is conducted to obtain the coefficient matrices of the time-frequency-domain characteristics using three typical algorithms:the wavelet transform,Hilbert-Huang transform,and Mel frequency cepstral coefficient extraction method.Subsequently,CNNs,long short-term memory(LSTM)networks,and combined deep CNN-LSTM networks are trained for vibration recognition,according to the time-frequencydomain characteristics.Finally,the performance of the trained deep neural networks is evaluated and validated.The results confirm the effectiveness of the proposed vibration recognition method combining signal preprocessing and deep learning. 相似文献
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中国电影资料馆珍藏着大量早期影片,其中许多具有珍贵的保存价值.1936年由蔡楚生编导、任光谱曲的<迷途的羔羊>是我国第一部以流浪儿童为题材的影片,也是我国儿童影片中的第一部有声片.此片在思想和艺术上都取得了突破,尤其是以童谣形式演唱的主题歌<月光光歌>感人至深,充分发挥了音乐的魅力,增强了整部影片的感染力.影片公映后,深受广大观众的欢迎和电影工作者的赞扬.七十多年过去了,当我们准备再次让它同观众见面时,却发现能够最真实、最原始记录影音效果的原底、声底片却出现了许多问题,给复制工作带来了空前的难度,这是我们从事资料影片复制工作三十多年来从未遇到过的难题.主要有以下几方面问题: 相似文献
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1989年是照片诞生后的第150周年.自从第一次将光影与化学结合起来用于从大自然中获得永恒的图片后,自然风光摄影就倍受争议.不管怎样,无论艺术还是科学,技艺还是职业,摄影都是产生于客观性与选择性之间,创造性与现实性之上的一种档案媒介.在最新的一次统计后,国家档案馆现今保存有1500万以上的照片档案.不管是百年前拍摄的还是上个星期刚刚拍摄的,照片所要传递出的要素通常是些非常独特的信息.无论照片、底片和幻灯片,是黑白的还是彩色的,无论旧与新,不管是退色了的还是色彩艳丽的,单独的还是成集合的,最为关键的是它们都见证了加拿大历史与社会的发展与兴衰. 相似文献
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科学哲学和技术哲学都是首先在欧美国家兴起的,可是,工程哲学却是于21世纪之初在中国和欧美发达国家同时兴起和基本同步发展的。文章简要介绍了2002年以来工程哲学在中国和欧美国家发展的重要事件和已经发表的重要著作,最后,简要评论了东、西方工程哲学发展的主要特点。 相似文献
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北京城区和远郊区大气细颗粒PM_(2.5)元素特征对比分析 总被引:4,自引:0,他引:4
为了对比大气悬浮颗粒PM2.5及其所含元素在北京城区与远郊区的特征,在2007年不同季节和2008年北京奥运会期间进行了PM2.5的采样分析。结果表明:城区PM2.5和元素的浓度均高于郊区,元素浓度在城区与郊区具有不同的季节变化特征,春、冬季地壳元素浓度在城区与郊区都有所增加,在城区S元素和其它污染元素在秋、冬季最高,而郊区S元素浓度在夏季最高。污染元素的富集程度夏秋季高于春冬季,郊区高于城区,城、郊两地PM2.5中元素来源相似。雾霾天PM2.5及元素浓度在城区增加明显,奥运期间污染元素的质量分数较奥运前明显降低。 相似文献
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Samit Kumar Gupta Yi Zou Xue-Yi Zhu Ming-Hui Lu Li-Jian Zhang Xiao-Ping Liu Yan-Feng Chen 《Advanced materials (Deerfield Beach, Fla.)》2020,32(27):1903639
The exploration of quantum-inspired symmetries in optical and photonic systems has witnessed immense research interest both fundamentally and technologically in a wide range of subject areas in physics and engineering. One of the principal emerging fields in this context is non-Hermitian physics based on parity-time symmetry, originally proposed in the studies pertaining to quantum mechanics and quantum field theory and recently ramified into a diverse set of areas, particularly in optics and photonics. The intriguing physical effects enabled by non-Hermitian physics and PT symmetry have enhanced significant application prospects and engineering of novel materials. In addition, there has been increasing research interest in many emerging directions beyond optics and photonics. Here, the state-of-the art developments in the field of complex non-Hermitian physics based on PT symmetry in various physical settings are brought together, and key concepts, a background, and a detailed perspective on new emerging directions are described. It can be anticipated that this trendy field of interest will be indispensable in providing new perspectives in maneuvering the flow of light in the diverse physical platforms in optics, photonics, condensed matter, optoelectronics, and beyond, and will offer distinctive application prospects in novel functional materials. 相似文献
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Earlier advances in air separation and liquefaction include improvements in: overall product recovery, feed air purification, more efficient heat exchange, optimum plant control, gradual improvement in efficiency of compressors and expanders. More recent improvements include use of structured packing in distillation columns, molecular sieve adsorbents for air purification, computer simulation and control of plants, and increased machinery efficiency. Advances in fabrication and construction techniques are aimed at reducing capital costs. This paper reviews modern developments in air separation and liquefaction and attempts in this context to suggest features that might be expected to arise in the early part of the third millennium. 相似文献
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文章通过对全国部分城市驾驶员交通事故和儿童意外伤害事故的流行病学研究结果发现 :(1 )驾驶员交通事故和儿童意外伤害事故检出率不存在地区性差异 ;(2 )驾驶员交通事故和儿童意外伤害事故的检出率无显著性的年龄差异 ;(3 )不同年龄段驾驶员和儿童 ,男性事故检出率均高于女性事故检出率 ;(4 )极少数的事故人群具有事故倾向性 :在驾驶人群中有 6%~ 8%的事故倾性驾驶员 ,其引起的交通事故数占总事故数的 3 0 %~ 40 % ,在 1~ 1 4岁儿童中有 1 %~ 2 %的事故倾性儿童 ,其发生的意外伤害数占意外伤害总数的2 5 %~ 3 5 % ;(5 )事故倾性驾驶员和事故倾性儿童再发事故的比率均比对照组高。文章从流行病学角度证实了事故倾性人群的存在 ,并对事故倾性的本质作了初步探讨。 相似文献
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为了探究江苏省各高校人文社科R&D效率影响因素和各高校人文社科R&D效率水平的差异,并考虑到评价单元投入的异质性问题,采用改进的DEA-CCR模型,对江苏省46所公办本科高校的人文社科R&D数据进行了实证分析。结果表明,江苏省46所公办本科高校在人文社会科学领域的科研效率水平尚可,但仍存在很大的进步空间,特别是“985”、“211”高校在人文社会科学的科研工作中需要取得突破性的进步,才能提高本校人文社会科学的科研效率。最后,根据所得结果,本文提出了各高校进一步提高在人文社会科学领域科研效率的针对性建议。 相似文献
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Ion-beam modifications of the surface morphology and conductivity in some polymer thin films 总被引:1,自引:0,他引:1
Studies on the surface micromorphology and surface conductivity in thin polymer films of poly vinyl alcohol (PVA) and poly
ethylene oxide (PEO) in both as-grown and ion-implanted polymer films have been carried out to reveal certain specific features
of the ordered state in these materials. Optical microscopic investigations revealed the existence and enhanced formation
in number of spherulites and dendrites in ion-implanted films relative to the as-grown films. The number and rate of formation
of spherulites indicated an increase in the degree of crystallinity in these films. Measurements of surface conductivity of
as-grown and ion-implanted polymer films, employing four-point probe method, indicated a decrease in electrical conductivity
on ion-implantation. Photomicrographic analysis of the PVA and PEO thin film surfaces, has enabled to propose a temperature-stress
induced mechanism of crystallization in conjunction with the surface conductivity measurements. The decrease in surface conductivity
on ion-implantation in both PVA and PEO thin films, is attributed to a decrease in mobility of macromolecular charged species
due to an increase in degree of crystallinity as has been observed by optical microscopy. 相似文献
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驾驶员与儿童事故倾性研究 总被引:4,自引:0,他引:4
文章通过对全国部分城市驾驶员交通事故和儿童意外伤害事故的流行病学研究结果发现:(1)驾驶员交通事故和儿童意外伤害事故检出率不存在地区性差异;(2)驾驶员交通事故和儿童意外伤害事故的检出率无显著性的年龄差异;(3)不同年龄段驾驶员和儿童,男性事故检出率均高于女性事故检出率;(4)极少数的事故人群具有事故倾向性:在驾驶人群中有6%~8%的事故倾性驾驶员,其引起的交通事故数占总事故数的30%~40%,在1~14岁儿童中有1%~2%的事故倾性儿童,其发生的意外伤害数占意外伤害总数的25%~35%;(5)事故倾性驾驶员和事故倾性儿童再发事故的比率均比对照组高。文章从流行病学角度证实了事故倾性人群的存在,并对事故倾性的本质作了初步探讨。 相似文献