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1.
《Ceramics International》2021,47(19):27386-27394
In order to control the pore characteristics and macroscopical performance of porous ceramics, roles of the freeze casting parameters are the key points. Herein, aligned dendritic porous SiC was fabricated by freeze casting of PCS-camphene solutions with different solid loading, freeze front velocity, temperature gradient, and freezing temperature. Influence of these parameters on the microstructure and compressive strength of porous SiC was investigated. With increasing the PCS content, freeze temperature, freeze front velocity or temperature gradient, degree of undercooling of the camphene was increased, resulting in the formation of smaller pore size, decreased porosity and increased compressive strength. Compared to variables of freeze temperature and temperature gradient, increased freeze front velocity was more efficiency in improving the compressive strength of porous SiC, owing to the formation of smaller pore size and longer secondary dendritic crystals. Promising micron-sized porous SiC with high porosity (79.93 vol%) and satisfactory strength (15.84 MPa) was achieved for 10% PCS-camphene solution under optimized freezing conditions.  相似文献   
2.
Coupling of side chain dynamics over long distances is an important component of allostery. Methionine side chains show the largest intrinsic flexibility among methyl-containing residues but the actual degree of conformational averaging depends on the proximity and mobility of neighboring residues. The 13C NMR chemical shifts of the methyl groups of methionine residues located at long distances in the same protein show a similar scaling with respect to the values predicted from the static X-ray structure by quantum methods. This results in a good linear correlation between calculated and observed chemical shifts. The slope is protein dependent and ranges from zero for the highly flexible calmodulin to 0.7 for the much more rigid calcineurin catalytic domain. The linear correlation is indicative of a similar level of side-chain conformational averaging over long distances, and the slope of the correlation line can be interpreted as an order parameter of the global side-chain flexibility.  相似文献   
3.
In the recent advancements in image and video analysis, the detection of salient regions in the image becomes the initial step. This plays a crucial role in deciding the performance of such algorithms. In this work, a Multi-Resolution Feature Extraction (MRFE) technique that makes use of Discrete Wavelet Convolutional Neural Network (DWCNN) for generating features is employed. An Enhanced Feature Extraction (EFE) module extracts additional features from the high level features of the DWCNN, which are used to frame both channel as well as spatial attention models for yielding contextual attention maps. A new hybrid loss function is also proposed, which is a combination of Balanced Cross Entropy (BCE) loss and Edge based Structural Similarity (ESSIM) loss that effectively identifies and segments the salient regions with clear boundaries. The method is tested exhaustively with five different benchmark datasets and is proved superior to the existing state-of-the-art methods with a minimum Mean Absolute error (MAE) of 0.03 and F-measure of 0.956.  相似文献   
4.
采用热重分析法研究了经KOH浸渍的甲壳素的热解特性,并考察了不同浸渍比对热解过程的影响;同时采用Coats-Redfern积分法拟合计算出热解动力学参数,探究了KOH对甲壳素主要热解过程中活化能的影响。热重分析结果表明:KOH的加入改变了甲壳素的热解行为,降低了热解所需的活化能,加快了反应速率,促进了甲壳素热解;当浸渍比即m(65% KOH)∶m(甲壳素)=2∶1或3∶1时,KOH浸渍后能使甲壳素在140℃左右开始迅速热解。热解动力学参数计算结果表明:无论反应级数选择多大,其线性拟合效果均比较好,相关系数基本都高于0.95;KOH作用下甲壳素热解是一个复杂的化学反应,而不是单一的某一级反应。  相似文献   
5.
We study the structure, crystallization, and performances of the sealing glasses with the composition (mol.%) of 12Al2O3·8B2O3·40SiO2·40RO (R = Mg, Ca, Sr) for solid oxide fuel cells (SOFCs) before and after isothermal treatment at 700°C, which is within the operation temperature range (600-800°C) of SOFCs. The crystallization behavior has been investigated by differential scanning calorimetry and X-ray diffraction under both dynamic and isothermal conditions. The structural evolution is probed using the Raman and nuclear magnetic resonance spectroscopies. The performances of the sealing glasses are characterized in terms of the coefficient of thermal expansion, the crystallization-induced stress at glass–steel interface. We find that strong crystallization occurs at the operation temperature (700°C) far below the crystallization onset temperature measured by DSC. The structure origin of this anomalous crystallization is discussed in terms of structural heterogeneity of the three studied glasses. We determine the residual stress at the interface between the Ca-containing glass and the steel after isothermal treatment at 700°C for 48 h, but this stress does not lead to falling off the glass layer from the steel. This indicates that this glass is a good candidate to be applied in SOFCs.  相似文献   
6.
Lipopolysaccharide (LPS), the major component of the outer membrane of Gram-negative bacteria, is important for bacterial viability in general and host–pathogen interactions in particular. Negative charges at its core oligosaccharide (core-OS) contribute to membrane integrity through bridging interactions with divalent cations. The molecular structure and synthesis of the core-OS have been resolved in various bacteria including the mammalian pathogen Pseudomonas aeruginosa. A few core-OS structures of plant-associated Pseudomonas strains have been solved to date, but the genetic components of the underlying biosynthesis remained unclear. We conducted a comparative genome analysis of the core-OS gene cluster in Pseudomonas syringae pv. tomato (Pst) DC3000, a widely used model pathogen in plant–microbe interactions, within the P. syringae species complex and to other plant-associated Pseudomonas strains. Our results suggest a genetic and structural conservation of the inner core-OS but variation in outer core-OS composition within the P. syringae species complex. Structural analysis of the core-OS of Pst DC3000 shows an uncommonly high phosphorylation and presence of an O-acetylated sugar. Finally, we combined the results of our genomic survey with available structure information to estimate the core-OS composition of other Pseudomonas species.  相似文献   
7.
An acoustic emission (AE) experiment was carried out to explore the AE location accuracy influenced by temperature. A hollow hemispherical specimen was used to simulate common underground structures. In the process of heating with the flame, the pulse signal of constant frequency was stimulated as an AE source. Then AE signals received by each sensor were collected and used for comparing localization accuracy at different temperatures. Results show that location errors of AE keep the same phenomenon in the early and middle heating stages. In the later stage of heating, location errors of AE increase sharply due to the appearance of cracks. This provides some beneficial suggestions on decreasing location errors of structural cracks caused by temperature and improves the ability of underground structure disaster prevention and control.  相似文献   
8.
为弥补传统设计理念和优化方法的不足,促进空间结构的发展与创新,结合前沿优化理论,依据模拟植物生长算法(PGSA)的基本原理,提出基于生长空间限定与并行搜索的模拟植物生长算法(GSL&PS-PGSA),并与空间结构优化相结合,建立了基于GSL&PS-PGSA的空间结构优化方法。给出了相应的结构优化流程,并采用MATLAB及ANSYS二次开发语言APDL编制了优化程序。通过单层球面网壳截面优化和弦支穹顶预应力优化的典型空间结构算例分析,结果表明:所提出的GSL&PS-PGSA为算法提供了有效的终止机制,且具有高效的计算效率及全局搜索能力;与遗传算法(GA)、粒子群算法(PSO)、ANSYS自带优化方法以及其他改进PGSA算法等相比,GSL&PS-PGSA的优化效果更为显著且具有明显优势;所建立的基于GSL&PS-PGSA的空间结构优化方法,可适用于各类传统和新型空间结构体系的优化问题。  相似文献   
9.
西安丝路国际会议中心悬挂幕墙吊柱最长45 m,吊挂幕墙面积26 000 m2,吊挂质量达12 100 t。悬挂幕墙上部吊挂在桁架端部(桁架最大悬挑35.6 m),下部支撑在通过圆管形月牙吊柱吊挂的下月牙桁架上,悬挂幕墙边界较为复杂,因此需对幕墙结构的吊柱和下月牙桁架支撑设计及关键技术进行研究。结合建筑设计中对幕墙吊柱的要求,对幕墙组合吊柱稳定性进行研究;对幕墙结构变形进行分析,确保变形满足幕墙围护系统设计需求;对幕墙结构和主体结构进行整体协同分析,考虑主体结构刚度对悬挂幕墙结构的影响,并针对如何保证吊柱始终受拉、卸载后幕墙变形与设计状态一致等问题,从设计和施工层面提出对应的解决办法和有效控制措施。结果表明,梯子形组合吊柱方案具有较好的侧向稳定性,适用于大跨度的悬挂式幕墙体系;增加横向构件、提高角部构件抗扭刚度能有效控制幕墙结构不均匀变形;结构预反拱、初张拉等施工措施,可以保证吊挂幕墙结构达到设计受力和成形状态。  相似文献   
10.
田应祥  张义平 《中国矿业》2021,30(7):171-175
为解决传统预裂爆破与光面爆破技术难以满足现如今高质量、高标准施工要求的难题,根据切缝药包的作用机理,对切缝药包在边坡预裂爆破中的应用进行研究。根据现场施工情况,设计相应爆破参数,进行切缝药包预裂爆破参数优化试验,并对切缝药包预裂爆破和传统预裂爆破的工程应用进行对比研究。试验结果表明:在中硬岩、90 mm直径预裂孔的条件下,采用外径40 mm、内径36 mm,切缝长度0.8m,切缝宽度10mm的PVC管作为切缝管进行切缝药包预裂爆破,其爆破效果较好;通过与传统预裂爆破相比,切缝药包预裂爆破后预裂缝宽度增加了1.12倍,预裂面不平整度减少了52.8%,半孔率提高了21%,振动速度峰值降低了29.02%,有效减少了爆破能量对保留边坡与周边构建筑物的损害,显著提高了爆破施工的质量。  相似文献   
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