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1.
《Soils and Foundations》2022,62(1):101103
The present study proposes a new elasto-plastic constitutive model that considers different types of hydrates in pore spaces. Many triaxial compression tests on both methane hydrate-bearing soils and carbon dioxide hydrate-bearing soils have been carried out over the last few decades. It has been revealed that methane hydrate-bearing soils and carbon dioxide hydrate-bearing soils have different strength and dilatancy properties even though they have the same hydrate contents. The reason for this might be due to the different types of hydrate morphology. In this study, therefore, the effect of the hydrate morphology on the mechanical response of gas-hydrate-bearing sediments is investigated through a model analysis by taking into account the different hardening rules corresponding to each type of hydrate morphology. In order to evaluate the capability of the proposed model, it is applied to the results of past triaxial compression tests on both methane hydrate-containing and carbon dioxide hydrate-containing sand specimens. The model is found to successfully reproduce the different stress–strain relations and dilatancy behaviors, by only giving consideration to the different morphology distributions and not changing the fitting parameters. The model is then used to predict a possible range in which the maximum deviator stress can move for various hydrate morphology ratios; the range is defined as the strength-band. The predicted curve of the maximum deviator stress obtained by the constitutive model matches the empirical equations obtained from past experiments. It supports the fact that the hydrate morphology ratio changes with the total hydrate saturation. These findings will contribute to a better understanding of the relation between the microscopic structures and macro-mechanical behaviors of gas-hydrate-bearing sediments.  相似文献   
2.
《Ceramics International》2022,48(5):6266-6276
Porous diatomite ceramics with hierarchical pores and high apparent porosity (50.29–56%) were successfully fabricated via direct stereolithography. The pre-ball-milling time, dispersant type and dispersant concentration were systematically investigated to prepare diatomite pastes with high solid loading, low viscosity and a self-supporting effect. The results showed that a pre-ball-milling time of 24 h was more suitable to prepare diatomite pastes with high solid loading, and Span80 at 2 wt% was the optimal dispersant to obtain 40 vol% diatomite paste with a low viscosity and a self-supporting effect. To restrain the formation of defects, a heating rate as low as 0.2 °C/min was allowed to control the pyrolysis rate in the multistage debinding process. At sintering temperatures ranging from 900 °C to 1000 °C, porous diatomite ceramics exhibited a typical bimodal porosity, high apparent porosity and great flexural strength.  相似文献   
3.
《Ceramics International》2022,48(21):31738-31745
In this study, novel polyborosilazane-derived SiBCN(O) ceramic was used as self-healing component in self-healing Cf/SiBCN(O) composite, which was prepared by polymer infiltration and pyrolysis (PIP) process. Molecular-level structure design of boron-containing ceramic precursors was utilized to achieve uniform dispersion of boron-containing self-healing components in prepared composites. No elemental diffusion was observed at the interface of ceramic matrix and carbon fibers, which resulted in stable SiBCN(O) structure. In addition, boron was uniformly distributed in Cf/SiBCN(O) composite ceramic matrix, which was beneficial for self-healing of cracks. Cracks and indentations were able to heal at high temperatures in air. The best crack-healing behavior occurred in air atmosphere at 1000 °C, with nearly complete crack healing. This excellent self-healing behavior was achieved because silicon and boron atoms in SiBCN(O) ceramic reacted with available oxygen at high temperatures to form SiO2(l), B2O3(l), and B2O3·xSiO2 liquid phases, which effectively filled cracks. In general, as-prepared Cf/SiBCN(O) composite exhibited excellent self-healing properties and shows great application potential in high-temperature environment applications such as aviation, aerospace, and nuclear power.  相似文献   
4.
诱导式卫星欺骗干扰可诱导航空器逐渐偏离预定航迹,难以被发现,因此及时有效地检测干扰是飞行安全的保障。在现有紧组合导航体制基础上,设计了一种基于误差估值累加开环校正的紧组合导航结构,并证明了其性能与传统闭环校正紧组合导航性能等效。在此结构中,将紧组合导航系统与自适应序贯概率比检测方法结合,提出了一种基于误差估值累加开环校正的诱导式欺骗检测方法,融合紧组合导航信息与其他不受欺骗影响的导航信息,构建欺骗检测统计量进行诱导式欺骗检测。仿真结果表明,开环校正结构可避免随时间累加的惯性导航系统误差所导致的组合导航滤波器发散问题,同时欺骗检测方法可进一步提高算法对“最坏”情形下微小诱导式欺骗的检测效果。  相似文献   
5.
刘亮 《兵工自动化》2022,41(6):35-40,52
针对传统网络信息服务质量评估模型客观性、适用性、扩展性不足的问题,提出基于用户信息行为的网 络信息服务质量评估模型。模型的建立以用户信息行为关键影响因素为基础,通过将网络信息服务分类、分析用户 信息行为的内涵和影响因素,总结出各类网络信息服务中用户的主要信息行为和质量构成要素,构建评估模型;阐 述模型适用和扩展的要点,并以电子政务为例进行分析。结果表明,该模型可为网络信息服务质量评估提供借鉴 参考。  相似文献   
6.
随着乙烷产品价值的进一步提升,国内各大油田正大力开展天然气乙烷回收,以提高油田的综合收益。以克拉美丽气田天然气乙烷回收工艺为例,基于序贯模块法建立了天然气乙烷回收系统模型;求解得到该系统的模拟顺序后,采用HYSYS软件建立了计算模型,分析了乙烷回收工艺中各关键参数的影响,并基于?分析方法对该乙烷回收系统进行了评价;最后,以乙烷产品最小比功耗为目标函数,采用序列二次规划(SQP)优化方法对乙烷回收工艺参数进行了优化。结果表明:采用序贯模块法模拟天然气乙烷回收系统具有较好的适用性;经参数优化后,乙烷收率由92.62%提高到97.01%,乙烷产品比功耗降低了约5.4%。  相似文献   
7.
目的 了解我国食品理化实验室专业技术人员食品安全知识、态度、行为现状,探讨其影响因素。方法 对我国15个省的省级、市级、区(县)级部门下属食品理化实验室及第三方机构、企业等非政府机构食品理化实验室的专业技术人员开展食品安全知识、态度、行为问卷调查,并对调查结果进行统计分析。结果 共回收有效问卷1339份。除性别对态度得分无显著影响,文化程度、就职年限等对行为无显著影响外,年龄、实验室类型、所在区域和最近一次接受培训时间等均是影响食品理化检验人员食品安全知识、态度、行为得分的因素,且知识、态度和行为得分存在正相关关系。结论 尽管存在满分问卷,但食品理化实验室专业技术人员KAP平均得分仅略高于及格水平。需要关注重点人群,如年龄25岁以下、就职年限2年以下或大专及以下学历的专业技术人员等食品安全知识水平的提升、态度的端正和行为的规范。  相似文献   
8.
Novel inks were formulated by dissolving polycaprolactone (PCL), a hydrophobic polymer, in organic solvent systems; polyethylene oxide (PEO) was incorporated to extend the range of hydrophilicity of the system. Hydroxyapatite (HAp) with a weight ratio of 55–85% was added to the polymer-based solution to mimic the material composition of natural bone tissue. The direct ink writing (DIW) technique was applied to extrude the formulated inks to fabricate the predesigned tissue scaffold structures; the influence of HAp concentration was investigated. The results indicate that in comparison to other inks containing HAp (55%, 75%, and 85%w/w), the ink containing 65% w/w HAp had faster ink recovery behavior; the fabricated scaffold had a rougher surface as well as better mechanical properties and wettability. It is noted that the 65% w/w HAp concentration is similar to the inorganic composition of natural bone tissue. The elastic modulus values of PCL/PEO/HAp scaffolds were in the range of 4–12 MPa; the values were dependent on the HAp concentration. Furthermore, vancomycin as a model drug was successfully encapsulated in the PCL/PEO/HAp composite scaffold for drug release applications. This paper presents novel drug-loaded PCL/PEO/HAp inks for 3D scaffold fabrication using the DIW printing technique for potential bone scaffold applications.  相似文献   
9.
张建超 《中州煤炭》2022,(5):255-261
为了分析矿井综采工作面不同复合顶板结构下开采岩压分布和显现特性,达到优化巷道支护设计的目的,采用理论分析和数值模拟相结合的方法,分析了复合顶板的结构特点及复合顶板开采效果。以陕西某矿井工作面为例,通过液压支架、巷道变形的现场监测数据,验证了理论研究的成果。结果表明,复合顶板中的软弱夹层在外力作用下极易破坏,夹层的矿压显现分布对顶板特性有重要影响。当软弱夹层位于顶板切割层范围中间时,巷道支护强度要求最高,当软弱夹层位于顶板切割层范围顶部时,巷道支护强度要求最低。  相似文献   
10.
为扩展非织造布在保鲜包装材料中的应用,以具有药用价值的沙棘作为抗氧化保鲜成分原料,通过负载不同体积分数的沙棘提取物(SBT)制备罗布麻纳米纤维素/壳聚糖基水凝胶,并与聚酯非织造布复合制备复合水凝胶非织造布保鲜材料,对其阻隔性能、释放行为、抗氧化活性、抗菌性以及保鲜性能进行分析。结果表明:随着SBT体积分数的增加,复合水凝胶非织造布的阻隔性增强且抗氧化活性显著提高;在18 d的释放行为测试中,复合水凝胶非织造布在酸性条件下SBT的最大累计释放率可达67.84%,对金黄色葡萄球菌和大肠杆菌的抑菌带宽度均超过1 mm,有较好的抗菌性能;添加体积分数为30% SBT的复合水凝胶非织造布综合保鲜能力最佳,可储存鲜切苹果时间最长达9 d。  相似文献   
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