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1.
本文采用高通测序方法对大凌河流域五刺金鱼藻、格菱、狐尾藻、水蓼及芦苇5种水生植物不同季节的微生物群落进行试验分析,分析表明:藻类密度在沉水植物表层要高于浮叶植物表层,微生物群落在浮叶植物根部的结构与其表面存在明显差异。各水生植物的优势生物群落依次为变形菌、梭菌、柔膜菌、鞭脂杆菌、杆菌、疣微菌门,且各微生物群落在季节丰度上存在明显差异性。由此可见,水环境对生物群落的影响要高于植物类型。研究成果可为大凌河流域生态修复工程提供重要理论依据。  相似文献   
2.
纤维与基体之间的粘结能力和机械锚固作用是基体将荷载传递给纤维的决定因素之一,不同类型的纤维和取向在拉拔时的受力形式和破坏形式决定试件承载能力。采用单根纤维拉拔试验探究了纤维类型、取向对超高性能混凝土(UHPC)界面拉伸性能的影响。结果表明:随着纤维取向的增加拔出荷载先增大后减小,在45°时拔出荷载达到最大值;随着纤维取向增加,纤维拔出时对基体破坏面积增大,纤维拔出时对于基体的破坏能力:波纹线>端勾型>直线型。由第一峰值荷载分析,波纹型钢纤维相比于直线型和端勾型钢纤维更容易脱黏。对纤维拔出时进行力学行为分析,波纹型钢纤维和端勾型钢纤维拔出过程中首先发生纤维屈服,随着荷载持续基体产生破坏,直线型钢纤维在拔出过程中最先发生纤维与基体脱黏。  相似文献   
3.
《Journal of dairy science》2022,105(6):5192-5205
We performed a genetic analysis of age at first insemination, including estimation of the heritability and genetic correlations with other economic traits, and the consequences of including this trait in the Israeli selection index. The genetic factors affecting age at first insemination were determined via GWAS. Five data sets were analyzed. Data sets 1, 2, and 3 were used to compute variance components among age at first insemination, first calving age, days from first insemination to calving, and the 9 traits included in the Israel breeding index. Heritabilities for age at first insemination, calving age, and days from first insemination to calving in Israeli Holsteins as computed by REML individual animal model analyses of 273,239 Israeli Holstein cows were 0.072, 0.042, and 0.014. The estimated genetic correlation between the first 2 traits was 0.88. In addition to the fact that heritability of age at first insemination is 1.7 times the heritability for calving, the former trait has the advantage that the number of records is greater, and the records are generated earlier. Absolute values of the genetic and residual correlations between age at first insemination and the 9 traits included in the Israeli index were all less than 0.2. Data set 4 included first insemination dates of 1,181,600 calves born from 1985 through 2018. Genetic evaluations were computed by a single trait animal model. Annual phenotypic and genetic trends for age at first calving for calves born since 1985 were “positive,” that is, economically negative, at 0.320 ± 0.003 and 0.169 ± 0.005 d, respectively. Applying the GCTA-GREML software, 54% of variance in the transmitting ability of 1,585 sires could be explained by considering all 40,498 markers included in the GWAS analysis. The significant markers were mainly associated with milk production genes. The SNP UA-IFASA-8854 on chromosome 11 had the lowest probability value, 1.2 × 10?24. This marker is located between the genes RETSAT and ELMOD3, both of which are overexpressed in human mammary glands. The gene RETSAT is reported to be essential for lipid accumulation and adipogenesis promotion. Gene enrichment analysis found that genes in the genomic region flanking significant markers are associated with vasopressin receptor activity, which was shown to mediate puberty in humans. If age at first insemination is included in the index with a weighting to account for 9% of the index, reductions of 2.8 and 2.6 d for age at first insemination and first calving age after 10 yr of selection are predicted, as compared with reductions of 1.4 and 1.1 d with the current index. Gains for the other index traits are only marginally affected. We suggest selection on age at first insemination as an alternative to selection for early calving.  相似文献   
4.
为了对矿山生产领域安全状况演化趋势准确预测,考虑生产实际中的季节性因素,本文构建季节-小波神经网络(WNN)组合预测模型来对生产事故进行预测。其中,采用X-12-ARIMA模型对安全事故时序进行季节调整,将其分成平稳时间序列和季节因子序列。季节因子序列按规律每年呈现相同规律,用WNN模型预测平稳时间序列,再按照乘法模型还原为真实预测序列。本文以我国煤矿生产安全为背景,将2015-2019年煤矿月度死亡人数作为观测值进行建模,预测2020年月度煤矿事故死亡人数,并将其与2020年煤矿事故月度死亡人数的真实值进行验证,将几种典型的预测模型与本文所构建模型对比分析。结果表明,我国煤矿事故存在显著的季节性特征,季节-小波神经网络组合预测模型的平均相对误差为1.1%,预测精度显著优于单一的预测模型,且与我国煤矿事故实际走势较为吻合,具有良好的预测效果。预测模型可为安全事故的预测提供方法和指导,也可为煤矿安全生产监管决策提供依据。  相似文献   
5.
任振宝  曹春平 《中国机械工程》2022,33(13):1622-1628
针对某动力电池壳首道次拉深成形过程中的起皱、破裂、厚度不均匀和模具接触力大的问题,提出了一种基于熵权的综合评价法对其进行多目标工艺参数优化来提高首道次成形质量。选取压边力、凹模圆角半径、凸模圆角半径、模具间隙、摩擦因数为影响因素,以最大减薄率、最大增厚率、最大凸模接触力、最大厚度差为评价指标,进行正交试验仿真。在此基础上应用熵值法和综合评价法,获得了最优的工艺参数组合,提高了动力电池壳首道次成形质量。  相似文献   
6.
实现室温超导是超导研究的终极目标。最近科学家在高压下富氢材料中发现了系列高温超导体,特别是首先被理论预测随后被实验证实的新型硫氢化物H3S和镧系氢化物LaH10,它们的超导转变温度均超过200K。富氢材料已经被认为是室温超导体的最佳候选体系,成为物理、材料、超导等多学科的研究热点。综述了本课题组在此领域的主要成果,包括:在高压下成功制备了多种新型的笼状结构超氢化物Pr H9和Nd H9,确定了它们的超导转变温度(Tc),首次发现了具有强磁功能特性的Nd H9,其磁性抑制了超导电性;设计了新型笼状超氢化物CaH9,其高压下的理论Tc达到了266 K;实验和理论紧密结合,在温和压力条件下合成了超导锆氢化合物ZrH3和Zr4H15;进一步将二元氢化物拓展到三元氢化物,设计了Tc超过60 K的Mg XH6(X=Si,Ge)。  相似文献   
7.
受全球气候变化影响和人类活动的加剧,干旱灾害发生频次增加且强度增大,严重威胁着我国的粮食安全和水安全。准确及时的旱情预报,对于制定科学有效的干旱应对策略、减少灾害造成的损失具有重大意义。从基于数理统计模型的预报技术和基于物理机制模型的预报技术两方面入手,梳理回顾了国内外研究进展,揭示了当前预报技术所存在的问题,并提出针对性的解决方案。未来研究应注重提高干旱监测数据的质量、突破核心关键技术、构建全国旱情预报业务化系统,为抗旱减灾事业提供强有力的科技支撑。  相似文献   
8.
The capture of sulfur dioxide (SO2) using dehydrated Na6[AlSiO4]6 sodalite was investigated using the first principles density functional theory calculations and thermodynamics analysis. The adsorption geometries, energetics, and electronic structures were predicted with the increasing number of SO2 adsorbates. Upon adsorption, the S atom of single SO2 molecule tends to align to the framework O2− and the two oxygen atoms are oriented to the framework Na+, through electrostatic interactions and with a minor charge transfer. Increasing the number of SO2 adsorbates, the Na6[AlSiO4]6 sodalite framework shrinks first and then expands. Statistical thermodynamics analysis suggests that the capture reaches its saturation limit of four SO2 molecules per Na6[AlSiO4]6 formula (~300 mg/g) at room temperature and a low SO2 partial pressure of 0.001 atm, indicating that dehydrated Na6[AlSiO4]6 can be an efficient SO2 sorbent even at its extremely low concentrations. Higher SO2 partial pressures lead to a higher capture capacity. A low baking temperature of 100-150°C can efficiently release the adsorbed SO2 and hence restore the capture capacity of Na6[AlSiO4]6.  相似文献   
9.
Model building and parameter estimation are traditional concepts widely used in chemical, biological, metallurgical, and manufacturing industries. Early modeling methodologies focused on mathematically capturing the process knowledge and domain expertise of the modeler. The models thus developed are termed first principles models (or white-box models). Over time, computational power became cheaper, and massive amounts of data became available for modeling. This led to the development of cutting edge machine learning models (black-box models) and artificial intelligence (AI) techniques. Hybrid models (gray-box models) are a combination of first principles and machine learning models. The development of hybrid models has captured the attention of researchers as this combines the best of both modeling paradigms. Recent attention to this field stems from the interest in explainable AI (XAI), a critical requirement as AI systems become more pervasive. This work aims at identifying and categorizing various hybrid models available in the literature that integrate machine-learning models with different forms of domain knowledge. Benefits such as enhanced predictive power, extrapolation capabilities, and other advantages of combining the two approaches are summarized. The goal of this article is to consolidate the published corpus in the area of hybrid modeling and develop a comprehensive framework to understand the various techniques presented. This framework can further be used as the foundation to explore rational associations between several models.  相似文献   
10.
围绕研制开发具有与AgCdO性能相媲美的银基电接触材料,报道了近3年来传统Ag/SnO_2、Ag/ZnO、Ag/CuO三种银基电接触材料体系的研究现状,主要论述国内外研究学者从掺杂改性、制备方法、材料模拟仿真、第一性原理计算等方面开展的大量优化研究;梳理了目前制备银基电接触材料体系的常规制备技术及其工作原理;简述了当前部分学者研制开发的诸如Zn_2SnO_4、La SrCuO_4、Ti_2AlN、La_2Sn_2O_7等新型增强相改性银基电接触材料体系;论述了关于材料模拟仿真、第一性原理等理论计算在电接触材料中的应用现状,这些理论计算为银基电接触材料的成分-结构-性能的优化设计提供了相应的指导意义,有助于缩短材料筛选与研发周期。采用新型表征技术检测Ag/CdO等电接触材料的本质特性,为新材料体系研发推导出最本质的设计判据,而关于电弧能量场作用下银基电接触材料的表面熔池特性、熔池内部冶金反应行为及其电寿命失效机制有待深入探究。  相似文献   
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