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321.
大型地下方厅多导洞施工力学效应分析 总被引:2,自引:2,他引:0
杜彬 《中国安全科学学报》2005,15(2):51-54
针对北京城铁 13号线东直门站地下方厅开挖跨度大、覆盖层薄、地质条件极差的施工难题 ,笔者采用三维有限元数值模型 ,模拟开挖支护施工流程 ,考虑到围岩介质的复杂特性 ,施工作业方式 ,包括分布开挖工序 ,支护结构形式和施作时机 ,以及开挖面推进过程中的空间效应 ;按形变压力理论 ,选用“连续体”计算模型 ,采用增量变弹性法和增量叠代的混合法进行计算分析 ,对多导洞开挖支护施工方案进行了计算分析 ;基本掌握了在覆土厚度小的情况下开挖大跨平顶直墙方厅时 ,周围土体的应力分布特征和变形特性 ,对于优化施工方案、修改支护参数、采取局部加固措施起到了重要作用。实践表明采用多导洞施工方案是科学合理的 ,有利地保证了周边环境和施工安全。 相似文献
322.
《组织行为杂志》2017,38(3):391-414
Building on the premises of the conservation of resources theory, the aim of this study was to investigate long‐term effects of job resources on vigor among native and immigrant employees in Israel. More specifically, we investigated the effects of baseline and change in job control and supervisor support on change in vigor levels, as well as the degree to which these effects differ among educated native and immigrant employees in Israel. We surveyed 235 white‐collar Eastern European and Russian immigrants and 235 white‐collar native Israelis matched on occupational and demographic characteristics at two points of measurement with a 30‐month time lag. Latent change score modeling revealed that among both immigrants and natives, change in job control was related to change in vigor. Multiple group analyses further revealed that among immigrant employees only, baseline levels of supervisor support were associated with change in vigor. In conclusion, these findings suggest that the utilization of resources as a means of acquiring new resources may be influenced by immigrant background. Managerial implications are discussed. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
323.
强膨胀软岩巷道的支护问题是西部地区矿井建设中普遍遇到的难题。为解决强膨胀软岩遇水泥化、崩解等给巷道掘进、支护等工程带来的困难,以强膨胀软岩巷道支护工程为研究对象,通过理论分析和现场调研,研究强膨胀软岩巷道变形机理;利用有限元分析软件MIDAS/GTS建立强膨胀软岩巷道数值仿真模型,分析了锚网喷架联合支护时巷道塑性区范围、表面位移和钢支架的受力特征。进行现场测试,获得了巷道围岩变形和锚杆受力变化规律。结果表明,采用钢支架与锚网喷构成联合支护体系可有效提高支护结构整体刚度,提升围岩的自稳能力和自承能力。 相似文献
324.
325.
Roman M. Wittig Catherine Crockford Robert M. Seyfarth Dorothy L. Cheney 《Behavioral ecology and sociobiology》2007,61(6):899-909
Theory predicts that females in species with matrilineal dominance hierarchies should use nepotistic support systems to maintain
their family’s rank. Female Old World monkeys, however, form alliances against other females at surprisingly low rates. Nonetheless,
in many species, females utter threat vocalizations when observing others’ disputes, suggesting that these vocalizations may
function as ‘vocal alliances’. We describe a playback experiment testing the efficacy of vocal alliances in free-ranging female
baboons. Subjects were played the same female’s threat-grunts under three separate conditions: after being threatened by the
signaller’s close relative to mimic kin support, after being threatened by a female maternally unrelated to the signaller
to mimic non-kin support, and after a friendly interaction with the signaller’s close relative as a control. Subjects responded
more strongly to the playback and avoided the signaller and her matrilineal relatives for a longer period of time in kin support
trials than in either non-kin support or no aggression trials. In contrast, there was no difference in subjects’ behaviour
between non-kin support and no aggression trials. These results corroborate observational data showing that vocal support
occurs at a higher rate than physical support in female baboons, and that kin are more likely to provide vocal support than
non-kin. We conclude that vocal support plays a similar role as physical support in the alliances of female baboons. 相似文献
326.
327.
Martin T. Schultz Mitchell J. Small Paul S. Fischbeck R. Scott Farrow 《Environmental Modeling and Assessment》2006,11(4):345-359
Environmental models are often too large and cumbersome for effective use in regulatory decision making or in the characterization of uncertainty. This paper describes and compares four response surfaces that could complement a large-scale water quality model, the U.S. National Water Pollution Control Assessment Model (NWPCAM), in simulation and regulatory decision support applications. Results show that a physically based reduced-form model that exploits the mathematical structure of the underlying water quality model is a better predictor of policy-relevant outputs than the polynomial expansions that are frequently used in response surface studies. 相似文献
328.
Erin M.K. Haacker Vaishali Sharda Amanda M. Cano R. Aaron Hrozencik Agustín Núez Zachary Zambreski Soheil Nozari Garvey Engulu B. Smith Lacey Moore Sumit Sharma Prasanna Gowda Chittaranjan Ray Meagan Schipanski Reagan Waskom 《Journal of the American Water Resources Association》2019,55(1):6-23
Agricultural water management (AWM) is an interdisciplinary concern, cutting across traditional domains such as agronomy, climatology, geology, economics, and sociology. Each of these disciplines has developed numerous process‐based and empirical models for AWM. However, models that simulate all major hydrologic, water quality, and crop growth processes in agricultural systems are still lacking. As computers become more powerful, more researchers are choosing to integrate existing models to account for these major processes rather than building new cross‐disciplinary models. Model integration carries the hope that, as in a real system, the sum of the model will be greater than the parts. However, models based upon simplified and unrealistic assumptions of physical or empirical processes can generate misleading results which are not useful for informing policy. In this article, we use literature and case studies from the High Plains Aquifer and Southeastern United States regions to elucidate the challenges and opportunities associated with integrated modeling for AWM and recommend conditions in which to use integrated models. Additionally, we examine the potential contributions of integrated modeling to AWM — the actual practice of conserving water while maximizing productivity. Editor's note : This paper is part of the featured series on Optimizing Ogallala Aquifer Water Use to Sustain Food Systems. See the February 2019 issue for the introduction and background to the series. 相似文献
329.
Dong Hwan Ko 《International journal of occupational safety and ergonomics》2019,25(4):568-574
This study aims to describe the characteristics of occupational injuries to educational support staff (service worker) in schools. In this research, 803 injured workers registered in 2015 were analyzed in terms of their gender, age, work experience, school type, work type, accident type, agency of accident, nature of injury and injured part of the body for each occupation. The workers were classified into after-school instructor, custodian and cooking staff. Accidents occurred mainly due to slips (35.6%) on floor/stair or contact with high temperature (18.1%). Also, the workers mostly fractured (41.2%) or had burns (19.3%) on their leg/foot (37.1%) or arm/hand/finger (29.8%). The results showed the difference in characteristics and injury pattern of injured persons for each occupation type, addressing the need for customized preventative measures for each situation. The results of this study can be a baseline in devising policies and guidelines for preventing accidents of service workers in schools. 相似文献
330.
使用支持向量机(SVM)方法对矿井通风系统进行故障诊断,存在惩罚系数(c)和核函数系数(g),通过人工方法选取效率低、难以达到较高准确率并且出现过拟合的问题。为了提高矿井通风故障诊断的效率、准确率,同时避免过拟合现象,提出了一种改进遗传算法(GA),在故障诊断过程中对支持向量机的c,g参数进行优化。经过多组试验分析,研究结果表明:用遗传算法优化的SVM矿井通风故障诊断系统相比于未优化系统的故障诊断准确率有所提升,参数未优化前故障诊断的准确率为60%,优化后的准确率为97.894 7%,并且优化参数经过大数据样本验证,未出现过拟合现象,证明了本文提出方法的有效性。 相似文献