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排序方式: 共有737条查询结果,搜索用时 54 毫秒
621.
622.
Kyung S. Park Un H. Kim 《International journal of occupational safety and ergonomics》2013,19(4):485-498
A posture control model has been developed on the basis of the 2-dimensional feedback control theory. Human postural characteristics were investigated in 5 healthy participants. Tests were performed with eyes open and eyes closed. After 5 s of quiet standing, each participant was unexpectedly pulled forward by 30 mm at his pelvis height and then released. Postural sway was measured over 20 s at a rate of 100 per second. Transfer functions to represent the posture control characteristic were identified by the least squares' method. These showed good results of the model's fitness, predictability, and stability. The response of the eyes-closed condition to perturbation is more oscillatory than that of the eyes-open condition. It seems that the model identified could be applicable to ergonomics, sports, or clinical situations. 相似文献
623.
为更准确地描述行人疏散动力学特征,利用目前行人疏散模型对行人疏散进行模拟研究发现:疏散空间行人拥堵时,会出现疏散区域某些位置的行人一直处于竞争劣势而保持位置不动的现象,这与行人实际疏散运动不符.考虑到现实情况,行人在等待的过程中会积极寻找机会,实现成功疏散;基于此,在疏散模型中引入了心理迫切因素的概念,表征了行人等待过程中竞争能力的变化,完善了行人疏散模型.对新模型模拟研究发现,在考虑等待时的心理迫切因素后,该模型能够更好地表达行人疏散的动力学特征,可更为准确地再现行人的疏散运动轨迹和路径,同时研究发现,引入等待迫切因素后并不会影响总的疏散时间. 相似文献
624.
Cesar Beltran N. R. Edwards A. B. Haurie J.-P. Vial D. S. Zachary 《Environmental Modeling and Assessment》2006,11(1):31-43
In this paper, we show how oracle-based optimization can be effectively used for the calibration of an intermediate complexity
climate model. In a fully developed example, we estimate the 12 principal parameters of the C-GOLDSTEIN climate model by using
an oracle-based optimization tool, Proximal-ACCPM. The oracle is a procedure that finds, for each query point, a value for
the goodness-of-fit function and an evaluation of its gradient. The difficulty in the model calibration problem stems from
the need to undertake costly calculations for each simulation and also from the fact that the error function used to assess
the goodness-of-fit is not convex. The method converges to a ‘best fit’ estimate over 10 times faster than a comparable test
using the ensemble Kalman filter. The approach is simple to implement and potentially useful in calibrating computationally
demanding models based on temporal integration (simulation), for which functional derivative information is not readily available. 相似文献
625.
Mirjam P. Fransen Marie-Louise Essink-Bot Anke Oenema Johan P. Mackenbach Eric A. P. Steegers Hajo I. J. Wildschut 《黑龙江环境通报》2007,27(10):938-950
Objective To develop a theoretical framework for analysing ethnic differences in determinants of participation and non-participation in prenatal screening for Down syndrome. Methods We applied Weinstein's Precaution Adoption Process (PAP) Model to the decision of whether or not to participate in prenatal screening for Down syndrome. The prenatal screening stage model was specified by reviewing the empirical literature and by data from seven focus group interviews with Dutch, Turkish and Surinamese pregnant women in the Netherlands. Results We identified 11 empirical studies on ethnic differences in determinants of participation and non-participation in prenatal screening for Down syndrome. The focus group interviews showed that almost all stages and determinants in the stage model were relevant in women's decision-making process. However, there were ethnic variations in the relevance of determinants, such as beliefs about personal consequences of having a child with Down syndrome or cultural and religious norms. Discussion The prenatal screening stage model can be applied as a framework to describe the decision-making process of pregnant women from different ethnic backgrounds. It provides scope for developing culturally sensitive, tailored methods to guide pregnant women towards informed decision-making on participation or non-participation in prenatal screening for Down syndrome. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
626.
A full probabilistic Explosion Risk Analysis (ERA) is commonly used to establish overpressure exceedance curves for offshore facilities. This involves modelling a large number of gas dispersion and explosion scenarios. Capturing the time dependant build up and decay of a flammable gas cloud size along with its shape and location are important parameters that can govern the results of an ERA. Dispersion simulations using Computational Fluid Dynamics (CFD) are generally carried out in detailed ERA studies to obtain these pieces of information. However, these dispersion simulations are typically modelled with constant release rates leading to steady state results. The basic assumption used here is that the flammable gas cloud build up rate from these constant release rate dispersion simulations would mimic the actual transient cloud build up rate from a time varying release rate. This assumption does not correctly capture the physical phenomena of transient gas releases and their subsequent dispersion and may lead to very conservative results. This in turn results in potential over design of facilities with implications on time, materials and cost of a project.In the current work, an ERA methodology is proposed that uses time varying release rates as an input in the CFD dispersion simulations to obtain the fully transient flammable gas cloud build-up and decay, while ensuring the total time required to perform the ERA study is also reduced. It was found that the proposed ERA methodology leads to improved accuracy in dispersion results, steeper overpressure exceedance curves and a significant reduction in the Design Accidental Load (DAL) values whilst still maintaining some conservatism and also reducing the total time required to perform an ERA study. 相似文献
627.
628.
在自行设计和搭建的模拟湿法脱硫烟气系统中,研究了基于控制冷凝法原理的SO_3/硫酸雾采集装置对湿法脱硫后SO_3/硫酸雾的捕集性能,重点考察了螺旋管与石英棉冷凝温度、采样枪温度、采样流量、采样时间和SO_3/硫酸雾质量浓度对SO_3/硫酸雾捕集性能的影响。结果表明,在研究范围内,湿法脱硫后SO_3/硫酸雾采集装置优化的操作参数为:螺旋管及石英棉冷凝温度95℃,采样枪温度280℃,采样流量17 L/min,采样时间30 min。SO_3/硫酸雾质量浓度较高时,螺旋冷凝管对SO_3/硫酸雾的捕集起主要作用,其捕集的SO_3/硫酸雾比例在75.8%~80.8%,远高于螺旋冷凝管与石英棉捕集SO_3/硫酸雾的比例;SO_3/硫酸雾质量浓度较低(约1mg/m3)时,采样枪对SO_3/硫酸雾的捕集起主要作用,其捕集SO_3/硫酸雾的比例大于50%。 相似文献
629.
630.