共查询到20条相似文献，搜索用时 500 毫秒
1.
Based on the factors impact strength model (FISM), we studied on calculation formulas of influence strength and key elements of FISM, and analyzed the turnover time of railway freight transportation of China. The results show that wagon transfer time is the most critical factor among the three subjective factors of wagons turnover time. The FISM based analysis of wagon transfer time show that the wagon turnover time is significantly correlated with transit time with resorting. Among the seven factors of detention time of transit time with resorting, the time of waiting to departing, converging, and waiting to break-up are key factors, while the time of make-up, break-up, arrival and departure are general factors. We carried out one empirical research based on the data of Baoji East Railway Station in 2015. The results of empirical research and FISM are consistent completely 相似文献
2.
Electromagnetic relay is a widely used apparatus which usually works in a magnetic disturbance environment. To evaluate its electromagnetic compatibility （EMC） in a static magnetic field, dynamic characteristics of a clapper relay in a uniform static magnetic field situation based on the finite element method （FEM） is studied. Influences of the magnetic field on dynamic parameters （delay time, pick-up time, end pressure, and final velocity） as well as a situation in which the relay cannot function normally are analyzed. Simulation reveals that the external magnetic field which weakens the relay＇s air-gap field has a greater influence on the relay＇s dynamic parameters than the one strengthening the field. The validity of the simulation is verified by measured results of coil current and armature displacement. 相似文献
3.
With the analysis on regulating system in 200 MW steam turbine, the necessity of appending the fast-opening function to the original system is set forth and a new type of fast-opening mechanism is devised. The mathematical model of system is built up. With the use of AMESIM software, the displacement curve of the piston, the force curve of the cartridge valve spool, the pressure curve and the flux curve in the regulation process are obtained based on simulation. The performances of three fast-opening systems composed of cartridge valves with different diameters are compared. Based on the analysis on factors that affect the execution time of fast-opening, the dead zone of the fast-opening system is put forward. To overcome the defect, different operation modes are adopted for different zones. The result shows that with the increase of the valve diameter, the regulating time in the dead zone significantly exceeds the fast-opening time in the whole journey. Accordingly, the optimization operation tactic in the dead zone and the qualification conditions are brought forward. The fast-opening system composed of 32 mm cartridge valves is taken as an example with use of the tactic. The simulation result shows that the maximum regulating time is shortened by 509 ms. 相似文献
4.
The indirect boundary element method (IBEM) is used to study the surface motion of an alluvial valley in layered half-space for incident plane P-waves based on Wolf’s theory. Firstly, the free field response can be solved by the direct stiffness method, and the scattering wave response is calculated by Green’s functions of distributed loads acting on inclined lines in a layered half-space. The method is verified by comparing its results with literature and numerical analyses are performed by taking the amplification of incident plane P-waves by an alluvial valley in one soil layer resting on bedrock as an example. The results show that there exist distinct differences between the wave amplification by an alluvial valley embedded in layered half-space and that in homogeneous half-space and there is interaction between the valley and the soil layer. The amplitudes are relatively large when incident frequencies are close to the soil layer’s resonant frequencies. 相似文献
5.
The dynamic response of moored crane-ship is studied. Governing equations for the dynamic response of a crane-ship coupled with the pendulum motion of the payload are derived based on Lagrange＇s equations. The boom is modeled based on finite element method, while the payload is modeled as a planar pendulum of point mass. The dynamic response was studied using numerical method. The calculation results show that the large-amplitude responses occur at wave periods near the natural period of the payload. Load swing angle is smaller for crane-ship with flexible boom, in comparison with rigid boom. The ship surge motions have large vibrations for crane-ship with flexible boom, which were not observed for a rigid boom. The analysis identifies the significance of key parameters and reveals how the system design can be adjusted to avoid critical conditions. 相似文献
6.
The indirect boundary element method (IBEM) is used to study the surface motion of an alluvial valley in layered half-space for incident plane P-waves based on Wolf’s theory. Firstly, the free field response can be solved by the direct stiffness method, and the scattering wave response is calculated by Green’s functions of distributed loads acting on inclined lines in a layered half-space. The method is verified by comparing its results with literature and numerical analyses are performed by taking the ampl... 相似文献
7.
The optimal evacuation scheme is studied based on the dam-break flood numerical simulation. A threedimensional dam-break mathematical model combined with the volume of fluid (VOF) method is adopted. According to the hydraulic information obtained from numerical simulation and selecting principles of evacuation emergency scheme, evacuation route analysis model is proposed, which consists of the road right model and random degree model. The road right model is used to calculate the consumption time in roads, and the random degree model is used to judge whether the roads are blocked. Then the shortest evacuation route is obtained based on Dijstra algorithm. Gongming Reservoir located in Shenzhen is taken as a case to study. The results show that industrial area Ⅰ is flooded at 2 500 s, and after 5 500 s, most of industrial area Ⅱ is submerged. The Hushan, Loucun Forest and Chaishan are not flooded around industrial area Ⅰand Ⅱ. Based on the above analysis, the optimal evacuation scheme is determined. 相似文献
8.
Dissolved oxygen sensor based on sol-gel matrix doped with tris(2,2’-bipyridine)ruthenium dichloride
To establish a immobilization method of oxygen sensitive dye, a dissolved oxygen sensor based on a sol-gel matrix doped with ruthenium complex ([Ru(bpy)3]2+) as the oxygen-sensitive material is reported. The results indicate that the I0 /I100 value of the [Ru(bpy)3]2+-doped in tetraethylorthosilane (TEOS) composite films are estimated to be 10.6, where I0 and I100 correspond to the detected fluorescence intensities in pure nitrogen saturated water and pure oxygen saturated water, respectively. Also, the Stern-Volmer plot shows a very good linearity at low dissolved oxygen concentrations. The response time of the composite films is 5 s upon switching from nitrogen saturated water to oxygen saturated water and 10 s from oxygen saturated water to nitrogen saturated water. The dissolved oxygen sensors based on the ruthenium complex/TEOS composite films exhibit greater sensitivity, stability and faster response time as compared to the existing ones. Furthermore, the thin films possess greatly minimized dye leaching effect. 相似文献
9.
The methodology of 5-axis cutter selection to avert collision for free-form surface machining by flat-end cutters is presented.The combination of different cutters is adopt aiming at short machining time and high precision.The optimal small cutter is determined based on the geometric information of the points where a cutter most probably collide with the machined surface.Several larger cutters are slected to machine the surface in order to find the interference-free area.The difference of machining time for this area between the optimal small cutter and the large cutters is calculated.The functional relationship between the machining time and the radius of a cutter is established,by which the optimal number of cutters is obtained.The combination of cutters,which possesses the minimum overall machining time,is selected as the optimal cutter sizes.A case study has demonstrated the validity of the proposed methodology and algorithms. 相似文献
10.
Traditional studies on integrated statistical process control and engineering process control (SPC-EPC) are based on linear autoregressive integrated moving average (ARIMA) time series models to describe the dynamic noise of the system.However,linear models sometimes are unable to model complex nonlinear autocorrelation.To solve this problem,this paper presents an integrated SPC-EPC method based on smooth transition autoregressive (STAR) time series model,and builds a minimum mean squared error (MMSE) controller as well as an integrated SPC-EPC control system.The performance of this method for checking the trend and sustained shift is analyzed.The simulation results indicate that this integrated SPC-EPC control method based on STAR model is effective in controlling complex nonlinear systems. 相似文献
11.
提出了一种基于流体随机Petri网的工作流响应时间概率分布计算方法.首先讨论了利用随机工作流网建模的一些相关问题,然后描述了如何将随机工作流网模型转化为流体随机Petri网模型,最后给出了该种流体随机Petri网模型的动态方程,说明工作流响应时间的概率分布可直接由流体随机Petri网模型的暂态解得到.该方法对工作流模型的结构没有提出任何限制,且工作流任务的处理时间可取任意概率分布,通过递归地使用网化简技术可有效地处理大型工作流模型. 相似文献
12.
This article addresses the issue of how to detect item preknowledge using item response time data in two computer‐based large‐scale licensure examinations. Item preknowledge is indicated by an unexpected short response time and a correct response. Two samples were used for detecting item preknowledge for each examination. The first sample was from the early stage of the operational test and was used for item calibration. The second sample was from the late stage of the operational test, which may feature item preknowledge. The purpose of this research was to explore whether there was evidence of item preknowledge and compromised items in the second sample using the parameters estimated from the first sample. The results showed that for one nonadaptive operational examination, two items (of 111) were potentially exposed, and two candidates (of 1,172) showed some indications of preknowledge on multiple items. For another licensure examination that featured computerized adaptive testing, there was no indication of item preknowledge or compromised items. Implications for detected aberrant examinees and compromised items are discussed in the article. 相似文献
13.
A developmental review of response time data that support a cognitive components model of reading 总被引：2，自引：0，他引：2
The present article provides a review of numerous studies that measured response times for cognitive tasks related to six components of the reading process. The component processes were single-letter recognition, multi-letter unit identification, word and pseudoword identification, semantic access/concept activation, phrase and sentence comprehension, and text comprehension. The response time data are presented in tables and summarized in the text. The data provide support for a componential view of reading. 相似文献
14.
李尧 《商丘师范学院学报》2002,18(5):50-52
介绍了Power Builder7.0的特点，提出了几种编程技巧。重点讨论了如何在Power Builder7.0编程中缩短响应时间、合理分配C／S的负载等问题，并对实施方法给出了具体说明。通过不同方法的响应时间的比较，证明了这些方法是可行的。 相似文献
15.
根据热电偶的响应特性，利用采样点的温度数据，采用在线式实时处理算法，较准确地求解出热电偶使用时刻的时间常数；并利用相关算法，可较大幅度地减小测量的动态误差，缩短测量时间。 相似文献
16.
James Soland 《Educational Measurement》2019,38(3):86-96
As computer‐based tests become more common, there is a growing wealth of metadata related to examinees’ response processes, which include solution strategies, concentration, and operating speed. One common type of metadata is item response time. While response times have been used extensively to improve estimates of achievement, little work considers whether these metadata may provide useful information on social–emotional constructs. This study uses an analytic example to explore whether metadata might help illuminate such constructs. Specifically, analyses examine whether the amount of time students spend on test items (after accounting for item difficulty and estimates of true achievement), and difficult items in particular, tell us anything about the student's academic motivation and self‐efficacy. While results do not indicate a strong relationship between mean item durations and these constructs in general, the amount of time students spend on very difficult items is highly correlated with motivation and self‐efficacy. The implications of these findings for using response process metadata to gain information on social–emotional constructs are discussed. 相似文献
17.
控制系统中的时滞现象是影响控制效果的不可忽视的因素。文章采用递归响应法对磁流变阻尼控制系统的算法进行仿真计算,分析在不同情况下递归响应法对磁流变阻尼控制系统的时滞补偿效果,并与主动控制系统进行比较。结果表明,递归响应法对磁流变阻尼控制系统有一定的补偿效果,对主动控制系统效果更加显著。 相似文献
18.
以北京、上海等10个热点城市为对象,选取1984~2008年入境客流量和旅游收入数据,分析了城市入境旅游发展的时间同步性及区域响应。结果显示：从1984~2008年,城市入境旅游发展具有较高的时间同步性,1984~1991年为快速增长,1992~2003年为平缓增长,2004~2008为加速增长,旅游增长率变化＂五涨四跌＂,波动周期＂同涨同落＂。依据增长指数和相关系数的差异,将10城市划分为两种类型。由于旅游投资、资源开发、交通区位等因素的差异,各城市入境旅游的发展具有不同的区域响应。文章分三个时段,分别统计了1984~1991,1992~2003和2004~2008年各城市入境旅游的基期值和平均增长率,依据各阶段基期值和平均增长率的大小,划分了入境旅游发展的区域响应类型。 相似文献
19.
AbstractOver the last years, the European Commission has heavily promoted various forms of digital education. In this article, we draw upon two recent European policy documents as key articulations of Europe’s contemporary governing apparatus: Opening Up Education and the Digital Education Action Plan. The article more particularly conceives of both policy documents as offering a point of departure to analyze how this apparatus is presently seeking to enact a specific mode of existence of the contemporary learner. We argue that this educational mode of existence is being enacted by the fabrication of highly specific sorts of time and space. In order to highlight the particularity of the enacted sorts of time and space exemplified in the policy documents, we start this article with a discussion of how a traditional, modern governing apparatus aims to fabricate linear time and institutional space. The article proceeds by arguing that the present-day European governing apparatus that is concerned with digital education fabricates different sorts of times and spaces, namely potential (rather than linear) temporalities and ecological/networked (rather than institutional) spatialities. Likewise, the concrete instruments (such as platforms, portals, credits and certificates) presently adopted in order to do so largely differ from modern instruments. Conclusively, we argue that the presence of these newly emerging (often digital) instruments, and the times and spaces that are fabricated through these instruments, call for an opportunistic mode of existing as a contemporary learner. 相似文献
20.
以重晶石、石英砂和凡士林等混合物作为铁路隧道软弱围岩的相似材料。基于响应面分析法中的二次回归通用旋转法设计实验,将有效应力条件下的有效粘聚力与有效内摩擦角作为铁路隧道软弱围岩的研究指标。通过应力控制式三轴试验仪,进行常规三轴试验。利用非线性回归分析的方法对相似材料配比与软弱围岩指标之间的关系进行分析,并对各回归系数进行实际试验与拟合检验,得出围岩物理力学指标与相似材料配比的变化规律。 相似文献