共查询到20条相似文献，搜索用时 125 毫秒
1.
With an improved Rayleigh fading model and a zero-mean stochastic sinusoid as the scattering and specular components respectively,a stochastic simulation model is proposed for the generation of Rayleigh and Rician fading waveforms.Compared with the existing stochastic models,the proposed simulator needs only one trial to obtain the desired statistical properties even if the number of samples is not large enough.Moreover,the proposed simulation model can directly generate multiple uncorrelated waveforms for different fading scenarios,such as single-input single-output frequency selective channels and multiple-input multiple-output channels.The performance evaluation and comparison show that the proposed simulator is efficient and accurate. 相似文献
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To predict the distortion of aerospace monolithic components, a model is established to simulate the numerical control （NC） milling process using 3D finite element method （FEM）. In this model, the cutting layer is simplified firstly. Then, the models of cutting force and cutting temperature are established to gain the cutting loads, which are applied to the mesh model of the part. Finally, a prototype of machining simulation environment is developed to simulate the milling process of a spar. Key factors influencing the distortion, such as initial residual stress, cutting loads, fixture layout, cutting sequence, and tool path are considered all together. The total distortion of the spar is predicted and an experiment is conducted to validate the numerical results. It is found that the maximum discrepancy between the simulation results and experiment values is 19.0%. 相似文献
3.
Fernandes E Pacheco A Penha-Gonçalves C 《Journal of Zhejiang University. Science. B》2007,8(11):792-801
In standard interval mapping (IM) of quantitative trait loci (QTL), the QTL effect is described by a normal mixture model. When this assumption of normality is violated, the most commonly adopted strategy is to use the previous model after data transformation. However, an appropriate transformation may not exist or may be difficult to find. Also this approach can raise interpretation issues. An interesting alternative is to consider a skew-normal mixture model in standard IM, and the resulting method is here denoted as skew-normal IM. This flexible model that includes the usual symmetric normal distribution as a special case is important, allowing continuous variation from normality to non-normality. In this paper we briefly introduce the main peculiarities of the skew-normal distribution. The maximum likelihood estimates of parameters of the skew-normal distribution are obtained by the expectation-maximization (EM) algorithm. The proposed model is illustrated with real data from an intercross experiment that shows a significant departure from the normality assumption. The performance of the skew-normal IM is assessed via stochastic simulation. The results indicate that the skew-normal IM has higher power for QTL detection and better precision of QTL location as compared to standard IM and nonparametric IM. 相似文献
4.
With the squeeze of electrode tips, the oxide film on aluminum (Al) alloy surface is broken and numbers of micro-gaps are formed randomly. The micro-gaps act as conducting spots at the beginning of welding, so the contact resistance is extremely high and unstable in spot welding of Al alloy. In this paper, a new contact resistance model is adopted to simulate the nugget forming process. This model describes the random distribution characteristic of conducting spots. The simulation results indicate that, within the first 5 ms of welding current (AC, 50 Hz), the temperature distribution at the workpieces interface is seriously irregular. In addition, the nugget does not nucleate from the weld center and grow continuously, however, it nucleates randomly from several points almost instantaneously and then merges into an entity quickly. Experimental results agreed with the numerical simulation. 相似文献
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In order to model the movement progress in case of risks such as dam collapse and coastal inundation, particle-based simulation methods, including the discrete-element method and smoothed particle hydrodynamics, which have specific advantages in modeling complex three-dimensional environmental fluid and particulate flows, are adopted as an effective way to illustrate environmental applications possibly happening in the real world. The theory of these methods and their relative advantages compared with traditional methods are discussed. Examples of 3-D flows on realistic topography including the flooding of a river valley as a result of a dam collapse and coastal inundation by a tsunami are introduced. Issues related to validation and quality data availability are also discussed. The results show that the simulations provide a valuable insight in a given situation for the security management of reservoir dams. Validation can only be performed where both the initial and final states can be very well characterized. 相似文献
6.
The Australian love of "heritage" buildings (most of them are unreinforced masonry (URM)) means that greater attention is required to secure their performance under seismic or impact loading in the future. A research project has been carried out to develop a new, economic and high strength retrofitting technique for masonry structures. A series of experimental testing on URM walls retrofitted with an innovative technique by cable system have been conducted. In this paper, an analytical model which is based on distinct element method (DEM) is developed to simulate the behaviour of retrofitted walls. In DEM, a solid is represented as an assembly of discrete blocks. Joints are modelled as interface between distinct bodies. It is a dynamic process and specially designed to model the behaviour of discontinuities. In order to assist the practising engineers to design this new retrofitted wall system, a simple mechanical model was also developed to predict the strength of the retrofitted walls. The results obtained from this simple mechanical model are compared with those from both experiments and distinct element model. 相似文献
7.
Simulation and analysis of resin flow in injection machine screw 总被引：1，自引：0，他引：1
Ling-feng LI Samir MEKID 《浙江大学学报(A卷英文版)》2008,9(3):338-345
A method with simulation and analysis of the resin flow in a screw is presented to ease the control of some problems that may affect the efficiency and the quality of the product among existing screws in an injection machine. The physical model of a screw is established to represent the stress, the strain, the relationship between velocity and stress, and the temperature of the cells. In this paper, a working case is considered where the velocity and the temperature distributions at any section of the flow are obtained. The analysis of the computational results shows an ability to master various parameters depending on the specifications. 相似文献
8.
Jun Li Nan Gao Guang-yi Cao Heng-yong Tu Ming-ruo Hu Xin-jian Zhu Jian Li 《浙江大学学报(A卷英文版)》2010,11(1):61-70
In this paper, an application of a nonlinear predictive controller based on a self recurrent wavelet network （SRWN） model for a direct internal reforming solid oxide fuel cell （DIR-SOFC） is presented. As operating temperature and fuel utilization are two important parameters, the SOFC is identified using an SRWN with inlet fuel flow rate, inlet air flow rate and current as inputs, and temperature and fuel utilization as outputs. To improve the operating performance of the DIR-SOFC and guarantee proper operating conditions, the nonlinear predictive control is implemented using the off-line trained and on-line modified SRWN model, to manipulate the inlet flow rates to keep the temperature and the fuel utilization at desired levels. Simulation results show satisfactory predictive accuracy of the SRWN model, and demonstrate the excellence of the SRWN-based predictive controller for the DIR-SOFC. 相似文献
9.
ZHUGE Yan CHUANG Shihwei 《天津大学学报(英文版)》2006,12(B09):171-176
The Australian love of ＂heritage＂ buildings （most of them are unreinforced masonry （URM） ） means that greater attention is required to secure their performance under seismic or impact loading in the future. A research project has been carried out to develop a new, economic and high strength retrofitting technique for masonry structures. A series of experimental testing on URM walls retrofitted with an innovative technique by cable system have been conducted. In this paper, an analytical model which is based on distinct element method（DEM） is developed to simulate the behaviour of retrofitted walls, in DEM, a solid is represented as an assembly of discrete blocks. Joints are modelled as interface between distinct bodies. It is a dynamic process and specially designed to model the behaviour of discontinuities. In order to assist the practising engineers to design this new retrofitted wall system, a simple mechanical model was also developed to predict the strength of the retrofitted walls. The results obtained from this simple mechanical model are compared with those from both experiments and distinct element model. 相似文献
10.
Any tidal defense engineering involves the collection and analysis of massive information about engineering structures and their surrounding environment. Traditional method, which is carried out mainly by means of twodimensional drawings and textures, is not efficient and intuitive enough to analyze the whole project and reflect its spatial relationship. Three-dimensional visual simulation provides an advanced technical means of solving this problem. In this paper, triangular irregular network (TIN) model simplified by non-uniform rational B-splines (NURBS) technique was used to establish the digital terrain model (DTM) of a super large region. Simulation of dynamic water surface was realized by combining noise function with sine wave superposition method. Models of different objects were established with different modeling techniques according to their characteristics. Application of texture mapping technology remarkably improved the authenticity of the models. Taking the tidal defense engineering in the new coastal region of Tianjin as a case study, three-dimensional visual simulation and dynamic roaming of the study area were realized, providing visual analysis and visible demonstration method for the management and emergency decision-making associated with construction. 相似文献
11.
In this article, we discuss and illustrate two centering and anchoring options available in differential item functioning (DIF) detection studies based on the hierarchical generalized linear and generalized linear mixed modeling frameworks. We compared and contrasted the assumptions of the two options, and examined the properties of their DIF estimates with a simulation study. For reference purposes, the results were compared to those obtained from using the Mantel-Haenszel procedure as well. Finally, we discuss some implications regarding the choice of model parameterizations for DIF detection using these frameworks. 相似文献
12.
Empirical studies and meta-analyses conducted during the past 35 years led to the development of a number of theoretical frameworks of teacher effectiveness. In this paper, we aim to summarize the main characteristics of three dominant frameworks within the field of educational effectiveness and discuss both their conceptual differences and their similarities, as well as, the different observational instruments used by each one to capture instructional quality. Specifically, the three frameworks are: a) the dynamic model of educational effectiveness; b) the International System for Teacher Observation and Feedback (ISTOF); and c) the Three Basic Dimensions of Teaching Quality (TBD). These frameworks were also used to analyze three videolessons for comparing the quality of teaching through the lens of each respective framework. Based on the results of the three lesson analyses, possibilities for combining different generic frameworks of effective teaching to provide a more complete view of teaching quality are discussed. 相似文献
13.
As a follow‐up to a previous article in which Baker and Friedman‐Nimz (2002a) recommended that gifted education advocates should focus on improving state funding of gifted education, this article provides an overview of state school finance policies for gifted education and frameworks for evaluating those policies. The frameworks are then applied for evaluating state school finance policies as of 1998–99 and state aid allocated to local districts for gifted education in 2000. In that year, only Florida provided both sufficient and equitable support for gifted education, assuming general education conditions to be adequate as well as equitable in that state. Gifted education funding in Virginia, while less adequate than supplemental funding in Florida, continues to be a model of equitable distribution. 相似文献
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This paper describes the SAM (Simulation and Multimedia) project and the rationales behind it. SAM focuses mainly on integrated simulation-based learning environments and creates a framework for authoring, modelling and learning. In these frameworks existing software tools are used where possible and an exchange of tools is enabled. Specialised tools support all actors: learners, authors and modellers. Emphasis will be put on methodologies and graphical tools supporting global course design and integration of simulations. Tools enable also the implementation of general and local course control including instructions for the monitor to recognise and evaluate learner behaviour.SAM methods and techniques are developed to design adaptable courses to meet different learner profiles and to integrate simulations in courseware. This implies a technical integration: the simulation package must accept external control and support an exchange of data. It also implies a conceptual integration: instructional domain concepts must be connected with the model entities; variables, parameters and relations. 相似文献
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在国家资历框架建设列入"十三五"规划后,建立资历框架破解终身教育的制度瓶颈成为教育改革实践中的重大课题.我国资历框架的建设采用了小步快走、分散创新和从阶段到全程、从区域到全国的建设模式,呈现了渐进性的特征.采用渐进模式的原因与庞杂的教育体系、教育政策的不稳定性和既有试点工作的推进程度密切相关.国家资历框架建设的渐进模式具有竞争力缺乏和改革乏力等风险,需要通过主动调整相关策略来消解. 相似文献
19.
Jason A. Parcover Jennifer Mettrick Cynthia A. D. Parcover Pamela Griffin‐Smith 《Journal of College Counseling》2009,12(2):149-161
Increasingly, university and college counselors are sought out by their institution's sports coaches for assistance in achieving team goals. Traditional sport psychology models that have the individual athlete as their primary focus are insufficient frameworks for team‐level consultations. The authors believe that systemic approaches may provide an effective alternative. In this article, the authors offer and illustrate S. Minuchin's (1974) Structural Family Therapy as a heuristic model for conceptualizing and intervening with athletic teams. 相似文献
20.
Thinking skills frameworks for use in education and training 总被引：2，自引：0，他引：2
《British Educational Research Journal》2005,31(3):367-390
This article details findings from a systematic review and evaluation of frameworks and taxonomies for understanding thinking, with particular reference to learning in post‐16 contexts. It describes the means used to identify and evaluate 35 frameworks and identifies three that appear to be particularly useful in the context of lifelong learning. In the light of this analysis, a schematic integrated model of thinking is outlined and discussed. 相似文献