共查询到20条相似文献，搜索用时 265 毫秒
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目的:推导一种高精度、使用简单且不含有分形维数的细颗粒泥沙沉速计算方法,以应用于原位观测和实现不同计算结果间的相互比较。创新点:1.推导出了不含有分形维数的泥沙絮团沉速公式;2.将LISST等高精度仪器应用于泥沙絮团密度计算中。方法:1.通过理论推导,得到不含分形维数的粘性细颗粒泥沙沉速公式;2.通过试验对该公式的精度进行研究,并在此基础上研究不同密度计算方法对该公式精度的影响;3.研究不同沉速状态下,泥沙絮团的沉降规律。结论:1.通过对比实测沉速与计算沉速的结果可以看出,本文提出的絮团沉速公式在计算泥沙絮团的沉速时精度较高;2.通过比较两种不同密度计算方法的结果可以看出,变密度方法具有更高的精度;3.通过拟合结果可以看出,公式(15)中的参数η与泥沙所处的沉降区间有关,参数γ与泥沙自身的性质有关。 相似文献
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李俊阳 《西安文理学院学报》2019,(3)
在加工有椭圆形状零件时,采用何种编程方法提高编程效率是编程员较难定夺的问题.通过对椭圆标准方程和参数方程不同的处理方法进行比较,进而讨论直线逼近和圆弧逼近方法的不同,得出直线逼近比圆弧逼近高效,后者比前者精度有所提高的结论. 相似文献
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利用数学工具软件Mathcad2001,对4Na2SO4·2H2O2·NaCl加合物的热分解动力学方程模型中的参数进行优化,得到了其热分解动力学方程式,优化的结果能准确地模拟4Na2SO4·2H2O2·NaCl的实际分解过程.Mathcad的使用大大减少了计算工作量.对于其它物质的热分解过程、非均相及均相体系反应的动力学方程式参数都可用Mathcad2001工具软件进行优化. 相似文献
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反应性溶质运移机理和模拟是地下水污染防治的前提和基础.为了考察化学反应和水流条件对溶质运移的影响,本文设计了承压含水层物理模型,以苯胺和1,2-萘醌-4-磺酸钠化学反应为例,开展了双分子化学反应条件下不同流速溶质运移实验和模拟研究,得到主要结论如下：（1）利用变系数二级反应率改进的ADRE模型能够较好地模拟在3种不同流速下双分子反应性溶质运移行为,峰值浓度相对误差分别为4.5％、5.0％及10.1％,模型可行,且模拟精度较高.（2）随着流速增大,模型参数m减小,而β0则增大.（3）模型对参数m值变化最敏感,其次是β0值,较不敏感的是弥散系数D.（4）随着流速增大,反应物和产物穿透曲线的不规则性加强,存在较明显的“拖尾”现象,今后需要进行机理方面的研究. 相似文献
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李维祖 《课程教材教学研究(小教研究)》2004,(Z3)
离子方程式的书写是中学化学的重点和难点之一。对于简单的离子反应,学生尚能熟练地书写其离子方程式,但对于较为复杂的离子反应,要书写其离子方程式,学生往往感到比较困难。例如:向NaHSO4溶液里,逐滴加入Ba(OH)2溶液至中性;请写出反应的离子方程式。该题中参加反应的离子种类较多,涉及到的反应类型既有中和反应又有沉淀反应,比较复杂,怎样快速准确地书写其离子方程式呢?现介绍一种方法仅供大家参考。该方法分以下三个步骤:(1)搞清溶液中离子间的反应情况。NaHSO4溶液中存在着Na+、H+、SO2-4;Ba(OH)2溶液中存在着Ba2+、OH-,当把两… 相似文献
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针对含自由曲面及标准解析曲面零件加工精度的高精度检测,本文提出一种形状公差评定的新方法——面向CAD模型的曲面形状误差检验。它实现了各种标准解析曲面和自由曲面形状的高精度检测,采用表达式精确地表示各种标准解析曲面和自由曲面;利用数据库技术研究CMM测量点云和CAD模型的最佳匹配算法;比较测量点云和CAD模型的法向偏移量即曲面形状误差,且用图形直观地显示出来。最后进行计算机仿真实验,实例验证算法可行性。 相似文献
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目前采用地震属性预测储层参数的方法层出不穷,但是这些方法多数是基于单变量、线性的机器学习算法,在已知样本较少的情况下精度得不到保证。为了获取高精度的储层参数,指导油气的勘探开发,迫切需要寻求一种新的方法最大限度地挖掘地震地质信息。支持向量机是以结构风险最小化原则为核心的新型机器学习算法,与传统的机器学习算法相比,其具有基于多变量、小样本、非线性和预测精度高的优点。以渤海湾SZ-361油田Ⅰ油组顶部储层参数预测为例,采用支持向量机算法,得到了较高精度的储层预测结果,证实了支持向量机算法可以应用于油气勘探领域。 相似文献
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研究目的：创新要点：研究方法：重要结论：采用广义估计方程模型对存在时间相关件的事故频次数据进行建模,并与传统广义线性模型的估计效果进行对比。
通过广义估计方程来考虑事故频次建模中数据的时间相关性,从而提高参数估计准确度以及模型预测精度。基于4年高速公路交通事故频次数据,建立考虑时间相关性的广义估计方程以及传统的广义线性模型,并采用统计指标对模型效果进行对比。1．事故频次数据样本最对预测精度影响很大;2．广义估引方程能够有效考虑事故频次数据中存住的时间相关性;3．广义估计方程的参数估计比传统广义线性模型史准确,且精度更高。 相似文献
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Modeling on flash flood disaster induced by bed load 总被引：1，自引：0，他引：1
Flash floods result from a complex interaction among hydro-meteorological, hydrological, and hydraulic processes across various
spatial and temporal scales. Sichuan Province suffers flash floods frequently owing to mountain weather and topography. A
flash flood and gravel bed load transport are two key relative problems in mountain river engineering. Bed materials are often
encountered in alternate scouring and deposition in mountain fluvial processes during a flash flood. In this circumstance,
CRS-1 bed load numerical model jointly with scale physical model is employed to predict water level and gravel bed scour and
deposition for design of flood control dykes and flash flood disaster mitigation. A case study on the mechanism of a flash
flood disaster induced by bed load transport for a hydropower station in Sichuan Province is conducted. Finally, suggestions
to protect the hydropower station are proposed.
Supported by the key project of National Natural Science Foundation of China(No.50739002).
CAO Shuyou, born in 1945, male, Dr, Prof. 相似文献
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This research focuses on the problem of model selection between the latent change score (LCS) model and the autoregressive cross-lagged (ARCL) model when the goal is to infer the longitudinal relationship between variables. We conducted a large-scale simulation study to (a) investigate the conditions under which these models return statistically (and substantively) different results concerning the presence of bivariate longitudinal relationships, and (b) ascertain the relative performance of an array of model selection procedures when such different results arise. The simulation results show that the primary sources of differences in parameter estimates across models are model parameters related to the slope factor scores in the LCS model (specifically, the correlation between the intercept factor and the slope factor scores) as well as the size of the data (specifically, the number of time points and sample size). Among several model selection procedures, correct selection rates were higher when using model fit indexes (i.e., comparative fit index, root mean square error of approximation) than when using a likelihood ratio test or any of several information criteria (i.e., Akaike’s information criterion, Bayesian information criterion, consistent AIC, and sample-size-adjusted BIC). 相似文献
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When people begin to study new material, they may first judge how difficult it will be to learn. Surprisingly, these ease of learning (EOL) judgments have received little attention by metacognitive researchers so far. The aim of this study was to systematically investigate how well EOL judgments can predict actual learning, and what factors may moderate their relative accuracy. In three experiments, undergraduate psychology students made EOL judgments on, then studied, and were tested on, lists of word-pairs (e.g., sun – warm). In Experiment 1, the Goodman-Kruskal gamma (G) correlations showed that EOL judgments were accurate (G = .74) when items varied enough in difficulty to allow for proper discrimination between them, but were less accurate (G = .21) when variation was smaller. Furthermore, in Experiment 1 and 3, we showed that the relative accuracy was reliably higher when the EOL judgments were correlated with a binary criterion (i.e., if an item was recalled or not on a test), compared with a trials-to-learn criterion (i.e., how many study and test trials were needed to recall an item). In addition, Experiments 2 and 3 indicate other factors to be non-influential for EOL accuracy, such as the task used to measure the EOL judgments, and whether items were judged sequentially (i.e., one item at a time in isolation from the other items) or simultaneously (i.e., each item was judged while having access to all other items). To conclude, EOL judgments can be highly accurate (G = .74) and may thus be of strategic importance for learning. Further avenues for research are discussed. 相似文献
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提出了一种利用非对称三点弯曲加载下的单边垂直切槽深梁试件(SEVNDB)开展岩石Ⅰ-Ⅱ复合断裂韧度测试方法。通过有限元法对试件的无量纲应力强度因子进行了数值分析与标定,研究了无量纲应力强度因子YⅠ、YⅡ及无量纲T应力T*与裂纹长度a、支座间距S1、S2之间的关系,定量刻画了实现纯Ⅱ型加载对应的裂纹长度a、支座间距(S1和S2)数值。研究结果表明,该方法在不改变试样裂缝倾角的前提下,通过调整裂缝长度a和支座间距S1、S2,即可方便地实现从纯Ⅰ型到纯Ⅱ型任意复合度载荷作用下的岩石断裂韧度测试。 相似文献
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William Balzer Nancy Boudreau Peter Hutchinson Ann Marie Ryan Todd Thorsteinson James Sullivan Robert Yonker Deanne Snavely 《Research in higher education》1996,37(6):633-658
Multiple regression procedures are commonly used to investigate gender equity in faculty salary. However, a review of 19 case studies indicates that many of them fail to (a) adequately develop a regression model that examines the linear and nonlinear (i.e., interactive and curvilinear) relations between predictors and the criterion and (b) appropriately apply regression diagnostic statistics throughout salary model development. A seven-step process is presented as a comprehensive framework for testing allegations of gender discrimination in faculty salary. Steps include (a) identifying predictors of faculty salary, (b) identifying and establishing criteria for interpreting statistical tests and diagnostic procedures, (c) determining the criterion variable used in the salary model, (d) developing a salary model, (e) testing for gender discrimination in pay, (f) conducting diagnostic procedures to confirm the appropriateness of the final salary model, and (g) testing the assumptions of the regression model. An application of this model is presented using a case study (N = 725 faculty). 相似文献
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新世纪我国基础教育课程改革的理念与体系 总被引：2，自引：0，他引：2
新世纪我国基础教育课程改革的目标在于以学生为本,具体包括：从“双基”到“四基”;以学科课程、活动课程、综合课程、问题中心课程等多类型课程体现目标;学生建构的课程设计,把学生的发展作为课程开发的出发点和归宿。落实这些目标必须确立终身学习的课程设计、多元文化的课程设计、开放系统的课程设计等全新的课程改革理念,试行国家课程、地方课程和学校课程。即三级课程、三级管理的基础教育课程体系。 相似文献
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This study investigated differences between two approaches to chained equipercentile (CE) equating (one‐ and bi‐direction CE equating) in nearly equal groups and relatively unequal groups. In one‐direction CE equating, the new form is linked to the anchor in one sample of examinees and the anchor is linked to the reference form in the other sample. In bi‐direction CE equating, the anchor is linked to the new form in one sample of examinees and to the reference form in the other sample. The two approaches were evaluated in comparison to a criterion equating function (i.e., equivalent groups equating) using indexes such as root expected squared difference, bias, standard error of equating, root mean squared error, and number of gaps and bumps. The overall results across the equating situations suggested that the two CE equating approaches produced very similar results, whereas the bi‐direction results were slightly less erratic, smoother (i.e., fewer gaps and bumps), usually closer to the criterion function, and also less variable. 相似文献
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Jee-Seon Kim 《Journal of Educational Measurement》2006,43(3):193-213
Simulation and real data studies are used to investigate the value of modeling multiple-choice distractors on item response theory linking. Using the characteristic curve linking procedure for Bock's (1972) nominal response model presented by Kim and Hanson (2002) , all-category linking (i.e., a linking based on all category characteristic curves of the linking items) is compared against correct-only (CO) linking (i.e., linking based on the correct category characteristic curves only) using a common-item nonequivalent groups design. The CO linking is shown to represent an approximation to what occurs when using a traditional correct/incorrect item response model for linking. Results suggest that the number of linking items needed to achieve an equivalent level of linking precision declines substantially when incorporating the distractor categories. 相似文献
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以美国著名后现代作家唐·德里罗的《白噪音》为例,在批评传统翻译观念中关于"忠实"性翻译标准的基础上,提出了目前在翻译活动中应遵守的原则,即后现代文化语境中的翻译标准。它们是:符合知识的客观性;理解的合理性与解释的普遍有效性;符合原文的定向性。用暴力颠覆原文的界限,从而寻求译文的真正越界。 相似文献
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本文结合土木工程毕业设计中建筑设计阶段教学,针对目前设计类课程在教学中存在的一些缺陷,提出采用教学两案（即教案和预案）的有效教学方法,并对设计类课程教学特点、教学组织等方面研究进行系统分析和研究。 相似文献