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《中国科技论文》2021,(1)
低温绝热气瓶储存低温液体,当气瓶处于额定充满率时,气瓶内部温度一般处于储存液体的饱和温度,但充满率降低时,由于气液两相物性参数的差异,其气相区温度分布会呈现出较液相明显的分层现象。为研究环境温度和充满率对低温绝热气瓶内部气相空间温度分布规律的影响,开展了实验和数值模拟研究,利用搭建的恒温箱,选取2种不同规格的气瓶,对不同恒温箱温度和充满率下的气瓶内部气相空间温度分布进行了实验研究。实验结果表明:恒温箱温度不变而充满率变化时,随着充满率的升高,气相区温度分层趋势加剧;而充满率不变时,恒温箱温度对气相区温度分布的影响较小。另外,对气瓶内壁面温度进行了数值模拟,模拟结果显示,壁面温度分布规律与气相温度分布规律具有一致性,同一高度处内壁面温度高于气相温度,对气相区内壁面温度取算术平均值时,充满率越低,其值越大。 相似文献
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INTRODUCTIONTolerancedesignisabridgetolinktherequirementofproductperformanceandthemanufacturingprocess;andaffectsnotonlytheproductperformance,butalsothecostoftheproductandthemanufacturingprocess.There foreComputerAidedTolerancing (CAT)be comesthekeytechniqueforintegratingCAD CAPP CAM (WuandYang,1999) .Tradition ally,thetoleranceisassignedtothecomponentdimensionsaccordingtotheminimumcost.Therestrictionofthemanufacturingabilityoftoolsthatthefactoryownsisneglected (Jietal.,1999) .Asa… 相似文献
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A prediction model of foreign language reading proficiency based on reading time and text complexity
In textbooks, foreign (second) language reading proficiency is often evaluated through comprehension questions. In case, authentic texts are used as reading material, such questions should be prepared by teachers. However, preparing appropriate questions may be a very demanding task for teachers. This paper introduces a method for automatically evaluating proficiency, wherein comprehension questions are not required. This method assesses a learner's reading proficiency on the basis of the linguistic features of the text and the learner's reading time. A reading model following this method predicted reading proficiency with an ER (error rate) of 18.2%. This ER is lower than those of models proposed in previous studies. Furthermore, the ER of the authors' reading model for various learner groups classified by their RS (reading speeds) was examined. The result of this examination showed that the error rate was the lowest for the group of learners with fast RS. 相似文献
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科学有效的教学质量评价是加强本科院校教学管理和提高教学质量的重要手段.为找出影响课堂教学效果的主要因素,利于教师教学水平的提高,采用模糊层次分析法(FAHP)对细胞生物学课堂教学效果进行综合评价. 相似文献
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Time series prediction has been successfully used in several application areas, such as meteorological forecasting, market
prediction, network traffic forecasting, etc., and a number of techniques have been developed for modeling and predicting
time series. In the traditional exponential smoothing method, a fixed weight is assigned to data history, and the trend changes
of time series are ignored. In this paper, an uncertainty reasoning method, based on cloud model, is employed in time series
prediction, which uses cloud logic controller to adjust the smoothing coefficient of the simple exponential smoothing method
dynamically to fit the current trend of the time series. The validity of this solution was proved by experiments on various
data sets.
Project (No. 2001AA112030) supported by the National Hi-Tech Development Program (863) of China 相似文献
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In order to overcome the inconvenience of manual bubble counting, a bubble counter based on photoelectric technique aiming for automatically detecting and measuring minute gas leakage of cryogenic valves is proposed. Experiments have been conducted on a self-built apparatus, testing the performance with different gas inlet strategies (bottom gas-inlet strategy and side gas-inlet strategy) and the influence of gas pipe length (0, 1, 2, 4, 6, 8, 10 m) and leakage rate (around 10, 20, 30, 40 bubbles/min) on first bubble time and bubble rate. A buffer of 110 cm^3 is inserted between leakage source and gas pipe to simulate the downstream cavum adjacent to the valve clack. Based on analyzing the experimental data, experiential parameters have also been summarized to guide leakage detection and measurement for engineering applications. A practical system has already been successfully applied in a cryogenic testing apparatus for cryogenic valves. 相似文献
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有源电力滤波器(active power filter, APF)补偿电流跟踪控制要求具有较高的稳态精度和较快的动态响应速度。文章将自适应预测滤波算法应用于无差拍控制,实现APF补偿电流精确控制。根据APF时域数学模型,推导滤波系统的无差拍控制离散方程;通过自适应(finite impulse response filter, FIR)预测滤波算法实现基波电流预测,消除控制系统的计算延迟,给无差拍控制提供所需的指令电流预测值。对预测算法进行MATLAB仿真,验证预测算法的稳态精度和动态跟踪快速性;实验室样机验证控制实验结果证明所提出的控制策略有效的,具有一定的实用性。 相似文献
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挤进时期的航空内弹道学是研究导带嵌入炮膛时弹丸运动的阻力,它对炮管寿命的研究和保障、射击时炮管的弹道保障、炮管和弹丸本身强度的计算以及弹丸射击密集度都具有重要的影响.因此,挤进压力的计算显得尤为重要.但目前还没有令人满意的计算方法.基于此,本文引入分析法研究某型航炮的挤进压力的计算问题,这种方法计算的挤进压力与实际情况比较吻合. 相似文献
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MO Guo-liang ZHAO Ya-nan 《浙江大学学报(A卷英文版)》2006,7(12):2043-2049
INTRODUCTION B-spline curves and surfaces have been widely used in Computer Graphics (CG) and Computer Aided Design (CAD) (Hoschek and Lasser, 1993; Piegl and Tiller, 1997). Many practical algorithms, such as those for position and derivatives evaluation, knot insertion, knot deletion and degree elevation, are usually implemented in a CAD system that uses B-spline as a shape design tool. In curve and surface design, a given B-spline curve or surface usually needs to be extended in … 相似文献
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通过对STL文件的分析和几种常用数据结构的比较,给出了一种层次环状数据结构,该结构是由快速排序顶点序列进行冗余顶点滤除,并建立顶点邻接表和三角面片邻接表而得到的.由于邻接表中存储的是点、面的索引号,从而提高了后续查找的效率,节省了存储空间.本方法已成功应用于虚拟牙齿矫正系统的开发,同时也适用于其它各种以STL为数据交换格式的系统. 相似文献
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文中深入讨论了利用支持向量机构造多分类器的方法,并比较了它们的优缺点,提出了基于赫夫曼树的SVM多分类构造算法,并在训练时间及判别时间上证明了该构造算法的优越性,减少了分类器的判别时间. 相似文献
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