共查询到20条相似文献，搜索用时 593 毫秒
1.
Aiming at disclosing the quantitative effects of Coulomb forces on the filtration efficiency of aerosol particles, a three-dimensional random fiber model was established to describe the microstructure of fibrous filters. Then, computational models including the flow model, particle model, and electric field model were constructed to estimate the filtration efficiency using the Fluent custom user-defined function program, neglecting the non-uniformity of the fiber potential and the particle charge distribution. The simulation results using the established models agreed with the data in the literature. In particular, the electric field force was found to be one of the important factors required to improve the filtration efficiency estimation accuracy for the ultrafine particles. Moreover, the variation tendencies of the filtration efficiency and the pressure drop of fibrous filters were studied based on the influence factors of the fiber potential, particle charge-to-mass ratio, solid volume fraction, fiber diameter, and face velocity. The established models and estimated results will provide important guidance on the design of high-efficiency particulate air filters for aerosol particles. 相似文献
2.
Visual perspective-taking skills in children 总被引：1，自引：0，他引：1
The present study evaluated the effects of stimulus complexity and rule usage on a visual perspective-taking task. Preschoolers, first, third, and fifth graders, and adults were shown arrays of dolls and performed a series of perspective-taking tasks. Errors decreased with age, and more errors occurred with the more complex visual arrays. A significant number of errors were made in self-view trials, especially by the preschoolers, showing that the ability to relate an array to a pictorial representation of it is not perfect. A conditional probability analysis showed that most egocentric errors were not due to an inability to relate the array to pictorial representations, but rather to a lack of mastery of Flavell's different positions--different views rule. When the array was covered, however, even first graders showed almost perfect mastery of this rule. There were also task effects on the use of Flavell's same position--same view rule: children performed better for a task involving self and other than for 2 others. Response latencies and effects for the observer's relative position provided evidence for a new rule: opposite positions--opposite views. In addition, front and back views of the dolls were significantly easier than the side views, which suggests a role of labeling or stimulus-discrimination skills. 相似文献
3.
纤维滤料新模型的阻力数值模拟研究 总被引：1，自引：0，他引：1
利用流体力学开源代码OpenFOAM验证了单圆柱体周围的流体特性（包括流型和阻力）,表明Open-FOAM能够用于模拟低Re数流,并发现Shaw的解析解是斯托克斯悖论的一种解.通过对纤维滤料进行试验以及对Tronville-Rivers二维纤维随机分布滤料新模型的阻力特性进行数值模拟,发现Kuwabara模型比Hap-pel模型更能精确预测纤维滤料的阻力,而且试验阻力值介于纤维表面为无滑移和全滑移边界条件下的数值模拟值之间. 相似文献
4.
应用FDTD方法分析TEM喇叭天线阵列的瞬态辐射特性，分析了阵列单元之间的互耦对天线阵列远场辐射的影响。TEM喇叭天线阵列单元沿E面叠状排列可以改善阵列的低频辐射。原理上阵元越多，天线阵列的增益越高。而线性阵列只压缩一个面的方向图。改变阵列单元间馈入信号的时延，可以实现阵列方向图主辩方向的偏移。用半TEM喇叭天线组成槽状排列二元线阵和四元线阵，进行了相应的原理性实验，实验结果与理论数值模拟基本一致。 相似文献
5.
邬刚 《潍坊教育学院学报》2002,15(3):40-41,72
通过对 1 0 0米途中跑腾空时的两条摆动腿的摆动技术分析得出结论 :腾空时 ,体前摆动腿作向后下方摆动的速度快慢 ,对缩小腾空时间和减小着地时人体受到的水平支撑反作用力起关键性的作用 ,体后摆动腿作快速折叠向前摆动的速度快慢 ,对体后摆动腿在有限时间内尽可能地完成大部分的体后折叠摆动 ,起着关键性的作用 ,并为支撑时的摆动创造良好的起始条件。 相似文献
6.
根据镱离子特性理论分析了掺镱光纤激光器的原理,借助阵列波导光栅、光谱分析仪等构建出相应装置对多波长掺镱光纤激光器24个不同的输入信道/输出光谱强度分别进行详细研究,证实了可调谐多波长掺镱光纤激光器稳定的工作特性。 相似文献
7.
Staggered pattern perforations are introduced to isolated isothermal plates, vertical parallel isothermal plates, and vertical
rectangular isothermal fins under natural convection conditions. The performance of perforations was evaluated theoretically
based on existing correlations by considering effects of ratios of open area, inclined angles, and other geometric parameters.
It was found that staggered pattern perforations can increase the total heat transfer rate for isolated isothermal plates
and vertical parallel plates, with low ratios of plate height to wall-to-wall spacing (H/s), by a factor of 1.07 to 1.21, while only by a factor of 1.03 to 1.07 for vertical rectangular isothermal fins, and the magnitude
of enhancement is proportional to the ratio of open area. However, staggered pattern perforations are detrimental to heat
transfer enhancement of vertical parallel plates with large H/s ratios. 相似文献
8.
模拟了一种常规快速式燃气热水器的燃烧系统,研究了不同压力状况下的燃烧工况.得到的数值模拟结果与实验获得的数据吻合得较好,证明了所用物理模型和数学模型的合理性.结果显示,火焰高度和过剩空气系数依赖于系统出口和入口的静压差,而与燃烧室内的绝对压力无关.该静压差和系统中用于燃烧的空气量显著影响CO的生成,与CO的生成量呈反比关系,并同时影响燃烧区域内的温度场和速度场.为降低CO排放水平,必须增加进入燃烧系统的空气量,因此需要增加风机输出功率以提供足够的空气压头.该研究为设计快速式燃气热水器提供了一种行之有效的方法. 相似文献
9.
Jacky Emmerton 《Learning & behavior》1998,26(3):243-256
Two experiments are described in which pigeons were trained in a simultaneous conditioning procedure to discriminate small arrays of dots that differed in numerosity. The birds successfully learned to choose the array of each pair that contained fewer dots when these choices were reinforced and choices of the array with more dots led to timeout. For the majority of numerosity values tested, discrimination performance for a fixed S+ value was better when the numerical difference between S+ and S-values was larger rather than smaller. This effect was seen in the first experiment when the numerical difference value was shifted between training trials and novel test trials. In the second experiment, too, performance level depended on the size of the numerosity difference when the birds were concurrently trained with two difference values that varied across trials within sessions. However, discrimination accuracy was influenced secondarily by variations in the density, or interdot spacing, of the stimulus arrays. In order to explain the latter finding, it is suggested that a tendency to “scan” a lowdensity array incompletely might alter the probability of accepting it as the smaller numerosity (S+) stimulus. This would increase error rates with S? arrays in which the dots are more widely spaced. 相似文献
10.
朱祎 《江苏广播电视大学学报》2003,14(6):28-30
为提高PHP程序的运行效率、规模支持能力和跨平台性，可以设计一个基于Java技术的编译器，将PHP程序直接编译成Java虚拟机的二进制字节代码。这个编译器采用经典的前端／后(font-end／back-end)式结构，前端程序对源程序进行扫描、分析后生成抽象语法树，后端程序遍历抽象语法树生成Kawa IR的表达式序列，并最终生成目标代码。 相似文献
11.
Ultrafiltration (UF) technique is prospective asalternative for conventional processes such as coagula-tion, flocculation, sedimentation and/or flotation,rapid and slowsand filtration[1]. Recentdevelopmentsin reducing energy consumption by (semi) dead-endfiltration and prevention of membrane fouling by back-washing (combined with chemicals), make UF moreand more an interestingoption forthe treatmentof sur-face water on a large scale[2]. At present, UF full-scale applications are evenlyspread… 相似文献
12.
A good efficiency performance of a pump over a wide range of displacement conditions is crucially important for variable pump control systems to save energy. However, according to the literature, less attention has been paid to the understanding of the efficiency, leakage flow, and compression flow characteristics of the pump with respect to displacement conditions. In this study, a test bench was built, and a novel explicit volumetric loss model was proposed to investigate these problems. The overall efficiency is found to drop considerably with the decreasing displacement. The volumetric losses range from 13% to 47% of the total power losses of pump at the rated speed, under the conditions of pressure ranging from 5 to 35 MPa and displacement ranging from 13% to 100% of full displacement. The highest proportion of compression flow losses in the total volumetric losses of pump at the rated speed can reach up to 41% when the pressure and displacement are greater than 30 MPa and 88% of full displacement, respectively; after that, the proportion gradually decreases with decreasing displacement. However, the leakage flow generally increases with decreasing displacement, or may decrease first and begin to increase after the minimum with the further decrease of displacement. In the components of leakage of slipper/swash plate pair, the squeeze leakage is found to reach a magnitude equal to that of the Poiseuille leakage. The findings can guide the further research and design of pumps with better efficiency performance. 相似文献
13.
A micro-sized tube heat exchanger(MTHE) was fabricated, and its performance in heat transfer and pressure drop was experimentally studied. The single-phase forced convection heat transfer correlation on the sides of the MTHE tubes was proposed and compared with previous experimental data in the Reynolds number range of 500—1 800. The average deviation of the correlation in calculating the Nusselt number was about 6.59%. The entrance effect in the thermal entrance region was discussed. In the same range of Reynolds number, the pressure drop and friction coefficient were found to be considerably higher than those predicted by the conventional correlations. The product of friction factor and Reynolds number was also a constant, but much higher than the conventional. 相似文献
14.
We previously reported that chimpanzees were unable to optimally select the smaller of two candy arrays in order to receive a larger reward. When Arabic numerals were substituted for the candy arrays, animals who had had prior training with numerical symbols showed an immediate and significant improvement in performance and were able to select reliably the smaller numeric representation in order to obtain a larger reward. Poor performance with candy arrays was interpreted as reflecting a response bias toward the intrinsic incentive and/or perceptual features of the larger array. In contrast, the Arabic numerals represent numerosity symbolically and appear to promote response choice on the basis of abstract processing of numerosity, with minimal interference from the inherent properties of the choice stimuli. The present study tested the hypothesis that, for mixed symbol-candy choice pairs, the requisite processing of the abstract numeral may foster a mode of numerical judgment that diminishes the interfering incentive/perceptual effects of the candy stimuli. The results were consistent with this hypothesis. Whereas performance on candy-candy arrays was significantly below chance levels, performance on numeral-candy choice pairs was significantly above chance and comparable with performance on numeral-numeral pairs. 相似文献
15.
徐四海 《常熟理工学院学报》2008,22(9):102-104
在现代汉语的许多方言中,前后鼻音是不分的,或者是分不清楚的。有的方言把后鼻音读成前鼻音,有的把前鼻音读成后鼻音。16个鼻韵母占普通话语音系统韵母总数的41％。鼻韵母中90％左右的字是形声字,通过形声字相同的声符可以类推出一系列同声符字的韵尾。掌握鼻韵母形声字韵尾呈现的规律,对于学习和推广普通话具有重要的意义。 相似文献
16.
There is conflicting evidence on the effect of seat location on student performance and participation in the classroom. The two major hypotheses are (1) that seat location influences student behavior and (2) that seat preference and selection is associated with personality traits of students. This study evaluated both hypotheses within a 55 student senior nutritional biochemistry class. Alternating every other seat, half of the class was randomly assigned a permanent seat while the other half was randomly reassigned a different seat each class period. Students sitting in the front of the classroom in the stay group made significantly more comments per student per day than stay group students in the back, in agreement with other studies. The move group, however, showed increased overall participation with no significant difference between the front and back of the classroom. Findings suggest a more flexible explanation—that students may adopt or reject an implied social role in which seat location and personality traits are influential factors. 相似文献
17.
时间是空间隐喻的结果,空间的位移性和顺序性投射在时间上表现为序列性和方向性。＂前/后＂是既可以表示空间意义也可以表示时间意义的一对语素。＂前/后＂有两种认知模式：强调时间的序列性时＂,前＂表过去,＂后＂表将来;强调时间的方向性时,＂前＂表将来＂,后＂表过去。 相似文献
18.
A micro turbo-expander capable of high working speed was specially manufactured for use in an organic Rankine cycle (ORC).
A series of tests were executed to examine the performance of the machine. In the experiment, the machine was tested under
different inlet pressure conditions (0.2–0.5 MPa). Data such as the compressed air pressure, temperatures of the inlet and
the outlet, rotational speed, and electric power generation were analyzed to discover underlying relationships. During the
test, the rotational speed of the machine reached as high as 54 000 r/min, the peak value of the temperature drop between
the inlet and the outlet reached 42 °C, the maximum electric power generated by the motor-generator attached to the machine
reached 630 W, and the efficiency of the machine reached 0.43. 相似文献
19.
黄国军 《黄冈职业技术学院学报》2010,12(3):9-10
C++语言中的指针变量和数组的关系非常密切。掌握指针变量与数组的关系是学好C++语言课程的难点,也是重点。就不同级别的指针变量与不同维数的数组之间的关系进行剖析,以便明确教学重难点。 相似文献
20.
在综合分析了微带平面天线阵列馈电网络的两种传统馈电方式的基础上,提出了一种在微波工程应用中实际使用的一种新型馈电网络,提高学生理论知识与实践相结合的能力,更好的掌握最新技术发展。其新型馈电网络由一种左-右手混合微带传输线构成,可以获得高于传统并联馈电网络的天线阵列增益;同时,可以修正传统串联馈电网络的天线阵列辐射方向图的波束偏移,给出了一个工作频率为35GHz的2×2微带面阵的馈电网络设计案例,验证了其理论的正确性。 相似文献