共查询到19条相似文献，搜索用时 671 毫秒
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用三维涡丝法对轴对称不可压射流进行了数值模拟，描述了轴对称射流在外加扰动下产生的拟序结构随时间的发展。文中应用了涡丝的增加与合并技术，模拟了在基波扰动作用下涡的卷起，以及在扰动中加入次谐波后涡的配对。通过对不同时刻涡量图的比较与分析，说明扰动中的基波导致涡的卷起，次谐波控制着涡的配对，所得结论与理论和实验结果相一致。 相似文献
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机械波是大学物理教学中的重点内容,本文以平面简谐波为例,阐明了波动方程所描述的物理意义,讨论了介质中两点之间的相位差,并对驻波进行了分析。 相似文献
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间谐波是频率介于两个谐波之间的信号.电力系统间谐波对人体健康状况的影响越来越受到人们的关注.某些家用电器中应用的ICC技术使其输出信号中含有大量的间谐波成分.本文对电烤炉的输出电流数据进行了FFT分析和有效值分析,并对二者进行了对比,证明其中含有大量的间谐波,对以后研究间谐波时人体健康的影响提供了理论依据. 相似文献
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《科技通报》2015,(11)
应用2004-2013年NCEP/NCAR再分析资料和浙江北部雨量资料,对梅雨期间低涡活动进行统计分类,并对低涡与浙北暴雨的关系进行了分析。结果表明:梅雨期平均每年有5.6个低涡活动,夜间02时生成的低涡最多,早晨最少,低涡生命期多在24~48 h之间;依据涡源,低涡可分为三类,其中西南涡最多,占总数的42%,生成后向东北方向移动;有低涡影响的暴雨约占暴雨总数的63%,其中73%受西南涡影响,且发生在夜间的暴雨受低涡影响概率比白天大;低涡东南侧暖区暴雨比低涡后部冷切暴雨略多,暖区暴雨发生时,低涡中心多位于安徽省,最远距浙北约400 km,高空多小槽活动;而在冷切暴雨中,切变线距离浙北200 km以内,75%的西风槽已移至我国东部沿海。 相似文献
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在正弦交流电路中,电流或电压的叠加不是简单的数值的叠加,而是相量的叠加,其结果与两个电量之间的相位差密切相关;能直接读出或显示相位差的相位仪不属于通用仪器,并且价格也相对较高,不可能每个实验台都予以配备;实践中利用通用仪器对两个正弦交流电量之间相位差进行测量仍然是一种简捷、有效的方法。 相似文献
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《科技通报》2017,(3)
针对三相四线制低压配电网中无功和谐波的综合治理困难的问题,该文利用SVG低压配电网进行综合治理。根据电网的负荷情况,以瞬时无功理论为基础,对传统ip-iq算法进行了改进,提出了可靠的数学模型,实现了负载电流中的基波有功电流的检测并计算出SVG输出的无功、谐波、零序和负序的补偿电流。SVG输出电流的控制采用电压外环和电流内环的双环控制策略,电压外环利用PI控制直流电容电压,电流内环利用比例谐振(PR)控制减少输出电流谐波含量,实现对SVG输出电流的精确控制。利用matlab/simlink仿真得到补偿后比补偿前负载电流波形有了明显改善;补偿后系统功率因数在0.99~1之间波动,比补偿前有了明显提高,验证了SVG在低压三相四线的无功和谐波综合治理问题上具有可行性。 相似文献
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本文对电能表在电力系统间谐波作用下的电能计量准确度影响因素及影响程度进行全面、深入的分析和研究.在理论研究基础上,利用电能功率标准源等间谐波标准源,在电压波形和电流波形畸变两种条件下,对两种电能表进行间谐波影响试验,给出电力系统间谐波对电能表电能计量影响的结论. 相似文献
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This paper reports a technique for temperature-induced merging of droplets in a microchannel. The multiphase system consists of water droplet and oil as the dispersed phase and the carrying continuous phase. A resistive heater provides heating in a rectangular merging chamber. The temperature of the chamber is controlled by the voltage applied to the heater. The merging process of two neighboring droplets was investigated with different applied voltage, flow rate ratio between water and oil and total flowrate. Merging is found to be effective at high flow rate ratio, high temperature, and low total flowrate. The presented technique could be used for merging and mixing in droplet-based lab-on-a-chip platforms. 相似文献
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An experimental study on isotachophoresis (ITP) in which an emulsion is used as leading electrolyte (LE) is reported. The study aims at giving an overview about the transport and flow phenomena occurring in that context. Generally, it is observed that the oil droplets initially dispersed in the LE are collected at the ITP transition zone and advected along with it. The detailed behavior at the transition zone depends on whether or not surfactants (polyvinylpyrrolidon, PVP) are added to the electrolytes. In a system without surfactants, coalescence is observed between the droplets collected at the ITP transition zone. After having achieved a certain size, the droplets merge with the channel walls, leaving an oil film behind. In systems with PVP, coalescence is largely suppressed and no merging of droplets with the channel walls is observed. Instead, at the ITP transition zone, a droplet agglomerate of increasing size is formed. In the initial stages of the ITP experiments, two counter rotating vortices are formed inside the terminating electrolyte. The vortex formation is qualitatively explained based on a hydrodynamic instability triggered by fluctuations of the number density of oil droplets. 相似文献
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This study examines the effects of the differences in organizational identities that emerged during a post-merger project that aimed at unifying the laboratory services of a large healthcare center that resulted from the merging of three hospitals by supporting them with a unique information system. We draw on the concepts of organizational identity and sensemaking to analyze the laboratory information system implementation project. Organizational identity is conceptualized as the mental representation that organizational members have of themselves as a social group in terms of practices, norms, and values and how they understand themselves to be different from members of other organizations. Data analysis suggests that divergent organizational identities and team members’ alternative interpretations of others’ practices, norms and organizational symbols, coexist during the post-merger integration phase. These interpretations are reflected in the final functionality of the information system that was different from the planned one. 相似文献
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Here, we introduce a solution to low stability of a two-phase slug flow with a chemical reaction occurring at the phase interface in a microfluidic reactor where substantial merging of individual reacting slugs results in the loss of uniformity of the flow. We create a three-phase slug flow by introducing a third fluid phase into the originally two-phase liquid-liquid slug flow, which generates small two-phase liquid slugs separated by gas phase. Introduction of the third phase into our system efficiently prevents merging of slugs and provides beneficial reaction conditions, such as uniform flow pattern along the whole reaction capillary, interfacial area with good reproducibility, and intensive water-oil interface renewal. We tested the three-phase flow on an enzyme hydrolysis of soybean oil and compared the reaction conversion with those from unstable two-phase slug flows. We experimentally confirmed that the three-phase slug flow arrangement provides conversions and pressure drops comparable or even better with two-phase liquid-liquid arrangements. 相似文献
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This study considers merging dynamical networks (relative sensing networks in this paper) in terms of a stability margin criterion. The main motivation of this consideration is that merging can cause a significant drop in the stability margin of merged network with respect to the original networks initially with ample stability margins. In this paper, various types of network merging (i.e. undirected/directed homogeneous/heterogeneous dynamical network merging via one-way/two-way links) are analysed to show their effects on the stability margin. In particular, it is shown that (1) merging with one-way links yields the stability margin less than the original networks’; (2) merging undirected homogeneous networks with two-way links results in a stability margin being at least a quantity solely characterized by the positive realness (PRness) of SISO (Single-Input-Single-Output) local dynamics; (3) the quantity depends both on the PRness of SISO local dynamics and the eigenvalues of Laplacian matrix, in case of merging directed homogeneous networks with two-way links; (4) two-way merging using multiple nodes may allow for a large increase in the stability margin; and (5) merging heterogeneous networks may be simply treated as merging homogeneous networks by exploiting the design of link dynamics. Several numerical results are presented to show their consistency with the performed analysis. 相似文献
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This paper proposes a learning approach for the merging process in multilingual information retrieval (MLIR). To conduct the learning approach, we present a number of features that may influence the MLIR merging process. These features are mainly extracted from three levels: query, document, and translation. After the feature extraction, we then use the FRank ranking algorithm to construct a merge model. To the best of our knowledge, this practice is the first attempt to use a learning-based ranking algorithm to construct a merge model for MLIR merging. In our experiments, three test collections for the task of crosslingual information retrieval (CLIR) in NTCIR3, 4, and 5 are employed to assess the performance of our proposed method. Moreover, several merging methods are also carried out for a comparison, including traditional merging methods, the 2-step merging strategy, and the merging method based on logistic regression. The experimental results show that our proposed method can significantly improve merging quality on two different types of datasets. In addition to the effectiveness, through the merge model generated by FRank, our method can further identify key factors that influence the merging process. This information might provide us more insight and understanding into MLIR merging. 相似文献
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QuickBird遥感影像的融合及在农业园区底图制作中的应用研究 总被引：4，自引：0，他引：4
应用比值变换、IHS变换、主成分变换和合成比值变量变换等4种影像融合方法对QuickBird多光谱和全色遥感影像进行融合,并利用偏差指数、平均梯度等指标对融合效果进行定量评价;运用最佳指数因子确定参与成图的多光谱影像的波段．研究结果表明,合成比值变量变换法的融合效果最佳;最优波段组合为431,并在此基础上建立了地物判读分析依据,用于QuickBird遥感影像目视解译;采用容差格网矢量化技术进行遥感影像的屏幕矢量化,制作了1：2000比例尺农业园区底图。 相似文献
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In this study, droplet formations in microfluidic double T-junctions (MFDTD) are investigated based on a two-dimensional numerical model with volume of fluid method. Parametric ranges for generating alternating droplet formation (ADF) are identified. A physical background responsible for the ADF is suggested by analyzing the dynamical stability of flow system. Since the phase discrepancy between dispersed flows is mainly caused by non-symmetrical breaking of merging droplet, merging regime becomes the alternating regime at appropriate conditions. In addition, the effects of channel geometries on droplet formation are studied in terms of relative channel width. The predicted results show that the ADF region is shifted toward lower capillary numbers when channel width ratio is less than unity. The alternating droplet size increases with the increase of channel width ratio. When this ratio reaches unity, alternating droplets can be formed at very high water fraction (wf = 0.8). The droplet formation in MFDTD depends significantly on the viscosity ratio, and the droplet size in ADF decreases with the increase of the viscosity ratio. The understanding of underlying physics of the ADF phenomenon is useful for many applications, including nanoparticle synthesis with different concentrations, hydrogel bead generation, and cell transplantation in biomedical therapy. 相似文献
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摘要：本文借鉴资源整合的视角,以陈克复院士团队为案例,从逻辑层面演绎了学术团队核心能力的成长路径与内在机理。研究发现：与资源整合的“资源判断能力--资源识别与获取能力--资源配置能力--资源运用能力”四个阶段相对应,学术团队核心能力成长过程可概括为“洞察技术需求与学术前沿--技术与知识资源的识别与获取--汲取、激活与融合形成新资源--运用整合资源创造价值”,并在此基础上提出了基于资源整合视角的学术团队核心能力成长过程及机理的“金字塔”模型。 相似文献