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2720篇 您的检索式:关键字=flow
    题名 作者 年代 出处 被引量
1Flow研究概述显示文摘Flow是一种重要的积极情绪,它是指人们对某一活动或事物表现出浓厚的兴趣并推动个体完全投入某项活动或事物的一种情绪体验。Flow体验具有九个特征,即所感知到的活动挑战性与技能水平相平衡、行动与意识相融合、明确的活动目的、清晰的即刻反馈、对当前活动的高度投入、控制感、丧失自我意识、活动的内在奖励以及时间体验失真。心理学界的Flow研究已主要在Flow自身属性和应用两个领域展开,而对Flow的测量主要有面谈、问卷调查和ESM等三种方法。任俊 施静 马甜语 2009心理科学进展2009,17,1:113
2Analysis on the ecological benefits of the stream water conveyance to the dried-up river of the lower reaches of Tarim River,China显示文摘This paper analyzes the monitored data of the 4 times of stream water conveyances to the river section where the stream flow was cut-off, of 9 groundwater-monitoring sections and 18 vegetation plots in the lower reaches of Tarim River. The results show that the groundwater depth in the lower reaches of Tarim River rose from 9.87 m before the conveyances to 7.74 m and 3.79 m after the first and second conveyances, 3.61 and 3.16 m after the 2 phases of the third conveyance, and 2.66 m after the fourth conveyance. The transverse response scope of groundwater level was gradually enlarged along both sides of the channel of conveyances, i.e., from 450 m in width after the first conveyance to 1050 m after the fourth conveyance, but the response degree of groundwater level was reduced with the increase of the distance away from the channel of conveyances. The composition, distribution and growth status of the natural vegetation are directly related to the groundwater depth. The indexes of Simpson’s biodiversity, McIntosh’s evenness and Margalef’s richness, which reflect the change of the quantity of species and the degree of biodiversity, are reduced from 0.70, 0.48 and 0.90 to 0.26, 0.17 and 0.37 re- spectively along with the drawdown of groundwater level from the upper reaches to the lower reaches. After the stream water conveyances, the natural vegetation in the lower reaches is saved and restored along with the rise of groundwater level, the response scope of vegetation is gradually enlarged, i.e., from 200— 250 m in width after the first conveyance to 800 m after the fourth conveyance. However, there is still a great disparity to the objective of protecting the “Green Corridor”in the lower reaches of Tarim River. Thus, it is suggested to convey the stream water in double-channel way, combine the conveyance with water supply in surface scope, or construct the modern pipe-conveyance network systems so as to save the natural vegetation in an intensive way, achieve the efficient water consumption and speed up the restoration and re- generation of the damaged ecosystems in the lower reaches of Tarim River.CHEN Yaning1,ZHANG Xiaolei1,ZHU Xiangmin2,LI Weihong1,ZHANG Yuanming1,XU Hailiang1,ZHANG Hongfeng1 & CHEN Yapeng1 1.Xinjiang Institute of Ecology and Geography,Chinese Academy of Sciences,Urumqi 830011,China 2.Management Beureau od Tarim River Basin,Kurle 831102,China Correspondence should be addressed to Chen Yaning(email: cheyn@ms.xjb.ac.cn) 2004Science China Earth Sciences2004,47,11:58
3Regulation of hepatic blood flow:The hepatic arterial buffer response revisited显示文摘The interest in the liver dates back to ancient times when it was considered to be the seat of life processes. The liver is indeed essential to life,not only due to its complex functions in biosynthesis,metabolism and clearance,but also its dramatic role as the blood volume reservoir. Among parenchymal organs,blood flow to the liver is unique due to the dual supply from the portal vein and the hepatic artery. Knowledge of the mutual communication of both the hepatic artery and the portal vein is essential to understand hepatic physiology and pathophysiology. To distinguish the individual importance of each of these inflows in normal and abnormal states is still a challenging task and the subject of on-going research. A central mechanism that controls and allows constancy of hepatic blood flow is the hepatic arterial buffer response. The current paper reviews the relevance of this intimate hepatic blood flow regulatory system in health and disease. We exclusively focus on the endogenous interrelationship between the hepatic arterial and portal venous inflow circuits in liver resection and transplantation,as well as inflammatory and chronic liver diseases. We do not consider the hepatic microvascular anatomy,as this has been the subject of another recent review.Christian Eipel Kerstin Abshagen Brigitte Vollmar 2010World Journal of Gastroenterology2010,16,48:49
4STUDY ON CONDITIONS AND MECHANISMS OF DEBRIS FLOW INITIATION BY MEANS OF EXPERIMENT显示文摘As a debris flow starts in the upper reaches of a gully or a ravine, its scale and destructive power are not very large. It rapidly strengthens in its flow process by eroding and carrying loose solid material along its running route, and at last, it accumulates great destructive power. If the initiation conditions may be regulated and controlled to prevent debris flows, practical benefits will be obtained. To study the conditions and崔鹏 1992Chinese Science Bulletin1992,37,9:41
5Advances in Computer Vision-Based Civil Infrastructure Inspection and Monitoring显示文摘Computer vision techniques, in conjunction with acquisition through remote cameras and unmanned aerial vehicles (UAVs), offer promising non-contact solutions to civil infrastructure condition assessment. The ultimate goal of such a system is to automatically and robustly convert the image or video data into actionable information. This paper provides an overview of recent advances in computer vision techniques as they apply to the problem of civil infrastructure condition assessment. In particular, relevant research in the fields of computer vision, machine learning, and structural engineering is presented. The work reviewed is classified into two types: inspection applications and monitoring applications. The inspection applications reviewed include identifying context such as structural components, characterizing local and global visible damage, and detecting changes from a reference image. The monitoring applications discussed include static measurement of strain and displacement, as well as dynamic measurement of displacement for modal analysis. Subsequently, some of the key challenges that persist toward the goal of automated vision-based civil infrastructure and monitoring are presented. The paper concludes with ongoing work aimed at addressing some of these stated challenges.Billie F. Spencer Jr. Vedhus Hoskere Yasutaka Narazaki 2019Engineering2019,5,2:44
6薄板冷轧厚度与板形高精度控制技术显示文摘介绍与分析目前最新薄板冷轧厚度控制技术 Mass Flow AGC及激光直接测量带钢速度技术 ,厚度偏差可控制在厚度的± (0 .7%~ 0 .6 % )范围内。分析和比较目前冷轧主流机型及其板形控制技术 。许健勇 2002钢铁2002,37,1:35
7Diagnostic accuracy of a deep learning approach to calculate FFR from coronary CT angiography显示文摘Background The computational fluid dynamics(CFD)approach has been frequently applied to compute the fractional flow reserve(FFR)using computed tomography angiography(CTA).This technique is efficient.We developed the DEEPVESSEL-FFR platform using the emerging deep learning technique to calculate the FFR value out of CTA images in five minutes.This study is to evaluate the DEEPVESSEL-FFR platform using the emerging deep learning technique to calculate the FFR value from CTA images as an efficient method.Methods A single-center,prospective study was conducted and 63 patients were enrolled for the evaluation of the diagnostic performance of DEEPVESSEL-FFR.Automatic quantification method for the three-dimensional coronary arterial geometry and the deep learning based prediction of FFR were developed to assess the ischemic risk of the stenotic coronary arteries.Diagnostic performance of the DEEPVESSEL-FFR was assessed by using wire-based FFR as reference standard.The primary evaluation factor was defined by using the area under receiver-operation characteristics curve(AUC)analysis.Results For per-patient level,taking the cut-off value<0.8 referring to the FFR measurement,DEEPVESSEL-FFR presented higher diagnostic performance in determining ischemia-related lesions with area under the curve of 0.928 compare to CTA stenotic severity 0.664.DEEPVESSEL-FFR correlated with FFR(R=0.686,P<0.001),with a mean di&ference of-0.006士0.0091(P=0.619).The secondary evaluation factors,indicating per vessel accuracy,sensitivity,specificity,positive predictive value,and negative predictive value were 87.3%,97.14%,75%,82.93%,and 95.45%,respectively.Conclusion DEEPVESSEL-FFR is a novel method that allows efficient assessment of the functional significance of coronary stenosis.Zhi-Qiang WANG Yu-Jie ZHOU Ying-Xin ZHAO Dong-Mei SHI Yu-Yang LIU Wei LIU Xiao-Li LIU Yue-Ping LI 2019Journal of Geriatric Cardiology2019,16,1:37
8Overtopping breaching of cohesive homogeneous earth dam with different cohesive strength显示文摘In consideration of the range of clay content of Chinese earth dams, the world's highest prototype tests have been made to research on the effects of cohesive strength of filling of cohesive homogeneous earth dam on breach formation. Three breach mechanisms were presented, they were the source-tracing erosion of dam body with the form of 'multilevel headcut', 'two-helix flow' erosion of dam crest and collapse of breach sidewalls due to instability. It can be concluded that the cohesive strength of filling of earth dam has great effect on breach formation. When the cohesive strength is bigger, the breach process becomes slower, and the peak outflow and the final width and depth of breach become smaller. The main character of the breach formation is head cutting and dumping collapse. When the cohesive strength is smaller, the breach process becomes faster, and the peak outflow, the final width and depth of breach become bigger. The main character of the breach formation is single level head cutting and shearing collapse.ZHANG JianYun LI Yun XUAN GuoXiang WANG XiaoGang LI Jun 2009Science China(Technological Sciences)2009,52,10:34
9Supersonic flow imaging via nanoparticles显示文摘Due to influence of compressibility,shock wave,instabilities,and turbulence on supersonic flows, current flow visualization and imaging techniques encounter some problems in high spatiotemporal resolution and high signal-to-noise ratio(SNR)measurements.Therefore,nanoparticle based planar laser scattering method(NPLS)is developed here.The nanoparticles are used as tracer,and pulse planar laser is used as light source in NPLS;by recording images of particles in flow field with CCD, high spatiotemporal resolution supersonic flow imaging is realized.The flow-following ability of nanoparticles in supersonic flows is studied according to multiphase flow theory and calibrating experiment of oblique shock wave.The laser scattering characteristics of nanoparticles are analyzed with light scattering theory.The results of theoretical and experimental studies show that the dynamic behavior and light scattering characteristics of nanoparticles highly enhance the spatiotemporal resolution and SNR of NPLS,with which the flow field involving shock wave,expansion,Mach disk,boundary layer,sliding-line,and mixing layer can be imaged clearly at high spatiotemporal resolution.ZHAO YuXin YI ShiHe TIAN LiFeng CHENG ZhongYu 2009Science China(Technological Sciences)2009,52,12:31
10Effects of the Biot and the squirt-flow coupling interaction on anisotropic elastic waves显示文摘Considering the velocity anisotropy of the solid/fluid relative motion and employment of the BISQ theory based on the one-dimensional porous isotropic case, we establish a two-phase anisotropic elastic wave equation to simultaneously include the Biot and the squirt mechanisms in terms of both the basic principles of the fluid’s mass conservation and the elastic-wave dynamical equations in the two-phase anisotropic rock. Numerical results, while the Biot-flow and the squirt-flow effects are simultaneously considered in the transversely isotropic (Tl) poroelastic medium, show that the attenuation of the quasi P-wave and the quasi SV-wave strongly depend on the permeability anisotropy, and the attenuation behavior at low and high frequencies is contrary. Meanwhile, the attenuation and dispersion of the quasi P-wave are also affected seriously by the anisotropic solid/fluid coupling additional density.YANG Dinghui & ZHANG Zhongjie Department of Mathematical Sciences, Tsinghua University, Beijing 100084, China Institute of Geophysics, Chinese Academy of Sciences, Beijing 100101, China 2000Chinese Science Bulletin2000,45,23:33
11DYNAMIC RECOVERY AND DYNAMIC RECRYSTALLIZATION OF 7005 ALUMINIUM ALLOY DURING HOT COMPRESSION显示文摘Dynamic recovery and dynamic recrystallizatin behaviors of AA7005 aluminium alloy (Al - Zn - Mg) during hot compression are investigated by isothermal compression testing.The interdependence of flow stress,stress, strain rate,true strain and deformation temperature for the alloy is analyzed by introduc- ing Zener-Hollomon parameter. A steady - state flow of the 7005 alloy is confirmed to be a thermal- ly activated process.which is governed by rate-controlling mechanisms of dislocations.A hyperbolic sine relationship can satisfactorily correlate temperature, strain rate with flow stress through an Arrhe- nius term that involves thermal activation parameters. The dynamic recovery mechanisms of the alloy are discussed.Cross- slip of jogged screw dislocations is the main dynamic recovery mechanism over the deformation temperatures and strain rates.Subgrains are highly developed in the originally elongat- ed grains.The size of the subgrain increases with decrease of the natural logarithm of Zener- Hol - lomon parameter.Local dynamic recrystallization is operative when the alloy is deformed at temperature of 500℃ and strain rate of 0. 001s - 1.J. Shen S. S. Xie and J. H. tang (General Research Institute for Non - ferrous Metals,Beijing 100088, China) 2000Acta Metallurgica Sinica(English Letters)2000,13,1:33
12SDN环境下基于KNN的DDoS攻击检测方法显示文摘DDo S攻击是当前互联网面临的主要威胁之一,如何快速准确地检测DDo S攻击是网络安全领域研究的热点问题。文中提出了一种在SDN环境下基于KNN算法的模块化DDo S攻击检测方法,该方法选取SDN网络的5个关键流量特征,采用优化的KNN算法对选取的流量特征进行流量异常检测,最后基于NOX控制器和Net FPGA交换机进行了实验验证。实验结果表明:相对其他的分类检测算法,所提的检测方案具有更高的识别率和更低的误报率。肖甫 马俊青 黄洵松 王汝传 2015南京邮电大学学报(自然科学版)2015,35,1:34
13Review of zero-net-mass-flux jet and its application in separation flow control显示文摘Since the zero-net-mass-flux (ZNMF) jet was first used as a laboratory flow control method in 1990's, it has attracted much attention. The ZNMF jet has unique features such as compact actuator, no requirement for external air supply, complex piping, etc., and becomes a hot topic research subject in fluid mechanics. This review introduces the state of the art in the development of ZNMF jet in the quiescent fluid, the interaction of the ZNMF jet with the cross flow and its application in the separation flow control. The evolution of the vortex ring/pair and the spacial flow structure of the ZNMF in quicent fluid or cross flow are presented, as well as the key parameter effects. At last, the applications of ZNMF jet in the wake control of the circular cylinder, the separation control on the airfoil and the aerodynamic force or moment control on MAV/UAV are presented.ZHANG PanFeng WANG JinJun FENG LiHao 2008Science China(Technological Sciences)2008,51,9:30
14Analytical method for softness abrasive flow field based on discrete phase model显示文摘Aiming at the problem of difficult contact finishing for mini structural surface in course of mould manufacturing,a new no-tool precision machining method based on soft abrasive flow machining (SAFM) was proposed. It allocated restrained component near surface machined,constituted restrained abrasive flow passage,and made the surface become a segment of passage wall. It could control turbulence abrasive flow in restrained passage,realize micro cutting for passage wall,and utilize the irregular motion of abrasive flow to eliminate the mono-directional marks on machined surfaces,and the precision could reach the specular level. A two-phase dynamic model of abrasive flow oriented to SAFM combined with discrete phase model (DPM) was established,the law of two-phase flow motion and the related physical parameters was obtained by corresponding numerical simulation method,and the mechanism of precision machining in SAFM was discussed. Simulation results show that the abrasive flow machining process mainly appears as translation of ablating location with the influence by granular pressure,and as the variation of machining efficiency with the influence by near-wall particle velocity. Thus via control of the inlet velocity and its corresponding machining time,it is supposed to work out the machining process according to the machining requirements by using the Preston equation to seek the relationship among velocity,pressure and material removing rate. By tracking near-wall particles,it can be confirmed that the movement of near-wall abrasive particles is similar to stream-wise vortices. The cutting traces on workpiece surfaces assume disorderly arrangement,so the feasibility of the SAFM method can be reaffirmed.JI ShiMing1,2, XIAO FengQing1,2 & TAN DaPeng1,2 1Key Laboratory of Special Purpose Equipment and Advanced Manufacturing Technology, (Zhejiang University of Technology), Ministry of Education, Hangzhou 310014, China 2Key Laboratory of Special Purpose Equipment and Advanced Manufacturing Technology of Zhejiang Province, Hangzhou 310014, China 2010Science China(Technological Sciences)2010,53,10:28
15Constructal entransy dissipation rate and flow-resistance minimizations for cooling channels显示文摘Based on constructal theory,a construct of a volume that generates heat at every point and is cooled by the coolant in the constant or tapered channel is optimized by minimizing entransy dissipation rate and flow resistance.The optimal constructs of the rectangular elements with dimensionless mean thermal resistance minimization as well as the first-,secondand thirdorder assemblies with dimensionless global flow resistance minimizations are obtained respectively.The results show that both the mean temperature difference and the limiting temperature difference of rectangular elements based on EDR (entransy dissipation rate) and MTD (maximum temperature difference) minimizations respectively are almost equal.Comparing heat transfer performances from the two optimization procedures,the dimensionless global flow resistance is decreased more for the former procedure when the assembly’s order is high.It may create great superiority for constructal optimization to combine the entransy dissipation extreme principle with heat convection.XIAO QingHua,CHEN LinGen & SUN FengRui Postgraduate School,Naval University of Engineering,Wuhan 430033,China 2010Science China(Technological Sciences)2010,53,9:27
16冰川泥石流形成机理研究进展显示文摘由于冰川泥石流的广泛分布及其发育地的特殊性使得对其开展全面治理较为困难,因此,有效开展冰川泥石流的预警预报具有重要意义。虽然近年来对冰川泥石流的研究有了较多的成果,但目前对其形成机理的认识还存在很大的局限,在很大程度上制约了防灾减灾的进展。为深入探讨冰川泥石流的形成机理,文章回顾了国内外学者在相关领域的研究成果,系统总结了现有冰川泥石流形成机理的研究现状,并对冰川泥石流形成机理的未来研究方向做了展望。铁永波 李宗亮 2010水科学进展2010,21,6:28
17The relationship between Th1/Th2-type cells and disease activity in patients with systemic lupus erythematosus显示文摘Obejctive To investigate the imbalance of Th1/Th2 type cytokines in patients with systemic lupus erythematosus (SLE) and its relation to disease activity Methods Intracellular cytokines were determined by flow cytometry following whole blood culture Results Patients with systemic lupus erythematosus disease activity index (SLEDAI) >10 had statistically significantly fewer CD4 + or CD8 + T cells producing IFN γ than patients with SLEDAI =0, SLEDAI 1-10 or healthy controls ( P <0 01, P <0 01 or P <0 05, respectively) Patients with SLEDAI>10 also had decreased ratio of IFN γ/IL 4 positive CD4 + or CD8 + T cells, compared with patients with SLEDAI =0, SLEDAI 1-10 or healthy controls ( P <0 05) The decreased Th1 or Tc1 cells and the ratios of IFN γ: IL 4 positive CD4 + T cells were significantly correlated with disease activity ( P <0 05) Conclusion SLE is characterized by an imbalance of Th1/Th2 and Tc1/Tc2 cytokines The decreased Th1 or Tc1 cells and the Th1/Th2 ratio are related to disease陈顺乐 胡大伟 石学耕 沈南 顾越英 鲍春 2000Chinese Medical Journal2000,,10:26
18The structure of turbulent flow through submerged flexible vegetation显示文摘The hydrodynamics of turbulent flow through submerged flexible vegetation is investigated in a flume using acoustic Doppler velocimetery(ADV)measurements.The flow characteristics such as the energetics and momentum transfer derived from convcntional spectral and quadrant analyses are considered as the flow encounters a finite vegetation patch.Consistent with numerous canopy flow experiments,a shear layer and coherent vortex structures near the canopy top emerge caused by Kelvin-Helmholtz instabilities after the flow equilibrates with the vegetated layer.These in stabilities are commonly attributed to velocity differences between non-vegetated and vegetated canopy layers in agreement with numerous experiments and simulations conducted on dense rigid canopies.The power-spectral density function for vertical velocity turbulent fluctuations at different downstream positions starting from the edge of the vegetation layer are also computed.For a preset water depth,the dominant dimensionless frequency is found to be surprisingly invariant around 0.027 despite large differences in vegetation densities.The ejection and sweep events significantly contribute to the Reynolds stresses near the top of the vegetation.The momentum flux carried by ejections is larger than its counterpart carried by the sweeps above the canopy top.However,the momentum flux carried by sweeps is larger below the top of the canopy.Wen-xin Huai Jiao Zhang Gabriel G.Katul Yong-guang Cheng Xue Tang Wei-jie Wang 2019Journal of Hydrodynamics2019,31,2:26
19Design concept of three-dimensional section controllable internal waverider hypersonic inlet显示文摘A new hypersonic inlet named three-dimensional section controllable internal waverider inlet is presented in this paper to achieve the goal of section shape geometric transition and complete capture of the upstream mass. On the basis of the association between hypersonic waverider airframe and streamtraced hypersonic inlet, the waverider concept is extended to yield results for the internal flows, namely internal waverider concept. It is proven theoretically that not osculating cones but osculating axisymmetric theory is appropriate for the design of section controllable internal waverider inlet. And two design methods out of the internal waverider concept are proposed subsequently to construct two inlets with specific section shape request, triangle to ellipse and rectangle to ellipse ones. The calculation results show that the inlets are capable of keeping their shock structures and the main flow characteristics exactly as their derived flowfield. Further, the inlets successfully capture all the upstream mass despite their complicated cross-section transitions. It is believed that the concept proposed ex- plores a new way of designing three-dimensional hypersonic inlets with special demand of section shape transition. However, the detailed flow characteristic and the performance of the internal waverider inlets are still under investigation.YOU YanCheng LIANG DeWang 2009Science China(Technological Sciences)2009,52,7:24
20S-wave crustal and upper mantle's velocity structure in the eastern Tibetan Plateau——Deep environment of lower crustal flow显示文摘A teleseismic profile consisting of 26 stations was deployed along 30°N latitude in the eastern Tibetan Plateau. By use of the inversion of P-wave receiver function, the S-wave velocity structures at depth from surface to 80 km beneath the profile have been determined. The inversion results reveal that there is significant lateral variation of the crustal structure between the tectonic blocks on the profile. From Linzhi north of the eastern Himalayan Syntaxis, the crust is gradually thickened in NE direction; the crustal thickness reaches to the maximum value (~72 km) at the Bangong-Nujiang suture, and then decreased to 65 km in the Qiangtang block, to 57―64 km in the Bayan Har block, and to 40―45 km in the Sichuan Basin. The eastern segment of the teleseismic profile (to the east of Batang) coincides geographically with the Zhubalong-Zizhong deep seismic sounding profile carried out in 2000, and the S-wave velocity structure determined from receiver functions is consistent with the P-wave velocity structure obtained by deep seismic sounding in respect of the depths of Moho and major crustal interfaces. In the Qiangtang and the Bayan Har blocks, the lower velocity layer is widespread in the lower crust (at depth of 30―60 km) along the profile, while there is a normal velocity distribution in lower crust in the Sichuan Basin. On an average, the crustal velocity ratio (Poisson ratio) in tectonic blocks on the profile is 1.73 (σ = 0.247) in the Lhasa block, 1.78 (σ = 0.269) in the Banggong-Nujiang suture, 1.80 (σ = 0.275) in the Qiangtang block, 1.86 (σ = 0.294) in the Bayan Har blocks, and 1.77 (σ = 0.265) in the Yangtze block, respectively. The Qiangtang and the Bayan Har blocks are characterized by lower S-wave velocity anomaly in lower crust, complicated Moho transition, and higher crustal Poisson ratio, indicating that there is a hot and weak medium in lower crust. These are considered as the deep environment of lower crustal flow in the eastern Tibetan Plateau. Flowage of the ductile material in lower crust may be attributable to the variation of the gravitational potential energy in upper crust from higher on the plateau to lower off plateau.Paul SILVER 2008Science China Earth Sciences2008,51,2:24
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