where d is a characteristic length of the pores or dispersed phases, ℓ a characteristic length of the averaging volume, and L is a characteristic length of the physical system.Solutions of local volume-averaged conservation equations call for expressing these local volume-averaged products in terms of products of averages. In nonturbulent flows, this can be achieved by expressing the “point” variable as the sum of its intrinsic volume average and a spatial deviation. In turbulent flows, the same can be achieved via subsequent time averaging over a duration T such that
τHFTτLF,
where τHF is a characteristic time of high-frequency fluctuation and τLF is a characteristic time of low-frequency fluctuation. In this case, and instantaneous “point” variable ψk of phase k is decomposed into a low-frequency component ψkLF and a high-frequency component ψk, similar to Reynolds analysis of turbulent flow. The low-frequency component consists of the sum of the local intrinsic volume average 3iψkLF and its local spatial deviation . Time averaging then reduces the volume-averaged products to products of averages plus terms representing eddy and dispersive diffusivities of mass, Reynolds and dispersive stresses, and eddy and dispersive conductivities of heat, etc. These terms arise from both high-frequency fluctuations and local spatial deviations. This procedure of time averaging after local volume averaging leads to a set of differential–integral equations of conservation for multiphase flow. This set of multiphase flow conservation equations is particularly suitable for numerical analysis with staggered grid computational systems.Attention is focused on multiphase flow in a region containing fixed and dispersed heat-generating and absorbing solid structures. The novel porous media formulation employs the concept of volume porosity, directional surface porosities, distributed resistance and distributed heat source and sink which is derived through local volume averaging of conservation of mass, momentum and energy equations. The directional surface porosities are defined as a fraction of free flow surface area to control surface area in three principal directions which are readily calculable quantities. The conventional porous media formulation employs the concept of volume porosity, distributed resistance and distributed heat source and sink. Most of engineering problems involve many complex shapes and sizes of structures which are impossible to quantify their distributed resistance accurately. The concept of directional surface porosities reduced the reliance of empirical estimate of distributed resistance and improved the resolution and modeling accuracy. The novel porous media formulation represents a significant advance for solving real engineering problems.  相似文献   
4.
Krylov precise time‐step integration method     
T. C. Fung  Z. L. Chen 《International journal for numerical methods in engineering》2006,68(11):1115-1136
An efficient precise time‐step integration (PTI) algorithm to solve large‐scale transient problems is presented in this paper. The Krylov subspace method and the Padé approximations are applied to modify the original PTI algorithm in order to improve the computational efficiency. Both the stability and accuracy characteristics of the resultant algorithms are investigated. The efficiency can be further improved by expanding the dimension to avoid the computation of the particular solutions. The present algorithm can also be extended to tackle nonlinear problems without difficulty. Two numerical examples are given to illustrate the highly accurate and efficient algorithm. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
5.
PSS/E--一种先进的电力系统分析仿真软件   总被引:6,自引:2,他引:4  
江全元  彭旭东  张宝星 《高电压技术》2005,31(1):60-62,76
介绍了PSS/E-29的基本功能及高级功能,与国内BPA程序比较,2种软件的原始数据均基于文本格式 的填卡式输入,但前者基于自由书写格式,原始数据输入工作量大为减轻,且其动态模型库更为全面,更适应电力 系统新技术的发展。仿真一算例系统的结果表明它提供的模型可靠,结果可信。  相似文献   
6.
固体绝缘材料耐电痕化指数的测试方法及要点     
孙小妹  何飞 《电子质量》2014,(2):55-57
固体绝缘材料的电痕化指数是判定材料好坏的一项重要指标,但材料的电痕化指数判定过程中涉及的环节和要求点很多,每个环节都会对材料电痕化指数的确定产生影响。故该文旨在指出电痕化指数测试过程中的若干细节,以期对今后的测试能有一定帮助。  相似文献   
7.
淮钢70 t电弧炉PTI JetBOx系统的应用   总被引:1,自引:0,他引:1  
刘阳春  王栋 《特殊钢》2003,24(3):50-51
淮钢70t电弧炉安装3套阿JetBOx集束射流氧枪系统后,冶炼周期降低3—5min,电耗降低25—40kWh/t,电极消耗降低0.4kg/t。  相似文献   
8.
基于单片机的真空冷冻干燥试验仪温度控制器设计     
陈大林  任祖平 《可编程控制器与工厂自动化(PLC FA)》2007,(11):79-81,62
介绍了一种真空冷冻干燥试验仪的温度控制器设计,以AT89C52为控制核心,选用PT100传感器,MC14433A/D,利用增量式PID算法来完成对电机执行机构的运动控制,从而实现温度的精确控制。  相似文献   
9.
数字机顶盒可编程传输接口方案分析     
张嵘  舒展  郭跃  王宏远 《计算机与数字工程》2007,35(3):73-74
介绍一种数字机顶盒系统中可编程传输接口的方案。可编程传输接口是从输入的传输流中获取特定数据的处理模块,并将获取的数据传输给对应的应用模块。  相似文献   
10.
PTI Jetbox系统在70 t电炉上的应用     
韩建淮  王栋  王忠英  张跃萍 《工业加热》2003,32(6):34-36
简要阐述了Jetbox集束射氧喷箱技术的原理,介绍了淮钢70t电炉安装Jetbox系统的情况以及使用效果。  相似文献   
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1.
Plants rely on multiple immune systems to protect themselves from pathogens. When pattern-triggered immunity (PTI)—the first layer of the immune response—is no longer effective as a result of pathogenic effectors, effector-triggered immunity (ETI) often provides resistance. In ETI, host plants directly or indirectly perceive pathogen effectors via resistance proteins and launch a more robust and rapid defense response. Resistance proteins are typically found in the form of nucleotide-binding and leucine-rich-repeat-containing receptors (NLRs). Upon effector recognition, an NLR undergoes structural change and associates with other NLRs. The dimerization or oligomerization of NLRs signals to downstream components, activates “helper” NLRs, and culminates in the ETI response. Originally, PTI was thought to contribute little to ETI. However, most recent studies revealed crosstalk and cooperation between ETI and PTI. Here, we summarize recent advancements in our understanding of the ETI response and its components, as well as how these components cooperate in the innate immune signaling pathways. Based on up-to-date accumulated knowledge, this review provides our current perspective of potential engineering strategies for crop protection.  相似文献   
2.
Puccinia striiformis f. sp. tritici (Pst) is an important pathogen of wheat (Triticum aestivum L.) stripe rust, and the effector protein secreted by haustoria is a very important component involved in the pathogenic process. Although the candidate effector proteins secreted by Pst haustoria have been predicted to be abundant, few have been functionally validated. Our study confirmed that chitin and flg22 could be used as elicitors of the pathogenic-associated molecular pattern-triggered immune (PTI) reaction in wheat leaves and that TaPr-1-14 could be used as a marker gene to detect the PTI reaction. In addition, the experimental results were consistent in wheat protoplasts. A rapid and efficient method for screening and identifying the effector proteins of Pst was established by using the wheat protoplast transient expression system. Thirty-nine Pst haustorial effector genes were successfully cloned and screened for expression in the protoplast. We identified three haustorial effector proteins, PSEC2, PSEC17, and PSEC45, that may inhibit the response of wheat to PTI. These proteins are localized in the somatic cytoplasm and nucleus of wheat protoplasts and are highly expressed during the infection and parasitism of wheat.  相似文献   
3.
Multiphase flows consist of interacting phases that are dispersed randomly in space and in time. An additional complication arises from the fact that the flow region of interest often contains irregularly shaped structures. While, in principle, the intraphase conservation equations for mass, momentum, and energy, and their initial and boundary conditions can be written, the cost of detailed fluid flow and heat transfer analysis with explicit treatment of these internal structures with complex geometry and irregular shape often is prohibitive, if not impossible. In most engineering applications, all that is required is to capture the essential features of the system and to express the flow and temperature field in terms of local volume-averaged quantities while sacrificing some of the details. The present study is an attempt to achieve this goal by applying time averaging after local volume averaging.Local volume averaging of conservation equations of mass, momentum, and energy for a multiphase system yields equations in terms of local volume-averaged products of density, velocity, energy, stresses, and field forces, together with interface transfer integrals. These averaging relations are subject to the following length scale restrictions:
dL,
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