共查询到20条相似文献，搜索用时 31 毫秒
1.
The quantum relaxation time of electrons in condensed matters is an important physical property, but its direct measurement has been elusive for a century. Here, we report a breakthrough that allows direct determination of quantum relaxation time at zero and non-zero frequencies using optical measurement. Through dielectric loss function, we connect bound electron effects to the physical parameters of plasma resonance and find an extra term of quantum relaxation time from inelastic scattering between bound electrons and conduction electrons at non-zero frequencies. We demonstrate here that the frequency-dependent inelastic polarization effect of bound electrons is the dominant contribution to quantum relaxation time of conduction electrons at optical frequencies, and the elastic polarization effect of bound electrons also dramatically changes the plasma resonance frequency through effective screening to charge carriers. 相似文献
2.
微型钢管外表面温度场可视化实验研究 总被引：1，自引：0，他引：1
为了准确测量微管外表面温度场的分布，并解决沿微管轴向导热对微管内部对流换热的影响，本文首次把非接触式测量温度方法引入到微尺度实验中。本次研究搭建了能够进行气体、液体流动与换热的微流动实验台，用蒸馏水作为工质，采用红外成像仪加专用红外放大镜头对微型钢管表面温度场作了可视化实验研究，得到了在Re数不变时，不同加热功率下内直径为168µm和外直径为406µm微型钢管外表面温度场的分布图，进而能得到了沿轴向温度对沿轴向长度的二次导数。建立简化的数学模型，并通过推导获得了沿轴向的导热对内部对流换热的关系式。实验与理论推导结果表明，在微圆管单相流情况下，其轴向的导热对管内对流换热影响很小，可以忽略不计。 相似文献
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收集了鸦片战争以前中国古代600多项科技成果,力图以定量的方法说明在中国古代这一特定的历史时期,科技始终以高低相间波浪向前的态势在发展,流行的中国古代科技自某一时期达到高峰后就衰落下去的观点是没有根据的。 相似文献
4.
文章研发了一种矿石破碎系统,包括送料机构和破碎机,其特点在送料机构和破碎机之间设计一个淌筛,其优点是对进入破碎机前的矿石进行筛选,对不需要进行破碎的矿石粉末或符合输送检测要求的矿石颗粒直接输送至下一工序,这样不仅可以有效解决破碎机在工作过程的堵塞问题,延长破碎机的使用寿命,而且大大提高了工作效率。 相似文献
5.
《Journal of The Franklin Institute》2001,338(2-3):335-351
This paper describes a set of delay-dependent IQCs for time-delay uncertainty. The set is linearly parameterized in terms of the frequency response of a complex scalar-valued multiplier. Using LMI optimization techniques, one may compute optimal multipliers and thereby obtain less conservative IQC stability robustness bounds for systems with uncertain time delays. 相似文献
6.
Stephen B. Margolis 《Journal of The Franklin Institute》1979,307(1):39-58
A multidimensional, time-dependent model of the thermocline degradation in a packed bed thermal storage tank is presented. The formulation includes the effects of finite tank length, multidimensional thermal conduction, heat transfer between the fluid and solid portions of the bed, and heat losses across all tank surfaces. The technique used to solve the coupled pair of parabolic partial differential equations describing the degradation of the thermocline is based on a vectorized separation of variables approach. Assuming cylindrical geometry, the analysis leads to separate eigenvalue problems for the radial, angular, and axial spatial dependencies of the fluid and solid temperatures in the bed. The eigenvalues are readily calculated and the corresponding eigenfunctions are shown to form a complete set of spatial basis functions for the solution space. The method and results are illustrated by several examples. 相似文献
7.
面向零时间企业的即时激励机制研究 总被引：2，自引：0，他引：2
本文探讨了零时间企业如何建立有效的即时激励机制这一富有实践意义的问题。论文首先在简要阐释零时间企业的内涵的基础之上,剖析了零时间企业激励的特点与原则;然后,阐述了即时激励的重要作用;最后,提出了即时激励的基本内容和“三位一体”的实现机制。 相似文献
8.
《Journal of The Franklin Institute》2021,358(15):7309-7332
The current paper addresses the fuzzy adaptive tracking control via output feedback for single-input single-output (SISO) nonlinear systems in strict-feedback form. Under the situation of system states being unavailable, the system output is used to set up the state observer to estimate the real system states. Furthermore, the estimation states are employed to design controller. During the control design process, fuzzy logic systems (FLSs) are used to model the unknown nonlinearities. A novel observer-based finite-time tracking control scheme is proposed via fuzzy adaptive backstepping and barrier Lyapunov function approach. The suggested fuzzy adaptive output feedback controller can force the output tracking error to meet the pre-specified accuracy in a fixed time. Meanwhile, all the closed-loop variables are bounded. Compared to some existing finite-time output feedback control schemes, the developed control strategy guarantees that the settling time and the error accuracy are independent of the uncertainties and can be specified by the designer. At last, the effectiveness and feasibility of the proposed control scheme are demonstrated by two simulation examples. 相似文献
9.
The CAS Dalian Institute of Chemical Physics(DICP)and BP Group will join efforts to set up an Energy Innovation Laboratory(BP- DICP EIL)at DICP.The agreement for the new initiative was signed by DICP Director ZHANG Tao and BP Group Vice President Tony Meggs on 5 December,2007 in Dalian. According to the agreement, BP will donate $3 million to the new lab,which will be part of the forthcoming National Laboratory for Clean Energy Sources.In addition,the company promises to annually contribute no less than ... 相似文献
10.
提高一堂课的教学效率,老师要做到精讲,哪些讲或不讲．这节课讲还是一定时候讲,源于对学生了解和对教材的把握。针对学生个体差异,有的反应快但欠准确,有的学生反应慢但很准确……设定目标层次教学。此外,课堂教学准备是非常重要的。 相似文献
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12.
中国科学奖励制度设立50余年来,国家自然科学奖先后颁发了17次,奖金数额也经历4次调整。但相对于城镇居民可支配收入的提高,实际奖励强度在整体上呈现明显的下降趋势,同时,奖金的财政负担也呈下降的趋势。鉴于基础研究具有重要的战略意义,考虑到当前的综合国力,中国有必要也有能力大幅度提高国家自然科学奖的奖励强度,以充分发挥科学奖励制度应有的激励作用。 相似文献
13.
在20世纪50年代,弗兰克率先在科学哲学界提出了类似于后来出现的"历史主义"的一些观点.虽然属于逻辑实证主义阵营,但他的视野不像一般的逻辑实证主义者那样狭窄,只注重对科学进行逻辑分析,而是在进行逻辑分析的同时,也重视对科学的社会背景和历史发展的考察.早在维也纳时期,弗兰克就已经开始从较为广阔的视野来研究科学哲学问题,后期的工作则更加接近历史主义学派.因此,可以认为,弗兰克在科学与哲学之间初步架起了桥梁. 相似文献
14.
Using the algebraic state space representation (ASSR) method, this paper investigates the set stability and synchronization of Boolean networks with probabilistic time delays (PTDs). Firstly, an equivalent stochastic system is established for the Boolean network with PTDs by using the ASSR method. Secondly, based on the probabilistic state transition matrix of equivalent stochastic system, a necessary and sufficient condition is proposed for the set stability of Boolean networks with PTDs. Thirdly, as an application of set stability, the synchronization of coupled Boolean networks with PTDs is studied, and a necessary and sufficient condition is presented. Finally, an illustrative example is given to demonstrate the effectiveness of the obtained new results. 相似文献
15.
Information filtering (IF) systems usually filter data items by correlating a set of terms representing the user’s interest (a user profile) with similar sets of terms representing the data items. Many techniques can be employed for constructing user profiles automatically, but they usually yield large sets of term. Various dimensionality-reduction techniques can be applied in order to reduce the number of terms in a user profile. We describe a new terms selection technique including a dimensionality-reduction mechanism which is based on the analysis of a trained artificial neural network (ANN) model. Its novel feature is the identification of an optimal set of terms that can classify correctly data items that are relevant to a user. The proposed technique was compared with the classical Rocchio algorithm. We found that when using all the distinct terms in the training set to train an ANN, the Rocchio algorithm outperforms the ANN based filtering system, but after applying the new dimensionality-reduction technique, leaving only an optimal set of terms, the improved ANN technique outperformed both the original ANN and the Rocchio algorithm. 相似文献
16.
Jianjun Bai Hongye Su Jinfeng Gao Tao Sun Zhengguang Wu 《Journal of The Franklin Institute》2012,349(7):2420-2430
The problem of modeling and stabilization of a wireless network control system (NCS) is considered in this paper, where packet loss and time delay exist simultaneously in the wireless network. A discrete-time switched system with time-varying delay model is first proposed to describe the system closed by a static state feedback controller. A sufficient criteria for the discrete-time switched system with time-varying delay to be stable is proposed, based on which, the corresponding state feedback controller is obtained by solving a set of linear matrix inequalities (LMIs). Numerical examples show the effectiveness of the proposed method. 相似文献
17.
现代经济增长：一个制度作为内生变量的模型 总被引：12，自引：0，他引：12
在以往经济增长模型中，经济学家主要是从资本、劳动力和技术三方面去研究的。随着经济研究的深入，人们越来越认识到仅有这三大要素是不够的。新制度经济学以强有力的证据向人们表明，制度对于经济增长起着重要的作用。本文将在以往对资本、劳动力和技术研究的基础上，从宏观角度出发，运用新制度经济学的研究方法，引入制度并将其作为经济增长的内生变量，力求全面反映经济增长，并揭示制度创新与长期经济稳定增长的关系。 相似文献
18.
针对重庆农村水利建设成本高、水利规划滞后等问题，建立并分析确定最优水利规模的基本模型，提出了总成本最小化的前提下扩建水利的具体工作思路。研究表明，水利建设的最优规模为一定水利需求下总成本最小的规模；水利建设要在推进水利工程产权、经营权制度改革的同时，还要加强水利部门的自身建设。 相似文献
19.
This paper addresses the problem of giving consistency conditions for constrained linear discrete time systems in state space form. Conditions for various significant cases are given and analysed. Finally, the structure of the set of initial states for which consistency prevails and the set of reachable states are studied. 相似文献
20.
This paper mainly considers the consensus for first-order discrete-time multi-agent systems w.r.t. two key parameters, the step size T and the delay τ. First, the consensus is recast into the concurrent stability for a series of trinomials. Then, for each associated trinomial, we derive a necessary and sufficient stability condition, based on proving the two invariance properties for the asymptotic behavior of the critical unitary roots. As a result, the exhaustive consensus region in the parameter space (i.e., the parameter set such that the multi-agent system reaches a consensus iff T and τ belong to that set) is determined. Furthermore, we show that the obtained result also applies to systems with diverse input delays, through an extra sufficient consensus condition. Finally, two illustrative examples are presented. 相似文献