CTR的导电机理研究

为了优化CTR(Critical Temperature Resister)产品性能,从微观上分析CTR晶粒体相变临界特征和粒界的电势垒,得出CTR临界阻温特性是由晶粒体导电性能和粒界电势垒共同决定,即"晶粒体-粒界"模型.运用此模型对不同配料比样品的临界阻温特性进行分析,得出V2O5:P2Os:Fe2O3配料比是影响CTR性能的关键因素.     

Fast response of undoped and Li-doped titania thick-films at low temperature

The fast response of undoped and Li-doped TiO₂ operating at low temperature to hydrogen and oxygen is investigated. The TiO₂ sensors are fabricated using thick-film technique. The prepared materials exhibit the presence of only rutile phase of TiO₂ but enlarged crystal lattice parameters were confirmed by X-ray diffraction (XRD). Scanning electron microscopy (SEM) shows that the grain size of the material has not obviously changed with different Li-doping (2–4 mol%), but the undoped is much smaller. Kroger–Vink model indicates that Li mainly substitutes for the lattice point of Ti. Because the material resistance decreases as the oxygen pressure increases, Li-doped samples can be regarded as a p-type semiconductor compared with pure TiO₂. The operating temperature of the Li-doped TiO₂ samples is found to be lower than that of pure TiO₂ in H₂ and O₂ environment. At less than 3 mol% Li content, the response time of the Li-doped TiO₂ gas sensors is much shorter than that of pure TiO_2, at the same temperature under both H₂ and O₂ environment. Moreover, the sample of 3 mol% Li-doping exhibits the best response characteristics. The response mechanism is suggested to arise from the conduction holes ionized by Li and the surface potential barrier change in different gas environments.     

亚硝酰氢与羟基自由基反应的密度泛函理论研究

用密度泛函理论研究了HNO OH反应机理。在(U)B3LYP/aug-cc-pVTZ水平上,优化了反应通道上各驻点(反应物、中间体、过渡态和产物)的几何构型,获得了零点能校正后的反应势能曲线。研究表明:根据进攻方式的不同,有3个反应通道,反应通道不同则产物不同。反应的主要产物是NO H_2O,次要产物是NH_2 O_2;主要产物和次要产物与反应物的总能量之差(经零点能校正后)分别为-133.42 kJ/mol和150.44 kJ/mol。生成主要产物时主要反应通道的活化能为102.11 kJ/mol。     

Ag掺杂的SnO_2酒敏薄膜敏感特性研究

采用非醇盐溶胶—凝胶工艺在A l2O3基片上旋转涂敷制得掺Ag的SnO2薄膜。原子力显微镜和扫描电子显微镜分析显示:薄膜晶粒呈球形,600℃热处理粒径为20 nm左右。热处理温度升高,晶粒尺寸增大。气敏性能采用静态法测试,掺Ag薄膜对体积分数为50×10-6乙醇和汽油气体的灵敏度分别为32.7和4.9,与未掺Ag薄膜的14.4和7.2相比较,提高了乙醇气体灵敏度,抑制了汽油气体灵敏度,使选择性得到改善。直流加热条件下,试样电阻和电容在老化初期变化较大,数天后趋于稳定,复阻抗分析表明:长期稳定性与晶粒间界处电阻和电容值的变化有关,来源于晶界势垒高度和势垒宽度的变化,其本质可能是直流偏压作用下晶界层中的离子迁移。     

Collaborative knowledge building using the Design Principles Database

In this study we describe a mechanism for supporting a community of learning scientists who are exploring educational technologies by helping them to share and collaboratively build design knowledge. The Design Principles Database (DPD) is intended to be built and used by this community to provide an infrastructure for participants to publish, connect, discuss and review design ideas, and to use these ideas to create new designs. The potential of the DPD to serve as a collaborative knowledge-building endeavor is illustrated by analysis of a CSCL study focused on peer-evaluation. The analysis demonstrates how the DPD was used by the researchers of the peer-evaluation study in three phases. In the first phase, design principles were articulated based on a literature review and contributed to the DPD. In the second phase, a peer-evaluation activity was designed based on these principles, and was enacted and revised in a three-iteration study. In the third phase, lessons learned through these iterations were fed back to the DPD. The analysis indicates that such processes can contribute to collaborative development of design knowledge in a community of the learning sciences. Readers of ijCSCL are invited to take part in this endeavor and share their design knowledge with the community.     

A change‐point perspective on the software failure process

In the software reliability growth phase, the nature of the failure data is, in a sense, determined by the software testing process. There are many factors that affect software testing. These factors are unlikely to all be kept stable during the entire process of software testing, with the result that the underlying statistics of the failure process is likely to experience major changes. In this case, it is appropriate to use the change‐point method in the reliability analysis. This paper considers a change‐point model and proposes a change‐point estimator for reliability analysis. Experimentally, the change‐point method is applied to a real dataset, which verifies the validity of the model. A Monte Carlo simulation study on the asymptotic properties of the estimator indicates that the model is consistent. Copyright © 2003 John Wiley & Sons, Ltd.     

Synchronization in relaxation oscillator networks with conduction delays

We study locally coupled networks of relaxation oscillators with excitatory connections and conduction delays and propose a mechanism for achieving zero phase-lag synchrony. Our mechanism is based on the observation that different rates of motion along different nullclines of the system can lead to synchrony in the presence of conduction delays. We analyze the system of two coupled oscillators and derive phase compression rates. This analysis indicates how to choose nullclines for individual relaxation oscillators in order to induce rapid synchrony. The numerical simulations demonstrate that our analytical results extend to locally coupled networks with conduction delays and that these networks can attain rapid synchrony with appropriately chosen nullclines and initial conditions. The robustness of the proposed mechanism is verified with respect to different nullclines, variations in parameter values, and initial conditions.     

Information transfer between rhythmically coupled networks: reading the hippocampal phase code.

There are numerous reports on rhythmic coupling between separate brain networks. It has been proposed that this rhythmic coupling indicates exchange of information. So far, few computational models have been proposed that explore this principle and its potential computational benefits. Recent results on hippocampal place cells of the rat provide new insight; it has been shown that information about space is encoded by the firing of place cells with respect to the phase of the ongoing theta rhythm. This principle is termed phase coding and suggests that upcoming locations (predicted by the hippocampus) are encoded by cells firing late in the theta cycle, whereas current location is encoded by early firing in the theta cycle. A network reading the hippocampal output must inevitably also receive an oscillatory theta input in order to decipher the phase-coded firing patterns. In this article, I propose a simple physiologically plausible mechanism implemented as an oscillatory network that can decode the hippocampal output. By changing only the phase of the theta input to the decoder, qualitatively different information is transferred: the theta phase determines whether representations of current or upcoming locations are read by the decoder. The proposed mechanism provides a computational principle for information transfer between oscillatory networks and might generalize to brain networks beyond the hippocampal region.     

基于COMSOL的接地网阴极保护仿真分析

针对土壤中施加电流的扁钢,研究电导率的改变对其表面电位、电流密度的影响.借助COMSOL软件腐蚀模块,建立扁钢的阴极保护模型,改变土壤电导率的大小,模拟扁钢的阴极保护情况,得到了扁钢表面电位、电流密度分布曲线.仿真结果表明,其他条件不变,仅增加土壤中的电导率,土壤中电解质电流密度也随之逐渐增大,扁钢的表面电位降低,说明...     

Reconfigurability and unified kinematics modeling of a 3rTPS metamorphic parallel mechanism with perpendicular constraint screws

This paper investigates reconfigurability and unified analytical kinematics analysis of a new 3rTPS metamorphic parallel mechanism consisting of three reconfigurable rTPS limbs in perpendicular base planes. Constraint screw systems show that in one phase the rTPS limb has no constraint to the platform and in the other phase obtained by altering the reconfigurable Hooke joint, it provides a constraint force. The two phases of the limb qualify the 3rTPS metamorphic parallel mechanism to have four topologies with ability of mobility change among 3R (three rotations), 3R1T (three rotations one translation), 3R2T and mobility 6. By considering the difference of the two phases of the limb, a unified kinematics modeling is proposed based on the actuation scheme analysis by taking one phase as a special case of the other. Following this, a unified kinematics modeling of the 3rTPS metamorphic parallel mechanism is obtained by covering all its four topologies. Both inverse and forward kinematics analysis are solved analytically and numerical examples confirm these theoretical results.     

立方晶系多晶体细观应力有限元分析

为研究多晶体宏细观力学响应,针对立方晶系单晶体提出形式与Hill屈服准则相关联的形状改变比能;以此为屈服考察量,建立适用于立方晶系的单参数Hill屈服准则;用MSCMare对立方晶系多晶体进行细观应力有限元分析．d—Fe多晶体样本单向拉伸有限元分析表明：多晶体的拉伸应力在细观尺度下分布不再均匀;多晶体3个样本的最大细观拉伸应力与最小细观拉伸应力的比值,在弹性状态下的平均值为2．1,在塑性强化阶段处于1．15～1．28之间．     

Studies in the modelling and control of a national economy

A survey of some elementary macroeconomic models is presented which indicates the potential that exists for the application of control theory in economics. An initial linear model is developed systematically to embrace an increasing degree of economic sophistication leading to a non-linear formulation, the need for which is soon made apparent. Examples are given to demonstrate the use of characteristic root analysis, of the root locus technique to examine parameter sensitivity and of phase plane and stability concepts. At the same time, important economic interpretations which can be drawn from the results are indicated.     

热泵相变储热器动态特性分析及强化传热研究

热泵相变储热器传输过程具有动态性,提出基于四阶动态响应特性分析的热泵相变储热器动态特性分析及强化传热模型。构建热泵相变储热器的欠阻尼振荡输出特征分析模型,以系统功率突变为控制状态约束对象进行热泵相变储热器动态驱动响应模拟,采用二项单调衰减分量、二项欠阻尼振荡分量作为控制约束变量进行热泵相变储热器动态强化传输控制,建立热泵相变储热器的输出功率调制模型,结合热泵相变储热器动态状态量初始值及变化值进行强化传热过程控制,提高热泵相变储热器的输出性能。仿真结果表明,采用该模型进行热泵相变储热器的输出动态控制能力较好,强化传输的输出增益较高,提高了热泵相变储热器的输出响应能力。     

(E)-N-(4-氨基正丁基)-3-(3-羟基-4-甲氧基-苯基)丙烯酰胺顺反构象异构化的理论研究

在HF/6-31G(d)水平上寻找(E)-N-(4-氨基正丁基)-3-(3-羟基-4-甲氧基-苯基)丙烯酰胺的顺反构象异构化的过渡态,计算得到了顺反异构化的势垒,揭示其在常温下反式和顺式异构体可迅速转化,但顺式异构体占绝大部分。在B3LYP/6-311 G(2d,p)水平上用GIAO方法计算两种异构体的~1H和~(13)C NMR的化学位移,通过对理论计算值与实验值的统计分析,显示顺式构象的计算值与实验值较为接近,实验结果证实了理论推断的正确性。     

耦合pre-B tzinger复合体神经元中混合簇放电的多时间尺度动力学分析

Pre-B tzinger复合体是新生哺乳动物呼吸节律起源的关键部位,是呼吸节律产生的中枢.本文以pre-B tzinger复合体中两个耦合的神经元为研究对象,并考虑钙离子动力学的耦合神经元模型.利用多时间尺度动力学、快慢尺度分解和分岔分析,研究混合簇同步放电模式及其产生机制,并研究了耦合神经元同相和反相簇放电类型及其同步转迁.结果表明钙离子的周期性波动对混合簇放电模式的产生有极大的影响,钙离子波动导致的时间尺度变化及分岔曲线相对位置的改变是混合簇放电产生的主要原因.本文的研究对认识pre-B tzinger中大规模网络的动力学有着重要的意义,为进一步探索呼吸节律的产生机制提供了一些有益的思考和见解.     

基于电力市场环境下的电网企业风险预警体系的管理创新与应用实践

随着电力体制改革的深入推进,未来发电、输配电、售电产业格局将发生根本改变,对电网企业的监管方式也将转变。电网企业必须以更低的成本、更高的效率和更优质的服务来提升企业竞争力,这样才能在改革的浪潮中站稳脚步。利用大数据挖掘技术探寻基础数据价值,打破专业壁垒,促进部门联动,促使各项指标可控、能控、在控,在异动发生前干预,将事后监测向事前预警有效转变,将为电网企业科学管理及决策提供有力支撑。通过利用大数据挖掘技术发掘各指标间潜在的关联关系,据此建立风险预警网络,一旦发现指标异动,其关联的其他指标自动提前预警,达到牵一发而动全身的效果。同时,建立横向协同机制,打破专业壁垒,各部门及时有效应对,最终实现提升公司运营效益和效率的目的。     

一种新型的分布式弱栅栏构建与移动算法

在传感器网络栅栏覆盖的研究中,针对如何减少移动节点带来的损耗,本论文提出了一种全新的分布式弱栅栏覆盖算法(Kuhn Select-box Distribute Exponential-smoothing,KSDE)。算法将弱栅栏覆盖中的栅栏模型化成若干个槽位相连接的方式,引入图论学中的库恩匹配(Kuhn.Munkras,KM)方法,完成槽位和节点集合之间的最小路径匹配,选出参与匹配的节点,进行弱栅栏的构建。为了进一步优化栅栏的闭合性,通过仿真调整分区的规模,找到最佳的分区方案。通过大量实验分析,KSDE可以在保证一定闭合性的前提下,大幅减少节点的平均移动距离。     

Electrical and photoelectrical characterizations of isotype GaAs15P85/GaP heterojunctions prepared by liquid phase epitaxy

The present work deals with the electrical and optoelectronic characterizations of the isotype GaAs₁₅P₈₅/GaP devices prepared by liquid phase epitaxy. The electrical properties of the fabricated junction were studied by analyzing its current–voltage (I–V) characteristics, capacitance–voltage (C–V) characteristics in the dark at different temperatures in the range of 300–450 K. The analysis of dark current–voltage (I–V) characteristics at different temperatures were presented in order to elucidate the conduction mechanism and to evaluate the important device parameters. The predominant charge transport mechanism in these devices was found to be thermionic emission in the depletion layer and over the barrier of GaAs₁₅P₈₅/GaP heterojunction at forward bias voltage. From the capacitance–voltage, measurements at high frequency (1 MHz) information can be obtained about the carrier concentration, the diffusion potential, the barrier height of GaAs₁₅P₈₅/GaP heterojunction. The current–voltage characteristics of the GaAs₁₅P₈₅/GaP heterojunction under different illumination intensities were studied. The power low dependence of the reverse current voltage is characterized by space charge limited conduction, SCLC dominated by exponential trap distribution at the higher reverse voltage region.     

微通道内两相流动的耗散粒子动力学模拟

使用了一种两相的耗散粒子动力学模型来模拟微通道内两相流动相变过程,采用改进了的Verlet速度算法,得到了微通道内流体的速度分布图.DPD粒子流动过程中,粒子出现团聚和稀化的现象,表明流体开始出现汽化.计算结果表明,耗散粒子动力学(DPD)方法可以用于对微通道里的相变过程进行模拟.     

About the gas sensitivity of metal–silicon contacts with the superthin nickel and titanium films to the ammonia environment

In the present paper, the processes occurring on the external interface of the superthin metal film at the adsorption of the ammonia molecule and the influence of these processes on the functionally important property of metal–silicon Schottky barrier structures were investigated. The simulation analysis by quantum-chemistry NDDO method was used. The quantum-chemical modeling results were compared with the results of experimental investigations of Schottky barrier structures with superthin nickel and titanium metal layers. The results show that the adsorption process leads to the change of the dielectrical permittivity of the Schottky barrier structures. This can be explained by taking into account the charges redistribution on the electronic bonds of the intermediate layer, which were formed by edge atoms of the Schottky barrier structures.