The theory of the electrical breakdown of gases at atmospheric pressures

After a brief summary and discussion of Townsend's theory of the electrical breakdown of gases in the light of certain recent criticisms, it is shown that these are compatible with his theory except for one serious discrepancy. This discrepancy lies in the fact that at the assumed fields at which breakdown occurs in air, at atmospheric pressure, and in inert gases at low pressures, the $\text{β}\text{P}$ of Townsend's theory cannot have the significance given it by Townsend, as the positive ions are incapable at these fields of acquiring the ionizing energy. Various solutions proposed are discussed and found inadequate. It seems necessary, in order to keep this otherwise successful theory, to doubt the validity of the assumption generally made for plane parallel electrodes, that the potential drop between the plates is uniform before the spark passes. If fields about ten times as great as those calculated from the uniform drop existed, the theory could be applied. It is shown that such fields are possible under the conditions of the spark potential experiments, due to space charges resulting from the difference of ionic and electronic velocities. The existence of such fields requires a finite spark lag interval of about 10^?4 seconds, as yet not definitely observed. Experiments should be undertaken in laboratories equipped for the purpose to look for both the spark lag and the non-uniform field.     

Behavior of dielectrics under alternating stress

The presence of maxima in the power factor-frequency and power factor-temperature curves of dielectrics has been explained by the Maxwell inhomogeneity theory and the Debye theory of polar molecular orientation. In order to ascertain the true cause of these maxima, a study has been made of the power factor of an essentially non-polar material with and without polar materials in dilute solution over extended ranges of frequency, 65 to 7.2 × 10⁶ c.p.s., and temperature, 2.9° C. to 90° C.The non-polar solvent is a mixture of paraffins having a pour point at 55° C. Small power factor maxima, 0.0003 in value, shifting over the audio frequency range with temperature variation, are observed for this solvent alone. Adding 3 per cent. phenol gives rise to molecular orientation maxima restricted largely to frequencies above 10⁷ c.p.s. At the lower temperatures, these maxima are greatly broadened, so that there is apparently a small contribution at power frequencies. Adding 10 per cent. stearic acid gives similar results. The failure of these maxima to shift to lower frequencies at the lower temperatures is due to the failure of the inner viscosity to increase very much in the solid state. The variation of the inner viscosity is calculated from the reciprocals of the short time conductivities since the degree of ionic dissociation is found to be essentially independent of temperature. The viscosity may be regarded as a function of particle size and varies within the medium. Where power factor maxima shift with essentially undiminished magnitude over a wide frequency range at ordinary temperatures, such as those observed here in the solvent above, it is believed that the cause is the orientation of associated or polymerized polar aggregates of such size as to be affected by the larger viscosity changes approaching the macroscopic.In the solid and amorphous states, the limited motion of ions leads to an ionic polarization as indicated by absorption curves of relatively large time constants and by high power factors in the low frequency range. The addition of organic acids greatly increases these effects and also increases the final conductivity. The true short time conductivity is largely caused by almost completely dissociated inorganic material.     

金属薄膜单轴拉伸过程中的等效性能研究

关注单轴拉伸条件下裂纹萌生扩展阶段的金属薄膜性能变化.通过运用Parallel、Maxwell和Hashin-Shtrikman等效理论,建立拉伸过程中金属薄膜的裂纹模型,得出了电阻值与应变的关系,并与现有实验结果进行了比较.结果表明,Maxwell等效理论条件下的理论值与实验结果吻合较好.然后运用有限元计算,比较了拉伸能量法和均匀化方法在计算等效弹性模量时的准确性,最后建立了等效电阻和等效弹性模量以及损伤变量的关联.     

论物理学中的类比方法 以汤姆森和麦克斯韦为例

类比方法是亚里士多德提出的逻辑学方法之一,但这一方法的严格性,乃至它是否可以被算作一种逻辑方法,在亚里士多德之后却一直饱受质疑。正因为如此,19世纪英国物理学家汤姆森和麦克斯韦将类比方法引入电磁学研究时曾受到严重的质疑。20世纪中叶,玛丽·海斯等西方哲学家试图将类比方法纳入到现代逻辑学体系中,并以此解释汤姆森和麦克斯韦的工作。但他们的出发点仍然是将类比置于一个基于事物间偶然联系的启发工具的地位上,这既不足以为物理类比方法的正当性提供辩护,也无法解释这种方法在物理学中表现出的广泛的适用性和有效性。本文将从重构汤姆森和麦克斯韦引入类比方法的过程入手,分析他们使用类比论证的依据。本文将论证,物理学中的类比方法是一种严格的科学方法,应明确地区别于一般逻辑学以及大众话语中所说的"类比"。这种方法的严格性来自于它所依据的唯一的类比基础,即不同物理现象的数学形式间的相似性。进而以此为基础浅论麦克斯韦的"数学分类"思想。     

《天演论》中的热力学

达尔文的生物演化论当年最显赫的论敌不在宗教界,而是物理学者汤姆生。他以热力学为武器,对莱尔地质学与天择论长达40多年的无情批评,甚至迫使斯宾塞、赫胥黎改变了他们原先为演化构思的乐观愿景。连达尔文也只能以“不可知论”来敷衍和搪塞。这是演化论史上的著名公案。严复据以做《天演论》的赫胥黎文本,留下了这段公案的线索,但严复似乎并不清楚详情。     

Characteristics of small grid-controlled hot-cathode mercury arcs or thyratrons

The principle of the grid-controlled arc or thyratron is briefly described and the norminal ratings as regards filament current, maximum plate current etc. of four important thyratrns are given in table form. Methods of measuring the grid current, critical grid potential, etc., with D.C. power supply are given along with the results obtained on the General Electric Company thyratrons FG-₁₇, FG-₂₇ and FG-₆₇. Characteristics obtained with A.C. power supply are also shown for these thyratrons and some of the relative advantages of the “phase-shift” and the “critical potential” methods of control are discussed when used in connection with photoelectric cell circuits. The A.C. measurements seem to show that a time of 10^?3 second is required to start a thyratron. An amplifier circuit is shown by which it is theoretically possible to control a thyratron circuit using an input current to the amplifier of 10^?11 ampere.     

Theory of broadband matching and the problem of compatible impedances

It is shown that Youla's theory of broadband matching between a passive load and a resistive generator with a preassigned transducer power gain characteristic is completely equivalent to Wohlers' solution to the problem of compatible impedences, which transforms a given passive impedance by a lossless coupling network into another specified one.     

Dynamical behavior in a harvested differential-algebraic prey-predator model with discrete time delay and stage structure

A differential-algebraic model system which considers a prey-predator system with stage structure for prey and harvest effort on predator is proposed. By using the differential-algebraic system theory and bifurcation theory, the dynamic behaviors of the proposed model system with and without discrete time delay are investigated. Local stability analysis of the model system without discrete time delay reveals that there is a phenomenon of singularity induced bifurcation due to variation of the economic interest of harvesting, and a state feedback controller is designed to stabilize the proposed model system at the interior equilibrium; on the other hand, the local stability of the model system with discrete time delay is also studied. The theoretical analysis shows that the discrete time delay has a destabilizing effect in the model of population dynamics, and a phenomenon of Hopf bifurcation occurs as the discrete time delay increases through a certain threshold. Numerical simulations are carried out to show the consistency with theoretical analysis.     

制造企业－知识型服务机构互动作用于运营绩效的机理研究

本文基于资源观、资源依赖理论和知识观,剖析制造企业－知识型服务机构互动作用于制造企业运营绩效的机理与路径。通过多元线性回归分析与结构方程模型分析发现：资源重组与资源重置在制造企业－知识型服务机构互动与运营绩效之间发挥中介作用;当制造企业与知识型服务机构进行互补型互动时,资源重组的中介作用要优于资源重置;当制造企业与知识型服务机构进行辅助型互动时,资源重置的中介作用要优于资源重组。本文的理论贡献在于剖析资源到竞争优势的作用机制,明确制造企业－知识型服务机构互动、资源重组、资源重置、运营绩效之间的内在联系,实践意义在于制造企业应该如何通过与知识型服务机构互动促进其资源重组与重置,以此来提升运营绩效。     

Integral sliding-mode fixed-time consensus tracking for second-order non-linear and time delay multi-agent systems

In this paper, fixed-time consensus tracking problems under directed interaction topologies for second-order non-linear multi-agent systems with disturbance and second-order multi-agent systems with input delay are investigated. Two continuous integral terminal sliding modes are designed, which can effectively eliminate the singularity and chattering. Correspondingly, two fixed-time distributed control protocols are proposed based on the designed continuous ITSM to ensure that the consensus tracking are achieved in fixed-time. It is shown that the upper bounds of settling time are regardless of initial conditions. The rigorous proofs are given by employing Lyapunov stability theory and fixed-time stability theory. Simulations are provided to verify the effectiveness of the theoretical results.     

Second-order observability of matrix-weight-based networks

This study focuses on the observability of second-order linear time invariant (LTI) systems with incommensurable output matrices through a matrix-weighted graph. Here, the observability of such systems refers to that the relative outputs have synchronized solutions for the identical LTI systems. Compared with most of existing results, relying on scalar networks (i.e., the weight of edges is a constant), this study investigates the observability in a matrix-weight-based network. Some necessary and sufficient conditions for the observability have been obtained by the space analysis, spectral analysis and matrix decomposition, respectively. Moreover, the relationship between the observability and the connectivity of its interconnection graph is also discussed. Examples and simulations are shown to verify the theoretical results.     

平台企业主导的生产性服务业集聚发展研究

"如何加速集聚进程、同时规避网络风险"是当前中国发展生产性服务业亟待统筹解决的现实问题,而理论界鲜有探讨。本文基于对浙江地区近年来若干创新个案的观察,主要运用产业集聚理论、双边平台理论和演化经济学理论,研究一种平台企业主导的生产性服务业集聚发展模式,为解决前述问题提供理论与经验支撑。文章首先从整体结构、交易与竞合关系、治理主体三个方面刻画了平台企业主导下服务交易网络的架构特征,并以此为基础剖析了前述创新个案中存在的多重集聚动力机制,以及平台企业对集聚网络的风险控制机制。文章对该模式加速集聚进程同时规避网络风险的机理给出了一个"架构功能主义"的理论解释,并进一步讨论了蕴含其中的理论与政策含义。     

Modeling of synchronous electric machines for real-time simulation and automotive applications

Recent research in the field of vehicle electrification has indicated that synchronous machines, which include the permanent magnet synchronous machine (PMSM) and the externally excited synchronous machine (EESM), represent a viable solution for electric propulsion. A challenging problem for synchronous machines drives employed in automotive applications is to obtain accurate mathematical models which can deal with parametric variation and which are suitable for real-time simulations and synthesis of control laws. The goal of this paper is to provide a mathematical modeling framework for synchronous machines that can answer to this challenging problem. To this end, using the rotor reference frame, the mathematical models of PMSMs and EESMs are constructed taking into account also the parametric variation due to magnetic saturation and temperature variation. Then, a complex state-space bilinear model for both EESM and PMSM with parametric variation due to magnetic saturation and temperature are developed. Considering the parametric variation as a polytopic bounded disturbance, it is then shown how to split the bilinear complex model in two PWA variable parameter state-space models suitable for a cascade control structure. Based on the developed models, a dynamic unified simulator was constructed in Matlab^®/Simulink^®. Measurement data obtained in a real test-bench system were used to verify the accuracy of the simulator. The discrete-time simulator was then integrated in an industrial hardware-in-the-loop test bench for real-time evaluation of a current control scheme in EESM drives.     

Some aspects of the present status of the thermodynamics of electrolytic solutions

We have surveyed in a brief manner some phases of the experimental thermodynamics of electrolytic solutions. A more complete review would be very voluminous, and would include a number of other topics. As examples, the investigations of electrolytes of higher valences types such as cadmium chloride (34), and iodide (8), barium chloride (85), and zinc sulphate (11) (55). It would also include a discussion of the important work of Gibson (14) who has measured the compressions of a number of aqueous salt solutions up to 1000 bars. Nor have we discussed the recent interpretations of the behaviors of strong electrolytes in solutions at higher concentrations where the theory of Debye and Hückel is no longer adequate without considerable extension. This complicated subject has been investigated most comprehensively by Scatchard (78) (80) and its discussion would lead beyond the intended limits of this survey. We trust that this sketch of our results will help somewhat to give a correct impression of the extent and direction of this part of solution chemistry. The development of method in these studies of equilibria has reached the stage where a really reliable and accurate body of evidence is becoming available. This is very important because accurate data will be required not only as criteria and as a guide to the approximate statistical and quantum mechanical interpretations of equilibrium constants, entropies, activation energies, and reaction velocity constants where ions are involved, but also in the further clarification of the state of ions in solution.     

Minimum mass convective fins with variable heat transfer coefficients

Pontryagin's maximum principles are applied to obtain the solution of minimum mass convective fins with variable heat transfer coefficients. It is shown that the volume and the width of the fin are uniquely related to the specified heat transfer rate and the properties of the material. For a power law spatial variation of the heat transfer coefficient, the results are set forth in a dimensionless form and they are given in tables or graphs, in order to aid design procedures. Several properties relating to the optimum volume, base thickness and the width of the fins with the properties of the material are also discussed. The method can also be used to solve problems of minimum mass fins having restricted width, often encountered in practice.     

Dynamical behavior in a hybrid stochastic triple delayed prey predator bioeconomic system with Lévy jumps

In this paper, a hybrid triple delayed prey predator bioeconomic system with prey refuge and Lévy jumps is established, where both maturation delay for prey and predator population and gestation delay for predator population are considered. For deterministic system, positivity and uniform permanence of solution are discussed. Local stability of deterministic system around interior equilibrium is investigated due to variations of triple time delays. For stochastic system without time delay, sufficient conditions for stochastically ultimate boundedness and stochastic permanence are discussed. Existence of stochastic Hopf bifurcation and stochastic stability are investigated. For stochastic system with triple time delays, existence and uniqueness of global positive solution are studied. Finally, combined dynamic effects of triple time delays and Lévy jumps on the hybrid stochastic system are discussed by constructing appropriate Lyapunov functions. Numerical simulations are supported to illustrate theoretical analysis.     

Information and communication technology adoption for business benefits: A case analysis of an integrated paperless system

This case study analyses the benefits of implementing a paperless software solution (Alert^®pfh–Alert Paperfree Hospital, developed by Alert Life Sciences Computing) in a Portuguese Hospital, the Espírito Santo Hospital, in the city of Évora. Alert^®pfh is a complete hospital clinical information system with real time clinical information input. It was implemented in emergency medical services, inpatient and outpatient services, and operating room services. Data were collected between 2006 and 2011 prior to, during and after the system's implementation. The case analysis demonstrates that paperless software systems have a significant potential when applied in healthcare organization services. Besides financial benefits, other important organizational features were identified, namely higher levels of patient and professional satisfaction; an increase in efficiency in hospital operations; improvement in the quality of information for management decision-making; and a reduction in medical errors. Lessons learned are noted and conclusions drawn for both theoretical and practical ICT benefits analysis.     

资源科学几个问题探讨

资源科学是一门新兴的综合性学科,其发展仍然面临着一系列需要探讨的理论问题。本文研究认为：资源科学是一门建立在各分支资源科学基础上的综合性学科。资源问题是资源科学迅速发展的社会动力。为了正确认识或解释世界范围内存在的严重的资源环境问题,资源科学必须进行横跨自然科学和社会科学的综合性研究,因为资源的利用过程实际上是人类利用现有的社会经济资源（资本、人力、技术、信息、管理等）对自然资源的加工利用过程。从世界范围看,特别是从处于经济高速增长的中国看,资源问题是人口、环境、经济复杂的问题的核心。最后,本文对几个重要的资源科学问题进行了初步研究：①资源过程论;②资源的生态经济平衡论;③资源生态系统论;④资源流动论;⑤资源产权论。     

Energy-Time optimal control of wheeled mobile robots

This paper focuses on the energy-time optimal control of wheeled mobile robots undergoing point-to-point transitions in an obstacles free space. Two interchangeable models are used to arrive at the necessary conditions for optimality. The first formulation exploits the Hamiltonian, while the second formulation considers the first variation of the augmented cost to derive the necessary conditions for optimality. Jacobi elliptic functions are shown to parameterize the closed form solutions for the states, control and costates. Analysis of the optimal control reveal that they are constrained to lie on a cylinder whose circular cross-section is a function of the weight penalizing the relative costs of time and energy. The evolving optimal costates for the second formulation are shown to lie on the intersection of two cylinders. The optimal control for the wheeled mobile robot undergoing point-to-point motion is also developed where the linear velocity is constrained to be time-invariant. It is shown that the costates are constrained to lie on the intersection of a cylinder and an extruded parabola. Numerical results for various point-to-point maneuvers are presented to illustrate the change in the structure of the optimal trajectories as a function of the relative location of the terminal and initial states.