Methods for controlling a linear asynchronous motor

This article describes the case of one of possible method of controlling a linear asynchronous motor (LAM) with a controlled normal component of the force of interaction between an inductor and a reactive bus. It is shown that the normal force in a unilateral linear asynchronous motor can affect significantly the operation of devices and systems on which a motor is installed. This normal force can attract an inductor to a reactive bus or repel it from a reactive bus. For the model of a motor, which is represented by four zones, namely, an inductor, an air gap, a conductive bus, and a steel core of a reactive bus, the analytical expressions for the calculation of the components of a magnetic field in an air gap were obtained. The effect of the longitudinal and transverse edge effects in the considered plane model of a motor is not considered. The expressions for the determination of the specific tangential and normal forces per area unit were found. It is shown that, under a change in the slide from negative to positive values, the tangential force changes similarly to the electromagnetic torque of a conventional asynchronous motor with a rotating rotor. Under a change in the slide, the normal force can attract an inductor to a reactive bus or repel it from a reactive bus. The force of attraction reaches the highest values under a zero slide. The slide under which the normal force is equal to zero is determined only by the pole pitch and the conductivity of material of a reactive bus and provides the operation of a motor at the highest power factor. It is proposed to use the measured normal force value as a parameter for the construction of a traction linear asynchronous motor-control system.     

Steady-state corona charging behavior of a corotron over a movingdielectric substrate

Charging up a dielectric surface through corona discharge from a thin wire has been a common practice in electrophotographic processes. One of the widely used corona charging devices is called a corotron, which consists of a coronating wire enclosed in a rectangular shield with one constituent side being the surface to be charged. Uniform surface charge can be deposited on a dielectric substrate, such as a photoreceptor in the absence of light, by moving the substrate at a constant velocity through a stationary corotron that consistently emits corona current. To design an efficient corotron for charging dielectric substrates, a fundamental understanding of the electrostatic nature of the device is desired. In this paper, the steady-state behavior of corona charging with a corotron over a moving dielectric substrate is analyzed by computationally solving the nonlinearly coupled equation system with Galerkin finite-element method and Newton iterations. The predictions based on a first-principle model are shown to agree well with experimental measurements     

Negotiating expert status: who gets taken seriously

A lay person may listen puzzled as a specialist in a public hearing discusses a technical point. Similarly, a challenging question from a technically knowledgeable member of the audience may be difficult to fathom. Failure to understand what a speaker discusses-despite one's interest in a topic-can cause frustration, anger and despair. It makes a listener wonder why they are there trying to engage, and why technical specialists persist in such a style of presentation. Breakdowns in communication between technical and nontechnical people are linked to the concept of “expert”. This link involves the process of the “negotiation of expert status”; this refers to the social construction of the role of the “expert” by the participants in a conversation. The term “negotiation” refers to the sometimes subtle and sometimes overtly contentious nature of a debate about who deserves to be listened to as a voice of authority on a particular topic     

新型制冷剂研究及应用冰箱压缩机的设计

为了解决R12的主流替代工质R134a作为冰箱制冷剂时存在的问题,提出给R134a系统加入R600a组成混合工质R134a/R600a的方案,提供物性和热力性能比较结果,证明R134a/R600a作为冰箱制冷剂比R134a和R600a更具有优势,并提出了采用新型制冷剂的冰箱压缩机的改进方案.R134a/R600a的性能试验结果证明其与矿物油的互溶性良好,成功的解决了R134a系统由于更换润滑油而产生的一系列问题.     

Teleoperation via computer network

In a teleoperation system, providing force information to a human operator can improve task performance. When a communication block between a master and a slave has a transmission delay, the system is easily destabilized. Anderson and Spong guaranteed passivity in the communication block by using scattering transformation and overcame this instability caused by the time delay. But this method can be applied to the communication block with a constant time delay. In a traditional teleoperation system, its communication block has a constant time delay. But time delay irregularly changes in a computer network because many users share telecommunication lines. This paper shows that the variable time delay destabilizes bilateral master-slave manipulator with scattering transformation and a new compensation method which keeps the time delay constant. This new compensation method has been implemented in a single-axis master-slave manipulator.     

A study of electric stress enhancement. Part 1. Implication in power cable design

The increase in electric stress due to a surface protrusion at the interface between a semiconductive shield and a polymer insulation layer in power cables can lead to localized electron injection into the polymer insulation and result in undesired material degradation. This paper reports the analyses of electric stress enhancement of surface protrusions in several commonly encountered medium- and high-voltage power cable configurations. First, a brief review of the electric stress enhancement theories is presented. Then evaluations using these theories for various power cable configurations are made, and it is shown that theories considering a hyperboloidal protrusion will exhibit more realistic stress enhancement results than the cases based on a spheroidal protrusion. Further examination reveals that, besides the sharpness of a protrusion, thickness of the insulation medium also plays a governing role in the stress enhancement at the interfaces between different dielectric media. Contrary to the conventional wisdom, it is a surprise to observe that a thicker insulation can actually cause higher stress enhancement at a protrusion tip, under a given applied voltage. Because of this, a flatter surface protrusion at a higher voltage setting, which usually has thicker insulation, can result in earlier degradation than a sharper protrusion at a lower voltage, even though sharper extrusions are expected to have higher stress enhancement. As a result, thicker insulation may not always be advantageous in the power cable design for higher voltage applications.     

Numerical Investigation of a Molecular Switch Based on Conformational Change, with the Inclusion of Contacts

We discuss the possibility of implementing a switch based on a conformational change, consisting in a relative rotation of a molecule containing two benzene rings, functionalized with proper substituents. Contacts are simulated with three-atom gold clusters, which are connected to the rest of the molecule via a thiol group. Relative rotation of the two rings, induced by a transverse electric field, determines a variation of the height of the potential barrier separating them, due to the change in the amount of conjugation of the π orbitals. The action of such a barrier is evaluated by computing the shift of the electron density as a function of a longitudinal electric field.     

Monitoring Around a Vehicle by a Spherical Image Sensor

This paper describes a prototype of a full-view spherical image sensor, gives a method for sensor calibration, and discusses display modalities of the captured full-view image for monitoring around a vehicle. To monitor the whole surrounding situation of a dynamic environment by a single camera, a spherical field of view (FOV) is divided into two hemispherical views. Each hemispherical FOV is imaged by a fisheye lens. Both of the hemispherical views are fused by a mirror to acquire them on a single image plane. To calibrate the full-view spherical image sensor, a three-dimensional (3-D) calibration pattern is used to compute the internal parameters of each fisheye lens and their relative orientation based upon a spherical camera model. Finally, several display modalities are discussed to show drivers the relevant spherical image information on planar displays for monitoring around a vehicle     

Computational finance models

The author discusses his involvement in developing computational finance software. These computational finance models attempt to model the randomness of a stock's price. At a fixed future time, a stock's price is modeled as a random variable with a normal distribution centered about the current price adjusted with a simple growth multiplier. The standard deviation of this normal distribution depends on the length of time into the future one peers and the volatility of the market. As the market becomes more volatile and we look further ahead, the less likely the stock will have a price near the adjusted current price. Implementing these ideas requires a tool borrowed from physics called the Brownian motion. In a sense, a stock's price is modeled as a point fluctuating about in "dollar space". Hence a financial modeler can no more predict what price a stock will have at a given instance in time than a physicist can predict where a particular air molecule might be.     

Unit commitment using Lagrangian relaxation and particle swarm optimization

Unit commitment (UC) is a NP-hard nonlinear mixed-integer optimization problem. This paper proposes ELRPSO, an algorithm to solve the UC problem using Lagrangian relaxation (LR) and particle swarm optimization (PSO). ELRPSO employs a state-of-the-art powerful PSO variant called comprehensive learning PSO to find a feasible near-optimal UC schedule. Each particle represents Lagrangian multipliers. The PSO uses a low level LR procedure, a reserve repairing heuristic, a unit decommitment heuristic, and an economic dispatch heuristic to obtain a feasible UC schedule for each particle. The reserve repairing heuristic addresses the spinning reserve and minimum up/down time constraints simultaneously. Moreover, the reserve repairing and unit decommitment heuristics consider committing/decommitting a unit for a consecutive period of hours at a time in order to reduce the total startup cost. Each particle is initialized using the Lagrangian multipliers obtained from a LR that iteratively updates the multipliers through an adaptive subgradient heuristic, because the multipliers obtained from the LR tend to be close to the optimal multipliers and have a high potential to lead to a feasible near-optimal UC schedule. Numerical results on test thermal power systems of 10, 20, 40, 60, 80, and 100 units demonstrate that ELRPSO is able to find a low-cost UC schedule in a short time and is robust in performance.     

水利工程模糊多模式工期-成本-质量均衡优化

针对不确定环境下水利工程建设项目的工期-成本-质量均衡优化问题,采用双指数函数和二次函数分段模拟工程质量和工期之间的关系,构建了水利工程模糊多模式离散工期-成本-质量均衡优化模型。运用微粒群算法对其进行求解,并将优化结果与相关文献进行对比分析,验证了模型的合理性和计算方法的有效性。最后,将该模型应用于水利工程实例,为决策者进行目标计划和控制提供理论依据。     

Heterodyne Mixing of Terahertz Quantum Cascade Lasers Using a Planar Schottky Diode

Terahertz quantum cascade lasers (QCLs) have been used together with a monolithic planar Schottky diode receiver to study the heterodyne mixing between dual internal modes of a QCL and between a single mode of a QCL and a known molecular line from a molecular gas laser. Dual-mode mixing shows that the intrinsic linewidth of a free-running QCL is les30 kHz . Mixing against a molecular laser line gives a high precision measurement of a QCL's absolute frequency and can show transient turn-on behavior in a pulsed QCL.     

换热器管壁圆形泄漏口空间辐射声场分布特征数值研究

根据可分离辐射源的声辐射，利用叠加原理和无穷级数迭代求和，建立了换热器管道壁面圆形口非分离泄漏声辐射源的空间声场分布数学模型。计算了圆形口均匀幅度非分离声辐射源的空间声场远场分布，给出了其远场相对声压级和位相的空间分布图案。与方形口均匀可分离辐射源的空间声场分布特征相比，发现两种情况具有相同的空间指向性特征，在较高频率时辐射声场空间分布出现盲区，在x—y平面内声场分布与泄漏口形状无关，但与辐射频率有密切关系。     

Evaluation of the Lorentz law by using a Barlow wheel

In this work, an evaluation of the Lorentz law has been carried out by a Barlow wheel. Basically, a Barlow wheel is a primitive dynamo-electric machine (invented by P. Barlow in 1828) which consists of a metallic cogwheel, which moves around a horizontal axis. The theoretical analysis includes the Lorentz law and the Petroff law, which characterizes the friction between the axis and the bearing. In the stationary state (when the angular velocity is constant), a simple formula can be obtained which relates the current intensity and the angular velocity. Experimental data approximately confirms this formula, and this device can be used as a simple and classical laboratory experiment in basic electromagnetism courses. Some modern complements were used for the acquisition of data, as a light barrier connected to a counter, a voltammeter and a direct-current power supply Therefore, the Barlow wheel, originally designed for qualitative demonstrations, can be used as a quantitative and useful assembly in a laboratory of General Physics     

Development of a web-based laboratory for control experiments on acoupled tank apparatus

The Internet provides a new environment for developing a variety of applications for educational and research purposes. This paper presents the implementation of a web-based laboratory experiment on a coupled tank apparatus, a multi-input-multi-output (MIMO) system. The web-based laboratory has been developed to serve students and staff in the Department of Electrical Engineering at the National University of Singapore (NUS). The laboratory is an educational tool for teaching students the basic principles and methodology in performing a series of experiments on a coupled tank apparatus at any time and from any location through the Internet. With the capability to implement strategies for manual, proportional integral derivative (PID), general state-space, and fuzzy logic control, the laboratory also provides a platform for research staff to test control algorithms. Video conferencing has been used to provide audio and video feedback, with a camera mounted on a movable platform so that the user can control both the zooming and viewing angle     

Modeling and performance of a static frequency converter starting a 300 MVA synchronous machine

This paper presents a study of the dynamic behavior of a static frequency converter driving a 300 MVA synchronous generator which is used in a pumped storage power plant of Taiwan Power Company. The static frequency converter, which consists of a three-phase AC/DC phase converter, a filtering inductance, and a six-step current-source inverter, is used to start a 300 MVA synchronous machine. In this paper, first the mathematical model of the whole system which consists of a synchronous machine, a static frequency converter, a microprocessor, and sensors is established. Then, the control method of the static frequency converter based on field oriented control is presented. Next, a filter circuit has been designed to reduce the harmonics of the AC source. By using this filter, the harmonics can be effectively reduced. Finally, some computer simulated and experimental results are shown to verify the theoretical analysis. This paper presents a new direction in the use of advanced power electronic technology to drive a very large synchronous machine.     

A practical approach to harmonic compensation in powersystems-series connection of passive and active filters

The authors present a combined system with a passive filter and a small-rated active filter, both connected in series with each other. The passive filter removes load produced harmonics just as a conventional filter does. The active filter plays a role in improving the filtering characteristics of the passive filter. This results in a great reduction of the required rating of the active filter and in eliminating all the limitations faced by using only the passive filter, leading to a practical and economical system. The active filter has a much smaller rating than a conventional active filter. Experimental results obtained from a prototype model are shown to verify the theory developed