检索结果-内蒙古大学图书馆

THEORETICAL BASIS FOR A UNIFIED CONSERVATION LAW DESCRIPTION OF THE ELECTROMAGNETIC ACOUSTIC TRANSDUCTION PROCESS

IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL 1992年第4期39卷 476-480页

作者： LUDWIG, R Department of Electrical and Computer Engineering Worcester Polytechnic Institute Worcester MA USA

A unified theoretical formulation describing the electro-acoustic transduction processes governing an electromagnetic acoustic transducer is presented. This new approach establishes separate electrical, mechanical and material subsystem descriptions based on the momentum conservation forms of Maxwell's field equations in the quasi-static limit and Cauchy's law of motion. Instead of accounting for the electromagnetic acoustic material interaction by direct linkage of mechanical stress and magnetic flux through constitutive relations, the coupling of the field tensors is achieved as part of an additional material subsystem. As a result, the complete set of governing equations and associated boundary conditions can be derived from first principles in a concise way that lends itself to a quantitative numerical implementation in the time domain. Aspects of the numerical formulation and the subsequent computer model predictions are discussed in a companion paper.

关键词： Magnetic materials Magnetic flux Tensile stress Magnetostriction Maxwell equations Electromagnetic fields Acoustic materials Acoustic transducers Electromagnetic coupling Surface acoustic waves

来源：评论

学校读者我要写书评

暂无评论

SHALLOW LEVEL RECOMBINATION CURRENT DOMINANCE IN TRANSISTOR BETAS

IEEE ELECTRON DEVICE LETTERS

引用

IEEE ELECTRON DEVICE LETTERS 1993年第2期14卷 49-50页

作者： LANYON, HPD Department of Electrical and Computer Engineering Worcester Polytechnic Institute Worcester MA USA

A new recombination mechanism, via the high density of shallow donor and acceptors present in the base-emitter junction of integrated circuit transistors, is suggested. In contrast to the recombination via deep centers, this mechanism has an ideal voltage dependence, leading to a beta essentially independent of the base-emitter voltage. It appears to be the dominant component to the base current of integrated circuit transistors. The temperature dependence of the beta of the transistors arises from the ionization energy of the donors and acceptors. The rate-setting capture cross section by neutral acceptor and donors is 1.3(5) x 10(-15) cm2.

关键词： Voltage Spontaneous emission Charge carrier processes Electron traps Silicon Temperature dependence Energy capture Ionization Doping Diodes

来源：评论

学校读者我要写书评

暂无评论

A finite-element time-domain method using prism elements for microwave cavities

引用

IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY 1995年第4期37卷 519-527页

作者： Sacks, ZS Lee, JF Department of Electrical and Computer Engineering Worcester Polytechnic Institute Worcester MA USA

A finite-element time-domain (FETD) method for solving Maxwell's equations was developed by combining prism-based edge elements with central differencing in the time domain. This method solves for the electric field as a vector function of space and time in finite cylindrical cavity geometries of arbitrary geometry. Two stability analyses of this method are performed using the growth factor technique and the Z-transform. Furthermore, the computational complexity of the present approach is also investigated. This method has been implemented and its validity tested by studying the resonant frequencies of various microwave cavities.

关键词： Finite element methods Time domain analysis Microwave theory and techniques Geometry Maxwell equations Difference equations Finite difference methods Magnetic fields Stability analysis Computational complexity

来源：评论

学校读者我要写书评

暂无评论

ANALYTICAL EXPRESSIONS FOR THE TIME-DOMAIN DISPLACEMENT RESPONSE OF A PIEZOELECTRIC PLATE RESONATOR

引用

IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL 1995年第4期42卷 801-803页

作者： USTUNDAG, A LUDWIG, R LEVIN, P Computational Electromagnetics and Ultrasonics Group Department of Electrical and Computer Engineering Worcester Polytechnic Institute Worcester MA USA

An analytical one-dimensional series solution for the time-domain displacement response of a piezoelectric plate is derived. Rather than the usual charge driven electric boundary value formulation, this paper develops the solution for a voltage-driven step function excitation where one electrode is stress-free and the other is displacement fixed. The advantage of this rapidly converging series lies in the ability to test numerical methods such as piezoelectric finite element time domain (FETD) algorithms.

关键词： Time domain analysis Electrodes Delay Finite element methods Equations Displays Dispersion Frequency dependence Acoustic reflection Time series analysis

来源：评论

学校读者我要写书评

暂无评论

A COMPARATIVE-STUDY OF NONPARAMETRIC SPECTRAL ESTIMATORS FOR APPLICATION IN MACHINE VIBRATION ANALYSIS

引用

MECHANICAL SYSTEMS AND SIGNAL PROCESSING 1992年第6期6卷 551-574页

作者： NAJAFI, B HAKIM, H Electrical and Computer Engineering Department Worcester Polytechnic Institute Worcester MA 01609 U.S.A.

The vibration of a machine carries important information about the health of its internal components; this information, if properly extracted, can be extremely useful in the detection of developing faults within the machine. One of the most effective methods to extract this information is the computation of the vibration power spectrum, but since the statistical properties of the vibration signal are generally unknown, the power spectrum has to be estimated from the available finite-length data. A number of methods have been proposed for vibration spectral estimation, each presenting advantages and disadvantages. In each specific application, it is often necessary to evaluate and choose the optimum spectral estimation method. This paper presents an analysis of four widely accepted non-parametric spectral estimation methods: Periodogram, Blackman-Tukey, Welch, and Nuttall-Carter. It compares them based on their mean, variance, resolution, and computational requirements. It is found that all methods, except the Periodogram, can achieve the same mean, variance, and resolution but differ in leakage suppression and computational complexity. The Welch method has the best leakage suppression and the Nuttall-Carter method has the lowest computational burden in most cases.

关键词：

来源：评论

学校读者我要写书评

暂无评论

INTEGRATION OF STEREO VISION AND OPTICAL-FLOW BY USING AN ENERGY-MINIMIZATION APPROACH

引用

JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION 1989年第6期6卷 900-907页

作者： NASRABADI, NM CLIFFORD, SP LIU, Y []Computer Vision Research Group Department of Electrical Engineering Worcester Polytechnic Institute Worcester Massachusetts 01609

A cooperative method is proposed in which image intensity (brightness) and optical-flow information are integrated into a single stereo technique by modeling the input data as coupled Markov random fields (MRF’s). The Bayesian probabilistic estimation method and the MRF–Gibbs equivalence theory are used to integrate the optical flow and the gray-level intensity information to obtain an energy function that will explicitly represent the depth discontinuity and occlusion constraints on the solution. This energy function involves the similarity in intensity (or edge orientation) and the optical flow between corresponding sites of the left and right images as well as the smoothness constraint on the disparity solution. If a simple MRF is used to model the data, the energy function will yield a poor disparity by smoothing across object boundaries, particularly when occluding objects are present. We use optical-flow information to indicate object boundaries (depth discontinuities) and occluded regions, in order to improve the disparity solution in occluded regions. A stochastic relaxation algorithm (simulated annealing) is used to find a favorable disparity solution by minimization of the energy equation.

关键词： Brightness Medical imaging Motion estimation Optical flow Remote sensing Stereo matching

来源：评论

学校读者我要写书评

暂无评论

Tolerance analysis based computer-aided setup planning

引用

Journal of the Chinese institute of Industrial Engineers 2003年第3期20卷 247-257页

作者： Zhang, Y. Hu, W. Rong, Y. Computer-aided Manufacturing Laboratory Department of Mechanical Engineering Worcester Polytechnic Institute Worcester MA 01609 United States Department of Mechanical Engineering United States Computer-aided Manufacturing Laboratory Worcester Polytechnic Institute United States

Setup Planning is to determine the number/sequence of setups in a production line and operation details in each setup. To bridge the gap between computer-aided process planning (CAPP) and computer-aided fixture design (CAFD), an automated setup planning and tolerance decomposition method is developed. Directed graph is extended to represent feature/dimension/tolerance relationships (FTG) and datum/machining feature relationships (DMG). According to different production schemes and manufacturing resource capabilities, setup planning principles and algorithms are explored to automatically extract DMG from FTG. Under the true positioning frame, tolerance decomposition models are concluded to partition a tolerance into interoperable machining errors, such as locating error, tool alignment error, and random process error. As one of the deterministic components of machining errors, locating error is primarily caused by positional variations of locating elements in fixture design and dimensional variations of locating features on workpieces. In this research, mathematical models are developed to analyze locating variations and their influences on machining features. The analysis results of locating error effects can be used in budgeting the locating precision and improving the setup plan. The technique has been implemented on a commercial CAD system with applications to automobile manufacturing industry.

关键词： computer aided design

来源：评论

学校读者我要写书评

暂无评论

STEREO VISION CORRESPONDENCE USING A MULTICHANNEL GRAPH MATCHING TECHNIQUE

引用

IMAGE AND VISION COMPUTING 1989年第4期7卷 237-245页

作者： NASRABADI, NM LIU, Y Computer Vision Research Group Department of Electrical Engineering Atwater Kent Laboratories Worcester Polytechnic Institute Worcester MA 01609 USA

A multichannel feature-based stereo vision technique is described in this paper where curve segments are used as the feature primitives in the matching process. Curve segments are extracted by tracking the zero-crossings of the left and right images. The generalized Hough transform of each curve and the curve length are used as a local feature vector in representing the distinctive characteristics of the curve segment. The feature vector of each curve segment in the left image is used as a constraint to find an instance of the same curve segment in the right image. The epipolar constraint on the centroids of the curve segment is used to limit the searching space in the right image. A relational graph is formed from the left image by treating the centroids of the curve segments as the nodes of the graph. The local features of the curve segments are used to represent the local properties of the nodes, and the relationship between the nodes represents the structural properties of the objects in the scene. A similar graph is also formed from the right image curve segments. A graph isomorphism is then formed between the two graphs by using the epipolar constraint on the centroids, the local properties of the nodes, node assignment and the structural relationship (compatibility) between the nodes.

关键词： stereo vision graph matching

来源：评论

学校读者我要写书评

暂无评论

Lessons on mobile apps for COVID-19 from China

引用

Journal of Safety Science and Resilience 2021年第2期2卷 40-49页

作者： Sophia L.Zhou Xianhan Jia Samuel P.Skinner William Yang Isabelle Claude Mass Academy of Math and Science Worcester Polytechnic Institute85 Prescott StreetWorcesterMA 01605United States Department of Computer Science Worcester Polytechnic Institute100 Institute RoadWorcesterMA 01609United States Department of Physics Worcester Polythenic Institute100 Institute RoadWorcesterMA 01609United States Department of Biomedical Engineering Worcester Polytechnic Institute100 Institute RoadWorcesterMA 10609United States

The COVID-19 pandemic has impacted the global society and human life *** countries have launched COVID-19 mobile apps with a wide range in how these apps *** it is hoped that these apps can assist in the fight against COVID-19,many are worried about user *** implemented“health code”systems,which assigned neighborhoods and citizens a specific health code,meant to indicate their risk of having been exposed to *** most widely used health code systems were hosted on the popular apps WeChat and Alipay,each with billions of *** experts argued that China’s use of mobile applications was essential to its successful combat against *** in this study are a summary of mobile technology usage in China,a review of previous studies of mobile technology in healthcare,and a brief survey of some existing mobile applications for COVID-19 that were *** included are outcomes of interviews with healthcare and public safety experts and a public survey to understand how mobile applications were used in China’s response to *** interviews revealed four important themes:personal privacy,community involvement,government involvement,and situational *** was found that a key concern was maintaining a balance between collecting and utilizing personal information,as well as protecting this *** addition,close collaboration between local communities and the national government was *** applications assisted in communication and coordination but did not replace the work of people such as delivery drivers and contact *** results also showed that there was room for improvement,especially accessibility for the elderly or those unfamiliar with *** results were obtained from our *** was interesting to find that the apps were mostly used for“accessing information on COVID-19.”In addition,respondents overwhelmingly identified“information”as the most valuable featur

关键词： Mobile apps COVID-19 response Survey Interview Lessons

来源：评论

学校读者我要写书评

暂无评论

Important considerations in the evaluation of absorbing boundary conditions

引用

ELECTROMAGNETICS 1996年第4期16卷 417-433页

作者： Lee, R Chen, Z Jevtic, JO Lee, JF [a] Department of Electrical Engineering ElectroScience Laboratory The Ohio State University Columbus OH USA [b] Department of Electrical and Computer Engineering Worcester Polytechnic Institute Worcester MA USA

In this paper, we study the interaction of an absorbing boundary condition (ABC) with the discretization error. In many cases the major source of error is due to the discretization error and how it couples to the ABC. In order to study the ABC, we consider three methods to solve the problem. Two of these are finite element methods with either nodal elements or the recently proposed solenoidal elements. The third is based on analytical methods. The effect of electrical size of the geometry as well as the excitation on the error is studied within the context of the interaction between numerical dispersion and the ABC errors.

关键词： Electromagnetic wave absorption

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：