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Articles 1 - 30 of 46
Full-Text Articles in Engineering
Semiconductor P-N Junction Space Charge Region Capacitance, Mohammad Humayun Habib
Semiconductor P-N Junction Space Charge Region Capacitance, Mohammad Humayun Habib
Dissertations and Theses
The classical capacitance voltage characteristics based on the depletion approximation, is adequate at reverse bias, but introduces errors at high forward bias. Because of its inherent simplicity and compactness this classical depletion model is well studied and widely used in circuit simulators. In this work, a new model for the semiconductor space charge region (SCR) capacitance, based on physical justification, will be derived. This new model takes three input parameters, C0 , Vbi and m, thus eliminating the fitting parameter FC currently used in SPICE. This new model is applicable for any applied voltage and will be compared with the …
Development And Analysis Of Non-Delay-Line Constant-Fraction Discriminator Timing Circuits, Including A Fully-Monolithic Cmos Implementation, David Martin Binkley
Development And Analysis Of Non-Delay-Line Constant-Fraction Discriminator Timing Circuits, Including A Fully-Monolithic Cmos Implementation, David Martin Binkley
Doctoral Dissertations
A constant-fraction discriminator (CFD) is a time pick-off circuit providing time derivation that is insensitive to input-signal amplitude and, in some cases, input-signal rise time. CFD time pick-off circuits are useful in Positron Emission Tomography (PET) systems where Bismuth Germanate (BGO)/photomultiplier scintillation detectors detect coincident, 511-keV annihilation gamma rays.
Time walk and noise-induced timing jitter in time pick-off circuits are discussed along with optimal and sub-optimal timing filters designed to minimize timing jitter. Additionally, the effects of scintillation-detector statistics on timing performance are discussed, and Monte Carlo analysis is developed to provide estimated timing and energy spectra for selected detector …
Fabrication And Characterization Of Gated Silicon Field Emission Micro Triodes, Nanchou Liu
Fabrication And Characterization Of Gated Silicon Field Emission Micro Triodes, Nanchou Liu
Dissertations
This dissertation describes the fabrication technology and characterization of a gated silicon field emission micro triode that is a novel electron tunneling device for generating electron emission into a vacuum. Conic (point) and wedge field emitter structures with nm-scale radii were fabricated in silicon and GaAs by etching, MOCVD and dry oxidation. A new self-aligned process was developed for fabrication of vertical field emission triodes. This process allows control of gate opening to less than 0.5 μm diameter without the need of electron-beam writing. It also provides a planar gate electrode and a thick dielectric layer for reduction of the …
Point Pattern Matching By Heuristic Methods : A Genetic Algorithm And Simulated Annealing, Erh-Chin Chen
Point Pattern Matching By Heuristic Methods : A Genetic Algorithm And Simulated Annealing, Erh-Chin Chen
Theses
The problem we consider is to find a subset of points in a pattern that best match to a subset of points in another pattern through a transformation in an optimal sense. Exhaustive search to find the best assignment mapping one set of points to another set is, if the number of points that are to be matched is large, computationally expensive. We propose two stochastic searching techniques - a genetic algorithm and simulated annealing to search for the best ("almost the best") assignment efficiently. To make the comparison between GA and SA fair, we introduce a piece-wise linear cooling …
Adaptive Map Configuration And Dynamic Routing To Optimize The Performance Of A Satellite Communication Network, Santhalingam Balasekar
Adaptive Map Configuration And Dynamic Routing To Optimize The Performance Of A Satellite Communication Network, Santhalingam Balasekar
Theses
Availability of alternate routes are shown to enhance the performance of non-hierarchical circuit switched networks at moderate load conditions on which the networks typically operate. But alternate routes introduce instability at heavy and overloaded conditions and at these load conditions the network performance is found to deteriorate. To alleviate this problem, one of the control mechanism used is to reserve a fraction of the capacity of each link for direct routed calls. In this work, the feasibility of changing the facilities of a satellite network is taken advantage in optimizing the performance of such a network. A mesh connected, circuit …
An Information Theoretic Approach To Dsn Evaluation, Vivek Mehrotra
An Information Theoretic Approach To Dsn Evaluation, Vivek Mehrotra
Theses
Evaluation of Distributed Sensor Networks (DSN's) for optimal detection using Bayesian cost formulation methods has been the objective of several studies. There have been a few studies on DSN evaluation using an information theoretic approach, wherein an assymetric channel models a detector. We look at the multi-sensor system at the receiver as a black-box and model it as an assymetric channel whose cross over probabilities depend on the probabilties of detection and of false alarm. These probabilities in turn depend on the thresholds of the local detectors and on the fusion rule used. We consider the case wherein the receiver …
Bragg Reflection Grating Waveguide, Wei Zhong
Bragg Reflection Grating Waveguide, Wei Zhong
Theses
Bragg reflection waveguides (BRW) are non-conventional optical guides in which optical confinement is achieved via periodic set of grooves or stratified media along the guiding path. BRW may also serve as optical filters, because of spectral discrimination of the guiding process. A novel UV laser ablation technique was used in this thesis to fabricate periodic metal-clad polymeric waveguides. Spin-on technique was applied to fabricate the waveguide core on glass substrates, evaporation of metal film and selective ablation process defined the optical guides. Various periodicities have been fabricated and the near field patterns have been measured to compare the different guiding …
Modification, Reimplementation And Studies Using The Meisner Model Of The Heart, Ari Zvi Zivotofsky
Modification, Reimplementation And Studies Using The Meisner Model Of The Heart, Ari Zvi Zivotofsky
Theses
The study of left ventricular filling in both the normal and the pathological heart is of great importance. A computer model simulation of the heart with emphasis on mitral flow was designed by Meisner in 1986 and implemented in QuickBASIC. This paper discusses how the original program was altered to be able to perform "Parameter vs. Parameter" runs in which it can be observed how varying an input parameter affects output parameters. The output data is then formatted in such a way that it can be used by QUATTRO PRO, a standard spreadsheet package, to yield graphical outputs.
In addition, …
Minimization Of Exclusive Sum Of Products Expressions For Multiple-Valued Input Incompletely Specified Functions, Ning Song
Dissertations and Theses
In recent years, there is an increased interest in the design of logic circuits which use EXOR gates. Particular interest is in the minimization of arbitrary Exclusive Sums Of Products (ESOPs). Functions realized by such circuits can have fewer gates, fewer connections, and take up less area in VLSI and especially, FPGA realizations. They are also easily testable. So far, the ESOPs are not as popular as their Sum of Products (SOP) counterparts. One of the main reasons it that the problem of the minimization of ESOP circuits was traditionally an extremely difficult one. Since exact solutions can be practically …
Text-Independent Automatic Speaker Identification Using Partitioned Neural Networks, Laszlo Rudasi
Text-Independent Automatic Speaker Identification Using Partitioned Neural Networks, Laszlo Rudasi
Electrical & Computer Engineering Theses & Dissertations
This dissertation introduces a binary partitioned approach to statistical pattern classification which is applied to talker identification using neural networks. In recent years artificial neural networks have been shown to work exceptionally well for small but difficult pattern classification tasks. However, their application to large tasks (i.e., having more than ten to 20 categories) is limited by a dramatic increase in required training time. The time required to train a single network to perform N-way classification is nearly proportional to the exponential of N. In contrast, the binary partitioned approach requires training times on the order of N2. …
Performance Evaluation Of Spread Spectrum System With Cochannel Interference Through A Nonlinear Channel, Yong H. Kim
Performance Evaluation Of Spread Spectrum System With Cochannel Interference Through A Nonlinear Channel, Yong H. Kim
Dissertations
This thesis deals with the problem of more than one subscriber transmitting data signals through a common satellite repeater using code division multiplexing to separate the signals. We are concerned with the problem of amplifying two DS spread spectrum signals, both QPSK or BPSK modulated, in a common device in which limiting occurs. One signal is considered the signal we desire to receive, and the other, having the same nominal carrier frequency with a small random offset, is considered to be a cochannel interferer. The case of a cochannel interferer on the uplink and downlink in QPSK signalling and BPSK …
Process Technology And Characterization For Field Emission Devices, Jong Min Kim
Process Technology And Characterization For Field Emission Devices, Jong Min Kim
Dissertations
Vacuum microelectronics is a new research field which applies semiconductor process technology to the fabrication of micron-dimensioned electron devices. Vacuum microelectronics is made possible by advances in microstructures and nanofabrication technology. Vacuum microelectronic devices are further characterized by a wide operating temperature range, nuclear radiation immunity, higher emission current density potential, and lower power consumption than that of thermionic emitters. The low mass of the electron provides a higher carrier mobility than GaAs or any solid state device. These features offer the potentials for wide variety of applications.
In this dissertation. electron field emission structures applicable to a variety of …
Investigation Of Epitaxial Lift-Off Gaas And Langmuir-Blodgett Films For Optoelectronic Device Applications, Divyang M. Shah
Investigation Of Epitaxial Lift-Off Gaas And Langmuir-Blodgett Films For Optoelectronic Device Applications, Divyang M. Shah
Dissertations
Epitaxial lift-off (ELO), a technique of removing an epitaxially grown GaAs layer from its growth substrate by selective etching of an AlAs sacrificial layer, is described for field-effect transistor fabrication independent of the GaAs growth substrate. Metal Semiconductor Field-Effect Transistors (MESFETs) and High Electron Mobility Transistors (HEMTs) fabricated on silicon and sapphire substrates using ELO are investigated. A 0.1 μm gate length depletion mode MESFET made on silicon exhibited a unity current gain frequency ft = 34 GHz. Excellent device isolation with subpicoampere leakage currents is obtained. A high input impedance amplifier has been implemented on silicon substrate using …
An Embedded Controller-Based Fiber Optic Sensor For Use In Fresh Concrete, Zhaowu Zhang
An Embedded Controller-Based Fiber Optic Sensor For Use In Fresh Concrete, Zhaowu Zhang
Theses
The principle of refraction and reflection of light in optical fibers is applied to detection of air bubbles in a previous thesis. In the earlier work, a microcomputer was employed in acquisition and processing of air bubble data. In the present thesis, an embedded controller system is interfaced and programmed in order to replace the microcomputer. In this way, the system can be more easily integrated into field construction operations. Reflected light intensity signals are detected and analyzed by a microcontroller. The entrained percentage of air in concrete is displayed immediately. The signal can be transferred through a UART (Universal …
Analysis Of Electric Field On Surface Of An Atomically Sharp Field Emitter, Ziyan Cheng
Analysis Of Electric Field On Surface Of An Atomically Sharp Field Emitter, Ziyan Cheng
Theses
In this thesis, exact calculation and computer simulation of an atomically sharp emitter are presented. In the theoretical analysis, the cathode-anode or cathode-gate complex is modeled for cone- and wedge-shaped emitters so that exact solution can be obtained. The exact solution reveals that the field on the emitter surface depends not only on the sharpness of the emitter, but also on the global geometry of the field emitter, gate, and anode complex. This finding is contrary to a widely accepted concept that field is predominantly determined only by local curvature of the tip.
The theoretical results are confirmed by computer …
Modeling And Performance Of Token Bus Lan With Petri Nets, Zhenggang Pan
Modeling And Performance Of Token Bus Lan With Petri Nets, Zhenggang Pan
Theses
A token bus local area network (LAN) is analyzed by Generalized Stochastic Petri Nets (GSPN). The GSPN models of both a single station and LAN for four types of service schemes are obtained and their liveness property is proved. The network performance parameters comprise throughput and delay. The performance analysis for both symmetric and asymmetric single-service systems is conducted for varying load. In order to analyze a token bus LAN with a large number of stations, an approximation method is developed to resolve the .state space explosion problem. A token bus LAN with twenty-one stations is used to show the …
Optimization Of A 3-Micron Bccd Process For High Density Ccd Registers, Mark Ratner
Optimization Of A 3-Micron Bccd Process For High Density Ccd Registers, Mark Ratner
Theses
In July 1991, Dr. Walter F. Kosonocky proposed a High-Frame-Rate-CCD Imager. The design of the imager is such that the CCD channel width be 3-microns and capable of handling at least 3000 - 5000 electrons per square micron. Using process (SUPREM III) and device (PISCES IIB) simulations, charge handling capacities as a function of implant energy and junction depth were studied. Arsenic implants ranging from 100 to 200keV were driven-in to obtain junction depths between 0.40µm and 0.80µm. As a result of this work it was determined that charge handling capacities as high as 9400 electrons/µm2 were achievable with …
Comparing Techniques Of Mapping Pyramid Algorithms Onto The Hypercube : A Case Study For The Connection Machine, Muhammad Ali Siddiqui
Comparing Techniques Of Mapping Pyramid Algorithms Onto The Hypercube : A Case Study For The Connection Machine, Muhammad Ali Siddiqui
Theses
The pyramid structure is most widely used for low-level and intermediate-level image processing and computer vision because of its efficient support of both local and global operations. However, the cost of pyramid computers (PC) may be very high. They also do not support the efficient implementation of the majority of the scientific algorithms. In contrast, the hypercube network has widely been used in the field of parallel processing because it offers a high degree of fault tolerance, a small diameter and rich interconnection structure that permits fast communication at a reasonable cost. Thus, several algorithms have been developed for the …
Improvement Of Light Collection Efficiency By Laser-Induced Patterning The Surface Of Schottky-Barrier Solar Cells, Kejia Fang
Theses
In order to achieve maximum light collection efficiency in silicon made solar cells, reflectivity of the silicon surface must be reduced to as low level as possible. In the past, researchers have concentrated on coating the Si surfaces with anti-reflection coatings. Another approach was to form textures on the Si wafers to capture further the light impinging on the solar cells.
Theoretical studies, which were based on ray tracing approach, revealed that some geometrical patterns are better capturing the light than others. In this work, different geometrical surface configurations on a Cu/n-Si Schottky-barrier solar cell have been investigated. The configurations …
Processor Allocation Strategies For Modified Hypercubes, Nagasimha G. Haravu
Processor Allocation Strategies For Modified Hypercubes, Nagasimha G. Haravu
Theses
Parallel processing has been widely accepted to be the future in high speed computing. Among the various parallel architectures proposed/implemented, the hypercube has shown a lot of promise because of its poweful properties, like regular topology, fault tolerance, low diameter, simple routing, and ability to efficiently emulate other architectures. The major drawback of the hypercube network is that it can not be expanded in practice because the number of communication ports for each processor grows as the logarithm of the total number of processors in the system. Therefore, once a hypercube supercomputer of a certain dimensionality has been built, any …
A New Method To Optimize The Satellite Broadcasting Schedules Using The Mean Field Annealing Of A Neural Network, Youyi Yu
Theses
This thesis reports a new method for optimizing satellite broadcasting schedules based on the Hopfield neural model in combination with the mean field annealing theory. A clamping technique is used with an associative matrix, thus reducing the dimensions of the solution space. A formula for estimating the critical temperature for the mean field annealing procedure is derived, hence enabling the updating of the mean field theory equations to be more economical. Several factors on the numerical implementation of the mean field equations using a straightforward iteration method that may cause divergence are discussed; methods to avoid this kind of divergence …
Applications Of Digital Signal Processing With Cardiac Pacemakers, Merry Thi Tran
Applications Of Digital Signal Processing With Cardiac Pacemakers, Merry Thi Tran
Dissertations and Theses
Because the voltage amplitude of a heart beat is small compared to the amplitude of exponential noise, pacemakers have difficulty registering the responding heart beat immediately after a pacing pulse. This thesis investigates use of digital filters, an inverse filter and a lowpass filter, to eliminate the effects of exponential noise following a pace pulse. The goal was to create a filter which makes recognition of a haversine wave less dependent on natural subsidence of exponential noise.
Research included the design of heart system, pacemaker, pulse generation, and sensor system simulations. The simulation model includes the following components:
- Signal source, …
A New Approach To The Decomposition Of Incompletely Specified Functions Based On Graph Coloring And Local Transformation And Its Application To Fpga Mapping, Wei Wan
Dissertations and Theses
The thesis presents a new approach to the decomposition of incompletely specified functions and its application to FPGA (Field Programmable Gate Array) mapping. Five methods: Variable Partitioning, Graph Coloring, Bond Set Encoding, CLB Reusing and Local Transformation are developed in order to efficiently perform decomposition and FPGA (Lookup-Table based FPGA) mapping. 1) Variable Partitioning is a high quality hemistic method used to find the "best" partitions, avoiding the very time consuming testing of all possible decomposition charts, which is impractical when there are many input variables in the input function. 2) Graph Coloring is another high quality heuristic\ used to …
Digital Model Of A Generic Infrared Tracker, James Michael Brown
Digital Model Of A Generic Infrared Tracker, James Michael Brown
Graduate Theses - Electrical and Computer Engineering
Personal computer based simulations are popular because of the wide availability of personal computers. In this thesis, a simple simulation model of a generic infrared tracker is developed for the personal computer. This thesis first centers on the definition of a generic infrared tracker and the development of a tracker model. The remainder of this thesis is a description of the personal computer based computer simulation model, and a discussion of results of simulation runs to characterize the tracker model response. The conclusion of this thesis is that the simple simulation model serves both as a prototype for developing a …
On Planar Routing Of Multi-Terminal Nets In Vlsi Physical Design, Jahangir A. Hashmi
On Planar Routing Of Multi-Terminal Nets In Vlsi Physical Design, Jahangir A. Hashmi
Masters Theses
In this thesis, we study two problems related to the physical design of VLSI circuits. One problem is related to the VLSI global routing and the other is related to the detailed routing in a bounded region.
We consider the routing of multiple multi-terminal nets on a single layer. We suggest a new approach for this problem. Our approach is based on simultaneously finding a forest of k non-intersecting spanning trees. We present an O(n^3) algorithm for finding two spanning trees corresponding to two nets on a single layer.
We also study the problem of finding a minimum Steiner tree …
Optimization Of Cryopreservation Protocols For Cardiovascular Tissue, Jianfei Hu
Optimization Of Cryopreservation Protocols For Cardiovascular Tissue, Jianfei Hu
Theses and Dissertations in Biomedical Sciences
The purpose of this research was to determine the effects of cryopreservation on the physical, biochemical and cellular aspects of heart valve tissue. The present study demonstrated that radiolabeled proline accumulation provides a quantitative estimate of total cellular metabolic viability. Radiolabeled inulin was demonstrated to be a useful marker for extracellular tissue space. Assessment of metabolic viability of the cellular population of leaflet tissue as a function of procurement and processing revealed that proline accumulation declined with increasing warm and cold ischemic times. Amphotericin B and streptomycin were toxic to the cells. Cefoxitin, lincomycin, polymyxin B, vancomycin and penicillin had …
Mapping Programs To Parallel Architectures In The Real World, Dezheng Tang
Mapping Programs To Parallel Architectures In The Real World, Dezheng Tang
Dissertations and Theses
Mapping an application program to a parallel architecture can be described as a multidimensional optimization problem. To simplify the problem, we divide the overall mapping process into three sequential substeps: partitioning, allocating, and scheduling, with each step using a few details of the program and architecture description. Due to the difficulty in accurately describing the program and architecture and the fact that each substep uses incomplete information, inaccuracy is pervasive in the real-world mapping process. We hypothesize that the inaccuracy and the use of suboptimal, heuristic mapping methods may greatly affect the mapping or submapping performance and lead to a …
Efficient Hypercube Communications, Shreyas R. Bhatt
Efficient Hypercube Communications, Shreyas R. Bhatt
Theses
Hypercube algorithms may be developed for a variety of communication-intensive tasks such as sending a message from one node to another, broadcasting a message from one node to all others, broadcasting a message from each node to all others, all-to-all personalized communication, one-to-all personalized communication, and exchanging messages between nodes via fixed permutations. All these communication patterns are special cases of many-to-many personalized communication. The problem of many-to-many personalized communication is investigated here.
Two routing algorithms for many-to-many personalized communication are presented here. The algorithms proposed yield very high performance with respect to the number of time steps and packet …
Ion Exchanged Glass Waveguides With Efficient Coupling To Fibers And Lasers, Shiqing Hu
Ion Exchanged Glass Waveguides With Efficient Coupling To Fibers And Lasers, Shiqing Hu
Theses
To be of practical use in optical communications networks, optical components must have both low on-chip losses and efficient coupling to fibers, semiconductor lasers and detectors. In this thesis work two types of channel waveguides were designed and fabricated on BK7 glass substrate using a low-cost ion-exchange process. The first type of waveguide was formed in a simple sequence of ion-exchange and post-exchange annealing. These single mode waveguides had large mode size and were efficiently coupled to single mode fibers. The lowest loss achieved in fiber-guide direct coupling was 1.25 dB. The second type of waveguide was formed in a …
Conditional Artificial Dielectric : Optically Controlled Microwave Modulator, J. Manuel Jimenez
Conditional Artificial Dielectric : Optically Controlled Microwave Modulator, J. Manuel Jimenez
Theses
A conditional artificial dielectric with embeddings of either CdS, GaAs or Si in PMMA form the dielectric material of a microstrip in a homodyne microwave detection system. The system consists of a Michelson or Mach-Zehnder interferometers with the microstrip placed in one arm. The index of refraction of the microstrip substrate is modulated by chopped incident light causing amplitude and phase variations in the incoming RF signal. Those variations are detected by mixing the light modulated microwave carrier(information channel) with the unmodulated carrier (reference channel) in the interferometer. The output is sensed by the square law detector and a lock-in …