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2006

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Articles 1861 - 1890 of 3391

Full-Text Articles in Engineering

Direct Torque Control Of Five-Phase Induction Motor Using Space Vector Modulation With Harmonics Elimination And Optimal Switching Sequence, Shuai Lu, Keith Corzine Mar 2006

Direct Torque Control Of Five-Phase Induction Motor Using Space Vector Modulation With Harmonics Elimination And Optimal Switching Sequence, Shuai Lu, Keith Corzine

Electrical and Computer Engineering Faculty Research & Creative Works

In this paper an effective direct torque control (DTC) for a 5-phase induction motor with sinusoidally distributed windings is developed. First by coordinate transformation, the converter/motor models are represented by two independent equivalent d-q circuit models; and the 5-phase VSI input are decoupled into the torque producing and non-torque producing harmonics sets. Then with the torque production component of the induction motor model, the space vector modulation (SVM) can be applied to the five-phase induction motor DTC control, resulting in considerable torque ripple reduction over the lookup table method. Based on the decoupled system model, the current distortion issue due …

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Intersection Safety, Aemal Khattak Mar 2006

Intersection Safety, Aemal Khattak

Nebraska Department of Transportation: Research Reports

The objectives of this project included a study to determine the safety effects of intersection type (unsignalized, signalized, and interchange) on Nebraska expressway intersections, quantification of the safety effects of a Collision Countermeasure System (CCS), and update of the Nebraska Department of Roads (NDOR) expressway intersection guidelines. The CCS is an Intelligent Transportation Systems (ITS) traffic control device to warn drivers of conflicting cross-traffic at rural, non-signalized intersections. The goal was that if found effective, the CCS will become part of the intersection designer’s options for expressway intersection design (other options being an interchange, traffic signals, and traffic control signs). …

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Restricted-Zone Requirements For Superpave Mixes Made With Local Aggregate Sources, Yong-Rak Kim Mar 2006

Restricted-Zone Requirements For Superpave Mixes Made With Local Aggregate Sources, Yong-Rak Kim

Nebraska Department of Transportation: Research Reports

No abstract provided.

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Using Case-Based Reasoning For Spam Filtering, Sarah Jane Delany Mar 2006

Using Case-Based Reasoning For Spam Filtering, Sarah Jane Delany

Doctoral

pam is a universal problem with which everyone is familiar. Figures published in 2005 state that about 75% of all email sent today is spam. In spite of significant new legal and technical approaches to combat it, spam remains a big problem that is costing companies meaningful amounts of money in lost productivity, clogged email systems, bandwidth and technical support. A number of approaches are used to combat spam including legislative measures, authentication approaches and email filtering. The most common filtering technique is content-based filtering which uses the actual text of the message to determine whether it is spam or …

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Long-Term Mechanical Behavior Of Yucca Mountain Tuff And Its Variability, Jaak J.K. Daemen, Lumin Ma, Guohua Zhao Mar 2006

Long-Term Mechanical Behavior Of Yucca Mountain Tuff And Its Variability, Jaak J.K. Daemen, Lumin Ma, Guohua Zhao

Publications (YM)

The study of the long term mechanical behavior of Yucca Mountain tuffs is important for several reasons. Long term stability of excavations will affect accessibility (e.g. for inspection purposes), and retrievability. Long term instabilities may induce loading of drip shields and/or emplaced waste, thus affecting drip shield and/or waste package corrosion. Failure of excavations will affect airflow, may affect water flow, and may affect temperature distributions. The long term mechanical behavior of “hard” rocks remains an elusive topic, loaded with uncertainties. A variety of approaches have been used to improve the understanding of this complex subject, but it is doubtful …

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Convergence Of Ipsec In Presence Of Resets, Chin-Tser Huang, Mohamed G. Gouda, E.N. Elnozahy Mar 2006

Convergence Of Ipsec In Presence Of Resets, Chin-Tser Huang, Mohamed G. Gouda, E.N. Elnozahy

Faculty Publications

IPsec is the current security standard for the Internet Protocol IP. According to this standard, a selected computer pair (p, q) in the Internet can be designated a “security association”. This designation guarantees that all sent IP messages whose original source is computer p and whose ultimate destination is computer q cannot be replayed in the future (by an adversary between p and q) and still be received by computer q as fresh messages from p. This guarantee is provided by adding increasing sequence numbers to all IP messages sent from p to q. Thus, p needs to always remember …

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Fusion Of Microwave And Eddy Current Data For A Multi-Modal Approach In Evaluating Corrosion Under Paint And In Lap Joints, Kapil Gupta, Mohammad Tayeb Ahmad Ghasr, Sergey Kharkovsky, R. Zoughi, R. Joe Stanley, Ajay Padwal, Matthew O'Keefe, Donald D. Palmer, J. Blackshire, Gary Steffes, N. Wood Mar 2006

Fusion Of Microwave And Eddy Current Data For A Multi-Modal Approach In Evaluating Corrosion Under Paint And In Lap Joints, Kapil Gupta, Mohammad Tayeb Ahmad Ghasr, Sergey Kharkovsky, R. Zoughi, R. Joe Stanley, Ajay Padwal, Matthew O'Keefe, Donald D. Palmer, J. Blackshire, Gary Steffes, N. Wood

Electrical and Computer Engineering Faculty Research & Creative Works

Critical aircraft structures are susceptible to hidden corrosion. Find-it and fix-it approaches are inefficient as it relates to managing the problems associated with corrosion. More comprehensive corrosion information may be obtained using data fusion from several detection and evaluation methods. To this end, microwave, conventional and pulsed eddy current data from a multi-layer corroded panel, representing an aircraft lap joint, are fused and used as inputs to a structural analysis model to obtain a comprehensive snapshot of the corroded environment. This paper presents the data fusion algorithm and the structural analysis model along with a discussion of the results.

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Acoustic Detection And Classification Of Microchiroptera Using Machine Learning: Lessons Learned From Automatic Speech Recognition, Mark D. Skowronski, John G. Harris Mar 2006

Acoustic Detection And Classification Of Microchiroptera Using Machine Learning: Lessons Learned From Automatic Speech Recognition, Mark D. Skowronski, John G. Harris

Electrical and Computer Engineering Faculty Research & Creative Works

Current automatic acoustic detection and classification of microchiroptera utilize global features of individual calls (i.e., duration, bandwidth, frequency extrema), an approach that stems from expert knowledge of call sonograms. This approach parallels the acoustic phonetic paradigm of human automatic speech recognition (ASR), which relied on expert knowledge to account for variations in canonical linguistic units. ASR research eventually shifted from acoustic phonetics to machine learning, primarily because of the superior ability of machine learning to account for signal variation. To compare machine learning with conventional methods of detection and classification, nearly 3000 search-phase calls were hand labeled from recordings of …

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Bs News Mar 2006

Bs News

Building Services Engineering

No abstract provided.

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Polarizing Properties Of Embedded Symmetric Trilayer Stacks Under Conditions Of Frustrated Total Internal Reflection, Rasheed M.A. Azzam, Siva R. Perla Mar 2006

Polarizing Properties Of Embedded Symmetric Trilayer Stacks Under Conditions Of Frustrated Total Internal Reflection, Rasheed M.A. Azzam, Siva R. Perla

Electrical Engineering Faculty Publications

An all-transparent symmetric trilayer structure, which consists of a high-index center layer coated on both sides by a low-index film and embedded in a high-index prism, can function as an efficient polarizer or polarizing beam splitter under conditions of frustrated total internal reflection over a wide range of incidence angles. For a given set of refractive indices, all possible solutions for the thicknesses of the layers that suppress the reflection of either the p or s polarization at a specified angle, as well as the reflectance of the system for the orthogonal polarization, are determined. A 633 nm design that …

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Effect Of Gravity On Methanol Diffusion Flames Burning Within A Forced Convective Environment, V. Raghavan, G. Gogos, V. Babu, T. Sundararajan Mar 2006

Effect Of Gravity On Methanol Diffusion Flames Burning Within A Forced Convective Environment, V. Raghavan, G. Gogos, V. Babu, T. Sundararajan

Combustion Research at University of Nebraska-Lincoln

Effect of Gravity on Methanol Diffusion Flames Burning within a Forced Convective Environment

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Doppler-Only Multistatic Radar, Dustin G. Mixon Mar 2006

Doppler-Only Multistatic Radar, Dustin G. Mixon

Theses and Dissertations

In order to estimate the position and velocity of a target, most multistatic radar systems require multiple independent target measurements, such as angle-of-arrival, time-of-arrival, and Doppler information. Though inexpensive and reliable, Doppler-only systems have not been widely implemented due to the inherent nonlinear problem of determining a target’s position and velocity from their measurements. We solve this problem. In particular, we first establish the lack of observability in the Doppler-only bistatic system, thereby demonstrating the need for multiple transmitters and/or receivers. Next, for a multistatic system with a sufficient number of transmitter-receiver pairs, we invoke classical optimization techniques, such as …

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A Climatological Study Of Equatorial Gps Data And The Effects On Ionospheric Scintillation, Katharine A. Wicker Mar 2006

A Climatological Study Of Equatorial Gps Data And The Effects On Ionospheric Scintillation, Katharine A. Wicker

Theses and Dissertations

Ionospheric scintillation is detrimental to radio signals, especially those from the global positioning system. Such scintillation is caused when a signal permeates the ionosphere through plasma bubbles. The signal’s phase and amplitude can be altered, and a receiver on the ground can lose lock on the GPS signal. Measured using a zero to one index known as S4, scintillation severity is based upon season, solar cycle, time of day, location and frequency. The most severe scintillation occurs at the equatorial anomaly, or fifteen degrees north and south of the equator. Seven years of data from fifteen different locations around the …

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Roadblocks To Software Modernization, Dyan E. Mcclamma Mar 2006

Roadblocks To Software Modernization, Dyan E. Mcclamma

Theses and Dissertations

Failed or troubled modernization efforts, such as the multi-million dollar 1997-2000 ROCC/SOCC failure, are a serious acquisition problem for the Air Force. Using both historical data and a survey of current Air Force software acquisition program key staff, this research examined the Air Forces ability to modernize legacy software systems. The search of historical program data, to identify trends or similarities between known failed software modernization efforts, failed to uncover sufficient data for analysis. This lack of project data indicates a knowledge management issue (i.e. lessons learned are not recorded and stored so that they can be accessed by other …

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Optimizing Mean Mission Duration For Multiple-Payload Satellites, John A. Flory Mar 2006

Optimizing Mean Mission Duration For Multiple-Payload Satellites, John A. Flory

Theses and Dissertations

This thesis addresses the problem of optimally selecting and specifying satellite payloads for inclusion on a satellite bus to be launched into a constellation. The objective is to select and specify payloads so that the total lifetime utility of the constellation is maximized. The satellite bus is limited by finite power, weight, volume, and cost constraints. This problem is modeled as a classical knapsack problem in one and multiple dimensions, and dynamic programming and binary integer programming formulations are provided to solve the problem. Due to the computational complexity of the problem, the solution techniques include exact methods as well …

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Polar Phase Screens: A Comparison With Other Methods Of Random Phase Screen Generation, Rebecca J. Eckert Mar 2006

Polar Phase Screens: A Comparison With Other Methods Of Random Phase Screen Generation, Rebecca J. Eckert

Theses and Dissertations

This research provides the first organized comparison of random phase screen generation methods, including logarithmic polar Fourier series, using structure functions. Random phase screens are essential elements of simulating light propagation through turbulent media. In order to be effective, they must accurately reflect theory and be practical to implement. This research explains and evaluates three methods of generating random phase screens: using a Fourier series upon a polar frequency grid with logarithmic spacing; using the fast Fourier transform, with its Cartesian frequency grid; and using Zernike polynomials. It provides a comparison of the Polar Fourier Series technique with the two …

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Power-Scavenging Mems Robots, Daniel J. Denninghoff Mar 2006

Power-Scavenging Mems Robots, Daniel J. Denninghoff

Theses and Dissertations

This thesis includes the design, modeling, and testing of novel, power-scavenging, biologically inspired MEMS microrobots. Over one hundred 500-μm and 990-μm microrobots with two, four, and eight wings were designed, fabricated, characterized. These microrobots constitute the smallest documented attempt at powered flight. Each microrobot wing is comprised of downward-deflecting, laser-powered thermal actuators made of gold and polysilicon; the microrobots were fabricated in PolyMUMPs® (Polysilicon Multi-User MEMS Processes). Characterization results of the microrobots illustrate how wing-tip deflection can be maximized by optimizing the gold-topolysilicon ratio as well as the dimensions of the actuator-wings. From these results, an optimum actuator-wing configuration was …

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Evaluating The Correlation Characteristics Of Arbitrary Am And Fm Radio Signals For The Purpose Of Navigation, Bryan S. Kim Mar 2006

Evaluating The Correlation Characteristics Of Arbitrary Am And Fm Radio Signals For The Purpose Of Navigation, Bryan S. Kim

Theses and Dissertations

The Global Positioning System (GPS) provides position estimates on the Earth at anytime, anywhere and in any weather. However, to provide robust positioning, GPS requires an unobstructed path to satellite signals. As such, GPS performance generally degrades or becomes non-existent in environments such as large urban areas. This research investigates and analyzes the correlation characteristics of arbitrary AM and FM radio signals for the purpose of navigation. Simulations are conducted with different combinations of correlation methods (`fixed' or `varying'), modulation types (AM or FM), and signal types (song or voice). Out of the eight different variations considered, only two provided …

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Investigation Of The Effects Of Target Feature Variations On Ballistic Missile Rcs, Sang H. Lee Mar 2006

Investigation Of The Effects Of Target Feature Variations On Ballistic Missile Rcs, Sang H. Lee

Theses and Dissertations

Uncertainties about certain features of target geometries can result in a loss of confidence in target signature assessment. This thesis describes the development of a general "rule-of-thumb" to determine how the radar signature of a target varies as a function of the target's specific features. The targets of interest in this study are fictitious ballistic missiles. Four target features of these missiles are investigated: fin size, nose cone shape, panel riveting along the sides of the missile, and heat shielding on the nose cone. By varying these target features in different missile configurations, and comparing them to each other, a …

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Characterization And Design Of High-Level Vhdl I/Q Frequency Downconverter Via Special Sampling Scheme, Jesse P. Somann Mar 2006

Characterization And Design Of High-Level Vhdl I/Q Frequency Downconverter Via Special Sampling Scheme, Jesse P. Somann

Theses and Dissertations

This study explores the characterization and implementation of a Special Sampling Scheme (SSS) for In-Phase and Quad-Phase (I/Q) down conversion utilizing top-level, portable design strategies. The SSS is an under-developed signal sampling methodology that can be used with military and industry receiver systems, specifically, United States Air Force (USAF) video receiver systems. The SSS processes a digital input signal-stream sampled at a specified sampling frequency, and down converts it into In-Phase (I) and Quad-Phase (Q) output signal-streams. Using the theory and application of the SSS, there are three main objectives that will be accomplished: characterization of the effects of input, …

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Multi-Dimensional Wave Front Sensing Algorithms For Embedded Tracking And Adaptive Optics Applications, Christopher C. Wood Mar 2006

Multi-Dimensional Wave Front Sensing Algorithms For Embedded Tracking And Adaptive Optics Applications, Christopher C. Wood

Theses and Dissertations

Current tracking and adaptive optics techniques cannot compensate for fast-moving extended objects, which is important for ground-based telescopes providing space situational awareness. To fill this need, a vector-projection maximum-likelihood wave-front sensing algorithm development and testing follows for this application. A derivation and simplification of the Cramer-Rao Lower Bound for wavefront sensing using a laser guide star bounds the performance of these systems and guides implementation of a vastly optimized maximum-likelihood search algorithm. A complete analysis of the bias, mean square error, and variance of the algorithm demonstrates exceptional performance of the new sensor. A proof of concept implementation shows feasibility …

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Evaluation Of Factors Contributing To Damping Of Coated And Uncoated Titanium Plates, Dustin W. Lee Mar 2006

Evaluation Of Factors Contributing To Damping Of Coated And Uncoated Titanium Plates, Dustin W. Lee

Theses and Dissertations

High Cycle Fatigue (HCF) is the leading cause of component failure in gas turbine engines today, which poses great risk to aircraft, engines, and their crews. Mitigation of HCF effects has become a priority topic, and the damping benefits of hard coatings are being reevaluated for this purpose. Research was conducted to further understanding of damping measurements on these coatings. This study continues work to characterize the damping effects of a magnesium aluminate spinel (mag spinel) coating applied to a titanium plate via vibration testing. Two different plate sizes were evaluated in a clamped-free-free-free condition and a free-free-free-free condition, respectively. …

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Optimal Coverage Of Theater Targets With Small Satellite Constellations, Axel Rendon Mar 2006

Optimal Coverage Of Theater Targets With Small Satellite Constellations, Axel Rendon

Theses and Dissertations

The daylight passes of a low-Earth orbit satellite over a targeted latitude and longitude are optimized by varying the inclination and eccentricity of an orbit at different altitudes. This investigation extends the work by Emery et al, in which the optimal Right Ascension of the Ascending Node was determined for a circular, matched inclination orbit. The optimal values were determined by a numerical research method based on Emery et al's Matlab program. Results indicate that small increases in inclination raise the number of daylight passes up to 33%. These optimal inclinations depend on the satellite semi-major axis. Eccentricity increases also …

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Experimental Investigation Into The Aerodynamic Ground Effect Of A Tailless Chevron And Lambda-Shaped Ucavs, Won In Mar 2006

Experimental Investigation Into The Aerodynamic Ground Effect Of A Tailless Chevron And Lambda-Shaped Ucavs, Won In

Theses and Dissertations

As future aircraft migrate toward tailless, blended wing body configurations, aircraft designers are faced with a lack of experimental data that represent these types of configurations. A wind tunnel investigation was conducted to identify the ground effect region of two unmanned combat air vehicle (UCAV) models. The AFIT low-speed wind tunnel (LSWT) and ground plane were used to study the forces and moments on the UCAV models in ground effect. The Chevron and Lambda planforms used in this study were originally tested in full-scale for stability and control without ground effects. A static ground plane was used in this study. …

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Structural Design Of Wing Twist For Pitch Control Of Joined Wing Sensor Craft, Fred A. Kimler Iii Mar 2006

Structural Design Of Wing Twist For Pitch Control Of Joined Wing Sensor Craft, Fred A. Kimler Iii

Theses and Dissertations

This research investigated two aspects of the aft wing structure of a joined wing SensorCraft. First, the efficacy of a novel approach for incorporating wing twist for pitch control was analyzed. This design involved adding a spanwise sliding joint into the wing structure at the lower aft spar of the vehicle's aft wing. Second, the joint section where the forward and aft wings connect and form the outboard wing was redesigned and analyzed to improve the load transmission between the wing spars. Using MSC.NASTRAN, linear and non-linear static analyses were performed to examine the efficiency of the wing twist sliding …

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Store Separations From A Supersonic Cone, Richard J. Simko Mar 2006

Store Separations From A Supersonic Cone, Richard J. Simko

Theses and Dissertations

The purpose of this research was to analyze the environment a store would travel through if ejected from a supersonic cone. This was done using the Beggar Computational Fluid Dynamics (CFD) code from the Air Force SEEK Eagle Office at Eglin Air Force Base, FL. CFD simulations were compared to experimental results from a previous AFIT thesis and conclusions were drawn based on whether or not the current wind tunnel setup at AFIT is capable of performing analyses of supersonic store separations. Also included in this research is a study of supersonic base pressure profiles, near-wake velocity profiles, wind tunnel …

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Cfd Investigation Of The Flow Dynamics Inside A Spherical Surface Indentation, Robert C. Vincent Mar 2006

Cfd Investigation Of The Flow Dynamics Inside A Spherical Surface Indentation, Robert C. Vincent

Theses and Dissertations

This study aims to identify the flow structure inside and around a dimple surface indentation that passively reduces flow separation, and to generate characterization parameters for the effectiveness of the aforementioned flow structure in boundary layer separation control. In this study the surface indentation is cut into a flat plate in a diverging channel that creates an adverse pressure gradient. In the baseline flat plate conditions, the shedding vortices formed by the pressure gradient create an oscillating pressure field in the dimple. This geometry has been chosen to simulate the adverse pressure gradient present in the flow regime found on …

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Comparison Of Variance-To-Mean Ratio Methods For Repairables Inventory Management, Lisa J. Mahon Mar 2006

Comparison Of Variance-To-Mean Ratio Methods For Repairables Inventory Management, Lisa J. Mahon

Theses and Dissertations

In an effort to improve aircraft availability, this research compared the efficiency of ten methods of determining variance-to-mean ratios (VTMRs, VMRs, V/Ms) for repairable, spare aircraft parts known as repairables. These methods are base pipeline quantity, Hill-Stevens (220 LRUs), a variation of Hill-Stevens (10 1s), Hill-Stevens (230 LRUs), the Sherbrooke, a variation of Sherbrooke (10 1s), historical data, a new regression function, variance-to-mean ratio equals 1.00 or variance-to-mean ratio equals 1.01. Using VTMRs derived from quarterly organizational intermediate maintenance (OIM) demands for line-replaceable units (LRUs) from the D200A Secondary Item Requirement System (SIRS) databases in aircraft sustainability model scenarios and …

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Least Squares Support Vector Machine Based Classification Of Abnormalities In Brain Mr Images, S. Thamarai Selvi, D. Selvathi, R. Ramkumar, Henry Selvaraj Mar 2006

Least Squares Support Vector Machine Based Classification Of Abnormalities In Brain Mr Images, S. Thamarai Selvi, D. Selvathi, R. Ramkumar, Henry Selvaraj

Electrical & Computer Engineering Faculty Research

The manual interpretation of MRI slices based on visual examination by radiologist/physician may lead to missing diagnosis when a large number of MRIs are analyzed. To avoid the human error, an automated intelligent classification system is proposed. This research paper proposes an intelligent classification technique to the problem of classifying four types of brain abnormalities viz. Metastases, Meningiomas, Gliomas, and Astrocytomas. The abnormalities are classified based on Two/Three/ Four class classification using statistical and textural features. In this work, classification techniques based on Least Squares Support Vector Machine (LS-SVM) using textural features computed from the MR images of patient are …

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Neutron Multiplicity Measurements For The Afci Program Final Quarterly Progress Report January-March 2006, Denis Beller Mar 2006

Neutron Multiplicity Measurements For The Afci Program Final Quarterly Progress Report January-March 2006, Denis Beller

Transmutation Sciences Physics (TRP)

This project was developed to test a Russian-built Neutron Multiplicity Detector System (NMDS) for measuring neutrons generated in a central target by a variety of accelerators. To assist in experiment design and evaluation, we use the most advanced high-energy radiation transport code, MCNPX, to model experiments. Experimental results are compared to computational predictions and discrepancies are investigated. Initial plans were to conduct experiments using a 70-MeV proton cyclotron at the Crocker Nuclear Laboratory at the University of California at Davis and/or a 20 to 40 MeV electron linac (linear accelerator) at the Idaho Accelerator Center (IAC) at Idaho State University …

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