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2008

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Articles 2341 - 2370 of 4190

Full-Text Articles in Engineering

Computational Design Of Upperstage Chamber, Aerospike, & Cooling Jacket For Dual-Expander Rocket Engine, David F. Martin Ii Mar 2008

Computational Design Of Upperstage Chamber, Aerospike, & Cooling Jacket For Dual-Expander Rocket Engine, David F. Martin Ii

Theses and Dissertations

To increase the performance of the current US satellite launch capability, new rocket designs must be undertaken. One concept that has been around since the 50s but yet to be utilized on a launch platform is the aerospike, or plug nozzle. The aerospike nozzle concept demonstrates globally better performance compared to a conventional bell nozzle, since the expansion of the jet is not bounded by a wall and therefore can adjust to the environment by changing the outer jet boundary. A dual-expander aerospike nozzle (DEAN) rocket concept would exceed the Integrated High Payoff Rocket Propulsion Technology initiative (IHPRPT) phase three …

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Optimal Guidance Of A Relay Mav For Isr Support Beyond Line-Of-Sight, John H. Hansen Mar 2008

Optimal Guidance Of A Relay Mav For Isr Support Beyond Line-Of-Sight, John H. Hansen

Theses and Dissertations

This thesis developed guidance laws to optimally position a relay Micro-UAV (MAV) to provide an operator with real-time Intelligence, Surveillance, and Reconnaissance (ISR) by relaying communication and video signals when there is no line-of-sight between the operator at the base and the rover MAV performing the ISR mission. The ISR system consists of two MAVs, the Relay and the Rover, and a Base. The Relay strives to position itself to minimize the radio frequency (RF) power required for maintaining communications between the Rover and the Base, while the Rover performs the ISR mission, which may maximize the required RF power. …

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Discrete Counting Of Short Lived Isotopes With Low Background Detectors, David E. Mather Mar 2008

Discrete Counting Of Short Lived Isotopes With Low Background Detectors, David E. Mather

Theses and Dissertations

We consider radiation counting experiments used to measure quantities of materials that are short-lived with respect to the count durations. The HPS 13.31 statistical analysis seriously overestimates the uncertainty when the quantity and background are very low. We consider the case in which the objective is to quantify the number of atoms, n, that were present in a sample when it was drawn. Mathews and Gerts [JRNC, 2008] analyzed this case and developed formulas for the probability distribution of n, in order to develop experiment design processes that minimize the smallest detectable quantity of material, thus maximizing sensitivity for the …

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Securing Manets With Bitsi: Danger Theory And Mission Continuity, Marco Carvalho, Richard A. Ford, William H. Allen, Gerald A. Marin Mar 2008

Securing Manets With Bitsi: Danger Theory And Mission Continuity, Marco Carvalho, Richard A. Ford, William H. Allen, Gerald A. Marin

Electrical Engineering and Computer Science Faculty Publications

MANET (Mobile Ad hoc Network) environments are becoming increasingly important as potential users recognize the benefits of being able to create a functional network using little or no fixed infrastructure. Unfortunately, the very properties that provide such flexibility also cause significant complications in terms of security. The collaborative nature of the system combined with its continual state of flux requires solutions that are highly dynamic, and that can adapt to massive changes in system resources, traffic patterns and network topology. In this paper, we outline a new approach to MANET security called BITSI (the Biologically-Inspired Tactical Security Infrastructure). BITSI is …

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Electrochemical Durability Of Carbon Nanotubes At 80 °C, Liang Li, Yangchuan Xing Mar 2008

Electrochemical Durability Of Carbon Nanotubes At 80 °C, Liang Li, Yangchuan Xing

Chemical and Biochemical Engineering Faculty Research & Creative Works

Carbon nanotubes (CNTs) have been studied as an alternative catalyst support in polymer electrolyte membrane (PEM) fuel cells. Recent studies showed that CNTs appear to be more resistant to electrochemical corrosion than carbon black (CB). in a previous study, we have demonstrated the room temperature durability of multiwalled CNTs in both non-catalyzed and catalyzed electrochemical oxidations. This paper is to report results conducted at 80 °C-an operational temperature of PEM fuel cells. It was found that multiwalled CNTs are still more resistant than CB at the elevated temperature. However, the electrochemical oxidation rate is more rapid than that at the …

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Factor Analysis Of Interface Problems Among Construction Parties - A Case Study Of Mrt, Rong-Yau Huang, Chin-Tien Huang, Hung Lin, Wen-Hsiang Ku Mar 2008

Factor Analysis Of Interface Problems Among Construction Parties - A Case Study Of Mrt, Rong-Yau Huang, Chin-Tien Huang, Hung Lin, Wen-Hsiang Ku

Journal of Marine Science and Technology–Taiwan

With the rapid development of technology and the increasingly bigger size of constructions, the involved parties are required to pay more attention to all types of difficult interface problems than ever before. By considering the mass rapid transit system (MRTS) as an example, several problems resulting from complicated mechanical, electrical, civil, and track interfaces led to enormously extra losses in the construction process. Accordingly, this paper intends to use quantitative methods to categorize a variety of interface problems in the MRTS construction projects as well as identify their individual impacts in order to clarify these interface problems. The analysis results …

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Robust Control Of Uncertain Time-Delay Systems Via Sliding Mode Control And Lmi- H∞ Technique, Ming-Chang Pai Mar 2008

Robust Control Of Uncertain Time-Delay Systems Via Sliding Mode Control And Lmi- H∞ Technique, Ming-Chang Pai

Journal of Marine Science and Technology–Taiwan

This paper presents a proportional-integral sliding mode control (PISMC) methodology for a class of linear uncertain systems with state delays. The systems are assumed to have structured, mismatched, and time-varying parameter uncertainties as well as mismatched and bounded external disturbances. Based on Lyapunov stability theorem and linear matrix inequality (LMI) H∞ technique, a sufficient condition is derived to guarantee the global stability of the dynamics and a prescribed H∞ norm bound of disturbance attenuation for all admissible uncertainties. Furthermore, this scheme assures robustness against state delays, parameter uncertainties and disturbances. Finally, an example is given to illustrate the feasibility of …

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Application Of Maximum-Efficiency Tracking Control To Backlight Module Based On Phase-Locked Loop Technique, Chang-Hua Lin, Ying Lu Mar 2008

Application Of Maximum-Efficiency Tracking Control To Backlight Module Based On Phase-Locked Loop Technique, Chang-Hua Lin, Ying Lu

Journal of Marine Science and Technology–Taiwan

Maximum-efficiency tracking control applied in the backlight module is proposed in this paper. The backlight system incorporates a phase-locked loop (PLL) as a feedback mechanism to promote both the system efficiency and stability. To overcome the drawbacks of the conventional electromagnetic transformer and to miniaturize the backlight module, the piezoelectric transformer (PT) is adopted for driving the cold cathode fluorescent lamp (CCFL). To avoid the system efficiency decreases due to the temperature effect of PT, the PLL is utilized to track immediately the optimal operating frequency of PT for achieving maximum output efficiency under various ambient temperatures. The feedback parameter …

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Design And Implementation Of An All-Digital Real-Time Underwater Acoustic Transceiver Using Digital Signal Processors, Fu-Sheng Lu, Ching-Hsiang Tseng, Bin-Chong Wu Mar 2008

Design And Implementation Of An All-Digital Real-Time Underwater Acoustic Transceiver Using Digital Signal Processors, Fu-Sheng Lu, Ching-Hsiang Tseng, Bin-Chong Wu

Journal of Marine Science and Technology–Taiwan

In this paper, an all-digital transceiver for real-time underwater acoustic (UWA) communications is developed using digital signal processors (DSPs). The design of the transceiver is based on the direct-sequence spread-spectrum (DS/SS) modulation scheme, in which the timing synchronization is efficiently achieved by employing a sliding correlator and a modified noncoherent delay-locked loop for code acquisition and tracking, respectively. In addition, an equal-gain combiner (EGC) and an adaptive decision-feedback equalizer (DFE) are included in the receiver to enhance its interference rejection capability under multipath fading environments. Several real-time UWA transmission tests are conducted in an experimental water tank to evaluate the …

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Profile Design Of Piston Ring Using Inverse Method, Li-Ming Chu, Yuh-Ping Chang, Jung-Hua Yang Mar 2008

Profile Design Of Piston Ring Using Inverse Method, Li-Ming Chu, Yuh-Ping Chang, Jung-Hua Yang

Journal of Marine Science and Technology–Taiwan

This study aims to develop an algorithm for designing the piston ring profile and pressure distribution using an inverse method. The proposed algorithm needs to obtain load and boundary conditions for estimating not only a smooth curve in the piston ring profile, but also in the pressure distribution. The algorithm is developed from Reynolds integral and force balance equations. The least-squares error method, variational method, Gauss-Seidel method and Newton-Raphson method are employed to calculate the piston ring profile. Simulation results reveal that the greater the degree of the polynomial function used, the greater the maximum pressure ( Pmax ), load …

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Guaranteed Cost Control Of Uncertain Linear Systems Via Discrete-Time Variable Structure Control, Ming-Chang Pai Mar 2008

Guaranteed Cost Control Of Uncertain Linear Systems Via Discrete-Time Variable Structure Control, Ming-Chang Pai

Journal of Marine Science and Technology–Taiwan

This paper presents a design of realizing the guaranteed cost control problem for uncertain linear systems via discrete-time variable structure control (VSC) scheme. The uncertainties in the system are assumed to be norm-bounded and time-varying. Based on the discrete-time VSC technique, the proposed controller can drive the system into a pre-specified switching surface to obtain the desired dynamic performance and the chattering phenomenon is eliminated. Sufficient conditions for the existence of guaranteed cost control are presented, and the problem of designing guaranteed cost control is converted to a convex optimization problem with linear matrix inequality (LMI) constraints. Finally, simulation results …

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Mesoscale Calculations Of The Dynamic Behavior Of A Granular Ceramic, John Borg, Tracy J. Vogler Mar 2008

Mesoscale Calculations Of The Dynamic Behavior Of A Granular Ceramic, John Borg, Tracy J. Vogler

Mechanical Engineering Faculty Research and Publications

Mesoscale calculations have been conducted in order to gain further insight into the dynamic compaction characteristics of granular ceramics. The primary goals of this work are to numerically determine the shock response of granular tungsten carbide and to assess the feasibility of using these results to construct the bulk material Hugoniot. Secondary goals include describing the averaged compaction wave behavior as well as characterizing wave front behavior such as the strain rate versus stress relationship and statistically describing the laterally induced velocity distribution. The mesoscale calculations were able to accurately reproduce the experimentally determined Hugoniot slope but under predicted the …

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Mobile Free Space Optical Communication System, Xian Wang, Chi Yeh Hsu, Xiaomin Jin Mar 2008

Mobile Free Space Optical Communication System, Xian Wang, Chi Yeh Hsu, Xiaomin Jin

Electrical Engineering

The paper discusses a low power consumption, light weight and low cost 10MHz free-space optical communication (FSO). The system is designed for mounting on mobile platforms, with effective range of at least 50 meters. Light-Emitting Diodes (LEDs) and Laser diodes (LDs) are used in the transmitter for comparison for their relative performance in the system. The receiver features a beam splitter that feeds part of the data link optical signal to a quadrant photodetector and controls a tracking/stabilization system using microcontroller. Since almost all commercial FSO systems are mounted on fixed positions such as buildings, the paper explores the possibility …

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Finite Element Simulation Methods For Dry Sliding Wear, Aaron J. Chmiel Mar 2008

Finite Element Simulation Methods For Dry Sliding Wear, Aaron J. Chmiel

Theses and Dissertations

The Holloman High Speed Test Track is a rocket sled track for testing at hypersonic velocities. However, there are customers that desire to test at even greater velocities. In order to achieve higher velocities there are several phenomena that must be overcome. One important phenomenon is wear of the shoe that holds the sled on the rail. This research is a look at the feasibility of using finite element analysis to predict the wear of the shoe during a test run down the track. Two methods are investigated, one is a macro-scale, incremental method utilizing traditional wear equations from Archard, …

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Filtered Rayleigh Scattering Measurements In A Buoyant Flow Field, Steven M. Meents Mar 2008

Filtered Rayleigh Scattering Measurements In A Buoyant Flow Field, Steven M. Meents

Theses and Dissertations

Filtered Rayleigh Scattering (FRS) is a non-intrusive, laser-based flow characterization technique that consists of a narrow linewidth laser, a molecular absorption filter, and a high resolution camera behind the filter to record images. Gases of different species have different molecular scattering cross-sections that become apparent as they pass through the interrogating laser light source, and this difference is used to discriminate between the different gaseous components. This study focuses on the behavior of a buoyant helium jet exiting horizontally into ambient air, and more specifically this jet’s tendency to form side lobes that are discharged from the core fluid under …

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A Static Aeroelastic Analysis Of A Flexible Wing Mini Unmanned Aerial Vehicle, Nathan A. Pitcher Mar 2008

A Static Aeroelastic Analysis Of A Flexible Wing Mini Unmanned Aerial Vehicle, Nathan A. Pitcher

Theses and Dissertations

The static aeroelastic behavior of the Nighthawk mini unmanned aerial vehicle is examined using a combined experimental and computational approach. Three wings are examined. In order of increasing stiffness they are: a flexible wing, a stiff wing, and a fictitious rigid wing with zero deflection. Photogrammetry is used during wind tunnel testing to measure the average deflected shape of the flexible and stiff wings during flight. The independent variables during wind tunnel tests are angle of attack (ranging from −5.1° through 13.4°) and velocity, which is 20 mph, 30 mph, and 40 mph. Roll angle and yaw angle are control …

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Biomimetic Micro Air Vehicle Testing Development And Small Scale Flapping-Wing Analysis, Craig E. Svanberg Mar 2008

Biomimetic Micro Air Vehicle Testing Development And Small Scale Flapping-Wing Analysis, Craig E. Svanberg

Theses and Dissertations

The purpose of this research was to develop testing methods capable of analyzing the performance of a miniature flapping-wing mechanism that can later be adapted to a biomimetic micro air vehicle (MAV). Three small scale flapping mechanisms capable of single plane flapping, flapping with active pitch control, and flapping/pitch with out-of-plane movement were designed using SolidWorks. The flapping-only model was fabricated on an Objet Eden 500V 3-dimensional printer. The flapping mechanism was mounted on an aluminum plate supported by air bearings, and thrust was measured for a variety of conditions. The testing was conducted using wings composed of carbon fiber …

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Minimizing Secular J2 Perturbation Effects On Satellite Formations, Jonathan W. Wright Mar 2008

Minimizing Secular J2 Perturbation Effects On Satellite Formations, Jonathan W. Wright

Theses and Dissertations

The purpose of this thesis is to examine the secular effects of the J2 oblateness perturbation on close proximity satellites. The main objective is to analyze the deputy’s position and velocity with respect to the chief and adjust the initial conditions of the deputy in an attempt to minimize the secular effects of J2 perturbations. Previous work has provided a method of obtaining a closed form solution for J2 invariance with co-planar orbits. Therefore, this work will primarily consider deputy orbits that experience motion outside of the chief’s orbital plane. Upon determining the required initial conditions, the …

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Modeling Gps Satellite Orbits Using Kam Tori, Rachel M. Derbis Mar 2008

Modeling Gps Satellite Orbits Using Kam Tori, Rachel M. Derbis

Theses and Dissertations

Global Positioning System (GPS) satellite orbits are modeled using Kolmogorov, Arnold, Moser (KAM) tori. Precise Global Positioning System satellite locations are analyzed using Fourier transforms to identify the three basis frequencies in an Earth Centered, Earth Fixed (ECEF) rotating reference frame. The three fundamental frequencies are 1) the anomalistic frequency, 2) a combination of earth’s rotational frequency and the nodal regression rate, and 3) the apsidial regression rate. A KAM tori model fit to the satellite data could be used to predict future satellite locations. This model would allow rapid determination with fewer computational requirements than the typical method of …

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Demonstration Of A Strategy To Perform Two-Dimensional Diode Laser Tomography, Ryan N. Givens Mar 2008

Demonstration Of A Strategy To Perform Two-Dimensional Diode Laser Tomography, Ryan N. Givens

Theses and Dissertations

Demonstration of a strategy to perform two-dimensional diode laser tomography using a priori knowledge from symmetry arguments and computational fluid dynamic (CFD) calculations is presented for a flat flame burner. The strategy uses an optimization technique to determine flame diameter and location using a vector quantization approach. Next, the variance in a training set, produced from CFD calculations, is captured using principal components analysis. The information in the training set allows interpolation between beam paths resulting in temperature and density maps. Finally, the TDLAS temperature and density maps are shown to agree with traditional thermocouple measurements of the flat flame …

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Analyzing Carbohydrate-Based Regenerative Fuel Cells As A Power Source For Unmanned Aerial Vehicles, Olek Wojnar Mar 2008

Analyzing Carbohydrate-Based Regenerative Fuel Cells As A Power Source For Unmanned Aerial Vehicles, Olek Wojnar

Theses and Dissertations

Based on current capabilities, we examine the feasibility of creating a carbohydrate-based regenerative fuel cell (CRFC) as the primary power source for unmanned aerial vehicles (UAV) for long endurance missions where station keeping is required. A CRFC power system is based on a closed-loop construct where carbohydrates are generated from zooxanthellae, algae that create excess carbohydrates during photosynthesis. The carbohydrates are then fed to a carbohydrate fuel cell where electric power is generated for the UAV’s propulsion, flight control, payload, and accessory systems. The waste products from the fuel cell are used by the zooxanthellae to create more carbohydrates, therefore …

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Look After The Risks, Ask The Right Questions – And Know How To Get Out, Lorcan Sirr Mar 2008

Look After The Risks, Ask The Right Questions – And Know How To Get Out, Lorcan Sirr

Media

No abstract provided.

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Utility Of Daily Vs. Monthly Large-Scale Climate Data: An Intercomparison Of Two Statistical Downscaling Methods, Edwin P. Maurer, Hugo G. Hidalgo Mar 2008

Utility Of Daily Vs. Monthly Large-Scale Climate Data: An Intercomparison Of Two Statistical Downscaling Methods, Edwin P. Maurer, Hugo G. Hidalgo

Civil, Environmental and Sustainable Engineering

Downscaling of climate model data is essential to local and regional impact analysis. We compare two methods of statistical downscaling to produce continuous, gridded time series of precipitation and surface air temperature at a 1/8-degree (approximately 140 km2 per grid cell) resolution over the western U.S. We use NCEP/NCAR Reanalysis data from 1950–1999 as a surrogate General Circulation Model (GCM). The two methods included are constructed analogues (CA) and a bias correction and spatial downscaling (BCSD), both of which have been shown to be skillful in different settings, and BCSD has been used extensively in hydrologic impact analysis. Both methods …

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C-5a Galaxy Systems Engineering Case Study, Air Force Center For Systems Engineering, John M. Griffin Mar 2008

C-5a Galaxy Systems Engineering Case Study, Air Force Center For Systems Engineering, John M. Griffin

AFIT Documents

The C-5 Systems Engineering Case Study captures the untold story of the application of systems engineering during the concept exploration, development, and production of the USAF C-5A and C-5B aircraft. The case study examines and dissects the systems engineering process as applied by the Air Force C-5 System Program Office and the prime contractor, Lockheed, Georgia, from the program s genesis in 1957 to the last delivery of the C-5A and the beginning of the C-5B program in 1973. Numerous interviews were conducted with the principals who managed and directed the program and a story of the systems engineering process …

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Evaluation Of The Applicability Of The Interactive Highway Safety Design Model To Safety Audit Of Two-Lane Rural Highways, Kaitlin Chuo Mar 2008

Evaluation Of The Applicability Of The Interactive Highway Safety Design Model To Safety Audit Of Two-Lane Rural Highways, Kaitlin Chuo

Theses and Dissertations

The Interactive Highway Safety Design Model (IHSDM) is a suite of software developed by the Federal Highway Administration (FHWA) for monitoring and analyzing two-lane rural highways in the United States. As IHSDM is a fairly "young" program a limited amount of research has been conducted to evaluate its practicability and reliability. To determine if IHSDM can be adopted into the engineering decision making process in Utah, a study was conducted under the supervision of the Utah Department of Transportation (UDOT) to evaluate its applicability to audit safety of two-lane rural highways in Utah. IHSDM consists of six modules: Policy Review …

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Thermal Characterization Of A Hall Effect Thruster, Alex M. Bohnert Mar 2008

Thermal Characterization Of A Hall Effect Thruster, Alex M. Bohnert

Theses and Dissertations

The thermal characteristics of a Hall thruster directly influence thruster and spacecraft design. High temperatures affect the magnetic coil capabilities and cause higher insulator erosion rates, influencing both thruster performance and lifetime. The Hall thruster transfers heat through both radiation and conduction, and the spacecraft must handle this additional thermal energy. An infrared camera provides a non-intrusive method to analyze the thermal characteristics of an operational Hall thruster. This thesis contains the thermal analysis of a Busek Co. Inc. 200 W Hall thruster, using a FLIR ThermaCAM SC640 infrared camera. The Space Propulsion Analysis and System Simulator Laboratory at the …

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Crew Exploration Vehicle (Cev) Skip Entry Trajectory, Emre Kaya Mar 2008

Crew Exploration Vehicle (Cev) Skip Entry Trajectory, Emre Kaya

Theses and Dissertations

This research effort develops a program using MATLAB® to solve the equations of motion for the atmospheric reentry of the Crew Exploration Vehicle (CEV) which is assumed to be in the phase of a lunar return trajectory that could be initiated any time during the mission. The essential reason for this research is to find a solution for the problem of an unplanned lunar return in addition to the normal procedures. Unlike Apollo type missions, the CEV would still be able to land on any preplanned available landing sites without any additional delay. In Apollo type missions, the return phase …

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Hubble Space Telescope Systems Engineering Case Study, Air Force Center For Systems Engineering, James J. Mattice Mar 2008

Hubble Space Telescope Systems Engineering Case Study, Air Force Center For Systems Engineering, James J. Mattice

AFIT Documents

The Hubble Space Telescope (HST) is an orbiting astronomical observatory operating in the spectrum from the near-infrared into the ultraviolet. Launched in 1990 and scheduled to operate through 2010, HST carries and has carried a wide variety of instruments producing imaging, spectrographic, astrometric, and photometric data through both pointed and parallel observing programs. Over 100,000 observations of more than 20,000 targets have been produced for retrieval. A macroscopic, cumulative representation of these observations is shown in the figure below to provide a sense of the enormous volume of astronomical data collected by the HST about our universe, our beginnings, and, …

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Six Dimensions Of Expertise: A More Comprehensive Definition Of Cognitive Expertise For Team Coordination, S K. Garrett, Barrett S. Caldwell, E C. Harris, M C. Gonzalez Mar 2008

Six Dimensions Of Expertise: A More Comprehensive Definition Of Cognitive Expertise For Team Coordination, S K. Garrett, Barrett S. Caldwell, E C. Harris, M C. Gonzalez

School of Industrial Engineering Faculty Publications

Looking at expertise from the vantage point of many knowledge domains allows the observations and resulting definitions to be useful across a broad range of subject areas. A stable set of definitions that work on a higher, more comprehensive level than the current literature offers is needed for an integrated description of expertise. A cohesive cross-domain definition and explanation of expertise can be used to optimise group interactions. Since group performance incorporates additional components of expertise that are not present in individual performance situations, these additional components must be examined in order to see a full picture of the successful …

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Force Measurement And Evaluation For Surgical Cutting Applications: Development Of An Effective Characterisation Testbed, Dean Callaghan Mar 2008

Force Measurement And Evaluation For Surgical Cutting Applications: Development Of An Effective Characterisation Testbed, Dean Callaghan

Conference Papers

Sensorized instruments that cater for accurate measurement of the interaction forces (between biological tissue and instrument end-effector) during surgical procedures offer surgeons a greater sense of immersion during minimally invasive robotic surgery (MIRS). There is much ongoing research into force measurement/evaluation involving surgical graspers. However, comparatively little corresponding effort has been expended in the measurement and subsequent evaluation of forces between scissor blades and tissue. This paper presents the design and development of a force/strain measurement test apparatus, which will ultimately serve as an effective sensor characterisation and evaluation platform. Data acquired from the testing platform can be used to …

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