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2007

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Articles 2701 - 2730 of 3831

Full-Text Articles in Engineering

Network Access In A Diversified Internet, M. Wilson, F. Kuhns, J. Turner Jan 2007

Network Access In A Diversified Internet, M. Wilson, F. Kuhns, J. Turner

All Computer Science and Engineering Research

There is a growing interest in virtualized network infrastructures as a means to enable experimental evaluation of new network architectures on a realistic scale. The National Science Foundation's GENI initiative seeks to develop a national experimental facility that would include virtualized network platforms that can support many concurrent experimental networks. Some researchers seek to make virtualization a central architectural component of a future Internet, so that new network architectures can be introduced at any time, without the barriers to entry that currently make this difficult. This paper focuses on how to extend the concept of virtualized networking through LAN-based access …

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Extending Bpel For Interoperable Pervasive Computing, Gregory Hackmann, Christopher Gill, Christopher Gill, Gruia-Catalin Roman Jan 2007

Extending Bpel For Interoperable Pervasive Computing, Gregory Hackmann, Christopher Gill, Christopher Gill, Gruia-Catalin Roman

All Computer Science and Engineering Research

The widespread deployment of mobile devices like PDAs and mobile phones has created a vast computation and communication platform for pervasive computing applications. However, these devices feature an array of incompatible hardware and software architectures, discouraging ad-hoc interactions among devices. The Business Process Execution Language (BPEL) allows users in wired computing settings to model applications of significant complexity, leveraging Web standards to guarantee interoperability. However, BPEL's inflexible communication model effectively prohibits its deployment on the kinds of dynamic wireless networks used by most pervasive computing devices. This paper presents extensions to BPEL that address these restrictions, transforming BPEL into a …

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Optimal Discrete Rate Adaptation For Distributed Real-Time Systems With End-To-End Tasks, Yingming Chen, Chenyang Lu, Xenofon Koutsoukos Jan 2007

Optimal Discrete Rate Adaptation For Distributed Real-Time Systems With End-To-End Tasks, Yingming Chen, Chenyang Lu, Xenofon Koutsoukos

All Computer Science and Engineering Research

Many distributed real-time systems face the challenge of dynamically maximizing system utility in response to fluctuations in system workload. We present the MultiParametric Rate Adaptation (MPRA) algorithm for discrete rate adaptation in distributed real-time systems with end-to-end tasks. The key novelty and advantage of MPRA is that it can efficiently produce optimal solutions in response to workload changes such as dynamic task arrivals. Through oline preprocessing MPRA transforms a NP-hard utility optimization problem to a set of simple linear functions in different regions expressed in term of CPU utilization changes caused by workload variations. At run time MPRA produces optimal …

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Configurable Component Middleware For Distributed Real-Time Systems With Aperiodic And Periodic Tasks, Yuanfang Zhang, Christopher Gill, Chenyang Lu Jan 2007

Configurable Component Middleware For Distributed Real-Time Systems With Aperiodic And Periodic Tasks, Yuanfang Zhang, Christopher Gill, Chenyang Lu

All Computer Science and Engineering Research

Many distributed real-time applications must handle mixed periodic and aperiodic tasks with diverse requirements. However, existing middleware lacks flexible configuration mechanisms needed to manage end-to-end timing easily for a wide range of different applications with both periodic and aperiodic tasks. The primary contribution of this work is the design, implementation and performance evaluation of the first configurable component middleware services for admission control and load balancing of aperiodic and periodic tasks in distributed real-time systems. Empirical results demonstrate the need for and effectiveness of our configurable component middleware approach in supporting different applications with periodic and aperiodic tasks.

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Fair Efficiency, Or Low Average Delay Without Starvation, Christoph Jechlitschek, Sergey Gorinsky Jan 2007

Fair Efficiency, Or Low Average Delay Without Starvation, Christoph Jechlitschek, Sergey Gorinsky

All Computer Science and Engineering Research

Elastic applications are primarily interested in minimal delay achievable for their messages under current network load. In this paper, we investigate how to transmit such messages over a bottleneck link efficiently and fairly. While SRPT (Shortest Remaining Processing Time) is an optimally efficient algorithm that minimizes average delay of messages, large messages might starve under SRPT in heavy load conditions. PS (Processor Sharing) and ViFi (Virtual Finish Time First) are fair but yield higher average delays than under SRPT. We explore the class of fair algorithms further and prove that no online algorithm in this class is optimally efficient. Then, …

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Scheduling Induced Bounds And The Verification Of Preemptive Real-Time Systems, Terry Tidwell, Christopher Gill, Venkita Subramonian Jan 2007

Scheduling Induced Bounds And The Verification Of Preemptive Real-Time Systems, Terry Tidwell, Christopher Gill, Venkita Subramonian

All Computer Science and Engineering Research

Distributed real-time and embedded (DRE) systems have stringent constraints on timeliness and other properties whose assurance is crucial to correct system behavior. Our previous research has shown that detailed models of essential middleware mechanisms can be developed, composed, and for constrained examples verified tractably, using state of the art timed automata model checkers. However, to apply model checking to a wider range of real-time systems, particularly those involving more general forms of preemptive concurrency, new techniques are needed to address decidability and tractability concerns. This paper makes three contributions to research on formal verification and validation of DRE systems. First, …

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Emergent Task Allocation For Mobile Robots Through Intentions And Directives, Nuzhet Atay, Burchan Bayazit Jan 2007

Emergent Task Allocation For Mobile Robots Through Intentions And Directives, Nuzhet Atay, Burchan Bayazit

All Computer Science and Engineering Research

Multi-robot systems require efficient and accurate planning in order to perform mission-critical tasks. However, algorithms that find the optimal solution are usually computationally expensive and may require a large number of messages between the robots as the robots need to be aware of the global spatiotemporal information. In this paper, we introduce an emergent task allocation approach for mobile robots. Each robot uses only the information obtained from its immediate neighbors in its decision. Our technique is general enough to be applicable to any task allocation scheme as long as a utilization criteria is given. We demonstrate that our approach …

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Perpetual: Byzantine Fault Tolerance For Federated Distributed Applications, Sajeeva L. Pallemulle, Haraldur D. Thorvaldsson, Kenneth J. Goldman Jan 2007

Perpetual: Byzantine Fault Tolerance For Federated Distributed Applications, Sajeeva L. Pallemulle, Haraldur D. Thorvaldsson, Kenneth J. Goldman

All Computer Science and Engineering Research

Modern distributed applications rely upon the functionality of services from multiple providers. Mission-critical services, possibly shared by multiple applications, must be replicated to guarantee correct execution and availability in spite of arbitrary (Byzantine) faults. Furthermore, shared services must enforce strict fault isolation policies to prevent cascading failures across organizational and application boundaries. Most existing protocols for Byzantine fault-tolerant execution do not support interoperability between replicated services while others provide poor fault isolation. Moreover, existing protocols place impractical limitations on application development by disallowing long-running threads of computation, asynchronous operation invocation, and asynchronous request processing. We present Perpetual, a protocol that …

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Expression Profiling Of Human Donor Lungs To Understand Primary Graft Dysfunction After Lung Transplantation, Monika Ray, Sekhar Dharmarajan, Johannes Freudenberg, Weixiong Zhang, Alexander G. Patterson Jan 2007

Expression Profiling Of Human Donor Lungs To Understand Primary Graft Dysfunction After Lung Transplantation, Monika Ray, Sekhar Dharmarajan, Johannes Freudenberg, Weixiong Zhang, Alexander G. Patterson

All Computer Science and Engineering Research

Lung transplantation is the treatment of choice for end-stage pulmonary diseases. A limited donor supply has resulted in 4000 patients on the waiting list. Currently, 10-20% of donor organs offered for transplantation are deemed suitable under the selection criteria, of which 15-25% fails due to primary graft dysfunction (PGD). This has resulted in increased efforts to search for alternative donor lungs selection criteria. In this study, we attempt to further our understanding of PGD by observing the changes in gene expression across donor lungs that developed PGD versus those that did not. Our second goal is to use a machine …

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Improving Individual Flow Performance With Multiple Queue Fair Queuing, Manfred Georg, Christopher Jechlitschek, Sergey Gorinsky Jan 2007

Improving Individual Flow Performance With Multiple Queue Fair Queuing, Manfred Georg, Christopher Jechlitschek, Sergey Gorinsky

All Computer Science and Engineering Research

Fair Queuing (FQ) algorithms provide isolation between packet flows, allowing max-min fair sharing of a link even when flows misbehave. However, fairness comes at the expense of per-flow state. To keep the memory requirement independent of the flow count, the router can isolate aggregates of flows, rather than individual flows. We investigate the feasibility of protecting individual flows under such aggregate isolation in the context of Multiple Queue Fair Queuing (MQFQ), where the router maintains a fixed number of queues and associates multiple queues with each flow. MQFQ places packets in the shortest queue associated with their flow. The redundancy …

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Splice: A Standardized Peripheral Logic And Interface Creation Engine, Justin Thiel Jan 2007

Splice: A Standardized Peripheral Logic And Interface Creation Engine, Justin Thiel

All Computer Science and Engineering Research

Recent advancements in FPGA technology have allowed manufacturers to place general-purpose processors alongside user-configurable logic gates on a single chip. At first glance, these integrated devices would seem to be the ideal deployment platform for hardware-software co-designed systems, but some issues, such as incompatibility across vendors and confusion over which bus interfaces to support, have impeded adoption of these platforms. This thesis describes the design and operation of Splice, a software-based code generation tool intended to address these types of issues by providing a bus-independent structure that allows end-users to easily integrate their customized peripheral logic into embedded systems. To …

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Byzantine Fault-Tolerant Web Services For N-Tier And Service Oriented Architectures, Sajeeva L. Pallemulle, Kenneth J. Goldman Jan 2007

Byzantine Fault-Tolerant Web Services For N-Tier And Service Oriented Architectures, Sajeeva L. Pallemulle, Kenneth J. Goldman

All Computer Science and Engineering Research

Web Services that provide mission-critical functionality must be replicated to guarantee correct execution and high availability in spite of arbitrary (Byzantine) faults. Existing approaches for Byzantine fault-tolerant execution of Web Services are inadequate to guarantee correct execution due to several major limitations. Some approaches do not support interoperability between replicated Web Services. Other approaches do not provide fault isolation guarantees that are strong enough to prevent cascading failures across organizational and application boundaries. Moreover, existing approaches place impractical limitations on application development by not supporting long-running active threads of computation, fully asynchronous communication, and access to host specific information. We …

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Efficient Fair Algorithms For Message Communication, Sergey Gorinsky, Eric J. Friedman, Shane Henderson, Christoph Jechlitschek Jan 2007

Efficient Fair Algorithms For Message Communication, Sergey Gorinsky, Eric J. Friedman, Shane Henderson, Christoph Jechlitschek

All Computer Science and Engineering Research

A computer network serves distributed applications by communicating messages between their remote ends. Many such applications desire minimal delay for their messages. Beside this efficiency objective, allocation of the network capacity is also subject to the fairness constraint of not shutting off communication for any individual message. Processor Sharing (PS) is a de facto standard of fairness but provides significantly higher average delay than Shortest Remaining Processing Time (SRPT), which is an optimally efficient but unfair algorithm. In this paper, we explore efficient fair algorithms for message communication where fairness means that no message is delivered later than under PS. …

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Strong Performance Guarantees For Asynchronous Buffered Crossbar Schedulers, Jonathon Turner Jan 2007

Strong Performance Guarantees For Asynchronous Buffered Crossbar Schedulers, Jonathon Turner

All Computer Science and Engineering Research

Crossbar-based switches are commonly used to implement routers with throughputs up to about 1 Tb/s. The advent of crossbar scheduling algorithms that provide strong performance guarantees now makes it possible to engineer systems that perform well, even under extreme traffic conditions. Until recently, such performance guarantees have only been developed for crossbars that switch cells rather than variable length packets. Cell-based crossbars incur a worst-case bandwidth penalty of up to a factor of two, since they must fragment variable length packets into fixed length cells. In addition, schedulers for cell-based crossbars may fail to deliver the expected performance guarantees when …

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Lower Bounds On Queuing And Loss At Highly Multiplexed Links, Maxim Podlesny, Sergey Gorinsky Jan 2007

Lower Bounds On Queuing And Loss At Highly Multiplexed Links, Maxim Podlesny, Sergey Gorinsky

All Computer Science and Engineering Research

Explicit and delay-driven congestion control protocols strive to preclude overflow of link buffers by reducing transmission upon incipient congestion. In this paper, we explore fundamental limitations of any congestion control with respect to minimum queuing and loss achievable at highly multiplexed links. We present and evaluate an idealized protocol where all flows always transmit at equal rates. The ideally smooth congestion control causes link queuing only due to asynchrony of flow arrivals, which is intrinsic to computer networks. With overprovisioned buffers, our analysis and simulations for different smooth distributions of flow interarrival times agree that minimum queuing at a fully …

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A Fingerspelling Sign Language Visualization , Carol S. Brickman Jan 2007

A Fingerspelling Sign Language Visualization , Carol S. Brickman

All Computer Science and Engineering Research

The goal of the Fingerspell Visualization Project is to research methods to improve learning of reading skills through sign language. The techniques are centered on Fingerspelling as the method to bridge stages of skill development. Visualization of a string of text in images of a hand performing the letters of the alphabet in standardized fingerspell sign language positions provide Full Motion Learning as opposed to learning from single pictures.

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Determining Alpha-Helix Correspondence For Protein Structure Prediction From Cryo-Em Density Maps, Master's Thesis, May 2007, Sasakthi S. Abeysinghe Jan 2007

Determining Alpha-Helix Correspondence For Protein Structure Prediction From Cryo-Em Density Maps, Master's Thesis, May 2007, Sasakthi S. Abeysinghe

All Computer Science and Engineering Research

Determining protein structure is an important problem for structural biologists, which has received a significant amount of attention in the recent years. In this thesis, we describe a novel, shape-modeling approach as an intermediate step towards recovering 3D protein structures from volumetric images. The input to our method is a sequence of alpha-helices that make up a protein, and a low-resolution volumetric image of the protein where possible locations of alpha-helices have been detected. Our task is to identify the correspondence between the two sets of helices, which will shed light on how the protein folds in space. The central …

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Dna Repair In Incipient Alzheimer's Disease, Monika Ray, Weixiong Zhang Jan 2007

Dna Repair In Incipient Alzheimer's Disease, Monika Ray, Weixiong Zhang

All Computer Science and Engineering Research

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder currently with no cure. Understanding the pathogenesis in the early stages of late-onset AD can help gain important mechanistic insights into this disease as well as aid in effective drug development. The analysis of incipient AD is steeped in difficulties due to its slight pathological and genetic differences from normal ageing. The difficulty also lies in the choice of analysis techniques as statistical power to analyse incipient AD with a small sample size, as is common in pilot studies, can be low if the proper analytical tool is not employed. In this …

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Nebraska Summary: S629 John Deere 6330, Nebraska Tractor Test Lab Jan 2007

Nebraska Summary: S629 John Deere 6330, Nebraska Tractor Test Lab

Nebraska Tractor Tests

ABOUT THE TEST REPORT AND USE OF THE DATA The test data contained in this report are a tabulation of the results of a series of tests. Due to the restricted format of these pages, only a limited amount of data and not all of the tractor specifications are included. The full OECD report contains usually about 30 pages of data and specifications. The test data were obtained for each tractor under similar conditions and therefore, provide a means of comparison of performance based on a limited set of reported data. EXPLANATION OF THE TEST PROCEDURES Purpose The purpose of …

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Nebraska Summary: S666 New Holland T6020 Delta, Nebraska Tractor Test Lab Jan 2007

Nebraska Summary: S666 New Holland T6020 Delta, Nebraska Tractor Test Lab

Nebraska Tractor Tests

ABOUT THE TEST REPORT AND USE OF THE DATA The test data contained in this report are a tabulation of the results of a series of tests. Due to the restricted format of these pages, only a limited amount of data and not all of the tractor specifications are included. The full OECD report contains usually about 30 pages of data and specifications. The test data were obtained for each tractor under similar conditions and therefore, provide a means of comparison of performance based on a limited set of reported data. EXPLANATION OF THE TEST PROCEDURES Purpose The purpose of …

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Investigating The Use Of Small-Diameter Softwood As Guardrail Posts (Dynamic Test Results), Jason A. Hascall, Ronald K. Faller, John D. Reid, Dean L. Sicking, David E. Kretschmann Jan 2007

Investigating The Use Of Small-Diameter Softwood As Guardrail Posts (Dynamic Test Results), Jason A. Hascall, Ronald K. Faller, John D. Reid, Dean L. Sicking, David E. Kretschmann

Mid-America Transportation Center: Final Reports and Technical Briefs

A modified version of the Midwest Guardrail System (MGS), utilizing small-diameter round wood posts, was developed, tested, and evaluated. Three systems were developed using different species of timber, Douglas Fir, Ponderosa Pine, and Southern Yellow Pine. A combination of Barrier VII computer simulation modeling and several series of cantilever bogie tests, conducted in both a rigid sleeve and soil, were used to determine the required diameter of post for each species in order to serve as an equivalent substitute for the standard steel post used in the barrier system. The final recommended nominal sizes were determined to be 184 mm …

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Dielectric Anisotropy And Phonon Modes Of Ordered Indirect-Gap Al0.52In0.48P Studied By Far-Infrared Ellipsometry, Tino Hofmann, V. Gottschalch, Mathias Schubert Jan 2007

Dielectric Anisotropy And Phonon Modes Of Ordered Indirect-Gap Al0.52In0.48P Studied By Far-Infrared Ellipsometry, Tino Hofmann, V. Gottschalch, Mathias Schubert

Materials Research Science and Engineering Center: Faculty Publications

The infrared (100–600 cm−1) optical properties of partially CuPt-type ordered Al0.52In0.48P deposited lattice matched on GaAs are studied by ellipsometry. The authors determine the ordinary and extraordinary dielectric functions and report on the evolution of the optical phonon mode frequencies of Al0.52In0.48P as a function of the degree of ordering. In addition to the InP- and AlP-like phonon modes, they observe two alloy-induced phonon modes which are anisotropic upon CuPt ordering. The observed modes are associated to vibrations with E and A1 symmetries. The alloy-induced phonon modes are useful …

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Demonstration Of An Ultraviolet Zno-Based Optically Pumped Third Order Distributed Feedback Laser, Daniel Hofstetter, Yargo Bonetti, Fabrizio Giorgetta, Abdel-Hamid El-Shaer, Andrey Bakin, Andreas Waag, Rudiger Schmidt-Grund, Mathias Schubert, Marius Grundmann Jan 2007

Demonstration Of An Ultraviolet Zno-Based Optically Pumped Third Order Distributed Feedback Laser, Daniel Hofstetter, Yargo Bonetti, Fabrizio Giorgetta, Abdel-Hamid El-Shaer, Andrey Bakin, Andreas Waag, Rudiger Schmidt-Grund, Mathias Schubert, Marius Grundmann

Materials Research Science and Engineering Center: Faculty Publications

The authors demonstrate an optically pumped ZnO distributed feedback laser operating at 383 nm. For a large temperature range between 10 and 270 K, the device lased in a single longitudinal mode. Mode selection was accomplished via a third order diffraction grating, which was dry etched into a 120 nm thick Si3N4 layer deposited on the ZnO active region. They observed a spectral linewidth of 0.4 nm, a pump threshold intensity of 0.12 MW/cm2, and a peak output power of 14 mW. From wavelength versus temperature measurements, they deduced a temperature tuning coefficient of the …

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Creating Micro- And Nanostructures On Tubular And Spherical Surfaces, O. Lima, L. Tan, A. Goel, Mehrdad Negahban, Z. Li Jan 2007

Creating Micro- And Nanostructures On Tubular And Spherical Surfaces, O. Lima, L. Tan, A. Goel, Mehrdad Negahban, Z. Li

Materials Research Science and Engineering Center: Faculty Publications

The authors developed a new technique to create micro- and nanometer scale structures on curved free-standing objects by combining embossing/imprinting lithography approaches with mechanical loadings on elastic films. Embossing/imprinting generates small structures and mechanical loading determines shape or geometry of the final object. As a result, a portion of the tubes with a radius between 0.5 and 3.5 mm and a portion of the spheres with a radius between 2.4 and 7.0 mm were fabricated with grating line features (period of 700 nm) and microlens array features (lens radius of 2.5 µm) atop, respectively. It was found that both static …

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Dielectric Constants And Phonon Modes Of Amorphous Hafnium Aluminate Deposited By Metal Organic Chemical Vapor Deposition, C. Bundesmann, O. Buiu, S. Hall, Mathias Schubert Jan 2007

Dielectric Constants And Phonon Modes Of Amorphous Hafnium Aluminate Deposited By Metal Organic Chemical Vapor Deposition, C. Bundesmann, O. Buiu, S. Hall, Mathias Schubert

Materials Research Science and Engineering Center: Faculty Publications

Dielectric constants and long-wavelength optical phonon modes of amorphous hafnium aluminate films with a maximum aluminum content of 19 at. % are studied by infrared spectroscopic ellipsometry (IRSE). The hafnium aluminate films were prepared by metal organic chemical vapor deposition on silicon substrates. IRSE revealed one polar lattice mode and one impurity-type mode, which show all a systematic shift in frequency with varying Al content. The static dielectric constant decreases from 10.1 for 4.6 at. % Al to 8.1 for 19 at. % Al. The absolute values were found to be between 50% and 70% smaller than the values obtained …

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Sequential Stretching Lithography, Haojing Lin, Ocelio V. Lima, Li Tan, Zheng Li, Jiangyu Li Jan 2007

Sequential Stretching Lithography, Haojing Lin, Ocelio V. Lima, Li Tan, Zheng Li, Jiangyu Li

Materials Research Science and Engineering Center: Faculty Publications

We developed an embossing/imprinting based nanofabrication technique, dubbed sequential stretching lithography (SSL). In this process, a master pattern is imprinted into an elastomer containing a film of uncured elastomer. The elastomer is cured and then elongated to increase feature density and reduce feature size. Replication of this substrate yields a new master that can be used in further reduction steps. One-dimensional grating features with a pitch size below 200 nm were fabricated from 750 nm-pitch grating lines. This process gives us a faithful pattern miniaturization in all aspects and, as a result, a much effective control on density and dimension …

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Nonvolatile Two-Terminal Molecular Memory, Jason Snodgrass, Glen Kennedy, Wai-Ning Mei, Renat F. Sabirianov Jan 2007

Nonvolatile Two-Terminal Molecular Memory, Jason Snodgrass, Glen Kennedy, Wai-Ning Mei, Renat F. Sabirianov

Materials Research Science and Engineering Center: Faculty Publications

We propose a nonvolatile two-terminal memory device with two resistance states based on the molecular tunnel junctions. This tunnel junction is composed of one or a few monolayers of polar molecules sandwiched between two electrodes made of materials with different screening length. As a prototype model system we study a rare earth endohedral metallofullerene molecule with reversible dipole moment sandwiched between metal and semiconducting electrodes, forming a double barrier junction. We use the Thomas-Fermi model to calculate the potential profile across the device. Calculated tunneling conductance through the proposed structure changes by order of magnitude upon the reversal of the …

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Geochemical Controls On Contaminant Uranium In Vadose Hanford Formation Sediments At The 200 Area And 300 Area, Hanford Site, Washington, James Mckinley, John M. Zachara, Jiamin Wan, David Mccready, Steven M. Heald Jan 2007

Geochemical Controls On Contaminant Uranium In Vadose Hanford Formation Sediments At The 200 Area And 300 Area, Hanford Site, Washington, James Mckinley, John M. Zachara, Jiamin Wan, David Mccready, Steven M. Heald

United States Department of Energy: Publications

Long-term historic spills of uranium at the 300 Area fuel fabrication site (58,000 kg of disposed uranium over 32 yr) and at the 200 East Area BX tank farm (7000 kg of spilled uranium in one event), both within the Hanford formation in the Hanford Site, Washington State, were investigated by subsurface sampling and subsequent microscale investigations of excavated samples. The 200 Area sediments contained uranyl silicate mineralization (sodium boltwoodite) in restrictive microfractures in granitic clasts, in the vadose zone over a narrow range in depth. Well logging and column experiments indicated that tank wastes migrated deeper than observed in …

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Hanford Site Vadose Zone Studies: An Overview, G. W. Gee, M. Oostrom, M. D. Freshley, M. L. Rockhold, John M. Zachara Jan 2007

Hanford Site Vadose Zone Studies: An Overview, G. W. Gee, M. Oostrom, M. D. Freshley, M. L. Rockhold, John M. Zachara

United States Department of Energy: Publications

Large quantities of radioactive and chemical wastes resulting from Pu production for nuclear weapons are located in the vadose zone at the USDOE’s Hanford Site, north of Richland, WA. The vadose zone here is characterized by often highly stratified glacial-fluvial sediments that give rise to complex subsurface-flow paths that contribute to uncertainty of contaminant fate and transport. Research efforts have focused on answering questions of contaminant transport from the viewpoint of geologic, biologic, geochemical, and hydrologic controls. This special section highlights key research topics concerning vadose zone problems at the Hanford Site. Research indicates that some of the contaminant species …

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Development Of A High Average Current Polarized Electron Source With Long Cathode Operational Lifetime, C. K. Sinclair, P. Adderley, B. M. Dunham, J. C. Hansknecht, P. Hartmann, M. Poelker, J. S. Price, P. M. Rutt, W. J. Schneider, M. Steigerwald Jan 2007

Development Of A High Average Current Polarized Electron Source With Long Cathode Operational Lifetime, C. K. Sinclair, P. Adderley, B. M. Dunham, J. C. Hansknecht, P. Hartmann, M. Poelker, J. S. Price, P. M. Rutt, W. J. Schneider, M. Steigerwald

United States Department of Energy: Publications

Substantially more than half of the electromagnetic nuclear physics experiments conducted at the Continuous Electron Beam Accelerator Facility of the Thomas Jefferson National Accelerator Facility (Jefferson Laboratory) require highly polarized electron beams, often at high average current. Spinpolarized electrons are produced by photoemission from various GaAs-based semiconductor photocathodes, using circularly polarized laser light with photon energy slightly larger than the semiconductor band gap. The photocathodes are prepared by activation of the clean semiconductor surface to negative electron affinity using cesium and oxidation. Historically, in many laboratories worldwide, these photocathodes have had short operational lifetimes at high average current, and have …

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