218 Matching Results

Search Results

Advanced search parameters have been applied.

Impact of the implementation of MPI point-to-point communications on the performance of two general sparse solvers

Description: We examine the mechanics of the send and receive mechanism of MPI and in particular how we can implement message passing in a robust way so that our performance is not significantly affected by changes to the MPI system. This leads us to using the Isend/Irecv protocol which will entail sometimes significant algorithmic changes. We discuss this within the context of two different algorithms for sparse Gaussian elimination that we have parallelized. One is a multifrontal solver called MUMPS, the other is a supernodal solver called SuperLU. Both algorithms are difficult to parallelize on distributed memory machines. Our initial strategies were based on simple MPI point-to-point communication primitives. With such approaches, the parallel performance of both codes are very sensitive to the MPI implementation, the way MPI internal buffers are used in particular. We then modified our codes to use more sophisticated nonblocking versions of MPI communication. This significantly improved the performance robustness (independent of the MPI buffering mechanism) and scalability, but at the cost of increased code complexity.
Date: October 10, 2001
Creator: Amestoy, Patrick R.; Duff, Iain S.; L'Excellent, Jean-Yves & Li, Xiaoye S.
Partner: UNT Libraries Government Documents Department

High Critical Current Densities in Nb3Sn Films with Engineered Microstructures--Artifical Pinning Microstructures

Description: Films with layers of Nb, Cu, and Sn have been fabricated to simulate a Nb{sub 3}Sn bronze-type process. These Nb{sub 3}Sn films have produced critical current densities greater than 1 x 10{sup 6} A/cm{sup 2} at 4.2 K and 7.5 T. Niobium films doped with Y, Sc, Dy, Al{sub 2}O{sub 3}, and Ti have been deposited with e-beam co-evaporation onto 75 mm diameter Si wafers with a 100 nm SiO{sub 2} buffer layer. The Nb layer was followed by a layer of Cu and a layer of Sn to complete the bronze-type process. The films with the highest J{sub c} had about 8 vol. % Sc and about 18 vol. % Al{sub 2}O{sub 3}. Characterization of the microstructure by TEM shows that these high J{sub c} films contained high density of inclusions about 5 nm in size and that the grain size of the Nb{sub 3}Sn is about 20-25 nm for samples heat treated at 700 C for up to eight hours.
Date: July 1, 1997
Creator: Dietderich, D.R.; Kelman, M.; Litty, J.R. & Scanlan, R.M.
Partner: UNT Libraries Government Documents Department

Wasco Riparian Buffer Project, Annual Report 2003-2004.

Description: This project implements riparian buffer systems in the Mid-Columbia, addressing limiting factors identified in the Deschutes River Sub-basin Summary, March 2, 2001. This project is providing the technical planning support needed to implement at least 20 riparian buffer system contracts on approximately 800 acres covering an estimated 36 miles of anadromous fish streams. During this second year of implementation, 17 buffer contracts were established on 173,462 ft. of stream (25.9 miles). Acreage included in the buffers totaled 891.6 acres. Average buffer width was 112 ft. on each side of the stream. Cumulative totals through the first two project years are 26 buffers on 36.6 stream miles covering 1,283.6 acres. Actual implementation costs, lease payments, and maintenance costs will be borne by existing USDA programs: Conservation Reserve (CRP) and Conservation Reserve Enhancement Programs (CREP). The lease period of each contract may vary from 10 to 15 years. During this year, the average lease period was 14.9 years. The total value of contracts established this year is $1,421,268 compared with $55,504 in BPA contract costs to provide the technical support needed to get the contracts implemented. Cumulative contract value for the first two years is $1,919,451 compared to $103,329 cost to BPA. This project provides technical staffing to conduct assessments and develop conservation plans required for riparian buffer systems to help keep pace with a growing backlog of potential buffer projects. This project meets a critical need in the lower Deschutes and lower John Day River basins and complements the Riparian Buffer project approved for Fifteenmile watershed, Project No. 2001-021-00 begun in fiscal year 2001. This project supports RPA 150 and 153 as required under the Federal Hydropower System biological opinion and benefits the mid-Columbia ESU of steelhead.
Date: July 1, 2003
Creator: Graves, Ron
Partner: UNT Libraries Government Documents Department

Gilliam County Riparian Buffers 2007-2008 Annual Report.

Description: During the contract year beginning July 1, 2007 and ending June 30, 2008, the CREP technician contacted 15 new landowners regarding an interest in either the CREP or the Continuous CRP programs. Most landowners requested a second meeting and most sites were visited to discuss possibilities of enrolling in a USDA riparian program. This year, a considerable amount of time was spent providing technical assistance to prior contracts as the practices are implemented. More time is being spent in planning site preparation so that NRCS and FSAs increasing concerns over plant survival are satisfied. A continued concern that the rate paid to the landowner for maintenance is not enough. Controlling competing vegetation is a major factor in increasing plant survival. Increasing costs in the methods used to control unwanted plants has made it difficult for contract holders to perform these methods as effectively as they would like. The projects that have continued maintenance are considerably more successful.
Date: November 4, 2008
Partner: UNT Libraries Government Documents Department

The Effect of High-Resistance SnO2 on CdS/CdTe Device Performance

Description: In this paper, we have studied the effect of high-resistance SnO2 buffer layers, deposited by low-pressure chemical-vapor deposition, on CdS/CdTe device performance. Our results indicate that when CdS/CdTe devices have a very thin layer of CdS or no CdS at all, the i-SnO2 buffer layer helps to increase device efficiency. When the CdS layer is thicker than 600{angstrom}, the device performance is dominated by CdS thickness, not the i-SnO2 layer. If a very thin CdS layer is to be used to enhance device performance, we conclude that a better SnO2 buffer layer is needed.
Date: October 6, 1998
Creator: Li, W.; Ribelin, R.; Mahathongdy, Y.; Albin, D.; Dhere, R.; Rose, D. et al.
Partner: UNT Libraries Government Documents Department

THE ROLE OF BUFFER GASES IN OPTOAOOUSTIC SPECTROSCOPY

Description: The dependence of an acoustically resonant optoacoustic signal on the molecular weight, and thermodynamic and transport properties of the buffer gas is reported. Our results show that careful selection of such gases can significantly increase the sensitivity and flexibility of optoacoustic spectroscopy. We also demonstrate that such thermodynamic quantities as {gamma} ({triple_bond} C{sub p}/C{sub v}) and sound velocity can now be measured readily and accurately. Other potential applications are suggested.
Date: November 1, 1977
Creator: Thomas III, L.J.; Kelly, M.J. & Amer, N.M.
Partner: UNT Libraries Government Documents Department

Fifteenmile Creek Riparian Buffers Project, Annual Report 2002-2003.

Description: This project implements riparian buffer systems in the Mid-Columbia, addressing limiting factors identified in the Fifteenmile Subbasin Summary, June 30, 2000. The project is providing the technical planning support needed to implement at least 36 riparian buffer system contracts on approximately 872 acres covering an estimated 40 miles of anadromous fish streams over a three year period. During this second year of the project, 11 buffer contracts were implemented on 10.9 miles of stream. Buffer widths averaged 132 ft. on each side of the stream. Implementation included prescribed plantings, fencing, and related practices. Actual implementation costs, lease payments, and maintenance costs are borne by existing USDA programs: Conservation Reserve and Conservation Reserve Enhancement Programs. The lease period of each contract may vary between 10 to 15 years. During this year the average was 14.6 years. The total value of contracts established this year is $666,121 compared with $71,115 in Bonneville Power Administration (BPA) contract costs to provide the technical support needed to get the contracts implemented. This project provides technical staffing to conduct assessments and develop plans to help keep pace with the growing backlog of potential riparian buffer projects. Word of mouth from satisfied customers has brought in many new sign-ups during the year. In addition, specific outreach efforts targeting the orchard areas of the county began to bear fruit with orchardists sign-ups as the project year ended. Progress this second year of project includes only work accomplished in the Fifteenmile subbasin. A similar but separate effort to implement buffers in the Columbia Plateau Province was initiated during the year under project number 2002-019-00. This project supports RPA 150 and 153 as required under the Federal Hydropower System biological opinion.
Date: February 1, 2004
Creator: Graves, Ron
Partner: UNT Libraries Government Documents Department

In Situ Redox Manipulation Proof-of-Principle Test at the Fort Lewis Logistics Center: Final Report

Description: Pacific Northwest National Laboratory conducted a proof-of-principle test at the Fort Lewis Logistics Center to determine the feasibility of using the innovative remedial technology In Situ Redox Manipulation (ISRM) to treat groundwater contaminated with dissolved TCE. ISRM creates a permeable treatment zone in the subsurface to remediate redox-sensitive contaminants in groundwater. The permeable treatment zone is created by injecting a chemical reducing agent (sodium dithionite with pH buffers) into the aquifer through a well to chemically reduce the naturally occurring ferric iron in the sediments to ferrous iron. Once the reducing agent has been given sufficient time to react with aquifer sediments, residual chemicals and reaction products are withdrawn through the same well. Redox-sensitive contaminants such as TCE, moving in a dissolved-phase plume through the treatment zone, are destroyed. TCE is degraded via reductive dechlorination within the treatment zone to benign degradation products (acetylene, ehtylene). Analyses of sediment samples collected from post-test boreholes showed a high degree of iron reduction, which confirmed the effectiveness of the treatment zone.
Date: October 25, 2000
Creator: Vermeul, Vincent R.; Williams, Mark D.; Evans, John C.; Szecsody, James E.; Bjornstad, Bruce N. & Liikala, Terry L.
Partner: UNT Libraries Government Documents Department

Hydrocarbon-free resonance transition 795-nm rubidium laser

Description: An optical resonance transition rubidium laser (5{sup 2}P{sub 1/2} {yields} 5{sup 2}S{sub 1/2}) is demonstrated with a hydrocarbon-free buffer gas. Prior demonstrations of alkali resonance transition lasers have used ethane as either the buffer gas or a buffer gas component to promote rapid fine-structure mixing. However, our experience suggests that the alkali vapor reacts with the ethane producing carbon as one of the reaction products. This degrades long term laser reliability. Our recent experimental results with a 'clean' helium-only buffer gas system pumped by a Ti:sapphire laser demonstrate all the advantages of the original alkali laser system, but without the reliability issues associated with the use of ethane.
Date: January 9, 2008
Creator: Wu, S Q; Soules, T F; Page, R H; Mitchell, S C; Kanz, V K & Beach, R J
Partner: UNT Libraries Government Documents Department

Resonance transition 795-nm Rubidium laser using 3He buffer gas

Description: We report the first demonstration of a 795-nm Rubidium resonance transition laser using a buffer gas consisting of pure {sup 3}He. This follows our recent demonstration of a hydrocarbon-free 795-nm Rubidium resonance laser which used naturally-occurring He as the buffer gas. Using He gas that is isotopically enriched with {sup 3}He yields enhanced mixing of the Rb fine-structure levels. This enables efficient lasing at reduced He buffer gas pressure, improving thermal management in high average power Rb lasers and enhancing the power scaling potential of such systems.
Date: August 2, 2007
Creator: Wu, S S; Soules, T F; Page, R H; Mitchell, S C; Kanz, V K & Beach, R J
Partner: UNT Libraries Government Documents Department

Developments toward a reliable diode-pumped hydrocarbon-free 795-nm rubidium laser

Description: We report a 795-nm diode-pumpable Rb laser using a buffer gas of pure {sup 3}He. {sup 3}He gas enhances mixing of the Rb fine-structure levels. This enables efficient lasing at reduced He pressures and improved thermal management.
Date: May 7, 2008
Creator: Wu, S S; Soules, T F; Page, R H; Mitchell, S C; Kanz, V K & Beach, R J
Partner: UNT Libraries Government Documents Department

DYNAMIC RIGHT-SIZING IN TCP.

Description: With the widespread arrival of bandwidth-intensive applications such as bulk-data transfer, multi-media web streaming and computational grids for high-performance computing, networking performance over the wide-area network has become a critical component in the infrastructure. Tragically, operating systems are still tuned for yesterday's WAN speeds and network applications. As a result, a painstaking process of manually tuning system buffers must be undertaken to make TCP flow-control scale to meet the needs of today's bandwidth-rich networks. Consequently, we propose an operating system technique called dynamic right-sizing that eliminates the need for this manual process. Previous work has also attacked this problem, but with less than complete solutions. Our solution is more efficient, more transparent, and applies to a wider set of applications, including those that require strict flow-control semantics because of performance disparities between the sender and receiver. Keywords--Wide-area networking, TCP, dynamic flow control, computational grid, high-performance networking, auto-tuning
Date: January 1, 2001
Creator: Fisk, M. E. (Mike E. ) & Feng, W. C. (Wu-Chun)
Partner: UNT Libraries Government Documents Department

Dynamic right-sizing in TCP : a simulation study /

Description: Virtually all network applications requiring reliable end-to-end communication depend on TCP. Unfortunately, the performance of any stock TCP is abysmal over wide-area networks (WANs) and even over local area networks (LANs) with wry high-bandwidth links. Currently, network researchers manually optimize TCP buffer sizes to achieve acceptable performance over a given connection. Unfortunately, this manual optimhtlon requires changes to the kernel on both end hosts involved in the network connection (changes that are only effective far connections Iuctween thesse two hosts). Furthermore, betruse two administrative domains must be coordinated to perform this optimization, thia process can be tedious and t h e consuming. To address these prohlem, this paper illustrates the benefits of B new technique called dynamic right-sizing. This technique dynamically and automatically determines the best buffer size, and hence flow-cantwl window size in TCP. Our simulation dtndy shows that dynamic right-sizing can Improve the performance of Rows by two orders of magnitude over stock TCP implernentations ihat have static flow-control windows.
Date: January 1, 2001
Creator: Weigle, E. H. (Eric H.) & Feng, W. C. (Wu-Chun)
Partner: UNT Libraries Government Documents Department

A dynamic kernel modifier for linux

Description: Dynamic Kernel Modifier, or DKM, is a kernel module for Linux that allows user-mode programs to modify the execution of functions in the kernel without recompiling or modifying the kernel source in any way. Functions may be traced, either function entry only or function entry and exit; nullified; or replaced with some other function. For the tracing case, function execution results in the activation of a watchpoint. When the watchpoint is activated, the address of the function is logged in a FIFO buffer that is readable by external applications. The watchpoints are time-stamped with the resolution of the processor high resolution timers, which on most modem processors are accurate to a single processor tick. DKM is very similar to earlier systems such as the SunOS trace device or Linux TT. Unlike these two systems, and other similar systems, DKM requires no kernel modifications. DKM allows users to do initial probing of the kernel to look for performance problems, or even to resolve potential problems by turning functions off or replacing them. DKM watchpoints are not without cost: it takes about 200 nanoseconds to make a log entry on an 800 Mhz Pentium-Ill. The overhead numbers are actually competitive with other hardware-based trace systems, although it has less 'Los Alamos National Laboratory is operated by the University of California for the National Nuclear Security Administration of the United States Department of Energy under contract W-7405-ENG-36. accuracy than an In-Circuit Emulator such as the American Arium. Once the user has zeroed in on a problem, other mechanisms with a higher degree of accuracy can be used.
Date: September 3, 2002
Creator: Minnich, R. G. (Ronald G.)
Partner: UNT Libraries Government Documents Department

Intelligent, onboard signal processing payload concept, addendum :

Description: This document addresses two issues in the original paper entitled 'An Intelligent, Onboard Signal Processing Payload Concept' submitted to the SPIE AeroSense 2003 C0nference.l Since the original paper submission, and prior to the scheduled presentation, a correction has been made to one of the figures in the original paper and an update has been performed to the software simulation of the payload concept. The figure, referred to as Figure 8. Simulation Results in the original paper, contains an error in the voltage versus the capacity drained chart. This chart does not correctly display the voltage changes experienced by the battery module due to the varying discharge rates. This error is an artifact of the procedure used to graph the data. Additionally, the original version of the Simulation related the algorithm execution rate to the lightning event rate regardless of the number of events in the ring buffer. This feature was mentioned in section 5. Simulation Results of the original paper. A correction was also made to the size of the ring buffer. Incorrect information was provided to the authors that placed the number of possible events at 18,310. Corrected information has since been obtained that specifies the ring buffer can typically hold only 1,000 events. This has a significant impact on the APM process and the number of events lost when the size of the ring buffer is exceeded. Also, upon further analysis, it was realized that the simulation contained an error in the recording of the number of events in the ring buffer. The faster algorithms, LMS and ML, should have been able to process all events during the simulation time interval, but the initial results did not reflect this characteristic. The updated version of the simulation appropriately handles the number of algorithm executions and recording of events in ...
Date: January 1, 2003
Creator: Shriver, P. M. (Patrick M.); Harikumar, J. (Jayashree); Briles, S. C. (Scott C.) & Gokhale, M. (Maya)
Partner: UNT Libraries Government Documents Department

Precision Power Supply Control Module

Description: A temperature stabilized, digital input circuit module using surface mount technology has been developed for use as the precision control element in a 10 A. bipolar trim magnet regulator. Regulators using this module have shown stability of 20 ppm over 8 hours. This circuit module combines the functions of a current measuring shunt, serial DAC, precision voltage reference, high gain error amplifier and readback buffer amplifier. Loop gain and compensation are done externally to the module. The module can be used in high current power supplies by replacing the internally derived current signal with the output signal from an external high current shunt or transductor.
Date: May 1, 1991
Creator: Mora, Bob; Larkin, J.; O'Sullivan, Michael & Dobeck, Nicholas
Partner: UNT Libraries Government Documents Department

Molecular Comb Development

Description: This CRADA was developed to enable ORNL to assist Protein Discovery, Inc. to develop a novel biomolecular separation system based on an ORNL patent application 'Photoelectrochemical Molecular Comb' by Thundat, Ferrell, and Brown. The Molecular Comb concept is based on creating light-induced charge carriers at a semiconductor-liquid interface, which is kept at a potential control such that a depletion layer is formed in the semiconductor. Focusing light from a low-power illumination source creates electron-hole pairs, which get separated in the depletion layer. The light-induced charge carriers reaching the surface attract oppositely charged biomolecules present in the solution. The solution is a buffer solution with very small concentrations of biomolecules. As the focused light is moved across the surface of the semiconductor-liquid interface, the accumulated biomolecules follow the light beam. A thin layer of gel or other similar material on the surface of the semiconductor can act as a sieving medium for separating the biomolecules according to their sizes.
Date: July 17, 2007
Creator: Ferrell, T.L.; Thundat, G.T. & Witkowski, C.E., III (Protein Discovery, Inc.)
Partner: UNT Libraries Government Documents Department

Streaming Compression of Tetrahedral Volume Meshes

Description: Geometry processing algorithms have traditionally assumed that the input data is entirely in main memory and available for random access. This assumption does not scale to large data sets, as exhausting the physical memory typically leads to IO-inefficient thrashing. Recent works advocate processing geometry in a 'streaming' manner, where computation and output begin as soon as possible. Streaming is suitable for tasks that require only local neighbor information and batch process an entire data set. We describe a streaming compression scheme for tetrahedral volume meshes that encodes vertices and tetrahedra in the order they are written. To keep the memory footprint low, the compressor is informed when vertices are referenced for the last time (i.e. are finalized). The compression achieved depends on how coherent the input order is and how many tetrahedra are buffered for local reordering. For reasonably coherent orderings and a buffer of 10,000 tetrahedra, we achieve compression rates that are only 25 to 40 percent above the state-of-the-art, while requiring drastically less memory resources and less than half the processing time.
Date: November 21, 2005
Creator: Isenburg, M; Lindstrom, P; Gumhold, S & Shewchuk, J
Partner: UNT Libraries Government Documents Department

Enabling compatibility between TCP Reno and TCP Vegas

Description: Despite research showing the superiority of TCP Vegas over TCP Reno, Reno is still the most widely deployed variant of TCP This predicament is due primarily to the alleged incompatibility of Vegas with Reno. While Yegas in isolation performs better with respect to overall network utilization, stability, fairness, throughput lznd packet loss, and burstiness; its perfarmance is generally mediocre in any environment where Reno connections exist. Hence, there exists no incentive for any operating system to adopt TCP Vegas. In this paper. we show that the accepted (default) configuration of Vegas is indeed incompatible with TCP Reno. However: with a careful analysis of how Reno and Vegas use buffer space in routers, Reno and Vegas can be compatible with one another if Vegas is conjigured properly Furthermore, we show that overall network performance actually improves with the addition of properly conjigured Vegas flows competing head-to-head with Reno flows.
Date: January 1, 2002
Creator: Feng, Wu-Chun & Vanichpun, Sarut
Partner: UNT Libraries Government Documents Department

Engineered microstructures and transport properties in YBCO coated conductors.

Description: Each process used to deposit or make the bi-axially textured template, buffer layer(s), and the superconductor in a coated conductor creates interfaces along which defects or interfacial reactions may result. These defects can be additive and propagate through the entire film structure to affect the growth and properties of the superconducting film. Defects within the films and their corresponding transport properties have been correlated with the differences in the thickness of the underlying buffer layer material. This knowledge can be used to control and engineer the structure of the coated conductor to maximize critical current densities.
Date: January 1, 2001
Creator: Holesinger, Terry G.; Gibbons, Brady J.; Coulter, James Y.; Foltyn, Stephen R. & Arendt, Paul N.
Partner: UNT Libraries Government Documents Department

Microstructural development and control in YBa[sub 2]Cu[sub 3]O[sub y]

Description: A study of some defect structures in Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7} (Y-123)coated conductors based on ion-beam -assisted-deposition (IBAD) of yttria-stabilized zirconia (YSZ) on nickel alloy substrates is presented. Defect structures can originate anywhere in the coated conductor architecture. Defects can be additive and propagate through the entire film structure to affect the growth, orientation, arid properties of the superconducting film. Interfacial Ieactions between Y- 123 and the underlying buffer layer and the corresponding effects on the transport properticis of the films can be controlled with the thickness of the underlying buffer layer. With a 9Ow ceria buffer layer on an IBAD YSZ coated metal substrate, a J, value of 1.7 MA/cm{sup 2} (self-field, 75K) was obtained in a 1.5{micro}m thick Y-123 film.
Date: January 1, 2001
Creator: Holesinger, T. G. (Terry G.); Gibbons, B. J. (Brady J.); Foltyn, S. R. (Stephen R.); Arendt, P. N. (Paul N.); Groves, J. R. (James R.) & Coulter, J. Y. (James Y.)
Partner: UNT Libraries Government Documents Department

Development of Substrate for RABiTS-based HTS Conductors

Description: During its fifteen years of life, this CRADA has evolved in both scope and purpose. Early efforts to develop high performance bismuth-based powder-in-tube first generation high temperature superconductors (HTS) have shifted toward efforts to understand and develop technologies required to fabricate second generation HTS coated conductors. Since the two original longstanding principal investigators from UT-Battelle and Oxford Superconducting Technology (OST) are not presently employed by their respective organizations, this final report shall focus primarily on results of the more recent past involving research and development of the deformation and annealing processes required to fabricate metallic substrates for RABiTS-based second generation coated conductors. The specific objectives of this recent work involve the development of OST Ni/3%W tape for HTS coated conductors and include: (a) to improve uniformity of cube texture through control of deformation and annealing parameters, (b) to minimize delamination and other buffer deposition problems through understanding and control of key parameters related to the metal substrate, (c) to ensure that the textured metal substrate allows well textured buffers with no delamination, and (d) to prepared a final report.
Date: June 5, 2009
Partner: UNT Libraries Government Documents Department