6,082 Matching Results

Search Results

Mechanism of strain release in carbon nanotubes

Description: Article on the mechanism of strain release in carbon nanotubes.
Date: February 15, 1998
Creator: Buongiorno Nardelli, Marco; Yakobson, Boris I. & Bernholc, Jerry
Partner: UNT College of Arts and Sciences

High-Temperature Fast-Flow Reactor Kinetics Studies of the Reactions of Al with Cl₂, Al with HCl, and AlCl, with Cl₂ over Wide Temperature Ranges

Description: Article on high-temperature fast-flow reactor kinetics studies of the reactions of aluminum with chlorine, aluminum with hydrogen chloride and aluminum monochloride with chlorine over wide temperature ranges.
Date: April 12, 1988
Creator: Rogowski, Donald F.; Marshall, Paul & Fontijn, A. (Arthur)
Partner: UNT College of Arts and Sciences

Numerical relativity in a distributed environment.

Description: We have found that the hardware and software infrastructure exists to simulate general relativity problems in a distributed computational environment, at some cost in performance. We examine two different issues for running the Cactus code in such a distributed environment The first issue is running a Cactus simulation on multiple parallel computer systems. Our objective is to perform larger simulations than are currently possible on a single parallel computer. We distribute Cactus simulations across multiple supercomputers using the mechanisms provided by the Globus toolkit. In particular, we use Globus mechanisms for authentication, access to remote computer systems, file transfer, and communication. The Cactus code uses MPI for communication and makes use of an MPI implementation layered atop Globus communication mechanisms. These communication mechanisms allow a MPI application to be executed on distributed resources. We find that without performing any code optimizations, our simulations ran 48% to 100% slower when using an Origin at the National Center for Supercomputing Applications (NCSA) and an Onyx2 at Argonne National Laboratory (ANL). We also ran simulations between Cray T3Es in Germany and a T3E at the San Diego Supercomputing Center (SDSC). Running between the T3Es in Germany resulted in an increase in execution time of 79% to 133%, and running between a German T3E and a T3E at the San Diego Supercomputing Center resulted in an execution time increase of 114% to 186%. We are very encouraged that we are able to run simulations on parallel computers that are geographically distributed, and we have identified several areas to investigate to improve the performance of Cactus simulations in this environment. The second issue we examine here is remote visualization and steering of the Cactus code. Cactus is a modular framework and we have implemented a module for this task. This module performs isosurfacing operations on ...
Date: February 8, 1999
Creator: Benger, W.; Foster, I.; Novotny, J.; Seidel, E.; Shalf, J.; Smith, W. et al.
Partner: UNT Libraries Government Documents Department

Ohmic contacts to Si-implanted and un-implanted n-type GaN

Description: We report on ohmic contacts to Si-implanted and un-implanted n-type GaN on sapphire. A ring shaped contact design avoids the need to isolate the contact structures by additional implantation or etching. Metal layers of Al and Ti/Al were investigated. On un-implanted GaN, post metalization annealing was performed in an RTA for 30 seconds in N{sub 2} at 700, 800, and 900 C. A minimum specific contact resistance (r{sub c}) of 1.4{times}10{sup -5} {Omega}{minus}cm{sup 2} was measured for Ti/Al at an annealing temperature of 800 C. Although these values are reasonably low, variations of 95% in specific contact resistance were measured within a 500 {mu}m distance on the wafer. These results are most likely caused by the presence of compensating hydrogen. Specific contact resistance variation was reduced from 95 to 10% by annealing at 900 C prior to metalization. On Si-implanted GaN, un-annealed ohmic contacts were formed with Ti/Al metalization. The implant activation anneal of 1120 C generates nitrogen vacancies that leave the surface heavily n-type, which makes un-annealed ohmic contacts with low contact resistivity possible.
Date: February 1996
Creator: Brown, J.; Ramer, J.; Zheng, L. F.; Hersee, S. D. & Zolper, J.
Partner: UNT Libraries Government Documents Department

Remediating the INEL`s buried mixed waste tanks

Description: The Idaho National Engineering Laboratory (INEL), formerly the National Reactor Testing Station (NRTS), encompasses 890 square miles and is located in southeast Idaho. In 1949, the United States Atomic Energy Commission, now the Department of Energy (DOE), established the NRTS as a site for the building and testing of nuclear facilities. Wastes generated during the building and testing of these nuclear facilities were disposed within the boundaries of the site. These mixed wastes, containing radionuclides and hazardous materials, were often stored in underground tanks for future disposal. The INEL has 11 buried mixed waste storage tanks regulated under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) ranging in size from 400 to 50,000 gallons. These tanks are constructed of either stainless or carbon steel and are located at 3 distinct geographic locations across the INEL. These tanks have been grouped based on their similarities in an effort to save money and decrease the time required to complete the necessary remediation. Environmental Restoration and Technology Development personnel are teaming in an effort to address the remediation problem systematically.
Date: February 28, 1996
Creator: Kuhns, D.J.; Matthern, G.E. & Reese, C.L.
Partner: UNT Libraries Government Documents Department

Experimental and modeling investigation of aromatic and polycyclic aromatic hydrocarbon formation in a premixed ethylene flame

Description: Experimental and detailed chemical kinetic modeling has been performed to investigate aromatic and polyaromatic hydrocarbon formation pathways in a rich, sooting, ethylene-oxygen-argon premixed flame. An atmospheric pressure, laminar flat flame operated at an equivalence ratio of 2.5 was used to acquire experimental data for model validation. Gas composition analysis was conducted by an on-line gas chromatograph/mass spectrometer (GC/MS) technique. Measurements were made in the flame and post-flame zone for a number of low molecular weight species, aliphatics, aromatics and polycyclic aromatic hydrocarbons (PAHs) ranging from two to five-aromatic fused rings. The modeling results show the key reaction sequences leading to aromatic and polycyclic aromatic hydrocarbon growth involve the combination of resonantly stabilized radicals. In particular, propargyl and 1-methylallenyl combination reactions lead to benzene and methyl substituted benzene formation, while polycyclic aromatics are formed from cyclopentadienyl radicals and fused rings that have a shared C{sub 5} side structure. Naphthalene production through the reaction step of cyclopentadienyl self-combination and phenanthrene formation from indenyl and cyclopentadienyl combination were shown to be important in the flame modeling study. The removal of phenyl by O{sub 2} leading to cyclopentadienyl formation is expected to play a pivotal role in the PAH or soot precursor growth process under fuel-rich oxidation conditions.
Date: February 1, 1996
Creator: Castaldi, M.J.; Marinov, N.M. & Melius, C.F.
Partner: UNT Libraries Government Documents Department

Repowering with clean coal technologies

Description: Repowering with clean coal technology can offer significant advantages, including lower heat rates and production costs, environmental compliance, incremental capacity increases, and life extension of existing facilities. Significant savings of capital costs can result by refurbishing and reusing existing sites and infrastructure relative to a greenfield siting approach. This paper summarizes some key results of a study performed by Parsons Power Group, Inc., under a contract with DOE/METC, which investigates many of the promising advanced power generation technologies in a repowering application. The purpose of this study was to evaluate the technical and economic results of applying each of a menu of Clean Coal Technologies in a repowering of a hypothetical representative fossil fueled power station. Pittsburgh No. 8 coal is used as the fuel for most of the cases evaluated herein, as well as serving as the fuel for the original unrepowered station. The steam turbine-generator, condenser, and circulating water system are refurbished and reused in this study, as is most of the existing site infrastructure such as transmission lines, railroad, coal yard and coal handling equipment, etc. The technologies evaluated in this study consisted of an atmospheric fluidized bed combustor, several varieties of pressurized fluid bed combustors, several types of gasifiers, a refueling with a process derived fuel, and, for reference, a natural gas fired combustion turbine-combined cycle.
Date: February 1, 1996
Creator: Freier, M.D.; Buchanan, T.L.; DeLallo, M.L. & Goldstein, H.N.
Partner: UNT Libraries Government Documents Department

A note on simulation and dynamical hierarchies

Description: This paper summarizes some of the problems associated with the generation of higher order emergent structures in formal dynamical systems as well as some of the formal properties of dynamical systems capable of generating higher order structures.
Date: February 22, 1996
Creator: Rasmussen, S.; Barrett, C. L.; Baas, N. A. & Olesen, M. W.
Partner: UNT Libraries Government Documents Department

Health monitoring studies on composite structures for aerospace applications

Description: This paper discusses ongoing work to develop structural health monitoring techniques for composite aerospace structures such as aircraft control surfaces, fuselage sections or repairs, and reusable launch vehicle fuel tanks. The overall project is divided into four tasks: Operational evaluation, diagnostic measurements, information condensation, and damage detection. Five composite plates were constructed to study delaminations, disbonds, and fluid retention issues as the initial step in creating an operational system. These four square feet plates were graphite-epoxy with nomex honeycomb cores. The diagnostic measurements are composed of modal tests with a scanning laser vibrometer at over 500 scan points per plate covering the frequency range up to 2000 Hz. This data has been reduced into experimental dynamics matrices using a generic, software package developed at the University of Colorado at Boulder. The continuing effort will entail performing a series of damage identification studies to detect, localize, and determine the extent of the damage. This work is providing understanding and algorithm development for a global NDE technique for composite aerospace structures.
Date: February 1, 1996
Creator: James, G.; Roach, D.; Hansche, B.; Meza, R. & Robinson, N.
Partner: UNT Libraries Government Documents Department

Enhanced work planning for reduction in landlord costs

Description: The cost of Landlord services constitutes a major portion of the Fernald Environmental Management Project (FEMP) budget. In order to place more resources in the area of actual remediation and cleanup, the Fernald Environmental Restoration Management Corporation (FERMCO) has established a new enhanced work planning initiative through the Integrated Safe Shutdown, Waste Management, and Landlord (ISWL) Project Team. The ISWL Project Team is a planning and coordination group which meets weekly at no additional cost to the DOE; actual field work is funded and implemented through the remedial or operational projects. The purpose of this team is to address issues that will facilitate safe shutdown and/or reduction of utilities in facilities thereby decreasing the infrastructure costs and increasing integration/advanced planning between Waste Management, Safe Shutdown, and Landlord Programs. The ISWL Project Team is the key planning and integration link for near term (one month to one year) integration activities. The ISWL Team is planning for the coordination of integration activities which must be completed to support and facilitate the FEMP`s (1) Safe Shutdown Program, (2) Utility Reduction Program, (3) Waste Programs Management, (4) remediation of all FEMP structures, and (5) ongoing remediation projects.
Date: February 1, 1996
Creator: Miller, L.K.; Houser, S.M.; Paine, D. & West, M.L.
Partner: UNT Libraries Government Documents Department

Non-proliferation issues for the disposition of fissile materials using reactor alternatives

Description: The Department of Energy (DOE) is analyzing long-term storage on options for excess weapons-usable fissile materials. A number of the disposition alternatives are being considered which involve the use of reactors. The various reactor alternatives are all very similar and include front-end processes that could convert plutonium to a usable form for fuel fabrication, a MOX fuel fab facility, reactors to bum the MOX fuel and ultimate disposal of spent fuel in some geologic repository. They include existing, partially completed, advanced or evolutionary light water reactors and Canadian deuterium uranium (CANDU) reactors. In addition to the differences in the type of reactors, other variants on these alternatives are being evaluated to include the location and number of the reactors, the location of the mixed oxide (MOX) fabrication facility, the ownership of the facilities (private or government) and the colocation and/or separation of these facilities. All of these alternatives and their variants must be evaluated with respect to non-proliferation resistance. Both domestic and international safeguards support are being provided to DOE`s Fissile Materials Disposition Program (FMDP) and includes such areas as physical protection, nuclear materials accountability and material containment and surveillance. This paper will focus on how the non-proliferation objective of reducing security risks and strengthening arms reduction will be accomplished and what some of the nonproliferation issues are for the reactor alternatives. Proliferation risk has been defined in terms of material form, physical environment, and the level of security and safeguards that is applied to the material. Metrics have been developed for each of these factors. The reactor alternatives will be evaluated with respect to these proliferation risk factors at each of the unit process locations in the alternative.
Date: February 1, 1996
Creator: Jaeger, C.D.; Duggan, R.A. & Tolk, K.M.
Partner: UNT Libraries Government Documents Department

Chemical treatment of mixed waste can be done.....Today!

Description: The Chemical Treatment Project is one in a series of projects implemented by the FEMP to treat mixed waste. The projects were initiated to address concerns regarding treatment capacity for mixed waste and to comply with requirements established by the Federal Facility Compliance Act. The Chemical Treatment Project is designed to utilize commercially available mobile technologies to perform treatment at the FEMP site. The waste in the Project consists of a variety of waste types with a wide range of hazards and physical characteristics. The treatment processes to be established for the waste types will be developed by a systematic approach including waste streams evaluation, projectization of the waste streams, and categorization of the stream. This information is utilized to determine the proper train of treatment which will be required to lead the waste to its final destination (i.e., disposal). This approach allows flexibility to manage a wide variety of waste in a cheaper, faster manner than designing a single treatment technology diverse enough to manage all the waste streams.
Date: February 1, 1996
Creator: Honigford, L.; Dilday, D.; Cook, D. & Sattler, J.
Partner: UNT Libraries Government Documents Department