200 Matching Results

Search Results

Advanced search parameters have been applied.

Nanoscience Research for Energy Needs. Report of the National Nanotechnology Initiative Grand Challenge Workshop, March 16-18, 2004

Description: This document is the report of a workshop held under NSET auspices in March 2004 aimed at identifying and articulating the relationship of nanoscale science and technology to the Nation's energy future.
Date: March 18, 2004
Creator: Alivisatos, P.; Cummings, P.; De Yoreo, J.; Fichthorn, K.; Gates, B.; Hwang, R. et al.
Partner: UNT Libraries Government Documents Department


Description: Basic studies of the kinetics of the reduction of copper oxide were made to establish the effect of the solid phase on the over-all reaction kinetics The reaction CuO + H/sub 2/ at the only rea Cu + H/sub 2/O consisted of an induction stage, an acceleration or autocatalytic stage terminating at about 35% reduction of the exide, and a decreasing-rate stage The reduction rates for each stage were dependent on the nature of the initial oxide, the degree of subdivision of the oxide, and the temperature but were independent of the mass of the oxide phase. Addition of the reaction product copper had no measurable effect on the reaction. Water vapor in concentrations of 25 mg per liter of H prevented reduction at 112 ction prod- C The inhibiting effect decreased rapidly as the temperature was increased and disappeared entirely at 190 ction prod- C. Once reduction bad started. water vapor had practically no effect The acceleration and decay stages were very closely approximated by a semiempirical equation based on the initial reaction occurring on certain active nuclei followed by a rapid growth of these nuclei by a branching-chain mechanism. The reduction rate reached a maximum and subsequentlv decreased as considerable interference occurred among the branching nuclei. Arrhenius plots gave an activation energy- of 13.5 plus or minus 1.2);cal for the reduction. (auth)
Date: March 30, 1960
Creator: Bond, W.D. & Clark, W.E.
Partner: UNT Libraries Government Documents Department


Description: A study was conducted to demonstrate the stripping and evaporation steps in a Purex-type uranium recovery prccess and to ascertain the operating behavior of the equipment under a range of conditions. The factors considered were control, effectiveness, and reliability of equipment and optimum feed pcint. Experimental procedures are described, and recominendations for equipment mcdifications are included. (J.R.D.)
Date: March 18, 1957
Creator: Long, J.T.
Partner: UNT Libraries Government Documents Department

BFS, a Legacy to the International Reactor Physics, Criticality Safety, and Nuclear Data Communities

Description: Interest in high-quality integral benchmark data is increasing as efforts to quantify and reduce calculational uncertainties accelerate to meet the demands of next generation reactor and advanced fuel cycle concepts. Two Organization for Economic Cooperation and Development (OECD) Nuclear Energy Agency (NEA) activities, the International Criticality Safety Benchmark Evaluation Project (ICSBEP), initiated in 1992, and the International Reactor Physics Experiment Evaluation Project (IRPhEP), initiated in 2003, have been identifying existing integral experiment data, evaluating those data, and providing integral benchmark specifications for methods and data validation for nearly two decades. Thus far, 14 countries have contributed to the IRPhEP, and 20 have contributed to the ICSBEP. Data provided by these two projects will be of use to the international reactor physics, criticality safety, and nuclear data communities for future decades The Russian Federation has been a major contributor to both projects with the Institute of Physics and Power Engineering (IPPE) as the major contributor from the Russian Federation. Included in the benchmark specifications from the BFS facilities are 34 critical configurations from BFS-49, 61, 62, 73, 79, 81, 97, 99, and 101; spectral characteristics measurements from BFS-31, 42, 57, 59, 61, 62, 73, 97, 99, and 101; reactivity effects measurements from BFS-62-3A; reactivity coefficients and kinetics measurements from BFS-73; and reaction rate measurements from BFS-42, 61, 62, 73, 97, 99, and 101.
Date: March 1, 2012
Creator: Briggs, J. Blair; Tsibulya, Anatoly & Rozhikhin, Yevgeniy
Partner: UNT Libraries Government Documents Department

A Compton-Vetoed Germanium Detector with Increased Sensitivity at Low Energies

Description: The difficulty to directly detect plutonium in spent nuclear fuel due to the high Compton background of the fission products motivates the design of a Gamma detector with improved sensitivity at low energies. We have built such a detector by operating a thin high-purity Ge detector with a large scintillator Compton veto directly behind it. The Ge detector is thin to absorb just the low-energy Pu radiation of interest while minimizing Compton scattering of high energy radiation from the fission products. The subsequent scintillator is large so that forward scattered photons from the Ge detector interact in it at least once to provide an anti-coincidence veto for the Ge detector. For highest sensitivity, additional material in the line-of-sight is minimized, the radioactive sample is kept thin, and its radiation is collimated. We will discuss the instrument design, and demonstrate the feasibility of the approach with a prototype that employs two large CsI scintillator vetoes. Initial spectra of a thin Cs-137 calibration source show a background suppression of a factor of {approx}2.5 at {approx}100 keV, limited by an unexpectedly thick 4 mm dead layer in the Ge detector.
Date: March 29, 2012
Creator: Friedrich, S; Bates, C; Drury, O B; Burks, M & DiPrete, D
Partner: UNT Libraries Government Documents Department

Macro-meso-microsystems integration in LTCC : LDRD report.

Description: Low Temperature Cofired Ceramic (LTCC) has proven to be an enabling medium for microsystem technologies, because of its desirable electrical, physical, and chemical properties coupled with its capability for rapid prototyping and scalable manufacturing of components. LTCC is viewed as an extension of hybrid microcircuits, and in that function it enables development, testing, and deployment of silicon microsystems. However, its versatility has allowed it to succeed as a microsystem medium in its own right, with applications in non-microelectronic meso-scale devices and in a range of sensor devices. Applications include silicon microfluidic ''chip-and-wire'' systems and fluid grid array (FGA)/microfluidic multichip modules using embedded channels in LTCC, and cofired electro-mechanical systems with moving parts. Both the microfluidic and mechanical system applications are enabled by sacrificial volume materials (SVM), which serve to create and maintain cavities and separation gaps during the lamination and cofiring process. SVMs consisting of thermally fugitive or partially inert materials are easily incorporated. Recognizing the premium on devices that are cofired rather than assembled, we report on functional-as-released and functional-as-fired moving parts. Additional applications for cofired transparent windows, some as small as an optical fiber, are also described. The applications described help pave the way for widespread application of LTCC to biomedical, control, analysis, characterization, and radio frequency (RF) functions for macro-meso-microsystems.
Date: March 1, 2007
Creator: De Smet, Dennis J.; Nordquist, Christopher Daniel; Turner, Timothy Shawn; Rohrer, Brandon Robinson; Walker, Charles A.; Ho, Clifford K.. et al.
Partner: UNT Libraries Government Documents Department


Description: Implanted medical devices such as pacemakers and neural prosthetics require that the electronic components that power these devices are protected from the harsh chemical and biological environment of the body. Typically, the electronics are hermetically sealed inside a bio-compatible package containing feedthroughs that transmit electrical signals, while being impermeable to particles or moisture. We present a novel approach for fabricating one of the highest densities of biocompatible hermetic feedthroughs in alumina (Al{sub 2}O{sub 3}). Alumina substrates with laser machined vias of 200 {mu}m pitch were conformally metallized and lithographically patterned. Hermetic electrical feedthroughs were formed by extruding metal studbumps partially through the vias. Hermeticity testing showed leak rates better than 9x10{sup -10} torr-l/s. Based on our preliminary results and process optimization, this extruded metal via approach is a high-density, low temperature, cost-effective, and robust method of miniaturizing electrical feedthroughs for a wide range of implantable bio-medical device applications.
Date: March 29, 2012
Creator: Tooker, A; Shah, K; Tolosa, V; Sheth, H; Felix, S; Delima, T et al.
Partner: UNT Libraries Government Documents Department

A Low-Cost Soft-Switched DC/DC Converter for Solid-Oxide Fuel Cells

Description: A highly efficient DC to DC converter has been developed for low-voltage high-current solid oxide fuel cells. The newly developed 'V6' converter resembles what has been done in internal combustion engine that split into multiple cylinders to increase the output capacity without having to increase individual cell size and to smooth out the torque with interleaving operation. The development was started with topology overview to ensure that all the DC to DC converter circuits were included in the study. Efficiency models for different circuit topologies were established, and computer simulations were performed to determine the best candidate converter circuit. Through design optimization including topology selection, device selection, magnetic component design, thermal design, and digital controller design, a bench prototype rated 5-kW, with 20 to 50V input and 200/400V output was fabricated and tested. Efficiency goal of 97% was proven achievable through hardware experiment. This DC to DC converter was then modified in the later stage to converter 35 to 63 V input and 13.8 V output for automotive charging applications. The complete prototype was tested at Delphi with their solid oxide fuel cell test stand to verify the performance of the modified DC to DC converter. The output was tested up to 3-kW level, and the efficiency exceeded 97.5%. Multiple-phase interleaving operation design was proved to be reliable and ripple free at the output, which is desirable for the battery charging. Overall this is a very successful collaboration project between the SECA Core Technology Team and Industrial Team.
Date: March 3, 2009
Creator: Lai, Jason
Partner: UNT Libraries Government Documents Department

Surrogate Nuclear Reactions - An Indirect Method for Determining Reaction Cross Sections

Description: An indirect method for determining cross sections of reactions proceeding through a compound nucleus is presented. Some applications of the Surrogate nuclear reaction approach are considered and challenges that need to be addressed are outlined.
Date: March 23, 2005
Creator: Escher, J; Ahle, L; Bernstein, L; Burke, J; Church, J A; Dietrich, F et al.
Partner: UNT Libraries Government Documents Department


Description: The Civil Effects Test Operation Exercise CEX-57.1 following Operation Plumbbob was carried out to obtain information on decontamination procedures that could be used as radiological countermeasures. The test was conducted on D + 1 and D + 2 days after shot Coulomb C. Data were obtained on reclamation of land areas by scraping with a motorgrader, on fire-hosing and scrubbing a concrete- slab roof, and on fire-hosing a composition roof. In addition, some shielding data were obtained for a small building with 6-in.-thick concrete walls and roof. The conceptual nature of a radiological defense system and the role of decontamination or reclamation in such a system are discussed. Most of the report deals with methods for reducing the observed data to interpretive form because the data were taken within a large contaminated area. The decontamination effectiveness in terms of the fraction of contamination remaining was computed. It is concluded that low levels of contamination at the Nevada Test Site could be utilized to advantage to obtain data on gamma -radiation properties, such as the effects of materials and source geometries on the attenuation of fission-product gamma rays. However, higher levels of fall-out in terms of the fall-out particle mass, are required to obtain useful information and training on decontamination techniques; therefore the use of low levels of contamination to conduct studies in this area is not recommended. (auth)
Date: March 1, 1958
Creator: Miller, C.F.
Partner: UNT Libraries Government Documents Department

Chemical Safety Alert: Anhydrous Ammonia Theft

Description: This publication of Alert presents the Environmental Protection Agency's analysis of anhydrous ammonia as used for agricultural fertilizer and industrial refrigerant.
Date: March 2000
Creator: United States. Environmental Protection Agency. Office of Solid Waste and Emergency Response.
Partner: UNT Libraries Government Documents Department

Fission Product Traps for Use in High-Temperature Gas-Cooled Graphite Reactors

Description: A proposal is given of an approach to a fission-product trapping system which appears feasible on the basis of thermodynamic and other data available. Reactor and trapping conditions are outlined. The half-lives, fission yields, and volatility of the fission products of interest are described. To provide the most effective retention at elevated temperatures, two types of reagents are required: a highly electropositive metal that will not melt or appreciably vaporize and which will form stable non-volatile compounds with non-metallic or near non-metallic fission products; and a reagent to provide a highly electronegative element to form stable, non-volatile compounds with metallic fission products. Thermodynamic properties are included for compounds formed by reactions between the fission products and the trapping reagents. (B.O.G.)
Date: March 13, 1958
Creator: Zumwalt, L. R.
Partner: UNT Libraries Government Documents Department

Exposure of Reactor Structural Materials to Impure Helium at Elevated Temperatures

Description: In the High-temperature Gas-cooled Reactor (HTGR), structural metals will be required to operate at temperatures of 1000 to 1400 deg F in an impure- helium environment for extended periods of time. Six candidate materials for such applications, including nickel alloys and stainless steels, were subjected to simulated reactor environments for times up to 3000 hr to evaluate the extent of corrosion and the changes in mechanical properties occasioned by I such exposures. Under the experimental exposure conditions (helium containing 200 to 300 ppm CO and 200 to 300 ppm H/sub 2/, or helium containing 2000 to 3000 ppm CO and 2000 to 3000 ppm H/sub 2/, at temperatures of 1200 or 1400 deg F), oxidation rather than carburization appears to be the major corrosion process; however, in some cases alternating carburization and decarburization were observed. Measurements of weight gains are described. None of the materials studied exhibited a large change in their mechanical properties after exposures at 1200 deg F. After exposures at 1400 deg F, moderate changes in mechanical properties were observed for all materials except Type 321H stainless steel, which exhibited a large decrease in ductility after l500-hr exposure to the higher impurity concentration. In general, the control specimens were affected as greatly as the specimens exposed to the impure helium environments, under the conditions of these tests. (R.J.S.)
Date: March 22, 1962
Creator: Weinberg, A. F. & Scoffin, J. M.
Partner: UNT Libraries Government Documents Department

The Nuclear Rocket: New Powerplant for Space Vehicle Propulsion

Description: A fundamental and practical survey is made of nuclear rocket application to space vehicle propulsion. The engine is described and propellant and radiation effects are discussed. Project Rover is summarized and performance requirements for a space vehicle are discussed. It is concluded that nuclear rockets can provide substantial performance, reliability, and economic advantages for difficult space missions. (T.R.H.)
Date: March 1, 1960
Creator: Schmidt, H. R. & Decker, R. S.
Partner: UNT Libraries Government Documents Department

Multi-Modality Phantom Development

Description: Multi-modality imaging has an increasing role in the diagnosis and treatment of a large number of diseases, particularly if both functional and anatomical information are acquired and accurately co-registered. Hence, there is a resulting need for multi modality phantoms in order to validate image co-registration and calibrate the imaging systems. We present our PET-ultrasound phantom development, including PET and ultrasound images of a simple prostate phantom. We use agar and gelatin mixed with a radioactive solution. We also present our development of custom multi-modality phantoms that are compatible with PET, transrectal ultrasound (TRUS), MRI and CT imaging. We describe both our selection of tissue mimicking materials and phantom construction procedures. These custom PET-TRUS-CT-MRI prostate phantoms use agargelatin radioactive mixtures with additional contrast agents and preservatives. We show multi-modality images of these custom prostate phantoms, as well as discuss phantom construction alternatives. Although we are currently focused on prostate imaging, this phantom development is applicable to many multi-modality imaging applications.
Date: March 20, 2009
Creator: Huber, Jennifer S.; Peng, Qiyu & Moses, William W.
Partner: UNT Libraries Government Documents Department

Kinetics, Stability, and Control. A Selected Bibliography

Description: References to 529 articles on nuclear reactor control, kinetics, and stability published before autumn 1962 are included. Emphasis is on calculations and theory since the references serve as an aid in analyzing the dynamic behavior of SNAP reactor systems. (D.C.W.)
Date: March 15, 1963
Creator: Johnson, R. L.
Partner: UNT Libraries Government Documents Department


Description: It is noted that in chemonuclear reaction systems the efficiency of conversion of nuclear to chemical energy is directly related to the fraction of the total fission fragment recoil energy liberated in the system which is directly absorbed by the chemical reactant. This fraction is termed the fission fragment energy deposition. The use of gas dosimetry for determining the deposition efficiency is described, and G value data are given for nitrogen fixation by fission fragment energy. (J.R.D.)
Date: March 1, 1963
Creator: Steinberg, M.; Loffelholz, M. & Pruzansky, J.
Partner: UNT Libraries Government Documents Department