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NUMERICAL SIMULATION OF VORTEX BREAKDOWN

Description: Vortex breakdown is simulated by a three dimensional Lagrangian method using vortex filaments. The filaments are approximated by vortex elements and their velocity is computed by a Biot-Savart type law of interaction. The numerical calculations show the development of an axisymmetric bubble with a recirculation zone and resemble in many respects the results obtained in the physical experiments on vortex breakdown.
Date: October 1, 1978
Creator: Prete, Vincenza Del
Partner: UNT Libraries Government Documents Department

Toxicological Benchmarks for Screening Potential Contaminants of Concern for Effects on Soil and Litter Invertebrates and Heterotrophic Process

Description: This report presents a standard method for deriving benchmarks for the purpose of ''contaminant screening,'' performed by comparing measured ambient concentrations of chemicals. The work was performed under Work Breakdown Structure 1.4.12.2.3.04.07.02 (Activity Data Sheet 8304). In addition, this report presents sets of data concerning the effects of chemicals in soil on invertebrates and soil microbial processes, benchmarks for chemicals potentially associated with United States Department of Energy sites, and literature describing the experiments from which data were drawn for benchmark derivation.
Date: January 1, 1994
Creator: Will, M. E.
Partner: UNT Libraries Government Documents Department

TPV Network Sensitivity: A Simulation Study

Description: A viable thermophotovoltaic power conversion system requires an electrically connected network of diodes that is designed to be fault tolerant for a prescribed power rating and generator life. This paper describes simulation studies investigating the sensitivity of various series/parallel network configurations to diode variability. The results show the effect of diode mismatch and reverse breakdown behavior on network performance.
Date: February 10, 2004
Creator: Vell, J.L.; Oppenlander, J.E.; Gaes, W.S.; Siganporia, D.M. & Danielson, L.R.
Partner: UNT Libraries Government Documents Department

Analysis Code for High Gradient Dielectric Insulator Surface Breakdown

Description: High voltage (HV) insulators are critical components in high-energy, accelerator and pulsed power systems that drive diverse applications in the national security, nuclear weapons science, defense and industrial arenas. In these systems, the insulator may separate vacuum/non-vacuum regions or conductors with high electrical field gradients. These insulators will often fail at electric fields over an order of magnitude lower than their intrinsic dielectric strength due to flashover at the dielectric interface. Decades of studies have produced a wealth of information on fundamental processes and mechanisms important for flashover initiation, but only for relatively simple insulator configurations in controlled environments. Accelerator and pulsed power system designers are faced with applying the fundamental knowledge to complex, operational devices with escalating HV requirements. Designers are forced to rely on “best practices” and expensive prototype testing, providing boundaries for successful operation. However, the safety margin is difficult to estimate, and system design must be very conservative for situations where testing is not practicable, or replacement of failed parts is disruptive or expensive. The Phase I program demonstrated the feasibility of developing an advanced code for modeling insulator breakdown. Such a code would be of great interest for a number of applications, including high energy physics, microwave source development, fusion sciences, and other research and industrial applications using high voltage devices.
Date: May 30, 2010
Creator: Ives, Robert Lawrence; Verboncoeur, John & Aldan, Manuel
Partner: UNT Libraries Government Documents Department

A SPARK-GAP TRIGGER SYSTEM

Description: The construction and operation of a trigger system designed to fire a 30-kV 5000 A spark gap with a minimum delay following the arrival of a small signal pulse is described. In this particular experiment a 150-MeV/c muon is detected with scintillators on three 6199 phototubes, and the output pulse of the attached tunnel-diode triple-coincidence circuit is amplified and used to trigger the gap. Approximately 32 nanoseconds are needed from passage of the muon to the coincidence output, and approximately 25 nanoseconds are required from the coincidence output to the time of complete breakdown of the gap. These delays represent the shortest times that we could achieve with the particular boundary conditions under which the circuit had to operate. Sufficient detail is given to show how additional savings of nanoseconds could be made under different operating conditions.
Date: August 6, 1963
Creator: Schrank, Glen E.; Henry, George R.; Kerns, Quentin A. & Swanson, Robert A.
Partner: UNT Libraries Government Documents Department

Comparison of buffered chemical polished and electropolished 3.9 GHz cavities

Description: Five 3.9 GHz 9 cell cavities have been measured for the DESY FLASH module. These cavities were BCP processed and reached gradients of typically about 25 MV/m with Q drop starting at about 20 MV/m. Recently a few one cell cavities have been processed with EP and at least one has tested to a gradient of 30 MV/m with Q drop starting at about 25 MV/m. We will compare the results and give an update to the thermal analysis in relation to global thermal breakdown at 3.9 GHz.
Date: October 1, 2009
Creator: Edwards, Helen; Cooper, Charlie A.; Ge, Mingqi; Gonin, Ivan V.; Harms, Elvin R.; Khabiboulline, Timergali N. et al.
Partner: UNT Libraries Government Documents Department

Formal Devices of Trance and House Music: Breakdowns, Buildups, and Anthems

Description: Trance and house music are sub-genres within the genre of electronic dance music. The form of breakdown, buildup and anthem is the main driving force behind trance and house music. This thesis analyzes transcriptions from 22 trance and house songs in order to establish and define new terminology for formal devices used within the breakdown, buildup and anthem sections of the music.
Date: December 2011
Creator: Iler, Devin
Partner: UNT Libraries

RF breakdown studies in X-Band klystron cavities

Description: RF breakdown studies are presently being carried out at SLAC with klystron cavities in a traveling wave resonator (TWR). Different kinds of fabrication methods and several kinds of semiconducting and insulating coatings have been applied to X-Band TM{sub 010} cavities. RF breakdown thresholds up to 250 MV/m have been obtained. Dark current levels were found to be depressed on TiN-coated and single-point diamond turned cavities. A new TM{sub 020} cavity with demountable electrodes has been designed and will be used to test a variety of materials, coatings, and processes. Recent tests of klystron output windows at 119 MW are also presented in this paper.
Date: May 1, 1997
Creator: Xu, X.; Callin, R.S. & Fowkes, W.R.
Partner: UNT Libraries Government Documents Department

GaAs Self-Aligned JFETS with Carbon-Doped P+ Region

Description: Self-aligned JFETs with a carbon-doped p{sup +} region have been reported for the first time. For these JFETs, both the channel and p{sup +} region were grown by metal organic chemical vapor deposition (MOCVD) and are termed epitaxial JFETs in this study. The epitaxial JFETs were compared to ion implanted JFETs of similar channel doping and threshold voltage. Both JFETs were fabricated using the same self-aligned process for doping the source and drain regions of the JFET and for eliminating excess gate capacitance of conventional JFETs. The gate turn-on voltage for the epitaxial JFETs was 1.06 V, about 0.1 V higher than for the implanted JFETs. The reverse breakdown voltage was similar for both JFETs but the reverse gate leakage current of the epitaxial JFETs was 1-3 orders of magnitude less than the implanted JFETs. The epitaxial JFETs also showed higher transconductance and lower knee voltage than the implanted JFETs.
Date: February 15, 1999
Creator: Allerman, A.A.; Baca, A.G.; Chang, P.C. & Drummond, T.J.
Partner: UNT Libraries Government Documents Department

High altitude atmospheric discharges according to the runaway air breakdown mechanism

Description: High altitude optical transients - red sprites, blue jets, and elves - are modeled in the context of the relativistic electron runaway air breakdown mechanism. These emissions are usually associated with large mesoscale convective systems (hereafter MCS). In thunderstorms cloud electrification proceeds over a time scale long enough to permit the conducting atmosphere above the cloud to polarize and short out the thunderstorm electric field. When a lightning strike rapidly neutralizes a cloud charge layer runaway driving fields can develop in the stratosphere and mesosphere. According to present simulations of the full runaway process the variety of observed optical emissions are due to the nature of the normal lightning event in the MCS that kick starts the runaway avalanche. In this paper the authors describe some details of the model, present the results of the evolution of the primary electron population, and summarize the initial conditions necessary for different types of discharges. Two companion papers present (a) the predicted optical, gamma ray, and radio emissions caused by these electrical discharges, and (b) the time evolution of the secondary electron population and its implications in terms of observables.
Date: April 1, 1997
Creator: Symbalisty, E.; Roussel-Dupre, R.; Yukhimuk, V. & Taranenko, Y.
Partner: UNT Libraries Government Documents Department

High-performance insulator structures for accelerator applications

Description: A new, high gradient insulator technology has been developed for accelerator systems. The concept involves the use of alternating layers of conductors and insulators with periods of order 1 mm or less. These structures perform many times better (about 1.5 to 4 times higher breakdown electric field) than conventional insulators in long pulse, short pulse, and alternating polarity applications. We describe our ongoing studies investigating the degradation of the breakdown electric field resulting from alternate fabrication techniques, the effect of gas pressure, the effect of the insulator-to-electrode interface gap spacing, and the performance of the insulator structure under bi-polar stress.
Date: May 1, 1997
Creator: Sampayan, S.E.; Caporaso, G.J.; Sanders, D.M.; Stoddard, R.D.; Trimble, D.O.; Elizondo, J. et al.
Partner: UNT Libraries Government Documents Department

A High-Voltage Pulse Transformer for Explosive Pulsed-Power Devices

Description: It is often necessary to use a high-voltage pulse transformer for impedance matching an explosive generator to a higher impedance load. Also, a particular application may require high-voltage rather than the high current which flux compressor generators (FCGs) normally deliver when driving suitable low impedance loads. We have designed and built transformers for use with FCGs. They are air-core transformers with measured coupling coefficients in the range of 0.88 to 0.94. The turns ratio for these transformers vary from 10 to 40. We have used these transformers in FCG shots and have measured 250 kV and 250 kA on the secondary, simultaneously and without breakdown. So far the FCG and not the transformer have limited the voltage. Experiments to determine a voltage limit are ongoing. Our design and results are presented.
Date: October 1, 1998
Creator: Fortgang, C.; Erickson, G.A. & Goettee, J.
Partner: UNT Libraries Government Documents Department

BIOMASS REBURNING - MODELING/ENGINEERING STUDIES

Description: This project is designed to develop engineering and modeling tools for a family of NO{sub x} control technologies utilizing biomass as a reburning fuel. The forth reporting period (July 1 - September 30) included ongoing kinetic modeling of the reburning process while firing biomass. Modeling of biomass reburning concentrated on description of biomass performance at different reburning heat inputs. Reburning fuel was assumed to undergo rapid breakdown to produce various gaseous products. Modeling shows that the efficiency of biomass is affected by its composition. The kinetic model agrees with experimental data for a wide range of initial conditions and thus can be used for process optimization. Experimental data on biomass reburning are included in Appendix 2.
Date: October 20, 1998
Partner: UNT Libraries Government Documents Department

Investigation of High Voltage Breakdown and Arc Localization in RF Structures

Description: An effort is underway to improve the voltage standoff capabilities of ion cyclotron range of frequencies (ICRF) heating and current drive systems. One approach is to develop techniques for determining the location of an electrical breakdown (arc) when it occurs. A technique is described which uses a measurement of the reflection coefficient of a swept frequency signal to determine the arc location. The technique has several advantages including a requirement for only a small number of sensors and very simple data interpretation. In addition a test stand is described which will be used for studies of rf arc behavior. The device uses a quarter-wave resonator to produce voltages to 90 kV in the frequency range of 55-80 MHz.
Date: April 12, 1999
Creator: Bigelow, T.S.; Goulding, R.H. & Swain, D.W.
Partner: UNT Libraries Government Documents Department

Breakdown During High-Field Bias-Temperature Stress

Description: Measurements of dielectric breakdown during high-field electrical stress are typically performed at or near room temperature via constant voltage or current stress methods. In this summary they explore whether useful information might also be obtained by performing current measurements during a temperature ramp at high electric field.
Date: August 5, 1999
Creator: Fleetwood, D.M.; Krisch, K.S. & Sexton, F.W.
Partner: UNT Libraries Government Documents Department

Final Report for "Simulation Tools for Parallel Microwave Particle in Cell Modeling"

Description: Transport of high-power rf fields and the subsequent deposition of rf power into plasma is an important component of developing tokamak fusion energy. Two limitations on rf heating are: (i) breakdown of the metallic structures used to deliver rf power to the plasma, and (ii) a detailed understanding of how rf power couples into a plasma. Computer simulation is a main tool for helping solve both of these problems, but one of the premier tools, VORPAL, is traditionally too difficult to use for non-experts. During this Phase II project, we developed the VorpalView user interface tool. This tool allows Department of Energy researchers a fully graphical interface for analyzing VORPAL output to more easily model rf power delivery and deposition in plasmas.
Date: September 25, 2008
Creator: Stoltz, Peter H
Partner: UNT Libraries Government Documents Department

Maltose Biochemistry and Transport in Plant Leaves

Description: Starch is a desirable plant product for both food and biofuel. Leaf starch is ideal for use in biofuels because it does not compete with grain starch, which is used for food. Starch is accumulated in plant leaves during the day and broken down at night. If we can manipulate leaf starch breakdown it may be possible to design a plant that provides both grain starch for food and leaf starch for biofuel. The pathway of leaf starch breakdown was not known when this work started. Preliminary evidence had shown that maltose was the primary product of leaf starch breakdown (Weise, Weber & Sharkey, 2004) and that it was metabolized by a disproportionating enzyme called amylomaltase but given the initials DPE2 (Lu & Sharkey, 2004). In this work we showed that only one form of maltose was metabolically active (Weise et al., 2005a) and that maltose was located in two different places when the amylomaltase was knocked out but only inside the chloroplast when the maltose transporter was knocked out (Lu et al., 2006a). This allowed us to estimate the energetics of maltose export and to show that maltose export is more efficient than glucose export (Weise et al., 2005b). We examined how daylength affected starch breakdown rate and found that starch breakdown rate could respond to changes in daylength within one day (Lu, Gehan & Sharkey, 2005). We also were able to show a second starch breakdown pathway by chloroplastic starch phosphorylase (Weise et al., 2006). Work to this point was summarized in a review (Lu & Sharkey, 2006). We were able to show that the amylomaltase in plants could substitute for the amylomaltase in bacteria (Lu et al., 2006b). In this paper we also showed the importance of a second enzyme called alpha-glucan phosphorylase in starch breakdown. Finally, ...
Date: May 3, 2012
Creator: Sharkey, Thomas D
Partner: UNT Libraries Government Documents Department

Non-invasive Technology to Study Local Passivity Breakdown of Metal Alloys in Aqueous Media

Description: Little is known about the basic mechanisms of passive oxide breakdown, repair, and localized corrosion of metals. A non-invasive instrument and methods have been developed to study local events and mechanisms that initiate passivity breakdown and subsequent corrosion of metals in aqueous media. The ''difference viewer imaging technique'' (DVIT) is a rapid, real time, non-invasive assay to study metal surfaces in corrosive solutions. It has a spatial resolution of less than 10.0 ?m (1cm x 1cm sample, 1000 x 1000 pixel CCD) to observe initial corrosion processes of the order of seconds. DVIT is a software-controlled video microscopy system and methods to collect and analyze pixel changes in video images. These images are recorded from a digital CCD video camera and frame grabber package using visible light for illumination. The DVIT system detects changes in video images that represent initial corrosive events that lead to passivity breakdown and re-passivation on metal surfaces in situ. This visual technique is easy to use and apply. It compliments other metal surface measurement techniques and can be used simultaneously with them. DVIT has proven to be more sensitive in detecting changes than scanning microelectrode techniques. DVIT is also much easier than other methods to apply and operate. It has the further advantage of providing a real time image of the entire metal surface under study instead of waiting for a microelectrode to scan a number of data points over a sample then plot the results. This project has fulfilled all specifications as outlined in the Department of Energy solicitation responsible for this grant application and award and exceeded a number of the specifications. Applicable Electronics, Inc. now has a marketable instrument and software package available for sale now. Further development of the system will be ongoing as driven by customer needs and discoveries. This ...
Date: March 9, 2005
Creator: Shipley, Alan M.
Partner: UNT Libraries Government Documents Department

Unraveling duality violations in hadronic tau decays

Description: There are some indications from recent determinations of the strong coupling constant alpha_s and the gluon condensate that the Operator Product Expansion may not be accurate enough to describe non-perturbative effects in hadronic tau decays. This breakdown of the Operator Product Expansion is usually referred to as being due to"Duality Violations." With the help of a physically motivated model, we investigate these duality violations. Based on this model, we argue how they may introduce a non-negligible systematic error in the current analysis, which employs finite-energy sum rules with pinched weights. In particular, this systematic effect might affect the precision determination of alpha_s from tau decays. With a view to a possible future application to real data, we present an alternative method for determining the OPE coefficients that might help estimating, and possibly even reducing, this systematic error.
Date: March 3, 2008
Creator: Cata, Oscar; Cata, Oscar; Golterman, Maarten & Peris, Santiago
Partner: UNT Libraries Government Documents Department