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DC surface-plasma source with high emission current density. (open access)

DC surface-plasma source with high emission current density.

None
Date: July 1, 2002
Creator: Dudnikov, V.; Schmidt, C.W.; Hren, R. & Wendt, J.
System: The UNT Digital Library
Performing Trade Studies in the CERCLA Environment (open access)

Performing Trade Studies in the CERCLA Environment

During almost any project, situations will arise that require project management and/or engineering personnel to make choices regarding project direction or product development. Often these choices are simply a part of the normal engineering development cycle (e.g., refinement or optimization of the product design). Frequently, on Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and other similar projects, trade studies are initiated to address concerns or issues raised by stakeholders (e.g., EPA, local and state governments, local tribes, public). Where CERCLA projects, by definition, deal with releases or threatened releases of hazardous substances that may endanger public health or the environment, these trade studies must balance safety, risk and health issues, as well as cost and engineering viability. How these trade studies are carried out and documented/presented to the stakeholders involved can often be the difference between continued project progress and a "stalemate" leaving the project in limbo. This document describes a basic trade study process, which has proved successful in addressing stakeholder concerns while at the same time balancing the desires of the various parties involved.
Date: July 1, 2002
Creator: Borland, Mark Wilson; Rice, Philip Matthew & Jamison, Ronald Kirt
System: The UNT Digital Library
Integrated X-ray and charged particle active pixel CMOS sensor arrays using an epitaxial silicon sensitive region (open access)

Integrated X-ray and charged particle active pixel CMOS sensor arrays using an epitaxial silicon sensitive region

Integrated CMOS Active Pixel Sensor (APS) arrays have been fabricated and tested using X-ray and electron sources. The 128 by 128 pixel arrays, designed in a standard 0.25 micron process, use a {approx}10 micron epitaxial silicon layer as a deep detection region. The epitaxial layer has a much greater thickness than the surface features used by standard CMOS APS, leading to stronger signals and potentially better signal-to-noise ratio (SNR). On the other hand, minority carriers confined within the epitaxial region may diffuse to neighboring pixels, blur images and reduce peak signal intensity. But for low-rate, sparse-event images, centroid analysis of this diffusion may be used to increase position resolution. Careful trade-offs involving pixel size and sense-node area verses capacitance must be made to optimize overall performance. The prototype sensor arrays, therefore, include a range of different pixel designs, including different APS circuits and a range of different epitaxial layer contact structures. The fabricated arrays were tested with 1.5 GeV electrons and Fe-55 X-ray sources, yielding a measured noise of 13 electrons RMS and an SNR for single Fe-55 X-rays of greater than 38.
Date: July 1, 2002
Creator: Kleinfelder, Stuart; Bichsel, Hans; Bieser, Fred; Matis, Howard S.; Rai, Gulshan; Retiere, Fabrice et al.
System: The UNT Digital Library
Elastic stability and the limit of strength (open access)

Elastic stability and the limit of strength

The upper limit of strength (the ''theoretical strength'') has been an active subject of research and speculation for the better part of a century. The subject has recently become important, for two reasons. First, given recent advances in ab initio techniques and computing machines, the limits of strength can be calculated with considerable accuracy, making this one of the very few problems in mechanical behavior that can actually be solved. Second, given recent advances in materials engineering, the limits of strength are being approached in some systems, such as hardened or defect-free films, and their relevance is becoming recognized in others. The present paper discusses some interesting results from recent research on the limits of strength, with an intermixture of speculations based on those results. Topics include the inherent nature of {l_brace}100{r_brace} cleavage and ''pencil slip'' in bcc metals, the inherent ductility of fcc metals, the anomalous properties of Al, and the possibility of measuring ideal strength with nanoindentation.
Date: July 1, 2002
Creator: Morris Jr., J.W.; Krenn, C.R.; Roundy, D. & Cohen, Marvin L.
System: The UNT Digital Library
HVAC component data modeling using industry foundation classes (open access)

HVAC component data modeling using industry foundation classes

The Industry Foundation Classes (IFC) object data model of buildings is being developed by the International Alliance for Interoperability (IAI). The aim is to support data sharing and exchange in the building and construction industry across the life-cycle of a building. This paper describes a number of aspects of a major extension of the HVAC part of the IFC data model. First is the introduction of a more generic approach for handling HVAC components. This includes type information, which corresponds to catalog data, occurrence information, which defines item-specific attributes such as location and connectivity, and performance history information, which documents the actual performance of the component instance over time. Other IFC model enhancements include an extension of the connectivity model used to specify how components forming a system can be traversed and the introduction of time-based data streams. This paper includes examples of models of particular types of HVAC components, such as boilers and actuators, with all attributes included in the definitions. The paper concludes by describing the on-going process of model testing, implementation and integration into the complete IFC model and how the model can be used by software developers to support interoperability between HVAC-oriented design and analysis tools.
Date: July 1, 2002
Creator: Bazjanac, Vladimir; Forester, James; Haves, Philip; Sucic, Darko & Xu, Peng
System: The UNT Digital Library
Very extended shapes in 108Cd: evidence for the occupation of 'hyper-intruder' orbitals (open access)

Very extended shapes in 108Cd: evidence for the occupation of 'hyper-intruder' orbitals

High-spin states in {sup 108}Cd were studied following the reaction {sup 64} Ni({sup 48}Ca,4n) at a beam energy of 207 MeV. Gamma rays were detected using the Gammasphere array. Two rotational bands have been observed at very high angular momentum. Measurements of fractional Doppler shifts yielded lower limits for the quadrupole moments and showed that the observed structures are at least as deformed as the superdeformed structures e.g. in the A {approx} 150 region, and possibly exceed a 2:1 axis ratio. The existence of very extended shapes has been predicted by cranked Strutinsky calculations, and recent projected shell model calculations suggest that the {pi}i{sub 13/2}hyper-intruder orbital is occupied in these newly observed bands.
Date: July 1, 2002
Creator: Gorgen, A.; Clark, R. M.; Fallon, P.; Cromaz, M.; Deleplanque, M. A.; Diamond, R. M. et al.
System: The UNT Digital Library
Physics of Off-Axis Electron Cyclotron Current Drive (open access)

Physics of Off-Axis Electron Cyclotron Current Drive

Electron cyclotron current drive is a key option for driving current off-axis in a tokamak, as needed for example for current profile control or for suppression of neoclassical tearing modes. Experiments in DIII-D at low beta have shown that the partial cancellation of the Fisch-Boozer co-current by the Ohkawa counter-current can cause strong deterioration of the current drive efficiency at larger minor radius. However, more recent experiments at higher power have shown that the loss in efficiency can be mostly recovered if the target plasma has higher electron beta, {beta}{sub e}. The improvement in efficiency with beta can be understood from a theoretical viewpoint by applying the Fokker-Planck code CQL3D, which shows excellent agreement with experiment over a wide range of parameters, thereby validating the code as an effective means of predicting the ECCD.
Date: July 1, 2002
Creator: Prater, R.; Petty, C. C.; Harvey, R.; Lin-Liu, Y. R.; Lohr, J. M. & Luce, T. C.
System: The UNT Digital Library
Development of Cryogenically Microwave Lossy Ceramics with Adjustable Properties (open access)

Development of Cryogenically Microwave Lossy Ceramics with Adjustable Properties

At cryogenic temperatures (below 20 K), most of the existing lossy materials become non-lossy, requiring the development of a new materials effective in these conditions. Results of an effort to develop a cryogenically lossy materials based on the AlN matrix are presented in the paper. Hot pressing with a wide range of possible lossy second phases was tried, followed by complex permitivity measurements. A promising second phase was selected, produced and evaluated under cryogenic conditions at the Thomas Jefferson National Accelerator Facility (Jefferson Lab). The developed material system allows the dielectric permitivity to be varied depending on the application requirements.
Date: July 1, 2002
Creator: Mikijeli, Biljana & Campisi, Isidoro
System: The UNT Digital Library
Damping in Yb nuclei (open access)

Damping in Yb nuclei

In a mixture of three Yb nuclei, we find the rotational damping widths vary from 180 keV at 1.1 MeV {gamma}-ray energy to 290 keV at 1.5 MeV, and the average compound damping widths (or spreading widths) vary from 40 keV at 1.1 MeV {gamma}-ray energy to 60 keV at 1.3 MeV. The simulations also suggest extensive motional narrowing.
Date: July 1, 2002
Creator: Stephens, F. S.; Deleplanque, M. A.; Lee, I. Y.; Ward, D.; Fallon, P.; Cromaz, M. et al.
System: The UNT Digital Library
Solenoid Magnets for the Front End of a Neutrino Factory. (open access)

Solenoid Magnets for the Front End of a Neutrino Factory.

This report describes the solenoid magnets in the front end (the section between the pion capture solenoid and the linear acceleration section) of the Level 2 study of a neutrino factory. The magnets described in the report start with the decay channel magnets that starts 18 meter downstream from the start of the pion production target. The magnet string ends with the transition solenoids that match the muon beam from the last cooling cell to the superconducting linear accelerator section. All of the magnets described in this report are solenoids. The field on axis in the solenoidal channel ranges from 1.25 T to just over 5.5 T. This report shows that the magnets in the front end of the neutrino factory are feasible.
Date: July 1, 2002
Creator: Green, M. A.; Yu, S. S.; Miller, J. R.; Prestemon, S. & Palmer, R. B.
System: The UNT Digital Library
Quantitative Tests of ELMs as Intermediate N Peeling-Ballooning Modes (open access)

Quantitative Tests of ELMs as Intermediate N Peeling-Ballooning Modes

OAK A271 QUANTITATIVE TESTS OF ELMS AS INTERMEDIATE N PEELING-BALLOONING MODES. Two of the major issues crucial for the design of the next generation tokamak burning plasma devices are the predictability of the edge pedestal height and control of the divertor heat load in H-mode configurations. Both of these are strongly impacted by edge localized modes (ELMs) and their size. A working model for ELMs is that they are intermediate toroidal mode number, n {approx} 5-30, peeling-ballooning modes driven by the large edge pedestal pressure gradient P{prime} and the associated large edge bootstrap current density J{sub BS}. the interplay between P{prime} and J{sub BS} as a discharge evolves can excite peeling-ballooning modes over a wide spectrum of n. The pedestal current density plays a dual role by stabilizing the high n ballooning modes via opening access to second stability but providing free energy to drive the intermediate n peeling modes. This makes a systematic evaluation of this model particularly challenging. This paper describes recent quantitative tests of this model using experimental data from the DIII-D and the JT-60U tokamaks. These tests are made possible by recent improvements to the ELITE MHD stability code, which allow an efficient evaluation of the …
Date: July 1, 2002
Creator: Lao, L. L.; Snyder, P. B.; Leonard, A. W.; Osborne, T. H.; Petrie, T. W.; Ferron, J. R. et al.
System: The UNT Digital Library
Oblique ion texturing of yttria-stabilized zirconia: The {l_brace}211{r_brace}<111> structure (open access)

Oblique ion texturing of yttria-stabilized zirconia: The {l_brace}211{r_brace}<111> structure

Amorphous (Zr,Y)O{sub x} films were synthesized by reactive magnetron sputtering and subsequently crystallized by oblique ion bombardment. Crystalline texture nucleated by the ion beam was replicated by solid-phase epitaxial growth throughout the formerly amorphous yttria-stabilized zirconia (YSZ) film. The resulting YSZ films have (211) orientation normal to the substrate with in-plane directions (111), parallel, and (110), transverse, to the azimuth of the ion beam. We hypothesize that the texture mechanism involves ion-induced film compression and shear. The results, taken together with prior work, show that oblique ion texturing of amorphous films is a general phenomenon that can be used to fabricate substrates with more than one type of crystallographic orientation.
Date: July 1, 2002
Creator: Berdahl, Paul; Reade, Ronald P.; Liu, Jinping; Russo, Richard E.; Fritzemeier, Les; Buczek, David et al.
System: The UNT Digital Library
Physics Processes in Disruption Mitigation Using Massive Noble Gas Injection (open access)

Physics Processes in Disruption Mitigation Using Massive Noble Gas Injection

Methods for detecting imminent disruptions and mitigating disruption effects using massive injection of noble gases (He, Ne, or Ar) have been demonstrated on the DIII-D tokamak [1]. A jet of high injected gas density (&gt; 10{sup 24} m{sup -3}) and pressure (&gt; 20 kPa) penetrates the target plasma at the gas sound speed ({approx}300-500 m/s) and increases the atom/ion content of the plasma by a factor of &gt; 50 in several milliseconds. UV line radiation from the impurity species distributes the plasma energy uniformly on the first wall, reducing the thermal load to the divertor by a factor of 10. Runaway electrons are almost completely eliminated by the large density of free and bound electrons supplied by the gas injection. The small vertical plasma displacement before current quench and high ratio of current decay rate to vertical growth rate result in a 75% reduction in peak halo current amplitude and attendant forces.
Date: July 1, 2002
Creator: Humphreys, D. A.; Whyte, D. G.; Jernigan, T. C.; Evans T. E.; Gray, D. S.; Hollmann, E. M. et al.
System: The UNT Digital Library
The Effect of Turbulent Stresses on the Experimental Determination of a Thermal Diffusivity Due to Turbulent Transport (open access)

The Effect of Turbulent Stresses on the Experimental Determination of a Thermal Diffusivity Due to Turbulent Transport

In plasmas where the transport processes are dominated by turbulence, it is not always straightforward to identify the magnitude of the experimental transport diffusion coefficients. This is primarily due to the fact that with turbulent transport, the separation of the convective and conductive terms depends upon the type of turbulence and/or the model which is used to describe it. For the energy transport it is not just a matter of deciding whether the convection term is 5/2 or 3/2 times the product of the particle flux and the temperature. It is also important to identify turbulence generated convection terms such as heat pinches which can obscure the correct evaluation of the thermal diffusivity. Here we show that inclusion of the turbulence induced stresses into the transport model identifies a heat pinch term and changes the expression for the thermal diffusivity. Comparison with experimental results shows that the new calculated ion thermal diffusivity is no longer less than the neoclassical value even for plasmas with very good ion thermal confinement.
Date: July 1, 2002
Creator: Baker, D. R.
System: The UNT Digital Library
Threshold charged current weak production of strangeness (open access)

Threshold charged current weak production of strangeness

The differential cross section for the charged current electroweak reaction {rvec e} + p {yields} {rvec v}{sub e} + {rvec {Lambda}} at threshold with polarization observables is presented. The form of the cross section at threshold for the reaction is simplified compared to higher energy. An expression is given for the invariant matrix element appropriate for the reaction when the incident electron is polarized, and the final state hyperon polarization is determined. The energy dependence of the resulting cross section is shown near threshold. Under the right kinematic conditions, there can be a sizeable enhancement in the cross section, making an experimental measurement of the weak axial-vector form factor feasible.
Date: July 1, 2002
Creator: Baker, O. K.
System: The UNT Digital Library
Effect of Particle Sources on the Structure of theH-Mode Pedestal (open access)

Effect of Particle Sources on the Structure of theH-Mode Pedestal

Techniques of dimensional analysis have been applied to deuterium and hydrogen plasmas in DIII-D to test the postulate that the edge particle source plays a role in forming the edge H-mode density profile. These experiments show that the pedestal density scale length is typically a factor of two to three larger in hydrogen plasmas than in deuterium plasmas with dimensionally similar ion parameters. These results are in agreement with the postulate [1,2] that the density scale length is primarily determined by the local particle source, rather than by the shape of a hypothetical particle transport barrier. The electron temperature scale length displays a similar trend, albeit with a weaker density dependence. Thus the pedestal pressure gradient scale length is larger in hydrogen. It is also observed that the frequency of a coherent mode, localized within the pedestal, increases with the local density (i.e. inversely with the local density scale length) irrespective of the working gas species. This frequency is a factor of two lower in a hydrogen discharge than in a dimensionally similar deuterium plasma, a result which cannot be explained solely in terms of plasma physics variables.
Date: July 1, 2002
Creator: Mahdavi, M. A.; Groebner, R. J.; Leonard, A. W.; Luce, T. C.; McKee, G. R.; Moyer, R. A. et al.
System: The UNT Digital Library
Becoming allies: Combining social science and technological perspectives to improve energy research and policy making (open access)

Becoming allies: Combining social science and technological perspectives to improve energy research and policy making

Within the energy research community, social sciences tends to be viewed fairly narrowly, often as simply a marketing tool to change the behavior of consumers and decision makers, and to ''attack market barriers''. As we see it, social sciences, which draws on sociology, psychology, political science, business administration, and other academic disciplines, is capable of far more. A social science perspective can re-align questions in ways that can lead to the development of technologies and technology policy that are much stronger and potentially more successful than they would be otherwise. In most energy policies governing commercial buildings, the prevailing R and D directives are firmly rooted in a technology framework, one that is generally more quantitative and evaluative than that fostered by the social sciences. To illustrate how social science thinking would approach the goal of achieving high energy performance in the commercial building sector, they focus on the US Department of Energy's Roadmap for commercial buildings (DOE 2000) as a starting point. By ''deconstructing'' the four strategies provided by the Roadmap, they set the stage for proposing a closer partnership between advocates of technology-based and social science-based approaches.
Date: July 1, 2002
Creator: Diamond, Rick & Moezzi, Mithra
System: The UNT Digital Library
List mode reconstruction for PET with motion compensation: A simulation study (open access)

List mode reconstruction for PET with motion compensation: A simulation study

Motion artifacts can be a significant factor that limits the image quality in high-resolution PET. Surveillance systems have been developed to track the movements of the subject during a scan. Development of reconstruction algorithms that are able to compensate for the subject motion will increase the potential of PET. In this paper we present a list mode likelihood reconstruction algorithm with the ability of motion compensation. The subject motion is explicitly modeled in the likelihood function. The detections of each detector pair are modeled as a Poisson process with time-varying rate function. The proposed method has several advantages over the existing methods. It uses all detected events and does not introduce any interpolation error. Computer simulations show that the proposed method can compensate simulated subject movements and that the reconstructed images have no visible motion artifacts.
Date: July 1, 2002
Creator: Qi, Jinyi & Huesman, Ronald H.
System: The UNT Digital Library
Comparison and Physical Interpretation of MCNP and TART Neutron and Gamma Monte Carlo Shielding Calculations for a Heavy-Ion ICF System (open access)

Comparison and Physical Interpretation of MCNP and TART Neutron and Gamma Monte Carlo Shielding Calculations for a Heavy-Ion ICF System

For heavy-ion beam driven inertial fusion ''liquid-protected'' reactor designs such as HYLIFE-II, a mixture of molten salts made of F{sup 10}, Li{sup -6}, Li{sup 7} and Be{sup 9} (called flibe) allows small chambers and final-focus magnets closer to the target with superconducting coils suffering higher radiation damage, though they can stand only a certain amount of energy deposited before quenching. This work has been primarily focusing on verifying that total energy deposited by fusion neutrons and induced gamma rays remain under such limit values and the final purpose is the optimization of the shielding of the magnetic lens system from the points of view of the geometrical configuration and of the physical nature of the materials adopted. The system is analyzed in terms of six geometrical models going from simplified up to much more realistic representations of a system of 192 beam lines, each focused by six magnets. A 3-D transport calculation of the radiation penetrating through ducts, that takes into account the complexity of the system, requires Monte Carlo methods. The quantities analyzed, using the two codes MCNP and TART include: neutron mean free path and total path length dependence on energy, energy deposited by neutrons and gamma photons, …
Date: July 1, 2002
Creator: Mainardi, E.; Premuda, F. & Lee, E.
System: The UNT Digital Library
Proliferation resistance assessment of the Integral Fast Reactor. (open access)

Proliferation resistance assessment of the Integral Fast Reactor.

The Integral Fast Reactor (IFR) concept includes a sodium-cooled fast reactor collocated with an integrated pyroprocess fuel recycling facility. The pyrochemical processes and the inert atmosphere of the heavily shielded fuel cycle facility provide inherent proliferation-resistant features for this advanced technology. The reactor can be designed to operate with a number of different conversion factors, so that it could be used for excess plutonium consumption or as a breeder if needed for rapid expansion of energy supply. The system contains a large quantity of plutonium and minor actinides, which at all times remain in extremely hostile environments and in chemical and physical forms that would require additional processing to extract weapons-suitable material. The aqueous processing equipment and facilities to accomplish such separation would not be available on site. Transportation would not be required in the reference deployment scenario. Nevertheless, the proliferation-resistance of some parts of the system could be considerably strengthened by advanced safeguards technologies. In spite of its inherent features, international deployment of the system would probably be limited to stable countries with a strong existing nuclear infrastructure.
Date: July 1, 2002
Creator: McFarlane, H. F.
System: The UNT Digital Library
Scalable cluster administration - Chiba City I approach and lessons learned. (open access)

Scalable cluster administration - Chiba City I approach and lessons learned.

Systems administrators of large clusters often need to perform the same administrative activity hundreds or thousands of times. Often such activities are time-consuming, especially the tasks of installing and maintaining software. By combining network services such as DHCP, TFTP, FTP, HTTP, and NFS with remote hardware control, cluster administrators can automate all administrative tasks. Scalable cluster administration addresses the following challenge: What systems design techniques can cluster builders use to automate cluster administration on very large clusters? We describe the approach used in the Mathematics and Computer Science Division of Argonne National Laboratory on Chiba City I, a 314-node Linux cluster; and we analyze the scalability, flexibility, and reliability benefits and limitations from that approach.
Date: July 1, 2002
Creator: Navarro, J. P.; Evard, R.; Nurmi, D. & Desai, N.
System: The UNT Digital Library
Clusters as large-scale development facilities. (open access)

Clusters as large-scale development facilities.

In this paper, the authors describe the use of a cluster as a generalized facility for development. A development facility is a system used primarily for testing and development activities while being operated reliably for many users. They are in the midst of a project to build and operate a large-scale development facility. They discuss the motivation for using clusters in this way and compare the model with a classic computing facility. They describe their experiences and findings from the first phase of this project. many of these observations are relevant to the design of standard clusters and to future development facilities.
Date: July 1, 2002
Creator: Evard, R.; Desai, N.; Navarro, J. P. & Nurmi, D.
System: The UNT Digital Library
Goals guiding design : PVM and MPI (open access)

Goals guiding design : PVM and MPI

PVM and MPI, two systems for programming clusters, are often compared. The comparisons usually start with the unspoken assumption that PVM and MPI represent different solutions to the same problem. In this paper we show that, in fact, the two systems often are solving different problems. In cases where the problems do match but the solutions chosen by PVM and MPI are different, we explain the reasons for the differences. Usually such differences can be traced to explicit differences in the goals of the two systems, their origins, or the relationship between their specifications and their implementations. For example, we show that the requirement for portability and performance across many platforms caused MPI to choose approaches different from those made by PVM, which is able to exploit the similarities of network-connected systems.
Date: July 1, 2002
Creator: Gropp, W. & Lusk, E.
System: The UNT Digital Library
Interplay of Hard and Soft Processes at JLAB Energies (open access)

Interplay of Hard and Soft Processes at JLAB Energies

Even at moderate energy machines, there is a regime where hard pion electroproduction proceeds by a perturbatively calculable process. The process, we claim, is not the leading twist fragmentation one but a rather higher twist process that produces kinematically isolated pions. Semiexclusive data may teach us more about parton distribution functions of the target and the pion distribution amplitude. In addition, there is a connection to generalized parton distribution calculations of exclusive processes in that the perturbative kernel is the same.
Date: July 1, 2002
Creator: Afanasev, Andrei & Carlson, Carl E.
System: The UNT Digital Library