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Thermal dissociation of SO₃ at 1000-1400 K

Description: Article on the thermal dissociation of SO3 at 1000 - 1400 K.
Date: January 12, 2006
Creator: Yilmaz, Ayten; Hindiyarti, Lusi; Jensen, Anker Degn; Glarborg, Peter & Marshall, Paul
Partner: UNT College of Arts and Sciences

Particle Velocity and Deposition Efficiency in the Cold Spray Process

Description: Copper powder was sprayed by the cold-gas dynamic method. In-flight particle velocities were measured with a laser-two-focus system as a function of process parameters such as gas temperature, gas pressure, and powder feed rate. Particle velocities were uniform in a relatively large volume within the plume and agreed with theoretical predictions. The presence of the substrate was found to have no significant effect on particle velocities. Cold-spray deposition efficiencies were measured on aluminum substrates as a function of particle velocity and incident angle of the plume. Deposition efficiencies of up to 95% were achieved. The critical velocity for deposition was determined to be about 640 meters per second. This work investigates both the in-flight characteristics of copper particles in a supersonic cold-spray plume and the build-up of the subsequent coating on aluminum substrates. Velocities were found to be relatively constant within a large volume of the plume. Particle counts dropped off sharply away from the central axis. The presence of a substrate was found to have no effect on the velocity of the particles. A substantial mass-loading effect on the particle velocity was observed; particle velocities begin to drop as the mass ratio of powder to gas flow rates exceeds 3%. The measured variation of velocity with gas pressure and pre-heat temperature was in fairly good agreement with theoretical predictions. Helium may be used as the driving gas instead of air in order to achieve higher particle velocities for a given temperature and pressure. Coating deposition efficiencies were found to increase with particle velocity and decrease with gun- substrate angle. There did not appear to be any dependence of the deposition efficiency on coating thickness. A critical velocity for deposition of about 640 mk appears to fit the data well. The cold-spray technique shows promise as a method for the ...
Date: November 12, 1998
Creator: Dykhuizen, R.C.; Gilmore, D.L.; Neiser, R.A.; Roemer, T.J. & Smith, M.F.
Partner: UNT Libraries Government Documents Department

Interaction between point defects and edge dislocation in BCC iron

Description: We present results of atomistic simulations of the interaction between self interstitial atoms and vacancies with edge dislocations in BCC iron. The calculations are carried out using molecular dynamics with an energy minimization scheme based on the quasi-Newton approach and use the Finnis-Sinclair interatomic potential for BCC iron developed by Ackland et al. Large anisotropy in the strain field of self interstitials is observed and it causes strong interaction with edge dislocations even when the defect is located on the dislocation glide plane. For vacancies, the relaxation volume is smaller and much more isotropic, which results in a far weaker interaction with the dislocation. A temperature dependent capture radius for vacancies and self interstitials is extracted from the simulations. The difference between the capture radii of vacancies and self interstitials is used to define the sink strength of the dislocation. Large deviations are observed from the predictions of elasticity based on treating point defects as isotropic dilatational centers. Further, the capture radius of edge dislocations in BCC iron is observed to be small and is of the order of l-3 nm for self interstitials.
Date: October 12, 1998
Creator: Diaz de la Rubia, T. & Shastry, V.
Partner: UNT Libraries Government Documents Department

Precision assembly and alignment of large optic modules for the National Ignition Facility

Description: The National Ignition Facility (NIF), currently under design and construction at Lawrence Livermore National Laboratory (LLNL), will be the world`s biggest laser. The optics for the multipass, 192-beam, high-power, neodymium-glass laser will be assembled and aligned in the NIF Optics Assembly Building (OAB), adjacent to the huge Laser and Target Area Building (LTAB), where they will be installed. To accommodate the aggressive schedule for initial installation and activation, rapid assembly and alignment of large aperture optics into line replaceable units (LRUs) will occur through the use of automated handling, semi-autonomous operations, and strict protocols. The OAB will have to maintain rigorous cleanliness levels, achieve both commonality and versatility to handle the various optic types, and allow for just-in-time processing and delivery of the optics into the LTAB without undoing their strict cleanliness and precise alignment. This paper describes the Project`s design philosophy of modularity and hardware commonality and presents the many design challenges encountered. It also describes how, by using a mixture of commercially available and newly designed equipment, we have developed unique systems for assembly and alignment, inspection and verification, and LRU loading and transfer.
Date: May 12, 1998
Creator: Hurst, P. & Grasz, E.
Partner: UNT Libraries Government Documents Department

High-average-power diode-end-pumped intracavity-doubled Nd:YAG laser

Description: A compact diode-pumped ND:YAG laser was frequency-doubled to 0.532 {mu}m with an intracavity KTP or LBO crystal using a `V` cavity configuration. Two acousto-optic Q-switches were employed at repetition rates of 10-30 kHz. Dichroic fold and end mirrors were used to output two beams with up to 140 W of 0.532 {mu}m power using KTP and 116 W using LBO as the frequency doubling crystal. This corresponds to 66% of the maximum output power at 1.064 {mu}m obtained with an optimized output coupler reflectivity. The minimum output pulse duration varied with repetition rate from 90 to 130 ns. The multimode output beam had a smooth profile and a beam quality of M{sup 2} = 5 1.
Date: February 12, 1998
Creator: Honea, E.C.; Ebbers, C.A.; Beach, R.J.; Speth, J.A.; Emanuel, M.S>; Skidmore, J.A. et al.
Partner: UNT Libraries Government Documents Department

Tevatron Run II performance and plans

Description: The Fermilab accelerator complex has been operating Run II for approximately one year. In this mode 36 proton bunches collide with 36 antiproton bunches at 2 interaction regions in the Tevatron at 980 GeV beam energy. The long range goal in Run II is to obtain a total integrated luminosity of 15 pb{sup -1}. The current status and performance of the accelerator complex is described, including the Tevatron, Main Injector, Antiproton Source, and Recycler Ring. Future upgrade plans and prospects for reaching the admittedly ambitious long range goal are presented.
Date: July 12, 2002
Creator: Church, Michael D
Partner: UNT Libraries Government Documents Department

Search for new particles at CDF II

Description: The authors report on the first results from the CDF experiment on search for physics beyond the Standard Model using data from the upgraded TeVatron collider running p{bar p} collisions at {radical}s = 1960 GeV. These first results, although obtained with a total integrated luminosity lower than the total integrated luminosity collected during Run I, are already competitive if not better, due to the increase in the center of mass energy and the improved detector capability.
Date: January 12, 2004
Creator: Rolli, Simona
Partner: UNT Libraries Government Documents Department


Description: Iterations to the cross section of the Relativistic Heavy Ion Collider (RHIC) D0 Insertion Dipole magnets were made during the production. This was included as part of the production plan because no R&D or pre-production magnets were built prior to the start of production. The first magnet produced had the desired coil pre-stress and low field harmonics in the body of the magnet and is therefore being used in the RHIC Machine. On the first eight magnets, iterations were carried out to minimize the iron saturation and to compensate for the end harmonics. This paper will discuss the details of the iterations made, the obstacles encountered, and the results obtained. Also included will be a brief summary of the magnet design and performance.
Date: May 12, 1997
Partner: UNT Libraries Government Documents Department

High Level Waste Tank Gamma Profiling

Description: Cleanup at the Savannah River Site brings with it the need to clean out and close down the radioactive waste tanks constructed in support of the fuel rod dissolution process. An innovative technique for assaying waste tanks has been developed at the Savannah River Site. The technique uses a gamma detector in the annular space between the inner and outer walls of double walled tanks. Unique shielding, counting electronics, and deployment techniques were developed to facilitate mapping interstitial liquid levels, sludge layers and other structures in the waste tank located near the tank walls. The techniques used, results, and lessons learned will be discussed.
Date: December 12, 2003
Creator: Moore, F.S. Jr.
Partner: UNT Libraries Government Documents Department


Description: Reaction rates depend on temperature as well as on the mechanical state. In shock wave initiation, experimental data almost always comprise mechanical measurements such as shock speed, material speed, compression, and pressure, and are accordingly modeled in terms of these parameters. Omission of temperature is one reason why mechanically based reaction rates do not extrapolate well out with the range of states used to normalize them. The model presented addresses chemical processes directly, enabling chemical kinetic data reported in terms of temperature (and at STP, generally) to be used in shock reaction models. We have recently extended a temperature-based model for use with ANFO-type formulations. Reactive material is treated as a heterogeneous mixture of components, each of which has its own model for response to dynamic loading (equation of state, strength model, reactions.) A finite-rate equilibration model is used to determine the overall response of the mixture to dynamic loading. In this model of ANFO, the ammonium nitrate and the fuel oil are treated as separate components in the unreacted mixture.
Date: June 12, 2002
Partner: UNT Libraries Government Documents Department

Toward improved environmental decisions.

Description: A common feature of many of the current environmental issues is that the immediate impact of risks, although considered to be small by many scientists, are uncertain and potentially wide spread and significant in the long term and thus of concern to potentially affected groups. The need to formulate decisions and commit major resources in the face of these uncertainties has led to the introduction of new environmental decision making frameworks that have as a central feature consideration of the broader environmental context and a greater involvement of the affected parties in the process. Various research activities and case studies are described which are targeted at aiding further development of the decision making frameworks into a more widely useable and effective approach.
Date: January 12, 2001
Creator: Habegger, L. & MacDonell, M.
Partner: UNT Libraries Government Documents Department

Synchrotron infrared spectromicroscopy as a novel bioanalytical microprobe for individual living cells: Cytotoxicity considerations

Description: Synchrotron radiation-based Fourier transform infrared (SR-FTIR) spectromicroscopy is a newly emerging analytical tool capable of monitoring the biochemistry within an individual living mammalian cell in real time. This unique technique provides infrared (IR)spectra, hence chemical information, with high signal-to-noise at spatial resolutions as fine as 3 to 10 microns. Mid-IR photons are too low in energy (0.05-0.5 eV) to either break bonds or to cause ionization, and the synchrotron IR beam has been shown to produce minimal sample heating. However, an important question remains, ''Does the intense synchrotron beam induce any cytotoxic effects in living cells?'' In this work, we present the results from a series of standard biological assays to evaluate any short-and/or long-term effects on cells exposed to the synchrotron radiation-based infrared (SR-IR) beam. Cell viability was tested using alcian blue dye-exclusion and colony formation assays. Cell-cycle progression was tested with bromodeoxyuridine (BrdU) uptake during DNA synthesis. Cell metabolism was tested using an 3-[4,5-Dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. All control, 5-, 10-, and 20-minute SR-IR exposure tests (267 total and over 1000 controls) show no evidence of cytotoxic effects. Concurrent infrared spectra obtained with each experiment confirm no detectable chemistry changes between control and exposed cells.
Date: December 12, 2001
Creator: Holman, Hoi-Ying N.; Bjornstad, Kathleen A.; McNamara, Morgan P.; Martin, Michael C.; McKinney, Wayne R. & Blakely, Eleanor A.
Partner: UNT Libraries Government Documents Department

All-optical beamlet train generation

Description: One of the critical issues for the development of Laser Wake Field Acceleration (LWFA), which has the promise of creating table-top, GeV accelerators, is the loading of beamlets into the accelerating buckets. All optical injection schemes, which include LILAC, beat-wave colliding pulse injection, wave breaking injection, and phase-kick injection, provide a technique for doing so. Although a single bunch can have desirable properties such as energy spread of the order of a few percent, femtosecond duration k and low emittance (<1 mm-mrad), recent simulations show that such methods lead to efficiencies of transfer of plasma wave energy to beam energy that are low compared with conventional RF accelerators when only a single pulse is generated. Our latest simulations show that one can improve on this situation through the generation of a beamlet train. This can occur naturally through phase-kick injection at the front of the train and transverse wave breaking for the trailing pulses. The result is an efficiency improvement of the order of the number of beamlets in the train.
Date: May 12, 2003
Creator: Cary, John; Giacone, Rodolfo; Nieter, Chet; Bruhwiler, David; Esarey, Eric; Fubiani, Gwenael et al.
Partner: UNT Libraries Government Documents Department

Evolution of pulse shapes during compressor scans in a CPA system and control of electron acceleration in plasmas

Description: The skewness of the envelope function of 20 - 100 femtosecond Ti:sapphire laser pulses has been controlled by appropriate choice of the higher order special phase coefficients, and used for optimization of a plasma wakefield electron accelerator.
Date: May 12, 2002
Creator: Toth, Csaba; de Groot, Joeri; van Tilborg, Jeroen; Geddes, Cameron G.R.; Faure, Jerome; Catravas, Palma et al.
Partner: UNT Libraries Government Documents Department

Recent results in search for new physics at the Tevatron (Run I)

Description: We present some new results on searches for new physics at the Tevatron Run 1 (1992-1996). The topics covered are searches for R-Parity violating and conserving mSUGRA, large extra dimensions in di-photon and monojet channels, leptoquark in jets + E{sub T} channel, and two model independent searches. All results were finalized during the past year.
Date: January 12, 2004
Creator: Zhou, John
Partner: UNT Libraries Government Documents Department

Melter Off-Gas Flammability Analysis

Description: The objective of this work was to develop predictive models to assess offgas flammability for a low activity radioactive waste melter. The models had to be comprehensive enough to explicitly describe the effects of key melter operating variables such as total organic carbon in the feed, melter air purge and vapor space temperature. Once validated against pilot melter data, these models were used to simulate a series of safety scenarios involving over-batching of sugar, used as a reducing agent, and off-gas surges. The overall scope of the work was broken down into two parts, each focusing on a physically distinct region in the melter.
Date: December 12, 2003
Creator: Smith, FG III
Partner: UNT Libraries Government Documents Department


Description: The INTRODUCTION to this paper summarizes the history of the Global Accelerator Network (GAN) concept and the recent workshops that discussed the relationship between GAN and Remote Operations. The REMOTE OPERATIONS SCENARIOS section brings out the organizational philosophy embodied in GAN-like and to non-GAN-like scenarios. The set of major TOPICS RAISED AT THE WORKSHOPS are only partially resolved. COLLABORATION TOOLS are described and discussed, followed by examples of REMOTE ACCELERATOR CONTROL PROJECTS around the world.
Date: May 12, 2003
Partner: UNT Libraries Government Documents Department

3-D full waveform inversion of seismic data; Part I. Theory

Description: Full waveform inversion of seismic data is a challenging subject partly because of the lack of precise knowledge of the source. Since currently available approaches involve some form of approximations to the source, inversion results are subject to the quality and the choice of the source information used. A new full waveform inversion scheme has been introduced (Lee and Kim, 2003) using normalized wavefield for simple two-dimensional (2-D) scalar problems. The method does not require source information, so potential inversion errors due to source estimation may be eliminated. A gather of seismic traces is first Fourier-transformed into the frequency domain and a normalized wavefield is obtained for each trace in the frequency domain. Normalization is done with respect to the frequency response of a reference trace selected from the gather, so the complex-valued normalized wavefield is source-independent and dimensionless. The inversion algorithm minimizes misfits between measured normalized wavefield and numerically computed normalized wavefield. In this paper the full waveform inversion is extended to three-dimensional (3-D) problems.
Date: May 12, 2003
Creator: Lee, Ki Ha
Partner: UNT Libraries Government Documents Department


Description: Operational aspects of the RHIC rf system are described. To date three different beam combinations have been collided for physics production: gold-gold, deuteron-gold, and proton-proton(polarized). To facilitate this flexibility the rf systems of the two rings are independent and self-sufficient. Techniques to cope with problems such as, injection/capture, beam loading, bunch shortening, and rf noise have evolved and are explained.
Date: May 12, 2003
Partner: UNT Libraries Government Documents Department

Biaxially aligned template films fabricated by inclined-substrate deposition for YBCO-coated conductor applications.

Description: Inclined substrate deposition (ISD) has the potential for rapid production of high-quality biaxially textured buffer layers, which are important for YBCO-coated conductor applications. We have grown biaxially textured MgO films by ISD at deposition rates of 20-100 {angstrom}/sec. Columnar grains with a roof-tile surface structure were observed in the ISD-MgO films. X-ray pole figure analysis revealed that the (002) planes of the ISD-MgO films are tilted at an angle from the substrate normal. A small {phi}-scan full-width at half maximum (FWHM) of {approx}9{sup o} was observed on MgO films deposited at an inclination angle of 55{sup o}. In-plane texture in the ISD MgO films developed in the first 0.5 {micro}m from the interface, then stabilized with further increases in film thickness. YBCO films deposited by pulsed laser deposition on ISD-MgO buffered Hastelloy C276 substrates were biaxially aligned with the c-axis parallel to the substrate normal. T{sub c} of 91 K with a sharp transition and transport J{sub c} of 5.5 x 10{sup 5} A/cm{sup 2} at 77 K in self-field were measured on a YBCO film that was 0.46-{micro}m thick, 4-mm wide, 10-mm long.
Date: August 12, 2002
Creator: Ma, B.; Li, M.; Koritala, R. E.; Fisher, B. L.; Erck, R. A.; Dorris, S. E. et al.
Partner: UNT Libraries Government Documents Department

The QCD/SM working group: Summary report

Description: Quantum Chromo-Dynamics (QCD), and more generally the physics of the Standard Model (SM), enter in many ways in high energy processes at TeV Colliders, and especially in hadron colliders (the Tevatron at Fermilab and the forthcoming LHC at CERN), First of all, at hadron colliders, QCD controls the parton luminosity, which rules the production rates of any particle or system with large invariant mass and/or large transverse momentum. Accurate predictions for any signal of possible ''New Physics'' sought at hadron colliders, as well as the corresponding backgrounds, require an improvement in the control of uncertainties on the determination of PDF and of the propagation of these uncertainties in the predictions. Furthermore, to fully exploit these new types of PDF with uncertainties, uniform tools (computer interfaces, standardization of the PDF evolution codes used by the various groups fitting PDF's) need to be proposed and developed. The dynamics of colour also affects, both in normalization and shape, various observables of the signals of any possible ''New Physics'' sought at the TeV scale, such as, e.g. the production rate, or the distributions in transverse momentum of the Higgs boson. Last, but not least, QCD governs many backgrounds to the searches for this ''New Physics''. Large and important QCD corrections may come from extra hard parton emission (and the corresponding virtual corrections), involving multi-leg and/or multi-loop amplitudes. This requires complex higher order calculations, and new methods have to be designed to compute the required multi-legs and/or multi-loop corrections in a tractable form. In the case of semi-inclusive observables, logarithmically enhanced contributions coming from multiple soft and collinear gluon emission require sophisticated QCD resummation techniques. Resummation is a catch-all name for efforts to extend the predictive power of QCD by summing the large logarithmic corrections to all orders in perturbation theory. In practice, the resummation ...
Date: January 12, 2004
Creator: al., W. Giele et
Partner: UNT Libraries Government Documents Department


Description: There has been a lot of interest in compact sources of high brightness, relativistic electron beams. One approach for developing such a source is to apply a high gradient that remains constant during the generation and acceleration of the electron beam. In this paper, we describe high voltage pulse generators that deliver up to 5 MV with 1 ns pulse duration. These devices are synchronizable to an external trigger with jitter of {approx}0.5 ns and can establish gradients in excess of 1 GV/m between two electrodes without breakdown. In the presence of field gradients up to 0.5 GV/m, electron beams of bunch lengths ranging from 1 ns to 0.3 ps and diameter < 300 {micro}m have been generated by irradiating the cathode with UV lasers. Characteristics of these electron beams as well as those produced via field emission at gradients up to 1 GV/m will be discussed.
Date: November 12, 2002
Partner: UNT Libraries Government Documents Department

Artificial Neural Network Solutions of Slab-Geometry Neutron Diffusion Problems

Description: Artificial neural network (ANN) methods have been researched extensively within the nuclear community for applications in systems control, diagnostics, and signal processing. We consider here the use of multilayer perceptron ANNs as an alternative to finite-difference and finite-element methods for obtaining solutions to neutron diffusion problems. This work is based on a method proposed by van Milligen et. al. to obtain solutions of the differential equations arising in plasma physics applications. This ANN method has the potential advantage of yielding an accurate, differentiable approximation to the solution of diffusion problems at all points in the spatial domain.
Date: June 12, 2000
Creator: Brantley, P. S.
Partner: UNT Libraries Government Documents Department