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Nonlinear optical spectroscopy of diamond surfaces

Description: Second harmonic generation (SHG) and infrared-visible sum frequency generation (SFG) spectroscopies have been shown to be powerful and versatile for studying surfaces with submonolayer sensitivity. They have been used in this work to study bare diamond surfaces and molecular adsorption on them. In particular, infrared-visible SFG as a surface vibrational spectroscopic technique has been employed to identify and monitor in-situ surface bonds and species on the diamond (111) surface. The CH stretch spectra allow us to investigate hydrogen adsorption, desorption, abstraction, and the nature of the hydrogen termination. The C(111) surface dosed with atomic hydrogen was found to be in a monohydride configuration with the hydrogen atoms situated at top-sites. The ratio of the abstraction rate to the adsorption rate was appreciable during atomic hydrogen dosing. Kinetic parameters for thermal desorption of H on C(111) were determined showing a near first-order kinetics. For the fully H-terminated (111) surface, a large (110 cm{sup {minus}1}) anharmonicity and {approximately}19 psec lifetime were measured for the first-excited CH stretch mode. The bare reconstructed C(111)-(2 {times} l) surface showed the presence of CC stretch modes which were consistent with the Pandey {pi}-bonded chain structure. When exposed to the methyl radical, the SFG spectra of the C(111) surface showed features suggesting the presence of adsorbed methyl species. After heating to sufficiently high temperatures, they were converted into the monohydride species. Preliminary results on the hydrogen-terminated diamond (100) surface are also presented.
Date: April 1, 1995
Creator: Chin, R.P.
Partner: UNT Libraries Government Documents Department

The {alpha}-induced thick-target {gamma}-ray yield from light elements

Description: The {alpha}-induced thick-target {gamma}-ray yield from light elements has been measured in the energy range 5.6 MeV {le} E{sub {alpha}} {le} 10 MeV. The {gamma}-ray yield for > 2.1 MeV from thick targets of beryllium, boron nitride, sodium fluoride, magnesium, aluminum and silicon were measured using the {alpha}-particle beam from the Lawrence Berkeley Laboratories 88 in. cyclotron. The elemental yields from this experiment were used to construct the {alpha}-induced direct production {gamma}-ray spectrum from materials in the SNO detector, a large volume ultra-low background neutrino detector located in the Creighton mine near Sudbury, Canada. This background source was an order of magnitude lower than predicted by previous calculations. These measurements are in good agreement with theoretical calculations of this spectrum based on a statistical nuclear model of the reaction, with the gross high energy spectrum structure being reproduced to within a factor of two. Detailed comparison of experimental and theoretical excitation population distribution of several residual nuclei indicate the same level of agreement within experimental uncertainties.
Date: October 1994
Creator: Heaton, R. K.
Partner: UNT Libraries Government Documents Department

Low p{sub t} pion enhancement in {sup 28}Si + Pb collisions at 14.6 A GeV/c

Description: The pion is produced copiously in nucleus-nucleus collisions at AGS energies and is expected to be easily thermalized due to its large cross section for interaction in dense nuclear matter. Pion enhancement at low transverse momentum has been predicted as the result of a variety of processes. For example, the decay of the {Delta}(1232) resonance is expected to be a major source of such enhancement and has been proposed as an alternative measure of the system temperature. The nucleons and pions produced as the daughters of the {Delta} share their parent`s energy and thereby produce a cold component of the pion spectrum. The delta resonance is believed to be a major contributor to the imaginary part of the scattering amplitude of the pion in dense baryon rich matter. Here the author presents the first results from identified pion spectra from AGS experiment E814.
Date: August 1, 1994
Creator: Hemmick, T. K.
Partner: UNT Libraries Government Documents Department

A wavenumber-partitioning scheme for two-dimensional statistical closures

Description: One of the principal advantages of statistical closure approximations for fluid turbulence is that they involve smoothly varying functions of wavenumber. This suggests the possibility of modeling a flow by following the evolution of only a few representative wavenumbers. This work presents two new techniques for the implementation of two-dimensional isotropic statistical closures that for the first time allows the inertial-range scalings of these approximation to be numerically demonstrated. A technique of wavenumber partitioning that conserves both energy and enstrophy is developed for two-dimensional statistical closures. Coupled with a new time-stepping scheme based on a variable integrating factor, this advance facilitates the computation of energy spectra over seven wavenumber decades, a task that will clearly remain outside the realm of conventional numerical simulations for the foreseeable future. Within the context of the test-field model, the method is used to demonstrate Kraichnan`s logarithmically-corrected scaling for the enstrophy inertial range and to make a quantitative assessment of the effect of replacing the physical Laplacian viscosity with an enhanced hyperviscosity.
Date: November 1, 1994
Creator: Bowman, J. C.
Partner: UNT Libraries Government Documents Department

On inertial range scaling laws

Description: Inertial-range scaling laws for two- and three-dimensional turbulence are re-examined within a unified framework. A new correction to Kolmogorov`s k{sup {minus}5/3} scaling is derived for the energy inertial range. A related modification is found to Kraichnan`s logarithmically corrected two-dimensional enstrophy cascade law that removes its unexpected divergence at the injection wavenumber. The significance of these corrections is illustrated with steady-state energy spectra from recent high-resolution closure computations. The results also underscore the asymptotic nature of inertial-range scaling laws. Implications for conventional numerical simulations are discussed.
Date: December 1, 1994
Creator: Bowman, J. C.
Partner: UNT Libraries Government Documents Department

Thermodynamic stabilities of U(VI) minerals: Estimated and observed relationships

Description: Gibbs free energies of formation ({Delta}G{degree}{sub f}) for several structurally related U(VI) minerals are estimated by summing the Gibbs energy contributions from component oxides. The estimated {Delta}G{degree}{sub f} values are used to construct activity-activity (stability) diagrams, and the predicted stability fields are compared with observed mineral occurrences and reaction pathways. With some exceptions, natural occurrences agree well with the mineral stability fields estimated for the systems SiO{sub 2}-CaO-UO{sub 3}-H{sub 2}O and CO{sub 2}-CaO-UO{sub 3}H{sub 2}O, providing confidence in the estimated thermodynamic values. Activity-activity diagrams are sensitive to small differences in {Delta}G{degree}{sub f} values, and mineral compositions must be known accurately, including structurally bound H{sub 2}O. The estimated {Delta}G{degree}{sub f} values are not considered reliable for a few minerals for two major reasons: (1) the structures of the minerals in question are not closely similar to those used to estimate the {Delta}G{sub f}* values of the component oxides, and/or (2) the minerals in question are exceptionally fine grained, leading to large surface energies that increase the effective mineral solubilities. The thermodynamic stabilities of uranium(VI) minerals are of interest for understanding the role of these minerals in controlling uranium concentrations in oxidizing groundwaters associated with uranium ore bodies, uranium mining and mill tailings and geological repositories for nuclear waste.
Date: December 31, 1996
Creator: Finch, R.J.
Partner: UNT Libraries Government Documents Department

Top quark studies at hadron colliders

Description: The techniques used to study top quarks at hadron colliders are presented. The analyses that discovered the top quark are described, with emphasis on the techniques used to tag {ital b} quark jets in candidate events. The most recent measurements of top quark properties by the CDF and D{null} collaborations are reviewed, including the top quark cross section, mass, branching fractions and production properties. Future top quark studies at hadron colliders are discussed, and predictions for event yields and uncertainties in the measurements of top quark properties are presented.
Date: August 1, 1996
Creator: Sinervo, P. K.
Partner: UNT Libraries Government Documents Department

Chiral symmetry and the threshold {gamma}p {yields} {pi}{sup 0}p reaction

Description: The threshold {gamma}p {yields} {pi}{sup 0}p reaction is investigated by using a chiral invariant {pi}N model in a unitary, gauge invariant, dynamical calculation based on a chiral Lagrangian. It is shown that the chiral invariant {pi}N final state interaction significantly suppresses the E{sub 0+} amplitude from the value {minus}2.4 {times} 10{sup {minus}3}m{sub {pi}}{sup {minus}1} predicted by the low energy theorem to {minus}0.66 {times} 10{sup {minus}3}m{sub {pi}}{sup {minus}1}. We discuss questions concerning the implications of the present results in interpreting the recent Mainz data and their multipole analysis. The experimental accuracy needed for investigating chiral symmetry breaking is illustrated.
Date: March 1, 1994
Creator: Lee, T. S. H. & Pearce, B. C.
Partner: UNT Libraries Government Documents Department

Summary of the extensions of the Standard Model working group

Description: The authors summarize the results of the extended gauge group working group of the Madison-Argonne Workshop on Present and Future Colliders. Contributions are described on the previously unexamined two photon fusion production of heavy leptons, new studies of Z{prime} couplings to {nu}{anti {nu}} and q{anti q}, and previously unexplored vector leptoquark production. More detailed accounts of these studies can be found in individual contributions.
Date: September 1, 1993
Creator: Godfrey, S. & Rizzo, T. G.
Partner: UNT Libraries Government Documents Department

Why Blue stragglers formed via collisions may not be rapid rotators

Description: We propose that the blue stragglers formed via collisions may not be rapid rotators due to magnetic braking during a Hayashi phase as they approach the main sequence. It is conceivable that just the envelopes of the blue stragglers are spun down, while their cores remain rapidly rotating. This would greatly extend the main-sequence lifetimes of the blue stragglers produced by collisions.
Date: March 1, 1993
Creator: Leonard, P. J. T. & Clement, M. J.
Partner: UNT Libraries Government Documents Department

Table of superdeformed nuclear bands and fission isomers

Description: A minimum in the second potential well of deformed nuclei was predicted and the associated shell gaps are illustrated in the harmonic oscillator potential shell energy surface calculations shown in this report. A strong superdeformed minimum in {sup 152}Dy was predicted for {beta}{sub 2}-0.65. Subsequently, a discrete set of {gamma}-ray transitions in {sup 152}DY was observed and, assigned to the predicted superdeformed band. Extensive research at several laboratories has since focused on searching for other mass regions of large deformation. A new generation of {gamma}-ray detector arrays is already producing a wealth of information about the mechanisms for feeding and deexciting superdeformed bands. These bands have been found in three distinct regions near A=l30, 150, and 190. This research extends upon previous work in the actinide region near A=240 where fission isomers were identified and also associated with the second potential well. Quadrupole moment measurements for selected cases in each mass region are consistent with assigning the bands to excitations in the second local minimum. As part of our committment to maintain nuclear structure data as current as possible in the Evaluated Nuclear Structure Reference File (ENSDF) and the Table of Isotopes, we have updated the information on superdeformed nuclear bands. As of April 1994, we have complied data from 86 superdeformed bands and 46 fission isomers identified in 73 nuclides for this report. For each nuclide there is a complete level table listing both normal and superdeformed band assignments; level energy, spin, parity, half-life, magneto moments, decay branchings; and the energies, final levels, relative intensities, multipolarities, and mixing ratios for transitions deexciting each level. Mass excess, decay energies, and proton and neutron separation energies are also provided from the evaluation of Audi and Wapstra.
Date: June 1, 1994
Creator: Firestone, R. B. & Singh, B.
Partner: UNT Libraries Government Documents Department

Discovery potential for new phenomena

Description: The authors examine the ability of future facilities to discover and interpret non-supersymmetric new phenomena. The authors first explore explicit manifestations of new physics, including extended gauge sectors, leptoquarks, exotic fermions, and technicolor models. They then take a more general approach where new physics only reveals itself through the existence of effective interactions at lower energy scales.
Date: March 1, 1997
Creator: Godfrey, S.; Hewett, J.L. & Price, L.E.
Partner: UNT Libraries Government Documents Department

Probing contact interactions at high energy lepton colliders

Description: Fermion compositeness and other new physics can be signaled by the presence of a strong four-fermion contact interaction. Here the authors present a study of {ell}{ell}qq and {ell}{ell}{ell}{prime}{ell}{prime} contact interactions using the reactions: {ell}{sup +}{ell}{sup {minus}} {r_arrow} {ell}{prime}{sup +} {ell}{prime}{sup {minus}}, b{anti b}, c{anti c} at future e{sup +}e{sup {minus}} linear colliders with {radical}s = 0.5--5 TeV and {mu}{sup +}{mu}{sup {minus}} colliders with {radical}s = 0.5, 4 TeV. They find that very large compositeness scales can be probed at these machines and that the use of polarized beams can unravel their underlying helicity structure.
Date: December 1, 1996
Creator: Cheung, K.; Godfrey, S. & Hewett, J.A.
Partner: UNT Libraries Government Documents Department

Nature of the Triple Point in Chromium Alloys: Mode-Softening of the Incommensurate Spin Density Wave

Description: The magnetic stiffness parameter, A2, associated with the critical fluctuations in the paramagnetic phase close to the incommensurate spin-density-wave (SDW) transition of a Cr+0.18at.%Re single crystal, when compared with that of in pure chromium and dilute alloys of vanadium in chromium, indicates that the singularity responsible for the onset of the commensurate SDW phase occurs when A2 approaches zero at a finite value of the incommensurability parameter, delta 0.017 rlu, instead of zero as usually assumed. The mode of the incommensurate SDW softens as delta approaches this critical value with rhenium doping, and conversely hardens as delta increases when vanadium is added to chromium. Also, the amplitude of the critical scattering increases as delta approaches its end point, by a factor of about two going from 0.2 and 0.5at.%V to pure chromium, and by another factor near two in going from pure Cr to Cr+0.18at.%Re.
Date: December 31, 1997
Creator: Noakes, D.R.; Fawcett, E.; Sternlieb, B.L.; Shirane, G. & Jankowska, J.
Partner: UNT Libraries Government Documents Department

The nature and fate of natural resins in the geosphere VI. Analysis of fossil resins from Axel Heiberg Island Canadian Arctic

Description: Ambers are well known and abundant in terrestrial sediments all over the world; however, due largely to the absence of definite morphological characteristics, the precise botanical origin of most amber samples, are at best, often a matter of speculation. This has severely restricted the usefulness of amber in paleobotanical and paleoecological interpretations. The molecular composition and structural characteristics of fossil resins however, may preserve evidence of their botanical origin, which could be of great value in both geochemical, paleobotanical, and paleoenvironmental studies. The remains of a number of exceptionally well-preserved Taxodiaceae-dominated swamp-forest communities have been identified in the sediments of the middle Eocene (45 million years old) Buchanan Lake Formation of Axel Heiberg Island, Canadian Arctic Archipelago. The amber collected from these ancient in situ forests provides a unique opportunity to characterize these resins chemically and taxonomically. Resinite associated with Metasequoia, Pinus and Pseudolarix has been characterized using Pyrolysis-Gas Chromatography-Mass Spectrometry. This method provides a direct analysis of the molecular structure and composition of the resin. In several cases, both bled resin and cone-resin samples have been characterized. The results of these analyses are presented and discussed. The implications of these results for the botanical origins of other ambers represented in the fossil record (including succinite) will also be discussed.
Date: June 1, 1995
Creator: Anderson, K.B. & LePage, B.A.
Partner: UNT Libraries Government Documents Department

Nonlinear symmetric stability of planetary atmospheres

Description: The energy-Casimir method is applied to the problem of symmetric stability in the context of a compressible, hydrostatic planetary atmosphere with a general equation of state. Linear stability criteria for symmetric disturbances to a zonally symmetric baroclinic flow are obtained. In the special case of a perfect gas the results of Stevens (1983) are recovered. Nonlinear stability conditions are also obtained that, in addition to implying linear stability, provide an upper bound on a certain positive-definite measure of disturbance amplitude.
Date: November 1, 1994
Creator: Bowman, J.C. & Shepherd, T.G.
Partner: UNT Libraries Government Documents Department

Is there flow at the AGS?

Description: We have employed the nearly 4{pi}-calorimetric coverage of the E877 apparatus in order to determine flow in different regions of pseudo-rapidity from the measured transverse energy in Au+Au collisions at 11.4 A{center_dot}GeV/c. Signatures for the side-splash in the reaction plane at forward and backward rapidities have been established. Indications of a non-zero eccentricity of particles in the reaction plane at mid-rapidity are also found. These observations complement analyses deriving collective longitudinal motion from dN/dy-spectra of protons, kaons, and pions as well as collective transverse motion of the same particles from m{sub t}-spectra at midrapidity.
Date: December 31, 1994
Creator: Wessels, J.P.; Zhang, Yingchao & Collaboration, E877
Partner: UNT Libraries Government Documents Department

First measurement of the vector analyzing power in muon capture by polarized muonic {sup 3}He

Description: This paper describes the first measurement of spin observables in nuclear muon capture by {sup 3}He. The sensitivity of spin observables to the pseudoscalar coupling is described. The triton asymmetry presented has to be corrected for small systematic effects in order to extract the vector analyzing power. The analysis of these effects is currently underway.
Date: September 1, 1995
Creator: Cummings, W.J.; Behr, J. & Bogorad, P.
Partner: UNT Libraries Government Documents Department

dN{sub ch}/d{eta} distributions in Au+Al, Cu, Au, and U collisions at 10.8 A{center_dot}GeV/c and E{sub t} per charged particle

Description: The pseudorapidity distributions are analyzed as a function of transverse energy produced in the target or central pseudorapidity regions. The transverse energy per charged particle is presented as a function of pseudorapidity and centrality.
Date: December 31, 1995
Creator: Voloshin, S.A. & Collaboration, E877
Partner: UNT Libraries Government Documents Department

Anomalous gauge boson interactions

Description: We discuss the direct measurement of the trilinear vector boson couplings in present and future collider experiments. The major goals of such experiments will be the confirmation of the Standard Model (SM) predictions and the search for signals of new physics. We review our current theoretical understanding of anomalous trilinear gauge-boson self interactions. If the energy scale of the new physics is {approximately} 1 TeV, these low energy anomalous couplings are expected to be no larger than {Omicron}(10{sup {minus}2}). Constraints from high precision measurements at LEP and low energy charged and neutral current processes are critically reviewed.
Date: March 1, 1995
Creator: Aihara, H.; Barklow, T. & Baur, U.
Partner: UNT Libraries Government Documents Department

Analysis of the high energy behavior of the forward scattering parameters -- {sigma}{sub tot}, {rho}, and B

Description: Recent experimental results, namely, the remeasurement of the {rho} value by UA4/2 at {radical}s = 546 GeV, together with a new analysis by the E710 group of {sigma}{sub tot}, {rho} and B at {radical}s = 1800 GeV, as well as their measurement of {sigma}{sub tot} and B at {radical}s = 1020 GeV, have provided important anchor points for the high energy behavior of {anti p}p scattering. The authors analyze high energy {anti p}p and pp data, using two distinct (and dissimilar) analysis techniques: (1) asymptotic amplitude analysis, under the assumption that they have reached {open_quotes}asymptopia{close_quotes}, and (2) an eikonal model whose amplitudes are designed to mimic real QCD amplitudes. The former gives strong evidence for a log (s/s{sub 0}) dependence at current energies and not log{sup 2}(s/s{sub 0}), and demonstrates that odderons are not necessary to explain the experimental data. The latter gives a unitary model for extrapolation into true {open_quote}asymptopia{close_quote} from current energies, allowing them to predict the values of the total cross section at future supercolliders. Using their QCD-model, the authors obtain {sigma}{sub tot}(16 TeV)= 106 {+-} 4 mb and {sigma}{sub tot}(40 TeV) = 120 {+-} 5 mb.
Date: December 31, 1993
Creator: Block, M. M.; Halzen, F.; Margolis, B. & White, A. R.
Partner: UNT Libraries Government Documents Department

The high energy behavior of the forward scattering parameters -- {sigma}{sub tot}, {rho}, and B

Description: Utilizing the most recent experimental data, the authors reanalyze high energy {anti p}p and pp data, using, two distinct (and dissimilar) analysis techniques: (1) asymptotic amplitude analysis, under the assumption that they have reached ``asymptopia``, and (2) an eikonal model whose amplitudes are designed to mimic real QCD amplitudes. The former gives strong evidence for a log(s/s{sub o}) dependence at current energies and not log{sup 2}(s/s{sub o}), and demonstrates that odderons are not necessary to explain the experimental data. The latter gives a unitary model for extrapolation into true ``asymptopia`` from current energies, allowing the authors to predict the values of the total cross section at future supercolliders. Using the QCD-model, they obtain {sigma}{sub tot}(16 TeV) = 109 {+-} 4mb and {sigma}{sub tot}(40 TeV) = 124 {+-} 4 mb.
Date: October 1994
Creator: Block, M. M.; Halzen, F.; Margolis, B. & White, A. R.
Partner: UNT Libraries Government Documents Department

Z-dependent barriers in multifragmentation from Poissonian reducibility and thermal scaling

Description: The authors explore the natural limit of binomial reducibility in nuclear multifragmentation by constructing excitation functions for intermediate mass fragments (IMF) of a given element Z. The resulting multiplicity distributions for each window of transverse energy are Poissonian. Thermal scaling is observed in the linear Arrhenius plots made from the average multiplicity of each element. Emission barriers are extracted from the slopes of the Arrhenius plots and their possible origin is discussed.
Date: January 1, 1998
Creator: Moretto, L. G.; Beaulieu, L.; Phair, L. & Wozniak, G. J.
Partner: UNT Libraries Government Documents Department

The role of statistics and thermodynamics in nuclear multifragmentation

Description: The natural limit of binomial reducibility in nuclear multifragmentation is observed in excitation functions for intermediate mass fragments (IMF) of a given element Z. The multiplicity distributions for each window of transverse energy are Poissonian. Thermal scaling is observed in the linear Arrhenius plots constructed from the average multiplicity of each element. Emission barriers are extracted from the slopes of the Arrhenius plots and their possible origin is discussed.
Date: March 1, 1998
Creator: Moretto, L. G.; Beaulieu, L.; Phair, L. & Wozniak, G. J.
Partner: UNT Libraries Government Documents Department