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Global warming potential estimates for the C₁–C₃ hydrochlorofluorocarbons (HCFCs) included in the Kigali Amendment to the Montreal Protocol

Description: This article reports global warming potentials (GWPs) for all C₁-C₃ hydrochlorofluorocarbons (HCFCs) based on estimated atmospheric lifetimes and theoretical methods used to calculate infrared absorption spectra.
Date: January 10, 2018
Creator: Papanastasiou, Dimitrios K.; Beltrone, Allison; Marshall, Paul & Burkholder, James B. (James Bart), 1954-
Partner: UNT College of Arts and Sciences

Energy From Biological Processes

Description: An assessment by the Office of Technology Assessment that examines the "energy potential of various sources of plant and animal matter (biomass)," giving an analysis of "prominent biomass issues, summaries of four biomass fuel cycles, a description of biomass' place in two plausible energy futures, and discussions of policy options for promoting energy from biomass" (p. iii).
Date: July 1980
Creator: United States. Congress. Office of Technology Assessment.
Partner: UNT Libraries Government Documents Department

Angular distributions of electrons photoemitted from core levels of oriented diatomic molecules: Multiple scattering theory in non-spherical potentials

Description: We use multiple scattering in non-spherical potentials (MSNSP) to calculate the angular distributions of electrons photoemitted from the 1s-shells of CO and N2 gas-phase molecules with fixed-in-space orientations. For low photoelectron kinetic energies (E<50 eV), as appropriate to certain shape-resonances, the electron scattering must be represented by non-spherical scattering potentials, which are naturally included in our formalism. Our calculations accurately reproduce the experimental angular patterns recently measured by several groups, including those at the shape-resonance energies. The MSNSP theory thus enhances the sensitivity to spatial electronic distribution and dynamics, paving the way toward their determination from experiment.
Date: September 6, 2001
Creator: Diez Muino, R.; Rolles, D.; Garcia de Abajo, F.J.; Fadley, C.S. & Van Hove, M.A.
Partner: UNT Libraries Government Documents Department

A weak microwave instability with potential well distortion and radial mode coupling

Description: In attempts to minimize the impedance of an accelerator by smoothing out its vacuum chamber, improvements are typically first made by reducing the inductive part of the impedance. As the inductance is reduced, however, the impedance becomes increasingly relatively resistive, and as a consequence, the nature of potential well distortion changes qualitatively. An inductive impedance lengthens the bunch (above transition) while maintaining more or less a head-tail symmetry of the bunch longitudinal distribution. A resistive impedance does not change the bunch length as much, but tends to cause a large head-tail asymmetry. We explore two ways which might in principle allevial this instability mechanism. (i) add a higher harmonic cavity: A higher harmonic rf voltage with appropriate and amplitude may compensate for the head-tail asymmetry and thus raise the instability threshold. (ii) operate the accelerator with a negative momentum compaction factor {eta}:(12) With {eta} > 0, the distorted beam distribution leans toward the head of the bunch; the bunch tail sees large wakefields. Operating with {eta} < 0 could conceivably help because the beam distribution now leans toward the tail of the bunch. Both (i) and (ii) were explored in this paper. We found that a higher harmonic cavity of a modest voltage can indeed eliminate this instability, while the advantage of operating with {eta}< 0 is less obvious.
Date: July 1, 1995
Creator: Chao, A.; Chen, Bo & Oide, Katsunobu
Partner: UNT Libraries Government Documents Department

Photoluminescence studies of modulation doped coupled double quantum wells in magnetic fields

Description: We have studied the photoluminescence spectra of a series of mudulation doped couple double quantum well structures in parallel and perpendicular magnetic fields to 62 tesla at 4K and 77K, for B{parallel}a, the spectra display distinct Landau level transitions which show anti-crossing with the e1-hh1 exciton. At high fields, the lowest conduction band-valence exciton approaches the extrapolated 0- 0 Landau level. About 25 Tesla, there is valence band mixing of the e1-lh1, e1-hh2, e1-hh1 transitions. The spectral peaks display a diamagnetic shift in low in-plane magnetic fields which become linear in high fields. At magnetic fields beyond 40T, spin splitting is observed for both B{parallel}z and B{perpendicular} geometries. The partial energy gap discovered in conductance measurements in in-plane fields was not conclusively observed using photoluminescence spectroscopy, although anomalies in the energy dependence of the lowest level with magnetic field were evident at similar field values.
Date: September 1, 1996
Creator: Kim, Y.; Perry, C.H.; Simmons, J.A.; Klem, J.F.; Jones, E.D. & Rickel, D.G.
Partner: UNT Libraries Government Documents Department

Development of global medium-energy nucleon-nucleus optical model potentials

Description: The authors report on the development of new global optical model potentials for nucleon-nucleus scattering at medium energies. Using both Schroedinger and Dirac scattering formalisms, the goal is to construct a physically realistic optical potential describing nucleon-nucleus elastic scattering observables for a projectile energy range of (perhaps) 20 meV to (perhaps) 2 GeV and a target mass range of 16 to 209, excluding regions of strong nuclear deformation. They use a phenomenological approach guided by conclusions from recent microscopic studies. The experimental database consists largely of proton-nucleus elastic differential cross sections, analyzing powers, spin-rotation functions, and total reaction cross sections, and neutron-nucleus total cross sections. They will use this database in a nonlinear least-squares adjustment of optical model parameters in both relativistic equivalent Schroedinger (including relativistic kinematics) and Dirac (second-order reduction) formalisms. Isospin will be introduced through the standard Lane model and a relativistic generalization of that model.
Date: August 1, 1997
Creator: Madland, D.G. & Sierk, A.J.
Partner: UNT Libraries Government Documents Department

Thermodynamics and kinetics of ion speciation in supercritical aqueous solutions: A molecular based study

Description: Molecular simulation of infinitely dilute NaCl aqueous solutions are performed to study the Na{sup +}/Cl{sup -} ion pairing in a polarizable and a nonpolarizable solvent at supercritical conditions. The Simple Point Charge, Pettitt-Rossky, and Fumi-Tosi models for the water-water, ion-water, and ion-ion interactions are used in determining the degree of dissociation, its temperature and density dependence, and the kinetics of the interconversion between ion-pair configurations in a nonpolarizable medium. To assess the effect of the solvent polarizability on the stability of the ion-pair configurations, we replace the Simple Point Charge by the Polarizable Point Charge water model and determine the anion-cation potential of mean force at T{sub r}=1.20 and {rho}{sub r}=1.5.
Date: May 1, 1997
Creator: Chialvo, A.A.; Cummings, P.T.; Simonson, J.M. & Mesmer, R.E.
Partner: UNT Libraries Government Documents Department

Beyond the adiabatic approximation: The impact of thresholds on the hadronic spectrum

Description: In the adiabatic approximation, most of the effects of quark-antiquark loops on spectroscopy can be absorbed into a static interquark potential. The author develops a formalism which can be used to treat the residual nonadiabatic effects associated with the presence of nearby hadronic thresholds for heavy quarks. He then defines a potential which includes additional high energy corrections to the adiabatic limit which would be present for finite quark masses. This improved potential allows a systematic low energy expansion of the impact of thresholds on hadronic spectra.
Date: January 1, 1999
Creator: Isgur, N.
Partner: UNT Libraries Government Documents Department

Mode-coupling instability and bunch lengthening in proton machines

Description: In proton machines, potential-well distortion leads to small amount of bunch lengthening with minimal head-tail asymmetry. Longitudinal mode-mixing instability occurs at higher azimuthal modes. When the driving resonance is of broad-band, the threshold corresponds to Keil-Schnell criterion for microwave instability. When the driving resonance is narrower than the bunch spectrum, the threshold corresponds to a similar criterion derived before.
Date: May 1, 1995
Creator: Ng, K.Y.
Partner: UNT Libraries Government Documents Department

Characterization of the passivation layer on disordered carbons in lithium-ion cells

Description: Intercalation anodes of graphite or disordered carbon in rechargeable Li-ion batteries (based on aprotic organic solvents) develop a passivating film during the first intercalation of Li{sup +}. The formation of this film reduces the cycling efficiency and results in excessive consumption of Li{sup +}. The exact nature of this film is not well defined, although there are many similarities in properties to the films that form on Li anodes under similar cycling conditions. In this study we report on characterization studies of films formed during galvanostatic cycling of disordered carbons derived from polymethylacryolintrile (PMAN) in a 1M LiPF{sub 6} solution in ethylene carbonateldimethyl carbonate solution (1:1 by vol.). Complementary tests were also conducted with glass carbon, where intercalation cannot occur. Complex-impedance spectroscopy was the primary measurement technique, supplemented by cyclic voltammetry.
Date: December 1, 1995
Creator: Guidotti, R. & Johnson, B.
Partner: UNT Libraries Government Documents Department

Magnetotunneling absorption in double quantum wells

Description: Tunneling absorption is calculated in weakly coupled n-type asymmetric double quantum wells in an in-plane magnetic field using a linear response theory. Photon-assisted tunneling occurs between the ground sublevels of the quantum wells. We show that the absorption threshold, the resonance energy of absorption, and the linewidth depend sensitively on the magnetic field and the temperature.
Date: June 1, 1996
Creator: Lyo, S.K.
Partner: UNT Libraries Government Documents Department

{ital Ab Initio} Pseudopotential calculations of dopant diffusion in Si

Description: The ab initio pseudopotential method is used to study transient-enhanced-diffusion (TED) related processes. The electronic degrees of freedom are included explicitly, together with the fully self-consistent treatment of the electron charge density. A large supercell and a fine k-point mesh are used to ensure numerical convergence. Such method has been demonstrated to give quantitative description of defect energetic. We will show that boron diffusion is significantly enhanced in the presence of the Si interstitial due to the substantial lowering of the migrational barrier through a kick-out mechanism. The resulting mobile boron can also be trapped by another substitutional boron, forming an immobile and elect rically inactive two-boron pair. Similarly, carbon diffusion is also enhanced significantly due to the pairing with Si interstitial. However, carbon binds to Si interstitial much more strongly than boron does, taking away most Si interstitial from boron at sufficiently large carbon concentration, which causes the suppression of the boron TED. We will also show that Fermi level effect plays an important role in both Si interstitial and boron diffusion.
Date: April 28, 1997
Creator: Zhu, J., LLNL
Partner: UNT Libraries Government Documents Department

Thermodynamics of anisotropic fluids using isotropic potentials

Description: We study the effectiveness and limitations of the median potential recipe for mixtures such as N{sub 2} + O{sub 2} and N{sub 2} + CO{sub 2}, that are important in detonation applications. Conversely, we treat effective spherical potentials extracted from Hugoniot experiments (e.g., N{sub 2} and O{sub 2}) as median potentials and invert them to extract atom-atom potentials. The resulting non-spherical potentials compare remarkably well with the atom - atom potentials used in studies of solid state properties. Finally, we propose a method to improve the median potential for stronger anisotropic fluids such as CO{sub 2} and its mixtures.
Date: August 16, 1999
Creator: Bastea, S & Ree, F H
Partner: UNT Libraries Government Documents Department

Hemispheric Interactions and Event-Related Potentials in Lateralized Stroop and Stroop Analog Tasks

Description: Classical Stroop stimuli and newly developed face/word Stroop analog stimuli were used to investigate hemispheric interactions in Stroop interference effects (SEs) and corresponding event-related potentials (ERPs). Lateralized stimuli were presented unilaterally and bilaterally as congruent or incongruent color strip-word or face-word pairs (to invoke right hemisphere (RH) and left hemisphere (LH) specialization, respectively, in the latter case). The common finding for such tasks is that responses for the congruent condition are faster and more accurate than for the incongruent condition (i.e., the SE). A primary prediction is that the SE will be maximized when both the distractor and target components, or distractor alone, are presented to the specialized hemisphere (i.e., LH for words and RH for faces). A total of 88 right-handed University of North Texas students participated in one of four experiments. Participants manually responded to one component of the stimuli (i.e., color, face, or word), while ignoring the other. Behaviorally, participants showed a robust SE across all experiments, especially for the face/word task with word targets. Findings from the face/word Stroop analog tasks also indicated that SEs were produced by selective attention to either faces or words, implicating a role for top-down (controlled) processes. Hemispheric asymmetries were observed only for bilateral presentations of the face/word Stroop analog stimuli and did not differ for word versus face targets. The results suggest that the LH is less susceptible to interference from the RH than vice versa. Electrophysiologically, anterior N1 and P1, posterior P1 and N1, N2, and P3 components were identified. A SE was found for P3 amplitudes, but not latencies, across all four experiments such that the congruent condition generated greater amplitudes than the incongruent condition, suggesting that the P3 is an index of task difficulty. Surprisingly, SEs were also observed for the early ERP components, albeit embedded in ...
Date: December 1997
Creator: Kavcic, Voyko
Partner: UNT Libraries

A preliminary study of the effects of selective-serotonin re-uptake inhibitors (SSRIs) on central auditory processing

Description: his study compared auditory behavioral and physiological measures among three subject groups: 1) Normal control subjects, 2) subjects who were on a prescribed SSRI for depression, and 3) subjects who were prescribed an SSRI for depression, but were not medicated at the time of testing. Test measures included: Standard audiological tests (audiometry and tympanometry), electrophysiological procedures for analysis of auditory- evoked brainstem and late responses, and standardized behavioral speech tests (SCAN-A, SSI, and the low predictability sentence list of the R-SPIN). Analysis of results indicated a statistically significant increase of group mean amplitude of the ABR peak V, from 15dBnSL to 55dBnSL, in the non-medicated group compared to controls. Also, the non-medicated group scored significantly less favorably than controls on the most challenging listening condition (-20 MCR) of the SSI, in the left ear. Although other test measures indicated consistent differences between these two groups, they were not, however, significant.
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Date: August 2001
Creator: Bishop, Charles E.
Partner: UNT Libraries

Coexistence of coherent and incoherent tunneling in asymmetric double-well potentials

Description: Double-well potentials are widely used to model phenomena in physics and chemistry. The system is assumed to be formed in a metastable state, its dynamical evolution providing the clues for the interpretation of the experimental data. Quantum mechanics predicts coherent oscillations of probability between wells if the double-well potential is nearly symmetric and irreversible exponential decay if the final well has an infinite width. For very asymmetric double-well potentials, these two extreme behaviors are expected to coexist. The purpose of the present paper is to investigate this coexistence and its evolution as a function of the width of (or density of states in) the second well. In this sense, increasing the density of states can be regarded as a mechanism for coherence breakdown. The dynamical evolution of the metastable state can be simulated by solving numerically the time-dependent Schroedinger equation (TDSE). This approach is general, intuitive, and gives access to time scales and dynamical effects. It also allows the inclusion of phenomenological dissipation.
Date: December 1, 1995
Creator: Carjan, N.; Grigorescu, M. & Strottman, D.
Partner: UNT Libraries Government Documents Department

CERTS Microgrid Laboratory Test Bed

Description: CERTS Microgrid concept captures the emerging potential of distributed generation using a system approach. CERTS views generation and associated loads as a subsystem or a 'microgrid'. The sources can operate in parallel to the grid or can operate in island, providing UPS services. The system can disconnect from the utility during large events (i.e. faults, voltage collapses), but may also intentionally disconnect when the quality of power from the grid falls below certain standards. CERTS Microgrid concepts were demonstrated at a full-scale test bed built near Columbus, Ohio and operated by American Electric Power. The testing fully confirmed earlier research that had been conducted initially through analytical simulations, then through laboratory emulations, and finally through factory acceptance testing of individual microgrid components. The islanding and resynchronization method met all Institute of Electrical and Electronics Engineers Standard 1547 and power quality requirements. The electrical protection system was able to distinguish between normal and faulted operation. The controls were found to be robust under all conditions, including difficult motor starts and high impedance faults.
Date: June 8, 2010
Creator: Lasseter, R. H.; Eto, J. H.; Schenkman, B.; Stevens, J.; Volkmmer, H.; Klapp, D. et al.
Partner: UNT Libraries Government Documents Department