Resource Type

95 Matching Results

Results open in a new window/tab.

Investigation of the 2p3/2-3d5/2 line emission of Au53+ -- Au69+ for diagnosing high energy density plasmas (open access)

Investigation of the 2p3/2-3d5/2 line emission of Au53+ -- Au69+ for diagnosing high energy density plasmas

Measurements of the L-shell emission of highly charged gold ions were made under controlled laboratory conditions using the SuperEBIT electron beam ion trap, allowing detailed spectral observations of lines from ironlike Au{sup 53+} through neonlike Au{sup 69+}. Using atomic data from the Flexible Atomic Code, we have identified strong 3d{sub 5/2} {yields} 2p{sub 3/2} emission features that can be used to diagnose the charge state distribution in high energy density plasmas, such as those found in the laser entrance hole of hot hohlraum radiation sources. We provide collisional-radiative calculations of the average ion charge <Z> as a function of temperature and density, which can be used to relate charge state distributions inferred from 3d{sub 5/2} {yields} 2p{sub 3/2} emission features to plasma conditions, and investigate the effects of plasma density on calculated L-shell Au emission spectra.
Date: January 29, 2008
Creator: Brown, G V; Hansen, S B; Trabert, E; Beiersdorfer, P; Widmann, K; Chen, H et al.
System: The UNT Digital Library
Dalitz Plot Analysis of B- -> D+ pi- pi- (open access)

Dalitz Plot Analysis of B- -> D+ pi- pi-

The author reports on a Dalitz plot analysis of B{sup -} {yields} D{sup +}{pi}{sup -}{pi}{sup -} decays, based on a sample of about 383 million {Upsilon}(4S) {yields} B{bar B} decays collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. They find the total branching fraction of the three-body decay: {Beta}(B{sup -} {yields} D{sup +} {pi}{sup -}{pi}{sup -}) = (1.08 {+-} 0.01 {+-} 0.05) x 10{sup -3}. the masses and widths of D*{sub 2}{sup 0} and D*{sub 0}{sup 0}, the 2{sup +} and 0{sup +} c{bar u} P-wave states decaying to D{sup +}{pi}{sup -}, are measured: m{sub D*{sub 2}{sup 0}} = (2460.4 {+-} 1.2 {+-} 1.2 {+-} 1.9) MeV/c{sup 2}, {Lambda}{sub D*{sub 2}{sup 0}} = (41.8 {+-} 2.5 {+-} 2.1 {+-} 2.0) MeV, m{sub D*{sub 0}{sup 0}} = (2297 {+-} 8 {+-} 5 {+-} 19) MeV/c{sup 2} and {Lambda}{sub D*{sub 0}{sup 0}} = (273 {+-} 12 {+-} 17 {+-} 45) MeV. The stated errors reflect the statistical and systematic uncertainties, and the uncertainty related to the assumed composition of signal events and the theoretical model.
Date: January 29, 2009
Creator: Aubert, B.
System: The UNT Digital Library
Rapid Reagentless Detection of M. tuberculosis H37Ra in Respiratory Effluents (open access)

Rapid Reagentless Detection of M. tuberculosis H37Ra in Respiratory Effluents

Two similar mycobacteria, Mycobacteria tuberculosis H37Ra and Mycobacteria smegmatis are rapidly detected and identified within samples containing a complex background of respiratory effluents using Single Particle Aerosol Mass Spectrometry (SPAMS). M. tuberculosis H37Ra (TBa), an avirulent strain, is used as a surrogate for virulent tuberculosis (TBv); M. smegmatis (MSm) is utilized as a near neighbor confounder for TBa. Bovine lung surfactant and human exhaled breath condensate are used as first-order surrogates for infected human lung expirations from patients with pulmonary tuberculosis. This simulated background sputum is mixed with TBa or MSm and nebulized to produce conglomerate aerosol particles, single particles that contain a bacterium embedded within a background respiratory matrix. Mass spectra of single conglomerate particles exhibit ions associated with both respiratory effluents and mycobacteria. Spectral features distinguishing TBa from MSm in pure and conglomerate particles are shown. SPAMS pattern matching alarm algorithms are able to distinguish TBa containing particles from background matrix and MSm for >50% of the test particles, which is sufficient to enable a high probability of detection and a low false alarm rate if an adequate number of such particles are present. These results indicate the potential usefulness of SPAMS for rapid, reagentless tuberculosis screening.
Date: January 29, 2008
Creator: Adams, K L; Steele, P T; Bogan, M J; Sadler, N M; Martin, S; Martin, A N et al.
System: The UNT Digital Library
Subaru Weak Lensing Measurements of Four Strong Lensing Clusters: Are Lensing Clusters Over-Concentrated? (open access)

Subaru Weak Lensing Measurements of Four Strong Lensing Clusters: Are Lensing Clusters Over-Concentrated?

We derive radial mass profiles of four strong lensing selected clusters which show prominent giant arcs (Abell 1703, SDSS J1446+3032, SDSS J1531+3414, and SDSS J2111-0115), by combining detailed strong lens modeling with weak lensing shear measured from deep Subaru Suprime-cam images. Weak lensing signals are detected at high significance for all four clusters, whose redshifts range from z = 0.28 to 0.64. We demonstrate that adding strong lensing information with known arc redshifts significantly improves constraints on the mass density profile, compared to those obtained from weak lensing alone. While the mass profiles are well fitted by the universal form predicted in N-body simulations of the {Lambda}-dominated cold dark matter model, all four clusters appear to be slightly more centrally concentrated (the concentration parameters c{sub vir} {approx} 8) than theoretical predictions, even after accounting for the bias toward higher concentrations inherent in lensing selected samples. Our results are consistent with previous studies which similarly detected a concentration excess, and increases the total number of clusters studied with the combined strong and weak lensing technique to ten. Combining our sample with previous work, we find that clusters with larger Einstein radii are more anomalously concentrated. We also present a detailed model …
Date: January 29, 2009
Creator: Oguri, Masamune; Hennawi, Joseph F.; Gladders, Michael D.; Dahle, Haakon; Natarajan, Priyamvada; Dalal, Neal et al.
System: The UNT Digital Library
Correlations between Optical, Chemical and Physical Properties of Biomass Burn Aerosols (open access)

Correlations between Optical, Chemical and Physical Properties of Biomass Burn Aerosols

Aerosols generated from burning different plant fuels were characterized to determine relationships between chemical, optical and physical properties. Single scattering albedo ({omega}) and Angstrom absorption coefficients ({alpha}{sub ap}) were measured using a photoacoustic technique combined with a reciprocal nephelometer. Carbon-to-oxygen atomic ratios, sp{sup 2} hybridization, elemental composition and morphology of individual particles were measured using scanning transmission X-ray microscopy coupled with near-edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS) and scanning electron microscopy with energy dispersion of X-rays (SEM/EDX). Particles were grouped into three categories based on sp2 hybridization and chemical composition. Measured {omega} (0.4-1.0 at 405 nm) and {alpha}{sub ap} (1.0-3.5) values displayed a fuel dependence. The category with sp{sup 2} hybridization >80% had values of {omega} (<0.5) and {alpha}{sub ap} ({approx}1.25) characteristic of light absorbing soot. Other categories with lower sp2 hybridization (20 to 60%) exhibited higher {omega} (>0.8) and {alpha}{sub ap} (1.0 to 3.5) values, indicating increased absorption spectral selectivity.
Date: January 29, 2008
Creator: Hopkins, Rebecca J.; Lewis, K.; Desyaterik, Yury; Wang, Z.; Tivanski, Alexei V.; Arnott, W. P. et al.
System: The UNT Digital Library
QUALIFICATION OF A RADIOACTIVE HIGH ALUMINUM GLASS FOR PROCESSINGIN THE DEFENSE WASTE PROCESSING FACILITY AT THE SAVANNAH RIVER SITE (open access)

QUALIFICATION OF A RADIOACTIVE HIGH ALUMINUM GLASS FOR PROCESSINGIN THE DEFENSE WASTE PROCESSING FACILITY AT THE SAVANNAH RIVER SITE

At the Savannah River Site (SRS) the Defense Waste Processing Facility (DWPF) has been immobilizing SRS's radioactive high level waste (HLW) sludge into a borosilicate glass for approximately eleven years. Currently the DWPF is immobilizing HLW sludge in Sludge Batch 4 (SB4). Each sludge batch is nominally two million liters of HLW and produces nominally five hundred stainless steel canisters 0.6 meters in diameter and 3 meters tall filled with the borosilicate glass. In SB4 and earlier sludge batches, the Al concentration has always been rather low, (less than 9.5 weight percent based on total dried solids). It is expected that in the future the Al concentrations will increase due to the changing composition of the HLW. Higher Al concentrations could introduce problems because of its known effect on the viscosity of glass melts and increase the possibility of the precipitation of nepheline in the final glass and decrease its durability. In 2006 Savannah River National Laboratory (SRNL) used DWPF processes to immobilize a radioactive HLW slurry containing 14 weight percent Al to ensure that this waste is viable for future DWPF processing. This paper presents results of the characterization of the high Al glass prepared in that demonstration. At …
Date: January 29, 2008
Creator: Bibler, N; John Pareizs, J; Tommy Edwards,T; Charles02 Coleman, C & Charles Crawford, C
System: The UNT Digital Library
Observation of B Meson Decays to omegaK* and Improved Measurements for omegarho and omegaf0 (open access)

Observation of B Meson Decays to omegaK* and Improved Measurements for omegarho and omegaf0

We present measurements of B meson decays to the final states {omega}K*, {omega}{rho}, and {omega}f{sub 0}, where K* indicates a spin 0, 1, or 2 strange meson. The data sample corresponds to 465 x 10{sup 6} B{bar B} pairs collected with the BABAR detector at the PEP-II e{sup +}e{sup -} collider at SLAC. B meson decays involving vector-scalar, vector-vector, and vector-tensor final states are analyzed; the latter two shed new light on the polarization of these final states. We measure the branching fractions for nine of these decays; five are observed for the first time. For most decays we also measure the charge asymmetry and, where relevant, the longitudinal polarization f{sub L}.
Date: January 29, 2009
Creator: Aubert, B.
System: The UNT Digital Library
MCSNA: Experimental Benchmarking of Pu Electronic Structure (open access)

MCSNA: Experimental Benchmarking of Pu Electronic Structure

The objective of this work is to develop and/or apply advanced diagnostics to the understanding of aging of Pu. Advanced characterization techniques such as photoelectron and x-ray absorption spectroscopy will provide fundamental data on the electronic structure of Pu phases. These data are crucial for the validation of the electronic structure methods. The fundamental goal of this project is to narrow the parameter space for the theoretical modeling of Pu aging. The short-term goal is to perform experiments to validate electronic structure calculations of Pu. The long-term goal is to determine the effects of aging upon the electronic structure of Pu. Many of the input parameters for aging models are not directly measurable. These parameters will need to be calculated or estimated. Thus a First Principles-Approach Theory is needed, but it is unclear what terms are important in the Hamiltonian. (H{Psi} = E{Psi}) Therefore, experimental data concerning the 5f electronic structure are needed, to determine which terms in the Hamiltonian are important. The data obtained in this task are crucial for reducing the uncertainty of Task LL-01-developed models and predictions. The data impact the validation of electronic structure methods, the calculation of defect properties, the evaluation of helium diffusion, and …
Date: January 29, 2007
Creator: Tobin, J G
System: The UNT Digital Library
PARTNERSHIP FOR THE DEVELOPMENT OF NEXT GENERATION SIMULATION TOOLS TO EVALUATE CEMENTITIOUS BARRIERS AND MATERIALS USED IN NUCLEAR APPLICATION - 8388 (open access)

PARTNERSHIP FOR THE DEVELOPMENT OF NEXT GENERATION SIMULATION TOOLS TO EVALUATE CEMENTITIOUS BARRIERS AND MATERIALS USED IN NUCLEAR APPLICATION - 8388

The US DOE has initiated a multidisciplinary cross cutting project to develop a reasonable and credible set of tools to predict the structural, hydraulic and chemical performance of cement barriers used in nuclear applications over extended time frames (e.g., > 100 years for operating facilities and > 1000 years for waste management). A partnership that combines DOE, NRC, academia, private sector, and international expertise has been formed to accomplish the project objectives by integrating existing information and realizing advancements where necessary. The set of simulation tools and data developed under this project will be used to evaluate and predict the behavior of cementitious barriers used in near surface engineered waste disposal systems, e.g., waste forms, containment structures, entombments and environmental remediation, including decontamination and decommissioning (D&D) activities. The simulation tools will also support analysis of structural concrete components of nuclear facilities (spent fuel pools, dry spent fuel storage units, and recycling facilities, e.g., fuel fabrication, separations processes). Simulation parameters will be obtained from prior literature and will be experimentally measured under this project, as necessary, to demonstrate application of the simulation tools for three prototype applications (waste form in concrete vault, high level waste tank grouting, and spent fuel pool). …
Date: January 29, 2008
Creator: Langton, C & Richard Dimenna, R
System: The UNT Digital Library
Modeling Estimated Personnel Needs for a Potential Foot and Mouth Disease Outbreak (open access)

Modeling Estimated Personnel Needs for a Potential Foot and Mouth Disease Outbreak

Foot and Mouth disease (FMD) is a highly infectious and contagious viral disease affecting cloven-hoofed livestock that was last detected in the United States (US) in 1929. The prevalence of FMD in other countries, as well as the current potential for this virus to be used as a form of agroterrorism, has made preparations for a potential FMD outbreak a national priority. To assist in the evaluation of national preparedness, all 50 states were surveyed via e-mail, telephone and web search to obtain emergency response plans for FMD or for foreign animal diseases in general. Information from 33 states was obtained and analyzed for estimates of personnel resources needed to respond to an outbreak. These estimates were consolidated and enhanced to create a tool that could be used by individual states to better understand the personnel that would be needed to complete various tasks over time during an outbreak response. The estimates were then coupled, post-processing, to the output from FMD outbreaks simulated in California using the Multiscale Epidemiological/Economic Simulation and Analysis (MESA) model at Lawrence Livermore National Laboratory to estimate the personnel resource demands, by task, over the course of an outbreak response.
Date: January 29, 2008
Creator: Simmons, K & Hullinger, P
System: The UNT Digital Library
On The Electronic Configuration in Pu (open access)

On The Electronic Configuration in Pu

X-Ray Absorption Spectroscopy (XAS) and Photoelectron Spectroscopy (PES) have been performed upon highly radioactive samples, particularly Plutonium, at the Advanced Light Source in Berkeley, CA, USA. First results from alpha and delta Plutonium are reported as well as a detailed analysis of sample quality.
Date: January 29, 2007
Creator: Tobin, J G; Soderlind, P; Landa, A; Moore, K T; Schwartz, A J; Chung, B W et al.
System: The UNT Digital Library
Ferrimagnetism and disorder of epitaxial Mn2-xCoxVAl Heusler compound thin films (open access)

Ferrimagnetism and disorder of epitaxial Mn2-xCoxVAl Heusler compound thin films

The quaternary full Heusler compound Mn{sub 2-x}Co{sub x}VAl with x = 1 is predicted to be a half-metallic antiferromagnet. Thin films of the quaternary compounds with x = 0-2 were prepared by dc and RF magnetron co-sputtering on heated MgO (0 0 1) substrates. The magnetic structure was examined by x-ray magnetic circular dichroism and the chemical disorder was characterized by x-ray diffraction. Ferrimagnetic coupling of V to Mn was observed for Mn{sub 2}VAl (x = 0). For x = 0.5, we also found ferrimagnetic order with V and Co antiparallel to Mn. The observed reduced magnetic moments are interpreted with the help of band structure calculations in the coherent potential approximation. Mn{sub 2}VAl is very sensitive to disorder involving Mn, because nearest-neighbour Mn atoms couple antiferromagnetically. Co{sub 2}VAl has B2 order and has reduced magnetization. In the cases with x {ge} 0.9 conventional ferromagnetism was observed, closely related to the atomic disorder in these compounds.
Date: January 29, 2011
Creator: Meinert, Markus; Schmalhorst, Jan-Michael; Reiss, Gunter & Arenholz, Elke
System: The UNT Digital Library
National Atmospheric Release Advisory Center Dispersion Modeling in Response to the Fukushima Daiichi Accident (open access)

National Atmospheric Release Advisory Center Dispersion Modeling in Response to the Fukushima Daiichi Accident

None
Date: January 29, 2013
Creator: Sugiyama, G.; Nasstrom, J.; Foster, K.; Pobanz, B.; Simpson, M.; Vogt, P. et al.
System: The UNT Digital Library
Pd/k for RTF and 232-H TCAP units (open access)

Pd/k for RTF and 232-H TCAP units

The Thermal Cycling Absorption Process (TCAP) will be used in the Replacement Tritium Facility (RTF) and 232-H Tritium Facility for separation of hydrogen isotopes. These TCAP units will be filled with palladium deposited on kieselguhr (Pd/k) that has been heat treated to reduce particle breakdown and sieved to remove particles smaller than 50 mesh (300{mu}m). Pd/k ordered for several applications in the RTF, including TCAP, was received at SRL in April 1989. Shortly thereafter, flow restriction caused by breakdown of the Pd/k particles was detected during operation of a TCAP unit in the Advanced Hydride Laboratory (AHL). Subsequent research at SRL showed that heating Pd/k at 1100{degrees}C in air for 2 hours greatly reduces mechanical breakdown. Based on these favorable results, sufficient Pd/k was heat treated to fill RTF and Building 232-H TCAP units. 11 refs., 11 figs., 7 tabs.
Date: January 29, 1991
Creator: Mosley, W. C.
System: The UNT Digital Library
DETERMINING THE EFFECTS OF RADIATION ON AGING CONCRETE STRUCTURES OF NUCLEAR REACTORS (open access)

DETERMINING THE EFFECTS OF RADIATION ON AGING CONCRETE STRUCTURES OF NUCLEAR REACTORS

The U.S. Department of Energy Office of Environmental Management (DOE-EM) is responsible for the Decontamination and Decommissioning (D&D) of nuclear facilities throughout the DOE Complex. Some of these facilities will be completely dismantled, while others will be partially dismantled and the remaining structure will be stabilized with cementitious fill materials. The latter is a process known as In-Situ Decommissioning (ISD). The ISD decision process requires a detailed understanding of the existing facility conditions, and operational history. System information and material properties are need for aged nuclear facilities. This literature review investigated the properties of aged concrete structures affected by radiation. In particular, this review addresses the Savannah River Site (SRS) isotope production nuclear reactors. The concrete in the reactors at SRS was not seriously damaged by the levels of radiation exposure. Loss of composite compressive strength was the most common effect of radiation induced damage documented at nuclear power plants.
Date: January 29, 2010
Creator: Serrato, M.
System: The UNT Digital Library
Theoretical Description of High-order Harmonic Generation in Solids (open access)

Theoretical Description of High-order Harmonic Generation in Solids

None
Date: January 29, 2013
Creator: Kemper, Alexander
System: The UNT Digital Library
Characterization of Niobium Oxide Films Deposited by High Target Utilization Sputter Sources (open access)

Characterization of Niobium Oxide Films Deposited by High Target Utilization Sputter Sources

High quality, refractory metal, oxide coatings are required in a variety of applications such as laser optics, micro-electronic insulating layers, nano-device structures, electro-optic multilayers, sensors and corrosion barriers. A common oxide deposition technique is reactive sputtering because the kinetic mechanism vaporizes almost any solid material in vacuum. Also, the sputtered molecules have higher energies than those generated from thermal evaporation, and so the condensates are smoother and denser than those from thermally-evaporated films. In the typical sputtering system, target erosion is a factor that drives machine availability. In some situations such as nano-layered capacitors, where the device's performance characteristics depends on thick layers, target life becomes a limiting factor on the maximizing device functionality. The keen interest to increase target utilization in sputtering has been addressed in a variety of ways such as target geometry, rotating magnets, and/or shaped magnet arrays. Also, a recent sputtering system has been developed that generates a high density plasma, directs the plasma beam towards the target in a uniform fashion, and erodes the target in a uniform fashion. The purpose of this paper is to characterize and compare niobia films deposited by two types of high target utilization sputtering sources, a rotating magnetron and …
Date: January 29, 2007
Creator: Chow, R; Ellis, A D; Loomis, G E & Rana, S I
System: The UNT Digital Library
NSLS-II DESIGN: A NOVEL APPROACH TO LIGHT SOURCE DESIGN (open access)

NSLS-II DESIGN: A NOVEL APPROACH TO LIGHT SOURCE DESIGN

The NSLS-II storage ring will be a replacement for the existing two NSLS light sources, which although innovative when proposed, have been exceeded by modern light source designs. NSLS-II design takes a new approach toward providing users with the very bright beams after commissioning and a strategy of evolving to higher brightness beams as more ID devices are installed during its operations. This is achieved not by pushing the basic lattice to lower emittance, an approach that hits severe limits in the control of the dynamic aperture of an ever increasing non-linear lattice. Our approach is rather to reduce the natural emittance using damping wigglers, in addition to damping from the user undulator's. Details on the lattice design are presented.
Date: January 29, 2007
Creator: KRAMER,S.
System: The UNT Digital Library
Polarization measurements of the Lyman-(alpha)1 x-ray emission lines of hydrogenlike Ar17+ and Fe25+ at high electron impact energies (open access)

Polarization measurements of the Lyman-(alpha)1 x-ray emission lines of hydrogenlike Ar17+ and Fe25+ at high electron impact energies

We have measured the polarization of the 2p{sub 3/2} {yields} 1s{sub 1/2} Lyman-{alpha}{sub 1} x-ray line of hydrogenlike Ar{sup 17+} and Fe{sup 25+} at electron impact energies ranging from 7 to 25 threshold units. The highly charged argon and iron ions were produced using the Lawrence Livermore National Laboratory SuperEBIT electron beam ion trap. A combination of two crystal spectrometers and a microcalorimeter were used to record the Lyman-{alpha} x-ray emission of Ar{sup 17+} and Fe{sup 25+} and to infer the polarization of the Lyman-{alpha}{sub 1} line. Our results show a systematic discrepancy with the predictions of distorted-wave calculations.
Date: January 29, 2006
Creator: Robbins, D. L.; Beiersdorfer, P.; Faenov, A. Y.; Pikuz, T. A.; Thorn, D. B.; Chen, H. et al.
System: The UNT Digital Library
RHIC STATUS (open access)

RHIC STATUS

As the first hadron accelerator and collider consisting of two independent superconducting rings RHIC has operated with a wide range of beam energies and particle species. Machine operation and performance will be reviewed that includes high luminosity gold-on-gold and copper-on-copper collisions at design beam energy (100 GeVh), asymmetric deuteron-on-gold collisions as well as high energy polarized proton-proton collisions (100 GeV on 100 GeV) with beam polarization of up to 65%. Plans for future upgrades of RHIC will also be discussed.
Date: January 29, 2007
Creator: ROSER, T.
System: The UNT Digital Library
China Spallation Neutron Source Design (open access)

China Spallation Neutron Source Design

The China Spallation Neutron Source (CSNS) is an accelerator-based high-power project currently in preparation under the direction of the Chinese Academy of Sciences (CAS). The complex is based on an H- linear accelerator, a rapid cycling proton synchrotron accelerating the beam to 1.6 GeV, a solid tungsten target station, and five initial instruments for spallation neutron applications. The facility will operate at 25 Hz repetition rate with a phase-I beam power of about 120 kW. The major challenge is to build a robust and reliable user's facility with upgrade potential at a fractional of ''world standard'' cost.
Date: January 29, 2007
Creator: Wei, J.
System: The UNT Digital Library
Optical Effects of Wakefields in the PEP-II Stanford Linear Accelerator Center B Factory (open access)

Optical Effects of Wakefields in the PEP-II Stanford Linear Accelerator Center B Factory

Wakefields defining beam stability affect also the beam optics and beam properties in high current machines. In this paper we present observations and analysis of the optical effects in the PEP-II SLAC B-factory, which has the record in achievement of high electron and positron currents. We study the synchronous phase and the bunch length variation along the train of bunches, overall bunch lengthening and effects of the wakes on the tune and on the Twiss parameters. This analysis is being used in upgrades of PEP-II and may be applied to future B-factories and damping rings for Linear Colliders.
Date: January 29, 2007
Creator: Heifets, S.; Novokhatski, S. & Teytelman, D.
System: The UNT Digital Library
Does Size Really Matter? The Steric Isotope Effect in a Supramolecular Host?Guest Exchange Reaction (open access)

Does Size Really Matter? The Steric Isotope Effect in a Supramolecular Host?Guest Exchange Reaction

Isotope effects (IEs), which arise from differences in zero point energies (ZPEs) between a parent and isotopically substituted bond, have been used extensively by chemists to probe molecular interactions and reactivity. Due to the anharmonicity of the C-H/D vibrational potential energy function and the lower ZPE of a C-D bond, the average C-D bond length is typically {approx}0.005 {angstrom} shorter than an equivalent C-H bond. It is this difference in size that is often invoked to explain the observation of secondary, inverse kinetic isotope effects (KIEs) in chemical processes which proceed through a sterically strained transition state. This so-called 'steric isotope effect' (SIE) has been observed in processes such as the racemization of ortho-substituted biphenyls[6] and phenanthrenes, ring flipping of cyclophanes, and more recently in the deslipping of rotaxanes, where substitution of the sterically less demanding deuterium for protium results in rate accelerations for these processes. Herein, we use deuterium substitution in a cationic guest molecule to probe the sensitivity limits of the guest exchange process from a highly-charged supramolecular host.
Date: January 29, 2010
Creator: Mugridge, Jeffrey; Bergman, Robert & Raymond, Kenneth
System: The UNT Digital Library
String Field Equations from Generalized Sigma Model (open access)

String Field Equations from Generalized Sigma Model

We propose a new approach for deriving the string field equations from a general sigma model on the world-sheet. This approach leads to an equation which combines some of the attractive features of both the renormalization group method and the covariant beta function treatment of the massless excitations. It has the advantage of being covariant under a very general set of both local and non-local transformations in the field space. We apply it to the tachyon, massless and first massive level, and show that the resulting field equations reproduce the correct spectrum of a left-right symmetric closed bosonic string.
Date: January 29, 1997
Creator: Bardakci, K. & Bernardo, L.M.
System: The UNT Digital Library