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Theoretical Studies of Elementary Hydrocarbon Species and their Reactions. Final Report, February 15, 1994--February 14, 1997
Highlights are described on acrtylene spectroscopy,oxirene and the Wolff Rearrangement, and the photodissociation of azoalkanes.
Date:
May 1, 1998
Creator:
Schaefer, Henry F. II
Object Type:
Report
System:
The UNT Digital Library
Theoretical studies of the structure and properties of cobalt-substituted aluminophosphates
Quantum chemical and atomistic forcefield based methods have been used to investigate models for the substitution of cobalt into aluminophosphate molecular sieves. Atomistic methods based on the Mott-Littleton approach were used to develop approximate models for cobalt substituted at the aluminum site in the AlPO{sub 4}-5 structure and from these structures clusters were constructed for quantum chemical calculations. The effect of termination with both hydride and hydroxyl groups was assessed. Full and constrained geometry optimization were performed to obtain geometrical parameters for the models which were compared to experimental data. Further calculations were performed on adducts consisting of the cluster models and small molecules to determine whether direct binding to the cobalt center is possible. The calculations were used to determine the stability of models proposed in the literature. Cobalt-substituted aluminophosphates have been shown to be active catalysts in a number of reactions including the homogeneous oxidation of cyclohexane to cyclohexanone.
Date:
December 31, 1998
Creator:
Henson, N. J.; Hay, P. J. & Redondo, A.
Object Type:
Article
System:
The UNT Digital Library
Theoretical studies of the structure and properties of cobalt-substituted aluminophosphates
There has been considerable debate regarding the structure and properties of cobalt-substituted aluminophosphate catalysts. In particular, the coordination environment, Co-O bond lengths and oxidation state are all thought to have important effects on the catalytic effectiveness of the material. This paper uses both atomistic modeling and quantum mechanical based methods to probe the local structure both of possible framework and extra-framework cobalt sites. The authors find that in the case of tetrahedral geometries, the bond lengths are similar to those found in cobalt oxides and measured from EXAFS experiments. The attractiveness of the cobalt sites for the direct binding of molecular oxygen is also investigated to assess the likelihood of the use of this oxidant in a catalytic process. In order to benchmark the computational methods calculations are also performed on a model biological system which is known to bind molecular oxygen reversibly. The authors find no evidence for direct oxygen binding in the zeolite models for a five coordinated framework cobalt center.
Date:
July 1998
Creator:
Henson, N. J.; Hay, P. J. & Redondo, A.
Object Type:
Article
System:
The UNT Digital Library
Theoretical uncertainties associated with the extraction of M{sub W} at hadron colliders
In this contribution I briefly summarize several topics related to the measurement of the W-boson mass, M{sub W}, at hadron colliders.
Date:
April 1, 1998
Creator:
Keller, S.
Object Type:
Article
System:
The UNT Digital Library
Theories of electromagnetic productions of pions.
The current theoretical approaches for investigating the {gamma}N {r_arrow} {pi}N and N(e,e{prime}{pi}) reactions are reviewed. It is shown that the dynamical approach can be used to test the predictions from hadron structure calculations. Some N* form factors calculated from using various chiral constituent quark models are presented.
Date:
September 11, 1998
Creator:
Lee, T. S. H.
Object Type:
Article
System:
The UNT Digital Library
Theories of hydrophobic effects and the description of free volume in complex liquids
Recent progress on molecular theories of hydration of nonpolar solutes in liquid aqueous solution has lead to new ways to thinking about the old issue of free volume in liquids. This article surveys the principal new results with particular attention to the context of general issues of packing in liquids.
Date:
December 1998
Creator:
Pratt, L. R.; Garde, S. & Hummer, G.
Object Type:
Report
System:
The UNT Digital Library
Theory and computational modeling: Medium reorganization and donor/acceptor coupling in electron transfer processes
The continuing goal is to convert the rapidly accumulating mechanistic information about electron transfer (et) kinetics (often representable in terms of simple rate constants) into precise tools for fine-tuned control of the kinetics and for design of molecular-based systems which meet specified et characteristics. The present treatment will be limited to the kinetic framework defined by the assumption of transition state theory (TST). The primary objective of this paper is to report recent advances in the theoretical formulation, calculation, and analysis of energetics and electronic coupling pertinent to et in complex molecular aggregates. The control of et kinetics (i.e., enhancing desired processes, while inhibiting others) involves, of course, both system energetics (especially reorganization energies (E{sub r}) and free energy changes ({Delta}G{sup 0})) and electronic coupling of local D and A sites, which for thermal processes is most directly relevant only after the system has reached the appropriate point (or region) along the reaction coordinate (i.e., the transition state). The authors first discuss TST rate constant models, emphasizing genetic features, but also noting some special features arising when metal electrodes are involved. They then turn to a consideration of detailed aspects of medium reorganization and donor/acceptor coupling. With these theoretical tools …
Date:
March 1998
Creator:
Newton, M. D.; Feldberg, S. W. & Smalley, J. F.
Object Type:
Report
System:
The UNT Digital Library
Theory of edge plasma in a spheromak
Properties of the edge plasma in the SSPX spheromak during the plasma formation and sustainment phases are discussed. For the breakdown and formation phase, the main emphasis is on the analysis of possible plasma contamination by impurities from the electrodes of the plasma gun (helicity injector). The issue of an azimuthally uniform breakdown initiation is also discussed. After the plasma settles down in the main vacuum chamber, one has to sustain the current between the electrodes, in order to continuously inject helicity. We discuss properties of the plasma on the field lines intersecting the electrodes. We conclude that the thermal balance of this plasma is maintained by Joule heating competing with parallel heat losses to the electrodes. The resulting plasma temperature is in the range of 15 - 30 eV. Under the expected operational conditions, the ``current`` velocity of the electrons is only slightly below their thermal velocity. Implications of this observation are briefly discussed.
Date:
May 1, 1998
Creator:
Hooper, E.B., LLNL
Object Type:
Article
System:
The UNT Digital Library
Theory of neutron emission in fission
A survey of theoretical representations of two of the observables in neutron emission in fission is given, namely, the prompt fission neutron spectrum N(E) and the average prompt neutron multiplicity {bar {nu}}{sub p}. Early representations of the two observables are presented and their deficiencies are discussed. This is followed by summaries and some examples of recent theoretical models for the calculation of these quantities. Emphasis is placed upon the predictability and accuracy of the recent models. In particular, the dependencies of N(E) and {bar {nu}}{sub p} upon the fissioning nucleus and its excitation energy are treated in detail for the Los Alamos model. Recent work in the calculation of the prompt fission neutron spectrum matrix N(E, E{sub n}), where E{sub n} is the energy of the neutron inducing fission, is then discussed. Concluding remarks address the current status of the ability to calculate these observables with confidence, the direction of future theoretical efforts, and limitations to current (and future) approaches. This paper is an extension of a similar paper presented at the International Centre for Theoretical Physics in 1996.
Date:
August 1998
Creator:
Madland, D. G.
Object Type:
Article
System:
The UNT Digital Library
Theory of point-defects, non-stoichiometry, and solute additions in SmCo{sub 5+x}-Sm{sub 2}Co{sub 17{minus}y} and related compounds
There is considerable interest in the possibility of producing Sm-Co-based nanocomposite magnets by rapid solidification and other far-from-equilibrium processing methods. Thermodynamic and kinetic models are quite valuable in understanding and optimizing such methods. This paper describes a method of estimation, utilizing tight-binding-based bond-order interatomic interaction potentials, of the thermodynamic properties of point defects such as vacancies, interstitials, antisite defects, and solute additions in the SmCo{sub 5+x} and Sm{sub 2}Co{sub 17{minus}y} phases and related rare-earth-transition metal compounds. Illustrative calculations for point defects in SmCo{sub 5} will be presented. The results suggest a unified model of the thermodynamic properties of the SmCo{sub 5+x}-Sm{sub 2}Co{sub 17{minus}y} region of the phase diagram, based on the 1-5 structure and the replacement of Sm by interacting dumb-bell interstitials to form the 2-17 structure; the model is similar in nature to theories of the thermodynamics of metal hydrides.
Date:
August 1, 1998
Creator:
Welch, D.O.
Object Type:
Article
System:
The UNT Digital Library
Theory of point-defects, non-stoichiometry, and solute additions in SmCo{sub 5+x}-Sm{sub 2}Co{sub 17{minus}y} and related compounds
There is considerable interest in the possibility of producing Sm-Co-based nanocomposite magnets by rapid solidification and other far-from-equilibrium processing methods. Thermodynamic and kinetic models are quite valuable in understanding and optimizing such methods. This paper describes a method of estimation, utilizing tight-binding-based bond-order interatomic interaction potentials, of the thermodynamic properties of point defects such as vacancies, interstitials, antisite defects, and solute additions in the SmCo{sub 5+x} and Sm{sub 2}Co {sub 17}-y phases and related rare-earth-transition metal compounds. Illustrative calculations for point defects in SmCo{sub 5} will be presented. The results suggest a unified model of the thermodynamic properties of the SmCo{sub 5+x} -- Sm{sub 2} Co{sub 17{minus}y} region of the phase diagram, based on the 1-5 structure and the replacement of Sm by interacting dumb-bell interstitials to form the 2-17 structure; the model is similar in nature to theories of the thermodynamics of metal hydrides.
Date:
September 3, 1998
Creator:
Welch, D. O.
Object Type:
Article
System:
The UNT Digital Library
Theory of RBE. Final report, January 1, 1967--October 31, 1998
The report begins with a historical survey of research activity. Next summaries of research accomplishments in the following areas are given: (1) Radiation Dose Distribution; (2) The 1-Hit Detector: Action Cross Sections; (3) Many Hit Detectors; (4) Biological Cells; (5) Implications for Radiation Protection; and (6) Implications for Radiation Oncology with Heavy Ion Beams.
Date:
October 31, 1998
Creator:
Katz, R.
Object Type:
Report
System:
The UNT Digital Library
Theory of Resonance Influence of Sawtooth Crashes on Ions with Large Orbit Width
The role of resonances in the sawtooth-crash-induced redistribution of fast ions is investigated. In particular, the conditions of wave-particle resonant interaction in the presence of the equilibrium electric field and the mode rotation are obtained, and effects of sawteeth on the resonant particles with arbitrary width of non-perturbed orbits are studied. It is found that resonances play the dominant role in the transport of ions having sufficiently high energy. It is shown that the resonance regions may overlap, in which case the resonant particles may constitute the main fraction of the fast ion population in the sawtooth mixing region. The behavior of the resonant particles is studied both by constructing a Poincaré map and analytically, by means of the adiabatic invariant derived in this paper and calculation of the characteristic frequencies of the particle motion.
Date:
February 1, 1998
Creator:
White, R. B.; Lutsenko, V. V.; Kolesnichenko, Y. I. & Yakovenko, Y. V.
Object Type:
Report
System:
The UNT Digital Library
Theory of tapered laser cooling
A theory of tapered laser cooling for fast circulating ion beams in a storage ring is constructed. The authors describe the fundamentals of this new cooling scheme, emphasizing that it might be the most promising way to beam crystallization. The cooling rates are analytically evaluated to study the ideal operating condition. They discuss the physical implication of the tapering factor of cooling laser, and show how to determine its optimum value. Molecular dynamics method is employed to demonstrate the validity of the present theory.
Date:
March 25, 1998
Creator:
Okamoto, Hiromi & Wei, J.
Object Type:
Report
System:
The UNT Digital Library
A thermal analysis and optimization of the APT 210 kW power coupler
This paper presents the thermal analysis and heat load optimization of the continuous power 210 kW, 700 MHz RF power coupler (PC) for the Accelerator Production of Tritium (APT). The PC is a co-axial design with RF power transmitted in the annular region between two concentric cylinders. Thermally, the PC represents a link from room temperature to the superconducting niobium cavities operating at 2 K. The analysis includes all the major heat transfer mechanisms: conduction, RF joule heating in normal and superconducting materials, infrared radiation, and, forced and natural convection cooling of the inner and outer conductors. A performance comparison is given for one and two single point thermal intercepts, versus a counter-flow heat exchanger on the outer conductor. The benefits of r4educing the operating temperature of the center conductor are discussed. The variation in thermal performance of the inner and outer conductors for several operating modes is also presented.
Date:
December 31, 1998
Creator:
Waynert, J. A. & Prenger, F. C.
Object Type:
Article
System:
The UNT Digital Library
Thermal Analysis of a D0 H-Disk Wedge
Each H-Disk ring assembly is comprised of 24 wedge assemblies. Figures 1-1 and 1-2 show the wedge mechanical layout. Each wedge consists of sets of two single-sided silicon detectors (referred to as inner and outer detectors, corresponding to their radial positioning) as provided by Moscow State University. Since these detectors are single sided, two mated inner/outer sets are arranged back-to-back such that they effectively become a double-sided detector with a 15{sup o} angle between the strips on either side. Six SVX II chips are mounted near the outboard edge of each outer detector since this location provides access to bond pads spanning the entire detector surface. Since the detector and chip bond pads are on significantly different pitches (approximately 80 vs. 48 microns), a pitch adapter is used to transition this jump, thus simplifying wirebonding. With the accompanying electronics required to support detector operation placed adjacent to the chips, the mountirig ring, which also acts as a means of cooling for the wedge, is by necessity located some distance from the chips, which are the primary heat source. The purpose of this report is to document the results of a thermal performance study of a wedge assembly. The methods, assumptions, …
Date:
March 30, 1998
Creator:
Derylo, G.
Object Type:
Report
System:
The UNT Digital Library
Thermal analysis of cold vacuum drying of spent nuclear fuel
The thermal analysis examined transient thermal and chemical behavior of the Multi canister Overpack (MCO) container for a broad range of cases that represent the Cold Vacuum Drying (CVD) processes. The cases were defined to consider both normal and off-normal operations at the CVD Facility for an MCO with Mark IV N, Reactor spent fuel in four fuel baskets and one scrap basket. This analysis provides the basis for the MCO thermal behavior at the CVD Facility for its Phase 2 Safety Analysis Report (revision 4).
Date:
July 20, 1998
Creator:
Piepho, M. G.
Object Type:
Report
System:
The UNT Digital Library
Thermal Analysis of the 9975 Package as a Plutonium Storage Container
None
Date:
July 1, 1998
Creator:
Hensel, S.
Object Type:
Report
System:
The UNT Digital Library
Thermal analysis of the APT materials irradiation samples
The accelerator production of tritium (APT) project proposes to use a 1.7 GeV, 100 mA proton beam to produce neutrons from an Inconel 718 clad tungsten target. The neutrons are multiplied and moderated in a lead/water blanket before being captured in He{sup 3} to form tritium. In this process, the materials in the target and blanket region are exposed to a wide range of different fluxes comprised of protons and neutrons with energies into the GeV range. To investigate the effect of irradiation on the mechanical properties of candidate APT materials (Inconel 718, 316L stainless steel, Al 6061-T6, Mod 9Cr-1Mo, 304L stainless steel and Al5052-0), the APT Engineering Design and Development group fielded an extensive materials irradiation using the LANSCE (Los Alamos Neutron Science Center) accelerator, which operates at an energy of 800 MeV and a current of 1 mA. The test set-up was designed to place mechanical test specimens in locations in and near the proton beam where the environment of proton and neutron fluxes and temperatures are prototypic to those expected in the APT target/blanket (50--170 C). After irradiating for about 3,600 hours, the maximum achieved proton fluence was 4--5 {times} 10{sup 21}p/cm{sup 2} for the materials in …
Date:
December 31, 1998
Creator:
Maloy, S. A.; Willcutt, G. J.; James, M. R.; Teague, J.; Siebe, D. A.; Sommer, W. F. et al.
Object Type:
Article
System:
The UNT Digital Library
Thermal analysis of the APT power coupler and similarities to superconducting magnet current leads
A detailed thermal analysis has been performed of the 210 kW, 700 MHz RF power coupler (PC) which transfers microwave energy from high power klystrons to the superconducting (SC) resonant cavities for the acceleration of protons. The work is part of the design for Accelerator Production of Tritium funded by the US Department of Energy. The PC is a co-axial design with the RF power transmitted in the annular region between two concentric cylinders. The PC provides a thermal connection from room temperature to superconducting niobium operating at 2.15 K. Heat transfer mechanisms considered are conduction, infra-red radiation, RF joule heating in normal and superconducting materials, and, forced and natural convection cooling. The objective of the thermal analysis is to minimize the required refrigeration power subject to manufacturability and reliability concerns. The problem is reminiscent of the optimization of superconducting magnet leads. The similarities and differences in the results between SC leads and PCs are discussed as well as the critical parameters in the PC optimization.
Date:
December 31, 1998
Creator:
Waynert, J. A.; Daney, D. E. & Prenger, F. C.
Object Type:
Article
System:
The UNT Digital Library
Thermal and Cold Neutron Computed Tomography at the Los Alamos Neutron Scattering Center Using an Amorphous Silicon Detector Array
The use of the EG and G-Heimann RTM 128 or dpiX FS20 amorphous silicon (a-Si) detector array for thermal neutron radiography/computed tomography has proven to be a quick and efficient means of producing high quality digital radiographic images. The resolution, although not as good as film, is about 750 pm with the RTM and 127 pm with the dpiX array with a dynamic range in excess of 2,800. In many respects using an amorphous silicon detector is an improvement over other techniques such as imaging with a CCD camera, using a storage phosphor plate or film radiography. Unlike a CCD camera, which is highly susceptible to radiation damage, a-Si detectors can be placed in the beam directly behind the object under examination and do not require any special optics or turning mirrors. The amorphous silicon detector also allows enough data to be acquired to construct a digital image in just a few seconds (minimum gate time 40 ms) whereas film or storage plate exposures can take many minutes and then need to be digitized with a scanner. The flat panel can therefore acquire a complete 3D computed tomography data set in just a few tens of minutes. While a-Si detectors …
Date:
July 19, 1998
Creator:
Claytor, T. N.; Schwab, M. J.; Farnum, E. H.; McDonald, T. E.; Summa, D. A.; Sheats, M. J. et al.
Object Type:
Article
System:
The UNT Digital Library
Thermal and flow analyses of the Nuclear Materials Storage Facility Renovation Title I 60% design
The authors are continuing to use the computational fluid dynamics code CFX-4.2 to evaluate the steady-state thermal-hydraulic conditions in the Nuclear Material Storage Facility Renovation Title 1 60% Design. The analyses build on those performed for the 30% design. They have run an additional 9 cases to investigate both the performance of the passive vault and of an individual drywell. These cases investigated the effect of wind on the inlet tower, the importance of resolving boundary layers in the analyses, and modifications to the porous-medium approach used in the earlier analyses to represent better the temperature fields resulting from the detailed modeling of the boundary layers. The difference between maximum temperatures of the bulk air inside the vault for the two approaches is small. They continued the analyses of the wind effects around the inflector fixture, a canopy and cruciform device, on the inlet tower by running a case with the wind blowing diagonally across the inflector. The earlier analyses had investigated a wind that was blowing parallel to one set of vanes on the inflector. Several subcases for these analyses investigated coupling the analysis to the facility analysis and design changes for the inflector.
Date:
August 1, 1998
Creator:
Knight, T. D.; Steinke, R. G. & Mueller, C.
Object Type:
Report
System:
The UNT Digital Library
Thermal and flow analysis of the Fluor Daniel, Inc., Nuclear Material Storage Facility renovation design (initial 30% effort of Title 1)
The computational fluid dynamics code CFX4.2 was used to evaluate steady-state thermal-hydraulic conditions in the Fluor Daniel, Inc., Nuclear Material Storage Facility renovation design (initial 30% of Title 1). Thirteen facility cases were evaluated with varying temperature dependence, drywell-array heat-source magnitude and distribution, location of the inlet tower, and no-flow curtains in the drywell-array vault. Four cases of a detailed model of the inlet-tower top fixture were evaluated to show the effect of the canopy-cruciform fixture design on the air pressure and flow distributions.
Date:
March 1, 1998
Creator:
Steinke, R. G.; Mueller, C. & Knight, T. D.
Object Type:
Report
System:
The UNT Digital Library
Thermal and molecular investigation of laser tissue welding
Despite the growing number of successful animal and human trials, the exact mechanisms of laser tissue welding remain unknown. Furthermore, the effects of laser heating on tissue on the molecular scale are not fully understood. To address these issues, a multi-front attack oil both extrinsic (solder/patch mediated) and intrinsic (laser only) tissue welding was launched using two-color infrared thermometry, computer modeling, weld strength assessment, biochemical assays, and vibrational spectroscopy. The coupling of experimentally measured surface temperatures with the predictive numerical simulations provided insight into the sub-surface dynamics of the laser tissue welding process. Quantification of the acute strength of the welds following the welding procedure enabled comparison among trials during an experiment, with previous experiments, and with other studies in the literature. The acute weld integrity also provided an indication of tile probability of long-term success. Molecular effects induced In the tissue by laser irradiation were investigated by measuring tile concentrations of specific collagen covalent crosslinks and characterizing the Fourier-Transform infrared (FTIR) spectra before and after the laser exposure.
Date:
June 1, 1998
Creator:
Small, W., IV
Object Type:
Report
System:
The UNT Digital Library