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Mark Vii-a Fuel Slugs--Computer Surveillance of Crystallographic Orientation

Description: Natural uranium fuel slugs are produced by a cortrolled process and definite averages and standard deviations exist for x-ray diffraction data. A change in a production variable, such as heat treatment, is readily discernible through statistical quality control. Programs for the IBM 1401 computer were developed which compute the average values and 3-sigma limits for texture coefficient and G3 growth index data. This information is updated weekly and is plotted by the computer in the form of average (X) and range (R) charts. Each month, an exception report and a G3 index are computed. These show only those charts which had X or R factors exceedirg 3-sigma limits during the month. Thus, trends are revealed in the crystallographic orientation characteristics of fuel slugs. (auth)
Date: November 1, 1962
Creator: Wood, R. S., Jr.
Partner: UNT Libraries Government Documents Department

Single, stretched membrane, structural module experiments

Description: This report describes tests done on stretched-membrane heliostats used to reflect solar radiation onto a central receiver. The tests were used to validate prior analysis and mathematical models developed to describe module performance. The modules tested were three meters in diameter and had reflective polymer film laminated to the membrane. The frames were supported at three points equally spaced around the ring. Three modules were pneumatically attached with their weight suspended at the bottom support, two were pneumatically attached with their weight suspended from the upper mounts, and one was rigidly attached with its weight suspended at the bottom mount. By varying the membrane tension we could simulate a uniform wind loading normal to the mirror's surface. A video camera 15+ meters away from the mirror recorded the virtual image of a target grid as reflected by the mirrors' surface. The image was digitized and stored on a microcomputer. Using the law of reflection and analytic geometry, we computed the surface slopes of a sampling of points on the surface. The dominant module response was consistent with prior SERI analyses. The simple analytical model is quite adequate for designing and sizing single-membrane modules if the initial imperfections and their amplification are appropriately controlled. To avoid potential problems resulting from the fundamentally n = 2 deformation phenomena, we advise using either relatively stiffer ring frames or more than three support points.
Date: February 1, 1986
Creator: Wood, R.L.
Partner: UNT Libraries Government Documents Department

Development of an experimental database and theories for prediction of thermodynamic properties of aqueous electrolytes and nonelectrolytes of geochemical significance at supercritical temperatures and pressures

Description: Volumetric measurements have been completed for CH{sub 4}, CO{sub 2}, and H{sub 2}S at temperatures from 25{degrees}C to 380{degrees}C and 2 or 3 pressures at each temperature. The H{sub 2}S and CO{sub 2} solutions are stored in aluminized mylar bags in PVC pipes with water surrounding the bags at a pressure of several atmospheres. The methane is stored in a one liter autoclave with a sliding teflon piston engaging the sides of the autoclave which separates the standard methane solution from the pressurizing fluid. The solutions are prepared at 100 to 200 atmospheres and do not need to be re-standardized after each experiment. We also have some measurements on aqueous ammonia, boric acid, and acetic acid. Preliminary calculations of the free energy of methane in water at room temperature as a function of the model parameters for the methane have been finished. In preparation for these calculations, the theory and practice of the free energy perturbation calculations was reviewed. In molecular dynamics and Monte Carlo calculations a system does not immediately equilibrate to a change in the Hamiltonian, so that there is a time lag or a configuration number lag in the response of the system. These lags cause errors in free energy calculations. 4 refs.
Date: May 2, 1991
Creator: Wood, R.H.
Partner: UNT Libraries Government Documents Department

Modeling of complex melting and solidification behavior in laser-irradiated materials (a description and users guide to the LASER8 computer program)

Description: The conceptual foundation of a computational model and a computer program based on it have been developed for treating various aspects of the complex melting and solidification behavior observed in pulsed laser-irradiated materials. A particularly important feature of the modeling is the capability of allowing melting and solidification to occur at temperatures other than the thermodynamic phase change temperatures. As a result, interfacial undercooling and overheating can be introduced and various types of nucleation events can be simulated. Calculations on silicon with the model have shown a wide variety of behavior, including the formation and propagation of multiple phase fronts. Although originally developed as a tool for studying certain problems arising in the field of laser annealing of semiconductors, the program should be useful in treating many types of systems in which phase changes and nucleation phenomena play important roles. This report describes the underlying physical and mathematical ideas and the basic relations used in LASER8. It also provides enough specific and detailed information on the program to serve as a guide for its use; a listing of one version of the program is given.
Date: November 1, 1985
Creator: Geist, G.A. & Wood, R.F.
Partner: UNT Libraries Government Documents Department

Theoretical calculations of the electronic and vibrational structure of point defects in ionic crystals

Description: The structure of the Hartree-Fock one-electron equations for simple point defects in ionic crystals are discussed. The importance of polarization effects due to the diffuse nature of the wavefunctions in the relaxed excited states are emphasized, and the usefulness of an effective mass approximation indicated. Several approaches to the calculation of the electronic structure are discussed and evaluated. The connection between electronic structure calculations and phonon perturbations are pointed out through a brief discussion of localized perturbation theory.
Date: January 1, 1981
Creator: Wood, R.F. & Wilson, T.M.
Partner: UNT Libraries Government Documents Department

High-{Tc} superconducting superlattices

Description: Superlattices composed of YBa{sub 2}CU{sub 3}O{sub 7} and PrBa{sub 2}Cu{sub 3}O{sub 7} have been studied extensively experimentally and several theoretical attempts to correlate the resistivity as a function of temperature with the superlattice structure have appeared in the literature. The theoretical interest in such structures comes about primarily because of insight into dimensionality effects, interlayer coupling, and interlayer charge redistribution in high-T {sub c}, superconductors. On the experimental side, there are possibilities for device applications that are just now beginning to be explored. After an overview of the experimental work and a discussion of charge transfer calculations, a description of how the experimental data can be explained using a model that incorporates Kosterlitz-Thouless (vortex-antivortex unbinding) and Azlamazov-Larkin (fluctuation-enhanced conductivity) theories in the resistive transition region and charge-transfer effects, variable-range hopping, etc. in the normal state. Difficulty in disentangling charge transfer and dimensionality effects in determining the nominal transition temperature is pointed out and other mechanisms that influence the width of the resistive transition are considered.
Date: June 1, 1993
Creator: Wood, R. F.
Partner: UNT Libraries Government Documents Department

Spin-polaron theory of high-{Tc} superconductivity: 2, electronic structure of the CuO{sub 2} planes

Description: After an introductory discussion of electronic structure calculations for the CuO{sub 2} planes in the copper-oxide based high-{Tc} superconductors, the method suggested by Slater for studying antiferromagnetic (AF) metals is described. In this method, as applied here, the chemical unit cell is doubled to form a magnetic unit cell which contains one Cu ion with predominantly up spin and one with predominantly down spin. Down spins are kept off up-spin sites, and conversely, by the introduction of a Hubbard U term. As a result, the band structure obtained is typical of that for a Mott-Hubbard (M-H) or, more generally, a charge transfer insulator. Conductivity in the a-b plane results when holes are introduced into the M-H valence band. The band structure as a function of the parameters in Koster-Slater type calculations is discussed and the Fermi surface is described. A calculation of the delocalization energy for spin-polaron formation is carried out within the context of the band calculations.
Date: June 1, 1993
Creator: Wood, R. F.
Partner: UNT Libraries Government Documents Department

Spin-polaron theory of high-{Tc} superconductivity: I, spin polarons and high-{Tc} pairing

Description: The concept of a spin polaron is introduced and contrasted with the more familiar ionic polaron picture. A brief review of aspects of ionic bipolaronic superconductivity is given with particular emphasis on the real-space pairing and true Bose condensation characteristics. The formation energy of spin polarons is then calculated in analogy with ionic polarons. The spin-flip energy of a Cu spin in an antiferromagnetically aligned CuO{sub 2} plane is discussed. It is shown that the introduction of holes into the CuO{sub 2} planes will always lead to the destruction of long-range AF ordering due to the formation of spin polarons. The pairing of two spin polarons can be expected because of the reestablishment of local (short-range) AF ordering; the magnitude of the pairing energy is estimated using a simplified model. The paper closes with a brief discussion of the formal theory of spin polarons.
Date: June 1, 1993
Creator: Wood, R. F.
Partner: UNT Libraries Government Documents Department

Spin-polaron theory of high-{Tc} superconductivity: 3, Gap function and critical temperature

Description: Results from previous papers in this series are used to derive approximate expressions for the gap and {Tc} within the framework of a Cooper-pairing approach. The possible symmetry types of the gap are discussed. It is shown how the proximity of the Fermi level to the Mott-Hubbard band edge and the interplay of O 2p{sigma} and 2p{pi} bands and/or localization effects can provide good fits to the variation of {Tc} with x in La{sub 2-x}Sr{sub x}CuO{sub 4} and YBa{sub 2}Cu{sub 3}O{sub 7-x}. It is concluded that the in-plane gap is either s- or d-like but anisotropic in either case. Other aspects and implications of the model and of the calculations are given and comparisons with Mott`s spin-bipolaron model are made.
Date: June 1, 1993
Creator: Wood, R. F.
Partner: UNT Libraries Government Documents Department

A stochastic method for nuclear power plant diagnosis

Description: The value of using neutron noise descriptors, especially the power spectral densities (PSDs) of ex-core detectors, to monitor core barrel motion and fuel element vibrations in pressurized water reactors (PWRs) is well established. Indeed, in the mid-frequency range (1 to 20 Hz), PWR neutron noise is dominated by vibration peaks in the neutron PSD that result from the motion of reactor internals. A qualitative examination of such descriptors from a 1150 MWE Westinghouse PWR plant, re-examination of such descriptors from a 1150 MWE Westinghouse PWR plant, revealed significant changes in the plant's noise signature (PSD) as its first fuel cycle proceeded. The purpose of this work is to use a mathematical model of the interaction between small mechanical motions and the core neutronics to provide a tool for quantitative investigation of the PSD structure in the vibrational frequency range. The purpose of neutron noise analysis is to provide information on plant conditions by the study of power traces from ex-core detectors. Due to the action of the coolant flow through the core and pump induced vibrations, the core barrel, which is bolted at the top of the reactor vessel, performs a pendular motion with a natural frequency determined by the mechanical parameters and constraints of the system. In addition, external forces deform the cylindrical shape of the core barrel by inducing vibrational modes which are excited by the turbulence of the coolant flow and by the /open quotes/table-shaker/close quotes/ effect of the core barrel motion. As a result of the various mechanical motions, the detector response will vary in a manner proportional to the importance function at the location of the disturbance. 7 refs., 4 figs., 1 tab.
Date: January 1, 1988
Creator: Perez, R. B. & Wood, R. T.
Partner: UNT Libraries Government Documents Department

Livermore Computing Production Control System, 3.0: Product description. Revision 1

Description: The purpose of this document is to introduce and describe the Livermore Computing Production Control System, commonly called the PCS. Resource management is very difficult in typical UNIX and related systems. The weakness involves the allocation, control and delivery of the usage of computer resources. Accounting also is weak, being generally limited to reporting that a user used an amount of time on a process. A process accounting record is made only after the completion of a process and then only if the process does not terminate as a result of a system panic. Resources can only be allocated to users. No cognizance can be taken of organizational structure or projects. Allocations cannot be managed at these levels. Denying service to a user who has access to a machine is crude. Large computing centers frequently have thousands of users working on hundreds of projects. These users and the projects are funded by several organizations with varying ability or willingness to pay for the computer services provided. With only typical UNIX tools, the appropriate delivery of resources to the correct organizations, projects, tasks and users requires continual human intervention. UNIX and related systems have become increasingly more reliable over the past few years. A consequence of this is that resource managers and accountants have been presented with an attendant problem of accurate accounting for resources used. Processes can now run for days or months without terminating. A run-away process or a malicious or uninformed user can use an organization`s budgeted resource allocation many times over before an accounting record to that effect is written. If a process`s accounting record is not written because of a panic, the computer center is faced with possibly significant financial loss.
Date: November 1, 1993
Creator: Wood, R. R.
Partner: UNT Libraries Government Documents Department

Production control system: A resource management and load leveling system for mainframe computers

Description: The Livermore Computing Production Control System, commonly called the PCS is described in this paper. The intended audiences for this document are system administrators and resource managers of computer systems. In 1990, the Livermore Computing Center committed itself to convert its supercomputer operations from the New Livermore TimeSharing System (NLTSS) to UNIX based systems. This was a radical change for Livermore Computing in that over thirty years had elapsed during which the only operating environments used on production platforms were LTSS and then later NLTSS. Elaborate, and sometimes obscure, paradigms (to others) were developed to help the lab`s scientists productively use the machines and to accurately account for their use to government oversight agencies. Resource management is difficult in typical UNIX and related systems. The weakness involves the allocation, control and delivery of the usage of computer resources. This is a result of the origins and subsequent development of UNIX which started as a system for small platforms in a collegial or departmental atmosphere without stringent or complex budgetary requirements. Accounting also is weak, being generally limited to reporting that a user used an amount of time on a process. A process accounting record is made only after the completion of a process and then only if the process does not terminate as a result of a system {open_quotes}panic.{close_quotes}
Date: March 1, 1994
Creator: Wood, R. R.
Partner: UNT Libraries Government Documents Department

Spin-polarons and high-{Tc} superconductivity

Description: The spin-polaron concept is introduced in analogy to ionic and electronic polarons and the assumptions underlying the author`s approach to spin-polaron mediated high-{Tc} superconductivity are discussed. Elementary considerations about the spin-polaron formation energy are reviewed and the possible origin of the pairing mechanism illustrated schematically. The electronic structure of the CuO{sub 2} planes is treated from the standpoint of antiferromagnetic band calculations that lead directly to the picture of holes predominantly on the oxygen sublattice in a Mott-Hubbard/charge transfer insulator. Assuming the holes to be described in a Bloch representation but with the effective mass renormalized by spin-polaron formation, equations for the superconducting gap, {Delta}, and transition temperature, {Tc}, are developed and the symmetry of {Delta} discussed. After further simplifications, {Tc} is calculated as a function of the carrier concentration, x. It is shown that the calculated behavior of {Tc}(x) follows the experimental results closely and leads to a natural explanation of the effects of under- and over-doping. The paper concludes with a few remarks about the evidence for the carriers being fermions (polarons) or bosons (bipolarons).
Date: March 1, 1994
Creator: Wood, R. F.
Partner: UNT Libraries Government Documents Department

Protection circuits for superconducting magnets

Description: As the technology of controlled nuclear fusion progresses, plans for new experimental reactors include much longer duty cycles than those of earlier experiments. Many of the magnet systems for these reactors must be superconducting due to the prolonged or continuous high current levels required. The large initial investment of a superconducting magnet system justifies a protective dump circuit. This circuit must operate if the magnet goes normal or in the event of failure of some of the critical auxiliary equipment. This paper examines two applications of superconducting magnet protection for fusion experiments. A novel dc interrupter being developed especially for this purpose is also discussed.
Date: January 1, 1980
Creator: Parsons, W.M. & Wood, R.J.
Partner: UNT Libraries Government Documents Department

Modified laser-annealing process for improving the quality of electrical P-N junctions and devices

Description: The invention is a process for producing improved electrical-junction devices. The invention is applicable, for example, to a process in which a light-sensitive electrical-junction device is produced by: (1) providing a body of crystalline semiconductor material having a doped surface layer; (2) irradiating the layer with at least one laser pulse to effect melting of the layer; (3) permitting recrystallization of the melted layer; and (4) providing the resulting body with electrical contacts. In accordance with the invention, the fill-factor and open-circuit-voltage parameters of the device are increased by conducting the irradiation with the substrate as a whole at a selected elevated temperature, the temperature being selected to effect a reduction in the rate of the recrystallization but insufficient to effect substantial migration of impurities within the body. In the case of doped silicon substrates, the substrate may be heated to a temperature in the range of from about 200/sup 0/C to 500/sup 0/C.
Date: February 19, 1982
Creator: Wood, R.F. & Young, R.T.
Partner: UNT Libraries Government Documents Department

Studies of pulsed laser melting and rapid solidification using amorphous silicon

Description: Pulsed-laser melting of ion implantation-amorphized silicon layers, and subsequent solidification were studied. Measurements of the onset of melting of amorphous silicon layers and of the duration of melting, and modified melting model calculations demonstrated that the thermal conductivity, K/sub a/, of amorphous silicon is very low (K/sub a/ approx. = 0.02 W/cm-K). K/sub a/ is also the dominant parameter determining the dynamical response of amorphous silicon to pulsed laser radiation. TEM indicates that bulk (volume) nucleation occurs directly from the highly undercooled liquid silicon that can be prepared by pulsed laser melting of amorphous silicon layers at low laser energy densities. A modified thermal melting model is presented. The model calculations demonstrate that the release of latent heat by bulk nucleation occurring during the melt-in process is essential to obtaining agreement with observed depths of melting. These calculations also show that this release of latent heat accompanying bulk nucleation can result in the existence of buried molten layers of silicon in the interior of the sample after the surface has solidified. The bulk nucleation implies that the liquid-to-amorphous phase transition (produced using picosecond or uv nanosecond laser pulses) cannot be explained using purely thermodynamic considerations.
Date: June 1, 1984
Creator: Lowndes, D.H. & Wood, R.F.
Partner: UNT Libraries Government Documents Department

Absolute calibration of a SPRED (Spectrometer Recording Extended Domain) EUV (extreme ultraviolet) spectrograph for use on the DIII-D tokamak

Description: We have performed an absolute intensity calibration of a SPRED multichannel EUV spectrograph using synchrotron radiation from the NBS SURF-II electron storage ring. The calibration procedure and results for both a survey grating (450 g/mm) and a high-resolution (2100 g/mm) grating are presented. The spectrograph is currently in use on the DIII-D tokamak with a tangential line-of-sight at the plasma midplane. Data is first acquired and processed by a microcomputer; the absolute line intensities are then sent to the DIII-D database for comparison with data from other diagnostics. Representative data from DIII-D plasma operations will be presented. 6 refs., 3 figs., 1 tab.
Date: January 1, 1988
Creator: Wood, R. D. & Allen, S. L.
Partner: UNT Libraries Government Documents Department

Electronic structure of the F center in the alkaline earth oxides

Description: The energy levels and wave functions of the ground and first few singlet and triplet excited states of the F center in MgO, CaO, and SrO were calculated as a function of the nearest neighbor ion positions. Configuration coordinate curves for A/sub 1g/, E/sub g/ and T/sub 2g/ displacements have been constructed and used to interpret the absorption and luminescence bands of the F center. The energy of the /sup 1/A/sub 1g/ ..-->.. /sup 1/T/sub 1u/ transition was set near the experimental value in each case by adjusting certain parameters in the model. The calculated energy level schemes partially support the interpretations of published experimental data on the luminescence bands in MgO and CaO and suggest that the /sup 3/T/sub 1u/ ..-->.. /sup 1/A/sub 1g/ luminescence in SrO should occur at roughly 0.4 eV. A luminescence band associated with the F center in SrO has not yet been reported. The calculations of the Jahn--Teller coupling constants indicate that the /sup 3/T/sub 1u/ state is strongly coupled to the E/sub g/ vibrational mode in CaO and to the T/sub 2g/ mode in MgO and SrO.
Date: August 1, 1976
Creator: Wilson, T. M. & Wood, R. F.
Partner: UNT Libraries Government Documents Department

Fundamental aspects of pulsed-laser irradiation of semiconductors

Description: Fundamental aspects of pulsed laser melting and solidification of crystalline silicon and germanium are reviewed. The discussion concentrates on time-resolved experiments performed with nanosecond pulsed lasers, although some picosecond and femtosecond experiments are also considered. The creation of amorphous material from crystalline material induced by ultrarapid melting and resolidification using either nanosecond or picosecond lasers is surveyed and the inverse process of recrystallization of a-Si by explosive crystallization is described. Finally, melting model calculations, which have proven to give a very accurate description of the pulsed laser irradiation process, are discussed.
Date: August 1, 1986
Creator: Jellison, G.E. Jr.; Lowndes, D.H. & Wood, R.F.
Partner: UNT Libraries Government Documents Department