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Hot nuclei -- Landau theory, thermal fluctuations and dissipation

Description: The basic ideas and theoretical methods used in the description of hot nuclei are reviewed. In particular, a macroscopic approach to shape transitions is discussed in the framework of the Landau theory in which the quadrupole shape degrees of freedom play the role of the order parameters. This theory describes the universal features of the nuclear shape evolution with temperature and spin. A unified description of fluctuations in all five quadrupole degrees of freedom is introduced and plays an important role in the calculation of physical observables. A macroscopic approach to the giant dipole resonance (GDR) in hot nuclei is developed. With all parameters fixed by the zero temperature nuclear properties, the theory predicts both the GDR cross-section and angular anisotropy of the {gamma}-rays in very good agreement with recent experiments. The intrinsic shape fluctuations are the main cause for the resonance broadening at higher temperatures, while the orientation fluctuations are responsible for the observed attenuation in the angular anisotropy. Dissipation at finite temperature is discussed in the framework of a Langevin-like equation describing the time-dependent shape fluctuations. Non-adiabatic effects may cause motional narrowing of the resonance.
Date: January 1, 1990
Creator: Alhassid, Y.
Partner: UNT Libraries Government Documents Department

Stability and performance of CDRL-FEL (Chemical Dynamics Research Laboratory-Free Electron Laser)

Description: We study the performance of a proposed infrared free electron laser at Lawrence Berkeley Laboratory, which would be a user facility and therefore has a unique set of requirements in intensity, spectrum and stability. The output performance in intensity and spectrum, and methods to optimize the performance, are studied in detail. The effect of the electron beam fluctuation on FEL stability is carefully evaluated to set a tolerance for the accelerator design. Use of intracavity gratings is studied as a means of further improving the spectral purity and stability. 19 refs., 12 figs., 2 tabs.
Date: November 1, 1990
Creator: Kim, K.J. & Xie, M.
Partner: UNT Libraries Government Documents Department

ATF (Advanced Toroidal Facility) edge plasma turbulence studies using a fast reciprocating Langmuir probe

Description: Electrostatic turbulence on the edge of the Advanced Torodial Facility (ATF) torsatron is investigated experimentally with a fast reciprocating Langmuir probe (FRLP) array. Initial measurements of plasma electron density n{sub e} and temperature T{sub e} and fluctuations in density ({tilde n}{sub e}) and plasma floating potential ({tilde {phi}}{sub f}) are made in ECH plasmas at 1 T. At the last closed flux surface (LCFS, r/{bar a} {approximately}1), T{sub e} {approx} 20--40 eV and n{sub e} {approx} 10{sup 12} cm{sup {minus}3} for a line-averaged electron density {bar n}{sub e} = (3--6) {times} 10{sup 12} cm{sup {minus}3}. Relative fluctuation levels, as the FRLP is moved into core plasma where T{sub e} > 20 eV, are {tilde n}{sub e}/n{sub e} {approx} 5%, and e {tilde {phi}}{sub f}/T{sub e} {approx} 2{tilde n}{sub e}/n{sub e} about 2 cm inside the LCFS. The observed fluctuation spectra are broadband (40--300 kHz) with {bar k}{rho}{sub s} {le} 0.1, where {bar k} is the wavenumber of the fluctuations and {rho}{sub s} is the ion Larmor radius at the sound speed. The propagation direction of the fluctuations reverses to the electron diamagnetic direction around r/{bar a} < 1. The phase velocity and the electron drift velocity are comparable (v{sub ph} {approximately} v{sub de}). The fluctuation-induced particle flux is comparable to fluxes estimated from the particle balance using the H{sub {alpha}} spectroscopic measurements. Many of the features seen in these experiments resemble the features of ohmically heated plasmas in the Texas Experimental Tokamak (TEXT). 17 refs., 10 figs.
Date: January 1, 1990
Creator: Uckan, T.; Hidalgo, C.; Bell, J.D.; Harris, J.H.; Dunlap, J.L.; Dyer, G.R. et al.
Partner: UNT Libraries Government Documents Department

Managing the global commons decision making and conflict resolution in response to climate change

Description: A workshop was convened to develop a better understanding of decision-making matters concerning management of the global commons and to resolve conflicts in response to climate change. This workshop report does not provide a narrative of the proceedings. The workshop program is included, as are the abstracts of the papers that were presented. Only the introductory paper on social science research by William Riebsame and the closing summary by Richard Rockwell are reprinted here. This brief report focuses instead on the deliberations of the working groups that developed during the workshop. 4 figs., 1 tab.
Date: July 1, 1990
Creator: Rayner, S. (Oak Ridge National Lab., TN (USA)); Naegeli, W. & Lund, P. (Tennessee Univ., Knoxville, TN (USA))
Partner: UNT Libraries Government Documents Department

Asymptotic analysis of the longitudinal instability of a heavy ion induction linac

Description: An Induction Linac accelerating high ion currents at sub-relativistic energies is predicted to exhibit unstable growth of current fluctuations at low frequencies. The instability is driven by the interaction between the beam and complex impedance of the induction modules. In general, the detailed form of the growing disturbance depends on the initial perturbation and ratio of pulse length to accelerator length, as well as the specific form of the impedance. An asymptotic analysis of the several regimes of interest is presented. 1 ref.
Date: September 1, 1990
Creator: Lee, E.P. & Smith, L.
Partner: UNT Libraries Government Documents Department

Comparison of experimental and theoretical XEDS cross-sections and k-factors as a function of accelerating voltage

Description: For nearly fifteen years k-factor measurements have been made by varying the composition of the standards at fixed accelerating voltage and reporting the change in the experimental k-factor with atomic number. From this data a best model of the ionization cross-section is frequently proposed for use in quantitative x ray analysis in the AEM, however it is valid only at that fixed voltage. It is usually difficult to judge the validity of the selection of cross-section using this type of plot and difference plots. These difference plots illustrate that the k-factor at a fixed voltage is not particularly sensitive for determination of the correct ionization cross-section parameterization, due to normalization effects which are inherent in it's definition. In fact, calculations show that the relative errors between cross-section models as shown in the difference plot are of the same order of magnitude as those which one would calculate due to inaccuracy in the thickness of the various Si(Li) detector parameters. In this paper experimental measurements of the absolute intensity variation of elemental standards are used to illustrate the differences cross-section models, which are then subsequently compared to experimental variations in the k-factor with accelerating voltage. With the advent of medium voltage analytical microscopes routinely available to the microscopy community, it becomes essential to understand how the k-factor varies with accelerating voltage in order that errors in quantitative analysis can be avoided should experimental or theoretical k-factors from lower voltage instruments be applied to the medium voltage regime. 8 refs., 5 figs.
Date: January 1, 1990
Creator: Zaluzec, N.J.
Partner: UNT Libraries Government Documents Department

Turbulence in slurry pipe flow

Description: The present state of knowledge of liquid-solid flows (slurries) is far behind than that for single phase flows. Very few geometries have been examined with a slurry and only with a limited variation of system parameters i.e. fluid viscosity, particle diameter, etc. This paper presents the first part of a study which examines the effects of the addition of a solid to the flow through a confined coaxial jet. Presented here will be the initial conditions for the jet which correspond to fully developed pipe flow. 6 refs., 9 figs.
Date: January 1, 1990
Creator: Gore, R.A. (Los Alamos National Lab., NM (USA)) & Crowe, C.T. (Washington State Univ., Pullman, WA (USA). Dept. of Mechanical and Materials Engineering)
Partner: UNT Libraries Government Documents Department

Uncertainties in forecasting future climate

Description: The increasing atmospheric concentrations of carbon dioxide, methane, chlorofluorocarbons, and other trace gases (collectively, greenhouse gases) pose a three-part challenge: (1) What the changes to atmospheric composition and the climate system will be; (2) What impacts (both detrimental and beneficial) these changes will induce on the biosphere and natural and societal resources; and (3) What the appropriate response, if any, might be when considering the changes themselves, the resulting impacts, and the benefits and other impacts of the activities generating the emissions. This brief summary will address only areas of agreement and areas of uncertainty related to the first challenge.
Date: November 1, 1990
Creator: MacCracken, M.C.
Partner: UNT Libraries Government Documents Department

A One-Body Transport Model of Fluctuation Processes in Nuclear Collisions

Description: Many aspects of a many-body system can be described in terms of one- body transport models in which the system at any time is characterized by its single-particle density rather than by the full many-body information. In these one-body models evaluation of the single-particle density is determined by a transport equation which contains the self-consistent mean-field potential and a collision term due to binary two-body collisions. Recently, this approach in a semi-classical limit with a Boltzmann-Uehling-Uhlenbeck (BUU) form of a collision term has been applied to nuclear collisions at intermediate energies. Common to all one-body models, only the average effects of two-body collisions are retained in the equation of motion and higher order correlations are entirely neglected. This approximation corresponds to an ensemble averaging which is evident, for example, from the molecular chaos assumption'' introduced in derivation of Boltzmann equation. As a result, these one-body models determine the ensemble averaged single-particle density and cannot provide a description for the fluctuation processes in nuclear collisions. On the other hand, at low and intermediate energies dynamical fluctuations are substantial due to large available phase space for decay into many final states. Therefore, it is of great interest to improve one-body transport models by incorporating dynamical fluctuations due to high order correlations into the equation of motion. 5 refs., 3 figs.
Date: January 1, 1990
Creator: Ayik, S.; Gregoire, C.; Suraud, E.; Stryjewski, J. & Belkacem, M.
Partner: UNT Libraries Government Documents Department

Concepts in strong Langmuir turbulence theory

Description: Some of the basic concepts of strong Langmuir turbulence (SLT) theory are reviewed. In SLT system, a major fraction of the turbulent energy is carried by local, time-dependent, nonlinear excitations called cavitons. Modulational instability, localization of Langmuir fields by density fluctuations, caviton nucleation, collapse, and burnout and caviton correlations are reviewed. Recent experimental evidence will be presented for SLT phenomena in the interaction of powerful HF waves with the ionosphere and in laser-plasma interaction experiments. 38 refs., 11 figs.
Date: January 1, 1990
Creator: DuBois, D.F. & Rose, H.A.
Partner: UNT Libraries Government Documents Department

Daytime wind valleys adjacent to the Great Salt Lake

Description: In 1986 Los Alamos National Laboratory was engaged by the US Army to study the meteorological aspects of emergency preparedness at several sites where toxic materials are stored and handled. The project included a series of tracer and meteorological field experiments in the vicinity of the Tooele Army Depot. These experiments generated a large data set for validating numerical simulations and for empirical analyses of the local meteorology. This paper discusses the main characteristics of the daytime, up-valley flow at the Utah site, including frequency of occurrence, horizontal and vertical structure, and temporal evolution. Some parameters controlling the variability in onset time for up-valley flow are identified, and an empirical forecasting scheme is discussed. 16 refs., 7 figs.
Date: January 1, 1990
Creator: Stone, G.L. (Los Alamos National Lab., NM (USA)) & Hoard, D.E. (Amparo Corp., Santa Fe, NM (USA))
Partner: UNT Libraries Government Documents Department

Charge and spin fluctuations in the density functional theory

Description: We introduce a conceptual framework which allow us to treat charge and spin fluctuations about the Local density Approximation (LDA) to the Density Functional Theory (DFT). We illustrate the approach by explicit study of the Disordered Local Moment (DLM) state in Fe above the Curie Temperature {Tc} and the Mott insulating state in MnO. 27 refs., 6 figs.
Date: January 1, 1990
Creator: Gyoerffy, B.L.; Barbieri, A. (Bristol Univ. (UK). H.H. Wills Physics Lab.); Staunton, J.B. (Warwick Univ., Coventry (UK). Dept. of Physics); Shelton, W.A. & Stocks, G.M. (Oak Ridge National Lab., TN (USA))
Partner: UNT Libraries Government Documents Department

Internal dynamics of electrical discharges

Description: The existence of thresholds for electrical discharge onset suggests a functional relation between macroscopic resistivity and current. At low current, the resistivity should be inversely proportional to the magnitude of the current. Macroscopic models which employ this scaling predict many empirically observed properties of transient electrical discharges, such as (1) thresholds for onset of current, (2) abrupt termination of current in active regions of a current channel, (3) current restart in passive regions of current channels, (4) leaders, and (5) residual charge, both in channels and at sources when current terminates. We present an overview of research with these models and use examples to illustrate the results that have been obtained. We also show how these models predict current channel formation and describe results of efforts to benchmark theory with experimental data. 12 refs., 9 figs.
Date: January 1, 1990
Creator: Kadish, A.; Maier, W.B. II (Los Alamos National Lab., NM (USA)) & Robiscoe, R.T. (Montana State Univ., Bozeman, MT (USA))
Partner: UNT Libraries Government Documents Department

Thermodynamic properties of fluids from Fluctuation Solution Theory

Description: Fluctuation Theory develops exact relations between integrals of molecular correlation functions and concentration derivatives of pressure and chemical potential. These quantities can be usefully correlated, particularly for mechanical and thermal properties of pure and mixed dense fluids and for activities of strongly nonideal liquid solutions. The expressions yield unique formulae for the desirable thermodynamic properties of activity and density. The molecular theory origins of the flucuation properties, their behavior for systems of technical interest and some of their successful correlations will be described. Suggestions for fruitful directions will be suggested.
Date: January 1, 1990
Creator: O'Connell, J.P.
Partner: UNT Libraries Government Documents Department

Elemental relationships in rock varnish as seen with SEM/EDX (scanning electron microscopy/energy dispersive x-ray) elemental line profiling

Description: The heterogeneous nature of rock varnish requires a thorough survey of elemental and mineralogic compositions before relating chemical variability of rock varnish to past geochemical environments. Elemental relationships in rock varnish can be examined using scanning electron microscopy (SEM) in conjunction with an elemental line profiling routine using semi-quantitative, energy dispersive x-ray (EDX) analysis. Results of SEM/EDX analysis suggest: variations in cation concentrations used in varnish cation ratio dating relate more specifically to variations in detritus within the varnish than to element mobility as defined by weathering indices; Mn concentration rather than Mn:Fe ratios may be a more appropriate indicator of paleoclimatic fluctuations; and the Mn-oxide phase existing in varnish is most likely a Ba-enriched phase rather than birnessite. Element line profiling offers great potential for gaining insights into geochemical processes affecting the deposition and diagenesis of rock varnish and for testing hypotheses relating to its chemical variability. 27 refs., 9 figs.
Date: January 1, 1990
Creator: Raymond, R. Jr.; Reneau, S.L. & Harrington, C.D.
Partner: UNT Libraries Government Documents Department

An optical technique for the direct measurement of the 2-D spectral density of a passive scalar in a turbulent flow

Description: A new optical technique for quantitatively measuring the spectral density of passive scalar fluctuations in a turbulent flow has been developed. The technique exploits the photorefractive properties of BaTiO{sub 3} to separate the optical signal of the turbulent field from the coherent illumination background. It is a major improvement over existing techniques in that it is non-intrusive, has excellent frequency response and spatial resolution, and is capable of simultaneously measuring two components of the three-dimensional spectral density, {Phi}{theta}({kappa}). The technique is thus especially well suited to the directly study of anisotropic flows. We have applied this technique to study the spectrum of temperature fluctuations in a fully developed turbulent channel flow with heat addition. The flow is highly anisotropic, yet the spectrum in directions transverse to the flow is seen to exhibit an inertial--convective subrange behavior which is characteristic of isotropic flows. The spectral behavior in the flow direction, due to the direct influence of the mean strain rate, is observed to be markedly different. 17 refs., 7 figs.
Date: April 6, 1990
Creator: Robey, H.F.; Albrecht, G.F. & Moore, T.R.
Partner: UNT Libraries Government Documents Department

TREAT (Transient Reactor Test Facility) reactor control rod scram system simulations and testing

Description: Air cylinders moving heavy components (100 to 300 lbs) at high speeds (above 300 in/sec) present a formidable end-cushion-shock problem. With no speed control, the moving components can reach over 600 in/sec if the air cylinder has a 5 ft stroke. This paper presents an overview of a successful upgrade modification to an existing reactor control rod drive design using a computer model to simulate the modified system performance for system design analysis. This design uses a high speed air cylinder to rapidly insert control rods (278 lb moved 5 ft in less than 300 msec) to scram an air-cooled test reactor. Included is information about the computer models developed to simulate high-speed air cylinder operation and a unique new speed control and end cushion design. A patent application is pending with the US Patent Trade Mark Office for this system (DOE case number S-68,622). The evolution of the design, from computer simulations thru operational testing in a test stand (simulating in-reactor operating conditions) to installation and use in the reactor, is also described. 6 figs.
Date: January 1, 1990
Creator: Solbrig, C. W. & Stevens, W. W.
Partner: UNT Libraries Government Documents Department

Aperiodicity in one-dimensional cellular automata

Description: Cellular automata are a class of mathematical systems characterized by discreteness (in space, time, and state values), determinism, and local interaction. A certain class of one-dimensional, binary site-valued, nearest-neighbor automata is shown to generate infinitely many aperiodic temporal sequences from arbitrary finite initial conditions on an infinite lattice. The class of automaton rules that generate aperiodic temporal sequences are characterized by a particular form of injectivity in their interaction rules. Included are the nontrivial linear'' automaton rules (that is, rules for which the superposition principle holds); certain nonlinear automata that retain injectivity properties similar to those of linear automata; and a wider subset of nonlinear automata whose interaction rules satisfy a weaker form of injectivity together with certain symmetry conditions. A technique is outlined here that maps this last set of automata onto a linear automaton, and thereby establishes the aperiodicity of their temporal sequences. 12 refs., 3 figs.
Date: January 1, 1990
Creator: Jen, E.
Partner: UNT Libraries Government Documents Department

The energy stabilization for the SLC scavenger beam

Description: The energy of the SLC scavenger beam which is used to produce positrons must be carefully maintained so that the beam can be transported through the collimators in the dispersive region of the extraction line which leads from the Linac to the positron target. A feedforward control loop has been developed to compensate the energy fluctuations due to the beam intensity fluctuations. The loop detects the beam intensities in the damping rings and then calculates how much energy needs to be compensated due to beam loading effects. The energy is corrected by adjusting the acceleration phases of two sets of klystrons right before the extraction. Because there is feedback loop using the same controls, their interaction needs to be carefully treated. This paper presents an overview of the feedforward algorithms. 3 figs.
Date: August 1, 1990
Creator: Hsu, Ian; Browne, M.; Himel, T.; Humphrey, R.; Jobe, K.; Ross, M. et al.
Partner: UNT Libraries Government Documents Department

Requirements and design of a high stable infrared free electron laser at LBL

Description: An infrared free electron laser (IRFEL) is being designed for the Chemical Dynamics Research Laboratory (CDRL) at LBL. The FEL is based on a 50 MeV RF linac operating in synchronization to the Advanced Light Source (ALS), and will produce intense (100 {mu}J per micropulse), narrow bandwidth (narrower than 0.1%) radiation between 3 {mu} and 50 {mu}. In the design, we pay particular attention to the FEL stability issues and require that the fluctuations in electron beam energy and in timing be less than 0.05% and 0.1 ps, respectively. The FEL spectrum can then be stabilized to about 10{sup {minus}3}, or if grating is used, to 10{sup {minus}4}. We discuss various sources of fluctuations in the gun, the bunchers and the accelerator sections, as well as the feedback and feedforward schemes to reduce these fluctuations. The accelerator structure is chosen to be of the side coupled, standing wave type for easier control. The beam transport is made isochronous to avoid the coupling between the energy and the timing fluctuations. 9 refs., 2 figs.
Date: June 1, 1990
Creator: Kim, K.J.; Berz, M.; Chattopadhyay, S.; Gough, R.; Kim, C.; Kung, A.H. et al.
Partner: UNT Libraries Government Documents Department

Hydrologic characterization of faults and other potentially conductive geologic features in the unsaturated zone

Description: The capability of characterizing near-vertical faults and other potentially highly conductive geologic features in the vicinity of a high-level-waste repository is of great importance in site characterization of underground waste-isolation projects. The possibility of using transient air pressure data at depth for characterizing these features in the unsaturated zone are investigated. Analytical solutions for calculating the pressure response of such systems are presented. Solutions are given for two types of barometric pressure fluctuations, step function and sinusoidal. 3 refs., 9 figs.
Date: January 1, 1990
Creator: Javandel, I. & Shan, C.
Partner: UNT Libraries Government Documents Department

Permeability and dispersivity of variable-aperture fracture systems

Description: A number of recent experiments have pointed out the need of including the effects of aperture variation within each fracture in predicting flow and transport properties of fractured media. This paper introduces a new approach in which medium properties, such as the permeability to flow and dispersivity in tracer transport, are correlated to only three statistical parameters describing the fracture aperture probability distribution and the aperture spatial correlation. We demonstrate how saturated permeability and relative permeabilities for flow, as well as dispersion for solute transport in fractures may be calculated. We are in the process of examining the applicability of these concepts to field problems. Results from the evaluation and analysis of the recent Stripa-3D field data are presented. 13 refs., 10 figs.
Date: January 1, 1990
Creator: Tsang, Y. W. & Tsang, C. F.
Partner: UNT Libraries Government Documents Department

Zonal statistics in (general circulation model) GCM/GCM/Data intercomparisons

Description: Comparisons of general circulation model (GCM) results with each other and with climate data are routinely made on a variety of spatial scales. In bridging the gap from larger scale behavior (global, hemispheric) to the regional, zonal statistics are commonly used. Here, statistics are developed using values at all longitudinal gridpoints at a specified latitude and these are displayed as a function of latitude. The zonal average is the most routinely used of these statistics, but there are many other statistics available, few of which are ever examined. These provide a rich array of diagnostic measures for intercomparing models with each other and with observational data. Several of these measures are explored here: (1) histograms or boxplots displaying the detailed distributions, (2) rms or average absolute pointwise differences between model and data sets and (3) cross correlations and auto correlations. 5 figs.
Date: November 1, 1990
Creator: Grotch, S.L.
Partner: UNT Libraries Government Documents Department

Evaluation of digital fault-tolerant architectures for nuclear power plant control systems

Description: Four fault tolerant architectures were evaluated for their potential reliability in service as control systems of nuclear power plants. The reliability analyses showed that human- and software-related common cause failures and single points of failure in the output modules are dominant contributors to system unreliability. The four architectures are triple-modular-redundant (TMR), both synchronous and asynchronous, and also dual synchronous and asynchronous. The evaluation includes a review of design features, an analysis of the importance of coverage, and reliability analyses of fault tolerant systems. An advantage of fault-tolerant controllers over those not fault tolerant, is that fault-tolerant controllers continue to function after the occurrence of most single hardware faults. However, most fault-tolerant controllers have single hardware components that will cause system failure, almost all controllers have single points of failure in software, and all are subject to common cause failures. Reliability analyses based on data from several industries that have fault-tolerant controllers were used to estimate the mean-time-between-failures of fault-tolerant controllers and to predict those failures modes that may be important in nuclear power plants. 7 refs., 4 tabs.
Date: January 28, 1990
Creator: Battle, R.E.
Partner: UNT Libraries Government Documents Department