1,417 Matching Results

Search Results

Advanced search parameters have been applied.

An information-theoretic look at branch-prediction

Description: Accurate branch-prediction is necessary to utilize deeply pipelined and Very Long Instruction-Word (VLIW) architectures. For a set of program traces we show the upper limits on branch predictability, and hence machine utilization, for important classes of branch-predictors using static (compiletime) and dynamic (runtime) program information. A set of optimal superpredictors'' is derived from these program traces. These optimal predictors compare favorably with other proposed methods of branch-prediction. 3 refs., 5 figs., 12 tabs.
Date: September 11, 1990
Creator: Ponder, C.G. (Lawrence Livermore National Lab., CA (USA)) & Shebanow, M.C. (Motorola, Inc., Austin, TX (USA))
Partner: UNT Libraries Government Documents Department

Measurement and simulation of whole beam brightness on the ETA-II (Experimental Test Accelerator-II) linear induction accelerator

Description: Measurement of beam radius as a function of focusing strength of an upstream solenoidal field allows simultaneous determination of the beam energy, brightness and tilt of the phase space ellipse. On ETA-II beam radius has been measured by analyzing foil emitted Cherenkov light with a gated (5 ns) image intensified CCD camera. The beam energy measurement is corroborated with a spectrometer magnet and core brightness with a two hole emittance diagnostic. For a 6 MeV, 1.6 kA beam, the whole beam brightness was measured to be 4.0 {times} 10{sup 8} A/(m-rad){sup 2} with an inner core (few percent) brightness of 1.2 {times} 10{sup 9} A/(m-rad){sup 2}. The data was simulated with a particle transport code that includes the effects of energy sweep and magnetic misalignment. The code predicts a halo produced by an orbital resonance that is also observed experimentally.
Date: August 7, 1990
Creator: Chen, Y.J.; CLark, J.C.; Paul, A.C.; Nexsen, W.E. & Turner, W.C.
Partner: UNT Libraries Government Documents Department

A 3d particle simulation code for heavy ion fusion accelerator studies

Description: We describe WARP, a new particle-in-cell code being developed and optimized for ion beam studies in true geometry. We seek to model transport around bends, axial compression with strong focusing, multiple beamlet interaction, and other inherently 3d processes that affect emittance growth. Constraints imposed by memory and running time are severe. Thus, we employ only two 3d field arrays ({rho} and {phi}), and difference {phi} directly on each particle to get E, rather than interpolating E from three meshes; use of a single 3d array is feasible. A new method for PIC simulation of bent beams follows the beam particles in a family of rotated laboratory frames, thus straightening'' the bends. We are also incorporating an envelope calculation, an (r, z) model, and 1d (axial) model within WARP. The BASIS development and run-time system is used, providing a powerful interactive environment in which the user has access to all variables in the code database. 10 refs., 3 figs.
Date: June 8, 1990
Creator: Friedman, A.; Bangerter, R.O.; Callahan, D.A.; Grote, D.P.; Langdon, A.B. (Lawrence Livermore National Lab., CA (USA)) & Haber, I. (Naval Research Lab., Washington, DC (USA))
Partner: UNT Libraries Government Documents Department

Design of long induction linacs

Description: A self-consistent design strategy for induction linacs is presented which addresses the issues of brightness preservation against space charge induced emittance growth, minimization of the beam breakup instability and the suppression of beam centroid motion due to chromatic effects (corkscrew) and misaligned focusing elements. A simple steering algorithm is described that widens the effective energy bandwidth of the transport system.
Date: September 6, 1990
Creator: Caporaso, G.J. & Cole, A.G.
Partner: UNT Libraries Government Documents Department

Application of linear magnetic loss model of ferrite to induction cavity simulation

Description: A linear, frequency independent model of the rf properties of unbiased, soft ferrite has been implemented in finite-difference, time-domain, electromagnetic simulation code AMOS for the purposes of studying linac induction cavities. The simple model consists of adding a magnetic conductivity term ({sigma}{sub m}H) to Faraday's Law. The value of {sigma}{sub m} that is appropriate for a given ferrite at a particular frequency is obtained via an rf reflection experiment on a very thin ferrite toroid in a shorted coaxial line. It was found that in the frequency range 100 to 1000 MHz, the required value of {sigma}{sub m} varies only slightly (<10%), and so we approximated it as a frequency independent parameter in AMOS. A description of the experimental setup and the technique used to extract the complex {mu} from the measurements is described. The model has been used to study the impedances of the DARHT induction cavity, and comparisons between these experimental measurements and AMOS calculations is presented. Implementation of a frequency dependent version of this model in AMOS is being pursued, and a discussion of this effort is given.
Date: September 5, 1990
Creator: DeFord, J.F. & Kamin, G.
Partner: UNT Libraries Government Documents Department

Bragg crystal polarimeter for the Spectrum-X-Gamma mission

Description: We are designing a Bragg crystal polarimeter for the focal plane of the SODART telescope on the Spectrum-X-Gamma mission. A mosaic graphite crystal will be oriented at 45{degree} to the optic axis of the telescope, thereby preferentially reflecting those x-rays which satisfy the Bragg condition and have electric vectors that are perpendicular to the plane defined by the incident and reflected photons. The reflected x-rays will be detected by an imaging proportional counter with the image providing direct x-ray aspect information. The crystal will be {approx}50 {mu}m thick to allow x-rays with energies {ge}4 keV to be transmitted to a lithium block mounted below the graphite. The lithium is used to measure the polarization of these high energy x-rays by exploiting the polarization dependence of Thomson scattering. The development of thin mosaic graphite crystals is discussed and recent reflectivity, transmission, and uniformity measurements are presented. 8 refs., 11 figs., 1 tab.
Date: August 13, 1990
Creator: Holley, J.; Silver, E.; Ziock, K.P. (Lawrence Livermore National Lab., CA (USA)); Novick, R.; Kaaret, P. (Columbia Univ., New York, NY (USA). Columbia Astrophysics Lab.); Weisskopf, M. et al.
Partner: UNT Libraries Government Documents Department

Falcon series data report: 1987 LNG vapor barrier verification field trials

Description: A series of five Liquefied Natural Gas Spills up to 66 m{sup 3} in volume were performed on water within a vapor barrier structure at Frenchman Flat on the Nevada Test Site as a part of a joint government/industry study. This data report presents a description of the tests, the test apparatus, the instrumentation, the meteorological conditions, and the data from the tests. 16 refs., 27 figs., 8 tabs.
Date: June 1, 1990
Creator: Brown, T.C.; Cederwall, R.T.; Chan, S.T.; Ermak, D.L.; Koopman, R.P.; Lamson, K.C. et al.
Partner: UNT Libraries Government Documents Department

Numerical simulation of the mitigating effects of an LNG vapor fence

Description: FEM3A, a fully three-dimensional numerical model for simulating the atmospheric dispersion of heavy gases involving complex geometry, has been used to investigate the mitigating effects of a vapor fence for LNG storage areas. In this paper, a brief description of the numerical model used to perform such calculations is given, the problem being simulated is described, and an intercomparison among the results from numerical simulations (with and without the vapor fence) and field data (with vapor fence) is made. The numerical results indicate that, with the present fence configuration, the maximum concentration on the cloud centerline was reduced by a factor of two or more within 250 m behind the fence, and the downwind distance to the 2.5% concentration was reduced from 365 m to 230 m. However, a vapor fence could also cause the vapor cloud to linger considerably longer in the source area, thus increasing the potential for ignition and combustion within the vapor fence and the area nearby over time. 8 refs., 10 figs.
Date: May 1, 1990
Creator: Chan, S.T.
Partner: UNT Libraries Government Documents Department

MGA (Multi-Group Analysis): A gamma-ray spectrum analysis code for determining plutonium isotopic abundances

Description: Nondestructive measurements of x-ray and gamma-ray emissions can be used to analyze a sample for plutonium. This report describes the methods and algorithms we have developed for analyzing gamma-ray spectra obtained by using a germanium detector system to accurately determine the relative abundances of various actinide isotopes in a sample. Our methodology requires no calibrations and can be used to measure virtually any size and type of plutonium sample. Measurement times can be as short as a few minutes; measurements are frequently accurate to within 1%. Our methods have been programmed into a computerized analysis code called MGA (Multi-Group Analysis). Our current versions can be run on personal computers (IBM type) and on the DEC VAX microcomputer. Spectral analysis times are usually far less than a minute. 28 refs., 26 figs., 1 tab.
Date: April 3, 1990
Creator: Gunnink, R
Partner: UNT Libraries Government Documents Department

Reduction of beam corkscrew motion on the ETAII linear induction accelerator

Description: The ETAII linear induction accelerator (6MeV, 3kA, 70ns) is designed to drive a microwave free electron laser (FEL) and demonstrate the front end accelerator technology for a shorter wavelength FEL. Performance to date has been limited by beam corkscrew motion that is driven by energy sweep and misalignment of the solenoidal focusing magnets. Modifications to the pulse power distribution system and magnetic alignment are expected to reduce the radius of corkscrew motion from its present value of 1 cm to less than 1 mm. The modifications have so far been carried out on the first 2.7 MeV (injector plus 20 accelerator cells) and experiments are beginning. In this paper we will present calculations of central flux line alignment, beam corkscrew motion and beam brightness that are anticipated with the modified ETAII. 10 refs., 4 figs., 1 tab.
Date: September 4, 1990
Creator: Turner, W.C.; Allen, S.L.; Brand, H.R.; Caporaso, G.J.; Chambers, F.W.; Chen, Y.-J. et al.
Partner: UNT Libraries Government Documents Department

Preliminary design for a recirculating induction accelerator for heavy ion fusion

Description: Substantial savings in size and cost over a linear machine may be achieved in an induction accelerator in which a heavy ion beam makes many ({approximately}50) passes through one or more circular accelerators. We examine a point design for such an accelerator, consisting of four rings. We discuss the consequences of this design on emittance growth, longitudinal instability growth, vacuum requirements, pulser requirements, pulsed-magnet requirements, acceleration schedule, and cost. 3 refs., 1 tab.
Date: December 1, 1990
Creator: Yu, S.S.; Barnard, J.J.; Caporaso, G.J.; Friedman, A.; Hewett, D.W.; Kirbie, H. et al.
Partner: UNT Libraries Government Documents Department

Superdeformation in the Hg-Tl-Pb region

Description: Superdeformation in the Hg-Tl-Pb region is discussed, with concentration on the experimental results. At least twenty-five superdeformed bands are known in this region, providing much new data to test theoretical calculations. 22 refs., 5 figs.
Date: October 1, 1990
Creator: Henry, E.A.; Becker, J.A.; Yates, S.W.; Wang, T.F.; Kuhnert, A. (Lawrence Livermore National Lab., CA (USA)); Brinkman, M.J. et al.
Partner: UNT Libraries Government Documents Department

Time-dependent two-dimensional radiation hydrodynamics of accreting matter onto highly magnetized neutron stars

Description: We present for the first time, the self-consistent solution of the two-dimensional, time-dependent equations of radiation-hydrodynamics governing the accretion of matter onto the highly magnetized polar caps of luminous x-ray pulsars. The calculations show a structure in the accretion column very different from previous one-zone uniform models. We have included all the relevant magnetic field corrections to both the hydrodynamics and the radiative transport. We include a new theory for the diffusion and advection of both radiation energy density and photon number density. For initially uniformly accreting models with super-Eddington flows, we have uncovered evidence of strong radiation-driven outflowing optically thin radiation filled regions of the accretion column embedded in optically-thick inflowing plasma. We follow the evolution of these photon bubbles for several dynamical timescales. The development of these photon bubbles'' indicates growth times on the order of a millisecond and show fluctuations on sub-millisecond timescales in agreement with a linear stability analysis. The photon bubbles are a consequence of the effect of radiative heat flux on the internal gravity waves in the strongly magnetized atmosphere and may result in observable fluctuations in the emitted luminosity leading to luminosity dependent changes in the pulse profile. This may provide important new diagnostics for conditions in accreting x-ray pulsars. 19 refs., 13 figs.
Date: November 20, 1990
Creator: Klein, R.I. (California Univ., Berkeley, CA (USA). Dept. of Astronomy Lawrence Livermore National Lab., CA (USA)) & Arons, J. (California Univ., Berkeley, CA (USA). Dept. of Astronomy California Univ., Berkeley, CA (USA). Dept. of Physics)
Partner: UNT Libraries Government Documents Department

3D particle simulation of beams using the WARP code: Transport around bends

Description: WARP is a discrete-particle simulation program which was developed for studies of space charge dominated ion beams. It combines features of an accelerator code and a particle-in-cell plasma simulation. The code architecture, and techniques employed to enhance efficiency, are briefly described. Current applications are reviewed. In this paper we emphasize the physics of transport of three-dimensional beams around bends. We present a simple bent-beam PIC algorithm. Using this model, we have followed a long, thin beam around a bend in a simple racetrack system (assuming straight-pipe self-fields). Results on beam dynamics are presented; no transverse emittance growth (at mid-pulse) is observed. 11 refs., 5 figs.
Date: November 30, 1990
Creator: Friedman, A.; Grote, D.P.; Callahan, D.A.; Langdon, A.B. (Lawrence Livermore National Lab., CA (USA)) & Haber, I. (Naval Research Lab., Washington, DC (USA))
Partner: UNT Libraries Government Documents Department

Influence of present and possible future aircraft emissions on the global ozone distribution

Description: This study has used the LLNL two-dimensional model of the global atmosphere in an evaluation of the effects on global ozone concentrations from current subsonic aircraft emissions and from the emissions of possible future high speed civil transports (HSCT). The authors have attempted to include more realistic representations of emissions as a function of altitude and latitude in these scenarios than were included in previous sensitivity analyses. Major findings from this study are: (1) Current aircraft emissions may be having an impact on upper tropospheric ozone, leading to increasing concentrations of ozone in the upper troposphere. (2) A matrix of HSCT scenarios evaluated over a wide range of mean flight altitudes and magnitudes of NO{sub x} emissions confirmed previous analyses showing that ozone destruction becomes larger as the emissions of NO{sub x} increase and as the altitude of injection increases. (3) Model calculations indicate that a major reduction in emissions would allow the stratosphere to recover to unperturbed conditions in about a decade. (4) Sensitivity studies indicate that water vapor emissions have a moderate effect on the change in total ozone, while carbon monoxide emissions had a negligible effect. (5) Injection of NO{sub x} as HNO{sub 3} had a moderate effect on the change in total ozone. (6) The calculated change in ozone for the HSCT scenarios was very sensitive to the background atmosphere, particularly to the levels of stratospheric chlorine and concentrations of carbon dioxide, methane, and nitrous oxide.
Date: October 1, 1990
Creator: Kinnison, D.E. & Wuebles, D.J.
Partner: UNT Libraries Government Documents Department

Chemical kinetic modeling of chlorinated hydrocarbons under stirred-reactor conditions

Description: The combustin of chloroethane is modeled as a stirred reactor so that we can study critical emission characteristics of the reactor as a function of residence time. We examine important operating conditions such as pressure, temperature, and equivalence ratio and their influence on destructive efficiency of chloroethane and production of other chlorinated products. The model uses a detailed chemical kinetic mechanism that we have developed previously for C{sub 3} hydrocarbons. We have added to this mechanism the chemical kinetic mechanism for C{sub 2} chlorinated hydrocarbons developed by Senkan and coworkers. Some reactions have been added to Senkan's mechanism and some of the reaction-rate expressions have been updated to reflect recent developments in the literature. In the modeling calculations, sensitivity coefficients are determined to find which reaction-rate constants have the largest effect on destructive efficiency. 25 refs., 6 figs., 1 tab.
Date: October 4, 1990
Creator: Pitz, W.J. & Westbrook, C.K.
Partner: UNT Libraries Government Documents Department

Nonequilibrium molecular dynamics

Description: The development of nonequilibrium molecular dynamics is described, with emphasis on massively-parallel simulations involving the motion of millions, soon to be billions, of atoms. Corresponding continuum simulations are also discussed. 14 refs., 8 figs.
Date: November 1, 1990
Creator: Hoover, W.G. (California Univ., Davis, CA (USA). Dept. of Applied Science Lawrence Livermore National Lab., CA (USA))
Partner: UNT Libraries Government Documents Department

Numerical methods for boundary value problems in differential-algebraic equations

Description: Differential-algebraic equation (DAE) boundary value problems arise in a variety of applications, including optimal control and parameter estimation for constrained systems. In this paper we survey these applications and explore some of the difficulties associated with solving the resulting DAE systems. For finite difference methods, the need to maintain stability in the differential part of the system often necessitates the use of methods based on symmetric discretizations. However, these methods can suffer from instability and loss of accuracy when applied to certain DAE systems. We describe a new class of methods, Projected Implicit Runge-Kutta Methods, which overcomes these difficulties. We give convergence and stability results, and present numerical experiments which illustrate the effectiveness of the new methods. 20 refs., 1 tab.
Date: September 24, 1990
Creator: Ascher, U.M. (British Columbia Univ., Vancouver, BC (Canada). Dept. of Computer Science) & Petzold, L.R. (Lawrence Livermore National Lab., CA (USA))
Partner: UNT Libraries Government Documents Department

The effects of climate change on the nitrogen cycle and acid deposition

Description: Increases in greenhouse gases are expected to lead to a number of changes to the atmosphere which may impact regional and global chemical cycles. With the increasing awareness of climate change and the possibility of global chemical changes to the atmosphere, it becomes important to ask whether these changes to global climate and chemical cycles might benefit or hinder control programs aimed at reducing acid deposition. In the following, we review several possible changes to climate that may be expected to impact the global cycle of reactive nitrogen. We then use our global model of the reactive nitrogen cycle to estimate the effects of several of the more important changes on the continental-scale deposition of nitric acid. 7 refs., 1 tab.
Date: September 1, 1990
Creator: Penner, J.E.; Walton, J.J. (Lawrence Livermore National Lab., CA (USA)) & Graboske, B.C. (California Univ., Berkeley, CA (USA))
Partner: UNT Libraries Government Documents Department

Policy route certification: Requirements and techniques

Description: The interconnection of separately administrated, autonomous communications networks into a large internetwork of global extent raises significant technical, managerial and security issues. Individual networks, or collections of networks, may exhibit different characteristics with respect to usage rules, cost, performance, and security services. In a large internetwork of autonomously administered constituent networks, clients of routing services may wish to obtain security and other service guarantees for their internetwork traffic. This paper analyzes requirements for these guarantees and suggests techniques to meet these requirements based on policy routing mechanisms.
Date: January 1, 1991
Creator: Nessett, D. (Lawrence Livermore National Lab., CA (USA)) & Solo, D. (BBN Communications Corp., Cambridge, MA (USA))
Partner: UNT Libraries Government Documents Department

Sterile neutrinos in the early universe

Description: We discuss the role played by right-handed sterile neutrinos in the early universe. We show how well known {sup 4}He constraint on the number of relativistic degrees of freedom at early times limits the equilibration of the right handed neutrino sea with the background plasma. We discuss how this allows interesting constraints to be placed on neutrino properties. In particular, a new limit on the Dirac mass of the neutrino is presented. 12 refs.
Date: November 14, 1990
Creator: Malaney, R.A. (Lawrence Livermore National Lab., CA (USA)) & Fuller, G.M. (California Univ., San Diego, La Jolla, CA (USA). Dept. of Physics)
Partner: UNT Libraries Government Documents Department

Shape isomers: Mean-field description and beyond

Description: Nuclear Hartree-Fock (HF) + BCS calculations have led to predictions of shape isomerism in isotopes of Pt, Hg and Os nuclei. These have been confirmed through the observation of superdeformed rotational bands in {sup 190,{hor ellipsis},194}Hg. Encouraged by these measurements and similar observations in {sup 194}Pb, we have extended these calculations to a wide range of contiguous nuclei. These HF results, for {sup 192,194}Pt, {sup 190,{hor ellipsis},198}Hg and {sup 194}Pb, have been employed in a Generator Coordinate Method (GCM) calculation utilizing the quadrupole deformation as the generating variable. The resulting spectra confirm the conclusions drawn from the HF results and agree with those experiments which have been performed. Adding a phenomenological assumption for the moments of inertia of our GCM states, we can construct the radiative transitions within and out of the superdeformed band. The results are in good agreement with the observed de-population of the superdeformed band built upon the shape isomer both in minimum angular momentum and in rapidity of de-population. Inferences for the existence of shape isomers will be drawn. 19 refs., 4 figs.
Date: November 19, 1990
Creator: Bonche, P.; Krieger, S.J.; Weiss, M.S. (Lawrence Livermore National Lab., CA (USA)); Dobaczewski, J. (Warsaw Univ. (Poland). Inst. Fizyki Teoretycznej); Flocard, H. (Paris-11 Univ., 91 - Orsay (France). Div. de Physique Theorique); Heenen, P.H. (Universite Libre de Bruxelles (Belgium)) et al.
Partner: UNT Libraries Government Documents Department

Superconducting energy gap and normal state conductivity of a single domain Y sub 1 Ba sub 2 Cu sub 3 O sub 7 crystal

Description: Using polarized reflectivity measurements of single domain crystals, we are able to distinguish chain and plane contributions to the infrared conductivity of Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7}. A substantial chain contribution to {sigma}({omega}) persisting to low frequency and temperature is observed. For the intrinsic conductivity of the CuO{sub 2} planes a superconducting energy gap of 500 cm{sup {minus}1} (2{Delta}/k{Tc} {approx equal} 8) is evident in the infrared data, while the normal state conductivity drops much more slowly with {omega} than the ordinary Drude form, and can be described in terms of a scattering rate {Dirac h}/{tau}* {approximately} kT + {Dirac h}{omega} at low frequency. The former result (2{Delta}/k{Tc} {approx equal} 8) suggests substantial suppression of {Tc}; the latter, that Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7} is not ordinary Fermi liquid. 26 refs., 4 figs.
Date: September 1, 1990
Creator: Schlesinger, Z.; Collins, R.T.; Holtzberg, F.; Feild, C.; Blanton, S.H. (International Business Machines Corp., Yorktown Heights, NY (USA). Thomas J. Watson Research Center); Welp, U. (Science and Technology Center for Superconductivity (USA) Argonne National Lab., IL (USA)) et al.
Partner: UNT Libraries Government Documents Department