Showing papers by "Lawrence Berkeley National Laboratory published in 1984"

Implementation techniques for main memory database systems

Abstract: With the availability of very large, relatively inexpensive main memories, it is becoming possible keep large databases resident in main memory In this paper we consider the changes necessary to permit a relational database system to take advantage of large amounts of main memory We evaluate AVL vs B+-tree access methods for main memory databases, hash-based query processing strategies vs sort-merge, and study recovery issues when most or all of the database fits in main memory As expected, B+-trees are the preferred storage mechanism unless more than 80--90% of the database fits in main memory A somewhat surprising result is that hash based query processing strategies are advantageous for large memory situations

Heat capacities and entropies of silicate liquids and glasses

Abstract: The heat capacities of several dozen silicate glasses and liquids composed of SiO2, TiO2, Al2O3, Fe2O3, FeO, MgO, CaO, BaO, Li2O, Na2O, K2O, and Rb2O have been measured by differential scanning and drop calorimetry. These results have been combined with data from the literature to fit C pas a function of composition. A model assuming ideal mixing (linear combination) of partial molar heat capacities of oxide components (each of which is independent of composition), reproduces the glass data within error. The assumption of constancy of ¯C p,iis less accurate for the liquids, but data are not sufficient to adequately constrain a more complex model. For liquids containing alkali metal and alkaline earth oxides, heat capacities are systematically greater in liquids with high “field strength” network modifying cations. Entropies of fusion (per g-atom) and changes of configurational entropy with temperature, are similarly affected by composition. Both smaller cation size and greater charge are therefore inferred to lead to greater development of new structural configurations with increasing temperature in silicate liquids.

Generalization/Specialization as a Basis for Software Specification

Abstract: This paper describes a software specification methodology based on the notion of concept specialization. The methodology, which is particularly useful for Information Systems, applies uniformly to the various components of such systems, such as data classes, transactions, exceptions, and user interfaces (scripts), and its goal is the systematic and structured description of highly detailed world models, where concepts occur in many variations. An example from the domain of university information systems is used to illustrate and motivate the approach.

Structural theory of graphite and graphitic silicon

Abstract: The graphitic phases of C and Si are studied with the use of the pseudopotential local-density-functional approach. For graphite, good agreement with experiment is obtained for the in-plane lattice constant, interlayer spacing, isotropic bulk modulus, and graphite-diamond structural energy difference. Graphitic Si has relatively weak bonding and its formation is unlikely since its energy is 0.71 eV/atom higher than the diamond phase and a large negative pressure of -69 kbar is required.

Silicon drift chambers - first results and optimum processing of signals

Abstract: A Semiconductor Drift Chamber was produced and tested. The paper describes: 1. 1)|principle of the chamber operation; 2. 2)|the performance of the test chamber; 3. 3)|the signal processing to obtain the best position resolution.

Radiative cooling with MgO and/or LiF layers.

Abstract: Resultats d'experiences montrant la meilleure performance de ces materiaux dans la refrigeration par rayonnement, utilisee notamment en conditionnement d'air

The Corrosion of Carbon Black Anodes in Alkaline Electrolyte I . Acetylene Black and the Effect of Cobalt Catalyzation

Abstract: 14C labeling of acetylene black was used together with mass spectroscopic analysis of the gas evolved to determine the current efficiencies for oxygen evolution, carbon dissolution, and carbon gasification (to carbon monoxide). The current efficiencies were found to depend dramatically on potential, temperature, and the presence of an evolution catalyst like . On uncatalyzed black, three regimes could be distinguished: (i) at potentials below 500 mV vs. and temperatures below 50°C, carbon dissolution is the primary anodic process, (ii) at 500–600 mV and 50°C or lower, carbon dissolution and oxygen evolution occur at equivalent rates, and (iii) above ca. 600 mV or above ca. 60°C, oxygen evolution and gasification of the carbon to carbon monoxide are the dominant processes. Catalyzation with collapsed these regimes so that all three anodic processes are concurrent throughout the potential region of interest, and the overall rate of corrosion increased significantly. In addition, catalyzation caused the production of organic products (ca. 5% current efficiency) in a potential region where none is produced from acetylene black alone. The mechanism of action of on the acetylene black corrosion is not yet understood, but there is evidence that direct physical contact between the particles and carbon particles is not required to produce accelerated corrosion of the carbon.

Application of the Godunov method and its second-order extension to cascade flow modeling

Abstract: The Godunov method and a new second-order accurate extension of the method are used for the solution of two-dimensional Euler equations. Both numerical schemes are described in detail. Their performances in the subsonic, transonic, and supersonic flow regimes are first tested on the problem of flow in a channel with a circular arc bump. The niethods are then applied to calculate the transonic flow through a supercritical com­ pressor cascade designed by J. Sanzo For this case, the solution with the second-order extension of the Godunov method gives verygood agreement with the design distribution of parameters given by Sanzo

Calculated surface electronic structure of ferromagnetic iron and the ferromagnetic ordered iron-cobalt alloy

Abstract: Calcul auto-coherent des proprietes electroniques et magnetiques des surfaces (100) et (110) du fer ferromagnetique et des alliages ferromagnetiques ordonnees Fe−Co. L'accord avec les donnees experimentales existantes est excellent. Tous les resultats peuvent etre interpretes correctement sur la base de l'aimantation a saturation de Co, de l'interaction electron-electron relativement faible de Fe, et du retrecissement en surface de la bande d electronique

Structural properties of NaCl

Abstract: A theoretical description of the static structural, vibrational, and solid-solid phase-transition properties of alkali halides is presented. The description is ab initio involving pseudopotentials and density-functional theory. Using NaCl as a prototypical example, we conclude that properties of alkali halides can be computed accurately using this first-principles approach.

Two-phase critical flow in slits

Abstract: The results of an experimental and theoretical investigation of the critical flashing flow of initially subcooled water through rectangular slits are described. The study of such flows is relevant ...

Structural and electronic properties of the high-pressure hexagonal phases of Si

Abstract: The pseudopotential method is used to examine the structural transitions of Si from $\ensuremath{\beta}$- Sn to simple hexagonal to hexagonal close packed. The calculated transition pressures, transition volumes, and $\frac{c}{a}$ ratios are in good agreement with the measured values. For the simple hexagonal phase, a soft-phonon mode and a high density of states at the Fermi level are found. These properties and the strong covalent interlayer bonding suggest the existence of superconductivity in this system. Investigation of the band structure reveals parallel bands separated by about 3 eV along the $\mathrm{LH}$ axis of the Brillouin zone; these are the likely origin of the main peak in the optical spectrum.

Behavioral studies with mice exposed to DC and 60-Hz magnetic fields

Abstract: Behavioral measures were evaluated in adult CD-1 and LAF-1 mice continuously exposed for 72 h to a 1.5-Tesla (1 T = 10(4) Gauss) homogeneous DC magnetic field, and in LAF-1 mice continuously exposed for 72 h to a sinusoidal 60-Hz, 1.65-mT (rms) homogeneous AC field. Three types of behavioral tests were employed: (1) Memory of an electroshock-motivated passive avoidance task was assessed in animals that had been trained immediately prior to the field exposure. The strength of memory was varied either by altering the strength of the electric footshock during training, or by administering a cerebral protein synthesis inhibitor, anisomycin, at the time of training. (2) General locomotor activity was measured using a quadrant-crossing test immediately after termination of the magnetic field exposure. (3) Sensitivity of the experimental subjects to the seizure-inducing neuropharmacological agent, pentylenetrazole , was assessed immediately after the field exposure on the basis of three criteria: (a) the percentage of subjects exhibiting a generalized seizure, (b) the mean time to seizure, and (c) the mean seizure level. The results of these studies revealed no behavioral alterations in exposed mice relative to controls in any of the experimental tests with the 1.5-T DC field or the 60-Hz, 1.65-mT (rms) AC field.

Electron capture by U(91+) and U(92+) and ionization of U(90+) and U(91+)

Abstract: U(92+)/U(91+) and U(91+)/U(90+) electron-capture and ionization cross sections and equilibrium charge-state distributions are measured experimentally in mylar, Cu and Ta of varying thickness. Relativistic U(68+) ions at 437 or 962 MeV/nucleon are produced by a heavy-ion linear accelerator and synchrotron in tandem and passed through the target material into a magnetic specrometer and position-sensitive proportional counter for evaluation of charge states. The results are presented graphically and discussed. At 962 MeV/nucleon, beams containing 85 percent bare U(92+) nuclei are obtained using 150-mg/sq cm Cu or 85-mg/sq cm Ta; at 437 MeV/nucleon, 50 percent bare U(92+) nuclei are obtained with 90-mg/sq cm Cu. The techniques decribed can be applied to produce beams of bare U nuclei for acceleration to ultrarelativistic speeds or beams of few-electron U for atomic-physics experiments on quantum electrodynamics.

Initial Characterization of a Bgo-Photodiode Detector for High Resolution Positron Emission Tomography

Abstract: Spatial resolution in positron emission tomography is currently limited by the resolution of the detectors. This work presents the initial characterization of a detector design using small bismuth germanate (BGO) crystals individually coupled to silicon photodiodes (SPOs) for crystal identification, and coupled in groups to phototubes (PMTs) for coincidence timing. A 3 mm × 3 mm × 3 mm BGO crystal coupled only to a SPD can achieve a 511 keV photopeak resolution of 8.7% FWHM at -150°C, using a pulse peaking time of 10 ?s. When two 3 mm × 3 mm × 15 mm BGO crystals are coupled individually to SPDs and also coupled to a common 14 mm diam PMT, the SPDs detect the 511 keV photopeak with a resolution of 30% FWHM at -76°C. In coincidence with an opposing 3 mm wide BGO crystal, the SPDs are able to identify the crystal of interaction with good signal-to-noise ratio, and the detector pair resolution is 2 mm FWHM.

High-temperature failure of polycrystalline alumina: II, creep crack growth and blunting

Abstract: Creep crack growth in fine-grain alumina is measured by using surface cracks. A narrow power-law crack growth regime occurs at both 1300° and 1400°C, wherein the power-law exponent and activation energy are comparable to steady-state creep values. Asymptotic crack velocity behavior is exhibited near both the critical stress intensity factor, KC, and the crack growth threshold, Kth. The threshold occurs near 0.4 K1C at both 1300° and 1400°C and is associated with a transition in the size and distribution of damage. Displacement measurements indicate that crack tip damage exerts a strong influence on the displacement field, as predicted by recent theories. Furthermore, use of the stress intensity factor as a loading parameter does not produce adequate correlation with displacement measurements and is, therefore, not strictly suitable for nonlinear creeping ceramic poly crystals.

Optical guiding in a free electron laser

Abstract: The coherent interaction between an optical wave and an electron beam in a free electron laser (FEL) is shown to be capable of optically guiding the light. The effect is analyzed using a two-dimensional approximation for the FEL equations, and using the properties of optical fibers. Results of two-dimensional (cylindrically symmetric) numerical simulations are presented, and found to agree reasonably well with the analytically derived criterion for guiding. Under proper conditions, the effect can be large and has important applications to short wavelength FELs and to directing intense light.