Showing papers by "Lawrence Berkeley National Laboratory published in 1988"
TL;DR: A new series of broadband heteronuclear decoupling sequences, called the DIPSI sequences, which give better quality decouplings of protons from carbon-13 than previous sequences like WALTZ-16 when there is scalar coupling among the protons.
728 citations
01 Jun 1988
TL;DR: A Monte Carlo technique computes the indirect contributions to illuminance at locations chosen by the rendering process, which speeds the process and provides a natural limit to recursion.
Abstract: An efficient ray tracing method is presented for calculating interreflections between surfaces with both diffuse and specular components. A Monte Carlo technique computes the indirect contributions to illuminance at locations chosen by the rendering process. The indirect illuminance values are averaged over surfaces and used in place of a constant "ambient" term. Illuminance calculations are made only for those areas participating in the selected view, and the results are stored so that subsequent views can reuse common values. The density of the calculation is adjusted to maintain a constant accuracy, permitting less populated portions of the scene to be computed quickly. Successive reflections use proportionally fewer samples, which speeds the process and provides a natural limit to recursion. The technique can also model diffuse transmission and illumination from large area sources, such as the sky.
402 citations
TL;DR: In this article, an electron beam ion trap has been built for the production of very highly-charged ions and the study of their collisions with electrons, where a high density electron beam is used to trap, ionize and excite the ions for spectroscopic measurements.
Abstract: An electron beam ion trap has been built for the production of very-highly-charged ions and the study of their collisions with electrons. A high density electron beam is used to trap, ionize and excite the ions for spectroscopic measurements. X-ray spectra from neon-like Ba46+ are reported and a theory of "evaporative" cooling is developed to explain why these ions are retained in the trap for surprisingly long times.
372 citations
TL;DR: In this article, the authors proposed an advanced unified defect model (AUDM) for GaAs, which is a refinement of the UDM proposed in 1979 to explain Fermi level pinning on 3-5 compounds due to metals or nonmetals.
Abstract: The advanced unified defect model (AUDM) for GaAs proposed in this paper can be looked upon as a refinement of the unified defect model (UDM) proposed in 1979 to explain Fermi level pinning on 3–5 compounds due to metals or nonmetals. The refinement lies in identifying the defect producing pinning at 0.75 and 0.5 eV above the valence band maximum as the AsGaantisite. Since the AsGaantisite is a double donor, a minority compensating acceptor is necessary. This is tentatively identified as the GaAsantisite. The concentration of As excess or deficiency due to processing or reactions at interfaces is particularly emphasized in this model. A wide range of experimental data is discussed in terms of this model and found to be in agreement with it. This includes the original data on which the UDM was based as well as more recent data including Fermi level pinning on the free-GaAs(100) molecular-beam epitaxy surface, Schottky barrier height for thick (∼ 1000 A) Ga films on GaAs, and the LaB6Schottky barrier height on GaAs(including thermal annealing effects). Of particular importance is the ability of this model to explain the changes in Schottky barrier height for Al and Au on GaAs due to thermal annealing and to relate these changes to interfacial chemistry.
318 citations
TL;DR: In this article, the decay of a standard model Higgs boson into a tau pair was considered as a possible signature at the SSC or LHC for a Higgs particle of mass between 110 and 160 GeV.
312 citations
TL;DR: Low temperature measurements of the escape rate for junctions that are either nearly undamped or moderately damped agree very closely with predictions for macroscopic quantum tunneling, with no adjustable parameters.
Abstract: Experiments to investigate the quantum behavior of a macroscopic degree of freedom, namely the phase difference across a Josephson tunnel junction, are described. The experiments involve measurements of the escape rate of the junction from its zero voltage state. Low temperature measurements of the escape rate for junctions that are either nearly undamped or moderately damped agree very closely with predictions for macroscopic quantum tunneling, with no adjustable parameters. Microwave spectroscopy reveals quantized energy levels in the potential well of the junction in excellent agreement with quantum-mechanical calculations. The system can be regarded as a "macroscopic nucleus with wires."
283 citations
TL;DR: In this paper, a construction of string theories with spontaneously broken supersymmetry and chiral fermion families, obtained by a suitable choice of boundary conditions in toroidal compactifications of ten-dimensional (1, 1) or heterotic models, is presented.
267 citations
TL;DR: In this paper, the same three strongly bound oxygenated species are formed after O2, CO2 and H2O adsorption, and some H2 is evolved at ca. 1300 K.
262 citations
01 Sep 1988-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: The Collider Detector at Fermilab (CDF) as mentioned in this paper is a 5000 t magnetic detector built to study 2 TeV p p collisions at the Fermielab Tevatron, which is based on charged particle tracking, magnetic momentum analysis and fine-grained calorimetry.
Abstract: The Collider Detector at Fermilab (CDF) is a 5000 t magnetic detector built to study 2 TeV p p collisions at the Fermilab Tevatron. Event analysis is based on charged particle tracking, magnetic momentum analysis and fine-grained calorimetry. The combined electromagnetic and hadron calorimetry has approximately uniform granularity in rapidity-azimuthal angle and extends down to 2° from the beam direction. Various tracking chambers cover the calorimeter acceptance and extend charged particle tracking down to 2 mrad from the beam direction. Charged particle momenta are analyzed in a 1.5 T solenoidal magnetic field, generated by a superconducting coil which is 3 m in diameter and 5 m in length. The central tracking chamber measures particle momenta with a resolution better then δpT/pT2 = 2 × 10−3 (GeV/c)−1 in the region 40°
259 citations
TL;DR: In this paper, a generalization of the double-porosity technique, the MINC-method permits a fully transient description of interporosity flow, using numerical methods, which has been successfully applied in the past to geothermal reservoir and chemical transport problems.
Abstract: This paper describes the application of the method of ''Multiple Interacting Continua'' (MINC) to the simulation of oil recovery in naturally fractured reservoirs. A generalization of the double-porosity technique, the MINC-method permits a fully transient description of interporosity flow, using numerical methods. The method has been successfully applied in the past to geothermal reservoir and chemical transport problems. In this paper, we present examples to demonstrate the utility of the MINC-method for modeling oil recovery mechanisms and field applications in fractured reservoirs. Specifically, results for water imbibition in individual matrix blocks obtained with the MINC method are compared with results from the conventional double-porosity method and with calculations using a detailed discretization of matrix blocks. The MINC-calculations are found to be accurate to better than 1 percent at all times, while double-porosity results can have large errors for matrix blocks of low permeability or large size. In addition, the MINC-method is used to match published results for five-spot waterfloods, and to study the coning behavior of a single well in the north China oil field. All results show that the MINC-method provides accurate predictions of the behavior of naturally fractured reservoirs, while requiring only a modest increase in computation workmore » in comparison to the double-porosity method. 21 refs., 15 figs., 5 tabs.« less
202 citations
TL;DR: NMR interferometry experiments in a three-level system are presented which demonstrate the Aharonov-Anandan phase and its topological invariance for different circuits.
Abstract: Aharonov and Anandan have recently reformulated and generalized Berry's phase by showing that a quantum system which evolves through a circuit C in projective Hilbert space acquires a geometrical phase \ensuremath{\beta}(C) related to the topology of the space and the geometry of the circuit. We present NMR interferometry experiments in a three-level system which demonstrate the Aharonov-Anandan phase and its topological invariance for different circuits.
TL;DR: An astronomer-turned-sleuth traces a German trespasser on military networks, who slipped through operating system security holes and browsed through sensitive databases.
Abstract: An astronomer-turned-sleuth traces a German trespasser on our military networks, who slipped through operating system security holes and browsed through sensitive databases. Was it espionage?
TL;DR: In this article, the error of a mass formula is defined in a rigorous way, which leads naturally to the use of experimental uncertainties and of the maximum-likelihood method to derive a set of equations for estimating the parameters and error of the theoretical model.
TL;DR: In this paper, a study of the Λ and λ content of jets resulting from reactions such as e+e − → γγ → jets and e + e − → Z → vv ∗ → jets could reveal the presence of baryon-number violation at the weak scale.
TL;DR: The equilibrium geometry and electronic structure of the boron-carbon compound, BC/sub 3/ is determined using the ab initio pseudopotential local orbital approach and the local-density functional formalism and is found to be less stable than graphite for the structures investigated.
Abstract: We have determined the equilibrium geometry and electronic structure of the compound, ${\mathrm{BC}}_{3}$ using the ab initio pseudopotential local orbital approach and the local-density functional formalism. The boron-carbon compound, ${\mathrm{BC}}_{3}$, is a layered material with gra- phitic structure, where every fourth carbon atom is substituted by boron. The nearest-neighbor distances are predicted to be 1.42 A\r{} for the C-C bond and 1.55 A\r{} for the B-C bond. A monolayer of ${\mathrm{BC}}_{3}$ is found to be a semiconductor, and the observed metallic behavior of the bulk sample arises from interactions between neighboring layers in ${\mathrm{BC}}_{3}$ with AA and AB stacking. Based on total-energy calculations, we find ${\mathrm{BC}}_{3}$ to be less stable than graphite for the structures investigated.
TL;DR: In this article, it is shown that the (three-dimensional) tetragonal to orthorhombic transition in the 1-2-3 superconducting compound can be mapped onto a two-dimensional Ising model with anisotropic second neighbor effective pair interactions.
Abstract: It is shown that the (three-dimensional) tetragonal to orthorhombic transition in the 1-2-3 superconducting compound can be mapped onto a two-dimensional Ising model with anisotropic second neighbor effective pair interactions The Cluster Variation Method (CVM) has been used to calculate a phase diagram based on interaction parameters provided by first principles linear muffin-tin orbital-atomic sphere approximation (LMTO-ASA) calculations performed by P Sterne at Lawrence Livermore National Laboratory At high temperature, agreement with experimental phase transition data is excellent At low temperatures, two-dimensional ordering gives way to quasi one-dimensional states of order as described by the linear chain Ising model for which the thermodynamics are known exactly Structures produced by Monte Carlo simulation and theoretical diffraction patterns are in striking agreement with recent experimental results
TL;DR: Forty-five consecutive patients with chordoma or chondrosarcoma at the base of skull or cervical spine were treated at the University of California Lawrence Berkeley Laboratory (UCLBL) andUniversity of California School of Medicine, San Francisco (UCSF) between November 1977 and October 1986.
Abstract: Forty-five consecutive patients with chordoma or chondrosarcoma at the base of skull or cervical spine were treated at the University of California Lawrence Berkeley Laboratory (UCLBL) and University of California School of Medicine, San Francisco (UCSF) between November 1977 and October 1986. All patients had undergone a subtotal surgical resection. Twenty-three patients were treated definitively with charged particles, 13 patients were treated with photons and particles, and 9 patients were treated for recurrent disease. Total doses ranged from 36 to 80 Gray equivalent (GyE). Thirty-three patients are alive with a minimum followup of 1 year. The actuarial survival and local control for all patients at 5 years is 62% and 59%, respectively. Patients treated for primary disease had a 78% actuarial local control rate at 2 years, whereas the rate for patients with recurrent disease was 33%. Patients with smaller visible tumor volumes (less than 20 cc) had a significantly better local control rate than patients with larger tumor volumes (80% vs 33% actuarial rate at 5 years). Patients with chondrosarcoma had the highest local control rate, as did patients treated with particles alone. Complications included 3 patients with unilateral visual loss, two patients who became blind, and 4 patients with radiation injury to the brainstem.
TL;DR: In this paper, the effects of potassium on ammonia synthesis over model iron single-crystal catalysts of (111), (100), and (110) orientation have been studied under high-pressure reaction conditions (20 atm reactant pressure of nitrogen and hydrogen).
TL;DR: The collocation method for obtaining the bound solutions of the Schrodinger equation was investigated in this paper, which does not require the evaluation of integrals and is very simple to implement.
TL;DR: In this paper, fully converged state-to-state integral cross sections are reported for the reaction H + H2 (ν1=j1=0)→ H, (ν2=1, j2 = 1 and 3) + H over a wide range of energy.
TL;DR: Single-crystal X-ray diffraction measurements on solid He-4 demonstrate that the structure of the solid is hexagonal close packed over this pressure-temperature range, contrary to both the interpretation of high-pressure optical studies and to theoretical predictions.
Abstract: Single-crystal X-ray diffraction measurements have been performed on solid He-4 from 15.6 to 23.3 GPa at 300 K with synchrotron radiation. The diffraction patterns demonstrate that the structure of the solid is hexagonal close packed over this pressure-temperature range, contrary to both the interpretation of high-pressure optical studies and to theoretical predictions. The solid is more compressible than is indicated by equations of state calculated with recently determined helium pair potentials. The results suggest that a significant revision of current views of the phase diagram and energetics of dense solid helium is in order.
TL;DR: The calculated valence electron charge density indicates that the bonding in WC consists of a metallic component similar to that found in solid W, and strong W-C bonds.
Abstract: We present the results of a pseudopotential local-orbital calculation on hexagonal WC. The calculated lattice constants and cohesive energy are in good agreement with experiment, and the calculated bulk modulus lies within the wide range of measured values. The band structure and Fermi surface obtained are also generally consistent with experimental data, and the Fermi level is found to lie in a deep minimum of the density of states. The calculated valence electron charge density indicates that the bonding in WC consists of a metallic component similar to that found in solid W, and strong W-C bonds.
TL;DR: The mode of O-alkylpyrimidine and alkyl phosphotriester repair in mammalian cells differs from that in E. coli, and new approaches and methods are needed to characterize these processes at the biochemical and molecular level.
Abstract: Enzymatic repair of the O-alkylpyrimidines (O2- and O4-alkylthymine, O2-alkylcytosine) and alkyl phosphotriesters has been studied in Escherichia coli, and the two proteins involved, a glycosylase (DNA-3-methyladenine glycosylase) and a methyltransferase (DNA-O6-methylguanine:protein-L-cysteine S-methyltransferase, EC 2.1.1.63), have been well characterized. In mammals or mammalian cells treated with carcinogenic alkylating agents, loss of these derivatives has been demonstrated repeatedly. Nevertheless, mammalian repair proteins that are analogous to those from E. coli do not detectably act on these alkyl derivatives. A variety of techniques has been used by many investigators in the United States and Europe, who conclude here that the mode of O-alkylpyrimidine and alkyl phosphotriester repair in mammalian cells differs from that in E. coli. New approaches and methods are needed to characterize these processes at the biochemical and molecular level.
TL;DR: The epitaxial growth of iron oxide overlayers on a platinum (111) single crystal, in the monolayer and the multilayer regimes, was reported in this article.
TL;DR: A new method of calculating total energies of solids using nonlocal pseudopotentials in conjunction with the variational quantum Monte Carlo approach is presented, which avoids the large fluctuations of the energies in the core region of the atoms which occur in Quantum Monte Carlo all-electron calculations.
Abstract: A new method of calculating total energies of solids using nonlocal pseudopotentials in conjunction with the variational quantum Monte Carlo approach is presented. By use of pseudopotentials, the large fluctuations of the energies in the core region of the atoms which occur in quantum Monte Carlo all-electron calculations are avoided. The method is applied to calculate the binding energy and structural properties of diamond. The results are in excellent agreement with experiment.
TL;DR: In this paper, an aethalometer was installed at the NOAA/GMCC South Pole Observatory to measure concentrations of the combustion effluent tracer species aerosol black carbon (BC) with a time resolution of one hour.
Abstract: In December 1986 an aethalometer was installed at the NOAA/GMCC South Pole Observatory to measure concentrations of the combustion effluent tracer species aerosol black carbon (BC) with a time resolution of one hour. We present data covering a 1-yr period from December 1986 through November 1987. The hourly data show infrequent events in which the concentrations increased greatly for periods of a few hours. We attribute these events to local contamination and identified them as such in the database. The remaining background data then yield daily average BC concentrations generally ranging from 50 pg m−3 to 5 ng m−3, with a minimum in the early austral winter. The results imply long-range transport of this aerosol species, and suggest a minimum value of the order of 10 pg m−3 for its global background concentration.
TL;DR: In this paper, it was shown that a similar reduction in the J/ψ signal can occur due to inelastic scattering of Jψ's in a hadronic resonance gas.
TL;DR: A key feature of this design is the inclusion of on-chip sparse read-out circuitry, which allows efficient management of low-occupancy events.
Abstract: A full-custom CMOS integrated circuit for silicon strip detector systems has been designed, fabricated, and tested. The circuit contains 128 parallel data-acquisition channels and considerable peripheral circuitry. Each channel consists of a low-noise, low-power, charge-sensitive amplifier, a multistage autobalanced comparator, an analog multiplexer, nearest-neighbor logic, priority-search logic, and a share of a position-encoding read-only memory. The analog system can substract both detector pedestal and leakage current on a channel-by-channel basis. A key feature of this design is the inclusion of on-chip sparse read-out circuitry, which allows efficient management of low-occupancy events. Designed for use at the Collider Detector Facility (CDF) at Fermilab, the circuit is suitable for large-scale silicon detector systems requiring a large, dense array of fast, low-power electronics. >
TL;DR: The cis and trans isomers of dicationic bis(4-N-methylpyridyl)diphenylporphine show a much greater tendency to aggregate than similar tetracationic porphyrins, giving intense circular dichroism signals whose profile reports the helical sense of the DNA.
TL;DR: In this paper, the (1 × 2) missing-row reconstruction of clean Pt(110) is studied with a new low-energy electron diffraction (LEED) intensity analysis.