Showing papers by "Lawrence Berkeley National Laboratory published in 1981"

Photothermal deflection spectroscopy and detection

Abstract: The theory for a sensitive spectroscopy based on the photothermal deflection of a laser beam is developed. We consider cw and pulsed cases of both transverse and collinear photothermal deflection spectroscopy for solids, liquids, gases, and thin films. The predictions of the theory are experimentally verified, its implications for imaging and microscopy are given, and the sources of noise are analyzed. The sensitivity and versatility of photothermal deflection spectroscopy are compared with thermal lensing and photoacoustic spectroscopy.

Catalytic Synthesis of Hydrocarbons over Group VIII Metals. A Discussion of the Reaction Mechanism

Abstract: A broad range of hydrocarbons and oxygenated products can be synthesized catalytically from CO and H2 produced by the gasification of coal, Since the earliest examples of such chemistry were reported by Fischer and Tropsch [1, 2] in 1926, the nonselective generation of organic compounds via the hydrogenation of CO has become known as Fischer-Tropsch synthesis. In the intervening 54 years, many efforts have been made to identify the mechanism by which reactants are converted to products. These studies have been motivated in large measure by the desire to understand how catalyst composition and reaction conditions govern the distribution of products formed. A brief review of the mechanistic hypotheses developed prior to 1970 will be presented here to serve as background for a discussion of more recent ideas, Details concerning the earlier studies can be found in a number of reviews [3–15] published previously.

Tomographical imaging with limited-angle input

Abstract: The theory of tomographical imaging with limited angular input, from which two reconstruction algorithms are derived, is discussed. The existence of missing information because of incomplete angular coverage is demonstrated, and an iteration algorithm to recover this information from a priori knowledge of the finite extent of the object is developed. Smoothing algorithms to stabilize reconstructions in the presence of noise are given. The effects of digitization and finite truncation of the reconstruction region in numerical computation are also analyzed. It is shown that the limited-angle problem is governed by a set of eigenvalues whose spectrum is determined by the imaging angle and the finite extent of the object. The distortion on a point source caused by the missing information is calculated; from the results some properties of the iteration scheme, such as spatial uniformity, are derived.

The Use of Filtering Methods to Compensate for Constant Attenuation in Single-Photon Emission Computed Tomography

Abstract: A back projection of filtered projection (BKFIL) reconstruction algorithm is presented that is applicable to single-photon emission computed tomography (ECT) in the presence of a constant attenuating medium such as the brain. The filters used in transmission computed tomography (TCT)-comprised of a ramp multiplied by window functions?are modified so that the single-photon ECT filter is a function of the constant attenuation coefficient. The filters give good reconstruction results with sufficient angular and lateral sampling. With continuous samples the BKFIL algorithm has a point spread function that is the Hankel transform of the window function. The resolution and statistical properties of the filters are demonstrated by various simulations which assume an ideal detector response. Statistical formulas for the reconstructed image show that the square of the percent-root-mean-square (percent-rms) uncertainty of the reconstruction is inversely proportional to the total measured counts. The results indicate that constant attenuation can be compensated for by using an attenuation-dependent filter that reconstructs the transverse section reliably. Computer time requirements are two times that of conventional TCT or positron ECT and there is no increase in memory requirements.

Analysis of Long Term File Reference Patterns for Application to File Migration Algorithms

Abstract: In most large computer installations files are moved between on-line disk and mass storage (tape, integrated mass storage device) either automatically by the system and/or at the direction of the user. In this paper we present and analyze long term file reference data in order to develop a basis for the construction of algorithms for file migration. Specifically, we examine the use of the on-line user (primarily text editor) data sets at the Stanford Linear Accelerator Center (SLAC) computer installation through the analysis of 13 months of file reference data. We find that most files are used very few times. Of those that are used sufficiently frequently that their reference patterns may be examined, we find that: 1) about a third show declining rates of reference during their lifetime, 2) of the remainder, very few (about 5 percent) show correlated interreference intervals, and 3) interreference intervals (in days) appear to be more skewed than would occur with the Bernoulli process. Thus, about two-thirds of all suffi1ciently active files appear to be referenced as a renewal process with a skewed interreference distribution. A large number of other file reference statistics (file lifetimes, interference distributions, moments, means, number of uses/ file, file sizes, file rates of reference, etc.) are computed and presented. Throughout, statistical tests are described and explained. The results of our analysis of file reference patterns are applied in a companion paper to the development and comparative evaluation of file migration algorithms.

Ground-state properties of diamond

Abstract: The ground-state properties of diamond are investigated using an ab initio density-functional pseudopotential scheme. The calculated equilibrium lattice constant, cohesive energy, and bulk modulus are in excellent agreement with experiment. Unlike Si and Ge, a double hump is found in the valence-electron charge density along the tetrahedral bonds.

QUANTUM NOISE THEORY FOR THE dc SQUID

Abstract: The noise temperature of a dc superconducting quantum interference device (SQUID) coupled to a tuned input circuit is computed using the complete quantum expression for the equilibrium noise in the shunt resistance of each junction. At T = 0, where the noise reduces to zero‐point fluctuations, the noise temperature for an optimized system is hn/kB ln2, where n is the signal frequency. The computation is extended to nonzero temperatures, and it is shown that a SQUID operated at 1K can approach the quantum limit.

Slow degradation and electron conduction in sodium/beta-aluminas

Abstract: Slow degradation was observed in sodium/beta-alumina electrolytes subjected to long term in cycling Na/S cells The degradation propagated as a layer from the sodium side It involves the internal deposition of sodium metal during current passage This Mode II degradation was distinct from chemical colouration and from the Mode I failure (Poiseuille pressure due to cathodic deposition driving isolated cracks) Degradation was also observed on the sulfur side of the electrolyte and was associated with the graphite felt “imprinting effect” It is thought that the Mode II degradation resulted from electron conduction into the solid electrolyte from the beta-alumina/sodium metal interface during the charging cycle

Near-millimeter spectrum of the microwave background

Abstract: A description is given of a method for the measurement of the cosmic microwave background (CMB) spectrum. A helium-cooled, balloon-borne spectrophotometer was used to measure the emission spectrum of the night sky over the frequency range 1.7-40/cm. The apparatus was calibrated using a blackbody source at a variety of temperatures both before and after the flight. It is shown that the spectrum of the CMB peaks at 6/cm and is approximately that of a blackbody out to several times that frequency. The measured flux is also found to be equivalent to that from a blackbody in the temperature range from 2.88 to 3.09 K. The data set resulting from the combination of these measurements with previous observations of the CMB covers three decades in frequency, and is compared with various CMB models.

Measurements of the Properties of d Meson Decays

Abstract: We present a study of the decay properties of charmed D mesons produced near the peak of the {psi}" (3770) resonance in e{sup +}e{sup -} annihilation. Branching fractions for nine Cabibbo-favored and three Cabibbo-suppressed decay modes are presented along with upper limits on one additional Cabibbo-favored and four additional Cabibbo-suppressed decay modes. A study of K{pi}{pi} decay mode Dalitz plots reveals a large quasi-two-body pseudoscalar-vector component for the D{sup 0} decays and an apparent nonuniform population an the Dalitz plot for the D{sup +} decay into K{sup -}{pi}{sup +}{pi}{sup +}. Using tagged events, we measure the charged particle multiplicity and strange particle content of D decays. A measurement of the D{sup +} and D{sup 0} semileptonic decay fractions indicates that the D{sup +} has a significantly longer lifetime than the D{sup 0}.

Equilibrium properties and the phase transition of grey and white tin

Abstract: The structural and thermodynamic properties of two phases of tin are reported. Equilibrium properties of both phases obtained from an ab initio nonrelativistic calculation are in good agreement with experiment. From our calculation, we suggest that the measured bulk modulus for grey tin reported in the literature is in error. The grey-to-white-tin transition is discussed using the total internal energy and the free energy [$E(T)$ and $F(T)$] curves as well as the valence charge distribution for each phase. Our method utilizes self-consistent pseudopotentials derived to identically reproduce results of all-electron calculations.

PERFORMANCE AND APPLICATION OF A DOUBLE-CRYSTAL MONOCHROMATOR IN THE ENERGY REGION 800 < hv < 4500 eV

Abstract: LBL-12729 WSltt Lawrence Berkeley Laboratory UNIVERSITY OF CALIFORNIA Materials & Molecular Research Division Presented at the Second National Conference on Synchrotron Radiation Instrumentation, Cornell University, Ithaca, NY, July 15-17, 1981; and to be published in Nuclear Instruments and Methods PERFORMANCE AND APPLICATION OF A DOUBLE-CRYSTAL MONOCHROMATOR IN THE ENERGY REGION 800 < hv < 4500 eV Z. Hussain, E. Umbach, D.A. Shirley, J. Stohr, and J. Feldhaus July 1981 Prepared for the U.S. Oepartment of Energy under Contract W-7405-ENG-48

Improved ab initio effective potentials for Ar, Kr, and Xe with applications to their homonuclear dimers

Abstract: Effective core potentials for the Ar, Kr, and Xe atoms derived from numerical Hartree–Fock and Dirac–Hartree–Fock wave functions are applied in SCF and CI calculations of homonuclear diatomic potential energy curves. Detailed comparisons are made with the all‐electron calculations of Wadt for the ground and lowest positive states. Relativistic effects, excluding spin–orbit coupling, are seen to be relatively unimportant. Plots of the potential energy curves and computed spectroscopic constants show excellent agreement with the all‐electron results. On the other hand, comparisons with results obtained using effective potentials derived using varients of Phillips–Kleinman procedures show dramatic differences for Xe2 and Xe2+. From SCF calculations on Xe2 and Xe2+ it was found that the explicit inclusion of the spin–orbit operator in the SCF procedure (using ω–ω coupling) results in essentially the same potential curves obtained by adding the spin–orbit correction as a final semiempirical perturbation.

Siderophilin metal coordination. 1. complexation of thorium by transferrin: structure-function implications

Abstract: LBL-11878 Preprint LIBFV·',RY ANL1 Submitted to the Journal of the American Chemical Society SIDEROPHILIN METAL COORDINATION. 1. COMPLEXATION OF THORIUM BY TRANSFERRIN: STRUCTURE-FUNCTION I:MPLI CATIONS Wesley R. Harris, Carl J. Carrano, Vincent L. Pecoraro, and Kenneth N. Raymond August 1980 TWO-WEEK LOAN COPY This is a Library which may borrowed For a personal Copy two weeks. Tech. Info. Divisiony Prepared for the U.S. Department of Energy under Contract W-7405-ENG-48

A unimolecular reaction ABC→A+B+C involving three product molecules and a single transition state. Photodissociation of glyoxal: HCOHCO→H2+CO+CO

Abstract: Following an earlier proposal [Y. Osamura and H. F. Schaefer, J. Chem. Phys. 74, 4576 (1981)], the unimolecular reaction HCOHCO→H2+CO+CO has been examined via nonempirical molecular electronic structure theory. Specifically, the constrained symmetric (point group C2v) transition state for this ABC→A+B+C reaction has been located at several levels of self‐consistent‐field (SCF) theory. Four different basis sets of contracted Gaussian functions were used: an STO‐3G minimum basis, the small split valence 3‐21G basis, the standard C(9s 5p/4s 2p) double zeta (DZ) set, and a double zeta plus polarization (DZ+P) basis. Vibrational analyses of the four stationary point structures (all of which are geometrically similar) yield a remarkable variety of results. The STO‐3G stationary point has three imaginary vibrational frequencies, 3‐21G has one imaginary frequency (and thus is a genuine transition state), while the DZ and DZ+P structures yield two imaginary vibrational frequencies. For the latter two cases, one of the two imaginary vibrations is a very small bending frequency, while the larger frequency clearly connects glyoxal with the three products H2+CO+CO. This suggests the existence of a slightly nonplanar true transition state. To our knowledge such a unimolecular transition state is without precedent. Configuration interaction (CI) suggests that the barrier for this ABC→A+B+C reaction is competitive with that for HCOHCO→H2CO+CO.

Polarization of the cosmic background radiation

Abstract: The technique and results of a measurement of the linear polarization of the cosmic background radiation at a wavelength of 9 mm are discussed. Data taken between 1978 May and 1980 February from both the Northern Hemisphere (Berkeley latitude 38 deg N) and the Southern Hemisphere (Lima latitude 12 deg S) over 11 declinations from -37 to +63 deg show the radiation to be essentially unpolarized over all areas surveyed. Fitting all data gives the 95% confidence level limit on a linearly polarized component of 0.3 mK for spherical harmonics through third order. A fit of all data to the anisotropic axisymmetric model of Rees (1968) yields a 95% confidence level limit of 0.15 mK for the magnitude of the polarized component. Constraints on various cosmological models are discussed in light of these limits.

Normal photoelectron diffraction of c(2 x 2)O(1s)-Ni(001) and c(2 x 2)S(2p)-Ni(001),with Fourier-transform analysis

Abstract: Normal photoelectron diffraction was used to study the structure of the $c(2\ifmmode\times\else\texttimes\fi{}2)\mathrm{O}$ and $c(2\ifmmode\times\else\texttimes\fi{}2)\mathrm{S}$ overlayers on Ni(001). The oxygen and sulfur atoms were found to lie above the fourfold hollow sites in the Ni(001) surface with ${d}_{1}$ spacings of 0.90\ifmmode\pm\else\textpm\fi{}0.04 and 1.30\ifmmode\pm\else\textpm\fi{}0.04 \AA{}, respectively, where ${d}_{1}$ is the perpendicular interplanar spacing between the adsorbate and surface layers. A Fourier-transform analysis was carried out on the experimental data. In both cases, the modulus of the Fourier transforms gave two large peaks in the real-space distribution function. The maxima of these peaks closely corresponded to ${d}_{1}+b$ and ${d}_{1}+2b$, where $b$ is the interlayer spacing in Ni(001). The range of experimental data in $k$ space was not large enough to yield the value of ${d}_{1}$ directly.

High-statistics study of π + p , π − p , and pp elastic scattering at 200 GeV/ c

Abstract: We have measured ${\ensuremath{\pi}}^{+}p$, ${\ensuremath{\pi}}^{\ensuremath{-}}p$, and $\mathrm{pp}$ elastic scattering at an incident-beam momentum of 200 GeV/c in the region of $\ensuremath{-}t$, four-momentum transfer squared, from 0.021 to 0.665 (${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$. The data allow an investigation of the $t$ dependence of the logarithmic forward slope parameter $b\ensuremath{\equiv}(\frac{d}{\mathrm{dt}})(\mathrm{ln}\frac{d\ensuremath{\sigma}}{\mathrm{dt}})$. In addition to standard parametrization, we use functional forms suggested by the additive quark model to fit the measured $\frac{d\ensuremath{\sigma}}{\mathrm{dt}}$ distributions. Within the context of this model we estimate the size of the clothed quark in the pion and proton. Limits on the elastic-scattering amplitude derived from unitarity bounds are checked, and no violations are observed.