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Stability of some stationary solutions for the forced KdV equation

Description: The forced KdV (fKdV) equation has been established by recent studies as a simple mathematical model capable of describing the physics of a shallow layer of fluid subject to external forcing. For a particular one-parameter family of forcings which is characterized by a wave amplitude parameter for supercritical forcing distributions, exact stationary solutions are known. We study the stability of these solutions as the parameter varies. The linear stability analysis is first carried out, and we discuss the structure of the spectrum of the associated eigenvalue problem using a perturbation approach, about isolated parameter values where eigenfunctions can be expressed in closed form and are the fixed-point solutions of the fKdV equation corresponding to zero eigenvalues. The results identify a set of intervals in the parameter space corresponding to different types of manifestation of instability. In the region of the parameter space where the linear stability analysis fails to provide an answer, we have developed a nonlinear analysis to provide a sufficient condition for stability. 13 refs.
Date: January 1, 1990
Creator: Camassa, R. (Los Alamos National Lab., NM (USA)) & Yao-tsu Wu, T. (California Inst. of Tech., Pasadena, CA (USA). Div. of Engineering and Applied Science)
Partner: UNT Libraries Government Documents Department

The Soviet-American gallium experiment at Baksan

Description: A gallium solar neutrino detector is sensitive to the full range of the solar neutrino spectrum, including the low-energy neutrinos from the fundamental proton-proton fusion reaction. If neutrino oscillations in the solar interior are responsible for the suppressed {sup 8}B flux measured by the Homestake {sup 37}Cl experiment and the Kamiokande water Cherenkov detector, then a comparison of the gallium, chlorine, and water results may make possible a determination of the neutrino mass difference and mixing angle. A 30-ton gallium detector is currently operating in the Baksan laboratory in the Soviet Union, with a ratio of expected solar signal to measured background (during the first one to two {sup 71}Ge half lives) of approximately one. 28 refs.
Date: January 1, 1990
Creator: Abazov, A. I.; Abdurashitov, D. N.; Anosov, O. L.; Danshin, S. N.; Eroshkina, L. A.; Faizov, E. L. et al.
Partner: UNT Libraries Government Documents Department

Transport of a passive tracer in time-dependent Rayleigh-Benard convection

Description: The transport of a passive tracer in a Rayleigh-Benard cell is considered, when the convection rolls are subject to oscillatory instability. We propose a mechanism for the roll to roll transport and introduce formulae for quantifying the spreading of the tracer, which are valid for as long as the molecular diffusivity can be neglected. A criterion for weighing the effects of diffusivity is discussed, and we provide some example by numerically simulating the flow in presence of molecular diffusivity. 8 refs., 6 figs.
Date: January 1, 1990
Creator: Camassa, R. & Wiggins, S.
Partner: UNT Libraries Government Documents Department

Pulsations of the white dwarf component in V471 tauri-like binaries

Description: The eclipsing spectroscopic binary V471 Tau has a compact DA component that has been observed to pulsate with multimode, low amplitude oscillations. We test three models with different masses (M/M{sub {circle dot}} = 0.6, 0.8, 1.0) against nonradial instability. Our models are derived from an evolutionary track calculated by Iben. The results confirm that the pulsations are driven by the {kappa} and {gamma} mechanisms operating in the ionization zones of carbon and oxygen. 18 refs., 1 fig., 1 tab.
Date: January 1, 1990
Creator: Stanghellini, L. (Osservatorio Astronomico di Bologna (Italy)); Cox, A.N. (Los Alamos National Lab., NM (USA)) & Starrfield, S.G. (Arizona State Univ., Tempe, AZ (USA). Dept. of Physics and Astronomy Los Alamos National Lab., NM (USA))
Partner: UNT Libraries Government Documents Department

Lobe area in adiabatic Hamiltonian systems

Description: We establish as analytically computable formula, based on the adiabatic Melnikov function, for lobe area in one-degree-of-freedom Hamiltonian systems depending on a parameter which varies slowly in time. We illustrate this lobe area result on a slowly parametrically forced pendulum, a paradigm problem for adiabatic chaos. Our analysis unties the theory of action from classical mechanics with the theory of the adiabatic Melnikov function from the field of global bifurcation theory.
Date: January 1, 1990
Creator: Kaper, T.J. & Wiggins, S. (California Inst. of Tech., Pasadena, CA (USA) Los Alamos National Lab., NM (USA). Center for Nonlinear Studies)
Partner: UNT Libraries Government Documents Department

Nonradial instability strips for post-AGB stars

Description: We test several pre-degenerate (PNN and DO) and degenerate (DB) models for stability against nonradial oscillations. These models lie on the 0.6 M{sub {circle dot}} evolutionary track calculated by Iben. The post-AGB stars have a residual CO core with only a little surface hydrogen and helium. In order to match all the observed pulsators. We use three different surface compositions for the DO stars, and a pure helium surface for the DB white dwarfs. We find 3 DO and 1 DB instability strips that we compare to the available observations. 16 refs., 1 fig.
Date: January 1, 1990
Creator: Stanghellini, L. (Osservatorio Astronomico di Bologna (Italy)); Cox, A.N. (Los Alamos National Lab., NM (USA)) & Starrfield, S.G. (Arizona State Univ., Tempe, AZ (USA). Dept. of Physics and Astronomy Los Alamos National Lab., NM (USA))
Partner: UNT Libraries Government Documents Department

A semi-analytical model of stellar flares

Description: We present a simplified point'' model to describe the hydrodynamic response of coronal loop plasma to the sudden release of energy which occurs at the time of a flare. Our simplification allows the full set of partial differential equations for energy, momentum, and mass conservation to be replaced by a corresponding set of ordinary differential equations for the plasma properties averaged over the loop volume. The temporal profiles of plasma temperature, density, and velocity are calculated over a time interval long enough to ensure that pre-flare conditions are re-established. The model is used for the interpretation of stellar flare data. In particular, we derive a set of representative loop geometries and flare energy inputs which allows us to reproduce the high emission measures typically inferred from observations of stellar flares. 4 refs., 1 fig.
Date: January 1, 1990
Creator: Kopp, R.A. (Los Alamos National Lab., NM (USA)) & Poletto, G. (Osservatorio Astrofisico di Arcetri, Florence (Italy))
Partner: UNT Libraries Government Documents Department

Texture-induced anisotropy and high-strain rate deformation in metals

Description: We have used crystallographic texture calculations to model anisotropic yielding behavior for polycrystalline materials with strong preferred orientations and strong plastic anisotropy. Fitted yield surfaces were incorporated into an explicit Lagrangian finite-element code. We consider different anisotropic orientations, as well as different yield-surface forms, for Taylor cylinder impacts of hcp metals such as titanium and zirconium. Some deformed shapes are intrinsic to anisotropic response. Also, yield surface curvature, as distinct from strength anisotropy, has a strong influence on plastic flow. 13 refs., 5 figs.
Date: January 1, 1990
Creator: Schiferl, S.K. & Maudlin, P.J.
Partner: UNT Libraries Government Documents Department

The gold/high temperature superconductor interface: Metallicity of the near surface region and a search for the proximity effect

Description: We have used high resolution photoemission spectroscopy to probe the electronic structure of a wide variety of gold/high temperature superconductor interfaces, the majority of which were formed by low-temperature (20K) gold evaporations on cleaved high quality single crystals. For c-axis interfaces formed on the 123 family of superconductors, we find that the gold deposition essentially destroys the metallicity of the superconducting substrate in the near surface region ({approximately}5{angstrom}), while the near surface region of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} remains metallic. We have also used photoemission spectroscopy to search for a proximity-effect superconducting gap in gold overlayers on c-axis single crystals and a-axis thin films, though no such effect was found. 30 refs., 6 figs.
Date: January 1, 1990
Creator: Dessau, D.S.; Shen, Z.X.; Wells, B.O.; Spicer, W.E. (Stanford Univ., CA (USA). Stanford Electronics Labs.); List, R.S.; Arko, A.J. et al.
Partner: UNT Libraries Government Documents Department

Observations of tornadoes and wall clouds with a portable FM-CW Doppler radar: 1989--1990 results

Description: The purpose of this paper is to report on our progress using a portable, 1 W,FM (frequency modulated)-CW (continuous wave) Doppler radar developed at the Los Alamos National Laboratory (LANL), to make measurements of the wind field in tornadoes and wall clouds along with simultaneous visual documentation. Results using a CW version of the radar in 1987--1988 are given in Bluestein and Unruh (1989). 18 refs., 2 figs., 1 tab.
Date: January 1, 1990
Creator: Bluestein, H.B. (Oklahoma Univ., Norman, OK (USA). School of Meteorology) & Unruh, W.P. (Los Alamos National Lab., NM (USA))
Partner: UNT Libraries Government Documents Department

Increasing output power of an 850 MHz tetrode with a floating-deck modulator

Description: Designers of high-power amplifiers generally regard the region above 300 MHz as a domain dominated by velocity-modulated (klystron/TWT) devices. However, as the power requirements diminish, there are attractive alternatives. The high-power 850-MHz requirements of the ground test accelerator (GTA) program can be filled by 1-MW klystrons, but it would be more efficient to use a lower-power device for a 50-kW requirement. To meet the 850-MHz medium-power requirements, Los Alamos National Laboratory is developing an 850-MHz tetrode amplifier. These amplifiers will provide rf power to the momentum compactor and bunch rotator cavities of the GTA. Available tubes provide only a limited safety margin for a low-risk design at the power levels and duty factor required for GTA cavities. At 850 MHz, the output power capability of available tubes is reduced because of transit time effects and limited anode voltage holdoff. Pulsing the anode of the output tetrode amplifier will allow higher output power with minimum design risk. A floating-deck modulator acts as a high-voltage/high-current switch, so voltage is applied to the anode of the gridded tube only during the rf pulse. The anode voltage holdoff capability of the tube is substantially enhanced by operating in this mode. This paper will describe the design of the floating deck modulator and its impact on the design risk of the 850-MHz tetrode amplifier.
Date: January 1, 1990
Creator: Rees, D. & Friedrichs, C.
Partner: UNT Libraries Government Documents Department

Relationship of cytochrome caa sub 3 from Thermus thermophilus to other heme- and copper-containing terminal oxidases

Description: Cytochrome oxidases are a key component of the energy metabolism of most aerobic organisms from mammals to bacteria. They are the final enzyme of the membrane associated respiratory chain responsible for converting the chemical energy of reduced substrates to a transmembrane electrochemical potential, which issused by the cell for a wide variety of energy-requiring processes. The most widely studied oxidase is the cytochrome c oxidase of the mammalian mitochondrion. This complex, integral membrane protein contains 13 subunits and four canonical metal centers: heme center a and a{sub 3}; copper centers CU{sub A} and CU{sub B}. It is responsible for electron transfer from reduced chytochrome c to dioxygen with the concomitant reduction of dioxygen to water and the coupled vectorial transfer of protons across the mitochondrial membrane. In this communication we will describe preliminary results of DNA sequencing experiments with the cytochrome caa{sub 3} oxidase, initially undertaken to determine the nature of the subunits of this oxidase and shed light on the distribution of the metal centers. We will speculate on oxidase gene and protein structures and evolutionary relationships in the light of these results and recent sequencing results from other groups. 47 refs., 4 figs., 1 tab.
Date: January 1, 1990
Creator: Mather, M.W.; Springer, P. & Fee, J.A.
Partner: UNT Libraries Government Documents Department

De Hass-van Alphen effect in YBCO

Description: Measurement of the de Haas-van Alphen effect in YBa{sub 2}Cu{sub 3}O{sub 6.97} in pulsed, magnetic fields peaking at 100 T in powdered material with the field applied along the c-axis reveal two pieces of the Fermi surface. Their cross sections are 0.56 kT (0.054 {angstrom}{sup {minus}2}) and 0.78 kT (0.075 {angstrom}{sup {minus}2}) with effective masses of 2.8 and 4.4 respectively.
Date: January 1, 1990
Creator: Smith, J.L.; Fowler, C.M.; Freeman, B.L.; Hults, W.L.; King, J.C. & Mueller, F.M.
Partner: UNT Libraries Government Documents Department

SiC reinforced-MoSi sub 2 based matrix composites

Description: SiC reinforced-MoSi{sub 2} based matrix composites possess very significant potential as high temperature structural materials for temperatures above 1200{degree}C in oxidizing environments, due to their combination of oxidation resistance, thermodynamic stability, machinability, elevated temperature ductility and strength, and ability to alloy the MoSi{sub 2} matrix with other silicides. The fabrication, microstructures, oxidation, and mechanical properties of these materials are described, and their current properties are compared to high temperature metals and structural ceramics. 22 refs., 5 figs., 2 tabs.
Date: January 1, 1990
Creator: Petrovic, J.J. & Honnell, R.E.
Partner: UNT Libraries Government Documents Department

rvec p + sup 13 rvec C elastic scattering at 500 MeV

Description: For the first time, an elastic scattering experiment was performed at LAMPF using polarized protons and a polarized target nucleus ({rvec p} + {sup 13}{rvec C}). The analyzing powers (A{sub ooon}({Theta})) and (A{sub oonn}({Theta})) were measured using an incident beam energy of 500 MeV over the laboratory angular range of 10{degree}--30{degree}. Motivation for the experiment and some preliminary results and conclusions are presented. 12 refs., 7 figs.
Date: January 1, 1990
Creator: Tanaka, N.
Partner: UNT Libraries Government Documents Department

Elemental mapping of planetary surfaces using gamma-ray spectroscopy

Description: The gamma rays escaping from a planet can be used to map the concentrations of various elements in its surface. In a planet, the high-energy particles in the galactic cosmic rays induce a cascade of particles that includes many neutrons. The {gamma} rays are made by the nuclear excitations induced by these cosmic-ray particles and their secondaries (especially capture or inelastic-scattering reactions induced by neutrons) and decay of the naturally-occurring radioelements. After a short history of planetary {gamma}-ray spectroscopy and its applications, the {gamma}-ray spectrometer planned for the Mars Observer mission is presented. The results of laboratory experiments that simulate the cosmic-ray bombardments of planetary surfaces or measure cross sections for the production of {gamma} rays and the status of the theoretical calculations for the processes that make and transport neutrons and {gamma} rays will be reviewed. The emphasis here is on studies of Mars and on new ideas, concepts, and problems that have arisen over the last decade, such as Doppler broadening and peaks from neutron scattering with germanium nuclei in a high-resolution {gamma}-ray spectrometer. 31 refs., 1 fig., 1 tab.
Date: January 1, 1990
Creator: Reedy, R.C.
Partner: UNT Libraries Government Documents Department

Gamma-ray and neutron leakage spectra calculated for unshieled reactors

Description: The spectra of neutrons and gamma rays escaping from unshielded reactors have been calculated for a number of simplified cases. Such spectra are important in connection with reactors operating in space orbit around the earth, which would normally have little or no heavy shielding. Reactors in space, such as the Soviet RORSAT spacecraft. Knowledge of the characteristics of their leakage spectra may be useful in understanding or minimizing such interference. The Monte Carlo Neutron-Photon (MCNP) code developed at Los Alamos has been used in these calculations. In the cases considered here the critical assembly is assumed to have spherically symmetrical geometry, with a central core of fissionable material surrounded by one or more shells of other material. The outer shells considered include beryllium, beryllium oxide, sodium, potassium, lithium, lithium hydride, and iron. The results obtained, presented as graphs, show that a number of materials that may be used in space reactors should lead to distinctive gamma-ray and neutron leakage spectra. Measurements of such spectra might well be useful in characterizing an unknown reactor type. 16 refs., 33 figs.
Date: May 1, 1990
Creator: Terrell, J.
Partner: UNT Libraries Government Documents Department

Structure and dynamics of a (1:1) drug-DNA complex: Analysis of 2D NMR data using molecular mechanics and molecular dynamics calculations

Description: 1D/2D NMR studies are reported for a (1:1) complex of d(GA{sub 4}T{sub 4}C){sub 2} and Dst2 (an analogue of distamycin A). Full- Matrix NOESY Simulations, Molecular Mechanics and Molecular Dynamics Calculations are performed to analyze the NMR data. Results show that drug-DNA complex formation is driven by static features like H-bonding and steric interactions in the minor-groove of DNA. As a consequence of drug binding, a non-linear oscillatory mode is activated. In this mode the molecule samples equilibrium structural states of difference degrees of bending. It is noted that these structures belong to three distinctly different energy wells that satisfy the same NMR data. 14 refs., 4 figs., 2 tabs.
Date: January 1, 1990
Creator: Sarma, R.H.; Sarma, M.H.; Umemoto, K. (State Univ. of New York, Albany, NY (USA). Dept. of Chemistry); Gupta, G. & Garcia, A.E. (Los Alamos National Lab., NM (USA))
Partner: UNT Libraries Government Documents Department

Pulsed laser fluorometry for environmental monitoring

Description: A compact pulsed laser fluorometer has been incorporated into a continuous flow system developed to detect acetylcholinesterase (AChE) inhibitors and/or primary amine compounds in air and water. A pulsed nitrogen laser pumped dye laser excites fluorescent reactants which flow continuously through a quartz flow cell. Data are collected, analyzed, and displayed using a Macintosh II personal computer. For detection of cholinesterase inhibitors the fluorogenic substrate N methylindoxyl acetate is used to monitor the activity of immobilized enzyme. Presence of inhibitors results in a decrease of steady state fluorescence. Detection of compounds containing primary amines is based on their reaction with fluorescamine to rapidly produce intensely fluorescent products. Compounds of interest to our research were amino acids, peptides, and proteins. An increase in steady state fluorescence could be cause to evaluate the reasons for the change. The detection limit of the protein, bovine serum albumin (BSA) in water is 10 ppT. Nebulized BSA concentrated by the LANL air sampler can be detected at sub ppT original air concentration. 16 refs., 14 figs., 3 tabs.
Date: January 1, 1990
Creator: Saunders, G. C.; Martin, J. C.; Jett, J. H.; Wilder, M. E.; Martinez, A.; Bentley, B. F. et al.
Partner: UNT Libraries Government Documents Department

Los Alamos science, Number 14

Description: Nine authored articles are included covering: natural heat engine, photoconductivity, the Caribbean Basin, energy in Central America, peat, geothermal energy, and the MANIAC computer. Separate abstracts were prepared for the articles. (DLC)
Date: January 1, 1986
Partner: UNT Libraries Government Documents Department

M51's spiral structure

Description: The M51 system (NGC 5194/5195) provides an excellent problem both in spiral structure and in galaxy interactions. We present an analytic study of a computer experiment on the excitation mechanisms for M51's spiral arms and whether or not a halo is important for these mechanisms. This work extends previous numerical studies of the M51 system by including self-gravitation in a two component disk: gas' and stars', and a dark halo. The analytic study provides two new observational constraints: the time ({approx}70-84 million years ago) and position angle of perigalacticon (300{degree}). By using these constraints and a simple conic approximation, the search for the companion's possible orbit is greatly simplified. This requires fewer N-body simulations than a fully self-gravitating orbit search. 8 refs., 4 figs.
Date: January 1, 1989
Creator: Howard, S. (Los Alamos National Lab., NM (USA)) & Byrd, G.G. (Alabama Univ., University, AL (USA))
Partner: UNT Libraries Government Documents Department

Multi-wavelength observations of novae in outburst

Description: This review serves as the introduction to the observational studies of novae and I will mention a number of results that will be emphasized by other reviewers. Therefore, I will try to provide the physical framework for multi-wavelength observations as applied to studies of novae. I divide the outburst into phases based on the physical effects that are occurring at that time. The first phase is the rise to bolometric maximum and occurs on a convective time scale. The second phase is the rise to visual maximum and occurs on the time scale for the envelope to expand to {approximately}10{sup 12}cm. The third phase is the time when the nova is emitting at constant bolometric luminosity, but declining optical magnitude, and it lasts until most of the accreted material has been either exhausted or eroded from the surface of the white dwarf. The fourth and final phase is the return is the return to quiescence (turn-off phase) and it occurs at the time that nuclear burning is ending. I will discuss each of these phases in turn and end with a discussion. 36 refs.
Date: January 1, 1989
Creator: Starrfield, S. (Los Alamos National Lab., NM (USA) Arizona State Univ., Tempe, AZ (USA). Dept. of Physics and Astronomy)
Partner: UNT Libraries Government Documents Department

Droplet shattering, vaporization and recondensation in cloud clearing with long pulse infrared chemical lasers

Description: Results of experimental attempts to produce an optically clear channel in a water cloud by evaporating the cloud droplets with a CO{sub 2} laser are presented. Using scattered light it is possible to visualize the clear channel produced. Measurements of the fraction of power transmitted through the channel at visible wavelengths give insight into the clearing mechanisms. The present data suggest that the water droplets explode in the process of clearing. A theoretical explanation of why this should occur is presented and predictions of the onset of droplet explosions are made. 4 refs., 5 figs.
Date: January 1, 1990
Creator: Caramana, E.J.; Kindel, J.L.; Morse, R.L.; Quigley, G.P.; Webster, R.B. & York, G.W.
Partner: UNT Libraries Government Documents Department

Toda lattice with transverse degree of freedom

Description: A transverse degree of freedom is introduced in the Toda lattice. The corresponding continuum approximations are discussed. 9 refs.
Date: January 1, 1989
Creator: Christiansen, P.L. (Los Alamos National Lab., NM (USA) Naples Univ. (Italy)); Lomdahl, P.S. & Muto, V. (Los Alamos National Lab., NM (USA))
Partner: UNT Libraries Government Documents Department