Article discussing research on the response of carbon nanotubes to a tensile load.

Advanced radiographic systems for stockpile stewardship require very small x-ray sources to achieve the required resolution. Focusing multi-kiloampere beams to diameters on the order of 1 mm onto a Bremsstrahlung target leads to the generation of axial electric fields on the order of several MV/cm which act to extract ions out of the surface plasma and accelerate them upstream into the beam. These backstreaming ions act as a distributed electrostatic lens which can perturb the focus of the electron beam in a time varying manner during the pulse. An analytic model of the ion extraction is presented for a particular target geometry along with scaling laws for the perturbation of the focal spot.

Mixed dark matter scenario can reconcile the COBE data and the observed large scale structure. So far the massive neutrino with a mass of a few eV has been the only discussed candidate for the hot dark matter component. We point out that the hadronic axion in the so-called hadronic axion window, f{sub a} {approx} 10{sup 6} GeV, is a perfect candidate as hot dark matter within the mixed dark matter scenario. The current limits on the hadronic axion are summarized. The most promising methods to verify the hadronic axion in this window are the resonant absorption of almost-monochromatic solar axions from M1 transition of the thermally excited {sup 57}Fe in the Sun, and the observation of the ''axion burst'' in water Cerenkov detectors from another supernova.

We have extracted polarized nucleon distributions from recent data at CERN, SLAC and DESY. The flavor-dependent valence and sea quark spin distributions are determined for each experiment. We take into account possible differences in the up and down sea distributions, and assume that the strange sea contribution is suppressed by mass effects. Physics results determined from different experiments are compared, including higher order corrections.

Quantum Monte Carlo calculations of ground and low-lying excited states for nuclei with A {le} 8 are made using a realistic Hamiltonian that fits NN scattering data. Results for more than 40 different (J{pi}, T) states, plus isobaric analogs, are obtained and the known excitation spectra are reproduced reasonably well. Various density and momentum distributions and electromagnetic form factors and moments have also been computed. These are the first microscopic calculations that directly produce nuclear shell structure from realistic NN interactions.

The (La{sub 1{minus}} x Sr{sub x}){sub 3}Mn{sub 2}O{sub 7} compounds are layered materials that exhibit higher magneto-resistance than the corresponding 3D manganite perovskites. Quasi-elastic neutron scattering on a polycrystalline sample of La{sub 1.4}Sr{sub 1.6}Mn{sub 2}O{sub 7} shows that the spin fluctuation spectrum of the these layered CMR materials is qualitatively similar to those found in the perovskite manganites (La,Ca)MnO{sub 3}; their concentration, lifetime, and coherence length increase as T decreases to T{sub c}. Unlike the perovskites we find a lower spin-diffusion constant above T{sub c} of {approximately}5 meV {angstrom}{sup 2}.

We introduce a novel type of spectrometer that provides a {micro}eV bandpass together with a tunability over a few meV. The technique relies on nuclear resonant scattering (Moessbauer effect) of synchrotrons radiation at the 14.4-keV resonance of {sup 57}Fe. Energy tuning is achieved by the Doppler effect in high speed rotary motion. The resonantly scattered monochromatic radiation is extracted by a polarization filtering technique or by spatial separation due to the ''nuclear lighthouse effect''.

Single ion impacts have been observed using in-situ transmission electron microscopy during irradiation. In addition to internal defects, single-ion impacts create surface craters as large as 12 nm on In, Ag, Pb and Au. Crater formation rates have been determined from video recordings with a time-resolution of 33 milliseconds. The cratering rate for Xe ions increases linearly with increasing target mass density above a threshold density of approximately 7 gm/cm{sup 3}. The cratering rate increases as the ion mass is increased. These results suggest that cratering requires a high energy-density, near-surface displacement cascade. TRIM calculations have been made in an effort to establish a near-surface energy-density criterion for cratering.

This paper addresses the statistical uncertainty of loads prediction using structural dynamics simulation codes and the requirements for the number and duration of simulations for obtaining robust load estimates.

Article on the solubility of anthracene in binary alkane + 2-ethyl-1-hexanol and alkane + 1-pentanol solvent mixtures at 298.2 K.

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We consider a simple model, based on currently accepted models for active galactic nuclei, for a quasi-stellar object (QSO or "quasar") and examine the influence that correlation-induced spectral changes ("The Wolf Effect") may have upon the redshifts of the optical emission lines.

A quantitative model is under development to assess the safety and efficiency of commercial aircraft operations under the Free Flight Program proposed for air traffic control for the US National Airspace System. The major objective of the Free Flight Program is to accommodate the dramatic growth anticipated in air traffic in the US. However, the potential impacts upon aircraft safety from implementing the Program have not been fully explored and evaluated. The model is directed at assessing aircraft operations at high altitude over the continental US airspace since this action is the initial step for Free Flight. Sequential steps with analysis, assessment, evaluation, and iteration will be required to satisfactorily accomplish the complete transition of US commercial aircraft traffic operations.

Beamlet measurements show that cone pinholes outperform other types tested with regard to both closure and back reflections. A ±150 µrad stainless steel cone remained open for a 15.5 kJ, 10:1 contrast shaped pulse with ±7.5 µrad of SSD divergence, which more than meets the requirements for a NIF ignition pulse. Measurements also showed the maximum tolerable pressures in the NIF spatial filters to be a few milliTorr, leading to recommendations of 0.1 and 0.6 mTorr for the NIF transport and cavity spatial filters, respectively.

The National Ignition Facility (NIF) is a 1.8 MJ (at 351 nm), 192 beam laser facility being built at the Lawrence Livermore National Laboratory (LLNL) to achieve inertial fusion ignition in the laboratory. The NIF Project is being designed and built by a team from LLNL, Los Alamos National Laboratory, Sandia National Laboratory, and the University of Rochester. When completed in 2003, it will be a multipurpose facility that will be used for many applications in national security, energy, and the basic sciences. In addition to the National Security Mission, these applications include, for example, electric power generation, space propulsion, and study of basic astrophysical phenomena in the laboratory. Such applications receive benefit both through the state- of-the-art technology developments necessary to build NIF and through specific experiments that will be performed on NIF.

The MACHO Project is a microlensing survey that monitors the brightnesses of -60 million stars in the Large Magellanic Cloud (LMC), Small Magellanic Cloud, and Galactic bulge. The database presently contains more photometric measurements than previously recorded in the history of astronomy. We describe the calibration of the MACHO two-color photometry and transformation to the standard Kron-Cousins V and R system. This allows for proper comparison with all other observations on the Kron-Cousins standard system. The highest precision calibrations are for -9 million stars in the LMC bar. For these stars, independent photometric measurements in field-overlap regions indicate standard deviations {sigma}{sub V} = {sigma}{sub R} = 0.020 mag. Calibrated MACHO photometry data are compared with published photometric sequences and with new Hubble Space Telescope observations. We additionally describe the first application of these calibrated data: the construction of the �efficiency� color-magnitude diagram which will be used to calculate our experimental sensitivity for detecting microlensing in the LMC.

The DOD uses the plastic bonded explosive (PBX) LX-14 in a wide variety of applications including shaped charges and explosively forged projectiles. LX- 19 is a higher energy explosive, which could be easily substituted for LX-14 because it contains the identical Estane 5703p binder and more energetic CL-20 explosive. Delivery systems for large shaped charges, such as TOW-2, include the Apache helicopter. Loads associated with vibrations and expansion from thermal excursions in field operations may, even at low levels over long time periods, cause flaws, already present in the PBX to grow. Flaws near the explosive/liner interface of a shaped charge can reduce performance. Small flaws in explosives are one mechanism (the hot spot mechanism) proposed for initiation and growth to detonation of PBXs like LX-14, PBXN 5, LX-04 and LX-17 among others. Unlike cast-cured explosives and propellants, PBXs cannot usually be compression molded to full density. Generally, the amount of explosive ignited by a shock wave is approximately equal to the original void volume. Whether or not these flaws or cracks grow during field operations to an extent sufficient to adversely affect the shaped charge performance or increase the vulnerability of the PBX is the ultimate question this effort …

A simple model is described for predicting the time evolution of the half-width h of a planar mixing layer between two immiscible incompressible fluids driven by an arbitrary time-dependent variable acceleration history <i>a(l)</i>a (t): The model is based on a heuristic expression for the kinetic energy per unit area of the mixing layer. This expression is based on that for the kinetic energy of a linearly perturbed interface, but with a dynamically renormalized wavelength which becomes proportional to h in the nonlinear regime. An equation of motion for h is then derived by means of Lagrange�s equations. This model reproduces the known linear growth rates of the Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities, as well as the quadratic RT and power-law RM growth laws in the nonlinear regime. The time exponent in the RM power law depends on the rate of kinetic energy dissipation. In the case of zero dissipation, this exponent reduces to 2/3 in agreement with elementary scaling arguments. A conservative numerical scheme is proposed to solve the model equations, and is used to perform calculations that agree well with published mixing data from linear electric motor experiments. Considerations involved in implementing the model in hydrodynamics codes are …

A phase-field model for grain growth is briefly described. In this model, a poly-crystalline microstructure is represented by multiple structural order parameter fields whose temporal and spatial evolutions follow the time-dependent Ginzburg-Landau (TDGL) equations. Results from phase-field simulations of two-dimensional (2D) grain growth will be summarized and preliminary results on three-dimensional (3D) grain growth will be presented. The physical interpretation of the structural order parameter fields and the efficient and accurate semi-implicit Fourier spectral method for solving the TDGL equations will be briefly discussed.

We have started a search for High Redshift Radio Galaxies (HzRGs) in an area covering 7 sr by selecting a sample of Ultra Steep Spectrum (USS) sources with a low flux density cut-off S{sub 1400} > 10 mJy and a steep spectral index {alpha} < -1 3 (S {alpha} {nu}{sup {alpha}}) using the WENSS, NVSS and TEXAS radio suveys. Preliminary results for 25 sources shows that we are almost twice as effective in finding HzRGs than previous searches using brighter radio sources and less steep radio spectra ({alpha} < -1 0) The redshift distribution is consistent with an extension of the z - {alpha} relation to {alpha} < -1 3, but a large fraction of our sample (40%) consists of objects which are too faint to observe with 3-4m class telescopes The first results from our Keck K- band imaging and spectroscopy program indicate that these faint objects are our best candidates to detect HzRGs at z > 3 5 Our search is aired at significantly increasing the number of very high redshift radio galaxies for further detailed studies of the formation and evolution of massive galaxies and their environment

We present the energy, propagation, and thermal modeling for a diode-pumped solid-state laser called Mercury being designed and built at LLNL using Yb:S-FAP [i.e., Yb{sup 3+}-doped Sr{sub 5}(PO{sub 4}){sub 3}F crystals] for the gain medium. This laser is intended to produce 100 J pulses at 1 to 10 ns at 10 Hz with an electrical efficiency of {approximately}10%. Our modeling indicates that the laser will be able to meet its performance goals.

High density plasma etching of GaAs, GaSb and AIGaAs was performed in IC1/Ar and lBr/Ar chemistries using an Inductively Coupled Plasma (ICP) source. GaSb and AlGaAs showed maxima in their etch rates for both plasma chemistries as a function of interhalogen percentage, while GaAs showed increased etch rates with plasma composition in both chemistries. Etch rates of all materials increased substantially with increasing rf chuck power, but rapidly decreased with chamber pressure. Selectivities > 10 for GaAs and GaSb over AlGaAs were obtained in both chemistries. The etched surfaces of GaAs showed smooth morphology, which were somewhat better with IC1/Ar than with IBr/& discharge. Auger Electron Spectroscopy analysis revealed equi-rate of removal of group III and V components or the corresponding etch products, maintaining the stoichiometry of the etched surface.