Intense, pulsed beams of low-energy positrons have been produced by a high-energy beam from an electron linac. The production efficiency for low-energy positrons has been determined for electrons with 60 to 120 MeV energy, low-energy positron beams from a linac can be of much higher intensity than those beams currently derived from radioactive sources.

Changes in the structure of (Mo /sub 6/Ru /sub 4/)/sub x/B/sub 1-x/ amorphous alloys were observed in positron annihilation analysis using both positron lifetime and Doppler broadening techniques. The changes were introduced into the alloy either by varying the boron fraction or by neutron irradiation. Similar results were observed both in the irradiated alloys and those with vacant boron sites. The positron annihilation data suggest that the modified structure contains regions of open volume and that the positrons interact with those regions.

This paper mathematically defines protocol translation which is a function employed to interconnect different computer networks. An example of an application is a gateway.

Annealed molybdenum was irradiated at room temperature by energetic protons or neutrons and the fluence and recoil energy dependence of two traps was measured. Comparison of trapping rates with calculations of damage energy correlates high energy recoils with the short lifetime trap and low energy recoils with the longer lifetime.

Compositional data are represented as vector variables with individual vector components ranging between zero and a positive maximum value representing a constant sum constraint, usually unity (or 100 percent). The earth sciences are flooded with spatial distributions of compositional data, such as concentrations of major ion constituents in natural waters (e.g. mole, mass, or volume fractions), mineral percentages, ore grades, or proportions of mutually exclusive categories (e.g. a water-oil-rock system). While geostatistical techniques have become popular in earth science applications since the 1970s, very little attention has been paid to the unique mathematical properties of geostatistical formulations involving compositional variables. The book 'Geostatistical Analysis of Compositional Data' by Vera Pawlowsky-Glahn and Ricardo Olea (Oxford University Press, 2004), unlike any previous book on geostatistics, directly confronts the mathematical difficulties inherent to applying geostatistics to compositional variables. The book righteously justifies itself with prodigious referencing to previous work addressing nonsensical ranges of estimated values and error, spurious correlation, and singular cross-covariance matrices.

In the context of eternal inflation we discuss the fate of Lambda = 0 bubbles when they collide with Lambda< 0 crunching bubbles. When the Lambda = 0 bubble is supersymmetric, it is not completely destroyed by collisions. If the domain wall separating the bubbles has higher tension than the BPS bound, it is expelled from the Lambda = 0 bubble and does not alter its long time behavior. If the domain wall saturates the BPS bound, then it stays inside the Lambda = 0 bubble and removes a finite fraction of future infinity. In this case, the crunch singularity is hidden behind the horizon of a stable hyperbolic black hole.

The evaporation rate of D{sub 2}O has been determined by Raman thermometry of a droplet train (12-15 {micro}m diameter) injected into vacuum ({approx}10{sup -5} torr). The cooling rate measured as a function of time in vacuum was fit to a model that accounts for temperature gradients between the surface and the core of the droplets, yielding an evaporation coefficient ({gamma}{sub e}) of 0.57 {+-} 0.06. This is nearly identical to that found for H{sub 2}O (0.62 {+-} 0.09) using the same experimental method and model, and indicates the existence of a kinetic barrier to evaporation. The application of a recently developed transition state theory (TST) model suggests that the kinetic barrier is due to librational and hindered translational motions at the liquid surface, and that the lack of an isotope effect is due to competing energetic and entropic factors. The implications of these results for cloud and aerosol particles in the atmosphere are discussed.

None

We investigate the climate forcing from and response to projected changes in short-lived species and methane under the A1B scenario from 2000-2050 in the GISS climate model. We present a meta-analysis of new simulations of the full evolution of gas and aerosol species and other existing experiments with variations of the same model. The comparison highlights the importance of several physical processes in determining radiative forcing, especially the effect of climate change on stratosphere-troposphere exchange, heterogeneous sulfate-nitrate-dust chemistry, and changes in methane oxidation and natural emissions. However, the impact of these fairly uncertain physical effects is substantially less than the difference between alternative emission scenarios for all short-lived species. The net global mean annual average direct radiative forcing from the short-lived species is .02 W/m{sup 2} or less in our projections, as substantial positive ozone forcing is largely offset by negative aerosol direct forcing. Since aerosol reductions also lead to a reduced indirect effect, the global mean surface temperature warms by {approx}0.07 C by 2030 and {approx}0.13 C by 2050, adding 19% and 17%, respectively, to the warming induced by long-lived greenhouse gases. Regional direct forcings are large, up to 3.8 W/m{sup 2}. The ensemble-mean climate response shows little regional …

Direct laser heating of molecular N2 to above 1400 K at 120-130 GPa results in the formation of a reddish amorphous phase and a transparent crystalline solid above 2000 K. Raman and x-ray data confirm that the transparent phase is cubic-gauche nitrogen (cg-N), while the reddish color of the amorphous phase might indicate the presence of N=N dish bonds. The quenched amorphous phase is stable down to at least 70GPa, analogous to cg-N, and could be a new non-molecular phase or an extension of the already known {eta}-phase. A chemo-physical phase diagram is presented which emphasizes the difference between pressure- and temperature-induced transitions from molecular to non-molecular solids, as found in other low Z systems.

We study the energy dependence of the transverse momentum (pT) spectra for charged pions, protons and anti-protons for Au+Au collisions at sqrt sNN = 62.4 and 200 GeV. Data are presented at mid-rapidity (lbar y rbar< 0.5) for 0.2< pT< 12 GeV/c. In the intermediate pT region (2< pT< 6 GeV/c), the nuclear modification factor is higher at 62.4 GeV than at 200 GeV, while at higher pT (pT> 7 GeV/c) the modification is similar for both energies. The p/pi+ and pbar/pi- ratios for central collisions at sqrt sNN = 62.4 GeV peak at pT _~;; 2 GeV/c. In the pT range where recombination is expected to dominate, the p/pi+ ratios at 62.4 GeV are larger than at 200 GeV, while the pbar/pi- ratios are smaller. For pT> 2 GeV/c, the pbar/pi- ratios at the two beam energies are independent of pT and centrality indicating that the dependence of the pbar/pi- ratio on pT does not change between 62.4 and 200 GeV. These findings challenge various models incorporating jet quenching and/or constituent quark coalescence.

We develop a new ab initio many-body approach capable of describing simultaneously both bound and scattering states in light nuclei, by combining the resonating-group method with the use of realistic interactions, and a microscopic and consistent description of the nucleon clusters. This approach preserves translational symmetry and Pauli principle. We present phase shifts for neutron scattering on {sup 3}H, {sup 4}He and {sup 10}Be and proton scattering on {sup 3,4}He, using realistic nucleon-nucleon potentials. Our A = 4 scattering results are compared to earlier ab initio calculations. We demonstrate that a proper treatment of the coupling to the n-{sup 10}Be continuum is essential to explain the parity-inverted ground state in {sup 11}Be.

Low energy theorems are derived for scattering of longitudinally polarized W and Z's, providing the basis for an estimate of the observable signal if electroweak symmetry breaking is due to new physics at the TeV scale. A pp collider with L, {radical}s {equals} 40 TeV, 10{sup 33}cm. {sup {minus}2}s{sup {minus}1} is just sufficient to observe the signal while pp colliders with 40, 10{sup 32} or 20, 10{sup 33} are not. A collider that is sensitive to the TeV-scale signal provides valuable information about symmetry breaking whether the masses of the associated new particles are below, within, or above the 1-2 TeV region. 6 refs., 6 figs., 2 tabs.

The major reported work on joining uranium comes from the USA, Great Britain, France and the USSR. The driving force for producing this technology base stems from the uses of uranium as a nuclear fuel for energy production, compact structures requiring high density, projectiles, radiation shielding, and nuclear weapons. This review examines the state-of-the-art of this technology and presents current welding process and parameter information. The welding metallurgy of uranium and the influence of microstructure on mechanical properties is developed for a number of the more commonly used welding processes.

An overview is presented of the LLNL High-Field Superconducting Magnet Development Program wherein the technology is being developed for producing fields in the range of 15 T and higher for both mirror and tokamak applications. Applications requiring less field will also benefit from this program. In addition, recent results on the thermomechanical performance of cable-in-conduit conductor systems are presented and their importance to high-field coil design discussed.

Grazing incidence mirrors used to focus synchrotron radiation beams through small distant apertures have severe optical requirements. The surface distortion due to heat loading of the first mirror in a bending magnet beam line is of particular concern when a large fraction of the incident beam is absorbed. In this paper we discuss mirror design considerations involved in minimizing the thermal/mechanical loading on vertically deflecting first surface mirrors required for SPEAR synchrotron radiation beam lines. Topics include selection of mirror material and cooling method, the choice of SiC for the substrate, optimization of the thickness, and the design of the mirror holder and cooling mechanism. Results obtained using two-dimensional, finite-element thermal/mechanical distortion analysis are presented for the case of a 6/sup 0/ grazing incidence SiC mirror absorbing up to 260 W at Beam Line VIII on the SPEAR ring. Test descriptions and results are given for the material used to thermally couple this SiC mirror to a water-cooled block. The interface material is limited to applications for which the equivalent normal heat load is less than 20 W/cm/sup 2/.

In contrast to failure approaches at the lamina level or the micromechanics level the present work concerns failure characterization at the laminate level. Specifically, attention is given to the ultimate failure characterization for quasi-isotropic laminates. This is in further contrast to the commonly used approaches for initial damage or progressive damage. It is shown that the analytical failure forms decompose into two modes, one for out of plane, delamination type failure and one for in plane, fiber controlled type failure. The work here is mainly given over to the delamination mode of failure. Experimental results are presented for laminates in this mode of failure. These results are then integrated with the analytical forms to give a simple criterion for delamination failure.

The usual approach to deal with noise present in many real-world optimization problems is to take an arbitrary number of samples of the objective function and use the sample average as an estimate of the true objective value. The number of samples is typically chosen arbitrarily and remains constant for the entire optimization process. This paper studies an adaptive sampling technique that varies the number of samples based on the uncertainty of deciding between two individuals. Experiments demonstrate the effect of adaptive sampling on the final solution quality reached by a genetic algorithm and the computational cost required to find the solution. The results suggest that the adaptive technique can effectively eliminate the need to set the sample size a priori, but in many cases it requires high computational costs.

QR and LU factorizations for dense matrices are important linear algebra computations that are widely used in scientific applications. To efficiently perform these computations on modern computers, the factorization algorithms need to be blocked when operating on large matrices to effectively exploit the deep cache hierarchy prevalent in today's computer memory systems. Because both QR (based on Householder transformations) and LU factorization algorithms contain complex loop structures, few compilers can fully automate the blocking of these algorithms. Though linear algebra libraries such as LAPACK provides manually blocked implementations of these algorithms, by automatically generating blocked versions of the computations, more benefit can be gained such as automatic adaptation of different blocking strategies. This paper demonstrates how to apply an aggressive loop transformation technique, dependence hoisting, to produce efficient blockings for both QR and LU with partial pivoting. We present different blocking strategies that can be generated by our optimizer and compare the performance of auto-blocked versions with manually tuned versions in LAPACK, both using reference BLAS, ATLAS BLAS and native BLAS specially tuned for the underlying machine architectures.

Nestled in a valley between the whitecaps of the Pacific and the snowcapped crests of the Sierra Nevada, Lawrence Livermore National Laboratory (LLNL) is home to the nearly complete National Ignition Facility (NIF). The purpose of NIF is to create a miniature star-on demand. An enormous amount of laser light energy (1.8 MJ in a pulse that is 20 ns in duration) will be focused into a small gold cylinder approximately the size of a pencil eraser. Centered in the gold cylinder (or hohlraum) will be a nearly perfect sphere filled with a complex mixture of hydrogen gas isotopes that is similar to the atmosphere of our Sun. During experiments, the laser light will hit the inside of the gold cylinder, heating the metal until it emits X-rays (similar to how your electric stove coil emits visible red light when heated). The X-rays will be used to compress the hydrogen-like gas with such pressure that the gas atoms will combine or 'fuse' together, producing the next heavier element (helium) and releasing energy in the form of energetic particles. 2010 will mark the first credible attempt at this world-changing event: the achievement of fusion energy 'break-even' on Earth using NIF, the …

X-ray FELs demand that the positions of undulator components be stable to less than 1 {mu}m per day. Simultaneously, the undulator length increases significantly in order to saturate at x-ray wavelengths. To minimize the impact of the outside environment, the Linac Coherent Light Source (LCLS) undulator is placed underground, but reliable data about ground motion inside such a tunnel was not available in the required stability range during the planning phase. Therefore, a new position monitor system had been developed and installed with the LCLS undulator. This system is capable of measuring x, y, roll, pitch and yaw of each of the 33 undulator quadrupoles with respect to stretched wires. Instrument resolution is about 10 nm and instrument drift is negligible. Position data of individual quadrupoles can be correlated along the entire 132-m long undulator. The system has been under continuous operation since 2009. This report describes long term experiences with the running system and the observed positional stability of the undulator quadrupoles.

Solid-state thermal neutron detectors are desired to replace {sup 3}He tube based technology for the detection of special nuclear materials. {sup 3}He tubes have some issues with stability, sensitivity to microphonics and very recently, a shortage of {sup 3}He. There are numerous solid-state approaches being investigated that utilize various architectures and material combinations. By using the combination of high-aspect-ratio silicon PIN pillars, which are 2 {micro}m wide with a 2 {micro}m separation, arranged in a square matrix, and surrounded by {sup 10}B, the neutron converter material, a high efficiency thermal neutron detector is possible. Besides intrinsic neutron detection efficiency, neutron to gamma discrimination is an important figure of merit for unambiguous signal identification. In this work, theoretical calculations and experimental measurements are conducted to determine the effect of structure design of pillar structured thermal neutron detectors including: intrinsic layer thickness, pillar height, substrate doping and incident gamma energy on neutron to gamma discrimination.

This talk deals with {Lambda}, K{sub s}{sup 0} and {bar {Lambda}} production with 14.5 GeV/c Silicon beams. Why study {Lambda}{sup 0} production Because the study of strangeness is an important part of the search for Quark Gluon Plasma (QGP). Many models predict an enhancement of strangeness in a QGP as compared to the amount of strangeness produced in a superposition of nucleon-nucleon interactions. The amount of enhancement varies from model to model. Even if no QGP is detected at AGS energies using Si beams, it is important to understand the production mechanisms in quantitative detail so that standard nucleon-nucleon production mechanism can be distinguished from QGP formation. The advantage of measuring strangeness production by measuring V{sup 0} production is that V{sup 0}'s can be identified by kinematics without the use of any special particle ID detectors. The disadvantage is that usually large aperture detectors are required. Experiment 810 has the needed large aperture. This talk describes the technique and results of V{sup 0} production from {approximately}9000 interactions of Si in a 1 mil (25 micron) Au target recorded in June 1989. 13 figs., 1 tab.

Although they are but a small fraction of the mass ejected in core-collapse supernovae, neutrino-driven winds (NDWs) from nascent proto-neutron stars (PNSs) have the potential to contribute significantly to supernova nucleosynthesis. In previous works, the NDW has been implicated as a possible source of r-process and light p-process isotopes. In this paper we present time-dependent hydrodynamic calculations of nucleosynthesis in the NDW which include accurate weak interaction physics coupled to a full nuclear reaction network. Using two published models of PNS neutrino luminosities, we predict the contribution of the NDW to the integrated nucleosynthetic yield of the entire supernova. For the neutrino luminosity histories considered, no true r-process occurs in the most basic scenario. The wind driven from an older 1.4M{sub {circle_dot}} model for a PNS is moderately neutron-rich at late times however, and produces {sup 87}Rb, {sup 88}Sr, {sup 89}Y, and {sup 90}Zr in near solar proportions relative to oxygen. The wind from a more recently studied 1.27M{sub {circle_dot}} PNS is proton-rich throughout its entire evolution and does not contribute significantly to the abundance of any element. It thus seems very unlikely that the simplest model of the NDW can produce the r-process. At most, it contributes to the …