Circular Dichroism of RbHe and RbN2_2 Molecules

We present measurements of the circular dichroism of optically pumped Rb vapor near the D1 resonance line. Collisions with the buffer gases $^3$He and N$_2$ reduce the transparency of the vapor, even when fully polarized. We use two methods to measure this effect, show that the He results can be understood from RbHe potential curves, and show how this effect conspires with the spectral profile of the optical pumping light to increase the laser power demands for optical pumping of very optically thick samples

Effects of Nitrogen Quenching Gas on Spin-Exchange Optical Pumping of He-3

We consider the degree of conservation of nuclear spin polarization in the process of optical pumping under typical spin-exchange optical pumping conditions. Previous analyses have assumed that negligible nuclear spin precession occurs in the brief periods of time the alkali-metal atoms are in the excited state after absorbing photons and before undergoing quenching collisions with nitrogen molecules. We include excited-state hyperfine interactions, electronic spin relaxation in collisions with He and N_2, spontaneous emission, quenching collisions, and a simplified treatment of radiation trapping

Extracting Electric Polarizabilities from Lattice QCD

Charged and neutral, pion and kaon electric polarizabilities are extracted from lattice QCD using an ensemble of anisotropic gauge configurations with dynamical clover fermions. We utilize classical background fields to access the polarizabilities from two-point correlation functions. Uniform background fields are achieved by quantizing the electric field strength with the proper treatment of boundary flux. These external fields, however, are implemented only in the valence quark sector. A novel method to extract charge particle polarizabilities is successfully demonstrated for the first time.Comment: 17 pages, 6 figures, a few clarifications added, published versio

Modelling self-piercing riveted joint failures in automotive crash structures

This paper describes a new model and method to predict Self-Piercing Riveted (SPR) joint interlock failures in aluminium sheet at crash speeds using explicit finite element simulation. SPR interlock failure is dependent on rivet direction, which is included in the model. A mesh independent approach is adopted for connection model which is capable of industrial application at the full vehicle crash analysis level. The paper provides an overview of the approach to validate connection model; typically by developing detailed physics based models of various joint configurations supported with high speed experimental data, through to model capable of industrial application. The framework to validate connection model for use in crash simulation tools is expected to have broader applicatio

Validating dynamic tensile mechanical properties of sheet steels for automotive crash applications

A thin-wall open channel beam, fabricated from high strength Dual Phase sheet steel, subjected to 3-point bending and constant velocity boundary condition, is investigated to validate material performance for automotive crash applications. Specifically quantitative validation of material tensile data determined from high speed tests and component models, and qualitative validation of materials resistance to fracture. The open channel beam is subjected to quasi-static and increasing loading speed and in all cases, large displacement in which deformation involves formation of a plastic hinge. This paper describes development of test procedure, notably beam specimen design, measurement system and boundary conditions, using both experimental and numerical techniques. The new test procedure, as a compliment to crush testing, will increase confidence in the modeling and application of new advanced higher strength materials in automotive crash structure

Development and characterization of Powder Metallurgy (PM) 2XXX series Al alloy products and Metal Matrix Composite (MMC) 2XXX Al/SiC materials for high temperature aircraft structural applications

The results of a series of material studies performed by the Lockheed Aeronautical Systems Company over the time period from 1980 to 1991 are discussed. The technical objective of these evaluations was to develop and characterize advanced aluminum alloy materials with temperature capabilities extending to 350 F. An overview is given of the first five alloy development efforts under this contract. Prior work conducted during the first five modifications of the alloy development program are listed. Recent developments based on the addition of high Zr levels to an optimum Al-Cu-Mg alloy composition by powder metallurgy processing are discussed. Both reinforced and SiC or B4C ceramic reinforced alloys were explored to achieve specific target goals for high temperature aluminum alloy applications