A Basis for Traceable NDE Standards

The National Bureau of Standards (NBS) is beginning to provide a mechanism for traceability for a number of NDE measurement procedures, an activity that is expected to have a significant, positive impact on the reproducibility and accuracy of NDE measurements. Much of the NDE standards activity has been in ultrasonics and acoustic emission, this effort leading to calibration services for ultrasonic reference blocks and ultrasonic and acoustic emission transducers. Additional NDE standards are also available or are being developed in radiography, eddy currents, magnetic particles, liquid penetrants and visual testing

Risky decision making : testing for violations of transitivity predicted by an editing mechanism

Transitivity is the assumption that if a person prefers A to B and B to C, then that person should prefer A to C. This article explores a paradigm in which Birnbaum, Patton and Lott (1999) thought people might be systematically intransitive. Many undergraduates choose C = ($96, .85;$90, .05; $12, .10) over A = ($96, .9; $14, .05;$12, .05), violating dominance. Perhaps people would detect dominance in simpler choices, such as A versus B = ($96, .9;$12, .10) and B versus C, and yet continue to violate it in the choice between A and C, which would violate transitivity. In this study we apply a true and error model to test intransitive preferences predicted by a partially effective editing mechanism. The results replicated previous findings quite well; however, the true and error model indicated that very few, if any, participants exhibited true intransitive preferences. In addition, violations of stochastic dominance showed a strong and systematic decrease in prevalence over time and viola

Availability of soil mutualists may not limit non‐native Acacia invasion but could increase their impact on native soil communities

The availability of compatible mutualistic soil microbes could influence the invasion success of non-native plant species. Specifically, there may be spatial variation in the distribution of compatible microbes, and species-specific variation in plant host ability to associate with available microbes. Although either or both factors could promote or limit invasion, the scale over which most studies are conducted makes it difficult to examine these two possibilities simultaneously. However, this is critical to identifying a role of soil microbes in invasion. A series of recent research projects focused on interactions between Australian Acacia and nitrogen-fixing bacteria (rhizobia) at multiple spatial scales, from the local to the inter-continental, has allowed us to evaluate this question. Collectively, this research reveals that nodulation, performance and rhizobial community composition are all broadly similar across spatial scales and differentially invasive species. Synthesis and applications. We argue that current research provides convincing evidence that interactions with rhizobia do not determine invasion success in Acacia, but instead highlights key knowledge gaps that remain unfilled. Importantly, the ease with which non-native Acacia species form mutualistic associations with rhizobia, regardless of invasive status, highlights the critical need to understand the impacts of all non-native Acacia on native soil communities

Energetics of hydrogen impurities in aluminum and their effect on mechanical properties

The effects of hydrogen impurities in the bulk and on the surface of aluminum are theoretically investigated. Within the framework of density functional theory, we have obtained the dependence on H concentration of the stacking fault energy, the cleavage energy, the Al/H surface energy and the Al/H/Al interface formation energy. The results indicate a strong dependence of the slip energy barrier in the $[\bar 211]$ direction the cleavage energy in the [111] direction and the Al/H/Al interface formation energy, on H concentration and on tension. The dependence of the Al/H surface energy on H coverage is less pronounced, while the optimal H coverage is $\leq 0.25$ monolayer. The calculated activation energy for diffusion between high symmetry sites in the bulk and on the surface is practically the same, 0.167 eV. From these results, we draw conclusions about the possible effect of H impurities on mechanical properties, and in particular on their role in embrittlement of Al.Comment: 9 pages, 5 figure

Strategies for Real-Time Position Control of a Single Atom in Cavity QED

Recent realizations of single-atom trapping and tracking in cavity QED open the door for feedback schemes which actively stabilize the motion of a single atom in real time. We present feedback algorithms for cooling the radial component of motion for a single atom trapped by strong coupling to single-photon fields in an optical cavity. Performance of various algorithms is studied through simulations of single-atom trajectories, with full dynamical and measurement noise included. Closed loop feedback algorithms compare favorably to open-loop "switching" analogs, demonstrating the importance of applying actual position information in real time. The high optical information rate in current experiments enables real-time tracking that approaches the standard quantum limit for broadband position measurements, suggesting that realistic active feedback schemes may reach a regime where measurement backaction appreciably alters the motional dynamics.Comment: 12 pages, 10 figures, submitted to J. Opt. B Quant. Semiclass. Op

Hydrogen-enhanced local plasticity in aluminum: an ab initio study

Dislocation core properties of Al with and without H impurities are studied using the Peierls-Nabarro model with parameters determined by ab initio calculations. We find that H not only facilitates dislocation emission from the crack tip but also enhances dislocation mobility dramatically, leading to macroscopically softening and thinning of the material ahead of the crack tip. We observe strong binding between H and dislocation cores, with the binding energy depending on dislocation character. This dependence can directly affect the mechanical properties of Al by inhibiting dislocation cross-slip and developing slip planarity.Comment: 4 pages, 3 figure