Effect of radial-electric-field polarity on wire-array Z-pinch dynamics

The formation of plasma in wire-array Z-pinch experiments was found to depend upon the polarity of the radial-electric field near the wires. Reversing the radial-electric field midway along the length of an array resulted in the ablation rate of one-half of the array being reduced by 50%, significantly delaying the start of its implosion and altering its acceleration towards the axis. The observed phenomena cannot be explained by the standard magnetohydrodynamic models of array behavior, suggesting that effects such as electron emission may be important, especially during wire initiation.     

Measuring magnetic fields in single aluminum wire plasmas with time-resolved optical spectroscopy

Using time-resolved emission spectroscopy at visible wavelengths, we explored the conditions of plasmas generated by current-driven explosions of single aluminum wires. The experiments were carried out with 15 μm aluminum wires driven by the Low Current Pulser 3 (LCP3) at Cornell University.The plasma conditions were studied as a function of time and radial position, including electron temperature, electron density, ionization state, and magnetic field. To determine the magnetic field, we are working toward employing a new diagnostic method which makes use of Zeeman-effect-produced differences in the line shapes of two fine structure components of a multiplet that are equally broadened by Stark effect and by Doppler broadening. Preliminary results and data collected by a spectroscopy system with 3.2 Å resolution are presented.     

Selective Propene Epoxidation on Immobilized Au6–10 Clusters: The Effect of Hydrogen and Water on Activity and Selectivity

Epoxidation made easy : Subnanometer gold clusters immobilized on amorphous alumina result in a highly active and selective catalyst for propene epoxidation. The highest selectivity is found for gas mixtures involving oxygen and water, thus avoiding the use of hydrogen. Ab initio DFT calculations are used to identify key reaction intermediates and reaction pathways. The results confirm the high catalyst activity owing to the formation of propene oxide metallacycles. Al green, Au yellow, O red, and C gray.

     

Structural contact problems for large deformations - Comparison of steady and non steady normal field

We will present a comparison between two formulations of the normal vector field for contact algorithms based on the mortar method. First the non steady normal field is discussed. The non steadiness is a result of the C⁰ continuity of the boundary discretization. This is the common result if one discretize the domain with classical finite element methods. Second we will present results for a special normal field distribution. We average the nodal normal vector of two ascending edges and interpolate this nodal normal throughout the edges. We have implemented both methods and present comparisons based on numerical experiments. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chiral recognition of organic molecules by atomic kinks on surfaces

Two distinct non-mirror-symmetric conformations of D- and L-cysteine were found after adsorption on Au(17 11 9)S. This demonstrates chiral heterorecognition, i.e., enantioselectivity of S kinks on vicinal Au(111). The structures as determined by angle scanned x-ray photoelectron diffraction agree well with those from density functional theory calculations. The calculations predict adsorption energies of approximately 2 eV where D-cysteine binds 140 meV stronger than L-cysteine. The classical three point contact model for molecular recognition fails to explain these findings.     

Orthogonal factor‐pair Latin squares of prime‐power order

We introduce a linear method for constructing factor‐pair Latin squares of prime‐power order and we identify criteria for determining whether two factor‐pair Latin squares constructed using this linear method are orthogonal. Then we show that families of pairwise mutually orthogonal diagonal factor‐pair Latin squares exist in all prime‐power orders.     

The size of the proton: Closing in on the radius puzzle

We analyze the recent electron-proton scattering data from Mainz using a dispersive framework that respects the constraints from analyticity and unitarity on the nucleon structure. We also perform a continued fraction analysis of these data. We find a small electric proton charge radius, r _E ^p = 0.84 _?0.01 ^+0.01 fm, consistent with the recent determination from muonic hydrogen measurements and earlier dispersive analyses. We also extract the proton magnetic radius, r _M ^p = 0.86 _?0.03 ^+0.02 fm, consistent with earlier determinations based on dispersion relations.     

Precise numerical results for limit cycles in the quantum three-body problem

The study of the three-body problem with short-range attractive two-body forces has a rich history going back to the 1930s. Recent applications of effective field theory methods to atomic and nuclear physics have produced a much improved understanding of this problem, and we elucidate some of the issues using renormalization group ideas applied to precise nonperturbative calculations. These calculations provide 11-12 digits of precision for the binding energies in the infinite cutoff limit. The method starts with this limit as an approximation to an effective theory and allows cutoff dependence to be systematically computed as an expansion in powers of inverse cutoffs and logarithms of the cutoff. Renormalization of three-body bound states requires a short range three-body interaction, with a coupling that is governed by a precisely mapped limit cycle of the renormalization group. Additional three-body irrelevant interactions must be determined to control subleading dependence on the cutoff and this control is essential for an effective field theory since the continuum limit is not likely to match physical systems (e.g., few-nucleon bound and scattering states at low energy). Leading order calculations precise to 11-12 digits allow clear identification of subleading corrections, but these corrections have not been computed.