Exclusive pion electroproduction off nucleons and nuclei

We present our results for the exclusive electroproduction of pions off nucleons and nuclei at high values of $Q^2$. In electroproduction of nuclei $A(e,e'\pi)$ we consider the Color Transparency (CT) effect recently observed at JLAB. It is shown that the description of $\pi$ production off nucleons is mandatory for the proof of the CT signal at JLAB. We further develop the models for exclusive production of $\pi$ off nucleons at JLAB and HERMES. At first we describe a model based on exclusive-inclusive connection. In the second approach we combine a Regge pole approach with the residual effect of nucleon resonances. The nucleon resonances are described using a dual connection between the exclusive form factors and inclusive deep inelastic structure functions. We present the results for the beam spin azimuthal asymmetries measured at JLAB in exclusive electroproduction of charged and neutral pions.Comment: 15 pages, 10 figures. Invited talk at the NAPP 2010 - 3rd International Conference on Nuclear and Particle Physics with CEBAF, October 3rd to 8th 2010, Dubrovnik, Croati

Deep exclusive electroproduction of π+\pi^+ at HERMES

Deeply virtual electroproduction of pion in exclusive reaction $p(e,e'\pi^+)n$ is studied using a two-component model which includes soft hadronic and hard partonic reaction mechanisms. The results are compared with the experimental data measured at HERMES in the deep inelastic region for values of $Q^2>1$ GeV$^2$ and $W^2 > 10$ GeV$^2$. At forward angles the $\pi^+$ cross section is longitudinal and is dominated by exchange of Regge poles, with $\pi$ the dominant trajectory. The off-forward region with $-t>1$ GeV$^2$ is transverse and shows the dominance of partonic subprocesses. An implication of present results for the future JLAB facilities are briefly discussed.Comment: 10 pages, 4 figure

Deep exclusive charged π\pi electroproduction above the resonance region

A description of exclusive charged pion electroproduction $(e,e'\pi^{\pm})$ off nucleons at high energies is proposed. The model combines a Regge pole approach with residual effect of nucleon resonances. The exchanges of $\pi$(140), vector $\rho(770)$ and axial-vector $a_1(1260)$ and $b_1(1235)$ Regge trajectories are considered. The contribution of nucleon resonances is described using a dual connection between the exclusive hadronic form factors and inclusive deep inelastic structure functions. The model describes the measured longitudinal, transverse and interference cross sections at JLAB and DESY. The scaling behavior of the cross sections is in agreement with JLAB and deeply virtual HERMES data. The results for a polarized beam-spin azimuthal asymmetry in $(\vec{e},e'\pi^{\pm})$ are presented. Model predictions for JLAB at 12 GeV are given.Comment: 29 page

Void growth in high strength aluminium alloy single crystals : a CPFEM based study

The author thankfully acknowledges the financial support of EPSRC funding (EP/L021714/1).Peer reviewedPostprin

Λ(1520)\Lambda(1520) and Σ(1385)\Sigma(1385) in the nuclear medium

Recent studies of the $\Lambda(1520)$ resonance within chiral unitary theory with coupled channels find the resonance as a dynamically generated state from the interaction of the decuplet of baryons and the octet of mesons, essentially a quasibound state of $\pi \Sigma^*(1385)$ in this case, although the coupling of the $\Lambda(1520)$ to the $\bar{K}N$ and $\pi \Sigma$ makes this picture only approximate. The $\pi \Sigma^*(1385)$ decay channel of the $\Lambda(1520)$ is forbidden in free space for the nominal mass of the $\Sigma^*(1385)$, but the coupling of the $\pi$ to $ph$ components in the nuclear medium opens new decay channels of the $\Lambda(1520)$ in the nucleus and produces a much larger width. Together with medium modifications of the $\bar{K}N$ and $\pi \Sigma$ decay channels, the final width of the $\Lambda(1520)$ at nuclear matter density is more than five times bigger than the free one. We perform the calculations by dressing simultaneously the $\Lambda(1520)$ and the $\Sigma^*(1385)$ resonances, finding moderate changes in the mass but substantial ones in the width of both resonances.Comment: 20 pages, 6 figures; comparison made to data, new references and new (small) decay channel include

Effect of prior cold work on the mechanical properties of weldments

Heat exchanger units used in steam raising power plant are often manufactured using many metres of austenitic stainless steel tubes that have been plastically formed (bent and swaged) and welded into complex shapes. The amount of plastic deformation (pre-straining) before welding varies greatly. This has a significant effect on the mechanical properties of the welded tubes and on the final residual stress state after welding. The aim of the present work was to measure and understand the combined effects of pre-straining and welding on the properties and residual stress levels in stainless steel tubing weldments. Effects of plastic deformation were simulated by plastically straining three identical stainless steel tubes to different strain levels (0%, 10% and 20%). Then each tube was cut into two halves and welding back together. The variation in mechanical properties across weldments was measured using digital image correlation (DIC) and a series of strain gauges (SG). Residual stresses were measured on the 0% (undeformed) and 20% prestrained and welded tubes by neutron diffraction. It was found that the welding process had a marked effect on the tensile properties of parent material within 25mm of the weld centre-line. Evidence of cyclic strain hardening was observed in the tube that had not been pre-strained, and evidence of softening seen in the 10% and 20% pre-strained tubes. Macroscopic residual stresses were measured to be near zero at distances greater than 25 mm from the weld centre-line, but measurements in the 20% pre-strained tube revealed the presence of micro residual stresses having a magnitude of up to 50 MPa

Convergence of numerical schemes for short wave long wave interaction equations

We consider the numerical approximation of a system of partial differential equations involving a nonlinear Schr\"odinger equation coupled with a hyperbolic conservation law. This system arises in models for the interaction of short and long waves. Using the compensated compactness method, we prove convergence of approximate solutions generated by semi-discrete finite volume type methods towards the unique entropy solution of the Cauchy problem. Some numerical examples are presented.Comment: 31 pages, 7 figure