Effect of thermodynamics on ion mixing

Ion mixing of elemental 4d-5d metallic bilayers at 77 K by 600 keV Xe + + ions has been studied to test the validity of the phenomenological model of ion mixing that predicts a dependence on the chemical heats of mixing, DeltaHmix, and on the cohesive energies, DeltaHcoh, of the bilayer elements. A series of samples was chosen to minimize the variation in kinematical properties between samples while maximizing the variation in heats of mixing. The experimental results agree well with the model's predictions, and the experimentally determined constants K1=0.034 Å and K2=27 agree with those of previous work

Correlation between the cohesive energy and the onset of radiation-enhanced diffusion in ion mixing

A correlation between the cohesive energy of elemental solids and the characteristic temperature Tc for the onset of radiation-enhanced diffusion during ion mixing is established. This correlation enables one to predict the onset of radiation-enhanced diffusion for systems which have not yet been investigated. A theoretical argument based on the current models of cascade mixing and radiation-enhanced diffusion is provided as a basis for understanding this observation

ADAP Faculty Needs Assessment for Improvement of Resident Instruction

The research reported in this publication provides an examination of the inservice training needs for Land Grant faculty in the U.S. affiliated Pacific region. It was conducted to prioritize the topics in a series of "Symposia for the Imporvement of Resident Instruction" under the Agricultural Development of the American Pacific (ADAP) initiative. These inservice training events were presented in 1991 based upon the results herein.Funded through the US Department of Agriculture Cooperative Extension Service

Remodelling of human atrial K+ currents but not ion channel expression by chronic β-blockade

Chronic β-adrenoceptor antagonist (β-blocker) treatment in patients is associated with a potentially anti-arrhythmic prolongation of the atrial action potential duration (APD), which may involve remodelling of repolarising K+ currents. The aim of this study was to investigate the effects of chronic β-blockade on transient outward, sustained and inward rectifier K+ currents (ITO, IKSUS and IK1) in human atrial myocytes and on the expression of underlying ion channel subunits. Ion currents were recorded from human right atrial isolated myocytes using the whole-cell-patch clamp technique. Tissue mRNA and protein levels were measured using real time RT-PCR and Western blotting. Chronic β-blockade was associated with a 41% reduction in ITO density: 9.3 ± 0.8 (30 myocytes, 15 patients) vs 15.7 ± 1.1 pA/pF (32, 14), p < 0.05; without affecting its voltage-, time- or rate dependence. IK1 was reduced by 34% at −120 mV (p < 0.05). Neither IKSUS, nor its increase by acute β-stimulation with isoprenaline, was affected by chronic β-blockade. Mathematical modelling suggested that the combination of ITO- and IK1-decrease could result in a 28% increase in APD90. Chronic β-blockade did not alter mRNA or protein expression of the ITO pore-forming subunit, Kv4.3, or mRNA expression of the accessory subunits KChIP2, KChAP, Kvβ1, Kvβ2 or frequenin. There was no reduction in mRNA expression of Kir2.1 or TWIK to account for the reduction in IK1. A reduction in atrial ITO and IK1 associated with chronic β-blocker treatment in patients may contribute to the associated action potential prolongation, and this cannot be explained by a reduction in expression of associated ion channel subunits

Form factors and photoproduction amplitudes

We examine the use of phenomenological form factors in tree level amplitudes for meson photoproduction. Two common recipes are shown to be fundamentally incorrect. An alternate form consistent with gauge invariance and crossing symmetry is proposed.Comment: To be published in PR

Extraction of the D13(1520) photon-decay couplings from pion- and eta-photoproduction data

We compare results for the D13(1520) photon-decay amplitudes determined in analyses of eta- and pion-photoproduction data. The ratio of helicity amplitudes (A_3/2 / A_1/2), determined from eta-photoproduction data, is quite different from that determined in previous analyses of pion-photoproduction data. We consider how strongly the existing pion-photoproduction data constrain both this ratio and the individual photon-decay amplitudes.Comment: 7 pages, 2 figure

Delta isobar masses, large N_c relations, and the quark model

Motivated by recent remarks on the Delta+ mass and comparisons between the quark model and relations based on large-N_c with perturbative flavor breaking, two sets of Delta masses consistent with these constraints are constructed. These two sets, based either on an experimentally determined mass splitting or a quark model of isospin symmetry breaking, are shown to be inconsistent. The model dependence of this inconsistency is examined, and suggestions for improved experiments are made. An explicit quark model calculation and mass relations based on the large-N_c limit with perturbative flavor breaking are compared. The expected level of accuracy of such relations is realized in the quark model, except for mass relations spanning more than one SU(6) representation. It is shown that the Delta0 and Delta++ pole masses and Delta0 - Delta+ = (Delta- - Delta++)/3 about 1.5 MeV are more consistent with model expectations than the analogous Breit-Wigner masses and their splittings.Comment: 10 pages, including 1 eps figure, revte

Present status of the nonstrange and other flavor partners of the exotic Theta+ baryon

Given the existing empirical information about the exotic Theta+ baryon, we analyze possible properties of its SU(3)F-partners, paying special attention to the nonstrange member of the antidecuplet N*. The modified piN partial-wave analysis presents two candidate masses, 1680 MeV and 1730 MeV. In both cases, the N* should be rather narrow and highly inelastic. Our results suggest several directions for experimental studies that may clarify properties of the antidecuplet baryons, and structure of their mixing with other baryons. Recent experimental evidence from the GRAAL and STAR Collaborations could be interpreted as observations of a candidate for the Theta+ nonstrange partner.Comment: 4 pages, 1 figure, talk given at the Topical Group on Hadron Physics (Fermilab, Oct. 24-26, 2004