Superconducting proximity effect in the presence of strong spin scattering

We report measurements of the four terminal temperature dependent resistance of narrow Au wires implanted with ~100 ppm Fe impurities in proximity to superconducting Al films. The wires show an initial decrease in resistance as the temperature is lowered through the superconducting transition of the Al films, but then show an increase in resistance as the temperature is lowered further. In contrast to the case of pure Au wires in contact with a superconducting film, the resistance at the lowest temperatures rises above the normal state resistance. Analysis of the data shows that, in addition to contributions from magnetic scattering and electron-electron interactions, the temperature dependent resistivity shows a substantial contribution from the superconducting proximity effect, which exists even in the presence of strong spin scattering.Comment: 4 pages, 3 figure

Correlation between the elastic-shear-instability-mechanism and empirical criteria for irradiation-induced amorphization

In an attempt to correlate the shear instability mechanism with empirical criteria for irradiation-induced amorphization, shear moduli of an A{sub 3}B-type fcc crystal were calculated as a function of the chemical long range order parameter (S) using a Morse potential. The shear moduli were found to decrease with decreasing S. When the depth and the curvature of the A-B potential were changed while keeping the A-A and B-B potentials constant, the magnitude of the decrease in shear moduli is greater for deeper and narrower A-B potentials. The present results indicate that a shear instability should occur more readily in compounds with larger ordering energy and larger elastic moduli. These results agree with the reported empirical criteria for irradiation-induced amorphization, therefore providing further support for the shear instability mechanism for solid-state amorphization. 9 refs., 3 figs

Distribution of Major Health Risks: Findings from the Global Burden of Disease Study

BACKGROUND: Most analyses of risks to health focus on the total burden of their aggregate effects. The distribution of risk-factor-attributable disease burden, for example by age or exposure level, can inform the selection and targeting of specific interventions and programs, and increase cost-effectiveness. METHODS AND FINDINGS: For 26 selected risk factors, expert working groups conducted comprehensive reviews of data on risk-factor exposure and hazard for 14 epidemiological subregions of the world, by age and sex. Age-sex-subregion-population attributable fractions were estimated and applied to the mortality and burden of disease estimates from the World Health Organization Global Burden of Disease database. Where possible, exposure levels were assessed as continuous measures, or as multiple categories. The proportion of risk-factor-attributable burden in different population subgroups, defined by age, sex, and exposure level, was estimated. For major cardiovascular risk factors (blood pressure, cholesterol, tobacco use, fruit and vegetable intake, body mass index, and physical inactivity) 43%–61% of attributable disease burden occurred between the ages of 15 and 59 y, and 87% of alcohol-attributable burden occurred in this age group. Most of the disease burden for continuous risks occurred in those with only moderately raised levels, not among those with levels above commonly used cut-points, such as those with hypertension or obesity. Of all disease burden attributable to being underweight during childhood, 55% occurred among children 1–3 standard deviations below the reference population median, and the remainder occurred among severely malnourished children, who were three or more standard deviations below median. CONCLUSIONS: Many major global risks are widely spread in a population, rather than restricted to a minority. Population-based strategies that seek to shift the whole distribution of risk factors often have the potential to produce substantial reductions in disease burden

Surface segregation during irradiation

Gibbsian adsorption is known to alter the surface composition of many alloys. During irradiation, four additional processes that affect the near-surface alloy composition become operative: preferential sputtering, displacement mixing, radiation-enhanced diffusion and radiation-induced segregation. Because of the mutual competition of these five processes, near-surface compositional changes in an irradiation environment can be extremely complex. Although ion-beam induced surface compositional changes were noted as long as fifty years ago, it is only during the past several years that individual mechanisms have been clearly identified. In this paper, a simple physical description of each of the processes is given, and selected examples of recent important progress are discussed. With the notable exception of preferential sputtering, it is shown that a reasonable qualitative understanding of the relative contributions from the individual processes under various irradiation conditions has been attained. However, considerably more effort will be required before a quantitative, predictive capability can be achieved. 29 refs., 8 figs

ANELASTIC RELAXATION IN IRRADIATED Cu-Be

Ultrasonic velocity measurements were made after thermal neutron irradiation of single-crystal Cu specimens containing 700 or 3700 appm Be. Ultrasonic attenuation was measured in similar specimens after 3 MeV electron irradiation. Three anelastic relaxation processes due to self-interstitial-Be complexes were observed. Cu-Be 1 was found to occur near liquid helium temperature ; the temperature dependence of the velocity change suggests that reorientation of the Cu-Be 1 complex may involve quantum mechanical tunneling. Cu-Be 2 produced an attenuation peak at ~2.5 K at a frequency of 10 MHz. Cu-Be 3 appeared simultaneously with 2 as a shoulder on the high temperature side of the 2.5 K attenuation peak

Radiation-induced segregation in Cu-Au alloys. [1 at. % Au]

Radiation-induced segregation in a Cu-1 at. % Au alloy was investigated using in situ Rutherford Backscattering Spectrometry. Irradiation with 1.8-MeV He produced nonequilibrium Au atom depletion in the near surface region. The amount of segregation was measured as a function of dose, dose rate and temperature. Segregation was observed between 300 and 500/sup 0/C. For a calculated dose rate of 3.9 x 10/sup -5/ dpa/s, the radiation-induced segregation rate peaked near 400/sup 0/C. Theoretical analysis based on the Johnson-Lam model predicted that the amount of segregation would be directly proportional to dose at the early stage of irradiation, would deviate from linearity with a continuously decreasing slope at intermediate doses, and finally approach a constant value after high doses. The analysis also predicted that the segregation rate would vary as the -1/4th power of the dose rate at constant dose in the low temperature region. These predictions were all verified experimentally. A procedure for extracting relative defect production efficiencies from similar measurements is discussed

Characterization of near surface regions in irradiated Ni(Si) alloys

Transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), Auger electron spectroscopy (AES), and infra-red pyrometry (IRP) have been used to characterize the growth of Ni/sub 3/Si films on the surfaces of irradiated Ni(Si) alloys. Results from each of the four techniques are presented and discussed, and comparisons are made between the different techniques. AES measurements are reported which suggest that Si concentrations significantly in excess of that found for stoichiometric Ni/sub 3/Si are induced in regions very near to the surface during irradiation