ESDA2008-59595 IN-SITU OBSERVATIONS OF DISLOCATION PATTERNING IN DEFORMED POLYCRYSTALLINE ALUMINUM

ABSTRACT The formation and evolution of dislocation patterns in pure polycrystalline aluminum was examined using transmission electron microscopy. The conventional characterization of the deformed samples was combined with in-situ tensile tests of prestrained samples which were carried out in order to get a better understanding of dislocation motion during deformation. The role of different types of boundaries was studied and it was found that while dense dislocation walls have an ordered structure since they are geometrically necessary, incidental dislocation boundaries can change their configuration from tangled to ordered

Deformation of as-fabricated and helium implanted 100 nm-diameter iron nano-pillars

〈101〉-oriented cylindrical single crystalline Fe samples with diameters of 100 nm and heights of 1 μm were implanted with 0.36±0.06 at% helium throughout their gauge sections. Uniaxial deformation experiments revealed a 40% higher yield and ultimate strengths in tension and a 25% higher yield strength and flow stress at 10% plastic strain in compression for implanted samples compared with as-fabricated ones. Observed tension–compression asymmetry in implanted pillars was attributed to the non-planarity of screw dislocation cores and to twinning-antitwinning deformation typical of bcc metals and the interaction between dislocations and He bubbles. Compressive stress–strain data in both sets of samples had three distinct regimes: (1) elastic loading followed by (2) discrete strain bursts during plastic flow with significant hardening up to strains of 5%, and (3) “steady state” discrete plasticity characterized by nearly-constant average flow stress. Each regime is discussed and explained in terms of competition in the rates of dislocation multiplication and dislocation annihilation

Helium Implantation Effects on the Compressive Response of Cu Nanopillars

A fabrication methodology for 120 nm-diameter, -oriented single crystalline Cu nanopillars which are uniformly implanted with helium is described. Uniaxial compression experiments reveal that their yield strength is 30% higher than that of their unimplanted counterparts. This study sheds light on the fundamental understanding of the deformation mechanism of irradiated metallic nanocrystals, and has important implications for the interplay between irradiation-induced defects and the external sample dimensions in the nanoscale

Neosporosis in Naturally Infected Sheep Herds, a Prospective Cohort Study over Three Years

Background: Neospora caninum is a protozoan parasite and a main cause of abortions in cattle worldwide. However, its role in abortions and decreased fertility in sheep is not completely understood, especially due to the complex, multifactorial etiology of abortions. This study aimed to perform a longitudinal field study to investigate the epidemiology of neosporosis and its effect on fertility in endemic sheep herds. Methods: Serological (IFAT) and clinical (outcome of pregnancy) data from 153 ewe-lambs was collected in four intensive management farms in Israel during three consecutive pregnancies. Results: The seroprevalence in ewe-lambs at different farms varied between 24% and 93%. The overall seroprevalence increased from 50% in ewe-lambs to 96.6% at the end of the third pregnancy. Horizontal infection was observed in all farms, with seroconversion in 59% of seronegative sheep. Abortion rates were lower (p = 0.004) in seropositive ewes in the first pregnancy and not significantly higher in seropositive sheep in consecutive pregnancies. Seropositivity or seroconversion were not associated with abortions or repeated abortions; however, many aborting ewes were removed from the flock. Conclusions: No direct short- or long-term association was found between Neopsora infection and abortions. The variations between flocks and pregnancies suggest a more complex etiology