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CAN THE MASSES OF ISOLATED PLANETARY-MASS GRAVITATIONAL LENSES BE MEASURED BY TERRESTRIAL PARALLAX?
Freeman, M.,Philpott, L. C.,Abe, F.,Albrow, M. D.,Bennett, D. P.,Bond, I. A.,Botzler, C. S.,Bray, J. C.,Cherrie, J. M.,Christie, G. W.,Dionnet, Z.,Gould, A.,Han, C.,Heyrovský,, D.,McCormick, J. IOP Publishing 2015 The Astrophysical journal Vol.799 No.2
<P>Recently Sumi et al. reported evidence for a large population of planetary-mass objects ( PMOs) that are either unbound or orbit host stars in orbits >= 10 AU. Their result was deduced from the statistical distribution of durations of gravitational microlensing events observed by the MOA collaboration during 2006 and 2007. Here we study the feasibility of measuring the mass of an individual PMO through microlensing by examining a particular event, MOA-2011-BLG-274. This event was unusual as the duration was short, the magnification high, the source-size effect large, and the angular Einstein radius small. Also, it was intensively monitored from widely separated locations under clear skies at low air masses. Choi et al. concluded that the lens of the event may have been a PMO but they did not attempt a measurement of its mass. We report here a re-analysis of the event using re-reduced data. We confirm the results of Choi et al. and attempt a measurement of the mass and distance of the lens using the terrestrial parallax effect. Evidence for terrestrial parallax is found at a 3 sigma level of confidence. The best fit to the data yields the mass and distance of the lens as 0.80 +/- 0.30 M-J and 0.80 +/- 0.25 kpc respectively. We exclude a host star to the lens out to a separation similar to 40 AU. Drawing on our analysis of MOA-2011-BLG-274 we propose observational strategies for future microlensing surveys to yield sharper results on PMOs including those down to super-Earth mass.</P>
Strength enhancement of high entropy alloy HfNbTaTiZr by severe plastic deformation
Č,í,ž,ek, J.,Hauš,ild, P.,Cieslar, M.,Melikhova, O.,Vlasá,k, T.,Janeč,ek, M.,Krá,l, R.,Harcuba, P.,Luká,č,, F.,Zý,ka, J.,Má,lek, J.,Moon, J Elsevier 2018 Journal of alloys and compounds Vol.768 No.-
<P><B>Abstract</B></P> <P>Refractory metal high entropy alloy HfNbTaTiZr with ultrafine grained structure and grain size of ≈80 nm was processed by high pressure torsion. The development of microstructure, lattice defects and mechanical properties with increasing strain was examined. Grain refinement of HfNbTaTiZr alloy deformed up to the equivalent strain <I>e</I> ≈ 50 resulted in a significant enhancement of strength while keeping sufficient ductility. However, further straining <I>e</I> > 100 led to a decrease of strength and the loss of ductility due to the decomposition of solid solution facilitated by vacancies introduced by severe plastic deformation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> High entropy alloy HfNbTaTiZr was nanostructured by high pressure torsion. </LI> <LI> Grain size of 80 nm was achieved by deformation to the equivalent strain e = 5. </LI> <LI> Structure refinement resulted in remarkable enhancement of strength of the alloy. </LI> <LI> Ductility remains sufficient for good workability. </LI> <LI> Further deformation to very high strains resulted in loss of strength. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>