Molecular Dynamics Study of Self-Diffusion in Zr

We employed a recently developed semi-empirical Zr potential to determine the diffusivities in the hcp and bcc Zr via molecular dynamics simulation. The point defect concentration was determined directly from MD simulation rather than from theoretical methods using T=0 calculations. We found that the diffusion proceeds via the interstitial mechanism in the hcp Zr and both the vacancy and interstitial mechanisms give contribution in diffusivity in the bcc Zr. The agreement with the experimental data is excellent for the hcp Zr and for the bcc Zr it is rather good at high temperatures but there is a considerable disagreement at low temperatures

Effect of Thermal Exposure on Structure of the Ultrafine-GrainedZr-1Nb Alloy

Effect of annealing at temperature range of 573–823 K on stability of the ultrafine-grained structure of the Zr-1wt.%Nb alloy was studied by methods of transmission electron microscopy. Growth kinetics of grain–subgrain structure elements of alloy was investigated

The evolution of bits and bottlenecks in a scientific workflow trying to keep up with technology: Accelerating 4D image segmentation applied to nasa data

In 2016, a team of earth scientists directly engaged a team of computer scientists to identify cyberinfrastructure (CI) approaches that would speed up an earth science workflow. This paper describes the evolution of that workflow as the two teams bridged CI and an image segmentation algorithm to do large scale earth science research. The Pacific Research Platform (PRP) and The Cognitive Hardware and Software Ecosystem Community Infrastructure (CHASE-CI) resources were used to significantly decreased the earth science workflow's wall-clock time from 19.5 days to 53 minutes. The improvement in wall-clock time comes from the use of network appliances, improved image segmentation, deployment of a containerized workflow, and the increase in CI experience and training for the earth scientists. This paper presents a description of the evolving innovations used to improve the workflow, bottlenecks identified within each workflow version, and improvements made within each version of the workflow, over a three-year time period

Effect of nonequilibrium hydrogen release in the ultrafine-grained Zr-1Nb alloy under the electron beam exposure

The evolution of structural and phase state and hydrogen release from the ultrafine-grained hydrogenated zirconium Zr-1Nb alloy during vacuum annealing and electron beams exposure were studied. The use of electron beam irradiation for hydrogen degassing is shown to decrease the temperature of active hydrogen release by 100-200 K and/or reduce the time required for hydrogen degassing from the alloy to concentrations corresponding to technical standards

Fingering Instability of Dislocations and Related Defects

We identify a fundamental morphological instability of mobile dislocations in crystals and related line defects. A positive gradient in the local driving force along the direction of defect motion destabilizes long-wavelength vibrational modes, producing a ``fingering'' pattern. The minimum unstable wavelength scales as the inverse square root of the force gradient. We demonstrate the instability's onset in simulations of a screw dislocation in Al (via molecular dynamics) and of a vortex in a 3-d XY ``rotator'' model.Comment: 4 pages, 3 figure

Measurement of the magnetic moment of the one-neutron halo nucleus 11^{11}Be

The magnetic moment of $^{11}$Be was measured by detecting nuclear magnetic resonance signals in a beryllium crystal lattice. The experimental technique applied to a $^{11}$Be$^+$ ion beam from a laser ion source includes in-beam optical polarization, implantation into a metallic single crystal and observation of rf resonances in the asymmetric angular distribution of the $\beta$-decay ($\beta$-NMR). The nuclear magnetic moment $\mu(^{11}{\rm Be}) = -1.6816(8)\,\mu_N$ provides a stringent test for theoretical models describing the structure of the 1/2$^+$ neutron halo state

Computational Modeling and Experimental Characterization of Martensitic Transformations in Nicoal for Self-Sensing Materials

Fundamental changes to aero-vehicle management require the utilization of automated health monitoring of vehicle structural components. A novel method is the use of self-sensing materials, which contain embedded sensory particles (SP). SPs are micron-sized pieces of shape-memory alloy that undergo transformation when the local strain reaches a prescribed threshold. The transformation is a result of a spontaneous rearrangement of the atoms in the crystal lattice under intensified stress near damaged locations, generating acoustic waves of a specific spectrum that can be detected by a suitably placed sensor. The sensitivity of the method depends on the strength of the emitted signal and its propagation through the material. To study the transition behavior of the sensory particle inside a metal matrix under load, a simulation approach based on a coupled atomistic-continuum model is used. The simulation results indicate a strong dependence of the particle's pseudoelastic response on its crystallographic orientation with respect to the loading direction and suggest possible ways of optimizing particle sensitivity. The technology of embedded sensory particles will serve as the key element in an autonomous structural health monitoring system that will constantly monitor for damage initiation in service, which will enable quick detection of unforeseen damage initiation in real-time and during onground inspections