Atomic displacements accompanying deformation twinning: shears and shuffles

Deformation twins grow by the motion of disconnections along their interfaces, thereby coupling shear with migration. Atomic-scale simulations of this mechanism have advanced to the point where the trajectory of each atom can be followed as it transits from a site in the shrinking grain, through the interface, and onwards to a site in the growing twin. Historically, such trajectories have been factorised into shear and shuffle components according to some defined convention. In the present article, we introduce a method of factorisation consistent with disconnection motion. This procedure is illustrated for the case of {10-12} twinning in hcp materials, and shown to agree with simulated atomic trajectories for Zr.Peer ReviewedPostprint (published version

The 2019 U.S. Government Orbital Debris Mitigation Standard Practices

The rapid expansion of space traffic enabled by the SmallSat revolution has enabled unparalleled opportunity for commercial, educational, and national interests. However, it is an ongoing truth of space operations that the number of functioning spacecraft in orbit is vastly exceeded by non-functional orbital objects that can destroy them. As with any other environment, orbital space is easily polluted by human activities, and at some point the pollution can significantly degrade the usefulness of that environment. Today, there are more threats to more spacecraft than ever before, and the current accelerated growth of space activity consequently accelerates the growth of its risks. As early as 1988, US national space policy established the priority to protect the space environment. Subsequently NASA and the US Department of Defense made first efforts on formal standard practices to control space debris as early as 1993. Their work was expanded with the participation of all involved US agencies in the publication of the first US Orbital Debris Mitigation Standard Practices (ODMSP) document in 2001. That document mandated minimum design and operations practices to best preserve the orbital environment with prudent, low-cost, mandatory steps. Subsequently, global coordination through the Interagency Debris Coordination Committee (IADC) has propagated many of these practices to all space-faring powers with varying levels of success, and has elevated orbital debris mitigation to be a global concern. Each US agency implements the standard practices within their own official regulatory/safety documents, such as NASA’s standard 8719.14 and DOD’s Directive 3100.10, and others. In the last decade innovative new practices, concepts, and massive constellation proposals have opened “future space” to realities not envisioned in the 2001 standard practices document. Therefore, under Presidential Space Policy Directive #3 (June 8, 2018) all US space-related agencies were directed to coordinate a major revision to the ODMSP to reflect expected best practices for this new era in space. This revised document was approved by the National Space Council in December 2019, and is reprinted here. All US agencies with any certification or development authority over space launchers and/or spacecraft are now working to assure compliance of their internal standards with these practices. In addition, a 2025 list of recommendations (non-mandatory) from the 18th Space Wing at the Central Space Operations Center introduces addition details of design and operations that are all useful in reducing the risks in small satellite operations. This document is proposed for revision as well. No matter the intended function of a space object or launch vehicle, its certification for flight by any US agency will now depend upon meeting the minimum set of debris mitigation practices of the 2019 ODMSP. Additionally, good recommended practices are embodied in the 2015 Recommendations for Optimal CubeSat Operations. Both documents are included with this presentation. The attached presentation slides highlight all ODMSP requirements, especially key new expected practices for large constellations, active debris removal, and un-trackable or minimally-trackable swarms. This paper consists of two exhibits: the 2019 ODMSP and the 2015 JSpOC Recommendations

Sediment dynamics of a nearshore sandbank: Results from TELEMAC-2D, TOMAWAC and SISYPHE modelling

Water Qualit

Implementation of a wind-farm specific operational wave forecasting tool in the North-Sea: methods and forcing sensitivity

Water Qualit

A new method for imaging nuclear threats using cosmic ray muons

Muon tomography is a technique that uses cosmic ray muons to generate three dimensional images of volumes using information contained in the Coulomb scattering of the muons. Advantages of this technique are the ability of cosmic rays to penetrate significant overburden and the absence of any additional dose delivered to subjects under study above the natural cosmic ray flux. Disadvantages include the relatively long exposure times and poor position resolution and complex algorithms needed for reconstruction. Here we demonstrate a new method for obtaining improved position resolution and statistical precision for objects with spherical symmetry

HST STIS spectroscopy of the triple nucleus of M31: two nested disks in Keplerian rotation around a Supermassive Black Hole

We present HST spectroscopy of the nucleus of M31 obtained with STIS. Spectra taken around the CaT lines at 8500 see only the red giants in the double bright- ness peaks P1 and P2. In contrast, spectra taken at 3600-5100 A are sensitive to the tiny blue nucleus embedded in P2, the lower surface brightness red nucleus. P2 has a K-type spectrum, but the embedded blue nucleus has an A-type spectrum with strong Balmer absorption lines. Given the small likelihood for stellar collisions, a 200 Myr old starburst appears to be the most plausible origin of the blue nucleus. In stellar population, size, and velocity dispersion, the blue nucleus is so different from P1 and P2 that we call it P3. The line-of-sight velocity distributions of the red stars in P1+P2 strengthen the support for Tremaine s eccentric disk model. The kinematics of P3 is consistent with a circular stellar disk in Keplerian rotation around a super-massive black hole with M_bh = 1.4 x 10^8 M_sun. The P3 and the P1+P2 disks rotate in the same sense and are almost coplanar. The observed velocity dispersion of P3 is due to blurred rotation and has a maximum value of sigma = 1183+-201 km/s. The observed peak rotation velocity of P3 is V = 618+-81 km/s at radius 0.05" = 0.19 pc corresponding to a circular rotation velocity at this radius of ~1700 km/s. Any dark star cluster alternative to a black hole must have a half-mass radius <= 0.03" = 0.11 pc. We show that this excludes clusters of brown dwarfs or dead stars on astrophysical grounds.Comment: Astrophysical Journal, Sep 20, 2005, 21 pages including 20 figure

Method and apparatus for electromagnetic powder deposition

The present invention provides a method for depositing powder particles on a substrate. The method comprises forming a planar plasma armature, accelerating the plasma armature, accelerating a column of gas with the plasma armature; and accelerating the powder particles with the column of gas. The present invention provides for a railgun, comprising first and second conducting rails, and first and second insulating rails. The insulating and conducting rails form a bore of the railgun. The first and second conducting rails are separated by the insulating rails. At least one of the rails has a port in the wall thereof, the port is adapted to introducing powder particles into the bore.Board of Regents, University of Texas Syste

Changes in the Economy and Ecology at Proposed Lake Sites in the Salt River Basin, Kentucky, During Early Construction of the Dam for Taylorsville Lake

This is an extension of the work reported in Project numbers B-005-KY, B-016-KY, and B-022-KY that extended from 1 July 1968 through 30 June 1972. Permanent collecting stations have been established at 67 sites throughout the Salt River, Beech Fork, and Chaplin River drainages. Turbidities increases quickly as flow and runoff increase, and subside quickly when the rain stops. Suspended solids range up to 1,700 mg/l in high turbidities and vary considerably as a result of local spates. Water chemistry generally reflects the limestone nature of the substrate and physico-chemical characteristics of a typically healthy limestone stream. Bottom organisms are abundant and diverse, more than 300 different benthic organisms have been identified to date