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Observations of grain-boundary phase transformations in an elemental metal 期刊论文
NATURE, 2020, 579 (7799) : 375-+
作者:  Valente, Luis;  Phillimore, Albert B.;  Melo, Martim;  Warren, Ben H.;  Clegg, Sonya M.;  Havenstein, Katja;  Tiedemann, Ralph;  Illera, Juan Carlos;  Thebaud, Christophe;  Aschenbach, Tina;  Etienne, Rampal S.
收藏  |  浏览/下载：38/0  |  提交时间：2020/07/03

Atomic-resolution observations combined with simulations show that grain boundaries within elemental copper undergo temperature-induced solid-state phase transformation to different structures  grain boundary phases can also coexist and are kinetically trapped structures.


The theory of grain boundary (the interface between crystallites, GB) structure has a long history(1) and the concept of GBs undergoing phase transformations was proposed 50 years ago(2,3). The underlying assumption was that multiple stable and metastable states exist for different GB orientations(4-6). The terminology '  complexion'  was recently proposed to distinguish between interfacial states that differ in any equilibrium thermodynamic property(7). Different types of complexion and transitions between complexions have been characterized, mostly in binary or multicomponent systems(8-19). Simulations have provided insight into the phase behaviour of interfaces and shown that GB transitions can occur in many material systems(20-24). However, the direct experimental observation and transformation kinetics of GBs in an elemental metal have remained elusive. Here we demonstrate atomic-scale GB phase coexistence and transformations at symmetric and asymmetric [111 over bar ] tilt GBs in elemental copper. Atomic-resolution imaging reveals the coexistence of two different structures at sigma 19b GBs (where sigma 19 is the density of coincident sites and b is a GB variant), in agreement with evolutionary GB structure search and clustering analysis(21,25,26). We also use finite-temperature molecular dynamics simulations to explore the coexistence and transformation kinetics of these GB phases. Our results demonstrate how GB phases can be kinetically trapped, enabling atomic-scale room-temperature observations. Our work paves the way for atomic-scale in situ studies of metallic GB phase transformations, which were previously detected only indirectly(9,15,27-29), through their influence on abnormal grain growth, non-Arrhenius-type diffusion or liquid metal embrittlement.


  
The politics of "usable" knowledge: examining the development of climate services in Tanzania 期刊论文
CLIMATIC CHANGE, 2019, 157 (1) : 61-80
作者:  Daly, Meaghan;  Dilling, Lisa
收藏  |  浏览/下载：26/0  |  提交时间：2020/02/17
Usable knowledge  Climate services  Co-production  Boundary work  Tanzania  
A Historical Evaluation of the U15 Complex, Nevada National Security Site, Nye County, Nevada 科技报告
来源：US Department of Energy (DOE). 出版年： 2014
作者:  Drollinger, Harold;  Holz, Barbara A;  Bullard, Thomas F;  Goldenberg, Nancy G;  Ashbaugh, Laurence J;  Griffin, Wayne R
收藏  |  浏览/下载：30/0  |  提交时间：2019/04/05
This report presents a historical evaluation of the U15 Complex on the Nevada National Security Site (NNSS) in southern Nevada. The work was conducted by the Desert Research Institute at the request of the U.S. Department of Energy  National Nuclear Security Administration Nevada Field Office and the U.S. Department of Defense  Defense Threat Reduction Agency. Three underground nuclear tests and two underground nuclear fuel storage experiments were conducted at the complex. The nuclear tests were Hard Hat in 1962  Tiny Tot in 1965  and Pile Driver in 1966. The Hard Hat and Pile Driver nuclear tests involved different types of experiment sections in test drifts at various distances from the explosion in order to determine which sections could best survive in order to design underground command centers. The Tiny Tot nuclear test involved an underground cavity in which the nuclear test was executed. It also provided data in designing underground structures and facilities to withstand a nuclear attack. The underground nuclear fuel storage experiments were Heater Test 1 from 1977 to 1978 and Spent Fuel Test - Climax from 1978 to 1985. Heater Test 1 was used to design the later Spent Fuel Test - Climax experiment. The latter experiment was a model of a larger underground storage facility and primarily involved recording the conditions of the spent fuel and the surrounding granite medium. Fieldwork was performed intermittently in the summers of 2011 and 2013  totaling 17 days. Access to the underground tunnel complex is sealed and unavailable. Restricted to the surface  four buildings  four structures  and 92 features associated with nuclear testing and fuel storage experiment activities at the U15 Complex have been recorded. Most of these are along the west side of the complex and next to the primary access road and are characteristic of an industrial mining site  albeit one with scientific interests. The geomorphological fieldwork was conducted over three days in the summer of 2011. It was discovered that major modifications to the terrain have resulted from four principal activities. These are road construction and maintenance  mining activities related to development of the tunnel complex  site preparation for activities related to the tests and experiments  and construction of drill pads and retention ponds. Six large trenches for exploring across the Boundary geologic fault are also present. The U15 Complex  designated historic district 143 and site 26NY15177  is eligible to the National Register of Historic Places under Criteria A  C  and D of 36 CFR Part 60.4. As a historic district and archaeological site eligible to the National Register of Historic Places  the Desert Research Institute recommends that the area defined for the U15 Complex  historic district 143 and site 26NY15117  be left in place in its current condition. The U15 Complex should also be included in the NNSS cultural resources monitoring program and monitored for disturbances or alterations.