Promising Copper Alloy for High Heat Load Applications in Neutron Environments

Four candidate copper alloys and two elemental coppers were irradiated in the Experimental Breeder Reactor to damage levels of about 3 and 15 dpa at 385/sup 0/C. The irradiated and control samples were evaluated to determine swelling, room temperature tensile properties, transmutation product levels, and electrical resistivity. Transmission electron microscopy was used to characterize the damaged microstructures. Among the six materials studied, the alumina-dispersed copper alloys (Glidcop Al-20 and Al-60 sheet material) exhibited the best, overall resistance to fast neutron damage, as they had minimal swelling and retained their original values of yield strength and electrical resistivity (corrected for transmuted elements) after irradiation. The two cold worked and age-hardened alloys (AMZIRC and MZC) suffered loss of yield strength after irradiation at 385/sup 0/C. The two elemental coppers and the AMZIRC alloy showed large swelling (3.6 to 6.8 vol %) due to void formation after the high neutron fluence. Further study is needed to understand microstructural alterations caused by neutron damage of the alumina-dispersed copper alloy. 10 refs

The long and the short of it: Mechanisms of synchronous and compensatory dynamics across temporal scales

Synchronous dynamics (fluctuations that occur in unison) are universal phenomena with widespread implications for ecological stability. Synchronous dynamics can amplify the destabilizing effect of environmental variability on ecosystem functions such as productivity, whereas the inverse, compensatory dynamics, can stabilize function. Here we combine simulation and empirical analyses to elucidate mechanisms that underlie patterns of synchronous versus compensatory dynamics. In both simulated and empirical communities, we show that synchronous and compensatory dynamics are not mutually exclusive but instead can vary by timescale. Our simulations identify multiple mechanisms that can generate timescale-specific patterns, including different environmental drivers, diverse life histories, dispersal, and non-stationary dynamics. We find that traditional metrics for quantifying synchronous dynamics are often biased toward long-term drivers and may miss the importance of short-term drivers. Our findings indicate key mechanisms to consider when assessing synchronous versus compensatory dynamics and our approach provides a pathway for disentangling these dynamics in natural systems

Multi-ancestry transcriptome-wide association analyses yield insights into tobacco use biology and drug repurposing

Most transcriptome-wide association studies (TWASs) so far focus on European ancestry and lack diversity. To overcome this limitation, we aggregated genome-wide association study (GWAS) summary statistics, whole-genome sequences and expression quantitative trait locus (eQTL) data from diverse ancestries. We developed a new approach, TESLA (multi-ancestry integrative study using an optimal linear combination of association statistics), to integrate an eQTL dataset with a multi-ancestry GWAS. By exploiting shared phenotypic effects between ancestries and accommodating potential effect heterogeneities, TESLA improves power over other TWAS methods. When applied to tobacco use phenotypes, TESLA identified 273 new genes, up to 55% more compared with alternative TWAS methods. These hits and subsequent fine mapping using TESLA point to target genes with biological relevance. In silico drug-repurposing analyses highlight several drugs with known efficacy, including dextromethorphan and galantamine, and new drugs such as muscle relaxants that may be repurposed for treating nicotine addiction

Radiation-disorder and Aperiodicity in Irradiated Ceramics

This final technical report documents the accomplishments of the program of research entitled Radiation Disorder and Aperiodicity in Irradiated Ceramics'' for the period June 22, 1989--June 21, 1992. This research forms the latest part on an on-going program, begun at MIT in 1983 under DOE support, which has had as its objectives investigation of the responses in radiation environments of ceramics heavily-irradiated with electrons, neutrons and ions, with potential applications to fusion energy technology and high-level nuclear waste storage. Materials investigated have included SiO{sub 2}, MgAl{sub 2}O{sub 4}, Al{sub 23}O{sub 27}N{sub 5}, SiC, BeO, LiAlO{sub 2}, Li{sub 2}ZrO{sub 3}, CaTiO{sub 3}KTaO{sub 3} and Ca(Zr, Pu)Ti{sub 2}O{sub 7}. The program initially proposed for 1989 had as its major objectives two main thrusts: (1) research on defect aggregation in irradiated non-oxide ceramics, and (2) research on irradiation-induced amorphization of network silicas and phosphates

Radiation-induced Aperiodicity in Irradiated Ceramics

The experimental program is designed to reveal details of the metamict (amorphization, or crystal-to-glass) transformation in irradiated ceramics (silica compounds, less-connected lead phosphates). The silica compounds were amorphized using electrons, neutrons, and ions, while the phosphates were amorphized using ions (primarily) and neutrons. Energy-filtered electron microdiffraction, high-resoltuion transmission electron microscopy, and high-performance liquid-phase chromatography are being used

POINT DEFECT STABILIZATION IN IONIC CRYSTALS AT HIGH DEFECT CONCENTRATIONS

Dans les cristaux ioniques, la stabilisation des défauts ponctuels diffère de celle dans les métaux ou dans d'autres solides monatomiques, par la nécessité de conserver la stœchiométrie (ou une stœchiométrie aménagée) et l'ordre. Dans ces solides, les défauts ponctuels primaires qu'ils soient produits thermiquement, chimiquement, ou par irradiation, sont rarement présents ou assemblés dans des proportions exactement stœchiométrie, et par conséquent pour de hautes concentrations de défauts se produisent des structures de défauts secondaires étendues qui peuvent être tout à fait distincts de celles formées dans des solides monatomiques. La non-stœchiométrie peut être aménagée de plusieurs façons. Dans les oxydes de métaux de transition déficients en oxygène, les lacunes d'oxygène peuvent être effectivement éliminées par altération de la mode de liaison des octaèdres initials d'oxygène, engendrant des plans de cisaillement cristallographiques. Ce processus délocalise effectivement un changement de valence cationique. Dans les systèmes ayant un défaut de cation ou un excès d'anion (par exemple Fe1-xO, UO2+x, CaF2 : YF3) l'adaptation peut se faire par un changement localisé de valence cationique (et souvent de position) et par la formation de complexes d'amas de défauts ponctuels (lacunes cationiques, interstitiels anioniques) ; ceux-ci peuvent, lorsqu'ils se rassemblent, former des germes embryoniques pour une nouvelle phase de la stœchiométrie altérée. Quand des changements de valence ne sont pas possibles, par exemple dans les halogénures alcalins ou dans les oxydes et halogénures de terres alcalines non dopés, des défauts de stœchiométrie étendus (tels que des boucles de dislocations) sont créés, mais ils doivent s'accompagner d'autres formes plus stables de défauts ponctuels. L'agglomération de défauts ponctuels de haute densité peut de plus conduire à la précipitation de phases élémentaires séparées, et aussi à la décomposition du solide.Stabilization of point defects in ionic crystals differs from that in metals or other monatomic solids in that there is the need to maintain both stoichiometry (or accommodate non-stoichiometry) and order. Primary point defects in these solids, whether produced thermally, chemically, or by irradiation, seldom are present or aggregate in exactly stoichiometric proportions, and in consequence at high defect concentrations extended secondary defect structures arise which can be quite distinct from those formed in monatomic solids. Non-stoichiometry can be accommodated in several ways. In oxygen-deficient transition metal oxides, oxygen vacancies can be effectively eliminated by alteration of the mode of linking metal-oxygen octahedra together, giving rise to so-called crystallographic shear planes. This process effectively delocalizes a change in cation valency. In cation deficient/anion excess systems (e. g. Fe1-xO, UO2+x, CaF2 : YF3), accommodation occurs by a localized change in cation valency (and often position) and formation of point defect cluster complexes (cation vacancies, anion interstitials) which when stacked together can form embryonic nuclei for a new phase of altered stoichiometry. Where valency changes are not possible, for example in alkali halides or undoped alkaline earth halides and oxides, stoichiometric extended defects (such as dislocation loops) are generated, but these must be accompanied by other more stable forms of point defect species. Aggregation of point defects at high density can additionally result in precipitation of separate elemental phases, and thus decomposition of the solid

STRUCTURE AND ENERGY OF Ni/NiO INTERFACES

La structure et l'énergie d'interfaces Ni/NiO développées par oxydation de nickel de haute pureté ont été étudiées par microscopie électronique en transmission. La préparation des échantillons de MET a été effectuée à l'aide d'une méthode permettant d'obtenir des sections parallèles ou perpendiculaires à l'interface. Les structures interfaciales sont discutées à l'aide de modèles de mailles en proche coïncidence (type CSL-DSC) ou de coïncidence des directions les plus denses. Des franges de moiré ont été observées dans le cas des interfaces correspondant aux relations topotactiques Ni/NiO les plus fortes ; un modèle a été développé pour décrire le comportement de ces franges de moiré dans le cas d'une interface inclinée. L'énergie des interfaces Ni/NiO a été estimée à partir des angles dihédraux mesurés aux jonctions triples entre les grains de Ni et NiO ; les résultats sont exprimés par le rapport entre l'énergie interfaciale Ni/NiO et l'énergie des joints de grains de Ni ou de NiO pour lesquels des estimations suffisamment précises sont disponibles.The structure and energy of Ni/NiO interfaces in oxidized high purity nickel were investigated using Transmission Electron Microscopy. Parallel and transverse section techniques were employed in producing TEM specimens. The Ni/NiO interface structures observed were compared with cell matching models (extended CSL-DSC) as well as models based on matching close-packed directions across the interface. Moiré fringes were observed in interfaces possessing strong topotactic relations between the Ni and NiO. Special attention was paid to the geometry of the moiré fringes and analytic models were developed to describe moiré fringe behavior in inclined interfaces. Estimates for the energy of Ni/NiO interfaces were obtained from dihedral angle measurements at triple grain junctions between Ni and NiO grains. The energies are reported as ratios of Ni/NiO interface energies to either Ni or NiO grain boundary energies for which reasonably precise estimates are available

Radiolysis and defect structure in electron-irradiated α-quartz

On a étudié par microscopie électronique à transmission la microstructure des défauts provoqués par irradiation aux électrons dans le quartz α. On observe la nucléation et la croissance hétérogènes des centres de contrainte et la transformation homogène état cristallin → état amorphe de la matrice. Les deux processus sont attribués à la radiolyse, dont un mécanisme est proposé.The defect microstructure of electron-irradiated α-quartz was studied by transmission electron microscopy. Formation of heterogeneously-nucleated disordered strain centers and a homogeneous crystalline → amorphous transformation of the surrounding matrix were observed. Both features are shown to be attributable to radiolysis, a mechanism for which is proposed

Oxidation and sulfidation resistance of a Nb-Cr alloy

Cr and Cr-bearing alloys possess satisfactorily good oxidation resistance at high temperatures, but they sulfidize catastrophically in sulfur-bearing environments which are encountered frequently in energy conversion systems and in petrochemical industries. Nb, on the other hand, has good sulfidation resistance but poor oxidation resistance at high temperatures. A combination of Cr and Nb is shown to improve the corrosion resistance at high temperatures in oxidizing and sulfidizing environments. Kinetic and microstructural studies of oxidation and sulfidation of Cr-40wt%Nb alloys were preformed at 1173 K in sulfur vapor (PS2 = 0.74 atm) . This two phase alloy consists of an fcc Cr2Nb intermetallic phase and small amount of Cr base alloy and shows very good oxidation resistance and appreciable sulfidation resistance in comparison with Fe-45Cr, pure Nb and Fe-40Mo. The dominant oxidation product is Cr2O3, while the sulfidation products are rhomobohedral Cr2S3 as an external scale and a Nb sulfide inner scale between the Cr2S3 and substrate