Mechanical response of self-ion irradiated, single crystal, FCC micropillars

Increasing energy demands and regulations on cleaner and more efficient energy sources has reinvigorated research into next generation nuclear reactors. The safe and optimal operation of the various proposed reactors requires the cladding and structural metals to perform under a combination of extreme environments including radiation damage levels \u3e100 dpa. This presentation will highlight a rapid screening technique developed at Sandia National Laboratories to determine the relative merit of implementing various advanced structural alloys and composites in high radiation environments. In addition to an overview of the technique and the wealth of alloy systems it has been applied to, this presentation will focus on the detailed mechanisms that can be elucidated from the micropillar compression of ion irradiated single crystal copper and nickel. Single crystal Cu micropillars self-ion irradiated up to 190 dpa at the end of range were compressed along the \u3c110\u3e to 10% strain. To elucidate the interaction of different length scales on the mechanical response, three specimen configurations were explored: large 10 μm tall, intermediate 5 μm tall, and small 4 μm tall pillars. In a similar manner, pristine and self-ion irradiated \u3c111\u3e Ni pillars were subject to in-situ microcompression in a scanning electron microscope (SEM). By performing these experiments during real time SEM observation a direct correlation between the mechanical responses and the pillars’ structural evolution can be obtained. Specifically, the dynamics resulting from the defect free channel formation and subsequent localization can be associated with heterogeneous plastic flow. This presentation will highlight the multiple length scale effects that are active during the micropillar compression of self-ion irradiated, single crystal, FCC micropillars. These results will be discussed in the context of an end of range effect, a damage gradient effect, and size effects, as well as compared to other small scale mechanical testing methods of ion and neutron irradiated materials. Finally, the benefits and limitations of applying these methods to rapidly screen advanced materials for potential future nuclear reactor applications will be discussed. This study is supported by the Division of Materials Science and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000

Local Dynamics and Strong Correlation Physics I: 1D and 2D Half-filled Hubbard Models

We report on a non-perturbative approach to the 1D and 2D Hubbard models that is capable of recovering both strong and weak-coupling limits. We first show that even when the on-site Coulomb repulsion, U, is much smaller than the bandwith, the Mott-Hubbard gap never closes at half-filling in both 1D and 2D. Consequently, the Hubbard model at half-filling is always in the strong-coupling non-perturbative regime. For both large and small U, we find that the population of nearest-neighbour singlet states approaches a value of order unity as $T\to 0$ as would be expected for antiferromagnetic order. We also find that the double occupancy is a smooth monotonic function of U and approaches the anticipated non-interacting limit and large U limits. Finally, in our results for the heat capacity in 1D differ by no more than 1% from the Bethe ansatz predictions. In addition, we find that in 2D, the heat capacity vs T for different values of U exhibits a universal crossing point at two characteristic temperatures as is seen experimentally in a wide range of strongly-correlated systems such as $^3He$, $UBe_3$, and $CeCu_{6-x}Al_x$. The success of this method in recovering well-established results that stem fundamentally from the Coulomb interaction suggests that local dynamics are at the heart of the physics of strongly correlated systems.Comment: 10 pages, 16 figures included in text, Final version for publication with a reference added and minor corrections. Phys. Rev. B, in pres

Scalable and accurate causality tracking for eventually consistent stores

Lecture Notes in Computer Science 8460, 2014In cloud computing environments, data storage systems often rely on optimistic replication to provide good performance and availability even in the presence of failures or network partitions. In this scenario, it is important to be able to accurately and efficiently identify updates executed concurrently. Current approaches to causality tracking in optimistic replication have problems with concurrent updates: they either (1) do not scale, as they require replicas to maintain information that grows linearly with the number of writes or unique clients; (2) lose information about causality, either by removing entries from client-id based version vectors or using server-id based version vectors, which cause false conflicts. We propose a new logical clock mechanism and a logical clock framework that together support a traditional key-value store API, while capturing causality in an accurate and scalable way, avoiding false conflicts. It maintains concise information per data replica, only linear on the number of replica servers, and allows data replicas to be compared and merged linear with the number of replica servers and versions.(undefined

Melting and Dimensionality of the Vortex Lattice in Underdoped YBa2Cu3O6.60

Muon spin rotation measurements of the magnetic field distribution in the vortex state of the oxygen deficient high-Tc superconductor YBa{2}Cu{3}O{6.60} reveal a vortex-lattice melting transition at much lower temperature than that in the fully oxygenated material. The transition is best described by a model in which adjacent layers of ``pancake'' vortices decouple in the liquid phase. Evidence is also found for a pinning-induced crossover from a solid 3D to quasi-2D vortex lattice, similar to that observed in the highly anisotropic superconductor Bi{2+x}Sr{2-x}CaCu{2}O{8+y}.Comment: 8 pages, 4 figures, 5 postscript file

The response of nematodes to deep-sea CO2 sequestration : a quantile regression approach

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 57 (2010): 696-707, doi:10.1016/j.dsr.2010.03.003.One proposed approach to ameliorate the effects of global warming is sequestration of the greenhouse gas CO2 in the deep sea. To evaluate the environmental impact of this approach, we exposed the sediment-dwelling fauna at the mouth of the Monterey Submarine Canyon (3262 m) and a site on the nearby continental rise (3607 m) to CO2- rich water. We measured meiobenthic nematode population and community metrics after ~30-day exposures along a distance gradient from the CO2 source and with sediment depth to infer the patterns of mortality. We also compared the nematode response with that of harpacticoid copepods. Nematode abundance, average sediment depth, tail-group composition, and length: width ratio did not vary with distance from the CO2 source. However, quantile regression showed that nematode length and diameter increased in close proximity to the CO2 source in both experiments. Further, the effects of CO2 exposure and sediment depth (nematodes became more slender at one site, but larger at the other, with increasing depth in the sediment) varied with body size. For example, the response of the longest nematodes differed from those of average length. We propose that nematode body length and diameter increases were induced by lethal exposure to CO2-rich water and that nematodes experienced a high rate of mortality in both experiments. In contrast, copepods experienced high mortality rates in only one experiment suggesting that CO2 sequestration effects are taxon specific.The Department of Energy Office of Biological and Environmental Research supported this research under award numbers DE‐FG02‐05ER64070 and DE‐FG03‐01ER63065 and the U.S. Department of Energy, Fossil Energy Group (award DE‐FC26‐00NT40929). We also appreciate significant support provided by the Monterey Bay Aquarium Research Institute (project 200002)

Nucleotide variation, haplotype structure, and association with end-stage renal disease of the human interleukin-1 gene cluster

A dense gene-based SNP map was constructed across a 360-kb region containing the interleukin-1 gene cluster (IL1A, IL1B, and IL1RN), focusing on IL1RN. In total, 95 polymorphisms were confirmed or identified primarily by direct sequencing. Polymorphisms were precisely mapped to completed BAC and genomic sequences spanning this region. The polymorphisms were typed in 443 case-control subjects from Caucasian and African American groups. Consecutive pair-wise marker linkage disequilibrium was not strictly correlated with distance and ranged from D′ = 0.0079 to 1.000 and D′ = 0.0521 to 1.0000 in Caucasians and African Americans, respectively. Single markers and haplotypes in IL1 cluster genes were evaluated for association with end-stage renal disease (ESRD). Eleven SNPs show some evidence of association with ESRD, with the strongest associations in two IL1A variants, one SNP, rs1516792-3, in intron 5 (p = 0.0015) and a 4-bp insertion/deletion within the 3′UTR, rs16347-2 (p = 0.0024), among African Americans with non-T2DM-associated ESRD

Late Winter Biogeochemical Conditions Under Sea Ice in the Canadian High Arctic

With the Arctic summer sea-ice extent in decline, questions are arising as to how changes in sea-ice dynamics might affect biogeochemical cycling and phenomena such as carbon dioxide (CO2) uptake and ocean acidification. Recent field research in these areas has concentrated on biogeochemical and CO2 measurements during spring, summer or autumn, but there are few data for the winter or winter–spring transition, particularly in the High Arctic. Here, we present carbon and nutrient data within and under sea ice measured during the Catlin Arctic Survey, over 40 days in March and April 2010, off Ellef Ringnes Island (78° 43.11′ N, 104° 47.44′ W) in the Canadian High Arctic. Results show relatively low surface water (1–10 m) nitrate (<1.3 µM) and total inorganic carbon concentrations (mean±SD=2015±5.83 µmol kg−1), total alkalinity (mean±SD=2134±11.09 µmol kg−1) and under-ice pCO2sw (mean±SD=286±17 µatm). These surprisingly low wintertime carbon and nutrient conditions suggest that the outer Canadian Arctic Archipelago region is nitrate-limited on account of sluggish mixing among the multi-year ice regions of the High Arctic, which could temper the potential of widespread under-ice and open-water phytoplankton blooms later in the season

Strong one-neutron emission from two-neutron unbound states in β decays of the r -process nuclei Ga 86,87

β-delayed one-neutron and two-neutron branching ratios (P1n and P2n) have been measured in the decay of A=84 to 87 Ga isotopes at the Radioactive-Isotope Beam Factory (RIBF) at the RIKEN Nishina Center using a high-efficiency array of He3 neutron counters (BRIKEN). Two-neutron emission was observed in the decay of Ga84,85,87 for the first time and the branching ratios were measured to be P2n=1.6(2)%,1.3(2)%, and 10.2(28)stat(5)sys%, respectively. One-neutron branching ratio of Ga87(P1n=81(9)stat(8)sys%) and half-life of 29(4) ms were measured for the first time. The branching ratios of Ga86 were also measured to be P1n=74(2)stat(8)sys% and 16.2(9)stat(6)sys% with better precision than a previous study. The observation that P1n>P2n for both Ga86,87 was unexpected and is interpreted as a signature of dominating one-neutron emission from the two-neutron unbound excited states in Ge86,87. In order to interpret the experimental results, shell-model and Hauser-Feshbach statistical model calculations of delayed particle and γ-ray emission probabilities were performed. This model framework reproduces the experimental results. The shell model alone predicts P2n significantly larger than P1n for the Ga87 decay, and it is necessary to invoke a statistical description to successfully explain the observation that P1n>P2n. Our new results demonstrate the relevance and importance of a statistical description of neutron emission for the prediction of the decay properties of multineutron emitters and that it must be included in the r-process modeling

Commissioning of the BRIKEN detector for the measurement of very exotic β-delayed neutron emitters

A new detection system has been installed at the RIKEN Nishina Center (Japan) to investigate decay properties of very neutron-rich nuclei. The setup consists of three main parts: a moderated neutron counter, a detection system sensitive to the implantation and decay of radioactive ions, and γ-ray detectors. We describe here the setup, the commissioning experiment and some selected results demonstrating its performance for the measurement of half-lives and β-delayed neutron emission probabilities. The methodology followed in the analysis of the data is described in detail. Particular emphasis is placed on the correction of the accidental neutron background