A critical analysis of existing models for plastic flow in Ni3Al: Comparisons with transient deformation experiments

A review of the intermediate temperature creep properties of Ni3Al indicates that octahedral glide, the mechanism associated with the anomalous temperature dependence of yielding in this alloy, is exhausted during primary creep. Comparisons of this primary creep transient with the various models proposed to explain the anomalous yielding behavior suggest that additional transient experiments are needed to fully characterize octahedral glide in this alloy. Cottrell-Stokes type temperature change experiments, stress relaxation experiments, and deformation exhaustion/temperature drop tests have been conducted in an attempt to better characterize octahedral glide in Ni3Al. The results of these transient experiments indicate that octahedral glide is only partially a thermally reversible process and that the formation of dislocation substructure, KW locks, plays an important role in determining the flow strength of this alloy. These experiments also suggest that flow in Ni3Al should not be viewed as a viscous drag process, but can best be described as a "pure-metal-like” process involving the rapid motion of a small number of highly mobile dislocations. The stochastic nature of dislocation motion and the importance of substructure formation are emphasized and a description of octahedral glide that is consistent with the transient deformation experiments is propose

Roman diet and trade: evidence from organic residues on pottery sherds recovered at the Roman town of Calleva Atrebatum (Silchester Hants.)

The analysis of organic residues from pottery sherds using Gas-Chromatography with mass-spectroscopy (GC-MS) has revealed information about the variety of foods eaten and domestic routine at Silchester between the second and fourth–sixth centuries A.D. Two results are discussed in detail: those of a second-century Gauloise-type amphora and a fourth-century SE Dorset black-burnished ware (BB1) cooking pot, which reveal the use of pine pitch on the inner surface of the amphora and the use of animal fats (ruminant adipose fats) and leafy vegetables in cooking at the Roman town of Silchester, Hants

Relaxed MHD states of a multiple region plasma

We calculate the stability of a multiple relaxation region MHD (MRXMHD) plasma, or stepped-Beltrami plasma, using both variational and tearing mode treatments. The configuration studied is a periodic cylinder. In the variational treatment, the problem reduces to an eigenvalue problem for the interface displacements. For the tearing mode treatment, analytic expressions for the tearing mode stability parameter $\Delta'$, being the jump in the logarithm in the helical flux across the resonant surface, are found. The stability of these treatments is compared for $m=1$ displacements of an illustrative RFP-like configuration, comprising two distinct plasma regions. For pressure-less configurations, we find the marginal stability conclusions of each treatment to be identical, confirming analytic results in the literature. The tearing mode treatment also resolves ideal MHD unstable solutions for which $\Delta' \to \infty$: these correspond to displacement of a resonant interface. Wall stabilisation scans resolve the internal and external ideal kink. Scans with increasing pressure are also performed: these indicate that both variational and tearing mode treatments have the same stability trends with $\beta$, and show pressure stabilisation in configurations with increasing edge pressure. Combined, our results suggest that MRXMHD configurations which are stable to ideal perturbations plus tearing modes are automatically in a stable state. Such configurations, and their stability properties, are of emerging importance in the quest to find mathematically rigorous solutions of ideal MHD force balance in 3D geometry.Comment: 11 pages, 3 figures, 22nd IAEA Fusion Energy Conference, Geneva, Switzerland. Submitted to Nuclear Fusio

The pace of plutonism

Beneath volcanoes are magmas that never erupt but that become frozen into feldspar- and quartz-rich rocks broadly called granite. Where the crystallized magmas form bodies with distinctive textures, they are grouped into named units-plutons. The rate (pace) at which magmas accumulate into plutons is fundamental to understanding both how room is made for the magmas and how unerupted and erupted magmas are connected. Dating plutonic rocks suggests that plutons accumulate slowly. Although the pace of magma accumulation does not preclude direct connections between plutons and small volcanic eruptions, it appears to be far too slow to support connections between most plutons and supereruptions

Direct sublattice imaging of interface dislocation structures in CdTe/GaAs(001)

This paper presents directly interpretable atomic resolution images of dislocation structures at interfaces in CdTe/GaAs(001) systems. This is achieved using the technique of Z-contrast imaging in a 300 kV scanning transmission electron microscope in conjunction with maximum entropy image analysis. In addition to being used to further the understanding of the relation between growth conditions and exhibited properties, the data presented provides direct information on the atomic arrangements at dislocation cores

The plutonic record of a silicic ignimbrite from the Latir volcanic field, New Mexico

Zircon U-Pb geochronologic data for plutonic rocks in the Latir volcanic field, New Mexico, demonstrate that the rocks are dominated by plutons that post-date ignimbrite eruption. Only zircon from the ring dike of the Questa caldera yields the same age (25.64±0.08 Ma) as zircon from the caldera-forming Amalia Tuff (25.52±0.06 Ma). The post-caldera Rio Hondo pluton was assembled incrementally over at least 400 ka. The magma accumulation rate for the exposed portion of the Rio Hondo pluton is estimated to be 0.0003 km3 a-1, comparable to rates for other plutons, and too slow to support accumulation of large eruptible magma volumes. Extrapolation of the accumulation rate for the Rio Hondo pluton over the history of the Latir volcanic field yields an estimated volume of plutonic rocks comparable to the calculated volume under the field as determined by geophysical studies. We propose that the bulk of the plutonic rocks beneath the volcanic center accumulated during periods of low volcanic effusivity. Furthermore, because the oldest portion of the Rio Hondo pluton is the granitic cap exposed beneath a gently dipping roof contact, the roof granite cannot be a silicic liquid fractionated from the deeper (younger) portions of the pluton. Instead, our data suggest that the compositional heterogeneity of the Rio Hondo pluton is inherited from lower crustal sources. We suggest that if magma fluxes are high enough, zoned ignimbrites can be formed by evolution of the melt compositions generated at the source with little or no shallow crustal differentiation

Behavioural and physiological correlates of impulsivity in the domestic dog (Canis familiaris)

Impulsivity is a trait related to inhibitory control which is expressed in a range of behaviours. Impulsive individuals show a decreased ability to tolerate delay of reinforcement, and more impulsive behaviour has been linked to decreased levels of serotonin and dopamine in a number of species. In domestic dogs, impulsivity is implicated in problem behaviours that result from a lack of self control, but currently there are no published studies that assess behavioural and physiological measures of impulsivity in relation to this trait. Impulsivity scores were calculated for 41 dogs using an owner-report assessment, the Dog Impulsivity Assessment Scale (DIAS). Twenty-three of these subjects completed an operant choice task based on a delayed reward paradigm, to assess their tolerance to delay of reinforcement. High Pressure Liquid Chromatography (HPLC) with Fluorometric Detection was used to detect levels of the metabolites of serotonin (5-HIAA) and dopamine (HVA) in the urine of 17 of the subjects. Higher impulsivity scores were found to be significantly correlated with more impulsive behaviour (reduced tolerance to delay of reinforcement) in the behaviour tests and lower levels of urinary 5-HIAA and 5-HIAA/HVA ratio. The results demonstrate convergent validity between impulsivity (as assessed by the DIAS) and behavioural and physiological parameters

Organic Pollutants, Heavy Metals and Toxicity in Oil Spill impacted Salt Marsh Sediment Cores, Staten Island, New York City, USA

Sediment cores from Staten Island's salt marsh contain multiple historical oil spill events that impact ecological health. Microtox solid phase bioassay indicated moderate to high toxicity. Multiple spikes of TPH (6524 to 9586 mg/kg) and Σ16 PAH (15.5 to 18.9 mg/kg) were co-incident with known oil spills. A high TPH background of 400–700 mg/kg was attributed to diffuse sources. Depth-profiled metals Cu (1243 mg/kg), Zn (1814 mg/kg), Pb (1140 mg/kg), Ni (109 mg/kg), Hg (7 mg/kg), Cd 15 (mg/kg) exceeded sediment quality guidelines confirming adverse biological effects. Changes in Pb206/207 suggested three metal contaminant sources and diatom assemblages responded to two contamination events. Organic and metal contamination in Saw Mill Creek Marsh may harm sensitive biota, we recommend caution in the management of the 20–50 cm sediment interval because disturbance could lead to remobilisation of pre-existing legacy contamination into the waterway

STN7 is not essential for developmental acclimation of Arabidopsis to light intensity

Plants respond to changing light intensity in the short term through regulation of light harvesting, electron transfer, and metabolism to mitigate redox stress. A sustained shift in light intensity leads to a long-term acclimation response (LTR). This involves adjustment in the stoichiometry of photosynthetic complexes through de novo synthesis and degradation of specific proteins associated with the thylakoid membrane. The light-harvesting complex II (LHCII) serine/threonine kinase STN7 plays a key role in short-term light harvesting regulation and was also suggested to be crucial to the LTR. Arabidopsis plants lacking STN7 (stn7) shifted to low light experience higher photosystem II (PSII) redox pressure than the wild type or those lacking the cognate phosphatase TAP38 (tap38), while the reverse is true at high light, where tap38 suffers more. In principle, the LTR should allow optimisation of the stoichiometry of photosynthetic complexes to mitigate these effects. We used quantitative label-free proteomics to assess how the relative abundance of photosynthetic proteins varied with growth light intensity in wild-type, stn7, and tap38 plants. All plants were able to adjust photosystem I, LHCII, cytochrome b6f, and ATP synthase abundance with changing white light intensity, demonstrating neither STN7 nor TAP38 is crucial to the LTR per se. However, stn7 plants grown for several weeks at low light (LL) or moderate light (ML) still showed high PSII redox pressure and correspondingly lower PSII efficiency, CO2 assimilation, and leaf area compared to wild-type and tap38 plants, hence the LTR is unable to fully ameliorate these symptoms. In contrast, under high light growth conditions the mutants and wild type behaved similarly. These data are consistent with the paramount role of STN7-dependent LHCII phosphorylation in tuning PSII redox state for optimal growth in LL and ML conditions