Grain morphology of as-cast wrought aluminium alloys

Two of the most important microstructural features of alloys are the grain size and the dendrite arm spacing (DAS). Both grain refinement and the DAS depend upon alloy composition through constitutional undercooling, but in different ways. Grain size tends to be related to the initial rate of development of constitutional undercooling, whilst the DAS is more related to the amount of solute build-up towards the end of the solidification process. This means that element additions that have a large effect on the grain size, e.g. Ti, have much less effect on the DAS. With examples from a range of wrought Al alloys, this paper investigates how the interaction between alloy content, grain refiner additions and cooling rate affect the grain size, DAS and the grain morphology obtained in an alloy

Fine-scale movement decisions of tropical forest birds in a fragmented landscape

The persistence of forest-dependent species in fragmented landscapes is fundamentally linked to the movement of individuals among subpopulations. The paths taken by dispersing individuals can be considered a series of steps built from individual route choices. Despite the importance of these fine-scale movement decisions, it has proved difficult to collect such data that reveal how forest birds move in novel landscapes. We collected unprecedented route information about the movement of translocated forest birds from two species in the highly fragmented tropical dry forest of Costa Rica. In this pasture-dominated landscape, forest remains in patches or riparian corridors, with lesser amounts of living fencerows and individual trees or "stepping stones." We used step selection functions to quantify how route choice was influenced by these habitat elements. We found that the amount of risk these birds were willing to take by crossing open habitat was context dependent. The forest-specialist Barred Antshrike (Thamnophilus doliatus) exhibited stronger selection for forested routes when moving in novel landscapes distant from its territory relative to locations closer to its territory. It also selected forested routes when its step originated in forest habitat. It preferred steps ending in stepping stones when the available routes had little forest cover, but avoided them when routes had greater forest cover. The forest-generalist Rufous-naped Wren (Campylorhynchus rufinucha) preferred steps that contained more pasture, but only when starting from non-forest habitats. Our results showed that forested corridors (i.e., riparian corridors) best facilitated the movement of a sensitive forest specialist through this fragmented landscape. They also suggested that stepping stones can be important in highly fragmented forests with little remaining forest cover. We expect that naturally dispersing birds and species with greater forest dependence would exhibit even stronger selection for forested routes than did the birds in our experiments

WR 110: A Single Wolf-Rayet Star With Corotating Interaction Regions In Its Wind?

A 30-day contiguous photometric run with the MOST satellite on the WN5-6b star WR 110 (HD 165688) reveals a fundamental periodicity of P = 4.08 +/- 0.55 days along with a number of harmonics at periods P/n, with n ~ 2,3,4,5 and 6, and a few other possible stray periodicities and/or stochastic variability on timescales longer than about a day. Spectroscopic RV studies fail to reveal any plausible companion with a period in this range. Therefore, we conjecture that the observed light-curve cusps of amplitude ~ 0.01 mag that recur at a 4.08 day timescale may arise in the inner parts, or at the base of, a corotating interaction region (CIR) seen in emission as it rotates around with the star at constant angular velocity. The hard X-ray component seen in WR 110 could then be a result of a high velocity component of the CIR shock interacting with the ambient wind at several stellar radii. Given that most hot, luminous stars showing CIRs have two CIR arms, it is possible that either the fundamental period is 8.2 days or, more likely in the case of WR 110, there is indeed a second weaker CIR arm for P = 4.08 days, that occurs ~ two thirds of a rotation period after the main CIR. If this interpretation is correct, WR 110 therefore joins the ranks with three other single WR stars, all WN, with confirmed CIR rotation periods (WR 1, WR 6, and WR 134), albeit with WR 110 having by far the lowest amplitude photometric modulation. This illustrates the power of being able to secure intense, continuous high-precision photometry from space-based platforms such as MOST. It also opens the door to revealing low-amplitude photometric variations in other WN stars, where previous attempts have failed. If all WN stars have CIRs at some level, this could be important for revealing sources of magnetism or pulsation in addition to rotation periods.Comment: 25 pages, 8 figures, 2 tables, accepted in Ap

Structural Variation and Chemical Performance—A Study of the Effects of Chemical Structure upon Epoxy Network Chemical Performance

Epoxy resins are used widely as protective coatings, in a wide range of harsh chemical environments. This work explores the influence of subtle structural variation in both epoxy and amine monomers upon chemical performance of cured networks, whether changing molecular geometry, the nature of the chemistry, or the mass between cross-linking reactive groups. To achieve this, four industrially relevant epoxy resins (two based on bisphenol A—Epikote 828 (E828) and Dow Epoxy Resin 332 (DER 332)—and two based on bisphenol F—Dow Epoxy Resin 354 (DER 354) and Araldite PY306 (PY306)) and the isomerically pure para–para-diglycidyl ether of bisphenol F (ppDGEBF) were used to explore variation caused by epoxy monomer variation. Four similar amines (meta-xylylenediamine (MXDA), para-xylylenediamine (PXDA), 1,3-bis(aminomethyl)cyclohexane (1,3-BAC), 1,4-bis(aminomethyl)cyclohexane (1,4-BAC)) were used to explore any variations caused by regioisomerism and aromaticity. Bisphenol F-based resins were found to outperform bisphenol A-based analogues, and chain extension within the epoxy component was found to be detrimental to performance. For amines, 1,3-substitution (vs 1,4) and aromaticity were both found to be beneficial to chemical performance

Body composition in older community-dwelling adults with hip fracture: portable field methods validated by dual-energy X-ray absorptiometry

Ageing is associated with weight loss and subsequently poor health outcomes. The present study assessed agreement between two field methods, bioelectrical impedance spectroscopy (BIS) and corrected arm muscle area (CAMA) for assessment of body composition against dual-energy X-ray absorptiometry (DXA), the reference technique. Agreement between two predictive equations estimating skeletal muscle mass (SMM) from BIS against SMM from DXA was also determined. Assessments occurred at baseline < 14 d post-surgery (n 79), and at 6 months (6M; n 75) and 12 months (12M; n 63) in community-living older adults after surgical treatment for hip fracture. The 95 % limits of agreement (LOA) between BIS and DXA, CAMA and DXA and the equations and DXA were assessed using Bland–Altman analyses. Mean bias and LOA for fat-free mass (FFM) between BIS and DXA were: baseline, 0·7 ( − 10·9, 12·4) kg; 6M, − 0·5 ( − 20·7, 19·8) kg; 12M, 0·1 ( − 8·7, 8·9) kg and for SMM between CAMA and DXA were: baseline, 0·3 ( − 11·7, 12·3) kg; 6M, 1·3 ( − 4·5, 7·1) kg; 12M, 0·9 ( − 5·4, 7·2) kg. Equivalent data for predictive equations against DXA were: equation 1: baseline, 15·1 ( − 9·5, 20·6) kg; 6M, 17·1 ( − 12·0, 22·2) kg; 12M, 17·5 ( − 13·0, 22·0) kg; equation 2: baseline, 12·6 ( − 7·3, 19·9) kg; 6M, 14·4 ( − 9·7, 19·1) kg; 12M, 14·8 ( − 10·7, 18·9) kg. Proportional bias (BIS: β = − 0·337, P< 0·001; CAMA: β = − 0·294, P< 0·001) was present at baseline but not at 6M or 12M. Clinicians should be cautious in using these field methods to predict FFM and SMM, particularly in the acute care setting. New predictive equations would be beneficial.This research was supported by the National Health and Medical Research Council (NHMRC), Australia

Small‐Scale Mechanical Testing of Nuclear Structural Materials

Material property changes due to harsh reactor environment conditions, such as neutron irradiation and high temperature, may limit the performance and the safe operating envelopes of all reactor types. Quantitative information on the material properties changes is needed to support ongoing life extension/ life management efforts of the existing global reactor fleet, as well as for design and development of future advanced reactor concepts. Testing of larger radioactive test specimens is challenging and expensive, as it requires their handling and testing in shielded facilities. Testing smaller sized specimens has an advantage in terms of their reduced activity that allows for safer handling and cost effective testing processes. Please click Additional Files below to see the full abstract

Wet scavenging of soluble gases in DC3 deep convective storms using WRF-Chem simulations and aircraft observations

We examine wet scavenging of soluble trace gases in storms observed during the Deep Convective Clouds and Chemistry (DC3) field campaign. We conduct high-resolution simulations with the Weather Research and Forecasting model with Chemistry (WRF-Chem) of a severe storm in Oklahoma. The model represents well the storm location, size, and structure as compared with Next Generation Weather Radar reflectivity, and simulated CO transport is consistent with aircraft observations. Scavenging efficiencies (SEs) between inflow and outflow of soluble species are calculated from aircraft measurements and model simulations. Using a simple wet scavenging scheme, we simulate the SE of each soluble species within the error bars of the observations. The simulated SEs of all species except nitric acid (HNO_3) are highly sensitive to the values specified for the fractions retained in ice when cloud water freezes. To reproduce the observations, we must assume zero ice retention for formaldehyde (CH_2O) and hydrogen peroxide (H_2O_2) and complete retention for methyl hydrogen peroxide (CH_3OOH) and sulfur dioxide (SO_2), likely to compensate for the lack of aqueous chemistry in the model. We then compare scavenging efficiencies among storms that formed in Alabama and northeast Colorado and the Oklahoma storm. Significant differences in SEs are seen among storms and species. More scavenging of HNO_3 and less removal of CH_3OOH are seen in storms with higher maximum flash rates, an indication of more graupel mass. Graupel is associated with mixed-phase scavenging and lightning production of nitrogen oxides (NO_x), processes that may explain the observed differences in HNO_3 and CH_3OOH scavenging