| 1. |
- Jakosky, B. M., et al.
(författare)
-
MAVEN observations of the response of Mars to an interplanetary coronal mass ejection
- 2015
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 350:6261
-
Tidskriftsartikel (refereegranskat)abstract
- Coupling between the lower and upper atmosphere, combined with loss of gas from the upper atmosphere to space, likely contributed to the thin, cold, dry atmosphere of modern Mars. To help understand ongoing ion loss to space, the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft made comprehensive measurements of the Mars upper atmosphere, ionosphere, and interactions with the Sun and solar wind during an interplanetary coronal mass ejection impact in March 2015. Responses include changes in the bow shock and magnetosheath, formation of widespread diffuse aurora, and enhancement of pick-up ions. Observations and models both show an enhancement in escape rate of ions to space during the event. Ion loss during solar events early in Mars history may have been a major contributor to the long-term evolution of the Mars atmosphere.
|
|
| 2. |
- Raffan, Eleanor, et al.
(författare)
-
A Deletion in the Canine POMC Gene Is Associated with Weight and Appetite in Obesity-Prone Labrador Retriever Dogs
- 2016
-
Ingår i: Cell Metabolism. - : Elsevier BV. - 1550-4131 .- 1932-7420. ; 23:5, s. 893-900
-
Tidskriftsartikel (refereegranskat)abstract
- Sequencing of candidate genes for obesity in Labrador retriever dogs identified a 14 bp deletion in pro-opiomelanocortin (POMC) with an allele frequency of 12%. The deletion disrupts the b-MSH and beta-endorphin coding sequences and is associated with body weight (per allele effect of 0.33 SD), adiposity, and greater food motivation. Among other dog breeds, the deletion was only found in the closely related flat-coat retriever (FCR), where it is similarly associated with body weight and food motivation. The mutation is significantly more common in Labrador retrievers selected to become assistance dogs than pets. In conclusion, the deletion in POMC is a significant modifier of weight and appetite in Labrador retrievers and FCRs and may influence other behavioral traits.
|
|
| 3. |
- Forber, K. J., et al.
(författare)
-
Plant-based diets add to the wastewater phosphorus burden
- 2020
-
Ingår i: Environmental Research Letters. - : IOP PUBLISHING LTD. - 1748-9326. ; 15:9
-
Tidskriftsartikel (refereegranskat)abstract
- Global food production and current reliance on meat-based diets requires a large share of natural resource use and causes widespread environmental pollution including phosphorus (P). Transitions to less animal-intensive diets address a suite of sustainability goals, but their impact on societys wastewater P burden is unclear. Using the UK as our example, we explored historical diet changes between 1942 and 2016, and how shifting towards plant-based diets might impact the P burden entering wastewater treatment works (WWTW), and subsequent effluent P discharge to receiving water bodies. Average daily per capita P intake declined from its peak in 1963 (1599 mg P pp(-1)d(-1)) to 1354 mg P pp(-1)d(-1)in 2016. Since 1942, the contribution of processed foods to total P consumption has increased from 21% to 52% in 2016, but consumption of total animal products has not changed significantly. Scenario analysis indicated that if individuals adopted a vegan diet or a low-meat (EAT- Lancet) diet by 2050, the P burden entering WWTW increased by 17% and 35%, respectively relative to baseline conditions in 2050. A much lower P burden increase (6%) was obtained with a flexitarian diet. An increasing burden of P to WWTW threatens greater non-compliance with regulatory targets for P discharge to water, but also presents an opportunity to the wastewater industry to recycle P in the food chain, and reduce reliance on finite phosphate rock resources. Sustainable diets that reduce food system P demand pre-consumption could also provide a source of renewable fertilizers through enhanced P recovery post-consumption and should be further explored.
|
|
| 4. |
- Lopez-Crespo, P., et al.
(författare)
-
Measuring overload effects during fatigue crack growth in bainitic steel by synchrotron X-ray diffraction
- 2015
-
Ingår i: International Journal of Fatigue. - : Elsevier BV. - 1879-3452 .- 0142-1123. ; 71, s. 11-16
-
Tidskriftsartikel (refereegranskat)abstract
- In this work we present the results of in situ synchrotron X-ray diffraction measurements of fatigue crack-tip strain fields following a 100% overload (OL) under plane strain conditions. The study is made on a bainitic steel with a high toughness and fine microstructure. This allowed a very high (60 mu m) spatial resolution to be achieved so that fine-scale changes occurring around the crack-tip were captured along the crack plane at the mid-thickness of the specimen. We have followed the crack as it grew through the plastic/residually stressed zone associated with the OL crack location. We observed two effects; one when the enhanced plastic zone is ahead of the crack and one after it has been passed. Regarding the former it was found that the compressive stress at the crack-tip initially falls sharply, presumably due to the increased plastic stretch caused by the OL. This is associated with a concomitant fall in peak tensile stress at K-max, the elastic excursion between K-min and K-max remaining essentially unchanged from before OL. Subsequently discontinuous closure as seen previously for plane stress caused by crack face contact at the OL location limits the elastic strain range experienced by the crack tip and thereby retards crack growth. (C) 2014 Elsevier Ltd. All rights reserved.
|
|
| 5. |
- Lopez-Crespo, P., et al.
(författare)
-
Overload effects on fatigue crack-tip fields under plane stress conditions: surface and bulk analysis
- 2013
-
Ingår i: Fatigue & Fracture of Engineering Materials & Structures. - : Wiley. - 1460-2695 .- 8756-758X. ; 36:1, s. 75-84
-
Tidskriftsartikel (refereegranskat)abstract
- The surface crack opening displacements are characterised by digital image correlation for a (thin) plane stress 316 stainless steel compact tension sample subjected to an overload event. This supports a traditional plasticity-induced closure interpretation showing a knee in the closure response prior to overload, an absence of closure in the accelerated growth regime followed by accentuated closure in the retardation regime. By contrast, measurement of the mid-thickness elastic strain field behind and ahead of the crack made by synchrotron X-ray diffraction shows no evidence of significant crack face contact stresses behind the crack tip on approaching minimum loading. Rather the changes during loading and overloading can mostly be explained by a simple elastic plastic analysis using a value of the yield stress intermediate between the initial yield stress and the UTS. This shows very significant compressive reverse plastic strains ahead of the crack that start to form early during unloading. At the moment it is not clear whether this difference is because of the increasing stress intensity applied as the crack grows, or for some other reason, such as prevention of the crack faces closing mid-thickness due to the reverse plastic zone.
|
|
| 6. |
- Steuwer, Axel, et al.
(författare)
-
A combined approach to microstructure mapping of an Al-Li AA2199 friction stir weld
- 2011
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1873-2453 .- 1359-6454. ; 59:8, s. 3002-3011
-
Tidskriftsartikel (refereegranskat)abstract
- A wide range of complementary techniques are used to build up a detailed picture of the microstructural zones found in friction stir welds (FSW) in an advanced AA2199 Al-Li alloy. Neutron and synchrotron X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, small angle X-ray scattering, scanning electron microscopy, electron backscatter diffraction (EBSD) and hardness mapping are brought together to build up a detailed two-dimensional picture of the grain morphology, precipitate type, size, volume fraction and matrix solute content across the weld cross section and to explain the general lack of a W-shaped hardness profile across FSW in third-generation Al-Li-Cu Mg alloys. Dissolution of the age-hardening phases occurred in different regions of the weld, depending on their respective solvus temperatures, with 5' dissolving within the heat-affected zone and T-1 coarsening in the thermo-mechanically affected zone before going into solution in the weld nugget. Changes to the precipitate distribution, and especially to the T1 phase, are linked to a significant reduction in hardness (strength) and unstrained lattice parameter across the weld zone. It was also possible to show that the low recovery of nugget zone hardness is primarily due to its poor natural ageing response. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
|
|
| 7. |
- Altenkirch, J., et al.
(författare)
-
Comparison of methods to determine variations in unstrained unit cell parameter across welds
- 2011
-
Ingår i: Journal of Strain Analysis for Engineering Design. - : SAGE Publications. - 0309-3247 .- 2041-3130. ; 46:7, s. 651-662
-
Tidskriftsartikel (refereegranskat)abstract
- Many alloys undergo complex changes in local chemistry in the vicinity of weldments due to the thermal excursion during welding. The resulting changes in solute concentrations can lead to significant local variations in the unstrained unit cell parameter which, if not accounted for, can lead to serious error when determining residual stress by diffraction methods. Age-hardening aluminium alloys are particularly susceptible to such effects. The present paper compares three methods (plane stress assumption, sin(2)psi method, and comb correction method) for evaluating the stress-free unit cell parameter variation for friction stir welds in AA7449-W51 plates of two different thicknesses. All three methods gave comparable results for thin (5 mm) sheet, but for the thicker (12.2 mm) plate the results calculated on the basis of the plane stress assumption diverged from the other two, largely because in this case the other methods indicate there to be a significant triaxiality of stress. In the example cases, hardness and unstrained unit cell parameter variations were found to be strongly correlated across the welds. The advantages and disadvantages of the three methods are compared.
|
|
| 8. |
- Altenkirch, J., et al.
(författare)
-
Mechanical Tensioning of High-Strength Aluminum Alloy Friction Stir Welds
- 2008
-
Ingår i: Symposium on Neutron and X-Ray Studies for Probing Materials Behavior held at the 137th TMS Annual Meeting and Exhibition. - : Springer Science and Business Media LLC. - 1073-5623. ; 39A, s. 3246-3259
-
Konferensbidrag (refereegranskat)abstract
- The extent to which in-situ global mechanical tensioning (GMT) can be used to modify the residual stress state in friction stir (FS) welds is investigated in this article. Residual stress distributions have been determined by synchrotron X-ray and neutron diffraction for four sets of FS welds in high-strength AA7449-W51 and lithium containing AA2199-T8 aerospace aluminum alloys subjected to a systematic range of GMT levels. For the cases studied, the results indicate that the level of residual stresses present in the as-welded state is a function of the alloy. The rate of residual stress reduction brought about by GMT, however, is basically alloy independent; indeed, it is essentially linear with respect to the GMT load, so that the tensioning required to reduce the weld stresses to zero can be calculated directly from the stresses present in the untensioned case. For thin plates, proximity to the yield stress in the hot-softened zone means that a guideline rule is that 1 MPa of tensioning during welding reduces the tensile stress by approximately 1 MPa. The GMT was found to be less effective at greater depths in thick plates. Furthermore, a reduction in bending distortion and an increase in angular distortion was observed with increased GMT, while no effects on the weld microstructure and hardness were observed.
|
|
| 9. |
- Altenkirch, J., et al.
(författare)
-
The extent of relaxation of weld residual stresses on cutting out cross-weld test-pieces
- 2009
-
Ingår i: Powder Diffraction. - : Cambridge University Press (CUP). - 0885-7156 .- 1945-7413. ; 24:2, s. 31-36
-
Tidskriftsartikel (refereegranskat)abstract
- Weld residual stress (RS) measurements are often undertaken on test-pieces which have been Cut Out from large components, yet it remains unclear to what extent the RSs in test-pieces are representative of those present in the original component. Similarly weld mechanical performance tests are frequently undertaken on cross-weld test-pieces without a proper understanding of the level or influence of retained RS. We present a systematic study of the relaxation of longitudinal RS in thin-plate butt welds produced using different materials and welding methods (FSW, laser-MIG, and pulsed-MIG). In each case the RSs were measured repeatedly in the same location as the welds were progressively and symmetrically cut down. Although cutting inevitably leads to stress redistribution, significant relaxation of the longitudinal RS was only observed when the weld length or width was reduced to below a certain value. This critical value appears to correlate with the lateral width of the tensile zone local to the weld-line and may be considered to be the characteristic length as defined in St. Venant's principle. Further, it was found that the level of stress relaxation as a function of weld length for all the welds studied could be collapsed onto a single empirical curve using a simple approach based on the characteristic length scales of the weld. Given the range of materials and welding methods used, this relation appears to be of general use for thin-plate welds although further work is required to test the limits of its applicability. (C) 2009 International Centre for Diffraction Data. [DOI: 10.1154/1.3152580]
|
|
| 10. |
- Andrews, David J., et al.
(författare)
-
MARSIS Observations of Field-Aligned Irregularities and Ducted Radio Propagation in the Martian Ionosphere
- 2018
-
Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 123:8, s. 6251-6263
-
Tidskriftsartikel (refereegranskat)abstract
- Knowledge of Mars's ionosphere has been significantly advanced in recent years by observations from Mars Express and lately Mars Atmosphere and Volatile EvolutioN. A topic of particular interest are the interactions between the planet's ionospheric plasma and its highly structured crustal magnetic fields and how these lead to the redistribution of plasma and affect the propagation of radio waves in the system. In this paper, we elucidate a possible relationship between two anomalous radar signatures previously reported in observations from the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument on Mars Express. Relatively uncommon observations of localized, extreme increases in the ionospheric peak density in regions of radial (cusp-like) magnetic fields and spread echo radar signatures are shown to be coincident with ducting of the same radar pulses at higher altitudes on the same field lines. We suggest that these two observations are both caused by a high electric field (perpendicular to B) having distinctly different effects in two altitude regimes. At lower altitudes, where ions are demagnetized and electrons magnetized, and recombination dominantes, a high electric field causes irregularities, plasma turbulence, electron heating, slower recombination, and ultimately enhanced plasma densities. However, at higher altitudes, where both ions and electrons are magnetized and atomic oxygen ions cannot recombine directly, the high electric field instead causes frictional heating, a faster production of molecular ions by charge exchange, and so a density decrease. The latter enables ducting of radar pulses on closed field lines, in an analogous fashion to interhemispheric ducting in the Earth's ionosphere.
|
|
