Haemonchus contortus is a haematophagous parasitic nematode of veterinary interest. We have performed a survey of its genome-wide diversity using single-worm whole genome sequencing of 223 ...individuals sampled from 19 isolates spanning five continents. We find an African origin for the species, together with evidence for parasites spreading during the transatlantic slave trade and colonisation of Australia. Strong selective sweeps surrounding the β-tubulin locus, a target of benzimidazole anthelmintic drug, are identified in independent populations. These sweeps are further supported by signals of diversifying selection enriched in genes involved in response to drugs and other anthelmintic-associated biological functions. We also identify some candidate genes that may play a role in ivermectin resistance. Finally, genetic signatures of climate-driven adaptation are described, revealing a gene acting as an epigenetic regulator and components of the dauer pathway. These results begin to define genetic adaptation to climate in a parasitic nematode.
Stress corrosion cracking of Al-Zn-Mg-Cu (AA7xxx) aluminum alloys exposed to saline environments at temperatures ranging from 293 K to 353 K (20 °C to 80 °C) has been reviewed with particular ...attention to the influences of alloy composition and temper, and bulk and local environmental conditions. Stress corrosion crack (SCC) growth rates at room temperature for peak- and over-aged tempers in saline environments are minimized for Al-Zn-Mg-Cu alloys containing less than ~8 wt pct Zn when Zn/Mg ratios are ranging from 2 to 3, excess magnesium levels are less than 1 wt pct, and copper content is either less than ~0.2 wt pct or ranging from 1.3 to 2 wt pct. A minimum chloride ion concentration of ~0.01 M is required for crack growth rates to exceed those in distilled water, which insures that the local solution pH in crack-tip regions can be maintained at less than 4. Crack growth rates in saline solution without other additions gradually increase with bulk chloride ion concentrations up to around 0.6 M NaCl, whereas in solutions with sufficiently low dichromate (or chromate), inhibitor additions are insensitive to the bulk chloride concentration and are typically at least double those observed without the additions. DCB specimens, fatigue pre-cracked in air before immersion in a saline environment, show an initial period with no detectible crack growth, followed by crack growth at the distilled water rate, and then transition to a higher crack growth rate typical of region 2 crack growth in the saline environment. Time spent in each stage depends on the type of pre-crack (“pop-in”
vs
fatigue), applied stress intensity factor, alloy chemistry, bulk environment, and, if applied, the external polarization. Apparent activation energies (
E
a
) for SCC growth in Al-Zn-Mg-Cu alloys exposed to 0.6 M NaCl over the temperatures ranging from 293 K to 353 K (20 °C to 80 °C) for under-, peak-, and over-aged low-copper-containing alloys (<0.2 wt pct) are typically ranging from 80 to 85 kJ/mol, whereas for high-copper-containing alloys (>~0.8 wt pct), they are typically ranging from 20 to 40 kJ/mol for under- and peak-aged alloys, and based on limited data, around 85 kJ/mol for over-aged tempers. This means that crack propagation in saline environments is most likely to occur by a hydrogen-related process for low-copper-containing Al-Zn-Mg-Cu alloys in under-, peak- and over-aged tempers, and for high-copper alloys in under- and peak-aged tempers. For over-aged high-copper-containing alloys, cracking is most probably under anodic dissolution control. Future stress corrosion studies should focus on understanding the factors that control crack initiation, and insuring that the next generation of higher performance Al-Zn-Mg-Cu alloys has similar longer crack initiation times and crack propagation rates to those of the incumbent alloys in an over-aged condition where crack rates are less than 1 mm/month at a high stress intensity factor.
Display omitted
•The HEAC behaviour of new generation 7xxx series has been compared in humid air.•The failure time can be reduced by at least an order of magnitude.•Crack growth rates are 6–20 times ...higher than for AA7050-T7651.•Shown, a strong association between crack growth rate and higher Zn.•The potential influences of differences in the alloy’s chemistries are discussed.
The hydrogen environmentally-assisted cracking (HEAC) behaviour of new generation (new-gen) Al-Zn-Mg-Cu thick-plate alloys (AA7449, AA7085, and AA7037), under accelerated humid warm-air exposure, has been compared to the aerospace industry benchmark alloy AA7050 in over-aged T7x type tempers. Constant load time-to-failure and DCB crack growth tests have been performed at a relative humidity of 85 %, at 70 °C. It has been found that in constant load tests the failure time of the new generation alloys can be reduced by at least an order of magnitude and in some cases cracking was observed in only a few days at stress levels of 85 % of yield. Analysis of the failed fractured specimens has confirmed that the fracture behaviour is predominantly intergranular, and highly localised to high angle grain boundaries. The progression from surface initiation to self-propagating cracks occurred much more rapidly in the new higher Zn content alloys, but with less prior surface chemical attack. In DCB v-K tests stage II crack growth rates were also found to be significantly higher (by a factor of 6–20 times) in the new-gen alloys and the K1HEAC threshold stress intensity was less than half that for AA7050-T7651. Under long crack growth conditions, propagation thus required a higher mechanical driving force and crack growth stagnated more readily in the AA7050-T7651 benchmark material, compared to in the new generation alloys. The results have been discussed in the context of the potential influences of differences in the alloy’s chemistries and microstructures.
•A copper content of ∼0.6wt% may be overaged when the quench-rate is not too rapid.•Crack arrest markings spacings could be related to the hydrogen diffusivity.•XPS showed that the oxide of AA7075 ...was slightly more hydrated than on AA7079.
Stress corrosion cracking (SCC) of two lower-copper Al–Zn–Mg–Cu alloys, AA7079 and AA7022 (0.6–0.9wt% Cu), and a higher-copper AA7075 (1.5wt% Cu) alloy are reported. In aqueous chloride, copper content of grain boundary precipitates is believed to be controlling, whereas in moist air it appears that the hydrogen diffusivity could be evident from the rate of crack growth between crack arrest markings. In moist air, the rate of hydrogen entry may control crack growth rates. X-ray photoelectron spectroscopy showed that the oxide formed in ambient conditions (e.g. ∼50% RH) was more hydrated on the AA7075-T651 than AA7079-T651.
Aluminum-magnesium alloys are ideal for a number of structural applications; however, alloys with magnesium content more than 3 wt% can become sensitized and susceptible to environmentally-assisted ...failure after exposure to moderately elevated temperatures for sufficient periods of time. Commercial Al-Mg alloys were tested in the as-received and sensitized conditions to investigate susceptibility to environmentally-enhanced cracking in fatigue crack growth. Slow strain rate testing (SSRT) of short-transverse (S-T) smooth tensile samples and fatigue crack growth testing of SEN bend specimens was also conducted in various loading orientations (L-T, L-S, S-L and S-T). Sensitization treatments included exposure to temperatures ranging from 60 °C – 175 °C for times ranging from 10 h to 20,000 h. Under specific loading conditions and the presence of a local hydrogen source, IGSCC manifested itself as ST and SL plane splits during the cyclic loading of sufficiently sensitized L-S and L-T test specimens. The regimes of grain boundary cracking have been determined. Initial findings using ESBD data is suggestive that the high angle grain boundaries most likely to suffer IGSCC are those with a sharp gradient in the Taylor factor. Remediation treatments were also conducted on sensitized Al-Mg alloys in an attempt to reverse sensitization and restore alloy properties. While thermal remediation was somewhat effective in reducing the environmentally-sensitive fracture, this condition occurred at the expense of a loss in strength and its long-term effectiveness remains questionable. SEM and EBSD were used to document the locus and orientation-dependence of grain boundary failure while TEM was used to determine species present at grain boundaries susceptible to environmentally-enhanced fracture. SSRT testing of S-T samples in various environments revealed different degrees of embrittlement depending on the environment and degree of sensitization. A change in alloy sensitization kinetics occurs at around 100 °C.
Imaging intact human organs from the organ to the cellular scale in three dimensions is a goal of biomedical imaging. To meet this challenge, we developed hierarchical phase-contrast tomography ...(HiP-CT), an X-ray phase propagation technique using the European Synchrotron Radiation Facility (ESRF)'s Extremely Brilliant Source (EBS). The spatial coherence of the ESRF-EBS combined with our beamline equipment, sample preparation and scanning developments enabled us to perform non-destructive, three-dimensional (3D) scans with hierarchically increasing resolution at any location in whole human organs. We applied HiP-CT to image five intact human organ types: brain, lung, heart, kidney and spleen. HiP-CT provided a structural overview of each whole organ followed by multiple higher-resolution volumes of interest, capturing organotypic functional units and certain individual specialized cells within intact human organs. We demonstrate the potential applications of HiP-CT through quantification and morphometry of glomeruli in an intact human kidney and identification of regional changes in the tissue architecture in a lung from a deceased donor with coronavirus disease 2019 (COVID-19).
New generation (new-gen) 7xxx series alloys have recently been shown to have higher susceptibility to environmental assisted cracking (EAC) in humid air, compared to AA7050, in T7651 tempers. ...Hydrogen (H)-EAC fracture features of brittle intergranular (IG) and transgranular (TG) fracture modes were observed with humidity levels as low as 20%. Initiation was favoured at sites of intermetallic particle clusters with gas pores. The higher performance of AA7050 was attributed to the difficulty of initiation in this alloy, where the grain structure, combined with an intrinsic resistance of the grain boundaries to IG-EAC, made the attainment of sustained cracking difficult.
Display omitted
•Strain rates as low as 10-8 s-1 were utilised to assess the EAC performance of aluminium alloy 7xxx series in humid air.•The complete sequence of EAC was presented through high-resolution fractography of well-preserved fracture surfaces.•Thick plate AA 7085 and AA 7449 were more susceptible to EAC in humid air compared to AA7050 in their T7651 tempers.•AA7050 high resistance to EAC in humid air was attributed to the difficulty of growing short cracks during EAC initiation.
Intergranular sustained-load cracking of Al-Zn-Mg-Cu (AA7xxx series) aluminum alloys exposed to moist air or distilled water at temperatures in the range 283 K to 353 K (10 °C to 80 °C) has been ...reviewed in detail, paying particular attention to local processes occurring in the crack-tip region during crack propagation. Distinct crack-arrest markings formed on intergranular fracture faces generated under fixed-displacement loading conditions are not generated under monotonic rising-load conditions, but can form under cyclic-loading conditions if loading frequencies are sufficiently low. The observed crack-arrest markings are insensitive to applied stress intensity factor, alloy copper content and temper, but are temperature sensitive, increasing from ~150 nm at room temperature to ~400 nm at 313 K (40 °C). A re-evaluation of published data reveals the apparent activation energy,
E
a
for crack propagation in Al-Zn-Mg(-Cu) alloys is consistently ~35 kJ/mol for temperatures above ~313 K (40 °C), independent of copper content or the applied stress intensity factor, unless the alloy contains a significant volume fraction of
S
-phase, Al
2
CuMg where
E
a
is ~80 kJ/mol. For temperatures below ~313 K (40 °C)
E
a
is independent of copper content for stress intensity factors below ~14 MNm
−3/2
, with a value ~80 kJ/mol but is sensitive to copper content for stress intensity factors above ~14 MNm
−3/2
, with
E
a
, ranging from ~35 kJ/mol for copper-free alloys to ~80 kJ/mol for alloys containing 1.5 pct Cu. The apparent activation energy for intergranular sustained-load crack initiation is consistently ~110 kJ/mol for both notched and un-notched samples. Mechanistic implications are discussed and processes controlling crack growth, as a function of temperature, alloy copper content, and loading conditions are proposed that are consistent with the calculated apparent activation energies and known characteristics of intergranular sustained-load cracking. It is suggested, depending on the circumstances, that intergranular crack propagation in humid air and distilled water can be enhanced by the generation of aluminum hydride, AlH
3,
ahead of a propagating crack and/or its decomposition after formation within the confines of the nanoscale volumes available after increments of crack growth, defined by the crack arrest markings on intergranular fracture surfaces.
Display omitted
•Entire colonies of environmentally induced cracks have been observed in 4D.•Cracks initiate continuously from 0.5σy until failure; the rate is highest under straining.•EIC cracks ...clearly propagate below KIEIC threshold but are susceptible to arrest.•Propagation of all cracks is discontinuous and ranges from 0 to 20x the average velocity.•Microstructural obstacles can be directly related to the propagation behaviour.
Environment Induced Cracking (EIC) has been observed in three dimensions (3D) at high spatial and temporal resolution for AA5083 H131 alloy using in situ synchrotron X-ray CT. The initiation of EIC cracks occurred in humid air at ∼0.5σy and started from corrosion sites associated with intermetallic particle clusters. Time-resolved monitoring of the crack growth confirmed cracks grow below threshold KIEIC and are susceptible to arrest under fixed displacement conditions. Even when the cracks exceed threshold KIEIC and enter sustained propagation they exhibit very uneven growth rates. Failure occurs when the K of the largest crack exceeds the fracture toughness KIC.
PDF
