Diode laser welding of stainless steel 304L

The feasibility to achieve deep penetration welding of stainless steel utilising a 15 kW laserline® diode laser has been studied. This was approached by first characterising the properties of melt run welds on stainless steel 304L plates and then transferring the gained knowledge to perform the butt welds. The results from the melt run analysis indicated that there was an increase in penetration and weld width with heat input, i. e. with either increasing the laser power (9–15 kW) or decreasing the welding velocity (3 m/min–1 m/min). Melt run penetrations up to 12 mm were achieved. The increased welding velocity was shown to reduce the solidification grain and subgrain size. Cracks along the weld centreline were observed at the higher heat inputs and sinking at the crowns at the lower. Good melt run welds were obtained at laser powers of 9–13 kW and a welding velocity of 1.5 m/min. Butt welding of 10 mm thick plates was successfully achieved with full penetration along the length of the weld at a laser power of 12 kW and a welding velocity of 1.5 m/min. The weld properties were comparable to the corresponding melt run welds using a similar parameter set of laser power and welding velocity. No detrimental subsurface defects were recorded with only the presence of a negligible amount of porosity. Oxidisation on the surface of the cap and sinking towards the end of the weld run was observed. It was demonstrated that high powered diode lasers are capable of deep penetration welding. Keyhole mode welding was achieved and the weld properties are comparable to that of other high energy density welding processes. For welding of plates in the 10 mm thickness range, the results suggested that the more economic high power diode lasers may become a competitor to different laser beam systems which may be more expensive in both procurement and operation

Evolution of Surface Morphology of Thermo-Mechanically Cycled NiCoCrAlY Bond Coats

We investigate morphological surface instabilities on bond coat surfaces of thermal barrier coatings, induced due to thermo-mechanical loading. Experimental results of hollow circular cylindrical specimens, consisting of a directionally solidified superalloy (IN 100 DS) coated with a NiCoCrAlY bond coat, show that the morphological instabilities are strongly dependent on the load conditions. In particular, the morphological instabilities develop during thermal cycling with a thermal gradient over the cylinder wall, whereas the surface remains smooth for thermal cyclic conditions without a gradient. Furthermore, if a cyclic, axial tensile force is applied (synchronized with the thermal cycling), the morphological instabilities become aligned with the axial direction. We discuss a model, quantified by finite element simulations, capturing this behavior and elucidating the thermo-mechanical response

Evolution of Surface Morphology of Thermo-Mechanically Cycled NiCoCrAlY Bond Coats

We investigate morphological surface instabilities on bond coat surfaces of thermal barrier coatings, induced due to thermo-mechanical loading. Experimental results of hollow circular cylindrical specimens, consisting of a directionally solidified superalloy (IN 100 DS) coated with a NiCoCrAlY bond coat, show that the morphological instabilities are strongly dependent on the load conditions. In particular, the morphological instabilities develop during thermal cycling with a thermal gradient over the cylinder wall, whereas the surface remains smooth for thermal cyclic conditions without a gradient. Furthermore, if a cyclic, axial tensile force is applied (synchronized with the thermal cycling), the morphological instabilities become aligned with the axial direction. We discuss a model, quantified by finite element simulations, capturing this behavior and elucidating the thermo-mechanical response

Sex-specific effects of microbiome perturbations on cerebral Aβ amyloidosis and microglia phenotypes.

We demonstrated that an antibiotic cocktail (ABX)-perturbed gut microbiome is associated with reduced amyloid-β (Aβ) plaque pathology and astrogliosis in the male amyloid precursor protein (APP)SWE /presenilin 1 (PS1)ΔE9 transgenic model of Aβ amyloidosis. We now show that in an independent, aggressive APPSWE/PS1L166P (APPPS1-21) mouse model of Aβ amyloidosis, an ABX-perturbed gut microbiome is associated with a reduction in Aβ pathology and alterations in microglial morphology, thus establishing the generality of the phenomenon. Most importantly, these latter alterations occur only in brains of male mice, not in the brains of female mice. Furthermore, ABX treatment lead to alterations in levels of selected microglial expressed transcripts indicative of the "M0" homeostatic state in male but not in female mice. Finally, we found that transplants of fecal microbiota from age-matched APPPS1-21 male mice into ABX-treated APPPS1-21 male restores the gut microbiome and partially restores Aβ pathology and microglial morphology, thus demonstrating a causal role of the microbiome in the modulation of Aβ amyloidosis and microglial physiology in mouse models of Aβ amyloidosis

Secondary contact and admixture between independently invading populations of the Western corn rootworm, diabrotica virgifera virgifera in Europe

The western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae), is one of the most destructive pests of corn in North America and is currently invading Europe. The two major invasive outbreaks of rootworm in Europe have occurred, in North-West Italy and in Central and South-Eastern Europe. These two outbreaks originated from independent introductions from North America. Secondary contact probably occurred in North Italy between these two outbreaks, in 2008. We used 13 microsatellite markers to conduct a population genetics study, to demonstrate that this geographic contact resulted in a zone of admixture in the Italian region of Veneto. We show that i) genetic variation is greater in the contact zone than in the parental outbreaks; ii) several signs of admixture were detected in some Venetian samples, in a Bayesian analysis of the population structure and in an approximate Bayesian computation analysis of historical scenarios and, finally, iii) allelic frequency clines were observed at microsatellite loci. The contact between the invasive outbreaks in North-West Italy and Central and South-Eastern Europe resulted in a zone of admixture, with particular characteristics. The evolutionary implications of the existence of a zone of admixture in Northern Italy and their possible impact on the invasion success of the western corn rootworm are discussed