An assessment of subsurface residual stresses analysis in SLM Ti 6Al 4V

Ti-6Al-4V bridges were additively fabricated by selective laser melting (SLM) under different scanning speed conditions, to compare the effect of process energy density on the residual stress state. Subsurface lattice strain characterization was conducted by means of synchrotron diffraction in energy dispersive mode. High tensile strain gradients were found at the frontal surface for samples in an as-built condition. The geometry of the samples promotes increasing strains towards the pillar of the bridges. We observed that the higher the laser energy density during fabrication, the lower the lattice strains. A relief of lattice strains takes place after heat treatment

Connecting Diffraction Based Strain with Macroscopic Stresses in Laser Powder Bed Fused Ti 6Al 4V

The laser powder bed fusion LPBF production process often results in large residual stress RS in the parts. Nondestructive techniques to determine RS are badly needed. However, a reliable quantification of macro RS i.e., stress at the component level by means of diffraction based techniques is still a great challenge, because the link between diffraction based strain and macro RS is not trivial. In this study, we experimentally determine by means of in situ synchrotron radiation diffraction this link for LPBF Ti 6Al 4V. We compare our results with commonly used models to determine the so called diffraction elastic constants DECs . We show that LPBF materials possess different DECs than wrought alloys, simply because their microstructural and mechanical properties are different. We also show that the existing models can be used to calculate DECs only if high accuracy of the RS values is not required. If the peculiarities of the microstructure have to be taken into account as is the case of additively manufactured materials , a radically new approach is desirabl

Phosphorylation of the Drosophila melanogaster RNA–Binding Protein HOW by MAPK/ERK Enhances Its Dimerization and Activity

Drosophila melanogaster Held Out Wings (HOW) is a conserved RNA–binding protein (RBP) belonging to the STAR family, whose closest mammalian ortholog Quaking (QKI) has been implicated in embryonic development and nervous system myelination. The HOW RBP modulates a variety of developmental processes by controlling mRNA levels and the splicing profile of multiple key regulatory genes; however, mechanisms regulating its activity in tissues have yet to be elucidated. Here, we link receptor tyrosine kinase (RTK) signaling to the regulation of QKI subfamily of STAR proteins, by showing that HOW undergoes phosphorylation by MAPK/ERK. Importantly, we show that this modification facilitates HOW dimerization and potentiates its ability to bind RNA and regulate its levels. Employing an antibody that specifically recognizes phosphorylated HOW, we show that HOW is phosphorylated in embryonic muscles and heart cardioblasts in vivo, thus documenting for the first time Serine/Threonine (Ser/Thr) phosphorylation of a STAR protein in the context of an intact organism. We also identify the sallimus/D-titin (sls) gene as a novel muscle target of HOW–mediated negative regulation and further show that this regulation is phosphorylation-dependent, underscoring the physiological relevance of this modification. Importantly, we demonstrate that HOW Thr phosphorylation is reduced following muscle-specific knock down of Drosophila MAPK rolled and that, correspondingly, Sls is elevated in these muscles, similarly to the HOW RNAi effect. Taken together, our results provide a coherent mechanism of differential HOW activation; MAPK/ERK-dependent phosphorylation of HOW promotes the formation of HOW dimers and thus enhances its activity in controlling mRNA levels of key muscle-specific genes. Hence, our findings bridge between MAPK/ERK signaling and RNA regulation in developing muscles

Geographic origin of the Y Chromosomes in “old” inbred strains of mice

Six distinct Y Chromosomes (Chr) were identified among 39 standard inbred strains of mice with five probes that identified Y Chr-specific restriction fragments on Southern blots. Three Y Chr types, distributed among 31 strains, were of Asian Mus musculus origin. The remaining three Y Chr types, distributed among eight strains, were of M. domesticus origin. The Asian source of the M. musculus Y Chr was confirmed by determining the DNA sequence of 221 bp from an open reading frame within the Sry (sex determining region Y) gene (Gubbay et al., Nature 346 245–250, 1990) in three inbred strains (C57BL/6J, AKR/J, and SWR/J) and comparing the sequence to the homologous sequences derived from wild caught European and Asian M. musculus males. These data indicate that a minimum of six male mice contributed to the formation of the old inbred strains.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46993/1/335_2004_Article_BF00292153.pd