Characterization of Loading Responses and Failure Loci of a Boron Steel Spot Weld

Boron steel, classed as an ultra high-strength steel (UHSS), has been utilized in anti-intrusion systems in automobiles, providing high strength and weight-saving potential through gage reduction. UHSS spot welds exhibit unique hardness distributions, with a hard nugget and outlying base material, but with a soft heat-affected zone in-between these regions. This soft zone reduces the strength of the weld and makes it susceptible to failure. Due to the interaction of various weld zones that occurs during loading, there is a need to characterize the loading response of the weld for accurate failure predictions. The loading response of certain weld zones, as well as failure loci, was obtained through physical simulation of the welding process. The results showed a significant difference in mechanical behavior through the weld length. An important result is that instrumented indentation was shown to be a valid, quantitative method for verifying the accuracy with which weld microstructure has been recreated with regard to the target weld microstructure

Cloning, expression and characterization of alcohol dehydrogenases in the silkworm Bombyx mori

Alcohol dehydrogenases (ADH) are a class of enzymes that catalyze the reversible oxidation of alcohols to corresponding aldehydes or ketones, by using either nicotinamide adenine dinucleotide (NAD) or nicotinamide adenine dinucleotide phosphate (NADP), as coenzymes. In this study, a short-chain ADH gene was identified in Bombyx mori by 5′-RACE PCR. This is the first time the coding region of BmADH has been cloned, expressed, purified and then characterized. The cDNA fragment encoding the BmADH protein was amplified from a pool of silkworm cDNAs by PCR, and then cloned into E. coli expression vector pET-30a(+). The recombinant His-tagged BmADH protein was expressed in E. coli BL21 (DE3), and then purified by metal chelating affinity chromatography. The soluble recombinant BmADH, produced at low-growth temperature, was instrumental in catalyzing the ethanol-dependent reduction of NAD+, thereby indicating ethanol as one of the substrates of BmADH

Simultaneous effects of strain rate and temperature on mechanical response of fabricated Mg–SiC nanocomposite

Mg–SiC nanocomposite samples were fabricated using split Hopkinson pressure bar for different SiC volume fractions and under different temperature conditions. The microstructures and mechanical properties of the samples including microhardness and stress–strain curves were captured from quasi-static and dynamic tests carried out using Instron and split Hopkinson pressure bar, respectively. Nanocomposites were produced by hot and high-rate compaction method using split Hopkinson pressure bar. Temperature also significantly affects relative density and can lead to 2.5% increase in density. Adding SiC-reinforcing particles to samples increased their Vickers microhardness from 46 VH to 68 VH (45% increase) depending on the compaction temperature. X-ray diffraction analysis showed that by increasing temperature from 25℃ to 450℃, the Mg crystallite size increases from 37 nm to 72 nm and decreases the lattice strain from 45% to 30%. In quasi-static tests, the ultimate compressive strength for the compaction temperature of 450℃ was improved from 123% for Mg–0 vol.% SiC to 200% for the Mg–10 vol.% SiC samples compared with those of the compaction at room temperature. In dynamic tests, the ultimate strength for Mg–10 vol.% SiC sample compacted at high strain rate increased remarkably by 110% compared with that for Mg–0 vol.% SiC sample compacted at low strain rate. </jats:p

Raman study of in vivo synthesized Zn(II)-metallothionein complexes: structural insight into metal clusters and protein folding.

Metallothioneins (MTs) are metal-chelating peptides that play an active role in zinc homeostasis. The participation of metal ligands other than cysteines and the presence of secondary structure elements in metal-MT complexes are fairly unknown, especially in nonvertebrate MTs. Here, four Zn(II) complexes of invertebrate MTs (mollusc, insect, nematode, and echinoderm) and the Zn(II)-MT complex of the mammalian MT1 isoform, heterologously synthesized in E. coli, were studied by analytic and spectroscopic techniques. By Raman and circular dichroism spectroscopy, new structural informations were obtained. The five analyzed MT isoforms consist largely of -turns with the near exclusion of -helical segments. Raman spectroscopy was revealed as an useful tool, providing information about the state of the cysteine sulfur atoms (metal coordinated and oxidized), the participation of histidine in metal coordination, and the molecular environment of tyrosine residues. In all the five Zn(II)-MT studied samples, acid-labile sulfide anions were found as nonproteic ligands, since sulfide-containing and sulfide-devoid species coexisted in the corresponding preparations. Significantly, Raman bands useful as markers of sulfide bridging ligands were identified. Overall, this work illustrates how the combination of analytical and spectroscopic techniques can be a very informative approach for the analysis of in vivo-synthesized metal-MT complexes, providing new data on the metal binding behavior of MTs from the most diverse organisms. \ua9 2008 Wiley Periodicals, Inc. Biopolymers 89: 1114-1124, 2008. This article was originally published online as an accepted preprint. The Published Online date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at [email protected]