Feeding and Distribution of Porosity in Cast Al-Si Alloys as Function of Alloy Composition and Modification

Unmodified, Na-modified, and Sr-modified castings of Al-7 pct Si and Al-12.5 pct Si alloys were cast in molds in which it was possible to create different cooling conditions. It is shown how solidification influences the distribution of porosity at the surface and the center of the castings as a function of modification and Si content in sand- and chill-cast samples. Eutectic modification, Si content, and cooling conditions have a great impact on the distribution of porosity. Unmodified and Na-modified castings are more easily fed with porosity tending to congregate near the centerline of the casting, while Sr-modified castings solidify in a mushy manner that creates a more homogeneous distribution of porosity in the casting. The amount of porosity was highest in the Sr-modified alloys, lower in the Na-modified alloys, and lowest in the unmodified alloys. The size of the porosity-free layer and the effectiveness of the feeders were greater in the castings made with the steel chills due to the increased thermal gradients and consequent increase in the directionality of solidification

Chinese Script vs Plate-Like Precipitation of Beta-Al9Fe2Si2 Phase in an Al-6.5Si-1Fe Alloy

The microstructure of a high-purity Al-6.5Si-1Fe(wt pct) alloy after solidification at various cooling rates was investigated. In most of the cases, the monoclinic beta-Al9Fe2Si2 phase was observed as long and thin lamellae. However, at a very slow cooling rate, Febearing precipitates with Chinese script morphology appeared together with lamellae. Further analysis showed all these Chinese script precipitates correspond also to the monoclinic beta phase. This finding stresses that differentiating second phases according to their shape may be misleading

Production and Characterization of Chimeric Monoclonal Antibodies against Burkholderia pseudomallei and B. mallei Using the DHFR Expression System

Burkholderia pseudomallei (BP) and B. mallei (BM) are closely related gram-negative, facultative anaerobic bacteria which cause life-threatening melioidosis in human and glanders in horse, respectively. Our laboratory has previously generated and characterized more than 100 mouse monoclonal antibodies (MAbs) against BP and BM, according to in vitro and in vivo assay. In this study, 3 MAbs (BP7 10B11, BP7 2C6, and BP1 7F7) were selected to develop into chimeric mouse-human monoclonal antibodies (cMAbs) against BP and/or BM. For the stable production of cMAbs, we constructed 4 major different vector systems with a dihydrofolate reductase (DHFR) amplification marker, and optimized transfection/selection conditions in mammalian host cells with the single-gene and/or double-gene expression system. These 3 cMAbs were stably produced by the DHFR double mutant Chinese hamster ovarian (CHO)-DG44 cells. By ELISA and Western blot analysis using whole bacterial antigens treated by heat (65°C/90 min), sodium periodate, and proteinase K, the cMAb BP7 10B11 (cMAb CK1) reacted with glycoproteins (34, 38, 48 kDa in BP; 28, 38, 48 kDa in BM). The cMAb BP7 2C6 (cMAb CK2) recognized surface-capsule antigens with molecular sizes of 38 to 52 kDa, and 200 kDa in BM. The cMAb CK2 was weakly reactive to 14∼28, 200 kDa antigens in BP. The cMAb BP1 7F7 (cMAb CK3) reacted with lipopolysaccharides (38∼52 kDa in BP; 38∼60 kDa in B. thailandensis). Western blot results with the outer surface antigens of the 3 Burkholderia species were consistent with results with the whole Burkholderia cell antigens, suggesting that these immunodominant antigens reacting with the 3 cMAbs were primarily present on the outer surface of the Burkholderia species. These 3 cMAbs would be useful for analyzing the role of the major outer surface antigens in Burkholderia infection

Recent progress in understanding eutectic solidification in aluminium-silicon foundry alloys

It is now well established that three different eutectic solidification mechanisms may occur in Al-Si foundry alloys. The operation of each mechanism can be controlled by altering the chemical composition and casting conditions. Recent research has focussed on the understanding of the mechanisms determining the eutectic solidification mode by investigating the growth mechanisms in ultra-high purity and commercial purity alloys, the effect of a wide range of different potential modifying elements and investigating the eutectic nucleation mode. It is concluded that nucleation of eutectic grains is prolific in unmodified commercial purity alloys. In contrast, high-purity alloys have relatively few nuclei and only a few eutectic grains nucleate. Nuclei can also be removed, or rendered inactive, by the addition of modifying elements to commercial purity alloys. There is a relationship between the number of eutectic grains and the morphology of the eutectic because the growth rate of the eutectic depends on the surface area, The three eutectic solidification modes have widely differing spatial distributions of growing eutectic and therefore significant effects on the feeding efficiency of the alloys. Porosity is significantly affected by eutectic solidification mode and there is a direct relationship between them

Eutectic modification and microstructure development in Al-Si alloys

Recent increasing applications for cast Al-Si alloys are particularly driven by the need for lightweighting components in the automotive sector. To improve mechanical properties, elements such as strontium, sodium and antimony can be added to modify the eutectic silicon from coarse and plate-like to fine and fibrous morphology. It is only recently being noticed that the morphological transformation resulting from eutectic modification is also accompanied by other, equally significant, but often unexpected changes. These changes can include a 10-fold increase in the eutectic grain size, redistribution of low-melting point phases and porosity as well as surface finish, consequently leading to variations in casting quality. This paper shows the state-of-the-art in understanding the mechanism of eutectic nucleation and growth in Al-Si alloys, inspecting samples, both quenched and uninterrupted, on the macro, micro and nano-scale. It shows that significant variations in eutectic nucleation and growth dynamics occur in AI-Si alloys as a function of the type and amount of modifier elements added. The key role of AIP particles in nucleating silicon is demonstrated. (c) 2005 Elsevier B.V. All rights reserved

Functional proteomic analysis of GS-NS0 murine myeloma cell lines with varying recombinant monoclonal antibody production rate

We previously compared changes in individual protein abundance between the proteomes of GS-NSO cell lines with varying rates of cell-specific recombinant monoclonal antibody production (qMab). Here we extend analyses of our proteomic clataset to statistically determine if particular cell lines have distinct functional capabilities that facilitate production of secreted recombinant Mab. We categorized 79 proteins identified by mass spectrometry according to their biological function or location in the cell and statistically compared the relative abundance of proteins in each category between GS-NSO cell lines with varying qMab. We found that the relative abundance of proteins in ER chaperone, non-ER chaperone, cytoskeletal, cell signaling, metabolic, and mitochondrial categories were significantly increased with qMab. As the GS-NSO cell line with highest qMab also had an increased intracellular abundance of unassembled Mab heavy chain (HC), we tested the hypothesis that the increased ER chaperone content was caused by induction of an unfolded protein response (UPR) signaling pathway. Immunoblot analyses revealed that spliced X-box binding protein 1 (XBP1), a marker for UPR induction, was not detectable in the GS-NSO cells with elevated qMab, although it was induced by chemical inhibitors of protein folding. These data suggest that qMab is functionally related to the abundance of specific categories of proteins that together facilitate recombinant protein production. We infer that individual cells within parental populations are more functionally equipped for high-level recombinant protein production than others and that this bias could be used to select cells that are more likely to achieve high qMab. (c) 2006 Wiley Periodicals, Inc

Post-transcriptional regulation of the breast cancer susceptibility gene BRCA1 by Hu Antigen-R

BRCA1 is a breast cancer susceptibility gene that is down-regulated in the majority of cases of sporadic breast cancer. In tumours with reduced BRCA1 protein expression, there can be a concomitant reduction in mRNA level, or no change, suggesting that disruption of multiple different regulatory processes may contribute to BRCA1 down-regulation. Despite this, efforts to date have chiefly focussed on transcriptional and epigenetic regulation of the gene, whilst post-transcriptional processes that regulate the dynamics of the BRCA1 transcript, such as decay, localisation and translation efficiency, are poorly understood. Post-transcriptional regulation of gene expression is often mediated by RNA-binding proteins (RNA-BPs) that recognise sequence motifs in the untranslated regions (UTRs) of certain mRNAs, and recruit, or shield them from macromolecular complexes involved in RNA metabolism, such as the translation apparatus and the exosome. Primary and secondary structure analysis of the BRCA1 3'UTR sequence revealed two predicted binding sites for the RNA-BP Hu-antigen R (HuR), known to regulate the stability and translation efficiency of other transcripts, including COX-2, TNF-α and TP53. Interestingly, HuR is frequently over-expressed in sporadic breast cancer. We present the results of RNA-protein-binding assays showing that HuR interacts directly with synthetic RNA probes containing one of the predicted HuR-binding sites in the BRCA1 3'UTR, and immunoprecipitation studies showing that this interaction occurs endogenously in human mammary epithelial cell lines. Over-expression of HuR conferred a reduction in BRCA1 protein expression, and the BRCA1 3'UTR sequence was sufficient for down-regulation of a luciferase reporter gene in cells expressing ectopic HuR. Experiments addressing the mechanism underlying the change in BRCA1 expression in HuR over-expressing cells, including reporter assays, mRNA and protein stability assays, suggest that the mechanism of regulation is post-transcriptional. Current and future work is aimed at understanding the relationship between HuR and BRCA1 in breast cancer