Phase Transformation and Residual Stress in a Laser Beam Spot-Welded TiAl-Based Alloy

The microstructure, chemical composition, residual stress, and lattice parameter evolution ofthe welding zone (WZ) and heat-affected zone (HAZ) of a laser-beam-welded TiAl-based alloywere investigated. It was found that both a2 and c phases remain highly restrained in the WZedge, and the stresses are relieved in the HAZ. A grain refinement mechanism is proposed,which works by heating the material to the b or a+b phase field for a short time. The lamellarcolonies are refined by the Nb-enriched segregations

Essential Roles for GPI-anchored Proteins in African Trypanosomes Revealed Using Mutants Deficient in GPI8

The survival of Trypanosoma brucei, the causative agent of Sleeping Sickness and Nagana, is facilitated by the expression of a dense surface coat of glycosylphosphatidylinositol (GPI)-anchored proteins in both its mammalian and tsetse fly hosts. We have characterized T. brucei GPI8, the gene encoding the catalytic subunit of the GPI:protein transamidase complex that adds preformed GPI anchors onto nascent polypeptides. Deletion of GPI8 (to give Δgpi8) resulted in the absence of GPI-anchored proteins from the cell surface of procyclic form trypanosomes and accumulation of a pool of non–protein-linked GPI molecules, some of which are surface located. Procyclic Δgpi8, while viable in culture, were unable to establish infections in the tsetse midgut, confirming that GPI-anchored proteins are essential for insect-parasite interactions. Applying specific inducible GPI8 RNAi with bloodstream form parasites resulted in accumulation of unanchored variant surface glycoprotein and cell death with a defined multinuclear, multikinetoplast, and multiflagellar phenotype indicative of a block in cytokinesis. These data show that GPI-anchored proteins are essential for the viability of bloodstream form trypanosomes even in the absence of immune challenge and imply that GPI8 is important for proper cell cycle progression