Surface Tension Measurements on CMSX-4 Superalloy by the Drop-Weight and Oscillating-Drop Methods

The surface tension of the CMSX-4^®reg; superalloy has been determined by the drop-weight and oscillating-drop methods which are well adapted to reactive materials. The recommended values are 1.59 J·m^–2 for the surface tension at the liquidus temperature and –0.14× 10^–3 J·m^–2· K^–1 for the temperature coefficient. A conclusion of the present work is that the interpretation of surface tension measurements performed on a complex alloy generally requires additional work to be performed on simpler associated binary or ternary systems, as well as some support from solidification experiments.     

Optimization techniques for small matrix multiplication

The complexity of matrix multiplication has attracted a lot of attention in the last forty years. In this paper, instead of considering asymptotic aspects of this problem, we are interested in reducing the cost of multiplication for matrices of small size, say up to 30. Following the previous work of Probert & Fischer, Smith, and Mezzarobba, in a similar vein, we base our approach on the previous algorithms for small matrices, due to Strassen, Winograd, Pan, Laderman, and others and show how to exploit these standard algorithms in an improved way. We illustrate the use of our results by generating multiplication codes over various rings, such as integers, polynomials, differential operators and linear recurrence operators.     

Capillary interactions between molten silicon and porous graphite

The capillary properties (wetting, infiltration) of the reactive Si/porous graphite system are studied by the sessile drop technique that enables the spreading and infiltration dynamics to be monitored in situ. The experiments are performed by varying the temperature, the type of graphite (porosity, grain size) and the vapour phase (inert gas or high vacuum). Further experiments are performed in order to quantify the influence of the exothermic reaction between Si and graphite on the temperature field close to the infiltration front. The effects of Si–graphite interactions on graphite mechanical integrity are also evidenced.     

Toxicity-based selection of Escherichia coli mutants for functional recombinant protein production: application to an antibody fragment

We propose a novel approach to the selection of Escherichia coli bacterial strains improved for the production of recombinant functional proteins. This approach is based on aggregation-induced toxicity of recombinant proteins. We show that selection of clones displaying a reduced toxicity is an efficient means of isolating bacteria producing recombinant protein with reduced aggregation in favour of correct folding. For an efficient selection, we found that time of toxicity induction must be precisely determined and recombinant protein must be expressed as a fusion with a protein whose activity is easily detectable on plates, thus allowing elimination of non-productive mutants. Choosing the expression to the periplasmic space of an scFv fragment fused to the N-terminus of alkaline phosphatase as a model, we selected chromosomal mutations that reduce aggregation-induced toxicity and showed that they concomitantly improve production of a functional recombinant hybrid. The effects of the mutations isolated could then be cumulated with those of other strategies used for recombinant scFv production. Thus, we could ensure a 6- to 16-fold increase in production of a functional scFv-PhoA hybrid. This is the first report demonstrating the possibility of directly selecting on agar plates E.coli strains improved for functional recombinant protein production from a large bacterial mutant library.     

Pd-Cu-Ni-P Bulk Metallic Glass: A Very Low Damping Material

The present work addresses damping experiments performed in a Pd-Cu-Ni-P bulk metallic glass. After an appropriated thermal treatment, this material exhibits a very low damping coefficient, down to 10⁻⁶. This result is discussed considering the different possible origins of the damping phenomena: thermoelasticity, energy dissipation by electrons, phonons, defects, and residual stresses. Thermoelasticity and defects appear to be the most important sources of mechanical damping. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25−March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.     

Transformation of a non-enzymatic toxin into a toxoid by genetic engineering

Curaremimetic toxins are typical non-enzymatic toxins that bind to their target [the nicotinic acetylcholine receptor (AChR)] through multiple residues. Nevertheless, we show that the concomitant substitutions of only three of the ten functionally important residues of such a toxin sufficed to cause an affinity decrease of the toxin for AChR that is higher than four orders of magnitude. Despite these triple mutations, the overall conformation of the mutated protein remains similar to that of a related recombinant toxin, as judged from both circular dichroism analysis and investigation of antigenicity, using monoclonal and polyclonal antibodies. Furthermore, we show that the detoxified toxin is capable of eliciting antibodies that neutralize the binding of a wild-type toxin to AChR. Therefore, transformation of a non-enzymatic toxin into a toxoid can be achieved, like in the case of enzymatic toxins, by introducing a small number of mutations at positions identified to be critical for expression of toxicity.     

Transformation of a non-enzymatic toxin into a toxoid by genetic engineering

Curaremimetic toxins are typical non-enzymatic toxins that bind to their target [the nicotinic acetylcholine receptor (AChR)] through multiple residues. Nevertheless, we show that the concomitant substitutions of only three of the ten functionally important residues of such a toxin sufficed to cause an affinity decrease of the toxin for AChR that is higher than four orders of magnitude. Despite these triple mutations, the overall conformation of the mutated protein remains similar to that of a related recombinant toxin, as judged from both circular dichroism analysis and investigation of antigenicity, using monoclonal and polyclonal antibodies. Furthermore, we show that the detoxified toxin is capable of eliciting antibodies that neutralize the binding of a wild-type toxin to AChR. Therefore, transformation of a non-enzymatic toxin into a toxoid can be achieved, like in the case of enzymatic toxins, by introducing a small number of mutations at positions identified to be critical for expression of toxicity.      

On the measurements of thermophysical properties during planar front solidification of an Sn-Bi alloy in microgravity: Results of the Mephisto-USMP1 experiments

We propose in this paper a procedure to deduce the values of some important thermophysical parameters, such as the solute diffusion and partition coefficients, from the analysis of solidification experiments. The data considered here were obtained during the first microgravity flight of the Mephisto experiment, as our procedure can only be applied when mass transport is purely diffusive. This is often impossible on earth due to unavoidable convective movements, but can be achieved in space. The numerical modelling of the initial solute transient using the deduced values was found to be in good agreement with the experimental results.