Henri Poincaré: The Status of Mechanical Explanations and the Foundations of Statistical Mechanics

The first goal of this paper is to show the evolution of Poincaré’s opinion on the mechanistic reduction of the principles of thermodynamics, placing it in the context of the science of his time. The second is to present some of his work in 1890 on the foundations of statistical mechanics. He became interested first in thermodynamics and its relation with mechanics, drawing on the work of Helm-holtz on monocyclic systems. After a period of skepticism concerning the kinetic theory, he read some of Maxwell’s memories and contributed to the foundations of statistical mechanics. I also show that Poincaré's contributions to the founda-tions of statistical mechanics are closely linked to his work in celestial mechanics and its interest in probability theory and its role in physics

Cell type-specific processing of the I-Ed-restricted hen egg lysozyme determinant 107-116.

Class II major histocompatibility complex heterodimers present to T cells determinants as sets of antigen fragments with ragged N and C termini. It is not yet elucidated whether different types of antigen-presenting cells generate identical sets of peptides containing the same determinant. Taking advantage of recombinant I-Ed molecules produced by insect cells as empty heterodimers, a sensitive T cell stimulation assay was developed to analyze naturally processed hen egg lysozyme (HEL) peptides. I-Ed preparations were isolated from antigen-presenting cells cultured with HEL. Following acid treatment, peptides eluted from I-Ed were chromatographed and the fractions incubated at acidic pH with purified recombinant I-Ed molecules, conditions which favor peptide binding. The stimulatory capacity of the reconstituted peptide-I-Ed complexes adsorbed on the well surface of cell culture plates was then evaluated by measuring interleukin-2 secreted by an HEL 107-116-specific, I-Ed-restricted T cell hybridoma. We found that the B lymphoma A20 and an I-Ed-transfected fibroblast cell line generated distinct sets of peptides containing the HEL sequence 107-116. Our results suggest the possibility that presentation of one determinant by different types of antigen-presenting cells stimulates populations of T cells with distinct fine antigen specificities

The processing routes determined by negatively charged residues in DR1-restricted T cell determinants

The presentation pathways followed by DR1-restricted determinants from the fusion protein of measles virus were studied. By assessing the capacity of various APC preparations to stimulate fusion protein-specific T cells, it was shown that the determinant contained within the fusion protein sequence 254-268 (F254) relies on newly synthesized DR1 protein for its presentation. By contrast, the determinant contained within the fusion protein sequence 314-328 (F314) is captured by DR1 protein recycled from the plasma membrane. In vitro binding analyses showed that the F254 and F314 peptides optimally bind to DR1 at pH 4 and pH 5, respectively. In addition, it was found that binding of the F254 peptide to DR1 is much poorer at pH 7 than at pH 4, while binding of the F314 peptide was decreased only moderately at pH 7 as compared with pH 5. Substitution of the glutamic acid 261 for an alanine in the F254 peptide resulted in an analogue with an improved capacity of binding to DR1 at neutral pH. By contrast, replacement of the valine 319 by a glutamic acid in the F314 peptide generated an analogue with a decreased binding capacity at pH 7. These findings indicated that determinants that do not bear acidic residues are captured efficiently by DR1 molecules over a broader range of pH than determinants containing acidic residues. Binding analyses between DR1 and four additional peptides further supported this conclusion. Altogether, these results suggested that acidic residues, by tuning the optimal pH for the assembly of peptide-DR1 complexes, determine the processing pathway followed by the determinants

Gain coupled DFB lasers with active layer grown on a corrugated substrate by molecular beam epitaxy

Using in situ hydrogen desorption before the growth of the 12nm thick active InGaAs layer over V-grooves, operation of gain coupled DFB lasers at 989nm is achieved al room temperature. As-cleaved lasers, 600 mu m long, have threshold current densities as low as 250A/cm(2) and typical sidemode suppression ratios of 40dB