Vectorial vortex mode transformation for a hollow waveguide using Pancharatnam-Berry phase optical elements

Transformation and inverse transformation between a free-space linearly polarized beam and the vectorial vortex mode of a circular hollow waveguide by use of Pancharatnam-Berry phase optical elements is proposed. Demonstration was achieved by fabricating GaAs subwavelength gratings and utilizing a 300 microm diameter hollow metallic waveguide for 10.6 microm wavelength CO(2) laser radiation. The mode transformations and the excitation of a single vectorial mode inside the hollow waveguide were verified by full polarization measurements. In addition, the inverse mode transformation of the single vectorial mode excitation in the waveguide enabled us to experimentally obtain a linearly polarized bright spot with a high central lobe.     

Radially and azimuthally polarized beams generated by space-variant dielectric subwavelength gratings

We present a novel method for forming radially and azimuthally polarized beams by using computer-generated subwavelength dielectric gratings. The elements were deposited upon GaAs substrates and produced beams with a polarization purity of 99.2% at a wavelength of 10.6 microm . We have verified the polarization properties with full space-variant polarization analysis and measurement, and we show that such beams have certain vortexlike properties and that they carry angular momentum.     

Hasse–Witt invariants of symmetric complexes: an example from geometryInvariants de Hasse–Witt de complexes symétriques : un exemple géométrique

Jardine has defined Hasse–Witt invariants for symmetric bundles over schemes. This definition can be extended to symmetric complexes, that is symmetric objects in the derived category of bounded complexes of vector bundles over a scheme. In this Note we show how one can use these generalized invariants to give a neater proof of a comparison result on Hasse–Witt invariants of symmetric bundles attached to tame coverings of schemes. To cite this article: P. Cassou-Noguès et al., C. R. Acad. Sci. Paris, Ser. I 334 (2002) 839–842.     

Atmospheric pressure chemical ionization of alkanes,alkenes, and cycloalkanes

Normal and cyclic alkanes and alkenes form stable gas-phase ions in air at atmospheric pressure from 40 to 200°C when moisture is below 1 ppm. Ionization of alkanes in a ⁶³Ni source favored charge transfer over proton transfer through pathways involving [M?1]⁺ and [M?3]⁺ ions. Ion mobility spectra for alkanes showed sharp and symmetrical profiles while spectra for alkenes suggested fragmentation. Ion identifications were made by using mass spectrometry, and ionization pathways were supported by using deuterated analogs of alkanes and alkenes. Alkanes were ionized seemingly through a hydrogen abstraction pathway and did not proceed through an alkene intermediate. New methods for interpretation of mobility spectra utilizing ion mobility spectrometry, atmospheric pressure chemical ionization mass spectrometry, chemical ionization mass spectrometry, and ion mobility spectrometry-mass spectrometry data were demonstrated.     

Oligonucleotide loaded polypeptide‐peptide nanoparticles towards mitochondrial‐targeted delivery

Nanoparticles (NPs) consisting of biodegradable and biocompatible polymers may have the ability to deliver a cargo to specific tissue, cell type, and organelle. Various diseases, which are linked to mitochondrial genome (mtDNA) mutations and have no effective treatments, may be approached by gene therapy strategies. In this study, we adapted the recently developed mitochondria delivering polypeptide‐peptide nanoparticles (PoP‐NPs) system to carry an oligonucleotide cargo to the proximity of the mitochondria. PoP‐NPs are formulated by self‐assembly of the negatively charged polypeptide, poly gamma glutamic acid (γ‐PGA), with an amphiphilic and cationic β‐sheet peptide (PFK). Here, we show that PFK interacts favorably with oligonucleotides and thereby enables the formation of DNA‐loaded PoP‐NPs (DNA‐PoP‐NPs). DNA‐PoP‐NPs could be assembled with different peptide to oligonucleotide (N/P) ratios, and their targeting to the proximity of mitochondria in cell culture could be facilitated through NPs coating with PFK peptide.     

Preferential attachment in the protein network evolution

The Saccharomyces cerevisiae protein-protein interaction map, as well as many natural and man-made networks, shares the scale-free topology. The preferential attachment model was suggested as a generic network evolution model that yields this universal topology. However, it is not clear that the model assumptions hold for the protein interaction network. Using a cross-genome comparison, we show that (a) the older a protein, the better connected it is, and (b) the number of interactions a protein gains during its evolution is proportional to its connectivity. Therefore, preferential attachment governs the protein network evolution. Evolutionary mechanisms leading to such preference and some implications are discussed.     

Singlet excitations in pyrochlore: a study of quantum frustration

We apply the contractor renormalization (CORE) method to the spin half Heisenberg antiferromagnet on the frustrated checkerboard and pyrochlore lattices. Their ground states are spin-gapped singlets which break lattice symmetry. Their effective Hamiltonians describe fluctuations of orthogonal singlet pairs on tetrahedral blocks, at an emergent low energy scale. We discuss low temperature thermodynamics and new interpretations of finite size numerical data. We argue that our results are common to many models of quantum frustration.     

Separating atmospheric layers in adaptive optics

Several optical schemes have been proposed to measure the separate contributions of atmospheric layers for astronomical adaptive optics. I show here that simple conjugation of the wave-front sensors to the layers is sufficient. Although a larger camera is required for a larger field of view, only the pixels that sense stars are being read out. The nearly periodic Hartmann data are analyzed by Fourier filtering so that the signals from all stars are added up while most of the noise is excluded. Acoustic Hartmann wave-front sensors [Opt. Lett. 26, 1834 (2001)1 that switch between layers improve flexibility and sensitivity.