Landauer–Büttiker and Thouless Conductance

In the independent electron approximation, the average (energy/charge/entropy) current flowing through a finite sample \({\mathcal{S}}\) connected to two electronic reservoirs can be computed by scattering theoretic arguments which lead to the famous Landauer–Büttiker formula. Another well known formula has been proposed by Thouless on the basis of a scaling argument. The Thouless formula relates the conductance of the sample to the width of the spectral bands of the infinite crystal obtained by periodic juxtaposition of \({\mathcal{S}}\). In this spirit, we define Landauer–Büttiker crystalline currents by extending the Landauer–Büttiker formula to a setup where the sample \({\mathcal{S}}\) is replaced by a periodic structure whose unit cell is \({\mathcal{S}}\). We argue that these crystalline currents are closely related to the Thouless currents. For example, the crystalline heat current is bounded above by the Thouless heat current, and this bound saturates iff the coupling between the reservoirs and the sample is reflectionless. Our analysis leads to a rigorous derivation of the Thouless formula from the first principles of quantum statistical mechanics.     

A Film-Flow Model to Describe Free Water Transport during Drying of a Hygroscopic Capillary Porous Medium

In this work, a two-phase film-flow model in a hygroscopic capillary tube is developed and extended to describe the two-phase capillary viscous transport in a network of parallel capillary tubes in terms of relative permeabilities. This film-flow approach is further considered to predict the longitudinal moisture transport in oak wood during drying. Numerical results obtained from this prediction are compared with data of convective drying experiments performed on samples of this wood. The comparison seems to confirm the physical relevance of a film-flow model to correctly represent the moisture transfer until the hygroscopic regime is reached.     

Proteome analysis of Aspergillus fumigatus identifies glycosylphosphatidylinositol-anchored proteins associated to the cell wall biosynthesis.

Previous studies in Aspergillus fumigatus (Mouyna I., Fontaine T., Vai M., Monod M., Fonzi W. A., Diaquin M., Popolo L., Hartland R. P., Latgé J.-P, J. Biol. Chem. 2000, 275, 14882-14889) have shown that a glucanosyltransferase playing an important role in fungal cell wall biosynthesis is glycosylphosphatidylinositol (GPI) anchored to the membrane. To identify other GPI-anchored proteins putatively involved in cell wall biogenesis, a proteomic analysis has been undertaken in A. fumigatus and the protein data were matched with the yeast genomic data. GPI-anchored proteins of A. fumigatus were released from membrane preparation by an endogenous GPI-phospholipase C, purified by liquid chromatography and separated by two-dimensional electrophoresis. They were characterized by their peptide mass fingerprint through matrix-assisted laser desorption/ionization-time of flight-(MALDI-TOF)-mass spectrometry and by internal amino acid sequencing. Nine GPI-anchored proteins were identified in A. fumigatus. Five of them were homologs of putatively GPI-anchored yeast proteins (Csa1p, Crh1p, Crh2p, Ecm33p, Gas1p) of unknown function but shown by gene disruption analysis to play a role in cell wall morphogenesis. In addition, a comparative study performed with chitin synthase and glucanosyl transferase mutants of A. fumigatus showed that a modification of the growth phenotype seen in these mutants was associated to an alteration of the pattern of GPI-anchored proteins. These results suggest that GPI-anchored proteins identified in this study are involved in A. fumigatus cell wall organization.     

Numerical simulation of the miscible displacement of radionuclides in a heterogeneous porous medium

The aim of this paper is to model and simulate the displacement of radioactive elements in a saturated heterogeneous porous medium. New schemes are proposed to solve accurately the convection–diffusion–reaction equations including nonlinear terms in the time derivative. Numerical tests show the stability and robustness of these schemes through strong heterogeneities of the medium. Finally the COUPLEX 1 benchmark concerning the far field simulation of a polluted flow by a leak of a nuclear waste disposal is performed and compared with the results available in the literature. Copyright © 2005 John Wiley & Sons, Ltd.     

Passive control of the flow around a square cylinder using porous media

The passive control of bluff body flows using porous media is investigated by means of the penalization method. This method is used to create intermediate porous media between solid obstacles and the fluid in order to modify the boundary layer behaviour. The study covers a wide range of two‐dimensional flows from low transitional flow to fully established turbulence by direct numerical simulation of incompressible Navier–Stokes equations. A parametric study is performed to illustrate the effect of the porous layer permeability and thickness on the passive control. The numerical results reveal the ability of porous media to both regularize the flow and to reduce the drag forces up to 30%. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis of new terpene derivatives via ruthenium catalysis: rearrangement of silylated enynes derived from terpenoids

Enyne rearrangement of silylated modified terpenoids has been used as the key step for the synthesis of new terpenes and terpenoids. The catalytic system generated in situ from [RuCl₂(p-cymene]₂, 1,3-bis(mesityl)imidazolinium chloride and cesium carbonate is able to perform the transformation of silylated 1,7-enynes into cyclic siloxanes. Selective cleavage of the silicon-carbon and silicon-oxygen bonds by simple reactions has been performed to afford new terpenes and terpenoids by formal addition of a C5 unit.     

CW HCN laser gain in a hollow dielectric rectangular cross-section discharge tube

This paper describes a 1 m-long CW HCN discharge laser with a hollow dielectric rectangular discharge tube of 5×20 cm² cross-section. For optimum working conditions, the characteristics of the amplifying medium have been made constant over the cross-section, by using an additional magnetic field. Then, the unsaturated gain for the 337 μm line is 6.8% m⁻¹. It is shown to be dependent on the smaller dimension of the cross-section rather than on the other dimension. By using the tube as a waveguide, laser output power of 1 Watt might be obtained with a discharge length of 4 m, instead of the 12m-long discharge required to get the same output power from a cylindrical waveguide laser.     

A Hamiltonian Model for Linear Friction in a Homogeneous Medium

 We introduce and study rigorously a Hamiltonian model of a classical particle moving through a homogeneous dissipative medium at zero temperature in such a way that it experiences an effective linear friction force proportional to its velocity (at small speeds). The medium consists at each point in a space of a vibration field modelling an obstacle with which the particle exchanges energy and momentum in such a way that total energy and momentum are conserved. We show that in the presence of a constant (not too large) external force, the particle reaches an asymptotic velocity proportional to this force. In a potential well, on the other hand, the particle comes exponentially fast to rest in the bottom of the well. The exponential rate is in both cases an explicit function of the model parameters and independent of the potential. Received: 18 July 2001 / Accepted: 20 April 2002 Published online: 12 August 2002