Large intrinsic birefringence in zinc-blende based artificial semiconductors

A new attempt to solve the phase matching problem for semiconductor-based frequency conversion devices, based on the implementation of intrinsic birefringence in artificial materials, is discussed. The first results concerning the growth and characterization of ultrashort period superlattices are presented. To cite this article: J.-M. Jancu et al., C. R. Physique 8 (2007).     

The refocused INADEQUATE MAS NMR experiment in multiple spin-systems: interpreting observed correlation peaks and optimising lineshapes

The robustness of the refocused INADEQUATE MAS NMR pulse sequence for probing through-bond connectivities has been demonstrated in a large range of solid-state applications. This pulse sequence nevertheless suffers from artifacts when applied to multispin systems, e.g. uniformly labeled (13)C solids, which distort the lineshapes and can potentially result in misleading correlation peaks. In this paper, we present a detailed account that combines product-operator analysis, numerical simulations and experiments of the behavior of a three-spin system during the refocused INADEQUATE pulse sequence. The origin of undesired anti-phase contributions to the spectral lineshapes are described, and we show that they do not interfere with the observation of long-range correlations (e.g. two-bond (13)C-(13)C correlations). The suppression of undesired contributions to the refocused INADEQUATE spectra is shown to require the removal of zero-quantum coherences within a z-filter. A method is proposed to eliminate zero-quantum coherences through dephasing by heteronuclear dipolar couplings, which leads to pure in-phase spectra.     

Drug-loaded nano/microbubbles for combining ultrasonography and targeted chemotherapy

A new class of multifunctional nanoparticles that combine properties of polymeric drug carriers, ultrasound imaging contrast agents, and enhancers of ultrasound-mediated drug delivery has been developed. At room temperature, the developed systems comprise perfluorocarbon nanodroplets stabilized by the walls made of biodegradable block copolymers. Upon heating to physiological temperatures, the nanodroplets convert into nano/microbubbles. The phase state of the systems and bubble size may be controlled by the copolymer/perfluorocarbon volume ratio. Upon intravenous injections, a long-lasting, strong and selective ultrasound contrast is observed in the tumor volume indicating nanobubble extravasation through the defective tumor microvasculature, suggesting their coalescence into larger, highly echogenic microbubbles in the tumor tissue. Under the action of tumor-directed ultrasound, microbubbles cavitate and collapse resulting in a release of the encapsulated drug and dramatically enhanced intracellular drug uptake by the tumor cells. This effect is tumor-selective; no accumulation of echogenic microbubbles is observed in other organs. Effective chemotherapy of the MDA MB231 breast cancer tumors has been achieved using this technique.     

Quark-hadron duality in neutron (3He) spin structure

We present experimental results of the first high-precision test of quark-hadron duality in the spin-structure function g_{1} of the neutron and 3He using a polarized 3He target in the four-momentum-transfer-squared range from 0.7 to 4.0 (GeV/c);{2}. Global duality is observed for the spin-structure function g_{1} down to at least Q;{2}=1.8 (GeV/c);{2} in both targets. We have also formed the photon-nucleon asymmetry A1 in the resonance region for 3He and found no strong Q2 dependence above 2.2 (GeV/c);{2}.     

The use of trehalose in the preparation of specimens for molecular electron microscopy

Biological specimens have to be prepared for imaging in the electron microscope in a way that preserves their native structure. Two-dimensional (2D) protein crystals to be analyzed by electron crystallography are best preserved by sugar embedding. One of the sugars often used to embed 2D crystals is trehalose, a disaccharide used by many organisms for protection against stress conditions. Sugars such as trehalose can also be added to negative staining solutions used to prepare proteins and macromolecular complexes for structural studies by single-particle electron microscopy (EM). In this review, we describe trehalose and its characteristics that make it so well suited for preparation of EM specimens and we review specimen preparation methods with a focus on the use of trehalose.     

Sur les valeurs propres d'un oscillateur harmonique perturbé

Sans résumé Dedicated to Professor Shmuel Agmon     

Anisotropic Analysis of Some Gaussian Models

Although the classical Fractional Brownian Motion is often used to describe porosity, it is not adapted to anisotropic situations. In the present work, we study a class of Gaussian fields with stationary increments and spectral density. They present asymptotic self-similarity properties and are good candidates to model a homogeneous anisotropic material, or its radiographic images. Unfortunately, the paths of all Gaussian fields with stationary increments have the same apparent regularity in all directions (except at most one). Hence we propose here a procedure to recover anisotropy from one realization: computing averages over all the hyperplanes which are orthogonal to a fixed direction, we get a process whose Hölder regularity depends explicitly on the asymptotic behavior of the spectral density in this direction.