Direct optical injection locking of 20 GHz superlattice oscillators

For the first time, a direct optically injection-locked oscillator based on the Esaki-Tsu effect in superlattices is reported. The microwave output power is -7 dBm at 20 GHz with an optical input power of -10 dBm at a wavelength of 1.3 μm     

A two-scale second-moment turbulence closure based on weighted spectrum integration

A two-scale second-moment turbulence closure has been derived based on the weighted integration of the dynamic equation for the covariance spectrum. The goal is to close the Reynolds stress equations with two additional scalar equations that provide separately the scales of the spectral energy transfer and of the turbulence energy dissipation rate. Such a model should provide better prediction of nonequilibrium turbulent flows. The derivation consists of analytical integration of the wave-number-weighted covariance spectrum using a model of the spectral equations with an assumed simple representation of the shape of the energy spectrum. The resulting closure consists of a set of three tensorial equations, one for the Reynolds stress and two for length scale tensors, the latter representing the energy containing- and dissipative eddies respectively. The trace of the two tensor-scale equations leads to a set of two scalar scale parameters. In the equilibrium limit, the model reduces to the standard second-moment single-scale closure. The approach makes it also possible to derive the scale equations in a more systematic manner as compared with the common single-scale and other multi-scale models. The performance of the model in capturing the scale dynamics is illustrated by predictions of several generic homogeneous and inhomogeneous unsteady flows, demonstrating the expected response of the two scale equations. PACS 03.50.De, 04.20-q, 42.65-k     

Hydrogels Incorporating GdDOTA: Towards Highly Efficient Dual T(1) /T(2) MRI Contrast Agents

Do not tumble dry: Gadolinium-DOTA encapsulated into polysaccharide nanoparticles (GdDOTA?NPs) exhibited high relaxivity (r(1) =101.7?s(-1) mM(-1) per Gd(3+) ion at 37?°C and 20?MHz). This high relaxation rate is due to efficient Gd loading, reduced tumbling of the Gd complex, and the hydrogel nature of the nanoparticles. The efficacy of the nanoparticles as a T(1) /T(2) dual-mode contrast agent was studied in C6 cells.     

Towards petascale spectral simulations for transition analysis in wall bounded flow

An efficient parallel spectral method for direct numerical simulations of transitional and turbulent flows is described in this paper. The parallelization is classically based on a bidimensional domain decomposition, but has been specifically developed for a solenoidal Fourier–Chebyshev spectral approximation where in one Fourier direction, the number of modes is very large compared with the two other directions. The approach therefore differs from classical libraries developed for cubic Fourier boxes. The strategy uses message‐passing interface (MPI) for message‐passing among nodes and is fairly portable. One of the originalities of this paper is the use of an efficient hybrid programming with MPI for internodes communications and a coarse grain parallelism using OpenMP for core shared‐memory computation, instead of the classical hybrid programming with MPI and a fine granularity parallelism at the loop level with OpenMP directives. This hybrid parallelism has been tested on the recent generation of high‐performance parallel supercomputers involving a few tens of cores per node. Performances are evaluated on different low‐frequency and high‐frequency processors massively parallel platforms. We demonstrate that spectral methods, which are known to be inherently ill‐fitted for the new generation of high‐performance distributed‐memory computers, can be implemented efficiently using this hybrid programming with good scalability and a very fast wall‐clock time per iteration. New numerical experiments are therefore now accessible on petascale computers, while keeping the attractive features of spectral methods such as accuracy, exponential convergence, computational efficiency and conservative properties. This is illustrated by a direct numerical simulation of the transition of the boundary layers developing from the entrance section of a plane channel and interacting to merge into a fully turbulent flow. Copyright © 2012 John Wiley & Sons, Ltd.     

Octanuclear cobalt and nickel cages featuring formate ligands

Two new octanuclear cages are reported which feature formate as a bridging carboxylate which has been formed in situ from decomposition of triphenylacetate used as a ligand.     

Cyclam-methylbenzimidazole: a selective OFF-ON fluorescent sensor for zinc

The coordination properties and the photophysical response of a new cyclam fluorescent probe for Zn(II), [L1H: 1-(benzimidazol-2-ylmethyl]-1,4, 8,11-tetraazacyclotetradecane] toward Cu(II), Zn(II), and Cd(II) are reported. The stability constants of the corresponding complexes were determined by means of potentiometric measurements in aqueous solution. The fluorescence of L1H was quenched by the presence of Cu(II), and L1H behaves as an OFF-ON sensor for Zn(II) even in the presence of a wide range of biological divalent cations. Furthermore, on addition of successive amounts of Zn(II), the fluorescence emission of L1H increases linearly by a factor of 12. This can be correlated to the efficient Zn(II) binding of L1H and to the participation of all the amine functions in the metal coordination which prevents the photoinduced electron transfer (PET) effect and promotes a good chelation-enhanced fluorescence (CHEF) effect; this confers to the cyclam probe better sensing properties than the cyclen ionophore.     

Enhancing U(eff) in oxime-bridged [Mn(III)6Ln(III)2] hexagonal prisms

The first 3d-4f clusters built using derivatised salicylaldoximes (R-saoH(2)) describe unusual hexagonal prisms. Replacement of the paramagnetic Gd(III) ions with diamagnetic Ln(III) ions allows for a more thorough understanding of the magnetic properties, whilst replacement with Tb(III) doubles U(eff).     

Biocompatible nanoparticles and gadolinium complexes for MRI applications

Performances of double-emulsion techniques (W/O/W and W/O/O) and ionotropic gelation process were compared to achieve encapsulation of gadolinium MRI contrast agents (GdCAs) into biocompatible polymeric nanoparticles (NPs) with high Gd-loadings. The better approach proved to be ionotropic gelation with H[Gd(DOTA)] as GdCA. Relaxometry evaluation of H[Gd(DOTA)]?NPs efficiency demonstrated that incorporation of H[Gd(DOTA)] inside an hydrogel matrix highly improved H[Gd(DOTA)] relaxivity. Particle efficacy as MR contrast agents was further demonstrated on a 3 T clinical imager: a significant improvement of T₁- and T₂- MR signals was obtained at doses much lower than the currently used.