Large Kerr effect in bulk Se-based chalcogenide glasses

High-speed optical communication requires ultrafast all-optical processing and switching capabilities. The Kerr nonlinearity, an ultrafast optical nonlinearity, is often used as the basic switching mechanism. A practical, small device that can be switched with ~1-pJ energies requires a large Kerr effect with minimal losses (both linear and nonlinear). We have investigated theoretically and experimentally a number of Se-based chalcogenide glasses. We have found a number of compounds with a Kerr nonlinearity hundreds of times larger than silica, making them excellent candidates for ultrafast all-optical devices.     

Acrylamide-based magnetic nanosponges: a new smart nanocomposite material

Nanocomposite materials consisting of CoFe2O4 magnetic nanoparticles and a polyethylene glycol-acrylamide gel matrix have been synthesized. The structure of such materials was studied by means of small-angle scattering of X-rays and polarized neutrons, showing that the CoFe2O4 nanoparticles were successfully and homogeneously embedded in the gel structure. Magnetic, viscoelastic, and water retention properties of the nanocomposite gel confirm that the properties of both nanoparticles and gel are combined in the resulting nanomagnetic gel. Scanning electron microscopy highlights the nanocomposite nature of the material, showing the presence of a gel structure with different pore size distributions (pores with micron and nano-size distributions) that can be used as active sponge-like nanomagnetic container for water-based formulations as oil-in-water microemulsions.     

Anionic Boraza-Crown Ethers

Making one out of two : Dimeric boraza-crown ethers bridge the gap between metallacrowns and aza-crown ethers with a strikingly simple synthesis. Dioxazaborocanes react with alkoxides to form the corresponding anionic boronates, which combine to form dimers upon ring-opening reactions. The presence of the dimers was proven in the solid state and in solution by X-ray crystallography and NMR spectroscopy, respectively. The influence of the sodium and potassium ions on the stability of boraza-crown ethers was examined using DFT calculations. The dissociation of the dimers to the monomeric species was found to be endothermic, independently of the counterion. Finally, their ability to engage in cross-coupling reactions was validated for two different compounds.     

Producing Slow Antihydrogen for a Test of CPT Symmetry with ATHENA

The ATHENA experiment at the Antiproton Decelerator facility at CERN aims at testing CPT symmetry with antihydrogen. An overview of the experiment, together with preliminary results of development towards the production of slow antihydrogen are reported. This revised version was published online in August 2006 with corrections to the Cover Date.     

Uniform Spectral Properties of One-Dimensional Quasicrystals,II. The Lyapunov Exponent

In this Letter we introduce a method that allows one to prove uniform local results for one-dimensional discrete Schrödinger operators with Sturmian potentials. We apply this method to the transfer matrices in order to study the Lyapunov exponent and the growth rate of eigenfunctions. This gives uniform vanishing of the Lyapunov exponent on the spectrum for all irrational rotation numbers. For irrational rotation numbers with bounded continued fraction expansion, it gives uniform existence of the Lyapunov exponent on the whole complex plane. Moreover, it yields uniform polynomial upper bounds on the growth rate of transfer matrices for irrational rotation numbers with bounded density. In particular, all our results apply to the Fibonacci case.     

Joint And Muscle Forces During Clenching

The masticatory system is highly redundant. Therefore, complete knowledge about the activation patterns of the chewing muscles belonging to a specific resultant bite force can only be gained either by simultaneous force- and EMG-measurement or with the help of optimization strategies. In this study, such EMG and force measurements were carried out with 10 test persons and the results compared to those computed with several objective functions. The results show an increase of the joint forces with an increase of the horizontal component of the resultant bite force. The test persons seem to favor energy minimization as control mechanism. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation of bone modeling around a screw implant in the mandible

On the basis of a biomechanical model for the bone healing process around a dental implant, the attainable degree of ossification in two‐phase implantation is studied for a screw implant and compared with corresponding results for a cylinder implant. It is shown that a screw implant delivers a better ossification of the repair zone than a cylinder implant which is in accordance with clinical observation.