Efficient Conversion of Light to Chemical Energy: Directional,Chiral Photoswitches with Very High Quantum Yields

Photochromic systems have been used to achieve a number of engineering functions such as light energy conversion, molecular motors, pumps, actuators, and sensors. Key to practical applications is a high efficiency in the conversion of light to chemical energy, a rigid structure for the transmission of force to the environment, and directed motion during isomerization. We present a novel type of photochromic system (diindane diazocines) that converts visible light with an efficiency of 18 % to chemical energy. Quantum yields are exceptionally high with >70 % for the cis–trans isomerization and 90 % for the back‐reaction and thus higher than the biochemical system rhodopsin (64 %). Two diastereomers (meso and racemate) were obtained in only two steps in high yields. Both isomers are directional switches with high conversion rates (76–99 %). No fatigue was observed after several thousands of switching cycles in both systems.     

High-speed all-optical switching in ion-implanted silicon-on-insulator microring resonators

We demonstrate high-speed all-optical switching via vertical excitation of an electron-hole plasma in an oxygen-ion implanted silicon-on-insulator microring resonator. Based on the plasma dispersion effect the spectral response of the device is rapidly modulated by photoinjection and subsequent recombination of charge carriers at artificially introduced fast recombination centers. At an implantation dose of 1 x 10(12) cm(-2) the carrier lifetime is reduced to 55 ps, which facilitates optical switching of signal light in the 1.55 mum wavelength range at modulation speeds larger than 5 Gbits/s.     

Die mafsanalytische Bestimmung des Berylliums

Ohne Zusammenfassung     

Thermodynamical properties of superconducting contacts

We investigate the thermodynamical properties of superconducting contacts, and concentrate on the calculation of the specific heat in the vicinity of the superconducting transition point. By considering the thick film limit, it is found that the reduction in the specific heat is a much more delicate measure of the proximity effect than is the change in transition temperature, for example. For the case that the normal film consists of a paramagnetic metal, it can be shown that for superconducting films even as thick as 100-times the coherence distance the reduction in the specific heat is still approximately 15%. Our computations apply to arbitrary mean free path. Finally we discuss experiments byShiffman et al. on eutectic Pb-Sn alloys and show that reasonable good agreement between theory and experiment can be obtained.     

Zur Theorie der Übergangstemperaturen von supraleitenden Doppelschichten (Proximity-Effekt)

A theory of the transition temperature of superconducting, superposed films is given by generalizing the methods ofde Gennes andWerthamer. It is shown that the transition temperature of nonhomogeneous superconductors obeys a general rule, which is formally of the same kind as the corresponding formula for homogeneous superconductors and is valid for all mean free paths. The results ofWerthamer follow analytically in the dirty limit if the transition temperatures of the superposed films are nearly equal, but there is numerical agreement for almost all superconductor-superconductor films. In the thin film limit and for normalconductor-superconductor films there are essential deviations. The theory is in good accord with the experimental data. By calculating the unknown interaction constant of copper from the experimental transition temperatures of superposed Cu-Pb films one gets for copper a transition temperature of the order of 10^?2°K.     

Dispersion properties of silicon nanophotonic waveguides investigated with Fourier optics

We experimentally investigate the dispersion relation of silicon-on-insulator waveguides in the 1.5 microm wavelength range by using a technique based on far-field Fourier-space imaging. The phase information of the propagating modes is transferred into the far field either by linear probe gratings positioned 1 microm away from the waveguide core or by residual gratings located on the sidewalls of the waveguide. As a result, the dispersion curve of rectangular and slot waveguides as well as the group index dispersion are accurately determined.     

A Facile Synthesis of 2-Aminonicotinaldehyde

A synthesis of 2-aminonicotinaldehyde (1) which does not require chromatography and is easily scaled up has been developed. Bromination of 2-amino-3-picoline, protected as a phthalimide (4), produced the gem-dibromide (5), which was reacted with Nh₄OH. The imine intermediate (7) was hydrolyzed with acid, producing (1) in a 56% conversion from 4.