Unidirectional optical Bloch oscillations in asymmetric waveguide arrays

We present an analytical proof of the existence of unidirectional optical Bloch oscillations in a waveguide array system. It is shown that the presence of nonreciprocity in the system allows for a complete normal-mode dephasing in one of the propagation directions, resulting in a unidirectional breakdown in Bloch oscillations. A model system consisting of an array of transversely magnetized asymmetric Si/SiO2 waveguides with a magneto-optic cover layer is presented. Large index contrasts between film and cover are critical for practical realizations.     

Metal carbonyl-promoted reactions of ferrocenylacetylene with sulfur to form thiophene, dithiine, thioketone and vinylthioketone derivatives

Photolysis of a hexane solution of ferrocenylacetylene and sulfur powder in presence of Cr(CO)₆ resulted in the formation of 2,6-diferrocenyldithiine and 2,5-diferrocenylthiophene. Similar reactions with Mo(CO)₆ or W(CO)₆ gave only the thiophene derivative. Formation of ferrocenyl-substituted thioketone complexes was observed in the reaction of ferrocenylacetylene with water and sulfur, in presence of W(CO)₆. Use of D₂O confirmed water as source of protons for the conversion of acetylenic CH to CH₃.     

1,4‐Dilithio‐1,1,4,4‐tetraphenylbutane in diethyl ether: An effective initiator for the living anionic polymerization of dienes

The anionic polymerization of butadiene initiated with 1,4‐dilithio‐1,1,4,4‐tetraphenylbutane (LiTPB) in diethyl ether (DEE) gives polybutadiene (PBD) with high 1,2 content (>70%), narrow polydispersities (1.04 < M_w/M_n < 1.20), and predicted molecular weights. In THF, this polymerization does not work very well. After removal of DEE and addition of THF, the PBD dianion is end capped quantitatively by addition of 1,1‐diphenylethylene (DPE) to give the diphenylalkyl end capped PBD dianion. Subsequent addition of methyl methacrylate at low temperatures results in the formation of well‐defined PMMA‐b‐PBD‐b‐PMMA triblock copolymers. The results are accounted for by taking into account the effects of Li ion solvation on the BD initiation and end capping of the PBD anion by DPE. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2198–2206, 2009     

Assembly-level reliability of flex-substrate BGA, elastomer-on-flex packages and 0.5 mm pitch partial array packages

The assembly-level reliability of the 0.8 mm pitch flex-substrate BGA, 0.65 mm pitch elastomer-on-flex package, and 0.5 mm pitch partial array BGA has been characterized in thermal fatigue, out-of-plane deformation, low frequency repeated bending, and thermal aging. Non-linear finite element models have been used to identify and predict the dominant failure mechanisms and identify the assembly parameters which have a dominant impact on reliability. The model predictions have been verified with accelerated test data. The results have been bench marked against other technologies including 1.5 mm pitch OMPAC^TM and 1 mm pitch, 196 I/O Glob-top BGA.     

Tetrapyridyl tetraphenylethylenes: supramolecular building blocks with aggregation-induced emission properties

Two tetrapyridyl-substituted tetraphenylethylenes have been prepared via Suzuki coupling between tetrabromo tetraphenylethylene and 3- or 4-pyridine boronic acid. Both compounds exhibit aggregation-induced emission as determined by solid state fluorescence spectroscopy and solution phase fluorescence measurements performed in aqueous/organic solvent mixtures. Solution phase fluorescence was also found to be switchable as a function of pH. 3-Pyridyl-substituted tetraphenylethylene has been structurally characterized by X-ray crystallography.