One-dimensional coupled cavities photonic crystal filters with tapered Bragg mirrors

The performance of one-dimensional (1D) coupled cavities photonic crystal (PC) filters has been analyzed by finite-difference time-domain (FDTD) simulation. It is shown that the addition of tapered Bragg mirrors at each side of the cavities, to create near-Gaussian field profiles for the cavity modes, results in the prediction of near flat-top passband filters with high out-of-band rejection ratio and near unity transmission. The tapered structures suppress the vertical radiation loss to allow optimization of the number of mirror periods for the best filter response whilst guaranteeing high transmission. A critical coupling condition (k = 2L_out/L_in = 1) for flat-top responses in doubly coupled cavities filters is proposed in the tapered structures. An optimized filter for 100 GHz optical communication system are demonstrated with 1 dB bandwidth of 0.17 nm, roll-off of 0.6 dB/GHz, out-of-band signal rejection of 33 dB and transmission of 95%. Further improvement of roll-off and out-of-band rejection is demonstrated in a triply coupled cavities filter.     

A suite of novel allenes from Australian melolonthine scarab beetles. Structure,synthesis, and stereochemistry

A suite of allenic hydrocarbons, previously unknown as a molecular class from insects, has been characterized from several Australian melolonthine scarab beetles. The allenes are represented by the formula CH(3)(CH(2))(n)()CH=*=CH(CH(2))(7)CH(3) with n being 11-15, 17 and 19, and thus, all have Delta(9,10)-unsaturation. These structures have been confirmed by syntheses and comparisons of spectral and chromatographic properties with those of the natural components. The enantiomers of (+/-)-Delta(9.10)-tricosadiene and Delta(9,10)-pentacosadiene were separable on a modified beta-cyclodextrin column (gas chromatography), and the natural Delta(9,10)-tricosadiene (n = 11) and Delta(9,10)-pentacosadiene (n = 13) were shown to be of >85% ee. Syntheses of nonracemic allenes of known predominating chirality were acquired using both organotin chemistry and sulfonylhydrazine intermediates, and comparisons then demonstrated that the natural allenes were predominantly (R)-configured.     

Wannier–Stark effect in strongly coupled three quantum well structures and superlattices

The Wannier–Stark effect has been investigated in strongly coupled three quantum well structures and 23.5 period superlattices consisting of 25Å wide GaAs wells separated by Al_0.25Ga_0.75As barriers of the same width. A blue shift associated with the Wannier–Stark localization of heavy holes states is observed for the first time, followed by a second blue shift at higher electric fields due to the electron localization. This is contrary to the widely reported single blue shift of the order of (e+hh)/2, where e and hh are the electron and heavy hole miniband widths respectively, produced by Wannier–Stark localization in superlattices.     

Molecular dynamics beyonds the limits: Massive scaling on 72 racks of a BlueGene/P and supercooled glass dynamics of a 1 billion particles system

We report scaling results on the world’s largest supercomputer of our recently developed Billions-Body Molecular Dynamics (BBMD) package, which was especially designed for massively parallel simulations of the short-range atomic dynamics in structural glasses and amorphous materials. The code was able to scale up to 72 racks of an IBM BlueGene/P, with a measured 89% efficiency for a system with 100 billion particles. The code speed, with 0.13 s per iteration in the case of 1 billion particles, paves the way to the study of billion-body structural glasses with a resolution increase of two orders of magnitude with respect to the largest simulation ever reported. We demonstrate the effectiveness of our code by studying the liquid–glass transition of an exceptionally large system made by a binary mixture of 1 billion particles.     

Effect of Vinyl Chloride Injection on the Morphology of Suspension-Polymerized PVC

The mechanism of growth of PVC granules was investigated by injecting additional vinyl chloride monomer into a conventional suspension polymerization process at two different conversions. Polymerization was sustained for long periods in both cases, with the injection before pressure drop producing a more rapid decrease in properties such as porosity and surface area. With injection after pressure drop, additional polymer growth produced a structure with noticeably inferior plasticizer absorption and gelation properties, even though porosity and surface area values were higher. A discussion of the growth mechanism of PVC granules under the two injection systems is presented and related to the conventional suspension process.     

Usage of 3D geometry descriptions and transformation techniques in log bucking and curve sawing

Detailed three dimensional models are nowadays frequently used in cross-cutting (bucking) tree stems into logs and in breakdown processes of logs into boards and flitches. Such models require increasingly sophisticated optimization models to assist planners (or automated decision support systems) in decision making. In this paper we develop two techniques that are linked to each other. The first is concerned with establishing high quality analytic approximations of full trees that are needed in full stem bucking applications. One important aspect is that inaccuracies due to measurement error can be reduced. The second is a transformation technique that makes it possible to apply curve sawing on logs in a standard straight sawing system. Numerical results based on real data are presented that support the usefulness of the techniques.     

Fair measures of performance: the World Cup of cricket

Luck can play a big part in tournament success, and progress is not necessarily the best measure of performance. A linear model is used to fit least squares ratings to margins of victory in the cricket World Cup. The Duckworth/Lewis rain interruption rules are used to project a winning second innings score and create a margin of victory in runs, equivalent to that used when the team batting first wins. Results show that, while the better teams progressed through the first round of the competition, some injustices occurred in the Super-Six round. This appears to be due to the double counting of selected matches. Ordering teams by average margin of victory gives similar results to the more complicated linear model, and its use as a tie breaker is suggested. Publication of the margin of victory as estimated by the Duckworth/Lewis method for second innings victories in all one-day matches would provide a common margin of victory suitable for analysis.     

Novel cuticular hydrocarbons from the cane beetle Antitrogus parvulus--4,6,8,10,16-penta- and 4,6,8,10,16,18-hexamethyldocosanes-unprecedented anti-anti-anti-stereochemistry in the 4,6,8,10-methyltetrad

The major cuticular hydrocarbons from the cane beetle species Antitrogus parvulus are 4,6,8,10,16-penta- and 4,6,8,10,16,18-hexamethyldocosanes, 1 and 2, respectively. Stereoisomers of 2,4,6,8-tetramethylundecanal of established relative stereochemistry were derived from 2,4,6-trimethylphenol and were then coupled with appropriate methyl-substituted phosphoranes 62 and 25 to furnish alkenes, which on reduction provided diastereomers of 1 and 2, respectively. Capillary gas chromatography, mass spectrometry, and high resolution 13C NMR spectroscopy confirmed 1 as either 84a or 84b and 2 as either 15a or 15b. The novelty of these structures and their relative stereochemistry is briefly related to polyketide assembly.