Tetrachlorfluorarsoran,AsCl4F

Tetrachlorofluoroarsorane, AsCl₄F The preparation of pure AsCl₄F is reported and the Raman spectrum is given. This chloro-fluoroarsorane is much more instable than AsCl₂F₃ and AsClF₄.     

A COMPARISON OF PHYCOCYANINS FROM THREE DIFFERENT SPECIES OF CYANOBACTERIA EMPLOYING RESONANCE-ENHANCED COHERENT ANTI-STOKES RAMAN SPECTROSCOPY

Resonance-enhanced coherent anti-Stokes Raman spectra are recorded for monomers and trimers of phycocyanin from three different cyanobacteria: Westiellopsis prolifica, Mastigocladus laminosus and Spirulina platensis. It is shown that upon aggregation from monomer to trimer the electronic structures of both the α84 and β84 chromophores are changed. The spectra of the trimers originating from S. platensis and M. laminosus are very similar to each other, but distinctly different from the spectrum of W. prolifica.     

Minimizing makespan for two parallel machines with job limit on each availability interval

We consider the problem of scheduling jobs on two parallel machines that are not continuously available for processing. The machine is not available after processing a fixed number of jobs in order to make precision adjustment of machines such as in wafer manufacturing, to reload the feeder in printed circuit board production, or to undertake any other maintenance works such as cleaning and safety inspections. The objective of the problem is to minimize the makespan. Two different scheduling horizons are investigated for this problem. For the short-term scheduling horizon, we consider only the time period before the unavailability interval, while for the long-term horizon, machines are allowed to restart processing after the unavailability interval. For both cases, which are strongly NP-hard, exact optimization algorithms based on the branch and bound method are proposed. Although the algorithms have exponential time complexities, computational results show that they can solve optimally the various-sized problems in reasonable computation time.     

Azabicycloalkenes as synthetic intermediates: application to the preparation of diazabicycloalkane scaffolds

[reaction: see text] A general method to synthesize bicyclic dipeptide mimetics is reported. Key intermediates are azabicycloalkenes 9 and 17, which are prepared via Diels-Alder reactions and subsequent mild deprotection. These unsaturated bicyclic heterocycles are versatile intermediates for different dipeptide mimetics of the aza- and diazabicycloalkane type, which is demonstrated by the synthesis of diazabicycloalkanes 11 and 19 in only 3-6 steps and good overall yield.     

Spin Hall effects for cold atoms in a light-induced gauge potential

We propose an experimental scheme to observe spin Hall effects with cold atoms in a light-induced gauge potential. Under an appropriate configuration, the cold atoms moving in a spatially varying laser field experience an effective spin-dependent gauge potential. Through numerical simulation, we demonstrate that such a gauge field leads to observable spin Hall currents under realistic conditions. We also discuss the quantum spin Hall state in an optical lattice.     

Steric hindrance as a mechanistic probe for olefin reactivity: variability of the hydrogenic canopy over the isomeric adamantylideneadamantane/sesquihomoadamantene pair (a combined experimental and theoretical study)

Access to each C=C face of adamantylideneadamantane (AA) and sesquihomoadamantene (SA) is hindered by the hydrogenic canopy consisting of four beta-hydrogens; otherwise, these olefins have quite normal environments. X-ray crystallography and density functional (DFT) calculations show a 0.5 A larger annular opening in the protective cover of AA than that in SA. This contributes to the remarkable differences in reactivity toward various reagents, not only by limiting access to the olefin site in SA but also by inhibiting reactions which force these hydrogens closer together. Thus, AA is subject to typical olefin-addition reactions with bromine, sulfuryl chloride, m-chloroperbenzoic acid, dioxygen, and so forth, albeit sometimes at attenuated rates. On the other hand, SA is singularly unreactive under identical reaction conditions, except for the notable exceptions that include Br?nsted (protonic) acids, a nitrosonium cation, and dichlorine. The exceptions are characterized as three sterically limited (electrophilic) reagents whose unique reactivity patterns are shown to be strongly influenced by steric access to the C=C center. As such, the different degrees of steric encumbrance in the isomeric donors AA and SA shed considerable light on the diverse nature of olefinic reactions. In particular, they evoke mechanistic features in electrophilic addition versus electron transfer, which are otherwise not readily discernible with other less hindered olefinic donors. Transient structures of the olefinic-reaction intermediates such as the protonated carbocations AA-H+ and SA-H+ as well as the cation radicals AA*+ and SA*+ are probed by the combination of X-ray crystallographic analyses and density functional theoretical computations.     

A pellet tracking system for the PANDA experiment

Frozen microspheres of hydrogen (pellets) will be one of the target types for the future hadron physics experiment PANDA at FAIR (GSI, Darmstadt, Germany) [1]. Pellets with a diameter of 25– μm are generated about 3 meters above the interaction region, to which they travel with a velocity around 80 m/s inside a narrow pipe. The interaction region is defined by the overlap of the pellet stream and the accelerator beam and has a size of a few millimeters. One would like to know the interaction point more precisely, to have better possibilities to reconstruct particle tracks and events e.g. in charmonium decay studies. One would also like to suppress background events that do not originate in a pellet, but e.g. may occur in rest gas, that is present in the beam pipe. A solution is provided by the presented pellet tracking system together with a target operation mode that provides one and only one pellet in the interaction region most of the time. The goal is to track individual pellets in order to know their position with a resolution of a few tenths of a millimeter at the time of an interaction. The system must also be highly efficient and provide tracking information for essentially all pellets that pass the interaction region. Presented results from the design studies show that the goals can be fulfilled by this solution.