Enhanced electro-catalytic degradation of chloroorganic compounds in the presence of ultrasound

The application of finely divided (black) Pd and Pd-Fe powder in the sono-electro-catalytic reduction of chlorophenoxy herbicides (2,4-D) and chlorophenols (2,4-DCP) in aqueous solutions allows for effective destruction of toxic chlorinated aromatic compounds. At 20 degrees C complete conversion of these compounds is observed within 10 min. On bimetallic Pd/Fe catalyst, intermediates due to the oxidation reaction are detected in addition to the products of dechlorination. The bimetallic catalyst appears to be energetically and economically superior to the Pd. In both cases, the reaction times were considerably shortened in comparison with traditional electro-catalytic processes.     

Solid-State Supramolecular Chemistry of Porphyrins. Ligand-Bridged Tetraphenylmetalloporphyrin Dimers

Eight new crystalline materialsbased on ligand-bridged dimers of either Zn(II)- orCo(II)-tetraphenylporphyrins have been prepared andcharacterized by X-ray diffraction analysis. These supramolecular entities have a ``wheel-and-axle' typeshape, the elongated bidentate ligands1,3-diaminopropane, 1,4-diaminobutane, 4,4'-bipyridyl, 1,2-bis(4-pyridyl)ethene or1,2-bis(4-pyridyl)ethane coordinating axially on bothsides to the metal centers of the porphyrin species. They vary from one another by the length of the ligandspacer, the distance between the two porphyrincomponents ranging from 9.4 Å to 14.0 Å. Theintermolecular organization in these structures ischaracterized by a similar chain motif in whichadjacent oligomeric units interlock into one another. In spite of the steric constraint imposed by thebridging ligand, this packing preserves the typicalcorrugated stacked arrangement of the porphyrinframeworks which has been commonly observed inclathrates of monomeric tetraarylporphyrins. It alsoinduces in most cases large voids between theinterlocked motifs, causing enclathration of solventmolecules in the crystal lattice. The experimentallyestablished geometries of these oligomers and theircrystal packing modes provide useful information forfurther crystal engineering efforts of polymericmultiporphyrin domains.     

Bis(μ‐pyrrolidine‐N:N)bis(dibromoboron), [(Br)2B(pyrrolidine)2B(Br)2]

The B atoms in the title compound, C₈H₁₆B₂Br₄N₂, bridge between the two monomeric moieties, forming a (BN)₂ four‐membered ring with partial bond orders of the B—N bonds.     

MaGMA: mobility and group management architecture for real‐time collaborative applications

We introduce MaGMA, a mobility and group management architecture, enabling real‐time collaborative group applications such as push‐to‐talk (PTT) for mobile users. MaGMA provides, for the first time, a comprehensive and scalable solution for group management, seamless mobility, and quality‐of‐service (QoS). MaGMA is a distributed IP‐based architecture consisting of an overlay server network deployed as part of the service infrastructure. MaGMA's architecture consists of a collection of mobile group managers (MGMs), which manage group membership and may also implement a multicast overlay for data delivery. The architecture is very flexible, and can co‐exist with current as well as emerging wireless network technologies. We see such services as essential components in beyond‐3G (B3G) networks. We propose two group management approaches in the context of MaGMA. We devise protocols for both approaches, evaluate both solutions using simulations, and validate the results through mathematical analysis. Finally, we present a proof‐of‐concept prototype implementation. Copyright © 2005 John Wiley & Sons, Ltd.     

Crystalline complexes of N,N'-ditritylurea (DTU) and N-tritylurea (NTU) hosts with molecular guests

This paper reports crystalline complexes of the new hosts N,N'-ditritylurea (DTU) and N-tritylurea (NTU) with various uncharged molecular guests. The crystal structures of the following complexes were elucidated by single crystal X-ray diffraction analysis at 115^oK: (I) 1:1 DTU-propanamide — space group C2/c, a=15.839Å, b=9.088Å, c=24.584Å, =111.05^o, Z=4; (II) 1:1 DTU-ethyl N-acetylglycinate — space group P1, a=9.010Å, b=10.800Å, c=19.810 Å, =105.29^o =94.33^o, =93.03^o, Z=2; (III) 2:1 NTU-N, N-dimethylformamide — space group Cc, a=29.614Å, b=8.906Å, c=16.127Å, =121.04^o, Z=4. The three crystal structures are stabilized mainly by a cooperative effect of hydrogen bonding between amide fragments displaced along the shortest axis of each crystal. This interaction occurs between host and guest in complexes I and II, and between host and host in complex III. The latter also represents a cage-type clathrate in which the guest molecules are accommodated in voids between the hydrophobic fragments of four neighboring NTU hosts. On the other hand, complexes of DTU are characterized by a more specific interaction between the two components, each guest molecule being inserted between two adjacent hosts (related by translation) and strongly bound to them via hydrogen bridges. These results illustrate a useful concept in the design of molecular species which can be potential hosts upon crystallization with neutral molecular guests. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82022 (7 pages).     

The Electronic State of Flavoproteins: Investigations with Proton Electron–Nuclear Double Resonance

Electron–nuclear double resonance (ENDOR) spectroscopy provides useful information on hyperfine interactions between nuclear magnetic moments and the magnetic moment of an unpaired electron spin. Because the hyperfine coupling constant reacts quite sensitively to polarity changes in the direct vicinity of the nucleus under consideration, ENDOR spectroscopy can be favorably used for the detection of subtle protein–cofactor interactions. A number of pulsed ENDOR studies on flavoproteins have been published during the past few years; most of them were designed to characterize the flavin cofactor by means of its protonation state, or to detect individual protein–cofactor interactions. The aim of this study is to compare the pulsed ENDOR spectra from different flavoproteins in terms of variations of characteristic proton hyperfine values. The general concept is to observe limits of possible influences on the cofactor’s electronic state by surrounding amino acids. Furthermore, we compare ENDOR data obtained from in vivo experiments with in vitro data to emphasize the potential of the method for gaining molecular information in complex media.     

An Alternative Approach to Understanding the Observed Positron Fraction

Space-based observations by PAMELA (Adriani et al., Nature 458, 607, 2009), Fermi-LAT (Ackerman et al., Phys. Rev. Lett. 105, 01103, 2012), and AMS (Aguilar et al., Phys. Rev. Lett. 110, 141102, 2013) have demonstrated that the positron fraction (e+/total-e) increases with increasing energy above about 10 GeV. According to the propagation model for Galactic cosmic rays in widespread use (Moskalenko & Strong, Astrophys. J. 493, 693, 1998), the production of secondary positrons from interaction of cosmic-ray protons and heavier nuclei with the interstellar medium gives a generally falling positron fraction between 10 and 100 GeV, with secondary positrons accounting for only ～20 % of the observed positron fraction at 100 GeV; so some other physical phenomena have been proposed to explain the data. An alternative approach to interpreting the positron observations is to consider these data as presenting an opportunity for re-examining models of Galactic cosmic-ray propagation. Following release of the PAMELA data, three groups published propagation models (Shaviv, et al., Phys. Rev. Lett. 103, 111302, 2009, Cowsik and Burch, Phys. Rev. D. 82, 023009, 2010, Katz et al., Mon. Not. R. Aston. Soc. 405, 1458 2010) in which the observed positron fraction is explained entirely by secondary positrons produced in the interstellar medium. In May of this year, stimulated by the AMS extension of the positron data to higher energy with excellent statistics, two of those groups presented further development of their calculations (Cowsik et al. 2013, Blum et al. 2013), again concluding that the observed positrons can be understood as secondaries. None of the authors of these five papers was registered for the 33rd International Cosmic Ray Conference (ICRC). Although I am not an author of any of these papers, I have some close familiarity with one of these recent papers, so the conference organizers invited me to bring this alternative approach to the attention of the conference. The present paper is a summary of the material I presented, along with a brief comment about reaction at the conference to this approach.     

Quadruplex CARS micro‐spectroscopy

We demonstrate a technique for simultaneous detection of coherent anti‐Stokes Raman scattering (CARS) at four vibrational frequencies, using simple passive optical elements and without spectrally resolved detection. The technique is based on pump and Stokes femtosecond pulses selectively exciting vibrational resonances through spectral focusing. By replicating the pump and Stokes pair into four pairs, each traveling through appropriate glass elements, we simultaneously excite four different vibrational frequencies. The resulting CARS is a periodic train of intensities detected by a single photomultiplier and frequency analyzed to retrieve its Fourier coefficients. We demonstrate detection of methanol and ethanol mixtures in water and quantitative determination of their concentration owing to the improved chemical selectivity of this quadruplex CARS scheme. Copyright © 2012 John Wiley & Sons, Ltd.     

Boundaries of Coxeter Matroids

The purpose of this paper is to introduce, for a finite Coxeter groupW, the mod 2 boundary operator on the space of all Coxeter matroids (also known asWP-matroids) forWandP, wherePvaries through all the proper standard parabolic subgroups ofW(Theorem 3 of the paper). A remarkably simple interpretation of Coxeter matroids as certain sets of faces of the generalized permutahedron associated with the Coxeter groupW(Theorem 1) yields a natural definition of the boundary of a Coxeter matroid. The latter happens to be a union of Coxeter matroids for maximal standard parabolic subgroupsQ_iofP(Theorem 2). These results have very natural interpretations in the case of ordinary matroids and flag-matroids (Section 3).     

Flatness of families induced by hypersurfaces of flag varieties

We show the family of tangent flags to smooth quadric hypersurfaces extends to a flat family parametrized by the variety of complete quadrics. This answers a question posed by S. Kleiman.Partially supported by CNP_q-Brasil.