Light Propagation in Linear Arrays of Spherical Particles

A propagation of dipolar radiation in a finite length linear chain of identical dielectric spheres is investigated using the multisphere Mie scattering formalism (MSMS). A frequency pass band is shown to be formed near every Mie resonances inherent in the spheres. The manifestation of the pass band depends on the polarization of the travelling radiation. To prove this effect, a point dipole placed by the end of the chain is used as an external source of radiation. It is found that, if this dipole is directed parallel to the to the chain axis, the frequency pass bands exist if the refractive index of dielectric spheres is sufficiently large. For the dipole normal to the chain axis, the pass band can always be formed if the chain is sufficiently long. Such a distinction is due to different behavior of the far-field dipolar interaction between the spheres induced by the external source. The edges of the pass bands are defined by the guiding wave criterion based on the light-cone constraint. The criterion of creation of the pass bands correlate with condition of formation of high quality factor modes in these systems found in our previous papers. A comparison with the results available for infinite chains is made. In particular, we clarify the nature of braking down the band structure for small enough wavevectors

Catalytic reactions in a Co12 cuboctahedral cage arising from guest encapsulation and cage-based redox activation

A Co12 coordination cage with a cuboctahedral architecture, and incorporating a mixture of tritopic (face-capping) and ditopic (edge-bridging) ligands, shows strong guest binding of large aromatic fluorophores (fluorescein and its derivatives 6-carboxyfluorescein and Eosin-Y) with 1 : 1 binding constants in water in the range log K = 6.7–7.9; its large central cavity (>1000 Å3) facilitates binding of much larger guests than was possible with the smaller Co8 cage that we have reported previously. Guest binding is accompanied by catalysed reactions of bound guests because the high positive charge on the cage surface (24+) also attracts anions, allowing the organic guests and anionic reaction partners to be co-located, resulting for example in cage-catalysed hydrolysis of phosphate esters (the insecticides Me-paraoxon and Et-paraoxon) and conversion of diacetyl fluorescein to fluorescein. In addition, we demonstrate a new type of cage-based catalysis which relies on the redox activity of the Co(II)/Co(III) couple in the cage to activate the peroxymonosulfate (PMS) anion by converting it to the highly reactive SO4˙− radical ion, which bleaches cavity-bound fluorescein by complete oxidation. This is an example of an ‘advanced oxidation process’ in which the host cage not only brings the fluorescein and the PMS together via orthogonal hydrophobic and electrostatic interactions, but also provides redox activation of the PMS via a Co(II)/Co(III) couple, with the cage taking an active role in the catalytic process rather than acting simply as a passive reaction vessel

Influence of Spatial Correlations on the Lasing Threshold of Random Lasers

The lasing threshold of a random laser is computed numerically from a generic model. It is shown that spatial correlations of the disorder in the medium (i.e., dielectric constant) lead to an increase of the decay rates of the eigenmodes and of the lasing threshold. This is in conflict with predictions that such correlations should lower the threshold. While all results are derived for photonic systems, the computed decay rate distributions also apply to electronic systems

Disentangling contributions to guest binding inside a coordination cage host : analysis of a set of isomeric guests with differing polarities

Binding of a set of three isomeric guests (1,2-, 1,3- and 1,4-dicyanobenzene, abbreviated DCB) inside an octanuclear cubic coordination cage host H (bearing different external substitutents according to solvent used) has been studied in water/dmso (98 : 2) and CD2Cl2. These guests have essentially identical molecular surfaces, volumes and external functional groups to interact with the cage interior surface; but they differ in polarity with dipole moments of ca. 7, 4 and 0 Debye respectively. In CD2Cl2 guest binding is weak but we observe a clear correlation of binding free energy with guest polarity, with 1,4-DCB showing no detectable binding by NMR spectroscopy but 1,2-DCB having −ΔG = 9 kJ mol−1. In water (containing 2% dmso to solubilise the guests) we see the same trend but all binding free energies are much higher due to an additional hydrophobic contribution to binding, with −ΔG varying from 16 kJ mol−1 for 1,4-DCB to 22 kJ mol−1 for 1,4-DCB: again we see an increase associated with guest polarity but the increase in −ΔG per Debye of dipole moment is around half what we observe in CD2Cl2 which we ascribe to the fact the more polar guests will be better solvated in the aqueous solvent. A van't Hoff analysis by variable-temperature NMR showed that the improvement in guest binding in water/dmso is entropy-driven, which suggests that the key factor is not direct electrostatic interactions between a polar guest and the cage surface, but the variation in guest desolvation across the series, with the more polar (and hence more highly solvated) guests having a greater favourable entropy change on desolvation

Coordination-cage binding and catalysed hydrolysis of organophosphorus chemical warfare agent simulants

The use of organophosphorus chemical warfare agents still remains an ongoing global threat. Here we investigate the binding of small-molecule organic guests including phosphate esters, sulfonate esters, carbonate esters and a sulfite ester – some of which act as simulants for organophosphorus chemical warfare agents – in the cavity of a water-soluble coordination cage. For several of these guest species, binding constants in the range 102 to 103 M−1 were determined in water/DMSO (98 : 2 v/v) solution, through a combination of fluorescence and 1H NMR spectroscopy, and subsequent fitting of titration data to a 1 : 1 binding isotherm model. For three cage/guest complexes crystallographic structure determinations were possible: in two cases (with guests phenyl methanesulfonate and phenyl propyl carbonate) the guest lies inside the cavity, forming a range of CH⋯O hydrogen-bonding interactions with the cage interior surface involving CH groups on the cationic cage surface that act as H-bond donors and O atoms on the guests that act as H-bond acceptors. In a third case, with the guest 4-nitrophenyl-methanesulfonate, the guest lies in the spaces outside a cage cavity between cages and forms weak CH⋯O interactions with the cage exterior surface: the cavity is occupied by a network of H-bonded water molecules, though this guest does show cavity binding in solution. For the isomeric guests 4-nitrophenyl-methanesulfonate and 4-nitrophenyl methyl sulfite, hydrolysis in water/DMSO (98 : 2 v/v) could be monitored colorimetrically via appearance of the 4-nitrophenolate anion; both showed accelerated hydrolysis rates in the presence of the host cage with second-order rate constants for the catalysed reactions in the range 10−3 to 10−2 M−1 s−1 at pH 9. The typical rate dependence on external pH and the increased reaction rates when chloride ions are present (which can bind inside the cavity and displace other cavity-bound guests) imply that the catalysed reaction actually occurs at the external surface of the cage rather than inside the cavity

Hydrodynamic turbulence cannot transport angular momentum effectively in astrophysical disks

The most efficient energy sources known in the Universe are accretion disks. Those around black holes convert 5 -- 40 per cent of rest-mass energy to radiation. Like water circling a drain, inflowing mass must lose angular momentum, presumably by vigorous turbulence in disks, which are essentially inviscid. The origin of the turbulence is unclear. Hot disks of electrically conducting plasma can become turbulent by way of the linear magnetorotational instability. Cool disks, such as the planet-forming disks of protostars, may be too poorly ionized for the magnetorotational instability to occur, hence essentially unmagnetized and linearly stable. Nonlinear hydrodynamic instability often occurs in linearly stable flows (for example, pipe flows) at sufficiently large Reynolds numbers. Although planet-forming disks have extreme Reynolds numbers, Keplerian rotation enhances their linear hydrodynamic stability, so the question of whether they can be turbulent and thereby transport angular momentum effectively is controversial. Here we report a laboratory experiment, demonstrating that non-magnetic quasi-Keplerian flows at Reynolds numbers up to millions are essentially steady. Scaled to accretion disks, rates of angular momentum transport lie far below astrophysical requirements. By ruling out purely hydrodynamic turbulence, our results indirectly support the magnetorotational instability as the likely cause of turbulence, even in cool disks.Comment: 12 pages and 4 figures. To be published in Nature on November 16, 2006, available at http://www.nature.com/nature/journal/v444/n7117/abs/nature05323.htm

Diagnosing mucopolysaccharidosis IVA

Mucopolysaccharidosis IVA (MPS IVA; Morquio A syndrome) is an autosomal recessive lysosomal storage disorder resulting from a deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS) activity. Diagnosis can be challenging and requires agreement of clinical, radiographic, and laboratory findings. A group of biochemical genetics laboratory directors and clinicians involved in the diagnosis of MPS IVA, convened by BioMarin Pharmaceutical Inc., met to develop recommendations for diagnosis. The following conclusions were reached. Due to the wide variation and subtleties of radiographic findings, imaging of multiple body regions is recommended. Urinary glycosaminoglycan analysis is particularly problematic for MPS IVA and it is strongly recommended to proceed to enzyme activity testing even if urine appears normal when there is clinical suspicion of MPS IVA. Enzyme activity testing of GALNS is essential in diagnosing MPS IVA. Additional analyses to confirm sample integrity and rule out MPS IVB, multiple sulfatase deficiency, and mucolipidoses types II/III are critical as part of enzyme activity testing. Leukocytes or cultured dermal fibroblasts are strongly recommended for enzyme activity testing to confirm screening results. Molecular testing may also be used to confirm the diagnosis in many patients. However, two known or probable causative mutations may not be identified in all cases of MPS IVA. A diagnostic testing algorithm is presented which attempts to streamline this complex testing process

Stability and instability of hydromagnetic Taylor–Couette flows

Decades ago S. Lundquist, S. Chandrasekhar, P. H. Roberts and R. J. Tayler first posed questions about the stability of Taylor–Couette flows of conducting material under the influence of large-scale magnetic fields. These and many new questions can now be answered numerically where the nonlinear simulations even provide the instability-induced values of several transport coefficients. The cylindrical containers are axially unbounded and penetrated by magnetic background fields with axial and/or azimuthal components. The influence of the magnetic Prandtl number Pm on the onset of the instabilities is shown to be substantial. The potential flow subject to axial fields becomes unstable against axisymmetric perturbations for a certain supercritical value of the averaged Reynolds number Rm¯=√Re⋅Rm (with Re the Reynolds number of rotation, Rm its magnetic Reynolds number). Rotation profiles as flat as the quasi-Keplerian rotation law scale similarly but only for Pm≫1 while for Pm≪1 the instability instead sets in for supercritical Rm at an optimal value of the magnetic field. Among the considered instabilities of azimuthal fields, those of the Chandrasekhar-type, where the background field and the background flow have identical radial profiles, are particularly interesting. They are unstable against nonaxisymmetric perturbations if at least one of the diffusivities is non-zero. For Pm≪1 the onset of the instability scales with Re while it scales with Rm¯ for Pm≫1. Even superrotation can be destabilized by azimuthal and current-free magnetic fields; this recently discovered nonaxisymmetric instability is of a double-diffusive character, thus excluding Pm=1. It scales with Re for Pm→0 and with Rm for Pm→∞. The presented results allow the construction of several new experiments with liquid metals as the conducting fluid. Some of them are described here and their results will be discussed together with relevant diversifications of the magnetic instability theory including nonlinear numerical studies of the kinetic and magnetic energies, the azimuthal spectra and the influence of the Hall effect

Penilaian Kinerja Keuangan Koperasi di Kabupaten Pelalawan

This paper describe development and financial performance of cooperative in District Pelalawan among 2007 - 2008. Studies on primary and secondary cooperative in 12 sub-districts. Method in this stady use performance measuring of productivity, efficiency, growth, liquidity, and solvability of cooperative. Productivity of cooperative in Pelalawan was highly but efficiency still low. Profit and income were highly, even liquidity of cooperative very high, and solvability was good

Differential cross section measurements for the production of a W boson in association with jets in proton–proton collisions at √s = 7 TeV

Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb[superscript −1]. The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pT distributions of the leading jets at high pT values, the distributions of the HT at high-HT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio