Broad Features (broad + feature)

Distribution by Scientific Domains

Selected Abstracts

A Polymer-Bound Oxidovanadium(IV) Complex Prepared from an L -Cysteine-Derived Ligand for the Oxidative Amination of Styrene

Mannar R. Maurya
Abstract The ligand H2sal-cys (I) derived from salicylaldehyde and L -cysteine has been covalently bonded to chloromethylated polystyrene cross-linked with 5,% divinylbenzene. Upon treatment with [VO(acac)2] in dimethylformamide (DMF) the polystyrene-bound ligand PS-H2sal-cys (II) gave the oxidovanadium(IV) complex, PS-[VO(sal-cys)·DMF] (1). The corresponding neat complex, [VO(sal-eta)]2 (2), has also been prepared similarly in methanol. These complexes have been characterised by IR, electronic, EPR spectroscopic studies, magnetic susceptibility measurements and thermal as well as scanning electron micrographs studies. Complex [VO(sal-eta)]2 exhibits a medium intensity band at 980 cm,1 in the IR spectrum due to ,(V=O) stretch. Broad features of the EPR spectrum for the neat complex along with magnetic susceptibility studies suggest the presence of antiferromagnetic exchange interaction between two vanadium centers in close proximity. Both complexes catalyze the oxidative amination of styrene, in mild basic conditions, with secondary amines (diethylamine, imidazole, and benzimidazole) and gave a mixture of two aminated products in good yields. Amongst the two aminated products, the anti-Markovnikov product is favored over the Markovnikov one due to the steric hindrance posed by the secondary amines. The polymer-anchored heterogeneous catalyst is free from leaching during catalytic action and recyclable.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Coriolis effects in mesoscale flows with sharp changes in surface conditions

J. C. R. Hunt
Abstract A general linearized ,shallow-layer' perturbation model, where the approximately neutral lower layer of thickness h0 is situated below a stable upper layer (i.e. an inversion with temperature change ,T), is developed for steady, mesoscale atmospheric flows over low-lying topography whose height is less than h0. With the Coriolis parameter f, sharp changes in surface conditions (surface roughness, terrain elevation, heat flux) are modelled as a distributed body force through the lower layer. The Froude number of this layer is small. Typical cases of mesoscale discontinuities are examined. The results are compared with those of a continuously stratified model and observations, and with numerical mesoscale model results for a meteorological case-study over the Dover Straits region of the English Channel. The main results are: (i) If the wind direction is parallel to the edge-line separating the change in surface roughness, there are marked increases and decreases in these coastal winds whose maxima can occur over the sea within a distance of order h0(,1 km) of a coast. The strength of these wind ,jets', which do not occur in the absence of Coriolis force, decrease away from the edge-line gradually over transverse length-scales of the order of the Rossby deformation radius . Changes to surface roughness lead to an increase in the wind speed perturbation in the downwind direction until limited by non-linear effects. When the wind is at an angle to a roughness change or coast, the maxima occur at the coastline. (ii) Where there are sharp changes in the orientation of contours of constant roughness length (e.g. at capes or bays on the coastline or wakes of high-drag areas), ,detached' jets are formed in the downwind direction. (iii) Changes in surface elevation at a coast produce effects different from those of roughness; a positive wind jet forms parallel to the coast in the direction of the wind when the coast is on the right (looking downwind) and a negative jet when the coast is on the left. These jets do not increase in strength along the flow and do not persist downwind. (iv) Coriolis effects also determine how the inversion height varies near coastlines and surface roughness changes; for example, increasing/decreasing inland over a distance LR when stable airflow approaches from the sea and the coast is on the right/left of an observer looking downwind (opposite in the southern hemisphere). This mechanism is consistent with observed increasing/decreasing cloudiness inland from a coast. (v) Other effects occur where the surface elevation changes gradually over a distance of order LR (e.g. a wide, shallow valley); frictional effects are comparable with buoyancy and Coriolis forces, and flows perpendicular to the elevation change are deflected to the left (in the northern hemisphere), as observed in the Rhine valley. (vi) The shallow-layer model simulates the major features of the low-level flow field computed using the numerical mesoscale model with a horizontal resolution of 2 km, i.e. of order h0. Broad features were captured using a coarser resolution of 12 km. (vii) The analysis provides a method of estimating errors associated with finite grid size in numerical mesoscale models. Copyright © 2004 Royal Meteorological Society [source]

The narrow-line quasar NAB 0205 + 024 observed with XMM,Newton

L. C. Gallo
ABSTRACT The XMM,Newton observation of the narrow-line quasar NAB 0205+024 reveals three striking differences since it was last observed in X-rays with ASCA. First, the 2,10 keV power law is notably steeper. Secondly, a hard X-ray flare is detected, very similar to that seen in I Zw 1. Thirdly, a strong and broad emission feature is detected with the bulk of its emission redward of 6.4 keV, and extending down to ,5 keV in the rest frame. The most likely explanation for the broad feature is neutral iron emission emitted from a narrow annulus of an accretion disc close to the black hole. The hard X-ray flare could be the mechanism that illuminates this region of the disc, allowing for the emission line to be detected. The combination of effects can be understood in terms of the ,thunder-cloud' model proposed by Merloni & Fabian. [source]

Optically pumped lasing and gain formation properties in blue Inx Ga1,x N MQWs

K. Kojima
Abstract Lasing and gain formation properties have been studied in an InxGaN1,x multiple quantum wells lasing at around 460 nm by employing the modified variable stripe length method (VSLM) and pump and probe spectroscopy (P&P). It was found that the spontaneous emission (Esp) appeared far below absorption edge (Ea) that is observed as a photo-bleaching negative-peak in P&P, indicating the formation of localized tail states. Lasing peaks appeared in between Esp and Ea with wide spectral distribution. This is consistent with the results where VSLM revealed the broad feature of optical gain spectra associated with rapid peak saturation of lasing even just above the threshold photo-pumping power density. Such mechanism observed in In-rich InxGa1,xN MQWs is contributed not only from the broad distribution of localized density-of-states but also from hot carrier distribution (determined by Maxwell,Boltzmann statistics), temperature of which is raised up due to long energy relaxation time to localized tail states. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Microstructured Surfaces for Directional Wetting

Ville Jokinen
Directional wetting on limited sectors of surfaces is achieved on partially wetting microstructured surfaces by placing nonsymmetrical microstructures in a regular rectangular lattice. Droplet spreading to a 90° sector is possible when the microstructures are designed to present broad features towards the right and top and sharp features towards the left and bottom (see image). [source]