Obliquely propagating ion-acoustic shock waves in a degenerate quantum plasma

A theoretical investigation has been carried out on the propagation of non-linear ion-acoustic shock waves (IASHWs) in a magnetized degenerate quantum plasma system composed of inertial non-relativistic positively charged light and heavy ions, inertialess non-relativistically or ultra-relativistically degenerate electrons and positrons. The reductive perturbation method has been employed to derive the Burgers' equation. It has been observed that under consideration, our plasma model supports only positive potential shock structure. It is also found that the amplitude and steepness of the IASHWs have been significantly modified by the variation of ion kinematic viscosity, oblique angle, number density, and charge state of the plasma species. The results of our present investigation will be helpful for understanding the propagation of IASHWs in white dwarfs and neutron stars.     

Influence of clay concentration on the gas barrier of clay-polymer nanobrick wall thin film assemblies

The influence of the clay deposition suspension concentration on gas barrier thin films of sodium montmorillonite (MMT) clay and branched polyethylenimine (PEI), created via layer-by-layer assembly, was investigated. Films grown with MMT suspension concentrations ranging from 0.05 to 2.0 wt % were analyzed for their growth as a function of deposited polymer-clay bilayers (BL) and their thickness, clay concentration, transparency, nanostructure, and oxygen barrier as a function of the suspension concentration. The film thickness doubles and the visible light transmission decreases less than 5% as a function of MMT concentration for 20-BL films. Atomic force and transmission electron microscope images reveal a highly aligned nanobrick wall structure, with quartz crystal microbalance measurements revealing a slight increase in the film clay concentration as the MMT suspension concentration increases. The oxygen transmission rate (OTR) through these 20-BL composites, deposited on a 179 μm poly(ethylene terephthalate) film, decreases exponentially as a function of the MMT clay concentration. A 24-BL film created with 2.0 wt % MMT has an OTR below the detection limit of commercial instrumentation (<0.005 cc/m(2)·day·atm). This study demonstrates an optimal clay suspension concentration to use when creating LbL barrier films, which minimizes deposition steps and the overall processing time.     

Screening structure-property correlations and device performance of Ir(III) complexes in multi-layer PhOLEDs

The structure-property correlations of a set of heteroleptic red- and green-emitting Ir(III) complexes with different temperature sensitivities and charge trapping capabilities are described, revealing superb performance in multi-layer phosphorescent organic light-emitting diodes (PhOLEDs) expressed by very high maximum luminous efficiencies up to 36.8 cd A(-1). Using 2-phenylpyridine and with 2-(naphthalen-1-yl)pyridine as the C^N ligand, the resulting red emitting complex featured a maximum luminous efficiency of 10.8 cd A(-1); one of the most excellent device performances within this class of red Ir(III) emitters.     

Commensurability oscillations in NdBa2Cu3Oy single crystals

Commensurability between inter-vortex distance and crystal lattice constant is investigated by angular dependent magnetization in very pure twinned and twin-free NdBa₂ Cu₃ O_y single crystals. With increasing temperature the incommensurate states split up and become finally commensurate with half the vortex distance. These new commensurate states are related to a substructure of the intrinsic pinning potential within the unit cell and discussed with respect to temperature, field, anisotropy, and twin structure.     

Random fluorene copolymers with on‐chain quinoxaline acceptor units

Two series of novel random polyfluorene copolymers containing quinoxaline units were prepared by stressing the coupling according to Yamamoto. The first series contains 2,3‐bis‐(4′‐tert‐butyl‐biphenyl‐4‐yl)benzo[g]quinoxaline and the second series 2,3‐bis‐(4′‐tert‐butyl‐biphenyl‐4‐yl)quinoxaline as energy accepting unit. The copolymers were identified by gel permeation chromatography, infrared spectroscopy, and nuclear magnetic resonance spectroscopy. Thermal properties were analyzed by thermal gravimetric analysis and differential scanning calorimetry revealing amorphous copolymers that are stable up to 430 °C. The morphology was investigated using atomic force microscopy. The optical properties in solutions and thin films were analyzed. Furthermore, the thin film electro‐optical properties were determined in monolayer polymer light‐emitting devices. Single layer devices were built with efficiencies ranging from 0.15 to 2.0 cd/A. For the random copolymers with 5 mol % benzo[g]quinoxazoline in the polyfluorene backbone some threefold efficiency enhancement from 1.1 to 3.0 cd/A was achieved by utilizing an ultra thin interlayer of poly(9,9‐di‐n‐octylfluorene‐2,7‐diyl)‐alt‐[1,4‐phenylene‐(4‐sec‐butylphenylimino)‐1,4‐phenylene] between PEDOT:PSS and the emissive random copolymer layer. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4773–4785, 2007     

Determining a 'safe' high-mass limit in matrix-assisted laser desorption/ionisation time-of-flight mass spectra of coal derived materials with reference to instrument noise

Three methods for determining a 'safe' estimate for high-mass limits of MALDI spectra of coal derived liquids were explored, using a sample of coal-tar pitch and its pyridine-insoluble fraction. Co-addition of increasing numbers of single-shot spectra (10, 30, 50 and 100 pulses) showed visually observable reductions in noise levels, consistent with robust and statistically meaningful signals. Three separate types of post-acquisition calculation were used to identify high-mass limits of the spectra. (i) A literature method indicated high-mass limits similar to those observed visually-as a shift from baseline at the highest masses, nearly 350 000 u for the coal tar pitch and about 390 000 u for its pyridine insoluble fraction. (ii) Comparing instrument signal with pre-selected multiples of the standard deviation, upper mass estimates of between 40-60 000 u for the coal-tar pitch and about 95 000 u for its pyridine-insoluble fraction were found. (iii) Calculation of the slope was used to identify 'lift-off' of the spectrum from baseline. The angle between the smoothed spectrum and the baseline was matched to a pre-selected value (e.g. 0.5 degrees and 1 degrees ). However, the arbitrary specification of the key parameter did not establish this last method on a firm basis. The choice of a criterion for estimating high-mass limits of MALDI spectra remains a semi-quantitative procedure; a reasonably conservative high-mass limit may be estimated by comparison of signal with five times the standard deviation. However, evaluation of size exclusion chromatograms of the present samples using polystyrene standards suggests that molecular mass distributions of pitch samples arrived at by MALDI mass spectrometry are, at least partly, determined by the limitations of available instruments. Copyright 1999 John Wiley & Sons, Ltd.     

The crystal structure of a bis(2,6-pyridinedicarboxylato)chromate(III) anion with an elaborate network of hydrogen bonding and π stacking

The synthesis, X-ray crystallography, spectroscopic, and electrochemical properties of the title compound, [Hdpa][Cr(dipic)₂]·3H₂O, 1, are reported. Compound 1 crystallized in the triclinic space group P-1 with a = 7.1057(11) ?, b = 12.965(2) ?, c = 14.269(2) ?, α = 80.306(3)°, β = 82.101(2)°, γ = 83.799(2)°, and V = 1278.6(4) ?³ with Z = 2. The distorted octahedral chromium anions are part of an elaborate network of hydrogen bonding formed by the waters of solvation, the anion, and cation as well as π-stacking interactions.     

Lamellar organic thin films through self-assembly and molecular recognition.

Molecular clips possessing U-shaped cavities have been functionalized on their convex side with long aliphatic tails. These molecules form dimers which self-assemble into malleable lamellar thin films. Upon addition of a guest (methyl 3,5-dihydroxybenzoate), a 1:1 host-guest complex is formed, which prohibits clip dimerization. As a result, the lamellar structure of the material is lost. Complexation of 3,5-dihydroxybenzoic acid in the clip results in host-guest complexes which dimerize by hydrogen bonding interactions between the carboxylic acid functions of the bound guests. This dimerization restores the lamellar type architecture of the material.     

Mechanism of the oxidation of l-ascorbic acid by the molyb-datopentaamminecobalt(III) ion in aqueous solution

Transition Metal Chemistry - Refer to PDF File     

GC-MS Determination of an Unknown Pesticide. II. An Experiment Investigating Quality of Analysis Using Random Sampling and Estimation of Variance

Newly devised components are described which significantly enhance both the scientific and pedagogical components of a previously published, qualitatively oriented experiment for students in an undergraduate instrumental analysis course. To provide a laboratory exercise containing as much real-world experience as possible, the earlier experiment was modified in such a way as to allow its use as a quantitative experiment illustrating such principles as sampling, experimental design, analysis of variance, and the use of internal standards.