Computational prediction of grain size during rapid laser surface modification of Al–O ceramic

The aim of this letter is to present a model including the fundamental non‐equilibrium effects to predict the microstructure evolution during the rapid solidification of laser surface modified Al–O ceramic system to understand grain growth and the physical process involved during the treatment. The obtained data is then compared with the actual measurements from micrographs. This approach is novel compared to other work in the similar field which have looked at the process only at the macroscopic level that included the extractions of macroscopic features such as melt depth and width. Such study is important as laser surface modification can be extended to dressing of alumina grinding wheel material, a part of the Al–O ceramic system. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Risk and Pitman closeness properties of feasible generalized double k-class estimators in linear regression models with non-spherical disturbances under balanced loss function

In this article, a family of feasible generalized double k-class estimator in a linear regression model with non-spherical disturbances is considered. The performance of this estimator is judged with feasible generalized least-squares and feasible generalized Stein-rule estimators under balanced loss function using the criteria of quadratic risk and general Pitman closeness. A Monte-Carlo study investigates the finite sample properties of several estimators arising from the family of feasible double k-class estimators.     

Sodium phenoxy­acetate hemihydrate

The structure of the hemihydrate of sodium phenoxy­acetate, Na⁺·C₈H₇O₃⁻·0.5H₂O, has been redetermined at low temperature (160 K). The structure consists of ribbons containing octahedral NaO₆ units, and half of the Na₂O₂ squares within the ribbon are bridged by water mol­ecules which lie across twofold rotation axes in C2/c. The phenyl substituents lie on the outside of the ribbon.     

Effect of Cetyltrimethyl Ammonium Bromide on Electrochemical Determination of Dexamethasone

The effect of surfactants on the electrochemical determination of dexamethasone at an edge plane pyrolytic graphite electrode (EPPGE), modified with single‐walled carbon nanotubes (SWNT) has been investigated. The unique electrocatalytic properties of SWNT along with the synergistic adsorption of CTAB on SWNT lead to sensitive voltammetric response of dexamethasone with the reduction peak at ca. ?1195 mV. The limit of detection and sensitivity of dexamethasone is estimated to be 9.1×10^?10 M and 0.727 µA µM^?1 respectively. The SWNT coated EPPGE had good stability and reproducibility. The analytical utility of the developed method was evaluated by applying it for sensing the drug in human body fluids and for the determination of dexamethasone content in several commercially available pharmaceutical preparations. A comparison of the observed results of proposed method with HPLC clearly indicates that the results of both the methods are in good agreement. The product obtained after the reduction of dexamethasone has also been characterized using ¹H NMR and carbonyl group at position 3 has been found to reduce. The method is instant, simple and accurate and can be easily applied for detecting cases of doping.     

Proton magnetic resonance spectroscopy and biochemical investigation of type 2 diabetes mellitus in Asian Indians: observation of high muscle lipids and C-reactive protein levels

We report the determination of intramyocellular lipids (IMCLs) of the soleus muscle of patients with type 2 diabetes mellitus (T2DM) using proton magnetic resonance spectroscopy. In addition, the various anthropometric and biochemical profiles of these patients were determined, including estimation of C-reactive protein (CRP), an inflammatory marker of coronary heart disease, and insulin resistance [Homeostasis Model Assessment (HOMA-IR)]. The estimated CRP level and the IMCL content in these patients were correlated with body mass index, percentage of body fat, other measures of abdominal obesity, serum lipoproteins, fasting and post-oral glucose load serum insulin levels and other surrogate markers of insulin resistance. The IMCL content (P=.04), CRP (P=.008) and insulin resistance (P=.0007) were significantly higher in T2DM patients compared to healthy controls. However, IMCL content did not correlate with values of fasting insulin, HOMA-IR or CRP in either group. These findings have strong implications of increased cardiovascular risk in Asian Indians with T2DM. The absence of relationship between CRP and IMCL needs to be explored further in a study using a large sample size.     

Luminescent Colloidal Dispersion of Silicon Quantum Dots from Microwave Plasma Synthesis: Exploring the Photoluminescence Behavior Across the Visible Spectrum

Aiming for a more practical route to highly stable visible photoluminescence (PL) from silicon, a novel approach to produce luminescent silicon nanoparticles (Si‐NPs) is developed. Single crystalline Si‐NPs are synthesized by pyrolysis of silane (SiH₄) in a microwave plasma reactor at very high production rates (0.1–10 g h^?1). The emission wavelength of the Si‐NPs is controlled by etching them in a mixture of hydrofluoric acid and nitric acid. Emission across the entire visible spectrum is obtained by varying the etching time. It is observed that the air oxidation of the etched Si‐NPs profoundly affects their optical properties, and causes their emission to blue‐shift and diminish in intensity with time. Modification of the silicon surface by UV‐induced hydrosilylation also causes a shift in the spectrum. The nature of the shift (red/blue) is dependent on the emission wavelength of the etched Si‐NPs. In addition, the amount of shift depends on the type of organic ligand on the silicon surface and the UV exposure time. The surface modification of Si‐NPs with different alkenes results in highly stable PL and allows their dispersion in a variety of organic solvents. This method of producing macroscopic quantities of Si‐NPs with very high PL stability opens new avenues to applications of silicon quantum dots in optoelectronic and biological fields, and paves the way towards their commercialization.     

Dielectric relaxation in a novel tapered chiral photochromatic liquid crystalline dendrimer

Temperature-dependent dielectric spectroscopic measurements of newly synthesised ribbon-shaped chiral liquid crystalline dendrimer with photochromic azobenzene mesogens and an isosorbide chiral centre on planar anchoring cell have been performed in the frequency range of 1.0 Hz to 5.5 MHz. Three dielectric dispersions in the relaxation frequency range of 10–80 Hz, 80–130 kHz and ~3.5 MHz have been observed not only in chiral smectic phase but also in isotropic phase in which two lower-frequency processes are retarded while the other one remained at same relaxation rate from isotropic to chiral smectic phase. Based on the dielectric and optical polarising microscopic results, the chiral smectic phase has been identified as SmC* phase. The relaxation mode observed at low-frequency region in the SmC* phase followed the dielectric characteristics of pinned Goldstone mode. Whereas the dielectric dispersions observed at high-frequency region have been analysed in the framework of the model given by Maier and Meier.     

Condensed two- and three-dimensional aromatic systems: a theoretical study on the relative stabilities of isomers of CB19H16+, B20H15Cl, and B20H14Cl2 and comparison to B12H10Cl22-, C6H4Cl2, C10H7Cl, and C10H6Cl2

DFT studies (B3LYP/6-31G) on mono- and dichloro derivatives of benzene, naphthalene, B12H12(2-), four-atom-sharing condensed systems B20H16, and monocarborane isomers of B20H16 are used to compare the variation of relative stability and aromaticity between condensed aromatics. The trends in the variation of the relative energies and aromaticity in these two- and three-dimensional systems are similar. Aromaticity, estimated by NICS values, does not change considerably with condensation or substitution. The minor variation in the relative energies of the isomers of chloro derivatives is explained by the topological charge stabilization rule of Gimarc. The compatibility of the cap and ring orbitals decides the relative stability of CB19H16+.     

Strong Coupling of Chiral Frenkel Exciton for Intense,Bisignate Circularly Polarized Luminescence

We show that chiral Frenkel excitons yield intense circularly polarized luminescence with an intrinsic dissymmetry factor in emission g_lum as high as 0.08. This outstanding value is measured through thin films of cyanine J-aggregates that form twisted bundles. Our measurements, obtained by a Mueller polarization analysis, are artifact-free and reveal a quasi-perfect correlation between the dissymmetry factors in absorption, g_abs, and in emission g_lum. We interpret the bisignate dissymmetry factors as the signature of a strong coupling between chiral Frenkel excitons longitudinally excited along the bundles. We further resolve by polarimetry analysis the split in energy between the excited states with a Davydov splitting as small as 28 meV. We finally show the anti-Kasha nature of the chiral emission bands with opposite optical chirality. These mirror-imaged emissive chiroptical features emerge from the structural rigidity of the bundles that preserves the ground- and excited-state chirality.