Slow flow of a conducting fluid past a non-conducting porous sphere with variable permeability

Slow flow of a conducting fluid past a non-conducting porous sphere of variable permeability in presence of a uniform radial magnetic field is studied. The drag experienced by the sphere is shown graphically and compared to that for a non-conducting fluid.Notation velocity vectors of the porous matrix and the conducting fluid - P, p pressures in the porous material and the free fluid - K permeability at a point of the porous medium - viscosity - v (=) kinematic viscosity - magnetic induction - current density - (r, , ) spherical coordinates - dimensionless constant - conductivity of the liquid The authors remain thankful to the referee for his valuable comments and helpful suggestions for improvement of the quality of the paper.     

A new, chiral aminoanthracene for the Diels-Alder/retro-Diels-Alder sequence in lactam and butenolide synthesis

9-(2-Phenylethyl)aminoanthracene has been prepared and used as a template in the Diels-Alder/retro-Diels-Alder sequence to produce α,β-butenolides and α,β-unsaturated lactams. In this sequence the aminoanthracene serves as a stereo- and regiocontrolling chaperone in guiding maleic anhydride or N-alkylmaleimides through transformations to the butenolide or lactam targets.     

Thermal and photochemical stability of polystyrene and its blends with polyvinyl chloride I.

The influence of a 1–20% content of PVC in PS films on their thermal stability was investigated. It was found that the thermal stabilities of these blends are higher than that of either of the two pure polymers. This indicated the mutual stabilizing effects of these polymers on each other. The effect is significant when the PVC content in the blends is 1–5%. A higher amount of PVC causes either no significant change or a lowering of the thermal stability. The miscibility of the polymer components in the blends clearly has an important influence on the course of the thermal processes.

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Zusammenfassung Der Einfluß von 1–20% PVC in PS-Filmen auf deren thermische Stabilität wurde untersucht. Es wurde festgestellt, daß die thermische Stabilität dieser Gemische höher ist, als die der beiden reinen Polymere für sich. Dies verdeutlicht den gegenseitigen Stabilisierungseffekt der beiden Polymere. Zu einem signifikanten Effekt kommt es bei einem PVC Gehalt der Gemische von 1–5%. Ein höherer Gehalt an PVC führt entweder zu keiner signifikanten Veränderung oder zu einer Abnahme der thermischen Stabilität. Die Mischbarkeit der Polymerkomponenten des Gemisches verfügt eindeutig über einen wichtigen Einfluß auf den Ablauf der thermischen Prozesse.

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A novel tryptamine-appended rhodamine-based chemosensor for selective detection of Hg2+ present in aqueous medium and its biological applications

A novel rhodamine–tryptamine conjugate–based fluorescent and chromogenic chemosensor (RTS) for detection of Hg²⁺ present in water was reported. After gradual addition of Hg²⁺ in aqueous methanol solution of RTS, a strong orange fluorescence and deep-pink coloration were observed. The probe showed high selectivity towards Hg²⁺ compared to other competitive metal ions. The 1:1 binding stoichiometry between RTS and Hg²⁺ was established by Job’s plot analysis and mass spectroscopy. Initial studies showed that the synthesized probe RTS possessed fair non-toxicity and effectively passed through cell walls of model cell systems, viz., human neuroblastoma (SHSY5Y) cells and cervical cells (HeLa) to detect intercellular Hg²⁺ ions, signifying its utility in biological system. The limit of detection (LOD) was found to be 2.1 nM or 0.42 ppb by fluorescence titration. Additionally, the potential relevance of synthesized chemosensor for detecting Hg²⁺ ions in environmental water samples has been demonstrated.

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Thermal and photochemical stability of polystyrene and its blends with polyvinyl chloride

The influence of some irregularities in polystyrene (PS) and polyvinyl chloride (PVC) chains on their thermal stability was investigated. UV irradiation caused an increase in the content of these irregularities in the polymers. It was found that the presence of carbonyl groups and crosslinking of the polymer chains hamper the thermal dehydrochlorination of PVC and the total decomposition of both polymers. On the other hand, weak peroxy linkages (which facilitate degradation processes) and conjugated double bonds decrease the temperature of total decomposition of PS and PVC blends.

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Zusammenfassung Es wurde der Einfluß von Unregmlmäßigkeiten in Polystyrol (PS)- und Polyvinylchlorid (PVC)-Ketten auf deren thermische Stabilität untersucht. UV-Bestrahlung verursacht ein Ansteigen des Gehaltes an Unregelmäßigkeiten in den Polymeren. Es wurde festgestellt, daß die Gegenwart von Carbonylgruppen und Querverbindungen der Polymerketten die thermische Dehydrochlorierung von PVC und eine vollständige Zersetzung beider Polymere verhindern. Andererseits senken Peroxidverknüpfungen (die die Degradierungsvorgänge erleichtern) und konjugierte Doppelbindungen die Temperatur für eine vollständige Zersetzung von PS und PVC Gemischen.

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Electronic structure and high pressure phase transition in LaSb and CeSb

The electronic structure and high pressure structural phase transition in lanthanum and cerium antimonides have been investigated using the tight binding LMTO method. Calculation of the total energy reveals that the simple tetragonal structure is stable at high pressure for both the compounds. In LaSb, the calculated values of the equilibrium cell volume and the cell volume at which phase transition occurs agree with the experimental results. However, in CeSb, the agreement is not so good. We have also predicted the most favouredc/a value in the simple tetragonal phase for these compounds. Further, we present the calculated results on the electronic structure of these systems at the equilibrium as well the reduced cell volumes.     

Imaging characteristics of a birefringent lens under broadband illumination

This paper reports the imaging characteristics of an optical system consisting of a lens made of a uniaxial birefringent crystal sandwiched between two linear polarizers under polychromatic input illumination. The optic axis of the birefringent crystal is perpendicular to the lens axis and for an initial investigation, the spectral profile of the input beam is considered to be uniform for all wavelengths. The study reveals that if the variation of the birefringence parameters of the device with the wavelength is less, a larger bandwidth may be used without considerably deviating from the imaging characteristics under strictly monochromatic illumination. The nonlinear variation of birefringence with wavelength results in an asymmetric axial irradiance distribution. This obviates an optimal operating wavelength as well as a proper choice of the lens material. It is found that no appreciable change in image quality under diffraction-limited condition results for an input beam having 632 nm operating wavelength and 60 nm bandwidth. Therefore, it may be feasible to use this system with a white light source in conjunction with a wavelength-selective filter.     

Half-life measurements in59Co,141Pr and227Ac

The half-lives of the 1291.6 keV level in⁵⁹Co, 145.43 keV level in¹⁴¹Pr and 27.35 keV level in²²⁷Ac have been measured using leading edge and zero-crossover timing techniques. The decay curves analysed by moments, Laplace transform and slope methods gave the following half-life values: $$\begin{gathered} T_{\tfrac{1}{2}} (1291.6 keV level in {}^{59}Co) = (0.538 \pm 0.004) ns \hfill \\ T_{\tfrac{1}{2}} (145.43 keV level in {}^{141}\Pr ) = (1.82 \pm 0.04) ns \hfill \\ T_{\tfrac{1}{2}} (27.35 keV level in {}^{227}Ac) = (41.0 \pm 1.1) ns. \hfill \\ \end{gathered} $$ From the measured half-lives, the reduced transition probabilitiesB(M1)↓,B(E2)↓ for gamma transitions de-exciting the above mentioned levels in⁵⁹Co and¹⁴¹Pr are determined and compared with single particle, intermediate coupling and Sorensen estimates. In²²⁷Ac, absolute transition probability for the 27.35 keV transition is determined and compared with single particle and Nilsson estimates.     

Morphological evolution of selenium micro‐crystals

A simple solution phase approach using dimethyl formamide (DMF) as solvent is utilized to obtain selenium (Se) microcrystals. Different morphological modifications of the products result from varied reaction environments. Solvothermal treatment of Se with DMF in an autoclave at 170°C yields rod‐like, and feather‐shaped microcrystalline structures while reduction of selenium dioxaide (SeO₂) by DMF generates microspheres at 30°C and 80°C, rods admixed with spherical particles at 120°C and predominantly micro rods at 150°C. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)