Low-macroscopic field emission from nanocrystalline Al doped SnO<Subscript>2</Subscript> thin films synthesized by sol–gel technique

We have observed low-macroscopic field electron emission from wide bandgap nanocrystalline Al doped SnO₂ thin films deposited on glass substrates. The emission properties have been studied for different anode-sample spacings and for different Al concentrations in the films. The turn-on field and approximate work function were calculated and we have tried to explain the emission mechanism from this. The turn-on field was found to vary in the range 5.6–7.5 V/μm for a variation of anode sample spacing from 80–120 μm. The turn-on field was also found to vary from 4.6–5.68 V/μm for a fixed anode-sample separation of 80 μm with a variation of Al concentration in the films 8.16–2.31%. The Al concentrations in the films have been measured by energy dispersive X-ray analysis. Optical transmittance measurement of the films showed a high transparency with a direct bandgap ∼3.98 eV. Due to the wide bandgap, the electron affinity of the film decreased. This, along with the nanocrystalline nature of the films, enhanced the field emission properties. PACS 81.20.Fw; 61.10.-i; 79.70.+q     

Synthesis of chiral oxa- and azacycle-fused anthraquinone derivatives

A convenient protocol for the synthesis of chiral pyran and piperidine ring-fused anthraquinone derivatives has been developed from (R)-2,3-O-cyclohexylidene-glyceraldehyde using sequential applications of enyne metathesis, Diels–Alder reaction and aromatization as key steps.     

An enantiodivergent synthesis of both (+)- and (−)-disparlure from (R)-2,3-cyclohexylideneglyceraldehyde

Reduction of ketone 3 derived from (R)-2,3-cyclohexylideneglyceraldehyde 1 with some common hydrides took place with syn-selectivity. The resulting major product 4a has been exploited as a common chiral template to prepare both enantiomers Ia,b of disparlure.     

A simple mathematical model for seasonal planktonic blooms

We show how the inclusion of the defense strategy by different species can alter the prediction of simple models. One of the defense strategy by the phytoplankton population against their grazer is the release of toxic chemicals. In turn the zooplankton population reduces there predation rate over toxin producing phytoplankton (TPP) to protect themselves from those toxic chemicals. Thus, when the level of toxicity is high, the grazing pressure is low and when the level of toxicity is low or when the toxin is absent, the grazing pressure is high. Here we have considered a TPP–zooplankton system where the rate of toxin liberation and the predation rate vary with zooplankton abundance. We observe that our proposed model has the potential to show different dynamical behaviour that are similar to that seen in real‐world situations. Further, we consider three different functional forms for the distribution of the toxins and compare them using latin hypercube sampling technique and found that the functional forms seem to have no effect in determining the final outcome of the system. Copyright © 2009 John Wiley & Sons, Ltd.     

A convenient synthesis of pyrrolopyridines and 2-substituted indoles by gold-catalyzed cycloisomerization

We have developed a gold-catalyzed intramolecular cyclization of variously substituted acetylenic amines under mild conditions, which yields pyrrolopyridines and 2-substituted indoles, quantitatively. The cycloisomerization of acetylenic amines was achieved with AuCl₃ as catalyst without the use of base, acid or N-protecting group.     

Wave reflection in slightly compressible, finitely deformed elastic media

Summary  In this paper, the reflection of a plane wave at an incrementally traction-free boundary of a half-space composed of nearly incompressible elastic material is considered. It is shown that two distinct cases exist, these being dependent on the underlying primary deformation. In the first case, the appropriate slowness sections are each approximately elliptical, and the corresponding reflection phenomena closely mirrors that associated with the corresponding linear isotropic theory. Specifically, an angular range of direction of incident wave exists, for which both a quasi-longitudinal and quasi-shear wave are reflected, the former being replaced by a surface wave outside this angular range. In the second case, the outer slowness section is re-enrant and, in addition to the scenarios previously mentioned, it is possible for two quasi-shear waves to be reflected. Numerical illustrations of reflection coefficients are presented in respect of a modified Varga material and the case of increasing bulk modulus is investigated. Received 17 January 2000; accepted for publication 22 February 2000     

Synthesis of a novel uracil-2,6-diaminopyridine-lithocholic acid conjugate that self-assembles into a cyclic dimer

Synthesis and self-association studies of a uracil-2,6-diaminopyridine-lithocholic acid conjugate are described. The dimeric supramolecular structure is characterized by NMR spectroscopic, ESI-MS, and size exclusion chromatographic studies.     

Oxidation reactions of 1,3-diphenylpropane-1,3-dione

The free radical scavenging properties and possible antioxidant activity of 1,3-diphenylpropane-1,3-dione (1) are reported. Pulse radiolysis technique was employed to study the one-electron oxidation of 1 with various radicals viz. CCl₃O₂ ^•, N₃ ^• and^•OH in homogeneous aqueous solution. All these radicals reacted with 1 under ambient conditions at almost diffusion controlled rates producing transient species with an absorption maximum around 420 nm that decayed at first order rates. The transient absorption peak was shifted in the case of CCl₃OO^• radical reaction with 1 due to change in the polarity of the medium. Formation of a stable product with a broad absorption band starting from 400 nm and cut off at 230 nm was observed in the oxidation of 1 with^•OH and^•N₃ radicals. In a biological system also, 1 showed significant inhibitory activity against Fe²⁺-mediatedlipidperoxidation. Based on these observations, a suitable mechanism for the oxidation of 1 has been proposed.