Range and frequency spreadF at Huancayo

The mean occurrence of frequency type of spreadF at Huancayo has been shown to have practically no solar cycle dependence. The occurrence of range type of spreadF is shown to be inversely related to sunspot number. The range spread occurs mostly around 2100 LT for any of the solar epoch, while frequency spread has maximum occurrence between 2300 and 0000 LT in high sunspot years and between 0000 and 0100 LT in low sunspot years. The seasonal variation in the occurrence of either type of spreadF shows minimum in northern solstices (June months) and maximum occurrence in southern solstices (December months). The post-sunset rise ofF layer is most predominant during high sunspot years. These results point out the inadequacy of the theory of spreadF based entirely on the post-sunset upward rise of theF region after sunset.     

On associative curves. I

Acta Mathematica Hungarica -     

Kinetics and mechanism of solid-state reaction between bismuth(III) oxide and molybdenum(VI) oxide

The mechanism of the following solid-state reactions between bismuth(III) oxide and molybdenum(VI) oxide was investigated within the temperature range 400–650°C.

$\text{(i)}\text{Bi}{}_2\text{O}{}_3\text{+ MoO}{}_3\text{→ Bi}{}_2\text{MoO}{}_6\text{, (ii)}\text{Bi}{}_2\text{O}{}_3\text{+ 2MoO}{}_3\text{→ Bi}{}_2\text{MO}{}_2\text{O}{}_9\text{, (iii)}\text{Bi}{}_2\text{O}{}_3\text{+ 3MoO}{}_3\text{→ Bi}{}_2\text{(MOO}{}_4\text{)}{}_3\text{, (iv)}\text{Bi}{}_2\text{MoO}{}_6\text{+ MoO}{}_3\text{→ Bi}{}_2\text{MO}{}_2\text{O}{}_9\text{, (v)}\text{Bi}{}_2\text{Mo}{}_2\text{O}{}_9\text{+ MoO}{}_3\text{→ Bi}{}_2\text{(MoO}{}_{\mathrm{2)3}}\text{.}$

Two types of experiments, capillary and particle size, were performed to ascertain whether MoO₃ diffuses into Bi₂O₃ or vice versa. These show that molybdenum trioxide diffuses into bismuth oxide grains. If α is the fraction of molybdenum trioxide reacted, the kinetics in all five cases are found to be governed by the equation αⁿ = kt throughout the temperature range, where n and k are constants at a given temperature and t is the time. Both n and k are temperature dependent. The characteristic feature of these reactions is that they proceed to completion. Results are also fitted by the relation $\text{α = k}{}_2\text{t}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{? k}{}_3\text{t}$, where k₂ and k₃ are constants, which shows that the reactions occur by bulk diffusion through grain boundary contacts. The number of grain boundary contact points decreases with time in the course of reaction.     

Photoelectric properties of pure and aluminium doped CdS films

Photoelectric properties of pure and Al doped vacuum deposited CdS films have been studied to explore the possibility of their application in photoactivated liquid crystal light valves. The effect of heat treatment in oxygen atmosphere, rate of deposition and the extent of Al doping, etc. on the resistivity, photo-response spectral characteristics, rise and decay time of photo-current, etc. have been investigated. It has been found that in contrast to pure CdS films, the properties of Al-doped films significantly depend on both the rate of deposition and the extent of Al doping. The dark resistivity in all cases was found to increase with heat treatment in oxygen. Unlike pure CdS films, Al doped films show photo-conductivity which is enhanced by heat treatment. Al doped films deposited at higher rates show better photo response even at lower light levels. At various light levels the rise and decay time of Al-doped films were found to be fairly constant and lower than that for pure CdS films. All these properties have been explained in terms of the presence of trapping levels due to doping. These trapping levels are also indicated by TSC, optical absorption and EPR studies.     

Additivity model study of EHT electron densities in some fluoro- and aza-substituted naphthalenes

It has been shown that a simple additivity model can be used quite successfully to predict EHT electron densities in a series of fluoro- and aza-substituted naphthalenes. The predicted electrondensities have been used to obtain good estimates of ¹H NMR chemical shifts in a series of aza-naphthalenes.     

Interface-mediated oscillatory phenomena

Oscillatory transport processes which occur in the far from equilibrium region have assumed great significance from the viewpoint of science of complexity. Oscillatory phenomena in the chemical reaction systems have been subjected to intense investigations both from theoretical and experimental angles. In the present review an effort has been made to bring transport processes other than conventional chemical reactions into focus: transport processes mediated by solid-liquid and liquid-liquid interfaces have been discussed. Transport through membranes including liquid membranes, liquid-liquid interfaces and the recently reported hydrodynamic oscillator have been covered. Applications of these systems in areas such as fabrication of sensors, phase transfer catalysis and, of course, the obvious biological action, e.g. excitation of biomembranes and tissues, have been reviewed. Theoretical frameworks proposed to rationalize the phenomena have also been critically reviewed.     

Solvent‐free neat synthetic route to tetrahydroacridinones

An environmentally benign approach for the synthesis of acridines using inorganic solid supports and “neat reaction'' technology is described. These methodologies completely eliminate the use of solvent during the course of reaction. Moreover, microwave‐assisted reactions reduce the reaction time from hours to minutes with improved yield. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:138–222, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20080