Sodar observation of elevated layers around Calcutta

Abstract

Sodar (sound radar) echograms recorded at the Indian Statistical Institute, Calcutta, often exhibit stratified or elevated layers over the ground-based inversion. These have been noticed often after the occurrences of thunderstorms and rain. These layers may be single or multiple, continuous or intermittent and are associated with some perturbations even as gravity wavelike structures. All these features of the lower atmospheric structures over this coastal station, as detected by a sound radar, are discussed in this paper.     

Study of Electrical Conductance of Pressed Chemically Pure MnO2 Powder†

Variation of electrical conductance and capacity of chemically pure MnO₂ in pressed powder form under a stress 6·0 × 10¹¹ dynes/sq. cm has been studied within the temperature range 26^°c to 110^°c at 1 MC/s, Electrical conductance of samples in tablet, form (3 mm thick and 15 mm in diameter) was measured between 26^° C and 110^° before and after heat treatment at 300^°c for 36 hours. Capacitance values were also measured simultaneously within the above temperature range. Electrical conductance was found to attain a maximum at about 78^°c. There is a marked hysteresis in ‘; ln conductance’ ? 1 / T graph when measurements are made while temperature is rising and while falling.

Differential thermal analysis of the samo MnO₂ powder was also carried out. Measurements were made while heating and also while cooling. Two marked changes are clearly seen, one at mean temperature of 56^°c and the other at mean temperature of 80^°c, suggesting some second-order solid to solid phase changes at these temperatures. Corresponding breaks occur in the ‘ln conductance ’ ? 1/T and capacity-temperature graphs at the above-mentioned temperatures.     

OCCURRENCE OF VIBRIO PARAHAEMOLYTICUS IN DIFFERENT FINFISH AND SHELLFISH SPECIES

Occurrence of Vibrio parahaemolyticus was examined in 293 samples of finfish and Penaeus monodon from wholesale fish markets in Kolkata, India, by standard culture technique. The bacterium was isolated from 45.83% of shellfish and 16.73% of finfish samples. Among finfishes, about 30% of Chela laubuca and Otolithoides biauritus, and 18–21% of Lates calcarifer, Ompok bimaculatus and Herpadon nehereus samples were contaminated. The bacterium was mostly recovered from intestinal contents (32.25%) as compared to skin (11.95%) and gill tissue (16.43%). Seasonal variation in occurrence of the bacterium was also recorded. The occurrence was slightly more in seafishes (21.74%) as compared to estuarine (16.04%) and freshwater fishes (13.83%), and in demersal fish species (19.35%) posing health risk to the consumers.

PRACTICAL APPLICATIONS / SIGNIFICANCE OF THE STUDY

Although seafoods, especially molluscan shellfishes, are known to carry Vibrio parahaemolyticus and are common sources of human infection, presence of the bacterium in finfishes is less documented. We have examined presence of V. parahaemolyticus in 20 finfish and shellfish species in India. Relative occurrences of the bacterium in finfishes from different habitats (sea, estuarine and freshwater) and in pelagic/benthopelagic or demersal fish species give new insights about distribution of the bacterium in nature. Data on unequal distribution of the pathogen in different fish and shellfish species will be helpful to the food industry, as well as the fish-eating community, ensuring fish food safety.     

Behaviour of volatile compounds during the shelf life of yoghurt

The production of acetaldehyde, diacetyl and ethanol was evaluated in whole plain yoghurts manufactured with commercial starter cultures, yoghurt acquired in a local market, and milk fermented by a single culture of either Streptococcus thermophilus or Lactobacillus delbrueckii ssp. bulgaricus . The headspace technique was used for sample preparation, following identification and quantification by gas chromatography. During an 8-h incubation period, mixed cultures were the most efficient in lowering the pH (from 6.30 to 4.8), followed by S. thermophilus (from 6.30 to 5.18) and L. bulgaricus (from 6.30 to 5.8). During the storage period, however, a single culture of L. bulgaricus decreased the pH more than S. thermophilus , but still less than the mixed commercial cultures. Plain yoghurts acquired in the market, those made with commercial starter cultures, and fermented milks obtained with single cultures showed, after 21 days of storage, concentrations of acetaldehyde from 11 to 35 mg/L, and of diacetyl from 0 to 0.85 mg/L. An increasing concentration of ethanol was observed during the storage period, and its production was observed even in the incubation stage of all products. It was also observed that the acetaldehyde concentration was inversely correlated to ethanol production in some products. The combination of headspace, identification and quantification techniques by gas chromatography in this work was efficient in the identification and quantification of the major aromatic compounds and ethanol content of yoghurt.     

Some studies on transient behaviours of sheath formation in dusty plasma with the effect of adiabatically heated electrons and ions

Based on quasipotential analysis, a plasma sheath is studied through the derivation of the Sagdeev potential equation in dusty plasma coexisting with adiabatically heated electrons and ions. Salient features as to the existence of sheaths are shown by solving the Sagdeev potential equation through the Runge–Kutta method, with appropriate consideration of adiabatically heated electrons and ions in the dynamical system. It has been shown that adiabatic heating of plasma sets a limit to the critical dust speed depending on the densities and Mach number, and it is believed that its role is very important to the sheath. One present problem is the contraction of the sheath region whereby dust grains levitated into the sheath lead to a crystallization similar to the formation of nebulons and are compressed to a larger chunk of the dust cloud by shrinking of the sheath. Our overall observations advance knowledge of sheath formation and are expected to be of interest in astroplasmas.     

Effect of extrusion on properties of Al-based composite

An aluminium alloy and its composite with dispersed SiC particles made by liquid metallurgy route were extruded under optimized conditions.The properties were characterized in terms of microstructure,hardness and sliding wear behaviour and then compared between the extruded and cast alloys and composites,in order to understand the benefits of composite and extrusion on the alloy.It was observed that composites drastically increased the hardness and the extruded composites further increased this value.The advantage of composites was realized in sliding wear tests.     

Economic design of dual-sampling-interval policies for X¯ charts with and without run rules

Recent studies show that the dual-sampling-interval (DSI) policies of X¯ control chart yield a smaller average time to signal (ATS) than Shewhart's classical fixed-sampling-interval (FSI) policy for off-target processes. An economic design approach for DSI policies has not been addressed in the literature. In this paper we develop a comprehensive cost model for DSI policies with and without run rules and steady-state performance. The expression for the unit cost of quality is used as the objective function in optimal design of DSI policy parameters. The design process and the sensitivities of some of the model input parameters are exposed through numerical examples.     

Dilatometric Sintering of Ti-2A1 and Ti-5AI Elemental Powders

The effect of Al addition (2 and 5 at. pct) on sintering kinetics of Ti power were investigated. Al reduces the sintering rates, sinter density, increases activation energy of sintering and accelerates the grain growth. Sintering was controlled by mixed mode, i.e. transient liquid phase sintering, formation of intermetallics, and Ti grain boundary diffusion in TiAl2 and other intermetallics.     

Multi-stage,multi-facility,batch production system with deterministic demand over a finite time horizon

Researches on multi-stage production systems, so far, have tended to schedule production according to the overall optimal batch size of the entire shop with little consideration of the influence of the individual stages of production on the batch sizes that are considered optimal. The authors have attempted, in this paper, to investigate the effects of scheduling according to the optimality of the respective production stages. The results are compared with those of the more common case of overall optimal batch scheduling