Electrical and Thermal Properties of Twin-Screw Extruded Multiwalled Carbon Nanotube/Epoxy Composites

This paper presents the experimental results of dispersing multiwalled carbon nanotubes (MWNTs) into epoxy (space grade structural adhesive) nanocomposites using co-rotating twin screw extrusion process. Two sets of specimens were prepared; set 1 with ultrasonication for predispersing MWNT before extrusion and set 2 direct dispersion of MWNT in the extruder. MWNT was loaded up to 8 vol.% in both the sets. The specimens were characterized for room temperature volume and surface resistivities as per ASTM D257 using Keithley Model 6517 and for thermal conductivity in the temperature range ?50 to 150 °C as per ASTM E 1530 using Thermal Conductivity Instrument (TCI) 2022 SX211. The volume resistivity of sets 1 and 2 decreased to an extent of 10¹¹ and 10⁹ respectively. The surface resistivity drop was of the order of 10⁹ for both the sets. These drops corresponded to the maximum MWNT loading of 8 vol.%. Electrical conductivity values of the specimens were fitted into the Power Law Model to evaluate the critical exponent. Both sets 1 and 2 showed increase in thermal conductivity with increase in temperature in the testing range. Thermal conductivity increased with increase in filler loading and the maximum increase was 60% at 150 °C in case of 8 vol.% MWNT nanocomposites for set 1. The corresponding value for the set 2 was 25%. Thermal conductivity values were predicted using Lewis Nielson model. DSC of the specimens showed increase in glass transition temperature with increase in filler loading. The dispersion of the nanofillers was studied using SEM and the surface morphology using AFM.     

Processing mango stones for fat

Stones of mango fruit (Mangifera indica) were processed for recovery of fat and the fat refined. Mango kernel fat is potentially edible and can substitute for tallow and cacao butter. Mango kernal meal can be used as a sizing material and as a feed.     

Approximate solutions for the structure of shock waves

Summary Approximate solutions of the B-G-K model equation are obtained for the structure of a plane shock, using various moment methods and a least squares technique. Comparison with available exact solution shows that while none of the methods is uniformly satisfactory, some of them can provide accurate values for the density slope shock thickness _n . A detailed error analysis provides explanations for this result. An asymptotic analysis of _n for largeMach numbers shows that it scales with theMaxwell mean free path on the hot side of the shock, and that their ratio is relatively insensitive to the viscosity law for the gas.

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Näherungsweise Lösungen für die Struktur von Stoßwellen

Zusammenfassung Unter Verwendung verschiedener Momentenmethoden und der Methode der kleinsten Quadrate werden Näherungslösungen der Gleichung des B-G-K-Modells für die Struktur eines ebenen Stoßes erhalten. Der Vergleich mit der verfügbaren exakten Lösung zeigt, daß zwar keine der Methoden durchwegs befriedigend ist, einige von ihnen aber genaue Werte für die Dichteanstiegs-Dicke _n des Stoßes liefern. Eine genaue Fehleruntersuchung gibt Erklärungen für dieses Ergebnis. Die asymptotische Analyse der Dicke _n für großeMachzahlen zeigt, daß sie mit derMaxwellschen mittleren freien Weglänge auf der heißen Seite des Stoßes vergleichbar ist und daß der Quotient aus beiden verhältnismäßig unempfindlich gegen das Viskositätsgesetz des Gases ist.

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With 7 Figures     

Quality of buffalo meat burger containing legume flours as binders

The effect of addition of different decorticated legume flours, viz., soya bean, bengal gram, green gram and black gram, on the quality of buffalo meat burger was studied. The burgers consisted of optimized quantities of roasted or unroasted legume flour, spices and common salt. Inclusion of roasted black gram flour registered the highest yield of 95.7%, lowest shrinkage of 5% and lowest fat absorption of 26.6% on frying. Protein content of 18-20% was highest in the soya flour formulation. Free fatty acid (FFA) values (as% oleic) increased from 14.3 to 17.3 in freshly prepared samples (before frying) to 16.0-19.4 in 4 m frozen (-16±2?°C) stored samples and fried samples had about 25% lower FFA values. Formulations with roasted flours registered lower thiobarbituric acid (TBA) values (mg malonaldehyde/kg sample) of 0.6-1.5 as against 0.6-2.1 for unroasted flours before frying. The burgers prepared with any of these binders were organoleptically acceptable even after storage at -16±2?°C for 4 months., However, the burger with black gram dhal (dehulled split legume) flour had better sensory quality attributes compared to other legumes.     

Thermoluminescence characteristics of Sm<Superscript>3+</Superscript> doped NaYF<Subscript>4</Subscript> crystals

Thermoluminescence (TL) characteristics of NaYF₄ crystals doped with Sm³⁺ have been studied after γ-ray irradiation. Dependence of luminescence efficiency on Sm³⁺ concentration and radiation dose has been measured and possible applications of NaYF₄: Sm³⁺ as a novel phosphor for TL dosimetry have been investigated. The efficiency of 0·3 mole% Sm³⁺ doped NaYF₄ crystal has been found to be maximum and comparable with commercial thermoluminescence dosimetric (TLD) materials.     

Influence of plant pigments on spectral reflectance of maize,groundnut and soybean grown in semi-arid environments

Abstract. Spectral reflectance of leaves is influenced primarily by plant pigments, chlorophyll and carotenoids. Such reflectance can be used to study the changes in chlorophyll content and nitrogen status and in turn measures the amount of biomass accumulation. A field experiment was laid out at the Research Farm of ANGR Agricultural University, Hyderabad. The reflectance observations were taken using a hand-held ground radiometer at an interval of 15 days beginning from 30 days after sowing (DAS) until harvest of the crops. The plant pigments were determined simultaneously using DMSO (dimethyl sulphoxide) method in the laboratory. The experimental results revealed the influence of plant pigments on spectral reflectance of maize, groundnut and soybean. It was observed that there was an increase in chlorophyll- a, chlorophyll- b, total chlorophyll and carotenoid content up to flowering and thereafter chlorophyll- a content declined at a faster rate than chlorophyll- b towards physiological maturity. With the increase in concentrations of chlorophyll and carotenoids, there was a decline in spectral reflectance of the blue band (450-520 nm) and the red band (620-680 nm). Whereas, NIR (near-infrared) reflectance in the case of soybean and groundnut was found to be higher than that of maize by 11% and 2%, respectively. This was attributed to canopy cover of soybean and groundnut crops, where the soil was fully covered with vegetation. In case of maize, due to wider spacing, the soil exposure is greater, which results in low reflectance values of the NIR band. Normalized Difference Vegetation Index (NDVI) is linearly related to total chlorophyll content and the growth stages of a crop up to flowering. The NDVI differs significantly during the peak vegetative growth period among the three crop types. The study revealed that the significant differences in reflectance of maize, groundnut and soybean in the red and NIR bands were influenced by concentrations of chlorophyll- a, chlorophyll- b and carotenoids, which indicates the photosynthetic behaviour of the crops.     

Pramila Rao · D. Sujatha · K. Rathina Raj · S. Vishwanatha · K. Narasimhamurthy · P. Saibaba · D. Narasimha Rao · S. Divakar

 Subchronic toxicity dietary studies were conducted in albino rats on the safety aspects of residual β-cyclodextrin in egg samples treated for cholesterol removal at concentrations of 250, 125 and 20 ppm for a period of 90 days. Daily food intake, body weight gain, relative organ weights, histopathology, haematology and serum enzyme activities were studied. The study however, did not reveal any toxicity at any of the levels tested. It can therefore be concluded from the present study that β-cyclodextrin-treated egg samples do not cause any toxicity. Received: 28 September 1999     

Knowledge-based learning using Conceptual Transformers

The notion of concept based on the semantics of objects is defined and illustrated. An underlying thread connecting a subset of concepts is identified. This class of concepts, called the Conceptual Transformer is defined and illustrated with real-world examples. This class finds a natural application in any area where objects can be characterized by functionality. Some interesting application areas are knowledge classification, manufacturing automation, and pattern synthesis. The salient features of this class are elaborated and a knowledge structure for representing concepts is proposed. The effect of these transformers on knowledge-directed classification, which results in the formation of virtual clusters, is examined in detail. We make use of examples from real life to bring out the efficacy of the proposed transformerbased, concept-directed classification.     

Influence of variable permeability on the dispersion of a chemically reacting solute in porous media

In this paper in the first part, the influence of variable permeability on the two MHD basic flows in porous media is studied numerically. It is seen that the variable permeability due to random packing causes the hydromagnetic channelling in both the flows. Further, it is also observed that the flow in both the cases is retarded for any increase in the magnetic parameter.

In the second part, the influence of variable permeability and the effects of homogeneous and heterogeneous reactions on the dispersion of a solute in the above two basic flows are investigated. In the case of diffusion with a first order homogeneous reaction, in both the flows, the variation of permeability increases the effective dispersion coefficient while it decreases with increase in the magnetic parameter. In the case of diffusion combined with homogeneous and heterogeneous chemical reactions, the variation in permeability again increases the effective dispersion coefficient while with increase in magnetic parameter causes a decrease in the effective dispersion coefficient. Several earlier results follow as particular cases of the present study.