Periodicity and bifurcations in capillary tube boiling with a concentric heating wire

Nucleate boiling from a vertical glass capillary in a pool of water is investigated here. Electrical heating is provided with a wire passing concentrically through the center of the capillary, and a fast-response thermocouple at the lip of the capillary records the instants of bubble departure. Different lengths and diameters of capillaries are used in the experiments. The average frequency of bubbling is seen to increase with applied heat flux, the relation being linear in the initial stages. With the heat flux used as a bifurcation parameter, one-dimensional return maps of the time interval between successive bubble emission events are used to study the transitions from the periodic state. The first bifurcation from the periodic to a two-period state is observed to be due to lateral instability of the liquid film adhering to the capillary wall. Further bifurcations to period two and then to period three bubbling are also observed. Simplified analysis of the different phases of the boiling process yields solutions which show close agreement with the experimental data.     

Low-temperature preparation of polycrystalline silicon from silicon tetrachloride

Polycrystalline silicon has been prepared by zinc reduction of silicon tetrachloride at a low temperature (≈550° C) in a vertical vapour phase reactor. Characterisation of the remelted polycrystalline ingot by X-ray, SEM and electrical methods shows that the material is p-type with an average grain size of 0.5 μm having a room-temperature resistivity in the range 1.0–1.5 Ω cm suitable for solar cell fabrication.     

Two-dimensional wave propagation in a micropolar thermo-elastic layer with stretch

This paper deals with the propagation of 2-dimensional waves in a thermo-elastic micropolar solid layer which can stretch and contract. Thermo-elastic Rayleigh wave velocity equation in the micropolar medium with stretch has been deduced from the above theory. The wave velocity equation obtained is in agreement with the classical result of Rayleigh when the layer is unstretched and thermal and micropolar effects are negligibly small.     

Pharmacological actions of Pongamia pinnata seeds--a preliminary study

Direct ethanolic and sequential petroleum ether, chloroform, acetone and ethanolic extracts (50-100 mg/kg, i.p.) of P. pinnata seeds given 30-60 min before revealed anti-inflammatory, analgesic and anti-ulcerogenic activities in rats. The activities were present maximum in petroleum ether and chloroform extracts. However, the extracts also showed shortening of pentobarbitone induced 'sleep time' in rats.     

Non-linear analysis of EEG signals at various sleep stages

Application of non-linear dynamics methods to the physiological sciences demonstrated that non-linear models are useful for understanding complex physiological phenomena such as abrupt transitions and chaotic behavior. Sleep stages and sustained fluctuations of autonomic functions such as temperature, blood pressure, electroencephalogram (EEG), etc., can be described as a chaotic process. The EEG signals are highly subjective and the information about the various states may appear at random in the time scale. Therefore, EEG signal parameters, extracted and analyzed using computers, are highly useful in diagnostics. The sleep data analysis is carried out using non-linear parameters: correlation dimension, fractal dimension, largest Lyapunov entropy, approximate entropy, Hurst exponent, phase space plot and recurrence plots. These non-linear parameters quantify the cortical function at different sleep stages and the results are tabulated.     

Entropies for detection of epilepsy in EEG

The electroencephalogram (EEG) is a representative signal containing information about the condition of the brain. The shape of the wave may contain useful information about the state of the brain. However, the human observer cannot directly monitor these subtle details. Besides, since bio-signals are highly subjective, the symptoms may appear at random in the time scale. Therefore, the EEG signal parameters, extracted and analyzed using computers, are highly useful in diagnostics. The aim of this work is to compare the different entropy estimators when applied to EEG data from normal and epileptic subjects. The results obtained indicate that entropy estimators can distinguish normal and epileptic EEG data with more than 95% confidence (using t-test). The classification ability of the entropy measures is tested using ANFIS classifier. The results are promising and a classification accuracy of about 90% is achieved.     

Solution-adaptive techniques in computational heat transfer and fluid flow

Recent contributions to solution-adaptive grid and solution-adaptive differencing techniques are breifly described in this paper. In solution-adaptive grid techniques, the grid points are dynamically reclustered or refined to improve the resolution in the important regions where the truncation error estimate is high. In solution-adaptive differencing techniques, the order of the differencing scheme in high error estimate region is dynamically increased. Thus both adaptive grid and adaptive differencing techniques represent error-equidistribution procedures. Two strategies for adaptive gridding are described in this paper. In one strategy, termed Global Adaptation, all grid points participate in the grid point redistribution process. In the other strategy, called Local Adaptation, grid refinement is performed only in local regions with high truncation error estimates. Results of various problems are presented which show the improvements obtained with solution-adaptive techniques.     

A Mobility-Prediction-Based Relay Deployment Framework for Conserving Power in MANETs

There has been a growing interest in designing mobile systems consisting of special relay nodes whose mobility can be controlled by the underlying network. In this paper, we consider the design of a heterogeneous mobile ad hoc network (MANET) consisting of two kinds of mobile nodes-traditional nodes with limited energy and a few controllable mobile relay nodes with relatively abundant energy resources. We propose a novel relay deployment framework that utilizes mobility prediction and works in tandem with the underlying MANET routing protocol to optimally define the movement of the relay nodes. We present two instances of the relay deployment problem, together with the solutions, to achieve different goals. Instance 1, termed Min-Total, aims to minimize the total energy consumed across all the traditional nodes during data transmission, while instance 2, termed Min-Max, aims to minimize the maximum energy consumed by a traditional node during data transmission. Our solutions also enable the prioritization of individual nodes in the network based on residual energy profiles and contextual significance. We perform an extensive simulation study to understand the trade-offs involved in deploying an increasing fraction of such relay nodes in the network. We also investigate the performance of the proposed framework under different mobility prediction schemes. Results indicate that even when the relay nodes constitute a small fraction of the total nodes in the network, the proposed framework results in significant energy savings. Further, we observed that while both the schemes have their potential advantages, the differences between the two optimization schemes are clearly highlighted in a sparse network.     

Active cellular preform derived from stems of jute and sticks of cane and their suitability for bulk porous Si/SiC ceramics

Stems of Jute (Corchorus capsularis L.) and sticks of Cane (Calamus rotang L.), plants of immense economic importance in the Indian subcontinent, were converted into carbonaceous perform (C-preform) maintaining the circular cylindrical shapes in lengths of 0.02–0.05 m by controlled thermal processing. Plant material precursors were characterized by analysis of elemental (C, H, N) and molecular (cellulose, hemicellulose, lignin) compositions, by determination of Bulk Density (BD) and ash content and by optical microscopy and X-ray diffractometry (XRD). C-preforms were also characterized by measurement of BD and by Scanning Electron Microscopy (SEM) and XRD. The C-preforms were further subjected to infiltration with Si-melt (1823–1923 K) under vacuum. Spontaneous infiltration and reaction yielded composite ceramics preserving the morphology of native Jute Stem (JS) and Cane Stick (CS) precursors on macro and micro scale. The materials were found to be duplex composites with Si and β-SiC as crystalline phases. The end ceramics were characterized by measurement of BD, and also by SEM and by XRD. Measured mean BD of the Si/SiC composites derived from JS and CS were 2190 Kg m⁻³ and 2250 Kg m⁻³. The respective volume fractions of large diameter (>100 μm) bulk pores were 0.134 and 0.204, in the composites derived from JS and CS. Taking into account the measured volume fraction internal pores of 0.11 and 0.149, the volume fractions of SiC were calculated to be 0.136 and 0.307 in the composites derived from JS and CS respectively, closely tallying with those calculated from the C-preform bulk densities. The cellular Si/SiC ceramics derived from JS and CS having special morphologies with long and large porous channels and oriented growth of constituent phases are likely to be suitable for devices such as high temperature insulators, catalyst support structures for gas phase reactions at elevated temperatures, molten metal filters and others.