Showing papers in "Journal of the Indian Institute of Science in 2004"

Fly ash characterization with reference to geotechnical applications

Abstract: Thermal power stations use pulverized coal as fuel. They produce enormous quantities of coal ash as a by-product of combustion. This calls for the development of strategies to encourage and establish technological concepts which will ensure consumption of fly ash in bulk. Among the various uses of fly ash, its bulk utilization is possible only in geotechnical engineering applications. This necessitates characterization of the fly ash with reference to geotechnical applications. This paper presents a review of such studies carried out. The results show that fly ash is a freely draining material with angle of internal friction of more than 30 degrees. The specific gravity is lower leading to lower unit weights resulting in lower earth pressures. It can be summarized that fly ash (with some modifications/additives, if required) can be effectively utilized in geotechnical applications.

Gauss Legendre quadrature over a triangle

Abstract: This paper presents a Gauss Legendre quadrature method for numerical int egration over the standard triangular surface: {(x, y) | 0, 1 ,1 } x y xy ≤≤ +≤ in the Cartesian two-dimensional (x, y) sp ace. Mathematical transformation from (x, y) space to ( ξ, η) space map the standard triangle in ( x, y) space to a standard 2-square in ( ξ, η) space: {(ξ, η)|–1 ≤ ξ, η ≤ 1}. This overcomes the difficulties associated with the derivation of new weight coeff icients and sampling points and yields results which are accurate and reliable. Results obtained with new formulae are compared with the existing formulae.

Design of FIR filters using variable window families: A comparative study

Abstract: In this paper, we report the design equations for FIR filter synthesis by using some recently reported combinational window functions. The performance of these filters is compared with FIR filters designed by using Kaiser window (prolate spheroidal wave function based). We also suggest some corrections in the set of design equations for FIR filter synthesis by using raised cosine window. The variable window functions used in this study other than Kaiser and raised cosine window provide filters with better side lobe fall off rate. This feature can be utilized for better suppression of images associated with interpolators.

A novel resonant transition push-pull DC-DC converter

Abstract: In hard-switched converters, the switching frequency is limited by switching losses and EMI problems. However, high-switching frequency is necessary to reduce the converter size. Hence, soft switching is imperative at high switching frequency to obtain good efficiency. Push-pull converter is a preferred topology at medium power level. This paper proposes a novel resonant transition topology for push-pull converter. The proposed topology uses two additional switches and two diodes when compared to hard-switched push-pull converter. These extra switches introduce freewheeling in the primary circuit and thus enable loss-less switching. In classical push-pull converters, the transformer primary is left open during two sub-intervals in a period making the turn-on of the switch hard. The new circuit topology converts these open circuit intervals into freewheeling ones. With such a modification, all trapped energy in the core is conserved to achieve zero-voltage switching during the entire transition. Switch stress, control and small signal model are similar to hard-switched PWM converter. Idealized analysis and design methodology are explained for the push-pull converter. A prototype-300 kHz, 200 W push-pull converter validates the design method. Dynamic analysis of the push-pull converter is presented. The proposed topology can be extended to half-bridge converter also. Its circuit diagram is presented.

Autecology of the endemic Crimson Rose butterfly Pachliopta hector (Lepidoptera : Rhopalocera : Papilionidae)

Abstract: The study including field observations on the distribution of eggs, larvae, purpae on the larval host Aristolochia indica and the laboratory study on the success rate of eggs, larvae and pupae established that Pachliopta hector Linn., endemic to Sri Lanka and south India, is on wings throughout the year with a higher density during August/September/October/November and also during AprilJune. It is multivoltine with 67 broods yearly, with development from egg to the adult requiring 3947 days. The species displayed single egg-laying habit, which coupled with host plant specialization of larve feeding on A. indica and A. bracteolata allowed efficient utiliza-tion of the food resource. The eggs hatched in seven days and the larvae passed through five instars. The last two instars consumed over 80% of the total food intake. Profiles of food consumption and body weight gain ran on similar lines, with increase through successive larvae. Both consumption index (CI) and growth rate (GR) de-clined as the larvae aged, the value of the former averaging 3.02 and the latter 0.37. The values of approximate digestibility (AD) are high: 9987%. The values of both efficiency of conversion of ingested food (ECI) and effi-ciency of conversion of digested food (ECD) increased as the larvae aged, the former averaging 18.02% and the latter 22.26%. Adults of P. hector utilized nearly 24 floral species as nectar sources, whose sugar concentrations (1258%) corresponded with 1550% in psychophilic flowers. They displayed a hovering habit while harvesting nectar, and frequently contacted the essential organs with probosics and head, thus promoting cross-pollination.

Analysis of quasi-saturation phenomena for SiGe double heterojunction bipolar transistors

Abstract: In this paper, a high-voltage current-switching NPN SiGe double-heterojunction bipolar transistor (DHBT) has been analyzed and simulated using two-dimensional device simulator MEDICI. The analysis includes conducti-vity modulation, quasi-saturation phenomenon and effect of valence band offset for holes in a high-voltage SiGe DHBT and is compared with a conventional Si bipolar junction transistor (Si BJT). The valence band offset for holes is responsible for the presence of a retarding potential barrier at collector-base junction for electrons in SiGe DHBT. The retarding potential barrier formation along with reduced conductivity modulation in SiGe DHBT leads to a fall in its short-circuit current gain hFE in comparison with Si BJT. As a consequence, the quasi-saturation current density limit JCQS of SiGe DHBT degrades and leads to high-power dissipation, setting a severe limitation on its performance at high collector current density. Keywords: SiGe DHBT, Si BJT, quasi-saturation, power dissipation, valenceformer averaging 18.02% and the latter 22.26%. Adults of P. hector utilized nearly 24 floral species as nectar sources, whose sugar concentrations (1258%) corresponded with 1550% in psychophilic flowers. They displayed a hovering habit while harvesting nectar, and frequently contacted the essential organs with probosics and head, thus promoting cross-pollination.