Formation of M23C6 type carbides in heat-treated extra low carbon Mn-Si and Mn-Si-Nb high strength low alloy “mar” steels

Structural investigations in extra low carbon mar steels with nominal compositions A1 (4 Mn-1.0 Si), A2 (4 Mn-1.0 Si – 0.042 Nb), A3 (～ 5 Mn-1.5 Si), A4 (2.6 Mn-1.0 Si) and A5 (～ 5 Mn-2.5 Si) in the heat treated condition by X-ray diffraction technique (Debye-Scherrer method) for identifying strengthening mechanisms. Results on the formation of M₂₃C₆ type carbide either singly (in most cases) or in combination with austenite. Discussion pertaining to 1. identification of factors promoting the structural changes and, 2. their likely effect on mechanical properties.     

An amorphous silicon thin film transistor: Theory and experiment

The volt-ampere characteristics for a thin film transistor fabricated with vacuum deposited amorphous silicon as the semiconductor is presented. The substrate is single crystalline silicon with a 3000 Å layer of thermally grown silicon dioxide as the insulator. The gate is a buried N⁺ phosphorus diffused region while the source and drain contacts are interdigited fingers of aluminum. By using the Cohen-Fritzsche-Ovshinsky model for the density of localized states in the mobility gap, the V_G vs I_D characteristic at small values of V_D is predicted and experimentally verified. This characteristic is used to theoretically predict the family of I_D curves for the TFT over a range of V_G and V_D. The theory and experiment agree exceptionally well below the gate-drain pinch-off, thereby verifying the theory of a TFT with a uniform distribution of traps in the band-gap.     

Theory of back surface field silicon solar cells

Back surface field silicon solar cells with n⁺pp⁺ (or sometimes p⁺nn⁺) structures are found to have better characteristics than the conventional solar cells. The existing theories have not been able to satisfactorily predict the experimentally observed parameters on these cells. A theory, based on the transport of both minority and majority carriers under the charge neutrality condition, has been developed in the present paper which explains the behavior of the back surface field solar cells. Good agreement is achieved between the results obtained by using this theory and the experimental observations of earlier workers.     

EvIA - Evidential Interval Algebra and Heuristic Backtrack-Free Algorithm

The Interval Algebra (IA) framework for temporal reasoning encodes indefinite knowledge in terms of disjunctions of relations. Many problems arising in practice can have evidences from past or from other external sources to indicate that some relations in a disjunction may be more probable than others. IA framework is inadequate to encode this information. The aim of the present study is two fold. First, to extend IA framework by associating numeric weights to the relations for capturing additional information and provide a reasoning methodology for the extended framework. Second, to apply the extended framework for developing a heuristic algorithm which finds a solution of the conventional IA network problem without backtrack. We make use of well-known evidential reasoning techniques to develop the new framework, Evidential Interval Algebra (EvIA). EvIA is an augmentation of interval algebra with evidential techniques. The constraint, constraint operators namely converse, composition and intersection, and path consistency algorithm of interval algebra are overlayed by evidential function and evidential operations to get enhanced expressiveness and efficient reasoning capability. The efficiency of the EvIA framework is demonstrated in the form of a heuristic which finds a solution of the interval algebra network without backtrack. Experimental results of the heuristic algorithm reveal that the algorithm is sound and for some specific types of the problems, the success of finding a solution is more than 90 percent. The results also show that the algorithm is efficient in terms of runtime when compared with a backtrack search algorithm.     

A Circularly Polarized Stacked Patch Aperture Coupled Microstrip Antenna for 2.6 GHz Band

A circularly polarized stacked patch microstrip antenna and a 2?×?2 subarray for circular polarization are proposed in this paper. The proposed design has the input impedance bandwidth and axial ratio bandwidth of about 10% and 4.7% respectively. Circular polarization is obtained with the help of slits cut in the patch. A size reduction of around 37% is also achieved with the help of the slits. A subarray based on sequentially rotated feeding technique for circular polarization is also presented in this paper. Array element was deigned using a high dielectric constant laminate for feed network. In addition to low boresight axial-ratio, the subarray has impedance and 3-dB axial-ratio bandwidths of 12% and 8% respectively.     

Nanostructured Thermoelectrics: Big Efficiency Gains from Small Features

The field of thermoelectrics has progressed enormously and is now growing steadily because of recently demonstrated advances and strong global demand for cost‐effective, pollution‐free forms of energy conversion. Rapid growth and exciting innovative breakthroughs in the field over the last 10–15 years have occurred in large part due to a new fundamental focus on nanostructured materials. As a result of the greatly increased research activity in this field, a substantial amount of new data—especially related to materials—have been generated. Although this has led to stronger insight and understanding of thermoelectric principles, it has also resulted in misconceptions and misunderstanding about some fundamental issues. This article sets out to summarize and clarify the current understanding in this field; explain the underpinnings of breakthroughs reported in the past decade; and provide a critical review of various concepts and experimental results related to nanostructured thermoelectrics. We believe recent achievements in the field augur great possibilities for thermoelectric power generation and cooling, and discuss future paths forward that build on these exciting nanostructuring concepts.     

State‐constrained stabilization of beam‐balance systems

We present nonlinear control techniques to stabilize a beam‐balance system with state constraints. We consider two different actuator configurations: the first one is actuated by a cart moving on the beam, while in the second case, the actuation is by a single electromagnet. In the first case, the constrained stabilization problem is solved via an output feedback controller designed using feedback linearization, Luenberger‐like observer and linear matrix inequality based optimization. In the second case, a Lyapunov‐based controller is proposed that takes care of both the input and state constraints. Copyright © 2007 John Wiley & Sons, Ltd.     

Above ground standing biomass and carbon storage in village bamboos in North East India

Bamboo forms an important component in the traditional landscape of North East India. For biomass estimation of village bamboos of Barak Valley, North East India, allometric relationships were developed by harvest method describing leaf, branch and culm biomass with DBH as an independent variable using a log linear model. The culm density of the stand was 8950 culms ha⁻¹ during 2005 of which 67% of growing stock was represented by Bambusa cacharensis, 17.88% by Bambusa vulgaris and 15.12% by Bambusa balcooa. Above ground stand biomass was 121.51 t ha⁻¹ of which 86% was contributed by culm component followed by branch (10%) and leaf (4%). With respect to species, B. cacharensis made up to 46% of total stand biomass followed by B. vulgaris (28%) and B. balcooa (26%). Carbon storage in the above ground biomass was 61.05 t ha⁻¹. Allocation of C was more in culm components (53.05 t ha⁻¹) than in branch (5.81 t ha⁻¹) and leaf (2.19 t ha⁻¹). Carbon storage in the litter floor mass was 2.40 t ha⁻¹, of which leaf litter made up the highest amount (1.37 t ha⁻¹) followed by sheath (0.86 t ha⁻¹) and branch (0.17 t ha⁻¹). Carbon stock in the soil up to 30 cm depth was 57.3 t ha⁻¹. Gross C stock in the plantation was estimated to be 120.75 t ha⁻¹. Carbon storage estimated in the bamboo stand of present study offers insights into the opportunity of village bamboos in the rural landscape for carbon storage through carbon sequestration. Management and utilization of village bamboos as a potential source of carbon sink by smallholder farmers are discussed in the context of their livelihood security and the Millennium Development Goals of the United Nations.