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.     

Effect of repeated dosages of superplasticizers on slump,strength and freeze-thaw resistance of concrete

Superplasticizers, when added to fresh concrete, cause large increases in its slump. However, this increase in slump is not sustained over long periods and within 60 minutes or so the concrete reverts to its original slump. In actual field applications of superplasticizers it may be necessary to add additional dosages to maintain the increased slump. This paper gives results of a laboratory investigation to determine the effect of repeated dosages of superplasticizers on workability, strength and durability of concrete. A series of air-entrained concrete mixes was made at a water/ cement ratio of 0.42 with a slump of 50 mm. Four commonly available superplasticizers were repeatedly added to the concrete, at the manufacture's recommended dosage rates, after completion of initial mixing. This was followed by additional mixing for 2 minutes. The properties of the fresh concrete were determined and test cylinders were cast after the addition of each dosage. Test prisms were also cast for strength and durability studies after the addition of the last dosage. The test results indicate that large increases in slumps of superplasticized concretes can be maintained for several hours by the addition of a second dosage. Apart from one instance, the addition of the third dosage is not considered desirable. The repeated additions of sulphonated melamine- and naphthalene-based superplasticizers caused substantial loss in entrained air content of the concrete; however, for concrete incorporating the lignosulphonate based superplasticizer, the reverse was true. The loss of entrained air adversely affected the performance of the concrete in freeze-thaw tests.     

Aggregation convergecast scheduling in wireless sensor networks

We consider the problem of scheduling in wireless sensor networks for the purposes of aggregation convergecast. We observe that existing schemes adopt essentially a two phase approach, consisting of, first, a tree construction and, second, a scheduling phase. Following a similar approach, we propose two new improvements, one to each of the two phases. Starting with a new lower bound on the schedule length, we make use of it in the tree construction phase. The tree construction phase consists of solutions to instances of bipartite graph semi-matchings. The scheduling phase is a weight-based priority scheme that obeys dependency (tree) and interference constraints. Our extensive experiments show that, overall, our proposed solution not only outperforms all previously proposed solutions in terms of schedule length, but it also significantly extends the network’s lifetime.     

Sustainable model for financial viability of decentralized biomass gasifier based power projects

This paper made a modest attempt for designing a sustainable model for financial viability of biomass gasifier power projects for enhancing electricity access in India and other developing countries. For long term sustainability of distributed generation projects in remote rural areas, viability from both project implementing agency (PIA) and the end-users need to be ensured. The minimum required prices of electricity from both PIA and end-user perspective have been estimated. While for PIA the cost recovery is the key for viability, the affordability to pay the electricity cost is crucial for the end users. Analysis carried out in this paper on the basis of data obtained from operational projects implemented in India reveal that it is essential to operate the system at a higher capacity utilization factor. While this can be achieved though creating convergence with locally relevant economic activity, it is also observed that micro-enterprises cannot pay beyond a certain price of electricity to keep it sustainable. This paper sets forth a case for developing a regulatory mechanism to extend the tariff fixation for the projects and providing cross-subsidies to ensure long term sustainability of off-grid project.     

Two-dimensional specification of universal quantification in agraphical database query language

A technique is proposed for specifying universal quantification and existential quantification (combined with negation) in a two-dimensional (graphical) database query language. Unlike other approaches that provide set operators to simulate universal quantification, this technique allows a direct representation of universal quantification. Syntactic constructs for specifying universal and existential quantifications, two-dimensional translation of universal quantification to existential quantification (with negation), and translation of existentially quantified two-dimensional queries to relational queries are presented. The resulting relational queries can be processed directly by many existing database systems. The authors claim that this technique renders universal quantifications easy to understand. To substantiate this claim, they provide a simple, easy-to-follow guideline for constructing universally quantified queries     

Effects of physical confinement (< 125 nm) on the curing behavior of phenolic resin

How the physical confinement of phenolic resin in nano porous silica (8 nm ≤ pore diameter (D_p) ≤ 125 nm) affected the polymer's curing behavior was examined by conducting differential scanning calorimetry experiments at 320 K ≤ T ≤500 K. Our results suggested that upon incorporating the phenolic resin into the silica, its curing temperature was lowered. However, what was interesting was that there was an inverse linear dependence between the pore size and the curing temperature, i.e., the smaller the pore diameter the higher the curing temperature. There was evidence that phenolic resin was unable to penetrate into 8 nm‐sized pores. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006