Showing papers by "National Institute of Technology, Silchar published in 2007"

Optical properties of thermally evaporated CdS thin films

Abstract: CdS thin films of varying thicknesses were deposited on cleaned glass substrates at room temperature by thermal evaporation technique in a vacuum of about 2 x 10-5 torr. UV-VIS spectra of the films were studied using the optical transmittance measurements which were taken in the spectral region from 300 nm to 1100 nm. The absorbance and reflectance spectra of the films in the UV-VIS region were also studied. Optical constants such as optical band gap, extinction coefficient, refractive index, optical conductivity and complex dielectric constant were evaluated from these spectra. All the films were found to exhibit high transmittance (∼ 60 - 93 %), low absorbance and low reflectance in the visible/near infrared region from ∼ 500 nm to 1100 nm. The optical band gap energy was found to be in the range 2.28 – 2.53 eV. All the films annealed at 300°C for 4 hours in vacuum (∼ 10-2 torr) showed a decrease in the optical transmittance with its absorption edge shifted towards the longer wavelength, leading to the result that the optical band gap decreases on annealing the films. Also, on annealing crystallinity of the films improves, resulting in decrease in the optical transmittance. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical and electrical studies on spray deposited ZnO thin films

Abstract: ZnO thin films were prepared by spray pyrolytic decomposition of zinc acetate onto a glass substrate. These films were analyzed for the optical and electrical properties. Optical studies show that in these films the electronic transition is of the direct transition type. The optical energy gap for the films of different thicknesses is estimated to be in the range 2.98 – 3.09 eV. Electrical studies indicate that the films exhibit thermally activated electronic conduction and the activation energies are found to be dependent on the film thickness. The complex impedance measurements were carried out over a wide range of frequencies at room temperature (300 K). All the impedance spectra contain only a single arc, but the arc has a non-zero intersection with the real axis in the high frequency region. Also, the arc has its centre lying below with the real axis which indicates the multirelaxation behavior of the films. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Experimental Investigation of Overlap and Blockage Effects on Three-Bucket Savonius Rotors

Abstract: Savonius vertical axis wind turbines (VAWT) have advantages over horizontal axis wind turbines (HAWT), such as simple construction, acceptance of wind from any direction without orientation, self-starting, inexpensive etc. These advantages make it a viable proposition for small-scale applications in developing countries. In spite of the above advantages, VAWT are not gaining popularity mainly because of their poor efficiency. Hence, a three-bucket Savonius model rotor, having 8 cm bucket diameter and 20 cm height, was designed, fabricated, and tested in a sub-sonic wind tunnel. Provisions for variations of ‘blade’ overlap were included. Experiments were conducted for overlap conditions in the range of 16% to 35%. From the experimental investigations, power-coefficients (Cp) were calculated with and without blockage correction factors for tunnel interference. In both analyses, the power-coefficient increased if there was overlap, with an optimum value at 20% overlap of 47% without blockage correction, and ...

Artificial Neural Networks Approximation of Density Dependent Saltwater Intrusion Process in Coastal Aquifers

Abstract: The flow and transport processes in a coastal aquifer are highly nonlinear, where both the flow and transport processes become density dependent. Therefore, numerical simulation of the saltwater intrusion process in such an aquifer is complex and time consuming. An approximate simulation of those complex flow and transport processes may be very useful, if sufficiently accurate, especially where repetitive simulations of these processes are necessary. A simulation methodology using a trained artificial neural network model (ANN) is developed to approximate the three-dimensional density dependent flow and transport processes in a coastal aquifer. The data required for initially training the ANN model is generated by using a numerical simulation model (FEMWATER). The simulated data consisting of corresponding sets of input and output patterns are used to train a multilayer perceptron using the back-propagation algorithm. The trained ANN predicts the concentration at specified observation locations at differe...

Optimal Design of a Stable Trapezoidal Channel Section Using Hybrid Optimization Techniques

Abstract: A cost effective channel section for a specified flow rate, roughness coefficients, longitudinal slope, and various cost parameters can be determined using an optimization technique. However, the derived optimal channel section may not be feasible for construction because of in situ conditions. The local soil conditions may not support the optimal side slope of the channel and if constructed, the slope may fail. It is therefore necessary to also incorporate the criteria for side slope stability in designing an optimal open channel section. In this paper, a new methodology has been developed to design a stable and optimal channel section using hybrid optimization techniques. A genetic algorithm based optimization model is developed initially to determine the factor of safety of a channel slope for given soil parameters. This optimization model is then externally linked with a separate sequential quadratic programming based optimization model to evaluate the parameters of the stable and optimal channel section. Solution for various example problems incorporating different soil parameters are illustrated to demonstrate the applicability of the developed methodology.

Multiple Inflows Muskingum Routing Model

Abstract: The Muskingum principle of flood routing is applicable to a single channel reach bounded by two measuring sections with no lateral inflow in the reach. The basic Muskingum model provides a forecasting form that may be used to predict the downstream flow, a finite time ahead on the basis of the current flow rates. To apply the Muskingum principle to a channel network having inflows from different subcatchments that join downstream to form a combined outflow, the inflows from the subcatchments may be substituted by an equivalent single inflow for an ideal Muskingum reach. This paper proposes a new multiple inflows Muskingum model; the parameters in the model can be estimated using channel properties, the model may be used for routing in ungauged river networks. The new model appropriately extends the Muskingum philosophy to multiple inflows routing and can be expressed in single inflow-single outflow form; a Muskingum-Cunge model and forecasting model for multiple inflows similar to the basic model can be d...

Wavelet-GA-ANN Based Hybrid Model for Accurate Prediction of Short-Term Load Forecast

Abstract: This paper proposes a hybrid model developed through wiser integration of wavelet transforms, floating point GA and artificial neural networks for prediction of short-term load The use of wavelet transforms has added the capability of capturing of both global trend and hidden templates in loads, which is otherwise very difficult to incorporate into the prediction model of ANN Auto-configuring RBF networks are used for predicting the wavelet coefficients of the future loads Floating point GA (FPGA) is used for optimizing the RBF networks The use of GA optimized RBF network has added to the model the online prediction capability of short-term loads accurately The performance of the proposed model is validated using Queensland electricity demand data from the Australian National Electricity Market Results demonstrate that the proposed model is more accurate as compared to RBF only model

A Pseudo Two-Dimensional Subthreshold Surface Potential Model for Dual-Material Gate MOSFETs

Abstract: An analytical subthreshold surface potential model for dual-material gate MOSFETs, which considers a varying depth of the channel depletion layer due to the difference in Hatband voltages, and also due to the depletion layers around the source/drain junctions, is presented. The model predictions are compared with the predictions by the 2-D numerical device simulator DESSIS, and a very good agreement between the two is observed.

Voice transformation by mapping the features at syllable level

Abstract: Voice transformation involves modifying the source speaker voice to target speaker voice. Voice characteristics of a speaker depends on the shape of the glottal pulse (source characteristics), shape of the vocal tract system (system characteristics) and the long term features (prosody or supra-segmental) of the speech signal produced by the speaker. In this paper we proposed the mapping functions to transform the vocal tract characteristics and intonation characteristics from source speaker to target speaker. Mapping functions are developed by the features extracted from syllable level. The shape of the vocal tract system is characterized by linear prediction coefficients, and the mapping function is realized by a five layer feedforward neural network. Mapping of the intonation characteristics (pitch contour) is provided by associating the code books derived fromthe pitch contours of the source and target speakers. The proposed mapping functions are used in voice transformation task. The target speaker's speech is synthesized and evaluated using listening tests. The results of the listening tests indicate that the proposed voice transformation provides better mapping of the voice characteristics compared to the earlier method proposed by the author. The original and the synthesized speech signals obtained usingmapping functions are available for listening at http://shilloi.iitg.ernet.in/~ksrao/result.html

A New Termination Detection Protocol for Mobile Distributed Systems

Abstract: In this paper, we propose an application layer based modified weight-throwing protocol for the distributed termination detection problem in a purely mobile distributed environment with no static hosts. The mobile hosts are considered with limited functionality. We discuss the effect of mobility on the proposed algorithm and analyze it.

A surface potential based subthreshold drain current model for short-channel MOS transistors

Abstract: Utilizing the concept of the splitting of the quasi-Fermi energy on the surface, a surface potential based subthreshold drain current model for the short-channel MOS transistor is presented. Both the drift and diffusion components are considered in this model. The model is based on an accurate surface potential model that takes into account the varying depth of the channel depletion layer around the source and drain junction which is very important for short-channel devices. The model predictions are compared with the predictions by the 2D numerical device simulator DESSIS, and a very good agreement is obtained.

Hybrid PSO/self-adaptive improved EP for economic dispatch with nonsmooth cost function

Abstract: This paper investigates the performance of a hybrid algorithm developed by hybridization between particle swarm optimization (PSO) and self-adaptive improved fast evolutionary programming (IFEP) techniques for solving economic load dispatch (ELD) problem with non-smooth cost curves where conventional gradient based methods are inapplicable. The reported excellent performance of both IFEP and PSO techniques in solving ELD problems has encouraged us in hybridizing them in the effort of enhancing the convergence capability of IFEP with PSO intelligence. The performance of the hybrid algorithm is demonstrated on a power system with 15 units and comparison is drawn in between CEP-PSO' and IFEP- PSO' in terms of the solution quality and computational efficiency. The simulation results show that IFEP-PSO' method is more efficient in finding higher quality solutions in non-convex ELD problems.

A process-based model on methane emission with its oxidation process from rice fields and corresponding control indices

Abstract: In this paper, a mathematical model is developed for net methane emission from rice fields by coupling methane production model with methane oxidation model. Several dynamical regimes were formed through qualitative analysis of the model, and corresponding dynamic features were interpreted through emission indices. Sensitivity of the model is discussed under the effects of temperature and oxygen concentration in methanogenic and methane oxidation phases, respectively, and interpreted by defining an index; in addition, control parameters are identified and their threshold limits defined. The out-busting emission tendency of methane is considered separately and a forcing strategy was defined to force emission level towards zero in the long term. Lastly, a complete control strategy is proposed for reducing methane emission.

A threshold voltage model for DMG-MOS transistors taking into account the varying depth of channel depletion layers around the source and drain

Abstract: In this paper, an analytical model for threshold voltage of dual material gate (DMG) MOS transistors is presented. For such devices, the depletion regions due to source/drain junctions occupy a large portion of the channel, and hence are very important for accurate modeling. The proposed threshold voltage model is based on a realistic physically-based model for the depletion layer depth along the channel that takes into account its variation due to the source and drain junctions as well as the work function difference of the metal gate materials. The proposed model can predict the drain induced barrier lowering (DIBL) effect and hence, the threshold voltage roll-off characteristics quite accurately. The model predictions are verified against the 2-D numerical device simulator, DESSIS of ISE TCAD.