Showing papers by "National Institute of Technology, Silchar published in 2008"

Al-doped ZnO thin films as methanol sensors

Abstract: Al-doped zinc oxide (ZnO) thin films were prepared by chemical spray pyrolysis technique. The dopant concentration (Al/Zn at%) varied from 0 to 1.5 at%. Structural analysis of the films reveals that all the films are of polycrystalline zinc oxide in nature, possessing hexagonal wurtzite structure with (0 0 2) preferred orientation. The lattice constants calculated from the most prominent peaks are found to be in good agreement with the ICDD reference pattern: zinc oxide, 01-080-0074 (a = 3.2535 A and c = 5.2151 A). The sensing properties of the films towards methanol vapour are investigated for various concentrations of methanol in air at different operating temperatures in the range 200–350 °C. It is observed that compared to the undoped ZnO film, Al-doped films show higher sensitivity to methanol vapour. Among all the Al-doped films studied, the 0.5 at% Al-doped ZnO film shows the maximum response (∼44%) at 275 °C to 500 ppm of methanol vapour in air. Further, the films show fast response and recovery to methanol vapour at higher operating temperatures. The methanol-sensing mechanism of the film has been explained.

Al-doped zinc oxide thin films for liquid petroleum gas (LPG) sensors

Abstract: Undoped and Al-doped zinc oxide thin films were prepared by chemical spray pyrolysis technique using Zn(CH3COO)2 as a precursor solution without or with AlCl3 as a doping solution, respectively. The dopant concentration (at% Al to Zn) was varied from 0 to 1.5 at%. Grazing incidence X-ray diffraction (GIXRD) analyses of the films confirm that all the films are of polycrystalline zinc oxide in nature, possessing hexagonal wurtzite structure. The films show the change in preferential orientation depending on the doping concentration of Al. The crystallite size in the 0.5 at% Al-doped film is found to be minimum (∼103 nm) among all the films. It is observed that the resistivity of the Al-doped films decreases with the Al dopant concentration up to 1 at%. At a higher doping concentration of 1.5 at%, the disorder produced in the lattice causes an increase in the resistivity of the film. It is found that compared to the undoped ZnO film, Al-doped films show high response to LPG. Among all the doped films studied, the 0.5 at% Al-doped ZnO film shows the maximum response (∼89%) to 1 vol% of LPG in air at 325 °C. Further, the response and recovery times of the films to LPG become shorter at higher operating temperatures. A possible mechanism of LPG sensing has been explained.

Experimental Investigation of Flow Past a Square Cylinder at an Angle of Incidence

Abstract: Flow past a square cylinder placed at an angle to the incoming flow is experimentally investigated using particle image velocimetry, hot wire anemometry, and flow visualization. The Reynolds number based on cylinder size and the average incoming velocity is set equal to 410. Data for four cylinder orientations =0, 22.5, 30, and 45° and two aspect ratios AR=16 and 28 are reported. Results are presented in terms of drag coefficient, Strouhal number, time averaged velocity, stream traces, turbulence intensity, power spectra, and vorticity field. In addition, flow visualization images in the near wake of the cylinder are discussed. The shape and size of the recirculation bubble downstream of the cylinder are strong functions of orientation. A minimum in drag coefficient and maximum in Strouhal number is observed at a cylinder orientation of 22.5°. The v-velocity profile and time-average stream traces show that the wake and the separation process are asymmetric at orientations of 22.5 and 30°. The corresponding power spectra show additional peaks related to secondary vortical structures that arise from nonlinear interaction between the Karman vortices. The flow visualization images show the streamwise separation distance between the alternating vortices to be a function of cylinder orientation. Further, the flow approaches three dimensionality early, i.e., closer to the cylinder surface for the 22.5° orientation. The drag coefficient decreases with an increase in aspect ratio, while the Strouhal number is seen to increase with aspect ratio. The turbulence intensity is higher for the large aspect ratio cylinder and the maximum turbulence intensity appears at an earlier streamwise location. The overall dependence of drag coefficient and Strouhal number on orientation is preserved for the two aspect ratios studied.

Studies on ac response of zinc oxide pellets

Abstract: The ac responses of the ZnO pellets have been studied by ac measurements (impedance, capacitance and phase angle) over the temperature range 300–435 K. The ac conductivity of the ZnO pellets is observed to be proportional to ωs, where ω is the angular frequency and the exponent s is a temperature- and frequency-dependent parameter. Based on the existing theories of ac conduction, it has been concluded that for low frequency region (20 Hz–2 kHz), the dominant conduction mechanism in the ZnO pellets is multihopping at all temperatures, whereas for high frequency region (500 kHz–2 MHz), the small polaron tunneling model is the dominant mechanism in the pellets. Activation energies for ac conduction processes are estimated to be in the range of 0.028–0.277 eV which are found to vary with the frequency of the ac signal. These results are found to be consistent with the hopping model. The ac capacitance and the dielectric loss tangent are found to be dependent on both frequency and temperature. Such dependences have been explained taking into account the equivalent circuit model comprising a frequency-independent capacitive element in parallel with a temperature-dependent resistive element, both in series with a low value resistance. Impedance spectroscopy studies show single semicircular arcs in the complex impedance spectra at all temperatures in the range 300–435 K, with their centres lying below the real axis at a particular angle of depression indicating a multirelaxation behaviour in the pellets.

Comparison of performances of several types of classical controller in automatic generation control for an interconnected multi-area thermal system

Abstract: This paper presents automatic generation control (AGC) of interconnected two equal area and three unequal area thermal systems provided with single reheat turbine and generation rate constraints of 3% per minute. A maiden attempt is made to apply integral plus double derivative (IDD) controller in AGC. Controller gains in the two area system are optimized using classical approach whereas in the three area system controller gains and governor speed regulation parameters (Ri) are simultaneously optimized by using a more recent and powerful evolutionary computational technique called bacterial foraging (BF) technique. Investigations reveal on comparison that Integral (I), proportional-integral (PI), integral-derivative (ID), or proportional-integral-derivative (PID) all provide more or less same response whereas integral-double derivative (IDD) controller provides much better response. Sensitivity analysis reveals the robustness of optimum gains of IDD controllers and optimum values of speed regulation parameters at nominal loading condition to wide changes in system parameters such as loading condition, inertia constant (H), reheat time constant (Tr) and reheat coefficient (Kr) from their nominal values. The system performance is examined considering 1% step load perturbation in area1.

A multi-objective evolutionary algorithm to exploit the similarities of resource allocation problems

Abstract: The complexity of a resource allocation problem (RAP) is usually NP-complete, which makes an exact method inadequate to handle RAPs, and encourages heuristic techniques to this class of problems for obtaining approximate solutions in polynomial time. Different heuristic techniques have already been investigated for handling various RAPs. However, since the properties of an RAP can help in characterizing other RAPs, instead of individual solution techniques, the similarities of different RAPs might be exploited for developing a common solution technique for them. Two RAPs of quite different nature, namely university class timetabling and land-use management, are considered here for such a study. The similarities between the problems are first explored, and then a common multi-objective evolutionary algorithm (a kind of heuristic techniques) for them is developed by exploiting those similarities. The algorithm is problem-dependent to some extent and can easily be extended to other similar RAPs. In the present work, the algorithm is applied to two real instances of the considered problems, and its properties are derived from the obtained results.

Evaluation of Liquefaction Potential of Pond Ash

Abstract: India is facing a serious problem of effective disposal of huge quantity of fly ash generated from thermal power plants. Fly ash is highly susceptible to liquefaction and thus the rehabilitation of ash ponds requires a detailed study on evaluation of liquefaction potential so that suitable densification measures can be adopted. This paper contains various steps of evaluation of liquefaction potential of pond ash.

GA optimized PID controllers for automatic generation control of two area reheat thermal systems under deregulated environment

Abstract: This paper proposes for a genetic algorithm (GA) tuned PID controllers for automatic generation control of two - area reheat thermal system under deregulated environment. A PID controller with its inherent superb capabilities of containing peak deviation, steady state errors and oscillatory behaviour of a dynamic system is an obvious choice for automatic generation control of interconnected power systems. The main issue towards the use of a PID controller is how to optimize the three gains of the controller. The trial and error method of finding the gains by indirect optimization using ISE technique with an appropriate performance index appears to be not wise enough because of its space complexity. GA appears to be the right choice in finding the optimum gains for the controllers. Hence, in this work, the gains of the PID controllers are optimized using floating point GA. The results of the GA optimized PID controllers on a two area reheat thermal system are compared with those with optimized through trial and error method. The GA optimized controllers are found to be superior in terms of peak transient deviation, settling times, and dynamic oscillations.

Graph partitioning through a multi-objective evolutionary algorithm: a preliminary study

Abstract: The graph partitioning problem has numerous applications in various scientific fields. It usually involves the effective partitioning of a graph into a number of disjoint sub-graphs/zones, and hence becomes a combinatorial optimization problem whose worst case complexity is NP-complete. The inadequacies of exact methods, like linear and integer programming approaches, to handle large-size instances of the combinatorial problems have motivated heuristic techniques to these problems. In the present work, a multi-objective evolutionary algorithm (MOEA), a kind of heuristic techniques, is developed for partitioning a graph under multiple objectives and constraints. The developed MOEA, which is a modified form of NSGA-II, is applied to four randomly generated graphs for partitioning them by optimizing three common objectives under five general constraints. The applications show that the MOEA is successful, in most of the cases, in achieving the expected results by partitioning a graph into a variable number of zones.

Genetic Algorithms for non-convex combined heat and power dispatch problems

Abstract: This paper investigates into performance of Genetic Algorithms (GA) for solving combined heat and power dispatch (CHPD) problems in power systems. Different algorithms in different combinations of crossover and mutation functions of GA are explored and tested on a test case of combined heat and power dispatch problem. The simulation results show that all the floating point GAs (FPGA) perform better than binary GA in solving non-convex CHPD problems. Amongst the FPGAs, the performance of the FPGA with heuristic crossover and multi-nonuniform mutation is the best in terms of the efficiency in achieving better quality solutions.

Design of a new rheometer for concrete

Abstract: A new concrete rheometer has been presented including its concept, actual design, working principle, calibration, and repeatability. Resistance offered by vertical wall of cylindrical container to concrete has been taken into consideration to represent actual flow condition of concrete during shearing. An expression for total shear stress has been derived whereby shear stress versus torque and overall shear strain rate versus rotational frequency relationships have been established for the given geometry of the rheometer. A magneto-rheological fluid has been tested with the present rheometer and the results have been compared with the test results obtained by HAAKE RS1 rheometer to validate the present analytical approach. Repeatability tests were conducted with different concrete mixes and results were found to be reasonable.

Flooding Probability-Based Optimal Design of Trapezoidal Open Channel Using Freeboard as a Design Variable

Abstract: A flooding probability based cost effective design of open channel section has been proposed using freeboard as an additional design variable. The freeboard of the channel is calculated based on the flooding probability value. The proposed model is solved using classical optimization techniques as well as a nondominated sorting genetic algorithm. The results of the model are compared with an earlier reported model to demonstrate its superiority and field applicability.

Genetic Algorithms for Solving Optimal Power Flow Problems

Abstract: This chapter contains sections titled: Introduction Genetic Algorithms Load Flow Problem Optimal Power Flow Problem OPF with FACTS Devices Conclusions References ]]>

Stability Analysis of an Articulated Loading Platform in Regular Sea

Abstract: Stability of the response of an articulated loading platform under regular wave, modeled as a SDOF nonlinear oscillator, is investigated. Relative velocity square drag force for harmonic wave appearing in the right hand side of the equation of motion is mathematically treated to bring the velocity dependent nonlinear hydrodynamic damping term to the left hand side of the equation of motion. Use of these two techniques makes the equation of motion amenable to the application of method IHBC. In order to trace different branches of the response curve and investigate different instability phenomena that may exist, the commonly used incremental harmonic balance method (IHB) is modified and integrated with an arc-length continuation technique to develop into incremental harmonic balance continuation (IHBC) method. Further, a technique for treating the nonlinear hydrodynamic damping term using a concept of distribution theory has been developed. The stability of the solution is investigated by the Floquet theory using Hsu's scheme. The stable solutions obtained by the IHBC method are compared with those obtained by the numerical integration of equation of motion wherever applicable.

GA based algorithm for optimum allocation of reactive power under deregulated environment

Abstract: An algorithm using floating point genetic algorithm (FPGA) was developed to solve the problem of optimum allocation of reactive power in power systems under open market environment. The performance of the proposed model is validated on IEEE-14 bus system with modifications to incorporate the varying working conditions of power systems like, change of tap settings of transformers, variable reactive power compensations, etc. Results of the FPGA demonstrate that the algorithm is well competent in achieving the near optimal allocation of reactive power under practical constraints and price based conditions.

Modeling of Fuel Cell Based Power Supply System for Grid Interface

Abstract: Renewable energy systems have developed wide interest to supply electricity in remote areas as well as for distributed power generation specially during peak loads Fuel cell based power generation is also gaining popularity due to its cleanliness, portability and suitability for electricity and heat generation This paper presents modeling of a fuel cell power plant in terms of fuel cell, converter and power system parameters, to facilitate operation with grid interface The mathematical model is developed in per unit (PU) system using qd0 reference frame theory, to define the power flow (real and reactive) limits, which can be supplied by the fuel cell power plant A single stage PWM inverter is selected as power electronic interface between fuel cell and grid

Effect of fringing fields on subthreshold surface potential of channel engineered short channel MOSFETs

Abstract: An analytical and accurate subthreshold surface potential model for short channel Conventional, LAC & double halo including the effect of inner fringing field is presented, considering the surface potential variation with the depth of the channel depletion layer. With this the drawback of existing models, the assumption of a constant channel depletion layer thickness is removed. A pseudo two dimensional method is adopted and we report a more accurate prediction of the surface potential including the fringing field effect.

A proportional intra-class scheduling for differentiated services model

Abstract: Aggregation of flows into classes is used to avoid the scalability problems of IntServ model and this requires per-class scheduling decisions. There are number of issues associated with such approach e.g. what will be per-flow guarantee, which flows are to be aggregated together, how to determine service order among multiple classes and within a class etc. DiffServ model is a framework wherein class based QoS support is provided. In this paper we propose an algorithm for intra-class scheduling (including a small modification in buffer management) when number of flows are aggregated within a single class. The algorithm proposed, dynamically selects a disjoint subset of flows to form a class (subgroup) and aggregation mechanisim allows us to define QoS requirement of the subgroup with the use of {Max, Min} operation. We show that the algorithm performs substantially better even under heavy network condition.

Development of software using fuzzy logic to predict erosive wear in slurry pipeline system

Abstract: The phenomenon of wear is a major challenge in transportation through slurry pipeline system. A predictive software tool has been devised using Fuzzy Logic for predicting the erosive wear rate in slurry pipeline system. It is based on published experimental results conducted in a pot tester for two materials namely brass and mild steel. The software is coded using Java Programming Language. It has been established that the predictive tool devised works with fair approximation in relation to the experimental results. So it is proposed that this predictive tool can be used in industries as a tool for carrying out predictive maintenance operations in the slurry pipeline system.

Voice conversion system using SVM for vocal tract modification and codebook based model for pitch contour modification

Abstract: The basic idea of this paper is to design an alternative voice conversion technique using support vector machine (SVM) as a regression tool that, converts the voice of a source speaker to specific standard target speaker. A nonlinear mapping function between the parameters for the acoustic features of the two speakers has been captured in our work. The vocal tract characteristics have been represented by the line spectral frequencies (LSFs). The kernel induced feature space using radial basis function network type SVM with Gaussian basis function have been used in our work. The codebook based technique has been used to modify the intonation characteristic (pitch contour). Mapping of the pitch contour has been achieved at the word level by associating the codebooks derived from the pitch contours of the source and the target speakers. The speech signals for the desired target speaker have been synthesized using the transformed LSFs along with the modified pitch contour and evaluated using both the subjective and the listening tests. The results signify that the proposed model improves the voice conversion performance in terms of capturing the speakerpsilas identity. However, the performance can further be improved by suitably modifying various user defined parameters used in regression analysis and using more training LSF vectors in the training stage.

A two-dimensional surface potential based subthreshold-slope model for short-channel MOS transistors

Abstract: An analytical model for the subthreshold-slope (SS) of short-channel MOS transistors is presented in this paper. The expression for the subthreshold current, which is the basis of the subthreshold-slope, utilizes the concept of splitting of quasi- Fermi levels along the channel. The current model is based on the surface potential for short-channel devices where two- dimensional effects are incorporated by solving a pseudo-2D Poisson's equation. To arrive at a simple analytical expression, some approximations with proper explanation are made. The model results are compared with that of two-dimensional numerical simulation results using DESSIS of ISE TCAD, and a very good agreement between the two is found.

Wavelet based speech enhancement technique using median function thresholding

Abstract: In modern day voice communication, reduction of noise is of great importance. The necessity of reduction of noise arises due to the interference of the external factors with the concerned signal. Hence to reduce the interference effects wavelet based time-frequency analysis of signals is performed. Time-frequency analysis is the process of determining what frequencies are present in a signal, how strong they are and how they change over time. Both Discrete Wavelet Transform (DWT) and Packet Wavelet Transform (PWT) are optimal methods for this purpose. In this work we use some real signals and process them with DWT and PWT.

Discussion of “Invertible Alternatives to Normal and Lognormal Distributions” by Prabhata K. Swamee and Pushpa N. Rathie

Abstract: The authors of the technical note have obtained functions which closely approximate the normal and lognormal distributions. The discusser would like to comment on the following points of the technical note. It is hoped that this additional information will be helpful to the readers of the technical note. 1. The authors of the note have given the following function which approximates the normal distribution