Showing papers by "Delhi Technological University published in 2006"

Bianchi type-ii cosmological models with constant deceleration parameter

Abstract: A special law of variation for Hubble's parameter in anisotropic space–time models that yields a constant value of the deceleration parameter is presented. Also, a spatially homogeneous and anisotropic but locally rotationally symmetric (LRS) Bianchi type-II cosmological model is studied with a perfect fluid and constant deceleration parameter. Assuming the equation of state p = γρ, where 0≤γ≤1, and using a special law of variation for the Hubble parameter, we are able to construct many new solutions to Einstein's field equations of LRS Bianchi type-II for four different physical models (dust, radiation, Zel'dovich and vacuum). We discuss the solutions with power-law and exponential expansion and examine a particular class of models. A detailed study of kinematic, geometrical and observational properties is carried out.

Plate–concrete interfacial bond strength of FRP and metallic plated concrete specimens

Abstract: Bonding of steel or fibre reinforced polymer (FRP) plates by adhesive to the surface of concrete structural elements have become increasingly popular for improving their strength and stiffness. However, these plates are susceptible to debonding prematurely before reaching the designed strength. Therefore, a thorough knowledge of bond behaviour of concrete–adhesive–plate interface is a prerequisite to develop guidelines to avoid failure through the different possible modes. The paper presents thirty six (36) test results for single shear tests conducted on concrete prisms bonded with variety of FRP and metallic plates to evaluate the bond strength and the critical bond length required to sustain the maximum stress on bond for a given plate–concrete interface. The elastic modulus and ultimate tensile strength of the plates of different materials vary between 32–300 GPa and 196–2800 MPa respectively. The design guidelines developed in this study are capable of predicting the critical bond length and ultimate bond strength of any type of plate–concrete interface with good accuracy. The predictability of the ultimate bond strength model is validated using numerous test results taken from the published literature.

Design of optical waveguide polarizer using photonic band gap.

Abstract: A new design of optical waveguide polarizer based on photonic band gap has been presented. A numerical approach based on the finite difference time domain method has been used to analyze and design photonic band gap polarizer. The performance of the device is investigated in terms of degree of polarization and transmittance. Polarizer action is achieved by engineering the defect modes in photonic band gap structures.

Engineering life through Synthetic Biology.

Abstract: Synthetic Biology is a field involving synthesis of novel biological systems which are not generally found in nature. It has brought a new paradigm in science as it has enabled scientists to create life from the scratch, hence helping better understand the principles of biology. The viability of living organisms that use unnatural molecules is also being explored. Unconventional projects such as DNA playing tic-tac-toe, bacterial photographic film, etc. are taking biology to its extremes. The field holds a promise for mass production of cheap drugs and programming bacteria to seek-and-destroy tumors in the body. However, the complexity of biological systems make the field a challenging one. In addition to this, there are other major technical and ethical challenges which need to be addressed before the field realizes its true potential.

Structural and electrical studies in La-substituted SrBi2Nb2O9 ferroelectric ceramics

Abstract: In this paper, structural and electrical studies of A-site lanthanum-substituted Sr1−xLaxBi2Nb2O9; x = 0.0 – 0.5 ceramics are reported. The introduction of lanthanum produces pore-free microstructure upto x = 0.3 . A diffuse ferroelectric to paraelectric phase transition is observed in the doped samples and positive temperature coefficient of resistance (PTCR) is observed in x = 0.0 , 0.4 and 0.5 samples whereas x = 0.1 – 0.3 samples show negative temperature coefficient of resistance (NTCR). Curie temperature decreases continuously with increase in lanthanum content.

A new mixed mode biquad using reduced number of active and passive elements

Abstract: The configuration that can work in mixed mode may be useful from IC realization viewpoint and application adaptability. This paper proposes a generalized mixed mode universal filter configuration that may be used in all possible modes i.e. voltage mode, current mode, trans-impedance mode and trans-admittance mode. The architecture uses minimum number of active and passive components reported till date and can realize all generic filter functions: low pass, band pass, high pass, notch and all pass. PSPICE simulation results agree well with experimental values.

Photonic band gap engineering in 2D photonic crystals

Abstract: The polarization-dependent photonic band gaps (TM and TE polarizations) in two-dimensional photonic crystals with square lattices composed of air holes in dielectric and vice versa i.e., dielectric rods in air, using the plane-wave expansion method are investigated. We then study, how the photonic band gap size is affected by the changing ellipticity of the constituent air holes/dielectric rods. It is observed that the size of the photonic band gap changes with changing ellipticity of the constituent air holes/dielectric rods. Further, it is reported, how the photonic band gap size is affected by the change in the orientation of the constituent elliptical air holes/dielectric rods in 2D photonic crystals.

A Steady State Analysis on Voltage and Frequency Control of Self-Excited Induction Generator in Micro-Hydro System

Abstract: This paper presents a steady state analysis of self-excited induction generator (SEIG) operating with an electronic load controller (ELC) for regulating its voltage and frequency under varying load condition The ELC consists of a rectifier and a chopper circuit whose operation generates harmonics on AC side of the SEIG system To achieve an adequate performance characteristics of the SEIG with ELC information of harmonic contents and real power is necessary In this paper a complete description of the AC current harmonics generated in the ELC operation and their effects on the performance of SEIG is presented in detail

Early Universe with Variable Gravitational and Cosmological Constants

Abstract: Einstein field equations are considered in zero-curvature Robertson–Walker (R–W) cosmology with perfect fluid source and time-dependent gravitational and cosmological “constants.” Exact solutions of the field equations are obtained by using the ’gamma-law' equation of state p = (γ − 1)ρ in which γ varies continuously with cosmological time. The functional form of γ (R) is used to analyze a wide range of cosmological solutions at early universe for two phases in cosmic history: inflationary phase and Radiation-dominated phase. The corresponding physical interpretations of the cosmological solutions are also discussed.

Computation of resonant frequency of annular-ring-loaded circular patch using cavity model analysis

Abstract: In this paper, the annular-ring-loaded (ARL) circular patch is revisited By applying suitable boundary conditions at the interfaces, the problem is solved The structure is considered as a disk with a ring slot etched in-between The narrow slot divides the entire region into two parts The slot is modeled as a π-type admittance network Using circuit theory, the modal-current discontinuity is deduced and a transcendental relation giving the resonant frequency for nth mode is obtained It is shown that the dominant-mode resonant frequency depends on where the probe is located inside the circle or the annular ring The theoretical predictions are compared with the results obtained using IE3D, a commercial method of moments (MoM)-based solver Comparison is also made with the published results as well as the experimental results and agreement of better than 2% to 3% is obtained The analytical tool presented is simple in approach and computationally fast © 2006 Wiley Periodicals, Inc Microwave Opt Technol Lett 48: 622–626, 2006; Published online in Wiley InterScience (wwwintersciencewileycom) DOI 101002/mop21426

Gerschgorin Theorem and its Applications in Control System Problems

Abstract: In this paper, we have presented application of Gerschgorin theorem in relative stability analysis of a system represented by a polynomial. We have also presented the applications of Gerschgorin Theorem in reduced order modeling by identifying time scales and stabilization for linear time invariant systems.

Analysis of flexibility requirements under uncertain environments

Abstract: Purpose – In the complex environment of manufacturing system, it is proper to design a production system which meets the market requirements in the most economical and competitive manner. Flexible manufacturing system (FMS) is one of the options to meet the uncertainty in demand and high variety of products. This paper aims to review the definition, classification, and measurement of manufacturing flexibility concerned with manufacturing flexibility management.Design/methodology/approach – The selection process consists of the synthesis and critical evaluation of the concepts put forward in the extant literature. As a consequence of this process, three primary flexibility dimensions are identified: volume, variety and machine. Simulation approach is used to study the behavior of FMS under different demand scenarios and levels of flexibility.Findings – Four hypotheses are tested in five different flexibility levels. The following conclusions are obtained from the study. For any flexibility level, as the tr...

Phase transition and electrical studies of wolframium doped SrBi2Ta2O9 ferroelectric ceramics

Abstract: In this study, crystalline structure, dielectric and impedance properties of SrBi2Ta2O9 (SBT) - based ferroelectric ceramics have been investigated with the substitution of wolframium/tungsten (W) onto the tantalum site. Wolframium doped SrBi2(W x Ta1 − x )2O9 (0.0 ≤ x ≤ 0.20) ceramics were synthesized by solid state reaction method. The X-ray diffractogram analysis revealed that the substitution formed a single phase layered perovskite structure for the doping content up to x ≤ 0.05. The dielectric measurements as a function of temperature show an increase in Curie temperature (T c ) over the composition range of x = 0.05 to 0.20. The W6 + substitution in perovskite-like units results in a sharp dielectric anomaly at the ferroelectric phase transition. Furthermore, the dielectric constant at their respective Curie temperature increases with wolframium doping. Both enhanced Curie temperatures and dielectric constants at the Curie points indicate an increase in polarizability, which could be attributed to the increased “rattling space” due to the incorporation of the smaller tungsten cations. The dielectric loss reduces significantly with tungsten addition. AC impedance properties vis-a-vis wolframium content has also been studied.

Design of a photonic band gap polarizer

Abstract: We explore the application of photonic band gaps PBGs in photonic crystal structures to propose the design of an ultracompact PBG polarizer. The existence of complete PBGs in certain photonic crystal structures and the variation introduced in the PBGs by the creation of defects has been utilized to design a PBG polarizer at 1.55 m with a degree of polarization equal to 1 leading to the formation of a super polarizer. © 2006 Society of Photo-Optical Instrumentation Engineers. DOI: 10.1117/1.2372461

Damping SSR in a series compensated power system

Abstract: In this paper, a new static VAr system (SVS) control scheme for damping torsional modes due to subsynchronous resonance (SSR) in a series compensated power system has been developed. The proposed scheme, called as the Narendra Kumar-subsynchronous resonance (NK-SSR) damping scheme, utilizes the effectiveness of combined reactive power and frequency (CRPF) SVS auxiliary controller in coordination with an induction machine-damping unit (IMDU) coupled to the T-G shaft. The studies are conducted on the first IEEE benchmark model. The scheme stabilizes all the torsional modes over a wide operating range of power transfer. The digital computer simulation study, using a nonlinear system model exhibits a remarkable improvement in the system transient performance. The optimal location of IMDU along the T-G shaft has been determined by performing eigen value analysis. It is found that locating IMDU after the IP turbine yields the maximum damping effect.

Electricity Industry Restructuring in India

Abstract: The electricity industry in India is going through a major change with the Electricity Act-2003 coming into force on June 10, 2003. The Act is stated to be the "distilled wisdom" of a series of commissioned international and national consultancy studies and seminars and conferences held at the all-India level for three years. This paper is an attempt to study the changes going on in the Indian electricity market, its components, salient features, and the challenges that are poised for future development. A brief overview of some electricity markets in other countries is presented and some comparisons are made with the Indian electricity market.

Rating Reduction of Static Compensator for Voltage Control of Three-Phase Self-Excited Induction Generator

Abstract: This paper describes the use of series capacitor in rating reduction of static compensator (STATCOM) for voltage regulation of three-phase self-excited induction generator (SEIG). A SEIG driven through a constant speed prime mover such as gasoline engine requires an appropriate combination of shunt and series capacitors to improve its voltage regulation under varying load conditions. Inclusion of fixed value of series capacitor provide additional VARs with increasing load to enhance the voltage regulation of the SEIG. However, the SEIG being a weak power supply system with limited kVA experiences large voltage dip with variable output power and fixed excitation in stand-alone applications. The problem of voltage dip arising from varying loads is reduced with use of STATCOM along with fixed excitation. The shunt excitation capacitor needs to supply the reactive power of demand of SEIG to generate rated voltage at no-load. In the present study the transient performance of series capacitor compensated SEIG-STATCOM system has been analyzed through simulation in MATLAB/Simulink environment. The simulation results have revealed that with inclusion of series capacitors along with STATCOM improves the voltage regulation of SEIG under varying loads. Moreover, the use of fixed value of series capacitor has resulted in significant reduction in the rating of STATCOM.

Design and Implementation of a Current Controlled Parallel Hybrid Power Filter

Abstract: This paper deals with the implementation of an indirect current control of parallel hybrid filter system (PHF) with rectifier load to eliminate generated harmonics The compensation principle, design and PHF implementation are discussed in detail The proposed control enhances the performance of the passive filters under unbalance situations existing in the passive filters under fault conditions Moreover, due to limited capacity of VSI a upper limit for such compensation may be imposed by proposed indirect current control based on synchronous reference frame employing decomposition of current in synchronously rotating reference frame (SRF) is used to control PHF The PHF is controlled using decomposition of load and source currents The implementation of the control scheme is carried out on dSpace with digital signal processor (DSP) for developed prototype of PHF Passive filters are developed keeping in view of its operation with PHF, so that, the total harmonic distortion (THD) in the source current gets minimized along with minimized fundamental frequency current sinking through the filter section The design has been carried out by genetic algorithm (GA), which optimizes the solution for multiple constraints Operation of PHF under dynamic change of load is also investigated through simulations under MATLAB and through experimentation

Unified Description of Early Universe with Variable Gravitational and Cosmological "constants"

Abstract: Einstein's field equations with variable gravitational and cosmological "constants" are considered in the presence of perfect fluid for a spatially homogeneous and isotropic universe. Exact solutions of the field equations are obtained by using the "gamma-law" equation of state p=(γ-1)ρ, where the adiabatic parameter γ, varies with cosmic time. The functional form of γ, which is assumed to be the function of scale factor R as proposed by Carvalho, is used to describe the early evolution of universe. A unified description of early universe is given in which an inflationary phase is followed by radiation-dominated phase. The various physical aspects of the models are also discussed.

Unified methodology for realizing fully-differential current-mode filters

Abstract: Using the concept of nullors, an unified methodology is presented which can be used for realizing fully differential current mode filters using a variety of building blocks which can be represented by nullators and norators. The workability of the proposed approach is verified by the SPICE simulation results of an exemplary universal biquad made from multiple-output-current-conveyors. This exemplary filter can realize low pass (LP), high pass (HP), band pass (BP), band elimination (BE) and all pass filters-all in fully differential form, from the same topology. The angular frequency and ω0/Q0 or Q0 of the realized filters are orthogonally controllable. The applicability of the developed approach to derive a variety of biquads as well as higher order FD CM filters (including the electronically-tunable ones), using a number of other building blocks such as FTFNs, Current Conveyors, Controlled Current Conveyors and OTAs, is conceptualized.

A systematic realization of current mode universal biquad filters

Abstract: A family of current mode universal biquads has been proposed. The biquad filters employ multiple output floating nullor (MOFN) configured as multiple output current conveyors (MOCC). The five-MOFN-based biquad has the property of independently tunable gain, bandwidth, and cut-off frequency without having any passive component matching constraint. Although the four/three MOFN-based universal biquads offer limited tunability of different parameters they do not have any parameter matching constraint on them and in addition, they offer the advantage of reduction in the number of MOFNs and resistances. The workability of all the proposed circuits has been verified using PSPICE simulations based CMOS MOFNs implemented in 0.35 µ CMOS technology.

Construction of Graceful Signed Graphs

Abstract: In this paper, the mathematical problem of automation of encoding a communication/ transportation network is considered for enabling design of appropriate plans for ground-troop movement on a complex terrain that motivated to discuss a general method of constructing infinite families of graceful signed graphs from a given gracefully numbered signed graph. This method gives graceful numberings for signed graphs on K 2 + K t c , t 1, where G c denotes the complement of the graph G.

Indirect Current Control of Series Hybrid Filter: An Experimental Study

Abstract: Series active filtering has been identified as an appropriate solution for voltage fed type harmonic producing loads. Moreover, the amicable configuration demands employment of a set of shunt connected passive filters so as to suitably compensate harmonics and retain the characteristics of multiple diverse connected loads. This paper presents experimental study of series hybrid filter system (SHF) to eliminate harmonics generated by nonlinear load and meeting the variable limited reactive power requirements corresponding to available rating of the voltage source inverter (VSI) employed as active filter (AF). The SHF is desired to operate in a way not to compensate negative sequence component, therefore, the indirect current control based on synchronous reference frame decomposition of current has been employed and discussed in details. The implementation of the control has been done on digital signal processor (DSP) for developed prototype of AF in SHF. The passive filters set has been developed keeping in view of its operation with SHF. Operation of SHF under dynamic change of load has also been investigated through simulations under MATLAB and through experimentation

Topology Optimization of Dispersion Properties in Optical Fibres

Abstract: In this paper, the possibility of using topology optimization for tailoring the dispersion properties in optical fibres is discussed. A method for finding the sensitivities of the dispersion coefficient is introduced, along with different constraints for confining the light to the centre of the fibre geometry. The modal analysis of the fibre geometries is carried out with a finite-difference approximation to the scalar Helmholtz wave equation. The results, obtained by optimizing the refractive index distribution over the cross section of the fibre, show that it is possible to match the value of the dispersion coefficient at both a single and at multiple wavelengths.

An embedded controller for greenhouse shade curtain

Abstract: A microprocessor based environment control system has been envisaged for greenhouses. Light control has been selected for this study. The controller will not only control the solar radiations but also indirectly, achieve a temperature balance inside the greenhouse. The automatic shading curtain has been designed using off the shelf components, with an 8-bit RISC micro-controller. An 8-bit AVR RISC controller with 1K Byte Flash (ATtiny15L) manufactured by ATMBL. The controller is designed to sense the light intensity and based on set limits it actuates a control motor to operate shade curtain open or close. The shade curtain is coupled mechanically with shade cloth mounting system.

Ergonomics in control centre design for power system

Abstract: The control centre in a SCADA set up is the place from where the operator/system engineer monitors the health of the power system and issues necessary control instructions. The operator/system engineer at the control centre undergoes a variety of muscular stresses while working for long durations, which degrades the quality of work. The proper design of the control center will ensure ease of functioning for the operator without experiencing stress in vital body parts. Care should be taken to install the different equipment for monitoring and controlling the power system in suitable atmosphere and housing. Hence, the authors in this paper have given emphasis on the various aspects of the ergonomics in designing the control room and housing rooms in the control centre for the power system.