Search

The present study deals with the non-catalytic and catalytic wet oxidation (CWO) for the removal of persistent organic compounds from the pulping effluent. Two activated carbon-supported heterogeneous catalysts (Cu/Ce/AC and Cu/Mn/AC) were used for CWO after characterization by the following techniques: temperature-programmed reduction, Fourier transform infrared spectroscopy and thermo-gravimetric analysis. The oxidation reaction was performed in a batch high-pressure reactor (capacity = 0.7 L) at moderate oxidation conditions (temperature = 190°C and oxygen pressure = 0.9 MPa). With Cu/Ce/AC catalyst, the maximum chemical oxygen demand (COD), total organic carbon (TOC) and lignin removals of 79%, 77% and 88% were achieved compared to only 50% removal during the non-catalytic process. The 5-day biochemical oxygen demand (BOD5) to COD ratio (a measure for biodegradability) of the pulping effluent was improved to 0.52 from an initial value of 0.16. The mass balance calculations for solid recovered after CWO reaction showed 8% and 10% deduction in catalyst mass primarily attributed to the loss of carbon and metal leaching. After the CWO process, carbon deposition was also observed on the recovered catalyst which was responsible for around 3–4% TOC reduction.

Organo-modified nanoclay has got considerable attention in recent years to improve the performance of asphalt binders. However, various aspects such as rutting performance using Multiple Stress Creep Recovery (MSCR) test, fatigue performance using Linear Amplitude Sweep (LAS) test and ageing resistivity potential using advanced rheological parameter are still unexplored for better rheological characterisation. The present study deals with rutting, ageing resistivity potential and fatigue performance of asphalt binder (AC-10) modified with organo-modified nanoclay (CL-30B). Different percentages (0, 2, 4 and 6% by weight of binder) of CL-30B were mixed with AC-10 using a high-shear mixer. Different rheological studies, such as Brookfield viscosity, Superpave performance grading, time-temperature sweep, MSCR and LAS tests, were conducted on CL-30B-modified asphalt binders. Effects of CL-30B on performance were observed to be predominant in intermediate to high-temperature range as obtained from the master curve. The ageing resistivity of asphalt binder increased with the addition of CL-30B. The Superpave rutting parameter (G*/Sin delta) increased and non-recoverable creep compliance (J(nr)) estimated from MSCR decreased with inclusion of CL-30B, indicating a better rutting performance of asphalt binders. The number of cycles to fatigue estimated from the LAS test showed improvement in fatigue performance of asphalt binder with addition of CL-30B. The high-temperature performance grade of CL-30B-modified binder was found to be higher compared to virgin binder. The relationship between J(nr) and G*/Sin delta, and recovery (R) and storage modulus (G') parameters are presented in this paper. In addition, ranking of asphalt binder based on various parameters (i.e. G*/Sin delta, AI, J(nr), R, N-f) is discussed in this paper.

This paper considers a low-level unit-load warehouse employing single-deep storage lanes and a single-command manual storage and retrieval policy. Analytical travel distance models are developed for class-based and full turnover storage policies under across-aisle, within-aisle and a newly proposed hybrid product placement schemes. Our computational studies show that the analytical models developed in this paper are very accurate as compared to simulation results and a comparative study with a real-world warehouse case. Hybrid storage policies proposed in this paper outperform all other traditional storage policies. The paper also presents insights and simple design rules to warehouse practitioners.

The paper presents a fast and efficient method for the detection and characterisation of delamination in photovoltaic (PV) modules by using active infrared thermography approach. A discrete part of PV module was irradiated by step heating and its thermal image sequence was used to detect and analyse delamination. Different types of heating source for thermal excitation for this application have been studied. An electro-thermal model was developed to simulate the active thermography approach for the characterisation of delamination in PV module by equivalent resistance-capacitance (RC) network using a circuit simulator. This simulation approach was used to estimate the extent of delamination in the module and to determine the optimum parameters for the characterisation of delamination. Different applications based on front and backsides of heating the module were also proposed in this paper. The proposed method has the potential to be employed for the quality check of PV modules during inline production as well as for the predictive maintenance of outdoor PV plants.

This paper reports a new design of microstrip directional coupler with high directivity. This directional coupler uses corrugated coupled lines and floating conductor in the ground plane of microstrip to enhance coupling. Based on this structure, directional coupler having 4.4% bandwidth has been designed at 4500 MHz with 10 dB coupling and 35 dB directivity. The designed directional coupler has been fabricated and tested for the validity of the design. Measured results are presented in this paper.

New frequency-domain 2-stability criteria are derived for nonlinear discrete-time MIMO systems, having a linear time-invariant block with the transfer function (z), in negative feedback with an aperiodic matrix gain A(k), k = 0, 1, 2,..., and a linear combination of a vector of certain classes of (generalised) first-and-third-quadrant non-monotone nonlinearities.(center dot), having arguments with constant and time-varying delays, but without restrictions on their slopes. The framework does not employ Lyapunov-Krasovskii functionals involving linear matrix inequalities (LMIs) or their equivalent. The new stability criteria seem to be the most general for nonlinear and time variying time-delay systems, and have the following structure: (1) positive definiteness of the real part (as evaluated on | z| = 1) of the product of (z) and an algebraic sum of general causal and anticausal matrix multiplier functions of z. (2) An upper bound on the L1-norm of the inverse Fourier transform of the multiplier function, the L1-norm being weighted by certain novel, quantitative characteristic parameters (CPs) of the nonlinearities.(center dot) without the asumptions of monotonicity, slope restrictions and the like. And (3) constraints on certain global averages of the generalised eigenvalues of (A(k + 1), A(k)), k = 1, 2,..., that are expressed in terms of (i) CPs of the nonlinearities, (ii) their coefficients, and, in general, (iii) time-delays in their arguments, a trade-off among all the three being possible. These global averages imply a restriction on the rate of variation of A(k) in a new sense. The literature results turn out to be special cases of the results of the present paper. Examples illustrate the stability theorems.

Prediction of cargo volumes is important for authorities such as port administrations and port operators, as cargo throughput affects port planning and operation. The forecasting results help planners and policy-makers to take decisions on issues such as port investment, port development, berth location selection, port operation, and freight rate. The success of the port operation policy depends on the accuracy of the cargo forecast. This paper presents an improved model known as dynamic regression (DR) model to forecast cargo demand simultaneously for ports within a port system; the model is applied to forecast cargo demand at major seaports in India. Past cargo flow data from years 1980-1981 to 2013-2014 at 11 major ports in India are used for estimating the proposed model. Average prediction error is found to be within 10% for most of the ports. The DR model is used to produce forecasts up to 2019-2020 for all the ports studied. The model forecast is compared with the projections of the Ministry of Shipping, Government of India. This study is intended to provide guidance to planners in taking decisions on issues related to port infrastructure development, such as construction of new terminals and improvement of access roads to ports for the major ports in India. The study will also be beneficial to shipping agencies for their investment strategies in the Indian ports sector.

Have you ever questioned why do we almost always use vector calculus and differential equations in electromagnetics? Are these the only tools at our disposal for studying and modelling electromagnetic problems? Well, the answer is no and this paper is about an alternative approach to model electromagnetic problems using algebraic topology. This approach has a few advantages compared to the familiar differential formulation-based methods in modelling electromagnetic and multiphysics problems. In differential formulation we need one of the several numerical methods like finite difference, finite element, method of moments and spectral methods to obtain approximate solution to the electromagnetic problem. In contrast, algebraic topology-based method leads directly to discrete formulation using global quantities. Furthermore, in the case of electromagnetics, all underlying global quantities are scalars. Hence, there is no need for vector calculus. In addition, we also avoid interpolating local vector field quantities as required in several numerical methods. Though algebraic topology offers powerful and elegant tools for solving various engineering problems, many applied physicists and engineers are not familiar with this subject. This is partly due to the fact that most publications on this topic burden us with complicated mathematical analysis filled with convoluted jargons. If one can introduce the key ideas of algebraic topology using familiar concepts, computational and applied physics, and engineering community can appreciate and benefit from its advantages over methods based on differential formulation. With this goal, we present the main ideas of algebraic topology applied to electromagnetics problems.

Delamination significantly affects the performance and reliability of photovoltaic (PV) modules. Recently, an active infrared thermography approach using step heating has been exploited for the detection and characterisation of delamination in PV modules. However, step heating takes longer observation time and causes overheating problems. This paper presents the effects of different thermal excitation waveforms namely rectangular, half-sine and short pulse, on the detection and characterisation of delamination in PV module by experiments and simulations. For simulation, a 3-dimensional electro-thermal model of heat conduction, based on resistance-capacitance network approach, has been exploited to study the variation in maximum thermal contrast and peak contrast time with the delamination thickness and heating parameters. Results show that the rectangular waveform provides better detection of delamination due to higher absolute contrast, while the half-sine waveform allows better characterisation of delamination in the PV modules with low-cost and low-power heat source. The high-energy short pulse enabled quick visualisation of delamination, but has limited practical implementation. The advantages and limitations of each waveform have been highlighted to assess the specific requirement for appropriate choice in the non-destructive thermographic inspection of delamination in PV modules at the manufacturing units or outdoor fields.

Information on existing landuse pattern and its spatial distribution is a pre-requisite for any watershed management programme. With the advent of remote sensing tools, with their inherent characteristics, it has been possible to prepare this dynamic resource map at various levels of confidence. But the application of multi-spectral classification techniques in vegetation discrimination has been the subject of discussion for many years. The paper describes a methodology developed to compile agricultural landuse map of a hilly watershed (where the rainfall erosivity is an ever-present threat) using geographical information systems (GIS). Multi-seasonal (monsoon-Kharif and post-monsoon-Rabi) and multi-sensor remotely-sensed data were used for mapping a landuse pattern of the watershed. The rasterised classified images, and the relevant watershed resources, were input and stored as separate layers in the GIS and then geometrically co-registered to a regular 30m grid. Knowledge-based rules were developed from the informed opinion of multi-disciplinary experts and field checkings, in addition to the knowledge of local landuse patterns. These expert rules were used to manipulate the information databases to discriminate various spectrally inseparable information classes, finding out the landuse/cover categories of the Kharif season under the cloud and its shadow areas. Finally, the improved and the agricultural landuse pattern map was classified into thick forest, sparse forest, degraded pastures, open (with/without scrub) areas, cropped (Kharif + Rabi) and fallow (Kharif + Rabi) lands. The areal extent of improved/final landuse map classes compared favourably with the natural conditions of the agro-climatic region of the watershed. The paper also envisages some future studies for watershed management policies.

Three phase 3-leg inverters are the most common interfaces for forming distributed generation and microgrids. However, in low voltage systems, loads are often 3-phase, 4-wire with frequent unbalances. The question of unbalanced loads on stand-alone microgrids can be handled in two ways. First, unbalanced load compensators can be provided near each unbalanced load. Second, unbalanced loads can be fed by 4-leg inverter interfaces with a 4-wire microgrid. This paper is concerned with the second approach. The design of closed-loop system for 4-leg inverter interface for microgrid with unbalanced loads is carried out. Detailed analysis of power flow dynamics and stability for a 3-phase, 4-wire microgrid with 4-leg inverters catering to unbalanced loads is reported. The analysis is supported by simulations and laboratory experiments. The proposed microgrid shows stable operation and maintains balanced voltages at unbalanced load terminals without any load compensators.

In the analysis of soil loss equation, the researchers have suggested two methods of deriving the slope steepness parameter. One method is having percentage slope term, while the other method is having sinθ as its term. In this paper, both the methods were analysed and compared in soil loss computation using Revised Universal Soil Loss Equation, over a Gangapur catchment area in India, having steep slopes. The soil loss rates derived were 0.98 million tonnes per year in case of steepness parameter derived by sinθ and 1.226 million tonnes per year in case of steepness parameter derived by percentage slope term. The observed rate of soil loss is 1.23 million tonnes per year. This methodology of soil loss estimation was also validated with similar catchment of Punegaon dam. It is concluded that for medium to steep terrain, percentage slope method estimates more accurate soil loss than other empirical methods for slope steepness estimation.

In wireless communications, a fading multiple-access channel (MAC) is typically used to model the uplink communication. Conventional MACs assume a centralized system, where the transmission rate and power are chosen centrally for every fading vector realization. On the other hand, there is considerable interest in the performance of distributed multiple access systems, where the lack of global channel state information (CSI) demands novel communication strategies. We consider a block-fading MAC where each transmitter is aware only of its own link CSI, which we term as the individual CSI MAC. The receiver has access to the full CSI of all links. This model was recently introduced in the information theory literature, and naturally leads to a distributed access system with several applications. An important utility of interest for this model is known as the power-controlled adaptive sum-capacity, whose evaluation is an open problem. This is the main subject of the current paper. We present the power-controlled adaptive sum-capacity of a wide class of popular fading MAC models. In particular, we characterize the sum-capacity when the statistics of the channel are identical across users. The proposed schemes also allow a low-complexity successive-cancellation decoding using rate-splitting. Furthermore, the optimal schemes are extended to situations in which each transmitter has additional finite-rate partial CSI on the link quality of others.

In this paper, the method to design the reduced-order switching function for an uncertain linear system in special coordinate basis (SCB) form is proposed. The sliding mode control with this method guarantees the asymptotic stability of all the states of system in presence of matched disturbance. The proposed design method is applicable to the system with unstable internal dynamics as well. This method enables the option of designing the control law with reduced-order states that are involved in the design of switching function. Also, a high performance sliding mode step-tracking control for non-minimum phase systems using reduced-order nonlinear switching function is proposed. The method is also extended to multiple-input and multiple-output (MIMO) systems. An effectiveness of sliding mode control with reduced-order switching function is shown through numerical examples.

In this paper, we have proposed a new decomposition technique for compact polarimetric (CP) synthetic aperture radar (SAR) data. In the proposed decomposition, the odd and the even bounce scattering powers P-S and P-D are, respectively, obtained by combining the powers received in the opposite-sense circular (OC) polarization and the same-sense circular (SC) polarization transmitted with the polarized power fraction (Omega). The volume scattering power P-V is obtained by combining the total power with the unpolarized power fraction (1 - Omega). The parameter Omega is a function of both the transmitting and the receiving ellipticities (chi(t), chi(r)) and orientations (psi(t)psi(r)). These parameters thus provide a wider degree of freedom to accommodate a range of scattering mechanisms which are not reflected in the existing approaches. The proposed method is applied on simulated CP-SAR data obtained from full-polarimetric E-SAR (Experimental Synthetic Aperture Radar) and AIRSAR (Airborne Synthetic Aperture Radar) L-band data sets. The proposed decomposition shows appreciable improvements in the scattering powers compared to the m - delta and the m - chi decompositions.

In this paper, we show how to incorporate cubic and hexagonal anisotropies in interfacial energies in phase field models; this incorporation is achieved by including upto sixth rank tensor terms in the free energy expansion, assuming that the free energy is only a function of coarse grained composition, its gradient, curvature and aberration. We derive the number of non-zero and independent components of these tensors. Further, by demanding that the resultant interfacial energy is positive definite for inclusion of each of the tensor terms individually, we identify the constraints imposed on the independent components of these tensors. The existing results in the invariant group theory literature can be used to simplify the process of construction of some (but not all) of the higher order tensors. Finally, we derive the relevant phase field evolution equations., Comment: About 14 pages; 2 figures, to be submitted for review

In this paper, a variant of nonlinear Galerkin method is proposed and analysed for equations of motions arising in a Kelvin-Voigt model of viscoelastic fluids in a bounded spatial domain in IRd (d = 2, 3). Some new a priori bounds are obtained for the exact solution when the forcing function is independent of time or belongs to L-infinity in time. As a consequence, existence of a global attractor is shown. For the spectral Galerkin scheme, existence of a unique discrete solution to the semidiscrete scheme is proved and again existence of a discrete global attractor is established. Further, optimal error estimate in L-infinity(L-2) and L-infinity(H-0(1))-norms are proved. Finally, a modified nonlinear Galerkin method is developed and optimal error bounds are derived. It is, further, shown that error estimates for both schemes are valid uniformly in time under uniqueness condition.

This paper considers a class of deploy and search strategies for multi-robot systems and evaluates their performance. The application framework used is a system of autonomous mobile robots equipped with required sensors and communication equipment deployed in a search space to gather information. The lack of information about the search space is modeled as an uncertainty density distribution over the search space. A {\em combined deploy and search} (CDS) strategy has been formulated as a modification to {\em sequential deploy and search} (SDS) strategy presented in our previous work. The optimal deployment strategy using Voronoi partition forms the basis for these two search strategies. The strategies are analyzed in presence of constraints on robot speed and limit on sensor range for convergence of trajectories with corresponding control laws responsible for the motion of robots. SDS and CDS strategies are compared with standard greedy and random search strategies on the basis of time taken to achieve reduction in the uncertainty density below a desired level. The simulation experiments reveal several important issues related to the dependence of the relative performances of the strategies on parameters such as number of robots, speed of robots, and their sensor range limits., 41 pages

To achieve cost effectiveness and reliability in design, this paper presents a probabilistic multi-objective model for optimal design of composite channels that have a cross-sectional shape of horizontal bottom and parabolic sides. The multiple objectives of channel design include minimizing the cost of channel construction, maximizing the probability of the expected channel capacity being greater than the design flow and minimizing the overtopping probability. In this study, the principles of first-order uncertainty analysis are adopted for handling uncertainty in parameters of the problem. The optimization model is solved using the particle swarm optimization method and Pareto-optimal solutions are generated for various combinations of overtopping probability and exceedance probability of channel capacity. The results show that the presented approach has good potential for exploring different alternative designs of open channels under input parameter uncertainty.

The planning problem in the context of a multi-site procurement-production-distribution system (MSPPDS) considered in this paper is motivated from a real life case of a multinational consumer goods company. A robust optimisation model considering model robustness and solution robustness in the objective function is developed for integrated planning in three dimensions. Detailed production, procurement and distribution plans are integrated; countrywide aggregate production plan is integrated with a detailed plan. Similarly the detailed production plans from the previous planning cycle are integrated with current production plans. Constraints on storage space, production capacity and the time lag between procurement, production and distribution activities are captured in the model. Procurement and production plans are treated as 'here-and-now' decisions and the distribution plans are treated as 'wait-and-see' decisions to be implemented based on the realised demand scenario. The model is illustrated using an example problem and also successfully applied to the data of a consumer goods company involving 104,000 variables (with 832 integer variables) and 21,000 constraints.

The analytical solution for vorticity, tangential velocity, circulation and pressure inside vortex cores in turbulent flows is presented in this paper. The analysis suggests a linear decrease in vorticity and polynomial variation for other quantities with distance from the vortex centre. The obtained solution is verified against experimental data in the literature.

Significant savings in cost and time can be achieved in rapid prototyping (RP) by manufacturing multiple parts in a single setup to achieve efficient machine volume utilization. This paper reports the design and implementation of a system for the optimal layout planning of 3D parts for a RP process. A genetic algorithm (GA) based search strategy has been used to arrive at a good packing layout for a chosen set of parts and RP process. A two stage approach has been proposed to initially short-list acceptable orientations for each part followed by the search for a layout plan which optimizes in terms of final product quality and build time. The GA uses a hybrid objective function comprising of the weighted measures like part build height, staircase effect, volume and area-of-contact of support structures. In essence it captures the key metrics of efficiency and goodness of packing for RP. The final layout plan is produced in the form of a composite part CAD model which can be directly exported to a RP machine for manufacturing. Design methodology of the system has been presented with some representative case studies.

Rapid tooling (RT) processes driven by rapid prototyping (such as stereolithography and selective laser sintering) can reduce mold development lead-time by 50% or more, though there are certain limitations in terms of mold materials, accuracy, and surface finish. This paper presents a systematic approach for manufacturability analysis of molds produced by rapid tooling methods, based on three aspects: mold feature manufacturability, secondary elements compatibility, and cost effectiveness. The geometric features of functional elements of the mold (core, cavity, side core, etc.) are evaluated for manufacturability using fuzzy-analytic hierarchy process (Fuzzy-AHP) methodology. The secondary elements of mold (parting surface, ejectors, cooling lines, etc.) are checked for compatibility with RT mold properties (machinability, wear resistance, and surface evenness). Finally, the cost of RT mold is estimated using a semi-empirical model based on cost drivers and cost modifiers, and compared with that of a conventional mold. The methodology has been demonstrated with an experimental mold. It is useful not only for RT mold process selection, but also for identifying minor modifications to a mold design to improve its manufacturability and economy.

A monolithic mixed integer linear goal programming (MILGP) model that is developed in this paper produces a time and capacity aggregated production plan, a detailed production plan, a detailed procurement plan and a detailed distribution plan simultaneously to overcome the drawbacks of the hierarchical/sequential planning approaches of not yielding a feasible and/or an optimal plan. The model uses different time-grids and planning horizons for aggregate and detailed planning to reduce the computational burden. The limitations of storage space, raw material availability and production capacity at plants and a requirement of maintaining a minimum level of inventory buffer or forward cover have been modelled. Two heuristics that are proposed to solve the MILGP model gave good quality solutions with an average and the worse case optimality gap of 1.17% and 4.4% respectively when applied to one hundred randomly generated industry size problem instances.

Chapter 7 of the Pearce Report (2003) elaborates succinctly on the role that technical progress should fulfil within a construction sector committed to the sustainable generation of social and economic value. Caught between technological macro-analysis and policy-steering objectives, and possibly overwhelmed by the difficulty of treating the subject within the limited scope of the report and time available, the chapter offers a few aggregate industrial data and some commendable, albeit generic, recommendations about innovation. Yet, as part of work conceived under the aegis of a strategic and development initiative, the chapter underplays the opportunity of highlighting two issues that have and should condition the policy debate on construction innovation in the future. The first issue is concerned with the project-based nature of the sector and its consequent ability to spur or thwart change. The second involves the definition or indication of practical institutional strategies that can trigger the changes foreseen or promoted within such a context. Based on this critique, a rationale is developed in the present paper for the strategic creation of technical progress by drawing attention to two specific elements: (1) the cost–benefit equation in the generation of new knowledge, and (2) the possible qualitative distribution of research investment opportunities in the industry. It is shown that although construction-related innovation and project-based innovation are naturally connected, a critical difference exists between the two. For the latter to develop and have an impact on the industry, both political support and wilful patronage are required. Le chaptire 7 du Rapport Pearce (2003) explique succinctement le rôle que le progrès technique devrait jouer au sein d'un secteur du bâtiment qui s'est engagé à générer de manière durable de la valeur sociale et économique. Pris entre une macroanalyse technologique et les objectifs de conduite de la politique, et peut-être submergé par la difficulté qu'il y a à traiter ce sujet dans le cadre limité du rapport et du temps disponible, ce chapitre propose quelques données industrielles agrégées et certaines recommandations louables, quoique génériques, concernant l'innovation. Cependant, dans le cadre de travaux conçus sous l'égide d'une initiative stratégique de développement, ce chapitre minimise la possibilité de mettre l'accent sur deux problèmes qui conditionnent et doivent conditionner les débats sur la politique en matière d'innovation future dans le bâtiment. Le premier problème porte sur la nature du secteur, basée sur les projets, et sur la capacité qui en résulte à encourager ou contrecarrer le changement. Le second problème implique la définition ou l'indication de stratégies institutionnelles pratiques pouvant déclencher les changements qui sont prévus ou favorisés dans un tel contexte. En se basant sur cette critique, des arguments sont développés dans le présent article en faveur de la création stratégique de progrès techniques en attirant l'attention sur deux éléments spécifiques: (1) l'équation coût–bénéfice dans la création de connaissances nouvelles, et (2) la possible répartition qualitative des possibilités d'investissement de recherche dans cette industrie. Il est montré que, bien que les innovations se rapportant à la construction et les innovations basées sur les projets soient naturellement liées, une différence cruciale existe entre les deux. Pour que les innovations basées sur les projets puissent se développer et avoir un impact sur cette industrie, il est nécessaire qu'il y ait à la fois un soutien politique et une volonté de parrainage.

Repeat-pass synthetic aperture radar interferometry (InSAR) appears to be an excellent tool for generating digital elevation models (DEMs) of high spatial and vertical resolution. However, in recent years, it has been noticed that the atmosphere causes errors in the elevation accuracy. The objective of this paper is to try to identify climatic regions in India where InSAR can be used for generating DEMs. A detailed study was carried out to quantify atmospheric effects on the DEMs derived from repeat-pass InSAR. Three test sites were selected for the analysis: one over Mumbai, which is a part of the western ghats region with hilly terrain, lakes and forests; another is the Kolar area with gently undulating terrain with agricultural and forested lands; and the last was Bhuj, an arid plains region which is close to the Rajasthan Thar desert, India. Six interferograms of the Bhuj area derived from two tandem pairs were analysed and it was found that there were varying atmospheric effects of the order of 0.2 lambda to 1 lambda and at specific locations more than l. In the case of the Mumbai and Kolar study areas with two interferograms each, the atmospheric effects were almost negligible. In these cases, it is shown that it was also possible to estimate the height of buildings to an accuracy of 1-2 m. Therefore, it is concluded that one should be cautious when using InSAR techniques for generating DEMs of desert/ arid regions where the climate may be very dynamic and only small amounts of water vapour can cause strong atmospheric artefacts.

Power-system stabilizers (PSSs) are added to excitation systems to enhance the damping during low-frequency oscillations. In this paper, the design of robust decentralized PSS for four machines with a 10-bus system using fast-output sampling feedback is proposed. The nonlinear model of a multimachine system is linearized at different operating points, and 16 linear state space models are obtained. For all of these plants, a common stabilizing state feedback gain, F, is obtained. A robust decentralized fast-output sampling feedback gain which realizes this state feedback gain is obtained using LMI approach. This method does not require all the states of the system for feedback and is easily implementable. This robust decentralized fast-output sampling control is applied to a nonlinear plant model of several machines at different operating ( equilibrium) points. This method yields encouraging results for the design of power-system stabilizers.

This paper presents the controllability properties of an underactuated 3R manipulator and the application of a discontinuous point-to-point control law for a three-degree-of-freedom (DOF) PPR manipulator. In the first half we present a controllability analysis at various actuator configurations of the manipulator. A novel contribution is that we use a single co-ordinate system to analyse the controllability at all the three possible configurations. In the second half we present a discontinuous feedback control law for point-to-point control of a 3 DOF PPR underactuated manipulator moving in a horizontal plane. Simulation results are presented that demonstrate the effectiveness of the controller.

Rare earth doped fluorides have been used in laser applications. Not much is known about the effect of ionizing radiation on the lasing and other properties of fluorides. Therefore, in recent years much attention has been paid to the study of radiation-induced defects in laser materials, as they affect the optical and stimulated emission properties. The defect formation by gamma-ray irradiation in Pr3+ activated LiYF4, powder prepared by melt method, have been studied by thermoluminescence and electron spin resonance techniques and are reported in this paper. It is shown that LiYF4:Pr3+ is sensitive to gamma-ray radiation. Characterization of this laser material using ESR and photoluminescence techniques is also described.

The paper presents a new algorithm for a variable structure model following controller (VSMFC) design for discrete time systems using a fast output sampling technique. The reaching law approach is used to guarantee the sliding mode motion. This methodology is easy to implement since the method is based on output feedback. It is shown that the proposed fast output sampling variable structure model following controller (FOS VSMFC) gives the same results as obtained by state feedback VSMFC. To demonstrate the design technique a VSMFC is designed for the tip position control of a single flexible link. The simulation results show the effectiveness of the proposed method.

Today, feature-based design has become a core technology for solid product modelling primarily because it can capture the designer's intent and provide the capability to satisfy the informational needs of the down-line application tasks for CAD/CAM integration. This paper reports the development of an intelligent environment, IFPP (Intelligent Feature-based Process Planning), for the feature-based design synthesis and process planning of prismatic parts to be produced on CNC machining centres. IFPP consists of two functional modules, namely Feature Based Modeller (FBM) and Automatic process Planner (AutoPlan). The FBM provides a graphical environment for the feature-based synthesis, validation and representation of the solid model of the part to be produced. AutoPlan maps this feature information to the corresponding machining processes to generate the operation plan and corresponding CNC code. This CNC code is unique in that it is functionally encapsulated with the feature data to provide a 'Variant' strategy utilizing the special parametric programming facilities provided on the controller. IFPP thus demonstrates an integrated part-process environment that enables quick turnaround from design to manufacture.

In this paper, the hyperspherical direction cosine transformation process of remotely-sensed data is explained. In particular, this transformation process is utilized to examine various land use and land cover classes in the Bombay suburban and Thana district area in India. A statistical approach to determine the transformed components and other statistical variables on different band combinations is discussed. The results are analysed, and the best possible combinations selected for accurate classification are presented. Separation of topographically induced illumination effects and spectral information (cover type) in digital scanner data can be accomplished by projecting measurement vectors on to a hypersphere.

In this paper, the rotational transformation process is explained as a problem of rotation of remotely sensed data in the variance-covariance space. In particular, the rotation which maximizes the covariance-variance ratio is examined in detail for various land use and land cover classes in the Bombay suburban and Thana district area in India. A statistical approach to determine transformed components and other statistical variables on different band combinations is discussed. The results are analysed, and the best possible combinations selected for accurate classification are presented.

This paper reports a system for automatic extraction of manufacturable features from 'engineering drawings' created in CADD format. It employs the techniques of string based pattern recognition and natural language processing. Drawing entities are processed to derive feature string patterns, which are syntactically analyzed to detect the feature topology and geometry. The information of the features so detected is augmented by non-geometric data like dimensions, position, tolerances and the relevant drawing callouts. The system is capable of detecting generic classes of features like holes, pockets, steps, slots, bosses, etc. The derived information can be easily linked to the downline CAD/CAM activities in the product cycle. The system, thus, demonstrates the feasibility of design automation from CADD models.

In this paper, a hybrid approach, employing both genetic and heuristic algorithms, is proposed for nesting of different rectangular parts in multiple rectangular sheets with the objective of utilizing the sheet material effectively. The proposed genetic approach gives the best sequence of sheets and parts to generate an effective nested pattern with a heuristic algorithm. The heuristic approach arranges each of the parts in the bottom-left-most position of the sheet(s) by considering the sequence of sheets and parts given by the genetic algorithm. The effectiveness of the proposed approach is shown by comparing the results obtained with the present approach to those obtained by Jakobs' approach when all the parts are nested in a single sheet. Finally, the application of the current approach for nesting of rectangular parts in multiple sheets is illustrated.

This paper presents a type of recurrent artificial neural network architecture for identification of an arbitrary, continuous dynamic system. The recurrent network is shown to be stable for a constant input with certain conditions on the parameters of the network. The proposed network has significant advantages over similar models in continuous time nonlinear system identification and is used to identify three nonlinear dynamic systems. Finally, the applicability of the radial basis function networks using the same network architecture to reduce the time-complexity of the training task is presented.

This paper reports the results of an experimental programme to study the effects of process parameters on the surface roughness and out-of-roundness error on components produced by the plunge feed centreless grinding process. Experiments have been planned based on the statistical response surface methodology (RSM) technique. Mathematical models correlating the process parameters to the process responses are obtained. In conclusion, optimal process conditions to minimize the out-of-roundness error and the surface roughness on the components are reported.

This paper reports the design and implementation of a semigenerative computer assisted process planning system (PRICAPP) for prismatic components used in the batch production of prismatic components used in the batch production of portable electric tools. The software incorporates various modules for components representation; automatic machine, tollings and process parameter selection; setup planning; production time calculation and report generation. The user friendly software package has been developed on an IBM compatible PC/XT system. It provides a quick and less costly method of generating consistent process plans.

The first step in any system identification procedure is the collection of data and its preliminary analysis. This step is generally neglected in the literature because in this step the maximum amount of human judgement, experience and decision-making is needed. In this paper Zadeh's fuzzy set theory is used to systematize this preliminary analysis of data. A fuzzy measure termed the ‘degree of difficulty’ (DOD) is derived, which quantifies in a fuzzy manner the difficulty and complexity involved in a system identification problem. The computation of DOD is based on the membership functions developed for nine fuzzy sets defined using nine characterizing properties of systems.

A thin-film effect transistor appears to be the most promising for an all thin-field integrated circuit. In this paper the authors have reported a coplanar device incorporating an evaporated CdSe film and an anodically grown aluminium oxide layer. The fabrication is based on optimized deposition conditions. The d.e. characteristics of the device are presented. For the transistor the device parameters are calculated from the I-T characteristics.

The paper presents a threc-thyristor inverter circuit for generating a three-level output voltage waveform. The operation of the circuit, in dcscribcd. Analysis of the commutation circuit is carried out to evolve optimum values of tho commutntion elements. Trapped energy problems are discussed. Experimental results on a 5 kVA prototype inverter are presented.

The philosophy of transform image coding is to transmit only relatively large magnitude transform coefficients and discard the remainder, The picture received is distorted, due to the presence of various noise sources at different stages of transmission. It is possible to design a non-recursive Wiener filter for the information transmission system from a knowledge of statistics of the image and the noise sources, as well as the interaction between them. In defining models, one should incorporate into them as much a priori knowledge about the system as possible. The success of the design is intimately tied to the accuracy of the models. In this paper the problem of spectral extrapolation, in which the rejected transform coefficients are estimated using statistical and correlation techniques, is solved by using different image models. The extrapolation results of the isotropic image model are much superior compared to the separable first-order Markov process model.

In this paper we present a method of incorporating spin-adapted configurations in a Many-Body Perturbation Theory (MBPT) framework. It has been demonstrated how the use of doubly excited Serber-type spinadapted configurations leads in a straightforward way to a well-defined MBPT series which in effect involves an infinite summation of orbital-diagonal ladders for all possible spin allocations. The formalism implicitly defines a partition of the hamiltonian in which the diagonal matrix elements of the hamiltonian in the Serber-type configurations figure as the unperturbed part. This may thus be called a spin-adapted Epstein-Nesbet (E-N) type of partition. The formalism has been tested on a selection of 6π-electron conjugated systems where we have calculated their orbital pair-correlation energies, and compared the performance against E-N perturbation results and a variational calculation of the same quantities. The comparison reveals that, with canonical Hartree-Fock orbitals, the E-N partition tends to ov...

A very general and numerically quite robust algorithm has been proposed by Sastry and Gauvrit (1980) for system identification. The present paper takes it up and examines its performance on a real test example. The example considered is the lateral dynamics of an aircraft. This is used as a vehicle for demonstrating the performance of various aspects of the algorithm in several possible modes.

This paper proposes a new technique based on eigenvalue assignment for the design of a variable structure load frequency controller for interconnected power systems. An important feature of the variable structure controller is that it can effectively improve the transient performance of the system while at the same time ensuring zero steady-state error. Further, when the variable structure system is operated in the so-called sliding mode, the response of the system becomes insensitive to plant parameter variations. The control problem is formulated and the results of a digital simulation study are presented for illustration. For comparison purposes, results obtained using a conventional integral controller and a linear optimal controller are also included.

In this paper, we study the temperature dependence of the barrier height for amorphous-silicon-Au Schottky barriers between 150 and 400 K for doped and undoped samples. We find that the temperature dependence of the barrier height is similar to that expected for the band gap. This suggests (a) the barrier height is pinned by surface states which are ‘valence band’ like and (b) the temperature dependence of the mobility edge is similar to that of the band gap in these samples.

The paper describes three methods that can be used for controlling the power of resistive loads. One of the methods described here aims at reducing any one unwanted harmonic to a very small value in the case of an a.c./a.c. phase-controlled converter feeding a resistive load. All three methods discussed are compared with the method suggested by Bland (1975) with regard to harmonics, power factor and practical realization of the power circuit. The power circuit and the control circuitry are described. Design criteria for choosing the components in the power circuit are also discussed.

This paper deals with simultaneous elimination of a number M of undesirable harmonics and variation of the output voltage in a pulse-width modulated (PWM) inverter. A general method of pulse-width modulation is suggested where the pulse positions are fixed for the elimination of M harmonics. Voltage control is then obtained by variation of the pulse width symmetricaly around the pulse position. By choosing M chops per quarter cycle, it is possible to eliminate M harmonics from the output. The theoretical results are experimentally verified. The proposed method is compared with the sinusoidal modulation technique and the Patel-Hoft method, and its advantages are discussed.

The paper describes a simple high-Q insensitive active band-pass filter having relatively few passive components and active elements with low closed-loop gains, using positive feedback Q enhancement scheme. The proposed filter has minimum dependence on the bandwidth of the operational amplifiers and is capable of operating over a wide frequency range with relatively stable Q and resonant frequency.

Various attempts have been made for the selective reduction of harmonics in the output of AC/AC converters. However, when some harmonics are reduced other harmonic amplitudes increase. Thus, to reduce the harmful effects of these harmonics on other equipment operating on the same line, it may be necessary to use filters. A suitable type of filter depending on the line inductance for such cases is suggested in this paper. Experimental results are also presented.