Perfectly matched layers for transient elastodynamics of unbounded domains

One approach to the numerical solution of a wave equation on an unbounded domain uses a bounded domain surrounded by an absorbing boundary or layer that absorbs waves propagating outward from the bounded domain. A perfectly matched layer (PML) is an unphysical absorbing layer model for linear wave equations that absorbs, almost perfectly, outgoing waves of all non‐tangential angles‐of‐incidence and of all non‐zero frequencies. In a recent work [Computer Methods in Applied Mechanics and Engineering 2003; 192: 1337–1375], the authors presented, inter alia, time‐harmonic governing equations of PMLs for anti‐plane and for plane‐strain motion of (visco‐) elastic media. This paper presents (a) corresponding time‐domain, displacement‐based governing equations of these PMLs and (b) displacement‐based finite element implementations of these equations, suitable for direct transient analysis. The finite element implementation of the anti‐plane PML is found to be symmetric, whereas that of the plane‐strain PML is not. Numerical results are presented for the anti‐plane motion of a semi‐infinite layer on a rigid base, and for the classical soil–structure interaction problems of a rigid strip‐footing on (i) a half‐plane, (ii) a layer on a half‐plane, and (iii) a layer on a rigid base. These results demonstrate the high accuracy achievable by PML models even with small bounded domains. Copyright © 2004 John Wiley & Sons, Ltd.     

My experiments with thin films—the nanostate of matter

The black art of thin films exhibiting whimsical properties and thus called ‘the fourth state of matter’ enticed the author to a challenge to unravel the mysteries of matter createdab-initio on a nanoscale. Nucleation and growth studies of evaporated and sputtered films (both polycrystalline and epitaxial) and the effects of kinetic energy, angle of incidence, electric field, substrate agitation, formation of metastable and amorphous structures, etc led to exciting discoveries. The fields of amorphous metal alloy and semiconducting films were thus born. Electron and optical transport investigations on pure and doped metal, semiconducting, oxide and polymer films established a variety of new phenomena of which the mean free path effects and specular scattering of conduction electrons in epitaxial metal films, giant thermopower in quenched metal films, sputter quenching, giant photocontraction effect in amorphous Ge-chalcogenide films, enhancement of superconducting transition temperature in transition metal films, nanosize multi layer coating (the first known superlattices) are noteworthy. A variety of new deposition processes such as solution growth of polymer films, solution growth of chalcogenide and oxide films, spray pyrolysis, coprecipitation of multicomponent oxides (for thick films), activated reactive evaporation/magnetron sputtering were innovated. This lecture will share the excitement of the contributions by the author, his 60 Ph.D students and a number of post doctoral fellows and faculty members at the Thin Film Laboratory, IIT Delhi and the Microscience Laboratory at IIT Kharagpur. Distinguished Materials Scientist Award Lecture presented at the MRSI Meeting, Kharagpur on February 8, 1995. Born in 1933 at Chahal Kalan, Panjab (now Pakistan), Kasturi Lal Chopra experienced along with his family the fiery turbulance of partition to reach Delhi. After topping in the matric examination from DAV School in 1948, he went on to earn his B. Sc. (Hons.) in 1952, and M. Sc. (1954) in Physics from Delhi University. As a World University Service Fellow, he took his Ph. D in Low Temperature Physics from the University of British Columbia, Canada. After being a post doctoral fellow at Royal Military College of Canada, and Max Planck Guest Scientist at the Fritz Haber Institute, Berlin, he took up the assignments of a Group Leader at Philco-Food Scientific Laboratory. Blue Bell in 1962 and later a Staff Scientist of Ledgemont Laboratory, Kennecott Copper Corp., USA. The IIT Delhi invited him in 1970 as a Senior Professor to head the Physics Department and establish a school of Solid State Physics. He founded the Thin Film Laboratory and served IIT Delhi for 17 years in various capacities as Head, Physics Department, Energy Centre, and Dean, Post Graduate Studies and Industrial Research and Development. He was appointed Director of IIT Kharagpur in 1987 and is presently serving a second term. He continues to actively pursue R/D activities along with research students and faculty in the Thin Film Laboratory in IIT Delhi, as also in the Microscience Laboratory founded by him at IIT Kharagpur. He has supervised over 60 Ph.D Theses, published over 400 papers and authored/coauthored: “Thin Film Solar Cells”, “Thin Film Phenomena”, “Thin Film Device Applications”, and has edited four other books. Several published papers are now Classic Citations and “Thin Film Phenomena” continues for the last 25 years to be considered a “Bible” of the field. Innovative developments of Prof. Chopra and colleagues have resulted in five US Patents, a dozen knowhow transfers to industry in India and abroad. He has served on the editorial boards of several international journals. He has lectured extensively abroad in various universities and R/D centres and consulted to several international companies. He has been elected a Fellow of the American Physical Society, Indian National Science Academy, Indian Academy of Sciences and Indian Academy of Engineering. He has delivered several memorial lectures and is the recipient of several awards: Bhatnagar Prize (Physics), Bhatnagar Award (Energy), FICCI Award (Science & Technology), Bhasin Award (Energy), Bhabha Award (Applied Sciences), INSA Krishnan Memorial Lecture Award.     

Lithographic patterning of superconducting YBCO films

Microbridges of YBa₂Cu₃O₇ thin films have been fabricated by conventional photolithography and wet chemical etching using EDTA, and by the lift-off lithography technique. The variation of etch rate with etch time, etchant temperature, and post-deposition sintering temperature has been studied. It has been shown that both techniques are useful for film patterning. However, an additional sintering step is necessary for the chemically etched sample to regain the original film properties. An order of increase in critical current density is observed for the patterned film.     

Conjoined gastric and mediastinal benign cystic teratomas. Case report of a rare occurrence and review of literature

In this study, we evaluated the permeation of piperacillin (PIPC), imipenem (IPM), amikacin (AKM), gentamicin (GM), ofloxacin (OFLX), levofloxacin (LVFX), ciprofloxacin (CPFX) and sparfloxacin (SPFX) through Pseudomonas aeruginosa biofilm with a simple new method. Bacteria used were a leucine-requiring mucoid mutant. Bacteria were grown on the membrane of a cell culture insert in chemically defined medium and incubated at 37 degrees C for 5 days. At days 0, 1, 3 and 5, the penetration rates through the biofilms were measured. PIPC and IPM demonstrated relatively high permeation both with penetration rates at day 5 of 50%, whereas AMK and GM, which are aminoglycosides, showed low permeation both with penetration rates after day 1 of less than 25%. Among the 4 fluoroquinolones, LVFX and SPFX demonstrated excellent permeation with penetration rates that reached 100% from day 0 to 5, while OFLX and CPFX showed almost the same permeation as IPM. This method of measuring penetration rates of antimicrobial agents through biofilm is very simple and useful for the evaluation of antibiotics against biofilm-forming bacteria.     

Microstructural characterization of transparent conducting aluminium doped zinc oxide films prepared by spray pyrolysis

X-ray diffraction patterns of pyrolytically sprayed aluminium doped zinc oxide films have been recorded and X-ray line profile analysis studies have been carried out after correcting for instrumental broadening. Different microstructural parameters such as crystallite size, r.m.s. strain and dislocation density have been determined from the variance analysis of X-ray line profiles. Texture coefficient, the degree of preferred orientation of the crystallites and stacking fault have been estimated from the X-ray diffraction data. It is observed that the figure of merit as a transparent conductor depends on the dopant concentration and microstructural parameters of the films deposited under identical growth conditions.     

Analysis of optimum matching of a DC series motor driven centrifugal pump to a photovoltaic generator

Direct coupling between a photovoltaic (PV) generator and a monoblock DC series motor connected with ventilator load torque centrifugal pump has been analyzed theoretically as a function of the no flow motor-pump speed (w₀) and the water head of the pump. The value of w₀ is directly related with motor terminal voltage which has been derived. The condition of the maximum motor-pump efficiency has been deduced mathematically in terms of the speed-torque constant K₁ at a given w₀ for different water heads. The variation of w₀ and perfectly matched motor constant (M₀) have been calculated at various solar insolation and different water heads. From these theoretical studies, the optimum matching condition has been suggested according to the requirements. One optimally matched monoblock DC series motor and centrifugal pump, of 125 W, was chosen for study. The calculated coupling efficiencies such as electrical energy, mechanical energy, and hydraulic energy of the pump, have been discussed. Some of these results are also compared to information available in the literature.     

a-Si:H/CuInS2 heterojunctions for photovoltaic conversion

Heterojunctions of hydrogenated a-Si films prepared by r.f. sputtering with spraypyrolyzed CuInS₂ films have been studied. Capacitance-voltage measurements establish the formation of abrupt heterojunction. The barrier height varies from 0·26 to 0·55 V as the resistivity of CuInS₂ film decrease from 1·5 × 10³ to 65 Θm. These junctions exhibit photovoltaic behaviour withV _oc = 220 mV andI _sc = 0·20 mA/cm².     

Nonlinear Model for Lead–Rubber Bearings Including Axial-Load Effects

Existing models for isolation bearings neglect certain aspects of their response behavior. For instance, rubber bearings have been observed to decrease in stiffness with increasing axial load, and soften in the vertical direction at large lateral deformations. The yield strength of lead–rubber bearings has also been observed to vary with axial load, such that a lightly loaded bearing may not achieve its theoretical strength. Models that include these axial-load effects in lead–rubber bearings are developed by extending an existing linear two-spring model to include nonlinear behavior. The nonlinearity includes an empirical equation for the experimentally observed variation of yield strength. For numerical implementation, the bearing forces are found by solving the nonlinear equilibrium and kinematic equations using Newton’s method, and the instantaneous bearing stiffness matrix is formed from the differentials of these equations. The response behavior of the models is confirmed by comparison with experimental data.     

Formation of atomic point contacts and molecular junctions with a combined mechanical break junction and electrodeposition method

A method to create atomic point contacts and molecular junctions by combining mechanically controlled break junction and electrochemical deposition/etching techniques is described. This approach provides both stability and flexibility, and is suitable for studying electron transport properties of single molecule junctions or atomic point contacts in aqueous solutions and under potential control. Using the approach, the electron transport properties of 4,4'-bipyridine as a function of electrochemical gate and Ni point contacts have been studied