Showing papers by "Indian Institute of Science published in 1988"

Optimal infinite-horizon feedback laws for a general class of constrained discrete-time systems: stability and moving-horizon approximations

Abstract: Stability results are given for a class of feedback systems arising from the regulation of time-varying discrete-time systems using optimal infinite-horizon and moving-horizon feedback laws. The class is characterized by joint constraints on the state and the control, a general nonlinear cost function and nonlinear equations of motion possessing two special properties. It is shown that weak conditions on the cost function and the constraints are sufficient to guarantee uniform asymptotic stability of both the optimal infinite-horizon and moving-horizon feedback systems. The infinite-horizon cost associated with the moving-horizon feedback law approaches the optimal infinite-horizon cost as the moving horizon is extended.

The structure of 2Zn pig insulin crystals at 1.5 A resolution.

Abstract: The paper describes the arrangement of the atoms within rhombohedral crystals of 2Zn pig insulin as seen in electron density maps calculated from X-ray data extending to 1.5 A (1 A = 10(-10) m = 10(-1) nm) at room temperature and refined to R = 0.153. The unit cell contains 2 zinc ions, 6 insulin molecules and about 3 x 283 water molecules. The atoms in the protein molecules appear well defined, 7 of the 102 side chains in the asymmetric unit have been assigned alternative disordered positions. The electron density over the water molecules has been interpreted in terms of 349 sites, 217 weighted 1.0, 126 weighted 0.5, 5 at 0.33 and 1 at 0.25 giving ca. 282 molecules. The positions and contacts of all the residues belonging to the two A and B chains of the asymmetric unit are shown first and then details of their arrangement in the two insulin molecules, 1 and 2, which are different. The formation from these molecules of a compact dimer and the further aggregation of three dimers to form a hexamer around two zinc ions, follows. It appears that in the packing of the hexamers in the crystal there are conflicting influences; too-close contacts between histidine B5 residues in neighbouring hexamers are probably responsible for movements of atoms at the beginning of the A chain of one of the two molecules of the dimer that initiate movements in other parts, particularly near the end of the B chain. At every stage of the building of the protein structure, residues to chains of definite conformation, molecules, dimers, hexamers and crystals, we can trace the effect of the packing of like groups to like, aliphatic groups together, aromatic groups together, hydrogen-bonded structures, positive and negative ions. Between the protein molecules, the water is distributed in cavities and channels that are continuous throughout the crystals. More than half the water molecules appear directly hydrogen bonded to protein atoms. These are generally in contact with other water molecules in chains and rings of increasing disorder, corresponding with their movement through the crystals. Within the established crystal structure we survey next the distribution of hydrogen bonds within the protein molecules and between water and protein and water and water; all but eight of the active atoms in the protein form at least one hydrogen bond.(ABSTRACT TRUNCATED AT 400 WORDS)

Interannual Variations of Sea Surface Temperature over the Arabian Sea and the Indian Monsoon: A New Perspective

Abstract: The interannual variation of surface fields over the Arabian Sea and Bay of Bengal are studied using data between 1900 and 1979. It is emphasized that the monthly mean sea surface temperature (SST) over the north Indian Ocean and monsoon rainfall are significantly affected by synoptic systems and other intraseasonal variations. To highlight the interannual signals it is important to remove the large-amplitude high-frequency noise and very low frequency long-term trends, if any. By suitable spatial and temporal averaging of the SST and the rainfall data and by removing the long-term trend from the SST data, we have been able to show that there exists a homogeneous region in the southeastern Arabian Sea over which the March–April (MA) SST anomalies are significantly correlated with the seasonal (June–September) rainfall over India. A potential of this premonsoon signal for predicting the seasonal rainfall over India is indicated. It is shown that the correlation between the SST and the seasonal mon...

Gaussian pure states in quantum mechanics and the symplectic group

Abstract: Gaussian pure states of systems with n degrees of freedom and their evolution under quadratic Hamiltonians are studied. The Wigner-Moyal technique together with the symplectic group Sp(2n,openR) is shown to give a convenient framework for handling these problems. By mapping these states to the set of n\ifmmode\times\else\texttimes\fi{}n complex symmetric matrices with a positive-definite real part, it is shown that their evolution under quadratic Hamiltonians is compactly described by a matrix generalization of the M\"obius transformation; the connection between this result and the ``abcd law'' of Kogelnik in the context of laser beams is brought out. An equivalent Poisson-bracket description over a special orbit in the Lie algebra of Sp(2n,openR) is derived. Transformation properties of a special class of partially coherent anisotropic Gaussian Schell-model optical fields under the action of Sp(4, openR) first-order systems are worked out as an example, and a generalization of the ``abcd law'' to the partially coherent case is derived. The relevance of these results to the problem of squeezing in multimode systems is noted.

The dynamics of polar solvation: Inhomogeneous dielectric continuum models

Abstract: The influence of an inhomogeneous dielectric response on the dynamics of solvation of ions and dipoles is investigated. Solvent models considered include discrete shell models as well as models in which the solvent dielectric constant varies continuously as a function of distance from a spherical solute. The effect of such dielectric inhomogeneity is to introduce additional, slower relaxation times into the solvation response when compared to the homogeneous case. For all models studied, the deviation of the average relaxation time from that predicted for a homogeneous continuum solvent increases as the dielectric constant and the length parameter, which specifies the rapidity of approach to bulk behavior, increase. For a given solvent model the solvation response to a change in a point dipole moment is slower than the response to a charge jump. The continuum results are compared to a recent molecular model based on the mean spherical approximation. The comparison suggests that deviations from homogeneous continuum behavior in the molecular model can be accounted for by inhomogeneity of the solvent dielectric constant extending only over the first solvation shell. Predictions of inhomogeneous continuum models are also compared to experimental data. Both the observed dependence of average relaxation time on dielectric constant, and the detailed time dependence of the relaxation in high dielectric constant solvents can be rationalized on the basis of such models.

Salinity Gradient Solar Ponds

Abstract: Salinity-gradient solar ponds are of interest as a means for collecting solar energy and storing it as heat for such low-temperature applications as space heating, industrial water heating, and crop drying Used in such applications, solar ponds may be significantly lower in cost than other solar collectors; and they combine at the same time the capability of long term storage In favorable sites where conventional fuel costs are unusually high, it is possible to use solar ponds for solar thermal power generation By far the largest solar ponds operated to date are those at the 5MW peaking power station at the north end of the Dead Sea in Israel Their intrinsic storage capability distinguishes solar pond power stations from other solar-electric systems

Three-Dimensional Unsteady Flow With Heat and Mass Transfer Over a Continuous Stretching Surface

Abstract: A numerical solution of the unsteady boundary layer equations under similarity assumptions is obtained. The solution represents the three-dimensional unsteady fluid motion caused by the time-dependent stretching of a flat boundary. It has been shown that a self-similar solution exists when either the rate of stretching is decreasing with time or it is constant. Three different numerical techniques are applied and a comparison is made among them as well as with earlier results. Analysis is made for various situations like deceleration in stretching of the boundary, mass transfer at the surface, saddle and nodal point flows, and the effect of a magnetic field. Both the constant temperature and constant heat flux conditions at the wall have been studied.

On the Suppression of Superconductivity in Y1-xPrxBa2Cu3O7-δ

Abstract: Y1-xPrxBa2Cu3O7-δ compounds exhibit a progressive decrease in superconducting transition temperature with increasing x. Using soft-X-ray absorption spectroscopy at the Pr-MIV,V thresholds, Pr is shown to be trivalent for all x in these compounds contrary to expectations, excluding an obvious mechanism for the suppression of Tc based on the tetravalency of Pr. From a discussion of other possible mechanisms it is suggested that Tc decreases through changes in electronic-band structure upon Pr substitution leading ultimately to a semiconducting behaviour for x = 1.0.

Role of lead in lead phosphomolybdate glasses and a model of structural units

Abstract: PbOMoO 3 P 2 O 5 glasses have been studied over a wide range of compositions. Their physical, thermal, and spectroscopic properties such as density, molar volume, microhardness, heat capacity, glass transition temperature and IR spectra have been investigated. Variation of Mo 5+ concentration as a function of PbO concentration has also been studied using ESR spectroscopy. A structural model is presented to rationalize the experimental observations. According to this model, binary phosphomolybdate glasses are built up of [ MoO 6 2 ] octahedral and [ POO 3 2 tetrahedral units which share corner Further, PbO plays a dual strutural role, both as a network former and as a network modifier. This aspect is discussed in the light of various experimental results. When PbO enters into the network modifier, itis assuuned to be present as four coordinated tetrahedral [ PbO 4 2 ] 2− units again with share corber. This is accompanied by the simulataneous conversion of [ POO 3 2 ] into [ PO 4 2 ] + units which thereby achieves charge neutrality in the system. When PbO acts as a network modifier, glasses are characterized by the presence of a number of polyhedral structural units carrying a net charge, while lead remains in the structure as Pb 2+ ions. The composition dependent structural changes are represented using a structural phase diagram.

Fault detection and diagnosis of automated manufacturing systems

Abstract: The authors develop a controller methodology for fault detection and diagnosis using Petri nets and fault trees in automated manufacturing systems. The controller has two levels. At the first level there are dedicated diagnostic systems for each of the subsystems, such as machine centers, robots, conveyers, etc. At the second level there is an intelligent controller monitoring the part flow and coordinating the local diagnostic systems and controllers. The authors assume that local controller and diagnostic systems exist for subsystem-level fault detection and diagnosis, and they present a Petri-net-based intelligent controller for system-level fault detection and diagnosis. The authors also describe fault-free-based diagnostics. >

Growth in the Asian elephant

Abstract: Records of captive Asian elephants (Elephas maximus) were used to derive parameters of the von Bertalanffy function for growth in height, body weight and circumference of tusks with age. There was some evidence for a post-pubertal secondary growth spurt in both male and female elephants. Domestic elephants which were born in captivity or captured at a young age also showed a reduced growth in height in both the sexes and in body weight in males compared to wild elephants. Aspects of allometric growth such as height-body weight relationship are examined. The height was twice the circumference of front foot throughout the life span, indicating an isometric relationship.

Cobalt(II), nickel(II) and copper(II) complexes of bidentate bibenzimidazoles

Abstract: Complexes of cobalt(II), nickel(II) and copper(II) with novel bidentate bibenzimidazoles, [M(L-L)Cl2], where L-L are methylenebis(1, 1′-benzimidazole), methylenebis(2, 2′-benzimidazole) and dimethylenebis(2, 2′-benzimidazole) are described and characterized by different physical measurements. The four coordinate complexes have distorted tetrahedral or square coplanar structures. The bridging entity between the two donor groups apparently influences the ligand field strength and the ligands occupy a higher position than that of benzimidazole in the spectrochemical series.

Molecular interactions and aggregation involving amino acids and peptides and their role in chemical evolution.

Abstract: The earth is believed to have originated some 4.5 billion years ago. The surface of the nascent earth was devoid of any trace of organic matter, let alone life. It is at present characterized by a rich variety of different forms of life. How did this come about? How did life originate and evolve into innumerable forms? The answer to this question is generally attempted in two phases. First, how did the molecules of life come into being and organize themselves into a primitive self-replicating system or primitive cell? Secondly, how did the present-day organisms evolve from the primitive cell or cells? The first question is concerned with chemical evolution and the subsequent origin of life, and the second with biological evolution. It may be noted that chemical evolution must have taken place in a comparatively short span of time on the geological time scale. There is evidence to suggest that life existed as early as 3.6 to 3.8 billion years ago (Nisbet, 1985). The earth, after its formation some 4.5 billion years ago, must have taken several hundred million years to cool down sufficiently for the formation of the crust and to be able to support water and organic matter on its surface. Allowing for this time lag and bearing in mind that life probably originated some 3.6 to 3.8 billion years ago, chemical evolution appears to have been completed in a few hundred million years in the early phase of earth's existence. No traces of the processes of chemical evolution remain. Therefore, direct answers to questions concerning chemical evolution cannot be obtained. Results of informed speculation, simulation experiments, observations of meteorites etc., need to be put together even to get a blurred picture of chemical evolution. Indeed such a picture, partly clear and partly hopelessly confusing, has emerged during the last few decades.

Pre-Imaginal Biasing of Caste in a Primitively Eusocial Insect

Abstract: Primitively eusocial insects often lack morphological caste differentiation, leading to considerable flexibility in the social and reproductive roles that the adult insects may adopt. Although this flexibility and its consequences for social organization have received much attention there has been relatively little effort to detect any pre-imaginal effects leading to a bias in the potential caste of eclosing females. Experiments reported here show that only about 50% of eclosing females of the tropical social wasp Ropalidia marginata build nests and lay eggs, in spite of being isolated from all conspecifics and being provided ad libitum food since eclosion. The number of empty cells in the parent nest, which we believe to be an indication of the queen's declining influence, and a wasp's own rate of feeding during adult life predict the probability of egg laying by eclosing females. These results call for an examination of the possibility that all females in primitively eusocial insect societies are not potentially capable of becoming egg layers and that reigning queens and possibly other adults exert an influence on the production of new queens.

Robust Observer Design with Application to Fault Detection

Abstract: A new scheme for robust estimation of the partial state of linear time-invariant multivariable systems is presented, and it is shown how this may be used for the detection of sensor faults in such systems. We consider an observer to be robust if it generates a faithful estimate of the plant state in the face of modelling uncertainty or plant perturbations. Using the Stable Factorization approach we formulate the problem of optimal robust observer design by minimizing an appropriate norm on the estimation error. A logical candidate is the 2-norm, corresponding to an H? optimization problem, for which solutions are readily available. In the special case of a stable plant, the optimal fault diagnosis scheme reduces to an internal model control architecture.