Showing papers by "Indian Institute of Science published in 1983"
TL;DR: In this article, the morphology and crystal growth of poly( l -lactic acid), PLLA have been studied from the melt as a function of undercooling and molecular weight using hot stage microscopy.
383 citations
TL;DR: A comprehensive and critical review of recent experimental studies of equilibrium critical phenomena in binary liquid mixtures can be found in this article, where it is shown that binary liquid mixture constitute ideal systems in which to attempt a detailed verification and evaluation of some predictions of the modern theories of critical phenomena.
205 citations
TL;DR: The crystal structures of the self-complementary octamer d(G-G-T-A-T, A-C-C) and its 5-bromouracil-containing analogue have been refined to R values of 20% and 14% at resolutions of 1·8 and 2·25 A, respectively as discussed by the authors.
176 citations
TL;DR: In this article, a systematic study of the various factors involved in zero-crossing measurements is presented, which shows that the dynamic range of the signal, the discriminator characteristics, filter frequency and noise contamination have a strong bearing on the results obtained.
Abstract: A primary motivation for this work arises from the contradictory results obtained in some recent measurements of the zero-crossing frequency of turbulent fluctuations in shear flows. A systematic study of the various factors involved in zero-crossing measurements shows that the dynamic range of the signal, the discriminator characteristics, filter frequency and noise contamination have a strong bearing on the results obtained. These effects are analysed, and explicit corrections for noise contamination have been worked out. New measurements of the zero-crossing frequency N0 have been made for the longitudinal velocity fluctuation in boundary layers and a wake, for wall shear stress in a channel, and for temperature derivatives in a heated boundary layer. All these measurements show that a zero-crossing microscale, defined as Λ = (2πN0)−1, is always nearly equal to the well-known Taylor microscale λ (in time). These measurements, as well as a brief analysis, show that even strong departures from Gaussianity do not necessarily yield values appreciably different from unity for the ratio Λ/λ. Further, the variation of N0/N0 max across the boundary layer is found to correlate with the familiar wall and outer coordinates; the outer scaling for N0 max is totally inappropriate, and the inner scaling shows only a weak Reynolds-number dependence. It is also found that the distribution of the interval between successive zero-crossings can be approximated by a combination of a lognormal and an exponential, or (if the shortest intervals are ignored) even of two exponentials, one of which characterizes crossings whose duration is of the order of the wall-variable timescale ν/U2*, while the other characterizes crossings whose duration is of the order of the large-eddy timescale δ/U[infty infinity]. The significance of these results is discussed, and it is particularly argued that the pulse frequency of Rao, Narasimha & Badri Narayanan (1971) is appreciably less than the zero-crossing rate.
143 citations
TL;DR: Magnetic resonance studies reveal a marked difference between the binding of α-tocopherol and that of the corresponding acetate (vitamin E acetate) with dipalmitoylphosphatidylcholine (DPPC) vesicles as mentioned in this paper.
121 citations
TL;DR: The AB-microELISA is not only rapid and inexpensive, but also more sensitive than other published ELISA procedures and comparable to solid-phase radioimmunoassays in the quantitation of total and allergen-specific IgE.
110 citations
TL;DR: In this paper, the authors present two dynamical aspects of interest in the trajectory of a spacecraft: the most obvious one is the trajectory traced by its center of mass which is governed by the classical Keplerian relations.
Abstract: Introduction M of a spacecraft presents two dynamical aspects of interest. The most obvious one is the trajectory traced by its center of mass which is governed by the classical Keplerian relations. However, spacecraft are not point masses as Kepler assumed in the analysis of planetary bodies. They have finite size and hence inertia. Thus a satellite, while negotiating a trajectory, may execute rotational motion about its center of mass, commonly referred to as libration.
102 citations
TL;DR: Analysis of time-activity budgets of several individually identified members of Ropalidia marginata colonies by multivariate statistical techniques including principal components analysis and hierarchical cluster analysis has demonstrated the presence of three different behavioural castes which are named Sitters, Fighters and Foragers.
87 citations
82 citations
TL;DR: By use of this immunochemical approach, this method is able to detect 5mC, 6mA and 7mG in human and Drosophila DNA and confirm their presence in the DNA of two mealybug species.
79 citations
TL;DR: The antitumour antibiotic, adriamycin, inhibited oxidative phosphorylation in freshly prepared mitochondria from the heart, liver and kidney of the rat, and was extremely sensitive to the drug when hexokinase was present in the reaction medium.
TL;DR: A working, hypothesis for a channel model is outlined and various aspects of the structural chemistry and membrane modifying properties of alamethicin and related Alb containing peptides are summarized.
Abstract: Alamethicin and several related microbial polypeptides, which contain a high proportion of alpha-aminoisobutyric acid (Aib) residues, possess the ability to modify the permeability properties of phospholipid bilayer membranes. Alamethicin induces excitability phenomena in model membranes and has served as an excellent model for the study of voltage sensitive transmembrane channels. This review summarizes various aspects of the structural chemistry and membrane modifying properties of alamethicin and related Aib containing peptides. The presence of Aib residues in these sequences, constrains the polypeptides to 3(10) or alpha-helical conformations. Functional membrane channels are formed by aggregation of cylindrical peptide helices, which span the lipid bilayer, forming a scaffolding for an aqueous column across the membrane. After consideration of the available data on the conductance characteristics of alamethicin channels, a working hypothesis for a channel model is outlined. Channel aggregates in the lipid phase may be stabilized by intermolecular hydrogen bonding, involving a central glutamine residue and also by interactions between the macro-dipoles of proximate peptide helices. Fluctuations between different conductance states are rationalized by transitions between states of different aggregation and hence altered dimensions of the aqueous core or by changes in net dipole moment of the aggregate. Ion fluxes through the channel may also be affected by the electric field within the aqueous core.
TL;DR: A molecular model is proposed for the transmembrane channels formed by alamethicin and related polypeptides and the helix dipole moment is considered to be the major factor modulating channel size, selectivity and field‐dependent transitions.
TL;DR: In this paper, the relativistic front form for the equations of the paraxial electromagnetic wave was developed and shown to be particularly suited to the description of paraxials.
Abstract: With the extension of the work of the preceding paper, the relativistic front form for Maxwell's equations for electromagnetism is developed and shown to be particularly suited to the description of paraxial waves. The generators of the Poincare group in a form applicable directly to the electric and magnetic field vectors are derived. It is shown that the effect of a thin lens on a paraxial electromagnetic wave is given by a six-dimensional transformation matrix, constructed out of certain special generators of the Poincare group. The method of construction guarantees that the free propagation of such waves as well as their transmission through ideal optical systems can be described in terms of the metaplectic group, exactly as found for scalar waves by Bacry and Cadilhac. An alternative formulation in terms of a vector potential is also constructed. It is chosen in a gauge suggested by the front form and by the requirement that the lens transformation matrix act locally in space. Pencils of light with accompanying polarization are defined for statistical states in terms of the two-point correlation function of the vector potential. Their propagation and transmission through lenses are briefly considered in the paraxial limit. This paper extends Fourier optics and completes it by formulating it for the Maxwell field. We stress that the derivations depend explicitly on the "henochromatic" idealization as well as the identification of the ideal lens with a quadratic phase shift and are heuristic to this extent.
TL;DR: In this article, surface concentrations of oxygen on both metal surfaces have been estimated over a wide range of alkali coverages, ranging from 1 \times 10^{14}$ to $1.8 ǫ/cm^{2})$ and temperatures (300 to 800 K).
TL;DR: In this paper, the effect of corundum particle content on the wear of aluminium was studied and the mechanism of reinforcement and its effect on the operative wear mode were discussed. But the wear decreased as the oxide content increased, showing an optimum value at a composition range of 25 wt.% −35 wt%.
TL;DR: Evidence is presented to show that castes living together in the same region had so organized their pattern of resource use as to avoid excessive intercaste competition for limiting resources, which favoured the cultural evolution of traditions ensuring sustainable use of natural resources.
Abstract: Indian society is an agglomeration of several thousand endogamous groups or castes each with a restricted geographical range and a hereditarily determine mode of subsistence. These reproductively isolated castes may be compared to biological species, and the society thought of as a biological community with each caste having its specific ecological niche. In this paper we examine the ecological-niche relationships of castes which are directly dependent on natural resources. Evidence is presented to show that castes living together in the same region had so organized their pattern of resource use as to avoid excessive intercaste competition for limiting resources. Furthermore, territorial division of the total range of the caste regulated intra-caste competition. Hence, a particular plant or animal resource in a given locality was used almost exclusively by a given lineage within a caste generation after generation. This favoured the cultural evolution of traditions ensuring sustainable use of natural resources. This must have contributed significantly to the stability of Indian caste society over several thousand years. The collapse of the base of natural resources and increasing monetarization of the economy has, however, destroyed the earlier complementarity between the different castes and led to increasing conflicts between them in recent years.
TL;DR: In this paper, the estimation of mean Doppler velocity in a coherent radar using a short complex time series is discussed. But the authors focus on the accuracy of the estimation and not the ease of implementation.
Abstract: Doppler weather radars with fast scanning rates must estimate spectral moments based on a small number of echo samples. This paper concerns the estimation of mean Doppler velocity in a coherent radar using a short complex time series. Specific results are presented based on 16 samples. A wide range of signal-to-noise ratios are considered, and attention is given to ease of implementation. It is shown that FFT estimators fare poorly in low SNR and/or high spectrum-width situations. Several variants of a vector pulse-pair processor are postulated and an algorithm is developed for the resolution of phase angle ambiguity. This processor is found to be better than conventional processors at very low SNR values. A feasible approximation to the maximum entropy estimator is derived as well as a technique utilizing the maximization of the periodogram. It is found that a vector pulse-pair processor operating with four lags for clear air observation and a single lag (pulse-pair mode) for storm observation may be a good way to estimate Doppler velocities over the entire gamut of weather phenomena.
TL;DR: The results of the bilingual comparison indicated the possibility that the phonetic influences on stuttering might be dependent on the number of languages spoken by the subjects as well as the specific language in which the effects were observed.
01 Dec 1983
TL;DR: In this article, the problem of designing a pair of controllers C1 and C2 such that their sum stabilizes a plant P, and each of them also stabilizes P should the other one fail is considered.
Abstract: Given a plant P, we consider the problem of designing a pair of controllers C1 and C2 such that their sum stabilizes P, and in addition, each of them also stabilizes P should the other one fail. This is referred to as the reliable stabilization problem. It is shown that every strongly stabilizable plant can be reliably stabilized; moreover, one of the two controllers can be specified arbitrarily, subject only to the constraint that it should be stable. The stabilization technique is extended to reliable regulation.
TL;DR: In this paper, a new model is presented to predict liquid holdup profiles in semi-batch cellular foams, which is based on two basic processes of film thinning and flow through Plateau borders.
01 Sep 1983
TL;DR: In this paper, it was shown that the set of first order systems that can be realized using axially symmetric thin lenses exhausts the entire SL(2, R) group; at most three lenses are needed to realize any element of this group.
Abstract: A first order optical system is investigated in full generality within the context of wave optics. The problem is reduced to a study of the ray transfer matrices. The simplest such systems correspond to axially symmetric propagation. Realization of such systems by centrally located lenses separated by finite distances is studied. It is shown that, contrary to the commonly held view, the set
of first order systems that can be realized using axially symmetric thin lenses exhausts the entire SL(2, R) group; at most three lenses are needed to realize any element of this group. In particular, the inverse of free propagation can be so realized. Among anisotropic systems it is again shown that every element of the lens group Sp(4, R) can be realized using a finite number of thin lenses.
TL;DR: In this paper, a very interesting and well-written expository paper on the Hamiltonian formulation for constrained systems and its symmetry from the geometrical point of view is presented.
Abstract: This is a very interesting and well-written expository paper on the Hamiltonian formulation for constrained systems and its symmetry from the geometrical point of view. Coordinate-free and coordinate-based methods are both used throughout the paper, making both geometrical and physical concepts transparent. The paper is divided into two parts. Part I is devoted to dynamics while part II deals with symmetries, and contains three appendices where some calculations and proofs are exhibited. Both the mathematically as well as the physically inclined reader will certainly find enough motivation to read this paper.
TL;DR: In this article, the copper complex, (N 2 H 5 ) 2 Cu(C 2 O 4 ) 2 ·H 2 O has a square planar geometry with no coordination of hydrazinium cations as confirmed by a single crystal X-ray study.
TL;DR: In this article, the authors derived climatic clusters of the Indian region using data on monthly mean profiles of the precipitation, the moisture index (defined as the ratio of precipitation and potential evapotranspiration) and of the minimum temperature.
Abstract: In this paper we derive climatic clusters of the Indian region using data on monthly mean profiles of the precipitation, the moisture index (defined as the ratio of precipitation and potential evapotranspiration) and of the minimum temperature. The delineation of regions over which the patterns of profiles of important climatic factors such as precipitation are similar is necessary for the determination of meteorological zones over which prediction can be made as well as for understanding the distribution of vegetation cover. The latter has been the major aim of the studies of climatic classification. In the traditional approach to this problem, the meteorological stations in the region are assigned to predetermined categories such as arid, semi-arid etc. on the basis of the values of the climatic factors (or of the bulk parameters derived therefrom) characterizing these stations.
Here the variation of the climatic patterns over the Indian region has been analysed to obtain climatic clusters, which represent natural grouping of the patterns and hence of the meteorological stations at which they occur, as well as the climatic boundaries separating these clusters. This analysis is facilitated by an initial reduction of dimensionality in the description of the patterns achieved by using principal component analysis. Sixteen clusters of the mean monthly profiles of the moisture index have been obtained. It is found that there is a close correspondence between these clusters and the distribution of the vegetation types in the country.
TL;DR: In this paper, it was shown that in two-dimensional supersymmetric theories, the energies of solitons do receive non-zero but finite quantum corrections, in contrast to the earlier work of D'Adda and Di Vecchia, who have claimed that, to order h, these corrections vanish exactly.
TL;DR: In this paper, continuous glass-fibre-reinforced epoxy composites were fabricated and their wear behaviour was studied and a rapid drop in the wear loss occurred with an increase in the sliding speed for the pure epoxy resin while the reinforced sample exhibited a mild decrease, a flat region and then a rise Optical microscopy examination indicates that the higher wear loss for the composite at higher speeds could be due to loss of glass fibres.
TL;DR: In this article, a pin-on-disc machine was used to wear Al-Si alloy pins under dry conditions and the surfaces of the worn alloys were examined by scanning electron microscopy to identify distinct topographical features to aid elucidation of the mechanisms of wear.
TL;DR: In this article, the authors showed that the micellar orientational effect is most effective only in those systems where the forces that control regiochemistry are weaker than hydrophobic association energies.
Abstract: Organized media such as micelles have shown great promise in achieving regio- and stereoselectivity in photochemical cycloaddition reactions as has been shown by recent reports. 7-Alkoxy- and 4-methyl-7-alkoxycoumarins dimerize in organic solvents to give the syn head-tail dimer. However, dimerization of these coumarins in SDS and CTAB micelles did not show any reversal in this trend. The results probably indicate that the micellar orientational effect is most effective only in those systems where the forces that control regiochemistry are weaker than hydrophobic association energies.