Showing papers by "Tata Institute of Fundamental Research published in 1980"

Moduli of Vector Bundles on Curves with Parabolic Structures.

Abstract: Let H be the upper half plane and T a discrete subgroup of AutH. Suppose that H mod Y is of finite measure. This work stems from the question whether there is an algebraic interpretation for the moduli of unitary representations of T similar to the case when H mod T is compact (cf. [3], [4], [5]). We show that this is indeed the case via the moduli of vector bundles on the compactification of H mod r , provided with some additional structures which we propose to call parabolic structures. The idea of parabolic structures is inspired from A. Weil's work [6, §2, Chapter I, p. 56]. Let Xbe a smooth, irreducible, projective curve defined, say, over an algebraically closed field k. By vector bundles on X we understand algebraic vector bundles. DEFINITION 1. Let V be a vector bundle on X and Q G X. Then a quasiparabolic structure of Vat Q is giving a flag on the fibre VQ of Fat Ô, i.e., giving linear subspaces F*VQ of VQ,

Criteria for the unitarizability of some highest weight modules

Abstract: For a linear semisimple Lie group we obtain a necessary and sufficient condition for a highest weight module with non-singular infinitesimal character to be unitarizable.

Tobacco-induced changes in oral leukoplakic epithelium.

Abstract: A study of 112 biopsy specimens from Danish oral leukoplakia patients and 145 biopsy specimens from Indian leukoplakia patients revealed a chevron-like keratinization of the epithelium in a number of cases. Clinically, this type of keratinization was often characterized by a pumice-like appearance. The clinical and histologic changes were only observed in tobacco users, and appeared to be associated particularly with use of pipes, snuff, and hooklis.

Condition for Nonexistence of Aharonov-Bohm Effect

Abstract: It is shown that electromagnetic effects of a vector potential on a charged particle confined to a region R (multiply or simply connected) are completely determined by field strengths in R, if the potential obeys certain conditions Such potentials are adequate in experiments purporting to show Aharonov-Bohm effect Therefore these experiments have not established effects of inaccessible fields

Olfactory Behavior of Drosophila Melanogaster

Abstract: The olfactory system of Drosophila is readily amenable to genetic dissection. The response to smell involves interaction between a chemical stimulant and the receptor surface, transduction, neural excitation, transmission across synapses and integration by the central nervous system finally leading to motor activity. By an appropriate choice of mutants, attention can be focussed on any one of this series of complex processes. In this paper I will describe the properties of olfactory mutations on the X-chromosome and compare the behavior of mutants with normal flies.

An oral lichen planus‐like lesion in Indian betel‐tobacco chewers

Abstract: During an epidemiologic study of oral cancer and precancerous lesions among Indian villagers, a lichen planus-like lesion was observed in Kerala. The lesion consisted of white, wavy, parallel, non-elevated lines that could not be scraped off. The lesion occurred exclusively among chewers and at the site of placement of quid. There were no subjective symptoms. The peak prevalence of the 35 diagnosed lesions was in the 35-44 years age-group for males and 45-54 for females. There was a marked female predominance. The histologic features were very similar to those seen in oral lichen planus.

Orbits of euclidean frames under discrete linear groups

Abstract: We obtain certain sufficient conditions for the orbit of a (euclidean)p-frame over a vector spaceV,p

Effect of disorder on relaxation in the one-dimensional Glauber model

Abstract: We study the long-time relaxation of magnetization in a disordered linear chain of Ising spins from an initially aligned state. The coupling constants are ferromagnetic and nearest-neighbor only, taking valuesJ0 andJ1 with probabilitiesp and 1−p, respectively. The time evolution of the system is governed by the Glauber master equation. It is shown that for large timest, the magnetizationM(t) varies as [exp(−λ0t]φ(t), where λ0 is a function of the stronger bond strengthJ0 only, and φ(t) decreases slower than an exponential. For very long times, we find that ln φ(t) varies as −t1/3. For low enough temperatures, there is an intermediate time regime when ln φ(t) varies as −t1/2. The results can be extended to more general probability distributions of ferromagnetic coupling constants, assuming thatM(t) can only increase if any bond in the chain is strengthened. If the coupling constants have a continuous distribution in which the probability density varies as a power law near some maximum valueJ0, we find that ln φ(t) varies as −t1/3(lnt)2/3 for large times.

Extremely relativistic electron-positron twin-jets form extragalactic radio sources

Abstract: The extended extragalactic double radio sources—quasars, BL Lac-type-objects (blazars), and radio galaxies—are commonly interpreted as synchrotron sources in which extremely relativistic electrons gyrate in enhanced magnetic fields. The detection of narrow emission bridges between hot spots inside these sources and the centre of an intermediate galaxy has strongly favoured the existence of a continuous power-line feeding the extended source1,3,5. Such beams may be a universal phenomenon occurring in many—if not all—massive galaxies, including our own4. But whereas early interpretations involved low-frequency electromagnetic waves and/or relativistic particle beams, more recent work favoured non-relativistic (β <10−1) (refs 3, 6–8), or mildly relativistic (γ <10) (refs 9–11) bulk velocities for the power supply. In particular, non-relativistic bulk velocities c β have been derived from estimates of the involved kinetic energy densities u and mass densities ρ in the form β≍(2u/ρ)1/2. This can lead to large underestimates of β when ρ is derived from Faraday rotation and depolarization data, because the observed jets are likely to have a two-fluid structure, with light relativistic plasma streaming inside of heavy ‘walls’ of thermal matter, or traversing ‘swarms’ of heavy quasistatic filaments12. We suggest here that these beams consist of extremely relativistic electrons and positrons, of typical Lorentz factor γ ≳102.

High-resolution narrow-band spectra by FFT pruning

Abstract: A new method of computing high-resolution narrow-band spectra faster than the chirp z transform (CZT) and direct computation of discrete Fourier transform (DFT) is presented. This is achieved by a generalization of Markel's pruning algorithm and in combination with Skinner's pruning algorithm for the decimation-in-time FFT formulation. However, for very high resolutions it is shown that the CZT is selectively superior to the new method.

On the canonical k -types in the irreducible unitary g -modules with non-zero relative cohomology

Abstract: Let G be a connected real semi-simple Lie group with finite center, and K a maximal compact subgroup of G. We denote by go and k o the Lie algebras of G and K respectively, g and [ stand for their respective complexifications. Let g = fGP be the corresponding Cartan decomposition and 0 the corresponding Cartan involution. Let (zt,/~) be an irreducible unitary representation of G on H. Let H denote the space of K-finite vectors in H. It is of current interest to study H(g, [:H) the relative (g, [)-cohomology of the g-module H. For this cohomology to be non-zero there is a necessary condition that the infinitesimal character of H coincides with the infinitesimal character of the trivial one dimensional representation of g. If this condition is satisfied then one knows Hi(g,t:H) =Homr(Aip, H). In particular an irreducible t-component of Aip occurs in H. The precise qualitative nature of such irreducible components is not known in general (see Remark below). The same problem arises in another context also. Let F be a discrete subgroup of G such that FIG/K is a compact manifold. Then one knows that G acts on I-?(FIG) via right regular representation and that as G-representation spaces,

Genetic Analysis of a Complex Chemoreceptor

Abstract: Taste responses of Dipterans have been extensively investigated for more than three decades. V.G. Dethier (1955) used the proboscis extention test to measure the natural preferences of the flies to different chemicals. He found that blowflies accepted sugars and rejected common salt or quinine. If a mixture of an attractant and a repellent was presented, the fly’s response was determined by the ratio of the two substances. Hodgson, Lettvin and Roeder (1955) first recorded the electrical responses of the Dipteran chemoreceptors. Since then a number of workers have attempted to correlate the electrophysiological and behavioral responses of a variety of flies. (See review by Hodgson, 1974.) It is evident that taste discrimination in insects, as in mammals, is based upon a small set of categoric distinctions, but the exact nature of the sensory code remains unknown (Perkel and Bullock, 1969).

Skylab measurements of low energy cosmic rays

Abstract: In this review the present state of our knowledge on the properties of heavy ions in low energy cosmic rays measured in the Skylab mission and in other spacecrafts is summarised and the possible mechanisms of their origin are discussed. A brief review of the general features of the galactic and solar cosmic rays is given in order to understand the special features of the low energy heavy ions of cosmic rays. The results of the cosmic ray experiment in the Skylab show that in the low energy interval of 8–30 MeV/N, the abundances of oxygen, nitrogen, and neon ions, relative to carbon are enhanced by a factor of 5 to 2 as compared to high energy cosmic rays; while Mg, Si, S, and A are depleted. In 50–150 MeV/N energy interval the abundance of nuclei of Ca-Cr relative to iron-group (Z = 25–28) is found to be highly enhanced, as compared to high energy cosmic rays. Furthermore the observations of the energy spectra of O, N, and Ne ions and their fairly large fluences in the energy interval of 8–30 MeV/N below the geomagnetic cut off energy of 50 MeV/N for fully stripped nuclei at the Skylab orbit indicate that these heavy ions are probably in partly ionised states. Thus, it is found that the Skylab results represent a new type of heavy ion population of low energy cosmic rays below 50 MeV/N, in the near Earth space and their properties are distinctly different from those of high energy cosmic rays and are similar to those of the anomalous component in the interplanetary space. The available data from the Skylab can be understood at present on the hypothesis that low energy interplanetary cosmic ray ions of oxygen etc. occur in partly ionised state such as O+1,O+2, etc. and these reach the inner magnetosphere at high latitudes where stripping process occurs near mirror points and this leads to temporarily trapped ions such as O+3, O+4, etc. It is noted that the origin of these low energy heavy cosmic ray ions in the magnetosphere and in interplanetary space is not yet fully understood and new type of sources or processes are responsible for their origin and these need further studies.

Nucleon-nucleon interaction as derived from the De Rujula, Georgi, Glashow phenomenological quark-quark potential

Abstract: The nucleon-nucleon interaction, originating from the phenomenological quark-quark interaction: one gluon exchange with an ad hoc confining potential, is rigorously derived. The coupling constants of this potential and the quark masses---which determine the strengths of the $\mathrm{NN}$ potentials in the various channels---had been previously reliably determined from the masses of the $s$-wave baryons. Two distinguishing features of this study are the reliable nature of the coupling constants and quark masses used and the inclusion of the detailed radial dynamics of quarks. The main results are as follows: (i) exchange of colored quarks among other things leads to short-range strongly repulsive central $\mathrm{NN}$ potentials in the odd channels alone, i.e., it yields the saturation property of nuclear forces; (ii) the spin-orbit (tensor) potential between quarks goes over to the spin-orbit (tensor) potential between nucleons; (iii) both these spin-orbit and tensor potentials between nucleons are found to have the correct signatures but they are very weak; (iv) there is insufficient attraction in the $\mathrm{NN}$ potentials in the intermediate range, so that the colored quark-exchange mechanism is not adequate to keep the deuteron bound. The $\mathrm{NN}$ potentials derived from one gluon exchange with an ad hoc confining potential are compared finally with the corresponding phenomenological ones.NUCLEAR STRUCTURE $\mathrm{NN}$ interaction from nonrelativistic quantum chromodynamics. Quark exchange, spin-orbit and tensor potentials, short-range repulsive core.

Peripheral and Central Nervous System Projections in Normal and Mutant (Bithorax) Drosophila Melanogaster

Abstract: Projections of axons from the wing, haltere and the head are described from silver intensified cobalt preparations of normal and bithorax mutant Drosophila. Dorsal projections from the homeotic wing into thoracic ganglia and to the brain are haltere-like. Ventral projections are wing-like. In general these results are in complete agreement with previous studies by Palka et al.1 and Ghysen2. However, considerable variation of projection patterns is seen between individual mutant animals some of which were previously described only from mosaics (clones of bithorax sensory fibers into normal ganglia).1 Evidence for possible transformations of the third thoracic ganglion in mutants is therefore ambiguous.

Kinks in general relativity

Abstract: The problem of classifying topologically distinct general relativistic metrics is discussed. For a wide class of parallelizable space-time manifolds it is shown that a certain integer-valued topological invariant n always exists, and that quantization when n is odd will lead to spinor wave functionals.

A class of exact solutions for doubly anharmonic oscillators

Abstract: The solution of a difference equation in the form of an infinite continued fraction is used to obtain a class of exact solutions for the eigenfunctions and eigenvalues of doubly anharmonic oscillators described by potentials of the type (1/2)ω2x2+(1/4)λx4+(1/6)ηx6, n>0, provided certain constraints on the couplings are satisfied. The class is denumerably infinite but not complete.

Kynurenine hydroxylase mutants of the nematode Caenorhabditis elegans.

Abstract: The relation of intestinal autofluorescence to tryptophan catabolism in the free-living nematode Caenorhabditis elegans has been investigated. L-Kynurenine hydroxylase (EC. 1.14.13.9) activity has been detected in normal (wild-type) individuals. Mutants in the gene flu-1 which are characterized by an altered autofluorescence of the intestine cells, i.e., more intense than wild type and bluish purple instead of light blue have also been examined. They show a markedly reduced activity of kynurenine hydroxylase. The finding supports the previously proposed model for altered fluorescence based on chromatographic identification of tryptophan catabolites present.

The unusual supernova remnant CTB80

Abstract: The low latitude (b = 2.8°) radio source CTB80 (ret. 1) is a probable, albeit unusual, supernova remnant2 (SNR). A compact high brightness region with a very flat spectrum dominates its centre, and we find optical emission associated with this feature. Here we discuss evidence that CTB80 may be young, and in particular the possibility that it was observed in China at the beginning of the fifteenth century.

Effect of Zeste on White Complementation

Abstract: The locus in which we are most interested is the white locus; it is on the first chromosome and maps at 1.5 map units. There are five recombinationally separable sites known in this locus (Judd, 1964). The site which maps right-most is called white-spotted (w sp ); the white (w) allele which has a pure white eye color as well as white-cherry (w ch ) which has a translucent pink eye phenotype also map at the next right-most site. Basically, white forms a single complementation group with the exception of w sp ; i.e. all white mutants fail to complement each other with the exception of w sp . The phenotype of w sp itself is unusual compared to other white mutants; w sp males and females have spotted eyes of yellowish to brown pigment facets in a light color background. We are here interested in the fact that the w sp mutation partially complements all other white mutations. This is clearly seen in the case of w/ w sp and w ch /w sp flies; both these trans-heterozygotes have uniformly pigmented brownish red eyes approaching the wild type. The new observation we have made is that this complementation between w sp and other white alleles depends on the allelic conditions of the zeste locus, where zeste is also a mutation on the first chromosome at 1.0 map units. Before we describe our observation, we will briefly summarize what is known about mutations at the zeste locus.