Showing papers by "Tata Institute of Fundamental Research published in 1984"

Oral submucous fibrosis as a precancerous condition.

Abstract: An evaluation of the malignant potential of submucous fibrosis, based on observations of 89 patients with the disease in Ernakulam District, Kerala, India was done. Out of the 89 patients, 12 were referred patients and 77 were diagnosed in population based studies. At the time of first examination oral cancer was found to be coexistent in nine (10%) cases. For 66 patients follow-up observations ranging from 4 to 15 yr (median 8 yr) were available. During this period malignant transformation was observed in three patients (4.5%). Considering malignant transformation and coexistence together, oral cancer was observed in 13% of the present material. Leukoplakia was found in 26% of the patients with submucous fibrosis. Out of 42 submucous fibrosis patients biopsied, 12% showed squamous cell carcinoma, 26% epithelial dysplasia, and 76% atrophic epithelium. These findings reinforced the hypothesis that submucous fibrosis is a precancerous condition.

Restriction of stable sheaves and representations of the fundamental group

Abstract: Let X be a projective smooth variety of dimension n over an algebraically closed field k. Let H be an ample line bundle on X. A torsion free sheaf V on X is said to be stable (respectively, semistable) with respect to the polarisation H if for every proper subsheaf W c V we have deg W/rk W < deg V / r k V (respectively <) where deg W= cl(W). H\"-1, c t(W ) the first chern class and r k = rank (see [7, 13]). In [10] we proved that the restriction of a semistable sheaf V on X to a complete intersection subvariety of X in general position and of high multidegree is again semistable. We prove here that the restriction of a stable sheaf also remains stable. This has some interesting consequences. When k=~2 and d imX =2 it follows from the recent results of Donaldson [2] and Kobayashi 1-6] that any stable vector bundle V with c l (V)=0 and c2(V)=0 on the surface X comes from an irreducible unitary representation of the fundamental group rcl(X ). It follows from this and our restriction theorem that the same result holds for higher dimensional varieties as well. This answers a question of Kobayashi [6, Sect. 4, p. 161].

Interval Methods for Processing Geometric Objects

Abstract: In this approach, the parametric form is applied without the usual computational nightmare. The key is to view the parametric range as an interval, relying on subdivision algorithms.

On orbits of unipotent flows on homogeneous spaces

Abstract: We show that if (ut) is a one-parameter subgroup of SL (n, ℝ) consisting of unipotent matrices, then for any e > 0 there exists a compact subset K of SL(n, ℝ)/SL(n, ℤ) such that the following holds: for any g ∈ SL(n, ℝ) either m({t ∈ [0, T] | utg SL (n, ℤ) ∈ K}) > (1 – e)T for all large T (m being the Lebesgue measure) or there exists a non-trivial (g−1utg)-invariant subspace defined by rational equations.Similar results are deduced for orbits of unipotent flows on other homogeneous spaces. We also conclude that if G is a connected semisimple Lie group and Γ is a lattice in G then there exists a compact subset D of G such that for any closed connected unipotent subgroup U, which is not contained in any proper closed subgroup of G, we have G = DΓ U. The decomposition is applied to get results on Diophantine approximation.

Fine structure of the sensory organs of Drosophila melanogaster Meigen larva (Diptera : Drosophilidae)

Abstract: Fine structure of the prominent external and internal sensory organs of Drosophila melaogaster Meigan (Diptera : Drosophilidae) larva was determined by transmission electron microscopy (TEM). The external sensory organs, namely, antennal, maxillary, ventral and labial organs, dorsal pits, sensory cones on the 8th and 9th abdominal segments, and the sensory hairs on the body of the larva, were studied. A new knob in pit (KIP) sensillum innervated by 3 dendrites was found on the dorsolateral surface on either side. Four tufts of hairs at the posterior end of each great lateral tracheal trunk were found to be sensory with a dendrite at the base of each tuft. Internally in the pharynx of the larva, 3 groups of symmetrically located sensory organs, namely, the anteroventral, dorsal, and posteroventral groups were found. In all they contain 10 pairs of sensilla. Amongst them, 2 pairs of sensilla were found to be of the compound type; one having 9 dendrites arranged in 3 groups of 4, 3 and 2; while the other had 6 dendrites grouped as 2 and 4. In addition, 2 groups of sensilla were found on the internal dorsal fold on either side. Similarities were observed in the dendritic organisation of sensilla in the internal mouthparts of the Drosophila larva and the adult. Unlike nerves of the adult, the larval nerves connected with the dorsal and maxillary organs have a significantly thick layer of glial cells ensheathing the bundle of axons.

Sensilla on the third antennal segment of Drosophila melanogaster meigen (Diptera : Drosophilidae)

Abstract: The distribution and morphology of the sensilla on the 3rd antennal segment of Drosophila melanogaster Meigen (Diptera : Drosophilidae) were studied with light and electron microscopy. Four types of hairs were identified. Three types of hairs innervated by dendrites are sensilla basiconica, sensilla coeloconica and sensilla trichodea. They occur amongst a large number of the 4th type of uninnervated hairs or spinules. Sensilla basiconica and coeloconica can be easily identified by light microscopy on staining with 0.1016 silver nitrate in 70% ethanol. The tips of sensilla basiconica and coeloconica appear dark brown. Most of the sensilla trichodea and spinules remain unstained. Sensilla basiconica conform to the single-walled, multiporous sensilla, having poretubules and branched dendrites. Sensilla coeloconica are double-walled and have longitudinal channels near the tip. No wall pores are found on sensilla trichodea. Dendrites do not branch in sensilla coelonica and trichodea. A mechanosensory dendrite with characteristic tubular body is absent in these sensilla. Populations of sensilla basiconica and sensilla trichodea occur in diametrically opposite, distinct regions on the 3rd antennal segment-the former in the dorsomedial and the latter in the ventrolateral regions, whereas sensilla coeloconica are distributed on most of the anterior and posterior surfaces, including the cavity walls of the sacculus. The axons are arranged in distinct groups in the antennal nerves at the stalk of the 3rd segment. This grouping becomes more pronounced in the nerve prior to its entry into the brain.

Nambu-Jona-Lasinio Model: An Effective Lagrangian for Quantum Chromodynamics at Intermediate Length Scales

Abstract: A Nambu--Jona-Lasinio type model is proposed as an effective Lagrangian for quantum chromodynamics at intermediate length scales. It is shown that the SU(n) x SU(n) nonlinear sigma model, including the Wess-Zumino term, can be derived from it in the low-energy limit. Also presented is the effective nonminimal action whose minima correspond to baryons in the many-color limit.

Observable Neutrino Dirac Mass and Supergrand Unification

Abstract: A new mechanism for generating an ultralight Dirac neutrino is given. A discussion is given of how it might possibly arise in a supergrand unified theory (SUSY GUT) with a geometric type of a hierarchy. The neutrino is scaled in mass relative to its charge-$\frac{2}{3}$ family member by $\frac{{M}_{\mathrm{SUSY}}}{{M}_{\mathrm{GUT}}}$.

Principal bundles on the affine line

Abstract: We prove that any principal bundle on the affine line over a perfect field with a reductive group as structure group comes from the base field by base change.

New perturbative approach to renormalizable field theories

Abstract: A new method for obtaining perturbative predictions in quantum field theory is developed. Our method gives finite predictions, which are free from scheme ambiguities, for any quantity of interest (like a cross section or a Green's function) starting directly from the bare regularized Lagrangian. The central idea in our approach is to incorporate directly the consequences of dimensional transmutation for the predictions of the theory. We thus completely bypass the conventional renormalization procedure and the ambiguities associated with it. The case of massless theories with a single dimensionless coupling constant is treated in detail to illustrate our approach.

The Evolution of Supernova Remnants as Radio Sources

Abstract: The acceleration of relativistic electrons by hydromagnetic turbulence in shell-type supernova remnants (SNRs) is examined within the framework of previous studies of their structural evolution through interaction with the interstellar medium. The predicted evolution of the synchrotron radio emission by the electrons is in agreement with a wide variety of observations.

Epidemiologic study of the association between alcohol habits and oral leukoplakia

Abstract: In a house-to-house survey in Ernakulam district Kerala State 10914 individuals were interviewed for their tobacco and alcohol habits and examined for the presence of oral leukoplakia. Very few females (1.6%) were found to be alcohol users and they were excluded from further analysis. Among 7604 males 30.4% used alcohol regularly 25.4% occasionally and 44.2% were non-users. The prevalence of leukoplakia was significantly higher among regular (5.7%) and occasional (3.9%) users than among non-users (2.9%) of alcohol. Alcohol usage was found to be related to age as well as tobacco habits. The prevalence of leukoplakia was higher among alcohol users in each age-group as well as in each tobacco habit category. After age-adjustment the difference between alcohol users and non-users although reduced remained significant. For most tobacco habit categories the trend remained similar after age-adjustment except for the mixed habits group for which there was a reversal of the trend. The alcohol habit may perhaps produce discernible effects only in association with other "weak" etiological risk factors such as the mixed habits of chewing and smoking. (authors)

On the Rogers-Ramanujan continued fraction

Abstract: In the “Lost” note book, Ramanujan had stated a large number of results regarding evaluation of his continued fraction $$R(\tau ) = \frac{{exp2\pi i\tau /}}{{1 + }}\frac{{5exp(2\pi i\tau )}}{{1 + }}\frac{{exp(4\pi i\tau )}}{{1 + }}...$$ for certain values of τ. It is shown that all these results and many more have their source in the Kronecker limit formula.

The Brush-Trajectory Approach to Figure Specification: Some Algebraic Solutions

Abstract: The brush-trajectory method, a very natural scheme for describing two-dimensional shapes used in graphic arts and typesetting applications, has been used in only a few systems largely ¢,wing to the computational complexity involved in transforming such descriptions into raster bit maps. This paper addresses the problem. For some specific brushes and trajectories we derive algebraic solutions for describing the resulting outlines. The result of dynamic transformations on the brush as it moves along the trajectory is also studied. A special closed, smooth, convex brush defined by a Jburth-order parametric equation is introduced to describe more complex shapes. An algorithmic solution to determining the outlines for an unconstrained brush is then presented. Finally, we present some ideas on a canonical brush and its use in solving the inverse problem, that is, determininl, the brushtrajectory description from given outlines.

Computational techniques for processing parametric surfaces

Abstract: This paper presents computational techniques using which subdivision algorithms may be devised for the processing (rendering, intersection detection, silhouette detection) of parametrically defined surfaces. These algorithms work by subdividing surface patches until they are simple enough for direct handling. For example, planar surface patches can be handled analytically. For interference it is necessary to box the surface as well. The computational techniques presented are essentially for efficient computation of surface properties needed by the processing tasks. The three properties considered are: (1) Euclidean bounds: this is done by working in extrema in x, y, and z over the patch; (2) planarity estimate: this test is defined in terms of the linearity of constituent curves; (3) Local visibility: which says whether a patch is totally visible, invisible, or partially visible from a given viewpoint. Rendering algorithms make use of this information. This too is done by working in extrema of the visibility function. All the techniques are based on the parametric form of the surface representation. The class of surfaces that can be handled by these techniques is very large, basically C2 continuous surfaces. A class of surfaces known as product surfaces is specially introduced as the above methods are extremely efficient for this class. Application of these methods to bicubic surfaces is also discussed.

Perfect-fluid higher-dimensional cosmologies. II.

Abstract: A higher-dimensional toroidal universe containing a perfect fluid obeying the equation of state /ital p/=(..gamma../minus/1)/rho/ is considered. A previousanalysis of the underlying equations of motion is extended to arbitrary valuesof ..gamma... Solutions to the latter are studied near their singular points.It is found that in these regimes the curvature and matter terms aregenerically unimportant (except when ..gamma..=2) and that thesuperexponential inflation of the external dimensions is driven by a cross term/similar to/(/ital R/dot ////ital R/)(/ital r/dot ////ital r/). This term could produce a large amountof entropy. This makes the resolution of the flatness and horizon problems inthese models even easier than believed previously.

Pyroelectric materials

Abstract: This paper presents a review of pyroelectric materials. The physics of pyroelectric materials is described. Various pyroelectric materials are compared for their efficiency in the detection of radiation. Current trends in pyroelectric material technology are highlighted.

Energy-extraction processes from a Kerr black hole immersed in a magnetic field. I. Negative-energy states

Abstract: This is the first of two papers on the energy-extraction processes near a Kerr black hole immersed in a magnetic field. In this paper we shall consider the consequences of a dipole field extending to infinity matched on to a uniform field in the interior which contains the Kerr black hole. The magnetic fields considered are perturbative in nature. The matching of the fields is imperative owing to the "no-hair theorem" and the second law of black-hole physics. Two intriguing situations arising in this context are discussed, namely, (1) the second law of black-hole physics and (2) the law of conservation of energy in an energy-extraction process. At first sight both these laws seem to be violated. These issues arise basically because in the presence of the magnetic field there can exist negative-energy states even for $Lg0$ particles. These issues get resolved by realizing that it is the sign of ${P}_{\ensuremath{\phi}}=L\ensuremath{-}e{A}_{\ensuremath{\phi}}$ and not $L$ which determines a corotating or counterrotating orbit. It is also shown that negative-energy states can exist away from the horizon in the presence of either of the fields, the dipole and the uniform, thus favoring energy-extraction processes away from the black hole. This type of energy extraction is solely a consequence of the magnetic field. Also, a fairly detailed analysis of the effective-potential curves is provided, mainly relevant to the existence of negative energies and energy extraction. The formalism of the energy-extraction process will be considered in the second paper.

Topological cross sections and charged particle multiplicities inpp interactions at 360 GeV/c

Abstract: Using data obtained with EHS equipped with the Rapid Cycling Bubble Chamber (RCBC) exposed to a proton beam of 360 GeV/c, we calculate topological cross sections. We present in great detail the procedure and the techniques used to correct raw data. Finally, we give multiplicity moments and multiplicity correlations and we compare the values obtained in our experiment, together with data at other energies, with different models.

Time-dependent Aharonov-Bohm Hamiltonian and admissibility criteria of quantum wave functions

Abstract: Self-adjointness of the time-independent Aharonov-Bohm Hamiltonian is shown to allow a continuous family of different dynamics including those following from Pauli's criterion of rotational invariance, Aharonov-Bohm criterion of single valuedness and a version of Pauli's criterion appropriate to cylindrical symmetry suggested by Henneberger. A time-dependent fluxF(t) linking the Aharonov-Bohm solenoid leads to the time-dependent AB Hamiltonian. Explicit solutions in cases with and without inaccessible regions for the charged particle rule out applicability of both versions of the Pauli criterion. The solutions contain one time-independent parameter α, integer values of which correspond to single-valued wave functions. Any real (integer or noninteger) value of α is allowed. Charge and current densities depend on α andF(t) only through the combination α−eF(t)/2π and lead to the conclusion that physical effects of changing the flux during an experiment can be understood as local effects of the electric field inevitably associated with changing magnetic flux.

Semistable sheaves on homogeneous spaces and abelian varieties

Abstract: In this paper we prove that semistable sheaves with zero Chern classes on homogeneous spaces are trivial and semistable sheaves on abelian varieties with zero Chern classes are filtered by line bundles numerically equivalent to zero. The method consists in reducing modp and then showing that the Frobenius morphism preserves semistability on the above class of varieties. For technical reasons, we have to assume boundedness of semistable sheaves in charp.

The Wess-Zumino term and fermionic solitons

Abstract: In [1, 2] Witten derived important consequences of the topological structure of σ-models. We rederive them from the canonical viewpoint and outline a systematic approach to similar questions.