Showing papers by "Tata Institute of Fundamental Research published in 1985"

Malignant transformation rate in oral submucous fibrosis over a 17-year period.

Abstract: Sixty-six patients with oral submucous fibrosis were followed-up for a period of 17 yr (median observation 10 yr) in Ernakulam District, Kerala, India. Oral cancer developed in five (7.6%) patients. The malignant transformation rate in the same sample was 4.5% over a 15-yr observation period (median 8 yr). These findings impart a high degree of malignant potential to this condition.

Distributed Processes and the Logic of Knowledge

Abstract: We establish a very natural connection between distributed processes and the logic of knowledge which promises to shed light on both areas.

Nambu-Jona-Lasinio-type effective Lagrangian: Anomalies and nonlinear Lagrangian of low-energy, large-N QCD

Abstract: We present a qualitative derivation of the chiral model from QCD. This is based on using a Nambu--Jona-Lasinio--type effective Lagrangian as an intermediate step. A detailed derivation of the anomalous low-energy Wess-Zumino term is presented. This includes vector, axial-vector, and pseudoscalar particles. The low-energy scale is set by H-barapprox.. We also present the low-energy nonlinear chiral model which generalizes the Skyrme model. The possibility of soliton solutions is indicated. There is a possible application of these ideas to electroweak theory.

Fine structure and primary sensory projections of sensilla on the maxillary palp of Drosophila melanogaster Meigen (Diptera : Drosophilidae)

Abstract: Three types of hairs were identified on the maxillary palp of Drosophila melanogaster Meigen (Diptera : Drosophilidae): (i) single-walled, multiporous sensilla basiconica, which constitute 75% of the innervated hairs; (ii) thick walled non-porous sensilla trichodea, which make up the remaining 25% of the innervated hairs; and (iii) numerous spinules, which are un-innervated. These sensilla basiconica uniformly contain 2 bipolar sense cells, whereas sensilla trichodea have a single dendrite with a tubular body at the base of each hair. A majority of the sensilla basiconica is located on the distal half of the dorsal surface, whereas sensilla trichodea are positioned on the tip and entire ventrolateral ridge of the palp. Approximately 125 axons of the sense cells join to form a single nerve. The structure of sensilla basiconica and sensilla trichodea suggests that they are olfactory and mechanosensory respectively. The contact chemoreceptors (gustatory sensilla) are conspicuously absent on the maxillary palp. Golgi silver impregnations and cobalt fills show that the primary sensory fibres from sensilla trichodea and sensilla basiconica on the maxillary palp project in the posterior suboesophageal ganglion (SOG) and the antennal lobe respectively. A single fibre projects separately either in the SOG or in the antennal lobe. In the antennal lobe, the input received from sensilla basiconica is usually bilateral and at least 5 glomeruli are innervated symmetrically on either side from both the palps. This study suggests that the sensory neurons are capable of making selective projections in the specific regions of the brain. Accordingly, the fibres from a sensillum project to the brain with respect to their functions and the individual glomeruli represent functional units of the brain, receiving inputs in a characteristic combination.

Planck length as the lower bound to all physical length scales

Abstract: The effect of quantum fluctuations of gravity on the measurement of proper distances is considered. It is shown that, when the length scales are of the order of Planck length, the concept of a unique distance between points ceases to exist. It is also shown that the quantum expectation value of the proper length is bounded from below by Planck length in any space-time.

A Priority Based Distributed Deadlock Detection Algorithm

Abstract: Deadlock handling is an important component of transaction management in a database system. In this paper, we contribute to the development of techniques for transaction management by presenting an algorithm for detecting deadlocks in a distributed database system. The algorithm uses priorities for transactions to minimize the number of messages initiated for detecting deadlocks. It does not construct any wait-for graph but detects cycles by an edge-chasing method. It does not detect any phantom deadlock (in the absence of failures), and for the resolution of deadlocks it does not need any extra computation. The algorithm also incorporates a post-resolution computation that leaves information characterizing dependence relations of remaining transactions of the deadlock cycle in the system, and this will help in detecting and resolving deadlocks which may arise in the future. An interesting aspect of this algorithm is that it is possible to compute the exact number of messages generated for a given deadlock configuration. The complexity is comparable to the best algorithm reported. We first present a basic algorithm and then extend it to take into account shared and exclusive lock modes, simultaneous acquisition of multiple locks, and nested transactions.

Primary sensory projections from the labella to the brain of Drosophila melanogaster Meigen (Diptera : Drosophilidae)

Abstract: Golgi silver impregnation of sensory neurons arising from labellar taste sensilla of Drosophila melanogaster Meigen (Diptera : Drosophilidae) revealed 7 distinct types I-VII of primary (sensory) fibres projecting to the suboesophageal ganglion (SOG) of the brain. Each fibre was classified on the bases of the neuropil volume occupied by its terminal arborisation, the shape of neuropil region receiving the arborisations and the detailed morphology of the arborisations. The primary sensory fibre projections from the labella are confined to the SOG where they project mainly in the anterior and central neuropils. No labellar sensory fibres project to posterior SOG. Of these 7 types of sensory fibres, three (III, IV and VII) show ipsilateral projections, while others have both ipsi-, and contralateral branches. Four types of interneurons are suggested to be associated with taste perception. Type A interneurons are local interneurons with arborisations confined only to the taste sensory neuropil of the SOG. The types B - D interneurons are interganglionic/output neurons with axons projecting to various brain regions-SOG, calyces of the mushroom bodies, tritocerebrum and thoracic ganglia. These projections suggest that more than one centre (SOG, tritocerebrum, calyces of the mushroom bodies and thoracic ganglia) are involved in processing gustatory information.

Two remarkable bright supernova remnants

Abstract: Statistical studies of supernova remnants (SNRs) indicate that the objects of high surface brightness are young1. This is confirmed by measurements of angular expansion for a number of such remnants and by the secular decrease in their radio flux densities2. Studies of these young SNRs are of particular interest as they can impose constraints on models of supernova outbursts and can reveal details of the initial interaction between the rapidly-expanding stellar material and the ambient interstellar medium3. Also, a high percentage of bright remnants belong to the comparatively-rare class of filled-centre SNRs. However, because of their small angular sizes, many have not been observed with sufficient resolution to determine detailed structures or, in some cases, even to verify an SNR classification. Between July 1981 and August 1984, we used the Very Large Array (VLA) of the National Radio Astronomy Observatory (NRAO) in its B, C and D configurations to clarify the morphology of several high-brightness sources from the Milne SNR catalogue4. Of these, the two sources G349.7+0.2 and G357.7−0.1 were found to be most unusual.

Chemical and magnetic stratigraphy of parts of Narmada Region, Deccan Basalt Province

Abstract: Field investigations of a 666 m thick Deccan volcanic sequence north of the River Narmada (Khalghat-Mhow traverse; 60 km) showed the presence of 21 flows, while a 549 m thick southern section comprises of 28 flows (Mandaleswar-Pipaljopa traverse: 110 km). The lava sequences essentially consist of PI and/or Pyx phyric to aphyric basalts with glassy vesicular - amygdular tops/flow breccia. On the basis of selected major and trace elements (Si, K, Ti, P, Ba, Sr, Zr), the Khalghat section is divided into three formations. The lowermost Narmada Formation is characterized by lower K, Ba, Sr, Ba/Ti, Ba/Sr and Ba/Zr than the succeeding Manpur Formation . The uppermost Mhow Formation is highly depleted in K, Ba, Sr compared to the two lower formations. Chemically, a four-unit informal stratigraphy has been adopted for the Mandaleswar section. The lower three may be correlated with the Narmada, Manpur and Mhow Fms of the Khalghat section and the upper one is labelled the Satpura Formatio n. Each formation is defined as a set of flows characterized by one or more chemical types such as 'primitive' and' evolved' ones. The palaeomagnetic results of the Khalghat section demonstrate that the lower 254m pile of flows belongs to normal polarity (N) (' Narmada Normal Epoch ') overlain by 412 m thick flows with reversed polarity (R) ('Malwa Reversed Epoch'). Interestingly, on the southern side of the river, about 21 m thick N flows are overlain by 476 m R flows, which in turn are capped by 52m thick N flows (' Satpura Normal Epoch ') resulting in an unambiguous NRN sequence in the Deccan basalt province. It appears that the northern side of the Narmada River has been thrown up relative to the southern side. Based on the correlation of the magnetic reversals in the Deccan as well as marine magnetic anomalies, it seems likely that the normally magnetized older Rajmahal traps (about 100 MA) of eastern India form the base of the Deccan basalts.

Classical diffusion on Eden trees.

Abstract: We study an aggregation process which gives rise to compact clusters with no loops. A generalization of the node-counting theorem, applicable to such branched graphs (trees), is proved. This is used to determine the spectral dimension of these clusters on square and cubic embedding lattices by Monte Carlo simulations. The results are explained in terms of the geometric structure of these trees.

A Decision Method for Temporal Logic Based on Resolution

Abstract: A decision method for linear temporal logic is presented. The given temporal formula is first converted into a normal form formula containing restricted nesting of temporal operators. The resulting formula is tested for satisfiability by using four crucial operations — Unwinding Resolution, SKIP and deletion of persistent eventual terms.

Ample divisors on abelian surfaces

Abstract: Let A be an abelian variety of dimension g, and let L be an ample line bundle on A. The algebraic equivalence class of L is determined by c^L) e H(A, Z). The latter can be viewed as the space of alternating bilinear forms on the free abelian group H^A, Z) of rank 2g. The ampleness of L implies that c^L) is (weakly) non-degenerate and consequently it determines positive integers <51} ...,Sg with Sx \S2 | . . . \Sg. Any line bundle in the algebraic equivalence class of L is a translate of L, so that the question of whether L is very ample on a fixed abelian variety A is a property of c^L). However, this is not so if A is allowed to vary. The classical theorem of Lefschetz asserts that if Si ^ 3, the line bundle L is always very ample. It is a necessary condition as well, if we require that whenever c^L) is of type (<5), L is very ample. For, it is obvious that if A = Ax x A2 and L = p*Li ® p*L2, where Lx is a line bundle of degree at most 2 on an elliptic curve Al} then L is not very ample. We wish to investigate the question of whether, given (S) = (<5l5 ...,Sg), there exist some abelian variety A and a very ample line bundle L on A of type {S\.

Time distributions for underground muons from the direction of Cygnus X-3.

Abstract: We have recently reported evidence from the Soudan-1 detector for underground muons apparently correlated with the x-ray binary Cygnus X-3. The measured, time-averaged flux was ~ 7 x l 0 ~ u c m 2 s 1 at a depth of 1800 m water equivalent. A similar observation has also been reported in data from the NUSEX (nucleon-stability experiment) detector under Mt. Blanc. These muon signals, if confirmed, may indicate either that high-energy photons or neutrinos have previously unknown interactions which produce muons with a high probability or that a new type of stable neutral particle is emitted by Cygnus X-3. In this paper, we extend our analysis of the underground-muon data presented in Ref. 1. We show that these data imply that the muon flux from Cygnus X-3 has a longer-term variability, in addition to the 4.8-h orbital period. This longer-term modulation provides additional evidence for the existence of a source. Knowledge about all time variations is important for flux comparisons with surface detectors. Such comparisons are needed to test proposed mechanisms for the production of underground muons by radiation from Cygnus X-3. The ability of a detector to separate the signal of an x-ray binary from a random background is considerably enhanced by the source periodicity. For Cygnus X-3, both the 4.8-h period and the absolute phase are accurately known from kiloelectronvolt x-ray data. The flux modulation (pulsed emission) of Cygnus X-3 at high energies according to the same ephemeris has been observed in air showers. Arrival times for air showers with primary energy ~ 1 TeV have been observed to cluster about two particular phases: 0.60 to 0.73, which dominates at teraelectronvolt energies, and 0.25, which is more common at higher energies. It is not clear what relation, if any, may exist between these air-shower data and observations of underground muons. Our data sample contains 784 000 muon events with at least eight proportional-tube hits in each of two orthogonal views. This 0.96-yr live-time sample is the same one discussed in Ref. 1. For 1183 events, the direction of arrival points within 3° of the nominal direction (declination 8 = 40.8°, right ascension a. = 307.6°) of Cygnus X-3. Using the ephemeris of Ref. 4 U0 = JD2440949.8986 (JD denotes Julian day), p0 = 0.199 6830 d, p = 1.18x 10~ ] , we calculate the Cygnus X-3 phase for each of these events. These phases can be histogrammed to produce the plot in Fig. 1(a). The peak between phases of 0.65 and 0.90 contains 60 ± 17 events, with use of a background level determined from off-source directions. The phase plot in Fig. 1(a) differs slightly from a similar plot in Ref. 1 because here we have selected the nominal direction of Cygnus X-3 rather than one about 2° off nominal, which yields about a 30% higher signal. We have used several alternative methods to estimate the statistical probability that Fig. 1 (a) represents a random fluctuation of a uniform background. Reference 1 relied principally on a X analysis. More specific tests for the presence of a Cygnus X-3 signal include a peak-over-background analysis, a Fourier-coefficient analysis, and a firstand second-moment analysis. In the case of the moment (or generalized Rayleigh) analysis, a particularly powerful constraint can be imposed by use of projections of the moments in directions specified by previous high-energy data on Cygnus X-3 (such as the 0.65-phase-peak direction). This method, which may be affected by systematic uncertainties concerning the relationship between airshower and underground-muon data, yields the phase-constrained probabilities discussed below. We have made empirical checks on the validity of these methods using both data from regions of the sky away from Cygnus X-3 and Monte Carlo-generated, simulated data samples. For Fig. 1(a), the results of our statistical analyses can be summarized as follows: A peak-over-

Search for a heavy neutrino in the β-decay of 35S

Abstract: Recent experimental evidence1 suggests that the neutrino (strictly, an antineutrino) emitted in the β-decay of tritium is a mixture of two mass eigen states ∣ν1〉 and ∣ν2〉 where ∣νe〉=cos θ∣ν1〉 + sin θ∣ν2〉 with <50 eV and =17.1±0.2 keV and sin2 θ=0.03. This conclusion is based on the observation of a ‘kink’ in the Fermi–Kurie plot2,3 of the electron energy spectrum at an energy 17.1 keV below the end point. Such an observation, if confirmed, will have far-reaching consequences in cosmology and particle physics4,5. In the experiment reported here, a search was made for such an admixture in the β-decay of 35S. We fail to confirm the presence of mixing of neutrinos with mass 17.1 keV and place an upper limit on such an admixture of 0.6% (90% confidence level).

Anomalous behavior of the Mössbauer resonance width in mixed-valence EuNi 2 P 2

Abstract: We present here the results of our detailed M\"ossbauer measurements on the mixed-valence system ${\mathrm{EuNi}}_{2}$${\mathrm{P}}_{2}$. The linewidth of the resonance exhibits a broad peak at \ensuremath{\sim}40 K. We argue that this feature is anomalous in that it cannot be understood in terms of the known mechanisms that can give rise to line broadening. The system exhibits strong mixed valence---the average valence being \ensuremath{\sim}2.5---even at T=1.4 K. This is the first Eu-based material having truly mixed valence behavior as T\ensuremath{\rightarrow}0; all others tend to approach the trivalent configuration as T\ensuremath{\rightarrow}0.

Geometrical and light-induced effects on back-gating in ion-implanted GaAs MESFET's

Abstract: Back-gating effects in GaAs MESFET's have been studied for small (10-30 µm) and large (~150 µm) back-gate separations and for different geometric positions of the back-gate. It is found that the substrate currents just at the onset of back-gating and when the channel is pinched off by the gate voltage are independent of the proximity of the back-gate. The geometric position of the back-gate is found to have a very strong influence on the back-gating characteristics. Illumination of the devices with white light gives rise to large substrate currents even for small back-gate voltages, and thus hastens the onset of back-gating. A simple qualitative model is presented to explain the observed results. Deep-level traps in the substrate, channel-substrate interface, and the channel have been studied by observing the drain current transients induced by a pulsed back-gate voltage or by a pulsed front-gate voltage. In addition to the EL2 electron trap with activation energy 0.82 eV detected in the substrate, a nondiscrete band of interface traps have been identified.

Ultra-relativistic bulk motion and radio flux variability of active galactic nuclei

Abstract: On a analyse 10 evenements importants publies de variabilite du flux en ondes metriques associes a 7 radiosources extragalactiques, dans l'hypothese ou les composantes variables dans ces sources ont un mouvement general relativiste et rayonnent selon un processus synchrotron incoherent. On a obtenu le facteur de Doppler pour chaque composante variable

Conformal invariance and string theory in compact space: Bosons

Abstract: The area law of the Nambu-Goto string is generalized to include a solid-angle-type term, which is purely topological in nature. Such a term exists and is unique provided the manifold M in which the string lives satisfies certain topological conditions. This generalization may be useful to maintain conformal invariance in case M is compact. Using methods of Polyakov and Friedan we identify the conformal anomaly coefficient with the central charge of the Virasoro algebra of this string theory. As an illustration we choose M to be a compact Lie group and compute the anomaly coefficient following the work of Knizhnik and Zamolodchikov.

Structure of the Crab Nebula: intensity and polarization at 20 cm

Abstract: On presente des cartes VLA a 20 cm de la nebuleuse du Crabe avec une resolution de 15×15 sec arc 2 . Elles revelent une emission radio renforcee associee aux filaments optiques et une excellente correlation entre la depolarisation a 20 cm et les filaments optiques brillants sur le bord de la nebuleuse. On discute de la structure generale de l'emission radio