Showing papers by "Tata Institute of Fundamental Research published in 1994"
Tohoku University1, University of Zurich2, Lawrence Berkeley National Laboratory3, Stanford University4, College of William & Mary5, University of Urbino6, CERN7, Budker Institute of Nuclear Physics8, University of California, Irvine9, Cornell University10, Argonne National Laboratory11, ETH Zurich12, Tata Institute of Fundamental Research13, Hillsdale College14, Spanish National Research Council15, Ohio State University16, University of Notre Dame17, Kent State University18, University of California, San Diego19, University of California, Berkeley20, University of Minnesota21, University of Alabama22, University of Helsinki23, Los Alamos National Laboratory24, California Institute of Technology25, George Washington University26, Syracuse University27, Lawrence Livermore National Laboratory28, Oklahoma State University–Stillwater29, University of Washington30, Max Planck Society31, Boston University32, University of California, Los Angeles33, Royal Holloway, University of London34, Université Paris-Saclay35, University of Pennsylvania36, University of Illinois at Urbana–Champaign37, University of Bristol38, University of Tokyo39, University of Delaware40, Carnegie Mellon University41, University of California, Santa Cruz42, Karlsruhe Institute of Technology43, Heidelberg University44, Florida State University45, University of Mainz46, University of Edinburgh47, Brookhaven National Laboratory48, Durham University49, University of Lausanne50, Massachusetts Institute of Technology51, University of Southampton52, Nagoya University53, University of Oxford54, Northwestern University55, University of British Columbia56, Columbia University57, Lund University58, University of Sheffield59, University of California, Santa Barbara60, Iowa State University61, University of Alberta62, University of Cambridge63
TL;DR: This biennial Review summarizes much of Particle Physics using data from previous editions, plus 2205 new measurements from 667 papers, and features expanded coverage of CP violation in B mesons and of neutrino oscillations.
Abstract: This biennial Review summarizes much of Particle Physics. Using data from previous editions, plus 2205 new measurements from 667 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors, probability, and statistics. This edition features expanded coverage of CP violation in B mesons and of neutrino oscillations. For the first time we cover searches for evidence of extra dimensions (both in the particle listings and in a new review). Another new review is on Grand Unified Theories. A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of this full Review. All tables, listings, and reviews (and errata) are also available on the Particle Data Group website: http://pdg.lbl.gov.
5,143 citations
TL;DR: In this article, the authors reported the discovery of bulk superconductivity at rather high (g10 K) values in samples having nominal compositions (i.e., they had nickel in large proportions) and showed that these materials are distinct superconductors.
Abstract: We report here our discovery of bulk superconductivity at rather high ${\mathit{T}}_{\mathit{c}}$ in samples having nominal compositions ${\mathrm{YNi}}_{4}$${\mathrm{BO}}_{0.2}$ (${\mathit{T}}_{\mathit{c}}$\ensuremath{\approxeq}12.5 K) and ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{3}$${\mathrm{O}}_{0.2}$ (${\mathit{T}}_{\mathit{c}}$\ensuremath{\approxeq}13.5 K). While ${\mathrm{YNi}}_{4}$${\mathrm{BC}}_{0.2}$ seems to be a single phase material, ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{3}$${\mathrm{C}}_{0.2}$ is a multiphase system. Our experimental results show that the two materials are distinct superconductors. Discovery of superconductivity in these materials is of significance since not only is their ${\mathit{T}}_{\mathit{c}}$ high (g10 K) but they also have nickel in large proportions. No nickel-based ternary superconductor was previously known.
535 citations
TL;DR: In this paper, it was shown that strong-weak coupling duality transformation implies the existence of supersymmetric bound states of monopoles and dyons in toroidally compactified heterotic string theory.
437 citations
TL;DR: In this article, the authors present several pieces of evidence for strong-weak coupling duality symmetry in the heterotic string theory, compactified on a six-dimensional torus, including symmetry of low energy effective action, allowed spectrum of electric and magnetic charges in the theory, allowed mass spectrum of particles saturating the Bogomol'nyi bound, and Yukawa couplings between massless neutral particles and massive charged particles.
Abstract: We present several pieces of evidence for strong–weak coupling duality symmetry in the heterotic string theory, compactified on a six-dimensional torus. They include symmetry of the (1) low energy effective action, (2) allowed spectrum of electric and magnetic charges in the theory, (3) allowed mass spectrum of particles saturating the Bogomol'nyi bound, and (4) Yukawa couplings between massless neutral particles and massive charged particles saturating the Bogomol'nyi bound. This duality transformation exchanges the electrically charged elementary string excitations with the magnetically charged soliton states in the theory. It is shown that the existence of a strong–weak coupling duality symmetry in four-dimensional string theory makes definite predictions about the existence of new stable monopole and dyon states in the theory with specific degeneracies, including certain supersymmetric bound states of monopoles and dyons. The relationship between strong–weak coupling duality transformation in string theory and target space duality transformation in the five-brane theory is also discussed.
413 citations
TL;DR: In this paper, a general procedure for constructing actions containing both potentials at the same time was described, such that the dual relationship of the field strengths arises as an equation of motion.
402 citations
TL;DR: In this paper, strong-weak coupling duality symmetry has been shown to exist in four-dimensional string theory with specific degeneracies, including certain supersymmetric bound states of monopoles and dyons.
Abstract: We present several pieces of evidence for strong-weak coupling duality symmetry in the heterotic string theory, compactified on a six dimensional torus. These include symmetry of the 1) low energy effective action, 2) allowed spectrum of electric and magnetic charges in the theory, 3) allowed mass spectrum of particles saturating the Bogomol'nyi bound, and 4) Yukawa couplings between massless neutral particles and massive charged particles saturating the Bogomol'nyi bound. This duality transformation exchanges the electrically charged elementary string excitations with the magnetically charged soliton states in the theory. It is shown that the existence of a strong-weak coupling duality symmetry in four dimensional string theory makes definite prediction about the existence of new stable monopole and dyon states in the theory with specific degeneracies, including certain supersymmetric bound states of monopoles and dyons. The relationship between strong-weak coupling duality transformation in string theory and target space duality transformation in the five-brane theory is also discussed. (Based on a talk given at the workshop on Strings and Gravity, Madras, India.)
349 citations
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15 Jan 1994-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: The DO detector as discussed by the authors is a large general purpose detector for the study of short-distance phenomena in high energy antiproton-proton collisions, now in operation at the Fermilab Tevatron collider.
Abstract: The DO detector is a large general purpose detector for the study of short-distance phenomena in high energy antiproton-proton collisions, now in operation at the Fermilab Tevatron collider. The detector focusses upon the detection of electrons, muons, jets and missing transverse momentum. We describe the design and performance of the major elements of the detector, including the tracking chambers, transition radiation detector, liquid argon calorimetry and muon detection. The associated electronics, triggering systems and data acquisition systems are presented. The global mechanical, high voltage, and experiment monitoring and control systems which support the detector are described. We also discuss the design and implementation of software and software support systems that are specific to DO.
268 citations
TL;DR: Molecular cloning, germline transformation, and biochemical experiments show that eas mutants are defective in the gene for ethanolamine kinase, which is required for a pathway of phosphatidylethanolamine synthesis.
209 citations
TL;DR: In this article, the authors obtained vertex representations for toroidal Lie algebras for any number of variables, which afford representations of certain n-variable generalizations of the Virasoro algebra that are abelian extensions of the Lie algebra of vector fields on a torus.
Abstract: Vertex representations are obtained for toroidal Lie algebras for any number of variables. These representations afford representations of certainn-variable generalizations of the Virasoro algebra that are abelian extensions of the Lie algebra of vector fields on a torus.
184 citations
172 citations
TL;DR: The picosecond time-resolved fluorescence decay data of nine single-tryptophan (trp) proteins and two multi-trp proteins in their native and denatured states were analyzed by the maximum entropy method (MEM), and the results (multimodal distributions) are contradictory to the unimodal Lorentzian distribution of lifetimes reported for some proteins in the native and Denatured state.
TL;DR: In this paper, the amplitude of the sound speed at the base of the overshoot layer below the solar convection zone is calibrated using a sequence of solar models constructed with varying extent of overshoot.
Abstract: The discontinuity in the derivatives of the sound speed at the base of the overshoot layer below the solar convection zone introduces a characteristic oscillatory component in the frequencies of solar p-modes as a function of the radial order n. The amplitude of this oscillatory part is calibrated as a function of the extent of overshoot using a sequence of solar models constructed with varying extent of overshoot. Using this calibration, an attempt is made to measure the extent of overshoot below the solar convection zone using the available frequencies of the p-modes. It is found that the observed frequencies are consistent with a solar model without overshoot. Further, taking account of the errors in observations, it is possible to put a 2-σ upper limit of 0.1 H p on the extent of overshoot.
TL;DR: In this paper, the intergalactic medium (IGM) was reionized at some redshift z≥ 5, probably due to discrete sources of ionizing photons like QSOs and young galaxies.
Abstract: Quasar spectra indicate that the intergalactic medium (IGM) was reionized at some redshift z≥ 5, probably due to discrete sources of ionizing photons like QSOs and young galaxies. In such a circumstance, ionization fronts will expand away from these sources until they percolate and encompass a substantial part of the IGM. The pressure gradients in the ionization front acting on electrons can lead to a thermally generated electric field. This field will have a non-vanishing curl and hence imply a growing magnetic field, provided the pressure gradient in the front is not parallel to the density gradient. Such a situation obtains naturally in the cosmological context because the IGM harbours primordial (growing) density fluctuations whose density gradients are not correlated with the pressure gradients produced by an arbitrarily placed ionizing source. In this process, magnetic fields can be thermally generated, over a good fraction of the IGM. In particular, they can have strengths ~3 × 10-20 G on galactic scales, and can serve as seed fields for further amplification by the galactic dynamo.
TL;DR: In this article, the authors explored the prospect of detecting a Higgs particle at LHC via its associated production with a gluon, Z or W boson, while the signal/background ratio is too small for the first process.
TL;DR: In this article, the authors give a complete proof of local background independence of the classical master action for closed strings by constructing explicitly a symplectic diffeomorphism between their state spaces mapping the corresponding non-polynomial string actions into each other.
23 May 1994
TL;DR: The minimum-degree greedy algorithm is shown to achieve a performance ratio of (Δ+2)/3 for approximating independent sets in graphs with degree bounded by Δ, and a precise characterization of the size of the independent sets found by the algorithm as a function of the independence number is found.
Abstract: Theminimum-degree greedy algorithm, or Greedy for short, is a simple and well-studied method for finding independent sets in graphs. We show that it achieves a performance ratio of (Δ+2)/3 for approximating independent sets in graphs with degree bounded by Δ. The analysis yields a precise characterization of the size of the independent sets found by the algorithm as a function of the independence number, as well as a generalization of Turan’s bound. We also analyze the algorithm when run in combination with a known preprocessing technique, and obtain an improved\((2\bar d + 3)/5\) performance ratio on graphs with average degree\(\bar d\), improving on the previous best\((\bar d + 1)/2\) of Hochbaum. Finally, we present an efficient parallel and distributed algorithm attaining the performance guarantees of Greedy.
TL;DR: In this paper, the viability of gb → tH → ttb charged-Higgs signals at the proposed LHC pp supercollider, in the decay channel tt → (bq q ′)(blν).
TL;DR: In this paper, the spherically symmetric gravitational collapse of a matter cloud with a general form of matter for the formation of a naked singularity was analyzed, and it was shown that this is related basically to the choice of initial data to the Einstein field equations, and would therefore occur in generic situations from regular initial data within the general context considered here.
Abstract: Generalizing earlier results of [1], we analyze here the spherically symmetric gravitational collapse of a matter cloud with a general form of matter for the formation of a naked singularity. It is shown that this is related basically to the choice of initial data to the Einstein field equations, and would therefore occur in generic situations from regular initial data within the general context considered here, subject to the matter satisfying the weak energy condition. The condition on initial data which leads to the formation of black hole is also characterized.
TL;DR: The organisation of the tritocerebrum of Drosophila melanogaster was studied by Bodian‐Protargol reduced silver staining, Golgi‐silver impregnation, horseradish peroxidase (HRP), and cobalt‐chloride labelling of neurones and transmission electron microscopy.
Abstract: The organisation of the tritocerebrum of Drosophila melanogaster was studied by Bodian-Protargol reduced silver staining, Golgi-silver impregnation, horseradish peroxidase (HRP), and cobalt-chloride labelling of neurones and transmission electron microscopy. Nerve fibres of six categories were found to project to the tritocerebrum. (1 and 2) The sensory fibres from the internal mouthpart sensilla known to course along pharyngeal and accessory pharyngeal nerves were found to project in mainly two tiers, in the tritocerebrum. (3) Stomodaeal nerve fibres also project along the pharyngeal nerve, to the tritocerebrum. (4) Cells of the pars intercerebralis (PI) project along the median bundle and arborise in the tritocerebrum. HRP labelling and subsequent examination by transmission electron microscopy indicated their neurosecretory nature. (5 and 6) Two tracts of ascending fibres, designated as dorsal and ventral ascending tracts, were found to project to the tritocerebrum. Some of the sensory fibres from the labial nerve extend close to the sensory projections of the tritocerebrum, suggesting a possible convergence of the two sensory inputs. In the tritocerebrum, the sensory input, the stomodaeal input, the neurosecretory fibres of PI, and the ascending fibres were found to have overlapping fields, suggesting mutual interaction. The medial subesophageal ganglion and the tritocerebrum may interact through the ventral ascending tract.
TL;DR: In this paper, a comprehensive nonequilibrium ionization (NEI) analysis of X-ray spectral data from the Einstein Observatory and EXOSAT for the supernova remnant G292.0+1.8 is presented.
Abstract: We present a comprehensive nonequilibrium ionization (NEI) analysis of X-ray spectral data from the Einstein Observatory and EXOSAT for the supernova remnant G292.0+1.8. The spectra are well described by a single-temperature, single-timescale NEI model with kT = 1.64(sub -0.19)(sup +0.29) keV and n(sub e)t = (5.55(sub -1.12)(sup +1.2) x 10(exp 10)s/cu cm, which establishes that this remnant is indeed young and in the ionizing phase of evolution of its X-ray spectrum. We determine the abundances of the elements O, Ne, Mg, Si, S, Ar, and Fe and examine their variation over the allowed range of column density, kT, and n(sub e)t. Numerical calculations of the nucleosynthesis expected for a 25 solar mass progenitor agree best with the fitted abundances; in fact the minimum rms percent difference between this model and the derived abundances is only 15%. From the fitted emission measure and a simple geometric model of the remnant we estimate the mass of X-ray-emitting plasma to be 9.3(sub -6.2)(sup +1.19) solar mass, for an assumed distance of 4.8 +/- 1.6 kpc. Additional errors on this mass estimate, from clumping of the ejecta, for example, may be substantial. No evidence was found for a difference in the thermodynamic state of the plasma as a function of elemental composition based on analysis of the individual ionization timescales of the various species. In this sense then, G292.0+1.8 resembles the remnant Cas A (another product of a massive star supernova), while it is different from the remnants of SN 1572 (Tycho) and SN 1006, both of which are believed to be from Type Ia supernovae.
TL;DR: In this article, a topological Landau-Ginzburg model with superpotential W ( X ) = X −1 was studied and the role of gravitational descendants in this theory was examined.
TL;DR: In this paper, it was proved that positive solutions of non linear equation involving the N-Laplacian in a ball in RN with Dirichlet boundary condition are radial and radially decreasing provided that the nonlinearity is a continuous function ƒ(t) (satisfying suitable growth conditions) which is strictly positive for t>0.
Abstract: In this paper, it is proved that positive solutions of non linear equation involving the N–Laplacian in a ball in RN with Dirichlet boundary condition are radial and radially decreasing provided that the nonlinearity is a continuous function ƒ(t) (satisfying suitable growth conditions) which is strictly positive for t>0. The method generalizes that of Lions for the Laplacian in two dimensions. The method of the present paper can also be extended to an analogous mixed boundary value problem in a convex cone.
TL;DR: In this article, the spherically symmetric gravitational collapse of a matter cloud with a general form of matter for the formation of a naked singularity is analyzed, and it is shown that this is related basically to the choice of initial data to the Einstein field equations and would therefore occur in generic situations from regular initial data within the general context considered here, subject to the matter satisfying the weak energy condition.
Abstract: Generalizing earlier results of Joshi and Dwivedi (Commun. Math. Phys. 146, 333 (1992); Lett. Math. Phys. 27, 235 (1993)), we analyze here the spherically symmetric gravitational collapse of a matter cloud with a general form of matter for the formation of a naked singularity. It is shown that this is related basically to the choice of initial data to the Einstein field equations, and would therefore occur in generic situations from regular initial data within the general context considered here, subject to the matter satisfying the weak energy condition. The condition on initial data which leads to the formation of black hole is also characterized.
TL;DR: In this paper, the amplitude of the oscillatory component in a solar model with an overshoot of 0.05H p is found to be consistent with that in the observed frequencies, when the composition gradient near the base of the convection zone is smooth.
Abstract: Discontinuities in the derivatives of the sound speed at the base of the overshoot layer below the solar convection zone introduce a characteristic oscillatory component in the frequencies of solar p-modes as a function of the radial order n. The amplitude of this oscillatory part may be used to measure the extent of overshoot. However, sharp changes in the mean molecular weight due to gravitational settling of helium, as well as sharp changes in the opacity due to diffusion of metals, can also give rise to an oscillatory component in the frequencies of solar p-modes. Thus the estimate of overshoot will be affected by the diffusion of helium and metals. It is found that helium diffusion tends to increase the amplitude of the oscillatory component in the frequencies of p-modes, while metal diffusion tends to decrease this amplitude, but the net effect is to increase the amplitude. Apart from diffusion, the amplitude also depends on the depth of the convection zone, and to a lesser extent on the hydrogen and metal abundance in the solar envelope. In the absence of diffusion, or when the composition gradient near the base of the convection zone is smooth, the amplitude of the oscillatory component in a solar model with an overshoot of 0.05H p is found to be consistent with that in the observed frequencies. Further, models with diffusion that have a sharp change in their composition profiles at the base of the solar convection zone do not seem to be favoured by observations.
TL;DR: In this paper, the authors present a study of the inclusive production of π0, η, Ks0 and Λ based on 929,000 hadronic Z decays recorded with the L3 detector at LEP.
TL;DR: In this paper, a review of non-linear optical investigations on dye-doped solids using low-power CW lasers is presented, where specific nonlinear processes such as self-diffraction, optical phase conjugation, two-beam coupling and polarization gratings are discussed.
Abstract: We present a brief review of non-linear optical investigations on dye-doped solids using low-power CW lasers. After a brief introduction to the photophysics of the dye molecules, we discuss specific nonlinear processes such as self-diffraction, optical phase conjugation, two-beam coupling and polarization gratings in these systems. The application potential of dye-doped solid devices is discussed.
06 Jul 1994
TL;DR: An algorithm schema for improving the approximation of algorithms for this problem, which is based on preprocessing the input by removing cliques is introduced, and an implementation of a theorem on the independence number of clique-free graphs is given, leading to the first o(Δ) ratio for the independent set problem.
Abstract: Finding maximum independent sets in graphs with bounded maximum degree is a well-studied NP-complete problem. We study two approaches for finding approximate solutions, and obtain several improved performance ratios.
TL;DR: In this paper, it was shown that the flux loops emerging from the bottom of the convection zone acquire a rotation velocity faster than the local plasma velocities, in complete contradiction to what angular momentum conservation would demand.
Abstract: Observations show that bipolar magnetic regions (BMRs) have differential rotation profiles that are faster than the local Doppler velocity profiles by about 5%, and thep-spots in the growing sunspot groups rotate faster than thef-spots. Also, the smaller spots rotate faster than the larger ones. We present detailed observations of the functional dependence of the residual rotation of sunspots on the spot size of thep- andf-spots of growing sunspot groups. Through numerical calculations of the dynamics of thin flux tubes we show that flux loops emerging from the bottom of the convection zone acquire a rotation velocity faster than the local plasma velocities, in complete contradiction to what angular momentum conservation would demand. The sunspot flux tubes need not be anchored to regions rotating faster than the surface plasma velocities to exhibit the observed faster rotation; we show that this occurs through a subtle interplay between the forces of magnetic buoyancy and drag, coupled with the important role of the Coriolis force acting on rising flux tubes. The dynamics of rising flux tubes also explains the faster rotation of smaller sunspots; we show that there is no need to evoke a radial differential rotation and anchoring of smaller spots to faster rotating regions. The simulated differential rotation profiles of thep- andf-legs of flux loops emerging in the convection zone, with a latitudinal differential rotation and velocity contours constant along cones, mimic the observed profiles for growing sunspot groups only when the flux loops emerge radially and obey Joy's law. (The ‘legs’ are defined to be the vertical part of the loops.) Also the rotation-size relation of growing sunspots is obeyed only by radially emerging loops which obey Joy's law. This constrains the fields at the bottom of the convection zone that are possible for producing the BMRs we see, to lie between 60 and 160 kG, which is in agreement with previous claims.
TL;DR: The inverse of particle addition process in the Abelian sandpile model is defined and the unique recurrent configuration corresponding to a single particle deletion is obtained by a sequence of operations called inverse avalanches.
Abstract: We define and study the inverse of particle addition process in the Abelian sandpile model. We show how to obtain the unique recurrent configuration corresponding to a single particle deletion by a sequence of operations called inverse avalanches. We study the probability distribution of ${\mathit{s}}_{1}$, the number of ``untopplings'' in the first inverse avalanche. For a square lattice, we determine Prob(${\mathit{s}}_{1}$) exactly for ${\mathit{s}}_{1}$=0, 1, 2, and 3. For large ${\mathit{s}}_{1}$, we show that Prob(${\mathit{s}}_{1}$) varies as ${\mathit{s}}_{1}^{\mathrm{\ensuremath{-}}11/8}$. In the direct avalanches, this is related to the probability distribution of the number of sites which topple as often as the site where the particle was added. These results are verified by numerical simulations.