335 research outputs found

    Commencement Address

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    Commencement address given by Arno A. Penzias, Vice President of Research at AT&T Bell Laboratories, to the Winter 1988 graduating class of The Ohio State University, St. John Arena, Columbus, Ohio, March 18, 1988

    Research at Bell

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    The molecular cloud Sagittarius B2

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    The structure of the Sgr B2 molecular cloud has been studied by detailed and extensive mappings of the CO, ^(13)CO, CS, and H_2CO (2-cm) transitions. The cloud consists of a dense core at the OH maser position plus a very large envelope 45 pc across. Sagittarius B2 is one of the most massive objects in the Galaxy, containing about 3 x 10^6 M_⊙ - an estimate arrived at independently from calculated ^(13)CO column densities, from application of the virial theorem, and from far-infrared measurements. The molecular gas has an average temperature T_k of ~ 20 K; that this is similar to the temperature of grains emitting far-infrared radiation is taken as evidence of near thermal equilibrium between dust grains and H_2. The dynamics of the gas in the cloud is found to be dominated by large-scale systematic motions with velocity not a monotonic function of radius

    Molecular Clouds in the Galactic Center Region: Carbon Monoxide Observations at 2.6 Millimeters

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    A preliminary CO emission line survey covering a strip at b = -2' from ℓ = 359°.7 to ℓ = 2°.8 is presented which shows a continuous band of emission connecting the region between Sgr A and Sgr B. A high-resolution map of the Sgr A cloud near the galactic center shows that there are at least two clouds centered within 3' of each other with a velocity difference of 35 km s^(-1). Measurement of the ^(13)C^(16)O and ^12)C^(18)O emission indicates isotopic abundances similar to those of the solar system

    The interstellar C18O/C17O ratio in the solar neighbourhood: The rho Oph cloud

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    Observations of up to ten carbon monoxide (CO and isotopomers) transitions are presented to study the interstellar C18O/C17O ratio towards 21 positions in the nearby (d~140pc) low-mass star forming cloud rho Oph. A map of the C18O J=1-0 distribution of parts of the cloud is also shown. An average 12C18O/12C17O isotopomeric ratio of 4.11 +/- 0.14, reflecting the 18O/17O isotope ratio, is derived from Large Velocity Gradient (LVG) calculations. From LTE column densities we derive a ratio of 4.17 +/-0.26. These calculations also show that the kinetic temperature decreases from about 30 K in the cloud envelope to about 10 K in the cloud cores. This decrease is accompanied by an increase of the average molecular hydrogen density from 10^4 cm-3 to >10^5 cm-3. Towards some lines of sight C18O optical depths reach values of order unity.Comment: 13 pages, 9 figures; accepted for publication in A&

    The molecular cloud Sagittarius B2

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    The structure of the Sgr B2 molecular cloud has been studied by detailed and extensive mappings of the CO, ^(13)CO, CS, and H_2CO (2-cm) transitions. The cloud consists of a dense core at the OH maser position plus a very large envelope 45 pc across. Sagittarius B2 is one of the most massive objects in the Galaxy, containing about 3 x 10^6 M_⊙ - an estimate arrived at independently from calculated ^(13)CO column densities, from application of the virial theorem, and from far-infrared measurements. The molecular gas has an average temperature T_k of ~ 20 K; that this is similar to the temperature of grains emitting far-infrared radiation is taken as evidence of near thermal equilibrium between dust grains and H_2. The dynamics of the gas in the cloud is found to be dominated by large-scale systematic motions with velocity not a monotonic function of radius

    Singularity: Raychaudhuri Equation once again

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    I first recount Raychaudhuri's deep involvement with the singularity problem in general relativity. I then argue that precisely the same situation has arisen today in loop quantum cosmology as obtained when Raychaudhuri discovered his celebrated equation. We thus need a new analogue of the Raychaudhuri equation in quantum gravity.Comment: 11 pages, Contribution to Special issue of Pramana on Raychaudhuri Equation at Cross-roads, edited by Naresh Dadhich, Pankaj Joshi and Probir Ro

    Arrival time and magnitude of airborne fission products from the Fukushima, Japan, reactor incident as measured in Seattle, WA, USA

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    We report results of air monitoring started due to the recent natural catastrophe on 11 March 2011 in Japan and the severe ensuing damage to the Fukushima Dai-ichi nuclear reactor complex. On 17-18 March 2011, we registered the first arrival of the airborne fission products 131-I, 132-I, 132-Te, 134-Cs, and 137-Cs in Seattle, WA, USA, by identifying their characteristic gamma rays using a germanium detector. We measured the evolution of the activities over a period of 23 days at the end of which the activities had mostly fallen below our detection limit. The highest detected activity amounted to 4.4 +/- 1.3 mBq/m^3 of 131-I on 19-20 March.Comment: 7 pages, 5 figures, published in Journal of Environmental Radioactivit

    Skewness in the Cosmic Microwave Background Anisotropy from Inflationary Gravity Wave Background

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    In the context of inflationary scenarios, the observed large angle anisotropy of the Cosmic Microwave Background (CMB) temperature is believed to probe the primordial metric perturbations from inflation. Although the perturbations from inflation are expected to be gaussian random fields, there remains the possibility that nonlinear processes at later epochs induce ``secondary'' non-gaussian features in the corresponding CMB anisotropy maps. The non-gaussianity induced by nonlinear gravitational instability of scalar (density) perturbations has been investigated in existing literature. In this paper, we highlight another source of non-gaussianity arising out of higher order scattering of CMB photons off the metric perturbations. We provide a simple and elegant formalism for deriving the CMB temperature fluctuations arising due to the Sachs-Wolfe effect beyond the linear order. In particular, we derive the expression for the second order CMB temperature fluctuations. The multiple scattering effect pointed out in this paper leads to the possibility that tensor metric perturbation, i.e., gravity waves (GW) which do not exhibit gravitational instability can still contribute to the skewness in the CMB anisotropy maps. We find that in a flat Ω=1\Omega =1 universe, the skewness in CMB contributed by gravity waves via multiple scattering effect is comparable to that from the gravitational instability of scalar perturbations for equal contribution of the gravity waves and scalar perturbations to the total rms CMB anisotropy. The secondary skewness is found to be smaller than the cosmic variance leading to the conclusion that inflationary scenarios do predict that the observed CMB anisotropy should be statistically consistent with a gaussian random distribution.Comment: 10 pages, Latex (uses revtex), 1 postscript figure included. Accepted for publication in Physical Review
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