16,469 research outputs found
The essential signature of a massive starburst in a distant galaxy
Observations of carbon monoxide (CO) emission in high redshift (z>2) galaxies
indicate the presence of large amounts of molecular gas. Many of these galaxies
contain an active galactic nucleus (AGN) powered by accretion of gas onto a
supermassive black hole, and a key question is whether their extremely high
infrared luminosities result from the AGN, or from bursts of massive star
formation (associated with the molecular gas), or both. In the Milky Way,
high-mass stars form in the dense cores of interstellar molecular clouds; gas
densities are n(H2)>105 cm-3 in the cores. Recent surveys show that virtually
all galactic sites of high-mass star formation have similarly high densities.
The bulk of the cloud material traced by CO observations is at a much lower
density. In galaxies in the local Universe, the HCN(J=1-0) line is an effective
tracer of the high-density molecular gas. Here we report observations of HCN
emission in the early Universe from the infrared luminous 'Cloverleaf' quasar
(at a redshift z=2.5579). The HCN line luminosity indicates the presence of 10
billion solar masses of very dense gas, an essential feature of an immense
starburst that contributes, together with the AGN it harbors, to its high
infrared luminosity.Comment: PDF pape
High Redshift HCN Emission: Dense Star-Forming Molecular Gas in IRAS F10214+4724
Hydrogen cyanide emission in the J=1-0 transition has been detected at
redshift z=2.2858 in IRAS F10214+4724 using the Green Bank Telescope . This is
the second detection of HCN emission at high redshift. The large HCN line
luminosity in F10214 is similar to that in the Cloverleaf (z=2.6) and the
ultra-luminous infrared galaxies Mrk231 and Arp220. This is also true of the
ratio of HCN to CO luminosities. The ratio of far-infrared luminosity to HCN
luminosity, an indicator of the star formation rate per solar mass of dense
gas, follows the correlation found for normal spirals and infrared luminous
starburst galaxies. F10214 clearly contains a starburst that contributes,
together with its embedded quasar, to its overall infrared luminosity. A new
technique for removing spectral baselines in the search for weak, broad
emission lines is presented.Comment: 9 pages, 2 figures; accepted ApJ(Letters
Energy Conversion Alternatives Study (ECAS), General Electric Phase 1. Volume 3: Energy conversion subsystems and components. Part 1: Bottoming cycles and materials of construction
Energy conversion subsystems and components were evaluated in terms of advanced energy conversion systems. Results of the bottoming cycles and materials of construction studies are presented and discussed
Some new results concerning the vacuum in Dirac Hole Theory
In Dirac's hole theory the vacuum state is generally believed to be the state
of minimum energy. It will be shown that this is not, in fact, the case and
that there must exist states in hole theory with less energy than the vacuum
state. It will be shown that energy can be extracted from the hole theory
vacuum state through the application of an electric field.Comment: Accepted by Physica Scripta, 19 page
Daytime ClO over McMurdo in September 1987: Altitude profile retrieval accuracy
During the 1987 National Ozone Expedition, mm-wave emission line spectra of the 278.6 GHz rotational stratospheric ClO were observed at McMurdo Station, Antarctica. The results confirm the 1986 discovery of a lower stratospheric layer with approximately 100 times the normal amount of ClO; the 1987 observations, made with a spectrometer bandwidth twice that used in 1986, make possible a more accurate retrieval of the altitude profile of the low altitude component of stratospheric ClO from the pressure broadened line shape, down to approximately 16 km. The accuracy of the altitude profile retrievals is discussed, using the daytime (09:30 to 19:30, local time) data from 20 to 24 September, 1987 as an example. The signal strength averaged over this daytime period is approx. 85 percent of the midday peak value. The rate of ozone depletion implied by the observed ClO densities is also discussed
Quantitative observations of the behavior of anomalous low altitude ClO in the Antarctic spring Stratosphere, 1987
During the second National Ozone Expedition ground-based observations at McMurdo Station Antarctica were performed which resulted in a second season's measurement of abnormally large amounts of ClO in the Antarctic spring stratosphere. The original measurements of 1986, in which the presence of this anomalous layer was first discovered, were limited in low altitude recovery of the ClO mixing ratio profile by the restrictions of the spectral bandwidth (256 MHz) which was used to measure the pressure-broadened ClO emission line shape. The 1987 measurements were marked by the use of twice the spectral bandpass employed the previous year, and allow a better characterization of the ClO mixing ratio profile in the critical altitude range 18 to 25 km. In-situ aircraft measurements of ClO made over the Palmer Peninsula during Aug. and Sept. of 1987 by Anderson, et al. effectively determined the important question of the ClO mixing ratio profile at altitudes inaccessible to our technique, below approximately 18 to 18.5 km. These flights did not penetrate further than 75 deg S, however, (vs 78 deg S for McMurdo) and were thus limited to coverage near the outer boundaries of the region of severest ozone depletion over Antarctica in 1987, did not reach an altitude convincingly above that of the peak mixing ratio for ClO, and were not able to make significant observations of the diurnal variation of ClO. The two techniques, and the body of data recovered by each, thus complement one another in producing a full picture of the anomalous ClO layer intimately connected with the region of Antarctic spring ozone depletion. An analysis is presented of the mixing ratio profile from approximately 18 to 45 km, the diurnal behavior, and the secular change in ClO over McMurdo Station during Sept. and early Oct. 1987
Hierarchical Dobinski-type relations via substitution and the moment problem
We consider the transformation properties of integer sequences arising from
the normal ordering of exponentiated boson ([a,a*]=1) monomials of the form
exp(x (a*)^r a), r=1,2,..., under the composition of their exponential
generating functions (egf). They turn out to be of Sheffer-type. We demonstrate
that two key properties of these sequences remain preserved under
substitutional composition: (a)the property of being the solution of the
Stieltjes moment problem; and (b) the representation of these sequences through
infinite series (Dobinski-type relations). We present a number of examples of
such composition satisfying properties (a) and (b). We obtain new Dobinski-type
formulas and solve the associated moment problem for several hierarchically
defined combinatorial families of sequences.Comment: 14 pages, 31 reference
Masses, luminosities and dynamics of galactic molecular clouds
Star formation in galaxies takes place in molecular clouds and the Milky Way is the only galaxy in which it is possible to resolve and study the physical properties and star formation activity of individual clouds. The masses, luminosities, dynamics, and distribution of molecular clouds, primarily giant molecular clouds in the Milky Way are described and analyzed. The observational data sets are the Massachusetts-Stony Brook CO Galactic Plane Survey and the IRAS far IR images. The molecular mass and infrared luminosities of glactic clouds are then compared with the molecular mass and infrared luminosities of external galaxies
Phase transitions in the q-voter model with two types of stochastic driving
In this paper we study nonlinear -voter model with stochastic driving on a
complete graph. We investigate two types of stochasticity that, using the
language of social sciences, can be interpreted as different kinds of
nonconformity. From a social point of view, it is very important to distinguish
between two types nonconformity, so called anti-conformity and independence. A
majority of works suggests that these social differences may be completely
irrelevant in terms of microscopic modeling that uses tools of statistical
physics and that both types of nonconformity play the role of so called 'social
temperature'. In this paper we clarify the concept of 'social temperature' and
show that different type of 'noise' may lead to qualitatively different
emergent properties. In particularly, we show that in the model with
anti-conformity the critical value of noise increases with parameter ,
whereas in the model with independence the critical value of noise decreases
with the . Moreover, in the model with anti-conformity the phase transition
is continuous for any value of , whereas in the model with independence the
transition is continuous for and discontinuous for
Tracer Applications of Noble Gas Radionuclides in the Geosciences
The noble gas radionuclides, including 81Kr (half-life = 229,000 yr), 85Kr
(11 yr), and 39Ar (269 yr), possess nearly ideal chemical and physical
properties for studies of earth and environmental processes. Recent advances in
Atom Trap Trace Analysis (ATTA), a laser-based atom counting method, have
enabled routine measurements of the radiokrypton isotopes, as well as the
demonstration of the ability to measure 39Ar in environmental samples. Here we
provide an overview of the ATTA technique, and a survey of recent progress made
in several laboratories worldwide. We review the application of noble gas
radionuclides in the geosciences and discuss how ATTA can help advance these
fields, specifically determination of groundwater residence times using 81Kr,
85Kr, and 39Ar; dating old glacial ice using 81Kr; and an 39Ar survey of the
main water masses of the oceans, to study circulation pathways and estimate
mean residence times. Other scientific questions involving deeper circulation
of fluids in the Earth's crust and mantle also are within the scope of future
applications. We conclude that the geoscience community would greatly benefit
from an ATTA facility dedicated to this field, with instrumentation for routine
measurements, as well as for research on further development of ATTA methods
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