3,495 research outputs found
The Interstellar Medium of IRAS 08572+3915 NW: H3+ and Warm High Velocity CO
We confirm the first detection of the molecular ion H3+ in an extragalactic
object, the highly obscured ultraluminous galaxy IRAS 08572+3915 NW. We also
have detected absorption lines of the fundamental band of CO in this galaxy.
The CO absorption consists of a cold component close to the systemic velocity
and warm, highly blueshifted and redshifted components. The warm blueshifted
component is remarkably strong and broad and extends at least to -350 km/s.
Some analogies can be drawn between the H3+ and cold CO in IRAS08572+3915 NW
and the same species seen toward the Galactic center. The profiles of the warm
CO components are not those expected from a dusty torus of the type thought to
obscure active galactic nuclei. They are probably formed close to the dust
continuum surface near the buried and active nucleus and are probably
associated with an unusual and energetic event there.Comment: 21 pages, 4 postscript figures, accepted by Ap
Absorption Line Survey of H3+ toward the Galactic Center Sources III. Extent of the Warm and Diffuse Clouds
We present follow-up observations to those of Geballe & Oka (2010), who found
high column densities of H3+ ~100 pc off of the Galactic center (GC) on the
lines of sight to 2MASS J17432173-2951430 (J1743) and 2MASS J17470898-2829561
(J1747). The wavelength coverages on these sightlines have been extended in
order to observe two key transitions of H3+, R(3,3)l and R(2,2)l, that
constrain the temperatures and densities of the environments. The profiles of
the H3+ R(3,3)l line, which is due only to gas in the GC, closely matches the
differences between the H3+ R(1,1)l and CO line profiles, just as it does for
previously studied sightlines in the GC. Absorption in the R(2,2)l line of H3+
is present in J1747 at velocities between -60 and +100 km/s. This is the second
clear detection of this line in the interstellar medium after GCIRS 3 in the
Central Cluster. The temperature of the absorbing gas in this velocity range is
350 K, significantly warmer than in the diffuse clouds in other parts of the
Central Molecular Zone. This indicates that the absorbing gas is local to Sgr B
molecular cloud complex. The warm and diffuse gas revealed by Oka et al. (2005)
apparently extends to ~100 pc, but there is a hint that its temperature is
somewhat lower in the line of sight to J1743 than elsewhere in the GC. The
observation of H3+ toward J1747 is compared with the recent Herschel
observation of H2O+ toward Sgr B2 and their chemical relationship and
remarkably similar velocity profiles are discussed.Comment: 6 pages, 3 figures, 2 tables, Accepted for publication in
Publications of the Astronomical Society of Japa
Conceptual Commitments of the LIDA Model of Cognition
Abstract
Significant debate on fundamental issues remains in the subfields of cognitive science, including perception, memory, attention, action selection, learning, and others. Psychology, neuroscience, and artificial intelligence each contribute alternative and sometimes conflicting perspectives on the supervening problem of artificial general intelligence (AGI). Current efforts toward a broad-based, systems-level model of minds cannot await theoretical convergence in each of the relevant subfields. Such work therefore requires the formulation of tentative hypotheses, based on current knowledge, that serve to connect cognitive functions into a theoretical framework for the study of the mind. We term such hypotheses âconceptual commitmentsâ and describe the hypotheses underlying one such model, the Learning Intelligent Distribution Agent (LIDA) Model. Our intention is to initiate a discussion among AGI researchers about which conceptual commitments are essential, or particularly useful, toward creating AGI agents.</jats:p
An Outbreak of Salmonella typhimurium at a teaching hospital
An outbreak of Salmonella typhimurium infection in December 1996 affected 52 patients, relatives, and staff of a large teaching hospital in southeast Queensland. Assorted sandwiches were identified as the vehicle of transmission. This article describes the outbreak investigation and demonstrates the importance of food hygiene and timely public health interventions
Observations of H3+ in the Diffuse Interstellar Medium
Surprisingly large column densities of H3+ have been detected using infrared
absorption spectroscopy in seven diffuse cloud sightlines (Cygnus OB2 12,
Cygnus OB2 5, HD 183143, HD 20041, WR 104, WR 118, and WR 121), demonstrating
that H3+ is ubiquitous in the diffuse interstellar medium. Using the standard
model of diffuse cloud chemistry, our H3+ column densities imply unreasonably
long path lengths (~1 kpc) and low densities (~3 cm^-3). Complimentary
millimeter-wave, infrared, and visible observations of related species suggest
that the chemical model is incorrect and that the number density of H3+ must be
increased by one to two orders of magnitude. Possible solutions include a
reduced electron fraction, an enhanced rate of H2 ionization, and/or a smaller
value of the H3+ dissociative recombination rate constant than implied by
laboratory experiments.Comment: To be published in Astrophysical Journal, March 200
Linear and nonlinear modulus surfaces in stress space, from stress-strain measurements on Berea sandstone
International audienceThe elastic response of many rocks to quasistatic stress changes is highly nonlinear and hysteretic, displaying discrete memory. Rocks also display unusual nonlinear response to dynamic stress changes. A model to describe the elastic behavior of rocks and other consolidated materials is called the Preisach-Mayergoyz (PM) space model. In contrast to the traditional analytic approach to stress-strain, the PM space picture establishes a relationship between the quasistatic data and a number density of hysteretic mesoscopic elastic elements in the rock. The number density allows us to make quantitative predictions of dynamic elastic properties. Using the PM space model, we analyze a complex suite of quasistatic stress-strain data taken on Berea sandstone. We predict a dynamic bulk modulus and a dynamic shear modulus surface as a function of mean stress and shear stress. Our predictions for the dynamic moduli compare favorably to moduli derived from time of flight measurements. We derive a set of nonlinear elastic constants and a set of constants that describe the hysteretic behavior of the sandstone
Enhanced cosmic-ray flux toward zeta Persei inferred from laboratory study of H3+ - e- recombination rate
The H3+ molecular ion plays a fundamental role in interstellar chemistry, as
it initiates a network of chemical reactions that produce many interstellar
molecules. In dense clouds, the H3+ abundance is understood using a simple
chemical model, from which observations of H3+ yield valuable estimates of
cloud path length, density, and temperature. On the other hand, observations of
diffuse clouds have suggested that H3+ is considerably more abundant than
expected from the chemical models. However, diffuse cloud models have been
hampered by the uncertain values of three key parameters: the rate of H3+
destruction by electrons, the electron fraction, and the cosmic-ray ionisation
rate. Here we report a direct experimental measurement of the H3+ destruction
rate under nearly interstellar conditions. We also report the observation of
H3+ in a diffuse cloud (towards zeta Persei) where the electron fraction is
already known. Taken together, these results allow us to derive the value of
the third uncertain model parameter: we find that the cosmic-ray ionisation
rate in this sightline is forty times faster than previously assumed. If such a
high cosmic-ray flux is indeed ubiquitous in diffuse clouds, the discrepancy
between chemical models and the previous observations of H3+ can be resolved.Comment: 6 pages, Nature, in pres
H3+ in Diffuse Interstellar Clouds: a Tracer for the Cosmic-Ray Ionization Rate
Using high resolution infrared spectroscopy we have surveyed twenty
sightlines for H3+ absorption. H3+ is detected in eight diffuse cloud
sightlines with column densities varying from 0.6x10^14 cm^-2 to 3.9x10^14
cm^-2. This brings to fourteen the total number of diffuse cloud sightlines
where H3+ has been detected. These detections are mostly along sightlines
concentrated in the Galactic plane, but well dispersed in Galactic longitude.
The results imply that abundant H3+ is common in the diffuse interstellar
medium. Because of the simple chemistry associated with H3+ production and
destruction, these column density measurements can be used in concert with
various other data to infer the primary cosmic-ray ionization rate, zeta_p.
Values range from 0.5x10^-16 s^-1 to 3x10^-16 s^-1 with an average of 2x10^-16
s^-1. Where H3+ is not detected the upper limits on the ionization rate are
consistent with this range. The average value of zeta_p is about an order of
magnitude larger than both the canonical rate and rates previously reported by
other groups using measurements of OH and HD. The discrepancy is most likely
due to inaccurate measurements of rate constants and the omission of effects
which were unknown when those studies were performed. We believe that the
observed column density of H3+ is the most direct tracer for the cosmic-ray
ionization rate due to its simple chemistry. Recent models of diffuse cloud
chemistry require cosmic-ray ionization rates on the order of 10^-16 s^-1 to
reproduce observed abundances of various atomic and molecular species, in rough
accord with our observational findings.Comment: Accepted to ApJ, 35 pages, 5 figures, 5 table
Insights from the 2006 Disease Management Colloquium
This roundtable discussion emanates from the presentations given and issues raised at the 2006 Disease Management Colloquium, which was held May 10â12, 2006 in Philadelphia, Pennsylvania
Stellar and gaseous abundances in M82
The near infrared (IR) absorption spectra of starburst galaxies show several
atomic and molecular lines from red supergiants which can be used to infer
reliable stellar abundances. The metals locked in stars give a picture of the
galaxy metallicity prior to the last burst of star formation. The enrichment of
the new generation of stars born in the last burst can be traced by measuring
the hot gas in the X-rays. For the first time detailed stellar abundances in
the nuclear region of the starburst galaxy M82 have been obtained. They are
compared with those of the hot gas as derived from an accurate re-analysis of
the XMM and Chandra nuclear X-ray spectra. The cool stars and the hot gas
suggest [Fe/H]=-0.35+/-0.2 dex, and an overall [Si,Mg/Fe] enhancement by 0.4
and 0.5 dex, respectively. This is consistent with a major chemical enrichment
by SNe II explosions in recursive bursts on short timescales. Oxygen is more
puzzling to interpret since it is enhanced by 0.3 dex in stars and depleted by
0.2 dex in the hot gas. None of the standard enrichment scenarios can fully
explain such a behavior when compared with the other alpha-elements.Comment: APJ, in pres
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