Cosmic evolution of extragalactic C 1, C 2, and CO luminosity

Carbon is the fourth most abundant element in the Galaxy with an abundance of approximately 4 x 10(exp -4) relative to hydrogen. Of all abundant metals it is the easiest to observe in the interstellar medium (ISM). Carbon can be found in four dominant forms: dust grains, C 2, C 1, and CO. The latter is the most abundant molecule (next to H2) in molecular clouds. All three gas-phase forms produce strong sub-mm wavelength emission lines and are the principal tracers of the warm and dense neutral phases of the ISM. We calculate the gas-phase abundances of neutral carbon (C 1), ionized carbon (C 2), and carbon monoxide (CO) as a function of cosmic time or redshift z in an idealized scenario of galactic evolution

Interstellar Bow Shocks around Fast Stars Passing through the Local Interstellar Medium

Bow-shocks are produced in the local interstellar medium by the passage of fast stars from the Galactic thin-disk and thick-disk populations with velocities $V_* =$ 40-80 km/s. Stellar transits of local H I clouds occur every 3500-7000 yr on average and last between $10^4$ and $10^5$ yr. There could be 10-20 active bow shocks around low-mass stars inside clouds within 10-15 pc of the Sun. At local cloud distances of 3-10 pc, their turbulent wakes have transverse radial extents $R_{\rm wake} \approx$ 10-300 AU, angular sizes 10-100 arcsec, and Lyman-alpha surface brightnesses of 2-8 Rayleighs in gas with total hydrogen density $n_H \approx 0.1~{\rm cm}^{-3}$ and $V_* =$ 40-80 km/s. These transit wakes may cover an area fraction $f_A \approx (R_{\rm wake}/R_{\rm cl}) \approx 10^{-3}$ of local H I clouds and be detectable in IR (dust), UV (Lya, two-photon), or non-thermal radio emission. Turbulent heating in these wakes could produce the observed elevated rotational populations of H$_2$ ($J \geq 2$) and influence the endothermic formation of CH$^+$ in diffuse interstellar gas at $T > 10^3$ K.Comment: Accepted to Astrophysical Journal, 12 pages with one tabl

The HI Environment of Nearby Lyman-alpha Absorbers

We present the results of a VLA and WSRT search for HI emission from the vicinity of seven nearby clouds, which were observed in Lya absorption with HST toward Mrk335, Mrk501 and PKS2155-304. We searched a volume of 40' x 40' x 1000 km/s. The HI mass sensitivity (5 sigma) varies from 5x10^6 to 5x10^8 Msun. We detected HI emission in the vicinity of four out of seven absorbers. The closest galaxy is a small dwarf galaxy at a projected distance of 68/h kpc from the sight line toward Mrk335. It has the same velocity (V=1970 km/s) as one of the absorbers, and has an HI mass of only 4x10^7 Msun. We found a more luminous galaxy at the velocity (V=5100 km/s) of one of the absorbers toward PKS2155-304, 230/h kpc from the sight line. Two other, stronger absorbers toward PKS2155-304 at V=17,000 km/s are associated with a loose group of three bright spiral galaxies, at projected distances of 300 to 600/h kpc. These results support the conclusion that most nearby Lya forest clouds trace the large-scale structures outlined by optically luminous galaxies. We do not find any evidence for a physical association between an absorber and its closest galaxy.Comment: 4 Tables, 11 Figures, to be published in Astron J. (Oct 1996) Vol 11

Effects of zinc oxide filler on the curing and mechanical response of alkyd coatings

The mechanical properties of an alkyd resin filled with zinc oxide pigment were studied at different concentrations over a wide range of time scales using dynamic mechanical analysis, quartz crystal rheometry and nanoindentation. The motivation for this work stems from the interest in accessing the long-term properties of paint coatings by studying the mechanical properties of historic paints. In this foundational work, we compare three different modalities of mechanical measurements and systematically determine the effect of pigment filler loading on the measured properties. Quantitative agreement between the methods is obtained when the characteristic time scales of each of the methods is taken into account. While nanoindentation is the technique most readily applied to historic paint samples, the rheometric quartz crystal microbalance (rheo-QCM) is the best suited for obtaining mechanistic information from measurements of paint properties over time, provided that appropriate thin-film samples can be produced. In these studies we find that ZnO increases the rate of oxidation of the alkyd during the initial stages of cure by an amount that depends on the ZnO content

Legal Mechanisms for Governing the Transition of Key Domain Name Functions to the Global Multi-Stakeholder Community

This Chapter proposes an alternative approach to the IANA transition that migrates the existing core contractual requirements imposed by the US government to the existing IANA functions customers. It also advances modest internal accountability revisions that could be undertaken within ICANN’s existing structure. Specifically, it advocates that the Independent Review Tribunal charged with reviewing certain ICANN board of directors-related decisions be selected by a multi-stakeholder committee rather than being subject to approval by ICANN and expanding the grounds for review to cover all of the rubrics recommended by ICANN’s “Improving Institutional Confidence” process in 2008-2009, including fairness, fidelity to the power, cogency of decision making and addressing the public interest. This new tribunal could be drawn from a standing panel of internationally recognized relevant technical experts, as well as internationally recognized jurists. Members of ICANN’s various stakeholder groups and the public should be able to make comments on the proposed bench before final appointment

Gamma-ray burst constraints on the galactic frequency of extra-solar Oort clouds

With the strong CGRO/BATSE evidence that most gamma-ray bursts do not come from galactic neutron stars, models involving the accretion of a comet onto a neutron star (NS) no longer appear to be strong contenders for explaining the majority of bursts. If this is the case, then it is worth asking whether the lack of an observed galactic gamma-ray burst population provides a useful constraint on the number of comets and comet clouds in the galaxy. Owing to the previously unrecognized structural weakness of cometary nuclei, we find the capture cross sections for comet-NS events to be much higher than previously published estimates, with tidal breakup at distances R(sub b) approximately equals to 4 x 10(exp 10) cm from the NS. As a result, impacts of comets onto field NS's penetrating the Oort Clouds of other stars are found to dominate all other galactic NS-comet capture rates by a factor of 100. This in turn predicts that if comet clouds are common, there should be a significant population of repeater sources with (1) a galactic distribution, (2) space-correlated repetition, and (3) a wide range of peak luminosities and luminosity time histories. If all main sequences stars have Oort Clouds like our own, we predict approximately 4000 such repeater sources in the Milky Way at any time, each repeating on timescales of months to years. Based on estimates of the sensitivity of the CGRO/BATSE instrument and assuming isotropic gamma-ray beaming from such events, we estimate that a population of approximately 20-200 of these galactic NS-Oort Cloud gamma-ray repeater sources should be detectable by CGRO. In addition, if giant planet formation is common in the galaxy, we estimate that the accretion of isolated comets injected to the interstellar medium by giant planet formation should produce an additional source of galactic, nonrepeating events. Comparing these estimates to the three to four soft gamma-ray repeater sources detected by BATSE, one is forced to conclude that (1) comet impacts on NS's are inefficient at producing gamma-rays; or (2) the gamma-rays from such events are highly beamed; or (3) the fraction of stars in the galaxy with Oort Cloud like our own is not higher than a few percent