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Sample records for dust clumps quantifying

  1. Glass Frit Clumping And Dusting

    SciTech Connect

    Steimke, J. L.

    2013-09-26

    DWPF mixes a slurry of glass frit (Frit 418) and dilute (1.5 wt%) formic acid solution with high level waste in the Slurry Mix Evaporator (SME). There would be advantages to introducing the frit in a non-slurry form to minimize water addition to the SME, however, adding completely dry frit has the potential to generate dust which could clog filters or condensers. Prior testing with another type of frit, Frit 320, and using a minimal amount of water reduced dust generation, however, the formation of hard clumps was observed. To examine options and behavior, a TTQAP [McCabe and Stone, 2013] was written to initiate tests that would address these concerns. Tests were conducted with four types of glass frit; Frit 320, DWPF Frit 418, Bekeson Frit 418 and Multi-Aspirator Frit 418. The last two frits are chemically identical to DWPF Frit 418 but smaller particles were removed by the respective vendors. Test results on Frit Clumping and Dusting are provided in this report. This report addresses the following seven questions. Short answers are provided below with more detailed answers to follow. 1. Will the addition of a small amount of water, 1.5 wt%, to dry DWPF Frit 418 greatly reduce the dust generation during handling at DWPF? a. Yes, a small scale test showed that adding a little water to the frit greatly reduced dust generation during handling. 2. Will the addition of small amounts of water to the frit cause clumping that will impair frit handling at DWPF? a. No, not with Frit 418. Although clumps were observed to form when 1.5 wt% water was mixed with DWPF Frit 418, then compressed and air-dried overnight, the clumps were easily crushed and did not form the hardened material noted when Frit 320 was tested. 3. What is the measured size distribution of dust generated when dry frit is handled? (This affects the feasibility and choice of processing equipment for removing the dust generating fraction of the frit before it is added to the SME.) a. The size distribution for

  2. Far-infrared Dust Temperatures and Column Densities of the MALT90 Molecular Clump Sample

    NASA Astrophysics Data System (ADS)

    Guzmán, Andrés E.; Sanhueza, Patricio; Contreras, Yanett; Smith, Howard A.; Jackson, James M.; Hoq, Sadia; Rathborne, Jill M.

    2015-12-01

    We present dust column densities and dust temperatures for ˜3000 young, high-mass molecular clumps from the Millimeter Astronomy Legacy Team 90 GHz survey, derived from adjusting single-temperature dust emission models to the far-infrared intensity maps measured between 160 and 870 μm from the Herschel/Herschel Infrared Galactic Plane Survey (Hi-Gal) and APEX/APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) surveys. We discuss the methodology employed in analyzing the data, calculating physical parameters, and estimating their uncertainties. The population average dust temperature of the clumps are 16.8 ± 0.2 K for the clumps that do not exhibit mid-infrared signatures of star formation (quiescent clumps), 18.6 ± 0.2 K for the clumps that display mid-infrared signatures of ongoing star formation but have not yet developed an H ii region (protostellar clumps), and 23.7 ± 0.2 and 28.1 ± 0.3 K for clumps associated with H ii and photo-dissociation regions, respectively. These four groups exhibit large overlaps in their temperature distributions, with dispersions ranging between 4 and 6 K. The median of the peak column densities of the protostellar clump population is 0.20 ± 0.02 g cm-2, which is about 50% higher compared to the median of the peak column densities associated with clumps in the other evolutionary stages. We compare the dust temperatures and column densities measured toward the center of the clumps with the mean values of each clump. We find that in the quiescent clumps, the dust temperature increases toward the outer regions and that these clumps are associated with the shallowest column density profiles. In contrast, molecular clumps in the protostellar or H ii region phase have dust temperature gradients more consistent with internal heating and are associated with steeper column density profiles compared with the quiescent clumps.

  3. FAR-INFRARED DUST TEMPERATURES AND COLUMN DENSITIES OF THE MALT90 MOLECULAR CLUMP SAMPLE

    SciTech Connect

    Guzmán, Andrés E.; Smith, Howard A.; Sanhueza, Patricio; Contreras, Yanett; Rathborne, Jill M.; Jackson, James M.; Hoq, Sadia

    2015-12-20

    We present dust column densities and dust temperatures for ∼3000 young, high-mass molecular clumps from the Millimeter Astronomy Legacy Team 90 GHz survey, derived from adjusting single-temperature dust emission models to the far-infrared intensity maps measured between 160 and 870 μm from the Herschel/Herschel Infrared Galactic Plane Survey (Hi-Gal) and APEX/APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) surveys. We discuss the methodology employed in analyzing the data, calculating physical parameters, and estimating their uncertainties. The population average dust temperature of the clumps are 16.8 ± 0.2 K for the clumps that do not exhibit mid-infrared signatures of star formation (quiescent clumps), 18.6 ± 0.2 K for the clumps that display mid-infrared signatures of ongoing star formation but have not yet developed an H ii region (protostellar clumps), and 23.7 ± 0.2 and 28.1 ± 0.3 K for clumps associated with H ii and photo-dissociation regions, respectively. These four groups exhibit large overlaps in their temperature distributions, with dispersions ranging between 4 and 6 K. The median of the peak column densities of the protostellar clump population is 0.20 ± 0.02 g cm{sup −2}, which is about 50% higher compared to the median of the peak column densities associated with clumps in the other evolutionary stages. We compare the dust temperatures and column densities measured toward the center of the clumps with the mean values of each clump. We find that in the quiescent clumps, the dust temperature increases toward the outer regions and that these clumps are associated with the shallowest column density profiles. In contrast, molecular clumps in the protostellar or H ii region phase have dust temperature gradients more consistent with internal heating and are associated with steeper column density profiles compared with the quiescent clumps.

  4. Will new horizons see dust clumps in the Edgeworth-Kuiper Belt?

    SciTech Connect

    Vitense, Christian; Krivov, Alexander V.; Löhne, Torsten

    2014-06-01

    Debris disks are thought to be sculptured by neighboring planets. The same is true for the Edgeworth-Kuiper debris disk, yet no direct observational evidence for signatures of giant planets in the Kuiper Belt dust distribution has been found so far. Here we model the dust distribution in the outer solar system to reproduce the dust impact rates onto the dust detector on board the New Horizons spacecraft measured so far and to predict the rates during the Neptune orbit traverse. To this end, we take a realistic distribution of trans-Neptunian objects to launch a sufficient number of dust grains of different sizes and follow their orbits by including radiation pressure, Poynting-Robertson and stellar wind drag, as well as the perturbations of four giant planets. In a subsequent statistical analysis, we calculate number densities and lifetimes of the dust grains in order to simulate a collisional cascade. In contrast to the previous work, our model not only considers collisional elimination of particles but also includes production of finer debris. We find that particles captured in the 3:2 resonance with Neptune build clumps that are not removed by collisions, because the depleting effect of collisions is counteracted by production of smaller fragments. Our model successfully reproduces the dust impact rates measured by New Horizons out to ≈23 AU and predicts an increase of the impact rate of about a factor of two or three around the Neptune orbit crossing. This result is robust with respect to the variation of the vaguely known number of dust-producing scattered disk objects, collisional outcomes, and the dust properties.

  5. The transiting dust clumps in the evolved disc of the Sun-like UXor RZ Psc

    PubMed Central

    Kenworthy, Matthew A.; Pepper, Joshua; Rodriguez, Joseph E.; Siverd, Robert J.; Stassun, Keivan G.; Wyatt, Mark C.

    2017-01-01

    RZ Psc is a young Sun-like star, long associated with the UXor class of variable stars, which is partially or wholly dimmed by dust clumps several times each year. The system has a bright and variable infrared excess, which has been interpreted as evidence that the dimming events are the passage of asteroidal fragments in front of the host star. Here, we present a decade of optical photometry of RZ Psc and take a critical look at the asteroid belt interpretation. We show that the distribution of light curve gradients is non-uniform for deep events, which we interpret as possible evidence for an asteroidal fragment-like clump structure. However, the clumps are very likely seen above a high optical depth midplane, so the disc’s bulk clumpiness is not revealed. While circumstantial evidence suggests an asteroid belt is more plausible than a gas-rich transition disc, the evolutionary status remains uncertain. We suggest that the rarity of Sun-like stars showing disc-related variability may arise because (i) any accretion streams are transparent and/or (ii) turbulence above the inner rim is normally shadowed by a flared outer disc. PMID:28280566

  6. The transiting dust clumps in the evolved disc of the Sun-like UXor RZ Psc.

    PubMed

    Kennedy, Grant M; Kenworthy, Matthew A; Pepper, Joshua; Rodriguez, Joseph E; Siverd, Robert J; Stassun, Keivan G; Wyatt, Mark C

    2017-01-01

    RZ Psc is a young Sun-like star, long associated with the UXor class of variable stars, which is partially or wholly dimmed by dust clumps several times each year. The system has a bright and variable infrared excess, which has been interpreted as evidence that the dimming events are the passage of asteroidal fragments in front of the host star. Here, we present a decade of optical photometry of RZ Psc and take a critical look at the asteroid belt interpretation. We show that the distribution of light curve gradients is non-uniform for deep events, which we interpret as possible evidence for an asteroidal fragment-like clump structure. However, the clumps are very likely seen above a high optical depth midplane, so the disc's bulk clumpiness is not revealed. While circumstantial evidence suggests an asteroid belt is more plausible than a gas-rich transition disc, the evolutionary status remains uncertain. We suggest that the rarity of Sun-like stars showing disc-related variability may arise because (i) any accretion streams are transparent and/or (ii) turbulence above the inner rim is normally shadowed by a flared outer disc.

  7. The transiting dust clumps in the evolved disc of the Sun-like UXor RZ Psc

    NASA Astrophysics Data System (ADS)

    Kennedy, Grant M.; Kenworthy, Matthew A.; Pepper, Joshua; Rodriguez, Joseph E.; Siverd, Robert J.; Stassun, Keivan G.; Wyatt, Mark C.

    2017-01-01

    RZ Psc is a young Sun-like star, long associated with the UXor class of variable stars, which is partially or wholly dimmed by dust clumps several times each year. The system has a bright and variable infrared excess, which has been interpreted as evidence that the dimming events are the passage of asteroidal fragments in front of the host star. Here, we present a decade of optical photometry of RZ Psc and take a critical look at the asteroid belt interpretation. We show that the distribution of light curve gradients is non-uniform for deep events, which we interpret as possible evidence for an asteroidal fragment-like clump structure. However, the clumps are very likely seen above a high optical depth midplane, so the disc's bulk clumpiness is not revealed. While circumstantial evidence suggests an asteroid belt is more plausible than a gas-rich transition disc, the evolutionary status remains uncertain. We suggest that the rarity of Sun-like stars showing disc-related variability may arise because (i) any accretion streams are transparent and/or (ii) turbulence above the inner rim is normally shadowed by a flared outer disc.

  8. Deriving Dust Properties in Star Forming Clumps: a Look Across the Perseus Molecular Cloud with Herschel and SCUBA-2

    NASA Astrophysics Data System (ADS)

    Chen, Michael Chun-Yuan

    2015-04-01

    Herschel and JCMT surveys of nearby star-forming regions have provided excellent images of cold dust emission across several wavelengths with unprecedented dynamic range and resolutions. Here we present spectral emissivity index and temperature maps of dust in the star-forming clumps of the Perseus molecular cloud determined from fitting SEDs to the combined Herschel and JCMT observations in the 160 μm, 250 μm, 350 μm, 500 μm, and 850 μm bands, employing the technique developed by Sadavoy et al. (2013). In NGC1333, the most complex and active star-forming clump in Perseus, we demonstrate that CO line contamination in the JCMT SCUBA-2 850 μm band is typically insignificant. The derived spectral emissivity index, β, and dust temperature, T, ranges between 0.8 - 3.0 and 7 - 50 K, respectively. Throughout Perseus, we see indications of heating from B stars and embedded protostars, and smooth β variations on the smaller scales. The distribution of β values seen in each clump differs from one clump to another, and is in general different from the diffuse ISM values (i.e., ~2), suggesting that dust grain evolution is significant in star-forming clumps. We also found coincidences between low β regions and local temperature peaks as well as locations of outflows, which may provide hints to the origins of these low β value grains, and dust grain evolution in star-forming clumps in general.

  9. The Small Magellanic Cloud Investigation of Dust and Gas Evolution (SMIDGE): The Dust Extinction Curve in the Small Magellanic Cloud from Red Clump Stars

    NASA Astrophysics Data System (ADS)

    Yanchulova Merica-Jones, Petia; Sandstrom, Karin; Johnson, Lent C.; SMIDGE Team

    2016-06-01

    We present preliminary measurements of the average dust extinction curve in a 200 pc x 100 pc region in the Small Magellanic Cloud (SMC) using multi-band Hubble Space Telescope observations of resolved stellar populations from SMIDGE. Extinction curve determinations from a fully-sampled region of the SMC are of great interest. SMC-like extinction is widely used to correct for the effects of dust in low metallicity or high redshift galaxies, however, there are currently very few extinction curve measurements in the SMC. We measure the extinction curve using color-magnitude diagrams of red clump stars experiencing reddening by dust along a vector from which the curve shape can theoretically be directly measured. In addition, our analysis of the extincted and unextincted red clump stars shows a substantial line-of-sight depth for the stellar distribution of the SMC, consistent with recent observations of Cepheids. With the deep multi-band photometry from SMIDGE we are able to separate these two effects and measure both the extinction curve and the line-of-sight depth. Our study implies that extinction curve measurements in nearby galaxies need to take into account the impact of an extended galactic structure on dust extinction along the line of sight.

  10. Quantifying global dust devil occurrence from meteorological analyses

    PubMed Central

    Jemmett-Smith, Bradley C; Marsham, John H; Knippertz, Peter; Gilkeson, Carl A

    2015-01-01

    Dust devils and nonrotating dusty plumes are effective uplift mechanisms for fine particles, but their contribution to the global dust budget is uncertain. By applying known bulk thermodynamic criteria to European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses, we provide the first global hourly climatology of potential dust devil and dusty plume (PDDP) occurrence. In agreement with observations, activity is highest from late morning into the afternoon. Combining PDDP frequencies with dust source maps and typical emission values gives the best estimate of global contributions of 3.4% (uncertainty 0.9–31%), 1 order of magnitude lower than the only estimate previously published. Total global hours of dust uplift by dry convection are ∼0.002% of the dust-lifting winds resolved by ECMWF, consistent with dry convection making a small contribution to global uplift. Reducing uncertainty requires better knowledge of factors controlling PDDP occurrence, source regions, and dust fluxes induced by dry convection. Key Points Global potential dust devil occurrence quantified from meteorological analyses Climatology shows realistic diurnal cycle and geographical distribution Best estimate of global contribution of 3.4% is 10 times smaller than the previous estimate PMID:26681815

  11. Star Formation Laws in Both Galactic Massive Clumps and External Galaxies: Extensive Study with Dust Coninuum, HCN (4-3), and CS (7-6)

    NASA Astrophysics Data System (ADS)

    Liu, Tie; Kim, Kee-Tae; Yoo, Hyunju; Liu, Sheng-yuan; Tatematsu, Ken'ichi; Qin, Sheng-Li; Zhang, Qizhou; Wu, Yuefang; Wang, Ke; Goldsmith, Paul F.; Juvela, Mika; Lee, Jeong-Eun; Tóth, L. Viktor; Mardones, Diego; Garay, Guido; Bronfman, Leonardo; Cunningham, Maria R.; Li, Di; Lo, Nadia; Ristorcelli, Isabelle; Schnee, Scott

    2016-10-01

    We observed 146 Galactic clumps in HCN (4-3) and CS (7-6) with the Atacama Submillimeter Telescope Experiment 10 m telescope. A tight linear relationship between star formation rate and gas mass traced by dust continuum emission was found for both Galactic clumps and the high redshift (z > 1) star forming galaxies (SFGs), indicating a constant gas depletion time of ˜100 Myr for molecular gas in both Galactic clumps and high z SFGs. However, low z galaxies do not follow this relation and seem to have a longer global gas depletion time. The correlations between total infrared luminosities (L TIR) and molecular line luminosities ({L}{mol}\\prime ) of HCN (4-3) and CS (7-6) are tight and sublinear extending down to clumps with L TIR ˜ 103 L ⊙. These correlations become linear when extended to external galaxies. A bimodal behavior in the L TIR-{L}{mol}\\prime correlations was found for clumps with different dust temperature, luminosity-to-mass ratio, and σ line/σ vir. Such bimodal behavior may be due to evolutionary effects. The slopes of L TIR-L‧mol correlations become more shallow as clumps evolve. We compared our results with lower J transition lines in Wu et al. (2010). The correlations between clump masses and line luminosities are close to linear for low effective excitation density tracers but become sublinear for high effective excitation density tracers for clumps with L TIR larger than L TIR ˜ 104.5 L ⊙. High effective excitation density tracers cannot linearly trace the total clump masses, leading to a sublinear correlations for both M clump-L‧mol and L TIR-L‧mol relations.

  12. ATLASGAL-selected massive clumps in the inner Galaxy. III. Dust continuum characterization of an evolutionary sample

    NASA Astrophysics Data System (ADS)

    König, C.; Urquhart, J. S.; Csengeri, T.; Leurini, S.; Wyrowski, F.; Giannetti, A.; Wienen, M.; Pillai, T.; Kauffmann, J.; Menten, K. M.; Schuller, F.

    2017-03-01

    Context. Massive-star formation and the processes involved are still poorly understood. The ATLASGAL survey provides an ideal basis for detailed studies of large numbers of massive-star forming clumps covering the whole range of evolutionary stages. The ATLASGAL Top100 is a sample of clumps selected by their infrared and radio properties to be representative for the whole range of evolutionary stages. Aims: The ATLASGAL Top100 sources are the focus of a number of detailed follow-up studies that will be presented in a series of papers. In the present work we use the dust continuum emission to constrain the physical properties of this sample and identify trends as a function of source evolution. Methods: We determine flux densities from mid-infrared to submillimeter wavelength (8-870 μm) images and use these values to fit their spectral energy distributions and determine their dust temperature and flux. Combining these with recent distances from the literature including maser parallax measurements we determine clump masses, luminosities and column densities. Results: We define four distinct source classes from the available continuum data and arrange these into an evolutionary sequence. This begins with sources found to be dark at 70 μm, followed by 24 μm weak sources with an embedded 70 μm source, continues through mid-infrared bright sources and ends with infrared bright sources associated with radio emission (i.e., H ii regions). We find trends for increasing temperature, luminosity, and column density with the proposed evolution sequence, confirming that this sample is representative of different evolutionary stages of massive star formation. Our sources span temperatures from approximately 11 to 41 K, with bolometric luminosities in the range 57 L⊙-3.8 × 106L⊙. The highest masses reach 4.3 × 104M⊙ and peak column densities up to 1.1 × 1024 cm-1, and therefore have the potential to form the most massive O-type stars. We show that at least 93 sources

  13. Dust as interstellar catalyst. I. Quantifying the chemical desorption process

    NASA Astrophysics Data System (ADS)

    Minissale, M.; Dulieu, F.; Cazaux, S.; Hocuk, S.

    2016-01-01

    Context. The presence of dust in the interstellar medium has profound consequences on the chemical composition of regions where stars are forming. Recent observations show that many species formed onto dust are populating the gas phase, especially in cold environments where UV- and cosmic-ray-induced photons do not account for such processes. Aims: The aim of this paper is to understand and quantify the process that releases solid species into the gas phase, the so-called chemical desorption process, so that an explicit formula can be derived that can be included in astrochemical models. Methods: We present a collection of experimental results of more than ten reactive systems. For each reaction, different substrates such as oxidized graphite and compact amorphous water ice were used. We derived a formula for reproducing the efficiencies of the chemical desorption process that considers the equipartition of the energy of newly formed products, followed by classical bounce on the surface. In part II of this study we extend these results to astrophysical conditions. Results: The equipartition of energy correctly describes the chemical desorption process on bare surfaces. On icy surfaces, the chemical desorption process is much less efficient, and a better description of the interaction with the surface is still needed. Conclusions: We show that the mechanism that directly transforms solid species into gas phase species is efficient for many reactions.

  14. Quantifying dust emissions from desert landforms, eastern Mojave Desert, USA

    NASA Astrophysics Data System (ADS)

    Sweeney, Mark R.; McDonald, Eric V.; Etyemezian, Vicken

    2011-12-01

    The measurement of natural dust emissions from desert landforms is crucial in environmental hazard assessment and field checking the accuracy of global dust models. More than 500 individual dust measurements from eight common desert landforms in southern California were collected using the PI-SWERL (Portable In Situ Wind Erosion Lab). The largest emitters of dust are dry washes (13.787 to 0.007 mg m - 2 s - 1 ), dunes, playa margins, distal alluvial fans, and lacustrine beaches. Low emitters include salt-crusted playas (0.692 to 0.002 mg m - 2 s - 1 ), silt-clay-crusted playas, and desert pavements. High emissions are a function of saltating sand that bombards the surface, liberating dust-sized particles for entrainment. Low dust emissions are primarily a function of surface crusting, gravel armoring, and vegetation density. PI-SWERL measurements reveal that emission rates can vary by at least three orders of magnitude, reflecting local variability in soil texture and continuity of surface crusts. Shear-stress partitioning models can be applied to dust data measured by the PI-SWERL to account for large surface roughness features, such as vegetation. The results presented here give an approximation of the contributions to atmospheric dust loading by landforms in the Mojave Desert, and can potentially be used to improve atmospheric dust models.

  15. Design and development of a dust dispersion chamber to quantify the dispersibility of rock dust.

    PubMed

    Perera, Inoka E; Sapko, Michael J; Harris, Marcia L; Zlochower, Isaac A; Weiss, Eric S

    2016-01-01

    Dispersible rock dust must be applied to the surfaces of entries in underground coal mines in order to inert the coal dust entrained or made airborne during an explosion and prevent propagating explosions. 30 CFR. 75.2 states that "… [rock dust particles] when wetted and dried will not cohere to form a cake which will not be dispersed into separate particles by a light blast of air …" However, a proper definition or quantification of "light blast of air" is not provided. The National Institute for Occupational Safety and Health (NIOSH) has, consequently, designed a dust dispersion chamber to conduct quantitative laboratory-scale dispersibility experiments as a screening tool for candidate rock dusts. A reproducible pulse of air is injected into the chamber and across a shallow tray of rock dust. The dust dispersed and carried downwind is monitored. The mass loss of the dust tray and the airborne dust measurements determine the relative dispersibility of the dust with respect to a Reference rock dust. This report describes the design and the methodology to evaluate the relative dispersibility of rock dusts with and without anti-caking agents. Further, the results of this study indicate that the dispersibility of rock dusts varies with particle size, type of anti-caking agent used, and with the untapped bulk density. Untreated rock dusts, when wetted and dried forming a cake that was much less dispersible than the reference rock dust used in supporting the 80% total incombustible content rule.

  16. How well can we quantify dust deposition to the ocean?

    NASA Astrophysics Data System (ADS)

    Anderson, R. F.; Cheng, H.; Edwards, R. L.; Fleisher, M. Q.; Hayes, C. T.; Huang, K.-F.; Kadko, D.; Lam, P. J.; Landing, W. M.; Lao, Y.; Lu, Y.; Measures, C. I.; Moran, S. B.; Morton, P. L.; Ohnemus, D. C.; Robinson, L. F.; Shelley, R. U.

    2016-11-01

    Deposition of continental mineral aerosols (dust) in the Eastern Tropical North Atlantic Ocean, between the coast of Africa and the Mid-Atlantic Ridge, was estimated using several strategies based on the measurement of aerosols, trace metals dissolved in seawater, particulate material filtered from the water column, particles collected by sediment traps and sediments. Most of the data used in this synthesis involve samples collected during US GEOTRACES expeditions in 2010 and 2011, although some results from the literature are also used. Dust deposition generated by a global model serves as a reference against which the results from each observational strategy are compared. Observation-based dust fluxes disagree with one another by as much as two orders of magnitude, although most of the methods produce results that are consistent with the reference model to within a factor of 5. The large range of estimates indicates that further work is needed to reduce uncertainties associated with each method before it can be applied routinely to map dust deposition to the ocean. Calculated dust deposition using observational strategies thought to have the smallest uncertainties is lower than the reference model by a factor of 2-5, suggesting that the model may overestimate dust deposition in our study area. This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'.

  17. Design and development of a dust dispersion chamber to quantify the dispersibility of rock dust

    PubMed Central

    Perera, Inoka E.; Sapko, Michael J.; Harris, Marcia L.; Zlochower, Isaac A.; Weiss, Eric S.

    2015-01-01

    Dispersible rock dust must be applied to the surfaces of entries in underground coal mines in order to inert the coal dust entrained or made airborne during an explosion and prevent propagating explosions. 30 CFR. 75.2 states that “… [rock dust particles] when wetted and dried will not cohere to form a cake which will not be dispersed into separate particles by a light blast of air …” However, a proper definition or quantification of “light blast of air” is not provided. The National Institute for Occupational Safety and Health (NIOSH) has, consequently, designed a dust dispersion chamber to conduct quantitative laboratory-scale dispersibility experiments as a screening tool for candidate rock dusts. A reproducible pulse of air is injected into the chamber and across a shallow tray of rock dust. The dust dispersed and carried downwind is monitored. The mass loss of the dust tray and the airborne dust measurements determine the relative dispersibility of the dust with respect to a Reference rock dust. This report describes the design and the methodology to evaluate the relative dispersibility of rock dusts with and without anti-caking agents. Further, the results of this study indicate that the dispersibility of rock dusts varies with particle size, type of anti-caking agent used, and with the untapped bulk density. Untreated rock dusts, when wetted and dried forming a cake that was much less dispersible than the reference rock dust used in supporting the 80% total incombustible content rule. PMID:26834390

  18. Quantifying the contribution of individual dust sources to the summertime dust hotspot in the central and western Sahara

    NASA Astrophysics Data System (ADS)

    Ashpole, Ian; Washington, Richard; Engelstaedter, Sebastian

    2014-05-01

    The central and western Sahara (CWS), a huge area encompassing parts of Algeria, Niger, Mali and Mauritania, is the dustiest place on Earth during the northern hemisphere summer. This dust is known to come from a large number of disperse sources across the region, which have been identified predominantly from satellite observations. We utilise an automated scheme that tracks individual dust plumes in data from the spaceborne Spinning Enhanced Visible and Infrared Imager (SEVIRI), available every 15 minutes at ~0.03° spatial resolution, to quantify the contribution of dust plumes from known sources to the overall CWS dust hotspot in terms of 1) frequency of dust detection and 2) total plume Aerosol Optical Depth (also derived from SEVIRI data). Results show that dust sources in the south of the region, whose activation is strongly linked to the dynamics of the West African Monsoon and convective processes, make a significantly greater contribution to the dust hotspot than sources in central Algeria and northwest Mali that, while equally or even more frequently active, give rise to plumes that are much more spatially constricted and short lived.

  19. Quantifying local-scale dust emission from the Arabian Red Sea coastal plain

    NASA Astrophysics Data System (ADS)

    Anisimov, Anatolii; Tao, Weichun; Stenchikov, Georgiy; Kalenderski, Stoitchko; Jish Prakash, P.; Yang, Zong-Liang; Shi, Mingjie

    2017-01-01

    Dust plumes emitted from the narrow Arabian Red Sea coastal plain are often observed on satellite images and felt in local population centers. Despite its relatively small area, the coastal plain could be a significant dust source; however, its effect is not well quantified as it is not well approximated in global or even regional models. In addition, because of close proximity to the Red Sea, a significant amount of dust from the coastal areas could be deposited into the Red Sea and serve as a vital component of the nutrient balance of marine ecosystems.In the current study, we apply the offline Community Land Model version 4 (CLM4) to better quantify dust emission from the coastal plain during the period of 2009-2011. We verify the spatial and temporal variability in model results using independent weather station reports. We also compare the results with the MERRA Aerosol Reanalysis (MERRAero). We show that the best results are obtained with 1 km model spatial resolution and dust source function based on Meteosat Second Generation Spinning Enhanced Visible and InfraRed Imager (SEVIRI) measurements. We present the dust emission spatial pattern, as well as estimates of seasonal and diurnal variability in dust event frequency and intensity, and discuss the emission regime in the major dust generation hot spot areas. We demonstrate the contrasting seasonal dust cycles in the northern and southern parts of the coastal plain and discuss the physical mechanisms responsible for dust generation.This study provides the first estimates of the fine-scale spatial and temporal distribution of dust emissions from the Arabian Red Sea coastal plain constrained by MERRAero and short-term WRF-Chem simulations. The estimate of total dust emission from the coastal plain, tuned to fit emissions in MERRAero, is 7.5 ± 0.5 Mt a-1. Small interannual variability indicates that the study area is a stable dust source. The mineralogical composition analysis shows that the coastal plain

  20. Quantifying the anthropogenic dust emission from agricultural land use and desiccation of the Aral Sea in Central Asia

    NASA Astrophysics Data System (ADS)

    Xi, Xin; Sokolik, Irina N.

    2016-10-01

    A regional dust model system is applied to quantify the anthropogenic dust emission in the post-Soviet Central Asia from 2000 to 2014. Two physically based dust schemes suggest that a proportion of 18.3-32.8% of total dust emissions is contributed by agricultural land use and the desiccation of Aral Sea, whereas a simplified dust scheme yields higher estimates in the range of 49.7-56.5% depending on whether a static or dynamic preferential dust source function is used. The dust schemes also differ greatly in the spatial distribution of anthropogenic dust and the sensitivity to the use of land use intensity in separating natural and human-made source areas, suggesting that the model representation of erosion threshold velocity, especially the role of vegetation, is a key source of model uncertainty in quantifying anthropogenic dust. The relative importance of agriculture and dried Aral Sea bed (Aralkum) differs greatly among the dust schemes. Despite the increased dust from the expansion of Aralkum, there is a negative trend in the anthropogenic dust proportion, indicating a shift of dust emission toward natural source areas. All dust schemes show a decrease in anthropogenic dust in response to land cover changes over agricultural lands.

  1. Quantifying the impact of dust on heterogeneous ice generation in midlevel supercooled stratiform clouds

    SciTech Connect

    Zhang, Damao; Wang, Zhien; Heymsfield, Andrew; Fan, Jiwen; Liu, Dong; Zhao, Ming

    2012-09-26

    Dust aerosols have been regarded as effective ice nuclei (IN), but large uncertainties regarding their efficiencies remain. Here, four years of collocated CALIPSO and CloudSat measurements are used to quantify the impact of dust on heterogeneous ice generation in midlevel supercooled stratiform clouds (MSSCs) over the ‘dust belt’. The results show that the dusty MSSCs have an up to 20% higher mixed-phase cloud occurrence, up to 8 dBZ higher mean maximum Ze (Ze_max), and up to 11.5 g/m2 higher ice water path (IWP) than similar MSSCs under background aerosol conditions. Assuming similar ice growth and fallout history in similar MSSCs, the significant differences in Ze_max between dusty and non-dusty MSSCs reflect ice particle number concentration differences. Therefore, observed Ze_max differences indicate that dust could enhance ice particle concentration in MSSCs by a factor of 2 to 6 at temperatures colder than -12°C. The enhancements are strongly dependent on the cloud top temperature, large dust particle concentration and chemical compositions. Finally, these results imply an important role of dust particles in modifying mixed-phase cloud properties globally.

  2. Quantifying the impact of dust on heterogeneous ice generation in midlevel supercooled stratiform clouds

    NASA Astrophysics Data System (ADS)

    Zhang, Damao; Wang, Zhien; Heymsfield, Andrew; Fan, Jiwen; Liu, Dong; Zhao, Ming

    2012-09-01

    Dust aerosols have been regarded as effective ice nuclei (IN), but large uncertainties regarding their efficiencies remain. Here, four years of collocated CALIPSO and CloudSat measurements are used to quantify the impact of dust on heterogeneous ice generation in midlevel supercooled stratiform clouds (MSSCs) over the ‘dust belt’. The results show that the dusty MSSCs have an up to 20% higher mixed-phase cloud occurrence, up to 8 dBZ higher mean maximum Ze (Ze_max), and up to 11.5 g/m2 higher ice water path (IWP) than similar MSSCs under background aerosol conditions. Assuming similar ice growth and fallout history in similar MSSCs, the significant differences in Ze_max between dusty and non-dusty MSSCs reflect ice particle number concentration differences. Therefore, observed Ze_max differences indicate that dust could enhance ice particle concentration in MSSCs by a factor of 2 to 6 at temperatures colder than -12°C. The enhancements are strongly dependent on the cloud top temperature, large dust particle concentration and chemical compositions. These results imply an important role of dust particles in modifying mixed-phase cloud properties globally.

  3. Quantifying atmospheric processing of mineral dust as a source of bioavailable phosphorus to the open oceans

    NASA Astrophysics Data System (ADS)

    Herbert, Ross; Stockdale, Anthony; Carslaw, Ken; Krom, Michael

    2016-04-01

    The transport and deposition of mineral dust is known to be the dominant source of phosphorus (P) to the surface waters of the open oceans. However, the fraction of this P that is deemed available for primary productivity remains a key uncertainty due to a limited understanding of the processes occurring during transport of the dust. Through a series of detailed laboratory experiments using desert dust and dust precursors, we show that the dissolution behaviour of P in these samples is controlled by a surface-bound labile pool, and an additional mineral pool primarily consisting of apatite. The acid dissolution of the apatite occurs rapidly and is controlled by the absolute number of H+ ions present in the solution surrounding the dust. Using these results we develop a new conceptual model that reproduces the major processes controlling P dissolution in the atmosphere. We then use a global aerosol microphysics model with a global soil database to quantify the deposition of bioavailable P to the open oceans and ice sheets. We show that, globally, the labile pool contributes 2.4 Gg P a-1 to the oceans and, from a potential pool of 11.5 Gg P a-1, the dissolved apatite pool contributes 0.24 Gg P a-1. A series of sensitivity studies identifying sources of acid in the atmosphere show that anthropogenic emissions of SO2 contribute 61% of the global mass of dissolved apatite, volcanic events contribute 11%, and DMS emissions contribute 10%. Finally, we show that the fraction of mineral dust P that is available for primary productivity varies, regionally, from <20% in the North Atlantic Ocean to >50% in the South Pacific Ocean; this explains the variability in the fraction of bioavailable P commonly observed in important oceanic regions.

  4. Astrochemical Properties of Planck Cold Clumps

    NASA Astrophysics Data System (ADS)

    Tatematsu, Ken’ichi; Liu, Tie; Ohashi, Satoshi; Sanhueza, Patricio; Nguyễn Lu’o’ng, Quang; Hirota, Tomoya; Liu, Sheng-Yuan; Hirano, Naomi; Choi, Minho; Kang, Miju; Thompson, Mark A.; Fuller, Gary; Wu, Yuefang; Li, Di; Di Francesco, James; Kim, Kee-Tae; Wang, Ke; Ristorcelli, Isabelle; Juvela, Mika; Shinnaga, Hiroko; Cunningham, Maria; Saito, Masao; Lee, Jeong-Eun; Tóth, L. Viktor; He, Jinhua; Sakai, Takeshi; Kim, Jungha; JCMT Large Program “SCOPE” collaboration; TRAO Key Science Program “TOP” collaboration

    2017-02-01

    We observed 13 Planck cold clumps with the James Clerk Maxwell Telescope/SCUBA-2 and with the Nobeyama 45 m radio telescope. The N2H+ distribution obtained with the Nobeyama telescope is quite similar to SCUBA-2 dust distribution. The 82 GHz HC3N, 82 GHz CCS, and 94 GHz CCS emission are often distributed differently with respect to the N2H+ emission. The CCS emission, which is known to be abundant in starless molecular cloud cores, is often very clumpy in the observed targets. We made deep single-pointing observations in DNC, HN13C, N2D+, and cyclic-C3H2 toward nine clumps. The detection rate of N2D+ is 50%. Furthermore, we observed the NH3 emission toward 15 Planck cold clumps to estimate the kinetic temperature, and confirmed that most targets are cold (≲20 K). In two of the starless clumps we observed, the CCS emission is distributed as it surrounds the N2H+ core (chemically evolved gas), which resembles the case of L1544, a prestellar core showing collapse. In addition, we detected both DNC and N2D+. These two clumps are most likely on the verge of star formation. We introduce the chemical evolution factor (CEF) for starless cores to describe the chemical evolutionary stage, and analyze the observed Planck cold clumps.

  5. Quantifying the Gas Inside Dust Cavities in Transitional Disks: Implications for Young Planets

    NASA Astrophysics Data System (ADS)

    van Dishoeck, E. F.; van der Marel, N.; Bruderer, S.; Pinilla, P.

    2015-12-01

    ALMA observations of a small sample of transitional disks with large dust cavities observed in Cycle 0 and 1 are summarized. The gas and dust surface density structures are inferred from the continuum and 12CO, 13CO and C18O line data using the DALI physical-chemical code. Thanks to its ability to self-shield, CO can survive inside dust cavities in spite of being exposed to intense UV radiation and can thus be used as a probe of the gas structure. Modeling of the existing data shows that gas is present inside the dust cavities in all cases, but at a reduced level compared with the gas surface density profile of the outer disk. The gas density decrease inside the dust cavity radius by factors of up to 104 suggests clearing by one or more planetary-mass companions. The accompanying pressure bumps naturally lead to trapping of the mm-sized dust grains observed in the ALMA images.

  6. QUANTIFYING NON-STAR-FORMATION-ASSOCIATED 8 {mu}m DUST EMISSION IN NGC 628

    SciTech Connect

    Crocker, Alison F.; Calzetti, Daniela; Thilker, David A.; Aniano, Gonzalo; Draine, Bruce T.; Hunt, Leslie K.; Kennicutt, Robert C.; Sandstrom, Karin; Smith, J. D. T.

    2013-01-10

    Combining H{alpha} and IRAC images of the nearby spiral galaxy NGC 628, we find that between 30% and 43% of its 8 {mu}m dust emission is not related to recent star formation. Contributions from dust heated by young stars are separated by identifying H II regions in the H{alpha} map and using these areas as a mask to determine the 8 {mu}m dust emission that must be due to heating by older stars. Corrections are made for sub-detection-threshold H II regions, photons escaping from H II regions, and for young stars not directly associated with H II regions (i.e., 10-100 Myr old stars). A simple model confirms that this amount of 8 {mu}m emission can be expected given dust and PAH absorption cross sections, a realistic star formation history, and the observed optical extinction values. A Fourier power spectrum analysis indicates that the 8 {mu}m dust emission is more diffuse than the H{alpha} emission (and similar to observed H I), supporting our analysis that much of the 8 {mu}m-emitting dust is heated by older stars. The 8 {mu}m dust-to-H{alpha} emission ratio declines with galactocentric radius both within and outside of H II regions, probably due to a radial increase in disk transparency. In the course of this work, we have also found that intrinsic diffuse H{alpha} fractions may be lower than previously thought in galaxies, if the differential extinction between H II regions and diffuse regions is taken into account.

  7. Quantifying particle size and turbulent scale dependence of dust flux in the Sahara using aircraft measurements

    NASA Astrophysics Data System (ADS)

    Rosenberg, Philip D.; Parker, Douglas J.; Ryder, Claire L.; Marsham, John H.; Garcia-Carreras, Luis; Dorsey, James R.; Brooks, Ian M.; Dean, Angela R.; Crosier, Jonathon; McQuaid, James B.; Washington, Richard

    2014-06-01

    The first size-resolved airborne measurements of dust fluxes and the first dust flux measurements from the central Sahara are presented and compared with a parameterization by Kok (2011a). High-frequency measurements of dust size distribution were obtained from 0.16 to 300 µm diameter, and eddy covariance fluxes were derived. This is more than an order of magnitude larger size range than previous flux estimates. Links to surface emission are provided by analysis of particle drift velocities. Number flux is described by a -2 power law between 1 and 144 µm diameter, significantly larger than the 12 µm upper limit suggested by Kok (2011a). For small particles, the deviation from a power law varies with terrain type and the large size cutoff is correlated with atmospheric vertical turbulent kinetic energy, suggesting control by vertical transport rather than emission processes. The measured mass flux mode is in the range 30-100 µm. The turbulent scales important for dust flux are from 0.1 km to 1-10 km. The upper scale increases during the morning as boundary layer depth and eddy size increase. All locations where large dust fluxes were measured had large topographical variations. These features are often linked with highly erodible surface features, such as wadis or dunes. We also hypothesize that upslope flow and flow separation over such features enhance the dust flux by transporting large particles out of the saltation layer. The tendency to locate surface flux measurements in open, flat terrain means these favored dust sources have been neglected in previous studies.

  8. Statistical clumped isotope signatures

    PubMed Central

    Röckmann, T.; Popa, M. E.; Krol, M. C.; Hofmann, M. E. G.

    2016-01-01

    High precision measurements of molecules containing more than one heavy isotope may provide novel constraints on element cycles in nature. These so-called clumped isotope signatures are reported relative to the random (stochastic) distribution of heavy isotopes over all available isotopocules of a molecule, which is the conventional reference. When multiple indistinguishable atoms of the same element are present in a molecule, this reference is calculated from the bulk (≈average) isotopic composition of the involved atoms. We show here that this referencing convention leads to apparent negative clumped isotope anomalies (anti-clumping) when the indistinguishable atoms originate from isotopically different populations. Such statistical clumped isotope anomalies must occur in any system where two or more indistinguishable atoms of the same element, but with different isotopic composition, combine in a molecule. The size of the anti-clumping signal is closely related to the difference of the initial isotope ratios of the indistinguishable atoms that have combined. Therefore, a measured statistical clumped isotope anomaly, relative to an expected (e.g. thermodynamical) clumped isotope composition, may allow assessment of the heterogeneity of the isotopic pools of atoms that are the substrate for formation of molecules. PMID:27535168

  9. Formation of the Martian Polar Layered Terrains: Quantifying Polar Water Ice and Dust Surface Deposition During Current and Past Orbital Epochs with the NASA Ames GCM

    NASA Astrophysics Data System (ADS)

    Emmett, J. A.; Murphy, J. R.

    2016-09-01

    The NASA Ames GCM will be used to quantify net annual polar deposition rates of water ice and dust on Mars during current and past orbital epochs to investigate the formation history, structure, and stratigraphy of the polar layered terrains.

  10. On the Formation of Molecular Clumps in QSO Outflows

    NASA Astrophysics Data System (ADS)

    Ferrara, A.; Scannapieco, E.

    2016-12-01

    We study the origin of the cold molecular clumps in quasar outflows, recently detected in CO and HCN emission. We first describe the physical properties of such radiation-driven outflows and show that a transition from a momentum- to an energy-driven flow must occur at a radial distance of R≈ 0.25 {kpc}. During this transition, the shell of swept-up material fragments due to Rayleigh-Taylor instabilities, but these clumps contain little mass and are likely to be rapidly ablated by the hot gas in which they are immersed. We then explore an alternative scenario in which clumps form from thermal instabilities at R≳ 1 {kpc}, possibly containing enough dust to catalyze molecule formation. We investigate this process with 3D two-fluid (gas+dust) numerical simulations of a kpc3 patch of the outflow, including atomic and dust cooling, thermal conduction, dust sputtering, and photoionization from the QSO radiation field. In all cases, dust grains are rapidly destroyed in ≈ {10}4 years; and while some cold clumps form at later times, they are present only as transient features, which disappear as cooling becomes more widespread. In fact, we only find a stable two-phase medium with dense clumps if we artificially enhance the QSO radiation field by a factor of 100. This result, together with the complete destruction of dust grains, renders the interpretation of molecular outflows a very challenging problem.

  11. Integrating laboratory and field data to quantify the immersion freezing ice nucleation activity of mineral dust particles

    DOE PAGES

    DeMott, P. J.; Prenni, A. J.; McMeeking, G. R.; ...

    2014-06-27

    Data from both laboratory studies and atmospheric measurements are used to develop a simple parametric description for the immersion freezing activity of natural mineral dust particles. Measurements made with the Colorado State University (CSU) continuous flow diffusion chamber (CFDC) when processing mineral dust aerosols at a nominal 105% relative humidity with respect to water (RHw) are taken to approximate the immersion freezing nucleation activity of particles. Ice active frozen fractions vs. temperature for dusts representative of Saharan and Asian desert sources were consistent with similar measurements in atmospheric dust plumes for a limited set of comparisons available. The parameterization developedmore » follows the form of one suggested previously for atmospheric particles of non-specific composition in quantifying ice nucleating particle concentrations as functions of temperature and the total number concentration of particles larger than 0.5 μm diameter. Such an approach does not explicitly account for surface area and time dependencies for ice nucleation, but sufficiently encapsulates the activation properties for potential use in regional and global modeling simulations, and possible application in developing remote sensing retrievals for ice nucleating particles. A correction factor is introduced to account for the apparent underestimate (by approximately 3, on average) of the immersion freezing fraction of mineral dust particles for CSU CFDC data processed at an RHw of 105% vs. maximum fractions active at higher RHw. Instrumental factors that affect activation behavior vs. RHw in CFDC instruments remain to be fully explored in future studies. Nevertheless, the use of this correction factor is supported by comparison to ice activation data obtained for the same aerosols from Aerosol Interactions and Dynamics of the Atmosphere (AIDA) expansion chamber cloud parcel experiments. Further comparison of the new parameterization to the immersion

  12. Integrating laboratory and field data to quantify the immersion freezing ice nucleation activity of mineral dust particles

    DOE PAGES

    DeMott, P. J.; Prenni, A. J.; McMeeking, G. R.; ...

    2015-01-13

    Data from both laboratory studies and atmospheric measurements are used to develop an empirical parameterization for the immersion freezing activity of natural mineral dust particles. Measurements made with the Colorado State University (CSU) continuous flow diffusion chamber (CFDC) when processing mineral dust aerosols at a nominal 105% relative humidity with respect to water (RHw) are taken as a measure of the immersion freezing nucleation activity of particles. Ice active frozen fractions vs. temperature for dusts representative of Saharan and Asian desert sources were consistent with similar measurements in atmospheric dust plumes for a limited set of comparisons available. The parameterizationmore » developed follows the form of one suggested previously for atmospheric particles of non-specific composition in quantifying ice nucleating particle concentrations as functions of temperature and the total number concentration of particles larger than 0.5 μm diameter. Such an approach does not explicitly account for surface area and time dependencies for ice nucleation, but sufficiently encapsulates the activation properties for potential use in regional and global modeling simulations, and possible application in developing remote sensing retrievals for ice nucleating particles. A calibration factor is introduced to account for the apparent underestimate (by approximately 3, on average) of the immersion freezing fraction of mineral dust particles for CSU CFDC data processed at an RHw of 105% vs. maximum fractions active at higher RHw. Instrumental factors that affect activation behavior vs. RHw in CFDC instruments remain to be fully explored in future studies. Nevertheless, the use of this calibration factor is supported by comparison to ice activation data obtained for the same aerosols from Aerosol Interactions and Dynamics of the Atmosphere (AIDA) expansion chamber cloud parcel experiments. Further comparison of the new parameterization, including calibration

  13. Fragmentation of Molecular Clumps and Formation of Massive Cores

    NASA Astrophysics Data System (ADS)

    Zhang, Qizhou

    2014-07-01

    Massive protostars are born in parsec-scale molecular clumps that collapse and fragment, leading to the formation of a cluster of stellar objects. The interplay among gravity, turbulence and magnetic fields affects the outcome of fragmentation. The physical condition (temperature and density) in molecular clumps limits the Jeans mass to about 1 Msun. This creates a theoretical puzzle for massive star formation since dense cores much larger than 1 Msun tend to further fragment into lower mass entities. In this talk, I will present recent high resolution observations of massive molecular clumps at very early evolutionary stages. I will discuss fragmentation, physical and chemical evolution of molecular coresand the implication of these findings to current theoretical ideas of massive star and cluster formation. I will also present measurements of dust polarization of a large sample of massive molecular clumps, which suggest that magnetic fields play an important role during the collapse of molecular clumps and the formation of dense cores.

  14. Assessing the performance of methods to detect and quantify African dust in airborne particulates.

    PubMed

    Viana, Mar; Salvador, Pedro; Artíñano, Begoña; Querol, Xavier; Alastuey, Andrés; Pey, Jorge; Latz, Achim J; Cabañas, Mercè; Moreno, Teresa; García dos Santos, Saúl; Herce, María Dolores; Diez Hernández, Pablo; Romero García, Dolores; Fernández-Patier, Rosalía

    2010-12-01

    African dust (AD) contributions to particulate matter (PM) levels may be reported by Member States to the European Commission during justification of exceedances of the daily limit value (DLV). However, the detection and subsequent quantification of the AD contribution to PM levels is complex, and only two measurement-based methods are available in the literature: the Spanish-Portuguese reference method (SPR), and the Tel Aviv University method (TAU). In the present study, both methods were assessed. The SPR method was more conservative in the detection of episodes (71 days identified as AD by SPR, vs 81 by TAU), as it is less affected by interferences with local dust sources. The mean annual contribution of AD was lower with the TAU method than with SPR (2.7 vs 3.5 ± 1.5 μg/m(3)). The SPR and TAU AD time series were correlated with daily aluminum levels (a known tracer of AD), as well as with an AD source identified by the Positive Matrix Factorization (PMF) receptor model. Higher r(2) values were obtained with the SPR method than with TAU in both cases (r(2) = 0.72 vs 0.56, y = 0.05x vs y = 0.06x with aluminum levels; r(2)=0.79 vs 0.43, y = 0.8x vs y = 0.4x with the PMF source). We conclude that the SPR method is more adequate from an EU policy perspective (justification of DLV exceedances) due to the fact that it is more conservative than the TAU method. Based on our results, the TAU method requires adaptation of the thresholds in the algorithm to refine detection of low-impact episodes and avoid misclassification of local events as AD.

  15. Quantitative characterization of clumping in Scots pine crowns

    PubMed Central

    Stenberg, Pauline; Mõttus, Matti; Rautiainen, Miina; Sievänen, Risto

    2014-01-01

    Background and Aims Proper characterization of the clumped structure of forests is needed for calculation of the absorbed radiation and photosynthetic production by a canopy. This study examined the dependency of crown-level clumping on tree size and growth conditions in Scots pine (Pinus sylvestris), and determined the ability of statistical canopy radiation models to quantify the degree of self-shading within crowns as a result of the clumping effect. Methods Twelve 3-D Scots pine trees were generated using an application of the LIGNUM model, and the crown-level clumping as quantified by the crown silhouette to total needle area ratio (STARcrown) was calculated. The results were compared with those produced by the stochastic approach of modelling tree crowns as geometric shapes filled with a random medium. Key Results Crown clumping was independent of tree height, needle area and growth conditions. The results supported the capability of the stochastic approach in characterizing clumping in crowns given that the outer shell of the tree crown is well represented. Conclusions Variation in the whole-stand clumping index is induced by differences in the spatial pattern of trees as a function of, for example, stand age rather than by changes in the degree of self-shading within individual crowns as they grow bigger. PMID:24431344

  16. Quantifying the climatological cloud-free shortwave direct radiative forcing of mineral dust aerosol over the Red Sea

    NASA Astrophysics Data System (ADS)

    Stenchikov, G. L.; Brindley, H. E.; Osipov, S.; Bantges, R. J.; Smirnov, A.; Prakash, P. J.

    2014-12-01

    While there have been a number of campaigns designed to probe dust-climate interactions over much of the world, relatively little attention has been paid to the Red Sea. Because of the remoteness of the area, satellite retrievals provide a crucial tool for assessing aerosol loading over the Sea. However, agreement between aerosol properties inferred from measurements from different instruments, and even in some cases from the same measurements using different retrieval algorithms can be poor, particularly in the case of mineral dust. Ground based measurements, which can be used to evaluate retrievals, are thus highly desirable. Here we take advantage of ship-based hand-held sun-photometer (microtops) observations gathered within the framework of NASA Aerosol Maritime Network from a series of cruises, which took place across the Red Sea during 2011 and 2013. To our knowledge these data represent the first set of detailed aerosol measurements from the Sea. They thus provide a unique opportunity to assess the performance of satellite retrieval algorithms in this region. Here we used the microtops measurements to evaluate the performance of co-located satellite retrievals from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) and the MODerate Imaging Spectrometer (MODIS). Both algorithms show good agreement with the ship-based measurements and with each other, although it appears that the MODIS cloud detection scheme in particular is rather conservative. The stand alone Rapid Radiative Transfer Model (RRTM) driven by reanalysis meteorological fields is used to estimate the cloud-free aerosol direct radiative effect at the surface and TOA along the ship tracks. The TOA effects are compared to co-located measurements from the Geostationary Earth Radiation Budget (GERB) instrument. Having evaluated both the quality of the retrievals and the ability of the model to capture the associated radiative effect, we will present a climatology of aerosol loading over the

  17. Mold Species in Dust from the International Space Station Identified and Quantified by Mold Specific Quantitative PCR - MCEARD

    EPA Science Inventory

    Dust was collected over a period of several weeks in 2007 from HEPA filters in the U.S. Laboratory Module of the International Space Station (ISS). The dust was returned on the Space Shuttle Atlantis, mixed, sieved, and the DNA was extracted. Using a DNA-based method called mo...

  18. Mold Species in Dust from the International Space Station Identified and Quantified by Mold Specific Quantitative PCR

    EPA Science Inventory

    Dust was collected over a period of several weeks in 2007 from HEPA filters in the U.S. Laboratory Module of the International Space Station (ISS). The dust was returned on the Space Shuttle Atlantis, mixed, sieved, and the DNA was extracted. Using a DNA-based method called mol...

  19. Mold Species in Dust from the International Space Station Identified and Quantified by Mold Specific Quantitative PCR

    NASA Technical Reports Server (NTRS)

    Vesper, Stephen J.; Wong, Wing; Kuo, C. Mike; Pierson, Duane L.

    2008-01-01

    Dust was collected over a period of several weeks in 2007 from various HEPA filters in the U.S. Laboratory Module of the International Space Station (ISS). The dust was returned on the Space Shuttle Atlantis, mixed, sieved, and the DNA was extracted. Using a DNA-based method called mold specific quantitative PCR (MSQPCR), 39 molds were measured in the dust. Opportunistic pathogens Aspergillus flavus and A. niger and toxin producers Penicillium chrysogenum and P. brevicompactum were found at relatively high concentrations (compared to U.S. homes). No cells of the opportunistic pathogens A. fumigatus, A. terreus, Fusarium solani or Candida albicans were detected.

  20. Mold species in dust from the International Space Station identified and quantified by mold-specific quantitative PCR.

    PubMed

    Vesper, Stephen J; Wong, Wing; Kuo, C Mike; Pierson, Duane L

    2008-01-01

    Dust was collected over a period of several weeks in 2007 from HEPA filters in the U.S. Laboratory Module of the International Space Station (ISS). The dust was returned on the Space Shuttle Atlantis, mixed, sieved and the DNA was extracted. Using a DNA-based method called mold-specific quantitative PCR (MSQPCR), 39 molds were measured in the dust. Potential opportunistic pathogens Aspergillus flavus and Aspergillus niger and potential moderate toxin producers Penicillium chrysogenum and Penicillium brevicompactum were noteworthy. No cells of the potential opportunistic pathogens Aspergillus fumigatus, Aspergillus terreus, Fusarium solani or Candida albicans were detected.

  1. COSMIC REIONIZATION ON COMPUTERS. III. THE CLUMPING FACTOR

    SciTech Connect

    Kaurov, Alexander A.; Gnedin, Nickolay Y. E-mail: gnedin@fnal.gov

    2015-09-10

    We use fully self-consistent numerical simulations of cosmic reionization, completed under the Cosmic Reionization On Computers project, to explore how well the recombinations in the ionized intergalactic medium (IGM) can be quantified by the effective “clumping factor.” The density distribution in the simulations (and, presumably, in a real universe) is highly inhomogeneous and more-or-less smoothly varying in space. However, even in highly complex and dynamic environments, the concept of the IGM remains reasonably well-defined; the largest ambiguity comes from the unvirialized regions around galaxies that are over-ionized by the local enhancement in the radiation field (“proximity zones”). That ambiguity precludes computing the IGM clumping factor to better than about 20%. We also discuss a “local clumping factor,” defined over a particular spatial scale, and quantify its scatter on a given scale and its variation as a function of scale.

  2. Cosmic Reionization On Computers III. The Clumping Factor

    SciTech Connect

    Kaurov, Alexander A.; Gnedin, Nickolay Y.

    2015-09-09

    We use fully self-consistent numerical simulations of cosmic reionization, completed under the Cosmic Reionization On Computers project, to explore how well the recombinations in the ionized intergalactic medium (IGM) can be quantified by the effective "clumping factor." The density distribution in the simulations (and, presumably, in a real universe) is highly inhomogeneous and more-or-less smoothly varying in space. However, even in highly complex and dynamic environments, the concept of the IGM remains reasonably well-defined; the largest ambiguity comes from the unvirialized regions around galaxies that are over-ionized by the local enhancement in the radiation field ("proximity zones"). This ambiguity precludes computing the IGM clumping factor to better than about 20%. Furthermore, we discuss a "local clumping factor," defined over a particular spatial scale, and quantify its scatter on a given scale and its variation as a function of scale.

  3. Cosmic Reionization On Computers III. The Clumping Factor

    DOE PAGES

    Kaurov, Alexander A.; Gnedin, Nickolay Y.

    2015-09-09

    We use fully self-consistent numerical simulations of cosmic reionization, completed under the Cosmic Reionization On Computers project, to explore how well the recombinations in the ionized intergalactic medium (IGM) can be quantified by the effective "clumping factor." The density distribution in the simulations (and, presumably, in a real universe) is highly inhomogeneous and more-or-less smoothly varying in space. However, even in highly complex and dynamic environments, the concept of the IGM remains reasonably well-defined; the largest ambiguity comes from the unvirialized regions around galaxies that are over-ionized by the local enhancement in the radiation field ("proximity zones"). This ambiguity precludesmore » computing the IGM clumping factor to better than about 20%. Furthermore, we discuss a "local clumping factor," defined over a particular spatial scale, and quantify its scatter on a given scale and its variation as a function of scale.« less

  4. Quantifying some of the impacts of dust and other aerosol on the Caspian Sea region using a regional climate model

    NASA Astrophysics Data System (ADS)

    Elguindi, N.; Solmon, F.; Turuncoglu, U.

    2016-01-01

    The Central Asian deserts are a major dust source region that can potentially have a substantial impact on the Caspian Sea. Despite major advances in the modeling and prediction of the Caspian Sea Level (CSL) during recent years, no study to date has investigated the climatic effects of dust on the hydrological budget of the Sea. In this study, we utilize a regional climate model coupled to an interactive emission and transport scheme to simulate the effects of dust and other aerosol in the Caspian region. First, we present a validation of the model using a variety of AOD satellite observations as well as a climatology of dust storms. Compared to the range of satellite estimates, the model's AOD climatology is closer to the lower end of the observations, and exhibit a significant underestimation over the clay deserts found on the Ustyurt plateau and north of the Aral Sea. Nevertheless, we find encouraging results in that the model is able to reproduce the gradient of increasing AOD intensity from the middle to the southern part of the Sea. Spatially, the model reproduces reasonably well the observed climatological dust storm frequency maps which show that the most intense dust source regions to be found in the Karakum desert in Turkmenistan and Kyzylkum desert in Uzbekistan east of the Aral Sea. In the second part of this study we explore some impacts of dust and other aerosol on the climatology of the region and on the energy budget of the Sea. We find that the overall direct radiative effects of dust and other aerosol reduce the amount of shortwave radiation reaching the surface, dampen boundary layer turbulence and inhibit convection over the region. We also show that by including dust and aerosol in our simulation, we are able to reduce the positive biases in sea surface temperatures by 1-2 °C. Evaporation is also considerably reduced, resulting in an average difference of approximately 10 mm year^{-1} in the Sea's hydrological budget which is substantial

  5. Remarks on the clump theory

    SciTech Connect

    Krommes, J.A.

    1986-07-01

    Further details are provided of a soon-to-be published dialog (Phys. Fluids 29 (July, 1986)) which discussed the role of the small scales in fluid clump theory. It is argued that the approximation of the clump lifetime which is compatible with exponentially rapid separation of adjacent orbits is inappropriate for the description of the dynamically important large scales. Various other remarks are made relating to the analytic treatment of strong drift-wave-like turbulence.

  6. QUANTIFYING THE HEATING SOURCES FOR MID-INFRARED DUST EMISSIONS IN GALAXIES: THE CASE OF M 81

    SciTech Connect

    Lu, N.; Zhao, Y.; Bendo, G. J.; Boselli, A.; Baes, M.; De Looze, I.; Wu, H.; Lam, M. I.; Madden, S. C.; Rémy-Ruyer, A.; Wilson, C. D.; Galametz, M.; Cooray, A.; Spinoglio, L.

    2014-12-20

    With the newly available photometric images at 250 and 500 μm from the Herschel Space Observatory, we study quantitative correlations over a sub-kiloparsec scale among three distinct emission components in the interstellar medium of the nearby spiral galaxy M 81 (NGC 3031): (1) I {sub 8} or I {sub 24}, the surface brightness of the mid-infrared emission observed in the Spitzer Space Telescope 8 or 24 μm band, with I {sub 8} and I {sub 24} being dominated by the emissions from polycyclic aromatic hydrocarbons (PAHs) and very small grains (VSGs) of dust, respectively; (2) I {sub 500}, that of the cold dust continuum emission in the Herschel Space Observatory 500 μm band, dominated by the emission from large dust grains heated by evolved stars; and (3) I {sub Hα}, a nominal surface brightness of the Hα line emission, from gas ionized by newly formed massive stars. The results from our correlation study, free from any assumption on or modeling of dust emissivity law or dust temperatures, present solid evidence for significant heating of PAHs and VSGs by evolved stars. In the case of M 81, about 67% (48%) of the 8 μm (24 μm ) emission derives its heating from evolved stars, with the remainder attributed to radiation heating associated with ionizing stars.

  7. Quantifying the impact of sub-grid surface wind variability on sea salt and dust emissions in CAM5

    NASA Astrophysics Data System (ADS)

    Zhang, Kai; Zhao, Chun; Wan, Hui; Qian, Yun; Easter, Richard C.; Ghan, Steven J.; Sakaguchi, Koichi; Liu, Xiaohong

    2016-02-01

    This paper evaluates the impact of sub-grid variability of surface wind on sea salt and dust emissions in the Community Atmosphere Model version 5 (CAM5). The basic strategy is to calculate emission fluxes multiple times, using different wind speed samples of a Weibull probability distribution derived from model-predicted grid-box mean quantities. In order to derive the Weibull distribution, the sub-grid standard deviation of surface wind speed is estimated by taking into account four mechanisms: turbulence under neutral and stable conditions, dry convective eddies, moist convective eddies over the ocean, and air motions induced by mesoscale systems and fine-scale topography over land. The contributions of turbulence and dry convective eddy are parameterized using schemes from the literature. Wind variabilities caused by moist convective eddies and fine-scale topography are estimated using empirical relationships derived from an operational weather analysis data set at 15 km resolution. The estimated sub-grid standard deviations of surface wind speed agree well with reference results derived from 1 year of global weather analysis at 15 km resolution and from two regional model simulations with 3 km grid spacing.The wind-distribution-based emission calculations are implemented in CAM5. In terms of computational cost, the increase in total simulation time turns out to be less than 3 %. Simulations at 2° resolution indicate that sub-grid wind variability has relatively small impacts (about 7 % increase) on the global annual mean emission of sea salt aerosols, but considerable influence on the emission of dust. Among the considered mechanisms, dry convective eddies and mesoscale flows associated with topography are major causes of dust emission enhancement. With all the four mechanisms included and without additional adjustment of uncertain parameters in the model, the simulated global and annual mean dust emission increase by about 50 % compared to the default model

  8. Quantifying the impact of sub-grid surface wind variability on sea salt and dust emissions in CAM5

    DOE PAGES

    Zhang, Kai; Zhao, Chun; Wan, Hui; ...

    2016-02-12

    This paper evaluates the impact of sub-grid variability of surface wind on sea salt and dust emissions in the Community Atmosphere Model version 5 (CAM5). The basic strategy is to calculate emission fluxes multiple times, using different wind speed samples of a Weibull probability distribution derived from model-predicted grid-box mean quantities. In order to derive the Weibull distribution, the sub-grid standard deviation of surface wind speed is estimated by taking into account four mechanisms: turbulence under neutral and stable conditions, dry convective eddies, moist convective eddies over the ocean, and air motions induced by mesoscale systems and fine-scale topography overmore » land. The contributions of turbulence and dry convective eddy are parameterized using schemes from the literature. Wind variabilities caused by moist convective eddies and fine-scale topography are estimated using empirical relationships derived from an operational weather analysis data set at 15 km resolution. The estimated sub-grid standard deviations of surface wind speed agree well with reference results derived from 1 year of global weather analysis at 15 km resolution and from two regional model simulations with 3 km grid spacing.The wind-distribution-based emission calculations are implemented in CAM5. In terms of computational cost, the increase in total simulation time turns out to be less than 3 %. Simulations at 2° resolution indicate that sub-grid wind variability has relatively small impacts (about 7 % increase) on the global annual mean emission of sea salt aerosols, but considerable influence on the emission of dust. Among the considered mechanisms, dry convective eddies and mesoscale flows associated with topography are major causes of dust emission enhancement. With all the four mechanisms included and without additional adjustment of uncertain parameters in the model, the simulated global and annual mean dust emission increase by about 50 % compared to the

  9. Quantifying the impact of sub-grid surface wind variability on sea salt and dust emissions in CAM5

    SciTech Connect

    Zhang, Kai; Zhao, Chun; Wan, Hui; Qian, Yun; Easter, Richard C.; Ghan, Steven J.; Sakaguchi, Koichi; Liu, Xiaohong

    2016-02-12

    This paper evaluates the impact of sub-grid variability of surface wind on sea salt and dust emissions in the Community Atmosphere Model version 5 (CAM5). The basic strategy is to calculate emission fluxes multiple times, using different wind speed samples of a Weibull probability distribution derived from model-predicted grid-box mean quantities.

    In order to derive the Weibull distribution, the sub-grid standard deviation of surface wind speed is estimated by taking into account four mechanisms: turbulence under neutral and stable conditions, dry convective eddies, moist convective eddies over the ocean, and air motions induced by mesoscale systems and fine-scale topography over land. The contributions of turbulence and dry convective eddy are parameterized using schemes from the literature. Wind variabilities caused by moist convective eddies and fine-scale topography are estimated using empirical relationships derived from an operational weather analysis data set at 15 km resolution. The estimated sub-grid standard deviations of surface wind speed agree well with reference results derived from 1 year of global weather analysis at 15 km resolution and from two regional model simulations with 3 km grid spacing.

    The wind-distribution-based emission calculations are implemented in CAM5. In terms of computational cost, the increase in total simulation time turns out to be less than 3 %. Simulations at 2° resolution indicate that sub-grid wind variability has relatively small impacts (about 7 % increase) on the global annual mean emission of sea salt aerosols, but considerable influence on the emission of dust. Among the considered mechanisms, dry convective eddies and mesoscale flows associated with topography are major causes of dust emission enhancement. With all the four mechanisms included and without additional adjustment of uncertain parameters in the model, the simulated global and annual mean dust emission increase by about 50 % compared to

  10. Quantifying the impact of sub-grid surface wind variability on sea salt and dust emissions in CAM5

    NASA Astrophysics Data System (ADS)

    Zhang, K.; Zhao, C.; Wan, H.; Qian, Y.; Easter, R. C.; Ghan, S. J.; Sakaguchi, K.; Liu, X.

    2015-08-01

    This paper evaluates the impact of sub-grid variability of surface wind on sea salt and dust emissions in the Community Atmosphere Model version 5 (CAM5). The basic strategy is to calculate emission fluxes multiple times, using different wind speed samples of a Weibull probability distribution derived from model-predicted grid-box mean quantities. In order to derive the Weibull distribution, the sub-grid standard deviation of surface wind speed is estimated by taking into account four mechanisms: turbulence under neutral and stable conditions, dry convective eddies, moist convective eddies over the ocean, and air motions induced by meso-scale systems and fine-scale topography over land. The contributions of turbulence and dry convective eddy are parameterized using schemes from the literature, while the wind variabilities caused by moist convective eddies and fine-scale topography are estimated using empirical relationships derived from an operational weather analysis dataset at 15 km resolution. The estimated sub-grid standard deviations of surface wind speed agree well with reference results derived from one year of global weather analysis at 15 km resolution and from two regional model simulations with 3 km grid spacing. The wind-distribution-based emission calculations are implemented in CAM5. Simulations at 2° resolution indicate that sub-grid wind variability has relatively small impacts (about 7 % increase) on the global annual mean emission of sea salt aerosols, but considerable influence on the emission of dust. Among the considered mechanisms, dry convective eddies and meso-scale flows associated with topography are major causes of dust emission enhancement. With all the four mechanisms included and without additional adjustment of uncertain parameters in the model, the simulated global and annual mean dust emission increase by about 50 % compared to the default model. By tuning the globally constant dust emission scale factor, the global annual mean

  11. Simulations of Supernova Reverse Shock Dust Destruction in Metal-Enriched Clouds

    NASA Astrophysics Data System (ADS)

    Silvia, Devin W.; Smith, B. D.; Shull, J. M.

    2011-01-01

    In following previous work, we present hydrodynamic simulations used to study the effects of dust destruction by sputtering in the reverse shocks of supernova remnants. As before (Silvia et al. 2010), we use an idealized setup of a planar shock impacting a dense, spherical clump implanted with a population of Lagrangian particles that act as tracers of dust. These tracers represent a distribution of dust grains that vary in both species and size. Specifically, we investigate those cases in which the cloud initially has super-solar metal abundances (Z 1000 Z⊙), as we expect the ejecta knots from supernova explosions to be extremely metal-enriched. A high abundance of metals has significant influence on both the cooling properties of the cloud and the thermal sputtering rates of the embedded dust grains. We also include a brief discussion about the difficulty of using the piecewise parabolic method for solving the hydrodynamic equations with high cooling rates produced by high metallicities. Through these simulations, we seek to quantify the fragmentation of ejecta clumps for comparison to observations of nearby supernova remnants and calculate the dust survival rate for these heavily metal-enriched cases. Estimates for dust survival in supernova shocks is critical in determining the source of dust at high redshift.

  12. Molecular Line Emission Towards High-Mass Clumps: The MALT90 Catalogue

    NASA Astrophysics Data System (ADS)

    Rathborne, J. M.; Whitaker, J. S.; Jackson, J. M.; Foster, J. B.; Contreras, Y.; Stephens, I. W.; Guzmán, A. E.; Longmore, S. N.; Sanhueza, P.; Schuller, F.; Wyrowski, F.; Urquhart, J. S.

    2016-07-01

    The Millimetre Astronomy Legacy Team 90 GHz survey aims to characterise the physical and chemical evolution of high-mass clumps. Recently completed, it mapped 90 GHz line emission towards 3 246 high-mass clumps identified from the ATLASGAL 870 μm Galactic plane survey. By utilising the broad frequency coverage of the Mopra telescope's spectrometer, maps in 16 different emission lines were simultaneously obtained. Here, we describe the first catalogue of the detected line emission, generated by Gaussian profile fitting to spectra extracted towards each clumps' 870 μm dust continuum peak. Synthetic spectra show that the catalogue has a completeness of > 95%, a probability of a false-positive detection of < 0.3%, and a relative uncertainty in the measured quantities of < 20% over the range of detection criteria. The detection rates are highest for the (1-0) transitions of HCO+, HNC, N2H+, and HCN (~77-89%). Almost all clumps (~95%) are detected in at least one of the molecular transitions, just over half of the clumps (~53%) are detected in four or more of the transitions, while only one clump is detected in 13 transitions. We find several striking trends in the ensemble of properties for the different molecular transitions when plotted as a function of the clumps' evolutionary state as estimated from Spitzer mid-IR images, including (1) HNC is relatively brighter in colder, less evolved clumps than those that show active star formation, (2) N2H+ is relatively brighter in the earlier stages, (3) that the observed optical depth decreases as the clumps evolve, and (4) the optically thickest HCO+ emission shows a `blue-red asymmetry' indicating overall collapse that monotonically decreases as the clumps evolve. This catalogue represents the largest compiled database of line emission towards high-mass clumps and is a valuable data set for detailed studies of these objects.

  13. Inter- and intra-annual variations of clumping index derived from the MODIS BRDF product

    NASA Astrophysics Data System (ADS)

    He, Liming; Liu, Jane; Chen, Jing M.; Croft, Holly; Wang, Rong; Sprintsin, Michael; Zheng, Ting; Ryu, Youngryel; Pisek, Jan; Gonsamo, Alemu; Deng, Feng; Zhang, Yongqin

    2016-02-01

    Clumping index quantifies the level of foliage aggregation, relative to a random distribution, and is a key structural parameter of plant canopies and is widely used in ecological and meteorological models. In this study, the inter- and intra-annual variations in clumping index values, derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) BRDF product, are investigated at six forest sites, including conifer forests, a mixed deciduous forest and an oak-savanna system. We find that the clumping index displays large seasonal variation, particularly for the deciduous sites, with the magnitude in clumping index values at each site comparable on an intra-annual basis, and the seasonality of clumping index well captured after noise removal. For broadleaved and mixed forest sites, minimum clumping index values are usually found during the season when leaf area index is at its maximum. The magnitude of MODIS clumping index is validated by ground data collected from 17 sites. Validation shows that the MODIS clumping index can explain 75% of variance in measured values (bias = 0.03 and rmse = 0.08), although with a narrower amplitude in variation. This study suggests that the MODIS BRDF product has the potential to produce good seasonal trajectories of clumping index values, but with an improved estimation of background reflectance.

  14. Chemistry of dense clumps near moving Herbig-Haro objects

    NASA Astrophysics Data System (ADS)

    Christie, H.; Viti, S.; Williams, D. A.; Girart, J. M.; Morata, O.

    2011-09-01

    Localized regions of enhanced emission from HCO+, NH3 and other species near Herbig-Haro objects (HHOs) have been interpreted as arising in a photochemistry stimulated by the HHO radiation on high-density quiescent clumps in molecular clouds. Static models of this process have been successful in accounting for the variety of molecular species arising ahead of the jet; however, recent observations show that the enhanced molecular emission is widespread along the jet as well as ahead. Hence, a realistic model must take into account the movement of the radiation field past the clump. It was previously unclear as to whether the short interaction time between the clump and the HHO in a moving source model would allow molecules such as HCO+ to reach high enough levels, and to survive for long enough to be observed. In this work we model a moving radiation source that approaches and passes a clump. The chemical picture is qualitatively unchanged by the addition of the moving source, strengthening the idea that enhancements are due to evaporation of molecules from dust grains. In addition, in the case of several molecules, the enhanced emission regions are longer lived. Some photochemically induced species, including methanol, are expected to maintain high abundances for ˜104 yr.

  15. Molecules and dust in Cassiopeia A. II. Dust sputtering and diagnosis of supernova dust survival in remnants

    NASA Astrophysics Data System (ADS)

    Biscaro, Chiara; Cherchneff, Isabelle

    2016-05-01

    We study the dust evolution in the supernova remnant Cassiopeia A. We follow the processing of dust grains that formed in the Type II-b supernova ejecta by modelling the sputtering of grains. The dust is located in dense ejecta clumps that are crossed by the reverse shock. We also investigate further sputtering in the inter-clump medium gas once the clumps have been disrupted by the reverse shock. The dust evolution in the dense ejecta clumps of Type II-P supernovae and their remnants is also explored. We study oxygen-rich clumps that describe the oxygen core of the ejecta, and carbon-rich clumps that correspond to the outermost carbon-rich ejecta zone. We consider the various dust components that form in the supernova, several reverse shock velocities and inter-clump gas temperatures, and derive grain-size distributions and masses for the dust as a function of time. Both non-thermal sputtering within clumps and thermal sputtering in the inter-clump medium gas are studied. We find that non-thermal sputtering in the clumps is important for all supernova types and accounts for reducing the grain population by ~ 40% to 80% in mass, depending on the clump gas over-density, the grain type and size, and the shock velocity in the clump. A Type II-b SN forms small grains that are sputtered within the clumps and in the inter-clump medium. For Cas A, silicate grains do not survive thermal sputtering in the inter-clump medium, while alumina, silicon carbide, and carbon dust may survive in the remnant. Our derived masses of currently processed silicate, alumina and carbon grains agree well with the values derived from the observations of warm dust, and seem to indicate that the dust is currently being processed within clumps by non-thermal sputtering. Out of the ~ 0.03M⊙ of dust formed in the ejecta, between 30% and 60% of this mass is present today in Cas A, and only 6% to 11% of the initial mass will survive the remnant phase. Grains formed in Type II-P supernovae are

  16. Dispersal patterns and clumping behaviors in the beetle Trichoton sordidum

    PubMed Central

    Gray, Carolyne N.

    2005-01-01

    this study to quantify relative clump sizes for Trichoton sordidum rather than total number of individuals in a clump. Homogeneous environment: Environment composed only of uniform, similar features with no irregular detail. In this experiment, open areas of sand, cloth, or fine debris were used. Habitat complexity: Structural interference in a habitat which leads to spatial variability. The result is predicted to be a change in the spatial distribution of individuals within the habitat. In this study pebbles were added to the homogeneous environment to break up a uniform surface area. PMID:16299601

  17. Clumped isotope thermometry and catagenesis

    NASA Astrophysics Data System (ADS)

    Eiler, J. M.; Clog, M. D.; Dallas, B.; Douglas, P. M.; Piasecki, A.; Sessions, A. L.; Stolper, D. A.

    2014-12-01

    Clumped- and site-specific isotopic compositions of organic compounds can constrain their formation temperatures, sources, and chemical reaction histories. The large number of isotopologues of organic molecules may allow for the isotopic composition of a single compound to illuminate many processes. For example, it is possible that clumping or site specific effects in different parts of the same molecule will differ in blocking temperature, such that a molecule's full isotopic structure could simultaneously constrain conditions of biosynthesis, catagenic 'cracking', and storage in the crust. Recent innovations in high-resolution mass spectrometry and methods of IR and NMR spectroscopy make it possible to explore these questions. Methane is the first organic molecule to have its clumped isotope geochemistry analyzed in a variety of natural environments and controlled experiments. Methane generated through catagenic cracking of kerogen and other organic matter forms in equilibrium with respect to isotopic clumping, and preserves that state through later storage or migration, up to temperatures of ~250 ˚C. This kinetic behavior permits a variety of useful geological applications. But it is unexpected because the bulk stable isotope composition of thermogenic methane is thought to reflect kinetic isotope effects on irreversible reactions. Our observations imply a new interpretation of the chemical physics of catagenic methane formation. Additional instrument and methods developments are currently extending the measurement of isotopic clumping and position specific effects to larger alkanes, other hydrocarbon compounds, and amino acids. These measurements will ultimately expand our capacity to understand the formational conditions and fates of organic molecules in high- and low-temperature environments through geological time.

  18. ATLASGAL: Chemical evolution of star forming clumps

    NASA Astrophysics Data System (ADS)

    Figura, Charles C.; Urquhart, James S.; Wyrowski, Friedrich

    2017-01-01

    Although massive stars are few in number, they impact their host molecular clouds, clusters, and galaxies in profound ways, playing a vital role in regulating star formation in their host galaxy. Understanding the formation of these massive stars is critical to understanding this evolution, but their rapid early development causes them to reach the main sequence while still shrouded in their natal molecular cloud. Many studies have investigated these regions in a targeted manner, but a full understanding necessitates a broader view at all stages of formation across many star forming regions.We have used mid-infrared continuum surveys to guide selection of a statistically large sample of massive dust clumps from the 10,000 such clumps identified in the ATLASGAL Compact Source Catalogue (CSC), ensuring that all stages of the evolutionary process are included. A final sample of 600 fourth-quadrant sources within 1 degree of the Galactic plane were observed with the Mopra telescope with an 8 GHz bandwidth between 85.2 and 93.4 GHz.We present an overview of our results. We have identified over 30 molecular lines, seven of which with detected hyperfine structure, as well as several mm-radio recombination line transitions. Source velocities indicate that these regions trace the Crux-Scutum, Norma, and Carina Sagitarius arms. We have performed an analysis of linewidth and line intensity ratios, correlating these with star formation stages as identified by IR brightness at the 70 and 24 μm bands, and present several molecular pairs whose linewidth and intensity might serve as significant tracers of the evolutionary stage of star formation. We comment on the results of PCA analysis of the measured parameters for the overall population and the star formation stage subgroups with an eye toward characterising early stellar development through molecular line observations.

  19. Gas of 96 Planck Cold Clumps in the Second Quadrant

    NASA Astrophysics Data System (ADS)

    Zhang, Tianwei; Wu, Yuefang; Liu, Tie; Meng, Fanyi

    2016-06-01

    Ninety-six Planck cold dust clumps in the second quadrant were mapped with 12CO (1-0), 13CO (1-0), and C18O (1-0) lines at the 13.7 m telescope of Purple Mountain Observatory. 12CO (1-0) and 13CO (1-0) emissions were detected for all 96 clumps, while C18O (1-0) emissions were detected in 81 of them. Fifteen clumps have more than one velocity component. In the 115 mapped velocity components, 225 cores were obtained. We found that 23.1% of the cores have non-Gaussian profiles. We acquired the V lsr, FWHM, and T A of the lines. Distances, T ex, velocity dispersions, {N}{{{H}}2}, and masses were also derived. Generally, turbulence may dominant the cores because {σ }{NT}/{σ }{Therm}\\gt 1 in almost all of the cores and Larson’s relationship is not apparent in our massive cores. Virial parameters are adopted to test the gravitational stability of cores and 51% of the cores are likely collapsing. The core mass function of the cores in the range 0-1 kpc suggests a low core-to-star conversional efficiency (0.62%). Only 14 of 225 cores (6.2%) have associated stellar objects at their centers, while the others are starless. The morphologies of clumps are mainly filamentary structures. Seven clumps may be located on an extension of the new spiral arm in the second quadrant while three are on the known outer arm.

  20. A process-based model for non-equilibrium clumped isotope effects in carbonates

    NASA Astrophysics Data System (ADS)

    Watkins, J. M.; Hunt, J. D.

    2015-12-01

    The equilibrium clumped isotope composition of carbonate minerals is independent of the composition of the aqueous solution. However, many carbonate minerals grow at rates that place them in a non-equilibrium regime with respect to carbon and oxygen isotopes with unknown consequences for clumped isotopes. We develop a process-based model that allows one to calculate the oxygen, carbon, and clumped isotope composition of calcite as a function of temperature, crystal growth rate, and solution pH. In the model, carbon and oxygen isotope fractionation occurs through the mass-dependent attachment/detachment kinetics of the isotopologues of HCO-3 and CO2-3 to and from the calcite surface, which in turn, influence the clumped isotope composition of calcite. At experimental and biogenic growth rates, the mineral is expected to inherit a clumped isotopic composition that is similar to that of the DIC pool, which helps to explain (1) why different organisms share the same clumped isotope versus temperature calibration curves, (2) why many inorganic calibration curves are slightly different from one another, and (3) why foraminifera, coccoliths, and deep sea corals can have near-equilibrium clumped isotope compositions but far-from-equilibrium carbon and oxygen isotope compositions. Some aspects of the model can be generalized to other mineral systems and should serve as a useful reference in future efforts to quantify kinetic clumped isotope effects.

  1. A Deuteration Survey of the Clump Population in the Gemini OB1 Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Henrici, Andrew Scott; Shirley, Yancy L.; Svoboda, Brian E.

    2017-01-01

    Recent maps of dust continuum emission from entire molecular clouds at submillimeter wavelengths have made it possible to survey and study the chemistry of entire core and clump populations within a single cloud. One very strong chemical process in star-forming regions is the fractionation of deuterium in molecules, which results in an increase in the deuterium ratio many orders of magnitude over the ISM [D]/[H] ratio and provides a chemical probe of cold, dense regions. We present a survey of DCO+ 3-2 and N2D+ 3-2 toward the clump population in the high-mass, star-forming Gemini OB1 Molecular Cloud identified from 1.1 mm continuum imaging by the Bolocam Galactic Plane Survey. The peak 1.1 mm continuum positions of 52 clumps in the range 188°≤ l ≤194° were observed with the 10m Heinrich Hertz Submillimeter Telescope. We find that DCO+ emission is detected toward 90% of the clumps with a median deuterium ratio of 0.01 while N2D+ emission is detected toward only 25% of the clumps. The DCO+ fractionation anti-correlates with gas kinetic temperature and linewidth, a measure of the amount of turbulence within the clumps. We compare the deuteration ratios of with physical properties of the clumps and their evolutionary stage.

  2. Formation of the Martian Polar Layered Terrains: Quantifying Polar Water Ice and Dust Surface Deposition during Current and Past Orbital Epochs with the NASA Ames GCM

    NASA Astrophysics Data System (ADS)

    Emmett, Jeremy; Murphy, Jim

    2016-10-01

    Structural and compositional variability in the layering sequences comprising Mars' polar layered terrains (PLT's) is likely explained by orbital-forced climatic variations in the sedimentary cycles of water ice and dust from which they formed [1]. The PLT's therefore contain a direct, extensive record of the recent climate history of Mars encoded in their structure and stratigraphy, but deciphering this record requires understanding the depositional history of their dust and water ice constituents. 3D Mars atmosphere modeling enables direct simulation of atmospheric dynamics, aerosol transport and quantification of surface accumulation for a range of past and present orbital configurations. By quantifying the net yearly polar deposition rates of water ice and dust under Mars' current and past orbital configurations characteristic of the last several millions of years, and integrating these into the present with a time-stepping model, the formation history of the north and south PLT's will be investigated, further constraining their age and composition, and, if reproducible, revealing the processes responsible for prominent features and stratigraphy observed within the deposits. Simulating the formation of the deposits by quantifying net deposition rates during past orbital epochs and integrating these into the present, effectively 'rebuilding' the terrains, could aid in understanding deeper stratigraphic trends, correlating between geographically-separated deposits, explaining the presence and shapes of large-scale polar features, and correlating stratigraphy with geological time. Quantification of the magnitude and geographical distribution of surface aerosol accumulation will build on the work of previous GCM-based investigations [3]. Construction and analysis of hypothetical stratigraphic sequences in the PLT's will draw from previous climate-controlled stratigraphy methodologies [2,4], but will utilize GCM-derived net deposition rates to model orbital

  3. A DELAUNAY TRIANGULATION APPROACH FOR SEGMENTING CLUMPS OF NUCLEI

    SciTech Connect

    Wen, Quan; Chang, Hang; Parvin, Bahram

    2009-05-07

    Cell-based fluorescence imaging assays have the potential to generate massive amount of data, which requires detailed quantitative analysis. Often, as a result of fixation, labeled nuclei overlap and create a clump of cells. However, it is important to quantify phenotypic read out on a cell-by-cell basis. In this paper, we propose a novel method for decomposing clumps of nuclei using high-level geometric constraints that are derived from low-level features of maximum curvature computed along the contour of each clump. Points of maximum curvature are used as vertices for Delaunay triangulation (DT), which provides a setof edge hypotheses for decomposing a clump of nuclei. Each hypothesis is subsequently tested against a constraint satisfaction network for a near optimum decomposition. The proposed method is compared with other traditional techniques such as the watershed method with/without markers. The experimental results show that our approach can overcome the deficiencies of the traditional methods and is very effective in separating severely touching nuclei.

  4. Cooperation, clumping and the evolution of multicellularity.

    PubMed

    Biernaskie, Jay M; West, Stuart A

    2015-08-22

    The evolution of multicellular organisms represents one of the major evolutionary transitions in the history of life. A potential advantage of forming multicellular clumps is that it provides an efficiency benefit to pre-existing cooperation, such as the production of extracellular 'public goods'. However, this is complicated by the fact that cooperation could jointly evolve with clumping, and clumping could have multiple consequences for the evolution of cooperation. We model the evolution of clumping and a cooperative public good, showing that (i) when considered separately, both clumping and public goods production gradually increase with increasing genetic relatedness; (ii) in contrast, when the traits evolve jointly, a small increase in relatedness can lead to a major shift in evolutionary outcome—from a non-clumping state with low public goods production to a cooperative clumping state with high values of both traits; (iii) high relatedness makes it easier to get to the cooperative clumping state and (iv) clumping can be inhibited when it increases the number of cells that the benefits of cooperation must be shared with, but promoted when it increases relatedness between those cells. Overall, our results suggest that public goods sharing can facilitate the formation of well-integrated cooperative clumps as a first step in the evolution of multicellularity.

  5. The Bolocam Galactic Plane Survey. XIV. Physical Properties of Massive Starless and Star-forming Clumps

    NASA Astrophysics Data System (ADS)

    Svoboda, Brian E.; Shirley, Yancy L.; Battersby, Cara; Rosolowsky, Erik W.; Ginsburg, Adam G.; Ellsworth-Bowers, Timothy P.; Pestalozzi, Michele R.; Dunham, Miranda K.; Evans, Neal J., II; Bally, John; Glenn, Jason

    2016-05-01

    We sort 4683 molecular clouds between 10° < ℓ < 65° from the Bolocam Galactic Plane Survey based on observational diagnostics of star formation activity: compact 70 μm sources, mid-IR color-selected YSOs, H2O and CH3OH masers, and UCH ii regions. We also present a combined NH3-derived gas kinetic temperature and H2O maser catalog for 1788 clumps from our own GBT 100 m observations and from the literature. We identify a subsample of 2223 (47.5%) starless clump candidates (SCCs), the largest and most robust sample identified from a blind survey to date. Distributions of flux density, flux concentration, solid angle, kinetic temperature, column density, radius, and mass show strong (>1 dex) progressions when sorted by star formation indicator. The median SCC is marginally subvirial (α ∼ 0.7) with >75% of clumps with known distance being gravitationally bound (α < 2). These samples show a statistically significant increase in the median clump mass of ΔM ∼ 170–370 M ⊙ from the starless candidates to clumps associated with protostars. This trend could be due to (i) mass growth of the clumps at \\dot{M}∼ 200{--}440 M ⊙ Myr‑1 for an average freefall 0.8 Myr timescale, (ii) a systematic factor of two increase in dust opacity from starless to protostellar phases, and/or (iii) a variation in the ratio of starless to protostellar clump lifetime that scales as ∼M ‑0.4. By comparing to the observed number of CH3OH maser containing clumps, we estimate the phase lifetime of massive (M > 103 M ⊙) starless clumps to be 0.37 ± 0.08 Myr (M/103 M ⊙)‑1 the majority (M < 450 M ⊙) have phase lifetimes longer than their average freefall time.

  6. The Planck Catalogue of Galactic Cold Clumps : PGCC

    NASA Astrophysics Data System (ADS)

    Montier, L.

    The Planck satellite has provided an unprecedented view of the submm sky, allowing us to search for the dust emission of Galactic cold sources. Combining Planck-HFI all-sky maps in the high frequency channels with the IRAS map at 100um, we built the Planck catalogue of Galactic Cold Clumps (PGCC, Planck 2015 results. XXVIII), counting 13188 sources distributed over the whole sky, and following mainly the Galactic structures at low and intermediate latitudes. This is the first all-sky catalogue of Galactic cold sources obtained with a single instrument at this resolution and sensitivity, which opens a new window on star-formation processes in our Galaxy.

  7. Clump Giants in the Hyades

    NASA Technical Reports Server (NTRS)

    Mushotzky, Richard F. (Technical Monitor); Brickhouse, Nancy

    2003-01-01

    The project is entitled 'Clump Giants in the Hyades.' This observation of one of the late-type Hyades giants (Gamma Tau) has implications for understanding the formation of late-type stellar coronae as a function of the evolutionary state of the star. The Hyades giants are interesting because they are all clump giants in the Helium burning phase, similar to the cool primary of Capella. The Hyades giants show significantly more magnetic activity than expected from their state of evolution (and slowed-down rotation). Thus these systems provide an important clue to dynamo action. The data were obtained by the satellite on 13 March 2001 for a total RGS exposure of 58220 seconds. These data were delivered to the PI on 7 August 2001. The data could not be reprocessed until SAS Version 5.3.3 which became available 7 June 2002. Although the guidelines for assessing background rates suggested that half the data were contaminated, it does not appear that the spectral region of the RGS was adversely affected by unusually high background. The spectra show strong lines of Fe XVII and XVIII, O VII and VIII, Ne IX and X, along with numerous weaker lines. The emission measure distribution is highly reminiscent of Capella; if anything, the emission measure distribution is steeper at 6 million K than for Capella. Gamma Tau is the second brightest of the Hyades clump giants. Pallavicini et al. have shown that the luminosity of the brightest Hyades giant (Theta Tau) is remarkably similar to its luminosity as measured by Einstein. Short-term variability is also modest. We are addressing the variability issue now for Gamma Tau. Initial results were reported at the 2003 Seattle AAS meeting. A paper is in preparation for submission to the Astrophysical Journal.

  8. Application of a combined measurement and modeling method to quantify windblown dust emissions from the exposed playa at Mono Lake, California.

    PubMed

    Ono, Duane; Kiddoo, Phill; Howard, Christopher; Davis, Guy; Richmond, Kenneth

    2011-10-01

    Particulate matter < or =10 microm (PM10) emissions due to wind erosion can vary dramatically with changing surface conditions. Crust formation, mechanical disturbance, soil texture, moisture, and chemical content of the soil can affect the amount of dust emitted during a wind event. A refined method of quantifying windblown dust emissions was applied at Mono Lake, CA, to account for changing surface conditions. This method used a combination of real-time sand flux monitoring, ambient PM10 monitoring, and dispersion modeling to estimate dust emissions and their downwind impact. The method identified periods with high emissions and periods when the surface was stable (no sand flux), even though winds may have been high. A network of 25 Cox sand catchers (CSCs) was used to measure the mass of saltating particles to estimate sand flux rates across a 2-km2 area. Two electronic sensors (Sensits) were used to time-resolve the CSC sand mass to estimate hourly sand flux rates, and a perimeter tapered element oscillating microbalance (TEOM) monitor measured hourly PM10 concentrations. Hourly sand flux rates were related by dispersion modeling to hourly PM10 concentrations to back-calculate the ratio of vertical PM10 flux to horizontal sand flux (K-factors). Geometric mean K-factor values (K(f)) were found to change seasonally, ranging from 1.3 x 10(-5) to 5.1 x 10(-5) for sand flux measured at 15 cm above the surface (q15). Hourly PM10 emissions, F, were calculated by applying seasonal K-factors to sand flux measurements (F = K(f) x q15). The maximum hourly PM10 emission rate from the study area was 76 g/m2 x hr (10-m wind speed = 23.5 m/sec). Maximum daily PM10 emissions were estimated at 450 g/m2 x day, and annual emissions at 1095 g/m2 x yr. Hourly PM10 emissions were used by the U.S. Environmental Protection Agency (EPA) guideline AERMOD dispersion model to estimate downwind ambient impacts. Model predictions compared well with monitor concentrations, with hourly PM10

  9. Application of a Combined Measurement and Modeling Method to Quantify Windblown Dust Emissions from the Exposed Playa at Mono Lake, California.

    PubMed

    Ono, Duane; Kiddoo, Phill; Howard, Christopher; Davis, Guy; Richmond, Kenneth

    2011-10-01

    Particulate matter ≤10 μm (PM10) emissions due to wind erosion can vary dramatically with changing surface conditions. Crust formation, mechanical disturbance, soil texture, moisture, and chemical content of the soil can affect the amount of dust emitted during a wind event. A refined method of quantifying windblown dust emissions was applied at Mono Lake, CA, to account for changing surface conditions. This method used a combination of real-time sand flux monitoring, ambient PM10 monitoring, and dispersion modeling to estimate dust emissions and their downwind impact. The method identified periods with high emissions and periods when the surface was stable (no sand flux), even though winds may have been high. A network of 25 Cox sand catchers (CSCs) was used to measure the mass of saltating particles to estimate sand flux rates across a 2-km(2) area. Two electronic sensors (Sensits) were used to time-resolve the CSC sand mass to estimate hourly sand flux rates, and a perimeter tapered element oscillating microbalance (TEOM) monitor measured hourly PM10 concentrations. Hourly sand flux rates were related by dispersion modeling to hourly PM10 concentrations to back-calculate the ratio of vertical PM10 flux to horizontal sand flux (K-factors). Geometric mean K-factor values (K f) were found to change seasonally, ranging from 1.3 × 10(-5) to 5.1 × 10(-5) for sand flux measured at 15 cm above the surface (q 15). Hourly PM10 emissions, F, were calculated by applying seasonal K-factors to sand flux measurements (F = K f × q 15). The maximum hourly PM10 emission rate from the study area was 76 g/m(2)·hr (10-m wind speed = 23.5 m/sec). Maximum daily PM10 emissions were estimated at 450 g/m(2)·day, and annual emissions at 1095 g/m(2)·yr. Hourly PM10 emissions were used by the U.S. Environmental Protection Agency (EPA) guideline AERMOD dispersion model to estimate downwind ambient impacts. Model predictions compared well with monitor concentrations, with

  10. Transient Clumps in Saturn's F Ring

    NASA Astrophysics Data System (ADS)

    Meinke, B. K.; Esposito, L. W.; Sremcevic, M.

    2011-10-01

    The Cassini Ultraviolet Imaging Spectrograph has detected 27 statistically significant features in 101 occultations by Saturn's F ring since July 2004. Of those 27 features, 17 likely correspond to transient clumps of material. We calculate from these observations the total number and total mass of transient clumps in the F ring. Constraints from observations place an upper limit on the number and total mass of such clumps. In turn, an upper limit on mass indicates that the clumps are not solid, spherical objects, rather they are loosely-packed, triaxial ellipsoids elongated in azimuth and vertically flattened. The total mass of clumps in the F ring is thus 6.1 x 1014 kg, the equivalent of a 6.8 km icy moon with a density equivalent to that of Prometheus. The differences in optical depth and morphology of the 17 significant features considered here also lead us to believe porosity differences exist among clumps. We investigate how the size distribution of clumps of different porosities evolves and how compaction of such clumps could lead to denser states that resemble moonlets, which describes 2 of the 17 features observed. The results presented here lead to a better model of how transient clumps form, evolve, and survive.

  11. Hidden Star Formation in High-Velocity Gas Clouds in Clump 2 near the Edge of the CMZ

    NASA Astrophysics Data System (ADS)

    Tolls, Volker; Smith, Howard Alan; Stark, Antony A.; Martin, Christopher L.; HIGGS Team

    2016-01-01

    The inner Galaxy can be divided into two main regions, the Central Molecular Zone (CMZ; Morris and Serabyn 1996) and the Galactic Bar region. Gas and dust moves from the end points of the Galactic Bar on dust lanes towards the CMZ, where it merges with the gas and dust located on a 100-pc molecular ring. The stream of gas and dust on the dust lanes is not continuous, but fragments into irregularly separated clumps of varying sizes. One of the most significant aggregations of clumps is the Clump 2 region (Roogour 1964, Bania 1977). Although the gas and dust clouds in this region are very dense, they were always considered quiet with no ongoing star formation. Selected regions of Clump 2 were the targets of Herschel HIFI and PACS observations of CO J=7-6, CI, CII, OI, NII, and OIII as part of the Herschel Inner Galactic Gas Survey (HIGGS). This poster will present an update of the ongoing data analysis, which may have yielded some surprising results.

  12. Photoevaporation of Clumps in Photodissociation Regions

    NASA Technical Reports Server (NTRS)

    Gorti, Uma; Hollenbach, David; DeVincenzi, D. (Technical Monitor)

    2002-01-01

    We present the results of an investigation of the effects of Far Ultraviolet (FUV) radiation (6.0eV < hv < 13.6eV) from hot early type OB stars on clumps in star-forming molecular clouds. Clumps in FUV-illuminated regions (or photodissociation regions or PDRs) undergo external heating and photodissociation as they are exposed to the FUV field, resulting in a loss of cold, molecular lump mass as it is converted to warm atomic gas. The heating, if rapid, creates strong photoevaporative mass flows off the clump surfaces, and drives shocks into the clumps, compressing them to high densities. The clumps lose mass on relatively short timescales. The evolution of an individual clump is found to be sensitive to three dimensionless parameters: Nc0, the ratio of the initial column density of the clump to the column N(0) approx. 10(exp 21) cm(exp -2) of a warm FUV-heated surface region; upsilon, the ratio of the sound speed in the heated surface to that in the cold clump material: and t(FUV)t(c), the ratio of the "turn-on time" t(FUV) of the heating flux on a clump to its initial sound crossing-time t(c). The evolution also depends on whether a confining interclump medium exists, or whether the interclump region has negligible pressure, as is the case for turbulence-generated clumps. In this paper, we use spherical 1-D numerical hydrodynamic models as well as approximate analytical models to study the dependence of clump photoevaporation on the physical parameters of the clump, and to derive the dynamical evolution, mass loss rates and photoevaporative timescales of a clump for a variety of astrophysical situations. Turbulent clumps evolve so that their column densities are equal to a critical value determined by the local FUV field, and typically have short photo evaporation timescales, approx. 10(exp 4-5) years for a 1 M(solar mass) clump in a typical star-forming region (Nc0 = 10, upsilon = 10). Clumps with insufficient magnetic pressure support, and in strong FUV fields

  13. The rate and latency of star formation in dense, massive clumps in the Milky Way

    NASA Astrophysics Data System (ADS)

    Heyer, M.; Gutermuth, R.; Urquhart, J. S.; Csengeri, T.; Wienen, M.; Leurini, S.; Menten, K.; Wyrowski, F.

    2016-04-01

    Context. Newborn stars form within the localized, high density regions of molecular clouds. The sequence and rate at which stars form in dense clumps and the dependence on local and global environments are key factors in developing descriptions of stellar production in galaxies. Aims: We seek to observationally constrain the rate and latency of star formation in dense massive clumps that are distributed throughout the Galaxy and to compare these results to proposed prescriptions for stellar production. Methods: A sample of 24 μm-based Class I protostars are linked to dust clumps that are embedded within molecular clouds selected from the APEX Telescope Large Area Survey of the Galaxy. We determine the fraction of star-forming clumps, f∗, that imposes a constraint on the latency of star formation in units of a clump's lifetime. Protostellar masses are estimated from models of circumstellar environments of young stellar objects from which star formation rates are derived. Physical properties of the clumps are calculated from 870 μm dust continuum emission and NH3 line emission. Results: Linear correlations are identified between the star formation rate surface density, ΣSFR, and the quantities ΣH2/τff and ΣH2/τcross, suggesting that star formation is regulated at the local scales of molecular clouds. The measured fraction of star forming clumps is 23%. Accounting for star formation within clumps that are excluded from our sample due to 24 μm saturation, this fraction can be as high as 31%, which is similar to previous results. Dense, massive clumps form primarily low mass (<1-2 M⊙) stars with emergent 24 μm fluxes below our sensitivity limit or are incapable of forming any stars for the initial 70% of their lifetimes. The low fraction of star forming clumps in the Galactic center relative to those located in the disk of the Milky Way is verified. Full Tables 2-4 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130

  14. SOFIA follow-ups of massive clumps from the ATLASGAL galactic plane survey

    NASA Astrophysics Data System (ADS)

    Wyrowski, F.; Güsten, R.; Menten, K. M.; Wiesemeyer, H.; Csengeri, T.; König, C.; Urquhart, J. S.

    2016-05-01

    With the GREAT receiver at the Stratospheric Observatory for Infrared Astronomy (SOFIA) we started a concerted observing effort towards a well selected sample of clumps with high masses covering a range of evolutionary stages based on their infrared properties. The sources were selected from the ATLASGAL sub-millimeter dust continuum survey of our Galaxy. The goal is threefold: (i) SOFIA/GREAT allows to study the cooling budget of the clumps, in particular with observations of the CII and OI cooling lines. (ii) With SOFIA/GREAT high-J CO lines can be observed to measure in combination with ground based data the CO SEDs of the sources. (iii) Using rotational transitions of ammonia at THz frequencies the kinematics of the clumps can be probed with absorption spectroscopy to search for infall. Here we will describe these efforts and in particular report new results from the ammonia 32+ - 22- (1.8 THz) observing program.

  15. Breakup of particle clumps on liquid surfaces

    NASA Astrophysics Data System (ADS)

    Gurupatham, S.; Hossain, M.; Dalal, B.; Fischer, I.; Singh, P.; Joseph, D.

    2011-11-01

    In this talk we describe the mechanism by which clumps of some powdered materials breakup and disperse on a liquid surface to form a monolayer of particles. We show that a clump breaks up because when particles on its outer periphery come in contact with the liquid surface they are pulled into the interface by the vertical component of capillary force overcoming the cohesive forces which keep them attached, and then these particles move away from the clump. In some cases, the clump itself is broken into smaller pieces and then these smaller pieces break apart by the aforementioned mechanism. The newly-adsorbed particles move away from the clump, and each other, because when particles are adsorbed on a liquid surface they cause a flow on the interface away from themselves. This flow may also cause particles newly-exposed on the outer periphery of the clump to break away. Since millimeter-sized clumps can breakup and spread on a liquid surface within a few seconds, their behavior appears to be similar to that of some liquid drops which can spontaneously disperse on solid surfaces.

  16. Recombination clumping factor during cosmic reionization

    SciTech Connect

    Kaurov, Alexander A.; Gnedin, Nickolay Y. E-mail: gnedin@fnal.gov

    2014-06-01

    We discuss the role of recombinations in the intergalactic medium, and the related concept of the clumping factor, during cosmic reionization. The clumping factor is, in general, a local quantity that depends on both the local overdensity and the scale below which the baryon density field can be assumed smooth. That scale, called the filtering scale, depends on over-density and local thermal history. We present a method for building a self-consistent analytical model of inhomogeneous reionization, assuming the linear growth rate of the density fluctuation, which simultaneously accounts for these effects. We show that taking into account the local clumping factor introduces significant corrections to the total recombination rate, compared to the model with a globally uniform clumping factor.

  17. Fragmentation of Molecular Clumps and Formation of a Protocluster

    NASA Astrophysics Data System (ADS)

    Zhang, Qizhou; Wang, Ke; Lu, Xing; Jiménez-Serra, Izaskun

    2015-05-01

    Sufficiently massive clumps of molecular gas collapse under self-gravity and fragment to spawn a cluster of stars that have a range of masses. We investigate observationally the early stages of formation of a stellar cluster in a massive filamentary infrared dark cloud, G28.34+0.06 P1, in the 1.3 mm continuum and spectral line emission using the Atacama Large Millimeter/Submillimeter Array. Sensitive continuum data reveal further fragmentation in five dusty cores at a resolution of several 103 AU. Spectral line emission from C18O, CH3OH, 13CS, H2CO, and N2D+ is detected for the first time toward these dense cores. We found that three cores are chemically more evolved as compared with the other two; interestingly, though, all of them are associated with collimated outflows as suggested by evidence from the CO, SiO, CH3OH, H2CO, and SO emission. The parsec-scale kinematics in exhibit velocity gradients along the filament, consistent with accretion flows toward the clumps and cores. The moderate luminosity and the chemical signatures indicate that the five cores harbor low- to intermediate-mass protostars that likely become massive ones at the end of the accretion. Despite the fact that the mass limit reached by the dust continuum sensitivity is 30 times lower than the thermal Jeans mass, there is a lack of a distributed low-mass protostellar population in the clump. Our observations indicate that in a protocluster, low-mass stars form at a later stage after the birth of more massive protostars.

  18. FRAGMENTATION OF MOLECULAR CLUMPS AND FORMATION OF A PROTOCLUSTER

    SciTech Connect

    Zhang, Qizhou; Lu, Xing; Wang, Ke; Jiménez-Serra, Izaskun

    2015-05-10

    Sufficiently massive clumps of molecular gas collapse under self-gravity and fragment to spawn a cluster of stars that have a range of masses. We investigate observationally the early stages of formation of a stellar cluster in a massive filamentary infrared dark cloud, G28.34+0.06 P1, in the 1.3 mm continuum and spectral line emission using the Atacama Large Millimeter/Submillimeter Array. Sensitive continuum data reveal further fragmentation in five dusty cores at a resolution of several 10{sup 3} AU. Spectral line emission from C{sup 18}O, CH{sub 3}OH, {sup 13}CS, H{sub 2}CO, and N{sub 2}D{sup +} is detected for the first time toward these dense cores. We found that three cores are chemically more evolved as compared with the other two; interestingly, though, all of them are associated with collimated outflows as suggested by evidence from the CO, SiO, CH{sub 3}OH, H{sub 2}CO, and SO emission. The parsec-scale kinematics in exhibit velocity gradients along the filament, consistent with accretion flows toward the clumps and cores. The moderate luminosity and the chemical signatures indicate that the five cores harbor low- to intermediate-mass protostars that likely become massive ones at the end of the accretion. Despite the fact that the mass limit reached by the dust continuum sensitivity is 30 times lower than the thermal Jeans mass, there is a lack of a distributed low-mass protostellar population in the clump. Our observations indicate that in a protocluster, low-mass stars form at a later stage after the birth of more massive protostars.

  19. Dust agglomeration

    NASA Technical Reports Server (NTRS)

    2000-01-01

    John Marshall, an investigator at Ames Research Center and a principal investigator in the microgravity fluid physics program, is studying the adhesion and cohesion of particles in order to shed light on how granular systems behave. These systems include everything from giant dust clouds that form planets to tiny compressed pellets, such as the ones you swallow as tablets. This knowledge should help us control the grains, dust, and powders that we encounter or use on a daily basis. Marshall investigated electrostatic charge in microgravity on the first and second U.S. Microgravity Laboratory shuttle missions to see how grains aggregate, or stick together. With gravity's effects eliminated on orbit, Marshall found that the grains of sand that behaved ever so freely on Earth now behaved like flour. They would just glom together in clumps and were quite difficult to disperse. That led to an understanding of the prevalence of the electrostatic forces. The granules wanted to aggregate as little chains, like little hairs, and stack end to end. Some of the chains had 20 or 30 grains. This phenomenon indicated that another force, what Marshall believes to be an electrostatic dipole, was at work.(The diagram on the right emphasizes the aggregating particles in the photo on the left, taken during the USML-2 mission in 1995.)

  20. The most massive gas clumps in the Milky Way

    NASA Astrophysics Data System (ADS)

    Zahorecz, Sarolta; Beuther, Henrik; Henning, Thomas; Linz, Hendrik; Tackenberg, Jochen; Schmiedeke, Anika; Schuller, Frederic; Urquhart, James; Wienen, Marion; Wyrowski, Friedrich

    2013-07-01

    In the recent years significant progress has been made in the understanding of high-mass star formation, although there are still open questions. Only a systematic survey can provide statistical data for unbiased studies. The APEX Telescope Large Area Survey of the Galaxy (ATLASGAL, Schuller et al. 2009, A&A, 605, 415) surveyed the southern sky at submillimeter wavelengths in dust continuum emission. We searched for the most massive dense gas condensations in the ATLASGAL survey within -60 < l < 60 degree and |b| < 1.5 degrees. We investigated the most luminous clumps and with the use of the Herschel Hi-GAL (Molinari et. al 2010, PASP, 122, 314) data we studied their basic physical parameters: distances, galactic distributions, temperatures, luminosites, masses.

  1. The Clumped Isotope Composition of Biogenic Methane.

    NASA Astrophysics Data System (ADS)

    Sessions, A. L.; Douglas, P. M.; Eiler, J. M.; Stolper, D. A.

    2015-12-01

    The excess or lack of 13CH3D, a doubly substituted ("clumped") isotopologue of methane, relative to that expected for a random distribution of isotopes across molecules, is a function of the processes that generated the methane. For high-temperature thermogenic methane, which typically achieves internal equilibrium, an excess of 13CH3D is expected and the amount of excess can serve as a thermometer. In contrast, biogenic methane often - though not always - has a smaller excess of clumped isotopologues, and sometimes even a deficit of clumped species ("anti-clumped"). The effect presumably arises from kinetic isotope effects accompanying enzymatic reactions in the methanogenic pathway, though the particular reaction(s) has not yet been positively identified. The decrease in clumping is also known to correlate with both the reversibility of the pathway and the methane flux. In this talk, we will present recent data bearing on the origin and utility of biologic fractionations of clumped isotopologues in methane. Preliminary data suggest that methane deriving from the fermentative pathway is enriched in D-bearing isotopologues, at the same level of clumping, relative to that derived from the CO2-reductive pathway. This property offers another potential means to distinguish biogenic methane sources in the environment. Recently, we have also begun to measure the 12CH2D2 isotopologue, for which equilibrium and kinetic isotope effects are predicted to be distinct from 13CH3D. Preliminary data suggest that the combination of both doubly-substituted isotopologues will be especially useful for disentangling mixtures containing biogenic gas.

  2. Clumps and Temporal Changes in the Jovian Ring System as Viewed by New Horizons

    NASA Astrophysics Data System (ADS)

    Showalter, Mark R.; Cheng, A. F.; Weaver, H. A.; Stern, S. A.; Spencer, J. R.; Throop, H.; Birath, E. M.; Rose, D.; Moore, J. M.

    2007-10-01

    New Horizons obtained 400 ring images of the Jovian ring system using the Long Range Reconnaissance Imager (LORRI). This camera has a broad bandpass spanning wavelengths λ = 0.35 to 0.85 µm. The ring was imaged at phase angles 7°-159°. In addition, one sequence of near-IR spectra (λ = 1.25 to 2.5 µm) was obtained by the Linear Etalon Imaging Spectral Array (LEISA) for compositional studies. Two ring rotation movies during Jupiter approach were used to search for small moons embedded within the system. These bodies might serve as source bodies for the prevalent ring dust. No moons were detected down to a threshold of 500 m radius, suggesting a sharp cutoff in the population of inner Jovian moons below 8-km Adrastea. Although this search focused on the main Jovian ring, any 1-km moons from orbital radius r = 100,000 km to beyond the orbit of Amalthea (r = 181,000 km) should have been detected multiple times. More surprisingly, the ring revealed two clusters of tiny clumps, one pair and one set of three. These are definitively not moons because they have longitudinal extents of a few tenths of a degree. Separations between clumps are 2 to 4° but are not uniform. These clump families both orbit within a brightness peak just interior to the orbit of Adrastea, at r = 128,740 km. Their origin is unknown. They are not visible at high phase angles, indicating that they are composed primarily of larger "parent” bodies, not dust. They are definitely not related to a clump detected in Cassini images of the Jovian ring from December 2000, indicating that at least some ring clumps are transient. The large quadrant asymmetries reported in earlier images from Voyager and Galileo are completely absent in the new data.

  3. IRDC G030.88+00.13: A TALE OF TWO MASSIVE CLUMPS

    SciTech Connect

    Zhang Qizhou; Wang Ke

    2011-05-20

    Massive stars (M {approx}>10 M{sub sun}) form from collapse of parsec-scale molecular clumps. How molecular clumps fragment to give rise to massive stars in a cluster with a distribution of masses is unclear. We search for cold cores that may lead to future formation of massive stars in a massive (>10{sup 3} M{sub sun}), low luminosity (4.6 x 10{sup 2} L{sub sun}) infrared dark cloud (IRDC) G030.88+00.13. The NH{sub 3} data from the Very Large Array (VLA) and Green Bank Telescope reveal that the extinction feature seen in the infrared consists of two distinctive clumps along the same line of sight. The C1 clump at 97 km s{sup -1} coincides with the extinction in the Spitzer 8 and 24 {mu}m. Therefore, it is responsible for the majority of the IRDC. The C2 clump at 107 km s{sup -1} is more compact and has a peak temperature of 45 K. Compact dust cores and H{sub 2}O masers revealed in the Submillimeter Array and VLA observations are mostly associated with C2, and none are within the IRDC in C1. The luminosity indicates that neither the C1 nor C2 clump has yet to form massive protostars. But C1 might be at a precluster forming stage. The simulated observations rule out 0.1 pc cold cores with masses above 8 M{sub sun} within the IRDC. The core masses in C1 and C2 and those in high-mass protostellar objects suggest an evolutionary trend that the mass of cold cores increases over time. Based on our findings, we propose an empirical picture of massive star formation that protostellar cores and the embedded protostars undergo simultaneous mass growth during the protostellar evolution.

  4. A Predator-Prey Model for Moon-Triggered Clumping in Saturn's Rings

    NASA Astrophysics Data System (ADS)

    Esposito, L. W.; Albers, N.; Meinke, B. K.; Sremcevic, M.; Madhusudhanan, P.; Colwell, J. E.; Jerousek, R. E.

    2011-10-01

    UVIS occultation data show clumping in Saturn's F ring and at the B ring outer edge, indicating aggregation and disaggregation at these locations that are perturbed by Mimas and by Prometheus. Timescales range from hours to months. Structure near the B ring edge is seen in power spectral analysis at scales 200m - 2000m. We quantify this sub-km structure using wavelet analysis that estimates the statistical significance of the features. Similar structure is also seen at the strongest density waves, with significance increasing with resonance strength (FIGURE 1). For the B ring outer edge, the strongest structure is seen at longitudes 90° and 270° relative to Mimas. This indicates a direct relation between the moon and the ring clumping. We propose that the collective behavior of the ring particles resembles a predatorprey system: the mean aggregate size is the prey, which feeds the velocity dispersion; conversely, increasing dispersion breaks up the aggregates. Moons may trigger clumping by streamline crowding, which reduces the relative velocity, leading to more aggregation and more clumping. Disaggregation may follow from disruptive collisions or tidal shedding as the clumps stir the relative velocity. For realistic values of the parameters this yields a limit cycle behavior, as for the ecology of foxes and hares or the "boom-bust" economic cycle. Solving for the longterm behavior of this forced system gives a periodic response at the perturbing frequency, with a phase lag roughly consistent with the UVIS occultation measurements (FIGURE 2).

  5. Self-shielding clumps in starburst clusters

    NASA Astrophysics Data System (ADS)

    Palouš, Jan; Wünsch, Richard; Ehlerová, Soňa; Tenorio-Tagle, Guillermo

    2017-03-01

    Young and massive star clusters above a critical mass form thermally unstable clumps reducing locally the temperature and pressure of the hot 107 K cluster wind. The matter reinserted by stars, and mass loaded in interactions with pristine gas and from evaporating circumstellar disks, accumulate on clumps that are ionized with photons produced by massive stars. We discuss if they may become self-shielded when they reach the central part of the cluster, or even before it, during their free fall to the cluster center. Here we explore the importance of heating efficiency of stellar winds.

  6. Hidden Star Formation in High-Velocity Gas Clouds in Clump 2 near the Edge of the CMZ

    NASA Astrophysics Data System (ADS)

    Tolls, Volker; Smith, Howard A.

    2017-01-01

    We present a snapshot of our ongoing investigation of molecular clouds in Clump 2 located in the Galactic Bar region at a projected distance of ~400pc from the Galactic Center. We show that the analysis of the Clump 2 molecular clouds is complicated because of many fore- and background clouds in the line of sight. Of all clouds, IGGC 22 is the most interesting one, showing very high dust column densities, significant high-J CO emission, and, potentially harbors star formations as eluded to by the detection of [OIII] emission.

  7. Probing Planck Cold Clump Sightlines through HST STIS UV Spectroscopy

    NASA Astrophysics Data System (ADS)

    Dirks, Cody; Meyer, David M.

    2017-01-01

    The Planck Catalogue of Galactic Cold Clumps (PGCC) has provided a wealth of information about the cold, dusty ISM across the entire sky, identifying regions ranging from relatively diffuse cold clouds to pre-stellar cores in giant molecular clouds. This catalogue uses sub-millimeter emission arising from cold dust to determine the physical properties, morphology, and temperature of these regions. Combining this information with the diagnostic capabilities of UV absorption line spectroscopy allows us to better characterize the interstellar gas associated with these dusty regions. We have identified numerous target stars with STIS high-resolution UV spectra in the Hubble Space Telescope data archive whose sightlines lie in the sky vicinity of PGCC objects. By analyzing select interstellar absorption lines along these target sightlines, we can investigate several important cloud properties. Here we investigate the gas thermal pressure using C I fine structure excitation, and find a similar distribution to previous studies of the broader diffuse ISM. We also investigate the potential destruction of dust grains by shock processing by determining abundance ratios of heavily depleted elements to those that are typically lightly depleted.

  8. DYNAMO-HST survey: clumps in nearby massive turbulent discs and the effects of clump clustering on kiloparsec scale measurements of clumps

    NASA Astrophysics Data System (ADS)

    Fisher, David B.; Glazebrook, Karl; Damjanov, Ivana; Abraham, Roberto G.; Obreschkow, Danail; Wisnioski, Emily; Bassett, Robert; Green, Andy; McGregor, Peter

    2017-01-01

    We present ˜100 pc resolution Hubble Space Telescope Hα images of 10 galaxies from the DYnamics of Newly-Assembled Massive Objects (DYNAMO) survey of low-z turbulent disc galaxies, and use these to undertake the first detailed systematic study of the effects of resolution and clump clustering on observations of clumps in turbulent discs. In the DYNAMO-HST sample, we measure clump diameters spanning the range dclump ˜ 100-800 pc, and individual clump star formation rates as high as ˜5 M⊙ yr-1. DYNAMO clumps have very high SFR surface densities, ΣSFR ˜ 1 - 15 M⊙ yr-1 kpc-2, ˜100 × higher than in H II regions of nearby spirals. Indeed, SFR surface density provides a simple dividing line between massive star-forming clumps and local star-forming regions, where massive star-forming clumps have ΣSFR > 0.5 M⊙ yr-1 kpc-2. When degraded to match the observations of galaxies in z ˜ 1-3 surveys, DYNAMO galaxies are similar in morphology and measured clump properties to clumpy galaxies observed in the high-z Universe. Emission peaks in the simulated high-redshift maps typically correspond to multiple clumps in full resolution images. This clustering of clumps systematically increases the apparent size and SFR of clumps in 1 kpc resolution maps, and decreases the measured SFR surface density of clumps by as much as a factor of 20×. From these results we can infer that clump clustering is likely to strongly affect the measured properties of clumps in high-z galaxies, which commonly have kiloparsec scale resolution.

  9. MOLECULAR ENVIRONMENTS OF 51 PLANCK COLD CLUMPS IN THE ORION COMPLEX

    SciTech Connect

    Liu Tie; Wu Yuefang; Zhang Huawei E-mail: ywu@pku.edu.cn

    2012-09-15

    A mapping survey of 51 Planck cold clumps projected on the Orion complex was performed with J = 1-0 lines of {sup 12}CO and {sup 13}CO with the 13.7 m telescope at the Purple Mountain Observatory. The mean column densities of the Planck gas clumps range from 0.5 to 9.5 Multiplication-Sign 10{sup 21} cm{sup -2}, with an average value of (2.9 {+-} 1.9) Multiplication-Sign 10{sup 21} cm{sup -2}. The mean excitation temperatures of these clumps range from 7.4 to 21.1 K, with an average value of 12.1 {+-} 3.0 K and the average three-dimensional velocity dispersion {sigma}{sub 3D} in these molecular clumps is 0.66 {+-} 0.24 km s{sup -1}. Most of the clumps have {sigma}{sub NT} larger than or comparable to {sigma}{sub Therm}. The H{sub 2} column density of the molecular clumps calculated from molecular lines correlates with the aperture flux at 857 GHz of the dust emission. By analyzing the distributions of the physical parameters, we suggest that turbulent flows can shape the clump structure and dominate their density distribution on large scales, but not function on small scales due to local fluctuations. Eighty-two dense cores are identified in the molecular clumps. The dense cores have an average radius and local thermal equilibrium (LTE) mass of 0.34 {+-} 0.14 pc and 38{sup +5}{sub -30} M{sub Sun }, respectively. The structures of low column density cores are more affected by turbulence, while the structures of high column density cores are more affected by other factors, especially by gravity. The correlation of velocity dispersion versus core size is very weak for the dense cores. The dense cores are found to be most likely gravitationally bounded rather than pressure confined. The relationship between M{sub vir} and M{sub LTE} can be well fitted with a power law. The core mass function here is much flatter than the stellar initial mass function. The lognormal behavior of the core mass distribution is most likely determined by internal turbulence.

  10. Clumping in hot-star winds

    NASA Astrophysics Data System (ADS)

    Hamann, Wolf-Rainer; Feldmeier, Achim; Oskinova, Lidia M.

    2008-04-01

    Stellar winds play an important role for the evolution of massive stars and their cosmic environment. Multiple lines of evidence, coming from spectroscopy, polarimetry, variability, stellar ejecta, and hydrodynamic modeling, suggest that stellar winds are non-stationary and inhomogeneous. This is referred to as 'wind clumping'. The urgent need to understand this phenomenon is boosted by its far-reaching implications. Most importantly, all techniques to derive empirical mass-loss rates are more or less corrupted by wind clumping. Consequently, mass-loss rates are extremely uncertain. Within their range of uncertainty, completely different scenarios for the evolution of massive stars are obtained. Settling these questions for Galactic OB, LBV and Wolf-Rayet stars is prerequisite to understanding stellar clusters and galaxies, or predicting the properties of first-generation stars. In order to develop a consistent picture and understanding of clumped stellar winds, an international workshop on 'Clumping in Hot Star Winds' was held in Potsdam, Germany, from 18. - 22. June 2007. About 60 participants, comprising almost all leading experts in the field, gathered for one week of extensive exchange and discussion. The Scientific Organizing Committee (SOC) included John Brown (Glasgow), Joseph Cassinelli (Madison), Paul Crowther (Sheffield), Alex Fullerton (Baltimore), Wolf-Rainer Hamann (Potsdam, chair), Anthony Moffat (Montreal), Stan Owocki (Newark), and Joachim Puls (Munich). These proceedings contain the invited and contributed talks presented at the workshop, and document the extensive discussions.

  11. Carbonate clumped isotope thermometry in continental tectonics

    NASA Astrophysics Data System (ADS)

    Huntington, Katharine W.; Lechler, Alex R.

    2015-04-01

    Reconstructing the thermal history of minerals and fluids in continental environments is a cornerstone of tectonics research. Paleotemperature constraints from carbonate clumped isotope thermometry have provided important tests of geodynamic, structural, topographic and basin evolution models. The thermometer is based on the 13C-18O bond ordering in carbonates (mass-47 anomaly, Δ47) and provides estimates of the carbonate formation temperature independent of the δ18O value of the water from which the carbonate grew; Δ47 is measured simultaneously with conventional measurements of carbonate δ13C and δ18O values, which together constrain the isotopic composition of the parent water. Depending on the geologic setting of carbonate growth, this information can help constrain paleoenvironmental conditions or basin temperatures and fluid sources. This review examines how clumped isotope thermometry can shed new light on problems in continental tectonics, focusing on paleoaltimetry, basin evolution and structural diagenesis applications. Paleoaltimetry is inherently difficult, and the precision in carbonate growth temperature estimates is at the limit of what is useful for quantitative paleoelevation reconstruction. Nevertheless, clumped isotope analyses have enabled workers to address previously intractable problems and in many settings offer the best chance of understanding topographic change from the geologic record. The portion of the shallow crust residing at temperatures up to ca. 200 °C is important as host to economic resources and records of tectonics and climate, and clumped isotope thermometry is one of the few proxies that can access this critical range with sensitivity to temperature alone. Only a handful of studies to date have used clumped isotopes to investigate diagenesis and other sub-surface processes using carbonate crystallization temperatures or the sensitivity of Δ47 values to a sample's thermal history. However, the thermometer is

  12. Equilibrium clumped-isotope effects in doubly substituted isotopologues of ethane

    NASA Astrophysics Data System (ADS)

    Webb, Michael A.; Wang, Yimin; Braams, Bastiaan J.; Bowman, Joel M.; Miller, Thomas F.

    2017-01-01

    We combine path-integral Monte Carlo methods with a new intramolecular potential energy surface to quantify the equilibrium enrichment of doubly substituted ethane isotopologues due to clumped-isotope effects. Ethane represents the simplest molecule to simultaneously exhibit 13C-13C, 13C-D, and D-D clumped-isotope effects, and the analysis of corresponding signatures may provide useful geochemical and biogeochemical proxies of formation temperatures or reaction pathways. Utilizing path-integral statistical mechanics, we predict equilibrium fractionation factors that fully incorporate nuclear quantum effects, such as anharmonicity and rotational-vibrational coupling which are typically neglected by the widely used Urey model. The magnitude of the calculated fractionation factors for the doubly substituted ethane isotopologues indicates that isotopic clumping can be observed if rare-isotope substitutions are separated by up to three chemical bonds, but the diminishing strength of these effects suggests that enrichment at further separations will be negligible. The Urey model systematically underestimates enrichment due to 13C-D and D-D clumped-isotope effects in ethane, leading to small relative errors in the apparent equilibrium temperature, ranging from 5 K at 273.15 K to 30 K at 873.15 K. We additionally note that the rotameric dependence of isotopologue enrichment must be carefully considered when using the Urey model, whereas the path-integral calculations automatically account for such effects due to configurational sampling. These findings are of direct relevance to future clumped-isotope studies of ethane, as well as studies of 13C-13C, 13C-D, and D-D clumped-isotope effects in other hydrocarbons.

  13. Interstellar Dust - A Review

    NASA Technical Reports Server (NTRS)

    Salama, Farid

    2012-01-01

    The study of the formation and the destruction processes of cosmic dust is essential to understand and to quantify the budget of extraterrestrial organic materials. Although dust with all its components plays an important role in the evolution of interstellar physics and chemistry and in the formation of organic materials, little is known on the formation and destruction processes of carbonaceous dust. Laboratory experiments that are performed under conditions that simulate interstellar and circumstellar environments to provide information on the nature, the size and the structure of interstellar dust particles, the growth and the destruction processes of interstellar dust and the resulting budget of extraterrestrial organic molecules. A review of the properties of dust and of the laboratory experiments that are conducted to study the formation processes of dust grains from molecular precursors will be given.

  14. Characterizing the zone of influence of dark matter clumps on image positions and flux ratios in gravitational lensing systems

    NASA Astrophysics Data System (ADS)

    Johnson, Jyothisraj; Keeton, Charles R.; Brennan, Sean

    2016-01-01

    The Cold Dark Matter (CDM) model of the universe predicts that there should be hundreds to thousands of clumps surrounding a massive galaxy. However, observations have shown that we only see dozens of dwarf galaxies and not the hundreds to thousands that are predicted. This means that either the CDM model prediction is wrong, or most of the substructure consists of dark matter that cannot be observed directly. Massive galaxies serve as natural gravitational lenses throughout the universe that allow us to indirectly observe these dark matter perturbations. Strong gravitational lensing occurs when these massive elliptical galaxies have the critical density required to bend light from a source located behind it and produce multiple images of that same source. Dark matter clumps located near these multiple images affect their positions and flux ratios. We used lensing simulations to quantify how dark matter clumps affect image properties and to characterize this zone of influence through color maps of chi-squared values. Our results showed regions around each of the image positions that display significant perturbations for low mass clumps. For higher mass clumps, however, these distinct regions bleed together. We found that there is a correlation between the mass of the dark matter clump and the area it perturbs.This research has been supported by NSF grant PHY-1263280.

  15. Properties of Starless Clumps through Protoclusters from the Bolocam Galactic Plane Survey

    NASA Astrophysics Data System (ADS)

    Svoboda, Brian E.; Shirley, Yancy

    2014-07-01

    High mass stars play a key role in the physical and chemical evolution of the interstellar medium, yet the evolution of physical properties for high-mass star-forming regions remains unclear. We sort a sample of ~4668 molecular cloud clumps from the Bolocam Galactic Plane Survey (BGPS) into different evolutionary stages by combining the BGPS 1.1 mm continuum and observational diagnostics of star-formation activity from a variety of Galactic plane surveys: 70 um compact sources, mid-IR color-selected YSOs, H2O and CH3OH masers, EGOs, and UCHII regions. We apply Monte Carlo techniques to distance probability distribution functions (DPDFs) in order to marginalize over the kinematic distance ambiguity and calculate distributions for derived quantities of clumps in different evolutionary stages. We also present a combined NH3 and H2O maser catalog for ~1590 clumps from the literature and our own GBT 100m observations. We identify a sub-sample of 440 dense clumps with no star-formation indicators, representing the largest and most robust sample of pre-protocluster candidates from a blind survey to date. Distributions of I(HCO+), I(N2H+), dv(HCO+), dv(N2H+), mass surface density, and kinetic temperature show strong progressions when separated by evolutionary stage. No progressions are found in size or dust mass; however, weak progressions are observed in area > 2 pc^2 and dust mass > 3 10^3 Msun. An observed breakdown occurs in the size-linewidth relationship and we find no improvement when sampling by evolutionary stage.

  16. Kinetic temperature of massive star forming molecular clumps measured with formaldehyde

    NASA Astrophysics Data System (ADS)

    Tang, X. D.; Henkel, C.; Menten, K. M.; Zheng, X. W.; Esimbek, J.; Zhou, J. J.; Yeh, C. C.; König, C.; Yuan, Y.; He, Y. X.; Li, D. L.

    2017-01-01

    Context. For a general understanding of the physics involved in the star formation process, measurements of physical parameters such as temperature and density are indispensable. The chemical and physical properties of dense clumps of molecular clouds are strongly affected by the kinetic temperature. Therefore, this parameter is essential for a better understanding of the interstellar medium. Formaldehyde, a molecule which traces the entire dense molecular gas, appears to be the most reliable tracer to directly measure the gas kinetic temperature. Aims: We aim to determine the kinetic temperature with spectral lines from formaldehyde and to compare the results with those obtained from ammonia lines for a large number of massive clumps. Methods: Three 218 GHz transitions (JKAKC = 303-202, 322-221, and 321-220) of para-H2CO were observed with the 15 m James Clerk Maxwell Telescope (JCMT) toward 30 massive clumps of the Galactic disk at various stages of high-mass star formation. Using the RADEX non-LTE model, we derive the gas kinetic temperature modeling the measured para-H2CO 322-221/303-202 and 321-220/303-202 ratios. Results: The gas kinetic temperatures derived from the para-H2CO (321-220/303-202) line ratios range from 30 to 61 K with an average of 46 ± 9 K. A comparison of kinetic temperature derived from para-H2CO, NH3, and the dust emission indicates that in many cases para-H2CO traces a similar kinetic temperature to the NH3 (2, 2)/(1, 1) transitions and the dust associated with the HII regions. Distinctly higher temperatures are probed by para-H2CO in the clumps associated with outflows/shocks. Kinetic temperatures obtained from para-H2CO trace turbulence to a higher degree than NH3 (2, 2)/(1, 1) in the massive clumps. The non-thermal velocity dispersions of para-H2CO lines are positively correlated with the gas kinetic temperature. The massive clumps are significantly influenced by supersonic non-thermal motions. The reduced spectra (FITS files) are only

  17. Nonequilibrium clumped isotope signals in microbial methane

    USGS Publications Warehouse

    Wang, David T.; Gruen, Danielle S.; Lollar, Barbara Sherwood; Hinrichs, Kai-Uwe; Stewart, Lucy C.; Holden, James F.; Hristov, Alexander N.; Pohlman, John W.; Morrill, Penny L.; Könneke, Martin; Delwiche, Kyle B.; Reeves, Eoghan P.; Sutcliffe, Chelsea N.; Ritter, Daniel J.; Seewald, Jeffrey S.; McIntosh, Jennifer C.; Hemond, Harold F.; Kubo, Michael D.; Cardace, Dawn; Hoehler, Tori M.; Ono, Shuhei

    2015-01-01

    Methane is a key component in the global carbon cycle with a wide range of anthropogenic and natural sources. Although isotopic compositions of methane have traditionally aided source identification, the abundance of its multiply-substituted “clumped” isotopologues, e.g., 13CH3D, has recently emerged as a proxy for determining methane-formation temperatures; however, the impact of biological processes on methane’s clumped isotopologue signature is poorly constrained. We show that methanogenesis proceeding at relatively high rates in cattle, surface environments, and laboratory cultures exerts kinetic control on 13CH3D abundances and results in anomalously elevated formation temperature estimates. We demonstrate quantitatively that H2 availability accounts for this effect. Clumped methane thermometry can therefore provide constraints on the generation of methane in diverse settings, including continental serpentinization sites and ancient, deep groundwaters.

  18. Nonequilibrium clumped isotope signals in microbial methane

    NASA Astrophysics Data System (ADS)

    Wang, David T.; Gruen, Danielle S.; Lollar, Barbara Sherwood; Hinrichs, Kai-Uwe; Stewart, Lucy C.; Holden, James F.; Hristov, Alexander N.; Pohlman, John W.; Morrill, Penny L.; Könneke, Martin; Delwiche, Kyle B.; Reeves, Eoghan P.; Sutcliffe, Chelsea N.; Ritter, Daniel J.; Seewald, Jeffrey S.; McIntosh, Jennifer C.; Hemond, Harold F.; Kubo, Michael D.; Cardace, Dawn; Hoehler, Tori M.; Ono, Shuhei

    2015-04-01

    Methane is a key component in the global carbon cycle, with a wide range of anthropogenic and natural sources. Although isotopic compositions of methane have traditionally aided source identification, the abundance of its multiply substituted “clumped” isotopologues (for example, 13CH3D) has recently emerged as a proxy for determining methane-formation temperatures. However, the effect of biological processes on methane’s clumped isotopologue signature is poorly constrained. We show that methanogenesis proceeding at relatively high rates in cattle, surface environments, and laboratory cultures exerts kinetic control on 13CH3D abundances and results in anomalously elevated formation-temperature estimates. We demonstrate quantitatively that H2 availability accounts for this effect. Clumped methane thermometry can therefore provide constraints on the generation of methane in diverse settings, including continental serpentinization sites and ancient, deep groundwaters.

  19. THE BOLOCAM GALACTIC PLANE SURVEY. XI. TEMPERATURES AND SUBSTRUCTURE OF GALACTIC CLUMPS BASED ON 350 μM OBSERVATIONS

    SciTech Connect

    Merello, Manuel; Evans II, Neal J.; Shirley, Yancy L.; Rosolowsky, Erik; Ginsburg, Adam; Bally, John; Battersby, Cara; Dunham, Michael M.

    2015-05-15

    We present 107 maps of continuum emission at 350 μm from Galactic molecular clumps. Observed sources were mainly selected from the Bolocam Galactic Plane Survey (BGPS) catalog, with three additional maps covering star-forming regions in the outer Galaxy. The higher resolution of the SHARC-II images (8.″5 beam) compared with the 1.1 mm images from BGPS (33″ beam) allowed us to identify a large population of smaller substructures within the clumps. A catalog is presented for the 1386 sources extracted from the 350 μm maps. The color temperature distribution of clumps based on the two wavelengths has a median of 13.3 K and mean of 16.3 ± 0.4 K, assuming an opacity law index of 1.7. For the structures with good determination of color temperatures, the mean ratio of gas temperature, determined from NH{sub 3} observations, to dust color temperature is 0.88 and the median ratio is 0.76. About half the clumps have more than 2 substructures and 22 clumps have more than 10. The fraction of the mass in dense substructures seen at 350 μm compared to the mass of their parental clump is ∼0.19, and the surface densities of these substructures are, on average, 2.2 times those seen in the clumps identified at 1.1 mm. For a well-characterized sample, 88 structures (31%) exceed a surface density of 0.2 g cm{sup −2}, and 18 (6%) exceed 1.0 g cm{sup −2}, thresholds for massive star formation suggested by theorists.

  20. ALMA survey of massive cluster progenitors from ATLASGAL. Limited fragmentation at the early evolutionary stage of massive clumps

    NASA Astrophysics Data System (ADS)

    Csengeri, T.; Bontemps, S.; Wyrowski, F.; Motte, F.; Menten, K. M.; Beuther, H.; Bronfman, L.; Commerçon, B.; Chapillon, E.; Duarte-Cabral, A.; Fuller, G. A.; Henning, Th.; Leurini, S.; Longmore, S.; Palau, A.; Peretto, N.; Schuller, F.; Tan, J. C.; Testi, L.; Traficante, A.; Urquhart, J. S.

    2017-04-01

    The early evolution of massive cluster progenitors is poorly understood. We investigate the fragmentation properties from 0.3 pc to 0.06 pc scales of a homogenous sample of infrared-quiet massive clumps within 4.5 kpc selected from the ATLASGAL survey. Using the ALMA 7 m array we detect compact dust continuum emission towards all targets and find that fragmentation, at these scales, is limited. The mass distribution of the fragments uncovers a large fraction of cores above 40 M⊙, corresponding to massive dense cores (MDCs) with masses up to 400 M⊙. Seventy-seven percent of the clumps contain at most 3 MDCs per clump, and we also reveal single clumps/MDCs. The most massive cores are formed within the more massive clumps and a high concentration of mass on small scales reveals a high core formation efficiency. The mass of MDCs highly exceeds the local thermal Jeans mass, and we lack the observational evidence of a sufficiently high level of turbulence or strong enough magnetic fields to keep the most massive MDCs in equilibrium. If already collapsing, the observed fragmentation properties with a high core formation efficiency are consistent with the collapse setting in at parsec scales. Full Table A.1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/600/L10

  1. ­­A Clumped Isotope Calibration for Terrestrial Microbial Carbonates

    NASA Astrophysics Data System (ADS)

    Petryshyn, V. A.; Mering, J. A.; Mitsunaga, B. A.; Eagle, R.; Dunbar, R. B.; Bhattacharya, A.; Tripati, A.

    2014-12-01

    Accurate terrestrial paleotemperature records are key pieces of information in the paleoenvironmental reconstruction of Earth history. These records aid in building reliable climate models and help scientists understand the links between continental and oceanic climate data. Many different types of analyses are used to estimate terrestrial climate shifts, including leaf margin analysis, palynology, glacial deposits, elemental ratios, organic geochemistry, and stable isotopes of lacustrine deposits. Here we report a carbonate clumped isotope calibration for microbial carbonates. Application of the clumped isotope paleothermometer can potentially provide a direct temperature measurement of the water at the time of carbonate formation. Although different calibrations of the paleothermometer have been published for both inorganic and biotic carbonate minerals, the effects of clumping in microbialites (structures built under the influence of microbial activity) have not yet been quantified. Lacustrine microbialites present a potentially large, untapped archive of terrestrial climate data, however they are not strictly biotic or abiotic, but bio-induced carbonate, meaning that organisms (such as photosynthetic bacteria) influence but do not directly control precipitation. We have measured modern microbialites from multiple lacustrine sites and will report a comparison of these results to known water temperatures. Additionally we will compare lacustrine samples to marine microbialites (e.g., samples from Shark Bay) to assess potential differences between lacustrine and marine intertidal environments on clumped isotope compositions.

  2. Mass-density relationship in molecular cloud clumps

    NASA Astrophysics Data System (ADS)

    Donkov, Sava; Veltchev, Todor V.; Klessen, Ralf S.

    2011-12-01

    We study the mass-density relationship n ∝ mx in molecular cloud condensations (clumps), considering various equipartition relations between their gravitational, kinetic, internal and magnetic energies. Clumps are described statistically, with a density distribution that reflects a lognormal probability density function in turbulent cold interstellar medium. The clump mass-density exponent x derived at different scales L varies in most of the cases within the range -2.5 ≲x≲-0.2, with a pronounced scale dependence and in consistency with observations. When derived from the global size-mass relationship ? for set of clumps, generated at all scales, the clump mass-density exponent has typical values -3.0 ≲x(γglob) ≲-0.3 that depend on the forms of energy, included in the equipartition relations, and on the velocity scaling law, whereas the description of clump geometry is important when magnetic energy is taken into account.

  3. Clumped Methane Isotopologue Temperatures of Microbial Methane

    NASA Astrophysics Data System (ADS)

    Ono, S.; Wang, D. T.; Gruen, D.; Delwiche, K.; Hemond, H.; Pohlman, J.

    2014-12-01

    We will report the abundance of 13CH3D, a clumped isotopologue of methane, in microbial methane sampled from natural environments. They yield some expected and some unexpected results reflecting both equilibrium and kinetic isotope effects controlling the abundance of 13CH3D in low temperature environments. The four isotopologues of methane (12CH4, 13CH4, 12CH3D and 13CH3D) were measured by a tunable infrared spectroscopy method at a precision of 0.2‰ and accuracy of 0.5‰ (Ono et al., 2014). Similar to carbonate clumped isotope thermometry, clumped isotopologues of methane become more stable at lower temperatures. The equilibrium constant for the isotope exchange reaction 13CH4 + 12CH3D ⇌ 13CH3D + 12CH4 deviates from unity by +6.3 to +3.5 ‰ for methane equilibrated between 4 and 121 °C, a range expected for microbial methanogenesis. This would be measurably-distinct from a thermogenic methane signal, which typically have apparent 13CH3D-based temperatures ranging from 150 to 220 °C (+3.0 to +2.2 ‰ clumped isotope effect; Ono et al., 2014; Stolper et al. 2014). Marine samples, such as methane clathrates and porewater methane from the Cascadia margin, have 13CH3D-based temperatures that appear to be consistent with isotopic equilibration at in situ temperatures that are reasonable for deep sedimentary environments. In contrast, methane from freshwater environments, such as a lake and a swamp, yield apparent temperatures that are much higher than the known or inferred environmental temperature. Mixing of two or more distinct sources of methane could potentially generate this high temperature bias. We suggest, however, that this high-temperature bias likely reflects a kinetic isotope fractionation intrinsic to methanogenesis in fresh water environments. In contrast, the low-temperature signals from marine methane could be related to the slow metabolic rates and reversibility of microbial methanogenesis and methanotrophy in marine sedimentary environments

  4. Clumped isotope thermometry of cryogenic cave carbonates

    NASA Astrophysics Data System (ADS)

    Kluge, Tobias; Affek, Hagit P.; Zhang, Yi Ge; Dublyansky, Yuri; Spötl, Christoph; Immenhauser, Adrian; Richter, Detlev K.

    2014-02-01

    Freezing of cave pool water that is increasingly oversaturated with dissolved carbonate leads to precipitation of a very specific type of speleothems known as cryogenic cave carbonates (CCC). At present, two different environments for their formation have been proposed, based on their characteristic carbon and oxygen isotope ratios. Rapidly freezing thin water films result in the fast precipitation of fine-grained carbonate powder (CCCfine). This leads to rapid physicochemical changes including CO2 degassing and CaCO3 precipitation, resulting in significantly 13C-enriched carbonates. Alternatively, slow carbonate precipitation in ice-covered cave pools results in coarse crystalline CCC (CCCcoarse) yielding strongly 18O-depleted carbonate. This is due to the formation of relatively 18O-enriched ice causing the gradual depletion of 18O in the water from which the CCC precipitates. Cryogenic carbonates from Central European caves were found to have been formed primarily during the last glacial period, specifically during times of permafrost thawing, based on the oxygen isotope ratios and U-Th dating. Information about the precise conditions of CCCcoarse formation, i.e. whether these crystals formed under equilibrium or disequilibrium conditions with the parent fluid, however, is lacking. An improved understanding of CCCcoarse formation will increase the predictive value of this paleo-permafrost archive. Here we apply clumped isotopes to investigate the formation conditions of cryogenic carbonates using well-studied CCCcoarse from five different cave systems in western Germany. Carbonate clumped isotope measurements yielded apparent temperatures between 3 and 18 °C and thus exhibit clear evidence of isotopic disequilibrium. Although the very negative carbonate δ18O values can only be explained by gradual freezing of pool water accompanied by preferential incorporation of 18O into the ice, clumped isotope-derived temperatures significantly above expected freezing

  5. Stellar age spreads in clusters as imprints of cluster-parent clump densities

    SciTech Connect

    Parmentier, G.; Grebel, E. K.; Pfalzner, S.

    2014-08-20

    It has recently been suggested that high-density star clusters have stellar age distributions much narrower than that of the Orion Nebula Cluster, indicating a possible trend of narrower age distributions for denser clusters. We show this effect to likely arise from star formation being faster in gas with a higher density. We model the star formation history of molecular clumps in equilibrium by associating a star formation efficiency per free-fall time, ε{sub ff}, to their volume density profile. We focus on the case of isothermal spheres and we obtain the evolution with time of their star formation rate. Our model predicts a steady decline of the star formation rate, which we quantify with its half-life time, namely, the time needed for the star formation rate to drop to half its initial value. Given the uncertainties affecting the star formation efficiency per free-fall time, we consider two distinct values: ε{sub ff} = 0.1 and ε{sub ff} = 0.01. When ε{sub ff} = 0.1, the half-life time is of the order of the clump free-fall time, τ{sub ff}. As a result, the age distributions of stars formed in high-density clumps have smaller full-widths at half-maximum than those of stars formed in low-density clumps. When the star formation efficiency per free-fall time is 0.01, the half-life time is 10 times longer, i.e., 10 clump free-fall times. We explore what happens if the duration of star formation is shorter than 10τ{sub ff}, that is, if the half-life time of the star formation rate cannot be defined. There, we build on the invariance of the shape of the young cluster mass function to show that an anti-correlation between the clump density and the duration of star formation is expected. We therefore conclude that, regardless of whether the duration of star formation is longer than the star formation rate half-life time, denser molecular clumps yield narrower star age distributions in clusters. Published densities and stellar age spreads of young clusters and star

  6. ION AND NEUTRAL MOLECULES IN THE W43-MM1(G30.79 FIR 10) INFALLING CLUMP

    SciTech Connect

    Cortes, Paulo C.

    2011-12-20

    The high-mass star-forming clump W43-MM1 has been mapped in N{sub 2}H{sup +}(4 {yields} 3), C{sup 18}O(3 {yields} 2), SiO(8 {yields} 7), and in a single pointing in DCO{sup +}(5 {yields} 4) toward the center of the clump. Column densities from these observations as well as previous HCO{sup +}(4 {yields} 3), H{sup 13}CO{sup +}(4 {yields} 3), HCN(4 {yields} 3), H{sup 13}CN(4 {yields} 3), and CS(7 {yields} 6) data have been derived using the RADEX code; results later have been used to derive chemical abundances at selected points in the MM1 main axis. We compare with chemical models to estimate an evolutionary age of 10{sup 4} years for a remarkable warm hot core inside MM1. We also proposed that the dust temperature derived from the spectral energy distribution fitting in MM1 is not representative of the gas temperature deep inside the clump because dust emission may have become optically thick. By deriving a deuterium fractionation of 1.2 Multiplication-Sign 10{sup 3}, we estimate an electron fraction of X(e) = 6.5 Multiplication-Sign 10{sup -8}. Thus, the coupling between the neutral gas and the magnetic field is estimated by computing the ambipolar diffusion Reynolds number R{sub m} = 18 and the wave coupling number W = 110. Considering that the infalling speed is slightly supersonic (M = 1.1) but sub-Alfvenic, we conclude that the MM1 clump has recently been or is in the process of decoupling the field from the neutral fluid. Thus, the MM1 clump appears to be in an intermediate stage of evolution in which a hot core has developed while the envelope is still infalling and not fully decoupled from the ambient magnetic field.

  7. MASSIVE CLUMPS IN LOCAL GALAXIES: COMPARISONS WITH HIGH-REDSHIFT CLUMPS

    SciTech Connect

    Elmegreen, Bruce G.; Elmegreen, Debra Meloy; Dewberry, J.; Putko, J.; Teich, Y.; Popinchalk, M.; Sanchez Almeida, J.; Munoz-Tunon, C.

    2013-09-01

    Local UV-bright galaxies in the Kiso survey include clumpy systems with kiloparsec-size star complexes that resemble clumpy young galaxies in surveys at high redshift. We compare clump masses and underlying disks in several dozen galaxies from each of these surveys to the star complexes and disks of normal spirals. Photometry and spectroscopy for the Kiso and spiral sample come from the Sloan Digital Sky Survey. We find that the largest Kiso clumpy galaxies resemble Ultra Deep Field (UDF) clumpies in terms of the star formation rates, clump masses, and clump surface densities. Clump masses and surface densities in normal spirals are smaller. If the clump masses are proportional to the turbulent Jeans mass in the interstellar medium, then for the most luminous galaxies in the sequence of normal:Kiso:UDF, the turbulent speeds and surface densities increase in the proportions 1.0:4.7:5.0 and 1.0:4.0:5.1, respectively, for fixed restframe B-band absolute magnitude. For the least luminous galaxies in the overlapping magnitude range, the turbulent speed and surface density trends are 1.0:2.7:7.4 and 1.0:1.4:3.0, respectively. We also find that while all three types have radially decreasing disk intensities when measured with ellipse-fit azimuthal averages, the average profiles are more irregular for UDF clumpies (which are viewed in their restframe UV) than for Kiso galaxies (viewed at g-band), and major axis intensity scans are even more irregular for the UDF than Kiso galaxies. Local clumpy galaxies in the Kiso survey appear to be intermediate between UDF clumpies and normal spirals.

  8. A Fractal Model for the Capacitance of Lunar Dust and Lunar Dust Aggregates

    NASA Technical Reports Server (NTRS)

    Collier, Michael R.; Stubbs, Timothy J.; Keller, John W.; Farrell, William M.; Marshall, John; Richard, Denis Thomas

    2011-01-01

    Lunar dust grains and dust aggregates exhibit clumping, with an uneven mass distribution, as well as features that span many spatial scales. It has been observed that these aggregates display an almost fractal repetition of geometry with scale. Furthermore, lunar dust grains typically have sharp protrusions and jagged features that result from the lack of aeolian weathering (as opposed to space weathering) on the Moon. A perfectly spherical geometry, frequently used as a model for lunar dust grains, has none of these characteristics (although a sphere may be a reasonable proxy for the very smallest grains and some glasses). We present a fractal model for a lunar dust grain or aggregate of grains that reproduces (1) the irregular clumpy nature of lunar dust, (2) the presence of sharp points, and (3) dust features that span multiple scale lengths. We calculate the capacitance of the fractal lunar dust analytically assuming fixed dust mass (i.e. volume) for an arbitrary number of fractal levels and compare the capacitance to that of a non-fractal object with the same volume, surface area, and characteristic width. The fractal capacitance is larger than that of the equivalent non-fractal object suggesting that for a given potential, electrostatic forces on lunar dust grains and aggregates are greater than one might infer from assuming dust grains are sphericaL Consequently, electrostatic transport of lunar dust grains, for example lofting, appears more plausible than might be inferred by calculations based on less realistic assumptions about dust shape and associated capacitance.

  9. Pressure-confined clumps in magnetized molecular clouds

    NASA Technical Reports Server (NTRS)

    Bertoldi, Frank; Mckee, Christopher F.

    1992-01-01

    A substantial fraction of the mass of a giant molecular cloud (GMC) in the Galaxy is confined to clumps which occupy a small fraction of the volume of the cloud. A majority of the clumps in several well-studied GMCs (Ophiuchus, Orion G, Rosette, Cepheus OB3) are not in gravitational virial equilibrium, but instead are confined by the pressure of the surrounding medium. These clumps thus violate one of 'Larson's (1981) laws'. Generalizing the standard virial analysis for spherical clouds to spheroidal clouds, we determine the Jeans mass and the magnetic critical mass for the clumps in these clouds. The Alfven Mach number, which is proportional to the internal velocity dispersion of the clumps divided by the Alfven velocity, is estimated to be of order unity for all the clumps. The more massive clumps, which are in gravitational virial equilibrium, are too massive to be supported by magnetic fields alone (i.e., they are magnetically supercritical). Internally generated turbulence must play a key role in supporting these clumps.

  10. Physical properties of high-mass clumps in different stages of evolution

    NASA Astrophysics Data System (ADS)

    Giannetti, A.; Brand, J.; Sánchez-Monge, Á.; Fontani, F.; Cesaroni, R.; Beltrán, M. T.; Molinari, S.; Dodson, R.; Rioja, M. J.

    2013-08-01

    Context. The details of the process of massive star formation are still elusive. A complete characterization of the first stages of the process from an observational point of view is needed to constrain theories on the subject. In the past 20 years we have made a thorough investigation of colour-selected IRAS sources over the whole sky. The sources in the northern hemisphere were studied in detail and used to derive an evolutionary sequence based on their spectral energy distribution. Aims: To investigate the first stages of the process of high-mass star formation, we selected a sample of massive clumps previously observed with the Swedish-ESO Submillimetre Telescope at 1.2 mm and with the ATNF Australia Telescope Compact Array at 1.3 cm. We want to characterize the physical conditions in such sources, and test whether their properties depend on the evolutionary stage of the clump. Methods: With ATCA we observed the selected sources in the NH3(1, 1) and (2, 2) transitions and in the H2O(616-523) maser line. Ammonia lines are a very good temperature probe that allow us to accurately determine the mass and the column, volume, and surface densities of the clumps. We also collected all data available to construct the spectral energy distribution of the individual clumps and to determine if star formation is already occurring through observations of its most common signposts, thus putting constraints on the evolutionary stage of the source. We fitted the spectral energy distribution between 1.2 mm and 70 μm with a modified black body to derive the dust temperature and independently determine the mass. Results: We find that the clumps are cold (T ~ 10-30 K), massive (M ~ 102-103 M⊙), and dense (n(H2) ≳ 105 cm-3) and that they have high column densities (N(H2) ~ 1023 cm-2). All clumps appear to be potentially able to form high-mass stars. The most massive clumps appear to be gravitationally unstable, if the only sources of support against collapse are turbulence and

  11. Dance into the fire: dust survival inside supernova remnants

    NASA Astrophysics Data System (ADS)

    Micelotta, Elisabetta R.; Dwek, Eli; Slavin, Jonathan D.

    2016-06-01

    Core collapse supernovae (CCSNe) are important sources of interstellar dust, potentially capable of producing 1 M_{⊙}) of dust in their explosively expelled ejecta. However, unlike other dust sources, the dust has to survive the passage of the reverse shock, generated by the interaction of the supernova blast wave with its surrounding medium. Knowledge of the net amount of dust produced by CCSNe is crucial for understanding the origin and evolution of dust in the local and high-redshift universe. Our goal is to identify the dust destruction mechanisms in the ejecta, and derive the net amount of dust that survives the passage of the reverse shock. To do so, we have developed analytical models for the evolution of a supernova blast wave and of the reverse shock, and the simultaneous processing of the dust inside the cavity of the supernova remnant. We have applied our models to the special case of the clumpy ejecta of the remnant of Cassiopeia A (Cas A), assuming that the dust (silicates and carbon grains) resides in cool oxygen-rich ejecta clumps which are uniformly distributed within the remnant and surrounded by a hot X-ray emitting plasma (smooth ejecta). The passage of the reverse shock through the clumps gives rise to a relative gas-grain motion and also destroys the clumps. While residing in the ejecta clouds, dust is processed via kinetic sputtering, which is terminated either when the grains escape the clumps, or when the clumps are destroyed by the reverse shock. In either case, grain destruction proceeds thereafter by thermal sputtering in the hot shocked smooth ejecta. We find that 12 and 16 percent of silicate and carbon dust, respectively, survive the passage of the reverse shock by the time the shock has reached the center of the remnant. These fractions depend on the morphology of the ejecta and the medium into which the remnant is expanding, as well as the composition and size distribution of the grains that formed in the ejecta. Results will

  12. Mycobacteria Clumping Increase Their Capacity to Damage Macrophages

    PubMed Central

    Brambilla, Cecilia; Llorens-Fons, Marta; Julián, Esther; Noguera-Ortega, Estela; Tomàs-Martínez, Cristina; Pérez-Trujillo, Miriam; Byrd, Thomas F.; Alcaide, Fernando; Luquin, Marina

    2016-01-01

    The rough morphotypes of non-tuberculous mycobacteria have been associated with the most severe illnesses in humans. This idea is consistent with the fact that Mycobacterium tuberculosis presents a stable rough morphotype. Unlike smooth morphotypes, the bacilli of rough morphotypes grow close together, leaving no spaces among them and forming large aggregates (clumps). Currently, the initial interaction of macrophages with clumps remains unclear. Thus, we infected J774 macrophages with bacterial suspensions of rough morphotypes of M. abscessus containing clumps and suspensions of smooth morphotypes, primarily containing isolated bacilli. Using confocal laser scanning microscopy and electron microscopy, we observed clumps of at least five rough-morphotype bacilli inside the phagocytic vesicles of macrophages at 3 h post-infection. These clumps grew within the phagocytic vesicles, killing 100% of the macrophages at 72 h post-infection, whereas the proliferation of macrophages infected with smooth morphotypes remained unaltered at 96 h post-infection. Thus, macrophages phagocytose large clumps, exceeding the bactericidal capacities of these cells. Furthermore, proinflammatory cytokines and granuloma-like structures were only produced by macrophages infected with rough morphotypes. Thus, the present study provides a foundation for further studies that consider mycobacterial clumps as virulence factors. PMID:27757105

  13. IN-SPIRALING CLUMPS IN BLUE COMPACT DWARF GALAXIES

    SciTech Connect

    Elmegreen, Bruce G.; Zhang Hongxin; Hunter, Deidre A.

    2012-03-10

    Giant star formation clumps in dwarf irregular galaxies can have masses exceeding a few percent of the galaxy mass enclosed inside their orbital radii. They can produce sufficient torques on dark matter halo particles, halo stars, and the surrounding disk to lose their angular momentum and spiral into the central region in 1 Gyr. Pairs of giant clumps with similarly large relative masses can interact and exchange angular momentum to the same degree. The result of this angular momentum loss is a growing central concentration of old stars, gas, and star formation that can produce a long-lived starburst in the inner region, identified with the blue compact dwarf (BCD) phase. This central concentration is proposed to be analogous to the bulge in a young spiral galaxy. Observations of star complexes in five local BCDs confirm the relatively large clump masses that are expected for this process. The observed clumps also seem to contain old field stars, even after background light subtraction, in which case the clumps may be long-lived. The two examples with clumps closest to the center have the largest relative clump masses and the greatest contributions from old stars. An additional indication that the dense central regions of BCDs are like bulges is the high ratio of the inner disk scale height to the scale length, which is comparable to 1 for four of the galaxies.

  14. Molecular clumps in the W51 giant molecular cloud

    NASA Astrophysics Data System (ADS)

    Parsons, H.; Thompson, M. A.; Clark, J. S.; Chrysostomou, A.

    2012-08-01

    In this paper, we present a catalogue of dense molecular clumps located within the W51 giant molecular cloud (GMC). This work is based on Heterodyne Array Receiver Programme 13CO J = 3-2 observations of the W51 GMC and uses the automated CLUMPFIND algorithm to decompose the region into a total of 1575 clumps of which 1130 are associated with the W51 GMC. We clearly see the distinct structures of the W51 complex and the high-velocity stream previously reported. We find the clumps have characteristic diameters of 1.4 pc, excitation temperatures of 12 K, densities of 5.6 × 1021 cm-2, surface densities 0.02 g cm-2 and masses of 90 M⊙. We find a total mass of dense clumps within the GMC of 1.5 × 105 M⊙, with only 1 per cent of the clumps detected by number and 4 per cent by mass found to be supercritical. We find a clump-forming efficiency of 14 ± 1 per cent for the W51 GMC and a supercritical clump-forming efficiency of 0.5-0.5+2.3 per cent. Looking at the clump mass distribution, we find it is described by a single power law with a slope of α=2.4-0.1+0.2 above ˜100 M⊙. By comparing locations of supercritical clumps and young clusters, we see that any future star formation is likely to be located away from the currently active W51A region.

  15. A Clumped Isotope Calibration for Lacustrine Carbonates

    NASA Astrophysics Data System (ADS)

    Mitsunaga, B. A.; Mering, J. A.; Petryshyn, V. A.; Dunbar, R. B.; Cohen, A. S.; Liu, X.; Kaufman, D. S.; Eagle, R.; Tripati, A.

    2014-12-01

    Our capacity to understand Earth's environmental history is highly dependent on the accuracy of past climate reconstructions. Unfortunately, many terrestrial proxies—tree rings, speleothems, leaf margin analyses, etc.—are influenced by the effects of both temperature and precipitation. Methods that can isolate the effects of temperature alone are needed, and clumped isotope thermometry has the potential to be a useful tool for determining terrestrial climates. Multiple studies have shown that the fraction of 13C—18O bonds in carbonates is inversely related to the temperature at which the rocks formed and may be a useful proxy for reconstructing temperatures on land. An in-depth survey of lacustrine carbonates, however, has not yet been published. Therefore we have been measuring the abundance of 13C18O16O in the CO2 produced by the dissolution of modern lake samples' carbonate minerals in phosphoric acid and comparing results to independently known estimates of lake water temperature and air temperature. Some of the sample types we have investigated include endogenic carbonates, freshwater gastropods, bivalves, microbialites, and ooids.

  16. Comparison Of Galaxies At Redshifts Z 2 With Star-forming Clumps From HST CANDELS Observations To Those From Hydrodynamical Simulations

    NASA Astrophysics Data System (ADS)

    Mozena, Mark; Faber, S. M.; Koo, D. C.; Primack, J. R.; Dekel, A.; CANDELS Team

    2012-01-01

    Massive, star-forming clumps have been observed in z 2 galaxies. These clumps have been hypothesized to be a major contributor to the build-up of stellar mass during this epoch of high star formation and AGN activity. Using the deepest optical (ACS) and near infra-red (WFC3) observations from the HST Multi-Cycle Treasury CANDELS (Cosmic Assembly Near Infra-Red Deep Extragalactic Legacy Survey - candels.ucolick.org), we compare the properties of these clumps in the rest-frame near-UV and optical to those predicted by the latest cosmologically motivated hydrodynamical simulations (Hydro-ART by Ceverino, Dekel and Primack and Eris by Guedes and Madau). We render these simulated galaxy images to mimic the observed ACS and WFC3 images in CANDELS, and include the effects of dust obscuration, and use the observed simulations to explore measurable differences between in-falling clumps and those that have formed in the disk. We will present our latest results of comparing the observations of CANDELS galaxies with those from the latest hydrodynamical models that provide new and important insights into the nature and role of clumps in the mass assembly of galaxies in the z 2 universe.

  17. ATLASGAL - towards a complete sample of massive star forming clumps

    NASA Astrophysics Data System (ADS)

    Urquhart, J. S.; Moore, T. J. T.; Csengeri, T.; Wyrowski, F.; Schuller, F.; Hoare, M. G.; Lumsden, S. L.; Mottram, J. C.; Thompson, M. A.; Menten, K. M.; Walmsley, C. M.; Bronfman, L.; Pfalzner, S.; König, C.; Wienen, M.

    2014-09-01

    By matching infrared-selected, massive young stellar objects (MYSOs) and compact H II regions in the Red MSX Source survey to massive clumps found in the submillimetre ATLASGAL (APEX Telescope Large Area Survey of the Galaxy) survey, we have identified ˜1000 embedded young massive stars between 280° < ℓ < 350° and 10° < ℓ < 60° with | b | < 1.5°. Combined with an existing sample of radio-selected methanol masers and compact H II regions, the result is a catalogue of ˜1700 massive stars embedded within ˜1300 clumps located across the inner Galaxy, containing three observationally distinct subsamples, methanol-maser, MYSO and H II-region associations, covering the most important tracers of massive star formation, thought to represent key stages of evolution. We find that massive star formation is strongly correlated with the regions of highest column density in spherical, centrally condensed clumps. We find no significant differences between the three samples in clump structure or the relative location of the embedded stars, which suggests that the structure of a clump is set before the onset of star formation, and changes little as the embedded object evolves towards the main sequence. There is a strong linear correlation between clump mass and bolometric luminosity, with the most massive stars forming in the most massive clumps. We find that the MYSO and H II-region subsamples are likely to cover a similar range of evolutionary stages and that the majority are near the end of their main accretion phase. We find few infrared-bright MYSOs associated with the most massive clumps, probably due to very short pre-main-sequence lifetimes in the most luminous sources.

  18. Adhesion of Lunar Dust

    NASA Technical Reports Server (NTRS)

    Walton, Otis R.

    2007-01-01

    This paper reviews the physical characteristics of lunar dust and the effects of various fundamental forces acting on dust particles on surfaces in a lunar environment. There are transport forces and adhesion forces after contact. Mechanical forces (i.e., from rover wheels, astronaut boots and rocket engine blast) and static electric effects (from UV photo-ionization and/or tribo-electric charging) are likely to be the major contributors to the transport of dust particles. If fine regolith particles are deposited on a surface, then surface energy-related (e.g., van der Walls) adhesion forces and static-electric-image forces are likely to be the strongest contributors to adhesion. Some measurement techniques are offered to quantify the strength of adhesion forces. And finally some dust removal techniques are discussed.

  19. RESONANT CLUMPING AND SUBSTRUCTURE IN GALACTIC DISKS

    SciTech Connect

    Molloy, Matthew; Smith, Martin C.; Shen, Juntai; Evans, N. Wyn E-mail: msmith@shao.ac.cn E-mail: nwe@ast.cam.ac.uk

    2015-05-10

    We describe a method to extract resonant orbits from N-body simulations, exploiting the fact that they close in frames rotating with a constant pattern speed. Our method is applied to the N-body simulation of the Milky Way by Shen et al. This simulation hosts a massive bar, which drives strong resonances and persistent angular momentum exchange. Resonant orbits are found throughout the disk, both close to the bar and out to the very edges of the disk. Using Fourier spectrograms, we demonstrate that the bar is driving kinematic substructure even in the very outer parts of the disk. We identify two major orbit families in the outskirts of the disk, one of which makes significant contributions to the kinematic landscape, namely, the m:l = 3:−2 family, resonating with the bar. A mechanism is described that produces bimodal distributions of Galactocentric radial velocities at selected azimuths in the outer disk. It occurs as a result of the temporal coherence of particles on the 3:−2 resonant orbits, which causes them to arrive simultaneously at pericenter or apocenter. This resonant clumping, due to the in-phase motion of the particles through their epicycle, leads to both inward and outward moving groups that belong to the same orbital family and consequently produce bimodal radial velocity distributions. This is a possible explanation of the bimodal velocity distributions observed toward the Galactic anticenter by Liu et al. Another consequence is that transient overdensities appear and dissipate (in a symmetric fashion), resulting in a periodic pulsing of the disk’s surface density.

  20. Extinctions and Distances of Dark Clouds from Ugrijhk Photometry of Red Clump Giants: the North America and Pelican Nebulae Complex

    NASA Astrophysics Data System (ADS)

    Straižys, V.; Laugalys, V.

    A possibility of applying 2MASS J, H, Ks, IPHAS r, i and MegaCam u, g photometry of red giants for determining distances to dark clouds is investigated. Red clump giants with a small admixture of G5--K1 and M2--M3 stars of the giant branch can be isolated and used in determining distances to separate clouds or spiral arms. Interstellar extinctions of background red giants can be also used for mapping dust surface density in the cloud.

  1. Finding ExoEarths: The Problem of Exozodical Dust

    NASA Technical Reports Server (NTRS)

    Roberge, Aki

    2009-01-01

    Dust coming from asteroids and comets will strongly affect direct imaging and characterization of terrestrial planets in the Habitable Zones of nearby stars. Such dust in the Solar System is called the zodiacal dust. Higher levels of similar dust are seen around many nearby stars, confined in disks called debris disks. Future high-contrast images of an Earth-like exoplanet (or "exoEarth") will very likely be background-limited by light scattered of both local Solar System zodiacal dust and circumstellar dust in the extrasolar system (exozodiacal dust). Clumps in the exozodiacal dust, which are expected in planet-hosting systems,, may also be a source of confusion. Here we discuss the problems associated with direct observations of an Earth-like planet in the presence of unknown levels of exozodiacal dust. Basic formulae showing the effect of zodiacal and exozodiacal dust on exoEarth direct imaging will be presented, and performance estimates for some future mission concepts summarized. Current detection limits for debris dust and future prospects for sensitive exozodiacal dust observations will also be discussed. Finally, we highlight a few additional problems relating to exozodiacal dust that have yet to be solved.

  2. The Planck Catalogue of Galactic Cold Clumps : Looking at the early stages of star-formation

    NASA Astrophysics Data System (ADS)

    Montier, Ludovic

    2015-08-01

    The Planck satellite has provided an unprecedented view of the submm sky, allowing us to search for the dust emission of Galactic cold sources. Combining Planck-HFI all-sky maps in the high frequency channels with the IRAS map at 100um, we built the Planck catalogue of Galactic Cold Clumps (PGCC, Planck 2015 results XXVIII 2015), counting 13188 sources distributed over the whole sky, and following mainly the Galactic structures at low and intermediate latitudes. This is the first all-sky catalogue of Galactic cold sources obtained with a single instrument at this resolution and sensitivity, which opens a new window on star-formation processes in our Galaxy.I will briefly describe the colour detection method used to extract the Galactic cold sources, i.e., the Cold Core Colour Detection Tool (CoCoCoDeT, Montier et al. 2010), and its application to the Planck data. I will discuss the statistical distribution of the properties of the PGCC sources (in terms of dust temperature, distance, mass, density and luminosity), which illustrates that the PGCC catalogue spans a large variety of environments and objects, from molecular clouds to cold cores, and covers various stages of evolution. The Planck catalogue is a very powerful tool to study the formation and the evolution of prestellar objects and star-forming regions.I will finally present an overview of the Herschel Key Program Galactic Cold Cores (PI. M.Juvela), which allowed us to follow-up about 350 Planck Galactic Cold Clumps, in various stages of evolution and environments. With this program, the nature and the composition of the 5' Planck sources have been revealed at a sub-arcmin resolution, showing very different configurations, such as starless cold cores or multiple Young Stellar objects still embedded in their cold envelope.

  3. Cosmic dust

    NASA Technical Reports Server (NTRS)

    Brownlee, Donald E.; Sandford, Scott A.

    1992-01-01

    Dust is a ubiquitous component of our galaxy and the solar system. The collection and analysis of extraterrestrial dust particles is important to exobiology because it provides information about the sources of biogenically significant elements and compounds that accumulated in distant regions of the solar nebula and that were later accreted on the planets. The topics discussed include the following: general properties of interplanetary dust; the carbonaceous component of interplanetary dust particles; and the presence of an interstellar component.

  4. Dust Dynamics in Kelvin-Helmholtz Instabilities

    NASA Astrophysics Data System (ADS)

    Hendrix, Tom; Keppens, Rony

    2013-04-01

    The Kelvin-Helmholtz instability (KHI) is a fluid instability which arises when two contacting flows have different tangential velocities. As shearing flows are very common in all sorts of (astro)physical fluid setups, the KHI is frequently encountered. In many astrophysical fluids the gas fluid in loaded with additional dust particles. Here we study the influence of these dust particles on the initiation of the KHI, as well as the effect the KHI has on the density distribution of dust species in a range of different particle sizes. This redistribution by the instability is of importance in the formation of dust structures in astrophysical fluids. To study the effect of dust on the linear and nonlinear phase of the KHI, we use the multi-fluid dust + gas module of the MPI-AMRVAC [1] code to perform 2D and 3D simulations of KHI in setups with physical quantities relevant to astrophysical fluids. A clear dependency on dust sizes is seen, with larger dust particles displaying significantly more clumping than smaller ones.

  5. The Application of Methane Clumped Isotope Measurements to Determine the Source of Large Methane Seeps in Alaskan Lakes

    NASA Astrophysics Data System (ADS)

    Douglas, P. M.; Stolper, D. A.; Eiler, J. M.; Sessions, A. L.; Walter Anthony, K. M.

    2014-12-01

    Natural methane emissions from the Arctic present an important potential feedback to global warming. Arctic methane emissions may come from either active microbial sources or from deep fossil reservoirs released by the thawing of permafrost and melting of glaciers. It is often difficult to distinguish between and quantify contributions from these methane sources based on stable isotope data. Analyses of methane clumped isotopes (isotopologues with two or more rare isotopes such as 13CH3D) can complement traditional stable isotope-based classifications of methane sources. This is because clumped isotope abundances (for isotopically equilibrated systems) are a function of temperature and can be used to identify pathways of methane generation. Additionally, distinctive effects of mixing on clumped isotope abundances make this analysis valuable for determining the origins of mixed gasses. We find large variability in clumped isotope compositions of methane from seeps in several lakes, including thermokarst lakes, across Alaska. At Lake Sukok in northern Alaska we observe the emission of dominantly thermogenic methane, with a formation temperature of at least 100° C. At several other lakes we find evidence for mixing between thermogenic methane and biogenic methane that forms in low-temperature isotopic equilibrium. For example, at Eyak Lake in southeastern Alaska, analysis of three methane samples results in a distinctive isotopic mixing line between a high-temperature end-member that formed between 100-170° C, and a biogenic end-member that formed in isotopic equilibrium between 0-20° C. In this respect, biogenic methane in these lakes resembles observations from marine gas seeps, oil degradation, and sub-surface aquifers. Interestingly, at Goldstream Lake in interior Alaska, methane with strongly depleted clumped-isotope abundances, indicative of disequilibrium gas formation, is found, similar to observations from methanogen culture experiments.

  6. Connecting Clump Sizes in Turbulent Disk Galaxies to Instability Theory

    NASA Astrophysics Data System (ADS)

    Fisher, David B.; Glazebrook, Karl; Abraham, Roberto G.; Damjanov, Ivana; White, Heidi A.; Obreschkow, Danail; Basset, Robert; Bekiaris, Georgios; Wisnioski, Emily; Green, Andy; Bolatto, Alberto D.

    2017-04-01

    In this letter we study the mean sizes of Hα clumps in turbulent disk galaxies relative to kinematics, gas fractions, and Toomre Q. We use ∼100 pc resolution HST images, IFU kinematics, and gas fractions of a sample of rare, nearby turbulent disks with properties closely matched to z∼ 1.5{--}2 main-sequence galaxies (the DYNAMO sample). We find linear correlations of normalized mean clump sizes with both the gas fraction and the velocity dispersion-to-rotation velocity ratio of the host galaxy. We show that these correlations are consistent with predictions derived from a model of instabilities in a self-gravitating disk (the so-called “violent disk instability model”). We also observe, using a two-fluid model for Q, a correlation between the size of clumps and self-gravity-driven unstable regions. These results are most consistent with the hypothesis that massive star-forming clumps in turbulent disks are the result of instabilities in self-gravitating gas-rich disks, and therefore provide a direct connection between resolved clump sizes and this in situ mechanism.

  7. Clump formation through colliding stellar winds in the Galactic Center

    NASA Astrophysics Data System (ADS)

    Calderón, Diego

    2016-07-01

    The gas cloud G2 is currently being tidally disrupted by the Galactic Center super-massive black hole, Sgr A*. The region around the black hole is populated by ˜30 Wolf-Rayet stars, which produce strong outflows. Following an analytical approach, we explore the possibility that gas clumps, such as G2, originate from the collision of identical stellar winds via the Non-Linear Thin Shell Instability. We have found that the collision of relatively slow (<750 km s^{-1}) and strong (˜10^{-5} M_{⊙} yr^{-1}) stellar winds from stars at short separations (<2000 AU) is a process that indeed could produce clumps of G2's mass and above. Such short separation encounters of single stars along their orbits are not common in the Galactic Centre, however close binaries, such as IRS 16SW, are promising clump sources (see Calderón et al. 2016). We also present the first results of 2D models of colliding wind systems using the hydrodynamics adaptive mesh refinement code RAMSES, aiming to obtain a clump mass function, and the rate of clump formation and ejection to the ISM. We study the effect of parameters such as wind properties, stellar separation and orbital motion, in order to understand how likely the formation of G2 is in this context.

  8. Equilibrium temperature in a clump of bacteria heated in fluid.

    PubMed Central

    Davey, K R

    1990-01-01

    A theoretical model was developed and used to estimate quantitatively the "worst case", i.e., the longest, time to reach equilibrium temperature in the center of a clump of bacteria heated in fluid. For clumps with 10 to 10(6) cells heated in vapor, such as dry and moist air, and liquid fluids such as purees and juices, predictions show that temperature equilibrium will occur with sterilization temperatures up to 130 degrees C in under 0.02 s. Model development highlighted that the controlling influence on time for heating up the clump is the surface convection thermal resistance and that the internal conduction resistance of the clump mass is negligible by comparison. The time for a clump to reach equilibrium sterilization temperature was therefore decreased with relative turbulence (velocity) of the heating fluid, such as occurs in many process operations. These results confirm widely held suppositions that the heat-up time of bacteria in vapor or liquid is not significant with usual sterilization times. PMID:2306095

  9. PARTICLE CLUMPING AND PLANETESIMAL FORMATION DEPEND STRONGLY ON METALLICITY

    SciTech Connect

    Johansen, Anders; Youdin, Andrew; Mac Low, Mordecai-Mark

    2009-10-20

    We present three-dimensional numerical simulations of particle clumping and planetesimal formation in protoplanetary disks with varying amounts of solid material. As centimeter-size pebbles settle to the mid-plane, turbulence develops through vertical shearing and streaming instabilities. We find that when the pebble-to-gas column density ratio is 0.01, corresponding roughly to solar metallicity, clumping is weak, so the pebble density rarely exceeds the gas density. Doubling the column density ratio leads to a dramatic increase in clumping, with characteristic particle densities more than 10 times the gas density and maximum densities reaching several thousand times the gas density. This is consistent with unstratified simulations of the streaming instability that show strong clumping in particle-dominated flows. The clumps readily contract gravitationally into interacting planetesimals on the order of 100 km in radius. Our results suggest that the correlation between host star metallicity and exoplanets may reflect the early stages of planet formation. We further speculate that initially low-metallicity disks can be particle enriched during the gas dispersal phase, leading to a late burst of planetesimal formation.

  10. ANALYSIS OF THE INSTABILITY DUE TO GAS–DUST FRICTION IN PROTOPLANETARY DISKS

    SciTech Connect

    Shadmehri, Mohsen

    2016-02-01

    We study the stability of a dust layer in a gaseous disk subject to linear axisymmetric perturbations. Instead of considering single-size particles, however, the population of dust particles is assumed to consist of two grain species. Dust grains exchange momentum with the gas via the drag force and their self-gravity is also considered. We show that the presence of two grain sizes can increase the efficiency of the linear growth of drag-driven instability in the protoplanetary disks (PPDs). A second dust phase with a small mass, compared to the first dust phase, would reduce the growth timescale by a factor of two or more, especially when its coupling to the gas is weak. This means that once a certain amount of large dust particles form, even though it is much smaller than that of small dust particles, the dust layer becomes more unstable and dust clumping is accelerated. Thus, the presence of dust particles of various sizes must be considered in studies of dust clumping in PPDs where both large and small dust grains are present.

  11. Dust Capture and Long-lived Density Enhancements Triggered by Vortices in 2D Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Surville, Clément; Mayer, Lucio; Lin, Douglas N. C.

    2016-11-01

    We study dust capture by vortices and its long-term consequences in global two-fluid inviscid disk simulations using a new polar grid code RoSSBi. We perform the longest integrations so far, several hundred disk orbits, at the highest resolution attainable in global disk simulations with dust, namely, 2048 × 4096 grid points. We vary a wide range of dust parameters, most notably the initial dust-to-gas ratio ɛ varies in the range of 10-4-10-2. Irrespective of the value of ɛ, we find rapid concentration of the dust inside vortices, reaching dust-to-gas ratios of the order of unity inside the vortex. We present an analytical model that describes this dust capture process very well, finding consistent results for all dust parameters. A vortex streaming instability develops, which invariably causes vortex destruction. After vortex dissipation large-scale dust rings encompassing a disk annulus form in most cases, which sustain very high dust concentration, approaching ratios of the order of unity they persist as long as the duration of the simulations. They are sustained by a streaming instability, which manifests itself in high-density dust clumps at various scales. When vortices are particularly long-lived, rings do not form but dust clumps inside vortices can survive a long time and would likely undergo collapse by gravitational instability. Rings encompass almost an Earth mass of solid material, while even larger masses of dust do accumulate inside vortices in the earlier stage. We argue that rapid planetesimal formation would occur in the dust clumps inside the vortices as well as in the post-vortex rings.

  12. Circumstellar dust

    NASA Technical Reports Server (NTRS)

    Dwek, E.

    1986-01-01

    The presence of dust in the general interstellar medium is inferred from the extinction, polarization, and scattering of starlight; the presence of dark nebulae; interstellar depletions; the observed infrared emission around certain stars and various types of interstellar clouds. Interstellar grains are subject to various destruction mechanisms that reduce their size or even completely destroy them. A continuous source of newly formed dust must therefore be present for dust to exist in the various phases of the interstellar medium (ISM). The working group has the following goals: (1) review the evidences for the formation of dust in the various sources; (2) examine the clues to the nature and composition of the dust; (3) review the status of grain formation theories; (4) examine any evidence for the processing of the dust prior to its injection into the interstellar medium; and (5) estimate the relative contribution of the various sources to the interstellar dust population.

  13. HCN Hyperfine Ratio Analysis of Massive Molecular Clumps

    NASA Astrophysics Data System (ADS)

    Schap, William; Barnes, Peter; Ginsburg, Adam; Ordonez, Antonio

    2017-03-01

    The CHaMP project has identified a uniform sample of 303 massive (20-8000 M⊙), dense (200-30,000 cm-3) molecular clumps in a large sector of the southern Milky Way that includes much of the Carina Arm. These are the kinds of clumps that are likely to be the precursors to IRDCs, large stellar clusters, and massive stars. We report new results of the physical conditions in these clouds based on the J=1 -> 0 emission at 3mm from the HCN molecule. Analysis of the HCN emission from these clumps reveals that the physical conditions in the gas (i.e., the excitation temperature, optical depth, and column density) do not follow the molecular line emissivity in a straightforward way. This means that large fractions of the molecular material involved in massive cluster formation, while not completely``dark'', are under-luminous and easily missed in certain studies.

  14. Methane cycling. Nonequilibrium clumped isotope signals in microbial methane.

    PubMed

    Wang, David T; Gruen, Danielle S; Lollar, Barbara Sherwood; Hinrichs, Kai-Uwe; Stewart, Lucy C; Holden, James F; Hristov, Alexander N; Pohlman, John W; Morrill, Penny L; Könneke, Martin; Delwiche, Kyle B; Reeves, Eoghan P; Sutcliffe, Chelsea N; Ritter, Daniel J; Seewald, Jeffrey S; McIntosh, Jennifer C; Hemond, Harold F; Kubo, Michael D; Cardace, Dawn; Hoehler, Tori M; Ono, Shuhei

    2015-04-24

    Methane is a key component in the global carbon cycle, with a wide range of anthropogenic and natural sources. Although isotopic compositions of methane have traditionally aided source identification, the abundance of its multiply substituted "clumped" isotopologues (for example, (13)CH3D) has recently emerged as a proxy for determining methane-formation temperatures. However, the effect of biological processes on methane's clumped isotopologue signature is poorly constrained. We show that methanogenesis proceeding at relatively high rates in cattle, surface environments, and laboratory cultures exerts kinetic control on (13)CH3D abundances and results in anomalously elevated formation-temperature estimates. We demonstrate quantitatively that H2 availability accounts for this effect. Clumped methane thermometry can therefore provide constraints on the generation of methane in diverse settings, including continental serpentinization sites and ancient, deep groundwaters.

  15. Isotope geochemistry. Biological signatures in clumped isotopes of O₂.

    PubMed

    Yeung, Laurence Y; Ash, Jeanine L; Young, Edward D

    2015-04-24

    The abundances of molecules containing more than one rare isotope have been applied broadly to determine formation temperatures of natural materials. These applications of "clumped" isotopes rely on the assumption that isotope-exchange equilibrium is reached, or at least approached, during the formation of those materials. In a closed-system terrarium experiment, we demonstrate that biological oxygen (O2) cycling drives the clumped-isotope composition of O2 away from isotopic equilibrium. Our model of the system suggests that unique biological signatures are present in clumped isotopes of O2—and not formation temperatures. Photosynthetic O2 is depleted in (18)O(18)O and (17)O(18)O relative to a stochastic distribution of isotopes, unlike at equilibrium, where heavy-isotope pairs are enriched. Similar signatures may be widespread in nature, offering new tracers of biological and geochemical cycling.

  16. Physical and Chemical Properties of Protocluster Clumps and Massive Young Stellar Objects Associated to Infrared Dark Clouds

    NASA Astrophysics Data System (ADS)

    Gomez Gonzalez, Laura

    2012-01-01

    than between these clumps and low-mass pre-stellar cores and protostellar objects. A non-LTE Monte Carlo code was used to model the N_2H^+ (1-0) and (3-2) lines in order to constrain the physical properties of two clumps. Six IRDC complexes have been mapped in the 870 um dust continuum emission with the LABOCA instrument on the APEX 12m telescope. Line observations have been carried out in order to obtain temperature and kinematic distances of selected clumps. Physical properties such as masses, effective radii, and column densities have been obtained. The mass spectrum of these clumps has been fitted with a power-law whose best-fitting index is alpha =-1.60. This value is consistent with the CO clump mass function reported in the literature. A relation between the dust emission at 870 um and the degree of extinction (contrast) at 24 um has been obtained by combining dust emission observations and extinction studies. A study with the Plateau de Bure Interferometer of a core in an archetypal filamentary IRDC at few arcsecond resolution has been carried out to determine its physical and chemical structure. Extended 4.5 um emission, "wings" in the CH_3OH 2_k -> 1_k spectra, and a CH_3OH abundance enhancement provide evidence of an outflow in the East-West direction. In addition, a gradient of ~4 km/s in the same direction has been found, which is interpreted as being produced by an outflow(s)-cloud interaction. Finally, Very Large Array interferometric observations of the 7_0-6_1 A^+ (class I) methanol maser transition at 44 GHz toward three high-mass star-forming regions have been carried out in order to provide accurate maser positions and parameters. For all three sources, the masers were well-separated from the HII region, with projected distances ranging from 0.1 to 0.3 pc.

  17. Clumped-isotope thermometry of magnesium carbonates in ultramafic rocks

    NASA Astrophysics Data System (ADS)

    García del Real, Pablo; Maher, Kate; Kluge, Tobias; Bird, Dennis K.; Brown, Gordon E.; John, Cédric M.

    2016-11-01

    Magnesium carbonate minerals produced by reaction of H2O-CO2 with ultramafic rocks occur in a wide range of paragenetic and tectonic settings and can thus provide insights into a variety of geologic processes, including (1) deposition of ore-grade, massive-vein cryptocrystalline magnesite; (2) formation of hydrous magnesium carbonates in weathering environments; and (3) metamorphic carbonate alteration of ultramafic rocks. However, the application of traditional geochemical and isotopic methods to infer temperatures of mineralization, the nature of mineralizing fluids, and the mechanisms controlling the transformation of dissolved CO2 into magnesium carbonates in these settings is difficult because the fluids are usually not preserved. Clumped-isotope compositions of magnesium carbonates provide a means to determine primary mineralization or (re)equilibration temperature, which permits the reconstruction of geologic processes that govern magnesium carbonate formation. We first provide an evaluation of the acid fractionation correction for magnesium carbonates using synthetic magnesite and hydromagnesite, along with natural metamorphic magnesite and low-temperature hydromagnesite precipitated within a mine adit. We show that the acid fractionation correction for magnesium carbonates is virtually indistinguishable from other carbonate acid fractionation corrections given current mass spectrometer resolution and error. In addition, we employ carbonate clumped-isotope thermometry on natural magnesium carbonates from various geologic environments and tectonic settings. Cryptocrystalline magnesite vein deposits from California (Red Mountain magnesite mine), Austria (Kraubath locality), Turkey (Tutluca mine, Eskişehir district) and Iran (Derakht-Senjed deposit) exhibit broadly uniform Δ47 compositions that yield apparent clumped-isotope temperatures that average 23.7 ± 5.0 °C. Based on oxygen isotope thermometry, these clumped-isotope temperatures suggest

  18. Quantifying resilience

    USGS Publications Warehouse

    Allen, Craig R.; Angeler, David G.

    2016-01-01

    Several frameworks to operationalize resilience have been proposed. A decade ago, a special feature focused on quantifying resilience was published in the journal Ecosystems (Carpenter, Westley & Turner 2005). The approach there was towards identifying surrogates of resilience, but few of the papers proposed quantifiable metrics. Consequently, many ecological resilience frameworks remain vague and difficult to quantify, a problem that this special feature aims to address. However, considerable progress has been made during the last decade (e.g. Pope, Allen & Angeler 2014). Although some argue that resilience is best kept as an unquantifiable, vague concept (Quinlan et al. 2016), to be useful for managers, there must be concrete guidance regarding how and what to manage and how to measure success (Garmestani, Allen & Benson 2013; Spears et al. 2015). Ideas such as ‘resilience thinking’ have utility in helping stakeholders conceptualize their systems, but provide little guidance on how to make resilience useful for ecosystem management, other than suggesting an ambiguous, Goldilocks approach of being just right (e.g. diverse, but not too diverse; connected, but not too connected). Here, we clarify some prominent resilience terms and concepts, introduce and synthesize the papers in this special feature on quantifying resilience and identify core unanswered questions related to resilience.

  19. The Dust and Gas Content of the Crab Nebula

    NASA Astrophysics Data System (ADS)

    Owen, P. J.; Barlow, M. J.

    2015-03-01

    We have constructed mocassin photoionization plus dust radiative transfer models for the Crab Nebula core-collapse supernova (CCSN) remnant, using either smooth or clumped mass distributions, in order to determine the chemical composition and masses of the nebular gas and dust. We computed models for several different geometries suggested for the nebular matter distribution but found that the observed gas and dust spectra are relatively insensitive to these geometries, being determined mainly by the spectrum of the pulsar wind nebula which ionizes and heats the nebula. Smooth distribution models are ruled out since they require 16-49 M ⊙ of gas to fit the integrated optical nebular line fluxes, whereas our clumped models require 7.0 M ⊙ of gas. A global gas-phase C/O ratio of 1.65 by number is derived, along with a He/H number ratio of 1.85, neither of which can be matched by current CCSN yield predictions. A carbonaceous dust composition is favored by the observed gas-phase C/O ratio: amorphous carbon clumped model fits to the Crab’s Herschel and Spitzer infrared spectral energy distribution imply the presence of 0.18-0.27 M ⊙ of dust, corresponding to a gas to dust mass ratio of 26-39. Mixed dust chemistry models can also be accommodated, comprising 0.11-0.13 M ⊙ of amorphous carbon and 0.39-0.47 M ⊙ of silicates. Power-law grain size distributions with mass distributions that are weighted toward the largest grain radii are derived, favoring their longer-term survival when they eventually interact with the interstellar medium. The total mass of gas plus dust in the Crab Nebula is 7.2 ± 0.5 M ⊙ , consistent with a progenitor star mass of ˜9 M ⊙ .

  20. The almost ubiquitous association of 6.7-GHz methanol masers with dust

    NASA Astrophysics Data System (ADS)

    Urquhart, J. S.; Moore, T. J. T.; Menten, K. M.; König, C.; Wyrowski, F.; Thompson, M. A.; Csengeri, T.; Leurini, S.; Eden, D. J.

    2015-02-01

    We report the results of 870-μm continuum observations, using the Large APEX Bolometer Camera, towards 77 class-II, 6.7-GHz methanol masers identified by the Methanol MultiBeam (MMB) survey to map the thermal emission from cool dust towards these objects. These data complement a study of 630 methanol masers associated with compact dense clumps identified from the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) survey. Compact dust emission is detected towards 70 sources, which implies a dust-association rate of 99 per cent for the full MMB catalogue. Evaluation of the derived dust and maser properties leads us to conclude that the combined sample represents a single population tracing the same phenomenon. We find median clump masses of a few 103 M⊙ and that all but a handful of sources satisfy the mass-size criterion required for massive star formation. This study provides the strongest evidence of the almost ubiquitous association of methanol masers with massive, star-forming clumps. The fraction of methanol-maser associated clumps is a factor of ˜2 lower in the outer Galaxy than the inner Galaxy, possibly a result of the lower metallicity environment of the former. We find no difference in the clump-mass and maser-luminosity distributions of the inner and outer Galaxy. The maser-pumping and clump formation mechanisms are therefore likely to be relatively invariant to Galactic location. Finally, we use the ratio of maser luminosity and clump mass to investigate the hypothesis that the maser luminosity is a good indicator of the evolutionary stage of the embedded source, however, we find no evidence to support this.

  1. On the Stellar Masses of Giant Clumps in Distant Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Dessauges-Zavadsky, Miroslava; Schaerer, Daniel; Cava, Antonio; Mayer, Lucio; Tamburello, Valentina

    2017-02-01

    We analyze stellar masses of clumps drawn from a compilation of star-forming galaxies at 1.1 < z < 3.6. Comparing clumps selected in different ways, and in lensed or blank field galaxies, we examine the effects of spatial resolution and sensitivity on the inferred stellar masses. Large differences are found, with median stellar masses ranging from ∼ {10}9 {M}ȯ for clumps in the often-referenced field galaxies to ∼ {10}7 {M}ȯ for fainter clumps selected in deep-field or lensed galaxies. We argue that the clump masses, observed in non-lensed galaxies with a limited spatial resolution of ∼1 kpc, are artificially increased due to the clustering of clumps of smaller mass. Furthermore, we show that the sensitivity threshold used for the clump selection affects the inferred masses even more strongly than resolution, biasing clumps at the low-mass end. Both improved spatial resolution and sensitivity appear to shift the clump stellar mass distribution to lower masses, qualitatively in agreement with clump masses found in recent high-resolution simulations of disk fragmentation. We discuss the nature of the most massive clumps, and we conclude that it is currently not possible to properly establish a meaningful clump stellar mass distribution from observations and to infer the existence and value of a characteristic clump mass scale.

  2. Studies of Resolved Stellar Clumps in High-Redshift Galaxy Analogs

    NASA Astrophysics Data System (ADS)

    Messa, Matteo Maria; Adamo, Angela; Östlin, Göran; Hayes, Matthew; Melinder, Jens

    2015-08-01

    The Lyman-alpha reference sample (LARS) is a sample of 14 local high-redshift analogues observed with the Hubble Space Telescope (HST). These local galaxies (z = 0.028 - 0.19) have been selected to have moderately high EW(Hα) to ensure the selection of star-forming systems and far UV luminosities ranging from log(LFUV) = 9.2 to 10.7 LSUN, comparable to those of high-redshift Lyα emitters and Lyman Break Galaxies. The survey is providing fundamental insights into Lyα emission process, allowing the investigation of Lyα radiation transport and photon escape.In this poster, we present the statistical study of the spatially resolved stellar cluster complexes and of the main star-forming regions of the LARS sample. The exquisite multiband HST coverage and the proximity of the galaxies of the sample allow us to derive the physical properties of these stellar clumps, such as ages, masses, extinction, and sizes. Using the UV fluxes, we constraint which fraction of the current star formation is condensed in these compact regions. We try to quantify their contribution to the total ionizing photon budget derived from total Hα fluxes. The properties of these cluster complexes are compared to clump properties detected in high-redshift galaxies.

  3. Protoplanetary Dust

    NASA Astrophysics Data System (ADS)

    Apai, D.´niel; Lauretta, Dante S.

    2014-02-01

    Preface; 1. Planet formation and protoplanetary dust Daniel Apai and Dante Lauretta; 2. The origins of protoplanetary dust and the formation of accretion disks Hans-Peter Gail and Peter Hope; 3. Evolution of protoplanetary disk structures Fred Ciesla and Cornelius P. Dullemond; 4. Chemical and isotopic evolution of the solar nebula and protoplanetary disks Dmitry Semenov, Subrata Chakraborty and Mark Thiemens; 5. Laboratory studies of simple dust analogs in astrophysical environments John R. Brucato and Joseph A. Nuth III; 6. Dust composition in protoplanetaty dust Michiel Min and George Flynn; 7. Dust particle size evolution Klaus M. Pontoppidan and Adrian J. Brearly; 8. Thermal processing in protoplanetary nebulae Daniel Apai, Harold C. Connolly Jr. and Dante S. Lauretta; 9. The clearing of protoplanetary disks and of the protosolar nebula Ilaira Pascucci and Shogo Tachibana; 10. Accretion of planetesimals and the formation of rocky planets John E. Chambers, David O'Brien and Andrew M. Davis; Appendixes; Glossary; Index.

  4. Clumped isotope thermometry of calcite and dolomite in a contact metamorphic environment

    NASA Astrophysics Data System (ADS)

    Lloyd, Max K.; Eiler, John M.; Nabelek, Peter I.

    2017-01-01

    Clumped isotope compositions of slowly-cooled calcite and dolomite marbles record apparent equilibrium temperatures of roughly 150-200 °C and 300-350 °C, respectively. Because clumped isotope compositions are sensitive to the details of T-t path within these intervals, measurements of the Δ47 values of coexisting calcite and dolomite can place new constraints on thermal history of low-grade metamorphic rocks over a large portion of the upper crust (from ∼5 to ∼15 km depth). We studied the clumped isotope geochemistry of coexisting calcite and dolomite in marbles from the Notch Peak contact metamorphic aureole, Utah. Here, flat-lying limestones were intruded by a pluton, producing a regular, zoned metamorphic aureole. Calcite Δ47 temperatures are uniform, 156 ± 12 °C (2σ s.e.), across rocks varying from high-grade marbles that exceeded 500 °C to nominally unmetamorphosed limestones >5 km from the intrusion. This result appears to require that the temperature far from the pluton was close to this value; an ambient temperature just 20 °C lower would not have permitted substantial re-equilibration, and should have preserved depositional or early diagenetic Δ47 values several km from the pluton. Combining this result with depth constraints from overlying strata suggests the country rock here had an average regional geotherm of 22.3-27.4 °C/km from the late Jurassic Period until at least the middle Paleogene Period. Dolomite Δ47 in all samples above the talc + tremolite-in isograd record apparent equilibrium temperatures of 328-12+13 °C (1σ s.e.), consistent with the apparent equilibrium blocking temperature we expect for cooling from peak metamorphic conditions. At greater distances, dolomite Δ47 records temperatures of peak (anchi)metamorphism or pre-metamorphic diagenetic conditions. The interface between these domains is the location of the 330 °C isotherm associated with intrusion. Multiple-phase clumped isotope measurements are complemented by

  5. Investigating the origin of discrepancies in clumped isotope calibrations

    NASA Astrophysics Data System (ADS)

    Eagle, R.

    2015-12-01

    The abundance of 13C-18O 'clumps' in calcite or aragonite of corals skeletons are a potentially valuable tool for reconstructing past ocean temperatures. However, corals are known to exhibit significant "vital effects" (i.e., non-equilibrium mineral compositions) in δ18O, which complicates its application in paleoclimate studies, and may also exhibit clumped isotope disequilibrium. Here we determined mass 47 anomalies (Δ47) in CO2 derived from cultured shallow water and live-collected deep-sea coral. In a species of cultured surface water coral, we find disequilibrium Δ47 and δ18O values that are consistent with a pH effect driving disequilibrium isotopic signatures. We go on to show that culturing specimens at elevated CO2 conditions drives changes in both Δ47 and δ18O that follows the same relationship defined for pH effects in inorganic carbonate precipitation experiments. This suggests that dissolved inorganic carbon speciation at the site of calcification and therefore fluid pH can effect the clumped isotope composition of biogenic minerals. In two different live-collected deep-sea coral taxa, we find distinct clumped isotope signatures and Δ47-temperature calibration relationships.

  6. Clumps of z 2 Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Guo, Yicheng; Giavalisco, M.; Cassata, P.; CANDELS Collaboration

    2011-05-01

    We study the properties of red clumps of star-forming galaxies at z 2. A sample of 15 galaxies with spectroscopic redshift is selected from the HUDF, where ultra--deep and high- resolution optical (HST/ACS) and near--IR (HST/WFC3 IR) images are available to resolve the internal structure of z 2 galaxies at the kpc scale. We generate rest-frame UV-optical color maps of these galaxies after carefully matching image PSFs. Clumps are identified through visual inspection on the (z-H) maps. We run SED-fitting using the seven-band BVizYJH HST photometry of each pixel and measure the spatial distributions of stellar population parameters, such as stellar mass, star-formation rate, age and obscuration. In order to understand the origin of sub-galactic structures, we study the distributions of these properties of the pixels that are part of clumps and compare them with those of the surrounding disks. Our results help answer two questions: (1) whether the clumps are the progenitor of bulges and (2) whether old stellar populations (with age of a few Gyr) exist in star-forming galaxies at z 2.

  7. Combinatorial effects on clumped isotopes and their significance in biogeochemistry

    NASA Astrophysics Data System (ADS)

    Yeung, Laurence Y.

    2016-01-01

    The arrangement of isotopes within a collection of molecules records their physical and chemical histories. Clumped-isotope analysis interrogates these arrangements, i.e., how often rare isotopes are bound together, which in many cases can be explained by equilibrium and/or kinetic isotope fractionation. However, purely combinatorial effects, rooted in the statistics of pairing atoms in a closed system, are also relevant, and not well understood. Here, I show that combinatorial isotope effects are most important when two identical atoms are neighbors on the same molecule (e.g., O2, N2, and D-D clumping in CH4). When the two halves of an atom pair are either assembled with different isotopic preferences or drawn from different reservoirs, combinatorial effects cause depletions in clumped-isotope abundance that are most likely between zero and -1‰, although they could potentially be -10‰ or larger for D-D pairs. These depletions are of similar magnitude, but of opposite sign, to low-temperature equilibrium clumped-isotope effects for many small molecules. Enzymatic isotope-pairing reactions, which can have site-specific isotopic fractionation factors and atom reservoirs, should express this class of combinatorial isotope effect, although it is not limited to biological reactions. Chemical-kinetic isotope effects, which are related to a bond-forming transition state, arise independently and express second-order combinatorial effects related to the abundance of the rare isotope. Heteronuclear moeties (e.g., Csbnd O and Csbnd H), are insensitive to direct combinatorial influences, but secondary combinatorial influences are evident. In general, both combinatorial and chemical-kinetic factors are important for calculating and interpreting clumped-isotope signatures of kinetically controlled reactions. I apply this analytical framework to isotope-pairing reactions relevant to geochemical oxygen, carbon, and nitrogen cycling that may be influenced by combinatorial

  8. Effects of Water on Carbonate Clumped Isotope Bond Reordering Kinetics

    NASA Astrophysics Data System (ADS)

    Brenner, D. C.; Passey, B. H.

    2015-12-01

    Carbonate clumped isotope geothermometry is a powerful tool for reconstructing past temperatures, both in surface environments and in the shallow crust. The method is based on heavy isotope "clumps" within single carbonate groups (e.g., 13C18O16O2-2), whose overabundance beyond levels predicted by chance is determined by mineralization temperature. The degree of clumped isotope overabundance can change at elevated temperatures (ca. >100ºC) owing to solid-state diffusion of C and O through the mineral lattice. Understanding the kinetics of this clumped isotope reordering process is a prerequisite for application to geological questions involving samples that have been heated in the subsurface. Thus far, the effect of water on reordering kinetics has not been explored. The presence of water dramatically increases rates of oxygen self-diffusion in calcite, but whether this water-enhanced diffusion is limited to the mineral surface or extends into the bulk crystal lattice is not clear. Here we present experimentally determined Arrhenius parameters for reordering rates in optical calcite heated under aqueous high pressure (100 MPa) conditions. We observe only marginal increases in reordering rates under these wet, high pressure conditions relative to rates observed for the same material reacted under dry, low pressure conditions. The near identical clumped isotope reordering rates for wet and dry conditions contrasts with the orders of magnitude increase in oxygen diffusivity at the mineral surface when water is present. This suggests the latter effect arises from surface reactions that have minimal influence on the diffusivity of C or O in the bulk mineral. Our results also imply that previously published reordering kinetics determined under dry, low pressure experimental conditions are applicable to geological samples that have been heated in the presence of water.

  9. INJECTION OF SUPERNOVA DUST IN NEARBY PROTOPLANETARY DISKS

    SciTech Connect

    Ouellette, N.; Desch, S. J.; Hester, J. J.

    2010-03-10

    The early solar system contained a number of short-lived radionuclides (SLRs) such as {sup 26}Al with half-lives <15 Myr. The one-time presence of {sup 60}Fe strongly suggests that the source of these radionuclides was a nearby supernova. In this paper, we investigate the 'aerogel' model, which hypothesizes that the solar system's SLRs were injected directly into the solar system's protoplanetary disk from a supernova within the same star-forming region. Previous work has shown that disks generally survive the impact of supernova ejecta, but also that little gaseous ejecta can be injected into the disk. The aerogel model hypothesizes that radionuclides in the ejecta condensed into micron-sized dust grains that were injected directly into the solar nebula disk. Here, we discuss the density structure of supernova ejecta and the observational support for dust condensation in the ejecta. We argue that supernova ejecta are clumpy and describe a model to quantify this clumpiness. We also argue that infrared observations may be underestimating the fraction of material that condenses into dust. Building on calculations of how supernova ejecta interact with protoplanetary disks, we calculate the efficiency with which dust grains in the ejecta are injected into a disk. We find that about 70% of material in grains roughly 0.4 {mu}m in diameter can be injected into disks. If ejecta are clumpy, the solar nebula was struck by a clump with higher-than-average {sup 26}Al and {sup 60}Fe, and these elements condensed efficiently into large grains, then the abundances of SLRs in the early solar system can be explained, even if the disk lies 2 pc from the supernova explosion. The probability that all these factors are met is low, perhaps {approx}10{sup -3}-10{sup -2}, and receiving as much {sup 26}Al and {sup 60}Fe as the solar system did may be a rare event. Still, the aerogel model remains a viable explanation for the origins of the radionuclides in the early solar system, and may

  10. China Dust

    Atmospheric Science Data Center

    2013-04-16

    ... SpectroRadiometer (MISR) nadir-camera images of eastern China compare a somewhat hazy summer view from July 9, 2000 (left) with a ... arid and sparsely vegetated surfaces of Mongolia and western China pick up large quantities of yellow dust. Airborne dust clouds from the ...

  11. The mass distribution of clumps within infrared dark clouds. A Large APEX Bolometer Camera study

    NASA Astrophysics Data System (ADS)

    Gómez, L.; Wyrowski, F.; Schuller, F.; Menten, K. M.; Ballesteros-Paredes, J.

    2014-01-01

    Aims: We present an analysis of the dust continuum emission at 870 μm in order to investigate the mass distribution of clumps within infrared dark clouds (IRDCs). Methods: We map six IRDCs with the Large APEX BOlometer CAmera (LABOCA) at APEX, reaching an rms noise level of σrms = 28-44 mJy beam-1. The dust continuum emission coming from these IRDCs was decomposed by using two automated algorithms, Gaussclumps and Clumpfind. Moreover, we carried out single-pointing observations of the N2H+ (3-2) line toward selected positions to obtain kinematic information. Results: The mapped IRDCs are located in the range of kinematic distances of 2.7-3.2 kpc. We identify 510 and 352 sources with Gaussclumps and Clumpfind, respectively, and estimate masses and other physical properties assuming a uniform dust temperature. The mass ranges are 6-2692 M⊙ (Gaussclumps) and 7-4254 M⊙ (Clumpfind), and the ranges in effective radius are ~0.10-0.74 pc (Gaussclumps) and 0.16-0.99 pc (Clumpfind). The mass distribution, independent of the decomposition method used, is fitted by a power law, dN/dM ∝ Mα, with an index (α) of -1.60 ± 0.06, consistent with the CO mass distribution and other high-mass star-forming regions. Based on data acquired with the Atacama Pathfinder Experiment (APEX). APEX is a collaboration between the Max-Planck-Institut für Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory.Full Tables 3 and 4 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/561/A148

  12. Andromeda's dust

    SciTech Connect

    Draine, B. T.; Aniano, G.; Krause, Oliver; Groves, Brent; Sandstrom, Karin; Klaas, Ulrich; Linz, Hendrik; Rix, Hans-Walter; Schinnerer, Eva; Schmiedeke, Anika; Walter, Fabian; Braun, Robert; Leroy, Adam E-mail: ganiano@ias.u-psud.fr

    2014-01-10

    Spitzer Space Telescope and Herschel Space Observatory imaging of M31 is used, with a physical dust model, to construct maps of dust surface density, dust-to-gas ratio, starlight heating intensity, and polycyclic aromatic hydrocarbon (PAH) abundance, out to R ≈ 25 kpc. The global dust mass is M {sub d} = 5.4 × 10{sup 7} M {sub ☉}, the global dust/H mass ratio is M {sub d}/M {sub H} = 0.0081, and the global PAH abundance is (q {sub PAH}) = 0.039. The dust surface density has an inner ring at R = 5.6 kpc, a maximum at R = 11.2 kpc, and an outer ring at R ≈ 15.1 kpc. The dust/gas ratio varies from M {sub d}/M {sub H} ≈ 0.026 at the center to ∼0.0027 at R ≈ 25 kpc. From the dust/gas ratio, we estimate the interstellar medium metallicity to vary by a factor ∼10, from Z/Z {sub ☉} ≈ 3 at R = 0 to ∼0.3 at R = 25 kpc. The dust heating rate parameter (U) peaks at the center, with (U) ≈ 35, declining to (U) ≈ 0.25 at R = 20 kpc. Within the central kiloparsec, the starlight heating intensity inferred from the dust modeling is close to what is estimated from the stars in the bulge. The PAH abundance reaches a peak q {sub PAH} ≈ 0.045 at R ≈ 11.2 kpc. When allowance is made for the different spectrum of the bulge stars, q {sub PAH} for the dust in the central kiloparsec is similar to the overall value of q {sub PAH} in the disk. The silicate-graphite-PAH dust model used here is generally able to reproduce the observed dust spectral energy distribution across M31, but overpredicts 500 μm emission at R ≈ 2-6 kpc, suggesting that at R = 2-6 kpc, the dust opacity varies more steeply with frequency (with β ≈ 2.3 between 200 and 600 μm) than in the model.

  13. Physical properties of high-mass star-forming clumps in different evolutionary stages from the Bolocam Galactic Plane Survey

    NASA Astrophysics Data System (ADS)

    Svoboda, Brian; Shirley, Yancy; Rosolowsky, Erik; Dunham, Miranda; Ellsworth-Bowers, Timothy; Ginsburg, Adam

    2013-07-01

    High mass stars play a key role in the physical and chemical evolution of the interstellar medium, yet the evolutionary sequence for high mass star forming regions is poorly understood. Recent Galactic plane surveys are providing the first systematic view of high-mass star-forming regions in all evolutionary phases across the Milky Way. We present observations of the 22.23 GHz H2O maser transition J(Ka,Kc) = 6(1,6)→5(2,3) transition toward 1398 clumps identified in the Bolocam Galactic Plane Survey using the 100m Green Bank Telescope (GBT). We detect 392 H2O masers, 279 (71%) newly discovered. We show that H2O masers can identify the presence of protostars which were not previously identified by Spitzer/MSX Galactic plane IR surveys: 25% of IR-dark clumps have an H2O maser. We compare the physical properties of the clumps in the Bolocam Galactic Plane Survey (BGPS) with observations of diagnostics of star formation activity: 8 and 24 um YSO candidates, H2O and CH3OH masers, shocked H2, EGOs, and UCHII regions. We identify a sub-sample of 400 clumps with no star formation indicators representing the largest and most robust sample of pre-protocluster candidates from an unbiased survey to date. The different evolutionary stages show strong separations in HCO+ linewidth and integrated intensity, surface mass density, and kinetic temperature. Monte Carlo techniques are applied to distance probability distribution functions (DPDFs) in order to marginalize over the kinematic distance ambiguity and calculate the distribution of derived quantities for clumps in different evolutionary stages. Surface area and dust mass show weak separations above > 2 pc^2 and > 3x10^3 solar masses. An observed breakdown occurs in the size-linewidth relationship with no differentiation by evolutionary stage. Future work includes adding evolutionary indicators (MIPSGAL, HiGal, MMB) and expanding DPDF priors (HI self-absorption, Galactic structure) for more well-resolved KDAs.

  14. Quantifying entanglement

    NASA Astrophysics Data System (ADS)

    Thapliyal, Ashish Vachaspati

    Entanglement is an essential element of quantum mechanics. The aim of this work is to explore various properties of entanglement from the viewpoints of both physics and information science, thus providing a unique picture of entanglement from an interdisciplinary point of view. The focus of this work is on quantifying entanglement as a resource. We start with bipartite states, proposing a new measure of bipartite entanglement called entanglement of assistance, showing that bound entangled states of rank two cannot exist, exploring the number of members required in the ensemble achieving the entanglement of formation and the possibility of bound entangled states that are negative under partial transposition (NPT bound entangled states). For multipartite states we introduce the notions of reducibilities and equivalences under entanglement non-increasing operations and we study the relations between various reducibilities and equivalences such as exact and asymptotic LOCC, asymptotic LOCCq, cLOCC, LOc, etc. We use this new language to attempt to quantify entanglement for multiple parties. We introduce the idea of entanglement span and minimal entanglement generating set and entanglement coefficients associated with it which are the entanglement measures, thus proposing a multicomponent measure of entanglement for three or more parties. We show that the class of Schmidt decomposable states have only GHZM or Cat-like entanglement. Further we introduce the class of multiseparable states for quantification of their entanglement and prove that they are equivalent to the Schmidt decomposable states, and thus have only Cat-like entanglement. We further explore the conditions under which LOCO equivalences are possible for multipartite isentropic states. We define Cat-distillability, EPRB-distillability and distillability for multipartite mixed states and show that distillability implies EPRB-distillability. Further we show that all non-factorizable pure states are Cat

  15. VizieR Online Data Catalog: Young clumps embedded in IRDC (Traficante+, 2015)

    NASA Astrophysics Data System (ADS)

    Traficante, A.; Fuller, G. A.; Peretto, N.; Pineda, J. E.; Molinari, S.

    2015-06-01

    Photometric parameters for 667 starless clumps (sources identified at 160um with a counterpart at 250 and 350um) and 1056 protostellar clumps (sources identified at 160um with a counterpart at 70, 250 and 350um). Photometric parameters obtained with Hyper photometry code (2015A&A...574A.119T). The photometry is corrected for aperture and colour corrections. The parameter list is the standard Hyper output (see description below). SED fit parameters for 650 starless clumps and 1034 protostellar clumps (all clumps with good SED fitting: Chi2<10, Temperature<40K. See the paper for details) (4 data files).

  16. Clumping in Massive Star Winds and Its Possible Connection to the B[e] Phenomenon

    NASA Astrophysics Data System (ADS)

    Kubátová, B.; Kubát, J.; Hamann, W.-R.; Oskinova, L.

    2017-02-01

    It has been observationally established that winds of hot massive stars have highly variable characteristics. The variability evident in the winds is believed to be caused by structures on a broad range of spatial scales. Small-scale structures (clumping) in stellar winds of hot stars are possible consequence of an instability appearing in their radiation hydrodynamics. To understand how clumping may influence calculation of theoretical spectra, different clumping properties and their 3D nature have to be taken into account. Properties of clumping have been examined using our 3D radiative transfer calculations. Effects of clumping for the case of the B[e] phenomenon are discussed.

  17. SMOOTH(ER) STELLAR MASS MAPS IN CANDELS: CONSTRAINTS ON THE LONGEVITY OF CLUMPS IN HIGH-REDSHIFT STAR-FORMING GALAXIES

    SciTech Connect

    Wuyts, Stijn; Foerster Schreiber, Natascha M.; Genzel, Reinhard; Lutz, Dieter; Guo Yicheng; Giavalisco, Mauro; Barro, Guillermo; Faber, Sandra M.; Kocevski, Dale D.; Koo, David C.; McGrath, Elizabeth; Dekel, Avishai; Ferguson, Henry C.; Grogin, Norman A.; Koekemoer, Anton M.; Lotz, Jennifer; Hathi, Nimish P.; Huang, Kuang-Han; Newman, Jeffrey A.; and others

    2012-07-10

    We perform a detailed analysis of the resolved colors and stellar populations of a complete sample of 323 star-forming galaxies (SFGs) at 0.5 < z < 1.5 and 326 SFGs at 1.5 < z < 2.5 in the ERS and CANDELS-Deep region of GOODS-South. Galaxies were selected to be more massive than 10{sup 10} M{sub Sun} and have specific star formation rates (SFRs) above 1/t{sub H} . We model the seven-band optical ACS + near-IR WFC3 spectral energy distributions of individual bins of pixels, accounting simultaneously for the galaxy-integrated photometric constraints available over a longer wavelength range. We analyze variations in rest-frame color, stellar surface mass density, age, and extinction as a function of galactocentric radius and local surface brightness/density, and measure structural parameters on luminosity and stellar mass maps. We find evidence for redder colors, older stellar ages, and increased dust extinction in the nuclei of galaxies. Big star-forming clumps seen in star formation tracers are less prominent or even invisible in the inferred stellar mass distributions. Off-center clumps contribute up to {approx}20% to the integrated SFR, but only 7% or less to the integrated mass of all massive SFGs at z {approx} 1 and z {approx} 2, with the fractional contributions being a decreasing function of wavelength used to select the clumps. The stellar mass profiles tend to have smaller sizes and M20 coefficients, and higher concentration and Gini coefficients than the light distribution. Our results are consistent with an inside-out disk growth scenario with brief (100-200 Myr) episodic local enhancements in star formation superposed on the underlying disk. Alternatively, the young ages of off-center clumps may signal inward clump migration, provided this happens efficiently on the order of an orbital timescale.

  18. NUMERICAL SIMULATIONS OF SUPERNOVA DUST DESTRUCTION. I. CLOUD-CRUSHING AND POST-PROCESSED GRAIN SPUTTERING

    SciTech Connect

    Silvia, Devin W.; Smith, Britton D.; Michael Shull, J. E-mail: britton.smith@colorado.ed

    2010-06-01

    We investigate through hydrodynamic simulations the destruction of newly formed dust grains by sputtering in the reverse shocks of supernova (SN) remnants. Using an idealized setup of a planar shock impacting a dense, spherical clump, we implant a population of Lagrangian particles into the clump to represent a distribution of dust grains in size and composition. We then post-process the simulation output to calculate the grain sputtering for a variety of species and size distributions. We explore the parameter space appropriate for this problem by altering the overdensity of the ejecta clumps and the speed of the reverse shocks. Since radiative cooling could lower the temperature of the medium in which the dust is embedded and potentially protect the dust by slowing or halting grain sputtering, we study the effects of different cooling methods over the timescale of the simulations. In general, our results indicate that grains with radii less than 0.1 {mu}m are sputtered to much smaller radii and often destroyed completely, while larger grains survive their interaction with the reverse shock. We also find that, for high ejecta densities, the percentage of dust that survives is strongly dependent on the relative velocity between the clump and the reverse shock, causing up to 50% more destruction for the highest velocity shocks. The fraction of dust destroyed varies widely across grain species, ranging from total destruction of Al{sub 2}O{sub 3} grains to minimal destruction of Fe grains (only 20% destruction in the most extreme cases). C and SiO{sub 2} grains show moderate to strong sputtering as well, with 38% and 80% mass loss. The survival rate of grains formed by early SNe is crucial in determining whether or not they can act as the 'dust factories' needed to explain high-redshift dust.

  19. Dust destruction by the reverse shock in the Cassiopeia A supernova remnant

    NASA Astrophysics Data System (ADS)

    Micelotta, Elisabetta R.; Dwek, Eli; Slavin, Jonathan D.

    2016-05-01

    Context. Core collapse supernovae (CCSNe) are important sources of interstellar dust, which are potentially capable of producing 1 M⊙ of dust in their explosively expelled ejecta. However, unlike other dust sources, the dust has to survive the passage of the reverse shock, generated by the interaction of the supernova blast wave with its surrounding medium. Knowledge of the net amount of dust produced by CCSNe is crucial for understanding the origin and evolution of dust in the local and high-redshift Universe. Aims: We identify the dust destruction mechanisms in the ejecta and derive the net amount of dust that survives the passage of the reverse shock. Methods: We use analytical models for the evolution of a supernova blast wave and of the reverse shock with special application to the clumpy ejecta of the remnant of Cassiopeia A (Cas A). We assume that the dust resides in cool oxygen-rich clumps, which are uniformly distributed within the remnant and surrounded by a hot X-ray emitting plasma (smooth ejecta), and that the dust consists of silicates (MgSiO3) and amorphous carbon grains. The passage of the reverse shock through the clumps gives rise to a relative gas-grain motion and also destroys the clumps. While residing in the ejecta clouds, dust is processed via kinetic sputtering, which is terminated either when the grains escape the clumps or when the clumps are destroyed by the reverse shock. In either case, grain destruction proceeds thereafter by thermal sputtering in the hot shocked smooth ejecta. Results: We find that 11.8 and 15.9 percent of silicate and carbon dust, respectively, survive the passage of the reverse shock by the time the shock has reached the centre of the remnant. These fractions depend on the morphology of the ejecta and the medium into which the remnant is expanding, as well as the composition and size distribution of the grains that formed in the ejecta. Results will therefore differ for different types of supernovae.

  20. HCN hyperfine ratio analysis of massive molecular clumps

    NASA Astrophysics Data System (ADS)

    Schap, W. J.; Barnes, P. J.; Ordoñez, A.; Ginsburg, A.; Yonekura, Y.; Fukui, Y.

    2017-03-01

    We report a new analysis protocol for HCN hyperfine data, based on the PYSPECKIT package, and results of using this new protocol to analyse a sample area of seven massive molecular clumps from the Census of High- and Medium-mass Protostars (CHaMP) survey, in order to derive maps of column density for this species. There is a strong correlation between the HCN integrated intensity, IHCN, and previously reported I_HCO+ in the clumps, but I_N_{2H+} is not well correlated with either of these other two 'dense gas tracers'. The four fitted parameters from PYSPECKIT in this region fall in the range of VLSR = 8-10 km s-1, σV = 1.2-2.2 km s-1, Tex = 4-15 K, and τ = 0.2-2.5. These parameters allow us to derive a column density map of these clouds, without limiting assumptions about the excitation or opacity. A more traditional (linear) method of converting IHCN to total mass column gives much lower clump masses than our results based on the hyperfine analysis. This is primarily due to areas in the sample region of low I, low Tex, and high τ. We conclude that there may be more dense gas in these massive clumps not engaged in massive star formation than previously recognized. If this result holds for other clouds in the CHaMP sample, it would have dramatic consequences for the calibration of the Kennicutt-Schmidt star formation laws, including a large increase in the gas depletion time-scale in such regions.

  1. OT1_mrubio_1: Clumping in OB-star winds

    NASA Astrophysics Data System (ADS)

    Rubio, M.

    2010-07-01

    Massive stars, their nature and evolution, play a important role at all stages of the Universe. Through their radiatively driven winds they influence on the dynamics and energetics of the interstellar medium. The winds of OB stars are the most studied case. Commonly, the mass-loss rates of luminous OB stars are inferred from several types of measurements, the strengths of UV P Cygni lines, H-alpha emission and radio and FIR continuum emission. Recent evidence indicates that currently accepted mass-loss rates may need to be revised downwards when small-scale density inhomogeneities (clumping) are taken into account. We argue that only a consistent treatment of ALL possible diagnostics, scanning different parts of the winds, and analyzed by means of state of the art model atmospheres, will permit the determination of true mass-loss rates. To this end we have assembled a variety of multi-wavelength data, but one crucial observational set is missing: far-IR diagnostics of free-free emission, which uniquely constrain the clumping properties of the wind at intermediate heights. We propose, therefore, to use PACS photometric mode to fill this crucial gap, studying the 70 and 110 micron fluxes of a carefully selected sample of 29 O4-B8 stars. These observations will provide the missing information to derive the clumping properties of the entire outflow, to understand the wind physics, and to obtain reliable massloss rates.

  2. OT2_mrubio_2: Clumping in OB-star winds

    NASA Astrophysics Data System (ADS)

    Rubio, M.

    2011-09-01

    Massive stars, their nature and evolution, play a important role at all stages of the Universe. Through their radiatively driven winds they influence on the dynamics and energetics of the interstellar medium. The winds of OB stars are the most studied case. Commonly, the mass-loss rates of luminous OB stars are inferred from several types of measurements, the strengths of UV P Cygni lines, H-alpha emission and radio and FIR continuum emission. Recent evidence indicates that currently accepted mass-loss rates may need to be revised downwards when small-scale density inhomogeneities (clumping) are taken into account. We argue that only a consistent treatment of ALL possible diagnostics, scanning different parts of the winds, and analyzed by means of state of the art model atmospheres, will permit the determination of true mass-loss rates. To this end we have assembled a variety of multi-wavelength data, but one crucial observational set is missing: far-IR diagnostics of free-free emission, which uniquely constrain the clumping properties of the wind at intermediate heights. We propose, therefore, to use PACS photometric mode to fill this crucial gap, studying the 70 and 110 micron fluxes of a carefully selected sample of 29 O4-B8 stars. These observations will provide the missing information to derive the clumping properties of the entire outflow, to understand the wind physics, and to obtain reliable massloss rates.

  3. Clump Accretion in Supergiant Fast X-Ray Transients

    NASA Astrophysics Data System (ADS)

    Chase, Eve; Raymer, E.; Blondin, J. M.

    2014-01-01

    Supergiant Fast X-Ray Transients (SFXTs) are a subclass of High-Mass X-Ray Binaries that consist of a neutron star and OB supergiant donor star. These systems display short, bright x-ray flares lasting a few minutes to a few hours with luminosities reaching 1036 erg/s, several orders of magnitude larger than the quiescent luminosities of 1032 erg/s. The clumpy wind hypothesis has been proposed as a possible mechanism for these transient flares; in this model, a portion of the stellar wind from the donor star forms into clumps and is accreted onto the neutron star, inducing flares. We use high-resolution 3D hydrodynamic simulations to test the clumpy wind hypothesis, tracking the mass and angular momentum accretion rates to infer properties of the resulting x-ray flare and secular evolution of the neutron star rotation. Our results are significantly different from the predictions of Hoyle-Lyttleton Accretion (HLA) theory, which assume steady, laminar, axisymmetric flow. For example, an off-axis clump initiated with an impact parameter greater than the clump radius (for which HLA predicts no effect) produces a small spike in mass accretion and induces a long period of disk-like flow that dramatically reduces the accretion rate below the steady HLA value. The result is a brief, weak flare with a net decrease in total accreted mass compared with steady wind accretion accompanied by a substantial accretion of angular momentum.

  4. Exozodiacal dust

    NASA Astrophysics Data System (ADS)

    Kuchner, Marc Jason

    Besides the sun, the most luminous feature of the solar system is a cloud of "zodiacal" dust released by asteroids and comets that pervades the region interior to the asteroid belt. Similar clouds of dust around other stars---exozodiacal clouds---may be the best tracers of the habitable zones of extra-solar planetary systems. This thesis discusses three searches for exozodiacal dust: (1) We observed six nearby main-sequence stars with the Keck telescope at 11.6 microns, correcting for atmosphere-induced wavefront aberrations and deconvolving the point spread function via classical speckle analysis. We compare our data to a simple model of the zodiacal dust in our own system based on COBE DIRBE observations and place upper limits on the density of exozodiacal dust in these systems. (2) We observed Sirius, Altair, and Procyon with the NICMOS Coronagraph on the Hubble Space Telescope to look for scattered light from exozodiacal dust and faint companions within 10 AU from these stars. (3) The planned nulling capability of the Keck Interferometer should allow it to probe the region <200 milliarcsecond from a bright star and to suppress on-axis starlight by factors of 10 -3 to reveal faint circumstellar material. We model the response of the Keck Interferometer to hypothetical exozodiacal clouds to derive detection limits that account for the effects of stellar leakage, photon noise, noise from null depth fluctuations, and the fact that the cloud's shape is not known a priori. We also discuss the interaction of dust with planets. We used the COBE DIRBE Sky and Zodi Atlas and the IRAS Sky Survey Atlas to search for dynamical signatures of three different planets in the solar system dust complex: (1) We searched the COBE DIRBE Sky and Zodi Atlas for a wake of dust trailing Mars. We compare the DIRBE images to a model Mars wake based on the empirical model of the Earth's wake as seen by the DIRBE. (2) We searched the COBE DIRRE Sky and Zodi Atlas for Tiojan dust near

  5. Long-lived Dust Asymmetries at Dead Zone Edges in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Miranda, Ryan; Li, Hui; Li, Shengtai; Jin, Sheng

    2017-02-01

    A number of transition disks exhibit significant azimuthal asymmetries in thermal dust emission. One possible origin for these asymmetries is dust trapping in vortices formed at the edges of dead zones. We carry out high-resolution, two-dimensional hydrodynamic simulations of this scenario, including the effects of dust feedback. We find that, although feedback weakens the vortices and slows down the process of dust accumulation, the dust distribution in the disk can nonetheless remain asymmetric for many thousands of orbits. We show that even after 104 orbits, or 2.5 Myr when scaled to the parameters of Oph IRS 48 (a significant fraction of its age), the dust is not dispersed into an axisymmetric ring, in contrast to the case of a vortex formed by a planet. This is because accumulation of mass at the dead zone edge constantly replenishes the vortex, preventing it from being fully destroyed. We produce synthetic dust emission images using our simulation results. We find that multiple small clumps of dust may be distributed azimuthally. These clumps, if not resolved from one another, appear as a single large feature. A defining characteristic of a disk with a dead zone edge is that an asymmetric feature is accompanied by a ring of dust located about twice as far from the central star.

  6. Clumped Isotopes in Bahamian Dolomites: A Rosetta Stone?

    NASA Astrophysics Data System (ADS)

    Murray, S.; Swart, P. K.; Arienzo, M. M.

    2014-12-01

    Low temperature dolomite formation continues to be an enigmatic process. However, with the advent of the clumped isotope technique, there is an opportunity to determine the temperature of formation as well as the δ18O of the fluid (δ18Ow) from which it formed. By using samples with a well constrained geologic and thermal history, we have attempted to accurately develop a technique for the application of clumped isotopes to varying dolomite systems. Samples for this study were taken from two cores, one from the island of San Salvador and one on Great Bahama Bank (known as Clino), located on the eastern and western edges respectively of the Bahamian Archipelago. Both cores penetrate through Pleistocene to Miocene aged carbonates. The San Salvador core has a 110m section of pure, near stoichiometric dolomite, while the Clino core is of a mixed carbonate composition with varying abundances (0% - 50%) of calcian dolomite (42-46 mol % MgCO3). The water temperature profile of the Bahamas can be assumed over time due to the stable geology and no influence of higher temperature waters. Because of its location and the present burial depth, the largest influence on dolomite formation has been changes in sea level. As the dolomites from San Salvador are 100% dolomite, the Δ47 was determined directly. The Clino dolomites however were only partially dolomitized and so were treated with buffered acetic acid to remove non-dolomite carbonates. This was carried out in stages, using X-ray diffraction to determine composition, followed by the measurement of Δ47 after each leaching episode. Because the dolomite formation temperature and δ18Ow can be constrained, it becomes possible to evaluate the applicability of the multitude of clumped isotope correction schemes that have been applied to various dolomite samples. Also tested were several different equations which link temperature to the δ18O of the dolomite allowing the δ18O of the water to be calculated. This is a necessary

  7. Molecules, dust, and protostars in NGC 3503

    NASA Astrophysics Data System (ADS)

    Duronea, N. U.; Vasquez, J.; Romero, G. A.; Cappa, C. E.; Barbá, R.; Bronfman, L.

    2014-05-01

    Aims: We present here a follow-up study of the molecular gas and dust in the environs of the star forming region NGC 3503. This study aims at dealing with the interaction of the Hii region NGC 3503 with its parental molecular cloud, and also with the star formation in the region, that was possibly triggered by the expansion of the ionization front against the parental cloud. Methods: To analyze the molecular gas we use CO(J = 2 → 1), 13CO(J = 2 → 1), C18O(J = 2 → 1), and HCN(J = 3 → 2) line data obtained with the on-the-fly technique from the APEX telescope. To study the distribution of the dust, we make use of unpublished images at 870 μm from the ATLASGAL survey and IRAC-GLIMPSE archival images. We use public 2MASS and WISE data to search for infrared candidate young stellar objects (YSOs) in the region. Results: The new APEX observations allowed the substructure of the molecular gas in the velocity range from ~-28 km s-1 to -23 km s-1 to be imaged in detail. The morphology of the molecular gas close to the nebula, the location of the PDR, and the shape of radio continuum emission suggest that the ionized gas is expanding against its parental cloud, and confirm the champagne flow scenario. We have identified several molecular clumps and determined some of their physical and dynamical properties such as density, excitation temperature, mass, and line width. Clumps adjacent to the ionization front are expected to be affected by the Hii region, unlike those that are distant from it. We have compared the physical properties of the two kinds of clumps to investigate how the molecular gas has been affected by the Hii region. Clumps adjacent to the ionization fronts of NGC 3503 and/or the bright rimmed cloud SFO 62 have been heated and compressed by the ionized gas, but their line width is not different from those that are too distant from the ionization fronts. We identified several candidate YSOs in the region. Their spatial distribution suggests that stellar

  8. Compact Dust Concentration in the MWC 758 Protoplanetary Disk

    NASA Astrophysics Data System (ADS)

    Marino, S.; Casassus, S.; Perez, S.; Lyra, W.; Roman, P. E.; Avenhaus, H.; Wright, C. M.; Maddison, S. T.

    2015-11-01

    The formation of planetesimals requires that primordial dust grains grow from micron- to kilometer-sized bodies. Dust traps caused by gas pressure maxima have been proposed as regions where grains can concentrate and grow fast enough to form planetesimals, before radially migrating onto the star. We report new VLA Ka and Ku observations of the protoplanetary disk around the Herbig Ae/Be star MWC 758. The Ka image shows a compact emission region in the outer disk, indicating a strong concentration of big dust grains. Tracing smaller grains, archival ALMA data in band 7 continuum shows extended disk emission with an intensity maximum to the northwest of the central star, which matches the VLA clump position. The compactness of the Ka emission is expected in the context of dust trapping, as big grains are trapped more easily than smaller grains in gas pressure maxima. We develop a nonaxisymmetric parametric model inspired by a steady-state vortex solution with parameters adequately selected to reproduce the observations, including the spectral energy distribution. Finally, we compare the radio continuum with SPHERE scattered light data. The ALMA continuum spatially coincides with a spiral-like feature seen in scattered light, while the VLA clump is offset from the scattered light maximum. Moreover, the ALMA map shows a decrement that matches a region devoid of scattered polarized emission. Continuum observations at a different wavelength are necessary to conclude whether the VLA-ALMA difference is an opacity or a real dust segregation.

  9. COMPACT DUST CONCENTRATION IN THE MWC 758 PROTOPLANETARY DISK

    SciTech Connect

    Marino, S.; Casassus, S.; Perez, S.; Avenhaus, H.; Lyra, W.; Roman, P. E.; Wright, C. M.; Maddison, S. T.

    2015-11-01

    The formation of planetesimals requires that primordial dust grains grow from micron- to kilometer-sized bodies. Dust traps caused by gas pressure maxima have been proposed as regions where grains can concentrate and grow fast enough to form planetesimals, before radially migrating onto the star. We report new VLA Ka and Ku observations of the protoplanetary disk around the Herbig Ae/Be star MWC 758. The Ka image shows a compact emission region in the outer disk, indicating a strong concentration of big dust grains. Tracing smaller grains, archival ALMA data in band 7 continuum shows extended disk emission with an intensity maximum to the northwest of the central star, which matches the VLA clump position. The compactness of the Ka emission is expected in the context of dust trapping, as big grains are trapped more easily than smaller grains in gas pressure maxima. We develop a nonaxisymmetric parametric model inspired by a steady-state vortex solution with parameters adequately selected to reproduce the observations, including the spectral energy distribution. Finally, we compare the radio continuum with SPHERE scattered light data. The ALMA continuum spatially coincides with a spiral-like feature seen in scattered light, while the VLA clump is offset from the scattered light maximum. Moreover, the ALMA map shows a decrement that matches a region devoid of scattered polarized emission. Continuum observations at a different wavelength are necessary to conclude whether the VLA-ALMA difference is an opacity or a real dust segregation.

  10. Sampling and analysis method for measuring airborne coal dust mass in mixtures with limestone (rock) dust

    PubMed Central

    Barone, T. L.; Patts, J. R.; Janisko, S. J.; Colinet, J. F.; Patts, L. D.; Beck, T. W.; Mischler, S. E.

    2016-01-01

    Airborne coal dust mass measurements in underground bituminous coal mines can be challenged by the presence of airborne limestone dust, which is an incombustible dust applied to prevent the propagation of dust explosions. To accurately measure the coal portion of this mixed airborne dust, the National Institute for Occupational Safety and Health (NIOSH) developed a sampling and analysis protocol that used a stainless steel cassette adapted with an isokinetic inlet and the low temperature ashing (LTA) analytical method. The Mine Safety and Health Administration (MSHA) routinely utilizes this LTA method to quantify the incombustible content of bulk dust samples collected from the roof, floor, and ribs of mining entries. The use of the stainless steel cassette with isokinetic inlet allowed NIOSH to adopt the LTA method for the analysis of airborne dust samples. Mixtures of known coal and limestone dust masses were prepared in the laboratory, loaded into the stainless steel cassettes, and analyzed to assess the accuracy of this method. Coal dust mass measurements differed from predicted values by an average of 0.5%, 0.2%, and 0.1% for samples containing 20%, 91%, and 95% limestone dust, respectively. The ability of this method to accurately quantify the laboratory samples confirmed the validity of this method and allowed NIOSH to successfully measure the coal fraction of airborne dust samples collected in an underground coal mine. PMID:26618374

  11. Sampling and analysis method for measuring airborne coal dust mass in mixtures with limestone (rock) dust.

    PubMed

    Barone, T L; Patts, J R; Janisko, S J; Colinet, J F; Patts, L D; Beck, T W; Mischler, S E

    2016-01-01

    Airborne coal dust mass measurements in underground bituminous coal mines can be challenged by the presence of airborne limestone dust, which is an incombustible dust applied to prevent the propagation of dust explosions. To accurately measure the coal portion of this mixed airborne dust, the National Institute for Occupational Safety and Health (NIOSH) developed a sampling and analysis protocol that used a stainless steel cassette adapted with an isokinetic inlet and the low temperature ashing (LTA) analytical method. The Mine Safety and Health Administration (MSHA) routinely utilizes this LTA method to quantify the incombustible content of bulk dust samples collected from the roof, floor, and ribs of mining entries. The use of the stainless steel cassette with isokinetic inlet allowed NIOSH to adopt the LTA method for the analysis of airborne dust samples. Mixtures of known coal and limestone dust masses were prepared in the laboratory, loaded into the stainless steel cassettes, and analyzed to assess the accuracy of this method. Coal dust mass measurements differed from predicted values by an average of 0.5%, 0.2%, and 0.1% for samples containing 20%, 91%, and 95% limestone dust, respectively. The ability of this method to accurately quantify the laboratory samples confirmed the validity of this method and allowed NIOSH to successfully measure the coal fraction of airborne dust samples collected in an underground coal mine.

  12. Carbonate "Clumped" Isotope Determination of Seawater Temperature During the End-Triassic Extinction Event

    NASA Astrophysics Data System (ADS)

    Gammariello, R. T., Jr.; Petryshyn, V. A.; Ibarra, Y.; Greene, S. E.; Corsetti, F. A.; Bottjer, D. J.; Tripati, A.

    2014-12-01

    Stromatolites are laminated sedimentary structures that are commonly thought to be created by cyanobacteria, either through the trapping and binding of sediment, or through metabolically-induced precipitation. However, stromatolite formation is poorly understood. In general, stromatolite abundance was higher in the Proterozoic than the Phanerozoic, but notable increases in stromatolite abundance occur in association with Phanerozoic mass extinction events. Here, we focus on stromatolites from the latest Triassic Cotham Marble (United Kingdom) that are associated with the extinction interval. The end-Triassic mass extinction is coincident with large-scale volcanism in the Central Atlantic Magmatic Province (CAMP) and the associated breakup of Pangea. Some hypothesize that CAMP-associated increases in atmospheric CO2 led to a rise in global temperatures and ocean acidification that caused or enhanced the extinction. In order to quantify the role of climate change with respect to the end-Triassic mass extinction, we applied the carbonate "clumped" isotope paleothermometer to the well-preserved Cotham Marble stromatolites. The stromatolites were deposited in the shallow Tethys Sea, and today occur in several localities across the southwestern UK. The stromatolites alternate on the cm scale between laminated and dendrolitic microstructures and each was microdrilled for clumped isotope analysis. The two microstructures display different temperatures of formation, where the dendrolitic portions apparently grew under cooler conditions than laminated layers, and younger layers grew in cooler conditions than older layers. Our results suggest that temperature fluctuated and potentially trended towards amelioration of the warm temperatures during the deposition of the Cotham Marble.

  13. Captive female gorilla agonistic relationships with clumped defendable food resources.

    PubMed

    Scott, Jennifer; Lockard, Joan S

    2006-07-01

    Minimal feeding competition among female mountain gorillas (Gorilla gorilla beringei) has resulted in egalitarian social relationships with poorly defined agonistic dominance hierarchies. Thus, gorillas are generally viewed as non-competitive egalitarian folivores that have had little need to develop effective competitive strategies to access food resources. However, this generalization is inconsistent with more recent research indicating that most gorillas are frugivorous, feeding on patchily distributed food resources. The current study at Howletts Wild Animal Park, Kent, England, explores the effects of clumped and defendable foods on female gorilla agonistic relationships among three groups of western lowland gorillas (G. g. gorilla), conditions that are predicted to lead to well-differentiated agonistic dominance hierarchies among female primates. The Howletts gorillas foraged all day on low-energy/-nutrient, high-fiber foods widely distributed around their enclosure by the keepers. However, they also had periodic access to high-energy foods (e.g., nuts, raisins, strawberries, etc.) that the keepers would spread in a clumped and defendable patch. Frequencies of agonistic and submissive behaviors between females and proximity data were gathered. High-status females were found to monopolize the food patch and kept the low-status females at bay with cough-grunt threat vocalizations or by chasing them away. Agonistic interactions were initiated mostly by females of high status; these were directed towards females of low status and were generally not reciprocal. In addition, females of low status engaged in submissive behaviors the most often, which they directed primarily at females of high status, especially in response to aggression by the latter. Agonistic interactions between high- and low-status females had decided outcomes more often than not, with low-status females the losers. Competition over highly desirable foods distributed in defendable clumps at

  14. Clumped isotope effects during OH and Cl oxidation of methane

    NASA Astrophysics Data System (ADS)

    Whitehill, Andrew R.; Joelsson, Lars Magnus T.; Schmidt, Johan A.; Wang, David T.; Johnson, Matthew S.; Ono, Shuhei

    2017-01-01

    A series of experiments were carried out to determine the clumped (13CH3D) methane kinetic isotope effects during oxidation of methane by OH and Cl radicals, the major sink reactions for atmospheric methane. Experiments were performed in a 100 L quartz photochemical reactor, in which OH was produced from the reaction of O(1D) (from O3 photolysis) with H2O, and Cl was from photolysis of Cl2. Samples were taken from the reaction cell and analyzed for methane (12CH4, 12CH3D, 13CH4, 13CH3D) isotopologue ratios using tunable infrared laser direct absorption spectroscopy. Measured kinetic isotope effects for singly substituted species were consistent with previous experimental studies. For doubly substituted methane, 13CH3D, the observed kinetic isotope effects closely follow the product of the kinetic isotope effects for the 13C and deuterium substituted species (i.e., 13,2KIE = 13KIE × 2KIE). The deviation from this relationship is 0.3‰ ± 1.2‰ and 3.5‰ ± 0.7‰ for OH and Cl oxidation, respectively. This is consistent with model calculations performed using quantum chemistry and transition state theory. The OH and Cl reactions enrich the residual methane in the clumped isotopologue in open system reactions. In a closed system, however, this effect is overtaken by the large D/H isotope effect, which causes the residual methane to become anti-clumped relative to the initial methane. Based on these results, we demonstrate that oxidation of methane by OH, the predominant oxidant for tropospheric methane, will only have a minor (∼0.3‰) impact on the clumped isotope signature (Δ13CH3D, measured as a deviation from a stochastic distribution of isotopes) of tropospheric methane. This paper shows that Δ13CH3D will provide constraints on methane source strengths, and predicts that Δ12CH2D2 can provide information on methane sink strengths.

  15. MOLECULAR CLUMPS AND INFRARED CLUSTERS IN THE S247, S252, AND BFS52 REGIONS

    SciTech Connect

    Shimoikura, Tomomi; Dobashi, Kazuhito; Saito, Hiro; Nakamura, Fumitaka; Matsumoto, Tomoaki; Nishimura, Atsushi; Kimura, Kimihiro; Onishi, Toshikazu; Ogawa, Hideo

    2013-05-01

    We present results of the observations carried out toward the S247, S252, and BFS52 H II regions with various molecular lines using the 1.85 m radio telescope and the 45 m telescope at Nobeyama Radio Observatory. There are at least 11 young infrared clusters (IR clusters) within the observed region. We found that there are two velocity components in {sup 12}CO (J = 2-1), and also that their spatial distributions show an anti-correlation. The IR clusters are located at their interfaces, suggesting that two distinct clouds with different velocities are colliding with each other, which may have induced the cluster formation. Based on {sup 13}CO (J = 1-0) and C{sup 18}O (J = 1-0) observations, we identified 16 clumps in and around the three H II regions. Eleven of the clumps are associated with the IR clusters and the other five clumps are not associated with any known young stellar objects. We investigated variations in the velocity dispersions of the 16 clumps as a function of the distance from the center of the clusters or the clumps. Clumps with clusters tend to have velocity dispersions that increase with distance from the cluster center, while clumps without clusters show a flat velocity dispersion over the clump extents. A {sup 12}CO outflow has been found in some of the clumps with IR clusters but not in the other clumps, supporting a strong relation of these clumps to the broader velocity dispersion region. We also estimated a mean star formation efficiency of {approx}30% for the clumps with IR clusters in the three H II regions.

  16. Discovery of Infalling Motion with Rotation of the Cluster-forming Clump S235AB and Its Implication to the Clump Structures

    NASA Astrophysics Data System (ADS)

    Shimoikura, Tomomi; Dobashi, Kazuhito; Matsumoto, Tomoaki; Nakamura, Fumitaka

    2016-12-01

    We report the discovery of infalling motion with the rotation of S235AB, a massive cluster-forming clump (˜ 1× {10}3 {M}⊙ ) in the S235 region. Our C18O observations with the 45 m telescope at the Nobeyama Radio Observatory have revealed an elliptical shape of the clump. A position-velocity diagram taken along its major axis exhibits two well-defined peaks symmetrically located, with respect to the clump center. This is similar to that found for a dynamically infalling envelope with rotation around a single protostar, modeled by N. Ohashi et al., indicating that the cluster-forming clump is also collapsing by the self-gravity toward the clump center. With analogue to Ohashi et al.'s model, we made a simple model of an infalling, rotating clump to fit the observed data. Based on the inferred model parameters, as well as results of earlier observations and simulations in the literature, we discuss the structures of the clump such as the relation among the global mass infall rate (˜ 1× {10}-3 {M}⊙ yr-1), formation of a compact core (with a mass and size of ˜4 {M}⊙ and ≲ 0.1 pc) at the center, and a massive star (˜11 {M}⊙ ) forming in the core.

  17. Analysis of Clumps in Saturn’s F Ring from Voyager and Cassini Observations

    NASA Astrophysics Data System (ADS)

    French, Robert S.; Hicks, S. K.; Showalter, M. R.; Antonsen, A. K.; Packard, D. R.

    2013-10-01

    Saturn's F ring is well known for its unique and dynamic features that change on timescales from hours to months. Among these features are clumps, localized bright areas spanning ~3-30 degrees in longitude. 34 clumps tracked in Voyager images (Showalter 2004, Icarus, 171, 356-371) were found to live for several months and have a ~100 km spread in semi-major axis around the F ring core. Several clumps appeared to "split" during their lifetimes. Unfortunately, the poor resolution of the Voyager images and limited temporal and longitudinal coverage prevented a more detailed analysis. In this study, we performed a similar analysis using six years' worth of images from the Cassini Orbiter. We tracked 96 clumps and found similar angular widths, lifetimes, and semi-major axes to those observed by Voyager. However, the number of clumps present at one time appears to have decreased and the clumps are generally less bright; there are also many fewer extremely bright clumps. The better quality images allowed us to investigate five "splitting" clumps and we found that the apparent splits were often caused by the passage of the inner shepherd moon Prometheus. We further found that the birth and death of clumps appears uncorrelated with the position of Prometheus or with other features such as "mini-jets" or "jets" often found in the ring. We speculate on the changes in the population of embedded moonlets that may have resulted in these changes.

  18. Galaxies Unveiled: Rest-frame UV Clumps at 0.5 < z < 1.5

    NASA Astrophysics Data System (ADS)

    Soto, Emmaris; de Mello, Duilia F.; Rafelski, Marc A.; Gardner, Jonathan P.; Koekemoer, Anton M.

    2017-03-01

    Studies of high redshift galaxies reveal compact sub-galactic regions of star formation, known as `clumps'. These `clumpy' galaxies are useful for the study of galactic outskirts by enabling us to examine the radial progression of clumps over large time scales. We use the first deep high resolution NUV image from the Hubble Space Telescope covering intermediate redshifts to explore the implications this radial progression may have on galaxy evolution. From the analysis of 209 clumpy galaxies, we find that higher redshift clumps dominate the outer regions of galactic outskirts. This indicates that clumps may be migrating from the outskirts inward toward their galactic centers.

  19. Dust explosions-cases, causes, consequences, and control.

    PubMed

    Abbasi, Tasneem; Abbasi, S A

    2007-02-09

    Dust explosions pose the most serious and widespread of explosion hazards in the process industry alongside vapour cloud explosions (VCE) and boiling liquid expanding vapour explosions (BLEVE). Dust explosions almost always lead to serious financial losses in terms of damage to facilities and down time. They also often cause serious injuries to personnel, and fatalities. We present the gist of the dust explosion state-of-the-art. Illustrative case studies and past accident analyses reflect the high frequency, geographic spread, and damage potential of dust explosions across the world. The sources and triggers of dust explosions, and the measures with which different factors associated with dust explosions can be quantified are reviewed alongside dust explosion mechanism. The rest of the review is focused on the ways available to prevent dust explosion, and on cushioning the impact of a dust explosion by venting when the accident does take place.

  20. Characterization of Settled Atmospheric Dust by the DART Experiment

    NASA Technical Reports Server (NTRS)

    Landis, Geoffrey A.; Jenkins, Phillip P.; Baraona, Cosmo

    1999-01-01

    The DART ("Dust Accumulation and Removal Test") package is an experiment which will fly as part of the MIP experiment on the Mars-2001 Surveyor Lander. Dust deposition could be a significant problem for photovoltaic array operation for long duration emissions on the surface of Mars. Measurements made by Pathfinder showed 0.3% loss of solar array performance per day due to dust obscuration. The DART experiment is designed to quantify dust deposition from the Mars atmosphere, measure the properties of settled dust, measure the effect of dust deposition on the array performance, and test several methods of mitigating the effect of settled dust on a solar array. Although the purpose of DART (along with its sister experiment, MATE) is to gather information critical to the design of future power systems on the surface of Mars, the dust characterization instrumentation on DART will also provide significant scientific data on the properties of settled atmospheric dust.

  1. A MALT90 study of the chemical properties of massive clumps and filaments of infrared dark clouds

    NASA Astrophysics Data System (ADS)

    Miettinen, O.

    2014-02-01

    Context. Infrared dark clouds (IRDCs) provide a useful testbed in which to investigate the genuine initial conditions and early stages of massive-star formation. Aims: We attempt to characterise the chemical properties of a sample of 35 massive clumps of IRDCs through multi-molecular line observations. We also search for possible evolutionary trends among the derived chemical parameters. Methods: The clumps are studied using the MALT90 (Millimetre Astronomy Legacy Team 90 GHz) line survey data obtained with the Mopra 22 m telescope. The survey covers 16 different transitions near 90 GHz. The spectral-line data are used in concert with our previous LABOCA (Large APEX BOlometer CAmera) 870 μm dust emission data. Results: Eleven MALT90 transitions are detected towards the clumps at least at the 3σ level. Most of the detected species (SiO, C2H, HNCO, HCN, HCO+, HNC, HC3N, and N2H+) show spatially extended emission towards many of the sources. Most of the fractional abundances of the molecules with respect to H2 are found to be comparable to those determined in other recent similar studies of IRDC clumps. We found that the abundances of SiO, HNCO, and HCO+ are higher in IR-bright clumps than in IR-dark sources, reflecting a possible evolutionary trend. A hint of this trend is also seen for HNC and HC3N. An opposite trend is seen for the C2H and N2H+ abundances. Moreover, a positive correlation is found between the abundances of HCO+ and HNC, and between those of HNC and HCN. The HCN and HNC abundances also appear to increase as a function of the N2H+ abundance. The HNC/HCN and N2H+/HNC abundance ratios are derived to be near unity on average, while that of HC3N/HCN is ~10%. The N2H+/HNC ratio appears to increase as the clump evolves, while the HNC/HCO+ ratio shows the opposite behaviour. Conclusions: The detected SiO emission is probably caused by shocks driven by outflows in most cases, although shocks resulting from the cloud formation process could also play a role

  2. PERSPECTIVE: Dust, fertilization and sources

    NASA Astrophysics Data System (ADS)

    Remer, Lorraine A.

    2006-11-01

    Aerosols, tiny suspended particles in the atmosphere, play an important role in modifying the Earth's energy balance and are essential for the formation of cloud droplets. Suspended dust particles lifted from the world's arid regions by strong winds contain essential minerals that can be transported great distances and deposited into the ocean or on other continents where productivity is limited by lack of usable minerals [1]. Dust can transport pathogens as well as minerals great distance, contributing to the spread of human and agricultural diseases, and a portion of dust can be attributed to human activity suggesting that dust radiative effects should be included in estimates of anthropogenic climate forcing. The greenish and brownish tints in figure 1 show the wide extent of monthly mean mineral dust transport, as viewed by the MODerate resolution Imaging Spectroradiometer (MODIS) satellite sensor. The monthly mean global aerosol system for February 2006 from the MODIS aboard the Terra satellite Figure 1. The monthly mean global aerosol system for February 2006 from the MODIS aboard the Terra satellite. The brighter the color, the greater the aerosol loading. Red and reddish tints indicate aerosol dominated by small particles created primarily from combustion processes. Green and brownish tints indicate larger particles created from wind-driven processes, usually transported desert dust. Note the bright green band at the southern edge of the Saharan desert, the reddish band it must cross if transported to the southwest and the long brownish transport path as it crosses the Atlantic to South America. Image courtesy of the NASA Earth Observatory (http://earthobservatory.nasa.gov). Even though qualitatively we recognize the extent and importance of dust transport and the role that it plays in fertilizing nutrient-limited regions, there is much that is still unknown. We are just now beginning to quantify the amount of dust that exits one continental region and the

  3. Condensation of dust in the ejecta of Type II-P supernovae

    NASA Astrophysics Data System (ADS)

    Sarangi, Arkaprabha; Cherchneff, Isabelle

    2015-03-01

    Aims: We study the production of dust in Type II-P supernova ejecta by coupling the gas-phase chemistry to the dust nucleation and condensation phases. We consider two supernova progenitor masses with homogeneous and clumpy ejecta to assess the chemical type and quantity of dust that forms. Grain size distributions are derived for all dust components as a function of post-explosion time. Methods: The chemistry of the gas phase and the simultaneous formation of dust clusters are described by a chemical network that includes all possible processes that are efficient at high gas temperatures and densities. The formation of key bimolecular species (e.g., CO, SiO) and dust clusters of silicates, alumina, silica, metal carbides, metal sulphides, pure metals, and amorphous carbon is considered. A set of stiff, coupled, ordinary, differential equations is solved for the gas conditions pertaining to supernova explosions. These master equations are coupled to a dust condensation formalism based on Brownian coagulation. Results: We find that Type II-P supernovae produce dust grains of various chemical compositions and size distributions as a function of post-explosion time. The grain size distributions gain in complexity with time, are slewed towards large grains, and differ from the usual Mathis, Rumpl, & Nordsieck power-law distribution characterising interstellar dust. Gas density enhancements in the form of ejecta clumps strongly affect the chemical composition of dust and the grain size distributions. Some dust type, such as forsterite and pure metallic grains, are highly dependent on clumpiness. Specifically, a clumpy ejecta produces large grains over 0.1 μm, and the final dust mass for the 19 M⊙ progenitor reaches 0.14 M⊙. Clumps also favour the formation of specific molecules, such as CO2, in the oxygen-rich zones. Conversely, the carbon and alumina dust masses are primarily controlled by the mass yields of alumina and carbon in the ejecta zones where the dust is

  4. ATCA Survey of Ammonia in the Galactic Center: The Temperatures of Dense Gas Clumps between Sgr A* and Sgr B2

    NASA Astrophysics Data System (ADS)

    Ott, Jürgen; Weiß, Axel; Staveley-Smith, Lister; Henkel, Christian; Meier, David S.

    2014-04-01

    We present a large-scale, interferometric survey of ammonia (1, 1) and (2, 2) toward the Galactic center observed with the Australia Telescope Compact Array. The survey covers Δl ~ 1° (~150 pc at an assumed distance of 8.5 kpc) and Δb ~ 0.°2 (~30 pc) which spans the region between the supermassive black hole Sgr A* and the massive star forming region Sgr B2. The resolution is ~20'' (~0.8 pc) and emission at scales >~ 2' (gsim 3.2 pc) is filtered out due to missing interferometric short spacings. Consequently, the data represent the denser, compact clouds and disregards the large-scale, diffuse gas. Many of the clumps align with the 100 pc dust ring and mostly anti-correlate with 1.2 cm continuum emission. We present a kinetic temperature map of the dense gas. The temperature distribution peaks at ~38 K with a width at half maximum between 18 K and 61 K (measurements sensitive within T kin ~ 10-80 K). Larger clumps are on average warmer than smaller clumps which suggests internal heating sources. Our observations indicate that the circumnuclear disk ~1.5 pc around Sgr A* is supplied with gas from the 20 km s-1 molecular cloud. This gas is substantially cooler than gas ~3-15 pc away from Sgr A*. We find a strong temperature gradient across Sgr B2. Ammonia column densities correlate well with SCUBA 850 μm fluxes, but the relation is shifted from the origin, which may indicate a requirement for a minimum amount of dust to form and shield ammonia. Around the Arches and Quintuplet clusters we find shell morphologies with UV-influenced gas in their centers, followed by ammonia and radio continuum layers.

  5. ATCA survey of ammonia in the galactic center: The temperatures of dense gas clumps between Sgr A* and Sgr B2

    SciTech Connect

    Ott, Jürgen; Weiß, Axel; Henkel, Christian; Staveley-Smith, Lister; Meier, David S. E-mail: aweiss@mpifr-bonn.mpg.de E-mail: Lister.Staveley-Smith@uwa.edu.au

    2014-04-10

    We present a large-scale, interferometric survey of ammonia (1, 1) and (2, 2) toward the Galactic center observed with the Australia Telescope Compact Array. The survey covers Δℓ ∼ 1° (∼150 pc at an assumed distance of 8.5 kpc) and Δb ∼ 0.°2 (∼30 pc) which spans the region between the supermassive black hole Sgr A* and the massive star forming region Sgr B2. The resolution is ∼20'' (∼0.8 pc) and emission at scales ≳ 2' (≳ 3.2 pc) is filtered out due to missing interferometric short spacings. Consequently, the data represent the denser, compact clouds and disregards the large-scale, diffuse gas. Many of the clumps align with the 100 pc dust ring and mostly anti-correlate with 1.2 cm continuum emission. We present a kinetic temperature map of the dense gas. The temperature distribution peaks at ∼38 K with a width at half maximum between 18 K and 61 K (measurements sensitive within T {sub kin} ∼ 10-80 K). Larger clumps are on average warmer than smaller clumps which suggests internal heating sources. Our observations indicate that the circumnuclear disk ∼1.5 pc around Sgr A* is supplied with gas from the 20 km s{sup –1} molecular cloud. This gas is substantially cooler than gas ∼3-15 pc away from Sgr A*. We find a strong temperature gradient across Sgr B2. Ammonia column densities correlate well with SCUBA 850 μm fluxes, but the relation is shifted from the origin, which may indicate a requirement for a minimum amount of dust to form and shield ammonia. Around the Arches and Quintuplet clusters we find shell morphologies with UV-influenced gas in their centers, followed by ammonia and radio continuum layers.

  6. Metabolic adaptations of Azospirillum brasilense to oxygen stress by cell-to-cell clumping and flocculation.

    PubMed

    Bible, Amber N; Khalsa-Moyers, Gurusahai K; Mukherjee, Tanmoy; Green, Calvin S; Mishra, Priyanka; Purcell, Alicia; Aksenova, Anastasia; Hurst, Gregory B; Alexandre, Gladys

    2015-12-01

    The ability of bacteria to monitor their metabolism and adjust their behavior accordingly is critical to maintain competitiveness in the environment. The motile microaerophilic bacterium Azospirillum brasilense navigates oxygen gradients by aerotaxis in order to locate low oxygen concentrations that can support metabolism. When cells are exposed to elevated levels of oxygen in their surroundings, motile A. brasilense cells implement an alternative response to aerotaxis and form transient clumps by cell-to-cell interactions. Clumping was suggested to represent a behavior protecting motile cells from transiently elevated levels of aeration. Using the proteomics of wild-type and mutant strains affected in the extent of their clumping abilities, we show that cell-to-cell clumping represents a metabolic scavenging strategy that likely prepares the cells for further metabolic stresses. Analysis of mutants affected in carbon or nitrogen metabolism confirmed this assumption. The metabolic changes experienced as clumping progresses prime cells for flocculation, a morphological and metabolic shift of cells triggered under elevated-aeration conditions and nitrogen limitation. The analysis of various mutants during clumping and flocculation characterized an ordered set of changes in cell envelope properties accompanying the metabolic changes. These data also identify clumping and early flocculation to be behaviors compatible with the expression of nitrogen fixation genes, despite the elevated-aeration conditions. Cell-to-cell clumping may thus license diazotrophy to microaerophilic A. brasilense cells under elevated oxygen conditions and prime them for long-term survival via flocculation if metabolic stress persists.

  7. Metabolic Adaptations of Azospirillum brasilense to Oxygen Stress by Cell-to-Cell Clumping and Flocculation

    PubMed Central

    Bible, Amber N.; Khalsa-Moyers, Gurusahai K.; Mukherjee, Tanmoy; Green, Calvin S.; Mishra, Priyanka; Purcell, Alicia; Aksenova, Anastasia; Hurst, Gregory B.

    2015-01-01

    The ability of bacteria to monitor their metabolism and adjust their behavior accordingly is critical to maintain competitiveness in the environment. The motile microaerophilic bacterium Azospirillum brasilense navigates oxygen gradients by aerotaxis in order to locate low oxygen concentrations that can support metabolism. When cells are exposed to elevated levels of oxygen in their surroundings, motile A. brasilense cells implement an alternative response to aerotaxis and form transient clumps by cell-to-cell interactions. Clumping was suggested to represent a behavior protecting motile cells from transiently elevated levels of aeration. Using the proteomics of wild-type and mutant strains affected in the extent of their clumping abilities, we show that cell-to-cell clumping represents a metabolic scavenging strategy that likely prepares the cells for further metabolic stresses. Analysis of mutants affected in carbon or nitrogen metabolism confirmed this assumption. The metabolic changes experienced as clumping progresses prime cells for flocculation, a morphological and metabolic shift of cells triggered under elevated-aeration conditions and nitrogen limitation. The analysis of various mutants during clumping and flocculation characterized an ordered set of changes in cell envelope properties accompanying the metabolic changes. These data also identify clumping and early flocculation to be behaviors compatible with the expression of nitrogen fixation genes, despite the elevated-aeration conditions. Cell-to-cell clumping may thus license diazotrophy to microaerophilic A. brasilense cells under elevated oxygen conditions and prime them for long-term survival via flocculation if metabolic stress persists. PMID:26407887

  8. Pseudothrombocytopenia due to Platelet Clumping: A Case Report and Brief Review of the Literature

    PubMed Central

    Tan, Geok Chin; Stalling, Melissa; Dennis, Gretchen; Nunez, Maria

    2016-01-01

    Platelet clumping is a common laboratory phenomenon that complicates or precludes reporting of platelet count. It is often, but not always, a phenomenon commonly caused by the anticoagulant EDTA. Herein, we discuss a case of a 14-year-old girl who was found to have platelet clumping and discuss the work-up she underwent to investigate her pseudothrombocytopenia. PMID:28044112

  9. The Keck Aperture Masking Experiment: Dust Enshrouded Red Giants

    NASA Technical Reports Server (NTRS)

    Blasius, T. D.; Monnier, J. D.; Tuthill, P. G.; Danchi, W. C.; Anderson, M.

    2012-01-01

    While the importance of dusty asymptotic giant branch (AGB) stars to galactic chemical enrichment is widely recognised, a sophisticated understanding of the dust formation and wind-driving mechanisms has proven elusive due in part to the difficulty in spatially-resolving the dust formation regions themselves. We have observed twenty dust-enshrouded AGB stars as part of the Keck Aperture Masking Experiment, resolving all of them in multiple near-infrared bands between 1.5 m and 3.1 m. We find 45% of the targets to show measurable elongations that, when correcting for the greater distances of the targets, would correspond to significantly asymmetric dust shells on par with the well-known cases of IRC +10216 or CIT 6. Using radiative transfer models, we find the sublimation temperature of Tsub(silicates) = 1130 90K and Tsub(amorphous carbon) = 1170 60 K, both somewhat lower than expected from laboratory measurements and vastly below temperatures inferred from the inner edge of YSO disks. The fact that O-rich and C-rich dust types showed the same sublimation temperature was surprising as well. For the most optically-thick shells ( 2.2 m > 2), the temperature profile of the inner dust shell is observed to change substantially, an effect we suggest could arise when individual dust clumps become optically-thick at the highest mass-loss rates.

  10. Circumstellar Dust in the Remnant of Kepler's Type Ia Supernova

    NASA Astrophysics Data System (ADS)

    Williams, Brian J.; Blair, W. P.; Borkowski, K. J.; Ghavamian, P.; Long, K. S.; Reynolds, S. P.; Sankrit, R.

    2012-01-01

    Kepler's Supernova Remnant, the remains of the supernova of 1604, is widely believed to be the result of a Type Ia supernova, and shows IR, optical, and X-ray evidence for an interaction of the blast wave with a dense circumstellar medium (CSM). We present low-resolution 7.5-38 μm IR spectra of selected regions within the remnant, obtained with the Spitzer Space Telescope. Spectra of those regions where the blast wave is encountering circumstellar material show strong features at 10 and 18 μm. These spectral features are most consistent with various silicate particles, likely formed in the stellar outflow from the progenitor system during the AGB stage of evolution. While it is possible that some features may arise from freshly formed ejecta dust, morphological evidence suggests that it is more likely that they originate from dust in the CSM. We isolate the dust grain absorption efficiencies for several regions in Kepler and compare them to laboratory data for dust particles of various compositions. The hottest dust in the remnant originates in the regions of dense, radiatively shocked clumps of gas, identified in optical images. Models of collisionally heated dust show that such shocks are capable of heating grains to temperatures of > 150 K. We confirm the finding that Kepler's SNR is still interacting with CSM in at least part of the remnant after 400 years. The significant quantities of silicate dust are consistent with a relatively massive progenitor.

  11. Clump detections and limits on moons in Jupiter's ring system.

    PubMed

    Showalter, Mark R; Cheng, Andrew F; Weaver, Harold A; Stern, S Alan; Spencer, John R; Throop, Henry B; Birath, Emma M; Rose, Debi; Moore, Jeffrey M

    2007-10-12

    The dusty jovian ring system must be replenished continuously from embedded source bodies. The New Horizons spacecraft has performed a comprehensive search for kilometer-sized moons within the system, which might have revealed the larger members of this population. No new moons were found, however, indicating a sharp cutoff in the population of jovian bodies smaller than 8-kilometer-radius Adrastea. However, the search revealed two families of clumps in the main ring: one close pair and one cluster of three to five. All orbit within a brighter ringlet just interior to Adrastea. Their properties are very different from those of the few other clumpy rings known; the origin and nonrandom distribution of these features remain unexplained, but resonant confinement by Metis may play a role.

  12. Towards Understanding Artifacts in the Clumped Isotope System

    NASA Astrophysics Data System (ADS)

    Swart, P. K.; Staudigel, P. T.; Murray, S.

    2015-12-01

    The clumped isotope system in carbonates (Δ47) relies on the extraction of CO2 from the carbonate minerals using phosphoric acid. Despite the fact that this method dates back to the original stable isotopic work in the 1950s, there are significant aspects of the fractionation of the 18O/16O (and by inference the ratio of mass 47 to 44) which are not understood. We believe that subtle variations in the isotopic fractionation as a function of temperature, acid density (and acid preparation method), and extraction line design cause variation between the clumped isotope data produced by different laboratories. One of the most obvious of these is difference in reaction temperatures. While most laboratories employ temperatures of between 75 and 90oC, the original method employed a temperature of 25oC. Although various estimate of the difference in fractionation of Δ47 between 25 and 90oC have been made, we have measured significantly different values for dolomites compared to published data. In order to understand this we have performed experiments in sealed Pyrex vessels to measure the exchange between CO2 and 103% phosphoric acid. We have determined there to be significant and measurable changes in the Δ47 of CO2 when exposed to phosphoric acid. This exchange is a function of temperature, time, acid strength, and the surface area of the acid exposed to the CO2. We postulate that, perhaps as a result of the lower reaction rate of dolomite, compared to calcite, that there is greater opportunity for CO2 to exchange with the phosphoric acid as bubbles of CO2 are retained within the acid for longer periods of time. Such a mechanism would predict that well-ordered dolomites will have different fractionation compared to protodolomite. Similar differences might account for different fractionation for other carbonate minerals.

  13. DENSE CLUMPS AND CANDIDATES FOR MOLECULAR OUTFLOWS IN W40

    SciTech Connect

    Shimoikura, Tomomi; Dobashi, Kazuhito; Nakamura, Fumitaka; Hara, Chihomi; Kawabe, Ryohei; Tanaka, Tomohiro; Shimajiri, Yoshito

    2015-06-20

    We report the results of the {sup 12}CO (J = 3−2) and HCO{sup +} (J = 4−3) observations of the W40 H ii region with the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope (HPBW ≃ 22″) to search for molecular outflows and dense clumps. We found that the velocity field in the region is highly complex, consisting of at least four distinct velocity components at V{sub LSR} ≃ 3, 5, 7, and 10 km s{sup −1}. The ∼7 km s{sup −1} component represents the systemic velocity of cold gas surrounding the entire region, and causes heavy absorption in the {sup 12}CO spectra over the velocity range 6 ≲ V{sub LSR} ≲ 9 km s{sup −1}. The ∼5 and ∼10 km s{sup −1} components exhibit high {sup 12}CO temperature (≳40 K) and are found mostly around the H ii region, suggesting that these components are likely to be tracing dense gas interacting with the expanding shell around the H ii region. Based on the {sup 12}CO data, we identified 13 regions of high velocity gas, which we interpret as candidate outflow lobes. Using the HCO{sup +} data, we also identified six clumps and estimated their physical parameters. On the basis of the ASTE data and near-infrared images from 2MASS, we present an updated three-dimensional model of this region. In order to investigate molecular outflows in W40, the SiO (J = 1−0, v = 0) emission line and some other emission lines at 40 GHz were also observed with the 45 m telescope at the Nobeyama Radio Observatory, but they were not detected at the present sensitivity.

  14. Entropy flattening, gas clumping, and turbulence in galaxy clusters

    SciTech Connect

    Fusco-Femiano, R.; Lapi, A.

    2014-03-10

    Several physical processes and formation events are expected in cluster outskirts, a vast region up to now essentially not covered by observations. The recent Suzaku (X-ray) and Planck (Sunyaev-Zel'dovich (SZ) effect) observations out to the virial radius have highlighted in these peripheral regions a rather sharp decline of the intracluster gas temperature, an entropy flattening in contrast with the theoretically expected power law increase, the break of the hydrostatic equilibrium even in some relaxed clusters, a derived gas mass fraction above the cosmic value measured from several cosmic microwave background experiments, and a total X-ray mass lower than the weak lensing mass determinations. Here we present the analysis of four clusters (A1795, A2029, A2204, and A133) with the SuperModel that includes a nonthermal pressure component due to turbulence to sustain the hydrostatic equilibrium also in the cluster outskirts. In this way, we obtain a correct determination of the total X-ray mass and of the gas mass fraction; this in turn allows us to determine the level of the gas clumping that can affect the shape of the entropy profiles reported by the Suzaku observations. Our conclusion is that the role of the gas clumping is very marginal and that the observed entropy flattening is due to the rapid decrement of the temperature in the cluster outskirts caused by non-gravitational effects. Moreover, we show that the X-ray/SZ joint analysis from ROSAT and Planck data, as performed in some recent investigations, is inadequate for discriminating between a power law increase and a flattening of the entropy.

  15. Highly Variable Young Massive Stars in ATLASGAL Clumps

    NASA Astrophysics Data System (ADS)

    Kumar, M. S. N.; Contreras Peña, C.; Lucas, P. W.; Thompson, M. A.

    2016-12-01

    High-amplitude variability in young stellar objects (YSOs) is usually associated with episodic accretion events. It has not been observed so far in massive YSOs. Here, the high-amplitude variable star sample of Contreras Peña et al. has been used to search for highly variable (ΔK ≥ 1 mag) sources coinciding with dense clumps mapped using the 850 μm continuum emission by the ATLASGAL survey. A total of 18 variable sources are centered on the submillimeter clump peaks and coincide (<1″) with a 24 μm point or compact (<10″) source. Of these 18 sources, 13 can be fit by YSO models. The 13 variable YSOs (VYSOs) have luminosities of ∼103 L ⊙, an average mass of 8 M ⊙, and a range of ages up to 106 yr. A total of 11 of these 13 VYSOs are located in the midst of infrared dark clouds. Nine of the 13 sources have ΔK > 2 mag, significantly higher compared to the mean variability of the entire VVV sample. The light curves of these objects sampled between 2010 and 2015 display rising, declining, or quasi-periodic behavior but no clear periodicity. Light-curve analysis using the Plavchan method shows that the most prominent phased signals have periods of a few hundred days. The nature and timescale of variations found in 6.7 Ghz methanol maser emission in massive stars are similar to that of the VYSO light curves. We argue that the origin of the observed variability is episodic accretion. We suggest that the timescale of a few hundred days may represent the frequency at which a spiraling disk feeds dense gas to the young massive star.

  16. Giant clumps in the FIRE simulations: a case study of a massive high-redshift galaxy

    NASA Astrophysics Data System (ADS)

    Oklopčić, Antonija; Hopkins, Philip F.; Feldmann, Robert; Kereš, Dušan; Faucher-Giguère, Claude-André; Murray, Norman

    2017-02-01

    The morphology of massive star-forming galaxies at high redshift is often dominated by giant clumps of mass ˜108-109 M⊙ and size ˜100-1000 pc. Previous studies have proposed that giant clumps might have an important role in the evolution of their host galaxy, particularly in building the central bulge. However, this depends on whether clumps live long enough to migrate from their original location in the disc or whether they get disrupted by their own stellar feedback before reaching the centre of the galaxy. We use cosmological hydrodynamical simulations from the FIRE (Feedback in Realistic Environments) project which implement explicit treatments of stellar feedback and interstellar medium physics to study the properties of these clumps. We follow the evolution of giant clumps in a massive (M* ˜ 1010.8 M⊙ at z = 1), discy, gas-rich galaxy from redshift z ≳ 2 to z = 1. Even though the clumpy phase of this galaxy lasts over a gigayear, individual gas clumps are short-lived, with mean lifetime of massive clumps of ˜20 Myr. During that time, they turn between 0.1 per cent and 20 per cent of their gas into stars before being disrupted, similar to local giant molecular clouds. Clumps with M ≳ 107 M⊙ account for ˜20 per cent of the total star formation in the galaxy during the clumpy phase, producing ˜1010 M⊙ of stars. We do not find evidence for net inward migration of clumps within the galaxy. The number of giant clumps and their mass decrease at lower redshifts, following the decrease in the overall gas fraction and star formation rate.

  17. Effect of Particle Shape on Mechanical Behaviors of Rocks: A Numerical Study Using Clumped Particle Model

    PubMed Central

    Rong, Guan; Liu, Guang; Zhou, Chuang-bing

    2013-01-01

    Since rocks are aggregates of mineral particles, the effect of mineral microstructure on macroscopic mechanical behaviors of rocks is inneglectable. Rock samples of four different particle shapes are established in this study based on clumped particle model, and a sphericity index is used to quantify particle shape. Model parameters for simulation in PFC are obtained by triaxial compression test of quartz sandstone, and simulation of triaxial compression test is then conducted on four rock samples with different particle shapes. It is seen from the results that stress thresholds of rock samples such as crack initiation stress, crack damage stress, and peak stress decrease with the increasing of the sphericity index. The increase of sphericity leads to a drop of elastic modulus and a rise in Poisson ratio, while the decreasing sphericity usually results in the increase of cohesion and internal friction angle. Based on volume change of rock samples during simulation of triaxial compression test, variation of dilation angle with plastic strain is also studied. PMID:23997677

  18. A Dust Characterization Experiment for Solar Cells Operating on Mars

    NASA Technical Reports Server (NTRS)

    Jenkins, Phillip; Landis, Geoffrey A.; Krasowski, Michael; Greer, Lawrence; Wilt, David; Baraona, Cosmo; Scheiman, David; Lekki, John

    2001-01-01

    During the Viking and Pathfinder missions to Mars, significant amounts of dust accumulated on the spacecrafts. In Pathfinder's case, the dust obscured the solar panels on the lander and the rover degrading their output current. The material adherence experiment aboard the Pathfinder rover quantified the rate of decrease in short circuit current at 0.28% per day. This rate is unacceptably high for long duration missions. In response, NASA has developed the Dust Accumulation and Removal Technology (DART) experiment. DART has three instruments for characterizing dust settling out of the atmosphere and tests two methods to keep dust from settling on solar cells.

  19. Volcanic loading: The dust veil index

    SciTech Connect

    Lamb, H.H.

    1985-09-01

    Dust ejected into the high atmosphere during explosive volcanic eruptions has been considered as a possible cause for climatic change. Dust veils created by volcanic eruptions can reduce the amount of light reaching the Earth`s surface and can cause reductions in surface temperatures. These climatic effects can be seen for several years following some eruptions and the magnitude and duration of the effects depend largely on the density or amount of tephra (i.e. dust) ejected, the latitude of injection, and atmospheric circulation patterns. Lamb (1970) formulated the Dust Veil Index (DVI) in an attempt to quantify the impact on the Earth`s energy balance of changes in atmospheric composition due to explosive volcanic eruptions. The DVI is a numerical index that quantifies the impact on the Earth`s energy balance of changes in atmospheric composition due to explosive volcanic eruptions. The DVI is a numerical index that quantifies the impact of a particular volcanic eruptions release of dust and aerosols over the years following the event. The DVI for any volcanic eruptions are available and have been used in estimating Lamb`s dust veil indices.

  20. Rotational support of giant clumps in high-z disc galaxies

    NASA Astrophysics Data System (ADS)

    Ceverino, Daniel; Dekel, Avishai; Mandelker, Nir; Bournaud, Frederic; Burkert, Andreas; Genzel, Reinhard; Primack, Joel

    2012-03-01

    We address the internal support against total free-fall collapse of the giant clumps that form by violent gravitational instability in high-z disc galaxies. Guidance is provided by an analytic model, where the protoclumps are cut from a rotating disc and collapse to equilibrium while preserving angular momentum. This model predicts prograde clump rotation, which dominates the support if the clump has contracted to a surface density contrast ≳10. This is confirmed in hydro adaptive mesh refinement zoom-in simulations of galaxies in a cosmological context. In most high-z clumps, the centrifugal force dominates the support, ?, where Vrot is the rotation velocity and the circular velocity Vcirc measures the potential well. The clump spin indeed tends to be in the sense of the global disc angular momentum, but substantial tilts are frequent, reflecting the highly warped nature of the high-z discs. Most clumps are in Jeans equilibrium, with the rest of the support provided by turbulence, partly driven by the gravitational instability itself. The general agreement between model and simulations indicates that angular momentum loss or gain in most clumps is limited to a factor of 2. Simulations of isolated gas-rich discs that resolve the clump substructure reveal that the cosmological simulations may overestimate ? by ˜30 per cent, but the dominance of rotational support at high z is not a resolution artefact. In turn, isolated gas-poor disc simulations produce at z= 0 smaller gaseous non-rotating transient clouds, indicating that the difference in rotational support is associated with the fraction of cold baryons in the disc. In our current cosmological simulations, the clump rotation velocity is typically more than twice the disc dispersion, Vrot˜ 100 km s-1, but when beam smearing of ≥0.1 arcsec is imposed, the rotation signal is reduced to a small gradient of ≤30 km s-1 kpc-1 across the clump. The velocity dispersion in the simulated clumps is comparable to the

  1. On the benefits of living in clumps: a case study on Polytrichastrum formosum.

    PubMed

    Zajączkowska, U; Grabowska, K; Kokot, G; Kruk, M

    2017-03-01

    The study concerns the mechanics and water relationships of clumps of a species of endohydric moss, Polytrichastrum formosum. Anatomical and morphological studies were done using optical and scanning electron microscopy. Experiments on waterdrop capture and their distribution to adjacent shoots within a moss clump were performed with the experimental set-up for the droplet collision phenomena and ultra-high speed camera. The mechanical strength of the moss clump was tested on an electromechanical testing machine. During the process of moss clump wetting, the falling water drops were captured by the apical stem part or leaves, then flowed down while adhering to the gametophore and never lost their surface continuity. In places of contact with another leaf, the water drop stops there and joins the leaves, enabling their hydration. Mathematical analysis of anatomical images showed that moss stems have different zones with varying cell lumen and cell wall/cell radius ratios, suggesting the occurrence of a periodic component structure. Our study provides evidence that the reaction of mosses to mechanical forces depends on the size of the clump, and that small groups are clearly stronger than larger groups. The clump structure of mosses acts as a net for falling rain droplets. Clumps of Polytrichastrum having overlapping leaves, at the time of loading formed a structure similar to a lattice. The observed reaction of mosses to mechanical forces indicates that this phenomenon appears to be analogous to the 'size effect on structural strength' that is of great importance for various fields of engineering.

  2. An extremely young massive clump forming by gravitational collapse in a primordial galaxy.

    PubMed

    Zanella, A; Daddi, E; Le Floc'h, E; Bournaud, F; Gobat, R; Valentino, F; Strazzullo, V; Cibinel, A; Onodera, M; Perret, V; Renaud, F; Vignali, C

    2015-05-07

    When cosmic star formation history reaches a peak (at about redshift z ≈ 2), galaxies vigorously fed by cosmic reservoirs are dominated by gas and contain massive star-forming clumps, which are thought to form by violent gravitational instabilities in highly turbulent gas-rich disks. However, a clump formation event has not yet been observed, and it is debated whether clumps can survive energetic feedback from young stars, and afterwards migrate inwards to form galaxy bulges. Here we report the spatially resolved spectroscopy of a bright off-nuclear emission line region in a galaxy at z = 1.987. Although this region dominates star formation in the galaxy disk, its stellar continuum remains undetected in deep imaging, revealing an extremely young (less than ten million years old) massive clump, forming through the gravitational collapse of more than one billion solar masses of gas. Gas consumption in this young clump is more than tenfold faster than in the host galaxy, displaying high star-formation efficiency during this phase, in agreement with our hydrodynamic simulations. The frequency of older clumps with similar masses, coupled with our initial estimate of their formation rate (about 2.5 per billion years), supports long lifetimes (about 500 million years), favouring models in which clumps survive feedback and grow the bulges of present-day galaxies.

  3. Improving dust emission characterization in dust models using dynamic high-resolution geomorphic erodibility map

    NASA Astrophysics Data System (ADS)

    Parajuli, S. P.; Yang, Z.; Kocurek, G.

    2013-12-01

    Dust is known to affect the earth radiation budget, biogeochemical cycle, precipitation, human health and visibility. Despite the increased research effort, dust emission modeling remains challenging because dust emission is affected by complex geomorphological processes. Existing dust models overestimate dust emission and rely on tuning and a static erodibility factor in order to make simulated results comparable to remote sensing and ground-based observations. In most of current models, dust emission is expressed in terms of threshold friction speed, which ultimately depends mainly upon the percentage clay content and soil moisture. Unfortunately, due to the unavailability of accurate and high resolution input data of the clay content and soil moisture, estimated threshold friction speed commonly does not represent the variability in field condition. In this work, we attempt to improve dust emission characterization by developing a high resolution geomorphic map of the Middle East and North Africa (MENA), which is responsible for more than 50% of global dust emission. We develop this geomorphic map by visually examining high resolution satellite images obtained from Google Earth Pro and ESRI base map. Albeit subjective, our technique is more reliable compared to automatic image classification technique because we incorporate knowledge of geological/geographical setting in identifying dust sources. We hypothesize that the erodibility is unique for different geomorphic landforms and that it can be quantified by the correlation between observed wind speed and satellite retrieved aerosol optical depth (AOD). We classify the study area into several key geomorphological categories with respect to their dust emission potential. Then we quantify their dust emission potential using the correlation between observed wind speed and satellite retrieved AOD. The dynamic, high-resolution geomorphic erodibility map thus prepared will help to reduce the uncertainty in current

  4. Interstellar Dust: Contributed Papers

    NASA Technical Reports Server (NTRS)

    Tielens, Alexander G. G. M. (Editor); Allamandola, Louis J. (Editor)

    1989-01-01

    A coherent picture of the dust composition and its physical characteristics in the various phases of the interstellar medium was the central theme. Topics addressed included: dust in diffuse interstellar medium; overidentified infrared emission features; dust in dense clouds; dust in galaxies; optical properties of dust grains; interstellar dust models; interstellar dust and the solar system; dust formation and destruction; UV, visible, and IR observations of interstellar extinction; and quantum-statistical calculations of IR emission from highly vibrationally excited polycyclic aromatic hydrocarbon (PAH) molecules.

  5. THE LIFE AND DEATH OF DENSE MOLECULAR CLUMPS IN THE LARGE MAGELLANIC CLOUD

    SciTech Connect

    Seale, Jonathan P.; Looney, Leslie W.; Wong, Tony; Ott, Juergen; Klein, Uli; Pineda, Jorge L.

    2012-05-20

    We report the results of a high spatial (parsec) resolution HCO{sup +} (J = 1 {yields} 0) and HCN (J = 1 {yields} 0) emission survey toward the giant molecular clouds of the star formation regions N 105, N 113, N 159, and N 44 in the Large Magellanic Cloud (LMC). The HCO{sup +} and HCN observations at 89.2 and 88.6 GHz, respectively, were conducted in the compact configuration of the Australia Telescope Compact Array. The emission is imaged into individual clumps with masses between 10{sup 2} and 10{sup 4} M{sub Sun} and radii of <1 pc to {approx}2 pc. Many of the clumps are coincident with indicators of current massive star formation, indicating that many of the clumps are associated with deeply embedded forming stars and star clusters. We find that massive young stellar object (YSO) bearing clumps tend to be larger ({approx}>1 pc), more massive (M {approx}> 10{sup 3} M{sub Sun }), and have higher surface densities ({approx}1 g cm{sup -2}), while clumps without signs of star formation are smaller ({approx}<1 pc), less massive (M {approx}< 10{sup 3} M{sub Sun }), and have lower surface densities ({approx}0.1 g cm{sup -2}). The dearth of massive (M > 10{sup 3} M{sub Sun }) clumps not bearing massive YSOs suggests that the onset of star formation occurs rapidly once the clump has attained physical properties favorable to massive star formation. Using a large sample of LMC massive YSO mid-IR spectra, we estimate that {approx}2/3 of the massive YSOs for which there are Spitzer mid-IR spectra are no longer located in molecular clumps; we estimate that these young stars/clusters have destroyed their natal clumps on a timescale of at least {approx}3 Multiplication-Sign 10{sup 5} yr.

  6. Clumped isotope composition of cold-water corals: A role for vital effects?

    NASA Astrophysics Data System (ADS)

    Spooner, Peter T.; Guo, Weifu; Robinson, Laura F.; Thiagarajan, Nivedita; Hendry, Katharine R.; Rosenheim, Brad E.; Leng, Melanie J.

    2016-04-01

    The carbonate clumped isotope thermometer is a promising tool for determining past ocean temperatures. It is based on the temperature dependence of rare isotopes 'clumping' into the same carbonate ion group in the carbonate mineral lattice. The extent of this clumping effect is independent of the isotope composition of the water from which carbonate precipitates, providing unique advantages over many other paleotemperature proxies. Existing calibrations of this thermometer in cold-water and warm-water corals suggest clumped isotope 'vital effects' are negligible in cold-water corals but may be significant in warm-water corals. Here, we test the calibration of the carbonate clumped isotope thermometer in cold-water corals with a recently collected and well characterised sample set spanning a range of coral genera (Balanophyllia, Caryophyllia, Dasmosmilia, Desmophyllum, Enallopsammia and Javania). The clumped isotope compositions (Δ47) of these corals exhibit systematic dependences on their growth temperatures, confirming the basis of the carbonate clumped isotope thermometer. However, some cold-water coral genera show Δ47 values that are higher than the expected equilibrium values by up to 0.05‰ (equivalent to underestimating temperature by ∼9 °C) similar to previous findings for some warm-water corals. This finding suggests that the vital effects affecting corals Δ47 are common to both warm- and cold-water corals. By comparison with models of the coral calcification process we suggest that the clumped isotope offsets in these genera are related to the kinetic isotope effects associated with CO2 hydration/hydroxylation reactions in the corals' calcifying fluid. Our findings complicate the use of the carbonate clumped isotope thermometer in corals, but suggest that species- or genus-specific calibrations could be useful for the future application of this paleotemperature proxy.

  7. Assessment and mitigation of combustible dust hazards in the plastics industry

    NASA Astrophysics Data System (ADS)

    Stern, Michael C.; Ibarreta, Alfonso; Myers, Timothy J.

    2015-05-01

    A number of recent industrial combustible dust fires and explosions, some involving powders used in the plastics industry, have led to heightened awareness of combustible dust hazards, increased regulatory enforcement, and changes to the current standards and regulations. This paper provides a summary of the fundamentals of combustible dust explosion hazards, comparing and contrasting combustible dust to flammable gases and vapors. The types of tests used to quantify and evaluate the potential hazard posed by plastic dusts are explored. Recent changes in NFPA 654, a standard applicable to combustible dust in the plastics industry, are also discussed. Finally, guidance on the primary methods for prevention and mitigation of combustible dust hazards are provided.

  8. Dynamical Fate of Clumps Formed in Satellite Mergers.

    NASA Astrophysics Data System (ADS)

    Cotto-Figueroa, Desireé; Asphaug, Erik; Reufer, Andreas

    2014-05-01

    The middle-sized moons (MSMs) of Saturn are icy bodies approximately 300-1500 km diameter, whose cumulative mass is approximately 5% the mass of Titan. Although it is generally thought that they accreted from a gas and particle disk around Saturn [Charnoz, S. et al. (2011), Canup, R. M. & Ward, W. R. (2006)], this classical scenario seems unable to explain their diverse geology and composition, ranging from pure ice to mostly rock. Recently the idea that the MSMs (and perhaps Titan) formed in a series of collisions has flourished [Sekine & Genda, H. (2012), Asphaug, E. & Reufer, A. (2013), Hamilton, D. P. (2013) AAS/DPS Meetings, Cuk, M. (2013) ASU, SESE Colloquium]. Sekine & Genda (2012) proposed that the MSMs are remnants of a hit and run collision into a disappeared Titan-like satellite of Saturn. Asphaug & Reufer (2013) proposed instead that they are unaccreted remnants from the few collisional mergers that formed Titan. In each scenario, the main uncertainty and skepticism, which motivates the research presented here, is whether unaccreted or hit and run remnants can attain stable orbits and avoid becoming accreted. We study the dynamical fate of clumps formed in satellite mergers by coupling N-body simulations with the results of collisional mergers in SPH simulations. We define stable orbital configurations of one or more satellites in a planetary system in which a collision (merger or other giant impact) is assumed to have occurred. The outcome of different SPH simulations, representative of realistic collisions (mergers, hit and runs, disruptions), is integrated using the N-body integrator Mercury [Chambers, J. E. (1999)]. We study a variety of scenarios, including: single major collisions, multiple major collisions and successions of major collisions. External perturbations that would cause the system to go unstable in the first place and trigger the major collisions are also studied. We aim to identify the characteristic fraction of clumps from

  9. Weighing the local dark matter with RAVE red clump stars

    NASA Astrophysics Data System (ADS)

    Bienaymé, O.; Famaey, B.; Siebert, A.; Freeman, K. C.; Gibson, B. K.; Gilmore, G.; Grebel, E. K.; Bland-Hawthorn, J.; Kordopatis, G.; Munari, U.; Navarro, J. F.; Parker, Q.; Reid, W.; Seabroke, G. M.; Siviero, A.; Steinmetz, M.; Watson, F.; Wyse, R. F. G.; Zwitter, T.

    2014-11-01

    We determine the Galactic potential in the solar neigbourhood from RAVE observations. We select red clump stars for which accurate distances, radial velocities, and metallicities have been measured. Combined with data from the 2MASS and UCAC catalogues, we build a sample of ~4600 red clump stars within a cylinder of 500 pc radius oriented in the direction of the South Galactic Pole, in the range of 200 pc to 2000 pc distances. We deduce the vertical force and the total mass density distribution up to 2 kpc away from the Galactic plane by fitting a distribution function depending explicitly on three isolating integrals of the motion in a separable potential locally representing the Galactic one with four free parameters. Because of the deep extension of our sample, we can determine nearly independently the dark matter mass density and the baryonic disc surface mass density. We find (i) at 1 kpc Kz/ (2πG) = 68.5 ± 1.0 M⊙ pc-2; and (ii) at 2 kpc Kz/ (2πG) = 96.9 ± 2.2 M⊙ pc-2. Assuming the solar Galactic radius at R0 = 8.5 kpc, we deduce the local dark matter density ρDM(z = 0) = 0.0143 ± 0.0011 M⊙pc-3 = 0.542 ± 0.042 Gev cm-3 and the baryonic surface mass density Σbar = 44.4 ± 4.1 M⊙pc-2. Our results are in agreement with previously published Kz determinations up to 1 kpc, while the extension to 2 kpc shows some evidence for an unexpectedly large amount of dark matter. A flattening of the dark halo of order 0.8 can produce such a high local density in combination with a circular velocity of 240 km s-1. It could also be consistent with a spherical cored dark matter profile whose density does not drop sharply with radius. Another explanation, allowing for a lower circular velocity, could be the presence of a secondary dark component, a very thick disc resulting either from the deposit of dark matter from the accretion of multiple small dwarf galaxies, or from the presence of an effective "phantom" thick disc in the context of effective galactic

  10. A lower fragmentation mass scale for clumps in high redshift galaxies: a systematic numerical study

    NASA Astrophysics Data System (ADS)

    Tamburello, Valentina; Mayer, Lucio; Shen, Sijing; Wadsley, James

    2015-08-01

    We perform a systematic study of the effect of sub-grid physics, resolution and structural parameters on the fragmentation of gas-rich galaxy discs into massive star forming clumps due to gravitational instability. We use the state-of-the-art zoom-in cosmological hydrodynamical simulation ARGO (Fiacconi et al. 2015) to set up the initial conditions of our models, and then carry out 26 high resolution controlled simulations of high-z galaxies using the GASOLINE2 code, which includes a modern, numerically robust SPH implementation.We find that when blast-wave feedback is included, the formation of long-lived, gravitationally bound clumps requires disc gas fractions of at least 50% and massive discs, which should have Vmax > 200 km/s at z ˜ 2, more massive than the typical galaxies expected at those redshifts.Less than 50 Myr after formation, clumps have stellar masses in the range 4 × 106 - 5 × 107 M⊙.Formation of clumps with mass exceeding ˜108 M⊙ is a rare occurrence, since it requires mergers between multiple massive clumps, as we verified by tracing back in time the particles belonging to such clumps. Such mergers happen after a few orbital times (˜200-300 Myr), but normally clumps migrate inward and are tidally disrupted on shorter timescales.Clump sizes are in the range 100-500 pc. We argue that giant clumps identified in observations (˜109 M⊙ and 1 kpc in size) might either have a different origin, such as minor mergers and clumpy gas accretion, or their sizes and masses may be overestimated due to resolution issues.Using an analytical model, already developed to explain the fragmentation scale in gravitationally unstable 3D protoplanetary discs, we can predict fairly accurately the characteristic gaseous masses of clumps soon after fragmentation, when standard Toome analysis becomes invalid.Due to their modest size, clumps have little effect on bulge growth as they migrate to the center. In our unstable discs a small bulge can form irrespective of

  11. The segregation of starless and protostellar clumps in the Hi-GAL ℓ = 224° region

    NASA Astrophysics Data System (ADS)

    Olmi, L.; Cunningham, M.; Elia, D.; Jones, P.

    2016-10-01

    Context. Stars form in dense, dusty structures, which are embedded in larger clumps of molecular clouds often showing a clear filamentary structure on large scales (≳1 pc). The origin (e.g., turbulence or gravitational instabilities) and evolution of these filaments, as well as their relation to clump and core formation, are not yet fully understood. A large sample of both starless and protostellar clumps can now be found in the Herschel Infrared GALactic Plane Survey (Hi-GAL) key project, which also provides striking images of the filamentary structure of the parent molecular clouds. Recent results indicate that populations of clumps on and off filaments may differ. Aims: One of the best-studied regions in the Hi-GAL survey can be observed toward the ℓ = 224° field. Here, a filamentary region has been studied and it has been found that protostellar clumps are mostly located along the main filament, whereas starless clumps are detected off this filament and are instead found on secondary, less prominent filaments. We want to investigate this segregation effect and how it may affect the clumps properties. Methods: We mapped the 12CO (1-0) line and its main three isotopologues toward the two most prominent filaments observed toward the ℓ = 224° field using the Mopra radio telescope, in order to set observational constraints on the dynamics of these structures and the associated starless and protostellar clumps. Results: Compared to the starless clumps, the protostellar clumps are more luminous, more turbulent and lie in regions where the filamentary ambient gas shows larger linewidths. We see evidence of gas flowing along the main filament, but we do not find any signs of accretion flow from the filament onto the Hi-GAL clumps. We analyze the radial column density profile of the filaments and their gravitational stability. Conclusions: The more massive and highly fragmented main filament appears to be thermally supercritical and gravitationally bound

  12. THE TRANSIT LIGHT CURVE OF AN EXOZODIACAL DUST CLOUD

    SciTech Connect

    Stark, Christopher C.

    2011-10-15

    Planets embedded within debris disks gravitationally perturb nearby dust and can create clumpy, azimuthally asymmetric circumstellar ring structures that rotate in lock with the planet. The Earth creates one such structure in the solar zodiacal dust cloud. In an edge-on system, the dust 'clumps' periodically pass in front of the star as the planet orbits, occulting and forward-scattering starlight. In this paper, we predict the shape and magnitude of the corresponding transit signal. To do so, we model the dust distributions of collisional, steady-state exozodiacal clouds perturbed by planetary companions. We examine disks with dusty ring structures formed by the planet's resonant trapping of in-spiraling dust for a range of planet masses and semi-major axes, dust properties, and disk masses. We synthesize edge-on images of these models and calculate the transit signatures of the resonant ring structures. The transit light curves created by dusty resonant ring structures typically exhibit two broad transit minima that lead and trail the planetary transit. We find that Jupiter-mass planets embedded within disks hundreds of times denser than our zodiacal cloud can create resonant ring structures with transit depths up to {approx}10{sup -4}, possibly detectable with Kepler. Resonant rings produced by planets more or less massive than Jupiter produce smaller transit depths. Observations of these transit signals may provide upper limits on the degree of asymmetry in exozodiacal clouds.

  13. The Exozodiacal Dust Problem for Direct Observations of ExoEarths

    NASA Technical Reports Server (NTRS)

    Roberge, Aki; Chen, Christine H.; Millan-Gabet, Rafael; Weinberger, Alycia J.; Hinz, Philip M.; Stapelfeldt, Karl R.; Absil, Olivier; Kuchner, Marc J.; Bryden, Geoffrey

    2012-01-01

    Debris dust in the habitable zones of stars otherwise known as exozodiacal dust comes from extrasolar asteroids and comets and is thus an expected part of a planetary system. Background flux from the Solar Systems zodiacal dust and the exozodiacal dust in the target system is likely to be the largest source of astrophysical noise in direct observations of terrestrial planets in the habitable zones of nearby stars. Furthermore, dust structures like clumps, thought to be produced by dynamical interactions with exoplanets, are a possible source of confusion. In this paper, we qualitatively assess the primary impact of exozodical dust on high-contrast direct imaging at optical wavelengths, such as would be performed with a coronagraph. Then we present the sensitivity of previous, current, and near-term facilities to thermal emission from debris dust at all distances from nearby solar-type stars, as well as our current knowledge of dust levels from recent surveys. Finally, we address the other method of detecting debris dust, through high-contrast imaging in scattered light. This method is currently far less sensitive than thermal emission observations, but provides high spatial resolution for studying dust structures. This paper represents the first report of NASA's Exoplanet Exploration Program Analysis Group (ExoPAG).

  14. Dust Measurements in Tokamaks

    SciTech Connect

    Rudakov, D; Yu, J; Boedo, J; Hollmann, E; Krasheninnikov, S; Moyer, R; Muller, S; Yu, A; Rosenberg, M; Smirnov, R; West, W; Boivin, R; Bray, B; Brooks, N; Hyatt, A; Wong, C; Fenstermacher, M; Groth, M; Lasnier, C; McLean, A; Stangeby, P; Ratynskaia, S; Roquemore, A; Skinner, C; Solomon, W M

    2008-04-23

    Dust production and accumulation impose safety and operational concerns for ITER. Diagnostics to monitor dust levels in the plasma as well as in-vessel dust inventory are currently being tested in a few tokamaks. Dust accumulation in ITER is likely to occur in hidden areas, e.g. between tiles and under divertor baffles. A novel electrostatic dust detector for monitoring dust in these regions has been developed and tested at PPPL. In DIII-D tokamak dust diagnostics include Mie scattering from Nd:YAG lasers, visible imaging, and spectroscopy. Laser scattering resolves size of particles between 0.16-1.6 {micro}m in diameter; the total dust content in the edge plasmas and trends in the dust production rates within this size range have been established. Individual dust particles are observed by visible imaging using fast-framing cameras, detecting dust particles of a few microns in diameter and larger. Dust velocities and trajectories can be determined in 2D with a single camera or 3D using multiple cameras, but determination of particle size is problematic. In order to calibrate diagnostics and benchmark dust dynamics modeling, pre-characterized carbon dust has been injected into the lower divertor of DIII-D. Injected dust is seen by cameras, and spectroscopic diagnostics observe an increase of carbon atomic, C2 dimer, and thermal continuum emissions from the injected dust. The latter observation can be used in the design of novel dust survey diagnostics.

  15. Physical Properties of Sub-galactic Clumps at 0.5 ≤ Z ≤ 1.5 in the UVUDF

    NASA Astrophysics Data System (ADS)

    Soto, Emmaris; de Mello, Duilia F.; Rafelski, Marc; Gardner, Jonathan P.; Teplitz, Harry I.; Koekemoer, Anton M.; Ravindranath, Swara; Grogin, Norman A.; Scarlata, Claudia; Kurczynski, Peter; Gawiser, Eric

    2017-03-01

    We present an investigation of clumpy galaxies in the Hubble Ultra Deep Field at 0.5≤slant z≤slant 1.5 in the rest-frame far-ultraviolet (FUV) using Hubble Space Telescope Wide Field Camera 3 broadband imaging in F225W, F275W, and F336W. An analysis of 1404 galaxies yields 209 galaxies that host 403 kpc scale clumps. These host galaxies appear to be typical star-forming galaxies, with an average of 2 clumps per galaxy and reaching a maximum of 8 clumps. We measure the photometry of the clumps and determine the mass, age, and star formation rates (SFR) using the spectral energy distribution fitting code FAST. We find that clumps make an average contribution of 19% to the total rest-frame FUV flux of their host galaxy. Individually, clumps contribute a median of 5% to the host galaxy SFR and an average of ∼4% to the host galaxy mass, with total clump contributions to the host galaxy stellar mass ranging widely from lower than 1% up to 93%. Clumps in the outskirts of galaxies are typically younger, with higher SFRs, than clumps in the inner regions. The results are consistent with clump migration theories in which clumps form through violent gravitational instabilities in gas-rich turbulent disks, eventually migrate toward the center of the galaxies, and coalesce into the bulge.

  16. Clumped isotope calibration data for lacustrine carbonates: A progress report

    NASA Astrophysics Data System (ADS)

    Tripati, A.

    2015-12-01

    Our capacity to understand Earth's environmental history is highly dependent on the accuracy of reconstructions of past climates. Lake sediments provide important archives of terrestrial climate change, and represent an important tool for reconstructing paleohydrology, paleoclimate, paleoenvironment, and paleoaltimetry. Unfortunately, while multiple methods for constraining marine temperature exist, quantitative terrestrial proxies are scarcer - tree rings, speleothems, and leaf margin analyses have all been used with varying degrees of accuracy. Clumped isotope thermometry has the potential to be a useful instrument for determining terrestrial climates: multiple studies have shown the fraction of 13C—18O bonds in carbonates is inversely related to the temperature at which the rocks formed. We have been measuring the abundance of 13C18O16O in the CO2 produced by the dissolution of carbonate minerals in phosphoric acid in modern lake samples and comparing results to independently known estimates of lake water temperature. Here we discuss an extensive calibration dataset comprised of 132 analyses of 97 samples from 44 localities, including microbialites, tufas, and micrites endogenic carbonates, freshwater gastropods, bivalves, microbialites, and ooids.

  17. Nucleosynthesis and Clump Formation in a Core-Collapse Supernova.

    PubMed

    Kifonidis; Plewa; Janka; Müller

    2000-03-10

    High-resolution two-dimensional simulations were performed for the first 5 minutes of the evolution of a core-collapse supernova explosion in a 15 M middle dot in circle blue supergiant progenitor. The computations start shortly after bounce and include neutrino-matter interactions by using a lightbulb approximation for the neutrinos and a treatment of the nucleosynthesis due to explosive silicon and oxygen burning. We find that newly formed iron-group elements are distributed throughout the inner half of the helium core by Rayleigh-Taylor instabilities at the (Ni + Si)/O and (C + O)/He interfaces, seeded by convective overturn during the early stages of the explosion. Fast-moving nickel mushrooms with velocities up to approximately 4000 km s-1 are observed. This offers a natural explanation for the mixing required in light-curve and spectral synthesis studies of Type Ib explosions. A continuation of the calculations to later times, however, indicates that the iron velocities observed in SN 1987A cannot be reproduced because of a strong deceleration of the clumps in the dense shell left behind by the shock at the He/H interface.

  18. Nucleosynthesis and Clump Formation in a Core-Collapse Supernova

    NASA Astrophysics Data System (ADS)

    Kifonidis, K.; Plewa, T.; Janka, H.-Th.; Müller, E.

    2000-03-01

    High-resolution two-dimensional simulations were performed for the first 5 minutes of the evolution of a core-collapse supernova explosion in a 15 Msolar blue supergiant progenitor. The computations start shortly after bounce and include neutrino-matter interactions by using a lightbulb approximation for the neutrinos and a treatment of the nucleosynthesis due to explosive silicon and oxygen burning. We find that newly formed iron-group elements are distributed throughout the inner half of the helium core by Rayleigh-Taylor instabilities at the (Ni + Si)/O and (C + O)/He interfaces, seeded by convective overturn during the early stages of the explosion. Fast-moving nickel mushrooms with velocities up to ~4000 km s-1 are observed. This offers a natural explanation for the mixing required in light-curve and spectral synthesis studies of Type Ib explosions. A continuation of the calculations to later times, however, indicates that the iron velocities observed in SN 1987A cannot be reproduced because of a strong deceleration of the clumps in the dense shell left behind by the shock at the He/H interface.

  19. Extinction and dust properties in a clumpy medium

    NASA Astrophysics Data System (ADS)

    Scicluna, P.; Siebenmorgen, R.

    2015-12-01

    The dust content of the universe is primarily explored via its interaction with stellar photons, which are absorbed or scattered by the dust, producing the effect known as interstellar extinction. However, owing to the physical extension of the observing beam, real observations may detect a significant number of dust-scattered photons. This may result in a change in the observed (or effective) extinction with a dependence on the spatial distribution of the dust and the spatial resolution of the instrument. We investigate the influence of clumpy dust distributions on the effective extinction toward both embedded sources and those seen through the diffuse interstellar medium (ISM). We use a Monte Carlo radiative transfer code to examine the effective extinction for various geometries. By varying the number, optical depth and volume-filling factor of clumps inside the model for spherical shells and the diffuse interstellar medium (ISM), we explore the evolution of the extinction curve and effective optical depth. Depending on the number of scattering events in the beam, the extinction curve is observed to steepen in homogeneous media and flatten in clumpy media. As a result, clumpy dust distributions are able to reproduce extinction curves with arbitrary RV,eff, the effective ratio of total-to-selective extinction. The flattening is also able to "wash out" the 2175 Å bump and results in a shift of the peak to shorter wavelengths. The mean RV,eff of a shell is shown to correlate with the optical depth of an individual clump and the wavelength at which a clump becomes optically thick. Similar behaviour is seen for edge-on discs or tori. However, at grazing inclinations the combination of extinction and strong forward scattering results in chaotic behaviour. Caution is therefore advised when attempting to measure extinction in AGN tori for example or toward SNIa or GRB afterglows. In face-on discs, the shape of the scattered continuum is observed to change significantly

  20. Dust feed mechanism

    DOEpatents

    Milliman, Edward M.

    1984-01-01

    The invention is a dust feed device for delivery of a uniform supply of dust for long periods of time to an aerosolizing means for production of a dust suspension. The device utilizes at least two tandem containers having spiral brushes within the containers which transport the dust from a supply to the aerosolizer means.

  1. Outflow Feedback Regulated Massive Star Formation in Parsec-Scale Cluster Forming Clumps

    SciTech Connect

    Wang, Peng; Li, Zhi-Yun; Abel, Tom; Nakamura, Fumitaka; /Niigata U.

    2010-02-15

    We investigate massive star formation in turbulent, magnetized, parsec-scale clumps of molecular clouds including protostellar outflow feedback using three dimensional numerical simulations of effective resolution 2048{sup 3}. The calculations are carried out using a block structured adaptive mesh refinement code that solves the ideal MHD equations including self-gravity and implements accreting sink particles. We find that, in the absence of regulation by magnetic fields and outflow feedback, massive stars form readily in a turbulent, moderately condensed clump of {approx} 1,600 M{sub {circle_dot}} (containing {approx} 10{sup 2} initial Jeans masses), along with a cluster of hundreds of lower mass stars. The massive stars are fed at high rates by (1) transient dense filaments produced by large-scale turbulent compression at early times, and (2) by the clump-wide global collapse resulting from turbulence decay at late times. In both cases, the bulk of the massive star's mass is supplied from outside a 0.1 pc-sized 'core' that surrounds the star. In our simulation, the massive star is clump-fed rather than core-fed. The need for large-scale feeding makes the massive star formation prone to regulation by outflow feedback, which directly opposes the feeding processes. The outflows reduce the mass accretion rates onto the massive stars by breaking up the dense filaments that feed the massive star formation at early times, and by collectively slowing down the global collapse that fuel the massive star formation at late times. The latter is aided by a moderate magnetic field of strength in the observed range (corresponding to a dimensionless clump mass-to-flux ratio {lambda} {approx} a few); the field allows the outflow momenta to be deposited more efficiently inside the clump. We conclude that the massive star formation in our simulated turbulent, magnetized, parsec-scale clump is outflow-regulated and clump-fed (ORCF for short). An important implication is that the

  2. Dust Formation in CCSNe with Extensive Mass Loss Histories

    NASA Astrophysics Data System (ADS)

    Andrews, Jennifer; Clayton, Geoffrey; Krafton, Kelsie; Sugerman, Ben; Barlow, Michael; Wesson, Roger; Gallagher, Joseph; Otsuka, Masaaki; Matsuura, Mikako; Meixner, Margaret

    2014-02-01

    The systematics of dust formation in core collapse supernovae (CCSNe), such as the timing, location, and amount of newly formed dust and the effects of progenitor mass and circumstellar environment, are still vague and unclear. Recent discoveries of massive amounts of cool dust in SN 1987A and the Crab nebula have once again brought this debate to the forefront. We are currently undertaking an ambitious program to better understand how the various dust formation indicators are related, and more importantly how to correctly interpret these indicators to make accurate estimates of the amount of dust formed in a typical CCSNe explosion. Our planned observations of SNe 2010jl and 2011ja, with Gemini/GMOS as part of our multi-wavelength and multi-;epoch campaign, will not only allow us to classify and quantify newly condensing dust in the cool dense shell and the ejecta, but will also allow us to accurately map out pre-existing circumstellar dust in light echoes. Measuring the location and mass of the dust around a SN, while the dust is still warm, is essential in deciphering the origin of the large masses of cold dust that have been discovered in SN 1987A and the Crab nebula. This increased understanding of dust formation from massive stars may then be applied to understanding the presence of large amounts of dust in primordial galaxies seen at high redshift.

  3. Metabolic Adaptations of Azospirillum brasilense to Oxygen Stress by Cell-to-Cell Clumping and Flocculation

    SciTech Connect

    Bible, Amber N.; Khalsa-Moyers, Gurusahai K.; Mukherjee, Tanmoy; Green, Calvin S.; Mishra, Priyanka; Purcell, Alicia; Aksenova, Anastasia; Hurst, Gregory B.; Alexandre, Gladys

    2015-09-25

    The ability of bacteria to monitor their metabolism and adjust their behavior accordingly is critical to maintain competitiveness in the environment. The motile microaerophilic bacteriumAzospirillum brasilensenavigates oxygen gradients by aerotaxis in order to locate low oxygen concentrations that can support metabolism. When cells are exposed to elevated levels of oxygen in their surroundings, motileA. brasilensecells implement an alternative response to aerotaxis and form transient clumps by cell-to-cell interactions. Clumping was suggested to represent a behavior protecting motile cells from transiently elevated levels of aeration. Using the proteomics of wild-type and mutant strains affected in the extent of their clumping abilities, we show that cell-to-cell clumping represents a metabolic scavenging strategy that likely prepares the cells for further metabolic stresses. Analysis of mutants affected in carbon or nitrogen metabolism confirmed this assumption. The metabolic changes experienced as clumping progresses prime cells for flocculation, a morphological and metabolic shift of cells triggered under elevated-aeration conditions and nitrogen limitation. The analysis of various mutants during clumping and flocculation characterized an ordered set of changes in cell envelope properties accompanying the metabolic changes. These data also identify clumping and early flocculation to be behaviors compatible with the expression of nitrogen fixation genes, despite the elevated-aeration conditions. Finally, cell-to-cell clumping may thus license diazotrophy to microaerophilicA. brasilensecells under elevated oxygen conditions and prime them for long-term survival via flocculation if metabolic stress persists.

  4. Metabolic Adaptations of Azospirillum brasilense to Oxygen Stress by Cell-to-Cell Clumping and Flocculation

    DOE PAGES

    Bible, Amber N.; Khalsa-Moyers, Gurusahai K.; Mukherjee, Tanmoy; ...

    2015-09-25

    The ability of bacteria to monitor their metabolism and adjust their behavior accordingly is critical to maintain competitiveness in the environment. The motile microaerophilic bacteriumAzospirillum brasilensenavigates oxygen gradients by aerotaxis in order to locate low oxygen concentrations that can support metabolism. When cells are exposed to elevated levels of oxygen in their surroundings, motileA. brasilensecells implement an alternative response to aerotaxis and form transient clumps by cell-to-cell interactions. Clumping was suggested to represent a behavior protecting motile cells from transiently elevated levels of aeration. Using the proteomics of wild-type and mutant strains affected in the extent of their clumping abilities,more » we show that cell-to-cell clumping represents a metabolic scavenging strategy that likely prepares the cells for further metabolic stresses. Analysis of mutants affected in carbon or nitrogen metabolism confirmed this assumption. The metabolic changes experienced as clumping progresses prime cells for flocculation, a morphological and metabolic shift of cells triggered under elevated-aeration conditions and nitrogen limitation. The analysis of various mutants during clumping and flocculation characterized an ordered set of changes in cell envelope properties accompanying the metabolic changes. These data also identify clumping and early flocculation to be behaviors compatible with the expression of nitrogen fixation genes, despite the elevated-aeration conditions. Finally, cell-to-cell clumping may thus license diazotrophy to microaerophilicA. brasilensecells under elevated oxygen conditions and prime them for long-term survival via flocculation if metabolic stress persists.« less

  5. From Dust Grains to Planetesimals: The Importance of the Streaming Instability in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Simon, Jacob B.; Armitage, Philip J.; Youdin, Andrew N.; Li, Rixin

    2016-01-01

    Planetesimals are the precursors to planets, and understanding their formation is an essential step towards developing a complete theory of planet formation. For small solid particles (e.g., dust grains) to coagulate into planetesimals, however, requires that these particles grow beyond centimeter sizes; with traditional coagulation physics, this is very difficult. The streaming instability, which is a clumping process akin to the pile-up of cars in a traffic jam, generates sufficiently high solid densities that the mutual gravity between the clumped particles eventually causes their collapse towards planetesimal mass and size scales. Exploring this transition from dust grains to planetesimals is still in its infancy but is extremely important if we want to understand the basics of planet formation. Here, I present a series of high resolution, first principles numerical simulations of protoplanetary disk gas and dust to study the clumping of particles via the streaming instability and the subsequent collapse towards planetesimals. These simulations have been employed to characterize the planetesimal population as a function of radius in protoplanetary disks. The results of these simulations will be crucial for planet formation models to correctly explain the formation and configuration of solar systems.

  6. LOOKING THROUGH THE GALACTIC PLANE: IMAGING COLD DUST TOWARD l = 44 DEG

    SciTech Connect

    Matthews, Henry; Kirk, Helen; Johnstone, Doug; Weferling, Bernd; Cohen, Martin; Jenness, Tim; Davis, Gary; Evans, Aneurin; Dent, William R. F.; Fuller, Gary; Jackson, James M.; Rathborne, Jill; Richer, John; Simon, Robert

    2009-11-15

    We present imaging observations of continuum emission from interstellar dust at 850 and 1200 {mu}m of a section of the Galactic Plane covering 2 deg{sup 2} centered at l = 44 DEG. Complementary jiggle-mapping and fast-scanning techniques were used, respectively, at these two wavelengths. The mapped area includes the well-known star formation regions W49 and G45.1/45.5. Using an automated clump-finding routine, we identify 132 compact 850 {mu}m emission features within the region above a completeness level of about 200 mJy beam{sup -1}. The positions of the latter objects were used to determine fluxes from the 1200 {mu}m image. Spectral line data were subsequently obtained with the same observing beamwidth as at 850 {mu}m for almost half of the objects; these were either imaged in the {sup 13}CO (3-2) line, or basic characteristics determined using the {sup 12}CO (3-2) transition. We use these data, supplemented by existing {sup 13}CO (1-0) and H I survey data, to determine distances and hence derive masses for the dust clump ensemble, assuming a uniform dust temperature of 15 K. From these data we find that the number-mass relationship for clumps in the field is similar to that found for individual star-forming regions.

  7. Modeling Active Galactic Nucleus Feedback in Cool-core Clusters: The Formation of Cold Clumps

    NASA Astrophysics Data System (ADS)

    Li, Yuan; Bryan, Greg L.

    2014-07-01

    We perform high-resolution (15-30 pc) adaptive mesh simulations to study the impact of momentum-driven active galactic nucleus (AGN) feedback in cool-core clusters, focusing in this paper on the formation of cold clumps. The feedback is jet-driven with an energy determined by the amount of cold gas within 500 pc of the super-massive black hole. When the intracluster medium in the core of the cluster becomes marginally stable to radiative cooling, with the thermal instability to the free-fall timescale ratio t TI/t ff < 3-10, cold clumps of gas start to form along the propagation direction of the AGN jets. By tracing the particles in the simulations, we find that these cold clumps originate from low entropy (but still hot) gas that is accelerated by the jet to outward radial velocities of a few hundred km s-1. This gas is out of hydrostatic equilibrium and so can cool. The clumps then grow larger as they decelerate and fall toward the center of the cluster, eventually being accreted onto the super-massive black hole. The general morphology, spatial distribution, and estimated Hα morphology of the clumps are in reasonable agreement with observations, although we do not fully replicate the filamentary morphology of the clumps seen in the observations, probably due to missing physics.

  8. Isolation of dihydrocurcuminoids from cell clumps and their distribution in various parts of turmeric (Curcuma longa).

    PubMed

    Kita, Tomoko; Imai, Shinsuke; Sawada, Hiroshi; Seto, Haruo

    2009-05-01

    In addition to well-known curcuminoids, three colored metabolites were isolated from cultured cell clumps that had been induced from buds on turmeric rhizomes. The isolated compounds were identified as dihydro derivatives of curcuminoids, dihydrocurcumin (dihydroCurc), dihydrodesmethoxycurcumin-a (dihydroDMC-a), and dihydrobisdesmethoxycurcumin (dihydroBDMC). The cell clumps did not contain dihydroDMC-b, an isomer of dihydroDMC-a. A comparison of the distribution profiles of curcuminoids and dihydrocurcuminoids in the cell clumps with those in the rhizomes, leaves, and roots revealed the following differences: Unlike rhizomes, the cell clumps, leaves, and roots contained dihydrocurcuminoids as the major colored constituents. Whereas dimethoxy compounds, curcumin and dihydrocurcumin, respectively, were most abundant in the rhizomes and leaves, one of the monomethoxy derivatives, dihydroDMC-a, was found most abundantly in the cell clumps and roots. While both dihydroDMC-a and b were detected in the rhizomes, dihydroDMC-b was not detectable in the cell clumps, leaves, or roots. The occurrence of only one of the two possible isomers of dihydroDMC suggests biosynthetic formation of dihydrocurcuminoids in turmeric.

  9. Giant Clumps in Star-forming Galaxies at z>1 in CANDELS Observations and CANDElized Simulations

    NASA Astrophysics Data System (ADS)

    Guo, Yicheng; Closson Ferguson, Henry; Ravindranath, Swara; Primack, Joel; Dekel, Avishai; Koo, David; Faber, Sandra

    2015-08-01

    A common feature of star-forming galaxies at z>1 is the existence of giant star-forming clumps, which are fundamental to our understanding of the accretion history of galaxies, formation of bulges, and evolution of gas-rich disks. In this talk, I will present our work on understanding the nature of clumps in high-redshift galaxies by comparing CANDELS observations with CANDELized high-resolution cosmological hydrodynamic simulations. The CANDELized simulations take into account of all observational effects, e.g., spatial resolution and sensitivity, of CANDELS images and thus provide a direct way to compare clumps identified in both observations and simulations. The comparison with the cosmological simulations also sheds a light on the roles that clumps play in the broad picture of galaxy formation and evolution. Our work focus on three questions: (1) When and how clumps are formed? (2) How they evolve once formed? (3) Can we use clumps as diagnostics of physical mechanisms that govern star formation, e.g., feedback? The three aspects provide important clues of tracing how distant clumpy galaxies evolve into galaxies seen in the local universe.

  10. Modeling active galactic nucleus feedback in cool-core clusters: The formation of cold clumps

    SciTech Connect

    Li, Yuan; Bryan, Greg L.

    2014-07-10

    We perform high-resolution (15-30 pc) adaptive mesh simulations to study the impact of momentum-driven active galactic nucleus (AGN) feedback in cool-core clusters, focusing in this paper on the formation of cold clumps. The feedback is jet-driven with an energy determined by the amount of cold gas within 500 pc of the super-massive black hole. When the intracluster medium in the core of the cluster becomes marginally stable to radiative cooling, with the thermal instability to the free-fall timescale ratio t{sub TI}/t{sub ff} < 3-10, cold clumps of gas start to form along the propagation direction of the AGN jets. By tracing the particles in the simulations, we find that these cold clumps originate from low entropy (but still hot) gas that is accelerated by the jet to outward radial velocities of a few hundred km s{sup –1}. This gas is out of hydrostatic equilibrium and so can cool. The clumps then grow larger as they decelerate and fall toward the center of the cluster, eventually being accreted onto the super-massive black hole. The general morphology, spatial distribution, and estimated Hα morphology of the clumps are in reasonable agreement with observations, although we do not fully replicate the filamentary morphology of the clumps seen in the observations, probably due to missing physics.

  11. A Novel Dust Telescope

    NASA Astrophysics Data System (ADS)

    Grün, E.; Srama, R.; Krüger, H.; Kempf, S.; Harris, D.; Conlon, T.; Auer, S.

    2001-11-01

    Dust particles in space, like photons, are born at remote sites in space and time. From knowledge of the dust particles' birthplace and the particles' bulk properties, we can learn about the remote environment out of which the particles were formed. This approach is carried out by means of a dust telescope on a dust observatory in space. A dust telescope is a combination of a dust trajectory sensor together with a chemical composition analyzer for dust particles. A novel dust telescope is described. It consists of a highly sensitive dust trajectory sensor, and a large area chemical dust analyzer. It can provide valuable information about the particles' birthplace which may not be accessible by other techniques. Dust particles' trajectories are determined by the measurement of the electric signals that are induced when a charged grain flies through an appropriately configured electrode systems. After the successful identification of a few charged micron-sized dust grains in space by the Cassini Cosmic Dust Analyzer, this dust telescope has a ten fold increased sensitivity of charge detection (10-16 Coulombs) and will be able to obtain trajectories for sub-micron sized dust grains. State-of-the art dust chemical analyzers have sufficient mass resolution to resolve ions with atomic mass numbers above 100. However, since their impact areas are small they can analyze statistically meaningful numbers of grains only in the dust-rich environments of comets or ringed planets. Therefore, this dust telescope includes a large area (0.1 m2) chemical dust analyzer of mass resolution > 100 that will allow us to obtain statistically significant measurements of interplanetary and interstellar dust grains in space.

  12. Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Crater wall dust avalanches in southern Arabia Terra.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

    Image information: VIS instrument. Latitude 10.3, Longitude 24.5 East (335.5 West). 19 meter/pixel resolution.

  13. Dust particle dynamics in atmospheric dust devils

    NASA Astrophysics Data System (ADS)

    Izvekova, Yulia; Popel, Sergey

    2016-04-01

    Dust particle dynamics is modeled in the Dust Devils (DDs). DD is a strong, well-formed, and relatively long-lived whirlwind, ranging from small (half a meter wide and a few meters tall) to large (more than 100 meters wide and more than 1000 meters tall) in Earth's atmosphere. We develop methods for the description of dust particle charging in DDs, discuss the ionization processes in DDs, and model charged dust particle motion. Our conclusions are consistent with the fact that DD can lift a big amount of dust from the surface of a planet into its atmosphere. On the basis of the model we perform calculations and show that DDs are important mechanism for dust uplift in the atmospheres of Earth and Mars. Influence of DD electric field on dynamics of dust particles is investigated. It is shown that influence of the electric field on dust particles trajectories is significant near the ground. At some altitude (more then a quarter of the height of DD) influence of the electric field on dust particles trajectories is negligible. For the calculation of the dynamics of dust electric field can be approximated by effective dipole located at a half of the height of DD. This work was supported by the Russian Federation Presidential Program for State Support of Young Scientists (project no. MK-6935.2015.2).

  14. Shear heating and clumped isotope reordering in carbonate faults

    NASA Astrophysics Data System (ADS)

    Siman-Tov, Shalev; Affek, Hagit P.; Matthews, Alan; Aharonov, Einat; Reches, Ze'ev

    2016-07-01

    Natural faults are expected to heat rapidly during seismic slip and to cool quite quickly after the slip event. Here we examine clumped isotope thermometry for its ability to identify such short duration elevated temperature events along frictionally heated carbonate faults. Our approach is based on measured Δ47 values that reflect the distribution of oxygen and carbon isotopes in the calcite lattice, measuring the abundance of 13Csbnd 18O bonds, which is affected by temperature. We examine three types of calcite rock samples: (1) crushed limestone grains that were rapidly heated and then cooled in static laboratory experiments, simulating the temperature cycle experienced by fault rock during an earthquake slip; (2) limestone samples that were experimentally sheared to simulate earthquake slip events; and (3) samples from Fault Mirrors (FMs) collected from principle slip surfaces of three natural carbonate faults. Extensive FM surfaces are believed to form during earthquake slip. Our experimental results show that Δ47 values decrease rapidly (in the course of seconds) with increasing temperature and shear velocity. On the other hand, carbonate shear zones from natural faults do not show such Δ47 decrease. We suggest that the Δ47 response may be controlled by nano-size grains, the high abundance of defects, and highly stressed/strained grain boundaries within the carbonate fault zone that can reduce the activation energy for diffusion, and thus lead to an increased rate of isotopic disordering during shear experiments. In our laboratory experiments the high stress and strain on grain contacts and the presence of nanograins thus allows for rapid disordering so that a change in Δ47 occurs in a very short and relatively low intensity heating events. In natural faults it may also lead to isotopic ordering after the cessation of frictional heating thus erasing the high temperature signature of Δ47.

  15. High Latitude Dust in the Earth System

    NASA Technical Reports Server (NTRS)

    Bullard, Joanna E.; Baddock, Matthew; Bradwell, Tom; Crusius, John; Darlington, Eleanor; Gaiero, Diego; Gasso, Santiago; Gisladottir, Gudrun; Hodgkins, Richard; McCulloch, Robert; McKenna-Neuman, Cheryl; Mockford, Tom; Stewart, Helena; Thorsteinsson, Throstur

    2016-01-01

    Natural dust is often associated with hot, subtropical deserts, but significant dust events have been reported from cold, high latitudes. This review synthesizes current understanding of high-latitude (> or = 50degN and > or = 40degS) dust source geography and dynamics and provides a prospectus for future research on the topic. Although the fundamental processes controlling aeolian dust emissions in high latitudes are essentially the same as in temperate regions, there are additional processes specific to or enhanced in cold regions. These include low temperatures, humidity, strong winds, permafrost and niveo-aeolian processes all of which can affect the efficiency of dust emission and distribution of sediments. Dust deposition at high latitudes can provide nutrients to the marine system, specifically by contributing iron to high-nutrient, low-chlorophyll oceans; it also affects ice albedo and melt rates. There have been no attempts to quantify systematically the expanse, characteristics, or dynamics of high-latitude dust sources. To address this, we identify and compare the main sources and drivers of dust emissions in the Northern (Alaska, Canada, Greenland, and Iceland) and Southern (Antarctica, New Zealand, and Patagonia) Hemispheres. The scarcity of year-round observations and limitations of satellite remote sensing data at high latitudes are discussed. It is estimated that under contemporary conditions high-latitude sources cover >500,000 sq km and contribute at least 80-100 Tg/yr1 of dust to the Earth system (approx. 5% of the global dust budget); both are projected to increase under future climate change scenarios.

  16. Mineral dust deposition in Western Mediterranean basin

    NASA Astrophysics Data System (ADS)

    Vincent, Julie; Laurent, Benoit; Bergmatti, Gilles; Losno, Rémi; Bon Nguyen, Elisabeth; Chevaillier, Servanne; Roulet, Pierre; Sauvage, Stéphane; Coddeville, Patrice; Ouboulmane, Noura; Siour, Guillaume; Tovar Sanchez, Antonio; Massanet, Ana; Morales Baquero, Rafael; Di Sarra, Giogio; Sferlazzo, Damiano; Dulac, François; Fornier, Michel; Coursier, Cyril

    2014-05-01

    North African deserts are the world's largest sources of atmospheric mineral dust produced by aeolian erosion. Saharan dust is frequently transported toward Europe over the Mediterranean basin. When deposited in oceanic areas, mineral dust can constitute a key input of nutrients bioavailable for the oceanic biosphere. For instance, Saharan dust deposited in the in the Mediterranean Sea can be a significant source of nutrient like Fe, P and N during summer and autumn. Our objective is to study the deposition Saharan mineral dust in the western Mediterranean basin and to improve how deposition processes are parameterized in 3D regional models. To quantify the deposition flux of Saharan dust in the western Mediterranean region a specific collector (CARAGA) to sample automatically the insoluble atmospheric particle deposition was developed (LISA-ICARE) and a network of CARAGA collectors have been set up. Since 2011, eight CARAGA are then deployed in Frioul, Casset, Montandon and Ersa in France, Mallorca and Granada in Spain, Lampedusa in Italia, and Medenine in Tunisia, along a South-North gradient of almost 2000km from the North African coast to the South of Europe. We observe 10 well identified dust Saharan deposition events at Lampedusa and 6 at Mallorca for a 1-yr sampling period. These dust events are sporadic and the South-North gradient of deposition intensity and frequency is observed (the highest dust mass sampled at the stations are : 2,66 g.m-2 at Lampedusa ; 0,54 g.m-2 at Majorque ; 0,33 g.m-2 at Frioul ; 0,16 g.m-2 at Casset). The ability of the CHIMERE model to reproduce the deposition measurements is tested. The mineral dust plumes simulated over the western Mediterranean basin are also compared to satellite observations (OMI, MODIS) and in-situ measurements performed during the ChArMEx campaign and in the AERONET stations.

  17. Clumped isotope paleothermometry of the Mio-Pliocene freshwater Lake Mohave. Lower ancestral Colorado River, USA

    NASA Astrophysics Data System (ADS)

    Lang, K. A.; Huntington, K. W.

    2015-12-01

    The fluvio-lacustrine deposits of the Bouse Formation are an archive of ancestral Colorado River integration in the Late Miocene and Early Pliocene. In Mohave Valley along the California-Arizona-Nevada border, exposures of the Bouse Formation are observed ~400 m above the modern river elevation, which has been interpreted as evidence of tectonic uplift following a regionally extensive marine incursion and integration of the ancestral Colorado River by capture. However, recent investigations instead favor a "top-down" process of river integration by sequential infilling of freshwater lakes that does not require subsequent tectonic uplift. Accurate interpretation of the Bouse Formation's depositional environment is needed to test these models and ultimately, constrain the timing and mechanism of southwestern Colorado Plateau uplift. To further constrain interpretations of depositional environment, we present new clumped isotope analyses with major and trace element geochemistry and scanning electron microscopy of carbonate samples from the Bouse Formation in Mohave Valley. Here the Bouse Formation contains three distinct facies: basal marl and limestone overlain by thick beds of calcareous claystone interbedded with siltstone and sandstone and locally overlain by tufa. Bulk geochemistry of all facies is consistent with a similar freshwater source yet each facies is isotopically distinct, potentially indicating a strong influence of facies-specific fractionation processes. Carbonate formation temperatures measured in tufa samples are variable, suggesting multiple generations of calcite precipitation. Formation temperatures from basal marl and claystone samples are generally consistent with near-surface lake temperatures, broadly supporting a lacustrine depositional environment and "top-down" process of ancestral Colorado River integration. More broadly, our results quantify the variability in carbonate formation temperatures with different lacustrine facies and

  18. Influence of climate change and uplift on Colorado Plateau paleotemperatures from carbonate clumped isotope thermometry

    NASA Astrophysics Data System (ADS)

    Huntington, K. W.; Wernicke, B. P.; Eiler, J. M.

    2010-06-01

    The elevation history of Earth's surface is key to understanding the geodynamic processes responsible for the rise of plateaus. We investigate the timing of Colorado Plateau uplift by estimating depositional temperatures of Tertiary lake sediments that blanket the plateau interior and adjacent lowlands using carbonate clumped isotope paleothermometry (a measure of the temperature-dependent enrichment of 13C-18O bonds in carbonates). Comparison of modern and ancient samples deposited near sea level provides an opportunity to quantify the influence of climate and therefore assess the contribution of changes in elevation to the variations of surface temperature on the plateau. Analysis of modern lake calcite from 350 to 3300 m elevation in the southwestern United States reveals a lake water carbonate temperature (LCT) lapse rate of 4.2 ± 0.6°C/km. Analysis of Miocene deposits from 88 to 1900 m elevation in the Colorado River drainage suggests that the ancient LCT lapse rate was 4.1 ± 0.7°C/km, and temperatures were 7.7 ± 2.0°C warmer at any one elevation than predicted by the modern trend. The inferred cooling is plausible in light of Pliocene temperature estimates off the coast of California, and the consistency of lapse rates through time supports the interpretation that there has been little or no elevation change for any of the samples since 6 Ma. Together with previous paleorelief estimates from apatite (U-Th)/He data from the Grand Canyon, our results suggest most or all of the plateau's lithospheric buoyancy was acquired ˜80-60 Ma and do not support explanations that ascribe most plateau uplift to Oligocene or younger disposal of either the Farallon or North American mantle lithosphere.

  19. The Exozodiacal Dust Problem for Direct Observations of Exo-Earths

    NASA Astrophysics Data System (ADS)

    Roberge, Aki; Chen, Christine H.; Millan-Gabet, Rafael; Weinberger, Alycia J.; Hinz, Philip M.; Stapelfeldt, Karl R.; Absil, Olivier; Kuchner, Marc J.; Bryden, Geoffrey

    2012-08-01

    Debris dust in the habitable zones of stars—otherwise known as exozodiacal dust—comes from extrasolar asteroids and comets and is thus an expected part of a planetary system. Background flux from the solar system’s zodiacal dust and the exozodiacal dust in the target system is likely to be the largest source of astrophysical noise in direct observations of terrestrial planets in the habitable zones of nearby stars. Furthermore, dust structures like clumps, thought to be produced by dynamical interactions with exoplanets, are a possible source of confusion. In this article, we qualitatively assess the primary impact of exozodiacal dust on high-contrast direct imaging at optical wavelengths, such as would be performed with a coronagraph. Then we present the sensitivity of previous, current, and near-term facilities to thermal emission from debris dust at all distances from nearby solar-type stars, as well as our current knowledge of dust levels from recent surveys. Finally, we address the other method of detecting debris dust, through high-contrast imaging in scattered light. This method is currently far less sensitive than thermal emission observations, but provides high spatial resolution for studying dust structures. This article represents the first report of NASA’s Exoplanet Exploration Program Analysis Group (ExoPAG).

  20. Giant clumps in simulated high- z Galaxies: properties, evolution and dependence on feedback

    NASA Astrophysics Data System (ADS)

    Mandelker, Nir; Dekel, Avishai; Ceverino, Daniel; DeGraf, Colin; Guo, Yicheng; Primack, Joel

    2017-01-01

    We study the evolution and properties of giant clumps in high-z disc galaxies using adaptive mesh refinement cosmological simulations at redshifts z ˜ 6-1. Our sample consists of 34 galaxies, of halo masses 1011-1012 M⊙ at z = 2, run with and without radiation pressure (RP) feedback from young stars. While RP has little effect on the sizes and global stability of discs, it reduces the amount of star-forming gas by a factor of ˜2, leading to a similar decrease in stellar mass by z ˜ 2. Both samples undergo extended periods of violent disc instability continuously forming giant clumps of masses 107-109 M⊙ at a similar rate, though RP significantly reduces the number of long-lived clumps (LLCs). When RP is (not) included, clumps with circular velocity ≲ 40 (20) km s- 1, baryonic surface density ≲ 200 (100)M⊙ pc- 2 and baryonic mass ≲ 108.2 (107.3) M⊙ are short-lived, disrupted in a few free-fall times. More massive and dense clumps survive and migrate towards the disc centre over a few disc orbital times. In the RP simulations, the distribution of clump masses and star formation rates (SFRs) normalized to their host disc is similar at all redshifts, exhibiting a truncated power law with a slope slightly shallower than -2. The specific SFR (sSFR) of the LLCs declines with age as they migrate towards the disc centre, producing gradients in mass, stellar age, gas fraction, sSFR and metallicity that distinguish them from the short-lived clumps which tend to populate the outer disc. Ex situ mergers comprise ˜37 per cent of the mass in clumps and ˜29 per cent of the SFR. They are more massive and with older stellar ages than the in situ clumps, especially near the disc edge. Roughly half the galaxies at redshifts z = 4-1 are clumpy, with ˜3-30 per cent of their SFR and ˜0.1-3 per cent of their stellar mass in clumps.

  1. Electric field generation in martian dust devils

    NASA Astrophysics Data System (ADS)

    Barth, Erika L.; Farrell, William M.; Rafkin, Scot C. R.

    2016-04-01

    Terrestrial dust devils are known to generate electric fields from the vertical separation of charged dust particles. The particles present within the dust devils on Mars may also be subject to similar charging processes and so likely contribute to electric field generation there as well. However, to date, no Mars in situ instrumentation has been deployed to measure electric field strength. In order to explore the electric environment of dust devils on Mars, the triboelectric dust charging physics from the Macroscopic Triboelectric Simulation (MTS) code has been coupled to the Mars Regional Atmospheric Modeling System (MRAMS). Using this model, we examine how macroscopic electric fields are generated within martian dust disturbances and attempt to quantify the time evolution of the electrodynamical system. Electric fields peak for several minutes within the dust devil simulations. The magnitude of the electric field is a strong function of the size of the particles present, the average charge on the particles and the number of particles lifted. Varying these parameters results in peak electric fields between tens of millivolts per meter and tens of kilovolts per meter.

  2. Electric Field Generation in Martian Dust Devils

    NASA Technical Reports Server (NTRS)

    Barth, Erika L.; Farrell, William M.; Rafkin, Scot C. R.

    2015-01-01

    Terrestrial dust devils are known to generate electric fields from the vertical separation of charged dust particles. The particles present within the dust devils on Mars may also be subject to similar charging processes and so likely contribute to electric field generation there as well. However, to date, no Marsin situ instrumentation has been deployed to measure electric field strength. In order to explore the electric environment of dust devils on Mars, the triboelectric dust charging physics from the MacroscopicTriboelectric Simulation (MTS) code has been coupled to the Mars Regional Atmospheric ModelingSystem (MRAMS). Using this model, we examine how macroscopic electric fields are generated within martian dust disturbances and attempt to quantify the time evolution of the electrodynamical system.Electric fields peak for several minutes within the dust devil simulations. The magnitude of the electric field is a strong function of the size of the particles present, the average charge on the particles and the number of particles lifted. Varying these parameters results in peak electric fields between tens of millivolts per meter and tens of kilovolts per meter.

  3. Clumped isotopes in near-surface atmospheric CO2 over land, coast and ocean in Taiwan and its vicinity

    NASA Astrophysics Data System (ADS)

    Hussain Laskar, Amzad; Liang, Mao-Chang

    2016-09-01

    Molecules containing two rare isotopes (e.g., 13C18O16O in CO2), called clumped isotopes, in atmospheric CO2 are powerful tools to provide an alternative way to independently constrain the sources of CO2 in the atmosphere because of their unique physical and chemical properties. We presented clumped isotope data (Δ47) in near-surface atmospheric CO2 from urban, suburban, ocean, coast, high mountain ( ˜ 3.2 km a.s.l.) and forest in Taiwan and its vicinity. The primary goal of the study was to use the unique Δ47 signature in atmospheric CO2 to show the extents of its deviations from thermodynamic equilibrium due to different processes such as photosynthesis, respiration and local anthropogenic emissions, which the commonly used tracers such as δ13C and δ18O cannot provide. We also explored the potential of Δ47 to identify/quantify the contribution of CO2 from various sources. Atmospheric CO2 over ocean was found to be in thermodynamic equilibrium with the surrounding surface sea water. Respired CO2 was also in close thermodynamic equilibrium at ambient air temperature. In contrast, photosynthetic activity result in significant deviation in Δ47 values from that expected thermodynamically. The disequilibrium could be a consequence of kinetic effects associated with the diffusion of CO2 in and out of the leaf stomata. We observed that δ18O and Δ47 do not vary similarly when photosynthesis was involved unlike simple water-CO2 exchange. Additionally we obtained Δ47 values of car exhaust CO2 that were significantly lower than the atmospheric CO2 but higher than that expected at the combustion temperature. In urban and suburban regions, the Δ47 values were found to be lower than the thermodynamic equilibrium values at the ambient temperature, suggesting contributions from local combustion emission.

  4. Structure and dynamics of the Milky Way disk as revealed from the radial velocity distributions of APOGEE red clump stars

    NASA Astrophysics Data System (ADS)

    Toyouchi, Daisuke; Chiba, Masashi

    2017-03-01

    We investigate the structure and dynamics of the Milky Way (MW) disk stars based on the analysis of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) data, to infer the past evolution histories of the MW disk component(s) possibly affected by radial migration and/or satellite accretions. APOGEE is the first near-infrared spectroscopic survey for a large number of the MW disk stars, providing their radial velocities and chemical abundances without significant dust extinction effects. We here adopt red-clump (RC) stars (Bovy et al. 2014), for which the distances from the Sun are determined precisely, and analyze their radial velocities and chemical abundances in the MW disk regions covering from the Galactocentric distance, R, of 5 kpc to 14 kpc. We investigate their dynamical properties, such as mean rotational velocities, and velocity dispersions, as a function of R, based on the MCMC Bayesian method. We find that at all radii, the dynamics of alpha-poor stars, which are candidates of young disk stars, is much different from that of alpha-rich stars, which are candidates of old disk stars. We find that our Jeans analysis for our sample stars reveals characteristic spatial and dynamical properties of the MW disk, which are generally in agreement with the recent independent work by Bovy et al. (2015) but with a different method from ours.

  5. Massive star formation in the GMC G345.5+1.0: spatial distribution of the dust emission

    NASA Astrophysics Data System (ADS)

    López, C.; Bronfman, L.; Nyman, L.-Å.; May, J.; Garay, G.

    2011-10-01

    Context. Massive condensations in giant molecular clouds (GMCs) are linked to the formation of high mass stars, which are the principal source of heavy elements and UV radiation, playing an important role in the evolution of galaxies. Aims: We attemp to make a complete census of massive-star formation within all of GMC G345.5+1.0. This cloud is located one degree above the Galactic plane and at 1.8 kpc from the Sun, thus there is little superposition of dust along the line-of-sight, minimizing confusion effects in identifying individual clumps. Methods: We observed the 1.2 mm continuum emission across the whole GMC using the Swedish-ESO Submillimetre Telescope (SEST) Imaging Bolometer Array (SIMBA) mounted on the SEST. Observations have a spatial resolution of 0.2 pc and cover 1.8° × 2.2° in the sky with a noise of 20 mJy beam-1. Results: We identify 201 clumps with diameters between 0.2 and 0.6 pc, masses between 3.0 and 1.3 × 103 M⊙, and densities between 5 × 103 and 4 × 105 cm-3. The total mass of the clumps is 1.2 × 104 M⊙, thus the efficiency in forming these clumps, estimated as the ratio of the total clump mass to the total GMC mass, is ~0.02. The clump mass distribution for masses between 10 and 103 M⊙ is well-fitted by a power law dN/dM ∝ M - α, with a spectral mass index α of 1.7 ± 0.1. Given their mass distribution, clumps do not appear to be the direct progenitors of single stars. Comparing the 1.2 mm continuum emission with infrared images taken by the Midcourse Space Experiment (MSX) and by the Spitzer satellite, we find that at least ~20% of the clumps are forming stars, and at most ~80% are starless. Six massive-star forming regions (MSFRs) embedded in clumps and associated with IRAS point sources have mean densities of ~105 cm-3, luminosities >103 L⊙, and spectral energy distributions that can be modeled with two dust components at different mean temperatures of 28 ± 5 and 200 ± 10 K. Table 5 is available in electronic form at

  6. Interactions Between Mineral Dust, Climate, and Ocean Ecosystems

    NASA Technical Reports Server (NTRS)

    Gasso, Santiago; Grassian, Vicki H.; Miller, Ron L.

    2010-01-01

    Over the past decade, technological improvements in the chemical and physical characterization of dust have provided insights into a number of phenomena that were previously unknown or poorly understood. In addition, models are now incorporating a wider range of physical processes, which will allow us to better quantify the climatic and ecological impacts of dust. For example, some models include the effect of dust on oceanic photosynthesis and thus on atmospheric CO 2 (Friedlingstein et al. 2006). The impact of long-range dust transport, with its multiple forcings and feedbacks, is a relatively new and complex area of research, where input from several disciplines is needed. So far, many of these effects have only been parameterized in models in very simple terms. For example, the representation of dust sources remains a major uncertainty in dust modeling and estimates of the global mass of airborne dust. This is a problem where Earth scientists could make an important contribution, by working with climate scientists to determine the type of environments in which easily erodible soil particles might have accumulated over time. Geologists could also help to identify the predominant mineralogical composition of dust sources, which is crucial for calculating the radiative and chemical effects of dust but is currently known for only a few regions. Understanding how climate and geological processes control source extent and characterizing the mineral content of airborne dust are two of the fascinating challenges in future dust research.

  7. Field Measurements of Terrestrial and Martian Dust Devils

    NASA Astrophysics Data System (ADS)

    Murphy, Jim; Steakley, Kathryn; Balme, Matt; Deprez, Gregoire; Esposito, Francesca; Kahanpää, Henrik; Lemmon, Mark; Lorenz, Ralph; Murdoch, Naomi; Neakrase, Lynn; Patel, Manish; Whelley, Patrick

    2016-11-01

    Surface-based measurements of terrestrial and martian dust devils/convective vortices provided from mobile and stationary platforms are discussed. Imaging of terrestrial dust devils has quantified their rotational and vertical wind speeds, translation speeds, dimensions, dust load, and frequency of occurrence. Imaging of martian dust devils has provided translation speeds and constraints on dimensions, but only limited constraints on vertical motion within a vortex. The longer mission durations on Mars afforded by long operating robotic landers and rovers have provided statistical quantification of vortex occurrence (time-of-sol, and recently seasonal) that has until recently not been a primary outcome of more temporally limited terrestrial dust devil measurement campaigns. Terrestrial measurement campaigns have included a more extensive range of measured vortex parameters (pressure, wind, morphology, etc.) than have martian opportunities, with electric field and direct measure of dust abundance not yet obtained on Mars. No martian robotic mission has yet provided contemporaneous high frequency wind and pressure measurements. Comparison of measured terrestrial and martian dust devil characteristics suggests that martian dust devils are larger and possess faster maximum rotational wind speeds, that the absolute magnitude of the pressure deficit within a terrestrial dust devil is an order of magnitude greater than a martian dust devil, and that the time-of-day variation in vortex frequency is similar. Recent terrestrial investigations have demonstrated the presence of diagnostic dust devil signals within seismic and infrasound measurements; an upcoming Mars robotic mission will obtain similar measurement types.

  8. Clumped Isotope Composition of Cold-Water Corals: A Role for Vital Effects?

    NASA Astrophysics Data System (ADS)

    Spooner, P.; Guo, W.; Robinson, L. F.

    2014-12-01

    Measurements on a set of cold-water corals (mainly Desmophyllum dianthus) have suggested that their clumped isotope composition could serve as a promising proxy for reconstructing paleocean temperatures. Such measurements have also offered support for certain isotope models of coral calcification. However, there are differences in the clumped isotope compositions between warm-water and cold-water corals, suggesting that different kinds of corals could have differences in their biocalcification processes. In order to understand the systematics of clumped isotope variations in cold-water corals more fully, we present clumped isotope data from a range of cold-water coral species from the tropical Atlantic and the Southern Ocean.Our samples were either collected live or recently dead (14C ages < 1,000 yrs) with associated temperature data. They include a total of 11 solitary corals and 1 colonial coral from the Atlantic, and 8 solitary corals from the Southern Ocean. The data indicate that coral clumped isotope systematics may be more complicated than previously thought. For example, for the genus Caryophyllia we observe significant variations in clumped isotope compositions for corals which grew at the same temperature with an apparent negative correlation between Δ47 and δ18O, different to patterns previously observed in Desmophyllum. These results indicate that existing isotope models of biocalcification may not apply equally well to all corals. Clumped isotope vital effects may be present in certain cold-water corals as they are in warm-water corals, complicating the use of this paleoclimate proxy.

  9. Dense Molecular Clumps Associated with the Large Magellanic Cloud Supergiant Shells LMC 4 and LMC 5

    NASA Astrophysics Data System (ADS)

    Fujii, Kosuke; Minamidani, Tetsuhiro; Mizuno, Norikazu; Onishi, Toshikazu; Kawamura, Akiko; Muller, Erik; Dawson, Joanne; Tatematsu, Ken'ichi; Hasegawa, Tetsuo; Tosaki, Tomoka; Miura, Rie E.; Muraoka, Kazuyuki; Sakai, Takeshi; Tsukagoshi, Takashi; Tanaka, Kunihiko; Ezawa, Hajime; Fukui, Yasuo

    2014-12-01

    We investigate the effects of supergiant shells (SGSs) and their interaction on dense molecular clumps by observing the Large Magellanic Cloud (LMC) star-forming regions N48 and N49, which are located between two SGSs, LMC 4 and LMC 5. 12CO (J = 3-2, 1-0) and 13CO(J = 1-0) observations with the ASTE and Mopra telescopes have been carried out toward these regions. A clumpy distribution of dense molecular clumps is revealed with 7 pc spatial resolution. Large velocity gradient analysis shows that the molecular hydrogen densities (n(H2)) of the clumps are distributed from low to high density (103-105 cm-3) and their kinetic temperatures (T kin) are typically high (greater than 50 K). These clumps seem to be in the early stages of star formation, as also indicated from the distribution of Hα, young stellar object candidates, and IR emission. We found that the N48 region is located in the high column density H I envelope at the interface of the two SGSs and the star formation is relatively evolved, whereas the N49 region is associated with LMC 5 alone and the star formation is quiet. The clumps in the N48 region typically show high n(H2) and T kin, which are as dense and warm as the clumps in LMC massive cluster-forming areas (30 Dor, N159). These results suggest that the large-scale structure of the SGSs, especially the interaction of two SGSs, works efficiently on the formation of dense molecular clumps and stars.

  10. Applying clumped isotopes of O2 to atmospheric and biogeochemical problems

    NASA Astrophysics Data System (ADS)

    Yeung, Laurence

    2016-04-01

    I will describe recent measurements of isotopic "clumps" in diatomic molecules, e.g., 18O18O in O2, which are being utilized to constrain atmospheric circulation on glacial-interglacial timescales and biogeochemical cycling in the oceans. While our understanding of these tracers is still evolving, several features of their geochemistry are apparent: (1) the proportional abundance of these isotopic "clumps" is governed by traditional chemical effects as well as combinatorial effects unique to clumped isotopes, and (2) when isotopic exchange reactions are disfavoured, chemical-kinetic and/or reservoir effects, rather than thermodynamic equilibrium, determine their clumped-isotope composition. Combinatorial clumped-isotope signatures imparted during photosynthesis are being developed as endmember signatures of gross primary productivity in the oceans. In addition, clumped-isotope measurements of O2 in the atmosphere (i.e., Δ36 values) suggest that isotopic clumping in O2 is continuously being altered by ozone photochemistry in the troposphere and stratosphere. Yet, the contrast in isotope-exchange rates between the stratosphere (where exchange is fast) and the troposphere (where exchange is slow) results in a gradient in Δ36 values with altitude, wherein stratospheric intrusions are detectable as elevated Δ36 values. Moreover, global chemical-transport model simulations suggest that ozone photochemistry in the troposphere re-orders the O2 reservoir in the troposphere on annual timescales. The Δ36 value at the surface is therefore sensitive to the tropospheric residence time of O2 with respect to stratosphere-troposphere exchange. Consequently, Δ36 values at the surface likely respond to changes in the strength of the global overturning circulation.

  11. The dust masses in the remnants of Cas A, SN1993J and SN 1980K

    NASA Astrophysics Data System (ADS)

    Barlow, Mike; Bevan, Antonia

    2016-06-01

    Using a recently developed 3D Monte Carlo dust line-scattering and absorption code, Bevan & Barlow (2016, MNRAS) have modeled the red-blue line asymmetries in the late-time Hα and [O i] spectra of SN 1987A caued by the preferential absorption by internal dust particles of redshifted photons from the far side of the ejecta. They found dust masses that grew from ≤ 10-3 M⊙ on day 714 to ≥ 0.10 M⊙ by day 3604, a trend that agrees with the day 615 - 9200 SED modeling results of Wesson et al. (2015) for SN 1987A, for which Herschel and ALMA observations indicate a dust mass of ˜0.7 M⊙ by day 9200. Similar red-blue emission line asymmetries are often observed in the late-time optical spectra of other supernova ejecta and remnants. With the aim of increasing the number of SNR dust mass determinations, we have modeled the red-blue emission line asymmetries in the late-time optical spectra of SN 1993J and SN 1980K published by Milisavljevic & Fesen (2013), as well as modeling similar red-blue line asymmetries seen in the integrated optical spectrum of Cas A published by Milisavljevic et al. (2013). Depending on grain composition, clumped dust masses of 0.1-0.4 M⊙ are required to provide fits to the Year-31 Hα and [O i] line profiles of SN 1980K, while fits to the Year-16 [O ii] and [O iii] line profiles of SN 1993J require up to 0.18 M⊙ of clumped ejecta dust. For Cas A, the fits to its [O i], [O ii] and [O iii] integrated line profiles require about 1 M⊙ of internal dust to be present.

  12. Dust Plume off Mauritania

    NASA Technical Reports Server (NTRS)

    2007-01-01

    A thick plume of dust blew off the coast of Mauritania in western Africa on October 2, 2007. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite observed the dust plume as it headed toward the southwest over the Atlantic Ocean. In this image, the dust varies in color from nearly white to medium tan. The dust plume is easier to see over the dark background of the ocean, but the plume stretches across the land surface to the east, as well. The dust plume's structure is clearest along the coastline, where relatively clear air pockets separate distinct puffs of dust. West of that, individual pillows of dust push together to form a more homogeneous plume. Near its southwest tip, the plume takes on yet another shape, with stripes of pale dust fanning out toward the northwest. Occasional tiny white clouds dot the sky overhead, but skies are otherwise clear.

  13. Siderite 'clumped' isotope thermometry: A new paleoclimate proxy for humid continental environments

    NASA Astrophysics Data System (ADS)

    Fernandez, Alvaro; Tang, Jianwu; Rosenheim, Brad E.

    2014-02-01

    Clumped isotope measurements can be used to exploit the paleoclimatic potential of pedogenic siderite (FeCO3); however, the applicability of this method is held back by the lack of clumped isotope calibrations of mineralogies other than calcite and aragonite. Here we present an inorganic calibration of siderites grown in the laboratory between 21 and 51 °C. Linear regression of Δ47 values and temperature (106/T2, K) yields the following relationship (r2 = 0.997): Δ={(0.0356±0.0018)×106}/{T}+(0.172±0.019) We demonstrate that this calibration is indistinguishable from calcite at current levels of analytical precision. Our observations suggest that there is likely no large systematic bias in the clumped isotope acid fractionation factors between the two different carbonate minerals. We also present clumped isotope measurements of a natural siderite collected from Holocene sediments of the Mississippi River Delta. We find that siderites record warm season marsh water temperatures instead of mean annual temperatures as it has long been presumed. This finding has important implications for the accuracy of siderite stable isotope and clumped isotope based climate reconstructions.

  14. A SPITZER-MIPS SEARCH FOR DUST IN COMPACT HIGH-VELOCITY H I CLOUDS

    SciTech Connect

    Williams, Rik J.; Mathur, Smita; Poindexter, Shawn; Elvis, Martin; Nicastro, Fabrizio

    2012-04-15

    We employ three-band Spitzer-MIPS observations to search for cold dust emission in three neutral hydrogen compact high-velocity clouds (CHVCs) in the vicinity of the Milky Way. Far-infrared emission correlated with H I column density was previously reported in HVC Complex C, indicating that this object contains dust heated by the Galactic radiation field at its distance of {approx}10 kpc. Assuming published Spitzer, IRAS, and Planck, IR-H I correlations for Complex C, our Spitzer observations are of sufficient depth to directly detect 160 {mu}m dust emission in the CHVCs if it is present at the same level as in Complex C, but no emission is detected in any of the targets. For one of the targets (CHVC289) which has well-localized H I clumps, we therefore conclude that it is fundamentally different from Complex C, with either a lower dust-to-gas ratio or a greater distance from the Galactic disk (and consequently cooler dust temperature). Firm conclusions cannot be drawn for the other two Spitzer-observed CHVCs since their small-scale H I structures are not sufficiently well known; nonetheless, no extended dust emission is apparent despite their relatively high H I column densities. The lack of dust emission in CHVC289 suggests that at least some compact high-velocity clouds objects may exhibit very low dust-to-gas ratios and/or greater Galactocentric distances than large HVC complexes.

  15. Niamey Dust Observations

    DOE Data Explorer

    Flynn, Connor

    2008-10-01

    Niamey aerosol are composed of two main components: dust due to the proximity of the Sahara Desert, and soot from local and regional biomass burning. The purpose of this data product is to identify when the local conditions are dominated by the dust component so that the properties of the dust events can be further studied.

  16. China Dust and Sand

    Atmospheric Science Data Center

    2013-04-16

    article title:  Dust and Sand Sweep Over Northeast China     ... (MISR) captured these views of the dust and sand that swept over northeast China on March 10, 2004. Information on the ... available at JPL March 10, 2004 - Dust and sand sweep the northeast region. project:  MISR ...

  17. Dust in the Universe

    ERIC Educational Resources Information Center

    Hemenway, Mary Kay; Armosky, Brad J.

    2004-01-01

    Space is seeming less and less like empty space as new discoveries and reexaminations fill in the gaps. And, ingenuity and technology, like the Spitzer Space Telescope, is allowing examination of the far reaches of the Milky Way and beyond. Even dust is getting its due, but not the dust everyone is familiar with. People seldom consider the dust in…

  18. Middle East Dust

    Atmospheric Science Data Center

    2013-04-16

    ... only some of the dust over eastern Syria and southeastern Turkey can be discerned. The dust is much more obvious in the center panel, ... 18, 2002 - A large dust plume extends across Syria and Turkey. project:  MISR category:  gallery ...

  19. Diesel Emissions Quantifier (DEQ)

    EPA Pesticide Factsheets

    .The Diesel Emissions Quantifier (Quantifier) is an interactive tool to estimate emission reductions and cost effectiveness. Publications EPA-420-F-13-008a (420f13008a), EPA-420-B-10-035 (420b10023), EPA-420-B-10-034 (420b10034)

  20. The most unusual dust event cases from Iceland

    NASA Astrophysics Data System (ADS)

    Dagsson Waldhauserova, Pavla; Arnalds, Olafur; Olafsson, Haraldur; Meinander, Outi; Gritsevich, Maria

    2016-04-01

    . Dust was transported over 250 km causing impurities on snow in the capital of Iceland, Reykjavik. This has been the first observation of clumping mechanism of particles on snow in natural conditions. Maximum one-minute PM10 concentration was measured as 6500 μg m-3 while the mean (median) PM10 concentration during 24-hour storm was 1,281 (1,170) μg m-3. Dust can be also suspended during rainy period as a result of surface heating. We measured particle number concentration (PM~0.3-10 μm) up to 149,954 particles cm-3 min-1 during wet and low wind/windless conditions in August 2013. The particles were mainly of the close-to-ultrafine size. Wet dust particles were mobilized within < 4 hours.

  1. Dust Formation and Light Echoes Around Core Collapse Supernovae

    NASA Astrophysics Data System (ADS)

    Andrews, Jennifer; Clayton, Geoffrey; Sugerman, Ben; Barlow, Mike; Meixner, Margaret; Wesson, Roger; Gallagher, Joseph; Matsuura, Mikako; Otsuka, Masaaki; Ercolano, Barbara

    2012-12-01

    The importance of core collapse supernovae (CCSNe) in the dust budget of the universe is still poorly understood. Recent discoveries of massive amounts of cool dust in SN 1987A and the Crab nebula have once again brought this debate to the forefront. We are proposing to continue observations of 7 CCSNe (SNe 1980K, 2002hh, 2008S, 2004et, 2010jl, 2011ja, and 2012aw) with Spitzer as part of our multi-wavelength campaign to both classify and quantify newly condensed dust in the SN ejecta as well as to accurately map out pre-existing circumstellar dust in light echoes. The proposed observations will be combined with previous epochs of Spitzer data and coordinated with other approved and proposed ground and space based observations with Gemini, and HST. We may be able to increase the small sample of CCSNe that show conclusive evidence of dust formation, as well as constrain pre-existing progenitor dust creation by studying the IR echoes around the older SNe. Measuring the location and mass of the dust around a SN, while the dust is still warm, is essential in deciphering the origin of the large masses of cold dust that have been discovered in nearby SN remnants, which is critical to understand the role of CCSNe as dust producers in the early universe.

  2. Effects of foliage clumping on the estimation of global terrestrial gross primary productivity

    NASA Astrophysics Data System (ADS)

    Chen, Jing M.; Mo, Gang; Pisek, Jan; Liu, Jane; Deng, Feng; Ishizawa, Misa; Chan, Douglas

    2012-03-01

    Sunlit and shaded leaf separation proposed by Norman (1982) is an effective way to upscale from leaf to canopy in modeling vegetation photosynthesis. The Boreal Ecosystem Productivity Simulator (BEPS) makes use of this methodology, and has been shown to be reliable in modeling the gross primary productivity (GPP) derived from CO2flux and tree ring measurements. In this study, we use BEPS to investigate the effect of canopy architecture on the global distribution of GPP. For this purpose, we use not only leaf area index (LAI) but also the first ever global map of the foliage clumping index derived from the multiangle satellite sensor POLDER at 6 km resolution. The clumping index, which characterizes the degree of the deviation of 3-dimensional leaf spatial distributions from the random case, is used to separate sunlit and shaded LAI values for a given LAI. Our model results show that global GPP in 2003 was 132 ± 22 Pg C. Relative to this baseline case, our results also show: (1) global GPP is overestimated by 12% when accurate LAI is available but clumping is ignored, and (2) global GPP is underestimated by 9% when the effective LAI is available and clumping is ignored. The clumping effects in both cases are statistically significant (p < 0.001). The effective LAI is often derived from remote sensing by inverting the measured canopy gap fraction to LAI without considering the clumping. Global GPP would therefore be generally underestimated when remotely sensed LAI (actually effective LAI by our definition) is used. This is due to the underestimation of the shaded LAI and therefore the contribution of shaded leaves to GPP. We found that shaded leaves contribute 50%, 38%, 37%, 39%, 26%, 29% and 21% to the total GPP for broadleaf evergreen forest, broadleaf deciduous forest, evergreen conifer forest, deciduous conifer forest, shrub, C4 vegetation, and other vegetation, respectively. The global average of this ratio is 35%.

  3. Intercomparison of clumping index estimates from POLDER, MODIS, and MISR satellite data over reference sites

    NASA Astrophysics Data System (ADS)

    Pisek, Jan; Govind, Ajit; Arndt, Stefan K.; Hocking, Darren; Wardlaw, Timothy J.; Fang, Hongliang; Matteucci, Giorgio; Longdoz, Bernard

    2015-03-01

    Clumping index is the measure of foliage grouping relative to a random distribution of leaves in space. It is a key structural parameter of plant canopies that influences canopy radiation regimes and controls canopy photosynthesis and other land-atmosphere interactions. The Normalized Difference between Hotspot and Darkspot (NDHD) index has been previously used to retrieve global clumping index maps from POLarization and Directionality of the Earth's Reflectances (POLDER) data at ∼6 km resolution and the Bidirectional Reflectance Distribution Function (BRDF) product from Moderate Resolution Imaging Spectroradiometer (MODIS) at 500 m resolution. Most recently the algorithm was also applied with Multi-angle Imaging SpectroRadiometer (MISR) data at 275 m resolution over selected areas. In this study for the first time we characterized and compared the three products over a set of sites representing diverse biomes and different canopy structures. The products were also directly validated with both in-situ vertical profiles and available seasonal trajectories of clumping index over several sites. We demonstrated that the vertical distribution of foliage and especially the effect of understory need to be taken into account while validating foliage clumping products from remote sensing products with values measured in the field. Satellite measurements responded to the structural effects near the top of canopies, while ground measurements may be biased by the lower vegetation layers. Additionally, caution should be taken regarding the misclassification in land cover maps as their errors can propagate into the foliage clumping maps. Our results indicate that MODIS data and MISR data, with 275 m in particular, can provide good quality clumping index estimates at spatial scales pertinent for modeling local carbon and energy fluxes.

  4. Energy Budget of Forming Clumps in Numerical Simulations of Collapsing Clouds

    NASA Astrophysics Data System (ADS)

    Camacho, Vianey; Vázquez-Semadeni, Enrique; Ballesteros-Paredes, Javier; Gómez, Gilberto C.; Fall, S. Michael; Mata-Chávez, M. Dolores

    2016-12-01

    We analyze the physical properties and energy balance of density enhancements in two SPH simulations of the formation, evolution, and collapse of giant molecular clouds. In the simulations, no feedback is included, so all motions are due either to the initial decaying turbulence or to gravitational contraction. We define clumps as connected regions above a series of density thresholds. The resulting full set of clumps follows the generalized energy equipartition relation, {σ }v/{R}1/2\\propto {{{Σ }}}1/2, where {σ }v is the velocity dispersion, R is the “radius,” and Σ is the column density. We interpret this as a natural consequence of gravitational contraction at all scales rather than virial equilibrium. Nevertheless, clumps with low Σ tend to show a large scatter around equipartition. In more than half of the cases, this scatter is dominated by external turbulent compressions that assemble the clumps rather than by small-scale random motions that would disperse them. The other half does actually disperse. Moreover, clump sub-samples selected by means of different criteria exhibit different scalings. Sub-samples with narrow Σ ranges follow Larson-like relations, although characterized by their respective values of Σ. Finally, we find that (i) clumps lying in filaments tend to appear sub-virial, (ii) high-density cores (n≥slant {10}5 cm3) that exhibit moderate kinetic energy excesses often contain sink (“stellar”) particles and the excess disappears when the stellar mass is taken into account in the energy balance, and (iii) cores with kinetic energy excess but no stellar particles are truly in a state of dispersal.

  5. Record of seasonal body fluid composition in Black Clam (Bivalve) using clumped isotope thermometric approach

    NASA Astrophysics Data System (ADS)

    Rahman, H.; Naidu, P. K.; Ghosh, P.

    2012-12-01

    Application of clumped isotope thermometry (Ghosh et al., 2006) is highly debated while resolving the issue of kinetic effect during biogenic carbonate precipitation. Mollusks are particularly attractive target to study the kinetic effect (Eiler, 2011) in the biological system owing to its incremental growth ring patterns. This allows understanding the role of environmental parameters other than temperature driving the distribution of heavier isotopologues. Guo et al., (2010) indicated role of pH in driving the distribution of heavier isotopolgues in the carbonates. We investigated here clumped isotopic composition of Black Calm (bivalve shell) caught live from a location in Southern Indian Estuary. The region experiences large change in seasonal condition. The physical environmental parameters at that location were monitored for last 3 years at monthly interval. The salinity, temperature, pH information are available for all the months when mollusc growth bands are deposited. The bottom water of estuary, where bivalve thrives experience maximum temperature of 32°C during November and December, while temperature during Monsoon months (July, August) drops lows to 26°C. Initial results on clumped isotope thermometry on the growth bands precipitated suggests that during the time in a year when pH level is alkaline i.e. 8.0±0.2 there is large consistency between actual temperature and estimated temperature using clumped isotope based thermometry. While the pH drops towards acidic i.e. 6.8±0.1 lower temperature estimates compared to actual was recorded. The effect of metabolic rate and body temperature variability is not been investigated as suggested in case of land snails based clumped isotope thermometry (Zaarur et al., 2011). Mollusc shell can be used to trace the composition of environmental water while pH variation is minimal. In this presentation analyses of more shell specimen and explore the role of pH and osmo-regulation in mollusc determining the clumped

  6. Dust and Planetary Rings

    NASA Astrophysics Data System (ADS)

    Siddiqui, Muddassir

    ABSTRACT Space is not empty it has comic radiations (CMBR), dust etc. Cosmic dust is that type of dust which is composed of particles in space which vary from few molecules to 0.1micro metres in size. This type of dust is made up of heavier atoms born in the heart of stars and supernova. Mainly it contains dust grains and when these dust grains starts compacting then it turns to dense clouds, planetary ring dust and circumstellar dust. Dust grains are mainly silicate particles. Dust plays a major role in our solar system, for example in zodiacal light, Saturn's B ring spokes, planetary rings at Jovian planets and comets. Observations and measurements of cosmic dust in different regions of universe provide an important insight into the Universe's recycling processes. Astronomers consider dust in its most recycled state. Cosmic dust have radiative properties by which they can be detected. Cosmic dusts are classified as intergalactic dusts, interstellar dusts and planetary rings. A planetary ring is a ring of cosmic dust and other small particles orbiting around a planet in flat disc shape. All of the Jovian planets in our solar system have rings. But the most notable one is the Saturn's ring which is the brightest one. In March 2008 a report suggested that the Saturn's moon Rhea may have its own tenuous ring system. The ring swirling around Saturn consists of chunks of ice and dust. Most rings were thought to be unstable and to dissipate over course of tens or hundreds of millions of years but it now appears that Saturn's rings might be older than that. The dust particles in the ring collide with each other and are subjected to forces other than gravity of its own planet. Such collisions and extra forces tend to spread out the rings. Pluto is not known to have any ring system but some Astronomers believe that New Horizons probe might find a ring system when it visits in 2015.It is also predicted that Phobos, a moon of Mars will break up and form into a planetary ring

  7. The population of giant clumps in simulated high-z galaxies: in situ and ex situ migration and survival

    NASA Astrophysics Data System (ADS)

    Mandelker, Nir; Dekel, Avishai; Ceverino, Daniel; Tweed, Dylan; Moody, Christopher E.; Primack, Joel

    2014-10-01

    We study the properties of giant clumps and their radial gradients in high-z disc galaxies using AMR cosmological simulations. Our sample consists of 770 snapshots in the redshift range z = 4-1 from 29 galaxies that at z = 2 span the stellar mass range (0.2-3) × 1011 M⊙. Extended gas discs exist in 83 per cent of the snapshots. Clumps are identified by gas density in 3D and their stellar and dark matter components are considered thereafter. While most of the overdensities are diffuse and elongated, 91 per cent of their mass and 83 per cent of their star formation rate (SFR) are in compact round clumps. Nearly all galaxies have a central, massive bulge clump, while 70 per cent of the discs show off-centre clumps, 3-4 per galaxy. The fraction of clumpy discs peaks at intermediate disc masses. Clumps are divided based on dark matter content into in situ and ex situ originating from violent disc instability (VDI) and minor mergers, respectively. 60 per cent of the discs are in a VDI phase showing off-centre in situ clumps, which contribute 1-7 per cent of the disc mass and 5-45 per cent of its SFR. The in situ clumps constitute 75 per cent of the off-centre clumps in terms of number and SFR but only half the mass, each clump containing on average 1 per cent of the disc mass and 6 per cent of its SFR. They have young stellar ages, 100-400 Myr, and high specific SFR (sSFR), 1-10 Gyr-1. They exhibit gradients resulting from inward clump migration, where the inner clumps are somewhat more massive and older, with lower gas fraction and sSFR and higher metallicity. Similar observed gradients indicate that clumps survive outflows. The ex situ clumps have stellar ages 0.5-3 Gyr and sSFR ˜0.1-2 Gyr-1, and they exhibit weaker gradients. Massive clumps of old stars at large radii are likely ex situ mergers, though half of them share the disc rotation.

  8. On the formation and evolution of clumps of galaxies in an expanding universe

    NASA Technical Reports Server (NTRS)

    Norman, C. A.; Silk, J.

    1978-01-01

    Results are derived for the development of phase-space clumps of mass points in a background spectrum of gravitational-potential fluctuations. The Vlasov equation and the pair correlation equation (in the weak coupling limit) are solved exactly in an Einstein-de Sitter cosmology, and the plasma-clumping theory is used to identify terms that yield important collective effects. Various astrophysical implications are discussed, including the formation of large-scale inhomogeneity and the enhanced generation of correlations in the distribution of galaxies.

  9. Dust in galaxy clusters

    NASA Astrophysics Data System (ADS)

    Polikarpova, O. L.; Shchekinov, Yu. A.

    2017-02-01

    The conditions for the destruction of dust in hot gas in galaxy clusters are investigated. It is argued that extinction measurements can be subject to selection effects, hindering their use in obtaining trustworthy estimates of dust masses in clusters. It is shown, in particular, that the ratio of the dust mass to the extinction M d / S d increases as dust grains are disrupted, due to the rapid destruction of small grains. Over long times, this ratio can asymptotically reach values a factor of three higher than the mean value in the interstellar medium in the Galaxy. This lowers dust-mass estimates based on measurements of extinction in galaxy clusters. The characteristic lifetime of dust in hot cluster gas is determined by its possible thermal isolation by the denser medium of gas fragments within which the dust is ejected from galaxies, and can reach 100-300 million years, depending on the kinematics and morphology of the fragments. As a result, the mass fraction of dust in hot cluster gas can reach 1-3% of the Galactic value. Over its lifetime, dust can also be manifest through its far-infrared emission. The emission characteristics of the dust change as it is disrupted, and the ratio of the fluxes at 350 and 850 μm can increase appreciably. This can potentially serve as an indicator of the state of the dust and ambient gas.

  10. Light Dust Devil Tracks

    NASA Technical Reports Server (NTRS)

    2004-01-01

    14 October 2004 Many Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images exhibit wild patterns of dark streaks thought to have formed by the passage of many dust devils. The dust devils disrupt the dust coating the martian surface, leaving behind a streak. However, not all dust devils make streaks, and not all dust devil streaks are dark. Some are light---it simply depends upon which is darker, the substrate or the dust that the spinning vortex disrupts. The example of light-toned dust devil streaks shown here is located in southern Schiaparelli Basin near 5.3oS, 343.3oW. The image covers an area about 3 km (1.9 mi) across; sunlight illuminates the scene from the left/upper left.

  11. DENSE, PARSEC-SCALE CLUMPS NEAR THE GREAT ANNIHILATOR

    SciTech Connect

    Hodges-Kluck, Edmund; Pound, Marc W.; Harris, Andrew I.; Lamb, James W.; Hodges, Mark

    2009-05-10

    We report on Combined Array for Research in Millimeter-Wave Astronomy and James Clerk Maxwell Telescope observations toward the Einstein source 1E 1740.7-2942, a low-mass X-ray binary commonly known as the 'Great Annihilator'. The Great Annihilator is known to be near a small, bright molecular cloud in a region largely devoid of emission in {sup 12}CO surveys of the Galactic center. This region is of interest because it is interior to the dust lanes which may be the shock zones where atomic gas from the HI nuclear disk is converted into molecular gas. We find that the region is populated with a large number of dense (n {approx} 10{sup 5} cm{sup -3}) regions of excited gas with small filling factors. The gas appears to have turbulent support and may be the result of sprays of material from collisions in the shock zone. We estimate that {approx}(1-3) x 10{sup 5} M {sub sun} of shocked gas resides in our r {approx} 3', {delta}v {sub LSR} = 100 km s{sup -1} field. If this gas has recently shocked and is interior to the inner Lindblad resonance of the dominant bar, it is in transit to the x {sub 2} disk, suggesting that a significant amount of mass may be transported to the disk by a low filling factor population of molecular clouds with low surface brightness in larger surveys.

  12. Constraints on the circumstellar dust around KIC 8462852

    NASA Astrophysics Data System (ADS)

    Thompson, M. A.; Scicluna, P.; Kemper, F.; Geach, J. E.; Dunham, M. M.; Morata, O.; Ertel, S.; Ho, P. T. P.; Dempsey, J.; Coulson, I.; Petitpas, G.; Kristensen, L. E.

    2016-05-01

    We present millimetre (Submillimeter Array) and submillimetre (SCUBA-2) continuum observations of the peculiar star KIC 8462852 which displayed several deep and aperiodic dips in brightness during the Kepler mission. Our observations are approximately confusion-limited at 850 μm and are the deepest millimetre and submillimetre photometry of the star that has yet been carried out. No significant emission is detected towards KIC 8462852. We determine upper limits for dust between a few 10-6 M⊕ and 10-3 M⊕ for regions identified as the most likely to host occluding dust clumps and a total overall dust budget of <7.7 M⊕ within a radius of 200 au. Such low limits for the inner system make the catastrophic planetary disruption hypothesis unlikely. Integrating over the Kepler light curve we determine that at least 10-9 M⊕ of dust is required to cause the observed Q16 dip. This is consistent with the currently most favoured cometary breakup hypothesis, but nevertheless implies the complete breakup of ˜30 Comet 1/P Halley type objects. Finally, in the wide SCUBA-2 field of view we identify another candidate debris disc system that is potentially the largest yet discovered.

  13. A SEARCH FOR DUST EMISSION IN THE LEO INTERGALACTIC CLOUD

    SciTech Connect

    Bot, Caroline; Helou, George; Puget, Jeremie; Latter, William B.; Schneider, Stephen; Terzian, Yervant

    2009-08-15

    We present a search for infrared dust emission associated with the Leo cloud, a large intergalactic cloud in the M96 group. Mid-infrared and far-infrared images were obtained with the InfraRed Array Camera and the Multiband Imaging Photometer for Spitzer on the Spitzer Space Telescope. Our analysis of these maps is done at each wavelength relative to the H I spatial distribution. We observe a probable detection at 8 {mu}m and a marginal detection at 24 {mu}m associated with the highest H I column densities in the cloud. At 70 and 160 {mu}m, upper limits on the dust emission are deduced. The level of the detection is low so that the possibility of a fortuitous cirrus clump or of an overdensity of extragalactic sources along the line of sight cannot be excluded. If this detection is confirmed, the quantities of dust inferred imply a dust-to-gas ratio in the intergalactic cloud up to a few times solar but no less than 1/20 solar. A confirmed detection would therefore exclude the possibility that the intergalactic cloud has a primordial origin. Instead, this large intergalactic cloud could therefore have been formed through interactions between galaxies in the group.

  14. Validation of a new method for directional dust monitoring

    NASA Astrophysics Data System (ADS)

    Datson, Hugh; Hall, David; Birch, Bill

    2012-04-01

    Fugitive dust from industrial sites is problematic to quantify and can be associated with nuisance complaints. Despite significant limitations, the British Standard 1747 Part 5 (BS 1747:5) directional dust gauge remains preferred for monitoring fugitive dust flux on site boundaries. An alternative directional dust gauge, DustScan, was developed at the University of Leeds, UK, and uses cylindrical adhesive 'sticky pads' to sample dust in flux. With this sampler, dust capture is measured as soiling, as opposed to mass, with the BS 1747:5 sampler. An Aerosol Test Tunnel (ATT) was developed to evaluate the performance of the DustScan sampler. Atmospheric turbulence was simulated using a coarse grid generator and maintained as rough-wall channel flow by roughness elements fixed to its floor and roof of the ATT. A polydisperse test dust was introduced upwind to form a cloud at the sampler. DustScan directional dust gauges were repeatedly exposed to aliquots of test dust at wind speeds of 2-10 m s-1 in the ATT. Dust soiling levels either side of the gauge's centreline (relative to the incident direction) were compared to demonstrate that the DustScan sampler is directionally accurate. Much lower proportions of antithetic sampling (dust catch on the downwind face of the gauge) occurred than for the BS 1747:5 sampler. The sampled particle size selection was related to the ratio of particle stop distance (s) to sampler diameter (D) ratio, s/D, showing that the particle size cut point fell with increasing wind speeds. A preliminary assessment of collection efficiency (CE) was made by determining dust mass after controlled ignition of selected sticky pad samples. Although dust saturation of the sticky pads can lead to sample loss over prolonged exposure periods, this loss is relatively small over the 1-2 week intervals established as appropriate for the DustScan sampler. This need for shorter sampling intervals is considered to outweigh the convenience of the longer exposure

  15. Constraints on Late Tertiary Elevation of the Colorado Plateau From Carbonate Clumped- Isotope Thermometry

    NASA Astrophysics Data System (ADS)

    Huntington, K. W.; Wernicke, B. P.; Eiler, J. M.

    2009-05-01

    Topography is a first-order expression of the buoyancy of the lithosphere, and the timing and pattern of elevation change can place fundamental constraints on mantle flow and continental dynamics. We investigate the timing of Colorado Plateau uplift using clumped-isotope thermometry to independently constrain both the temperature and isotopic composition of ancient surface waters based on the 13C-18O bond enrichment in carbonates. Analyses of ancient lake sediments from the plateau interior and adjacent lowlands are compared to signals recorded by modern sediments collected over 3 km of elevation in the region. Comparison of modern and ancient samples deposited near sea level provides an opportunity to quantify the influence of climate on changes in temperature, and therefore more accurately assess the contribution from changes in elevation. Both modern and ancient (Miocene-Pliocene) carbonates record near-surface spring/summer lake water temperatures that vary strongly with elevation. Modern and ancient lake carbonate temperature lapse rates of -4.2±0.7°C/km and -4.1±0.6°C/km, respectively, suggest that little if any post-16 Ma change in elevation of the southern plateau is required to explain the data. Agreement of δ18O data for modern and ancient surface waters supports this interpretation. The zero-elevation intercept of the ancient trend is 7.7±2.0°C warmer than the modern trend, indicating significant cooling due to climate change since Late Miocene time. The temperature data are permissive of up to 450 m of uplift or 250 m of subsidence of the plateau interior since 6 Ma, but do not support km-scale changes. Combined with previous constraints, the data suggest that most uplift of the south-central plateau occurred during Late Cretaceous/earliest Tertiary time, favoring uplift mechanisms such as crustal thickening by channel flow, hydration of the mantle lithosphere due to volatile flux from the Laramide flat slab, or dynamic topography associated with

  16. Gas Emissions in Planck Cold Dust Clumps—A Survey of the J = 1-0 Transitions of 12CO, 13CO, and C18O

    NASA Astrophysics Data System (ADS)

    Wu, Yuefang; Liu, Tie; Meng, Fanyi; Li, Di; Qin, Sheng-Li; Ju, Bing-Gang

    2012-09-01

    A survey toward 674 Planck cold clumps of the Early Cold Core Catalogue (ECC) in the J = 1-0 transitions of 12CO, 13CO, and C18O has been carried out using the Purple Mountain Observatory 13.7 m telescope. Six hundred seventy-three clumps were detected with 12CO and 13CO emission, and 68% of the sample has C18O emission. Additional velocity components were also identified. A close consistency of the three line peak velocities was revealed for the first time. Kinematic distances are given for all the velocity components, and half of the clumps are located within 0.5 and 1.5 kpc. Excitation temperatures range from 4 to 27 K, slightly larger than those of Td . Line width analysis shows that the majority of ECC clumps are low-mass clumps. Column densities N_{H_{2}} span from 1020 to 4.5 × 1022 cm-2 with an average value of (4.4 ± 3.6) × 1021 cm-2. N_{H_{2}} cumulative fraction distribution deviates from the lognormal distribution, which is attributed to optical depth. The average abundance ratio of the 13CO to C18O in these clumps is 7.0 ± 3.8, higher than the terrestrial value. Dust and gas are well coupled in 95% of the clumps. Blue profile asymmetry, red profile asymmetry, and total line asymmetry were found in less than 10% of the clumps, generally indicating that star formation is not yet developed. Ten clumps were mapped. Twelve velocity components and 22 cores were obtained. Their morphologies include extended diffuse, dense, isolated, cometary, and filament, of which the last is the majority. Twenty cores are starless, and only seven cores seem to be in a gravitationally bound state. Planck cold clumps are the most quiescent among the samples of weak red IRAS, infrared dark clouds, UC H II candidates, extended green objects, and methanol maser sources, suggesting that Planck cold clumps have expanded the horizon of cold astronomy.

  17. Deposition Rates and Characterization of Arabian Mineral Dust

    NASA Astrophysics Data System (ADS)

    Puthan Purakkal, J.; Stenchikov, G. L.; Engelbrecht, J. P.

    2015-12-01

    Airborne mineral dust directly and indirectly impacts on global climate, continental and marine biochemistry, human and animal health, agriculture, equipment, and visibility. Annual global dust emissions are poorly known with estimates differing by a factor of at least two. Local dust emission and deposition rates are even less quantified. Dust deposition rate is a key parameter, which helps to constrain the modeled dust budget of the atmosphere. However, dust deposition remains poorly known, due to the limited number of reliable measurements. Simulations and satellite observations suggest that coastal dusts contribute substantially to the total deposition flux into the Red Sea. Starting December 2014, deposition samplers, both the "frisbee" type, and passive samplers for individual particle scanning electron microscopy were deployed at King Abdullah University of Science and Technology (KAUST), along the Red Sea in Saudi Arabia. Sampling periods of one month were adopted. The deposition rates range from 3 g m-2 month-1 for fair weather conditions to 23 g m-2 month-1 for high dust events. The X-ray diffraction (XRD) analyses of deposited dust samples show mineralogical compositions different from any of the parent soils, the former consisting mainly of gypsum, calcite, and smaller amounts of albite, montmorillonite, chlorite, quartz and biotite. The deposited dust samples on the other hand contain more gypsum and less quartz than the previously collected soil samples. This presentation discusses the results from XRD, chemical analysis and SEM-based individual particle analysis of the soils and the deposited dust samples. The monthly dust accumulation rates and their seasonal and spatial variability are compared with the regional model predictions. Data from this study provide an observational basis for validating the regional dust mass balance along the Arabian Red Sea coastal plain.

  18. Multi-wavelength View of Kiloparsec-scale Clumps in Star-forming Galaxies at z ~ 2

    NASA Astrophysics Data System (ADS)

    Guo, Yicheng; Giavalisco, Mauro; Ferguson, Henry C.; Cassata, Paolo; Koekemoer, Anton M.

    2012-10-01

    This paper studies the properties of kiloparsec-scale clumps in star-forming galaxies at z ~ 2 through multi-wavelength broadband photometry. A sample of 40 clumps is identified from Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) z-band images through auto-detection and visual inspection from 10 galaxies with 1.5 < z < 2.5 in the Hubble Ultra Deep Field, where deep and high-resolution HST/WFC3 and ACS images enable us to resolve structures of z ~ 2 galaxies down to the kiloparsec scale in the rest-frame UV and optical bands and to detect clumps toward the faint end. The physical properties of clumps are measured through fitting spatially resolved seven-band (BVizYJH) spectral energy distribution to models. On average, the clumps are blue and have similar median rest-frame UV-optical color as the diffuse components of their host galaxies, but the clumps have large scatter in their colors. Although the star formation rate (SFR)-stellar mass relation of galaxies is dominated by the diffuse components, clumps emerge as regions with enhanced specific star formation rates, contributing individually ~10% and together ~50% of the SFR of the host galaxies. However, the contributions of clumps to the rest-frame UV/optical luminosity and stellar mass are smaller, typically a few percent individually and ~20% together. On average, clumps are younger by 0.2 dex and denser by a factor of eight than diffuse components. Clump properties have obvious radial variations in the sense that central clumps are redder, older, more extincted, denser, and less active on forming stars than outskirt clumps. Our results are broadly consistent with a widely held view that clumps are formed through gravitational instability in gas-rich turbulent disks and would eventually migrate toward galactic centers and coalesce into bulges. Roughly 40% of the galaxies in our sample contain a massive clump that could be identified as a proto-bulge, which seems qualitatively consistent with

  19. MULTI-WAVELENGTH VIEW OF KILOPARSEC-SCALE CLUMPS IN STAR-FORMING GALAXIES AT z {approx} 2

    SciTech Connect

    Guo Yicheng; Giavalisco, Mauro; Cassata, Paolo; Ferguson, Henry C.; Koekemoer, Anton M.

    2012-10-01

    This paper studies the properties of kiloparsec-scale clumps in star-forming galaxies at z {approx} 2 through multi-wavelength broadband photometry. A sample of 40 clumps is identified from Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) z-band images through auto-detection and visual inspection from 10 galaxies with 1.5 < z < 2.5 in the Hubble Ultra Deep Field, where deep and high-resolution HST/WFC3 and ACS images enable us to resolve structures of z {approx} 2 galaxies down to the kiloparsec scale in the rest-frame UV and optical bands and to detect clumps toward the faint end. The physical properties of clumps are measured through fitting spatially resolved seven-band (BVizYJH) spectral energy distribution to models. On average, the clumps are blue and have similar median rest-frame UV-optical color as the diffuse components of their host galaxies, but the clumps have large scatter in their colors. Although the star formation rate (SFR)-stellar mass relation of galaxies is dominated by the diffuse components, clumps emerge as regions with enhanced specific star formation rates, contributing individually {approx}10% and together {approx}50% of the SFR of the host galaxies. However, the contributions of clumps to the rest-frame UV/optical luminosity and stellar mass are smaller, typically a few percent individually and {approx}20% together. On average, clumps are younger by 0.2 dex and denser by a factor of eight than diffuse components. Clump properties have obvious radial variations in the sense that central clumps are redder, older, more extincted, denser, and less active on forming stars than outskirt clumps. Our results are broadly consistent with a widely held view that clumps are formed through gravitational instability in gas-rich turbulent disks and would eventually migrate toward galactic centers and coalesce into bulges. Roughly 40% of the galaxies in our sample contain a massive clump that could be identified as a proto-bulge, which

  20. The Lunar Dust Environment

    NASA Astrophysics Data System (ADS)

    Szalay, Jamey Robert

    Planetary bodies throughout the solar system are continually bombarded by dust particles, largely originating from cometary activities and asteroidal collisions. Surfaces of bodies with thick atmospheres, such as Venus, Earth, Mars and Titan are mostly protected from incoming dust impacts as these particles ablate in their atmospheres as 'shooting stars'. However, the majority of bodies in the solar system have no appreciable atmosphere and their surfaces are directly exposed to the flux of high speed dust grains. Impacts onto solid surfaces in space generate charged and neutral gas clouds, as well as solid secondary ejecta dust particles. Gravitationally bound ejecta clouds forming dust exospheres were recognized by in situ dust instruments around the icy moons of Jupiter and Saturn, and had not yet been observed near bodies with refractory regolith surfaces before NASA's Lunar Dust and Environment Explorer (LADEE) mission. In this thesis, we first present the measurements taken by the Lunar Dust Explorer (LDEX), aboard LADEE, which discovered a permanently present, asymmetric dust cloud surrounding the Moon. The global characteristics of the lunar dust cloud are discussed as a function of a variety of variables such as altitude, solar longitude, local time, and lunar phase. These results are compared with models for lunar dust cloud generation. Second, we present an analysis of the groupings of impacts measured by LDEX, which represent detections of dense ejecta plumes above the lunar surface. These measurements are put in the context of understanding the response of the lunar surface to meteoroid bombardment and how to use other airless bodies in the solar system as detectors for their local meteoroid environment. Third, we present the first in-situ dust measurements taken over the lunar sunrise terminator. Having found no excess of small grains in this region, we discuss its implications for the putative population of electrostatically lofted dust.

  1. Dust outflows from quiescent spiral disks.

    NASA Astrophysics Data System (ADS)

    Alton, P. B.; Rand, R. J.; Xilouris, E. M.; Bevan, S.; Ferguson, A. M.; Davies, J. I.; Bianchi, S.

    2000-07-01

    We have conducted a search for ``dust chimneys'' in a sample of 10 highly-inclined spiral galaxies (i=86-90deg) which we had previously observed in the Hα emission line (Rand 1996). We have procured B-band CCD images for this purpose and employed unsharp-masking techniques to accentuate the structure of the dust lane. A scattering+absorption radiation transfer model enabled us to separate 5 galaxies from the sample which are sufficiently inclined (i>87deg) for us to reliably identify and quantify dust clouds residing at over 2 scale-heights above the disk. Three of these galaxies possess numerous curvi-linear chimney structures stretching up to 2 kpc from the midplane and the fraction of total galactic dust contained in such structures is of order 1%. Optical extinction offers a lower limit to the amount of dust contained in the extraplanar layer but, by examining the transparent submm thermal emission from NGC 891, we fix an upper limit of 5%. Our results are consistent with a similar recent study by Howk & Savage (1999) which indicates that about half of quiescent spiral disks possess detectable dust chimneys. We have compared our optical images with the corresponding Hα emission-line radiation. We do not find a detailed spatial correspondance between dust chimneys and either sites of recent star-formation or the extraplanar diffuse ionized gas. This is somewhat surprising given that FIR-bright galaxies, such as M 82, are known to entrain dust at the working surface of the starburst-driven outflow (traced in Hα ). It is possible a global correlation exists, with disks experiencing overall higher rates of star-formation also possessing the greatest number of chimneys. This may indicate a timescale difference between the two phenomena with the Hα phase lasting ~ 106 yr but chimneys requiring ~ 107 yr to form. Additionally, we have investigated the edge-on disk NGC 55 which, being ten times closer than galaxies in our main sample, allows us to examine in greater

  2. MLAOS: a multi-point linear array of optical sensors for coniferous foliage clumping index measurement.

    PubMed

    Qu, Yonghua; Fu, Lizhe; Han, Wenchao; Zhu, Yeqing; Wang, Jindi

    2014-05-23

    The canopy foliage clumping effect is primarily caused by the non-random distribution of canopy foliage. Currently, measurements of clumping index (CI) by handheld instruments is typically time- and labor-intensive. We propose a low-cost and low-power automatic measurement system called Multi-point Linear Array of Optical Sensors (MLAOS), which consists of three above-canopy and nine below-canopy optical sensors that capture plant transmittance at different times of the day. Data communication between the MLAOS node is facilitated by using a ZigBee network, and the data are transmitted from the field MLAOS to a remote data server using the Internet. The choice of the electronic element and design of the MLAOS software is aimed at reducing costs and power consumption. A power consumption test showed that, when a 4000 mAH Li-ion battery is used, a maximum of 8-10 months of work can be achieved. A field experiment on a coniferous forest revealed that the CI of MLAOS may reveal a clumping effect that occurs within the canopy. In further work, measurement of the multi-scale clumping effect can be achieved by utilizing a greater number of MLAOS devices to capture the heterogeneity of the plant canopy.

  3. Using red clump stars to decompose the galactic magnetic field with distance

    SciTech Connect

    Pavel, Michael D.

    2014-09-01

    A new method for measuring the large-scale structure of the Galactic magnetic field is presented. The Galactic magnetic field has been probed through the Galactic disk with near-infrared starlight polarimetry; however, the distance to each background star is unknown. Using red clump stars as near-infrared standard candles, this work presents the first attempt to decompose the line-of-sight structure of the sky-projected Galactic magnetic field. Two example lines of sight are decomposed: toward a field with many red clump stars and toward a field with few red clump stars. A continuous estimate of magnetic field orientation over several kiloparsecs of distance is possible in the field with many red clump stars, while only discrete estimates are possible in the sparse example. Toward the outer Galaxy, there is a continuous field orientation with distance that shows evidence of perturbation by the Galactic warp. Toward the inner Galaxy, evidence for a large-scale change in the magnetic field geometry is consistent with models of magnetic field reversals, independently derived from Faraday rotation studies. A photo-polarimetric method for identifying candidate intrinsically polarized stars is also presented. The future application of this method to large regions of the sky will begin the process of mapping the Galactic magnetic field in a way never before possible.

  4. Estimation of intervention effect using paired interval-censored data with clumping below lower detection limit.

    PubMed

    Xu, Ying; Lam, K F; Cowling, Benjamin J; Cheung, Yin Bun

    2015-01-30

    Outcome variables that are semicontinuous with clumping at zero are commonly seen in biomedical research. In addition, the outcome measurement is sometimes subject to interval censoring and a lower detection limit (LDL). This gives rise to interval-censored observations with clumping below the LDL. Level of antibody against influenza virus measured by the hemagglutination inhibition assay is an example. The interval censoring is due to the assay's technical procedure. The clumping below LDL is likely a result of the lack of prior exposure in some individuals such that they either have zero level of antibodies or do not have detectable level of antibodies. Given a pair of such measurements from the same subject at two time points, a binary 'fold-increase' endpoint can be defined according to the ratio of these two measurements, as it often is in vaccine clinical trials. The intervention effect or vaccine immunogenicity can be assessed by comparing the binary endpoint between groups of subjects given different vaccines or placebos. We introduce a two-part random effects model for modeling the paired interval-censored data with clumping below the LDL. Based on the estimated model parameters, we propose to use Monte Carlo approximation for estimation of the 'fold-increase' endpoint and the intervention effect. Bootstrapping is used for variance estimation. The performance of the proposed method is demonstrated by simulation. We analyze antibody data from an influenza vaccine trial for illustration.

  5. MLAOS: A Multi-Point Linear Array of Optical Sensors for Coniferous Foliage Clumping Index Measurement

    PubMed Central

    Qu, Yonghua; Fu, Lizhe; Han, Wenchao; Zhu, Yeqing; Wang, Jindi

    2014-01-01

    The canopy foliage clumping effect is primarily caused by the non-random distribution of canopy foliage. Currently, measurements of clumping index (CI) by handheld instruments is typically time- and labor-intensive. We propose a low-cost and low-power automatic measurement system called Multi-point Linear Array of Optical Sensors (MLAOS), which consists of three above-canopy and nine below-canopy optical sensors that capture plant transmittance at different times of the day. Data communication between the MLAOS node is facilitated by using a ZigBee network, and the data are transmitted from the field MLAOS to a remote data server using the Internet. The choice of the electronic element and design of the MLAOS software is aimed at reducing costs and power consumption. A power consumption test showed that, when a 4000 mAH Li-ion battery is used, a maximum of 8–10 months of work can be achieved. A field experiment on a coniferous forest revealed that the CI of MLAOS may reveal a clumping effect that occurs within the canopy. In further work, measurement of the multi-scale clumping effect can be achieved by utilizing a greater number of MLAOS devices to capture the heterogeneity of the plant canopy. PMID:24859029

  6. A study of the dust distribution and extinction law in Mon R2

    NASA Technical Reports Server (NTRS)

    Natta, A.; Beckwith, S.; Beck, S. C.; Evans, N. J., II; Moorwood, A. F. M.

    1986-01-01

    Observations were obtained at wavelengths from 1.5 to 7.5 microns with beams varying in diameter from 4 to 28 arcsec of infrared hydrogen recombination lines toward the Mon R2 IRS1 H II region. It is found that the data cannot be fitted with the extinction law which characterizes the interstellar medium unless the obscuring matter is clumped on a small scale of not greater than 0.3 arcsec; in which case considerable fluctuations in the amount of extinction on scales smaller than 1 arcsec are expected. The data of Simon et al. (1983) suggest a dip in the extinction about 5 arcsec from the 2-micron and radio continuum peak, and rule out models with uniform dust and clump distributions.

  7. CHEMISTRY IN INFRARED DARK CLOUD CLUMPS: A MOLECULAR LINE SURVEY AT 3 mm

    SciTech Connect

    Sanhueza, Patricio; Jackson, James M.; Foster, Jonathan B.; Finn, Susanna C.; Garay, Guido; Silva, Andrea

    2012-09-01

    We have observed 37 Infrared Dark Clouds (IRDCs), containing a total of 159 clumps, in high-density molecular tracers at 3 mm using the 22 m ATNF Mopra Telescope located in Australia. After determining kinematic distances, we eliminated clumps that are not located in IRDCs and clumps with a separation between them of less than one Mopra beam. Our final sample consists of 92 IRDC clumps. The most commonly detected molecular lines are (detection rates higher than 8%) N{sub 2}H{sup +}, HNC, HN{sup 13}C, HCO{sup +}, H{sup 13}CO{sup +}, HCN, C{sub 2}H, HC{sub 3}N, HNCO, and SiO. We investigate the behavior of the different molecular tracers and look for chemical variations as a function of an evolutionary sequence based on Spitzer IRAC and MIPS emission. We find that the molecular tracers behave differently through the evolutionary sequence and some of them can be used to yield useful relative age information. The presence of HNC and N{sub 2}H{sup +} lines does not depend on the star formation activity. On the other hand, HC{sub 3}N, HNCO, and SiO are predominantly detected in later stages of evolution. Optical depth calculations show that in IRDC clumps the N{sub 2}H{sup +} line is optically thin, the C{sub 2}H line is moderately optically thick, and HNC and HCO{sup +} are optically thick. The HCN hyperfine transitions are blended, and, in addition, show self-absorbed line profiles and extended wing emission. These factors combined prevent the use of HCN hyperfine transitions for the calculation of physical parameters. Total column densities of the different molecules, except C{sub 2}H, increase with the evolutionary stage of the clumps. Molecular abundances increase with the evolutionary stage for N{sub 2}H{sup +} and HCO{sup +}. The N{sub 2}H{sup +}/HCO{sup +} and N{sub 2}H{sup +}/HNC abundance ratios act as chemical clocks, increasing with the evolution of the clumps.

  8. The Spherically Symmetric Gravitational Collapse of a Clump of Solids in a Gas

    NASA Astrophysics Data System (ADS)

    Shariff, Karim; Cuzzi, Jeffrey N.

    2015-05-01

    In the subject of planetesimal formation, several mechanisms have been identified that create dense particle clumps in the solar nebula. The present work is concerned with the gravitational collapse of such clumps, idealized as being spherically symmetric. Fully nonlinear simulations using the two-fluid model are carried out (almost) up to the time when a central density singularity forms. We refer to this as the collapse time. The end result of the study is a parametrization of the collapse time, in order that it may be compared with timescales for various disruptive effects to which clumps may be subject in a particular situation. An important effect that determines the collapse time is that as the clump compresses, it also compresses the gas due to drag. This increases gas pressure, which retards particle collapse and can lead to oscillation in the size and density of the clump. In the limit of particles perfectly coupled to the gas, the characteristic ratio of gravitational force to gas pressure becomes relevant and defines a two-phase Jeans parameter, {{J}t}, which is the classical Jeans parameter with the speed of sound replaced by an effective wave speed in the coupled two-fluid medium. The parameter {{J}t} remains useful even away from the perfect coupling limit because it makes the simulation results insensitive to the initial density ratio of particles to gas (Φ0) as a separate parameter. A simple ordinary differential equation model is developed. It takes the form of two coupled non-linear oscillators and reproduces key features of the simulations. Finally, a parametric study of the time to collapse is performed and a formula (fit to the simulations) is developed. In the incompressible limit {{J}t}\\to 0, collapse time equals the self-sedimentation time, which is inversely proportional to the Stokes number. As {{J}t} increases, the collapse time decreases with {{J}t} and eventually becomes approximately equal to the dynamical time. Values of collapse

  9. A predator-prey model for moon-triggered clumping in Saturn's rings

    NASA Astrophysics Data System (ADS)

    Esposito, Larry W.; Albers, Nicole; Meinke, Bonnie K.; Sremčević, Miodrag; Madhusudhanan, Prasanna; Colwell, Joshua E.; Jerousek, Richard G.

    2012-01-01

    UVIS occultation data show clumping in Saturn's F ring and at the B ring outer edge, indicating aggregation and disaggregation at these locations that are perturbed by Prometheus and by Mimas. The inferred timescales range from hours to months. Occultation profiles of the edge show wide variability, indicating perturbations by local mass aggregations. Structure near the B ring edge is seen in power spectral analysis at scales 200-2000 m. Similar structure is also seen at the strongest density waves, with significance increasing with resonance strength. For the B ring outer edge, the strongest structure is seen at longitudes 90° and 270° relative to Mimas. This indicates a direct relation between the moon and the ring clumping. We propose that the collective behavior of the ring particles resembles a predator-prey system: the mean aggregate size is the prey, which feeds the velocity dispersion; conversely, increasing dispersion breaks up the aggregates. Moons may trigger clumping by streamline crowding, which reduces the relative velocity, leading to more aggregation and more clumping. Disaggregation may follow from disruptive collisions or tidal shedding as the clumps stir the relative velocity. For realistic values of the parameters this yields a limit cycle behavior, as for the ecology of foxes and hares or the "boom-bust" economic cycle. Solving for the long-term behavior of this forced system gives a periodic response at the perturbing frequency, with a phase lag roughly consistent with the UVIS occultation measurements. We conclude that the agitation by the moons in the F ring and at the B ring outer edge drives aggregation and disaggregation in the forcing frame. This agitation of the ring material may also allow fortuitous formation of solid objects from the temporary clumps, via stochastic processes like compaction, adhesion, sintering or reorganization that drives the denser parts of the aggregate to the center or ejects the lighter elements. Any of

  10. The Influence of Kinetic Growth Factors on the Clumped Isotope Composition of Calcite

    NASA Astrophysics Data System (ADS)

    Hunt, J. D.; Watkins, J. M.; Tripati, A.; Ryerson, F. J.; DePaolo, D. J.

    2014-12-01

    Clumped isotope paleothermometry is based on the association of 13C and 18O within carbonate minerals. Although the influence of temperature on equilibrium 13C-18O bond ordering has been studied, recent oxygen isotope studies of inorganic calcite demonstrate that calcite grown in laboratory experiments and in many natural settings does not form in equilibrium with water. It is therefore likely that the carbon and clumped isotope composition of these calcite crystals are not representative of true thermodynamic equilibrium. To isolate kinetic clumped isotope effects that arise at the mineral-solution interface, clumped isotopic equilibrium of DIC species must be maintained. This can be accomplished by dissolving the enzyme carbonic anhydrase (CA) into the solution, thereby reducing the time required for isotopic equilibration of DIC species by approximately two orders of magnitude between pH 7.7 and 9.3. We conduct calcite growth experiments aimed specifically at measuring the pH-dependence of kinetic clumped isotope effects during non-equilibrium precipitation of calcite. We precipitated calcite from aqueous solution at a constant pH and controlled supersaturation over the pH range 7.7-9.3 in the presence of CA. For each experiment, a gas mixture of N2 and CO2 is bubbled through a beaker of solution without seed crystals. As CO2 from the gas dissolves into solution, calcite crystals grow on the beaker walls. The pH of the solution is maintained by use of an autotitrator with NaOH as the titrant. We control the temperature, pH, the pCO2 of the gas inflow, and the gas inflow rate, and monitor the total alkalinity, the pCO2 of the gas outflow, and the amount of NaOH added. A constant crystal growth rate of ~1.6 mmol/m2/hr is maintained over all experiments. Results from these experiments are compared to predictions from a recently-developed isotopic ion-by-ion growth model of calcite. The model describes the rate, temperature and pH dependence of oxygen isotope uptake

  11. Imaging-based dust sensors: equipment and methods

    NASA Astrophysics Data System (ADS)

    Bonifazi, Giuseppe; Greco, Sonia

    2004-05-01

    Dust detection and control in real time, represent one of the most challenging problem in all those environments where fine and ultrafine airborne particulate solids products are present. The presence of such products can be linked to several factors, often directly related and influenced by the working-production actions performed. Independently from the causes generating dust, airborne contaminants are an occupational problem of increasing interest as they are related to a wide number of diseases. In particular, airborne dusts are well known to be associated with several classical occupational lung diseases, such as the pneumoconiosis, especially at high levels of exposure. Nowadays there is also an increasing interest in other dust related diseases, from the most serious as cancer and asthma, to those related with allergies or irritation and other illnesses, also occurring at lower levels of exposure. Among the different critical factors influencing health risk for airborne dust exposure, mainly four have to be considered, that is: i) nature of the dust resulting from working in terms of presence of specific poisoning material, i.e. free silica, and morphological and morphometrical attributes of particulates constituting airborne dust; ii) size of the particles, iii) duration of exposure time and, finally, iv) airborne dust concentration in the breathing zone where the worker performs his activity. A correct dust detection is not easy, especially if some of the previous mentioned factors, have to be detected and quantified in real time in order to define specific "on-line" control actions aimed to reduce the level of the exposure to dust of the workers, as for example: i) modification of aspirating devices operating condition, change of filtering cleaning sequence, etc. . The more severe are the environmental conditions, in terms of dust presence (in quantity and quality) more difficult is to utilize efficient sampling devices. Detection devices, in fact, tend

  12. Reducing float coal dust

    PubMed Central

    Patts, J.R.; Colinet, J.F.; Janisko, S.J.; Barone, T.L.; Patts, L.D.

    2016-01-01

    Controlling float coal dust in underground coal mines before dispersal into the general airstream can reduce the risk of mine explosions while potentially achieving a more effective and efficient use of rock dust. A prototype flooded-bed scrubber was evaluated for float coal dust control in the return of a continuous miner section. The scrubber was installed inline between the face ventilation tubing and an exhausting auxiliary fan. Airborne and deposited dust mass measurements were collected over three days at set distances from the fan exhaust to assess changes in float coal dust levels in the return due to operation of the scrubber. Mass-based measurements were collected on a per-cut basis and normalized on the basis of per ton mined by the continuous miner. The results show that average float coal dust levels measured under baseline conditions were reduced by more than 90 percent when operating the scrubber. PMID:28018004

  13. DUST FORMATION IN MACRONOVAE

    SciTech Connect

    Takami, Hajime; Ioka, Kunihito; Nozawa, Takaya E-mail: kunihito.ioka@kek.jp

    2014-07-01

    We examine dust formation in macronovae (as known as kilonovae), which are the bright ejecta of neutron star binary mergers and one of the leading sites of r-process nucleosynthesis. In light of information about the first macronova candidate associated with GRB 130603B, we find that dust grains of r-process elements have difficulty forming because of the low number density of the r-process atoms, while carbon or elements lighter than iron can condense into dust if they are abundant. Dust grains absorb emission from ejecta with an opacity even greater than that of the r-process elements, and re-emit photons at infrared wavelengths. Such dust emission can potentially account for macronovae without r-process nucleosynthesis as an alternative model. This dust scenario predicts a spectrum with fewer features than the r-process model and day-scale optical-to-ultraviolet emission.

  14. Dust devils on Mars

    NASA Technical Reports Server (NTRS)

    Thomas, P. G.; Gierasch, P.

    1985-01-01

    Large columns of dust have been discovered rising above plains on Mars. The storms are probably analogous to terrestrial dust devils, but their size indicates that they are more similar to tornadoes in intensity. They occur at locations where the soil has been strongly warmed by the Sun, and there the surface is smooth and fine grained. These are the same conditions that favor dust devils on Earth. Warm gas from the lowest atmospheric layer converges and rises in a thin column, with intense swirl developing at the edge of the column. In one area a mosaic of Viking images shows 97 vortices in a three day period. This represents a density of vortices of about one in each 900 square kilometers. Thus, these dust devils may be important in moving dust or starting over dust storms.

  15. Interstellar Dust: Physical Processes

    NASA Technical Reports Server (NTRS)

    Jones, A. P.; Tielens, A. G. G. M.

    1993-01-01

    Dust is formed in stellar environments, and destroyed by sputtering, shattering and vaporization in shock waves due to cloud-cloud collisions and supernova blast waves. Dust is also destroyed during star formation. We review the dust formation and destruction balance. The calculated destruction time-scale is less than or equal to one billion years and the star dust injection time-scale is approx. 2.5 billion years. Hence, the fractions of elemental carbon and silicon locked up in stardust are less than 0.3 and less than 0.15, respectively. An efficient ISM dust formation route is therefore implied. In particular, in dense clouds dust grows; through the processes of coagulation and the accretion of gas phase molecules e.g. H20, CO, CH4. These icy materials may then be photoprocessed to refractory materials in more diffuse regions. The resulting carbonaceous grain mantle may actually be the glue that holds the coagulated grains together.

  16. Dust Formation and Destruction

    NASA Astrophysics Data System (ADS)

    Wiebe, Dmitry

    Recent infrared and sub-millimeter observations have opened up a new window in dust evolution studies. High angular resolution of Spitzer and Herschel space telescopes from near to far-infrared wavelengths allows observing dust emission in galactic and extragalactic star-forming complexes, covering a broad range of metallicities, radiation field properties, etc. A wide-scale picture of dust evolution starts to arise from these observations. In my contribution I will try to cover major recent advances in studies of dust formation and destruction, including such topics as a diverse role of supernovae in dust evolution, possibility of dust formation and/or growth in molecular clouds, and VSG and PAH evolution in HII regions and complexes.

  17. Empirical High-Temperature Calibration for the Carbonate Clumped Isotopes Paleothermometer

    NASA Astrophysics Data System (ADS)

    Kluge, T.; John, C. M.; Jourdan, A.; Davis, S.; Crawshaw, J.

    2013-12-01

    The clumped isotope paleothermometer is being used in a wide range of applications related to carbonate mineral formation, focusing on temperature and fluid δ18O reconstruction. Whereas the range of typical Earth surface temperatures has been the focus of several studies based on laboratory experiments and biogenic carbonates of known growth temperatures, the clumped isotope-temperature relationship above 70 °C has not been assessed by direct precipitation of carbonates. We investigated the clumped isotope-temperature relationship by precipitating carbonates between 20 and 200°C in the laboratory. The setup consists of a pressurized vessel in which carbonate minerals are precipitated from the mixture of two solutions (CaCl2, NaHCO3). Both solutions are thermally and isotopically equilibrated before injection in the pressure vessel. Minerals precipitated in this setup generally consist of calcite. Samples were reacted with 105% orthophosphoric acid for 10 min at 90°C. The evolved CO2 was continuously collected and subsequently purified with a Porapak trap held at -35°C. Measurements were performed on a MAT 253 using the protocol of Huntington et al. (2009) and Dennis et al. (2011). Clumped isotope values from 20-90°C are consistent with carbonates that were precipitated from a CaCO3 super-saturated solution using the method of McCrea (1950). This demonstrates that the experimental setup does not induce any kinetic fractionation, and can be used for high-temperature carbonate precipitation. The new clumped isotope calibration at high temperature follows the theoretical calculations of Schauble et al. (2006) adjusted for phosphoric acid digestion at 90°C. We gratefully acknowledge funding from Qatar Petroleum, Shell and the Qatar Science and Technology Park.

  18. Carbonate clumped isotope constraints on Silurian ocean temperature and seawater δ18O

    NASA Astrophysics Data System (ADS)

    Cummins, Renata C.; Finnegan, Seth; Fike, David A.; Eiler, John M.; Fischer, Woodward W.

    2014-09-01

    Much of what we know about the history of Earth's climate derives from the chemistry of carbonate minerals in the sedimentary record. The oxygen isotopic compositions (δ18O) of calcitic marine fossils and cements have been widely used as a proxy for past seawater temperatures, but application of this proxy to deep geologic time is complicated by diagenetic alteration and uncertainties in the δ18O of seawater in the past. Carbonate clumped isotope thermometry provides an independent estimate of the temperature of the water from which a calcite phase precipitated, and allows direct calculation of the δ18O of the water. The clumped isotope composition of calcites is also highly sensitive to recrystallization and can help diagnose different modes of diagenetic alteration, enabling evaluation of preservation states and identification of the most pristine materials from within a sample set-critical information for assessing the quality of paleoproxy data generated from carbonates. We measured the clumped isotope composition of a large suite of calcitic fossils (primarily brachiopods and corals), sedimentary grains, and cements from Silurian (ca. 433 Ma) stratigraphic sections on the island of Gotland, Sweden. Substantial variability in clumped isotope temperatures suggests differential preservation with alteration largely tied to rock-buffered diagenesis, complicating the generation of a stratigraphically resolved climate history through these sections. Despite the generally high preservation quality of samples from these sections, micro-scale observations of calcite fabric and trace metal composition using electron backscatter diffraction and electron microprobe analysis suggest that only a subset of relatively pristine samples retain primary clumped isotope signatures. These samples indicate that Silurian tropical oceans were likely warm (33 ± 7 °C) and similar in oxygen isotopic composition to that estimated for a "modern" ice-free world (δ18OVSMOW of -1.1 ± 1

  19. Early evolution of clumps formed via gravitational instability in protoplanetary discs: precursors of Hot Jupiters?

    NASA Astrophysics Data System (ADS)

    Galvagni, M.; Mayer, L.

    2014-01-01

    Although it is fairly established that Gravitational Instability (GI) should occur in the early phases of the evolution of a protoplanetary disc, the fate of the clumps resulting from disc fragmentation and their role in planet formation is still unclear. In the present study we investigate semi-analytically their evolution following the contraction of a synthetic population of clumps with varied initial structure and orbits coupled with the surrounding disc and the central star. Our model is based on recently published state-of-the-art 3D collapse simulations of clumps with varied thermodynamics. Various evolutionary mechanisms are taken into account, and their effect is explored both individually and in combination with others: migration and tidal disruption, mass accretion, gap opening and disc viscosity. It is found that, in general, at least 50 per cent of the initial clumps survive tides, leaving behind potential gas giant progenitors after ˜105 yr of evolution in the disc. The rest might either be disrupted or produce super-Earths and other low-mass planets provided that a solid core can be assembled on a sufficiently short time-scale, a possibility that we do not address in this paper. Extrapolating to million year time-scales, all our surviving protoplanets would lead to close-in gas giants. This outcome might in part reflect the limitations of the migration model adopted, and is reminiscent of the analogous result found in core-accretion models in absence of fine-tuning of the migration rate. Yet it suggests that a significant fraction of the clumps formed by GI could be the precursors of Hot Jupiters.

  20. The Robustness of Clumped Isotope Temperatures to Bond Reordering: Evidence from Deeply Buried Carbonate Reservoirs

    NASA Astrophysics Data System (ADS)

    MacDonald, J.; John, C. M.; Girard, J. P.

    2014-12-01

    Numerous studies have shown that clumped isotope thermometry records the temperature of precipitation for carbonate minerals in surface and near-surface environments. However, the ability of a mineral to retain its clumped isotope signature at deeper, hotter burial conditions is still debated. Dolomite has been shown to be more robust to clumped isotope bond reordering than calcite. In this contribution we measure clumped isotopes in calcite veins from Southern Europe that have been buried to up to 7 km to test the robustness of calcite and dolomite to bond reordering. First, we analysed finely crystalline dolostone matrix samples collected in industry wells from Southwest France and buried to between 2 and 5.5 km, Results indicated a temperatures of ~40-60 °C, interpreted to represent formation in an early burial environment. By contrast, coarser dolomite crystals that are petrographically distinct from the fine-grained dolomite record higher temperatures and are interpreted to reflect a deeper, hotter phase of dolomite formation. Preliminary analysis of a calcite vein from a Cretaceous dolostone in Southern Europe buried to 6.3 km records a temperature of 41±3 °C; the calcite matrix around this records a similarly low temperature. This is well below the present-day well temperature of 130-140 °C. Our results indicate that both calcite and dolomite are not affected by bond reordering at the range of depths and temperatures investigated here. Furthermore, this suggests that clumped isotope thermometry can be applied to deeply-buried samples (i.e. >5km).

  1. Dust Devil Formation

    NASA Astrophysics Data System (ADS)

    Rafkin, S.; Jemmett-Smith, B.; Fenton, L.; Lorenz, R.; Takemi, T.; Ito, J.; Tyler, D.

    2016-11-01

    The essential dynamical characteristic of convective vortices, including dust devils, is a highly localized vorticity tube that extends into the vertical. This chapter is concerned with both the generation of vorticity and the subsequent focusing of that vorticity into a tight vortex, and with the environmental conditions that are conducive to the formation of convective vortices in general and dust devils in particular. A review of observations, theory, and modeling of dust devil formation is provided.

  2. Galaxy formation by dust

    NASA Technical Reports Server (NTRS)

    Wang, Boqi; Field, Goerge B.

    1989-01-01

    It has been known since the early 1940's that radiation can cause an instability in the interstellar medium. Absorbing dust particles in an isotropic radiation field shadow each other by a solid angle which is inversely proportional to the square of the distance between the two particles, leading to an inverse-square attractive force - mock gravity. The effect is largest in an optically thin medium. Recently Hogan and White (HW, hereafter) proposed that if the pre-galactic universe contained suitable sources of radiation and dust, instability in the dust distribution caused by mock gravity may have led to the formation of galaxies and galaxy clusters. In their picture of a well-coupled dust-gas medium, HW show that mock gravity begins to dominate gravitational instability when the perturbation becomes optically thin, provided that the radiation field at the time is strong enough. The recent rocket observation of the microwave background at submillimeter wavelengths by Matsumoto et al. might be from pre-galactic stars, the consequence of the absorption of ultraviolet radiation by dust, and infrared reemission which is subsequently redshifted. HW's analysis omits radiative drag, incomplete collisional coupling of gas and dust, finite dust albedo, and finite matter pressure. These effects could be important. In a preliminary calculation including them, the authors have confirmed that mock gravitational instability is effective if there is a strong ultraviolet radiation at the time, but any galaxies that form would be substantially enriched in heavy elements because the contraction of the dust is more rapid than that of the gas. Moreover, since the dust moves with supersonic velocity through the gas soon after the perturbation becomes optically thin, the sputtering of dust particles by gas is significant, so the dust could disappear before the instability develops significantly. They conclude that the mock gravity by dust is not important in galaxy formations.

  3. Operational Dust Prediction

    NASA Technical Reports Server (NTRS)

    Benedetti, Angela; Baldasano, Jose M.; Basart, Sara; Benincasa, Francesco; Boucher, Olivier; Brooks, Malcolm E.; Chen, Jen-Ping; Colarco, Peter R.; Gong, Sunlin; Huneeus, Nicolas; Jones, Luke; Lu, Sarah; Menut, Laurent; Morcrette, Jean-Jacques; Mulcahy, Jane; Nickovic, Slobodan; Garcia-Pando, Carlos P.; Reid, Jeffrey S.; Sekiyama, Thomas T.; Tanaka, Taichu Y.; Terradellas, Enric; Westphal, Douglas L.; Zhang, Xiao-Ye; Zhou, Chun-Hong

    2014-01-01

    Over the last few years, numerical prediction of dust aerosol concentration has become prominent at several research and operational weather centres due to growing interest from diverse stakeholders, such as solar energy plant managers, health professionals, aviation and military authorities and policymakers. Dust prediction in numerical weather prediction-type models faces a number of challenges owing to the complexity of the system. At the centre of the problem is the vast range of scales required to fully account for all of the physical processes related to dust. Another limiting factor is the paucity of suitable dust observations available for model, evaluation and assimilation. This chapter discusses in detail numerical prediction of dust with examples from systems that are currently providing dust forecasts in near real-time or are part of international efforts to establish daily provision of dust forecasts based on multi-model ensembles. The various models are introduced and described along with an overview on the importance of dust prediction activities and a historical perspective. Assimilation and evaluation aspects in dust prediction are also discussed.

  4. Dust Devil Tracks

    NASA Technical Reports Server (NTRS)

    2002-01-01

    (Released 8 May 2002) The Science This image, centered near 50.0 S and 17.7 W displays dust devil tracks on the surface. Most of the lighter portions of the image likely have a thin veneer of dust settled on the surface. As a dust devil passes over the surface, it acts as a vacuum and picks up the dust, leaving the darker substrate exposed. In this image there is a general trend of many of the tracks running from east to west or west to east, indicating the general wind direction. There is often no general trend present in dust devil tracks seen in other images. The track patterns are quite ephemeral and can completely change or even disappear over the course of a few months. Dust devils are one of the mechanisms that Mars uses to constantly pump dust into the ubiquitously dusty atmosphere. This atmospheric dust is one of the main driving forces of the present Martian climate. The Story Vrrrrooooooooom. Think of a tornado, the cartoon Tasmanian devil, or any number of vacuum commercials that powerfully suck up swirls of dust and dirt. That's pretty much what it's like on the surface of Mars a lot of the time. Whirlpools of wind called

  5. The Influence of Climate Change and Uplift on Colorado Plateau Paleotemperatures From Clumped Isotope (Δ47) Carbonate Thermometry

    NASA Astrophysics Data System (ADS)

    Huntington, K. W.; Wernicke, B. P.; Eiler, J. M.

    2008-12-01

    The elevation history of Earth's surface is key to understanding the geodynamic processes responsible for the rise of continental plateaus and orogens, and topography's influence on the circulation of the atmosphere and global climate in the past. Yet few available tools can provide quantitative paleoelevation constraints independently of climatic conditions. 'Clumped isotope' carbonate paleothermometry - a new technique based on measurement of the 13C-18O bond enrichment in carbonates - independently constrains both the temperature and isotopic composition of ancient surface waters, offering a potentially powerful approach to reconstruct past elevations and climate. We investigate the timing of Colorado Plateau uplift by comparing measurements of both modern and ancient depositional temperatures of lake sediments that blanket the plateau interior and adjacent lowlands. In particular, we find that comparison of modern and ancient samples deposited near sea level provides an opportunity to quantify the influence of climate on changes in temperature, and therefore more accurately assess the contribution from changes in elevation. Clumped isotope thermometry of modern lake calcite from 350-3300 m elevation in the southwestern United States reveals a lapse rate of 4.2°C/km, consistent with modern climatic data for the region. Lacustrine carbonates of the Late Miocene Bidahochi Formation (ca. 1900 m above sea level) record temperatures of 22-25°C, 8°C warmer than the temperature predicted by the modern trend. Temperature estimates for the low elevation (88-125 m above sea level) Late Miocene Bouse Formation suggest that a warmer Late Miocene climate can explain 2.6 to 5.8°C of the observed 8°C Bidahochi temperature anomaly, leaving approximately 2.2 to 5.4°C of the anomaly that can be attributed to elevation gain. Using our best- fit carbonate temperature-elevation slope of 4.2°C/km, the data suggest that this cooling was accompanied by 520 to 1300 m of uplift of

  6. Cold dust in hot regions

    SciTech Connect

    Sreenilayam, Gopika; Fich, Michel; Ade, Peter; Bintley, Dan; Chapin, Ed; Chrysostomou, Antonio; Jenness, Tim; Dunlop, James S.; Holland, Wayne S.; Ivison, Rob; Gibb, Andy; Halpern, Mark; Scott, Douglas; Greaves, Jane S.; Robson, Ian

    2014-03-01

    We mapped five massive star-forming regions with the SCUBA-2 camera on the James Clerk Maxwell Telescope. Temperature and column density maps are obtained from the SCUBA-2 450 and 850 μm images. Most of the dense clumps we find have central temperatures below 20 K, with some as cold as 8 K, suggesting that they have no internal heating due to the presence of embedded protostars. This is surprising, because at the high densities inferred from these images and at these low temperatures such clumps should be unstable, collapsing to form stars and generating internal heating. The column densities at the clump centers exceed 10{sup 23} cm{sup –2}, and the derived peak visual extinction values are from 25 to 500 mag for β = 1.5-2.5, indicating highly opaque centers. The observed cloud gas masses range from ∼10 to 10{sup 3} M {sub ☉}. The outer regions of the clumps follow an r {sup –2.36±0.35} density distribution, and this power-law structure is observed outside of typically 10{sup 4} AU. All these findings suggest that these clumps are high-mass starless clumps and most likely contain high-mass starless cores.

  7. Detecting Exoplanets with the New Worlds Observer: The Problem of Exozodiacal Dust

    NASA Technical Reports Server (NTRS)

    Roberge, A.; Noecker, M. C.; Glassman, T. M.; Oakley, P.; Turnbull, M. C.

    2009-01-01

    Dust coming from asteroids and comets will strongly affect direct imaging and characterization of terrestrial planets in the Habitable Zones of nearby stars. Such dust in the Solar System is called the zodiacal dust (or 'zodi' for short). Higher levels of similar dust are seen around many nearby stars, confined in disks called debris disks. Future high-contrast images of an Earth-like exoplanet will very likely be background-limited by light scattered of both the local Solar System zodi and the circumstellar dust in the extrasolar system (the exozodiacal dust). Clumps in the exozodiacal dust, which are expected in planet-hosting systems, may also be a source of confusion. Here we discuss the problems associated with imaging an Earth-like planet in the presence of unknown levels of exozodiacal dust. Basic formulae for the exoplanet imaging exposure time as function of star, exoplanet, zodi, exozodi, and telescope parameters will be presented. To examine the behavior of these formulae, we apply them to the New Worlds Observer (NWO) mission. NWO is a proposed 4-meter UV/optical/near-IR telescope, with a free flying starshade to suppress the light from a nearby star and achieve the high contrast needed for detection and characterization of a terrestrial planet in the star's Habitable Zone. We find that NWO can accomplish its science goals even if exozodiacal dust levels are typically much higher than the Solar System zodi level. Finally, we highlight a few additional problems relating to exozodiacal dust that have yet to be solved.

  8. Whither Cometary Dust?

    NASA Astrophysics Data System (ADS)

    Lisse, Carey M.

    2010-10-01

    In this paper I will discuss recent findings that have important implications for our understanding of the formation and evolution of primitive solar system dust, including: - Nesvorny et al. (2010), following up on their dynamical analyses of the zodiacal dust bands as sourced by the breakup of the Karin (5Mya) and Veritas (8Mya) asteroid families, argue that over 90% of the interplanetary dust cloud at 1 AU comes from JFC comets with near-circularized, low inclination orbits. This implies that the noted IPD collections of anhydrous and hydrous dust particles are likely to be from Oort cloud and JFC comets, respectively, not from asteroids and comets as thought in the past. Hydrous dust particles from comets like 85P/Wild2 and 9P/Tempel 1 would be consistent with results from the STARDUST and Deep Impact experiments. - Estimates of the dust particle size distributions (PSDs) in the comae of 85P/Wild2 (Green et al. 2004, 2007) and 73P/SW-3 (Sitko et al. 2010, Vaubaillon & Reach 2010) and in the trails of comets (Reach et al. 2007) have broken power law structure, with a plateau enhancement of particles of 1 mm - 1 cm in size. This size is also the size of most chondritic inclusions, and the predicted size range of the "aggregational barrier", where collisions between dust particles become destructive. - Studies of the albedo and polarization properties of cometary dust (Kolokolova et al. 2007) suggest there are 2 major groupings, one with low scattering capability and one with high. While these families could possibly have been explained by systematics in the PSDs of the emitted dust, independent work by Lisse et al. (2008) on the mineralogy of a number of highly dusty comets has shown evidence for one family of comets with highly crystalline dust and another with highly amorphous dust.

  9. Effects of cutting time, stump height, parent tree characteristics, and harvest variables on development of bigleaf maple sprout clumps

    USGS Publications Warehouse

    Tappeiner, J. C.; Zasada, J.; Maxwell, B.

    1996-01-01

    In order to determine the effects of stump height, year of cutting, parent-tree size, logging damage, and deer browsing on bigleaf maple (Acer macrophyllum) sprout clump development, maple trees were cut to two stump heights at three different times. Stump height had the greatest impact on sprout clump size. Two years after clearcutting, the sprout clump volume for short stumps was significantly less than that for tall stumps. The sprout clump volume, area, and number of sprouts were significantly less for trees cut 1 and 2 yr before harvest than for trees cut at harvest. Sprout clump size was positively correlated with parent tree stem diameter and stump volume, and negatively correlated with the percentage of bark removed during logging. Browsing had no significant impact on average clump size. Uncut trees produced sprout clumps at their base and epicormic branches along the length of their stems; thus their crown volume averaged four to five times that of cut trees. Cutting maple in clearcuts to low stumps may reduce maple competition with Douglas-fir regeneration and still maintain maple in the next stand.

  10. The long lives of giant clumps and the birth of outflows in gas-rich galaxies at high redshift

    SciTech Connect

    Bournaud, Frédéric; Renaud, Florent; Daddi, Emanuele; Duc, Pierre-Alain; Elbaz, David; Gabor, Jared M.; Juneau, Stéphanie; Kraljic, Katarina; Le Floch', Emeric; Dekel, Avishai; Elmegreen, Bruce G.; Elmegreen, Debra M.; Teyssier, Romain

    2014-01-01

    Star-forming disk galaxies at high redshift are often subject to violent disk instability, characterized by giant clumps whose fate is yet to be understood. The main question is whether the clumps disrupt within their dynamical timescale (≤50 Myr), like the molecular clouds in today's galaxies, or whether they survive stellar feedback for more than a disk orbital time (≈300 Myr) in which case they can migrate inward and help building the central bulge. We present 3.5-7 pc resolution adaptive mesh refinement simulations of high-redshift disks including photoionization, radiation pressure, and supernovae feedback. Our modeling of radiation pressure determines the mass loading and initial velocity of winds from basic physical principles. We find that the giant clumps produce steady outflow rates comparable to and sometimes somewhat larger than their star formation rate, with velocities largely sufficient to escape the galaxy. The clumps also lose mass, especially old stars, by tidal stripping, and the stellar populations contained in the clumps hence remain relatively young (≤200 Myr), as observed. The clumps survive gaseous outflows and stellar loss, because they are wandering in gas-rich turbulent disks from which they can reaccrete gas at high rates compensating for outflows and tidal stripping, overall keeping realistic and self-regulated gaseous and stellar masses. The outflow and accretion rates have specific timescales of a few 10{sup 8} yr, as opposed to rapid and repeated dispersion and reformation of clumps. Our simulations produce gaseous outflows with velocities, densities, and mass loading consistent with observations, and at the same time suggest that the giant clumps survive for hundreds of Myr and complete their migration to the center of high-redshift galaxies. These long-lived clumps are gas-dominated and contain a moderate mass fraction of stars; they drive inside-out disk evolution, thickening, spheroid growth, and fueling of the central

  11. SHORT-LIVED STAR-FORMING GIANT CLUMPS IN COSMOLOGICAL SIMULATIONS OF z Almost-Equal-To 2 DISKS

    SciTech Connect

    Genel, Shy; Genzel, Reinhard; Foerster Schreiber, Natascha M.; Naab, Thorsten; Oser, Ludwig; Sternberg, Amiel; Johansson, Peter H.; Dave, Romeel; Oppenheimer, Benjamin D.; Burkert, Andreas E-mail: genzel@mpe.mpg.de E-mail: amiel@wise.tau.ac.il E-mail: oser@usm.lmu.de E-mail: phjohans@astro.helsinki.fi E-mail: oppenheimer@strw.leidenuniv.nl

    2012-01-20

    Many observed massive star-forming z Almost-Equal-To 2 galaxies are large disks that exhibit irregular morphologies, with Almost-Equal-To 1 kpc, Almost-Equal-To 10{sup 8}-10{sup 10}M{sub o-dot} clumps. We present the largest sample to date of high-resolution cosmological smoothed particle hydrodynamics simulations that zoom-in on the formation of individual M{sub *} Almost-Equal-To 10{sup 10.5}M{sub o-dot} galaxies in Almost-Equal-To 10{sup 12}M{sub o-dot} halos at z Almost-Equal-To 2. Our code includes strong stellar feedback parameterized as momentum-driven galactic winds. This model reproduces many characteristic features of this observed class of galaxies, such as their clumpy morphologies, smooth and monotonic velocity gradients, high gas fractions (f{sub g} Almost-Equal-To 50%), and high specific star formation rates ({approx}>1 Gyr{sup -1}). In accord with recent models, giant clumps (M{sub clump} Almost-Equal-To (5 Multiplication-Sign 10{sup 8}-10{sup 9})M{sub o-dot}) form in situ via gravitational instabilities. However, the galactic winds are critical for their subsequent evolution. The giant clumps we obtain are short-lived and are disrupted by wind-driven mass loss. They do not virialize or migrate to the galaxy centers as suggested in recent work neglecting strong winds. By phenomenologically implementing the winds that are observed from high-redshift galaxies and in particular from individual clumps, our simulations reproduce well new observational constraints on clump kinematics and clump ages. In particular, the observation that older clumps appear closer to their galaxy centers is reproduced in our simulations, as a result of inside-out formation of the disks rather than inward clump migration.

  12. Quantifying Faculty Workloads.

    ERIC Educational Resources Information Center

    Archer, J. Andrew

    Teaching load depends on many variables, however most colleges define it strictly in terms of contact or credit hours. The failure to give weight to variables such as number of preparations, number of students served, committee and other noninstructional assignments is usually due to the lack of a formula that will quantify the effects of these…

  13. Catalysis: Quantifying charge transfer

    NASA Astrophysics Data System (ADS)

    James, Trevor E.; Campbell, Charles T.

    2016-02-01

    Improving the design of catalytic materials for clean energy production requires a better understanding of their electronic properties, which remains experimentally challenging. Researchers now quantify the number of electrons transferred from metal nanoparticles to an oxide support as a function of particle size.

  14. Dust and Smoke

    Atmospheric Science Data Center

    2014-05-15

    ... dust, the most common non-spherical aerosol type, from pollution and forest fire particles. Determining aerosol characteristics is a ... aerosol is quite thick, and in some places, the dust over water is too optically thick for MISR to retrieve the aerosol amount. For the ...

  15. Combustible dust tests

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The sugar dust explosion in Georgia on February 7, 2008 killed 14 workers and injured many others (OSHA, 2009). As a consequence of this explosion, OSHA revised its Combustible Dust National Emphasis (NEP) program. The NEP targets 64 industries with more than 1,000 inspections and has found more tha...

  16. Space dust in Paris

    NASA Astrophysics Data System (ADS)

    2017-02-01

    Next time you take a stroll in Paris, Oslo or Berlin, you might be breathing in big particles of cosmic dust after a study led by earth scientist Matthew Genge from Imperial College London found tiny specks of space dust on the rooftops of the three European capitals.

  17. Dust resuspension without saltation

    PubMed Central

    Loosmore, Gwen A.; Hunt, James R.

    2010-01-01

    Wind resuspension (or entrainment) provides a source of dust and contaminants for the atmosphere. Conventional wind erosion models parameterize dust resuspension flux with a threshold velocity or with a horizontal abrasion flux; in the absence of abrasion the models assume dust flux is transient only. Our experiments with an uncrusted, fine material at relative humidities exceeding 40% show a long-term steady dust flux in the absence of abrasion, which fits the approximate form: Fd = 3.6(u*)3, where Fd is the dust flux (in μg/m2 s), and u* is the friction velocity (in m/s). These fluxes are generally too small to be significant sources of dust in most models of dust emission. However, they provide a potential route to transport contaminants into the atmosphere. In addition, dust release is substantial during the initial transient phase. Comparison with field data suggests that the particle friction Reynolds number may prove a better parameter than u* for correlating fluxes and understanding the potential for abrasion. PMID:20336175

  18. Dust in supernova remnants

    NASA Astrophysics Data System (ADS)

    Gomez, H.

    In this Review, I will discuss our changing view on supernovae as interstellar dust sources. In particular I will focus on infrared and submillimetre studies of the historical supernova remnants Cassiopeia A, the Crab Nebula, SN 1987A, Tycho and Kepler. In the last decade (and particularly in recent years), SCUBA, Herschel and ALMA have now demonstrated that core-collapse supernovae are prolific dust factories, with evidence of 0.1 - 0.7 M⊙ of dust formed in the ejecta, though there is little evidence (as yet) for significant dust production in Type Ia supernova ejecta. There is no longer any question that dust (and molecule) formation is efficient after some supernova events, though it is not clear how much of this will survive over longer timescales. Current and future instruments will allow us to investigate the spatial distribution of dust within corecollapse ejecta, and whether this component contributes a significant amount to the dust content of the Universe or if supernovae ultimately provide a net loss once dust destruction by shocks is taken into account.

  19. Supernova Dust Factories

    NASA Astrophysics Data System (ADS)

    Gomez, Haley; Consortium, MESS; LCOGT

    2013-01-01

    The origin of interstellar dust in galaxies is poorly understood, particularly the relative contribution from supernovae. We present infrared and submillimeter photometry and spectroscopy from the Herschel Space Observatory of the Galactic remnants Tycho, Kepler and the Crab Nebula, taken as part of the Mass Loss from Evolved StarS program (MESS). Although we detect small amounts of dust surrounding Tycho and Kepler (the remnants of Type Ia supernovae), we show this is due to swept-up interstellar and circumstellar material respectively. The lack of dust grains in the ejecta suggests that Type Ia remnants do not produce substantial quantities of iron-rich dust grains and has important consequences for the ‘missing’ iron mass observed in ejecta. After carefully subtracting the synchrotron and line emission from the Crab, the remaining far-infrared continuum originates from 0.1-0.2 solar masses of dust. These observations suggest that the Crab Nebula has condensed most of the relevant refractory elements into dust and that these grains appear well set to survive their journey into the interstellar medium. In summary, our Herschel observations show that significantly less dust forms in the ejecta of Type Ia supernovae than in the remnants of core-collapse explosions, placing stringent constraints on the environments in which dust and molecules can form.

  20. Talc dust pneumoconiosis.

    PubMed

    Berner, A; Gylseth, B; Levy, F

    1981-01-01

    Various types of mineral dust can induce interstitial pulmonary fibrosis, but there is no definite correlation between lung X-ray findings, tissue lesions and the type of dust. In this paper, we report on the post mortem verification of talcosis by lung tissue analysis, using light microscopy, scanning electron microscopy, energy dispersive x-ray microanalysis and x-ray diffractometry.

  1. Laboratory and Natural Constraints on the Temperature Limit for Preservation of the Dolomite Clumped Isotope Thermometer

    NASA Astrophysics Data System (ADS)

    Lloyd, M. K.; Eiler, J. M.

    2014-12-01

    Kinetic barriers generally inhibit intercrystalline equilibration of cations and isotopic compositions at temperatures below ~350˚C, greatly limiting the geothermometers available to study the upper 10-15 km of the crust. Calcite 'clumped' isotopes commonly appear to record homogeneous equilibrium during crystallization at surface temperatures, but kinetic models predict that reordering due to solid-state exchange among nearby carbonate groups modifies primary compositions at temperatures above ~115˚C on timescales of 10^6 - 10^8 years and fully re-equilibrates above 200˚C in most geological environments1. Slowly cooled dolomitic marbles commonly preserve apparent temperatures of ~300˚C, indicating that dolomite may have slower reordering kinetics and thus greater preservation of primary crystallization temperatures. If so, dolomite clumped isotope thermometry may be a useful geothermometer in much of the the shallow crust. We measured the kinetics of clumped isotope reordering in dolomite with heating experiments at 400-800˚C in a TZM cold seal apparatus pressurized with CO2. Results predict that no detectable reordering occurs in dolomite held at temperatures less than ~250˚C over timescales of up to 10^8 years, demonstrating the viability of the system as a shallow crustal geothermometer. The non-first order behavior observed in calcite1,2,3is exhibited by dolomite as well, albeit at higher temperatures. To test these predictions, we measured the clumped isotopic compositions of coexisting calcite and dolomite in marbles from the Notch Peak aureole, UT. Dolomite clumped isotope temperatures in the outer aureole match peak conditions predicted by thermal models up to ~275˚C, indicating that the system resisted reordering below this grade. Calcite clumped isotope temperatures are never greater than ~150˚C at all grades in the aureole; this is consistent with the ambient burial temperature in the section and indicates that all metamorphic calcite was fully

  2. Pixel-based dust-extinction mapping in nearby galaxies: A new approach to lifting the veil of dust

    NASA Astrophysics Data System (ADS)

    Tamura, Kazuyuki

    In the first part of this dissertation, I explore a new approach to mapping dust extinction in galaxies, using the observed and estimated dust-free flux- ratios of optical V -band and mid-IR 3.6 micro-meter emission. Inferred missing V -band flux is then converted into an estimate of dust extinction. While dust features are not clearly evident in the observed ground-based images of NGC 0959, the target of my pilot study, the dust-map created with this method clearly traces the distribution of dust seen in higher resolution Hubble images. Stellar populations are then analyzed through various pixel Color- Magnitude Diagrams and pixel Color-Color Diagrams (pCCDs), both before and after extinction correction. The ( B - 3.6 microns) versus (far-UV - U ) pCCD proves particularly powerful to distinguish pixels that are dominated by different types of or mixtures of stellar populations. Mapping these pixel- groups onto a pixel-coordinate map shows that they are not distributed randomly, but follow genuine galactic structures, such as a previously unrecognized bar. I show that selecting pixel-groups is not meaningful when using uncorrected colors, and that pixel-based extinction correction is crucial to reveal the true spatial variations in stellar populations. This method is then applied to a sample of late-type galaxies to study the distribution of dust and stellar population as a function of their morphological type and absolute magnitude. In each galaxy, I find that dust extinction is not simply decreasing radially, but that is concentrated in localized clumps throughout a galaxy. I also find some cases where star-formation regions are not associated with dust. In the second part, I describe the application of astronomical image analysis tools for medical purposes. In particular, Source Extractor is used to detect nerve fibers in the basement membrane images of human skin-biopsies of obese subjects. While more development and testing is necessary for this kind of work

  3. Dust evolution from comets

    NASA Technical Reports Server (NTRS)

    Sekanina, Z.

    1977-01-01

    The studies of the evolution of cometary debris are reviewed. The subject is divided into three major sections: (1) the developments in the immediate vicinity of the cometary nucleus, which is the source of the dust; (2) the formation of the dust tail; and (3) the blending of the debris with the dust component of interplanetary matter. The importance of the physical theory of comets is emphasized for the understanding of the early phase of the evolution of cometary dust. A physico-dynamical model designed to analyze the particle-emission mechanism from the distribution of light in the dust tails is described and the results are presented. Increased attention is paid to large particles because of their importance for the evolution of the zodiacal cloud. Finally, implications are discussed for the future in situ investigations of comets.

  4. Dust escape from Io

    NASA Astrophysics Data System (ADS)

    Flandes, Alberto

    2004-08-01

    The Dust ballerina skirt is a set of well defined streams composed of nanometric sized dust particles that escape from the Jovian system and may be accelerated up to >=200 km/s. The source of this dust is Jupiter's moon Io, the most volcanically active body in the Solar system. The escape of dust grains from Jupiter requires first the escape of these grains from Io. This work is basically devoted to explain this escape given that the driving of dust particles to great heights and later injection into the ionosphere of Io may give the particles an equilibrium potential that allow the magnetic field to accelerate them away from Io. The grain sizes obtained through this study match very well to the values required for the particles to escape from the Jovian system.

  5. Lunar Dust Mitigation Screens

    NASA Astrophysics Data System (ADS)

    Knutson, Shawn; Holloway, Nancy

    With plans for the United States to return to the moon, and establish a sustainable human presence on the lunar surface many issues must be successfully overcome. Lunar dust is one of a number of issues with the potential to create a myriad of problems if not adequately addressed. Samples of dust brought back from Apollo missions show it to be soft, yet sharp and abrasive. The dust consists of a variety of morphologies including spherical, angular blocks, shards, and a number of irregular shapes. One of the main issues with lunar dust is its attraction to stick to anything it comes in contact with (i.e. astronauts, equipment, habitats, etc.). Ionized radiation from the sun strikes the moon's surface and creates an electrostatic charge on the dust. Further, the dust harbors van der Waals forces making it especially difficult to separate once it sticks to a surface. During the Apollo missions, it was discovered that trying to brush the lunar dust from spacesuits was not effective, and rubbing it caused degradation of the suit material. Further, when entering the lunar module after moonwalks, the astronauts noted that the dust was so prolific inside the cabin that they inhaled and ingested it, causing at least one of them, Harrison "Jack" Schmidt, to report irritation of the throat and lungs. It is speculated that the dust could also harm an astronaut's nervous and cardiovascular systems, especially during an extended stay. In addition to health issues, the dust can also cause problems by scouring reflective coatings off of thermal blankets, and roughening surfaces of windows and optics. Further, panels on solar cells and photovoltaics can also be compromised due to dust sticking on the surfaces. Lunar dust has the capacity to penetrate seals, interfere with connectors, as well as mechanisms on digging machines, all of which can lead to problems and failure. To address lunar dust issues, development of electrostatic screens to mitigate dust on sur-faces is currently

  6. A COMPACT CONCENTRATION OF LARGE GRAINS IN THE HD 142527 PROTOPLANETARY DUST TRAP

    SciTech Connect

    Casassus, Simon; Marino, Sebastian; Pérez, Sebastian; Christiaens, Valentin; Plas, Gerrit van der; Wright, Chris M.; Maddison, Sarah T.; Wootten, Al; Roman, Pablo; Moral, Victor; Pinilla, Paola; Wyatt, Mark; Ménard, Francois

    2015-10-20

    A pathway to the formation of planetesimals, and eventually giant planets, may occur in concentrations of dust grains trapped in pressure maxima. Dramatic crescent-shaped dust concentrations have been seen in recent radio images at submillimeter wavelengths. These disk asymmetries could represent the initial phases of planet formation in the dust trap scenario, provided that grain sizes are spatially segregated. A testable prediction of azimuthal dust trapping is that progressively larger grains should be more sharply confined and should follow a distribution that is markedly different from the gas. However, gas tracers such as {sup 12}CO and the infrared emission from small grains are both very optically thick where the submillimeter continuum originates, so previous observations have been unable to test the trapping predictions or to identify compact concentrations of larger grains required for planet formation by core accretion. Here we report multifrequency observations of HD 142527, from 34 to 700 GHz, that reveal a compact concentration of grains approaching centimeter sizes, with a few Earth masses, embedded in a large-scale crescent of smaller, submillimeter-sized particles. The emission peaks at wavelengths shorter than ∼1 mm are optically thick and trace the temperature structure resulting from shadows cast by the inner regions. Given this temperature structure, we infer that the largest dust grains are concentrated in the 34 GHz clump. We conclude that dust trapping is efficient enough for grains observable at centimeter wavelengths to lead to compact concentrations.

  7. A Compact Concentration of Large Grains in the HD 142527 Protoplanetary Dust Trap

    NASA Astrophysics Data System (ADS)

    Casassus, Simon; Wright, Chris M.; Marino, Sebastian; Maddison, Sarah T.; Wootten, Al; Roman, Pablo; Pérez, Sebastian; Pinilla, Paola; Wyatt, Mark; Moral, Victor; Ménard, Francois; Christiaens, Valentin; Cieza, Lucas; van der Plas, Gerrit

    2015-10-01

    A pathway to the formation of planetesimals, and eventually giant planets, may occur in concentrations of dust grains trapped in pressure maxima. Dramatic crescent-shaped dust concentrations have been seen in recent radio images at submillimeter wavelengths. These disk asymmetries could represent the initial phases of planet formation in the dust trap scenario, provided that grain sizes are spatially segregated. A testable prediction of azimuthal dust trapping is that progressively larger grains should be more sharply confined and should follow a distribution that is markedly different from the gas. However, gas tracers such as 12CO and the infrared emission from small grains are both very optically thick where the submillimeter continuum originates, so previous observations have been unable to test the trapping predictions or to identify compact concentrations of larger grains required for planet formation by core accretion. Here we report multifrequency observations of HD 142527, from 34 to 700 GHz, that reveal a compact concentration of grains approaching centimeter sizes, with a few Earth masses, embedded in a large-scale crescent of smaller, submillimeter-sized particles. The emission peaks at wavelengths shorter than ∼1 mm are optically thick and trace the temperature structure resulting from shadows cast by the inner regions. Given this temperature structure, we infer that the largest dust grains are concentrated in the 34 GHz clump. We conclude that dust trapping is efficient enough for grains observable at centimeter wavelengths to lead to compact concentrations.

  8. Pathways of high-latitude dust in the North Atlantic

    NASA Astrophysics Data System (ADS)

    Baddock, Matthew C.; Mockford, Tom; Bullard, Joanna E.; Thorsteinsson, Throstur

    2017-02-01

    The contribution of mineral dust from high-latitude sources has remained an under-examined feature of the global dust cycle. Dust events originating at high latitudes can provide inputs of aeolian sediment to regions lying well outside the subtropical dust belt. Constraining the seasonal variability and preferential pathways of dust from high-latitude sources is important for understanding the potential impacts that the dust may have on wider environmental systems, such as nearby marine or cryospheric domains. This study quantifies dust pathways from two areas exhibiting different emission dynamics in the north and south of Iceland, which is a prominent Northern Hemisphere dust source. The analysis uses air parcel trajectory modelling, and for the first time for high-latitude sources, explicitly links all trajectory simulations to time-specific (meteorological) observations of suspended dust. This approach maximises the potential for trajectories to represent dust, and illustrates that trajectory climatologies not limited to dust can grossly overestimate the potential for dust transport. Preferential pathways emerge that demonstrate the role of Iceland in supplying dust to the Northern Atlantic and sub-Arctic oceans. For dust emitted from northern sources, a dominant route exists to the northeast, into the Norwegian, Greenland and Barents Seas, although there is also potential for delivery to the North Atlantic in summer months. From the southern sources, the primary pathway extends into the North Atlantic, with a high density of trajectories extending as far south as 50°N, particularly in spring and summer. Common to both southern and northern sources is a pathway to the west-southwest of Iceland into the Denmark Strait and towards Greenland. For trajectories simulated at ≤500 m, the vertical development of dust plumes from Iceland is limited, likely due to the stable air masses of the region suppressing the potential for vertical motion. Trajectories rarely

  9. On the morphology of dust lanes in galactic bars

    NASA Astrophysics Data System (ADS)

    Sánchez-Menguiano, L.; Pérez, I.; Zurita, A.; Martínez-Valpuesta, I.; Aguerri, J. A. L.; Sánchez, S. F.; Comerón, S.; Díaz-García, S.

    2015-07-01

    The aim of our study is to use dynamical simulations to explore the influence of two important dynamical bar parameters, bar strength and bar pattern speed on the shape of the bar dust lanes. To quantify the shape of the dust lanes we have developed a new systematic method to measure the dust lane curvature. Previous numerical simulations have compared the curvature of bar dust lanes with the bar strength, predicting a relation between both parameters which has been supported by observational studies but with a large spread. We take into account the bar pattern speed to explore, simultaneously, the effect of both parameters on the dust lane shape. To that end, we separate our galactic bars in fast bars (1 < {R} < 1.4 ) and slow bars ({R} > 1.4 ), obtaining, as previous simulations, an inverse relation between the dust lane curvature and the bar strength for fast bars. For the first time, we extend the study to slow bars, finding a constant curvature as a function of the bar strength. As a result, we conclude that weak bars with straight dust lanes are candidates for slow bars. Finally, we have analysed a pilot sample of 10 S4G galaxies, obtaining dust lane curvatures lying within the range covered by the simulations.

  10. Methane seep carbonates yield clumped isotope signatures out of equilibrium with formation temperatures

    PubMed Central

    Loyd, S. J.; Sample, J.; Tripati, R. E.; Defliese, W. F.; Brooks, K.; Hovland, M.; Torres, M.; Marlow, J.; Hancock, L. G.; Martin, R.; Lyons, T.; Tripati, A. E.

    2016-01-01

    Methane cold seep systems typically exhibit extensive buildups of authigenic carbonate minerals, resulting from local increases in alkalinity driven by methane oxidation. Here, we demonstrate that modern seep authigenic carbonates exhibit anomalously low clumped isotope values (Δ47), as much as ∼0.2‰ lower than expected values. In modern seeps, this range of disequilibrium translates into apparent temperatures that are always warmer than ambient temperatures, by up to 50 °C. We examine various mechanisms that may induce disequilibrium behaviour in modern seep carbonates, and suggest that the observed values result from several factors including kinetic isotopic effects during methane oxidation, mixing of inorganic carbon pools, pH effects and rapid precipitation. Ancient seep carbonates studied here also exhibit potential disequilibrium signals. Ultimately, these findings indicate the predominance of disequilibrium clumped isotope behaviour in modern cold seep carbonates that must be considered when characterizing environmental conditions in both modern and ancient cold seep settings. PMID:27447820

  11. Methane seep carbonates yield clumped isotope signatures out of equilibrium with formation temperatures.

    PubMed

    Loyd, S J; Sample, J; Tripati, R E; Defliese, W F; Brooks, K; Hovland, M; Torres, M; Marlow, J; Hancock, L G; Martin, R; Lyons, T; Tripati, A E

    2016-07-22

    Methane cold seep systems typically exhibit extensive buildups of authigenic carbonate minerals, resulting from local increases in alkalinity driven by methane oxidation. Here, we demonstrate that modern seep authigenic carbonates exhibit anomalously low clumped isotope values (Δ47), as much as ∼0.2‰ lower than expected values. In modern seeps, this range of disequilibrium translates into apparent temperatures that are always warmer than ambient temperatures, by up to 50 °C. We examine various mechanisms that may induce disequilibrium behaviour in modern seep carbonates, and suggest that the observed values result from several factors including kinetic isotopic effects during methane oxidation, mixing of inorganic carbon pools, pH effects and rapid precipitation. Ancient seep carbonates studied here also exhibit potential disequilibrium signals. Ultimately, these findings indicate the predominance of disequilibrium clumped isotope behaviour in modern cold seep carbonates that must be considered when characterizing environmental conditions in both modern and ancient cold seep settings.

  12. Methane seep carbonates yield clumped isotope signatures out of equilibrium with formation temperatures

    NASA Astrophysics Data System (ADS)

    Loyd, S. J.; Sample, J.; Tripati, R. E.; Defliese, W. F.; Brooks, K.; Hovland, M.; Torres, M.; Marlow, J.; Hancock, L. G.; Martin, R.; Lyons, T.; Tripati, A. E.

    2016-07-01

    Methane cold seep systems typically exhibit extensive buildups of authigenic carbonate minerals, resulting from local increases in alkalinity driven by methane oxidation. Here, we demonstrate that modern seep authigenic carbonates exhibit anomalously low clumped isotope values (Δ47), as much as ~0.2‰ lower than expected values. In modern seeps, this range of disequilibrium translates into apparent temperatures that are always warmer than ambient temperatures, by up to 50 °C. We examine various mechanisms that may induce disequilibrium behaviour in modern seep carbonates, and suggest that the observed values result from several factors including kinetic isotopic effects during methane oxidation, mixing of inorganic carbon pools, pH effects and rapid precipitation. Ancient seep carbonates studied here also exhibit potential disequilibrium signals. Ultimately, these findings indicate the predominance of disequilibrium clumped isotope behaviour in modern cold seep carbonates that must be considered when characterizing environmental conditions in both modern and ancient cold seep settings.

  13. Using red clump stars to correct the Gaia DR1 parallaxes

    NASA Astrophysics Data System (ADS)

    Davies, Guy R.; Lund, Mikkel N.; Miglio, Andrea; Elsworth, Yvonne; Kuszlewicz, James S.; North, Thomas S. H.; Rendle, Ben; Chaplin, William J.; Rodrigues, Thaíse S.; Campante, Tiago L.; Girardi, Léo; Hale, Steven J.; Hall, Oliver; Jones, Caitlin D.; Kawaler, Steven D.; Roxburgh, Ian; Schofield, Mathew

    2017-01-01

    Recent results have suggested that there is tension between the Gaia DR1 TGAS distances and the distances obtained using luminosities determined by eclipsing binaries or asteroseismology on red giant stars. We use the Ks-band luminosities of red clump stars, identified and characterized by asteroseismology, to make independent distance estimates. Our results suggest that Gaia TGAS distances contain a systematic error that decreases with increasing distance. We propose a correction to mitigate this offset as a function of parallax that is valid for the Kepler field and values of parallax that are less than 1.6 mas. For parallaxes greater than this, we find agreement with previously published values. We note that the TGAS distances to the red clump stars of the open cluster M67 show a high level of disagreement that is difficult to correct for.

  14. Dense Molecular Clumps Associated with the LMC Supergiant Shell LMC 4 & LMC 5

    NASA Astrophysics Data System (ADS)

    Fujii, K.; Minamidani, T.; Mizuno, N.; Onishi, T.; Kawamura, A.; Muller, E.; Dawson, J.; Fukui, Y.

    2015-12-01

    The 12CO(J=3-2/1-0) and 13CO(J=3-2/1-0) observations with ASTE and Mopra telescopes have been carried out toward the giant molecular clouds (GMCs) in the N48/N49 regions in the Large Magellanic Cloud (LMC), which are located at the boundary of two kpc-scale Supergiant Shell (SGS) LMC 4 & LMC 5. The star formation is relatively evolved in the N48 region, which is just located at the boundary of SGSs, than in the N49 region. The clumps in the N48 show higher n(H2) and Tkin than those in the N49, but their densities are not so high as the LMC cluster forming clumps. The collision of two SGSs actually enhances the star formation but further evolution seem to be necessary for subsequent cluster formation.

  15. Molecular Gas Clumps from the Destruction of Icy Bodies in the beta Pictoris Debris Disk

    NASA Technical Reports Server (NTRS)

    Dent, W. R. F.; Wyatt, M. C.; Roberge, A.; Augereau, J. -C.; Casassus, S.; Corder, S.; Greaves, J. S.; DeGregorio-Monsalvo, I.; Hales, A.; Jackson, A. P.; Hughes, A. Meredith; Lagrange, A. -M.; Matthews, B.; Wilner, D.

    2014-01-01

    Many stars are surrounded by disks of dusty debris formed in the collisions of asteroids, comets and dwarf planets. But is gas also released in such events? Observations at sub-mm wavelengths of the archetypal debris disk around ß Pictoris show that 0.3% of a Moon mass of carbon monoxide orbits in its debris belt. The gas distribution is highly asymmetric, with 30% found in a single clump 85 AU from the star, in a plane closely aligned with the orbit of the inner planet, beta Pic b. This gas clump delineates a region of enhanced collisions, either from a mean motion resonance with an unseen giant planet, or from the remnants of a collision of Mars-mass planets.

  16. THE EDGE OF THE MILKY WAY STELLAR DISK REVEALED USING CLUMP GIANT STARS AS DISTANCE INDICATORS

    SciTech Connect

    Minniti, D.; Saito, R. K.; Alonso-Garcia, J.; Hempel, M.; Lucas, P. W.

    2011-06-01

    We use the clump giants of the disk as standard candles calibrated from Hipparcos parallaxes in order to map their distribution with two new near-infrared surveys of the Galactic plane: UKIDSS-GPS and VISTA Variables in the VIa Lactea (VVV). We explore different selection cuts of clump giants. We conclude that there is an edge of the stellar disk of the Milky Way at R = 13.9 {+-} 0.5 kpc along various lines of sight across the Galaxy. The effect of the warp is considered, taking fields at different longitudes and above and below the plane. We demonstrate that the edge of the stellar disk of the Milky Way can now be mapped in the near-infrared in order to test different models, and to establish our own place within the Galaxy.

  17. Predator-prey interactions between blue crabs and ribbed mussels living in clumps

    NASA Astrophysics Data System (ADS)

    Lin, Junda

    1991-01-01

    Predator-prey interactions between blue crabs ( Callinectes sapidus) and ribbed mussels ( Geukensia demissa) were studied by manipulating different components of mussel clump structure in the laboratory to test their effects on the mussels' susceptibility to crab predation. Mussels with stronger attachment strength or those buried deeper in the sediment suffered lower mortality. Blue crabs showed no significant size selectivity when two size classes of mussles (30-40 and 50-60 mm in shell heights) were offered. When juvenile mussels were attached to adult conspecifics and completely buried in the centres of clumps as in the field, blue crabs did not actively search for them. The crabs, however, did consume juveniles as by-products when they preyed upon the adult mussels to which the juveniles were attached.

  18. Quantifying Ubiquitin Signaling

    PubMed Central

    Ordureau, Alban; Münch, Christian; Harper, J. Wade

    2015-01-01

    Ubiquitin (UB)-driven signaling systems permeate biology, and are often integrated with other types of post-translational modifications (PTMs), most notably phosphorylation. Flux through such pathways is typically dictated by the fractional stoichiometry of distinct regulatory modifications and protein assemblies as well as the spatial organization of pathway components. Yet, we rarely understand the dynamics and stoichiometry of rate-limiting intermediates along a reaction trajectory. Here, we review how quantitative proteomic tools and enrichment strategies are being used to quantify UB-dependent signaling systems, and to integrate UB signaling with regulatory phosphorylation events. A key regulatory feature of ubiquitylation is that the identity of UB chain linkage types can control downstream processes. We also describe how proteomic and enzymological tools can be used to identify and quantify UB chain synthesis and linkage preferences. The emergence of sophisticated quantitative proteomic approaches will set a new standard for elucidating biochemical mechanisms of UB-driven signaling systems. PMID:26000850

  19. How to quantify ripple

    NASA Astrophysics Data System (ADS)

    Geib, H.; Kuehne, C.; Morgenbrod, E.

    In the present attempt to render the small area errors in large telescope mirror manufacture, known as 'ripple', numerically quantifiable, two-dimensional regularity is omitted, yielding greater clarity and comparability of results. In the measurement of the interference fringe, the central fringe is photometered in equidistant steps. Application of Fourier analysis to the average value obtained is followed by a power spectrum calculation. The test method is evaluated through the numerical examination of a ripple structure of known size and period length.

  20. Quantification of Spore-forming Bacteria Carried by Dust Particles

    NASA Technical Reports Server (NTRS)

    Lin, Ying; Cholakian, Tanya; Gao, Wenming; Osman, Shariff; Barengoltz, Jack

    2006-01-01

    In order to establish a biological contamination transport model for predicting the cross contamination risk during spacecraft assembly and upon landing on Mars, it is important to understand the relationship between spore-forming bacteria and their carrier particles. We conducted air and surface sampling in indoor, outdoor, and cleanroom environments to determine the ratio of spore forming bacteria to their dust particle carriers of different sizes. The number of spore forming bacteria was determined from various size groups of particles in a given environment. Our data also confirms the existence of multiple spores on a single particle and spore clumps. This study will help in developing a better bio-contamination transport model, which in turn will help in determining forward contamination risks for future missions.

  1. VizieR Online Data Catalog: Planck Catalogue of Galactic cold clumps (PGCC) (Planck+, 2016)

    NASA Astrophysics Data System (ADS)

    Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartolo, N.; Battaner, E.; Benabed, K.; Benoit, A.; Benoit-Levy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Catalano, A.; Chamballu, A.; Chiang, H. C.; Christensen, P. R.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Combet, C.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; De Rosa, A.; de Zotti, G.; Delabrouille, J.; Desert, F.-X.; Dickinson, C.; Diego, J. M.; Dole, H.; Donzelli, S.; Dore, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Ensslin, T. A.; Eriksen, H. K.; Falgarone, E.; Fergusson, J.; Fergusson, J.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Giard, M.; Giraud-Heraud, Y.; Gjerlow, E.; Gonzalez-Nuevo, J.; Gorsk, I. K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Hansen, F. K.; Hanson, D.; Harrison, D. L.; Helou, G.; Henrot-Versille, S.; Hernandez-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihanen, E.; Keskitalo, R.; Kisner, T. S.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leonardi, R.; Lesgourgues, J.; Levrier, F.; Liguori, M.; Lilje, P. B.; Linden-Vornle, M.; Lopez-Caniego, M.; Lubin, P. M.; Macias-Perez, J. F.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Marshall, D. J.; Martin, P. G.; Martinez-Gonzalez, E.; Masi, S.; Matarrese, S.; Mazzotta, P.; McGehee, P.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschenes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Norgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Pasian, F.; Patanchon, G.; Pearson, T. J.; Pelkonen, V.-M.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Pratt, G. W.; Prezeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rubino-Martin, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Spencer, L. D.; Stolyarov, V.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Umana, G.; Valenziano, L.; Valiviita, J.; van Tent, B.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; Yvon, D.; Zacchei, A.; Zonca, A.

    2017-01-01

    The Planck Catalogue of Galactic Cold Clumps (PGCC) is a list of 13188 Galactic sources and 54 sources located in the Small and Large Magellanic Clouds. The sources have been identified in Planck data as sources colder than their environment. It has been built using the 48 months Planck data at 857, 545, and 353GHz combined with the 3THz IRAS data. (1 data file).

  2. Star Cluster Formation from Turbulent Clumps. I. The Fast Formation Limit

    NASA Astrophysics Data System (ADS)

    Farias, Juan P.; Tan, Jonathan C.; Chatterjee, Sourav

    2017-04-01

    We investigate the formation and early evolution of star clusters, assuming that they form from a turbulent starless clump of a given mass bounded inside a parent self-gravitating molecular cloud characterized by a particular mass surface density. As a first step, we assume instantaneous star cluster formation and gas expulsion. We draw our initial conditions from observed properties of starless clumps. We follow the early evolution of the clusters up to 20 Myr, investigating the effects of different star formation efficiencies, primordial binary fractions and eccentricities, and primordial mass segregation levels. We investigate clumps with initial masses of {M}{cl}=3000 {M}ȯ embedded in ambient cloud environments with mass surface densities {{{Σ }}}{cloud}=0.1 and 1 {{g}} {{cm}}-2. We show that these models of fast star cluster formation result, in the fiducial case, in clusters that expand rapidly, even considering only the bound members. Clusters formed from higher {{{Σ }}}{cloud} environments tend to expand more quickly and thus are soon larger than clusters born from lower {{{Σ }}}{cloud} conditions. To form a young cluster of a given age, stellar mass, and mass surface density, these models need to assume a parent molecular clump that is many times denser, which is unrealistic compared to observed systems. We also show that, in these models, the initial binary properties are only slightly modified by interactions, meaning that the binary properties, e.g., at 20 Myr, are very similar to those at birth. With this study, we set up the foundation for future work, where we will investigate more realistic models of star formation compared to this instantaneous, baseline case.

  3. Filamentary flow and magnetic geometry in evolving cluster-forming molecular cloud clumps

    NASA Astrophysics Data System (ADS)

    Klassen, Mikhail; Pudritz, Ralph E.; Kirk, Helen

    2017-02-01

    We present an analysis of the relationship between the orientation of magnetic fields and filaments that form in 3D magnetohydrodynamic simulations of cluster-forming, turbulent molecular cloud clumps. We examine simulated cloud clumps with size scales of L ∼ 2-4 pc and densities of n ∼ 400-1000 cm-3 with Alfvén Mach numbers near unity. We simulated two cloud clumps of different masses, one in virial equilibrium, the other strongly gravitationally bound, but with the same initial turbulent velocity field and similar mass-to-flux ratio. We apply various techniques to analyse the filamentary and magnetic structure of the resulting cloud, including the DISPERSE filament-finding algorithm in 3D. The largest structure that forms is a 1-2 parsec-long filament, with smaller connecting sub-filaments. We find that our simulated clouds, wherein magnetic forces and turbulence are comparable, coherent orientation of the magnetic field depends on the virial parameter. Sub-virial clumps undergo strong gravitational collapse and magnetic field lines are dragged with the accretion flow. We see evidence of filament-aligned flow and accretion flow on to the filament in the sub-virial cloud. Magnetic fields oriented more parallel in the sub-virial cloud and more perpendicular in the denser, marginally bound cloud. Radiative feedback from a 16 M⊙ star forming in a cluster in one of our simulation's ultimately results in the destruction of the main filament, the formation of an H II region, and the sweeping up of magnetic fields within an expanding shell at the edges of the H II region.

  4. Microlensing Optical Depth towards the Galactic Bulge Using Clump Giants from the MACHO Survey

    SciTech Connect

    Popowski, P; Griest, K; Thomas, C L; Cook, K H; Bennett, D P; Becker, A C; Alves, D R; Minniti, D; Drake, A J; Alcock, C; Allsman, R A; Axelrod, T S; Freeman, K C; Geha, M; Lehner, M J; Marshall, S L; Nelson, C A; Peterson, B A; Quinn, P J; Stubbs, C W; Sutherland, W; Vandehei, T; Welch, D

    2005-07-14

    Using 7 years of MACHO survey data, we present a new determination of the optical depth to microlensing towards the Galactic bulge. We select the sample of 62 microlensing events (60 unique) on clump giant sources and perform a detailed efficiency analysis. We use only the clump giant sources because these are bright bulge stars and are not as strongly affected by blending as other events. Using a subsample of 42 clump events concentrated in an area of 4.5 deg{sup 2} with 739000 clump giant stars, we find {tau} = 2.17{sub -0.38}{sup +0.47} x 10{sup -6} at (l,b) = (1{sup o}.50, -2{sup o}.68), somewhat smaller than found in most previous MACHO studies, but in excellent agreement with recent theoretical predictions. We also present the optical depth in each of the 19 fields in which we detected events, and find limits on optical depth for fields with no events. The errors in optical depth in individual fields are dominated by Poisson noise. We measure optical depth gradients of (1.06 {+-} 0.71) x 10{sup -6}deg{sup -1} and (0.29 {+-} 0.43) x 10{sup -6}deg{sup -1} in the galactic latitude b and longitude l directions, respectively. Finally, we discuss the possibility of anomalous duration distribution of events in the field 104 centered on (l,b) = (3{sup o}.11, -3{sup o}.01) as well as investigate spatial clustering of events in all fields.

  5. Quantifying concordance in cosmology

    NASA Astrophysics Data System (ADS)

    Seehars, Sebastian; Grandis, Sebastian; Amara, Adam; Refregier, Alexandre

    2016-05-01

    Quantifying the concordance between different cosmological experiments is important for testing the validity of theoretical models and systematics in the observations. In earlier work, we thus proposed the Surprise, a concordance measure derived from the relative entropy between posterior distributions. We revisit the properties of the Surprise and describe how it provides a general, versatile, and robust measure for the agreement between data sets. We also compare it to other measures of concordance that have been proposed for cosmology. As an application, we extend our earlier analysis and use the Surprise to quantify the agreement between WMAP 9, Planck 13, and Planck 15 constraints on the Λ CDM model. Using a principle component analysis in parameter space, we find that the large Surprise between WMAP 9 and Planck 13 (S =17.6 bits, implying a deviation from consistency at 99.8% confidence) is due to a shift along a direction that is dominated by the amplitude of the power spectrum. The Planck 15 constraints deviate from the Planck 13 results (S =56.3 bits), primarily due to a shift in the same direction. The Surprise between WMAP and Planck consequently disappears when moving to Planck 15 (S =-5.1 bits). This means that, unlike Planck 13, Planck 15 is not in tension with WMAP 9. These results illustrate the advantages of the relative entropy and the Surprise for quantifying the disagreement between cosmological experiments and more generally as an information metric for cosmology.

  6. Dust Devil Dynamics

    NASA Astrophysics Data System (ADS)

    Horton, W.; Miura, H.

    2008-11-01

    A dust devil is a rotating updraft, with coherent structures ranging from small (H/D ˜ 5m/1m) to large (H/D ˜ 1000 m/10 m). Common in west Texas and Arizona, dust devils are formed unstable stratification of the air by solar heating over a sandy floor. Unstable gravity waves grow exponentially in the low density, hot air, rising into the upper layer of stably stratified atmosphere creating the large, 3D vortex. Dust devils are common on Mars. On Earth radio noise and electrical fields greater than 100kV/m are inferred [Kok J. F., N. O. Renno (2006), Geophys. Res. Lett., 33, L19S10]. Dust devils pick up small dirt and dust particles. The whirling charged dust particles (30 -50 microns) create a magnetic field that fluctuates between 3 and 30 times each second. The electric fields created assist the vortices in lifting materials off the ground and into the atmosphere. We use the theory and simulation tools of fusion plasma physics to describe dust devils. The Grad-Shafranov equation governs the vorticity dynamics and gives a solution for steady axisymmetric flows. The high core velocity is limited by the vortex model with viscous dissipation. The Reynolds number is not large, so these structures are well represented with super computers, in contrast to collisionless plasmas. 1mm Research supported by NIFS, Japan and the NSF through ATM-0638480 at UT Austin.

  7. Utilizing Pyrosequencing and Quantitative pCR to Characterize Fungal Populations among House Dust Samples

    EPA Science Inventory

    Molecular techniques are an alternative to culturing and counting methods in quantifying indoor fungal contamination. Pyrosequencing offers the possibility of identifying unexpected indoor fungi. In this study, 50 house dust samples were collected from homes in the Yakima Valley,...

  8. NOISE AND HYSTERESIS IN CHARGED STRIPE, CHECKERBOARD, AND CLUMP FORMING SYSTEMS

    SciTech Connect

    Reichhardt, Charles; Reichhardt, Cynthia J.; Bishop, Alan R.

    2007-05-07

    We numerically examine noise fluctuations and hysteresis phenomena in charged systems that form stripe, labyrinth or clump patterns. It is believed that charge inhomogeneities of this type arise in two-dimensional (2D) quantum hall systems and in electron crystal structures in high temperature superconductors, while related patterns appear in manganites and type-I superconductors. Recent noise and transport experiments in twodimensional electron gases and high temperature superconducting samples revealed both 1/ fα. noise signatures and hysteretic phenomena. Using numerical simulations we show that 1/ fα. noise fluctuations and hysteresis are generic features that occur in charge systems which undergo a type of phase separation that results in stripes, clumps, checkerboards, or other inhomogeneous patterns. We find that these systems exhibit 1/ fα. fluctuations with 1.2 < α < 1.8, rather than simple 1/ f or 1/ f 2 fluctuations. We also propose that the 2D metal insulator transition may be associated with a clump electron glass phase rather than a Wigner glass phase.

  9. Disc Dynamics In The Early Universe: Instabilities, Giant Clumps, Feedback & Outflows

    NASA Astrophysics Data System (ADS)

    Bournaud, Frédéric

    2016-10-01

    Star-forming galaxies at high redshift (z=1-3) have irregular, clumpy morphologies. These are best explained by a violent, ubiquitous gravitational instability in gas-rich disks, causing fragmentation in giant clumps and other irregular features. The instability can rapidly redistribute the baryons within galaxies, by inward migration of the giant clumps and other rapid inflows of mass. The promotes the growth of central bulges and other galactic components, and models predict that the resulting properties may finely match those observed in today's Milky Way-like spirals. The instability-driven inflow may also feed the central black hole in a moderate but steady mode and drive a high fraction of active galaxies, promoting earlier supermassive black hole growth. At the same time, intense stellar feedback in the giant gas-rich clumps and from the active nucleus drive intense gas outflows that regulate the galaxy mass to realistic levels, but the outflows are largely decoupled from the dense gas phases, which continue to form stars continuously. Hence the high-redshift progenitors of massive galaxies evolve in a steady unstable state lasting a couple of Gyr during which they build their fondamental structural components before evolving secularly into modern, quasi-stable spiral disks and spheroids.

  10. Radiation Pressure on Bacterial Clumps in the Solar Vicinity and Their Survival Between Interstellar Transits

    NASA Astrophysics Data System (ADS)

    Wickramasinghe, N. C.; Wickramasinghe, J. T.

    Radiation pressure cross-sections for clumps of hollow bacterial grains with thin coatings of graphite are calculated using rigorous Guttler formulae. The carbonized skins are expected to form through exposure to solar ultraviolet radiation, but a limiting thickness of about 0.03 μm is determined by opacity effects. The ratios of radiation pressure to gravity P/G are calculated for varying sizes of the clumps and for varying thickness of the graphite coatings. Bacterial clumps and individual desiccated bacteria without coatings of radii in the range 0.3-8 μm have P/G ratios less than unity, whereas particles with coatings of 0.02 μm thickness have ratios in excess of unity. Such coatings also provide protection from damaging ultraviolet radiation. Putative cometary bacteria, such as have been recently collected in the stratosphere, are thus not gravitationally bound in the solar system provided they possess carbonised exterior coatings. They are rapidly expelled from the solar system reaching nearby protosolar nebulae in timescales of a few million years. Even with the most pessimistic assumptions galactic cosmic rays are unable to diminish viability to an extent that vitiates the continuity of panspermia.

  11. The Origin of the Split Red Clump in the Galactic Bulge of the Milky Way

    NASA Astrophysics Data System (ADS)

    Ness, M.; Freeman, K.; Athanassoula, E.; Wylie-De-Boer, E.; Bland-Hawthorn, J.; Lewis, G. F.; Yong, D.; Asplund, M.; Lane, R. R.; Kiss, L. L.; Ibata, R.

    2012-09-01

    Near the minor axis of the Galactic bulge, at latitudes b < -5°, the red giant clump stars are split into two components along the line of sight. We investigate this split using the three fields from the ARGOS survey that lie on the minor axis at (l, b) = (0°, -5°), (0°, -7fdg5), (0°, -10°). The separation is evident for stars with [Fe/H] > - 0.5 in the two higher-latitude fields, but not in the field at b = -5°. Stars with [Fe/H] < - 0.5 do not show the split. We compare the spatial distribution and kinematics of the clump stars with predictions from an evolutionary N-body model of a bulge that grew from a disk via bar-related instabilities. The density distribution of the peanut-shaped model is depressed near its minor axis. This produces a bimodal distribution of stars along the line of sight through the bulge near its minor axis, very much as seen in our observations. The observed and modeled kinematics of the two groups of stars are also similar. We conclude that the split red clump of the bulge is probably a generic feature of boxy/peanut bulges that grew from disks, and that the disk from which the bulge grew had relatively few stars with [Fe/H] < - 0.5.

  12. Galactic cold cores. VI. Dust opacity spectral index

    NASA Astrophysics Data System (ADS)

    Juvela, M.; Demyk, K.; Doi, Y.; Hughes, A.; Lefèvre, C.; Marshall, D. J.; Meny, C.; Montillaud, J.; Pagani, L.; Paradis, D.; Ristorcelli, I.; Malinen, J.; Montier, L. A.; Paladini, R.; Pelkonen, V.-M.; Rivera-Ingraham, A.

    2015-12-01

    Context. The Galactic Cold Cores project has carried out Herschel photometric observations of 116 fields where the Planck survey has found signs of cold dust emission. The fields contain sources in different environments and different phases of star formation. Previous studies have revealed variations in their dust submillimetre opacity. Aims: The aim is to measure the value of dust opacity spectral index and to understand its variations spatially and with respect to other parameters, such as temperature, column density, and Galactic location. Methods: The dust opacity spectral index β and the dust colour temperature T are derived using Herschel and Planck data. The relation between β and T is examined for the whole sample and inside individual fields. Results: Based on IRAS and Planck data, the fields are characterised by a median colour temperature of 16.1 K and a median opacity spectral index of β = 1.84. The values are not correlated with Galactic longitude. We observe a clear T-β anti-correlation. In Herschel observations, constrained at lower resolution by Planck data, the variations follow the column density structure and βFIR can rise to ~2.2 in individual clumps. The highest values are found in starless clumps. The Planck 217 GHz band shows a systematic excess that is not restricted to cold clumps and is thus consistent with a general flattening of the dust emission spectrum at millimetre wavelengths. When fitted separately below and above 700 μm, the median spectral index values are βFIR ~ 1.91 and β(mm) ~ 1.66. Conclusions: The spectral index changes as a function of column density and wavelength. The comparison of different data sets and the examination of possible error sources show that our results are robust. However, β variations are partly masked by temperature gradients and the changes in the intrinsic grain properties may be even greater. Planck http://www.esa.int/Planck is a project of the European Space Agency - ESA - with instruments

  13. Dust Emissions from Undisturbed and Disturbed, Crusted Playa Surfaces: Cattle Trampling Effect

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dry playa lake beds can be a significant source of fine dust emissions during high wind events in arid and semiarid landscapes. The physical and chemical properties of the playa surface control the amount and properties of the dust emitted. In this study, we use a field wind tunnel to quantify the...

  14. Dust storms: recent developments.

    PubMed

    Goudie, Andrew S

    2009-01-01

    Dust storms have a number of impacts upon the environment including radiative forcing, and biogeochemical cycling. They transport material over many thousands of kilometres. They also have a range of impacts on humans, not least on human health. In recent years the identification of source areas for dust storms has been an important area or research, with the Sahara (especially Bodélé) and western China being recognised as the strongest sources globally. Another major development has been the recognition of the degree to which dust storm activity has varied at a range of time scales, millennial, century, decadal, annual and seasonal.

  15. Spirit Feels Dust Gust

    NASA Technical Reports Server (NTRS)

    2007-01-01

    On sol 1149 (March 28, 2007) of its mission, NASA's Mars Exploration Rover Spirit caught a wind gust with its navigation camera. A series of navigation camera images were strung together to create this movie. The front of the gust is observable because it was strong enough to lift up dust. From assessing the trajectory of this gust, the atmospheric science team concludes that it is possible that it passed over the rover. There was, however, no noticeable increase in power associated with this gust. In the past, dust devils and gusts have wiped the solar panels of dust, making it easier for the solar panels to absorb sunlight.

  16. A Galactic Molecular Cloud Clump Catalog from Hi-GAL Data: Method and Initial Results Comparison with BGPS

    NASA Astrophysics Data System (ADS)

    Zetterlund, Erika; Glenn, Jason; Rosolowsky, Erik

    2017-02-01

    As the precursors to stellar clusters, it is imperative that we understand the distribution and physical properties of dense molecular gas clouds and clumps. Such a study has been done with the ground-based Bolocam Galactic Plane Survey (BGPS). Now the Herschel infrared GALactic plane survey (Hi-GAL) allows us to do the same with higher-quality data and complete coverage of the Galactic plane. We have made a pilot study comparing dense molecular gas clumps identified in Hi-GAL and BGPS, using six 2° × 2° regions centered at Galactic longitudes of {\\ell }=11^\\circ , 30°, 41°, 50°, 202°, and 217°. We adopted the BGPS methodology for identifying clumps and estimating distances, leading to 6198 clumps being identified in our substudy, with 995 of those having well-constrained distances. These objects were evenly distributed with Galactic longitude, a consequence of Hi-GAL being source confusion limited. These clumps range in mass from 10‑2 to 105 M⊙ and have heliocentric distances of up to 16 kpc. When clumps found in both surveys are compared, we see that distances agree within 1 kpc and ratios of masses are of the order of unity. This serves as an external validation for BGPS and instills confidence as we move forward to cataloging the clumps from the entirety of Hi-GAL. In addition to the sources that were in common with BGPS, Hi-GAL found many additional sources, primarily due to the lack of atmospheric noise. We expect Hi-GAL to yield 2 × 105 clumps, with 20% having well-constrained distances, an order of magnitude above what was found in BGPS.

  17. Characterization, validation and intercomparison of clumping index maps from POLDER, MODIS, and MISR satellite data over reference sites

    NASA Astrophysics Data System (ADS)

    Pisek, Jan; He, Liming; Chen, Jing; Govind, Ajit; Sprintsin, Michael; Ryu, Youngryel; Arndt, Stefan; Hocking, Darren; Wardlaw, Timothy; Kuusk, Joel; Oliphant, Andrew; Korhonen, Lauri; Fang, Hongliang; Matteucci, Giorgio; Longdoz, Bernard; Raabe, Kairi

    2015-04-01

    Vegetation foliage clumping significantly alters its radiation environment and therefore affects vegetation growth as well as water and carbon cycles. The clumping index is useful in ecological and meteorological models because it provides new structural information in addition to the effective leaf area index (LAI) retrieved from mono-angle remote sensing and allows accurate separation of sunlit and shaded leaves in the canopy. Not accounting for the foliage clumping in LAI retrieval algorithms leads to substantial underestimation of actual LAI, especially for needleleaf forests. Normalized Difference between Hotspot and Darkspot (NDHD) index has been previously used to retrieve global clumping index maps from POLarization and Directionality of the Earth's Reflectances (POLDER) data at ~6 km resolution, from Moderate Resolution Imaging Spectroradiometer (MODIS) Bidirectional Reflectance Distribution Function (BRDF) product at 500 m resolution. Most recently the algorithm was applied with Multi-angle Imaging SpectroRadiometer (MISR) data at 275 m resolution over selected areas. In this presentation we characterize and intercompare the three products over a set of sites representing diverse biomes and different canopy structures. The products are also directly validated with both in-situ vertical profiles and seasonal trajectories of clumping index. We illustrate that the vertical distribution of foliage and especially the effect of understory needs to be taken into account while validating foliage clumping products from remote sensing products with values measured in the field. Satellite measurements respond to the structural effects near the top of canopies, while ground measurements may be biased by the lower vegetation layers. Additionally, caution should be taken regarding the misclassification in land cover maps as their errors can be propagated into the foliage clumping maps. Our results indicate that MODIS data and MISR data with 275 m in particular can

  18. Characterization, Validation and Intercomparison of Clumping Index Maps from POLDER, MODIS, and MISR Satellite Data Over Reference Sites

    NASA Astrophysics Data System (ADS)

    Pisek, J.; He, L.; Chen, J. M.; Govind, A.; Sprintsin, M.; Ryu, Y.; Arndt, S. K.; Hocking, D.; Wardlaw, T.; Kuusk, J.; Oliphant, A. J.; Korhonen, L.; Fang, H.; Matteucci, G.; Longdoz, B.; Raabe, K.

    2015-12-01

    Vegetation foliage clumping significantly alters its radiation environment and therefore affects vegetation growth as well as water and carbon cycles. The clumping index is useful in ecological and meteorological models because it provides new structural information in addition to the effective leaf area index (LAI) retrieved from mono-angle remote sensing and allows accurate separation of sunlit and shaded leaves in the canopy. Not accounting for the foliage clumping in LAI retrieval algorithms leads to substantial underestimation of actual LAI, especially for needleleaf forests. Normalized Difference between Hotspot and Darkspot (NDHD) index has been previously used to retrieve global clumping index maps from POLarization and Directionality of the Earth's Reflectances (POLDER) data at ~6 km resolution, from Moderate Resolution Imaging Spectroradiometer (MODIS) Bidirectional Reflectance Distribution Function (BRDF) product at 500 m resolution. Most recently the algorithm was applied with Multi-angle Imaging SpectroRadiometer (MISR) data at 275 m resolution over selected areas. In this presentation we characterize and intercompare the three products over a set of sites representing diverse biomes and different canopy structures. The products are also directly validated with both in-situ vertical profiles and seasonal trajectories of clumping index. We illustrate that the vertical distribution of foliage and especially the effect of understory needs to be taken into account while validating foliage clumping products from remote sensing products with values measured in the field. Satellite measurements respond to the structural effects near the top of canopies, while ground measurements may be biased by the lower vegetation layers. Additionally, caution should be taken regarding the misclassification in land cover maps as their errors can be propagated into the foliage clumping maps. Our results indicate that MODIS data and MISR data with 275 m resolution in

  19. Photoevaporation of Disks and Clumps by Nearby Massive Stars: Application to Disk Destruction in the Orion Nebula

    NASA Astrophysics Data System (ADS)

    Johnstone, Doug; Hollenbach, David; Bally, John

    1998-05-01

    We present a model for the photoevaporation of circumstellar disks or dense clumps of gas by an external source of ultraviolet radiation. Our model includes the thermal and dynamic effects of 6-13.6 eV far-ultraviolet (FUV) photons and Lyman continuum EUV photons incident upon disks or clumps idealized as spheres of radius rd and enclosed mass M*. For sufficiently large values of rd/M*, the radiation field evaporates the surface gas and dust. Analytical and numerical approximations to the resulting flows are presented; the model depends on rd, M*, the flux of FUV and EUV photons, and the column density of neutral gas heated by FUV photons to high temperatures. Application of this model shows that the circumstellar disks (rd ~ 1014-1015 cm) in the Orion Nebula (``proplyds'') are rapidly destroyed by the external UV radiation field. Close (d <~ 1017 cm) to θ1 Ori C, the ionizing EUV photon flux controls the mass-loss rate, and the ionization front (IF) is approximately coincident with the disk surface. Gas evaporated from the cold disk moves subsonically through a relatively thin photodissociation region (PDR) dominated by FUV photons and heated to ~1000 K. As the distance from θ1 Ori C increases, the Lyman continuum flux declines, the PDR thickens, and the IF moves away from the disk surface. At d ~ 3 × 1017 cm, the thickness of the PDR becomes comparable to the disk radius. Between 3 × 1017 cm <~ d <~ 1018 cm, spherical divergence and the resultant pressure gradient in the 103 K PDR forms a mildly supersonic (~3-6 km s-1) but neutral Parker wind. This wind flows outward until it passes through a shock, beyond which gas moves subsonically through a stationary D-type IF. The IF is moved away from the disk surface to a standoff distance rIF >~ 2.5rd. In this regime, the mass-loss rate is determined by the incident FUV photon flux and not the ionizing flux. However, at very large distances, d >~ 1018 cm, the FUV photon flux drops to values that cannot maintain the

  20. Calibration of the carbonate `clumped isotope' paleotemperature proxy using mollusc shells and benthic foraminiferal tests

    NASA Astrophysics Data System (ADS)

    Came, R. E.; Curry, W. B.; Weidman, C. R.; Eiler, J. M.

    2007-12-01

    It has recently been shown that the carbonate `clumped isotope' thermometer can provide temperature constraints that depend only on the isotopic composition of carbonate (in particular, on the proportion of 13C and 18O that form bonds with each other), and that do not require assumptions about the isotopic composition of the water in which the carbonate formed (Ghosh et al., 2006). Furthermore, this novel method permits the calculation of seawater δ18O based on the clumped isotope temperature estimates and the simultaneously obtained δ18O of carbonate, thereby enabling the extraction of global ice volume estimates for both the recent and distant geologic past. Here we present clumped isotope analyses of several naturally occurring marine carbonates that calcified at known temperatures in the modern ocean. First, we analyzed benthic foraminiferal tests from six high-quality multicore tops collected in the Florida Strait, spanning a temperature range of 9.3-20.2 degrees C. Second, we analyzed shallow-water mollusc shells from a variety of different climate regimes, spanning a temperature range of 2.5-26.0 degrees C. We find that the calcitic foraminiferal species Cibicidoides spp. agrees well with the inorganic calcite precipitation experiments of Ghosh et al. (2006), while the aragonitic species Hoeglundina elegans is significantly offset. Similarly, clumped isotope results obtained from aragonitic mollusc shells also reveal an offset from the Ghosh et al. (2006) trend, although the offset observed in mollusc aragonite is quite different in nature from that observed in foraminiferal aragonite. Assuming our estimates of the growth temperatures of these naturally occurring organisms are correct, these results suggest that there are vital effects associated with the stable isotope compositions of the aragonite-precipitating organisms examined in this study; further work will be required to determine their cause. Nevertheless, the internal coherence of trends for

  1. Clumped isotope geochemistry of mid-Cretaceous (Barremian-Aptian) rudist shells: paleoclimatic and paleoenvironmental implications

    NASA Astrophysics Data System (ADS)

    Huck, S.; Steuber, T.; Bernasconi, S.; Weissert, H.

    2012-04-01

    The Cretaceous period is generally considered to have been a time of climate warmth, but there is an ongoing dispute about the existence of Cretaceous cool episodes - including the short-termed installation of polar ice caps. The Late Barremian-Early Aptian represents a Cretaceous key interval in terms of paleoclimate and paleoceanography, as it provides evidence for (i) a cooler climate (Pucéat et al., 2003) and (ii) a considerable seasonality of sea surface temperatures (SSTs) at low latitudes (Steuber et al., 2005). The timing and significance of these cool episodes, however, are not well constrained. Recently published TEX86 data, in contrast to oxygen isotope paleotemperature estimates, now are in support of a climate scenario with equable hot (~30° C) tropical SSTs from the Early Cretaceous onwards. The aim of this project is to reconstruct the evolution of Barremian-Aptian sea-surface temperatures (SSTs) in the tropical Tethyan realm by use of a combined geochemical approach including oxygen isotope analysis and carbonate clumped-isotope thermometry. Paleotemperature proxies are based on the isotope geochemistry of low-Mg calcite of pristine rudist bivalve shells (Toucasia, Requienia) collected from different carbonate platform settings, including the Provence platform in SE France and the Adriatic Carbonate platform in Croatia. Carbonate clumped-isotope geochemistry deals with the state of ordering of rare isotopes in molecules, in particular with their tendency to form bonds with other rare isotopes (13C-18O) rather than with the most abundant ones. Carbonate clumped-isotope thermometry has been shown to allow for reconstructing (i) the temperature of carbonate mineral formation and calculating (ii) the isotopic composition of the water from which carbonate minerals were formed (by using the δ18O of the analysed carbonate sample). Our approach seeks to provide insights into possible biases in temperature estimates of different paleothermometers

  2. Assessment of the clumped isotope composition of fossil bone carbonate as a recorder of subsurface temperatures

    NASA Astrophysics Data System (ADS)

    Suarez, Marina B.; Passey, Benjamin H.

    2014-09-01

    Bone is susceptible to early diagenesis, and its carbon and oxygen isotopic compositions have been suggested to reflect conditions in the soil environment and shallow subsurface during fossilization. This implies open-system recrystallization involving mass exchange of carbon and oxygen among bioapatite, soil water, and DIC. Such recrystallization would also redistribute isotopic clumping (including 13C-18O bonds), leading to the possibility that the carbonate clumped isotope compositions of fossil bone record ground temperature during early diagenesis. We assess this possibility by studying Quaternary mammalian fossil bone from subtropical to polar latitudes: if recrystallization is early and pervasive, clumped isotope derived temperatures, T(Δ47), should closely mirror latitudinal gradients in ground temperature. Excluding results from a mummified specimen yielding T(Δ47) = 38 °C (that is, indistinguishable from mammalian body temperature), we find that T(Δ47) values are intermediate between mammalian body temperature and ground temperature, suggesting partial recrystallization of bone carbonate. XRD analyses show that the nature and extent of diagenesis varies among the samples and does not relate in a straightforward manner to T(Δ47). No clear correlation exists between T(Δ47) and mean annual temperature or mean warm season temperature. Furthermore, bone tends to retain the 18O-enriched signature of body water, suggesting incomplete oxygen isotope exchange with meteoric waters. Incomplete carbon and oxygen isotope exchange between bone carbonate and soil waters is also indicated for a set of late Miocene bone-enamel pairs from a sequence of stacked paleosols in northern China. Analysis of bone as old as Early Cretaceous shows that bone carbonate is susceptible to later diagenesis at elevated burial temperatures, although T(Δ47) does not closely conform to maximum burial temperature, again suggesting partial recrystallization, or recrystallization during

  3. Understanding and constraining global controls on dust emissions from playas

    NASA Astrophysics Data System (ADS)

    Bryant, Robert; Eckardt, Frank; Vickery, Kate; Wiggs, Giles; Hipondoka, Martin; Murray, Jon; Baddock, Matt; Brindley, Helen; King, James; Nield, Jo; Thomas, Dave; Washington, Richard; Haustein, Karsten

    2016-04-01

    and transport capacity limiting factors either seasonally or on an inter-annual basis. Using a range of examples drawn from ongoing and past research [e.g. the DO4Models project] to provide an overview of key controls on critical thresholds and feedbacks (climate, geochemistry, groundwater regime) for dust emission on playas. Pathways to understanding and quantifying the global emission potential of ephemeral lakes will be presented. Implications for dust emission modelling and future dust scenarios will also be outlined.

  4. Far-Reaching Impacts of African Dust- A Calipso Perspective

    NASA Technical Reports Server (NTRS)

    Yu, Hongbin; Chin, Mian; Yuan, Tianle; Bian, Huisheng; Prospero, Joseph; Omar, Ali; Remer, Lorraine; Winker, David; Yang, Yuekui; Zhang, Yan; Zhang, Zhibo

    2014-01-01

    African dust can transport across the tropical Atlantic and reach the Amazon basin, exerting far-reaching impacts on climate in downwind regions. The transported dust influences the surface-atmosphere interactions and cloud and precipitation processes through perturbing the surface radiative budget and atmospheric radiative heating and acting as cloud condensation nuclei and ice nuclei. Dust also influences biogeochemical cycle and climate through providing nutrients vital to the productivity of ocean biomass and Amazon forests. Assessing these climate impacts relies on an accurate quantification of dust transport and deposition. Currently model simulations show extremely large diversity, which calls for a need of observational constraints. Kaufman et al. (2005) estimated from MODIS aerosol measurements that about 144 Tg of dust is deposited into the tropical Atlantic and 50 Tg of dust into the Amazon in 2001. This estimated dust import to Amazon is a factor of 3-4 higher than other observations and models. However, several studies have argued that the oversimplified characterization of dust vertical profile in the study would have introduced large uncertainty and very likely a high bias. In this study we quantify the trans-Atlantic dust transport and deposition by using 7 years (2007-2013) observations from CALIPSO lidar. CALIPSO acquires high-resolution aerosol extinction and depolarization profiles in both cloud-free and above-cloud conditions. The unique CALIPSO capability of profiling aerosols above clouds offers an unprecedented opportunity of examining uncertainties associated with the use of MODIS clear-sky data. Dust is separated from other types of aerosols using the depolarization measurements. We estimated that on the basis of 7-year average, 118142 Tg of dust is deposited into the tropical Atlantic and 3860 Tg of dust into the Amazon basin. Substantial interannual variations are observed during the period, with the maximum to minimum ratio of about 1

  5. Field-testing a new directional passive air sampler for fugitive dust in a complex industrial source environment.

    PubMed

    Ferranti, E J S; Fryer, M; Sweetman, A J; Garcia, M A Solera; Timmis, R J

    2014-01-01

    Quantifying the sources of fugitive dusts on complex industrial sites is essential for regulation and effective dust management. This study applied two recently-patented Directional Passive Air Samplers (DPAS) to measure the fugitive dust contribution from a Metal Recovery Plant (MRP) located on the periphery of a major steelworks site. The DPAS can collect separate samples for winds from different directions (12 × 30° sectors), and the collected dust may be quantified using several different measurement methods. The DPASs were located up and down-prevailing-wind of the MRP processing area to (i) identify and measure the contribution made by the MRP processing operation; (ii) monitor this contribution during the processing of a particularly dusty material; and (iii) detect any changes to this contribution following new dust-control measures. Sampling took place over a 12-month period and the amount of dust was quantified using photographic, magnetic and mass-loading measurement methods. The DPASs are able to effectively resolve the incoming dust signal from the wider steelworks complex, and also different sources of fugitive dust from the MRP processing area. There was no confirmable increase in the dust contribution from the MRP during the processing of a particularly dusty material, but dust levels significantly reduced following the introduction of new dust-control measures. This research was undertaken in a regulatory context, and the results provide a unique evidence-base for current and future operational or regulatory decisions.

  6. The formulation of Lamb's Dust Veil Index

    NASA Technical Reports Server (NTRS)

    Kelly, P. M.; Sear, C. B.

    1982-01-01

    A catalog of the major explosive volcanic eruptions since 1500 AD and formulated the Dust Veil Index (DVI) is presented. The DVI quantifies the impact on the Earth's energy balance of changes in atmospheric composition due to explosive volcanic eruptions. The DVI for a particular eruption quantifies the climatic impact of the dust and aerosol injection from the eruption integrated over the years following the event. The formulation of the DVI is described. All references are to Lamb (1970). A distinction is made between the catalog of volcanic activity, and the tabulation of the northern hemisphere DVI apportioned over the years. The DVI data are updated to 1975 for any particular eruption, the catalog gives three DVI values: global, Southern Hemisphere, and Northern Hemisphere. The global DVI given in the catalog is considered. The other two DVIs relate to the impact on the hemispheres considered separately and their estimation involves an additional factor apportioning the dust veil between the hemispheres on the basis of the latitude of injection.

  7. Dust Mite Allergy

    MedlinePlus

    ... a pollen allergy may be noticeable because the allergy is seasonal. For example, you may have more difficulty managing your asthma for a short time during the summer. Dust mite allergy, on the other hand, is due to something ...

  8. 1983 Transatlantic Dust Event

    NASA Video Gallery

    This visualization (prepared in 2001) shows dust being blown westward over the Atlantic from northern Africa in early 1983, from aerosol measurements taken by Nimbus 7's TOMS instrument. Saharan du...

  9. Composite circumstellar dust grains

    NASA Astrophysics Data System (ADS)

    Gupta, Ranjan; Vaidya, Dipak B.; Dutta, Rajeshwari

    2016-10-01

    We calculate the absorption efficiencies of composite silicate grains with inclusions of graphite and silicon carbide in the spectral range 5-25 μm. We study the variation in absorption profiles with volume fractions of inclusions. In particular we study the variation in the wavelength of peak absorption at 10 and 18 μm. We also study the variation of the absorption of porous silicate grains. We use the absorption efficiencies to calculate the infrared flux at various dust temperatures and compare with the observed infrared emission flux from the circumstellar dust around some M-type and asymptotic giant branch stars obtained from IRAS and a few stars from Spitzer satellite. We interpret the observed data in terms of the circumstellar dust grain sizes, shape, composition and dust temperature.

  10. Dust evolution from comets

    NASA Technical Reports Server (NTRS)

    Sekanina, Z.

    1976-01-01

    The studies of the evolution of cometary debris are reviewed. The subject is divided into three major sections: (1) the developments in the immediate vicinity of the cometary nucleus, which is the source of the dust; (2) the formation of the dust tail; and (3) the blending of the debris with the dust component of interplanetary matter. The importance of the physical theory of comets is emphasized for the understanding of the early phase of evolution. A physico-dynamical model designed to analyze the particle-emission mechanism from the distribution of light in the dust tail is described and the results are presented. Increased attention is paid to large particles because of their importance for the evolution of the zodiacal cloud. Finally, implications are discussed for the future in situ investigations of comets.

  11. The Lunar Dust Pendulum

    NASA Technical Reports Server (NTRS)

    Collier, Michael R.; Stubbs, Timothy J.; Farrell, William M.

    2011-01-01

    Shadowed regions on the lunar surface acquire a negative potential. In particular, shadowed craters can have a negative potential with respect to the surrounding lunar regolith in sunlight, especially near the terminator regions. Here we analyze the motion of a positively charged lunar dust grain in the presence of a shadowed crater at a negative potential in vacuum. Previous models describing the transport of charged lunar dust close to the surface have typically been limited to one-dimensional motion in the vertical direction, e.g. electrostatic levitation; however, the electric fields in the vicinity of shadowed craters will also have significant components in the horizontal directions. We propose a model that includes both the horizontal and vertical motion of charged dust grains near shadowed craters. We show that the dust grains execute oscillatory trajectories and present an expression for the period of oscillation drawing an analogy to the motion of a pendulum.

  12. The Lunar Dust Pendulum

    NASA Technical Reports Server (NTRS)

    Kuntz, Kip; Collier, Michael R.; Stubbs, Timothy J.; Farrell, William M.

    2011-01-01

    Shadowed regions on the lunar surface acquire a negative potential. In particular, shadowed craters can have a negative potential with respect to the surrounding lunar regolith in sunlight, especially near the terminator regions. Here we analyze the motion of a positively charged lnnar dust grain in the presence of a shadowed crater at a negative potential in vacuum. Previous models describing the transport of charged lunar dust close to the surface have typically been limited to one-dimensional motion in the vertical direction, e.g. electrostatic levitation; however. the electric fields in the vicinity of shadowed craters will also have significant components in the horizontal directions. We propose a model that includes both the horizontal and vertical motion of charged dust grains near shadowed craters. We show that the dust grains execute oscillatory trajectories and present an expression for the period of oscillation drawing an analogy to the motion of a pendulum.

  13. Carbonate "clumped" isotope signatures in aragonitic scleractinian and calcitic gorgonian deep-sea corals

    NASA Astrophysics Data System (ADS)

    Kimball, Justine; Eagle, Robert; Dunbar, Robert

    2016-12-01

    Deep-sea corals are a potentially valuable archive of the temperature and ocean chemistry of intermediate and deep waters. Living in near-constant temperature, salinity, and pH and having amongst the slowest calcification rates observed in carbonate-precipitating biological organisms, deep-sea corals can provide valuable constraints on processes driving mineral equilibrium and disequilibrium isotope signatures. Here we report new data to further develop "clumped" isotopes as a paleothermometer in deep-sea corals as well as to investigate mineral-specific, taxon-specific, and growth-rate-related effects. Carbonate clumped isotope thermometry is based on measurements of the abundance of the doubly substituted isotopologue 13C18O16O2 in carbonate minerals, analyzed in CO2 gas liberated on phosphoric acid digestion of carbonates and reported as Δ47 values. We analyzed Δ47 in live-collected aragonitic scleractinian (Enallopsammia sp.) and high-Mg calcitic gorgonian (Isididae and Coralliidae) deep-sea corals and compared results to published data for other aragonitic scleractinian taxa. Measured Δ47 values were compared to in situ temperatures, and the relationship between Δ47 and temperature was determined for each group to investigate taxon-specific effects. We find that aragonitic scleractinian deep-sea corals exhibit higher values than high-Mg calcitic gorgonian corals and the two groups of coral produce statistically different relationships between Δ47-temperature calibrations. These data are significant in the interpretation of all carbonate clumped isotope calibration data as they show that distinct Δ47-temperature calibrations can be observed in different materials recovered from the same environment and analyzed using the same instrumentation, phosphoric acid composition, digestion temperature and technique, CO2 gas purification apparatus, and data handling. There are three possible explanations for the origin of these different calibrations. The offset

  14. Carbonate "clumped" isotope signatures in aragonitic scleractinian and calcitic gorgonian deep-sea corals

    NASA Astrophysics Data System (ADS)

    Kimball, J.; Tripati, R. E.; Dunbar, R.

    2015-12-01

    Deep-sea corals are a potentially valuable archive of the temperature and ocean chemistry of intermediate and deep waters. Living in near constant temperature, salinity and pH, and having amongst the slowest calcification rates observed in carbonate-precipitating biological organisms, deep-sea corals can provide valuable constraints on processes driving mineral equilibrium and disequilibrium isotope signatures. Here we report new data to further develop "clumped" isotopes as a paleothermometer in deep-sea corals as well as to investigate mineral-specific, taxon-specific, and growth-rate related effects. Carbonate clumped isotope thermometry is based on measurements of the abundance of the doubly-substituted isotopologue 13C18O16O2 in carbonate minerals, analyzed in CO2 gas liberated on phosphoric acid digestion of carbonates and reported as Δ47 values. We analyzed Δ47 in live-collected aragonitic scleractinian (Enallopsammia sp.) and calcitic gorgonian (Isididae and Coralliidae) deep-sea corals, and compared results to published data for other aragonitic scleractinian taxa. Measured Δ47 values were compared to in situ temperatures and the relationship between Δ47 and temperature was determined for each group to investigate taxon-specific effects. We find that aragonitic scleractinian deep-sea corals exhibit higher values than calcitic gorgonian corals and the two groups of coral produce statistically different relationship between Δ47-temperature calibrations. These data are significant in the interpretation of all carbonate "clumped" isotope calibration data as they show that distinct Δ47-temperature calibrations can be observed in different materials recovered from the same environment and analyzed using the same instrumentation, phosphoric acid composition, digestion temperature and technique, CO2 gas purification apparatus, and data handling. There are three possible explanations for the origin of these different calibrations. The offset between the

  15. Using Clumped Isotopes to Investigate the Causes of Pluvial Conditions in the Southeastern Basin and Range during the Last Deglaciation

    NASA Astrophysics Data System (ADS)

    Kowler, A.; Lora, J. M.; Mitchell, J.; Risi, C.; Lee, H. I.; Tripati, A.

    2015-12-01

    The last deglacial interval (~19-11 ka) was marked by major perturbations to Earth's climate coupled with rising atmospheric temperatures and CO2 concentrations, reaching near-modern levels by the early Holocene. Several discharges of freshwater into the North Atlantic caused by melting and collapse of continental ice sheets affected ocean circulation and sea-surface temperatures, triggering abrupt changes in terrestrial climate worldwide. While the timing and amount of associated temperature changes have been quantified from ice core records at high latitudes, corresponding information from lower latitudes is comparatively low and concentrated along coastlines, at high elevations, and in tropical and mesic regions. This is problematic for efforts to improve the reliability of long-term climate forecasts, reliant on models lacking sufficient validation from paleoclimate reconstructions for interior drylands that comprise nearly half of Earth's land surface. Evidence for past hydrologic changes in arid regions comes from ancient lake-shoreline deposits in internally drained basins, allowing quantitative comparison of the recorded effective moisture increases. However, the utility of these records depends on our relatively limited ability to deconvolve the contributions of temperature and precipitation to these changes. Here we explore the possible role of the summer monsoon in causing deglacial-age highstands in the southern Basin and Range. We employ clumped isotope analysis to generate paleotemperature and surface-water d18O estimates from carbonates in fossil shoreline and wetland deposits for comparison to output from PMIP3 coupled climate models and the model ensemble. Additionally, we present higher resolution output from LMDZ, the atmosphere-only component of the IPSL coupled model, employing LGM boundary conditions along with a hosing experiment designed to simulate Heinrich 1. For all simulations, we present analysis of changes in moisture transport

  16. Dust opacities inside the dust devil column in the Taklimakan Desert

    NASA Astrophysics Data System (ADS)

    Luan, Zhaopeng; Han, Yongxiang; Zhao, Tianliang; Liu, Feng; Liu, Chong; Rood, Mark J.; Yang, Xinghua; He, Qing; Lu, Huichao

    2017-01-01

    The distribution of dust aerosols in dust devils (DDs) is quantitatively characterized here based on a field observation. We applied the digital optical method (DOM) with digital still cameras to quantify the opacity of the DDs in the Taklimakan Desert, China. This study presents the following unique and important results: (1) the distinct horizontal distributions of opacity proved the existence of DDs' eye, similarly to the eye of tropical cyclone; (2) the opacity of the DDs decreases with increasing height; however, the dust aerosols do appear to settle out, and the relatively calm eye leads to a minimum in dust opacity at the eye; (3) the horizontal distribution of opacity is quasi-symmetric with a bimodal across the eye of the DDs, which could be resulted from the ambient air conditions; and (4) a new method is developed for characterizing the three-dimensional structure of DDs based on the observed two-dimensional opacity provided by DOM. This study not only proposes a highly reliable, low-cost and efficient methodology to capture the optical structure of DDs, but it could also provide the information on estimation of dust emissions driven by DDs.

  17. Comments on Dust Reverberation

    NASA Astrophysics Data System (ADS)

    Peterson, B.

    2015-09-01

    Dust reverberation is an important technique for studying the inner structure of AGNs and probing the properties of astrophysical dust, and even has some potential as a cosmological probe. We will discuss two recent results that pose a serious limitation to understanding dust reverberation at the present time. First, recent high-cadence monitoring of the UV and optical continuum in two AGNs, NGC 2617 and NGC 5548, have yielded unambiguous lags between variations of the UV continuum and corresponding variations of the continuum at longer wavelengths. In the absence of UV data, this leads to a systematic underestimate of the innermost radius where dust is found. This similarly leads to an underestimate of the size of the broad emission-line region, although it does not affect the AGN black hole mass scale, which calibrates out this effect. Second, broad-band monitoring of continuum variations in the optical through near-IR show that the innermost dust is not necessarily at the 'instantaneous sublimation radius.' The innermost dust can be considerably cooler than expected at the sublimation radius and thus can heat up without sublimating when the central continuum source becomes more luminous (see the poster by Pott).

  18. The Galileo Dust Detector

    NASA Technical Reports Server (NTRS)

    Gruen, Eberhard; Fechtig, Hugo; Hanner, Martha S.; Kissel, Jochen; Lindblad, Bertil-Anders; Linkert, Dietmar; Maas, Dieter; Morfill, Gregor E.; Zook, Herbert A.

    1992-01-01

    The Galileo Dust Detector is intended to provide direct observations of dust grains with masses between 10 exp -19 and 10 exp -9 kg in interplanetary space and in the Jovian system, to investigate their physical and dynamical properties as functions of the distances to the sun, to Jupiter and to its satellites, and to study its interaction with the Galilean satellites and the Jovian magnetosphere. The investigation is performed with an instrument that measures the mass, speed, flight direction and electric charge of individual dust particles. It is a multicoincidence detector with a mass sensitivity 1 000 000 times higher than that of previous in situ experiments which measured dust in the outer solar system. The instrument weighs 4.2 kg, consumes 2.4 W, and has a normal data transmission rate of 24 bits/s in nominal spacecraft tracking mode. On December 29, 1989 the instrument was switched-on. After the instrument had been configured to flight conditions cruise science data collection started immediately. In the period to May 18, 1990 at least 168 dust impacts have been recorded. For 81 of these dust grains masses and impact speeds have been determined. First flux values are given.

  19. Hebes Chasma Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    These dust avalanches are located in Hebes Chasma.

    Image information: VIS instrument. Latitude -1.4, Longitude 286.6 East (73.4 West). 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  20. Selecting baghouse dust collectors

    SciTech Connect

    Moore, S.; Rubak, J.; Jolin, M. |

    1996-10-01

    Control of nuisance or process dusts generated within a plant is a vital concern with today`s growing emphasis on indoor air quality. In the past, many companies simply moved these contaminants away from workers and discharged them into the atmosphere. More stringent pollution control requirements now make this course of action unacceptable. Also, in some cases there is a need to recover high-value dusts, such as chemicals or precious metals. As a result, proper design and selection of a dust collection system are more critical than ever. There are two types of fabric filter dust collection systems commonly used today: baghouses and cartridges. Baghouses were the first collection systems with fabric media (in the form of long tubes, or bags) for removal of contaminants. The versatility of the baghouse--coupled with constant technological refinements--have made it a long-standing favorite among specifiers of pollution control equipment. In fact, baghouses account for more than 80% of all fabric filter dust collection systems in use today. Cartridge dust collectors use rigidly pleated filter elements instead of bags, making it possible to accommodate a large amount of filter surface area in a comparatively small package. Cartridge collectors also offer high efficiency and low pressure drop.

  1. Quantifying surface normal estimation

    NASA Astrophysics Data System (ADS)

    Reid, Robert B.; Oxley, Mark E.; Eismann, Michael T.; Goda, Matthew E.

    2006-05-01

    An inverse algorithm for surface normal estimation from thermal polarimetric imagery was developed and used to quantify the requirements on a priori information. Building on existing knowledge that calculates the degree of linear polarization (DOLP) and the angle of polarization (AOP) for a given surface normal in a forward model (from an object's characteristics to calculation of the DOLP and AOP), this research quantifies the impact of a priori information with the development of an inverse algorithm to estimate surface normals from thermal polarimetric emissions in long-wave infrared (LWIR). The inverse algorithm assumes a polarized infrared focal plane array capturing LWIR intensity images which are then converted to Stokes vectors. Next, the DOLP and AOP are calculated from the Stokes vectors. Last, the viewing angles, θ v, to the surface normals are estimated assuming perfect material information about the imaged scene. A sensitivity analysis is presented to quantitatively describe the a priori information's impact on the amount of error in the estimation of surface normals, and a bound is determined given perfect information about an object. Simulations explored the impact of surface roughness (σ) and the real component (n) of a dielectric's complex index of refraction across a range of viewing angles (θ v) for a given wavelength of observation.

  2. Newton to Einstein — dust to dust

    SciTech Connect

    Kopp, Michael; Uhlemann, Cora; Haugg, Thomas E-mail: cora.uhlemann@physik.lmu.de

    2014-03-01

    We investigate the relation between the standard Newtonian equations for a pressureless fluid (dust) and the Einstein equations in a double expansion in small scales and small metric perturbations. We find that parts of the Einstein equations can be rewritten as a closed system of two coupled differential equations for the scalar and transverse vector metric perturbations in Poisson gauge. It is then shown that this system is equivalent to the Newtonian system of continuity and Euler equations. Brustein and Riotto (2011) conjectured the equivalence of these systems in the special case where vector perturbations were neglected. We show that this approach does not lead to the Euler equation but to a physically different one with large deviations already in the 1-loop power spectrum. We show that it is also possible to consistently set to zero the vector perturbations which strongly constrains the allowed initial conditions, in particular excluding Gaussian ones such that inclusion of vector perturbations is inevitable in the cosmological context. In addition we derive nonlinear equations for the gravitational slip and tensor perturbations, thereby extending Newtonian gravity of a dust fluid to account for nonlinear light propagation effects and dust-induced gravitational waves.

  3. Comet 'Bites the Dust' Around Dead Star

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Infrared Spectrometer Graph

    This artist's concept illustrates a comet being torn to shreds around a dead star, or white dwarf, called G29-38. NASA's Spitzer Space Telescope observed a cloud of dust around this white dwarf that may have been generated from this type of comet disruption. The findings suggest that a host of other comet survivors may still orbit in this long-dead solar system.

    The white dwarf G29-38 began life as a star that was about three times as massive as our sun. Its death involved the same steps that the sun will ultimately undergo billions of years from now. According to theory, the G29-38 star became brighter and brighter as it aged, until it bloated up into a dying star called a red giant. This red giant was large enough to engulf and evaporate any terrestrial planets like Earth that happened to be in its way. Later, the red giant shed its outer atmosphere, leaving behind a shrunken skeleton of star, called a white dwarf. If the star did host a planetary system, outer planets akin to Jupiter and Neptune and a remote ring of icy comets would remain.

    The Spitzer observations provide observational evidence for this orbiting outpost of comet survivors. Astronomers speculate that one such comet was knocked into the inner regions of G29-38, possibly by an outer planet. As the comet approached very close to the white dwarf, it may have been torn apart by the star's tidal forces. Eventually, all that would be left of the comet is a disk of dust.

    This illustration shows a comet in the process of being pulverized: part of it still exists as a chain of small clumps, while the rest has already spread out into a dusty disk. Comet Shoemaker-Levy 9 broke apart in a similar fashion when it plunged into Jupiter in 1994. Evidence for Comets Found in Dead Star's Dust The graph of data, or spectrum, from NASA's Spitzer Space Telescope indicates that a dead star, or white dwarf, called G29

  4. High-latitude dust in the Earth system

    NASA Astrophysics Data System (ADS)

    Bullard, Joanna E.; Baddock, Matthew; Bradwell, Tom; Crusius, John; Darlington, Eleanor; Gaiero, Diego; Gassó, Santiago; Gisladottir, Gudrun; Hodgkins, Richard; McCulloch, Robert; McKenna-Neuman, Cheryl; Mockford, Tom; Stewart, Helena; Thorsteinsson, Throstur

    2016-06-01

    Natural dust is often associated with hot, subtropical deserts, but significant dust events have been reported from cold, high latitudes. This review synthesizes current understanding of high-latitude (≥50°N and ≥40°S) dust source geography and dynamics and provides a prospectus for future research on the topic. Although the fundamental processes controlling aeolian dust emissions in high latitudes are essentially the same as in temperate regions, there are additional processes specific to or enhanced in cold regions. These include low temperatures, humidity, strong winds, permafrost and niveo-aeolian processes all of which can affect the efficiency of dust emission and distribution of sediments. Dust deposition at high latitudes can provide nutrients to the marine system, specifically by contributing iron to high-nutrient, low-chlorophyll oceans; it also affects ice albedo and melt rates. There have been no attempts to quantify systematically the expanse, characteristics, or dynamics of high-latitude dust sources. To address this, we identify and compare the main sources and drivers of dust emissions in the Northern (Alaska, Canada, Greenland, and Iceland) and Southern (Antarctica, New Zealand, and Patagonia) Hemispheres. The scarcity of year-round observations and limitations of satellite remote sensing data at high latitudes are discussed. It is estimated that under contemporary conditions high-latitude sources cover >500,000 km2 and contribute at least 80-100 Tg yr-1 of dust to the Earth system (~5% of the global dust budget); both are projected to increase under future climate change scenarios.

  5. Simulation of the Radiative Impact of High Dust Loading during a Dust Storm in March 2012

    NASA Astrophysics Data System (ADS)

    Puthan Purakkal, J.; Kalenderski, S.; Stenchikov, G. L.

    2013-12-01

    We investigated a severe dust storm that developed over vast areas of the Middle East on 18-19 March 2012 and affected Saudi Arabia, Sudan, Egypt, Jordan, United Arab Emirates, Bahrain, Qatar, Oman, Kuwait, Iraq, Iran, Israel, and Pakistan. The visible aerosol optical depth recorded by the AERONET station on the KAUST campus (22.30o N 39.10o E) during the storm reached 4.5, exceeding the average level by an order of magnitude. To quantify the effects of the dust on atmospheric radiation and dynamics, we analyzed available ground-based and satellite observations and conducted numerical simulations using a fully coupled meteorology-chemistry-aerosol model (WRF-Chem). The model was able to reproduce the spatial and temporal patterns of the aerosol optical depths (AOD) observed by airborne and ground-based instruments. The major dust sources included river valleys of lower Tigris and Euphrates in Iraq, desert areas in Kuwait, Iran, United Arab Emirates, central Arabia including Rub' al Khali, An Nafud, and Ad Dahna, as well as the Red Sea coast of the Arabian Peninsula. The total amount of dust generated across the entire domain during the period of the simulation reached 93.76 Mt; 73.04 Mt of dust was deposited within the domain; 6.56 Mt of dust sunk in the adjacent sea waters, including 1.20 Mt that sedimented into the Red Sea. The model predicted a well-mixed boundary layer expanding up to 3.5 km in the afternoon. Some dust plumes were seen above the Planetary Boundary layer. In our simulations, mineral dust heated the lower atmosphere with a maximum heating rate of 9 K/day. The dust storm reduced the downwelling shortwave radiation at the surface to a maximum daily average value of -134 Wm-2 and the daily averaged long-wave forcing at the surface increased to 43 Wm-2. The combined short-wave cooling and long-wave warming effects of dust aerosols caused significant reduction in the surface air temperature -6.7 K at 1200 UTC on 19 March 2013.

  6. Interstellar and Cometary Dust

    NASA Technical Reports Server (NTRS)

    Mathis, John S.

    1997-01-01

    'Interstellar dust' forms a continuum of materials with differing properties which I divide into three classes on the basis of observations: (a) diffuse dust, in the low-density interstellar medium; (b) outer-cloud dust, observed in stars close enough to the outer edges of molecular clouds to be observed in the optical and ultraviolet regions of the spectrum, and (c) inner-cloud dust, deep within the cores of molecular clouds, and observed only in the infrared by means of absorption bands of C-H, C=O, 0-H, C(triple bond)N, etc. There is a surprising regularity of the extinction laws between diffuse- and outer-cloud dust. The entire mean extinction law from infrared through the observable ultraviolet spectrum can be characterized by a single parameter. There are real deviations from this mean law, larger than observational uncertainties, but they are much smaller than differences of the mean laws in diffuse- and outer-cloud dust. This fact shows that there are processes which operate over the entire distribution of grain sizes, and which change size distributions extremely efficiently. There is no evidence for mantles on grains in local diffuse and outer-cloud dust. The only published spectra of the star VI Cyg 12, the best candidate for showing mantles, does not show the 3.4 micro-m band which appreciable mantles would produce. Grains are larger in outer-cloud dust than diffuse dust because of coagulation, not accretion of extensive mantles. Core-mantle grains favored by J. M. Greenberg and collaborators, and composite grains of Mathis and Whiffen (1989), are discussed more extensively (naturally, I prefer the latter). The composite grains are fluffy and consist of silicates, amorphous carbon, and some graphite in the same grain. Grains deep within molecular clouds but before any processing within the solar system are presumably formed from the accretion of icy mantles on and within the coagulated outer-cloud grains. They should contain a mineral

  7. Large and small-scale structures and the dust energy balance problem in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Saftly, W.; Baes, M.; De Geyter, G.; Camps, P.; Renaud, F.; Guedes, J.; De Looze, I.

    2015-04-01

    The interstellar dust content in galaxies can be traced in extinction at optical wavelengths, or in emission in the far-infrared. Several studies have found that radiative transfer models that successfully explain the optical extinction in edge-on spiral galaxies generally underestimate the observed FIR/submm fluxes by a factor of about three. In order to investigate this so-called dust energy balance problem, we use two Milky Way-like galaxies produced by high-resolution hydrodynamical simulations. We create mock optical edge-on views of these simulated galaxies (using the radiative transfer code SKIRT), and we then fit the parameters of a basic spiral galaxy model to these images (using the fitting code FitSKIRT). The basic model includes smooth axisymmetric distributions along a Sérsic bulge and exponential disc for the stars, and a second exponential disc for the dust. We find that the dust mass recovered by the fitted models is about three times smaller than the known dust mass of the hydrodynamical input models. This factor is in agreement with previous energy balance studies of real edge-on spiral galaxies. On the other hand, fitting the same basic model to less complex input models (e.g. a smooth exponential disc with a spiral perturbation or with random clumps), does recover the dust mass of the input model almost perfectly. Thus it seems that the complex asymmetries and the inhomogeneous structure of real and hydrodynamically simulated galaxies are a lot more efficient at hiding dust than the rather contrived geometries in typical quasi-analytical models. This effect may help explain the discrepancy between the dust emission predicted by radiative transfer models and the observed emission in energy balance studies for edge-on spiral galaxies.

  8. On quantifying insect movements

    SciTech Connect

    Wiens, J.A.; Crist, T.O. ); Milne, B.T. )

    1993-08-01

    We elaborate on methods described by Turchin, Odendaal Rausher for quantifying insect movement pathways. We note the need to scale measurement resolution to the study insects and the questions being asked, and we discuss the use of surveying instrumentation for recording sequential positions of individuals on pathways. We itemize several measures that may be used to characterize movement pathways and illustrate these by comparisons among several Eleodes beetles occurring in shortgrass steppe. The fractal dimension of pathways may provide insights not available from absolute measures of pathway configuration. Finally, we describe a renormalization procedure that may be used to remove sequential interdependence among locations of moving individuals while preserving the basic attributes of the pathway.

  9. Fractal dust grains in plasma

    SciTech Connect

    Huang, F.; Peng, R. D.; Liu, Y. H.; Chen, Z. Y.; Ye, M. F.; Wang, L.

    2012-09-15

    Fractal dust grains of different shapes are observed in a radially confined magnetized radio frequency plasma. The fractal dimensions of the dust structures in two-dimensional (2D) horizontal dust layers are calculated, and their evolution in the dust growth process is investigated. It is found that as the dust grains grow the fractal dimension of the dust structure decreases. In addition, the fractal dimension of the center region is larger than that of the entire region in the 2D dust layer. In the initial growth stage, the small dust particulates at a high number density in a 2D layer tend to fill space as a normal surface with fractal dimension D = 2. The mechanism of the formation of fractal dust grains is discussed.

  10. Clumped isotope thermometry in deeply buried sedimentary carbonates: The effects of C-O bond reordering and recrystallization

    NASA Astrophysics Data System (ADS)

    Passey, B. H.; Shenton, B.; Grossman, E. L.; Henkes, G. A.; Laya, J. C.; Perez-Huerta, A.

    2014-12-01

    Constraining the thermal histories of sedimentary basins is fundamental to a range of geologic applications including tectonics, petroleum system analysis, and the genesis of ore deposits. Carbonate rocks can serve as archives of basin thermal histories through solid-state reordering of their 13C-18O, or 'clumped isotope', bonds at elevated burial temperatures. Here we present one of the first applied studies of carbonate clumped isotope reordering to explore the diagenetic and thermal histories of exhumed brachiopods, crinoids, cements, and host rock in the Permian Palmarito Formation, Venezuela and the Carboniferous Bird Spring Formation, Nevada, USA. Carbonate components in the Palmarito Formation, buried to ~4 km depth, yield statistically indistinguishable clumped isotope temperatures (T(∆47)) ranging from 86 to 122 °C. Clumped isotope temperatures of components in the more deeply buried Bird Spring Formation (>5 km), range from ~100 to 165 °C and differ by component type, with brachiopods and pore-filling cements yielding the highest T(∆47) (mean = 153 and 141 °C, respectively) and crinoids and host rock yielding significantly cooler T(∆47) (mean = 103 and 114 °C). New high-resolution thermal histories are coupled with kinetic models to predict the extent of solid-state C-O bond reordering during burial and exhumation for both sites. Application of these models suggests that brachiopods in the Palmarito Formation experienced partial bond reordering without complete equilibration of clumped isotopes at maximum burial temperature. In contrast, clumped isotope bonds of brachiopods from the Bird Spring Formation appear to have completely equilibrated at maximum burial temperature, and now reflect blocking temperatures 'locked-in' during cooling. The 40-50 °C cooler clumped isotope temperatures measured in Bird Spring Formation crinoids and host rock can be explained by both recrystallization and cementation during shallow burial and a greater inherent

  11. Determining inert content in coal dust/rock dust mixture

    DOEpatents

    Sapko, Michael J.; Ward, Jr., Jack A.

    1989-01-01

    A method and apparatus for determining the inert content of a coal dust and rock dust mixture uses a transparent window pressed against the mixture. An infrared light beam is directed through the window such that a portion of the infrared light beam is reflected from the mixture. The concentration of the reflected light is detected and a signal indicative of the reflected light is generated. A normalized value for the generated signal is determined according to the relationship .phi.=(log i.sub.c `log i.sub.co) / (log i.sub.c100 -log i.sub.co) where i.sub.co =measured signal at 0% rock dust i.sub.c100 =measured signal at 100% rock dust i.sub.c =measured signal of the mixture. This normalized value is then correlated to a predetermined relationship of .phi. to rock dust percentage to determine the rock dust content of the mixture. The rock dust content is displayed where the percentage is between 30 and 100%, and an indication of out-of-range is displayed where the rock dust percent is less than 30%. Preferably, the rock dust percentage (RD%) is calculated from the predetermined relationship RD%=100+30 log .phi.. where the dust mixture initially includes moisture, the dust mixture is dried before measuring by use of 8 to 12 mesh molecular-sieves which are shaken with the dust mixture and subsequently screened from the dust mixture.

  12. Expanding shell and star formation in the infrared dust bubble N6

    SciTech Connect

    Yuan, Jing-Hua; Li, Jin Zeng; Liu, Hongli; Wu, Yuefang E-mail: ywu@pku.edu.cn

    2014-12-10

    We have carried out a multiwavelength study of the infrared dust bubble N6 to extensively investigate the molecular environs and star-forming activities therein. Mapping observations in {sup 12}CO J = 1-0 and {sup 13}CO J = 1-0 performed with the Purple Mountain Observatory 13.7 m telescope have revealed four velocity components. Comparison between distributions of each component and the infrared emission suggests that three components are correlated with N6. There are 10 molecular clumps detected. Among them, five have reliable detections in both {sup 12}CO and {sup 13}CO and have similar LTE and non-LTE masses ranging from 200 to higher than 5000 M {sub ☉}. With larger gas masses than virial masses, these five clumps are gravitationally unstable and have the potential to collapse to form new stars. The other five clumps are only reliably detected in {sup 12}CO and have relatively small masses. Five clumps are located on the border of the ring structure, and four of them are elongated along the shell. This is well in agreement with the collect-and-collapse scenario. The detected velocity gradient reveals that the ring structure is still under expansion owing to stellar winds from the exciting star(s). Furthermore, 99 young stellar objects (YSOs) have been identified based on their infrared colors. A group of YSOs reside inside the ring, indicating active star formation in N6. Although no confirmative features of triggered star formation are detected, the bubble and the enclosed H II region have profoundly reconstructed the natal cloud and altered the dynamics therein.

  13. Kiloparsec-scale Dust Disks in High-redshift Luminous Submillimeter Galaxies

    NASA Astrophysics Data System (ADS)

    Hodge, J. A.; Swinbank, A. M.; Simpson, J. M.; Smail, I.; Walter, F.; Alexander, D. M.; Bertoldi, F.; Biggs, A. D.; Brandt, W. N.; Chapman, S. C.; Chen, C. C.; Coppin, K. E. K.; Cox, P.; Dannerbauer, H.; Edge, A. C.; Greve, T. R.; Ivison, R. J.; Karim, A.; Knudsen, K. K.; Menten, K. M.; Rix, H.-W.; Schinnerer, E.; Wardlow, J. L.; Weiss, A.; van der Werf, P.

    2016-12-01

    We present high-resolution (0.″16) 870 μm Atacama Large Millimeter/submillimeter Array (ALMA) imaging of 16 luminous ({L}{IR}˜ 4× {10}12 {L}⊙ ) submillimeter galaxies (SMGs) from the ALESS survey of the Extended Chandra Deep Field South. This dust imaging traces the dust-obscured star formation in these z˜ 2.5 galaxies on ˜1.3 kpc scales. The emission has a median effective radius of R e = 0.″24 ± 0.″02, corresponding to a typical physical size of {R}e= 1.8 ± 0.2 kpc. We derive a median Sérsic index of n = 0.9 ± 0.2, implying that the dust emission is remarkably disk-like at the current resolution and sensitivity. We use different weighting schemes with the visibilities to search for clumps on 0.″12 (˜1.0 kpc) scales, but we find no significant evidence for clumping in the majority of cases. Indeed, we demonstrate using simulations that the observed morphologies are generally consistent with smooth exponential disks, suggesting that caution should be exercised when identifying candidate clumps in even moderate signal-to-noise ratio interferometric data. We compare our maps to comparable-resolution Hubble Space Telescope {H}160-band images, finding that the stellar morphologies appear significantly more extended and disturbed, and suggesting that major mergers may be responsible for driving the formation of the compact dust disks we observe. The stark contrast between the obscured and unobscured morphologies may also have implications for SED fitting routines that assume the dust is co-located with the optical/near-IR continuum emission. Finally, we discuss the potential of the current bursts of star formation to transform the observed galaxy sizes and light profiles, showing that the z˜ 0 descendants of these SMGs are expected to have stellar masses, effective radii, and gas surface densities consistent with the most compact massive ({M}* ˜ 1-2 × 1011 {M}⊙ ) early-type galaxies observed locally.

  14. Sahara Dust Cloud

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Dust Particles Click on the image for Quicktime movie from 7/15-7/24

    A continent-sized cloud of hot air and dust originating from the Sahara Desert crossed the Atlantic Ocean and headed towards Florida and the Caribbean. A Saharan Air Layer, or SAL, forms when dry air and dust rise from Africa's west coast and ride the trade winds above the Atlantic Ocean.

    These dust clouds are not uncommon, especially during the months of July and August. They start when weather patterns called tropical waves pick up dust from the desert in North Africa, carry it a couple of miles into the atmosphere and drift westward.

    In a sequence of images created by data acquired by the Earth-orbiting Atmospheric Infrared Sounder ranging from July 15 through July 24, we see the distribution of the cloud in the atmosphere as it swirls off of Africa and heads across the ocean to the west. Using the unique silicate spectral signatures of dust in the thermal infrared, AIRS can detect the presence of dust in the atmosphere day or night. This detection works best if there are no clouds present on top of the dust; when clouds are present, they can interfere with the signal, making it much harder to detect dust as in the case of July 24, 2005.

    In the Quicktime movie, the scale at the bottom of the images shows +1 for dust definitely detected, and ranges down to -1 for no dust detected. The plots are averaged over a number of AIRS observations falling within grid boxes, and so it is possible to obtain fractional numbers. [figure removed for brevity, see original site] Total Water Vapor in the Atmosphere Around the Dust Cloud Click on the image for Quicktime movie

    The dust cloud is contained within a dry adiabatic layer which originates over the Sahara Desert. This Saharan Air Layer (SAL) advances Westward over the Atlantic Ocean, overriding the cool, moist air nearer the surface. This burst of very dry air is visible in the

  15. Electrodynamic Dust Shield Demonstrator

    NASA Technical Reports Server (NTRS)

    Stankie, Charles G.

    2013-01-01

    The objective of the project was to design and manufacture a device to demonstrate a new technology developed by NASA's Electrostatics and Surface Physics Laboratory. The technology itself is a system which uses magnetic principles to remove regolith dust from its surface. This project was to create an enclosure that will be used to demonstrate the effectiveness of the invention to The Office of the Chief Technologist. ONE of the most important challenges of space exploration is actually caused by something very small and seemingly insignificant. Dust in space, most notably on the moon and Mars, has caused many unforeseen issues. Dirt and dust on Earth, while a nuisance, can be easily cleaned and kept at bay. However, there is considerably less weathering and erosion in space. As a result, the microscopic particles are extremely rough and abrasive. They are also electrostatically charged, so they cling to everything they make contact with. This was first noted to be a major problem during the Apollo missions. Dust would stick to the spacesuits, and could not be wiped off as predicted. Dust was brought back into the spacecraft, and was even inhaled by astronauts. This is a major health hazard. Atmospheric storms and other events can also cause dust to coat surfaces of spacecraft. This can cause abrasive damage to the craft. The coating can also reduce the effectiveness of thermal insulation and solar panels.' A group of engineers at Kennedy Space Center's Electrostatics and Surface Physics Laboratory have developed a new technology, called the Electrodynamic Dust Shield, to help alleviate these problems. It is based off of the electric curtain concept developed at NASA in 1967. "The EDS is an active dust mitigation technology that uses traveling electric fields to transport electrostatically charged dust particles along surfaces. To generate the traveling electric fields, the EDS consists of a multilayer dielectric coating with an embedded thin electrode grid

  16. Derivation of an observation-based map of North African dust emission

    SciTech Connect

    Evan, Amato T.; Fiedler, Stephanie; Zhao, Chun; Menut, Laurent; Schepanski, Kerstin; Flamant, C.; Doherty, Owen

    2015-03-01

    Changes in the emission, transport and deposition of aeolian dust have profound effects on regional climate, so that characterizing the lifecycle of dust in observations and improving the representation of dust in global climate models is necessary. A fundamental aspect of characterizing the dust cycle is quantifying surface dust fluxes, yet no spatially explicit estimates of this flux exist for the World’s major source regions. Here we present a novel technique for creating a map of the annual mean emitted dust flux for North Africa based on retrievals of dust storm frequency from the Meteosat Second Generation Spinning Enhanced Visible and InfraRed Imager (SEVIRI) and the relationship between dust storm frequency and emitted mass flux derived from the output of five models that simulate dust. Our results suggest that 64 (±16)% of all dust emitted from North Africa is from the Bodélé depression, and that 13 (±3)% of the North African dust flux is from a depression lying in the lee of the Aïr and Hoggar Mountains, making this area the second most important region of emission within North Africa.

  17. Saharan dust deposition in the Carpathian Basin and its possible effects on interglacial soil formation

    NASA Astrophysics Data System (ADS)

    Varga, György; Cserháti, Csaba; Kovács, János; Szalai, Zoltán

    2016-09-01

    Several hundred tons of windblown dust material are lifted into the atmosphere and are transported every year from Saharan dust source areas towards Europe having an important climatic and other environmental effect also on distant areas. According to the systematic observations of modern Saharan dust events, it can be stated that dust deflated from North African source areas is a significant constituent of the atmosphere of the Carpathian Basin and Saharan dust deposition events are identifiable several times in a year. Dust episodes are connected to distinct meteorological situations, which are also the determining factors of the different kinds of depositional mechanisms. By using the adjusted values of dust deposition simulations of numerical models, the annual Saharan dust flux can be set into the range of 3.2-5.4 g/m2/y. Based on the results of past mass accumulation rates calculated from stratigraphic and sedimentary data of loess-paleosol sequences, the relative contribution of Saharan dust to interglacial paleosol material was quantified. According to these calculations, North African exotic dust material can represent 20-30% of clay and fine silt-sized soil components of interglacial paleosols in the Carpathian Basin. The syngenetic contribution of external aeolian dust material is capable to modify physicochemical properties of soils and hereby the paleoclimatic interpretation of these pedogene stratigraphic units.

  18. Insights into Methane Formation Temperatures, Biogenic Methanogenesis, and Natural Methane Emissions from Clumped Isotopes

    NASA Astrophysics Data System (ADS)

    Douglas, P. M.; Stolper, D. A.; Walter Anthony, K. M.; Dallimore, S.; Paull, C. K.; Wik, M.; Crill, P. M.; Winterdahl, M.; Smith, D. A.; Luhmann, A. J.; Ding, K.; Seyfried, W. E., Jr.; Eiler, J. M.; Ponton, C.; Sessions, A. L.

    2015-12-01

    Multiply substituted isotopologues of methane are a valuable new tool for characterizing and understanding the source of methane in different Earth environments. Here we present methane clumped isotope results from natural gas wells, hydrothermal vents, marine and lacustrine methane seeps, and culture experiments. We observe a wide range of formation temperatures for thermogenic methane. Methane samples from low-maturity reservoirs indicate formation temperatures between 102-144° C, high-maturity conventional and shale gasses indicate temperatures between 158-246 °C, and thermogenic coal gases indicate temperatures between 174-267 °C. Methane formation temperatures generally correlate positively with δ13C, and negatively with gas wetness indices. Methane samples from a set of marine hydrothermal vents indicate a formation temperature of 290-350 °C. Methane sampled from subsurface and marine biogenic sources typically indicate temperatures consistent with the formation environment (0-64° C). In contrast, freshwater biogenic methane samples, and cultures of hydrogenotrophic and methylotrophic methanogens, express low levels of isotopic clumping inconsistent with their formation temperature. These data and complementary models suggest that kinetic isotope effects, likely modulated by rates and pathways of methanogenesis, affect biogenic methane in cultures and freshwater environments. Alternatively, non-equilibrium signatures may result from mixing of methane with widely differing δD and δ13C values. Analyses of biogenic methane emissions from lakes indicate a correlation between methane flux and non-equilibrium clumped isotope fractionations in a given lake. Results from large methane seeps in Alaskan lakes confirm that some seeps emit thermogenic methane, but also indicate that other seeps emit subsurface biogenic methane or variable mixtures of biogenic and thermogenic methane. These results point to diverse sources for large Arctic methane seeps.

  19. "Anticlumping" and Other Combinatorial Effects on Clumped Isotopes: Implications for Tracing Biogeochemical Cycling

    NASA Astrophysics Data System (ADS)

    Yeung, L.

    2015-12-01

    I present a mode of isotopic ordering that has purely combinatorial origins. It can be important when identical rare isotopes are paired by coincidence (e.g., they are neighbors on the same molecule), or when extrinsic factors govern the isotopic composition of the two atoms that share a chemical bond. By itself, combinatorial isotope pairing yields products with isotopes either randomly distributed or with a deficit relative to a random distribution of isotopes. These systematics arise because of an unconventional coupling between the formation of singly- and multiply-substituted isotopic moieties. In a random distribution, rare isotopes are symmetrically distributed: Single isotopic substitutions (e.g., H‒D and D‒H in H2) occur with equal probability, and double isotopic substitutions (e.g., D2) occur according to random chance. The absence of symmetry in a bond-making complex can yield unequal numbers of singly-substituted molecules (e.g., more H‒D than D‒H in H2), which is recorded in the product molecule as a deficit in doubly-substituted moieties and an "anticlumped" isotope distribution (i.e., Δn < 0). Enzymatic isotope pairing reactions, which can have site-specific isotopic fractionation factors and atom reservoirs, should express this class of combinatorial isotope effect. Chemical-kinetic isotope effects, which are related to the bond-forming transition state, arise independently and express second-order combinatorial effects. In general, both combinatorial and chemical factors are important for calculating and interpreting clumped-isotope signatures of individual reactions. In many reactions relevant to geochemical oxygen, carbon, and nitrogen cycling, combinatorial isotope pairing likely plays a strong role in the clumped isotope distribution of the products. These isotopic signatures, manifest as either directly bound isotope clumps or as features of a molecule's isotopic anatomy, could be exploited as tracers of biogeochemistry that can

  20. Temporal clumping of bark beetle arrival at pheromone traps: Modeling anemotaxis in chaotic plumes.

    PubMed

    Byers, J A

    1996-11-01

    The sequence of arrival of the bark beetlesIps typographus andPityogenes chalcographus (Coleoptera: Scolytidae) at traps baited with their synthetic pheromones was monitored with a portable fraction collector. Histograms of the natural arrival patterns of both species were nonrandom and clumped at shorter time scales (1-, 2-, 4-, 5-, or 6-min cells) but appeared random at larger time scales (10, 20 or 30 min). Monte Carlo generation of similar histograms showed them to be random at all of these time scales. A stochastic computer model could graphically simulate insect orientation to odor sources based on present theories of odor-modulated anemotaxis and casting. Although this model was used throughout, since it assumes only that insects cast perpendicular to the current wind direction, a second model could slightly improve orientation success. However, the second model requires that the insect remember its ground path (upwind) prior to losing the plume (after an abrupt wind direction change). The effects of casting and flight parameters on orientation success and randomness of arrival sequence within various plumes were determined by simulation. Similarly, the effects of random walks in plume direction, plume width, and wind speed were explored. The results showed that dynamic random variations in plume direction and especially wind speed could cause an otherwise random arrival sequence (e.g., under constant wind) to become clumped and nonrandom. Therefore, the clumped arrival patterns of bark beetles and other insects, includingSpodoptera litura, at pheromone sources could result from random-walk fluctuations in wind speed and wind direction.

  1. A molecular line study towards massive extended green object clumps in the southern sky: chemical properties

    NASA Astrophysics Data System (ADS)

    Yu, Naiping; Wang, Jun-Jie

    2015-08-01

    We present a molecular line study towards 31 extended green object (EGO) clumps in the southern sky using data from MALT90 (Millimetre Astronomy Legacy Team 90 GHz). According to previous multiwavelength observations, we divide our sample into two groups: massive young stellar objects (MYSOs) and H II regions. The most detected lines are N2H+ (J = 1 - 0), HCO+ (J = 1 - 0), HNC (J = 1 - 0), HCN (J = 1 - 0), HC3N (J = 10 - 9), H13CO+ (J = 1 - 0), C2H (N = 1 - 0) and SiO (J = 2 - 1), indicating that most EGOs are indeed associated with dense clumps and recent outflow activities. The velocity widths of the N2H+ (J = 1 - 0), H13CO+ (J = 1 - 0), C2H (N = 1 - 0) and HC3N (J = 10 - 9) lines are comparable to each other in MYSOs. However, in H II regions the velocity widths of the N2H+ (J = 1 - 0) and C2H (N = 1 - 0) lines tend to be narrower than those of H13CO+ (J = 1 - 0) and HC3N (J = 10 - 9). Our results seem to support that N2H+ and C2H emissions mainly come from the gas inside quiescent clumps. In addition, we also find that the [N2H+]/[H13CO+] and [C2H]/[H13CO+] relative abundance ratios decrease from MYSOs to H II regions. These results suggest depletion of N2H+ and C2H in the late stages of massive-star formation, probably caused by the formation of H II regions inside. N2H+ and C2H might be used as chemical clocks for massive-star formation by comparing with other molecules such as H13CO+ and HC3N.

  2. A super lithium-rich red-clump star in the open cluster Trumpler 5

    NASA Astrophysics Data System (ADS)

    Monaco, L.; Boffin, H. M. J.; Bonifacio, P.; Villanova, S.; Carraro, G.; Caffau, E.; Steffen, M.; Ahumada, J. A.; Beletsky, Y.; Beccari, G.

    2014-04-01

    Context. The existence of lithium-rich low-mass red giant stars still represents a challenge for stellar evolution models. Stellar clusters are privileged environments for this kind of investigation. Aims: To investigate the chemical abundance pattern of the old open cluster Trumpler 5, we observed a sample of four red-clump stars with high-resolution optical spectrographs. One of them (#3416) reveals extremely strong lithium lines in its spectrum. Methods: One-dimensional, local thermodynamic equilibrium analysis was performed on the spectra of the observed stars. A 3D-NLTE analysis was performed to derive the lithium abundance of star #3416. Results: Star #3416 is super Li-rich with A(Li) = 3.75 dex. The lack of 6Li enrichment (6Li/7Li < 2%), the low carbon isotopic ratio (12C/13C = 14 ± 3), and the lack of evidence for radial velocity variation or enhanced rotational velocity (vsini = 2.8 km s-1) all suggest that lithium production has occurred in this star through the Cameron & Fowler mechanism. Conclusions: We identified a super Li-rich core helium-burning, red-clump star in an open cluster. Internal production is the most likely cause of the observed enrichment. Given the expected short duration of a star's Li-rich phase, enrichment is likely to have occurred at the red clump or in the immediately preceding phases, namely during the He-flash at the tip of the red giant branch (RGB) or while ascending the brightest portion of the RGB. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 088.D-0045(A).Appendix A is available in electronic form at http://www.aanda.org

  3. Clumping in the Cassini Division and C Ring: Constraints from Stellar Occultations

    NASA Astrophysics Data System (ADS)

    Colwell, J. E.; Jerousek, R. G.; Esposito, L. W.

    2014-12-01

    Particles in Saturn's rings are engaged in a constant tug-of-war between interparticle gravitational and adhesive forces that lead to clumping, on the one hand, and Keplerian shear that inhibits accretion on the other. Depending on the surface mass density of the rings and the local orbital velocity, ephemeral clumps or self-gravity wakes can form, giving the rings granularity on the scale of the most-unstable length scale against gravitational collapse. The A ring and many regions of the B ring are dominated by self-gravity wakes with a typical radial wavelength of ~50-100 m. A characteristic of self-gravity wakes is that they can effectively shadow the relatively empty spaces in between them, depending on viewing geometry. This leads to geometry-dependent measurements of optical depth in occultations of the rings. The C ring and Cassini Division have significantly lower surface mass densities than the A and B ring such that in most of these regions the most-unstable wavelength is comparable to the size of the ring particles (~1 m) so that self-gravity wake formation is not expected nor have its characteristics in various measurements been observed. Here we present measurements of the optical depth of the C ring and Cassini Division with the Cassini Ultraviolet Imaging Spectrograph (UVIS) showing variations with viewing geometry in the "ramp" regions and the Cassini Division "triple band". These variations are characteristic of self-gravity wakes. We place limits on clumping in other regions of the C ring and Cassini Division.

  4. The Kinematic and Chemical Properties of a Potential Core-forming Clump: Perseus B1-E

    NASA Astrophysics Data System (ADS)

    Sadavoy, S. I.; Shirley, Y.; Di Francesco, J.; Henning, Th.; Currie, M. J.; André, Ph.; Pezzuto, S.

    2015-06-01

    We present 13CO and {{C}18}O (1-0), (2-1), and (3-2) maps toward the core-forming Perseus B1-E clump using observations from the James Clerk Maxwell Telescope, the Submillimeter Telescope of the Arizona Radio Observatory, and the IRAM 30 m telescope. We find that the 13CO and {{C}18}O line emission both have very complex velocity structures, indicative of multiple velocity components within the ambient gas. The (1-0) transitions reveal a radial velocity gradient across B1-E of ˜ 1 km {{s}-1} p{{c}-1} that increases from northwest to southeast, whereas the majority of the Perseus cloud has a radial velocity gradient increasing from southwest to northeast. In contrast, we see no evidence of a velocity gradient associated with the denser Herschel-identified substructures in B1-E. Additionally, the denser substructures have much lower systemic motions than the ambient clump material, which indicates that they are likely decoupled from the large-scale gas. Nevertheless, these substructures themselves have broad line widths (˜0.4 km {{s}-1}) similar to that of the {{C}18}O gas in the clump, which suggests they inherited their kinematic properties from the larger-scale, moderately dense gas. Finally, we find evidence of {{C}18}O depletion only toward one substructure, B1-E2, which is also the only object with narrow (transonic) line widths. We suggest that as prestellar cores form, their chemical and kinematic properties are linked in evolution, such that these objects must first dissipate their turbulence before they deplete in CO.

  5. EVIDENCE FOR INFLOW IN HIGH-MASS STAR-FORMING CLUMPS

    SciTech Connect

    Reiter, Megan; Shirley, Yancy L.; Wu Jingwen; Brogan, Crystal; Wootten, Alwyn; Tatematsu, Ken'ichi E-mail: yshirley@as.arizona.edu E-mail: cbrogan@nrao.edu E-mail: k.tatematsu@nao.ac.jp

    2011-10-10

    We analyze the HCO{sup +} 3-2 and H{sup 13}CO{sup +} 3-2 line profiles of 27 high-mass star-forming regions to identify asymmetries that are suggestive of mass inflow. Three quantitative measures of line asymmetry are used to indicate whether a line profile is blue, red, or neither-the ratio of the temperature of the blue and red peaks, the line skew, and the dimensionless parameter {delta}v. We find nine HCO{sup +} 3-2 line profiles with a significant blue asymmetry and four with significant red asymmetric profiles. Comparing our HCO{sup +} 3-2 results to HCN 3-2 observations from Wu et al., we find that eight of the blue and three of the red have profiles with the same asymmetry in HCN. The eight sources with blue asymmetries in both tracers are considered strong candidates for inflow. Quantitative measures of the asymmetry (e.g., {delta}v) tend to be larger for HCN. This, combined with possible HCO{sup +} abundance enhancements in outflows, suggests that HCN may be a better tracer of inflow. Understanding the behavior of common molecular tracers like HCO{sup +} in clumps of different masses is important for properly analyzing the line profiles seen in a sample of sources representing a broad range of clump masses. Such studies will soon be possible with the large number of sources with possible self-absorption seen in spectroscopic follow-up observations of clumps identified in the Bolocam Galactic Plane Survey.

  6. A new calibration curve for carbonate clumped isotope thermometer of land snail shells (aragonite)

    NASA Astrophysics Data System (ADS)

    Zhang, N.; Yamada, K.; Yoshida, N.

    2013-12-01

    Clumped isotope data (Δ47) of carbonate is considered as a useful tool to reflect both the temperature and oxygen isotopic composition of water where the carbonate grew [1]. Zarrur et al. reported the relationship between snail shell calcification temperatures and the mean annual/ activity season ambient temperatures based on a calibration curve established by Ghosh et al. [2]. However, the clumped isotope temperature is always higher than the environment temperature. For better understanding this phenomenon, we present a new empirical calibration curve based on land snail shells (aragonite) cultured in the controlled temperature environment. In 2012, we cultured the land snails ';Euhadra' which were collected from Yokohama, Japan. They were cultured from eggs to adults around 6-8 months under the temperature of 20°, 25° and 30°, respectively. Each temperature group contains 15-20 snails. All of them were fed by cabbages during their life span. To study the effect of ingested carbonate, some of them were fed by Ca3(PO4)2 powder while others were fed by CaCO3 powder. Clumped isotope data for all samples were analyzed by a Thermo Finnigan MAT 253 Mass Spectrometer and calibrated by an ';absolute reference frame' [3]. We found an empirical linear relationship between Δ47 and controlled ambient temperature, which is slightly deviated from the published theoretical and experimental calibration curves based on both inorganic and biogenic materials. We will discuss the potential controlling factors caused this kind of deviation combine with the land snail growth environment. [1] Ghosh et al., 2006, Geochimica et Cosmochimica Acta. 70, 1439-1456 [2] Zaarur et al. 2011. Geochimica et Cosmochimica Acta, 75, 6859-6869 [3] Dennis et al., 2011. Geochimica et Cosmochimica Acta 75, 7117-7131

  7. An automated method for 'clumped-isotope' measurements on small carbonate samples.

    PubMed

    Schmid, Thomas W; Bernasconi, Stefano M

    2010-07-30

    Clumped-isotope geochemistry deals with the state of ordering of rare isotopes in molecules, in particular with their tendency to form bonds with other rare isotopes rather than with the most abundant ones. Among its possible applications, carbonate clumped-isotope thermometry is the one that has gained most attention because of the wide potential of applications in many disciplines of earth sciences. Clumped-isotope thermometry allows reconstructing the temperature of formation of carbonate minerals without knowing the isotopic composition of the water from which they were formed. This feature enables new approaches in paleothermometry. The currently published method is, however, limited by sample weight requirements of 10-15 mg and because measurements are performed manually. In this paper we present a new method using an automated sample preparation device coupled to an isotope ratio mass spectrometer. The method is based on the repeated analysis (n = 6-8) of 200 microg aliquots of sample material and completely automated measurements. In addition, we propose to use precisely calibrated carbonates spanning a wide range in Delta(47) instead of heated gases to correct for isotope effects caused by the source of the mass spectrometer, following the principle of equal treatment of the samples and standards. We present data for international standards (NBS 19 and LSVEC) and different carbonates formed at temperatures exceeding 600 degrees C to show that precisions in the range of 10 to 15 ppm (1 SE) can be reached for repeated analyses of a single sample. Finally, we discuss and validate the correction procedure based on high-temperature carbonates instead of heated gases.

  8. Dust Growth by RF Sputtering

    SciTech Connect

    Churton, B.; Samarian, A. A.; Coueedel, L.

    2008-09-07

    The effect of the dust particle growth by RF sputtering on glow discharge has been investigated. It has been found that the growth of dust particles modifies the electrical characteristics of the discharge. In particularly, the absolute value of the self-bias voltage decreases during the particle growth due to the electron losses on the dust particles. To find the correlation between the dust growth and the self bias evolution, dust particles have been collected at different times. The dust particle growth rate is found to be linear.

  9. Interstellar dust at our doorstep

    NASA Astrophysics Data System (ADS)

    Sterken, V. J.

    2013-12-01

    Interstellar dust has long been researched by astronomical methods to learn about its size distribution, grain properties and composition. However, interstellar dust grains also move through the solar system. They were detected for the first time in-situ with the Ulysses dust detector in 1993. In addition, in 2006, the Stardust mission returned three interstellar dust grain candidates back to Earth after a collection period of 195 days. In this talk we elaborate on how the current in-situ ISD measurement methods are a valuable addition to the knowledge about interstellar dust inferred from classical astronomy. We also discuss the role of interstellar dust dynamics and simulations herein.

  10. Oblique dust density waves

    NASA Astrophysics Data System (ADS)

    Piel, Alexander; Arp, Oliver; Menzel, Kristoffer; Klindworth, Markus

    2007-11-01

    We report on experimental observations of dust density waves in a complex (dusty) plasma under microgravity. The plasma is produced in a radio-frequency parallel-plate discharge (argon, p=15Pa, U=65Vpp). Different sizes of dust particles were used (3.4 μm and 6.4μm diameter). The low-frequency (f 11Hz) dust density waves are naturally unstable modes, which are driven by the ion flow in the plasma. Surprisingly, the wave propagation direction is aligned with the ion flow direction in the bulk plasma but becomes oblique at the boundary of the dust cloud with an inclination of 60^o with respect to the plasma boundary. The experimental results are compared with a kinetic model in the electrostatic approximation [1] and a fluid model [2]. Moreover, the role of dust surface waves is discussed. [1] M. Rosenberg, J. Vac. Sci. Technol. A 14, 631 (1996) [2] A. Piel et al, Phys. Rev. Lett. 97, 205009 (2006)

  11. Conveyor dust control

    SciTech Connect

    Goldbeck, L.

    1999-11-01

    In the past, three different approaches have been used to control dust arising at conveyor load zones. They are: Dust Containment consists of those mechanical systems employed to keep material inside the transfer point with the main material body. Dust Suppression systems increase the mass of suspended dust particles, allowing them to fall from the air stream. Dust Collection is the mechanical capture and return of airborne material after it becomes airborne from the main material body. Previously, these three approaches have always been seen as separate entities. They were offered by separate organizations competing in the marketplace. The three technologies vied for their individual piece of the rock, at the expense of the other technologies (and often at the expense of overall success). There have been considerable amounts of I`m better selling, as well as finger pointing at the other systems when problems arose. Each system claimed its own technology was the best, providing the most effective, most cost-efficient, most maintenance-free solution to fugitive material.

  12. 13C 18O clumping in speleothems: Observations from natural caves and precipitation experiments

    NASA Astrophysics Data System (ADS)

    Daëron, M.; Guo, W.; Eiler, J.; Genty, D.; Blamart, D.; Boch, R.; Drysdale, R.; Maire, R.; Wainer, K.; Zanchetta, G.

    2011-06-01

    The oxygen isotope composition of speleothems is an important proxy of continental paleoenvironments, because of its sensitivity to variations in cave temperature and drip water δ 18O. Interpreting speleothem δ 18O records in terms of absolute paleotemperatures and δ 18O values of paleo-precipitation requires quantitative separation of the effects of these two parameters, and correcting for possible kinetic isotope fractionation associated with precipitation of calcite out of thermodynamic equilibrium. Carbonate clumped-isotope thermometry, based on measurements of Δ47 (a geochemical variable reflecting the statistical overabundance of 13C 18O bonds in CO 2 evolved from phosphoric acid digestion of carbonate minerals), potentially provides a method for absolute speleothem paleotemperature reconstructions independent of drip water composition. Application of this new technique to karst records is currently limited by the scarcity of published clumped-isotope studies of modern speleothems. The only modern stalagmite reported so far in the literature yielded a lower Δ47 value than expected for equilibrium precipitation, possibly due to kinetic isotope fractionation. Here we report Δ47 values measured in natural speleothems from various cave settings, in carbonate produced by cave precipitation experiments, and in synthetic stalagmite analogs precipitated in controlled laboratory conditions designed to mimic natural cave processes. All samples yield lower Δ47 and heavier δ 18O values than predicted by experimental calibrations of thermodynamic equilibrium in inorganic calcite. The amplitudes of these isotopic disequilibria vary between samples, but there is clear correlation between the amount of Δ47 disequilibrium and that of δ 18O. Even pool carbonates believed to offer excellent conditions for equilibrium precipitation of calcite display out-of-equilibrium δ 18O and Δ47 values, probably inherited from prior degassing within the cave system. In addition

  13. The calibration of clumped-isotope thermometry on modern marine mollusk

    NASA Astrophysics Data System (ADS)

    Canavan, R. R.; Affek, H. P.; Zaarur, S.; Douglas, P. M.; Wang, Z.

    2013-12-01

    Clumped-isotope (Δ47) thermometry is a novel method to reconstruct paleotemperatures that can be applied to studying past coastal and marine environments using marine mollusk shells. Macrofossil mollusk shells are common in the fossil record and provide enough material to satisfy the relatively large-sample requirement for Δ47 analysis, making them ideal for clumped-isotope paleothermometry. If consistent with the clumped isotope thermometer, mollusk Δ47 derived temperatures should record local water temperatures during shell growth season. Recent studies, however, show strong deviations from the empirical Δ47-T calibration derived from synthetic calcite in some modern mollusk shells (cephalopods, gastropods and bivalves; Dennis et al., 2013; Henkes et al., 2013; Eagle et al., 2013) but not in others (bivalves; Douglas et al., submitted; Came et al., 2007). The source of these discrepancies has been hypothesized to be related to 1) different laboratory techniques (including sample preparation and instrument standardization), 2) growth of CaCO3 polymorphs (calcite, aragonite or vaterite) in shells, and 3) variable environmental growth conditions such as salinity and pH. We test the effect of CaCO3 polymorph, taxonomy, and mollusk growth conditions by comparing among Δ47 values of calcitic shells from eastern oysters (Crassostrea virginica), those of clam shells that are mostly aragonitic (collected along the United States' Atlantic coast), and published calibrations of the clumped isotope thermometer. Atlantic oysters were collected from 37°N to 43°N latitude, with temperatures ranging between ~ 10-25°C, and brackish to marine salinities ranging from 14.5 - 34 PSU. Clam genera were similarly collected along the coast between Florida up north to Maine with growth temperatures ranging from ~ 10-22 °C. We further examine whether the deviation from the calibration is related to the relatively low reproducibility observed in modern mollusk Δ47 measurements, and

  14. Quantifier Comprehension in Corticobasal Degeneration

    ERIC Educational Resources Information Center

    McMillan, Corey T.; Clark, Robin; Moore, Peachie; Grossman, Murray

    2006-01-01

    In this study, we investigated patients with focal neurodegenerative diseases to examine a formal linguistic distinction between classes of generalized quantifiers, like "some X" and "less than half of X." Our model of quantifier comprehension proposes that number knowledge is required to understand both first-order and higher-order quantifiers.…

  15. MID-INFRARED EXTINCTION MAPPING OF INFRARED DARK CLOUDS. II. THE STRUCTURE OF MASSIVE STARLESS CORES AND CLUMPS

    SciTech Connect

    Butler, Michael J.; Tan, Jonathan C.

    2012-07-20

    We develop the mid-infrared extinction (MIREX) mapping technique of Butler and Tan (Paper I), presenting a new method to correct for the Galactic foreground emission based on observed saturation in independent cores. Using Spitzer GLIMPSE 8 {mu}m images, this allows us to accurately probe mass surface densities, {Sigma}, up to {approx_equal} 0.5 g cm{sup -2} with 2'' resolution and mitigate one of the main sources of uncertainty associated with Galactic MIREX mapping. We then characterize the structure of 42 massive starless and early-stage cores and their surrounding clumps, selected from 10 infrared dark clouds, measuring {Sigma}{sub cl}(r) from the core/clump centers. We first assess the properties of the core/clump at a scale where the total enclosed mass as projected on the sky is M{sub cl} = 60 M{sub Sun }. We find that these objects have a mean radius of R{sub cl} {approx_equal} 0.1 pc, mean {Sigma}{sub cl} = 0.3 g cm{sup -} and, if fitted by a power-law (PL) density profile {rho}{sub cl}{proportional_to}r{sup -k{sub {rho}}{sub ,}{sub c}{sub l}}, a mean value of k{sub {rho},cl} = 1.1. If we assume a core is embedded in each clump and subtract the surrounding clump envelope to derive the core properties, then we find a mean core density PL index of k{sub {rho},c} = 1.6. We repeat this analysis as a function of radius and derive the best-fitting PL plus uniform clump envelope model for each of the 42 core/clumps. The cores have typical masses of M{sub c} {approx} 100 M{sub Sun} and {Sigma}-bar{sub c} {approx} 0.1 g cm{sup -2}, and are embedded in clumps with comparable mass surface densities. We also consider Bonnor-Ebert density models, but these do not fit the observed {Sigma} profiles as well as PLs. We conclude that massive starless cores exist and are well described by singular polytropic spheres. Their relatively low values of {Sigma} and the fact that they are IR dark may imply that their fragmentation is inhibited by magnetic fields rather than

  16. Research allays longwall dust

    SciTech Connect

    Scott, F.E.

    1984-02-01

    Longwall shearer operators have to walk with their machines along the face to mine coal, but some must endure more respirable dust than others. The Bureau of Mines is willing to help any mine having trouble keeping dust levels below the Federal standard of 2.0 mg/m/sup 3/. Recently, Robert A. Jankowski and others at the Bureau of Mines (BoM) completed a survey of twelve US longwall mines. With the cooperation of mine operators and Mine Safety and Health Administration (MSHA) officials, they gathered information on longwall double-drum shearer installations from compliance records. Six of the operations examined were ''clean'' or regularly in compliance with the dust standard, while the other six had great difficulty in complying. Subsequently, BoM conducted an investigation into the reasons for the non-compliance and a search for possible solutions to the problems.

  17. Dust control for draglines

    SciTech Connect

    Grad, P.

    2009-09-15

    Monitoring dust levels inside draglines reveals room for improvement in how filtration systems are used and maintained. The Australian firm BMT conducted a field test program to measure airflow parameters, dust fallout rates and dust concentrations, inside and outside the machine house, on four draglines and one shovel. The study involved computational fluid dynamics (CFD) simulations. The article describes how the tests were made and gives results. It was not possible to say which of the two main filtration systems currently used on Australian draglines - Dynavane or Floseps - performs better. It would appear that more frequent maintenance and cleaning would increase the overall filtration performance and systems could be susceptible to repeat clogging in a short time. 2 figs., 1 photos.

  18. Selecting baghouse dust collectors

    SciTech Connect

    Moore, S.; Rubak, J.; Jolin, M. |

    1997-04-01

    A thorough analysis of the dust to be captured and determination of specific application requirements are necessary when designing a baghouse collection system. Independent consultants specializing in pollution control equipment and manufacturers with experience in several types of collectors are possible sources of assistance. These experts typically have testing facilities to analyze the dust characteristics. This final article of a two-part series on baghouse design and selection concentrates on application considerations created by the type of dust handled, selecting the best filtration media, selecting the best filtration media, and determining the air-to-cloth (A/C) ratio. The first article discussed bag sizing and cleaning methods and housing and hopper designs.

  19. High concentration dust monitor

    NASA Astrophysics Data System (ADS)

    Lilienfeld, P.

    1981-06-01

    The development, design, fabrication, and testing of a portable, self-contained prototype monitoring instrument capable of detecting and measuring airborne coal dust levels as concentrations in the range of 20 to 500 g/cu m is described. The output of the high concentration dust monitor is essentially independent of particle size and composition, with a response time of 10 seconds. Direct concentration readout as well as internal memory or recording capabilities are incorporated in the device. The operation of the instrument is based on direct sensing of the mass concentration of airborne dust by air-path beta radiation attenuation. The monitor is battery operated and incorporates a microprocessor that controls periodic automatic zero referencing, executes the mass computations, records the data for subsequent playback, and performs internal diagnostic checks.

  20. Evidence from carbonate clumped isotope (Δ47) thermometry for the Late Cretaceous `Nevadaplano' in the northern Basin and Range Province

    NASA Astrophysics Data System (ADS)

    Snell, K. E.; Koch, P. L.; Eiler, J.

    2010-12-01

    From the middle Mesozoic to the present, the topography of the Basin and Range province (BRP) of the western Cordillera of North America has evolved in response to diverse tectonic forces, though the details are unclear for most of this period over most of this area. Much of the research on this region has focused on the Cenozoic record of paleoelevation during extension in the BRP. Some geodynamic models of this episode require high elevation prior to extension, but few studies have quantified the elevation of the pre-existing topography that developed during the Mesozoic in response to sustained convergence along the western coast of North America. Some workers have argued that the region was a high elevation plateau, the ‘Nevadaplano,’ analogous to the South American Altiplano. We tested this hypothesis using carbonate clumped isotope (Δ47) temperature estimates from Late Cretaceous lacustrine and paleosol carbonates. These samples come from the Sheep Pass Formation in east-central Nevada (presumed from geologic indications to be atop the plateau), and the North Horn Formation in central Utah on the eastern edge of the Sevier fold and thrust belt (presumably lower elevation). The textural characteristics, stable isotope compositions and carbonate clumped isotope temperature estimates from secondary carbonates in these units suggest that, despite moderate burial, primary carbonate samples have undergone little diagenetic alteration. Average temperatures from these two sites (23°C for the NV suite and 38°C for the UT suite) suggest that during the late Cretaceous (~66.5 Ma for the NV suite and 72 Ma for the UT suite), the NV site was ~15°C cooler than the UT site. This thermal gradient implies an elevation difference between the two sites of ~2.5 km, given certain assumptions: 1) there was little global or regional climate change during the ~5 million years between formation of these samples, 2) precipitation of both the lacustrine and paleosol carbonates

  1. Quantifying the adaptive cycle

    USGS Publications Warehouse

    Angeler, David G.; Allen, Craig R.; Garmestani, Ahjond S.; Gunderson, Lance H.; Hjerne, Olle; Winder, Monika

    2015-01-01

    The adaptive cycle was proposed as a conceptual model to portray patterns of change in complex systems. Despite the model having potential for elucidating change across systems, it has been used mainly as a metaphor, describing system dynamics qualitatively. We use a quantitative approach for testing premises (reorganisation, conservatism, adaptation) in the adaptive cycle, using Baltic Sea phytoplankton communities as an example of such complex system dynamics. Phytoplankton organizes in recurring spring and summer blooms, a well-established paradigm in planktology and succession theory, with characteristic temporal trajectories during blooms that may be consistent with adaptive cycle phases. We used long-term (1994–2011) data and multivariate analysis of community structure to assess key components of the adaptive cycle. Specifically, we tested predictions about: reorganisation: spring and summer blooms comprise distinct community states; conservatism: community trajectories during individual adaptive cycles are conservative; and adaptation: phytoplankton species during blooms change in the long term. All predictions were supported by our analyses. Results suggest that traditional ecological paradigms such as phytoplankton successional models have potential for moving the adaptive cycle from a metaphor to a framework that can improve our understanding how complex systems organize and reorganize following collapse. Quantifying reorganization, conservatism and adaptation provides opportunities to cope with the intricacies and uncertainties associated with fast ecological change, driven by shifting system controls. Ultimately, combining traditional ecological paradigms with heuristics of complex system dynamics using quantitative approaches may help refine ecological theory and improve our understanding of the resilience of ecosystems.

  2. Quantifying T Lymphocyte Turnover

    PubMed Central

    De Boer, Rob J.; Perelson, Alan S.

    2013-01-01

    Peripheral T cell populations are maintained by production of naive T cells in the thymus, clonal expansion of activated cells, cellular self-renewal (or homeostatic proliferation), and density dependent cell life spans. A variety of experimental techniques have been employed to quantify the relative contributions of these processes. In modern studies lymphocytes are typically labeled with 5-bromo-2′-deoxyuridine (BrdU), deuterium, or the fluorescent dye carboxy-fluorescein diacetate succinimidyl ester (CFSE), their division history has been studied by monitoring telomere shortening and the dilution of T cell receptor excision circles (TRECs) or the dye CFSE, and clonal expansion has been documented by recording changes in the population densities of antigen specific cells. Proper interpretation of such data in terms of the underlying rates of T cell production, division, and death has proven to be notoriously difficult and involves mathematical modeling. We review the various models that have been developed for each of these techniques, discuss which models seem most appropriate for what type of data, reveal open problems that require better models, and pinpoint how the assumptions underlying a mathematical model may influence the interpretation of data. Elaborating various successful cases where modeling has delivered new insights in T cell population dynamics, this review provides quantitative estimates of several processes involved in the maintenance of naive and memory, CD4+ and CD8+ T cell pools in mice and men. PMID:23313150

  3. Quantifying the Adaptive Cycle.

    PubMed

    Angeler, David G; Allen, Craig R; Garmestani, Ahjond S; Gunderson, Lance H; Hjerne, Olle; Winder, Monika

    2015-01-01

    The adaptive cycle was proposed as a conceptual model to portray patterns of change in complex systems. Despite the model having potential for elucidating change across systems, it has been used mainly as a metaphor, describing system dynamics qualitatively. We use a quantitative approach for testing premises (reorganisation, conservatism, adaptation) in the adaptive cycle, using Baltic Sea phytoplankton communities as an example of such complex system dynamics. Phytoplankton organizes in recurring spring and summer blooms, a well-established paradigm in planktology and succession theory, with characteristic temporal trajectories during blooms that may be consistent with adaptive cycle phases. We used long-term (1994-2011) data and multivariate analysis of community structure to assess key components of the adaptive cycle. Specifically, we tested predictions about: reorganisation: spring and summer blooms comprise distinct community states; conservatism: community trajectories during individual adaptive cycles are conservative; and adaptation: phytoplankton species during blooms change in the long term. All predictions were supported by our analyses. Results suggest that traditional ecological paradigms such as phytoplankton successional models have potential for moving the adaptive cycle from a metaphor to a framework that can improve our understanding how complex systems organize and reorganize following collapse. Quantifying reorganization, conservatism and adaptation provides opportunities to cope with the intricacies and uncertainties associated with fast ecological change, driven by shifting system controls. Ultimately, combining traditional ecological paradigms with heuristics of complex system dynamics using quantitative approaches may help refine ecological theory and improve our understanding of the resilience of ecosystems.

  4. THE MYSTERIOUS SICKLE OBJECT IN THE CARINA NEBULA: A STELLAR WIND INDUCED BOW SHOCK GRAZING A CLUMP?

    SciTech Connect

    Ngoumou, Judith; Preibisch, Thomas; Ratzka, Thorsten; Burkert, Andreas

    2013-06-01

    Optical and near-infrared images of the Carina Nebula show a peculiar arc-shaped feature, which we call the ''Sickle'', next to the B-type star Trumpler 14 MJ 218. We use multi-wavelength observations to explore and constrain the nature and origin of the nebulosity. Using submillimeter data from APEX/LABOCA as well as Herschel far-infrared maps, we discovered a dense, compact clump with a mass of {approx}40 M{sub Sun} located close to the apex of the Sickle. We investigate how the B star MJ 218, the Sickle, and the clump are related. Our numerical simulations show that, in principle, a B-type star located near the edge of a clump can produce a crescent-shaped wind shock front, similar to the observed morphology. However, the observed proper motion of MJ 218 suggests that the star moves with high velocity ({approx}100 km s{sup -1}) through the ambient interstellar gas. We argue that the star is just about to graze along the surface of the clump, and the Sickle is a bow shock induced by the stellar wind, as the object moves supersonically through the density gradient in the envelope of the clump.

  5. STAR FORMATION AND DISTRIBUTIONS OF GAS AND DUST IN THE CIRCINUS CLOUD

    SciTech Connect

    Shimoikura, Tomomi; Dobashi, Kazuhito

    2011-04-10

    We present results of a study on the Circinus cloud based on {sup 13}CO (J = 1 - 0) data as well as visual to near-infrared (JHK{sub S}) extinction maps, to investigate the distributions of gas and dust around the cloud. The global {sup 13}CO distribution of the Circinus cloud is revealed for the first time, and the total molecular mass of the cloud is estimated to be 2.5 x 10{sup 4} M{sub sun} for the assumed distance 700 pc. Two massive clumps in the cloud, called Circinus-W and Circinus-E, have a mass of {approx}5 x 10{sup 3} M{sub sun}. These clumps are associated with a number of young stellar objects (YSOs) searched for in the literature, indicating that they are the most active star-forming sites in Circinus. All of the extinction maps show good agreement with the {sup 13}CO distribution. We derived the average N({sup 13}CO)/A{sub V} ratio in the Circinus cloud to be 1.25 x 10{sup 15} cm{sup -2} mag{sup -1} by comparing the extinction maps with the {sup 13}CO data. The extinction maps also allowed us to probe into the reddening law over the Circinus cloud. We found that there is a clear change in dust properties in the densest regions of Circinus-W and Circinus-E, possibly due to grain growth in the dense cloud interior. Among the YSOs found in the literature, we attempted to infer the ages and masses of the H{alpha} emission-line stars forming in the two clumps, and found that they are likely to be younger than 1 Myr, having a relatively small mass of {approx}<2 M{sub sun} at the zero-age main sequence.

  6. Tikhonravov Crater Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    These dust avalanches are located within a small crater inside Tikhonravov Crater.

    Image information: VIS instrument. Latitude 12.6, Longitude 37.1 East (322.9 West). 36 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  7. Lycus Sulci Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    These dust avalanches occur on the slopes of Lycus Sulci near Olympus Mons.

    Image information: VIS instrument. Latitude 28.1, Longitude 220.4 East (139.6 West). 18 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  8. Crater Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    These dust avalanches are located in a small canyon within a crater rim northeast of Naktong Vallis.

    Image information: VIS instrument. Latitude 7.1, Longitude 34.7 East (325.3 West). 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  9. Crater Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    This region of dust avalanches is located in and around a crater to the west of yesterday's image.

    Image information: VIS instrument. Latitude 14.7, Longitude 32.7 East (327.3 West). 18 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  10. Combustibility determination for cotton gin dust and almond huller dust

    Technology Transfer Automated Retrieval System (TEKTRAN)

    It has been documented that some dusts generated while processing agricultural products, such as grain and sugar (OSHA, 2009), can constitute combustible dust hazards. After a catastrophic dust explosion in a sugar refinery in 2008, OSHA initiated action to develop a mandatory standard to comprehen...

  11. Dust Devils : How many, how big, and how deadly ?

    NASA Astrophysics Data System (ADS)

    Lorenz, R. D.

    2015-12-01

    Dust devils are significant agents of dust-lifting on Mars, but their importance on Earth has been debated. Accurate quantification of the amount of dust-lifting by devils on Earth requires an understanding of the population of devils (i.e. the formation rate of devils of different diameters as a function of meteorological conditions, their longevity and their dust-lifting intensity). Correlation among these parameters (e.g. large devils last longer) means great care must be taken in evaluating the population integral - the contribution of 'average' devils may be dwarfed by the few largest ones, but large area-time surveys are needed to detect the rare giants. Significant progress has been made in quantifying the vortex population in the field using new pressure-logging instrumentation to generate robust statistics which appear also consistent with Large Eddy Simulations, and the vortex population can be reconciled with visual dust devil counts using Monte Carlo modeling, where core pressure drop is a useful intensity metric, and a threshold of about 0.3 hPa corresponds to visible dust lifting. Further field measurements are exploring the parameter correlation, and vortex model-fitting is being use to estimate diameter and core pressure drop by combining pressure and wind speed/direction data at a single station, a technique that may be useful in the upcoming InSight mission at Mars, where dust devils may be a useful seismic source to probe the near-surface regolith structure. Array measurements with multiple stations are also yielding powerful results. The core pressure drop can also be related to the weight-loading of structures for the quantification of dust devils as a hazard. In fact, dust devils are responsible for a number of deaths on the ground (in addition to aircraft and parachuting accidents) which will be briefly reviewed.

  12. Lunar Horizon Glow: A Quantitative Indicator of Exospheric Dust

    NASA Astrophysics Data System (ADS)

    Glenar, D. A.; Stubbs, T. J.; Vondrak, R. R.

    2008-12-01

    During the Apollo missions, horizon glow (HG) was observed by astronauts in lunar orbit just prior to orbital sunrise. These observations were further supported by excess brightness which appeared along the horizon in coronal photographs from Apollo 15 and 17. Horizon glow may also be present in star tracker measurements acquired during the Clementine mission, though it would be heavily masked by coronal and zodiacal light (CZL). The most likely cause of HG is thought to be forward scattering of sunlight by submicron dust grains in the lunar exosphere above the terminator, extending to 10's of km or higher in altitude. Such a dust population is thought to arise from charged lunar dust that has been electrostatically lofted from the surface, since strong surface electric fields are believed to exist at the terminator. Additional contributions to exospheric dust will arise from meteoritic ejecta. With many missions now returning to the Moon, it is important to be able to distinguish and quantify the observable sources of UV-VIS optical emission, specifically HG from lunar exospheric dust, CZL, and line emission from exospheric gases. We have developed a code which simulates 3D (2D spatial plus spectral) intensities of horizon glow arising from lunar exospheric dust, as it would be viewed from an orbiter in lunar shadow. The dust vertical profile used is the semi-empirical model proposed by Murphy and Vondrak. Dust scattering properties as a function of grain size are computed using Mie Theory. The code also incorporates CZL intensities as formulated by Hahn et al., as well as Na D-line emission as observed by Potter and Morgan, in order to contrast these three emission sources near the limb via their distinct spatial distributions, spectral intensities and dependence on solar elongation angle. We include a simulation of lunar HG, as it might be observed by the UV/Vis spectrometer aboard the Lunar Atmosphere and Dust Environment Explorer (LADEE).

  13. Syrian Dust Devil

    NASA Technical Reports Server (NTRS)

    2005-01-01

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a dust devil in far western Syria Planum. The dust devil is located near the left-center of the image. It is casting a shadow toward the lower right (southeast).

    Location near: 14.5oS, 109.6oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Winter

  14. Dust Devil Tracks

    NASA Astrophysics Data System (ADS)

    Reiss, Dennis; Fenton, Lori; Neakrase, Lynn; Zimmerman, Michael; Statella, Thiago; Whelley, Patrick; Rossi, Angelo Pio; Balme, Matthew

    2016-11-01

    Dust devils that leave dark- or light-toned tracks are common on Mars and they can also be found on the Earth's surface. Dust devil tracks (hereinafter DDTs) are ephemeral surface features with mostly sub-annual lifetimes. Regarding their size, DDT widths can range between ˜1 m and ˜1 km, depending on the diameter of dust devil that created the track, and DDT lengths range from a few tens of meters to several kilometers, limited by the duration and horizontal ground speed of dust devils. DDTs can be classified into three main types based on their morphology and albedo in contrast to their surroundings; all are found on both planets: (a) dark continuous DDTs, (b) dark cycloidal DDTs, and (c) bright DDTs. Dark continuous DDTs are the most common type on Mars. They are characterized by their relatively homogenous and continuous low albedo surface tracks. Based on terrestrial and martian in situ studies, these DDTs most likely form when surficial dust layers are removed to expose larger-grained substrate material (coarse sands of ≥500 μm in diameter). The exposure of larger-grained materials changes the photometric properties of the surface; hence leading to lower albedo tracks because grain size is photometrically inversely proportional to the surface reflectance. However, although not observed so far, compositional differences (i.e., color differences) might also lead to albedo contrasts when dust is removed to expose substrate materials with mineralogical differences. For dark continuous DDTs, albedo drop measurements are around 2.5 % in the wavelength range of 550-850 nm on Mars and around 0.5 % in the wavelength range from 300-1100 nm on Earth. The removal of an equivalent layer thickness around 1 μm is sufficient for the formation of visible dark continuous DDTs on Mars and Earth. The next type of DDTs, dark cycloidal DDTs, are characterized by their low albedo pattern of overlapping scallops. Terrestrial in situ studies imply that they are formed when sand

  15. Natural variability versus human impact: Hydroclimate variability and the role of agriculture in changing dust emissions from Australia.

    NASA Astrophysics Data System (ADS)

    Marx, Samuel; Kamber, Balz; McGowan, Hamish; Hooper, James; Zawadzki, Atun

    2016-04-01

    Broad-scale dust emissions play an important role in Earth systems, for example influencing oceanic productivity via phytoplankton fertilisation. Existing palaeo dust records show that dust emissions vary significantly in time, implying its impact is similarly variable. There remains, however, a paucity of records which quantify variability in dust emissions. This study presents continuous, Holocene-aged, records of dust emissions from Australia, an important global dust source. Records demonstrate that rates of dust export have varied by 8-30 times over the mid to late Holocene. This variability is largely attributed to hydroclimate variability and its associated feedbacks within dust source areas. Significantly, however, a major disruption of dust emission rates is recorded in the past 200 years when dust emissions increased by between 2-10 times rates of natural variability in dust export. This change is concomitant with the arrival of Europeans in Australia and is primarily attributed to the development of agriculture which resulted in unprecedented environmental change in Australia's arid interior. This result broadly accords with the few other existing empirical dust records which both pre-date and post-date the onset of agriculture in various arid and semi-arid regions. Collectively, these records imply the impact of dust in Earth systems has changed as a result of agricultural development.

  16. Sensitivity of dust emissions to aerosol feedback and the impact of dust loading on climate forcing with varied resolutions using FIM-Chem

    NASA Astrophysics Data System (ADS)

    Zhang, Li; Grell, Georg; Henze, Daven; Mckeen, Stuart; Sun, Shan; Li, Haiqin

    2016-04-01

    Meteorological conditions directly impact aerosol loading, especially dust emissions. Variations in dust emissions on the other hand, will also impact meteorology and climate through direct and indirect aerosol forcing. To study these impacts in more detail we use the global Flow-following finite-volume Icosahedra Model (FIM, http://fim.noaa.gov/), a new global weather prediction model currently under development in the Global Systems Division of NOAA/ESRL, as it is coupled online with the aerosol modules from the Goddard Gobal Ozone Chemistry Aerosol Radiation and Transport (GOCART) model (FIM-Chem). FIM-Chem includes direct and semi direct feedback, and uses the dust schemes of GOCART and the Air Force Weather Agency (AFWA). FIM-Chem is able to investigate the contribution of climate feedbacks to simulated hyperspectral data by considering a range of simulations with different dust emissions and different levels of aerosol feedbacks enabled at four different spatial resolutions. The emitted dust flux and total emissions are highly depending on the wind, soil moisture and model resolution. We compare the dust emissions by including and excluding the aerosol radiative feedback in the simulations to quantify the sensitivity of dust emissions to aerosol feedback. The results show that all aerosol-induced dust emissions increase about 10% globally, which is mainly dominated by the contributions of anthropogenic black carbon (EC) aerosol. While the dust-induced percentage changes of dust emissions are about -5.5%, that indicates reduction effect globally. Also, the simulations based on different resolutions of 240x240 km, 120x120 km, 60x60 km and 30x30 km are performed to test the impacts of model resolution on total dust emissions. By comparing the dust emission sensitivity to aerosol feedback and model resolution, we can estimate the uncertainty of model resolution versus aerosol feedback. We also conduct FIM-Chem simulations to investigate the sensitivity of dust

  17. Dust Devils Whip by Spirit

    NASA Technical Reports Server (NTRS)

    2007-01-01

    On sol 1120 (February 26, 2007), the navigation camera aboard NASA's Mars Exploration Rover Spirit captured one of the best dust devils it's seen in its three-plus year mission. The series of navigation camera images were put together to make a dust devil movie.

    The dust devil column is clearly defined and is clearly bent in the down wind direction. Near the end of the movie, the base of the dust devil becomes much wider. The atmospheric science team thinks that this is because the dust devil encountered some sand and therefore produced a 'saltation skirt,' an apron of material that is thrown out of the dust devil because it is too large to be carried up into suspension.

    Also near the end of the movie the dust devil seems to move faster across the surface. This is because Spirit began taking pictures less frequently, and not because the dust devil sped up.

  18. Quantifying Anderson's fault types

    USGS Publications Warehouse

    Simpson, R.W.

    1997-01-01

    Anderson [1905] explained three basic types of faulting (normal, strike-slip, and reverse) in terms of the shape of the causative stress tensor and its orientation relative to the Earth's surface. Quantitative parameters can be defined which contain information about both shape and orientation [Ce??le??rier, 1995], thereby offering a way to distinguish fault-type domains on plots of regional stress fields and to quantify, for example, the degree of normal-faulting tendencies within strike-slip domains. This paper offers a geometrically motivated generalization of Angelier's [1979, 1984, 1990] shape parameters ?? and ?? to new quantities named A?? and A??. In their simple forms, A?? varies from 0 to 1 for normal, 1 to 2 for strike-slip, and 2 to 3 for reverse faulting, and A?? ranges from 0?? to 60??, 60?? to 120??, and 120?? to 180??, respectively. After scaling, A?? and A?? agree to within 2% (or 1??), a difference of little practical significance, although A?? has smoother analytical properties. A formulation distinguishing horizontal axes as well as the vertical axis is also possible, yielding an A?? ranging from -3 to +3 and A?? from -180?? to +180??. The geometrically motivated derivation in three-dimensional stress space presented here may aid intuition and offers a natural link with traditional ways of plotting yield and failure criteria. Examples are given, based on models of Bird [1996] and Bird and Kong [1994], of the use of Anderson fault parameters A?? and A?? for visualizing tectonic regimes defined by regional stress fields. Copyright 1997 by the American Geophysical Union.

  19. Progress of the Dust Accumulation and Removal Technology Experiment (DART) for the Mars 2001 Lander

    NASA Technical Reports Server (NTRS)

    Jenkins, Phillip; Landis, Geoffrey A.; Wilt, David; Krasowski, Michael; Greer, Lawrence; Baraona, Cosmo; Scheiman, David

    2005-01-01

    Dust deposition could be a significant problem for photovoltaic array operation for long duration missions on the surface of Mars. Measurements made by Pathfinder showed 0.3 percent loss of solar array performance per day due to dust obscuration. We have designed an experiment package, "DART", which is part of the Mars ISPP Precursor (MIP) package, to fly on the Mars-2001 Surveyor Lander. This mission, to launch in April 2001, will arrive on Mars in January 2002. The DART experiment is designed to quantify dust deposition from the Mars atmosphere, measure the properties of settled dust, measure the effect of dust deposition on array performance, and test several methods of clearing dust from solar cells.

  20. Equator To Pole in the Cretaceous: A Comparison of Clumped Isotope Data and CESM Model Runs

    NASA Astrophysics Data System (ADS)

    Petersen, S. V.; Tabor, C. R.; Meyer, K.; Lohmann, K. C.; Poulsen, C. J.; Carpenter, S. J.

    2015-12-01

    An outstanding issue in the field of paleoclimate is the inability of models to reproduce the shallower equator-to-pole temperature gradients suggested by proxies for past greenhouse periods. Here, we focus on the Late Cretaceous (Maastrichtian, 72-66 Ma), when estimated CO2 levels were ~400-1000ppm. New clumped isotope temperature data from more than 10 sites spanning 65°S to 48°N are used to reconstruct the Maastrichtian equator-to-pole temperature gradient. This data is compared to CESM model simulations of the Maastrichtian, run using relevant paleogeography and atmospheric CO2 levels of 560 and 1120 ppm. Due to a reduced "proxy toolkit" this far in the past, much of our knowledge of Cretaceous climate comes from the oxygen isotope paleothermometer, which incorporates an assumption about the oxygen isotopic composition of seawater (δ18Osw), a quantity often related to salinity. With the clumped isotope paleothermometer, we can directly calculate δ18Osw. This will be used to test commonly applied assumptions about water composition, and will be compared to modeled ocean salinity. We also discuss basin-to-basin differences and their implications for paleo-circulation patterns.

  1. Formation of clumps and patches in self-aggregation of finite-size particles

    NASA Astrophysics Data System (ADS)

    Holm, Darryl D.; Putkaradze, Vakhtang

    2006-08-01

    New model equations are derived for the dynamics of self-aggregation of finite-size particles. Differences from standard Debye-Hückel [P. Debye, E. Hückel, Zur Theorie der Elektrolyte: (2): Das Grenzgesetz für die Elektrische Leiftfahrigkeit (On the theory of electrolytes 2: limiting law of electrical conductivity), Phys. Z. 24 (1923) 305-325] and Keller-Segel [E.F. Keller, L.A. Segel, J. Theoret. Biol. 26 (1970) 399-415; E.F. Keller, L.A. Segel, J. Theoret. Biol. 30 (1971) 225-234] models are: (a) the mobility μ of particles depends on the locally averaged particle density and (b) linear diffusion acts on that locally averaged particle density. The cases both with and without diffusion are considered here. Surprisingly, these simple modifications of standard models allow progress in the analytical description of evolution as well as the complete analysis of stationary states. When μ remains positive, the evolution of collapsed states in our model reduces exactly to finite-dimensional dynamics of interacting particle clumps. Simulations show these collapsed (clumped) states emerging from smooth initial conditions, even in one spatial dimension. If μ vanishes for some averaged density, the evolution leads to the spontaneous formation of jammed patches (a weak solution with the density having compact support). Simulations confirm that a combination of these patches forms the final state for the system.

  2. GAMMA-RAY EMISSION FROM SUPERNOVA REMNANT INTERACTION WITH MOLECULAR CLUMPS

    NASA Astrophysics Data System (ADS)

    Tang, Xiaping; Chevalier, R.

    2014-01-01

    Observations of the middle-aged supernova remnants IC 443, W28, and W51C indicate that the brightnesses at GeV and TeV energies are correlated with each other and with regions of molecular clump interaction, but not with the radio synchrotron brightness. We suggest that the radio emission is primarily associated with a radiative shell in the interclump medium of a molecular cloud, while the Gamma-ray emission is primarily associated with the interaction of the radiative shell with molecular clumps. The shell interaction produces a high pressure region, so that the Gamma-ray luminosity can be approximately reproduced even if shock acceleration of particles is not efficient, provided that energetic particles are trapped in the cooling shell. In addition, the GeV through TeV emission can be produced in the interaction region if the trapping occurs to sufficiently high energies. Alternatively, diffusive acceleration may be efficient; in this case the observed GeV emission can be approximately reproduced, but not the TeV emission.

  3. The Cusp/Core problem: supernovae feedback versus the baryonic clumps and dynamical fr