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  • 1
    Electronic Resource
    Electronic Resource
    Detection of accreting circumstellar gas around weak emission-line Herbig Ae/Be stars (1994)
    Springer
    Astrophysics and space science 212 (1994), S. 107-114 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present archival and recent IUE high dispersion spectra of late B stars which reveal the presence of accreting gas with velocities as high as 350 km s−1, collisional ionization of the accreting gas to temperatures above the stellar Teff, and column densities intermediate between those observed toward classical Herbig Ae/Be stars and the nearby proto-planetary systemβ Pictoris. One of the stars, HD 176386, while lacking obvious optical signatures of youth, is a member of the R CrA star formation region, and with an inferred age of 2.8 Myr has not yet arrived on the zero-age main sequence (ZAMS). The other object, an isolated, field B star with pronounced IR excess due to warm, circumstellar dust, 51 Oph, exhibits only modest hα emission. The combination of high velocity, accreting gas in systems with IR excesses due to circumstellar dust suggests that not only are these objects candidate proto-planetary systems, but that they may represent an extension to higher stellar masses of the weak-emission pre-main sequence (PMS) stars.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00984514
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  • 2
    Electronic Resource
    Electronic Resource
    The evidence for clumpy accretion in the Herbig Ae star HR 5999 (1994)
    Springer
    Astrophysics and space science 212 (1994), S. 115-124 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Analysis of IUE high- and low-dispersion spectra of the young Herbig Ae star HR 5999 (HD 144668) covering 1978–1992 has revealed dramatic changes in the Mg II h and k (2795.5, 2802.7 Å) emission profiles, changes in the column density and distribution in radial velocity of accreting gas, and flux in the Lyα, OI and CIV emission lines, which are correlated with the UV excess luminosity. We also observe variability in the spectral type inferred from the UV spectral energy distribution, ranging from A5 IV-III in high state to A7 III in the low state. The trend of earlier inferred spectral type with decreasing wavelength and with increasing UV continuum flux has previously been noted as a signature of accretion disks in lower mass pre-main sequence stars (PMS) and in systems undergoing FU Orionis-type outbursts. Our data represent the first detection of similar phenomena in an intermediate mass (M ≥ 2M ⊙) PMS star. Recent IUE spectra show gas accreting toward the star with velocities as high as +300 km s−1, much as is seen towardβ Pic, and suggest that we also view this system through the debris disk. The absence of UV lines with the rotational broadening expected given the optical data (A7 IV,v sini = 180 ± 20 km s−1) for this system also suggests that most of the UV light originates in the disk, even in the low continuum state. The dramatic variability in the column density of accreting gas, consistent with clumpy accretion, such as has been observed towardβ Pic, is a hallmark of accretion onto young stars, and is not restricted to the clearing phase, since detectable amounts of accretion are present for stars with 0.5 〈t age 〈 2.8 Myr. The implications for models ofβ Pic and similar systems are briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00984515
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of media composition on substrate removal by pure and mixed bacterial cultures (1993)
    Springer
    Biodegradation 4 (1993), S. 23-38 
    Details
    ISSN: 1572-9729
    Keywords: 2-chlorophenol ; continuous culture ; L-lysine ; mixed microbial community ; multicomponent substrate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Continuous culture experiments with identical experimental designs were run with a mixed microbial community of activated sludge origin and an axenic bacterial culture derived from it. Each culture received 2-chlorophenol (2-CP) at a concentration of 160 mg/L as COD and L-lysine at a concentration of 65 mg/L as COD. A factorial experimental design was employed with dilution rate and media composition as the two controlled variables. Three dilution rates were studied: 0.015, 0.0325, and 0.05 h−1. Media composition was changed by adding four biogenic compounds (butyric acid, thymine, glutamic acid and lactose) in equal COD proportions at total concentrations of 0, 34, 225, and 1462 mg/L as COD. The measured variables were the effluent concentrations of 2-CP as measured by the 4-aminoantipyrene test and lysine as measured by the o-diacetylbenzene procedure. The results suggest that community structure and substrate composition play important roles in the response of a microbial community to mixed substrates. The addition of more biogenic substrates to the axenic culture had a deleterious effect on the removal of both lysine and 2-CP, although the effect was much larger on lysine removal. In contrast, additional substrates had a positive effect on the removal of 2-CP by the mixed community and much less of a negative effect on the removal of lysine. The dilution rate at which the cultures were growing had relatively little impact on the responses to the additional substrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00701452
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  • 4
    Electronic Resource
    Electronic Resource
    Ecological Engineering of Bioreactors for Wastewater Treatment (2000)
    Springer
    Water, air & soil pollution 123 (2000), S. 117-132 
    Details
    ISSN: 1573-2932
    Keywords: biological nutrient removal ; ecological engineering ; filamentous bulking ; glycogen accumulating organisms ; nitrifying bacteria ; phosphorus accumulating organisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Biological nutrient removal (BNR) systems remove carbon, nitrogen, and phosphorus from wastewaters through biodegradation of organic compounds, oxidation of ammonia-N to nitrate-N, reduction of nitrate-N to N2 gas, and sequestration of phosphorus as polyphosphate. The microbial community in such systems is complex because it must contain heterotrophic bacteria capable of aerobic respiration, anaerobic respiration, and fermentation; specialized heterotrophic bacteria that can store polyphosphate; and autotrophic nitrifying bacteria that can withstand long periods without oxygen. Although the basic design principles for BNR systems are reasonably well established, it is becoming apparent that a greater understanding of the microbial interactions involved is required to increase system reliability. For example, although the environment established for the selection of phosphorus accumulating organisms was thought to give them a strong competitive advantage over other heterotrophic bacteria, this has turned out not to be the case. Rather, glycogen accumulating organisms can compete quite effectively in the same environment. Furthermore, BNR systems have suffered from problems with sludge settleability, even though many of the system characteristics are considered to be conducive to the suppression of filamentous bacteria. Finally, the use of molecular techniques has revealed that the autotrophic nitrifying bacteria are different from those that had been considered to be present. This paper reviews the microbial ecology of BNR systems, establishes how molecular biology techniques are changing our understanding of that ecology, and suggests ways in which engineering control can be exerted over community structure, thereby increasing the reliability of BNR systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005201528411
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  • 5
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    Detection of accreting circumstellar gas around weak emission-line Herbig Ae/Be stars (1994)
    Springer
    Details
    Publication Date: 1994-02-01
    Print ISSN: 0004-640X
    Electronic ISSN: 1572-946X
    Topics: Physics
    Published by Springer
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  • 6
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    The evidence for clumpy accretion in the Herbig Ae star HR 5999 (1994)
    Springer
    Details
    Publication Date: 1994-02-01
    Print ISSN: 0004-640X
    Electronic ISSN: 1572-946X
    Topics: Physics
    Published by Springer
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  • 7
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    The outer disks of Herbig stars from the UV to NIR (2014)
    Springer
    Details
    Publication Date: 2014-12-16
    Print ISSN: 0004-640X
    Electronic ISSN: 1572-946X
    Topics: Physics
    Published by Springer
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  • 8
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    Effects of media composition on substrate removal by pure and mixed bacterial cultures (1993)
    Springer
    Details
    Publication Date: 1993-03-01
    Print ISSN: 0923-9820
    Electronic ISSN: 1572-9729
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Springer
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