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1.
J. J. MacFarlane 《Astrophysics and Space Science》1994,221(1-2):287-294
Results from wind ionization calculations are presented which show how the P-Cygni profiles of superionized species such as O VI can provide information about the X-ray source characteristics of early-type stars. Using detailed radiative and atomic physics models, we find that a significant source of X-ray emission from Pup (O4 If) comes from a region in the wind located within roughly 1 to 2 stellar radii of the photosphere. Our results suggest that X-rays sources in which emission occurs exclusively at large radii (r a fewR
*
) are inconsistent with UV P-Cygni profiles for O VI. Instead, we find that X-ray emission from shocks distributed throughout the lower regions of the wind (r 1 – 2R
*
) is consistent with both X-ray and UV data, as well as mass loss rates deduced from radio andH
observations. 相似文献
2.
R.Bruch MacFarlane 《Geochimica et cosmochimica acta》1978,42(10):1579-1582
The molecular weight distribution of the humic and fulvic acid fractions of two sediments was determined using Amicon ultrafiltrat ion techniques. All fractions of humic substances had a molecular weight range of less than 500 to greater than 300,000. The largest component of humic acids was in the greater than 300,000 molecular weight range, whereas, the largest percentages of fulvic acids were in the less than 500 molecular weight range and the 100,000–300,000 molecular weight range. From this preliminary investigation there appears to be a qualitative relationship between the molecular weight composition of the humic substances in the sediment and the salinity of the overlying water within an estuarine environment. 相似文献
3.
Toxicity,growth and accumulation relationships of copper,lead and zinc in the grey mangrove Avicennia marina (Forsk.) Vierh 总被引：12，自引：0，他引：12
The effects of three heavy metals Copper (Cu), lead (Pb) and zinc (Zn), and the interaction of an essential (Zn) and non-essential (Pb) metal on germination, growth, and accumulation of metals in the grey mangrove, Avicennia marina (Forsk.) Vierh var. australasica (Walp.) Moldenke, were studied under laboratory conditions. Avicennia marina was found to be highly tolerant to the metals applied. Copper was accumulated in root tissue in a linear relationship at lower sediment concentrations, but at concentrations of 200 microg/g and higher, no further increases in root Cu levels occurred. Translocation of Cu from the root to leaf tissue was low, yet revealed similar accumulation patterns as root tissue. Significant reductions in seedling height leaf number and area were found with significant increases in Cu concentrations in tissues at 100 microg/g sediment Cu. At Cu sediment levels of 400 microg/g, a decrease in total biomass and root growth inhibition was observed. Emergence was retarded with increasing copper concentration, with 800 microg/g sediment Cu resulting in a total inhibition of emergence. The LC50 for emergence and EC50 for biomass was 566 and 380 microg/g Cu respectively. Lead accumulation in root tissue was lower that other metals, yet increased in a dose dependant fashion across the sediment Pb concentration range examined. Lead was excluded from leaf tissue at Pb sediment concentrations up to 400 microg/g, above which limited transport of Pb occurred. Little negative effects on growth were observed due to the low accumulation of Pb. Zinc uptake was high, and was accumulated in a linear fashion in root tissue across the sediment Zn concentration range applied. Zinc translocation to leaf tissue exhibited a dose dependant relationship with both root and sediment Zn levels. Emergence decreased with increasing sediment Zn concentrations, with 1000 microg/g sediment Zn showing 100% mortality. Significant reductions in seedling height, leaf number, area, biomass and root growth inhibition were found at concentrations of 500 microg/g sediment Zn. The LC50 for emergence and EC50 for biomass was 580 and 392 microg/g Zn respectively. Lead and Zn in combination resulted in an increased accumulation of both metals in leaf tissue and increased toxicity than individual metals alone, and is the first noted occurrence of a Pb and Zn additive response in angiosperms. Possible mechanisms of accumulation and toxicity are discussed. 相似文献
4.
I. M. Hall T. Durmaz R. C. Mancini J. E. Bailey G. A. Rochau M. J. Rosenberg D. H. Cohen I. E. Golovkin J. J. MacFarlane M. E. Sherril J. Abdallah R. F. Heeter M. E. Foord S. H. Glenzer H. A. Scott 《Astrophysics and Space Science》2009,322(1-4):117-121
Photoionised plasmas are common in astrophysical environments and new high resolution spectra from such sources have been recorded in recent years by the Chandra and XMM-Newton satellites. These provide a wealth of spectroscopic information and have motivated recent efforts aimed at obtaining a detailed understanding of the atomic-kinetic and radiative characteristics of photoionised plasmas. The Z-pinch facility at the Sandia National Laboratories is the most powerful terrestrial source of X-rays and provides an opportunity to produce photoionised plasmas in a well characterised radiation environment. We present modelling work and experimental design considerations for a forthcoming experiment at Sandia in which X-rays from a collapsing Z-pinch will be used to photoionise low density neon contained in a gas cell. View factor calculations were used to evaluate the radiation environment at the gas cell; the hydrodynamic characteristics of the gas cell were examined using the Helios-CR code, in particular looking at the heating, temperature and ionisation of the neon and the absorption of radiation. Emission and absorption spectra were also computed, giving estimates of spectra likely to be observed experimentally. 相似文献
5.
Phenomena associated with small ice cap instability (SICI) are investigated using a general circulation model (GCM: NCAR Community Climate Model version 0) and a noise-forced nonlinear energy balance model (EBM). Both make use of idealized boundary conditions consisting of an all-land planet without topography and mean annual insolation. Ice is prescribed to exist on surface areas for which the instantaneous temperature lies below freezing. The adjustable parameters of the EBM were chosen to match the GCM solutions. For the regions in parameter space where SICI might occur we do not find the corresponding icefree steady state solution with the GCM. Our simulations with the EBM show that SICI phenomena in the presence of fluctuations are strongly dependent on the amplitude of the noise forcing. When the strength of noise forcing is adjusted to match the fluctuations in the GCM, we do not find a SICI in the EBM. With weaker levels of forcing the SICI reappears. In all cases steady stable ice caps smaller than a critical size are not found to exist. 相似文献
6.
MacFarlane GR 《Marine pollution bulletin》2002,44(3):244-256
Sediment loadings and leaf accumulation of the heavy metals copper (Cu), lead (Pb) and zinc (Zn) with accompanying changes in leaf chlorophylls' (a + b), carotenoids and the antioxidant enzyme peroxidase were examined in the grey mangrove Avicennia marina (Forsk.) Vierh, in order to determine the applicability of these parameters as biomarkers of heavy metal stress under field conditions. Copper was found to show limited accumulation to leaf tissue, following a linear relationship at lower sediment concentrations, with saturation at higher sediment Cu concentrations. Copper accumulation relationships to leaf tissue were maintained temporally, and increases in sediment Cu, salinity, and decreases in sediment pH and Zn contributed to the accumulation of Cu to leaf tissue. Lead showed a significant relationship between sediment and leaf Pb levels, but accumulation was minimal. Accumulation relationships for Pb were not maintained temporally, and high sediment Pb, low pH and organic content increased bioavailability and accumulation of Pb. Zinc was the most mobile of all metals and was accumulated to the greatest quantities in leaf tissue in a dose-dependant relationship. Some temporal variation in Zn accumulation occurred, and higher sediment pH, organic content Zn and Pb promoted leaf Zn accumulation. Leaf Cu and Zn showed the strongest relationship with peroxidase activity and to a lesser degree Pb. Zinc was the only accumulated metal to show relationship maintenance with peroxidase activity over time. It was found that peroxidase activity best reflects the total phytotoxic effect from the combined metal stress of all three accumulated leaf metals. The only significant photopigment relationship evidenced was that of leaf Zn with the chlorophyll a/b ratio, but was not maintained temporally. Peroxidase activity may be an appropriate biomarker for Zn or total metal accumulation in leaf tissue, and the chlorophyll a/b ratio a suitable biomarker of Zn accumulation though requires temporal monitoring under field conditions. 相似文献
7.
Ground‐penetrating radar has not been applied widely to the recognition of ancient carbonate platform geometries. This article reports the results of an integrated study performed on an Upper Jurassic outcrop from the south‐east Paris basin, where coral bioherms laterally change into prograding depositional sequences. Ground‐penetrating radar profiles illustrate the different bedding planes and major erosional unconformities visible at outcrop. A ground‐penetrating radar profile conducted at the base of the cliff displays a palaeotopographic surface on which the outcropping bioherms settled. The excellent penetration depths of the ground‐penetrating radar (20 m with a monostatic 200 MHz antenna) images the carbonate platform geometries, ranging between outcrop workscale (a few metres) and seismic scale (several hundreds of metres). This study supports recent evidence of icehouse conditions and induced sea‐level fluctuations controlling the Upper Jurassic carbonate production. 相似文献
8.
Using current concepts for the origin of the Jovian planets and current constraints on their interior structure, we argue that the presence of large amounts of “ice” (H2O, CH4, and NH3) in Uranus and Neptune indicates temperatures low enough to condense these species at the time Uranus and Neptune formed. Yet such low temperatures imply orders-of-magnetude fractionation effects for deuterium into the “ice” component if isotopic equilibration can occur. Our models thus imply that Uranus and Neptune should have a D/H ratio at least four times primordial, contrary to observation for Uranus. We find that the Jovian and Saturnian D/H should be close to primordial regardless of formation scenario. The Uranus anomaly could indicate that there was a strong initial radial gradient in D/H in the primordial solar nebula, or that Uranus is so inactive that no significant mixing of its interior has occurred over the age of the solar system. Observation of Neptune's atmospheric D/H may help to resolve the problem. 相似文献
9.
The Valanginian is a period of global environmental change as illustrated by sedimentary, palaeontological, geochemical and climatic perturbations. A production crisis in most of the carbonate platforms suggests important changes in palaeoenvironmental conditions. During the same time interval, a major positive excursion in δ13C, the Weissert Event, suggests perturbations of the carbon cycle from the latest Early Valanginian to the Early Hauterivian. In order to better understand the link between these changes, sea‐level fluctuations have been reconstructed in detail from the Middle Berriasian to the earliest Hauterivian. Sections from the Peri‐Vocontian Zone (South‐east France) have been investigated because of the good quality of outcrops on the carbonate platforms, their margins and in the Vocontian Basin. Sections ranging from the most proximal zone (Swiss Jura) to the basin were interpreted in terms of sequence stratigraphy and cyclostratigraphy, and correlated at high resolutions. Using the identified small, medium and large‐scale sequences as well as depositional geometries, sea‐level fluctuations were reconstructed. Two main trends are evidenced during the studied interval: (i) the peak amplitude (magnitude) of the sea‐level fluctuations increased gradually from the Middle Berriasian to the Early Valanginian, and reached a maximum (more than 50 m) from the middle Early Valanginian to the Valanginian/Hauterivian boundary; and (ii) sea‐level variations were quite symmetrical during the Late Berriasian, slightly asymmetrical during the Early Valanginian and strongly asymmetrical (fast sea‐level rise, slow fall) from the latest Early Valanginian to the earliest Hauterivian. Moreover, three orders of sea‐level fluctuations were recognized in the sedimentary rocks of the Peri‐Vocontian Zone. Platform‐basin correlations and cyclostratigraphic interpretations of the basinal sections evidence an astronomical control on the sea‐level variations, mainly by the two eccentricity cycles of 100 and 400 kyr. The increase in the amplitude of the sea‐level fluctuations and their change from symmetrical to asymmetrical can be related to the onset of a major cooling event in the Early Valanginian. Fast transgressions followed by slower regressions would correspond to waxing and waning of high‐latitudinal ice during most of the Valanginian, especially from the latest Early Valanginian to the latest Late Valanginian. Glacio‐eustatic sea‐level fluctuations in tune with the 100 and 400 kyr eccentricity cycles are in agreement with glaciations during the Valanginian. 相似文献
10.
准噶尔盆地南缘新生代构造特征及其与砂岩型铀矿成矿作用初析 总被引：5，自引：0，他引：5
准噶尔盆地南缘盆山结合部中新生界沉积巨厚,新生代变形强烈,是研究新盆山耦合的理想场所,也是我国砂岩型铀矿找矿的远景区段。本文在综合前人资料和野外观测分析基础上,根据新生代构造活动特征,将准噶尔盆地南缘划分为博格达山前和西部断褶带两个构造分区,博格达山前以强烈的逆冲推覆为特征,发育多条活动的逆冲推覆断裂; 乌鲁木齐以西至乌苏南的西部断褶带则发育三-四排的褶皱-逆冲断裂构造带。对采自博格达山前逆冲推覆断裂带内的方解石和断层泥,利用电子自旋共振测年手段,推测博格达山前的富康-吉木萨尔断裂带和北三台断裂带分别在0.7~1Ma和0.25Ma期间,经历了一期重要的逆冲推覆作用。结合盆地南缘砂岩型铀矿的展布规律及其成矿条件的分析,探讨了新生代构造运动对砂岩型铀矿成矿的控制作用,认为西部断褶带的第一排构造带具有较好的成矿前景,而博格达山前由于新生代构造活动强烈而相对成矿不利,为此提出了准噶尔盆地南缘砂岩型铀矿成矿“构造优先权”的构造控矿模式,进而指出了区域找矿的优选区段。 相似文献