Sulfide intrusion in the tropical seagrasses Thalassia testudinum and Syringodium filiforme     

Marianne Holmer  Ole Pedersen  Dorte Krause-Jensen  Birgit Olesen  Malene Hedegrd Petersen  Stephanie Schopmeyer  Marguerite Koch  Bente Aa. Lomstein  Henning S. Jensen 《Estuarine, Coastal and Shelf Science》2009,85(2):319-326

Sulfur and oxygen dynamics in the seagrasses Thalassia testudinum and Syringodium filiforme and their sediments were studied in the US Virgin Islands (USVI) in order to explore sulfide intrusion into tropical seagrasses. Four study sites were selected based on the iron concentration in sediments and on proximity to anthropogenic nutrient sources. Meadow characteristics (shoot density, above- and below-ground biomass, nutrient content) were sampled along with sediment biogeochemistry. Sulfide intrusion was high in T. testudinum, as up to 96% of total sulfur in the plant was derived from sediment-derived sulfides. The sulfide intrusion was negatively correlated to the turnover of sulfides in the sediments regulated by both plant parameters and sediment sulfur pools. Sediment iron content played an indirect role by affecting sulfide turnover rates. Leaf production was negatively correlated with sulfide intrusion suggesting that active growth reduced sulfide intrusion. Sulfide intrusion was lower in S. filiforme (up to 44%) compared to T. testudinum consistent with a higher internal nighttime oxygen concentrations found for S. filiforme. When S. filiforme can take advantage of its ability to maintain high internal oxygen concentrations, as was the case on the USVI, it could increase its success in colonizing unvegetated disturbed sediments with potentially high sulfide concentrations.  相似文献   

On the properties of very young massive infrared sources (Mitteilungen der Universitäts-Sternwarte zu Jena Nr. 169)     

J. Gürtler  T. H. Henning  J. Dorschner  C. Friedmann 《Astronomische Nachrichten》1985,306(6):311-327

The data compiled for 34 very young massive compact infrared source (Becklin-Neugebauer objects) in a separately published catalogue serve as the basis for an investigation of their general properties. First, the correlations of the strength of the ice and silicate bands at 3.1 μm and 10 μm, resp., with each other and with other parameters of the sources are investigated. In accordance with theoretical expectations the strengths of both bands are not well correlated with each other. The ratio τ₁₀/τ₃ of their optical depths veries from 0.85 to 8 (and possibly up to 22). That implies for the number densities of the grains that (naked) silicate grains always are considerably more abundant than ice grains (grains with ice mantles). It follows from the discussion of the relationships between τ₁₀, the temperature parameter of the sources, and their luminosity that relations between τ₁₀ and temperature and possibly between τ₁₀ and the luminosity exist. Stellar wind models for the ionized region around the embedded star are favoured after the analysis of the intensities of the hydrogen infrred emission lines and the radio continuum. The limited observational data do not yet allow a decision on a correlation between the silicate band depth and energy content and/or the velocity of the bipolar outflow detected in a number of sources. The BN objects are clearly more frequently associated with H₂O masers than OH masers. The linear separations of the infrared peaks from the masers are compatible with models where the H₂O masers are situated near the edges the gas-dust shells of the BN objects.  相似文献   

Preface     

Th. Henning  B. Stecklum 《Astrophysics and Space Science》1986,128(1):1-1

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Some physical properties and stability of an exact model of a relativistic star     

Henning Knutsen 《Astrophysics and Space Science》1988,140(2):385-401

An exact solution of Einstein's field equations for an isentropic fluid sphere is examined. It turns out that the crucial factor for the physical properties and the stability of this model is the degree of incompressibility. Necessary and sufficient conditions are given for the weak and the strong energy conditions to be fulfilled and for the speed of sound to be less than the speed of light. The speed of sound always has a minimum at the center of the fluid sphere. But two possibilities exist: either the speed of sound is increasing all the way outwards to the surface of the sphere, or the speed of sound is first increasing, then reaching a maximum when still inside the fluid sphere, and thereafter decreasing outwards to the surface. The adiabatic index is investigated and is found to be increasing outwards for the actual degrees of compressibility. This adiabatic index is always greater than unity, and the temperature is thus decreasing throughout the sphere. The necessary and sufficient condition for the adiabatic index to be greater than 4/3 is also given. (This is a necessary condition for the fluid sphere to be stable.) Chandrasekhar's pulsation equation with boundary conditions is investigated, and the fluid sphere is found to bestable if and only if the degree of incompressibility is greater than a certain value.Dedicated to the memory of the late Bronislaw Kuchowicz.  相似文献   

Parameters of very young and massive stars with dust shells     

Th. Henning 《Astrophysics and Space Science》1985,114(2):401-411

A radiative transfer model for newly formed hot stars surrounded by optically thick dust shells is applied to a number of compact infrared sources. The model parameters are derived by fitting the synthetic spectra to the observed one between 8 and 13 m and used to derive additional properties of the shells and the embedded stars.  相似文献   

Geology of the Severnaya Zemlya Archipelago and the North Kara Terrane in the Russian high Arctic     

Henning Lorenz  Peep Männik  David Gee  Vasilij Proskurnin 《International Journal of Earth Sciences》2008,97(3):519-547

The Severnaya Zemlya Archipelago is located at 80°N near the continental shelf break, between the Kara and Laptev seas. Sedimentary successions of Neoproterozoic and Palaeozoic age dominate the bedrock geology. Together with Northern Tajmyr, Severnaya Zemlya constitutes the main land areas of the North Kara Terrane (NKT), which is inferred here to have been a part of the Timanide margin of Baltica, i.e. an integral part of Baltica at least since the Vendian. Vendian turbidites derived from the Timanide Orogen are inferred to have been deposited on Neoproterozoic greenschist facies, granite-intruded basement. Shallow-water siliclastic deposition in the Early to Mid-Cambrian was followed by highly organic-rich shales in the Late Cambrian and influx of more turbidites. An episode of folding, the Kan’on River deformation, separates these formations from the overlying Tremadocian conglomerates and sandstones. In the Early Ordovician, rift-related magmatic rocks accompanied the deposition of variegated marls, sandstones, carbonates and evaporites. Dark shales and gypsiferous limestones characterise the Mid-Ordovician. Late Ordovician quartz-sandstones mark a hiatus, followed by carbonate rocks that extend up into and through most of the Silurian. The latter give way upwards into Old Red Sandstones, which are inferred to have been deposited in a Caledonian foreland basin. Deformation, reaching the area in the latest Devonian or earliest Carboniferous and referred to as the Severnaya Zemlya episode, is thought to be Caledonian-related. The dominating E-vergent structure was controlled by décollement zones in Ordovician evaporite-bearing strata; detachment folds and thrusts developed in the west and were apparently impeded by a barrier of Ordovician igneous rocks in the east. Below the décollement zones, the Neoproterozoic to Early Ordovician succession was deformed into open to close folds. The exposed strata in the lower structural level have been juxtaposed with those in the upper structural level along the major N-trending Fiordovoe Lake Fault Zone, which involved several kilometres of dextral strike-slip movement and downthrow to the west. A major Early Carboniferous unconformity separates the folded Mid-Palaeozoic and older rocks from overlying Carboniferous formations, as on Franz Joseph Land and Svalbard. Subsequent latest Palaeozoic to Early Mesozoic orogeny, as on Taimyr, apparently had little influence on the Severnaya Zemlya successions.  相似文献   

Cl,Br and I analyses of metamorphic and sedimentary rocks by isotope dilution mass spectrometry     

M. Boneß  K. G. Heumann  U. Haack 《Contributions to Mineralogy and Petrology》1991,107(1):94-99

Isotope dilution mass spectrometry with negative thermal ions was applied to determine Cl, Br and I in rocks which, in part, contained less than 100 ppb of Br and I. Two sets of samples have been investigated: a) a series of Al-rich metapelites of increasing metamorphic grade from the Damara Orogen, Namibia and b) fresh and hydrothermally altered greywackes from the Pb−Zn deposit Bad Grund in Germany. It was found that regional metamorphism of Al-rich metapelites causes no strong fractionation of the halides. The Br/Cl ratios in the metapelites are similar to those of sea water. The I/Cl and I/Br ratios, however, are 500 times higher. The I depleted in the ocean most probably is associated with organic matter stored in sediments. The unaltered greywackes from near the Pb−Zn vein have about the same concentrations of halides as the metamorphic Al-rich pelites. By contrast, the hydrothemally altered greywackes contain about twice as much Cl and I, and about 2–5 times as much Br as the unaltered samples. The element ratios, however, are similar for all three categories of rocks, thereby indicating that sea water played no role in the hydrothermal system.  相似文献   

Radar speckle reduction and derived texture measures for land cover/use classification: a case study     

Terry Idol  Barry Haack 《国际地球制图》2017,32(1):18-29

This study examined the appropriateness of radar speckle reduction for deriving texture measures for land cover/use classifications. Radarsat-2 C-band quad-polarised data were obtained for Washington, DC, USA. Polarisation signatures were extracted for multiple image components, classified with a maximum-likelihood decision rule and thematic accuracies determined. Initial classifications using original and despeckled scenes showed despeckled radar to have better overall thematic accuracies. However, when variance texture measures were extracted for several window sizes from the original and despeckled imagery and classified, the accuracy for the radar data was decreased when despeckled prior to texture extraction. The highest classification accuracy obtained for the extracted variance texture measure from the original radar was 72%, which was reduced to 69% when this measure was extracted from a 5 × 5 despeckled image. These results suggest that it may be better to use despeckled radar as original data and extract texture measures from the original imagery.  相似文献   

Geochemical tables | H.J. Rösler and H. Lange, 1972. Elsevier,Amsterdam, 468 pp., Dfl. 80.00     

V. Haack 《Earth》1974,10(1):80-81

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BN objects — A class of very young and massive stars     

Th. Henning  J. Gürtler 《Astrophysics and Space Science》1986,128(1):199-216

The Becklin-Neugebauer objects are identified by means of a wide range of observable features as a separate class of very young and massive stars surrounded by optically thick dust shells. We show that they evolutionarily connect real protostars to compactHii regions. We give criteria which should be appropriate to segregate the BN objects from compactHii regions. Finally, we describe the structure of a typical BN object.Paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March, 1986.  相似文献