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91.
Equivalent widths of weak and moderately strong Fraunhofer lines observed in an area roughly 3500 × 10000 km in extent are found to show small variations of the order of 1 mÅ, on a time scale of minutes. The dependence of amplitude on line strength and excitation closely fits that predicted for a compressional disturbance associated with temperature variations that manifest themselves in the equivalent widths. The rms amplitude is about 20K near τ5000 = 10-2. These equivalent width variations frequently exhibit a 5-min periodicity and are accompanied by prominent oscillations of velocity. Power spectra of both quantities closely resemble each other and demonstrate that most of the equivalent width variations in the range 200 to 500 s are due to the thermal response of the atmosphere to 5-min oscillations. A systematic phase lag between velocity and equivalent width is observed, in the sense that temperature leads velocity by an average angle of 120°. This deviates significantly from 90° valid for standing adiabatic waves, showing that in the line-forming layers, τ5000 ≈ 10-2, the 5-min oscillations are markedly affected by radiative exchange. The observed phase lag implies a radiative decay time of ≈40 s, a value which agrees with modelatmosphere predictions for the line-forming layers. Since the observed wave trains frequently show constant amplitude over a much longer time, a continuous feed-back of energy seems to occur. 相似文献
92.
93.
Gabriele Trommer Michael Siccha Marcel T.J. van der Meer Stefan Schouten Jaap S. Sinninghe Damsté Hartmut Schulz Christoph Hemleben Michal Kucera 《Organic Geochemistry》2009,40(6):724-731
The Red Sea represents an extreme marine environment, with high salinity, high temperature and low level of nutrients, complicating the application of standard geochemical palaeotemperature proxies. In order to investigate the applicability of the TEX86 (TetraEther indeX of GDGTs with 86 carbons) proxy for sea surface temperature (SST) in the Red Sea, the distribution of glycerol dialkyl glycerol tetraether membrane lipids (GDGTs) in sediments from the Red Sea and the Gulf of Aden were examined. Against expectations, TEX86 values for the Red Sea do not show a simple linear relationship with SST and deviate from the global core top calibration. In the northern Red Sea, at temperatures between 25 and 28 °C, the values increase linearly with SST, whereas in the southern Red Sea, at temperatures above 28 °C, TEX86 decreases with increasing temperature. Factors like seasonality and depth of production, salinity and nutrient availability, as well as diagenetic overprint or influence of allochtonous terrestrial lipids, cannot explain this pattern. However, the observed TEX86 relationship with SST could be explained by the presence of a hypothetical endemic Crenarchaeota population in the Red Sea with a specific TEX86 vs. SST relationship. In the Southern Red Sea, a two-component mixing model implies an exponential decrease in the endemic population towards the Gulf of Aden. Thus, the application of the TEX86 as a palaeotemperature proxy in the Red Sea is likely only possible for the northern Red Sea area with the specific SST vs. TEX86 relationship determined in this study and potentially for the whole Red Sea basin during glacials, when water exchange with the Indian Ocean was more restricted than today and the endemic archaeal lipid distribution was not affected by transport from the Indian Ocean. Our results suggest that distinct populations of Crenarchaeota in extreme environments such as evaporitic basins may have different membrane composition, necessitating application of another calibration than the global core top calibration for TEX86 palaeothermometry. 相似文献
94.
Ralf Srama Thomas Stephan Eberhard Grün Norbert Pailer Anton Kearsley Amara Graps Rene Laufer Pascale Ehrenfreund Nicolas Altobelli Kathrin Altwegg Siegfried Auer Jack Baggaley Mark J. Burchell James Carpenter Luigi Colangeli Francesca Esposito Simon F. Green Hartmut Henkel Mihaly Horanyi Annette Jäckel Sascha Kempf Neil McBride Georg Moragas-Klostermeyer Harald Krüger Pasquale Palumbo Andre Srowig Mario Trieloff Peter Tsou Zoltan Sternovsky Oliver Zeile Hans-Peter Röser 《Experimental Astronomy》2009,23(1):303-328
The scientific community has expressed strong interest to re-fly Stardust-like missions with improved instrumentation. We
propose a new mission concept, SARIM, that collects interstellar and interplanetary dust particles and returns them to Earth.
SARIM is optimised for the collection and discrimination of interstellar dust grains. Improved active dust collectors on-board
allow us to perform in-situ determination of individual dust impacts and their impact location. This will provide important
constraints for subsequent laboratory analysis.
The SARIM spacecraft will be placed at the L2 libration point of the Sun–Earth system, outside the Earth’s debris belts and
inside the solar-wind charging environment. SARIM is three-axes stabilised and collects interstellar grains between July and
October when the relative encounter speeds with interstellar dust grains are lowest (4 to 20 km/s). During a 3-year dust collection
period several hundred interstellar and several thousand interplanetary grains will be collected by a total sensitive area
of 1 m2. At the end of the collection phase seven collector modules are stored and sealed in a MIRKA-type sample return capsule.
SARIM will return the capsule containing the stardust to Earth to allow for an extraction and investigation of interstellar
samples by latest laboratory technologies. 相似文献
95.
Eberhard Grün Ralf Srama Nicolas Altobelli Kathrin Altwegg James Carpenter Luigi Colangeli Karl-Heinz Glassmeier Stefan Helfert Hartmut Henkel Mihaly Horanyi Annette Jäckel Sascha Kempf Markus Landgraf Neil McBride Georg Moragas-Klostermeyer Pasquale Palumbo Han Scholten Andre Srowig Zoltan Sternovsky Xavier Vo 《Experimental Astronomy》2009,23(3):981-999
The DuneXpress observatory will characterize interstellar and interplanetary dust in-situ, in order to provide crucial information
not achievable with remote sensing astronomical methods. Galactic interstellar dust constitutes the solid phase of matter
from which stars and planetary systems form. Interplanetary dust, from comets and asteroids, represents remnant material from
bodies at different stages of early solar system evolution. Thus, studies of interstellar and interplanetary dust with DuneXpress
in Earth orbit will provide a comparison between the composition of the interstellar medium and primitive planetary objects.
Hence DuneXpress will provide insights into the physical conditions during planetary system formation. This comparison of
interstellar and interplanetary dust addresses directly themes of highest priority in astrophysics and solar system science,
which are described in ESA’s Cosmic Vision. The discoveries of interstellar dust in the outer and inner solar system during
the last decade suggest an innovative approach to the characterization of cosmic dust. DuneXpress establishes the next logical
step beyond NASA’s Stardust mission, with four major advancements in cosmic dust research: (1) analysis of the elemental and
isotopic composition of individual interstellar grains passing through the solar system, (2) determination of the size distribution
of interstellar dust at 1 AU from 10 − 14 to 10 − 9 g, (3) characterization of the interstellar dust flow through the planetary system, (4) establish the interrelation of interplanetary
dust with comets and asteroids. Additionally, in supporting the dust science objectives, DuneXpress will characterize dust
charging in the solar wind and in the Earth’s magnetotail. The science payload consists of two dust telescopes of a total
of 0.1 m2 sensitive area, three dust cameras totaling 0.4 m2 sensitive area, and a nano-dust detector. The dust telescopes measure high-resolution mass spectra of both positive and negative
ions released upon impact of dust particles. The dust cameras employ different detection methods and are optimized for (1)
large area impact detection and trajectory analysis of submicron sized and larger dust grains, (2) the determination of physical
properties, such as flux, mass, speed, and electrical charge. A nano-dust detector searches for nanometer-sized dust particles
in interplanetary space. A plasma monitor supports the dust charge measurements, thereby, providing additional information
on the dust particles. About 1,000 grains are expected to be recorded by this payload every year, with 20% of these grains
providing elemental composition. During the mission submicron to micron-sized interstellar grains are expected to be recorded
in statistically significant numbers. DuneXpress will open a new window to dusty universe that will provide unprecedented
information on cosmic dust and on the objects from which it is derived. 相似文献
96.
Laurent Deguillaume Andreas Tilgner Roland Schrödner Ralf Wolke Nadine Chaumerliac Hartmut Herrmann 《Journal of Atmospheric Chemistry》2009,64(1):1-35
Mechanism reductions of the detailed aqueous phase chemistry mechanism CAPRAM 3.0i are performed. Manual methods and automatic
techniques are both applied in order to provide a less computationally intensive mechanism which is operational in regional
chemistry transport models (CTMs). The finally reduced mechanism contains less than 200 reactions (4 times smaller than the
detailed CAPRAM 3.0i) and describes the main characteristics of inorganic and organic aqueous phase processes occurring in
tropospheric warm clouds. Most of the chemical reduction potential is realized in the CAPRAM 3.0i organic chemistry. The number
of aqueous phase species decreases from 380 in the full mechanism to 130 in the final reduced version. The calculated percentage
deviations between the full and reduced mechanism are on average below 5% for the most important organic and inorganic target
compounds such as oxidants, inorganic and organic acids, carbonyls and alcohols. Comparisons of the required CPU times between
the full and reduced mechanisms show reductions of approximately 40%. 2-D test simulations with the CTM MUSCAT were performed
using prescribed meteorological conditions in order to examine the applicability of the reduced mechanism at regional scale.
Simulations with the reduced CAPRAM 3.0i mechanism and a much less complex mechanism with only limited inorganic chemistry
(INORG) were compared to evaluate the effects of more detailed chemistry. The model results show large differences in the
level of oxidants and the inorganic and organic mass processing. Prospectively, the reduced mechanism represents the basis
for studying aerosol cloud processing effects at regional scale with future CTMs and will allow more adequate interpretation
of field data. 相似文献
97.
We present a vertex-centered finite volume method for the fully coupled, fully implicit discretization of two-phase flow in fractured porous media. Fractures are discretely modeled as lower dimensional elements. The method works on unstructured, locally refined grids and on parallel computers with distributed memory. An implicit time discretization is employed and the nonlinear systems of equations are solved with a parallel Newton-multigrid method. Results from two-dimensional and three-dimensional simulations are presented. 相似文献
98.
99.
A glass of composition NaAlSi3O8 with small contents of Fe has been crystallized in the presence of water vapor under 1000 bars, at temperatures in the range of 250 to 700° C for varying periods of time. The synthetic crystals were investigated microscopically and by x-ray powder diffraction methods. Most of the crystals are twinned according to the albite law, but other twins are found too. Size and form of the crystals seem to depend on the temperature of crystallization. The optic axial angles (2V
x
) of the albites being measurable on the universal stage are in the range of 50 to 100 degrees. There seems to exist a linear relation between the 2131–21¯31 values (used as an indicator for the degree of ordering) and the 2V
x
values. The change of the lattice parameters from albite (D) to albite (O) is suggested to deviate slightly from linearity.In contrast to previous investigations the steady value of 2131–21¯31 which is characteristic of the temperature of crystallization was reached more rapidly. These results suggest that small content of Fe in the glass had a catalytic effect on the Al/Si ordering.
Herrn Dr. F. Seifert (Ruhruniversität Bochum) danken wir herzlich für die Einweisung in die experimentellen Untersuchungsmethoden sowie für manchen kritischen Hinweis. Danken möchten wir auch Herrn Dr. P. K. Hörmann für die Kontrolle der chemischen Zusammensetzung des Albitglases sowie Herrn Dr. C. W. Burnham (Harvard University) für die Bereitstellung des Rechenprogramms. Nicht zuletzt danken wir Herrn Prof. Dr. F. Karl für die kritische Durchsicht des Manuskriptes. 相似文献
Herrn Dr. F. Seifert (Ruhruniversität Bochum) danken wir herzlich für die Einweisung in die experimentellen Untersuchungsmethoden sowie für manchen kritischen Hinweis. Danken möchten wir auch Herrn Dr. P. K. Hörmann für die Kontrolle der chemischen Zusammensetzung des Albitglases sowie Herrn Dr. C. W. Burnham (Harvard University) für die Bereitstellung des Rechenprogramms. Nicht zuletzt danken wir Herrn Prof. Dr. F. Karl für die kritische Durchsicht des Manuskriptes. 相似文献
100.
Hartmut Holweger 《Earth and Planetary Science Letters》1977,34(1):152-154
Solar abundances based on recent laboratory oscillator strengths confirm the relationship between solar matter and carbonaceous chondrites. Within spectroscopic uncertainties (typically±40%) these meteorites contain refractory and volatile elements in solar proportions. Significant improvement of accuracy at present seems restricted to a few abundant elements having reliable quantum-mechanical oscillator strengths, and necessitates strictly differential spectrum analysis. Taking this into account, the solar abundance ratios Na/Ca and S/Ca have been determined to an accuracy of±15%. The results are:Na/Ca= 0.91and S/Ca= 6.8. These volatile/refractory ratios just match type 1 carbonaceous chondrites, but contrast with other types.These and related interstellar abundance features place constraints on the condensation process and a potential heterogeneity of the solar nebula. There is evidence that no drastic pre-solar separation of interstellar gas and grains has occurred, but minor imbalance may be a common mechanism co-determining stellar metal content. 相似文献