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排序方式: 共有661条查询结果,搜索用时 312 毫秒
221.
222.
R. Silvotti A. Bonanno A. Frasca S. Bernabei R. Janulis R. Østensen S.-L. Kim B.-G. Park J. Xiaojun J. Guo Z. Liu M.D. Reed R.S. Patterson K.M. Gietzen P.J. Clark G.W. Wolf Y. Lipkin L. Formiggini E. Leibowitz T.D. Oswalt M. Rudkin K. Johnston 《Astrophysics and Space Science》2004,289(3-4):445-448
I present a model for the formation and evolution of a massive disk galaxy, within a growing dark halo whose mass evolves according to cosmological simulations of structure formation. The galactic evolution is simulated with a new 3D chemo-dynamical code, including dark matter, stars and a multi-phase ISM. We follow the evolution from redshift z = 4.85 until the present epoch. The energy release by massive stars and supernovae prevents a rapid collapse of the baryonic matter and delays the maximum star formation until redshift z ≈ 1. The galaxy forms radially from inside-out and vertically from top-to-bottom. The feedback of stars leads to turbulent motions and large-scale flows in the ISM. As one result the galactic disk is significantly enriched by chemical elements synthesized in bulge stars. 相似文献
223.
A systematic calibration procedure for the constitutive model gUTS using conventional triaxial data for all but one of the material constants is described. Typical ranges for the constants for clay and sand are specified together with default values. When all default values are adopted, just eight material constants need to be determined (gUTS-lite). A comprehensive series of 49 simulations on clays, silt and sands in loose and dense states under a wide range of monotonic and cyclic stress paths, initial states and drainage conditions provide very satisfactory agreement with experimental results. 相似文献
224.
Christian Koeberl Wolf Uwe Reimold Hanna E. Horsch Roland K. W. Merkle 《Meteoritics & planetary science》1990,25(1):23-26
Abstract— The Machinga, southern Malawi, Africa, L6 chondrite (observed fall, 22 January 1981) contains accessory phases of metal, troilite, chromite, and native Cu (which is associated with limonite and found in zones of aqueous alteration). Rare accessory phases are apatite and pentlandite, which are uncommon in L6 chondrites. Major mineral constituents (olivine, orthopyroxene, and plagioclase) indicate shock effects at a level of about 15–20 GPa shock pressure. The meteorite is thus classified to be of L6d type. Melt pockets of widely variable composition are abundant. 相似文献
225.
Andrea Borch Klaus Meisenheimer Christian Wolf Meghan Gray 《Astrophysics and Space Science》2003,284(2):965-968
The COMBO-17 survey cite(Wolf et al., 2002) contains ≈ 40000 galaxies down to R=24 mag on an area of one square degree, obtained
with the wide field imager at the 2.2 m telescope at La Silla. A multi-colour classification on the basis of 5 broadband and
12 medium band filters (=17 bands) yields accurate redshifts (σ
z
≤ 0.01 at the bright end up to σ
z
≈ 0.1 at the faint end) and spectral energy distribution types (SEDs) when using observed galaxy templates from (Kinney et
al.,1996). However, there is an obvious weakness in this classification scheme: The relation between star formation history
and SED remains unclear. It is therefore impossible to draw firm conclusions about the age of the underlying stellar population
and the expected aging between z ≈ 1 and z ≈ 0 can not be quantified. We will present first results of our attempt to replace
the observed templates with model spectra from the PEGASE code (Fioc and Rocca-Volmerange, 1997), in order to get a better
handle on the star formation history.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
226.
H.-M. Schulz H. W. Hagemann M. Wolf A. Brammertz H.-J. Einbrodt 《Environmental Geology》1997,30(1-2):72-80
The fibrogenic and cytotoxic potential of coal mine dust is independent of the amount of quartz and other inorganic parameters.
Results of coal petrographical and organic geochemical investigations of coals and coal mine dust from the Ruhr and Ibbenbüren
Region of Germany demonstrate variations of organic dust amount possibly influencing these noxious properties. Coal mine dust
of high rank coals is characterized by a pronounced fibrogenic risk. This risk, independent of the quantity of quartz, is
probably based on shape variations of different coal macerals. With increasing coalification of the corresponding seam, the
vitrinite is enriched in its dust; however, lower concentrations have been determined for inertinite. Vitrinite shows constant
shapes and sizes independent of the rank of coal. Inertinite particles with elongated to fibrous shapes tend to larger sizes
with increasing coalification. Strikingly, coal mine dust from miners' lungs with high degrees of coal mine workers' pneumoconiosis
(CWP) is enriched in inertinite. In contrast, high cytotoxicities in cell tests are known for coal mine dust from low coalified
coals. High concentrations of phenolic compounds can be extracted by dichloromethane from low coalified coal mine dust. These
compounds, which are characterized by a high water solubility and therefore high bioavailability, explain the high cytotoxicities
of coal mine dust. Contamination of dust by diesel emissions in the coal mine can act as additionally supporting parameters
for extended cytotoxicities.
Received: 18 August 1995 · Accepted: 15 October 1995 相似文献
227.
Pavel Mayer Marek Wolf P. G. Niarchos K. D. Gazeas V. N. Manimanis Drahomír Chochol 《Astrophysics and Space Science》2006,304(1-4):39-41
New precise times of minimum light for several early-type eclipsing binaries were obtained at three observatories. The changes of period of the following measured binaries are discussed: V1182 Aql, LY Aur, SZ Cam, FZ CMa, QZ Car, LZ Cen, V606 Cen, AH Cep and TU~Mus. 相似文献
228.
229.
Dion Brandt Wolf Uwe Reimold Raymond J. Durrheim 《Meteoritics & planetary science》1994,29(3):379-384
Abstract— The genesis of the 1.13-km-diameter Pretoria Saltpan crater has long been the focus of a controversy. Its origin has been explained by either meteorite impact or “cryptoexplosive” volcanic activity, but it was recently confirmed, through detailed petrographic and chemical analysis of a breccia layer forming part of the crater fill, that the crater was formed by impact. As the limited previous geophysical work failed to support an impact origin, a more detailed gravity and magnetic study was conducted. A possible 400-m-diameter circular crater located 3 km to the southwest of the main crater was also investigated with geophysical methods, including resistivity, seismics and ground-probing radar. The gravity signature of the main crater is compatible with that of a simple impact crater and the magnetic signature (no magnetic anomaly could be detected) rules out the possibility of a central magnetic volcanic body below the crater-fill sediments. The results for the possible twin or satellite crater are inconclusive. As it is the only such feature in the entire region, it should not be overlooked. A drilling program may reveal interesting results. 相似文献
230.
A reactor building founded on a large number of piles situated in a layered site is analysed for an historic earthquake assumed to be propagating horizontally. Pile-soil-pile interaction is properly accounted for, incorporating the frequency-dependent stiffness and radiation damping. Compared to vertical incidence, the pile forces are increased and the piles close to the boundary are loaded more heavily than those in the centre region of the basemat. 相似文献