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1.
R. D. Vis A. Mrowiec P. J. Kooyman K. Matsubara D. Heymann 《Meteoritics & planetary science》2002,37(10):1391-1399
Abstract— High‐resolution transmission electron microscopy micrographs of acid‐resistant residues of the Allende, Leoville, and Vigarano meteorites show a great variety of carbon structures: curved and frequently twisted and intertwined graphene sheets, abundant carbon black‐like particles, and hollow “sacs”. It is suggested that perhaps all of these are carriers for the planetary Q‐noble gases in these meteorites. Most of these materials are pyrocarbons that probably formed by the pyrolysis of hydrocarbons either in a gas phase, or on hot surfaces of minerals. An attempt was made to analyze for argon with particle‐induced x‐ray emission in 143 spots of grains of floating and suspended matter from freeze‐dry cycles of an Allende bulk sample in water, and floating “black balls” from sonication in water of samples from the Allende meteorite. The chemical compositions of these particles were obtained, but x‐ray signals at the wavelength of argon were obtained on only a few spots. 相似文献
2.
D. Heymann C.C.A.H. Van Der Stap R.N. Vis H. Verheul 《Meteoritics & planetary science》1987,22(1):3-15
Carbon contents of three Dark Inclusions (DI's) of the Allende meteorite, measured chemically, range from 0.56 to 1.17 weight %. When one includes the data reported by Bunch, Chang, and Ott (two DI's), the lower limit is 0.44%. The C-concentration map of a 1.6 × 1.6 mm2 area straddling the boundary of a DI and matrix, or else of a DI and its dark halo, obtained with a 12C (d,p)13 C nuclear microprobe, shows that the C-content of the core of the DI is very uniform, and that the C-content of the rim is 2.9 ± 0.3 times larger. Variability of C-content of matrix and matrix-like areas of Allende appears to be the rule. DI's cannot be reworked bulk Allende, or precursor for bulk Allende without the addition, respectively removal of significant amounts of carbon. However, some Type 1 DI's might be reworked Allende matrix or precursor matter for that matrix. 相似文献
3.
During the last few years it has been shown that the results of model tests of harbour basins and moored ships are highly dependent on the correct reproduction of wave groups and the attached long waves. Although these bounded long waves are of second order and thus of a rather limited height, resonance and shoaling effects can increase their influence on the results of model investigations. In traditional first order wave generation, the boundary conditions at the wave board are not fulfilled for the bounded long waves, and consequently various spurious, free long waves are unintentionally produced. This paper outlines the general equations and the solution for a rotating and translating wave board. The translatory case is treated in detail, i.e. a physical interpretation of all the second order terms is given, and an approximate control signal for the suppression of spurious long waves for practical use is described. Finally, laboratory experiments successfully verify the various long wave terms and the effectiveness of the suppression terms. 相似文献
4.
The output of material from 11 small drainage basins in the Keuper region of central Luxembourg is considered. Attention is given to differences between forested and cultivated basins. Whilst the output of suspended solids from the cultivated Mosergriecht catchment may be as much as five times higher than from the forested Keiwelsbaach, the solute load is only 50 per cent and the runoff 20 per cent higher. Relationships between dispersed clay in suspension and the water chemistry observed for the forested drainage basins are not present in the cultivated catchments. Water having a milky appearance and containing dispersed clay is of more frequent occurrence in forested basins where subsurface runoff occurs in macropores and cracks in the undisturbed soil. 相似文献
5.
Dieter Heymann Franco Cataldo Mark h. Thiemens Roelof Fokkens Nico m. m. Nibbering Ronald d. Vis 《Meteoritics & planetary science》2000,35(2):355-361
Abstract— Toluene extracts from two (CSn)x photopolymers were examined with high‐performance liquid chromatography (HPLC), matrix‐assisted laser desorption ionization time‐of‐flight (MALDI‐TOF) mass spectrometry, particle‐induced x‐ray emission (PIXE), and 12C(d,p)13C nuclear microprobing. the extracts contained elemental s and at least from 17 to 20 distinct cmsn compounds with m/z less than ～500 amu. Whereas H2S is the dominant S‐bearing compound of the normal jovian atmosphere, elemental S, CS, and CS2 were observed at Shoemaker‐Levy 9 cometary impact sites and at altitudes of the transiently disturbed jovian atmosphere where photodissociation and photopolymerization occur. It is uncertain whether the CS2 molecular densities were sufficiently large for both to occur, but photopolymerization could have occurred during larger impacts of Jupiter's history. Because the known stable CmSn compounds are yellow, orange and deep red, they could contribute significantly to the colors of the jovian clouds. 相似文献
6.
ABSTRACTGoodness-of-fit measures are important for an objective evaluation of runoff model performance. The Kling-Gupta efficiency (RKG), which has been introduced as an improvement of the widely used Nash-Sutcliffe efficiency, considers different types of model errors, namely the error in the mean, the variability, and the dynamics. The calculation of RKG is implicitly based on the assumptions of data linearity, data normality, and the absence of outliers. In this study, we propose a modification of RKG as an efficiency measure comprising non-parametric components, i.e. the Spearman rank correlation and the normalized flow–duration curve. The performances of model simulations for 100 catchments using the new measure were compared to those obtained using RKG based on a number of statistical metrics and hydrological signatures. The new measure resulted overall in better or comparable model performances, and thus it was concluded that efficiency measures with non-parametric components provide a suitable alternative to commonly used measures. 相似文献
7.
Abstract— Carbon in the petrologic matrices of a number of ordinary chondrites of groups H, L, and LL, and of types 3 through 6 was studied with a nuclear microprobe and a Raman microprobe. The majority of the matrices had carbon contents in the narrow range between 0.03 and 0.2 wt%. The carbon content decreased only slightly with increasing petrologic type. Carbon-rich coats around troilite and/or metal phases occured in five meteorites. Poorly ordered carbon was found in the matrices. The carbon in the meteorites of higher petrologic types was slightly better ordered than in the meteorites of lower types. The narrow range of carbon contents and the similarity of the structural form of carbon in the matrices of the measured ordinary chondrites, which represent all groups and types, imply that their matrices may contain a common component, which might be of interstellar origin. 相似文献
8.
Late Holocene sedimentary changes in floodplain and shelf environments of the Tagus River (Portugal)
Geert-Jan Vis Cornelis Kasse Simon Jung Alexander Prick 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(2):203-217
Sedimentary changes during the last ∼2500 years have been reconstructed from cored sedimentary records from the deltaic floodplain of the Lower Tagus Valley and the Tagus mudbelt on the continental shelf offshore Lisbon. We used a multi-proxy approach consisting of sedimentology, grainsize, pollen data and magnetic susceptibility. In the floodplain grainsize coarsened and sedimentation rate and magnetic susceptibility increased during the late Holocene due to an increased flooding frequency and/or intensity. On the Tagus shelf the mudbelt grainsize fined, together with a higher sedimentation rate and increased magnetic susceptibility. The fining grainsize is explained by an increased suspended sediment flux towards the shelf and subdued winnowing. Floodplain and shelf records were correlated by radiocarbon dating and changes in sediment characteristics. We identified four depositional phases (∼2300/∼1600/∼1100/∼670 cal BP) on the floodplain and the shelf. These are tentatively explained by land-use changes in the Tagus catchment. 相似文献
9.
Interception,drop size distributions and rainfall kinetic energy in four colombian forest ecosystems 总被引：1，自引：0，他引：1
M. Vis 《地球表面变化过程与地形》1986,11(6):591-603
Interception losses, rain and throughfall drop size spectra and kinetic energy were studied in four relatively undisturbed tropical forest ecosystems along a transect across the Central Andean Cordillera of Colombia at altitudes between 3000 and 1000 m above sea level. Interception amounts ranged from 11 to more than 20 per cent of the total rainfall and fell within the normal range of interception figures observed in natural tropical forests. Drop size spectra were established using the filter paper method; the drop size distributions of the open field rainfall were unimodal while the throughfall had bimodal distributions, with a higher percentage of the volume of rain falling as large drops. Disturbance of the natural forests, for example by logging activities or cattle grazing, will further increase the throughfall kinetic energy and may lead to higher splash erosion rates inside the forests than in the open field. The kinetic energy of the throughfall was higher than that of the open field rainfall (20-70 per cent), even after correcting for interception losses (4-30 per cent). Splash-cup experiments, conducted both in the field and in the laboratory, indicated that the kinetic energy is a good index of rainfall erosivity. Inside the forests the amounts of sand splashed from the splash-cups was, after correction for interception losses, 2-16 per cent higher than outside the forests. 相似文献
10.
Because of the deep glacial incision, the Lower Tagus Valley hosts a sedimentary record since 20 000 cal BP, making this a unique site along the European Atlantic margin with respect to palaeogeographic and sea level changes. Based on nine cross-sections and 55 radiocarbon dates together with a newly created relative sea level curve, we constructed five palaeogeographic maps of the infill of the Lower Tagus Valley since 20 000 cal BP. We illustrate that relative sea level rise and fluvial sediment supply were the prime forcing factors determining the depositional history and palaeogeographic changes. Around 20 000 cal BP a deeply incised braided river existed, which was directly connected to the ocean across the narrow continental shelf. After that (12 000 cal BP) the gradually moister and warmer climate caused a change to a single-channel river. During the following period (12 000–7000 cal BP) relative sea level rise resulted in a transgression in the Lower Tagus Valley and the establishment of extensive tidal environments. After relative sea level rise had ended (7000 cal BP) the valley was progressively filled by a fluvial wedge and tidally influenced bayhead delta. Since 1000 cal BP the valley-fill history was dominated by increased sediment input due to human-induced degradation of catchment slopes. Generally, climate was of subordinate importance during the entire studied period, merely causing a single-channel river resulting from the change from the cold Heinrich event 1 to the temperate Bölling–Allerød interstadial. Despite the tectonic activity in the region, neotectonic uplift or subsidence was limited, as supported by the horizontal relative sea level curve since 7000 cal BP. Neotectonics played a minor role due to the large distance from the Fennoscandian ice sheet and the narrow continental shelf, which prohibited strong glacio- and hydro-isostatic movements. 相似文献