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71.
Matthew J. Payne Giuseppe Lodato 《Monthly notices of the Royal Astronomical Society》2007,381(4):1597-1606
Recent observations point to the presence of structured dust grains in the discs surrounding young brown dwarfs, thus implying that the first stages of planet formation take place also in the substellar regime. Here, we investigate the potential for planet formation around brown dwarfs and very low-mass stars according to the sequential core accretion model of planet formation. We find that, for a brown dwarf mass 0.05 M⊙ , our models predict a maximum planetary mass of ∼5 M⊕ , orbiting with semimajor axis ∼ 1 au. However, we note that the predictions for the mass–semimajor axis distribution are strongly dependent upon the models chosen for the disc surface density profiles and the assumed distribution of disc masses. In particular, if brown dwarf disc masses are of the order of a few Jupiter masses, Earth-mass planets might be relatively frequent, while if typical disc masses are only a fraction of Jupiter mass, we predict that planet formation would be extremely rare in the substellar regime. As the observational constraints on disc profiles, mass dependencies and their distributions are poor in the brown dwarf regime, we advise caution in validating theoretical models only on stars similar to the Sun and emphasize the need for observational data on planetary systems around a wide range of stellar masses. We also find that, unlike the situation around solar-like stars, Type II migration is totally absent from the planet formation process around brown dwarfs, suggesting that any future observations of planets around brown dwarfs would provide a direct measure of the role of other types of migration. 相似文献
72.
P. S. Arun R. Jana M. S. Nathawat 《Journal of the Indian Society of Remote Sensing》2005,33(2):189-201
Efficient micro-watershed management needs characterization of it to optimize natural resources, which is especially important
in drought prone areas. In the present study micro-watersheds of Gandheshwari tributary in Chotta-Nagpur Plateau are characterized
based on physiographic properties towards agricultural potentiality. An algorithm interpolating elevation values using an
empirical formula is proposed to obtain an improved Digital Elevation Model (DEM). IRS LISS-Ill Satellite data is used to
acquire important parameters like landuse/ landcover and drainage. Image processing techniques like edge enhancement, edge
detection, and principal components analysis are used for improving lineament detection. For characterization of watershed
landform analysis using physiographic parameters is done in Geographic Information System (GIS). Detailed drainage network
obtained from satellite image, the improved DEM and other GIS layers of land based information are used to delineate micro-watersheds.
The Agricultural 1-lydrologic Response Units (AHRU) targeting agricultural use of the land are derived by overlaying the delineated
parameters and are grouped into thirty response units based on their agricultural potential. Micro-watersheds are characterized
based on the dominant Al-IRU giving spatial information about agricultural suitability, emphasizing availability and scarcity
of water so that respective water conservation practices can be improved to use the potential AHRU. 相似文献
73.
Summary Induction response has been investigated at 57 field stations covering the Bohemian Massif (BM) and the Bruno-Vistulicum (BV),
and at 93 temporary observing sites across the West Carpathians (WCP). Induction response data at 958 localities covering
mainly the Central European area were also collected and analysed. Components of transfer functions (TF), moduli and arguments
of corresponding induction vectors are analyzed for individual profiles. Pseudo-sections of induction parameters at profiles
are used to visualize the period dependence of induction response and computer generated contour maps of TF components define
zones of anomalous induction and their relation to large scale anomalies. Depths of anomalous field source are estimated by
separating variations into internal and external parts. Correlations among induction response characteristics and the results
of other geophysical investigations are discussed. 相似文献
74.
Karel Pěč Jana Pěčová Oldřich Praus Reviewer M. Hvoždara 《Studia Geophysica et Geodaetica》1988,32(4):368-391
Summary The theory of methods of computing single- and inter-station transfer functions in both the spectral and time domains was developed in paper[1]. Both approaches are applied to the variation data recorded at field stations along two non-simultaneous profiles traversing the eastern margin of the Bohemian Massif, where a zone of anomalous induction seems to mark an important geological boundary of formations with different histories of development. The results of both analyses are found to coincide within reasonable bounds of 20–30% in the principal induction characteristics.
u m¶rt; ama ¶rt;-u -mau n¶rt;am u nma u am a ua am[1]. am nua m am a n¶rt;¶rt;a nu ¶rt; aaua ¶rt;aaum auau aumua a n mau ¶rt; u nu, nau m au aua,¶rt; aa a aa u¶rt;uu. a, u¶rt;u, mamau a¶rt;a ¶rt; ¶rt; ¶rt;uuau au umuu aumu. mam aau nma u am auam a 20–30% ¶rt; u¶rt;u naam.相似文献
75.
Different experimental conditions (fed large, fed small, starved large, starved small groups, batch offered ration during experiment and low fish loading for a constant volume of water) of the carnivorous fish Clarias batrachus resulted in marked changes in the concentration of different N species (ammonium-N, nitrate-N, nitrate-N, organic-N as well as the sum of all forms of N) in aquaria water. Organic forms of nitrogen were the most important species of nitrogen excreted by the test fish. The maintenance nitrogen excretion rate was distinctly higher in larger fishes than in smaller ones. Different species of N were found to differ significantly depending upon the fed or starved conditions as well as small or large groups. A reduced level of oxygen in experimental aquaria inhibited the synthesis of nitrate which was maximum in control aquaria with considerably higher values of oxygen. 相似文献
76.
The plankton collected from three fish ponds shows a considerable variability within a pond, between the ponds and in the course of the year. The individual volumes or weights are (minimum—mean—maximum): Gleotrichia echinulata 41–252–879 μg3, Chlorella vulgaris 18–42–94 μm3, Oscillatoria amphigranulata 99–306–827 μm3, Brachionus plicatilis 1–4.918 μg, nauplia 0.5–1.25–2.35 μg, Mesocyclops hyalinus 4–45–369—μg, Heliodiaptomus viduus 41–202–288 μg, Daphnia carinata 186–1468–4578 μg. 相似文献
77.
Jana Konopásková Vlastislav Červený Reviewer I. Pšenčík 《Studia Geophysica et Geodaetica》1984,28(1):19-35
m¶rt;au n unm ¶rt; u ¶rt;uau uu n m nm ¶rt; ¶rt;. a uau ¶rt;m a ma m nau a¶rt;a, amu aa mu. au mu uu naam, m m¶rt;au n ¶rt;am ¶rt;mam m mam ¶rt;a u amu aa mu (. u. 9). aumu amu, uauau n ma nam ¶rt;a . ¶rt; amu m am ¶rt;m ¶rt;am mumm mam a naama am, an. aa uuau n, naama uauau n, um¶rt;. 相似文献
78.
79.
J. S. Lin M. C. Payne V. Heine J. D. C. McConnell 《Physics and Chemistry of Minerals》1994,21(3):150-155
Ab initio total energy calculations based on a new optimized oxygen psuedopotential have been used to study the structures
and relative energies of α-quartz, a partly (OH)4 substituted version of the α-quartz structure, and interstitial water molecules in α-quartz. Hydrogen bonds formed from two hydroxyl groups of the (OH)4 defects in the substituted α-quartz structure promote a stable structure for the defect α-quartz at low temperature. Comparable ab initio calculation of the energy of the interstitial water molecule in the quartz
structure indicates that, energetically, the (OH)4 defect is likely to be strongly favoured as a mode for the incorporation of water. Ab initio stress calculations confirm
that the (OH)4 defect in quartz has a large associated stress field which is likely to lead to segregation of these defects on supersaturation
in wet quartz. The calculations indicate that segregation should occur in the plane (10
0) of the α-quartz structure. 相似文献
80.
M M Jana 《Journal of the Indian Society of Remote Sensing》2002,30(1-2):61-72
The piedmont zone, located between the foothills of Darjeeling Sub-Himalaya and the flat plains of North Bengal is elongated from west to east and its average height varies from 150 m in the north to 50 m in the south. Morphologically, the region is divided into three distinct physiographic units. Many large and small rivers originated from the Darjeeling Sub-Himalayas intersect it. Most of these rivers have their large catchment area in the mountainous tract. The study area has about 350 cm of annual rainfall and peak discharge in the rivers is very high during monsoon period. Rivers carry large amount of sediments, gravels, and pebbles both in suspension and traction and these materials are deposited in the foothills of the Sub-Himalaya as fan deposits and on the riverbeds making braided channels. Landforms in the study area are mainly complex and their origins are influenced by neotectonic and fluvial activities. Many rivers terraces, palaeo-channels, out wash plains, valley-fills and channel bars are formed in the region due to both erosion and depositional processes. These processes and modifications of landforms are still going on in the region. 相似文献