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91.
The neutrally stratified flow over the Askervein Hill was simulatedusing a terrain-following coordinatesystem and a two-equation(k - ) turbulence model. Calculations were performed on awide range of numerical grids to assess, among other things, theimportance of spatial discretization and the limitations of theturbulence model. Our results showed that a relatively coarse gridwas enough to resolve the flow in the upstream region of the hill;at the hilltop, 10 m above the ground, the speed-up was 10% lessthan the experimental value. The flow's most prominent feature wasa recirculating region in the lee of the hill, which determinedthe main characteristics of the whole downstream flow. This regionhad an intermittent nature and could be fully captured only in the caseof a time-dependent formulation and a third-order discretization ofthe advective terms. The reduction of the characteristic roughnessnear the top of the hill was also taken into account, showing theimportance of this parameter, particularly in the flow close to theground at the summit and in the downstream side of the hill.Calculations involving an enlarged area around the Askervein Hillshowed that the presence of the nearby topography affected the flowneither at the top nor downstream of the Askervein Hill. 相似文献
92.
93.
In the present study, an attempt has been made to characterize the biophysical land units in Kanholi bara river basin of sub-humid
tropical ecosystem of central India using remotely sensed data, field surveys and GIS based multi-criteria overlay analysis.
The geo-spatial database on elevation, slope, landforms, soil depth, soil erosion, land use/land cover and hydrogeomorphological
parameters has been generated using IRS-ID LISS-III satellite data coupled with soil survey data in GIS. The methodology followed
in characterization of biophysical land units in GIS includes assigning scores for different classes of the layers and weighatges
for different layers based on their characteristics and degree of influence on desired output. GIS based ‘multi criteria overlay’
analysis reveals seventeen distinct biophysical land units in the river basin. Severe (50.5-59.5) to very severe (59.5) biophysical
stress units are found in plateau spurs, isolated mounds, linear ridges, dissected plateau and escarpments. These zones are
associated with severe to very severe erosion, steep to very steep, extremely shallow soils, poor to very poor groundwater
prospects, wastelands and scrublands. The characterization of biophysical land units helps in analysis of their potentials,
problems and stress environment to plan and execute site-specific landscape management practices and maximize the productivity
from each biophysical land unit. The present study demonstrates that generation of geo-spatial database based on remotely
sensed data and field surveys in GIS and their analysis helps great extent in characterization of biophysical land units and
analysis of their stress environment for management. 相似文献
94.
JosA. D. Lopes Eugênio V. Santos Neto Mrcio R. Mello Francisco De A.M. Reis 《Organic Geochemistry》1997,26(11-12)
A novel series of 3-alkyl and 3-carboxyalkyl-5β(H)-steranes 7–10 along with a full homologous series of carboxyalkyl-sterane (C1 to C6) 4–6 with 3α(H)5α(H) configuration have been identified in marine-evaporitic oils from Fazenda Belém, Potiguar Basin (Brazil) on the basis of mass spectral interpretation. The synthesis of enantiomerically pure 3α-alkyl-5β(H)-cholestane and 3β-alkyl-5α(H)-cholestane standards and their coinjection with petroleum fractions confirmed the structural assignments. 相似文献
95.
SHARE Asia自动气象站网络:喜马拉雅山—喀喇昆仑山地区气候研究的一个必要组成部分 总被引:1,自引:0,他引:1
E. Vuillermoz L. Bertolani C. Smiraglia GP. Verza G. Tartari A. Marinoni P. Bonasoni 《地球科学进展》2006,21(12):1244-1253
Ev K2 CNR SHARE Asia计划的目标就是建立一个沿喜马拉雅山—喀喇昆仑山脉的监测网络,为气象学和气候研究提供参数,特别是为季风变化、大气化学、冰川学、高海拔湖沼学和古湖沼学等研究,同时也为准确地确定地球表面坐标。SHARE Asia 计划的一个特殊的目的是发展一套完整的测量系统,以满足不断进步的环境与地球科学;促进当地的技术升级和建设的能力。
就像WMO CEOP 和UNEP ABC一样,SHARE Asia 气象—气候及大气化学观测站已经成为重要的国际科学计划的一部分。 相似文献
96.
Damineli A Kaufer A Wolf B Stahl O Lopes DF de Araújo FX 《The Astrophysical journal》2000,536(2):L101-L104
Gas giant planets have been detected in orbit around an increasing number of nearby stars. Two theories have been advanced for the formation of such planets: core accretion and disk instability. Core accretion, the generally accepted mechanism, requires several million years or more to form a gas giant planet in a protoplanetary disk like the solar nebula. Disk instability, on the other hand, can form a gas giant protoplanet in a few hundred years. However, disk instability has previously been thought to be important only in relatively massive disks. New three-dimensional, "locally isothermal," hydrodynamical models without velocity damping show that a disk instability can form Jupiter-mass clumps, even in a disk with a mass (0.091 M middle dot in circle within 20 AU) low enough to be in the range inferred for the solar nebula. The clumps form with initially eccentric orbits, and their survival will depend on their ability to contract to higher densities before they can be tidally disrupted at successive periastrons. Because the disk mass in these models is comparable to that apparently required for the core accretion mechanism to operate, the models imply that disk instability could obviate the core accretion mechanism in the solar nebula and elsewhere. 相似文献
97.
David Lopes de Castro Digenes Custdio de Oliveira Raimundo Mariano Gomes Castelo Branco 《Journal of South American Earth Sciences》2007,24(2-4):184-202
A geophysical perspective based on well-acquired gravity, magnetic, and radiometric data provides good insights into the basin architectural elements and tectonic evolution of the Rio do Peixe Basin (RPB), an Early Cretaceous intracontinental basin in the northeast Brazilian rift system, which developed during the opening of the South Atlantic. NW–SE-trending extensional forces acting over an intensively deformed Precambrian basement yielded a composite basin architecture strongly controlled by preexisting, mechanically weak fault zones in the upper crust. Reactivated NE–SW and E–W ductile shear zones of Brasiliano age (0.6 Ga) divided the RPB into three asymmetrical half-grabens (Brejo das Freiras, Sousa, and Pombal subbasins), separated by basement highs of granite bodies that seem to anchor and distinguish the mechanical subsidence of the subbasins. Radiometric and geopotential field data highlight the relationship between the tectonic stress field and the role of a preexisting structural framework inserted in the final rift geometry. The up-to-2000 m thick half-grabens are sequentially located at the inflexion of sigmoidal-shaped shear zones and acquire a typical NE–SW-oriented elliptic shape. The Sousa Subbasin is the single exception. Because of its uncommon E–W elongated form, three-dimensional gravity modeling reveals an E–W axis of depocenters within the Sousa Subbasin framework, in which the eastern shoulders are controlled by NE–SW-trending faults. These faults belong to the Precambrian structural fabric, as is well illustrated by the gamma ray and magnetic signatures of the basement grain. Release faults were identified nearly perpendicular or oblique to master faults, forming marginal strike ramps and horst structures in all subbasins. The emplacement mechanism of Brasiliano granites around the RPB was partially oriented by the same structural framework, as is indicated by the gravity signature of the granitic bodies after removal of the gravity effect of the basin-filling deposits. The RPB major-fault occurrence along the releasing bend of a strong discontinuity – the so-called Portalegre Shear Zone – in addition to the configuration of a gentle crustal thinning, according to gravity field studies, suggests that a crustal discontinuity governs the nucleation of the RPB, followed probably by small displacement in deep crustal levels accommodating low-rate stretching during basin subsidence. 相似文献
98.
99.
Zeferino Joel Carvalho Maria Rosrio Lopes Ana Rita Jesus Rosrio Afonso Maria Jos Freitas Liliana Carvalho Jos Martins Chamin Helder I. 《Hydrogeology Journal》2021,29(6):2267-2283
Hydrogeology Journal - Nitrate contamination of groundwater is an important public health issue worldwide. For environmental and public health reasons, water should not contain more than... 相似文献
100.
Lopes Namir Domingos Raimundo Li Tianxin Matomela Nametso Sá Rui Moutinho 《Natural Hazards》2022,114(1):989-1013
Natural Hazards - Guinea-Bissau's coasts are considered highly vulnerable to coastal hazards, and this vulnerability is expected to increase under future climate change scenarios. Multi-hazards... 相似文献