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1.
GP. Horedt 《Celestial Mechanics and Dynamical Astronomy》1972,6(2):232-241
We consider a large massM and two small massesm
1 andm
2 (m
1 m
2;m
1,m
2M). The orbit ofm
1 is initially circular and the motion ofm
2 hyperbolic with respect toM. The orbital elements of the small masses are strongly modified after a close, single encounter betweenm
1 andm
2.An approximative method, similar to the theory of stellar encounters, is used to determine the probabilities of collisions, hyperbolas, direct and retrograde ellipses, as well as the mean values of the semimajor axes and their root mean square deviation after the encounter.The results are close to those which are obtained if the massm
2 is negligibly small, (Mm
1m
2;m
2 0), as should be also expected on general grounds. 相似文献
2.
Sediment resuspension during and after mechanical excavation of macrophytes may have a significant impact on resident fish populations. Unfortunately, little is known about the influence of this sediment on the respiratory performance and feeding abilities of fishes in New Zealand waterways. We examined the effects of suspended sediment (SS) concentrations previously observed after a large-scale macrophyte removal operation on oxygen consumption (MO2) and feeding rates of brown trout (Salmo trutta). MO2 at 0 mg L?1, 150 mg L?1, 300 mg L?1, 450 mg L?1 and 600 mg L?1 of SS was measured using semi-closed respirometry. Feeding rates at the same SS concentrations were also measured using laboratory tank experiments. Results suggest that SS concentrations up to 600 mg L?1 have no effect on MO2. Conversely, feeding rates were significantly reduced at 450 mg L?1 (22% reduction) and 600 mg L?1 (31% reduction), indicating that sediment concentrations above 450 mg L?1 may negatively affect brown trout populations. 相似文献
3.
GP. Horedt 《Earth, Moon, and Planets》1976,15(3-4):439-443
If the mass of the Earth was not considerably larger than at present, the pre-capture orbit of the Moon was in the range 0.9–1.1 A.U. Capture occurred within several 108 years after formation of the Moon. 相似文献
4.
GP Jones 《新西兰海洋与淡水研究杂志》2013,47(3):334-359
Abstract This review examines the history and current understanding of the ecology of rocky reef fishes in northeastern New Zealand, marking the fiftieth anniversary of the Leigh Marine Laboratory. The cumulative number of publications increased steadily to c. 180 by 2012. Most attention has been on the snapper (Pagrus auratus, f. Sparidae), the largest in size and economically most important species, and on triplefins (Tripterygiidae), the smallest in size and most diverse family. A strong quantitative school emerged in the 1980s, a period when there was little research on temperate reef fishes elsewhere. A ‘bottom-up’ view of the effects of habitat structure on fish emerged, identifying the key roles of depth, topography and macroalgae. By 2000, attention shifted to using marine reserves as laboratories for ecological research. A ‘top-down’ view of fish as predators emerged, documenting cascading effects on prey communities and habitats. The two different viewpoints have not yet been integrated. Research gaps, including population connectivity and climate change, represent major challenges for the next 50 years. 相似文献
5.
Quantitative recruitment of ichthyofauna into a South African temporarily open/closed estuary (TOCE) was investigated during three distinct hydrological phases: closed overwash, open outflow and tidal mouth conditions. Maximum recruitment densities occurred during outflow conditions and declined when the system became tidally inundated. Recruitment densities were lowest during overwash events. Selective diel variation was evident, with higher night-time densities for each phase. This study highlights the importance of seasonal timing and duration of open conditions and overwash events for structuring ichthyofaunal community composition of southern African TOCEs. 相似文献
6.
华南西部地区晚中生代与W-Sn矿有关花岗岩的年代学格架及地质意义 总被引:10,自引:3,他引:7
华南西部地区是我国重要的大型-超大型锡多金属矿床分布区。本文根据近年来新获得的花岗岩LA-ICP-MS锆石U-Pb数据,结合近几年以来新报道的高精度成岩成矿年代学资料和地球动力学研究进展,总结发现华南西部地区中生代岩浆-成矿作用的时代主要集中在晚白垩世(76~98Ma)。通过分别总结华南东、西部地区晚白垩岩浆作用及相应的成矿作用的特征,发现华南东、西部的成岩成矿作用特征表现出明显的差异,但是这两地内部各自却表现出高度的一致性;且东部地区明显要比西部地区更为复杂,但二者之间的共同点在于该时期均处于岩石圈伸展的环境和壳幔间的相互作用明显。晚白垩世华南西部地区主要受控于华南陆块陆内背景下岩石圈伸展而导致的岩浆-成矿作用这一因素,而东部地区除此之外还受到太平洋古板块北北东向走滑带来的影响。 相似文献
7.
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
8.
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
9.
Herold M Román-Cuesta RM Mollicone D Hirata Y Van Laake P Asner GP Souza C Skutsch M Avitabile V Macdicken K 《Carbon balance and management》2011,6(1):13
Measuring forest degradation and related forest carbon stock changes is more challenging than measuring deforestation since
degradation implies changes in the structure of the forest and does not entail a change in land use, making it less easily
detectable through remote sensing. Although we anticipate the use of the IPCC guidance under the United Framework Convention
on Climate Change (UNFCCC), there is no one single method for monitoring forest degradation for the case of REDD+ policy.
In this review paper we highlight that the choice depends upon a number of factors including the type of degradation, available
historical data, capacities and resources, and the potentials and limitations of various measurement and monitoring approaches.
Current degradation rates can be measured through field data (i.e. multi-date national forest inventories and permanent sample
plot data, commercial forestry data sets, proxy data from domestic markets) and/or remote sensing data (i.e. direct mapping
of canopy and forest structural changes or indirect mapping through modelling approaches), with the combination of techniques
providing the best options. Developing countries frequently lack consistent historical field data for assessing past forest
degradation, and so must rely more on remote sensing approaches mixed with current field assessments of carbon stock changes.
Historical degradation estimates will have larger uncertainties as it will be difficult to determine their accuracy. However
improving monitoring capacities for systematic forest degradation estimates today will help reduce uncertainties even for
historical estimates. 相似文献
10.
GP. Horedt 《Astrophysics and Space Science》1976,45(2):353-367
In dense interstellar clouds or in the surroundings of just-formed stars, the larger grains form proto-cores by segregating from the gas under the influence of the gravitational field of the cloud during intervals of the order 108 yr.If the mass of the proto-cores is smaller than a certain limit, the object possesses a negligible atmosphere and remains composed mainly of solid grain material. If the mass of the proto-core exceeds the limiting mass, the proto-core can bind around it an atmosphere. When the temperature of the opaque part of the atmosphere is only fractions of a degree above the temperature of the surrounding tenuous gas, gravitational contraction of the opaque part of the atmosphere sets in, forming gaseous objects up to stellar mass range.Binary and multiple systems originate from neighbouring proto-cores, through gravitational contraction of both their separate and common outer atmospheres.Pycnonuclear reactions are not able to prevent a star with mass 0.08M
from cooling to the black dwarf stadium. 相似文献