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51.
As a large and dynamic land‐use category, tropical secondary forests may affect climate, soils, and hydrology in a manner different from primary forests or agricultural areas. We investigated the saturated hydraulic conductivity Ksat of a Kandiudult under different land uses in Rondonia, Brazil. We measured Ksat at four depths (12·5, 20, 30 and 50 cm) under (a) primary forest, (b) a former banana–cacao plantation (SF1), and (c) an abandoned pasture (SF2). At 12·5 cm, all three land uses differ significantly (α = 0·1), but not at the 20 and 30 cm depths. At 50 cm, Ksat was significantly greater in the former pasture than in other land uses. Lateral subsurface flow is expected during intense rainfall (about 30 times per year) at 30 cm depth in SF1 and at 50 cm depth in the forest, whereas the relatively low permeability at shallow 12·5 cm in the SF2 may result not only in lateral subsurface flow, but also saturation overland flow. For modelling purposes, recovering systems seem to have Ksat values distinct from primary forest at shallow depths, whereas at deeper layers (>20 cm) they may be considered similar to forests. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
52.
HelmutA.Abt 《天文学进展》2002,20(4):299-301
对如何撰写将要在国际上发表的天文学论文给出一些建议。讲述了论文的每一部分(题目、摘要、引言、主要内容、图表及参考文献等)如何可以写得简洁而又能清晰地表达出观点。这是作者根据在多年的编辑生涯中审阅了许多效果迥异的论文后的经验之谈。 相似文献
53.
Bringfried Stecklum Helmut Meusinger Dirk Froebrich 《Astrophysics and Space Science》2007,311(1-3):63-67
Herbig-Haro objects (HHOs) are caused by outflows from young objects. Since the outflow relies on mass accretion from a circumstellar
disk, it indicates ongoing growth. Recent results of infrared observations yielded evidence for disks around brown dwarfs.
This suggests that at least a certain fraction of brown dwarfs forms like stars. Thus, young sub-stellar objects might cause
HHOs as well. We present selected results of a general survey for HHOs based on DSS-II plates and CCD images taken with the
Tautenburg Schmidt telescope. Numerous young objects could be identified due to their association with newly detected HHOs.
In some cases the luminosity is consistent with very low-mass stars or close to sub-stellar values. This holds for L1415-IRS
and a few infrared sources embedded in other dark clouds (e.g., GF9, BHR111). The question on the minimum mass for outflow
activity is addressed. 相似文献
54.
The variation of abundance of elements across the transition layer between a magnetoplasma and neutral gas is studied for the case of a plasma-gas system containing two different elements. It is shown that the steady states discussed by Bonnevier (1976) represent special situations, a much wider class of steady states being possible. 相似文献
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Żelaźniewicz Andrzej Dörr Wolfgang Bylina Paweł Franke Wolfgang Haack Udo Heinisch Helmut Schastok Janina Grandmontagne Klaus Kulicki Cyprian 《International Journal of Earth Sciences》2004,93(5):773-781
We report U–Pb single zircon ages from three pre-Variscan granitoids in the NE part of the Bohemian Massif. The Platerówka granodiorite from the Lausitz-Izera Unit, the Polish Sudetes, has been dated at 533±9 Ma. The Bitouchov granite form the SW part of the South Krkonoe Unit, the Czech Sudetes, gave an age of 540+11/–10 Ma, and the Wdroe granodiorite in the Fore-Sudetic Block yielded 548±9 Ma. All these latest Vendian/Early Cambrian granitoids represent the post-tectonic expression of a late Proterozoic Cadomian orogenic cycle and demonstrate the eastward extent of the Cadomian basement into the Variscan orogen. Granodiorites of similar age have so far been reported from Brittany and especially from the Saxo-Thuringian Terrane to the NE and SW of the Elbe Fault Zone. We conclude that the Saxo-Thuringian Terrane extends across the Elbe and Sudetic Marginal Fault Zones into the Fore-Sudetic Block. 相似文献
57.
Jorge Arigony-Neto Helmut Saurer Jefferson C. Simões Frank Rau Ricardo Jaña Steffen Vogt Hermann Gossmann 《Climatic change》2009,94(1-2):19-33
Drastic changes were detected in glacial systems of the Antarctic Peninsula in the last decades. The observed phenomena comprise the disintegration of ice shelves, acceleration and thinning of glaciers, and retreat of glacier fronts. However, due to the lack of consistent systematic observations in particular of the higher parts of the glacial systems, it is difficult to predict further responses of the Antarctic Peninsula glaciers to climatic change. The present paper analyses spatial and temporal variations of changes in the dry-snow line altitude on the Antarctic Peninsula as extracted from a time series (1992–2005) of ERS-1/2 SAR and Envisat ASAR data. Upward changes in dry-snow line altitude were observed in general, and are attributed to extreme high-temperature events impacting the central plateaus of the Antarctic Peninsula and the increasing duration of warming periods. A mean decrease in dry-snow line altitude was detected on the west side of the peninsula and is identified as a response to recorded increase in precipitation and accumulation. These results validate the capability of SAR data for deriving superficial parameters of glaciers to be used as indicators of climatic changes in high-latitude regions where operational restrictions limit conventional meteorological observations. 相似文献
58.
Luminescence-dated aeolian deposits of late Quaternary age in the southern Tibetan Plateau and their implications for landscape history 总被引:5,自引:0,他引:5
Aeolian deposits are widely distributed in the interior of the Tibetan Plateau, and their chronology is poorly known. It is not yet clear whether they accumulated only after the last deglaciation, or over a longer time. We applied quartz OSL dating to aeolian samples from the Lhasa area with OSL ages ranging from 2.9 ± 0.2 to at least 118 ± 11 ka. The probability density frequency (PDF) distribution of 24 ages reveals age clusters at about 3, 8, 16–21, 33, and 79–83 ka, indicating enhanced sediment accumulation then. The results show that aeolian deposition occurred throughout most of the last 100 ka. This implies that: 1) an ice sheet covering the whole Tibetan Plateau during the last glacial maximum (LGM) could not have existed; and 2) erosion during the last deglaciation was not as strong as previously proposed, such that not all pre-Holocene loess was removed. The age distribution shown in the PDF indicates that aeolian accumulation is episodic. Sand-formation events revealed by age clusters at 3, 8, and 16–21 ka imply roughly synchronous environmental responses to corresponding global-scale arid events. 相似文献
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