Tidal interactions and disruptions of giant planets on highly eccentric orbits     

Joshua A. Faber  Frederic A. Rasio  Bart Willems 《Icarus》2005,175(1):248-262

We calculate the evolution of planets undergoing a strong tidal encounter using smoothed particle hydrodynamics (SPH), for a range of periastron separations. We find that outside the Roche limit, the evolution of the planet is well-described by the standard model of linear, non-radial, adiabatic oscillations. If the planet passes within the Roche limit at periastron, however, mass can be stripped from it, but in no case do we find enough energy transferred to the planet to lead to complete disruption. In light of the three new extrasolar planets discovered with periods shorter than two days, we argue that the shortest-period cases observed in the period-mass relation may be explained by a model whereby planets undergo strong tidal encounters with stars, after either being scattered by dynamical interactions into highly eccentric orbits, or tidally captured from nearly parabolic orbits. Although this scenario does provide a natural explanation for the edge found for planets at twice the Roche limit, it does not explain how such planets will survive the inevitable expansion that results from energy injection during tidal circularization.  相似文献   

The usefulness of outcrop analogue air permeameter measurements for analyzing aquifer heterogeneity: quantifying outcrop hydraulic conductivity and its spatial variability          下载免费PDF全文

Bart Rogiers  Koen Beerten  Tuur Smeekens  Dirk Mallants  Matej Gedeon  Marijke Huysmans  Okke Batelaan  Alain Dassargues 《水文研究》2014,28(20):5176-5188

Saturated hydraulic conductivity (K) is one of the most important parameters determining groundwater flow and contaminant transport in both unsaturated and saturated porous media. Although several well‐established laboratory methods exist for determining K, in situ measurements of this parameter remain very complex and scale dependent. Often, the limited accessibility of subsurface sediments for sampling means an additional impediment to our ability to quantify subsurface K heterogeneity. One potential solution is the use of outcrops as analogues for subsurface sediments. This paper investigates the use of air permeameter measurements on outcrops of unconsolidated sediments to quantify K and its spatial heterogeneity on a broad range of sediment types. The Neogene aquifer in northern Belgium is used as a case study for this purpose. To characterize the variability in K, 511 small‐scale air permeability measurements were performed on outcrop sediments representative over five of the aquifer's lithostratigraphic units. From these measurements, outcrop‐scale equivalent K tensors were calculated using numerical upscaling techniques. Validation of the air permeameter‐based K values by comparison with laboratory constant head K measurements reveals a correlation of 0.93. Overall, the results indicate that hand‐held air permeameters are very efficient and accurate tools to characterize saturated K, as well as its small‐scale variability and anisotropy on a broad range of unconsolidated sediments. The studied outcrops further provided a qualitative understanding of aquifer hydrostratigraphy and quantitative estimates about K variability at the centimetre‐scale to metre‐scale. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Pleistocene glacial history of the NW European continental margin   总被引：3，自引：3，他引：3  

Hans Petter Sejrup  Berit Oline Hjelstuen  K.I. Torbjrn Dahlgren  Haflidi Haflidason  Antoon Kuijpers  Atle Nygrd  Daniel Praeg  Martyn S. Stoker  Tore O. Vorren 《Marine and Petroleum Geology》2005,22(9-10):1111

In this paper new and previously published data on the Pleistocene glacial impact on the NW European margin from Ireland to Svalbard (between c. 48°N–80°N) are compiled. The morphology of the glaciated part of the European margin strongly reflects repeated occurrence of fast-moving ice streams, creating numerous glacial troughs/channels that are separated by shallow bank areas. End-moraines have been identified at several locations on the shelf, suggesting shelf-edge glaciation along the major part of the margin during the Last Glacial Maximum. Deposition of stacked units of glacigenic debris flows on the continental slope form fans at a number of locations from 55°N and northwards, whereas the margin to the south of this is characterised by the presence of submarine canyons. Glaciation curves, based primarily on information from the glacial fed fan systems, that depict the Pleistocene trends in extent of glaciations along the margin have been compiled. These curves suggest that extensive shelf glaciations started around Svalbard at 1.6–1.3 Ma, while repeated periods of shelf-edge glaciations on the UK margin started with MIS 12 (c. 0.45 Ma). The available evidence for MIS 2 suggest that shelf-edge glaciation for the whole margin was reached between c. 28 and 22 ¹⁴C ka BP and maximum positions after this were more limited in some regions (North Sea and Lofoten). The last glacial advance on the margin has been dated to 15–13.5 ¹⁴C ka BP, and by c. 13 ¹⁴C ka BP the shelf areas were completely deglaciated. The Younger Dryas (Loch Lomond) advance reached the coastal areas in only a few regions.  相似文献   

Implications of Country-Level Decisions on the Specification of Crown Cover in the Definition of Forests for Land Area Eligible for Afforestation and Reforestation Activities in the CDM     

Louis V. Verchot  Robert Zomer  Oliver Van Straaten  Bart Muys 《Climatic change》2007,81(3-4):415-430

Within the Kyoto Protocol, countries have significant latitude to define a forest. The most important parameter affecting area designated as forest is the minimum crown density which can be set between 10 and 30 percent. The choice will have implications for the amount of land available in a country for afforestation and reforestation (A/R) activities within the Clean Development Mechanism (CDM). In this paper, we used GIS analysis to look at four case studies from countries involved in the EU-funded ENCOFOR project: Bolivia, Ecuador, Uganda and Kenya. We also looked at the effects of other factors that would exclude land from eligibility for A/R projects. A low threshold of 10 percent crown cover resulted in exclusion of 70 to 90 percent of the land area of all countries except Kenya, which differed from the other countries by its large dryland areas. Much less area was excluded when higher thresholds were used. The spatial analyses showed not only the effects of the choice of the crown cover criterion, but also where the land was available for CDM activities within each country at different thresholds. This is the first time that the effect of the crown cover element of the Kyoto forest definition on land availability and distribution for CDM A/R activities has been quantified. While there are a number of reasons to choose different thresholds, this analysis suggests that countries that are considering using CDM finance for rural development might want to select the higher minimum threshold for crown cover in order to maximize their participation and flexibility.  相似文献   

Structural evidence for the sorption of Ni(II) atoms on the edges of montmorillonite clay minerals: a polarized X-ray absorption fine structure study   总被引：1，自引：0，他引：1  

Rainer Dähn  André M Scheidegger  Michel L Schlegel  Bart Baeyens  Daniel Chateigner 《Geochimica et cosmochimica acta》2003,67(1):1-15

The nature of surface complexes formed on Ni uptake onto montmorillonite (a dioctahedral smectite) has been investigated over an extended time period by polarized extended X-ray absorption fine structure (P-EXAFS) spectroscopy. Self-supporting films of Ni-sorbed montmorillonite were prepared by contacting Ni and montmorillonite at pH 7.2, high ionic strength (0.3 M NaClO₄), and low Ni concentration ([Ni]_initial = 19.9 μM) for 14- and 360-d reaction time. The resulting Ni concentration on the clay varied from 4 to 7 μmol/g. Quantitative texture analysis indicates that the montmorillonite particles were well orientated with respect to the plane of the film. The full width at half maximum of the orientation distribution of the c* axes of individual clay platelets about the normal to the film plane was 44.3° (14-d reaction time) and 47.1° (360-d reaction time). These values were used to correct the coordination numbers determined by P-EXAFS for texture effects. Ni K-edge P-EXAFS spectra were recorded at angles between the incident beam and the film normal equal to 10, 35, 55, and 80°. Spectral analysis led to the identification of three nearest cationic subshells containing 2.0 ± 0.5 Al at 3.0 Å and 2.0 ± 0.5 Si at 3.12 Å and 4.0 ± 0.5 Si at 3.26 Å. These distances are characteristic of edge-sharing linkages between Al and Ni octahedra and of corner-sharing linkages between Ni octahedra and Si tetrahedra, as in clay structures. The angular dependence of the Ni-Al and Ni-Si contributions indicates that Ni-Al pairs are oriented parallel to the film plane, whereas Ni-Si pairs are not. The study reveals the formation of Ni inner-sphere mononuclear surface complexes located at the edges of montmorillonite platelets and thus that heavy metals binding to edge sites is a possible sorption mechanism for dioctahedral smectites. Data analysis further suggests that either the number of neighboring Al atoms slightly increases from 1.6 to 2 or that the structural order of the observed surface complexes increases from 0.01 Ų to 0.005 Ų with increasing reaction time. On the basis of the low Ni-Al coordination numbers, it appears that over an extended reaction time period of 1 yr the diffusion of Ni atoms in the octahedral layer is not the major uptake mechanism of Ni onto montmorillonite.  相似文献   

Thermal metamorphism of primitive meteorites—XL The enstatite meteorites: origin and evolution of a parent body     

Swarajranjan Biswas  Thomas Walsh  Gerhard Bart  Michael E. Lipschutz 《Geochimica et cosmochimica acta》1980,44(12):2097-2110

We report neutron activation data for Ag, As, Bi, Cd, Co, Cs, Cu, Ga, In, Rb, Se, Te, Tl and Zn in samples of Abee heated at temperatures of 1000–1400°C in a low-pressure environment (initially ~ 10^?5 atm H₂) and in 9 enstatite achondrites (aubrites) and the silicate portion of the unique stony-iron, Mt Egerton. Trace element losses in heated Abee progress with temperature, the lowest retention being 2.4 × 10^?6 of initial contents. These data indicate trace element loss above 1000°C via diffusion-controlled processes having apparent activation energies of 8–55 kcal/mol ; only Co exhibits a significantly higher energy. These trace element data and those for aubrites, Mt Egerton and E4–6 chondrites, and mineralogic and isotopic evidence link all enstatite meteorites to a common parent body. Volatile, mobile elements vary inversely with cobalt content in aubrites and Mt Egerton but directly in E4–6 chondrites; this is inconsistent with all genetic models positing fractionation of such elements during nebular condensation and accretion. However, the data are consistent with the idea that aubrites and Mt. Egerton reflect fractional crystallization of a magma produced from enstatite chondrite-like parent material (probably E6) and late introduction of chalcophiles and mobile elements transported by FeS-Fe eutectic from an E4–6 region experiencing open-system metamorphism. As suggested earlier, the only primary process that affected enstatite meteorites involved fractionation of non-volatile lithophiles from sulfides and metal during condensation and accretion of chondritic parent material from the nebula. If, as seems likely, volatile/mobile elements reflect secondary processes, they can only be used to establish alteration conditions within the enstatite parent body and not to estimate temperatures during primary nebular condensation and accretion.  相似文献   

Quantifying the effectiveness of climate change mitigation through forest plantations and carbon sequestration with an integrated land-use model     

Jelle G van Minnen  Bart J Strengers  Bas Eickhout  Rob J Swart  Rik Leemans 《Carbon balance and management》2008,3(1):1-20

Background

Carbon plantations are introduced in climate change policy as an option to slow the build-up of atmospheric carbon dioxide (CO₂) concentrations. Here we present a methodology to evaluate the potential effectiveness of carbon plantations. The methodology explicitly considers future long-term land-use change around the world and all relevant carbon (C) fluxes, including all natural fluxes. Both issues have generally been ignored in earlier studies.

Results

Two different baseline scenarios up to 2100 indicate that uncertainties in future land-use change lead to a near 100% difference in estimates of carbon sequestration potentials. Moreover, social, economic and institutional barriers preventing carbon plantations in natural vegetation areas decrease the physical potential by 75–80% or more. Nevertheless, carbon plantations can still considerably contribute to slowing the increase in the atmospheric CO₂ concentration but only in the long term. The most conservative set of assumptions lowers the increase of the atmospheric CO₂ concentration in 2100 by a 27 ppm and compensates for 5–7% of the total energy-related CO₂ emissions. The net sequestration up to 2020 is limited, given the short-term increased need for agricultural land in most regions and the long period needed to compensate for emissions through the establishment of the plantations. The potential is highest in the tropics, despite projections that most of the agricultural expansion will be in these regions. Plantations in high latitudes as Northern Europe and Northern Russia should only be established if the objective to sequester carbon is combined with other activities.

Conclusion

Carbon sequestration in plantations can play an important role in mitigating the build-up of atmospheric CO₂. The actual magnitude depends on natural and management factors, social barriers, and the time frame considered. In addition, there are a number of ancillary benefits for local communities and the environment. Carbon plantations are, however, particularly effective in the long term. Furthermore, plantations do not offer the ultimate solution towards stabilizing CO₂ concentrations but should be part of a broader package of options with clear energy emission reduction measures.  相似文献   

Evaluation of Two Low‐Cost–High‐Performance Adsorbent Materials in the Waste‐to‐Product Approach for the Removal of Pesticides from Drinking Water     

Pham Thi Thuy  Nguyen Viet Anh  Bart van der Bruggen 《洁净——土壤、空气、水》2012,40(3):246-253

This study evaluates the performance of two low cost and high performance adsorption materials, i.e., activated carbon produced from two natural waste products: Bamboo and coconut shell, in the removal of three pesticides from drinking water sources. Due to the fact that bamboo and coconut shell are abundant and inexpensive materials in many parts of the world, they respond to the “low‐cost” aspect. The adsorption capacities of two local adsorbents have been compared with commercial activated carbon to explore their potential to respond to the “high quality” aspect. Two pesticides were selected, namely dieldrin and chlorpyrifos, because they are commonly used in agriculture activities, and may remain in high concentrations in surface water used as drinking water sources. The results indicate that the adsorption of pesticides on activated carbons is influenced by physico‐chemical properties of the activated carbon and the pesticides such as the presence of an aromatic ring, and their molar mass. The activated carbon produced from bamboo can be employed as low‐cost and high performance adsorbent, alternative to commercial activated carbon for the removal of pesticides during drinking water production. The performance of activated carbon from bamboo was better due to its relatively large macroporosity and planar surface. The effect of adsorbent and pesticide characteristics on the performance was derived from batch experiments in which the adsorption behavior was studied on the basis of Freundlich isotherms.  相似文献   

Upstream and downstream controls of recent avulsions on the Taquari megafan,Pantanal, south‐western Brazil     

Bart Makaske  Ben H. P. Maathuis  Carlos R. Padovani  Chris Stolker  Erik Mosselman  Rob H. G. Jongman 《地球表面变化过程与地形》2012,37(12):1313-1326

Avulsion, the natural relocation of a river, is a key process in the evolution of subaerial fans, river floodplains and deltas. The causes of avulsion are poorly understood, which is partly due to the scarcity of field studies of present avulsions. At present, two avulsions are occurring on the middle and lower Taquari megafan, Pantanal basin, south‐western Brazil. Here we present an analysis of the causes of these avulsions based on field and remote sensing data and show that avulsions on megafans can be controlled by both upstream and downstream processes. The middle fan avulsion (started in 1997–1998) is a result of upstream control: overbank aggradation was caused by the (variable) input of sandy sediment into the system, which caused channel‐belt superelevation and also created an easily erodible subsurface favouring bank retreat, crevassing, and scour of deep floodplain channels. The sandy subsurface in this area is inferred to have been a major factor in the causation of this avulsion under conditions of little gradient advantage. The lower fan avulsion (started c. 1990) results from interplay of upstream and downstream controls, the latter being related to the local base level (the Paraguay River floodplain) at the toe of the fan. Channel and overbank aggradation on the lower fan was influenced by fan sub‐lobe progradation and channel backfilling. Fan sub‐lobe progradation caused a significant gradient advantage of the avulsion channel over the parent channel. Avulsions are commonly supposed to be preferentially triggered by high‐magnitude floods, when there is considerable channel‐belt superelevation. However, both avulsions studied by us were triggered by small to average floods, with modest channel‐belt superelevation. We conclude that flood magnitude and channel‐belt superelevation have been overrated as causes of avulsion, and demonstrate additional causes that influence the growth of crevasses into avulsions. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Hydraulic and sedimentary processes causing anastomosing morphology of the upper Columbia River, British Columbia, Canada   总被引：2，自引：0，他引：2  

Bart Makaske  Derald G. Smith  Henk J.A. Berendsen  Arjan G. de Boer  Marinka F. van Nielen-Kiezebrink  Tracey Locking 《Geomorphology》2009,111(3-4):194-205

The upper Columbia River, British Columbia, Canada, shows typical anastomosing morphology — multiple interconnected channels that enclose floodbasins — and lateral channel stability. We analysed field data on hydraulic and sedimentary processes and show that the anastomosing morphology of the upper Columbia River is caused by sediment (bedload) transport inefficiency, in combination with very limited potential for lateral bank erosion because of very low specific stream power (≤ 2.3 W/m²) and cohesive silty banks. In a diagram of channel type in relation to flow energy and median grain size of the bed material, data points for the straight upper Columbia River channels cluster separately from the data points for braided and meandering channels. Measurements and calculations indicate that bedload transport in the anastomosing reach of the upper Columbia River decreases downstream. Because of lateral channel stability no lateral storage capacity for bedload is created. Therefore, the surplus of bedload leads to channel bed aggradation, which outpaces levee accretion and causes avulsions because of loss of channel flow capacity. This avulsion mechanism applies only to the main channel of the system, which transports 87% of the water and > 90% of the sediment in the cross-valley transect studied. Because of very low sediment transport capacity, the morphological evolution of most secondary channels is slow. Measurements and calculations indicate that much more bedload is sequestered in the relatively steep upper anastomosing reach of the upper Columbia River than in the relatively gentle lower anastomosing reach. With anastomosing morphology and related processes (e.g., crevassing) being best developed in the upper reach, this confirms the notion of upstream rather than downstream control of upper Columbia River anastomosis.  相似文献