Determination of efficiency of Vaseline slide and Wilson and Cooke sediment traps by wind tunnel experiments     

Feras Youssef  Gunay Erpul  Pieter Bogman  Wim M. Cornelis  Donald Gabriels 《Environmental Geology》2008,55(4):741-750

The trap efficiency of a catcher in wind erosion measurements plays a significant role, and in many cases suspension trap efficiencies at high wind velocities are still unknown. The sediment trap efficiency generally changes with particles size and with wind speed. In this study, the efficiency of Vaseline Slide (VS) and Modified Wilson and Cooke (MWAC) catchers were determined with different sand particle sizes (<50, <75, 50–75, 200–400, and 400–500 μm) at a fixed wind speed (13.3 ms⁻¹) and with different soil textures at different wind velocities (10.3, 12.3, and 14.3 ms⁻¹) in the wind tunnel of the International Center for Eremology (ICE), Ghent University, Belgium. The traps were placed at different heights (4, 6.5, 13, 20, 120, and 192 cm for VS and 1.5, 3, 5, 8, 11, and 30 cm for MWAC) to catch saltating and suspended sediments in a 12-m long, 1.2-m wide and 3.2-m high working section of the wind tunnel. In the sand particle experiments, the efficiency of the VS catcher was 92% for particles smaller than 50 μm and decreased with increasing particles size, falling to 2.2% for 400–500 μm particle size at 13.4 ms⁻¹. However, the MWAC’s efficiency was 0% for particles smaller than 50 μm and increased with increasing particle size to 69.5% at 400–500 μm. In the experiments with different soil textures, the efficiency of each catcher significantly changed with soil and with wind speed. It also considerably varied with the catchers: for instance, for sand (S), the MWAC efficiency was very high (67.4, 113.4, and 90.5% at 10.3, 12.3, and 14.4 ms⁻¹, respectively) while the efficiency of VS was relatively very low (5.2, 4.4, and 1.9% at 10.3, 12.3, and 14.4 ms⁻¹, respectively). Results indicated that the efficiency depends critically on the particle size, type of catcher, and wind speed, and these could be helpful to increase the robustness of wind erosion measurements.  相似文献   

Spatial development of X-ray emission during the impulsive phase of a solar flare     

Cornelis De Jager  André Boelee  David M. Rust 《Solar physics》1984,92(1-2):245-258

The flare of 11 November, 1980, 1725 UT occurred in a magnetically complex region. It was preceded by some ten minutes by a gradual flare originating over the magnetic inversion line, close to a small sunspot. This seems to have triggered the main flare (at 70 000 km distance) which originated between a large sunspot and the inversion line. The main flare started at 172320 UT with a slight enhancement of hard X-rays (E > 30 keV) accompanied by the formation of a dark loop between two H bright ribbons. In 3–8 keV X-rays a southward expansion started at the same time, with - 500 km s ^–1. At the same time a surge-like expansion started. It was observable slightly later in H, with southward velocities of 200 km s^–1. The dark H loop dissolved at 1724 UT at which time several impulsive phenomena started such as a complex of hard X-ray bursts localized in a small area. At the end of the impulsive phase at 172540 UT, a coronal explosion occurred directed southward with an initial expansion velocity of 1800 km s^–1, decreasing in 40 s to 500 km s^–1.Now at Fokker Aircraft Industries, Schiphol, The Netherlands.  相似文献   

Tracing mechanisms controlling the release of dissolved silicon in forest soil solutions using Si isotopes and Ge/Si ratios     

J.-T. Cornelis  B. Delvaux  L. André  S. Opfergelt 《Geochimica et cosmochimica acta》2010,74(14):3913-289

The terrestrial biogenic Si (BSi) pool in the soil-plant system is ubiquitous and substantial, likely impacting the land-ocean transfer of dissolved Si (DSi). Here, we consider the mechanisms controlling DSi in forest soil in a temperate granitic ecosystem that would differ from previous works mostly focused on tropical environments. This study aims at tracing the source of DSi in forest floor leachates and in soil solutions under various tree species at homogeneous soil and climate conditions, using stable Si isotopes and Ge/Si ratios. Relative to granitic bedrock, clays minerals were enriched in ²⁸Si and had high Ge/Si ratios, while BSi from phytoliths was also enriched in ²⁸Si, but had a low Ge/Si ratio. Such a contrast is useful to infer the relative contribution of silicate weathering and BSi dissolution in the shallow soil on the release of DSi in forest floor leachate solutions. The δ³⁰Si values in forest floor leachates (−1.38‰ to −2.05‰) are the lightest ever found in natural waters, and Ge/Si ratios are higher in forest floor leachates relative to soil solution. These results suggest dissolution of ²⁸Si and Ge-enriched secondary clay minerals incorporated by bioturbation in organic-rich horizons in combination with an isotopic fractionation releasing preferentially light Si isotopes during this dissolution process. Ge/Si ratios in soil solutions are governed by incongruent weathering of primary minerals and neoformation of secondary clays minerals. Tree species influence Si-isotopic compositions and Ge/Si ratios in forest floor leachates through differing incorporation of minerals in organic horizons by bioturbation and, to a lesser extent, through differing Si recycling.  相似文献   

Instability regions in the upper HR diagram     

Cornelis de Jager  Alex Lobel  Hans Nieuwenhuijzen  Richard Stothers 《Monthly notices of the Royal Astronomical Society》2001,327(2):452-458

The following instability regions for blueward evolving-supergiants are outlined and compared. (1) Areas in the Hertzsprung–Russell (HR) diagram where stars are dynamically unstable. (2) Areas where the effective acceleration in the upper part of the photospheres is negative, hence directed outward. (3) Areas where the sonic points of the stellar winds (where     are situated inside the photospheres, at a level deeper than     . We compare the results with the positions of actual stars in the HR diagram and we find evidence that the recent strong contraction of the yellow hypergiant HR 8752 was initiated in a period during which     , whereupon the star became dynamically unstable. The instability and extreme shells around IRC+10420 are suggested to be related to three factors:     the sonic point is situated inside the photosphere; and the star is dynamically unstable.  相似文献   

Properties and emergence patterns of bipolar active regions     

Karen L. Harvey  Cornelis Zwaan 《Solar physics》1993,148(1):85-118

Patterns in the properties of bipolar active regions are determined throughout Cycle 21. Active regions that emerged on the visible hemisphere were identified on NSO/KP full-disk magnetograms during 29 solar rotations selected from 1975 through 1986. The bipolar active regions are included only once in this sampling; their properties are derived at the time of maximum development. In order to study an unbiased sample over the entire range of areas larger than 2.5 square degrees (or 373 Mm²), their counts are corrected for size-dependent effects that reduce the chance of their identifications.The size distribution of bipolar active regions is a well-defined function that decreases with increasing size. Except for the smallest regions, the shape of the size distribution is independent of the phase of a cycle, only the scaling factor varies. The shape of the size distribution function for bipoles emerging within existing sunspot regions is virtually the same as that for bipoles emerging outside existing regions. Over the cycle, at least 44% of the regions larger than 3.5 square degrees emerge within existing sunspot regions. Hence, the rate at which new regions emerge is much higher within the boundaries of existing sunspot regions than it is in the activity belts outside existing regions. For regions emerging outside of existing sunspot regions, this rate increases by a factor of 3.5 from cycle minimum to maximum, while for new bipoles within existing active regions, the emergence rate varies with a significantly lower magnitude.Through the cycle, for regions in all size bins, the emergence frequencies appear to vary in phase. The frequencies increase by a factor of more than 8 from minimum to maximum for regions larger than 3.5 square degrees, but no more than 4.7 for the smaller regions. Short-term variations in the emergence frequency of regions do not necessarily occur simultaneously for regions of all sizes, implying that the size distribution is variable on time scales of less than six rotations.  相似文献   

New techniques for integral field spectroscopy – II. Performance of the GNIRS IFU     

Jeremy Allington-Smith  Cornelis M. Dubbeldam  Robert Content  David Robertson  James Turner  Bernadette Rodgers  Jonathan Elias  Joris Gerssen †  Mark Swinbank 《Monthly notices of the Royal Astronomical Society》2007,376(2):785-792

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Stability of pyrochlores in alkaline matrices: Solubility of calcium antimonate   总被引：1，自引：0，他引：1  

Geert Cornelis  Tom Van Gerven  Ruben Snellings  Bram Verbinnen  Jan Elsen  Carlo Vandecasteele 《Applied Geochemistry》2011,26(5):809-817

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Biological carbon sequestration and carbon trading re-visited     

G. Cornelis van Kooten 《Climatic change》2009,95(3-4):449-463

Biological activities that sequester carbon create CO₂ offset credits that could obviate the need for reductions in fossil fuel use. Credits are earned by storing carbon in terrestrial ecosystems and wood products, although CO₂ emissions are also mitigated by delaying deforestation, which accounts for one-quarter of anthropogenic CO₂ emissions. However, non-permanent carbon offsets from biological activities are difficult to compare with each other and with emissions reduction because they differ in how long they prevent CO₂ from entering the atmosphere. This is the duration problem. It results in uncertainty and makes it hard to determine the legitimacy of biological activities in mitigating climate change. Measuring, verifying and monitoring the carbon sequestered in sinks greatly increases transaction costs and leads to rent seeking by sellers of dubious sink credits. While biological sink activities undoubtedly help mitigate climate change and should not be neglected, it is shown that there are limits to the substitutability between temporary offset credits from these activities and emissions reduction, and that this has implications for carbon trading. A possible solution to inherent incommensurability between temporary and permanent credits is also suggested.  相似文献   

Microfocus X-ray computed tomography analysis of corroded glass objects     

Florias Mees  Etienne Cornelis  Patric Jacobs  Maria Teresa Domnech Crbo  Hannelore Rmich 《Engineering Geology》2009,103(3-4):93-99

Microfocus X-ray computed tomography (µCT) is a useful tool for non-destructive analysis of corroded archaeological glass objects and for monitoring restoration and conservation processes for these materials. This was demonstrated by µCT analysis of artificially corroded laboratory-produced glasses and corroded archaeological glasses retrieved from soil environments. Corrosion layers with a thickness of 20 µm or more can be detected as areas with lower X-ray attenuation values than the non-corroded glass. Features that are revealed by µCT analyses include the degree and patterns of corrosion and the presence of various internal structures in the corrosion layers. The study of restored corroded glasses demonstrates that mechanical and laser cleaning can be monitored efficiently. The study of consolidation practices, using test objects, requires the use of additives to increase X-ray attenuation values of the organic compounds that are used.  相似文献   

Chromospheric and coronal explosions in solar flares     

Cornelis De Jager 《Solar physics》1987,110(2):337-342

The phenomenon described as a coronal explosion results directly from a chromospheric explosion. These two phenomena always occur together. They are the manifestations of the impulsive phase explosions in solar flares. These explosive processes occur during and immediately after the onset of the impulsive phase of flares. A previously presented model, describing the relation between the two kinds of explosions, appears to be able to explain qualitatively, and in many cases also quantitatively, the observations relevant to these explosive processes.  相似文献