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排序方式: 共有244条查询结果,搜索用时 15 毫秒
11.
Presently, the soil water balance of flood‐influenced soils in fluvial plains is insufficiently described. The new development of a weighable groundwater lysimeter is the basis for recording the water‐balance components precipitation, evapotranspiration, groundwater recharge, capillary rise, and interaction with the water course. Soil‐hydrologic measuring setups at two floodplain sites of the Elbe river serve for direct comparability of lysimeter measurements with data obtained on site. A groundwater control was designed for lysimeters that automatically adjusts the current groundwater level at the floodplain measuring setups and quantifies inflow into or outflow from the lysimeter. It turned out that the lysimeter developed is capable of identifying the individual water‐balance quantities at high accuracy. Contrary to previous assumptions, it was possible to prove groundwater recharge for the floodplain sites. 相似文献
12.
Georg Avramidis Gunthard Scholz Evelyn Nothnick Holger Militz Wolfgang Viöl Arndt Wolkenhauer 《Wood Science and Technology》2011,45(2):359-368
In this study, the impact of a plasma treatment using dielectric barrier discharge at atmospheric pressure on wax-treated
beech was investigated by surface energy determination and adhesion tests. Measurements of the surface energy revealed a strong
increase in surface polarity along with increased surface energy as a result of the plasma treatment, pointing to increased
adhesion properties. To evaluate the adhesion properties of a polyvinyl acetate (PVAc) adhesive on beech treated with montan
ester wax and synthetic Fischer–Tropsch wax, a special peel test was applied. This peel test provided evidence of increased
adhesion of the PVAc after plasma treatment of both materials investigated. 相似文献
13.
14.
Hafezparast M Klocke R Ruhrberg C Marquardt A Ahmad-Annuar A Bowen S Lalli G Witherden AS Hummerich H Nicholson S Morgan PJ Oozageer R Priestley JV Averill S King VR Ball S Peters J Toda T Yamamoto A Hiraoka Y Augustin M Korthaus D Wattler S Wabnitz P Dickneite C Lampel S Boehme F Peraus G Popp A Rudelius M Schlegel J Fuchs H Hrabe de Angelis M Schiavo G Shima DT Russ AP Stumm G Martin JE Fisher EM 《Science (New York, N.Y.)》2003,300(5620):808-812
Degenerative disorders of motor neurons include a range of progressive fatal diseases such as amyotrophic lateral sclerosis (ALS), spinal-bulbar muscular atrophy (SBMA), and spinal muscular atrophy (SMA). Although the causative genetic alterations are known for some cases, the molecular basis of many SMA and SBMA-like syndromes and most ALS cases is unknown. Here we show that missense point mutations in the cytoplasmic dynein heavy chain result in progressive motor neuron degeneration in heterozygous mice, and in homozygotes this is accompanied by the formation of Lewy-like inclusion bodies, thus resembling key features of human pathology. These mutations exclusively perturb neuron-specific functions of dynein. 相似文献
15.
Oxygen (O(2)) is a critical constraint on marine ecosystems. As oceanic O(2) falls to hypoxic concentrations, habitability for aerobic organisms decreases rapidly. We show that the spatial extent of hypoxia is highly sensitive to small changes in the ocean's O(2) content, with maximum responses at suboxic concentrations where anaerobic metabolisms predominate. In model-based reconstructions of historical oxygen changes, the world's largest suboxic zone, in the Pacific Ocean, varies in size by a factor of 2. This is attributable to climate-driven changes in the depth of the tropical and subtropical thermocline that have multiplicative effects on respiration rates in low-O(2) water. The same mechanism yields even larger fluctuations in the rate of nitrogen removal by denitrification, creating a link between decadal climate oscillations and the nutrient limitation of marine photosynthesis. 相似文献
16.
Anaerobic CO dehydrogenases catalyze the reversible oxidation of CO to CO2 at a complex Ni-, Fe-, and S-containing metal center called cluster C. We report crystal structures of CO dehydrogenase II from Carboxydothermus hydrogenoformans in three different states. In a reduced state, exogenous CO2 supplied in solution is bound and reductively activated by cluster C. In the intermediate structure, CO2 acts as a bridging ligand between Ni and the asymmetrically coordinated Fe, where it completes the square-planar coordination of the Ni ion. It replaces a water/hydroxo ligand bound to the Fe ion in the other two states. The structures define the mechanism of CO oxidation and CO2 reduction at the Ni-Fe site of cluster C. 相似文献
17.
Keller HU Jorda L Küppers M Gutierrez PJ Hviid SF Knollenberg J Lara LM Sierks H Barbieri C Lamy P Rickman H Rodrigo R 《Science (New York, N.Y.)》2005,310(5746):281-283
The OSIRIS cameras (optical, spectroscopic, and infrared remote imaging system) onboard the European Space Agency's Rosetta spacecraft observed comet 9P/Tempel 1 for 17 days continuously around the time of NASA's Deep Impact mission. The cyanide-to-water production ratio was slightly enhanced in the impact cloud, compared with that of normal comet activity. Dust particles were flowing outward in the coma at >160 meters per second, accelerated by the gas. The slope of the brightness increase showed a dip about 200 seconds after the impact. Dust Afrho values before and long after the impact confirm the slight decrease of cometary activity. The dust-to-water mass ratio was much larger than 1. 相似文献
18.
Within this paper we summarize the results of the Thaumetopoea processionea monitoring at two observation sites and try to interpret population dynamics from 2006 to 2010 considering meteorological data. Furthermore, observations on the behaviour of neonates associated with oak budburst are presented and discussed. In 2007 large larval colonies occurred and population densities peaked. Massive defoliation and larval migration due to food shortage were observed regularly leading to reduced female moth fecundity. Unfavourable weather conditions probably abetted OPM population decline in spring 2008. Additionally oak budburst was delayed remarkably. More detailed observations on the hatching process and the behaviour of single colonies revealed increasing mortality after two and a half weeks of starvation. The 2009 results indicated another increase of population densities, but exceeded cool and humid weather conditions in May 2010 presumably prevented a new OPM outbreak. In accordance with previous studies egg parasitisation seems to play a minor role in OPM population dynamics. 相似文献
19.
Sandford SA Aléon J Alexander CM Araki T Bajt S Baratta GA Borg J Bradley JP Brownlee DE Brucato JR Burchell MJ Busemann H Butterworth A Clemett SJ Cody G Colangeli L Cooper G D'Hendecourt L Djouadi Z Dworkin JP Ferrini G Fleckenstein H Flynn GJ Franchi IA Fries M Gilles MK Glavin DP Gounelle M Grossemy F Jacobsen C Keller LP Kilcoyne AL Leitner J Matrajt G Meibom A Mennella V Mostefaoui S Nittler LR Palumbo ME Papanastassiou DA Robert F Rotundi A Snead CJ Spencer MK Stadermann FJ Steele A 《Science (New York, N.Y.)》2006,314(5806):1720-1724
Organics found in comet 81P/Wild 2 samples show a heterogeneous and unequilibrated distribution in abundance and composition. Some organics are similar, but not identical, to those in interplanetary dust particles and carbonaceous meteorites. A class of aromatic-poor organic material is also present. The organics are rich in oxygen and nitrogen compared with meteoritic organics. Aromatic compounds are present, but the samples tend to be relatively poorer in aromatics than are meteorites and interplanetary dust particles. The presence of deuterium and nitrogen-15 excesses suggest that some organics have an interstellar/protostellar heritage. Although the variable extent of modification of these materials by impact capture is not yet fully constrained, a diverse suite of organic compounds is present and identifiable within the returned samples. 相似文献
20.
Steven De Decker DVM PhD Emma Davies DVM Diplomate ECVN Livia Benigni DVM Diplomate ECVDI Helen Wilson BVSc Ludovic Pelligand DVM PhD Diplomate ECVAA Emma L. Rayner BSc BVetMed FRCPath MRCVS Nadia Shihab MA VetMB Diplomate ECVN Holger A. Volk DVM PhD Diplomate ECVN 《Veterinary surgery : VS》2012,41(6):766-771