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排序方式: 共有935条查询结果,搜索用时 15 毫秒
851.
Catherine L. Docherty Stephen J. Dugdale Alexander M. Milner Jakob Abermann Magnus Lund David M. Hannah 《河流研究与利用》2019,35(8):1212-1227
Climate change in the Arctic is expected to have a major impact on stream ecosystems, affecting hydrological and thermal regimes. Although temperature is important to a range of in‐stream processes, previous Arctic stream temperature research is limited—focused on glacierised headwaters in summer—with limited attention to snowmelt streams and winter. This is the first high‐resolution study on stream temperature in north‐east Greenland (Zackenberg). Data were collected from five streams from September 2013 to September 2015 (24 months). During the winter, streams were largely frozen solid and water temperature variability low. Spring ice‐off date occurred simultaneously across all streams, but 11 days earlier in 2014 compared with 2015 due to thicker snow insulation. During summer, water temperature was highly variable and exhibited a strong relationship with meteorological variables, particularly incoming shortwave radiation and air temperature. Mean summer water temperature in these snowmelt streams was high compared with streams studied previously in Svalbard, yet was lower in Swedish Lapland, as was expected given latitude. With global warning, Arctic stream thermal variability may be less in summer and increased during the winter due to higher summer air temperature and elevated winter precipitation, and the spring and autumn ice‐on and ice‐off dates may extend the flowing water season—in turn affecting stream productivity and diversity. 相似文献
852.
Erik Fridell Annika Amberntsson Louise Olsson Ann W. Grant Magnus Skoglundh 《Topics in Catalysis》2004,(1):143-146
Flow reactor experiments and X-ray photoelectron spectroscopy (XPS) measurements were used to investigate the importance of platinum oxide formation on Pt/BaO/Al2O3 NO
x
storage catalysts during reactions conditions. The reaction studied was NO(g) + 1/2 O2(g) NO2(g). During NO2 exposure of the catalyst the NO2 dissociation rate decreased during the reaction. This activity decrease with time was also studied with XPS and it was found to be due to platinum oxide formation. The influence of sulphur exposure conditions on the performance of the NO
x
storage catalysts was studied by exposing the samples to lean and/or rich gas mixtures, simulating the conditions in a mixed lean application, containing SO2. The main results show that all samples are sensitive to sulphur and that the deactivation proceeds faster when SO2 is present in the feed under rich conditions than under lean or continuous SO2 exposure. Additionally, the influence of the noble metals present in the catalysts was investigated regarding sulphur sensitivity and it was found that a combination of platinum and rhodium seems to be preferable to retain high performance of the catalyst under SO2 exposure and subsequent regeneration. Finally, the behaviour of micro-fabricated model NO
x
storage catalysts was studied as a function of temperature and gas composition with area-resolved XPS. These model catalysts consisted of a thin film of Pt deposited on one-half of a BaCO3 pellet. It was found that the combination of SO2 and O2 resulted in migration of Pt on the BaCO3 support up to one mm away from the Pt/BaCO3 interface. 相似文献
853.
Esther Ochoa-Fernndez Hans Kristian Rusten Hugo Atle Jakobsen Magnus Rnning Anders Holmen De Chen 《Catalysis Today》2005,106(1-4):41-46
The kinetics of CO2 sorption on a solid adsorbent, namely lithium zirconate, have been studied in an oscillating microbalance. The solid sorbent has been prepared by a novel route resulting in a high capacity, good stability and much improved sorption rates, making it suitable for its application in sorption enhanced hydrogen production by steam methane reforming. A kinetic equation for the sorption kinetics as a function of CO2 partial pressure and temperature has been developed. The hydrogen production by sorption enhanced reaction process has been simulated by a dynamic one-dimensional pseudo-homogenous model of a fixed-bed reactor, where a hydrotalcite-derived Ni catalyst has been used as steam reforming catalysts. Simulation results show that hydrogen purer than 95% with a concentration of carbon monoxide lower than 0.2 mol% can be produced in a single step. 相似文献
854.
In this article we investigate how to optimally activate regulating bids to handle bottlenecks in power system operation. This will lead to an optimal stopping problem, and activation of a regulating bid is to be performed when the transfer through a specific system bottleneck reaches a certain value. Compared to previous research in the area the work presented in this article includes a more detailed model of the structure of the regulating market, and reaction times of actors on the regulating market is taken into consideration. The emphasis of the presentation will be application to a two area test system. The method is compared to Monte Carlo simulation in a numerical example. The example shows a promising result for the suggested method. 相似文献
855.
The catalytic activity and stability in the water–gas shift reaction have been tested for Au-based catalysts prepared by deposition of Au from colloid solutions. The supports that have been used are TiO2, TiO2 supported on carbon nanofibres (CNF) and CNF. Thermal treatments of the samples show that the Au particle size depends on the support material and hence the interaction between the Au particles and the support. In situ X-ray absorption spectroscopic (XAS) measurements during the water–gas shift reaction show no changes in the first Au–Au coordination number for the catalysts containing CNF. Furthermore, improved short-time stability is obtained compared to the AuTiO2 catalysts. The improved stability is achieved by the CNF stabilising small TiO2 particles and hence prevent subsequent sintering of the Au particles. 相似文献
856.
Johan Magnusson Anders Klarbring Magnus Sethson 《Structural and Multidisciplinary Optimization》2009,37(4):335-350
Neuro mechanical network (NMN) is a new concept of adaptronic character. The governing idea is to include geometry, topology,
load carrying, energy transfer, actuating, sensing and control of a machine in one single mathematical state model and, thereby,
enable a formulation of the design and configuration problem as an optimization problem. We have focused our attention on
a type of NMN consisting of what we call active trusses. For these, we have established a state model and given a design optimization
problem from which we have obtained numerical solutions. These solutions show that the approach has the possibility to suggest
new families of designs that are superior to those of classical passive trusses. We also indicate how activation may result
in singularities, the treatment of which is, so far, essentially an open problem. 相似文献
857.
Ingvar Kvande Stein Trygve Briskeby Mikhail Tsypkin Magnus Rønning Svein Sunde Reidar Tunold De Chen 《Topics in Catalysis》2007,45(1-4):81-85
A study of the suitability of different methods for preparing highly loaded, well dispersed carbon nanofiber (CNF) supported
Pt catalysts intended for application in fuel cells is reported. Preparation routes that are successfully applied on conventional
carbon supports are hampered by the lower surface area and number of surface groups on CNFs. Ion exchange, homogeneous deposition
precipitation and impregnation are all techniques that are limited to low metal loading on this CNF support. The most promising
methods are the colloidal methods. By the modified polyol method, a Pt-content of 24 wt% with a particle size of 2–4 nm was
achieved. CNFs could also be completely covered by 2–3 nm Pt oxide particles by using the metal–oxide colloid route, reaching
a Pt-content of 17 wt%. The merits that make these methods more suitable than the other methods and the mechanism for deposition
of Pt particles on CNFs are discussed. 相似文献
858.
K. Meerbeck F. Sauter K. Hawbitz L. Collatz L. Collatz H. Behrboym Fraedrich Keune H. D. Baehr K. Magnus W. de Beauclair W. Gröbner H. W. Hahnemann H. Bufler 《Forschung im Ingenieurwesen》1961,27(3):93-96
Ohne Zusammenfassung
VDI 相似文献
859.
Johanne Mouzon Alexandre Maitre Lars Frisk Niklas Lehto Magnus Odén 《Journal of the European Ceramic Society》2009,29(2):311-316
This method consists of a combination of vacuum sintering at 1600 °C followed by hot isostatic pressing (HIP) at 1500 °C of a highly agglomerated commercial powder. The use of evacuated glass capsules to perform HIP treatment allowed samples that showed open porosity after vacuum sintering to be sintered to transparency. The sintering response of the investigated powder was studied by careful microstructural observations using scanning electron microscopy and optical microscopy both in reflection and transmission. The successful key of this method was to keep porosity intergranular during pre-sintering, so that it can be removed subsequently by HIP treatment. It was found that agglomerates of closely packed particles are helpful to reach that purpose, since they densify fully and leave only intergranular porosity. However, performing HIP treatment at 1625 °C was found to result in opaque samples. This was attributed to the diffusion of argon inside the capsule. Contamination at different steps of processing was also investigated by inductively coupled plasma mass spectrometry (ICP-MS). 相似文献
860.