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排序方式: 共有238条查询结果,搜索用时 15 毫秒
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R.?L.?M.?SchilsEmail author A.?Verhagen H.?F.?M.?Aarts L.?B.?J.??ebek 《Nutrient Cycling in Agroecosystems》2005,71(2):163-175
Ruminant livestock systems are a significant source of greenhouse gases (GHGs). Thus far, mitigation options for GHG emissions mainly focused on a single gas, and are treated as isolated activities. The present paper proposes a framework for a farm level approach for the full accounting of GHG emissions. The methodology accounts for the relevant direct and indirect emissions of methane, nitrous oxide and carbon dioxide, including carbon sequestration. Furthermore, the potential trade-off with ammonia volatilisation and nitrate leaching are taken into account. A ruminant livestock farm is represented with a conceptual model consisting of five pools: animal, manure, soil, crop and feed. The carbon and nitrogen inputs, throughputs and outputs are described, and the direct emissions are related to the carbon and nitrogen flows. The indirect emissions included in the methodology are mainly carbon dioxide emissions from energy use and nitrous oxide emissions related to imported resources and nitrogen losses. The whole farm approach is illustrated with a case of two dairy farms with contrasting livestock density and grassland management. It is shown that the inclusion of carbon sequestration and all indirect emissions have a major impact on the GHG budget of the farm. For one farm, the effect of four mitigation options on the GHG emissions was quantified. It was concluded that a whole farm approach of full accounting contributes to a better insight in the interactions between the carbon and nitrogen flows and the resulting emissions, within and outside the farm boundaries. Consequently, the methodology can be used to develop efficient and effective mitigation strategies. 相似文献
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Y.?Gao A.?van?Reenen M.?A.?Hulsen A.?M.?de?Jong M.?W.?J.?Prins J.?M.?J.?den?ToonderEmail author 《Microfluidics and nanofluidics》2014,16(1-2):265-274
We report experimental results on chaotic mass transport induced by alternating topological changes of magnetic particle chains actuated by a rotating magnetic field. Results on the induced fluid flows, through particle tracing experiments and mixing experiments, are obtained for (1) the regime of rigid chain rotation and (2) the regime wherein chains periodically fragment and reform. In the case of rigid rotating chains, the overall tracer particle trajectories are steady, slightly modulated circles around the center of the microparticle chains. In the regime of periodic chain breaking and reformation, the tracer particle trajectories become chaotic. The level of mixing is measured by using a mixing index (M) in a water–dye system, i.e., in a perfectly mixed system M = 0, while in an unmixed system M = 1. When particle chains periodically break and reform, we observe that the mixing index M decreases from 1 to 0.1 within 15 rotational cycles. For rigid rotating chains, M reaches a minimum of only 0.5. We also report the effect of the different actuation regimes on a biological binding reaction in the solution and indeed found that the reaction product (at equal actuation time) is significantly enhanced (3 times) by the dynamic chain regime as compared to the rigid chain regime. We conclude that the alternating topological change of microparticle chains—with repetitive chain breakup and chain reformation—is an effective mechanism to achieve chaotic mixing and thereby promote and homogenize reactions in lab-on-a-chip systems. 相似文献
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Jan Willem?van?GroenigenEmail author Pieter Jan?Georgius Chris?van?Kessel Eduard W.J.?Hummelink Gerard L.?Velthof Kor B.?Zwart 《Nutrient Cycling in Agroecosystems》2005,72(1):13-25
Studies on emissions of nitrous oxide (N2O) from agricultural soils mostly focus on fluxes between the soil and the atmosphere or are limited to the atmosphere in
the topsoil. However, in soils with shallow water tables, significant N2O formation may occur closer to the groundwater. The aims of this study were (i) to determine the importance of subsoil N2O formation in a sandy soil; and (ii) to obtain a quantitative insight in the contribution of subsoil N2O to the overall losses of N2O to the environment. We applied 15N labeled fertilizer at a rate of 5.22 kg 15N ha−1; 50% as Ca(NO3)2 and 50% as NH4Cl, on a mesic typic Haplaquod seeded with potatoes (Solanum tuberosum L.), and traced soil N2O concentrations and fluxes over a one-year period. Throughout the year, total N2O and the amount of 15N recovered in soil N2O were highest in the subsoil, with a maximum concentration at 48 cm depth in mid-February of 19900 μl m−3 and 24 μg 15N m−3, respectively. The maximum concentration coincided with the highest water-filled pore space of 71%. The cumulative flux of
N2O was 446 g N2O-N ha−1, the recovery of 15N in this flux was 0.06%. During the summer, maximum fluxes followed high soil N2O concentrations. During winter, no such relation was found. We concluded that the formation of N2O was the highest in the subsoil, largely controlled by water-filled pore space rather than NO3− concentration or temperature. Although high subsoil N2O concentrations did not lead to high surface fluxes of N2O in the winter, artificial draining may lead to high indirect N2O emissions through supersaturated drainage water. 相似文献
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Robbert?Jongeling Proshanta?Sarkar Subhajit?Datta Alexander?SerebrenikEmail authorView authors OrcID profile 《Empirical Software Engineering》2017,22(5):2543-2584
Recent years have seen an increasing attention to social aspects of software engineering, including studies of emotions and sentiments experienced and expressed by the software developers. Most of these studies reuse existing sentiment analysis tools such as SentiStrength and NLTK. However, these tools have been trained on product reviews and movie reviews and, therefore, their results might not be applicable in the software engineering domain. In this paper we study whether the sentiment analysis tools agree with the sentiment recognized by human evaluators (as reported in an earlier study) as well as with each other. Furthermore, we evaluate the impact of the choice of a sentiment analysis tool on software engineering studies by conducting a simple study of differences in issue resolution times for positive, negative and neutral texts. We repeat the study for seven datasets (issue trackers and Stack Overflow questions) and different sentiment analysis tools and observe that the disagreement between the tools can lead to diverging conclusions. Finally, we perform two replications of previously published studies and observe that the results of those studies cannot be confirmed when a different sentiment analysis tool is used. 相似文献
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Bram?KlievinkEmail authorView authors OrcID profile Bart-Jan?Romijn Scott?Cunningham Hans?de?Bruijn 《Information Systems Frontiers》2017,19(2):267-283
Big data is being implemented with success in the private sector and science. Yet the public sector seems to be falling behind, despite the potential value of big data for government. Government organizations do recognize the opportunities of big data but seem uncertain about whether they are ready for the introduction of big data, and if they are adequately equipped to use big data. This paper addresses those uncertainties. It presents an assessment framework for evaluating public organizations’ big data readiness. Doing so demystifies the concept of big data, as it is expressed in terms of specific and measureable organizational characteristics. The framework was tested by applying it to organizations in the Dutch public sector. The results suggest that organizations may be technically capable of using big data, but they will not significantly gain from these activities if the applications do not fit their organizations and main statutory tasks. The framework proved helpful in pointing out areas where public sector organizations could improve, providing guidance on how government can become more big data ready in the future. 相似文献
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C. Yürdü S. Işçi C. Ünlü O. Atici Ö. I. Ece N. Güngör 《Bulletin of Materials Science》2005,28(6):623-628
In this study, the rheologic and colloidal characterizations of sodium montmorillonite (NaMMT) were examined. Hexadecylamine
(CH3(CH2)15NH2, HDA) was added to the bentonite water dispersion (2%, w/w) in different concentrations in the range 5.6 × 10−4−9.4 × 10−3 mmol/l. The rheological and electrokinetic behaviour of aqueous montmorillonite dispersions was investigated as a function
of solid content and HDA concentration. The basal spacings of the HDA/NaMMT composites were studied by X-ray diffraction.
The FTIR spectra were obtained from the modified bentonite products, which revealed the characteristic absorbances after treatment
with HDA. 相似文献
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