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排序方式: 共有286条查询结果,搜索用时 15 毫秒
1.
Henrik H. Jessen Huruma F. Mgana Peter Grønkjær Torben L. Lauridsen 《Journal of Great Lakes research》2019,45(6):1205-1214
The pelagic fishery of Lake Tanganyika, which is largely made up of the three species Lates stappersii, Limnothrissa miodon, and Stolothrissa tanganicae, has been in decline, and there is no clear understanding of the primary underlying causes. It has been suggested that climate change has altered the primary productivity of the system, but detailed knowledge of the system's food web is required to elucidate the effect on higher trophic levels. The aim of this study is to determine the diet of the three commercially important fish species. Muscle tissue samples for stable isotope analysis were taken from February through April 2017, supplemented with stomach samples from L. stappersii for use in stomach content analysis. The stomach analysis showed an ontogenetic change in the diet composition of L. stappersii, shifting from copepods to fish larvae, supplemented with shrimp, to whole fish prey as the fish grew larger. Stable carbon and nitrogen isotope values from fish muscle were consistent with this observation, and also seemed to indicate that fish of similar sizes had similar diets, irrespective of species. This suggests that the diet of the pelagic fish species might be better explained by size, rather than species. The isotope data revealed a short range of δ15N values from primary consumers to fish, which may help explain the high fisheries productivity of Lake Tanganyika, and the strong impact of primary productivity changes on fisheries yield. 相似文献
2.
Joost Duvigneau Edit Kutnyanszky In Yee Phang Hong-Jing Chung Hairong Wu Lionel Dos Ramos Torben Gädt Siti Fairus M. Yusoff Mark A. Hempenius Ian Manners G. Julius Vancso 《Polymer》2014
We report on the morphology evolution during heating and melting of lamellar poly(isoprene)-block-poly(ferrocenyldimethylsilane) (PI76-b-PFDMS76) raft crystals deposited at the native oxide surface of silicon (SiO2) or at a highly ordered pyrolytic graphite (HOPG) surface, studied by in situ temperature controlled atomic force microscopy. Crystals deposited on hydrophilic SiO2 surfaces revealed an irreversible decrease in length at temperatures of up to tens of degrees above their expected melting temperature, while maintaining their platelet-like structure. Crystals deposited on hydrophobic HOPG surfaces initially decreased in length below their expected melting temperature, while at 120 °C and above a typical molten morphology was observed. In addition, the irreversible formation of a PI76-b-PFDMS76 wetting layer around the crystals was observed upon increasing the temperature. These observations in the morphological behavior upon heating emphasize the role of interfacial energy between a surface deposited block copolymer based macromolecular nanostructure and its supporting substrate. 相似文献
3.
Mohammed Taleb-Berrouane Kelly Hawboldt Richard Eckert Torben Lund Skovhus 《腐蚀工程科学与技术》2018,53(5):378-392
Corrosion is one of the major causes of failure in onshore and offshore oil and gas operations. Microbiologically influenced corrosion (MIC) is inherently more complex to predict, detect and measure because, for instance, the presence of biofilm and/or bacterial products is not sufficient to indicate active microbiological corrosion. The major challenge for current MIC models is to correlate factors that influence corrosion (i.e. chemical, physical, biological and molecular variables) with the potential of having MIC. Previous work has proposed the potential for MIC as a simple product of multiple factors, without fully considering the synergy or the interference among the factors. The present work proposes a network-based approach to analyse and predict MIC potential considering the complex interactions among a total of 60 influencing factors and 20 screening parameters. The proposed model has the ability to capture the complex interdependences and the synergic interactions of the factors used to assess MIC potential and uses an object-oriented approach based on a Bayesian Network. The model has been tested and verified using real data from a pipeline leakage incident that was a result of MIC. The proposed model constitutes a significant step in deepening the understanding of when MIC occurs and its predictability.
List of acronyms: APB: acid producing bacteria; Aw: water activity; BN: Bayesian network; MIC: microbiologically influenced corrosion; MMMs: molecular microbiological methods; NRB: nitrate-reducing bacteria; OOBN: object-oriented Bayesian network; PWRI: produced water re-injection; SPs: screening parameters; SRB: sulphate-reducing bacteria; SRPs: sulphate-reducing prokaryotes; TDSs: total dissolved solids 相似文献
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6.
Kasper T. Møller Mathias Jørgensen Jacob G. Andreasen Jørgen Skibsted Zbigniew Łodziana Yaroslav Filinchuk Torben R. Jensen 《International Journal of Hydrogen Energy》2018,43(1):311-321
A new potassium tetraamidoboranealuminate, K[Al(NH2BH3)4], has been synthesized by a mechanochemical reaction between KAlH4 and NH3BH3. The compound, K[Al(NH2BH3)4], crystallizes in a triclinic unit cell with space group symmetry P?1. The crystal structure consists of [K(NH2BH3)6]5? octahedra which facilitate the bridging between K+ in 1D chains, while also bridging K+ to Al3+ to connect the 1D chains in a 3D network. Thermal analysis reveals that K[Al(NH2BH3)4] decomposes in two exothermic steps at T ~ 94 and 138 °C and releases primarily hydrogen. The total gas release amounts to ~6.0 wt% H2. The decomposition products are investigated ex situ by powder X-ray diffraction, infrared spectroscopy, and 11B and 27Al NMR and identified as KBH4 and amorphous phases, possibly BN3, N2BH, and/or NBH2 whereas aluminum is found in four-, five-, and six-fold coordination. Unfortunately, the decomposed sample shows no hydrogen absorption at T = 260 °C and p(H2) = 110 bar. 相似文献
7.
In order to analyze various process characteristics, grinding simulations can be used, which need accurate models of the tool and the individual grains. For this purpose, grinding tools can be digitized. To identify characteristic grains from a large number of measurements, each individual grain has to be analyzed and separated from the bond manually. Therefore, a deep learning-based methodology was developed to achieve a high segmentation accuracy of the grain boundaries efficiently. Additionally, a data augmentation approach was investigated to limit the data necessary for learning. The model transferability was quantified by analyzing different states of tool wear. 相似文献
8.
Thomas Bak Angus Graham Alla Sapronova Mihai Florian John Dalsgaard Sørensen Torben Knudsen Peng Hou Zhe Chen 《风能》2017,20(9):1665-1683
The paper presents a model of a reference wind farm. The model considers the wind and wave climatologies for a specific site from which two different wind farm layouts are derived. These layouts are examined through the effective wake‐enhanced turbulence intensity at the hub height for a given climatology, and a simple model for the influence on capital expenditures is proposed. An electrical design is presented, the cable losses are calculated and the energy yield is determined. An operation and maintenance model is established, and the associated operating expenditure is obtained. All of the models are then summarized in terms of a levelized cost of energy using a numerical simulation tool, which allows the layouts to be compared. The data and models are freely available online for others to use and may serve as a baseline for benchmarking and allow researchers to compare and discuss their results. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
9.
Inductively powered devices are finding increasing use in many applications, such as biomedical implants and radio frequency
identification (RFID) tags. In these systems, because of transmitter and receiver movements, the receiver coil may get close
to the transmitter coil, which results in more than needed power delivered to the receiver load. This increases heat dissipated
in the receiver circuit. In order to avoid overheating the receiver in such a high magnetic field (short coil separation distance)
condition, the received power should be monitored and controlled. This paper introduces a clocked power control circuit integrated
in the implant receiver, which is an independent, automatic power adjustment solution to limit heat dissipation with response
to the coil separation distance. In this circuit, the rectified voltage across the load is monitored, and converted to a digital
representation to selectively detune the receiver inductor-capacitor (LC) tank. To demonstrate this concept, a design example
applied to inductively powered implants is given. Measurements on the prototype with a varied coil separation distance validate
the desired power control functionality. Less power dissipation is achieved for the receiver compared to no power control
condition. 相似文献
10.
Thomas Erlebach Torben Hagerup Klaus Jansen Moritz Minzlaff Alexander Wolff 《Theory of Computing Systems》2010,47(3):613-636
For t>0 and g≥0, a vertex-weighted graph of total weight W is (t,g)-trimmable if it contains a vertex-induced subgraph of total weight at least (1−1/t)W and with no simple path of more than g edges. A family of graphs is trimmable if for every constant t>0, there is a constant g≥0 such that every vertex-weighted graph in the family is (t,g)-trimmable. We show that every family of graphs of bounded domino treewidth is trimmable. This implies that every family
of graphs of bounded degree is trimmable if the graphs in the family have bounded treewidth or are planar. We also show that
every family of directed graphs of bounded layer bandwidth (a less restrictive condition than bounded directed bandwidth)
is trimmable. As an application of these results, we derive polynomial-time approximation schemes for various forms of the
problem of labeling a subset of given weighted point features with nonoverlapping sliding axes-parallel rectangular labels
so as to maximize the total weight of the labeled features, provided that the ratios of label heights or the ratios of label
lengths are bounded by a constant. This settles one of the last major open questions in the theory of map labeling. 相似文献