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171.
Alexander Klippel Marc Scheid January Koperski Mike Wappler Ulrich Krause 《Journal of Loss Prevention in the Process Industries》2013,26(6):1433-1441
A new safety characteristic the “dustiness” according to VDI 2263 – part 9 (Verein Deutscher Ingenieure, 2008) is investigated. Dustiness means the tendency of a dust to form clouds. The paper deals with the physical reasons for the different behavior of dusts, even if they have similar properties such as particle size and density and the influence of the dustiness on dust explosions. In order to study the effects of the dustiness on dust cloud formation for different dispersion methods experiments in a vertical dust dispersion glass tube apparatus were carried out. Furthermore vented dust explosion experiments were done for two different dispersion methods and two static activation pressures.Experiments show that particle size and density are not the only factors which influence dispersibility. Particle shape, specific surface area, flow and dispersion method have an influence which can outweigh size and density. Preliminary explosion experiments showed that the dustiness has an influence on the reduced explosion pressure and flame speed in a vented 75 L test apparatus. In order to verify the results for applications in the process industries further tests with industrial scale experiments are planned. 相似文献
172.
Journal of Polymers and the Environment - Algae-based materials appear to be promising substitutes for plastics in many applications due to their eco-friendly belongings. However, high solubility,... 相似文献
173.
This study evaluates chemical trends of seven acidified reservoirs and 22 tributaries in the Erzgebirge from 1993 to 2003. About 85% of these waters showed significantly (p < 0.05) declining concentrations of protons (-69%), nitrate (-41%), sulfate (-27%), and reactive aluminum (-50% on average). This reversal is attributed to the intense reduction of industrial SO2 and NOx emissions from formerly high levels, which declined by 99% and 82% in the German-Czech border region between 1993 and 1999. The deposition rates of protons and sulfur decreased by 70-90%. Since 1993, the dry deposition of total inorganic nitrogen diminished to a minor degree, but the wet deposition remained unchanged. The surface waters reflect a substantial decrease in Al exchange processes, a release of sulfur previously stored in soils, and an uptake of nitrate by forest vegetation. The latter effect may be supported by soil protection liming which contributed to the chemical reversal in almost 20% of the study waters. 相似文献
174.
Reliability data acquisition and evaluation in process plants 总被引:1,自引:0,他引:1
Ulrich Hauptmanns 《Journal of Loss Prevention in the Process Industries》2011,24(3):266-273
Based on the practical experience of assessing reliability data in two plants of the explosives industry, the organization and scope of the data collection, the component delimitation, the procedures of quality assurance and the data evaluation for their final use in PSA studies are presented. An example is given for the type of detection and repair, etc. The mathematical background for evaluating observed component lifetimes is discussed. Both frequentist and Bayesian methods are addressed. The resulting failure rate distributions and their approximations by log-normal distributions for several key components are presented. They were obtained using a Bayesian approach with a non-informative prior. Remarks on uncertainty, their treatment and a proposal for transferring data to plants other than the ones investigated conclude the presentation. 相似文献
175.
Climate-related scientific analyses of meteorological–marine systems are often based on numerical long-term simulations at
high spatial and temporal detail. Such comprehensive data sets require much resources and specific evaluation tools, which
sometimes hampers their use within interdisciplinary projects. In the present study, we propose the use of a Bayesian network
to represent simulated transports in the North Sea depending on variable external forcing in terms of conditional probabilities.
Eliciting probability tables from multi-decadal numerical simulations ensures that all realistic weather and resulting sea
state conditions are covered in agreement with the frequency of their occurrence. The probabilistic representation conveniently
allows for conditioning numerical simulations on either external forcing (weather conditions) or observed transports. In the
latter case, the Bayesian inversion formula becomes involved to transfer information in a direction opposite to causal dependencies
encoded in the underlying mechanistic model. We show that simulated travel time distributions even allow for taking into account
a substance’s specific half-life, although this was not an issue in the original passive tracer simulations. 相似文献
176.
Gabriele C. Hegerl Ulrich Cubasch 《Environmental science and pollution research international》1996,3(2):99-102
Simulations using global coupled climate models predict a climate change due to the increasing concentration of greenhouse gases and aerosols in the atmosphere. Both are associated with the burning of fossil fuels. There has been considerable debate if this postulated human influence is already evident. This paper gives an overview on some recent material on this question. One particular study using optimal fingerprints (Hegerl et al., 1996) is explained in more detail. In this study, an optimal fingerprint analysis is applied to temperature trend patterns over several decades. The results show the probability being less than 5% that the most recently observed 30 year trend is due to naturally occurring climate fluctuations. This result suggests that the present warming is caused by some external influence on climate, e.g. by the increasing concentrations of greenhouse gases and aerosols. More work is needed to address the uncertainties in the magnitude of naturally occurring climate fluctuations. Also, other external influences on climate need to be investigated to uniquely attribute the present climate change to the human influence. 相似文献
177.
N. Aberle Thomas Hansen Ruth Boettger-Schnack Antje Burmeister Anton F. Post Ulrich Sommer 《Marine Biology》2010,157(1):157-169
Mesozooplankton communities in the meso-oligotrophic Gulf of Aqaba, Northern Red Sea, were investigated over a 2 years period
(2005–2007) with emphasis on the trophodynamic relations among different taxonomic groups ranging from primary consumers to
carnivorous predators. Based on stable isotope analyses, we present evidence for a strong contribution of ‘new’ nitrogen mainly
derived from the utilization of aerosol nitrate by unicellular cyanobacteria especially during summer stratification and the
propagation of exceptionally low δ15N onto higher trophic levels. In contrast, N2-fixation by diazotrophs seemed to play a minor role, while the utilization of deep water nitrate by cyanobacteria and eukaryotic
algae might be of importance during winter mixing. Based on 15N enrichment of consumers, clear differences between exclusively herbivorous organisms (doliolids, appendicularians, pteropods)
and those with omnivorous feeding modes were detected. The category of omnivores comprised a large variety of taxons ranging
from small meroplanktonic larvae to non-calanoid copepods (harpacticoids, cyclopoids and poecilostomatoids) that together
form a diverse and complex community with overlapping feeding modes. In addition, distinct seasonality patterns in δ15N of copepods were found showing elevated trophic positions during periods of winter mixing, which were most pronounced for
non-calanoid copepods. In general, feeding modes of omnivores appeared rather unselective, and relative contributions of heterotrophic
protists and degraded material to the diets of non-calanoid copepods are discussed. At elevated trophic positions, four groups
of carnivore predators were identified, while calanoid copepods and meroplanktonic predators showing lowest 15N enrichment within the carnivores. The direct link between ‘new’ nitrogen utilization by primary producers and the 15N enrichment of consumers in the planktonic food web of the Gulf of Aqaba emphasizes the significant contribution of ‘new’
nitrogen to the nitrogen budget and ecosystem functions in subtropical and tropical oligotrophic oceans. 相似文献
178.
Mucus released by scleractinian corals can act as an important energy and nutrient carrier in coral reef ecosystems, and a
distinct isotopic signature would allow following the fate of this material. This study investigates the natural C and N stable
isotopic signatures of mucus released by four scleractinian coral genera (Acropora, Fungia, Pocillopora and Stylophora) in comparison with those of suspended particulate organic matter (POM) in seawater of a Northern Red Sea fringing coral
reef near Aqaba, Jordan. The natural δ13C and δ15N signatures of coral mucus differed significantly from seawater POM for the majority of seasonal comparisons, but were inappropriate
for explicit tracing of mucus in the coral reef food web. Thus, a labeling technique using stable isotope tracers (13C and 15N) was developed that produced δ13C values of up to 122 ± 5‰ (mean ± SE) and δ15N of up to 2,100 ± 151‰ in mucus exuded by Fungia corals. 13C and 15N-enriched compounds were rapidly (within 3 h) and light-dependently transferred from the endosymbiotic zooxanthellae to the
mucus-producing coral host. The traceability of 15N-labeled mucus was examined by evaluating its uptake and potential utilization by epizoic acoelomorph Waminoa worms naturally occurring on a range of scleractinian coral taxa. This tracer experiment resulted in uptake of coral mucus
by the coral-associated acoelomorphs and further demonstrated the possibility to trace stable isotope-labeled coral mucus
by revealing a new trophic pathway in coral reef ecosystems. 相似文献
179.
Driving factors of phytoplankton spring blooms have been discussed since long, but rarely analyzed quantitatively. Here, we use a mechanistic size-based ecosystem model to reconstruct observations made during the Kiel mesocosm experiments (2005–2006). The model accurately hindcasts highly variable bloom developments including community shifts in cell size. Under low light, phytoplankton dynamics was mostly controlled by selective mesozooplankton grazing. Selective grazing also explains initial dominance of large diatoms under high light conditions. All blooms were mainly terminated by aggregation and sedimentation. Allometries in nutrient uptake capabilities led to a delayed, post-bloom dominance of small species. In general, biomass and trait dynamics revealed many mutual dependencies, while growth factors decoupled from the respective selective forces. A size shift induced by one factor often changed the growth dependency on other factors. Within climate change scenarios, these indirect effects produced large sensitivities of ecosystem fluxes to the size distribution of winter phytoplankton. These sensitivities exceeded those found for changes in vertical mixing, whereas temperature changes only had minimal impacts. 相似文献
180.
Monika Winder Stella A. Berger Aleksandra Lewandowska Nicole Aberle Kathrin Lengfellner Ulrich Sommer Sebastian Diehl 《Marine Biology》2012,159(11):2491-2501
Shifts in the timing and magnitude of the spring plankton bloom in response to climate change have been observed across a wide range of aquatic systems. We used meta-analysis to investigate phenological responses of marine and freshwater plankton communities in mesocosms subjected to experimental manipulations of temperature and light intensity. Systems differed with respect to the dominant mesozooplankton (copepods in seawater and daphnids in freshwater). Higher water temperatures advanced the bloom timing of most functional plankton groups in both marine and freshwater systems. In contrast to timing, responses of bloom magnitudes were more variable among taxa and systems and were influenced by light intensity and trophic interactions. Increased light levels increased the magnitude of the spring peaks of most phytoplankton taxa and of total phytoplankton biomass. Intensified size-selective grazing of copepods in warming scenarios affected phytoplankton size structure and lowered intermediate (20–200?μm)-sized phytoplankton in marine systems. In contrast, plankton peak magnitudes in freshwater systems were unaffected by temperature, but decreased at lower light intensities, suggesting that filter feeding daphnids are sensitive to changes in algal carrying capacity as mediated by light supply. Our analysis confirms the general shift toward earlier blooms at increased temperature in both marine and freshwater systems and supports predictions that effects of climate change on plankton production will vary among sites, depending on resource limitation and species composition. 相似文献