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11.
Fire and explosion accidents are frequently caused by combustible dust, which has led to increased interest in this area of research. Although scholars have performed some research in this field, they often ignored interesting phenomena in their experiments. In this paper, we established a 2D numerical method to thoroughly investigate the particle motion and distribution before ignition. The optimal time for the corn starch dust cloud to ignite was determined in a semi-closed tube, and the characteristics of the flame propagation and temperature field were investigated after ignition inside and outside the tube. From the simulation, certain unexpected phenomena that occurred in the experiment were explained, and some suggestions were proposed for future experiments. The results from the simulation showed that 60–70 ms was the best time for the dust cloud to ignite. The local high-temperature flame clusters were caused by the agglomeration of high-temperature particles, and there were no flames near the wall of the tube due to particles gathering and attaching to the wall. Vortices formed around the nozzle, where the particle concentration was low and the flame spread slowly. During the explosion venting, particles flew out of the tube before the flame. The venting flame exhibited a “mushroom cloud” shape due to interactions with the vortex, and the flame maintained this shape as it was driven upward by the vortex. 相似文献
12.
13.
运用有限元软件ABAQUS计算L形带肋钢管混凝土柱阴角相邻两面受火全过程下的耐火极限,分析了阴角邻面受火方式下构件内部温度场和应力场的变化规律,在此基础上分析荷载比、宽厚比、计算长度、加劲肋纵向间距、荷载偏心率、荷载角等参数对耐火极限的影响规律。数据表明:荷载比、计算长度对构件耐火极限影响较大,随着荷载比和计算长度的增大,耐火极限基本呈线性下降;加劲肋间距对构件耐火性能影响较小;由于L形柱的特殊形式,偏心荷载对耐火极限的影响规律较复杂,荷载作用点偏向低温区可以提高耐火极限。 相似文献
14.
C. Duchet Th. Caquet C. Lagneau 《Environmental pollution (Barking, Essex : 1987)》2010,158(5):1825-1833
The present study was undertaken to assess the impact of a candidate mosquito larvicide, spinosad (8, 17 and 33 μg L−1) on a field population of Daphnia magna under natural variations of water temperature and salinity, using Bti (0.16 and 0.50 μL L−1) as the reference larvicide. Microcosms (125 L) were placed in a shallow temporary marsh where D. magna was naturally present. The peak of salinity observed during the 21-day observation period may have been partly responsible for the decrease of daphnid population density in all the microcosms. It is also probably responsible for the absence of recovery in the microcosms treated with spinosad which caused a sharp decrease of D. magna abundance within the first two days following treatment whereas Bti had no effect. These results suggest that it may be difficult for a field population of daphnids to cope simultaneously with natural (water salinity and temperature) and anthropogenic (larvicides) stressors. 相似文献
15.
Temperature-dependent sorption of polycyclic aromatic hydrocarbons on natural and treated sediments 总被引:1,自引:0,他引:1
In aqueous environment temperature is considered to play a significant role in the sorption process of polycyclic aromatic hydrocarbons (PAHs) and its influence on the sorption equilibrium is indicative of sorption energies and mechanisms. In this study, sorptions of five PAHs on three heterogeneous sorbents including one river sediment (YHR), one estuary sediment (YRD) and one treated sediment with organic matter removed (IM) were carried out at a range of temperature from 5 °C to 35 °C. Stronger sorptions were observed at lower temperatures, with the equilibrium sorption coefficient Kd increasing 2-5 times as the temperature decreases 30 °C. The increase of Kd value was attributed primarily to the change of PAH water solubility, which predicted 40-75% of the increase of Kd in the sorption process. To provide insight into the sorption mechanism, enthalpy change (ΔHS) for the sorption process was calculated and the values were observed to be negative for all of the interactions, suggesting that the exothermal sorption of PAHs inversely dependents on temperature. Based on the values of ΔHS, van der Waals forces were inferred as the main sorption mechanism for the PAHs, especially on the YHR sediment which contained more organic matter. For sorption of larger size PAHs on the sorbents with low organic matter, specific interactions were deduced to contribute to the overall sorption. 相似文献
16.
Bioremediation of sandy soil contaminated with fish-biodiesel, conventional diesel, and blends of both was studied in microcosm experiments at different temperatures, simulating the subarctic environment. While distinct lag, exponential, and stationary phases were observed at 20 °C, degradation at 6 °C was slow and the lag phase continued throughout the 4-week experiment. A three-phase 1st order kinetic model successfully described respiration at 20 °C, a one-phase model was sufficient at 6 °C. For temperatures fluctuating between ∼6 and ∼20 °C, higher than expected microbial activity persisted at 6 °C for several days, due to the presence of active cultures, even though the soil temperature closely followed the air temperature. At 20 °C, respiration peaked already after 1 week, and 18-51% of the initially added fuel was mineralized within 4 weeks, whereby degradation was higher at higher biodiesel percentages. Biodiesel addition accelerated mineralization of blends with regular diesel beyond expectations. In blends with 20% biodiesel, the degradation rate constant was twice as high as for conventional diesel. These synergistic effects are likely due to an active microbial population. Addition of biodiesel to conventional diesel could reduce the impact of diesel spills. 相似文献
17.
Long-range atmospheric transport of three toxaphene congeners across Europe. Modeling by chained single-box FATEMOD program 总被引:1,自引:1,他引:0
Jaakko Paasivirta Seija Sinkkonen Vladimir Nikiforov Fedor Kryuchkov Erkki Kolehmainen Katri Laihia Arto Valkonen Manu Lahtinen 《Environmental science and pollution research international》2009,16(2):191-205
Background, aims, and scope Since toxaphene (polychlorocamphene, polychloropinene, or strobane) mixtures were applied for massive insecticide use in the
1960s to replace the use of DDT, some of their congeners have been found at high latitudes far away from the usage areas.
Especially polychlorinated bornanes have demonstrated dominating congeners transported by air up to the Arctic areas. Environmental
fate modeling has been applied to monitor this phenomenon using parallel zones of atmosphere around the globe as interconnected
environments. These zones, shown in many meteorological maps, however, may not be the best way to configure atmospheric transport
in air trajectories. The latter could also be covered by connecting a chain of simple model boxes. We aim to study this alternative
approach by modeling the trajectory chain using catchment boxes of our FATEMOD model. Polychlorobornanes analyzed in biota
of the Barents Sea offered one case to study this modeling alternative, while toxaphene has been and partly still is used
massively at southern East Europe and around rivers flowing to the Aral Sea.
Materials and methods Pure model substances of three polychlorobornanes (toxaphene congeners P26, P50, and P62) were synthesized, their environmentally
important thermal properties measured by differential scanning calorimetry, as evaluated from literature data, and their temperature
dependences estimated by the QSPR programs VPLEST, WATSOLU, and TDLKOW. The evaluated property parameters were used to model
their atmospheric long-range transport from toxaphene heavy usage areas in Ukraine and Aral/SyrDarja/AmuDarja region areas,
through East Europe and Northern Norway (Finnmarken) to the Barents Sea. The time period used for the emission model was June
1997. Usual weather conditions in June were applied in the model, which was constructed by chaining FATEMOD model boxes of
the catchment’s areas along assumed maximal air flow trajectories. Analysis of the three chlorobornanes in toxaphene mixtures
function as a basis for the estimates of emission levels caused by its usage. High estimate (A) was taken from contents in
a Western product chlorocamphene and low estimate (B) from mean contents in Russian polychloroterpene products to achieve
modeled water concentrations. Bioaccumulation to analyzed lipid of aquatic biota at the target region was estimated by using
statistical calculation for persistent organic pollutants in literature.
Results The results from model runs A and B (high and low emission estimate) for levels in sea biota were compared to analysis results
of samples taken in August 1997 at Barents Sea. The model results (ng g−1 lw): 4–95 in lipid of planktovores and 7–150 in lipid of piscivores, were in fair agreement with the analysis results from
August 1997: 21–31 in Themisto libellula (chatka), 26–42 in Boreocadus saida (Polar cod), and 5–27 in Gadus morhua (cod) liver.
Discussion The modeling results indicate that the application of chained simple multimedia catchment boxes on predicted trajectory is
a useful method for estimation of volatile airborne persistent chemical exposures to biota in remote areas. For hazard assessment
of these pollutants, their properties, especially temperature dependences, must be estimated by a reasonable accuracy. That
can be achieved by using measurements in laboratory with pure model compounds and estimation of properties by thermodynamic
QSPR methods. The property parameters can be validated by comparing their values at an environmental temperature range with
measured or QSPR-estimated values derived by independent methods. The chained box method used for long-range air transport
modeling can be more suitable than global parallel zones modeling used earlier, provided that the main airflow trajectories
and properties of transported pollutants are predictable enough.
Conclusions Long-range air transport modeling of persistent, especially photo-resistant organic compounds using a chain of joint simple
boxes of catchment’s environments is a feasible method to predict concentrations of pollutants at the target area. This is
justified from model results compared with analytical measurements in Barents Sea biota in August 1997: three of six modeled
values were high and the other three low compared to the analysis results. The order of magnitude level was similar in both
modeled (planktovore and piscivore) and observed (chatka and polar cod) values of lipid samples. The obtained results were
too limited to firm validation but are sufficient to justify feasibility of the method, which prompts one to perform more
studies on this modeling system.
Recommendations and perspectives For assessment of the risk of environmental damages, chemical fate determination is an essential tool for chemical control,
e.g., for EU following the REACH rules. The present conclusion of applicability of the chained single-box multimedia modeling
can be validated by further studies using analyses of emissions and target biota in various other cases. To achieve useful
results, fate models built with databases having automatic steps for most calculations and outputs accessible to all chemical
control professionals are essential. Our FATEMOD program catchments at environments and compound properties listed in the
database represent a feasible tool for local, regional, and, according our present test results, for global exposure predictions.
As an extended use of model, emission estimates can be achieved by reversed modeling from analysis results of samples corresponding
to the target area.
This article is dedicated to the memory of Professor Alexander B Terentiev (who passed away in November 2006), our true friend.
With his Institute of Organo-Element Compounds, Russian Academy of Science, Moscow, he was an important main organizer of
the six joint Finnish–Russian seminars (every third year since 1989) on the field (‘Chemistry and Ecology of Organo-Element
Compounds’). He prompted us especially to search properties and environmental fates for various polyhalogen compounds. We
remember him for his friendly character and great sense of humor. 相似文献
18.
Mackenzie BR Meier HE Lindegren M Neuenfeldt S Eero M Blenckner T Tomczak MT Niiranen S 《Ambio》2012,41(6):626-636
Understanding how climate change, exploitation and eutrophication will affect populations and ecosystems of the Baltic Sea can be facilitated with models which realistically combine these forcings into common frameworks. Here, we evaluate sensitivity of fish recruitment and population dynamics to past and future environmental forcings provided by three ocean-biogeochemical models of the Baltic Sea. Modeled temperature explained nearly as much variability in reproductive success of sprat (Sprattus sprattus; Clupeidae) as measured temperatures during 1973-2005, and both the spawner biomass and the temperature have influenced recruitment for at least 50 years. The three Baltic Sea models estimate relatively similar developments (increases) in biomass and fishery yield during twenty-first century climate change (ca. 28 % range among models). However, this uncertainty is exceeded by the one associated with the fish population model, and by the source of global climate data used by regional models. Knowledge of processes and biases could reduce these uncertainties. 相似文献
19.
Previous studies have demonstrated that the commercial feed of aquacultured fish contains trace amounts of toxic and essential metals which can accumulate in tissues and finally be ingested by consumers. Recently rising temperatures, associated to the global warming phenomenon, have been reported as a factor to be taken into consideration in ecotoxicology, since temperature-dependent alterations in bioavailability, toxicokinetics and biotransformation rates can be expected. Sparus aurata were kept at 22 °C, 27 °C and 30 °C for 3 months in order to determine the temperature effect on metallothionein induction and metal bioaccumulation from a non-experimentally contaminated commercial feed. A significant temperature-dependent accumulation of cadmium (Cd), copper (Cu), mercury (Hg), zinc (Zn), lead (Pb) and iron (Fe) was found in liver, together with that of manganese (Mn), Fe and Zn in muscle. Hg presented the highest bioaccumulation factor, and essential metal homeostasis was disturbed in both tissues at warm temperatures. An enhancement of hepatic metallothionein induction was found in fish exposed to the highest temperature. 相似文献
20.
C. S. Withers D. P. Krouse C. P. Pearson S. Nadarajah 《Environmental Modeling and Assessment》2009,14(2):231-249
If global warming is accelerating, then one might expect temperatures for most stations to be accelerating and perhaps variability
to be increasing. In this study, we examine 57 New Zealand temperature time series for evidence of non-linearity and changing
variability. These correspond to time series for annual minima, annual means and annual maxima for 19 stations. Estimation
is by an extended least-squares method. We find a surprising diversity of behaviour of these series – presumably reflecting
their different geographic factors as well as series length. We give evidence of regions where temperatures are decreasing. For series where a linear trend is significant, it is downwards in about one third of the cases. This proportion was higher in the South Island, especially for series of minima. Where a
non-linear trend is significant, temperatures are decelerating in about one half of the cases. The ratio of downward to upward trends is highest among annual maxima and South Island minima
and smallest in annual means. Where a linear trend in the variability is significant, it is decreasing in 13 cases and increasing in 5 cases, although possibly this is partly due to poorer quality
data last century. Where a non-linear trend in the variability is significant, variability is decelerating in about two thirds of the cases. The results are used to project upper and lower return levels of minima, means and maxima
for each of the series to the year 2010. 相似文献