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931.
932.
Deterministic, size-structured models are widely used to describe consumer-resource interactions. Such models typically ignore potentially large random variability in juvenile development rates. We present simple representations of this variability and show five approaches to calculating the model parameters for Daphnia pulex interacting with its algal food. Using our parameterized models of growth variability, we investigate the robustness of a recently proposed stabilizing mechanism for Daphnia populations. Growth rate variability increases the range of enrichments over which small-amplitude cycles or quasi-cycles occur, thus increasing the plausibility that the underlying mechanism contributes to the prevalence of small-amplitude cycles in the field and in experiments. More generally, our approach allows us to relate commonly available information on variance of development times to population stability. 相似文献
933.
Haibo Niu Zhengkai Li Kenneth Lee Paul Kepkay Joseph V. Mullin 《Environmental Modeling and Assessment》2011,16(1):61-75
Spilled oil can interact with suspended particles in marine environments and form oil–mineral aggregates (OMAs). Some OMAs
with densities higher than seawater density can settle to the seedbed to pose potential risks to benthic organisms. To understand
the transport and fate of oil associated with OMAs and evaluate their potential risks, an integrated hydrodynamic and fate/transport
model has been used in a hypothetical case study of 1,000 tonnes of South Louisiana oil spilled in the Bristol Channel. Several
scenarios have been simulated under different wave and current conditions. By using OMA properties derived from laboratory
measurements reported in literature, it has been found that the risk to the benthos is unlikely for the two hypothetical cases
with strong currents, but it is likely for the wave only (weak current) case. The effects of other factors such as OMA properties
and sediment concentration were also examined in terms of their effects on the transport process and risks. 相似文献
934.
Zeccola P 《Disasters》2011,35(2):308-328
This paper examines the interface between human rights and humanitarian action in the context of the conflict and tsunami in Aceh, Indonesia, between 1998 and 2007. It looks at the challenges international humanitarian non-governmental organisations (NGOs) faced as they engaged in human rights work in the conflict period and in conflict-related activities in the post-tsunami period. The paper argues that many large NGOs may have compromised what some would hold to be essential principles for humanitarian action because of domestic political concerns, donor restrictions and resistance among certain NGO chiefs. In contrast with the pre-tsunami period, in which NGOs worked for years amid military operations, in the post-tsunami period NGOs were decidedly apolitical, neglecting the conflict in their tsunami response--despite significant developments that permitted greater political engagement in Aceh's post-conflict transformation. The evidence suggests that NGOs are challenged in contextualising humanitarian responses and that there is a need to underscore donor flexibility and independence in humanitarian action. 相似文献
935.
Daniel RodríguezJosé Ricardo Cure José Miguel CotesAndrew Paul Gutierrez Fernando Cantor 《Ecological modelling》2011,222(19):3626-3639
This paper is the first of three on the coffee production system consisting of (1) the coffee plant, (2) coffee berry borer (CBB) and (3) the role of CBB parasitoids. A previous simulation model of the coffee plant was developed using data from Brazil where coffee phenology is characterized by distinct seasonal flowering (Gutierrez et al., 1998). In contrast, flowering in Colombia is continuous with low seasonality. To capture the differences in coffee phenology and growth in the two climatic regions, the Gutierrez et al. (1998) model was modified using new data from Colombia.The modifications to the model include:
- (1)
- The effect of solar radiation on floral buds initiation;
- (2)
- An age structure population model to track the daily input and development of the floral buds;
- (3)
- The effect of leaf water potential on breaking dormancy in flower buds, and hence on the timing and intensity of flowering;
- (4)
- The incorporation of both the vegetative and the reproductive demands to predict the photosynthetic rate.
- (5)
- The effect of low temperature on photosynthesis and defoliation.
936.
Detlef Markus Aljoscha Hallermann Michael Paul Tim Langer Frank Lienesch 《Journal of Loss Prevention in the Process Industries》2013,26(2):324-328
Repetitive streamer discharges caused by transients, e.g. due to high frequency overvoltages, can ignite combustible mixtures, which has to be taken into account concerning the safety assessment of electrical apparatus for usage in hazardous areas. Hydrogen/air mixtures were ignited inside a closed vessel using a rod/plane electrode configuration. Alternating voltage with a frequency between 600 and 750 kHz and amplitudes of up to 20 kV was used to produce streamer discharges. The ignition process and the subsequent flame front propagation were examined with respect to mixture composition and several electrical parameters using time-resolved measurements of planar laser-induced fluorescence (PLIF) of OH radicals. A multiple pulse laser and detection system was used to assemble four images during one experiment. These measurements have given detailed information about the point of ignition and flame velocities. The experimental results will be used to validate numerical simulations of ignition by streamer discharges, which will yield deep insights into this specific ignition process. 相似文献
937.
This Incubator contends that the concept of validity generalization has been overgeneralized in its capacity to predict work performance for three reasons: sampling bias in the occupations selected for analysis, the prediction of acceptable performance to the exclusion of superior performance, and the conflation of statistical prediction and psychological meaning. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
938.
Simon P. Boilard Paul R. Amyotte Faisal I. Khan Ashok G. Dastidar Rolf K. Eckhoff 《Journal of Loss Prevention in the Process Industries》2013,26(6):1646-1654
Explosibility of micron- and nano-titanium was determined and compared according to explosion severity and likelihood using standard dust explosion equipment. ASTM methods were followed using a Siwek 20-L explosion chamber, MIKE 3 apparatus and BAM oven. The explosibility parameters investigated for both size ranges of titanium include explosion severity (maximum explosion pressure (Pmax) and size-normalized maximum rate of pressure rise (KSt)) and explosion likelihood (minimum explosible concentration (MEC), minimum ignition energy (MIE) and minimum ignition temperature (MIT)). Titanium particle sizes were ?100 mesh (<150 μm), ?325 mesh (<45 μm), ≤20 μm, 150 nm, 60–80 nm, and 40–60 nm. The results show a significant increase in explosion severity as the particle size decreases from ?100 mesh with an apparent plateau being reached at ?325 mesh and ≤20 μm. Micron-size explosion severity could not be compared with that for nano-titanium due to pre-ignition of the nano-powder in the 20-L chamber. The likelihood of an explosion increases significantly as the particle size decreases into the nano range. Nano-titanium is very sensitive and can self-ignite under the appropriate conditions. The explosive properties of the nano-titanium can be suppressed by adding nano-titanium dioxide to the dust mixture. Safety precautions and procedures for the nano-titanium are also discussed. 相似文献
939.
Chris T. Cloney Robert C. Ripley Paul R. Amyotte Faisal I. Khan 《Journal of Loss Prevention in the Process Industries》2013,26(6):1574-1582
Computational fluid dynamics is used to investigate the preconditioning aspect of overdriving in dust explosion testing. The results show that preconditioning alters both the particle temperature and distribution prior to flame propagation in the 20-L chamber. A parametric study gives the fluid pressure and temperature, and particle temperature and concentration at an assumed flame kernel development time (10 ms) for varying ignitor size and particle diameter. For the 10 kJ ignitor with 50% efficiency, polyethylene particles under 50 μm reach 400 K and may melt prior to flame propagation. Gases from the ignitor detonation displace the dust from the center of the chamber and may increase local particle concentration up to two times the nominal value being tested. These effects have important implications for explosive testing of dusts in the 20-L chamber and comparing to larger 1-m3 testing, where these effects may be negligible. 相似文献
940.
Nima Khakzad Faisal Khan Paul Amyotte 《Process Safety and Environmental Protection》2013,91(1-2):46-53
Among the various techniques used for safety analysis of process systems, bow-tie (BT) analysis is becoming a popular technique as it represents an accident scenario from causes to effects. However, the BT application in the dynamic safety analysis is limited due to the static nature of its components, i.e. fault tree and event tree. It is therefore difficult in BT to take accident precursors into account to update the probability of events and the consequent risk. Also, BT is unable to represent conditional dependency. Event dependency is common among primary events and safety barriers. The current paper illustrates how Bayesian network (BN) helps to overcome these limitations. It has also been shown that BN can be used in dynamic safety analysis of a wide range of accident scenarios due to its flexible structure. This paper also introduces the application of probability adapting in dynamic safety analysis rather than probability updating. A case study from the U.S. Chemical Safety Board has been used to illustrate the application of both BT and BN techniques, with a comparison of the results from each technique. 相似文献