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11.
12.
Problem
To simplify the computation of the variance in before-after studies, it is generally assumed that the observed crash data for each entity (or observation) are Poisson distributed. Given the characteristics of this distribution, the observed value (xi) for each entity is implicitly made equal to its variance. However, the variance should be estimated using the conditional properties of this observed value (defined as a random variable), that is, f(xi|μi), since the mean of the observed value is in fact unknown.Method
Parametric and non-parametric bootstrap methods were investigated to evaluate the conditional assumption using simulated and observed data.Results
The results of this study show that observed data should not be used as a substitute for the variance, even if the entities are assumed to be Poisson distributed. Consequently, the estimated variance for the parameters under study in traditional before-after studies is likely to be underestimated.Conclusions
The proposed methods offer more accurate approaches for estimating the variance in before-after studies. 相似文献13.
Pamela N. Melki Frédéric Ledoux Samer Aouad Sylvain Billet Bilal El Khoury Yann Landkocz Roula M. Abdel-Massih Dominique Courcot 《Environmental science and pollution research international》2017,24(23):18782-18797
In this work, the main objectives were to assess the mutagenic and genotoxic effects of fine particulate matter collected in an industrial influenced site in comparison with a non-industrial influenced one (rural site) and to relate the particulate matter (PM) composition to the observed genotoxic effects. At the industrial influenced site, higher concentrations of phosphates, trace metals, and polycyclic aromatic hydrocarbons (PAHs) in particles could be related to the contributions of quarries, fertilizer producer, cement plants, and tires burning. Gasoline and diesel combustion contributions were evidenced in particles collected at both sites. Particles collected under industrial influence showed a higher mutagenic potential on three tested strains of Salmonella typhimurium (TA98, YG1041, and TA102), and especially on the YG1041, compared to particles from the rural site. Furthermore, only particles collected in the vicinity of the industrial site showed a tendency to activate the SOS responses in Escherichia coli PQ37, which is indicative of DNA damage as a result of exposure of the bacteria cells to the action of mutagenic samples. The mutagenicity and genotoxicity of the industrial PM2.5–0.3 particulates may be attributed to its composition especially in organic compounds. This study showed that proximity of industries can affect local PM composition as well as PM genotoxic and mutagenic potential. 相似文献
14.
Although a number of manufactured nanoparticles are applied for the medical and clinical purposes, the understanding of interaction between nanomaterials and biological systems are still insufficient. Using nematode Caenorhabditis elegans model organism, we here investigated the in vivo toxicity or safety of hydroxylated fullerene nanoparticles known to detoxify anti-cancer drug-induced oxidative damages in mammals. The survival ratio of C. elegans rapidly decreased by the uptake of nanoparticles from their L4 larval stage with resulting in shortened lifespan (20 d). Both reproduction rate and body size of C. elegans were also reduced after exposure to 100 μg mL−1 of fullerol. We found ectopic cell corpses caused by apoptotic cell death in the adult worms grown with fullerol nanoparticles. By the mutation of core pro-apoptotic regulator genes, ced-3 and ced-4, these nanoparticle-induced cell death were significantly suppressed, and the viability of animals consequently increased despite of nanoparticle uptake. The apoptosis-mediated toxicity of nanoparticles particularly led to the disorder of digestion system in the animals containing a large number of undigested foods in their intestine. These results demonstrated that the water-soluble fullerol nanoparticles widely used in medicinal applications have a potential for inducing apoptotic cell death in multicellular organisms despite of their antioxidative detoxifying property. 相似文献
15.
Pratt IS Anderson WA Crowley D Daly SF Evans RI Fernandes AR Fitzgerald M Geary MP Keane DP Malisch R McBride J Morrison JJ Reilly A Tlustos C 《Chemosphere》2012,88(7):865-872
The 2008 dioxin incident in Ireland resulted in elevated concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) in Irish pork and pork products, due to the consumption of contaminated animal feed by pigs. In order to investigate any resulting impact on the Irish population, these contaminants were measured in pooled breast milk samples from 109 first-time mothers, collected in 2010. A comparison of the results with similar data from 2002 revealed generally lower concentrations of PCDD/Fs and dioxin-like PCBs in the 2010 samples, confirming the declining trend reported by many authors. Contaminant concentration levels for both 2002 and 2010 were generally slightly lower than those reported internationally, with a mean combined PCDD/F and PCB WHO-TEQ of 9.66 pg g−1 fat, for an overall pooled sample of milk from 2010. An apparent slight increase in PCDFs was observed between 2002 and 2010 (from 2.73 pg WHO-TEQ g−1 fat to 3.21 pg WHO-TEQ g−1 fat), with the main contributory congener being 2,3,4,7,8-PentaCDF. While it cannot be totally discounted that the slight increase in 2,3,4,7,8-PentaCDF and in the overall PCDF WHO-TEQ in breast milk could be attributable to consumption of Irish pork during the 2008 incident, we consider that it is more likely that this was due to other factors, including the predominantly urban/industrial sampling locations for the 2010 samples, compared to 2002. 相似文献
16.
Assia Kaci Fabienne Petit Patrick Lesueur Dominique Boust Anne Vrel Thierry Berthe 《Environmental science and pollution research international》2014,21(18):10787-10802
In estuarine ecosystems, trace metals are mainly associated with fine grain sediments which settle on mudflats. Over time, the layers of sediments accumulate and are then transformed by diagenetic processes, recording the history of the estuary’s chemical contamination. In such a specific environment, we investigated to what extent a chronic exposure to contaminants could affect metal-resistant sedimentary bacteria in subsurface sediments. The occurrence and diversity of cadmium resistance genes (cadA, czcA) was investigated in 5- and 33-year-old sediments from a highly contaminated estuary (Seine France). Primers were designed to detect a 252-bp fragment of the czcA gene, specifically targeting a transmembrane helice domain (TMH IV) involved in the proton substrate antiport of this efflux pump. Although the cadA gene was not detected, the highest diversity of the sequence of the czcA gene was observed in the 5-year-old sediment. According to the percentage of identity at the amino acid level, the closest CzcA relatives were identified among Proteobacteria (α, β, γ, and δ), Verrucomicrobia, Nitrospirae, and Bacteroidetes. The most abundant sequences were affiliated with Stenotrophomonas. In contrast, in the 33-year-old sediment, CzcA sequences were mainly related to Rhodanobacter thiooxydans and Stenotrophomonas, suggesting a shaping of the metal-resistant microbial communities over time by both diagenetic processes and trace metal contamination. 相似文献
17.
Aymen Amine Assadi Abdelkrim Bouzaza Dominique Wolbert Philippe Petit 《Environmental science and pollution research international》2014,21(19):11178-11188
A proposal for scaling-up the photocatalytic reactors is described and applied to the coated catalytic walls with a thin layer of titanium dioxide under the near ultraviolet (UV) irradiation. In this context, the photocatalytic degradation of isovaleraldehyde in gas phase is studied. In fact, the removal capacity is compared at different continuous reactors: a photocatalytic cylindrical reactor, planar reactor, and pilot unit. Results show that laboratory results can be useful for reactor design and scale-up. The flowrate increases lead to the removal capacity increases also. For example, with pilot unit, when flowrate extends four times, the degradation rate varies from 0.14 to 0.38 g h?1 mcat ?2. The influence of UV intensity is also studied. When this parameter increases, zboth degradation rate and overall mineralization are enhanced. Moreover, the effects of inlet concentration, flowrate, geometries, and size of reactors on the removal capacity are also studied. 相似文献
18.
Kupper T de Alencastro LF Gatsigazi R Furrer R Grandjean D Tarradellas J 《Chemosphere》2008,71(6):1173-1180
Many substances related to human activities end up in wastewater and accumulate in sewage sludge. The present study focuses on two classes of brominated flame retardants: polybrominated diphenyl ethers (BDE28, BDE47, BDE49, BDE66, BDE85, BDE99, BDE100, BDE119, BDE138, BDE153, BDE154, BDE183, BDE209) and hexabromocyclododecane (HBCD) detected in sewage sludge collected from a monitoring network in Switzerland. Mean concentrations (n=16 wastewater treatment plants) were 310, 149, 95 and 17microg per kg dry matter for decaBDE, HBCD, penta- and octaBDE, respectively. These numbers correspond well with other studies from European countries. DecaBDE, HBCD, penta- and octaBDE showed average specific loads (load per connected inhabitant per year) in sludge of 6.1, 3.3, 2.0 and 0.3mgcap(-1)yr(-1), respectively. This is in line with consumption and storage of the compounds in the environment and the anthroposphere. Discrepancies observed for octaBDE and HBCD can be explained by the release from materials where these compounds are incorporated in and/or their degradation during anaerobic sludge treatment. Loads from different types of monitoring sites showed that brominated flame retardants ending up in sewage sludge originate mainly from surface runoff, industrial and domestic wastewater. 相似文献
19.
Vincent Careau Jean-François Giroux Dominique Berteaux 《Behavioral ecology and sociobiology》2007,62(1):87-96
Food-hoarding animals are expected to preferentially cache items with lower perishability and/or higher consumption time.
We observed arctic foxes (Alopex lagopus) foraging in a greater snow goose (Anser caerulescens atlanticus) colony where the main prey of foxes consisted of goose eggs, goslings, and lemmings (Lemmus and Dicrostonyx spp.). We recorded the number of prey consumed and cached and the time that foxes invested in these activities. Foxes took
more time to consume a goose egg than a lemming or gosling but cached a greater proportion of eggs than the other prey type.
This may be caused by the eggshell, which presumably decreases the perishability and/or pilfering risk of cached eggs, but
also increases egg consumption time. Arctic foxes usually recached goose eggs but rarely recached goslings or lemmings. We
tested whether the rapid-sequestering hypothesis could explain this recaching behavior. According to this hypothesis, arctic
foxes may adopt a two-stage strategy allowing both to maximize egg acquisition rate in an undefended nest and subsequently
secure eggs in potentially safer sites. Foxes spent more time carrying an egg and traveled greater distances when establishing
a secondary than a primary cache. To gain further information on the location and subsequent fate of cached eggs, we used
dummy eggs containing radio transmitters. Lifespan of primary caches increased with distance from the goose nest. Secondary
caches were generally located farther from the nest and had a longer lifespan than primary caches. Behavioral observations
and the radio-tagged egg technique both gave results supporting the rapid-sequestering hypothesis. 相似文献
20.
Development and Operational Testing of a Super‐Ensemble Artificial Intelligence Flood‐Forecast Model for a Pacific Northwest River
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Dominique R. Bourdin Dave Campbell Roland B. Stull Tobi Gardner 《Journal of the American Water Resources Association》2015,51(2):502-512
Coastal catchments in British Columbia, Canada, experience a complex mixture of rainfall‐ and snowmelt‐driven contributions to flood events. Few operational flood‐forecast models are available in the region. Here, we integrated a number of proven technologies in a novel way to produce a super‐ensemble forecast system for the Englishman River, a flood‐prone stream on Vancouver Island. This three‐day‐ahead modeling system utilizes up to 42 numerical weather prediction model outputs from the North American Ensemble Forecast System, combined with six artificial neural network‐based streamflow models representing various slightly different system conceptualizations, all of which were trained exclusively on historical high‐flow data. As such, the system combines relatively low model development times and costs with the generation of fully probabilistic forecasts reflecting uncertainty in the simulation of both atmospheric and terrestrial hydrologic dynamics. Results from operational testing by British Columbia's flood forecasting agency during the 2013‐2014 storm season suggest that the prediction system is operationally useful and robust. 相似文献