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871.
Mohammad Salehi Mohammad Mohammadi J. N. K. Rao Yves G. Berger 《Environmental and Ecological Statistics》2010,17(1):111-123
Adaptive cluster sampling (ACS) is an efficient sampling design for estimating parameters of rare and clustered populations.
It is widely used in ecological research. The modified Hansen-Hurwitz (HH) and Horvitz-Thompson (HT) estimators based on small
samples under ACS have often highly skewed distributions. In such situations, confidence intervals based on traditional normal
approximation can lead to unsatisfactory results, with poor coverage properties. Christman and Pontius (Biometrics 56:503–510,
2000) showed that bootstrap percentile methods are appropriate for constructing confidence intervals from the HH estimator.
But Perez and Pontius (J Stat Comput Simul 76:755–764, 2006) showed that bootstrap confidence intervals from the HT estimator
are even worse than the normal approximation confidence intervals. In this article, we consider two pseudo empirical likelihood
functions under the ACS design. One leads to the HH estimator and the other leads to a HT type estimator known as the Hájek
estimator. Based on these two empirical likelihood functions, we derive confidence intervals for the population mean. Using
a simulation study, we show that the confidence intervals obtained from the first EL function perform as good as the bootstrap
confidence intervals from the HH estimator but the confidence intervals obtained from the second EL function perform much
better than the bootstrap confidence intervals from the HT estimator, in terms of coverage rate. 相似文献
872.
Vittorio Barale 《Journal of Coastal Conservation》2010,14(4):317-326
The ecosystem approach requires that all elements of an ecosystem, and their mutual interactions, be taken into consideration
in any management effort. The selection of suitable geographical units, where this approach can be taken, requires the assessment
of ecological provinces, characterized by a coherent set of environmental traits. The marine side of coastal zones, where
the interaction between atmosphere, land and sea is not bounded by evident geographic markers, represents a critical factor
in this assessment. A coastal province can be defined by physical setting, but also by its bio-geo-chemical features, ideally
on the basis of synoptic remote sensing data, collected at space/time scales not accessible by other means. Classifications
based on indicators such as temperature, wind speed and chlorophyll-like pigments, demonstrate the identification of potential
ecological provinces in the Mediterranean Sea. The results suggest remote sensing as the ideal tool to set up the basis for
an ecosystem approach to the management of each province. 相似文献
873.
874.
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the urban atmosphere and the atmospheric pollutants to be identified
as the most suspected carcinogens. In early measurements of urban PAH concentrations in Tehran area, the correlation between
concentrations of different species indicated that automobiles were the predominant source of emission of PAHs in this city.
From the diagnostic ratios, the results indicated that PAHs in the ambient air in Tehran originate primarily from diesel and
gasoline engines, but contribution of the related diesel emission is apparently higher, or dominant, at the sampling sites
and therefore considered as the major emission of PAHs in the ambient air. 相似文献
875.
Ali Akbar Safari Sinegani Hossein Mirahamdi Araki 《Environmental Chemistry Letters》2010,8(4):323-330
Sequential extraction has been used as a suitable method for fractionation of chemical forms of trace elements and study of
their plant availability. Surface soils were sampled from Guilan and Hamadan provinces in north and northwest of Iran with
temperate and semiarid climates. The chemical forms of Pb in the Pb(NO3)2-treated (400 μg Pb g−1) soils have been studied in solid state incubation (FC) at 27°C in sterile and unsterile conditions. After 20 min and 3600 h
a sequential extraction scheme was also used to fractionate Pb of incubated samples into soluble-exchangeable (Sol-Exch),
carbonates associated (ACar), organic matter associated (AOM), Mn oxide associated (AMnOx), Fe oxide associated (AFeOx), and
residual (Res) forms. Temperate soil samples had higher clay content, cation exchange capacity (CEC), dichromate oxidable
organic carbon (OC), total Kjeldahl-nitrogen (TN), biological activity, amorphous and crystalline Fe and Al, but semiarid
soil samples had higher sand content, pH, equivalent calcium carbonate (ECC), available P and K. Soil lead fractionation revealed
that in both groups of soils Pb largely changed to exchangeable, carbonates associated and organic associated forms after
20 min. The chemical forms of Pb differed widely among soils after 3600-h incubation. The conversion rate of Pb from more
available forms to less available forms was higher in temperate soils with higher Fe–Mn oxides and OM contents compared to
semiarid soils. In temperate soils after 3600-h incubation, greater content of Pb was observed in Res (68%), AOM (14%), ACar
(7%), and AMnOx (5%) fractions. However, in semiarid soils greater content of Pb was observed in Res (61%), ACar (16%), Sol-Exch
(8%), and AOM (8%) fractions. The sum of AMnOx and AFeOx chemical forms for Pb in semiarid soils compared to temperate soils
was lower. It was only 7% against 9% in temperate soils. Soil microorganisms in unsterile soils had significant effect on
AOM, AFeOx and Res fractions of Pb. They not only increased AOM and AFeOx fractions of Pb in soils but also decreased Res
fraction of Pb significantly. 相似文献
876.
Distribution and availability of potentially toxic metals in soil in central area of Belgrade,Serbia 总被引:1,自引:0,他引:1
Rabia Ahmed Ghariani Ivan Gržetić Mališa Antić Snežana Nikolić Mandić 《Environmental Chemistry Letters》2010,8(3):261-269
Belgrade, capital city of Serbia, has over 1,600,000 inhabitants and over 400,000 vehicles trafficking every day on its streets.
The investigation of soil pollution was performed by sequential extraction analysis to investigate the availability of potentially
toxic metals (Zn, Cd, Pb, Co, Ni, Cu, Cr and Mn) under different oxidation and pH conditions. All investigated metals were
mainly extracted from soils with neutral or acidic extractants. Serious pollution was observed along roads and streets with
high traffic frequency, but Pb and Ni pollution was the highest since their concentrations exceed both soil Serbian standard
and Canadian guidance values and is characteristic for all investigated sites. Cd, Cu, Cr and Zn concentrations are moderately
high since they are between Canadian guideline and Serbian standard. 相似文献
877.
Photochemical reaction of nitro-polycyclic aromatic hydrocarbons: effect by solvent and structure 总被引:1,自引:0,他引:1
Stewart G Smith K Chornes A Harris T Honeysucker T Dasary SR Yu H 《Environmental Chemistry Letters》2010,8(4):301-306
Photochemical degradation of 1-nitropyrene, 2-nitrofluorene, 2,7-dinitrofluorene, 6-nitrochrysene, 3-nitrofluoranthene, 5-nitroacenaphthene,
and 9-nitroanthracene was examined in CHCl3, CH2Cl2, DMF, DMF/H2O (80/20), CH3CN, or CH3CN/H2O (80/20). The degradation mostly follows the first order kinetics; but a few follow second order kinetics or undergo self-catalysis.
The photodegradation rates follow the order: CHCl3 > CH2Cl2 > DMF > DMF/H2O > CH3CN > CH3CN/H2O. DMF is an exceptional solvent because three of the seven compounds undergo self-catalytic reaction. 9-Nitroanthracene,
which has a perpendicular nitro group, is the fastest, while the more compact 1-nitropyrene and 3-nitrofluoranthene are the
slowest degrading compounds. 相似文献
878.
Caio F. Gromboni George L. Donati Wladiana O. Matos Eduardo F. A. Neves Ana Rita A. Nogueira Joaquim A. Nóbrega 《Environmental Chemistry Letters》2010,8(1):73-77
Efficiency of metabisulfite and a commercial steel wool as reducing agents in the removal of Cr(VI) from wastewaters was evaluated.
Chromium(VI) was converted to Cr(III), precipitated with NaOH, and removed by filtration. A reduction of more than 1.0 × 105 and 4.0 × 105 fold in total Cr and the Cr(VI) concentrations, respectively, was observed by employing steel wool masses as low as 0.4420 g
to 30-mL solutions of wastewater. Chromium(III) hydroxide obtained after the treatment was recycled and used as marker in
cattle nutrition studies. The liquid residue obtained after the treatment was reused as precipitation agent replacing NaOH. 相似文献
879.
A surfactant mediated cloud point extraction (CPE) procedure has been developed to remove color from wastewater containing
malachite green using Triton X-100 as non-ionic surfactant. The effects of the concentration of the surfactant, temperature
and salt concentration on the different concentrations of dye have been studied and optimum conditions were obtained for the
removal of malachite green. The concentration of malachite green in the dilute phase was measured using UV–Vis spectrophotometer.
It was found that the separation of phases was complete and the recovery of malachite green was very effective in the presence
of NaCl as an electrolyte. The results showed that up to 500 ppm of malachite green can quantitatively be removed (>95%) by
CPE procedure in a single extraction using optimum conditions. 相似文献
880.
Davide Vione Daniele Bagnus Valter Maurino Claudio Minero 《Environmental Chemistry Letters》2010,8(2):193-198
We measured the formation rate and the steady-state concentration of hydroxyl radicals and of singlet oxygen upon irradiation
of lake water. There is controversy about the importance of singlet oxygen in the environmental photochemistry, but here we
show that the steady-state concentration of 1O2 under irradiation can be higher by about two orders of magnitude compared to the hydroxyl radical. The higher occurrence
of singlet oxygen in surface waters is mainly due to a higher rate of formation, because the transformation rate constants
of 1O2 (collision with the solvent) and of ·OH (reaction with dissolved compounds) are comparable. 相似文献