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221.
The photochemical behaviour of chlorophenols is different to that of non-halogenated phenols. In the former, the first step is a C-Cl bond scission, which is not influenced by oxygen. Chlorine is converted into hydrochloric acid. For monochlorophenols, the position of the chlorine on the ring strongly influences the transformation. In the molecular form, 2-chlorophenol is converted into pyrocatechol. In the anionic form however, it is reduced in a cyclopentadienic acid which dimerizes according to a Diels-Alder reaction. The irradiation of 3-chlorophenol leads to resorcinol whatever the pH. This would appear to suggest a photohydrolysis mechanism. With 4-chlorophenol, the photochemical conversion is not so specific. Hydroquinone is formed (mainly in aerated solution), along with polyphenolic oligomers. A radical mechanism is proposed. 相似文献
222.
In order to study the effect of thevegetation structure on atmospheric ammonia(NH3) dispersion and deposition, anexperiment was set up near Paris, in July 1997.Between 12 and 162 m downwind of a 200 m line-source releasing 600 to 1200 g NH3hr-1placed at the top of a maize canopy, NH3concentration was measured, within and above thecanopy, with a set of 30 active, acid-coateddenuders over periods of 2 to 3 hr. Eight datasets were collected over a one-month period.NH3 concentration decreased sharply withdistance to the source, from up to800 g NH3 m-3 at 12 m, to lessthan 10 g NH3 m-3 at 162 m andshowed strong vertical gradients. Within thecanopy, the concentration scaled using thefriction velocity, the canopy height, and thesource strength, exhibited a universal power lawrelationship as a function of the normaliseddownwind distance from the source. A mass balancemethod and a resistance model approach were usedas independent estimates of the cumulateddeposition at 162 m downwind from the source,which range between 1 and 29% of the emittedNH3. Both methods agreed approximately inmagnitude. A sensitivity analysis showed that thecuticular uptake and the compensation point aremajor parameters that needs to be bettercharacterised under high NH3 concentrationif one wants to improve NH3 short-rangedeposition modelling. 相似文献
223.
Pierre Lasserre 《Journal of Environmental Economics and Management》1984,11(3):191-201
Arrow and Chang (J. Econom. Environ. Manag.9, 1–10 (1982) analyze an exploration-extraction model with uncertainty about the distribution of deposits. Reserve prices do not exhibit any rising trend when the unexplored land area is big but, in order to know what happens when the unexplored area is smaller, “a probabilistic analysis not yet performed” (ibid. p. 10) is required. Their conjecture of a rising trend at less than the discount rate is confirmed. However, land prices can be expected to grow faster than reserve prices, which helps discriminate between Arrow and Chang's, and other rationalizations of the failure of resource prices to rise at the discount rate. 相似文献
224.
A mathematical model describing the dissolution of nuclear glass directly disposed in clay combines a first-order dissolution rate law with the diffusion of dissolved silica in clay. According to this model, the main parameters describing the long-term dissolution of the glass are etaR, the product of the diffusion accessible porosity eta and the retardation factor R, and the apparent diffusion coefficient D(app) of dissolved silica in clay. For determining the migration parameters needed for long-term predictions, four Through-Diffusion (T-D) experiments and one percolation test have been performed on undisturbed clay cores. In the Through-Diffusion experiments, the concentration decrease after injection of 32Si (radioactive labelled silica) was measured in the inlet compartment. At the end of the T-D experiments, the clay cores were cut in thin slices and the activity of labelled silica in each slice was determined. The measured activity profiles for these four clay cores are well reproducible. Since no labelled silica could be detected in the outlet compartments, the Through-Diffusion experiments are fitted by two In-Diffusion models: one model assuming linear and reversible sorption equilibrium and a second model taking into account sorption kinetics. Although the kinetic model provides better fits, due to the sufficiently long duration of the experiments, both models give approximately similar values for the fit parameters. The single percolation test leads to an apparent diffusion coefficient value about two to three times lower than those of the Through-Diffusion tests. Therefore, dissolved silica appears to be strongly retarded in Boom Clay. A retardation factor R between 100 and 300 was determined. The corresponding in situ distribution coefficient K(d) is in the range 25-75 cm(3) g(-1). The apparent diffusion coefficient of dissolved silica in Boom Clay is estimated between 2 x 10(-13) and 7 x 10(-13) m(2) s(-1). The pore diffusion coefficient is in the range from 6 x 10(-11) to 1 x 10(-10) m(2) s(-1). 相似文献
225.
Pierre Desprairies 《Natural resources forum》1989,13(1):33-35
The oil crisis has ended on a worldwide scale. Risks of excessive price rises have disappeared. Between now and the year 2000, oil resources costing less than $15/bbl (1988 dollars) will be abundant. Twenty to 25% of the oil consumed in 2000 for thermal uses will be replaced by less costly natural gas and coal. Consumption of these last two energy sources will increase if the cost of oil rises above $20/bbl (1988 dollars). The cost of oil will rise sharply when it becomes reserved for the uses for which it is irreplaceable, ie transport, petrochemicals, the Third World and non-energy uses — probably after 2010. 相似文献
226.
Denyse Lajeunesse Gérald Domon Pierre Drapeau Alain Cogliastro André Bouchard 《Environmental management》1995,19(4):481-495
Preservation of small natural areas is not in itself a sufficient measure to maintain the integrity of the ecosystems for
which they were initially set aside. Intense pressure from recreational use is just one of the many human-caused stresses
that may degrade natural areas. Therefore, land-use planning and management from an ecological perspective is necessary to
assess, ensure, and in some cases increase, the ecological integrity of protected natural areas. An ecosystem management approach
for small protected natural areas with high recreational use is presented, based on three interrelated components: an ecological
evaluation procedure of ecosystems, the implementation of management interventions on ecosystems, and the development of a
monitoring scheme of ecosystem components. The ecological evaluation procedure combines two concepts: the biotic value of
vegetation and wildlife and the abiotic fragility of the soils. This combined evaluation process results in the creation of
a sensitivity map that can be used as a management tool for planners and managers. Management interventions, the second component
of the management approach, are derived from concepts of ecological succession. Intentional human interventions are used to
maintain the ecological integrity of ecosystems or in some cases to restore degraded sites. For the third component, only
the basic principles of the monitoring program will be discussed. A pilot project in one of the Montreal urban community protected
areas is presented to illustrate aspects of the proposed ecosystem management approach. 相似文献
227.
Pierre Y. Julien Bahram Saghafian Fred L. Ogden 《Journal of the American Water Resources Association》1995,31(3):523-536
ABSTRACT: The proliferation of watershed databases in raster Geographic Information System (GIS) format and the availability of radar-estimated rainfall data foster rapid developments in raster-based surface runoff simulations. The two-dimensional physically-based rainfall-runoff model CASC2D simulates spatially-varied surface runoff while fully utilizing raster GIS and radar-rainfall data. The model uses the Green and Ampt infiltration method, and the diffusive wave formulation for overland and channel flow routing enables overbank flow storage and routing. CASC2D offers unique color capabilities to display the spatio-temporal variability of rainfall, cumulative infiltrated depth, and surface water depth as thunderstorms unfold. The model has been calibrated and independently verified to provide accurate simulations of catchment response to moving rainstorms on watersheds with spatially-varied infiltration. The model can accurately simulate surface runoff from flashfloods caused by intense thunderstorms moving across partial areas of a watershed. 相似文献
228.
Analysis of HO-PCBs and PCP in blood plasma from individuals with high PCB exposure living on the Chukotka Peninsula in the Russian Arctic 总被引:1,自引:0,他引:1
Sandanger TM Dumas P Berger U Burkow IC 《Journal of environmental monitoring : JEM》2004,6(9):758-765
A trace analytical method is presented for the analysis of hydroxylated polychlorinated biphenyl metabolites (HO-PCBs) and pentachlorophenol (PCP) in human plasma. The described methodology is a modification of a previously validated method used for PCB and organochlorine pesticide analysis. The modified method enables the combined analysis of phenolic and neutral halogenated compounds. A tandem Florisil column is used for separating the HO-PCBs and PCP from the neutral fraction, instead of the more common chemical partitioning. In the same step the neutral fraction is purified for GC analysis. The extraction of the HO-PCBs and PCP was found to be highly dependent on sufficient acidification of the sample and the polarity of the extracting solvent. Analysis of plasma samples gave recovery rates for (13)C(6)-PCP and (13)C(12)-4-HO-CB 187 of 64 and 72%, respectively. The limit of detection ranged between 2-20 pg g(-1) plasma for the HO-PCBs and 5 pg g(-1) plasma for PCP. No matrix interferences were observed in the chromatograms. In plasma samples (n = 15) from the native Chukchi people in Uelen (Russian Arctic), a population with high PCB exposure, the median ratio of sum HO-PCBs to sum PCBs was as high as 0.4 and the sum HO-PCBs and PCBs were significantly correlated (r(2) > 0.7, p < 0.01). The median sum HO-PCBs (10 congeners) was 5920 pg g(-1) plasma with 4-HO-CB 107 as the dominating congener (median: 1670 pg g(-1) plasma). The median PCP level was measured at 642 pg g(-1) plasma. 相似文献
229.
Raia-Silvia Massad Benjamin Loubet Andre Tuzet Herv Autret Pierre Cellier 《Agriculture, ecosystems & environment》2009,133(3-4):170
The plant can be a source or a sink of ammonia (NH3) depending on its nitrogen (N) supply, metabolism and on the background atmospheric concentrations. Thus plants play a major role in regulating atmospheric NH3 concentrations. For a better understanding of the factors influencing the NH3 stomatal compensation point, it is important to analyse the dynamics of leaf NH3 fluxes. The relationship between the leaf NH3 fluxes and the leaf apoplast ammonium and nitrate concentrations, N nutrition and the light and dark periods was studied here.We designed an experiment to quantitatively assess leaf-atmosphere NH3 exchange and the stomatal compensation point and to identify the main factors affecting the variation of NH3 fluxes in oilseed rape. We tested day and night dynamics as well as the effect of five different N treatments. Two experimental methods were used: a dynamic open flux chamber and extraction of the apoplastic solution.Chamber measurements showed that there was a good correlation between plant NH3 fluxes and water fluxes. Compensation points were calculated by two different methods and ranged between 0.8 and 12.2 μg m−3 NH3 (at 20 °C) for the different N treatments. Apoplastic solution measurements showed that there was no significant differences in the apoplastic NH4+ concentrations ([NH4+]apo) extracted in dark and light periods for the same N treatment. Statistical analysis also showed that [NH4+]apo was correlated with [NH4+] in the nutrient solution and weakly correlated with [NO3−]. Apoplast NH4+ concentrations ranged between 0.1 and 2.1 mM, bulk tissue NH4+ concentrations between 3.9 and 6.6 mM and xylem concentrations between 2.4 and 6.1 mM depending on the N supply.Calculated NH3 emission potential from the extraction measurements were over-estimated when compared with the value calculated from chamber measurements. Errors related to chamber measurements included separation of the cuticular and stomatal fluxes and the calculation of total resistance to NH3 exchange. Errors related to the extraction measurements included assessing the amount of cytoplasmic contamination. We do not have another method to assess the NH3 stomatal compensation point and the choice between these two measurement techniques should depend on the scales to which the measurements apply and the processes to be studied. 相似文献
230.
Fureix C Hausberger M Seneque E Morisset S Baylac M Cornette R Biquand V Deleporte P 《Die Naturwissenschaften》2011,98(7):583-592
Describing postures has always been a central concern when studying behaviour. However, attempts to compare postures objectively
at phylogenetical, populational, inter- or intra-individual levels generally either rely upon a few key elements or remain
highly subjective. Here, we propose a novel approach, based on well-established geometric morphometrics, to describe and to
analyse postures globally (i.e. considering the animal’s body posture in its entirety rather than focusing only on a few salient
elements, such as head or tail position). Geometric morphometrics is concerned with describing and comparing variation and
changes in the form (size and shape) of organisms using the coordinates of a series of homologous landmarks (i.e. positioned
in relation to skeletal or muscular cues that are the same for different species for every variety of form and function and
that have derived from a common ancestor, i.e. they have a common evolutionary ancestry, e.g. neck, wings, flipper/hand).
We applied this approach to horses, using global postures (1) to characterise behaviours that correspond to different arousal
levels, (2) to test potential impact of environmental changes on postures. Our application of geometric morphometrics to horse
postures showed that this method can be used to characterise behavioural categories, to evaluate the impact of environmental
factors (here human actions) and to compare individuals and groups. Beyond its application to horses, this promising approach
could be applied to all questions involving the analysis of postures (evolution of displays, expression of emotions, stress
and welfare, behavioural repertoires…) and could lead to a whole new line of research. 相似文献