The thermodynamics of quadrilateral pyroxene solutions have been analysed with the ternary non-convergent site-disorder model developed in Part I. Solution parameters have been refined for this model with a non-linear least squares technique to fit experimentally determined phase equilibria for the assemblages orthopyroxene-clinopyroxene (opx-cpx), pigeonite-augite (pig-aug), and opx-pig-aug. Calculated phase relations agree, within error, with experiments. Predicted cation distributions and enthalpies of solution for opx are also in agreement with measurements. Predicted cation distributions for cpx are more disordered than indicated by most available measurements. Two types of pyroxene thermometers are presented: (a) a single-pyroxene (aug) thermometer, and (b), a two-pyroxene thermometer which approximates the temperature of an observed pig-aug or cpx-opx assemblage as that of its nearest model tieline. Pyroxene pairs from two granulite suites, whose compositions were projected to the ternary system by the method of Lindsley and Andersen (1983), yield temperatures that are 25° C higher by thermometers (a) and (b) than determined from Lindsley's (1983) graphical thermometer. Temperatures calculated for projected compositions of coexisting pig-aug are within 20° C of run temperatures in experiments by Grove and Bryan (1983). 相似文献
The ratios of the carbon isotopes 13C and 12C of twenty-four graphite samples from Bogala Mine, Sri Lanka have been determined. The graphites are isotopically very similar (mean value ; range ). Three models for the biogenic or abiogenic origin of the graphite deposit are discussed. 相似文献
Recent environmental developments have stimulated an interest in conservation and restoration of the historical Willamette River flood plain, both to protect against flooding and to provide wildlife habitat. In order to best utilize scarce resources, we characterized historical and modern river channel and flood‐plain conditions to evaluate changes and help prioritize restoration sites. Using cartographic and photographic data sources, we developed a Geographic Information System (GIS) to map active channels, side channels, islands and tributaries for four separate dates, as well as riparian and flood‐plain vegetation characteristics for pre‐European settlement and modern time periods. Coverages based on flood records and other boundaries were used to partition the flood plain into spatial subsets for analysis. The GIS allowed comparisons between historical and present conditions for a variety of environmental factors. Much of the pre‐settlement channel complexity has been removed. Total channel length in 1995 was 26% less than in 1850, with almost 58% of the river's side channels disconnected from the system. In addition, we found a 72% loss of flood‐plain forest from 1850 to 1995, since it was converted to agricultural and urban land uses. Selected river and flood‐plain variables were made available for a spatial model to prioritize potential locations for flood‐plain restoration. 相似文献
This paper presents an analysis of critical thresholds for bedload transport based on field measurements conducted in two small, high gradient streams: the Rio Cordon (Italian Alps) and the Tres Arroyos (Chilean Andes). The threshold of incipient motion was identified by using marked particles displacement and both flood and flow competence approaches. The findings are expressed in terms of Shields parameter, dimensionless discharge, and specific stream power, and are used to identify the effects of relative grain size, relative depth, and bedform resistance. Overall, particle entrainment tends to be size selective, rather than exhibiting equal mobility, and the high values of dimensionless critical shear stress observed at both study sites confirm the additional roughness effects of step–pool morphologies that are very effective in reducing the bed shear stress and causing an apparent increase in critical shear stress. 相似文献
The assessment of vulnerability provides valuable knowledge in the risk assessment steps of a risk governance process. Given the multiscale, multilevel, and multisectorial aspects of flood risk, the diversified entities that directly and indirectly intervene in risk management require specific outputs from the assessment studies. Urban areas in estuarine margins are particularly exposed and vulnerable to flooding. Such interface conditions are found in the Old City Centre of the Seixal, located in the Tagus estuary, Portugal. Here, two distinct methodologies were applied for the assessment of territorial vulnerability. A regional, lower-scale, methodology explores the application of the statistical procedure based on the SoVI® at the statistical block level. A second, local and higher-scale, methodology is based in data collected through field matrices at the building and statistical sub-block level. Comparison of results revealed that the lower-scale assessment provides information on the vulnerability drivers at the regional and municipal level. Nevertheless, only at a higher-scale, it is possible to characterize and differentiate the smaller geographical units of analysis that compose the Old City Centre of Seixal. The lower-scale vulnerability assessment allows a strategic response, based on adaptation measures such as spatial planning, institutional capacity building and public awareness. The local level assessment provides more accurate knowledge to support local emergency planning and the allocation of operational and material resources at the urban level. Nevertheless, rather than antagonistic, both models can be considered as complementary, having in mind the requirements of an holistic flood risk governance model.
The effect of different organic-rich sewage concentration (0%, 20% and 60% diluted in seawater) and absence or presence of mangrove trees on the survival, bioturbation activities and burrow morphology of fiddler crabs species was assessed. After 6 months, males of both species always showed higher survival (80%) when compared to females (20%). Crabs inhabiting pristine conditions achieved higher survival (67–87%) than those living in sewage-exposed mesocosms (40–71%). At 60% sewage loading, fiddler crabs processed less sediment (34–46%) during feeding and excavated slightly more sediment (45–80%) than at pristine conditions. While percent volume of the burrow chambers increased (13–66%) at contaminated mesocosms for both vegetation conditions, burrows were shallower (33%) in bare cells loaded with sewage. The results show that fiddler crabs presented moderate mortality levels in these artificial mangrove wetlands, but mainly in sewage impacted cells. However, they still function as ecosystem engineers through bioturbation activities and burrow construction. 相似文献
Ultra-low-volume (ULV) aerosol applications of insecticides are used to manage high densities of adult mosquitoes. We used
two-dimensional probabilistic risk assessment methodologies to evaluate three pyrethroid insecticides (phenothrin, resmethrin,
and permethrin), pyrethrins, and two organophosphate insecticides (malathion and naled), applied by truck-mounted ULV sprayer.
Piperonyl butoxide, a synergist commonly used in pyrethroid and pyrethrins formulations, was also assessed. The objective
of our study was to evaluate probabilistically if a deterministic human-health risk assessment of mosquito insecticides was
sufficiently conservative to protect human-health. Toddlers and infants were the highest risk groups while adult males were
the lowest risk group assessed in this study. Total acute exposure ranged from 0.00003 to 0.0003 mg/kg day−1 for the chemicals and subgroups assessed examining inhalation, dermal, oral, and hand-to-mouth exposure. We used the risk
quotient (RQ) method for our risk assessment, which is calculated by dividing the total potential exposure for each subgroup
and chemical by its ingestion toxic endpoint value (RfD). Mean RQs ranged from 0.000004 to 0.034 for all subgroups and chemicals,
with none exceeding the RQ level of concern. Naled had the highest RQs of any chemical assessed while PBO had the lowest.
Sensitivity analysis demonstrated that the exposure from inhalation and deposition contributed the largest variance to the
model output. Results support the findings of previous studies that the risks from adult mosquito management are most likely
negligible, and that the human-health deterministic risk assessment is most likely sufficiently conservative. 相似文献
Natural Hazards - Understanding the culture of preparedness is essential to improve public policies and programs aimed to promote population preparedness to cope with natural hazards. The present... 相似文献
Natural Hazards - Historically, during periods of extreme drought, food security in the drylands of the semiarid region of Northeast Brazil (NEB) is under severe risk due to agricultural collapse.... 相似文献