The oxidation of Cr(III) has been studied in NaCl solutions in the presence of two siderophore models, acetohydroxamic acid (Aha) and benzohydroxamic acid (Bha), the natural siderophore Desferal (DFOB) and the synthetic aminocarboxilate (ethylenedinitrilo)-tetra-acetic acid (EDTA) as a function of pH (8-9), ionic strength (0.01-2 M) and temperature (10-50 °C), at different Cr(III)-organic compound ratios. The addition of Aha and Bha caused the rates to increase at low ligand/Cr(III) ratios and decrease at high ratios. The variation of the pseudo first order rate constant (k1) as a function of the ligand concentration has been attributed to the formation of three Cr(III)-organo species (1:1, 1:2, 1:3), which can form in the presence of monohydroxamic acids. A kinetic model has been developed that gives a value of 600 (min−1) for the pseudo first order rate constant k1CrAha2+ and values approaching zero for and k1CrAha3. These kinetic results demonstrate that these monohydroxamic acids are able to bind with Cr(III) under experimental conditions that may occur in natural waters and can increase the oxidation rates of Cr(III) with H2O2 by a factor of 3.5 at an Aha/Cr(III) ratio of about 50-100.The monohydroxamic acids also affect the rates on aged products of Cr(III), suggesting that these ligands are able to affect the oxidation rates by releasing reactive Cr(III). DFOB and EDTA do not have a great effect on the oxidation of Cr(III) with H2O2. This is thought to be due to the much longer times they need to form complexes with Cr(III) compared to Aha and Bha. The rates for the formation of DFOB and EDTA complexes with Cr(III) are not competitive with the rates of the formation of aged Cr(III). After allowing Cr(III) and DFOB to react for 5 days to form the complex, reaction rates of Cr(III) with H2O2 appear to be lowered probably because of steric hindrance of the chelated Cr(III). 相似文献
The provenance and paleogeography of the Upper Triassic deep-sea flysch Langjiexue Group(LG) of the Shannan Terrane in the northeastern Himalaya orogen, south of Yarlung Zangbo, have been disputed in recent years since its affinity to the Tethys Himalaya was suspected during the early 2000 s. Based on the earlier discoveries of the Upper Permian–Triassic basalts and mafic dykes from the LG and of coeval detrital zircons from the Qulonggongba Formation(QF) in shallow shelf sediments of the Tethys Himalaya, the previous viewpoints on the basin and tectonics of the LG have been recently rejected. We compared the two units of the Upper Triassic, and our results reveal a number of differences,discrepancies, and inconsistencies in the debate, raising crucial questions on the postulation and provenance model of the remote Gondwanide Orogen for the LG. It is suggested that more observations and evidence are needed to further improve the paleogeographic understanding and relationship of the two units. 相似文献
The non-marine bivalve species Trigonioides (Kumamotoa) quadratus Gu and Ma is described from the Fourth Member of the Hekou Formation in western Fujian, southeastern China. This species previously was regarded to belong to the subgenus Trigonioides (s.s.), which is restricted to the Early Cretaceous. Herein, it is included into the subgenus Kumamotoa. It is compared to Cenomanian (early Late Cretaceous) species from Japan and Korea such as Trigonioides (Kumamotoa) mifunensis Tamura, Trigonioides (Kumamotoa) matsumotoi Kobayashi and Suzuki and Trigonioides (Kumamotoa) paucisulcatus Suzuki. The age of the Fourth Member of the Hekou Formation is discussed. 相似文献
China has experienced considerable migration from inland to coastal areas since the reforms of 1978, with migrants becoming
an important population in many coastal cities. Compared with non-migrants (long-term residents), migrant vulnerability to
typhoons is considered high due to limited access to job opportunities, social security, information, and other resources;
however, there is no research on vulnerability of this population sector to natural hazards. This initial study analysed the
perceptions and personal experiences of migrants living in Shanghai of typhoon hazards. During May 2010, empirical data were
collected using an online questionnaire and face–face interviews. Response data indicated that risk knowledge of migrants
was significantly lower than among non- migrants; differing risk perceptions between the groups were consistent with levels
of personal typhoon experience; statistically significant differences in hazard knowledge within the sample also related to
education and occupation; a variety of strategies to cope with typhoon hazards was being applied by residential committees;
and that migrants were not generally recognised as a vulnerable group requiring special consideration in hazard risk management.
To reduce the vulnerability of migrants to typhoons, we recommend expanding the range of accessible communication technologies
distributing warning information; organising more educational and training programmes, at government and corporate level,
to increase community awareness of natural hazards; encouraging local residential committees to promote social networks and
engagement for migrants; and providing corporate incentives to develop insurances specifically for migrant needs. Further
research is necessary to assess the differences in vulnerability between different types of migrants. 相似文献
An area-differentiated model approach (MEPhos) for the quantification of mean annual P-inputs from point and diffuse sources
is presented. The following pathways are considered: artificial drainage, wash-off, groundwater outflow, soil erosion, rainwater
sewers, combined sewer overflows, municipal waste water treatment plants and industrial effluents. Two retention functions
for rivers and reservoirs are included in order to model P-sinks within a river basin. This allows a complete record of P-loads
in heterogeneous meso- and macroscale river basins and enables validation of modeling results with water quality data on a
load basis. The model is applied to the River Ruhr basin (4,485 km2) in Germany, which includes contrasting natural conditions, land use patterns as well as population and industry densities.
Based on validated modelling results sub-areas of high P-loads are localized and management options for the reduction of P-inputs
to surface waters are proposed taking into account the site conditions of the sub-areas relevant for high P-inputs into surface
waters. 相似文献
Chemical diffusion profiles in molten CaO---Al2O3---SiO2 have been measured over a large range of compositions at 1500°C and l GPa. The diffusion profiles have been inverted for effective binary diffusion coefficients (EBDCs) and for the chemical diffusion matrix. The EBDCs are shown to depend strongly on both composition and direction of diffusion in composition space. The dependence of EBDCs on direction in composition space, which for the system studied here can be as large as a factor of seven, severely limits the applicability of EBDCs to interdiffusion in any direction other than the one used to derive the EBDCs.
The chemical diffusion matrix for molten CaO---Al2O3---SiO2 was determined using diffusion profiles from two or three mutually orthogonal diffusion couples in the ternary composition space. All features of the diffusion profiles shown in this work can be reproduced by representing the chemical fluxes in the three-component system as a linear combination of concentration gradients via a 2 × 2 diffusion matrix. Chemical diffusion in molten CaO---Al2O3---SiO2 shows clear evidence of strong diffusive coupling among the components. This can be seen in the uphill diffusion profiles of components that were initially uniform, in the fact that the apparent rate of diffusion of some components is a strong function of direction in composition space, and most quantitatively in the magnitude of off-diagonal elements of the diffusion matrix relative to the magnitude of the diagonal elements. SiO2 for example, is found to be strongly coupled with CaO in relatively silicic melts, whereas Al2O3 is strongly coupled with CaO in less silicic melts. Furthermore, the coupling of CaO with either Al2O3 or Si02 reverses sign between more and less polymerized compositions. Interdiffusion profiles in natural melts have numerous features that suggest similar coupling between Al2O3 and CaO and between SiO2 and CaO. 相似文献
Pliocene to recent volcanic rocks from the Bulusan volcanic complex in the southern part of the Bicol arc (Philippines) exhibit
a wide compositional range (medium- to high-K basaltic-andesites, andesites and a dacite/rhyolite suite), but are characterised
by large ion lithophile element enrichments and HFS element depletions typical of subduction-related rocks. Field, petrographic
and geochemical data indicate that the more silicic syn- and post-caldera magmas have been influenced by intracrustal processes
such as magma mixing and fractional crystallisation. However, the available data indicate that the Bicol rocks as a group
exhibit relatively lower and less variable 87Sr/86Sr ratios (0.7036–0.7039) compared with many of the other subduction-related volcanics from the Philippine archipelago. The
Pb isotope ratios of the Bicol volcanics appear to be unlike those of other Philippine arc segments. They typically plot within
and below the data field for the Philippine Sea Basin on 207Pb/204Pb versus 206Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb diagrams, implying a pre-subduction mantle wedge similar to that sampled by the Palau Kyushu Ridge, east of the Philippine
Trench. 143Nd/144Nd ratios are moderately variable (0.51285–0.51300). Low silica (<55 wt%) samples that have lower 143Nd/144Nd tend to have high Th/Nd, high Th/Nb, and moderately low Ce/Ce* ratios. Unlike some other arc segments in the Philippines
(e.g. the Babuyan-Taiwan segment), there is little evidence for the involvement of subducted terrigenous sediment. Instead,
the moderately low 143Nd/144Nd ratios in some of the Bicol volcanics may result from subduction of pelagic sediment (low Ce/Ce*, high Th/Nd, and high
Th/Nb) and its incorporation into the mantle wedge via a slab-derived partial melt. 相似文献
Coastal regions are vulnerable to storm surge and flooding due to tropical and extratropical storms. It is necessary to build
robust resiliency of the coastal communities to these hazards. The main objectives of operational surge and inundation forecast
and coastal warning systems are to protect life and to sustain economic prosperity. The National Oceanic and Atmospheric Administration
of the United States has initiated an integrated effort through pilot demonstration projects, and model-based ocean and coastal
forecasting systems, to build improved operational warnings and forecasts capability for storm surge and inundation. This
note describes the overall strategy and progress to date, with an emphasis on forecasting extratropical storm surge. 相似文献
Here, I describe a theoretical approach to the structure and chemical composition of minerals based on their bond topology. This approach allows consideration of many aspects of minerals and mineral behaviour that cannot be addressed by current theoretical methods. It consists of combining the bond topology of the structure with aspects of graph theory and bond-valence theory (both long range and short range), and using the moments approach to the electronic energy density-of-states to interpret topological aspects of crystal structures. The structure hierarchy hypothesis states that higher bond-valence polyhedra polymerize to form the (usually anionic) structural unit, the excess charge of which is balanced by the interstitial complex (usually consisting of large low-valence cations and (H2O) groups). This hypothesis may be justified within the framework of bond topology and bond-valence theory, and may be used to hierarchically classify oxysalt minerals. It is the weak interaction between the structural unit and the interstitial complex that controls the stability of the structural arrangement. The principle of correspondence of Lewis acidity–basicity states that stable structures will form when the Lewis-acid strength of the interstitial complex closely matches the Lewis-base strength of the structural unit, and allows us to examine the factors that control the chemical composition and aspects of the structural arrangements of minerals. It also provides a connection between a structure, the speciation of its constituents in aqueous solution and its mechanism of crystallization. The moments approach to the electronic energy density-of-states provides a link between the bond topology of a structure and its thermodynamic properties, as indicated by correlations between average anion coordination number and reduced enthalpy of formation from the oxides for [6]Mgm[4]SinO(m+2n) and MgSO4(H2O)n. 相似文献