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101.
Mineral particles could have influenced on the climate of Oviedo, a non-industrial city situated in the centre of an industrial
zone of the North of Spain, increasing the temperature and the precipitations, in spite of the fact that “greenhouse gases”
concentrations have diminished in this city in recent years. The directive (1999/30/EC) of the European Commission began to
be applied in Oviedo in the year 2003. In agreement with this norm, our first aim was the identification of the inorganic
particulate matter of the PM10 and PM2.5 fractions sampled in this city. X-ray diffraction and scanning electron microscopy
coupled with X-ray dispersive energy spectrometry were used. The percentages of the different mineral phases of the PM were
obtained by a Rietveld refinement of powder X-ray diffraction data. The compositions of the PM10 and PM2.5 fractions of this
city are similar. Sulphates are the most abundant particles in the both fractions. Most sulphates, nitrates and sal-ammoniac
would have formed by reaction between solid, liquid and/or gas particles and they could be associated with the power stations
near to the city and traffic. Wüstite and haematites come from the iron and steel industries of Gijón and Avilés. The main
natural sources of halite and carbonates and silicates are sea spray and soil resuspension by the wind, respectively. 相似文献
102.
In this paper, we present a complete morphological characterization of the ash particles erupted on 18 December 2002 from
Etna volcano, Italy. The work is based on the acquisition and processing of bidimensional digital images carried out by scanning
electron microscopy (SEM) to obtain shape parameters by image analysis. We measure aspect ratio (AR), form factor (FF), compactness
(CC), and rectangularity (RT) of 2065 ash particles with size between 0.026 and 1.122 mm. We evaluate the variation of these
parameters as a function of the grain-size. Ash particles with a diameter of <0.125 mm vary from mostly equant to very equant,
ash particles between 0.125 and 0.250 mm have an intermediate shape, and particles with diameters >0.250 mm are subelongate.
We find that, on average, particles with a diameter of <0.250 mm are subrounded, particles between 0.250 and 0.50 mm are subangular,
and particles >0.50 mm are angular. Using this morphological analysis and an empirical relation between the drag coefficient
(C
D) and Reynolds number (R
e) of Wilson and Huang (Earth Planet Sci Lett 44:311–324, 1979), we calculate the terminal settling velocities (V
WH). The comparisons between these velocities and those calculated with the formula of Kunii and Levenspiel (Fluidization engineering. Wiley, New York, pp 97, 1969) (V
KL), which considers ash particles as spheres, show that V
KL are in average 1.28 greater than V
WH. Hence, we quantify the systematic error on the spatial distribution of the mass computed around the volcano carried out
by tephra dispersal models when the particles are assumed to be spherical. 相似文献
103.
Beta-eucryptite as grown by the flux method has been investigated by in-situ cold- and hot-stage transmission electron microscopy
(TEM). Using electron diffraction and dark-field TEM imaging, we found no evidence for the merohedral twinning that accompanies
structural collapse at the β-to-α-quartz transition, suggesting a true hexagonal symmetry for the aluminosilicate framework
of β-eucryptite. Selected-area electron diffraction (SAED) patterns exhibited a variety of incommensurate structures along
the three a axes with an average modulation period of about 6.5 a. These modulated structures arise from superperiodic stacking parallel to (100) of two structural units with different Li
configurations. In-situ heating experiments show that the modulated structures undergo a reversible transition to the disordered
modification at elevated temperatures. This transition arises from positional order-disorder of Li ions along the main structural
channels. In addition, it appears that at constant low temperature, electron beam irradiation alone can induce a sequence
of transitions similar to those that are thermally induced from the ordered modification to modulated states.
Received: 12 November 1998 / Revised and accepted: 31 December 1998 相似文献
104.
105.
Benthic control upon the morphology of transported fine sediments in a low‐gradient stream 下载免费PDF全文
The structure of fluvial sediments in streams has environmental implications to contaminant fate, nutrient budgeting and the carbon flux associated with fine particulate organic matter (FPOM). However, the influence of sediment structure is lacking in environmental predictive models. To this end, the present study links field‐based results of sediment aggregate structure to seasonal biological functions in the surface fine‐grained laminae (SFGL) of a low‐gradient stream. Fluvial sediment collection, microscopy and image analysis are used to show that aggregates collected over a 20 month time period support the concept that aggregate structure can vary seasonally in low‐gradient streams where temporarily stored sediment is prominent. Results show that the structure of the transported aggregates is more irregular in the summer with the structure being elongated about the long axes. In the winter, the aggregate structure is compacted and more spherical. Statistical analysis and results suggest that heterotrophic and autotrophic biological activity within the SFGL exhibits seasonal control upon the morphology of transported sediments. Implications of this research are highlighted through calculations of the reactive surface area of the transported suspended sediment load. The surface area of transported sediment is estimated to be 40% greater in the summer as compared to the winter time period, which implies that (i) the affinity of sediments to sorb contaminants is higher in summer months and (ii) the downstream reactivity of FPOM in large rivers, lakes and estuaries is not just a function of microbial drivers but also the seasonally dependent structure of transported FPOM derived from low‐order streams. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
106.
The limited depth of focus of microscope optics precludes the observation of a three-dimensional surface in a single view. For an efficient operation of a planetary microscope observing a highly irregular surface, an autofocus algorithm must detect partially focused views and merge them into a completely focused image (extended depth of focus). In this paper we investigate the suitability of different algorithms for autonomous image focusing onboard a Mars lander. We show that all methods under study, except for the Variance method, produce reasonable results and that their performance depends (amongst other factors) on sample morphology. For reasons of simplicity and reduced computational requirements we favor Gradient and Roberts methods and present an efficient implementation thereof. 相似文献
107.
Stephan A. Klapp Gerhard Bohrmann Werner F. Kuhs M. Mangir Murshed Thomas Pape Helmut Klein Kirsten S. Techmer Katja U. Heeschen Friedrich Abegg 《Marine and Petroleum Geology》2010
Gas hydrate samples from various locations in the Gulf of Mexico (GOM) differ considerably in their microstructure. Distinct microstructure characteristics coincide with discrete crystallographic structures, gas compositions and calculated thermodynamic stabilities. 相似文献
108.
<正>A new genus Microelectrona gen.nov.and species Microelectrona cladara sp.nov.of the extinct tribe Protodikraneurini of the leafhoppers(Cicadeilidae:Typhlocybinae) from the Eocene Baltic amber is described. The piece of amber containing leafhopper inclusion is broken,unveiling some of the morphological structures,and enabling their studies using scanning electron microscopy. 相似文献
109.
Paul F. Schofield Andrew D. Smith J. Frederick W. Mosselmans Hendrik Ohldag Andreas Scholl Simone Raoux Gordon Cressey Barbara A. Cressey Paul D. Quinn Caroline A. Kirk Simon C. Hogg 《Geostandards and Geoanalytical Research》2010,34(2):145-159
This work describes the application of microfocus X-ray absorption spectroscopy (XAS) and X-ray photo-emission electron microscopy (XPEEM) to the study of the complex mineralogical intergrowths within the Santa Catharina meteorite. The Santa Catharina meteorite of this study (BM52283 from the meteorite collection of the Natural History Museum, London, UK) primarily comprises a taenite bulk host phase (Fe:Ni ratio = 70.9 ± 0.8%:29.1 ± 0.8%) with a set of oxide-bearing cloudy zone textured regions (Fe:Ni:O ratio = 40.4 ± 0.3%:49.0 ± 0.7%:10.6 ± 0.8% at the core and Fe:Ni:O ratio = 34.4 ± 1.5%:42.7 ± 0.6%:22.9 ± 1.8% towards the rims) and numerous schreibersite (Fe:Ni:P ratio = 38.6 ± 1.6%:38.4 ± 0.9%:23.0 ± 0.5%) inclusions. Between the schreibersite and the taenite are rims up to 50 μm across of Ni-rich kamacite (Fe:Ni ratio = 93.4 ± 0.4%:6.6 ± 0.5%). No chemical zoning or spatial variations in the Fe and Ni speciation was observed within either the schreibersite or the kamacite phases. The oxide-bearing cloudy zone textured regions mostly comprise metallic Fe–Ni alloy, predominantly tetrataenite. Within the oxide phases, the Fe is predominantly, but not entirely, tetrahedrally co-ordinated Fe3+ and the Ni is octahedrally co-ordinated Ni2+. Structural analysis supports the suggestion that non-stoichiometric Fe2NiO4 trevorite is the oxide phase. The trevorite:tetrataenite ratio increases at the edges of the oxide-bearing cloudy zone textured regions indicating increased oxidation at the edges of these zones. The spatial resolution of the XPEEM achieved was between 110 and 150 nm, which precluded the study of either the previously reported ∼ 10 nm precipitates of tetrataenite within the bulk taenite or any antitaenite. 相似文献
110.
Soils in the Knersvlakte are particularly prone to crusting and have lower inherent infiltrability than other soils across western southern Africa. Micromorphological techniques were used to examine the structure and porosity of soil crusts in the Knersvlakte to ascertain why crusting is so intense in this region. Quantile regression using boundary lines was employed to examine the relationships between infiltrability and soil properties for all samples (n = 67). This analysis showed that infiltrability is potentially maximal at low water- dispersible 'clay plus silt' content and low silt content (r^2 = 0.72 and 0.64; respectively, n = 67) (Figure 2). The strength of crusts, pH, EC, clay mineralogy, and water-dispersible clay, silt and 'clay plus silt' content were compared, and a pore analysis using optical microscopy was undertaken on images of six soil thin sections (n = 6) (circular and parallel polarizers). Pore analysis was further undertaken on five horizontal slices of equal dimensions taken through each soil thin section. The porosity samples with low infiltrability (〈 100 mm·hr^-1, n = 4) had greater crust strength, lower porosity (both total and in the least porous slice) and greater water-dispersible 'day plus silt' and silt content than the porosity samples with high infiltrability (〉 100mm·hr^-1, n = 2). The porosity samples with low infiltrability showed a trend of lower pH and greater water dispersible clay percentage. Porosity varied within the porosity samples due to the presence of dense clay/silt bands (〈 0.5 mm in width) with relatively few air vesicles. The porosity samples with horizontal slices of low porosity (but large numbers of air vesicles) had low infiltrability, while those without slices of low porosity (and relatively few air vesicles) had high infiltrability. We conclude that the intense crusting and resultant low infiltrability of soils in the Knersvlakte appears to be related to the formation of thin, dense clay/silt bands in the pedoderm. 相似文献