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41.
Effect of heat treatment on tourmaline from Brazil 总被引:4,自引:0,他引:4
Cristiane Castañeda Sigrid G. Eeckhout Geraldo Magela da Costa Nilson F. Botelho Eddy De Grave 《Physics and Chemistry of Minerals》2006,33(3):207-216
The crystal-chemical behaviour of tourmaline from Araçuaí, Minas Gerais state, Brazil, when subjected to heating in air atmosphere has been studied by several techniques, including EMPA, UV–Vis, TGA, and Mössbauer spectroscopy. The tourmaline samples are typically intermediate members of the elbaite-schorl series. The origin of colour and of its change after treatment has been discussed in terms of local disorder, presence of metal transition elements, oxidation of ferrous iron at the octahedral site, and simultaneous trap of the excess electron. These findings may be used to enhance the colour in tourmaline crystals or generate wanted colour changes. 相似文献
42.
一次诱发山地灾害突发性暴雨数值模拟及诊断分析 总被引:5,自引:0,他引:5
应用MM5V3.5中尺度非静力数值模式对2003年7月14~15日发生在陕西省一次区域性暴雨过程进行数值模拟和诊断分析,结果发现,西太平洋副热带高压西侧的暖湿气流和新疆冷空气是这次暴雨的主要影响系统,充沛的水汽输送、能量的积聚和强烈的上升运动为暴雨的发生提供了充分的条件,700hPa低涡、切变线是暴雨形成的触发机制.模拟结果表明:涡度场和散度场及垂直上升运动互耦;特强辐合辐散柱的出现早于强涡度柱,而深厚的强气旋性涡柱则几乎与暴雨最强盛时期同时出现. 相似文献
43.
44.
The ability of an atmospheric general circulation model to reproduce fundamental features of the wintertime extratropical Southern Hemisphere (SH) circulation is evaluated with emphasis on the daily variability of the SH mean flow and the mean flow-transient perturbations interaction. Two 10-year simulations using a new version of the LMDZ GCM with a stretched grid scheme centered at 45 °S and forced by climatological SST are performed: a high (144Ꮡ) and low (64Ꭹ) horizontal resolution runs. The performance of both simulations was determined by comparing several simulated fields (zonal wind, temperature, kinetic energy, transient eddy momentum and heat fluxes, Eliassen-Palm fluxes, Eady growth rate and baroclinic conversion term) against the European Centre for Medium Range Weather Forecast reanalyses (ERA). High and low-resolution simulations are similar in many respects; in particular, both experiments reproduce the main patterns of the southern extratropical large-scale circulation satisfactorily. Increasing resolution does not improve universally some spurious aspects of the low resolution simulation (e.g. the cold bias in the high polar troposphere, the debilitated subtropical jet, the low baroclinic conversion rate). Those aspects present little sensitivity to the model resolution. The interaction between transient eddies and zonal mean flow are examined. The low-resolution experiment is able to qualitatively represent the acceleration/deceleration of the mean flow by transient perturbations, south/north of 30 °S with an accuracy similar to that of the high-resolution experiment. Although both experiments represent the baroclinic structure of the mean flow satisfactorily, the model underestimates some transient properties due to the underestimation of the baroclinic conversion term in middle latitudes. Such misrepresentation does not improve with increasing resolution and is related to the relatively weak meridional temperature gradient and the inadequate geographical distribution of the eddy heat fluxes. In particular, the eddy kinetic energy is always underestimated. Eddy kinetic energy does not improve convincingly with increasing resolution, suggesting that the adequate representation of the storm tracks is highly influenced by the physical parametrizations. 相似文献
45.
Mariano Barriendos Javier Martín-Vide Juan Carlos Peña Roberto Rodríguez 《Climatic change》2002,53(1-3):151-170
Meteorological observations in the city of Cádiz are acknowledged as having been made from the middle of the 18th century onwards although they were only recorded and preserved in documentary form from 1789 onwards. Data readings were taken at the new Naval Observatory in San Fernando, ten kilometres from Cádiz, from 1797 onwards. Continuous series for temperature and atmospheric pressure at a daily resolution have been compiled and constructed from 1817 until 1996. The data series is composed of thrice daily observations made at Cádiz (1821–1880) by local observers and hourly data from Naval Observatory at San Fernando (1870–1996). 相似文献
46.
Victor Pinto Xavier Font Miquel Salgot Jose Tapias Tomas Mañá 《Environmental Geology》2002,41(5):495-503
One of the most important environmental impacts resulting from opencast mining, and especially quarries, is the visual impact. Evaluation of this impact considers two aspects: first, the area occupied by the quarry as seen by an observer from a specific place, and, second, the chromatic contrast existing between landscape and exploitation. In this study we develop a methodology to assess the chromatic impact in an objective and comparable form. To assess this impact we developed a method based on image analysis that allows us to obtain from a picture or image its equivalent as a function of chromatic impact, according to the sensibility of the human eye to different wavelengths. The methodology was applied to the Martinenca limestone quarry (Alcanar, Tarragona) and to Cerro Kori Kollo mine, La Joya district (Bolivia). 相似文献
47.
48.
The anisotropy of magnetic susceptibility (AMS) of lava flows is an innovative method which has been proved to be directly related to the shear history of lava. One of the advantages of this method is that it can be used in the absence of other morphological features commonly employed to study the mechanism of emplacement of lava flows. This feature of the AMS method makes it very attractive to gain insight into the mechanism of emplacement of massive, relatively featureless, long lava flows such as those forming flood basalt provinces. In this work, we report the results of the measurement of AMS as a function of vertical position within the Birkett lava flow, one of the Columbia River Basalt Group flows. The observed variation of AMS allows us to identify at least 16 discrete events of lava injection and to estimate the thickness of individual injection events. The AMS-estimated thickness of each injection event (in the range of 0.5-4.0 m) coincides with the range inferred for injected lava pulses in modern Hawaiian lava flows. Thus, the evidence provided by the AMS method supports the notion that at least some flood basalt lava flows were emplaced by the same mechanism as many present-day inflated pahoehoe flows. Regarding the orientation of the principal susceptibilities, in the central part of the flow they define a preferred orientation along an E-W trend, whereas in the outer parts of the flow they have a NNE-SSW trend. This difference in the orientation of the principal susceptibilities is interpreted as the result of a change of flow direction of the lava as emplacement progressed. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00445-002-0203-8. 相似文献
49.
50.
Arantxa Luzón Angel González Arsenio Muñoz Belén Sánchez-Valverde 《Journal of Paleolimnology》2002,28(4):441-456
The lacustrine facies from two sections (Candasnos and Fraga) ofthe Oligocene-Miocene Torrente de Cinca lithostratigraphic Unit in thecentral part of the Ebro Basin (Spain) have been analysed to determine theinfluence of orbital parameters in lacustrine sedimentation. The unit ispredominantly composed of limestones and marls, and represents a shallowlacustrine freshwater system. The sedimentological features of the faciesstudied demonstrate that the lower part of the Candasnos section representsoffshore lacustrine subenvironments whereas the upper part, and the whole ofthe Fraga section, characterise marginal lacustrine areas. Series of stratalthickness variations of limestone, marl, and limestone/marl couplets fromboth sections have been analysed using spectral analysis. This shows thatinformation corresponding to periodic cycles only appears in the offshorefacies, that is to say, in the lower part of Candasnos section, and disappearsin the marginal facies where non-periodic cycles exist. Furthermore, thespectral analysis of the offshore facies highlights the existence of a peak inthe power spectrum with a period of around 7 (6.8 to 7.8) that can berecognised in the field as shallowing-upward lacustrine sequences.Magnetostratigraphic data from the Candasnos section allow us to establish atime span of 2,808 years for the limestone/marl couplet from the lower partof this section, and between 19,000 and 22,000 years for the periodic cycleidentified, thus representing the climatic precession cycle. Shallowingsequences from marginal areas do not correspond with any periodiccycle. 相似文献