Critical antecedent rainfall conditions for shallow landslides in Chittagong City of Bangladesh   总被引：4，自引：2，他引：2  

Younus Ahmed Khan  Habibah Lateh  M. Azizul Baten  Anton Abdulbasah Kamil 《Environmental Earth Sciences》2012,67(1):97-106

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Single-crystal EPR study of three radiation-induced defects (Al–O2 3?, Ti3+ and W5+) in stishovite     

Yuanming Pan  Mao Mao  Zucheng Li  Sanda M. Botis  Rudolf I. Mashkovtsev  Anton Shatskiy 《Physics and Chemistry of Minerals》2012,39(8):627-637

Single-crystal electron paramagnetic resonance spectra of electron-irradiated stishovite, measured at temperatures from 3.5 to 294?K, reveal three S?=?1/2 radiation-induced defects: an aluminum-associated oxygen hole center and two nd ¹ centers (Ti³⁺ and W⁵⁺). The aluminum-associated oxygen hole center, characterized by an orthorhombic site symmetry, coaxial matrices of the electronic Zeeman g, nuclear hyperfine A(²⁷Al) and nuclear quadrupole P(²⁷Al), and the orientation of the g-minimum axis along an O–O direction and those of the unique A(²⁷Al) and P(²⁷Al) axes perpendicular to the O–O direction, is an Al–O₂ ^3? center, with the unpaired electron equally distributed on two equatorial oxygen atoms of a substitutional Al³⁺ ion at the octahedral Si site. Fully optimized Al-doped structure, theoretical ²⁷Al nuclear hyperfine and quadrupole coupling constants and directions, and 3D spin densities from periodic hybrid density functional theory calculations provide further support for this structural model. Spin Hamiltonian parameters of the Ti³⁺ and W⁵⁺ centers, which are confirmed by their diagnostic ⁴⁷Ti, ⁴⁹Ti and ¹⁸³W hyperfine structures, arise from electron trapping on substitutional Ti⁴⁺ and W⁶⁺ ions at the octahedral Si site.  相似文献   

Spectroscopic characterisation and crystal field calculations of varicoloured kyanites from Loliondo, Tanzania     

Manfred Wildner  Anton Beran  Friedrich Koller 《Mineralogy and Petrology》2013,107(2):289-310

Orange, ochre-coloured, light green and dark blue varieties of kyanite, ideally Al₂SiO₅, from Loliondo, Tanzania, have been characterised by electron microprobe analysis and polarised infrared and optical absorption spectroscopy. All colour varieties show elevated Fe contents of 0.39 to 1.31 wt.% FeO, but Ti contents only in the range of the EMP detection limit. Orange and ochre-coloured crystals have Mn contents of 0.23 and 0.06 wt.% MnO, respectively, the dark blue kyanite contains 0.28 wt.% Cr₂O₃, while the light green sample is nearly free from transition metal cations other than Fe. Polarised infrared spectra reveal OH defect concentrations of 3 to 17 wt.ppm H₂O with structural OH defects partially replacing the O_B (O2) oxygen atoms. Polarised optical absorption spectra show that the colour of all four varieties is governed by crystal field d-d transitions of trivalent cations, i.e. Fe³⁺ (all samples), Mn³⁺ (orange and ochre) and Cr³⁺ (blue kyanite), replacing Al in sixfold coordinated triclinic sites of the kyanite structure. Intervalence charge transfer, the prevalent colour-inducing mechanism in ‘usual’ (Cr-poor) blue kyanites, seems to play a very minor, if any, role in the present samples. Crystal field calculations in both a ‘classic’ tetragonal and in the semiempirical Superposition Model approach, accompanied by distance- and angle-least-squares refinements, indicate that Fe³⁺ preferably occupies the Al4 site, Cr³⁺ prefers the Al1 and Al2 sites, and Mn³⁺ predominantly enters the Al1 site. In each case specific local relaxation effects were observed according to the crystal chemical preferences of these transition metal cations. Furthermore, the high values obtained in the calculations for the interelectronic repulsion parameter Racah B correspond to a high ionic contribution to Me³⁺–O bonding in the kyanite structure. In the particular case of the blue sample, band positions specifically related to the high Racah B value enable this ‘unusual’ type of blue colouration of kyanite solely due to Cr³⁺ cations.  相似文献   

岩溶表层带水生动物研究进展   总被引：2，自引：1，他引：1  

刘伟  周翠英  袁爱华  BRANCELJ Anton 《中国岩溶》2016,35(6):712-719

本文旨在介绍岩溶表层带水生生态研究中微小甲壳类生物的最新研究进展,相关研究国内还少有涉及。岩溶表层带不仅仅是岩溶地下含水层的一个重要组成,而且是岩溶发育的活跃地带,同时也是大量地下生物生存的栖息地。目前,岩溶表层带内甲壳类主要采自洞穴滴水,残留的滴水水洼以及裂隙中的水体。这些甲壳类主要是桡足类,也有其他甲壳类,如端足目和介形虫,它们主要为暗层生物（stygobiont）,也包括一些陆生物种。以斯洛文尼亚为例,在所调查的洞穴中平均每个洞穴有近9个暗层桡足类物种,为了适应表层带特殊的地质环境,这些物种在形体上存在适当的进化。表层带的众多地质因子如顶板厚度、栖息地的连通性、及栖息地的大小等,以及水文因子包括水文动态特征、水化学特征等,都对这些物种的组成与分布有较大的影响。虽然岩溶表层带及其水生动物的独特性和重要性已逐步得到了许多地质学家和生物学家的认可,但还有很多问题有待进一步的解答,譬如邻近群落间差异性,以及桡足类对非饱和带水流指示作用等。   相似文献   

Pitfalls of microseismic data inversion in the case of strong anisotropy     

Sergey Yaskevich  Georgy Loginov  Anton Duchkov  Alexandr Serdukov 《应用地球物理》2016,13(2):326-332

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Location Performance and Detection Magnitude Threshold of the Romanian National Seismic Network     

Antonino D’Alessandro  Anton D?ne?  Bogdan Grecu 《Pure and Applied Geophysics》2012,169(12):2149-2164

Romania is an earthquake prone area with a few destructive earthquakes per century. The National Institute for Earth Physics carries out the seismic survey of Romania through the Romanian National Seismic Network (RNSN) consisting of 65 real-time seismic stations. Daily reports and monthly bulletins are delivered after routinely analyzing and processing the recorded data. In the present paper we applied the Seismic Network Evaluation through Simulation method for the RNSN configuration as it was in August 2011 to estimate the background noise level, assess the appropriateness of the velocity model adopted in routine location procedure, evaluate the hypocenter location uncertainty and determine the detection magnitude threshold. Areas of greater (southern Romania) and lower (Carpathians and Apuseni Mountains) background noise within the RNSN are identified by mapping the average power of noise in 1–12?Hz frequency range. The statistical study of the P and S phases residual times allow us to assess the appropriateness of the velocity model used in routine location. Both P- and S-wave velocity models can be optimized to improve the quality of the hypocenter location. As shown by our analysis, the RNSN is able to detect and locate earthquakes with M _L magnitude above 2.5 anywhere on the Romanian territory, except the border areas, such as the Crisana–Maramures seismic source zone. Merging data from both sides of the border significantly improves the quality of hypocenter location in these areas.  相似文献   

Spring mating period in Orconectes limosus: the reason for movement     

Miloš Buřič  Antonín Kouba  Pavel Kozák 《Aquatic Sciences - Research Across Boundaries》2009,71(4):473-477

Thirteen adult Orconectes limosus males (carapace length 32.5 ± 2.48 mm; weight 10.8 ± 2.63 g) were radio-tagged and tracked during and after the spring mating period, April–June 2008. Average distances moved per day were higher in the mating period (14.9 ± 21.4 m) due to mate searching activity. During the mating period, movement did not correlate with water temperature, and crayfish were active during daylight hours. They moved rapidly upstream and downstream, a maximum 118 and 95 m per day, respectively. When water temperature increased over 10°C, this initiated the end of mating and the start of spawning, and the spring migration abruptly ceased. An influence of water temperature on movements was observed during the non-reproductive period. Orconectes limosus was highly mobile in small watercourses, signifying a threat of penetration into native crayfish habitats, and potentially enabling the transmission of crayfish plague. This threat was increased during the mating period due to increased activity.  相似文献   

A critical evaluation of calcium isotope ratios in tests of planktonic foraminifers   总被引：1，自引：0，他引：1  

Nikolaus Gussone  Bärbel Hönisch  Anton Eisenhauer  Christoph Hemleben 《Geochimica et cosmochimica acta》2009,73(24):7241-5818

We critically evaluate the applicability of Ca-isotope ratios in planktonic foraminifers as proxy for past sea surface temperatures (SST) and isotope composition of paleo-seawater (δ⁴⁴Ca_sw) reconstructions. Previous studies have shown discrepancies regarding the temperature sensitivity of Ca isotope fractionation in foraminifers of more than one order of magnitude. We present new data from the planktonic foraminifer species Orbulina universa, Globigerinoides sacculifer and Neogloboquadrina pachyderma (sinistral) from culture experiments, multinet deployments and coretop samples. Specimens of G. sacculifer cultured at low salinities (33-34.5) show predominantly no major temperature dependent Ca isotope fractionation, in contrast to previous individuals cultured at higher salinities of 34.5-36. The new data of O. universa are consistent with previously published results, revealing a small but significant temperature sensitivity. Calcium isotope fractionation in tests of N. pachyderma shows a significant variation with temperature, which is not uniform over the total investigated temperature range (−1.6 °C to +10 °C), possibly reflecting the influence of additional controlling factors besides temperature. Controlled dissolution experiments in the laboratory indicate that the Ca-isotope composition of G. sacculifer and N. pachyderma is relatively insensitive to partial dissolution of their tests.Calcium isotope ratios in the planktonic foraminifers G. sacculifer and N. pachyderma (s) reveal a complex Ca isotope fractionation behaviour, which is not yet fully understood. Additional validation studies are crucial to enhance the basic understanding of the calcium isotope systematics in planktic foraminifer shells, and the potential for applying Ca-isotope ratios as proxies for seawater temperature and the oceanic Ca budget.  相似文献   

The Rožná uranium deposit (Bohemian Massif, Czech Republic): shear zone-hosted, late Variscan and post-Variscan hydrothermal mineralization     

Bohdan Kříbek  Karel Žák  Petr Dobeš  Jaromír Leichmann  Marta Pudilová  Miloš René  Bohdan Scharm  Marta Scharmová  Antonín Hájek  Daniel Holeczy  Ulrich F. Hein  Bernd Lehmann 《Mineralium Deposita》2009,44(1):99-128

Three major mineralization events are recorded at the Rožná uranium deposit (total mine production of 23,000 t U, average grade of 0.24% U): (1) pre-uranium quartz-sulfide and carbonate-sulfide mineralization, (2) uranium, and (3) post-uranium quartz-carbonate-sulfide mineralization. (1) K–Ar ages for white mica from wall rock alteration of the pre-uranium mineralization style range from 304.5 ± 5.8 to 307.6 ± 6.0 Ma coinciding with the post-orogenic exhumation of the Moldanubian orogenic root and retrograde-metamorphic equilibration of the high-grade metamorphic host rocks. The fluid inclusion record consists of low-salinity aqueous inclusions, together with H₂O-CO₂-CH₄, CO₂-CH₄, and pure CH₄ inclusions. The fluid inclusion, paragenetic, and isotope data suggest that the pre-uranium mineralization formed from a reduced low-salinity aqueous fluid at temperatures close to 300°C. (2) The uraniferous hydrothermal event is subdivided into the pre-ore, ore, and post-ore substages. K–Ar ages of pre-ore authigenic K-feldspar range from 296.3 ± 7.5 to 281.0 ± 5.4 Ma and coincide with the transcurrent reorganization of crustal blocks of the Bohemian Massif and with Late Stephanian to Early Permian rifting. Massive hematitization, albitization, and desilicification of the pre-ore altered rocks indicate an influx of oxidized basinal fluids to the crystalline rocks of the Moldanubian domain. The wide range of salinities of fluid inclusions is interpreted as a result of the large-scale mixing of basinal brines with meteoric water. The cationic composition of these fluids indicates extensive interaction with crystalline rocks. Chlorite thermometry yielded temperatures of 260°C to 310°C. During this substage, uranium was probably leached from the Moldanubian crystalline rocks. The hydrothermal alteration of the ore substage followed, or partly overlapped in time, the pre-ore substage alteration. K–Ar ages of illite from ore substage alteration range from 277.2 ± 5.5 to 264.0 ± 4.3 Ma and roughly correspond with the results of chemical U–Pb dating of authigenic monazite (268 ± 50 Ma). The uranium ore deposition was accompanied by large-scale decomposition of biotite and pre-ore chlorite to Fe-rich illite and iron hydrooxides. Therefore, it is proposed that the deposition of uranium ore was mostly in response to the reduction of the ore-bearing fluid by interaction with ferrous iron-bearing silicates (biotite and pre-ore chlorite). The Th data on primary, mostly aqueous, inclusions trapped in carbonates of the ore substage range between 152°C and 174°C and total salinity ranges over a relatively wide interval of 3.1 to 23.1 wt% NaCl eq. Gradual reduction of the fluid system during the post-ore substage is manifested by the appearance of a new generation of authigenic chlorite and pyrite. Chlorite thermometry yielded temperatures of 150°C to 170°C. Solid bitumens that post-date uranium mineralization indicate radiolytic polymerization of gaseous and liquid hydrocarbons and their derivatives. The origin of the organic compounds can be related to the diagenetic and catagenetic transformation of organic matter in Upper Stephanian and Permian sediments. (3) K–Ar ages on illite from post-uranium quartz-carbonate-sulfide mineralization range from 233.7 ± 4.7 to 227.5 ± 4.6 Ma and are consistent with the early Tethys-Central Atlantic rifting and tectonic reactivation of the Variscan structures of the Bohemian Massif. A minor part of the late Variscan uranium mineralization was remobilized during this hydrothermal event.  相似文献   

微波消解法在水泥工业样品分析中的应用     

奥地利安东帕有限公司 《岩矿测试》2009,28(2):202

在过去的几年中,辅助燃料(如旧轮胎和塑料垃圾)在水泥行业应用越来越重要,不仅是价格原因,更重要的是这些应用在经济和环境方面对于处理废弃材料起到了重要作用。水泥回转窑的高温是塑料垃圾焚烧的最好条件。旧轮胎作为辅助燃料的应用已经很长时间了,因为它们的材料、反应行为及对最终产品的影响都已经得到了很好的认知,而塑料垃圾的分析相对比较困难。如塑料瓶子及塑料薄膜往往添加各种不同的色素及添加剂。水泥对锌和其他痕量元素非常敏感,尤其是氯元素。因此,在燃烧前,必须先将PVC材料挑出,而食品包装材料必须先经过清洗避免氯化钠残留而带入氯元素。这就是粉碎垃圾需要完全消解及分析的关键原因。因为垃圾的组成是不均一的,完全  相似文献