Thermal stability of extended clusters in dravite: a combined EMP,SREF and FTIR study     

Ferdinando Bosi  Henrik Skogby  Tonči Balić-Žunić 《Physics and Chemistry of Minerals》2016,43(6):395-407

A dravite from Yemen of near end-member composition was treated in air and hydrogen atmospheres at 600–900 °C to reveal changes in Mg and Al order over the octahedrally coordinated Y and Z sites, and to explore related changes in the characteristic vibrational bands in the principal (OH)-stretching frequency. Relevant information was obtained using electron microprobe analysis (EMPA), structural refinement (SREF) and polarized infrared (IR) single-crystal spectroscopy. Overall, the EMPA, SREF and IR data show that only minor changes occur during thermal treatment up to at least 800 °C, including variations in structural parameters, Mg–Al order–disorder and (OH)-stretching bands, indicating limited hydrogen loss. Untreated and treated dravite samples have very similar long-range and short-range atomic structures, which may be related to the occurrence of stable Al–Mg extended clusters around the O1 (=W) and O3 (=V) sites: ^W(F)–^Y(MgMgMg)–^V(OH)₃–^Z[AlAlAlAlAl(Al,Mg)]; ^W(OH)–^Y(MgMgAl)–^V(OH)₃–^Z[AlAlAlAlAl(Al,Mg)]; ^W(O^2–)–^Y(AlAlAl)–^V(OH)₃–^Z[AlAlAlAlAl(Al,Mg)]. These extended clusters remain stable to temperatures close to the observed start of decomposition (~900 °C).  相似文献   

A method for estimating microporosity of fine‐grained sediments and sedimentary rocks via scanning electron microscope image analysis          下载免费PDF全文

Michael Nole  Hugh Daigle  Kitty L. Milliken  Maša Prodanović 《Sedimentology》2016,63(6):1507-1521

This study presents a method of two‐dimensional scanning electron microscope image analysis that directly quantifies microporosity abundance in clay‐rich, fine‐grained sediments. The method is novel in that it is specifically designed to circumvent the challenge to porosity quantification posed by mineral surface charging and topographical artifacts created during Ar‐ion cross‐section polishing. It utilizes the finding that differences in circularity values can be used to distinguish micropores from blemishes in a thresholded image. This method is powerful because it is fast and provides a direct microporosity estimation technique to augment or replace experimental data. The pore size range to which the method is applicable is clear and can be selected depending on the application of the analysis. When used appropriately, the method can be implemented on microporous sediments and sedimentary rock in general. The method is developed using marine muds of Pliocene and Miocene ages from the Nankai margin (burial depths from approximately 200 to 1100 m). The close match between imaging‐derived microporosity and bulk N₂ microporosity measurements shows that porosity in these young and relatively shallowly buried sediments is dominated by pores of sizes that can be imaged by scanning electron microscopy. In Kumano, forearc basin sediments of the Nankai Trough, results of this method show a significant increase in microporosity with burial depth, probably due to microporosity preservation during compaction and possibly early volcanic ash diagenesis.  相似文献   

Metal concentrations around thermal power plants,rural and urban areas using honeybees (Apis mellifera L.) as bioindicators     

N. M. Zarić  K. Ilijević  L. Stanisavljević  I. Gržetić 《International Journal of Environmental Science and Technology》2016,13(2):413-422

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Analysis of the Drava and Danube rivers floods in Osijek (Croatia) and possibility of their coincidence     

Lidija Tadić  Ognjen Bonacci  Tamara Dadić 《Environmental Earth Sciences》2016,75(18):1238

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Manganese mineralization in andesites of Brestovačka Banja,Serbia: evidence of sea-floor exhalations in the Timok Magmatic Complex     

Aleksandar Pačevski  Vladica Cvetković  Kristina Šarić  Miodrag Banješević  Heidi Eva Hoefer  Aleksandar Kremenović 《Mineralogy and Petrology》2016,110(4):491-502

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Spatial indices for measuring three-dimensional patterns in a voxel-based space     

Anthony Jjumba  Suzana Dragićević 《Journal of Geographical Systems》2016,18(3):183-204

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Limits of warm and cold bioclimatic stress in different climatic regions     

K. Zaninović 《Theoretical and Applied Climatology》1992,45(1):65-70

Summary Limits of warm and cold stress in different climatic regions are determined by means of temperature, wind speed and humidity for the period 1976–1985. These values are measured at 2 PM local time during July for warm stress and at 7 AM local time during January for cold stress. Hvar (20 m ASL) is used to represent maritime climate, Zavian on the top of Mount Velebit (1594 m ASL) and Skrad (668 m ASL) in Gorski Kotar are representative of mountainous climate, and Zagreb (128 m ASL) is representative of continental low-land climate. Values of a biometeorological Temperature-Wind Speed-Humidity (TWH)-index higher than the 98% value of the theoretical distribution fitted to empirical data represent above normal extreme conditions at a given location, and TWH values less than 2% value of the theoretical distribution represent below normal extreme conditions. For similar temperatures, it will be extremely above normal at the top of Mount Velebit (Zavian) whilst normal on the coast (Hvar), and similarly, it will be extremely below normal in Hvar but normal at Zavian.With 4 Figures  相似文献   

An analysis of active close binaries (CB) based on photometric measurements     

Gojko Djurašević 《Astrophysics and Space Science》1992,196(2):267-282

For the purpose of analysing light curves of active CB with an accretion disc being at the evolutional phase of an intensive matter exchange between the components a model for light-curve synthesis has been realized where the attention is given to systems like W Ser not sufficiently examined yet with regard that in them the accretion disc is formed around an ordinary star. In the paper one uses the elements presented in the first paper of this series. The model can successfully describe the essential characteristics of the observed light curves due to existence of an accretion disc and a hot spot, as well as those originated in the temperature distribution along the disc radius. The system components are considered in the framework of the nonsynchronous Roche model and the accretion disc of a constant thickness lies in the orbital plane around the star capturing the matter of the neighbouring component.The primary surrounded by the disc is situated relatively well within the Roche oval and its rotation can be significantly nonsynchronous. Near the Lagrange equilibrium pointL ₁ flows from the secondary (which fills the Roche limit) the gas stream nourishing the disc. In the zone where the stream touches the lateral side of the disc a hot spot is formed.The proposed model enables estimating of the basic orbital and physical parameters of active type W Ser CB (Djuraevi, 1991) on the basis of photometric measurements by applying the inverse-problem method.  相似文献   

Orbital eccentricity study for the spherical component of our galaxy     

Slobodan Ninković 《Astrophysics and Space Science》1987,136(2):299-314

An analysis of the data concerning high-velocity stars from Eggen's catalogue aimed at a determination of the approximate slope of the mass function for the spherical component of our Galaxy, and at estimating the local circular velocity, as well as the local rotation velocity, as by-products, has been performed. Our conclusions are that:

1. A linear dependence of the mass on the radius is very likely;
2. the value of the limiting radius is most likely equal to (40±10) kpc;
3. the two local velocities are approximately equal to each other, being both equal to (230±30) km s^?1;
4. the local escape velocity appears to be most likely equal to (520±30) km s^?1;
5. the total mass of a corona, obtained in this way, is (5±1)×10¹¹ M _⊙.

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The chronostratigraphy of the latest Middle Pleistocene aeolian and alluvial activity on the Island of Hvar,eastern Adriatic,Croatia          下载免费PDF全文

Lara Wacha  Igor Vlahović  Sumiko Tsukamoto  Marijan Kovačić  Ozren Hasan  Davor Pavelić 《Boreas: An International Journal of Quaternary Research》2016,45(1):152-164

Pleistocene aeolian sands and alluvial deposits can frequently be traced along the Mediterranean coast. Such deposits also exist along the eastern Adriatic coast and the nearby islands. Four stratigraphical sections of these deposits were studied on the Island of Hvar with the purpose of establishing a chronological framework of the aeolian–alluvial depositional system, using luminescence dating and magnetic susceptibility stratigraphy. Luminescence dating was applied on coarse‐grained feldspar and quartz grains separated from the sands. Both quartz optically stimulated luminescence (OSL) and feldspar post‐IR infrared stimulated luminescence (pIRIR) age estimates are in good agreement, with values ranging between 167±24 to 120±12 ka (OSL) and 179±18 to 131±18 ka (pIRIR measured at 290 °C) after a fading correction for the pIRIR signal. The results can be clearly correlated to around the end of oxygen isotope stage (OIS) 6 and the beginning of OSI 5, indicating that the aeolian accumulation of sands was a result of the Penultimate Glacial and climate fluctuations at the beginning of the Last Interglacial. Variations in magnetic susceptibility (MS) data can be interpreted alongside these dating results; several stronger peaks detected at the very end of the Penultimate Glacial and the initial stage of the Last Interglacial cycle most probably indicates more intensive pedogenesis resulting from a more favourable climate, probably because of climate changes. Breccias related to major bounding surfaces in association with evidence of soil formation and bioturbation could be the result of more favourable climate conditions and changes during the transition from OIS 6 to OIS 5 (Penultimate Glacial–Last Interglacial). These results are in agreement with similar data from the wider Mediterranean area.  相似文献