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991.
M. N.?TaranEmail author A. N.?Tarashchan H.?Rager St.?Schott K.?Schürmann W.?Iwanuch 《Physics and Chemistry of Minerals》2003,30(9):546-555
Variously colored gem-quality topazes from Ouro Preto, Minas Gerais, Brazil, were studied by optical absorption spectroscopy and photoluminescence methods. In the near infrared range (750–2500 nm) the absorption spectra display an identical pattern of narrow intense absorption lines caused by overtones and combination vibrations of OH groups, which do not relate to the coloration of the topazes studied. Their colors were found to be caused by combination of three sets of absorption features, (1), (2), and (3) in the visible and near-UV range, which are due to different color center. (1) denotes a pair of broad split bands with maxima 18 000 and 25 000 cm–1 caused by electronic spin-allowed dd transitions of Cr3+ ions. They cause a light rose to deep violet color and characteristic pleochroism of Cr3+-containing topazes. Photoluminescence evidences of at least three different types of Cr3+ complexes which, most probably, differ by ligand surroundings, O4F2, O4F(OH) and O4(OH) (2) Corresponds to the intense weakly polarized UV absorption edge. Two different parts, the thermally stable one, caused by ligand-to-metal charge transfer, and the thermally unstable one, caused by some defect center(s), contribute to the edge. (3) denotes a system of two broad unstructured bands with maxima around 19 000 cm–1 (X>Y Z) and 24 000 cm–1 (Y Z
X). They cause the unique orange color and characteristic pleochroism of Brazilian Imperial topazes. Combinations of (1) and (3) absorption features cause various yellow-rose colors of the samples. Investigations of natural irradiated and thermally treated topazes show that the color centers (1) and (3) transform to each other at annealing and X- or gamma irradiation. The color of natural orange-red Imperial topazes is assumed to be caused by Cr4+, stabilized by other impurity ions and/or defect irradiation EPR centers. At T=300 °C Cr4+ reduces to Cr3+, the color of Imperial topazes changes to pale rose, caused by spin-allowed bands of Cr3+. In artificially irradiated crystals the (3)-center, Cr4+, may be induced according to the reaction 2Cr3+ Cr4+ + Cr2+, which involves chromium pairs in adjacent Al sites of the structure. Such artificially induced color is unstable at room temperature and in daylight. The process of the decay of (3)-centers may be described as a recombination Cr4++Cr2+ 2Cr3+ that results in vanishing of the (3)-bands accompanied by the appearance or increase in Cr3+
dd bands, the original orange color turning to a pale rose. 相似文献
992.
Gerhard Vavra 《Contributions to Mineralogy and Petrology》1994,117(4):331-344
The internal morphologies of zircon crystals from different types of granitoids (alkaline, calcalkaline and anatectic) are revealed by cathodoluminescence imaging and are described in terms of growth rates of the crystal faces relative to each other. Zircons in the alkaline granitoids are characterized by high and constant growth rates of {010} relative to the pyramidal forms and by symmetric grwoth of {011}. Zircons in the calcalkaline and anatectic granitoids are characterized by fluctuating or gradually decreasing relative growth rates of {010}, by asymmetric and highly variable growth of {011}, and by a tendency of {110} to become grwoth-inhibited. Corrosion events are interspersed during zircon growth in the calcalkaline magmas. In the calcalkaline and anatectic magmas, a discontinuity breaks the morphological evolution at late stages of crystallization. The discontinuity coincides with a sharp drop in cathodoluminescence. The growth behaviour of each crystal form is analysed and compared with predictions made by the periodic bond chain (PBC) theory. It is argued that the relative growth rate of {010} depends on supersaturation, that the growth rates of {011} faces are changed in response to different ratios of adsorbing cations (Na, K, Al), and that {110} faces become growth-inhibited by the adsorption of H2O or trace elements enriched in the residual liquid. Morphological and chemical discontinuities at late stages of crystallization are reasonably explained by the formation of larger growth units (from smaller ionic entities) in the residual liquid. Important factors controlling the zircon morphology in different types of granitoids are: high cooling rates (alkaline magmas), magma mixing (calcalkaline magmas), enrichment of H2O and trace elements in residual liquids (calcalkaline and anatectic magmas), and the major element chemistry of the magma, possibly the ratio of Na and K to Al (agpaicity). 相似文献
993.
Images from the High Resolution Stereo Camera on Mars Express reveal the surface of the Red Planet in unprecedented detail – and should have the whole planet mapped at high resolution in just two years. Over the next six pages, Ernst Hauber and Gerhard Neukum set the scene and reveal some of the spectacular images already captured.
(All images are courtesy of ESA/DLR/FU Berlin/G Neukum unless otherwise credited.) 相似文献
(All images are courtesy of ESA/DLR/FU Berlin/G Neukum unless otherwise credited.) 相似文献
994.
2006年冬末春初,在德国POLARSTERN科学考察船执行南极威德尔海西北海域考察期间,调查了考察区海冰物理和海洋生物。本文观测了航线上钻取的27支海冰冰芯的组构和71个冰晶体薄片;分析得到393组冰温数据;348组盐度、密度数据和311组叶绿素a和脱镁叶绿素含量数据;通过302组冰内相同深度孔隙率和叶绿素a含量数据分析,发现海冰物理参数影响冰内叶绿素a含量的新证据;利用收集的雪、冰厚度数据以及环境容量制约生态平衡的规律,建立了雪、冰厚度对冰底叶绿素繁荣的影响以及;确立了南极粒状冰和柱状冰内叶绿素a上限含量同卤水体积的关系。从而表达了冰晶体对卤水排泄的效应和冰物理性质对南极春季冰底和冰-水界面叶绿素a增长的贡献。此外,还得出海冰物理性质影响冰藻,并且是南极冰区水体浮游植物繁荣的关键控制因素。 相似文献
995.
Andreas Borchers Elisabeth Dietze Gerhard Kuhn Oliver Esper Ines Voigt Kai Hartmann Bernhard Diekmann 《Marine Geophysical Researches》2016,37(1):49-70
A multi-proxy study including sedimentological, mineralogical, biogeochemical and micropaleontological methods was conducted on sediment core PS69/849-2 retrieved from Burton Basin, MacRobertson Shelf, East Antarctica. The goal of this study was to depict the deglacial and Holocene environmental history of the MacRobertson Land–Prydz Bay region. A special focus was put on the timing of ice-sheet retreat and the variability of bottom-water formation due to sea ice formation through the Holocene. Results from site PS69/849-2 provide the first paleo-environmental record of Holocene variations in bottom-water production probably associated to the Cape Darnley polynya, which is the second largest polynya in the Antarctic. Methods included end-member modeling of laser-derived high-resolution grain size data to reconstruct the depositional regimes and bottom-water activity. The provenance of current-derived and ice-transported material was reconstructed using clay-mineral and heavy-mineral analysis. Conclusions on biogenic production were drawn by determination of biogenic opal and total organic carbon. It was found that the ice shelf front started to retreat from the site around 12.8 ka BP. This coincides with results from other records in Prydz Bay and suggests warming during the early Holocene optimum next to global sea level rise as the main trigger. Ice-rafted debris was then supplied to the site until 5.5 cal. ka BP, when Holocene global sea level rise stabilized and glacial isostatic rebound on MacRobertson Land commenced. Throughout the Holocene, three episodes of enhanced bottom-water activity probably due to elevated brine rejection in Cape Darnley polynya occured between 11.5 and 9 cal. ka BP, 5.6 and 4.5 cal. ka BP and since 1.5 cal. ka BP. These periods are related to shifts from warmer to cooler conditions at the end of Holocene warm periods, in particular the early Holocene optimum, the mid-Holocene warm period and at the beginning of the neoglacial. In contrast, between 7.7 and 6.7 cal. ka BP, brine rejection shut down, maybe owed to warm conditions and pronounced open-water intervals. 相似文献
996.
Late Turonian, Coniacian and Santonian source rock samples from a recently drilled well (Tafaya Sondage No. 2; 2010) in the Tarfaya Basin were analyzed for quantity, quality, maturity and depositional environment of the organic matter (OM). To our knowledge such a thick sequence of organic matter-rich Turonian to Santonian source rocks was investigated in that great detail for the first time. Organic geochemical and organic petrological investigations were carried out on a large sample set from the 200 m thick sequence. In total 195 core samples were analyzed for total organic carbon (Corg), total inorganic carbon contents and total sulfur (TS) contents. Rock-Eval pyrolysis and vitrinite reflectance measurements were performed on 28 samples chosen on the basis of their Corg content. Non-aromatic hydrocarbons were analyzed on selected samples by way of gas chromatography–flame ionization detection (GC–FID) and GC–mass spectrometry (GC–MS). The organic matter-rich carbonates revealed a high source rock potential, representing type I kerogen and a good preservation of the organic matter, which is mainly of marine (phytoplankton) origin. HI values are high (400–900 mg/g Corg) and in a similar range as those described for more recent upwelling sediments along the continental slope of North Africa. TS/Corg ratios as well as pristane over phytane ratios indicate variable oxygen content during sediment deposition. All samples are clearly immature with respect to petroleum generation which is supported by maturity parameters such as vitrinite reflectance (0.3–0.4%), Tmax values (401–423 °C), production indices (S1/(S1 + S2) > 0.1) as well as maturity parameters based on ratios of specific steranes and hopanes. 相似文献
997.
998.
Teresa Amaro Harry Witte Gerhard J. Herndl Marina R. Cunha David S.M. Billett 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1834-1843
Deposit-feeding holothurians often dominate the megafauna in bathyal deep-sea settings, in terms of both abundance and biomass. Molpadia musculus is particularly abundant at about 3400 m depth in the Nazaré Canyon on the NE Atlantic Continental Margin. However, these high abundances are unusual for burrowing species at this depth. The objective of this research was to understand the reasons of the massive occurrence of these molpadiid holothurians in the Nazaré Canyon. To address this question we investigated possible trophic interactions with bacteria at sites where the organic content of the sediment was different (Setúbal and Cascais Canyons, NE Atlantic Continental Margin). The molecular fingerprinting technique of Denaturing Gradient Gel Electrophoresis (DGGE) with band sequencing, combined with non-metric multi-dimensional scaling and statistical analyses, was used to compare the bacterial community diversity in canyon sediments and holothurian gut contents. Our results suggest that M. musculus does not need to develop a specialised gut bacterial community to aid digestion where the sediment is rich in organic matter (Nazaré Canyon); in contrast, such a community may be developed where the sediment is poorer in organic matter (Cascais Canyon). 相似文献
999.
Helas Günter Lobert Jürgen Scharffe Dieter Schäfer Luise Goldammer Johann Baudet Jean Ajavon Ayité-Lô Ahoua Brou Lacaux Jean-Pierre Delmas Robert Andreae Meinrat O. 《Journal of Atmospheric Chemistry》1995,22(1-2):217-239
We measured CO2, CO, CH4, H2, and NO2 in air masses polluted by savanna fires over Côte d'Ivoire, western Africa. Elevated concentrations of these trace gases were found in fire plumes and also in extensive haze layers. Trace gas mixing ratios ranged as high as 605 ppmv for CO2, 14.8 ppmv for CO, 2.7 ppmv for CH4, 4.2 ppmv for H2, and 25 ppbv for NO2. We compare our emission ratios to those obtained in previous field and laboratory studies. The emission ratios, expressed as an average and as a range or as an average only, were: dCO/dCO2 5.3×10–2 (3–18×10–2); dCH4/dCO 5.3×10–2; dH2/dCO 2.4×10–1 and dNO2/dCO2 1.8×10–4 (1.5–2.2×10–4). The values found match those found during similar measurements, though our results point to rather vigorous burning in the savanna of western Africa. 相似文献
1000.
W. Schüepp 《Theoretical and Applied Climatology》1960,10(3):311-341
Résumé Une étude théorique permet d'estimer les sommes journalières soit du rayonnement global tombant sur un récepteur plan et horizontal, soit du rayonnement sphérique ou circumglobal tombant sur une sphère. Ces deux sommes dépendent fortement des conditions atmosphèriques: atmosphère pure, brume, humidité et nébulosité, ainsi que de la latitude géographique, de la déclinaison du soleil et de l'albédo du sol. On montre qu'il est quand-même possible de trouver une relation du deuxième ou troisième degré entre les deux types de mesures où les coefficients ne dépendent que de la différence – entre latitude et déclinaison et de l'albédo du sol. Cette relation est valable dans les basses latitudes <30° avec une faible dispersion des valeurs journalières; dans les latitudes plus élevées sa validité semble limitée au semestre estival.
Avec 8 Figures 相似文献
Summary The daily totals of radiation falling on a horizontal receiver as well as on a spherical one are calculated by theoretical approach. Both types of values change very much with atmospherical conditions, such as pure atmosphere, haze and humidity of the atmosphere and cloudiness and furthermore with the geographical latitude, the declination of sun and finally with the albedo of the ground. It is demonstrated that it is nevertheless possible to establish a relation of second or third order between both these types of values. The coefficients are function only of –, the difference between latitude and declination and of the albedo . This relation is valid in low latitudes <30° for daily totals; in higher latitudes its validity is limited to days of the summer period.
Zusammenfassung Auf theoretischem Wege werden die Tagessummen sowohl der auf einen horizontalen Empfänger fallenden Globalstrahlung von Sonne und Himmel als auch der auf eine Kugel fallenden Zirkumglobalstrahlung ermittelt. Beide Werte hängen sehr stark von den atmosphärischen Verhältnissen, wie Reinheit der Atmosphäre, Dunst, Feuchtigkeit und Bewölkung, sowie von der geographischen Breite, der Deklination der Sonne und der Albedo der Bodenoberfläche ab. Es wird nun gezeigt, daß es trotzdem möglich ist, eine Beziehung zweiten oder dritten Grades zwischen den beiden Arten von Tagessummen herzuleiten, in der die Koeffizienten nur von der Differenz – zwischen geographischer Breite und Deklination der Sonne einerseits und der Albedo andererseits abhängen. Diese Beziehung gilt in niederen Breiten <30° für alle Einzelwerte, in höheren Breiten nur im Sommerhalbjahr.
Avec 8 Figures 相似文献