Gel synthesis of magnesium silicates: A 29Si magic angle spinning NMR study     

J. Stephen Hartman  Roberta L. Millard 《Physics and Chemistry of Minerals》1990,17(1):1-8

The formation of the magnesium silicate minerals forsterite, enstatite, and roedderite by heating of amorphous “protosilicate” gels precipitated from aqueous solution has been studied by ²⁹Si MAS nmr. Gentle drying of the hydrogels at 110° C gives materials with broad nmr signals that do not differ appreciably with preparation conditions, but the minerals formed by heating at 750° C or higher are greatly dependent on the precipitation and washing conditions of the original gel. The rare mineral roedderite, best known from studies of unequilibrated enstatite chondrite meteorites, becomes a major species along with forsterite when the hydrogels are washed with sodium hydroxide solution before drying and heating to 750° C.  相似文献   

Cs baseline levels in the Mediterranean and Black Sea: A cross-basin survey of the CIESM Mediterranean Mussel Watch programme     

Herv Thbault  Alessia M. Rodriguez y Baena  Bruno Andral  Delko Barisic  Jos Benedicto Albaladejo  Alexandru S. Bologa  Redouane Boudjenoun  Roberta Delfanti  Victor N. Egorov  Tahar El Khoukhi  Heleni Florou  Goran Kniewald  Abdelkader Noureddine  Vasile Patrascu  Mai Khanh Pham  Alfonso Scarpato  Nikolay A. Stokozov  Sayhan Topcuoglu  Michel Warnau 《Marine pollution bulletin》2008,57(6-12):801

The common mussel Mytilus galloprovincialis was selected as unique biomonitor species to implement a regional monitoring programme, the CIESM Mediterranean Mussel Watch (MMW), in the Mediterranean and Black Seas. As of today, and upon standardization of the methodological approach, the MMW Network has been able to quantify ¹³⁷Cs levels in mussels from 60 coastal stations and to produce the first distribution map of this artificial radionuclide at the scale of the entire Mediterranean and Black Seas. While measured ¹³⁷Cs levels were found to be very low (usually <1 Bq kg⁻¹ wet wt) ¹³⁷Cs activity concentrations in the Black Sea and North Aegean Sea were up to two orders of magnitude higher than those in the western Mediterranean Basin. Such effects, far from representing a threat to human populations or the environment, reflect a persistent signature of the Chernobyl fallout in this area.  相似文献   

Intercomparison and Evaluation of Precipitation Forecasts for MAP Seasons 1995 and 1996     

R. Mladek  J. Barckicke  P. Binder  P. Bougeault  N. Brzovic  C. Frei  J. F. Geleyn  J. Hoffman  W. Ott  T. Paccagnella  P. Patruno  P. Pottier  A. Rossa 《Meteorology and Atmospheric Physics》2000,72(2-4):111-129

Summary  The precipitation forecasts of four operational numerical weather prediction models over the Alpine region are evaluated and intercompared for two periods of interest to the Mesoscale Alpine Programme (MAP). The new analysis of Alpine rainfall of Frei and Scha?r (1998) is used to validate the models. It is found that the models have a tendency to overestimate the total precipitation and the frequency of intense rain events over high orography. The skill scores show good consistency between models, except for the ability to forecast light rain or heavy rain events. The partition between convective and stratiform rainfall is rather variable between the models. Received March 15, 1999/Revised July 12, 1999  相似文献   

Underestimation of fine grain quartz OSL dating towards the Eemian: Comparison with palynostratigraphy from Azzano Decimo,northeastern Italy     

Sally E. Lowick  Frank Preusser  Roberta Pini  Cesare Ravazzi 《Quaternary Geochronology》2010,5(5):583-590

Palynostratigraphical records have been used to understand the response of vegetation to climate change, and benefit from independent dating to ensure a robust correlation with global climate and sea-level change. In order to constrain the pollen chronology of a long sedimentary core taken at Azzano Decimo in the Friulian foreland of northeastern Italy, optically stimulated luminescence (OSL) has been applied to fine grain quartz. The samples meet all the standard performance criteria set to test the reliability of the single-aliquot regenerative-dose (SAR) protocol, and still show increasing dose response at 500 Gy. OSL ages are in good agreement with radiocarbon dating and the pollen interpretation down to 70 ka, and with D_e values of ～140 Gy, but below this point, they display an increasing age underestimation towards the Eemian and beyond. The comparison of D_e values measured using both a SAR and single-aliquot regeneration and added-dose (SARA) protocol, confirmed that both were successfully correcting for sensitivity changes in the quartz during measurement of the burial dose, and this was not the reason for the age underestimation. The quartz OSL dose response curve for all samples is best described by a saturating exponential plus linear (SEPL) function. Although all underestimated ages are derived from D_e values that fall on the high dose linear region of this curve, it is unclear if this is the cause of the underestimation.  相似文献   

Production and energy flow in relation to age and shore level in the bivalve Choromytilus meridionalis (Kr.)     

Roberta J. Griffiths 《Estuarine, Coastal and Shelf Science》1981,13(5):477-493

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Fluid inclusions in high-grade gneisses of the Kapuskasing structural zone,Ontario: metamorphic fluids and uplift/erosion path     

Roberta L. Rudnick  Lewis D. Ashwal  Darrell J. Henry 《Contributions to Mineralogy and Petrology》1984,87(4):399-406

Fluid inclusions in quartz grains from five samples of high-grade rocks (two paragneisses, an amphibolite, a mafic gneiss and a tonalite dike) from the 2.7 Ga Kapuskasing structural zone (KSZ), Ontario, were examined with petrographic, microthermometric and laser Raman techniques. Three types of fluid inclusions were observed: CO₂-rich, H₂O-rich and mixed CO₂-H₂O. CO₂-rich fluid inclusions are pseudosecondary or secondary in nature and are generally pure CO₂; a few contain varying amounts of CH₄·H₂O-rich fluid inclusions are secondary in nature, contain variable amounts of dissolved salts, and generally contain daughter crystals. Mixed CO₂-H₂O fluid inclusions occur where trails of H₂O-rich inclusions intersect trails of CO₂-rich inclusions. Isochores for high density (p=1.03 g/cm³) pseudosecondary, pure CO₂ inclusions intersect the lower pressure portion of the estimated P-T field for high-grade metamorphism, implying that pure CO₂ was the peak metamorphic fluid. The variable CH₄ content of CO₂ inclusions within graphite-bearing samples suggests that CH₄ was introduced locally after the formation of the CO₂ inclusions; however the origin of the CH₄ remains problematic. An aqueous fluid clearly penetrated the gneisses after the peak metamorphism (during uplift/erosion), forming secondary inclusions and contributing to the minor retrogressive hydration observed in these rocks. The presence of the pseudosecondary, high-density CO₂ inclusions in quartz crystals in the KSZ rocks constrains the uplift/ erosion path for the KSZ to one of simultaneous decrease in pressure and temperature.  相似文献   

Dating the lower crust by ion microprobe     

Roberta L. Rudnick  Ian S. Williams 《Earth and Planetary Science Letters》1987,85(1-3)

Ion microprobe UThPb ages of zircons from granulite facies lower crustal xenoliths from north Queensland, Australia, correlate well with the ages of major orogenic episodes manifest at the earth's surface. About half of the xenoliths contain Proterozoic zircons which are similar in age to the episodes of high-grade metamorphism of the older surface rocks. All the xenoliths contain late Paleozoic zircons which show a real 100 Ma range in²⁰⁶Pb²³⁸/U ages (from 320 to 220 Ma), which is attributed to granulite facies metamorphism followed by slow cooling in the deep crust. The Paleozoic zircon ages coincide in time with the prolonged episode of eruption of voluminous felsic ash-flows and intrusion of high-level granites in this region (320-270 Ma). Mineral and melt inclusions in the zircons provide clues to the origin of some of the xenoliths, and coupled with the age information, can be used to infer the geological processes operating in the lower crust. The zircons from two mafic xenoliths contain felsic and intermediate melt inclusions implying at least a two-stage history for these rocks, involving either partial melting of a more felsic protolith or crystal accumulation from an evolved melt. Some of the zircons from the felsic xenoliths contain CO₂-rich fluid inclusions, indicating that those zircons grew during high-grade metamorphism. The isotopic and chemical data for the whole rock xenoliths show that they originate from a segment of the lower crust which is a heterogeneous mixture of supracrustal and mafic, mantle-derived, lithologies. The major orogenic event responsible for the formation of that crust occurred in the late Paleozoic, when Proterozoic supracrustal rocks were emplaced into the lower crust, possibly along thin-skinned thrust slices. This was accompanied by intrusion of high-temperature, mantle-derived melts which caused partial melting of pre-existing crust. The most likely setting for such tectonism is a continental margin subduction zone.  相似文献   

Landslide susceptibility assessment in Apulian Southern Apennine: heuristic vs. statistical methods   总被引：2，自引：1，他引：1  

Roberta Pellicani  Paolo Frattini  Giuseppe Spilotro 《Environmental Earth Sciences》2014,72(4):1097-1108

In this paper, a bivariate-heuristic model (modified Stevenson’s method) and two multivariate statistical procedures (discriminant analysis and logistic regression) were used in order to assess and map landslide susceptibility in the north-western side of Daunia region (Apulia, Southern Italy). The whole Daunia region is characterized by complex and composite landslides, which are located on clayey slopes, near urban centers, affecting structures and infrastructures. The high predisposition to landsliding of the Daunia hillslopes is related to the very poor strength properties of clayey formations. The comparative analysis of landslide susceptibility using different methods, on the same test site and with the same inventory map allowed understanding the dependence of the results from the dataset and the capability of models under different levels of use, from expert to simple operator. By comparing the performance of the three models through the success rate curves, it emerges that the simple modified Stevenson’s method produces reliable outcomes, comparable with those deriving from more complex multivariate statistical models. This result is related to the characteristics of clayey slopes, in which the landslide occurrence is so much controlled by the poor strength properties of the clayey formations that the multivariate analysis of a large set of morphometric, geological and land-use variables results to be somehow superfluous. This suggests that, for clayey slopes, a simple, easy-to-manage bivariate-heuristic model based on expert opinion can be used with reliable results.  相似文献   

Erratum to: On the criteria to create a susceptibility map to debris flow at a regional scale using Flow-R     

Roberta Pastorello  Tamara Michelini  Vincenzo d’Agostino 《山地科学学报》2017,14(5):1008-1008

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