A thermochemical study of glasses and crystals along the joins silica-calcium aluminate and silica-sodium aluminate     

Alexandra Navrotsky  Gilles Peraudeau  Paul McMillan  Jean-Pierre Coutures 《Geochimica et cosmochimica acta》1982,46(11):2039-2047

Enthalpies of solution in molten 2PbO · B₂O₃ at 985 K are reported for series of glasses xCa_0.5AlO₂-(1?x)SiO₂ (O ≤ x ≤ 0.99) and xNaAlO₂-(1?x)SiO₂ (0 ≤ x ≤ 0.56). The data are compared to values for the corresponding crystalline aluminosilicates and to preliminary data for systems containing KAlO₂ and Mg_0.5AlO₂. The enthalpies of mixing of glasses become more exothermic with increasing basicity of the mono- or divalent oxide. The tendency toward immiscibility on the silica-rich side, indicated by the shape of the heat of mixing curve between x = 0 and x = 0.4, is pronounced in the calcium aluminate system, but not in the sodium aluminate system. The shape of the heat of mixing curve, which is roughly symmetrical about x = 0.5, can be rationalized in terms of glass structure by considering essentially random substitution of Si and Al on a continuous three dimensional tetrahedral framework, with stabilization arising from electrostatic interactions between aluminum and the nonframework cation balancing the destabilizing effects arising from perturbation of the aluminosilicate framework by the nonframework cation. These trends are consistent with the variation of physical properties of aluminosilicate melts.  相似文献   

Lysosomal membrane stability and metallothioneins in digestive gland of Mussels (Mytilus galloprovincialis Lam.) as biomarkers in a field study     

Petrović S  Ozretić B  Krajnović-Ozretić M  Bobinac D 《Marine pollution bulletin》2001,42(12):1373-1378

The lysosomal membrane destabilization and the metallothionein content in the digestive gland cells of mussels (Mytilus galloprovincialis Lam.), collected along the east coast of the North Adriatic (Istrian and Kvarnerine coast, Croatia), were examined over a period of four years (1996–1999). The lysosomal membrane stability, as a biomarker of general stress, showed that the membrane labilization period in mussels from polluted, urban- and industrial-related areas was significantly decreased (p<0.05) when compared to mussels from control, clean sea water sites. In the harbour of Rijeka, the most contaminated site, the lysosomal membrane stability was reduced by more than 70% compared to the control. This method also proved to be a useful biomarker for detection of additional stress caused by short-term hypoxia that occurred once during this study inside the polluted and periodically quite eutrophic Pula Harbour. The concentration of metallothioneins in the mussel digestive gland, as a specific biomarker of exposure to heavy metals, did not reveal significant differences (p<0.05) between sites covered by this study.  相似文献   

Special Issue: Cvijic Karst 2005: “Water Resources and Environmental Problems in Karst”, held in Belgrade and Kotor, Serbia and Montenegro, 14–19 September 2005     

Petar Milanović 《Environmental Geology》2007,51(5):673-674

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Derivation Of Refractive Index And Temperature Gradients From Optical Scintillometry To Correct Atmospherically Induced Errors For Highly Precise Geodetic Measurements     

Alexandra I. Weiss  Maria Hennes  Mathias W. Rotach 《Surveys in Geophysics》2001,22(5-6):589-596

Refraction effects of optical beams are generally caused by an inhomogeneous propagation medium and are a major source of systematic errors in the precise optical determination of angles and distances in the atmospheric surface layer. In this contribution a method for deriving vertical temperature and refractive index gradients from optical scintillation is presented. Knowledge of these gradients is required for the compensation of atmospherically induced errors for highly precise terrestrial geodetic measurements, like direct transfer and levelling. The advantage of the present optical method is, that temperature and refractive index gradients can be derived as line-averaged values over the propagation path, which is not possible by meteorological point measurements. Field observations have been carried out with a displaced-beam scintillometer over flat terrain and under different atmospheric conditions in order to verify this method. The experiments show, that this method allows to derive accurate correction values for precise terrestrial geodetic measurements.  相似文献   

Application of the photoacoustic method for characterization of natural galena (PbS)     

P. M. Nikolić  S. Ðurić  D. M. Todorović  D. Vasiljević-Radović  V. Blagojević  P. Mihajlović  J. Elazar  K. T. Radulović  A. I. Bojičić  D. Urošević 《Physics and Chemistry of Minerals》2001,28(1):44-51

Electron transport properties of single crystal and polycrystalline natural mineral galena (PbS) samples from the Trep?a mine, Yugoslavia, were determined using the photoacoustic frequency transmission technique. Their thermal diffusivity (D _T≈0.16 × 10^?5 m² s^?1), the coefficient of diffusion (D between 0.15×10^?2 0.16×10^?2 m² s^?1) and lifetime of the excess carrier (τ≈35 μs and the front and rear recombination velocity (s _g≈65.5 m s^?1 and s _b≈66.4 m s^?1, respectively), were calculated by comparing the experimental results and the theoretical photoacoustic amplitude and phase signals. The lattice parameter obtained by X-ray work was a?=5.936?Å. The free carrier concentration of these single-crystal samples was measured using the Hall method (N?=?3×10¹⁸ cm^?3). Measurements of the optical reflectivity of the same samples, as a function of wavelength, in the infrared and far infrared ranges, were performed. In the far infrared range a free electron plasma frequency was observed and numerically analyzed, using the least-squares fitting procedure. The values of optical parameters were calculated and the value of the free carrier concentration obtained by the Hall method was confirmed.  相似文献   

Numerical model for quantitative precipitation forecasting     

Djuro Radinović 《Pure and Applied Geophysics》1972,93(1):159-176

Summary A numerical model for the quantitative precipitation forecasting has been formulated. In this model precipitation is computed as a function of the vertical velocity and humidity distribution in the atmosphere. The orographic influence on the vertical velocity was taken into consideration. Further, the relation between vertical velocity and static stability of the atmosphere has been considered and, as an important factor in the condensation process, was introduced into the equation of the model. This numerical model for the precipitation forecasting has been applied in the North Adriactic Sea region, which is characterized by a strong vertical gradient of the specific humidity and pronounced orographic influence. The results achieved show that this model could successfully be used as an objective method in the routine forecasting of the amount of precipitation.  相似文献   

Dolomitmarmor in der Umgebung der Stadt Prilep und die in ihm vorkommenden Minerale     

Lj. Barić 《Mineralogy and Petrology》1969,13(3-4):233-249

Zusammenfassung In der Umgebung der Stadt Prilep in Mazedonien kommen an mehreren Stellen in einer hochmetamorphen, aus Glimmerschiefern und Amphiboliten bestehenden Zone Calcit- und Dolomitmarmore vor. In den letzterwähnten wurden bisher Dolomit, Calcit, Korund, Diaspor, -Zoisit, Rutil, Fluorit, Achroit, Pyrit, Muskovit, Illit, Margarit und Chlorit (vonErdmannnsdörfer auch Kossmatit) festgestellt. Diese Paragenese ist regionalmetamorph entstanden.

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Dolomite-marble in the surroundings of the town prilep, macedonia, and its minerals

Summary Calcite- and dolomite-marbles occur in a highly metamorphic series together with micaschists and amphibolites at several localities in the surroundings of Prilep, Macedonia. In the dolomite-marbles, dolomite, calcite, corundum, diaspore, -zoisite, rutile, fluorite, achroite pyrite, muscovite, illite, margarite, chlorite, and kossmatite (the last only byErdmannsdörffer) have been found. The paragenesis is of regional metamorphic origin.

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Mit 1 Abbildung  相似文献   

A two-stage time series model for monthly hydrological projections under climate change in the Lim River basin (southeast Europe)     

Milan Stojković  Jasna Plavšić  Stevan Prohaska  Dragutin Pavlović  Jovan Despotović 《水文科学杂志》2020,65(3):387-400

ABSTRACT

Climate change projections of precipitation and temperature suggest that Serbia could be one of the most affected regions in southeastern Europe. To prepare adaptation measures, the impact of climate changes on water resources needs to be assessed. Pilot research is carried out for the Lim River basin, in southeastern Europe, to predict monthly flows under different climate scenarios. For estimation of future water availability, an alternative approach of developing a deterministic-stochastic time series model is chosen. The proposed two-stage time series model consists of several components: trend, long-term periodicity, seasonality and the stochastic component. The latter is based on a transfer function model with two input variables, precipitation and temperature, as climatic drivers. The Nash-Sutcliffe model efficiency for the observed period 1950–2012 is 0.829. The model is applied for the long-term hydrological prediction under the representative concentration pathway (RCP) emissions scenarios for the future time frame 2013–2070.  相似文献   

Application of Generalized Likelihood Uncertainty Estimation (GLUE) at different temporal scales to reduce the uncertainty level in modelled river flows     

Ragab Ragab  Alexandra Kaelin  Muhammad Afzal  Ioanna Panagea 《水文科学杂志》2020,65(11):1856-1871

ABSTRACT

In this study, the distributed catchment-scale model, DiCaSM, was applied on five catchments across the UK. Given its importance, river flow was selected to study the uncertainty in streamflow prediction using the Generalized Likelihood Uncertainty Estimation (GLUE) methodology at different timescales (daily, monthly, seasonal and annual). The uncertainty analysis showed that the observed river flows were within the predicted bounds/envelope of 5% and 95% percentiles. These predicted river flow bounds contained most of the observed river flows, as expressed by the high containment ratio, CR. In addition to CR, other uncertainty indices – bandwidth B, relative bandwidth RB, degrees of asymmetry S and T, deviation amplitude D, relative deviation amplitude RD and the R factor – also indicated that the predicted river flows have acceptable uncertainty levels. The results show lower uncertainty in predicted river flows when increasing the timescale from daily to monthly to seasonal, with the lowest uncertainty associated with annual flows.  相似文献   

Formation Of Coronal Mhd Shock Waves – I. The Basic Mechanism     

B. Vršnak  S. Lulić 《Solar physics》2000,196(1):157-180

The formation and evolution of a large amplitude MHD perturbation propagating perpendicular to the magnetic field in a perfectly conducting low plasma is studied. The perturbation is generated by an abrupt expansion of the source region. Explicit expressions for the time and the distance needed for the transformation of the perturbation's leading edge into a shock wave are derived. The results are applied to coronal conditions and the dynamic spectra of the radio emission excited by the shock are synthesized, reproducing metric and kilometric type II bursts. The features corresponding to the metric type II burst precursor and the moving type IV burst in the case of kilometric type II bursts are identified. A specific radio signature that is sometimes observed at the onset of a metric type II burst is found to appear immediately before the shock wave formation due to the associated growth of the magnetic field gradient. Time delays and starting frequencies of bursts' onsets are calculated and presented as a function of the impulsiveness of the source-region expansion, using different values of the ambient Alfvén velocity and various time profiles of the expansion velocity. The results are confronted with the observations of metric and kilometric type II solar radio bursts.  相似文献