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121.
122.
An outdoor experiment testing the effect of water flea (Daphnia longispina) and zebra mussels (Dreissena polymorpha) on physical and chemical water parameters and chlorophyll concentration changes was carried out in 12 containers filled with 150 l of unfiltered water from a lowland reservoir. During the 11 weeks of the experiment, the following physical, chemical and biological measurements were recorded: temperature (°C), oxygen concentration (mg dm−3), pH, conductivity (S cm−1), concentration of phosphate phosphorus (PO4-P) and ammonia nitrogen (NH4-N) (g dm−3), total nitrogen (TN) and total phosphorus (TP) (g dm−3), phytoplankton community structure and chlorophyll a concentration (g dm−3). The amount of ammonia ions was the highest in the treatment with zooplankton, while phosphate ions reached the highest values in treatments with zebra mussels. The results confirmed the ability of Daphnia to increase the NH4:PO4 ratio, whereas excretion from zebra mussels resulted in a decrease in both the N:P ratio (ranging from 9 to 13) and the NH4:PO4 ratio in water. In both treatments containing zebra mussels, P-rich water enabled sudden growth of Chlorophyta, resulting in blooms of Hydrodictyon reticulatum after 3–4 weeks of the experiment. Such phenomena were not observed in the control and Daphnia treatments. Our results indicate that zebra mussels, in contrast to Daphnia, may increase the symptoms of water eutrophication and contribute to blooms of expansive phytoplankton species. 相似文献
123.
The mass-dependent equilibrium stable isotope fractionation between different materials is an important geochemical process. Here we present an efficient method to compute the isotope fractionation between complex minerals and fluids at high pressure, P, and temperature, T, representative for the Earth’s crust and mantle. The method is tested by computation of the equilibrium fractionation of lithium isotopes between aqueous fluids and various Li bearing minerals such as staurolite, spodumene and mica. We are able to correctly predict the direction of the isotope fractionation as observed in the experiments. On the quantitative level the computed fractionation factors agree within 1.0‰ with the experimental values indicating predictive power of ab initio methods. We show that with ab initio methods we are able to investigate the underlying mechanisms driving the equilibrium isotope fractionation process, such as coordination of the fractionating elements, their bond strengths to the neighboring atoms, compression of fluids and thermal expansion of solids. This gives valuable insight into the processes governing the isotope fractionation mechanisms on the atomic scale. The method is applicable to any state and does not require different treatment of crystals and fluids. 相似文献
124.
Janusz W. Krzyścin Piotr S. Sobolewski Janusz Jarosławski Jerzy Podgórski Bonawentura Rajewska-Więch 《Acta Geophysica》2011,59(1):155-182
Measurements of erythemal irradiance have been carried out continuously at Belsk since May 1975. We present a homogenization
procedure of the UV time series for the period of 1976–2008. Long-term oscillations discovered in the homogenized data set
agree with those extracted from the reconstructed UV data for all-sky and clear-sky conditions. The UV climatology was established
and the UV variability was determined. Positive UV trends were found for the period of 1976-2008 in the annual mean (5.6±0.9%
per decade), in the seasonal mean for the warm subperiod of the year (April–October, 5.5±1.0% per decade), and in monthly
means (∼2–9% per decade). A satisfactory agreement between the trend extracted from the homogenized ground-based data and
that found in satellite UV data for Belsk (1979–2008) supports the reliability of satellite trend analyses over wider areas
during snowless periods. 相似文献
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127.
Piotr Kowalczuk William J. Cooper Michael J. Durako Amanda E. Kahn Michael Gonsior Heather Young 《Marine Chemistry》2010,118(1-2):22-36
In this study, the CDOM absorption coefficient at 350 nm [aCDOM(350)] and CDOM excitation emission matrix (EEM) fluorescence were used to estimate annual fluxes of dissolved organic carbon (DOC) from the Cape Fear River to Long Bay in the South Atlantic Bight. Water samples were collected during a 3.5 year period, from October 2001 through March 2005, in the vicinity of the Cape Fear River (CFR) outlet and adjacent Onslow Bay (OB). Parallel factor analysis (PARAFAC) of CDOM EEM spectra identified six components: three terrestrial humic-like, one marine humic-like and two protein-like. Empirical relationships were derived from the PARAFAC model between DOC concentration and aCDOM(350), total fluorescence intensity and the intensities of respective EEM components. DOC concentration and CDOM optical parameters were very well correlated and R2 values ranged from 0.77 to 0.90. Regression analyses revealed that the non-absorbing DOC fraction, in DOC concentration estimated from CDOM optical parameters, varied with the qualitative composition of the CDOM. DOC concentration and intensity of the humic-like CDOM components characterized by excitation maxima at longer wavelengths have significantly higher estimated non-absorbing DOC compared to the analogous relationships between DOC and intensity of the humic-like CDOM components characterized by excitation maxima at shorter wavelengths. The relationships between DOC concentration and intensity of one of the protein-like components resulted in significantly reduced non-absorbing DOC fraction in DOC concentration estimation. Results of regression analyses between fluorescence intensities of specific EEM components and CDOM-specific absorption coefficients suggest that the relative proportion of humic-like CDOM components (characterized by excitation maximum at longer wavelengths) and the main protein-like component have the most impact on the values of a?CDOM(350). Based on the relationships between aCDOM(350), Cape Fear River flow, and DOC concentrations, DOC fluxes were estimated for 2002, 2003 and 2004. DOC fluxes varied from 1.5 to 6.2 × 1010 g C yr? 1, depending on river flow. 相似文献
128.
Piotr Popowski 《Monthly notices of the Royal Astronomical Society》2001,321(3):502-506
I explore the consequences of making the RR Lyrae and clump giant distance scales consistent in the solar neighbourhood, Galactic bulge and Large Magellanic Cloud (LMC). I employ two major assumptions: (i) that the absolute magnitude–metallicity, M V (RR)–[Fe/H], relation for RR Lyrae stars is universal, and (ii) that absolute I magnitudes of clump giants, M I (RC), in Baade's Window are known (e.g. can be inferred from the local Hipparcos -based calibration or theoretical modelling). A comparison between the solar neighbourhood and Baade's Window sets M V (RR) at [Fe/H]=−1.6 in the range (0.59±0.05, 0.70±0.05), somewhat brighter than the statistical parallax solution. More luminous RR Lyrae stars imply younger globular clusters, which would be in better agreement with the conclusions from the currently favoured stellar evolution and cosmological models. A comparison between Baade's Window and the LMC sets M LMC(RC) I in the range (−0.33±0.09,−0.53±0.09). The distance modulus to the LMC is μ LMC ∈(18.24±0.08,18.44±0.07). Unlike M LMC(RC) I , this range in μ LMC does not depend on the adopted value of the dereddened LMC clump magnitude, I LMC(RC) 0 . I argue that the currently available information is insufficient to select the correct distance scale with high confidence. 相似文献
129.
Piotr Gronkowski 《Astrophysics and Space Science》2001,278(4):459-464
It is examined whether the destruction of heterogeneous cometary grains can explain the variation of cometary brightness and comet outburst.Calculations were carried out for water ice grains with carbonoxideinclusions. It was shown that for realistic chosen values of parametersthe comet luminosity can increase by even a few stellar magnitudes. 相似文献
130.
National borders play an important role in everyday life. Interest in border studies has increased with recent changes in geographical locations of the border or the fluctuation of the permeability of the border between some countries, such as in the European Union. Whether the nations are trying to increase traffic flow of the border or to implement stricter border control, having appropriate information of the border is crucial for effective policymaking. The objective of this research was to identify areas of high porosity, or high permeability, for pedestrians along the southern national border region in Carinthia, Austria using terrain, land use, and road data along with geocomputational methods. Two unsupervised classification methods, the fuzzy K-means clustering and the Self-Organizing Map, were applied to segment the border into homogeneous zones according to topographic and infrastructural attributes. The fuzzy K-means clustering method was chosen for its ability to allow for a continuous approach to classification. With this method, an object can belong, with different degrees of membership, to multiple classes, which is a more realistic reflection of the natural world than discrete clustering, where each object can only belong to one class. However, the fuzzy K-means clustering method does have disadvantages, i.e. the user must determine the number of classes and the input parameters are required to be in continuous format. The second classification method, the Self-Organizing Map, is a type of artificial neural network and was chosen for its ability to automatically determine the number of classes and handle categorical data. The Self-Organizing Map is unique because it can transform high dimensional data into low dimensional display while preserving the topology and spatial distribution of the input parameters. The results of the two classification methods suggest that the fuzzy K-means classification is more effective than the Self-Organizing Map for this situation. However, more research is needed to determine the fit of these algorithms for particular spatial data classification tasks. The results obtained from this research provide an insight into the permeability of the border region of Carinthia, Slovenia, and Italy to pedestrian traffic and can be potentially useful for decision making processes for tourism development and road transportation management in that region. Furthermore, the approach presented in this article can be applied to other national borders to identify zones permeable to pedestrian traffic. 相似文献