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Kristian Finlator Feryal Özel Romeel Davé 《Monthly notices of the Royal Astronomical Society》2009,393(4):1090-1106
We introduce a new code for computing time-dependent continuum radiative transfer and non-equilibrium ionization states in static density fields with periodic boundaries. Our code solves the moments of the radiative transfer equation, closed by an Eddington tensor computed using a long characteristics (LC) method. We show that traditional short characteristics and the optically thin approximation are inappropriate for computing Eddington factors for the problem of cosmological re-ionization. We evolve the non-equilibrium ionization field via an efficient and accurate (errors <1 per cent) technique that switches between fully implicit or explicit finite differencing depending on whether the local time-scales are long or short compared to the time-step. We tailor our code for the problem of cosmological re-ionization. In tests, the code conserves photons, accurately treats cosmological effects and reproduces analytic Strömgren sphere solutions. Its chief weakness is that the computation time for the LC calculation scales relatively poorly compared to other techniques ( t LC ∝ N ∼1.5 cells ) ; however, we mitigate this by only recomputing the Eddington tensor when the radiation field changes substantially. Our technique makes almost no physical approximations, so it provides a way to benchmark faster but more approximate techniques. It can readily be extended to evolve multiple frequencies, though we do not do so here. Finally, we note that our method is generally applicable to any problem involving the transfer of continuum radiation through a periodic volume. 相似文献
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Feryal Akbal Levent Gürel Tolga Bahadır İlknur Güler Gülfem Bakan Hanife Büyükgüngör 《Environmental Earth Sciences》2011,64(5):1387-1395
The aim of this study was to investigate the water and sediment quality in the mid-Black Sea coast of Turkey. The samples
were collected from six stations during 2007. Investigated parameters were total carbon (TC), total inorganic carbon (TIC),
total organic carbon (TOC), ammonium-nitrogen (NH4-N), nitrate-nitrogen (NO3-N), nitrite-nitrogen (NO2-N), total phosphorus (TP), sulphate, total hardness, methylene blue active substances (MBAS), phenol, adsorbable organic
halogens (AOX), dissolved oxygen (DO), pH and electrical conductivity (EC) in water samples and TC, TIC, TOC, TP, pH, electrical
conductivity (EC), redox potential (Eh) and water content (WC) in sediment samples. Different multivariate statistical techniques
were used to evaluate variations in surface water and sediment quality. Principal component analysis helped in identifying
the factors or sources responsible for water and sediment quality variations. Five factors were found responsible for 87.63%
of the total variance in the surface waters. In sediments, three factors explained 84.73% of the observed total variance.
Cluster analysis classified the monitoring sites into two groups based on similarities of water and sediment quality characteristics. 相似文献
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