Starch-assisted sol–gel synthesis of magnetic CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript> powder as photo-Fenton catalysts in the presence of oxalic acid

Magnetic photo-Fenton catalysts based on spinel CuFe₂O₄ were successfully prepared by the starch-assisted sol–gel method. Various synthetic conditions such as annealing temperatures (700, 800 and 900 °C) and molar ratios of Cu²⁺/Fe³⁺/C₆H₁₀O₅ in the precursor solution (from 1:2:2 to 1:2:4) were, respectively, used in order to study the influences of annealing temperatures and precursor starch contents on the magnetic and catalytic properties of CuFe₂O₄ powders. The photo-Fenton catalytic activity was evaluated via the degradation of methylene blue under ultraviolet and visible irradiation with H₂C₂O₄ as a new oxidizing agent. According to the results, when the annealing temperature increased to 800 °C, the spinel CuFe₂O₄ phase amount was increased, which strongly enhances the photo-Fenton catalytic performance. However, above 800 °C, the catalytic activity was reduced, due to the increase in particle size. The starch content also affected the surface Cu²⁺ content and the particle size of catalysts. The catalyst prepared at 800 °C with the molar Cu²⁺/Fe³⁺/C₆H₁₀O₅ ratio of 1:2:3 presented the best photo-Fenton performance, owing to its highest surface Cu²⁺ content. This catalyst also exhibits ferromagnetic properties (saturation magnetization of 25.836 emu/g and coercivity of 1010.23 Oe), which allows them to be easily separated from the solution by a magnet.     

Streamflow generation regarding storage components and runs' characteristics

An attempt is made in this study to search for a model which is capable of reproducing the reservoir storage components and runs' characteristics along with the mean, standard deviation, skewness and correlation coefficients of historical monthly streamflows. The model based upon the method of fragments and a scheme devised for annual values is found to yield satisfactory results and is, therefore, recommended for use.     

Moments of the run-sum for independent sequences

General expressions for the first four moments of the positive run-sum for independent sequences are derived and their computation scheme is indicated. The formulae for the moments of the truncated variable, which are needed in obtaining those of the positive run-sum, are then given for the case when the sequence under consideration follows one of the normal, log-normal, gamma or Rayleigh distributions.     

Mathematical model for the dynamics of radionuclides,heavy metals,and petroleum hydrocarbons in the Arctic basin

This paper discusses a mathematical model for the dynamics of pollution in the Arctic basin, considering spatial non-uniformities in the distribution of ecological and hydrodynamic parameters. The model features blocks simulating contaminant fluxes through the tropic chains. The results of numerical experiments are provided which demonstrate the model's capability to predict and assess the dynamics of heavy metals, radionuclides, and petroleum hydrocarbons in the Arctic basin. The model is adaptable to a global model. Climatic phenomena and anthropogenic forcing are described in the form of scenarios.Translated by Vladimir A. Puchkin.