Biodegradable poly-3-hydroxybutyrate [P(3HB)] and natural materials (fillers)clay, peat, and birch wood powderwere used to prepare powdered blends and, then, pellets and granules. Pellets were produced by cold pressing of polymer and filler powders; granules were produced from the powders wetted with ethanol. Properties of initial P(3HB) and fillers and blends thereof were studied using IR spectroscopy, DSC, X-ray analysis, and electron microscopy. No chemical bonds between the components were revealed: the blends were physical mixtures. The degree of crystallinity of the blends was lower than that of the initial polymer, suggesting different crystallization kinetics of the blends. Introduction of increasing amounts of the fillers into the polymer progressively decreased mechanical strength of the pellets, as confirmed by the decrease in Young's modulus. The study of degradation of the blends in soil showed that the mass loss of the blends over 35 days of incubation in soil varied between 30 and 50% of the initial mass of the products, depending on the type of the filler.
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The present study addresses the herbicidal activity and biological effects of the metribuzin (MET) and tribenuron-methyl (TBM) herbicides used to control various weed species (Amaranthus retroflexus, Sinapis arvensis, and Leucanthemum maximum). The effects of the free herbicides and the herbicides embedded in granules of degradable polymer poly-3-hydroxybutyrate [P(3HB)] blended with birch wood flour were compared. Metribuzin, regardless of the form, caused 100% mortality of the three weeds by day 21. The herbicidal activity of tribenuron-methyl was lower than that of metribuzin, but the embedded TBM was superior to the free herbicide in the length and strength of its action on the weeds. Both metribuzin forms dramatically decreased the main parameters of fluorescence: maximum quantum yield of photosystem-II [Y(II) max ], maximum quantum yield of non-photochemical quenching [Y(NPQ) max ], and maximum rate of non-cyclic electron transport [ETR max ] and concentrations of chlorophyll a and b. The effect of the embedded TBM on the photosynthetic activity of the weeds was lower in the first two weeks of the growth of herbicidetreated plants but lasted longer than the effect of the free TBM and increased over time. Embedding of metribuzin in the matrix of degradable blend did not decrease its herbicidal activity.
To study the patterns of response of the immune system to viruses detected in the body, a very diverse range of models has been developed. The simplest infectious disease model, which describes the most general mechanisms of immune protection, built on the assumption that the environment of the «organism» is homogeneous, in which all components of the process are instantly mixed by Marchuk is known. The infectious disease mathematical model by Marchuk for generalization of diffusion perturbations and various concentrated influences is generalized. The corresponding singularly perturbed model problem with delay is reduced to a sequence of problems without delay, for which the corresponding asymptotic developments of solutions are obtained. The results of numerical experiments, which illustrate the influence of spatially distributed diffusion «redistributions» on the nature of the viral disease in the presence of concentrated sources of antigens and donor antibodies are presented. A model decrease in the maximum level of antigens in the infection epicenter due to their diffusion «erosion» in the process of infectious disease development has been demonstrated. It is emphasized that even if the initial concentration or intensity of the pulsed viral source in a certain part of the infection will exceed some critical value (immunological barrier) due to diffusion «redistribution» for a short period of time, the supercritical concentration of viral agents may decrease to lower than the critical level and further neutralization of antigens can be provided by the available level of antibodies and a more economical procedure of injection solution with donor antibodies. That is, within this model, the «severity» of the viral disease in such cases can be reduced more rationally, at lower cost.
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