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This paper provides a step-by-step description of integrated methodology for quantification and prediction of gas (methane, CH4) content dynamics in shallow aquatic sediments under changing spatial and temporal conditions. Presence of gas bubbles even in small concentrations significantly affects sediment compressibility, which in turn decreases sound speed in sediment. Our integrated methodology consists of two basic steps. In the first step, free gas content is evaluated by acoustic applications based on the sound speed inferred from the reflection coefficient from gassy bottom. The experimental bottom reflections are registered and compared to the simulated ones, using a geoacoustic inversion technique. The best match between the model and the experiment provides sediment sound speed estimate, which is converted into free gas content using a basic relation. In the second step, a multivariate linear regression is fitted for gas content and closed form expression of gas content dependence on the following predictors, which change spatially and temporally over the aquatic ecosystem, is obtained: 1) water depth, 2) short-leaving CH4 production rate peaks fueled by punctuated organic matter deposition; and 3) CH4 bubble dissolution rates.•Gas content and sound speed in the sediment are estimated via the geoacoustic inversion technique by matching the experimentally recorded and simulated bottom reflections•Only single source and receiver are required for the acoustic methodology•A multivariate linear regression is fitted for gas content to indicate its dependence on various predictors that change spatially and temporally over the lake.

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Spatiotemporal variability of the low-frequency sound field in a coastal wedge in the presence of an internal Kelvin wave (IKW) is studied both experimentally and theoretically. The experiments were carried out in Lake Kinneret, Israel (also known as the Sea of Galilee) in August 2021, with a wideband sound source deployed near the shore and receiving vertical line arrays located at the lake's center. Parameters of the IKW were obtained earlier from long-term thermistor string measurements combined with conductivity, temperature, and depth data. The IKW initiated range-dependent vertical displacements of the thermocline with a maximum amplitude near the shore and almost zero amplitude in the center of the lake. It corresponded to a thermocline inclination angle of ±0.08° with respect to the horizontal. Temporal variations in depth-averaged acoustic intensity, reaching almost 8 dB, and remarkable changes in the normal mode composition were registered. These effects are explained based on simulations using a parabolic equation and normal mode models. The role of mode coupling in acoustic intensity variations is assessed.

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Uncontrolled bleeding that occurs during surgery, trauma, and in combat conditions is critical and require immediate action. Chitosan is a polysaccharide, obtained from natural sources with unique biological properties. It is often used as basis for local hemostatic agents (LHA). We summarized the data on hemostatic properties of chitosan, commercially available chitosan-based products with focus in the field of chemical modification of chitosan. Various approaches are used to enhance hemostatic activity of chitosan-based materials. The approach with chemical modification of chitosan allows changing the properties of the polymer in order to obtain an active macromolecule that contributes to hemostasis. Ongoing research on the mechanism of interaction with blood components in the case of different chitosan derivatives will make it possible to identify promising directions for chemical modification to obtain an effective LHA.

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We studied hemocompatibility of silver nanoparticles synthesized on the basis of a conjugate of quaternized chitosan with gallic acid (QChit-Gal). For the three variants of silver particles (Nos. 1, 2, and 3), the QChit-Gal:AgNO3 ratio was 5:1, 5:3, and 1:1, respectively. Anticoagulant activity of all samples of silver nanoparticles was lower than that of the conjugate. Samples of nanoparticles Nos. 1 and 2 in a concentration of 0.0233 mg/ml did not affect plasma clotting time and can be used for intravenous administration. However, their concentration in the blood should not exceed 0.01 mg/ml, because in this concentration they do not affect erythrocyte membrane, do not induce platelet aggregation, and do not affect platelet aggregation induced by ADP.

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In this review, we present the data on the natural occurrence of chitin and its partially or fully deacetylated derivative chitosan, as well as their properties, methods of modification, and potential applications of derivatives with bactericidal, fungicidal, and antioxidant activities. The structure and physicochemical characteristics of the polymers, their functions, and features of chitin microbial synthesis and degradation, including the processes occurring in nature, are described. New data on the hydrolytic microorganisms capable of chitin degradation under extreme conditions are presented. Special attention is focused on the effect of physicochemical characteristics of chitosan, including molecular weight, degree of deacetylation, polydispersity index, and number of amino group derivatives (quaternized, succinyl, etc.) on the antimicrobial and antioxidant properties of modified polymers that can be of particular interest for biotechnology, medicine, and agriculture. Analysis of the available literature data confirms the importance of fundamental research to broaden our knowledge on the occurrence of chitin and chitosan in nature, their role in global biosphere cycles, and prospects of applied research aimed at using chitin, chitosan, and their derivatives in various aspects of human activity.

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