The effect of cobalt acetylacetonate (Co(acac)2) on heavy oil oxidation under in-situ combustion (ISC) conditions was investigated using DSC, TG, XRD, and SEM analyses. The results show that the compound does not behave as an active catalyst at low temperature but instead undergoes thermal decomposition as temperature increases. Around 350 degrees C, close to the transition between low-temperature oxidation (LTO) and high-temperature oxidation (HTO), an oxide-based Co3O4 phase is formed. This change in state is reflected in the oxidation behavior. Only a limited variation is observed in the LTO region, where the peak shifts slightly toward higher temperature, while a much stronger effect appears in the HTO region. In this stage, the apparent activation energy decreases from 150.602 to 101.357 kJ/mol, indicating that the main catalytic contribution occurs at elevated temperatures. SEM observations show that the decomposition process leads to the formation of particles in the nanometer range, mostly between 40 and 80 nm. Although no direct correlation is established, such dimensions are generally associated with increased surface accessibility and may contribute to the observed enhancement in high-temperature oxidation. Overall, the results suggest that the catalytic effect is governed by the thermal evolution of the precursor rather than its initial form. This temperature-dependent activation results in a differential effect across oxidation stages, with limited influence on LTO and a more pronounced effect on HTO. This differential response is favorable for heat release and may improve combustion stability under ISC conditions. The study provides a basis for further investigation of oil-soluble precursors as controllable catalytic systems in thermal recovery processes.
Guitar nebula is a prime example of a class of bow-shock pulsar wind nebulae (PWNe), powered by a wind of a supersonically moving neutron star. Bow-shock PWNe can probe particle acceleration processes in relativistic pulsar winds, as well as the structure of the interstellar medium (ISM). We demonstrate that Guitar is an exceptional object in a number of ways. First, particles escaping the PWN and forming the X-ray “kinetic jet” need to be accelerated to the energies corresponding to the maximal electric potential of the neutron star ηacc≳3/4 : it is another example of the class of extreme accelerators. Second, exceptionally bright Hα emission requires that the central pulsar PSR J2225+6535 passes through a dense, low ionization ISM region. Bright X-ray emission of the “kinetic jet” then also requires exceptionally high magnetic field, ∼ 100 μG. We hypothesize that Guitar passes through the one of long-predicted, narrow dense shells of an old supernova remnant, currently in the “pressure-driven snowplow” regime.
This work aims to study the distribution features of eight potentially toxic heavy metals (Cd, Pb, Co, Cu, Ni, Zn, Cr, and Mn) and two biogenic elements (N and P) in the bottom sediments of beaver ponds in two small rivers of the Volga Upland’s far north of the East European Plain. In 27 most typical beaver ponds, differing in their morphometric characteristics, as well as in some sections of the studied rivers unaffected by beaver activity, bottom sediments were collected in their upper, middle and lower reaches. The content of heavy metals and biogenic elements in the rivers’ water was also determined. The obtained results were processed using statistical methods. The concentration of mobile forms of Co, Cu, Ni, and Mn in the sampled sediments significantly exceeds their concentration in the soils of basin areas and in the sediments of riverbeds not affected by beavers. At the same time, the content of total Cd, Zn, and Mn, as well as N and P in the sediments of the upper reaches of the rivers is somewhat higher than in their lower reaches. The distribution of gross forms of heavy metals is significantly affected by the granulometric composition of bottom sediments and the content of organic matter in them. Statistically significant factors influencing the presence of mobile forms are the distance from the river mouth, the length of beaver dams and ponds, and the content of organic matter in bottom sediments. The distribution of biogenic elements correlates well with the height and length of beaver dams, the distance from the river mouth, and the content of organic matter in the sediments. It was revealed that the bottom sediments of beaver ponds of the studied rivers are not contaminated with either gross or mobile forms of the studied chemical elements. For mobile forms, a moderate enrichment of Pb, Co, and Ni was found. Of all the analyzed heavy metals in the bottom sediments, compared with sections of the riverbed unaffected by beaver activity, an excess was observed only for Co, Cu, Ni, and Mn.
In this study, the effect of various polysaccharides including dextran, hyaluronic acid, κ-, ι-, and λ-carrageenans, on the kinetics of bovine serum albumin (BSA) fibrillation at 65°C was investigated using thioflavin T (ThT) assay. It was found that these polysaccharides modulate the fibrillation process differently: dextran weakly promotes fibrillation, hyaluronic acid shows almost no impact, while carrageenans demonstrate the most pronounced effects, which depends on polysaccharide concentration. The addition of sodium chloride was shown to affect the protein-polysaccharide interactions primarily by weakening the electrostatic contribution and stabilizing the native protein form. The results expand our understanding on protein aggregation processes in the presence of polysaccharides and may be useful for developing the methods to design biopolymer complexes with tailorable properties.
We have studied the physical parameters of a group of 15 OBA stars from which X-ray emission was detected by the SRG/eROSITA telescope. Whereas the X-ray emission from cool FGKM stars is directly produced near their surface zones—in their chromospheres and coronae—the nature of the X-ray emission from OBA stars requires a separate study in each specific case, since single OBA stars are not intrinsic X-ray sources. We have determined the main physical characteristics of the stars under study, including their effective temperature T_eff and surface gravity log g , based on the spectral energy distribution and the optical spectra obtained with the 1.5-m Russian–Turkish RTT-150 telescope. An additional analysis of the H α line profiles has allowed the possible X-ray emission mechanisms to be assessed: generation in non-stationary stellar winds, collisional processes in circumstellar envelopes, and coronal emission of hidden cool companions. As a result of the analysis, we have concluded that the X-ray emission from eight stars with typical X-ray luminosities in the range log L_X=28.5-30.0 is determined by their hidden late-type companions.
