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  • 1
    In: Minerals, MDPI AG, Vol. 10, No. 11 ( 2020-10-28), p. 964-
    Abstract: Here, we present new results from seismic, geological, and geochemical studies conducted in 2015–2019 in the Petrozavodsk Bay of Lake Onego, NW Russia. The aims of these investigations were to (i) to characterize the structure of Quaternary deposits and (ii) provide new evidence of modern geodynamic movements and gas-seepage in Holocene sediments. The structure of the recovered deposits was composed of lacustrine mud, silt and sands from the Holocene, limno-glacial clays (varved clays) from the Late Glacial–Interglacial Transition, and glacial deposits (till) from the Late Pleistocene. The thickness of these deposits varied in different parts of the bay. Many pockmarks created by gases escaping and reaching sediment-water interface were observed in these deposits. Such pockmarks can play a significant role in the geochemical and biological processes in the bottom sediment surface, and gases that escape might modify the physicochemical characteristics of the environment.
    Type of Medium: Online Resource
    ISSN: 2075-163X
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2655947-X
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  • 2
    Online Resource
    Online Resource
    MDPI AG ; 2023
    In:  Physics Vol. 5, No. 2 ( 2023-05-09), p. 537-546
    In: Physics, MDPI AG, Vol. 5, No. 2 ( 2023-05-09), p. 537-546
    Abstract: In this paper, we review our findings concerning fractal entropy of microscopic configurations corresponding to the production of KS0 mesons in AuAu collisions in the z-scaling approach. The entropy is expressed via structural and fragmentation fractal dimensions, and model parameter cAuAu is interpreted as a specific heat of produced medium. These parameters are related to the respective momentum fractions of the colliding nuclei, the momentum fractions of the scattered constituents that fragment into the produced hadrons, and the multiplicity density of negative particles in the central interaction region. The dependence of the entropy on the collision energy over the range of 7.7–200 GeV for most central and most peripheral events is studied as a function of the transverse momentum of the produced KS0 mesons. A non-trivial dependence of the entropy on the collision energy with decreasing transverse momentum is found. This reflects the irregularity of the behavior of the specific heat, cAuAu, and can point to a manifestation of phase transition in nuclear matter.
    Type of Medium: Online Resource
    ISSN: 2624-8174
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2965324-1
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  • 3
    Online Resource
    Online Resource
    MDPI AG ; 2020
    In:  Entropy Vol. 22, No. 8 ( 2020-07-23), p. 808-
    In: Entropy, MDPI AG, Vol. 22, No. 8 ( 2020-07-23), p. 808-
    Abstract: Adsorptive Heat Transformation systems are at the interface between thermal and chemical engineering. Their study and development need a thorough thermodynamic analysis aimed at the smart choice of adsorbent-adsorptive pair and its fitting with a particular heat transformation cycle. This paper addresses such an analysis for a new “Heat from Cold” cycle proposed for amplification of the ambient heat in cold countries. A comparison of four working fluids is made in terms of the useful heat per cycle and the temperature lift. The useful heat increases in the row water 〉 ammonia ≥ methanol 〉 hydrofluorocarbon R32. A threshold mass of exchanged adsorbate, below which the useful heat equals zero, raises in the same sequence. The most promising adsorbents for this cycle are activated carbons Maxsorb III and SRD 1352/2. For all the adsorptives studied, a linear relationship F = A·ΔT is found between the Dubinin adsorption potential and the driving temperature difference ΔT between the two natural thermal baths. It allows the maximum temperature lift during the heat generation stage to be assessed. Thus, a larger ΔT-value promotes the removal of the more strongly bound adsorbate.
    Type of Medium: Online Resource
    ISSN: 1099-4300
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2014734-X
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  • 4
    In: Symmetry, MDPI AG, Vol. 15, No. 4 ( 2023-04-01), p. 846-
    Abstract: Nowadays, commercial electric double-layer supercapacitors mainly use porous activated carbons due to their high specific surface area, electrical conductivity, and chemical stability. A feature of carbon materials is the possibility of obtaining them from renewable plant biomass. In this study, fungi (Fomes fomentarius) were used as a bio-template for the preparation of carbon fibers via a combination of thermochemical conversion approaches, including a general hydrothermal pre-carbonization step, as well as subsequent carbonization, physical, or chemical activation. The relationships between the preparation conditions and the structural and electrochemical properties of the obtained carbon materials were determined using SEM, TEM, EDAX, XPS, cyclic voltammetry, galvanostatic measurements, and EIS. It was shown that hydrothermal pretreatment in the presence of phosphoric acid ensured the complete removal of inorganic impurities of raw fungus hyphae, but at the same time, saved some heteroatoms, such as O, N, and P. Chemical activation using H3PO4 increased the amount of phosphorus in the carbon material and saved the natural fungus’s structure. The combination of a hierarchical pore structure with O, N, and P heteroatom doping made it possible to achieve good electrochemical properties (specific capacitance values of 220 F/g) and excellent stability after 25,000 charge/discharge cycles in a three-electrode cell. The electrochemical performance in both three- and two-electrode cells exceeded or was comparable to other biomass-derived porous carbons, making it a prospective candidate as an electrode material in symmetrical supercapacitors.
    Type of Medium: Online Resource
    ISSN: 2073-8994
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2518382-5
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  • 5
    In: Fluids, MDPI AG, Vol. 8, No. 8 ( 2023-08-10), p. 228-
    Abstract: Adsorption energy storage is a promising resource-saving technology that allows the rational use of alternative heat sources. One of the most important parts of the adsorption heat accumulator is the adsorber heat exchanger. The parameters of heat transfer in this unit determine how fast heat from an alternative energy source, such as the Sun, will be stored. For the design of adsorption heat accumulators, plate fin heat exchangers are mainly used. In this paper, the procedure for the estimation of the global heat transfer coefficient for the adsorber heat exchanger depending on its geometry is considered. The heat transfer coefficient for a LiCl/SiO2 sorbent flat layer under conditions of heat storage stage was measured. Based on these data, the global heat transfer coefficients for a number of industrial heat exchangers were theoretically estimated and experimentally measured for the adsorption cycle of daily heat storage. It was shown that theoretically obtained values are in good agreement with the values of the global heat transfer coefficients measured experimentally. Thus, the considered technique makes it possible to determine the most promising geometry of the plate fin heat exchanger for a given adsorption heat storage cycle without complicated experiments.
    Type of Medium: Online Resource
    ISSN: 2311-5521
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2882362-X
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  • 6
    Online Resource
    Online Resource
    MDPI AG ; 2020
    In:  Energies Vol. 13, No. 22 ( 2020-11-13), p. 5920-
    In: Energies, MDPI AG, Vol. 13, No. 22 ( 2020-11-13), p. 5920-
    Abstract: We apply deep reinforcement learning to active closed-loop control of a two-dimensional flow over a cylinder oscillating around its axis with a time-dependent angular velocity representing the only control parameter. Experimenting with the angular velocity, the neural network is able to devise a control strategy based on low frequency harmonic oscillations with some additional modulations to stabilize the Kármán vortex street at a low Reynolds number Re=100. We examine the convergence issue for two reward functions showing that later epoch number does not always guarantee a better result. The performance of the controller provide the drag reduction of 14% or 16% depending on the employed reward function. The additional efforts are very low as the maximum amplitude of the angular velocity is equal to 8% of the incoming flow in the first case while the latter reward function returns an impressive 0.8% rotation amplitude which is comparable with the state-of-the-art adjoint optimization results. A detailed comparison with a flow controlled by harmonic oscillations with fixed amplitude and frequency is presented, highlighting the benefits of a feedback loop.
    Type of Medium: Online Resource
    ISSN: 1996-1073
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2437446-5
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  • 7
    In: Nanomaterials, MDPI AG, Vol. 13, No. 9 ( 2023-04-27), p. 1490-
    Abstract: The results of experimental studies of ohmic conductivity degradation in the ensembles of nanostructured anatase bridges under a long-term effect of direct current are presented. Stochastic sets of partially conducting inter-electrode bridges consisting of close-packed anatase nanoparticles were formed by means of the seeding particles from drying aqueous suspensions on the surfaces of silica substrates with interdigital platinum electrodes. Multiple-run experiments conducted at room temperature have shown that ohmic conductivity degradation in these systems is irreversible. It is presumably due to the accumulated capture of conduction electrons by deep traps in anatase nanoparticles. The scaling analysis of voltage drops across the samples at the final stage of degradation gives a critical exponent for ohmic conductivity as ≈1.597. This value satisfactorily agrees with the reported model data for percolation systems. At an early stage of degradation, the spectral density of conduction current fluctuations observed within the frequency range of 0.01–1 Hz decreases approximately as 1/ω, while near the percolation threshold, the decreasing trend changes to ≈1/ω2. This transition is interpreted in terms of the increasing contribution of blockages and subsequent avalanche-like breakdowns of part of the local conduction channels in the bridges into electron transport near the percolation threshold.
    Type of Medium: Online Resource
    ISSN: 2079-4991
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2662255-5
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  • 8
    In: Fluids, MDPI AG, Vol. 8, No. 1 ( 2022-12-30), p. 14-
    Abstract: In this work, four radiators with different core geometries were tested using a wind tunnel. The values of the global heat transfer coefficient (UA = 5 ÷ 65 W/K) were measured depending on the flow of air and water. The obtained UA values correlate well with the data of sorption experiments described in the literature. The found correlations between the Nusselt and Reynolds numbers made it possible to propose an algorithm for ranging commercial air radiators for the use in adsorption heat transformers. It is shown that the use of a wind tunnel can serve as an effective tool for express assessment of the prospects of using air radiators for adsorption heat conversion without destroying radiators or their direct testing in a complex adsorption installation requiring vacuum maintenance.
    Type of Medium: Online Resource
    ISSN: 2311-5521
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2882362-X
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  • 9
    In: Separations, MDPI AG, Vol. 10, No. 9 ( 2023-08-28), p. 473-
    Abstract: The different adsorption applications require the development of sorbents with predetermined properties. One of the ways for fine tuning the adsorption properties of the material is using a binary salt system as an active sorbing component. The aim of this work is to conduct a precision investigation of thermodynamic data on the sorption equilibrium of composite sorbents “(CaCl2 + CaBr2) confined to the silica gel pores” with water vapour. The isotherms and isosteres (at an uptake of N = 1.5 and 3.6 mole/mole) of water sorption on the composites were measured. It was shown that at a fixed temperature, the composites based on solid solutions of CaCl2 in CaBr2 form complexes with water at a pressure that is dependent on the CaCl2/CaBr2 molar ratio. The isosteric enthalpy and entropy of water sorption (ΔH = −48 ± 3 kJ/mol ΔS = −108 ± 2 J/(mol·K)) at N = 3.6 mole/mole were midway between the same parameters for composites on the base of the pure salts CaCl2 and CaBr2. The novelty of this work is in the design of sorbents optimized for air conditioning in hot climates and air drying cycles. It was shown that the use of the binary CaCl2 + CaBr2 system confined to the silica pores can be an effective tool for designing innovative materials with predetermined properties.
    Type of Medium: Online Resource
    ISSN: 2297-8739
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2869930-0
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  • 10
    Online Resource
    Online Resource
    MDPI AG ; 2019
    In:  Energies Vol. 12, No. 21 ( 2019-10-23), p. 4037-
    In: Energies, MDPI AG, Vol. 12, No. 21 ( 2019-10-23), p. 4037-
    Abstract: A full scale lab prototype of an adsorptive heat transformer (AHT), consisting of two adsorbers, an evaporator, and a condenser, was designed and tested in subsequent cycles of heat upgrading. The composite LiCl/SiO2 was used as an adsorbent with methanol as an adsorbtive substance under boundary temperatures of TL/TM/TH = −30/20/30 °C. Preliminary experiments demonstrated the feasibility of the tested AHT in continuous heat generation, with specific power output of 520 W/kg over 1–1.5 h steady-state cycling. The formal and experimental thermal efficiency of the tested rig were found to be 0.5 and 0.44, respectively. Although the low potential heat to be upgraded was available for free from a natural source, the electric efficiency of the prototype was found to be as high as 4.4, which demonstrates the promising potential of the “heat from cold” concept. Recommendations for further improvements are also outlined and discussed in this paper.
    Type of Medium: Online Resource
    ISSN: 1996-1073
    Language: English
    Publisher: MDPI AG
    Publication Date: 2019
    detail.hit.zdb_id: 2437446-5
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