Semiclassical approach to the description of the basic properties of nanoobjects

Present paper is a review of results, obtained in the framework of semiclassical approach in nanophysics. Semiclassical description, based on Electrostatics and Thomas-Fermi model was applied to calculate dimensions of the electronic shell of a fullerene molecule and a carbon nanotube. This simplified approach yields surprisingly accurate results in some cases. Semiclassical approach provides rather good description of the dimensions of the electronic shell of a fullerene molecule. Two types of dipole oscillations in a fullerene molecule were considered and their frequencies were calculated. Similar calculations were performed for a carbon nanotube also. These results look rather reasonable. Three types of dipole oscillations in carbon nanotube were considered and their frequencies were calculated. Frequencies of the longitudinal collective oscillations of delocalized electrons in carbon peapod were calculated as well. Metallic cluster was modeled as a spherical ball. It was shown that metallic cluster is stable; its bulk modulus and the frequency of the dipole oscillation of the electronic shell relative to the ions were calculated.Comment: Semiclassical description based on Thomas-Fermi model and Electrostatic

On the effective conductivity of composite materials

A composite conductive material, which consists of fibers of a high conductivity in a matrix of low conductivity, is discussed. The effective conductivity of the system considered is calculated in Clausius-Mossotti approximation. Obtained relationships can be used to calculate the conductivity of a matrix, using experimentally measured parameters. Electric fields in the matrix and the inclusions are calculated. It is shown that the field in a low-conductivity matrix can be much higher than the external applied one.Comment: Russian version is include

Prediction of remission of type 2 diabetes mellitus after bariatric surgery

Type 2 diabetes prevalence is increasing dramatically worldwide. Conservative therapy doesn’t bring stable effect and is often insufficient, not to mention the lack of prospects to cure the disease. Fortunately, accumulating evidence points towards the notion that a complete remission of type 2 diabetes is feasible following a choice of surgical interventions. The efficacy of bariatric surgery in particular for achieving glycemic control has highlighted surgery as a candidate curative intervention for type 2 diabetes. When compared to intensive medical therapy and lifestyle intervention, metabolic surgery has shown superiority in achieving reducing number of medications and metabolic factors improvement, which translates in long-term benefits on diabetes progression and complications. Understanding factors that predict diabetes remission can help to select patients who will benefit most from bariatric surgery and to choose the most effective type of operation. This literature review analyzes studies of the most significant clinical and biochemical predictors of remission of type 2 diabetes mellitus after bariatric interventions, as well as highlights well-known mathematical prediction models

Влияние активирующих добавок на процесс холодного спекания высокоэнтропийной керамики (MnFeCoNiCu)3O4

Objectives. To obtain experimental data on the effect of activating additive type on the cold sintering process of (MnFeCoNiCu)3O4 high-entropy ceramic. The following substances were used as activating additives: ammonium acetate (CH3COONH4), acetic acid (CH3COOH), ammonium chloride (NH4Cl), potassium fluoride dihydrate (КF·2H2O), lithium fluoride (LiF), sodium fluoride (NaF), and sodium hydroxide (NaOH).Methods. Synthesis of the initial powder by low-temperature self-propagating method; investigation of the powder particles size distribution by laser diffraction method; analysis of the particle shape and compacted sample microstructure by scanning electron microscopy; investigation of the phase composition by X-ray phase analysis; high-entropy ceramic sample consolidation by cold sintering process. The density of the initial powder and the relative density of cold sintered samples were determined by the Archimedes method.Results. Samples with a relative density of over 0.70 were obtained using distilled water, CH3COONH4 and NaOH during cold sintering at 300 °C, with a holding time of 30 min and pressure 315 MPa.Conclusions. For the first time, the effect of the type of activating additive on the relative density of high-entropy ceramics (MnFeCoNiCu)3O4 samples obtained by cold sintering process has been experimentally demonstrated. The samples microstructures have pronounced differences: 20 wt % distilled water does not lead to grain growth, with only their compaction to 0.71 relative density observed; however, the addition of 0.1 wt % CH3COONH4 and NaOH increases the average grain size when reaching similar relative densities (0.70 and 0.71, respectively). X-ray diffraction analysis showed that the cold sintering process does not lead to a change in the phase composition of the initial (MnFeCoNiCu)3O4 powder, confirming the preservation of the high-entropy structure.Цели. Получение экспериментальных данных о влиянии вида активирующей добавки на процесс холодного спекания высокоэнтропийной керамики состава (MnFeCoNiCu)3O4. В качестве активирующих добавок были использованы: ацетат аммония (CH3COONH4), уксусная кислота (CH3COOH), аммоний хлористый (NH4Cl), калий фтористый 2-х водный (КF·2H2O), литий фтористый (LiF), натрий фтористый (NaF), гидроксид натрия (NaOH).Методы. Синтез исходного порошка методом низкотемпературного самораспространяющегося синтеза; исследование гранулометрического состава порошка методом лазерной дифракции; анализ формы частиц и микроструктуры скомпактированных образцов методом сканирующей электронной микроскопии; анализ фазового состава методом рентгенофазового анализа; консолидация образцов высокоэнтропийной керамики методом холодного спекания; плотность исходного порошка и относительная плотность образцов керамики холодного спекания определялись методом Архимеда.Результаты. Образцы с относительной плотностью свыше 0.70 получены с применением дистиллированной воды, CH3COONH4 и NaOH в процессе холодного спекания при температуре 300 °С, времени выдержки 30 мин и давлении прессования 315 МПа.Выводы. Впервые экспериментально показано влияние вида активирующей добавки на относительную плотность образцов высокоэнтропийной керамики (MnFeCoNiCu)3O4, полученных с помощью процесса холодного спекания. Микроструктуры образцов имеют выраженные отличия: 20 мас. % дистиллированной воды не приводит к росту зерен, наблюдается только их уплотнение до 0.71 относительной плотности; при добавлении 0.1 мас. % CH3COONH4 и NaOH наблюдается рост среднего размера зерен при достижении близких показателей относительной плотности (0.70 и 0.71 соответственно). Рентгенодифракционный анализ показал, что процесс холодного спекания порошка (MnFeCoNiCu)3O4 не приводит к изменению фазового состава исходного порошка, что свидетельствует о сохранении высокоэнтропийной структуры

PROJECTION-MATRIX FORM OF DESCRIPTION OF DYNAMICS OF A TURBOGENERATOR AS A REGULATION OBJECT

The article deals with the projection-matrix form of description of dynamics of a turbogenerator as an object of regulation. The initial model of a synchronous generator in coordinates contains several nonlinear elements performing the operation of two processes multiplication. The authors propose to calculate the matrix multiplication operator of two processes in advance, rather than in the process of the main procedure for further synthesis of the necessary regulators. The obtained form of the description of the turbo generator makes it possible to use it for synthesis of regulation algorithms in deterministic, statistical, and also in robust formulation of problems by advanced projection-matrix methods. The pre-calculated matrix operator for multiplying of two processes makes it possible to reduce the number of iterative processes in the algorithms of regulator synthesis, which makes it possible to build more efficient computational algorithms in real time. The authors proved that synthesis algorithms can be applied to the developed projection-matrix model of the turbogenerator, and such algorithms take into account the random nature of perturbations, the uncertainty of the mathematical model and the identification algorithms

Occurrence of Entomopathogenic Nematodes (Rhabditida: Steienernematidae, Heterorhabditidae) from Agricultural Ecosystems in Forest (Polissya) and Forest-Steppe Natural Zones of Ukraine

A survey for entomopathogenic nematodes (EPNs) of the Steienernematidae and Heterorhabditidae in soils of different crop types of agricultural lands (household plots, commercial fields) in the forest (Polissya) and forest-steppe (Lisostep) zones of Ukraine was carried out in spring, summer and autumn months from 2016 to 2018. In total, 205 soil samples and 92 live-traps were processed. In addition, 98 samples of soil-living larvae and adults of insect crop pests, including cockchafer beetles, click beetle larvae, darkling beetle larvae, caterpillars of the scoops were collected. It is shown that the EPNs distribution and frequency of occurrence depends on the natural geographical features (regional characteristics) and habitat types. EPNs were found in 46 (15.4 %) out 297 samples. The incidence (% of samples) of the entomopathogenic nematodes, and their diversity varied depending on the location-based sampling, the type of agrocenosis, and the predominant agricultural plant species or typical species-edificators. The proportion of entomopathogenic nematodes (Steinernema spp., Heterorhabditis spp.) recovery from regions of Lisostep zone was 16.9 %, and 13.6 % from regions of Polissya zone. The highest number among all positive samples was recorded from the apple trees, Malus domestica Borkh., 1803 (10 samples). The least number of positive samples (one sample) was obtained from sweet cherry trees, Prúnus cérasus L., 1753, junipers, Juniperus communis L., 1753, alfalfa, Medicago sativa L., 1753, common beans, Phaseolus vulgaris L., 1753, and common pumpkin, Cucurbita pepo L., 1753. The steinernematid nematodes were noticeably dominant over heterorhabditid nematodes: 60.8 % vs 39.2 % respectively. Steinernema spp. is widespread in different regions and plots, whereas Heterorhabditis spp. are common in fruit orchards and coniferous decorative perennial plantings

Water-Assisted Cold Sintering of Alumina Ceramics in SPS Conditions

A developing energy-saving approach of cold sintering in a pure aqueous medium was applied to the preparation of α-Al2O3 ceramics and performed on spark plasma sintering equipment. The initial γ-Al(OH)3 and γ-AlOOH powders and the cold-sintered ceramics were studied by X-ray diffraction analysis, infrared spectroscopy, thermal analysis, and scanning electron microscopy to reveal the chemical and structural transformations they experienced during the cold sintering. At 450 °C and 70 MPa, initially γ-AlOOH transformed into a fragile α-Al2O3 material. Porous α-Al2O3 ceramics with about 60% porosity were obtained after cold sintering of γ-Al(OH)3 in the same conditions combined with subsequent annealing at 1250 °C for 3 h. The role of water molecules in the studied processes was considered as the enhancement of structural mobility in the cold-sintered material due to its reversible hydroxylation similar to earlier investigated supercritical water actions on the precursors during α-Al2O3 formation. Further improvement of the cold sintering setup and regimens would open prospects in α-Al2O3 ceramics manufacturing by an ecologically benign route

Cold Sintering Process of Zinc Oxide Ceramics: Powder Preparation and Sintering Conditions Effects on Final Microstructure

Although the activating effect of an acetate medium in the cold sintering process of zinc oxide ceramics is well known, some problems need to be solved on the effect of process conditions and the initial powder’s preparation methods on the ceramic’s density and microstructure. This article describes an effect of the zinc acetate introduction method, its concentration in zinc oxide powder as well as that of the die sealing configuration on the density and microstructure of zinc oxide ceramics obtained by the cold sintering process at 244 °C. The activating additive of zinc acetate was applied in two ways: (1) impregnation in aqueous solution and (2) impregnation with subsequent treatment in water vapor. Zinc oxide powders and ceramics were analyzed using SEM, TGA/DSC/MS and XRD to reveal the effect of powder pre-treatment and sintering conditions on the material microstructure. Cold sintered ZnO ceramics samples with a relative density up to 0.99 and with average grain sizes from 0.28 to 1.71 μm were obtained. The die sealing by two Teflon sealing rings appeared to be the most effective

Evaluation of the Role of the Activating Application Method in the Cold Sintering Process of ZnO Ceramics Using Ammonium Chloride

The influence of the method of applying the activating additive ammonium chloride and its concentration on the density and microstructure of zinc oxide ceramic obtained by cold sintering at 244 °C was investigated. The activating agent was applied by two methods: impregnation and subsequent autoclave treatment. When the powder was activated by the impregnation method, the crystal sizes remained at the initial level of 0.17–0.19 μm. After the autoclave treatment, the crystal sizes increased to 0.31–0.53 μm. Samples of cold sintering ZnO with relative density up to 0.96 and average grain sizes 0.29–0.86 μm were obtained. ZnO powders and ceramic samples were analyzed using SEM, TGA/DSC, and XRD to reveal the effect of the powder activation method and cold sintering conditions on the material microstructure. The effect of ammonium chloride concentration on grain growth and microstructure of ceramic samples is shown. It was found that the average grain size of ceramic samples with an increase in additive concentration passes through a minimum. In cold sintering of the autoclave activated powder, the effect of reducing the average grain size was observed. The results of this work are discussed on the basis of the idea of the solid-phase mobility of the crystal structure arising when interacting with an aqueous medium