Investigation of the influence of technological conditions of microarc oxidation of magnesium alloys on their structural state and mechanical properties

Наведені дослідження структури і властивостей покриттів, отриманих при мікродуговій обробці на магнієвому сплаві. Обробка проводилася при анодно-катодному режимі в лужному електроліті з різними домішками. Показана можливість формування кристалічних оксидних покриттів різного фазового складу (MgO, MgAl₂O₄, Mg₂Sі₄, Mg₃(PO₄)₂) товщиною до 300 мкм, що мають високу адгезію з основою, гарні захисні властивості і високу твердість, яка досягає 6,6 ГПа

Magnetic properties of ferrofluid emulsions: The effect of droplet elongation

The paper is concerned with a theoretical explanation of the experimentally observed effect of non-monotonic field dependence of the effective magnetic permeability of ferrofluid emulsion. In a weak magnetic field, the growth of the induced droplet magnetic moment is faster than the linear one due to the droplet elongation accompanied by the reduction of the demagnetizing field. Thus, the emulsion magnetic permeability increases in weak magnetic fields. Further strengthening of the external magnetic field cannot lead to a significant decrease of the demagnetizing field, as the droplets are already highly elongated. On the other hand, the magnetic susceptibility of the ferrofluid reduces with the field strength. Hence, the effective magnetic permeability of the ferrofluid emulsion starts decreasing. The developed theoretical model describes well the experimental observations

Influence of the thermal factor on the composition of electron-beam high-entropy ALTiVCrNbMo coatings

This paper reports results of studying the element and phase compositions of electron-beam coatings based on the high-entropy alloy AlTiVCrNbMo, depending on the deposition temperature (in the range of 300...700 °С). The high-entropy alloys were melted in an arc furnace in an atmosphere of high-purity argon. Vacuum condensates of the high-entropy alloy (AlTiVCrNbMo) with a thickness of 3–5 µm were obtained in the vacuum setup UVN-2M-1 at a working vacuum of 5·10-5 mТоrr. The alloy evaporation was performed from the water-cooled ingot mold using an electron-beam gun with a power of 5 kW. Condensation of vapors of all the elements of the alloy was performed onto copper substrates at temperatures of 300, 500, 700 °C. Based on analysis of the element composition of materials of the target made of the high-entropy six-element alloy AlTiVCrNbMo and electron-beam coatings, based on it, we established the critical parameter (specific heat of vaporization of an element) that defined a selective change in the element composition. In accordance with a characteristic change in the composition of coatings of the multi-element high-entropy alloy, 3 groups of elements were distinguished: with a specific heat of evaporation of 280...350 kJ/mol (group 1), 420…460 kJ/mol (group 2), and 590…680 kJ/mol (group 3). It was shown that the formation of a single-phase coating of the high-entropy alloy (based on BCC of the crystalline lattice) occurs at the higher deposition temperature of 500...700 °C when the coating consists of not less than 5 elements. It was established that based on the conditions for an electron-beam process of materials formation, the results obtained can be divided into two types: those determined by the condition of evaporation of the target and those determined by the conditions of coating deposition. The density of flows of elements, evaporated from the target, is determined by their specific heat of evaporation. However, the ratio of atoms in the flow, derived in this way, may not be retained in the formed coating due to the secondary evaporation of elements from the growth surface. The obtained results allow us to substantiate principles for the selection of components for achieving the optimal element and phase compositions of high-entropy alloys.На основі аналізу елементного складу матеріалів мішені з високоентропійного шестиелементного сплаву AlTiVCrNbMo і електронно-променевих покриттів на його основі встановлено критичний параметр (питома теплота випаровування елемента), який визначає селективну зміну елементного складу. Показано, що формування однофазного покриття високоентропійного сплаву відбувається, коли до складу покриття входить не менше 5 елементів. Отримані результати дозволяють обґрунтувати принципи підбору компонент для досягнення оптимальних елементного та фазового складу високоентропійних сплавів

On the inner structure of 3-dimensional Leibniz algebras

Let $L$ be an algebra over a field $F$ with the binary operations $+$ and $[,]$. Then $L$ is called a left Leibniz algebra if $[[a,b],c]=[a,[b,c]]-[b,[a,c]]$ for all $a,b,c\in L$. We describe the inner structure of left Leibniz algebras having dimension 3

Phase behavior and structure formation of hairy-rod supramolecules

Phase behavior and microstructure formation of rod and coil molecules, which can associate to form hairy-rod polymeric supramolecules, are addressed theoretically. Association induces considerable compatibility enhancement between the rod and coil molecules and various microscopically ordered structures can appear in the compatibility region. The equilibria between microphase-separated states, the coil-rich isotropic liquid and the rod-rich nematic are discussed in detail. In the regime where hairy-rod supramolecules with a high grafting density appear as a result of the association, three phase diagram types are possible depending on the value of the association energy. In the low grafting density regime only the lamellar microstructure is proven to be stable

Influence of the thermal factor on the composition of electron-beam high-entropy ALTiVCrNbMo coatings

This paper reports results of studying the element and phase compositions of electron-beam coatings based on the high-entropy alloy AlTiVCrNbMo, depending on the deposition temperature (in the range of 300...700 °С). The high-entropy alloys were melted in an arc furnace in an atmosphere of high-purity argon. Vacuum condensates of the high-entropy alloy (AlTiVCrNbMo) with a thickness of 3–5 µm were obtained in the vacuum setup UVN-2M-1 at a working vacuum of 5·10-5 mТоrr. The alloy evaporation was performed from the water-cooled ingot mold using an electron-beam gun with a power of 5 kW. Condensation of vapors of all the elements of the alloy was performed onto copper substrates at temperatures of 300, 500, 700 °C. Based on analysis of the element composition of materials of the target made of the high-entropy six-element alloy AlTiVCrNbMo and electron-beam coatings, based on it, we established the critical parameter (specific heat of vaporization of an element) that defined a selective change in the element composition. In accordance with a characteristic change in the composition of coatings of the multi-element high-entropy alloy, 3 groups of elements were distinguished: with a specific heat of evaporation of 280...350 kJ/mol (group 1), 420…460 kJ/mol (group 2), and 590…680 kJ/mol (group 3). It was shown that the formation of a single-phase coating of the high-entropy alloy (based on BCC of the crystalline lattice) occurs at the higher deposition temperature of 500...700 °C when the coating consists of not less than 5 elements. It was established that based on the conditions for an electron-beam process of materials formation, the results obtained can be divided into two types: those determined by the condition of evaporation of the target and those determined by the conditions of coating deposition. The density of flows of elements, evaporated from the target, is determined by their specific heat of evaporation. However, the ratio of atoms in the flow, derived in this way, may not be retained in the formed coating due to the secondary evaporation of elements from the growth surface. The obtained results allow us to substantiate principles for the selection of components for achieving the optimal element and phase compositions of high-entropy alloys.На основі аналізу елементного складу матеріалів мішені з високоентропійного шестиелементного сплаву AlTiVCrNbMo і електронно-променевих покриттів на його основі встановлено критичний параметр (питома теплота випаровування елемента), який визначає селективну зміну елементного складу. Показано, що формування однофазного покриття високоентропійного сплаву відбувається, коли до складу покриття входить не менше 5 елементів. Отримані результати дозволяють обґрунтувати принципи підбору компонент для досягнення оптимальних елементного та фазового складу високоентропійних сплавів

MODELS OF IMAGES WITH RADIAL-CIRCULAR STRUCTURE

The overwhelming majority of known image models are varieties of random fields defined on rectangular two-dimensional grids or grids of higher dimension, for example. In some practical situations, the images have an annular, radial or radial-circular structure. For example, images of the facies (thin film) of dried biological fluid, eyes, cut of a tree trunk or a fruit, blood vessel, erythrocyte, blast pattern, end face detail, etc. In addition, radar and other images are physically obtained in polar or spherical coordinates. These features of images require their consideration in their mathematical models. In this paper, an autoregressive models of homogeneous and inhomogeneous random fields defined on a circle or oval are considered as representations of images with radial or radial-circular structure

A rare combination of noncompact myocardium and coronary dilatation with type 1 neurofibromatosis

The article describes the observation of a child with a very rare combination of noncompact left ventricular myocardium and coronary dilatation in type 1 neurofibromatosis (NF1). The first of these complications, undifferentiated cardiomyopathy, also known as noncompact myocardium, is not described in combination with nF 1 in available literature, although cases of hypertrophic cardiomyopathy in patients with NF 1 have been previously reported. Dilatation of the coronary arteries also refers to infrequent manifestations of vascular pathology against the background of neurofibromatosis, and the combination of all three signs (NF 1, noncompact myocardium and coronary dilatation) has not yet been reported by other authors. When examining the patient, we found the characteristic signs of NF 1 (foci of "coffee" pigmentation on the skin, multiple nevuses, fibroids of the forearm, cognitive disorders), electrocardiogram features of left ventricular hypertrophy, negative T-tooth and ST-segment displacement 1 mm below the isoline in Leads V4-6, in echocardiography - pronounced trabecularity, thinning of the compact myocardium layer and a "spongy myocardium" in the region of the left ventricle apex, dilatation of the coronary arteries. With magnetic resonance imaging, signs of noncompact myocardium of the left ventricle were found, with selective coronary angiography - slowing of the coronary blood flow. The patient receives the permanent treatment for heart failure and aspirin, his condition remains stable for 4 years of follow-u

Ultrasound diagnostics of left ventricular noncompaction

The clinical cases of rare, genetically heterogeneous cardiomyopathy are described - the left ventricular noncompaction (LVNC) cardiomyopathy for four children (three boys and one girl) in age from two months to 6 years. Description of echocardiography signs is presented in accordance with modern diagnostic criteria. Noncompaction of the left ventricle is recognized in three patients, of the left and right ventricle - in one. In three patients out of four, LVNC was a separate disease, and yet in one it was associated with neurofibromatosis type 1, in combination with dilatation of coronary arteries and pericardial effusion. Three of four patients were admitted with congestive heart failure (CHF) of New York Heart Association (NYHA) functional class 3-4 (FC), and one - with CHF 2 FC. The echocardiograms are brought with description of characteristic features of LVNC (hypertrabecularity, spongy myocardium on the apex of the left ventricle, typical correlation of incompact and compact layer from 2.0 to 2.6). All four patients received treatment for CHF (diuretics, beta-blockers, captopril, in one case - digoxin); two out of four got antithrombotic therapy (aspirin, warfarin). Results of follow-up observation of the patients are described with the estimation of echocardiography signs, including dilatation of coronary arteries. Left ventricular ejection fraction - both by Simpson and Teicholz - increased in two patients, with therapy of chronic heart failure at a follow-up visits over > 5 years simultaneously with the decline of severity of CHF. Another two patients have been examined from 2 months to 5 years and have had CHF 3 FC; their left ventricular ejection fraction increased too, but cardiomegaly and right ventricular heart failure preserved