Contact probing of stretched membranes and adhesive interactions: graphene and other two-dimensional materials

Contact probing is the preferable method for studying mechanical properties of thin two-dimensional (2D) materials. These studies are based on analysis of experimental force–displacement curves obtained by loading of a stretched membrane by a probe of an atomic force microscope or a nanoindenter. Both non-adhesive and adhesive contact interactions between such a probe and a 2D membrane are studied. As an example of the 2D materials, we consider a graphene crystal monolayer whose discrete structure is modelled as a 2D isotropic elastic membrane. Initially, for contact between a punch and the stretched circular membrane, we formulate and solve problems that are analogies to the Hertz-type and Boussinesq frictionless contact problems. A general statement for the slope of the force–displacement curve is formulated and proved. Then analogies to the JKR (Johnson, Kendall and Roberts) and the Boussinesq–Kendall contact problems in the presence of adhesive interactions are formulated. General nonlinear relations among the actual force, displacements and contact radius between a sticky membrane and an arbitrary axisymmetric indenter are derived. The dimensionless form of the equations for power-law shaped indenters has been analysed, and the explicit expressions are derived for the values of the pull-off force and corresponding critical contact radius

Thermally activated motion of dislocations in irradiated KBr crystals

Dynamics of thermally activated motion of dislocations in real time were studied by recording the pulses of electrical potential on the surface of the KBr crystals (in situ). It is shown that the radiation influence leads to crystals hardening, activation energy increasing and movement of dislocations initial stage shift to higher temperatures

Magnetically Stabilized Luminescent Excitations in Hexagonal Boron Nitride

Magnetically stabilized luminescence is observed in hexagonal boron nitride. The luminescence is induced by absorption of cold neutrons and is in the visible region. In the absence of a magnetic field, the photon emission level is observed to decay over several hundred seconds. A fraction of this luminescence can be suppressed if the temperature is T <~ 0.6 K and the magnetic field is B >~ 1.0 T. Subsequent to irradiation and suppression, luminescence can be induced by an increase in T or lowering of B. Possible explanations include stabilization of triplet states or the localization and stabilization of excitons.Comment: 11 pages, 7 figures, to appear in the Journal of Luminescenc

Microwave plasma torch for processing hydrocarbon gases

AbstractWe designed and developed an ultrahigh-frequency (microwave) plasma torch with a combined (nitrogen, methane) plasma-forming environment, and microwave output of up to 2 kW, continuously. We demonstrate the possibility of using it in order to process natural and associated petroleum (APG) gas into valuable products (hydrogen and carbon nanomaterial CNM) with up to 70% efficiency. Based on the developed microwave plasma torch, we developed an apparatus capable of converting hydrocarbon feedstock at a capacity of 50 g/h yielding CNM and hydrogen of up to 70 vol. %. In its mobile small-tonnage version, this technology can be used on gas-condensate fields

Low temperature sintering of electroexplosive nanopowders

By means of the methods of conductivity measurement and transmitting electron microscopy of sintered metal layer it has been shown that electroexplosive copper and zink powders are sintered with the formation of strong aggregates of corresponding compact metals. It has been also shown that sels-sintereing is a cause of below reduction of metal powder particle size obtained by the method of semiconductor electrical explosion

Influence of concentration modifier on the structure and functional properties of aluminum oxyhydroxide modified

Studying the properties of nanomaterials is an important task, but nanomaterials with desired properties is a promising direction. The aim of this work is to investigate the influence of the value of the concentration of the modifier (ions Mn{2+}) on the structural and functional properties of modified aluminum oxyhydroxide. In this paper, using methods such as the X-ray diffraction studies, differential thermal analysis, electron microscopy, chromatography. The paper found that increasing the concentration of the modifier result in significant changes in the morphology, the appearance of metallic aluminum, which is well seen on X-ray data samples. The influence of thermal effects on a modified aluminum oxyhydroxide argon. Set the phase transition temperatures in the synthesized samples. It is shown that with increasing sodeozhaniya manganese in the composition of the synthesized samples decreases the value of specific surface area. Study of the functional properties showed that the synthesized material has catalytic properties in the oxidation of methane. It is shown that the effective sample is a sample with a manganese content of 2.7 wt. %. By XRD results calcined in air samples modified aluminum oxyhydroxide was shown that only in the sample with a manganese content of 2.7 wt. % MnAl[2]O[4] phase is formed, which is catalytically active phase

The JKR-type adhesive contact problems for transversely isotropic elastic solids

The JKR (Johnson, Kendall, and Roberts) and Boussinesq–Kendall models describe adhesive frictionless contact between two isotropic elastic spheres or between a flat end punch and an elastic isotropic half-space. Here adhesive contact is studied for transversely isotropic materials in the framework of the JKR theory. The theory is extended to much more general shapes of contacting axisymmetric solids, namely the distance between the solids is described by a monomial (power-law) function of an arbitrary degree d⩾1d⩾1. The classic JKR and Boussinesq–Kendall models can be considered as two particular cases of these problems, when the degree of the punch d is equal to two or it goes to infinity, respectively. It is shown that the formulae for extended JKR contact model for transversely isotropic materials have the same mathematical form as the corresponding formulae for isotropic materials; however the effective elastic contact moduli have different expression for different materials. The dimensionless relations between the actual force, displacements and contact radius are given in explicit form. Connections of the problems to nanoindentation of transversely isotropic materials are discussed

CHANGING THE NATURE OF STOCK RISK OVER TIME THE LONG-TERM ASPECT

Background: The risk of stock return is of paramount importance for a stock trader, but for an investor who owns an investment portfolio or stocks for a long time, the risk associated with a sharp drop in stock prices, usually characteristic of a stock crisis, or crisis risk comes first. The timing of the stock market crisis and its duration are unknown, and historical analogy is usually used for its approximate forecasting. Purpose: The study proposes theoretical model that represented relationship between stock price and company's equity per share depending on a number of main economic indicators. Results: If we proceed from the position that a stock crisis occurs when the stock price significantly exceeds its economic basis in the form of the company's own capital, then it becomes possible to assess the crisis risk by the degree of excess of the stock price of its objective basis. However, as the analysis shows, such a basis is not directly the equity capital of a joint-stock company, but such a value that reflects both the use of borrowed capital and the most important proportions of profit distribution, which are characteristic both for an individual company and for the stock market as a whole. Therefore, as an indicator of crisis risk, it is proposed to use a coefficient showing the ratio of the actual excess of the price over its economic basis to the normative, or economically justified, excess. Conclusion: Calculations of the crisis risk index can be useful for predicting "soap bubbles" in the stock market and stock crises

Dependence of the preparation method on the phase composition and particle size of the binary NiO–ZrO2 system oxides

Was studied how preparation method influences phase composition, oxide particle size and catalytic activity of the binary NiO–ZrO2 systems. The processes taking place under the thermal influence while NiO–ZrO2 catalysts are formed from precursors, obtained using a variety of methods, were determinated using the methods of simultaneous TGA-DTG/DSC analysis and XFA. Was studied the influence of the precursor preparation method upon the catalysts' phase composition, sizes of the nickel oxide and zirconium dioxide particles. The research revealed that preparation of precursor using coprecipitation method makes it possible to obtain a binary system, where nickel oxide has minimal size, determined by CSR, and monoclinic phase prevails in ZrO2, after heating it to 800 °C. The research unearthed that the catalyst exhibiting maximal catalytic activity by deep oxidation of methane is nickel oxide-zirconium dioxide, containing equal amounts of monoclinic and tetragonal phases of ZrO2