This paper describes an approximate theoretical analysis of a new method for testing explosive materials for sensitivity to mechanical impact, which is known as the shell fracture method. In this ...nonimpact method, the shell fracture releases the solid explosive material contained in it from the compressive load and allows it to free lateral expansion. During a high-velocity flow, the substance explodes if the created compressive stress is sufficiently strong. The explosion pattern as a whole seems to be similar to the phenomenon of initiating an explosion in the case where a charge of a solid explosive material is destroyed by an impact on a pile driver. Therefore, the test procedure under consideration is often mathematically described partially by the previously developed model of the radial flow of a viscoplastic explosive material, its dissipative heating, and thermal ignition in the hot spots of the fluid. The data obtained on various parameters changing during the initiation of an explosion allow one to visualize its course not only within the framework of the method considered, but also to generalize them to explosion-like processes in many materials that are suddenly released from a high load.
The expediency of using a new explosive or mixed composition is often decided by the results of their tests on their sensitivity to mechanical stresses (impact, friction, etc.), which are usually ...performed by standard methods: state, industry, etc. However, the experience of using these methods shows that often they are not sufficiently effective and that the level of danger of explosives in circulation is often underestimated. Based on the results of the analysis of laboratory methods of testing explosives for impact sensitivity—critical pressures and critical energies, based on the search for the optimal parameters for the initiation of the given mechanical explosion—ways to make the existing testing standards more accurate when obtaining data on the sensitivity of explosives are considered in this article.
The experimental data on the sensitivity to impact, characterized by the critical pressures of the initiation of the explosion, of charges from a mixture of okfol-3,5 with aluminum particles with ...dispersion ranging from 0.1 to 160 µm in the entire range of variation of the concentrations of the components are presented. We note that the explosion initiation pressures are constant on the size of metal microparticles when the content of the latter in the mixture is 0.1 < α < 0.7 and nanoparticles are 0.4 < α < 0.7. Analysis of various models of friction showed that the results obtained can be explained using a model of frictional heating of particles during dry friction with plastic wear in a flow of flying fragments during the destruction of an explosive charge upon impact. Additional information is presented to clarify the previously proposed formulations of the mechanism for initiating the explosion of metallized explosives.
On the example of mixtures of octogen with aluminum powders of various dispersities, an approximate theoretical analysis of the method of testing solid explosive materials (EMs) for sensitivity to ...mechanical stress, known as the collapsing shell (CS) method, is carried out. A physical model of the mechanical behavior of the mixture during friction in the flow of the destroyed material is developed and an analytical expression is obtained for the law of heat release during the thermal decomposition of a mixture of octogen with aluminum to calculate the critical parameters of the initiation of an explosion during the removal of the load on an EM (pressure, velocity of the substance, etc.). The mixture’s explosion initiation pattern is numerically modeled under the assumption of the physical and mechanical similarity of the processes of destruction of charges in the CS method and in conventional tests of EMs for sensitivity to impact on a pile driver. An analysis of the obtained time dependences of the parameters of the spreading material shows that the chemical interaction between the components of the mixture is actively manifested during the dynamic unloading of octogen charges with nanosized aluminum particles and is practically absent in mixtures with aluminum with micron-sized particles.
A class of exact solutions of the system of Navier–Stokes equations corresponding to the vortex flow of an incompressible fluid in a cylinder and a coaxial cylinder is obtained. The behavior of the ...solution in the vicinity of singular points lying on the axis of the cylinder is studied. The temperature field is calculated based on the control volume method corresponding to the found class of exact solutions.
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•Chitosan thermoresponsivity is induced by glycerophosphate binding.•Binding stimulates formation of highly ordered hydrate structure of chitosan.•Hydrate structure melting triggers ...phase separation of the system.•Restoration of chitin-like structures after phase separation results in gelation.
Thermoresponsivity of chitosan induced by β-glycerophosphate (GP) in diluted aqueous solutions has been first studied by high-sensitivity differential scanning calorimetry. It has been found that the GP solutions of chitosan undergo a first-order phase transition upon heating. The onset of this transition coincides with the cloud point of the system. This allows one to identify the thermoresponsivity of chitosan as a macroscopic demonstration of the phase separation transition. The transition temperature, enthalpy, heat capacity increment, and width were determined as functions of GP and chitosan concentrations, and the dielectric constant of the solvent. Based on this data, we suggested that GP binds cooperatively to the chitosan matrix at low temperatures. The standard free energy of GP binding (Δbgint= −6 ± 1 kJ mol−1) was estimated from the DSC data. It was shown that the Okada–Tanaka model of cooperative hydration of polymers adequately describes the thermogram of the GP induced phase transition of chitosan.
For problems describing incompressible flows in time-varying domains, classes of exact solutions are obtained within the potential flow model. The resulting exact solutions are used to verify ...numerical results produced by the control volume method. The solution of problems of this class is important for the control of incompressible fluid parameters by varying the flow region.
The mathematical model of the accelerated thermal decomposition of a composite explo-sive, the rate of which is nonadditive with respect to the decomposition rates of the compo-nents, is considered ...using a solid composite explosive of nitrotriazolone with trinitrotoluene with the weight ratio 1: 1 as an example. The formation of an unstable 1: 1 complex at the stage of preliminary heating up of the composition is assumed to be a reason for this decom-position. The subsequent fast thermal decomposition of the complex imparts a necessary acceleration to the decomposition of the composite explosive as a whole, which occurs with a high rate to the end of experiment.
•The growth conditions to produce a ZnWO4:Sm single crystals were determined.•The Sm3+ segregation coefficient in the ZnWO4 single crystal was estimated to be 0.023.•The effect of Sm3 + segregation ...on the ZnWO4 crystal lattice parameters has been investigated.•ZnWO4:148,149Sm crystals were obtained following the established growth technique.
The growth conditions to produce a high quality ZnWO4:Sm single crystals by the Czochralski method were determined in this work. The role of the Sm impurity in the formation of bubbles in a ZnWO4 single crystal is discussed. The Sm3+ ions segregation coefficient in the ZnWO4 single crystal was estimated to be 0.023. The effect of non-isomorphic substitution of Sm3 + for Zn2 + ions on the ZnWO4 crystal lattice parameters has been investigated. The X-ray luminescence spectra of ZnWO4:Sm3+ crystals are discussed. Two ZnWO4 crystals doped with samarium enriched in 148Sm and 149Sm isotopes were obtained following the established growth technique, which demonstrates its feasibility and reliability for production of detector for rare nuclear processes studies.
The dynamics of water physicochemical properties and hydrochemical characteristics in the Dubna River was studied from April 18, 2021 to July 4, 2021. The study showed an increase in pH with ...increasing water temperature and considerable variation in the concentrations of ammonium, nitrite, and phosphate ions in it. Promising approaches were shown to be the use of mathematical processing of UV-spectra of water samples by Gauss method and model biological systems based on natural lipids (low-temperature oxidation of lecithin, and its ability to spontaneously aggregate in a polar environment) for assessing the quality of natural water and its effect on the regulation of oxidation processes in biological objects. Thus, analysis of UV-spectra revealed the presence in water of hydrophobic organic compounds throughout the observation period, compounds with conjugated double bonds and N-containing compounds in late April, free fatty acids, organic compounds with a carbonyl group and P-containing compounds at the end of May and an increase in the diversity of components in water samples in late June. Water samples taken in summer, increased the rate of lecithin oxidation by a factor of more than 1.8, and, throughout the observation period, they caused staged changes in the size of aggregates formed by it and produced a considerable effect on their dzeta-potential.
