Calculation scheme for the evaluation of polymer thermal conductivity

A calculation scheme for evaluating the thermal conductivities of polymers from the data on their chemical structures and degrees of crystallinity has been developed. The scheme is a version of the Vargaftik equation for organic liquids that is modified for polymers. In the modified equation, the heat capacity of a polymer, its density, and the reduced molecular mass of the repeating unit are involved. The effect of polar groups responsible for dipole-dipole interactions or the formation of hydrogen bonds and the effect of the van der Waals volume of the repeating unit of a polymer or the repeating fragment of the network are analyzed. It has been taken into account that atoms in the polymer backbone and in side chains contribute differently to thermal conductivity. The effects of temperature and the degree of crystallinity on the studied characteristic are considered.     

The two-step exponential decay reaction network: analysis of the solutions and relation to epidemiological SIR models with logistic and Gompertz type infection contact patterns

Journal of Mathematical Chemistry - We mathematically analyze the solutions to the dynamical system induced by the two-step exponential (growth-)decay (2SED) reaction network involving three...     

Structural Features of Ni–W Alloy Deposited from Pyrophosphate Electrolyte

Russian Journal of Applied Chemistry - The composition and structure of Ni–W alloys prepapred from pyrophosphate electrolyte have been studied. It was demionstrated that, regardless of the...     

Nanostructured oxide membranes

Porous aluminum (Al 99.99%) foil membranes prepared by electrochemical anodizing and subsequent removing the continuous barrier layer by ion-plasma irradiation are described. As a result, Al₂O₃ membranes about 2–5 μm thick with regular arrangement of channels have been obtained. The possibility has been shown of regulation of a channel diameter in a range of 20–100 nm by changing the oxidation conditions. The experimental dependences of Al and Al₂O₃ sputtering coefficients on the xenon ion energy (100–400 eV) and the angle of incidence have been obtained.     

Numerical simulation of spinning detonation in circular section channels

Numerical simulation of three-dimensional structures of gas detonation in circular section channels that emerge due to the instability when the one-dimensional flow is initiated by energy supply at the closed end of the channel is performed. It is found that in channels with a large diameter, an irregular three-dimensional cellular detonation structure is formed. Furthermore, it is found that in channels with a small diameter circular section, the initially plane detonation wave is spontaneously transformed into a spinning detonation wave, while passing through four phases. A critical value of the channel diameter that divides the regimes with the three-dimensional cellular detonation and spinning detonation is determined. The stability of the spinning detonation wave under perturbations occurring when the wave passes into a channel with a greater (a smaller) diameter is investigated. It is found that the spin is preserved if the diameter of the next channel (into which the wave passes) is smaller (respectively, greater) than a certain critical value. The computations were performed on the Lomonosov supercomputer using from 0.1 to 10 billions of computational cells. All the computations of the cellular and spinning detonation were performed in the whole long three-dimensional channel (up to 1 m long) rather than only in its part containing the detonation wave; this made it possible to adequately simulate and investigate the features of the transformation of the detonation structure in the process of its propagation.     

Calculating the boundary conditions of the formation of solid-phase metal sulfides and selenides by deposition with thio- and selenourea

Calculation equations that allow one to determine the boundary conditions of the formation of solid-phase metal sulfides and selenides with different valences according to the decomposition constants of thio- and selenourea and the kinetic dependence of the accumulation of chalcogenide ions in the reaction system are proposed. The contribution from the crystallization factor to the determination of the boundary conditions of the formation of the solid phase is shown with allowance for the nucleation of metal chalcogenide. The calculation equations determining the boundary conditions of the formation of the main admixture phases upon the hydrochemical deposition of chalcogenides, metal hydroxide, and cyanamide are derived.     

Population inversion induced by collisions in a two level system under nonresonance optical excitation

When the gas particles, which can be considered as a two level quantum system, are affected by frequent collisions with buffer gas particles (thermal reservoir), the spectral densities of the Einstein coefficients for absorption and induced emission are unequal to each other far from the absorption (emission) line. The relationship between the spectral densities at the specified condition reveals new physical phenomena. The mostly convincing example is the fact that population inversion is established in a two level system under nonresonance optical excitation. This effect is experimentally observed as a lasing on sodium resonance transitions.     

Radiative decays and quark content of f 0(980) and φ(1020)

The quark structure of φ(1020) and f ₀(980) is studied on the basis of data on the radiative decays φ(1020) → γπ ⁰, γη, γη′, γ a ₀(980), γ f ₀(980) and f ₀(980) → γγ. The partial widths are calculated under the assumption that all the mesons under consideration are $\bar qq$ states: φ(1020) is a dominantly $s\bar s$ state ( $\eta ' = n\bar nsin\theta + s\bar scos\theta $ component contributes not more than 1%); η, η′, and π ⁰ are standard $q\bar q$ states, $\eta = n\bar ncos\theta - s\bar ssin\theta $ and $\eta ' = n\bar nsin\theta + s\bar scos\theta $ with θ?37°; and f ₀(980) is a e5 meson with the flavor wave function $n\bar ncos\varphi + s\bar ssin\varphi $ . The transition φ → γπ ⁰ specifies the admixture of the $n\bar n$ component in the φ meson: it is on the order of 0.5%. We argue that this order of $n\bar n$ value does not contradict data on the decay φ(1020) → γ a ₀(980). The partial widths calculated for the decays φ → γη, γη? are in reasonable agreement with experimental data. The measured branching-ratio value Br(φ→γf ₀(980))=(3.4±0.4 _?0.5 ^+1.5 ×10^?4) requires 25°≤|?|≤90°. For the decay f ₀(980) → γγ, the agreement with data, Γ(f ₀(980) → γγ)=0.28 _?0.13 ^+0.09 keV, is attained at either ?=85°±8° or ?=?46°±8°. A simultaneous analysis of the decays φ(1020) → γ f ₀(980) and f ₀(980) → γγ favors the solution with the negative mixing angle of ?=?48°±6°, setting f ₀(980) very close to the flavor octet (? _octet=±54.7°).     

Display and applied holography in museum practice

Possible applications of holography for cultural heritage study, demonstration and restoration, particularly in practical museum applications, are discussed. In this respect two main applications of holography are of interest: display holography and technical holography. The latter includes holographic NDT methods, three-dimensional measurements of objects, memory systems, and so on.