Silver and palladium nanoparticles-containing products of the low-temperature wave conversion of an energetic material: Catalytic activity in piperylene hydrogenation

The hydrogenation of 1,3-pentadiene into pentenes over the commercial 0.5% Pd/Al₂O₃ catalyst and over a new catalyst containing 1.0% Pd and 3.7% Ag (μ-catalyst) has been investigated. The new catalyst has been prepared via the flameless wave conversion of cyclotrimethylenetrinitramine in a porous composite. The catalytic properties of the new composite in the hydrogenation reaction depend on the hydrogen/1,3-pentadiene ratio and on the catalyst activation temperature. The reaction conditions for selective 1,3-pentadiene hydrogenation have been optimized. The pentenes yield as a function of temperature passes through a maximum at any H₂/C₅H₈ ratio between 1 and 2. The 2-pentene/1-pentene ratio in the reaction products increases as the temperature is raised.     

High-rate combustion of cellulose nitrate in filled polymer systems

It was found that, at a certain external pressure, the conventional slow flameless combustion of nitrocellulose in filled compositions can go over into a high-rate low-temperature mode, with a burning velocity increasing by more than 40-fold. It was shown that the critical external pressure at which the changeover of the combustion modes occurs decreases with the sample porosity. It was assumed that the high-rate combustion of nitrocellulose in filled systems proceeds by the well-known mechanism of convective combustion of energetic condensed systems with some specific features.     

Investigation of the possibility of suppressing the mixing induced by the Rayleigh-Taylor instability by means of reflected waves

The salient features of the reflection of compression waves traveling in a closed channel are studied in the presence of a contact boundary separating gases with different densities. The effect of the reflection nature on the evolution of the mixing region formed due to the Rayleigh-Taylor instability development is shown. The mixing rates are determined in all evolution stages.     

Search for sterile neutrinos in the neutrino-4 experiment

An experimental search for sterile neutrinos has been carried out at a neutrino facility based on the SM-3 nuclear reactor in Dimitrovgrad, Russia. The movable detector with passive shielding against the external radiation may be positioned at a distance varying between 6 and 12 m from the center of the reactor. The antineutrino flux has for the first time been measured using a movable detector placed close to the antineutrino source. The accuracy of the measurements is largely restricted by the cosmic background. The results of the measurements performed at small and large distances are analyzed in terms of the sterile-neutrino model parameters Δm ₁₄ ² and sin²2θ₁₄.     

Averaging in systems containing several small parameters

In this note we consider a system of differential equations containing several small parameters with various orders of smallness. We propose a method of obtaining a “diagonally” averaged system, based on successive application of an averaging process along the trajectories of so-called degenerate systems.     

Effective elastic properties of two-phase composites

Expressions for the effective elastic constants of two-phase composites in the form of series obtained with Fourier transforms have been analyzed. In certain cases, such series are shown to be fully summed up; as a result, one can directly obtain exact expressions for the effective bulk modulus of a composite. It is found that the symmetry of the coefficients in series for the shear modulus and Young’s modulus and the corresponding reciprocal quantities can be used to relate these series to each other. Thus, all well-known exact relations for the effective elastic constants can be derived. A set of equations is proposed to compute the effective constants of a two-dimensional isotropic symmetrical composite with arbitrary properties of its phases.     

Theoretical study of X-ray photoelectron spectrum of germanium valence electrons

The density of states and X-ray photoelectron spectra of germanium valence electrons have been calculated. It is shown that to describe the shape of the photoelectron energy distribution curve of the greatest importance is precise allowance for the particularities of energy band structure and the ratio between excitation probabilities of s- and p-electrons. This is possible if the valence electron states are described with a linear combination of atomic orbitals while the excited electron states are described with the orthogonalized plane wave.     

The effect of transition probability on the shape of X-ray photoelectron spectra of diamond and silicon

X-ray photoelectron spectra of valence bands in diamond and silicon have been calculated. It is shown that the probability of electron excitation from s-states is higher than that from p-states. The density of the electron states in the valence band of these crystals differs markedly from the energy distribution of photoelectrons.     

Resonant bar simulations in media with localized damage

As a rule, problems of wave propagation in finite media with non-uniform spatial distribution of material properties can only be tackled by numerical models. In addition, the modeling of damage features in a material requires the introduction of locally non-linear and--more important--non-unique equations of state. Using a multiscale approach, we have implemented a non-linear hysteretic stress-strain relation based on the Preisach-Mayergoyz (PM) model, into a numerical elastodynamic finite integration technique program, which has originally been developed for linearly elastic wave propagation in inhomogeneous media. The simulation results show qualitatively good agreement with data of non-linear resonant bar experiments in homogeneously non-linear and hysteretic media. When the PM density distribution of hysteretic units at the mesoscopic level is not uniform and/or confined to a finite area in stress-stress space, the response at high amplitude excitation tend to deviate from the quasi-analytical results obtained in the case of a uniform PM-space density. Localized microdamage features in an intact medium can be modeled by conceiving finite zones with pronounced hysteretic stress-strain relations within a "linear" surrounding. Forward calculations reveal a significant influence of the amplitude dependent resonance behavior on the location (edge versus center of a bar), the extend (width of the zone) and the degree (density of hysteretic units) of damage.