Search

This paper presents the results of experimental and computational studies of instability development and mixing at the contact boundaries between gases of different densities. It has been shown that instability and mixing at two contact boundaries in a three-layer gas systems occur after a shock wave with a Mach number M = 1.3 that forms on the left end and moves along the tube has passed through the contact boundaries. Two experiments were performed, in the first of which the central layer was filled with a heavy gas (SF6 gas), and in the second experiment, it was filled with a light gas (helium). On the left and right of the central layer was air at atmospheric pressure. A comparison of the results was performed.

The experimental data and the results of direct numerical simulation of the flow developed in a constant-cross-section tube in passage of a shock wave through a three-layer gas system are presented. The three-layer systemis formed as a result ofmounting two thin films in the tube and filling the space between them with gases of different densities. The first interface (thin film) makes an angle of 45◦ with the shock front and the second interface is located in parallel to the front. The shock wave is formed at the left tube end and moves towards the first interface at the Mach number M = 2.4. The results of simulation of the problem are compared with the experimental data.

The results of the SERP-E-184 experiment at the U-70 accelerator (IHEP, Protvino) are presented. Interactions of the 70GeV proton beam with carbon, silicon and lead targets were studied to detect decays of charmed \(D^{0}\), \(\bar{D}^{0}\), \(D^{+}\), \(D^{-}\) mesons and \(\Lambda_{c}^{+}\) baryon near their production threshold. Measurements of lifetimes and masses have shown a good agreement with PDG data. The inclusive cross-sections of charm production and their A-dependences have been obtained. The yields of these particles are compared with the theoretical predictions and the data of other experiments. The measured cross-section of the total open charm production ( \(\sigma_{\rm tot}(c\bar{c}) = 7.1 \pm 2.3({\rm stat}) \pm 1.4({\rm syst})\) μb/nucleon) at the collision c.m. energy \(\surd s = 11.8\) GeV is well above the QCD model predictions. The contributions of different kinds of charmed particles to the total cross-section of the open charm production in proton-nucleus interactions vary with energy.

Data from the SVD-2 experiment that were obtained at the IHEP accelerator in 70-GeV/c proton-nucleus interactions are analyzed with the aim of searches for an exotic Θ+ baryon that decays through the pK S 0 channel. The reaction pN → pK S 0 + X characterized by a bounded multiplicity of charged secondaries is used for this analysis. A resonance of mass M = 1526 ± 3(stat.) ± 3(syst.) MeV/c 2 and width Γ < 24 MeV/c 2 is observed in the invariant-mass spectrum of the pK S 0 system at a statistical significance of 5.6σ. The mass and the width of this resonance correspond to the recently found positive-strangeness Θ+ baryon, which was predicted to be an exotic baryon consisting of five quarks (pentaquark), $$uudd\bar s$$ . The total cross section for the production of a Θ+ baryon in pA interactions is estimated at a value within the range 30–120 μb for x F ≥ 0. An analysis of the A dependence of the cross section for Θ+-baryon production does not reveal a significant deviation from the A dependence for inelastic events (∼A 0.7).

The critical properties of Ising model on the dynamical triangulated random surface embedded in D-dimensional Euclidean space are investigated. The strong coupling expansion method is used. The transition to thermodynamical limit is performed by means of continuous fractions.