τ → K–π0ντ Decay in the Nambu–Jona-Lasinio Model Including the Final-State Interaction of Mesons

JETP Letters - The $$\tau \to {{K}^{ - }}{{\pi }^{0}}{{\nu }_{\tau }}$$ decay has been described within the Nambu–Jona-Lasinio model including the contact term and the contribution from an...     

Metallation of poly(1-trimethylsilyl-1-prop-1-yne) and poly(vinyltrimethylsilane) with superbases

The pathway and degree of metallation of polymers were studied depending on the the conditions (temperature, concentration, nature, and component ratio) of metallation of poly(1-trimethylsilylprop-1-yne) (PTMSP) and poly(vinyltrimethylsilane) (PVTMS) by superbases, viz., BuⁿLi and Bu^sLi, in combination with potassium tert-pentyl oxide (Pe^tOK). For the BuⁿLi—Pe^tOK system (1 : 3), the yield of modified PTMSP reached 90%. In the case of PTMSP, only the Me groups at the double bonds and at the Si atoms undergo metallation, whereas only the Me groups at the Si atoms are metallated in PVTMS. The kinetics of metallation with the BuⁿLi—Pe^tOK system was studied.     

Electronic excitation energy transfer in solid solution of 7-diethylamino-3,4-benzophenoxazine-2-one (Nile Red dye) in bis[N-2-(oxybenzylidene)-4-tert-butylaniline]zinc

Transfer of electronic excitation energy from the host material to guest molecules was studied taking the solid-phase system bis[N-(2-oxybenzylidene)-4-tert-butylaniline]zinc + 7-diethylamino-3,4-benzophenoxazine-2-one (the guest compound) as an example. The luminescence excitation spectra and the concentration quenching of green fluorescence of the host compound and the excitation of sensitized red fluorescence of the guest molecules were studied. Among the exciton mechanism of energy migration and Förster"s long-range, single-jump mechanism, the former dominates. The number of jumps (m) and the mean diffusion length of the singlet exciton (l), calculated in the framework of the model of partially delocalized, randomly hopping exciton, were estimated at 1.5·10³ and 450 , respectively.     

Three-dimensional convective interactions in an inclined longitudinal air layer

The results of a three-dimensional numerical simulation of thermal-gravitational convection for an arbitrary direction of the gravity force are presented. The calculations were carried out for a rectangular domain with the solid-wall aspect ratio 4:0.5:1. The cavity filled with air was heated from below. The convection regime was laminar with Rayleigh numbers Ra = 10³–10⁵. The cavity was gradually turned about the short side in different directions in the range 0–90° to study how the initial conditions affect the convection. The average heat transfer characteristics and the spatial flow patterns are presented. A comparison with two-dimensional calculations is given. The conditions of the occurrence of a hysteresis in the steady state of convection are found, a regime map is constructed, and the specific features of the interaction of heat fluxes are described.     

Studies of relativistic electron scattering at planar alignment in a thin Si crystal

Experiments on 255-MeV electron scattering under (220) planar channeling conditions in a Si crystal were carried out at the linac of the SAGA Light Source. The spatial and angular distributions of electrons penetrating through a 20-μm thick Si crystal at different incident angles with respect to the (220) plane were measured, and features characteristic of the planar alignment were identified. The experimental results were compared with computer simulations, and showed a reasonable agreement. A comparison with doughnut scattering at axial channeling in the same crystal was also performed. It was confirmed that the planar alignment effect is weaker than the axial alignment effect. These studies are important for understanding the basic mechanism of electron scattering and radiation processes in a crystal.     

Diffracted channeling radiation for axial electron channeling

It is shown that, in contrast to diffracted channeling radiation (DCR) in the case of planar channeling, transitions of type 2 → 1, 3 → 2, 4 → 3, and so on make the main contribution to DCR in the case of axial channeling along an isolated axis. The angular DCR distributions for channeling of electrons with the energy corresponding to the Lorentz factor γ = 100 are calculated for an isolated axis using the Coulomb-type potential.