Regime of superhigh reactivity of the YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6 + δ</Subscript> superconductor toward the components of air

Physicochemical features of the YBa₂Cu₃O_{6 + δ} superconductor synthesized via ceramic route and subjected to a kind of modification by long-term exposure to an atmosphere with low pH₂O have been studied by X-ray diffraction, thermal analysis, and magnetometry. The resulting material had a high degree of saturation with air components at room temperature and 30% humidity, up to 1.5 wt % in 30 days, which is not inherent in YBa₂Cu₃O_{6 + δ}.     

On the construction of solutions of terminal problems for multidimensional affine systems in quasicanonical form

We consider the construction of solutions of terminal problems for multidimensional affine systems. We show that the terminal problem for a regular system in quasicanonical form can be reduced to a boundary value problem for a system of ordinary differential equations of lower order with right-hand side depending on a vector parameter. We prove a sufficient condition for the existence of a solution of the above-mentioned boundary value problem. A method for constructing a numerical solution is developed.     

Terminal control problem for affine systems

We suggest a method for solving the terminal control problem for multidimensional affine systems that are not linearizable by feedback. We prove a sufficient condition for the existence of a solution and present a numerical procedure for its construction.     

Effect of annealing temperature on the optical properties of nanosilicon produced from silicon monoxide

Silicon nanoparticles (Si-NPs) capable of photoluminescence (PL) over the energy range from 790 nm to 900 nm were synthesized from silicon monoxide by increasing annealing temperatures from 25 °C to 950 °C. The PL of nanoparticles has remained stable for more than ten months from the date of the hydrosilylation of their surface by 1-octadecene. Solid samples of Si-NPs grafted with 1-octadecene are stable in the air up to 220 °C. The mean sizes of particles and their size distribution density function were derived from SAXS and XRD experiments and compared with TEM and HRTEM images and values calculated by the quantum limit model in accordance with the experimental optical absorption gap values. The absorption spectra of Si-NPs synthesized at 25 °C, 200 °C and 300 °C exhibited a blue shift of the fundamental absorption edge with respect to silicon single crystals; the absorption of Si600 and Si950 at the same incident photon shows energies increase. The PL peak of Si-NPs shifted toward longer waves as the synthesis temperature increased and exhibited a stronger red shift with respect to the photoexcitation wavelength. An analysis of the red shift led us to conclude that the surface states related to (Si-O) bonds influenced the effectiveness of PL. The Si-NPs PL quantum yield increased as the annealing temperature grew and reached a maximum of ∼12% for Si-NPs at 950 °C.     

Fermi motion in hypernuclear production

The effects of target-nucleon motion in the (K, π) reaction are studied. The distortion of meson waves and the full transition amplitude are taken into account. The renormalization of the A-body transition matrix due to Fermi motion does not reduce theoretical cross sections substantially.     

Spin-orbit splitting in σ-hypernuclei

The shell model analysis of experimental 0⁺, 2⁺ spectra of and as obtained from (K ^–, ⁺) in-flight and stoppedK ^– reactions, is performed. It suggests a large (twice that for nucleons) spin-orbit splitting of hyperon levelsp _3/2 andp _1/2. Certain constraints on effective central N interaction arise, as well. Some experiments are put forward to further test this value and to extend it to hypernuclei.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.