Use of a Split Microtron for Instrumental Gamma Activation Analysis

The potentials of a split microtron with an electron beam energy of up to 70 MeV for the gamma activation analysis of some natural samples were studied. Certified reference materials of bottom sediments—terrigenous clay (SDO-1), volcanic-terrigenous mud (SDO-2), and lime mud (SDO-3)—were used as model samples. The samples were irradiated with photons generated upon the deceleration of an electronic beam with an energy of 20–50 MeV. The beam was controlled by placing a gold foil before the test sample. Activation products of C, Cl, Na, Mg, Ti, Fe, Ca, Zr, Mn, Rb, Sr, Ni, Co, Y, As, Ba, Zn, Cs, Sc, Cr, and Ce were identified by gamma lines using a high-purity germanium detector.     

Heat capacity and the magnetocaloric effect in Pr0.6Sr0.4Mn1–x Fe x O3 manganite

The heat capacity and the magnetocaloric effect of Pr_0.6Sr_0.4Mn_1–xFe_xO₃(x = 0 and 0.1) manganite have been studied in the temperature range 80–350 K and magnetic fields to 18 kOe. The magnetocaloric effect is estimated using two independent methods: the method of magnetic field modulation (direct method) and from the data on the heat capacity in magnetic field and without magnetic field (indirect method). The substitution of Fe atoms for Mn atoms (x = 0.1) shifts T _C by 167 K to lower temperatures; in this case, the magnetocaloric effect (MCE) is changed insignificantly in magnetic field 18 kOe with ΔS _M = 2.05 and 2.31 J/kg K for x = 0 and 0.10, respectively.

     

Quasi-static surface modes of plasma layer with anisotropic electron temperature

Quasi-static surface wave propagation in a plasma layer with anisotropic electron temperature is considered. The case is analyzed where the electron temperature in the direction normal to the plasma boundary is considered to be zero, while in the direction along the boundary, electrons are described by the Maxwellian velocity distribution. It is shown that the modes of such a layer are described by equations for bulk plasma waves with renormalization of the electron density affecting the surface wave dispersion and damping.     

Effect of Frequency of the Alternating Electric Field on Temperature Impedance Spectra of LuFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Ceramic Multiferroic

Temperature impedance spectra are measured on LuFe₂O₄ ceramic multiferroics over a temperature range of 100–400 K, upon applying a sinusoidal voltage with a frequency varying between 20 Hz and 120MHz. At signal frequencies of 30–70 MHz, spectra exhibit features such as an abnormal positive temperature resistance coefficient within the temperature range of 200–260 K, which are interpreted in the context of the generalized barrier model.     

Optical Properties of Nonstoichiometric Tantalum Oxide TaO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (<Emphasis Type="Italic">x</Emphasis> &lt; 5/2) According to Spectral-Ellipsometry and Raman-Scattering Data

Optical properties of amorphous nonstoichiometric tantalum-oxide films of variable composition (TaO_x, x = 1.94–2.51) in the spectral range of 1.12–4.96 eV, obtained by ion-beam sputtering-deposition of metallic tantalum at different partial oxygen pressures (0.53–9.09 × 10^–3 Pa), have been investigated. It is shown by spectral ellipsometry that the character of dispersion of the absorption coefficient and refractive index in TaO_x of variable composition suggests that light-absorbing films with dispersion similar to that in metals are formed at oxygen pressures in the growth chamber below 2.21 × 10^–3 Pa, whereas transparent films with dielectric dispersion are formed at pressures above 2.81 × 10^–3 Pa. According to the data of quantumchemical simulation, the absorption peak at a photon energy of 4.6 eV in TaO_x observed in the absorptioncoefficient dispersion spectrum is due to oxygen vacancy. The peak in the Raman-scattering spectra of TaO_x films with metallic dispersion at frequencies of 200–230 cm^–1 is presumably related to tantalum nanoclusters.     

Measurement of Angular Distributions of Gamma Rays from the Inelastic Scattering of 14.1-MeV Neutrons by Carbon and Oxygen Nuclei

The results obtained by measuring the angular and energy distributions of gamma rays originating from the inelastic scattering of 14.1-MeV neutrons by carbon and oxygen nuclei are presented. The measurements in question were performed by the tagged-neutron method in a beam of an ING-27 standard portable neutron generator. The angular distributions of gamma rays emitted by the 2⁺ state of ¹²С at 4.43 MeVand the 3^? state of ¹⁶O at 6.13 MeV were obtained.     

Electric quadrupole and magnetic octupole moments of the light decuplet baryons within light cone QCD sum rules

The electric quadrupole and magnetic octupole moments of the light decuplet baryons are calculated in the framework of the light cone QCD sum rules. The obtained non-vanishing values for the electric quadrupole and magnetic octupole moments of these baryons show nonspherical charge distribution. The sign of electric quadrupole moment is positive for Ω⁻, Ξ^*−, Σ^*− and negative for Σ^*+, which correspond to the prolate and oblate charge distributions, respectively. A comparison of the obtained results with the predictions of non-covariant quark model which shows a good consistency between two approaches is also presented. Comparison of the obtained results on the multipole moments of the decuplet baryons containing strange quark with those of Δ baryons shows a large SU(3) flavor symmetry breaking.     

Optimization problems for periodic systems

Quadratic optimization algorithms for discrete-time linear periodic systems are discussed. Consideration is given to the conventional linear-quadratic problem statement where the optimal controller is found by solving the discrete algebraic Riccati equation and to input-feedback controller design problems. Considerable attention is focused on the synthesis of a reliable controller with a guaranteed stability margin. The following inverse problem is solved: given plant and controller matrices, find the weight matrices of the functional being optimized. The efficiency of the algorithms is demonstrated by way of examples     

Effect of radial density gradient on dispersion of guided helicon mode

The effect of the radial density gradient on the dispersion of guided helicon mode is considered. For the parabolic density profile, the conditions under which the wave frequency is proportional to the axial wavenumber squared (ω ≈ k _z ² ) are obtained.