Changes in K-208 glass transmittance spectra under ionizing radiation and molecular fluxes

The effect of 40-keV electron and proton radiation with a flux density of 5 × 10 cm^?2 s^?1 on the deposition of products of thermostimulated gas release from a polymer composite on a substrate made from protective K-208 glass used for the protection of spacecraft solar panels is experimentally investigated. Analysis of the obtained results shows that, unlike proton radiation, electron radiation results in an increase in the optical density of the glass and stimulates the deposition of gas-release products. It is established that the majority of effects generated as a result of exposure of the substrate to electron radiation are neutralized by protons upon combined irradiation with electrons and protons.     

Self-diffusion in liquid lithium and lead from coherent quasi-elastic neutron scattering data

The temperature dependence of the self-diffusion coefficient of liquid lithium in the temperature range of 500–830 K has been investigated using coherent quasi-elastic neutron scattering. Good agreement with the results obtained from incoherent quasi-elastic neutron scattering experiments traditionally used for this purpose has been achieved, as well as with the corresponding literature data. In addition, one temperature point (623 K) has been obtained for the self-diffusion coefficient of liquid lead, which is a pure coherent scatterer.     

Regularities of lamellae ordering in the formation of polypropylene membrane porous structure

The lamellar structure of porous polypropylene membranes prepared by the extrusion of the polymer melt, annealing of extruded films, and their uniaxial extension has been investigated using data of computer analysis of scanning electron microscopy images. It has been shown that the formation of pores at the stage of uniaxial extension is accompanied by an ordering of lamellae or their self-organization controlled by the annealing temperature T _ann. It has been found that the self-organization of lamellae can occur through two mechanisms depending on the spin draw ratio at the stage of extrusion of the polymer melt: in the first case, an increase in the temperature T _ann leads to a gradual transition of the disorder-order type; in the second case, a bifurcation transition occurs with a nonmonotonic change in the order parameter. The conditions of the preparation of regular spatial lattices of lamellae have been discussed.     

Microphase separation in a cross-linked epoxy phenol polymer

The microphase separation on the surface of samples of a cross-liked epoxy phenol (EP) polymer produced by the curing of a composition containing an epoxy diane oligomer (EO) and a phenol formaldehyde oligomer (PO) has been investigated using electron microscopy with decoration by silver chloride. It has been shown that, in the cross-liked EP polymer, there is a quasi-lattice of mixed-type AgCl nanoparticles, which consists of two sublattices. The formation of simple lattices of particles is caused by the microphase separation according to the type of nucleation and growth of fractal clusters of the cross-liked EO; the spinodal decomposition in the binary system; and the formation of interpenetrating polymer networks represented by the superposition of two lattices of particles or two infinite phase clusters (cross-liked EO and PO, respectively).     

Necessary and sufficient conditions for the vibrations of a bounded string with directional derivatives in the boundary conditions

We obtain a closed-form expression for the classical solutions of a mixed problem describing the forced vibrations of a bounded string for two boundary modes with directional derivatives and time-dependent coefficients. We derive necessary and sufficient conditions on the right-hand side of the equation and the initial and boundary data.     

Mössbauer spectroscopy with high velocity resolution: an increase of analytical possibilities in biomedical research

Mössbauer spectroscopy is a useful technique for biomedical applications. To increase analytical possibilities and quality of its biomedical applications a new Mössbauer spectrometric system was developed. This system based on a highly stable, sensitive and precision spectrometer SM-2201 with high velocity resolution and a temperature variable liquid nitrogen cryostat with a moving absorber. The first results of Mössbauer spectroscopy with high velocity resolution demonstrated a decrease in the experimental error in the determination of ⁵⁷Fe hyperfine parameters and, therefore, an increase of accuracy in analysis of small variations of the iron electronic structure, as well as more reliable fitting of complicated spectra.     

Unusual aluminum chloride-assisted conversion of isopropenyl acetate into 3-acetyl- and 3,5-diacetyl-2,6-dimethyl- 4<Emphasis Type="Italic">H</Emphasis>-pyran-4-ones

Reflux of isopropenyl acetate with an excess of AlCl₃ in 1,2-dichloroethane affords 3,5-diacetyl-2,6-dimethyl-4H-pyran-4-one in 17% yield. The mild acidic cleavage of the latter (2% HCl, 20 °C, 16 h) gives 3-acetyl-2,6-dimethyl-4H-pyran-4-one in 87% yield, whereas this reaction under more drastic conditions (17% HCl, reflux, 3 h) gives 2,6-dimethyl-4H-pyran-4-one in 61% yield.     

X-ray diffraction analysis of multilayer porous InP(001) structure

Multilayer structures composed of four porous bilayers have been studied by high-resolution X-ray diffraction using synchrotron radiation, and the photoluminescence of these structures has been investigated at 4 K. The porous structures were formed by anodic oxidation of InP(001) substrates in aqueous HCl solution. The structural parameters of the sublayers were varied by changing the electrochemical etching mode (potentiostatic/galvanostatic). The X-ray scattering intensity maps near the InP 004 reflection are obtained. A model for scattering from such systems is proposed based on the statistical dynamical diffraction theory. Theoretical scattering maps have been fitted to the experimental ones. It is shown that a mathematical analysis of the scattering intensity maps makes it possible to determine the structural parameters of sublayers. The reconstructed parameters (thickness, strain, and porosity of sublayers and the shape and arrangement of pores) are in satisfactory agreement with the scanning electron microscopy data.     

Intramolecular cycloaddition of azomethine ylides, from imines of O-acylsalicylic aldehyde and ethyl diazoacetate, to ester carbonyl--experimental and DFT computational study

Intramolecular 1,3-dipolar cycloaddition of alkoxycarbonyl-substituted azomethine ylides to ester carbonyl was realized for the first time in the reaction of imines of O-acylsalicylic aldehyde with ethyl diazoacetate in the presence of Cu(tfacac)(2). The stereoselectivity of the cycloaddition is explained using DFT calculations.     

Optical properties of spherical gold mesoparticles

Optical properties of spherical gold particles with diameters of 150–650 nm (mesoparticles) are studied by reflectance spectroscopy. Particles are fabricated by laser-induced transfer of metallic droplets onto metal and dielectric substrates. Contributions of higher multipoles (beyond the quadrupole) in the scattering spectra of individual spherical particles are experimentally observed. These observations are performed for particles in a homogeneous environment and for particles located in air on a metal surface. Good agreement between calculations on the basis of Mie theory and experimental results obtained in homogeneous environment is demonstrated. Multipole resonance features in the experimental reflection spectra of particles located on a gold substrate, in the wavelength range of 500–1000 nm, are discussed and theoretically analyzed on the basis of finite-difference time-domain simulations. High-resolution Raman images of mesoparticle pairs at different polarizations of light are also presented.