Modeling of Microwave Images of Buried Cylindrical Objects

Tomographic methods of image reconstruction of two-dimensional cross-sections of volumetric objects in millimeter wavelengths band are suggested and considered. It is shown that in the frequency band under consideration, the images of investigated objects may be obtained by first-order diffraction tomography method (Born, Rytov or high frequency approximation of the first-order for scattered electromagnetic field).     

Project of CW race-track microtron-recuperator for free-electronlasers

A project for a race-track microtron-the beam source for a free-electron laser (FEL)-is considered. Utilized in the FEL, the beam will liberate its energy to the RF microtron system when, being decelerated, it passes along the same microtron orbits in inverse sequence. The layout of the microtron is depicted. The microtron comprises an injector, two magnetic straight systems with 180° separating bend, a common straight section with RF cavities (the section is common to electrons of different energy), magnets for the injection and extraction systems, solenoidal magnetic lenses, four separated straight sections with magnetic quadrupole lenses, a FEL magnetic system placed in the fourth straight section, and a beam dump. The design energy of electrons is 35 MeV and the mean current ranges from 0.1 to 1 A     

Optical properties of porous nanosized GaAs

The optical properties of porous GaAs layers obtained by electrochemical etching of single-crystal n-and p-GaAs(100) wafers are studied. It is shown that the shape of the nanocrystals, their mean diameter, and their surface states depend on the conductivity type of the initial crystal. A shift of the peaks corresponding to the main optical phonons to lower frequencies in the Raman spectra is observed. Surface-phonon frequencies determined from the Raman spectra coincide with those determined from the reflection spectra in the infrared spectral region. The forms of the spectral dependences of the reflection coefficient in the phonon-resonance region in bulk GaAs differ from those in porous GaAs. This is caused by the appearance of additional oscillators related to spatially confined lattice vibrations in GaAs nanocrystals. Atomic-force microscopy is used to study the surface morphology of porous GaAs samples formed on the n-GaAs substrates, and a nanosized surface profile is observed. Estimations made for the mean diameter of GaAs nanocrystals based on data from the Raman scattering, infrared spectroscopy, photoluminescence, and atomic-force microscopy yield results that are in good agreement with each other.     

The synthesis of single phase WC nanoparticles/C composite by solid state reaction involving nitrogen-rich carbonized polyaniline

Single phase tungsten carbide nanoparticles (WC-NPs), (mean particle diameter 5.4 nm), distributed over carbonized polyaniline (C-PANI) nanotubes/nanosheets were synthesized by a solid state reaction between WO₃ and nitrogen-rich carbonized polyaniline at 1000 °C in a reducing atmosphere. The resulting composite was characterized by X-ray diffractometry, electron microscopy, thermogravimetry in oxidizing and reduction atmospheres and elemental analysis. We suggested that the synthesis of WC as a single phase was facilitated by reactive C atoms with dangling bonds, formed upon nitrogen removal.     

Enhancement of electrocatalytic properties of carbonized polyaniline nanoparticles upon a hydrothermal treatment in alkaline medium

The electrocatalytic activity of carbonized polyaniline nanostructures (Carb-nanoPANI) towards oxygen reduction reaction (ORR), estimated in 0.1 mol dm⁻³ KOH solution, was significantly improved upon a hydrothermal treatment in 1 mol dm⁻³ KOH solution. Namely, the onset of ORR was shifted by ∼70 mV to more positive potentials, and the number of electrons consumed per O₂ molecule was enhanced in comparison to the original material. The number of electrons involved in ORR depended on loading, and with a loading of 0.5 mg cm⁻², for the potentials lower than −0.5 V vs SCE, the number of electrons approached 4. For this material, high stability of electrochemical behavior and resistance to the poisoning by ethanol was evidenced by potentiodynamic cycling.     

Thermal Properties of n-Hexane at Temperatures of 298.15–363.5 K and Pressures of 0.098–147 MPa

The thermal-expansion coefficient and isobaric heat capacity c _p of n-hexane at 298.15–363.5 K and 0.098–147 MPa are measured by flux calorimetry. Observed and calculated c _p data are compared, and a general equation for determining c _p is suggested.     

A self-heated hollow cathode made of compacted TiN powder: the preparation method and test results

A method for the formation of a tubular hollow self-heated cathode using magnetic-pulse pressing of a mixture of TiN (90%) and Ti (10%) powders with subsequent annealing and sintering during operation of the compact as a cathode in a high-current (5–45 А) discharge at temperatures of 2000–2200°C is described. Massive tubular cathodes with a 2.5-mm-thick wall and a large (up to 12 mm) inner diameter were manufactured. The erosion rate of a TiN cathode was 2.3 × 10^–7 g/C for the operation in an Ar/N₂ mixture and increased by a factor of 1.6 in the oxygen–argon plasma generation mode with separate feeding of gases.     

Change of the wear resistance of a superhigh-molecular-weight polyethylene plate upon its modification by a mechanically activated ceramic nanopowder

The object of investigation is superhigh-molecular-weght polyethylene (SMWP) with a molecular weight of up to 8 × 10⁶ g/mole and a particle size from 63 to 315 μm obtained by the technique developed at the Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. The purpose of this work is to create structural polymer materials with high physical and technical characteristics and to extend the scope of the application of this polymer in industry. The problem is solved by the modification of SMWP powder particles via the introduction of nanodispersed ceramic materials. Based on the data obtained, the methods of the production of the article samples from nanocomposite materials based on SMWP via the hot-pressing technique were developed and the influence of the nanomodifiers on the properties of the composite material was studied.     

Silica and Magnesia Dopant Distributions in Alumina by High-Resolution Scanning Secondary Ion Mass Spectrometry

Trace SiO₂ and MgO additive distributions in sintered alumina have been studied using high-resolution scanning secondary ion mass spectrometry (SIMS). When doped with each additive individually, evidence is seen for both strong silicon segregation to grain boundaries ( C _gb/ C _grain similar/congruent 300) in SiO₂-doped alumina and strong magnesium segregation to grain boundaries ( C _gb/ C _grain similar/congruent 400) in MgO-doped alumina. When codoped with both SiO₂ and MgO, segregation of both ions to grain boundaries is reduced by a factor of 5 or more over single doping. The additive concentrations increase proportionally in the grains, and both dopants become more uniformly distributed throughout the bulk. It is concluded that codoping with these additives increases their mutual bulk solid solubility and decreases their interfacial segregation over single doping. The beneficial effect of MgO additions in controlling microstructure development in alumina and improving corrosion resistance to aqueous HF stems from its ability to redistribute silicon ions from grain boundaries into the bulk.