Search

An improved method for parallel MRI reconstruction based on a modified GRAPPA technique is proposed. The method uses an extended linear mapping kernel and an optimized k-space configuration. The results of MRI reconstruction are compared to those obtained using other methods. Essential advantages of the proposed method at high values of the acceleration factor are demonstrated.

The photoluminescent properties of CeO2 nanoparticles ablated by pulsed laser radiation are studied. Annealing nanoparticles in the range 400–1000°C changes the luminescence spectrum. The results are consistent with oxygenvacancy defects in the surface layers of ablated nanoparticles. The activation energy of photoluminescence centers is determined. A qualitative explanation of the observed regularities is presented.

The paper investigates the size and morphological composition of ablated cerium dioxide nanoparticles after ultrasonic dispersion at centrifugation speeds from 800 to 13400 rpm. A nanodispersed solution of cerium dioxide was deposited onto silicon substrates by the drop method. To characterize the size and morphological composition of cerium dioxide nanoparticles, methods of scanning electron and atomic microscopy were used, and X-ray phase analysis was performed. It was found that ablated cerium dioxide particles in an aqueous solution agglomerated and without centrifugation their average size was 162 nm, after centrifugation their average size varied from 86 nm to 142.5 nm. X-ray phase analysis showed that with an increase in the centrifuge speed, the size of the coherent scattering region decreases, which affects the effectiveness of antioxidant properties, for example, in the Fenton reaction.

The article discusses the results of ordering a composite of carbon nanoparticles (CNPs) coated copper oxide (CuO) on the silicon substrate by the electrophoresis method and, particles size and chemical composition have analyzed by Raman spectroscopy, an Atomic Force Microscope, and Scanning Electron Microscope. Carbon nanoparticles from Single-walled Carbon Nanotubes (SWCNTs) using the centrifugation method are applied by a pipette (by the drop method) on the silicon substrate with copper electrodes under the direct electric field to obtain CNPs-CuO nanocomposite films. It has been shown that carbon nanoparticles in solutions upon dispersion in an ultrasonic bath and subsequent centrifugation have a limiting particle size of 38 nm and CNPs solution can be controlled to obtain the nanocomposite films by the electrophoretic forces.

The synthesis of nanotubes and faceted nanocrystals of titanium dioxide doped with alkali metals cations has been performed. It has been established that TiO2 nanotubes with lengths of up to 100 nm and thicknesses of 50–500 nm obtained by solvothermal synthesis have an anatase structure in the direction of crystal growth. Faceted TiO2 particles with sizes of 80–150 nm doped with Na and K cations (2–7 at % calculated to a yield of TiO2 yield) preserve the anatase structure, whereas doping with Li induces the formation of a mixture of anatase and rutile. An analysis of the diffuse reflectance spectra showed that dopants had an insignificant effect on optic properties of TiO2 nanoparticles. The high activity of these catalysts is explained by a decrease in the rate of recombination of charge carriers, rather than by the increase of their photo-generation yield.

Cerium-dioxide nanoparticles are prepared by laser ablation, and their structure is studied by transmission electron microscopy and X-ray-diffraction analysis. The semiquantitative elemental composition is determined by electron energy-loss spectroscopy. Based on the spectral data obtained before and after annealing of particles, the significant oxygen-vacancy concentration in the structure of ablated CeO2 nanoparticles is established.

Thermostable monodisperse nanoparticles of anatase with a diameter of 35–50 nm doped with tungsten were obtained by the method of hydrothermal synthesis. It was found that the temperature of the phase transition from anatase to rutile decreases from 905 to 650°С with the increase in the content of tungsten oxide from 0.35 to 4% in the precursor. Diffuse reflection spectra of the synthesized nanoparticles were obtained, and the values of the band gap were determined. The band gap varies with changes in tungsten content from 3.15 eV for pure anatase to 2.91 eV for TiO2/WO3(4%), leading to an increase in the optical absorption in the visible and the ultraviolet regions.

The synthesis of nanowhiskers (NW) of WOx/W composites has been performed on a nickel substrate in flow of WO2(OH)2 vapor and CO and Ar gases at temperatures of 850–1000°C. Individual and bundled NWs grow in the form of nanorods at an angle to the substrate surface. Their length (5–30 µm) and diameter (100–300 nm) depend on the synthesis temperature conditions. The presence of an oxide film WOx of variable stoichiometric composition (x = 2.72–3) on the surface of tungsten NWs has been revealed using transmission and atomic force microscopy (TEM and AFM): the thickness of the oxide layer reaches 5 nm.

Photocatalytic decomposition of a polymer film with TiO2 nanoparticles of different sizes and morphologies was investigated using transmission electron microscopy. Electron energy loss spectroscopy found that UV irradiation of the polymer-film–TiO2-nanoparticle composite decreased the carbon content in the polymer film. It was shown that this method could be used to study the activity of photocatalysts for decomposing organic matter.

The methods of scanning and transmission electron microscopy, energy-dispersive analysis, and electron energy loss spectroscopy are used for the study of the interaction of soluble sodium and magnesium sulfates, as well as sodium chloride (in the presence of Na and Mg sulfates), with clay minerals: kaolinite and smectite. It is shown that the interaction of clay minerals with salt solutions initiates the reorganization of crystallites of the minerals and results in the formation of clay-salt microaggregates. The manifestation of the formation of clay-salt microaggregates and their composition, size, shape, and particle-packing state depend on the nature of the minerals and the properties of the salt participating in the interaction. In addition, the interaction of sodium chloride in the presence of sulfates results in the formation of peculiarly shaped pen tagonal clay–salt ultramicroaggregates. Their microdiffraction patterns are characterized by the presence of reflections corresponding to fivefold rotational symmetry; this may be evidence of their quasicrystalline structure.

The absorption and photoluminescence spectra of laser-ablated hafnium dioxide nanoparticles are studied by optical spectroscopy. The band gap of the nanoparticles is determined from the intrinsic absorption edge. The influence of the parameters of the laser ablation and the subsequent thermal annealing on the optical properties of the nanoparticles is studied.

The author's second affiliation was inadvertently omitted. The affiliations should read Far Eastern State Transport University, 47 Seryshev Str., Khabarovsk, 680042, Russia; Southwest State University, 94 50-let Oktyabrya Str., Kursk, 305040, Russia.

Nanocrystals of TiO2 of various shapes have been obtained by the solvothermal synthesis technique. It is found that the morphology of TiO2 particles is determined by the type of solvent, while their crystallinity and the sizes of particles depend on the temperature and duration of the synthesis. The conditions needed for nanocrystals of anatase to be formed in the shape of spherical particles with a diameter of 10–15 nm, cubic particles with ribs of 25–30 nm, and nanowires with diameters of 50–100 nm and lengths of more than 100 μm are determined. The structural and geometric parameters of synthesis products are determined with the help of the PEM technique.

The photocatalytic properties of titania (titanium dioxide) nanoparticles ablated by pulsed laser radiation are studied in this work. The influence of the subsequent annealing in a furnace at various temper� atures on the properties of particles is studied. It is shown that the photocatalytic activity of particles decreases as the temperature of annealing rises. The degradation of the properties is associated with the growth in size of TiO2 nanoparticles and the decrease in surface defects in the process of thermal annealing.

The nanoparticles of cerium dioxide have been produced by laser ablation. The ultraviolet (UV) absorption spectra of the synthesized nanoparticles are studied. The band gap of the particles and the effect exerted on it by laser radiation intensity during the synthesis of nanoparticles are determined from the analysis of the spectra. Electron energy loss spectra (EELS) of the nanoparticles are investigated on a transmission electron microscope. Comparative analysis of the UV and EELS spectra has been carried out.

A method for obtaining titanium dioxide (TiO2) nanoparticles by laser ablation has been developed. Pulsed laser irradiation at an intensity of 109 W/m2 leads to sputtering of titanium dioxide in the form of particles with dimensions within 10–50 nm. The phase composition and morphology of obtained nanoparticles have been studied by the methods of transmission electron microscopy and X-ray diffraction. Thermal annealing above 600°C leads to an increase in the average particle size and induces the structural transition of titanium dioxide from anatase to rutile modification. Quantitative dependences of the particle size and phase composition on the annealing temperature are established. It is established that, using the laser ablation method, it is possible to obtain the anatase phase of TiO2 with increased thermal stability.

A technique for producing ZrO2 dioxide nanoparticles under the action of pulsed laser radiation is developed. By the methods of transmission electron microscopy and X-ray phase analysis, it is shown that the high-temperature cubic phase of ZrO2 is formed during laser ablation. The dependence of the size of ZrO2 dispersed particles on the laser radiation intensity is determined. A thermodynamic one-dimensional model of laser ablation of zirconium dioxide is analyzed. The results of analytical computations of ablation of ZrO2 particles are confirmed by experimental data.

The microstructure and phase composition of a copper foil subjected to single low-voltage discharges of different duration and power have been studied. It was found that the grain size decreases from 200 μm to 10 nm with approaching the center of the discharge-affected zone. The electron-microscopic examinations showed that the compounds formed by electrode materials and oxygen were regularly distributed depending on the distance from the center of the discharge-affected region.

The ultraviolet (UV) absorption spectra of titanium dioxide nanoparticles synthesized by laser ablation are studied. The band gap of the particles and the effect exerted on it by various factors, such as the laser radiation intensity during the synthesis of nanoparticles and the temperature of subsequent annealing of the particles in a furnace, are determined from the analysis of the spectra. The dependence of the peak positions in the UV spectra on the type of defects in the structure of the nanoparticles is discussed.

A circuit and the structural features of apparatus for the synchronous recording of the electrical and optical characteristics of spark discharges, which occur between two electrodes at low voltages, are described. The parameters are recorded in digital form with a discreteness of 4 μsec.

The elastic properties of tungsten nanowires (NWs) grown by the carbothermal reduction of nickel tungstate (NiWO4) have been studied using atomic force microscopy (AFM). Based on the AFM data, the elastic moduli of NWs with various dimensions have been calculated. It is concluded that the elastic properties of tungsten NWs are determined by grain boundaries.