Search

The article addresses a practicable and economic low-temperature method of TiO synthesis, which allows us in a specific manner to influence structure-sorption characteristics and photocatalytic activity of samples not at the expense of the change of temperature of finite treatment, but rather by way of varying additions of the precipitant and modifier. This method helped obtain nanodisperse TiO with a developed specific area of the surface and high photocatalytic activity with respect to dyes of the anionic and cationic types. Individually obtained TiO samples display activity even higher than commercial products. [ABSTRACT FROM AUTHOR]

The paper presents an overview of theoretical aspects of ultrasound image reconstruction techniques based on the circular Radon transform inversion. Their potential application in ultrasonography in a similar way as it was successfully done in the x-ray computer tomography is demonstrated. The methods employing Radon transform were previously extensively explored in the synthetic aperture radars, geophysics, and medical imaging using x-ray computer tomography. In this paper the main attention is paid to the ultrasound imaging employing monostatic transmit-receive configuration. Specifically, a single transmit and receive omnidirectional source placed at the same spatial location is used for generation of a wide-band ultrasound pulse and detection of back-scattered waves. The paper presents derivation of the closed-form solution of the CRT inversion algorithms by two different approaches: the range-migration algorithm (RMA) and the deconvolution algorithm (DA). Experimentally determined data of ultrasound phantom obtained using a 32-element 5 MHz linear transducer array with 0.48 mm element pitch and 0.36 mm element width and 5 mm height, excited by a 2 sine cycles burst pulse are used for comparison of images reconstructed by the RMA, DA, and conventional synthetic aperture focusing technique (SAFT). It is demonstrated that both the RMA and SAFT allow better lateral resolution and visualization depth to be achieved as compared to the DA approach. Comparison of the results obtained by the RMA method and the SAFT indicates slight improvement of the lateral resolution for the SAFT of approximately 1.5 and 1.6% at the depth of 12 and 32 mm, respectively. Concurrently, however, the visualization depth increase for the RMA is shown in comparison with the SAFT. Specifically, the scattered echo amplitude increase by the factor of 1.36 and 1.12 at the depth of 22 and 32 mm is demonstrated. It is also shown that the RMA runs about 30% faster than the SAFT and about 12% faster than the DA method [ABSTRACT FROM AUTHOR]

At lower mantle conditions, subducted mid oceanic ridge basalts (MORB) will crystallize more than 20 vol% of an aluminum-rich phase, which is referred to generally as the new aluminum (NAL) phase. Given that a significant proportion of the lower mantle may be comprised of subducted crust, the NAL phase may contribute to the bulk elastic properties of the lower mantle. In this study we report for the first time the structure, Raman spectrum and elasticity of single crystals of Na0.41 [Na0.125Mg0.79Al0.085]2[Al0.79 Si0.21]6O12 NAL phase, synthesized at 2260 °C and 20 GPa. The single-crystal structure refinement of NAL, which is consistent with the space group P63/m, reveals dynamic disorder of Na atoms along channels within the structure. The elastic tensor was experimentally determined at ambient conditions by Brillouin scattering spectroscopy. The elastic modulii obtained from the Voigt-Reuss-Hill approximation using the elastic constants determined in this study are KS= 206 GPa and μ = 129 GPa, whereas the isotropic compressional and shear sound velocities are vP = 9.9 km/s and vS = 5.8 km/s. The NAL phase is elastically anisotropic, displaying 13.9% compressional and shear wave anisotropy. Elastic constants as well as Raman active modes of NAL have also been calculated using density-functional theory and density-functional perturbation theory. [ABSTRACT FROM AUTHOR]

Structural and elastic properties of chalcopyrite-type CuInSe are determined in almost full stability range of temperature from 11 to 1,073 K, by in situ X-ray diffraction, employing a synchrotron-radiation source. The studied polycrystalline sample was prepared from a stoichiometric single crystal. Phase analysis reveals the formation of a trace amount of indium oxide impurity phase at the highest temperatures studied. From the obtained smooth lattice-parameter dependencies on temperature, the temperature dependencies of thermal expansion coefficients are derived. These coefficients are found to follow the trends previously reported for narrow temperature intervals. The present results provide a clear experimental evidence that the linear expansion coefficient is slightly negative below 47 K in both, a and c, directions; this temperature limit is in between the previously reported theoretical value (35 K) and the experimental ones (60 and 80 K) of such limit. [ABSTRACT FROM AUTHOR]

Structural features of Li-extraction from the LiCrMnO4 cathode material in Li-electrochemical cells were investigated by in situ synchrotron powder diffraction and completed by ex situ neutron powder diffraction and magnetization measurements on delithiated products. The observed diffraction patterns reveal that both Li-extraction during the cell charge up to 5.15 V and the following Li-insertion upon the discharge down to 3.2 V vs. Li+/Li are one-phase solid-solution processes. According to the Rietveld structure refinement Li atoms were completely removed from the tetrahedral 8a site during the cell charge with the C/10 rate. However, only about 40% Li atoms were inserted during the cell discharge with the same rate. The unit cell parameter a and the average metal-oxygen distance (Cr,Mn-O) show non-linear dependence on the lithium content upon extraction, with the slope changing at 4.9 V and manifesting a change in the mechanism of redox behavior. While the first step between 3 V and 4.9 V is presumably accompanied by the oxidation of Cr3+ to Cr4+, the charging above 4.9 V requires a further oxidation of Cr4+ toward Cr6+. The paramagnetic effective moment of LixCrMnO4 compounds changes non-monotonously with decreasing Li-content. [ABSTRACT FROM AUTHOR]

In situ synchrotron X-ray powder diffraction measurements using a Paris-Edinburgh pressure cell were performed to investigate the nature of the high-pressure breakdown reaction of magnetite (Fe3O4). Refinement of diffraction patterns reveals that magnetite breaks down via a disproportionation reaction to Fe4O5 and hematite (Fe2O3) rather than undergoing an isochemical phase transition. This result, combined with literature data indicates (1) that this reaction occurs at ~9.5-11 GPa and 973-1673 K, and (2) these two phases should recombine at yet higher pressures to produce an h-Fe3O4 phase. [ABSTRACT FROM AUTHOR]

Abstract: The modified synthetic transmit aperture (STA) algorithm is described. The primary goal of this work was to assess the possibility to improve the image quality achievable using synthetic aperture (SA) approach and to evaluate the performance and the clinical applicability of the modified algorithm using phantoms. The modified algorithm is based on the coherent summation of back-scattered RF echo signals with weights calculated for each point in the image and for all possible combinations of the transmit–receive pairs. The weights are calculated using the angular directivity functions of the transmit–receive elements, which are approximated by a far-field radiation pattern of a narrow strip transducer element vibrating with uniform pressure amplitude over its width. In this way, the algorithm takes into account the finite aperture of each individual element in the imaging transducer array. The performance of the approach developed was tested using FIELD II simulated synthetic aperture data of the point reflectors, which allowed the visualization (penetration) depth and lateral resolution to be estimated. Also, both simulated and measured data of cyst phantom were used for qualitative assessment of the imaging contrast improvement. The experimental data were obtained using 128 elements, 4MHz, linear transducer array of the Ultrasonix research platform. The comparison of the results obtained using the modified and conventional (unweighted) STA algorithms revealed that the modified STA exhibited an increase in the penetration depth accompanied by a minor, yet discernible upon the closer examination, degradation in lateral resolution, mainly in the proximity of the transducer aperture. Overall, however, a considerable (12dB) improvement in the image quality, particularly in the immediate vicinity of the transducer’s surface was demonstrated. The modified STA method holds promise to be of clinical importance, especially in the applications where the quality of the “near-field” image, that is the image in the immediate vicinity of the scanhead is of critical importance such as for instance in skin- and breast-examinations. [Copyright &y& Elsevier]