306 research outputs found

    Magnetic properties and structure of TiO2-Mn (0.73 %) nanopowders: The effects of electron irradiation and vacuum annealing

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    Nanopowder TiO2-0.73 % Mn was synthesized by the sol-gel method. Thermal treatment of the samples was carried out in vacuum at a temperature of 500°C. Magnetic properties were studied in the temperature range from 2 to 850 K. The effects of electron irradiation and vacuum annealing on the EPR spectra and magnetic properties of TiO2-Mn powder are discussed. It was established that a part of manganese ions in the anatase crystal lattice interacts antiferromagnetically, which causes a decrease in magnetization as compared to the result of the calculation for non-interacting ions. Vacuum annealing leads to the formation of oxygen vacancies and, at the same time, to a noticeable increase in the ferromagnetic contribution to magnetization, especially, after preliminary electron irradiation. We assume that the ferromagnetic contribution to the magnetization appears either due to incomplete compensation of antiferromagnetically directed moments of manganese ions, or due to positive exchange interactions of Mn ions via defects in the TiO2 lattice. It is shown that the temperature of magnetic disordering in samples with a spontaneous magnetic moment exceeds 600°C. © 2019, Institute for Metals Superplasticity Problems of Russian Academy of Sciences. All rights reserved

    Unconventional magnetism of non-uniform distribution of Co in TiO2 nanoparticles

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    High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) analysis, electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS), magnetic methods, and density-functional theory (DFT) calculations were applied for the investigations of Co-doped anatase TiO2 nanoparticles (∼20 nm). It was found that high-spin Co2+ ions prefer to occupy the interstitial positions in the TiO2 lattice which are the most energetically favourable in compare to the substitutional those. A quantum mechanical model which operates mainly on two types of Co2+ – Co2+ dimers with different negative exchange interactions and the non-interacting paramagnetic Co2+ ions provides a satisfactorily description of magnetic properties for the TiO2:Co system. © 2020 Elsevier B.V.Russian Foundation for Basic Research. Ministry of Science and Higher Education of the Russian Federatio

    Social Distancing and the Deficit of Presence (Philosophical Reflection of the Covid-19 Pandemic)

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    The paper claims that if the COVID-19 pandemic turned out to be a man-made risk (А. Giddens), i.e. an unforeseen consequence of a person’s own behavior and actions, then in order to avoid such fatal contingences that occur so unexpectedly, it is necessary to change the type of behavior and actions that have established in the culture of the Modern Period. During the pandemic people are forced to observe the spatial order. Distancing, self-isolation, the Red Zone and other spatial limitations made people acutely aware of the deficit of presence, the lack of their independent active participation in life. The new virus, on the one hand, returned a person to the awareness of the biological, natural origin of human existence, which has been forgotten by culture (science). On the other hand, the practices of social rationing and restriction revealed the influence of various forms of alienation — social, political, economic, cultural — on the fate of each individual. The introduction of the bioprinciple (the virus) into the social, cultural and political space radically changes the relationship between people and nature. This situation makes one think about the meaning of the notion of culture, which got its definition in the 18th century and is understood as non-nature reflected in the formula culture vs nature. The paper shows that the cultural ideal of human activity, which was established in modern times, became the reason of the alienation of technogenic civilization and social forms of life from nature. By destroying nature, turning it into the material for people’s various techne, people found themselves in conflict with their own life. Culture has lost its inner meaning of the presence of the world and of an individual which dissolved in various interpretations and ideas. Contemporary history is moving towards the establishment of a culture of Presence, where the world is viewed not as a mere material to be used, but an area for humans to engage with. What we see today is the assertion of the right to difference and the right to the presence of diversity — in nature, culture, politics (struggle for a multipolar world), in the personal domain (selfies, blogs, chats, etc.)

    The MFA ground states for the extended Bose-Hubbard model with a three-body constraint

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    We address the intensively studied extended bosonic Hubbard model (EBHM) with truncation of the on-site Hilbert space to the three lowest occupation states n=0,1,2 in frames of the S=1 pseudospin formalism. Similar model was recently proposed to describe the charge degree of freedom in a model high-Tc cuprate with the on-site Hilbert space reduced to the three effective valence centers, nominally Cu^{1+;2+;3+} . With small corrections the model becomes equivalent to a strongly anisotropic S=1 quantum magnet in an external magnetic field. We have applied a generalized mean-field approach and quantum Monte-Carlo technique for the model 2D S=1 system with a two-particle transport to find the ground state phase with its evolution under deviation from half-filling.Comment: 9 pages, 3 figure

    Efficient Certified Resolution Proof Checking

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    We present a novel propositional proof tracing format that eliminates complex processing, thus enabling efficient (formal) proof checking. The benefits of this format are demonstrated by implementing a proof checker in C, which outperforms a state-of-the-art checker by two orders of magnitude. We then formalize the theory underlying propositional proof checking in Coq, and extract a correct-by-construction proof checker for our format from the formalization. An empirical evaluation using 280 unsatisfiable instances from the 2015 and 2016 SAT competitions shows that this certified checker usually performs comparably to a state-of-the-art non-certified proof checker. Using this format, we formally verify the recent 200 TB proof of the Boolean Pythagorean Triples conjecture

    COMPARATIVE ANALYSIS OF RADIOLOGIC ASPECTS OF FACET JOINTS IN SURGICAL TREATMENT OF PATIENTS WITH DEGENERATIVE DISEASES OF THE LUMBAR SPINE

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    Objective To study the radiologic characteristics of facet joints at different stages of the degenerative process in the lumbar spine to determine the indications for various methods of fixing the affected segment and to evaluate the results of treatment.Material and Methods To determine the radiologic aspects of facet joints in the affected area and in  adjacent segments of the lumbar spine, two groups were formed, including 136 patients who underwent multispiral computed tomography in two-energy mode before surgery and 12 months after surgery. Group I included patients who underwent rigid fixation of the spine (360°), and group II included patients who underwent dynamic fixation using nitinol rods (180°).Results Based on a comprehensive instrumental study, it was found that the degeneration of the intervertebral disc according to Pfirrmann II and III revealed an increase in the density of the cartilaginous plate in facet joints (HU). These digital indicators confirm the preservation of joint functionality, both in the affected area and in adjacent segments. With severe degrees of disk degeneration in Pfirrmann IV and V and facet joints, deep pathological changes occurred, directed towards the loss of facet joints functionality.Conclusion The obtained digital indicators of dual-energy computed tomography for the state of facet joints  in combination with the results of magnetic resonance imaging can be used as criteria in a complex of patient studies to assess the degree of degeneration of the vertebral motion segment in the affected area and adjacent segments. We recommend using these criteria as a diagnostic component for finding optimal methods of surgical treatment

    Magnetism and temperature dependence of nano-TiO2: Fe EPR spectra

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    Nanocrystalline TiO2 samples of various compositions (up to 5 at.% Fe) with anatase structure and an average particle size of about 20 nm were synthesized using sol-gel technology. The magnetic properties of nano-TiO2: Fe was studied by electron paramagnetic resonance (EPR) and Faraday balance. The existence of an inhomogeneous magnetic state in TiO2: Fe samples of different compositions were revealed by EPR spectroscopy in a wide temperature range. The analysis of the EPR spectra in the L -, X - and Q-bands allowed us to calculate the quadratic fine structure (D, E) parameters, “axial” and “rhombic” ones, respectively. The value of D turned out to be quite small, which indicates an insignificant anisotropy, which can be ignored describing the magnetic properties of TiO2:Fe. It was shown that the temperature behavior of different separate components of the integral EPR spectra can be qualitatively interpreted in the model of coexistence in the TiO2: Fe system, mainly, dimers with a strong negative exchange interaction and isolated paramagnetic centers. No ferromagnetic state in TiO2: Fe-based samples after etching of aE-prepared state were detected. © 202

    Two different types of ferromagnetic state in TiO2-Co nanopowders

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    TiO2-Co nanopowders were synthesized by the sol-gel method and gas condensation method. The structure of powders and its change during various heat treatments in air and hydrogen was investigated. The samples obtained by the gas condensation method contain ferromagnetic regions in the as-prepared state. This ferromagnetism does not disappear when annealed in air at 773 K. The magnetization curves of these powders are measured in the temperature range from 2 up to 773 K and the temperature dependence of the ferromagnetic contribution is analyzed. © Published under licence by IOP Publishing Ltd

    NATURAL HYDROXYAPATITE AS A DETECTOR OF THE ACCUMULATED DOSE OF IONIZING RADIATION

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    The purpose of the present study is developing a new dosimeter detector based on biological hydroxyapatite having several advantages over the existing analogs, and methods of its application. Properties of the biological materials were studied by continuous and pulsed EPR in order to determine their suitability for application as dosimetric materials. Possible differences in the mechanisms of formation of radiation-induced stable free radicals in the biological hydroxyapatite of different origin were considered, and radiation sensitivity of this materials was determined. Studies were also aimed at finding a binder having the properties of neutrality to radiation and biocompatibility. A test batch of artificial radiation detectors based on the chosen material, epoxy resin, was produced and tested. Detectors were tested for their usefulness in the calibration of artificial radiation beams as well as for radioecological studies
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