The influence of local correlations on the phase states in the model of semi-hard-core bosons on a square lattice

The work considers a model of charged "semi-hard-core" bosons on a square lattice with a possible filling number at each node, ranging from 0 to 2. Temperature phase diagrams of the model are obtained using numerical Monte Carlo quantum simulation methods, and the influence of local charge correlations is examined. Comparison with results from mean-field methods shows that local charge correlations contribute to an increased role of quantum fluctuations in the formation of phase states.Comment: 5 pages, 2 figure

Unconventional phase transitions in strongly anisotropic 2D (pseudo)spin systems

We have applied a generalized mean-field approach and quantum Monte-Carlo technique for the model 2D S = 1 (pseudo)spin system to find the ground state phase with its evolution under application of the (pseudo)magnetic field. The comparison of the two methods allows us to clearly demonstrate the role of quantum effects. Special attention is given to the role played by an effective single-ion anisotropy (»on-site correlation»). © 2018 The Authors, published by EDP Sciences.The research was supported by the Government of the Russian Federation, Program 02.A03.21.0006 and by the Ministry of Education and Science of the Russian Federation, projects Nos. 2277 and 5719

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

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

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

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.)

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

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

The Health in the Value System of Russian Youth: Contradictory Discursive Practices

The axiological aspects of the self-preserving behaviour of Russian youth are considered on the basis of the data of sociological studies. The contradiction between the high value of health in the minds of modern youth declared and the underdevelopment of daily practices aimed at its preservation and strengthening is revealed. The probable causes of the contradiction are listed; they are related as to the specifics of this socio-demographic group, to its hedonistic orientation, to situational orientation of thinking, and also to the limited capacity of youth in relation to receiving medical and preventive services. Conclusion was made that it is necessary to form the axiological-and-motivational foundations of self-preserving behaviour of Russian youth as one of the most important directions in the implementation of the state policy to protect public health in general

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

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

Study of the switching characteristics of gas S-diodes

In the study, the switching properties of avalanche GaAs S-diodes are investigated. We studied diode assemblies of various configurations. It is shown that when using two or more diodes connected in series, the edge of the voltage pulse can be sharpened to about 1 ns