Superconductivity in model cuprate as an S=1 pseudomagnon condensation

We make use of the S=1 pseudospin formalism to describe the charge degree of freedom in a model high-$T_c$ cuprate with the on-site Hilbert space reduced to the three effective valence centers, nominally Cu$^{1+,\,2+,\,3+}$. Starting with a parent cuprate as an analogue of the quantum paramagnet ground state and using the Schwinger boson technique we found the pseudospin spectrum and conditions for the pseudomagnon condensation with phase transition to a superconducting state.Comment: Version to be published in JLT

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

Design and Investigation of de Vries Liquid Crystals Based on 5-Phenyl-Pyrimidine and (R,R)-2,3-Epoxyhexoxy backbone.

Calamitic liquid crystals based on 5-phenyl-pyrimidine derivatives have been designed, synthesized, and characterized. The 5-phenyl pyrimidine core was functionalized with a chiral (R,R)-2,3-epoxyhexoxy chain on one side and either siloxane or perfluoro terminated chains on the opposite side. The one involving a perfluorinated chain shows SmA^{*} phase over a wide temperature range of 82 °C, whereas the siloxane analog exhibits both SmA^{*} and SmC^{*} phases over a broad range of temperatures, and a weak first-order SmA^{*}-SmC^{*} transition is observed. For the siloxane analog, the reduction factor for the layer shrinkage R (relative to its thickness at the SmA^{*}-SmC^{*} transition temperature, T_{AC}) is ∼0.373, and layer shrinkage is 1.7% at a temperature of 13 °C below the T_{AC}. This compound is considered to have de Vries smectic characteristics with the de Vries coefficient C_{deVries} of ∼0.86 on the scale of zero (maximum-layer shrinkage) to 1 (zero-layer shrinkage). A three-parameter mean-field model is introduced for the orientational distribution function (ODF) to reproduce the electro-optic properties. This model explains the experimental results and leads to the ODF, which exhibits a crossover from the sugar-loaf to diffuse-cone ODF some 3 °C above T_{AC}

Representations of teachers and elder schoolchildren about the risks of interacting with the internet

The paper explores the notions of risks on the Internet in teachers and high school students. The study was carried out on a sample of teachers (n = 294) and school students of 9-11 grades (n = 180) using the analysis of social representations (Abric coefficient). The results confirmed that only a small part (5 out of 29) of the teachers' notions about the riskiness of Internet communication is related to the use of the Internet; mostly they are based on some general ideas concerning risk behaviours in adolescents. At the same time, the teachers were not quite ready to cooperate with their colleagues to help reduce such risks: only 41.5% of the teachers showed readiness, given that they receive appropriate training. The study confirmed that the notions of risks associated with the active use of the Internet differ significantly in teachers and students, which can be explained by at least two reasons. Firstly, by the fact that the active use of the Internet does not affect the subjective well-being of the adolescents. Secondly, by the fact that for high school students, the Internet is a natural tool and a necessary attribute of their daily life, whereas, according to the outcomes of our study, only 20% of the teachers believe that they have the necessary skills to freely use the Internet as a means of their teaching activities. For the rest of the teachers, the Internet is still an object that must be mastered and treated as a source of threats and risks to the psychological development of schoolchildren. © 2020 Escuela Militar de Cadetes. All rights reserved.Russian Foundation for Basic Research, RFBR : 19-29-14067Представления педагогов и подростков о рисках во взаимодействиях в интернет-среде Психологическая наука и образование . 2020 . Т . 25 . № 3 Funding: The reported study was funded by Russian Foundation for Basic Research (RFBR), project number 19-29-14067