462 research outputs found

    Critical behavior of three-dimensional magnets with complicated ordering from three-loop renormalization-group expansions

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    The critical behavior of a model describing phase transitions in 3D antiferromagnets with 2N-component real order parameters is studied within the renormalization-group (RG) approach. The RG functions are calculated in the three-loop order and resummed by the generalized Pade-Borel procedure preserving the specific symmetry properties of the model. An anisotropic stable fixed point is found to exist in the RG flow diagram for N > 1 and lies near the Bose fixed point; corresponding critical exponents are close to those of the XY model. The accuracy of the results obtained is discussed and estimated.Comment: 10 pages, LaTeX, revised version published in Phys. Rev.

    A characterization of those automata that structurally generate finite groups

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    Antonenko and Russyev independently have shown that any Mealy automaton with no cycles with exit--that is, where every cycle in the underlying directed graph is a sink component--generates a fi- nite (semi)group, regardless of the choice of the production functions. Antonenko has proved that this constitutes a characterization in the non-invertible case and asked for the invertible case, which is proved in this paper

    Monte Carlo renormalization group study of the Heisenberg and XY antiferromagnet on the stacked triangular lattice and the chiral ϕ4\phi^4 model

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    With the help of the improved Monte Carlo renormalization-group scheme, we numerically investigate the renormalization group flow of the antiferromagnetic Heisenberg and XY spin model on the stacked triangular lattice (STA-model) and its effective Hamiltonian, 2N-component chiral ϕ4\phi^4 model which is used in the field-theoretical studies. We find that the XY-STA model with the lattice size 126×144×126126\times 144 \times 126 exhibits clear first-order behavior. We also find that the renormalization-group flow of STA model is well reproduced by the chiral ϕ4\phi^4 model, and that there are no chiral fixed point of renormalization-group flow for N=2 and 3 cases. This result indicates that the Heisenberg-STA model also undergoes first-order transition.Comment: v1:15 pages, 15 figures v2:updated references v3:added comments on the higher order irrelevant scaling variables v4:added results of larger sizes v5:final version to appear in J.Phys.Soc.Jpn Vol.72, No.

    The critical behavior of frustrated spin models with noncollinear order

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    We study the critical behavior of frustrated spin models with noncollinear order, including stacked triangular antiferromagnets and helimagnets. For this purpose we compute the field-theoretic expansions at fixed dimension to six loops and determine their large-order behavior. For the physically relevant cases of two and three components, we show the existence of a new stable fixed point that corresponds to the conjectured chiral universality class. This contradicts previous three-loop field-theoretical results but is in agreement with experiments.Comment: 4 pages, RevTe

    Risk-based Regulation of Russian Universities: Risk Indicators and Their Use for State Control Purposes

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    The article is devoted to the identification and analysis of indicators of the risk of low-quality education in Russian universities. In 2021-2022, the approach to higher education inspections has changed significantly: accreditation monitoring has been introduced, it includes eight indicators. However, this monitoring was formed by the expert community, so the results of its testing in practice have yet to be analyzed. The purpose of this work is to identify risk factors for estimation the likelihood of violations of mandatory requirements by universities, and to develop recommendations for expanding the set of risk indicators included in accreditation monitoring. The main methods used in the work are methods of quantitative analysis, including econometric modeling. The novelty of the work is determined by the approach used: risk indicators are identified using a quantitative econometric analysis of data on the observed characteristics and results of inspections of Russian universities in 2015-2019. The results of the study indicate the possibility of supplementing the set of accreditation monitoring indicators. As additional indicators, first of all, various characteristics of research activities of universities can be used. Such a change in accreditation monitoring will increase its effectiveness as a preliminary assessment tool used in the implementation of a risk-based approach to state control. In cases where the assessment of even extended monitoring is ambiguous, the quantitative model proposed by the authors can be used
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