Neural networks art: solving problems with multiple solutions and new teaching algorithm

A new discrete neural networks adaptive resonance theory (ART), which allows solving problems with multiple solutions, is developed. New algorithms neural networks teaching ART to prevent degradation and reproduction classes at training noisy input data is developed. Proposed learning algorithms discrete ART networks, allowing obtaining different classification methods of input

Dzyaloshinskii--Moriya interaction: How to measure its sign in weak ferromagnetics?

Three experimental techniques sensitive to the sign of the Dzyaloshinskii--Moriya interaction are discussed: neutron diffraction, Moessbauer gamma-ray diffraction, and resonant x-ray scattering. Classical examples of hematite (alpha-Fe2O3) and MnCO3 crystals are considered in detailComment: 5 pages, 1 figure; to be published in JETP Letter

Comment on "X-ray resonant scattering studies of orbital and charge ordering in Pr1-xCaxMnO3"

In a recent published paper [Phys. Rev. B 64, 195133 (2001)], Zimmermann et al. present a systematic x-ray scattering study of charge and orbital ordering phenomena in the Pr1-xCaxMnO3 series with x= 0.25, 0.4 and 0.5. They propose that for Ca concentrations x=0.4 and 0.5, the appearance of (0, k+1/2, 0) reflections are originated by the orbital ordering of the eg electrons in the a-b plane while the (0, 2k+1, 0) reflections are due to the charge ordering among the Mn3+ and Mn4+ ions. Moreover, for small Ca concentrations (x<0.3), the orbital ordering is only considered and it occurs at (0, k, 0) reflections. A rigorous analysis of all these resonance reflections will show the inadequacy of the charge-orbital model proposed to explain the experimental results. In addition, this charge-orbital model is highly inconsistent with the electronic balance. On the contrary, these reflections can be easily understood as arising from the anisotropy of charge distribution induced by the presence of local distortions, i.e. due to a structural phase transition.Comment: 10 pages, 2 figures.To be published Phys. Rev.

Relative contributions of lattice distortion and orbital ordering to resonant x-ray scattering in manganites

We investigated the origin of the energy splitting observed in the resonant x-ray scattering (RXS) in manganites. Using thin film samples with controlled lattice parameters and orbital states at a fixed orbital filling, we estimated that the contribution of the interatomic Coulomb interaction relative to the Jahn-Teller mechanism is insignificant and at most 0.27. This indicates that RXS probes mainly Jahn-Teller distortion in manganites.Comment: 8 pages, 4 figure

Surface Activity of Stars in the Praesepe Cluster Observed by the Mission K2

We present estimations of spottedness parameters S (the fraction of the visible surface of the star occupied by spots) of 674 stars in the Praesepe Cluster (age 650 Myr). Compared with parameters S of stars in the Pleiades Cluster (age 125 Myr) they reveal surface activity evolution of stars with different masses. We also present estimation of rotation periods and spottedness parameters of sun-like stars from both clusters compared with contemporary Sun properties.Представлены оценки доли видимой поверхности звезды, занимаемой пятнами (параметр S) для 674 звезд скопления Ясли возрастом 650 млн лет. Произведено сравнение с параметром S для звезд скопления Плеяды возрастом 125 млн лет. Представлена эволюция поверхностной активности звезд разных масс за 500 млн лет. Произведено сравнение периодов вращения и параметров запятненности звезд солнечных масс из этих скоплений с соответствующими параметрами современного Солнца.Работа выполнена при поддержке гранта РФФИ 17–52–45048

Surface Differential Rotation of Stars in Young Clusters Observed by the Mission K2

We present calculated periodograms and relative shear of possible differential rotators in Pleiades and Praesepe clusters. For some stars we are able to estimate inclinations roughly from theoretical predictions.По периодограммам звезд скоплений Плеяды и Ясли обнаружены объекты, предположительно имеющие дифференциальное вращение. Представлены оценки параметров дифференциального вращения, для небольшого числа звезд представлены оценки угла наклона оси вращения к лучу зрения.Работа выполнена при поддержке гранта РФФИ 17–52–45048