The influence of phonon anharmonicity on thermal and elastic properties of neptunium

A self-consistent thermodynamic model describing the thermal and elastic properties of α- and β-phases of neptunium was developed. The presence of strong phonon anharmonicity of Np is established. The obtained results are in good agreement with the experimental data and enable to predict the Np properties in wide temperature range. © 2013 Elsevier B.V. All rights reserved

Thermodynamic simulation of thermophysical and elastic properties of plutonium

A self-consistent thermodynamic model taking into account phonon anharmonicity effects is used for calculating the temperature dependences of the lattice components of thermophysical and elastic properties of the alpha-phase of plutonium. The theoretical curves are in good agreement with experimental data and make it possible to compare the mechanisms of formation of thermophysical and elastic properties of the alpha- and delta-phases of plutonium. The entropy of both phases is estimated, the role of the lattice magnetic anharmonicity is analyzed, and the key question concerning the reasons for stabilization of the delta-phase of plutonium relative to its α-phase is considered. © 2013 Pleiades Publishing, Ltd

A possible spin-fluctuation mechanism in the emergence of superconductivity in a region of magnetic instability, using the example of PuCoGa5

The spin-fluctuation superconductivity mechanism of strongly correlated d-f electrons is considered within the Hubbard model. It is shown that the emergence of superconductivity is possible under conditions of strong spin anharmonicity. Evaluations of the superconductivity temperature in the model developed for the electron structure of PuCoGa5 agree with the experimental data. © 2013 Allerton Press, Inc

A thermodynamic model of thermal end elastic properties of curium

A self-consistent thermodynamic model of curium is developed. In the framework of this model the temperature dependencies of heat capacity, coefficient of thermal expansion, bulk modulus and Debye temperature of Cm are calculated. It is shown that the phonon anharmonicity of Cm is weaker than in the case of Np and δ-Pu, but stronger than in lanthanides. © 2013 Elsevier B.V. All rights reserved

Principles of using NI LabVIEW system in the course of practical physics at technical university

В статье обсуждаются принципы использования системы NI LabVIEW в физическом практикуме технического университета.Principles of using NI LabVIEW system in the course of practical physics are discussed

Electron heat capacity and lattice properties of Americium

The temperature dependence of the electron heat capacity of americium is calculated using the concepts on the electronic structure and magnetic properties of this element. The Debye temperature, the thermal expansion coefficient, and the bulk modulus of americium are determined on the basis of the results of calculations and experimental data on heat capacity. © 2013 Pleiades Publishing, Ltd

Machine Learning Methods for Predicting the Lattice Characteristics of Materials

Data on 5244 crystalline compounds from the open AFLOWlib repository are used to build machine learning models, which enable to predict important features of phonon spectrum of a material (Debye temperature and Gruneisen parameter) required for simulation of its lattice properties. We build two types of descriptors: the first one contains data solely on the chemical composition of a compound and the second one incorporates information on the elemental properties of atoms that make up the compound and additionally contains several features regarding its crystal structure. The regression models are built using four popular approaches - gradient boosting (GB), random forests (RF), artificial neural networks (ANN) and support vector machines (SVM). Prior the regression a search for the best values of hyperparameters has been performed for each of the model supplemented with a 5-fold cross validation. We compare prediction accuracy of models based on different methods as well as trained on each of the descriptors. © 2020 IEEE

Phase transitions induced by concentration and thermodynamic magnetic fluctuations in chiral ferromagnets Fe1-xCoxSi

Taking into account the results of LDA+U+SO-modeling of the electronic structure of Fe1-xCoxSi, temperature-prolonged magnetic phase transitions of the first order in strongly correlated alloys with a broken crystal structure of the B20 type are investigated. It is shown that such phase transitions are induced by concentration and thermodynamic fluctuations for compositions with 0.2<x<0.65 and are accompanied by a change in the sign of the mode-mode coupling parameter. In this case, an intermediate region appears between the long-range order phases and the paramagnetic phase, with the short-range spin order characterized by ferromagnetic and helicoidal spatial fluctuations. We have defined the intervals of external magnetic fields, at which skyrmion microstructures spatially limited by the crossover of helicoidal and ferromagnetic fluctuations appear in the considered region of the extended phase transition. The peculiarities of the temperature dependences of the magnetic susceptibility in an external magnetic field, characteristic of the appearance of skyrmions, are obtained. © 2021 Author(s)

The inverse scattering problem at fixed energy based on the Marchenko equation for an auxiliary Sturm-Liouville operator

A new approach is proposed to the solution of the quantum mechanical inverse scattering problem at fixed energy. The method relates the fixed energy phase shifts to those arising in an auxiliary Sturm-Liouville problem via the interpolation theory of the Weyl-Titchmarsh m-function. Then a Marchenko equation is solved to obtain the potential.Comment: 6 pages, 8 eps figure