1,204 research outputs found
Metal-Insulator Transition and Lattice Instability of Paramagnetic V2O3
We determine the electronic structure and phase stability of paramagnetic
VO at the Mott-Hubbard metal-insulator phase transition, by employing a
combination of an ab initio method for calculating band structures with
dynamical mean-field theory. The structural transformation associated with the
metal-insulator transition is found to occur upon a slight expansion of the
lattice volume by %, in agreement with experiment. Our results show
that the structural change precedes the metal-insulator transition, implying a
complex interplay between electronic and lattice degrees of freedom at the
transition. Electronic correlations and full charge self-consistency are found
to be crucial for a correct description of the properties of VO.Comment: 5 pages, 4 figure
The neural network art which uses the Hamming distance to measure an image similarity score
This study reports a new discrete neural network of Adaptive Resonance Theory (ART-1H) in which the Hamming distance is used for the first time to estimate the measure of binary images (vectors) proximity. For the development of a new neural network of adaptive resonance theory, architectures and operational algorithms of discrete neural networks ART-1 and discrete Hamming neural networks are used. Unlike the discrete neural network adaptive resonance theory ART-1 in which the similarity parameter which takes into account single images components only is used as a measure of images (vectors) proximity in the new network in the Hamming distance all the components of black and white images are taken into account. In contrast to the Hamming network, the new network allows the formation of typical vector classes representatives in the learning process not using information from the teacher which is not always reliable. New neural network can combine the advantages of the Hamming neural network and ART-1 by setting a part of source information in the form of reference images (distinctive feature and advantage of the Hamming neural network) and obtaining some of typical image classes representatives using learning algorithms of the neural network ART-1 (the dignity of the neural network ART-1). The architecture and functional algorithms of the new neural network ART which has the properties of both neural network ART-1 and the Hamming network were proposed and investigated. The network can use three methods to get information about typical image classes representatives: teacher information, neural network learning process, third method uses a combination of first two methods. Property of neural network ART-1 and ART-1H, related to the dependence of network learning outcomes or classification of input information to the order of the vectors (images) can be considered not as a disadvantage of the networks but as a virtue. This property allows to receive various types of input information classification which cannot be obtained using other neural networks
Correlation strength, Lifshitz transition and the emergence of a two- to three-dimensional crossover in FeSe under pressure
We report a detailed theoretical study of the electronic structure, spectral
properties, and lattice parameters of bulk FeSe under pressure using a fully
charge self-consistent implementation of the density functional theory plus
dynamical mean-field theory method (DFT+DMFT). In particular, we perform a
structural optimization and compute the evolution of the lattice parameters
(volume, ratio, and the internal position of Se) and the electronic
structure of the tetragonal (space group ) paramagnetic FeSe. Our
results for the lattice parameters are in good quantitative agreement with
experiment. The ratio is slightly overestimated by about ~\%,
presumably due to the absence of the van der Waals interactions between the
FeSe layers in our calculations. The lattice parameters determined within DFT
are off the experimental values by a remarkable -~\%, implying a
crucial importance of electron correlations. Upon compression to ~GPa, the
ratio and the lattice volume show a decrease by and ~\%,
respectively, while the Se coordinate weakly increases by ~\%.
Most importantly, our results reveal a topological change of the Fermi surface
(Lifshitz transition) which is accompanied by a two- to three-dimensional
crossover. Our results indicate a small reduction of the quasiparticle mass
renormalization by about ~\% for the and less than ~\% for
the states, as compared to ambient pressure. The behavior of the
momentum-resolved magnetic susceptibility shows no topological
changes of magnetic correlations under pressure, but demonstrates a reduction
of the degree of the in-plane stripe-type nesting. Our results for
the electronic structure and lattice parameters of FeSe are in good qualitative
agreement with recent experiments on its isoelectronic counterpart
FeSeS.Comment: 10 pages, 6 figure
The Study of Nitrogen Transformation in Fresh Water: Experiments and Mathematical Modeling
Two main transformations occur in water environments -- one due to the effect of microorganisms and the other due to chemical reactions. Both transformations are very closely interwoven. Of the transformation processes in the water environment, nitrogen transformation is perhaps the most interesting because nitrogen and its compounds (both organic and mineral), affect the development of practically all aquatic microorganisms and therefore determine the trophic state and the quality of a water environment. Nitrogen compounds are present in sewage and other waste water discharged into water bodies. Therefore, it is quite understandable why during the last few years nitrogen transformation is the subject of study at descriptive and experimental levels, as well as by mathematical modeling techniques. This paper reports on the results of a collaborative study between IIASA and the Institute of Experimental Biology and Ecology of the Slovak Academy of Sciences in Bratislava, on nitrogen transformations. The data of twelve experiments covering a broad set of initial conditions in nitrogen concentrations and at two temperatures (180 degrees Celsius and 120 degrees Celsius) are presented in this report. These experimental data were analyzed with the help of the mathematical model developed at IIASA (WP-80-86) and intended for understanding processes of nitrogen transformation in water environments. The results of model description of nitrogen compound dynamics are evaluated by statistics to find a quantitative criteria in model assessment. In the discussion of simulation results, attention was focused on the analysis of bacterial activities in the conversion of organic as well as mineral nitrogen forms. The results reported here are considered to be the basis for the simulation of nitrogen dynamics in water bodies and for studying various aspects of ecology and aquatic ecosystem behavior
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
Hidden attractors in fundamental problems and engineering models
Recently a concept of self-excited and hidden attractors was suggested: an
attractor is called a self-excited attractor if its basin of attraction
overlaps with neighborhood of an equilibrium, otherwise it is called a hidden
attractor. For example, hidden attractors are attractors in systems with no
equilibria or with only one stable equilibrium (a special case of
multistability and coexistence of attractors). While coexisting self-excited
attractors can be found using the standard computational procedure, there is no
standard way of predicting the existence or coexistence of hidden attractors in
a system. In this plenary survey lecture the concept of self-excited and hidden
attractors is discussed, and various corresponding examples of self-excited and
hidden attractors are considered
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