Structure and three-body decay of 9^9Be resonances

The complex-rotated hyperspherical adiabatic method is used to study the decay of low-lying $^9$Be resonances into one neutron and two $\alpha$-particles. We investigate the six resonances above the break-up threshold and below 6 MeV: $1/2^\pm$, $3/2^\pm$ and $5/2^\pm$. The short-distance properties of each resonance are studied, and the different angular momentum and parity configurations of the $^8$Be and $^5$He two-body substructures are determined. We compute the branching ratio for sequential decay via the $^8$Be ground state which qualitatively is consistent with measurements. We extract the momentum distributions after decay directly into the three-body continuum from the large-distance asymptotic structures. The kinematically complete results are presented as Dalitz plots as well as projections on given neutron and $\alpha$-energy. The distributions are discussed and in most cases found to agree with available experimental data.Comment: 12 pages, 10 figures. To appear in Physical Review

Laser cooling with induced radiation

Theoretical model is constructed for radiation balanced solid state lasers with up-conversion cooling effect. Kinetic equations are derived for such lasers in the framework of nonequilibrium statistical operator method and estimations are made for limiting temperatures of generation. Calculations are performed also for radiation balanced pulsed lasers where excess heat is removed by induced radiation

Laser cooling of extended crystals and optical fibers

The equation obtained earlier by the authors from a starting model Hamiltonian for the thermal conductivity of solids under conditions of laser cooling has been converted to a form that contains on its right-hand side an expression for the load power and the removed power. Numerical and analytical solutions are presented for this equation under conditions far from saturation. They give the time-dependent temperature distribution inside a sample for laser cooling of optical fibers and extended crystals. © 2003 Optical Society of America

Model of the global distribution of the total electron content based on deep dense convolutional autoencoder

© 2018 Institute of Physics Publishing. All rights reserved. Nowadays the prediction of ionospheric parameters is an important and acute problem in the field of ensuring stable operation of radio communication and radio navigation facilities. The network of two-frequency GPS receivers data is used for monitoring the ionospheric condition. Based on these data, a number of laboratories are building global maps of total electron content (TEC). There are strong spatial and temporal correlations in the TEC maps. As a result, in order to successfully solve the problem of TEC prediction, it is advisable to perform preliminary processing of maps data with dimensionality reduction. In this paper, the problem of constructing a low-dimensional model of global distribution of the TEC is solved. In addition, the model of global distribution of the TEC can be useful for the ionosphere dynamics investigation. In this paper, it is proposed to use dense convolutional auto encoders as a base element of the model. This architecture allows us to speed up the neural network learning process and avoid the gradient-vanishing problem in error backpropagation algorithm

Optimal regimes for laser cooling of solids

In the framework of nonequilibrium statistical operator, the equations are derived for number of phonons, photons and collective population difference, describing the process of laser cooling for solids. With the use of these equations, the expressions are obtained for the coefficient of performance of optical thermal machine in reverse thermodynamic cycle and for limiting temperature of cooling. The criteria are formulated for the determination of type of samples, of temperature diapasons and spectral ranges that are the most perspective for the experiments on laser cooling. Numerical calculations substituting these conclusions are carried out

Quantum theory of radiation-balanced generation

Quantum statistical theory of radiation-balanced laser is constructed within method of nonequilibrium statistical operator. System of equations is derived for number of phonons and collective population difference. Their numerical solutions are obtained and discussed

Archimedean-type force in a cosmic dark fluid: II. Qualitative and numerical study of a multistage Universe expansion

In this (second) part of the work we present the results of numerical and qualitative analysis, based on a new model of the Archimedean-type interaction between dark matter and dark energy. The Archimedean-type force is linear in the four-gradient of the dark energy pressure and plays a role of self-regulator of the energy redistribution in a cosmic dark fluid. Because of the Archimedean-type interaction the cosmological evolution is shown to have a multistage character. Depending on the choice of the values of the model guiding parameters,the Universe's expansion is shown to be perpetually accelerated, periodic or quasiperiodic with finite number of deceleration/acceleration epochs. We distinguished the models, which can be definitely characterized by the inflation in the early Universe, by the late-time accelerated expansion and nonsingular behavior in intermediate epochs, and classified them with respect to a number of transition points. Transition points appear, when the acceleration parameter changes the sign, providing the natural partition of the Universe's history into epochs of accelerated and decelerated expansion. The strategy and results of numerical calculations are advocated by the qualitative analysis of the instantaneous phase portraits of the dynamic system associated with the key equation for the dark energy pressure evolution.Comment: 15 pages, 12 figures, Part II, typos corrected, Fig.4 replaced, references correcte

Universals versus historical contingencies in lexical evolution

© 2014 The Author(s) Published by the Royal Society. All rights reserved. The frequency with which we use different words changes all the time, and every so often, a new lexical item is invented or another one ceases to be used. Beyond a small sample of lexical items whose properties are well studied, little is known about the dynamics of lexical evolution. How do the lexical inventories of languages, viewed as entire systems, evolve? Is the rate of evolution of the lexicon contingent upon historical factors or is it driven by regularities, perhaps to do with universals of cognition and social interaction?We address these questions using the Google Books N-Gram Corpus as a source of data and relative entropy as a measure of changes in the frequency distributions of words. It turns out that there are both universals and historical contingencies at work. Across several languages, we observe similar rates of change, but only at timescales of at least around five decades. At shorter timescales, the rate of change is highly variable and differs between languages. Major societal transformations as well as catastrophic events such as wars lead to increased change in frequency distributions, whereas stability in society has a dampening effect on lexical evolution