Diagrammatic calculation of energy spectrum of quantum impurity in degenerate Bose-Einstein condensate

In this paper we considered a quantum particle moving through delute Bose-Einstein condensate at zero temperature. In our formulation the impurity particle interacts with the gas of uncoupled Bogoliubov's excitations. We constructed the perturbation theory for the Green's function of the impurity particle with respect to the impurity-condensate interaction employing the coherent-state path integral approach. The perturbative expansion for the Green's function is resumed into the expansion for its poles with the help of the diagrammatic technique developed in this work. The dispersion relation for the impurity clothed by condensate excitations is obtained and effective mass is evaluated beyond the Golden rule approximation

Fast and slow microphysics regimes in a minimalist model of cloudy Rayleigh-Bénard convection

A minimalist model of microphysical properties in cloudy Rayleigh-Bénard convection is developed based on mass and number balances for cloud droplets growing by vapor condensation. The model is relevant to a turbulent mixed-layer in which a steady forcing of supersaturation can be defined, e.g., a model of the cloudy boundary layer or a convection-cloud chamber. The model assumes steady injection of aerosol particles that are activated to form cloud droplets, and the removal of cloud droplets through sedimentation. Simplifying assumptions include the consideration of mean properties in steady state, neglect of coalescence growth, and no detailed representation of the droplet size distribution. Closed-form expressions for cloud droplet radius, number concentration, and liquid water content are derived. Limits of fast and slow microphysics, compared to the turbulent mixing time scale, are explored, and resulting expressions for the scaling of microphysical properties in fast and slow regimes are obtained. Scaling of microphysics with layer thickness is also explored, suggesting that liquid water content and cloud droplet number concentration increase, and mean droplet radius decreases with increasing layer thickness. Finally, the analytical model is shown to compare favorably to solutions of the fully-coupled set of governing ordinary differential equations that describe the system, and the predicted power law for liquid water mixing ratio versus droplet activation rate is observed to be consistent with measurements from the Pi convection-cloud chamber

Organizational and methodological approaches to development of accounting policy for formation of integrated accounting of interrelated agricultural companies

The purpose of the article is to determine advantages and drawbacks of existing organizational and methodological approaches to development of accounting policy and develop optimal approach to formation of integrated accounting of interrelated agricultural enterprises. For this purpose, the article uses methods of problem and comparative analysis, method of optimization, and methods of graphical presentation of information. The authors conduct comparative analysis of existing organizational and methodological approaches to development of accounting policy of enterprise and develop optimal approach to formation of integrated accounting of interrelated agricultural enterprises. As a result of the research, the authors come to the conclusion that Russian and international approach to development of accounting policy differ from each other, but neither of these approaches is optimal for formation of integrated accounting of interrelated agricultural enterprises. The developed optimal approach to formation of integrated accounting allows unifying the process of development of accounting policy of enterprise and thus is the best for interrelated agricultural enterprises. This approach is oriented at consumers, due to which it is able not only to simplify the process of formation of corporate accounting of interrelated agricultural enterprises but to turn it into the factor of their competitiveness.peer-reviewe

Rotational dynamics of fullerenes in the molecular crystal of fullerite

The work is devoted to the study of gyroscopic phenomena in the interaction of a rotating fullerene molecule and a xenon atom incident on it. The methods of classical molecular physics are used: intermolecular potentials, Newton's equations for describing the motion of particles, and the Runge–Kutta numerical method of high order of accuracy. A mathematical model is constructed and implemented for the rotation frequencies of fullerene up to 1014 Hz and the speed of the incident xenon atom of the order of 103 m s−1. For such parameters of the problem, the de Broglie wavelength of the incident atom and the fullerene molecule become smaller than the diameter of the carbon atomic nucleus. This made it possible to apply the Newtonian approach without involving quantum mechanics. The aim of this work is the consistent application of the apparatus of classical mechanics to reveal the effect of the precession of rotating fullerene inside fullerite. © 2020 Wiley-VCH Gmb

Enhancements in Cloud Condensation Nuclei Activity From Turbulent Fluctuations in Supersaturation

The effect of aerosols on the properties of clouds is a large source of uncertainty in predictions of weather and climate. These aerosol-cloud interactions depend critically on the ability of aerosol particles to form cloud droplets. A challenge in modeling aerosol-cloud interactions is the representation of interactions between turbulence and cloud microphysics. Turbulent mixing leads to small-scale fluctuations in water vapor and temperature that are unresolved in large-scale atmospheric models. To quantify the impact of turbulent fluctuations on cloud condensation nuclei (CCN) activation, we used a high-resolution Large Eddy Simulation of a convective cloud chamber to drive particle-based cloud microphysics simulations. We show small-scale fluctuations strongly impact CCN activity. Once activated, the relatively long timescales of evaporation compared to fluctuations causes droplets to persist in subsaturated regions, which further increases droplet concentrations

Microstructure and mechanical properties of V-4Ti-4Cr alloy as a function of the chemical heat treatment regimes

The regularities of the formation of a heterophase structure and mechanical properties of V–4Ti–4Cr alloy as a function of thermomechanical and chemical heat treatments are studied. The regimes of thermomechanical treatment which provide the formation of a heterophase structure with a homogeneous volume distribution of oxycarbonitride nanoparticles with a size of about 10 nm and an increase in the volume content and thermal stability of this phase and which provide an increase in the temperature of alloy recrystallization are developed. The formation of the heterophase structure results in a substantial (up to 70%) increase in the short-term high-temperature strength of the alloy at T = 800°C. The increase in the strength is achieved while keeping a rather high level of plasticity

Excited states of linear polyenes

We present density matrix renormalisation group calculations of the Pariser- Parr-Pople-Peierls model of linear polyenes within the adiabatic approximation. We calculate the vertical and relaxed transition energies, and relaxed geometries for various excitations on long chains. The triplet (3Bu+) and even- parity singlet (2Ag+) states have a 2-soliton and 4-soliton form, respectively, both with large relaxation energies. The dipole-allowed (1Bu-) state forms an exciton-polaron and has a very small relaxation energy. The relaxed energy of the 2Ag+ state lies below that of the 1Bu- state. We observe an attraction between the soliton-antisoliton pairs in the 2Ag+ state. The calculated excitation energies agree well with the observed values for polyene oligomers; the agreement with polyacetylene thin films is less good, and we comment on the possible sources of the discrepencies. The photoinduced absorption is interpreted. The spin-spin correlation function shows that the unpaired spins coincide with the geometrical soliton positions. We study the roles of electron-electron interactions and electron-lattice coupling in determining the excitation energies and soliton structures. The electronic interactions play the key role in determining the ground state dimerisation and the excited state transition energies.Comment: LaTeX, 15 pages, 9 figure

High - Temperature Superconductivity in Iron Based Layered Compounds

We present a review of basic experimental facts on the new class of high - temperature superconductors - iron based layered compounds like REOFeAs (RE=La,Ce,Nd,Pr,Sm...), AFe_2As_2 (A=Ba,Sr...), AFeAs (A=Li,...) and FeSe(Te). We discuss electronic structure, including the role of correlations, spectrum and role of collective excitations (phonons, spin waves), as well as the main models, describing possible types of magnetic ordering and Cooper pairing in these compounds.Comment: 43 pages, 30 figures, review talk on 90th anniversary of Physics Uspekh