Comment on "Large Difference in the Elastic Properties of fcc and hcp Hard-Sphere Crystals"

As is well known, hard-sphere crystals of the fcc and hcp type differ very little in their thermodynamic properties. Nonetheless, recent computer simulations by Pronk and Frenkel indicate that the elastic response to mechanical deformation of the two types of crystal should be quite different. By invoking a geometrical argument put forward by R. Martin some time ago, we suggest that this is largely due to the different symmetries of the fcc and hcp crystal structures. Indeed, we find that elastic constants obtained by means of computer simulations for the fcc hard-sphere crystal can be mapped onto the equivalent ones of the hcp crystal to very high accuracy. The same procedure applied to density functional theoretical predictions for the elastic properties of the fcc hard-sphere crystal also produces remarkably accurate predictions for those of the hcp hard-sphere crystal.Comment: 7 pages, 5 figure

Density functional theory for the elastic moduli of a model polymeric solid

We apply a recently developed density functional theory for freely hinged, hard polymeric chains to calculate the elastic moduli of an idealized polymeric solid lacking long-range bond order. We find that for such a model packing effects dominate the elastic behavior of the polymeric solid in a similar way as is the case in the hard-sphere crystal, which we reexamine. Our calculations show that the elastic stiffness of the model polymeric solid is essentially determined by how far one is removed from its melting point. The main role of the chain connectivity is to destabilize the solid relative to the equivalent solid of hard monomers. Comparison of our results with experimental data on semicrystalline polymers shows order-of-magnitude agreement

Brief view in the development of agricultural sector: space information technologies

Modern development of agricultural industry is impossible without the use of innovations and technological solutions, the comprehensive implementation of which helps to save resources, reduce the cost of agri-food products, and increase the volumes and efficiency of agricultural production, which affects investment

Психологический отбор в игровых видах спорта на примере баскетбола

For the first time, an integrated approach based on the assessment of the technical and tactical skills of basketball players in combination with the psychological selection was used for selectionthe candidates for the Ukrainian cadet team. From the 144 athletes, who participated in the Ukrainian Championship, 36 players were selected based on the level of technical and tactical skills. According to the results of the psychological tests main characteristics of basketball players were defended and recommendations for coaches were given. As a result, 18 players, who were selected using psychological methods, had better technical and tactical mastery. They took part in the training process for preparation for the main competitions of the year (European Championship).Вперше застосовано комплексний підхід на основі оцінки техніко-тактичної мастерності баскетболістів в поєднанні з психологічним відбором кандидатів у кадетську збірну команду України для проведення навчально-тренувальних зборів. Зі 144 спортсменів, які брали участь у чемпіонаті України, відібрано 36 гравців по результатам визначення рівня техніко-тактичної майстерності. За підсумками проведених досліджень по вивченню психологічних характеристик баскетболістів відібрано 18 гравців для проведення навчально-тренувального процесу по підготовці до головних змагань року (чемпіонату Європи).Впервые был применен комплексный подход на основе оценки технико-тактического мастерства баскетболистов в сочетании с психологическим отбором кандидатов в кадетскую сборную Украины для проведения учебно-тренировочных сборов. Из 144 спортсменов, которые участвовали в чемпионате Украины, отобрано 36 игроков по результатам определения уровня технико-тактического мастерства. По итогам проведенных исследований по изучению психологических характеристик баскетболистов отобрано 18 игроков для проведения учебно-тренировочного процесса по подготовке к главным соревнованиям года (чемпионату Европы)

Моделирование цен авиаперевозок пассажиров

The pricing policy of airlines is developed based on a retrospective analysis of the price dynamics of air transportation and forecasting the market situation of supply and demand. The price dynamics of passenger air transportation has a certain structure and patterns, the identification of which helps to develop a competitive price offer for consumers.The objective of the work is to determine the structure of price dynamics and identify patterns of price fluctuations in passenger air transportation from 2008 to 2022, which is important to consider when developing the pricing policy of airlines and the range of tariffs. Studies of the price dynamics of airline tickets by econometric methods allowed to identify the structure of the time series of prices and develop several models.The study of the price dynamics structure, first, identified and analysed the seasonal component of the dynamics of airline ticket prices. Its calculation was carried out using additive and multiplicative models. The range of seasonal changes was -8,5% to +12,5%. The autocorrelation function of the dynamics of average monthly prices showed that the time series of airline ticket prices contained a trend. In addition to trend and seasonal components, cyclical fluctuations were identified in the price dynamics, the modelling of which was carried out based on regression analysis. Cyclical changes in the dynamics of air ticket prices, identified from 2008 to the present, are not sustainable.Analysed dynamics revealed several medium-term cycles with a duration of 4–6 years. The cyclical dynamics of air transportation prices largely coincides with the general economic medium-term cycles, but there are time lags or lagging growth and decline rates.Thus, the change in prices for civil air transportation has a natural trend-cyclical character shaped under the influence of fundamental macroeconomic factors and new determinants, the effect of which may result in a stronger change but with shorter impact or lag effect. Additive and multiplicative models will help predict average annual prices.Ценовая политика авиакомпаний разрабатывается на основании ретроспективного анализа ценовой динамики авиаперевозок и прогнозирования рыночной ситуации спроса и предложения. Ценовая динамика пассажирских авиаперевозок имеет определённую структуру и закономерности, выявление которых помогает формировать конкурентоспособное ценовое предложение для пассажиров.Цель работы заключается в исследовании структуры ценовой динамики с 2008 года по 2022 год и выявлении закономерностей движения цен на пассажирские авиаперевозки, что важно учитывать при определении ценового курса и диапазона цен тарифов. Исследования ценовой динамики авиабилетов эконометрическими методами позволили выявить структуру временного ряда цен и разработать ряд моделей.При исследовании структуры ценовой динамики в первую очередь была выделена и проанализирована сезонная компонента, расчёт которой проводился по аддитивным и мультипликативным моделям. Диапазон сезонных изменений составляет -8,5 % до +12,5 %. Автокорреляционная функция динамики среднемесячных цен показала, что временной ряд цен на авиабилеты содержит тренд. Кроме трендовых и сезонных компонент в динамике цен выделены циклические колебания, моделирование которых проводилось на основе регрессионного анализа. Циклические изменения динамики цен на авиабилеты, выявленных с 2008 года по настоящее время, не имеют устойчивого характера.В анализируемой динамике выделено несколько среднесрочных циклов продолжительностью 4–6 лет. Цикличность динамики цен на авиаперевозки во многом совпадает с общеэкономическими среднесрочными циклами, но присутствуют временные лаги запаздывания или отставание темпов роста или снижения.Таким образом, изменение цен на гражданские авиаперевозки имеет закономерный трендциклический характер, формирующийся под действием фундаментальных макроэкономических факторов и новых детерминант, действие которых может вызывать более сильное изменение, но с кратким периодом воздействия, или лаговое влияние. Аддитивные и мультипликативные модели помогут спрогнозировать среднегодовые цены авиатарифов

Dynamical chaos and power spectra in toy models of heteropolymers and proteins

The dynamical chaos in Lennard-Jones toy models of heteropolymers is studied by molecular dynamics simulations. It is shown that two nearby trajectories quickly diverge from each other if the heteropolymer corresponds to a random sequence. For good folders, on the other hand, two nearby trajectories may initially move apart but eventually they come together. Thus good folders are intrinsically non-chaotic. A choice of a distance of the initial conformation from the native state affects the way in which a separation between the twin trajectories behaves in time. This observation allows one to determine the size of a folding funnel in good folders. We study the energy landscapes of the toy models by determining the power spectra and fractal characteristics of the dependence of the potential energy on time. For good folders, folding and unfolding trajectories have distinctly different correlated behaviors at low frequencies.Comment: 8 pages, 9 EPS figures, Phys. Rev. E (in press

Spin Fluctuation-Induced Superconductivity in Organic Compounds

Spin fluctuation-induced superconductivity in two-dimensional organic compounds such as \kappa-(ET)_2-X is investigated by using a simplified dimer Hubbard model with right-angled isosceles triangular lattice (transfer matrices -\tau, -\tau^\prime). The dynamical susceptiblity and the self-energy are calculated self-consistently within the fluctuation exchange approximation and the value for T_c as obtained by solving the linearized Eliashberg-type equations is in good agreement with experiment. The pairing symmetry is of d_{x^2-y^2} type. The calculated (U/\tau)-dependence of T_c compares qualitatively well with the observed pressure dependence of T_c. Varying the value for \tau^\prime/\tau from 0 to 1 we interpolate between the square lattice and the regular triangular lattice and find firstly that values of T_c for \kappa-(ET)_2-X and cuprates scale well and secondly that T_c tends to decrease with increasing \tau^\prime/\tau and no superconductivity is found for \tau^\prime/\tau=1, the regular triangular lattice.Comment: 4 pages, 6 eps figures, uses jpsj.st

Modelling charge self-trapping in wide-gap dielectrics: Localization problem in local density functionals

We discuss the adiabatic self-trapping of small polarons within the density functional theory (DFT). In particular, we carried out plane-wave pseudo-potential calculations of the triplet exciton in NaCl and found no energy minimum corresponding to the self-trapped exciton (STE) contrary to the experimental evidence and previous calculations. To explore the origin of this problem we modelled the self-trapped hole in NaCl using hybrid density functionals and an embedded cluster method. Calculations show that the stability of the self-trapped state of the hole drastically depends on the amount of the exact exchange in the density functional: at less than 30% of the Hartree-Fock exchange, only delocalized hole is stable, at 50% - both delocalized and self-trapped states are stable, while further increase of exact exchange results in only the self-trapped state being stable. We argue that the main contributions to the self-trapping energy such as the kinetic energy of the localizing charge, the chemical bond formation of the di-halogen quasi molecule, and the lattice polarization, are represented incorrectly within the Kohn-Sham (KS) based approaches.Comment: 6 figures, 1 tabl

Perturbation Theory on the Transition Temperature and Electronic Properties of Organic Superconductor

We study the superconducting transition temperature and the electronic properties of the metallic phase of $\kappa$-type (BEDT-TTF)$_2$X which shows unconventional properties in experiments, on the basis of the third order perturbation theory for a simple effective Hubbard model of a nearly triangular lattice. Appropriate transition temperatures and $d_{x^2-y^2}$ symmetry of the gap function are obtained in good agreement with experimental results. We also calculate the transition temperature by the fluctuation-exchange approximation(FLEX) in order to compare the two approaches; FLEX gives higher transition temperatures rather than the perturbation approach. However, it is also found that the vertex corrections, which are ignored in FLEX, have a crucial effect on $T_{\rm c}$ for strongly frustrated systems. The density of states and the normal self-energy calculated in this perturbation scheme show the nature of the conventional Fermi liquid near the Mott-insulator. Thus, our perturbation approach is applicable to the conventional metallic phase of this compound, while it cannot explain the (pseudo-)spin gap phenomenon which signals the non-Fermi liquid

Magnetic Phase Diagram and Metal-Insulator Transition of NiS2-xSex

Magnetic phase diagram of NiS2-xSex has been reexamined by systematic studies of electrical resistivity, uniform magnetic susceptibility and neutron diffraction using single crystals grown by a chemical transport method. The electrical resistivity and the uniform magnetic susceptibility exhibit the same feature of temperature dependence over a wide Se concentration. A distinct first order metal-insulator (M-I) transition accompanied by a volume change was observed only in the antiferromagnetic ordered phase for 0.50<x<0.59. In this region, the M-I transition makes substantial effects to the thermal evolution of staggered moments. In the paramagnetic phase, the M-I transition becomes broad; both the electrical resistivity and the uniform magnetic susceptibility exhibit a broad maximum around the temperatures on the M-I transition-line extrapolated to the paramagnetic phase.Comment: 6 pages, 8 figures, corrected EPS fil