Stationary States in Bistable System Driven by L\'evy Noise

We study the properties of the probability density function (PDF) of a bistable system driven by heavy tailed white symmetric L\'evy noise. The shape of the stationary PDF is found analytically for the particular case of the L\'evy index \alpha = 1 (Cauchy noise). For an arbitrary L\'evy index we employ numerical methods based on the solution of the stochastic Langevin equation and space fractional kinetic equation. In contrast with the bistable system driven by Gaussian noise, in the L\'evy case the positions of maxima of the stationary PDF do not coincide with the positions of minima of the bistable potential. We provide a detailed study of the distance between the maxima and the minima as a function of the potential's depth and L\'evy noise parameters.Comment: Accepted to EPJS

Determination of chemical composition of the atmosphere of Venus by the interplanetary station ''Venera-4''

Venera-4 observation of chemical composition of Venus atmospher

Rook placements in G2G_2 and F4F_4 and associated coadjoint orbits

Let $\mathfrak{n}$ be a maximal nilpotent subalgebra of a simple complex Lie algebra with root system $\Phi$. A subset $D$ of the set $\Phi^+$ of positive roots is called a rook placement if it consists of roots with pairwise non-positive scalar products. To each rook placement $D$ and each map $\xi$ from $D$ to the set $\mathbb{C}^{\times}$ of nonzero complex numbers one can naturally assign the coadjoint orbit $\Omega_{D,\xi}$ in the dual space $\mathfrak{n}^*$. By definition, $\Omega_{D,\xi}$ is the orbit of $f_{D,\xi}$, where $f_{D,\xi}$ is the sum of root covectors $e_{\alpha}^*$ multiplied by $\xi(\alpha)$, $\alpha\in D$. (In fact, almost all coadjoint orbits studied at the moment have such a form for certain $D$ and $\xi$.) It follows from the results of Andr\`e that if $\xi_1$ and $\xi_2$ are distinct maps from $D$ to $\mathbb{C}^{\times}$ then $\Omega_{D,\xi_1}$ and $\Omega_{D,\xi_2}$ do not coincide for classical root systems $\Phi$. We prove that this is true if $\Phi$ is of type $G_2$, or if $\Phi$ is of type $F_4$ and $D$ is orthogonal.Comment: 16 pages, 4 figure

A direction finding technique for the ULF electromagnetic source

International audienceA technique of direction finding is proposed, which can be applied to the magnetic-dipole type source located in the conductive ground. To distinguish a weak ULF source signal from the natural noise a network of multicomponent magnetometers is supposed to be used. The data obtained by the ground-based stations is processed in such a way that a set of partial derivatives of the magnetic perturbations due to the source are found. Comparing these derivatives with theoretical formulae makes it possible, in principle, to find the ULF source parameters such as the distance and amplitude. Averaging the data and a special procedure are proposed in order to exclude random fluctuations in the magnetic moment orientation and to avoid hydrogeological and other local factors

azTotMD 2.0: Molecular Dynamics with the Radiative Thermostat and Temperature-Dependent Force Field (CUDA Version)

azTotMD 2.0 is a parallel molecular dynamics program which includes both conventional algorithms and a novel “radiative” thermostat and a temperature-dependent force field. The radiative thermostat is based on the black-body radiation law and acts like virtual adsorption and radiation of photons. The thermostat algorithm has complexity of O(N), it can accelerate and decelerate atoms and this action over time leads to a Maxwell-like distribution of velocities. The temperature-dependent pair potential includes atomic radii, which are functions of the thermal excitation of atoms. The combination of the radiative thermostat and the potential allows to reproduce many phenomena such as phase transitions, thermal expansion, defect formation, surface tension, vapor saturation, glass formation and devitrification. © 2022 The Author(s).The reported study was funded by RFBR, Russia, project number 20-03-00897

Oxygen isotope composition of dissolved sulphate in deep-sea sediments: Eastern Equatorial Pacific Ocean

High-resolution analyses of the oxygen isotope ratio (18O/16O) of dissolved sulfate in pore waters have been made to depths of >400 meters below seafloor (mbsf) at open-ocean and upwelling sites in the eastern equatorial Pacific Ocean. 18O values of dissolved sulfate (18O-SO4) at the organic-poor open-ocean Site 1231 gave compositions close to modern seawater (+9.5 vs. Vienna-standard mean ocean water, providing no chemical or isotopic evidence for microbial sulfate reduction (MSR). In contrast, the maximum 18O values at Sites 1225 and 1226, which contain higher organic matter contents, are +20 and +28, respectively. Depth-correlative trends of increasing 18O-SO4, alkalinity, and ammonium and the presence of sulfide indicate significant oxidation of sedimentary organic matter by sulfate-reducing microbial populations at these sites. Although sulfate concentration profiles at Sites 1225 and 1231 both show similarly flat trends without significant net MSR, 18O-SO4 values at Site 1225 reveal the presence of significant microbial sulfur-cycling activity, which contrasts to Site 1231. This activity may include contributions from several processes, including enzyme-catalyzed equilibration between oxygen in sulfate and water superimposed upon bacterial sulfate reduction, which would tend to shift 18O-SO4 toward higher values than MSR alone, and sulfide oxidation, possibly coupled to reduction of Fe and Mn oxides and/or bacterial disproportionation of sulfur intermediates. Large isotope enrichment factors observed at Sites 1225 and 1226 ( values between 42 and 79) likely reflect concurrent processes of kinetic isotope fractionation, equilibrium fractionation between sulfate and water, and sulfide oxidation at low rates of sulfate reduction. The oxygen isotope ratio of dissolved pore water sulfate is a powerful tool for tracing microbial activity and sulfur cycling by the deep biosphere of deep-sea sediments

Mechanochemical conversion of acetylene in quartz – ultrafine metal powder system

We have studied the effect of nano-sized metal powders (Zn, Ni), obtained by electric explosion of wires, on mechanochemical conversions of acetylene in the presence of quartz. In the process of acetylene mechanical treatment (MT) in the presence of quartz, benzene is formed. During the mechanical grinding of quartz in planetary-centrifugal mills, active radical sites are formed on quartz surface. It is possible to suppose that due to the influence of mechanical energy acetylene triple bond breaks to form ethyl radicals, which are subjected to chemosorption on active quartz sites with subsequent formation of benzene. The addition of ultrafine Zn powder decreased, while Ni powder considerably increased benzene yield. In the process of MT, particles of ultrafine Zn powder are agglomerated which results in the decrease of its catalytic activity. The increase in benzene yield at the use of ultrafine Ni powder as the additives is associated with catalytic conversion of acetylene into benzene on the newly formed nickel surface. The injection of ultrafine Zn and Ni powders in quartz-acetylene system caused no changes in quantitative composition of acetylene conversion products but affected the amounts of one or other component formation

Management of patent ductus arteriosus in premature infants.

Closure of hemodynamically significant patent ductus arterios (HSPDA)  is one of the most important questions in modern neonatal intensive care, especially for preterm babies. Long-term functioning of the hemodynamically significant  arterial duct leads to a large number of complications in premature babies, such as: bronchopulmonary dysplasia, periventricular leucomalacia, intraventricular hemorrhage, retinopathy of the premature. To prevent all these complications, the PDA should be closed pharmacologically or surgically as soon as possible without any hesitation. COX inhibitors are commonly used nowa days. Ibuprofen and indomethacin show the equal efficacy and no significant adverse events. But some patients still need surgical treatment. The aim of the study was to determine the feasibility, effectiveness and safety of using various volumes of infusion in combination with COX inhibitors and to determine its effect on the timing of the closure of PDA. 91 premature infants with a gestational age of 26-31 weeks with manifestations of respiratory distress syndrome and НSPDA were studied retrospectively. Premies were divided into 2 groups. Research groups were representative as to gestational age, gender, and weight (1205.0±435.0 g). Therapy for PDA closure included the use of various volumes of restrictive or liberal infusion therapy (from 50 to 100 ml/kg/day) and COX inhibitors (indomethacin, ibuprofen). The volume of infusion therapy was limited in the first group. Preemies received 53.5±6.4 ml/kg/day on DOL1 and 2. From the third day urine excretion increased and the volume of infusion therapy also raised to 63.6±5.6 ml/kg/day, and on day 5 – to 89.7±6.8 ml/kg/day. In the second group there was no strict limitation of the volume of infusion therapy (especially in the first 5 days). Delayed period of PDA closure (on average from 14.55±0.56 DOL) was associated with absence of limitation of the infusion volume. In the first group, volume of infusion therapy was restricted in the first 5 days, and the closure of the ductus arteriosus occurred extremely early (on 2.35±0.48 DOL). COX inhibitors were prescribed according to the standard scheme: in the first 3 days indomethacin was administered orally in doses of 0.2/0.1/0.1 mg/kg/day. If the premature baby had symptoms of intestinal paresis ( this restricted oral administration of indomethacin), ibuprofen was prescribed in a three-day course in doses of 10/5/5 mg/kg/day intravenously or 20/10/10 mg/kg/day in rectal form. In all  groups, standard PDA closure therapy was used. In the more remote periods (14 and 28 days), there was no fundamental difference in the volume of infusion in all groups. For early PDA closure limitation of infusion therapy in the first 3-5 days in combination with COX is principle

Объединение экономических прогнозов с использованием экспертной информации

Purpose of the study. The aim of this work is to consider the possibility of using expert information when combining forecasts as an additional factor in improving the accuracy of economic forecasting. Using the methodology of combining forecasts is increasingly found in the domestic practice of economic forecasting. Most researchers agree that combining forecasts improves forecasting accuracy by using all available information about the process under study, which is included in individual forecasting methods.  Today, there are many methods for constructing weighting factors when combining forecasts, but all of them are primarily based on the use of only statistical information about the process under study. But economic forecasting cannot be linear in its dynamics, many external factors constantly affect the forecasted process, and some internal ones may not be affected by the methods used. In this case, it is necessary to attract expert information or external information about the forecast obtained in order to increase its accuracy and adjust the further development of the economic process. This is especially true today, during the period of digitalization of the economy and the increasing influence of social and political factors on the dynamics of economic phenomena.  Materials and methods. For this purpose, methods of constructing integral indicators based on expert information or directly using such information at the stage of constructing a joint forecast can be directly used to make adjustments to the resulting combined forecast. Some of these approaches are already used in foreign practice of economic forecasting, while in domestic practice they are still little known. One of such approaches may be the use of the pairwise preference method or the application of Fishburn formulas for ranking particular forecasting methods by accuracy. The approaches considered in this work can be used as tools for constructing weight coefficients or as a correction of the obtained forecasting results.  Results. As a result of this article, attempts have been made to propose possible methods for combining forecasts using expert information, a summary table has been compiled with an assessment of one or another method of combining forecasts, and conclusions are drawn on the appropriateness of their application in practice. Such a table will make it possible to better understand the direction of attracting expert information to combine forecasts and choose the most suitable approach for further use in practice.  Conclusion. Combining forecasts has long established itself as an effective method for increasing forecast accuracy. This technique cannot degrade the result, in most cases increasing accuracy. The use of expert information in combining forecasts is the next step in improving this technique and requires a separate further practical study of possible tools for attracting expert information to the pool.  Цель исследования. Целью настоящей работы является рас­смотрение возможности использования экспертной информации при объединении прогнозов как дополнительного фактора по­вышения точности экономического прогнозирования. Использо­вание методики объединения прогнозов все чаще встречается в отечественной практике экономического прогнозирования. Большинство исследователей сходятся во мнении что объеди­нение прогнозов повышает точность прогнозирования через ис­пользование всей доступной информации об изучаемом процессе, включаемой в отдельные методы прогнозирования.  На сегодняшний день существует множество методов постро­ения весовых коэффициентов при объединении прогнозов, но все они в первую очередь основываются на использовании только статистической информации об изучаемом процессе. Но эко­номическое прогнозирование не может быть линейным в своей динамике, множество внешних факторов постоянно оказывают влияние на прогнозируемый процесс, а некоторые внутренние мо­гут не затрагиваться используемыми методами. В этом случае необходимо привлечение экспертной информации или внешней информации о полученном прогнозе для повешения его точности и корректировки дальнейшего развития экономического процесса. Это особенно актуально на сегодняшний день, в период цифрови­зации экономики и увеличения влияния социальных и политических факторов на динамику экономических явлений.  Материалы и методы. Для этой цели, непосредственно могут использоваться методы построения интегральных показателей на основе экспертной информации или же привлечение такой информации на стадии построения объединенного прогноза, для внесения корректировок полученного объединенного прогноза. Некоторые из этих подходов уже используются в зарубежной практике экономического прогнозирования, в отечественной же практике они пока что мало известны. Одним из таких подходов может являться использование метода попарных предпочтений или же применение формул Фишберна для ранжирования частных методов прогнозирования по точности. Рассмотренные в работе подходы могут использоваться в качестве инструментов по построению весовых коэффициентов или же в качестве коррек­тировки полученных результатов прогнозирования.  Результаты. В качестве итога настоящей статьи сделаны попытки по предложению возможных методов объединения прогнозов, с использованием экспертной информации, сфор­мирована сводная таблица с оценкой того или иного метода объединения прогнозов и сделаны выводы о целесообразности их применения на практике. Такая таблица позволит лучше разобраться в направлении привлечения экспертной информации в объединение прогнозов и выбрать наиболее подходящий подход для дальнейшего иго использования на практике.  Заключение. Объединение прогнозов уже давно зарекомендовало себя как эффективный метод повышения точности прогнози­рования. Данная методика не может ухудшить получаемый результат, в большинстве случаев увеличивая точность. Использование экспертной информации в объединении прогно­зов является следующим этапом совершенствования данной методики и требует отдельного дальнейшего практического исследования возможных инструментов по привлечению экс­пертной информации в объединение.