Evolution of dwarf galaxies in the Centaurus A group

We consider star formation properties of dwarf galaxies in Cen A group observed within our HST/ACS projects number 9771 and 10235. We model color-magnitude diagrams of the galaxies under consideration and measure star formation rate and metallicity dependence on time. We study environmental dependence of the galaxy evolution and probable origin of the dwarf galaxies in the group.Comment: To appear in proceedings IAU Symp 244, 'Dark Galaxies and Lost Baryons', June 200

Unconstrained Astrometric Orbits for Hipparcos Stars with Stochastic Solutions

A considerable number of astrometric binaries whose positions on the sky do not obey the standard model of mean position, parallax and linear proper motion, were observed by the Hipparcos satellite. Some of them remain non-discovered, and their observational data have not been properly processed with the more adequate astrometric model that includes nonlinear orbital motion. We develop an automated algorithm based on "genetic optimization", to solve the orbital fitting problem with no prior information about the orbital elements is available (from, e.g., spectroscopic data or radial velocity monitoring). We test this method on Hipparcos stars with known orbital solutions in the catalog, and further apply it to stars with stochastic solutions, which may be unresolved binaries. At a confidence level of 99%, orbital fits are obtained for 65 stars, most of which have not been known as binary. A few of the new probable binaries with A-type primaries with periods 444-2015 d are chemically peculiar stars, including Ap and \lambda Boo type. The anomalous spectra of these stars are explained as admixture of the light from the unresolved, sufficiently bright and massive companions. We estimate the apparent orbits of four stars which have been identified as members of the 300 Myr-old UMa kinematic group. Another four new nearby binaries may include low-mass M-type or brown dwarf companions. Similar astrometric models and algorithms can be used for binary stars and planet hosts observed by SIM PlanetQuest and Gaia

Simulation of population’s reproductive behaviour patterns within an agent-oriented regional model

The study focuses on the research on how the unevenness of demographic transition affects the social and demographic characteristics and their dynamics of a region’s population. The research was conducted by means of computerized experiments (simulations) set within an original agent-oriented model. The study features the structure of the model represented by an artificial society, with its members (agents) being attributed their personal characteristics in such a way that they would imitate the gender and age of the region’s population. The agents are divided into two groups which differ in their reproductive strategy. Agents from Group 1 adhere to the traditional strategy characterized by a high birth rate, while the agents from Group 2 follow the modern strategy resulting in a markedly low birth rate. With the application of probabilistic mechanisms, the natural birth-death processes are imitated within the model. The extinction of agents occurs in accordance with the death rates adjusted for age and gender but remaining the same for the whole population. In the model, the appearance of new agents (birth of children) results from the choice made by reproductive-aged female agents, and their choice is influenced by the subjective traits determined by their group. The age and social structure of the regional population are generally formed as a result of the aggregation of particular agents’ activity. The model has been applied in a range of experiments on forecasting the number and structure of the population in an assumed region. The results showed that despite the apparent simplification of the reality, the developed agent-oriented model correctly represents both the initial condition of the regional population including the gender, age and social structure and the dynamics of the population’s basic characteristics.The research has been supported by the Russian Science Foundation (Project № 14-18-01968)

A Kinetic Model for the Enzymatic Action of Cellulase

We develop a mechanochemical model for the dynamics of cellulase, a two-domain enzyme connected by a peptide linker, as it extracts and hydrolyzes a cellulose polymer from a crystalline substrate. We consider two random walkers, representing the catalytic domain (CD) and the carbohydrate binding module (CBM), whose rates for stepping are biased by the coupling through the linker and the energy required to lift the cellulose polymer from the crystalline surface. Our results show that the linker length and stiffness play a critical role in the cooperative action of the CD and CBM domains and that, for a given linker length, the steady-state hydrolysis shows a maximum at some intermediate linker stiffness. The maximum hydrolysis rate corresponds to a transition of the linker from a compressed to an extended conformation, where the system exhibits maximum fluctuation, as measured by the variance of the separation distance between the two domains and the dispersion around the mean hydrolysis speed. In the range of experimentally known values of the parameters of our model, improving the intrinsic hydrolytic activity of the CD leads to a proportional increase in the overall hydrolysis rate