SMC protein RecN drives translocation and remodelling of RecA filament for homology search

While the molecular repertoire of the homologous recombination pathway is well studied, the search mechanism that enables recombination between distant homologous regions is poorly understood. Here, we follow the dynamics of the recombinase RecA, an essential component of homology search, after induction of a single double-strand break on the Caulobacter chromosome. We find that the RecA-nucleoprotein filament translocates in a directional manner in the cell, undergoing several pole-to-pole traversals, until homology search is complete. Simultaneously, the filament undergoes dynamic remodelling; both translocation and dynamic remodelling are contingent on the action of the SMC protein RecN via its ATPase cycle. We provide a stochastic description of RecN regulated changes in filament length during translocation via modulation of RecA assembly-disassembly. Together, the observed RecN driven RecA dynamics points to a novel optimal search strategy.

Formation of initial projection data in reflection tomography in the implementation of technical vision

The known principles of active monostatic radar are based on the effect of radio wave scattering on objects located on the path of the probing signal, and the subsequent registration of a part of the wave reflected in the direction of the emitter. However, within the framework of this study, it is of interest to register objects that do not return a reflected radio echo towards the emitter. When fixing the position of an object, it is assumed that there is a possible absence of an echo signal characteristic of classical active radar with a passive response. The absence of a characteristic echo signal does not exclude its return as a result of repeated reflection inside the scene, including along other routes and from other objects. Purpose – within the framework of the implementation of technical vision in the course of tomographic observation of a complex radar scene that solves the problems of multidimensional reconstruction, a stochastic model based on the principles of tomography describing the subject area of a complex radar scene is developed. In the indicated relevance of the development of methods for radar detection of hidden objects inaccessible for registration by classical methods, a variant of using tomographic observation of a complex radar scene is proposed. In connection with the admitted lowangle and the emerging problems of an unambiguous deterministic definition, a description of the subject area of the scene from a stochastic position is proposed. In the proposed tomographic method, in conditions of limited initial data, when a deterministic approach to the reconstruction of the radar scene is not possible, an acceptable solution is sought in the stochastic description. At a given value by sampling the space, determined by the hexagonal lattice cell, the scene reconstruction is carried out by selecting and analyzing the echo signal trajectories from the possible set of proposed ones. The decision on the choice of one or another proposed trajectory and its transfer to the category of a possible solution is carried out on the basis of a preliminary calculation of the characteristics of the stochastic description.

A Simple Model to Assess the Performance of an Overtopping Wave Energy Converter Embedded in a Port Breakwater

A numerical model for the optimization of the performance of an innovative overtopping breakwater for wave energy conversion is proposed. The model is based on the stochastic description of the overtopping phenomenon based on the results of extensive laboratory tests, and it is able to simulate the behavior of the device operating under any assigned sequence of sea states, thus allowing to easily obtain results that would otherwise require time consuming and costly physical model tests. The model is used here to identify the main geometrical parameters affecting the performance of the device and to optimize such parameters in order to maximize the average yearly output power. An application to a device embedded in the breakwater of Pantelleria Port (Sicily, Italy) is presented. The model is also proved to be useful to verify the possibility of further increasing the output power through the implementation of specific control strategies concerning the operation of the turbines. The work provides a better understanding of the influence that such a system could have on the energy system of small Mediterranean islands, for example in terms of contribution to the CO2 emission reduction.

On Exact and Approximate Approaches for Stochastic Receptor-Ligand Competition Dynamics—An Ecological Perspective

Cellular receptors on the cell membrane can bind ligand molecules in the extra-cellular medium to form ligand-bound monomers. These interactions ultimately determine the fate of a cell through the resulting intra-cellular signalling cascades. Often, several receptor types can bind a shared ligand leading to the formation of different monomeric complexes, and in turn to competition for the common ligand. Here, we describe competition between two receptors which bind a common ligand in terms of a bi-variate stochastic process. The stochastic description is important to account for fluctuations in the number of molecules. Our interest is in computing two summary statistics—the steady-state distribution of the number of bound monomers and the time to reach a threshold number of monomers of a given kind. The matrix-analytic approach developed in this manuscript is exact, but becomes impractical as the number of molecules in the system increases. Thus, we present novel approximations which can work under low-to-moderate competition scenarios. Our results apply to systems with a larger number of population species (i.e., receptors) competing for a common resource (i.e., ligands), and to competition systems outside the area of molecular dynamics, such as Mathematical Ecology.

Distribution of the components of the building mixture in the presence of secondary raw materials during rotary mixing

The purpose of this study is a stochastic description of the distribution of solid dispersed components, including those from secondary raw materials, according to the characteristic angle of scattering ϴij when receiving a construction mixture at the first stage of operation of the rotary apparatus. Two stages of the formation of rarefied flows are assumed: when scattering particles of components by elastic blades of a rotating drum and when interacting with the baffle surface. Modeling method this is energy method of Klimontovich Yu.L. The analysis of the efficiency of the first stage (rotary mixing) is carried out based on the obtained distribution functions of the number of particles of bulk components over the scattering angle, taking into account their physical and mechanical properties and a variety of design and operating parameters of the apparatus. The bulk of the particles of the mixed components are scattered at the initial angles of rotation of the mixing drum, when the deformation of the elastic blades is most significant. This is accompanied by the characteristic first bursts of the obtained distribution curves (ϴij< 0.1 rad) for the number of particles of the tested bulk materials at the given ranges of parameters.