The recently noticed ability of restart to reduce the expected completion time of first-passage processes allows appealing opportunities for performance improvement in a variety of settings. However, complex stochastic processes often exhibit several possible scenarios of completion which are not equally desirable in terms of efficiency. Here we show that restart may have profound consequences on the splitting probabilities of a Bernoulli-like first-passage process, i.e., of a process which can end with one of two outcomes. Particularly intriguing, in this respect, is the class of problems where a carefully adjusted restart mechanism maximizes the probability that the process will complete in a desired way. We reveal the universal aspects of this kind of optimal behavior by applying the general approach recently proposed for the problem of first-passage under restart.

Chromosomes are exceedingly long polymers compacted in a cell nucleus. While it was long suggested that mammalian chromosomes are folded into loops, experimental detection of such loops has remained a daunting task. The most comprehensive experimental information about chromosome spatial organization is provided by Hi-C experiments that measure the frequency of contacts between all chromosomal positions. The lack of a tractable physical model of a polymer folded into loops limits our ability to interpret experimental data. It thus remains unknown how to obtain accurate and quantitative information about the nature of chromosomal looping from Hi-C. Here, we introduce a model of a polymer with random loops, solve it analytically and extend it by simulations for real chains. Remarkably, our model faithfully reproduces complex shapes of experimental contact probability curves universal among mammalian cells. This agreement suggests that chromosomes are indeed organized into a sequence of randomly positioned loops and allows to estimate loop sizes. We further show that excluded volume in real chains can induce osmotic and topological repulsion between loops. Thus, our new framework allows interpretation of experimental data and suggests that interphase chromosomes are crumpled polymers further folded into a sequence of randomly positioned loops.

Small aerosols drift down temperature or turbulence gradient since faster particles fly longer distances before equilibration. That fundamental phenomenon, called thermophoresis or turbophoresis, is widely encountered in nature and used in industry [1][2][3][4][5][6]. It is universally believed that particles moving down the kinetic energy gradient must concentrate in minima (say, on walls in turbulence). Here we show that this is incorrect: escaping minima is possible for inertial particles whose time of equilibration is longer than the time to reach the minimum. The best way out is always through: particles escape by flying through minima or reflecting from walls. We solve the problem analytically and find the phase transition as a sign change of the mean velocity. That means separation: light particles concentrate in a minimum while heavy particles spread away from it (gravity can reverse the effect). That discovery changes understanding of that fundamental phenomenon and may find numerous applications.Small particles in a fluid are agitated by thermal or turbulent fluctuations. In a spatial gradient of temperature or turbulence intensity, an inertial particle which flies from the hot side moves faster and travels longer distance before equilibration than a particle flying from a colder side. That produces net flux of particles towards the minima of kinetic energy of the fluid. Discovery of thermophoresis, wherein particles go with the heat flow, goes back to Maxwell, Tyndall and Rayleigh. A common example is the blackening of the kerosene lantern glass: the temperature gradient drives the carbon particles away from the flame. There are special cases where the sign of a drift can be opposite (like for particles driven by a colored noise [7], some cases of Soret effect in liquids etc) but we consider here the simplest situation. Since particles flow towards temperature minima, it was invariably concluded that they must accumulate there. That statement was then generalized from thermal diffusion to turbulent diffusion predicting the so-called turbophoresis: it is widely accepted that heavy particles migrate toward the turbulence minima, particularly to walls [6,[8][9][10][11]. Turbophoresis is ubiquitous in nature and industry, from droplets in clouds to coal fire burners; it determines, for instance, how chemicals remaining near walls are washed out into the bulk of reactor, how dust is raised from the ground by a turbulent wind or deposited on surfaces. Thermophoresis also is of interest both as a fundamental phenomenon and because of practical importance in many industrial applications, such as thermal precipitators removing sub-micron sized particles from gas streams, laser Doppler velocimetry, manufacturing by vapor deposition, manipulations of nano-particles, etc [12].Here we predict a new phenomenon: sufficiently inertial particles can have a net flux against the gradient, escaping kinetic energy minima. We show below that upon the change of the inertia parameter, the system undergoes localization-deloca...

The results of sensing of the gas and aerosol composition of the atmosphere with the Optik Tu‐134 aircraft laboratory in the period from 31 July to 1 August 2012 are presented. The measurements were conducted along the flight route Novosibirsk‐Tomsk‐Mirny‐Yakutsk‐Bratsk‐Novosibirsk. A significant part of the Siberian territory during this period was covered by numerous forest fires. The synoptic situation during the measurements was characterized by the presence of low‐gradient field. This fact determined the low rate of transport and diffusion of pollutants and their accumulation in the region under study. The maximal concentrations of CO2, CH4, and CO over fire zones achieved 432 ppm, 2367 ppb, and 4036 ppb, respectively. The aerosol particle number density in emission plumes achieved 4400 cm−3. Outside emission plumes, the concentration ranged within 400–1000 cm−3 depending on the region. The mass concentration of aerosol in plumes increased approximately 7 times (6.9). The enrichment of the concentration of some elements and ions in the plume with respect to the background varied from 1.3 to 9.1 times. The generation of ozone from biomass burning products was observed at plume boundaries. Two versions of this process are possible: ozone generation under and above the plume.