Active particles with chirality: Application to pedestrian flows

We analyse pattern formation in systems of active particles with right/left asymmetry of the interaction forces in the context of pedestrian dynamics. To describe the inter-particle interactions we use the standard social force model and supplement it with the new type of force, reflecting the chirality of pedestrians. We perform numerical simulations of two pedestrian flows moving in opposite directions in a long corridor. We observe phase transition from disordered motion to multi-lane motion and quantify it in terms of the order parameter. Also we observe a phase transition from the multi-lane to two-lane motion, which occurs with varying number density of pedestrians and strength of the chirality force. We perform a qualitative analysis to predict the critical density of this transition and its dependence on the chirality. The results of our analysis agree fairly well with the simulation data. Our findings may find applications in urbanistic and transport problems

A model of ballistic aggregation and fragmentation

A simple model of ballistic aggregation and fragmentation is proposed. The model is characterized by two energy thresholds, Eagg and Efrag, which demarcate different types of impacts: If the kinetic energy of the relative motion of a colliding pair is smaller than Eagg or larger than Efrag, particles respectively merge or break; otherwise they rebound. We assume that particles are formed from monomers which cannot split any further and that in a collision-induced fragmentation the larger particle splits into two fragments. We start from the Boltzmann equation for the mass-velocity distribution function and derive Smoluchowski-like equations for concentrations of particles of different mass. We analyze these equations analytically, solve them numerically and perform Monte Carlo simulations. When aggregation and fragmentation energy thresholds do not depend on the masses of the colliding particles, the model becomes analytically tractable. In this case we show the emergence of the two types of behavior: the regime of unlimited cluster growth arises when fragmentation is (relatively) weak and the relaxation towards a steady state occurs when fragmentation prevails. In a model with mass-dependent Eagg and Efrag the evolution with a cross-over from one of the regimes to another has been detected

Трехкомпонентная модель механической активности легких

The article provides a review of key studies of the hypothesis about an independent pulmonary mechanical activity: from phylogenic analysis of respiratory movements in amphibians and mammals to respiratory mechanics research. The airflow interruption method revealed negative elastic lung hysteresis. Given the basic physical laws (the first and the second laws of thermodynamics), this paradox was considered as evidence of the independent mechanical activity of the lungs. Predominance of breathing-related pressure fluctuations in an obstructed bronchus over the intrathoracic pressure amplitude was considered as a manifestation of the regional pulmonary mechanical activity. Experimental studies of respiratory mechanics allowed formulation a hypothesis about three levels of pulmonary mechanical activity. The integral pulmonary mechanical activity provides inspiratory and expiratory movements. Smooth muscles of the bronchial wall keep the bronchial lumen during expiration and preclude valvular obstruction of the bronchus (the second level of the mechanical activity). The inspiratory action of the smooth muscles in distal parts of the lungs is a functional component along with surfactant that provides the consistency of alveoli during expirations (the third component).Представлен обзор основных работ, в которых определено формирование гипотезы о самостоятельной механической активности легких, а также важнейшие этапы ее развития – от размышлений с позиции филогенетического анализа дыхательных движений у земноводных и млекопитающих животных до исследования механики дыхания. При использовании методики прерывания воздушного потока выявлен отрицательный эластический гистерезис легких. С позиции фундаментальных законов физики (I и II законов термодинамики) этот парадокс был расценен как доказательство самостоятельной механической активности легких. Преобладание дыхательных колебаний давления в заклиненном бронхе над амплитудой внутригрудного давления расценивается как проявление регионарной механической активности легких. Клинико-экспериментальные исследования механики дыхания позволили сформировать гипотезу о функционировании 3 уровней механической активности легких. Интегральная механическая активность легких обеспечивает соучастие легких в инспираторном и экспираторном движении легких. Гладкая мускулатура бронхов поддерживает просвет бронхов на выдохе, противодействуя клапанной их обструкции (2-й уровень механической активности). Инспираторное действие гладкой мускулатуры терминальных отделов легких является функциональным компонентом наряду с сурфактантом, обеспечивающим стабильность альвеол на выдохе (3-й компонент)

Abstracts from the 20th International Symposium on Signal Transduction at the Blood-Brain Barriers

https://deepblue.lib.umich.edu/bitstream/2027.42/138963/1/12987_2017_Article_71.pd