Quasisolitons in self-diffusive excitable systems, or Why asymmetric diffusivity does not violate the Second Law

Solitons, defined as nonlinear waves which can reflect from boundaries or transmit through each other, are found in conservative, fully integrable systems. Similar phenomena, dubbed quasi-solitons, have been observed also in dissipative, "excitable" systems, either at finely tuned parameters (near a bifurcation) or in systems with cross-diffusion. Here we demonstrate that quasi-solitons can be robustly observed in excitable systems with excitable kinetics and with self-diffusion only. This includes quasi-solitons of fixed shape (like KdV solitons) or envelope quasi-solitons (like NLS solitons). This can happen in systems with more than two components, and can be explained by effective cross-diffusion, which emerges via adiabatic elimination of a fast but diffusing component. We describe here a reduction procedure can be used for the search of complicated wave regimes in multi-component, stiff systems by studying simplified, soft systems.Comment: 11 pages, 2 figures, as accepted to Scientific Reports on 2016/07/0

Pursuit-evasion predator-prey waves in two spatial dimensions

We consider a spatially distributed population dynamics model with excitable predator-prey dynamics, where species propagate in space due to their taxis with respect to each other's gradient in addition to, or instead of, their diffusive spread. Earlier, we have described new phenomena in this model in one spatial dimension, not found in analogous systems without taxis: reflecting and self-splitting waves. Here we identify new phenomena in two spatial dimensions: unusual patterns of meander of spirals, partial reflection of waves, swelling wavetips, attachment of free wave ends to wave backs, and as a result, a novel mechanism of self-supporting complicated spatio-temporal activity, unknown in reaction-diffusion population models.Comment: 15 pages, 15 figures, submitted to Chao

Soliton-like phenomena in one-dimensional cross-diffusion systems: a predator-prey pursuit and evasion example

We have studied properties of nonlinear waves in a mathematical model of a predator-prey system with pursuit and evasion. We demonstrate a new type of propagating wave in this system. The mechanism of propagation of these waves essentially depends on the ``taxis'', represented by nonlinear ``cross-diffusion'' terms in the mathematical formulation. We have shown that the dependence of the velocity of wave propagation on the taxis has two distinct forms, ``parabolic'' and ``linear''. Transition from one form to the other correlates with changes in the shape of the wave profile. Dependence of the propagation velocity on diffusion in this system differs from the square-root dependence typical of reaction-diffusion waves. We demonstrate also that, for systems with negative and positive taxis, for example, pursuit and evasion, there typically exists a large region in the parameter space, where the waves demonstrate quasisoliton interaction: colliding waves can penetrate through each other, and waves can also reflect from impermeable boundaries.Comment: 15 pages, 18 figures, submitted to Physica

Envelope quasisolitons in dissipative systems with cross-diffusion

Copyright © 2011 American Physical SocietyJournal ArticleWe consider two-component nonlinear dissipative spatially extended systems of reaction-cross-diffusion type. Previously, such systems were shown to support "quasisoliton" pulses, which have a fixed stable structure but can reflect from boundaries and penetrate each other. Herein we demonstrate a different type of quasisolitons, with a phenomenology resembling that of the envelope solitons in the nonlinear Schrödinger equation: spatiotemporal oscillations with a smooth envelope, with the velocity of the oscillations different from the velocity of the envelope

Classification of wave regimes in excitable systems with linear cross diffusion

Copyright © 2014 American Physical SocietyWe consider principal properties of various wave regimes in two selected excitable systems with linear cross diffusion in one spatial dimension observed at different parameter values. This includes fixed-shape propagating waves, envelope waves, multienvelope waves, and intermediate regimes appearing as waves propagating at a fixed shape most of the time but undergoing restructuring from time to time. Depending on parameters, most of these regimes can be with and without the "quasisoliton" property of reflection of boundaries and penetration through each other. We also present some examples of the behavior of envelope quasisolitons in two spatial dimensions.Russian Foundation for Basic Research (RFBR

“Надо, чтоб каждый в Союзе читал…”: Читатель как институция советской культуры

[Rev. of: Reading Russia. A History of Reading in Modern Russia. Volume 3. Edited by Damiano Rebecchini and Raffaella Vassena. Milano: Università degli Studi di Milano, 2020] The present review focuses on the third volume of the collective study Reading Russia: A History of Reading in Modern Russia and aims at analyzing the methods of studying reading practices proposed in the aforementioned publication. The articles included in the peer-reviewed volume are studied in detail against the background of previously published scholarly literature on the history of reading, as well as in relation to archival and previously (un)published materials that have so escaped researchers’ attention. The broad historical and literary material shows that the «narratives» proposed in the reviewed volume do not present a full-fledged history of reading practices, but describe only individual disparate reading strategies of typologically different readers. The forms of institutionalization of reading in the USSR that were left out are sometimes much more important in the context of transformations in reading practices than the total collection of the «cases» offered in the volume. At the same time, the case study review offers an opportunity to talk about ‘the reader of the 20th century’ as a special institution of Soviet culture. This is why much of the review presents an attempt to find other principles and strategies of analysis on which the history of reading in the «small twentieth century» can be based. The article offers a sociological portrait of the average reader, whose main features were formed during the Stalinist era and remained unchanged throughout the previous century. These features have existed in the same form for almost a quarter of the present century. The material that has been excluded from the present research can be divided into three groups: facts that characterize the Soviet state of affairs; information about the most important forms of institutionalized reading in the USSR-specific cultural environment; information concerning aesthetic and economic aspects of the book. A detailed commentary on each of these groups is intended to supplement and elaborate on the authors' concept. Along with the analysis of archival documents, we draw on materials from the funds of various public organizations and bodies, as well as periodicals, published memoirs, diaries and other materials available to us. DOI: 10.31168/2305-6754.2022.11.2.16[Рец.: Reading Russia. A History of Reading in Modern Russia. Volume 3. Edited by Damiano Rebecchini and Raffaella Vassena. Milano: Università degli Studi di Milano, 2020] Предлагаемый обзор посвящен третьему тому коллективного исследования «Reading Russia: A History of Reading in Modern Russia» и имеет своей задачей анализ предложенных в издании методов изучения читательских практик. Вошедшие в рецензируемый том статьи подробно рассматриваются как на фоне ранее вышедшей научной литературы по истории чтения, так и в связи с архивными и ранее (не)опубликованными материалами, которые оказались вне поля зрения исследователей. На широком историко-литературном материале показывается, что предложенные в рецензируемом томе «сюжеты» не образуют полноценной истории читательских практик, но описывают лишь частные разрозненные стратегии чтения типологически разных читателей. Оставленные без внимания формы институализации чтения в СССР подчас оказываются куда весомее в контексте трансформаций читательских практик, чем вся совокупность предложенных в сборнике «кейсов». Вместе с тем обзор конкретного исследования становится поводом к разговору о читателе прошлого столетия как об особой институции советской культуры. Именно поэтому большая часть обзора представляет собой попытку поиска иных принципов и стратегий анализа, на которых может быть основана история чтения в «малом двадцатом веке». В статье предлагается социологический портрет усредненного реципиента, основные черты которого сформировались в эпоху сталинизма и остались неизменными на протяжении всего прошлого столетия и в прежнем виде продолжают существовать уже почти четверть нынешнего века. Не вошедший в исследование материал условно подразделяется на три группы: факты, характеризующие собственно советское положение дел; сведения о важнейших для культурной ситуации СССР формах институционализации чтения; данные об эстетическом и экономическом аспектах бытования книги. Подробный комментарий к каждой из этих групп призван дополнить и детализировать предложенную авторами концепцию. Наряду с анализом архивных документов, нами привлекаются материалы фондов различных общественных организаций и органов, а также периодика, опубликованные воспоминания, дневниковые/мемуарные свидетельства и другие доступные нам материалы. DOI: 10.31168/2305-6754.2022.11.2.1

Natural and chemotherapy-induced clonal evolution of tumors

Evolution and natural selection of tumoral clones in the process of transformation and the following carcinogenesis can be called natural clonal evolution. Its main driving factors are internal: genetic instability initiated by driver mutations and microenvironment, which enables selective pressure while forming the environment for cell transformation and their survival. We present our overview of contemporary research dealing with mechanisms of carcinogenesis in different localizations from precancerous pathologies to metastasis and relapse. It shows that natural clonal evolution establishes intratumoral heterogeneity and enables tumor progression. Tumors of monoclonal origin are of low-level intratumoral heterogeneity in the initial stages, and this increases with the size of the tumor. Tumors of polyclonal origin are of extremely high-level intratumoral heterogeneity in the initial stages and become more homogeneous when larger due to clonal expansion. In cases of chemotherapy-induced clonal evolution of a tumor, chemotherapy becomes the leading factor in treatment. The latest research shows that the impact of chemotherapy can radically increase the speed of clonal evolution and lead to new malignant and resistant clones that cause tumor metastasis. Another option of chemotherapy-induced clonal evolution is formation of a new dominant clone from a clone that was minor in the initial tumor and obtained free space due to elimination of sensitive clones by chemotherapy. As a result, in ~20% of cases, chemotherapy can stimulate metastasis and relapse of tumors due to clonal evolution. The conclusion of the overview formulates approaches to tumor treatment based on clonal evolution: in particular, precision therapy, prediction of metastasis stimulation in patients treated with chemotherapy, methods of genetic evaluation of chemotherapy efficiency and clonal-oriented treatment, and approaches to manipulating the clonal evolution of tumors are presented