Modeling emergent tissue organization involving high-speed migrating cells in a flow equilibrium

There is increasing interest in the analysis of biological tissue, its organization and its dynamics with the help of mathematical models. In the ideal case emergent properties on the tissue scale can be derived from the cellular scale. However, this has been achieved in rare examples only, in particular, when involving high-speed migration of cells. One major difficulty is the lack of a suitable multiscale simulation platform, which embeds reaction-diffusion of soluble substances, fast cell migration and mechanics, and, being of great importance in several tissue types, cell flow homeostasis. In this paper a step into this direction is presented by developing an agent-based mathematical model specifically designed to incorporate these features with special emphasis on high speed cell migration. Cells are represented as elastic spheres migrating on a substrate in lattice-free space. Their movement is regulated and guided by chemoattractants that can be derived from the substrate. The diffusion of chemoattractants is considered to be slower than cell migration and, thus, to be far from equilibrium. Tissue homeostasis is not achieved by the balance of growth and death but by a flow equilibrium of cells migrating in and out of the tissue under consideration. In this sense the number and the distribution of the cells in the tissue is a result of the model and not part of the assumptions. For purpose of demonstration of the model properties and functioning, the model is applied to a prominent example of tissue in a cellular flow equilibrium, the secondary lymphoid tissue. The experimental data on cell speed distributions in these tissues can be reproduced using reasonable mechanical parameters for the simulated cell migration in dense tissue.Comment: 27 pages, 7 figures v2 major conceptual changes: stronger focus on model architecture; new Fig 6, fitting of migration parameters; reduced Fig 7 (formerly Fig 6), shortened presentation of the application; equation (3) provided in more detail; Fig 5 extende

Pulling all the pedagogic pieces together to provide good electronic feedback: an example from science education

The aim of Nefreduca project was to develop digital science materials for chronically ill children and to assist them to cope more rationally with their illness. The Nefreduca system was developed in 2 stages.The first was a teaching-learning sequence about nutrition and kidney function, which was tested with the students and their teachers from the hospital school. The second phase was the construction of an automatic feedback system for Nefreduca. This paper reports the findings from both phases and makes the case that good feedback models must build upon on a good learning design that addresses students' misconceptions and introduces well structured e-activitie

Digit-Type Mechanisms in Cell Differentiation Process: a Theoretical Study

According to inductive conception, the interference of neighboring cells causes a production of broken spatial symmetry in an initially homogenous system (cell differentiation process) during embryo development. A concentration gradient of a specific substance (morphogen), which serves as an analog-type control signal, is proposed as an agent to provide this process. It is known fact, that genes’ activity are of a discreet-type (digit) and, therefore, cell differentiation mechanism based on the control digit-type signals in comparison with the analog-type signals is more or less probable. A model presented here simulates the cell differentiation process. The model is based on the assumption that only the digit-type interactions take place between adjacent cells (not analog-type interactions that are typical for the concentration gradient field). Within model assumptions, the genes’ interaction algorithms and boundary condition are postulated. Under the model assumptions, the cell differentiation process starts with the homogeneous blastula formation and comprises three consecutive stages. 1) The loop-like inhomogeneous cell formation development and corresponding set of the self-blocking genes activation - the set of the asymmetric pattern genes governs the process. 2) The line-type inhomogeneous cell formations, with their origins at different cells of the loop-type formation, development and corresponding self-blocking genes activation - the sets of the symmetric pattern genes govern the process. 3) The variety of the function genes activation in the complex inhomogeneous cell formation - the sets of the self-blocking genes govern the process. Under model assumptions the multi level tree-type inhomogeneous cell structures creation is possible. The number of the pattern genes limits the complexity of the inhomogeneous structure. According to the model, in order to provide the further blastula development process, the concentration gradient fields may appear after the initial stages of the cell differentiation process. As simulated by the model, results qualitatively coincide with some of the experimental facts

Neurotoxicity

Neurotoxicity refers to the direct or indirect effect of chemicals that disrupt the nervous system of humans or animals. Numerous chemicals can produce neurotoxic diseases in humans, and many more are used as experimental tools to disturb or damage the nervous system of animals. Some act directly on neural cells, others interfere with metabolic processes on which the nervous system is especially dependent. Some disrupt neural function, others induce maldevelopment or damage to the adult nervous system. Perturbations may appear and disappear rapidly, evolve slowly over days or weeks and regress over months or years, or cause permanent deficits. Neurotoxicity is usually self-limiting after exposure ceases and rarely progressive in the absence of continued exposure, although there may be a significant delay between exposure and manifestation of neurotoxic effects

Public health and landfill sites

Landfill management is a complex discipline, requiring very high levels of organisation, and considerable investment. Until the early 1990’s most Irish landfill sites were not managed to modern standards. Illegal landfill sites are, of course, usually not managed at all. Landfills are very active. The traditional idea of ‘put it in the ground and forget about it’ is entirely misleading. There is a lot of chemical and biological activity underground. This produces complex changes in the chemistry of the landfill, and of the emissions from the site. The main emissions of concern are landfill gases and contaminated water (which is known as leachate). Both of these emissions have complex and changing chemical compositions, and both depend critically on what has been put into the landfill. The gases spread mainly through the atmosphere, but also through the soil, while the leachate (the water) spreads through surface waters and the local groundwater. Essentially all unmanaged landfills will discharge large volumes of leachate into the local groundwater. In sites where the waste accepted has been properly regulated, and where no hazardous wastes are present, there is a lot known about the likely composition of this leachate and there is some knowledge of its likely biological and health effects. This is not the case for poorly regulated sites, where the composition of the waste accepted is unknown. It is possible to monitor the emissions from landfills, and to reduce some of the adverse health and environmental effects of these. These emissions, and hence the possible health effects, depend greatly on the content of the landfill, and on the details of the local geology and landscape. There is insufficient evidence to demonstrate a clear link between cancers and exposure to landfill, however, it is noted that there may be an association with adverse birth outcomes such as low birth weight and birth defects. It should be noted, however, that modern landfills, run in strict accordance with standard operation procedures, would have much less impact on the health of residents living in proximity to the site

Переклад у галузі електроенергетики. Методичні рекомендації до практичних занять з дисципліни для студентів спеціальності 7.030507 «Переклад» напряму підготовки 035 «Філологія»

Методичні матеріали призначено для самостійної роботи студентів спеціальності 7.030507 “Переклад” напряму підготовки 035 «Філологія» для організації практичних занять із дисципліни «Переклад у галузі електроенергетики». Рекомендації орієнтовано на вдосконалення навичок перекладу науково-технічних текстів