Author: toschi
Francesca Tesser
Title
Population dynamics under flow
Aim
Simulations and experiments on populations of organisms living in aquatic environments and growing under flow conditions.
Summary
Ocean, rivers and lakes are natural environments for many living organisms. In these ecosystems they reproduce, compete for food, swim and die. The presence of a flow can have a strong effect on their dynamics both at individual and population scales. The dynamics of these systems are complicated because both transport and growth play a role. We are mainly interested in a population of individuals expanding in new territories and how the propagation speed is changed by the flow. Another question is how different species compete in such environments and, for example, how the extinction probability depends on the fluid dynamics. Population dynamics can be studied with numerical models but also experiments are performed with bacteria inside microfluidic devices. Bacteria are injected in micro-channels and observed for many days using microscopy equipment. We investigate how they colonize the channels and the way the colony propagates both upstream and downstream under flow. In order to measure these phenomena, the bacteria are modified and made fluorescent. It is possible to modify them in various ways so that they can be detected using different optical filters since they emit different colors. In this way also the competition between different growing species can be measured in space and time.
3CS03 - Caput Theoretical Physics: Theory of liquids
Liquids lack the long-range order typical for solids. Collisional processes and short-range correlations distinguish liquids from dilute gases. Therefore, no idealized models comparable with the perfect gas or the harmonic solid are available for even simple liquids. During the last half of the 20th century a rapid progress has been made in our understanding of the microscopic structure and the dynamics of simple liquids. With advances in experiments (light and neutron scattering), theoretical analysis (statistical mechanics, kinetic theory of strongly correlated systems) and numerical tools (Molecular Dynamics and Monte Carlo simulations) a rather clear and complete picture emerged on the properties of simple atomic liquids. Since the last few decades a variety of more complicated systems are being studied: ionic, molecular and polar liquids, liquid metals, liquid-vapor interfaces, liquid crystals, and colloidal suspensions. In this lecture we will address the basic theory of the liquid state based on a statistical mechanical description of liquids. Topics that will be discussed include static properties of liquids, distribution function theories, perturbation theory and inhomogeneous fluids. We will conclude with an outlook to more complex fluids.
Introduction (week 1-2)
Liquid state, intermolecular forces
Liouville equation, BBGKY hierarchy
Statistical mechanics and ensemble averages
Static properties of liquids (week 3-4)
Particle densities and distribution functions
Computer simulations (MD and MC)
Diagrammatic expansions, virial expansion of the equation of state
Equation of state of a hard sphere fluid
Distribution function theories (week 5-6)
Static structure factor
Ornstein-Zernike direct correlation function
Percus-Yevick solution for hard spheres, mean spherical approximation
Outlook (week 7)
Perturbation theories
Complex liquids
3FMX0 - Fysisch modelleren en simuleren
Study guide De cursus biedt een overzicht van een aantal fundamentele problemen uit verschillende domeinen in de fysica. Hiermee wordt geïllustreerd hoe fysische problemen langs klassieke analytische en numerieke weg kunnen worden gemodelleerd. Deze aanpak is van wijdverbreide nut voor verschillende wetenschappelijke disciplines. Het college illustreert welke stappen nodig zijn voor de definitie van analytische en numerieke modellen voor fysische verschijnselen. Klassieke voorbeelden worden besproken in de context van problemen uit de mechanica, elektromagnetisme, statistische fysica, klassieke mechanica, chaos en de theoretische kwantumfysica. De cursus behandelt modellen met relevantie voor veel fysische problemen en presenteert standaard methoden voor het oplossen van de analytische en numerieke modellen. Inhoud: Partiële differentiaalvergelijkingen; Klassieke analytische modelleringstechnieken; Op deeltjes gebaseerde methoden; Numerieke modellering.
3T350 - Chaos
This course is the continuation of 3T220 (Chaos), but now with a greater emphasis on the application of Chaos concepts to fluids. Chaos is the seemingly erratic behavior of simple deterministic, but nonlinear dynamical systems. We will first discuss the route to chaos, where we will already encounter the scaling concepts that will return in the description of chaotic fluid flow and turbulence. After a discussion of basic concepts, such as the sensitivity to variation in initial conditions, and the multifractal organization of phase space, we will introduce chaotic behavior and synchronization in coupled systems. These scaling ideas will then be carried over to the description of turbulence, the erratic flow of a fluid. We will do this in both the Eulerian and Lagrangian frame, where we move with the flow. While turbulence is wild chaos, also stirred viscous fluids may be chaotic, which may help to efficiently stir tracers. Also this case will be analyzed with the tools introduced in this course, such as local sensitivity to perturbations, and scaling of the concentration field of the stirred material. Central to the course is the exposure to the modern literature, in particular papers which appeared in Physical Review Letters (the most famous Physics journal). These papers can serve as inspiration for student presentations. Of course, adequate coaching is offered here.
COST Action MP1305 "Flowing matter"
Flowing matter lies at the crossroads between industrial processes, fundamental physics, engineering and Earth Sciences. Depending on the microscopic interactions, an assembly of molecules or of mesoscopic particles can flow like a simple Newtonian fluid, deform elastically like a solid or behave in a complex manner. When the internal constituents are active, as for biological entities, one generally observes complex large-scale collective motions. The phenomenology is further complicated by the invariable tendency of fluids to display chaos at the large scales or when stirred strong enough. A fundamental understanding of flowing matter is still missing impeding scientific progress, effective control on industrial processes, as well as accurate predictions of natural phenomena. Flowing matter frequently presents a tight coupling between small-scale structures and large-scale flow urging for a unifying approach. The Action will coordinate existing research efforts into a synergetic plan of collaborations and exchanges to develop an innovative multi-scale approach able to encompass the traditional micro-, meso-, and macro-scales descriptions. Breakthroughs in the understanding of flowing matter will impact on fundamental key scientific issues, such as the glass, the elasto-plastic and the jamming transitions, as well as industrial applications including health, energy, cosmetics, detergents, food, paints, inks, oil and gas.
COST Action MP0806 "Particles in turbulence"
Fluid turbulence is ubiquitous and so is its ability to transport particulate matter such as dust, soot or droplets. The dynamics of particles in a turbulent flow is fundamental to everyday life - examples of open scientific and technological issues include rain formation in clouds, pollution dispersion in the atmosphere, optimization and emission reduction in combustion, plankton population dynamics - and constitute a major scientific challenge with immediate practical implications and applications. Open scientific issues such as inertia, finite particles sizes, collisions, advection in complex flow geometries are examples of fundamental key ingredients which pose challenging theoretical problems and need to be understood in order to have an impact on applications. By joining forces within the experimental and numerical community of turbulence major breakthroughs can be achieved. The present COST action will create the needed platform for direct communication and interaction between participating laboratories and towards the wider scientific community alike.