Analysis of mixed motion in deterministic ratchets via experiment and particle simulation

Deterministic lateral displacement (DLD) ratchets are microfluidic devices, which are used for size-based sorting of cells or DNA. Based on their size, particles are showing different kinds of motion, leading to their fractionation. In earlier studies, so-called zigzag and displacement motions are observed, and in recent study by our group (Kulrattanarak et al., Meas Sci Technol, 2010a; J Colloid Interface Sci, 2010b), we have shown that also mixed motion occurs, which is an irregular alternation of zigzag and displacement motion. We have shown that the mixed motion is due to asymmetry of the flow lane distribution, induced by the symmetry breaking of the oblique primitive lattice cell (Kulrattanarak et al. 2010b). In this study, we investigate mixed motion in depth by numerical and experimental analysis. Via 3D simulations, we have computed explicit particle trajectories in DLD, and are able to show that there are two critical length scales determining the type of motion. The first length scale d f,1 is the first flow lane width, which determines the transition between zigzag motion and mixed motion. The other length scale, d f,c , determines the transition between mixed motion and displacement motion. Based on our experimental and numerical results we have been able to correlate the migration angle of particles showing mixed motion to the particle size, relative to the two critical length scales d f,1 and d f,

Ethylene and flooding resistance : I. An ecophysiological approach with Rumex as a model

Contains fulltext : 15908.pdf (publisher's version ) (Open Access

Effectiviteit van ervarend leren op de boerderij

In Noord-Brabant zijn individuele woon-werktrajecten op boerderijen ontwikkeld voor jongeren tussen de 16 en 20 jaar met ernstige problemen. Er is sprake van problemen en ruzie in het gezin, de jongeren gaan niet meer naar school en ze hebben geen goede vrijetijdsinvulling. De jongeren verblijven een half jaar op de boerderij. Daarna volgt nog een nabegeleiding van een half jaar. De resultaten van de door de jongeren ingevulde vragenlijsten laten zien dat het traject met name een positief effect heeft op probleemgedrag en zelfwaardering en in iets mindere mate op het copinggedrag. De positieve veranderingen zijn ook een half jaar na afsluiting van het nabegeleidingstraject nog zichtbaar. Uit de scores van de begeleiders blijkt dat er verbeteringen opgetreden zijn in het contact met het gezin, schooluitval, politiecontact, drugsgebruik, vrijetijdsbesteding, welzijn, gedragsproblemen en zelfvertrouwen

Reproductive Allocation and Maternal Investment in Intertidal Whelks

Parental investment per offspring is a key life history trait in which offspring size and number combinations are balanced in order to maximise fitness. When food is scarce and energy for reproduction is reduced, changes in reproductive allocation can be expected. These adjustments may go on to influence the growth and survival of the next generation. Trade-offs in reproductive allocation in response to food availability occurred differently in each of the three whelks species of this study. However, each species traded numbers of offspring rather than size of offspring when fed low food. Offspring size was more variable among and within capsules than among food treatments. Capsule size was a plastic trait that varied in response to food treatments in each of the species and varied among populations of the same species. Carry-over effects of maternal nutrition influenced juvenile growth in all three species. However, while juvenile growth was greater when adults were fed high food in two of the species, high adult food suppressed the growth of juveniles of the third species. This may be a mechanism to prevent potential negative consequences of rapid growth. There was no evidence of a maternal effect of mortality in any of the three species. Greater variation in hatchling size occurred in the species in which nurse egg feeding occurred. Nurse egg feeding may be a successful strategy in unpredictable environments where optimal offspring size changes from year to year. Regional differences in reproductive allocation between whelks separated by small distances suggest that populations may be isolated from one another and may need to be managed separately for conservation purposes. This study highlights the influence of maternal nutritional effects on life history and the potential impacts that these may have on population and community structure

Temporally-coherent terawatt attosecond XFEL synchronized with a few cycle laser

Attosecond metrology using laser-based high-order harmonics has been significantly advanced and applied to various studies of electron dynamics in atoms, molecules and solids. Laser-based high-order harmonics have a limitation of low power and photon energies. There is, however, a great demand for even higher power and photon energy. Here, we propose a scheme for a terawatt attosecond (TW-as) X-ray pulse in X-ray free-electron laser controlled by a few cycle IR pulse, where one dominant current spike in an electron bunch is used repeatedly to amplify a seeded radiation to a terawatt level. This scheme is relatively simple, compact, straightforward, and also produces a temporally and spectrally clean pulse. The viability of this scheme is demonstrated in simulations using Pohang accelerator laboratory (PAL)-XFEL beam parameters.1183Ysciescopu

Galilean invariant lattice Boltzmann scheme for natural convection on square and rectangular lattices

In this paper we present lattice Boltzmann (LB) schemes for convection diffusion coupled to fluid flow on two-dimensional rectangular lattices. Via inverse Chapman-Enskog analysis of LB schemes including source terms, we show that for consistency with physics it is required that the moments of the equilibrium distributions equal those of the Maxwell-Boltzmann distribution. These constraints can be satisfied for the rectangular D2Q9 lattice for only fluid flow in the weakly compressible regime. The analysis of source terms shows that fluxes are really defined on the boundaries of the Wigner-Seitz cells, and not on the lattice sites where the densities are defined¿which is quite similar to the staggered grid finite-volume schemes. Our theoretical findings are confirmed by numerical solutions of benchmark problems for convection diffusion and natural convection. The lattice Boltzmann scheme shows remarkably good performance for convection diffusion, showing little to non-numerical diffusion or numerical dispersion, even at high grid Peclet number

Lattice Boltzmann schemes for convection-diffusion phenomena : application to packages of agricultural products

Packaging is crucial for the control of quality of fresh agricultural products. How to optimise the packaging design for a particular product and distribution chain, is still not fully understood. Various empirical studies have shown that existing packaging designs can still be improved significantly. The packaging design process can be greatly enhanced by the use of computer models, describing the physical and physiological processes.In transport packaging systems with vent holes, the dominant physical processes are convection-diffusion of heat and water vapour. The numerical solution of convection-diffusion problems is a complex matter. Traditionally, solutions are obtained with specific Finite Element or Finite Difference schemes, which require a highly-specialised knowledge of numerical mathematics. /P>In this thesis, the Lattice Boltzmann method is investigated as an alternative numerical method to solve the convection-diffusion problems in packaging systems. It simulates physical transport phenomena with quasi-particles, which move and collide on a lattice. Space, time and particle speed are discrete.The dynamics of the quasi-particles are governed by a discretised Boltzmann equation. Since the Lattice Boltzmann method has shown to be able to model Navier-Stokes flow, it has recieved a rapidly growing interest from the scientific community. This interest can be attributed to the simplicity and the appeal to physical intuition of the Lattice Boltzmann method.In the first part of this thesis several test case problems, taken from the practice of packing agricultural products, are solved with the Lattice Boltzmann method. Accurate and efficient schemes have been developed for the following applications: the cooling of cut flowers, the natural convection in a potato container, and the water vapour transfer in a potato container with vent holes.In order to solve these test case problems, the Lattice Boltzmann method has been extended with:a scheme for convection-diffusion on an orthorhombic lattice,a scheme for porous media flow as described by Darcy's law,interactions modelling heat and mass transfer between solid and fluid phase of a porous medium,boundary conditions for heat conducting and water permeating packaging material, andboundary conditions for vent holes.Despite the successful solution of the test case problems, the Lattice Boltzmann schemes have up to now have had drawbacks, which make them difficult to compete with Finite Element and Finite Difference schemes.Because the lack of a clear theoretical foundation, and the inability to Support grid refinements, it is difficult for the Lattice Boltzmann method to compete with the Finite Element and Finite Difference method in solving convection-diffusion problems. Hence, in the latter part of the thesis we investigate whether these drawbacks of the Lattice Boltzmann scheme can be resolved.Theoretical analysis shows that the diffusion Lattice Boltzmann scheme can be derived from the basic principle that the hydrodynamic moments of the equilibrium particle distribution must equal those of the Maxwell-Boltzmann distribution up to second order.By extending this theoretical framework to convection-diffusion, LB schemes are developed for orthorhombic lattices and irregular grids. These new Lattice Boltzmann schemes are compared to several Finite Difference and Finite Element schemes by solving benchmark problems. Analysis of the numerical solutions shows that the accuracy of the Lattice Boltzmann schemes is comparable to high-order Finite Element schemes, but can be achieved with much less computer resources, i.e., memory and computing time. Its good performance, the existence of a theoretical framework clearly linked with physics, and the algorithmic simplicity, make the Lattice Boltzmann method a strong competitor for conventional numerical schemes.From the results of this thesis it can be concluded that the Lattice Boltzmann method is a very suitable framework for modelling convection-diffusion phenomena and can be applied to packaging systems. It has attractive properties in simplicity, efficiency, and accuracy. Thereby, it can greatly contribute to better quality management of packed, fresh agricultural products.</p