RESUMEN
We present a coarse-grained model of DNA-functionalized colloids that is computationally tractable. Importantly, the model parameters are solely based on experimental data. Using this highly simplified model, we can predict the phase behavior of DNA-functionalized nanocolloids without assuming pairwise additivity of the intercolloidal interactions. Our simulations show that, for nanocolloids, the assumption of pairwise additivity leads to substantial errors in the estimate of the free energy of the crystal phase. We compare our results with available experimental data and find that the simulations predict the correct structure of the solid phase and yield a very good estimate of the melting temperature. Current experimental estimates for the contour length and persistence length of single-stranded (ss) DNA sequences are subject to relatively large uncertainties. Using the best available estimates, we obtain predictions for the crystal lattice constants that are off by a few percent: this indicates that more accurate experimental data on ssDNA are needed to exploit the full power of our coarse-grained approach.
Asunto(s)
Coloides/química , ADN de Cadena Simple/química , Modelos Químicos , Nanopartículas/química , Modelos Moleculares , Transición de Fase , TermodinámicaRESUMEN
Margination of white blood cells (WBCs) towards vessel walls is an essential precondition for their efficient adhesion to the vascular endothelium. We perform numerical simulations with a two-dimensional blood flow model to investigate the dependence of WBC margination on hydrodynamic interactions of blood cells with the vessel walls, as well as on their collective behavior and deformability. We find WBC margination to be optimal in intermediate ranges of red blood cell (RBC) volume fractions and flow rates, while, beyond these ranges, it is substantially attenuated. RBC aggregation enhances WBC margination, while WBC deformability reduces it. These results are combined in state diagrams, which identify WBC margination for a wide range of flow and cell suspension conditions.
Asunto(s)
Endotelio Vascular/citología , Agregación Eritrocitaria/fisiología , Hemodinámica , Leucocitos/citología , Adhesión Celular , Movimiento Celular , Simulación por Computador , Endotelio Vascular/metabolismo , Humanos , Leucocitos/metabolismo , Estrés MecánicoRESUMEN
We analyze the phonon spectra of periodic structures formed by two-dimensional mixtures of dipolar colloidal particles. These mixtures display an enormous variety of complex ordered configurations [J. Fornleitner, Soft Matter 4, 480 (2008)], allowing for the systematic investigation of the ensuing phonon spectra and the control of phononic gaps. We show how the shape of the phonon bands and the number and width of the phonon gaps can be controlled by changing the susceptibility ratio, the composition, and the mass ratio between the two components.
RESUMEN
Using a highly efficient and reliable optimization tool that is based on ideas of genetic algorithms, we have systematically studied the pattern formation of the two-dimensional square-shoulder system. An overwhelming wealth of complex ordered equilibrium structures emerge from this investigation as we vary the shoulder width. With increasing pressure three structural archetypes could be identified: cluster lattices, where clusters of particles occupy the sites of distorted hexagonal lattices, lane formation, and compact particle arrangements with high coordination numbers. The internal complexity of these structures increases with increasing shoulder width.
Asunto(s)
Biofisica/métodos , Algoritmos , Análisis por Conglomerados , Modelos Genéticos , Modelos Estadísticos , Modelos Teóricos , Conformación Molecular , Método de Montecarlo , Polímeros/química , Presión , Temperatura , TermodinámicaRESUMEN
Two-dimensional dipolar mixtures consisting of spherical particles with unequal susceptibilities are shown to order to an enormous variety of crystalline structures, whose geometry can be tuned by the stoichiometry of the compound, the susceptibility ratio, as well as the density. Our results are based on the application of genetic algorithms, which allow for an efficient and unbiased search over the parameter space. Structures that are practically degenerate energetically are discovered at various parameter combinations. Implications on the ability to tune the phononic spectra of such composite materials are discussed.
RESUMEN
We employ genetic algorithms (GA), which allow for an unbiased search for the global minimum of energy landscapes, to identify the ordered equilibrium configurations formed by binary dipolar systems confined on a plane. A large variety of arrangements is identified, the complexity of which grows with increasing asymmetry between the two components and with growing concentration of the small particles. The effects of the density are briefly discussed and a comparison with results obtained via conventional lattice-sum minimization is presented. Our results can be confirmed by experiments involving Langmuir monolayers of polystyrene dipolar spheres or superparamagnetic colloids confined on the air-water interface and polarized by an external, perpendicular magnetic field.