Results 1 - 10 of 27563
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[en] We have used a variety of different applied fields to control the density, growth, and structure of colloidal crystals. Gravity exerts a body force proportional to the buoyant mass and in equilibrium produces a height-dependent concentration profile. A similar body force can be obtained with electric fields on charged particles (electrophoresis), a temperature gradient on all particles, or an electric field gradient on uncharged particles (dielectrophoresis). The last is particularly interesting since its magnitude and sign can be changed by tuning the applied frequency. We study these effects in bulk (making 'dielectrophoretic bottles' or traps), to control concentration profiles during nucleation and growth and near surfaces. We also study control of non-spherical and optically anisotropic particles with the light field from laser tweezers
[en] We examine the ultimate fate of individual opinions in a socially interacting population of leftists, centrists and rightists. In an elemental interaction between agents, a centrist and a leftist can both become centrists or both become leftists with equal rates (and similarly for a centrist and a rightist). However leftists and rightists do not interact. This interaction step between pairs of agents is applied repeatedly until the system can no longer evolve. In the mean-field limit, we determine the exact probability that the system reaches consensus (either leftist, rightist or centrist) or a frozen mixture of leftists and rightists as a function of the initial composition of the population. We also determine the mean time until the final state is reached. Some implications of our results for the ultimate fate in a limit of the Axelrod model are discussed
[en] A complex mathematical model of processes of plant nutrition from a special regulated gas medium containing nanoparticles of basic macro- and microelements is formulated. The variation of the number of nanoparticles and the variation of the total nanoparticle volume with time, which form during the cooling process of the initial gas mixture, were investigated. The calculations of the structures, compositions and shapes of nanoparticles and the movement of nanoparticles were carried out
[en] The interaction potential of two like-charged colloid spheres with nonuniform surface charge distribution suspended in an electrolyte confined in a long charged cylinder wall is calculated in this paper. Two models of boundary conditions on the cylinder wall are considered. One is the fixed potential model, and the other is the fixed charge density model. The confinement makes a quantitative or even qualitative change to the spheres' interaction compared with the unconfined system. A long-ranged attraction emerges in the confined system, though they are repulsive in the unconfined system under the same other conditions
[en] In this paper, we report a new method for size-based capturing of suspended particles by a specially designed micro fluidic structure named 'vernier walls'. A number of particles in suspension can be captured based on their sizes by a series of gaps between the closest walls, one standing on the ceiling and the other on the bottom of a wide microfluidic channel. The dimensions of the gaps narrow stepwise along the flow direction with a fixed step size per gap, which can be determined according to the required capturing resolution. Particles are captured based on their sizes in a line along each of the gaps with their corresponding dimensions. A part of the wide channel works as a bypass area, where the gap is constant to avoid clogging, letting the excess number of particles go through the channel. To realize the proposed structure, a new device assembly method has also been developed adopting planar gear-shaped structures surrounding the microfluidic channel solely for the fine and easy alignment of the narrowing gaps. The performance of the present method was evaluated using a device designed and fabricated for size-based capturing with a 5 µm resolution, and it was demonstrated that three kinds of particles with diameters from 10 to 26 µm were successfully captured by size. Additionally, we confirmed that the capturing rate was no less than 20% under the experimental condition. The present method can be used as a basic tool for handling particles with certain ranges of sizes.
[en] The magnetically induced yield stress in a sample of suspension of magnetic particles is associated with formation of a field-oriented structure, the strength of which depends on the degree of particles magnetization. This factor is largely defined by the actual magnetic field strength in the sample. At the same time it is common practice to present and analyze magnetorheological characteristics as a function of the applied magnetic field. Uncertainty of an influence function in magnetorheology hampers interpretation of data obtained with different measurement configurations. It was shown in this paper that rheological response of magnetorheological fluid to the applied magnetic field is defined by the sample's actual (internal) magnetic field intensity, which, in turn, depends on sample geometry and field orientation all other factors being equal. Utilization of the sample's actual field as an influence function in magnetorheology allows proper interpretation of data obtained with different measuring system configurations. Optimization of the actual internal field is a promising approach in designing of energy efficient magnetorheological devices.
[en] Colloidal dispersions are commonly encountered in everyday life and represent an important class of complex fluid. Of particular significance for many commercial products and industrial processes is the ability to control and manipulate the macroscopic flow response of a dispersion by tuning the microscopic interactions between the constituents. An important step towards attaining this goal is the development of robust theoretical methods for predicting from first-principles the rheology and nonequilibrium microstructure of well defined model systems subject to external flow. In this review we give an overview of some promising theoretical approaches and the phenomena they seek to describe, focusing, for simplicity, on systems for which the colloidal particles interact via strongly repulsive, spherically symmetric interactions. In presenting the various theories, we will consider first low volume fraction systems, for which a number of exact results may be derived, before moving on to consider the intermediate and high volume fraction states which present both the most interesting physics and the most demanding technical challenges. In the high volume fraction regime particular emphasis will be given to the rheology of dynamically arrested states. (topical review)
[en] The effect the initial structure of a two-component reaction powder mixture has on the dynamics of its isothermal homogenization is investigated. Relations for determining the duration of homogenization are obtained. A technique for calculating kinetic parameters is proposed.