Dynamical density functional theory with hydrodynamic interactions and colloids in unstable traps

A density functional theory for colloidal dynamics is presented which includes hydrodynamic interactions between the colloidal particles. The theory is applied to the dynamics of colloidal particles in an optical trap which switches periodically in time from a stable to unstable confining potential. In the absence of hydrodynamic interactions, the resulting density breathing mode, exhibits huge oscillations in the trap center which are almost completely damped by hydrodynamic interactions. The predicted dynamical density fields are in good agreement with Brownian dynamics computer simulations

Concentration Dependen Sedimentation of Collidal Rods

In the first part of this paper, an approximate theory is developed for the leading order concentration dependence of the sedimentation coefficient for rod-like colloids/polymers/macromolecules. To first order in volume fraction $\phi$ of rods, the sedimentation coefficient is written as $1+\alpha \phi$. For large aspect ratio L/D (L is the rod length, D it's thickness) $\alpha$ is found to very like $\propto (\frac{L}{D})^2/\log (\frac{L}{D})$. This theoretical prediction is compared to experimental results. In the second part, experiments on {\it fd}-virus are described, both in the isotropic and nematic phase. First order in concentration results for this very long and thin (semi-flexible) rod are in agreement with the above theoretical prediction. Sedimentation profiles for the nematic phase show two sedimentation fronts. This result indicates that the nematic phase becomes unstable with the respect to isotropic phase during sedimentation.Comment: Submitted to J. Chem. Phys. See related webpage http://www.elsie.brandeis.ed

A Case Study of Sedimentation of Charged Colloids: The Primitive Model and the Effective One-Component Approach

Sedimentation-diffusion equilibrium density profiles of suspensions of charge-stabilized colloids are calculated theoretically and by Monte Carlo simulation, both for a one-component model of colloidal particles interacting through pairwise screened-Coulomb repulsions and for a three-component model of colloids, cations, and anions with unscreened-Coulomb interactions. We focus on a state point for which experimental measurements are available [C.P. Royall et al., J. Phys.: Cond. Matt. {\bf 17}, 2315 (2005)]. Despite the apparently different picture that emerges from the one- and three-component model (repelling colloids pushing each other to high altitude in the former, versus a self-generated electric field that pushes the colloids up in the latter), we find similar colloidal density profiles for both models from theory as well as simulation, thereby suggesting that these pictures represent different view points of the same phenomenon. The sedimentation profiles obtained from an effective one-component model by MC simulations and theory, together with MC simulations of the multi-component primitive model are consistent among themselves, but differ quantitatively from the results of a theoretical multi-component description at the Poisson-Boltzmann level. We find that for small and moderate colloid charge the Poisson-Boltzmann theory gives profiles in excellent agreement with the effective one-component theory if a smaller effective charge is used. We attribute this discrepancy to the poor treatment of correlations in the Poisson-Boltzmann theory.Comment: 9 pages, 7 figure

Врахування ризиків у процесі взаємодії електронних магазинів та користувачів

Розглядаються ризики, які виникають у відвідувачів електронних магазинів, а також пропонуються можливі заходи безпеки при онлайн-купівлі товарів. Описуються ризики, яким підлягають самі Інтернет-магазини, та наводяться пропозиції щодо підвищення безпеки веб-ресурсу, розміщеного в мереж і Інтернет.Describing the risks arising at visitors of electronic shops are considered, and also possible security' measures are offered at online purchase of the goods. Risks to which Internet shops are exposed are described and offers on improvement of safety of a web resource which Internet is in a network are resulted

Depletion forces in non-equilibrium

The concept of effective depletion forces between two fixed big colloidal particles in a bath of small particles is generalized to a non-equilibrium situation where the bath of small Brownian particles is flowing around the big particles with a prescribed velocity. In striking contrast to the equilibrium case, the non-equilibrium forces violate Newton's third law, are non-conservative and strongly anisotropic, featuring both strong attractive and repulsive domains.Comment: 4 pages, 3 figure

Depletion-Induced Chiral Chain Formation of Magnetic Spheres

Experimental evidence is presented for the spontaneous formation of chiral configurations in bulk dispersions of magnetized colloids that interact by a combination of anisotropic dipolar interactions and isotropic depletion attractions. The colloids are superparamagnetic silica spheres, magnetized and aligned by a carefully tuned uniform external magnetic field; isotropic attractions are induced by using poly(ethylene oxide) polymers as depleting agents. At specific polymer concentrations, sphere chains wind around each other to form helical structures–of the type that previously have only been observed in simulations on small sets of unconfined dipolar spheres with additional isotropic interactions

Self-assembly of charged colloidal cubes

In this work, we show how and why the interactions between charged cubic colloids range from radially isotropic to strongly directionally anisotropic, depending on tuneable factors. Using molecular dynamics simulations, we illustrate the effects of typical solvents to complement experimental investigations of cube assembly. We find that in low-salinity water solutions, where cube self-assembly is observed, the colloidal shape anisotropy leads to the strongest attraction along the corner-to-corner line, followed by edge-to-edge, with a face-to-face configuration of the cubes only becoming energetically favorable after the colloids have collapsed into the van der Waals attraction minimum. Analysing the potential of mean force between colloids with varied cubicity, we identify the origin of the asymmetric microstructures seen in experiment. This journal is © The Royal Society of Chemistry.Austrian Science Fund, FWF: START-Projekt Y 627-N27Russian Science Foundation, RSF: 19-12-00209We thank Prof. A. Ivanov for helpful discussions. F. D. wants to acknowledge Dr Leon Bremer and Dr Harm Langermans for their help with the Langmuir–Blodgett experiments. This research has been supported by the Russian Science Foundation Grant No. 19-12-00209. The authors acknowledge support from the Austrian Research Fund (FWF), START-Projekt Y 627-N27. Computer simulations were performed using the Vienna Scientific Cluster (VSC-3 and VSC-4)

Colloidal iron(III) pyrophosphate particles

a b s t r a c t Ferric pyrophosphate is a widely used material in the area of mineral fortification but its synthesis and properties in colloidal form are largely unknown. In this article, we report on the synthesis and characterisation of colloidal iron(III) pyrophosphate particles with potential for application as a food additive in iron-fortified products. We present a convenient and food grade synthetic method yielding stable colloids of nanometre size with a distinctive white colour, a unique characteristic for iron-containing colloids. Physical properties of the colloids were investigated using different techniques, to assess particle crystallinity, surface charge, mass density, refractive index, internal structure, elemental composition and magnetic properties. The findings of this research are especially relevant for food and beverage science and technology and will help develop a more effective use of these fortifiers in colloidal form

Формирование приоритетов интенсификации факторов производства угольного предприятия на основе структурно-иерархического анализа

Проведено оцінку взаємного впливу чинників виробництва і пріоритетів їх формування на базі підприємств вугільної галузі на основі структурно-ієрархічного підходу. Обґрунтовано можливості йі умови аналізу багатоваріантності впливів чинників праці і капіталу на зниження трудомісткості і капіталомісткості очисних робіт. Доведено доцільність застосування методу аналізу ієрархій, за допомогою якого побудовано матриці парних порівнянь. Ключові слова: інтенсифікація чинників виробництва, матриця попарних порівнянь, метод аналізу ієрархій, структурно-ієрархічний метод, чинники виробництва.Проведена оценка взаимного влияния факторов производства и приоритетов их формирования на базе предприятий угольной отрасли на основе структурно-иерархического подхода. Обоснованы возможности и условия анализа многовариантности воздействия факторов труда и капитала на снижение трудоемкости и капиталоемкости очистных работ. Доказана целесообразность применения метода анализа иерархий, с помощью которого построены матрицы парных сравнений. Ключевые слова: интенсификация факторов производства, матрица попарных сравнений, метод анализа иерархий, структурно-иерархический метод, факторы производства.In new economics which is based on the knowledge system the level and complicity of innovation development of industrial complexenterprise is determined by such deep transformational phenomena as change of structure of technological modes in world economy, change of qualitative and quantitative proportions of production factors and, in particular, intensification of production factors, which is able to solve such actual problem as migration to primary intensive way of development. That is why the purpose of this research is development and improvement of methodological approach to formation of priority variants of production factors intensification on the basis of method of hierarchies analysis. For solution ofthis task the method of hierarchies analysis is usedwhich is systematic procedure for hierarchical expressing the elements determining the essence of any problem. The assessment of mutual influence of production factors and priorities of their formation by the example of coal industry enterprise on the basis of structural-hierarchic approach is given in the article. On the basis of structural-hierarchic approach the criteriawere formed, which, each in different ways and with different level of intensity, make influence on meaning of coal enterprise factors. There were proved the possibilities and conditions of multipart influence of labor factors and capital on decrease of labor and capital intensity of coal-face works, which will allow giving rise in increasing effectiveness while securing necessary labor safety. Practicability of method of hierarchies analysis, with the help of which the comparison-of-pairs matrix were built, was proved. Investigation conducted allowed choosing the directions of capital investments for the purpose of getting maximum effect. Keywords: production factors intensification, comparison-of-pairs matrix, method of hierarchies analysis, structural-hierarchic method, production factors