Self-propulsion of pure water droplets by spontaneous Marangoni stress driven motion

We report spontaneous motion in a fully bio-compatible system consisting of pure water droplets in an oil-surfactant medium of squalane and monoolein. Water from the droplet is solubilized by the reverse micellar solution, creating a concentration gradient of swollen reverse micelles around each droplet. The strong advection and weak diffusion conditions allow for the first experimental realization of spontaneous motion in a system of isotropic particles at sufficiently large P\'eclet number according to a straightforward generalization of a recently proposed mechanism. Experiments with a highly concentrated solution of salt instead of water, and tetradecane instead of squalane, confirm the above mechanism. The present swimming droplets are able to carry external bodies such as large colloids, salt crystals, and even cells.Comment: 5 pages, 5 figure

Project Panorama - vistas on validated information

Internet has become the foremost information source for a large majority of people, young and old, in the Netherlands certainly not less than in other European countries. Search is a ubiquitous functionality available at any website. General search engines like Google, Yahoo! or Bing have become the primary tool for locating information for almost everybody. What you find (discover) in Google is immediately displayed (delivered) on your screen; a mechanism very unlike classical library practice. As a result a user-expectation of "instant satisfaction" of any information need has developed. Unfortunately, often these facts also trigger the general notion that no other information exists than what can be found by these search engines

Palaeo-ecological and archaeological analysis of two Dutch Celtic fields (Zeijen-Noordse Veld and Wekerom-Lunteren): solving the puzzle of local Celtic field bank formation

Celtic fields are the best preserved and most widely distributed type of prehistoric agricultural landscape in the Netherlands, and occur throughout northwestern Europe. In this contribution, data from two excavated Dutch Celtic fields are used to explain the process of bank formation and to unravel the agricultural regime of Celtic fields. To this end, traditional archaeological methodologies and geochemical analyses are combined with detailed palaeo-ecological analyses. It is shown that Celtic field banks were constructed from a mixture of non-local soil, wetland vegetation, dung and settlement debris such as charcoal and sherds. A system was in place in which sods and plants were cut in lower-lying wetland landscapes and which were transported to the settlement, where they were presumably used as byre-bedding, became enriched with dung and were mixed with settlement debris. This mixture was carted to the fields, most likely to be spread across fallow plots as a manuring agent. From this primary, functional location, a composite sediment of agricultural sediments and the added manure was incorporated into the field banks. This process of incorporation was very slow and probably started with the uprooting of arable weeds from the fields, which were tossed to the side against the wattlework fences—together with minute quantities of soil attached to their root clusters. As a consequence of this chain of events, over the course of centuries, banks of anthropogenic sediment came to enclose fields within the Celtic field landscape

Realisation of the Brazil-nut effect in charged colloids without external driving

Sedimentation is a ubiquitous phenomenon across many fields of science, such as geology, astrophysics, and soft matter. Sometimes, sedimentation leads to unusual phenomena, such as the Brazil-nut effect, where heavier (granular) particles reside on top of lighter particles after shaking. We show experimentally that a Brazil-nut effect can be realised in a binary colloidal system of long-range repulsive charged particles driven purely by Brownian motion and electrostatics without the need for activity. Using theory, we argue that not only the mass-per-charge for the heavier particles needs to be smaller than the mass-per-charge for the lighter particles, but that at high overall density, the system can be trapped in a long-lived metastable state, which prevents the occurrence of the equilibrium Brazil-nut effect. Therefore, we envision that our work provides valuable insights into the physics of strongly interacting systems, such as partially glassy and crystalline structures. Finally, our theory, which quantitatively agrees with the experimental data, predicts that the shapes of sedimentation density profiles of multicomponent charged colloids are greatly altered when the particles are charge regulating with more than two ion species involved. Hence, we hypothesise that sedimentation experiments can aid in revealing the type of ion-adsorption processes that determine the particle charge and possibly the value of the corresponding equilibrium constants.Comment: 13 pages, 4 figures. In ancillary files: SI and 2 SI videos, published manuscript with improved explanation on quantification of parameter

О финансово-экономическом кризисе

У статті для визначення позиції молодих учених, стосовно фінансово-економічної кризи 2008–2010 р. використаний метод нечіткої кластеризації даних, що працює в режимі паралельної їхньої обробки. Наведено заходи щодо зниження наслідків кризи для України.В статье для определения позиции молодых ученых, применительно к финансово-экономическому кризису 2008—2010 гг. использован метод нечеткой кластеризации данных, который работает в режиме параллельной их обработки. Приведены мероприятия по снижению последствий кризиса для Украины.In an article for determining the position of young scientists, in relation to financial and economic crisis, 2008— 2010. used the method of fuzzy clustering, which operates in parallel processing. Shows the measures to reduce the impact of the crisis in Ukraine

Speed-Dispersion Induced Alignment : a 1D model inspired by swimming droplets experiments

We investigate the collective dynamics of self-propelled droplets, confined in a one dimensional micro-fluidic channel. On one hand, neighboring droplets align and form large trains of droplets moving in the same direction. On the other hand, the droplets condensates, leaving large regions with very low density. A careful examination of the interactions between two "colliding" droplets demonstrates that local alignment takes place as a result of the interplay between the dispersion of their speeds and the absence of Galilean invariance. Inspired by these observations, we propose a minimalistic 1D model of active particles reproducing such dynamical rules and, combining analytical arguments and numerical evidences, we show that the model exhibits a transition to collective motion in 1D for a large range of values of the control parameters. Condensation takes place as a transient phenomena which tremendously slows down the dynamics, before the system eventually settles into a homogeneous aligned phase.Comment: 5 pages, 5 figure

Formation of dodecagonal quasicrystals in two-dimensional systems of patchy particles

The behaviour of two-dimensional patchy particles with 5 and 7 regularly-arranged patches is investigated by computer simulation. For higher pressures and wider patch widths, hexagonal crystals have the lowest enthalpy, whereas at lower pressures and for narrower patches, lower-density crystals with five nearest neighbours and that are based on the (3^2,4,3,4) tiling of squares and triangles become lower in enthalpy. Interestingly, in regions of parameter space near to that where the hexagonal crystals become stable, quasicrystalline structures with dodecagonal symmetry form on cooling from high temperature. These quasicrystals can be considered as tilings of squares and triangles, and are probably stabilized by the large configurational entropy associated with all the different possible such tilings. The potential for experimentally realizing such structures using DNA multi-arm motifs are discussed.Comment: 12 pages, 12 figure

Realization of the Brazil-nut effect in charged colloids without external driving

Sedimentation is a ubiquitous phenomenon across many fields of science, such as geology, astrophysics, and soft matter. Sometimes, sedimentation leads to unusual phenomena, such as the Brazil-nut effect, where heavier (granular) particles reside on top of lighter particles after shaking. We show experimentally that a Brazil-nut effect can be realized in a binary colloidal system of long-range repulsive charged particles driven purely by Brownian motion and electrostatics without the need for activity. Using theory, we argue that not only the mass-per-charge for the heavier particles needs to be smaller than the mass-per-charge for the lighter particles but also that at high overall density, the system can be trapped in a long-lived metastable state, which prevents the occurrence of the equilibrium Brazil-nut effect. Therefore, we envision that our work provides valuable insights into the physics of strongly interacting systems, such as partially glassy and crystalline structures. Finally, our theory, which quantitatively agrees with the experimental data, predicts that the shapes of sedimentation density profiles of multicomponent charged colloids are greatly altered when the particles are charge-regulating with more than one ion species involved. Hence, we hypothesize that sedimentation experiments can aid in revealing the type of ion adsorption processes that determine the particle charge and possibly the value of the corresponding equilibrium constants