281 research outputs found
Artificial Rheotaxis
Motility is a basic feature of living microorganisms, and how it works is
often determined by environmental cues. Recent efforts have focused on develop-
ing artificial systems that can mimic microorganisms, and in particular their
self-propulsion. Here, we report on the design and characterization of syn-
thetic self-propelled particles that migrate upstream, known as positive rheo-
taxis. This phenomenon results from a purely physical mechanism involving the
interplay between the polarity of the particles and their alignment by a
viscous torque. We show quantitative agreement between experimental data and a
simple model of an overdamped Brownian pendulum. The model no- tably predicts
the existence of a stagnation point in a diverging flow. We take advantage of
this property to demonstrate that our active particles can sense and
predictably organize in an imposed flow. Our colloidal system represents an
important step towards the realization of biomimetic micro-systems withthe
ability to sense and respond to environmental changesComment: Published in Science Advances [Open access journal of Science
Magazine
Hopping and crawling DNA-coated colloids
Understanding the motion of particles with ligand-receptors is important for
biomedical applications and material design. Yet, even among a single design,
the prototypical DNA-coated colloids, seemingly similar micrometric particles
hop or roll, depending on the study. We shed light on this problem by observing
DNA-coated colloids diffusing near surfaces coated with complementary strands
for a wide array of coating designs. We find colloids rapidly switch between 2
modes: they hop - with long and fast steps - and crawl - with short and slow
steps. Both modes occur at all temperatures around the melting point and over a
wide array of designs. The particles become increasingly subdiffusive as
temperature decreases, in line with subsequent velocity steps becoming
increasingly anti-correlated. Overall, crawling (or hopping) phases are more
predominant at low (or high) temperatures; crawling is also more efficient at
low temperatures than hopping to cover large distances. We rationalize this
behavior within a simple model: at lower temperatures, the number of bound
strands increases, and detachment of all bonds is unlikely, hence, hopping is
prevented and crawling favored. We thus reveal the mechanism behind a common
design rule relying on increased strand density for long-range self-assembly:
dense strands on surfaces are required to enable crawling, possibly
facilitating particle rearrangements
Self Assembled Particles
A self-assembling structure using non-equilibrium driving forces leading to 'living crystals' and other maniputable particles with a complex dynamics. The dynamic self-assembly assembly results from a competition between self-propulsion of particles and an attractive interaction between the particles. As a result of non-equilibrium driving forces, the crystals form, grow, collide, anneal, repair themselves and spontaneously self-destruct, thereby enabling reconfiguration and assembly to achieve a desired property
Human relaxometry and MRI using fast field-cycling
Peer reviewedPublisher PD
In vivo human brain imaging at 0.2 T using a whole-body fast field-cycling MRI system
Peer reviewedPublisher PD
Соматоформная вегетативная дисфункция у лиц молодого возраста в свете современньїх представлений об этиопатогенезе, диагностике и методах восстановительного лечения
Guiding the self-assembly of materials by controlling the shape of the individual particle constituents is a powerful approach to material design. We show that colloidal silica superballs crystallize into canted phases in the presence of depletants. Some of these phases are consistent with the so-called "Λ1" lattice that was recently predicted as the densest packing of superdisks. As the size of the depletant is reduced, however, we observe a transition to a square phase. The differences in these entropically stabilized phases result from an interplay between the size of the depletants and the fine structure of the superball shape. We find qualitative agreement of our experimental results both with a phase diagram computed on the basis of the volume accessible to the depletants and with simulations. By using a mixture of depletants, one of which is thermosensitive, we induce solid-to-solid phase transitions between square and canted structures. The use of depletant size to leverage fine features of the shape of particles in driving their self-assembly demonstrates a general and powerful mechanism for engineering novel materials
Understanding value creation and word-of-mouth behaviour at cultural events
Cultural value is a highly contested concept, despite its undoubted importance to practitioners and policy makers. Reseach into cultural value has, meanwhile, tended to employ a unidimensional value framework. This has hamprered the understanding of behaviour related to the word-of-mouth (WOM) communication behaviour of cultural values. This paper presents a cultural value segmentation based on a multidimensional value framework, allowing a profile of WOM behaviour (both online and offline) of each segment to be developed. The segmentation has four distinct segments of cultural consumer, each with different combinations of cultural values and WOM communication preferences. In this way, the study challenges current understandings of value creation and transfer in cultural settings. By way of practical recommendations, the study favours the use of market segmentation based on multi-dimensional value ‘constellations’, which can not only achieve better audience development but also to encourage wider WOM communication of the values in question
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