Self-propelled droplet driven by Marangoni flow and its applications

We developed a new class of self-propelled droplet, which is made of water/ethanol dispersed in squalane/monoolein. During the propulsion, a spontaneous phase separation of the droplet occurs due to the release of ethanol and the uptake of monoolein. This phase separation can lead to the formation of a Janus droplet consisting of a water-rich phase and an ethanol-rich phase. The droplet moves as a pusher, which is determined by µPIV, before the phase separation and as a neutral squirmer after it. The time before phase separation can be quantified by a model. Additionally the quantitative analysis of the driving mechanisms before and after the phase separation are presented. Depending on salt concentration, added DNA or RNA can be controlled to accumulate either in the water-rich or in the ethanol-rich phase as a 'cargo'. This 'cargo' can be selectively delivered to a target controlled by hydrodynamic interaction and wettability. The same water/ethanol droplet in an ethanol-saturated squalane shows chemotaxic attraction. In this system, the droplet uptakes ethanol from squalane and droplets are attracted to each other supposably driven by this ethanol gradient, which is created by themselves. Large numbers of droplets can form patterns with different shapes, which is controlled by number density and vertical confinement.Wir haben eine neue Klasse von selbst-angetriebenen Tropfen entwickelt, die aus Wasser / Ethanol bestehen und in Squalan / Monoolein dispergiert sind. Während der Bewegung kommt es zu einer spontanen Phasentrennung des Tropfens aufgrund der Abgabe von Ethanol und der Aufnahme von Monoolein. Diese Phasentrennung kann zur Ausbildung eines Janus-Tropfens führen, der aus einer wasserreichen Phase und einer ethanolreichen Phase besteht. Der Tropfen bewegt sich vor der Phasentrennung als 'Pusher', der durch µPIV bestimmt wird, und danach als neutraler 'Squirmer'. Die Zeit vor der Phasentrennung kann durch ein Modell quantifiziert. Zusätzlich wird die quantitative Analyse der Antriebsmechanismen vor und nach der Phasentrennung vorgestellt. Abhängig von der Salzkonzentration kann die zugesetzte DNA oder RNA so gesteuert werden, dass sie sich entweder in der wasserreichen oder in der ethanolreichen Phase als "Ladung" ansammelt. Diese 'Ladung' kann selektiv an ein Ziel geliefert werden und durch hydrodynamische Wechselwirkung und Benetzbarkeit gesteuert werden. Der gleiche Wasser/Ethanol Tropfen in ethanolgesättigten Squalan zeigt eine chemotaktische Anziehungskraft. In diesem System nehmen die Tropfen Ethanol aus Squalan auf und die Tropfen werden vermutlich durch diesen Ethanolgradienten, der von ihnen selbst erzeugt wird, voneinander angezogen. Die Ansammlung vieler Tropfen können Muster bilden. Das Muster wird von der Tropfendichte und der vertikalen Ausdehnung kontrolliert

Transformer Based Multi-Grained Features for Unsupervised Person Re-Identification

Multi-grained features extracted from convolutional neural networks (CNNs) have demonstrated their strong discrimination ability in supervised person re-identification (Re-ID) tasks. Inspired by them, this work investigates the way of extracting multi-grained features from a pure transformer network to address the unsupervised Re-ID problem that is label-free but much more challenging. To this end, we build a dual-branch network architecture based upon a modified Vision Transformer (ViT). The local tokens output in each branch are reshaped and then uniformly partitioned into multiple stripes to generate part-level features, while the global tokens of two branches are averaged to produce a global feature. Further, based upon offline-online associated camera-aware proxies (O2CAP) that is a top-performing unsupervised Re-ID method, we define offline and online contrastive learning losses with respect to both global and part-level features to conduct unsupervised learning. Extensive experiments on three person Re-ID datasets show that the proposed method outperforms state-of-the-art unsupervised methods by a considerable margin, greatly mitigating the gap to supervised counterparts. Code will be available soon at https://github.com/RikoLi/WACV23-workshop-TMGF.Comment: Accepted by WACVW 2023, 3rd Workshop on Real-World Surveillance: Applications and Challenge

Local orbital-angular-momentum dependent surface states with topological protection

Chiral surface states along the zigzag edge of a valley photonic crystal in the honeycomb lattice are demonstrated. By decomposing the local fields into orbital angular momentum (OAM) modes, we find that the chiral surface states present OAM-dependent unidirectional propagation characteristics. Particularly, the propagation directivities of the surface states are quantified by the local OAM decomposition and are found to depend on the chiralities of both the source and surface states. These findings allow for the engineering control of the unidirectional propagation of electromagnetic energy without requiring an ancillary cladding layer. Furthermore, we examine the propagation of the chiral surface states against sharp bends. It turns out that although only certain states successfully pass through the bend, the unidirectional propagation is well maintained due to the topology of the structure.Comment: 9 pages, 6 figure

Active Janus Droplet as a Micro‐Reactor for Automatic DNA/RNA Precipitation and Extraction

We explore the possibility to precipitate and to extract DNA, or RNA using an active water/ethanol Janus droplet. The active Janus droplet is initially formed by a single droplet made of a water/ethanol mixture in an oil/surfactant solution. This active droplet self-propels and absorbs surfactant molecules, by advection, while moving in the oily phase. The surfactant absorption leads to a phase separation of the water/ethanol mixture and the formation of an active Janus droplet. This active Janus droplet is made of a water-rich leading droplet and an ethanol-rich trailing droplet. We employ this phase separation method to precipitate and to extract DNA, RNA, or DNA/RNA mixtures independently, in an automatic manner. This automatic precipitation and extraction of DNA, or RNA, is achieved by tuning their water solubility with the addition of salt and then it is demonstrated by fluorescence