Conditional stability of particle alignment in finite-Reynolds-number channel flow

Finite-size neutrally buoyant particles in a channel flow are known to accumulate at specific equilibrium positions or spots in the channel cross-section if the flow inertia is finite at the particle scale. Experiments in different conduit geometries have shown that while reaching equilibrium locations, particles tend also to align regularly in the streamwise direction. In this paper, the Force Coupling Method was used to numerically investigate the inertia-induced particle alignment, using square channel geometry. The method was first shown to be suitable to capture the quasi-steady lift force that leads to particle cross-streamline migration in channel flow. Then the particle alignment in the flow direction was investigated by calculating the particle relative trajectories as a function of flow inertia and of the ratio between the particle size and channel hydraulic diameter. The flow streamlines were examined around the freely rotating particles at equilibrium, revealing stable small-scale vortices between aligned particles. The streamwise inter-particle spacing between aligned particles at equilibrium was calculated and compared to available experimental data in square channel flow (Gao {\it et al.} Microfluidics and Nanofluidics {\bf 21}, 154 (2017)). The new result highlighted by our numerical simulations is that the inter-particle spacing is unconditionally stable only for a limited number of aligned particles in a single train, the threshold number being dependent on the confinement (particle-to-channel size ratio) and on the Reynolds number. For instance, when the particle Reynolds number is $\approx1$ and the particle-to-channel height size ratio is $\approx0.1$, the maximum number of stable aligned particles per train is equal to 3. This agrees with statistics realized on the experiments of (Gao {\it et al.} Microfluidics and Nanofluidics {\bf 21}, 154 (2017)).Comment: 13 pages, 13 figure

Waves, rings, and trails: The scenic landscape of axonal actin.

The goal of this article is to provide the reader a snapshot of recent studies on axonal actin--largely emerging from superresolution and live-imaging experiments--and place this new information in context with earlier studies

Fuel Efficient Computation in Passive Self-Assembly

In this paper we show that passive self-assembly in the context of the tile self-assembly model is capable of performing fuel efficient, universal computation. The tile self-assembly model is a premiere model of self-assembly in which particles are modeled by four-sided squares with glue types assigned to each tile edge. The assembly process is driven by positive and negative force interactions between glue types, allowing for tile assemblies floating in the plane to combine and break apart over time. We refer to this type of assembly model as passive in that the constituent parts remain unchanged throughout the assembly process regardless of their interactions. A computationally universal system is said to be fuel efficient if the number of tiles used up per computation step is bounded by a constant. Work within this model has shown how fuel guzzling tile systems can perform universal computation with only positive strength glue interactions. Recent work has introduced space-efficient, fuel-guzzling universal computation with the addition of negative glue interactions and the use of a powerful non-diagonal class of glue interactions. Other recent work has shown how to achieve fuel efficient computation within active tile self-assembly. In this paper we utilize negative interactions in the tile self-assembly model to achieve the first computationally universal passive tile self-assembly system that is both space and fuel-efficient. In addition, we achieve this result using a limited diagonal class of glue interactions

Hessian characterization of a vortex in a maze

Recent advances in vortex imaging allow for tracing the position of individual vortices with high resolution. Pushing an isolated vortex through the sample with the help of a controlled $dc$ transport current and measuring its local $ac$ response, the pinning energy landscape could be reconstructed along the vortex trajectory [$\text{L. Embon } et\ al.$, $\text{Scientific Reports}$ $\mathbf{5}$, $7598$ $(2015)$]. This setup with linear tilts of the potential landscape reminds about the dexterity game where a ball is balanced through a maze. The controlled motion of objects through such tilted energy landscapes is fundamentally limited to those areas of the landscape developing local minima under appropriate tilt. We introduce the Hessian stability map and the Hessian character of a pinning landscape as new quantities to characterize a pinning landscape. We determine the Hessian character, the area fraction admitting stable vortex positions, for various types of pinning potentials: assemblies of cut parabolas, Lorentzian- and Gaussian-shaped traps, as well as a Gaussian random disordered energy landscape, with the latter providing a universal result of $(3-\sqrt{3})/6 \approx 21\%$ of stable area. Furthermore, we discuss various aspects of the vortex-in-a-maze experiment.Comment: 17 pages, 9 figure

Pulse-coupled relaxation oscillators: from biological synchronization to Self-Organized Criticality

It is shown that globally-coupled oscillators with pulse interaction can synchronize under broader conditions than widely believed from a theorem of Mirollo \& Strogatz \cite{MirolloII}. This behavior is stable against frozen disorder. Beside the relevance to biology, it is argued that synchronization in relaxation oscillator models is related to Self-Organized Criticality in Stick-Slip-like models.Comment: 4 pages, RevTeX, 1 uuencoded postscript figure in separate file, accepted for publication in Phys. Rev. Lett

Congress In India - Crisis And Split

Asian Studie

Interconvertible soft articles

Robust, soft, interconvertible articles constructed from soft, resilient members, which articles adopt a substantially different geometry upon an interior to exterior interconversion. The articles of the invention provide a significant visual effect and are useful as educational aids, magician's props, and toys.Published versio