Liquid walls and interfaces in arbitrary directions stabilized by vibrations

Gravity shapes liquids and plays a crucial role in their internal balance. Creating new equilibrium configurations irrespective of the presence of a gravitational field is challenging with applications on Earth as well as in zero-gravity environments. Vibrations are known to alter the shape of liquid interfaces and also to change internal dynamics and stability in depth. Here, we show that vibrations can also create an “artificial gravity” in any direction. We demonstrate that a liquid can maintain an inclined interface when shaken in an arbitrary direction. A necessary condition for the equilibrium to occur is the existence of a velocity gradient determined by dynamical boundary conditions. However, the no-slip boundary condition and incompressibility can perturb the required velocity profile, leading to a destabilization of the equilibrium. We show that liquid layers provide a solution, and liquid walls of several centimeters in height can thus be stabilized. We show that the buoyancy equilibrium is not affected by the forcing.

Self-Organized UAV Flocking Based Only on Relative Range and Bearing

In this work, we address the problem of convergence and cohesiveness of an unmanned aerial vehicle (UAV) flocking. Thus, we propose a proximal control-based method for UAV self-organized flocking. Our method efficiently achieves flocking in the absence of alignment control and moves into an arbitrary direction without any direction control or informed robots. Robots use a Lennard-Jones potential function to maintain the cohesiveness of the flocking while avoiding collision within the teammates. We evaluate our approach using the order metric, the steady-state value, and the settling time that can be used as a cohesiveness indicator.

On the photon-pseudoscalar particle mixing in media and external fields

In this work, I study the mixing of photons with pseudoscalar particles and vice-versa in the presence of an external magnetic field and a pseudoscalar field. I solve exactly for the first time in the literature the equations of motion of the electromagnetic field coupled with a pseudoscalar field in the presence of a constant magnetic field with arbitrary direction with respect to the direction of propagation of the fields in vacuum. In addition, I also solve exactly the equations of motion in a magnetized plasma/gas for perpendicular propagation with respect to the external magnetic field. By finding exact solutions to the equations of motion, I find exact expressions for the transition efficiencies of photons into pseudoscalar particles in different situations. The expressions of the transition efficiencies generalize and correct those previously found in the literature by using approximate WKB methods on solving the equations of motion. In the case when the direction of propagation of fields with respect to the external magnetic field is not perpendicular, a longitudinal state of the electromagnetic field is generated even in a magnetized vacuum. The appearance of the longitudinal electric field state could be used for laboratory searches of pseudoscalar particles such as the axion and/or axion-like particles.

Minimal Deterministic Traversable Vertex Labelling of Infinite Square Grid Graph

Automata walking on graphs are a mathematical formalization of autonomous mobile agents with limited memory operating in discrete environments. Under this model a broad area of studies of the behaviour of automata in labyrinths arose and intensively developing last decades (a labyrinth is an embedded directed graph of special form). Research in this regard received a wide range of applications, for example, in the problems of image analysis and navigation of mobile robots. Automata operating in labyrinths can distinguish directions, that is, they have a compass. This paper deals with the problem of constructing square grid graph vertex labelling thanks to which a finite automaton without a compass can walk on graph in any arbitrary direction. The automaton looking over neighbourhood of the current vertex and may travel to some neighbouring vertex selected by its label. In this paper, we propose a minimal deterministic traversable vertex labelling that satisfies the required property. A labelling is said to be deterministic if all vertices in closed neighbourhood of every vertex have different labels. In previous works we have proved that minimal deterministic traversable vertex labelling of square grid graph uses labels of five different types. In this paper we prove that a collective of one automaton and three pebbles can construct this labelling on initially unlabelled infinite square grid graph. We consider pebbles as automata of the simplest form, whose positions are completely determined by the remaining automata of the collective.

Morphological improvement after multi-directional cranial distraction osteogenesis procedure for syndromic craniosynostosis

The multidirectional cranial distraction osteogenesis (MCDO) procedure, which uses an external distraction device, enables tailor-made distraction in an arbitrary direction, eliminating the disadvantage of unidirectional distraction with an internal distraction device. Multiple-suture synostosis cases for syndromic craniosynostosis patients are better indicated for this procedure. Here the authors describe seven cases in which the MCDO procedure was used to treat syndromic craniosynostosis. In each case, the MCDO procedure and postoperative distraction, with reference to midsagittal vector analysis of normal morphology in Japanese children, resulted in morphological improvement. The video can be found here: https://vimeo.com/519006555