Atmospheric Memory

In 1860, Édouard-Léon Scott de Martinville recorded the song “Au clair de la lune” on the phonautograph, making the first recording of human speech. Here the phrase is depicted as a sculpture to be viewed, rather than heard. Exhaled breath from words, phrases and sounds become moving clouds of vapor containing layers of complex folds and vortices. These structures are 3D scanned, formed into a solid, and later printed to immortalize the speech.

The video shows the motion of air coming from the mouth of someone saying the word “yes”. The flow is made visible through the Schlieren technique, which is based on the fact that rays of light are bent differently whenever they encounter changes in density of a fluid, between the warm air coming from the mouth and the cooler surrounding air.

Each frame of the video represents a section of the 3D scanned volume of the cloud generated by saying “Au clair de la lune” .

Collective motion

Schooling, flocking, and swarming are all powerful examples of collective motion. The classical Vicsek model allows for simulating several emergent features of collective motion, starting from simple interactions of active self-propelled particles. In this model, particles tend to align with their neighbors, against the effect of internal random noise. Here, we demonstrate a fluid-like behavior, consisting of a self-organized vortex motion superimposed to local fluctuations. This collective motion appears when a large number of particles interact under the effect of a moderate noise, below the phase transition.

Immutable Swell

A wave an oscillation or vibration of a physical medium or a field. The wave transfers energy but no (or little) mass. The waves on the surface of a fluid are called gravity waves because the restoring force is gravity. The ocean waves are driven by wind, and they last even after the wind has stopped. The restoring force of the smaller capillary waves, or ripples is instead the surface tension. These waves die quickly after the wind stops. Much bigger waves are the so called rogue waves, which are usually more than twice the size of surrounding waves.

Nimbus Atlas

Clouds are made by microscopic droplets of liquid water (warm clouds), crystals of ice (cold clouds), or both (mixed phase clouds). Clouds in the atmosphere originate from supersaturated air, created by the cooling of wet air, as cold air has a lower saturation point than warm air. The water vapor comes in contact with small particles and in a process of nucleation create the droplets of the cloud. These small particles, as small as 0.1 microns, can be dust, ice or seasalt.

There are still open questions regarding cloud formation and dissipation, and in general clouds are the source of most of the uncertainty in climate models. Other planets also have clouds. Mars has clouds of carbon dioxide and water ice crystals, Saturn’s moon Titan has clouds of methane and ethane, while Jupiter has clouds made of ammonia.

Quantum vortices

The word turbolenza was used for the first time to describe the chaotic motion of water by Leonardo Da Vinci. Since Leonardo, turbulence stands as the last unsolved problem of classical physics, even though the most illustrious mathematicians, engineers and physicists have tried to crack the problem. A better understanding of turbulence could have far reaching consequences in industries like aerospace, automotive, maritime and energy production. We study a special kind of turbulence called quantum turbulence.

When helium is cooled below about 2 degrees above absolute zero, it becomes a superfluid. A superfluid has zero viscosity, meaning that flows without friction. This unique characteristic arises because quantum effects become important on a macroscopic scale. The superfluid is populated by quantized vortices, centimeter-sized filamentary quantum tornados with atomic-sized cores. These vortices interact in a process called quantum turbulence. We study in particular a phenomenon called vortex reconnection, a situation in which two vortices intersect, exchange tails and rapidly retract. To visualize the vortices we sprinkle in solid hydrogen particles that get trapped on their cores and that we illuminate with a laser and image with a camera.

By studying the motion of these vortices, which appear alive, we hope to shed light on the foundations of quantum as well as classical turbulence. Understanding quantum turbulence is not only interesting from a basic standpoint but could provide insight into the behaviour of neutron stars, trapped atom systems and superconductors. Learning about reconnections could shed light on analogous phenomena in magnetic field lines, cosmic strings, polymers, liquid crystals and even filaments of DNA.