How archer fish achieve a powerful impact

Archer fish swimming

Our recent paper in PLOS ONE investigates the physics of the water jet used by archer fish to down their prey. 


Archer fish are known for their ability of shooting down aerial insects anchored to vegetation by hitting them from a distance with a precisely aimed jet of water. The analysis of high-speed video recordings reveals that the impact of the jet with preys is way more powerful than what bare muscular power would allow, thus apparently defying the laws of physics. The study demonstrates that archer fish make a subtle use of the laws of fluid dynamics to produce a liquid projectile that grows in size during its travel to the prey, leading eventually to a striking impact with the prey.

The archer fish represents a notable example of animal making use of a highly sophisticated external tool – in this case a hydrodynamic lever – to amplify muscular power, just like an archer would do with his bow. In retrospect the genus name Toxotes (Greek word for archer), originated by their ability of shooting darts of water, appears to be farsighted and well deserved.



SMART NANOFLUIDS FOR HEAT TRANSFER


waves in smart nanofluid

In the paper "Bistable heat transfer in a nanofluid", published in the issue of March 13, 2009 of Physical Review Letters, we have shown that nanofluids can act as smart materials that can be switched on and off to dissipate heat efficiently or poorly. Heating and cooling are of cardinal importance to attain optimal performances in any technological device. In the past, the attention of scientists and engineers has been mostly focused on the dissipation of great amounts of heat, the rationale behind that being  that a high dissipation prevents overheating and thus enhances the efficiency of a device: the old good “the more powerful-the better!”. In recent times, the lack of abundant sources of clean energy and the widespread dissemination of battery operated devices, such as cell-phones and laptops, have highlighted the need for a smart technological handling of energetic resources.

We have shown that a particular class of nanofluids can be used as a smart material working as a heat valve to control the flow of heat. The nanofluid can be easily configured either in a “low” state, where it conducts heat poorly, or in a “high” state, where the dissipation is more efficient.

 

For an introductory description of the physics of "smart nanofluids" see the articles written by scientific journalists linked in the press review section.


 PATTERN FORMATION AND FLUCTUATIONS IN NONEQUILIBRIUM SYSTEMS

Experimental investigation of the patterns originated in nonequilibrium fluids such as suspensions of nanoparticles (nanofluids) under the action of a thermal gradient. Depending on whether the nanofluid is heated from above and from below, the nanoparticles either organize into macroscopic convective patterns or give rise to giant concentration fluctuations.


CONVECTION IN NANOFLUIDS

The great interest of convection in suspension of nanoparticles is generated by the fact that, beyond its fundamental relevance, it represents a model system mimicking some of the features of the convective heat transfer inside the Earth mantle.

The patterns generated by convection in a nanofluid (a) are strikingly similar to those predicted by simulations of convection in the Earth mantle by D. Yuen and F. Dubuffet (b)


TOPOLOGY OF CONVECTIVE PATTERNS

 

 The analysis of the topological properties of the convective patterns in nanofluids unveils a structure based on a mutual Voronoi tesselation. Read paper in PRL 

DIFFUSIVE REMIXING IN MICROGRAVITY


  The investigation of giant fluctuations occurring during the diffusive remixing of two liquids (read paper in Nature) is of great applicative relevance for the processing of materials in the absence of gravity. For this reason in September 2007 we have investigated such fluctuations under microgravity conditions during the GRADFLEX experiment aboard the FOTON M3 spaceship of the European Space Agency 


ADVANCED OPTICAL TECHNIQUES FOR THE INVESTIGATION OF COMPLEX FLUIDS

Development of novel optical techniques for the investigation of complex fluids. These techniques include small angle static and dynamic light scattering, quantitative shadowgraphy, Near Field Scattering, wavelet transform spectrum analyzer.


OPTICAL GENERATION OF VORONOI DIAGRAMS 
The determination of Voronoi diagrams is of great 

relevance in many fields as different as archaeology, physics, crystallography, linguistics, geology, ecology, marketing and finance. Examples of Voronoi diagrams include basins of predation in ecosystems, the texture of giraffe hide, grain boundaries in materials, and urban districts
 We have shown experimentally that  
the Voronoi diagram associated wit h a set of points on a plane can be generated optically from the in terference of the diffraction patterns generated by a set of circular apertures. This opens new perspectives in the parlallel optical processing of Voronoi Diagrams. Read paper in Optics Express








  QUANTITATIVE SHADOWHGRAPH

Shadowgraph is a very sensitive optical technique that can be used to image faint perturbations of the index of refraction, such as the hot air rising from the flame of a candle

 

We have developed a sophisticated diagnostics based on the processing of shadowgraph images. The diagnostics allows to perform static and dynamic light scattering experiments at ultra-small angles and has been used for the development of the GRADFLEX facility of the European Space Agency.


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Alberto Vailati,
19 nov 2012, 02:59
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