Maze solvers demystified and some other thoughts

There is a growing interest towards implementation of maze solving in spatially-extended physical, chemical and living systems. Several reports of prototypes attracted great publicity, e.g. maze solving with slime mould and epithelial cells, maze navigating droplets. We show that most prototypes utilise one of two phenomena: a shortest path in a maze is a path of the least resistance for fluid and current flow, and a shortest path is a path of the steepest gradient of chemoattractants. We discuss that substrates with so-called maze-solving capabilities simply trace flow currents or chemical diffusion gradients. We illustrate our thoughts with a model of flow and experiments with slime mould. The chapter ends with a discussion of experiments on maze solving with plant roots and leeches which show limitations of the chemical diffusion maze-solving approach.Comment: This is a preliminary version of the chapter to be published in Adamatzky A. (Ed.) Shortest path solvers. From software to wetware. Springer, 201

Propagation et atténuation du son dans la silice - étude par spectroscopie Brillouin et acoustique picoseconde

We study propagation and attenuation of sound waves in silica with two complementary experimental techniques, Brillouin light scattering and picosecond acoustics. Analysis of new accurate Brillouin data obtained in a large temperature range (4-1300 K), supplemented with literature data on a broad frequency range, shows that internal friction results from two main mechanisms: the interaction of sound with relaxing defects and with modes of the thermal bath (anharmonicity). Brillouin spectroscopy at high pressure (0-6 GPa) reveals the existence of a structural modification around 2~GPa in silica at room temperature. High frequency sound is observed for the first time around 250~GHz in silica with a new picosecond acoustic technique. These data demonstrates that the sound attenuation is still dominated by the anharmonicity at these mesoscopic wavelengths. The relation with a strong scattering regime of the attenuation at THz frequencies is discussed.Nous étudions la propagation et l'atténuation du son dans la silice avec deux techniques expérimentales complémentaires, la diffusion Brillouin de la lumière et l'acoustique picoseconde. L'analyse de nouvelles données Brillouin précises obtenues dans une large gamme de températures (4-1300 K), complétées avec les données de la littérature sur un large intervalle de fréquences, montre que le frottement interne résulte de deux principaux mécanismes : l'interaction du son avec les défauts relaxants et avec les modes du bain thermique (anharmonicité). La spectroscopie Brillouin à haute pression (0-6 GPa) révèle l'existence d'une modification structurale à environ 2 GPa à température ambiante. L'atténuation du son est observée pour la première fois autour de 250 GHz avec une nouvelle technique acoustique picoseconde. Ce résultat démontre que l'atténuation du son est encore dominée par l'anharmonicité à l'échelle des longueurs d'onde mésoscopiques. La relation avec un régime de forte atténuation au THz est discutée

The Transportation of the Djehutihotep Statue Revisited

The transportation of a colossus painted in the ancient Egyptian tomb of Djehutihotep (Dayr al-Barsha) is known as an example of lubrication application. However the benefits and the nature of lubrication used by ancient Egyptians are controversial. In order to clarify this issue, the physical parameters involved in the transportation are carefully reviewed. The traction force is a key parameter, and is evaluated by simple physical models and the results of biomechanical and ergonomic studies. The results of this work suggest high traction force can be produced only with an excellent team coordination, and the friction coefficient between sledge and ground is efficiently reduced by hypothetical methods which exclude probably wood-on-wood or wood-on-sand surface contacts

Propagation et atténuation du son dans la silice (étude par Spectroscopie Brillouin et acoustique picoseconde)

Nous étudions la propagation et l'atténuation des phonons acoustiques dans la silice avec deux techniques, la diffusion Brillouin de la lumière et une technique acoustique picoseconde. L'étude Brillouin en fonction de la température (4 K-1300 K) combinée à une analyse des données de la littérature sur une large gamme de fréquence, montre que la friction interne (à 35 GHz) résulte de deux mécanismes principaux : l'interaction du son avec d'une part des défauts relaxants activés thermiquement et avec d'autre part les modes du bain thermique (anharmonicité). Une estimation quantitative du poids de chacun d'eux est proposée. Notre étude permet d'expliquer de manière quantitative le minimum observé à 50 K dans la vitesse et de déduire la vitesse non-relaxée. L'augmentation de cette dernière avec la température traduit le durcissement structural anormal de la silice. Une étude Brillouin en fonction de la pression (0-6 GPa) en cellule à enclumes de diamant révèle l'existence d'un pic d'atténuation intense en coïncidence avec le minimum observé dans la vitesse à 2 GPa. Nous montrons que ce dernier résulte principalement d'une modification structurale tandis que le pic d'atténuation semble associé aux relaxations activées thermiquement. Enfin, nous mesurons l'atténuation hypersonique à 250 GHz dans la silice pour la première fois avec une nouvelle technique acoustique utilisant des impulsions laser picoseconde. Nous montrons que dans cette gamme de fréquence le frottement interne est uniquement dû à l'anharmonicité. Cette technique ouvre la perspective de pouvoir observer pour la première fois le régime de forte atténuation des ondes acoustiques attendu dans la gamme sub-THzWe study propagation and attenuation of the acoustics phonons in silica with two technics, the Brillouin spectroscopy of light and an acoustical picosecond technology. The Brillouin study in function of the temperature (4 K-1300 K) combined with an analysis of the data of literature on a broad range of frequency, show internal friction (at 35 GHz) results from two main mechanisms: the interaction of sound with relaxing defects thermally activated and on with modes of the thermal bath (anharmonicity). A quantitative estimation of the weight of each of them is offered. Our study allows to explain in a quantitative way the minimum noticed at 50 K in the velocity and to deduct the non-relaxed velocity. The increase of this last with the temperature reveals abnormal structural hardening of silica. A Brillouin study in function of pressure (0-6 GPa) in diamond anvils cell reveals the existence of an intense attenuation peak in coincidence with the minimum noticed in the velocity in 2 GPa. We show that this last results in most cases from a structural modification while the peak of attenuation seems linked to thermally activated relaxations. Finally, we measure hypersonic attenuation in 250 GHz in silica for the first time with a new acoustic technology using picoseconds impulsions laser. We show that in this range of frequency internal friction is only owed to the anharmonicity. This technology opens perspective to observe for the first time the regime of strong attenuation of the acoustical waves expected in the range Sub-THzMONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Subterahertz hypersound attenuation in silica glass studied via picosecond acoustics

International audienceWe report picosecond acoustic measurements in silica-glass films grown by wet thermal oxidation on a (111) silicon substrate. The longitudinal acoustic phonons are observed over the range from 150 to 300 GHz using an infrared pump and a second harmonic blue probe. The transducer is an aluminum thin film deposited on top. Multiple interference effects are analyzed and fully taken into account. They lead to a signal presenting rapid oscillations as a function of the sample thicknesses. The latter are determined by separate interferometry. Our remarkably precise acoustic attenuation results are found to follow rather well a model combining thermally activated relaxations and anharmonicity. New values for the optical absorption of silicon in the 400-to-500-nm region of the spectrum are obtained as a by-product

Stability of lauric acid at high pressure studied by Raman spectroscopy and picosecond acoustics

International audienceLauric acid is commonly used as a coating agent which efficiently protects against oxidation and/or coalescence a set of inorganic nanocrystals obtained by chemical process. Its stability under pressure is likely to be informative on the stability and ordering of compressed supercrystals of nanocrystals. Therefore the elastic behaviour of lauric acid submitted to high pressures up to 25 GPa is studied. This elastic behavior has been probed by two complementary in situ techniques at high pressure : Raman spectroscopy and picosecond acoustics. Comparison between pressure-induced transformations as observed with the two techniques suggests that lauric acid remains elastically stable above 2 GPa up to 25 GPa

Sound velocity and equation of state of liquid Cesium at high pressure and high temperature

International audienceLiquid cesium (l-Cs) sound velocity at high densities was investigated along a 500 K isotherm using high-pressure picosecond acoustics measurements. At 2.0 GPa, the liquid sound velocity goes through a maximum versus pressure without any change on the reflectivity and interferometry acoustic signals. Upon further compression, a softening of the l-Cs visco-elastic properties is observed from 2.0 up to 4.0 GPa, pressure at which the reflectometric signal is abruptly reversed whereas the interferometric signal remains qualitatively the same. This anomalous behaviour could be related to an electronic transformation within the l-Cs state, which here again could reflect what happens at lower temperature within the solid state. If so, such liquid-liquid transition may be driven by the progressive collapse of the 6s electronic orbital onto the 5d ones. Above 4.0 GPa, the l-Cs sound velocity starts again to increase as commonly expected upon compression

High pressure transformations in liquid rubidium

International audienceAn electronic-driven liquid-liquid phase transition in rubidium is revealed by picosecond acoustic measurements combined with ab initio calculations. Picosecond acoustics were used to measure the melting line up to 10 GPa, finding the maximum in the melting curve at 7 GPa and 555 K. We observe the onset of a continuous liquid-liquid phase transition beginning around the melting maxima through until 16 GPa. Sound velocity shows a softening similar to that reported for liquid caesium, caused by a change in the bulk modulus during a crossover from the low-density to the high-density liquid. Guided by the ab initio calculations, we relate the changes in the thermo-elastic properties to the progressive localization of the valence electrons in the pressure range of 6-16 GPa. At high pressure rubidium forms an electride liquid quantified by the appearance of interstitial quasi atoms (ISQs) localised in the valence electron density

High-pressure transformations in liquid rubidium

International audienceAn electronic-driven liquid-liquid phase transition in rubidium is revealed by picosecond acoustic measurements combined with ab initio calculations. Picosecond acoustics were used to measure the melting line up to 10 GPa, finding the maximum in the melting curve at 7 GPa and 555 K. We observe the onset of a continuous liquid-liquid phase transition beginning around the melting maxima through until 16 GPa. Sound velocity shows a softening similar to that reported for liquid caesium, caused by a change in the bulk modulus during a crossover from the low-density to the high-density liquid. Guided by the ab initio calculations, we relate the changes in the thermoelastic properties to the progressive localization of the valence electrons in the pressure range of 6-16 GPa. At high pressure rubidium forms an electride liquid quantified by the appearance of interstitial quasiatoms localized in the valence electron density