A mathematical model for Tsunami generation using a conservative velocity-pressure hyperbolic system

By using the Hugoniot curve in detonics as a Riemann invariant of a velocity-pressure model, we get a conservative hyperbolic system similar to the Euler equations. The only differences are the larger value of the adiabatic constant (= 8.678 instead of 1.4 for gas dynamics) and the mass density replaced by a strain density depending on the pressure. The model is not homogeneous since it involves a gravity and a friction term. After the seismic wave reaches up the bottom of the ocean, one gets a pressure wave propagating toward the surface, which is made of a frontal shock wave followed by a regular decreasing profile. Since this regular profile propagates faster than the frontal shock waves, the amplitude of the pressure wave is strongly reduced when reaching the surface. Only in the case of a strong earth tremor the residual pressure wave is still sufficient to generate a water elevation with a sufficient wavelengths enable to propagate as a SaintVenant water wave and to become a tsunami when reaching the shore. We describe the construction of the model and the computation of the wave profile and discuss about the formation or not of a wave

Annular shear of cohesionless granular materials: from inertial to quasistatic regime

Using discrete simulations, we investigate the behavior of a model granular material within an annular shear cell. Specifically, two-dimensional assemblies of disks are placed between two circular walls, the inner one rotating with prescribed angular velocity, while the outer one may expand or shrink and maintains a constant radial pressure. Focusing on steady state flows, we delineate in parameter space the range of applicability of the recently introduced constitutive laws for sheared granular materials (based on the inertial number). We discuss the two origins of the stronger strain rates observed near the inner boundary, the vicinity of the wall and the heteregeneous stress field in a Couette cell. Above a certain velocity, an inertial region develops near the inner wall, to which the known constitutive laws apply, with suitable corrections due to wall slip, for small enough stress gradients. Away from the inner wall, slow, apparently unbounded creep takes place in the nominally solid material, although its density and shear to normal stress ratio are on the jammed side of the critical values. In addition to rheological characterizations, our simulations provide microscopic information on the contact network and velocity fluctuations that is potentially useful to assess theoretical approaches

Sound travellingwaves in wind instruments as solutions to non linear homogeneous gas dynamics equations

The sound propagation is usually described by a linear homogeneous wave equation, though the air flow in a duct is described by the gas dynamics equations, using a variable cross section, which corresponds to a non linear non homogneous system. The aim of this paper is to exhibit a common periodic solution to both models, with several free parameters such as frequency or amplitude, able to represent any sound. By taking in account a friction term linked to the material (wood or brass for instance) of the duct, it is possible to build an analytic such solution when the cross section fullfills some condition which corresponds exactly to the general shape of the wind instruments. The conclusion is that in the wind intruments, the shape brings the linearity

How to coexist with fire ants: The roles of behaviour and cuticular compounds

tBecause territoriality is energetically costly, territorial animals frequently respond less aggressively toneighbours than to strangers, a reaction known as the “dear enemy phenomenon” (DEP). The contrary,the “nasty neighbour effect” (NNE), occurs mainly for group-living species defending resource-basedterritories. We studied the relationships between supercolonies of the pest fire ant Solenopsis saevissimaand eight ant species able to live in the vicinity of its nests plus Eciton burchellii, an army ant predatorof other ants. The workers from all of the eight ant species behaved submissively when confrontedwith S. saevissima (dominant) individuals, whereas the contrary was never true. Yet, S. saevissima weresubmissive towards E. burchellii workers. Both DEP and NNE were observed for the eight ant species, withsubmissive behaviours less frequent in the case of DEP. To distinguish what is due to chemical cues fromwhat can be attributed to behaviour, we extracted cuticular compounds from all of the nine ant speciescompared and transferred them onto a number of S. saevissima workers that were then confronted withuntreated conspecifics. The cuticular compounds from three species, particularly E. burchellii, triggeredgreater aggressiveness by S. saevissima workers, while those from the other species did not

Arboreal ants use the "Velcro® principle" to capture very large prey

Plant-ants live in a mutualistic association with host plants known as "myrmecophytes" that provide them with a nesting place and sometimes with extra-floral nectar (EFN) and/or food bodies (FBs); the ants can also attend sap-sucking Hemiptera for their honeydew. In return, plant-ants, like most other arboreal ants, protect their host plants from defoliators. To satisfy their nitrogen requirements, however, some have optimized their ability to capture prey in the restricted environment represented by the crowns of trees by using elaborate hunting techniques. In this study, we investigated the predatory behavior of the ant Azteca andreae which is associated with the myrmecophyte Cecropia obtusa. We noted that up to 8350 ant workers per tree hide side-by-side beneath the leaf margins of their host plant with their mandibles open, waiting for insects to alight. The latter are immediately seized by their extremities, and then spread-eagled; nestmates are recruited to help stretch, carve up and transport prey. This group ambush hunting technique is particularly effective when the underside of the leaves is downy, as is the case for C. obtusa. In this case, the hook-shaped claws of the A. andreae workers and the velvet-like structure of the underside of the leaves combine to act like natural VelcroH that is reinforced by the group ambush strategy of the workers, allowing them to capture prey of up to 13,350 times the mean weight of a single worker

Perceived Head-Trunk Angle During Microgravity Produced by Parabolic Flight

International audienceIntroduction: Neck proprioceptors are essential for orienting the head relative to the trunk. However, it has been shown that the available information about the relationship of gravity to different body parts would augment the clues about their relative orientation. In weightlessness , the absence of relevant body position signals from the otoliths and other inertial graviceptors requires the substitution of other sensory information. The aim of the present study was to investigate the ability of humans to accurately locate the head relative to the trunk in microgravity.Methods: Experiments were conducted during two separate sessions: 1) on Earth and 2) during parabolic fl ights. Volunteers were asked to adjust a visual rod until it looked parallel to their head or trunk axis in two different segmental confi gurations: head and trunk aligned or head tilted. Results: There was no effect of microgravity when the head and trunk were aligned. However, when the head was tilted with respect to the trunk, the orientation of the visual rod relative to the head or the trunk (visual egocentric coordinates) was deviated toward the head tilt, although the orientation between the body parts themselves (head-trunk angle) was correctly estimated.Discussion: These results suggested that, in microgravity, the proprioceptive signals from neck muscles seem suf-fi cient to provide accurate head on trunk information. However, the representation of orientation in visual space was modifi ed. This experiment provides evidence for the role of gravity on the visual perception of head-and trunk-based egocentric coordinates

Feifei Li, Robert Sabella and David Liu eds., Nanking 1937: Memory and Healing

This small volume contains the papers presented at the international conference with the same title held on November 22nd 1997 at Princeton University. The participants at that conference took every care to be as scrupulous as possible in their approach to the major controversy that had been raging in China and Japan since the 1980s over the sacking of Nanking from December 13th 1937 to early March 1938, when it was still the capital of Nationalist China. This war crime, among several others,..

Lucien Bianco, Jacqueries et révolution dans la Chine du XXe siècle

Patiently, passionately, Lucien Bianco has successfully concluded a mission that looked impossible : to explore the immensity of the Chinese peasantry and to describe the behaviour, over the half-century preceding the conquest of power by the Chinese Communist Party (CCP), of those 400 million people who cultivated in the traditional way 100 million hectares and eked out a miserable existence from it. From his very first article (“Les paysans et la révolution : Chine 1919-1969”, followed by “..