Tardigrada Tardigrades, Oursons d'eau Longs de 0,1 à un peu plus de 1 mm, les tardigrades sont des animaux extrêmophiles, c'est-à-dire qu'ils peuvent survivre dans des environnements extrêmement hostiles. (températures de −272 à +150 °C et pressions jusqu'à 6 000 bar[6], milieu anhydrique ou exposé aux rayonnements ultraviolets ou X, vide spatial[7]). Privés d'eau et de nourriture, ils se replient en cryptobiose, ce qui signifie que les processus métaboliques observables sont considérablement réduits : le tardigrade est alors en état de stase jusqu'à réactivation de ses processus métaboliques (sortie de stase). La stase peut durer une trentaine d’années[8]. Description[modifier | modifier le code] Un tardigrade vu au microscope. Tous les tardigrades adultes de la même espèce ont le même nombre de cellules (Eutélie). Physiologie[modifier | modifier le code] La lenteur des déplacements des tardigrades est due à l'absence de muscles transverses (ils n'ont que des muscles longitudinaux lisses)[4].
Le dilemme du prisonnier a enfin été testé... sur des prisonniers Les humains sont-ils moins égoïstes, calculateurs et méfiants que ne le supposent certaines théories économiques lorsqu’ils agissent en société? Les chercheurs Menusch Khadjavi et Andreas Lange du département d’économie de l’université de Hambourg ont testé, sans doute pour la première fois, le célèbre dilemme du prisonnier sur des prisonnières d’un pénitencier de Basse-Saxe ainsi que sur des étudiants, relate Business Insider. Leurs résultats complets seront publiés en août dans la revue Journal of Economic Behavior & Organization. Et ces résultats sont surprenants. publicité Le dilemme du prisonnier, le plus célèbre de la théorie des jeux, démontre normalement que face à une incertitude concernant le choix d’un autre individu, le premier a intérêt à le trahir. Dans le cas fictif du dilemme du prisonnier, les participants risquent jusqu'à 10 ans de prison. À lire aussi sur Slate.fr
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Quorum sensing Quorum sensing is a system of stimulus and response correlated to population density. Many species of bacteria use quorum sensing to coordinate gene expression according to the density of their local population. In similar fashion, some social insects use quorum sensing to determine where to nest. In addition to its function in biological systems, quorum sensing has several useful applications for computing and robotics. Quorum sensing can function as a decision-making process in any decentralized system, as long as individual components have: (a) a means of assessing the number of other components they interact with and (b) a standard response once a threshold number of components is detected. Bacteria[edit] Some of the best-known examples of quorum sensing come from studies of bacteria. Mechanism[edit] Model of quorum sensing. Examples[edit] Aliivibrio fischeri[edit] Escherichia coli[edit] Salmonella enterica[edit] Salmonella encodes a LuxR homolog, SdiA, but does not encode an AHL synthase.
Quantum Levitation Syndrome from Pixar's The Incredibles levitates things on zero-point energy. We study methods [1,2] for the manipulation of the force of the quantum vacuum known as the Casimir force. It is possible to turn the Casimir force from attraction to repulsion and to use it for levitating mirrors on, literally, nothing. This research may be interesting for applications in nanotechnology, because the Casimir force is the ultimate source of friction for micro- and nano-machines. In the following we explain the science behind Quantum Levitation [1]. Gecko feet [3]. A gecko can hang on a glass surface using only one toe. Field lines of the van der Waals force between two atoms or molecules. What is the van der Waals force? The physics behind the van der Waals force: neutral atoms or molecules electrically polarize each other. However, the dipole of one molecule does only form in the presence of another particle. Imagine that you replace the molecules by larger bodies, say glass or metal plates. U.
Scientists use iPods, car batteries to build a frog surveillance net Put this on your playlist: scientists at the University of Puerto Rico have developed a system to monitor wildlife in tropical rainforests, using captured audio in real time to remotely record the sounds made by animals. Using hardware that includes iPods, solar panels, and car batteries, the scientists created a network of radio-connected listening posts around the world that allows them to collect data 24 hours a day over long periods of time. The sound will help them track the effects of environmental changes—such as deforestation and climate change—on endangered species. The system, called Arbimon (Automated Remote Biodiversity Monitoring Network), was created by a team led by Dr. Mitchel Aide and Dr. Carlos Corrada-Bravo of the University of Puerto Rico. The collected audio is then transmitted over a 900MHz radio signal back to a collection base station—which can be up to 24 miles away—and is uploaded over the Internet to the team's server in Puerto Rico.
Loi de Zipf On nomme Loi de Zipf une observation empirique de la fréquence des mots dans un texte. Elle a pris le nom de son auteur, George Kingsley Zipf (1902-1950). Cette loi a été par la suite généralisée par Benoit Mandelbrot. Genèse Zipf avait entrepris d'analyser une œuvre monumentale de James Joyce, Ulysse, d'en compter les mots distincts, et de les présenter par ordre de nombre (La notion de nombre en linguistique est traitée à l’article « Nombre grammatical ».) décroissants d'occurrences. le mot le plus courant revenait 8 000 fois ; le dixième mot 800 fois ; le centième, 80 fois ; et le millième, 8 fois. Ces résultats semblent, à la lumière (La lumière est l'ensemble des ondes électromagnétiques visibles par l'œil humain, c'est-à-dire comprises dans des longueurs d'onde de 380nm (violet)...) d'autres études que l'on peut faire en quelques minutes ( Forme première d'un document : Droit : une minute est l'original d'un acte. où s est juste légèrement plus grand que 1. La synthèse de Mandelbrot
Smart People Choke Under Pressure People perceived as the most likely to succeed might also be the most likely to crumble under pressure. A new study finds that individuals with high working-memory capacity, which normally allows them to excel, crack under pressure and do worse on simple exams than when allowed to work with no constraints. Those with less capacity score low, too, but they tend not to be affected by pressure. "The pressure causes verbal worries, like 'Oh no, I can't screw up,'" said Sian Beilock, assistant professor of psychology at Miami University of Ohio. "When they begin to worry, then they're in trouble," Beilock told LiveScience. The findings are detailed this week's issue of Psychological Science. Working memory, also known as short-term memory, holds information that is relevant to performance and ensures task focus. The study analyzed 93 undergraduate students from Michigan State University to determine their working-memory capacities.
Finding the limits of speciation Despite their small size, organisms smaller than a thousandth of a meter (1 mm) contribute greatly to biodiversity and ecosystem function. Unfortunately, categorizing small organisms—even defining those categories—is difficult. Do small organisms form discrete species? Advances in DNA sequencing, combined with large surveys of small organisms, suggest that they may not. The process of defining a species is a historical practice. They start by asking a biological question: are there circumstances where species formation breaks down? Modeling species Studying the relationship of organisms to one another and their environment helps define something as a “species.” DNA sequencing technology is advancing at such a dizzying pace that biologists increasingly rely on mathematical models to understand complex systems. Do species form at all scales? For both ecological and genetic versions of the model, the higher the mutation rate or population size, the less likely it was for a species to form.
Fungus and bacteria play game theory to make biofuels To ensure that biofuel production doesn't compete with material that could otherwise provide food, researchers have been trying to produce biofuels from cellulose, the tough polymer that gives wood its strength. Unfortunately, cellulose isn't easy to digest, and the organisms that can digest it are bad at using it to produce something we could burn in an engine. To get around this, many researchers have attempted to create a single microbe that can do both—digest the cellulose and directly convert it to a usable fuel. So far, however, efforts to engineer all the pathways to digest haven't worked out as well as we might hope, so a team of researchers has decided to use a pair of organisms instead. And, by testing a variety of conditions, they found that their behavior was predictable based on game theory. Cellulose is a polymer of the sugar glucose, which can readily be digested and used to power cellular processes.
Lonely lemurs listen to, understand other species’ warning calls While not the brightest of primates, one species of lemur has shown that it can still learn a trick or two, staying safe from predators by heeding the alarm calls of other creatures in the forest. Of all the species of lemur living on the island of Madagascar, only one, Lepilemur sahamalazensis, has been found to exhibit this trait. The solitary, nocturnal creatures were found to respond to the alarm calls of the blue-eyed black lemur and to those from several different species of bird. A team of researchers from Bristol University, Bristol Zoo, and Torino University in Italy studied the behaviour of the Lepilemur, called the Sahamalaza sportive lemur because of the way it leaps between trees. As a solitary creature, the Sahamalaza sportive lemur doesn’t have the benefit of relying on others from its group to warn it of predators. Watching the behavior of sportive lemurs suggested that they might be very aware of what goes on in the forest.