Contents contributed and discussions participated by Jac Londe
Why is space three-dimensional? - 0 views
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(Phys.org)-The question of why space is three-dimensional (3D) and not some other number of dimensions has puzzled philosophers and scientists since ancient Greece. Space-time overall is four-dimensional, or (3 + 1)-dimensional, where time is the fourth dimension. It's well-known that the time dimension is related to the second law of thermodynamics: time has one direction (forward) because entropy (a measure of disorder) never decreases in a closed system such as the universe.
MERN - Statistiques énergétiques - 0 views
Kepller Star Burst Styrk - 0 views
Nobel-Prize Economist Condemns Obama's 'Trade' Deals Washington's Blog - 0 views
Sr2IrO4 - 0 views
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As it turns out, the new phase that the Hsieh group identified is precisely this type of multipolar order.
To detect multipolar order, Hsieh's group utilized an effect called
optical harmonic generation, which is exhibited by all solids but is
usually extremely weak. Typically, when you look at an object
illuminated by a single frequency of light, all of the light that you
see reflected from the object is at that frequency. When you shine a red
laser pointer at a wall, for example, your eye detects red light.
However, for all materials, there is a tiny amount of light bouncing off
at integer multiples of the incoming frequency. So with the red laser
pointer, there will also be some blue light bouncing off of the wall.
You just do not see it because it is such a small percentage of the
total light. These multiples are called optical harmonics.
The Hsieh group's experiment exploited the fact that changes in the
symmetry of a crystal will affect the strength of each harmonic
differently. Since the emergence of multipolar ordering changes the
symmetry of the crystal in a very specific way-a way that can be largely
invisible to conventional probes-their idea was that the optical
harmonic response of a crystal could serve as a fingerprint of
multipolar order.
"We found that light reflected at the second harmonic frequency
revealed a set of symmetries completely different from those of the
known crystal structure, whereas this effect was completely absent for
light reflected at the fundamental frequency," says Hsieh. "This is a
very clear fingerprint of a specific type of multipolar order."
The specific compound that the researchers studied was strontium-iridium oxide (Sr2IrO4),
a member of the class of synthetic compounds broadly known as iridates.
Over the past few years, there has been a lot of interest in Sr2IrO4
owing to certain features it shares with copper-oxide-based compounds,
or cuprates. Cuprates are the only family of materials known to exhibit
superconductivity at high temperatures-exceeding 100 Kelvin (-173
degrees Celsius). Structurally, iridates and cuprates are very similar.
And like the cuprates, iridates are electrically insulating
antiferromagnets that become increasingly metallic as electrons are
added to or removed from them through a process called chemical doping. A
high enough level of doping will transform cuprates into
high-temperature superconductors, and as cuprates evolve from being
insulators to superconductors, they first transition through a
mysterious phase known as the pseudogap, where an additional amount of
energy is required to strip electrons out of the material. For decades,
scientists have debated the origin of the pseudogap and its relationship
to superconductivity-whether it is a necessary precursor to
superconductivity or a competing phase with a distinct set of symmetry
properties. If that relationship were better understood, scientists
believe, it might be possible to develop materials that superconduct at
temperatures approaching room temperature.
Recently, a pseudogap phase also has been observed in Sr2IrO4-and
Hsieh's group has found that the multipolar order they have identified
exists over a doping and temperature window where the pseudogap is
present. The researchers are still investigating whether the two overlap
exactly, but Hsieh says the work suggests a connection between
multipolar order and pseudogap phenomena.
"There is also very recent work by other groups showing signatures of
superconductivity in Sr2IrO4 of the same variety as that found in
cuprates," he says. "Given the highly similar phenomenology of the
iridates and cuprates, perhaps iridates will help us resolve some of the
longstanding debates about the relationship between the pseudogap and
high-temperature superconductivity."
Hsieh says the finding emphasizes the importance of developing new
tools to try to uncover new phenomena. "This was really enabled by a
simultaneous technique advancement," he says.
Furthermore, he adds, these multipolar orders might exist in many more materials. "Sr2IrO4
is the first thing we looked at, so these orders could very well be
lurking in other materials as well, and that's exactly what we are
pursuing next."
Read more at: http://phys.org/news/2015-10-physicists-uncover-phase.html#jCp
2015 - Learning brain - 1 views
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Il existe une dichotomie très souvent utilisée pour caractériser les différences hémisphériques dans le traitement de l'information : l'hémisphère gauche serait plus efficace pour effectuer un traitement local et séquentiel de l'information tandis que l'hémisphère droit favorise un traitement holistique et parallèle. L'hémisphère droit serait aussi avantagé dans les traitements visuo-spatiaux et les émotions.
Google Alertes - 0 views
FeedEk jQuery RSS/ATOM Feed Plugin - 0 views
visoft/jquery-rss · GitHub - 0 views
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jquery-rss /
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sdepold authored 2 years ago lib use instances + readme 2 years ago src fixed indexOf bug in ie 2 years ago .gitignore ignore node_modules 2 years ago CHANGELOG.md fixed indexOf bug in ie 2 years ago MIT-LICENSE license 2 years ago README.md added index and totalEntries 2 years ago index.html minfied version 2 years ago package.json fixed indexOf bug in ie
Loi sur le droit d'auteur - 0 views
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Loi sur le droit d’auteur1 - TITRE ABRÉGÉ 2 - DÉFINITIONS ET DISPOSITIONS INTERPRÉTATIVES 3 - PARTIE I - DROIT D’AUTEUR ET DROITS MORAUX SUR LES OEUVRES
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PARTIE II - DROIT D’AUTEUR SUR LES PRESTATIONS, ENREGISTREMENTS SONORES ET SIGNAUX DE COMMUNICATION ET DROITS MORAUX SUR LES PRESTATIONS
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PARTIE III - VIOLATION DU DROIT D’AUTEUR ET DES DROITS MORAUX, ET CAS D’EXCEPTION
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Forbes list of billionaires - Wikipedia, the free encyclopedia - 0 views
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2013 1,426 $5.4 trillion 2012 1,226 $4.6 trillion 2011 1,210 $4.5 trillion 2010 1,011 $3.6 trillion 2009 793 $2.4 trillion 2008 1,125 $4.4 trillion 2007 946 $3.5 trillion 2006 793 $2.6 trillion 2005 691 $2.2 trillion 2004 587 $1.9 trillion 2003 476 $1.4 trillion 2002 497 $1.5 trillion 2001 538 $1.8 trillion 2000 470 $0.9 trillion$898 billion
Ce poisson en armure qui tient tête aux piranhas | Passeur de sciences - 0 views
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Ce poisson en armure qui tient tête aux piranhas
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l'arapaima porte un gilet pare-dents. La preuve vient d'en être faite dans une étude américaine publiée en janvier par la revue Advanced Engineering Materials. Le titre – "Bataille dans l'Amazone : arapaima contre piranha" – résume bien l'approche que les auteurs, chercheurs à l'université de Californie, ont suivie : confronter les armes des piranhas, leurs dents, à l'armure de l'arapaima, ses écailles. Les premières sont impressionnantes, comme on peut le voir sur la photo ci-dessus. Même si la musculature de la bouche du piranha n'est pas particulièrement puissante, le poisson compense avec des dents aussi aiguisées que des lames de rasoir.
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L'analyse a montré que cette zone de l'écaille est ondulée et que les bosses concentrent du calcium, ce qui explique la dureté de ce matériau bio-minéral. La partie cachée est, elle, plus mince et plus tendre. L'écaille est donc une superposition de deux épaisseurs, la première hautement minéralisée et la seconde faite de plusieurs couches de fibres de collagène. Ce matériau composite est donc à la fois très résistant en surface et flexible, une propriété indispensable à la nage du poisson. Les ondulations de la couche supérieure facilitent d'ailleurs cette flexibilité.
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We are living in a bacterial world, and it's impacting us more than previously thought - 0 views
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""The true number of bacterial species in the world is staggeringly huge, including bacteria now found circling the Earth in the most upper layers of our atmosphere and in the rocks deep below the sea floor," "
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""The true number of bacterial species in the world is staggeringly huge, including bacteria now found circling the Earth in the most upper layers of our atmosphere and in the rocks deep below the sea floor," "