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La struttura degli origami

Geek   31.10.17  

Lo studio delle pieghe degli origami immaginati come atomi in un reticolo sta aiutando i ricercatori a scoprire i comportamenti complessi e strani nascosti in strutture semplici.

In 1970, an astrophysicist named Koryo Miura conceived what would become one of the most well-known and well-studied folds in origami: the Miura-ori. The pattern of creases forms a tessellation of parallelograms, and the whole structure collapses and unfolds in a single motion — providing an elegant way to fold a map. It also proved an efficient way to pack a solar panel for a spacecraft, an idea Miura proposed in 1985 and then launched into reality on Japan's Space Flyer Unit satellite in 1995.

Back on Earth, the Miura-ori has continued to find more uses. The fold imbues a floppy sheet with form and stiffness, making it a promising metamaterial — a material whose properties depend not on its composition but on its structure. The Miura-ori is also unique in having what's called a negative Poisson's ratio. When you push on its sides, the top and bottom will contract. But that's not the case for most objects. Try squeezing a banana, for example, and a mess will squirt out from its ends.

Researchers have explored how to use Miura-ori to build tubes, curves and other structures, which they say could have applications in robotics, aerospace and architecture. Even fashion designers have been inspired to incorporate Miura-ori into dresses and scarves.

Now Michael Assis, a physicist at the University of Newcastle in Australia, is taking a seemingly unusual approach to understanding Miura-ori and related folds: by viewing them through the lens of statistical mechanics.

Assis' new analysis, which is under review at Physical Review E, is the first to use statistical mechanics to describe a true origami pattern. The work is also the first to model origami using a pencil-and-paper approach that produces exact solutions — calculations that don’t rely on approximations or numerical computation.


Sorvolare l'Italia in meno di 3 minuti

Geek   28.10.17  

L'Italia vista dallo spazio, ripresa dall'astronauta dell'ESA Paolo Nespoli durante la sua permanenza sulla ISS, nell'ambito della missione VITA dell'Agenzia Spaziale Italiana.

Da Vipiteno a Siracusa in meno di tre minuti.


La tesi di Stephen Hawking

Geek   23.10.17  

La tesi di dottorato di Stephen Hawking sulle implicazioni dell'espansione dell'universo, discussa a Cambridge nel 1966, è gratuitamente scaricabile dal sito dell'università.

By making my PhD thesis Open Access, I hope to inspire people around the world to look up at the stars and not down at their feet; to wonder about our place in the universe and to try and make sense of the cosmos.
Anyone, anywhere in the world should have free, unhindered access to not just my research, but to the research of every great and enquiring mind across the spectrum of human understanding.

Each generation stands on the shoulders of those who have gone before them, just as I did as a young PhD student in Cambridge, inspired by the work of Isaac Newton, James Clerk Maxwell and Albert Einstein. It's wonderful to hear how many people have already shown an interest in downloading my thesis - hopefully they won't be disappointed now that they finally have access to it!


Dot Piano

Geek   19.10.17  

Dot Piano è un simulatore web di un pianoforte che funziona una normale tastiera di computer o con quella diuna periferica MIDI.
La musica danza sullo schermo grazie a punti colorati che registrano la pressione dei tasti e le note.
Dot Piano è musica per gli occhi.


Esplorare il sistema Solare su Google Maps

Geek   16.10.17  
Esplorare il sistema Solare su Google Maps
Esplorare il sistema Solare su Google Maps

Ora Google Maps permette di visitare virtualmente 16 tra pianeti, pianeti nani e lune del sistema Solare, oltre alla Stazione Spaziale Internazionale presente su Google Street View, grazie anche alle immagini raccolte dalla sonda Cassini.

Twenty years ago, the spacecraft Cassini launched from Cape Canaveral on a journey to uncover the secrets of Saturn and its many moons. During its mission, Cassini recorded and sent nearly half a million pictures back to Earth, allowing scientists to reconstruct these distant worlds in unprecedented detail. Now you can visit these places—along with many other planets and moons—in Google Maps right from your computer. For extra fun, try zooming out from the Earth until you're in space!


Storia del calcestruzzo

Geek   14.10.17  

È difficile precisare quali siano le origini della tecnica di costruire in conglomerato.
Secondo gli storici già Assiri e Egizi erano in grado di realizzare costruzioni impiegando materiale minuto. I Greci conoscevano questa tecnica, utilizzata per la realizzazione dell'acquedotto di Argo e del serbatoio di Sparta tra le più importanti opere costruite ancora esistenti.

Fu però l'ingegno dei Romani a dare l'impulso decisivo all'uso del calcestruzzo per l'edilizia civile e nella costruzioni di strade.
Le tecniche dell'opus incertum, dell'opus reticulatum e dell'opus caementicium sono descritte da Vitruvio nel suo De Architectura.
L'opus caementicium consisteva nell'elevare muri deponendo strati sovrapposti di malta e materiali inerti. I paramenti esterni in mattoni o pietre squadrate, che fungevano da casseri permanenti, venivano rapidamente riempiti di malta, all'interno della quale erano conficcati rottami di pietra o mattone.

La storia del calcestruzzo ripercorsa da Popular Mechanics.


Cosa c'è dentro un iPhone

Geek   13.10.17  
I componenti interni dell'iPhone
I componenti interni dell'iPhone

La storia dell'evoluzione dell'iPhone vista da dentro.
Tutti i componenti di tutti i modelli di iPhone analizzati in un'infografica realizzata da Bloomberg in collaborazione con iFixit.


Scoperta la metà della massa mancante dell'universo

Geek   11.10.17  
La struttura delle galassie e della materia barionica nell'universo
La struttura delle galassie e della materia barionica nell'universo

Non si tratta di materia oscura, ma di materia barionica individuata in filamenti di gas caldo e diffuso che collega le galassie le une alle altre.

"The missing baryon problem is solved," says Hideki Tanimura at the Institute of Space Astrophysics in Orsay, France, leader of one of the groups. The other team was led by Anna de Graaff at the University of Edinburgh, UK.

Because the gas is so tenuous and not quite hot enough for X-ray telescopes to pick up, nobody had been able to see it before.

"There's no sweet spot – no sweet instrument that we've invented yet that can directly observe this gas," says Richard Ellis at University College London. "It's been purely speculation until now."

So the two groups had to find another way to definitively show that these threads of gas are really there.

Both teams took advantage of a phenomenon called the Sunyaev-Zel'dovich effect that occurs when light left over from the big bang passes through hot gas. As the light travels, some of it scatters off the electrons in the gas, leaving a dim patch in the cosmic microwave background – our snapshot of the remnants from the birth of the cosmos.


Singapore sotterranea

Geek   05.10.17  
Lo schema sotterraneo della città-stato di Singapore
Lo schema sotterraneo della città-stato di Singapore

Negli ultimi decenni la città-stato di Singapore nel tentativo di aumentare la sua scarsa superficie si è concentrata su imponenti progetti di bonifica e riempimenti, ma il suo sviluppo è stato anche sotterraneo.
Yp svela cosa si cela sotto il manto stradale della metropoli del sud-est asiatico.


Breve storia delle onde gravitazionali

Geek   03.10.17  

Il Washington Post ripercorre la storia, la teoria e la fisica delle onde gravitazionali, la cui scoperta è valsa il Premio Nobel per la fisica a Rainer Weiss, Kip Thorne e Barry Barish.

Gravity is invisible, as you may have noticed, and a little bit spooky, because it seems to reach across space to cause actions at a distance without any obvious underlying mechanism. What goes up must come down, but why that is so has never been obvious.

Physicists tell us there are four fundamental forces in the universe: Gravity, electromagnetism, the strong nuclear force and the weak nuclear force. Of these, gravity is the most anemic, and yet over cosmic expanses it has shaped the universe. In our solar system, it governs the planets and moons in their orbits. On Earth, it motivates the apple to fall from the tree. You can feel it in your bones.

Aristotle believed that an object fell to Earth because it sought its natural place. Heavier objects, Aristotle believed, fell faster; weight was an inherent property of the object.

In the late 16th and early 17th centuries, Galileo brought scientific experiments into the conversation, and he discovered that a heavy object and a light object actually fall at the same speed. [...]

Galileo also discovered that objects always fall with constant acceleration and along a parabolic curve. [...]

Then came Isaac Newton. In the second half of the 17th century, he developed a universal law of gravity. He calculated that the attraction between two bodies was equal to the product of their masses divided by the square of the distance between them. This is true on Earth as well as in space. It explains the tides. It explains the motions of the planets around the sun. This is a basic law of nature, true anywhere in the universe.

But even Newton admitted that he didn’t understand the fundamental nature of this force. Newton could describe gravity mathematically, but he didn’t know how it achieved its effects.

In the early 20th century, Albert Einstein finally came up with an explanation, and it's rather astonishing. First he grasped that gravity and acceleration are the same thing. His General Theory of Relativity, formulated in 1915, describes gravity as a consequence of the way mass curves "spacetime," the fabric of the universe. It's all geometry. Objects in motion will move through space and time on the path of least resistance. A planet will orbit a star not because it is connected to the star by some kind of invisible tether, but because the space is warped around the star.

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