Gli oceani? Grandi, vasti, addirittura smisurati. Così sono descritti dai viaggiatori e dai poeti e chi è stato in una spiaggia oceanica quest'impressione la capisce bene. Eppure di acqua non ne hanno poi tanta, almeno in confronto ad APM +5255 08 279 un ben strano corpo celeste, un quasar, che sta a 12 miliardi di anni luce da noi. Praticamente ai confini dell'Universo visibile, dato che pensiamo che la sua età sia di 13,5 miliardi di anni. Bene già allora, agli albori dell'espansione, di acqua ce ne era da vendere, dato che questo quasar attorno ne ha una quantità pari a 140 trilioni di volte quella di tutti gli oceani terrestri. E un trilione equivale a un milione di miliardi.
Quindi lontanissima, antichissima e abbondantissima. È la scoperta del giorno, molto sicura dato che è stata fatta e confermata indipendentemente da due gruppi di ricerca americani, gli astronomi del Jet Propulsion Laboratory (Jpl) della Nasa e del California Institute of Technology (Caltech). Un quasar è uno degli oggetti celesti più strani ed enigmatici, presenti fin dalle prime epoche dell'Universo, composto da un enorme buco nero che assorbe costantemente, e potremmo dire voracemente, materia da un altrettanto enorme disco circostante di gas e polveri.
Man mano che il materiale gassoso e le polveri vengono "catturate" dal buco nero, il quasar emette enormi quantità di energia e per questo è ben visibile anche da distanze per noi inimmaginabili, come i 12 miliardi di anni luce in questione. Questo quasar poi è effettivamente di grandi dimensioni, dato che ospita un buco nero almeno 20 miliardi di volte più massiccio del nostro Sole e produce tanta energia, ad ogni secondo, quanto un migliaio di miliardi di stelle simile alla nostra. Tutto insomma in una scala difficile da immaginare, da "Universo violento" come si legge in qualche testo di fantascienza.
...
read more
Sunday 24 July 2011
Friday 1 July 2011
Water good idea
Biomimicry: An improved way to harvest drinking water from fog in remote areas takes its inspiration from an African beetle: this a good idea!
IN THE dry desert on the west coast of Namibia, where the annual average rainfall is a meagre 40mm, the Namib beetle (Stenocara gracilipes) has evolved a unique mechanism to drink. It collects moisture from the early morning fog that is produced when ocean breezes from the Atlantic collide with the hot desert air. Drawing inspiration from this fog-harvesting trick, Shreerang Chhatre, a graduate student at the Massachusetts Institute of Technology, and his colleagues, have developed a simple and inexpensive way to produce drinking water.
The Namibian mist rapidly dissipates once the sun rises, so the beetle has just a brief opportunity to collect water. The insect typically finds a ridge of sand and faces the breeze, tilting its lower body upwards with its specially adapted wings outstretched. The wings have bumps made of a hydrophilic substance that attracts minute water droplets. As they accumulate, the droplets grow larger until their weight causes them to run off into troughs in the beetle’s wings. These troughs are covered with a waxy water-repelling substance which has the effect of rolling the droplets down the beetle’s inclined body and into its mouth.
Fog harvesting is not a new idea. FogQuest, a Canadian charity, has been installing devices using a metallic mesh to catch water droplets in developing countries for more than a decade. But Mr Chhatre says he and his colleagues have increased the efficiency of water collection using a variety of surface coatings.
Water droplets in fog are very small, typically between 1 to 50 microns (one-millionth of a metre) across. Hydrophilic surfaces gather and hold droplets with electrostatic attraction, which prevents them being picked up and carried away in the wind. As more droplets are attracted, they spread out and eventually join together and run off the surface—as they do on a pane of glass. Hydrophobic coatings, like Teflon, are then needed to repel the water and stream it as quickly as possible to a reservoir so it does not evaporate.
Mr Chhatre, a chemist, studied the so-called “wettability” of various coatings and found mathematical formulae which could determine the ideal combination of coatings for the different sizes of fog particles found in any particular region. The surface texture of the coatings also turned out to be important.
The ideal locations for fog harvesting are mountainous and desert regions where fog is present but water sources are far away. Mr Chhatre is setting up a pilot project in South Africa and hopes to organise another in India. Using a coated aluminium mesh, he conservatively estimates that it is possible to collect about one litre of water daily from a mesh of one square metre. Under ideal conditions, he says, that could increase tenfold.
The Economist 2-6-2011
IN THE dry desert on the west coast of Namibia, where the annual average rainfall is a meagre 40mm, the Namib beetle (Stenocara gracilipes) has evolved a unique mechanism to drink. It collects moisture from the early morning fog that is produced when ocean breezes from the Atlantic collide with the hot desert air. Drawing inspiration from this fog-harvesting trick, Shreerang Chhatre, a graduate student at the Massachusetts Institute of Technology, and his colleagues, have developed a simple and inexpensive way to produce drinking water.
The Namibian mist rapidly dissipates once the sun rises, so the beetle has just a brief opportunity to collect water. The insect typically finds a ridge of sand and faces the breeze, tilting its lower body upwards with its specially adapted wings outstretched. The wings have bumps made of a hydrophilic substance that attracts minute water droplets. As they accumulate, the droplets grow larger until their weight causes them to run off into troughs in the beetle’s wings. These troughs are covered with a waxy water-repelling substance which has the effect of rolling the droplets down the beetle’s inclined body and into its mouth.
Fog harvesting is not a new idea. FogQuest, a Canadian charity, has been installing devices using a metallic mesh to catch water droplets in developing countries for more than a decade. But Mr Chhatre says he and his colleagues have increased the efficiency of water collection using a variety of surface coatings.
Water droplets in fog are very small, typically between 1 to 50 microns (one-millionth of a metre) across. Hydrophilic surfaces gather and hold droplets with electrostatic attraction, which prevents them being picked up and carried away in the wind. As more droplets are attracted, they spread out and eventually join together and run off the surface—as they do on a pane of glass. Hydrophobic coatings, like Teflon, are then needed to repel the water and stream it as quickly as possible to a reservoir so it does not evaporate.
Mr Chhatre, a chemist, studied the so-called “wettability” of various coatings and found mathematical formulae which could determine the ideal combination of coatings for the different sizes of fog particles found in any particular region. The surface texture of the coatings also turned out to be important.
The ideal locations for fog harvesting are mountainous and desert regions where fog is present but water sources are far away. Mr Chhatre is setting up a pilot project in South Africa and hopes to organise another in India. Using a coated aluminium mesh, he conservatively estimates that it is possible to collect about one litre of water daily from a mesh of one square metre. Under ideal conditions, he says, that could increase tenfold.
The Economist 2-6-2011
Subscribe to:
Posts (Atom)