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WITNESS a howling gale or an ocean storm, and it's hard to believe that humans could make a dent in the awesome natural forces that created them. Yet that is the provocative suggestion of one physicist who has done the sums.

He concludes that it is a mistake to assume that energy sources like wind and waves are truly renewable. Build enough wind farms to replace fossil fuels, he says, and we could seriously deplete the energy available in the atmosphere, with consequences as dire as severe climate change.

Axel Kleidon of the Max Planck Institute for Biogeochemistry in Jena, Germany, says that efforts to satisfy a large proportion of our energy needs from the wind and waves will sap a significant proportion of the usable energy available from the sun. In effect, he says, we will be depleting green energy sources. His logic rests on the laws of thermodynamics, which point inescapably to the fact that only a fraction of the solar energy reaching Earth can be exploited to generate energy we can use.


When energy from the sun reaches our atmosphere, some of it drives the winds and ocean currents, and evaporates water from the ground, raising it high into the air. Much of the rest is dissipated as heat, which we cannot harness.

At present, humans use only about 1 part in 10,000 of the total energy that comes to Earth from the sun. But this ratio is misleading, Kleidon says. Instead, we should be looking at how much useful energy - called "free" energy in the parlance of thermodynamics - is available from the global system, and our impact on that.

Humans currently use energy at the rate of 47 terawatts (TW) or trillions of watts, mostly by burning fossil fuels and harvesting farmed plants, Kleidon calculates in a paper to be published in Philosophical Transactions of the Royal Society. This corresponds to roughly 5 to 10 per cent of the free energy generated by the global system.

"It's hard to put a precise number on the fraction," he says, "but we certainly use more of the free energy than [is used by] all geological processes." In other words, we have a greater effect on Earth's energy balance than all the earthquakes, volcanoes and tectonic plate movements put together.

Radical as his thesis sounds, it is being taken seriously. "Kleidon is at the forefront of a new wave of research, and the potential prize is huge," says Peter Cox, who studies climate system dynamics at the University of Exeter, UK. "A theory of the thermodynamics of the Earth system could help us understand the constraints on humankind's sustainable use of resources." Indeed, Kleidon's calculations have profound implications for attempts to transform our energy supply.

Of the 47 TW of energy that we use, about 17 TW comes from burning fossil fuels. So to replace this, we would need to build enough sustainable energy installations to generate at least 17 TW. And because no technology can ever be perfectly efficient, some of the free energy harnessed by wind and wave generators will be lost as heat. So by setting up wind and wave farms, we convert part of the sun's useful energy into unusable heat.

"Large-scale exploitation of wind energy will inevitably leave an imprint in the atmosphere," says Kleidon. "Because we use so much free energy, and more every year, we'll deplete the reservoir of energy." He says this would probably show up first in wind farms themselves, where the gains expected from massive facilities just won't pan out as the energy of the Earth system is depleted.

Using a model of global circulation, Kleidon found that the amount of energy which we can expect to harness from the wind is reduced by a factor of 100 if you take into account the depletion of free energy by wind farms. It remains theoretically possible to extract up to 70 TW globally, but doing so would have serious consequences.

Although the winds will not die, sucking that much energy out of the atmosphere in Kleidon's model changed precipitation, turbulence and the amount of solar radiation reaching the Earth's surface. The magnitude of the changes was comparable to the changes to the climate caused by doubling atmospheric concentrations of carbon dioxide (Earth System Dynamics, DOI: 10.5194/esd-2-1-2011).

"This is an intriguing point of view and potentially very important," says meteorologist Maarten Ambaum of the University of Reading, UK. "Human consumption of energy is substantial when compared to free energy production in the Earth system. If we don't think in terms of free energy, we may be a bit misled by the potential for using natural energy resources."

This by no means spells the end for renewable energy, however. Photosynthesis also generates free energy, but without producing waste heat. Increasing the fraction of the Earth covered by light-harvesting vegetation - for example, through projects aimed at "greening the deserts" - would mean more free energy would get stored. Photovoltaic solar cells can also increase the amount of free energy gathered from incoming radiation, though there are still major obstacles to doing this sustainably (see "Is solar electricity the answer?").

In any event, says Kleidon, we are going to need to think about these fundamental principles much more clearly than we have in the past. "We have a hard time convincing engineers working on wind power that the ultimate limitation isn't how efficient an engine or wind farm is, but how much useful energy nature can generate." As Kleidon sees it, the idea that we can harvest unlimited amounts of renewable energy from our environment is as much of a fantasy as a perpetual motion machine.

Is solar electricity the answer?

A solar energy industry large enough to make a real impact will require cheap and efficient solar cells. Unfortunately, many of the most efficient of today's thin-film solar cells require rare elements such as indium and tellurium, whose global supplies could be depleted within decades.

For photovoltaic technology to be sustainable, it will have to be based on cheaper and more readily available materials such as zinc and copper, says Kasturi Chopra of the Indian Institute of Technology, New Delhi.

Researchers at IBM showed last year that they could produce solar cells from these elements along with tin, sulphur and the relatively rare element selenium. These "kesterite" cells already have an efficiency comparable with commercially competitive cells, and it may one day be possible to do without the selenium.

Even if solar cells like this are eventually built and put to work, they will still contribute to global warming. That is because they convert only a small fraction of the light that hits them, and absorb most of the rest, converting it to heat that spills into the environment. Sustainable solar energy may therefore require cells that reflect the light they cannot use.

Source: NewScientist

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Siete molto social? Vi piace condividere con gli amici via Facebook, Twitter e Buzz assortiti tutto ciò che state leggendo/guardando/ascoltando in Rete? La vostra privacy è rischio: lo sostiene una recente inchiesta pubblicata dal Wall Street Journal che mette in guardia dai pericoli dei social widget, cioè i pulsanti come "I like" o "Share" che permettono la condivisione dei contenuti.

social network

Pedinamenti digitali

Secondo quanto si legge nell’articolo, queste applicazioni permetterebbero a vari Facebook, Twitter e Google di tracciare i percorsi di navigazione degli utenti anche se non hanno cliccato o condiviso nulla in tempi recenti. In pratica i social network saprebbero tutto ciò che avete fatto in rete, che siti avete visitato, per quanto tempo e quando.
La questione è spinosa perché i social network, Facebook in particolare, hanno a disposizione molte informazioni sui loro iscritti: nome e cognome, amicizie, parentele, preferenze musicali ma anche politiche o religiose. E collegandole ai siti che avete visitato potrebbero scoprire molte altre cose: per esempio dove vi piace andare in vacanza, cosa vi piace mangiare, se soffrite di alitosi o se siete interessati a prodotti contro la sudorazione dei piedi.

Ti piace questo elemento?

Lo scenario è effettivamente agghiacciante. E, secondo l’autore dell’inchiesta, perché questo meccanismo si metta in moto è sufficiente che abbiate cliccato un "mi piace" o un "condividi" negli ultimi 30 giorni.
Non serve a niente chiudere il browser o spegnere il computer: per disinnescare i siti spioni occorre effettuare il log out da Facebook, Twitter o Google al termine di ogni sessione. Ma loro, i social network, come si difendono da queste pesanti accuse?

La parola alla difesa

Non negano, ma minimizzano: Facebook e Google sostengono di utilizzare i dati di navigazione raccolti tramite i widget solo per meglio calibrare le pubblicità che vengono mostrate agli utenti. Le aziende spiegano che tutti i dati vengono "anonimizzati", e non è possibile ricondurli a uno specifico utente. Facebook in particolare ha dichiarato al Wall Street Jorunal di cancellare tutte queste informazioni ogni 90 giorni.
Il problema della privacy è ancor più pressante per gli utenti degli smartphone, che temono di essere seguiti non solo online nei loro percorsi virtuali, ma anche nella realtà attraverso i GPS e i sistemi di geolocalizzazione dei loro dispositivi.


Ecco il colpevole

Il Wall Street Journal ha fatto analizzare da esperti informatici i social widget presenti nei 1000 siti più visitati del web ed è emerso che 331 di loro inviano dati a Facebook e 250 a Google. Ma dov’è il trucco? In un programmino di pochi kb di peso chiamato cookie che i social network inviano al browser dell’utente ogni volta che questo si collega, condivide o fa altre operazioni che prevedono un log-in.
Da quel momento in poi il cookie riconoscerà tutti i siti ai quali l’utente si collega e nei quali è presente il social widget, raccoglierà i dati e li invierà al social network.

Non è vero, ma ci credo

Facebook però rassicura: Bret Taylor, responsabile tecnico dell’azienda di Mark Zuckberg, spiega al Wall Street Journal che i cookie servono solo a mostrare ad un utente quali contenuti di quella pagina sono stati visitati o condivisi dai propri amici. "Non sono stati progettati per tracciare nessuno" afferma.
Eppure Facebook continua a piazzare i propri cookie sui PC di chiunque abbia visitato la sua homepage anche se non è membro della sua community. Taylor sostiene che è una misura di sicurezza finalizzata a evitare attacchi informatici.
Sarà, ma nel dubbio il  consiglio è quello di effettuare il log-out dai social network ogni volta che si è finito di utilizzarli.


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On July 6, 2010, Private Bradley Manning, a 22 year old intelligence analyst with the United States Army in Baghdad, was charged with disclosing this video (after allegedly speaking to an unfaithful journalist). The whistleblower behind the Pentagon Papers, Daniel Ellsberg, has called Mr. Manning a 'hero'. He is currently imprisoned in Kuwait. The Apache crew and those behind the cover up depicted in the video have yet to be charged. To assist Private Manning, please see

5th April 2010 10:44 EST WikiLeaks has released a classified US military video depicting the indiscriminate slaying of over a dozen people in the Iraqi suburb of New Baghdad -- including two Reuters news staff.

Reuters has been trying to obtain the video through the Freedom of Information Act, without success since the time of the attack. The video, shot from an Apache helicopter gun-sight, clearly shows the unprovoked slaying of a wounded Reuters employee and his rescuers. Two young children involved in the rescue were also seriously wounded.

Short version

Full version

WikiLeaks' Collateral Murder: U.S. Soldier Ethan McCord's Eyewitness Story

The military did not reveal how the Reuters staff were killed, and stated that they did not know how the children were injured.

After demands by Reuters, the incident was investigated and the U.S. military concluded that the actions of the soldiers were in accordance with the law of armed conflict and its own "Rules of Engagement".

Consequently, WikiLeaks has released the classified Rules of Engagement for 2006, 2007 and 2008, revealing these rules before, during, and after the killings.

WikiLeaks has released both the original 38 minutes video and a shorter version with an initial analysis. Subtitles have been added to both versions from the radio transmissions.

WikiLeaks obtained this video as well as supporting documents from a number of military whistleblowers. WikiLeaks goes to great lengths to verify the authenticity of the information it receives. We have analyzed the information about this incident from a variety of source material. We have spoken to witnesses and journalists directly involved in the incident.

WikiLeaks wants to ensure that all the leaked information it receives gets the attention it deserves. In this particular case, some of the people killed were journalists that were simply doing their jobs: putting their lives at risk in order to report on war. Iraq is a very dangerous place for journalists: from 2003- 2009, 139 journalists were killed while doing their work.


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The expectations people have about how others will behave play a large role in determining whether people cooperate with each other or not. And moreover that very first expectation, or impression, is hard to change. "This is particularly true when the impression is a negative one," says Michael Kurschilgen from the Max Planck Institute for Research on Collective Goods in Bonn, summarising the key findings of a study in which he and his colleagues Christoph Engel and Sebastian Kube examined the results of so-called public good games. One's own expectation thereby becomes a self-fulfilling prophecy: those who expect people to act selfishly, actually experience uncooperative behavior from others more often.

In previous studies, other researchers had successfully put participants in Bonn and London into a social dilemma with such games, which are very popular in experimental economics. Engel, Kube and Kurschilgen used them as a template for their study, which focuses on an aspect that ought to be of interest to social policymakers and town planners too. "We wanted to find out whether the 'broken windows' theory held true in the lab as well," explained Michael Kurschilgen.

According to this theory, minor details, like broken windows in abandoned buildings or rubbish on the streets, can give rise to desolate conditions like the utter neglect of a district. "Such signs of neglect give people the impression that social standards do not apply there," says Kurschilgen, explaining the idea behind the theory, which was the motivation behind New York mayor Rudy Giuliani's decision to embark on the zero-tolerance strategy he employed to clean up the city in the 1990s.

In their study, the three MPI scientists tested the theory in a scientific experiment. Using the kind of public good games that are often applied in the field of experimental economics, their aim was to find out the extent to which first impressions determine how people will behave, and the extent to which this can be influenced by selective information. The games are set up around the classic dilemma of self-interest and socially minded behaviour: each member of a group of four players is given the sum of 20 tokens They can either keep these for themselves or invest them in a community project. Each player receives 0.4 tokens in return for each tokens they invest in the community project. If all four group members invest their 20 tokens, each one of them receives 32 tokens, in other words 12 tokens more than if they all keep the money for themselves. But if only three of them invest their money in the community, the selfish fourth player gets 44 tokens.

So even the free rider profits from the other players' investment in the community fund. "The public good game thus creates a social dilemma," explains the economist. That's because it would be best for the community if everybody invested in the collective. However, on an individual level the free rider gets the best out of it. They ultimately receive the bonus without having made the investment.

Surprisingly, there are significant differences between Bonn and London in the willingness to invest in the common good. Londoners invested a mere 43 per cent, on average, in the common good. In Bonn, on the other hand, the figure was 82 per cent. "This is probably down to differing expectations of what constitutes normal behaviour," postulates Kurschilgen. Individuals who assume that the others will act selfishly too are hardly likely to commit altruistic deeds themselves. "From that point of view, Londoners have a more pessimistic view of man than do the participants in Bonn," he concludes in respect of the Brits' reticence. Consequently, whether a person decides to behave cooperatively or not depends strongly on how that person thinks the other players will behave.

In their series of experiments, Engel, Kube and Kurschilgen told their newly recruited players from Bonn the results of the London study. The players in the new round of games evidently reacted very negatively to the information that few of the players in the previous experiments in London had exhibited cooperative behaviour. Unlike the virtuous people of Bonn from the previous rounds, they showed far fewer pretensions of being good citizens: instead of investing more than 80 per cent in the common good, the participants in these experiments contributed just 51 per cent, on average. Therefore, the negative information was enough to revise the previously positive image held by the Bonn residents. This model did not really work the other way around – good examples did not make bad teammates into goody two-shoes.

"Our findings demonstrate that the core of the 'broken windows' theory does actually hold true. Faced with a social dilemma, people are guided to a very great extent by their original expectations of what other people will do, but they are also particularly sensitive to negative impressions," says Kurschilgen, summing up the observations.

Given this conclusion, it is clear to him that every cent spent on maintaining residential districts does more than just make the neighbourhood look prettier – it also represents a sound investment against crime.

More information: Engel C., et al. Can we manage first impressions in cooperation problems? An experimental study on “Broken (and Fixed) Windows," Preprints of the Max Planck Institute for Research on Collective Goods, 2011/05


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 In Bucuresti exista un razboi rece care, uneori, degenereaza in confruntari verbale, intre aparatorii si „opozantii” cainilor vagabonzi. Cei dintai pledeaza pentru vietile lor in conditii optime, ceilalti pentru eutanasierea lor. In unele tari europene, problema cainilor vagabonzi a fost de mult rezolvata. In schimb a aparut cea a animalelor care fac obiectul experimentelor medicale. Aparatorii acestora trec, uneori, cu nonsalanta bariera protestelor pasnice, organizand actiuni de o violenta extrema.

 In Franta a fost elaborata Carta nationala de sustinere a eticii experimentelor animale. Un text care atrage atentia asupra faptului ca animalul nu e o masina si nici un obiect de laborator ci o fiinta sensibila. Carta nu se refera insa si la folosirea cobailor. Un „detaliu” care nu-i va calma pe inflacaratii militanti antivivisectie care cer „abolirea” totala si definitiva a experimentelor pe animale.

Aparatorii cei mai extremisti ai drepturilor animalelor ameninta cu acte de violenta. Anglia, Tarile de Jos, Belgia si Spania au inregistrat deja anul trecut mai multe atacuri asupra unor laboratoare de cercetare. Si in Franta s-au petrecut lucruri similare. In ianuarie a.c. cativa militanti ai drepturilor animalelor s-au instalat in fata sediului unei companii farmaceutice din Paris proferand sloganuri virulente de genul: „Nazisti responsabili de genocid!” Renasterea si radicalizarea acestei miscari au fost initiate de activistii din cadrul SHAC veniti special din Anglia, Bulgaria si Tarile de Jos.

Primele lor actiuni in Hexagon au avut drept tinta birourile din Sanofi, GSK, Novartis etc. cu participarea simpatizantilor francezi. Miscarile radicale orientate spre actiuni directe sunt putine dar militantii lor sunt deosebit de duri. In aprilie 2007 ALF, o organizatie clandestina a revendicat incendiul care a distrus o parte din intreprinderea Techniplast din apropiere de Lyon, unde se produceau custi pentru animale destinate experimentelor medicale. In decembrie 2007, la domiciliul unui blanar din Bordeaux, cativa activisti au dat foc garajului sau in timp ce fiica sa handicapata dormea in camera sa aflata deasupra garajului. Din fericire, incendiul a fost stins la timp. Grupul de origine engleza ARM nu ezita sa ameninte viata umana pentru a o apara pe cea a animalelor...

One Voice, una din marile asociatii care se opun experimentelor pe animale, a obtinut semnaturile a 400 de deputati europeni pentru oprirea acestei practici asupra primatelor. O „victorie” care-i nelinisteste pe cercetatori. Daca acest lucru s-ar intampla, ar fi o catastrofa pentru cercetarea medicala. Mai ales in maladiile neurodegenerative unde s-au obtinut succese notabile.


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Secondo il chirurgo italiano uno dei fattori scatenanti la sclerosi multipla sarebbe un’anomalia a livello venoso (CCSVI), risolvibile tramite un intervento di angioplastica. Nel commento di Roger Chafe del Memorial University of Newfoundland si parla del Canada, uno dei paesi, insieme all'Italia, dove il dibattito è più acceso.E dove i pazienti premono di più sulla comunità scientifica perché accolga l'ipotesi Zamboni.

In Canada, infatti, la teoria del medico ferrarese ha avuto un’ampia diffusione mediatica, ma è rimasta fuori dai consessi scientifici. Né la Multiple Sclerosis Society of Canada (MSSC), né gli enti di ricerca indipendenti sparsi sul territorio, infatti, hanno dato inizio a trial clinici per verificare l’efficacia del trattamento chirurgico. E, ovviamente, non hanno dato il loro benestare a eseguire le angioplastiche sui malati. La posizione dei medici e delle società scientifiche canadesi è chiara: in assenza di evidenze certe, lo sviluppo di trial interventistici potrebbe essere troppo rischioso per i pazienti. Per ora, la MSSC si limita a finanziare studi osservazionali per verificare l’associazione tra le due patologie, proprio come sta facendo in Italia l’Aism-Fism.

C’è un risvolto della medaglia: alcuni pazienti hanno fatto le valigie e sono partiti diretti verso cliniche private estere per sottoporsi a interventi di angioplastica. Non senza rischi. Nel frattempo i sostenitori del metodo Zamboni hanno continuato a crescere, grazie soprattutto a Facebook e Youtube, usati per diffondere le testimonianze positive di chi si è già sottoposto alla cosiddetta “terapia della liberazione”. E dai social media continuano le richieste di accesso pubblico agli interventi di angioplastica o di trial clinici, “senza -  come sottolinea Nature  - che se ne conoscano necessariamente le potenziali limitazioni”. Secondo la rivista, il fenomeno dei social media pone due diversi quesiti. Il primo di comunicazione medico-paziente: ovvero, se il pubblico usa i social network per organizzarsi e diffondere informazioni, forse gli scienziati dovrebbero fare lo stesso, cercando di spiegare tutti gli aspetti di una problematica.

Il secondo è questo: può la mobilitazione sociale influenzare il funzionamento della ricerca? Normalmente infatti, i trial interventistici hanno luogo solo dopo studi osservazionali incoraggianti. C’è però la possibilità che la voce dei social network possa esercitare una forte pressione nei confronti delle istituzioni politiche e scientifiche per favorire l’inizio di trial clinici, prima ancora che sia raggiunto un consenso scientifico. Una posizione giustificabile in determinati casi, secondo Nature, quando viene adottata per esempio per evitare che i malati scelgano di farsi operare chissà dove, esponendosi a ulteriori rischi. Una situazione, questa, non lontana da quella che si è verificata in Italia, dove, come dichiarato dal professor Massimo Del Sette, per motivi di “salute pubblica” si è deciso di dare il via a un “studio scientifico rigoroso” di intervento, come BRAVE DREAMS in cui includere i pazienti.

Fonte: - Riferimenti: Nature, Volume: 472, 410–411, doi:10.1038/472410°

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Come in un effetto domino, l’impatto delle guerre e delle rivoluzioni nei paesi del Nord Africa si sta facendo sentire negli altri paesi. Come rispondono l’Europa e l’Italia? Stando ai messaggi dei politici e agli umori della gente sembra regnare un clima di paura e di chiusura. Più che la complessità della situazione geo-politica, a preoccupare è soprattutto la questione immigrazione. Quanti profughi dovranno ancora arrivare? Come possiamo tenerli lontani? Se bombardiamo la Libia, arriveranno in massa? L’allarme è però eccessivo. Con questo aggettivo lo ha definito Laurens Jolles, rappresentante per l’Italia dell’Alto Commissariato Onu per i rifugiati (Unhcr), nel corso di un incontro organizzato da Link2007 a Roma.

Detail-libia immigrazione

Secondo Jolles, lo stato di paura che regna sta facendo dimenticare gli impegni e i doveri di protezione che l’Italia e gli altri paesi hanno nei confronti di queste persone. Sulle coste di Lampedusa ne sono sbarcate 23 mila dalla Tunisia, e la maggior parte è stata trasferita in qualche altro paese europeo. Poi, a metà marzo, è cominciato il secondo flusso dalla Libia, di circa 8 mila persone, quasi tutti somali, eritrei, nigeriani. “Se si tiene conto che dalla Libia sono partite ben 700 mila persone, accolte per lo più in Tunisia, Egitto o in qualche altro paese africano, il numero di persone giunte in Italia è molto piccolo”, spiega Jolles. “Ciò non vuol dire che non dobbiamo essere preparati a un’ondata maggiore di profughi. Potrebbero essere 50mila, come dice il governo italiano, e la maggior parte richiederà asilo. Serve un piano di intervento per accoglierli e chiarezza sui fatti”.

Troppo spesso, infatti, si tende a includere sotto il cappello della clandestinità tutti i fenomeni migratori, senza considerare che molti fuggono dal proprio paese per motivi economici o perché perseguitati per ragioni politiche, religiose o etniche. Questi profughi, in base alle norme internazionali, hanno diritto di fare richiesta di asilo e di vedersi riconosciuto lo status di rifugiati. Il principio del “non respingimento” sancito dalla Convenzione di Ginevra del 1951 trova applicazione anche in acque internazionali e vincola l’Europa. “Per quanto riguarda la procedura di accesso all’asilo in Italia, il sistema sta funzionando abbastanza bene. Il tasso dei riconoscimenti è alto rispetto alla media europea”, continua Jolles, che teme però la possibilità di un ritorno a quelle politiche di respingimento in mare attuate fino a poco tempo fa. “Ciò che preoccupa è la mozione approvata in questi giorni dalla Lega e dal Pdl, che impegna il governo a insistere affinché l’Unione europea ‘renda immediatamente operativa un’azione di pattugliamento del Mediterraneo’ allo scopo di fare prevenzione migratoria”.

L’atteggiamento di chiusura e di paura non riguarda solo l’Italia. Da quando sono iniziati gli sbarchi, altri paesi europei hanno cercato di bloccare l’entrata dei migranti nel proprio territorio. “Esistono norme che limitano la libera circolazione dei rifugiati tra i paesi; il Trattato di Dublino impone che chi arriva in uno stato e vi chiede rifugio debba rimanere lì”, spiega ancora Jolles. “L’Italia ha il diritto di dare i permessi di soggiorno, ma è sbagliato presentarli come la garanzia di una libera circolazione tra paesi. Per affrontare in maniera collaborativa la questione dei rifugiati, servono regole e standard comuni di accoglienza e di trattamento”.

Il problema non è solo politico ma sociale. Gli stranieri rifugiati in Italia, a differenza di quanto avviene in altri paesi europei, spesso vivono nel degrado, non hanno accesso ai servizi sociali e sanitari, non lavorano e stentano a integrarsi a causa della mancanza di una rete di sostegno e di accoglienza. “Serve una politica migratoria realistica, con delle quote di ingresso legali, basate sui bisogni del paese che ospita”, ha aggiunto Laura Boldrini, portavoce dell’Unhcr. “Ogni anno entrano nel nostro paese tantissimi migranti in possesso di regolare visto di studio e lavoro, che poi diventano irregolari e clandestini perché manca un sistema di integrazione e di supporto”.


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Graphene is the material from which graphite, the core of your No. 2 pencil, is made. It is also the latest "wonder material," and may be the electronics industry’s next great hope for the creation of extremely fast electronic devices. Researchers at North Carolina State University have found one of the first roadblocks to utilizing graphene by proving that its conductivity decreases significantly when more than one layer is present.

Graphene’s structure is what makes it promising for electronics. Because of the way its carbon atoms are arranged, its electrons are very mobile. Mobile electrons mean that a material should have high conductivity. But NC State physicist Dr. Marco Buongiorno-Nardelli and NC State electrical and computer engineer Dr. Ki Wook Kim wanted to find a way to study the behavior of “real” graphene and see if this was actually the case.

“You can talk about the electronic structure of graphene, but you must consider that those electrons don’t exist alone in the material,” Buongiorno-Nardelli says. “There are impurities, and most importantly, there are vibrations present from the atoms in the material. The electrons encounter and interact with these vibrations, and that can affect the material’s conductivity.”

Buongiorno-Nardelli, Kim and graduate students Kostya Borysenko and Jeff Mullen developed a computer model that would predict the actual conductivity of graphene, both as a single layer and in a bilayer form, with two layers of graphene sitting on top of one another. It was important to study the bilayer model because actual electronic devices cannot work with only a single layer of the material present.

“You cannot make a semiconductor with just one graphite layer,” Buongiorno-Nardelli explains. “To make a device, the conductive material must have a means by which it can be turned off and on. And bilayer provides such ability.”

With the help of the high performance computers at Oak Ridge National Laboratories, the NC State team discovered both good and bad news about graphene. Their results appear as an Editor’s Suggestion in the April 15 edition of Physical Review B.

With a single layer of graphene, the mobility – and therefore conductivity – shown by the researchers’ simulations turned out to be much higher than they had originally thought. This good news was balanced, however, by the results from the bilayer state.

“We expected that the electrons’ conductivity in bilayer graphene could be somewhat worse, due to the ways in which the vibrations from the atoms in each individual layer interact with one another,” Mullen says. “Surprisingly, we found that the mobility of electrons in bilayer graphene is roughly an order of magnitude lower than in a single graphene sheet.”

“The reduction is substantial, but even this reduced number is higher than in many conventional semiconductors,” Borysenko adds.

Buongiorno-Nardelli says that the NC State researchers are turning their attention to remedying this problem.

“If we put the graphene on a substrate that can ‘siphon off’ some of the heat generated by the electric current, the crystal vibrations will decrease and the mobility will increase. Those are our next steps – running the simulations withgraphene and substrates that have this property.”

Source: PhysOrg

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By Admin (from 08/07/2011 @ 14:00:51, in ro - Stiinta si Societate, read 1706 times)

 Lucrand la bazele militare de la Peenemunde si Hillersleben, in cel mai deplin secret, oamenii de stiinta germani au realizat sau au fost pe punctul de a realiza multe „super-arme”, menite sa aduca victoria lui Hitler in cel de-al doilea razboi mondial. Dar sansa a fost de partea aliatilor care, beneficiari ai unei baze umane si materiale mult mai mari, si ai unor resurse superioare, au reusit sa invinga masina de razboi nazista. Cand Germania s-a predat, in mai 1945, savantii din aceste baze secrete au fost obligati sa abandoneze o serie intreaga de inovatii revolutionare, in diverse stadii de realizare.

Inventiile diabolice ale nazistilor

Printre armele la care nemtii lucrau se numara o baterie de artilerie care avea drept proiectile rachete inteligente, capabile sa atinga tinte situate la cativa kilometri departare, un mortier ce putea lansa o singura data o tona de proiectile autopropulsate, care faceau prapad la locul impactului, ajungand pana la 5 km distanta, un tanc Tiger modificat care arunca proiectile de 250 kilograme la zece kilometri si un lant de rachete de mici dimensiuni ce puteau atinge tinte situate la 200 km distanta! Dar cele mai sinistre ambitii ale inginerilor militari germani constau in realizarea asa numitului Sonnengewehr (Tunul Solar), un dispozitiv orbital destinat sa distruga total inamicii Reichului si sa stabileasca dominatia rasei ariene asupra „rasei inferioare” de pe Pamant.

„Raza mortii”, inventata involuntar de Oberth

Cel care a avut prima data ideea realizarii unui astfel de dispozitiv a fost compatriotul nostru, Herman Oberth, savant nascut la Sibiu si considerat pe buna dreptate, alaturi de Constantin Tiolkovski, parintele aeronauticii moderne. In cartea lui „Wege zur Raumschiffahrt” (Modalitati de a zbura in spatiul cosmic), tiparita in 1929, Oberth prezenta descrierea stiintifica a unei statii spatiale cu echipaj uman capabile sa orbiteze in jurul Terrei, la o mie de kilometri altitudine. El detalia metodele de constructie, pledand pentru folosirea sectiunilor prefabricate, descria un ciclu rotational pentru producerea gravitatiei centrifugale in interiorul statiei si un sistem ingenios, pentru aprovizionarea periodica a misiunilor spatiale.

Desigur, genialul savant dorea ca aceste „raumstationen” sa serveasca drept observatoare astronomice sau posturi telegrafice, sa transmita date meteorologice, sa supravegheze operatiuni de salvare etc. Dar ceea ce ii interesa pe nazisti era sugestia lui, potrivit careia o oglinda concava, cu diametrul de 100 metri, ar fi putut fi folosita pentru a reflecta razele solare intr-un anumit punct de pe suprafata Pamantului. Ideea lui Oberth avea destinatii pasnice – utilizarea intensei calduri rezultate astfel pentru a genera electricitate cu ajutorul turbinelor de aburi. Nazistii voiau insa altceva: realizarea unei „raze a mortii” de putere colosala, care putea incendia in cateva minute orase intregi!

Arhimede – omul care si-a depasit epoca

Ideea „Tunului solar” avea radacini adanci in istoria omenirii. In 212 i.Hr., romanii au incercat sa cucereasca orasul grec Siracuza; potrivit unei legende, primul atac asupra asezarii ar fi fost respins de aparatori intr-un mod ingenios: Arhimede, renumitul matematician, inventator si astronom grec, ar fi folosit puterea razelor solare pentru ca, prin intermediul unor oglinzi de cupru, sa incendieze la mare distanta corabiile romane. In zilele noastre au fost facute numeroase experimente pentru a confirma sau nega fezabilitatea unei asemenea arme, rezultatele fiind insa diferite. Cel mai celebru este cel realizat in anul 2006, in cadrul emisiunii „Distrugatorii de mituri”, concluzia fiind ca o serie de oglinzi de metal pot incendia o nava de lemn dar numai dupa o expunere de cateva minute asupra tintei.

O forta distrugatoare

Folosind planurile lui Oberth, savantii germani de la Hillersleben au dezvoltat considerabil conceptul oglinzilor spatiale. Calculele lor pledau pentru realizarea unei oglinzi parabolice de cel putin trei kilometri patrati, pentru a atinge puterea distructiva dorita – de peste o suta de mii de ori mai mare decat legendarele „raze ale mortii” imaginate de Arhimede, si o orbita ideala de 8200 kilometri. Dupa ce s-au luat in calcula o serie intreaga de materiale stralucitoare, s-a optat pentru sodiul metalic, element relativ abundent printre compusii naturali.

In conditii obisnuite, sodiul reactioneaza violent la umezeala, dar avand in vedere ca dispozitivul urma sa fie lansat pe orbita, in vid, aceasta nu reprezenta o problema. Pentru a trimite pe orbita piesele pre-asamblate, inginerii intentioneau sa foloseasca versiuni modificate, mult mai puternice, ale rachetei V-2, cu care Hitler terorizase Anglia.

Pamantul, distrus la ordin

In interiorul suprafetei locuibile a statiei spatiale, electricitatea urma sa fie asigurata de dinamuri speciale, puse in miscare de forta aburului si care de asemenea puteau utiliza caldura radiatiilor solare brute. Astronautii nazisti ar fi urmat sa poarte incaltaminte magnetica pentru a se acomoda cu imponderabilitatea si rezervele lor de oxigen ar fi fost constant reimprospatate de catre sere cu plante mari consumatoare de dioxid de carbon. Echipajul unei asemenea statii spatiale urma sa primeasca ordine cifrate prin radio, in timp ce supraveghea atent activitatea dusmanilor Reichului.

Cand li se ordona un atac asupra unei tinte terestre, cei de la bordul statiei roteau masivul reflector, ca pe o teava de tun anti-aerian, in directia dorita, calculand atent pozitia de tragere. Odata plasat pe traiectorie, oglinda capta razele puternice de Soare, inmagazinandu-le si trimitandu-le spre Pamant sub forma unei raze superconcentrate. In mod teoretic, aceasta raza era suficient de puternica spre a parjoli campuri, a incinera orase, a vaporiza rezervoare de combustibil si a pulveriza, pur si simplu, oamenii aflati la sol. Orice natiune care n-ar fi avut rachete spatiale ar fi fost neputincioasa in fata unei asemenea amenintari. Dupa distrugerea tintei, oglinda era intoarsa intr-o directie nepericuloasa pentru Pamant.

Americanii intra pe fir

Dar acest ambitios proiect a trebuit intrerupt in primavara lui 1945, cand victoria Aliatilor devenea tot mai evidenta. Serviciile secrete americano-britanice au reusit sa puna mana pe savantii germani si pe echipamentul acestora, pentru a-i impiedica pe sovietici sa beneficieze de ele. Ofiterul insarcinat cu interogarea cercetatorilor nazisti a fost colonelul american John A. Keck, a aflat de la acestia ca, daca razboiul s-ar mai fi prelungit cu inca un an, Germania ar fi putut dispune de arme redutabile, pe care le-au descris in detaliu, spre uimirea americanilor.

Desigur, cea mai puternica impresie a facut „Tunul solar”, inventie care a fost luata foarte in serios de partea americana. S-a facut chiar un calcul de fezabilitate privind aplicarea proiectului de catre US Army dar s-a apreciat in cele din urma ca resursele materiale, financiare si umane necesare transportarii si montarii oglinzilor in spatiu ar fi fost prea mari pentru finalitatea dorita. Aceasta cu atat mai mult cu cat intre timp savantii americani realizasera arma atomica, suficienta pentru a le asigura suprematia in urmatorii ani.

Oricum, savantii germani precum Oberth sau Wernher von Braun au pus stiinta mai presus decat patriotismul si vor participa la programul spatial american. Racheta lui von Braun, A 11, care urma sa transporte pe orbita componentele tunului solar, este precursoarea lui Saturn V, racheta care a purtat pe orbita astronautii misiunilor Apollo.

Soarele, folosit in scopuri pasnice

Chiar daca transformarea Soarelui intr-o arma a fost un concept niciodata realizat in epoca moderna, dispozitive similare „tunului solar” al nazistilor sunt puse in practica. Furnale solare folosind oglinzi parabolice asigura caldura pentru gatit, electricitate, metalurgie si producerea de oxigen. Cea mai mare instalatie de acest gen se gaseste in comuna franceza Odeillo, din Pirinei: o cladire de opt etaje, cuprinzand 10.000 de oglinzi concentrate pentru a capta razele solare si a produce temperaturi de pana la 3000 grade Celsius! Un concept similare este folosit la turnurile solare, unde o baterie de oglinzi reflecta razele de soare catre un receptor central, pentru a produce abur, din care rezulta electricitate, prin invartirea unor turbine.


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CAPE CANAVERAL, Fla. (AP) -- NASA fueled space shuttle Atlantis for liftoff Friday on the final flight of the 30-year program, even though stormy weather threatened to delay the launch.

Forecasters stuck to their original 70 percent chance of thunderstorms or rain, as fuel filled Atlantis' tank in the pre-dawn hours.

Mission managers acknowledged it might seem foolish to proceed with fueling, given the dismal forecast, NASA spokesman Allard Beutel said. They said they would take another look at the forecast and decide whether it makes sense to keep counting down.


The four shuttle astronauts suited up after sunrise despite the still-iffy launch prospects.

"Have you done your rain dance for the day?" joked Aly Mendoza, the tank and booster rocket vehicle manager.

Atlantis holds a year's worth of supplies – more than 8,000 pounds – for the International Space Station.

An estimated 750,000 people are expected to jam Cape Canaveral and surrounding towns for this final shuttle launch, reminiscent of the crowds that gathered for the Apollo moon shots.

Among the expected VIPs: 14 members of Congress, Joint Chiefs of Staff Chairman Adm. Mike Mullen, four members of the Kennedy family, two former NASA administrators, singers Jimmy Buffett and Gloria Estefan, and the first shuttle pilot of them all, Robert Crippen.

By 6 a.m., cars and RV were packed into almost every available space along U.S. 1 in Titusville, with cameras already trained on the launch pad in the hazy clouds across the Indian River. Many had planted chairs and staked out viewing locations just feet from the water. Some were still cocooned in sleeping bags as the sun rose.

Kenneth Cox, 25, an airport employee from Danville, Ind., joined three friends at the riverside. Hauling Lucky Charms, fixings for s'mores and a bottle of champagne to celebrate the launch, they slept off and on as the sun rose.

"It's the closing chapter of 30 years," said Cox, who went to Space Camp when he was in the fifth grade and has been enamored with the shuttle program as long as he could remember.

"I definitely think it's a somber attitude out here, because it's the last one," said Cox's friend, Simon Lin, 26, who works at Walt Disney World in Orlando. "It's brought so much to the tourist industry in Florida, and that's what we are. Closing it down, it's going to be sad."

Cherie Cabrera, 23, a Disney World employee, tried to explain the attraction.

"It's just powerful," she said. "There are so few people who have the ability to go to space, and for all of us to be here on the river, watching it launch and feeling it rise and feeling the wind, you feel like you're a part of it. You feel connected."

John and Jennifer Cardwell came from Fairhope, Ala., for their third attempt to see the shuttle launch. Twice before they made the trip only to have a flight canceled and they weren't able to stay. They brought their sons, Isaac, 6, and 3-year-old Eli.

"This is our last-ditch chance to see one," said 38-year-old Jennifer Cardwell, cradling a sleepy Eli in her arms just after dawn. "This is the end of an era, and I wanted to be able to experience it. My son is interested in space and science, and I wanted to encourage that.

"It's that last frontier, that last place left for us to explore," she said. "We've gone all over the world, and this is what's left."

NASA must launch Atlantis by Sunday or Monday or it will have to wait until at least July 16 because of an unmanned rocket launch scheduled for next week.

The 12-day mission will close out the space shuttle program, which began with the launch of Columbia in 1981. Atlantis will join Discovery and Endeavour in retirement, so NASA can focus on sending astronauts to asteroids and Mars. Private companies will take over the business of getting space station cargo and crews to orbit.

Once Atlantis soars, it will be another three years – possibly five or more – before astronauts blast off again from U.S. soil.

This will be the 33rd flight for Atlantis and the 135th shuttle mission overall.

"Everybody should be really proud how we've ended and just finishing strong," Mendoza said.


Associated Press Writer Mitch Stacy contributed from Titusville, Fla.

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