Immagine
 Trilingual World Observatory: italiano, english, română. GLOBAL NEWS & more... di Redazione
   
 
Di seguito tutti gli interventi pubblicati sul sito, in ordine cronologico.
 
 

 Prima constructie creata de roboti zburatori a fost proiectata de arhitectii Fabio Gramazio si Matthias Kohler si a fost asamblata în doar câteva zile de masinile create de ETH Zurich.

Primul turn construit de roboţi zburători (VIDEO)

Turnul a fost construit de o armata de roboti zburatori ghidati cu ajutorul unei camere instalete în plafon si care detecteaza miscarea. Pentru a evita coliziunile si a le permite robotilor sa construiasca concomitent, masinile au fost ghidate pe doua trasee care înconjoara structura. Utilizarea traseelor este dictatata de un "sistem de rezervare a spatiului" prin care fiecare vehicul îsi retine spatiul de care are nevoie. Odata ce masina a parcurs drumul si a pus caramida la locul potrivit, spatiul îi este alocat alteia.

Fiecare robot este dotat cu un dispozitiv de aspirare, cu ajutorul caruia poate ridica si transporta caramizile din polistiren. Atunci când un robot este suprasolicitat, se conecteaza singur la un încarcator, urmând ca un altul sa îi ia locul.

Acum, turnul construit din 1500 de caramizi are o înaltime de 6m si o latime de 3,35m si poate fi admirat la galeria de arta FRAC.

Sursa: inhabitat - via descopera.ro

Articolo (p)Link Commenti Commenti (0)  Storico Storico  Stampa Stampa
 

The incorporation of such single-molecule elements could enable smaller, faster, and more energy-efficient electronics.

The research findings, supported by a $1 million grant from the W.M. Keck Foundation, were published online in the Nov. 14 issue of Nano Letters.

"This new switch is superior to existing single-molecule concepts," said Hrvoje Petek, principal investigator and professor of physics and chemistry in the Kenneth P. Dietrich School of Arts and Sciences and codirector of the Petersen Institute for NanoScience and Engineering (PINSE) at Pitt. "We are learning how to reduce electronic circuit elements to single molecules for a new generation of enhanced and more sustainable technologies."

The switch was discovered by experimenting with the rotation of a triangular cluster of three metal atoms held together by a nitrogen atom, which is enclosed entirely within a cage made up entirely of carbon atoms. Petek and his team found that the metal clusters encapsulated within a hollow carbon cage could rotate between several structures under the stimulation of electrons. This rotation changes the molecule's ability to conduct an electric current, thereby switching among multiple logic states without changing the spherical shape of the carbon cage. Petek says this concept also protects the molecule so it can function without influence from outside chemicals.

Because of their constant spherical shape, the prototype molecular switches can be integrated as atom-like building blocks the size of one nanometer (100,000 times smaller than the diameter of a human hair) into massively parallel computing architectures.

The prototype was demonstrated using an Sc3N@C80 molecule sandwiched between two electrodes consisting of an atomically flat copper oxide substrate and an atomically sharp tungsten tip. By applying a voltage pulse, the equilateral triangle-shaped Sc3N could be rotated predictably among six logic states.

The research was led by Petek in collaboration with chemists at the Leibnitz Institute for Solid State Research in Dresden, Germany, and theoreticians at the University of Science and Technology of China in Hefei, People's Republic of China. The experiments were performed by postdoctoral researcher Tian Huang and research assistant professor Min Feng, both in Pitt's Department of Physics and Astronomy.

Source: ScienceDaily

Articolo (p)Link Commenti Commenti (0)  Storico Storico  Stampa Stampa
 

Previously, the maximum resolution of optical instruments, including cameras and microscopes, was fundamentally limited to a precision that corresponded to approximately half of the wavelength of incoming light.

The new scheme, developed by researchers from the RIKEN SPring-8 Center in Harima and Nagoya University, has a resolution up to 380 times better than the UV light used in the experiments. For microscopes using visible light, which means wavelengths of a few hundred nanometers, the best achievable resolution is around 100 nanometers, which fails to resolve the smallest structures on a computer chip. Imaging smaller nanostructures, or even atoms, requires light of much shorter wavelengths, such as x-rays that are difficult to handle, and which provide different types of images to those captured using visible light.

Figure 1: The optical response of a diamond crystal (left) can now be analyzed at the atomic scale with extreme ultraviolet light (center). This technique can provide additional information to the crystal structure (right) typically obtained using x-rays. Credit: Reproduced, in part, from Ref. 1 © 2011 Kenji Tamasaku

Led by Kenji Tamasaku of RIKEN, the researchers used a non-linear optical effect to achieve atomic resolution in diamond. Their process is based on the intrinsic interaction between the electrons of the material’s crystal atoms and UV light that splits an incoming x-ray beam into a UV beam and a lower energy x-ray beam. The combined energy of these scattered beams is the same as that of the incoming beam. This process depends strongly on the activation of the UV beam, which occurs only in the vicinity of the electrons in the atoms, and only if the optical response of the electrons is a match to the incoming x-ray beam, Tamasaku explains.

Analyzing the scattered beams allowed a precise reconstruction of the motion of the electrons under UV illumination. Using a diamond crystal as an imaging object, the researchers demonstrated a resolution of 0.054 nanometers (Fig. 1). Because Tamasaku and colleagues used a non-linear optical effect, they obtained new information not only about how electrons move but also about atomic position.

There are many possibilities for using this new method, says Tamasaku. “This technique is very useful for the study of the physical properties of materials that couple to light.” An example is the study of electronic materials, in which the sensitivity of the technique to the electron’s electronic states can be used to probe electrical charges in materials such as high-temperature superconductors. Using the team's new approach, this will now be possible with atomic resolution.

Source: RIKEN

Articolo (p)Link Commenti Commenti (0)  Storico Storico  Stampa Stampa
 

Il mantello dell’invisibilità alla Harry Potter non è ancora stato creato, ma i ricercatori sanno da tempo come costruire oggetti che ingannano occhio e strumenti elettronici, rimanendo impercettibili alla vista. Ora la scienza potrebbe superare la fantascienza: un gruppo di fisici della Cornell University ha costruito, infatti, un apparecchio in grado di nascondere eventi nel tempo. Come spiegano su Nature, bisogna usare delle particolari lenti temporali, che funzionano proprio come quelle ottiche, ma agiscono nella dimensione del tempo invece che in quella dello spazio.

Per rendere invisibili degli oggetti basta scegliere elementi con il giusto indice di rifrazione, una delle proprietà intrinseche dei materiali che indica come luce e radiazione elettromagnetiche vengano rallentate o accelerate quando li attraversano. Per esempio, se questo indice ha valore negativo o pari a quello dell’aria che circonda l’oggetto, la luce quando lo incontra viene accelerata o deviata, nascondendolo così alla nostra vista.

Può sembrare strano, ma qualcosa di simile può avvenire anche nella dimensione temporale, tramite l’uso di particolari lenti. “Grazie ad esse abbiamo creato una specie di buco temporale, all’interno del quale le sonde elettromagnetiche non sono capaci di registrare variazioni della luce”, hanno spiegato i ricercatori statunitensi nello studio.

In ottica una lente è un oggetto capace di cambiare direzione ai raggi luminosi, facendoli divergere o convergere. Ma da un punto di vista strettamente matematico, le equazioni che descrivono come si sposta un raggio di luce nello spazio sono simili a quelle che mostrano come esso viaggia nel tempo. Per questo, secondo i ricercatori, allo stesso modo che per i materiali invisibili, è possibile ingannare gli strumenti in modo che non siano più capaci di rilevare un evento sulla linea temporale.

Ogni lente di invisibilità creata dai fisici è formata di due parti: la prima aumenta la frequenza della radiazione luminosa, rendendola più blu, la seconda la ridiminuisce, rendendola più rossa. Se avviene nel giusto mezzo di dispersione (in questo caso una fibra ottica), questo gioco di frequenze fa sì che in un primo momento il raggio di luce venga accelerato e in un secondo rallentato, e in questo modo si dà inizio a una finestra temporale in cui gli eventi sono nascosti.

“Il concetto è simile a quello che succede nel traffico quando si deve superare un passaggio a livello”, hanno spiegato Robert Boyd e Zhimin Shi dell’ Università di Rochester in un commento alla ricerca pubblicato sempre su Nature:  “Quando deve passare il treno le macchine rallentano e si fermano, il che crea una sorta di buco nel traffico.

Quando poi il passaggio viene riaperto, le automobili accelerano per raggiungere di nuovo quelle che le precedono, e quando questo succede non c’è più modo di distinguere se il treno sia passato oppure no”.

Successivamente, infatti, il buco nel tempo può essere chiuso facendo passare il raggio di luce in un mezzo con caratteristiche di dispersione opposte al primo e attraverso una seconda lente invertita rispetto alla precedente. Così gli eventi che si verificano nell’intervallo di tempo che si crea con questo metodo non sono percepibili dagli strumenti. I ricercatori hanno per ora verificato il funzionamento del metodo con un singolo impulso laser ripetuto nel tempo: esso veniva correttamente nascosto quando il “mantello” era acceso, ed era invece visibile in condizioni normali.

A oggi, il gap temporale può essere lungo appena cinquanta picosecondi (1ps è pari a un millesimo di miliardesimo di secondo). Questo intervallo può sembrare un tempo brevissimo, ma potrebbe essere sufficiente a nascondere una serie di impulsi laser molto veloci. In ogni caso gli scienziati stanno cercando di aumentare la durata del buco nel tempo, e pensano di poterla portare dall’ordine dei picosecondi a quello dei microsecondi (milionesimi di secondo) o addirittura dei millisecondi (un millesimo di secondo).

Se combinato con i metodi che permettono di nascondere materiali diversi nello spazio, questo approccio potrebbe portare allo sviluppo di apparecchi capaci di rendere alcuni oggetti invisibili in tutto lo spazio-tempo. A parte quest’applicazione futuribile – affascinante, ma per ora lontana - i ricercatori hanno già fatto sapere che il procedimento potrebbe trovare uso anche nel presente, per esempio per migliorare la sicurezza delle comunicazioni via fibra ottica.

Fonte: wired.it

Articolo (p)Link Commenti Commenti (0)  Storico Storico  Stampa Stampa
 

Uluitoarea tehnica, cunoscuta sub termenul stiintific de "levitatie diamagnetica", permite apei si substantelor organice sa devina fara greutate atunci când se întrunesc unele conditii specifice de laborator.

Savanţii britanici au reuşit să facă să leviteze o... muscă!

Rezultatele studiului au fost publicate în premiera în Journal of the Royal Society Interface.

"Levitatia diamagnetica ne-a permis sa mentinem un control ridicat al conditiilor fizice ale experimentului nostru. Pe lânga acest aspect, levitatia diamagnetica ne-a ajutat sa descoperim modalitatea în care alterarea gravitatiei efective ajunsese sa fie o cauza a comportamentului anormal al mustelor.

Cele 4 miliarde ani de evolutie a vietii pe Terra au dus la adaptarea tuturor organismelor vii la conditiile gravitatiei terestre. Aici, cu ocazia experimentului nostru încheiat cu succes, am evidentiat influenta levitatiei diamagnetice asupra organismelor vii de pe Terra si am comparat rezultatele cu cele obtinute în cazul experimentarii imponderabilitatii din spatiul cosmic. Materialele cu proprietati diamagnetice sunt respinse de câmpurile magnetice, în timp ce materialele cu puternice proprietati magnetice, precum fierul, sunt puternic atrase de câmpul magnetic.

Forta diamagnetica are proprietatea de a echilibra greutatea obiectului care leviteaza si functioneaza chiar la nivel molecular, la fel cum forta centrifuga echilibreaza forta gravitationala asupra unui obiect de pe orbita Terrei.", declara profesorul Richard Hill, conducatorul experimentului efectuat de un grup de cercetatori din cadrul Universitatii din Nottingham.

Cercetatorii au reusit experimentul dupa ce au suspendat câteva musculite de otet în fluxul unui puternic câmp magnetic.

Câmpurile magnetice au fost folosite în alte experimente si studii pentru a induce levitatia unor fragmente de material organic, precum si a unor marunte organisme vii microscopice si chiar a a unei broaste vii.

Sursa: Google News

Articolo (p)Link Commenti Commenti (0)  Storico Storico  Stampa Stampa
 

"Israel was born out of Jewish Terrorism" Tzipi Livnis Father was a Terrorist" Astonishing claims in the House of Parliament. SIR Gerald Kaufman, the veteran Labour MP, yesterday compared the actions of Israeli troops in Gaza to the Nazis who forced his family to flee Poland.

During a Commons debate on the fighting in Gaza, he urged the government to impose an arms embargo on Israel.

Sir Gerald, who was brought up as an orthodox Jew and Zionist, said: "My grandmother was ill in bed when the Nazis came to her home town a German soldier shot her dead in her bed.

"My grandmother did not die to provide cover for Israeli soldiers murdering Palestinian grandmothers in Gaza. The present Israeli government ruthlessly and cynically exploits the continuing guilt from gentiles over the slaughter of Jews in the Holocaust as justification for their murder of Palestinians."

He said the claim that many of the Palestinian victims were militants "was the reply of the Nazi" and added: "I suppose the Jews fighting for their lives in the Warsaw ghetto could have been dismissed as militants."

He accused the Israeli government of seeking "conquest" and added: "

They are not simply war criminals, they are fools."

Articolo (p)Link Commenti Commenti (0)  Storico Storico  Stampa Stampa
 

Researchers working at the Clarendon Laboratory at the University of Oxford in England have managed to get one small diamond to communicate with another small diamond utilizing "quantum entanglement," one of the more mind-blowing features of quantum physics.

Entanglement has been proven before but what makes the Oxford experiment unique is that concept was demonstrated with substantial solid objects at room temperature.

Previous entanglements of matter involved submicroscopic particles, often at cold temperatures.

 

The vibrational states of two spatially separated, millimeter-sized diamonds are entangled at room temperature by scattering a pair of strong pump pulses (green). The generated motional entanglement is verified by observing nonclassical correlations in the inelastically scattered light. Credit: Dr. Lee and colleagues, Image Copyright Science|AAAS

This experiment employed millimeter-scale diamonds, "not individual atoms, not gaseous clouds," said Ian Walmsley, professor of experimental physics at Oxford's Clarendon Laboratory, one of the international team of researchers.

The experiment is reported in this week's edition of Science.

When zapping one artificial diamond with ultrashort laser pulses they managed to change the vibrations of a second diamond sitting a half a foot away without touching it.

Entanglement originated in the mind of Albert Einstein, who ironically came up with the notion trying to disprove quantum mechanics, a branch of physics he mistrusted all his life.

Under the theory, if two particles, say electrons, are created together, some of their attributes will become "entangled." If the two are then separated, doing something to one instantly affects the other. This would happen whether they were next to each other or across the universe.

For instance, electrons act as if they have tiny bar magnets that point up or down, described by an attribute called "spin." If the two electrons are entangled through their spins -- up or down -- and a scientist measures the spin of one, the spin of the other will react even if one is on a lab table in Oxford and the other were on a planet near the star Antares, 1,000 light years away. Instantly.

This would mean that the information about the change traveled faster than the speed of light -- which Einstein said was impossible -- or that long distances are some kind of illusion.

Einstein disparaged it as "spooky action at a distance." The German physicist Erwin Schrodinger used the term "entanglement" in a letter to Einstein. He didn't believe in quantum mechanics either.

"I think I can safely say no one understands quantum mechanics," the late physicist Richard Feynman once famously explained.

Nonetheless, quantum mechanics is now the paradigm for nature at the atomic level. It serves as the foundation of much of modern technology, from lasers to transistors. And entanglement comes as part of the package. Physicists have been demonstrating it in laboratories since the 1980s, and it is being used in laboratories experimenting with the building blocks of quantum computers.

The diamonds Walmsley and his international team used were approximately 3 millimeters (a tenth of an inch) square and 1 millimeter thick.

"We used short pulse lasers with pulse durations of around 100 femtoseconds (a quadrillionth of a second). A femtosecond is to a second as a nickel is to the debt of the federal government generally speaking," he said.

They chose diamonds because they are crystals, so it was easier to measure molecular vibrations, and because they are transparent in visible wavelengths. Light from the lasers altered a kind of mass vibration in the diamond crystal called phonons, and the measurements showed they were entangled: The vibrations of the second diamond reacted to what happened to the vibrations of the first.

Performing the experiment with ultrafast laser pulses enabled the researchers to catch entanglement, which is usually very short-lived in large objects at room temperature.

"It remains a counterintuitive way of thinking about objects," Walmsley admitted.

"It's a very nice and clever piece of work with potentially big implications," said Sidney Perkowitz, a physicist at Emory University in Atlanta, and author of "Slow Light: Invisibility, Teleportation and Other Mysteries of Light," a book partially about entanglement. The macroscopic size, and the fact that this was done at room temperature, would be important steps toward a practical quantum technology for telecommunications and computing, and toward deeper understanding of how the quantum world and the human-scale world are related."

Source: Inside Science News Service

Articolo (p)Link Commenti Commenti (0)  Storico Storico  Stampa Stampa
 

16mila euro (lordi) al mese, il 60% in più rispetto alla media comunitaria e 11mila e spiccioli dei quali di indennità parlamentare. Dalla Camera è giunta una repentina smentita, l'indennità parlamentare dei deputati italiani " è pari mediamente a 5mila euro netti" e inferiore a quella di altri paesi Ue, ma ormai la frittata (mediatica) è fatta: almeno per qualche giorno, il primo problema del paese riguarda il gonfiore dei portafogli di chi lo governa.

Dimensioni, smisurate o meno, delle buste paga, si tratta di dati che vanno analizzati a braccetto con quelli sull'attività dei soggetti in esame. In parole povere: quanto guadagnano, ma soprattutto cosa fanno per guadagnarsi lo stipendio? In soccorso di chi vuol farsi un'idea più strutturata giunge Openpolis, associazione che monitora online l'attività di Camera e Senato e che ha tolto il velo proprio in queste ore sul rapporto Camere aperte 2011.

L'analisi, aggiornata a fine 2010, tiene il dito premuto sul polso della situazione grazie al calcolo dell'indice di produttività parlamentare, cioè la somma di una serie di variabili (atti e tipologia di atti presentati, presenza ai lavori, consenso dei colleghi, ecc) che dia un'idea quanto più precisa della partecipazione attiva dei nostri, e riapre il vaso di Pandora della pubblicazione in Rete dei redditi ( qui ci chiedevamo sia giusto pubblicare quelli dei cittadini). I trasparenti, quanti mettono online la loro dichiarazione patrimoniale, sono solo 45 (22 del Pd, 4 dell'Udc, 11 del Pdl, 3 del  Gruppo Misto, 3 della Lega e 2 di Fli).

Tornando alla produttività, a distinguersi fra i deputati sono Antonio Borghesi (IdV), Pier Paolo Baretta (Pd) e Franco Narducci (Pd). Sul podio dei senatori, Gianpiero D'Alia (Udc), Carlo Vizzini (Udc) e Lucio Malan (Pdl). Maglia nera, invece, per i deputati Niccolò Ghedini (Pdl), Antonio Angelucci (Pdl) e lo scomparso  Mirko Tremaglia (Fli) e per i senatori Sebastiano Burgaretta Aparo (Pdl), Alberto Tedesco (Pd) e Vladimiro Crisafulli (Pd). A livello di gruppi, i personaggi più virtuosi appartengono all' Idv, sia in Camera sia in Senato. La Lega si distingue con percentuali particolarmente basse, 6,3 Camera e 3,6 Senato, per ciò che concerne le assenze.

E di mancate presenze parlando quando c'è da alzare la mano, svettano i deputati Antonio Gaglione (Misto), ancora Ghedini (Pdl) e Tremaglia (Fli) con, rispettivamente, il 92% (!), il 76% e il 76,% delle assenze. Stesso discorso per i senatori Umberto Veronesi (Pd e 72% delle assenze), Emma Bonino (Pd, 68%) e Giovanni Pistorio (Misto 67%). Non se ne perdono una, invece, i deputati Remigo Ceroni (Pdl, 99% delle presenze), Rosy Bindi (Pd, 99%) e Paolo Vella (Pdl, 99%) e i senatori Cristiano De Eccher (Pdl, 99%), Madell Valli (Lega, 99%) e Mario Ferrara (Pdl, 99%). Per citare un'altra delle graduatorie stilate, i più attivi nella presentazione di progetti di legge sono la deputata Gabriella Carlucci (Pdl), 95 ddl messi sul tavolo e uno diventato legge, e il senatore Rosario Costa (Pdl), 76 ddl e una legge.

Fonte: wired.it

Articolo (p)Link Commenti Commenti (0)  Storico Storico  Stampa Stampa
 

Specialistii au ajuns la aceasta concluzie dupa ce au analizat 14 studii, din Statele Unite, Canada si Africa de Sud, care au inclus, fiecare, între 53 si 12.000 de copii cu vârste între 6 si 18 ani.

Dr. Amika Singh si colegii sai de la VU University Medical Center, Amsterdam, au decis sa abordeze aceasta problema ca urmare a faptului ca, în ultimul timp, accentul cade tot mai mult pe învatare, alocându-se din ce în ce mai putin timp pentru activitatile în aer liber si cele care presupun miscare.

Sportul înlesneşte învăţarea

Doua dintre cele 14 studii au fost catalogate ca având o calitate superioara si au indicat clar existenta unei relatii între activitatea fizica si performantele scolare.

Este cunoscut faptul ca exercitiile fizice ajuta la cresterea fluxului sangvin si a celui de oxigen la nivelul creierului. Totusi, specialistii explica existenta relatiei si prin faptul ca exercitiile fizice ajuta la îmbunatatirea dispozitiei si la reducerea nivelului de stres. De asemenea, dr. Singh a declarat ca "atunci când copiii fac sport, învata sa se supuna regulilor si sa le respecte. Astfel, ei devin mai disciplinati si se pot concentra mai bine în timpul orelor".

Desi expertii recunosc ca va fi nevoie si de alte cercetari pentru a putea demonstra oficial aceasta legatura, ei afirma ca "este bine ca un copil sa fie activ cel putin o ora pe zi pentru a se mentine sanatos".

Sursa: BBC

Articolo (p)Link Commenti Commenti (0)  Storico Storico  Stampa Stampa
 

Switching from hydrocarbon-based transportation to systems powered by state-of-the-art fuel cells therefore seems a natural choice, but numerous obstacles have kept this technology confined to laboratories. A prime example is the problem of on-board hydrogen storage for vehicles: because ambient hydrogen gas is roughly 10,000 times less dense than gasoline, it would require impractically large tanks to obtain comparable mileage.

Compressing hydrogen gas or liquefying it at -250 °C are two ways to increase its energy content by volume. However, chemists are developing a more attractive strategy using specially designed compounds, called metal hydride clusters, to produce high hydrogen-storage densities without extreme temperatures or pressures. The metal atoms within these molecules bind to large numbers of hydrogen atoms, producing a solid that can reversibly add or remove hydrogen using mild heating or cooling.

Now, Zhaomin Hou from the RIKEN Advanced Science Institute in Wako and an international team of colleagues have isolated a new class of ‘heterometallic’ hydride clusters (Fig. 1) that may spur development of lighter and longer-lived fuel cell devices. By incorporating multinuclear rare-earth metals into their compounds, the team has produced the first high-density storage molecules that have hydrogen addition properties that can be monitored directly using x-ray diffraction—a technique that provides clear insights into cluster structure and functionality.

Rare combinations

For the past 25 years, chemists have paired so-called ‘d-block transition metals’, such as tungsten (W) and molybdenum (Mo), with lightweight rare-earth metals, such as yttrium (Y), to increase the storage capacity of hydride clusters. Because the nuclei of rare earths are shielded by many electrons, these metals can pack high numbers of hydrogen atoms into small crystal volumes without suffering electronic repulsions. Unfortunately, once hydrogen gas binds to a rare-earth metal, it tends to stay there. Mixing in d-block metals alters the rare-earth reactivity so that on-demand hydrogen storage and release can occur.

Figure 1: Heterometallic hydride clusters containing molybdenum atoms (purple spheres) and rare-earth yttrium metals (green spheres) are promising materials for on-board storage and release of hydrogen gas (light blue spheres). Credit: 2011 Zhaomin Hou

Until now, most of these combined metal hydrides were constructed using mononuclear rare-earth building blocks, such as YH, with a mononuclear d-block metal. Using a different strategy, Hou and his colleagues recently devised innovative protocols to isolate polynuclear rare-earth hydrides using large molecular ligands to trap these typically unstable compounds in place. Polynuclear hydrides feature dense, interconnected networks of ‘bridging’ hydrogen atoms connected to two or more metals—characteristics that led the researchers to explore their potential for hydrogen storage applications.

“It is not difficult to imagine that hydrogen atoms could bond to multiple metal atoms in a polynuclear polyhydride complex, and the [mode of] bonding could be different with different metal combinations,” says Hou. “However, it is not easy to prepare quality polyhydride samples for high-precision structure determinations. Hydride complexes containing both rare-earth and d-block transition metals are even more difficult to prepare because of their air- and moisture-sensitivity.”

A five-way first


Figure 2: Monitoring the reversible addition and release of a hydrogen gas molecule to a molybdenum-yttrium cluster in real time with x-ray crystallography has revealed the first atom-resolved insights into hydrogen storage by organometallic crystals. Credit: 2011 Zhaomin Hou

Performing their experiments inside nitrogen-filled and humidity-free enclosures, the team mixed one of their carefully prepared polynuclear complexes—four yttrium metals and eight hydrogen atoms held together by bulky organic ligands—with either a Mo or W pentahydride. After precipitating crystals out of the reaction, they used x-ray and neutron diffraction experiments to view their product’s atomic structure. These measurements showed that the two metallic components fused together, yielding a Y4MH11 (M = Mo, W) hydride with double-, triple-, and quadruple-bridged hydrogen atoms.

Zapping the penta-metallic polyhydride with ultraviolet light enabled the team to remove a protective phosphorus ligand and increase the hydrogen bridging density within the cluster. This produced the first hydride cluster where hydrogen is bonded to five metals in a distinctive symmetry known as trigonal bipyramidal. “The confirmation of a penta-coordinated hydrogen atom in this geometry is unprecedented,” says Hou.

Step-by-step scrutiny

Hou and colleagues’ experiments then demonstrated that their heterometallic clusters possessed critical hydrogen storage and release capabilities. Heating H2 and Y4WH11 to 80 °C caused an oxidative addition of the gas molecule to the cluster, which they could reverse through ultraviolet-light treatment. Despite the Y4MoH11 molecule not responding to the same chemical tricks, the researchers discovered that applying a vacuum could suck H2 from the cluster, giving a new Y4MoH9 complex. Exposing this compound to hydrogen gas at room temperature spontaneously regenerated the original molecule (Fig. 2).

According to Hou, the most striking aspect of this chemistry is that the hydrogen addition to the Y4MoH9 cluster can be followed from single crystal to single crystal—meaning that the starting material, the reaction intermediates, and the product all retain the same rigid morphology. “No metal hydrides have previously shown such excellent crystallinity,” he notes.

After gingerly sealing a Y4MoH9 crystal into a thin, hydrogen-filled capillary tube, the researchers monitored the spontaneous addition reaction over 60 hours. As the cluster gradually took in hydrogen and changed color from black to red, they watched—at precision greater than one-millionth of a meter—yttrium and molybdenum atoms separate and shift within the crystal unit cell. By providing the first-ever atom-resolved views of active sites and bonding modes for hydrogen addition to an organometallic crystal, these findings should aid design of more sophisticated alloys in the future.

Theoretical calculations performed by the researchers indicated that combining two metals with starkly different electronic properties played a big role in giving the clusters their unique reactivity. With wide swaths of the periodic table available for exploring using this technique, breakthroughs in heterometallic hydride materials may have only just begun.

Source: RIKEN

Articolo (p)Link Commenti Commenti (0)  Storico Storico  Stampa Stampa
 
Ci sono 2510 persone collegate

< ottobre 2019 >
L
M
M
G
V
S
D
 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
     
             

Titolo
en - Global Observatory (605)
en - Science and Society (594)
en - Video Alert (346)
it - Osservatorio Globale (503)
it - Scienze e Societa (555)
it - Video Alerta (132)
ro - Observator Global (399)
ro - Stiinta si Societate (467)
ro - TV Network (149)
z - Games Giochi Jocuri (68)

Catalogati per mese - Filed by month - Arhivate pe luni:

Gli interventi piů cliccati

Ultimi commenti - Last comments - Ultimele comentarii:
Hi, it's Nathan!Pretty much everyone is using voice search with their Siri/Google/Alexa to ask for services and products now, and next year, it'll be EVERYONE of your customers. Imagine what you are ...
15/01/2019 @ 17:58:25
By Nathan
Now Colorado is one love, I'm already packing suitcases;)
14/01/2018 @ 16:07:36
By Napasechnik
Nice read, I just passed this onto a friend who was doing some research on that. And he just bought me lunch since I found it for him smile So let me rephrase that Thank you for lunch! Whenever you ha...
21/11/2016 @ 09:41:39
By Anonimo


Titolo

Latest NEWS @
www.TurismoAssociati.it

Non-Hodgkin lymphoma cured by CANNABIS. The video of Stan and Barb Rutner.

Dr. Joycelyn Elders, U.S. surgeon general: Myths About Medical Marijuana in The Providence Journal, 2004.

Marihuana vindeca CANCERUL: marturii despre uleiul de cocos si canabis.

Yahoo Incorporated Mail. My account recovery information is incorrect. The Password Helper says my password can't be reset online. "First time signing in here?" message.

All information in a video about Donatio Mortis Causa and The Venus Project

What is TOR browser?

China says it hopes to reach phased trade pact with U.S. as early as possible

UAW, GM leaders have a deal to end strike, now workers will decide

Exclusive: Satellite images reveal China's aircraft carrier 'factory,' analysts say

Pence to urge Turkey to halt Syria offensive as threat of further sanctions loom

Hungary would have to 'use force' to fend off new wave of migrants: PM

Exclusive: Iran-backed militias deployed snipers in Iraq protests - sources

Ultimele articole - Antena3.roDoliu în lumea sportului. Un pugilist a murit la patru zile dupa un KO

BCR opre?te sistemul de carduri. Anun? important pentru clien?i

Gheorghe Dinca, fata în fata cu procurorii DIICOT. Criminalul din Caracal afla cât mai ramâne dupa gratii - VIDEO

Concert The Motans ?i un spectacol de flamenco în închiderea Festivalului Tânar de la Sibiu 2019

Drama „5 Minute”, regizata de Dan Chi?u, premiera mondiala astazi la Var?ovia IFF

HOROSCOP. Sufletul tau pereche în func?ie de zodie. Descopera cine este jumatatea ta adevarata





17/10/2019 @ 10:54:07
script eseguito in 2018 ms