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ewmayer 2010-03-02 23:14

Quantum Comp.: Electron Spin Control Breakthrough
[url=] Breakthrough in Electron Spin Control Brings Quantum Computers Closer to Reality[/url]: [i]Research allows control of a single electron without disturbing other nearby electrons[/i]
[quote]The method developed by a team of researchers led by Jason Petta, assistant professor of physics at Princeton University, traps one or two electrons in microscopic corrals created by applying voltages to minuscule electrodes giving them an ability to control spin orientation.

The accomplishment overcomes a major challenge to creating scalable semiconductor-based quantum computers that use the intrinsic spin of individual electrons to store and manipulate information. Previous methods, namely electron spin resonance or ESR, unselectively sprayed microwave radiation on a sample, causing all the electrons in the sample to adopt the same spin orientation. This defeated the goal of having distinct electrons work together to represent data.

In their latest research, Petta and his team control electron spin using a method similar to splitting a beam of light. The path length of one of the resulting two beams is carefully adjusted so that when they recombine, their peaks and troughs either reinforce or cancel out each other. By doing this, researchers can control the constructive or destructive outcome of the resultant beam after recombination. Likewise, by carefully adjusting how the peaks and troughs of two quantum spin waves align, Petta's team is able to constructively or destructively manage the condition of an electron's spin and control its orientation.

What's more, the new method controls the spin of electrons in approximately one-billionth of a second. "This is nearly 100 times faster than conventional electron spin resonance," said Petta.

The spin of an electron forms a quantum bit, also called a qubit. Qubits are to quantum computing what "bits" are to conventional computing--a basic unit of information representing either a 1 or 0. But in quantum computing, a qubit can represent 1 and 0 at the same time making way for a dramatic increase in computing speed for certain types of computation.

Researchers ultimately would like to have a quantum computer consisting of many densely packed single electron spins. But in order to make this new type of computer a reality, they would need to control the spin orientation of a selected qubit without disturbing the other nearby spin qubits.

The challenge has been achieving the fast single spin rotations that are required to control a spin qubit without allowing the system to suffer "decoherence" or loss of quantum mechanical behavior.

"Think of a spinning top," said Petta. "Sooner or later it falls down due to friction. Our quantum system in some sense does the same thing. In order for a qubit to be technologically relevant, we need to be able to manipulate its state many times before it loses its quantum coherence."

Regarding future research, Petta explained that "the next big step for the spin qubit community is to coherently couple two spin qubits, implementing what is called a "two-qubit gate." Our work demonstrates single qubit control. In the long run, it is necessary to couple adjacent qubits and have them interact."[/quote]

ewmayer 2010-03-25 23:51

DNA identifies new ancient human species
[url=]DNA identifies new ancient human dubbed 'X-woman'[/url]: [i]Scientists have identified a previously unknown type of ancient human through analysis of DNA from a finger bone unearthed in a Siberian cave.[/i]
[quote]The extinct "hominin" (human-like creature) lived in Central Asia between 48,000 and 30,000 years ago.

An international team has sequenced genetic material from the fossil showing that it is distinct from that of Neanderthals and modern humans.

Details of the find, dubbed "X-woman", have been published in Nature journal.

Ornaments were found in the same ground layer as the finger bone, including a bracelet.

Professor Chris Stringer, human origins researcher at London's Natural History Museum, called the discovery "a very exciting development".

"This new DNA work provides an entirely new way of looking at the still poorly-understood evolution of humans in central and eastern Asia."

The discovery raises the intriguing possibility that three forms of human - Homo sapiens, Neanderthals and the species represented by X-woman - could have met each other and interacted in southern Siberia.

The tiny fragment of bone from a fifth finger was uncovered by archaeologists working at Denisova Cave in Siberia's Altai Mountains in 2008.

An international team of researchers extracted mitochondrial DNA from the bone and compared the genetic sequence with those from modern humans and Neanderthals.[/quote]

Spherical Cow 2010-03-30 00:49

An interesting news article from an MIT publication on theories of gravity. (And the reader's comments section suggests that the Mersenne Forum certainly does not have a monopoly on "gibberish".)



retina 2010-03-30 01:51

[QUOTE=Spherical Cow;210014]An interesting news article from an MIT publication on theories of gravity. (And the reader's comments section suggests that the Mersenne Forum certainly does not have a monopoly on "gibberish".)


[URL=""][/URL][/QUOTE]Wow, there sure some very high quality nonsense posted there. I wonder if it is even human generated? It seems more like some random number generator was used to select words from a lexicon and then pass them through a Markoff chain generator of some sort.

xilman 2010-04-08 18:36

Dust ring eclipsing ε Aur.
Beuatiful pictures of an eclipse of ε Aurigae here:



cheesehead 2010-04-08 18:46

[quote=xilman;211033]Beuatiful pictures of an eclipse of ε Aurigae here:



A dust ring shepherded by a single B-type companion, not a black hole or neutron star.

... except ...

it's the bright F-type star we see that's the companion! It's about 2-3 solar masses, whereas the "dwarf" (4 times as wide as our Sun) B-type star mostly hidden within the dust cloud is 5.9 solar masses.

So, it's really the B-type primary within the dust ring, with the F-type secondary (135 times as wide as our Sun) orbiting it outside the dust ring. (Yeah, [I]really[/I] they both swing around their barycenter outside the dust ring.)

The 7.6-AU-wide ring would fit comfortably inside Jupiter's orbit. (Jupiter is 5.2 AU from the Sun.)

The F and B stars orbit 18.1-19.6 AU apart. (Uranus is 19.2 AU from the Sun.)

This table has the latest figures:


Numbers in other articles below are sometimes outdated estimates from before 2009.




Catch an artist's concept picture here: [URL][/URL], but note that one comment says, "The image shown is wrong and not at all proportional. The F star from that perspective would be much smaller."

I remember reading about ε Aurigae in old Sky & Telescope articles, but hadn't marked my calendar. In the early 1980s I was too occupied with non-astronomy stuff.

cheesehead 2010-04-09 06:13

Another periodic astronomical phenomenon
"Cassini eavesdrops on orbit-swapping moons"


[quote]. . .

But there’s more to these moons. Amazingly, Janus and Epimetheus are on almost — but not [I]quite [/I] — the same orbit around Saturn! Currently, Janus is a bit closer to Saturn than Epimetheus.

I say "currently", because every four years [I]these moons swap orbits![/I] Since Janus has an orbit slightly closer to Saturn, it is moving faster around the planet than Epimetheus. It slowly but eventually catches up to the outer moon. As they approach, Janus pulls back slightly on Epimetheus, and Epimetheus pulls Janus forward. In other words, Janus steals orbital energy [from] Epimetheus! This means Epimetheus drops into a slightly lower orbit, and Janus gets boosted into a slightly higher one, effectively swapping the orbits of the two moons. Although the two orbital paths are separated by only about 50 km (30 miles) — smaller than the radii of either moon — they never collide. The swap takes place when the moons are still more than 10,000 km apart, so they never get a chance to bump uglies.

. . .[/quote]Furthermore, there's an animation sequence of photos, taken by the Cassini spacecraft, of Janus passing Epimethus in 2005 (i.e., one swap earlier than the latest). A forum entry at [URL][/URL] explains it. The animation is at [URL][/URL]

There's another animation at [URL][/URL], but this is a cut-and-paste of actual Cassini moon photos overlaid on a more detailed star background, showing fainter stars than are actually visible in the first animation.

cheesehead 2010-04-09 06:23

A Martian phenomenon
[B]"[/B]Martian avalanche crashes the party"


[quote]... These pictures from the orbiting HiRISE camera never get old because they’re frakking amazing! [URL=""]Here is another awesome avalanche[/URL] caught in the act… on Mars!

This may be my favorite Red Planet avalanche of them all. On the left you can see the surface of Mars: that’s frozen carbon dioxide — dry ice — covering the ground. The red brick-like pattern to the right of the ice is actually the face of a scarp, a steep cliff. We’re looking almost straight down on it, so it’s foreshortened, but don’t let that fool you; it’s 700 meters (2000 feet) high! On the right is the greyish floor, dusty basaltic rock. You can see sand dunes rippling across it, as well as a few boulders here and there.

But right there is the plume of a large avalanche, the cloud still rising above the floor! Clearly this was caught within seconds of the landslide hitting the floor of the scarp. The shadow of the plume is clear and obvious below and to the left. That’s particularly cool because knowing the Sun angle in the image means the plume height can be determined. They generally rise to 50 or more meters.

It’s spring in the northern hemisphere of Mars, and the warming temperatures are sublimating the dry ice. This may be causing the slides; the CO2 gets in the cracks of the rocks and dust, and when it goes away the loose debris can be free to fall. The folks at HiRISE have been targeting scarps like this one just in case they can catch avalanches like this.

I like this avalanche shot in particular because you can really see the contrast between the layer of ice, the scarp wall, and the floor. It makes for a wonderfully complete scene, and for some reason reminds me of Earth… maybe it’s because I live in Boulder, and I’m used to seeing ice covered red rocks with lots of interesting geological bits around. I’m not sure. But like all the other avalanche shots, it reminds me that Mars is a planet, a world, a location, an actual [I]place[/I]. It may lack the dynamic and diverse weather we get here on Earth, but there’s still plenty going on at that little ball.[/quote]

ewmayer 2010-04-16 22:45

New Exoplanets Shake Up Space Theory
[url=]New Exoplanets Shake Up Space Theory[/url][quote]Apr 13 2010, 3:00 PM ET

Researchers [url=]have discovered nine new exoplanets[/url], overturning a pillar of planetary theory. Previously, astronomers thought that all planets orbit their suns in the same direction as the suns rotate, but two of the new exoplanets have opposite, or retrograde, orbits.

Planets were thought to develop from dust and gas orbiting a young star, thus developing an orbit in the same direction as the star's rotation. The retrograde orbits, however, suggest that some developing planets could get caught in a long-term "gravitational tug-of-war" between other stars and planets, pushing the new planets into eccentric orbits around their transit stars. Such a development process would exclude the possibility of an Earth-like planet developing alongside the Jupiter-sized retrograde planets, since the latter's jerky movements would knock out smaller competition.

The new exoplanets are also notable for the way they were discovered. Scientists have found most of the 452 recorded exoplanets by noting their gravitational pull on their transit stars' light. Researchers found the newcomers, however, when the planets passed directly in front of their transit stars.

The same method recently disclosed another exoplanet, this one notable for its similarities to the members of our solar system: it resembles Jupiter in size but Mercury in orbit, giving it much lower temperatures than the gas giant. Since astronomers can learn more about this planet every 95 days, when it orbits past its sun, they will be able to conduct much more thorough research than if they had found it using traditional methods.[/quote]

ewmayer 2010-05-04 00:01

"Loop Current" Could Push Oil Spill Up East Coast

Not looking good ...

cheesehead 2010-05-07 22:45

A little uplift to contemplate instead of the spill, perhaps ...

"Peak Picked for World's Largest Scope"


[quote]Yesterday officials from the European Southern Observatory [URL=""]announced[/URL][/quote][URL][/URL]
[quote]where they plan to build the E-ELT, short for European Extremely Large Telescope.

. . .

... Its primary's mosaic of 1,000 hexagonal mirrors will create an aperture 138 feet (42 meters) across. That's a huge engineering leap: four times the diameter of the largest single-aperture optical telescopes today. To put the optics in perspective, the E-ELT's [I]secondary[/I] mirror will be bigger than the venerable Hale Telescope's 200-inch primary.

. . .[/quote]I've visited Mt. Palomar. 200 inches looked pretty big.

BTW, recall that the observer's cage at the primary focus of the 200-inch Hale telescope is big enough for a man to sit in. It obscures only a small percentage of the 200-inch aperture.

42 * 39.37 inches = 1654 inches (and a man-sized cage would obscure only a small percentage of its secondary mirror)

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