My Science Books

Glasses-free 3-D TV looks nearer (w/ Video)

2012-07-12T03:08:00.001-07:00

A new glasses-free 3-D video system uses three layered LCD panels displaying bizarre patterns (top three images) that collectively produce a coherent, high-resolution, multiperspective 3-D image. The bottom image illustrates, roughly, the composite image that would reach one eye at one viewing angle. Images courtesy of the Camera Culture group

Despite impressive recent advances, holographic television, which would present images that vary with varying perspectives, probably remains some distance in the future. But in a new paper featured as a research highlight at this summer’s Siggraph computer-graphics conference, the MIT Media Lab’s Camera Culture group offers a new approach to multiple-perspective, glasses-free 3-D that could prove much more practical in the short term.

Instead of the complex hardware required to produce holograms, the Media Lab system, dubbed a Tensor Display, uses several layers of liquid-crystal displays (LCDs), the technology currently found in most flat-panel TVs. To produce a convincing 3-D illusion, the LCDs would need to refresh at a rate of about 360 times a second, or 360 hertz. Such displays may not be far off: LCD TVs that boast 240-hertz refresh rates have already appeared on the market, just a few years after 120-hertz TVs made their debut.

“Holography works, it’s beautiful, nothing can touch its quality,” says Douglas Lanman, a postdoc at the Media Lab and one of the new paper’s co-authors. “The problem, of course, is that holograms don’t move. To make them move, you need to create a hologram in real time, and to do that, you need … little tiny pixels, smaller than anything we can build at large volume at low cost. So the question is, what do we have now? We have LCDs. They’re incredibly mature, and they’re cheap.”

Layers of research

The Nintendo 3DS — a portable, glasses-free 3-D gaming device introduced last year — uses two layered LCD screens to produce the illusion of depth, with the bottom screen simply displaying alternating dark and light bands. Two slightly offset images, which represent the different perspectives of the viewer’s two eyes, are sliced up and interleaved on the top screen. The dark bands on the bottom screen block the light coming from the display’s backlight in such a way that each eye sees only the image intended for it.

This technique is in fact more than a century old and produces a stereoscopic image, the type of single-perspective illusion familiar from 3-D movies. The bottom screen displays the same pattern of light and dark bands no matter the image on the top screen. But Lanman, graduate student Matthew Hirsch and professor Ramesh Raskar, who leads the Camera Culture group, reasoned that by tailoring the patterns displayed on the top and bottom screens to each other, they could filter the light emitted by the display in more sophisticated ways, creating an image that would change with varying perspectives. In a project they dubbed HR3D, they developed algorithms for generating the top and bottom patterns as well as a prototype display, which they presented at Siggraph Asia in 2010.

The problem is that, whereas a stereoscopic system such as a 3-D movie projector or the 3DS needs to display only two perspectives on a visual scene — one for each eye — the system the Media Lab researchers envisioned had to display hundreds of perspectives in order to accommodate a moving viewer. That was too much information to display at once, so for every frame of 3-D video, the HR3D screen in fact flickered 10 times, displaying slightly different patterns each time. With this approach, however, producing a convincing 3-D illusion would require displays with a 1,000-hertz refresh rate.

To get the refresh rate down to 360 hertz, the Tensor Display adds another LCD screen, which displays yet another pattern. That makes the problem of calculating the patterns exponentially more complex, however. In solving that problem, Raskar, Lanman and Hirsch were joined by Gordon Wetzstein, a new postdoc in the Camera Culture group.

The researchers’ key insight was that, while some aspects of a scene change with the viewing angle, some do not. The pattern-calculating algorithms exploit this natural redundancy, reducing the amount of information that needs to be sent to the LCD screens and thus improving the resolution of the final image.

CT in reverse

As it turns out, the math behind the Tensor Display is similar to that behind computed tomography, or CT, an X-ray technique used to produce three-dimensional images of internal organs. In a CT scan, a sensor makes a slow circle around the subject, making a series of measurements of X-rays passing through the subject’s body. Each measurement captures information about the composition of tissues at different distances from the sensor; finally, all the information is stitched together into a composite 3-D image.

“The way I like to think about it is, we’re building a patient whose CT scan is the view,” Lanman says.

At Siggraph, the Media Lab researchers will demonstrate a prototype Tensor Display that uses three LCD panels. They’ve also developed another prototype that uses only two panels, but between the panels they introduce a sheet of lenses that refract light left and right. The lenses were actually developed for stereoscopic display systems; an LCD panel beneath the lenses alternately displays one image intended for the left eye, which is diffracted to the left, and another for the right eye, which is diffracted to the right. The MIT display also takes advantage of the ability to project different patterns in different directions, but the chief purpose of the lenses is to widen the viewing angle of the display. With the three-panel version, the 3-D illusion is consistent within a viewing angle of 20 degrees, but with the refractive-lens version, the viewing angle expands to 50 degrees.

“The paper reveals how you would greatly improve the realism, and image depth, and physical simplicity of 3-D display systems, particularly those that don’t require you to wear glasses,” says Gregg Favalora, a principal at the engineering consultancy Optics for Hire and co-chair of the SPIE Stereoscopic Displays and Applications Conference. “It’s only possible when you have these really good mathematicians and signal-processing guys and optics experts all sitting in the same room.”

“It’s definitely suitable for commercial applications, because each component is commonplace, and it sounds easy to manufacture, so this ought to be something that a consumer-electronics company would license,” Favalora adds. “Honestly, this is a really big deal.”

SOURCE PHYS

Dark galaxies of the early Universe spotted for the first time

2012-07-11T05:32:00.000-07:00

Dark galaxies are small, gas-rich galaxies in the early Universe that are very inefficient at forming stars. They are predicted by theories of galaxy formation and are thought to be the building blocks of today's bright, star-filled galaxies. Astronomers think that they may have fed large galaxies with much of the gas that later formed into the stars that exist today.

Because they are essentially devoid of stars, these dark galaxies don't emit much light, making them very hard to detect. For years astronomers have been trying to develop new techniques that could confirm the existence of these galaxies. Small absorption dips in the spectra of background sources of light have hinted at their existence. However, this new study marks the first time that such objects have been seen directly.

"Our approach to the problem of detecting a dark galaxy was simply to shine a bright light on it." explains Simon Lilly (ETH Zurich, Switzerland), co-author of the paper. "We searched for the fluorescent glow of the gas in dark galaxies when they are illuminated by the ultraviolet light from a nearby and very bright quasar. The light from the quasar makes the dark galaxies light up in a process similar to how white clothes are illuminated by ultraviolet lamps in a night club."

The team took advantage of the large collecting area and sensitivity of the Very Large Telescope (VLT), and a series of very long exposures, to detect the extremely faint fluorescent glow of the dark galaxies. They used the FORS2 instrument to map a region of the sky around the bright quasar HE 0109-3518, looking for the ultraviolet light that is emitted by hydrogen gas when it is subjected to intense radiation. Because of the expansion of the Universe, this light is actually observed as a shade of violet by the time it reaches the VLT.

"After several years of attempts to detect fluorescent emission from dark galaxies, our results demonstrate the potential of our method to discover and study these fascinating and previously invisible objects," says Sebastiano Cantalupo (University of California, Santa Cruz), lead author of the study.

This image shows 12 close-up images of dark galaxies. These are essentially devoid of stars and would normally be invisible to telescopes. However, their gas is being illuminated by the intense light from a nearby quasar, making them visible to the VLT. Credit: ESO, Digitized Sky Survey 2 and S. Cantalupo (UCSC)

The team detected almost 100 gaseous objects which lie within a few million light-years of the quasar. After a careful analysis designed to exclude objects where the emission might be powered by internal star-formation in the galaxies, rather than the light from the quasar, they finally narrowed down their search to 12 objects. These are the most convincing identifications of dark galaxies in the early Universe to date.

The astronomers were also able to determine some of the properties of the dark galaxies. They estimate that the mass of the gas in them is about 1 billion times that of the Sun, typical for gas-rich, low-mass galaxies in the early Universe. They were also able to estimate that the star formation efficiency is suppressed by a factor of more than 100 relative to typical star-forming galaxies found at similar stage in cosmic history.

"Our observations with the VLT have provided evidence for the existence of compact and isolated dark clouds. With this study, we've made a crucial step towards revealing and understanding the obscure early stages of galaxy formation and how galaxies acquired their gas", concludes Sebastiano Cantalupo.

The MUSE integral field spectrograph, which will be commissioned on the VLT in 2013, will be an extremely powerful tool for the study of these objects.

SOURCE PHYS

New nanodevice builds electricity from tiny pieces

2012-07-06T09:37:00.001-07:00

A team of scientists at the National Physical Laboratory (NPL) and University of Cambridge has made a significant advance in using nano-devices to create accurate electrical currents. Electrical current is composed of billions and billions of tiny particles called electrons. They have developed an electron pump - a nano-device - which picks these electrons up one at a time and moves them across a barrier, creating a very well-defined electrical current.

The device drives electrical current by manipulating individual electrons, one-by-one at very high speed. This technique could replace the traditional definition of electrical current, the ampere, which relies on measurements of mechanical forces on current-carrying wires.

The key breakthrough came when scientists experimented with the exact shape of the voltage pulses that control the trapping and ejection of electrons. By changing the voltage slowly while trapping electrons, and then much more rapidly when ejecting them, it was possible to massively speed up the overall rate of pumping without compromising the accuracy.

By employing this technique, the team were able to pump almost a billion electrons per second, 300 times faster than the previous record for an accurate electron pump set at the National Institute of Standards and Technology (NIST) in the USA in 1996.

Although the resulting current of 150 picoamperes is small (ten billion times smaller than the current used when boiling a kettle), the team were able to measure the current with an accuracy of one part-per-million, confirming that the electron pump was accurate at this level. This result is a milestone in the precise, fast, manipulation of single electrons and an important step towards a re-definition of the unit ampere.

As reported in Nature Communications, the team used a nano-scale semiconductor device called a 'quantum dot' to pump electrons through a circuit. The quantum dot is a tiny electrostatic trap less than 0.0001 mm wide. The shape of the quantum dot is controlled by voltages applied to nearby electrodes.

The dot can be filled with electrons and then raised in energy. By a process known as 'back-tunneling', all but one of the electrons fall out of the quantum dot back into the source lead. Ideally, just one electron remains trapped in the dot, which is ejected into the output lead by tilting the trap. When this is repeated rapidly this gives a current determined solely by the repetition rate and the charge on each electron - a universal constant of nature and the same for all electrons.

The research makes significant steps towards redefining the ampere by developing the application of an electron pump which improves accuracy rates in primary electrical measurement.

Masaya Kataoka of the Quantum Detection Group at NPL explains: "Our device is like a water pump in that it produces a flow by a cyclical action. The tricky part is making sure that exactly the same number of electronic charge is transported in each cycle.

The way that the electrons in our device behave is quite similar to water; if you try and scoop up a fixed volume of water, say in a cup or spoon, you have to move slowly otherwise you'll spill some. This is exactly what used to happen to our electrons if we went too fast."

Stephen Giblin also part of the Quantum Detection Group, added: "For the last few years, we have worked on optimising the design of our device, but we made a huge leap forward when we fine-tuned the timing sequence. We've basically smashed the record for the largest accurate single-electron current by a factor of 300.

Although moving electrons one at a time is not new, we can do it much faster, and with very high reliability - a billion electrons per second, with an accuracy of less than one error in a million operations.

Using mechanical forces to define the ampere has made a lot of sense for the last 60 or so years, but now that we have the nanotechnology to control single electrons we can move on.

The technology might seem more complicated, but actually a quantum system of measurement is more elegant, because you are basing your system on fundamental constants of nature, rather than things which we know aren't really constant, like the mass of the standard kilogram."

SOURCE PHYS

Dark matter underpinnings of cosmic web found

2012-07-05T03:35:00.001-07:00

THE skeleton of dark matter that undergirds the cosmic web of matter in the universe has been clearly detected for first time.

We know that matter in the cosmos forms a web, with galaxies and clusterslinked by filaments across mostly empty space. Filaments are made of normal matter and dark matter - the unseen stuff that makes up about 85 per cent of the universe's mass. Recent observations have seen the normal matter in such filaments.

Now Jörg Dietrich at the University Observatory in Munich, Germany, and his team have detected the dark matter component in a filament in a supercluster about 2.7 billion light years from us, called Abell 222/223.

The massive filament's gravity focuses the light travelling towards Earth from more distant background galaxies. The team used this light to calculate the filament's mass and shape. X-rays from the hot gas of normal matter in the vicinity showed that this matter lined up with the filament but made up only about 10 per cent of its mass. The rest must be dark matter (Nature, DOI: 10.1038/nature11224). This shows that the filament is "part of a network of dark matter that connects galaxy clusters throughout the universe", says Dietrich.

source NEW SCIENTIST

Confirmed: the Higgs boson does exist

2012-07-04T04:15:00.000-07:00

To cheers and standing ovations from scientists, the world's biggest atom smasher claimed the discovery of a new subatomic particle Wednesday, calling it "consistent" with the long-sought Higgs boson -- popularly known as the "God particle" -- that helps explain what gives all matter in the universe size and shape.

"We have now found the missing cornerstone of particle physics," Rolf Heuer, director of the European Center for Nuclear Research (CERN), told scientists.

He said the newly discovered subatomic particle is a boson, but he stopped just shy of claiming outright that it is the Higgs boson itself -- an extremely fine distinction.

"As a layman, I think we did it," he told the elated crowd. "We have a discovery. We have observed a new particle that is consistent with a Higgs boson."

The Higgs boson, which until now has been a theoretical particle, is seen as the key to our understanding of why matter has mass, which combines with gravity to give an object weight. The idea is much like gravity and Isaac Newton's discovery of it: Gravity was there all the time before Newton explained it. But now scientists know what a boson is and can put that knowledge to further use.

CERN's atom smasher, the $10 billion Large Hadron Collider on the Swiss-French border, has been creating high-energy collisions of protons to investigate dark matter, antimatter and the creation of the universe, which many theorize occurred in a massive explosion known as the Big Bang.

Two independent teams at CERN said Wednesday they have both "observed" a new subatomic particle -- a boson. Heuer called it "most probably a Higgs boson, but we have to find out what kind of Higgs boson it is. "
Asked whether the find is a discovery, Heuer answered, "As a layman, I think we have it. But as a scientist, I have to say, `"What do we have?' "

The leaders of the two teams -- Joe Incandela, head of CMS with 2,100 scientists, and Fabiola Gianotti, head of ATLAS with 3,000 scientists -- each presented in complicated scientific terms what was essentially extremely strong evidence of a new particle.

Incandela said it was too soon to say definitively whether it is the "standard model" Higgs that Scottish physicist Peter Higgs and others predicted in the 1960s. That was part of a standard model theory of physics involving an energy field where particles interact with a key particle, the Higgs boson. Asked his opinion, Higgs said he also could not yet say.
The stunning work elicited standing ovations and frequent applause at a packed auditorium in CERN as Gianotti and Incandela each took their turn.
Incandela called it "a Higgs-like particle" and said "we know it must be a boson and it's the heaviest boson ever found."

"Thanks, nature!" Gianotti said to laughs, giving thanks for the discovery.
The phrase "God particle" was coined by Nobel Prize-winning physicist Leon Lederman but is used by laymen, not physicists, as an easier way of explaining how the subatomic universe works and got started.

SOURCE FOX NEWS

A Rare Look at Quantum Mechanics in Action

2012-06-30T23:36:00.001-07:00

In a world where seeing is believing, one of the chief disadvantages of quantum physics, unlike Newtonian physics, is that it’s largely invisible. The wonderfully bizarre rules that allow a vanishingly small particle to exist in two places simultaneously, or two seemingly isolated particles to influence each other across space—what Einstein called spooky action at distance—usually apply at scales too small to be seen by the naked eye. But not always. Here, physicist Boaz Almog of Israeli’s Tel Aviv University gives audience members of the 5th Annual World Science Festival Gala Celebration—and now the rest of us—a rare macroscopic view of the magical properties of quantum mechanics. Sharing the stage with fellow physicist Brian Green, Almog conducts the first public demonstration of an ethereal phenomenon he calls quantum levitation, sending a thin wafer super-chilled below -301 degrees F zipping around a circular track like a miniature flying saucer. Boaz also makes the wafer hover in midair, frozen as though trapped in a vat of invisible glue. How? Watch as Greene explains.

source world science festival

Is Death An Illusion? Evidence Suggests Death Isn’t the End

2012-06-22T22:45:00.000-07:00

After the death of his old friend, Albert Einstein said “Now Besso has departed from this strange world a little ahead of me. That means nothing. People like us … know that the distinction between past, present and future is only a stubbornly persistent illusion.”

New evidence continues to suggest that Einstein was right – death isan illusion.

Our classical way of thinking is based on the belief that the world has an objective observer-independent existence. But a long list of experiments shows just the opposite. We think life is just the activity of carbon and an admixture of molecules – we live awhile and then rot into the ground.

We believe in death because we’ve been taught we die. Also, of course, because we associate ourselves with our body and we know bodies die. End of story. But biocentrism – a new theory of everything – tells us death may not be the terminal event we think. Amazingly, if you add life and consciousness to the equation, you can explain some of the biggest puzzles of science. For instance, it becomes clear why space and time – and even the properties of matter itself – depend on the observer. It also becomes clear why the laws, forces, and constants of the universe appear to be exquisitely fine-tuned for the existence of life.

Until we recognize the universe in our heads, attempts to understand reality will remain a road to nowhere.

Consider the weather ‘outside’: You see a blue sky, but the cells in your brain could be changed so the sky looks green or red. In fact, with a little genetic engineering we could probably make everything that is red vibrate or make a noise, or even make you want to have sex like with some birds. You think its bright out, but your brain circuits could be changed so it looks dark out. You think it feels hot and humid, but to a tropical frog it would feel cold and dry. This logic applies to virtually everything. Bottom line: What you see could not be present without your consciousness.

In truth, you can’t see anything through the bone that surrounds your brain. Your eyes are not portals to the world. Everything you see and experience right now – even your body – is a whirl of information occurring in your mind. According to biocentrism, space and time aren’t the hard, cold objects we think. Wave your hand through the air – if you take everything away, what’s left? Nothing. The same thing applies for time. Space and time are simply the tools for putting everything together.

Consider the famous two-slit experiment. When scientists watch a particle pass through two slits in a barrier, the particle behaves like a bullet and goes through one slit or the other. But if you don’t watch, it acts like a wave and can go through both slits at the same time. So how can a particle change its behavior depending on whether you watch it or not? The answer is simple – reality is a process that involves your consciousness.

Or consider Heisenberg’s famous uncertainty principle. If there is really a world out there with particles just bouncing around, then we should be able to measure all their properties. But you can’t. For instance, a particle’s exact location and momentum can’t be known at the same time. So why should it matter to a particle what you decide to measure? And how can pairs of entangled particles be instantaneously connected on opposite sides of the galaxy as if space and time don’t exist? Again, the answer is simple: because they’re not just ‘out there’ – space and time are simply tools of our mind.

Death doesn’t exist in a timeless, spaceless world. Immortality doesn’t mean a perpetual existence in time, but resides outside of time altogether.

Our linear way of thinking about time is also inconsistent with another series of recent experiments. In 2002, scientists showed that particles of light “photons” knew – in advance – what their distant twins would do in the future. They tested the communication between pairs of photons. They let one photon finish its journey – it had to decide whether to be either a wave or a particle. Researchers stretched the distance the other photon took to reach its own detector. However, they could add a scrambler to prevent it from collapsing into a particle. Somehow, the first particle knew what the researcher was going to do before it happened – and across distances instantaneously as if there were no space or time between them. They decide not to become particles before their twin even encounters the scrambler. It doesn’t matter how we set up the experiment. Our mind and its knowledge is the only thing that determines how they behave. Experiments consistently confirm these observer-dependent effects.

Bizarre? Consider another experiment that was recently published in the prestigious scientific journal Science (Jacques et al, 315, 966, 2007). Scientists in France shot photons into an apparatus, and showed that what they did could retroactively change something that had already happened in the past. As the photons passed a fork in the apparatus, they had to decide whether to behave like particles or waves when they hit a beam splitter. Later on – well after the photons passed the fork – the experimenter could randomly switch a second beam splitter on and off. It turns out that what the observer decided at that point, determined what the particle actually did at the fork in the past. At that moment, the experimenter chose his past.

Of course, we live in the same world. But critics claim this behavior is limited to the microscopic world. But this ‘two-world’ view (that is, one set of physical laws for small objects, and another for the rest of the universe including us) has no basis in reason and is being challenged in laboratories around the world. A couple years ago, researchers published a paper in Nature (Jost et al, 459, 683, 2009) showing that quantum behavior extends into the everyday realm. Pairs of vibrating ions were coaxed to entangle so their physical properties remained bound together when separated by large distances (“spooky action at a distance,” as Einstein put it). Other experiments with huge molecules called ‘Buckyballs’ also show that quantum reality extends beyond the microscopic world. And in 2005, KHC03 crystals exhibited entanglement ridges one-half inch high, quantum behavior nudging into the ordinary world of human-scale objects.

We generally reject the multiple universes of Star Trek as fiction, but it turns out there is more than a morsel of scientific truth to this popular genre. One well-known aspect of quantum physics is that observations can’t be predicted absolutely. Instead, there is a range of possible observations each with a different probability. One mainstream explanation, the “many-worlds” interpretation, states that each of these possible observations corresponds to a different universe (the ‘multiverse’). There are an infinite number of universes and everything that could possibly happen occurs in some universe. Death does not exist in any real sense in these scenarios. All possible universes exist simultaneously, regardless of what happens in any of them.

Life is an adventure that transcends our ordinary linear way of thinking. When we die, we do so not in the random billiard-ball-matrix but in the inescapable-life-matrix. Life has a non-linear dimensionality – it’s like a perennial flower that returns to bloom in the multiverse.

“The influences of the senses,” said Ralph Waldo Emerson “has in most men overpowered the mind to the degree that the walls of space and time have come to look solid, real and insurmountable; and to speak with levity of these limits in the world is the sign of insanity.

FACEBOOK ACQUIRES FACE RECOGNITION SITE

2012-06-20T01:11:00.000-07:00

Facebook has announced plans to buy the face recognition site Face.com, along with its free mobile app,Klik, which recognizes friends in photos to make tagging on Facebook easier. The acquisition means this feature could be added to Facebook’s mobile app or to the site itself, with possible Instagram integration.

Facebook announced Monday that it will acquire facial recognition firm Face.com, an Israeli company that has worked with the social network for nearly two years to identify and tag people in uploaded photos.

Integrating Face.com's facial recognition capabilities into Facebook marks an effort to encourage even more photo sharing on the social network and, further down the road, could yield new advertising opportunities or even features that bring facial recognition to the physical world, experts say. That extra convenience, tagging photos based on friends' faces, whether on a smartphone or laptop, is also likely to bring a fresh round of privacy concerns over the limits of Facebook's reach into its users' lives.

"Today, facial recognition for Facebook is about photographs. But future uses of this technology could absolutely extend to recognizing people in the real world," said Forrester analyst Sarah Rotman Epps. "Facebook is becoming a search engine for people. It's building a catalog of humans, and today that’s a two dimensional experience. Tomorrow it will take place in the physical world."

Facebook declined to specify how it will integrate Face.com's team and technology into its offerings. A spokeswoman for the social network told The Huffington Post in an email, “People who use Facebook enjoy sharing photos and memories with their friends, and Face.com’s technology has helped to provide the best photo experience. This transaction simply brings a world-class team and a long-time technology vendor in house.”

Face.com's technology, which has been available to Facebook members since 2010, enhances the social network's core strength: photos. Face.com's facial recognition tools spare users the trouble of manually tagging friends in each image they upload, and instead scans the faces of people in photos to suggest names.

For Facebook, an uploaded photograph is good, but an uploaded photograph that's been tagged is even better: It's more likely to be seen by a greater number of people, and in turn helps Facebook provide the up-to-the-minute personal information that keeps users returning to the site. The visibility of photos depends on a user's privacy settings, but generally speaking, if my friend Jason uploads a photo of me and doesn't tag me in it, only Jason's friends will be able to see the image. On the other hand, if Jason tags me in the picture, friends of mine who don't know Jason will see the image of me in their News Feed.

Who needs particle accelerators when you can just use black holes?

2012-06-18T22:41:00.000-07:00

As any particle physicist will tell you, if you want to find new particles, you're going to need a lot of energy. This is why huge accelerators are used to propel particles to nearly the speed of light.

But scientists are now suggesting that there may be another way — if we can detect some previously undiscovered particles, called axions, as they accumulate around black holes. An axion is a hypothetical elementary particle with a very low mass. It was postulated by the Peccei-Quinn theory in 1977 to resolve a nasty problem in quantum physics.

Because Einstein said that mass is directly related to energy, it is assumed that very little energy is required to produce these axions. The trick now is for scientists to find them.

And to perform that trick, Daniel Grumiller and Gabriela Mocanu of the Vienna University of Technology have turned their attention to quantum physics, which suggests that every particle can be described as a wave. Because the wavelength corresponds to a particle's energy, heavy particles have small wavelengths, but the low-energy axions would have wavelengths that extend many kilometers.

Research by Grumiller and Mocanu, in conjunction with work done by Asmina Arvanitaki and Sergei Dubovsky, show that axions can circle a black hole, similar to electrons circling the nucleus of an atom. But instead of the electromagnetic force, it is the gravitational force which acts between the axions and the black hole.

There's another very important difference that distinguishes electrons and atoms from axions and black holes: Electrons are fermions and axions are bosons. Fermions can never be in the same state, whereas many bosons can occupy the same quantum state at the same time. This results in the so-called "boson-cloud" which surrounds a black hole. It is supposed that the boson-cloud continuously draws energy from the black hole, causing the number of axions in the cloud to increase.

But the researchers suggest that this cloud is not necessarily stable — which is good news. In apress release, Daniel Grumiller explained: "Just like a loose pile of sand, which can suddenly slide, triggered by one single additional grain of sand, this boson cloud can suddenly collapse." When this collapse happens, a "bose-nova" (no, not Brazilian dance music) could be measured, an event that would make space and time vibrate and emit gravity waves.

So, are Grumiller and Mocanu right? We won't know until at least 2016 – the year a new gravity wave detector will be constructed with enough sensitivity to detect the ones emitted by the bose-novas. In the meantime, we'll just have to stick with particle accelerators.

Image provided by the Vienna University of technology

Technical: Line follower Robot - without using Microcontrolle...

2012-06-17T22:46:00.001-07:00

Technical: Line follower Robot - without using Microcontrolle...: Difficulty Rating : 3/10 Ever wanted to make a Line follower Robot, 'without' using Microcontroller ??? Then you have visited a right p...

GATE Electronics and Communication Syllabus

2012-06-17T02:48:00.000-07:00

SYLLABUS FOR ELECTRONICS ANDCOMMUNICATION ENGINEERING (EC)

Engineering Mathematics

Linear Algebra:

Matrix Algebra, Systems of linear equations, Eigen values and eigen vectors.

Calculus:

Mean value theorems, Theorems of integral calculus, Evaluation of definite and

improper integrals, Partial Derivatives, Maxima and minima, Multiple integrals, Fourier

series. Vector identities, Directional derivatives, Line, Surface and Volume integrals,

Stokes, Gauss and Green's theorems.

Differential equations:

First order equation (linear and nonlinear), Higher order linear differential equations with
constant coefficients, Method of variation of parameters, Cauchy's and Euler's
equations, Initial and boundary value problems, Partial Differential Equations and
variable separable method.

Complex variables:

Analytic functions, Cauchy's integral theorem and integral formula, Taylor's and Laurent'
series, Residue theorem, solution integrals.

Probability and Statistics:

Sampling theorems, Conditional probability, Mean, median, mode and standard
deviation, Random variables, Discrete and continuous distributions, Poisson, Normal
and Binomial distribution, Correlation and regression analysis.

Numerical Methods:

Solutions of non-linear algebraic equations, single and multi-step methods for
differential equations.

Transform Theory:

Fourier transform, Laplace transform, Z-transform.

Electronics and Communication Engineering

Networks:

Network graphs: matrices associated with graphs; incidence, fundamental cut set and
fundamental circuit matrices. Solution methods: nodal and mesh analysis. Network
theorems: superposition, Thevenin and Norton's maximum power transfer, Wye-Delta
transformation. Steady state sinusoidal analysis using phasors. Linear constant
coefficient differential equations; time domain analysis of simple RLC circuits, Solution
of network equations using Laplace transform: frequency domain analysis of RLC
circuits. 2-port network parameters: driving point and transfer functions. State equations
for networks.

Electronic Devices:

Energy bands in silicon, intrinsic and extrinsic silicon. Carrier transport in silicon:
diffusion current, drift current, mobility, and resistivity. Generation and recombination of
carriers. p-n junction diode, Zener diode, tunnel diode, BJT, JFET, MOS capacitor,
MOSFET, LED, p-I-n and avalanche photo diode, Basics of LASERs. Device
technology: integrated circuits fabrication process, oxidation, diffusion, ion implantation,
photolithography, n-tub, p-tub and twin-tub CMOS process.

Analog Circuits:

Small Signal Equivalent circuits of diodes, BJTs, MOSFETs and analog CMOS. Simple
diode circuits, clipping, clamping, rectifier. Biasing and bias stability of transistor and
FET amplifiers. Amplifiers: single-and multi-stage, differential and operational, feedback,
and power. Frequency response of amplifiers. Simple op-amp circuits. Filters.
Sinusoidal oscillators; criterion for oscillation; single-transistor and op-amp
configurations. Function generators and wave-shaping circuits, 555 Timers. Power
supplies.

Digital circuits:

Boolean algebra, minimization of Boolean functions; logic gates; digital IC families (DTL,
TTL, ECL, MOS, CMOS). Combinatorial circuits: arithmetic circuits, code converters,
multiplexers, decoders, PROMs and PLAs. Sequential circuits: latches and flip-flops,
counters and shift-registers. Sample and hold circuits, ADCs, DACs. Semiconductor
memories. Microprocessor(8085): architecture, programming, memory and I/O
interfacing.

Signals and Systems:

Definitions and properties of Laplace transform, continuous-time and discrete-time
Fourier series, continuous-time and discrete-time Fourier Transform, DFT and FFT, ztransform.
Sampling theorem. Linear Time-Invariant (LTI) Systems: definitions and
properties; causality, stability, impulse response, convolution, poles and zeros, parallel
and cascade structure, frequency response, group delay, phase delay. Signal
transmission through LTI systems.

Control Systems:

Basic control system components; block diagrammatic description, reduction of block
diagrams. Open loop and closed loop (feedback) systems and stability analysis of these
systems. Signal flow graphs and their use in determining transfer functions of systems;
transient and steady state analysis of LTI control systems and frequency response.
Tools and techniques for LTI control system analysis: root loci, Routh-Hurwitz criterion,
Bode and Nyquist plots. Control system compensators: elements of lead and lag
compensation, elements of Proportional-Integral-Derivative (PID) control. State variable
representation and solution of state equation of LTI control systems.

Communications:

Random signals and noise: probability, random variables, probability density function,
autocorrelation, power spectral density. Analog communication systems: amplitude and
angle modulation and demodulation systems, spectral analysis of these operations,
superheterodyne receivers; elements of hardware, realizations of analog
communication systems; signal-to-noise ratio (SNR) calculations for amplitude
modulation (AM) and frequency modulation (FM) for low noise conditions.
Fundamentals of information theory and channel capacity theorem. Digital
communication systems: pulse code modulation (PCM), differential pulse code
modulation (DPCM), digital modulation schemes: amplitude, phase and frequency shift
keying schemes (ASK, PSK, FSK), matched filter receivers, bandwidth consideration
and probability of error calculations for these schemes. Basics of TDMA, FDMA and
CDMA and GSM.

Electromagnetics:

Elements of vector calculus: divergence and curl; Gauss' and Stokes' theorems,
Maxwell's equations: differential and integral forms. Wave equation, Poynting vector.
Plane waves: propagation through various media; reflection and refraction; phase and
group velocity; skin depth. Transmission lines: characteristic impedance; impedance
transformation; Smith chart; impedance matching; S parameters, pulse excitation.
Waveguides: modes in rectangular waveguides; boundary conditions; cut-off
frequencies; dispersion relations. Basics of propagation in dielectric waveguide and
optical fibers. Basics of Antennas: Dipole antennas; radiation pattern; antenna gain.

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Switchable Nano Magnets May Revolutionize Data Storage: Magnetism of Individual Molecules Switched

2012-06-14T21:39:00.000-07:00

ScienceDaily (June 14, 2012) — Using individual molecules instead of electronic or magnetic memory cells would revolutionise data storage technology, as molecular memories could be thousand-fold smaller. Scientists of Kiel University took a big step towards developing such molecular data storage. They succeeded in selectively switching on and off the magnetism of individual molecules, so-called spin-crossover complexes, by electrons.

The interdisciplinary study is part of the Collaborative Research Centre 677 "Functions by Switching," which is funded by the German Research Foundation (DFG). The results prove that it is technically possible to store information using molecules. The study will be published on June 25th in the German science magazineAngewandte Chemie (Applied Chemistry).

"In principle information may be stored in a single molecule. However, techniques that would make such an approach feasible are becoming available just now," explains project leader Professor Richard Berndt of the Institute of Experimental and Applied Physics at Kiel University. Since the 1980s scientists are able to image individual molecules on surfaces with scanning tunnelling microscopes, he continues. Current research aims at controlling the characteristics of single molecules in order to facilitate future technical applications. The Collaborative Research Centre 677 "Functions by Switching" at Kiel University is a large-scale project engaged in such investigations, which aim at constructing molecular machines.

The current study is focused on the magnetism of molecules. Using a scanning tunnelling microscope Dr. Thiruvancheril Gopakumar, who carried out the study, was able to switch individual molecules between two magnetic states. Despite their dense packing in a molecular layer he was able to target individual molecules for switching. "Many research groups are striving to control the magnetic characteristics of molecules. Gopakumar's studies have taken us one step ahead," says Berndt.

The molecules (spin-crossover complexes) were synthesised at the Institute of Inorganic Chemistry at Kiel University. "Even though it took us a long time to find adequate molecules, we are very pleased with the outcome," states Professor Felix Tuczek, head of the research group "Inorganic Molecular Chemistry." The next step will be to adapt the molecules in a way that would allow scientists to switch them with light instead of electrons and at higher temperatures.

Breaking the limits of classical physics

2012-06-14T02:27:00.000-07:00

In the quantum optical laboratories at the Niels Bohr Institute, researchers have conducted experiments that show that light breaks with the classical physical principles. The studies show that light can have both an electrical and a magnetic field, but not at the same time. That is to say, light has quantum mechanical properties.

In physics there are two categories: classical physics and quantum physics. In classical physics, objects, e.g. a car or a ball, have a position and a velocity. This is how we classically look at our everyday world. In the quantum world objects can also have a position and a velocity, but not at the same time. At the atomic level, quantum mechanics says that nature behaves quite differently than you might think. It is not just that we do not know the position and the velocity, rather, these two things simply do not exist simultaneously. But how do we know that they do not exist simultaneously? And where is the border of these two worlds? Researchers have found a new way to answer these questions.

Light on quantum mechanics

“Our goal is to use quantum mechanics in a new way. It is therefore important for us to know that a ‘system’ really behaves in a way that has no classical explanation. To this end, we first examined light,” explains Eran Kot, PhD-student in the research group, Quantum Optics at the Niels Bohr Institute at the University of Copenhagen.

Based on a series of experiments in the quantum optics laboratories, they examined the state of light. In classical physics, light possesses both an electric and a magnetic field.

“What our study demonstrated was that light can have both an electric and a magnetic field, but not at the same time. We thus provide a simple proof that an experiment breaks the classical principles. That is to say, we showed light possesses quantum properties, and we can expand this to other systems as well” says Eran Kot.

Classical and non-classical mechanics

The aim of the research is both to fundamentally understand the world, but there is also a practical challenge in being able to exploit quantum mechanics in larger contexts. For light it is no great surprise that it behaves quantum mechanically, but the methods that have been developed can also be used to study other systems.

“We are endeavouring to develop future quantum computers and we therefore need to understand the borders for when something behaves quantum mechanically and when it is classical mechanics,” says professor of quantum physics Anders S. Sørensen, explaining that quantum computing must necessarily be comprised of systems with non-classical properties.

Graphene on boron nitride work may lead to breakthrough in microchip technology

2012-06-14T02:19:00.001-07:00

Graphene is the wonder material that could solve the problem of making ever faster computers and smaller mobile devices when current silicon microchip technology hits an inevitable wall. Graphene, a single layer of carbon atoms in a tight hexagonal arrangement, has been highly researched because of its incredible electronic properties, with theoretical speeds 100 times greater than silicon. But putting the material into a microchip that could outperform current silicon technology has proven difficult.

The answer may lie in new nanoscale systems based on ultrathin layers of materials with exotic properties. Called two-dimensional layered materials, these systems could be important for microelectronics, various types of hypersensitive sensors, catalysis,tissue engineering and energy storage. Researchers at Penn State have applied one such 2D layered material, a combination of graphene and hexagonal boron nitride, to produce improved transistor performance at an industrially relevant scale.

“Other groups have shown that graphene on boron nitride can improve performance two to three times, but not in a way that could be scaled up. For the first time, we have been able to take this material and apply it to make transistors at wafer scale,” said Joshua Robinson, assistant professor of materials science and engineering at Penn State and the corresponding author on a paper reporting their work in the online version of the journal ACS Nano.

In the article, the Penn State team describes a method for integrating a thin layer of graphene only one or two atoms thick, with a second layer of hexagonal boron nitride (hBN) with a thickness of a few atoms up to several hundred atoms. The resulting bilayer material constitutes the next step in creating functional graphene field effect transistors for high frequency electronic and optoelectronic devices.

Previous research by other groups has shown that a common material called hexagonal boron nitride (hBN), a synthetic mixture of boron and nitrogen that is used as an industrial lubricant and is found in many cosmetics, is a potential replacement for silicon dioxide and other high-performance dielectrics that have failed to integrate well with graphene. Because boron sits next to carbon on the periodic table, and hexagonal boron nitride has a similar arrangement of atoms as graphene, the two materials match up well electronically. In fact, hBN is often referred to as white graphene. To be of more than academic interest in the lab, however, the hBN-graphene bilayer had to be grown at wafer scale – from around 3 inches (75 mm) to almost 12 inches (300 mm).

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My Science Books: PIN CONFIGURATION OF 8085

2012-06-12T23:06:00.001-07:00

My Science Books: PIN CONFIGURATION OF 8085

PIN CONFIGURATION OF 8085

2012-06-12T22:46:00.002-07:00

AAA
Address bus (A6 -A15)
The most significant 8 bits of the memory address or the 8 bits of the I/0

address,3 stated during Hold and Halt modes.

Mulitiplexed Address/DataBus (AD0 - AD7 )

Multiplexed Address/Data Bus; Lower 8 bits of the memory address (or I/0 address)
appear on the bus during the first clock cycle of a machine state. It then becomes the
data bus during the second and third clock cycles. 3 stated during Hold and Halt
modes.

ALE (Output)

Address Latch Enable: It occurs during the first clock cycle of a machine state and
enables the address to get latched into the on chip latch of peripherals. The falling
edge of ALE is set to guarantee setup and hold times for the address information.
ALE can also be used to strobe the status information. ALE is never 3stated.

SO, S1 (Output)

S1 S0
O O HALT
0 1 WRITE
1 0 READ
1 1 FETCH

S1 can be used as an advanced R/W status.

RD
READ; indicates the selected memory or 1/0 device is to be read and that the Data
Bus is available for the data transfer.

WR
WRITE; indicates the data on the Data Bus is to be written into the selected memory
or 1/0 location. Data is set up at the trailing edge of WR. 3stated during Hold and Halt
modes.

READY (Input)

If Ready is high during a read or write cycle, it indicates that the memory or
peripheral is ready to send or receive data. If Ready is low, the CPU will wait for
Ready to go high before completing the read or write cycle.

HOLD (Input)

HOLD; indicates that another Master is requesting the use of the Address and Data
Buses. The CPU, upon receiving the Hold request. will relinquish the use of buses as
soon as the completion of the current machine cycle. Internal processing can continue.
The processor can regain the buses only after the Hold is removed. When the Hold is
acknowledged, the Address, Data, RD, WR, and IO/M lines are 3stated.

HLDA
HOLD ACKNOWLEDGE; indicates that the CPU has received the Hold request and
that it will relinquish the buses in the next clock cycle. HLDA goes low after the Hold
request is removed. The CPU takes the buses one half clock cycle after HLDA goes
low.

INTR (Input)
INTERRUPT REQUEST; is used as a general purpose interrupt. It is sampled only
during the next to the last clock cycle of the instruction. If it is active, the Program
Counter (PC) will be inhibited from incrementing and an INTA will be issued. During
this cycle a RESTART or CALL instruction can be inserted to jump to the interrupt
service routine. The INTR is enabled and disabled by software. It is disabled by Reset
and immediately after an interrupt is accepted.

INTA (Output)
INTERRUPT ACKNOWLEDGE; is used instead of (and has the same timing as) RD
during the Instruction cycle after an INTR is accepted. It can be used to activate the
8259 Interrupt chip or some other interrupt port.
RST 5.5
RST 6.5 - (Inputs)
RST 7.5

RESTART INTERRUPTS; These three inputs have the same timing as I NTR except
they cause an internal RESTART to be automatically inserted.
RST 7.5 ~~ Highest Priority
RST 6.5
RST 5.5 o Lowest Priority
The priority of these interrupts is ordered as shown above. These interrupts have a
higher priority than the INTR.

TRAP (Input)
Trap interrupt is a nonmaskable restart interrupt. It is recognized at the same time as
INTR. It is unaffected by any mask or Interrupt Enable. It has the highest priority of
any interrupt.

RESET IN (Input)
Reset sets the Program Counter to zero and resets the Interrupt Enable and HLDA
flipflops. None of the other flags or registers (except the instruction register) are
affected The CPU is held in the reset condition as long as Reset is applied.

RESET OUT (Output)
Indicates CPlJ is being reset. Can be used as a system RESET. The signal is
synchronized to the processor clock.

X1, X2 (Input)
Crystal or R/C network connections to set the internal clock generator X1 can also be
an external clock input instead of a crystal. The input frequency is divided by 2 to
give the internal operating frequency.

CLK (Output)
Clock Output for use as a system clock when a crystal or R/ C network is used as an
input to the CPU. The period of CLK is twice the X1, X2 input period.

IO/M (Output)

IO/M indicates whether the Read/Write is to memory or l/O Tristated during Hold and
Halt modes.

SID (Input)
Serial input data line The data on this line is loaded into accumulator bit 7 whenever a
RIM instruction is executed.

SOD (output)

Serial output data line. The output SOD is set or reset as specified by the SIM
instruction.

Vcc
+5 volt supply.

Vss
Ground Reference.

How the Universe escaped its 'dark ages'

2012-06-12T02:34:00.000-07:00

or some time astronomers have known that following the big bang, a dense hydrogen ‘fog’ settled over the Universe. During this time, a lot of the light produced by the first stars could only travel short distances before it was absorbed by the fog. They call this period the ‘dark ages’ of the Universe, but little is known about what was happening at this time.

“During the dark ages, the hydrogen fog condensed in certain places, which allowed the formation of stars, black holes and the first galaxies,” said Swinburne University of Technology astrophysicist Dr Lee Spitler.

“These objects were the first significant sources of ultraviolet radiation, which eventually started to burn off the hydrogen fog much like the Sun burns off a morning fog on Earth. We call this process reionisation, because the hydrogen atoms are ionised by the ultraviolet light.

"But what was happening during the Universe’s dark ages is somewhat of a mystery because there are few light sources embedded in the hydrogen fog.

“Obtaining information about reionisation is quite challenging as it occurred so long ago. Since light takes time to reach us, astronomers can observe what was happening at that time, but it is very difficult and pushes modern telescopes to their limits.”

To address this problem, an international research team, led by Dr Spitler, tried a different approach: they looked for signs of reionisation in nearby galaxies, which are easier to observe.

“We used nearby galaxies to understand something that happened long ago, in much the same way fossils are used to understand Earth’s history,” said Swinburne Professor Duncan Forbes.

“We can see regions around galaxies where reionisation has just finished and use that information to understand important questions about the dark ages: What were the first stars like; how were the first galaxies formed; and were there many supermassive black holes?”

When reionisation occurs in a galaxy and clears out the hydrogen fog, it also disrupts the condensation of the fog into locations of new star formation.

The research team looked for signs of this stalled star formation in ancient star clusters and were able to measure when reionisation passed through the region around a galaxy.

By measuring when reionisation took place around three galaxies, including the Milky Way, the researchers found evidence that the hydrogen fog burned off first in isolated, low-density regions of the Universe. A few hundred million years later, reionisation took place in the dense, crowded regions of the Universe.

This suggests that galaxies in crowded regions of the Universe were more likely to be shrouded in very dense pockets of hydrogen fog. Such dense regions would therefore require larger numbers of light sources and more time to burn off the fog compared to regions with relatively light fog.

“Understanding how reionisation moved through the Universe is very, challenging. Our technique provides a novel way to tackle this problem,” Dr Spitler said.

The researchers used the Keck and Subaru telescopes in Hawaii for this work, which has been published in the Monthly Notices of the Royal Astronomical Society.

Silicene: substitute for graphene

2012-06-11T09:21:00.002-07:00

AFTER only a few years basking in the limelight, wonder material graphene has a competitor in the shape of silicene. For the first time, silicon has been turned into a sheet just one atom thick. Silicene is thought to have similar electronic properties to graphene but ought to be more compatible with silicon-based electronic devices.

Patrick Vogt of Berlin's Technical University in Germany, and colleagues at Aix-Marseille University in France created silicene by condensing silicon vapour onto a silver plate to form a single layer of atoms. They then measured the optical, chemical and electronic properties of the layer, showing it closely matched those predicted by theory (Physical Review Letters, DOI: 10.1103/PhysRevLett.108.155501).

Silicene may turn out to be a better bet than graphene for smaller and cheaper electronic devices because it can be integrated more easily into silicon chip production lines.

In 2010, another Aix-Marseille group led by Bernard Aufray attempted create silicene using a similar approach but failed to present convincing evidence that it was present. Michel Houssa of the Catholic University of Leuven (KUL) in Belgium, who was not involved in the new work, says: "In my opinion, this is the first compelling evidence that silicene can be grown on silver."

He says an important challenge now will be to grow silicene on insulating substrates to learn more about its electrical properties and understand how they can be exploited to build future electronic devices.

Einstein was right, neutrino researchers admit

2012-06-11T02:11:00.000-07:00

Researchers working at the European Centre for Nuclear Research (CERN) caused a storm last year when they published experimental results showing that neutrinos could out-pace light by some six kilometres (3.7 miles) per second.

The findings threatened to upend modern physics and smash a hole in Albert Einstein's 1905 theory of special relativity, which described the velocity of light as the maximum speed in the cosmos.

But CERN now says that the earlier results were wrong and faulty kit was to blame.

"Although this result isn't as exciting as some would have liked, it is what we all expected deep down," said the centre's research director Sergio Bertolucci.

"The story captured the public imagination, and has given people the opportunity to see the scientific method in action.

"An unexpected result was put up for scrutiny, thoroughly investigated and resolved in part thanks to collaboration between normally competing experiments. That's how science moves forward."

The neutrinos were timed on the journey from CERN's giant underground lab near Geneva to the Gran Sasso Laboratory in Italy, after travelling 732 kilometres (454 miles) through the Earth's crust.

To do the trip, the neutrinos should have taken 0.0024 seconds. Instead, the particles were recorded as hitting the detectors in Italy 0.00000006 seconds sooner than expected, the preliminary experiment had shown.

Researchers updated the science community on Friday at the International Conference on Neutrino Physics and Astrophysics, being held in Japan's ancient capital of Kyoto.

"The previous data taken up to 2011 with the neutrino beam from CERN to Gran Sasso were revised taking into account understood instrumental effects," the team said.

"A coherent picture has emerged with both previous and new data pointing to a neutrino velocity consistent with the speed of light."

The initial findings had been greeted with a combination of excitement and scepticism, even from those involved in the experiment, who urged other physicists to carry out their own checks to corroborate or refute what had been seen.

"If this result at CERN is proved to be right, and particles are found to travel faster than the speed of light, then I am prepared to eat my shorts, live on TV," Jim Al-Khalili, a professor of theoretical physics at Britain's University of Surrey, declared at the time.

Self Sculpting Sand

2012-06-10T23:11:00.001-07:00

Research currently underway at MIT’s Distributed Robotic Laboratory (DRL) could lead to an innovative replicative manufacturing technique with the disruptive potential equal to that of 3D printing. Imagine a sand-like material that could autonomously assemble itself into a replica of any object encased within. Incredible though this may sound, the DRL researchers have already managed to build a large scale proof-of-concept, with 10-mm cubes acting as the grains.

Before we go into how these cubes - or "smart pebbles" - work, let’s sketch out the general concept. The idea is to create objects using a subtractive method, where excess material is removed just like when carving in stone. Each grain of smart sand would be a self-contained micro computer. These tiny machines would use an elaborate algorithm to communicate with the neighboring particles in order to establish the exact position and shape of the input object so that it can be replicated.

The already mentioned smart pebbles demonstrate this principle in a more easily understandable 2D setting. First the pebbles establish which of them border on the perimeter of the object to be replicated. Once identified, these particles pass on a message to their neighbors, and effectively specific particles selected by the algorithm are notified that an identical (or scaled) arrangement should be recreated a safe distance away, so that the two shapes do not overlap.Once the perimeter of the copy is identified, the pebbles within that area bond to each other, while the redundant material simply falls away. The resultant object would be solid, but it could be easily deconstructed simply by putting it back into the heap of smart sand. The constituent grains would detach from each other and the whole process could be repeated with an entirely new shape.

Each smart pebble cube used for testing was equipped with a set of electro-permanent magnets on four sides. The magnetic properties of such magnets can be switched on and off using electrical impulses, but unlike electromagnets, they do not require electricity to sustain these properties over time. With each particle neighboring on eight other particles in a 2D scenario, the magnets allow for selective bonding with any of the neighbors. However, the magnets also play a role in communication and power sharing.

Each smart pebble was also fitted with a rudimentary microprocessor capable of storing 32 kilobytes of code and boasting two kilobytes of working memory. With such limited processing power at the disposal of a single unit, the main computational heft had to fall on the distributed intelligence algorithm that constitutes the core of the current DRL endeavors.
"How do you develop efficient algorithms that do not waste any information at the level of communication and at the level of storage?" asks Daniela Rus, a computer science and engineering professor at MIT. The answer to that question is likely to be found in a paper that Rus co-authored with her student, Kyle Gilpin, and which is going to be presented in May at the IEEE International Conference on Robotics and Automation.

The algorithms developed at DRL have already been shown to work robustly with 3D scenarios, where the bed of smart sand would be divided into layers, each constituting a separate 2D grid. Now the only thing that stops smart sand from joining 3D printing in revolutionizing the world of rapid manufacturing is getting the scale right.

But according to Robert Wood, an associate professor of electrical engineering at Harvard University, this is not an issue. Wood reckons recreating the functionalities of the smart pebbles in smaller scale is feasible. Yes, it would require quite a lot of engineering, but the goal is well defined and reachable. “That’s a well-posed but very difficult set of engineering challenges that they could continue to address in the future.”, he says. If Wood is right, the future of subtractive manufacturing is bright.

Watch the video below to find out more about the algorithm behind smart pebbles.

Source: MIT

Hawking's 'Escher-verse' could be theory of everything

2012-06-10T22:36:00.001-07:00

Stephen Hawking has come up with a way to describe the universe that suggests it may have the same geometry as mind-boggling images by M. C. Escher

THE universe may have the same surreal geometry as some of art's most mind-boggling images. That's the upshot of a study by the world's most famous living scientist, Stephen Hawking of the University of Cambridge.

The finding may delight fans of Dutch artist M. C. Escher, but Hawking's team claim that their study provides a way to square the geometric demands of string theory, a still-hypothetical "theory of everything", with the universe we observe.

Their calculations rely on a mathematical twist that was previously considered impossible. If it stands up, it could explain how the universe emerged from the big bang and unite gravity and quantum mechanics.

"We have a new route towards constructing string theory models of our world," says Hawking's colleague Thomas Hertog of the Institute for Theoretical Physics at the Catholic University of Leuven (KUL) in Belgium.

On the face of it, the idea that Escher's images can describe the layout of the universe seems to contradict what we know about it.

The images in question are tessellations, arrangements of repeated shapes, such as the images of interlocking bats and angels seen in Circle Limit IV. Although these are flat, they serve as "projections" of an alternative geometry called hyperbolic space, rather like a flat map of the world is a projection of a globe. For example, although the bats in the flat projection appear to shrink at an exponential rate at the edges, in hyperbolic space they are all the same size. These distortions in the projection arise because hyperbolic space cannot lie flat. Instead, it resembles a twisting, wiggly landscape of saddle-like hills.

That is not what our universe seems to look like. Measurements of the cosmic microwave background - the echo of the big bang - and distances to supernovae have revealed that our universe is flat, not twisted.

It is also expanding at an accelerating rate, because of a mysterious entity known as dark energy. We don't know what dark energy is or where it came from, but the mathematical language provided by Einstein's theory of general relativity has a way to describe this accelerated expansion. Sticking a constant - known as the cosmological constant - into the general-relativity equations keeps the universe expanding forever, but only if the constant has a positive sign. Until now, saying we live in an ever-expanding universe has been the same as saying our universe has a positive cosmological constant.

There are some outstanding problems, however. General relativity covers this aspect of the universe, but it can't describe the big bang. Nor can it unite gravity, which works on large scales, with quantum mechanics, which works on very small scales. "That means you cannot predict why we live in the universe that we live in," Hertog says.

String theory, in the meantime, offers a beautifully complete picture of the universe's history and connects gravity to quantum mechanics - but is most comfortable in a universe with a negatively curved, Escher-like geometry and with a negative cosmological constant.

This left physicists with a deep chasm to cross: on one side is a universe that works but lacks a complete theory, and on the other is a complete theory that doesn't describe the actual universe.

Now, Hawking, Hertog and James Hartle of the University of California, Santa Barbara, are proposing a bridge. They have found a way to produce expanding, accelerating universes using a negative cosmological constant. This means that string theory may, after all, describe the universe that we observe. The proposal grew from an idea that Hawking and Hartle had in the 1980s to get around general relativity's shortcomings by looking for a quantum picture of cosmology.

In quantum mechanics, a single equation called the wave function describes all the possible states that a quantum object can be in, and assigns each of them a certain probability. Hawking and Hartle sought a similar wave function that can generate the probability of various universes arising from the big bang. It would describe all the possible universes that could have been - including ones in which the solar system never formed, or in which life might have evolved very differently.

Over the past 30 years, Hawking and Hartle have been forcing a positive cosmological constant into their wave function, because that was considered necessary. But that meant sacrificing precision: they just couldn't get these universes to be anything more than clunky approximations of reality.

Tip the balanceString theorists had also been struggling with universes with positive cosmological constants, which tend to be unstable. Building them is a bit like trying to balance a pencil on its tip: it might work for a while, but the pencil's most energetically stable state is lying flat on the table, and eventually it will fall over. The most successful versions of string theory would rather live in the Escher-verse.

"String theory with a negative cosmological constant just goes much better," Hertog says.

But Hawking's latest work suggests that this supposed flaw may actually be the thing that knits string theory back to reality. In a paper posted online, Hawking and colleagues describe how they produced a plethora of universes from wave functions with negative cosmological constants, some of which are expanding and accelerating (arxiv.org/abs/1205.3807).

"Some of those universes are accelerating, just like our universe," Hertog says. "It turns out the quantum state includes both kinds of universes, automatically." For a certain wave function, these accelerating and expanding universes even turn out to be the most likely ones.

The key to this insight was recognising that the universes generated by the team's wave function could evolve to look a lot like a particular formulation of string theory, produced by Juan Maldacena of the Institute for Advanced Study in Princeton, New Jersey in 1997 (arxiv.org/abs/hep-th/9711200). "There was a mathematical connection, a very elegant connection," Hertog says.

Once they had spotted its connection to their wave function, Hawking's team decided to try to stitch the two together by writing a new wave function with a negative cosmological constant. They reasoned that this would allow them to borrow the beautifully complete mathematical picture of the universe provided by string theory and produce universes that accelerate outwards.

What about the observations suggesting that our universe is flat? Similar to how Newton's laws of motion work for everyday objects but give way to the more comprehensive laws of Einstein on cosmological scales, Hawking's team thinks that the universe's apparent flatness may describe it well as far as we can see but ultimately gives way to an underlying Escher-like geometry.

It is too soon to declare the universe solved. Maldacena says the Hawking team's model leaves out aspects of complete versions of string theory, such as provisions for the stability of some particles. "It would be wonderful if it was all we need to do," he says. "But I think it's too simplified. It's hard to see how it can be expanded to a more complete theory."

Hertog agrees that their work isn't finished - but thinks that the negative cosmological constant will eventually lead to a complete, description of the universe we observe. "It's an avenue that is opening up now," he says, "not something we have yet."