The butterfly-shaped pattern was first theorized by physicist Douglas Hofstadter in 1976, but it took the tools and technology now available at the MagLab to prove its existence.

"The observation of the 'Hofstadter butterfly' marks a real landmark in condensed matter physics and high magnetic field research," said Greg Boebinger, director of the MagLab. "It opens a new experimental direction in materials research."

This groundbreaking research demanded the ability to measure samples of materials at very low temperatures and very high magnetic fields, up to 35 tesla. Both of those conditions are available at the MagLab, making it an international destination for scientific exploration.

The unique periodic structure used to observe the butterfly pattern was composed of boron nitride (BN) and graphene. Graphene is a Nobel Prize-winning material that holds tremendous promise in revolutionizing computers, batteries, cell phones, televisions and even airplanes. A one-atom thick, honeycomb array of carbon atoms, graphene is virtually see-through, yet 300 times stronger than steel and 1,000 times more conducting than silicon.

"This is about a puzzle that has been solved," said Eric Palm, deputy director at the MagLab. "It is really about scientific curiosity. It is an exciting confirmation of a theory that was made years ago."

MagLab physicist Nicholas Bonesteel agreed, adding "The Hofstadter butterfly is a beautiful fractal energy pattern that has intrigued physicists for decades. Seeing clear experimental evidence for it is a real breakthrough."

One research team was led by Columbia University's Philip Kim and included researchers from City University of New York, the University of Central Florida, Tohoku University and the National Institute for Materials Science in Japan.

The team's work will be published today in the Advanced Online Publication of the journal Nature. Similar results were discovered at the MagLab by a group led by Pablo Jarillo-Herrero and Raymond Ashoori at MIT, as well as scientists from Tohoku University and the National Institute for Materials Science in Japan. Their work is expected to be published soon.

]]> Thu, 23 MAY 2013 22:52:52 AEST College Park MD (SPX) May 21, 2013 - Entanglement, by general consensus of physicists, is the weirdest part of quantum science. To say that two particles, A and B, are entangled means that they are actually two parts of an inseparable quantum thing. An important consequence of this inherent kinship is that measuring a property of A (say, the particle's polarization) is necessarily to know the corresponding property of B, even if you're not there with a detector to observe B and even if (as explained below) the existence of that property had no prior fixed value until the moment particle A was detected.

To create such entanglement it is generally necessary to generate particles two at a time and to generate them so that they are born with this connected property. The most basic step in measuring such a system is to measure and detect both particles and to do so efficiently. So it had better be the case that if one detector registers a particle, the other detector should collect and register the other particle.

Because we know that if we see one particle, the other must exist, we say that the detection of one particle "heralds" the existence of the other, just as medieval heralds, with their banners and bugles, signified the arrival of a king. Although in this case, because with these particles born in twos, one photon is no more regal than the other, so we can equally well say that one photon heralds the other and vice versa. But as in the case of a king, in real life even though the herald announces the king he may be waylaid and never appear.

An experiment conducted at the Joint Quantum Institute (*) establishes a new record for heralding efficiency for a pair of entangled photons (particles of light). The JQI work is published in the May 15 issue of the journal Optics Letters (**). What happens is this: about 84% of the time the researchers observe photon A they also observe photon B just where it should be, and vice versa.

The JQI detection scheme will be useful for a number of reasons: it should help experiments to tighten remaining loopholes over the fundamental sway of quantum reality; it shows that sources of single heralded photons can achieve a certain level of reliability; and that might be a critical ingredient in producing a source of random numbers in a way that guarantees that any nefarious attempts to "load the dice" are impossible.

Indeterminacy
The JQI experiment demonstrates a photon source which could allow one to get to the heart of counter-intuitive nature of quantum reality by looking at indeterminacy. In common experience a coin facing up has a definite value: it is a head or a tail. Even if you don't look at the coin you trust that it must be a head or tail. In quantum experience the situation is more unsettling: material properties of things do not exist until they are measured. Until you "look" (measure the particular property) at the coin, as it were, it has no fixed face up.

What this indeterminacy means is that until it is observed an object has no definite value for that property. So the property in question, whether it is position, velocity, charge, polarization, or some other attribute, cannot even be said to exist. Instead the object is said to be in a superposition of states and its physical attributes can potentially take on a variety of values.

When describing the existence of this particle, we can do no more than specify a set of probabilities that the object's properties have certain values. At the moment measurement occurs the object undergoes a "collapse of probability." The probability estimates in play just before measurement become superfluous. The property being measured - the polarization of a photon, say - has assumed a definite value, horizontal or vertical in this case.

Einstein's Reservations
Describing reality in terms of indeterminacy and probability bothered Albert Einstein. Surely, he said, a particle's property exists before it is measured and a theory more complete than quantum mechanics would include the existence of those properties before they were measured. Those properties before measurement must be contained in some variables hidden from the standard quantum mechanical representation. The search for those "hidden variables" pertaining to the existence of things occupied a lot of Einstein's time in the latter part of his life, and has been a topic of concern with physicists ever since.

In the 1960s John Bell proposed a number of experiments designed to test the validity of things like entanglement and indeterminacy. So far all such tests have supported the validity of quantum indeterminacy and have discouraged the idea of any hidden variables. But for some skeptics, loopholes remain, and they argue that the reality of entanglement has not yet been adequately demonstrated.

One reason for this is the difficulty in measuring properties of two or more (supposedly entangled) objects with sufficient efficiency. The relatively poor measurement efficiency, resulting in the failure to detect one or the other of the pair of entangled photons, allowed skeptics to assert that the measured sample of pairs did not constitute a good enough representation of the overall set of objects to be able to say something definitive about entanglement.

JQI Experiment
The experiment effort in Alan Migdall's JQI lab specifically targets the efficiency of the heralding process. To start, the researchers send a beam of ultraviolet photons into a special crystal where, at a rate of about one per billion, a UV photon is turned into a pair of entangled photons.

This process is called spontaneous parametric down-conversion (PDC). The laws of physics dictate that the momentum and energy of the incoming photon (from the pump beam) should be split between the daughter photons (one is called the "signal" and the other the "idler"). In this picture omega is the frequency of the respective photon and is proportional to its energy.

The daughters might, for instance, be a green photon plus a near-infrared photon, or two red photons, or any other combination of colors so long as the sum of the energies of the photons adds up the energy of the pump photon.

Each of the two photons makes its way through a lens and into a fiber so narrow that only a single mode can propagate. That is, if we think of the light not as a particle (photon) but as a bundle of electric and magnetic fields, the lateral profile of the ray will have a simple Gaussian shape. This kind of fiber, aligned to exacting standards, ensures that photons of a very specific energy and direction will be channeled into a photodetector where its presence and time of arrival can be determined.

Photon Or Vacuum?
"In effect the observation of photon A brings photon B into existence," says Alan Migdall, "at least if these are true entangled photons." This entanglement between the existence of a photon and no photon (or vacuum) is not what is usually considered to be entanglement but it is nonetheless.

The aim of this JQI experiment is not itself to test the Bell criteria for entanglement (as it turns out the polarizations of photons A and B are known be forehand), but rather to optimize the process of heralding - the ability to say that if A is here then B is there. For some theories a heralding efficiency must at least 82% if entanglement loopholes are to be closed.

New Heralding Record
The JQI physicists have now exceeded this yardstick. They typically observe about 50,000 signal photons (photon A) per second in their detector. And when this happens about 84% of the time a photon is seen in detector B. And simultaneously, when the roles of the two detectors are reversed a comparable percentage is registered. This is the highest symmetric heralding efficiency for a single-mode fiber yet seen in any experiment.

Migdall says that because of the random nature of observing a photon with an appropriately prepared polarization state, the measurement of a heralded photon can be turned into a number that is truly random and guaranteed to be free of tampering. Such random numbers can, in turn, be used in various schemes to encrypt messages that can never be cracked.

(*)The Joint Quantum Institute is operated jointly by the National Institute of Standards and Technology in Gaithersburg, MD and the University of Maryland in College Park.

(**) "Demonstrating highly symmetric single-mode, single-photon heralding efficiency in spontaneous parametric downconversion," Marcelo Da Cunha Pereira, Francisco E Becerra, Boris L Glebov, Jingyun Fan, Sae Woo Nam, and Alan Migdall, Optics Letters, May 15, 2013.

]]> Thu, 23 MAY 2013 22:52:52 AEST Wallops Island VA (SPX) May 21, 2013 - When did the first stars and galaxies form in the universe? How brightly did they burn their nuclear fuel?\

Scientists will seek to gain answers to these questions with the launch of the Cosmic Infrared Background ExpeRIment (CIBER) on a Black Brant XII suborbital sounding rocket between 11 and 11:59 p.m. EDT, June 4 from the Wallops Flight Facility in Virginia.

Jamie Bock, CIBER principal investigator from the California Institute of Technology, said, "The first massive stars to form in the universe produced copious ultraviolet light that ionized gas from neutral hydrogen.

CIBER observes in the near infrared, as the expansion of the universe stretched the original short ultraviolet wavelengths to long near-infrared wavelengths today. CIBER investigates two telltale signatures of first star formation - the total brightness of the sky after subtracting all foregrounds, and a distinctive pattern of spatial variations."

"The objectives of the experiment are of fundamental importance for astrophysics, to probe the process of first galaxy formation, but the measurement is also extremely difficult technically," he noted.

This will be the fourth flight for CIBER on a NASA sounding rocket. The previous launches were in 2009, 2010, and 2012 from the White Sands Missile Range, New Mexico. After each flight the experiment or payload was recovered for post-calibrations and re-flight.

For this flight CIBER will fly on a larger and more powerful rocket than before. This will loft CIBER to a higher altitude than those previously obtained, thus providing longer observation time for the instruments. The experiment, which will safely splash down in the Atlantic Ocean more than 400 miles off the Virginia coast, will not be recovered.

CIBER previously flew on two-stage Black Brant IX sounding rockets. Bock said, "The collection of data from the three flights allows us to compare data and rigorously test sources of potential systematic error from both the instrument and astrophysical foregrounds.

"We have been through the end-to-end process in analyzing our data, so we understand the benefits of going with a non-recovered Black Brant XII. We also know the performance of the instrument very well from these flights and that makes us confident going forward with this more capable but final flight."

The 70-foot tall four-stage Black Brant XII rocket will carry CIBER to an altitude of about 350 miles. According to Bock, "This flight is pioneering a new direction in the astrophysics program in that we are flying our instrument on a non-recovered Black Brant XII.

The XII gives us a significantly higher trajectory, providing about 560 seconds of flight time above 250 km (155 miles) altitude, compared with 250 seconds on standard Black Brant IX flights out of White Sands."

"Our experience in the near-infrared waveband is that we see appreciable emission from the atmosphere up to 250 km. The higher trajectory allows us to do some new things that are not possible on a Black Brant IX.

"For example, we expect to have enough independent images of the sky to directly determine the in-flight gain of the infrared cameras, which will allow us to measure background fluctuations in single exposures.

"This gives us a much more direct way to compare with satellite data than the statistical combinations we have had to use to date. The higher trajectory of course comes with a price in that the payload is not recovered," he said.

CIBER is a cooperative instrument designed and built by the California Institute of Technology, University of California Irvine, the Japan Aerospace Exploration Agency (JAXA), and the Korean Astronomy and Space Science Institute (KASI). The same team is also developing an improved follow-on experiment, with more capable optics and detector arrays, that will be completed next year.

Backup launch days for this project are June 5 - 10.

]]> Thu, 23 MAY 2013 22:52:52 AEST Huntsville AL (SPX) May 22, 2013 - This composite image of a galaxy illustrates how the intense gravity of a supermassive black hole can be tapped to generate immense power. The image contains X-ray data from NASA's Chandra X-ray Observatory (blue), optical light obtained with the Hubble Space Telescope (gold) and radio waves from the NSF's Very Large Array (pink).

This multi-wavelength view shows 4C+29.30, a galaxy located some 850 million light years from Earth. The radio emission comes from two jets of particles that are speeding at millions of miles per hour away from a supermassive black hole at the center of the galaxy. The estimated mass of the black hole is about 100 million times the mass of our Sun. The ends of the jets show larger areas of radio emission located outside the galaxy.

The X-ray data show a different aspect of this galaxy, tracing the location of hot gas. The bright X-rays in the center of the image mark a pool of million-degree gas around the black hole. Some of this material may eventually be consumed by the black hole, and the magnetized, whirlpool of gas near the black hole could in turn, trigger more output to the radio jet.

Most of the low-energy X-rays from the vicinity of the black hole are absorbed by dust and gas, probably in the shape of a giant doughnut around the black hole. This doughnut, or torus blocks all the optical light produced near the black hole, so astronomers refer to this type of source as a hidden or buried black hole. The optical light seen in the image is from the stars in the galaxy.

The bright spots in X-ray and radio emission on the outer edges of the galaxy, near the ends of the jets, are caused by extremely high energy electrons following curved paths around magnetic field lines. They show where a jet generated by the black hole has plowed into clumps of material in the galaxy (mouse over the image for the location of these bright spots).

Much of the energy of the jet goes into heating the gas in these clumps, and some of it goes into dragging cool gas along the direction of the jet. Both the heating and the dragging can limit the fuel supply for the supermassive black hole, leading to temporary starvation and stopping its growth.

This feedback process is thought to cause the observed correlation between the mass of the supermassive black hole and the combined mass of the stars in the central region or bulge of a galaxy.

These results were reported in two different papers. The first, which concentrated on the effects of the jets on the galaxy, is available online and was published in the May 10, 2012 issue of The Astrophysical Journal.

]]> Thu, 23 MAY 2013 22:52:52 AEST Orlando FL (SPX) May 20, 2013 - A team of researchers from several universities - including UCF -has observed a rare quantum physics effect that produces a repeating butterfly-shaped energy spectrum in a magnetic field, confirming the longstanding prediction of the quantum fractal energy structure called Hofstadter's butterfly.

This discovery by the team paves the way for engineering new types of extraordinary nanoscale materials that can be used to develop smaller, lighter and faster electronics, including sensors, cell phones, tablets and laptops.

First predicted by American physicist Douglas Hofstadter in 1976, the butterfly pattern emerges when electrons are confined to a two-dimensional plane and subjected to both a periodic potential energy and a strong magnetic field.

The Hofstadter butterfly is a fractal pattern-meaning that it contains shapes that repeat on smaller and smaller size scales. Fractals are common in systems such as fluid mechanics, but rare in the quantum mechanical world. The Hofstadter butterfly is one of the first quantum fractals theoretically discovered in physics but, until now, there has been no direct experimental proof of this spectrum.

Columbia University led the study and also involved scientists from the City University of New York, Tohoku University and the National Institute for Materials Science in Japan. Columbia prepared the sample and the UCF team measured the regular recurrence of the high-fidelity periodic pattern, engineered by inducing nanoscale ripples on graphene, a carbon material.

The measured recurrence served as the essential proof that the measured spectrum was indeed the Hofstadter butterfly. The image that captured the evidence was taken in UCF Assistant Professor Masa Ishigami's laboratory.

Jyoti Katoch, Ishigami's graduate student, used a non-contact atomic force high-resolution microscope to image the ripples, which have the height of only 0.2 angstroms (twenty trillionth of a meter), to confirm that the observed Hofstadter butterfly spectrum indeed matched the theoretical prediction.

"The arrangement of individual atoms, even just one atom can drastically alter properties of nanoscale materials. That is the basis for nanotechnology," Ishigami said.

"Atomic structures must be resolved to understand the properties of nanoscale materials. What we do here at UCF is to explain why nanoscale materials behave so different by resolving their atomic structures.

"Only when we understand the origin of the extraordinary properties of nanoscale materials, we can propel nanoscience and technology forward. What Jyoti has done here is to image how graphene is rippled to explain the observed Hofstadter spectrum."

UCF's laboratory utilizes a novel, the state-of-the-art microscopy technique to simultaneously determine the atomic structure and electronic properties of nanoscale materials such as graphene.

Katoch has been working with Ishigami since 2008, when Ishigami joined UCF. Katoch helped build the laboratory and developed the atomic-resolution capability critical to capturing the picture proof for this study.

Ishigami has a Ph.D. in physics from the University of California at Berkeley and a bachelor's degree in physics from the Massachusetts Institute of Technology. He has won multiple awards, including the Intelligence Community postdoctoral fellowship and the Hertz graduate fellowship, and has published more than 30 papers in journals including Science.

The study is published in Nature.

]]> Thu, 23 MAY 2013 22:52:52 AEST Singapore (SPX) May 15, 2013 - Like small children, scientists are always asking the question 'why?'. One question they've yet to answer is why nature picked quantum physics, in all its weird glory, as a sensible way to behave. Researchers Corsin Pfister and Stephanie Wehner at the Centre for Quantum Technologies at the National University of Singapore tackle this perennial question in a paper published 14 May in Nature Communications.

We know that things that follow quantum rules, such as atoms, electrons or the photons that make up light, are full of surprises. They can exist in more than one place at once, for instance, or exist in a shared state where the properties of two particles show what Einstein called "spooky action at a distance", no matter what their physical separation.

Because such things have been confirmed in experiments, researchers are confident the theory is right. But it would still be easier to swallow if it could be shown that quantum physics itself sprang from intuitive underlying principles.

One way to approach this problem is to imagine all the theories one could possibly come up with to describe nature, and then work out what principles help to single out quantum physics. A good start is to assume that information follows

Einstein's special relativity and cannot travel faster than light. However, this alone isn't enough to define quantum physics as the only way nature might behave. Corsin and Stephanie think they have come across a new useful principle. "We have found a principle that is very good at ruling out other theories," says Corsin.

In short, the principle to be assumed is that if a measurement yields no information, then the system being measured has not been disturbed.

Quantum physicists accept that gaining information from quantum systems causes disturbance. Corsin and Stephanie suggest that in a sensible world the reverse should be true, too. If you learn nothing from measuring a system, then you can't have disturbed it.

Consider the famous Schrodinger's cat paradox, a thought experiment in which a cat in a box simultaneously exists in two states (this is known as a 'quantum superposition'). According to quantum theory it is possible that the cat is both dead and alive - until, that is, the cat's state of health is 'measured' by opening the box.

When the box is opened, allowing the health of the cat to be measured, the superposition collapses and the cat ends up definitively dead or alive. The measurement has disturbed the cat.

This is a property of quantum systems in general. Perform a measurement for which you can't know the outcome in advance, and the system changes to match the outcome you get. What happens if you look a second time? The researchers assume the system is not evolving in time or affected by any outside influence, which means the quantum state stays collapsed.

You would then expect the second measurement to yield the same result as the first. After all, "If you look into the box and find a dead cat, you don't expect to look again later and find the cat has been resurrected," says Stephanie. "You could say we've formalised the principle of accepting the facts", says Stephanie.

Corsin and Stephanie show that this principle rules out various theories of nature. They note particularly that a class of theories they call 'discrete' are incompatible with the principle. These theories hold that quantum particles can take up only a finite number of states, rather than choose from an infinite, continuous range of possibilities.

The possibility of such a discrete 'state space' has been linked to quantum gravitational theories proposing similar discreteness in spacetime, where the fabric of the universe is made up of tiny brick-like elements rather than being a smooth, continuous sheet.

As is often the case in research, Corsin and Stephanie reached this point having set out to solve an entirely different problem altogether. Corsin was trying to find a general way to describe the effects of measurements on states, a problem that he found impossible to solve. In an attempt to make progress, he wrote down features that a 'sensible' answer should have. This property of information gain versus disturbance was on the list. He then noticed that if he imposed the property as a principle, some theories would fail.

Corsin and Stephanie are keen to point out it's still not the whole answer to the big 'why' question: theories other than quantum physics, including classical physics, are compatible with the principle. But as researchers compile lists of principles that each rule out some theories to reach a set that singles out quantum physics, the principle of information gain versus disturbance seems like a good one to include.

"An information-theoretic principle implies that any discrete physical theory is classical", Nature Communications, doi: 10.1038/ncomms2821 (2013).

]]> Thu, 23 MAY 2013 22:52:52 AEST Madrid, Spain (SPX) May 15, 2013 - Improving our understanding of the human brain, gathering insights into the origin of our universe through the detection of gravitational waves, or optimizing the precision of GPS systems- all are difficult challenges to master because they require the ability to visualize highly fragile elements, which can be terminally damaged by any attempt to observe them.

Now, quantum physics has provided a solution. In an article published in Nature Photonics, researchers at the Institute of Photonic Sciences (ICFO) report the observation of a highly fragile and volatile body through a new quantum-mechanical measurement technique.

Researchers from the group led by Morgan Mitchell applied the so-called "quantum non-demolition measurement" to a tiny cloud of atoms. They were able to observe the spinning of the electrons in the atoms, and more importantly, the atom cloud was not disturbed in the process.

It is the first time quantum non-demolition measurement has been demonstrated with any material object. The same method could be extended to permit the observation of individual atoms.

In the experiment, scientists prepared light pulses with photons in complementary states, and then sent them through the cloud of atoms, measuring their polarization on the way out.

"A first measurement gives us information reflecting the action of the first light pulse. A second measurement, taken with photons in a complementary state from the first, cancels the influence of the preliminary pulse, allowing us to observe the original characteristics of the object," explains Dr. Robert Sewell, researcher at ICFO. This process has enabled the team to gather precise information on the magnetic field of the atom's surroundings.

The information obtained exceeds the so-called "standard quantum limit", which quantifies the maximum amount of information obtainable with any traditional probing.

Two achievements made this possible. On one hand, researchers were able to structure the observation so that the noise resulting from the visualization was shifted away from the object being measured and into a different variable.

In addition, they introduced quantum statistical correlations among the atoms so that they were able to gather in one measurement what previously they needed a collection of measurements to observe. "This experiment provides rigorous proof of the effectiveness of quantum physics for measuring delicate objects" concludes Sewell.

Link to the paper.

]]> Thu, 23 MAY 2013 22:52:52 AEST New York NY (SPX) May 15, 2013 - New York University physicists have uncovered how energy is released and dispersed in magnetic materials in a process akin to the spread of forest fires, a finding that has the potential to deepen our understanding of self-sustained chemical reactions.

The study, which appears in the journal Physical Review Letters, also included researchers from the University of Barcelona, City College of New York, and the University of Florida. It may be downloaded here: http://bit.ly/18FKwFO.

Forest fires spread because an initial flame or spark will heat a substance-a trunk or branch-causing it to burn, which releases heat that causes the fire to spread to other trunks or branches, turning a small spark into a self-sustained, propagating front of fire that can be deadly and is irreversible.

In the Physical Review Letters study, the researchers sought to understand how energy is sustained and spreads in magnetic materials-"magnetic fire." Such knowledge is important in designing magnetic materials for energy storage applications. This is because magnetic fire can lead to a rapid and uncontrolled release of stored energy, producing significant energy loss in, for example, an electrical generator.

Research on bursts of energy within magnetic systems dates back two decades. But scientists haven't been able to measure and understand what prompts this phenomenon, known as "magnetic deflagration."

Part of this mystery lies in the nature of chemical reactions. In such reactions, which produce heat, the energy released is determined by the chemical constituents and cannot be easily varied. What is known as an "activation energy" is typically necessary to start a chemical reaction; energy is then released as the reaction proceeds. In other words, scientists have concluded that a spark is needed to begin this process-much the same way a forest fire begins with a single lit match.

But in magnetic materials the energies can be manipulated by magnetic fields and are therefore very easily varied in an experiment. Thus the activation energy and the energy released are controllable, enabling systematic studies of the physical mechanisms of energy flow.

To achieve this, the researchers surmised they could produce such a "spark" through a series of spins-the chemical equivalent of striking a match. In this case, they employed small single crystals of a molecular magnet- each magnetic molecule being just one billionth of a meter-that could be magnetized, much like the needle of a compass.

The researchers provided a pulse of heat as the spark, causing molecular spins near the heaters to flip in a magnetic field, a process that released energy and transmitted it to nearby material.

"When the molecules' spins are aligned opposite the applied field direction, they possess a high level of energy," explained Andrew Kent, a professor in NYU's Department of Physics and the study's senior researcher. "And then when the spins 'flip,' energy is released and dispersed into surrounding magnetic material that can cause a runaway reaction."

Moreover, the scientists were able to control the speed of this process by adjusting the make-up of the magnetic field in their experiments. Through this detailed examination, they could see under what conditions energy is released and how it propagates.

"These are exciting results and ones that have prompted us to further consider whether a spark is even necessary to start a magnetic fire," added Kent. "We hope to observe and study situations in which the fire starts spontaneously, without a spark."

The study was conducted at NYU by Pradeep Subedi and Saul Velez, both doctoral candidates, as well as Ferran Macia, a postdoctoral researcher, and included: Shiqi Li, a City College of New York (CCNY) doctoral candidate; Myriam Sarachik, a professor at CCNY; Javier Tejada, a professor at the University of Barcelona; Shreya Mukherjee, a University of Florida doctoral candidate; and George Christou, a professor at University of Florida.

]]> Thu, 23 MAY 2013 22:52:52 AEST Liverpool UK (SPX) May 14, 2013 - Scientists at the University of Liverpool have shown that some atomic nuclei can assume the shape of a pear which contributes to our understanding of nuclear structure and the underlying fundamental interactions.

Most nuclei that exist naturally are not spherical but have the shape of a rugby ball. While state-of-the-art theories are able to predict this, the same theories have predicted that for some particular combinations of protons and neutrons, nuclei can also assume very asymmetric shapes, like a pear where there is more mass at one end of the nucleus than the other.

The experimental observation of nuclear pear shapes is important for understanding the theory of nuclear structure and for helping with experimental searches for electric dipole moments (EDM) in atoms.

The Standard Model of particle physics predicts that the value of the EDM is so small that it lies well below the current observational limit. However, many theories that try to refine this model predict EDMs that should be measurable.

In order to test these theories the EDM searches have to be improved and the most sensitive method is to use exotic atoms whose nucleus is pear-shaped. Quantifying this shape will therefore help with experimental programmes searching for atomic EDMs.

Professor Peter Butler, from the University's Department of Physics who carried out the measurements, said: "Our findings contradict some nuclear theories and will help refine others. The measurements will also help direct the searches for atomic EDMs currently being carried out in North America and in Europe, where new techniques are being developed to exploit the special properties of radon and radium isotopes.

"Our expectation is that the data from our nuclear physics experiments can be combined with the results from atomic trapping experiments measuring EDMs to make the most stringent tests of the Standard Model, the best theory we have for understanding the nature of the building blocks of the universe."

Most nuclear isotopes predicted to have pear shapes have been out of reach of experimental techniques to measure them.

Now, at the ISOLDE facility at CERN, beams of very heavy, radioactive nuclei can be produced in high-energy proton collisions with a uranium carbide target. They are then selectively extracted using their chemical and physical properties before being accelerated to 8% of the speed of light and allowed to impinge on a target foil of isotopically pure nickel, cadmium or tin.

When this happens the relative motion of the heavy accelerated nucleus and the target nucleus creates an electromagnetic impulse that excites the nuclei. By studying the details of this excitation process it is possible to understand the nuclear shape.

This method has been used successfully to study the shape of short-lived isotopes 220Rn and 224Ra. The data show that while 224Ra is pear-shaped, 220Rn does not assume the fixed shape of a pear but rather vibrates about this shape.

The findings are published in Nature.

]]> Thu, 23 MAY 2013 22:52:52 AEST Madrid, Spain (SPX) May 14, 2013 - The so-called Elephant's Tomb in the Roman necropolis of Carmona (Seville, Spain) was not always used for burials. The original structure of the building and a window through which the sun shines directly in the equinoxes suggest that it was a temple of Mithraism, an unofficial religion in the Roman Empire. The position of Taurus and Scorpio during the equinoxes gives force to the theory.

The Carmona necropolis (Spain) is a collection of funeral structures from between the 1st century B.C. and the 2nd century A.D. One of these is known as the Elephant's Tomb because a statue in the shape of an elephant was found in the interior of the structure.

The origin and function of the construction have been the subject of much debate. Archaeologists from the University of Pablo de Olavide (Seville, Spain) have conducted a detailed analysis of the structure and now suggest that it may originally not have been used for burials but for worshipping the God Mithras. Mithraism was an unofficial religion that was widespread throughout the Roman Empire in the early centuries of our era.

Researchers have identified four stages in which the building was renovated, giving it different uses.

"In some stages, it was used for burial purposes, but its shape and an archaeoastronomical analysis suggest that it was originally designed and built to contain a Mithraeum [temple to Mithras]," as explained to SINC by Inmaculada Carrasco, one of the authors of the study.

Carrasco and her colleague Alejandro Jimenez focus their studies on a window in the main chamber built during the first stage. Earlier studies had already suggested that the purpose of the window was not to provide light, but that rather it may have served a symbolic and spiritual purpose.

The Sun, the Moon and the stars
"From our analysis of the window, we have deduced that it was positioned so that the rays of the sun reached the centre of the chamber during the equinoxes, in the spring and autumn, three hours after sunrise" explains Carrasco.

The authors believe that at that moment a statue of the tauroctony, the statue of Mithras slaying the bull (which has been lost), would have been illuminated.

In addition, during the winter and summer solstice, the sun would light up the north and south walls respectively.

Moreover, the position of the heavenly bodies at that time in the 2nd century reinforces the theory that the building was constructed for Mithraic worship, a religion that gave considerable importance to the constellations.

As the sun shines through the window during the spring equinox, Taurus rises to the East and Scorpio hides to the West. The opposite occurred during the autumn equinox.

Taurus and Scorpio were of special significance to the Mithraics. The main image of the cult is that of the God Mithras slaying a bull, and in the majority of these images there is also a scorpion stinging the animal's testicles.

Other constellations such as Aquarius, Orion or Leo, which were also of significance in this religion, appear in the path of the sun in the equinoxes and solstices at that time.

Moreover, according to the authors, the Moon, although having a secondary role, may have lit up the face of Mithras with a full moon on nights near to the equinoxes.

Four stages of renovation
Apart from the window, the architecture of the original building has similarities to other Mithraic constructions.

Carrasco explained that it is "an underground structure, with a room divided into three chambers, with a shrine or altar illuminated by the window at the head. The presence of a fountain is also highly significant as these are commonly found in the Mithraeums".

According to the authors, after its period as a Mithraic temple, the building was renovated three times, giving it new functions more in line with the functions of a necropolis. A burial chamber was built and at a later date, the roof was removed, leaving open courtyards. Lastly, it was filled with rubble and used as an area for burials.

However, there are some objections to the theory that it was a Mithraic temple as it is in a necropolis, an uncommon site for buildings used for this cult which were more often found in domestic, urban or rural environments.

"A similar case is that of Sutri (Italy) where the Mithraeum is on the outskirts of the town. The structure in Carmona is in a multi-purpose space, next to the Via Augusta which connected Cadiz to Rome, close to the amphitheatre and the circus, and consequently its position should not be considered an objection," says Jimenez.

A. Jimenez, I. Carrasco. "The tomb of the Elephant at the Roman Necropolis of carmona. A necessary review through the Building Archaeology and Archaeostromy" Archivo espanol de arqueologia. DOI: 10.3989/aespa.085.012.007

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