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Jul

2

BELLA: Building a Table-Top Accelerator

July 2, 2009 | Leave a Comment

BELLA: Accelerating Science by Accelerating Electrons: Berkeley Lab scientists stunned the world in 2006 when they proved they could accelerate electrons to very high energies (1 GeV, or a billion electron volts) in a distance of centimeters rather than hundreds of meters. Using the same concepts, those scientists plan to take the project to the next level and build a laser-based accelerator capable of zapping electron beams to energies exceeding 10 GeV in a distance of just one meter.

When completed in about four years, the Berkeley Lab Laser Accelerator, or BELLA, will demonstrate the promise of a novel and compact method of accelerating high-energy particles, by making use of a series of synchronized laser systems. The results will be of interest not only to high-energy particle physicists but also to chemists, biologists, doctors, and national security officials.

Related reading from Berkeley Labs: BELLA – The Next Stage in Laser Wakefield Acceleration

Popularity: 1% [?]

Jan

11

All About Richard Feynman

January 11, 2008 | Leave a Comment

Feynman Online. ‘This web site is dedicated to Richard P. Feynman (1918-1988), scientist, teacher, raconteur, and musician. He assisted in the development of the atomic bomb, expanded the understanding of quantum electrodynamics, translated Mayan hieroglyphics, and cut to the heart of the Challenger disaster. But beyond all of that, Richard Feynman was a unique and multi-faceted individual.’

Popularity: 10% [?]

Nov

9

Large Hadron Collider: Cold and Ready for Physics

November 9, 2007 | Leave a Comment

CERN: LHC completes the circle. ‘At a brief ceremony deep under the French countryside today, CERN Director General Robert Aymar sealed the last interconnect between the main magnet systems in the Large Hadron Collider (LHC). This is the latest milestone in commissioning the LHC, the world’s most powerful particle accelerator.

The LHC’s superconducting main magnets will operate at a temperature of just 1.9 degrees above absolute zero (-271.3 oC), colder than outer space. To cool the magnets, over 10 000 tonnes of liquid nitrogen and 130 tonnes of liquid helium will be deployed through a cryogenic system including more than 40 000 leak-tight welds. Today’s ceremony marks the end of a two year programme of work to connect all the main dipole and quadrupole magnets in the LHC. This complex task included both electrical and fluid connections.

“This is a huge accomplishment,” said Lyn Evans, LHC project leader. “Now that it is done, we can concentrate on getting the machine cold and ready for physics.”

The LHC is a circular machine, 27 kilometres around and divided into eight sectors, each of which can be cooled down to its operating temperature of 1.9 degrees above absolute zero and powered-up individually. One sector was cooled down, powered and warmed up in the first half of 2007. This was an important learning process, allowing subsequent sectors to be tested more quickly.’

Popularity: 5% [?]

Oct

28

Supersolidity

October 28, 2007 | Leave a Comment

Evidence for “Supersolidity” Becomes More Solid. ‘In recent years, no topic in condensed matter physics has been hotter than the study of ultracold solid helium. Subtle experiments suggest that as temperatures dip toward absolute zero, crystalline helium can bizarrely flow like a liquid with no viscosity, a phenomenon known as supersolidity. Now, a new experiment lends credence to that controversial claim by revealing a possible second sign of the transition.’

Penn State Live: High-quality helium crystals show supersolid behavior. ‘High-quality, single-crystal, ultra-cold solid helium exhibits supersolid behavior, suggesting that this frictionless solid flow is not a consequence of defects and grain boundaries in poor-quality, polycrystalline, solid helium, according to a team of Penn State researchers.

In 2004, Penn state physicists — Eunseong Kim, then-graduate student and Moses Chan, the Evan Pugh professor of physics– announced the observance of frictionless superflow in solid helium at nearly absolute zero. This new phenomenon is a cousin of Bose-Einstein condensate observed in gases in 1995 and in liquid helium in 1938.

Since then, their results have been replicated at the University of Tokyo, Keio University, Japan, and Cornell University. While the experiment was duplicated at Cornell, one experiment there found that if the solid helium was annealed –- cooled slowly from the melting point –- the supersolid behavior disappeared. This suggested that the theoretical idea of supersolidity is possible only in poor-quality solid helium and that the superflow is due to defects in the poorly grown crystals.

To create solid helium, the gaseous helium must be cooled very close to absolute zero and put under at least 25 atmospheres. Unlike other gases, helium remains a liquid at ambient pressure all the way down to absolute zero. Determining that the solid helium acts as a supersolid or Bose Einstein condensate is tricky. In a Bose-Einstein condensate all the atoms are at the lowest possible energy state, and they all behave in unison. The supersolid portion of the crystalized helium appears to flow without friction. For liquids and gases, this idea is less difficult because the atoms of both move around more and can easily slide past each other. But, in a solid, especially a very cold one, atoms do not usually flow easily or without friction.’

PhysicsWorld: The quantum solid that defies expectation. ‘In 2004 researchers reported the first clear evidence for superfluidity in solid helium-4. However, Matthew Chalmers describes recent experimental and theoretical work that has brought the very existence of such a “supersolid” into question.’

Physical Review Focus: Supersolid, with a Twist. ‘The strange quantum phenomenon known as supersolidity occurs when atoms flow without friction through a solid block of helium, possibly along a network of defects extending through an otherwise perfect crystal. In the 20 July Physical Review Letters, physicists find such a flow in computer simulations even when the atoms that make up the defects form a regular pattern, unlike the disorderly arrangement used in previous calculations. The results open a new way of understanding this extraordinary state of matter, which has properties of both solids and liquids.’

Kavli Institute Rapid Response to Supersolidity: ‘Is It There or Is It Not?’ May Be the Answer as Well as the Question (PDF).

Popularity: 5% [?]

Oct

17

2007 Physics Nobel Prize Laureates Articles Freely Available

October 17, 2007 | Leave a Comment

The American Physical Society has announced that both of the original articles describing the work that led to this year’s physics Nobel Prize have been made free-to-read. While the Nobel Laureates made their discoveries independently, both published their fundamental work in papers submitted to the Physical Review journals in 1988:

Enhanced magnetoresistance in layered magnetic structures with antiferromagnetic interlayer exchange, G. Binasch, P. Grünberg, F. Saurenbach and W. Zinn, Phys. Rev. B 39, 4828 (1989);

Giant Magnetoresistance of (001)Fe/(001)Cr Magnetic Superlattices, M. N. Baibich, J. M. Broto, A. Fert, F. Nguyen Van Dau, F. Petroff, P. Eitenne, G. Creuzet, A. Friederich, and J. Chazelas, Phys. Rev. Lett. 61, 2472 (1988).

Access AIP Journal Articles from Albert Fert and Peter Grünberg – Winners of the 2007 Nobel Prize in Physics. The American Institute of Physics made a selection of articles published in their journals by Albert Fert (Université Paris-Sud, Orsay, France) and Peter Grünberg (Forschungszentrum Jülich, Germany) since 1998 – the year of their prize-winning discovery of giant magnetoresistance. Articles from 1988 to 1997 are freely available.

Popularity: 5% [?]

Oct

9

Nobel Prize in Physics 2007: Discovery of Giant Magnetoresistance (GMR)

October 9, 2007 | 1 Comment

Nobel Prize in Physics 2007 – “for the discovery of Giant Magnetoresistance“: Albert Fert and Peter Grünberg. ‘This year’s physics prize is awarded for the technology that is used to read data on hard disks. It is thanks to this technology that it has been possible to miniaturize hard disks so radically in recent years. Sensitive read-out heads are needed to be able to read data from the compact hard disks used in laptops and some music players, for instance.

In 1988 the Frenchman Albert Fert and the German Peter Grünberg each independently discovered a totally new physical effect: Giant Magnetoresistance or GMR. Very weak magnetic changes give rise to major differences in electrical resistance in a GMR system. A system of this kind is the perfect tool for reading data from hard disks when information registered magnetically has to be converted to electric current. Soon researchers and engineers began work to enable use of the effect in read-out heads. In 1997 the first read-out head based on the GMR effect was launched and this soon became the standard technology. Even the most recent read-out techniques of today are further developments of GMR.’

Information for the Public (PDF)

The Giant Magnetoresistive Head: A giant leap for IBM Research. ‘The “giant magnetoresistive” (GMR) effect was discovered in the late 1980s by two European scientists working independently: Peter Grünberg of the KFA research institute in Jülich, Germany, and Albert Fert of the University of Paris-Sud . They saw very large resistance changes – 6 percent and 50 percent, respectively – in materials comprised of alternating very thin layers of various metallic elements. This discovery took the scientific community by surprise; physicists did not widely believe that such an effect was physically possible. These experiments were performed at low temperatures and in the presence of very high magnetic fields and used laboriously grown materials that cannot be mass-produced, but the magnitude of this discovery sent scientists around the world on a mission to see how they might be able to harness the power of the Giant Magnetoresistive effect.’

Applications of Giant Magnetoresistance. ‘Giant magnetoresistance (GMR) already has magnetic appeal: It allows more data to be packed on computer disks. If improvements are made in the interfaces between magnetic layers in thin-film structures, the number of new applications could prove irresistible.’

An overview of Giant Magnetoresistance (GMR) by Evgeny Tsymbal, University of Nebraska-Lincoln.

Popularity: 5% [?]

Oct

9

h-Index for Non-Prominent Scientists: A Case Study by Michael Schreiber

October 9, 2007 | Leave a Comment

A case study of the Hirsch index for 26 non-prominent physicists, Michael Schreiber, 10.1002/andp.200710252. Abstract: ‘The h index was introduced by Hirsch to quantify an individual’s scientific research output. It has been widely used in different fields to show the relevance of the research work of prominent scientists. I have worked out 26 practical cases of physicists which are not so prominent. Therefore this case study should be more relevant to discuss various features of the Hirsch index which are interesting or disturbing or both for the more average situation. In particular, I investigate quantitatively some pitfalls in the evaluation and the influence of self-citations.’

And from Summary and outlook: ‘The popularity of the Hirsch index is increasing. I believe that it would be fairer and safer to utilize the sharpened index hs. Both comprise the information about publication quantity and citation quality into a single number. The main disadvantages are the same: firstly the number of co-authors has no influence on the calculation of the index, and secondly it is not sensitive to one or several outstandingly high citation counts because, once a paper has reached the h-defining set, it is no longer relevant whether or not it is further cited. Nevertheless, it is a reasonable assumption that the Hirsch index will be more frequently used in the future when assessing the scientific achievement of scientists for evaluation and promotion purposes.’

Popularity: 6% [?]

Sep

14

Dipositronium: The Matter-Antimatter Molecule

September 14, 2007 | Leave a Comment

Matter-antimatter molecule makes its debut. ‘The first ever molecule made from matter-antimatter pairs has been created by physicists in the US. Dubbed “dipositronium”, it contains two electrons and two positrons that are bound together in much the same way as molecular hydrogen. The researchers claim that their technique could be improved to make the first matter-antimatter Bose Einstein condensate and ultimately the first “annihilation gamma-ray laser”, which could be used to study objects as small as atomic nuclei (Nature 449 195).’

Molecules of Positronium Observed in the Laboratory for the First Time – Research by UCR physicists could help the development of gamma-ray lasers; explain how matter came to dominate the universe. ‘Physicists at UC Riverside have created molecular positronium, an entirely new object in the laboratory. Briefly stable, each molecule is made up of a pair of electrons and a pair of their antiparticles, called positrons.

The research paves the way for studying multi-positronium interactions – useful for generating coherent gamma radiation – and could one day help develop fusion power generation as well as directed energy weapons such as gamma-ray lasers. It also could help explain how the observable universe ended up with so much more matter than “antimatter”.

The researchers made the positronium molecules by firing intense bursts of positrons into a thin film of porous silica, which is the chemical name for the mineral quartz. Upon slowing down in silica, the positrons were captured by ordinary electrons to form positronium atoms.

Positronium atoms, by nature, are extremely short-lived. But those positronium atoms that stuck to the internal pore surfaces of silica, the way dirt particles might cling to the inside surface of the holes in a sponge, lived long enough to interact with one another to form molecules of positronium, the physicists found.’

Popularity: 5% [?]

Sep

5

Theory for Everything

September 5, 2007 | Leave a Comment

Stringscape. ‘In its near 40-year history, string theory has gone from a theory of hadrons to a theory of everything to, possibly, a theory of nothing. Indeed, modern string theory is not even a theory of strings but one of higher-dimensional objects called branes. Matthew Chalmers attempts to disentangle the immense theoretical framework that is string theory, and reveals a world of mind-bending ideas, tangible successes and daunting challenges – most of which, perhaps surprisingly, are rooted in experimental data.’

Popularity: 4% [?]

Aug

18

Super Crystals in Organic Semiconductors

August 18, 2007 | Leave a Comment

UA Physicists Discover ‘Super Crystals’ in a Semiconductor. ‘University of Arizona physicists have discovered that “super crystals” – crystals which are hundreds to thousands times larger than conventional crystals – exist in certain organic semiconducting solids.
Pure super-crystalline organic semiconductors will conduct electricity much differently than conventional solids. Super-crystalline semiconductors, for example, could create splashes of current on electrical contacts, even in a uniform electric field, say UA physicist Andrei Lebed and graduate student Si Wu.

If experiments do confirm Lebed’s and Wu’s results, the novel, exotic solid phase in organic semiconductors promises important technological applications. Such semiconductors will conduct electricity in novels ways. Another striking feature of the super-crystalline semiconductor is that its period and electronic properties might be tuned by changing the strength of the external magnetic field, Lebed said.’

Popularity: 4% [?]

Aug

16

Article: Hollywood Blockbusters – Unlimited Fun but Limited Science Literacy

August 16, 2007 | Leave a Comment

Hollywood Blockbusters: Unlimited Fun but Limited Science Literacy, C.J. Efthimiou and R.A. Llewellyn, arXiv:0707.1167v1. Abstract: In this article, we examine specific scenes from popular action and sci-fi movies and show how they blatantly break the laws of physics, all in the name of entertainment, but coincidentally contributing to science illiteracy. [via EETimes]

Excerpt: Hollywood directors and special effects creators work hard to create impressive scenes in movies to excite the audience. However, many scenes are created with absolute disregard of the physical laws in our universe. Sometimes the scene is so profoundly wrong that it is hard to be missed. However, often the absurdity is hard to detect by people not very fluent in science literacy and untrained in critical thinking. In this way, Hollywood is reinforcing (or even creating) incorrect scientific attitudes that can have negative results for the society. This is a good reason to recommend that all citizens be taught critical thinking and be required to develop basic science and quantitative literacy. (Download article, PDF)

Popularity: 4% [?]

Aug

16

How to Quantify the Uncertainty of “Instantaneously”

August 16, 2007 | Leave a Comment

‘We have broken speed of light’. ‘A pair of German physicists claim to have broken the speed of light – an achievement that would undermine our entire understanding of space and time. According to Einstein’s special theory of relativity, it would require an infinite amount of energy to propel an object at more than 186,000 miles per second. However, Dr Gunter Nimtz and Dr Alfons Stahlhofen, of the University of Koblenz, say they may have breached a key tenet of that theory.

The pair say they have conducted an experiment in which microwave photons – energetic packets of light – travelled “instantaneously” between a pair of prisms that had been moved up to 3ft apart.’

Popularity: 4% [?]

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