Membrane protein structure can be seen using new X-ray free-electron lasers

About 70% of drugs on the market today depend on the activity ofmembrane proteins, which are complexmoleculesthat form the membranes of thecellsin our body.

A major problem for the design of new pharmaceuticals, often known as the“membrane protein problem”, is that they do not form the crystals needed to enable further investigation of the structure to design better drugs.

A major international effort is being mounted to determine the structures of membrane proteins using XFELs - large facilities that create such a bright beam of X-rays it is possible to see the X-ray light bouncing off a single molecule without forming a crystal.

Professor Keith Nugent, Laureate Professor and ARC Federation Fellow and Director of the Australian Research Council Centre of Excellence for Coherent X-ray Science (CXS) at the University of Melbourne said a key problem was that the light from an XFEL was so bright a molecule would start to disintegrate in less than one thousandth of a millionth of a millionth of a second.

In a paper published today in the journalNature Physics, Professor Nugent and Associate Professor Harry Quiney from the ARC Centre of Excellence for Coherent X-ray Science (CXS) have developed a method by which the damage from the XFEL pulse may be included in the data analysis.

Associate Professor Quiney, also of the School of Physics at the University of Melbourne, said results showed that high-resolution molecular structures may be obtained from X-ray scattering data using a few-femtosecond pulse from an XFEL, even if the interaction resulted in significant electronic damage to the target.

“This result has far-reaching implications for the future development of structural biology, because it removes a significant obstacle to the practical realisation of the molecular microscope using XFEL sources,” he said.

It also provides important insights into the complex, turbulent and poorly-understood interactions that are driven by the interaction of an XFEL pulse with an atom, molecule or solid.

Their approach uses sophisticated molecular physics and careful data analysis to determine a new approach to measuring molecular structure.

Although still at the theoretical and computation level when put into practice this discovery will remove a major road-block in the path to solving the membrane protein problem.

This year, CXS signed an agreement with Japanese colleagues and will host the 4th Asia-Oceania Workshop on Science with X-ray Free Electron Lasers in 2011.

Professor Nugent said this was an extremely exciting time for X-ray science.

“My colleagues and I are convinced that our recent work is a critically important step forward,” he said.

“We are very much looking forward to working with our Japanese colleagues in the coming years”.

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Dutch researchers build affordable alternative to mega-laser X-FEL

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It's one of the few remaining 'holy grails' of science: a system that allows you to observe the extremely high-speed molecular processes at anatomic scale. You could call it an ultra-fast video microscope. Instead of visible light this kind of system uses X-rays or electrons, because it requires radiation with a wavelength of less than a nanometer. The X-rays or electrons have to be emitted in ultra short pulses, so that the exposure time is extremely short. However these pulses are not easy to generate. An X FEL uses X-ray pulses for this purpose, generated by accelerating electrons in an accelerator of a kilometer, or longer. These electrons are then converted into X-rays. An installation of this kind is very costly, uses large amounts of energy and needs a whole team to operate it. A European X-FEL, which will cost a billion euro, is currently under construction in Hamburg (Germany).

TU/e doctoral candidate ir. Thijs van Oudheusden has developed a machine that in many respects can compete with this billion-euro facility, based on ideas from his co supervisor dr.ir. Jom Luiten. The essence of their 'poor man's X-FEL' is that it uses electrons instead of X-rays."Why convert electrons into X-rays if you can use the electrons themselves?", asks Van Oudheusden."As well as that you only need to give the electrons a low energy, so you can accelerate them in just a centimeter. That's why the whole system fits on a tabletop."

The physical barrier that Van Oudheusden had to overcome is that the electrons in electron bunches repel each other. This causes the electron bunches to expand, making them longer than the desired 100 femtoseconds (1 femtosecond is 10-15 second), which in turn would make the 'video microscope' too slow. Jom Luiten thought of a solution to prevent the undesired expansion. The key was to create bunches of exactly the right shape, so they can be controlled and focused by means of electrical fields into bunches of the desired type and length. All with a number ofelectrons(1 million) that is sufficient to create a diffraction pattern in just a single shot.

Supervisor prof.dr. Marnix van der Wiel believes that half to three-quarters of the kind of research that can be done on an X-FEL can also be done with the 'poor man's X_FEL'. But this doesn't immediately mean that the latter is automatically a lot cheaper in relation to the scientific output that can be generated with it."The X-FEL at Stanford works non-stop, all year round, and is used by thousands of research groups over several decades. So if you're allocated time on the system you have to take all your equipment to the USA, where you have to stick to a very strict schedule. Our finding is a good alternative for people who want to have the freedom to do research in their own labs. As far as the costs are concerned, it depends on the user if our system will turn out to be cheaper on a per publication basis."

TU/e spin-off AccTec BV intends to build the machine developed by Van Oudheusden and Luiten and to sell it to scientific users. AccTec expects the total price to be below half a million euro.

Thijs van Oudheusden gained his PhD on 13 December with his doctoral thesis entitled 'Electron source for sub-relativistic single-shot femtosecond diffraction'.

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Trapped micro-cylinders act a bit like neurons

Both the micro-cylinders and theneuronsare 'excitable', i.e. they respond to an external disturbance by producing a pulse (e.g. a voltage) of a given, fixed size. The results of this study was published online on theNature Physicswebsite on December 19th.

Simultaneously, the researchers have shown that the rotating micro-cylinders can detect the presence of microscopic particles in liquid. This is because the presence of such particles in the vicinity of a rotating micro-cylinder produces a clearly measurable disturbance in the torque experienced by the cylinder. This provides a means of detecting, counting, or separating cells (or other microscopic particles) in liquids.

For the purposes of this study, the researchers employed optical torque tweezers. This unique instrument is capable of measuring both the force and angular momentum exerted on microscopic objects, including biological molecules such as DNA.

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Researchers develop first high-temperature spin-field-effect transistor

The team has developed an electrically controllable device whose functionality is based on an electron'sspin. Their results, the culmination of a 20-year scientific quest involving many international researchers and groups, are published in the current issue ofScience.

The team, which also includes researchers from the Hitachi Cambridge Laboratory and the Universities of Cambridge and Nottingham in the United Kingdom as well as the Academy of Sciences and Charles University in the Czech Republic, is the first to combine the spin-helix state and anomalous Hall effect to create a realistic spin-field-effect transistor (FET) operable at high temperatures, complete with an AND-gate logic device— the first such realization in the type of transistors originally proposed by Purdue University's Supriyo Datta and Biswajit Das in 1989.

"One of the major stumbling blocks was that to manipulate spin, one may also destroy it,"Sinova explains."It has only recently been realized that one could manipulate it without destroying it by choosing a particular set-up for the device and manipulating the material. One also has to detect it without destroying it, which we were able to do by exploiting our findings from our study of the spin Hall effect six years ago. It is the combination of these basic physics research projects that has given rise to the first spin-FET."

Sixty years after the transistor's discovery, its operation is still based on the same physical principles of electrical manipulation and detection of electronic charges in a semiconductor, says Hitachi's Dr. Jorg Wunderlich, senior researcher in the team. He says subsequent technology has focused on down-scaling the device size, succeeding to the point where we are approaching the ultimate limit, shifting the focus to establishing new physical principles of operation to overcome these limits— specifically, using its elementary magnetic movement, or so-called"spin,"as the logic variable instead of the charge.

This new approach constitutes the field of"spintronics,"which promises potential advances in low-power electronics, hybrid electronic-magnetic systems and completely new functionalities.

Wunderlich says the 20-year-old theory of electrical manipulation and detection of electron's spin in semiconductors— the cornerstone of which is the"holy grail"known as the spin transistor— has proven to be unexpectedly difficult to experimentally realize.

"We used recently discovered quantum-relativistic phenomena for both spin manipulation and detection to realize and confirm all the principal phenomena of the spin transistor concept,"Wunderlich explains.

To observe the electrical manipulation and detection of spins, the team made a specially designed planar photo-diode (as opposed to the typically used circularly polarized light source) placed next to the transistor channel. By shining light on the diode, they injected photo-excited electrons, rather than the customary spin-polarized electrons, into the transistor channel. Voltages were applied to input-gate electrodes to control the procession of spins via quantum-relativistic effects. These effects— attributable to quantum relativity— are also responsible for the onset of transverse electrical voltages in the device, which represent the output signal, dependent on the local orientation of processing electron spins in the transistor channel.

The new device can have a broad range of applications in spintronics research as an efficient tool for manipulating and detecting spins in semiconductors without disturbing the spin-polarized current or using magnetic elements.

Wunderlich notes the observed output electrical signals remain large at high temperatures and are linearly dependent on the degree of circular polarization of the incident light. The device therefore represents a realization of an electrically controllable solid-state polarimeter which directly converts polarization of light into electric voltage signals. He says future applications may exploit the device to detect the content of chiral molecules in solutions, for example, to measure the blood-sugar levels of patients or the sugar content of wine.

This work forms part of wider spintronics activity within Hitachi worldwide, which expects to develop new functionalities for use in fields as diverse as energy transfer, high-speed secure communications and various forms of sensor.

While Wunderlich acknowledges it is yet to be determined whether or not spin-based devices will become a viable alternative to or complement of their standard electron-charge-based counterparts in current information-processing devices, he says his team's discovery has shifted the focus from the theoretical academic speculation to prototype microelectronic device development.

"For spintronics to revolutionize information technology, one needs a further step of creating a spin amplifier,"Sinova says."For now, the device aspect— the ability to inject, manipulate and create a logic step with spin alone— has been achieved, and I am happy that Texas A&M University is a part of that accomplishment."

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Antarctic IceCube observatory to hunt dark matter

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Building theIceCube, the world's largest neutrino observatory, has taken a gruelling decade of work in the Antarctic tundra and will help scientists study space particles in the search fordark matter, invisible material that makes up most of the Universe's mass.

The observatory, located 1,400 metres underground near the US Amundsen-Scott South Pole Station, cost more than 270 million dollars, according to the US National Science Foundation (NSF).

The cube is a network of 5,160optical sensors, each about the size of a basketball, which have been suspended on cables in 86 holes bored into the ice with a specially-designed hot-water drill.

NSF said the final sensor was installed in the cube, which is one kilometre (0.62 miles) long in each direction, on December 18. Once in place they will be forever embedded in thepermafrostas the drill holes fill with ice.

The point of the exercise is to study neutrinos,subatomic particlesthat travel at close to the speed of light but are so small they can pass through solid matter without colliding with any molecules.

Scientists believe neutrinos were first created during the Big Bang and are still generated by nuclear reactions in suns and when adying starexplodes, creating a supernova.

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A handout picture taken on December 18, released by the US National Science Foundation (NSF) on December 23, shows the final Digital Optical Module (DOM) IceCube project members. An extraordinary underground observatory for subatomic particles has been completed in a huge cube of ice one kilometre on each side deep under the South Pole, researchers said.

Trillions of them pass through the entire planet all the time without leaving a trace, but the IceCube seeks to detect the blue light emitted when an occasional neutrino crashes into an atom in the ice.

"Antarcticpolar icehas turned out to be an ideal medium for detecting neutrinos,"the NSF said in a statement announcing the project's completion.

"It is exceptionally pure, transparent and free of radioactivity."

Scientists have hailed the IceCube as a milestone for international research and say studying neutrinos will help them understand the origins of the Universe.

"From its vantage point at the end of the world, IceCube provides an innovative means to investigate the properties of fundamental particles that originate in some of the most spectacular phenomena in the Universe,"NSF said.

Most of the IceCube's funding came from the NSF, with contributions from Germany, Belgium and Sweden.

Researchers from Canada, Japan, New Zealand, Switzerland, Britain and Barbados also worked on the project.

It is operated by the University of Wisconsin-Madison.

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Santa: A Claus-et physicist

Several professors in the school's Department of Mechanical and Aerospace Engineering recently asked their students to explore the aerodynamic and thermodynamic challenges of delivering gifts to millions of children worldwide in a single night from an airborne sleigh.

The results, posted atweb.ncsu.edu/abstract/tag/science-of-santa, posit thatSanta Clausis a brilliant engineer and physicist.

One of the professors, Dr. Larry Silverberg, said the students concluded that Santa has expanded Einstein's theory of relativity to take advantage of"relativity clouds"that stretch time and bend the universe."Relativity clouds are controllable domains - rips in time - that allow him months to deliver presents while only a few minutes pass on Earth,"he said.

The site reports that his sleigh must be an advanced aerodynamic design made of honeycombed titanium alloy, capable of altered shape in flight and yet stable enough for landings on steep roofs. Laser sensors would help select the fastest route, and a porous, nano-structured skin outfitted with a low-pressure system reduces drag up to 90 percent, Silverberg said.

Silverberg confessed that he really didn't understand all of it, even though he's an expert in unified field theory.

"The man is a genius,"Silverberg said of Santa, whom he described as"jolly, but learned."

What about figuring out who is naughty and nice? Theory: A mile-wide antenna of super-thin mesh relying on electromagnetic induction principles picks up brain waves of children around the world. Filter algorithms organize desires and behaviors, and microprocessors feed the data to an onboard sleigh guidance system.

Also, Santa must be checking kids' Facebook and Twitter accounts.

And does Santa carry all those presents in a single sleigh? Not possible, according to Silverberg.

More plausible: He creates them on-site, i.e., on each rooftop, using a reversible thermodynamic processor - a sort of nano-toymaker known as the"magic sack."The carbon from chimney soot would be a common building block.

But the students theorized that he still delivers presents the old-fashioned way, climbing down chimneys, dressed in a fire-resistant halocarbon polymer suit.

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Chameleon model tries to explain the origin of dark energy

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According to thechameleon model, dark energy stems from particles that change their mass depending upon the local environment.

In the presence of ordinary matter, chameleons are massive particles that mediate a short-range force– too short to have appeared in searches for new forces. But in the vacuum of space, chameleons would have small masses. In principle, chameleons would interact with electromagnetic fields and, under certain conditions, could create photons, and photons could create chameleons.

Scientists of the Chameleon Afterglow Search (CHASE) explore this possibility by shining a laser beam into a vacuum chamber located inside a long, strong magnet. Traversing the magnetic field, the laser light might produce a population of chameleon particles within the chamber. When the laser is turned off, the chameleons would continue to interact with the magnetic field and produce an observable afterglow of photons.

No chameleon afterglow signal was seen in the CHASE data, which allowed the collaboration to place more stringent limits on chameleon models ofdark energy. The new limits span a range of nearly four orders of magnitude in chameleon mass (see graphic) and are nearly five orders of magnitude more stringent than previous bounds from particle collider experiments.

The results are available in thearXiv preprint serverand will soon appear inPhysical Review Letters.

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