Large Hadron Collider smashes another record

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"Last night, a symbolic frontier was crossed,"said Michel Spiro, president of the board of the European Organisation forNuclear Research(CERN), explaining that the rate of sub-atomic smashups in its vast machine had multiplied 10-fold in the space of a month.

CERN's Large Hadron Collider (LHC) is housed in a 27-kilometre (16.9-mile) ring-shaped tunnel 100 metres (325 feet) below ground, straddling the French-Swiss border.

It is designed to accelerate beams ofprotonsto nearly thespeed of lightin contra-rotating directions.

Then, using magnets, the beams are then directed into labs where some of the protons collide while others escape.

Detectors record the seething sub-atomic debris, hoping to find traces of particles that can strengthen fundamental understanding of physics.

A month ago, the LHC set a record of 10 million collisions per second.

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The director general of the European Organization for Nuclear Research (CERN), Rolf-Dieter Heuer, speaks to journalists in May 2011. CERN runs the world's biggest particle collider, located on the outskirts of Geneva. It set a new record, a feat that should accelerate the quest to pinpoint the elusive particle known as the Higgs Boson, a senior physicist said.

"This is now 100 million collisions per second,"Spiro said at a conference in Paris on the"infinitely small and the infinitely big."

Among the puzzles that physicists are seeking to answer is the existence of the Higgs, which has been dubbed"theGod particle"for being mysterious yet ubiquitous.

If found, it would explain the nature of mass, filling a major piece of the theoretical construct of physics known as theStandard Model.

In London last week, CERN physicists said they believed that by the end of 2012 they could determine once and for all whether the Higgs existed or not.

Spiro said that this search would certainly be helped by the stepped-up pace of collision, which is the equivalent to sifting more earth in search of nuggets of gold.

"If we're lucky, and it (the Higgs) is in the right zone for expected mass, we may be able to find it this summer,"he said."On the other hand, ruling it out will take us to the end of next year."

To provide a confirmation would require notching up"at least 15"detections, he said.

The first proton collisions at theLHCoccurred on September 10, 2008. The smasher then had to endure a 14-month shutdown to fix technical problems.

It had been due to shut down in early 2012 for work enabling it to crank up to full power. But a decision was made several weeks ago to delay closure for a year to help the Higgs hunt.

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Long-standing question about swimming in elastic liquids, answered

Paulo Arratia, assistant professor ofmechanical engineeringand applied mechanics, along with student Xiaoning Shen, conducted the experiment. Their findings were published in the journalPhysical Review Letters.

Many animals,microorganismsand cells move by undulation, and they often do so through elastic fluids. From worms aeratingwet soilto sperm racing toward an egg,swimmingdynamics in elastic fluids is relevant to a number of facets of everyday life; however, decades of research in this area have been almost entirely theoretical or done with computer models. Only a few investigations involved live organisms.

“There have been qualitative observations of sperm cells, for example, where you put sperm in water and watch their tails, then put them in an elastic fluid and see how they swim differently,” Arratia said.“But this difference has never been characterized, never put into numbers to quantify exactly how muchelasticityaffects the way they swim, is it faster or slower and why.”

The main obstacle for quantitatively testing these theories with live organisms is developing an elastic fluid in which they can survive, behave normally and in which they can be effectively observed under a microscope.

Arratia and Shen experimented on the nematode C. elegans, building a swimming course for the millimeter-longworms. The researchers filmed them through a microscope while the creatures swam the course in many different liquids with different elasticity but the same viscosity.

Though the two liquid traits, elasticity and viscosity, sound like they are two sides of the same coin, they are actually independent of each other. Viscosity is a liquid’s resistance to flowing; elasticity describes its tendency to resume its original shape after it has been deformed. All fluids have some level of viscosity, but certain liquids like saliva or mucus, under certain conditions, can act like a rubber band.

Increased viscosity would slow a swimming organism, but how one would fare with increased elasticity was an open question.

“The theorists had a lot of different predictions,” Arratia said.“Some people said elasticity would make things go faster. Others said it would make things go slower. It was all over the map.

“We were the first ones to show that, with this animal, elasticity actually brings the speed and swimming efficiency down.”

The reason the nematodes swam slower has to do with how viscosity and elasticity can influence each other.

“In order to make our fluids elastic, we put polymers in them,” Arratia said.“DNA, for example, is a polymer. What we use is very similar to DNA, in that if you leave it alone it is coiled. But if you apply a force to it, the DNA or our polymer, will start to unravel.

“With each swimming stroke, the nematode stretches the polymer. And every time the polymers are stretched, the viscosity goes up. And as theviscositygoes up, it's more resistance to move through.”

Beyond giving theorists and models a real-world benchmark to work from, Arratia and Shen’s experiment opens the door for more live-organism experiments. There are still many un-answered questions relating to swimming dynamics and elasticity.

“We can increase the elasticity and see if there is a mode in which speed goes up again. Once the fluid is strongly elastic, or closer to a solid, we want to see what happens,” Arratia said.“Is there a point where it switches from swimming to crawling?”

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'Kinks' in tiny chains reveal Brownian rotation

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Biswal, an assistant professor in chemical and biomolecular engineering, said it's easy to view microscopic rods as they wiggle and weave under the influence of Brownian forces. But it's never been easy to see one spin along its axis, let alone measure that motion.

The technique created by Biswal and her team involves micron-scale rigid chains in liquid that act like perfect cylinders as they exhibit Brownian motion. But the rodlike chains incorporate the slightest ofimperfections. These nearly invisible"kinks"are just big enough to the measure the chain's rotation without influencing it.

Knowing how elongated molecules move in a solution is important to those who study the structure of liquid crystals orbiological processeslike the dynamics of lipid bilayers, the gatekeepers in living cells, Biswal said.

The research follows her lab's creation of a technique to build stiff chains ofparticlesthat mimic rod-like polymer or biological molecules. Using them like Legos, the lab assembles chains from DNA-grafted paramagneticpolystyreneparticles, which line up when exposed to a magnetic field and link together where the strands of DNA meet.

The result looks like a string of beads. Depending on the length and type of the DNA linkers, the rods can be stiff or flexible. Slight variations in the paramagnetic properties of each particle account for the kinks."We can make them robust; we can make them stable,"Biswal said."Now we're actually using them as a model forpolymer chains."

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See video of the microscopic rods turning

It's long been known that stiff rods in a solution rotate as they dance and are pushed by the atoms around them. Nearly two centuries ago, Robert Brown observed the rotation of flatarsenic trioxideflakes but had no way to characterize that motion. While Albert Einstein and others have since made progress in applying formulas to Brownian motion, the particulars of rotation have remained a relative mystery.

Dichuan Li, a graduate student in Biswal's lab and lead author of the new paper, was inspired to look at rotation after reading Brown's 1827 report in a classic-paper reading club."He noticed what he thought must be axial rotation, but he wasn't able to measure how fast it was moving,"Li said.

The new method is the first systematic approach to measuring the axial rotation of particles, he said. Once chains are formed, themagnetic fieldis released and the chains are free to move in a solution between two cover plates. Li isolated and filmed the structures as they twisted, and he later analyzed the kinks to quantify the chains' motion.

The finding opens a door to further study of longer or more complex polymer or biological chains, Biswal said. She said the paramagnetic beads could be used to model rods of varying stiffness,"even more flexible structures that can actually curve and bend, just like DNA, or branch-like structures. Then we can apply forces to them and see what happens."

Biswal hopes to take a closer look at how polymers entangle in materials of varying density."How they're stabilized by entanglement is not well understood,"she said."We're moving toward being able to create not just single chains for study, but large collections of these chains to see if they provide good models to look at things like entanglement."

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AMS is ready to discover the particle universe

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Cosmic rays are high-energy particles that shoot through space close to the speed of light. The newly installedAlpha Magnetic Spectrometer(AMS-02) will detect and catalogue these rays looking for new clues into the fundamental nature of matter.

One of the biggest mysteries that AMS will attempt to solve is where the cosmic rays originate. The fearsome energies of the particles could be generated in the tangled magnetic fields of exploded stars, or perhaps in the hearts of active galaxies, or maybe in places as yet unseen by astronomers.

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AMS-02 on ISS. Credits: NASA

By collecting and measuring vast numbers of cosmic rays and their energies, particle physicists hope to understand more about how and where they are born.

AMS-02 is the culmination of a programme that launched a prototype detector aboard theSpace Shuttlein 1998. Known as AMS-01, the experiment showed the great potential for discovery.

AMS-02 will operate on theInternational Space Stationto 2020 and beyond. Part of its mission is to search for antimatter within thecosmic rays. A European satellite package– Payload for Antimatter Matter Exploration and Light-Nuclei Astrophysics (PAMELA)– has already shown that there is more antimatter in space than conventional astrophysics expects.

One possibility that AMS-02 will investigate is whether it is coming from collisions between particles of‘dark matter’. This is the mysterious substance that astronomers believe may pervade the Universe, outweighing normal matter by about ten to one.

There is also the remote chance that AMS-02 will detect a particle of anti-helium, left over from the Big Bang itself.

“The most exciting objective of AMS is to probe the unknown; to search for phenomena which exist in nature that we have not yet imagined nor had the tools to discover,” says Nobel Prize Laureate Samuel Ting, who leads the international project.

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Assembling the AMS-02 magnet. Credits: CERN / AMS-02 Collaboration

Significant European participation has gone into the AMS collaboration. The instrument is a unique suite of different detectors and was mostly built in Europe by institutes in Italy, France, Germany, Spain, Portugal and Switzerland, together with the participation of US, China, Russia and Taiwan.

In all, the experiment’s team consists of more than 600 scientists from 56 institutes in 16 countries, with the European involvement coordinated by Prof. Roberto Battiston.

The installation of AMS-02 is part of the‘DAMA’ (dark matter) mission of ESA astronaut Roberto Vittori, one of the six astronauts on Space Shuttle Endeavor.

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'Critical baby step' taken for spying life on a molecular scale

In a study published today, Thursday, 19 May, in the Institute of Physics and the German Physical Society'sNew Journal of Physics, researchers have developed a technique, exploiting a specific defect in the lattice structure of diamond, to externally detect the spins of individual molecules.

Magnetic Resonance Imaging(MRI) has already taken advantage of a molecule's spin to give clear snapshots of organs and tissue within the human body, however to get a more detailed insight into the workings of disease, the imaging scale must be brought down to individualbiomolecules, and captured whilst thecellsare still alive.

Co-lead author Professor Phillip Hemmer, Electrical&Computer Engineering, Texas A&M University, said,"Many conditions, such as cancer and aging, have their roots at the molecular scale. Therefore if we could somehow develop a tool that would allow us to do magnetic resonance imaging of individual biomolecules in a living cell then we would have a powerful new tool for diagnosing and eventually developing cures for such stubborn diseases."

To do this, the researchers, from Professor Joerg Wrachtrup's group at the University of Stuttgart and Texas A&M University, used a constructed defect in the structure of diamond called a nitrogen vacancy (NV)—a position within thelattice structurewhere one of thecarbon atomsis replaced with a nitrogen atom.

Instead of bonding to four other carbon atoms, the nitrogen atom only bonds to three carbon atoms leaving a spare pair of electrons, acting as one of the strongest magnets on an atomic scale.

The most important characteristic of a diamond NV is that it has an optical readout—it emits bright red light when excited by a laser, which is dependent on which way the magnet is pointing.

The researchers found that if an external spin is placed close to the NV it will cause the magnet to point in a different direction, therefore changing the amount of light emitted by it.

This change of light can be used to gauge which way the external molecule is spinning and therefore create a one-dimensional image of the external spin. If combined with additional knowledge of the surface, or a second NV nearby, a more detailed image with additional dimensions could be had.

To test this theory, nitrogen was implanted into a sample of diamond in order to produce the necessary NVs. Externalmoleculeswere brought to the surface of the diamond, using several chemical interactions, for their spins to be analyzed.

Spins that exist within the diamond structure itself have already been modelled, so to test that the spins were indeed external, the researchers chemically cleaned the diamond surface and performed the analysis again to prove that the spins had been washed away.

Professor Hemmer continued,"Currently, biological interactions are deduced mostly by looking at large ensembles. In this case you are looking only at statistical averages and details of the interaction which are not always clear. Often the data is taken after killing the cell and spreading its contents onto a gene chip, so it is like looking at snapshots in time when you really want to see the whole movie."

"Clearly there is much work to be done before we can, if ever, reach our long-term goal of spying on the inner workings of life on the molecular scale. But we have to learn to walk before we can run, and this breakthrough represents one of the first critical baby steps."

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Some particles are able to flow up small waterfalls, physicists show

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With just a small bit of research, the team was able to show what seems to be counterintuitive; that it truly is possible for someparticles(and some of the liquid itself) to travel up a very small waterfall and into the reservoir behind it. While most anyone that has observedmoving waterhas likely noted the whirls and eddies that form when water tries to flow along or past obstacles, it’s difficult to imagine such counter-flows being created with sufficient force to actually push the fluid uphill. Althsuler et al. show that in fact, it can.

To see what was going on, they used two lab containers; one to hold the room temperature water, the other to hold the chalk they used instead of mate leaf bits (figuring it would be much easier to follow with the naked eye). They then placed an open half-cylinder shapedchannelbetween the two containers that would allow water to flow smoothly from the first container down the channel, where it would then drop into the second container. With this setup, they discovered that as the liquid came rushing down the channel, the main mass ofwatertraveled down the center, creating vortices that caused small amounts of fluid to travel along the edges of the channel in the opposite direction, allowing the chalk to work its way up to the higher level container. But, they also discovered by varying the height of the channel, that it only occurred when the dropping distance was very slight; in this case, 1 centimeter, or less.

As a result of this study, it’s likely that certain industrial processes might have to be modified to make certain unintentional contamination doesn’t occur that is currently being overlooked. Also, its likely future research on thisphenomenonwill need to be done to determine if other factors can affect the height of the fall or the amount of particulate that is able to travel uphill to another vessel.

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Physicists accelerate simulations of thin film growth

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Jacques Amar, Ph.D., professor of physics at the University of Toledo (UT), studies the modeling and growth of materials at the atomic level. He uses Ohio Supercomputer Center (OSC) resources and Kinetic Monte Carlo (KMC) methods to simulate the molecularbeam epitaxy(MBE) process, where metals are heated until they transition into a gaseous state and then reform as thin films by condensing on a wafer in single-crystal thick layers.

"One of the main advantages of MBE is the ability to control the deposition of thin films and atomic structures on theatomic scalein order to create nanostructures,"explained Amar.

Thin filmsare used in industry to create a variety of products, such as semiconductors, optical coatings, pharmaceuticals andsolar cells.

"Ohio's status as a worldwide manufacturing leader has led OSC to focus on the field of advanced materials as one of our areas of primary support,"noted Ashok Krishnamurthy, co-interim co-executive director of the center."As a result, numerous respected physicists, chemists and engineers, such as Dr. Amar, have accessed OSC computation and storage resources to advance their vital materials science research."

Recently, Amar leveraged the center's powerful supercomputers to implement a"first-passage time approach"to speed up KMC simulations of the creation of materials just a few atoms thick.

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In tests run on Ohio Supercomputer Systems, Jacques Amar, Ph.D., compared the surface simulations of thin film copper growth using regular (a) Kinetic Monte Carlo methods (KMC) and (b) first-passage-time distribution KMC simulations. Credit: Amar/University of Toledo

"The KMC method has been successfully used to carry out simulations of a wide variety of dynamical processes over experimentally relevant time and length scales,"Amar noted."However, in some cases, much of the simulation time can be 'wasted' on rapid, repetitive, low-barrier events."

While a variety of approaches to dealing with the inefficiencies have been suggested, Amar settled on using a first-passage-time (FPT) approach to improve KMC processing speeds. FPT, sometimes also called first-hitting-time, is a statistical model that sets a certain threshold for a process and then estimates certain factors, such as the probability that the process reaches that threshold within a certain amount time or the mean time until which the threshold is reached.

"In this approach, one avoids simulating the numerous diffusive hops of atoms, and instead replaces them with the first-passage time to make a transition from one location to another,"Amar said.

In particular, Amar and colleagues from the UT department of Physics and Astronomy targeted two atomic-level events for testing the FPT approach: edge-diffusion and corner rounding. Edge-diffusion involves the"hopping"movement of surface atoms– called adatoms– along the edges of islands, which are formed as the material is growing. Corner rounding involves the hopping of adatoms around island corners, leading to smoother islands.

Amar compared the KMC-FPT and regular KMC simulation approaches using several different models of thin film growth: Cu/Cu(100), fcc(100) and solid-on-solid (SOS). Additionally, he employed two different methods for calculating the FPT for these events: the mean FPT (MFPT), as well as the full FPT distribution.

"Both methods provided"very good agreement"between the FPT-KMC approach and regular KMC simulations,"Amar concluded."In addition, we find that our FPT approach can lead to a significant speed-up, compared to regular KMC simulations."

Amar's FPT-KMC approach accelerated simulations by a factor of approximately 63 to 100 times faster than the corresponding KMC simulations for the fcc(100) model. The SOS model was improved by a factor of 36 to 76 times faster. For the Cu/Cu(100) tests, speed-up factors of 31 to 42 and 22 to 28 times faster were achieved, respectively, for simulations using the full FPT distribution and MFPT calculations.

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