APS Physics Tip Sheet – Feb 11, 2014

In this issue: Biocompatible Carbon, Quantum Lego, A Microscopic View of Cracking

* Need an outside expert to comment on your science story? Check out the APS Science Expert Exchange:http://apsphysicsnewsticker.blogspot.com/2014/01/aps-science-expert-exchange.html

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Biocompatible Carbon 

Simulations show that lipid membranes called liposomes can be used as biocompatible solvents for carbon nanoparticles in medical applications. 

C₆₀ fullerenes, aka buckyballs, are being investigated for applications in nanomedicine, from drug delivery vectors to diagnostic contrast agents. Their use faces an important challenge: there are few solvents for fullerenes that are nontoxic and biocompatible. Recent work has shown that liposomes (vesicles made of lipid bilayers) may be an efficient fullerene solvent, but little is known on how to design optimal fullerene-carrying liposomes. Now, a research team in France has presented simulations that explain how liposomes dissolve fullerene clusters and suggest they may be regarded as biocompatible solvents that can be chemically tuned to specific medical applications.  

* J Barnoud, G Rossi, Luca Monticelli (contact author), “Lipid membranes as solvents for carbon nanoparticles”, Physical Review Letters (expected publication date: Feb 12)

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Quantum Lego

Theorists have proposed a modular design for quantum computers that can be used to assemble large numbers of qubits into a fault-tolerant device. 

A major challenge of quantum computing is the assembly of individual qubits into an actual working device: a large number of logic elements need to communicate over data channels while preserving the fragile entanglement between qubits that is the basis of any quantum advantage. A team of researchers from the US, Canada and China has confronted this problem with a proposed modular quantum computing design that is scalable to a large number of qubits while remaining fault tolerant. The scheme is based on building blocks made of arrays of trapped ions controlled with optical or microwave pulses and connected via optical fibers.

* C Monroe, Jungsang Kim (contact author), “Large Scale Modular Quantum Computer Architecture with Atomic Memory and Photonic Interconnects”, Physical Review A (expected publication date: Feb 13)

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A Microscopic View of Cracking

A new microscopic model describes how porous materials such as sandstone break, providing good agreement with the behavior observed in experiments.

Modeling the catastrophic failure of materials has a wide range of applications, from earthquake science to civil engineering. The description of such fracture processes is complicated by the fact that microscopic cracks can propagate all the way up to the size of mountains. As a consequence, most currently used models are too simplistic to connect to experiments. A team of researchers from Hungary and Scotland presents an improved model of cracking in a porous material (such as sedimentary rock), which better describes the microscopic material structure. They found that cracks spread through the material in cascading avalanches that happen at erratic intervals, separated by quiescent periods. Their model can reproduce well the complex behavior observed in experiments, including many features of cracking deduced from measurements of the sound waves that accompany the propagation of cracks. 

* Ferenc Kun (contact author), I Varga, S Lennartz-Sassinek, IG Main, Physical Review Letters (expected publication date:Feb 14)

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Journal articles and preprints are available to journalists on request. 

Contact: Matteo Rini Tel: +1 631 591 4224 (office), +1 646 288 5441 (cell), email: mrini@aps.org

Matteo Rini, PhD 

Deputy Editor, Physics 

mrini@aps.org  

http://physics.aps.org

Experiments explain the shapes of curly hair

By observing elastic rods hanging under their own weight, each with a different amount of "natural" curvature, researchers described several type of curls that occur in hair and the conditions that lead to them. 

 Abstract from manuscript LL14067, to be published in Phys. Rev. Lett.:

We investigate how natural curvature affects the configuration of a thin elastic rod suspended under its own weight, as when a single strand of hair hangs under gravity. We combine precision desktop experiments, numerics, and theoretical analysis to explore the equilibrium shapes set by the coupled effects of elasticity, natural curvature, nonlinear geometry, and gravity. A phase diagram is constructed in terms of the control parameters of the system, namely the dimensionless curvature and weight, where we identify three distinct regions: planar curls, localized helices and global helices. We analyze the stability of planar configurations, and describe the localization of helical patterns for long rods, near their free end. The observed shapes and their associated phase boundaries are then rationalized based on the underlying physical ingredients.

Contact:
Matteo Rini
631 591 4224 (office)
646 288 5441 (cell)
mrini@aps.org

APS Science Expert Exchange

The APS Science Expert Exchange is a new resource available to professional journalists. It consists of database of hundreds of American Physical Society members who have identified areas where they would be willing to serve as experts for the press.

Physicists listed in the database can offer insight to a wide range of topics, from accelerators to x-rays.

To gain access to the APS Science Expert Exchange contact James Riordon at riordon@aps.org

The following is a complete list of the subject ares currently covered in the APS Science Expert Exchange. (New subject areas are being added daily.)

• Accelerator and Beam Physics
  • Experimental
  • Theoretical
• Acoustics
  • Architectural
  • Music
• Aerosol
  • Chemistry
  • Physics
• Astrophysics

APS Physics Tip Sheet – Jan 14, 2013

In this issue: Moving Objects with Sound, Ball Lightning Captured on Film, No Dark Matter Detected at LHC, More Four-Quark Clovers

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Moving Objects with Sound

Researchers have demonstrated a contactless technique that uses sound waves to levitate and manipulate tiny objects.

The ability to manipulate matter without touching it might be of interest for many applications, from handling high-purity samples to microgravity experiments that would otherwise require expensive space-borne set-ups. Researchers at the ETH in Switzerland have now reported a technique for lifting and spinning small droplets, as well as putting them into tiny orbits, by means of acoustic waves. The team was able to perform such levitation tricks by creating acoustic standing waves between an acoustic transducer and a reflector. By varying the geometry of the waves, they could trap a spherical droplet, squish it into an oblate shape, and make it spin while suspended in air, or drive the droplet in a controlled orbital motion without causing its breakup.

* D Foresti, Dimos Poulikakos (contact author), “Acoustophoretic Contactless Elevation, Orbital Transport and Spinning of Matter in Air”, Physical Review Letters (expected publication date: Jan 15)

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Ball Lightning Captured on Film

A fortuitous observation has allowed researchers to record ball lightning and analyze its light, providing insights into the origin of the mysterious atmospheric phenomenon.

Ball lightning - a rare and transient electrical phenomenon - is still very poorly understood. It typically appears during thunderstorms as a glowing sphere whose size may range from that of a golf ball to several meters, floating in the air for up to tens of seconds. But a fortuitous observation during field experiments on ordinary lightning has now allowed a Chinese research team to record a ball lightning event and analyze its size, colors and light. The results offer important clues about what the glowing balls are made of: the observation of spectral lines of soil elements such as silicon, iron and calcium support the hypothesis that such ball lightning is generated by conventional lightning striking the soil on the ground.

* Jianyong Cen (contact author), P Yuan, and S Xue, “Observation of the optical and spectral characteristics of ball lightning”, Physical Review Letters (expected publication date: Jan 17)

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No Dark Matter Detected at LHC

The ATLAS collaboration has found no evidence of dark matter production in LHC particle collisions.

Most dark matter searches are trying to catch dark-matter particles as they stream through the Earth. But many theories suggest dark matter particles could be generated in the high-energy particle collisions produced at the LHC. Such particles would escape through the LHC detectors unnoticed, but their existence could be inferred from the amount of energy or momentum missing after a collision. The ATLAS collaboration at the LHC has searched for signals of dark matter production during the 2012 LHC run. It found no evidence of such production and used this to place some of the strongest constraints to date on dark-matter models.

* ATLAS collaboration (contact: atlas.publications@cern.ch) et al, “Search for Dark Matter in Events with a Hadronically Decaying W or Z Boson and Missing Transverse Momentum in pp Collisions at √s = 8 TeV with the ATLAS Detector”, Physical Review Letters (expected publication date: Jan 16)

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More Four-Quark Clovers

In April 2013, particle physicists discovered a particle, called Zc(3900) that appeared to be composed of four quarks rather than the usual two or three. The BESIII Collaboration — one of the two groups to first spot the new particle — has now studied a similar set of reactions, finding further hints of a four-quark particle with very similar mass and characterizing for the first time its properties, such as angular momentum and symmetry.

* BESIII Collaboration (contact author: Stephen L Olsen) et al, “Observation of a charged (DD̄*)± mass peak in e+e-→πDD̄* at √s=4.26 GeV”, Physical Review Letters (expected publication date: Jan 14)

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Journal articles and preprints are available to journalists on request. 

Contact: Matteo Rini Tel: +1 631 591 4224 (office), +1 646 288 5441 (cell), email: mrini@aps.org

Matteo Rini, PhD 

Deputy Editor, Physics 

mrini@aps.org  

http://physics.aps.org

APS Physics Tip Sheet – Dec 17, 2013

In this issue: Plant Power, New Light On Uranium Chemistry, Not a Lumpy Universe

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Plant Power

Light-harvesting molecules in plants inspire a proposal for more efficient solar cells.

In solar cells, the energy of photons is absorbed by electrons, which become unbound and can generate an electrical current. But the electrons can also quickly recombine, which poses limits on the efficiency of most photoelectric materials. Molecules in plants, on the other hand, can, under certain conditions, convert photons to electrons with near perfect efficiency, and recent results suggest this is the result of quantum-mechanical effects. Researchers in Cambridge (UK) have proposed a model photocell inspired by how plants convert sunlight into useful energy. According to their calculation, their system of three molecules, thanks to quantum effects, could have a 35% higher efficiency than a cell that works based on classical physics only. 

* Celestino Creatore (contact author), MA Parker, S Emmott, and AW Chin, “An efficient biologically-inspired photocell enhanced by delocalised quantum states”, Physical Review Letters (expected publication date: Dec 18)

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New Light On Uranium Chemistry

The X-ray analysis of uranium oxides calls for a revision of the current thinking on uranium chemistry.

The storage of spent fuel poses one of the most challenging problems to the nuclear industry. Safe disposal, for instance in deep geological repositories, requires a thorough understanding of the possible chemical forms of uranium in a fuel rod: different oxides may have different properties, such as their solubility in water. At the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, a research team has used X-ray techniques to probe several oxides of uranium. The authors were able to study how uranium dioxide – the main component of nuclear fuel rods – transforms into other types of oxides. The results will help predict uranium’s behavior in a number of chemical reactions relevant to long term nuclear-fuel storage.

* Kristina O Kvashnina (contact author), SM Butorin, P Martin, and P Glatzel, “Chemical state of complex uranium oxides”, Physical Review Letters (expected publication date: Dec 17)

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Not a Lumpy Universe

Astrophysical observations suggest the expansion of the universe is accelerating – a puzzling fact attributed to the presence of the yet-to-be-deciphered dark energy. But there are alternative theories that do not invoke a new form of energy. A popular one explains the observed expansion rates by assuming the universe is “lumpy”, i.e. its density is not uniform on large scales. But a team of theorists at the University of Texas (Dallas) has now shown a lumpy universe model would be at odds with observations of the speed by which clusters of galaxies grow. Instead, the authors show that some form of dark energy would still be needed to model galaxy-cluster growth.  

* Mustapha Ishak (contact author), A Peel, and MA Troxel, “Stringent restriction from the growth of large-scale structure on apparent acceleration in inhomogeneous cosmological models”, Physical Review Letters (expected publication date: Dec 19)

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Journal articles and preprints are available to journalists on request. 

Contact: Matteo Rini Tel: +1 631 591 4224 (office), +1 646 288 5441 (cell), email: mrini@aps.org

Physical Review Applied Call for Papers APS is now accepting submissions for Physical Review Applied, the newest member of thePhysical Review family. Dedicated to publishing the highest quality research at the intersection of physics and engineering, Physical Review Applied will debut in early 2014. Troy Shinbrot, Professor of Biomedical Engineering at Rutgers University, is the Editor forPhysical Review Applied and will work closely with a distinguished and diverse Editorial Board. Professor Shinbrot received his Ph.D. in Physics from the University of Maryland and held positions in industry before joining the Rutgers faculty in 1998. His research focuses on computational biology and multiphase flow. He was selected as an APS Outstanding Referee in 2008. Physical Review Applied expands the current APS family of journals to provide comprehensive coverage of applied physics research. This new journal will include Letters, Research Articles, and Review Articles and follow the same high-quality peer-review process as the other Physical Review journals. More information about Physical Review Applied, including manuscript submission, is available online at journals.aps.org/prapplied. Contact: prapplied@aps.org The American Physical Society (www.aps.org) is a non-profit membership organization working to advance and diffuse the knowledge of physics through its outstanding research journals, scientific meetings, and education, outreach, advocacy and international activities. APS represents 50,000 members, including physicists in academia, national laboratories and industry in the United States and throughout the world. Society offices are located in College Park, MD (Headquarters), Ridge, NY, and Washington, DC.

APS Physics Tip Sheet – Dec 10, 2013

In this issue: Dark Matter Signatures?, Detecting Molecules on a Chip, Liquid-Crystal Flowers, Counting Atoms Up To 1200

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Dark Matter Signatures?

Results from one the leading dark-matter-detection collaborations have revealed potential signatures of dark-matter particles, but more recent experiments suggest dark matter has yet to be detected.

The Cryogenic Dark Matter Search (CDMS) experiment at Fermilab in Illinois and the Large Underground Xenon (LUX) experiment in South Dakota have reported results from their most extensive search for dark-matter candidate particles called Weakly Interacting Massive Particles (WIMPs). In underground facilities providing shielding from cosmic radiation, CDMS detectors have recorded three blips that could signal a dark-matter particle hitting the detector. The finding would point to the existence of WIMPs nine times as massive as protons. But more recently, a similar experiment at the Large Underground Xenon (LUX) experiment in South Dakota, which nominally features a much higher sensitivity, announced it has seen no evidence for dark matter. Scientists are still debating whether the new LUX result rules out the CDMS finding. 

* CDMS Collaboration (contact author: Enectali Figueroa-Feliciano) et al, “Silicon detector dark matter results from the final exposure of CDMS II”, Physical Review Letters (expected publication date: Dec 16)

* LUX Collaboration (contact author: Blair Edwards), “First results from the LUX dark matter experiment at the Sanford Underground Research Facility”, http://arxiv.org/abs/1310.8214

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Detecting Molecules on a Chip

A new setup allows the detection of molecules trapped on the surface of a microchip.

Modern labs-on-a-chip can perform experiments on atoms or ions trapped on the surface of microchips, with applications ranging from quantum computing to gravitation sensing. Molecules would offer much richer properties than atoms and ions, but molecule-chips have lagged behind, partly because molecules are more difficult to cool, control and observe. A research group at the Fritz Haber Institute of the Max Planck Society, Germany, has developed the first on-chip molecular detector. The researchers use a laser to ionize a few carbon-monoxide molecules trapped on the chip, and then image the resulting ion cloud on a phosphor screen several centimeters above the chip.

* S Marx, Gabriele Santambrogio (contact author) et al, “Imaging cold molecules on a chip”, Physical Review Letters (expected publication date: Dec 12)

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Liquid-Crystal Flowers

Researchers at the University of Pennsylvania have demonstrated a method for engineering flower-shaped liquid-crystal structures, in which the molecules are aligned around multiple ellipses resembling the petals on a daisy. The structures could be used to make microlenses that focus light efficiently. 

* DA Beller, Randal D Kamien (contact author) et al, “Focal conic flower textures at curved interfaces”, Physical Review X (expected publication date: Dec 10)

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Counting Atoms Up To 1200

Many experiments with cold atoms rely on the exact determination of the number of atoms, in particular high-precision metrology applications like atomic clocks. Researchers at the University of Heidelberg have set a record for the number of atoms that can be counted with single-atom precision. By monitoring the light emitted by an ensemble of cold, trapped atoms, the researchers were able to count up to 1200 atoms, improving on the previous record by almost an order of magnitude. 

* DB Hume (contact author) et al, “Accurate atom counting in mesoscopic ensembles”, Physical Review Letters (expected publication date: Dec 16)

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Journal articles and preprints are available to journalists on request. 

Contact: Matteo Rini Tel: +1 631 591 4224 (office), +1 646 288 5441 (cell), email: mrini@aps.org