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

APS Physics Tip Sheet – Dec 3, 2013

In this issue: Distributing Entanglement on the Cheap, Asking Photons Where They Have Been, Why Swimming Particles Aggregate

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Distributing Entanglement on the Cheap

Three new experiments demonstrate how entanglement can be shared between two distant parties without the need of sending an entangled carrier.

Entangled states lie at the heart of quantum physics and can be used as a powerful resource in emerging quantum technologies such as quantum key cryptography. The disruption of entanglement, which can be caused by any interaction with the environment, poses the hardest challenge to practical applications. But three different international research teams have now demonstrated experiments that distribute entanglement between two distant parties by sending a non-entangled carrier. Their arrangements place this carrier in a "cheaper," so-called separable state, which is still tied, or “correlated,” to the two parties, but in a way that is less fragile to environmental disturbance than entanglement is. The scheme may thus help realize communication schemes that are more robust to noise.

* Christian Peuntinger (contact author) et al, “Distributing entanglement with separable states”, Physical Review Letters (expected publication date: Dec 4)

* CE Vollmer, Roman Schnabel (contact author) et al, “Experimental entanglement distribution by separable states”, Physical Review Letters (expected publication date: Dec 4)

* A Fedrizzi, Tomasz Paterek (contact author) et al, “Experimental distribution of entanglement with separable carriers”, Physical Review Letters (expected publication date: Dec 4)

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Asking Photons Where They Have Been

A new experiment exposes the path taken by photons in an optical setup, revealing an unconventional quantum phenomenon.

A research team at the Tel-Aviv University has demonstrated a technique that is able to find out what path – among a few possible ones – photons have taken in an optical apparatus. The experiment allowed them to reveal a bizarre quantum mechanical phenomenon: photons pass through a section of the setup that they neither enter nor exit. The authors explain the effect by invoking an alternative interpretation of quantum mechanics called a “two-state vector formalism”, in which any quantum state in the present is described through a relationship between quantum states in the future and quantum states in the past.

* A Danan, D Farfurnik, S Bar-Ad, Lev Vaidman (contact author), “Asking photons where they have been”, Physical Review Letters (expected publication date: Dec 9)

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Why Swimming Particles Aggregate

Simulations explain why ensembles of swimming particles in solution sometimes aggregate in clusters.

Particles that move of their own accord, such as bacteria or beads propelled by chemical reactions, can organize themselves into diverse arrangements, such as coherently moving swarms or ordered arrays. A commonly observed behavior is the formation of a number of clusters, which may achieve a stable size or aggregate into a single dense phase. The reasons for the diverse behaviors are clarified by the work of a team of researchers from Europe (UK, Spain, Germany) and the US. The authors’ simulations explain why clustering may occur, depending on a fine balance of different forces: the attractive or repulsive forces between particles and the swimming intensity of the self-propelled particles. The model could be used to describe the behavior of biologically relevant systems or to design new ways of assembling tiny particles into well-defined structures.

* BM Mognetti, Chantal Valeriani (contact author) et al, “Living clusters and crystals from low-density suspensions of active colloids”, Physical Review Letters (expected publication date: Dec 6)

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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