Faster-than-light neutrinos may leave trails at the LHC

DKR1045

- Is Einstein's venerated theory of special relativity challenged by
neutrinos? Our work suggests that the LHC may help provide the answer.

The OPERA experiment, at the Gran Sasso Laboratory in Italy, has reported
observation of neutrinos that travel faster than light. This result, if
confirmed, would violate one of the defining laws of special relativity --
a pillar of fundamental physics for over a century-- that forbids
superluminal (faster-than-light) travel. If neutrinos, which are extremely
elusive by nature, can travel at superluminal speeds it has been predicted
that they would emit easy-to-detect particles, such as electron
anti-electron pairs, along their paths. In our paper, we suggest looking
for these conspicuous trails that would be left in the wake of neutrinos
-- if they traversed the LHC detectors faster than light -- as a way of
testing the superluminal neutrino hypothesis implied by the OPERA results.
The requisite neutrinos can originate from decays of top quarks that are
copiously produced at the LHC.

Why it is hard to see Schroedinger's Cat

LH12959

- Why do we not see quantum physical effects in our daily lives? This question was raised already by Schroedinger, one of the founding fathers of quantum physics, in his famous cat paradox. One answer is that quantum superposition states, such as the cat being both dead and alive at the same time, are very fragile. When the cat interacts with its environment even just a tiny bit, the superposition is destroyed.

This effect is known as decoherence, and it has been studied intensively over the last few decades. But it turns out that decoherence is not the only reason why quantum effects are hard to see. In a recent paper in Physical Review Letters, researchers point out an even more basic difficulty: seeing quantum effects requires extremely precise measurements. Studying a concrete example for such a "cat" motivated by recent experiments, a particular quantum state involving a large number of photons, they show that in order to see the quantum nature of this state, one has to be able to count the number of photons in it perfectly. This becomes more and more difficult as the total number of photons is increased.

Distinguishing one photon from two photons is within reach of current technology, but distinguishing a million photons from a million plus one is not. This shows that seeing Schroedinger's cat is hard also because it would require exceptionally good eyesight.

Leonardo's Rule of Tree Branching

LE13207

- Leonardo da Vinci observed in his notebooks that "all the branches of a tree at every stage of its height when put together are equal in thickness to the trunk." There have been surprisingly few assessments of this rule, but the available data indicate that the Leonardo rule holds for a large number of species. Despite this scarcity of experimental evidence, it is safe to state that Leonardo's rule has not been disproved. As a matter of fact, it is so natural to the eye that it is routinely used in computer-generated trees. In this Letter, it is proposed that this rule is a consequence of the tree skeleton having a self-similar structure and the branch diameters being adjusted to resist wind-induced loads.

Radical Role Reversal

LE13164

- It is an elementary principle of chemistry that radicals, i.e. atoms or molecules with an unpaired electron orbiting their nucleus, are highly reactive, while closed-shell species, i.e. atoms and molecules where the electrons are all paired, are relatively stable. In this paper, atoms and ions are produced and confined at ultracold temperatures in a novel hybrid trap, dubbed the MOTION trap. By carefully monitoring the interaction of the ultracold atoms and ions in this trap, it is observed that at these ultracold temperatures closed-shell species can in fact be thousands of times more reactive than radicals. This role-reversal is found to be the consequence of the underlying quantum dynamics driving the chemical reaction, which are normally obscured at room temperature. Given that reactions of the type observed in this work are important for determining astrophysical processes and in planned hybrid atom-ion devices, this work highlights both the need for a renewed effort in laboratory astrophysics and fully-quantum chemical reaction calculations on a case-by-case basis to guide the next generation of atom-ion device design.

How hard is it to generate a complex birdsong?

EH10901

- Behavior emerges from the interaction between a nervous system and a peripheral bio-mechanical device executing those instructions. In that perspective, how much of the complexity is coded in the driving commands, and how much emerges in the physical device? In this work we study the acoustically challenging song the Zebra finch, and test the hypothesis that much of its acoustic complexity is due to the nonlinear nature of the avian vocal organ. We test it by reconstructing the parameters of a simple model, and comparing those results with direct measurements of the physiological parameters driving the vocal organ. Simple instructions, driving the nonlinear device, generate the most peculiar and acoustically rich song of the Zebra finch.

High-brightness multi-wavelength remote laser for detecting multiple hazard gases in air

LE13721AR

- Since the first ruby laser was demonstrated in 1960, there have been enormous requirements for a variety of coherent light sources in a broad spectrum of fields covering science and engineering. In environmental science, there has been a large amount of research effort aiming at measuring atmospheric trace species over a long distance. The ability to control the generation of coherent light source with different frequencies at a designed location would provide a new strategy to meet the pressing needs of various environmental issues from monitoring global warming and stratospheric ozone depletion to early detection of nuclear reactor radiation leak and biological treat agents in air. To date, a multi-wavelength remote laser in air that allows for dynamically switching the operating wavelength has not yet been achieved, although this type of laser is certainly of high importance for detecting multiple hazard gases. Here, we demonstrate a harmonic-seeded switchable multi-wavelength laser in air driven by intense mid-infrared femtosecond laser pulses. Furthermore, population inversion in the multi-wavelength remote laser occurs at an unexpected ultrafast time-scale (i.e., less than ~200 fs) owing to direct formation of excited molecular nitrogen ions by strong-field ionization of inner-valence electrons. The bright multi-wavelength laser in air opens the perspective for remote detection of multiple pollutants based on nonlinear spectroscopy.

New way to pack marbles and buckyballs

LJ12785ER


- Spherical objects inside a cylinder can now be packed more efficiently than ever. With a suitable template, the densest packings can surprisingly be obtained from a very simple deposition procedure. The findings will have a broad range of applications in physics, from the macro- to the nano-scale, and also in commercial packaging.

Indications of a spatial variation of the fine structure constant

LV12409

- One of the most cherished principles in science - the constancy of physics – apparently may not be true. A new study, using data from the world’s largest optical telescopes, suggests that one of the four fundamental forces of Nature, electromagnetism - measured by the so-called fine-structure constant and denoted by the symbol alpha - seems to vary across the Universe.

The very first hints that alpha might not be constant arose in 1999 from data collected with the Keck Observatory in Hawaii but there was insufficient data to explore any dependence on location in the Universe. Now, newer data from the European Southern Observatory’s “Very Large Telescope” in Chile suggests a “preferred direction” in the Universe, along which alpha varies, slightly, but significantly.

The discovery, if confirmed, has profound implications for our understanding of space and time and violates one of the fundamental principles underlying Einstein's General Relativity theory. The continuous drift in alpha may also imply a much larger universe than our observable patch, possibly infinite and also offer a natural explanation for a question that puzzled scientists for decades: why do the laws of physics seem to be so finely-tuned for the existence of life?

Peering Out from Under an Invisibility Cloak

PRE 84, 046607 (2011)

- Most invisibility cloak designs have one serious drawback - they make it impossible for anyone hiding under the cloak to see what's going on in the outside world. Researchers have now come up with an approach that, in theory, should allow us to make cloaks that allow you to peek out while remaining entirely hidden. In effect, they propose making a tiny tear in the cloak, and then stitching the hole with a two types of materials chosen to effectively cancel each other out when seen from the outside, while still allowing light to enter. Although the invisibility cloak design currently exists only on paper, it theoretically ensures that aspiring Harry Potters remain invisible while keeping an eye on the Voldemorts and Snapes all around them.

Self-organizing patterns help to conceal secret communication

EF10894


- Steganography is a science of hiding data in a communication in such a way that only the sender and the receiver know of its existence. In this paper, we propose a steganographic communication algorithm based on self-organizing patterns. The dot-skeleton representation of the secret image is embedded into the initial random perturbation around the unstable stationary state. The pattern of stripes is allowed to evolve for a pre-determined number of forward time steps and is transmitted to the receiver. The receiver has to generate the identical initial perturbation (without the dot-skeleton representation of the secret image). The difference between the pattern produced by the receiver and the pattern received via the communication channel reveals the secret image.

Complex nonlinear pattern formation processes govern the formation of stripes interconnecting dot-skeleton points in the difference image. The proposed communication system is fully functional when grayscale levels of the dot-skeleton representation of the secret are well below the noise level of the initial random perturbation. The ability of the proposed scheme to hide information and to avoid suspicion outperforms traditional steganographic techniques if the security of communication is considered as a primary objective.

Building towers drop by drop

LH13533

- We show an unprecedented variety of smooth symmetric, corrugated, zig-zag shaped slender structures that can be observed by simply dripping a mixture of sand and water on a liquid absorbing surface such as a dry bed of sand or blotting paper. The various shapes are in contrast with the liquid drops which can splash, spread or bounce upon hitting a surface. Successive drops are observed to freeze rapidly upon impact due to the drainage of a small fraction of liquid, literally stacking on top of each other into surprisingly slender structures named granular towers. Further, twisted pagoda dome-like structures are observed by increasing the flux into the jetting regime. We show that the towers are held together because of capillary and friction forces, and the shape of the towers depends on a subtle balance between dripping frequency, density of grains, and impact speed. Besides applications in surface patterning, this tower building technique may be a new and easy way to probe the flow properties of dense granular suspensions using the shape of the tower.

A story of colliding sea ice floes

EG10801

- As has been so often the case over the last several years, alarming news again arrived from the Arctic a few weeks ago. On 9th September, at the maximum of the summer melting season, the sea ice extent in the Arctic Ocean reached the second lowest value in the satellite record: 4.6 million square kilometers. Increasing areas of open water in the summer mean larger and larger areas where new ice forms in winter. Thick and strong perennial ice gets gradually replaced by thinner seasonal ice, more susceptible to breaking and deformation. What do we know about the dynamics of that increasingly abundant – and thus increasingly important – ice type, composed of separate floes? Incomparably less than about the dynamics of the perennial ice. In this paper, sea ice is viewed as a discontinuous medium built of floes of different sizes moving on the sea surface and colliding with each other. The model presented, deriving from analogies with other granular materials, reproduces a number of hitherto unexplained phenomena observed in sea ice at low concentrations – including the formation of floe clusters (see the attached image), important for the dynamics and freezing/melting of ice – and thus it may contribute to a better performance of state-of-the-art sea-ice and climate models.

Different mechanics of snap-trapping in the two closely related carnivorous plants, Dionaea muscipula and Aldrovanda vesiculosa

LG13128E


- The carnivorous aquatic Waterwheel Plant (Aldrovanda
vesiculosa L.) and the closely related terrestrial Venus Flytrap
(Dionaea muscipula SOL. EX J. ELLIS) both feature elaborate
snap-traps, which shut after reception of an external mechanical
stimulus by prey animals. Traditionally, Aldrovanda is considered as a
miniature, aquatic Dionaea, an assumption which was already
established by Charles Darwin. However, videos of snapping traps from
both species suggest completely different closure mechanisms. Indeed,
the well- described snapping mechanism in Dionaea comprises abrupt
curvature inversion of the two trap lobes, while the closing movement
in Aldrovanda involves deformation of the trap midrib but not of the
lobes, which do not change curvature. In this paper, we present the
first detailed mechanical models for these plants, which are based on
the theory of thin solid membranes and explain this difference by
showing that the fast snapping of Aldrovanda is due to kinematic
amplification of the bending deformation of the midrib, while that of
Dionaea unambiguously relies on the buckling instability that affects
the two lobes.

Pair Creation Constrains Superluminal Neutrino Propagation

LK12734

- The OPERA collaboration claims that muon neutrinos with mean energy of 17.5 GeV travel 730 km from CERN to the Gran Sasso at a speed exceeding that of light by about 7.5 km/s or 25 ppm. However, we show that superluminal neutrinos may lose energy rapidly via the bremsstrahlung of electron-positron pairs ( ! + e− + e+). For the claimed superluminal velocity and at the stated mean energy, we find that most of the neutrinos would have suffered several pair emissions en route, causing the beam to be depleted of higher energy neutrinos. This presents a significant challenge to the superluminal interpretation of the OPERA data. Furthermore, we appeal to Super-Kamiokande and IceCube data to establish strong new limits on the superluminal propagation of
high-energy neutrinos.

Impact craters: grains against grains

LH13515


- Nowadays it is well accepted that craters in the moons and planets were created by asteroid collisions. But, why some craters are completely flat and others show central peaks? The actual paradigm explains that central peaks arise due to the surface fluidization produced by the impact and/or the crater collapse. However, based on the granular nature of the asteroids we developed impact experiments of “granular projectiles” in sand, obtaining similar morphologies to those observed in celestial bodies. So we claim that the crater morphology is due to the granularity of the projectile: low-packed projectiles completely spread after collision producing bowl- shaped craters, high-packed projectiles confine the internal material during the impact giving rise to central peaks.

How a quintessential quantum test was fooled -- or why quantum physicists should always read the fine print

LH12960

- When it comes to pitting quantum theory against classical notions of
the world, there’s one experiment that physicists say makes quantum
theory the clear winner: a test of Bell’s inequalities. We have found
that it’s possible to fake quantum results using classical physics in
such a test, reminding us to be cautious about the assumptions in
experiments. Bell inequalities measure the strength of correlations
between two particles, or how much their behaviors are coordinated.
Quantum physics allows for stronger correlations than classical physics,
violating a Bell inequality. In our experiment, a typical apparatus for
measuring Bell violations by photons was cheated using bright pulses of
light to manipulate the output of single-photon detectors. Researchers
thinking ahead to quantum devices for communication and computation have
proposed incorporating tests of Bell inequalities in such devices to act
as safeguards. Our work highlights the practical challenges of such
schemes. It also reminds us that no Bell tests so far have been without
seemingly reasonable ‘fine print’ assumptions about how the experiments
worked. In our case, we exploited the so-called detection loophole. Our
attack was an evil intervention. We have no reason to think the Universe
conspired to trick past experiments, but one would prefer to eliminate
the need for fine print. Various experimental groups worldwide are
working towards this goal.

Switching the light fantastic

LH12759

- Quantum mechanics says that light consists of small indivisible packets of energy or quanta known as photons. In this paper, we show that the passage of a light beam through an optical fiber can be controlled by just a few quanta of energy (photons) in another light beam.

Photons are introverts by nature and usually don’t interact with each other, unless they are in large numbers. One of the holy grails of physics is single-photon all-optical switching, where one photon controls the passage of another photon through a medium. It is a critical goal for the development of future quantum information networks, promising ultrahigh speed computation and ultra-secure communication.

Our paper takes a significant step towards this goal by demonstrating all-optical switching with less than twenty photons and that too at fast timescales of around five billionths of a second. We confine the light, along with an atomic vapor, to the core of an optical fiber that has a size less than a tenth of the width of a human hair. This architecture forces light to strongly interact with the atoms, causing the absorption of photons of two different colors only if they are simultaneously present, but not if one type is absent.

BATS CHANGE EAR SHAPE AND RESHAPE THEIR SPATIAL HEARING

LC13795

- Certain bats can deform the shapes of their ears in a way that changes the animal's ultrasonic hearing spotlight. Within just one tenth of a second, these bats are able to change the configurations of their outer ear shapes from one extreme to another. As a result of these shape changes, the shape of the ultrasonic spotlight also undergoes a qualitative change. Using a combination of methods that included high-speed stereo vision and high-resolution tomography, researchers have now been able to reconstruct the three-dimensional geometries of the outer ears from live horseshoe bats as they deform on these short time scales. Using computer analysis of the deforming shapes, the researchers found ultrasonic hearing spotlights associated with the different ear configurations that could suit different hearing tasks performed by the animals. Hence, the ear deformation in horsehoe bats could be a substrate for adapting the spatial hearing of the animals on a very short time scale.

World’s fastest maze solver

LC13533E

- The authors of a recently accepted PRE paper demonstrate that a network of memristors (resistors with memory) solves the maze problem much faster than any existing supercomputer. Such an extraordinary advance in computation power is due to a massively-parallel network dynamics in which all network components are simultaneously involved in the calculation. This type of parallelism could be dubbed as “analog parallelism” which is different from that used in conventional supercomputer. It is anticipated that massively-parallel memristive processors will provide an efficient solution of many other optimization problems.

Hot electron ‘coolness’ through tunable energy transfer in nanowires

LC13992

- Harnessing and transfer of excess energy of electrons generated by light via rapid transfer of electrons across semiconductor interfaces is key to developing more efficient solar cells. In addition, hot-electron transfer is one process involved in obtaining a region of negative electrical resistance, a non-linear feature that is important in many advanced electronic devices. Researchers now report highly tunable and fast photo-excited hot electron transfer across the cylindrical interface of a co-axial core-shell semiconductor nanowire hetero-structure. The onset of the negative resistance region is shown to be highly tunable by one of three different modes, owing to the reduced dimensionality of a nanowire. Until now, the onset of negative resistance has been fixed by the selection of materials, thus requiring a network of integrated circuit components to produce tunable components important for computing, signal processing and communications. This nano-scaled multiply-tunable optically-addressed device element opens possibilities for gaining new insight into hot electron transfer processes for solar energy conversion, and for constructing complex electronic circuits using far fewer, simpler and much smaller components with the potential for requiring much less energy to operate.

An All-optical, Pain-free Method for Blood Glucose Testing

EC11052

- Pain-free blood glucose testing is highly desirable for diabetes management which requires frequent blood glucose monitoring. For many decades a search for a non-invasive blood glucose concentration detection method has been a major, yet elusive goal. Optical methods have been confined in the near-infrared where glucose has absorption peaks but is hard to identify due to multiple overlapping absorptions by other blood constituents. The development of clinically viable non-invasive glucose biosensors has been hampered by lack of specificity and sensitivity. In this paper we introduce theoretically and experimentally a new non-invasive method, Wavelength-Modulated Differential Photothermal Radiometry (WM-DPTR), for non-invasive, non-contact blood glucose monitoring. WM-DPTR features glucose specificity and sensitivity by combining laser excitation by two out-of-phase modulated beams at wavelengths near the peak and the baseline of a prominent and isolated mid-IR glucose absorption band. A theoretical photothermal model of WM-DPTR signal generation and detection has been developed. Simulation results on water-glucose phantoms within the human blood-range glucose concentration (0-300 mg/dl) demonstrated high sensitivity and resolution to meet wide clinical detection requirements. The model has also been validated by experimental data of the glucose-water system obtained using WM-DPTR.

The Fastest Way to Pour Syrup

LC13080ER

- A thick liquid flows quickest if you pour it from the corner, rather than the side, of a carton.

Pouring a fluid out of a container is an everyday process that is also relevant in a wide range of industrial situations. Despite this fundamental interest, this fundamental problem has apparently never been addressed before. The authors derive the time required for the fluid to begin discharging after tipping the container and the volume of the fluid yet to be discharged at subsequent times. The authors consider two different geometric configurations and find noticably different pouring characteristics. The theoretical predictions are compared successfully with experiments.

The results of the present study are applicable to situations where it is desirable to retrieve viscous fluids in minimal time from containers, such as buckets of detergent, cans of paint, and tanks of oil. They provide a point of reference to gauge the influence of a rich variety of effects that could be incorporated to extend the simplified model.

Deciphering the very first contact between virus particles and host cells

LD13184

- A virus replication cycle is initiated by virus binding to receptors presented on the surface of a host cell. An in-depth understanding of the very first steps of virus binding to cell membranes is therefore crucial for the development of antiviral therapies, vaccines and high-performance diagnostics. Studies of the initial interaction between a virus and the host cell membrane were so far mainly focused on identifying the binding sites on the virus and / or the cell membrane, while significantly less is known about the kinetics of the interaction. With single virus sensitivity, we quantify in this work the energy barrier for the virus-membrane association. We were able to discriminate between two structurally very similar receptors, which interaction kinetics could not be distinguished using conventional methods. We also observed that the virus release kinetics appears logarithmic over a long time span. Such interaction behavior is rarely observed in natural sciences and was earlier not reported in the context of virus binding. In our study, this feature has been explained by multiple receptor-virus contact points and membrane deformation. Such situations may occur at receptor-enriched cell-membrane regions with positive curvature, allowing us to suggest that the logarithmic kinetics may take place in vivo.



Description of the illustration:

Illustration of how surface-bound virus-like particles were used to probe their interaction with cell-membrane receptors incorporated into fluorescent-labeled lipid vesicles. By probing the rate of binding and the time individual vesicles remain bound (the residence time), we could simultaneously investigate weak (few receptor contacts) and strong (multiple receptor contacts) interactions. The virus-like particle was from the norovirus genogroup II.4 Dijon strain, being the major causative agent of acute viral gastroenteritis worldwide causing yearly up to 200, 000 children deaths, and the receptors were glycosylated sphingolipids.

X-rays vaporize water

LF13057EJ

- When ionizing radiation i s illuminated to water, it removes electrons from water molecules and ! ionizes them. This ionization can modify water surface tension (PRL 100, 217403, 2008), potentially affecting thermodynamic behavior of water: an important example is vaporization, since vaporization enthalpy depends on surface tension. The interaction between ionizing photons (x-rays or gamma-rays) and soft matter becomes important to scientists, with growing applications of x-ray techniques to soft matter systems.

In a paper in Physical Review E, researchers address for the first time (on a quantitative basis) that liquid water is vaporized by x-rays. They precisely measure the vaporization rate of water confined in a capillary tube during x-ray irradiation using high-resolution, high-speed x-ray microscopy. Intere! stingly, a reversible switching between vaporization and condensation repeatedly occurs with x-ray on-off switching.

The group finds a hidden fundamental linkage among ionization, surface tension, and vaporization: how effectively photons vaporize water depends on charging density. This finding could provide insights into topics concerning radiological or electrohydrodynamic phenomena such as radiation-induced bubble formation or cosmic-ray-induced cloud formation.

Sand physics: taking the rough with the smooth.

EE11020


- Why do the slopes of some piles of soil or sand slip very easily, while
other piles remain extremely stable? Answering this question holds the
key to the understanding of many fundamental physical questions, for
example the onset of landslides. For a long time scientists have assumed
that the surface roughness of the individual grains plays a keys role in
this process. However, this common-sense assumption has never been
verified experimentally. Here, for the first time, we provide the
necessary methodological concepts and succeed in proving this
hypothesis. We do so as follows.

We have invented a chemical recipe to increase the roughness of glass
and we use it to systematically tune the roughness of sub-mm glass spheres.

We measure the roughness of individual grains using light interference,
and the roughness of the whole granular sample using Coca-Cola.

We then measure the friction between the grains by looking at the slope
of the pile they form at the bottom of an hour glass.

We look at the correlation between roughness and friction. Our results
show that changing the roughness of grains allows us to tune the
friction between them, making friction a control parameter. And this
hands us the key to understanding real-life granular systems.