Author(s): U. Briskot, I. A. Dmitriev, and A. D. Mirlin

We present a theoretical analysis of the relaxation cascade of a photoexcited electron in graphene in the presence of screened electron-electron interaction in the random phase approximation. We calculate the relaxation rate of high energy electrons and the jump-size distribution of the random walk ...

[Phys. Rev. B 89, 075414] Published Thu Feb 13, 2014

Author(s): J. T. Miller, A. Lazarus, B. Audoly, and P. M. Reis

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 ...

[Phys. Rev. Lett. 112, 068103] Published Thu Feb 13, 2014

Mosaic two-lengthscale quasicrystals

Nature 506, 7487 (2014). doi:10.1038/nature12938

Authors: T. Dotera, T. Oshiro & P. Ziherl

Over the past decade, quasicrystalline order has been observed in many soft-matter systems: in dendritic micelles, in star and tetrablock terpolymer melts and in diblock copolymer and surfactant micelles. The formation of quasicrystals from such a broad range of ‘soft’ macromolecular micelles suggests that they assemble by a generic mechanism rather than being dependent on the specific chemistry of each system. Indeed, micellar softness has been postulated and shown to lead to quasicrystalline order. Here we theoretically explore this link by studying two-dimensional hard disks decorated with step-like square-shoulder repulsion that mimics, for example, the soft alkyl shell around the aromatic core in dendritic micelles. We find a family of quasicrystals with 10-, 12-, 18- and 24-fold bond orientational order which originate from mosaics of equilateral and isosceles triangles formed by particles arranged core-to-core and shoulder-to-shoulder. The pair interaction responsible for these phases highlights the role of local packing geometry in generating quasicrystallinity in soft matter, complementing the principles that lead to quasicrystal formation in hard tetrahedra. Based on simple interparticle potentials, quasicrystalline mosaics may well find use in diverse applications ranging from improved image reproduction to advanced photonic materials.

Number crunch

Nature 506, 7487 (2014). doi:10.1038/506131b

The correct use of statistics is not just good for science — it is essential.

Science at the sharp end of oppressive politics

Nature 506, 7487 (2014). http://www.nature.com/doifinder/10.1038/506133a

Author: Andreas Kreiter

Andreas Kreiter describes his frightening and surreal ordeal at the hands of animal-rights extremists and their political allies.

Scientific method: Statistical errors

Nature 506, 7487 (2014). http://www.nature.com/doifinder/10.1038/506150a

Author: Regina Nuzzo

P values, the 'gold standard' of statistical validity, are not as reliable as many scientists assume.

Read 15 remaining paragraphs | Comments

If you made a beach using grains the proportionate size of the stars in the Milky Way, what would that beach look like?

Jeff Wartes

Sand is interesting.^{[Citation needed]}

"Are there more grains of sand than stars in the sky?" is a popular question which has been tackled by many people. The upshot is that there are probably more stars in the visible universe than grains of sand on all of Earth's beaches.

When people do those calculations, they often dig up some good data on the number of stars, then do some hand-waving about sand grain size to come up with a number for the sand grains on Earth.[1]From a practical point of view, geology and soil science are more complicated than astrophysics. We're not going to tackle that issue today, but to answer Jeff's question, we do need to figure out what the deal with sand is.[2]"i like sand because i don't really know what it is and there's so many of it"

—@darth__mouth Specifically, we need to have some idea of what grain sizes correspond to clay, silt, fine sand, coarse sand, and gravel, so we can understand how our galaxy would look and feel if it were a beach.[3]Instead of just containing a bunch of them.

Fortunately, there's a wonderful chart by the US Geologic Survey that answers all these questions and more. For some reason, I find this chart very satisfying—it's like the erosion geology edition of the electromagnetic spectrum chart.

According to surveys of sand,[4]There are apparently lots of them. the grains found on beaches tend to run from 0.2mm to 0.5mm (with the finest layers on top). This corresponds to medium-to-coarse sand in the chart. The individual grains are about this big:

If we assume the Sun corresponds to a typical sand grain, then multiply by the number of stars in the galaxy, we come up with a large sandbox worth of sand.[5]I mean, you come up with a bunch of numbers, but imagination turns them into a sandbox.

However, this is wrong. The reason: Stars aren't all the same size.

There are a number of widely-circulated YouTube videos comparing star sizes. They do a good job of getting across just how staggeringly large some stars are. Although it's easy to get lost in the videos and lose track of scale, it's clear that some of the grains in our sandbox universe would be more like boulders.

Here's how the main-sequence[6]The stars in the main part of their fuel-burning lifecycle. star-sand grains look:

They mostly fall into the "sand" category, though the larger Daft Punk stars cross the line into "granules" or "small pebbles".

However, that's just the main sequence stars. Dying stars get much, much bigger.

When a star runs out of fuel, it expands into a red giant. Even ordinary stars can produce huge red giants, but when a star that's already massive enters this phase, it can become a true monster. These red supergiants are the largest stars in the universe.

These beachball-sized sand stars would be rare, but the grape-sized and baseball-sized red giants are relatively common. While they're not nearly as abundant as Sun-like stars or red dwarfs, their huge volume means that they'd constitute the bulk of our sand. We would have a large sandbox worth of grains ... along with a field of gravel that went on for miles.

The little sand patch would contain 99% of the pile's individual grains, but less than 1% of its total volume. Our Sun isn't a grain of sand on a soft galactic beach; instead, the Milky Way is a field of boulders with some sand in between.

But, as with the real Earth seashore, it's the rare little stretches of sand between the rocks where all the fun seems to happen.

Modelling the effects of subjective and objective decision making in scientific peer review

Nature 506, 7486 (2014). doi:10.1038/nature12786

Authors: In-Uck Park, Mike W. Peacey & Marcus R. Munafò

The objective of science is to advance knowledge, primarily in two interlinked ways: circulating ideas, and defending or criticizing the ideas of others. Peer review acts as the gatekeeper to these mechanisms. Given the increasing concern surrounding the reproducibility of much published research, it is critical to understand whether peer review is intrinsically susceptible to failure, or whether other extrinsic factors are responsible that distort scientists’ decisions. Here we show that even when scientists are motivated to promote the truth, their behaviour may be influenced, and even dominated, by information gleaned from their peers’ behaviour, rather than by their personal dispositions. This phenomenon, known as herding, subjects the scientific community to an inherent risk of converging on an incorrect answer and raises the possibility that, under certain conditions, science may not be self-correcting. We further demonstrate that exercising some subjectivity in reviewer decisions, which serves to curb the herding process, can be beneficial for the scientific community in processing available information to estimate truth more accurately. By examining the impact of different models of reviewer decisions on the dynamic process of publication, and thereby on eventual aggregation of knowledge, we provide a new perspective on the ongoing discussion of how the peer-review process may be improved.

Article

The coherence of light is vital for applications like imaging and sensing, but is hard to measure with normal photodetectors. Stoklasa et al. show that, when combined with methods from quantum information processing, wavefront sensors can measure the complete coherence properties of a signal in a single-shot.

Nature Communications doi: 10.1038/ncomms4275

Authors: B. Stoklasa, L. Motka, J. Rehacek, Z. Hradil, L. L. Sánchez-Soto

Broderick

As happens from time to time, the suggestion has been made that Microsoft cancel Windows Phone, and instead fork Android. It's not the first time this suggestion has been made. It's probably not the last, either.

It's a poor idea. Google has worked to make Android functionally unforkable, with no practical way to simultaneously fork the platform and take advantage of its related strengths: abundant developers, and abundant applications.

The outline of the "Microsoft should fork Android" argument is as follows: Windows Phone doesn't have huge developer buy-in or sales success, but Android has both. By forking Android, Microsoft could provide unique value—corporate integration with things like Exchange, Active Directory, and System Center or InTune; full Office support; a polished user experience—and make the platform depend on its own cloud services (Bing, Bing Maps, Azure) rather than Google's. But simultaneously, it would still have access to all the Android applications that people depend on.

Read 31 remaining paragraphs | Comments

Faulty forensic science under fire

Nature 506, 7486 (2014). http://www.nature.com/doifinder/10.1038/506013a

Author: Sara Reardon

US panels aim to set standards for crime labs.

UK visa problems worry scientists

Nature 506, 7486 (2014). http://www.nature.com/doifinder/10.1038/506014a

Author: Daniel Cressey

Immigration policies scare off foreign talent, warn critics.

Trust funds PhDs

Nature 506, 7486 (2014). doi:10.1038/nj7486-123c

Doctoral studentships offered for UK universities.

Author(s): Michael A. Taylor, Jiri Janousek, Vincent Daria, Joachim Knittel, Boris Hage, Hans-A. Bachor, and Warwick P. Bowen

Quantum effects may help devise new imaging schemes that can overcome classical constraints posed by noise and diffraction. By using squeezed states of light in photonic force microscopy (PFM), scientists have demonstrated a 14% quantum enhancement of PFM’s spatial resolution, imaging details of living yeast cells with a resolution of 10 nm.

[Phys. Rev. X 4, 011017] Published Tue Feb 04, 2014

Observation of Dirac monopoles in a synthetic magnetic field

Nature 505, 7485 (2014). doi:10.1038/nature12954

Authors: M. W. Ray, E. Ruokokoski, S. Kandel, M. Möttönen & D. S. Hall

Magnetic monopoles—particles that behave as isolated north or south magnetic poles—have been the subject of speculation since the first detailed observations of magnetism several hundred years ago. Numerous theoretical investigations and hitherto unsuccessful experimental searches have followed Dirac’s 1931 development of a theory of monopoles consistent with both quantum mechanics and the gauge invariance of the electromagnetic field. The existence of even a single Dirac magnetic monopole would have far-reaching physical consequences, most famously explaining the quantization of electric charge. Although analogues of magnetic monopoles have been found in exotic spin ices and other systems, there has been no direct experimental observation of Dirac monopoles within a medium described by a quantum field, such as superfluid helium-3 (refs 10, 11, 12, 13). Here we demonstrate the controlled creation of Dirac monopoles in the synthetic magnetic field produced by a spinor Bose–Einstein condensate. Monopoles are identified, in both experiments and matching numerical simulations, at the termini of vortex lines within the condensate. By directly imaging such a vortex line, the presence of a monopole may be discerned from the experimental data alone. These real-space images provide conclusive and long-awaited experimental evidence of the existence of Dirac monopoles. Our result provides an unprecedented opportunity to observe and manipulate these quantum mechanical entities in a controlled environment.

Article

While a quantum system is always disturbed by any observation, one can exploit the back action of measurements and strong couplings to tailor the system evolution via quantum Zeno dynamics. Schäfer et al. demonstrate quantum Zeno dynamics in a five-level Hilbert space using a 87 Rb Bose–Einstein condensate.

Nature Communications doi: 10.1038/ncomms4194

Authors: F. Schäfer, I. Herrera, S. Cherukattil, C. Lovecchio, F.S. Cataliotti, F. Caruso, A. Smerzi

Article

The coupling of particles with physical waves is a generic phenomenon observed in various systems, but its differentiation from quantum effect is still unclear. Perrard et al. address this issue using a bouncing liquid drop confined in a magnetic potential well, where quantized motions are obtained.

Nature Communications doi: 10.1038/ncomms4219

Authors: Stéphane Perrard, Matthieu Labousse, Marc Miskin, Emmanuel Fort, Yves Couder

Article

The Aharonov–Bohm effect describes the influence of an electromagnetic vector potential on the phase of a charged particle. Here, Li et al. demonstrate that photon–phonon interactions can lead to the Aharonov–Bohm effect also for the electrically neutral photons.

Nature Communications doi: 10.1038/ncomms4225

Authors: Enbang Li, Benjamin J. Eggleton, Kejie Fang, Shanhui Fan

Nature Methods 11, 141 (2014). doi:10.1038/nmeth.2805

Authors: Xudong Fan & Seok-Hyun Yun