Author(s): Manuchehr Aminian, Francesca Bernardi, Roberto Camassa, and Richard M. McLaughlin
Calculations of the motion of particles carried by a fluid flowing through a pipe find a surprising effect of the pipe’s shape.
[Phys. Rev. Lett. 115, 154503] Published Mon Oct 05, 2015
Nature Physics 11, 791 (2015). doi:10.1038/nphys3494
Authors: Roberta Sinatra, Pierre Deville, Michael Szell, Dashun Wang & Albert-László Barabási
An analysis of Web of Science data spanning more than 100 years reveals the rapid growth and increasing multidisciplinarity of physics — as well its internal map of subdisciplines.
| Piled Higher & Deeper by Jorge Cham |
www.phdcomics.com
|
|
 |
||
|
title:
"Academics don't read" - originally published
9/28/2015
For the latest news in PHD Comics, CLICK HERE! |
||
Article
The design of all-passive nonreciprocal metastructures is a challenging task as there are trade-offs between the nonreciprocal transmission ratio and insertion loss. Here, Mahmoud et al . propose a concept for all-passive, high-throughput metastructures that exhibit nonreciprocal properties and wave-flow isolation.
Nature Communications doi: 10.1038/ncomms9359
Authors: Ahmed M. Mahmoud, Arthur R. Davoyan, Nader Engheta
Nature Photonics 9, 663 (2015). doi:10.1038/nphoton.2015.159
Authors: Martin Aeschlimann, Tobias Brixner, Dominik Differt, Ulrich Heinzmann, Matthias Hensen, Christian Kramer, Florian Lükermann, Pascal Melchior, Walter Pfeiffer, Martin Piecuch, Christian Schneider, Helmut Stiebig, Christian Strüber & Philip Thielen
The enhancement of light absorption in absorber layers is crucial in a number of applications, including photovoltaics and thermoelectrics. The efficient use of natural resources and physical constraints such as limited charge extraction in photovoltaic devices require thin but efficient absorbers. Among the many different strategies used, light diffraction and light localization at randomly nanotextured interfaces have been proposed to improve absorption. Although already exploited in commercial devices, the enhancement mechanism for devices with nanotextured interfaces is still subject to debate. Using coherent two-dimensional nanoscopy and coherent light scattering, we demonstrate the existence of localized photonic states in nanotextured amorphous silicon layers as used in commercial thin-film solar cells. Resonant absorption in these states accounts for the enhanced absorption in the long-wavelength cutoff region. Our observations establish that Anderson localization—that is, strong localization—is a highly efficient resonant absorption enhancement mechanism offering interesting opportunities for the design of efficient future absorber layers.
Author(s): Liyi Zhao, Chushun Tian, Yury P. Bliokh, and Valentin Freilikher
When a wave is incident on an open random medium it is decomposed into a number of “partial waves” that propagate independently along natural channels, the so-called transmission eigenchannels, and are superposed again when they leave the medium. Here, the authors propose the use of asymmetric edge reflection (the asymmetry in the reflections of the sample edges) to control the perfectly transmitting eigenchannel in a quasi-one-dimensional diffusive medium.
[Phys. Rev. B 92, 094203] Published Mon Sep 21, 2015
Wedding rings spinning on a surface can follow surprising boomeranglike trajectories.
[Physics] Published Tue Sep 22, 2015
Article
Bloch oscillations consist of periodic spreading and relocalization of particle wave functions, but have been so far observed only in separable states. Here the authors observe them for two-photon N00N states in integrated photonic circuits, revealing transitions from particle bunching to anitbunching.
Nature Communications doi: 10.1038/ncomms9273
Authors: Maxime Lebugle, Markus Gräfe, René Heilmann, Armando Perez-Leija, Stefan Nolte, Alexander Szameit
The theory of musical scales involves mathematical ratios, harmonic resonators, beats, and human perception and provides an interesting application of the physics of waves and sound. We first review the history and physics of musical scales, with an emphasis on four historically important scales: twelve-tone equal temperament, Pythagorean, quarter-comma meantone, and Ptolemaic just intonation. We then present an easy way for students and teachers to directly experience the qualities of different scales using MIDI synthesis.
The quantum mechanical behavior of a particle in a double well defies our intuition based on classical reasoning. Not surprisingly, an asymmetry in the double well will restore results more consistent with the classical picture. What is surprising, however, is how a very small asymmetry can lead to essentially classical behavior. In this paper, we use the simplest version of a double-well potential to demonstrate these statements. We also show how this system accurately maps onto a two-state system, which we refer to as a “toy model.”
C’era una volta un esperimento che poteva cambiare il volto della Fisica Nucleare
Article
Various approaches based on the iterative search have failed in the deterministic creation of bandgaps in random networks. Here Yu et al . reveal a deterministic pathway to bandgaps in random-walk potentials by applying the notion of supersymmetry to the wave equation.
Nature Communications doi: 10.1038/ncomms9269
Authors: Sunkyu Yu, Xianji Piao, Jiho Hong, Namkyoo Park
D-Wave, a company we have covered extensively in the past, has taken some heat because a number of tests have shown that its adiabatic quantum optimizer is no faster than a regular computer. But the company is now claiming that its machine is between two to 600 times faster than a classical computer. What happened to obtain such a huge speed-up? A new benchmark, that's what.
I remember when every OS manufacturer, chip maker, and video card vendor would either cheat or invent a new benchmark in order to claim to be the fastest. So my eyes initially rolled so hard that Newton's third law just about kicked me out of my chair. After recovering from the muscle strain, I got a hold of the paper, and much to my surprise, I agree with the authors.
Before I get to the D-Wave benchmark, let's take a quick look at how a naive benchmark might work. You can set your computer a task and time how long it takes to perform it. Or you can set it a repetitive set of fundamental operations (say multiplying two numbers) and see how many operations it can perform per second.
Author(s): M. J. A. Schuetz, E. M. Kessler, G. Giedke, L. M. K. Vandersypen, M. D. Lukin, and J. I. Cirac
Surface acoustic waves may work as a “quantum bus” that carries information to different parts of a quantum computer.
[Phys. Rev. X 5, 031031] Published Thu Sep 10, 2015
Arithmetic and local circuitry underlying dopamine prediction errors
Nature 525, 7568 (2015). doi:10.1038/nature14855
Authors: Neir Eshel, Michael Bukwich, Vinod Rao, Vivian Hemmelder, Ju Tian & Naoshige Uchida
Dopamine neurons are thought to facilitate learning by comparing actual and expected reward. Despite two decades of investigation, little is known about how this comparison is made. To determine how dopamine neurons calculate prediction error, we combined optogenetic manipulations with extracellular recordings in the ventral tegmental area while mice engaged in classical conditioning. Here we demonstrate, by manipulating the temporal expectation of reward, that dopamine neurons perform subtraction, a computation that is ideal for reinforcement learning but rarely observed in the brain. Furthermore, selectively exciting and inhibiting neighbouring GABA (γ-aminobutyric acid) neurons in the ventral tegmental area reveals that these neurons are a source of subtraction: they inhibit dopamine neurons when reward is expected, causally contributing to prediction-error calculations. Finally, bilaterally stimulating ventral tegmental area GABA neurons dramatically reduces anticipatory licking to conditioned odours, consistent with an important role for these neurons in reinforcement learning. Together, our results uncover the arithmetic and local circuitry underlying dopamine prediction errors.
Ballmer: Lo chiamiamo Surface [“superficie”].
Pubblico: Buuuuu! Il tuo iPad fa schifo.
Ballmer: Non è un iPad! È un Surface.
Pubblico: Succhiami la superficie! Quella del mio uccello!
Ballmer: Ha un supporto estraibile e anche un portabicchiere.
Pubblico: Il tuo iPad fa schifo lo stesso.
Ballmer: Ehi, amico, vaffanculo! Abbiamo messo una tastiera direttamente nella copertina! Tra tre anni, quando Apple ce lo copierà, voi stronzi penserete che è geniale.
Pubblico: Facci il ballo della scimmia!
WWDC 2015 – Tim Cook: Lo chiamiamo Smart Cover Touch, e crediamo che lo amerete.
Pubblico: Lo avete inventato voi!
Tim Cook: Sì, sì, lo abbiamo inventato noi.
Author(s): Matthias Kraft, Yu Luo, S. A. Maier, and J. B. Pendry
Solar cell technology benefits from increased photocurrents. New research uses transformation optics to preferentially concentrate light in hotspots in a metal grating.
[Phys. Rev. X 5, 031029] Published Tue Sep 08, 2015
Article
In measurements that employ phase retrieval algorithms, such as coherent diffraction imaging, reconstruction of one-dimensional signals is challenging due to ambiguity issues. Here, the authors demonstrate super-resolution coherent imaging of one-dimensional objects by utilizing sparsity prior information.
Nature Communications doi: 10.1038/ncomms9209
Authors: Pavel Sidorenko, Ofer Kfir, Yoav Shechtman, Avner Fleischer, Yonina C. Eldar, Mordechai Segev, Oren Cohen
Author(s): David W. Zhou, David D. Mowrey, Pei Tang, and Yan Xu
A computer model of a network of neurons shows that a sudden breakdown in the net’s ability to transmit information mimics the brain wave changes that accompany anesthesia.
[Phys. Rev. Lett. 115, 108103] Published Fri Sep 04, 2015
Negative refractive index and acoustic superlens from multiple scattering in single negative metamaterials
Nature 525, 7567 (2015). doi:10.1038/nature14678
Authors: Nadège Kaina, Fabrice Lemoult, Mathias Fink & Geoffroy Lerosey
Metamaterials, man-made composite media structured on a scale much smaller than a wavelength, offer surprising possibilities for engineering the propagation of waves. One of the most interesting of these is the ability to achieve superlensing—that is, to focus or image beyond the diffraction limit. This originates from the left-handed behaviour—the property of refracting waves negatively—that is typical of negative index metamaterials. Yet reaching this goal requires the design of ‘double negative’ metamaterials, which act simultaneously on the permittivity and permeability in electromagnetics, or on the density and compressibility in acoustics; this generally implies the use of two different kinds of building blocks or specific particles presenting multiple overlapping resonances. Such a requirement limits the applicability of double negative metamaterials, and has, for example, hampered any demonstration of subwavelength focusing using left-handed acoustic metamaterials. Here we show that these strict conditions can be largely relaxed by relying on media that consist of only one type of single resonant unit cell. Specifically, we show with a simple yet general semi-analytical model that judiciously breaking the symmetry of a single negative metamaterial is sufficient to turn it into a double negative one. We then demonstrate that this occurs solely because of multiple scattering of waves off the metamaterial resonant elements, a phenomenon often disregarded in these media owing to their subwavelength patterning. We apply our approach to acoustics and verify through numerical simulations that it allows the realization of negative index acoustic metamaterials based on Helmholtz resonators only. Finally, we demonstrate the operation of a negative index acoustic superlens, achieving subwavelength focusing and imaging with spot width and resolution 7 and 3.5 times better than the diffraction limit, respectively. Our findings have profound implications for the physics of metamaterials, highlighting the role of their subwavelength crystalline structure, and hence entering the realm of metamaterial crystals. This widens the scope of possibilities for designing composite media with novel properties in a much simpler way than has been possible so far.
Article
Multicolour information is required to study the complex interplay of biological tissues. Here, Jahr et al. acquire spectral information at high resolution for each pixel in a hyperspectral light sheet microscope, while maintaining its perpendicular illumination and low phototoxicity.
Nature Communications doi: 10.1038/ncomms8990
Authors: Wiebke Jahr, Benjamin Schmid, Christopher Schmied, Florian O. Fahrbach, Jan Huisken