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  • Baby penguins benefit from fishing bans
    Nature (IF 40.137) Pub Date : 

    Baby penguins benefit from fishing bans Baby penguins benefit from fishing bans, Published online: 17 January 2018; doi:10.1038/d41586-018-00836-6 South African survey provides rare evidence on fishery impacts.

    更新日期:2018-01-17
  • Train robots to self-certify their safe operation
    Nature (IF 40.137) Pub Date : 
    Valentin Robu, David Flynn, David Lane

    Train robots to self-certify their safe operation Train robots to self-certify their safe operation, Published online: 16 January 2018; doi:10.1038/d41586-018-00646-w Train robots to self-certify their safe operation

    更新日期:2018-01-17
  • Support for US postdocs is growing slowly
    Nature (IF 40.137) Pub Date : 

    Support for US postdocs is growing slowly Support for US postdocs is growing slowly, Published online: 16 January 2018; doi:10.1038/d41586-018-00559-8 Report from National Postdoctoral Association highlights progress and pain points.

    更新日期:2018-01-17
  • The dark side of light: how artificial lighting is harming the natural world
    Nature (IF 40.137) Pub Date : 
    Aisling Irwin

    The dark side of light: how artificial lighting is harming the natural world The dark side of light: how artificial lighting is harming the natural world , Published online: 16 January 2018; doi:10.1038/d41586-018-00665-7 The world is lit at night like never before, and ecologists are assessing the damage.

    更新日期:2018-01-17
  • Egyptian tombs depict seldom-seen creatures
    Nature (IF 40.137) Pub Date : 

    Egyptian tombs depict seldom-seen creatures Egyptian tombs depict seldom-seen creatures, Published online: 16 January 2018; doi:10.1038/d41586-018-00790-3 Imaging technique reveals painted details lost to time.

    更新日期:2018-01-17
  • Research kudos does not need a price tag
    Nature (IF 40.137) Pub Date : 
    Tim Caro, Sasha R. X. Dall

    Research kudos does not need a price tag Research kudos does not need a price tag, Published online: 16 January 2018; doi:10.1038/d41586-018-00644-y Research kudos does not need a price tag

    更新日期:2018-01-17
  • Fixing statistics is more than a technical issue
    Nature (IF 40.137) Pub Date : 
    Andrea Saltelli, Philip Stark

    Fixing statistics is more than a technical issue Fixing statistics is more than a technical issue, Published online: 16 January 2018; doi:10.1038/d41586-018-00647-9 Fixing statistics is more than a technical issue

    更新日期:2018-01-17
  • The evolution of attraction, rare brains and how to hack time: Books in brief
    Nature (IF 40.137) Pub Date : 
    Barbara Kiser

    The evolution of attraction, rare brains and how to hack time: Books in brief The evolution of attraction, rare brains and how to hack time: Books in brief, Published online: 16 January 2018; doi:10.1038/d41586-018-00581-w Barbara Kiser reviews five of the week’s best science picks.

    更新日期:2018-01-17
  • Revealing the topology of Fermi-surface wavefunctions from magnetic quantum oscillations
    Phys. Rev. X (IF 12.789) Pub Date : 
    A. Alexandradinata, Chong Wang, Wenhui Duan, and Leonid Glazman

    The modern semiclassical theory of a Bloch electron in a magnetic field now encompasses the orbital magnetic moment and the geometric phase. These two notions are encoded in the Bohr-Sommerfeld quantization condition as a phase (\lambda) that is subleading in powers of the field; \lambda is measurable in the phase offset of the de Haas-van Alphen oscillation, as well as of fixed-bias oscillations of the differential conductance in tunneling spectroscopy. In some solids and for certain field orientations, \lambda/\pi are robustly integer-valued owing to the symmetry of the extremal orbit, i.e., they are the topological invariants of magnetotransport. Our comprehensive symmetry analysis identifies solids in any (magnetic) space group for which \lambda is a topological invariant, as well as identifies the symmetry-enforced degeneracy of Landau levels. The analysis is simplified by our formulation of ten (and only ten) symmetry classes for closed, Fermi-surface orbits. Case studies are discussed for graphene, transition metal dichalchogenides, 3D Weyl and Dirac metals, and crystalline and \Z_2 topological insulators. In particular, we point out that a \pi phase offset in the fundamental oscillation should \emph{not} be viewed as a smoking gun for a 3D Dirac metal.

    更新日期:2018-01-17
  • Probing the topology of density matrices
    Phys. Rev. X (IF 12.789) Pub Date : 
    Charles-Edouard Bardyn, Lukas Wawer, Alexander Altland, Michael Fleischhauer, and Sebastian Diehl

    The mixedness of a quantum state is usually seen as an adversary to topological quantization of observables. For example, exact quantization of the charge transported in a so-called Thouless adiabatic pump is lifted at any finite temperature in symmetry-protected topological insulators. Here, we show that certain directly observable many-body correlators preserve the integrity of topological invariants for mixed Gaussian quantum states in one dimension. Our approach relies on the expectation value of the many-body momentum-translation operator, and leads to a physical observable --- the ``ensemble geometric phase'' (EGP) --- which represents a bona fide geometric phase for mixed quantum states, in the thermodynamic limit. In cyclic protocols, the EGP provides a topologically quantized observable which detects encircled spectral singularities (``purity-gap'' closing points) of density matrices. While we identify the many-body nature of the EGP as a key ingredient, we propose a conceptually simple, interferometric setup to directly measure the latter in experiments with mesoscopic ensembles of ultracold atoms.

    更新日期:2018-01-16
  • He3−Xe129Comagnetometery usingRb87Detection and Decoupling
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-16
    M. E. Limes, D. Sheng, and M. V. Romalis
    更新日期:2018-01-16
  • Amorphous topological insulators constructed from random point sets
    Nat. Phys. (IF 22.806) Pub Date : 2018-01-15
    Noah P. Mitchell, Lisa M. Nash, Daniel Hexner, Ari M. Turner, William T. M. Irvine

    The discovery that the band structure of electronic insulators may be topologically non-trivial has revealed distinct phases of electronic matter with novel properties1,2. Recently, mechanical lattices have been found to have similarly rich structure in their phononic excitations3,4, giving rise to protected unidirectional edge modes5,6,7. In all of these cases, however, as well as in other topological metamaterials3,8, the underlying structure was finely tuned, be it through periodicity, quasi-periodicity or isostaticity. Here we show that amorphous Chern insulators can be readily constructed from arbitrary underlying structures, including hyperuniform, jammed, quasi-crystalline and uniformly random point sets. While our findings apply to mechanical and electronic systems alike, we focus on networks of interacting gyroscopes as a model system. Local decorations control the topology of the vibrational spectrum, endowing amorphous structures with protected edge modes—with a chirality of choice. Using a real-space generalization of the Chern number, we investigate the topology of our structures numerically, analytically and experimentally. The robustness of our approach enables the topological design and self-assembly of non-crystalline topological metamaterials on the micro and macro scale.

    更新日期:2018-01-15
  • Superconductivity in few-layer stanene
    Nat. Phys. (IF 22.806) Pub Date : 2018-01-15
    Menghan Liao, Yunyi Zang, Zhaoyong Guan, Haiwei Li, Yan Gong, Kejing Zhu, Xiao-Peng Hu, Ding Zhang, Yong Xu, Ya-Yu Wang, Ke He, Xu-Cun Ma, Shou-Cheng Zhang, Qi-Kun Xue

    A single atomic slice of α-tin—stanene—has been predicted to host the quantum spin Hall effect at room temperature, offering an ideal platform to study low-dimensional and topological physics. Although recent research has focused on monolayer stanene, the quantum size effect in few-layer stanene could profoundly change material properties, but remains unexplored. By exploring the layer degree of freedom, we discover superconductivity in few-layer stanene down to a bilayer grown on PbTe, while bulk α-tin is not superconductive. Through substrate engineering, we further realize a transition from a single-band to a two-band superconductor with a doubling of the transition temperature. In situ angle-resolved photoemission spectroscopy (ARPES) together with first-principles calculations elucidate the corresponding band structure. The theory also indicates the existence of a topologically non-trivial band. Our experimental findings open up novel strategies for constructing two-dimensional topological superconductors.

    更新日期:2018-01-15
  • Erratum: Optimal Continuous Variable Quantum Teleportation with Limited Resources [Phys. Rev. Lett.119, 120503 (2017)]
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Pietro Liuzzo-Scorpo, Andrea Mari, Vittorio Giovannetti, and Gerardo Adesso

    DOI:https://doi.org/10.1103/PhysRevLett.120.029904

    更新日期:2018-01-12
  • Mean-Potential Law in Evolutionary Games
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Paweł Nałęcz-Jawecki and Jacek Miękisz

    The Letter presents a novel way to connect random walks, stochastic differential equations, and evolutionary game theory. We introduce a new concept of a potential function for discrete-space stochastic systems. It is based on a correspondence between one-dimensional stochastic differential equations and random walks, which may be exact not only in the continuous limit but also in finite-state spaces. Our method is useful for computation of fixation probabilities in discrete stochastic dynamical systems with two absorbing states. We apply it to evolutionary games, formulating two simple and intuitive criteria for evolutionary stability of pure Nash equilibria in finite populations. In particular, we show that the 1 / 3 law of evolutionary games, introduced by Nowak et al. [Nature, 2004], follows from a more general mean-potential law.

    更新日期:2018-01-12
  • Stable Liquid Jets Bouncing off Soft Gels
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Dan Daniel, Xi Yao, and Joanna Aizenberg

    A liquid jet can stably bounce off a sufficiently soft gel by following the contour of the dimple created upon impact. This new phenomenon is insensitive to the wetting properties of the gels and was observed for different liquids over a wide range of surface tensions, γ = 24 − 72    mN / m . In contrast, other jet rebound phenomena are typically sensitive to γ : only a high γ jet rebounds off a hard solid (e.g. superhydrophobic surface) and only a low γ jet bounces off a liquid bath. This is because an air layer must be stabilized between the two interfaces. For a soft gel, no air layer is necessary and the jet rebound remains stable even when there is direct liquid-gel contact.

    更新日期:2018-01-12
  • Surfactant Variations in Porous Media Localize Capillary Instabilities during Haines Jumps
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Yaniv Edery, David Weitz, and Steffen Berg

    We use confocal microscopy to measure velocity and interfacial tension between a trapped wetting phase with a surfactant and a flowing, invading nonwetting phase in a porous medium. We relate interfacial tension variations at the fluid-fluid interface to surfactant concentration and show that these variations localize the destabilization of capillary forces and lead to rapid local invasion of the nonwetting fluid, resulting in a Haines jump. These spatial variations in surfactant concentration are caused by velocity variations at the fluid-fluid interfaces and lead to localization of the Haines jumps even in otherwise very uniform pore structure and pressure conditions. Our results provide new insight into the nature of Haines jumps, one of the most ubiquitous and important instabilities in flow in porous media.

    更新日期:2018-01-12
  • Mean-Field Scenario for the Athermal Creep Dynamics of Yield-Stress Fluids
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Chen Liu, Kirsten Martens, and Jean-Louis Barrat

    We develop a theoretical description based on an existent mean-field model for the transient dynamics prior to the steady flow of yielding materials. The mean-field model not only reproduces the experimentally observed nonlinear time dependence of the shear-rate response to an external stress, but also allows for the determination of the different physical processes involved in the onset of the reacceleration phase after the initial slowing down and a distinct fluidization phase. The fluidization time displays a power-law dependence on the distance of the applied stress to an age-dependent yield stress, which is not universal but strongly dependent on initial conditions.

    更新日期:2018-01-12
  • Inner Phases of Colloidal Hexagonal Spin Ice
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    A. Libál, C. Nisoli, C. J. O. Reichhardt, and C. Reichhardt
    更新日期:2018-01-12
  • Switching of Magnons by Electric and Magnetic Fields in Multiferroic Borates
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    A. M. Kuzmenko, D. Szaller, Th. Kain, V. Dziom, L. Weymann, A. Shuvaev, Anna Pimenov, A. A. Mukhin, V. Yu. Ivanov, I. A. Gudim, L. N. Bezmaternykh, and A. Pimenov

    Electric manipulation of magnetic properties is a key problem of materials research. To fulfill the requirements of modern electronics, these processes must be shifted to high frequencies. In multiferroic materials, this may be achieved by electric and magnetic control of their fundamental excitations. Here we identify magnetic vibrations in multiferroic iron borates that are simultaneously sensitive to external electric and magnetic fields. Nearly 100% modulation of the terahertz radiation in an external field is demonstrated for SmFe 3 ( BO 3 ) 4 . High sensitivity can be explained by a modification of the spin orientation that controls the excitation conditions in multiferroic borates. These experiments demonstrate the possibility to alter terahertz magnetic properties of materials independently by external electric and magnetic fields.

    更新日期:2018-01-12
  • Electromagnon with Sensitive Terahertz Magnetochromism in a Room-Temperature Magnetoelectric Hexaferrite
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Sae Hwan Chun, Kwang Woo Shin, Hyung Joon Kim, Seonghoon Jung, Jaehun Park, Young-Mi Bahk, Hyeong-Ryeol Park, Jisoo Kyoung, Da-Hye Choi, Dai-Sik Kim, Gun-Sik Park, J. F. Mitchell, and Kee Hoon Kim

    An electromagnon in the magnetoelectric (ME) hexaferrite Ba 0.5 Sr 2.5 Co 2 Fe 24 O 41 ( Co 2 Z -type) single crystal is identified by time-domain terahertz (THz) spectroscopy. The associated THz resonance is active on the electric field ( E ω ) of the THz light parallel to the c axis ( ∥   [ 001 ] ), whose spectral weight develops at a markedly high temperature, coinciding with a transverse conical magnetic order below 410 K. The resonance frequency of 1.03 THz at 20 K changes − 8.7 % and + 5.8 % under external magnetic field ( H ) of 2 kOe along [001] and [120], respectively. A model Hamiltonian describing the conical magnetic order elucidates that the dynamical ME effect arises from antiphase motion of spins which are coupled with modulating electric dipoles through the exchange striction mechanism. Moreover, the calculated frequency shift points to the key role of the Dzyaloshinskii-Moriya interaction that is altered by static electric polarization change under different H .

    更新日期:2018-01-12
  • Evidence for Spin Singlet Pairing with Strong Uniaxial Anisotropy inURu2Si2Using Nuclear Magnetic Resonance
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    T. Hattori, H. Sakai, Y. Tokunaga, S. Kambe, T. D. Matsuda, and Y. Haga

    In order to identify the spin contribution to superconducting pairing compatible with the so-called “hidden order”, Si 29 nuclear magnetic resonance measurements have been performed using a high-quality single crystal of URu 2 Si 2 . A clear reduction of the Si 29 Knight shift in the superconducting state has been observed under a magnetic field applied along the crystalline c axis, corresponding to the magnetic easy axis. These results provide direct evidence for the formation of spin-singlet Cooper pairs. Consequently, results indicating a very tiny change of the in-plane Knight shift reported previously demonstrate extreme uniaxial anisotropy for the spin susceptibility in the hidden order state.

    更新日期:2018-01-12
  • Edge Modes and Nonlocal Conductance in Graphene Superlattices
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Rory Brown, Niels R. Walet, and Francisco Guinea

    We study the existence of edge modes in gapped moiré superlattices of graphene monolayer ribbons on a hexagonal boron nitride substrate. We find that the superlattice bands acquire finite Chern numbers, which lead to a valley Hall effect. The presence of dispersive edge modes is confirmed by calculations of the band structure of realistic nanoribbons using tight binding methods. These edge states are only weakly sensitive to disorder, as short-range scattering processes lead to mean free paths of the order of microns. The results explain the existence of edge currents when the chemical potential lies within the bulk superlattice gap, and offer an explanation for existing nonlocal resistivity measurements in graphene ribbons on boron nitride.

    更新日期:2018-01-12
  • Higher-Order Topological Insulators and Semimetals on the Breathing Kagome and Pyrochlore Lattices
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Motohiko Ezawa

    A second-order topological insulator in d dimensions is an insulator which has no d − 1 dimensional topological boundary states but has d − 2 dimensional topological boundary states. It is an extended notion of the conventional topological insulator. Higher-order topological insulators have been investigated in square and cubic lattices. In this Letter, we generalize them to breathing kagome and pyrochlore lattices. First, we construct a second-order topological insulator on the breathing Kagome lattice. Three topological boundary states emerge at the corner of the triangle, realizing a 1 / 3 fractional charge at each corner. Second, we construct a third-order topological insulator on the breathing pyrochlore lattice. Four topological boundary states emerge at the corners of the tetrahedron with a 1 / 4 fractional charge at each corner. These higher-order topological insulators are characterized by the quantized polarization, which constitutes the bulk topological index. Finally, we study a second-order topological semimetal by stacking the breathing kagome lattice.

    更新日期:2018-01-12
  • Longitudinal Negative Magnetoresistance and Magnetotransport Phenomena in Conventional and Topological Conductors
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    A. V. Andreev and B. Z. Spivak

    Recently, a large negative longitudinal (parallel to the magnetic field) magnetoresistance was observed in Weyl and Dirac semimetals. It is believed to be related to the chiral anomaly associated with topological electron band structure of these materials. We show that in a certain range of parameters such a phenomenon can also exist in conventional centrosymmetric and time-reversal invariant conductors, lacking topological protection of the electron spectrum and the chiral anomaly. We also discuss the magnetic field enhancement of the longitudinal components of the thermal conductivity and thermoelectric tensors.

    更新日期:2018-01-12
  • Topological Nodal-Net Semimetal in a Graphene Network Structure
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Jian-Tao Wang, Simin Nie, Hongming Weng, Yoshiyuki Kawazoe, and Changfeng Chen

    Topological semimetals are characterized by the nodal points in their electronic structure near the Fermi level, either discrete or forming a continuous line or ring, which are responsible for exotic properties related to the topology of bulk bands. Here we identify by ab initio calculations a distinct topological semimetal that exhibits nodal nets comprising multiple interconnected nodal lines in bulk and have two coupled drumheadlike flat bands around the Fermi level on its surface. This nodal net semimetal state is proposed to be realized in a graphene network structure that can be constructed by inserting a benzene ring into each C ─ C bond in the bct- C 4 lattice or by a crystalline modification of the (5,5) carbon nanotube. These results expand the realm of nodal manifolds in topological semimetals, offering a new platform for exploring novel physics in these fascinating materials.

    更新日期:2018-01-12
  • On-the-Fly Machine Learning of Atomic Potential in Density Functional Theory Structure Optimization
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    T. L. Jacobsen, M. S. Jørgensen, and B. Hammer

    Machine learning (ML) is used to derive local stability information for density functional theory calculations of systems in relation to the recently discovered SnO 2 ( 110 ) − ( 4 × 1 ) reconstruction. The ML model is trained on (structure, total energy) relations collected during global minimum energy search runs with an evolutionary algorithm (EA). While being built, the ML model is used to guide the EA, thereby speeding up the overall rate by which the EA succeeds. Inspection of the local atomic potentials emerging from the model further shows chemically intuitive patterns.

    更新日期:2018-01-12
  • Direct Measurement of the Surface Energy of Bimetallic Nanoparticles: Evidence of Vegard’s Rulelike Dependence
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Adrian Chmielewski, Jaysen Nelayah, Hakim Amara, Jérôme Creuze, Damien Alloyeau, Guillaume Wang, and Christian Ricolleau

    We use in situ transmission electron microscopy to monitor in real time the evaporation of gold, copper, and bimetallic copper-gold nanoparticles at high temperature. Besides, we extend the Kelvin equation to two-component systems to predict the evaporation rates of spherical liquid mono- and bimetallic nanoparticles. By linking this macroscopic model to experimental TEM data, we determine the surface energies of pure gold, pure copper, Cu 50 Au 50 , and Cu 25 Au 75 nanoparticles in the liquid state. Our model suggests that the surface energy varies linearly with the composition in the liquid Cu-Au nanoalloy; i.e., it follows a Vegard’s rulelike dependence. To get atomic-scale insights into the thermodynamic properties of Cu-Au alloys on the whole composition range, we perform Monte Carlo simulations employing N -body interatomic potentials. These simulations at a microscopic level confirm the Vegard’s rulelike behavior of the surface energy obtained from experiments combined with macroscopic modeling.

    更新日期:2018-01-12
  • Phase Diagram of Hydrogen and a Hydrogen-Helium Mixture at Planetary Conditions by Quantum Monte Carlo Simulations
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Guglielmo Mazzola, Ravit Helled, and Sandro Sorella

    Understanding planetary interiors is directly linked to our ability of simulating exotic quantum mechanical systems such as hydrogen (H) and hydrogen-helium (H-He) mixtures at high pressures and temperatures. Equation of state (EOS) tables based on density functional theory are commonly used by planetary scientists, although this method allows only for a qualitative description of the phase diagram. Here we report quantum Monte Carlo (QMC) molecular dynamics simulations of pure H and H-He mixture. We calculate the first QMC EOS at 6000 K for a H-He mixture of a protosolar composition, and show the crucial influence of He on the H metallization pressure. Our results can be used to calibrate other EOS calculations and are very timely given the accurate determination of Jupiter’s gravitational field from the NASA Juno mission and the effort to determine its structure.

    更新日期:2018-01-12
  • mRNA vaccines — a new era in vaccinology
    Nat. Photon. (IF 37.852) Pub Date : 2018-01-12
    Norbert Pardi, Michael J. Hogan, Frederick W. Porter, Drew Weissman

    mRNA vaccines represent a promising alternative to conventional vaccine approaches because of their high potency, capacity for rapid development and potential for low-cost manufacture and safe administration. However, their application has until recently been restricted by the instability and inefficient in vivo delivery of mRNA. Recent technological advances have now largely overcome these issues, and multiple mRNA vaccine platforms against infectious diseases and several types of cancer have demonstrated encouraging results in both animal models and humans. This Review provides a detailed overview of mRNA vaccines and considers future directions and challenges in advancing this promising vaccine platform to widespread therapeutic use.

    更新日期:2018-01-12
  • Connecting Dissipation and Phase Slips in a Josephson Junction between Fermionic Superfluids
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    A. Burchianti, F. Scazza, A. Amico, G. Valtolina, J. A. Seman, C. Fort, M. Zaccanti, M. Inguscio, and G. Roati

    We study the emergence of dissipation in an atomic Josephson junction between weakly coupled superfluid Fermi gases. We find that vortex-induced phase slippage is the dominant microscopic source of dissipation across the Bose-Einstein condensate–Bardeen-Cooper-Schrieffer crossover. We explore different dynamical regimes by tuning the bias chemical potential between the two superfluid reservoirs. For small excitations, we observe dissipation and phase coherence to coexist, with a resistive current followed by well-defined Josephson oscillations. We link the junction transport properties to the phase-slippage mechanism, finding that vortex nucleation is primarily responsible for the observed trends of conductance and critical current. For large excitations, we observe the irreversible loss of coherence between the two superfluids, and transport cannot be described only within an uncorrelated phase-slip picture. Our findings open new directions for investigating the interplay between dissipative and superfluid transport in strongly correlated Fermi systems, and general concepts in out-of-equilibrium quantum systems.

    更新日期:2018-01-12
  • Raman Amplification with a Flying Focus
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    D. Turnbull, S. Bucht, A. Davies, D. Haberberger, T. Kessler, J. L. Shaw, and D. H. Froula

    We propose a new laser amplifier scheme utilizing stimulated Raman scattering in plasma in conjunction with a “flying focus”—a chromatic focusing system combined with a chirped pump beam that provides spatiotemporal control over the pump’s focal spot. Pump intensity isosurfaces are made to propagate at v = − c so as to be in sync with the injected counterpropagating seed pulse. By setting the pump intensity in the interaction region to be just above the ionization threshold of the background gas, an ionization wave is produced that travels at a fixed distance ahead of the seed. Simulations show that this will make it possible to optimize the plasma temperature and mitigate many of the issues that are known to have impacted previous Raman amplification experiments, in particular, the growth of precursors.

    更新日期:2018-01-12
  • Nonlinear Large Scale Flow in a Precessing Cylinder and Its Ability To Drive Dynamo Action
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    André Giesecke, Tobias Vogt, Thomas Gundrum, and Frank Stefani

    We have conducted experimental measurements and numerical simulations of a precession-driven flow in a cylindrical cavity. The study is dedicated to the precession dynamo experiment currently under construction at Helmholtz-Zentrum Dresden-Rossendorf and aims at the evaluation of the hydrodynamic flow with respect to its ability to drive a dynamo. We focus on the strongly nonlinear regime in which the flow is essentially composed of the directly forced primary Kelvin mode and higher modes in terms of standing inertial waves arising from nonlinear self-interactions. We obtain an excellent agreement between experiment and simulation with regard to both flow amplitudes and flow geometry. A peculiarity is the resonance-like emergence of an axisymmetric mode that represents a double roll structure in the meridional plane. Kinematic simulations of the magnetic field evolution induced by the time-averaged flow yield dynamo action at critical magnetic Reynolds numbers around Rm c ≈ 430 , which is well within the range of the planned liquid sodium experiment.

    更新日期:2018-01-12
  • Model-Free Prediction of Large Spatiotemporally Chaotic Systems from Data: A Reservoir Computing Approach
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Jaideep Pathak, Brian Hunt, Michelle Girvan, Zhixin Lu, and Edward Ott

    We demonstrate the effectiveness of using machine learning for model-free prediction of spatiotemporally chaotic systems of arbitrarily large spatial extent and attractor dimension purely from observations of the system’s past evolution. We present a parallel scheme with an example implementation based on the reservoir computing paradigm and demonstrate the scalability of our scheme using the Kuramoto-Sivashinsky equation as an example of a spatiotemporally chaotic system.

    更新日期:2018-01-12
  • Chaotic Properties of a Turbulent Isotropic Fluid
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Arjun Berera and Richard D. J. G. Ho

    By tracking the divergence of two initially close trajectories in phase space in an Eulerian approach to forced turbulence, the relation between the maximal Lyapunov exponent λ and the Reynolds number Re is measured using direct numerical simulations, performed on up to 204 8 3 collocation points. The Lyapunov exponent is found to solely depend on the Reynolds number with λ ∝ Re 0.53 and that after a transient period the divergence of trajectories grows at the same rate at all scales. Finally a linear divergence is seen that is dependent on the energy forcing rate. Links are made with other chaotic systems.

    更新日期:2018-01-12
  • Ultracold Heteronuclear Three-Body Systems: How Diabaticity Limits the Universality of Recombination into Shallow Dimers
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    P. Giannakeas and Chris H. Greene

    The mass-imbalanced three-body recombination process that forms a shallow dimer is shown to possess a rich Efimov-Stückelberg landscape, with corresponding spectra that differ fundamentally from the homonuclear case. A semianalytical treatment of the three-body recombination predicts unusual spectra with intertwined resonance peaks and minima and yields in-depth insight into the behavior of the corresponding Efimov spectra. In particular, the patterns of the Efimov-Stückelberg landscape are shown to depend inherently on the degree of diabaticity of the three-body collisions, which strongly affects the universality of the heteronuclear Efimov states.

    更新日期:2018-01-12
  • Measuring Anomalous Heating in a Planar Ion Trap with Variable Ion-Surface Separation
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Ivan A. Boldin, Alexander Kraft, and Christof Wunderlich

    Cold ions trapped in the vicinity of conductive surfaces experience heating of their oscillatory motion. Typically, the rate of this heating is orders of magnitude larger than expected from electric field fluctuations due to thermal motion of electrons in the conductors. This effect, known as anomalous heating, is not fully understood. One of the open questions is the heating rate’s dependence on the ion-electrode separation. We present a direct measurement of this dependence in an ion trap of simple planar geometry. The heating rates are determined by taking images of a single Yb + 172 ion’s resonance fluorescence after a variable heating time and deducing the trapped ion’s temperature from measuring its average oscillation amplitude. Assuming a power law for the heating rate versus ion-surface separation dependence, an exponent of − 3.79 ± 0.12 is measured.

    更新日期:2018-01-12
  • Analysis of the Daya Bay Reactor Antineutrino Flux Changes with Fuel Burnup
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    A. C. Hayes, Gerard Jungman, E. A. McCutchan, A. A. Sonzogni, G. T. Garvey, and X. B. Wang

    We investigate the recent Daya Bay results on the changes in the antineutrino flux and spectrum with the burnup of the reactor fuel. We find that the discrepancy between current model predictions and the Daya Bay results can be traced to the original measured U 235 / Pu 239 ratio of the fission β spectra that were used as a base for the expected antineutrino fluxes. An analysis of the antineutrino spectra that is based on a summation over all fission fragment β decays, using nuclear database input, explains all of the features seen in the Daya Bay evolution data. However, this summation method still allows for an anomaly. We conclude that there is currently not enough information to use the antineutrino flux changes to rule out the possible existence of sterile neutrinos.

    更新日期:2018-01-12
  • First Measurement of thegFactor in the Chiral Band: The Case of theCs128Isomeric State
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    E. Grodner, J. Srebrny, Ch. Droste, L. Próchniak, S. G. Rohoziński, M. Kowalczyk, M. Ionescu-Bujor, C. A. Ur, K. Starosta, T. Ahn, M. Kisieliński, T. Marchlewski, S. Aydin, F. Recchia, G. Georgiev, R. Lozeva, E. Fiori, M. Zielińska, Q. B. Chen, S. Q. Zhang, L. F. Yu, P. W. Zhao, and J. Meng

    The g factor of the 56 ns half-life isomeric state in Cs 128 has been measured using the time-differential perturbed angular distribution method. This state is the bandhead of the positive-parity chiral rotational band, which emerges when an unpaired proton, an unpaired neutron hole, and an even-even core are coupled such that their angular momentum vectors are aplanar (chiral configuration). g -factor measurements can give important information on the relative orientation of the three angular momentum vectors. The measured g factor g = + 0.59 ( 1 ) shows that there is an important contribution of the core rotation in the total angular momentum of the isomeric state. Moreover, a quantitative theoretical analysis supports the conclusion that the three angular momentum vectors lie almost in one plane, which suggests that the chiral configuration in Cs 128 demonstrated in previous works by characteristic patterns of electromagnetic transitions appears only above some value of the total nuclear spin.

    更新日期:2018-01-12
  • Lossless Brownian Information Engine
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Govind Paneru, Dong Yun Lee, Tsvi Tlusty, and Hyuk Kyu Pak

    We report on a lossless information engine that converts nearly all available information from an error-free feedback protocol into mechanical work. Combining high-precision detection at a resolution of 1 nm with ultrafast feedback control, the engine is tuned to extract the maximum work from information on the position of a Brownian particle. We show that the work produced by the engine achieves a bound set by a generalized second law of thermodynamics, demonstrating for the first time the sharpness of this bound. We validate a generalized Jarzynski equality for error-free feedback-controlled information engines.

    更新日期:2018-01-12
  • Defect in the Joint Spectrum of Hydrogen due to Monodromy
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Holger R. Dullin and Holger Waalkens
    更新日期:2018-01-12
  • Quantum States with a Positive Partial Transpose are Useful for Metrology
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Géza Tóth and Tamás Vértesi

    We show that multipartite quantum states that have a positive partial transpose with respect to all bipartitions of the particles can outperform separable states in linear interferometers. We introduce a powerful iterative method to find such states. We present some examples for multipartite states and examine the scaling of the precision with the particle number. Some bipartite examples are also shown that possess an entanglement very robust to noise. We also discuss the relation of metrological usefulness to Bell inequality violation. We find that quantum states that do not violate any Bell inequality can outperform separable states metrologically. We present such states with a positive partial transpose, as well as with a nonpositive partial transpose.

    更新日期:2018-01-12
  • Light-Cone and Diffusive Propagation of Correlations in a Many-Body Dissipative System
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2018-01-12
    Jean-Sébastien Bernier, Ryan Tan, Lars Bonnes, Chu Guo, Dario Poletti, and Corinna Kollath

    We analyze the propagation of correlations after a sudden interaction change in a strongly interacting quantum system in contact with an environment. In particular, we consider an interaction quench in the Bose-Hubbard model, deep within the Mott-insulating phase, under the effect of dephasing. We observe that dissipation effectively speeds up the propagation of single-particle correlations while reducing their coherence. In contrast, for two-point density correlations, the initial ballistic propagation regime gives way to diffusion at intermediate times. Numerical simulations, based on a time-dependent matrix product state algorithm, are supplemented by a quantitatively accurate fermionic quasiparticle approach providing an intuitive description of the initial dynamics in terms of holon and doublon excitations.

    更新日期:2018-01-12
  • Frankenstein lives on
    Science (IF 37.205) Pub Date : 2018-01-12
    Henk van den Belt

    It was 200 years ago that Mary Shelley's Frankenstein; or, The Modern Prometheus was published. Over the decades, this gothic tale has captured the popular imagination through the numerous theater productions and films it inspired. The story is commonly taken to imply a dire warning about the dangers of scientific hubris. Just mention the name Frankenstein and laypersons think of scientists “playing God.” In the common view, the inevitable consequence of Frankenstein's alleged transgression—bestowing life on inanimate matter—was that he created a monster that would wreak havoc on his family and friends. Frankenstein's name is repeatedly invoked in debates about emerging technologies like biotech, nanotech, synthetic biology, and artificial intelligence. However, the view of Shelley's story as a cautionary tale about scientific hubris, although dominant, is only one possible interpretation. Her novel, actually, is a multilayered story full of ambivalences and much subtler than most Hollywood versions. It naturally lends itself to diverse interpretations.

    更新日期:2018-01-12
  • News at a glance
    Science (IF 37.205) Pub Date : 2018-01-12
    American Association for the Advancement of Science

    In science news around the world, the U.S. National Football League provides $16 million for medical research on concussions and other football-related illnesses, and the World Health Organization approves a new, long-lasting vaccine for typhoid fever. China announces it will build a new research and development park in Beijing to develop artificial intelligence technologies, and South Korean universities refuse to renew their contracts with Elsevier for access to its ScienceDirect database because of a price hike. Scientists install new devices at the South Pole to measure neutrinos, and a volunteer discovers the largest prime number, containing more than 23 million digits. And the U.S. Department of the Interior decides to review certain grants to universities and nonprofit groups to ensure they align with the priorities of President Donald Trump's administration.

    更新日期:2018-01-12
  • DOE pushes for useful quantum computing
    Science (IF 37.205) Pub Date : 2018-01-12
    Adrian Cho

    The U.S. Department of Energy (DOE) is joining the quest to develop quantum computers, devices that would exploit quantum mechanics to crack problems that overwhelm conventional computers. The initiative comes as Google and other companies race to build a quantum computer that can demonstrate "quantum supremacy" by beating classical computers on a test problem. But reaching that milestone will not mean practical uses are at hand, and the new $40 million DOE effort is intended to spur the development of useful quantum computing algorithms for its work in chemistry, materials science, nuclear physics, and particle physics. With the resources at its 17 national laboratories, DOE could play a key role in developing the machines, researchers say, although finding problems with which quantum computers can help isn't so easy.

    更新日期:2018-01-12
  • In Pakistan, surveillance for polio reveals a paradox
    Science (IF 37.205) Pub Date : 2018-01-12
    Leslie Roberts

    Last year polio fighters could smell victory in Pakistan, which many believe will be the last country on Earth to harbor the virus. Cases dropped to an all-time low. Blood tests showed that immunity to the poliovirus had never been higher. Surely, there were not enough susceptible children to sustain transmission, and the virus would burn itself out within a year. Unsettling new findings, however, show it is far from gone. In the most extensive effort in any country to scour the environment for traces of the virus, polio workers are finding it widely across Pakistan, in places they thought it had disappeared. They are wondering "just what the hell is going on" and how worried they should be, says epidemiologist Chris Maher of the World Health Organization in Geneva, Switzerland, who runs polio operations in the eastern Mediterranean region. Does this mean the virus is more entrenched than anyone realized and is poised to resurge? Or is this how a virus behaves in its final days—persisting in the environment but not causing disease until it fades out? 

    更新日期:2018-01-12
  • Earth scientists list top priorities for space missions
    Science (IF 37.205) Pub Date : 2018-01-12
    Paul Voosen

    Earth scientists hope a new priority setting effort will help them make the most of NASA's limited budget for satellite missions that watch over the planet. The so-called decadal survey, issued in January by the National Academies of Sciences, Engineering, and Medicine, laid out the community's consensus wish list, ranging from cloud monitoring to multiwavelength imaging—and recommends a strong dose of competition to keep costs down. The report prioritizes five observations for launch, including hyperspectral imaging, clouds, atmospheric particles, and missions to chart gravity variations and tiny crustal movements. It also advocates creating a new line of $350 million missions targeting seven observations, with competitions to choose three for flight in the next 10 years.

    更新日期:2018-01-12
  • Cuba's 100-year plan for climate change
    Science (IF 37.205) Pub Date : 2018-01-12
    Richard Stone

    On its deadly run through the Caribbean last September, Hurricane Irma lashed northern Cuba, inundating coastal settlements and scouring away vegetation. Irma lent new urgency to a Cuban national plan, called Tarea Vida, or Project Life, that bans construction of new homes in threatened coastal areas, mandates relocating people from communities doomed by rising sea levels, calls for an overhaul of the country's agricultural system to shift crop production away from saltwater-contaminated areas, and spells out the need to shore up coastal defenses, including by restoring degraded habitat. Project Life stands out for taking a long view: It intends to prepare Cuba for climatological impacts over the next century. Much of the initial funding could come from a $100 million proposal that Cuba plans to submit soon to the Global Climate Fund.

    更新日期:2018-01-12
  • Cliffs of ice spied on Mars
    Science (IF 37.205) Pub Date : 2018-01-12
    Paul Voosen

    Scientists have discovered eight cliffs of nearly pure water ice on Mars, some of which stand nearly 100 meters tall. The discovery points to large stores of underground ice buried only a meter or two below the surface at surprisingly low martian latitudes, in regions where ice had not yet been detected. Each cliff seems to be the naked face of a glacier, tantalizing scientists with the promise of a layer-cake record of past martian climates and space enthusiasts with a potential resource for future human bases. Scientists discovered the cliffs with a high-resolution camera on the Mars Reconnaissance Orbiter, revisiting the sites to show their subsequent retreat as a result of vaporization, and their persistence in the martian summer. The hunt should now be on, scientists say, for similar sites closer to the equator.

    更新日期:2018-01-12
  • The long shadow of Frankenstein
    Science (IF 37.205) Pub Date : 2018-01-12
    Kai Kupferschmidt

    In January 1818, Mary Shelley published her book Frankenstein, a terrifying story of a doctor who builds a creature from scavenged body parts, then recoils in horror, spurns it, and sees his friends and family destroyed by the monster. Two hundred years later, Frankenstein is still essential reading for anyone working in science. In this special issue, Science examines the lasting legacy of Shelley's book on science and popular culture as well as the potential risks from modern-day, real-life Frankensteins.

    更新日期:2018-01-12
  • How a horror story haunts science
    Science (IF 37.205) Pub Date : 2018-01-12
    Jon Cohen

    In conceiving her novel Frankenstein, Mary Shelley was influenced by the nascent medical science of the day and by early experiments on electricity. In return, Frankenstein has haunted science ever since. Shelley's book and subsequent films and plays have become what one author calls "the governing myth of modern biology": a cautionary tale of scientific hubris. The scientific literature, like the popular press, is rife with references to Frankenfood, Frankencells, and Frankendrugs—most of them supposedly monstrous creations. Other papers mentioning Frankenstein analyze the science behind the novel, analyze Shelley's state of mind, or even, in a bizarre twist, draw inspiration from the tale.

    更新日期:2018-01-12
  • Creating a modern monster
    Science (IF 37.205) Pub Date : 2018-01-12
    David Shultz

    When Mary Shelley published her story of Victor Frankenstein and his misshapen monster in 1818, she provided little detail about how exactly the doctor built his creation, except that "the dissecting room and the slaughter-house furnished many of [his] materials" and that he infused "a spark of being in the lifeless thing." But what if Shelley had written her book today? Here is an overview of current and future technologies—from lab-grown organs and bionics to gene editing—that she might call on to produce her iconic creature.

    更新日期:2018-01-12
  • Taming the monsters of tomorrow
    Science (IF 37.205) Pub Date : 2018-01-12
    Kai Kupferschmidt

    In Mary Shelley's novel, the scientist Victor Frankenstein fears that creating a female companion to his unhappy monster could lead to a "race of devils" that could drive humanity extinct. Today, some scientists worry about scientific advances in the real world that could kill all of humanity, or at least end civilization as we know it. Some two dozen researchers at three academic centers are studying these "existential risks"—including labmade viruses, armies of nanobots, and artificial intelligence—and what can be done about them. But critics say their scenarios are far-fetched and distract from real existential dangers, including climate change and nuclear war.

    更新日期:2018-01-12
  • A glossary of Frankenwords
    Science (IF 37.205) Pub Date : 2018-01-12
    Jon Cohen

    Along with fears about scientific overreach, Mary Shelley's novel has inspired hundreds of whimsical names for products and phenomena—from Frankencells and Frankengenes to Frankenslime and Frankenswine. Here's a selection.

    更新日期:2018-01-12
  • Detecting the building blocks of aromatics
    Science (IF 37.205) Pub Date : 2018-01-12
    Christine Joblin, José Cernicharo

    Interstellar clouds are sites of active organic chemistry (1). Many small, gasphase molecules are found in the dark parts of the clouds that are protected from ultraviolet (UV) photons, but these molecules photodissociate in the external layers of the cloud that are exposed to stellar radiation (see the photo). These irradiated regions are populated by large polycyclic aromatic hydrocarbons (PAHs) with characteristic infrared (IR) emission features. These large aromatics are expected to form from benzene (C6H6), which is, however, difficult to detect because it does not have a permanent dipole moment and can only be detected via its IR absorption transitions against a strong background source (2). On page 202 of this issue, McGuire et al. (3) report the detection of benzonitrile (c-C6H5CN) with radio telescopes. Benzonitrile likely forms in the reaction of CN with benzene; from its observation, it is therefore possible to estimate the abundance of benzene itself.

    更新日期:2018-01-12
  • Improbable Big Birds
    Science (IF 37.205) Pub Date : 2018-01-12
    Catherine E. Wagner

    Darwin's finches, a group of 18 species endemic to the Galápagos archipelago, are a classic example of adaptive radiation—the process whereby a single ancestral species multiplies in number to produce divergent species, often in rapid succession (1). These birds are evolutionary biologists' most celebrated example of natural selection in action. On page 224 of this issue, Lamichhaney et al. (2) have succeeded in observing a process even more elusive than natural selection—the formation of a new species (speciation). Because speciation typically takes place on time scales that are too long for direct human observation, before now it was only in organisms with very fast generation times, such as viruses and bacteria, that scientists had directly observed this process [for example, (3)]. Lamichhaney et al. show through direct observation and DNA sequencing that new species can form very rapidly: within three generations. The key, in this case, is hybridization between different species.

    更新日期:2018-01-12
  • Malaria parasite evolution in a test tube
    Science (IF 37.205) Pub Date : 2018-01-12
    Jane M. Carlton

    Malaria is an infectious disease caused by the Plasmodium parasite, and transmitted by Anopheles mosquitoes. In 2016, a staggering 216 million cases of malaria and 445,000 deaths were recorded, mostly in Africa, although half of the world's population in 91 countries is at risk of the disease (1). Malaria prevention methods include control of the mosquito with insecticide-treated bed nets and indoor residual spraying of insecticides. Prompt diagnosis through the use of rapid diagnostic tests is also key. Although there is a malaria vaccine, RTS,S/AS01, it shows limited efficacy and has yet to be used widely. However, the frontline against malaria is antimalarial drugs, in particular artemisinin-based combination therapies (ACTs), which are mixtures of artemisinin and its derivatives from the Chinese sweet wormwood herb, with drugs such as piperaquine. Alarmingly, the parasite is now resistant to most drugs that have been developed (see the figure). It is imperative that we identify new inhibitors if progress in reducing malaria is to be sustained. On page 191 of this issue, Cowell et al. (2) present a major step forward, revealing new antimalarial drug targets and their possible resistance mechanisms.

    更新日期:2018-01-12
  • TRPM channels come into focus
    Science (IF 37.205) Pub Date : 2018-01-12
    Chanhyung Bae, Andres Jara-Oseguera, Kenton J. Swartz

    Transient receptor potential (TRP) channels were first identified in photoreceptors of the fruit fly (1, 2). In mammals, six major families of TRP channels play key roles in sensing stimuli such as light, temperature, membrane lipids, and intracellular Ca2+. In 2013, two landmark publications revealed the cryo–electron microscopy (cryo-EM) structure of the heat- and capsaicin-activated TRPV1 channel (3, 4). Two articles in this issue report cryo-EM structures of cation-selective TRPM channels. On page 228, Autzen et al. (5) describe TRPM4, which is activated by intracellular Ca2+ and involved in controlling arterial tone, cardiac rhythm, and the immune response (6). On page 237, Yin et al. (7) report on TRPM8, which senses cold and menthol and may serve as a cancer biomarker (8).

    更新日期:2018-01-12
  • Coherent excitations revealed and calculated
    Science (IF 37.205) Pub Date : 2018-01-12
    Antoine Georges

    Quantum entities manifest themselves as either particles or waves. In a physical system containing a very large number of identical particles, such as electrons in a material, individualistic (particle-like) behavior prevails at high temperatures. At low temperatures, collective behavior emerges, and excitations of the system in this regime are best described as waves—long-lived phenomena that are periodic in both space and time and often dubbed “coherent excitations” by physicists. On page 186 of this issue, Goremychkin et al. (1) used experiment and theory to describe the emergence of coherent excitations in a complex quantum system with strong interactions. They studied a cerium-palladium compound, CePd3, in which the very localized electrons of 4f orbitals of Ce interact with the much more itinerant conduction electrons of the extended d orbitals of Pd at low temperatures to create a wavelike state.

    更新日期:2018-01-12
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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