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Nature is the international weekly journal of science: a magazine style journal that publishes full-length research papers in all disciplines of science, as well as News and Views, reviews, news, features, commentaries, web focuses and more, covering all branches of science and how science impacts upon all aspects of society and life.
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Materials science: Superlattice substitution

Tue, 08/25/2015 - 23:00

Materials science: Superlattice substitution

Nature 524, 7566 (2015). doi:10.1038/524418a

Authors: Daniel Vanmaekelbergh

What happens if some of the particles of a superlattice — an array of identical nanoscale crystals — are replaced with foreign ones? It emerges that the properties of superlattices can be radically altered in this way. See Letter p.450

Categories: Journal Articles

Particle physics: Positrons ride the wave

Tue, 08/25/2015 - 23:00

Particle physics: Positrons ride the wave

Nature 524, 7566 (2015). doi:10.1038/524422a

Authors: Philippe Piot

Experiments reveal that positrons — the antimatter equivalents of electrons — can be rapidly accelerated using a plasma wave. The findings pave the way to high-energy electron–positron particle colliders. See Letter p.442

Categories: Journal Articles

Photonics: A stable narrow-band X-ray laser

Tue, 08/25/2015 - 23:00

Photonics: A stable narrow-band X-ray laser

Nature 524, 7566 (2015). doi:10.1038/524424a

Authors: Linda Young

An atomic laser operating at the shortest wavelength yet achieved has been created by bombarding a copper foil with two X-ray pulses tuned to slightly different energies. The results may lead to ultrastable X-ray lasers. See Letter p.446

Categories: Journal Articles

The disruption of multiplanet systems through resonance with a binary orbit

Tue, 08/25/2015 - 23:00

The disruption of multiplanet systems through resonance with a binary orbit

Nature 524, 7566 (2015). doi:10.1038/nature14873

Authors: Jihad R. Touma & S. Sridhar

Most exoplanetary systems in binary stars are of S-type, and consist of one or more planets orbiting a primary star with a wide binary stellar companion. Planetary eccentricities and mutual inclinations can be large, perhaps forced gravitationally by the binary companion. Earlier work on single planet systems appealed to the Kozai–Lidov instability wherein a sufficiently inclined binary orbit excites large-amplitude oscillations in the planet’s eccentricity and inclination. The instability, however, can be quenched by many agents that induce fast orbital precession, including mutual gravitational forces in a multiplanet system. Here we report that orbital precession, which inhibits Kozai–Lidov cycling in a multiplanet system, can become fast enough to resonate with the orbital motion of a distant binary companion. Resonant binary forcing results in dramatic outcomes ranging from the excitation of large planetary eccentricities and mutual inclinations to total disruption. Processes such as planetary migration can bring an initially non-resonant system into resonance. As it does not require special physical or initial conditions, binary resonant driving is generic and may have altered the architecture of many multiplanet systems. It can also weaken the multiplanet occurrence rate in wide binaries, and affect planet formation in close binaries.

Categories: Journal Articles

Multi-gigaelectronvolt acceleration of positrons in a self-loaded plasma wakefield

Tue, 08/25/2015 - 23:00

Multi-gigaelectronvolt acceleration of positrons in a self-loaded plasma wakefield

Nature 524, 7566 (2015). doi:10.1038/nature14890

Authors: S. Corde, E. Adli, J. M. Allen, W. An, C. I. Clarke, C. E. Clayton, J. P. Delahaye, J. Frederico, S. Gessner, S. Z. Green, M. J. Hogan, C. Joshi, N. Lipkowitz, M. Litos, W. Lu, K. A. Marsh, W. B. Mori, M. Schmeltz, N. Vafaei-Najafabadi, D. Walz, V. Yakimenko & G. Yocky

Electrical breakdown sets a limit on the kinetic energy that particles in a conventional radio-frequency accelerator can reach. New accelerator concepts must be developed to achieve higher energies and to make future particle colliders more compact and affordable. The plasma wakefield accelerator (PWFA) embodies one such concept, in which the electric field of a plasma wake excited by a bunch of charged particles (such as electrons) is used to accelerate a trailing bunch of particles. To apply plasma acceleration to electron–positron colliders, it is imperative that both the electrons and their antimatter counterpart, the positrons, are efficiently accelerated at high fields using plasmas. Although substantial progress has recently been reported on high-field, high-efficiency acceleration of electrons in a PWFA powered by an electron bunch, such an electron-driven wake is unsuitable for the acceleration and focusing of a positron bunch. Here we demonstrate a new regime of PWFAs where particles in the front of a single positron bunch transfer their energy to a substantial number of those in the rear of the same bunch by exciting a wakefield in the plasma. In the process, the accelerating field is altered—‘self-loaded’—so that about a billion positrons gain five gigaelectronvolts of energy with a narrow energy spread over a distance of just 1.3 metres. They extract about 30 per cent of the wake’s energy and form a spectrally distinct bunch with a root-mean-square energy spread as low as 1.8 per cent. This ability to transfer energy efficiently from the front to the rear within a single positron bunch makes the PWFA scheme very attractive as an energy booster to an electron–positron collider.

Categories: Journal Articles

Atomic inner-shell laser at 1.5-ångström wavelength pumped by an X-ray free-electron laser

Tue, 08/25/2015 - 23:00

Atomic inner-shell laser at 1.5-ångström wavelength pumped by an X-ray free-electron laser

Nature 524, 7566 (2015). doi:10.1038/nature14894

Authors: Hitoki Yoneda, Yuichi Inubushi, Kazunori Nagamine, Yurina Michine, Haruhiko Ohashi, Hirokatsu Yumoto, Kazuto Yamauchi, Hidekazu Mimura, Hikaru Kitamura, Tetsuo Katayama, Tetsuya Ishikawa & Makina Yabashi

Since the invention of the first lasers in the visible-light region, research has aimed to produce short-wavelength lasers that generate coherent X-rays; the shorter the wavelength, the better the imaging resolution of the laser and the shorter the pulse duration, leading to better temporal resolution in probe measurements. Recently, free-electron lasers based on self-amplified spontaneous emission have made it possible to generate a hard-X-ray laser (that is, the photon energy is of the order of ten kiloelectronvolts) in an ångström-wavelength regime, enabling advances in fields from ultrafast X-ray spectrosopy to X-ray quantum optics. An atomic laser based on neon atoms and pumped by a soft-X-ray (that is, a photon energy of less than one kiloelectronvolt) free-electron laser has been achieved at a wavelength of 14 nanometres. Here, we use a copper target and report a hard-X-ray inner-shell atomic laser operating at a wavelength of 1.5 ångströms. X-ray free-electron laser pulses with an intensity of about 1019 watts per square centimetre tuned to the copper K-absorption edge produced sufficient population inversion to generate strong amplified spontaneous emission on the copper Kα lines. Furthermore, we operated the X-ray free-electron laser source in a two-colour mode, with one colour tuned for pumping and the other for the seed (starting) light for the laser.

Categories: Journal Articles

Substitutional doping in nanocrystal superlattices

Tue, 08/25/2015 - 23:00

Substitutional doping in nanocrystal superlattices

Nature 524, 7566 (2015). doi:10.1038/nature14872

Authors: Matteo Cargnello, Aaron C. Johnston-Peck, Benjamin T. Diroll, Eric Wong, Bianca Datta, Divij Damodhar, Vicky V. T. Doan-Nguyen, Andrew A. Herzing, Cherie R. Kagan & Christopher B. Murray

Doping is a process in which atomic impurities are intentionally added to a host material to modify its properties. It has had a revolutionary impact in altering or introducing electronic, magnetic, luminescent, and catalytic properties for several applications, for example in semiconductors. Here we explore and demonstrate the extension of the concept of substitutional atomic doping to nanometre-scale crystal doping, in which one nanocrystal is used to replace another to form doped self-assembled superlattices. Towards this goal, we show that gold nanocrystals act as substitutional dopants in superlattices of cadmium selenide or lead selenide nanocrystals when the size of the gold nanocrystal is very close to that of the host. The gold nanocrystals occupy random positions in the superlattice and their density is readily and widely controllable, analogous to the case of atomic doping, but here through nanocrystal self-assembly. We also show that the electronic properties of the superlattices are highly tunable and strongly affected by the presence and density of the gold nanocrystal dopants. The conductivity of lead selenide films, for example, can be manipulated over at least six orders of magnitude by the addition of gold nanocrystals and is explained by a percolation model. As this process relies on the self-assembly of uniform nanocrystals, it can be generally applied to assemble a wide variety of nanocrystal-doped structures for electronic, optical, magnetic, and catalytic materials.

Categories: Journal Articles

Western US intermountain seismicity caused by changes in upper mantle flow

Tue, 08/25/2015 - 23:00

Western US intermountain seismicity caused by changes in upper mantle flow

Nature 524, 7566 (2015). doi:10.1038/nature14867

Authors: Thorsten W. Becker, Anthony R. Lowry, Claudio Faccenna, Brandon Schmandt, Adrian Borsa & Chunquan Yu

Understanding the causes of intraplate earthquakes is challenging, as it requires extending plate tectonic theory to the dynamics of continental deformation. Seismicity in the western United States away from the plate boundary is clustered along a meandering, north–south trending ‘intermountain’ belt. This zone coincides with a transition from thin, actively deforming to thicker, less tectonically active crust and lithosphere. Although such structural gradients have been invoked to explain seismicity localization, the underlying cause of seismicity remains unclear. Here we show results from improved mantle flow models that reveal a relationship between seismicity and the rate change of ‘dynamic topography’ (that is, vertical normal stress from mantle flow). The associated predictive skill is greater than that of any of the other forcings we examined. We suggest that active mantle flow is a major contributor to seismogenic intraplate deformation, while gravitational potential energy variations have a minor role. Seismicity localization should occur where convective changes in vertical normal stress are modulated by lithospheric strength heterogeneities. Our results on deformation processes appear consistent with findings from other mobile belts, and imply that mantle flow plays a significant and quantifiable part in shaping topography, tectonics, and seismic hazard within intraplate settings.

Categories: Journal Articles

Heroism in Syria

Mon, 08/24/2015 - 23:00

Heroism in Syria

Nature 524, 7566 (2015). doi:10.1038/524387b

A tribute to scholars of extraordinary courage.

Categories: Journal Articles

Minnesota bog study turns up the heat on peat

Mon, 08/24/2015 - 23:00

Minnesota bog study turns up the heat on peat

Nature 524, 7566 (2015). http://www.nature.com/doifinder/10.1038/524397a

Author: Alexandra Witze

Experiment boosts temperature and carbon dioxide to gauge global-warming response.

Categories: Journal Articles

Ecologists embrace their urban side

Mon, 08/24/2015 - 23:00

Ecologists embrace their urban side

Nature 524, 7566 (2015). http://www.nature.com/doifinder/10.1038/524399a

Author: Daniel Cressey

Climate change and the rise of cities have broadened what it means to study ecosystems.

Categories: Journal Articles

The growing global battle against blood-sucking ticks

Mon, 08/24/2015 - 23:00

The growing global battle against blood-sucking ticks

Nature 524, 7566 (2015). http://www.nature.com/doifinder/10.1038/524406a

Author: Melinda Wenner Moyer

Scientists have no shortage of ideas about how to stop tick-borne illnesses. What is holding them back?

Categories: Journal Articles

Hurricane Katrina’s psychological scars revealed

Sun, 08/23/2015 - 23:00

Hurricane Katrina’s psychological scars revealed

Nature 524, 7566 (2015). http://www.nature.com/doifinder/10.1038/524395a

Author: Sara Reardon

Mental health worsened in the disaster’s aftermath, but survivors also showed resilience.

Categories: Journal Articles

North Pacific ‘blob’ stirs up fisheries management

Wed, 08/19/2015 - 23:00

North Pacific ‘blob’ stirs up fisheries management

Nature 524, 7566 (2015). http://www.nature.com/doifinder/10.1038/nature.2015.18218

Author: Virginia Gewin

Unusually warm ocean strengthens calls to consider ecosystem variables in setting catch limits.

Categories: Journal Articles

Conference tweeting rule frustrates ecologists

Tue, 08/18/2015 - 23:00

Conference tweeting rule frustrates ecologists

Nature 524, 7566 (2015). doi:10.1038/524391f

Author: Chris Woolston

Complaints ensued when attendees at an ecology meeting were asked to get permission before live-tweeting.

Categories: Journal Articles

Evolution: Gene transfer in complex cells

Tue, 08/18/2015 - 23:00

Evolution: Gene transfer in complex cells

Nature 524, 7566 (2015). doi:10.1038/nature15205

Authors: John M. Archibald

A comparative genomic study shows that, during evolution, nucleus-containing cells acquired DNA from bacteria primarily by endosymbiosis — the uptake and integration of one cell by another. See Article p.427

Categories: Journal Articles

Endosymbiotic origin and differential loss of eukaryotic genes

Tue, 08/18/2015 - 23:00

Endosymbiotic origin and differential loss of eukaryotic genes

Nature 524, 7566 (2015). doi:10.1038/nature14963

Authors: Chuan Ku, Shijulal Nelson-Sathi, Mayo Roettger, Filipa L. Sousa, Peter J. Lockhart, David Bryant, Einat Hazkani-Covo, James O. McInerney, Giddy Landan & William F. Martin

Chloroplasts arose from cyanobacteria, mitochondria arose from proteobacteria. Both organelles have conserved their prokaryotic biochemistry, but their genomes are reduced, and most organelle proteins are encoded in the nucleus. Endosymbiotic theory posits that bacterial genes in eukaryotic genomes entered the eukaryotic lineage via organelle ancestors.

Categories: Journal Articles

Sidekick 2 directs formation of a retinal circuit that detects differential motion

Tue, 08/18/2015 - 23:00

Sidekick 2 directs formation of a retinal circuit that detects differential motion

Nature 524, 7566 (2015). doi:10.1038/nature14682

Authors: Arjun Krishnaswamy, Masahito Yamagata, Xin Duan, Y. Kate Hong & Joshua R. Sanes

In the mammalian retina, processes of approximately 70 types of interneurons form specific synapses on roughly 30 types of retinal ganglion cells (RGCs) in a neuropil called the inner plexiform layer. Each RGC type extracts salient features from visual input, which are sent deeper into the brain for further processing. The specificity and stereotypy of synapses formed in the inner plexiform layer account for the feature-detecting ability of RGCs. Here we analyse the development and function of synapses on one mouse RGC type, called the W3B-RGC. These cells have the remarkable property of responding when the timing of the movement of a small object differs from that of the background, but not when they coincide. Such cells, known as local edge detectors or object motion sensors, can distinguish moving objects from a visual scene that is also moving. We show that W3B-RGCs receive strong and selective input from an unusual excitatory amacrine cell type known as VG3-AC (vesicular glutamate transporter 3). Both W3B-RGCs and VG3-ACs express the immunoglobulin superfamily recognition molecule sidekick 2 (Sdk2), and both loss- and gain-of-function studies indicate that Sdk2-dependent homophilic interactions are necessary for the selectivity of the connection. The Sdk2-specified synapse is essential for visual responses of W3B-RGCs: whereas bipolar cells relay visual input directly to most RGCs, the W3B-RGCs receive much of their input indirectly, via the VG3-ACs. This non-canonical circuit introduces a delay into the pathway from photoreceptors in the centre of the receptive field to W3B-RGCs, which could improve their ability to judge the synchrony of local and global motion.

Categories: Journal Articles

Cell mixing induced by myc is required for competitive tissue invasion and destruction

Tue, 08/18/2015 - 23:00

Cell mixing induced by myc is required for competitive tissue invasion and destruction

Nature 524, 7566 (2015). doi:10.1038/nature14684

Authors: Romain Levayer, Barbara Hauert & Eduardo Moreno

Cell–cell intercalation is used in several developmental processes to shape the normal body plan. There is no clear evidence that intercalation is involved in pathologies. Here we use the proto-oncogene myc to study a process analogous to early phase of tumour expansion: myc-induced cell competition. Cell competition is a conserved mechanism driving the elimination of slow-proliferating cells (so-called ‘losers’) by faster-proliferating neighbours (so-called ‘winners’) through apoptosis and is important in preventing developmental malformations and maintain tissue fitness. Here we show, using long-term live imaging of myc-driven competition in the Drosophila pupal notum and in the wing imaginal disc, that the probability of elimination of loser cells correlates with the surface of contact shared with winners. As such, modifying loser–winner interface morphology can modulate the strength of competition. We further show that elimination of loser clones requires winner–loser cell mixing through cell–cell intercalation. Cell mixing is driven by differential growth and the high tension at winner–winner interfaces relative to winner–loser and loser–loser interfaces, which leads to a preferential stabilization of winner–loser contacts and reduction of clone compactness over time. Differences in tension are generated by a relative difference in F-actin levels between loser and winner junctions, induced by differential levels of the membrane lipid phosphatidylinositol (3,4,5)-trisphosphate. Our results establish the first link between cell–cell intercalation induced by a proto-oncogene and how it promotes invasiveness and destruction of healthy tissues.

Categories: Journal Articles

Multimetallic catalysed cross-coupling of aryl bromides with aryl triflates

Sun, 08/16/2015 - 23:00

Multimetallic catalysed cross-coupling of aryl bromides with aryl triflates

Nature 524, 7566 (2015). doi:10.1038/nature14676

Authors: Laura K. G. Ackerman, Matthew M. Lovell & Daniel J. Weix

The advent of transition-metal catalysed strategies for forming new carbon-carbon bonds has revolutionized the field of organic chemistry, enabling the efficient synthesis of ligands, materials, and biologically active molecules. In cases where a single metal fails to promote a selective or efficient transformation, the synergistic cooperation of two distinct catalysts—multimetallic catalysis—can be used instead. Many important reactions rely on multimetallic catalysis, such as the Wacker oxidation of olefins and the Sonogashira coupling of alkynes with aryl halides, but this approach has largely been limited to the use of metals with distinct reactivities, with only one metal catalyst undergoing oxidative addition. Here, we demonstrate that cooperativity between two group 10 metal catalysts—(bipyridine)nickel and (1,3-bis(diphenylphosphino)propane)palladium—enables a general cross-Ullmann reaction (the cross-coupling of two different aryl electrophiles). Our method couples aryl bromides with aryl triflates directly, eliminating the use of arylmetal reagents and avoiding the challenge of differentiating between multiple carbon–hydrogen bonds that is required for direct arylation methods. Selectivity can be achieved without an excess of either substrate and originates from the orthogonal reactivity of the two catalysts and the relative stability of the two arylmetal intermediates. While (1,3-bis(diphenylphosphino)propane)palladium reacts preferentially with aryl triflates to afford a persistent intermediate, (bipyridine)nickel reacts preferentially with aryl bromides to form a transient, reactive intermediate. Although each catalyst forms less than 5 per cent cross-coupled product in isolation, together they are able to achieve a yield of up to 94 per cent. Our results reveal a new method for the synthesis of biaryls, heteroaryls, and dienes, as well as a general mechanism for the selective transfer of ligands between two metal catalysts. We anticipate that this reaction will simplify the synthesis of pharmaceuticals, many of which are currently made with pre-formed organometallic reagents, and lead to the discovery of new multimetallic reactions.

Categories: Journal Articles