Under an uncaring sky

Nature 524, 7566 (2015). doi:10.1038/524510a

Author: William Meikle

Ill met by starlight.

Questioning evidence of group selection in spiders

Nature 524, 7566 (2015). doi:10.1038/nature14595

Authors: Lena Grinsted, Trine Bilde & James D. J. Gilbert

arising from J. N. Pruitt & C. J. Goodnight Nature514, 359–362 (2014); doi:10.1038/nature13811Any field study showing convincing evidence of group selection would be a significant contribution to the field of evolutionary biology. Pruitt and Goodnight

Group selection versus group adaptation

Nature 524, 7566 (2015). doi:10.1038/nature14596

Author: Andy Gardner

arising from J. N. Pruitt & C. J. Goodnight Nature514, 359–362 (2014); doi:10.1038/nature13811Pruitt and Goodnight describe how the ratio of aggressive versus docile females varies among naturally occurring colonies of the social spider Anelosimus

Pruitt & Goodnight reply

Nature 524, 7566 (2015). doi:10.1038/nature14597

Authors: Jonathan N. Pruitt & Charles J. Goodnight

replying to L. Grinsted, T. Bilde & J. D. J. Gilbert Nature524, http://dx.doi.org/10.1038/nature14595 (2015); A. Gardner Nature524, http://dx.doi.org/10.1038/nature14596 (2015)In Pruitt and Goodnight we provided experimental evidence that group selection has contributed

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

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

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

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.

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.

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.

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.

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.

by Tim Genewein, Eduard Hez, Zeynab Razzaghpanah, Daniel A. Braun

Previous studies have shown that sensorimotor processing can often be described by Bayesian learning, in particular the integration of prior and feedback information depending on its degree of reliability. Here we test the hypothesis that the integration process itself can be tuned to the statistical structure of the environment. We exposed human participants to a reaching task in a three-dimensional virtual reality environment where we could displace the visual feedback of their hand position in a two dimensional plane. When introducing statistical structure between the two dimensions of the displacement, we found that over the course of several days participants adapted their feedback integration process in order to exploit this structure for performance improvement. In control experiments we found that this adaptation process critically depended on performance feedback and could not be induced by verbal instructions. Our results suggest that structural learning is an important meta-learning component of Bayesian sensorimotor integration.

Journal of the American Chemical SocietyDOI: 10.1021/jacs.5b04366

Abstract

1,4-Dihydropyridines (DHPs) have been developed to treat hypertension, angina, and nerve system disease. They are thought to mainly target the L-type calcium channels, but low selectivity prompts them to block Cav1.2 and Cav3.1 channels simultaneously. Recently, some novel DHPs with different hydrophobic groups have been synthesized and among them M12 has a higher selectivity for Cav3.1. However, the structural information about Cav3.1-DHPs complexes is not available in the experiment. Thus, we combined homology modeling, molecular docking, molecular dynamics simulations, and binding free energy calculations to quantitatively elucidate the inhibition mechanism of DHPs. The calculated results indicate that our model is in excellent agreement with experimental results. On the basis of conformational analysis, we identify the main interactions between DHPs and calcium channels and further elaborate on the different selectivity of ligands from the micro perspective. In conjunction with energy distribution, we propose that the binding sites of Cav3.1-DHPs is characterized by several interspersed hydrophobic amino acid residues on the IIIS6 and IVS6 segments. We also speculate the favorable function groups on prospective DHPs. Besides, our model provides important information for further mutagenesis experiments.

Abstract

Cytoplasmic domains of transmembrane bacterial chemoreceptors are largely extended four-helix coiled coils. Previous observations suggested the domain was structurally dynamic. We probed directly backbone dynamics of this domain of the transmembrane chemoreceptor Tar from Escherichia coli using site-directed spin labeling and electron paramagnetic resonance (EPR) spectroscopy. Spin labels were positioned on solvent-exposed helical faces because EPR spectra for such positions reflect primarily polypeptide backbone movements. We acquired spectra for spin-labeled, intact receptor homodimers solubilized in detergent or inserted into native E. coli lipid bilayers in Nanodiscs, characterizing 16 positions distributed throughout the cytoplasmic domain and on both helices of its helical hairpins, one amino terminal to the membrane-distal tight turn (N-helix), and the other carboxyl terminal (C-helix). Detergent solubilization increased backbone dynamics for much of the domain, suggesting that loss of receptor activities upon solubilization reflects wide-spread destabilization. For receptors in either condition, we observed an unanticipated difference between the N- and C-helices. For bilayer-inserted receptors, EPR spectra from sites in the membrane-distal protein-interaction region and throughout the C-helix were typical of well-structured helices. In contrast, for approximately two-thirds of the N-helix, from its origin as the AS-2 helix of the membrane-proximal HAMP domain to the beginning of the membrane-distal protein-interaction region, spectra had a significantly mobile component, estimated by spectral deconvolution to average approximately 15%. Differential helical dynamics suggests a four-helix bundle organization with a pair of core scaffold helices and two more dynamic partner helices. This newly observed feature of chemoreceptor structure could be involved in receptor function.

Heroism in Syria

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

A tribute to scholars of extraordinary courage.

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.

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.

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?