Nature

The four hundred years of planetary science since Galileo and Kepler

The four hundred years of planetary science since Galileo and Kepler

Nature 466, 575 (2010). doi:10.1038/nature09215

Authors: Joseph A. Burns

For 350 years after Galileo’s discoveries, ground-based telescopes and theoretical modelling furnished everything we knew about the Sun’s planetary retinue. Over the past five decades, however, spacecraft visits to many targets transformed these early notions, revealing the diversity of Solar System bodies and displaying active planetary processes at work. Violent events have punctuated the histories of many planets and satellites, changing them substantially since their birth. Contemporary knowledge has finally allowed testable models of the Solar System’s origin to be developed and potential abodes for extraterrestrial life to be explored. Future planetary research should involve focused studies of selected targets, including exoplanets.

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Observation of neutral modes in the fractional quantum Hall regime

Observation of neutral modes in the fractional quantum Hall regime

Nature 466, 585 (2010). doi:10.1038/nature09277

Authors: Aveek Bid, N. Ofek, H. Inoue, M. Heiblum, C. L. Kane, V. Umansky & D. Mahalu

The quantum Hall effect takes place in a two-dimensional electron gas under a strong magnetic field and involves current flow along the edges of the sample. For some particle–hole conjugate states of the fractional regime (for example, with fillings between 1/2 and 1 of the

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Global phytoplankton decline over the past century

Global phytoplankton decline over the past century

Nature 466, 591 (2010). doi:10.1038/nature09268

Authors: Daniel G. Boyce, Marlon R. Lewis & Boris Worm

In the oceans, ubiquitous microscopic phototrophs (phytoplankton) account for approximately half the production of organic matter on Earth. Analyses of satellite-derived phytoplankton concentration (available since 1979) have suggested decadal-scale fluctuations linked to climate forcing, but the length of this record is insufficient to resolve longer-term

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Pinning quantum phase transition for a Luttinger liquid of strongly interacting bosons

Pinning quantum phase transition for a Luttinger liquid of strongly interacting bosons

Nature 466, 597 (2010). doi:10.1038/nature09259

Authors: Elmar Haller, Russell Hart, Manfred J. Mark, Johann G. Danzl, Lukas Reichsöllner, Mattias Gustavsson, Marcello Dalmonte, Guido Pupillo & Hanns-Christoph Nägerl

Quantum many-body systems can have phase transitions even at zero temperature; fluctuations arising from Heisenberg’s uncertainty principle, as opposed to thermal effects, drive the system from one phase to another. Typically, during the transition the relative strength of two competing terms in the system’s Hamiltonian changes across a finite critical value. A well-known example is the Mott–Hubbard quantum phase transition from a superfluid to an insulating phase, which has been observed for weakly interacting bosonic atomic gases. However, for strongly interacting quantum systems confined to lower-dimensional geometry, a novel type of quantum phase transition may be induced and driven by an arbitrarily weak perturbation to the Hamiltonian. Here we observe such an effect—the sine–Gordon quantum phase transition from a superfluid Luttinger liquid to a Mott insulator—in a one-dimensional quantum gas of bosonic caesium atoms with tunable interactions. For sufficiently strong interactions, the transition is induced by adding an arbitrarily weak optical lattice commensurate with the atomic granularity, which leads to immediate pinning of the atoms. We map out the phase diagram and find that our measurements in the strongly interacting regime agree well with a quantum field description based on the exactly solvable sine–Gordon model. We trace the phase boundary all the way to the weakly interacting regime, where we find good agreement with the predictions of the one-dimensional Bose–Hubbard model. Our results open up the experimental study of quantum phase transitions, criticality and transport phenomena beyond Hubbard-type models in the context of ultracold gases.

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Direct generation of photon triplets using cascaded photon-pair sources

Direct generation of photon triplets using cascaded photon-pair sources

Nature 466, 601 (2010). doi:10.1038/nature09175

Authors: Hannes Hübel, Deny R. Hamel, Alessandro Fedrizzi, Sven Ramelow, Kevin J. Resch & Thomas Jennewein

Non-classical states of light, such as entangled photon pairs and number states, are essential for fundamental tests of quantum mechanics and optical quantum technologies. The most widespread technique for creating these quantum resources is spontaneous parametric down-conversion of laser light into photon pairs. Conservation of energy and momentum in this process, known as phase-matching, gives rise to strong correlations that are used to produce two-photon entanglement in various degrees of freedom. It has been a longstanding goal in quantum optics to realize a source that can produce analogous correlations in photon triplets, but of the many approaches considered, none has been technically feasible. Here we report the observation of photon triplets generated by cascaded down-conversion. Each triplet originates from a single pump photon, and therefore quantum correlations will extend over all three photons in a way not achievable with independently created photon pairs. Our photon-triplet source will allow experimental interrogation of novel quantum correlations, the generation of tripartite entanglement without post-selection and the generation of heralded entangled photon pairs suitable for linear optical quantum computing. Two of the triplet photons have a wavelength matched for optimal transmission in optical fibres, suitable for three-party quantum communication. Furthermore, our results open interesting regimes of non-linear optics, as we observe spontaneous down-conversion pumped by single photons, an interaction also highly relevant to optical quantum computing.

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Following a chemical reaction using high-harmonic interferometry

Following a chemical reaction using high-harmonic interferometry

Nature 466, 604 (2010). doi:10.1038/nature09185

Authors: H. J. Wörner, J. B. Bertrand, D. V. Kartashov, P. B. Corkum & D. M. Villeneuve

The study of chemical reactions on the molecular (femtosecond) timescale typically uses pump laser pulses to excite molecules and subsequent probe pulses to interrogate them. The ultrashort pump pulse can excite only a small fraction of molecules, and the probe wavelength must be carefully chosen to discriminate between excited and unexcited molecules. The past decade has seen the emergence of new methods that are also aimed at imaging chemical reactions as they occur, based on X-ray diffraction, electron diffraction or laser-induced recollision—with spectral selection not available for any of these new methods. Here we show that in the case of high-harmonic spectroscopy based on recollision, this apparent limitation becomes a major advantage owing to the coherent nature of the attosecond high-harmonic pulse generation. The coherence allows the unexcited molecules to act as local oscillators against which the dynamics are observed, so a transient grating technique can be used to reconstruct the amplitude and phase of emission from the excited molecules. We then extract structural information from the amplitude, which encodes the internuclear separation, by quantum interference at short times and by scattering of the recollision electron at longer times. The phase records the attosecond dynamics of the electrons, giving access to the evolving ionization potentials and the electronic structure of the transient molecule. In our experiment, we are able to document a temporal shift of the high-harmonic field of less than an attosecond (1 as = 10−18 s) between the stretched and compressed geometry of weakly vibrationally excited Br2 in the electronic ground state. The ability to probe structural and electronic features, combined with high time resolution, make high-harmonic spectroscopy ideally suited to measuring coupled electronic and nuclear dynamics occurring in photochemical reactions and to characterizing the electronic structure of transition states.

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Triggering of New Madrid seismicity by late-Pleistocene erosion

Triggering of New Madrid seismicity by late-Pleistocene erosion

Nature 466, 608 (2010). doi:10.1038/nature09258

Authors: E. Calais, A. M. Freed, R. Van Arsdale & S. Stein

The spatiotemporal behaviour of earthquakes within continental plate interiors is different from that at plate boundaries. At plate margins, tectonic motions quickly reload earthquake ruptures, making the location of recent earthquakes and the average time between them consistent with the faults’ geological, palaeoseismic and seismic histories. In contrast, what determines the activation of a particular mid-continental fault and controls the duration of its seismic activity remains poorly understood. Here we argue that the concentration of magnitude-7 or larger earthquakes in the New Madrid seismic zone of the central United States since the end of the last ice age results from the recent, climate-controlled, erosional history of the northern Mississippi embayment. We show that the upward flexure of the lithosphere caused by unloading from river incision between 16,000 and 10,000 years ago caused a reduction of normal stresses in the upper crust sufficient to unclamp pre-existing faults close to failure equilibrium. Models indicate that fault segments that have already ruptured are unlikely to fail again soon, but stress changes from sediment unloading and previous earthquakes may eventually be sufficient to bring to failure other nearby segments that have not yet ruptured.

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Pathogenic LRRK2 negatively regulates microRNA-mediated translational repression

Pathogenic LRRK2 negatively regulates microRNA-mediated translational repression

Nature 466, 637 (2010). doi:10.1038/nature09191

Authors: Stephan Gehrke, Yuzuru Imai, Nicholas Sokol & Bingwei Lu

Gain-of-function mutations in leucine-rich repeat kinase 2 (LRRK2) cause familial as well as sporadic Parkinson’s disease characterized by age-dependent degeneration of dopaminergic neurons. The molecular mechanism of LRRK2 action is not known. Here we show that LRRK2 interacts with the microRNA (miRNA) pathway to regulate protein synthesis. Drosophila e2f1 and dp messenger RNAs are translationally repressed by let-7 and miR-184*, respectively. Pathogenic LRRK2 antagonizes these miRNAs, leading to the overproduction of E2F1/DP, previously implicated in cell cycle and survival control and shown here to be critical for LRRK2 pathogenesis. Genetic deletion of let-7, antagomir-mediated blockage of let-7 and miR-184* action, transgenic expression of dp target protector, or replacement of endogenous dp with a dp transgene non-responsive to let-7 each had toxic effects similar to those of pathogenic LRRK2. Conversely, increasing the level of let-7 or miR-184* attenuated pathogenic LRRK2 effects. LRRK2 associated with Drosophila Argonaute-1 (dAgo1) or human Argonaute-2 (hAgo2) of the RNA-induced silencing complex (RISC). In aged fly brain, dAgo1 protein level was negatively regulated by LRRK2. Further, pathogenic LRRK2 promoted the association of phospho-4E-BP1 with hAgo2. Our results implicate deregulated synthesis of E2F1/DP caused by the miRNA pathway impairment as a key event in LRRK2 pathogenesis and suggest novel miRNA-based therapeutic strategies.

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New class of gene-termini-associated human RNAs suggests a novel RNA copying mechanism

New class of gene-termini-associated human RNAs suggests a novel RNA copying mechanism

Nature 466, 642 (2010). doi:10.1038/nature09190

Authors: Philipp Kapranov, Fatih Ozsolak, Sang Woo Kim, Sylvain Foissac, Doron Lipson, Chris Hart, Steve Roels, Christelle Borel, Stylianos E. Antonarakis, A. Paula Monaghan, Bino John & Patrice M. Milos

Small (<200 nucleotide) RNA (sRNA) profiling of human cells using various technologies demonstrates unexpected complexity of sRNAs with hundreds of thousands of sRNA species present. Genetic and in vitro studies show that these RNAs are not merely degradation products of longer transcripts but could indeed have a function. Furthermore, profiling of RNAs, including the sRNAs, can reveal not only novel transcripts, but also make clear predictions about the existence and properties of novel biochemical pathways operating in a cell. For example, sRNA profiling in human cells indicated the existence of an unknown capping mechanism operating on cleaved RNA, a biochemical component of which was later identified. Here we show that human cells contain a novel type of sRNA that has non-genomically encoded 5′ poly(U) tails. The presence of these RNAs at the termini of genes, specifically at the very 3′ ends of known mRNAs, strongly argues for the presence of a yet uncharacterized endogenous biochemical pathway in cells that can copy RNA. We show that this pathway can operate on multiple genes, with specific enrichment towards transcript-encoding components of the translational machinery. Finally, we show that genes are also flanked by sense, 3′ polyadenylated sRNAs that are likely to be capped.

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Asymptomatic deer excrete infectious prions in faeces

Asymptomatic deer excrete infectious prions in faeces

Nature 466, 652 (2010). doi:10.1038/nature09031

Authors: Gültekin Tamgüney, Michael W. Miller, Lisa L. Wolfe, Tracey M. Sirochman, David V. Glidden, Christina Palmer, Azucena Lemus, Stephen J. DeArmond & Stanley B. Prusiner

Nature461, 529–532 (2009)In this Letter, there was an error in the calculation of infectious doses. The correct sentence should read: Assuming a constant infectious dose of 0 log ID50 units in 3 mg of faeces (equivalent

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NLRP3 inflammasomes are required for atherogenesis and activated by cholesterol crystals

NLRP3 inflammasomes are required for atherogenesis and activated by cholesterol crystals

Nature 466, 652 (2010). doi:10.1038/nature09316

Authors: Peter Duewell, Hajime Kono, Katey J. Rayner, Cherilyn M. Sirois, Gregory Vladimer, Franz G. Bauernfeind, George S. Abela, Luigi Franchi, Gabriel Nuñez, Max Schnurr, Terje Espevik, Egil Lien, Katherine A. Fitzgerald, Kenneth L. Rock, Kathryn J. Moore, Samuel D. Wright, Veit Hornung & Eicke Latz

Nature464, 1357–1361 (2010)In this Letter, the address for author Veit Hornung was listed incorrectly. The correct address is: The Institute of Clinical Chemistry and Pharmacology, University Hospitals, University of Bonn, 53127 Bonn, Germany. Also, Veit Hornung was

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How to feed a hungry world

How to feed a hungry world

Nature 466, 531 (2010). doi:10.1038/466531a

Producing enough food for the world's population in 2050 will be easy. But doing it at an acceptable cost to the planet will depend on research into everything from high-tech seeds to low-tech farming practices.

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Save the census

Save the census

Nature 466, 532 (2010). doi:10.1038/466532a

The Canadian government should rethink its decision to change the way census data are collected.

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Palaeontology: Burrow builders

Palaeontology: Burrow builders

Nature 466, 534 (2010). doi:10.1038/466534a

Geology38, 711–714 (2010) 10.1130/G30829.1Fossil burrows in ocean sediments from the Precambrian–Cambrian period about 540 million years ago are ubiquitous in the fossil record, but the creatures that created these Treptichnus burrows (pictured, left) remained a mystery.

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Physics: Mini mass

Physics: Mini mass

Nature 466, 534 (2010). doi:10.1038/466534b

Phys. Rev. Lett. doi:10.1103/PhysRevLett.105.031301 (2010)The mass of the elusive neutrino is less than 0.28 electronvolts — the lowest upper limit predicted so far — according to Shaun Thomas and his colleagues at University College London.Neutrinos are abundant in

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Geoscience: When sea ice melts

Geoscience: When sea ice melts

Nature 466, 534 (2010). doi:10.1038/466534c

Geophys. Res. Lett. doi:10.1029/2010GL042496 (2010)Rapid loss of floating sea ice is contributing a tiny amount, 50 micrometres, to the current annual global sea-level rise of around 3 millimetres.Andrew Shepherd of the University of Leeds, UK, and his colleagues

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Materials science: Shape shifts heat tolerance

Materials science: Shape shifts heat tolerance

Nature 466, 534 (2010). doi:10.1038/466534d

J. Am. Chem. Soc. doi:10.1021/ja104691j (2010)Poorly soluble drugs and other chemicals can be dissolved in liquid by packaging them inside micelles — soluble molecular assemblies that often assume hollow spherical or floral shapes. Heat can rattle these structures apart,

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Ecology: Shrubs survive warming

Ecology: Shrubs survive warming

Nature 466, 534 (2010). doi:10.1038/466534e

J. Ecol. doi:10.1111/j.1365-2745.2010.01690.x (2010)Unlike most tundra plant species, Arctic evergreen shrubs seem to be resilient to climate change. James Hudson and Greg Henry at the University of British Columbia in Vancouver were surprised to find that increases of 1–1.3

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Neuroscience: Movement decoded

Neuroscience: Movement decoded

Nature 466, 534 (2010). doi:10.1038/466534f

J. Neurosci.30, 9659–9669 (2010) 10.1523/JNEUROSCI.5443-09.2010Brain signals in monkeys have been decoded and used to reconstruct three-dimensional arm movements, raising the possibility of future neuroprosthetic devices that people who are paralysed could use to control robotic arms for

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Remote sensing: Great heights

Remote sensing: Great heights

Nature 466, 535 (2010). doi:10.1038/466535a

Geophys. Res. Lett. doi:10.1029/2010GL043622 (2010)Towering more than 40 metres high, the Douglas firs, coast redwoods and giant sequoias of the North American Pacific coast stand out as some of the world's tallest trees, according to a map charting the

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