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Sommaires des Revues - Sciences

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How to govern geoengineering?  Voir?

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News at a glance  Voir?

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NIH redefines clinical trials, attracting critics  Voir?

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Gender discrimination lawsuit at Salk ignites controversy  Voir?

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The first Australians arrived early  Voir?

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Unlocking a key to maize's amazing success  Voir?

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Zika rewrites maternal immunization ethics  Voir?

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Saving Europe's salamanders  Voir?

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Sulfur injections for a cooler planet  Voir?

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A cirrus cloud climate dial?  Voir?

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Sliding chains keep particles together  Voir?

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Tuna fin hydraulics inspire aquatic robotics  Voir?

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A twist on the Majorana fermion  Voir?

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Can immunotherapy treat neurodegeneration?  Voir?

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Promote scientific integrity via journal peer review data  Voir?

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Acknowledging Africa  Voir?

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About face  Voir?

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Flawed environmental justice analyses  Voir?

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Mexico's basic science funding falls short  Voir?

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Fringe on the brink: Intertidal reefs at risk  Voir?

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Ecosystem protection payments pay off  Voir?

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Volcanoes find a new carbon platform  Voir?

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Pulling on bonds counterintuitively  Voir?

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Hydraulic fins  Voir?

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Getting loaded--make mine a double!  Voir?

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Reaching out as a way to grow  Voir?

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Greater gait with gravity  Voir?

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A stretchy binder protects the silicon  Voir?

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Cancer epigenetics in the driver's seat  Voir?

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Untangling aggregates one step at a time  Voir?

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Lighting the way to carbon borylation  Voir?

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A propagating Majorana mode  Voir?

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Making a large-gap topological insulator  Voir?

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Hitting the highs in solid state  Voir?

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Finding a more flexible mechanical sensor  Voir?

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Geoengineering for temperature control  Voir?

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The amyloid connection in Parkinson's  Voir?

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Wasp venom evolution  Voir?

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Making a quantum-classical hybrid  Voir?

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Get ready, get set, get wet  Voir?

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A setback for immune checkpoint therapy?  Voir?

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Evolutionarily, the beat goes on  Voir?

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Babies favor facelike stimuli before birth  Voir?

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A rhodium catalyst hogs the spotlight  Voir?

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Cash for carbon: A randomized trial of payments for ecosystem services to reduce deforestation  Voir?

We evaluated a program of payments for ecosystem services in Uganda that offered forest-owning households annual payments of 70,000 Ugandan shillings per hectare if they conserved their forest. The program was implemented as a randomized controlled trial in 121 villages, 60 of which received the program for 2 years. The primary outcome was the change in land area covered by trees, measured by classifying high-resolution satellite imagery. We found that tree cover declined by 4.2% during the study period in treatment villages, compared to 9.1% in control villages. We found no evidence that enrollees shifted their deforestation to nearby land. We valued the delayed carbon dioxide emissions and found that this program benefit is 2.4 times as large as the program costs.

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Ratchet-like polypeptide translocation mechanism of the AAA+ disaggregase Hsp104  Voir?

Hsp100 polypeptide translocases are conserved members of the AAA+ family (adenosine triphosphatases associated with diverse cellular activities) that maintain proteostasis by unfolding aberrant and toxic proteins for refolding or proteolytic degradation. The Hsp104 disaggregase from Saccharomyces cerevisiae solubilizes stress-induced amorphous aggregates and amyloids. The structural basis for substrate recognition and translocation is unknown. Using a model substrate (casein), we report cryo–electron microscopy structures at near-atomic resolution of Hsp104 in different translocation states. Substrate interactions are mediated by conserved, pore-loop tyrosines that contact an 80-angstrom-long unfolded polypeptide along the axial channel. Two protomers undergo a ratchet-like conformational change that advances pore loop–substrate interactions by two amino acids. These changes are coupled to activation of specific nucleotide hydrolysis sites and, when transmitted around the hexamer, reveal a processive rotary translocation mechanism and substrate-responsive flexibility during Hsp104-catalyzed disaggregation.

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Highly elastic binders integrating polyrotaxanes for silicon microparticle anodes in lithium ion batteries  Voir?

Lithium-ion batteries with ever-increasing energy densities are needed for batteries for advanced devices and all-electric vehicles. Silicon has been highlighted as a promising anode material because of its superior specific capacity. During repeated charge-discharge cycles, silicon undergoes huge volume changes. This limits cycle life via particle pulverization and an unstable electrode-electrolyte interface, especially when the particle sizes are in the micrometer range. We show that the incorporation of 5 weight % polyrotaxane to conventional polyacrylic acid binder imparts extraordinary elasticity to the polymer network originating from the ring sliding motion of polyrotaxane. This binder combination keeps even pulverized silicon particles coalesced without disintegration, enabling stable cycle life for silicon microparticle anodes at commercial-level areal capacities.

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Photoinduced decarboxylative borylation of carboxylic acids  Voir?

The conversion of widely available carboxylic acids into versatile boronic esters would be highly enabling for synthesis. We found that this transformation can be effected by illuminating the N-hydroxyphthalimide ester derivative of the carboxylic acid under visible light at room temperature in the presence of the diboron reagent bis(catecholato)diboron. A simple workup allows isolation of the pinacol boronic ester. Experimental evidence suggests that boryl radical intermediates are involved in the process. The methodology is illustrated by the transformation of primary, secondary, and tertiary alkyl carboxylic acids as well as a diverse range of natural-product carboxylic acids, thereby demonstrating its broad utility and functional group tolerance.

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Bismuthene on a SiC substrate: A candidate for a high-temperature quantum spin Hall material  Voir?

Quantum spin Hall materials hold the promise of revolutionary devices with dissipationless spin currents but have required cryogenic temperatures owing to small energy gaps. Here we show theoretically that a room-temperature regime with a large energy gap may be achievable within a paradigm that exploits the atomic spin-orbit coupling. The concept is based on a substrate-supported monolayer of a high–atomic number element and is experimentally realized as a bismuth honeycomb lattice on top of the insulating silicon carbide substrate SiC(0001). Using scanning tunneling spectroscopy, we detect a gap of ~0.8 electron volt and conductive edge states consistent with theory. Our combined theoretical and experimental results demonstrate a concept for a quantum spin Hall wide-gap scenario, where the chemical potential resides in the global system gap, ensuring robust edge conductance.

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Remobilization of crustal carbon may dominate volcanic arc emissions  Voir?

The flux of carbon into and out of Earth’s surface environment has implications for Earth’s climate and habitability. We compiled a global data set for carbon and helium isotopes from volcanic arcs and demonstrated that the carbon isotope composition of mean global volcanic gas is considerably heavier, at –3.8 to –4.6 per mil (), than the canonical mid-ocean ridge basalt value of –6.0. The largest volcanic emitters outgas carbon with higher 13C and are located in mature continental arcs that have accreted carbonate platforms, indicating that reworking of crustal limestone is an important source of volcanic carbon. The fractional burial of organic carbon is lower than traditionally determined from a global carbon isotope mass balance and may have varied over geological time, modulated by supercontinent formation and breakup.

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Chiral Majorana fermion modes in a quantum anomalous Hall insulator-superconductor structure  Voir?

Majorana fermion is a hypothetical particle that is its own antiparticle. We report transport measurements that suggest the existence of one-dimensional chiral Majorana fermion modes in the hybrid system of a quantum anomalous Hall insulator thin film coupled with a superconductor. As the external magnetic field is swept, half-integer quantized conductance plateaus are observed at the locations of magnetization reversals, giving a distinct signature of the Majorana fermion modes. This transport signature is reproducible over many magnetic field sweeps and appears at different temperatures. This finding may open up an avenue to control Majorana fermions for implementing robust topological quantum computing.

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Experimentally realized mechanochemistry distinct from force-accelerated scission of loaded bonds  Voir?

Stretching polymer chains accelerates dissociation of a variety of internal covalent bonds, to an extent that correlates well with the force experienced by the scissile bond. Recent theory has also predicted scenarios in which applied force accelerates dissociation of unloaded bonds and kinetically strengthens strained bonds. We report here unambiguous experimental validation of this hypothesis: Detailed kinetic measurements demonstrate that stretching phosphotriesters accelerates dissociation of the unloaded phosphorus-oxygen bond orthogonal to the pulling axis, whereas stretching organosiloxanes inhibits dissociation of the aligned loaded silicon-oxygen bonds. Qualitatively, the outcome is determined by phosphoester elongation and siloxane contraction along the pulling axis in the respective rate-determining transition states. Quantitatively, the results agree with a simple mechanochemical kinetics model.

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Tailored semiconductors for high-harmonic optoelectronics  Voir?

The advent of high-harmonic generation in gases 30 years ago set the foundation for attosecond science and facilitated ultrafast spectroscopy in atoms, molecules, and solids. We explore high-harmonic generation in the solid state by means of nanostructured and ion-implanted semiconductors. We use wavelength-selective microscopic imaging to map enhanced harmonic emission and show that the generation medium and the driving field can be locally tailored in solids by modifying the chemical composition and morphology. This enables the control of high-harmonic technology within precisely engineered solid targets. We demonstrate customized high-harmonic wave fields with wavelengths down to 225 nanometers (ninth-harmonic order of 2-micrometer laser pulses) and present an integrated Fresnel zone plate target in silicon, which leads to diffraction-limited self-focusing of the generated harmonics down to 1-micrometer spot sizes.

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An organic-inorganic perovskite ferroelectric with large piezoelectric response  Voir?

Molecular piezoelectrics are highly desirable for their easy and environment-friendly processing, light weight, low processing temperature, and mechanical flexibility. However, although 136 years have passed since the discovery in 1880 of the piezoelectric effect, molecular piezoelectrics with a piezoelectric coefficient d33 comparable with piezoceramics such as barium titanate (BTO; ~190 picocoulombs per newton) have not been found. We show that trimethylchloromethyl ammonium trichloromanganese(II), an organic-inorganic perovskite ferroelectric crystal processed from aqueous solution, has a large d33 of 185 picocoulombs per newton and a high phase-transition temperature of 406 kelvin (K) (16 K above that of BTO). This makes it a competitive candidate for medical, micromechanical, and biomechanical applications.

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Hydraulic control of tuna fins: A role for the lymphatic system in vertebrate locomotion  Voir?

The lymphatic system in teleost fish has genetic and developmental origins similar to those of the mammalian lymphatic system, which is involved in immune response and fluid homeostasis. Here, we show that the lymphatic system of tunas functions in swimming hydrodynamics. Specifically, a musculo-vascular complex, consisting of fin muscles, bones, and lymphatic vessels, is involved in the hydraulic control of median fins. This specialization of the lymphatic system is associated with fish in the family Scombridae and may have evolved in response to the demand for swimming and maneuvering control in these high-performance species.

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Bidirectional eukaryotic DNA replication is established by quasi-symmetrical helicase loading  Voir?

Bidirectional replication from eukaryotic DNA replication origins requires the loading of two ring-shaped minichromosome maintenance (MCM) helicases around DNA in opposite orientations. MCM loading is orchestrated by binding of the origin recognition complex (ORC) to DNA, but how ORC coordinates symmetrical MCM loading is unclear. We used natural budding yeast DNA replication origins and synthetic DNA sequences to show that efficient MCM loading requires binding of two ORC molecules to two ORC binding sites. The relative orientation of these sites, but not the distance between them, was found to be critical for MCM loading in vitro and origin function in vivo. We propose that quasi-symmetrical loading of individual MCM hexamers by ORC and directed MCM translocation into double hexamers acts as a unifying mechanism for the establishment of bidirectional replication in archaea and eukaryotes.

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New Products  Voir?

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The call of the wild  Voir?

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Epigenetic plasticity and the hallmarks of cancer  Voir?

Chromatin and associated epigenetic mechanisms stabilize gene expression and cellular states while also facilitating appropriate responses to developmental or environmental cues. Genetic, environmental, or metabolic insults can induce overly restrictive or overly permissive epigenetic landscapes that contribute to pathogenesis of cancer and other diseases. Restrictive chromatin states may prevent appropriate induction of tumor suppressor programs or block differentiation. By contrast, permissive or "plastic" states may allow stochastic oncogene activation or nonphysiologic cell fate transitions. Whereas many stochastic events will be inconsequential "passengers," some will confer a fitness advantage to a cell and be selected as "drivers." We review the broad roles played by epigenetic aberrations in tumor initiation and evolution and their potential to give rise to all classic hallmarks of cancer.

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Comment on "The [4Fe4S] cluster of human DNA primase functions as a redox switch using DNA charge transport"  Voir?

O’Brien et al. (Research Article, 24 February 2017, eaag1789) proposed a novel mechanism of primase function based on redox activity of the iron-sulfur cluster buried inside the C-terminal domain of the large primase subunit (p58C). Serious problems in the experimental design and data interpretation raise concerns about the validity of the conclusions.

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Response to Comments on "The [4Fe4S] cluster of human DNA primase functions as a redox switch using DNA charge transport"  Voir?

Baranovskiy et al. and Pellegrini argue that, based on structural data, the path for charge transfer through the [4Fe4S] domain of primase is not feasible. Our manuscript presents electrochemical data directly showing charge transport through DNA to the [4Fe4S] cluster of a primase p58C construct and a reversible switch in the DNA-bound signal with oxidation/reduction, which is inhibited by mutation of three tyrosine residues. Although the dispositions of tyrosines differ in different constructs, all are within range for microsecond electron transfer.

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Comment on "The [4Fe4S] cluster of human DNA primase functions as a redox switch using DNA charge transport"  Voir?

O’Brien et al. (Research Article, 24 February 2017, eaag1789) report that the iron-sulfur cluster of primase has a redox role in enzyme activity. Their analysis is based on a partially misfolded structure of the iron-sulfur cluster domain of primase. In the correctly folded structure, two of the three tyrosines putatively involved in electron transfer, Y345 and Y347, contact the RNA/DNA helix, providing an alternative explanation for the data of O’Brien et al.

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Dernière mise à jour : 27/07/2017 : 08:56


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