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Sommaires des Revues - Sciences

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Rebuilding Caribbean science  Voir?

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News at a glance  Voir?

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Drug-resistant malaria advances in Mekong  Voir?

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Cold, clear view of molecules nets chemistry prize  Voir?

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How Africans evolved a palette of skin tones  Voir?

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Evolution accelerated when life set foot on land  Voir?

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'Science wars veteran has a new mission  Voir?

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Most distant Milky Way outpost mapped  Voir?

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Publishers take academic networking site to court  Voir?

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A cold case  Voir?

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Addressing supply issues for natural products in the clinic  Voir?

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A direct look at halogen bonds  Voir?

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Helping robots blend into the background  Voir?

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Quantum emitters in two dimensions  Voir?

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Life, death, and antibodies  Voir?

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Atlas...t, patterns from every cell  Voir?

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Sir Patrick Bateson (1938-2017)  Voir?

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Reproductive health in culture wars crossfire  Voir?

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Tracking today  Voir?

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A future on fire  Voir?

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Brazil's development turns river into sea  Voir?

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Brazil's scientists and churches share goals  Voir?

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Sand in demand: Trapped behind dams  Voir?

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Measuring the far side of the Galaxy  Voir?

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3D gene expression blueprint of the fly  Voir?

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Mechanical systems at the quantum level  Voir?

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3D texture morphing for camouflage  Voir?

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A signature event for organoids  Voir?

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Forests out of balance  Voir?

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Fevers, TRPV channels, and birth defects  Voir?

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Newborn brain imaging made easier  Voir?

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Light- and dark-zone death dynamics  Voir?

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A radical route from methane to methanol  Voir?

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Visualizing halogen bonding  Voir?

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A gram-scale route to bryostatin  Voir?

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Teaching an enzyme to switch sites  Voir?

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An expanded view of disordered proteins  Voir?

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Type III interferons prime neutrophils  Voir?

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Coffee plants benefit from ant dung  Voir?

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For diabetes screening, race matters  Voir?

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Blood test for early-stage cancer  Voir?

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Not missing the origins of lncRNAs  Voir?

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More undergraduates, more publications  Voir?

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Subtleties of growing iron sulfides  Voir?

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Aqueous azobenzene switching  Voir?

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Measuring Earth's carbon cycle  Voir?

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The Drosophila embryo at single-cell transcriptome resolution  Voir?

By the onset of morphogenesis, Drosophila embryos consist of about 6000 cells that express distinct gene combinations. Here, we used single-cell sequencing of precisely staged embryos and devised DistMap, a computational mapping strategy to reconstruct the embryo and to predict spatial gene expression approaching single-cell resolution. We produced a virtual embryo with about 8000 expressed genes per cell. Our interactive Drosophila Virtual Expression eXplorer (DVEX) database generates three-dimensional virtual in situ hybridizations and computes gene expression gradients. We used DVEX to uncover patterned expression of transcription factors and long noncoding RNAs, as well as signaling pathway components. Spatial regulation of Hippo signaling during early embryogenesis suggests a mechanism for establishing asynchronous cell proliferation. Our approach is suitable to generate transcriptomic blueprints for other complex tissues.

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Quantum acoustics with superconducting qubits  Voir?

Mechanical objects have important practical applications in the fields of quantum information and metrology as quantum memories or transducers for measuring and connecting different types of quantum systems. The field of electromechanics is in pursuit of a robust and highly coherent device that couples motion to nonlinear quantum objects such as superconducting qubits. Here, we experimentally demonstrate a high-frequency bulk acoustic wave resonator that is strongly coupled to a superconducting qubit using piezoelectric transduction with a cooperativity of 260. We measure qubit and mechanical coherence times on the order of 10 microseconds. Our device requires only simple fabrication methods and provides controllable access to a multitude of phonon modes. We demonstrate quantum control and measurement on gigahertz phonons at the single-quantum level.

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Hanbury Brown and Twiss interferometry of single phonons from an optomechanical resonator  Voir?

Nano- and micromechanical solid-state quantum devices have become a focus of attention. Reliably generating nonclassical states of their motion is of interest both for addressing fundamental questions about macroscopic quantum phenomena and for developing quantum technologies in the domains of sensing and transduction. We used quantum optical control techniques to conditionally generate single-phonon Fock states of a nanomechanical resonator. We performed a Hanbury Brown and Twiss–type experiment that verified the nonclassical nature of the phonon state without requiring full state reconstruction. Our result establishes purely optical quantum control of a mechanical oscillator at the single-phonon level.

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Imaging the halogen bond in self-assembled halogenbenzenes on silver  Voir?

Halogens are among the most electronegative elements, and the variations in size and polarizability of halogens require different descriptions of the intermolecular bonds they form. Here we use the inelastic tunneling probe (itProbe) to acquire real-space imaging of intermolecular-bonding structures in the two-dimensional self-assembly of halogenbenzene molecules on a metal surface. Direct visualization is obtained for the intermolecular attraction and the "windmill" pattern of bonding among the fully halogenated molecules. Our results provide a hitherto missing understanding of the nature of the halogen bond.

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Stretchable surfaces with programmable 3D texture morphing for synthetic camouflaging skins  Voir?

Technologies that use stretchable materials are increasingly important, yet we are unable to control how they stretch with much more sophistication than inflating balloons. Nature, however, demonstrates remarkable control of stretchable surfaces; for example, cephalopods can project hierarchical structures from their skin in milliseconds for a wide range of textural camouflage. Inspired by cephalopod muscular morphology, we developed synthetic tissue groupings that allowed programmable transformation of two-dimensional (2D) stretchable surfaces into target 3D shapes. The synthetic tissue groupings consisted of elastomeric membranes embedded with inextensible textile mesh that inflated to within 10% of their target shapes by using a simple fabrication method and modeling approach. These stretchable surfaces transform from flat sheets to 3D textures that imitate natural stone and plant shapes and camouflage into their background environments.

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Anti-Markovnikov alkene oxidation by metal-oxo-mediated enzyme catalysis  Voir?

Catalytic anti-Markovnikov oxidation of alkene feedstocks could simplify synthetic routes to many important molecules and solve a long-standing challenge in chemistry. Here we report the engineering of a cytochrome P450 enzyme by directed evolution to catalyze metal-oxo–mediated anti-Markovnikov oxidation of styrenes with high efficiency. The enzyme uses dioxygen as the terminal oxidant and achieves selectivity for anti-Markovnikov oxidation over the kinetically favored alkene epoxidation by trapping high-energy intermediates and catalyzing an oxo transfer, including an enantioselective 1,2-hydride migration. The anti-Markovnikov oxygenase can be combined with other catalysts in synthetic metabolic pathways to access a variety of challenging anti-Markovnikov functionalization reactions.

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Scalable synthesis of bryostatin 1 and analogs, adjuvant leads against latent HIV  Voir?

Bryostatin 1 is an exceedingly scarce marine-derived natural product that is in clinical development directed at HIV/AIDS eradication, cancer immunotherapy, and the treatment of Alzheimer’s disease. Despite this unique portfolio of indications, its availability has been limited and variable, thus impeding research and clinical studies. Here, we report a total synthesis of bryostatin 1 that proceeds in 29 total steps (19 in the longest linear sequence, >80% average yield per step), collectively produces grams of material, and can be scaled to meet clinical needs (~20 grams per year). This practical solution to the bryostatin supply problem also opens broad, facile, and efficient access to derivatives and potentially superior analogs.

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Aqueous Au-Pd colloids catalyze selective CH4 oxidation to CH3OH with O2 under mild conditions  Voir?

The selective oxidation of methane, the primary component of natural gas, remains an important challenge in catalysis. We used colloidal gold-palladium nanoparticles, rather than the same nanoparticles supported on titanium oxide, to oxidize methane to methanol with high selectivity (92%) in aqueous solution at mild temperatures. Then, using isotopically labeled oxygen (O2) as an oxidant in the presence of hydrogen peroxide (H2O2), we demonstrated that the resulting methanol incorporated a substantial fraction (70%) of gas-phase O2. More oxygenated products were formed than the amount of H2O2 consumed, suggesting that the controlled breakdown of H2O2 activates methane, which subsequently incorporates molecular oxygen through a radical process. If a source of methyl radicals can be established, then the selective oxidation of methane to methanol using molecular oxygen is possible.

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Mapping spiral structure on the far side of the Milky Way  Voir?

Little is known about the portion of the Milky Way lying beyond the Galactic center at distances of more than 9 kiloparsec from the Sun. These regions are opaque at optical wavelengths because of absorption by interstellar dust, and distances are very large and hard to measure. We report a direct trigonometric parallax distance of 20.4–2.2+2.8 kiloparsec obtained with the Very Long Baseline Array to a water maser source in a region of active star formation. These measurements allow us to shed light on Galactic spiral structure by locating the Scutum-Centaurus spiral arm as it passes through the far side of the Milky Way and to validate a kinematic method for determining distances in this region on the basis of transverse motions.

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Tropical forests are a net carbon source based on aboveground measurements of gain and loss  Voir?

The carbon balance of tropical ecosystems remains uncertain, with top-down atmospheric studies suggesting an overall sink and bottom-up ecological approaches indicating a modest net source. Here we use 12 years (2003 to 2014) of MODIS pantropical satellite data to quantify net annual changes in the aboveground carbon density of tropical woody live vegetation, providing direct, measurement-based evidence that the world’s tropical forests are a net carbon source of 425.2 ± 92.0 teragrams of carbon per year (Tg C year–1). This net release of carbon consists of losses of 861.7 ± 80.2 Tg C year–1 and gains of 436.5 ± 31.0 Tg C year–1. Gains result from forest growth; losses result from deforestation and from reductions in carbon density within standing forests (degradation or disturbance), with the latter accounting for 68.9% of overall losses.

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Use of CRISPR-modified human stem cell organoids to study the origin of mutational signatures in cancer  Voir?

Mutational processes underlie cancer initiation and progression. Signatures of these processes in cancer genomes may explain cancer etiology and could hold diagnostic and prognostic value. We developed a strategy that can be used to explore the origin of cancer-associated mutational signatures. We used CRISPR-Cas9 technology to delete key DNA repair genes in human colon organoids, followed by delayed subcloning and whole-genome sequencing. We found that mutation accumulation in organoids deficient in the mismatch repair gene MLH1 is driven by replication errors and accurately models the mutation profiles observed in mismatch repair–deficient colorectal cancers. Application of this strategy to the cancer predisposition gene NTHL1, which encodes a base excision repair protein, revealed a mutational footprint (signature 30) previously observed in a breast cancer cohort. We show that signature 30 can arise from germline NTHL1 mutations.

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Innovative scattering analysis shows that hydrophobic disordered proteins are expanded in water  Voir?

A substantial fraction of the proteome is intrinsically disordered, and even well-folded proteins adopt non-native geometries during synthesis, folding, transport, and turnover. Characterization of intrinsically disordered proteins (IDPs) is challenging, in part because of a lack of accurate physical models and the difficulty of interpreting experimental results. We have developed a general method to extract the dimensions and solvent quality (self-interactions) of IDPs from a single small-angle x-ray scattering measurement. We applied this procedure to a variety of IDPs and found that even IDPs with low net charge and high hydrophobicity remain highly expanded in water, contrary to the general expectation that protein-like sequences collapse in water. Our results suggest that the unfolded state of most foldable sequences is expanded; we conjecture that this property was selected by evolution to minimize misfolding and aggregation.

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New Products  Voir?

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Sponsored Collection | Accelerating the path from structure to function through integrated structural biology solutions  Voir?

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AAAS 2018 Annual Meeting Program  Voir?

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I am a United Academic Worker  Voir?

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Cover stories: Making the Orbiting Carbon Observatory-2 cover  Voir?

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The microanatomic segregation of selection by apoptosis in the germinal center  Voir?

B cells undergo rapid cell division and affinity maturation in anatomically distinct sites in lymphoid organs called germinal centers (GCs). Homeostasis is maintained in part by B cell apoptosis. However, the precise contribution of apoptosis to GC biology and selection is not well defined. We developed apoptosis-indicator mice and used them to visualize, purify, and characterize dying GC B cells. Apoptosis is prevalent in the GC, with up to half of all GC B cells dying every 6 hours. Moreover, programmed cell death is differentially regulated in the light zone and the dark zone: Light-zone B cells die by default if they are not positively selected, whereas dark-zone cells die when their antigen receptors are damaged by activation-induced cytidine deaminase.

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Contrasting carbon cycle responses of the tropical continents to the 2015-2016 El Nino  Voir?

The 2015–2016 El Niño led to historically high temperatures and low precipitation over the tropics, while the growth rate of atmospheric carbon dioxide (CO2) was the largest on record. Here we quantify the response of tropical net biosphere exchange, gross primary production, biomass burning, and respiration to these climate anomalies by assimilating column CO2, solar-induced chlorophyll fluorescence, and carbon monoxide observations from multiple satellites. Relative to the 2011 La Niña, the pantropical biosphere released 2.5 ± 0.34 gigatons more carbon into the atmosphere in 2015, consisting of approximately even contributions from three tropical continents but dominated by diverse carbon exchange processes. The heterogeneity of the carbon-exchange processes indicated here challenges previous studies that suggested that a single dominant process determines carbon cycle interannual variability.

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The Orbiting Carbon Observatory-2 early science investigations of regional carbon dioxide fluxes  Voir?

NASA’s Orbiting Carbon Observatory-2 (OCO-2) mission was motivated by the need to diagnose how the increasing concentration of atmospheric carbon dioxide (CO2) is altering the productivity of the biosphere and the uptake of CO2 by the oceans. Launched on 2 July 2014, OCO-2 provides retrievals of the column-averaged CO2 dry-air mole fraction (XCO2) as well as the fluorescence from chlorophyll in terrestrial plants. The seasonal pattern of uptake by the terrestrial biosphere is recorded in fluorescence and the drawdown of XCO2 during summer. Launched just before one of the most intense El Niños of the past century, OCO-2 measurements of XCO2 and fluorescence record the impact of the large change in ocean temperature and rainfall on uptake and release of CO2 by the oceans and biosphere.

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OCO-2 advances photosynthesis observation from space via solar-induced chlorophyll fluorescence  Voir?

Quantifying gross primary production (GPP) remains a major challenge in global carbon cycle research. Spaceborne monitoring of solar-induced chlorophyll fluorescence (SIF), an integrative photosynthetic signal of molecular origin, can assist in terrestrial GPP monitoring. However, the extent to which SIF tracks spatiotemporal variations in GPP remains unresolved. Orbiting Carbon Observatory-2 (OCO-2)’s SIF data acquisition and fine spatial resolution permit direct validation against ground and airborne observations. Empirical orthogonal function analysis shows consistent spatiotemporal correspondence between OCO-2 SIF and GPP globally. A linear SIF-GPP relationship is also obtained at eddy-flux sites covering diverse biomes, setting the stage for future investigations of the robustness of such a relationship across more biomes. Our findings support the central importance of high-quality satellite SIF for studying terrestrial carbon cycle dynamics.

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Influence of El Nino on atmospheric CO2 over the tropical Pacific Ocean: Findings from NASAs OCO-2 mission  Voir?

Spaceborne observations of carbon dioxide (CO2) from the Orbiting Carbon Observatory-2 are used to characterize the response of tropical atmospheric CO2 concentrations to the strong El Niño event of 2015–2016. Although correlations between the growth rate of atmospheric CO2 concentrations and the El Niño–Southern Oscillation are well known, the magnitude of the correlation and the timing of the responses of oceanic and terrestrial carbon cycle remain poorly constrained in space and time. We used space-based CO2 observations to confirm that the tropical Pacific Ocean does play an early and important role in modulating the changes in atmospheric CO2 concentrations during El Niño events—a phenomenon inferred but not previously observed because of insufficient high-density, broad-scale CO2 observations over the tropics.

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Spaceborne detection of localized carbon dioxide sources  Voir?

Spaceborne measurements by NASA’s Orbiting Carbon Observatory-2 (OCO-2) at the kilometer scale reveal distinct structures of atmospheric carbon dioxide (CO2) caused by known anthropogenic and natural point sources. OCO-2 transects across the Los Angeles megacity (USA) show that anthropogenic CO2 enhancements peak over the urban core and decrease through suburban areas to rural background values more than ~100 kilometers away, varying seasonally from ~4.4 to 6.1 parts per million. A transect passing directly downwind of the persistent isolated natural CO2 plume from Yasur volcano (Vanuatu) shows a narrow filament of enhanced CO2 values (~3.4 parts per million), consistent with a CO2 point source emitting 41.6 kilotons per day. These examples highlight the potential of the OCO-2 sensor, with its unprecedented resolution and sensitivity, to detect localized natural and anthropogenic CO2 sources.

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Comment on "Selective anaerobic oxidation of methane enables direct synthesis of methanol"  Voir?

Sushkevich et al. (Reports, 5 May 2017, p. 523) report on the use of water to oxidize methane to methanol. This seems problematic because the reaction of CH4 and water to generate methanol and H2 is highly unfavorable at any temperature (G of reaction +28 kcal/mol at 200°C, equilibrium constant K 10–13). Consequently, even if the reaction is separated into two steps, it seems inconceivable to carry out such a net reaction in a practical manner.

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Response to Comment on "Selective anaerobic oxidation of methane enables direct synthesis of methanol"  Voir?

Periana argues that the stepwise reaction of methane with water is thermodynamically unfavorable and therefore impractical. We reply by presenting an in-depth thermodynamic analysis of each step in the process and show that the surface concentrations of the reactants and products as well as the stabilizing effect of additional water molecules, as discussed in the original paper, fully support the feasibility of the proposed reaction.

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Dernière mise à jour : 16/10/2017 : 14:48


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