A precise measurement of the magnetic field in the corona of the black hole binary V404 Cygni

<p>Observations of binary stars containing an accreting black hole or neutron star often show x-ray emission extending to high energies (&gt;10 kilo&shy;&ndash;electron volts), which is ascribed to an accretion disk corona of energetic particles akin to those seen in the solar corona. Despite their ubiquity, the physical conditions in accretion disk coronae remain poorly constrained. Using simultaneous infrared, optical, x-ray, and radio observations of the Galactic black hole system V404 Cygni, showing a rapid synchrotron cooling event in its 2015 outburst, we present a precise 461 &plusmn; 12 gauss magnetic field measurement in the corona. This measurement is substantially lower than previous estimates for such systems, providing constraints on physical models of accretion physics in black hole and neutron star binary systems.</p>

Imaging resonant dissipation from individual atomic defects in graphene

<p>Conversion of electric current into heat involves microscopic processes that operate on nanometer length scales and release minute amounts of power. Although central to our understanding of the electrical properties of materials, individual mediators of energy dissipation have so far eluded direct observation. Using scanning nanothermometry with submicrokelvin sensitivity, we visualized and controlled phonon emission from individual atomic-scale defects in graphene. The inferred electron-phonon "cooling power spectrum" exhibits sharp peaks when the Fermi level comes into resonance with electronic quasi-bound states at such defects. Rare in the bulk but abundant at graphene&rsquo;s edges, switchable atomic-scale phonon emitters provide the dominant dissipation mechanism. Our work offers insights for addressing key materials challenges in modern electronics and enables control of dissipation at the nanoscale.</p>

Renewable acrylonitrile production

<p>Acrylonitrile (ACN) is a petroleum-derived compound used in resins, polymers, acrylics, and carbon fiber. We present a process for renewable ACN production using 3-hydroxypropionic acid (3-HP), which can be produced microbially from sugars. The process achieves ACN molar yields exceeding 90% from ethyl 3-hydroxypropanoate (ethyl 3-HP) via dehydration and nitrilation with ammonia over an inexpensive titanium dioxide solid acid catalyst. We further describe an integrated process modeled at scale that is based on this chemistry and achieves near-quantitative ACN yields (98 &plusmn; 2%) from ethyl acrylate. This endothermic approach eliminates runaway reaction hazards and achieves higher yields than the standard propylene ammoxidation process. Avoidance of hydrogen cyanide as a by-product also improves process safety and mitigates product handling requirements.</p>

Quantized chiral edge conduction on domain walls of a magnetic topological insulator

<p>Electronic ordering in magnetic and dielectric materials forms domains with different signs of order parameters. The control of configuration and motion of the domain walls (DWs) enables nonvolatile responses against minute external fields. Here, we realize chiral edge states (CESs) on the magnetic DWs of a magnetic topological insulator. We design and fabricate the magnetic domains in the quantum anomalous Hall state with the tip of a magnetic force microscope and prove the existence of the chiral one-dimensional edge conduction along the prescribed DWs through transport measurements. The proof-of-concept devices based on reconfigurable CESs and Landauer-Bu&#x0308;ttiker formalism are realized for multiple-domain configurations with well-defined DW channels. Our results may lead to the realization of low-power-consumption spintronic devices.</p>

Signatures of exciton condensation in a transition metal dichalcogenide

<p>Bose condensation has shaped our understanding of macroscopic quantum phenomena, having been realized in superconductors, atomic gases, and liquid helium. Excitons are bosons that have been predicted to condense into either a superfluid or an insulating electronic crystal. Using the recently developed technique of momentum-resolved electron energy-loss spectroscopy (M-EELS), we studied electronic collective modes in the transition metal dichalcogenide semimetal 1<I>T</I>-TiSe<SUB>2</SUB>. Near the phase-transition temperature (190 kelvin), the energy of the electronic mode fell to zero at nonzero momentum, indicating dynamical slowing of plasma fluctuations and crystallization of the valence electrons into an exciton condensate. Our study provides compelling evidence for exciton condensation in a three-dimensional solid and establishes M-EELS as a versatile technique sensitive to valence band excitations in quantum materials.</p>

Spatiotemporal gene expression trajectories reveal developmental hierarchies of the human cortex

<p>Systematic analyses of spatiotemporal gene expression trajectories during organogenesis have been challenging because diverse cell types at different stages of maturation and differentiation coexist in the emerging tissues. We identified discrete cell types as well as temporally and spatially restricted trajectories of radial glia maturation and neurogenesis in developing human telencephalon. These lineage-specific trajectories reveal the expression of neurogenic transcription factors in early radial glia and enriched activation of mammalian target of rapamycin signaling in outer radial glia. Across cortical areas, modest transcriptional differences among radial glia cascade into robust typological distinctions among maturing neurons. Together, our results support a mixed model of topographical, typological, and temporal hierarchies governing cell-type diversity in the developing human telencephalon, including distinct excitatory lineages emerging in rostral and caudal cerebral cortex.</p>

Firearms and accidental deaths: Evidence from the aftermath of the Sandy Hook school shooting

<p>Exposure to firearms increased substantially after the December 2012 shooting at Sandy Hook Elementary School in Newtown, Connecticut, where 20 children and 6 adults were killed. Gun sales spiked by 3 million, on the basis of the increase in the number of background checks for firearm purchases. Google searches for buying and cleaning guns increased. We used Vital Statistics mortality data to examine whether a spike in accidental firearm deaths occurred at the same time as the greater exposure to firearms. We also assessed whether the increase in these deaths was larger in those states where the spike in gun sales per capita was larger. We find that an additional 60 deaths overall, including 20 children, resulted from unintentional shootings in the immediate aftermath of Sandy Hook.</p>

Paradoxical escape responses by narwhals (Monodon monoceros)

<p>Until recent declines in Arctic sea ice levels, narwhals (<I>Monodon monoceros</I>) have lived in relative isolation from human perturbation and sustained predation pressures. The resulting nai&#x0308;vety has made this cryptic, deep-diving cetacean highly susceptible to disturbance, although quantifiable effects have been lacking. We deployed a submersible, animal-borne electrocardiograph-accelerometer-depth recorder to monitor physiological and behavioral responses of East Greenland narwhals after release from net entanglement and stranding. Escaping narwhals displayed a paradoxical cardiovascular down-regulation (extreme bradycardia with heart rate &le;4 beats per minute) superimposed on exercise up-regulation (stroke frequency &gt;25 strokes per minute and energetic costs three to six times the resting rate of energy expenditure) that rapidly depleted onboard oxygen stores. We attribute this unusual reaction to opposing cardiovascular signals&mdash;from diving, exercise, and neurocognitive fear responses&mdash;that challenge physiological homeostasis.</p>

A small-molecule inhibitor of TRPC5 ion channels suppresses progressive kidney disease in animal models

<p>Progressive kidney diseases are often associated with scarring of the kidney&rsquo;s filtration unit, a condition called focal segmental glomerulosclerosis (FSGS). This scarring is due to loss of podocytes, cells critical for glomerular filtration, and leads to proteinuria and kidney failure. Inherited forms of FSGS are caused by Rac1-activating mutations, and Rac1 induces TRPC5 ion channel activity and cytoskeletal remodeling in podocytes. Whether TRPC5 activity mediates FSGS onset and progression is unknown. We identified a small molecule, AC1903, that specifically blocks TRPC5 channel activity in glomeruli of proteinuric rats. Chronic administration of AC1903 suppressed severe proteinuria and prevented podocyte loss in a transgenic rat model of FSGS. AC1903 also provided therapeutic benefit in a rat model of hypertensive proteinuric kidney disease. These data indicate that TRPC5 activity drives disease and that TRPC5 inhibitors may be valuable for the treatment of progressive kidney diseases.</p>

Structural basis for methylphosphonate biosynthesis

<p>Methylphosphonate synthase (MPnS) produces methylphosphonate, a metabolic precursor to methane in the upper ocean. Here, we determine a 2.35-angstrom resolution structure of MPnS and discover that it has an unusual 2-histidine-1-glutamine iron-coordinating triad. We further solve the structure of a related enzyme, hydroxyethylphosphonate dioxygenase from <I>Streptomyces albus</I> (<I>Sa</I>HEPD), and find that it displays the same motif. <I>Sa</I>HEPD can be converted into an MPnS by mutation of glutamine-adjacent residues, identifying the molecular requirements for methylphosphonate synthesis. Using these sequence markers, we find numerous putative MPnSs in marine microbiomes and confirm that MPnS is present in the abundant <I>Pelagibacter ubique.</I> The ubiquity of MPnS-containing microbes supports the proposal that methylphosphonate is a source of methane in the upper, aerobic ocean, where phosphorus-starved microbes catabolize methylphosphonate for its phosphorus.</p>

Comment on "Cognition-mediated evolution of low-quality floral nectars"

<p>Nachev <I>et al</I>. (Reports, 6 January 2017, p. 75) present dilute nectar in bat-pollinated plants as "paradoxical" because bats prefer concentrated nectar, but paradox disappears with realistic assumptions about nectar evolution. We argue that they make unrealistic assumptions about the cognitive abilities of bat pollinators, invoke Weber&rsquo;s law inappropriately, and cannot predict observed nectar concentrations of bat flowers or negative correlations between pollinator body size and average concentration.</p>

A generative vision model that trains with high data efficiency and breaks text-based CAPTCHAs

<p>Learning from a few examples and generalizing to markedly different situations are capabilities of human visual intelligence that are yet to be matched by leading machine learning models. By drawing inspiration from systems neuroscience, we introduce a probabilistic generative model for vision in which message-passing&ndash;based inference handles recognition, segmentation, and reasoning in a unified way. The model demonstrates excellent generalization and occlusion-reasoning capabilities and outperforms deep neural networks on a challenging scene text recognition benchmark while being 300-fold more data efficient. In addition, the model fundamentally breaks the defense of modern text-based CAPTCHAs (Completely Automated Public Turing test to tell Computers and Humans Apart) by generatively segmenting characters without CAPTCHA-specific heuristics. Our model emphasizes aspects such as data efficiency and compositionality that may be important in the path toward general artificial intelligence.</p>

Response to Comment on "Cognition-mediated evolution of low-quality floral nectars"

<p>Pyke and Waser claim that our virtual pollination ecology model makes unrealistic assumptions and fails to predict observed nectar concentrations of bat flowers and negative correlations between pollinator body size and sugar concentration. In their comment, crucial model features are misrepresented, misunderstood, or ignored. Sensitivity to the supply/demand ratio explains both the equilibrium concentrations and the selection for lower concentrations by larger pollinators.</p>

On the origin of modern humans: Asian perspectives

<p>The traditional "out of Africa" model, which posits a dispersal of modern <I>Homo sapiens</I> across Eurasia as a single wave at ~60,000 years ago and the subsequent replacement of all indigenous populations, is in need of revision. Recent discoveries from archaeology, hominin paleontology, geochronology, genetics, and paleoenvironmental studies have contributed to a better understanding of the Late Pleistocene record in Asia. Important findings highlighted here include growing evidence for multiple dispersals predating 60,000 years ago in regions such as southern and eastern Asia. Modern humans moving into Asia met Neandertals, Denisovans, mid-Pleistocene <I>Homo</I>, and possibly <I>H. floresiensis</I>, with some degree of interbreeding occurring. These early human dispersals, which left at least some genetic traces in modern populations, indicate that later replacements were not wholesale.</p>

Comment on "Water harvesting from air with metal-organic frameworks powered by natural sunlight"

<p>Kim <I>et al</I>. (Reports, 28 April 2017, p. 430) presented results for the solar-driven harvesting of water from air via metal-organic frameworks as a prodigious potential advance toward remedying global water shortages. Basic thermodynamics and a survey of multiple off-the-shelf technologies show that their approach is vastly inferior in efficiency (and thereby in feasibility) to available alternatives.</p>

Ocean biogeochemistry modeled with emergent trait-based genomics

<p>Marine ecosystem models have advanced to incorporate metabolic pathways discovered with genomic sequencing, but direct comparisons between models and "omics" data are lacking. We developed a model that directly simulates metagenomes and metatranscriptomes for comparison with observations. Model microbes were randomly assigned genes for specialized functions, and communities of 68 species were simulated in the Atlantic Ocean. Unfit organisms were replaced, and the model self-organized to develop community genomes and transcriptomes. Emergent communities from simulations that were initialized with different cohorts of randomly generated microbes all produced realistic vertical and horizontal ocean nutrient, genome, and transcriptome gradients. Thus, the library of gene functions available to the community, rather than the distribution of functions among specific organisms, drove community assembly and biogeochemical gradients in the model ocean.</p>

Stripe order in the underdoped region of the two-dimensional Hubbard model

<p>Competing inhomogeneous orders are a central feature of correlated electron materials, including the high-temperature superconductors. The two-dimensional Hubbard model serves as the canonical microscopic physical model for such systems. Multiple orders have been proposed in the underdoped part of the phase diagram, which corresponds to a regime of maximum numerical difficulty. By combining the latest numerical methods in exhaustive simulations, we uncover the ordering in the underdoped ground state. We find a stripe order that has a highly compressible wavelength on an energy scale of a few kelvin, with wavelength fluctuations coupled to pairing order. The favored filled stripe order is different from that seen in real materials. Our results demonstrate the power of modern numerical methods to solve microscopic models, even in challenging settings.</p>

Numerical evidence of fluctuating stripes in the normal state of high-Tc cuprate superconductors

<p>Upon doping, Mott insulators often exhibit symmetry breaking where charge carriers and their spins organize into patterns known as stripes. For high&ndash;transition temperature cuprate superconductors, stripes are widely suspected to exist in a fluctuating form. We used numerically exact determinant quantum Monte Carlo calculations to demonstrate dynamical stripe correlations in the three-band Hubbard model, which represents the local electronic structure of the copper-oxygen plane. Our results, which are robust to varying parameters, cluster size, and boundary conditions, support the interpretation of experimental observations such as the hourglass magnetic dispersion and the Yamada plot of incommensurability versus doping in terms of the physics of fluctuating stripes. These findings provide a different perspective on the intertwined orders emerging from the cuprates&rsquo; normal state.</p>

Observations and modeling of the elastogravity signals preceding direct seismic waves

<p>After an earthquake, the earliest deformation signals are not expected to be carried by the fastest (<I>P</I>) elastic waves but by the speed-of-light changes of the gravitational field. However, these perturbations are weak and, so far, their detection has not been accurate enough to fully understand their origins and to use them for a highly valuable rapid estimate of the earthquake magnitude. We show that gravity perturbations are particularly well observed with broadband seismometers at distances between 1000 and 2000 kilometers from the source of the 2011, moment magnitude 9.1, Tohoku earthquake. We can accurately model them by a new formalism, taking into account both the gravity changes and the gravity-induced motion. These prompt elastogravity signals open the window for minute time-scale magnitude determination for great earthquakes.</p>

Organocalcium-mediated nucleophilic alkylation of benzene

<p>The electrophilic aromatic substitution of a C&ndash;H bond of benzene is one of the archetypal transformations of organic chemistry. In contrast, the electron-rich -system of benzene is highly resistant to reactions with electron-rich and negatively charged organic nucleophiles. Here, we report that this previously insurmountable electronic repulsion may be overcome through the use of sufficiently potent organocalcium nucleophiles. Calcium <I>n</I>-alkyl derivatives&mdash;synthesized by reaction of ethene, but-1-ene, and hex-1-ene with a dimeric calcium hydride&mdash;react with protio and deutero benzene at 60&deg;C through nucleophilic substitution of an aromatic C&ndash;D/H bond. These reactions produce the <I>n-</I>alkyl benzenes with regeneration of the calcium hydride. Density functional theory calculations implicate an unstabilized Meisenheimer complex in the C&ndash;H activation transition state.</p>

The image-forming mirror in the eye of the scallop

<p>Scallops possess a visual system comprising up to 200 eyes, each containing a concave mirror rather than a lens to focus light. The hierarchical organization of the multilayered mirror is controlled for image formation, from the component guanine crystals at the nanoscale to the complex three-dimensional morphology at the millimeter level. The layered structure of the mirror is tuned to reflect the wavelengths of light penetrating the scallop&rsquo;s habitat and is tiled with a mosaic of square guanine crystals, which reduces optical aberrations. The mirror forms images on a double-layered retina used for separately imaging the peripheral and central fields of view. The tiled, off-axis mirror of the scallop eye bears a striking resemblance to the segmented mirrors of reflecting telescopes.</p>

Spectroscopic signatures of localization with interacting photons in superconducting qubits

<p>Quantized eigenenergies and their associated wave functions provide extensive information for predicting the physics of quantum many-body systems. Using a chain of nine superconducting qubits, we implement a technique for resolving the energy levels of interacting photons. We benchmark this method by capturing the main features of the intricate energy spectrum predicted for two-dimensional electrons in a magnetic field&mdash;the Hofstadter butterfly. We introduce disorder to study the statistics of the energy levels of the system as it undergoes the transition from a thermalized to a localized phase. Our work introduces a many-body spectroscopy technique to study quantum phases of matter.</p>

Giant nonlinear response at a plasmonic nanofocus drives efficient four-wave mixing

<p>Efficient optical frequency mixing typically must accumulate over large interaction lengths because nonlinear responses in natural materials are inherently weak. This limits the efficiency of mixing processes owing to the requirement of phase matching. Here, we report efficient four-wave mixing (FWM) over micrometer-scale interaction lengths at telecommunications wavelengths on silicon. We used an integrated plasmonic gap waveguide that strongly confines light within a nonlinear organic polymer. The gap waveguide intensifies light by nanofocusing it to a mode cross-section of a few tens of nanometers, thus generating a nonlinear response so strong that efficient FWM accumulates over wavelength-scale distances. This technique opens up nonlinear optics to a regime of relaxed phase matching, with the possibility of compact, broadband, and efficient frequency mixing integrated with silicon photonics.</p>

Photoredox-catalyzed deuteration and tritiation of pharmaceutical compounds

<p>Deuterium- and tritium-labeled pharmaceutical compounds are pivotal diagnostic tools in drug discovery research, providing vital information about the biological fate of drugs and drug metabolites. Herein we demonstrate that a photoredox-mediated hydrogen atom transfer protocol can efficiently and selectively install deuterium (D) and tritium (T) at &alpha;-amino sp<sup>3</sup> carbon-hydrogen bonds in a single step, using isotopically labeled water (D<SUB>2</SUB>O or T<SUB>2</SUB>O) as the source of hydrogen isotope. In this context, we also report a convenient synthesis of T<SUB>2</SUB>O from T<SUB>2</SUB>, providing access to high-specific-activity T<SUB>2</SUB>O. This protocol has been successfully applied to the high incorporation of deuterium and tritium in 18 drug molecules, which meet the requirements for use in ligand-binding assays and absorption, distribution, metabolism, and excretion studies.</p>

Selective increase in CO2 electroreduction activity at grain-boundary surface terminations

<p>Altering a material&rsquo;s catalytic properties requires identifying structural features that give rise to active surfaces. Grain boundaries create strained regions in polycrystalline materials by stabilizing dislocations and may provide a way to create high-energy surfaces for catalysis that are kinetically trapped. Although grain-boundary density has previously been correlated with catalytic activity for some reactions, direct evidence that grain boundaries create surfaces with enhanced activity is lacking. We used a combination of bulk electrochemical measurements and scanning electrochemical cell microscopy with submicrometer resolution to show that grain-boundary surface terminations in gold electrodes are more active than grain surfaces for electrochemical carbon dioxide (CO<SUB>2</SUB>) reduction to carbon monoxide (CO) but not for the competing hydrogen (H<SUB>2</SUB>) evolution reaction. The catalytic footprint of the grain boundary is commensurate with its dislocation-induced strain field, providing a strategy for broader exploitation of grain-boundary effects in heterogeneous catalysis.</p>

A generic interface to reduce the efficiency-stability-cost gap of perovskite solar cells

<p>A major bottleneck delaying the further commercialization of thin-film solar cells based on hybrid organohalide lead perovskites is interface loss in state-of-the-art devices. We present a generic interface architecture that combines solution-processed, reliable, and cost-efficient hole-transporting materials without compromising efficiency, stability, or scalability of perovskite solar cells. Tantalum-doped tungsten oxide (Ta-WO<I><SUB>x</SUB></I>)/conjugated polymer multilayers offer a surprisingly small interface barrier and form quasi-ohmic contacts universally with various scalable conjugated polymers. In a simple device with regular planar architecture and a self-assembled monolayer, Ta-WO<I><SUB>x</SUB></I>&ndash;doped interface&ndash;based perovskite solar cells achieve maximum efficiencies of 21.2% and offer more than 1000 hours of light stability. By eliminating additional ionic dopants, these findings open up the entire class of organics as scalable hole-transporting materials for perovskite solar cells.</p>

Egg accumulation with 3D embryos provides insight into the life history of a pterosaur

<p>Fossil eggs and embryos that provide unique information about the reproduction and early growth of vertebrates are exceedingly rare, particularly for pterosaurs. Here we report on hundreds of three-dimensional (3D) eggs of the species <I>Hamipterus tianshanensis</I> from a Lower Cretaceous site in China, 16 of which contain embryonic remains. Computed tomography scanning, osteohistology, and micropreparation reveal that some bones lack extensive ossification in potentially late-term embryos, suggesting that hatchlings might have been flightless and less precocious than previously assumed. The geological context, including at least four levels with embryos and eggs, indicates that this deposit was formed by a rare combination of events, with storms acting on a nesting ground. This discovery supports colonial nesting behavior and potential nesting site fidelity in the Pterosauria.</p>

Host DNases prevent vascular occlusion by neutrophil extracellular traps

<p>Platelet and fibrin clots occlude blood vessels in hemostasis and thrombosis. Here we report a noncanonical mechanism for vascular occlusion based on neutrophil extracellular traps (NETs), DNA fibers released by neutrophils during inflammation. We investigated which host factors control NETs in vivo and found that two deoxyribonucleases (DNases), DNase1 and DNase1-like 3, degraded NETs in circulation during sterile neutrophilia and septicemia. In the absence of both DNases, intravascular NETs formed clots that obstructed blood vessels and caused organ damage. Vascular occlusions in patients with severe bacterial infections were associated with a defect to degrade NETs ex vivo and the formation of intravascular NET clots. DNase1 and DNase1-like 3 are independently expressed and thus provide dual host protection against deleterious effects of intravascular NETs.</p>

3.9 A structure of the yeast Mec1-Ddc2 complex, a homolog of human ATR-ATRIP

<p>The ataxia telangiectasia&ndash;mutated and Rad3-related (ATR) kinase is a master regulator of DNA damage response and replication stress in humans, but the mechanism of its activation remains unclear. ATR acts together with its partner ATRIP. Using cryo&ndash;electron microscopy, we determined the structure of intact Mec1-Ddc2 (the yeast homolog of ATR-ATRIP), which is poised for catalysis, at a resolution of 3.9 angstroms. Mec1-Ddc2 forms a dimer of heterodimers through the PRD and FAT domains of Mec1 and the coiled-coil domain of Ddc2. The PRD and Bridge domains in Mec1 constitute critical regulatory sites. The activation loop of Mec1 is inhibited by the PRD, revealing an allosteric mechanism of kinase activation. Our study clarifies the architecture of ATR-ATRIP and provides a structural framework for the understanding of ATR regulation.</p>

Response to Comment on "Water harvesting from air with metal-organic frameworks powered by natural sunlight"

<p>In their comment, Bui <I>et al</I>. argue that the approach we described in our report is vastly inferior in efficiency to alternative off-the-shelf technologies. Their conclusion is invalid, as they compare efficiencies in completely different operating conditions. Here, using heat transfer and thermodynamics principles, we show how Bui <I>et al</I>.&rsquo;s conclusions about the efficiencies of off-the-shelf technologies are fundamentally flawed and inaccurate for the operating conditions described in our study.</p>