显示样式:     当前期刊: Science Advances    加入关注       排序: 导出
我的关注
我的收藏
您暂时未登录!
登录
  • Heritable stress response dynamics revealed by single-cell genealogy
    Sci. Adv. Pub Date : 2018-04-01
    Meenakshi Chatterjee, Murat Acar

    Cells often respond to environmental stimuli by activating specific transcription factors. Upon exposure to glucose limitation stress, it is known that yeast Saccharomyces cerevisiae cells dephosphorylate the general stress response factor Msn2, leading to its nuclear localization, which in turn activates the expression of many genes. However, the precise dynamics of Msn2 nucleocytoplasmic translocations and whether they are inherited over multiple generations in a stress-dependent manner are not well understood. Tracking Msn2 localization events in yeast lineages grown on a microfluidic chip, here we report how cells modulate the amplitude, duration, frequency, and dynamic pattern of the localization events in response to glucose limitation stress. Single yeast cells were found to modulate the amplitude and frequency of Msn2 nuclear localization, but not its duration. Moreover, the Msn2 localization frequency was epigenetically inherited in descendants of mother cells, leading to a decrease in cell-to-cell variation in localization frequency. An analysis of the time dynamic patterns of nuclear localizations between genealogically related cell pairs using an information theory approach found that the magnitude of pattern similarity increased with stress intensity and was strongly inherited by the descendant cells at the highest stress level. By dissecting how general stress response dynamics is contributed by different modulation schemes over long time scales, our work provides insight into which scheme evolution might have acted on to optimize fitness in stressful environments.

    更新日期:2018-04-19
  • Elimination of established tumors with nanodisc-based combination chemoimmunotherapy
    Sci. Adv. Pub Date : 2018-04-01
    Rui Kuai, Wenmin Yuan, Sejin Son, Jutaek Nam, Yao Xu, Yuchen Fan, Anna Schwendeman, James J. Moon

    Although immune checkpoint blockade has shown initial success for various cancers, only a small subset of patients benefits from this therapy. Some chemotherapeutic drugs have been reported to induce antitumor T cell responses, prompting a number of clinical trials on combination chemoimmunotherapy. However, how to achieve potent immune activation with traditional chemotherapeutics in a manner that is safe, effective, and compatible with immunotherapy remains unclear. We show that high-density lipoprotein–mimicking nanodiscs loaded with doxorubicin (DOX), a widely used chemotherapeutic agent, can potentiate immune checkpoint blockade in murine tumor models. Delivery of DOX via nanodiscs triggered immunogenic cell death of cancer cells and exerted antitumor efficacy without any overt off-target side effects. “Priming” tumors with DOX-carrying nanodiscs elicited robust antitumor CD8+ T cell responses while broadening their epitope recognition to tumor-associated antigens, neoantigens, and intact whole tumor cells. Combination chemoimmunotherapy with nanodiscs plus anti–programmed death 1 therapy induced complete regression of established CT26 and MC38 colon carcinoma tumors in 80 to 88% of animals and protected survivors against tumor recurrence. Our work provides a new, generalizable framework for using nanoparticle-based chemotherapy to initiate antitumor immunity and sensitize tumors to immune checkpoint blockade.

    更新日期:2018-04-19
  • Parallel evolution of Batesian mimicry supergene in two Papilio butterflies, P. polytes and P. memnon
    Sci. Adv. Pub Date : 2018-04-01
    Takuro Iijima, Rei Kajitani, Shinya Komata, Chung-Ping Lin, Teiji Sota, Takehiko Itoh, Haruhiko Fujiwara

    Batesian mimicry protects animals from predators when mimics resemble distasteful models. The female-limited Batesian mimicry in Papilio butterflies is controlled by a supergene locus switching mimetic and nonmimetic forms. In Papilio polytes, recent studies revealed that a highly diversified region (HDR) containing doublesex (dsx-HDR) constitutes the supergene with dimorphic alleles and is likely maintained by a chromosomal inversion. In the closely related Papilio memnon, which exhibits a similar mimicry polymorphism, we performed whole-genome sequence analyses in 11 butterflies, which revealed a nearly identical dsx-HDR containing three genes (dsx, Nach-like, and UXT) with dimorphic sequences strictly associated with the mimetic/nonmimetic phenotypes. In addition, expression of these genes, except that of Nach-like in female hind wings, showed differences correlated with phenotype. The dimorphic dsx-HDR in P. memnon is maintained without a chromosomal inversion, suggesting that a separate mechanism causes and maintains allelic divergence in these genes. More abundant accumulation of transposable elements and repetitive sequences in the dsx-HDR than in other genomic regions may contribute to the suppression of chromosomal recombination. Gene trees for Dsx, Nach-like, and UXT indicated that mimetic alleles evolved independently in the two Papilio species. These results suggest that the genomic region involving the above three genes has repeatedly diverged so that two allelic sequences of this region function as developmental switches for mimicry polymorphism in the two Papilio species. The supergene structures revealed here suggest that independent evolutionary processes with different genetic mechanisms have led to parallel evolution of similar female-limited polymorphisms underlying Batesian mimicry in Papilio butterflies.

    更新日期:2018-04-19
  • Freshening by glacial meltwater enhances melting of ice shelves and reduces formation of Antarctic Bottom Water
    Sci. Adv. Pub Date : 2018-04-01
    Alessandro Silvano, Stephen Rich Rintoul, Beatriz Peña-Molino, William Richard Hobbs, Esmee van Wijk, Shigeru Aoki, Takeshi Tamura, Guy Darvall Williams

    Strong heat loss and brine release during sea ice formation in coastal polynyas act to cool and salinify waters on the Antarctic continental shelf. Polynya activity thus both limits the ocean heat flux to the Antarctic Ice Sheet and promotes formation of Dense Shelf Water (DSW), the precursor to Antarctic Bottom Water. However, despite the presence of strong polynyas, DSW is not formed on the Sabrina Coast in East Antarctica and in the Amundsen Sea in West Antarctica. Using a simple ocean model driven by observed forcing, we show that freshwater input from basal melt of ice shelves partially offsets the salt flux by sea ice formation in polynyas found in both regions, preventing full-depth convection and formation of DSW. In the absence of deep convection, warm water that reaches the continental shelf in the bottom layer does not lose much heat to the atmosphere and is thus available to drive the rapid basal melt observed at the Totten Ice Shelf on the Sabrina Coast and at the Dotson and Getz ice shelves in the Amundsen Sea. Our results suggest that increased glacial meltwater input in a warming climate will both reduce Antarctic Bottom Water formation and trigger increased mass loss from the Antarctic Ice Sheet, with consequences for the global overturning circulation and sea level rise.

    更新日期:2018-04-19
  • Decline of genetic diversity in ancient domestic stallions in Europe
    Sci. Adv. Pub Date : 2018-04-01
    Saskia Wutke, Edson Sandoval-Castellanos, Norbert Benecke, Hans-Jürgen Döhle, Susanne Friederich, Javier Gonzalez, Michael Hofreiter, Lembi Lõugas, Ola Magnell, Anna-Sapfo Malaspinas, Arturo Morales-Muñiz, Ludovic Orlando, Monika Reissmann, Alexandra Trinks, Arne Ludwig

    Present-day domestic horses are immensely diverse in their maternally inherited mitochondrial DNA, yet they show very little variation on their paternally inherited Y chromosome. Although it has recently been shown that Y chromosomal diversity in domestic horses was higher at least until the Iron Age, when and why this diversity disappeared remain controversial questions. We genotyped 16 recently discovered Y chromosomal single-nucleotide polymorphisms in 96 ancient Eurasian stallions spanning the early domestication stages (Copper and Bronze Age) to the Middle Ages. Using this Y chromosomal time series, which covers nearly the entire history of horse domestication, we reveal how Y chromosomal diversity changed over time. Our results also show that the lack of multiple stallion lineages in the extant domestic population is caused by neither a founder effect nor random demographic effects but instead is the result of artificial selection—initially during the Iron Age by nomadic people from the Eurasian steppes and later during the Roman period. Moreover, the modern domestic haplotype probably derived from another, already advantageous, haplotype, most likely after the beginning of the domestication. In line with recent findings indicating that the Przewalski and domestic horse lineages remained connected by gene flow after they diverged about 45,000 years ago, we present evidence for Y chromosomal introgression of Przewalski horses into the gene pool of European domestic horses at least until medieval times.

    更新日期:2018-04-19
  • Noninvasive ovarian cancer biomarker detection via an optical nanosensor implant
    Sci. Adv. Pub Date : 2018-04-01
    Ryan M. Williams, Christopher Lee, Thomas V. Galassi, Jackson D. Harvey, Rachel Leicher, Maria Sirenko, Madeline A. Dorso, Janki Shah, Narciso Olvera, Fanny Dao, Douglas A. Levine, Daniel A. Heller

    Patients with high-grade serous ovarian carcinoma (HGSC) exhibit poor 5-year survival rates, which may be significantly improved by early-stage detection. The U.S. Food and Drug Administration–approved biomarkers for HGSC—CA-125 (cancer antigen 125) and HE4 (human epididymis protein 4)—do not generally appear at detectable levels in the serum until advanced stages of the disease. An implantable device placed proximal to disease sites, such as in or near the fallopian tube, ovary, uterine cavity, or peritoneal cavity, may constitute a feasible strategy to improve detection of HGSC. We engineered a prototype optical sensor composed of an antibody-functionalized carbon nanotube complex, which responds quantitatively to HE4 via modulation of the nanotube optical bandgap. The complexes measured HE4 with nanomolar sensitivity to differentiate disease from benign patient biofluids. The sensors were implanted into four models of ovarian cancer, within a semipermeable membrane, enabling the optical detection of HE4 within the live animals. We present the first in vivo optical nanosensor capable of noninvasive cancer biomarker detection in orthotopic models of disease.

    更新日期:2018-04-19
  • Origin of Phobos and Deimos by the impact of a Vesta-to-Ceres sized body with Mars
    Sci. Adv. Pub Date : 2018-04-01
    Robin Canup, Julien Salmon

    It has been proposed that Mars’ moons formed from a disk produced by a large impact with the planet. However, whether such an event could produce tiny Phobos and Deimos remains unclear. Using a hybrid N-body model of moon accumulation that includes a full treatment of moon-moon dynamical interactions, we first identify new constraints on the disk properties needed to produce Phobos and Deimos. We then simulate the impact formation of disks using smoothed particle hydrodynamics, including a novel approach that resolves the impact ejecta with order-of-magnitude finer mass resolution than existing methods. We find that forming Phobos-Deimos requires an oblique impact by a Vesta-to-Ceres sized object with ~10−3 times Mars’ mass, a much less massive impactor than previously considered.

    更新日期:2018-04-19
  • Dynamic coding of predatory information between the prelimbic cortex and lateral amygdala in foraging rats
    Sci. Adv. Pub Date : 2018-04-01
    Eun Joo Kim, Mi-Seon Kong, Sang Geon Park, Sheri J. Y. Mizumori, Jeiwon Cho, Jeansok J. Kim

    Predation is considered a major selective pressure in the evolution of fear, but the neurophysiology of predator-induced fear is unknown. We simultaneously recorded lateral amygdala (LA) and prelimbic (PL) area neuronal activities as rats exited a safe nest to search for food in an open space before, during, and after encountering a “predator” robot programmed to surge from afar. Distinct populations of LA neurons transiently increased spiking as rats either advanced or fled the robot, whereas PL neurons showed longer-lasting spike trains that preceded and persisted beyond LA activity. Moreover, discrete LA-PL cell pairs displayed correlated firings only when the animals either approached or fled the robot. These results suggest a general fear function of the LA-PL circuit where the PL participates in the initial detection of potential threats, the LA signals the occurrence of real threats, and the dynamic LA-PL interaction optimizes defensive readiness for action.

    更新日期:2018-04-19
  • Low-input and multiplexed microfluidic assay reveals epigenomic variation across cerebellum and prefrontal cortex
    Sci. Adv. Pub Date : 2018-04-01
    Sai Ma, Yuan-Pang Hsieh, Jian Ma, Chang Lu

    Extensive effort is under way to survey the epigenomic landscape of primary ex vivo tissues to establish normal reference data and to discern variation associated with disease. The low abundance of some tissue types and the isolation procedure required to generate a homogenous cell population often yield a small quantity of cells for examination. This difficulty is further compounded by the need to profile a myriad of epigenetic marks. Thus, technologies that permit both ultralow input and high throughput are desired. We demonstrate a simple microfluidic technology, SurfaceChIP-seq, for profiling genome-wide histone modifications using as few as 30 to 100 cells per assay and with up to eight assays running in parallel. We applied the technology to profile epigenomes using nuclei isolated from prefrontal cortex and cerebellum of mouse brain. Our cell type–specific data revealed that neuronal and glial fractions exhibited profound epigenomic differences across the two functionally distinct brain regions.

    更新日期:2018-04-19
  • Strong coupling superconductivity in a quasiperiodic host-guest structure
    Sci. Adv. Pub Date : 2018-04-01
    Philip Brown, Konstantin Semeniuk, Diandian Wang, Bartomeu Monserrat, Chris J. Pickard, F. Malte Grosche

    We examine the low-temperature states supported by the quasiperiodic host-guest structure of elemental bismuth at high pressure, Bi-III. Our electronic transport and magnetization experiments establish Bi-III as a rare example of type II superconductivity in an element, with a record upper critical field of ~ 2.5 T, unusually strong electron-phonon coupling, and an anomalously large, linear temperature dependence of the electrical resistivity in the normal state. These properties may be attributed to the peculiar phonon spectrum of incommensurate host-guest structures, which exhibit additional quasi-acoustic sliding modes, suggesting a pathway toward strong coupling superconductivity with the potential for enhanced transition temperatures and high critical fields.

    更新日期:2018-04-14
  • High-performance and scalable metal-chalcogenide semiconductors and devices via chalco-gel routes
    Sci. Adv. Pub Date : 2018-04-01
    Sung Min Kwon, Jong Kook Won, Jeong-Wan Jo, Jaehyun Kim, Hee-Joong Kim, Hyuck-In Kwon, Jaekyun Kim, Sangdoo Ahn, Yong-Hoon Kim, Myoung-Jae Lee, Hyung-ik Lee, Tobin J. Marks, Myung-Gil Kim, Sung Kyu Park

    We report a general strategy for obtaining high-quality, large-area metal-chalcogenide semiconductor films from precursors combining chelated metal salts with chalcoureas or chalcoamides. Using conventional organic solvents, such precursors enable the expeditious formation of chalco-gels, which are easily transformed into the corresponding high-performance metal-chalcogenide thin films with large, uniform areas. Diverse metal chalcogenides and their alloys (MQx: M = Zn, Cd, In, Sb, Pb; Q = S, Se, Te) are successfully synthesized at relatively low processing temperatures (<400°C). The versatility of this scalable route is demonstrated by the fabrication of large-area thin-film transistors (TFTs), optoelectronic devices, and integrated circuits on a 4-inch Si wafer and 2.5-inch borosilicate glass substrates in ambient air using CdS, CdSe, and In2Se3 active layers. The CdSe TFTs exhibit a maximum field-effect mobility greater than 300 cm2 V−1 s−1 with an on/off current ratio of >107 and good operational stability (threshold voltage shift < 0.5 V at a positive gate bias stress of 10 ks). In addition, metal chalcogenide–based phototransistors with a photodetectivity of >1013 Jones and seven-stage ring oscillators operating at a speed of ~2.6 MHz (propagation delay of < 27 ns per stage) are demonstrated.

    更新日期:2018-04-14
  • Bursting at the seams: Rippled monolayer bismuth on NbSe2
    Sci. Adv. Pub Date : 2018-04-01
    Alan Fang, Carolina Adamo, Shuang Jia, Robert J. Cava, Shu-Chun Wu, Claudia Felser, Aharon Kapitulnik

    Bismuth, one of the heaviest semimetals in nature, ignited the interest of the materials physics community for its potential impact on topological quantum material systems that use its strong spin-orbit coupling and unique orbital hybridization. In particular, recent theoretical predictions of unique topological and superconducting properties of thin bismuth films and interfaces prompted intense research on the growth of submonolayers to a few monolayers of bismuth on different substrates. Similar to bulk rhombohedral bismuth, the initial growth of bismuth films on most substrates results in buckled bilayers that grow in either the (111) or (110) directions, with a lattice constant close to that of bulk Bi. By contrast, we show a new growth pattern for bismuth monolayers on NbSe2. We find that the initial growth of Bi can form a strongly bonded commensurate layer, resulting in a compressively strained two-dimensional (2D) triangular lattice. We also observed unique pattern of 1D ripples and domain walls is observed. The single layer of bismuth also introduces strong marks on the electronic properties at the surface.

    更新日期:2018-04-14
  • Accelerated discovery of metallic glasses through iteration of machine learning and high-throughput experiments
    Sci. Adv. Pub Date : 2018-04-01
    Fang Ren, Logan Ward, Travis Williams, Kevin J. Laws, Christopher Wolverton, Jason Hattrick-Simpers, Apurva Mehta

    With more than a hundred elements in the periodic table, a large number of potential new materials exist to address the technological and societal challenges we face today; however, without some guidance, searching through this vast combinatorial space is frustratingly slow and expensive, especially for materials strongly influenced by processing. We train a machine learning (ML) model on previously reported observations, parameters from physiochemical theories, and make it synthesis method–dependent to guide high-throughput (HiTp) experiments to find a new system of metallic glasses in the Co-V-Zr ternary. Experimental observations are in good agreement with the predictions of the model, but there are quantitative discrepancies in the precise compositions predicted. We use these discrepancies to retrain the ML model. The refined model has significantly improved accuracy not only for the Co-V-Zr system but also across all other available validation data. We then use the refined model to guide the discovery of metallic glasses in two additional previously unreported ternaries. Although our approach of iterative use of ML and HiTp experiments has guided us to rapid discovery of three new glass-forming systems, it has also provided us with a quantitatively accurate, synthesis method–sensitive predictor for metallic glasses that improves performance with use and thus promises to greatly accelerate discovery of many new metallic glasses. We believe that this discovery paradigm is applicable to a wider range of materials and should prove equally powerful for other materials and properties that are synthesis path–dependent and that current physiochemical theories find challenging to predict.

    更新日期:2018-04-14
  • Crystal nucleation in metallic alloys using x-ray radiography and machine learning
    Sci. Adv. Pub Date : 2018-04-01
    Enzo Liotti, Carlos Arteta, Andrew Zisserman, Andrew Lui, Victor Lempitsky, Patrick S. Grant

    The crystallization of solidifying Al-Cu alloys over a wide range of conditions was studied in situ by synchrotron x-ray radiography, and the data were analyzed using a computer vision algorithm trained using machine learning. The effect of cooling rate and solute concentration on nucleation undercooling, crystal formation rate, and crystal growth rate was measured automatically for thousands of separate crystals, which was impossible to achieve manually. Nucleation undercooling distributions confirmed the efficiency of extrinsic grain refiners and gave support to the widely assumed free growth model of heterogeneous nucleation. We show that crystallization occurred in temporal and spatial bursts associated with a solute-suppressed nucleation zone.

    更新日期:2018-04-14
  • Multiple heteroatom substitution to graphene nanoribbon
    Sci. Adv. Pub Date : 2018-04-01
    Shigeki Kawai, Soichiro Nakatsuka, Takuji Hatakeyama, Rémy Pawlak, Tobias Meier, John Tracey, Ernst Meyer, Adam S. Foster

    Substituting heteroatoms into nanostructured graphene elements, such as graphene nanoribbons, offers the possibility for atomic engineering of electronic properties. To characterize these substitutions, functionalized atomic force microscopy (AFM)—a tool to directly resolve chemical structures—is one of the most promising tools, yet the chemical analysis of heteroatoms has been rarely performed. We synthesized multiple heteroatom-substituted graphene nanoribbons and showed that AFM can directly resolve elemental differences and can be correlated to the van der Waals radii, as well as the modulated local electron density caused by the substitution. This elemental-sensitive measurement takes an important step in the analysis of functionalized two-dimensional carbon materials.

    更新日期:2018-04-14
  • Experimental signatures of spin superfluid ground state in canted antiferromagnet Cr2O3 via nonlocal spin transport
    Sci. Adv. Pub Date : 2018-04-01
    Wei Yuan, Qiong Zhu, Tang Su, Yunyan Yao, Wenyu Xing, Yangyang Chen, Yang Ma, Xi Lin, Jing Shi, Ryuichi Shindou, X. C. Xie, Wei Han

    Spin superfluid is a novel emerging quantum matter arising from the Bose-Einstein condensate (BEC) of spin-1 bosons. We demonstrate the spin superfluid ground state in canted antiferromagnetic Cr2O3 thin film at low temperatures via nonlocal spin transport. A large enhancement of the nonlocal spin signal is observed below ~20 K, and it saturates from ~5 down to 2 K. We show that the spins can propagate over very long distances (~20 μm) in such spin superfluid ground state and that the nonlocal spin signal decreases very slowly as the spacing increases with an inverse relationship, which is consistent with theoretical prediction. Furthermore, spin superfluidity has been investigated in the canted antiferromagnetic phase of the (110)-oriented Cr2O3 film, where the magnetic field dependence of the associated critical temperature follows a 2/3 power law near the critical point. The experimental demonstration of the spin superfluid ground state in canted antiferromagnet will be extremely important for the fundamental physics on the BEC of spin-1 bosons and paves the way for future spin supercurrent devices, such as spin-Josephson junctions.

    更新日期:2018-04-14
  • Multiple episodes of extensive marine anoxia linked to global warming and continental weathering following the latest Permian mass extinction
    Sci. Adv. Pub Date : 2018-04-01
    Feifei Zhang, Stephen J. Romaniello, Thomas J. Algeo, Kimberly V. Lau, Matthew E. Clapham, Sylvain Richoz, Achim D. Herrmann, Harrison Smith, Micha Horacek, Ariel D. Anbar

    Explaining the ~5-million-year delay in marine biotic recovery following the latest Permian mass extinction, the largest biotic crisis of the Phanerozoic, is a fundamental challenge for both geological and biological sciences. Ocean redox perturbations may have played a critical role in this delayed recovery. However, the lack of quantitative constraints on the details of Early Triassic oceanic anoxia (for example, time, duration, and extent) leaves the links between oceanic conditions and the delayed biotic recovery ambiguous. We report high-resolution U-isotope (δ238U) data from carbonates of the uppermost Permian to lowermost Middle Triassic Zal section (Iran) to characterize the timing and global extent of ocean redox variation during the Early Triassic. Our δ238U record reveals multiple negative shifts during the Early Triassic. Isotope mass-balance modeling suggests that the global area of anoxic seafloor expanded substantially in the Early Triassic, peaking during the latest Permian to mid-Griesbachian, the late Griesbachian to mid-Dienerian, the Smithian-Spathian transition, and the Early/Middle Triassic transition. Comparisons of the U-, C-, and Sr-isotope records with a modeled seawater PO43− concentration curve for the Early Triassic suggest that elevated marine productivity and enhanced oceanic stratification were likely the immediate causes of expanded oceanic anoxia. The patterns of redox variation documented by the U-isotope record show a good first-order correspondence to peaks in ammonoid extinctions during the Early Triassic. Our results indicate that multiple oscillations in oceanic anoxia modulated the recovery of marine ecosystems following the latest Permian mass extinction.

    更新日期:2018-04-12
  • Fossil scales illuminate the early evolution of lepidopterans and structural colors
    Sci. Adv. Pub Date : 2018-04-01
    Qingqing Zhang, Wolfram Mey, Jörg Ansorge, Timothy A. Starkey, Luke T. McDonald, Maria E. McNamara, Edmund A. Jarzembowski, Wilfried Wichard, Richard Kelly, Xiaoyin Ren, Jun Chen, Haichun Zhang, Bo Wang

    Lepidopteran scales exhibit remarkably complex ultrastructures, many of which produce structural colors that are the basis for diverse communication strategies. Little is known, however, about the early evolution of lepidopteran scales and their photonic structures. We report scale architectures from Jurassic Lepidoptera from the United Kingdom, Germany, Kazakhstan, and China and from Tarachoptera (a stem group of Amphiesmenoptera) from mid-Cretaceous Burmese amber. The Jurassic lepidopterans exhibit a type 1 bilayer scale vestiture: an upper layer of large fused cover scales and a lower layer of small fused ground scales. This scale arrangement, plus preserved herringbone ornamentation on the cover scale surface, is almost identical to those of some extant Micropterigidae. Critically, the fossil scale ultrastructures have periodicities measuring from 140 to 2000 nm and are therefore capable of scattering visible light, providing the earliest evidence of structural colors in the insect fossil record. Optical modeling confirms that diffraction-related scattering mechanisms dominate the photonic properties of the fossil cover scales, which would have displayed broadband metallic hues as in numerous extant Micropterigidae. The fossil tarachopteran scales exhibit a unique suite of characteristics, including small size, elongate-spatulate shape, ridged ornamentation, and irregular arrangement, providing novel insight into the early evolution of lepidopteran scales. Combined, our results provide the earliest evidence for structural coloration in fossil lepidopterans and support the hypothesis that fused wing scales and the type 1 bilayer covering are groundplan features of the group. Wing scales likely had deep origins in earlier amphiesmenopteran lineages before the appearance of the Lepidoptera.

    更新日期:2018-04-12
  • Systematic reconstruction of autism biology from massive genetic mutation profiles
    Sci. Adv. Pub Date : 2018-04-01
    Weijun Luo, Chaolin Zhang, Yong-hui Jiang, Cory R. Brouwer

    Autism spectrum disorder (ASD) affects 1% of world population and has become a pressing medical and social problem worldwide. As a paradigmatic complex genetic disease, ASD has been intensively studied and thousands of gene mutations have been reported. Because these mutations rarely recur, it is difficult to (i) pinpoint the fewer disease-causing versus majority random events and (ii) replicate or verify independent studies. A coherent and systematic understanding of autism biology has not been achieved. We analyzed 3392 and 4792 autism-related mutations from two large-scale whole-exome studies across multiple resolution levels, that is, variants (single-nucleotide), genes (protein-coding unit), and pathways (molecular module). These mutations do not recur or replicate at the variant level, but significantly and increasingly do so at gene and pathway levels. Genetic association reveals a novel gene + pathway dual-hit model, where the mutation burden becomes less relevant. In multiple independent analyses, hundreds of variants or genes repeatedly converge to several canonical pathways, either novel or literature-supported. These pathways define recurrent and systematic ASD biology, distinct from previously reported gene groups or networks. They also present a catalog of novel ASD risk factors including 118 variants and 72 genes. At a subpathway level, most variants disrupt the pathway-related gene functions, and in the same gene, they tend to hit residues extremely close to each other and in the same domain. Multiple interacting variants spotlight key modules, including the cAMP (adenosine 3′,5′-monophosphate) second-messenger system and mGluR (metabotropic glutamate receptor) signaling regulation by GRKs (G protein–coupled receptor kinases). At a superpathway level, distinct pathways further interconnect and converge to three biology themes: synaptic function, morphology, and plasticity.

    更新日期:2018-04-12
  • Light-induced dynamic structural color by intracellular 3D photonic crystals in brown algae
    Sci. Adv. Pub Date : 2018-04-01
    Martin Lopez-Garcia, Nathan Masters, Heath E. O’Brien, Joseph Lennon, George Atkinson, Martin J. Cryan, Ruth Oulton, Heather M. Whitney

    Natural photonic crystals are responsible for strong reflectance at selective wavelengths in different natural systems. We demonstrate that intracellular opal-like photonic crystals formed from lipids within photosynthetic cells produce vivid structural color in the alga Cystoseira tamariscifolia. The reflectance of the opaline vesicles is dynamically responsive to environmental illumination. The structural color is present in low light–adapted samples, whereas higher light levels produce a slow disappearance of the structural color such that it eventually vanishes completely. Once returned to low-light conditions, the color re-emerges. Our results suggest that these complex intracellular natural photonic crystals are responsive to environmental conditions, changing their packing structure reversibly, and have the potential to manipulate light for roles beyond visual signaling.

    更新日期:2018-04-12
  • Differential expression of voltage-gated sodium channels in afferent neurons renders selective neural block by ionic direct current
    Sci. Adv. Pub Date : 2018-04-01
    Fei Yang, Michael Anderson, Shaoqiu He, Kimberly Stephens, Yu Zheng, Zhiyong Chen, Srinivasa N. Raja, Felix Aplin, Yun Guan, Gene Fridman

    The assertion that large-diameter nerve fibers have low thresholds and small-diameter fibers have high thresholds in response to electrical stimulation has been held in a nearly axiomatic regard in the field of neuromodulation and neuroprosthetics. In contrast to the short pulses used to evoke action potentials, long-duration ionic direct current has been shown to block neural activity. We propose that the main determinant of the neural sensitivity to direct current block is not the size of the axon but the types of voltage-gated sodium channels prevalent in its neural membrane. On the basis of the variants of voltage-gated sodium channels expressed in different types of neurons in the peripheral nerves, we hypothesized that the small-diameter nociceptive fibers could be preferentially blocked. We show the results of a computational model and in vivo neurophysiology experiments that offer experimental validation of this novel phenomenon.

    更新日期:2018-04-12
  • Evo-devo models of tooth development and the origin of hominoid molar diversity
    Sci. Adv. Pub Date : 2018-04-01
    Alejandra Ortiz, Shara E. Bailey, Gary T. Schwartz, Jean-Jacques Hublin, Matthew M. Skinner

    The detailed anatomical features that characterize fossil hominin molars figure prominently in the reconstruction of their taxonomy, phylogeny, and paleobiology. Despite the prominence of molar form in human origins research, the underlying developmental mechanisms generating the diversity of tooth crown features remain poorly understood. A model of tooth morphogenesis—the patterning cascade model (PCM)—provides a developmental framework to explore how and why the varying molar morphologies arose throughout human evolution. We generated virtual maps of the inner enamel epithelium—an indelibly preserved record of enamel knot arrangement—in 17 living and fossil hominoid species to investigate whether the PCM explains the expression of all major accessory cusps. We found that most of the variation and evolutionary changes in hominoid molar morphology followed the general developmental rule shared by all mammals, outlined by the PCM. Our results have implications for the accurate interpretation of molar crown configuration in hominoid systematics.

    更新日期:2018-04-12
  • Isoprene photo-oxidation products quantify the effect of pollution on hydroxyl radicals over Amazonia
    Sci. Adv. Pub Date : 2018-04-01
    Yingjun Liu, Roger Seco, Saewung Kim, Alex B. Guenther, Allen H. Goldstein, Frank N. Keutsch, Stephen R. Springston, Thomas B. Watson, Paulo Artaxo, Rodrigo A. F. Souza, Karena A. McKinney, Scot T. Martin

    Nitrogen oxides (NOx) emitted from human activities are believed to regulate the atmospheric oxidation capacity of the troposphere. However, observational evidence is limited for the low-to-median NOx concentrations prevalent outside of polluted regions. Directly measuring oxidation capacity, represented primarily by hydroxyl radicals (OH), is challenging, and the span in NOx concentrations at a single observation site is often not wide. Concentrations of isoprene and its photo-oxidation products were used to infer the equivalent noontime OH concentrations. The fetch at an observation site in central Amazonia experienced varied contributions from background regional air, urban pollution, and biomass burning. The afternoon concentrations of reactive nitrogen oxides (NOy), indicative of NOx exposure during the preceding few hours, spanned from 0.3 to 3.5 parts per billion. Accompanying the increase of NOy concentration, the inferred equivalent noontime OH concentrations increased by at least 250% from 0.6 × 106 to 1.6 × 106 cm−3. The conclusion is that, compared to background conditions of low NOx concentrations over the Amazon forest, pollution increased NOx concentrations and amplified OH concentrations, indicating the susceptibility of the atmospheric oxidation capacity over the forest to anthropogenic influence and reinforcing the important role of NOx in sustaining OH concentrations.

    更新日期:2018-04-12
  • Limiting parental interaction during vocal development affects acoustic call structure in marmoset monkeys
    Sci. Adv. Pub Date : 2018-04-01
    Yasemin B. Gultekin, Steffen R. Hage

    Human vocal development is dependent on learning by imitation through social feedback between infants and caregivers. Recent studies have revealed that vocal development is also influenced by parental feedback in marmoset monkeys, suggesting vocal learning mechanisms in nonhuman primates. Marmoset infants that experience more contingent vocal feedback than their littermates develop vocalizations more rapidly, and infant marmosets with limited parental interaction exhibit immature vocal behavior beyond infancy. However, it is yet unclear whether direct parental interaction is an obligate requirement for proper vocal development because all monkeys in the aforementioned studies were able to produce the adult call repertoire after infancy. Using quantitative measures to compare distinct call parameters and vocal sequence structure, we show that social interaction has a direct impact not only on the maturation of the vocal behavior but also on acoustic call structures during vocal development. Monkeys with limited parental interaction during development show systematic differences in call entropy, a measure for maturity, compared with their normally raised siblings. In addition, different call types were occasionally uttered in motif-like sequences similar to those exhibited by vocal learners, such as birds and humans, in early vocal development. These results indicate that a lack of parental interaction leads to long-term disturbances in the acoustic structure of marmoset vocalizations, suggesting an imperative role for social interaction in proper primate vocal development.

    更新日期:2018-04-12
  • Discovery of a hypersaline subglacial lake complex beneath Devon Ice Cap, Canadian Arctic
    Sci. Adv. Pub Date : 2018-04-01
    Anja Rutishauser, Donald D. Blankenship, Martin Sharp, Mark L. Skidmore, Jamin S. Greenbaum, Cyril Grima, Dustin M. Schroeder, Julian A. Dowdeswell, Duncan A. Young

    Subglacial lakes are unique environments that, despite the extreme dark and cold conditions, have been shown to host microbial life. Many subglacial lakes have been discovered beneath the ice sheets of Antarctica and Greenland, but no spatially isolated water body has been documented as hypersaline. We use radio-echo sounding measurements to identify two subglacial lakes situated in bedrock troughs near the ice divide of Devon Ice Cap, Canadian Arctic. Modeled basal ice temperatures in the lake area are no higher than −10.5°C, suggesting that these lakes consist of hypersaline water. This implication of hypersalinity is in agreement with the surrounding geology, which indicates that the subglacial lakes are situated within an evaporite-rich sediment unit containing a bedded salt sequence, which likely act as the solute source for the brine. Our results reveal the first evidence for subglacial lakes in the Canadian Arctic and the first hypersaline subglacial lakes reported to date. We conclude that these previously unknown hypersaline subglacial lakes may represent significant and largely isolated microbial habitats, and are compelling analogs for potential ice-covered brine lakes and lenses on planetary bodies across the solar system.

    更新日期:2018-04-12
  • Anatomy of Mississippi Delta growth and its implications for coastal restoration
    Sci. Adv. Pub Date : 2018-04-01
    Elizabeth L. Chamberlain, Torbjörn E. Törnqvist, Zhixiong Shen, Barbara Mauz, Jakob Wallinga

    The decline of several of the world’s largest deltas has spurred interest in expensive coastal restoration projects to make these economically and ecologically vital regions more sustainable. The success of these projects depends, in part, on our understanding of how delta plains evolve over time scales longer than the instrumental record. Building on a new set of optically stimulated luminescence ages, we demonstrate that a large portion (~10,000 km2) of the late Holocene river–dominated Mississippi Delta grew in a radially symmetric fashion for almost a millennium before abandonment. Sediment was dispersed by deltaic distributaries that formed by means of bifurcations at the coeval shoreline and remained active throughout the life span of this landform. Progradation rates (100 to 150 m/year) were surprisingly constant, producing 6 to 8 km2 of new land per year. This shows that robust rates of land building were sustained under preindustrial conditions. However, these rates are several times lower than rates of land loss over the past century, indicating that only a small portion of the Mississippi Delta may be sustainable in a future world with accelerated sea-level rise.

    更新日期:2018-04-12
  • HEx: A heterologous expression platform for the discovery of fungal natural products
    Sci. Adv. Pub Date : 2018-04-01
    Colin J. B. Harvey, Mancheng Tang, Ulrich Schlecht, Joe Horecka, Curt R. Fischer, Hsiao-Ching Lin, Jian Li, Brian Naughton, James Cherry, Molly Miranda, Yong Fuga Li, Angela M. Chu, James R. Hennessy, Gergana A. Vandova, Diane Inglis, Raeka S. Aiyar, Lars M. Steinmetz, Ronald W. Davis, Marnix H. Medema, Elizabeth Sattely, Chaitan Khosla, Robert P. St. Onge, Yi Tang, Maureen E. Hillenmeyer

    For decades, fungi have been a source of U.S. Food and Drug Administration–approved natural products such as penicillin, cyclosporine, and the statins. Recent breakthroughs in DNA sequencing suggest that millions of fungal species exist on Earth, with each genome encoding pathways capable of generating as many as dozens of natural products. However, the majority of encoded molecules are difficult or impossible to access because the organisms are uncultivable or the genes are transcriptionally silent. To overcome this bottleneck in natural product discovery, we developed the HEx (Heterologous EXpression) synthetic biology platform for rapid, scalable expression of fungal biosynthetic genes and their encoded metabolites in Saccharomyces cerevisiae. We applied this platform to 41 fungal biosynthetic gene clusters from diverse fungal species from around the world, 22 of which produced detectable compounds. These included novel compounds with unexpected biosynthetic origins, particularly from poorly studied species. This result establishes the HEx platform for rapid discovery of natural products from any fungal species, even those that are uncultivable, and opens the door to discovery of the next generation of natural products.

    更新日期:2018-04-12
  • Active nematic emulsions
    Sci. Adv. Pub Date : 2018-04-01
    Pau Guillamat, Žiga Kos, Jérôme Hardoüin, Jordi Ignés-Mullol, Miha Ravnik, Francesc Sagués

    The formation of emulsions from multiple immiscible fluids is governed by classical concepts such as surface tension, differential chemical affinity and viscosity, and the action of surface-active agents. Much less is known about emulsification when one of the components is active and thus inherently not constrained by the laws of thermodynamic equilibrium. We demonstrate one such realization consisting in the encapsulation of an active liquid crystal (LC)–like gel, based on microtubules and kinesin molecular motors, into a thermotropic LC. These active nematic emulsions exhibit a variety of dynamic behaviors that arise from the cross-talk between topological defects separately residing in the active and passive components. Using numerical simulations, we show a feedback mechanism by which active flows continuously drive the passive defects that, in response, resolve the otherwise degenerated trajectories of the active defects. Our experiments show that the choice of surfactant, which stabilizes the active/passive interface, allows tuning the regularity of the self-sustained dynamic events. The hybrid active-passive system demonstrated here provides new perspectives for dynamic self-assembly driven by an active material but regulated by the equilibrium properties of the passive component.

    更新日期:2018-04-07
  • Beyond triplet: Unconventional superconductivity in a spin-3/2 topological semimetal
    Sci. Adv. Pub Date : 2018-04-01
    Hyunsoo Kim, Kefeng Wang, Yasuyuki Nakajima, Rongwei Hu, Steven Ziemak, Paul Syers, Limin Wang, Halyna Hodovanets, Jonathan D. Denlinger, Philip M. R. Brydon, Daniel F. Agterberg, Makariy A. Tanatar, Ruslan Prozorov, Johnpierre Paglione

    In all known fermionic superfluids, Cooper pairs are composed of spin-1/2 quasi-particles that pair to form either spin-singlet or spin-triplet bound states. The “spin” of a Bloch electron, however, is fixed by the symmetries of the crystal and the atomic orbitals from which it is derived and, in some cases, can behave as if it were a spin-3/2 particle. The superconducting state of such a system allows pairing beyond spin-triplet, with higher spin quasi-particles combining to form quintet or septet pairs. We report evidence of unconventional superconductivity emerging from a spin-3/2 quasi-particle electronic structure in the half-Heusler semimetal YPtBi, a low-carrier density noncentrosymmetric cubic material with a high symmetry that preserves the p-like j = 3/2 manifold in the Bi-based Γ8 band in the presence of strong spin-orbit coupling. With a striking linear temperature dependence of the London penetration depth, the existence of line nodes in the superconducting order parameter Δ is directly explained by a mixed-parity Cooper pairing model with high total angular momentum, consistent with a high-spin fermionic superfluid state. We propose a k ⋅ p model of the j = 3/2 fermions to explain how a dominant J = 3 septet pairing state is the simplest solution that naturally produces nodes in the mixed even-odd parity gap. Together with the underlying topologically nontrivial band structure, the unconventional pairing in this system represents a truly novel form of superfluidity that has strong potential for leading the development of a new series of topological superconductors.

    更新日期:2018-04-07
  • Time-resolved structural evolution during the collapse of responsive hydrogels: The microgel-to-particle transition
    Sci. Adv. Pub Date : 2018-04-01
    Rico Keidel, Ali Ghavami, Dersy M. Lugo, Gudrun Lotze, Otto Virtanen, Peter Beumers, Jan Skov Pedersen, Andre Bardow, Roland G. Winkler, Walter Richtering

    Adaptive hydrogels, often termed smart materials, are macromolecules whose structure adjusts to external stimuli. Responsive micro- and nanogels are particularly interesting because the small length scale enables very fast response times. Chemical cross-links provide topological constraints and define the three-dimensional structure of the microgels, whereas their porous structure permits fast mass transfer, enabling very rapid structural adaption of the microgel to the environment. The change of microgel structure involves a unique transition from a flexible, swollen finite-size macromolecular network, characterized by a fuzzy surface, to a colloidal particle with homogeneous density and a sharp surface. In this contribution, we determine, for the first time, the structural evolution during the microgel-to-particle transition. Time-resolved small-angle x-ray scattering experiments and computer simulations unambiguously reveal a two-stage process: In a first, very fast process, collapsed clusters form at the periphery, leading to an intermediate, hollowish core-shell structure that slowly transforms to a globule. This structural evolution is independent of the type of stimulus and thus applies to instantaneous transitions as in a temperature jump or to slower stimuli that rely on the uptake of active molecules from and/or exchange with the environment. The fast transitions of size and shape provide unique opportunities for various applications as, for example, in uptake and release, catalysis, or sensing.

    更新日期:2018-04-07
  • Nonlinear fracture toughness measurement and crack propagation resistance of functionalized graphene multilayers
    Sci. Adv. Pub Date : 2018-04-01
    Changhong Cao, Sankha Mukherjee, Jane Y. Howe, Doug D. Perovic, Yu Sun, Chandra Veer Singh, Tobin Filleter

    Despite promising applications of two-dimensional (2D) materials, one major concern is their propensity to fail in a brittle manner, which results in a low fracture toughness causing reliability issues in practical applications. We show that this limitation can be overcome by using functionalized graphene multilayers with fracture toughness (J integral) as high as ~39 J/m2, measured via a microelectromechanical systems–based in situ transmission electron microscopy technique coupled with nonlinear finite element fracture analysis. The measured fracture toughness of functionalized graphene multilayers is more than two times higher than graphene (~16 J/m2). A linear fracture analysis, similar to that previously applied to other 2D materials, was also conducted and found to be inaccurate due to the nonlinear nature of the stress-strain response of functionalized graphene multilayers. A crack arresting mechanism of functionalized graphene multilayers was experimentally observed and identified as the main contributing factor for the higher fracture toughness as compared to graphene. Molecular dynamics simulations revealed that the interactions among functionalized atoms in constituent layers and distinct fracture pathways in individual layers, due to a random distribution of functionalized carbon atoms in multilayers, restrict the growth of a preexisting crack. The results inspire potential strategies for overcoming the relatively low fracture toughness of 2D materials through chemical functionalization.

    更新日期:2018-04-07
  • Stimuli-responsive and on-chip nanomembrane micro-rolls for enhanced macroscopic visual hydrogen detection
    Sci. Adv. Pub Date : 2018-04-01
    Borui Xu, Ziao Tian, Jiao Wang, Heetak Han, Taeyoon Lee, Yongfeng Mei

    Nanomembrane rolling offers advanced three-dimensional (3D) mesostructures in electronics, optics, and biomedical applications. We demonstrate a high-density and on-chip array of rolled-up nanomembrane actuators with stimuli-responsive function based on the volume expansion of palladium in hydrogen milieu. The uniform stimuli-responsive behavior of high-density nanomembrane rolls leads to huge macroscopic visual detection with more than 50% transmittance change under optimization of micropattern design. The reversible shape changing between rolled and flat (unrolled) statuses can be well explained on the basis of the elastic mechanical model. The strain change in the palladium layer during hydrogen absorption and desorption produces a marked change in the diameter of nanomembrane rolls. We found that a functional palladium layer established an external compressive strain after hydrogen stimuli and thus also reduced the rolls’ diameters. The large area of the nanomembrane roll array performs excellent nonelectrical hydrogen detection, with response and recovery speeds within seconds. Our work suggests a new strategy to integrate high-density 3D mesoscale architectures into functional devices and systems.

    更新日期:2018-04-07
  • Inducing ferromagnetism and Kondo effect in platinum by paramagnetic ionic gating
    Sci. Adv. Pub Date : 2018-04-01
    Lei Liang, Qihong Chen, Jianming Lu, Wytse Talsma, Juan Shan, Graeme R. Blake, Thomas T. M. Palstra, Jianting Ye

    Electrically controllable magnetism, which requires the field-effect manipulation of both charge and spin degrees of freedom, has attracted growing interest since the emergence of spintronics. We report the reversible electrical switching of ferromagnetic (FM) states in platinum (Pt) thin films by introducing paramagnetic ionic liquid (PIL) as the gating media. The paramagnetic ionic gating controls the movement of ions with magnetic moments, which induces itinerant ferromagnetism on the surface of Pt films, with large coercivity and perpendicular anisotropy mimicking the ideal two-dimensional Ising-type FM state. The electrical transport of the induced FM state shows Kondo effect at low temperature, suggesting spatially separated coexistence of Kondo scattering beneath the FM interface. The tunable FM state indicates that paramagnetic ionic gating could serve as a versatile method to induce rich transport phenomena combining field effect and magnetism at PIL-gated interfaces.

    更新日期:2018-04-07
  • Light-sheet microscopy with attenuation-compensated propagation-invariant beams
    Sci. Adv. Pub Date : 2018-04-01
    Jonathan Nylk, Kaley McCluskey, Miguel A. Preciado, Michael Mazilu, Zhengyi Yang, Frank J. Gunn-Moore, Sanya Aggarwal, Javier A. Tello, David E. K. Ferrier, Kishan Dholakia

    Scattering and absorption limit the penetration of optical fields into tissue. We demonstrate a new approach for increased depth penetration in light-sheet microscopy: attenuation-compensation of the light field. This tailors an exponential intensity increase along the illuminating propagation-invariant field, enabling the redistribution of intensity strategically within a sample to maximize signal and minimize irradiation. A key attribute of this method is that only minimal knowledge of the specimen transmission properties is required. We numerically quantify the imaging capabilities of attenuation-compensated Airy and Bessel light sheets, showing that increased depth penetration is gained without compromising any other beam attributes. This powerful yet straightforward concept, combined with the self-healing properties of the propagation-invariant field, improves the contrast-to-noise ratio of light-sheet microscopy up to eightfold across the entire field of view in thick biological specimens. This improvement can significantly increase the imaging capabilities of light-sheet microscopy techniques using Airy, Bessel, and other propagation-invariant beam types, paving the way for widespread uptake by the biomedical community.

    更新日期:2018-04-07
  • Near-infrared light–responsive dynamic wrinkle patterns
    Sci. Adv. Pub Date : 2018-04-01
    Fudong Li, Honghao Hou, Jie Yin, Xuesong Jiang

    Dynamic micro/nanopatterns provide an effective approach for on-demand tuning of surface properties to realize a smart surface. We report a simple yet versatile strategy for the fabrication of near-infrared (NIR) light–responsive dynamic wrinkles by using a carbon nanotube (CNT)–containing poly(dimethylsiloxane) (PDMS) elastomer as the substrate for the bilayer systems, with various functional polymers serving as the top stiff layers. The high photon-to-thermal energy conversion of CNT leads to the NIR-controlled thermal expansion of the elastic CNT-PDMS substrate, resulting in dynamic regulation of the applied strain (ε) of the bilayer system by the NIR on/off cycle to obtain a reversible wrinkle pattern. The switchable surface topological structures can transfer between the wrinkled state and the wrinkle-free state within tens of seconds via NIR irradiation. As a proof-of-concept application, this type of NIR-driven dynamic wrinkle pattern was used in smart displays, dynamic gratings, and light control electronics.

    更新日期:2018-04-07
  • Mechanism of the 2015 volcanic tsunami earthquake near Torishima, Japan
    Sci. Adv. Pub Date : 2018-04-01
    Yoshio Fukao, Osamu Sandanbata, Hiroko Sugioka, Aki Ito, Hajime Shiobara, Shingo Watada, Kenji Satake

    Tsunami earthquakes are a group of enigmatic earthquakes generating disproportionally large tsunamis relative to seismic magnitude. These events occur most typically near deep-sea trenches. Tsunami earthquakes occurring approximately every 10 years near Torishima on the Izu-Bonin arc are another example. Seismic and tsunami waves from the 2015 event [Mw (moment magnitude) = 5.7] were recorded by an offshore seafloor array of 10 pressure gauges, ~100 km away from the epicenter. We made an array analysis of dispersive tsunamis to locate the tsunami source within the submarine Smith Caldera. The tsunami simulation from a large caldera-floor uplift of ~1.5 m with a small peripheral depression yielded waveforms remarkably similar to the observations. The estimated central uplift, 1.5 m, is ~20 times larger than that inferred from the seismologically determined non–double-couple source. Thus, the tsunami observation is not compatible with the published seismic source model taken at face value. However, given the indeterminacy of Mzx, Mzy, and M{tensile} of a shallow moment tensor source, it may be possible to find a source mechanism with efficient tsunami but inefficient seismic radiation that can satisfactorily explain both the tsunami and seismic observations, but this question remains unresolved.

    更新日期:2018-04-05
  • Bioinspired polarization vision enables underwater geolocalization
    Sci. Adv. Pub Date : 2018-04-01
    Samuel B. Powell, Roman Garnett, Justin Marshall, Charbel Rizk, Viktor Gruev

    With its never-ending blue color, the underwater environment often seems monotonic and featureless. However, to an animal with polarization-sensitive vision, it is anything but bland. The rich repertoire of underwater polarization patterns—a consequence of light’s air-to-water transmission and in-water scattering—can be exploited both as a compass and for geolocalization purposes. We demonstrate that, by using a bioinspired polarization-sensitive imager, we can determine the geolocation of an observer based on radial underwater polarization patterns. Our experimental data, recorded at various locations around the world, at different depths and times of day, indicate that the average accuracy of our geolocalization is 61 km, or 6 m of error for every 1 km traveled. This proof-of-concept study of our bioinspired technique opens new possibilities in long-distance underwater navigation and suggests additional mechanisms by which marine animals with polarization-sensitive vision might perform both local and long-distance navigation.

    更新日期:2018-04-05
  • Geoelectrochemical CO production: Implications for the autotrophic origin of life
    Sci. Adv. Pub Date : 2018-04-01
    Norio Kitadai, Ryuhei Nakamura, Masahiro Yamamoto, Ken Takai, Yamei Li, Akira Yamaguchi, Alexis Gilbert, Yuichiro Ueno, Naohiro Yoshida, Yoshi Oono

    Wächtershäuser’s proposal of the autotrophic origin of life theory and subsequent laboratory demonstrations of relevant organic reactions have opened a new gate for the exploration of the origin of life. However, this scenario remains controversial because, at present, it requires a high pressure of CO as a source of carbon and reducing energy, although CO must have been a trace C species on the Hadean Earth. We show that, simulating a geoelectrochemical environment in deep-sea hydrothermal fields, CO production with up to ~40% Faraday efficiency was attainable on CdS in CO2-saturated NaCl solution at ≤–1 V (versus the standard hydrogen electrode). The threshold potential is readily generated in the H2-rich, high-temperature, and alkaline hydrothermal vents that were probably widespread on the early komatiitic and basaltic ocean crust. Thus, Wächtershäuser’s scenario starting from CO2 was likely to be realized in the Hadean ocean hydrothermal systems.

    更新日期:2018-04-05
  • Organic fertilizer as a vehicle for the entry of microplastic into the environment
    Sci. Adv. Pub Date : 2018-04-01
    Nicolas Weithmann, Julia N. Möller, Martin G. J. Löder, Sarah Piehl, Christian Laforsch, Ruth Freitag

    The contamination of the environment with microplastic, defined as particles smaller than 5 mm, has emerged as a global challenge because it may pose risks to biota and public health. Current research focuses predominantly on aquatic systems, whereas comparatively little is known regarding the sources, pathways, and possible accumulation of plastic particles in terrestrial ecosystems. We investigated the potential of organic fertilizers from biowaste fermentation and composting as an entry path for microplastic particles into the environment. Particles were classified by size and identified by attenuated total reflection-Fourier transform infrared spectroscopy. All fertilizer samples from plants converting biowaste contained plastic particles, but amounts differed significantly with substrate pretreatment, plant, and waste (for example, household versus commerce) type. In contrast, digestates from agricultural energy crop digesters tested for comparison contained only isolated particles, if any. Among the most abundant synthetic polymers observed were those used for common consumer products. Our results indicate that depending on pretreatment, organic fertilizers from biowaste fermentation and composting, as applied in agriculture and gardening worldwide, are a neglected source of microplastic in the environment.

    更新日期:2018-04-05
  • Whole-genome sequencing of the blue whale and other rorquals finds signatures for introgressive gene flow
    Sci. Adv. Pub Date : 2018-04-01
    Úlfur Árnason, Fritjof Lammers, Vikas Kumar, Maria A. Nilsson, Axel Janke

    Reconstructing the evolution of baleen whales (Mysticeti) has been problematic because morphological and genetic analyses have produced different scenarios. This might be caused by genomic admixture that may have taken place among some rorquals. We present the genomes of six whales, including the blue whale (Balaenoptera musculus), to reconstruct a species tree of baleen whales and to identify phylogenetic conflicts. Evolutionary multilocus analyses of 34,192 genome fragments reveal a fast radiation of rorquals at 10.5 to 7.5 million years ago coinciding with oceanic circulation shifts. The evolutionarily enigmatic gray whale (Eschrichtius robustus) is placed among rorquals, and the blue whale genome shows a high degree of heterozygosity. The nearly equal frequency of conflicting gene trees suggests that speciation of rorqual evolution occurred under gene flow, which is best depicted by evolutionary networks. Especially in marine environments, sympatric speciation might be common; our results raise questions about how genetic divergence can be established.

    更新日期:2018-04-05
  • Improved de novo genomic assembly for the domestic donkey
    Sci. Adv. Pub Date : 2018-04-01
    Gabriel Renaud, Bent Petersen, Andaine Seguin-Orlando, Mads Frost Bertelsen, Andrew Waller, Richard Newton, Romain Paillot, Neil Bryant, Mark Vaudin, Pablo Librado, Ludovic Orlando

    Donkeys and horses share a common ancestor dating back to about 4 million years ago. Although a high-quality genome assembly at the chromosomal level is available for the horse, current assemblies available for the donkey are limited to moderately sized scaffolds. The absence of a better-quality assembly for the donkey has hampered studies involving the characterization of patterns of genetic variation at the genome-wide scale. These range from the application of genomic tools to selective breeding and conservation to the more fundamental characterization of the genomic loci underlying speciation and domestication. We present a new high-quality donkey genome assembly obtained using the Chicago HiRise assembly technology, providing scaffolds of subchromosomal size. We make use of this new assembly to obtain more accurate measures of heterozygosity for equine species other than the horse, both genome-wide and locally, and to detect runs of homozygosity potentially pertaining to positive selection in domestic donkeys. Finally, this new assembly allowed us to identify fine-scale chromosomal rearrangements between the horse and the donkey that likely played an active role in their divergence and, ultimately, speciation.

    更新日期:2018-04-05
  • Implantation of hyaluronic acid hydrogel prevents the pain phenotype in a rat model of intervertebral disc injury
    Sci. Adv. Pub Date : 2018-04-01
    Isma Liza Mohd Isa, Sunny A. Abbah, Michelle Kilcoyne, Daisuke Sakai, Peter Dockery, David P. Finn, Abhay Pandit

    Painful intervertebral disc degeneration is mediated by inflammation that modulates glycosylation and induces hyperinnervation and sensory sensitization, which result in discogenic pain. Hyaluronic acid (HA) used as a therapeutic biomaterial can reduce inflammation and pain, but the effects of HA therapy on glycosylation and pain associated with disc degeneration have not been previously determined. We describe a novel rat model of pain induced by intervertebral disc injury, with validation of the pain phenotype by morphine treatment. Using this model, we assessed the efficacy of HA hydrogel for the alleviation of pain, demonstrating that it reduced nociceptive behavior, an effect associated with down-regulation of nociception markers and inhibition of hyperinnervation. Furthermore, HA hydrogel altered glycosylation and modulated key inflammatory and regulatory signaling pathways, resulting in attenuation of inflammation and regulation of matrix components. Our results suggest that HA hydrogel is a promising clinical candidate for the treatment of back pain caused by degenerated discs.

    更新日期:2018-04-05
  • Differences in extinction rates drove modern biogeographic patterns of tropical marine biodiversity
    Sci. Adv. Pub Date : 2018-04-01
    Emanuela Di Martino, Jeremy B. C. Jackson, Paul D. Taylor, Kenneth G. Johnson

    Marine biodiversity in the Coral Triangle is several times higher than anywhere else, but why this is true is unknown because of poor historical data. To address this, we compared the first available record of fossil cheilostome bryozoans from Indonesia with the previously sampled excellent record from the Caribbean. These two regions differ several-fold in species richness today, but cheilostome diversity was strikingly similar until the end of the Miocene 5.3 million years ago so that the modern disparity must have developed more recently. However, the Miocene faunas were ecologically very different, with a greater proportion of erect and free-living species in the Caribbean compared to the less well-known Coral Triangle. Our results support the hypothesis that modern differences in diversity arose primarily from differential extinction of Caribbean erect and free-living species concomitant with oceanographic changes due to the uplift of the Isthmus of Panama, rather than exceptional rates of diversification in the Indo-Pacific.

    更新日期:2018-04-05
  • BIG1/Arfgef1 and Arf1 regulate the initiation of myelination by Schwann cells in mice
    Sci. Adv. Pub Date : 2018-04-01
    Yuki Miyamoto, Tomohiro Torii, Kenji Tago, Akito Tanoue, Shou Takashima, Junji Yamauchi

    During development of the peripheral nervous system in mammals, Schwann cells wrap their plasma membranes around neuronal axons, forming multiple myelin sheaths. A mature myelin sheath insulates axons and increases nerve conduction velocity while protecting nerve fibers from various stresses such as physical ones. Despite this functional importance, the molecular units that underlie dynamic morphological changes in formation of myelin sheaths are not sufficiently understood. Arf1 is a small guanosine triphosphate–binding protein that plays multiple roles in intracellular trafficking and related signaling, both of which are processes involved in cell morphogenesis. We demonstrate that the Arf1 guanine nucleotide exchange factor, brefeldin A–inhibited guanine nucleotide-exchange protein 1 (BIG1)/Arfgef1, and the effector Arf1 regulate the initiation of myelination of axons by Schwann cells. Schwann cell–specific BIG1 conditional knockout mice, which have been generated here, exhibit reduced myelin thickness and decreased localization of myelin protein zero in the myelin membrane, compared with their littermate controls. BIG1 knockout mouse nerves specifically decrease the amounts of Arf1 in the AP1 clathrin adaptor protein subunits but not the Arf1 binding to GGA1 (Golgi-localized, gamma-adaptin ear-containing, Arf-binding protein 1) transporting proteins. The amounts of Arf1 in the COPI coatomer protein subunits were comparable in the knockout mice and controls. Similar results in myelin thickness are observed in Arf1 conditional knockout mice, which have also been generated here. Thus, the BIG1 and Arf1 unit plays a key role in Schwann cell myelination, newly adding it to the list of molecular units controlling myelination.

    更新日期:2018-04-05
  • A low-barrier hydrogen bond mediates antibiotic resistance in a noncanonical catalytic triad
    Sci. Adv. Pub Date : 2018-04-01
    Prashasti Kumar, Engin H. Serpersu, Matthew J. Cuneo

    One group of enzymes that confer resistance to aminoglycoside antibiotics through covalent modification belongs to the GCN5-related N-acetyltransferase (GNAT) superfamily. We show how a unique GNAT subfamily member uses a previously unidentified noncanonical catalytic triad, consisting of a glutamic acid, a histidine, and the antibiotic substrate itself, which acts as a nucleophile and attacks the acetyl donor molecule. Neutron diffraction studies allow for unambiguous identification of a low-barrier hydrogen bond, predicted in canonical catalytic triads to increase basicity of the histidine. This work highlights the role of this unique catalytic triad in mediating antibiotic resistance while providing new insights into the design of the next generation of aminoglycosides.

    更新日期:2018-04-05
  • Nonequilibrium optical control of dynamical states in superconducting nanowire circuits
    Sci. Adv. Pub Date : 2018-03-01
    Ivan Madan, Jože Buh, Vladimir V. Baranov, Viktor V. Kabanov, Aleš Mrzel, Dragan Mihailovic

    Optical control of states exhibiting macroscopic phase coherence in condensed matter systems opens intriguing possibilities for materials and device engineering, including optically controlled qubits and photoinduced superconductivity. Metastable states, which in bulk materials are often associated with the formation of topological defects, are of more practical interest. Scaling to nanosize leads to reduced dimensionality, fundamentally changing the system’s properties. In one-dimensional superconducting nanowires, vortices that are present in three-dimensional systems are replaced by fluctuating topological defects of the phase. These drastically change the dynamical behavior of the superconductor and introduce dynamical periodic long-range ordered states when the current is driven through the wire. We report the control and manipulation of transitions between different dynamically stable states in superconducting δ3-MoN nanowire circuits by ultrashort laser pulses. Not only can the transitions between different dynamically stable states be precisely controlled by light, but we also discovered new photoinduced hidden states that cannot be reached under near-equilibrium conditions, created while laser photoexcited quasi-particles are outside the equilibrium condition. The observed switching behavior can be understood in terms of dynamical stabilization of various spatiotemporal periodic trajectories of the order parameter in the superconductor nanowire, providing means for the optical control of the superconducting phase with subpicosecond control of timing.

    更新日期:2018-03-31
  • Electrically tunable single- and few-layer MoS2 nanoelectromechanical systems with broad dynamic range
    Sci. Adv. Pub Date : 2018-03-01
    Jaesung Lee, Zenghui Wang, Keliang He, Rui Yang, Jie Shan, Philip X.-L. Feng

    Atomically thin semiconducting crystals [such as molybdenum disulfide (MoS2)] have outstanding electrical, optical, and mechanical properties, thus making them excellent constitutive materials for innovating new two-dimensional (2D) nanoelectromechanical systems (NEMS). Although prototype structures have recently been demonstrated toward functional devices such as ultralow-power, high-frequency tunable oscillators and ultrasensitive resonant transducers, both electrical tunability and large dynamic range (DR) are critical and desirable. We report the first experimental demonstration of clearly defined single-, bi-, and trilayer MoS2 2D resonant NEMS operating in the very high frequency band (up to ~120 MHz) with outstanding electrical tunability and DR. Through deterministic measurement and calibration, we discover that these 2D atomic layer devices have remarkably broad DR (up to ~70 to 110 dB), in contrast to their 1D NEMS counterparts that are expected to have limited DR. These 2D devices, therefore, open avenues for efficiently tuning and strongly coupling the electronic, mechanical, and optical properties in atomic layer semiconducting devices and systems.

    更新日期:2018-03-31
  • Poro-elasto-capillary wicking of cellulose sponges
    Sci. Adv. Pub Date : 2018-03-01
    Jonghyun Ha, Jungchul Kim, Yeonsu Jung, Giseok Yun, Do-Nyun Kim, Ho-Young Kim

    We mundanely observe cellulose (kitchen) sponges swell while absorbing water. Fluid flows in deformable porous media, such as soils and hydrogels, are classically described on the basis of the theories of Darcy and poroelasticity, where the expansion of media arises due to increased pore pressure. However, the situation is qualitatively different in cellulosic porous materials like sponges because the pore expansion is driven by wetting of the surrounding cellulose walls rather than by increase of the internal pore pressure. We address a seemingly so simple but hitherto unanswered question of how fast water wicks into the swelling sponge. Our experiments uncover a power law of the wicking height versus time distinct from that for nonswelling materials. The observation using environmental scanning electron microscopy reveals the coalescence of microscale wall pores with wetting, which allows us to build a mathematical model for pore size evolution and the consequent wicking dynamics. Our study sheds light on the physics of water absorption in hygroscopically responsive multiscale porous materials, which have far more implications than everyday activities (for example, cleaning, writing, and painting) carried out with cellulosic materials (paper and sponge), including absorbent hygiene products, biomedical cell cultures, building safety, and cooking.

    更新日期:2018-03-31
  • Machine learning–enabled identification of material phase transitions based on experimental data: Exploring collective dynamics in ferroelectric relaxors
    Sci. Adv. Pub Date : 2018-03-01
    Linglong Li, Yaodong Yang, Dawei Zhang, Zuo-Guang Ye, Stephen Jesse, Sergei V. Kalinin, Rama K. Vasudevan

    Exploration of phase transitions and construction of associated phase diagrams are of fundamental importance for condensed matter physics and materials science alike, and remain the focus of extensive research for both theoretical and experimental studies. For the latter, comprehensive studies involving scattering, thermodynamics, and modeling are typically required. We present a new approach to data mining multiple realizations of collective dynamics, measured through piezoelectric relaxation studies, to identify the onset of a structural phase transition in nanometer-scale volumes, that is, the probed volume of an atomic force microscope tip. Machine learning is used to analyze the multidimensional data sets describing relaxation to voltage and thermal stimuli, producing the temperature-bias phase diagram for a relaxor crystal without the need to measure (or know) the order parameter. The suitability of the approach to determine the phase diagram is shown with simulations based on a two-dimensional Ising model. These results indicate that machine learning approaches can be used to determine phase transitions in ferroelectrics, providing a general, statistically significant, and robust approach toward determining the presence of critical regimes and phase boundaries.

    更新日期:2018-03-31
  • Hydrophilic directional slippery rough surfaces for water harvesting
    Sci. Adv. Pub Date : 2018-03-01
    Xianming Dai, Nan Sun, Steven O. Nielsen, Birgitt Boschitsch Stogin, Jing Wang, Shikuan Yang, Tak-Sing Wong

    Multifunctional surfaces that are favorable for both droplet nucleation and removal are highly desirable for water harvesting applications but are rare. Inspired by the unique functions of pitcher plants and rice leaves, we present a hydrophilic directional slippery rough surface (SRS) that is capable of rapidly nucleating and removing water droplets. Our surfaces consist of nanotextured directional microgrooves in which the nanotextures alone are infused with hydrophilic liquid lubricant. We have shown through molecular dynamics simulations that the physical origin of the efficient droplet nucleation is attributed to the hydrophilic surface functional groups, whereas the rapid droplet removal is due to the significantly reduced droplet pinning of the directional surface structures and slippery interface. We have further demonstrated that the SRS, owing to its large surface area, hydrophilic slippery interface, and directional liquid repellency, outperforms conventional liquid-repellent surfaces in water harvesting applications.

    更新日期:2018-03-31
  • Molecular engineered conjugated polymer with high thermal conductivity
    Sci. Adv. Pub Date : 2018-03-01
    Yanfei Xu, Xiaoxue Wang, Jiawei Zhou, Bai Song, Zhang Jiang, Elizabeth M. Y. Lee, Samuel Huberman, Karen K. Gleason, Gang Chen

    Traditional polymers are both electrically and thermally insulating. The development of electrically conductive polymers has led to novel applications such as flexible displays, solar cells, and wearable biosensors. As in the case of electrically conductive polymers, the development of polymers with high thermal conductivity would open up a range of applications in next-generation electronic, optoelectronic, and energy devices. Current research has so far been limited to engineering polymers either by strong intramolecular interactions, which enable efficient phonon transport along the polymer chains, or by strong intermolecular interactions, which enable efficient phonon transport between the polymer chains. However, it has not been possible until now to engineer both interactions simultaneously. We report the first realization of high thermal conductivity in the thin film of a conjugated polymer, poly(3-hexylthiophene), via bottom-up oxidative chemical vapor deposition (oCVD), taking advantage of both strong C=C covalent bonding along the extended polymer chain and strong π-π stacking noncovalent interactions between chains. We confirm the presence of both types of interactions by systematic structural characterization, achieving a near–room temperature thermal conductivity of 2.2 W/m·K, which is 10 times higher than that of conventional polymers. With the solvent-free oCVD technique, it is now possible to grow polymer films conformally on a variety of substrates as lightweight, flexible heat conductors that are also electrically insulating and resistant to corrosion.

    更新日期:2018-03-31
  • Nanostructure, osteopontin, and mechanical properties of calcitic avian eggshell
    Sci. Adv. Pub Date : 2018-03-01
    Dimitra Athanasiadou, Wenge Jiang, Dina Goldbaum, Aroba Saleem, Kaustuv Basu, Michael S. Pacella, Corinna F. Böhm, Richard R. Chromik, Maxwell T. Hincke, Alejandro B. Rodríguez-Navarro, Hojatollah Vali, Stephan E. Wolf, Jeffrey J. Gray, Khanh Huy Bui, Marc D. McKee

    Avian (and formerly dinosaur) eggshells form a hard, protective biomineralized chamber for embryonic growth—an evolutionary strategy that has existed for hundreds of millions of years. We show in the calcitic chicken eggshell how the mineral and organic phases organize hierarchically across different length scales and how variation in nanostructure across the shell thickness modifies its hardness, elastic modulus, and dissolution properties. We also show that the nanostructure changes during egg incubation, weakening the shell for chick hatching. Nanostructure and increased hardness were reproduced in synthetic calcite crystals grown in the presence of the prominent eggshell protein osteopontin. These results demonstrate the contribution of nanostructure to avian eggshell formation, mechanical properties, and dissolution.

    更新日期:2018-03-31
  • Shaken and stirred: Random organization reduces viscosity and dissipation in granular suspensions
    Sci. Adv. Pub Date : 2018-03-01
    Christopher Ness, Romain Mari, Michael E. Cates

    The viscosity of suspensions of large (≥10 μm) particles diverges at high solid fractions due to proliferation of frictional particle contacts. Reducing friction, to allow or improve flowability, is usually achieved by tuning the composition, either by changing particle sizes and shapes or by adding lubricating molecules. We present numerical simulations that demonstrate a complementary approach whereby the viscosity divergence is shifted by driven flow tuning, using superimposed shear oscillations in various configurations to facilitate a primary flow. The oscillations drive the suspension toward an out-of-equilibrium, absorbing state phase transition, where frictional particle contacts that dominate the viscosity are reduced in a self-organizing manner. The method can allow otherwise jammed states to flow; even for unjammed states, it can substantially decrease the energy dissipated per unit strain. This creates a practicable route to flow enhancement across a broad range of suspensions where compositional tuning is undesirable or problematic.

    更新日期:2018-03-31
  • Room temperature solid-state quantum emitters in the telecom range
    Sci. Adv. Pub Date : 2018-03-01
    Yu Zhou, Ziyu Wang, Abdullah Rasmita, Sejeong Kim, Amanuel Berhane, Zoltán Bodrog, Giorgio Adamo, Adam Gali, Igor Aharonovich, Wei-bo Gao

    On-demand, single-photon emitters (SPEs) play a key role across a broad range of quantum technologies. In quantum networks and quantum key distribution protocols, where photons are used as flying qubits, telecom wavelength operation is preferred because of the reduced fiber loss. However, despite the tremendous efforts to develop various triggered SPE platforms, a robust source of triggered SPEs operating at room temperature and the telecom wavelength is still missing. We report a triggered, optically stable, room temperature solid-state SPE operating at telecom wavelengths. The emitters exhibit high photon purity (~5% multiphoton events) and a record-high brightness of ~1.5 MHz. The emission is attributed to localized defects in a gallium nitride (GaN) crystal. The high-performance SPEs embedded in a technologically mature semiconductor are promising for on-chip quantum simulators and practical quantum communication technologies.

    更新日期:2018-03-31
  • Highly efficient electrochemical reforming of CH4/CO2 in a solid oxide electrolyser
    Sci. Adv. Pub Date : 2018-03-01
    Jinhai Lu, Changli Zhu, Changchang Pan, Wenlie Lin, John P. Lemmon, Fanglin Chen, Chunsen Li, Kui Xie

    Reforming CH4 into syngas using CO2 remains a fundamental challenge due to carbon deposition and nanocatalyst instability. We, for the first time, demonstrate highly efficient electrochemical reforming of CH4/CO2 to produce syngas in a solid oxide electrolyser with CO2 electrolysis in the cathode and CH4 oxidation in the anode. In situ exsolution of an anchored metal/oxide interface on perovskite electrode delivers remarkably enhanced coking resistance and catalyst stability. In situ Fourier transform infrared characterizations combined with first principle calculations disclose the interface activation of CO2 at a transition state between a CO2 molecule and a carbonate ion. Carbon removal at the interfaces is highly favorable with electrochemically provided oxygen species, even in the presence of H2 or H2O. This novel strategy provides optimal performance with no obvious degradation after 300 hours of high-temperature operation and 10 redox cycles, suggesting a reliable process for conversion of CH4 into syngas using CO2.

    更新日期:2018-03-31
  • Giant perpendicular magnetic anisotropy in Fe/III-V nitride thin films
    Sci. Adv. Pub Date : 2018-03-01
    Jie-Xiang Yu, Jiadong Zang

    Large perpendicular magnetic anisotropy (PMA) in transition metal thin films provides a pathway for enabling the intriguing physics of nanomagnetism and developing broad spintronics applications. After decades of searches for promising materials, the energy scale of PMA of transition metal thin films, unfortunately, remains only about 1 meV. This limitation has become a major bottleneck in the development of ultradense storage and memory devices. We discovered unprecedented PMA in Fe thin-film growth on the N-terminated surface of III-V nitrides from first-principles calculations. PMA ranges from 24.1 meV/u.c. in Fe/BN to 53.7 meV/u.c. in Fe/InN. Symmetry-protected degeneracy between x2 − y2 and xy orbitals and its lift by the spin-orbit coupling play a dominant role. As a consequence, PMA in Fe/III-V nitride thin films is dominated by first-order perturbation of the spin-orbit coupling, instead of second-order in conventional transition metal/oxide thin films. This game-changing scenario would also open a new field of magnetism on transition metal/nitride interfaces.

    更新日期:2018-03-31
  • Submesoscale Rossby waves on the Antarctic circumpolar current
    Sci. Adv. Pub Date : 2018-03-01
    John R. Taylor, Scott Bachman, Megan Stamper, Phil Hosegood, Katherine Adams, Jean-Baptiste Sallee, Ricardo Torres

    The eastward-flowing Antarctic circumpolar current (ACC) plays a central role in the global ocean overturning circulation and facilitates the exchange of water between the ocean surface and interior. Submesoscale eddies and fronts with scales between 1 and 10 km are regularly observed in the upper ocean and are associated with strong vertical circulations and enhanced stratification. Despite their importance in other locations, comparatively little is known about submesoscales in the Southern Ocean. We present results from new observations, models, and theories showing that submesoscales are qualitatively changed by the strong jet associated with the ACC in the Scotia Sea, east of Drake Passage. Growing submesoscale disturbances develop along a dense filament and are transformed into submesoscale Rossby waves, which propagate upstream relative to the eastward jet. Unlike their counterparts in slower currents, the submesoscale Rossby waves do not destroy the underlying frontal structure. The development of submesoscale instabilities leads to strong net subduction of water associated with a dense outcropping filament, and later, the submesoscale Rossby waves are associated with intense vertical circulations.

    更新日期:2018-03-29
  • Universal characteristics of particle shape evolution by bed-load chipping
    Sci. Adv. Pub Date : 2018-03-01
    Tímea Novák-Szabó, András Árpád Sipos, Sam Shaw, Duccio Bertoni, Alessandro Pozzebon, Edoardo Grottoli, Giovanni Sarti, Paolo Ciavola, Gábor Domokos, Douglas J. Jerolmack

    River currents, wind, and waves drive bed-load transport, in which sediment particles collide with each other and Earth’s surface. A generic consequence is impact attrition and rounding of particles as a result of chipping, often referred to in geological literature as abrasion. Recent studies have shown that the rounding of river pebbles can be modeled as diffusion of surface curvature, indicating that geometric aspects of impact attrition are insensitive to details of collisions and material properties. We present data from fluvial, aeolian, and coastal environments and laboratory experiments that suggest a common relation between circularity and mass attrition for particles transported as bed load. Theory and simulations demonstrate that universal characteristics of shape evolution arise because of three constraints: (i) Initial particles are mildly elongated fragments, (ii) particles collide with similarly-sized particles or the bed, and (iii) collision energy is small enough that chipping dominates over fragmentation but large enough that sliding friction is negligible. We show that bed-load transport selects these constraints, providing the foundation to estimate a particle’s attrition rate from its shape alone in most sedimentary environments. These findings may be used to determine the contribution of attrition to downstream fining in rivers and deserts and to infer transport conditions using only images of sediment grains.

    更新日期:2018-03-29
  • Oxygen isotopic evidence for accretion of Earth’s water before a high-energy Moon-forming giant impact
    Sci. Adv. Pub Date : 2018-03-01
    Richard C. Greenwood, Jean-Alix Barrat, Martin F. Miller, Mahesh Anand, Nicolas Dauphas, Ian A. Franchi, Patrick Sillard, Natalie A. Starkey

    The Earth-Moon system likely formed as a result of a collision between two large planetary objects. Debate about their relative masses, the impact energy involved, and the extent of isotopic homogenization continues. We present the results of a high-precision oxygen isotope study of an extensive suite of lunar and terrestrial samples. We demonstrate that lunar rocks and terrestrial basalts show a 3 to 4 ppm (parts per million), statistically resolvable, difference in Δ17O. Taking aubrite meteorites as a candidate impactor material, we show that the giant impact scenario involved nearly complete mixing between the target and impactor. Alternatively, the degree of similarity between the Δ17O values of the impactor and the proto-Earth must have been significantly closer than that between Earth and aubrites. If the Earth-Moon system evolved from an initially highly vaporized and isotopically homogenized state, as indicated by recent dynamical models, then the terrestrial basalt-lunar oxygen isotope difference detected by our study may be a reflection of post–giant impact additions to Earth. On the basis of this assumption, our data indicate that post–giant impact additions to Earth could have contributed between 5 and 30% of Earth’s water, depending on global water estimates. Consequently, our data indicate that the bulk of Earth’s water was accreted before the giant impact and not later, as often proposed.

    更新日期:2018-03-29
  • Saturation of charge-induced water alignment at model membrane surfaces
    Sci. Adv. Pub Date : 2018-03-01
    Lisa B. Dreier, Yuki Nagata, Helmut Lutz, Grazia Gonella, Johannes Hunger, Ellen H. G. Backus, Mischa Bonn

    The electrical charge of biological membranes and thus the resulting alignment of water molecules in response to this charge are important factors affecting membrane rigidity, transport, and reactivity. We tune the surface charge density by varying lipid composition and investigate the charge-induced alignment of water molecules using surface-specific vibrational spectroscopy and molecular dynamics simulations. At low charge densities, the alignment of water increases proportionally to the charge. However, already at moderate, physiologically relevant charge densities, water alignment starts to saturate despite the increase in the nominal surface charge. The saturation occurs in both the Stern layer, directly at the surface, and in the diffuse layer, yet for distinctly different reasons. Our results show that the soft nature of the lipid interface allows for a marked reduction of the surface potential at high surface charge density via both interfacial molecular rearrangement and permeation of monovalent ions into the interface.

    更新日期:2018-03-29
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
化学 • 材料 期刊列表