bluuebunny/crossref_metadata_2025_split huggingface dataset:
Heavy Ion Flows in the Upper Ionosphere of the Venusian North Pole
Authors: Persson M. , Futaana Y. , Nilsson H. , Stenberg Wieser G. , Hamrin M. , Fedorov A. , Zhang T. L. , Barabash S. 
Published: May 2019

AbstractWe investigate the heavy ion density and velocity in the Venusian upper ionosphere near the North Pole, using the Ion Mass Analyzer, a part of the Analyzer of Space Plasmas and Energetic Atoms 4, together with the magnetic field instruments on Venus Express. The measurements were made during June–July 2014, covering the aerobraking campaign with lowered altitude measurements (~130 km). The plasma scale heights are ~15 km below 150‐km altitude and ~200 km at 150–400‐km altitude. A clear trend of dusk‐to‐dawn heavy ion flow across the polar ionosphere was found, with speeds of ~2–10 km/s. In addition, the flow has a significant downward radial velocity component. The flow pattern does not depend on the interplanetary magnetic field directions nor the ionospheric magnetization states. Instead, we suggest a thermal pressure gradient between the equatorial and polar terminator regions, induced by the decrease in density between the regions, as the dominant mechanism driving the ion flow.
Effect of Digital Elevation Model Resolution on the Simulation of the Snow Cover Evolution in the High Atlas
Authors: Baba Mohamed Wassim , Gascoin Simon , Kinnard Christophe , Marchane Ahmed , Hanich Lahoucine 
Published: May 2019

AbstractThe snow melt from the High Atlas represents a crucial water resource for crop irrigation in the semiarid regions of Morocco. Recent studies have used assimilation of snow cover area data from high‐resolution optical sensors to compute the snow water equivalent and snow melt in other mountain regions. These techniques however require large model ensembles, and therefore it is a challenge to determine the adequate model resolution that yields accurate results with reasonable computation time. Here we study the sensitivity of an energy balance model to the resolution of the model grid for a pilot catchment in the High Atlas. We used a time series of 8‐m resolution snow cover area maps with an average revisit time of 7.5 days to evaluate the model results. The digital elevation model was generated from Pléiades stereo images and resampled from 8 to 30, 90, 250, 500, and 1,000 m. The results indicate that the model performs well from 8 to 250 m but the agreement with observations drops at 500 m. This is because significant features of the topography were too smoothed out to properly characterize the spatial variability of meteorological forcing, including solar radiation. We conclude that a resolution of 250 m might be sufficient in this area. This result is consistent with the shape of the semivariogram of the topographic slope, suggesting that this semivariogram analysis could be used to transpose our conclusion to other study regions.
Global and Regional Increase of Precipitation Extremes Under Global Warming
Authors: Papalexiou Simon Michael , Montanari Alberto 
Published: May 2019

AbstractGlobal warming is expected to change the regime of extreme precipitation. Physical laws translate increasing atmospheric heat into increasing atmospheric water content that drives precipitation changes. Within the literature, general agreement is that extreme precipitation is changing, yet different assessment methods, data sets, and study periods may result in different patterns and rates of change. Here we perform a global analysis of 8,730 daily precipitation records focusing on the 1964–2013 period when the global warming accelerates. We introduce a novel analysis of the N largest extremes in records having N complete years within the study period. Based on these extremes, which represent more accurately heavy precipitation than annual maxima, we form time series of their annual frequency and mean annual magnitude. The analysis offers new insights and reveals (1) global and zonal increasing trends in the frequency of extremes that are highly unlikely under the assumption of stationarity and (2) magnitude changes that are not as evident. Frequency changes reveal a coherent spatial pattern with increasing trends being detected in large parts of Eurasia, North Australia, and the Midwestern United States. Globally, over the last decade of the studied period we find 7% more extreme events than the expected number. Finally, we report that changes in magnitude are not in general correlated with changes in frequency.
Effect of Surface Water Stage Fluctuation on Mixing‐Dependent Hyporheic Denitrification in Riverbed Dunes
Authors: Hester Erich T. , Eastes Lauren A. , Widdowson Mark A. 
Published: May 2019

AbstractThe hyporheic zone, where surface water (SW) and groundwater (GW) interact in shallow sediments beneath rivers, is uniquely reactive and attenuates pollutants. Mixing of reactants from SW and GW enables mixing‐dependent (MD) reactions, which may be the last opportunity for GW contaminants to react before entering SW. Yet little is known about hyporheic MD reactions, particularly how they respond to daily or seasonal SW fluctuations or sediment heterogeneity. We used MODFLOW and SEAM3D to simulate non‐mixing‐dependent (NMD) aerobic respiration and MD denitrification in a riverbed dune with nitrate from SW and dissolved organic carbon from GW. We varied SW heads and heterogeneity of sediment hydraulic conductivity. For longer‐term fluctuations (i.e., seasons), increasing SW depth from 0.1 to 1.0 m increased NMD aerobic respiration by 270% and MD denitrification by 78% in homogeneous sediment. MD reactions thus were controlled by mixing zone length or size and would be stronger when SW stage is elevated, for example, during wintertime. Adding sediment heterogeneity to the long‐term scenarios, particularly by increasing hydraulic conductivity correlation length, increased flow focusing and consequently increased MD denitrification by 20–30%. By contrast, the net effect of daily SW fluctuations on MD denitrification in homogeneous sediment was minor. In sum, SW fluctuations are an important control on hyporheic MD reactions, primarily by controlling mixing zone length. The hyporheic zone may attenuate nitrate in upwelling GW plumes, but temporal fluctuations may be considerable as quantified above.
Paleosensitivity of Hydrogen Isotope Ratios of Long‐Chain Alkenones to Salinity Changes at the Chile Margin
Authors: Weiss G. M. , de Bar M. W. , Stolwijk D. J. , Schouten S. , Sinninghe Damsté J. S. , van der Meer M. T. J. 
Published: May 2019

AbstractHydrogen isotope ratios of long‐chain alkenones (δ2HC37 ratios) have been shown to correlate with salinity in several culture studies. However, it is uncertain how applicable the δ2HC37‐salinity relationship is to reconstruct past salinity. The δ2HC37 ratios were measured on sediments from a drill core (ODP site 1234) at the Chilean Margin covering the last ~150 kyr. High δ2HC37 values corresponded to glacial time periods and interglacial periods are characterized by lower δ2HC37 values, aligning with δ18O ratios measured on planktonic foraminifera from the same core. Effects of parameters such as species composition, the δ2H‐δ18O relationship used for ice volume corrections, and nutrient‐ or light‐controlled growth rate, did not appear to significantly alter δ2HC37 ratios at ODP 1234. We used linear regression equations from batch culture experiments, marine surface sediments, and suspended particulate organic matter to quantitatively characterize salinity changes over the last ~150 kyr at ODP 1234. However, most of these equations yielded larger salinity shifts than previously suggested, a phenomenon also observed for other δ2HC37 records. This suggests that the paleosensitivity of δ2HC37 ratios to salinity was larger in the geologic record than has been observed in any modern environment or laboratory settings, or that glacial to interglacial salinity shifts might have been larger than currently believed.
MicroRNA-181a-5p and microRNA-181a-3p cooperatively restrict vascular inflammation and atherosclerosis
Authors: Su Yingxue , Yuan Jiani , Zhang Feiran , Lei Qingqing , Zhang Tingting , Li Kai , Guo Jiawei , Hong Yu , Bu Guolong , Lv Xiaofei , Liang Sijia , Ou Jingsong , Zhou Jiaguo , Luo Bin , Shang Jinyan 
Published: May 2019

AbstractMicroRNAs have emerged as important post-transcriptional regulators of gene expression and are involved in diverse diseases and cellular process. Decreased expression of miR-181a has been observed in the patients with coronary artery disease, but its function and mechanism in atherogenesis is not clear. This study was designed to determine the roles of miR-181a-5p, as well as its passenger strand, miR-181a-3p, in vascular inflammation and atherogenesis. We found that the levels of both miR-181a-5p and miR-181a-3p are decreased in the aorta plaque and plasma of apoE−/− mice in response to hyperlipidemia and in the plasma of patients with coronary artery disease. Rescue of miR-181a-5p and miR-181a-3p significantly retards atherosclerotic plaque formation in apoE−/− mice. MiR-181a-5p and miR-181a-3p have no effect on lipid metabolism but decrease proinflammatory gene expression and the infiltration of macrophage, leukocyte and T cell into the lesions. In addition, gain-of-function and loss-of-function experiments show that miR-181a-5p and miR-181a-3p inhibit adhesion molecule expression in HUVECs and monocytes-endothelial cell interaction. MiR-181a-5p and miR-181a-3p cooperatively receded endothelium inflammation compared with single miRNA strand. Mechanistically, miR-181a-5p and miR-181a-3p prevent endothelial cell activation through blockade of NF-κB signaling pathway by targeting TAB2 and NEMO, respectively. In conclusion, these findings suggest that miR-181a-5p and miR-181a-3p are both antiatherogenic miRNAs. MiR-181a-5p and miR-181a-3p mimetics retard atherosclerosis progression through blocking NF-κB activation and vascular inflammation by targeting TAB2 and NEMO, respectively. Therefore, restoration of miR-181a-5p and miR-181a-3p may represent a novel therapeutic approach to manage atherosclerosis.
Self-healing materials for soft-matter machines and electronics
Authors: Bartlett Michael D. , Dickey Michael D. , Majidi Carmel 
Published: May 2019

AbstractThe emergence of soft machines and electronics creates new opportunities to engineer robotic systems that are mechanically compliant, deformable, and safe for physical interaction with the human body. Progress, however, depends on new classes of soft multifunctional materials that can operate outside of a hard exterior and withstand the same real-world conditions that human skin and other soft biological materials are typically subjected to. As with their natural counterparts, these materials must be capable of self-repair and healing when damaged to maintain the longevity of the host system and prevent sudden or permanent failure. Here, we provide a perspective on current trends and future opportunities in self-healing soft systems that enhance the durability, mechanical robustness, and longevity of soft-matter machines and electronics.
Extraordinarily transparent compact metallic metamaterials
Authors: Palmer Samuel J. , Xiao Xiaofei , Pazos-Perez Nicolas , Guerrini Luca , Correa-Duarte Miguel A. , Maier Stefan A. , Craster Richard V. , Alvarez-Puebla Ramon A. , Giannini Vincenzo 
Published: May 2019

AbstractThe design of achromatic optical components requires materials with high transparency and low dispersion. We show that although metals are highly opaque, densely packed arrays of metallic nanoparticles can be more transparent to infrared radiation than dielectrics such as germanium, even when the arrays are over 75% metal by volume. Such arrays form effective dielectrics that are virtually dispersion-free over ultra-broadband ranges of wavelengths from microns up to millimeters or more. Furthermore, the local refractive indices may be tuned by altering the size, shape, and spacing of the nanoparticles, allowing the design of gradient-index lenses that guide and focus light on the microscale. The electric field is also strongly concentrated in the gaps between the metallic nanoparticles, and the simultaneous focusing and squeezing of the electric field produces strong ‘doubly-enhanced’ hotspots which could boost measurements made using infrared spectroscopy and other non-linear processes over a broad range of frequencies.
Controlling CRISPR-Cas9 with ligand-activated and ligand-deactivated sgRNAs
Authors: Kundert Kale , Lucas James E. , Watters Kyle E. , Fellmann Christof , Ng Andrew H. , Heineike Benjamin M. , Fitzsimmons Christina M. , Oakes Benjamin L. , Qu Jiuxin , Prasad Neha , Rosenberg Oren S. , Savage David F. , El-Samad Hana , Doudna Jennifer A. , Kortemme Tanja 
Published: May 2019

AbstractThe CRISPR-Cas9 system provides the ability to edit, repress, activate, or mark any gene (or DNA element) by pairing of a programmable single guide RNA (sgRNA) with a complementary sequence on the DNA target. Here we present a new method for small-molecule control of CRISPR-Cas9 function through insertion of RNA aptamers into the sgRNA. We show that CRISPR-Cas9-based gene repression (CRISPRi) can be either activated or deactivated in a dose-dependent fashion over a >10-fold dynamic range in response to two different small-molecule ligands. Since our system acts directly on each target-specific sgRNA, it enables new applications that require differential and opposing temporal control of multiple genes.
Deep-ocean mixing driven by small-scale internal tides
Authors: Vic Clément , Naveira Garabato Alberto C. , Green J. A. Mattias , Waterhouse Amy F. , Zhao Zhongxiang , Melet Angélique , de Lavergne Casimir , Buijsman Maarten C. , Stephenson Gordon R. 
Published: May 2019

AbstractTurbulent mixing in the ocean is key to regulate the transport of heat, freshwater and biogeochemical tracers, with strong implications for Earth’s climate. In the deep ocean, tides supply much of the mechanical energy required to sustain mixing via the generation of internal waves, known as internal tides, whose fate—the relative importance of their local versus remote breaking into turbulence—remains uncertain. Here, we combine a semi-analytical model of internal tide generation with satellite and in situ measurements to show that from an energetic viewpoint, small-scale internal tides, hitherto overlooked, account for the bulk (>50%) of global internal tide generation, breaking and mixing. Furthermore, we unveil the pronounced geographical variations of their energy proportion, ignored by current parameterisations of mixing in climate-scale models. Based on these results, we propose a physically consistent, observationally supported approach to accurately represent the dissipation of small-scale internal tides and their induced mixing in climate-scale models.
Synthesis of an aromatic N-heterocycle derived from biomass and its use as a polymer feedstock
Authors: Qi Yu , Wang Jinyan , Kou Yan , Pang Hongchang , Zhang Shouhai , Li Nan , Liu Cheng , Weng Zhihuan , Jian Xigao 
Published: May 2019

AbstractAromatic N-heterocyclic compounds are very important chemicals, which are currently produced mostly from petroleum. Here we report that a pyridazine-based compound 6-(4-hydroxy-3-methoxyphenyl)pyridazin-3(2H)-one (GSPZ) can be efficiently synthesized by the Friedel-Crafts reaction of guaiacol and succinic anhydride, both of which can be derived from biomass. GSPZ is then treated with bio-based epichlorohydrin to prepare the epoxy resin precursor GSPZ-EP. With 4,4'-diaminodiphenylmethane as curing agent, GSPZ-EP possesses higher glass transition temperature (187 oC vs. 173 oC) and shows a 140%, 70 and 93% increase in char yield (in N2), storage modulus (30 oC) and Young’s modulus, respectively when compared with a standard petroleum-based bisphenol A epoxy resin. Moreover, the cured GSPZ-EP shows good intrinsic flame retardancy properties and is very close to the V-0 rating of UL-94 test. This work opens the door for production of aromatic N-heterocyclic compounds, which can be derived from biomass and employed to construct high performance polymers.
A database of atmospheric nitrogen concentration and deposition from the nationwide monitoring network in China
Authors: Xu Wen , Zhang Lin , Liu Xuejun 
Published: May 2019

AbstractAtmospheric nitrogen (N) deposition has increased substantially across China since 1980; however, data for N deposition fluxes since the 2000s has been very limited. Understanding and mitigating the impacts of N deposition requires long-term quantification of dry as well as wet deposition of key reactive nitrogen (Nr) species. Here we present a dataset for inorganic N concentrations and deposition for the period 2010–2015 in China, compiled from the nationwide deposition monitoring network. The dataset comprises information from 32 monitoring sites on concentrations and bulk deposition (wet plus part of dry deposition) fluxes of NH4+-N and NO3−-N, air concentrations and dry deposition fluxes of the major Nr species NH3, NO2, HNO3, and particulate NH4+ and NO3−. This unique database is available inter alia to advance understanding of the spatial patterns of inorganic N concentrations and deposition in China and its associated effects, constrain primary Nr (e.g., NH3, NOx) emission inventories, and validate outputs of atmospheric chemistry and transport models.
Essential Mycoplasma Glycolipid Synthase Adheres to the Cell Membrane by Means of an Amphipathic Helix
Authors: Romero-García Javier , Biarnés Xevi , Planas Antoni 
Published: May 2019

AbstractBecause of the lack of cell wall, Micoplasma species require a fine control of membrane fluidity and integrity. mg517 is an essential gene of Mycoplasma genitalium responsible for the biosynthesis of membrane glycoglycerolipids. It encodes for a unique glycosyltransferase (MG517) with processive activity, transferring activated glycosyl donors to either nude diacylglycerol or already glycosylated diacylglycerol. This dual activity, asserted to different enzymes in other species, is sensitive to and regulated by the presence of anionic lipid vesicles in vitro. We present here a computational model of the C-terminus domain of MG517 that complements a previous structural model of the N-terminus domain. By means of sequence analysis, molecular dynamics and metadynamics simulations, we have identified a short α-helix at the apical C-terminus of MG517 with clear amphipathic character. Binding to a membrane model is thermodynamically favored which suggests that this structural element guides the adhesion of MG517 to the cell membrane. We have experimentally verified that truncation of part of this helix causes a substantial reduction of glycoglycerolipids synthesis. The model proposes that MG517 recognizes and binds the diacylglycerol substrate embedded in the membrane by means of this α-helix at the C-terminus together with a previously identified binding pocket at the N-terminus.
Biogeographical origin and timing of the founder ichthyosis TGM1 c.1187G > A mutation in an isolated Ecuadorian population
Authors: Esperón-Moldes U. S. , Pardo-Seco J. , Montalván-Suárez M. , Fachal L. , Ginarte M. , Rodríguez-Pazos L. , Gómez-Carballa A. , Moscoso F. , Ugalde-Noritz N. , Ordóñez-Ugalde A. , Tettamanti-Miranda D. , Ruiz J. C. , Salas A. , Vega A. 
Published: May 2019

AbstractAn unusually high frequency of the lamellar ichthyosis TGM1 mutation, c.1187G > A, has been observed in the Ecuadorian province of Manabí. Recently, the same mutation has been detected in a Galician patient (Northwest of Spain). By analyzing patterns of genetic variation around this mutation in Ecuadorian patients and population matched controls, we were able to estimate the age of c.1187G > A and the time to their most recent common ancestor (TMRCA) of c.1187G > A Ecuadorian carriers. While the estimated mutation age is 41 generations ago (~1,025 years ago [ya]), the TMRCA of Ecuadorian c.1187G > A carrier haplotypes dates to just 17 generations (~425 ya). Probabilistic-based inferences of local ancestry allowed us to infer a most likely European origin of a few (16% to 30%) Ecuadorian haplotypes carrying this mutation. In addition, inferences on demographic historical changes based on c.1187G > A Ecuadorian carrier haplotypes estimated an exponential population growth starting ~20 generations, compatible with a recent founder effect occurring in Manabí. Two main hypotheses can be considered for the origin of c.1187G > A: (i) the mutation could have arisen in Spain >1,000 ya (being Galicia the possible homeland) and then carried to Ecuador by Spaniards in colonial times ~400 ya, and (ii) two independent mutational events originated this mutation in Ecuador and Galicia. The geographic and cultural characteristics of Manabí could have favored a founder effect that explains the high prevalence of TGM1 c.1187G > A in this region.
Modern Iron Ooids of Hydrothermal Origin as a Proxy for Ancient Deposits
Authors: Di Bella Marcella , Sabatino Giuseppe , Quartieri Simona , Ferretti Annalisa , Cavalazzi Barbara , Barbieri Roberto , Foucher Frédéric , Messori Fabio , Italiano Francesco 
Published: May 2019

AbstractWe constrained the origin and genetic environment of modern iron ooids (sand-sized grains with a core and external cortex of concentric laminae) providing new tools for the interpretation of their fossil counterparts as well as the analogous particles discovered on Mars. Here, we report an exceptional, unique finding of a still active deposit of submillimetric iron ooids, under formation at the seabed at a depth of 80 m over an area characterized by intense hydrothermal activity off Panarea, a volcanic island north of Sicily (Italy). An integrated analysis, carried out by X-ray Powder Diffraction, Environmental Scanning Electron Microscopy, X-ray Fluorescence and Raman spectroscopy reveals that Panarea ooids are deposited at the seafloor as concentric laminae of primary goethite around existing nuclei. The process is rapid, and driven by hydrothermal fluids as iron source. A sub-spherical, laminated structure resulted from constant agitation and by degassing of CO2-dominated fluids through seafloor sediments. Our investigations point the hydrothermal processes as responsible for the generation of the Panarea ooids, which are neither diagenetic nor reworked. The presence of ooids at the seawater-sediments interface, in fact, highlights how their development and growth is still ongoing. The proposed results show a new process responsible for ooids formation and gain a new insight into the genesis of iron ooids deposits that are distributed at global scale in both modern and past sediments.
Parametrical Optomechanical Oscillations in PhoXonic Whispering Gallery Mode Resonators
Authors: Roselló-Mechó Xavier , Farnesi Daniele , Frigenti Gabriele , Barucci Andrea , Fernández-Bienes Alberto , García-Fernández Tupak , Ratto Fulvio , Delgado-Pinar Martina , Andrés Miguel V. , Nunzi Conti Gualtiero , Soria Silvia 
Published: May 2019

AbstractWe report on the experimental and theoretical analysis of parametrical optomechanical oscillations in hollow spherical phoxonic whispering gallery mode resonators due to radiation pressure. The optically excited acoustic eigenmodes of the phoxonic cavity oscillate regeneratively leading to parametric oscillation instabilities.