bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tropical Dominance of N2 Fixation in the North Atlantic Ocean
Authors: Marconi Dario , Sigman Daniel M. , Casciotti Karen L. , Campbell Ethan C. , Alexandra Weigand M. , Fawcett Sarah E. , Knapp Angela N. , Rafter Patrick A. , Ward Bess B. , Haug Gerald H. 
Published: September 2017

AbstractTo investigate the controls on N2 fixation and the role of the Atlantic in the global ocean's fixed nitrogen (N) budget, Atlantic N2 fixation is calculated by combining meridional nitrate fluxes across World Ocean Circulation Experiment sections with observed nitrate 15N/14N differences between northward and southward transported nitrate. N2 fixation inputs of 27.1 ± 4.3 Tg N/yr and 3.0 ± 0.5 Tg N/yr are estimated north of 11°S and 24°N, respectively. That is, ~90% of the N2 fixation in the Atlantic north of 11°S occurs south of 24°N in a region with upwelling that imports phosphorus (P) in excess of N relative to phytoplankton requirements. This suggests that, under the modern iron‐rich conditions of the equatorial and North Atlantic, N2 fixation occurs predominantly in response to P‐bearing, N‐poor conditions. We estimate a N2 fixation rate of 30.5 ± 4.9 Tg N/yr north of 30°S, implying only 3 Tg N/yr between 30° and 11°S, despite evidence of P‐bearing, N‐poor surface waters in this region as well; this is consistent with iron limitation of N2 fixation in the South Atlantic. Since the ocean flows through the Atlantic surface in <2,500 years, similar to the residence time of oceanic fixed N, Atlantic N2 fixation can stabilize the N‐to‐P ratio of the global ocean. However, the calculated rate of Atlantic N2 fixation is a small fraction of global ocean estimates for either N2 fixation or fixed N loss. This suggests that, in the modern ocean, an approximate balance between N loss and N2 fixation is achieved within the combined Indian and Pacific basins.
Postinjection Normal Closure of Fractures as a Mechanism for Induced Seismicity
Authors: Ucar E. , Berre I. , Keilegavlen E. 
Published: September 2017

AbstractUnderstanding the controlling mechanisms underlying injection‐induced seismicity is important for optimizing reservoir productivity and addressing seismicity‐related concerns related to hydraulic stimulation in Enhanced Geothermal Systems. Hydraulic stimulation enhances permeability through elevated pressures, which cause normal deformations and the shear slip of preexisting fractures. Previous experiments indicate that fracture deformation in the normal direction reverses as the pressure decreases, e.g., at the end of stimulation. We hypothesize that this normal closure of fractures enhances pressure propagation away from the injection region and significantly increases the potential for postinjection seismicity. To test this hypothesis, hydraulic stimulation is modeled by numerically coupling flow in the fractures and matrix, fracture deformation, and matrix deformation for a synthetic reservoir in which the flow and mechanics are strongly affected by a complex three‐dimensional fracture network. The role of the normal closure of fractures is verified by comparing simulations conducted with and without the normal closure effect.
Wave‐Related Reynolds Number Parameterizations of CO2 and DMS Transfer Velocities
Authors: Brumer Sophia E. , Zappa Christopher J. , Blomquist Byron W. , Fairall Christopher W. , Cifuentes‐Lorenzen Alejandro , Edson James B. , Brooks Ian M. , Huebert Barry J. 
Published: September 2017

AbstractPredicting future climate hinges on our understanding of and ability to quantify air‐sea gas transfer. The latter relies on parameterizations of the gas transfer velocity k, which represents physical mass transfer mechanisms and is usually parameterized as a nonlinear function of wind forcing. In an attempt to reduce uncertainties in k, this study explores empirical parameterizations that incorporate both wind speed and sea state dependence via wave‐wind and breaking Reynolds numbers, RH and RB. Analysis of concurrent eddy covariance gas transfer and measured wavefield statistics supplemented by wave model hindcasts shows for the first time that wave‐related Reynolds numbers collapse four open ocean data sets that have a wind speed dependence of CO2 transfer velocity ranging from lower than quadratic to cubic. Wave‐related Reynolds number and wind speed show comparable performance for parametrizing dimethyl sulfide (DMS) which, because of its higher solubility, is less affected by bubble‐mediated exchange associated with wave breaking.
Global Three‐Dimensional Simulation of Earth's Dayside Reconnection Using a Two‐Way Coupled Magnetohydrodynamics With Embedded Particle‐in‐Cell Model: Initial Results
Authors: Chen Yuxi , Tóth Gábor , Cassak Paul , Jia Xianzhe , Gombosi Tamas I. , Slavin James A. , Markidis Stefano , Peng Ivy Bo , Jordanova Vania K. , Henderson Michael G. 
Published: September 2017

AbstractWe perform a three‐dimensional (3‐D) global simulation of Earth's magnetosphere with kinetic reconnection physics to study the flux transfer events (FTEs) and dayside magnetic reconnection with the recently developed magnetohydrodynamics with embedded particle‐in‐cell model. During the 1 h long simulation, the FTEs are generated quasi‐periodically near the subsolar point and move toward the poles. We find that the magnetic field signature of FTEs at their early formation stage is similar to a “crater FTE,” which is characterized by a magnetic field strength dip at the FTE center. After the FTE core field grows to a significant value, it becomes an FTE with typical flux rope structure. When an FTE moves across the cusp, reconnection between the FTE field lines and the cusp field lines can dissipate the FTE. The kinetic features are also captured by our model. A crescent electron phase space distribution is found near the reconnection site. A similar distribution is found for ions at the location where the Larmor electric field appears. The lower hybrid drift instability (LHDI) along the current sheet direction also arises at the interface of magnetosheath and magnetosphere plasma. The LHDI electric field is about 8 mV/m, and its dominant wavelength relative to the electron gyroradius agrees reasonably with Magnetospheric Multiscale (MMS) observations.
Neutron Monitors and Cosmogenic Isotopes as Cosmic Ray Energy‐Integration Detectors: Effective Yield Functions, Effective Energy, and Its Dependence on the Local Interstellar Spectrum
Authors: Asvestari Eleanna , Gil Agnieszka , Kovaltsov Gennady A. , Usoskin Ilya G. 
Published: September 2017

AbstractThe method of assessment of galactic cosmic rays (GCR) variability over different timescales, using energy‐integrating ground‐based detectors such as a neutron monitor and cosmogenic isotopes 10Be and 14C stored in natural archives is revisited here. The effective yield functions for cosmogenic 14C (globally mixed in the atmosphere) and 10Be (realistically deposited in the polar region) are calculated and provided, in a tabulated form, in the supporting information. The effective energy of a detector is redefined so that the variability of the flux of GCR particles at this energy is equal to that of the detector's count rate. The effective energy is found as 11–12 GeV/nucleon for the standard polar neutron monitor, and 6–7 GeV/nucleon and 5.5–6 GeV/nucleon for 14C and 10Be, respectively. New “calibration” relations between the force‐field modulation potentials, based on different models of local interstellar spectra (LIS) are provided. While such relations are typically based on refitting the modeled cosmic ray spectra with a prescribed LIS model, the method introduced here straightforwardly accounts for the exact type of the detector used to assess the spectrum. The relations are given separately for ground‐based neutron monitors and cosmogenic isotopes. This work allows for harmonization of different works related to variability of galactic cosmic ray flux in the vicinity of Earth, on long‐term scale.
Seasonal‐Scale Dating of a Shallow Ice Core From Greenland Using Oxygen Isotope Matching Between Data and Simulation
Authors: Furukawa Ryoto , Uemura Ryu , Fujita Koji , Sjolte Jesper , Yoshimura Kei , Matoba Sumito , Iizuka Yoshinori 
Published: September 2017

AbstractA precise age scale based on annual layer counting is essential for investigating past environmental changes from ice core records. However, subannual scale dating is hampered by the irregular intraannual variabilities of oxygen isotope (δ18O) records. Here we propose a dating method based on matching the δ18O variations between ice core records and records simulated by isotope‐enabled climate models. We applied this method to a new δ18O record from an ice core obtained from a dome site in southeast Greenland. The close similarity between the δ18O records from the ice core and models enables correlation and the production of a precise age scale, with an accuracy of a few months. A missing δ18O minimum in the 1995/1996 winter is an example of an indistinct δ18O seasonal cycle. Our analysis suggests that the missing δ18O minimum is likely caused by a combination of warm air temperature, weak moisture transport, and cool ocean temperature. Based on the age scale, the average accumulation rate from 1960 to 2014 is reconstructed as 1.02 m yr−1 in water equivalent. The annual accumulation rate shows an increasing trend with a slope of 3.6 mm yr−1, which is mainly caused by the increase in the autumn accumulation rate of 2.6 mm yr−1. This increase is likely linked to the enhanced hydrological cycle caused by the decrease in Arctic sea ice area. Unlike the strong seasonality of precipitation amount in the ERA reanalysis data in the southeast dome region, our reconstructed accumulation rate suggests a weak seasonality.
AERONET‐Based Nonspherical Dust Optical Models and Effects on the VIIRS Deep Blue/SOAR Over Water Aerosol Product
Authors: Lee Jaehwa , Hsu N. Christina , Sayer Andrew M. , Bettenhausen Corey , Yang Ping 
Published: September 2017

AbstractAerosol Robotic Network (AERONET)‐based nonspherical dust optical models are developed and applied to the Satellite Ocean Aerosol Retrieval (SOAR) algorithm as part of the Version 1 Visible Infrared Imaging Radiometer Suite (VIIRS) NASA “Deep Blue” aerosol data product suite. The optical models are created using Version 2 AERONET inversion data at six distinct sites influenced frequently by dust aerosols from different source regions. The same spheroid shape distribution as used in the AERONET inversion algorithm is assumed to account for the nonspherical characteristics of mineral dust, which ensures the consistency between the bulk scattering properties of the developed optical models and the AERONET‐retrieved microphysical and optical properties. For the Version 1 SOAR aerosol product, the dust optical model representative for Capo Verde site is used, considering the strong influence of Saharan dust over the global ocean in terms of amount and spatial coverage. Comparisons of the VIIRS‐retrieved aerosol optical properties against AERONET direct‐Sun observations at five island/coastal sites suggest that the use of nonspherical dust optical models significantly improves the retrievals of aerosol optical depth (AOD) and Ångström exponent by mitigating the well‐known artifact of scattering angle dependence of the variables, which is observed when incorrectly assuming spherical dust. The resulting removal of these artifacts results in a more natural spatial pattern of AOD along the transport path of Saharan dust to the Atlantic Ocean; that is, AOD decreases with increasing distance transported, whereas the spherical assumption leads to a strong wave pattern due to the spurious scattering angle dependence of AOD.
Three‐Dimensional Evolution of the Early Paleozoic Western Laurentian Margin: New Insights From Detrital Zircon U‐Pb Geochronology and Hf Isotope Geochemistry of the Harmony Formation of Nevada
Authors: Linde G. M. , Trexler J. H. , Cashman P. H. , Gehrels G. , Dickinson W. R. 
Published: September 2017

AbstractUranium‐lead (U‐Pb) geochronology and Hafnium (Hf) isotope geochemistry of detrital zircons of the Harmony Formation of north central Nevada provide new insights into the tectonic evolution of the Late Paleozoic western Laurentian margin. Using laser‐ablation inductively coupled plasma mass spectrometry, 10 arenite samples were analyzed for U‐Pb ages, and 8 of these samples were further analyzed for Hf isotope ratios. Three of the sampled units have similar U‐Pb age peaks and Hf isotope ratios, including a 1.0–1.4 Ga peak with εHf values of +12 to −3 and a 2.5–2.7 Ga peak with εHf values of +7 to −5. The remaining seven samples differ significantly from these three, but are similar to one another; having age peaks of 1.7–1.9 Ga with εHf of +10 to −20 and age peaks of 2.3–2.7 Ga with εHf of +6 to −8. The data confirm the subdivision of the Harmony Formation into two petrofacies: quartzose (Harmony A) and feldspathic (Harmony B). The three samples with 1.0–1.4 and 2.5–2.7 Ga peaks are the Harmony A, which originated in the central Laurentian craton. The other seven samples are the Harmony B, which originated in eastern Alberta‐western Saskatchewan, north of the Harmony A source. We propose that all Harmony Formation strata were deposited near eastern Alberta and subsequently tectonically interleaved with Roberts Mountains allochthon strata. We interpret that the entire package was tectonically transported south along the western Laurentian margin and then emplaced eastward onto the craton during the Late Devonian‐Early Mississippian Antler orogeny.
Characterization of auxiliary iron–sulfur clusters in a radical S‐adenosylmethionine enzyme PqqE from Methylobacterium extorquens AM1
Authors: Saichana Natsaran , Tanizawa Katsuyuki , Ueno Hiroshi , Pechoušek Jiří , Novák Petr , Frébortová Jitka 
Published: September 2017

PqqE is a radical S‐adenosyl‐l‐methionine (SAM) enzyme that catalyzes the initial reaction of pyrroloquinoline quinone (PQQ) biosynthesis. PqqE belongs to the SPASM (subtilosin/PQQ/anaerobic sulfatase/mycofactocin maturating enzymes) subfamily of the radical SAM superfamily and contains multiple Fe–S clusters. To characterize the Fe–S clusters in PqqE from Methylobacterium extorquens AM1, Cys residues conserved in the N‐terminal signature motif (CX3CX2C) and the C‐terminal seven‐cysteine motif (CX9–15GX4CXnCX2CX5CX3CXnC; n = an unspecified number) were individually or simultaneously mutated into Ser. Biochemical and Mössbauer spectral analyses of as‐purified and reconstituted mutant enzymes confirmed the presence of three Fe–S clusters in PqqE: one [4Fe–4S]2+ cluster at the N‐terminal region that is essential for the reductive homolytic cleavage of SAM into methionine and 5′‐deoxyadenosyl radical, and one each [4Fe–4S]2+ and [2Fe–2S]2+ auxiliary clusters in the C‐terminal SPASM domain, which are assumed to serve for electron transfer between the buried active site and the protein surface. The presence of [2Fe–2S]2+ cluster is a novel finding for radical SAM enzyme belonging to the SPASM subfamily. Moreover, we found uncommon ligation of the auxiliary [4Fe–4S]2+ cluster with sulfur atoms of three Cys residues and a carboxyl oxygen atom of a conserved Asp residue.
A New Passivation Route Leading to Over 8% Efficient PbSe Quantum‐Dot Solar Cells via Direct Ion Exchange with Perovskite Nanocrystals
Authors: Zhang Zhilong , Chen Zihan , Yuan Lin , Chen Weijian , Yang Jianfeng , Wang Bo , Wen Xiaoming , Zhang Jianbing , Hu Long , Stride John A. , Conibeer Gavin J. , Patterson Robert J. , Huang Shujuan 
Published: September 2017

AbstractColloidal quantum dots (QDs) are promising candidate materials for photovoltaics (PV) owing to the tunable bandgap and low‐cost solution processability. Lead selenide (PbSe) QDs are particularly attractive to PV applications due to the efficient multiple‐exciton generation and carrier transportation. However, surface defects arising from the oxidation of the PbSe QDs have been the major limitation for their development in PV. Here, a new passivation method for chlorinated PbSe QDs via ion exchange with cesium lead halide (Br, I) perovskite nanocrystals is reported. The surface chloride ions on the as‐synthesized QDs can be partially exchanged with bromide or iodide ions from the perovskite nanocrystals, hence forming a hybrid halide passivation. Consistent with the improved photoluminescence quantum yield, the champion PV device fabricated with these PbSe QDs achieves a PCE of 8.2%, compared to 7.3% of that fabricated with the untreated QDs. This new method also leads to devices with excellent air‐stability, retaining at least 93% of their initial PCEs after being stored in ambient conditions for 57 d. This is considered as the first reported PbSe QD solar cell with a PCE of over 8% to date.
Formation of Ni–Fe Mixed Diselenide Nanocages as a Superior Oxygen Evolution Electrocatalyst
Authors: Nai Jianwei , Lu Yan , Yu Le , Wang Xin , Lou Xiong Wen (David) 
Published: September 2017

AbstractExploring effective electrocatalysts is a crucial requirement for boosting the efficiency of water splitting to obtain clean fuels. Here, a self‐templating strategy is reported to synthesize Ni–Fe mixed diselenide cubic nanocages for the electrocatalytic oxygen evolution reaction (OER). The diselenide nanocages are derived from corresponding Prussian‐blue analog nanocages, which are first obtained by treating the nanocube precursor with a site‐selective ammonia etchant. The resulting Ni–Fe mixed diselenide nanocages perform as a superior OER electrocatalyst, which affords a current density of 10 mA cm−2 at a small overpotential of 240 mV; a high current density, mass activity, and turnover frequency of 100 mA cm−2, 1000 A g−1, and 0.58 s−1, respectively, at the overpotential of 270 mV; a Tafel slope as small as 24 mV dec−1; and excellent stability in alkaline medium.
A Case Study of Thiourea‐Assisted Iminium Formation by Hydroxyl Anion Binding: Kinetic, Spectroscopic and Computational Evidences
Authors: Juste‐Navarro Veronica , Prieto Liher , Delso Ignacio , Manzano Rubén , Tejero Tomas , Reyes Efraim , Vicario Jose L. , Merino Pedro 
Published: September 2017

AbstractThe experimental and computational study of the mechanism of the iminium‐organocatalyzed formation of N‐hydroxypyrrolidines from nitrones, revealed up to three activation levels of the Schreiner's thiourea used as co‐catalyst, i.e: (i) formation of the iminium ion through hydroxyl anion recognition forming a stable ion pair; (ii) enolization of the nitrone through a H‐bond network and (iii) activation of the nitrone moiety towards the final ring closure. The computational model supports the mechanism and the catalytic cycle. This mechanistic rationale is supported by the lack of reactivity of preformed iminium ion with the nitrone in the absence of thiourea‐hydroxyl complex and the observed reactivity when a complex thiourea‐tetrabutylammonium hydroxide is added.magnified image
Photodetectors Based on Organic–Inorganic Hybrid Lead Halide Perovskites
Authors: Zhou Jiachen , Huang Jia 
Published: September 2017

AbstractRecent years have witnessed skyrocketing research achievements in organic–inorganic hybrid lead halide perovskites (OIHPs) in the photovoltaic field. In addition to photovoltaics, more and more studies have focused on OIHPs‐based photodetectors in the past two years, due to the remarkable optoelectronic properties of OIHPs. This article summarizes the latest progress in this research field. To begin with, the factors influencing the performance of photodetectors are discussed, including both internal and external factors. In particular, the channel width and the incident power intensities should be taken into account to precisely and objectively evaluate and compare the output performance of different photodetectors. Next, photodetectors fabricated on single‐component perovskites in terms of different micromorphologies are discussed, namely, 3D thin‐film and single crystalline, 2D nanoplates, 1D nanowires, and 0D nanocrystals, respectively. Then, bilayer structured perovskite‐based photodetectors incorporating inorganic and organic semiconductors are discussed to improve the optoelectronic performance of their pristine counterparts. Additionally, flexible OIHPs‐based photodetectors are highlighted. Finally, a brief conclusion and outlook is given on the progress and challenges in the field of perovskites‐based photodetectors.
CuI/I2‐Mediated Intramolecular Oxidative Cyclization Reaction of N‐(2‐pyridyl)amidines by the Direct Double C−H Functionalization of a C(sp3)−H Bond
Authors: Yi Fengping , Zhang Songxing , Zhang Lirong , Yi Weiyin , Yu Rui 
Published: September 2017

AbstractA facile approach to a rare class of 3,3‐disubstituted 2‐iminoimidazo[1,2‐a]‐pyridines bearing a hydroxyl group at the 3 position in good to excellent yields from N‐(2‐pyridyl)amidines substrates in the presence of CuI/I2/KI/KOtBu is described. According to the investigation, the use of a Cu catalyst and the presence of sulfonyl groups in the substrates has a remarkable influence on the success of the oxidative cyclization reaction. Moreover, the oxygen source of the hydroxyl group may be from the incorporation of water in the reaction system or KOtBu. The successful implementation of the reaction further indicates that amidines have abundant reactivity under various reaction conditions. The methodology is operationally simple and has a broad substrate scope.
Structures of the Heme Acquisition Protein HasA with Iron(III)‐5,15‐Diphenylporphyrin and Derivatives Thereof as an Artificial Prosthetic Group
Authors: Uehara Hiromu , Shisaka Yuma , Nishimura Tsubasa , Sugimoto Hiroshi , Shiro Yoshitsugu , Miyake Yoshihiro , Shinokubo Hiroshi , Watanabe Yoshihito , Shoji Osami 
Published: September 2017

AbstractIron(III)‐5,15‐diphenylporphyrin and several derivatives were accommodated by HasA, a heme acquisition protein secreted by Pseudomonas aeruginosa, despite possessing bulky substituents at the meso position of the porphyrin. Crystal structure analysis revealed that the two phenyl groups at the meso positions of porphyrin extend outside HasA. It was shown that the growth of P. aeruginosa was inhibited in the presence of HasA coordinating the synthetic porphyrins under iron‐limiting conditions, and that the structure of the synthetic porphyrins greatly affects the inhibition efficiency.
Characterization of Doubly Ionic Hydrogen Bonds in Protic Ionic Liquids by NMR Deuteron Quadrupole Coupling Constants: Differences to H‐bonds in Amides, Peptides, and Proteins
Authors: Khudozhitkov Alexander E. , Stange Peter , Golub Benjamin , Paschek Dietmar , Stepanov Alexander G. , Kolokolov Daniil I. , Ludwig Ralf 
Published: September 2017

AbstractWe present the first deuteron quadrupole coupling constants (DQCCs) for selected protic ionic liquids (PILs) measured by solid‐state NMR spectroscopy. The experimental data are supported by dispersion‐corrected density functional theory (DFT‐D3) calculations and molecular dynamics (MD) simulations. The DQCCs of the N−D bond in the triethylammonium cations are the lowest reported for deuterons in PILs, indicating strong hydrogen bonds between ions. The NMR coupling parameters are compared to those in amides, peptides, and proteins. The DQCCs show characteristic behavior with increasing interaction strength of the counterion and variation of the H‐bond motifs. We report the similar presence of the quadrupolar splitting pattern and the narrow liquid line in the NMR spectra over large temperature ranges, indicating the heterogeneous nature of PILs.