bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seismic structure of the lithosphere beneath NWNamibia: Impact of the Tristan da Cunha mantle plume
Authors: Yuan Xiaohui , Heit Benjamin , Brune Sascha , Steinberger Bernhard , Geissler Wolfram H. , Jokat Wilfried , Weber Michael 
Published: January 2017

AbstractNorthwestern Namibia, at the landfall of the Walvis Ridge, was affected by the Tristan da Cunha mantle plume during continental rupture between Africa and South America, as evidenced by the presence of the Etendeka continental flood basalts. Here we use data from a passive‐source seismological network to investigate the upper mantle structure and to elucidate the Cretaceous mantle plume‐lithosphere interaction. Receiver functions reveal an interface associated with a negative velocity contrast within the lithosphere at an average depth of 80 km. We interpret this interface as the relic of the lithosphere‐asthenosphere boundary (LAB) formed during the Mesozoic by interaction of the Tristan da Cunha plume head with the pre‐existing lithosphere. The velocity contrast might be explained by stagnated and “frozen” melts beneath an intensively depleted and dehydrated peridotitic mantle. The present‐day LAB is poorly visible with converted waves, indicating a gradual impedance contrast. Beneath much of the study area, converted phases of the 410 and 660 km mantle transition zone discontinuities arrive 1.5 s earlier than in the landward plume‐unaffected continental interior, suggesting high velocities in the upper mantle caused by a thick lithosphere. This indicates that after lithospheric thinning during continental breakup, the lithosphere has increased in thickness during the last 132 Myr. Thermal cooling of the continental lithosphere alone cannot produce the lithospheric thickness required here. We propose that the remnant plume material, which has a higher seismic velocity than the ambient mantle due to melt depletion and dehydration, significantly contributed to the thickening of the mantle lithosphere.
The impact of rapid sediment accumulation on pore pressure development and dehydration reactions during shallow subduction in the Gulf of Alaska
Authors: Meridth Lanie N. , Screaton Elizabeth J. , Jaeger John M. , James Stephanie R. , Villaseñor Tania 
Published: January 2017

AbstractIn the Gulf of Alaska region, sediment has rapidly accumulated (>1 km/my) in the trench sourced from intensified glaciation in the past ∼1.2 million years. This rapid sediment accumulation increases overburden and should accelerate dehydration of hydrous minerals by insulating the underlying sediment column. These processes have the potential to generate fluid overpressures in the low permeability sediments entering the subduction zone. A 1‐D model was developed to simulate dehydration reaction progress and investigate excess pore pressures as sediments approach the trench and are subducted. At the deformation front, simulated temperatures increase by ∼30°C due to the insulating effect of trench sediments. As a result, opal‐A begins to react to form quartz while smectite remains mostly unreacted. Loading due to the trench sediments elevates excess pore pressures to ∼30% of lithostatic pressure at the deformation front; however, deformation front excess pore pressures are sensitive to assumptions about the permeability of outer wedge sediments. If the outer wedge sediments are coarse‐grained and high‐permeability rather than mud‐dominated, excess pore pressures are lower but still have an insulating effect. During early subduction, simulated pore pressures continue to rise and reach ∼70% of lithostatic by 60 km landward. The 1‐D modeling results suggest that the elevated pore pressures are primarily due to loading and that dehydration reactions are not a significant component of excess pore pressure generation at this margin.
TerraFERMA: The Transparent Finite Element Rapid Model Assembler for multiphysics problems in Earth sciences
Authors: Wilson Cian R. , Spiegelman Marc , van Keken Peter E. 
Published: January 2017

AbstractWe introduce and describe a new software infrastructure TerraFERMA, the Transparent Finite Element Rapid Model Assembler, for the rapid and reproducible description and solution of coupled multiphysics problems. The design of TerraFERMA is driven by two computational needs in Earth sciences. The first is the need for increased flexibility in both problem description and solution strategies for coupled problems where small changes in model assumptions can lead to dramatic changes in physical behavior. The second is the need for software and models that are more transparent so that results can be verified, reproduced, and modified in a manner such that the best ideas in computation and Earth science can be more easily shared and reused. TerraFERMA leverages three advanced open‐source libraries for scientific computation that provide high‐level problem description (FEniCS), composable solvers for coupled multiphysics problems (PETSc), and an options handling system (SPuD) that allows the hierarchical management of all model options. TerraFERMA integrates these libraries into an interface that organizes the scientific and computational choices required in a model into a single options file from which a custom compiled application is generated and run. Because all models share the same infrastructure, models become more reusable and reproducible, while still permitting the individual researcher considerable latitude in model construction. TerraFERMA solves partial differential equations using the finite element method. It is particularly well suited for nonlinear problems with complex coupling between components. TerraFERMA is open‐source and available at http://terraferma.github.io, which includes links to documentation and example input files.
Note on the Pantellini et al. process for dust impact signals on spacecraft
Authors: Kellogg Paul J. 
Published: January 2017

AbstractIn some recent papers it has been proposed that thick antennas are much more sensitive for the detection of dust impacts than thin wire antennas. This proposal attributes a large part of the signal on the antenna to a disruption of the photoelectron cloud around the antenna, and the signal is larger on thick antennas because there are more photoelectrons. However, comparison of thick and thin wire antennas on the Wind spacecraft has shown that thick antennas are somewhat more sensitive than thin wire antennas, but the difference is not as great as first supposed. Here an attempt is made to understand the quantitative difference between the responses of thick and thin antennas. It is found that a recent conjecture by the present author that the necessary increase in angular momentum for photoelectrons to avoid returning to a thick antenna would compensate for the larger number of photoelectrons is not correct. It is shown, however, that there is a significant difference in sensitivity between thin and thick antennas. An accurate calculation of the antenna sensitivities is not done here, as it depends on a number of factors, including a large difference in electric field around the antennas. Nevertheless, the photoelectron disruption mechanism is an important advance in understanding the coupling of dust impacts to antennas.
Implications of MAVEN's planetographic coordinate system for comparisons to other recent Mars orbital missions
Authors: Withers Paul , Jakosky B. M. 
Published: January 2017

AbstractThe Mars Atmosphere and Volatile EvolutioN (MAVEN) mission uses a planetographic coordinate system to report altitude, latitude, and longitude on Mars. By contrast, Mars Global Surveyor, Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter generally used a planetocentric coordinate system. These two coordinate systems are different: latitudes differ by up to 0.34° and altitudes differ by up to 2 km. These differences are large enough to affect the scientific results of comparisons between MAVEN and other orbital data sets. This is illustrated with three examples. (a) Comparisons of neutral density inferred from ionospheric peak altitude could contain errors of 25%. (b) Comparisons of mesopause altitude found from ultraviolet stellar occultations could contain errors of 2 km. (c) Comparisons of zonal variations in thermospheric density found from accelerometer observations could contain errors of 12%. Scientists who compare MAVEN data to other data sets, or to models derived from other data sets, should be aware of these differences in the coordinate systems and make appropriate adjustments.
Acidic weathering of basalt and basaltic glass: 1. Near‐infrared spectra, thermal infrared spectra, and implications for Mars
Authors: Horgan Briony H. N. , Smith Rebecca J. , Cloutis Edward A. , Mann Paul , Christensen Philip R. 
Published: January 2017

AbstractAcid‐leached rinds and coatings occur in volcanic environments on Earth and have been identified using orbital spectroscopy on Mars, but their development is poorly understood. We simulated long‐term open‐system acidic weathering in a laboratory by repeatedly rinsing and submerging crystalline and glassy basalts in pH ~ 1 and pH ~ 3 acidic solutions for 213 days and compared their visible/near‐infrared (0.3–2.5 µm) and thermal infrared (5–50 µm) spectral characteristics to their microscopic physical and chemical properties from scanning electron microscopy (SEM). We find that while alteration at moderately low pH (~3) can produce mineral precipitates from solution, it has very little spectral or physical effect on the underlying parent material. In contrast, alteration at very low pH (~1) results in clear silica spectral signatures for all crystalline samples while glasses exhibit strong blue concave‐up near‐infrared slopes. SEM indicates that these spectral differences correspond to different modes of alteration. In glass, alteration occurs only at the surface and produces a silica‐enriched leached rind, while in more crystalline samples, alteration penetrates the interior to cause dissolution and replacement by silica. We confirm that glass is more stable than crystalline basalt under long‐term acidic leaching, suggesting that glass could be enriched and common in terrains on Mars that have been exposed to acidic weathering. Leached glasses are consistent with both OMEGA and Thermal Emission Spectrometer (TES) spectra of the Martian northern lowlands and may contribute to the high‐silica phases detected globally in TES Surface Type 2. Thus, both glass‐rich deposits and acidic weathering may have been widespread on Mars.
Gypsum veins in Triassic Moenkopi mudrocks of southern Utah: Analogs to calcium sulfate veins on Mars
Authors: Young B. W. , Chan M. A. 
Published: January 2017

AbstractWell‐exposed gypsum veins in the Triassic Moenkopi formation in southern Utah, USA, are similar to veins at Endeavour and Gale Craters on Mars. Both Moenkopi and Mars veins are hydrated calcium sulfate, have fibrous textures, and crosscut other diagenetic features. Moenkopi veins are stratigraphically localized with strontium and sulfur isotope ratios similar to primary Moenkopi sulfate beds and are thus interpreted to be sourced from within the unit. Endeavour veins seem to be distributed by lithology and may have a local source. Gale veins cut across multiple lithologies and appear to be sourced from another stratigraphic interval. Evaluation of vein network geometries indicates that horizontal Moenkopi veins are longer and thicker than vertical veins. Moenkopi veins are also generally oriented with the modern stress field, so are interpreted to have formed in the latest stages of exhumation. Endeavour veins appear to be generally vertical and oriented parallel to the margins of Cape York and are interpreted to have formed in response to topographic collapse of the crater rim. Gale horizontal veins appear to be slightly more continuous than vertical veins and may have formed during exhumation. Abrupt changes in orientation, complex crosscutting relationships, and fibrous (antitaxial) texture in Moenkopi and Mars veins suggest emplacement via hydraulic fracture at low temperatures. Moenkopi and Mars veins are interpreted as late‐stage diagenetic features that have experienced little alteration since emplacement. Moenkopi veins are useful terrestrial analogs for Mars veins because vein geometry, texture, and chemistry record information about crustal deformation and vein emplacement.
Evaluating waterpoint sustainability and access implications of revenue collection approaches in ruralKenya
Authors: Foster T. , Hope R. 
Published: January 2017

AbstractWater policies in many sub‐Saharan African countries stipulate that rural communities are responsible for self‐financing their waterpoint's operation and maintenance. In the absence of policy consensus or evidence on optimal payment models, rural communities adopt a diversity of approaches to revenue collection. This study empirically assesses waterpoint sustainability and access outcomes associated with different revenue collection approaches on the south coast of Kenya. The analysis draws on a unique data set comprising financial records spanning 27 years and 100 communities, operational performance indicators for 200 waterpoints, and water source choices for more than 2000 households. Results suggest communities collecting pay‐as‐you‐fetch fees on a volumetric basis generate higher levels of revenue and experience better operational performance than communities charging flat fees. In both cases, financial flows mirror seasonal rainfall peaks and troughs. These outcomes are tempered by evidence that households are more likely to opt for an unimproved drinking water source when a pay‐as‐you‐fetch system is in place. The findings illuminate a possible tension between financial sustainability and universal access. If the Sustainable Development Goal of “safe water for all” is to become a reality, policymakers and practitioners will need to address this issue and ensure rural water services are both sustainable and inclusive.
Lithium n‐Doped Polyaniline as a High‐Performance Electroactive Material for Rechargeable Batteries
Authors: Jiménez Pablo , Levillain Eric , Alévêque Olivier , Guyomard Dominique , Lestriez Bernard , Gaubicher Joël 
Published: January 2017

AbstractThe discovery of conducting lithium‐doped polyaniline with reversible redox chemistry allows simultaneous unprecedented capacity and stability in a non‐aqueous Li battery. This compound (lithium emeraldinate) was synthesized by lithium–proton exchange on the emeraldine base in an anhydrous lithium‐based electrolyte. A combination of UV/Vis‐NIR spectroelectrochemistry, XPS, FTIR, and EQCM characterization allowed a unified description of the chemical and electrochemical behavior, showing facile charge delocalization of the doped states and the reversibility of the redox processes in this form of polyaniline. From a practical point of view, lithium emeraldinate behaves as a high‐capacity organic active material (230 mAh g−1) that enables preparation of relatively thick composite electrodes with a low amount of carbon additives and high energy density (460 Wh kg−1). Concomitantly, at 1C rate, 400 cycles were achieved without significant capacity loss, while the coulombic efficiency is greater than 99 %.
meta‐C−H Bromination on Purine Bases by Heterogeneous Ruthenium Catalysis
Authors: Warratz Svenja , Burns David J. , Zhu Cuiju , Korvorapun Korkit , Rogge Torben , Scholz Julius , Jooss Christian , Gelman Dmitri , Ackermann Lutz 
Published: January 2017

AbstractMethods for positionally selective remote C−H functionalizations are in high demand. Herein, we disclose the first heterogeneous ruthenium catalyst for meta‐selective C−H functionalizations, which enabled remote halogenations with excellent site selectivity and ample scope. The versatile heterogeneous Ru@SiO2 catalyst was broadly applicable and could be easily recovered and reused, which set the stage for the direct fluorescent labeling of purines. In contrast to palladium, rhodium, iridium, or cobalt complexes, solely the ruthenium catalysis manifold provided access to meta‐halogenated purine derivatives, illustrating the unique power of ruthenium C−H activation catalysis.
Ligand‐Enabled β‐C–H Arylation of α‐Amino Acids Without Installing Exogenous Directing Groups
Authors: Chen Gang , Zhuang Zhe , Li Gen‐Cheng , Saint‐Denis Tyler G. , Hsiao Yi , Joe Candice L. , Yu Jin‐Quan 
Published: January 2017

AbstractHerein we report acid‐directed β‐C(sp3)‐H arylation of α‐amino acids enabled by pyridine‐type ligands. This reaction does not require the installation of an exogenous directing group, is scalable, and enables the preparation of Fmoc‐protected unnatural amino acids in three steps. The pyridine‐type ligands are crucial for the development of this new C(sp3)‐H arylation.
CO2‐Assisted Fabrication of Two‐Dimensional Amorphous Molybdenum Oxide Nanosheets for Enhanced Plasmon Resonances
Authors: Liu Wei , Xu Qun , Cui Weili , Zhu Chuanhui , Qi Yuhang 
Published: January 2017

AbstractAs a remarkable class of plasmonic materials, two dimensional (2D) semiconductor compounds have attracted attention owing to their controlled manipulation of plasmon resonances in the visible light spectrum, which outperforms conventional noble metals. However, tuning of plasmonic resonances for 2D semiconductors remains challenging. Herein, we design a novel method to obtain amorphous molybdenum oxide (MoO3) nanosheets, in which it combines the oxidation of MoS2 and subsequent supercritical CO2‐treatment, which is a crucial step for the achievement of amorphous structure of MoO3. Upon illumination, hydrogen‐doped MoO3 exhibits tuned surface plasmon resonances in the visible and near‐IR regions. Moreover, a unique behavior of the amorphous MoO3 nanosheets has been found in an optical biosensing system; there is an optimum plasmon resonance after incubation with different BSA concentrations, suggesting a tunable plasmonic device in the near future.
A Double Allylation Strategy for Gram‐Scale Guaianolide Production: Total Synthesis of (+)‐Mikanokryptin
Authors: Hu Xirui , Xu Silong , Maimone Thomas J. 
Published: January 2017

AbstractWith over 5000 members isolated to date, sesquiterpene lactones represent a prolific source of medicinal agents with several derivatives in human clinical trials. The guaianolides, a major subset of this group, have been intensely investigated from both medicinal and chemical‐synthesis perspectives for decades. To date, the myriad stereochemical permutations presented by this enormous family have precluded the synthesis of many unique members. Herein we report the total synthesis of the trans‐fused 8,12‐guaianolide (+)‐mikanokryptin in 10 steps from (+)‐carvone. Notably, this synthesis is the first gram‐scale total synthesis of a guaianolide natural product.
Vertically Aligned Porous Nickel(II) Hydroxide Nanosheets Supported on Carbon Paper with Long‐Term Oxygen Evolution Performance
Authors: Xiong Dehua , Li Wei , Liu Lifeng 
Published: January 2017

AbstractVertically aligned Ni(OH)2 nanosheets were grown on carbon paper (CP) current collectors through a simple and cost‐effective hydrothermal approach. The as‐grown nanosheets are porous and highly crystallized. If used as a monolithic electrode for electrochemical water oxidation in alkaline solution, the carbon paper supported Ni(OH)2 nanosheets [CP@Ni(OH)2] exhibit high electrocatalytic activity and excellent long‐term stability. The electrode can attain an anodic current density of 20 mA cm−2 at a low overpotential of 338 mV, comparable to that of state‐of‐the‐art RuO2 nanocatalysts supported on CP (CP/RuO2) with the same catalyst loading. Significantly, CP@Ni(OH)2 shows much better long‐term stability than CP/RuO2 upon continuous galvanostatic electrolysis, particularly at a high industry‐relevant current density such as 100 mA cm−2. CP@Ni(OH)2 can sustain water oxidation at 100 mA cm−2 for 50 h without any degradation, whereas the performance of CP/RuO2 is much poorer and deteriorates gradually over time. CP@Ni(OH)2 electrodes hold substantial promise for use as low‐costing water oxidation anodes in electrolyzers.
Synthesis of β‐Keto Sulfones by a Catalyst‐Free Reaction of Aryldiazonium Tetrafluoroborates, Sulfur Dioxide, and Silyl Enol Ethers
Authors: Liu Tianshuo , Zheng Danqing , Ding Yechun , Fan Xiaona , Wu Jie 
Published: January 2017

AbstractA green approach for the generation of β‐keto sulfones through a reaction of aryldiazonium tetrafluoroborates and sulfur dioxide with silyl enol ether under catalyst‐ and additive‐free conditions has been realized. This reaction proceeds efficiently at room temperature and goes to completion in half an hour. During the reaction process, aryldiazonium tetrafluoroborate is treated with DABCO⋅(SO2)2 (DABCO=1,4‐diazabicyclo[2.2.2]octane) to provide a sulfonyl radical as the key intermediate, which then initiates the transformation. Oxidants or metal catalysts are avoided, and the presence of DABCO also plays an important role in the reaction.
Ion‐Pair Halogen Bonds in 2‐Halo‐Functionalized Imidazolium Chloride Receptors: Substituent and Solvent Effects
Authors: Nunes Rafael , Costa Paulo J. 
Published: January 2017

AbstractThe interaction of 2‐halo‐functionalized imidazolium derivatives (n‐X+; X=Cl, Br, I) with a chloride anion through ion‐pair halogen bonds (n‐X⋅Cl) was studied by means of DFT and ab initio calculations. A method benchmark was performed on 2‐bromo‐1H‐imidazol‐3‐ium in association with chloride (1‐Br⋅Cl); MP2 yielded the best results when compared with CCSD(T) calculations. The interaction energies (ΔE) in the gas phase are high and, although the electrostatic interaction is strong owing to the ion‐pair nature of the system, large X⋅⋅⋅Cl− Wiberg bond orders and contributions from charge transfer (n
→σ*C−X) are obtained. These values drop considerably in chloroform and water; this shows that solvent plays a role in modulating the interaction and that gas‐phase calculations are particularly unrealistic for experimental applications. The introduction of electron‐withdrawing groups in the 4,5‐positions of the imidazolium (e.g., −NO2, −F) increases the halogen‐bond strength in both the gas phase and solvent, including water. The effect of the substituents on the 1,3‐positions (N−H groups) also depends on the solvent. The variation of ΔE can be predicted through a two‐parameter linear regression that optimizes the weights of charge‐transfer and electrostatic interactions, which are different in vacuum and in solvent (chloroform and water). These results could be used in the rational design of efficient chloride receptors based on halogen bonds that work in solution, in particular, in an aqueous environment.
A Convenient One‐Pot Route to Screw‐Shaped [5]Azahelicenes via Rhodium(III)‐Catalyzed Multiple C−H Bond Activation
Authors: Li Shuai‐Shuai , Liu Chen‐Fei , Zhang Guo‐Tai , Xia Ying‐Qi , Li Wei‐Huan , Dong Lin 
Published: January 2017

AbstractA convenient rhodium(III)‐catalyzed cascade reaction of 7‐azaindoles and alkynes through multiple C−H bond activation for the synthesis of unique [5]azahelicenes has been developed. The optical property of these screw‐shaped helicene derivatives could be further utilized in electronic devices to recognize mercury ions.