bluuebunny/crossref_metadata_2025_split huggingface dataset:
Field‐aligned currents in Saturn's magnetosphere: Local time dependence of southern summer currents in the dawn sector between midnight and noon
Authors: Hunt G. J. , Cowley S. W. H. , Provan G. , Bunce E. J. , Alexeev I. I. , Belenkaya E. S. , Kalegaev V. V. , Dougherty M. K. , Coates A. J. 
Published: August 2016

AbstractWe examine and compare the magnetic field perturbations associated with field‐aligned ionosphere‐magnetosphere coupling currents at Saturn, observed by the Cassini spacecraft during two sequences of highly inclined orbits in 2006/2007 and 2008 under late southern summer conditions. These sequences explore the southern currents in the dawn‐noon and midnight sectors, respectively, thus allowing investigation of possible origins of the local time (LT) asymmetry in auroral Saturn kilometric radiation (SKR) emissions, which peak in power at ~8 h LT in the dawn‐noon sector. We first show that the dawn‐noon field data generally have the same four‐sheet current structure as found previously in the midnight data and that both are similarly modulated by “planetary period oscillation” (PPO) currents. We then separate the averaged PPO‐independent (e.g., subcorotation) and PPO‐related currents for both LT sectors by using the current system symmetry properties. Surprisingly, we find that the PPO‐independent currents are essentially identical within uncertainties in the dawn‐dusk and midnight sectors, thus providing no explanation for the LT dependence of the SKR emissions. The main PPO‐related currents are, however, found to be slightly stronger and narrower in latitudinal width at dawn‐noon than at midnight, leading to estimated precipitating electron powers, and hence emissions, that are on average a factor of ~1.3 larger at dawn‐noon than at midnight, inadequate to account for the observed LT asymmetry in SKR power by a factor of ~2.7. Some other factors must also be involved, such as a LT asymmetry in the hot magnetospheric auroral source electron population.
Relativistic electron precipitation as seen by NOAA POES
Authors: Yahnin A. G. , Yahnina T. A. , Semenova N. V. , Gvozdevsky B. B. , Pashin A. B. 
Published: August 2016

AbstractWe performed a survey of relativistic electron precipitation (REP) events revealed by the Medium Energy Proton and Electron Detector instrument on board NOAA Polar‐orbiting Operational Environmental Satellites during a 38 day interval. We have divided the observed REP events into three groups with respect to the simultaneous observations of energetic (>30 keV) electron and proton precipitation. The first group consists of REP enhancements forming the isotropy zone at the poleward edge of trapped relativistic electron fluxes. These REP events are observed on the nightside, and they are, apparently, produced by isotropization process related to nonadiabatic motion of particles in the stretched magnetic field. The second group are the REP events related to simultaneous enhancements of energetic >30–300 keV electrons. These events have a wider magnetic local time range of occurrence with a maximum in the premidnight sector. They can be related to the interaction of electrons with waves whose possible nature is briefly discussed on the basis of comparison with the cold plasma density in the conjugated region of the equatorial plane. The third group consists of the REP events correlated with the burst‐like precipitation of >30–keV protons within an anisotropy zone, where the trapped flux dominates. These events are found in the dusk sector in association with enhanced cold plasma density in the conjugate equatorial magnetosphere. As is known, proton bursts within the anisotropy zone indicate the location of the electromagnetic ion cyclotron (EMIC) wave source. Such REP events can be due to scattering of the relativistic electrons by EMIC waves. However, we noted that some of these REP events are associated with precipitation of energetic electrons with low‐energy cutoff below 100 keV. We suggest that in such cases the electrons within a wide energy range are precipitated by other waves (probably, by plasmaspheric hiss).
Electric and magnetic radial diffusion coefficients using the Van Allen probes data
Authors: Ali Ashar F. , Malaspina David M. , Elkington Scot R. , Jaynes Allison N. , Chan Anthony A. , Wygant John , Kletzing Craig A. 
Published: August 2016

AbstractULF waves are a common occurrence in the inner magnetosphere and they contribute to particle motion, significantly, at times. We used the magnetic and the electric field data from the Electric and Magnetic Field Instrument Suite and Integrated Sciences (EMFISIS) and the Electric Field and Waves instruments (EFW) on board the Van Allen Probes to estimate the ULF wave power in the compressional component of the magnetic field and the azimuthal component of the electric field, respectively. Using L∗, Kp, and magnetic local time (MLT) as parameters, we conclude that the noon sector contains higher ULF Pc‐5 wave power compared with the other MLT sectors. The dawn, dusk, and midnight sectors have no statistically significant difference between them. The drift‐averaged power spectral densities are used to derive the magnetic and the electric component of the radial diffusion coefficient. Both components exhibit little to no energy dependence, resulting in simple analytic models for both components. More importantly, the electric component is larger than the magnetic component by one to two orders of magnitude for almost all L∗ and Kp; thus, the electric field perturbations are more effective in driving radial diffusion of charged particles in the inner magnetosphere. We also present a comparison of the Van Allen Probes radial diffusion coefficients, including the error estimates, with some of the previous published results. This allows us to gauge the large amount of uncertainty present in such estimates.
In situ stress state and strength in mudrocks
Authors: Casey Brendan , Germaine John T. , Flemings Peter B. , Fahy Brian P. 
Published: August 2016

AbstractThe stress state of mudrocks buried under uniaxial strain conditions is defined through a large number of laboratory triaxial tests performed on water‐saturated resedimented mudrocks from a diverse set of geologic backgrounds. Unique relationships are found between the horizontal stresses that develop during normal uniaxial compression (given by K0NC), critical state friction angle, and shear strength during undrained loading. Tests were performed over the effective stress range of 0.1 to 100 MPa. Smectite‐rich mudrocks display a more rapid reduction in shear strength with increasing effective stress, which corresponds with a more rapid increase in horizontal stresses. The relationship between horizontal stresses and critical state friction angle found in this study compares favorably with the well‐known correlation of Jâky (1948), which was developed for very low stresses, even for friction angle values as low as 11°. Results for one mudrock suggest that this relationship also applies to mudrocks sheared from an unloaded (overconsolidated) state. The correlation between friction angle and K0NC is independent of the stress path applied during the compression phase of a test. This is not the case for shearing under undrained conditions, however, and the application of a stress path that produces uniaxial compression is necessary to measure a reliable shear strength. Systematic variations in K0NC and strength properties reflect an overall change in the shape and orientation of a mudrock's yield surface with effective stress level. The results of this study can aid in estimating the in situ stress state and strength properties of mudrocks, and this will have significant impact on a range of geoscience and engineering problems.
Joint inversion of teleseismic and ambient noise Rayleigh waves for phase velocity maps, an application to Iceland
Authors: Harmon Nicholas , Rychert Catherine A. 
Published: August 2016

AbstractWe present a method for joint inversion of teleseismic and ambient noise Rayleigh wave data for phase velocity maps from 18 to 50 s period. We adapt the two‐plane wave method for teleseismic data to include ambient noise phase data. We apply the method to data from Iceland's ICEMELT and HOTSPOT arrays. Checkerboard tests show that the joint inversion improves phase velocity model recovery over methods that use the data sets independently, particularly at 18 s period. The addition of ambient noise data also extends resolution to shallower depths and shorter periods in comparison to previous teleseismic results beneath Iceland. We show there are significant differences in the phase velocity maps from the joint approach in comparison to other approaches, for instance, using only teleseismic data, only ambient noise data, or the mean of the two. The difference in phase velocities in turn affects the resulting shear velocity models. The advantage of the joint inversion is that it produces a single phase velocity map that satisfies both data sets simultaneously. Our phase velocity maps show a transition from low velocities centered beneath the main volcanic centers in Iceland at 18–25 s period, primarily crustal depths, to a low‐velocity region that traces the rift zones from the Reykjanes Ridge in the south to the Kolbeinsey Ridge in the north at 29–50 s period, greater depths. These results are consistent with previous studies, although with an extended and improved region of resolution, which extends further into the Atlantic and Arctic Ocean.
Evaluating the use of 1‐D transit time distributions to infer the mean state and variability of oceanic ventilation
Authors: Shao Andrew E. , Mecking Sabine , Thompson LuAnne , Sonnerup Rolf E. 
Published: August 2016

AbstractAn offline tracer transport model transport is used to simulate chlorofluorocarbon (CFCs), sulfur hexafluoride (SF6), oxygen, ideal age, and model transit time distributions (TTDs) to evaluate how well tracers can be used to constrain both the mean state and variability of oceanic ventilation. Using climatological transports, the two‐parameter 1‐D inverse Gaussian approximation of the model TTD is found to be an adequate representation of ventilation pathways within the parts of the subtropical gyres with simple ventilation dynamics, but a poor approximation for regions with large gradients in ideal age (i.e., near the base of the thermocline and the continental boundaries). TTDs inferred from CFC‐12 and SF6 using a Peclet number‐based lookup table approach yield poor representations of the model TTD with a consistent bias toward ventilation being strongly dominated by along‐isopycnal diffusion. In a run with variable circulation, ideal age is used to track changes in thermocline ventilation. Variability in both apparent oxygen utilization (AOU) and tracer‐inferred TTD mean ages inferred using CFC‐12 (assuming fixed Peclet number) and dual tracers (SF6 and CFC‐12) are well‐correlated to ideal age variability in most of the thermocline. Changes in AOU are correlated with ideal age variability in even more regions compared to the TTD ages both horizontally and vertically down to intermediate depths. Generally, when changes in TTD mean age and AOU agreed in sign, correlations of both with ideal age changes were positive indicating the usefulness of tracers in diagnosing ventilation changes.
Bomb‐produced radiocarbon in the western tropical Pacific Ocean: Guam coral reveals operation‐specific signals from the Pacific Proving Grounds
Authors: Andrews Allen H. , Asami Ryuji , Iryu Yasufumi , Kobayashi Donald R. , Camacho Frank 
Published: August 2016

AbstractHigh‐resolution radiocarbon (14C) analyses on a coral core extracted from Guam, a western tropical Pacific island, revealed a series of early bomb‐produced 14C spikes. The typical marine bomb 14C signal—phase lagged and attenuated relative to atmospheric records—is present in the coral and is consistent with other regional coral records. However, 14C levels well above what can be attributed to air‐sea diffusion alone punctuate this pattern. This anomaly was observed in other Indo‐Pacific coral records, but the Guam record is unmatched in magnitude and temporal resolution. The Guam coral Δ14C record provided three spikes in 1954–1955, 1956–1957, and 1958–1959 that are superimposed on a normal 14C record. Relative to mean prebomb levels, the first peak rises an incredible ∼700‰ and remained elevated for ∼1.2 years. A follow up assay with finer resolution increased the peak by ∼300‰. Subsequent spikes were less intense with a rise of ∼35 and ∼70‰. Each can be linked to thermonuclear testing in the Pacific Proving Grounds at Bikini and Enewetak atolls in Operations Castle (1954), Redwing (1956), and Hardtack I (1958). These 14C signals can be explained by vaporization of coral reef material in the nuclear fireball, coupled with neutron activation of atmospheric nitrogen (14C production), and subsequent absorption of 14CO2 to form particulate carbonates of close‐in fallout. The lag time in reaching Guam and other coral records abroad was tied to ocean surface currents and modeling provided validation of 14C arrival observations.
Estimates of greenhouse gas and black carbon emissions from a major Australian wildfire with high spatiotemporal resolution
Authors: Surawski N. C. , Sullivan A. L. , Roxburgh S. H. , Polglase P. J. 
Published: August 2016

AbstractEstimates of greenhouse gases and particulate emissions are made with a high spatiotemporal resolution from the Kilmore East fire in Victoria, Australia, which burnt approximately 100,000 ha over a 12 h period. Altogether, 10,175 Gigagrams (Gg) of CO2 equivalent (CO2‐e) emissions occurred, with CO2 (∼68%) being the dominant chemical species emitted followed by CH4 (∼17%) and black carbon (BC) (∼15%). About 63% of total CO2‐e emissions were estimated to be from coarse woody debris, 22% were from surface fuels, 7% from bark, 6% from elevated fuels, and less than 2% from tree crown consumption. To assess the quality of our emissions estimates, we compared our results with previous estimates which used the Global Fire Emissions Database version 3.1 (GFEDv3.1) and the Fire INventory from the National Center for Atmospheric Research version 1.0 (FINNv1), as well as Australia's National Inventory System (and its revision). The uncertainty in emission estimates was addressed using truncated Monte Carlo analysis, which derived a probability density function for total emissions from the uncertainties in each input. The distribution of emission estimates from Monte Carlo analysis was lognormal with a mean of 10,355 Gigagrams (Gg) and a ±1 standard deviation (σ) uncertainty range of 7260–13,450 Gg. Results were in good agreement with the global data sets (when using the same burnt area), although they predicted lower total emissions by 15–37% due to underestimating fuel consumed. Emissions estimates can be improved by obtaining better estimates of fuel consumed and BC emission factors. Overall, this study presents a methodological template for high‐resolution emissions accounting and its uncertainty, enabling a step toward process‐based emissions accounting to be achieved.
Enhancement of volcanism and geothermal heat flux by ice‐age cycling: A stress modeling study of Greenland
Authors: Stevens Nathan T. , Parizek Byron R. , Alley Richard B. 
Published: August 2016

AbstractIce‐age cycling of the Greenland ice sheet likely contributed to locally elevated subglacial geothermal heat fluxes (GHFs), based on recent thermal modeling. Borehole and geophysical data indicate higher GHF in some areas than suggested by current knowledge of underlying geology, particularly at the head of the Northeast Greenland Ice Stream. Changes in lithospheric loading during ice‐sheet growth and decay cycles produce large and geologically rapid changes in the effective stress state beneath and near the ice sheet. Oscillations in melt fraction from cyclic loading through multiple ice‐age cycles will enhance upward magma migration through the nonlinear increase of melt migration velocity with melt fraction. We simulate periodic ice‐sheet loading scenarios along an east‐west transect across central Greenland on an Elastic Lithosphere, Relaxed Asthenosphere Earth model. Under likely parameter ranges, deviatoric stresses in the elastic lithosphere across widespread regions are sufficiently high to meaningfully enhance dike emplacement and also allow vug‐wave propagation in some scenarios. Stress patterns migrate laterally in response to ice‐sheet dynamics, favoring multistage magma ascent. If melt occurs at depth, our modeling suggests that ice‐age cycling could help it migrate upward to shallow depth or erupt, contributing to the high observed GHF. Furthermore, shallow magma emplacement might feed hydrothermal systems exploiting enhanced faulting or fracturing from ice‐age cycling, adding to elevated GHF. The preglacial passage of the Iceland‐Jan Mayen hot spot could have sourced such magmas. Direct observations of these lithospheric processes needed to further constrain our models are limited, highlighting the value of more targeted geophysical studies informing future modeling.
Simulating effects of a wind‐turbine array using LES and RANS
Authors: Vanderwende Brian J. , Kosović Branko , Lundquist Julie K. , Mirocha Jeffrey D. 
Published: August 2016

AbstractGrowth in wind power production has motivated investigation of wind‐farm impacts on in situ flow fields and downstream interactions with agriculture and other wind farms. These impacts can be simulated with both large‐eddy simulations (LES) and mesoscale wind‐farm parameterizations (WFP). The Weather Research and Forecasting (WRF) model offers both approaches. We used the validated generalized actuator disk (GAD) parameterization in WRF‐LES to assess WFP performance. A 12‐turbine array was simulated using the GAD model and the WFP in WRF. We examined the performance of each scheme in both convective and stable conditions. The GAD model and WFP produced qualitatively similar wind speed deficits and turbulent kinetic energy (TKE) production across the array in both stability regimes, though the magnitudes of velocity deficits and TKE production levels were underestimated and overestimated, respectively. While wake growth slowed in the latter half of the WFP array as expected, wakes did not approach steady state by the end of the array as simulated by the GAD model. A sensitivity test involving the deactivation of explicit TKE production by the WFP resulted in turbulence levels within the array well that were below those produced by the GAD in both stable and unstable conditions. Finally, the WFP overestimated downwind power production deficits in stable conditions because of the lack of wake stabilization in the latter half of the array.
Single‐ion spectroscopy system for the 2S1/2(F = 0) − 2D3/2(F = 2) transition in 171Yb+
Authors: Imai Yasutaka , Nishi Tatsuya , Nishizaki Masatoshi , Kawajiri Sho , Muroki Yuto , Ikuta Rikizo , Matsumoto Kai , Kitano Masao , Sugiyama Kazuhiko 
Published: August 2016

AbstractWe report on our system and scheme for single‐ion spectroscopy of the
clock transition in 171Yb+. Spectroscopy of the clock transition requires decoupling of the
state from the laser cooling cycle. We investigate this decoupling of the
state by using independent light sources for driving of all the transitions between the hyperfine structures contained in the cooling and repumping transitions. We observe the carrier spectrum of the
magnetic‐insensitive transition with a spectral width of 380 Hz.
Physics‐based RF/microwave characterization of wave interactions within electrical connectors with partial insertion faults
Authors: Tokgöz Çağatay , Dardona Sameh 
Published: August 2016

AbstractElectrical failures in avionics systems may result from connector faults. If fault precursors are not detected in advance, they may lead to hard failures such as open and short circuits that could ultimately result in fire or loss of flight critical systems. Therefore, It is crucial to detect, locate, and characterize fault precursors for timely preventive maintenance and mitigation before hard failures occur. In this paper, a physics‐based connector model consisting of multiple coaxial line sections with different characteristic impedances and lengths is proposed. Method of Moments (MoM) analyses were performed using commercial electromagnetic simulation software, FEKO, for transverse electric and magnetic (TEM) wave propagation through a connector. The physical parameters of the connector were optimized to match the measured S parameters for multiple insertion depths. The proposed models represent the connector for multiple insertion depths by varying only two length parameters at a time while other parameters are fixed. Insertion depth‐dependent resonant frequency shifts observed during measurement are also captured by the model over the full range of fully inserted to barely touching contacts. Hence, the models provide accurate representations of the connector and properly detect precursors to partial insertion faults.
Morphological Investigation of Poly(2‐aminothiazole) Prepared by Rapid Initiated Polymerization
Authors: Nabid Mohammad Reza , Bide Yasamin 
Published: August 2016

AbstractThe bulk and template‐free method to synthesize poly(2‐aminothiazole) (P2AT) and also morphological investigation by scanning electron microscopy are presented. The approach uses rapid initiated strategy by sodium hypochlorite as the oxidant and acetic acid, hydrochloric acid or camphorsulfonic acid as the dopant. Moreover, size controlling of P2AT nanoparticles was accomplished by employing different dopants, molar ratios of reactants, temperature and time, ranged from 20 to 380 nm in diameter. These nanoparticles can self‐assemble into plate‐like microstructures under certain conditions. According to the results, the amount of doping agent has a critical role in tailoring the nano‐ and microstructure of P2AT. The as‐obtained P2AT with plate‐like microstructure containing nanoparticles exhibited fluorescence emission at 430 nm. According to the nitrogen adsorption isotherm, the P2AT has a porous structure as the surface area was determined to be 38.54 m2 g−1 with the average pore size of 2.1 nm.
On the Effect of Prevalent Carbazole Homocoupling Defects on the Photovoltaic Performance of PCDTBT:PC71BM Solar Cells
Authors: Lombeck Florian , Komber Hartmut , Fazzi Daniele , Nava Diego , Kuhlmann Jochen , Stegerer Dominik , Strassel Karen , Brandt Josef , de Zerio Mendaza Amaia Diaz , Müller Christian , Thiel Walter , Caironi Mario , Friend Richard , Sommer Michael 
Published: August 2016

The photophysical properties and solar cell performance of the classical donor–acceptor copolymer PCDTBT(poly(N‐9′‐heptadecanyl‐2,7‐carbazole‐alt ‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole))) in relation to unintentionally formed main chain defects are investigated. Carbazole–carbazole homocouplings (Cbz hc) are found to significant extent in PCDTBT made with a variety of Suzuki polycondensation conditions. Cbz hc vary between 0 and 8 mol% depending on the synthetic protocol used, and are quantified by detailed nuclear magnetic resonance spectroscopy including model compounds, which allows to establish a calibration curve from optical spectroscopy. The results are corroborated by extended time‐dependent density functional theory investigations on the structural, electronic, and optical properties of regularly alternating and homocoupled chains. The photovoltaic properties of PCDTBT:fullerene blend solar cells significantly depend on the Cbz hc content for constant molecular weight, whereby an increasing amount of Cbz hc leads to strongly decreased short circuit currents JSC. With increasing Cbz hc content, JSC decreases more strongly than the intensity of the low energy absorption band, suggesting that small losses in absorption cannot explain the decrease in JSC alone, rather than combined effects of a more localized LUMO level on the TBT unit and lower hole mobilities found in highly defective samples. Homocoupling‐free PCDTBT with optimized molecular weight yields the highest efficiency up to 7.2% without extensive optimization.