bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermoremanent Behavior in Synthetic Samples Containing Natural Oxyexsolved Titanomagnetite
Authors: Hodgson Emma , Grappone J. Michael , Biggin Andrew J. , Hill Mimi J. , Dekkers Mark J. 
Published: May 2018

AbstractUnderstanding Earth's geodynamo provides us a window into the evolution of the Earth's core, which requires accurate data about how its strength varies with time. Classic Thellier‐style paleointensity experiments assume that studied specimens contain only noninteracting single‐domain (SD) magnetic particles. Interacting grains commonly occur in volcanic rocks but are generally assumed to behave like equivalently sized SD grains. Multidomain (MD) grains can cause erroneous PI estimates or cause Thellier‐style experiments to fail entirely. Synthetic specimens containing naturally formed magnetite with MD grains and oxyexsolved titanomagnetite (closely packed SD grains) were subjected to various partial thermoremanent magnetization (pTRM) experiments, which tested nonideal behavior as a function of pTRM acquisition and loss inequality, thermal history, and repeated heating steps. For all grain sizes and domain states, pTRMc (heating and cooling in a nonzero field) gives larger values, compared to pTRMb (heating in a zero field and cooling in a nonzero field), by ∼5.5%. Oxyexsolved grains appear prone to the same concave‐up, nonideal Arai plots commonly observed in MD specimens, which also has potential implications for the multiple‐specimen, domain‐state corrected protocol. Repeated heatings cause additive deviations from ideality with relatively small impacts on Arai plot curvature for both grain types. Experiments with higher initial demagnetization temperatures had lower curvatures, with the most SD‐like behavior occurring in the uppermost 20
C of the (un)blocking temperature range. Samples containing mixtures of magnetic domain sizes are likely to behave less ideally at lower temperatures but become more ideal with increasing temperature as the nonideal grains unblock.
Thermodynamic and Elastic Properties of Magnesite at Mantle Conditions: First‐Principles Calculations
Authors: Yao Chao , Wu Zhongqing , Zou Fan , Sun Weidong 
Published: May 2018

AbstractMagnesite (MgCO3) is a likely main host of carbonates in the mantle and plays an important role in the transport and storage of carbon in the Earth's mantle. Its physical properties at high pressure and high temperature (PT) are crucial for understanding the deep carbon cycle. Here we investigated thermodynamic and elastic properties of magnesite under the mantle PT conditions using first‐principles calculations with local density approximation (LDA). Magnesite has the seismic velocities close to those of forsterite. The effect of the magnesite on seismic velocity of the carbonated peridotite and eclogite is subtle in the upper mantle. However, magnesite has much smaller seismic velocities and far larger elastic anisotropy than major minerals in the transition zone and lower mantle. The enrichment of magnesite in the transition zone and lower mantle will likely produce seismically detectable low‐velocity zone and velocity anisotropy.
The First Fermi‐GBM Terrestrial Gamma Ray Flash Catalog
Authors: Roberts O. J. , Fitzpatrick G. , Stanbro M. , McBreen S. , Briggs M. S. , Holzworth R. H. , Grove J. E. , Chekhtman A. , Cramer E. S. , Mailyan B. G. 
Published: May 2018

AbstractWe present the first Fermi Space Telescope Gamma Ray Burst Monitor (GBM) catalog of 4,144 terrestrial gamma ray flashes (TGFs), detected since launch in 11 July 2008 through 31 July 2016. We discuss the updates and improvements to the triggered data and off‐line search algorithms, comparing this improved detection rate of ∼800 TGFs per year with event rates from previously published TGF catalogs from other missions. A Bayesian block algorithm calculated the temporal and spectral properties of the TGFs, revealing a delay between the hard (>300 keV) and soft (≤300 keV) photons of around 27 μs. Detector count rates of “low‐fluence” events were found to have average rates exceeding 150 kHz. Searching the World‐Wide Lightning Location Network data for radio sferics within ±5 min of each TGF revealed a clean sample of 1,314 World‐Wide Lightning Location Network locations, which were used to to accurately locate TGF‐producing storms. It also revealed lightning and storm activity for specific regions, as well as seasonal and daily variations of global lightning patterns. Correcting for the orbit of Fermi, we quantitatively find a marginal excess of TGFs being produced from storms over land near oceans (i.e., narrow isthmuses and small islands). No difference was observed between the duration of TGFs over the ocean and land. The distribution of TGFs at a given local solar time for predefined American, Asian, and African regions were confirmed to correlate well with known regional lightning rates.
Comments on “Long‐Term Variations of Exospheric Temperature Inferred From foF1 Observations: A Comparison to ISR Ti Trend Estimates” by Perrone and Mikhailov
Authors: Zhang Shun‐Rong , Holt John M. , Erickson Philip J. , Goncharenko Larisa P. 
Published: May 2018

AbstractPerrone and Mikhailov (2017, https://doi.org/10.1002/2017JA024193) and Mikhailov et al. (2017, https://doi.org/10.1002/2017JA023909) have recently examined thermospheric and ionospheric long‐term trends using a data set of four thermospheric parameters (Tex, [O], [N2], and [O2]) and solar EUV flux. These data were derived from one single ionospheric parameter, foF1, using a nonlinear fitting procedure involving a photochemical model for the F1 peak. The F1 peak is assumed at the transition height ht with the linear recombination for atomic oxygen ions being equal to the quadratic recombination for molecular ions. This procedure has a number of obvious problems that are not addressed or not sufficiently justified. The potentially large ambiguities and biases in derived parameters make them unsuitable for precise quantitative ionospheric and thermospheric long‐term trend studies. Furthermore, we assert that Perrone and Mikhailov (2017, https://doi.org/10.1002/2017JA024193) conclusions regarding incoherent scatter radar (ISR) ion temperature analysis for long‐term trend studies are incorrect and in particular are based on a misunderstanding of the nature of the incoherent scatter radar measurement process. Large ISR data sets remain a consistent and statistically robust method for determining long term secular plasma temperature trends.
Survey of Ionospheric Pc3‐5 ULF Wave Signatures in SuperDARN High Time Resolution Data
Authors: Shi X. , Ruohoniemi J. M. , Baker J. B. H. , Lin D. , Bland E. C. , Hartinger M. D. , Scales W. A. 
Published: May 2018

AbstractIonospheric signatures of ultralow frequency (ULF) wave in the Pc3‐5 band (1.7–40.0 mHz) were surveyed using ∼6‐s resolution data from Super Dual Auroral Radar Network (SuperDARN) radars in the Northern Hemisphere from 2010 to 2016. Numerical experiments were conducted to derive wave period‐dependent thresholds for automated detection of ULF waves using the Lomb‐Scargle periodogram technique. The spatial occurrence distribution, frequency characteristics, seasonal effects, solar wind condition, and geomagnetic activity level dependence have been studied. Pc5 wave events were found to dominate at high and polar latitudes with a most probable frequency of 2.08 ± 0.07 mHz, while Pc3‐4 waves were relatively more common at midlatitudes on the nightside with a most probable frequency of 11.39 ± 0.14 mHz. At high latitudes, the occurrence rate of Pc4‐5 waves maximizes in the dusk sector and during winter. These events tend to occur during low geomagnetic activity and northward interplanetary magnetic field. For the category of radially bounded but longitudinally extended Pc4 events in the duskside ionosphere, an internal driving source is suggested. At midlatitudes, the poloidal Pc3‐4 occurrence rate maximizes premidnight and during equinox. This tendency becomes more prominent with increasing auroral electrojet (AE) index and during southward interplanetary magnetic field, which suggests that many of these events are Pi2 and Pc3‐4 pulsations associated with magnetotail dynamics during active geomagnetic intervals. The overall occurrence rate of Pc3‐5 wave events is lowest in summer, which suggests that the ionospheric conductivity plays a role in controlling ULF wave occurrence.
Core Complex Segmentation in North Aegean, A Dynamic View
Authors: Brun Jean‐Pierre , Sokoutis Dimitrios 
Published: May 2018

AbstractThe core complexes of the North Aegean result from the gravity spreading of a thrust wedge, driven by the Hellenic slab rollback, since middle Eocene. The development of the Southern Rhodope Core Complex occurred in two stages: (i) core complex exhumation accommodated by the Kerdylion detachment and (ii) steep normal faulting controlling the deposition of Neogene sedimentary basins that segmented the core complex. Both stages have been controlled by a clockwise rotation of the detachment hanging wall. The bulk amount of extension along the Aegean coastline in Northern Greece reached 120 km. The transition between the two stages occurred in middle Miocene due to an increase in extensional displacement by a factor 5. This transition between two different modes of extension, from localized detachment (i.e., core complex mode) to distributed steep normal faulting (i.e., wide rift mode), occurred at Aegean scale as a result of an acceleration of slab rollback. The Neogene basins emplaced close to the detachment, where brittle upper crust was thin (around 7 km) but containing weak marble layers allowing the formation of ramp‐flat extensional systems with rollover‐type basin fill. Since Pliocene, the stretching direction changed, from NE‐SW to NS, due to the propagation of the North Anatolian Fault in the North Aegean domain.
Pore Geometry Characterization by Persistent Homology Theory
Authors: Jiang Fei , Tsuji Takeshi , Shirai Tomoyuki 
Published: May 2018

AbstractRock pore geometry has heterogeneous characteristics and is scale dependent. This feature in a geological formation differs significantly from artificial materials and makes it difficult to predict hydrologic and elastic properties. To characterize pore heterogeneity, we propose an evaluation method that exploits the recently developed persistent homology theory. In the proposed method, complex pore geometry is first represented as sphere cloud data using a pore‐network extraction method. Then, a persistence diagram (PD) is calculated from the point cloud, which represents the spatial distribution of pore bodies. A new parameter (distance index H) derived from the PD is proposed to characterize the degree of rock heterogeneity. Low H value indicates high heterogeneity. A new empirical equation using this index H is proposed to predict the effective elastic modulus of porous media. The results indicate that the proposed PD analysis is very efficient for extracting topological feature of pore geometry.
Rethinking the Use of Seabed Sediment Temperature Profiles to Trace Submarine Groundwater Flow
Authors: Kurylyk B. L. , Irvine D. J. , Mohammed A. A. , Bense V. F. , Briggs M. A. , Loder J. W. , Geshelin Y. 
Published: May 2018

AbstractSubmarine groundwater fluxes across the seafloor facilitate important hydrological and biogeochemical exchanges between oceans and seabed sediment, yet few studies have investigated spatially distributed groundwater fluxes in deep‐ocean environments such as continental slopes. Heat has been previously applied as a submarine groundwater tracer using an analytical solution to a heat flow equation assuming steady state conditions and homogeneous thermal conductivity. These assumptions are often violated in shallow seabeds due to ocean bottom temperature changes or sediment property variations. Here heat tracing analysis techniques recently developed for terrestrial settings are applied in concert to examine the influences of groundwater flow, ocean temperature changes, and seabed thermal conductivity variations on deep‐ocean sediment temperature profiles. Temperature observations from the sediment and bottom ocean water on the Scotian Slope off eastern Canada are used to demonstrate how simple thermal methods for tracing groundwater can be employed if more comprehensive techniques indicate that the simplifying assumptions are valid. The spatial distribution of the inferred groundwater fluxes on the slope suggests a downward groundwater flow system with recharge occurring over the upper‐middle slope and discharge on the lower slope. We speculate that the downward groundwater flow inferred on the Scotian Slope is due to density‐driven processes arising from underlying salt domes, in contrast with upward slope systems driven by geothermal convection. Improvements in the design of future submarine hydrogeological studies are proposed for thermal data collection and groundwater flow analysis, including new equations that quantify the minimum detectable flux magnitude for a given sensor accuracy and profile length.
Tomographic Estimation of Exospheric Hydrogen Density Distributions
Authors: Cucho‐Padin G. , Waldrop L. 
Published: May 2018

AbstractFor the past decade, the Lyman‐alpha detectors on board National Aeronautics and Space Administration's Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS) mission have obtained routine measurements of solar Lyman‐α photons (121.6 nm) resonantly scattered by atomic hydrogen (H) in the terrestrial exosphere. These data have been used to derive global three‐dimensional (3‐D) models of exospheric H density beyond 3 RE, which are needed to understand various aspects of aeronomy and heliophysics, such as atmospheric chemistry and energetics, magnetospheric energy dissipation, ion‐neutral coupling, and atmospheric evolution through gravitational escape. These empirical distributions are obtained through parametric fitting of assumed functional forms that have little observational justification, thus limiting confidence in conclusions drawn from analysis of the resulting exospheric structure. In this work, we present a new means of global 3‐D reconstruction of exospheric H density through tomographic inversion of the scattered H Lyman‐α emission. Our approach avoids the conventional dependence on ad hoc parametric formulations and, based on the case studies reported here, appears to enable a more accurate characterization of the global structure of the H density in the outer exosphere. We evaluate the bounds of technique feasibility using simulated TWINS data and report new geophysical insights gained from applying this promising new approach to an example of actual TWINS data.
Satellite‐Based Analysis of CO Seasonal and Interannual Variability Over the Amazon Basin
Authors: Deeter M. N. , Martínez‐Alonso S. , Andreae Meinrat O. , Schlager H. 
Published: May 2018

AbstractThe “Measurements of Pollution in the Troposphere” (MOPITT) satellite record is applied to study the geographical and temporal variability of carbon monoxide (CO) from biomass burning in the Amazon Basin. The presented analysis demonstrates the use of satellite observations for interpreting the effects of deforestation and climate on past and future emissions of CO. The study exploits the MOPITT “multispectral” retrieval product which effectively resolves tropospheric CO into two independently measured layers. New validation results based on in situ measurements during the ACRIDICON‐CHUVA aircraft campaign in 2014 are used for bias correction. Contrasting CO monthly climatologies are presented for the Amazon Basin for the lower and upper troposphere (“LT” and “UT”) with an emphasis on the Amazonian dry season. Climatologically, spatial patterns of UT CO over the Amazon Basin appear to be related to both deep convection and anticyclonic flow. Strongly enhanced LT basin‐mean CO concentrations are observed for the dry season months in 2005, 2007, 2010, and 2015, while the record also indicates a decreasing long‐term trend. These observations are consistent with the expected effects of falling deforestation rates since 2004, punctuated by CO spikes in drought years due to large‐scale wildfires.
Hyporheic Exchange Driven by Three‐Dimensional Sandy Bed Forms: Sensitivity to and Prediction from Bed Form Geometry
Authors: Chen Xiaobing , Cardenas M. Bayani , Chen Li 
Published: May 2018

AbstractBed form‐driven hyporheic exchange is vital to biogeochemical processes occurring within aquatic sediment. The integrated effects of hyporheic processes in a bed form ultimately impact watershed‐scale water quality. However, much of what is understood regarding bed hyporheic exchange is based on idealized two‐dimensional bed forms despite the prevalence of potentially complex three‐dimensional (3‐D) bed forms in sandy riverbeds. We thus examined the impact of bed form three‐dimensionality on hyporheic exchange. Bed form three‐dimensionality was represented by two groups of geometric parameters: (1) crest planform curvature and (2) transverse and longitudinal wavelength and amplitude. A wide variety of synthetic bed forms was generated based on the geometric parameters. Then, surface flow over and hyporheic flow through each bed form was calculated using a 3‐D multiphysics computational fluid dynamics model implemented across a range of Reynolds Number. We found that hyporheic exchange is sensitive to both types of parameters that determine the bed form three‐dimensionality. Hyporheic exchange is dominated however by the three‐dimensionality caused by out‐of‐phase superimposed sinusoidal surfaces. The results of the complex flow models were synthesized into simple equations for predicting hyporheic flux and bulk residence time based on bed form longitudinal and transverse wavelengths, bed form height, and Reynolds Number.
iASPP–PP1 complex is required for cytokinetic abscission by controlling CEP55 dephosphorylation
Authors: Gao Kun , Zhang Yuanyuan , Shi Qing , Zhang Jianong , Zhang Liang , Sun Huiru , Jiao Dongyue , Zhao Xiayin , Tao Hongru , Wei Youheng , Wang Yuqi , Saiyin Hexige , Zhao Shi-Min , Li Yao , Zhang Pingzhao , Wang Chenji 
Published: May 2018

AbstractCytokinesis is the last step of cell division and is concluded by the abscission of the intercellular bridge that connects two daughter cells. The tight regulation of cytokinesis completion is essential because cytokinesis failure is associated with various human diseases. Here, we report that iASPP, a member of the apoptosis-stimulating proteins of p53 (ASPP) family, is required for proper cell division. iASPP depletion results in abnormal midbody structure and failed cytokinesis. We used protein affinity purification methods to identify the functional partners of iASPP. We found that iASPP associates with centrosomal protein of 55 kDa (CEP55), an important cytokinetic abscission regulator. Mechanically, iASPP acts as a PP1-targeting subunit to facilitate the interaction between PP1 and CEP55 and to remove PLK1-mediated Ser436 phosphorylation in CEP55 during late mitosis. The latter step is critical for the timely recruitment of CEP55 to the midbody. The present observations revealed a previously unrecognized function of iASPP in cytokinesis. This function, in turn, likely contributes to the roles of iASPP in tumor development and genetic diseases.
Sphingosine kinase 1-associated autophagy differs between neurons and astrocytes
Authors: Moruno-Manchon Jose F. , Uzor Ndidi-Ese , Ambati Chandrashekar R. , Shetty Vivekananda , Putluri Nagireddy , Jagannath Chinnaswamy , McCullough Louise D. , Tsvetkov Andrey S. 
Published: May 2018

AbstractAutophagy is a degradative pathway for removing aggregated proteins, damaged organelles, and parasites. Evidence indicates that autophagic pathways differ between cell types. In neurons, autophagy plays a homeostatic role, compared to a survival mechanism employed by starving non-neuronal cells. We investigated if sphingosine kinase 1 (SK1)-associated autophagy differs between two symbiotic brain cell types—neurons and astrocytes. SK1 synthesizes sphingosine-1-phosphate, which regulates autophagy in non-neuronal cells and in neurons. We found that benzoxazine autophagy inducers upregulate SK1 and neuroprotective autophagy in neurons, but not in astrocytes. Starvation enhances SK1-associated autophagy in astrocytes, but not in neurons. In astrocytes, SK1 is cytoprotective and promotes the degradation of an autophagy substrate, mutant huntingtin, the protein that causes Huntington’s disease. Overexpressed SK1 is unexpectedly toxic to neurons, and its toxicity localizes to the neuronal soma, demonstrating an intricate relationship between the localization of SK1’s activity and neurotoxicity. Our results underscore the importance of cell type-specific autophagic differences in any efforts to target autophagy therapeutically.
Genipin alleviates vascular hyperpermeability following hemorrhagic shock by up-regulation of SIRT3/autophagy
Authors: Shumin Cai , Wei Xu , Yunfeng Li , Jiangshui Liang , Youguang Gao , Zhongqing Chen , Tao Li 
Published: May 2018

AbstractGenipin (GP) is commonly used to treat cardiovascular diseases; however, the protective action of GP against vascular hyperpermeability (VH) has not been reported. We previously reported that intrinsic apoptotic signaling (IAS) is involved in VH following hemorrhagic shock (HS). GP inhibits apoptosis, but the specific mechanism remains unclear. In the present study, we observed that GP protects against HS-induced VH in vitro and in vivo. We report that this protective effect is related to the inhibition of IAS by up-regulation of autophagy via sirtuin 3 (SIRT3). The endothelial cell hyperpermeability induced by HS was enhanced by GP; this was attenuated by 3-methyladenine (3MA), a specific inhibitor of autophagy, indicating the involvement of autophagy. Consistent with these results, we found that 3MA reversed the effects of GP on up-regulation of autophagy, and also diminished the protective effect of GP against IAS activation following HS. Furthermore, knockout of SIRT3 inhibited GP-induced autophagy, indicating the requirement of SIRT3 in the regulation of autophagy by GP. In rats, GP improved HS-induced VH, which was repressed by 3MA and 3-(1H-1,2,3-triazol-4-yl)pyridine (3-TYP), a SIRT3 inhibitor. In conclusion, these findings suggest that autophagy plays a protective effect in VH following HS; the protective effect of autophagy is reinforced by GP, which protects against IAS and VH by up-regulating SIRT3.