bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling Amateur Radio Soundings of the Ionospheric Response to the 2017 Great American Eclipse
Authors: Frissell N. A. , Katz J. D. , Gunning S. W. , Vega J. S. , Gerrard A. J. , Earle G. D. , Moses M. L. , West M. L. , Huba J. D. , Erickson P. J. , Miller E. S. , Gerzoff R. B. , Liles W. , Silver H. W. 
Published: May 2018

AbstractOn 21 August 2017, a total solar eclipse traversed the continental United States and caused large‐scale changes in ionospheric densities. These were detected as changes in medium‐ and high‐frequency radio propagation by the Solar Eclipse QSO Party citizen science experiment organized by the Ham Radio Science Citizen Investigation (hamsci.org). This is the first eclipse‐ionospheric study to make use of measurements from a citizen‐operated, global‐scale HF propagation network and develop tools for comparison to a physics‐based model ionosphere. Eclipse effects were observed ±0.3 hr on 1.8 MHz, ±0.75 hr on 3.5 and 7 MHz, and ±1 hr on 14 MHz and are consistent with eclipse‐induced ionospheric densities. Observations were simulated using the PHaRLAP raytracing toolkit in conjunction with the eclipsed SAMI3 ionospheric model. Model results suggest 1.8, 3.5, and 7 MHz refracted at h≥125 km altitude with elevation angles θ≥22°, while 14 MHz signals refracted at h < 125 km with elevation angles θ < 10°.
Intrathermocline Eddies Embedded Within an Anticyclonic Vortex Ring
Authors: Meunier Thomas , Tenreiro M. , Pallàs‐Sanz Enric , Ochoa Jose , Ruiz‐Angulo Angel , Portela Esther , Cusí Simò , Damien Pierre , Carton Xavier 
Published: May 2018

AbstractHigh‐resolution hydrographic measurements reveal the presence of three intrathermocline eddies (ITEs) embedded within a loop current eddy. ITEs are lenticular bodies of nearly homogeneous water, which contrasts with the well‐stratified surrounding water. Their radii and thickness ranged between 19–32 km and 150–250 m. Negative relative vorticity within their cores (down to −0.85 times the Coriolis frequency), along with a large negative stratification anomaly, results in low Ertel potential vorticity and intense negative Ertel potential vorticity anomalies. Vortex stretching and relative vorticity have comparable contributions to potential vorticity anomaly, resulting in Burger numbers of order unity. The similarity of thermohaline properties within the ITE's cores and the surrounding loop current eddy water suggests that these ITEs likely form by intense mixing events followed by Rossby adjustment.
Opposite Aerosol Index‐Cloud Droplet Effective Radius Correlations Over Major Industrial Regions and Their Adjacent Oceans
Authors: Ma X. , Jia H. , Yu F. , Quaas J. 
Published: May 2018

AbstractThe Moderate Resolution Imaging Spectroradiometer (MODIS) C6 L3 and the European Centre for Medium‐Range Weather Forecasts (ECMWF) ERA‐Interim reanalysis data from 2003 to 2016 are employed to study aerosol‐cloud correlations over three industrial regions and their adjacent oceans, as well as explore the impact of meteorological conditions on the correlations. The analysis focusing on liquid and single‐layer clouds indicates an opposite aerosol‐cloud correlation between land and ocean; namely, cloud effective radius is positively correlated with aerosol index over industrial regions (positive slopes), but negatively correlated over their adjacent oceans (negative slopes), for a quasi‐constant liquid water path. The positive slopes are relatively large under low lower‐tropospheric stability (LTS; weakly stable condition), but much weaker or even become negative under high LTS (stable conditions) and high liquid water path. The occurrence frequency of cloud top height (CTH) and LTS suggests that positive correlations are more likely corresponding to relatively high CTH and low LTS, while negative to low CTH and high LTS.
Fluid Injection and Time‐Dependent Seismic Hazard in the Barnett Shale, Texas
Authors: Zhai Guang , Shirzaei Manoochehr 
Published: May 2018

AbstractThe Barnett Shale in Texas experienced an increase in seismicity since 2008, coinciding with high‐volume deep fluid injection. Despite the spatial proximity, the lack of a first‐order correlation between seismic records and the total volume of injected fluid requires more comprehensive geomechanical analysis, which accounts for local hydrogeology. Using time‐varying injections at 96 wells and employing a coupled linear poroelastic model, we simulate the spatiotemporal evolution of pore pressure and poroelastic stresses during 2007–2015. The overall contribution of poroelastic stresses to Coulomb failure stress change is ~10% of that of pore pressure; however, both can explain the spatiotemporal distribution of earthquakes. We use a seismicity rate model to calculate earthquake magnitude exceedance probability due to stress changes. The obtained time‐dependent seismic hazard is heterogeneous in space and time. Decreasing injection rates does not necessarily reduce probabilities immediately.
High‐Latitude Observations of a Localized Wind Wall and Its Coupling to the Lower Thermosphere
Authors: Shepherd Gordon G. , Shepherd Marianna G. 
Published: May 2018

AbstractReversals in the thermospheric zonal winds at altitudes of 140 to 250 km from eastward to westward have been found at southern geographic latitudes between 60° and 70°. These are confined to a narrow region between 100° and 200° in longitude with zonal velocities regularly of −400 m/s, sometimes reaching −600 m/s, so sharply defined that the authors describe it as a “wind wall.” The observations were made by the Wind Imaging Interferometer on National Aeronautics and Space Administration's Upper Atmosphere Research Satellite, and they occur as the field of view crosses the high polar cap wind field. The wind reversals at the wall boundaries create a convergence on the west side of the wall and a divergence on the east side that potentially generate vertical flows, consistent with observed perturbations in the O(1S) emission rate. They are present about one half of the time in local summer and autumn.
The Mars Topside Ionosphere Response to the X8.2 Solar Flare of 10 September 2017
Authors: Thiemann E. M. B. , Andersson L. , Lillis R. , Withers P. , Xu S. , Elrod M. , Jain S. , Pilinski M. D. , Pawlowski D. , Chamberlin P. C. , Eparvier F. G. , Benna M. , Fowler C. , Curry S. , Peterson W. K. , Deighan J. 
Published: May 2018

AbstractOn 10 September 2017, irradiance from a magnitude X8.2 solar flare impacted Mars while the Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter was characterizing the Mars upper atmosphere. This solar flare was the largest to occur during the MAVEN mission to date, nearly tripling the ionizing irradiance impacting Mars in tens of minutes, and provides an opportunity to study the planet's response to extreme irradiance changes. This letter reports in situ observations of the Mars topside ionosphere's response to this flare above 155 km made 1.67 hr after the flare soft X‐ray peak. The observed plasma density increase is higher than expected based solely on increased ionization, and the electron temperature decreases below 225 km; both effects can be explained by an expanded neutral atmosphere, which efficiently dissipates any flare‐induced heating of the thermal electrons at altitudes where CO2 is the dominant species. Further, the ion density and composition change significantly at both fixed altitude and pressure level, which can be explained by a change in the O:CO2 density ratio, highlighting the importance this ratio has in determining ionospheric structure.
Ocean Carbon Cycle Feedbacks Under Negative Emissions
Authors: Schwinger Jörg , Tjiputra Jerry 
Published: May 2018

AbstractNegative emissions will most likely be needed to achieve ambitious climate targets, such as limiting global warming to 1.5°. Here we analyze the ocean carbon‐concentration and carbon‐climate feedback in an Earth system model under an idealized strong CO2 peak and decline scenario. We find that the ocean carbon‐climate feedback is not reversible by means of negative emissions on decadal to centennial timescales. When preindustrial surface climate is restored, the oceans, due to the carbon‐climate feedback, still contain about 110 Pg less carbon compared to a simulation without climate change. This result is unsurprising but highlights an issue with a widely used carbon cycle feedback metric. We show that this metric can be greatly improved by using ocean potential temperature as a proxy for climate change. The nonlinearity (nonadditivity) of climate and CO2‐driven feedbacks continues to grow after the atmospheric CO2 peak.
Machine Learning Seismic Wave Discrimination: Application to Earthquake Early Warning
Authors: Li Zefeng , Meier Men‐Andrin , Hauksson Egill , Zhan Zhongwen , Andrews Jennifer 
Published: May 2018

AbstractPerformance of earthquake early warning systems suffers from false alerts caused by local impulsive noise from natural or anthropogenic sources. To mitigate this problem, we train a generative adversarial network (GAN) to learn the characteristics of first‐arrival earthquake P waves, using 300,000 waveforms recorded in southern California and Japan. We apply the GAN critic as an automatic feature extractor and train a Random Forest classifier with about 700,000 earthquake and noise waveforms. We show that the discriminator can recognize 99.2% of the earthquake P waves and 98.4% of the noise signals. This state‐of‐the‐art performance is expected to reduce significantly the number of false triggers from local impulsive noise. Our study demonstrates that GANs can discover a compact and effective representation of seismic waves, which has the potential for wide applications in seismology.
Test‐Particle Simulations of Linear and Nonlinear Interactions Between a 2‐D Whistler‐Mode Wave Packet and Radiation Belt Electrons
Authors: da Silva C. L. , Denton R. E. , Hudson M. K. , Millan R. M. , Liu K. , Bortnik J. 
Published: May 2018

AbstractUsing test‐particle simulations, we describe (in 2‐D) the interaction of an ensemble of electrons with a discrete whistler‐mode wave packet, which propagates with a moderate wave‐normal angle with respect to the background magnetic field. We evaluate both the average transport coefficients used in quasi‐linear diffusion transport and also the full nonlinear wave‐particle interactions. The magnitude of the calculated diffusion coefficients is found to increase proportionally to the wave amplitude squared, in agreement with quasi‐linear diffusion theory. Cyclotron resonance of counterstreaming electrons (n = 1 harmonic number) is more important for pitch angle scattering than Landau resonance. Landau resonance of costreaming electrons (n = 0) is comparable to cyclotron resonance for energy diffusion and advection. Strong acceleration of high pitch angle, costreaming electrons arises in nonlinear wave‐particle interactions with high‐amplitude waves. In our simulations with zero parallel electric field, the energy source for electron acceleration is the wave's perpendicular electric field, in both the cyclotron and Landau resonances. The Landau resonance can happen even with zero parallel electric field, if the wave packet propagates with a finite wave‐normal angle. This resonance between the particle's azimuthal velocity and the wave fields leads to trapping and substantial parallel acceleration.
Arctic Sea Ice Decline Significantly Contributed to the Unprecedented Liquid Freshwater Accumulation in the Beaufort Gyre of the Arctic Ocean
Authors: Wang Qiang , Wekerle Claudia , Danilov Sergey , Koldunov Nikolay , Sidorenko Dmitry , Sein Dmitry , Rabe Benjamin , Jung Thomas 
Published: May 2018

AbstractThe Beaufort Gyre (BG) is the largest liquid freshwater reservoir of the Arctic Ocean. The liquid freshwater content (FWC) significantly increased in the BG in the 2000s during an anticyclonic wind regime and remained at a high level despite a transition to a more cyclonic state in the early 2010s. It is not well understood to what extent the rapid sea ice decline during this period has modified the trend and variability of the BG liquid FWC in the past decade. Our numerical simulations show that about 50% of the liquid freshwater accumulated in the BG in the 2000s can be explained by the sea ice decline caused by the Arctic atmospheric warming. Among this part of the FWC increase, 60% can be attributed to surface freshening associated with the reduction of the net sea ice thermodynamic growth rate, and 40% to changes in ocean circulation, which makes freshwater more accessible to the BG for storage. Thus, the rapid increase of the BG FWC in the 2000s was due to the concurrence of the anticyclonic wind regime and the high freshwater availability. We also find that if the Arctic sea ice had not declined, the liquid FWC in the BG would have shown a stronger decreasing tendency at the beginning of the 2010s owing to the cyclonic wind regime. From our results we argue that changes in sea ice conditions should be adequately taken into account when it comes to understanding and predicting variations of BG liquid FWC in a changing climate.
Saturn's Planetary Period Oscillations During the Closest Approach of Cassini's Ring‐Grazing Orbits
Authors: Hunt G. J. , Provan G. , Cowley S. W. H. , Dougherty M. K. , Southwood D. J. 
Published: May 2018

AbstractSaturn's planetary period oscillations (PPOs) are ubiquitous throughout its magnetosphere. We investigate the PPO's azimuthal magnetic field amplitude interior to the field‐aligned currents, during the closest approaches of Cassini's ring‐grazing orbits (October 2016 to April 2017), with periapses at ~2.5 RS. The amplitudes of the northern and southern PPO systems are shown to vary as a function of latitude. The amplitude ratio between the two PPO systems shows that the northern system is dominant by a factor of ~1.3 in the equatorial plane, and it is dominant to ~ −15° latitude in the southern hemisphere. The dayside amplitudes are approximately half of the 2008 nightside amplitudes, which agree with previous local time‐related amplitude observations. Overall, there is clear evidence that the PPOs are present on field lines that map to the outer edge of Saturn's rings, closer to Saturn than previously confirmed.
Robust Broadband Maritime Communications: Theoretical and Experimental Validation
Authors: Couillard Denis , Dahman Ghassan , GrandMaison Marie‐Eve , Poitau Gwenael , Gagnon Francois 
Published: May 2018

AbstractAtmospheric ducts, which are caused by the rapid decrease in the refractive index of the lower atmosphere, have been recognized as the dominant propagation mechanism for long range maritime links. Recent advances in radio technology are making reliable high‐capacity overwater links a reality. A ray‐tracing simulation model was developed to obtain reliable prediction of maritime link performance beyond 30 km for realistic conditions. A series of static and mobile long range maritime multiple‐input multiple‐output links were tested with representative antenna heights at 1.39 (Band 3 or L‐Band) and 4.5 GHz (Band 4 or C‐Band) during periods with various levels of ducting activities, for example, sunset and sunrise times. Measured link performance and observed ducting occurrences are compared to predictions to validate the model ability to accurately predict and explain link performance for various ducting conditions. The test results agree with the model predictions and illustrate the various Received Signal Level degradation, enhancement, and fluctuations that can be expected in long range maritime links below 6 GHz. We also report on short‐term (few to several minutes) fluctuations of the received signal level at the two measurement frequency bands during high ducting activity periods. Measurements and theoretical analysis of the effect of ducting on the quality of maritime communication links indicate that both reflection‐induced and ducting‐induced disruptions are different and more frequent in higher‐frequency bands. This work opens interesting perspectives on providing more robust and more predictable communications in the presence of ducting.
DDB2 represses ovarian cancer cell dedifferentiation by suppressing ALDH1A1
Authors: Cui Tiantian , Srivastava Amit Kumar , Han Chunhua , Wu Dayong , Wani Nissar , Liu Lu , Gao Zhiqin , Qu Meihua , Zou Ning , Zhang Xiaoli , Yi Ping , Yu Jianhua , Bell Erica H. , Yang Shyh-Ming , Maloney David J. , Zheng Yanfang , Wani Altaf A. , Wang Qi-En 
Published: May 2018

AbstractCancer stem cells (CSCs), representing the root of many solid tumors including ovarian cancer, have been implicated in disease recurrence, metastasis, and therapeutic resistance. Our previous study has demonstrated that the CSC subpopulation in ovarian cancer can be limited by DNA damage-binding protein 2 (DDB2). Here, we demonstrated that the ovarian CSC subpopulation can be maintained via cancer cell dedifferentiation, and DDB2 is able to suppress this non-CSC-to-CSC conversion by repression ofALDH1A1transcription. Mechanistically, DDB2 binds to theALDH1A1gene promoter, facilitating the enrichment of histone H3K27me3, and competing with the transcription factor C/EBPβ for binding to this region, eventually inhibiting the promoter activity of theALDH1A1gene. The de-repression of ALDH1A1 expression contributes to DDB2 silencing-augmented non-CSC-to-CSC conversion and expansion of the CSC subpopulation. We further showed that treatment with a selective ALDH1A1 inhibitor blocked DDB2 silencing-induced expansion of CSCs, and halted orthotopic xenograft tumor growth. Together, our data demonstrate that DDB2, functioning as a transcription repressor, can abrogate ovarian CSC properties by downregulating ALDH1A1 expression.
Palmitic acid, but not high-glucose, induced myocardial apoptosis is alleviated by N‑acetylcysteine due to attenuated mitochondrial-derived ROS accumulation-induced endoplasmic reticulum stress
Authors: He Yang , Zhou Lingyun , Fan Zhiqiang , Liu Shikun , Fang Weijin 
Published: May 2018

AbstractPharmacological inhibition of reactive oxygen species (ROS) is a potential strategy to prevent diabetes-induced cardiac dysfunction. This study was designed to investigate precise effects of antioxidant N‑acetylcysteine (NAC) in alleviating diabetic cardiomyopathy (DCM). Echocardiography and histologic studies were performed 12 weeks after streptozocin injection. Protein levels involved in endoplasmic reticulum stress (ERS) and apoptosis were analyzed by western blotting in diabetic hearts or high-glucose (HG, 30 mM)- and palmitic acid (PA, 300 μM)-cultured neonatal rat cardiomyocytes (NRCMs). ROS generation and structural alterations of mitochondria were also assessed. We report that NAC alleviated diabetes-induced cardiac abnormality, including restored ejection fraction (EF %), fraction shortening (FS %), peak E to peak A ratio (E/A) and reduced cardiac hypertrophy and fibrosis. These effects were concomitant with blocked ERS and apoptosis, as evidenced by inactivation of phosphorylated inositol-requiring enzyme-1α (IRE1α)/spliced X-box binding protein 1 (XBP1), phosphorylated protein kinase-like kinase (PERK)/phosphorylated eukaryotic initiation factor 2α (eIF2α) and glucose-regulated protein 78 (GRP78)/activating transcription factor 6 (ATF6α)/C/EBP homologous protein (CHOP) pathways, as well as suppressed Bcl-2-associated X protein (BAX)/B-cell lymphoma-2 (Bcl-2) and cleaved caspase 3 expressions. Mechanistically, PA mediated excessive mitochondrial ROS generation and oxidative stress, which were antagonized by NAC and Mito-TEMPO, a mitochondrial ROS inhibitor. No effects were noted by addition of apocynin, a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor, and NADPH oxidase 4 (NOX 4) and NOX 2 expressions were not altered, indicating that PA-induced ROS generation is independent of NADPH oxidases. Most intriguingly, HG failed to promote ROS production despite its ability to promote ERS and apoptosis in NRCMs. Collectively, these findings indicate that NAC primarily abrogates PA-mediated mitochondrial ROS through ERS and therefore alleviates myocardial apoptosis but has little effect on HG-induced cardiac injury. This uncovers a potential role for NAC in formulating novel cardioprotective strategies in DCM patients.
Activation of TGF-β-activated kinase 1 (TAK1) restricts Salmonella Typhimurium growth by inducing AMPK activation and autophagy
Authors: Liu Wei , Jiang Yuanyuan , Sun Jing , Geng Shizhong , Pan Zhiming , Prinz Richard A. , Wang Chengming , Sun Jun , Jiao Xinan , Xu Xiulong 
Published: May 2018

AbstractAutophagy is a conserved cellular process that functions as a first-line defense to restrict the growth of invading parasitic bacteria. As an intracellular pathogen, Salmonella (S) Typhimurium invades host cells through two Type III secretion systems (T3SS) and resides in the Salmonella-containing vacuole (SCV). When the SCV membrane is perforated and ruptured by T3SS-1, a small portion of the Salmonella egresses from the SCV and replicates rapidly in the nutrient-rich cytosol. Cytosolic Salmonella and those residing in the membrane-damaged SCV are tagged by ubiquitination and marked for autophagy through the ubiquitin-binding adaptor proteins such as p62, NDP52, and optineurin. Prior studies suggest that transient intracellular amino-acid starvation and subsequent inactivation of the mechanistic target of rapamycin (mTOR), a key molecule that phosphorylates Unc-51 like autophagy activating kinase (ULK1) and inhibits its activity, can trigger autophagy in S. Typhimurium-infected cells. Other studies suggest that energy stress in S. Typhimurium-infected cells leads to AMP-activated protein kinase (AMPK) activation and autophagy. In the present study, we report that autophagy was rapidly induced in S. Typhimurium-infected cells, as evidenced by increased LC3 lipidation and decreased p62 levels. However, S. Typhimurium infection drastically increased AKT phosphorylation but decreased S6K1T389, 4E-BPT37/46, and ULK1S757 phosphorylation, suggesting that mTOR activation by AKT is subverted. Further studies showed that AMPK was activated in S. Typhimurium-infected cells, as evidenced by increased ULK1S317 and ACCS79 phosphorylation. AMPK activation was mediated by Toll-like receptor-activated TAK1. Functional studies revealed that AMPK and TAK1 inhibitors accelerated S. Typhimurium growth in HeLa cells. Our results strongly suggest that TAK1 activation leads to AMPK activation, which activates ULK1 by phosphorylating ULK1S317 and suppressing mTOR activity and ULK1S757 phosphorylation. Our study has unveiled a previously unrecognized pathway for S. Typhimurium-induced autophagy.
Caspase-3 suppresses diethylnitrosamine-induced hepatocyte death, compensatory proliferation and hepatocarcinogenesis through inhibiting p38 activation
Authors: Shang Na , Bank Thomas , Ding Xianzhong , Breslin Peter , Li Jun , Shi Baomin , Qiu Wei 
Published: May 2018

AbstractIt is critical to understand the molecular mechanisms of hepatocarcinogenesis in order to prevent or treat hepatocellular carcinoma (HCC). The development of HCC is commonly associated with hepatocyte death and compensatory proliferation. However, the role of Caspase-3, a key apoptotic executor, in hepatocarcinogenesis is unknown. In this study, we used Caspase-3-deficient mice to examine the role of Caspase-3 in hepatocarcinogenesis in a chemical (diethylnitrosamine, DEN)-induced HCC model. We found that Caspase-3 deficiency significantly increased DEN-induced HCC. Unexpectedly, Caspase-3 deficiency increased apoptosis induced by DEN and the subsequent compensatory proliferation. Intriguingly, we discovered that Caspase-3 deficiency increased the activation of p38 with and without DEN treatment. Moreover, we demonstrated that TNFα and IL1α stimulated increased activation of p38 in Caspase-3 KO hepatocytes compared with wild-type hepatocytes. Finally, we found that inhibition of p38 by SB202190 abrogated enhanced hepatocyte death, compensatory proliferation and HCC induced by DEN in Caspase-3-deficient mice. Overall, our data suggest that Caspase-3 inhibits chemical-induced hepatocarcinogenesis by suppressing p38 activation and hepatocyte death.