bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Scale Characteristics and Formation Mechanism of Aeolian Sand Streamers Based on Large Eddy Simulation
Authors: Wang Ping , Feng ShengJun , Zheng XiaoJing , Sung Hyung Jin 
Published: October 2019

AbstractAeolian sand transport near the surface in the field often occurs in the form of sand streamers, which is very important to understand in‐depth the physics of aeolian transport and accurately predict the sand transport rate. In this paper, sand streamers were successfully reproduced by combining the Lagrangian trajectory simulation of particles with large eddy simulation of turbulence. The simulated sand streamers are hill‐like. Their characteristic scales are extracted by the two‐point correlation of sand concentration. It is found that sand streamers corresponding to the correlation threshold of
are 2.0–4.5 m long and 0.3–0.4 m wide, while 30–100 m long and 1.2–2.4 m wide for
, which are substantially consistent with the existing field observation results and increases with particle size. Conditional averaging method provided an ensemble‐mean visualization of flow structures that are responsible for the formation of streamers. It is found that sand streamers on a flat and erodible surface exist in the near‐surface wake area of large/very large scale turbulent motions (LSMs/VLSMs), indicating that sand streamers are the footprint of LSMs/VLSMs. Moreover, the characteristic scales of sand streamers will be affected by the splashing process of sand saltation. On a nonerodible surface, sand streamers trailing from upstream sandy surface become narrow though it can propagate downstream for a long distance.
Extreme Wet‐Bulb Temperatures in China: The Significant Role of Moisture
Authors: Wang Pinya , Leung L. Ruby , Lu Jian , Song Fengfei , Tang Jianping 
Published: October 2019

AbstractThis paper investigates the extreme wet‐bulb temperatures (TWs) in China, with a focus on understanding the relative contributions of temperature and moisture to the extremes. Analysis of station observations shows that daily extreme temperatures (T), specific humidity (q), and TWs generally co‐occur in Southeastern China, while extreme TW and T rarely overlap in the arid and semiarid North and Northwest China. Overall, q contributes more than T to extreme TWs, especially in North and Northwest China. Based on the relative contributions of q and T, regional extreme TW events are classified as q dominated and T dominated, respectively, to study their large‐scale environment. Cluster analysis of global reanalysis data shows that extreme TWs are generally accompanied by increased surface air temperature and humidity, concomitant with anomalous high pressure and notable water vapor flux convergence. However, important differences are also seen in the large‐scale environment during q‐dominated and T‐dominated extreme TWs. During q‐dominated extreme TWs, the large‐scale environment favors convection, as indicated by ascending motions, decreased downward solar radiation as well as increased precipitable water and near‐surface relative humidity. In contrast, during T‐dominated extreme TWs, convection is inhibited by the large‐scale environment that features descending motion and increased downward solar radiation, decreased precipitable water, and decreased relative humidity. Consistent with the contrasting environments, we demonstrate that T‐dominated extreme TWs tend to last longer than q‐dominated extremes. Given the significant role of moisture in extreme TWs, more research is needed to understand its impacts on heat stress now and in the future.
Hyporheic Zone Microbiome Assembly Is Linked to Dynamic Water Mixing Patterns in Snowmelt‐Dominated Headwater Catchments
Authors: Saup C. M. , Bryant S. R. , Nelson A. R. , Harris K. D. , Sawyer A. H. , Christensen J. N. , Tfaily M. M. , Williams K. H. , Wilkins M. J. 
Published: October 2019

AbstractTerrestrial and aquatic elemental cycles are tightly linked in upland fluvial networks. Biotic and abiotic mineral weathering, microbially mediated degradation of organic matter, and anthropogenic influences all result in the movement of solutes (e.g., carbon, metals, and nutrients) through these catchments, with implications for downstream water quality. Within the river channel, the region of hyporheic mixing represents a hot spot of microbial activity, exerting significant control over solute cycling. To investigate how snowmelt‐driven seasonal changes in river discharge affect microbial community assembly and carbon biogeochemistry, depth‐resolved pore water samples were recovered from multiple locations around a representative meander on the East River near Crested Butte, CO, USA. Vertical temperature sensor arrays were also installed in the streambed to enable seepage flux estimates. Snowmelt‐driven high river discharge led to an expanding zone of vertical hyporheic mixing and introduced dissolved oxygen into the streambed that stimulated aerobic microbial respiration. These physicochemical processes contributed to microbial communities undergoing homogenizing selection, in contrast to other ecosystems where lower permeability may limit the extent of mixing. Conversely, lower river discharge conditions led to a greater influence of upwelling groundwater within the streambed and a decrease in microbial respiration rates. Associated with these processes, microbial communities throughout the streambed exhibited increasing dissimilarity between each other, suggesting that the earlier onset of snowmelt and longer periods of base flow may lead to changes in the composition (and associated function) of streambed microbiomes, with consequent implications for the processing and export of solutes from upland catchments.
Space‐Based Observations for Understanding Changes in the Arctic‐Boreal Zone
Authors: Duncan Bryan N. , Ott Lesley E. , Abshire James B. , Brucker Ludovic , Carroll Mark L. , Carton James , Comiso Josefino C. , Dinnat Emmanuel P. , Forbes Bruce C. , Gonsamo Alemu , Gregg Watson W. , Hall Dorothy K. , Ialongo Iolanda , Jandt Randi , Kahn Ralph A. , Karpechko Alexey , Kawa Stephan R. , Kato Seiji , Kumpula Timo , Kyrölä Erkki , Loboda Tatiana V. , McDonald Kyle C. , Montesano Paul M. , Nassar Ray , Neigh Christopher S.R. , Parkinson Claire L. , Poulter Benjamin , Pulliainen Jouni , Rautiainen Kimmo , Rogers Brendan M. , Rousseaux Cecile S. , Soja Amber J. , Steiner Nicholas , Tamminen Johanna , Taylor Patrick C. , Tzortziou Maria A. , Virta Henrik , Wang James S. , Watts Jennifer D. , Winker David M. , Wu Dong L. 
Published: October 2019

AbstractObservations taken over the last few decades indicate that dramatic changes are occurring in the Arctic‐Boreal Zone (ABZ), which are having significant impacts on ABZ inhabitants, infrastructure, flora and fauna, and economies. While suitable for detecting overall change, the current capability is inadequate for systematic monitoring and for improving process‐based and large‐scale understanding of the integrated components of the ABZ, which includes the cryosphere, biosphere, hydrosphere, and atmosphere. Such knowledge will lead to improvements in Earth system models, enabling more accurate prediction of future changes and development of informed adaptation and mitigation strategies. In this article, we review the strengths and limitations of current space‐based observational capabilities for several important ABZ components and make recommendations for improving upon these current capabilities. We recommend an interdisciplinary and stepwise approach to develop a comprehensive ABZ Observing Network (ABZ‐ON), beginning with an initial focus on observing networks designed to gain process‐based understanding for individual ABZ components and systems that can then serve as the building blocks for a comprehensive ABZ‐ON.
A New Method for Deriving the Nightside Thermospheric Density Based on GUVI Dayside Limb Observations
Authors: Yu Tingting , Ren Zhipeng , Yu You , Wan Weixing 
Published: October 2019

AbstractWe propose a new method to derive the nightside thermospheric density by extending Global Ultraviolet Imager (GUVI) dayside limb observations using empirical orthogonal function (EOF) analysis. First, we acquire the GUVI dayside total mass density during 2002–2005 to construct a preliminary empirical model (EM). Simultaneously, we decompose the background thermospheric density from U.S. Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar Extended model into different EOFs. The decomposed EOFs are then used to fit the continuous density from EM, to develop a new nightside extended model (NEM). The preliminary EM and developed NEM are further evaluated with Challenging Minisatellite Payload (CHAMP) satellite observations. Higher correlation coefficients and smaller relative standard errors between CHAMP observations and the NEM results are obtained than those between CHAMP observations and the EM results, and the NEM results are in good agreement with the CHAMP observations in time series during both daytime and nighttime, which all prove the NEM method is effective to the reproduction and extension of GUVI original dayside observations. Furthermore, the NEM reveals two typical seasonal variation features, the semiannual variation and equinoctial asymmetry of thermospheric density. The model provides an effective tool to derive the nightside thermospheric density and explore the thermospheric intrinsic structure, and needs the further development to achieve more widespread application of the thermosphere.
On Imaging South African Regional Ionosphere Using 4D‐var Technique
Authors: Ssessanga Nicholas , Kim Yong Ha , Habarulema John Bosco , Kwak Young‐Sil 
Published: October 2019

AbstractOne of the major research areas in the space weather community is the ability to understand, characterize, and model a time‐space variant ionosphere through which transionospheric signals propagate. In this paper a strong constraint four‐dimensional variational data assimilation (4D‐var) technique was used to more accurately estimate the South African regional ionosphere (bound latitude 20–35°S, longitude 20–40°E, and altitude 100–1,336 km). The altitude was capped to the JASON‐1 satellite orbital altitude for the purpose of eliminating the plasmasphere contribution hence reducing the computation expense. Background densities were obtained from an empirical internationally recognized ionosphere model (IRI‐2016) and propagated in time using a Gauss‐Markov filter. Ingested data were STECs (slant total electron content) obtained from the South African Global Navigation Satellite System receiver network (TrigNet). The vertically integrated electron content was validated using Global ionosphere Maps and JASON‐3 data over the continent and ocean areas, respectively. Further, vertical profiles after assimilation were compared with data from a network of ground‐based regional ionosondes Hermanus (34.25°S, 19.13°E), Grahamstown (33.3°S, 26.5°E), Louisvale (21.2°S, 28.5°E), and Madimbo (22.4°S, 30.9°E). Results show that assimilation of STEC data has a profound improvement on the estimation of both the horizontal and vertical structures during quiet and storm periods. Accuracy of the horizontal structure decreases from the continent toward the ocean area where GPS receivers are less abundant. Superiority of assimilating STEC is best pronounced during daytime especially when estimating maximum electron density of theF2 layer (NmF2), with a 60% root‐mean‐square error improvement over the background values.
Evapotranspiration Estimation for Tibetan Plateau Headwaters Using Conjoint Terrestrial and Atmospheric Water Balances and Multisource Remote Sensing
Authors: Li Xueying , Long Di , Han Zhongying , Scanlon Bridget R. , Sun Zhangli , Han Pengfei , Hou Aizhong 
Published: October 2019

AbstractSatellite remote sensing combined with water balance calculations provides a promising approach to estimating evapotranspiration (ET), a critical variable in water‐energy exchange. Here we compare ET estimates from terrestrial and atmospheric water balances, multisource remote sensing (AVHRR, GLEAM, and MOD16), and a land surface model (GLDAS NOAH) for headwaters on the Tibetan Plateau (TP), that is, headwaters of the Brahmaputra (HBR), Salween (HSR), Mekong (HMR), Yangtze (HYR), and Huang (Yellow; HHR) Rivers, for the 2003–2012 period. Results show that (1) ET estimated from terrestrial and atmospheric water balances agrees closely in three basins (HMR, HYR, and HHR) but has large discrepancies in the other two basins (HBR and HSR), mainly caused by uncertainties in the terrestrial water balance; (2) agreement between various ET products and water balance‐derived ET baselines is highest for GLEAM in two basins (HMR and HYR) and GLDAS NOAH in another two basins (HSR and HHR); and (3) large discrepancies between water balance‐derived ET and all ET products are found in the most glacierized HBR, which may reflect the importance of sublimation in the ET process. The decadal mean ET based on water balance‐derived ET baselines is highest in the HHR (447 mm/year) and HSR (430 mm/year) and lowest in the HBR (238 mm/year), ranging from 51% to 78% of mean precipitation in the five TP headwaters. These findings have important implications for ET estimation on the TP headwaters, which greatly influences downstream water availability.
Activation of Nrf2 by lead sulfide nanoparticles induces impairment of learning and memory
Authors: Cao Yanhua , Wang Dong , Li Qingzhao , Liu Huajie , Jin Cuihong , Yang Jinghua , Wu Shengwen , Lu Xiaobo , Cai Yuan 
Published: October 2019

Abstract
Lead sulfide nanoparticles (PbS NPs) are semiconductor materials that have been widely applied to light-emitting diodes (LEDs), biological fluorescent probes, infrared detection, solar receivers, ion-selective electrodes, and ion-sensitive materials. However, the effects of PbS NPs on the central nervous system are still unclear. Thus, this study aimed to determine, using rats, the mechanism of action of PbS NPs, exposure to which results in persistent alterations in nervous system function. The results of the Morris water maze test showed that PbS NPs significantly impaired learning and memory. Compared with that in the control group, the lead content in the hippocampal tissue was significantly elevated after PbS NP exposure. Exposure to PbS NPs led to increased oxidative damage in blood and hippocampal tissues, and significantly inhibited the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) while increasing the serum malondialdehyde (MDA) content. In addition, reactive oxygen species triggered the activation of Nrf2 and the antioxidant system, including HO-1, r-GCS, and GSH-Px. Moreover, we observed significant apoptosis in the hippocampi of the rats using the TUNEL assay and transmission electron microscopy. The MOD values from the TUNEL assay of the hippocampi were all significantly higher than those of the control group, which increased as the concentration of the PbS NPs increased. There were also changes in the ultrastructure of the hippocampal neurons and synapses in the PbS-treated rats, including a shorter synaptic active zone, smaller curvature of the synaptic interface, and thicker postsynaptic density. Therefore, PbS NP exposure could lead to increased brain lead content, oxidative damage, and apoptosis.
Anti‐icing measures in the Italian power system
Authors: Quaia Stefano , Marchesin Alessio , Rampazzo Davide , Mancuso Cristian 
Published: October 2019

Despite the good operating results of passive anti‐icing devices installed by the Italian transmission system operator (TSO) on high‐voltage overhead lines (OHLs), the increasing number and consequences of wet snow events have prompted consideration of other anti‐icing measures. In particular, attention focuses on the thermal approach, which is intended to achieve – before, or in the early stage of wet snow events – the anti‐icing current in OHL phase conductors where snow sleeve formation is foreseen. The authors carried out a specific anti‐icing study with reference to a 132 kV critical path in an area of the Apennines, with simulation results illustrated in this study. Anti‐icing measures investigated were (i) load shifting actions and (ii) insertion of shunt reactors used as ballast loads. The results show that shunt reactors are the most effective anti‐icing measure. The main disadvantage of this innovative solution is the degradation of voltage regulation in the area. However, this downside can be limited by combining the insertion of reactors with control of autotransformers under load tap changers. Similar results are obtained from analyses of other critical areas. As a result of these findings, the Italian TSO is now undertaking the installation of the first ballast reactors.
Boost‐integrated LCL resonant converter with high voltage gain
Authors: Yuan Yisheng , Zhang Zhongyi , Mei Xianglong 
Published: October 2019

A boost‐integrated LCL resonant DC–DC converter is proposed, which is constituted by a full‐bridge inverter module, the main transformer and a flyback transformer, resonant unit, and a rectifier module. The primary winding of the flyback transformer is also used as a resonant inductor and a boost inductor to improve the power density and the voltage gain. In order to meet different output environments, the converter can operate in low voltage‐gain mode or high voltage gain mode. In low voltage‐gain mode, the converter operates in PWM with LCL resonance. In high voltage‐gain mode, the converter operates in PWM with boost and LCL resonance, in which boost modulation plays a role before the LCL resonance to increase the output voltage. Compared with the conventional LCL resonant converter, the new converter has higher voltage gain and is more suitable for a wide output range with the same resonant parameters. The operation principles of the proposed converter are clarified. A prototype with 80–140V output and maximum output current 2.9 A is built, and experimental data shows that the maximum efficiency of the prototype can be 94.5%, verifying the correctness of the theoretical analysis.
Low‐cost analogue active gate driver for SiC MOSFET to enable operation in higher parasitic environment
Authors: Krishna Miryala Vamshi , Hatua Kamalesh 
Published: October 2019

Operating silicon carbide (SiC) metal–oxide–semiconductor field‐effect transistor (MOSFET) at its rated switching speed may not be always feasible due to excessive voltage and current overshoot and ringing caused by layout parasitic inductance and load parasitic capacitance. This study proposes a low‐cost analogue active gate driver technique for switching SiC MOSFET in the presence of moderate amount of layout parasitic inductance (<200 nH) and load parasitic capacitance (<300 pF). In this study, a based closed‐loop active gate driver circuit is implemented using low‐cost signal level transistors. The present work explains the working of the gate driver during turn‐on and turn‐off switching transients. A detailed design methodology for the gate driver is presented using its high‐frequency model. The proposed active gate driver (AGD) has been verified in hardware platform using a double pulse test setup and in a boost converter test setup. Cree make 1200 V, 36 A SiC MOSFET (C2M0080120D) is used for evaluating the proposed active gate driver. The proposed circuit has sufficient operating bandwidth to drive SiC MOSFET and it is realised with low‐cost transistors.
Enhanced beamspace MUSIC for cost‐effective FMCW automotive radar
Authors: Li Yang , Zhang Cheng , Song Yixin , Huang Yongming 
Published: October 2019

As one important sensor for automotive applications, frequency modulated continuous wave (FMCW) radars working at millimetre wave frequency, e.g. 24 or 77 GHz, are drawing much attention in recent years. Compared with range and radial velocity measurement, direction of arrival (DOA) estimation is more challenging in FMCW automotive radars due to the space limitation and computational complexity constraint. The feature of the signal processing procedure further results in the problem of single snapshot and relatively low signal‐to‐noise ratio (SNR) level. In this study, the authors propose a low‐complexity beamspace multiple signal classification (MUSIC) scheme to improve the DOA estimation performance, where (i) the prior information is exploited to improve beamformer design, (ii) a modified MUSIC estimator is formulated to alleviate the performance degradation due to low SNR, (iii) a joint sub‐matrix averaging and Toeplitz structure recovery processing is utilised to compensate the sample covariance estimation error resulted from single snapshot, especially for closely located targets. Simulations are given to demonstrate the efficiency of the authors’ proposed enhanced beamspace DOA estimation for cost‐effective FMCW automotive radar.
Tomography of cool giant and supergiant star atmospheres
Authors: Kravchenko K. , Chiavassa A. , Van Eck S. , Jorissen A. , Merle T. , Freytag B. , Plez B. 
Published: October 2019

Context. Red supergiants are cool massive stars and are the largest and the most luminous stars in the Universe. They are characterized by irregular or semi-regular photometric variations, the physics of which is not clearly understood.
Aims. The paper aims to derive the velocity field in the red supergiant star μ Cep and to relate it to the photometric variability with the help of the tomographic method.
Methods. The tomographic method allows one to recover the line-of-sight velocity distribution over the stellar disk and within different optical-depth slices. This method was applied to a series of high-resolution spectra of μ Cep, and these results are compared to those obtained from 3D radiative-hydrodynamics CO5BOLD simulations of red supergiants. Fluctuations in the velocity field are compared with photometric and spectroscopic variations, the latter were derived from the TiO band strength and serve, at least partly, as a proxy of the variations in effective temperature.
Results. The tomographic method reveals a phase shift between the velocity and spectroscopic and photometric variations. This phase shift results in a hysteresis loop in the temperature – velocity plane with a timescale of a few hundred days, which is similar to the photometric one. The similarity between the hysteresis loop timescale measured in μ Cep and the timescale of acoustic waves disturbing the convective pattern suggests that such waves play an important role in triggering the hysteresis loops.