Flashover Performance and Process of Suspension Insulator Strings Artificially Covered with Snow

Snow accumulates on the surface of insulator string, causing a decrease in its electrical performance, seriously threatening the reliable operation of the power grid. Most previous studies have focused on iced insulators; however, there is a lack of research on snow-covered insulators. In this paper, to reveal the influencing mechanism that snow has on the electrical characteristics of insulator string, based on an artificial snowing test in a chamber, the effects of equivalent salt deposit density, applied voltage type, and snow thickness on the flashover performance of snow-covered insulators are analyzed, and the flashover process is investigated. The results show that the relationship between the arc flashover gradient and the equivalent salt deposit density is a power function with a negative exponent, which is similar to that of polluted and ice-covered insulator strings. For the insulator strings with the same snow accretion, the direct current (DC) arc flashover gradient is lower than the alternating current (AC) arc flashover gradient. The relationship between arc flashover gradient and snow thickness is also a power function. The formation of a dry band during the flashover of snow-covered insulator string is similar to the flashover of the polluted insulator, and the arc propagation along the surface of the snow-covered insulator is similar to the flashover of the iced insulator

Collaborative Reinforcement Learning Based Unmanned Aerial Vehicle (UAV) Trajectory Design for 3D UAV Tracking

In this paper, the problem of using one active unmanned aerial vehicle (UAV)and four passive UAVs to localize a 3D target UAV in real time is investigated.In the considered model, each passive UAV receives reflection signals from thetarget UAV, which are initially transmitted by the active UAV. The receivedreflection signals allow each passive UAV to estimate the signal transmissiondistance which will be transmitted to a base station (BS) for the estimation ofthe position of the target UAV. Due to the movement of the target UAV, eachactive/passive UAV must optimize its trajectory to continuously localize thetarget UAV. Meanwhile, since the accuracy of the distance estimation depends onthe signal-to-noise ratio of the transmission signals, the active UAV mustoptimize its transmit power. This problem is formulated as an optimizationproblem whose goal is to jointly optimize the transmit power of the active UAVand trajectories of both active and passive UAVs so as to maximize the targetUAV positioning accuracy. To solve this problem, a Z function decompositionbased reinforcement learning (ZD-RL) method is proposed. Compared to valuefunction decomposition based RL (VD-RL), the proposed method can find theprobability distribution of the sum of future rewards to accurately estimatethe expected value of the sum of future rewards thus finding better transmitpower of the active UAV and trajectories for both active and passive UAVs andimproving target UAV positioning accuracy. Simulation results show that theproposed ZD-RL method can reduce the positioning errors by up to 39.4% and64.6%, compared to VD-RL and independent deep RL methods, respectively

Influence of water temperature, habitat complexity and light on the predatory performance of the dark sleeperOdontobutis potamophila(Gunther, 1861)

Recently, the dark sleeper [Odontobutis potamophila(Gunther, 1861)] was selected as a potential aquaculture target. However, the feeding behavior of this species remains unclear. In this study, we investigated the influence of water temperature, habitat type, light intensity and photoperiod on the predatory performance of dark sleepers against juvenile demersal mrigal carp [Cirrhinus mrigala(Hamilton, 1822)] in the laboratory. Our results showed that both the prey consumption and the feeding rate of dark sleepers increased significantly with increases in water temperature (22-34 degrees C) and stabilized between 26-34 degrees C. Additionally, both the prey consumption and the feeding rate were higher in vegetated habitats than those in open areas at 22-30 degrees C, although no significant differences were detected. The prey consumption and the feeding rate of dark sleepers increased significantly with decreased light intensity (0-1350 lx) and shortened light duration (0-14 h), indicating that this fish prefers feeding in dark environments. These results will help elucidate the influence of environmental variables on this species' predatory performance and create suitable protocols for its culture

Divergent adaptation to Qinghai Tibetan Plateau implicated from transciptome study of Gymnocypris dobula and Schizothorax nukiangensis

The Schizothoracine fishes are widely distributed in the Qinghai-Tibetan Plateau (QTP) area and its peripheral regions, which provide a prime example of adaptation in highland aquatic environments. Recent progresses have revealed various genetic adaptations of these fishes by comparing to distantly related lowerland species, however, comparative studies on closely-related species of different altitudes are still lacking. In this study, we sequenced and annotated a primitive Schizothoracine fish Schizothorax nukiangensis Tsao and a highly specialized one Gymnocypris dobula. We performed evolutionary analyses to investigate the candidate genes and signaling pathways involved QTP highland adaptation in both Schizothoracine fishes. Analysis of the 11,007 one-copy orthologs to the primitive cyprinid species, Danio rerio, revealed that both G. dobula and S. nukiangensis showed elevated evolutionary rates. A large number of genes related to hypoxia, including genes involved metabolic processes and cardiovascular system development, exhibited signatures of positive selection in both Schizothoracine fishes, but very few positively selected genes were found overlapping among these Schizothoracines. Our results indicated divergent genetic adaptation to highland environment for aquatic species living in QTP. (C) 2017 Elsevier Ltd. All rights reserved

Data from: Evolutionary suppression of erythropoiesis via the modulation of TGF-β signaling in an Antarctic icefish

The Antarctic icefish, a family (Channichthyidae) of teleosts within the perciform suborder Notothenioidei, are the only known vertebrates without oxygen-transporting haemoglobins and that are largely devoid of circulating erythrocytes. To elucidate the evo-devo mechanisms underpinning the suppressed erythropoiesis in the icefish, we conducted comparative studies on the transcriptomes and microRNAomes of the primary haematopoietic tissues between an icefish (Chionodraco hamatus) and two red-blooded notothenioids (Trematomus bernacchii and Gymnodraco acuticeps). We identified substantial remodelling of the haematopoietic programs in the icefish through which erythropoiesis is selectively suppressed. Experimental verification showed that erythropoietic suppression in the icefish may be attributable to the upregulation of TGF-β signalling, which coincides with reductions in multiple transcription factors essential for erythropoiesis and the upregulation of hundreds of microRNAs, the majority (> 80%) of which potentially target erythropoiesis regulating factors. Of the six microRNAs selected for verification, three miRNAs (miR-152, miR-1388 and miR-16b) demonstrated suppressive functions on GATA1 and ALAS2, which are two factors important for erythroid differentiation, resulting in reduced numbers of erythroids in microinjected zebra fish embryos. Codon substitution analyses of the genes of the TGF-β superfamily revealed signs of positive selection in TGF-β1 and endoglin in the lineages leading to Antarctic notothenioids. Both genes are previously known to function in erythropoietic suppression. These findings implied a general trend of erythropoietic suppression in the cold-adapted notothenioid lineages through evolutionary modulation of the multi-functional TGF-β signalling pathway. This trend is more pronounced in the haemoglobin-less icefish, which may pre-emptively hinder the otherwise defective erythroids from production

Genetic Adaptation of Schizothoracine Fish to the Phased Uplifting of the Qinghai-Tibetan Plateau

Many species of Schizothoracine, a subfamily of Cyprinidae, are highly endemic to the Qinghai-Tibetan Plateau (QTP). To characterize the adaptive changes associated with the Schizothoracine expansion at high altitudes, we sequenced tissue transcriptomes of two highland and two subhighland Schizothoracines and analyzed gene evolution patterns by comparing with lowland cyprinids. Phylogenetic tree reconstruction and divergence time estimation indicated that the common ancestor of Schizothoracine fish lived approximate to 32.7 million years ago (MYA), coinciding with the timing of the first phase of QTP uplifting. Both high- and subhigh-Schizothoracines demonstrated elevated dN/dS ratios in the protein-coding genes compared to lowland cyprinids, from which some biological processes implicated in altitude adaptation were commonly identified. On the other hand, the highland and subhighland lineages presented drastically divergent landscapes of positively selected genes (PSGs), enriched with very different gene ontology (GO) profiles, including those in sensory organ morphogenesis, regulation of protein ubiquitination, blood circulation, and blood vessel development. These results indicated different selection pressures imposed on the highland and subhighland lineages of the Schizothoracine subfamily, with a higher number of genes in the high-altitude species involved in adaptations such as sensory perception, blood circulation, and protein metabolism. Our study indicated divergent genetic adaptations in the aquatic species facing the phased uplifting of QTP

Magnetostratigraphy of the Fenghuoshan Group in the Hoh Xil Basin and its tectonic implications for India?Eurasia collision and Tibetan Plateau deformation

Early Cenozoic plate collision of India and Eurasia was a significant geological event, which resulted in Tibetan Plateau (TP) uplift and altered regional and global atmospheric circulations. However, the timing of initial collision is debated. It also remains unclear whether the TP was deformed either progressively northward, or synchronously as a whole. As the largest basin in the hinterland of the TP, evolution of the Hoh Xil Basin (HXB) and its structural relationship with development of the Tanggula Thrust System (TTS) have important implications for unraveling the formation mechanism and deformation history of the TP. In this study, we present results from a long sedimentary sequence from the HXB that dates the Fenghuoshan Group to ∼72–51 Ma based on magnetostratigraphy and radiometric ages of a volcanic tuff layer within the group. Three depositional phases reflect different stages of tectonic movement on the TTS, which was initialized at 71.9 Ma prior to the India–Eurasia collision. An abrupt sediment accumulation rate increase from 53.9 Ma is a likely response to tectonic deformation in the plateau hinterland, and indicates that initial India–Eurasia collision occurred at no later than that time. This remote HXB tectonosedimentary response implies that compressional deformation caused by India–Eurasia collision likely propagated to the central TP shortly after the collision, which supports the synchronous deformation model for TP.This work was supported by the “Strategic Priority Research Program” (Pan-Third Pole Environment Study for a Green Silk Road) of the CAS, National Basic Research Program of China (2013CB956403), and the NSFC (41421002, 41672168, 41672200 and 41772200)

Intrinsic room-temperature ferromagnetism in a two-dimensional semiconducting metal-organic framework

Abstract The development of two-dimensional (2D) magnetic semiconductors with room-temperature ferromagnetism is a significant challenge in materials science and is important for the development of next-generation spintronic devices. Herein, we demonstrate that a 2D semiconducting antiferromagnetic Cu-MOF can be endowed with intrinsic room-temperature ferromagnetic coupling using a ligand cleavage strategy to regulate the inner magnetic interaction within the Cu dimers. Using the element-selective X-ray magnetic circular dichroism (XMCD) technique, we provide unambiguous evidence for intrinsic ferromagnetism. Exhaustive structural characterizations confirm that the change of magnetic coupling is caused by the increased distance between Cu atoms within a Cu dimer. Theoretical calculations reveal that the ferromagnetic coupling is enhanced with the increased Cu-Cu distance, which depresses the hybridization between 3d orbitals of nearest Cu atoms. Our work provides an effective avenue to design and fabricate MOF-based semiconducting room-temperature ferromagnetic materials and promotes their practical applications in next-generation spintronic devices

Polaronic Trions Induced by Strong Interfacial Coupling in Monolayer WSe2

The weak dielectric screening in 2D semiconducting transition metal dichalcogenides give rise to strongly bound quasiparticles, which provides a platform to investigate the diverse excitonic phenomena and correlated physics. However, how to effectively control these quasiparticles is still a challenge for their applications in optoelectronic and valleytronic devices. Herein, by means of fabricating monolayer WSe2 and transition metal oxide (TMO) heterostructures, polaronic trion, that is a trion dressed with soft rotational optical (RO) phonons, is realized due to the strong interfacial coupling. This Fröhlich bound state of trion dramatically increases the trion binding energy (BE) from room temperature to 65 meV at 80 K in WSe2/LaAlO3 (LAO). However, the increase of the trion BE for WSe2/SrTiO3 (STO) occurs below the phase transition temperature. This work expands the possibilities of the TMDs/TMOs heterostructures and promotes the development of 2D van der Waals materials for quasiparticle-based devices