Nodal and Nematic Superconducting Phases in NbSe2_2 Monolayers from Competing Superconducting Channels

Transition metal dichalcogenides like 2H-NbSe$_2$ in their two-dimensional (2D) form exhibit Ising superconductivity with the quasiparticle spins are firmly pinned in the direction perpendicular to the basal plane. This enables them to withstand exceptionally high magnetic fields beyond the Pauli limit for superconductivity. Using field-angle-resolved magnetoresistance experiments for fields rotated in the basal plane we investigate the field-angle dependence of the upper critical field (Hc$_2$), which directly reflects the symmetry of the superconducting order parameter. We observe a six-fold nodal symmetry superposed on a two-fold symmetry. This agrees with theoretical predictions of a nodal topological superconducting phase near Hc$_2$, together with a nematic superconducting state. We demonstrate that in NbSe$_2$ such unconventional superconducting states can arise from the presence of several competing superconducting channels

Nodal and Nematic Superconducting Phases in NbSe2_2 Monolayers from Competing Superconducting Channels

Transition metal dichalcogenides like 2H-NbSe$_2$ in their two-dimensional (2D) form exhibit Ising superconductivity with the quasiparticle spins are firmly pinned in the direction perpendicular to the basal plane. This enables them to withstand exceptionally high magnetic fields beyond the Pauli limit for superconductivity. Using field-angle-resolved magnetoresistance experiments for fields rotated in the basal plane we investigate the field-angle dependence of the upper critical field (Hc$_2$), which directly reflects the symmetry of the superconducting order parameter. We observe a six-fold nodal symmetry superposed on a two-fold symmetry. This agrees with theoretical predictions of a nodal topological superconducting phase near Hc$_2$, together with a nematic superconducting state. We demonstrate that in NbSe$_2$ such unconventional superconducting states can arise from the presence of several competing superconducting channels

Low-frequency oscillation of train–network system considering traction power supply mode

Abstract The low-frequency oscillation (LFO) has occurred in the train–network system due to the introduction of the power electronics of the trains. The modeling and analyzing method in current researches based on electrified railway unilateral power supply system are not suitable for the LFO analysis in a bilateral power supply system, where the trains are supplied by two traction substations. In this work, based on the single-input and single-output impedance model of China CRH5 trains, the node admittance matrices of the train–network system both in unilateral and bilateral power supply modes are established, including three-phase power grid, traction transformers and traction network. Then the modal analysis is used to study the oscillation modes and propagation characteristics of the unilateral and bilateral power supply systems. Moreover, the influence of the equivalent inductance of the power grid, the length of the transmission line, and the length of the traction network are analyzed on the critical oscillation mode of the bilateral power supply system. Finally, the theoretical analysis results are verified by the time-domain simulation model in MATLAB/Simulink

Effective Real-Time Android Application Auditing

Mobile applications can access both sensitive personal data and the network, giving rise to threats of data leaks. App auditing is a fundamental program analysis task to reveal such leaks. Currently, static analysis is the de facto technique which exhaustively examines all data flows and pinpoints problematic ones. However, static analysis generates false alarms for being over-estimated and requires minutes or even hours to examine a real app. These shortcomings greatly limit the usability of automatic app auditing. To overcome these limitations, we design AppAudit that relies on the synergy of static and dynamic analysis to provide effective real-time app auditing. AppAudit embodies a novel dynamic analysis that can simulate the execution of part of the program and perform customized checks at each program state. AppAudit utilizes this to prune false positives of an efficient but over-estimating static analysis. Overall, AppAudit makes app auditing useful for app market operators, app developers and mobile end users, to reveal data leaks effectively and efficiently. We apply AppAudit to more than 1,000 known malware and 400 real apps from various markets. Overall, AppAudit reports comparative number of true data leaks and eliminates all false positives, while being 8.3x faster and using 90% less memory compared to existing approaches. AppAudit also uncovers 30 data leaks in real apps. Our further study reveals the common patterns behind these leaks: 1) most leaks are caused by 3rd-party advertising modules; 2) most data are leaked with simple unencrypted HTTP requests. We believe AppAudit serves as an effective tool to identify data-leaking apps and provides implications to design promising runtime techniques against data leaks. Keywords-approximated execution; program analysis; pri-vacy; mobile application; I

Progress of HDDR NdFeB powders modulated by the diffusion of low melting point elements and their alloys

The hydrogenation-disproportionation-desorption-recombination (HDDR) process is the main technique for the fabrication of anisotropic NdFeB magnetic powder.But the intrinsic coercivity (HC) of HDDR magnetic powder is low.The addition of heavy rare earth element Dy could improve its HC.It was found that the added Dy is mainly distributed in the grain boundary of HDDR magnets,which regulates grain boundary phase and increases the thickness of grain boundary to improve the anisotropy field (HA) and HC of the magnets.However,Dy becomes scarcer and more expensive,which limits the practical application of HDDR magnets.To reduce the dependence on heavy rare earth elements and cost,researchers replaced the heavy rare earth element Dy by low melting point elements and their alloys through grain boundary diffusion technique.During diffusion process low melting point metal exists as liquid phase that increases the diffusion coefficient of diffusion medium as well as its contact area with grain boundary phases of HDDR magnets,and benefits its diffusion along grain boundaries and regulation of grain boundary phase.The modified grain boundary in magnets improve HC.This review paper focuses on the research progress in improving HC of HDDR NdFeB magnets by low melting point elements and their alloys

Mechanism of Land Subsidence Mutation in Beijing Plain under the Background of Urban Expansion

Under the background of over-exploitation of groundwater and urban expansion, the land subsidence in the Beijing Plain has dramatically increased recently, and has demonstrated obvious mutation characteristics. Firstly, this paper used the land-use transfer matrix (LUTM) to quantify the urban expansion of Beijing, from 1990 to 2015. Secondly, the gravity center migration model (GCM) and standard deviation ellipse (SDE) methods were employed in order to quantitatively reveal the response relationship between urban expansion and land subsidence in the study area. Finally, the research innovatively combines multi-disciplinary (remote sensing, geophysical prospecting, spatial analysis, and hydrogeology), to analyze the mechanism of land subsidence mutation in the Beijing Plain, at multiple scales. The results showed the following: 1. The development direction of the urban expansion and the subsidence bowl (subsidence rate > 50 mm/year) were highly consistent, with values of 116.8° and 113.3°, respectively. 2. At the regional scale, the overall spatial distribution of subsidence mutations is controlled by the geological conditions, and the subsidence mutation time was mainly in 2005 and 2015. The area where mutation occurred in 2005 was basically located in the subsidence bowls, and the correlation between the confined water level and the subsidence rate was relatively high (r > 0.62). The area where the settlement mutation occurred in 2015, was mainly located outside the subsidence bowls, and the correlation between the confined water level and the subsidence rate was relatively low (r < 0.71). 3. In the typical subsidence area, the subsidence mutation occurred mostly in the places where the stratigraphic density is reduced, due to human activities (such as groundwater exploitation). Human activities caused the reduction in stratigraphic density, at 20 m and 90 m vertical depth in urban and rural areas, respectively. 4. At the local scale, clusters of subsidence mutation were located in the fault buffer zone, with a lateral influence range of nearly 1 km in Tongzhou. The scattered settlement mutation is distributed as a spot pattern, and the affected area is relatively small, which basically includes high-rise buildings

Progress of sintered NdFeB permanent magnets by the diffusion of non-rare earth elements and their alloy compounds

It has been found that the coercivity (HC) and corrosivity of sintered NdFeB magnets are closely related to the components and microstructure of their intergranular phase.The traditional smelting NdFeB magnets with adding heavy rare earth elements can modify intergranular phase to improve the HC and corrosion resistance of magnets.However,it makes the additives be homogenously distributed on the main phase,and causes magnetic decrease and cost increase.With the addition of non-rare earth materials into grain boundary,the microstructure of intergranular phase as well as its electrochemical potential and wettability can be optimized.As a result,the amount of heavy rare earth elements and cost of magnets could be reduced whilst the HC and corrosion resistance of magnets can be improved.This paper summarized the research on regulating the components and the microstructure of intergranular phase in sintered NdFeB magnets by non-rare earth metals and compounds,and its influence on coercivity and corrosion resistance

Change in regional land subsidence in Beijing after south-to-north water diversion project observed using satellite radar interferometry

Over-exploitation of groundwater has caused severe land subsidence in Beijing during the past two decades. Since the middle route of South-to-North Water Diversion Project (SNWDP), the biggest water diversion project in China, started to deliver water to Beijing in December 2014, the groundwater shortage has been greatly alleviated. This study aims to analyze the impact of SNWDP on the spatiotemporal evolution of land subsidence in Beijing. Change in surface displacement in Beijing after SNWDP was retrieved and the spatiotemporal patterns of the change were analyzed based on long time-series Envisat Advanced Synthetic Aperture Radar (ASAR) (2004–2010), Radarsat-2 (2011–2014), and Sentinel-1 (2015–2017) satellite datasets using Permanent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) techniques. Land subsidence unevenness index (LSUI) was proposed to represent the spatial unevenness of surface displacement. PS-Time approach was then adapted to examine the time series evolution of LSUI. The results showed that the InSAR measurements agree well with leveling measurements with R2 over 0.96. Although the maximum annual displacement rate reached −159.7 mm/year by 2017, over 57% of the area within 25 mm/year contour line showed decreasing or unchanged displacement rate after the south-north water delivered to Beijing. The settlement rate in Chaoyang-Dongbalizhuang (CD) subsidence center has decreased for 26 mm/year from 2011–2014 to 2015–2017. Only around 15% of the area experienced continued accelerating settlement rate through the three time periods, which was mainly located in the area with the compressible layer thickness over 190 m, while the magnitude of velocity increment considerably decreased after SNWDP. Land subsidence unevenness, represented by LSUI, developed more slowly after SNWDP than that during 2011–2014. However, LSUI at the edge of settlement funnel has kept developing and reached 1.7‰ in 2017. Decreasing groundwater level decline after SNWDP and the positive relationship (R2 > 0.74) between land subsidence and groundwater level clearly showed impacts of SNWDP on the alleviating land subsidence. Other reasons include geological background, increasing precipitation, and strict water management policies implemented during these years

A New Hybrid Algorithm to Image Lightning Channels Combining the Time Difference of Arrival Technique and Electromagnetic Time Reversal Technique

Very-high-frequency (VHF) electromagnetic signals have been well used to image lightning channels with high temporal and spatial resolution due to their capability to penetrate clouds. A lightning broadband VHF interferometer with three VHF antennas configured in a scalene-triangle shape has been installed in Lhasa since 2019, to detect the lightning VHF signals. Using the signals from the VHF interferometer, a new hybrid algorithm, called the TDOA-EMTR technique, combining the time difference of arrival (TDOA) and the electromagnetic time reversal (EMTR) technique is introduced to image the two-dimensional lightning channels. The TDOA technique is firstly applied to calculate the initial solutions for the whole lightning flash. According to the results by the TDOA method, the domain used for the EMTR technique is predetermined, and then the EMTR technique is operated to obtain the final positioning result. Unlike the original EMTR technique, the low-power frequency points for each time window are removed based on the FFT spectrum. Metrics used to filter noise events are adjusted. Detailed imaging results of a negative cloud-to-ground (CG) lightning flash and an intra-cloud (IC) lightning flash by the TDOA method and the TDOA-EMTR are presented. Compared with the original EMTR method, the positioning efficiency can be improved by more than a factor of 3 to 4, depending on the scope of the pre-determined domain. Results show that the new algorithm can obtain much weaker radiation sources and simultaneously occurring sources, compared with the TDOA method