bluuebunny/crossref_metadata_2025_split huggingface dataset:
Constraining the population of isolated massive stars within the Central Molecular Zone
Authors: Clark J. S. , Patrick L. R. , Najarro F. , Evans C. J. , Lohr M. 
Published: February 2021

Context. Many galaxies host pronounced circumnuclear starbursts, fuelled by infalling gas. Such activity is expected to drive the secular evolution of the nucleus and generate super winds which enrich the interstellar and intergalactic medium. Moreover, given the intense radiation fields and extreme gas and cosmic ray densities present within such regions, one might question whether star formation proceeds in a different manner to that occurring in more quiescent regions of the galactic disc, potentially leading to a dependence of the stellar initial mass function on the local environment.
Aims. To address the physics of circumnuclear starbursts, we are driven to observe the centre of our own Galaxy, which is the only example where individual stars may be resolved. Previous studies have revealed a rich population of very massive stars, found in three young massive clusters as well as being distributed, in apparent isolation, throughout the inner ∼500 pc of the Galaxy. In this paper we investigate the size and composition of the latter cohort in order to constrain its origin and role in the lifecycle of the Galactic Centre.
Methods. To accomplish this, we utilised the Very Large Telescope + K-band Multi-Object Spectrograph to obtain homogeneous, high signal-to-noise ratio observations of known and candidate massive stars suitable for spectral classification and quantitative analysis.
Results. We identified 17 new isolated massive stars and reclassified a further 19 known examples, leading to a total of at least 83 within the Galactic Centre. Due to the selection criteria employed, these were strongly biased towards stars with powerful stellar winds and/or extensive circumstellar envelopes; as such, we suspect the resultant census to be incomplete. No further stellar clusters, or their tidally stripped remnants, were identified, although an apparent overdensity of very young and massive stars is found to be coincident with the Sgr B1 star forming region.
Conclusions. Despite the limitations of the current dataset, the size of the cohort of outlying massive stars within the Galactic Centre is directly comparable to that of the known clusters and, assuming a comparable mass function, is expected to exceed this number. Combining both cluster and isolated populations yields ≳320 spectroscopically classified stars within the Galactic Centre that are sufficiently massive that they might be anticipated to undergo core collapse within the next ∼20 Myr. Given this is almost certainly a substantial underestimate of the true number, the population of massive stars associated with the Galactic Centre appears unprecedented within the Milky Way, and it appears unavoidable that they play a substantial role in the energetics and evolution of this region.
A study of the H I gas fractions of galaxies at z ∼ 1
Authors: Zhang Wei , Kauffmann Guinevere , Wang Jing , Chen Yanmei , Fu Jian , Wu Hong 
Published: February 2021

Aims. Due to the fact that H I mass measurements are not available for large galaxy samples at high redshifts, we apply a photometric estimator of the H I-to-stellar mass ratio (MHI/M*), calibrated using a local Universe sample of galaxies, to a sample of galaxies at z ∼ 1 in the DEEP2 survey. We use these H I mass estimates to calculate H I mass functions (HIMFs) and cosmic H I mass densities (ΩHI) as well as to examine the correlation between star formation rates and H I gas content for galaxies at z ∼ 1.
Methods. We have estimated H I gas masses for ∼7000 galaxies in the DEEP2 survey with redshifts in the range 0.75 < z < 1.4 and stellar masses M* ≳ 1010 M⊙ using a combination of the rest-frame ultraviolet-optical colour (NUV − r) and stellar mass density (μ*) to estimate MHI/M*.
Results. It is found that the high-mass end of the high-z HIMF is quite similar to that of the local HIMF. The lower limit of ΩHI,limit = 2.1 × 10−4 h70−1, obtained by directly integrating the H I mass of galaxies with M* ≳ 1010 M⊙, confirms that massive star-forming galaxies do not dominate the neutral gas at z ∼ 1. We study the evolution of the H I-to-stellar mass ratio from z ∼ 1 to today and find a steeper relation between the H I gas mass fraction and stellar mass at higher redshifts. Specifically, galaxies with M* = 1011 M⊙ at z ∼ 1 are found to have 3−4 times higher neutral gas fractions than local galaxies, while the increase is as high as 4−12 times at M* = 1010 M⊙. The quantity MHI/SFR exhibits very large scatter, and the scatter increases from factors of 5−7 at z = 0 to factors close to 100 at z = 1. This implies that there is no relation between H I gas and star formation in high-redshift galaxies. The H I gas must be linked to cosmological gas accretion processes at high redshifts.
Probing core overshooting using subgiant asteroseismology: The case of KIC10273246
Authors: Noll A. , Deheuvels S. , Ballot J. 
Published: February 2021

Context.The size of convective cores remains uncertain, despite their substantial influence on stellar evolution, and thus on stellar ages. The seismic modeling of young subgiants can be used to obtain indirect constraints on the core structure during main sequence, thanks to the high probing potential of mixed modes.Aims.We selected the young subgiant KIC10273246, observed byKepler, based on its mixed-mode properties. We thoroughly modeled this star, with the aim of placing constraints on the size of its main-sequence convective core. A corollary goal of this study is to elaborate a modeling technique that is suitable for subgiants and can later be applied to a larger number of targets.Methods.We first extracted the parameters of the oscillation modes of the star using the fullKeplerdata set. To overcome the challenges posed by the seismic modeling of subgiants, we propose a method that is specifically tailored to subgiants with mixed modes and uses nested optimization. We then applied this method to perform a detailed seismic modeling of KIC10273246.Results.We obtain models that show good statistical agreements with the observations, both seismic and non-seismic. We show that including core overshooting in the models significantly improves the quality of the seismic fit, optimal models being found forαov = 0.15. Higher amounts of core overshooting strongly worsen the agreement with the observations and are thus firmly ruled out. We also find that having access to twog-dominated mixed modes in young subgiants allows us to place stronger constraints on the gradient of molecular weight in the core and on the central density.Conclusions.This study confirms the high potential of young subgiants with mixed modes to investigate the size of main-sequence convective cores. It paves the way for a more general study including the subgiants observed withKepler, TESS, and eventually PLATO.
Anomalous vortex liquid in charge-ordered cuprate superconductors
Authors: Hsu Yu-Te , Berben Maarten , Čulo Matija , Adachi Seiji , Kondo Takeshi , Takeuchi Tsuneshiro , Wang Yue , Wiedmann Steffen , Hayden Stephen M. , Hussey Nigel E. 
Published: February 2021

Significance
The magnetic-field scale at which superconducting vortices persist in underdoped cuprate superconductors has remained a controversial subject. Here we present an electrical transport study on three distinctly different cuprate families, at temperatures down to 0.32 K and magnetic fields up to 45 T. We reveal the presence of an anomalous vortex liquid state with a highly nonohmic resistivity in all three materials, irrespective of the level of disorder or structural details. The doping and field regime over which this anomalous vortex state persists suggests its occurrence is tied to the presence of long-range charge order under high magnetic field. Our results demonstrate that the intricate interplay between charge order and superconductivity can lead to an exotic vortex state.
Fighting monetary colonialism in francophone Africa: Samir Amin’s contribution
Authors: Sylla Ndongo Samba 
Published: February 2021

ABSTRACTThis article discusses Samir Amin’s intellectual and activist contribution to the political economy of decolonisation in sub-Saharan Africa. It focuses on his fight from 1969 to 1975 for the monetary sovereignty of West African countries using the CFA franc, a colonial currency that survived independence. Amin was an advisor to Niger’s President Hamani Diori alongside whom he fought to end monetary colonialism. As an alternative to the CFA franc, Amin recommended an ambitious economic integration for the West Africa region based on mutually supportive national currencies. Although his proposal would meet opposition from France, Senegal and Côte d’Ivoire, his economic case against the CFA franc is still relevant. With regard to the ongoing protests against the CFA franc, it is important to recall a major teaching from Amin: although monetary autonomy is necessary for economic development in peripheral countries, without a delinking strategy its effects will be limited.
Improved anchor design for flat MEMS structure by suppressing deformation due to buried-oxide stress on silicon-on-insulator wafer
Authors: Fujiyoshi Motohiro , Ozaki Takashi , Omura Yoshiteru , Funabashi Hirofumi , Akashi Teruhisa , Nonomura Yutaka 
Published: February 2021

Abstract
Silicon-on-insulator (SOI) wafers are used in many micro-electromechanical system (MEMS) devices because of their stable mechanical properties. However, one of the disadvantages of using the SOI configuration is residual stress deformation; strong residual stresses in the buried-oxide layer deform the device and deteriorate its performance. This could prevent the development of high-precision sensors and actuators. In recent years, a new deformation mode caused by this residual stress has been reported, involving tilting of the suspended MEMS structure owing to local deformation of the anchor. However, methods to solve this problem have not yet been proposed. In this study, we propose a simple T-shaped support as a solution to the tilt deformation. We verified its effects by finite element analysis and experiments; the proposed structure was observed to successfully reduce the tip displacement of a SOI-based cantilever by one-fourth. In addition, we applied the proposed method to a parallel-plate accelerometer as a demonstration to confirm that the sensitivity variations of the device reduced from 10.8% to 6.8% using the proposed support structure. Thus, we believe that the proposed design can contribute to the development of extremely accurate MEMS sensors and optical devices.
Implementation of smartphone-based experimental exercises for physics courses at universities
Authors: Kaps A , Splith T , Stallmach F 
Published: February 2021

Abstract
A concept for undergraduate mechanics courses at universities is introduced where traditional pencil-paper based exercises are partially replaced by experimental exercises, in which smartphones are used as measurement devices. A detailed guidance for practical realization and implementation of these tasks formats into the course is presented. Three smartphone-based experimental exercises ‘The tilting smartphone’, ‘The oscillation balance’ and ‘Using the Smartphone in a Torsion Pendulum’ are presented. First empirical results with respect to the learning achievement indicate a mid size effect on the understanding of the physical concepts. Compared to the traditional pencil-paper based exercises, the students performance in the experimental exercises is slightly lower, although the motivation to solve these tasks is higher.
An Approach to Analyze Duality of Current-type DC-DC Circuit and Voltage-type DC-DC circuit based on Gyrator
Authors: Zheng Zhenhong , Ran Li 
Published: February 2021

Abstract
This paper proposes a method that can derive the current-type (C-T) DC-DC circuit topology from the voltage-type (V-T) DC-DC circuit topology by the duality of two-ports gyrator. In addition, the mathematical relationships between C-T DC-DC circuit and V-T DC-DC circuit parameters are established using the gyration resistance and the duty cycle of power switching device. Hence, C-T DC-DC parameters of the passive components, and the expressions of the mathematical relationships between the input and output, including the ripples of inductance current and capacitance voltage are obtained by analysing and calculating the V-T DC-DC circuit. Finally, the analysis results are verified by simulation in SIMULINK.
CAE-based classification method of electric power business
Authors: Ma Ruiheng , Xiang Min , Lei Rujie , Huang Chunmei 
Published: February 2021

Abstract
Aiming at the problem that abnormal data in the business classification of power data communication networks will reduce the business classification accuracy, a classification method based on convolutional autoencoder combined with lightGBM was proposed. First, the flow features of the electric power business were extracted through the convolutional autoencoder. Then, anomaly detection was realized according to the relationship between the reconstruction loss of the convolutional autoencoder and the set threshold. Finally, the electric power business was classified through the LightGBM classifier. The Moore data set used for simulation verification. The results show that the proposed method can effectively detect abnormalities, thereby improving the accuracy of the electric power business classification.
Research on DC Charger Interoperability Test for Electric Vehicles
Authors: Li Yulan , Wang Guangyan 
Published: February 2021

Abstract
DC charger is an important facility for electric vehicles to quickly replenish electric energy. Its operation safety, reliability and interoperability are of great significance for improving the popularity of charging facilities and the development of electric vehicles. Starting from the charging process of DC charger, this paper develops a set of DC charger interoperability testing device in combination with relevant testing specifications of DC charger, and carries out relevant tests on DC charger to verify the effectiveness of this set of equipment.
Power Grid Safety Assessment Based on an Improved Generative Adversarial Network
Authors: Aidong XU , Yunan ZHANG , Yixin JIANG 
Published: February 2021

Abstract
Critical clearing time (CCT) is one of the important indices for transient stability evaluation. From the data-driven perspective, the research on CCT prediction is troubled by changing models and insufficient samples, that is, the small sample characteristics of the target system may be submerged by the large sample characteristics of the source system. In this paper, a prediction method of CCT based on improved generative adversarial network (WGAN) is put forward to solve this problem, and the network structure of WGAN is redesigned. This method is suitable for the transition phase of power grid when the operation mode changes. Through the unsupervised training of WGAN, the neural network will automatically learn the complex relationship between the small sample data of the target system, so that the generator can produce small sample data with high precision. Then the CCT prediction model was built on the expanded balanced dataset. Results validate that the method can effectively learn the distribution law of samples, improve the CCT prediction ability, and has the advantage of precision in the transition phase of power grid with insufficient samples.
Vehicle Ethernet Flow Estimation Using Intelligent Methods
Authors: Hu ZhengWei , Li Hui , Li Yang , Li XueZhen , Li Peng 
Published: February 2021

Abstract
For modern vehicle communications systems, it is vital to utilize advanced networks such as Ethernet to enhance the network speed, improve the service, and avoid the congestion. To this end, it is necessary to develop a hardware platform as well as a flow estimation scheme for system optimization. In this paper, we formulate the vehicle Ethernet platform using Duagon cards under the standard of IEC 61375. Then, we propose three intelligent methods for vehicle flow estimation, i.e., the support vector machine (SVM), the back propagation (BP) neural network, and recurrent neural network (RNN) using improved back-propagation through time (BPTT). Comparative studies are performed to validate the proposed scheme. The results provide technical support for statistical characters analysis and high speed monitoring of modern vehicles.
PMSM double loop predictive control based on Luenberger observer
Authors: Chen Dongdong , Li Zongwei , Chen Ying , Lei Hongdan , Zhu Hongguan , Zeng Qiyi 
Published: February 2021

Abstract
Predictive control strategy is applied to permanent magnet synchronous motor (PMSM) control system, it can achieve fast dynamic response and high-precision tracking control, but depending on the mathematical model of the (PMSM), the load disturbance will affect the control performance of system. Therefore, a control method based on the combination of Luenberger observer and predictive control is proposed to construct a double closed-loop predictive control system. Through the load disturbance estimated by the Luenberger observer, the torque current compensation produced is used as the feedforward compensation of the speed loop to achieve disturbance suppression. The simulation results under Simulink environment show that this method can improve the dynamic response performance and steady-state accuracy of the control system, and greatly improve the robustness.
Research on Control Strategy of Three-Phase Inverter Based on Fractional Calculus
Authors: kai YAN , chaojun WU , zhang LIU , qi ZHANG 
Published: February 2021

Abstract
Three-level inverters has widely used in Medium pressure due to its advantages of low total harmonics, low voltage resistance of power switch tubes and low switching losses. In order to further improve the output voltage waveform quality and optimal control effect of the Three-level inverter, this paper introduces fractional calculus in the control method of the three-level inverter circuit. First, designed a control strategy for the fractional voltage outer loop. Secondly, the use of vector representation simplifies the parameter tuning of fractional-order controller, the optimization process of the parameters of the fractional order PIλ and integer-order PI is completed by utilizing the ITAE rules. At the same time, the Oustaloup approximation method realizes the fractional integral operator in the controller, thereby achieving the purpose of improving the output voltage of the system. For three-level inverter circuit model, comparative analysis of the control effects of the fractional-order PIλ and integer-order PI. Finally, simulation results show that fractional-order PIλ controllers have excellent flexibility, robustness.
Application of Short-time Fourier Transform in Feeder Fault Detection of Flexible Multi-state Switch
Authors: Cheng Yimin , Zhang Guorong , Yu Chong , Peng Bo , Wu Xuewei , Xu Feng 
Published: February 2021

Abstract
Flexible multi-state switch (FMSS) is widely used in active distribution networks. However, the medium voltage distribution network that includes FMSS requires more accurate fault detection method. To solve this problem, the application of short-time Fourier transform (STFT) in the design of FMSS fault detection methods is studied. The data of power spectrum density in the STFT spectrogram is used to define the Fault Index, Λ. The A can be used to accurately detect the fault type of FMSS in a relatively short time. In order to verify the effectiveness of this fault detection method, this paper builds a control structure for each port based on the FMSS topology and mathematical model. The FMSS model is simulated in MATLAB/Simulink, and the fault signal is analysed by STFT in MATLAB. The results show that the proposed fault detection method can accurately detect the fault type. The STFT parameters have a great influence on the fault detection result, which is studied in the parameters influence analysis.
Direct Power Control Strategy for Three-phase Vienna Rectifier
Authors: Chen Lan , Xiao Huihui , Guo Qiang , Liu Shuxi , Sun Chaojun 
Published: February 2021

Abstract
Firstly, through a detailed analysis of the working principle of the voltage-type Vienna rectifier, the mathematical model of the rectifier power control is established according to the mathematical model of the Vienna rectifier based on the equivalent switch function in the d-q two-phase synchronous rotation coordinate system. Secondly, according to the mathematical model of power control, using the principle of direct power control (DPC), the outer loop of the DC bus voltage PI control of the Vienna rectifier is described in detail, the dual loop structure of the direct power control inner loop and the overall system structure. Finally, the control strategy was verified by Simulink simulation. The results show that the Vienna rectifier based on direct power control has good steady state and dynamic performances, and verify the correctness and feasibility of the control strategy.
Simulation analysis and suppression measures of harmonic resonance of offshore wind farm
Authors: Quanchun YAN , Wen GU , Yanan LIU , Chenglong LI , Tao WU 
Published: February 2021

Abstract
Large-capacity long-distance offshore wind farm adopts high-voltage AC submarine cable outgoing line and collecting system. Due to the high capacitance of submarine cable to ground, the harmonic resonance problem of wind farm is increasingly prominent. First of all, through the actual measurement of the wind turbine yaw system exiting due to the 5th harmonic resonance when the wind turbine is shut down in an offshore wind farm along Jiangsu coast, and the analysis of harmonic current and impedance frequency, the reason of resonance is further analyzed. Finally, the ETAP simulation software is used to analyze the measured data, and then several kinds of causes of offshore wind power resonance are obtained, and the corresponding improvement measures are put forward.
Simulation of Vector Control System of Permanent Magnet Synchronous Motor
Authors: Wang Luyao , Chen Biyun , Sui Lihui 
Published: February 2021

Abstract
The article analysed and studied the structure performance and mathematical model of the permanent magnet synchronous motor, and it further researched the principle of vector control technology and the SVPWM algorithm on this basis. A closed-loop simulation model of permanent magnet synchronous motor speed/current was built. The waveform of the simulation result is consistent with the theoretical analysis, which verifies the effectiveness of the simulation experiment platform and mathematical model. It also verifies the superiority of the id=0 control algorithm and vector control. A theory for the research and design of the permanent magnet synchronous motor vector control system basis is provided.