bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic analysis and oscillation elimination of brushless doubly fed wind power generation system during symmetrical voltage dips
Authors: Nie Pengcheng , Wang Xuefan , Kong Ming 
Published: January 2021

AbstractIn the dynamics of grid‐connected operation of brushless doubly‐fed generators, grid voltage dips can cause the extreme imbalance between the voltage and the back electromotive forces in power winding. When these imbalances are combined with the influence of the inertia link composed of converter and generator, a serious over‐current and current oscillation forms in power winding and control winding. This paper gives a process analysis and proposes an improved control to the system during the low voltage ride through event. According to the mathematical model of the generators, the correlation between the power winding and control winding currents is established and then a fully equivalent simplified model is obtained accordingly. When the voltage suddenly drops to zero, the analytic expressions of power winding and control winding are calculated in the complex frequency domain and the influence factors of overshoot and oscillations are analyzed. The conventional control method relies on limited PI regulation that cannot eliminate the oscillations completely. It is found that after adjusting a proportional coefficient and eliminating the integral link of the control winding current controller, the order of the control system reduces. Therefore, the generation system can quickly recover to a steady state without oscillations. Finally, the analysis and improvement are verified by the simulation model and experimental results.
EDA‐based optimized global control for PV inverters in distribution grids
Authors: Cañadillas David , Valizadeh Hamed , Kleissl Jan , González‐Díaz Benjamín , Guerrero‐Lemus Ricardo 
Published: January 2021

AbstractOperating distribution grids is increasingly challenging due to the increasing penetration of photovoltaic systems. To address these challenges, modern photovoltaic inverters include features for local control, which sometimes lead to suboptimal results. Improved communication infrastructure and photovoltaic inverters favour global control strategies, which receive information from all the systems in the grid. An estimation of distribution algorithm is used to optimize a global control strategy that minimizes active power curtailment and use of reactive power of the photovoltaic inverters, while maintaining voltage stability. Optimized global control outperforms every other local control evaluated in terms of apparent energy used for control (9.9% less usage compared to the second best alternative in all scenarios studied) and ranks second in terms of voltage stability (with a 0.14% of total time outside the voltage limits). Two new indicators to compare control strategies are proposed, and optimized global control strategy ranks best for both efficiency index (0.98) and average apparent power use (0.48 kVA).
Comprehensive analysis of distributed energy resource penetration and placement using probabilistic framework
Authors: Paliwal Priyanka 
Published: January 2021

AbstractIntegration of distributed energy resources (DERs) affect system performance in multitude of ways such as reliability, losses and voltage profile. Thus, increasing distributed energy resource penetration necessitates impact assessment particularly when DERs comprise of stochastic RES based distributed generators (DGs) and storage system. This paper presents a formulation for the analysis of DER penetration and placement on system losses and voltage profile in probabilistic framework. Penetration level has been defined, giving due consideration to stochastic behaviour of RES based distributed generators. The work presented incorporates analysis and consideration of two important factors in placement problem, that is, intermittent nature of RES based distributed generators and dual nature of storage units. In order to account for uncertainties inherently present in RES, probabilistic load flow has been used in this work. Placement problem is solved for three different penetration levels, that is, 20%, 40% and 60% using utterfly particle swarm optimisation. The impact of seasonal effect on system losses and voltage profile in correlation with penetration levels has also been investigated. Results provide useful insights for identification of optimum penetration level.
Effect of Nb addition on high-temperature oxidation behavior, oxide layer structure, and its exfoliation resistance of Ti-Nb Alloys
Authors: Miura-Fujiwara Eri , Ogawa Yuya , Niinomi Mitsuo , Yamasaki Tohru 
Published: January 2021

The authors proposed an oxide coating on Ti alloys for the dental abutment tooth, and they had reported that Ti–29Nb–13Ta–4.6Zr (TNTZ) alloy forms a dense oxide layer by high-temperature oxidation. On the other hand, CP Ti forms a multilayered oxide consisted of rutile monolayers and the void layer. This morphological change by alloying is supposed to be mainly caused by Nb addition in Ti since the dense oxide layer of TNTZ mainly consists of rutile TiO2and TiNb2O7.Therefore, in this study, oxidation behaviors of various range of Nb content of Ti-xNb alloys (x = 1 ~ 32 mol%) were investigated, and exfoliation resistance was evaluated. And in this paper, the oxide/metal interfacial microstructure of oxidized CP Ti, TNTZ alloy, and Ti-Nb alloy was studied by a transmission electron microscopy (TEM) and by a scanning transmission electron microscopy with an electron dispersive spectroscopy (STEM-EDS).The cross-sectional observations suggested that the substrate was gradually oxidized during heat treatment, and nucleation and grain growth of TiO2and TiNb2O7proceed at the metal/oxide interface. Consequently, the gradual oxidation process in TNTZ and Ti-Nb alloys could lead to its continuous interfacial microstructure and dense oxide structure, which can achieve high exfoliation resistance.
An Ugi Reaction/Intramolecular Cyclization/Oxidation Cascade towards Tetrazole-Linked Dibenzoxazepines
Authors: Dömling Alexander , Zheng Qiang , Boltjes André 
Published: January 2021

AbstractA series of tetrazole-linked dibenzo[b,f][1,4]oxazepines is synthesized through a short sequence involving an Ugi tetrazole reaction. The intermediate tetrazole undergoes a potassium carbonate mediated SNAr cyclization, followed by oxidation to afford the target tricyclic heterocyclic scaffold. The optimization, scope and limitations of this two-step and efficient methodology are investigated. A 1000-member library of tetrazole-linked dibenzo[b,f][1,4]oxazepines is generated and the physicochemical properties are analyzed. great
Surface acoustic waves increase magnetic domain wall velocity
Authors: Adhikari A. , Adenwalla S. 
Published: January 2021

Domain walls in magnetic thin films are being explored for memory applications and the speed at which they move has acquired increasing importance. Magnetic fields and currents have been shown to drive domain walls with speeds exceeding 500 m/s. We investigate another approach to increase domain wall velocities, using high frequency surface acoustic waves to create standing strain waves in a 3 micron wide strip of magnetic film with perpendicular anisotropy. Our measurements, at a resonant frequency of 248.8 MHz, indicate that domain wall velocities increase substantially, even at relatively low applied voltages. Our findings suggest that the strain wave derived effective magnetic field acts as an additional driver for domain wall motion.
Locally transitive analytic actions of Lie groups on compact surfaces
Authors: Gorbatsevich V. V. 
Published: January 2021

Abstract
We investigate locally transitive analytic actions of Lie groups on surfaces. We indicate compact surfaces on which locally transitive actions of Lie groups can be globalized (in particular, with certain conditions on the set of fixed points) and describe the schemes of irreducible locally transitive actions of Lie groups on these surfaces.
Bibliography: 13 titles.
The natural axis of transmitter receptor distribution in the human cerebral cortex
Authors: Goulas Alexandros , Changeux Jean-Pierre , Wagstyl Konrad , Amunts Katrin , Palomero-Gallagher Nicola , Hilgetag Claus C. 
Published: January 2021

Significance
Communication between cells in the brain relies on different types of transmitter receptors. Can we uncover organizational principles that harness the diversity of such signatures across the brain? We focus on the human cerebral cortex and demonstrate that the distribution of receptors forms a natural axis that stretches from association to sensory areas. Moreover, traversing this axis entails changes in the diversity, excitability, and mirrored density that reflect a basic division in receptor types, that is, ionotropic and metabotropic receptors. The unraveled principles offer explanatory depth for diverse phenomena and entail concrete, testable predictions.
A simple method to measure DC electric field with space charges
Authors: Zhang Bo , Meng Yongchang , He Jinliang 
Published: January 2021

Abstract
DC partial discharge in gas generates many space charges. Because these charges move with the electric field, change the electric field and accumulate on the surface of sensors, it is difficult to measure the electric field in the space. Based on the relationship between the charge accumulated on the surface of the dielectric in the ion flow field and the applied electric field, this paper proposes a simple method to measure the electric field with space charges using a suspended dielectric as a sensor. By testing the charge accumulated on the suspended dielectric, the applied electric field can be determined. The method is verified and the factors that affect the measurement result are investigated by experiments in a predictable and controllable ion flow field. The results show that when saturation of the accumulation of the space charge on the suspended disc is reached, the total accumulated surface charges are linear with the normal component of the external applied electric field. The ion flow density just affects the speed of the charge accumulation and does not affect the amount of saturated surface charges. The relationship coefficient between the surface charge and the electric field can be obtained through calibration. Unlike other methods that regard the accumulation of charge on the sensor as the key interference, the method in this article just uses the accumulation characteristics of the charge on the sensor, which is simple and feasible.
Focused laser differential interferometer response to shock waves
Authors: Lawson J M , Austin J M 
Published: January 2021

Abstract
The focused laser differential interferometer (FLDI) can be used to measure rapid density fluctuations non-intrusively in high-speed flow applications. Being a non-imaging shearing interferometer, FLDI response can be accurately modeled using a paraxial ray-tracing scheme. We present the details of a new numerical implementation of this scheme, capable of accepting flow-field input from analytical models, computational fluid dynamics (CFD) results, and experimental data. This implementation has previously been validated for static (laminar jet) and dynamic (ultrasound-generated) changes in index of refraction by Lawson et al. In this work, we examine the FLDI response to shock waves propagating at up to Mach 10, in Caltech’s hypervelocity expansion tube. While the timescale and approximate form of the signal can be recovered using a simple inviscid, planar shock model, it is found that the inclusion of viscous shock effects allows an accurate simulation of both the magnitude and detailed shape of the experimental response. This is a further analytical validation of the FLDI model that extends beyond the results of the existing dynamic validation case. The model implementation is then coupled to a CFD code, and predictions reproduce experimental FLDI response to a complex shock-dominated flow-field.
A designed flow-through microsystem for accurate and fast measurement of gas sensors at the ppb level
Authors: Zhang Jingjing , Ning Zhanwu , Zhao Peng , Liu Jinhua , Zhang Yanni , Liu Weijie , Liu Ning , Jia Yiting 
Published: January 2021

Abstract
The characteristic parameters of gas sensors depend highly on the method used to evaluate them. This paper presents a flow-through microsystem for accurate and fast measurement of gas sensors, especially for the sensor with a fast response and high sensitivity at the ppb level. The microsystem consists of four parts, i.e. a dynamic multiple gas handling unit, a test gas preheater, an olive-like test chamber with an inner volume of 4.98 ml and data analysis apparatus. Thereinto, the multiple gas handling unit was constructed to meet the needs of dynamical sensor response tests, and the olive-like test chamber was designed based on the principles of low background interference and fast replacement of ambient conditions, which was optimized by computational fluid dynamics simulation and verified by its airtightness and applicable flow rate range. For a flow rate of 300 ml min−1, it can discern that the replacement time for the chamber ambient gas test was about 1 s. Finally, performance tests for two commercial sensors and one home-made sensor were carried out on this microsystem. The results showed that this system can serve as a means of highly sensitive (ppb level) and fast gas sensor evaluation, and the measured values obtained by this system can be considered to be closer to a sensor’s true values.
Experimental and numerical characterization of a radio-frequency plasma source with a DC-grounded electrode configuration using a quarter-wavelength filter
Authors: Soni Kunal , Moser Lucas , Donkó Zoltán , Hartmann Peter , Korolov Ihor , Antunes Rodrigo , Juhasz Zoltan , Steiner Roland , Marot Laurent , Meyer Ernst 
Published: January 2021

Abstract
We present a combined experimental and numerical investigation of the plasma properties in an asymmetric capacitively coupled radio frequency plasma source using argon discharge. Besides driving the system in the conventional way, which results in a high negative self-bias voltage

V

DC

due to the asymmetric configuration, we also connect a ‘quarter-wavelength filter’ to the powered electrode, which lifts its DC potential to zero. At the powered side of the plasma, we employ electrodes with conducting and insulating surfaces, as well as electrodes combining both in different proportions (‘hybrid electrodes’). Measurements are carried out for the plasma potential, the electron density and temperature in the bulk plasma, as well as for the flux-energy distribution of the ions at the grounded surface of the system. The nature of the surface of the powered electrode as well as the presence of the quarter-wavelength filter are found to highly influence the plasma potential,

V

p

‾

. For the electrode with a conducting surface

V

p

‾

∼

20 V and ∼150 V are found in the absence and the presence of the filter, respectively. For the electrode with an insulating surface, the self-bias voltage builds up directly at the plasma interface, thus the filter has no effect and a plasma potential of ∼20 V is found. For the electrodes with different conducting/insulating proportions of their surface,

V

p

‾

ranges between the above values. Particle-in-Cell/Monte Carlo Collisions calculations for identical conditions with hybrid electrodes predict double-peaked ion energy distribution at the powered electrode with peaks corresponding to

e

V

p

‾

and

e
(

V

p

‾

−

V

DC

)

along with a lowering of the plasma potential (whencompared to wholly conducting electrode), a trend that is observed experimentally. These studies are of great importance for the application of similar plasma sources with in-situ cleaning of mirrors in fusion devices and the results can be extended to a variety of plasma processing applications.
Soliton trains after interaction quenches in Bose mixtures
Authors: Cidrim André , Salasnich Luca , Macrì Tommaso 
Published: January 2021

Abstract
We investigate the quench dynamics of a two-component Bose mixture and study the onset of modulational instability, which leads the system far from equilibrium. Analogous to the single-component counterpart, this phenomenon results in the creation of trains of bright solitons. We provide an analytical estimate of the number of solitons at long times after the quench for each of the two components based on the most unstable mode of the Bogoliubov spectrum, which agrees well with our simulations for quenches to the weak attractive regime when the two components possess equal intraspecies interactions and loss rates. We also explain the significantly different soliton dynamics in a realistic experimental homonuclear potassium mixture in terms of different intraspecies interaction and loss rates. We investigate the quench dynamics of the particle number of each component estimating the characteristic time for the appearance of modulational instability for a variety of interaction strengths and loss rates. Finally we evaluate the influence of the beyond-mean-field contribution, which is crucial for the ground-state properties of the mixture, in the quench dynamics for both the evolution of the particle number and the radial width of the mixture. In particular, even for quenches to strongly attractive effective interactions we do not observe the dynamical formation of solitonic droplets.
Potential Applications of Big Data for Managing the COVID-19 Pandemic
Authors: Pradana A R , Madjid S R , Prayitno H J , Utami R D , Dharmawan Y 
Published: January 2021

AbstractCOVID-19 caused by SARS-CoV-2 is being global pandemic which the number of positive confirmed cases and deaths increase massively and rapidly. Big data is a technology can be used for analysing the trend pattern of coronavirus and prevent the spreading of it. Few countries already use big data as a strategy in managing the ongoing of COVID-19 pandemic. This research uses descriptive analytical research to describe the findings of previous research information with a simplified approach. The aim of this research is knowing how big data used for managing the outbreak of COVID-19 by detecting cases, predicting cases and tracking contact through the use of various data characteristics in some countries around the world. Several countries that have used big data to help manage COVID-19 pandemic are Taiwan, China, Korea, Australia. Taiwan uses credit card and geographic route for tracking the routes of tourists, China uses Baidu Maps Traffic Flow as local maps for knowing distribution of aircraft passenger who have potential high risk to get infected by COVID-19, Korea uses insurance data from Korean National Health Insurance Service for knowing the community with hypertension history who have protentional high risk to get infected by COVID-19 and Australia uses application COVIDSafe for handling the spreading by detecting ambient contact. The ongoing of COVID-19 pandemic in the world has caused the big data technology to be considered to be applied in a country so it hopes can reduce the negative impacts caused in several fields.
Mathematical creative thinking ability and problem centered learning
Authors: Desmayanasari D , Hardianti D , Machromah I U , Rohaeti T , Arsisari A 
Published: January 2021

Abstract
This research aims to determine the improvement of students’ mathematical creative thinking ability through Problem Centered Learning (PCL) approach. This research is a quasi-experimental with a non-equivalent research design. The population of this research were the eighth-grade students of SMP Negeri in Bandung. The sample of this research was determined by purposive sampling. The sample consisted of 62 students who were divided into two classes, experimental class and control class. The experimental class uses the PCL approach, while the control class uses conventional learning. Each class consists of 31 students. The data of students’ mathematical creative thinking ability were obtained by using test techniques. The improvement was proven by n-gain value of students’ pre-test and post-test. The conclusions obtained from the data analysis and discussion, there is a significant difference in the improvement mathematical creative thinking ability between high EMA in the PCL group and medium EMA in conventional learning. Based on EMA, PCL can be applied in high EMA classes. While students with medium and low EMA need further research so that students’ mathematical abilities can be improved by PCL.
Improving The Quality of Mathematics Learning Based On Society’s Potency in Junior High School
Authors: Nur Hafida Siti Hadiyati , Santoso  , Sutama  , Nurhidayat  , Dalman  , Hesti  , Kusumaningtyas Dian Artha 
Published: January 2021

AbstractThe objectives of this study were to describe the society’s empowerment in improving the quality of the learning media, learning process, and learning assessment in school. This research applied qualitative with ethnography research design. The data were collected by in-depth interview, observation, and documentation; while the data analysis technique used was the interactive analysis. The results of the study showed the following conclusions. (1) In order to gain good quality learning, it is a must to prepare a good learning media. The minimum component in developing the learning media (syllabus and lesson plan) must content the learning objectives, learning material, study source, and learning assessment. (2) The learning process must use various ways to encourage students’ interest and curiosity, including using various methods, using language styles that are not monotonous, asking questions that guide students’ creativity, using multi-method and multimedia, and giving assignments individually and in groups to students. (3) The assessment becomes a very important thing to determine the level of success in the learning that has been done.
Computational Thinking Lesson in Improving Digital Literacy for Rural Area Children via CS Unplugged
Authors: Yuliana Irma , Hermawan Hardika Dwi , Prayitno Harun Joko , Ratih Koesomo , Adhantoro Muhammad Syahriandi , Hidayati Herlina , Ibrahim Mohd Hairy 
Published: January 2021

Abstract
The advantage of computational tools over human brains is the speed, but the initiative ability of human brains is not owned by computational tools. The perfect combination of thinking and computing lays the foundation of science and gives birth to a series of achievements in technology. The introduction of technology through the subjects of Information and Communication Technology (ICT) in schools nowadays is just limited to using the applications. Computational thinking gives knowledge that builds structural thinking, critical power, and creativity by learning the computing process itself. These are what people need to enhance digital literacy. The way to learn it could be in many strategies. CS Unplugged was used in this research to deliver computational thinking in a simple way related to minimum infrastructure in the remote area for the children at elementary schools. Some activities were done as kinaesthetic learning in certain topics of CS Unplugged. This kind of method does not need some computer devices to get children closer to computer science. A challenge was given to assess the ability of ICT learning which is computational thinking. The children show their enthusiasm for learning, proved by their final score in a challenge. The children’s score significantly improved in learning ICT by using CS Unplugged.