Study of the spectrum effect on the threshold of resonant magnetic perturbation penetration on J-TEXT

The spectrum effect on the penetration of resonant magnetic perturbation(RMP) is studied with upgraded in-vessel RMP coils on J-TEXT.The poloidal spectrum of the RMP field,especially the amplitudes of 2/1 and 3/1 components,can be varied by the phase difference between the upper and lower coil rows,ΔΦ=Φ_(top)-Φ_(bottom),where Φ_(top)and Φ_(bottom)are the toroidal phases of the n=1 field of each coil row.The type of RMP penetration is found to be related to ΔΦ,including the RMP penetration of either 2/1 or 3/1 RMP and the successive penetrations of 3/1 RMP followed by the 2/1 RMP.For cases with penetration of only one RMP component,the penetration thresholds measured by the corresponding resonant component are close for variousΔΦ.However,the 2/1 RMP penetration threshold is significantly reduced if the 3/1 locked island is formed in advance.The changes in the rotation profile due to 3/1 locked island formation could partially contribute to the reduction of the 2/1 thresholds.

Power supply for generating frequency-variable resonant magnetic perturbations on the J-TEXT tokamak

To further research the response of the tearing mode（TM） to dynamic resonant magnetic perturbation（DRMP） on the J-TEXT tokamak, a modified series resonant inverter power supply（MSRIPS） with a function of discrete variable frequency is designed for DRMP coils in this study. The MSRIPS is an AC–DC–AC converter, including a phase-controlled rectifier, an LC filter, an insulated gate bipolar transistor（IGBT） full bridge, a matching transformer, three resonant capacitors with different capacitance values, and three corresponding silicon controlled rectifier（SCR） switches. The function of discrete variable frequency is realized by switching over different resonant capacitors with corresponding SCR switches while matching the corresponding driving frequency of the IGBT full bridge. A detailed switching strategy of the SCR switch is put forward to obtain sinusoidal current waveform and realize current waveform smooth transition during frequency conversion. In addition, a resistor and thyristor bleeder is designed to protect the SCR switch from overvoltage. Manufacturing of the MSRIPS is completed, and the MSRIPS equipment can output current with an amplitude of 1.5 kA when its working frequency jumps among different frequencies. Moreover, the current waveform is sinusoidal and can smoothly transition during frequency conversion. Furthermore, the transition time when the current amplitude rises from zero to a steady state is less than 2 ms during frequency conversion. By using the MSRIPS, the expected discrete variable frequency DRMP is generated, and the phenomenon of the TM being locked to the discrete variable frequency DRMP is observed on the J-TEXT tokamak.

The spectrum analysis of RMP coils with multiple connection modes and the design of high field side coils on J-TEXT

The phase difference Δξ between locked islands(2/1 and 3/1) has been found to influence the heat transport on the thermal quench during disruptions by numerical modeling [Hu Q et al 2019Nucl.Fusion 59,016005].To verify this experimentally,a set of resonant magnetic perturbation(RMP) coils is required to excite coupled magnetic islands with different Δξ.The spectrum analysis shows that the current RMP coils on J-TEXT can only produce sufficient 2/1 and 3/1RMP fields with a limited phase difference of Δξ∈[-75°,75°].In order to broaden the adjustable range of Δξ,a set of coils on the high field side(HFS) is proposed to generate 2/1 and 3/1 RMP fields with Δξ=180°.As a result,RMPs with adjustable Δξ∈[-180°,180°] and sufficient amplitudes could be achieved by applying the HFS coils and the low field side(LFS)coils.This work provides a feasible solution for flexible adjustment of the phase difference between m and m+1 RMP,which might facilitate the study of major disruptions and their control.

Characteristics of the Cochlear Symptoms and Functions in Meniere＇s Disease

Background：Meniere＇s disease is a unique,progressive disease of the inner ear.The complex manifestation presents diagnostic challenges.The cochlear symptoms often present before vertigo and tend to be ignored.This study aimed to analyze the characteristics of cochlear symptoms and functions associated with Meniere＇s disease to investigate the regularity of the development of this disorder.Methods：One-hundred fifteen patients who were diagnosed with definite unilateral Meniere＇s disease at the Hearing and Vestibular Clinic of the Department of Otorhinolaryngology of Beijing Tongren Hospital from August 2013 to November 2015 were recruited in this retrospective study.Initial symptoms,duration from initial symptoms to the diagnosis,hearing thresholds,audiogram patterns,and caloric test results were collected and analyzed for each patient.Data were analyzed using SPSS 13.0 statistical software by Spearman＇s correlation,Kruskal-Wallis H test,Chi-square test,and Fisher＇s exact test.Results：The average hearing threshold of these patients was 45.24 ± 18.40 dB HL.A majority of the patients （55.65%） were in Stage 3.The initial presentation of the disorder in 58 cases （50.43%） comprised only cochlear symptoms without vertigo.A weak,positive correlation was found between the degree of hearing loss and duration of the disease from initial symptoms to the diagnosis （rs =0.288,P =0.002）.Upward-sloping,inverted ＂V,＂ downward-sloping,and flat pattern were the main audiometric patterns observed with a distinctive distribution between stages （P 〈 0.001）.Based on the configurations of audiograms,the audiometric patterns had a weak correlation to the duration （rs =0.269,P =0.004）,and there was a tendency of duration to rising from upward-sloping,inverted ＂V＂,downward-sloping to flat pattern.（H =10.024,P =0.018）.Frequencies of tinnitus in 56 patients （64.4%） were at the lowest points of the audiograms,i.e.,the frequencies of the poorest hearing threshold.The patients at an advanced stage （Stage 3 [56] and Stage 4 [73]） exhibited a significantly higher abnormality of canal paresis than those at the earlier stages （Stage 1 [23] and Stage 2 [42]） （χ^2 =5.973,P=0.015）.Conclusions：Patients with definite Meniere＇s disease always have a moderate to severe sensorineural hearing loss before diagnosis.Cochlear symptoms are the most common initial presentation.With the progression of the duration,the hearing impairment becomes more severe and the distribution of the audiometric pattem is distinctive between stages.

How machine learning informs ride-hailing services:A survey

In recent years,online ride-hailing services have emerged as an important component of urban transportation system,which not only provide significant ease for residents’travel activities,but also shape new travel behavior and diversify urban mobility patterns.This study provides a thorough review of machine-learning-based methodologies for on-demand ride-hailing services.The importance of on-demand ride-hailing services in the spatiotemporal dynamics of urban traffic is first highlighted,with machine-learning-based macro-level ride-hailing research demonstrating its value in guiding the design,planning,operation,and control of urban intelligent transportation systems.Then,the research on travel behavior from the perspective of individual mobility patterns,including carpooling behavior and modal choice behavior,is summarized.In addition,existing studies on order matching and vehicle dispatching strategies,which are among the most important components of on-line ridehailing systems,are collected and summarized.Finally,some of the critical challenges and opportunities in ridehailing services are discussed.