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Experiment and simulation of tearing mode evolution with electron cyclotron current drive in KSTAR
Kim, Kyungjin,Na, Yong-Su,Kim, Minhwa,Jeon, Y.M.,Lee, K.D.,Bak, J.G.,Choi, M.J.,Yun, G.S.,Lee, S.G.,Park, S.,Jeong, J.H.,Terzolo, L.,Na, D.H.,Yoo, M.G. Elsevier 2015 CURRENT APPLIED PHYSICS Vol.15 No.4
<P><B>Abstract</B></P> <P>The tearing mode (TM) plasma instability was observed in low confinement (L-mode) plasmas when non-axisymmetric magnetic perturbation (MP) was applied using external coils during 2011 campaign of KSTAR. Based on the collected information of the magnetic island location in a plasma, a discharge was designed for suppression of a (2,1) TM mode by adjusting electron cyclotron (EC) launcher angles to the estimated island position. Here, the (m,n) notation describes the poloidal mode number and the toroidal mode number of the TM, respectively. The discharge is analysed with experimental observations and numerical simulations. Mirnov coil (MC) arrays and electron cyclotron emission (ECE) are used for analysis of the island width and the location as well as the mode number. The EC deposition and its alignment with the island are estimated by X-ray imaging crystal spectroscopy (XICS) and ECE measurements. An integrated numerical system is employed for modelling of this discharge to analyse a temporal evolution of the mode activity by integrating plasma equilibrium, transport, heating and current drive, and the magnetic island evolution, in a self-consistent way. The effect of EC current drive is discussed by comparing with another TM discharge but without ECCD. Some possibilities for classifying this mode to neoclassical tearing mode (NTM) and stabilisation effect of ECCD are suggested based on the experimental observation and the simulation results.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Suppression of (2,1) TM/NTM by applying ECH/CD for the first time in KSTAR. </LI> <LI> Suppression of the mode examined by experimental observations and simulations. </LI> <LI> Simulation of a mode without ECCD to compare with/without the applied control. </LI> </UL> </P>
Influence of Sr substitution on thermoelectric properties of La1−xSrxFeO3 ceramics
H.C. Wang,C.L. Wang,J.L. Zhang,W.B. Su,J. Liu,M.L. Zhao,N. Yin,Y.G. Lv,L.M. Mei 한국물리학회 2010 Current Applied Physics Vol.10 No.3
Perovskite La1-xSrxFeO3 (0.10 ≤ x ≤ 0.20) ceramics have been synthesized by the conventional solid-state reaction technique. Their electrical resistivity, Seebeck coefficient and thermal conductivity have been measured. It has been found that the increase of Sr content reduces significantly both the electrical resistivity and the Seebeck coefficient, but slightly increases the high-temperature thermal conductivity. An adiabatic hopping conduction mechanism of small polaron is suggested from the analysis of the temperature dependence of the electrical resistivity. Seebeck coefficients decrease with increasing temperature,and saturate at temperature above 573 K. The saturated value of Seebeck coefficient decreases with increasing of Sr contents, from 200 μV/K for x = 0.10 to 100 μV/K for x = 0.20. All samples exhibit lower thermal conductivity with values around 2.6 W/m K. The highest dimensionless figure of merit is 0.031at temperature 973 K in La0.88Sr0.12FeO3.
Seismic assessment of transfer plate high rise buildings
Su, R.K.L.,Chandler, A.M.,Li, J.H.,Lam, N.T.K. Techno-Press 2002 Structural Engineering and Mechanics, An Int'l Jou Vol.14 No.3
The assessment of structural performance of transfer structures under potential seismic actions is presented. Various seismic assessment methodologies are used, with particular emphasis on the accurate modelling of the higher mode effects and the potential development of a soft storey effect in the mega-columns below the transfer plate (TP) level. Those methods include response spectrum analysis (RSA), manual calculation, pushover analysis (POA) and equivalent static load analysis (ESA). The capabilities and limitations of each method are highlighted. The paper aims, firstly, to determine the appropriate seismic assessment methodology for transfer structures using these different approaches, all of which can be undertaken with the resources generally available in a design office. Secondly, the paper highlights and discusses factors influencing the response behaviour of transfer structures, and finally provides a general indication of their seismic vulnerability. The representative Hong Kong building considered in this paper utilises a structural system with coupled shear walls and moment resisting portal-frames, above and below the TP, respectively. By adopting the wind load profile stipulated in the Code of Practice on Wind Effects: Hong Kong-1983, all the structural members are sized and detailed according to the British Standards BS8110 and the current local practices. The seismic displacement demand for the structure, when built on either rock or deep soil sites, was determined in a companion paper. The lateral load-displacement characteristic of the building, determined herein from manual calculation, has indicated that the poor ductility (brittle nature) of the mega-columns, due mainly to the high level of axial pre-compression as found from the analysis, cannot be effectively alleviated solely by increasing the quantity of confinement stirrups. The interstorey drift demands at lower and upper zones caused by seismic actions are found to be substantially higher than those arising from wind loads. The mega-columns supporting the TP and the coupling beams at higher zones are identified to be the most vulnerable components under seismic actions.
C.L. Lu,Q. S. Li,S.H. Huang,Alex Y. Tuan,L.H. Zhi,Sheng-chung Su 한국풍공학회 2016 Wind and Structures, An International Journal (WAS Vol.23 No.4
Taipei 101 Tower, which has 101 stories with height of 508 m, is located in Taipei where typhoons and earthquakes commonly occur. It is currently the second tallest building in the world. Therefore, the dynamic performance of the super-tall building under strong wind actions requires particular attentions. In this study, Large Eddy Simulation (LES) integrated with a new inflow turbulence generator and a new sub-grid scale (SGS) model was conducted to simulate the wind loads on the super-tall building. Three-dimensional finite element model of Taipei 101 Tower was established and used to evaluate the wind-induced responses of the high-rise structure based on the simulated wind forces. The numerical results were found to be consistent with those measured from a vibration monitoring system installed in the building. Furthermore, the equivalent static wind loads on the building, which were computed by the time-domain and frequency-domain analysis, respectively, were in satisfactory agreement with available wind tunnel testing results. It has been demonstrated through the validation studies that the numerical framework presented in this paper, including the recommended SGS model, the inflow turbulence generation technique and associated numerical treatments, is a useful tool for evaluation of the wind loads and wind-induced responses of tall buildings.
Multisite campaign on the open cluster M67 – III. δ Scuti pulsations in the blue stragglers
Bruntt, H.,Stello, D.,Suá,rez, J. C.,Arentoft, T.,Bedding, T. R.,Bouzid, M. Y.,Csubry, Z.,Dall, T. H.,Dind, Z. E.,Frandsen, S.,Gilliland, R. L.,Jacob, A. P.,Jensen, H. R.,Kang, Y. B.,Kim, S.-L. Blackwell Publishing Ltd 2007 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.378 No.4
<P>ABSTRACT</P><P>We have made an asteroseismic analysis of the variable blue stragglers in the open cluster M67. The data set consists of photometric time-series from eight sites using nine 0.6–2.1 m telescopes with a time-baseline of 43 d. In two stars, EW Cnc and EX Cnc, we detect the highest number of frequencies (41 and 26) detected in δ Scuti stars belonging to a stellar cluster, and EW Cnc has the second highest number of frequencies detected in any δ Scuti star. We have computed a grid of pulsation models that take the effects of rotation into account. The distribution of observed and theoretical frequencies shows that in a wide frequency range a significant fraction of the radial and non-radial low-degree modes are excited to detectable amplitudes. Despite the large number of observed frequencies we cannot constrain the fundamental parameters of the stars. To make progress we need to identify the degrees of some of the modes from either multicolour photometry or spectroscopy.</P>
Solar Coronal Loops Associated with Small-scale Mixed Polarity Surface Magnetic Fields
Chitta, L. P.,Peter, H.,Solanki, S. K.,Barthol, P.,Gandorfer, A.,Gizon, L.,Hirzberger, J.,Riethmü,ller, T. L.,Noort, M. van,Rodrí,guez, J. Blanco,Iniesta, J. C. Del Toro,Suá,rez, D. Or American Astronomical Society 2017 The Astrophysical journal, Supplement series Vol.229 No.1
<P>How and where are coronal loops rooted in the solar lower atmosphere? The details of the magnetic environment and its evolution at the footpoints of coronal loops are crucial to understanding the processes of mass and energy supply to the solar corona. To address the above question, we use high-resolution line-of-sight magnetic field data from the Imaging Magnetograph eXperiment instrument on the SUNRISE balloon-borne observatory and coronal observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory of an emerging active region. We find that the coronal loops are often rooted at the locations with minor small-scale but persistent opposite-polarity magnetic elements very close to the larger dominant polarity. These opposite-polarity small-scale elements continually interact with the dominant polarity underlying the coronal loop through flux cancellation. At these locations we detect small inverse Y-shaped jets in chromospheric Ca II H images obtained from the SUNRISE Filter Imager during the flux cancellation. Our results indicate that magnetic flux cancellation and reconnection at the base of coronal loops due to mixed polarity fields might be a crucial feature for the supply of mass and energy into the corona.</P>
Lu, C.L.,Li, Q.S.,Huang, S.H.,Tuan, Alex Y.,Zhi, L.H.,Su, Sheng-chung Techno-Press 2016 Wind and Structures, An International Journal (WAS Vol.23 No.4
Taipei 101 Tower, which has 101 stories with height of 508 m, is located in Taipei where typhoons and earthquakes commonly occur. It is currently the second tallest building in the world. Therefore, the dynamic performance of the super-tall building under strong wind actions requires particular attentions. In this study, Large Eddy Simulation (LES) integrated with a new inflow turbulence generator and a new sub-grid scale (SGS) model was conducted to simulate the wind loads on the super-tall building. Three-dimensional finite element model of Taipei 101 Tower was established and used to evaluate the wind-induced responses of the high-rise structure based on the simulated wind forces. The numerical results were found to be consistent with those measured from a vibration monitoring system installed in the building. Furthermore, the equivalent static wind loads on the building, which were computed by the time-domain and frequency-domain analysis, respectively, were in satisfactory agreement with available wind tunnel testing results. It has been demonstrated through the validation studies that the numerical framework presented in this paper, including the recommended SGS model, the inflow turbulence generation technique and associated numerical treatments, is a useful tool for evaluation of the wind loads and wind-induced responses of tall buildings.