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Discovery of four W UMa type eclipsing binaries in the field of open cluster ASCC 5

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Research in Astronomy and Astrophysics 2013年第9期13卷 1052-1062页

作者： Xiang-Song Fang sheng-hong gu Li-Yun Zhang Qing-Feng Pi National Astronomical Observatories/Yunnan Observatory Chinese Academy of Sciences Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences University of Chinese Academy of Sciences College of Science/Department of Physics & NAOC-GZU-Sponsored Center for Astronomy Research Guizhou University

We carried out time-series photometric observations in the Re-band of the young, poorly studied open cluster ASCC 5 during November and December, 2012, to search for magnetically active stars, and discovered four eclipsing binary stars in this field. In order to characterize these four newly discovered binaries, we derived their orbital periods by their times of light minimum, estimated their effective tem- peratures based on their （J - H） colors and analyzed their light curves using the Wilson-Devinney light curve modeling technique. Our analyses reveal that all of them are contact binaries with short orbital periods of less than 0.5 d, with spectral types from late-F to mid-K. Among them, one is a typical A subtype contact binary with a mass ratio around 0.5 and a period of 0.44 d, and one is an H subtype contact binary with a high mass ratio around 0.9 and a short period of about 0.27 d. The other two systems show low amplitudes of light variation （Ant 〈0.11m）; their actual photomet- ric mass ratios could not be determined by the light curve modelings, probably due to their attributes of being partially eclipsing stars. A preliminary analysis for these two systems indicates that both of them are likely to be W subtype contact binaries with low orbital inclinations. In addition, both of these two low amplitude variables show asymmetric distorted light curves （e.g., O＇Connell effect of ARc --~0.02m） during the observing runs, suggesting the presence of starspots on these two systems. More inter- estingly, the one showing a large case of the O＇Connell effect presented a remarkable variation in the shape of the light curve on a time scale of one day, indicating that this star is in a very active state. Therefore, these two stars need spectroscopic observations to precisely determine their parameters, as well as further photometric observations to understand the properties of their magnetic activity, e.g., the evolution of starspots.

关键词： stars:binaries: close -- stars:binaries: eclipsing -- stars: spots

A newly discovered active contact binary in the field of NGC 1348

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Research in Astronomy and Astrophysics 2012年第1期12卷 93-103页

作者： Xiang-Song Fang sheng-hong gu Ho-Keung Hui Chi-Tai Kwok Bill Yeung Kam-Cheung Leung National Astronomical Observatories / Yunnan Observatory Chinese Academy of SciencesKunming 650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming 650011 China Graduate University of Chinese Academy of Sciences Beijing 100049 China Hokoon Nature Education cum Astronomical Centre Sik Sik-Yuen Hong Kong China hong Kong Astronomical Society Hong Kong China

We present a CCD photometry study of a newly discovered active eclipsing binary in the field of open cluster NGC 1348 based on the first time-series photometric observation. From the minimum times, we determined an orbital period of P = 0.691363 d. Among our datasets, the BV（.RI）c light curves obtained in November 2008 were analyzed using the Wilson-Devinney light curve modeling tech- nique. Because of the uncertainty of the membership of this binary in open cluster NGC 1348, we have analyzed the photometric data in two cases with different primary effective temperatures： Case A （T1 = 7750K） and Case B （T1 = 5250K）. Our anal- yses reveal that, for Case A, it is a deep （f 〉 70%）, very low mass ratio （q - 0.096） binary system, indicating that it is now in the late evolution stage of a contact binary; while for Case B, it is a red system with extraordinarily long orbital period with respect to the period-color relation for normal contact binaries, which suggests that this binary has evolved off the main sequence. The well known O＇Connell effect （e.g., AB 0.03 mag） was found in the dataset obtained in November 2008, which could be due to the existence of starspots on the components, therefore the corresponding spot properties （for Case A： hot spot; for Case B： dark spot） were determined using the Wilson-Devinney code. With the purpose of analyzing the dark spot activity for Case B, we compared the light curves derived in different observing runs, and found that a slight change appeared from November to December, 2008, which indicates the evolution of spot activity on at least one component over a time scale of about one month.

关键词： stars: binaries: close -- stars: binaries: eclipsing -- stars: spots

The refined physical parameters of transiting exoplanet system HAT-P-24

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Research in Astronomy and Astrophysics 2013年第5期13卷 593-603页

作者： Xiao-Bin Wang sheng-hong gu Andrew Collier Cameron hong-Bo Tan Ho-Keung Hui Chi-Tai Kwok Bill Yeung Kam-Cheung National Astronomical Observatories/Yunnan Observatory Chinese Academy of Sciences Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences School of Physics and Astronomy University of St Andrews North Haugh St Andrews Fife KY16 9SS UK University of Chinese Academy of Sciences Hokoon Nature Education cum Astronomical Centre Sik Sik Yuen hong Kong Astronomical Society

The transiting exoplanet system HAT-P-24 was observed by using CCD cameras at Yunnan Observatory and Hokoon Astronomical Centre, China in 2010 and 2012. In order to enhance the signal to noise ratio of transit events, the observed data are corrected for systematic errors according to Collier Cameron et al.＇s coarse de- correlation and Tamuz et al.＇s SYSREM algorithms. Three new complete transit light curves are analyzed by means of the Markov chain Monte Carlo technique, and the new physical parameters of the system are derived. They are consistent with the old ones from the discovered paper except for a new larger radius Rp = 1.364 Rj of HAT- P-24b, which confirms its inflated nature. By combining the five available epochs of mid-transit derived from complete transit light curves, the orbital period of HAT-P- 24b is refined to P = 3.3552479 d and no obvious transit timing variation signal can be found from these five transit events during 2010-2012.

关键词： exoplanet system -- transit -- individual: HAT-P-24

Magnetic activity of the spotted dwarf AP149 in the α Persei open cluster

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Research in Astronomy and Astrophysics 2010年第3期10卷 253-265页

作者： Xiang-Song Fang sheng-hong gu Sze-Leung Cheung Ho-Keung Hui Chi-Tai Kwok Kam-Cheung Leung National Astronomical Observatories / Yunnan Observatory Chinese Academy of Sciences Kunming 650011 China Graduate University of Chinese Academy of Sciences Beijing 100049 China Ho Koon Nature Education cum Astronomical Centre Sik Sik Yuen Hong Kong China hong Kong Astronomical Society Hong Kong China

The simultaneous photometric and spectroscopic observations of the spotted G dwarf AP149 in the young open cluster α Persei are analyzed here. We reconstruct the observed light curves with a two-starspot model by means of a light curve modeling technique, and find that the active regions shift oppositely along longitude on a time scale of one day. Combining with the observational data obtained by other groups, we discuss the evolution of spotted regions in the photosphere, and find that its starspots evolve not only on a short time scale but also on a long time scale. The pure chromospheric emissions for Ca IIHK and Hβ lines are derived by using the spectral subtraction technique. The variation of Ca IIHK lines＇ excess emission is spatially correlated to the starspot regions. There is no clear rotational modulation for the Hβ line＇s excess emission, probably due to the contamination of prominence emission.

关键词： stars: activity -- stars: late-type -- stars: spots -- stars: individual AP149

Physical modification of polyetheretherketone for orthopedic implants

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Frontiers of Materials Science 2014年第4期8卷 313-324页

作者： Ya-Wei DU Li-Nan ZHANG Zeng-Tao HOU Xin YE hong-sheng gu guo-Ping YAN Peng SHANG School of Materials Science and Engineering Wuhan Institute of Technology Wuhan 430073 China Center for Translational Medicine Research and Development Shenzhen Instituies of Advanced Technology Chinese Academy of Sciences Shenzhen 518055 China Department of Spine Surgery Shenzhen Second People's Hospital Shenzhen 518035 China

Polyetheretherketone （PEEK） is regarded as one of the most potential candidates for replacing current implant applications. To obtain good bone-implant interfaces, many modification methods have been developed to enable PEEK and PEEK- based composites from bio-inert to bioactive. Among them, physical methods have aroused significant attention and been widely used to modify PEEK for orthopedic implants. This review summarizes current physical modification techniques of PEEK for orthopedic applications, which include composite strategies, surface coating methods and irradiation treatments. The positive consequences of those modification methods will encourage continuing investigations and stimulate the wide range of applications of PEEK-based implants in orthopedics.

关键词： polyetheretherketone (PEEK) modification bioactivity bone-implantinterface

Volume of fluid simulation of single argon bubble dynamics in liquid steel under RH vacuum conditions

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Journal of Iron and Steel Research International 2024年第4期31卷 828-837页

作者： gu-jun Chen sheng-ping He College of Materials Science and Engineering Yangtze Normal UniversityChongqing 400044China College of Materials Science and Engineering Chongqing UniversityChongqing 400044China

Single argon bubble dynamics in liquid steel under Ruhrstahl-Heraeus(RH)vacuum conditions were simulated using the volume of fluid method,and the ideal gas law was used to consider bubble growth due to heat transfer and pressure *** simulation with a constant bubble density was also performed to validate the numerical method,and the predicted terminal bubble shape and velocity were found to agree with those presented in the Grace diagram and calculated by drag correlation,*** simulation results under RH conditions indicate that the terminal bubble shape and velocity cannot be *** primary bubble growth occurs within a rising distance of 0.3 m owing to heating by the high-temperature liquid steel;subsequently,the bubble continues to grow under equilibrium with the hydrostatic *** the initial diameter is 8-32 mm,the bubble diameter and rising velocity near the liquid surface are 80-200 mm and 0.5-0.8 m/s,*** bubble rises rectilinearly with an axisymmetric shape,and the shape evolution history includes an initial sphere,(dimpled)ellipsoid,and spherical cap with satellite bubbles.

关键词： Bubble dynamics Liquid steel Volume of fluid Bubble growth Bubble shape Rising velocity

Prediction of liquid circulation flow rate in RH degasser:improvement of decarburization at low atmospheric pressure

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Journal of Iron and Steel Research International 2024年第7期31卷 1661-1667页

The two-fluid model coupled with population balance model was used for simulating the gas-liquid flow in the Ruhrstahl-Heraeus(RH)*** predicted circulation flow rate was compared with that measured from a water model experiment to validate the mathematical ***,influence of snorkel immersion depth on liquid circulation flow rate was numerically investigated under an atmospheric pressure of 101 and 84 kPa,*** result indicates that the circulation flow rate of the RH degasser in the high-altitude area was severely reduced because of the decrease in atmospheric ***,increasing the snorkel immersion depth from 0.5 to 0.7 m can compensate for the decrease in atmospheric *** test result indicates that decarburization rate is significantly enhanced by increasing the snorkel immersion *** optimization,the percentage of heats with a final carbon content less than 0.002 wt.%is significantly increased from 22.0%to 96.4%.

关键词： RH degasser Two-fluid model Population balance model-Circulation flow rate Decarburization Snorkel immersion depth

H∞ Robustness for Distributed Control in Autonomous Microgrids Considering Cyber Disturbances

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CSEE Journal of Power and Energy Systems 2024年第2期10卷 696-706页

作者： Ge Cao guannan Lou Wei gu Lina sheng School of Electrical Engineering Southeast UniversityNanjing 210096China

The physical connections and logical relationships between microgrids and communication networks allow microgrids to develop into typical cyber-physical systems(CPSs).With the extensive use of open communication mechanisms,the impact of cyber disturbances in public communication networks cannot be *** this paper,a parameter optimal method for a distributed secondary controller based on the robust control theory and consensus algorithm is presented to enhance the robustness of a secondary control system under data disturbance,parameter perturbation,and time ***,a distributed secondary control strategy of microgrids is demonstrated that coordinates frequency and voltage restoration and power ***,considering the impact of cyber events on the secondary control,a distributed robust controller gain design method is proposed to satisfy the H∞ performance *** solution of the distributed robust control is transformed into a linear matrix in equation problem and latency margin is simultaneously ***,a test microgrid CPS is simulated with and without time delay to investigate the impact of cyber events on system operational states and the effectiveness and robustness of the proposed method.

关键词： Cyber disturbance cyber-physical lsystem distributed control microgrid robust H∞control

Transient Stability Analysis and Design of VSGs with Different DC-Link Voltage Controllers

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CSEE Journal of Power and Energy Systems 2024年第2期10卷 593-604页

作者： Chao Shen Wei gu Wanxing sheng Keyan Liu School of Electrical Engineering Southeast UniversityNanjingChina Power Distribution Research Department China Electric Power Research InstituteBeijing 100192China

Virtual synchronous control has been widely studied for the advantages of emulating inertia for voltage source converters (VSCs). A constant dc-link voltage is usually assumed in existing literature to estimate transient stability of virtual synchronous generators (VSGs). However, actual power supply in the dc-side of VSGs is limited and different dc-link voltage controllers are needed to achieve power balance between DC side and AC side. Addition of dc-link voltage controller has great influence on transient behavior of VSGs, which has not been investigated by previous research. To fill this gap, this paper gives insights into the effect of dc-link voltage dynamics on transient stability of VSGs. First, two typical kinds of VSGs with dc-link voltage controllers are introduced. Then, mathematical models considering dc-link dynamics are established and the effect of dc-link voltage controllers on transient synchronization stability of VSGs is revealed through equal area criterion (EAC). It is found that dc-link voltage controller would reduce stability margin of VSGs and design-oriented transient stability analysis is carried out quantitively using critical clearing time (CCT). Finally, simulation results are given to validate correctness of theoretical analysis.

关键词： DC-link voltage dynamics equal area criterion(eac) transient synchronization stability virtual synchronous generator(VSG)