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Search Results: 1 - 10 of 2905 matches for " Chuanyi Tu "
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Independent Directors, Female Directors and Performance of Financial Listed Companies in China  [PDF]
Chuanyi Zeng
Modern Economy (ME) , 2018, DOI: 10.4236/me.2018.94042
Abstract: Both independent and female directors are important parts of the board composition. This paper empirically examines the impact of independent directors’ background and the size of independent directors and female directors. The background of independent directors has positive effect on the performance of Chinese financial listed companies. The size of independent directors, female directors and female independent directors has no significant effect on corporate performance. This result provides an empirical evidence for the reform of corporate governance in China.
Multi-scale pressure-balanced structures in the solar wind observed by WIND
Shuo Yao,ChuanYi Tu,JianSen He,WenBo Wei,XiaoHong Meng
Chinese Science Bulletin , 2012, DOI: 10.1007/s11434-011-4966-1
Abstract: This work detects multi-scale, from hour to seconds, pressure-balanced structures (PBSs) in the solar wind based on the anti-correlation between the plasma thermal pressure and the magnetic pressure measured by WIND at 1 AU on April 5th, 2001. In our former research based on Cluster measurements, we showed the anti-correlation between the electron density and the magnetic field strength in multi-scales, and we supposed these structures may be pressure-balanced structures. Thus, in this work we aim to prove our speculation by the direct evidence on pressure measurements. Different from our previous work, we apply the WIND measurements this time, for they have both the magnetic pressure and the plasma pressure which Cluster could not offer. We use the wavelet cross-coherence method to analyze the correlation between the plasma pressure (P th ) and the magnetic pressure (P B ), and also the electron density (N e ) and the magnetic field strength (B) on various scales. We observe the anti-correlation between P th and P B distributed at different temporal scales ranging from 1000 s down to 10 s. This result directly indicates the existence of pressure-balanced structures (PBSs) with different sizes in the solar wind. Further, We compare the wavelet cross correlation spectrum of P th -P B and N e -B. We notice that the two spectra are similar in general. Thus this result confirms that the relation between P th -P B and N e -B are consistent with each other in the PBSs we study. Moreover, we compare the power spectrum density (PSD) of relative N e fluctuation with our previous work based on Cluster measurements. The two spectra show similar trend with Komolgorov’s 5/3 as their slopes. This may imply the similarity of the structures observed by both WIND and Cluster spacecrafts. Finally, we discuss the possible formation mechanisms for these multi-scale pressure-balanced structures. Our result is important to support the existence of multi-scale PBSs from one-hour scale down to one-minute, and is helpful to understand the role of compressive fluctuation in the solar wind turbulence dominated by Alfvéenic cascading.
New views on the emission and structure of the solar transition region
Hui Tian,Eckart Marsch,Chuanyi Tu,Werner Curdt,Jiansen He
Physics , 2010, DOI: 10.1016/j.newar.2010.08.001
Abstract: The Sun is the only star that we can spatially resolve and it can be regarded as a fundamental plasma laboratory of astrophysics. The solar transition region (TR), the layer between the solar chromosphere and corona, plays an important role in solar wind origin and coronal heating. Recent high-resolution observations made by SOHO, TRACE, and Hinode indicate that the TR is highly nonuniform and magnetically structured. Through a combination of spectroscopic observations and magnetic field extrapolations, the TR magnetic structures and plasma properties have been found to be different in coronal holes and in the quiet Sun. In active regions, the TR density and temperature structures also differ in sunspots and the surrounding plage regions. Although the TR is believed to be a dynamic layer, quasi-steady flows lasting from several hours to several days are often present in the quiet Sun, coronal holes, and active regions, indicating some kind of plasma circulation/convection in the TR and corona. The emission of hydrogen Lyman lines, which originates from the lower TR, has also been intensively investigated in the recent past. Observations show clearly that the flows and dynamics in the middle and upper TR can greatly modify the Lyman line profiles.
Radial evolution of the wave-vector anisotropy of solar wind turbulence between 0.3 and 1 AU
Jiansen He,Chuanyi Tu,Eckart Marsch,Sofiane Bourouaine,Zhongtian Pei
Physics , 2013, DOI: 10.1088/0004-637X/773/1/72
Abstract: We present observations of the power spectral anisotropy in wave-vector space of solar wind turbulence, and study how it evolves in interplanetary space with increasing heliocentric distance. For this purpose we use magnetic field measurements made by the Helios-2 spacecraft at three positions between 0.29 and 0.9 AU. To derive the power spectral density (PSD) in $(k_\parallel, k_\bot)$-space based on single-satellite measurements is a challenging task not yet accomplished previously. Here we derive the spectrum $\rm{PSD}_{\rm{2D}}$($\rm{k}_\parallel$, $\rm{k}_\bot$) from the spatial correlation function $\rm{CF}_{\rm{2D}}(r_\parallel, r_\bot)$ by a transformation according to the projection-slice theorem. We find the so constructed PSDs to be distributed in k-space mainly along a ridge that is more inclined toward the $\rm{k}_\bot$ than $\rm{k}_\parallel$ axis, a new result which probably indicates preferential cascading of turbulent energy along the $\rm{k}_\bot$ direction. Furthermore, this ridge of the distribution is found to gradually get closer to the $\rm{k}_\bot$ axis, as the outer scale length of the turbulence becomes larger while the solar wind flows further away from the Sun. In the vicinity of the $\rm{k}_\parallel$ axis, there appears a minor spectral component that probably corresponds to quasi-parallel Alfv\'enic fluctuations. Their relative contribution to the total spectral density tends to decrease with radial distance. These findings suggest that solar wind turbulence undergoes an anisotropic cascade transporting most of its magnetic energy towards larger $\rm{k}_\bot$, and that the anisotropy in the inertial range is radially developing further at scales that are relatively far from the ever increasing outer scale.
Occurrence Rates and Heating Effects of Tangential and Rotational Discontinuities as Obtained from Three-dimensional Simulation of Magnetohydrodynamic Turbulence
Lei Zhang,Jiansen He,Chuanyi Tu,Liping Yang,Xin Wang,Eckart Marsch,Linghua Wang
Physics , 2015, DOI: 10.1088/2041-8205/804/2/L43
Abstract: In solar wind, magnetohydrodynamic (MHD) discontinuities are ubiquitous and often found to be at the origin of turbulence intermittency. They may also play a key role in the turbulence dissipation and heating of the solar wind. The tangential (TD) and rotational (RD) discontinuities are the two most important types of discontinuities. Recently, the connection between turbulence intermittency and proton thermodynamics has been being investigated observationally. Here we present numerical results from three-dimensional MHD simulation with pressure anisotropy and define new methods to identify and to distinguish TDs and RDs. Three statistical results obtained about the relative occurrence rates and heating effects are highlighted: (1) RDs tend to take up the majority of the discontinuities along with time; (2) the thermal states embedding TDs tend to be associated with extreme plasma parameters or instabilities, while RDs do not; (3) TDs have a higher average T as well as perpendicular temperature $T_\perp$. The simulation shows that TDs and RDs evolve and contribute to solar wind heating differently. These results will inspire our understanding of the mechanisms that generate discontinuities and cause plasma heating.
Origin of Both the Fast Hot Jet and the Slow Cool Jet from Magnetic Flux Emergence and Advection in the Solar Transition Region
Liping Yang,Hardi Peter,Jiansen He,Chuanyi Tu,Linghua Wang,Lei Zhang,Xueshang Feng
Physics , 2015,
Abstract: In the solar atmosphere, the jets are ubiquitous and found to be at various spatia-temporal scales. They are significant to understand energy and mass transport in the solar atmosphere. Recently, the high-speed transition region jets are reported from the observation. Here we conduct a numerical simulation to investigate the mechanism in their formation. Driven by the supergranular convection motion, the magnetic reconnection between the magnetic loop and the background open flux occurring in the transition region is simulated with a two-dimensional magnetohydrodynamics model. The simulation results show that not only a fast hot jet, much resemble the found transition region jets, but also a adjacent slow cool jet, mostly like classical spicules, is launched. The force analysis shows that the fast hot jet is continually driven by the Lorentz force around the reconnection region, while the slow cool jet is induced by an initial kick through the Lorentz force associated with the emerging magnetic flux. Also, the features of the driven jets change with the amount of the emerging magnetic flux, giving the varieties of both jets. These results will inspire our understanding of the formation of the prevalence of both the fast hot jet and slow cool jet from the solar transition region and chromosphere.
A Numerical Investigation of the Recurrent High-speed Jets as a Possibility of Solar Wind Origin
Liping Yang,Jiansen He,Hardi Peter,Chuanyi Tu,Lei Zhang,Eckart Marsch,Linghua Wang,Xueshang Feng
Physics , 2015,
Abstract: In the solar atmosphere, jets are prevalent and they are significant for the mass and energy transport. Here we conduct numerical simulations to investigate the mass and energy contributions of the recently observed high-speed jets to the solar wind. With a one-dimensional hydrodynamic solar wind model, the time-dependent pulses are imposed at the bottom to simulate the jets. The simulation results show that without other energy source, the injected plasmas are accelerated effectively to be a transonic wind with a substantial mass flux. The rapid acceleration occurs close to the Sun, and the resulting asymptotic speed, number density at 0.3 AU, as well as mass flux normalized to 1 AU are compatible with in situ observations. As a result of the high speed, the imposed pulses generate a train of shocks traveling upward. By tracing the motions of the injected plasma, it is found that these shocks heat and accelerate the injected plasmas successively step by step to push them upward and eventually allow them to escape. The parametric studies show that increasing the speed of the imposed pulses or their temperature gives a considerably faster, and hotter solar wind, while increasing their number density or decreasing their recurring period only bring a denser solar wind. These studies provide a possibility that the ubiquitous high-speed jets are a substantial mass and energy contributions to the solar wind.
Self-absorption in the solar transition region
Limei Yan,Hardi Peter,Jiansen He,Hui Tian,Lidong Xia,Linghua Wang,Chuanyi Tu,Lei Zhang,Feng Chen,Krzysztof Barczynski
Physics , 2015, DOI: 10.1088/0004-637X/811/1/48
Abstract: Transient brightenings in the transition region of the Sun have been studied for decades and are usually related to magnetic reconnection. Recently, absorption features due to chromospheric lines have been identified in transition region emission lines raising the question of the thermal stratification during such reconnection events. We analyse data from the Interface Region Imaging Spectrograph (IRIS) in an emerging active region. Here the spectral profiles show clear self-absorption features in the transition region lines of Si\,{\sc{iv}}. While some indications existed that opacity effects might play some role in strong transition region lines, self-absorption has not been observed before. We show why previous instruments could not observe such self-absorption features, and discuss some implications of this observation for the corresponding structure of reconnection events in the atmosphere. Based on this we speculate that a range of phenomena, such as explosive events, blinkers or Ellerman bombs, are just different aspects of the same reconnection event occurring at different heights in the atmosphere.
Formation of Rotational Discontinuities in Compressive three-dimensional MHD Turbulence
Liping Yang,Lei Zhang,Jiansen He,Chuanyi Tu,Linghua Wang,Eckart Marsch,Xin Wang,Shaohua Zhang,Xueshang Feng
Physics , 2015, DOI: 10.1088/0004-637X/809/2/155
Abstract: Measurements of solar wind turbulence reveal the ubiquity of discontinuities. In this study, we investigate how the discontinuities, especially rotational discontinuities (RDs), are formed in magnetohydrodynamic (MHD) turbulence. In a simulation of the decaying compressive three-dimensional (3-D) MHD turbulence with an imposed uniform background magnetic field, we detect RDs with sharp field rotations and little variations of magnetic field intensity as well as mass density. At the same time, in the de Hoffman-Teller (HT) frame, the plasma velocity is nearly in agreement with the Alfv\'{e}n speed, and is field-aligned on both sides of the discontinuity. We take one of the identified RDs to analyze in details its 3-D structure and temporal evolution. By checking the magnetic field and plasma parameters, we find that the identified RD evolves from the steepening of the Alfv\'{e}n wave with moderate amplitude, and that steepening is caused by the nonuniformity of the Alfv\'{e}n speed in the ambient turbulence.
Characterizations of vector-valued weakly almost periodic functions
Chuanyi Zhang
International Journal of Mathematics and Mathematical Sciences , 2003, DOI: 10.1155/s0161171203111325
Abstract: We characterize the weak almost periodicity of a vector-valued,bounded, continuous function. We show that if the range of thefunction is relatively weakly compact, then the relative weakcompactness of its right orbit is equivalent to that of its leftorbit. At the same time, we give the function some otherequivalent properties.
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