HKUST Institutional Repository
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Repository of Hong Kong University of Science and Technology. Managed by the HKUST Library.
Mostrando recursos 1 - 6 de 6
1.
Velociety oscillations in turbulent rayleigh-benard convection - Qiu, X.-L.; Shang, X.-D.; Tong, Penger; Xia, K.-Q.
A systematic study of velocity oscillations in turbulent thermal convection is
carried out in small aspect-ratio cells filled with water. Local velocity fluctuations and temperature-velocity cross-correlation functions are measured over varying Rayleigh numbers and spatial positions across the entire convection cell. These structural measurements reveal how the thermal plumes interact with the bulk fluid in a closed cell and provide an interesting physical picture for the dynamics of the temperature and velocity oscillations in turbulent convection.
PACS numbers: 47.27.-i, 44.25.+f, 05.40.-a.
3.
Limit cycle theory of temporal current self-oscillations in sequential tunneling of superlattices - Sun, Zhouzhou; Wang, Shidong; Duan, S. Q.; Wang, Xiang-Rong
A unified theory of the temporal current self-oscillations is presented. We establish these oscillations as the manifestations of limit cycles, around unstable steady-state solutions caused by the negative differential conductance. This theory implies that both the generation and the motion of an electric-field domain boundary are universal in the sense that they do not depend on the initial conditions. Under an extra weak ac bias with a frequency Wac, the frequency must be either Wac or an integer fractional of Wac if the tunneling current oscillates periodically in time, indicating the periodic doubling for this non-linear dynamical system.
4.
Phenomenological considerations in percolating magnetic nanostructures - Wong, S. K.; Zhao, B.; Ng, Tai-Kai; Jing, X. N.; Yan, X.
Transport and magnetotransport properties were analysized systematically in percolating magnetic nanostructures such as Ni-rich NiFe - SiO2 and Fe - SiO2 films, where universal features unique to percolating magnetic nanostructures exhibiting giant Hall effect are pointed out. Assuming the presence of nanometer sized particles in the percolating conduction channels whose contribution to the conduction is sensitive to the temperature and external magnetic field, a phenomenological model was developed which explains the essence of these universal features.
5.
Properties of a magnetic superconductor with weak magnetization : application to ErNi2B2C - Ng, Tai-Kai; Leung, Wai-Tak
Using a Ginsburg-Landau free energy functional, we study the H - T phase diagram of a weak magnetic superconductor, where the magnetization from the magnetic component is marginal in supporting a spontaneous vortex phase in absence of external magnetic field. In particular, the competition between the spiral state and spontaneous vortex phase is analysed. Our theory is applied to understand the magnetic properties of ErNi2B2C.
6.
Magnetization reversal through synchronization with a microwave - Sun, Zhouzhou; Wang, Xiang-Rong
Based on the Landau-Lifshitz-Gilbert equation, it can be shown that a circularly-polarized microwave can reverse the magnetization of a Stoner particle through synchronization. In comparison with magnetization reversal induced by a static magnetic field, it can be shown that when a proper microwave frequency is used the minimal switching field is much smaller than that of precessional magnetization reversal. A microwave needs only to overcome the energy dissipation of a Stoner particle in order to reverse magnetization unlike the conventional method with a static magnetic field where the switching field must be of the order of magnetic anisotropy.
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