Wang Li-Feng

Jet-Like Long Spike in Nonlinear Evolution of Ablative Rayleigh-Taylor Instability

We report the formation of jet-like long spike in the nonlinear evolution of the ablative Rayleigh-Taylor instability (ARTI) experiments by numerical simulations. A preheating model ?(T) = ?SH[1 + f(T)], where ?SH is the Spitzer-H?rm (SH) electron conductivity and f(T) interprets the preheating tongue effect in the cold plasma ahead of the ablative front [Phys. Rev. E 65 (2002) 57401], is introduced in simulations. The simulation results of the nonlinear evolution of the ARTI are in general agreement with the experiment results. It is found that two factors, i.e., the suppressing of ablative Kelvin-Helmholtz instability (AKHI) and the heat flow cone in the spike tips, contribute to the formation of jet-like long spike in the nonlinear evolution of the ARTI.

Generation and Measurement of Isolated 160-Attosecond XUV Laser Pulses at 82 eV

Isolated attosecond extreme-ultraviolate (XUV) pulses are generated based on high-harmonic-generation from a neon gas cell driven by carrier-envelope phase stabilized sub-5-fs Ti:sapphire laser pulses at repetition rate of 1 kHz. Temporal characterization of isolated attosecond XUV pulses is demonstrated to be 160-attosecond by attosecond streaking spectroscopy. The development of attosecond source and streaking spectroscopy will allow scientists to explore the electron dynamics in matter.

On the Second Harmonic Generation through Bell—Plesset Effects in Cylindrical Geometry

Generation of the second harmonic initiated by Bell—Plesset effects in a cylindrical geometry is studied analytically. For an initial single-mode velocity perturbation, the second-order mode-coupling formula is obtained by expanding the perturbation displacement and velocity potential up to the second-order accuracy. It is found that the initially symmetric interface evolves into a significant bubble-spike asymmetric pattern. The second-order solutions clearly show that the amplitude of the spike grows faster than that of the bubble. The temporal evolutions of the amplitudes of the bubble and spike are dependent on the interface velocity V0. The larger interface velocity leads to the smaller amplitude of the perturbation at an arbitrary interface position in a cylindrically convergent geometry.

Nonlinear Evolution of Jet-Like Spikes from the Single-Mode Ablative Rayleigh-Taylor Instability with Preheating

In this research, the nonlinear evolution of jet-like spikes in the single-mode ablative Rayleigh-Taylor instability (ARTI) in the presence of preheating, is studied numerically. It is demonstrated that the preheating plays an essential role in the formation of jet-like spikes in the nonlinear ARTI. The evolution of jet-like spikes in the ARTI with preheating consists of three stages with distinctly different distinguishing features. In the early stage, the preheating contributes to significantly increase the density-gradient scale length and broaden the velocity profile of the ablation surface, where the former can reduce the linear growth of the ARTI and mitigate the growth of its harmonics. In the middle stage, the ablative Kelvin-Helmholtz instability is dramatically suppressed due to the ablation effects. In the late stage, the jets length (i.e. bubble-spike amplitude) is further increased by the bubble acceleration in the highly nonlinear ARTI, resulting eventually in the formation of jet-like spikes.

A Lightweight Video Encryption Algorithm for Wireless Application

Protecting the confidentiality and integrity of video information is one of the crucial security elements for many wireless video applications. Taking limited power, processor resource and bandwidth of mobile device into account, a lightweight luminance transform coefficients encryption (LTCE) algorithm, is proposed based on the special feature of the H.264 video coding standard. In LTCE algorithm, the luminance transform coefficients of residual data before entropy coding are adjustably partially encrypted by stream cipher, and it is discussed when ciphertext value are equal to zero in detail. Experimental results demonstrate the proposed algorithm that encrypts much less important data can achieve good security and high efficiency, as well as obtain low complexity and time cost. LTCE algorithm is suitable for security multimedia services for wireless application.

Incompressible Magnetohydrodynamic Kelvin—Helmholtz Instability with Continuous Profiles

Effects of a continuous magnetic field in the direction of streaming on the incompressible Kelvin—Helmholtz instability (KHI) are investigated by solving the linear ideal magnetohydrodynamic equations. It is found that the frequency of the KHI is not influenced by the magnetic field. The magnetic field strength effect decreases the linear growth of the KHI, while the magnetic field gradient scale length effect increases its linear growth. The KHI can even be completely suppressed when the magnetic field is strong enough. The linear growth rate approaches a maximum when the magnetic field gradient scale length is large enough.

Implementation of 72 point DST-IV for 60 channel TDM-FDM transmultiplexer

The implementation of 72 point DST-IV (discrete sine transform L type four) is presented in this paper. This design is used for the 60 channel transmultiplexer (TMUX) which implements the conversion between time division multiplex (TDM) signals and frequency division multiplex (FDM) signals. Based on a newly developed fast algorithm, two cascaded printed circuit boards are designed. They are composed of general high speed integrated circuits, with structures suitable for pipeline and parallel computation. A ROM direct control mode is adopted. Combined with the use of multiplexing techniques, the above measures promise the real-time implementation of 72-point DST-IV equipment with 125 mu s time duration at 9.216 MHz clock rate.<<ETX>>