Peculiarities of the UV continuum energy distribution for T Tauri stars

In the UV spectra of BP Tau, GW Ori, T Tau, and RY Tau obtained with the Hubble Space Telescope, we detected an inflection near 2000 Å in the F _λ ^c (λ) curve that describes the continuum energy distribution. The inflection probably stems from the fact that the UV continuum in these stars consists of two components: the emission from an optically thick gas with T<8000 K and the emission from a gas with a much higher temperature. The total luminosity of the hot component is much lower than that of the cool component, but the hot-gas radiation dominates at λ<1800 Å. Previously, other authors have drawn a similar conclusion for several young stars from low-resolution IUE spectra. However, we show that the short-wavelength continuum is determined from these spectra with large errors. We also show that, for three of the stars studied (BP Tau, GW Ori, and T Tau), the accretion-shock radiation cannot account for the observed dependence F _λ ^c (λ) in the ultraviolet. We argue that more than 90% of the emission continuum in BP Tau at λ>2000 Å originates not in the accretion shock but in the inner accretion disk. Previously, a similar conclusion was reached for six more classical T Tau stars. Therefore, we believe that the high-temperature continuum can be associated with the radiation from the disk chromosphere. However, it may well be that the stellar chromosphere is its source.     

Is LkHα 264 like a young, extremely active Sun?

We combine calibrated International Ultraviolet Explorer ( IUE ) archive data and new low-resolution optical data for the T Tauri star LkH α 264 covering the region from 1200 to 7000 Å. The UV continuum is well fitted by the combination of a blackbody at 4300 K plus hydrogenic free–free and free–bound emission from a dense plasma at 3.5×10⁴ K plus the emission by a second blackbody. This last component is at T ≈8700 K and covers about 4 per cent of the stellar surface. We interpret this last component to be the result of emission from one or various hotspots. The interesting result is that this combined emission also fits the observed optical continuum well. We conclude that this star is an analogue of the Sun, however displaying a much higher level of activity.     

一种H.264帧内模式选择快速算法

基于空域的帧内预测是H．264采用的一项重要技术，对编码性能的提高具有重要作用。但是由于支持的帧内预测模式较多，使用率失真优化模型计算的编码复杂度很高。利用像素边缘方向信息，相邻块预测模式间的相关性提出了一种帧内模式选择快速算法，可以预先排除约60％的预测模式，从而减小对率失真优化模型的调用。实验结果表明，算法在基本保持H．264原算法性能的同时，编码时间减少70％以上。     

基于H．264编码标准的远程视频采集系统的设计与实现

通过对如何构建远程视频采集（监控）系统的关键技术进行了较深入的研究，解决了非宽带环境下视频数据连续性和视频数据丢包等问题，视频编解码使用H．264压缩卡完成。     

Time-variability analysis of the Hα, He i and Na i D lines in the T Tauri star LkHα 264

We present a time-series analysis of quasi-simultaneous high-resolution profiles of the Hα, He i (λ5876 Å) and Na i D lines for the highly active T Tauri star LkHα 264.
Our data include repeated observations on time-scales ranging from approximately 1 d down to less than 1 h, at two different epochs. For the three lines we have analysed the time variability of the equivalent width and of the profile, using in this case both the normalized variance and correlation matrix analysis.
The behaviours of the equivalent widths of the He i and Na i lines on time-scales of the order of 1 d were found to correlate well. The correlation is more conspicuous when the level of variability of the lines is more dramatic. We conclude that there is a common region of formation for these lines, very close to the star. However, the Hα equivalent width follows such behaviour only when the He i and Na i D lines are less variable.
In terms of profile variations, He i and Na i differ from Hα. The He i and Na i D variations occur coherently over the entire profile, independently of the time-scales, although there are indications that such behaviour may break down for time-scales shorter than ≈20 min. In contrast, the variability of Hα occurs mainly on the blue side of the line. Variations on short time-scales seem to be associated with a secondary blue emission peak. Variations on time-scales of 1 d are linked to two weak blueshifted absorptions. These absorptions occur in an outer region and their behaviour can be understood in terms of an optical depth effect.
We conclude that the Hα line is formed in two distinct regions. The inner region, which is not too distinct from the one producing the He i and Na i D lines, is highly sensitive to the level of activity. The outer and more extended region dominates the contribution to the flux in Hα when the general level of stellar activity is high.     

适用于H.264的高性能快速运动估计算法

提出了一种适用于H .2 6 4的快速运动估计方法 :使用一维映射作为块排除准则 ,并充分利用H .2 6 4中的运动估计模式间的匹配冗余 ,使得 7种运动估计模式并行执行。试验结果表明 ,在估计精度几乎无损的情况下 ,本文算法比传统的全局搜索速度快 6倍以上     

基于Window CE.NET的H.264实时解码系统实现

设计实现了一套基于嵌入式操作系统Windows CE.NET的H.264视频实时解码系统。系统主要由视频解码、网络传输、网络质量控制、视频显示4部分组成。采用H.264编码技术对视频进行解码,采用UDP/RTP/RTCP协议传输多媒体流信息和控制信息。实验表明系统可以稳定实时解码、播放QCIF视频序列。     

基于H.264编码标准的远程视频采集系统的设计与实现

通过对如何构建远程视频采集(监控)系统的关键技术进行了较深入的研究,解决了非宽带环境下视频数据连续性和视频数据丢包等问题,视频编解码使用H.264压缩卡完成。     

一种改进的H．264差错隐藏算法

针对H.264的参考模型JM中P帧差错隐藏算法的不足,设计了改进的P帧差错隐藏方案.介绍了该方案中算法的理论基础及实现原理,并基于JM86平台对改进方案和原方案进行了对比测试,验证了改进方案具有一定的优越性.