Generalized one-sided forbidding grammars

In generalized one-sided forbidding grammars (GOFGs), each context-free rule has associated a finite set of forbidding strings, and the set of rules is divided into the sets of left and right forbidding rules. A left forbidding rule can rewrite a nonterminal if each of its forbidding strings is absent to the left of the rewritten symbol. A right forbidding rule is applied analogically. Apart from this, they work like any generalized forbidding grammar. This paper proves the following three results. (1) GOFGs where each forbidding string consists of at most two symbols characterize the family of recursively enumerable languages. (2) GOFGs where the rules in one of the two sets of rules contain only ordinary context-free rules without any forbidding strings characterize the family of context-free languages. (3) GOFGs with the set of left forbidding rules coinciding with the set of right forbidding rules characterize the family of context-free languages.     

Multi grammars

The theory of selective substitution grammars is an attempt to provide a common framework for a number of seemingly different rewriting systems. The core of a selective substitution grammar is its selector (language), which prescribes which occurrences of letters in a current sentential form must be rewritten. Three rudimentary forms of selectors, studied until now are sequential, parallel, and continuous selectors. This paper is concerned with building more involved selectors, starting with rudimentary ones and using operations of union and concatenation. The language generating power of several classes of rewriting systems obtained in this way is investigated.     

A decidable word problem without equivalent canonical term rewriting system

We present a weak associative single-axiom system having the following property: the word problem is decidable with an efficient algorithm even though there does not exist any finite equivalent canonical term rewriting system.     

H.264熵解码器的研究与实现

在H.264/AVC标准中,基于上下文的自适应可变长编码(CAVLC)解码算法的复杂度较高。为此,提出一种基于熵解码算法的新型熵解码器,在对视频压缩码流实现熵解码的过程中,引入并行处理方式,并改进二叉树法。通过采用QuartusⅡ7.2版环境波形仿真和FPGA硬件实现方法进行实验,结果表明该熵解码器在硬件资源节省和解码速度方面具有较好的性能。     

H.264帧内预测快速模式选择

H.264/AVC视频编码标准中用率失真优化(RDO)方法为一个宏块(MB)判决最佳编码模式来提高编码效果,加大了算法复杂度并且计算冗余大。为了克服这一缺点,一种快速帧内预测模式选择算法被提出。在色度预测中,根据宏块的色度纹理复杂度,把原先的4种模式降到1或2种;在亮度16×16块模式判决中,根据最小哈达玛变换的绝对误差和(SATD)来选择最佳模式;在亮度4×4块模式判决中,该算法在9种模式中选择3种可能模式作为候选模式。通过比较16个4×4块总代价与1个16×16块的代价来选择最佳块选择模式,实验表明,该算法能在节省69%左右编码时间的情况下,比特率与峰值信噪比(PSNR)保持不变。     

H.264/AVC的自适应时域错误隐藏方法

针对视频传输时容易发生损坏或丢失的特点,为了更好地恢复图像质量,提出了基于H.264/AVC平台的自适应时域错误隐藏方法,该方法依据边界失真准则自适应转换两种隐藏方法,一种是初次隐藏,另一种是集成隐藏。集成隐藏采用自适应加权集成初次隐藏和增强隐藏。实验仿真结果表明方法改善了隐藏性能。     

地区电网地县一体调控技术支持系统AVC功能实现方案

应用网络拓扑分析功能,以220kV母线节点为单位将地区电网划分为若干个电网子区,提出了一种基于电网分区的分布式地区电网AVC功能实现方案.     

H.264/AVC解码芯片验证系统及验证策略

H.264/AVC视频编码标准是目前应用广泛的视频压缩标准,具有压缩比高、算法复杂等特点,给视频解码系统的设计和验证带来了挑战。文中基于一款H.264/AVC解码芯片架构,针对H.264/AVC视频解码系统的复杂性,构建了验证系统,提出多形式、分层次的验证策略,在解码芯片设计实现的各个阶段实施验证。根据RTL虚拟仿真、FPGA原型和后仿真等验证手段的特点,分别规划不同阶段的测试激励,形成基于H.264/AVC解码芯片的验证项策划,对类似H.264/AVC解码器的验证工作具有一定的帮助。     

H.264/AVC中基于决策树的P帧快速模式选择

目的 H.264/AVC帧间预测编码需要对所有可能编码模式计算并比较率失真代价,众多的模式类型导致了P帧编码的计算复杂度非常高。为此提出一种针对P帧的基于决策树的快速候选模式选择算法。方法在对宏块进行16×16的帧间运动估计后,首先根据残差宏块中4×4全零系数块个数对部分宏块直接选择出候选模式;然后使用16个4×4块的变换域系数绝对值之和(SATD)值,采用决策树分类方法对其余宏块选择候选模式。结果由于只需对候选模式进行编码,因此有效降低了编码器的计算复杂度。实验结果表明,与原始全搜索编码算法相比,该算法对不同运动程度的视频序列获得了较一致的编码时间的节省,同时平均峰值信噪比的损失和平均比特率的增加均较少。结论新的P帧帧间预测候选模式选择算法,根据帧间运动估计后的残差宏块信息,采用决策树方法对候选模式集进行分类。实验结果表明,该算法能在保证视频编码质量的前提下,有效地降低编码过程中的计算量,缩短编码时间。     

URL重写技术实现网站伪静态

介绍网站伪静态的概念,提出动态网站实现伪静态的几种生成方式,并选用ISAPI_Rewrite重写技术,详细阐述网站伪静态的实现过程,包括ISAPI筛选器的配置、URL重写规则的设计等关键步骤,最后说明伪静态技术在完善网站方面的作用。