This paper discusses the problem that constructing a curve to satisfy the given endpoint constraints and chord-length parameters. Based on the research of Lu, the curve construction method for the entire tangent angle...This paper discusses the problem that constructing a curve to satisfy the given endpoint constraints and chord-length parameters. Based on the research of Lu, the curve construction method for the entire tangent angles region （α0, α1）∈（-r, r）×（-r, r） is given. Firstly, to ensure the weights are always positive, the three characteristics of cubic rational Bezier curve is proved, then the segment construction idea for the other tangent angles are presented in view of the three characteristics. The curve constructed with the new method satisfies the endpoint constraint and chord-length parameters, it＇s G1 continuous in every segment curve, and the shapes of the curve are well.展开更多
具有通配符间隙约束的模式匹配问题在信息检索、计算生物学和序列模式挖掘等研究领域有重要的应用.提出了更一般性的模式匹配问题,即一般间隙和长度约束的严格模式匹配(strict pattern matching with general gaps and length constrain...具有通配符间隙约束的模式匹配问题在信息检索、计算生物学和序列模式挖掘等研究领域有重要的应用.提出了更一般性的模式匹配问题,即一般间隙和长度约束的严格模式匹配(strict pattern matching with general gaps and length constraints,简称SPANGLO).该问题具有如下4个特点:它是一种严格的精确模式匹配;允许序列中任意位置的字符被多次使用;模式串中可以包含多个一般间隙;对出现的总体长度进行了约束.最坏情况下,一个SPANGLO实例将转换出指数个非负间隙的严格模式匹配实例.为了有效地解决该问题,提出了子网树及其相关概念和性质.在此基础上提出了求解算法SubnettreeSpanglo(SETS),并给出算法的正确性和完备性证明,同时指出该算法的空间复杂度与时间复杂度分别为O(m MaxLen W)和O(MaxLen W m2 n),其中,m,n,MaxLen和W分别是模式和序列的长度、出现的最大长度约束和模式的最大间距.实验结果既验证了SPANGLO问题转换方法的正确性,又验证了该算法的正确性和有效性.展开更多
具有长度约束的简单路径(Simple Paths with Length Constraint,SPLC)问题是指求解图中任意两点间路径长度为m的简单路径数,是k-path问题的一种特殊情况.该文基于网树数据结构提出了在有向无环图中求解SPLC问题的算法(Nettree for SPLC ...具有长度约束的简单路径(Simple Paths with Length Constraint,SPLC)问题是指求解图中任意两点间路径长度为m的简单路径数,是k-path问题的一种特殊情况.该文基于网树数据结构提出了在有向无环图中求解SPLC问题的算法(Nettree for SPLC in Directed Acyclic Graphs,NSPLCDAG).网树是一种多树根多双亲的数据结构.NSPLCDAG算法将该问题转化为一棵网树后,利用树根路径数这一性质对其进行求解.对NSPLCDAG算法进行改造,可以求解有向无环图中最长路径问题并形成网树求解最长路径算法(Nettree for the Longest Path inDAGs,NLPDAG),NLPDAG算法可找到所有最长路径,对NLPDAG算法做进一步改进形成改进的NLPDAG算法,改进的NLPDAG算法可在线性时间复杂度内给出有向无环图中的一条最长路径.实验结果验证了NSPLCDAG和改进的NLPDAG算法的正确性与有效性.展开更多
Progressive solidification is usually considered an effective strategy to reduce the hot tearing susceptibility of a cast component.In this study,special constrained plate castings with progressive changes in cross-se...Progressive solidification is usually considered an effective strategy to reduce the hot tearing susceptibility of a cast component.In this study,special constrained plate castings with progressive changes in cross-section were designed,which enabled progressive solidification.The hot tearing behavior of a newly developed NZ30 K Mg alloy(Mg-3.0 Nd-0.2 Zn-Zr,wt.%)was studied under progressive solidification using various mold temperature distributions and constraint lengths.Of these,a homogeneous mold temperature distribution is found to be the best option to avoid hot tearing,followed by a local low mold temperature distribution(with a chiller),then a gradient mold temperature distribution.Unexpectedly,compared with the homogeneous mold temperature distribution,adding a chiller does not provide any further reduction in the hot tearing susceptibility of the NZ30 K Mg alloy.A high mold temperature and a short constraint length increase the hot tearing resistance of cast Mg alloys.Progressive solidification is not a sufficient and necessary condition to avoid the formation of hot tearing.The two key factors that determine the occurrence of hot tearing under progressive solidification are the maximum cooling rate and the constraint length.Decreasing these values can reduce the incidence of hot tearing.展开更多
正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)技术作为802.11物理层标准,已经广泛应用于无线通信系统中。通过Matlab编程实现了OFDM系统的仿真,采用高斯白噪声信道,并使用卷积码作为系统的差错编码,对不同编码速率...正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)技术作为802.11物理层标准,已经广泛应用于无线通信系统中。通过Matlab编程实现了OFDM系统的仿真,采用高斯白噪声信道,并使用卷积码作为系统的差错编码,对不同编码速率和不同约束长度下的卷积码对OFDM系统带来的误码率影响进行了仿真。结果表明在中低码率情况下使用卷积码作为信道编码可使OFDM系统的抗干扰能力有明显的提升,并且系统的传输时延较小,采用低速率编码结构或增加约束长度都会增强卷积码的纠错能力。展开更多
基金Supported by Shandong Province Higher Educational Science and Technology Program(No.J12LN34)Shandong Ji'nan College and Institute Independent Innovation Project(No.201303011,No.201303021,No.201303016)
文摘This paper discusses the problem that constructing a curve to satisfy the given endpoint constraints and chord-length parameters. Based on the research of Lu, the curve construction method for the entire tangent angles region （α0, α1）∈（-r, r）×（-r, r） is given. Firstly, to ensure the weights are always positive, the three characteristics of cubic rational Bezier curve is proved, then the segment construction idea for the other tangent angles are presented in view of the three characteristics. The curve constructed with the new method satisfies the endpoint constraint and chord-length parameters, it＇s G1 continuous in every segment curve, and the shapes of the curve are well.
文摘具有通配符间隙约束的模式匹配问题在信息检索、计算生物学和序列模式挖掘等研究领域有重要的应用.提出了更一般性的模式匹配问题,即一般间隙和长度约束的严格模式匹配(strict pattern matching with general gaps and length constraints,简称SPANGLO).该问题具有如下4个特点:它是一种严格的精确模式匹配;允许序列中任意位置的字符被多次使用;模式串中可以包含多个一般间隙;对出现的总体长度进行了约束.最坏情况下,一个SPANGLO实例将转换出指数个非负间隙的严格模式匹配实例.为了有效地解决该问题,提出了子网树及其相关概念和性质.在此基础上提出了求解算法SubnettreeSpanglo(SETS),并给出算法的正确性和完备性证明,同时指出该算法的空间复杂度与时间复杂度分别为O(m MaxLen W)和O(MaxLen W m2 n),其中,m,n,MaxLen和W分别是模式和序列的长度、出现的最大长度约束和模式的最大间距.实验结果既验证了SPANGLO问题转换方法的正确性,又验证了该算法的正确性和有效性.
文摘具有长度约束的简单路径(Simple Paths with Length Constraint,SPLC)问题是指求解图中任意两点间路径长度为m的简单路径数,是k-path问题的一种特殊情况.该文基于网树数据结构提出了在有向无环图中求解SPLC问题的算法(Nettree for SPLC in Directed Acyclic Graphs,NSPLCDAG).网树是一种多树根多双亲的数据结构.NSPLCDAG算法将该问题转化为一棵网树后,利用树根路径数这一性质对其进行求解.对NSPLCDAG算法进行改造,可以求解有向无环图中最长路径问题并形成网树求解最长路径算法(Nettree for the Longest Path inDAGs,NLPDAG),NLPDAG算法可找到所有最长路径,对NLPDAG算法做进一步改进形成改进的NLPDAG算法,改进的NLPDAG算法可在线性时间复杂度内给出有向无环图中的一条最长路径.实验结果验证了NSPLCDAG和改进的NLPDAG算法的正确性与有效性.
基金supported by the National Key Research and Development Program of China(Grant Nos.:2016YFB0701204 and 2016YFB0301002)the National Natural Science Foundation of China(Grant Nos.:51671128,51771113,and 51821001)the Shanghai Rising-Star Program(Grant No.:15QB1402700)。
文摘Progressive solidification is usually considered an effective strategy to reduce the hot tearing susceptibility of a cast component.In this study,special constrained plate castings with progressive changes in cross-section were designed,which enabled progressive solidification.The hot tearing behavior of a newly developed NZ30 K Mg alloy(Mg-3.0 Nd-0.2 Zn-Zr,wt.%)was studied under progressive solidification using various mold temperature distributions and constraint lengths.Of these,a homogeneous mold temperature distribution is found to be the best option to avoid hot tearing,followed by a local low mold temperature distribution(with a chiller),then a gradient mold temperature distribution.Unexpectedly,compared with the homogeneous mold temperature distribution,adding a chiller does not provide any further reduction in the hot tearing susceptibility of the NZ30 K Mg alloy.A high mold temperature and a short constraint length increase the hot tearing resistance of cast Mg alloys.Progressive solidification is not a sufficient and necessary condition to avoid the formation of hot tearing.The two key factors that determine the occurrence of hot tearing under progressive solidification are the maximum cooling rate and the constraint length.Decreasing these values can reduce the incidence of hot tearing.
文摘正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)技术作为802.11物理层标准,已经广泛应用于无线通信系统中。通过Matlab编程实现了OFDM系统的仿真,采用高斯白噪声信道,并使用卷积码作为系统的差错编码,对不同编码速率和不同约束长度下的卷积码对OFDM系统带来的误码率影响进行了仿真。结果表明在中低码率情况下使用卷积码作为信道编码可使OFDM系统的抗干扰能力有明显的提升,并且系统的传输时延较小,采用低速率编码结构或增加约束长度都会增强卷积码的纠错能力。
