联结CPG(connectionist central pattern generator,CCPG)模型适于控制机器人生成步态,但是传统的CCPG模型无法很好地生成3维步态.为此,本文根据生物学原理,提出了一个改进的神经元模型和一个改进的层次化CCPG(hierarchical CCPG,HCCPG...联结CPG(connectionist central pattern generator,CCPG)模型适于控制机器人生成步态,但是传统的CCPG模型无法很好地生成3维步态.为此,本文根据生物学原理,提出了一个改进的神经元模型和一个改进的层次化CCPG(hierarchical CCPG,HCCPG)模型.HCCPG模型能够生成相位协调的多自由度运动控制信号,从而解决了传统CCPG模型的步态生成问题.基于该模型,提出了一个统一方法来生成机器人的2维、3维步态.对转弯步态的特性进行了系统化深入分析,以便更好地利用该步态来适应狭窄的弯道环境.本文提出的HCCPG模型以及得到的步态特性,有助于提高机器人的环境适应能力.展开更多
提高蛇形机器人的三维运动控制能力是提高蛇形机器人环境适应能力的关键之一.虽然联结中枢模式生成器(Connectionist central pattern generator,CCPG)模型具有复杂度小、适合硬件实现等优点,但是目前的CCPG模型难以生成相位协调的多自...提高蛇形机器人的三维运动控制能力是提高蛇形机器人环境适应能力的关键之一.虽然联结中枢模式生成器(Connectionist central pattern generator,CCPG)模型具有复杂度小、适合硬件实现等优点,但是目前的CCPG模型难以生成相位协调的多自由度运动的控制信号,从而限制了它的三维步态控制能力.本文根据生物CPG机制的分层结构和运动神经元的功能,提出一个有层次化结构的CCPG(Hierarchical CCPG,HCCPG)模型.HCCPG模型由基本节律信号生成层、模式形成层、运动信号调整层这三个部分组成.运动信号调整层的运动神经元能够独立地对模式形成层的输出信号的幅值、相位等进行调整,从而较好地解决了CCPG模型难以生成相位协调的多自由度运动控制信号的问题.HCCPG模型具有步态控制能力强、复杂度小、有良好的扩展性等优点,从而适合用于控制三维步态.在HCCPG模型的基础上提出一个三维步态控制方法.仿真验证了这个控制方法的有效性.展开更多
Global DNA hypomethylation at CpG islands coupled with local hypermethylation is a hallmark for breast cancer, yet the mechanism underlying this change remains elusive. In this study, we showed that DNMT1, which encod...Global DNA hypomethylation at CpG islands coupled with local hypermethylation is a hallmark for breast cancer, yet the mechanism underlying this change remains elusive. In this study, we showed that DNMT1, which encodes a methylation maintenance enzyme, is a transcriptional target of BRCA1. BRCA1 binds to the promoter of the DNMT1 gene through a potential OCT1 site and the binding is required for maintaining a transcriptional active configuration of the promoter in both mouse and human cells. We further demonstrated that impaired function of BRCA1 leads to global DNA hypomethylation, loss of genomic imprinting, and an open chromatin configuration in several types of tissues examined in a BRCA1 mutant mouse model at premaligant stages. BRCA1 deficiency is also associated with significantly increased expression levels of several protooncogenes, including c-Fos, Ha-Ras, and c-Myc, with a higher expression in tumors, while premalignant mammary epithelial cells displayed an intermediate state between tumors and controls. In human clinical samples, reduced expression of BRCA1 correlates with decreased levels of DNMT1, and reduced methylation of CpG islands. Thus, BRCA1 prevents global DNA hypomethylation through positively regulating DNMT1 expression, and this provides one of mechanisms for BRCAl-associated breast cancer formation.展开更多
文摘联结CPG(connectionist central pattern generator,CCPG)模型适于控制机器人生成步态,但是传统的CCPG模型无法很好地生成3维步态.为此,本文根据生物学原理,提出了一个改进的神经元模型和一个改进的层次化CCPG(hierarchical CCPG,HCCPG)模型.HCCPG模型能够生成相位协调的多自由度运动控制信号,从而解决了传统CCPG模型的步态生成问题.基于该模型,提出了一个统一方法来生成机器人的2维、3维步态.对转弯步态的特性进行了系统化深入分析,以便更好地利用该步态来适应狭窄的弯道环境.本文提出的HCCPG模型以及得到的步态特性,有助于提高机器人的环境适应能力.
文摘提高蛇形机器人的三维运动控制能力是提高蛇形机器人环境适应能力的关键之一.虽然联结中枢模式生成器(Connectionist central pattern generator,CCPG)模型具有复杂度小、适合硬件实现等优点,但是目前的CCPG模型难以生成相位协调的多自由度运动的控制信号,从而限制了它的三维步态控制能力.本文根据生物CPG机制的分层结构和运动神经元的功能,提出一个有层次化结构的CCPG(Hierarchical CCPG,HCCPG)模型.HCCPG模型由基本节律信号生成层、模式形成层、运动信号调整层这三个部分组成.运动信号调整层的运动神经元能够独立地对模式形成层的输出信号的幅值、相位等进行调整,从而较好地解决了CCPG模型难以生成相位协调的多自由度运动控制信号的问题.HCCPG模型具有步态控制能力强、复杂度小、有良好的扩展性等优点,从而适合用于控制三维步态.在HCCPG模型的基础上提出一个三维步态控制方法.仿真验证了这个控制方法的有效性.
文摘Global DNA hypomethylation at CpG islands coupled with local hypermethylation is a hallmark for breast cancer, yet the mechanism underlying this change remains elusive. In this study, we showed that DNMT1, which encodes a methylation maintenance enzyme, is a transcriptional target of BRCA1. BRCA1 binds to the promoter of the DNMT1 gene through a potential OCT1 site and the binding is required for maintaining a transcriptional active configuration of the promoter in both mouse and human cells. We further demonstrated that impaired function of BRCA1 leads to global DNA hypomethylation, loss of genomic imprinting, and an open chromatin configuration in several types of tissues examined in a BRCA1 mutant mouse model at premaligant stages. BRCA1 deficiency is also associated with significantly increased expression levels of several protooncogenes, including c-Fos, Ha-Ras, and c-Myc, with a higher expression in tumors, while premalignant mammary epithelial cells displayed an intermediate state between tumors and controls. In human clinical samples, reduced expression of BRCA1 correlates with decreased levels of DNMT1, and reduced methylation of CpG islands. Thus, BRCA1 prevents global DNA hypomethylation through positively regulating DNMT1 expression, and this provides one of mechanisms for BRCAl-associated breast cancer formation.
