Computational approaches to cellular rhythms

Oscillations arise in genetic and metabolic networks as a result of various modes of cellular regulation. In view of the large number of variables involved and of the complexity of feedback processes that generate oscillations, mathematical models and numerical simulations are needed to fully grasp the molecular mechanisms and functions of biological rhythms. Models are also necessary to comprehend the transition from simple to complex oscillatory behaviour and to delineate the conditions under which they arise. Examples ranging from calcium oscillations to pulsatile intercellular communication and circadian rhythms illustrate how computational biology contributes to clarify the molecular and dynamical bases of cellular rhythms.     

Fidelity in planar cell polarity signalling

The polarity of Drosophila wing hairs displays remarkable fidelity. Each of the approximately 30,000 wing epithelial cells constructs an actin-rich prehair that protrudes from its distal vertex and points distally. The distal location and orientation of the hairs is virtually error free, thus forming a nearly perfect parallel array. This process is controlled by the planar cell polarity signalling pathway. Here we show that interaction between two tiers of the planar cell polarity signalling mechanism results in the observed high fidelity. The first tier, mediated by the cadherin Fat, dictates global orientation by transducing a directional signal to individual cells. The second tier, orchestrated by the 7-pass transmembrane receptor Frizzled, aligns each cell's polarity with that of its neighbours through the action of an intercellular feedback loop, enabling polarity to propagate from cell to cell. We show that all cells need not respond correctly to the presumably subtle signal transmitted by Fat. Subsequent action of the Frizzled feedback loop is sufficient to align all the cells cooperatively. This economical system is therefore highly robust, and produces virtually error-free arrays.     

海嘧啶对人胃癌BGC-823细胞形态、细胞核DNA及细胞间通讯的影响

目的研究海嘧啶对人胃癌细胞BGC-283细胞形态、细胞核DNA及细胞间通讯的影响。方法采用激光扫描共聚焦技术观察海嘧啶对人胃癌细胞及细胞核DNA的影响。采用划痕标记染料示踪技术观察海嘧啶对细胞间通讯的影响。结果海嘧啶可改变细胞形态,使细胞DNA缺损,可促进肿瘤细胞间通讯的恢复。结论通过影响细胞DNA和恢复细胞间通讯是海嘧啶抗肿瘤的作用机理。     

线性系统极点配置的神经网络算法

利用人工神经网络，讨论了线性定常控制系统关于状态反馈，输出反馈及动态补偿器的极点配置问题，对状态反馈问题采用一个二级四层BP网求解，对输出反馈问题采用一个二级五层BP网求解，而对动态补偿器问题亦可采用一个二级五层BP网求解，这些极点配置方法便于计算机实现。     

飞机纵向控制中的法向过载设计

以某飞机为研究对象，通过在俯仰角速度控制回路上加上法向过载回路作为外回路，实现飞机纵向控制中的法向过载设计．反馈增益的设计则选用输出反馈线性二次型算法，该算法可以同时闭合所有反馈环节，设计出所需要的反馈系数．分析了选用法向过载控制回路的合理性．最后，分别给出了低空、中空、高空该控制回路的阶跃响应，验证了该控制规律的有效性和正确性。     

不同耦合反馈对结肠细胞中信号噪声的影响

在结肠隐窝中,干细胞分化为短暂扩增细胞,短暂扩增细胞再分化为完全分化细胞.为了维持体内平衡,这2个分化概率必受到线性反馈(L)或饱和反馈(S)的调节.不同细胞可以采用不同的调节方式,产生LL、LS、SL和SS这4种耦合反馈.该文借鉴信号转导理论,引入增益因子,运用Fokker-Planck方程,推导出信号-噪声公式,并借助数值模拟,比较4种耦合反馈对信号噪声的影响.研究结果表明:相对于LL耦合反馈和LS耦合反馈,SL耦合反馈和SS耦合反馈更能合理地解释结直肠癌的“腺瘤”或“良性阶段”以及“最佳治疗”时期.因此,SL和SS耦合反馈可能是调节细胞分化的最佳耦合方式.研究结果可以为临床上正确认识结直肠癌的发展过程并制定有效的治疗方案提供理论依据.     

Feedback strategies for iterative channel estimation in OFDM underwater acoustic communications

The extremely limited bandwidth in underwater acoustic communication makes channel estimation using fewer pilot symbols more challenging. Iterative channel estimation( ICE) can be used to refine channel estimation with limited number of pilots,by coupling the channel estimator with channel decoder. In this paper,various feedback strategies in ICE are discussed. The performance of a decision feedback based on the cost function is improved by modifying the design and another four feedback strategies are summarized,including hard/soft decision feedback and their threshold-controlled versions. Simulation results show that ICE can achieve impressive gains over the non-iterative receiver and the gains are more significant with fewer pilots. Furthermore,soft decision feedback outperforms hard decision feedback; while the feedback based on the cost function and soft decision feedback have quite close performance.     

两种混沌同步法及其用于通讯的比较

用Ｌｏｒｅｎｚ系统对两种混沌同步方法－变量替换法和变量反馈法进行了数值研究。结果表明用单变量反馈可混沌同步，并比变量替换法有较快的收敛速率和较高的同步稳定性。用单变量反馈法同步的混沌系统同样可以用于通讯，且结构简单，便于应用。     

用短路法、开路法分析负反馈电路的组态

根据反馈网络从电路输出回路的不同取样电量和在输入回路的不同连接方式,可把交流负反馈电路的组态分为电压串联、电压并联、电流串联和电流并联4种.通过构建电路存在反馈的必要条件和充要条件,可引出令反馈电路的负载和信号源内阻分别短路或开路的方法,用于分析负反馈电路的组态.实例说明,两者互为对偶,物理意义明确,因果关系等价,逻辑概念清晰,通用性强,适用面广,应用灵活.     

运用反馈信息卡片进行挺身式跳远技术教学的研究

鉴于田径教学中普遍采用的常规技术教学方法存在着对反馈信息运用不够的缺陷,笔者在挺身式跳远技术教学中运用反馈信息卡片进行了实验研究.研究结果表明,运用反馈信息卡片进行教学有利于发挥教师在教学中的主导性和学生的主体性;有利于促进教学过程中反馈信息的流动、交换和储存;有利于促进学生对运动技术的掌握,提高运动技能,激发学习兴趣,提高教学效果.     

结构振动的反馈控制

针对结构振动的反馈控制方法，考虑作动器的动态特性，给出保证位移正反馈、速度负反馈和加速度负反馈控制稳定的时延界限和增益幅度．比较了三种反馈方法的优缺点，指出加速度负反馈具有大范围的稳定特性．     

学习者性格类型与教师修正性反馈形式研究

目前,大学英语写作教学中的教师修正性反馈方式与学生需求差距甚大,且不同性格类型的学习者对反馈方式的偏好有显著差异：内向型学习者倾向获得语言提示反馈,其次是标记反馈,而外向型学习者对反馈的明晰度要求更高,偏爱直接反馈。因此,教师应对不同性格学习者进行针对性反馈,这将有助于学生对习作进行积极有效的修改。     

外部光反馈对半导体激光器混沌同步系统同步性能的影响

采用单向耦合光反馈半导体激光器混沌同步系统,对外部光反馈对系统实现同步的情况进行了比较,并进一步分析了不同反馈下激光器的参数失配对同步性能的影响.研究表明:光反馈半导体激光器混沌同步系统只在两个反馈区域可以实现完全(超前)同步,且在较强反馈区域实现的同步具有对参数失配更加敏感的特点;另外,当接收端处于强注入锁定的状态下,随着反馈系数的变化,系统会出现由广义同步向完全同步的切换,这会为一种新的混沌键控通信方案提供参考.     

反馈受限的多用户MIMO下行链路预编码算法研究

在上行链路反馈受限的MIMO信道系统中,通过最大化反馈的信道质量信息可以获得相关门限阈值。现有研究在提高用户和速率方面已达到较好效果,但同时也提高了算法复杂度。为了在不损失多用户分集增益的前提下降低反馈开销,提出一种基于门限的次优下行链路预编码方案。在反馈信道方向信息(CDI)和信道质量信息(CQI)的基础上,应用迫零波束成形(ZFBF)算法进行预编码。实验结果表明,该算法在保证较高和速率的同时有效降低了计算复杂度。     

二次型性能的优化降阶控制器设计

在静态输出反馈控制器设计的基础上,设计线性系统在二次型性能指标下的优化降阶动态输出反馈控制器.动态反馈控制器可表示为一个最优降维状态估值器和一个最优静态反馈增益阵.控制器的输入阵,可用全维控制器输入阵的一个线性组合来表示.通过求解利用降维状态观测器的静态输出反馈,可得到降阶控制的最优反馈增益阵.最后,通过一个例子,说明本文提出的给定解控制器设计方法.     

大学英语写作中教师反馈和同伴反馈有效性的行动研究

以行动研究的方法在一年级非英语专业学生写作课中将教师反馈与同伴反馈相结合,对教师反馈和同伴反馈合理性和采纳率进行了研究。结果显示：教师反馈的正确率与学生写作水平呈正相关,同伴反馈的合理性较低。因此教师反馈应在大学英语写作课中大力提倡,同伴反馈应设计合理,操作严谨,作为教师反馈方式的一种补充,从而提高学生的写作水平。     

双向中继通信系统中的信道信息反馈和用户选择性能分析

在多用户放大转发双向中继通信网络中,文章分别基于两种信道状态信息(CSI)反馈模式:无CSI反馈和存在基站-中继链路CSI反馈,推导了中断概率闭合表达式,并提出一种最优用户选择方法使平均和速率最大化.仿真结果显示,CSI的反馈有助于系统性能的提高,所提的用户选择方法能显著提升系统和速率.     

基于min型表现外延的反馈外延外包络

相对于max型表现外延,给出min型表现外延的定义,利用min型表现外延构造了概念关于因素的min型反馈外延.研究了min型反馈外延与概念外延以及复杂因素min型反馈外延与简单因素min型反馈外延之间的关系,得到了与min型反馈外延相关的一些重要性质.定义了min型反馈外延外包络,给出一种从概念外延"内部"对概念外延进行逼近的方法.     

A sensing array of radically coupled genetic 'biopixels'

Although there has been considerable progress in the development of engineering principles for synthetic biology, a substantial challenge is the construction of robust circuits in a noisy cellular environment. Such an environment leads to considerable intercellular variability in circuit behaviour, which can hinder functionality at the colony level. Here we engineer the synchronization of thousands of oscillating colony 'biopixels' over centimetre-length scales through the use of synergistic intercellular coupling involving quorum sensing within a colony and gas-phase redox signalling between colonies. We use this platform to construct a liquid crystal display (LCD)-like macroscopic clock that can be used to sense arsenic via modulation of the oscillatory period. Given the repertoire of sensing capabilities of bacteria such as Escherichia coli, the ability to coordinate their behaviour over large length scales sets the stage for the construction of low cost genetic biosensors that are capable of detecting heavy metals and pathogens in the field.     

On Limited Feedback in Wireless Communication Systems

We provide a broad look at the field of limited feedback in wireless communication.We review works of limited feedback with various combinations of single antenna,multiple antenna,single-user and multiuser technology and provide a synopsis of the role of limited feedback in wireless communication systems.We also study how the feedback rate can be minimized without losing the gains due to adaptive transmission and multiuser diversity.It seems that the best possible feedback scheme is not invented yet.As anot...