A chemokine-driven positive feedback loop organizes lymphoid follicles

Lymphoid follicles are B-cell-rich compartments of lymphoid organs that function as sites of B-cell antigen encounter and differentiation. CXC chemokine receptor-5 (CXCR5) is required for B-cell migration to splenic follicles, but the requirements for homing to B-cell areas in lymph nodes remain to be defined. Here we show that lymph nodes contain two types of B-cell-rich compartment: follicles containing follicular dendritic cells, and areas lacking such cells. Using gene-targeted mice, we establish that B-lymphocyte chemoattractant (BLC/BCA1) and its receptor, CXCR5, are needed for B-cell homing to follicles in lymph nodes as well as in spleen. We also find that BLC is required for the development of most lymph nodes and Peyer's patches. In addition to mediating chemoattraction, BLC induces B cells to up-regulate membrane lymphotoxin alpha1beta2, a cytokine that promotes follicular dendritic cell development and BLC expression, establishing a positive feedback loop that is likely to be important in follicle development and homeostasis. In germinal centres the feedback loop is overridden, with B-cell lymphotoxin alpha1beta2 expression being induced by a mechanism independent of BLC.     

A local positive feedback of the tropical Pacific ocean-atmosphere system on interdecadal timescales

SINCE THE 1990S, THE CLIMATIC VARIABILITY ON INTERDE- CADAL TIME SCALES BECAME THE FOCUS OF THE INTERNATIONAL CLIMATOLOGY RESEARCH MISSIONS[1―3]. ON TIME SCALES OF A DECADE OR MORE, THE OCEAN CIRCULATION PREDOMINATEDHEAT BALANCE AND HYDROLOGICAL CYCLE, S…     

智能系统开发环境中agent的一种协商机制

介绍了一种面向智能体的智能系统开发环境ＡＯＤＥ中ａｇｅｎｔ间具有正交互关系的协商机制，给出了相应的协商算法和应用实例     

一种解空间机构运动分析问题的新方法

针对目前在空间机构的运动研究中缺少高效的研究工具的现状,提出了一种解空间机构运动分析问题的新方法--三维矢量的复指数形式,并探讨了应用该方法表示三维矢量的坐标变换形式.在机械手实例中,分别采用复指数变换法和坐标矩阵变换法进行求解.对比求解过程,可以看出复指数变换法是一种解决空间机构运动分析问题的有效和便捷的方法.     

Possible positive autocrine feedback in the prereplicative phase of human fibroblasts

The growth of normal diploid fibroblasts is generally thought to be tightly controlled by exogenous growth factors such as platelet-derived growth factor (PDGF) and epidermal growth factor (EGF). Subversion of a growth factor pathway at a regulatory point is considered to be a key event in neoplastic transformation and tumorigenesis. Thus, simian sarcoma virus has acquired the gene encoding the B-chain of PDGF and there is direct experimental proof that SSV-transformation is mediated by a PDGF-like growth factor. There is accumulating evidence that PDGF-like molecules are also synthesized and released by certain normal cells, suggesting an important role of cellularly produced PDGF in development and tissue regeneration. We now present evidence that a transient expression of the gene encoding the PDGF A-chain, and the synthesis and release of functional A-chain homodimers, is an early event in the prereplicative phase of normal human foreskin fibroblasts exposed to PDGF or EGF. Since these cells are PDGF-responsive, the results imply the existence of a positive autocrine signal that may serve as an amplifier of the mitogenic response under certain conditions.     

一种基于注意力机制的绝缘子状态反馈认知方法

针对已有绝缘子状态识别模型,以及细节识别深层网络开环认知模式和损失函数泛化能力不足的缺陷,模仿人工巡检模式,即实时评估认知结果可信度自寻优调节多尺度图像知识空间决策,提出一种基于注意力机制的绝缘子状态反馈认知方法。首先,针对预处理后的绝缘子图像,设计自适应尺度堆叠的卷积神经网络架构,使得网络输入由整体图像缩放至细节局部区域,每个尺度的网络共享相同的架构具有不同的参数,确保不同分辨率输入的可区分能力并为下一尺度生成一个细节注意区域。其次,随机配置网络面向多个尺度特征,建立具有强泛化能力的绝缘子状态分类准则。再次,构建类间分类和类内尺度间排序损失函数优化注意力网络,较前次预测生成更高置信度得分排名。最后,借鉴闭环控制思想,定义广义误差熵性能指标实时评测绝缘子不确定状态认知结果可信度,动态调节网络尺度等级,实现不确定认知结果约束下的特征空间自优化调节和分类准则重构,反馈再认知绝缘子状态。实验结果表明了本文方法与其他网络架构相比,增强了模型的泛化能力,提升了模型的认知精度。     

双臂空间机器人系统动力学与关节运动的非线性反馈控制

利用拉格朗日方程建立了漂浮基双臂空间机器人系统的动力学方程,给出了载体位置、姿态均不受控制情况下,双臂空间机器人关节运动的非线性反馈控制规律.结果表明,在系统动力学模型及参数较精确确定情况下,本文提出的控制方案能够有效地控制双臂空间机器人系统完成关节空间的指定运动,而不需对其载体的位置、姿态进行主动控制.仿真计算结果证实了方法的有效性.     

LFRBM系统的自适应控制

通过坐标变换和线性状态反馈,分别在系统参数已知和未知的情况下研究了LFRBM系统的控制问题．当参数已知时,给出了反馈增益的范围;当参数未知时,设计了一自适应控制器,自动调整控制增益k.利用Lyapunov稳定性理论证明所给控制器能将受控混沌系统全局渐近稳定于它的5个平衡点,最后Matlab的数值仿真证明了所给方法的有效性。     

机械手夹持机构运动与控制的联合仿真

设计一种基于凸轮运动原理的简易机械手夹持机构,以期将其应用于机械臂的末端夹持装置和管道攀爬机器人的手爪。建立夹持机构的简化三维模型,在ADAMS环境下对其进行运动学与动力学仿真。通过ADAMS／Control接口模块,在Simulink中搭建夹持机构的联合仿真控制系统,利用三闭环PID控制方法进行机械系统与控制系统的联合仿真分析。仿真结果表明,所设计的夹持机构系统具有良好的动态响应和轨迹跟踪特性。     

反馈平衡调节自适应机制在搜索引擎中的应用

介绍了反馈平衡调节自适应机制在循环工作链中的研究和实现 ,经实践证明运行效果良好 ,设计达到了预期目标     

Nucleation and growth mechanism of ferroelectric domain-wall motion

The motion of domain walls is critical to many applications involving ferroelectric materials, such as fast high-density non-volatile random access memory. In memories of this sort, storing a data bit means increasing the size of one polar region at the expense of another, and hence the movement of a domain wall separating these regions. Experimental measurements of domain growth rates in the well-established ferroelectrics PbTiO3 and BaTiO3 have been performed, but the development of new materials has been hampered by a lack of microscopic understanding of how domain walls move. Despite some success in interpreting domain-wall motion in terms of classical nucleation and growth models, these models were formulated without insight from first-principles-based calculations, and they portray a picture of a large, triangular nucleus that leads to unrealistically large depolarization and nucleation energies. Here we use atomistic molecular dynamics and coarse-grained Monte Carlo simulations to analyse these processes, and demonstrate that the prevailing models are incorrect. Our multi-scale simulations reproduce experimental domain growth rates in PbTiO3 and reveal small, square critical nuclei with a diffuse interface. A simple analytic model is also proposed, relating bulk polarization and gradient energies to wall nucleation and growth, and thus rationalizing all experimental rate measurements in PbTiO3 and BaTiO3.     

指令正反馈敦促法的原理及其在《生物化学》教学中的应用

以生物化学知识为载体,分别采用学导式、讲授式和指令正反馈敦促教学法进行生物化学教学探索,通过分组实验法对教学效果进行了对比实验研究.研究结果表明,指令正反馈敦促法显著优于学导式与讲授式两种方法,且能较好地消除学生中良莠不齐的现象,有效提高全体学生的成绩,具有优越的教学效果,不失为一种优良的新型教学方法.     

Structure of the yeast polarity protein Sro7 reveals a SNARE regulatory mechanism

Polarized exocytosis requires coordination between the actin cytoskeleton and the exocytic machinery responsible for fusion of secretory vesicles at specific sites on the plasma membrane. Fusion requires formation of a complex between a vesicle-bound R-SNARE and plasma membrane Qa, Qb and Qc SNARE proteins. Proteins in the lethal giant larvae protein family, including lethal giant larvae and tomosyn in metazoans and Sro7 in yeast, interact with Q-SNAREs and are emerging as key regulators of polarized exocytosis. The crystal structure of Sro7 reveals two seven-bladed WD40 beta-propellers followed by a 60-residue-long 'tail', which is bound to the surface of the amino-terminal propeller. Deletion of the Sro7 tail enables binding to the Qbc SNARE region of Sec9 and this interaction inhibits SNARE complex assembly. The N-terminal domain of Sec9 provides a second, high-affinity Sro7 interaction that is unaffected by the tail. The results suggest that Sro7 acts as an allosteric regulator of exocytosis through interactions with factors that control the tail. Sequence alignments indicate that lethal giant larvae and tomosyn have a two-beta-propeller fold similar to that of Sro7, but only tomosyn appears to retain the regulatory tail.     

程序设计类课程中建立实践教学环节反馈机制的探讨

对程序设计类课程的实践教学环节中存在的一些问题进行了分析,有针对性地引入反馈机制,重点探讨了如何构建反馈机制及相应措施的实施,使反馈机制成为促进教师有效教学和学生有效学习的重要手段。     

曲柄滑块机构运动分析的简便图解法

结合传统图解法进行运动分析。介绍一种简便实用、作图误差小，且不必选速度比例尺、加速度比例尺，直接在机构运动筒图上作速度多边形和加速度多边形的图解法。     

基于分层网络和反馈机制的细胞重编程

在多潜能细胞分化并最终形成相应的谱系结构的过程中, 多潜能细胞可能发生重编程.主要研究细胞分化过程中由双重负反馈回路的层级网络如何产生细胞重编程. 通过建立数学模型对整个系统的分叉进行分析, 揭示分层网络以及反馈机制产生细胞重编程的机理.     

严格正实广义系统的鲁棒性分析与输出反馈控制

讨论了一类广义系统的鲁棒严格正实分析与综合问题,其中各个不确定参数矩阵具有线性分式形式.基于线性矩阵不等式,给出了这类系统对所有容许不确定性扩展严格正实的条件,并设计动态输出反馈控制器,使闭环系统容许且扩展严格正实.结果表明,这一问题可以转化为确定广义系统的正实控制问题.     

时滞反馈磁浮控制系统的周期运动稳定性分析

研究了控制回路中速度反馈信号存在的时滞对非线性悬浮系统稳定性的影响.以时滞为参量,给出了系统发生Hopf分岔的条件.运用规范型法和中心流形法解析地确定出表征时滞磁浮系统中Hopf分岔方向、周期解的稳定性及周期变化的特征量.通过数值模拟验证了主要结果的可靠性,且分析表明,当时滞量达到临界值时,系统将会经历一个亚临界Hopf分岔而产生不稳定的周期振动.     

一种用于锁相环的正反馈互补型电荷泵电路

给出了一种新型的互补型电荷泵电路．采用正反馈技术,电路由CSMC1．2μm CMOS工艺实现,可工作在2V的低电压下．Spectre仿真结果显示,电荷泵的工作频率为100MHz时,功耗为0．08mW,输出信号的电压范围宽(0～2V),电路速度快,波形平滑,抖动小,在不增加电路功耗的前提下消除了传统电荷泵电路的电压跳变现象．该电荷泵电路可以很好地应用于低电源电压、高频锁相环电路．