Impedance control is selectively tuned to multiple directions of movement

Humans are able to learn tool-handling tasks, such as carving, demonstrating their competency to make movements in unstable environments with varied directions. When faced with a single direction of instability, humans learn to selectively co-contract their arm muscles tuning the mechanical stiffness of the limb end point to stabilize movements. This study examines, for the first time, subjects simultaneously adapting to two distinct directions of instability, a situation that may typically occur when using tools. Subjects learned to perform reaching movements in two directions, each of which had lateral instability requiring control of impedance. The subjects were able to adapt to these unstable interactions and switch between movements in the two directions; they did so by learning to selectively control the end-point stiffness counteracting the environmental instability without superfluous stiffness in other directions. This finding demonstrates that the central nervous system can simultaneously tune the mechanical impedance of the limbs to multiple movements by learning movement-specific solutions. Furthermore, it suggests that the impedance controller learns as a function of the state of the arm rather than a general strategy. © 2011 the American Physiological Society.

Movements of haplochromines (Pisces: Cichlidae) in Lake George, Uganda

In Lake George, the abundance of haplochromines in inshore regions during the day and at night differs significantly. Futhermore, while by day there are more haplochromines in the lower than the upper layers, at night these fishes appear to be uniformly distributed throught the water column. Regions of the lake near river mouths had fewer haplochromines during the wet than the dry season, while the reverse was true of regions distant form the river mouths. Possible causes of these movements are discussed.

The response of buildings to movements induced by deep excavations

Deep excavations and tunnelling can cause ground movements that affect buildings within their influence zone. The current approach for building damage assessment is based on tensile strains estimated from the deflection ratio and the horizontal strains at the building foundation. For tunnelling-induced deformations, Potts & Addenbrooke (1997) suggested a method to estimate the building response from greenfield conditions using the relative building stiffness. However, there is not much guidance for building response to excavation-induced movements. This paper presents a numerical study on the response of buildings to movements caused by deep excavations in soft clays, and proposes design guidance to estimate the deflection ratio and the horizontal strains of the building from the building stiffness. © 2012 Taylor & Francis Group.

The horizontal response of framed buildings on individual footings to excavation-induced movements

Deep excavations and tunnelling can cause ground movements that affect buildings within their influence zone. The current approach for building damage assessment is based on tensile strains estimated from the deflection ratio and the horizontal strains at the building foundation. This paper examines the significance of horizontal strains in buildings on individual footings. The first part of the paper presents a case study of a framed building in Singapore which was subjected to the effects of bored tunnelling, where significant horizontal strains were observed. The second part of the paper suggests a method to relate the horizontal strains induced in a building to the stiffness of the frame structure. Using a combination of simplified structural analysis and finite element models, design guidance is proposed to estimate excavation-induced horizontal strains in frame buildings on individual footings. © 2012 Taylor & Francis Group.

Control of bimanual rhythmic movements: Trading efficiency for robustness depending on the context

This paper investigates how the efficiency and robustness of a skilled rhythmic task compete against each other in the control of a bimanual movement. Human subjects juggled a puck in 2D through impacts with two metallic arms, requiring rhythmic bimanual actuation. The arms kinematics were only constrained by the position, velocity and time of impacts while the rest of the trajectory did not influence the movement of the puck. In order to expose the task robustness, we manipulated the task context in two distinct manners: the task tempo was assigned at four different values (hence manipulating the time available to plan and execute each impact movement individually); and vision was withdrawn during half of the trials (hence reducing the sensory inflows). We show that when the tempo was fast, the actuation was rhythmic (no pause in the trajectory) while at slow tempo, the actuation was discrete (with pause intervals between individual movements). Moreover, the withdrawal of visual information encouraged the rhythmic behavior at the four tested tempi. The discrete versus rhythmic behavior give different answers to the efficiency/robustness trade-off: discrete movements result in energy efficient movements, while rhythmic movements impact the puck with negative acceleration, a property preserving robustness. Moreover, we report that in all conditions the impact velocity of the arms was negatively correlated with the energy of the puck. This correlation tended to stabilize the task and was influenced by vision, revealing again different control strategies. In conclusion, this task involves different modes of control that balance efficiency and robustness, depending on the context. © 2008 Springer-Verlag.

Comparative Expression of Zebrafish Lats1 and Lats2 and Their Implication in Gastrulation Movements

Large tumor suppressor (Lats) is a Ser/Thr kinase, and it presents an important function in tumor suppression. lats was originally identified in Drosophila and recently in mammals. In mammals, it contains two homologues, lats1 and lats2. In the present study, lats1 and lats2 were characterized from zebrafish (Danio rerio), which is the first report of lats in a nonmammalian vertebrate. The primary structure, genomic organization, and phylogenesis of lats from different species were studied, and the results suggest that lats1 is the direct descendant of invertebrate lats, whereas lats2 is formed by genome duplication. In zebrafish, both lats genes are maternally expressed, while they show distinctly different expression profiles during gastrulation. lats1 is almost ubiquitously expressed through development, and lats2 is more prominently expressed in the non-neural ectoderm region of zebrafish gastrula. Most intriguingly, as revealed by cell tracing and gene expression analysis, morpholino-mediated knockdown of either lats1 or lats2 led to obvious defects of cell migration in gastrulation, indicating the functional significance of lats in gastrulation movements. Developmental Dynamics 238:28502859, 2009. (C) 2009 Wiley-Liss, Inc.

Zebrafish eaf1 and eaf2/u19 Mediate Effective Convergence and Extension Movements through the Maintenance of wnt11 and wnt5 Expression

Studies have attributed several functions to the Eaf family, including tumor suppression and eye development. Given the potential association between cancer and development, we set forth to explore Eaf1 and Eaf2/U19 activity in vertebrate embryogenesis, using zebrafish. In situ hybridization revealed similar eaf1 and eaf2/u19 expression patterns. Morpholino-mediated knockdown of either eaf1 or eaf2/u19 expression produced similar morphological changes that could be reversed by ectopic expression of target or reciprocal-target mRNA. However, combination of Eaf1 and Eaf2/U19 (Eafs)-morpholinos increased the severity of defects, suggesting that Eaf1 and Eaf2/U19 only share some functional redundancy. The Eafs knockdown phenotype resembled that of embryos with defects in convergence and extension movements. Indeed, knockdown caused expression pattern changes for convergence and extension movement markers, whereas cell tracing experiments using kaeda mRNA showed a correlation between Eafs knockdown and cell migration defects. Cardiac and pancreatic differentiation markers revealed that Eafs knockdown also disrupted midline convergence of heart and pancreatic organ precursors. Noncanonical Wnt signaling plays a key role in both convergence and extension movements and midline convergence of organ precursors. We found that Eaf1 and Eaf2/U19 maintained expression levels of wnt11 and wnt5. Moreover, wnt11 or wnt5 mRNA partially rescued the convergence and extension movement defects occurring in eafs morphants. Wnt11 and Wnt5 converge on rhoA, so not surprisingly, rhoA mRNA more effectively rescued defects than either wnt11 or wnt5 mRNA alone. However, the ectopic expression of wnt11 and wnt5 did not affect eaf1 and eaf2/u19 expression. These data indicate that eaf1 and eaf2/u19 act upstream of noncanonical Wnt signaling to mediate convergence and extension movements.

基于ARM和DSP的CSR主环电源控制系统

介绍了基于ARM和DSP的CSR主环磁场电源控制系统的设计和开发。系统以以太网作为连接各个单元的传输介质,以ARM板卡作为以太网中的一个通信节点,由DSP板卡完成实际的电源控制。实验表明控制效果良好,超过了预期的设计目标。

基于ARM、CPLD和MCU的冷却储存环真空控制系统设计

以ARM(S3C4510B)、CPLD(XC95288XL)和微控制器(MSP430F149)为核心进行实时多路数据采集和控制的冷却储存环(CSR)真空控制系统设计。着重分析了控制系统组成、工作原理、功能实现、硬件电路和软件开发。该控制系统具有适应性与灵活性强、响应速度快、精度高、稳定性好、可靠性高、性价比优越、自我连锁保护等优点,现已成功应用于CSR真空控制系统中。

基于ARM Linux的门禁系统的设计与实现

门禁系统主要负责对出入通道进行管制，是社区楼宇安全监控系统的一部分。传统的门禁系统通常采用密码识别、卡片识别的方式进行验证，由于密码、卡片容易被盗用、丢失，系统安全性不高。在通信方式上传统门禁系统通常采用RS485或者RS232连接，传输距离、速度和连接终端数均受限制。本文提出的人像识别门禁系统解决方案采用ARM-Linux系统平台，依靠社区宽带综合业务网的传输和存储能力，结合密码、RFID和人像识别三种识别方式，利用网络技术和生物识别技术达到识别率高、响应速度快、扩展能力强的要求，并能够与驻地网的其它业务集成，提供业务级的联动服务。此外，该门禁系统还支持用户使用电话开门，由服务器完成对用户来电的识别和防伪验证。本文工作的主要贡献是：参与了ARM-Linux系统的裁剪、移植和声卡驱动的修改；建立了ARM-Linux交叉编译环境；完成了门禁前端软件系统的整体设计和实现；完成了服务器软件电话呼叫响应子系统的设计。