Browsing by Subject "tracking"

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Attractive membrane domains control lateral diffusion
(2008-05) Forstner, Martin B.; Martin, Douglas S.; Ruckerl, Florian; Kas, Josef A.; Selle, Carsten; Forstner, Martin B.; Martin, Douglas S.
Lipid membranes play a fundamental role in vital cellular functions such as signal transduction. Many of these processes rely on lateral diffusion within the membrane, generally a complex fluid containing ordered microdomains. However, little attention has been paid to the alterations in transport dynamics of a diffusing species caused by long-range interactions with membrane domains. In this paper, we address the effect of such interactions on diffusive transport by studying lateral diffusion in a phase-separated Langmuir phospholipid monolayer via single-particle tracking. We find that attractive dipole-dipole interactions between condensed phase domains and diffusing probe beads lead to transient confinement at the phase boundaries, causing a transition from two- to one-dimensional diffusion. Using Brownian dynamics simulations, the long-term diffusion constant for such a system is found to have a sensitive, Boltzmann-like, dependence on the interaction strength. In addition, this interaction strength is shown to be a strong function of the ratio of domain to particle size. As similar interactions are expected in biological membranes, the modulation of. diffusive transport dynamics by varying interaction strength and/or domain size may offer cells selective spatial and temporal control over signaling processes.
CMIP5 Climate Model Analyses Climate Extremes in the United States
(2014-04) Wuebbles, Donald; Meehl, Gerald; Hayhoe, Katharine; Karl, Thomas R.; Kunkel, Kenneth; Santer, Benjamin; Wehner, Michael; Colle, Brian; Fischer, Erich M.; Fu, Rong; Goodman, Alex; Janssen, Emily; Kharin, Viatcheslav; Lee, Huikyo; Li, Wenhong; Long, Lindsey N.; Olsen, Seth C.; Pan, Zaitao; Seth, Anji; Sheffield, Justin; Sun, Liqiang; Fu, Rong
Design and development of a high precision, high payload telescope dual drive system
(2010-07) Worthington, M.S.; Beets, T.A; Beno, J.H; Mock, J.R; Murphy, B.T; South, B.J; Good, J.M.
A high precision, dual drive system has been designed and developed for the Wide Field Upgrade to the Hobby-Eberly Telescope* at McDonald Observatory in support of the Hobby-Eberly Telescope Dark Energy Experiment‡. Analysis,design and controls details will be of interest to designers of large scale, high precision robotic motion devices. The drive system positions the 19,000 kg star tracker to a precision of less than 5 microns along its 4-meter travel. While positioning requirements remain essentially equal to the existing HET, tracker mass increases by a factor greater than 5. The 10.5-meter long tracker is driven at each end by planetary roller screws, each having two distinct drive sources dictated by the desired operation: one slowly rotates the screw when tracking celestial objects and the second rotates the nut for rapid displacements. Key results of the roller screw rotordynamics analysis are presented. A description of the complex bearing arrangement providing required degrees of freedom as well as the impact of a detailed Failure Modes and Effects Analysis addressing necessary safety systems is also presented. Finite element analysis results demonstrate how mechanical springs increase the telescope's natural frequency response by 22 percent. The critical analysis and resulting design is provided.
Securing Our Future: The Importance of Quality Education for Minorities, PRP 96
(LBJ School of Public Affairs, 1992) Marshall, Ray; Glover, Robert W.; Plascencia, Luis; Garza-Lubeck, Maria; Nielsen, Robert
Tracker controls development and control architecture for the Hobby-Eberly Telescope Wide Field Upgrade
(2010-07) Mock, J.R.; Beno, J; Rafferty, T.H; Cornell, M.E.
To enable the Hobby-Eberly Telescope Wide Field Upgrade, the University of Texas Center for Electromechanics and McDonald Observatory are developing a precision tracker system – a 15,000 kg robot to position a 3,100 kg payload within 10 microns of a desired dynamic track. Performance requirements to meet science needs and safety requirements that emerged from detailed Failure Modes and Effects Analysis resulted in a system of 14 precision controlled actuators and 100 additional analog and digital devices (primarily sensors and safety limit switches). This level of system complexity and emphasis on fail-safe operation is typical of large modern telescopes and numerous industrial applications. Due to this complexity, demanding accuracy requirements, and stringent safety requirements, a highly versatile and easily configurable centralized control system that easily links with modeling and simulation tools during the hardware and software design process was deemed essential. The Matlab/Simulink simulation environment, coupled with dSPACE controller hardware, was selected for controls development and realization. The dSPACE real-time operating system collects sensor information; motor commands are transmitted over a PROFIBUS network to servo amplifiers and drive motor status is received over the same network. Custom designed position feedback loops, supplemented by feed forward force commands for enhanced performance, and algorithms to accommodate self-locking gearboxes (for safety), reside in dSPACE. To interface the dSPACE controller directly to absolute Heidenhain sensors with EnDat 2.2 protocol, a custom communication board was developed. This paper covers details of software and hardware, design choices and analysis, and supporting simulations (primarily Simulink).