A Bayesian approach to tracking in single molecule fluorescence microscopy

Using fluorescence microscopy with single molecule sensitivity it is now possible to follow the movement of individual fluorophore tagged molecules such as proteins and lipids in the cell membrane with nanometer precision. These experiments are important as they allow many key biological processes on the cell membrane and in the cell, such as transcription, translation and DNA replication, to be studied at new levels of detail. Computerized microscopes generate sequences of images (in the order of tens to hundreds) of the molecules diffusing and one of the challenges is to track these molecules to obtain reliable statistics such as speed distributions, diffusion patterns, intracellular positioning, etc. The data set is challenging because the molecules are tagged with a single or small number of fluorophores, which makes it difficult to distinguish them from the background, the fluorophore bleaches irreversibly over time, the number of tagged molecules are unknown and there is occasional loss of signal from the tagged molecules. All these factors make accurate tracking over long trajectories difficult. Also the experiments are technically difficulty to conduct and thus there is a pressing need to develop better algorithms to extract the maximum information from the data. For this purpose we propose a Bayesian approach and apply our technique to synthetic and a real experimental data set.

Nonautonomous elementary net systems and their application to programmable logic control

In this paper, a novel approach to Petri net modeling of programmable logic controller (PLC) programs is presented. The modeling approach is a simple extension of elementary net systems, and a graphical design tool that supports the use of this modeling approach is provided. A key characteristic of the model is that the binary sensory inputs and binary actuation outputs of the PLC are explicitly represented. This leads to the following two improvements: outputs are unambiguous, and interaction patterns are more clearly represented in the graphical form. The use of this modeling approach produces programs that are simple, lightweight, and portable. The approach is demonstrated by applying it to the development of a control module for a MonTech Positioning Station. © 2008 IEEE.

Superconducting micro-bearings

This paper presents research into superconducting Micro-Bearings for MEMS systems. Advanced silicon processing techniques developed for the Very Large Scale Integration (VLSI) industry have been exploited in recent years to enable the production of micro-engineered moving mechanical systems. These devices commonly known as Micro-ElectroMechanical Systems (MEMS) have many potential advantages. In many respects the effect of scaling a machine from macro-sized to micro-sized are either neutral or beneficial. However in one important respect the scaling produces a severely detrimental effect. That respect is in the tribology and the subsequent wear on the high speed rotating machines. This leads to very short device lifetimes. This paper presents results obtained from a MEMS motor supported on superconducting bearings. The bearings are self-positioning, relying on, the Meissner effect to provide a levitation force which moves the rotor into position and flux pinning to provide stability thereafter. The rotor is driven by a simple electrostatic type motor in which photo resist is used to pattern the motor poles directly onto the rotor. © 2005 IEEE.

Micro-ramp control for oblique shock wave / boundary layer interactions

Supersonic engine intakes operating supercritically feature shock wave / boundary layer interactions (SBLIs), which are conventionally controlled using boundary layer bleed. The momentum loss of bleed flow causes high drag, compromising intake performance. Micro-ramp sub-boundary layer vortex generators (SBVGs) have been proposed as an alternative form of flow control for oblique SBLIs in order to reduce the bleed requirement. Experiments have been conducted at Mach 2.5 to characterise the flow details on such devices and investigate their ability to control the interaction between an oblique shock wave and the naturally grown turbulent boundary layer on the tunnel floor. Micro-ramps of four sizes with heights ranging from 25% to 75% of the uncontrolled boundary layer thickness were tested. The flow over all sizes of microramp was found to be similar, featuring streamwise counter-rotating vortices which entrain high momentum fluid, locally reducing the boundary layer displacement thickness. When installed ahead of the shock interaction it was found that the positioning of the micro-ramps is of limited importance. Micro-ramps did not eliminate flow separation. However, the previously two-dimensional separation was broken up into periodic three-dimensional separation zones. The interaction length was reduced and the pressure gradient across the interaction was increased.