Controlled Lagrangian Methods and Tracking of Accelerated Motions

Matching techniques are applied to the problem of stabilization of uniformly accelerated motions of mechanical systems with symmetry. The theory is illustrated with a simple model-a wheel and pendulum system

Exponential ε-tracking and ε-stabilization of second-order nonholonomic SE(2) vehicles using dynamic state feedback

In this paper, we address the problem of ε-tracking and ε-stabilization for a class of SE(2) vehicles with second-order nonholonomic constraints. We introduce a class of transformations called near-identity diffeomorphism that allow dynamic partial feedback linearization of the translational dynamics of this class of SE(2) vehicles. This allows us to achieve global exponential ε-stabilization and ε-tracking (in position) for the aforementioned classes of autonomous vehicles using a coordinate-independent dynamic state feedback. This feedback is only discontinuous w.r.t. the augmented state. We apply our results to ε-stabilization and ε-tracking for an underactuated surface vessel

The cytodisk: A cytometer based upon a new principle of cell alignment

A new method is described for one-dimensional alignment of small particles such as biological cells. A drop of the particle suspension is spread out on a flat disk or plate equipped with V-shaped grooves such as are present on a gramophone disk. After drying, the particles are located on the bottom of the grooves and are thus aligned in a one-dimensional array. The new alignment procedure is demonstrated with a suspension of fluorescent polystyrene micropheres (diameter 3.8 µm) and a suspension of the unicellular algae chlorella vulgaris (diameter about 3 µm). It appears that the alignment of cells and spheres is very good. \ud When using microspheres, more than 95% of the particles in the grooves are located within ±2 µm of the centre line of the groove. Based upon this cell-alignment principle, a new cytometer, named the cytodisk, is proposed. The proposed system has a number of advantages over the flow cytometer, among which is the unique ability of relocating a previously measured cell for further measurement or visual examination. \ud A prototype of a cytodisk, developed for initial test measurements, was built in our laboratory. The apparatus, constructed from a record player and ordinary long-playing records, uses a simple mechanical tracking system and a single optical fiber for fluorescence excitation and detection. With this apparatus it is demonstrated that a cytodisk can indeed perform quite well: A histogram of fluorescing microspheres could be measured with a coefficient of variation of 4.1%. The performance of this prototype is limited by the quality of the mechanical tracking system and the optical system used. It is expected that considerable improvements may be obtained by using a more sophisticated optical detection system such as the tracking system in use in optical disk players

Causal Induction from Continuous Event Streams: Evidence for Delay-Induced Attribution Shifts

Contemporary theories of Human Causal Induction assume that causal knowledge is inferred from observable contingencies. While this assumption is well supported by empirical results, it fails to consider an important problem-solving aspect of causal induction in real time: In the absence of well structured learning trials, it is not clear whether the effect of interest occurred because of the cause under investigation, or on its own accord. Attributing the effect to either the cause of interest or alternative background causes is an important precursor to induction. We present a new paradigm based on the presentation of continuous event streams, and use it to test the Attribution-Shift Hypothesis (Shanks & Dickinson, 1987), according to which temporal delays sever the attributional link between cause and effect. Delays generally impaired attribution to the candidate, and increased attribution to the constant background of alternative causes. In line with earlier research (Buehner & May, 2002, 2003, 2004) prior knowledge and experience mediated this effect. Pre-exposure to a causally ineffective background context was found to facilitate the discovery of delayed causal relationships by reducing the tendency for attributional shifts to occur. However, longer exposure to a delayed causal relationship did not improve discovery. This complex pattern of results is problematic for associative learning theories, but supports the Attribution-Shift Hypothesi