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X-ray fluorescence (XRF) microscopy is an important tool for studying trace metals in biology, enabling simultaneous detection of multiple elements of interest and allowing quantification of metals in organelles without the need for subcellular fractionation. Currently, analysis of XRF images is often done using manually defined regions of interest (ROIs). However, since advances in synchrotron instrumentation have enabled the collection of very large data sets encompassing hundreds of cells, manual approaches are becoming increasingly impractical. We describe here the use of soft clustering to identify cell ROIs based on elemental contents, using data collected over a sample of the malaria parasite Plasmodium falciparum as a test case. Soft clustering was able to successfully classify regions in infected erythrocytes as “parasite,” “food vacuole,” “host,” or “background.” In contrast, hard clustering using the k-means algorithm was found to have difficulty in distinguishing cells from background. While initial tests showed convergence on two or three distinct solutions in 60% of the cells studied, subsequent modifications to the clustering routine improved results to yield 100% consistency in image segmentation. Data extracted using soft cluster ROIs were found to be as accurate as data extracted using manually defined ROIs, and analysis time was considerably improved.
LOFAR (Low Frequency Array) is an innovative radio telescope optimized for the frequency range 30–240 MHz. The telescope is realized as a phased aperture array without any moving parts. Digital beam forming allows the telescope to point to any part of the sky within a second. Transient buffering makes retrospective imaging of explosive short-term events possible. The scientific focus of LOFAR will initially be on four key science projects (KSPs): (i) Detection of the formation of the very first stars and galaxies in the universe during the so-called epoch of reionization by measuring the power spectrum of the neutral hydrogen 21-cm line (Shaver et al. 1999) on the ∼ 5′ scale; (ii) Low-frequency surveys of the sky with of order 108 expected new sources; (iii) All-sky monitoring and detection of transient radio sources such as γ-ray bursts, X-ray binaries, and exo-planets (Farrell et al. 2004); and (iv) Radio detection of ultra-high energy cosmic rays and neutrinos (Falcke & Gorham 2003) allowing for the first time access to particles beyond 1021 eV (Scholten et al. 2006). Apart from the KSPs open access for smaller projects is also planned. Here we give a brief description of the telescope.
A central aim of imitation research is to identify how complex patterns of motor output are generated based on observing a similarly complex pattern of motion produced by a model. How is imitative action informed by perception? During the 1990s a number of findings, and most markedly the discovery of “mirror neurons” by Rizzolatti and coworkers, supported the idea that motor structures are already involved in action perception and not only when reproducing the observed action. On first sight, this idea appears to provide a clear answer to the issue of imitative perception-action mediation: a motor representation of the observed act is formed already during model observation, which should allow its reproduction with high fidelity, at least when the model's action is in the behavioral repertoire of the observer. Also, this idea seems to depart from earlier theorizing about imitation and observational learning, in which typically two temporally distinct stages were implied: the formation of a cognitive (e.g., verbal or iconic) representation during action observation, and the later “translation” of this cognitive representation into action (e.g., Carroll & Bandura, 1990; Keele, 1986; Meltzoff, 1988). These two stages could be a few seconds, or even days, apart. Accordingly, this view may be characterized as late mediation between perception and action, whereas mirror neurons indicate the possibility of early mediation. In this chapter, I investigate the consequences of early mediation accounts for functional theories of human imitative behavior.
We share the authors' general approach to the study of perception and action, but rather than singling out a particular level of “late perceptual” and “early motor” processing for sensorimotor interactions, we argue that these can arise at multiple levels during action preparation and execution. Recent data on action-perception transfer are used to illustrate this perspective.
We outline a view of imitative behaviour as largely internally
driven and discuss, based on experimental research, the distinction
between program versus action level imitation, the role of organismic
constraints, observational learning as vicarious exploration, and
imitation as selection in speeded response paradigms.