Laron Walker

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The force-constancy hypothesis states that the user of a force-feedback device maintains a constant penetration force when stroking virtual surfaces in order to perceive their topography. The hypothesis was developed to address a real-world data perceptualization problem where the perception of surface topography was distorted when the surface stiffness was(More)
This study is concerned with the distorted perception of surface topography when both surface height and surface stiffness vary. Three psychophysical experiments were conducted using virtual surfaces rendered with a force-feedback device. In Exp. I, we found that the threshold for detecting a height difference between two adjacent planes was quite small(More)
This paper outlines major challenges that we are facing in interfacing a human user with objects in the nanoworld via a haptic interface. After a review of prior efforts at haptically-enabled nanomanipulation systems, we present the current state of our nanomanipulator system. We then discuss current research issues including the direct-Z mode, force(More)
Machine vision-based weighing of pigs is a non-intrusive, fast and relatively accurate approach that could reduce stress on both the animal and the stockman during the weighing process. An image-based walk-through system was developed in this study for pig liveweight approximation without having to restrain the pig to a certain area for stationary imaging.(More)
A method has been developed for the analysis of sulphonamides in bovine and porcine muscle, based on solid-phase dispersion. Muscle tissue was blended with pre-washed C18 coated silica (55-105 microns), and the resulting homogeneous solid packed into a polypropylene syringe barrel. Fatty material was washed from the sample using hexane, and the sulphonamide(More)
A method is presented for the determination of the three tetracyclines oxytetracycline, tetracycline and chlortetracycline in muscle, spiked at 100 ng/g, using high-performance liquid chromatography (HPLC). The concentration and extraction steps are carried out using Waters Environmental Sep-Pak cartridges. The principal steps involve homogenizing the(More)
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