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An investigation of collagen fiber reorientation, as well as fluid and matrix movement of equine articular cartilage and subchondral bone under compressive mechanical loads, was undertaken using small angle X-ray scattering measurements and optical microscopy. Small angle X-ray scattering measurements were made on healthy and diseased samples of equine articular cartilage and subchondral bone mounted in a mechanical testing apparatus on station IDI8F of ESRF, Grenoble, together with fiber orientation analysis using polarized light and displacement measurements of the cartilage matrix and fluid using tracers. At surface pressures of up to approximately 1.5 MPa, there was reversible compression of the tangential surface fibers and immediately subjacent zone. As load increased, deformation in these zones reached a maximum and then reorientation propagated to the radial deep zone. Between surface pressures of 4.8 MPa and 6.0 MPa, fiber orientation above the tide mark rotated 10 deg from the radial direction, with an overall loss of alignment. With further increase in load, the fibers 'crimped' as shown by the appearance of subsidiary peaks approximately [+ or -] 10 deg either side of the principal fiber orientation direction. Failure at higher loads was characterized by a radial split in the deep cartilage, which propagated along the tide mark while the surface zone remained intact. In lesions, the fiber organization was disrupted and the initial response to load was consistent with early rupture of fibers, but the matrix relaxed to an organization very similar to that of the unloaded tissue. Tracer measurements revealed anisotropic solid and fluid displacement, which depended strongly on depth within the tissue. [DOI: 10.1115/1.3049478] Keywords: SAXS, polarized light, articular cartilage, load, collagen orientation

The normal direction of the bone contour in computed tomography (CT) images provides important anatomical information and can guide segmentation algorithms. Since various bones in CT images have different sizes, and the intensity values of bone pixels are generally nonuniform and noisy, estimation of the normal direction using a single scale is not reliable. We propose a multiscale approach to estimate the normal direction of bone edges. The reliability of the estimation is calculated from the estimated results and, after re-scaling, the reliability is used to further correct the normal direction. The optimal scale at each point is obtained while estimating the normal direction; this scale is then used in a simple edge detector. Our experimental results have shown that use of this estimated/corrected normal direction improves the segmentation quality by decreasing the number of unexpected edges and discontinuities (gaps) of real contours. The corrected normal direction could also be used in postprocessing to delete false edges. Our segmentation algorithm is automatic, and its performance is evaluated on CT images of the human pelvis, leg, and wrist. Index Terms--Edge-tracing, image segmentation, Kalman filtering, normal direction, postprocessing, reliability, seed.

An important problem in the field of force-reflecting systems and telerobotics is poor rendering of contact, particularly of contact with stiff surfaces. There are numerous possible sources of poor performance, including poor contact models, sampling errors, and delays due to computation or data transmission. In this paper we examine effects due to sample-and-hold, which is a fundamental property of both the discrete domain and also of the sensors and power amplifiers used in a force-reflecting system. We propose sample-and-hold be generalized to sample-estimate-hold. We show why ordinary sample-and-hold generates an active contact interface, and provide ways of improving the feeling of the interface. We have developed a suite of numerical methods for improving the performance of rendering of surfaces by force reflection. We have conducted both simulations and experiments to demonstrate the efficacy of the proposed scheme. Our contributions are a new method of digitally processing force data, and a systematic method for coupling force-processing systems that run at different rates.

A common approach to formulating the dynamics of closed-chain mechanisms requires finding the forces of constraint at the loop closures. However, there are indications that this approach leads both to ill conditioned systems that must be inverted and to numerically unstable differential equations of motion. We derive a sufficient condition for ill conditioning of augmented dynamical systems - that the mechanism's trajectory passes through, or very near, a kinematic singularity. In singular regions the equations of motion are also numerically stiff, and they frequently require special numerical methods for computer solution. We propose a new method of calculating closed-chain dynamics, based on the systematic elimination of variables that are both redundant and that may adversely affect the computations. This approach produces numerically stable solutions of the differential equations of motion, and the equations are apparently much less stiff than the equations produced by the traditional force-closure approach.

The co-ordination of respiration and swallowing was recorded electronically in three groups of patients who complained of dysphagia following a stroke, or associated with multiple sclerosis or motor neurone disease. The test used was simple and the equipment easily taken to the patient, in bed if necessary. All the patients showed differences from normal subjects and there were differences between each of the neurologically impaired groups. The technique appears to allow an assessment of the state of oropharyngeal motor and sensory functions separately during swallowing.

Simple, non-invasive equipment was designed to record respiratory patterns associated with swallowing food or drink in young and elderly healthy adults, to compare with neurologically impaired patients who complained of dysphagia. The timing of the entry of the test drink from a spoon into the mouth, the swallow event and respiration were recorded electronically and were presented in chart form. The equipment proved to be easy to use and the results were consistent. All 33 subjects showed a well-defined respiratory pattern, with individual minor variations, but different from the pattern of their resting respiration. The direction of respiration during spoon contact was consistent for each individual and the pharyngeal stage of swallowing was almost always followed by a large expiration. Thus the resting respiration is not simply arrested during swallowing, but is substituted by a different, well-controlled pattern.

In mammals, cyclic GMP and cGMP-dependent protein kinases (cGKs) have been implicated in the regulation of many neuronal functions including long-term potentiation and long-term depression of synaptic efficacy. To develop Caenorhabditis elegans as a model system for studying the neuronal function of the cGKs, we cloned and characterized the cgk-1 gene. A combination of approaches showed that cgk-1 produces three transcripts, which differ in their first exon but are similar in length. Northern analysis of C. elegans RNA, performed with a probe designed to hybridize to all three transcripts, confirmed that a major 3.0 kb cgk-1 transcript is present at all stages of development. To determine if the CGK-1C protein was a cGMP-dependent protein kinase, CGK-1C was expressed in Sf9 cells and purified. CGK-1C shows a K[sub a] of 190 ± 14 nm for cGMP and 18.4 ± 2 µm for cAMP. Furthermore, CGK-1C undergoes autophosphorylation in a cGMP-dependent manner and is inhibited by the commonly used cGK inhibitor, KT5823. To determine which cells expressed CGK-1C, a 2.4-kb DNA fragment from the promoter of CGK-1C was used to drive GFP expression. The CGK-1C reporter construct is strongly expressed in the ventral nerve cord and in several other neurons as well as the marginal cells of the pharynx and intestine. Finally, RNA-mediated interference of CGK-1 resulted in movement defects in nematode larvae. These results provide the first demonstration that cGMP-dependent protein kinase is present in neurons of C.elegans and show that this kinase is required for normal motility. [ABSTRACT FROM AUTHOR]

Focuses on the discovery of a new gene, ced-9, that seems to regulate the activities of ced-3 and ced-4. Control of potentially lethal activities like those of ced-3 and ced-4; Preventing cell death during normal Caenorhabditis elegans development; Role of naturally occurring or programmed cell death in animal development and homeostasis; Phenotypes of ced-9(lf) mutants; More.