PubMed · 7845081
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T Leuthner. 1994. Development system for pulse oximetry.. https://doi.org/10.1007/bf02515323
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We present a stable regime of asymmetric bound states for spiral pairs in a generic numerical model of a homogeneous excitable medium. In this regime, one spiral tip (slave) rotates around the other (master). Master-slave dynamics occur for both same-chirality and opposite-chirality spiral pairs in a range of parameters and initial conditions. We study the dependency of master-slave characteristics on the medium's excitation threshold and present a phenomenological model that accounts for the qualitative properties of master-slave dynamics.
The presence or absence of loops in the emergent transportation networks, that are characterized by a minimum overall cost, is shown to depend on the convexity of the cost function for the local transportation of material. Our results are directly applicable to a variety of situations across disciplines.
Methods of assessing the imaging characteristics of intravascular ultrasound systems are described and applied to an HP Sonos 3000 system imaging at 12, 20 and 30 MHz. The presence of geometrical image distortion associated with bending of the catheter was detected by imaging silk filaments positioned at 45 degrees around a circle. Distortion was clearly present indicating that it is likely to occur in clinical studies. Resolution measurements (-12 dB) were made from images of 30 microns Nylon. The axial resolution did not change with depth and was in the range 150-400 microns. The lateral resolution increased linearly with depth for all frequencies, with values in the range 0.9-1.7 mm at a depth of 5 mm. High frequency catheter transducers therefore generate ultrasound with beamshapes similar to those expected from the familiar performance of devices in the 2-10 MHz range. Penetration measurements were made with material known to be tissue equivalent at 3-7 MHz. The penetration depth varied from 4.5 to 14 mm depending on catheter and frequency. There is a need for the manufacture of tissue equivalent materials for use in the frequency range 20-30 MHz, and also for the design of phantoms based on these materials for the measurement of contrast-detail performance and penetration depth.