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At least 433 records · Page 24Linked to original sources
PubMed2006

Complexity analysis of stride interval time series by threshold dependent symbolic entropy.

The stride interval of human gait fluctuates in complex fashion. It reflects the rhythm of the locomotor system. The temporal fluctuations in the stride interval provide us a non-invasive technique to evaluate the effects of neurological impairments on gait and its changes with age and disease. In this paper, we have used threshold dependent symbolic entropy, which is based on symbolic nonlinear time series analysis to study complexity of gait of control and neurodegenerative disease subjects. Symbolic entropy characterizes quantitatively the complexity even in time series having relatively few data points. We have calculated normalized corrected Shannon entropy (NCSE) of symbolic sequences extracted from stride interval time series. This measure of complexity showed significant difference between control and neurodegenerative disease subjects for a certain range of thresholds. We have also investigated complexity of physiological signal and randomized noisy data. In the study, we have found that the complexity of physiological signal was higher than that of random signals at short threshold values.

Biological Clocks↗
PubMedDate not supplied

Boiling nucleation on melanosomes and microbeads transiently heated by nanosecond and microsecond laser pulses.

Selective tissue damage on the cellular level can be achieved by microbubble formation around laser-heated intracellular pigments. To acquire a more detailed understanding of the laser tissue interaction in the highly pigmented retinal pigment epithelium (RPE), we irradiate aqueous suspensions of absorbing microparticles by short pulsed laser irradiation (12 ns, 240 ns, and 1.8 micros). Porcine retinal pigment epithelial melanosomes, gold beads, and magnetic silica beads are used as absorbers. Pulsed laser heating of the particles leads to vaporization of the surrounding liquid. The resulting transient microbubbles on the particle surface are imaged directly on a microscopic level by fast flash light photography. Furthermore, the bubble dynamics is probed by a low power laser. Threshold radiant exposures for bubble formation and nucleation temperatures are experimentally determined. Superheating of the surrounding water to 150 degrees C for melanosomes and to more than 200 degrees C for magnetic silica beads (psi = 3 microm) and gold beads (psi = 500 nm) is achieved. With these data, the absorption coefficient of a melanosome is calculated by thermal modeling of the experimental thresholds for bubble formation.

Absorption↗
PubMed1996

Rotation and radical motion thresholds support a two-stage model of differential-motion analysis.

Lower motion thresholds for rotational and radial flow have been measured for stimuli consisting of four closely packed circular apertures, each containing patches of drifting grating or plaid. Detection and direction thresholds were measured for gratings and plaids as a function of the relative orientation of the pattern components. There was a similarity between both types of threshold, supporting the existence of specialised rotation and radial-flow detectors. Further, thresholds increased with the relative component orientation for both gratings and plaids. This suggests that component information from a first stage, tuned spatiotemporally and to orientation, is being used directly to compute the optic flow in a two-stage process. A model based on this architecture is described by means of simple template receptive-field arrays with separable temporal and spatial tuning at the first stage.

Humans↗