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Biomedical subjects

S Lehman

Publications and source records attributed to S Lehman.

7 recordsLinked to original sources
PubMed1992

Sensitivity coefficients, trajectories and graphs of a human head-movement model.

With time as the criterion to be optimized, the divergences from optimal head movements show systematic differences in their control signal variables with respect to single behaviours. To clarify these relationships, this study applies manipulation and mathematical analysis of the 6th-order nonlinear head movement model, using the three-fold approach of sensitivity analysis. The sensitivity analysis of the improved and refined head movement model explains the different tasks of the control parameters and their relation to the plant. It shows that width more than height of the agonistic and antagonistic pulses dominate the important behaviours of the movement: acceleration, magnitude and duration.

Head↗
PubMed1988

Regional differentiation in the stomach of the green anole.

The stomach of Anolis carolinensis (Reptilia: Iguanidae) has four histologically and histochemically distinct regions. The gastroesophageal junction has an acidic surface mucin and no glands. The cardia has an acidic surface mucin and mucous glands. This acidic mucin appears to contain neither sulfates nor sialic acid. The fundus has a neutral surface mucin and mucoserous glands. The pylorus has a neutral surface mucin and mucous glands.

Animals↗
PubMed1981

Simulation of head movement trajectories: model and fit to main sequence.

A sixth order nonlinear model for horizontal head rotations in humans is presented and investigated using experimental results on head movement trajectories and neck muscle EMG. The controller signals, structured in accordance with time optimal control theory, are parameterized, and controller signal parameter variations show a dominating influence on different aspects of the head movement trajectory. The model fits the common head acceleration types over a wide range of amplitudes, and also less common (dynamic overshoot) trajectories.

Electromyography↗
PubMed1981

Sensitivity analysis and optimization for a head movement model.

A sixth order nonlinear model for horizontal head rotations in humans is analyzed using an extended parameter sensitivity analysis and a global optimization algorithm. The sensitivity analysis is used in both the direct sense, as a model fitting tool, and in the indirect sense, as a guide to experimental design. Resolution is defined in terms of the sensitivity table, and is used to interpret the sensitivity results. Using sensitivity analyses, the head and eye movement systems are compared and contrasted. Controller signal parameters are the most influential. Their variations and effects on head movement trajectories and accelerations are investigated, and the conclusions are compared with clinical neurological findings. The global optimization algorithm, in addition to automating the fitting of various types of data, is combined with time optimality theory to give theoretical time-optimal inputs to the model.

Computers↗