Global Response Characteristics Research Articles

Anisotropic continuum models for beamlike lattice trusses

A simple procedure is presented for developing anisotropic continuum models for repetitive beamlike lattice trusses having four or more longerons and rectangular cross-sections. The beam models account for the couplings between the axial and shear effects, and between the bending and twisting effects. Two groups of beam models are developed. The first group has six degrees of freedom (three displacements and three rotations) at each cross-section and is adequate for predicting the global response characteristics of the lattice (e.g., vibration frequencies and buckling loads). The second group has more than six degrees of freedom, accounts for local deformations of the cross-section, and provides accurate prediction of the detailed displacement and force distributions in the lattice. The accuracy and effectiveness of the continuum models developed are demonstrated by means of numerical examples.

A method for parameter sensitivity analysis in differential equation models

A numeric method for analyzing global parameter sensitivity about a fixed point in parameter space for differential equation models is presented. The method is suitable for large‐scale, multiresponse systems which may not be in steady state. By using a quadratic model, the relationship between several global response characteristics and parameter perturbations is examined. Sensitivity relationships are defined with both backward elimination regression model selection procedures and eigenvalue‐eigenvector analyses. An example of the method is given using an ecosystem model consisting of 14 coupled differential equations.

Response patterns of primary vestibular neurons to thermal and rotational stimuli

The neural responses of vestibular ganglion cells to quantified thermal and rotational stimulation were studied in anesthetized squirrel monkeys. All cells exhibited a spontaneous discharge rate with the average being 72 ± 27.8 spikes/sec. The observed increases and decreases in discharge rates during sinusoidal angular rotation were consistent with the morphological polarization patterns of the hair cells. Likewise, the ganglion cell responses resulting from thermal stimulation by a controlled temperature air stream directed on the lateral portion of the horizontal canal were in agreement with those expected on the basis of Barany's convective current theory and the polarization pattern of the hair cells. In an attempt to determine the relationship between thermal and rotational stimuli, the sensitivities of individual cells to both types of stimuli were determined. Those cells most sensitive to angular rotation were also most sensitive to caloric stimulation. An equivalency value for the two types of stimuli was defined and found to be 1.84 °C/radian·sec −1. The global response characteristics of the vestibular endorgan were studied by simultaneous thermal and rotational stimuli. The thermal stimulus was used to bias the cupula at a new equilibrium position while a rotational stimulus was used to determine the differential sensitivity at that cupular position. For the cells with a more regular spontaneous discharge rate, the differential sensitivity was observed to be a function of the instantaneous discharge rate. No such relationship was observed for the more irregular cells.