Frequency Response Profiles Research Articles

Stability and parameter studies of a stretch reflex loop model.

A model of the arm muscle stretch reflex loop is considered. Investigations are carried out on a system consisting of models of the forearm, the muscle spindle in a feedback structure, and the arm muscle. Specifically, the forearm is modeled as an inverted pendulum, the experimentally derived fourth-order muscle spindle model is taken from the literature, and two linear muscle models are employed. The stability of the feedback structure is investigated as a function of various free parameters in the component models. Frequency response profiles are analyzed for the muscle/muscle spindle combination, and are compared to experimentally derived data available in the literature. Finally, digital computer simulations are exhibited for a system corresponding to a quick release experiment, and for a system in which a periodic force is applied to the forearm.

Vagal stimulation-induced gastric acid secretion in the anesthetized rat

The dynamics of gastric acid secretion induced by electrical stimulation of the cervical vagus in the anesthetized rat were investigated using a continuous collection-titration system permitting high temporal resolution. Stimulation with pulse rates of 2 or 4 impulses/s (pps) produced maximal gastric acid responses with small cardiovascular effects. With continuous stimulation, secretion was sustained for at least 1 h. Frequency-response profiles suggested that the parietal cells are innervated predominantly by fine-caliber C-fibers. Continuous stimulation was 3 times as effective as stimulation in bursts of higher frequencies. The minimal latency for the onset of secretion was 2.6 min at 4 pps, however, one- and two-min stimulations still produced proportionate but delayed secretory responses. It is concluded that, with low frequency cervical vagus stimulation, the rat stomach preparation described and employed in the present experiment is a useful model for further studies on the interaction of neural and humoral factors on gastric acid secretion.

Thermal cycling for piezoelectric gas detector systems

The effect of temperature (0–60°C) on the operation of a piezoelectric gas monitor is discussed. The development and application of small solid-state systems incorporating Peltier devices to allow rapid thermal cycling or isothermal operation of these monitors are evaluated. Thermal performance of the Peltier/gas monitor system is discussed, and frequency response profiles for a model analysis gas/crystal coating system (sulphur dioxide/triethanolamine) are reported.

Central control of cardiac and scaphognathite pacemakers in the crab,Cancer magister

Command fibers located in the circumesophageal connectives which modify scaphognathite and heart rhythms have been mapped and characterized in the crab,Cancer magister. Behavior: Crabs show a variety of responses to external stimuli often including simultaneous cessation of cardiac and scaphognathite “pumping”. Habituation and a return to prestimulus rhythms results from continued stimulation. The response to short stimulus durations, on the other hand, generally outlasts the stimulus indicating the playing-out of a motor program. Neurophysiology: Small bundles of fibers have been isolated from desheathed connectives. Activity in these fibers resulting from stimulation of various anterior sensory receptors was recordeden passant with suction electrodes. When sensory stimulation produced both electrical activity in the nerves under examination and a cardiac and/or scaphognathite response it was assumed such units were involved in inducing this response. This was tested by electrical stimulation delivered through the same electrode. Those units which produced similar responses to natural and artificial stimulation were deemed “command fibers”. It was invariably found that the minimum stimulating frequency needed to mimic naturally induced responses was much greater than the frequency at which the units discharged in response to those stimuli. During mapping experiments, command fibers were characterized with respect to their positions in the connectives and by the responses they produced at different frequencies of stimulation. 68% of the fibers identified affected both cardiac and scaphognathite systems, 29% the scaphognathites alone and 3% the heart alone. The frequency-response profiles of single bivalent command fibers were often different from the heart and scaphognathites. These findings help explain the responses of both systems to natural stimuli and also indicate that the circulatory and respiratory systems not only perform in concert, but are often under common control.

Fourier transform faradaic admittance measurements II. Ultra-rapid, high precision acquisition of the frequency response profile

Fourier transform faradaic admittance measurements II. Ultra-rapid, high precision acquisition of the frequency response profile

Fourier transform faradaic admittance measurements II. Ultra-rapid, high precision acquisition of the frequency response profile

Fourier transform faradaic admittance measurements II. Ultra-rapid, high precision acquisition of the frequency response profile

Biological system transfer-function extraction using swept-frequency and correlation techniques

The paper describes the application of a swept-frequency-system identification technique to biological systems. By linearly sweeping the frequency of the sinusoidal input signal over the range of frequencies of interest, the frequency-response profile of the biological system can be rapidly determined. System transfer characteristics are extracted from the input-power spectral density and output-input crosspower spectral-density computations. Noise, harmonic distortion and sweeptime considerations are given. Logarithmic frequencysweeping is suggested as a means of avoiding harmonic distortion.