Amplitude Of Undershoot Research Articles

Electrical properties of the sensory neuron and defense reactions of mollusc Lymnaea stagnalis at conditions of prolonged hyperglycemia

Hemolymph glucose level rise (from 0.12 (0.05; 0.18) to 4.10 (3.18; 6.08) mmol/L) modify the defensive behaviour of molluscs. This results in increase of the degree of animal’s body retracted into the shell and in reinforcement of weak defense reactions in response to tentacles’ tactile stimulation. No fluctuations in the tentacles length and the duration of the latent period of protraction were found. At experimental hyperglycemia (incubation of the isolated CNS preparation in 10 mmol/L D-glucose solution for 2 h), the basic electrical characteristics of FMRFamide-containing neuron RPaD1, involved in sensory stimuli detection and heart beat regulation in Lymnaea, were changed. Membrane depolarisation, accompanied by firing rate increase were observed, while current-voltage curve characteristics, as well as membrane resistance, capacity and time constant remains unchanged in comparison with control. An increase in rising and falling phases duration, undershoot amplitude were noted, while other parameters of the RPaD1 spike remained unchanged. Based on the revealed features of the action potential shape at hyperglycemia, it is assumed that these changes can be caused by the activation of the Na+-glucose co-transporter and ATP-sensitive K+-channels of the RPaD1 membrane. The action of glucose should be considered as a metabolic signal also in relation to non-feeding neurons in the mollusc brain.

Load frequency regulation by de-loaded tidal turbine power plant units using fractional fuzzy based PID droop controller

This study presents a model to analyse and simulate tidal power generation for hybrid power system in the presence of highly infiltrated tidal units. The response of the hybrid system may be at risk without suitable frequency enhancement techniques. The complete load frequency model is a combination of conventional automatic generation control (AGC) and automatic voltage regulator (AVR). AVR is employed to keep the output voltage magnitude of conventional generator at a particular level. The purpose of integrating AGC with AVR is to maintain the equilibrium between system’s generation and load as well as to keep the frequency of system within suitable range. Owing to inclusion of nonconventional sources, the total inertia of the power system is eventually diminished. Conventional PID droop controller demonstrates inefficacy in diminishing the frequency deviations due to slow controlling action. This research proposes a fractional order (FO) fuzzy PID droop in de-loaded area to improvise the frequency excursion over fixed/Fuzzy PID/PID droop controllers. Imperialist competitive algorithm (ICA) is employed to tune the parameters of the controllers. ICA optimized fractional order PID droop control strategy unveils best performance (settling time = 11.65 s, undershoot amplitude = 0.26pu, performance index = 0.072e−6) over the integer order fuzzy PID control (settling time = 12.02 s, undershoot amplitude = 0.278 pu, performance index = 0.189e−6) and PID droop control (settling time = 30.68 s, undershoot amplitude = 0.95 pu, performance index = 0.215e−6). Examination of dynamic responses for abrupt changes in load request divulges the pre-eminence of proposed droop controller strategy with others controllers. The comprehensive study carried out in this paper implies that ICA optimized controller operates properly and has proven its robustness for ±10% variations in system parameters and physical constraints (Generation rate constraints, governor dead band, and time delay). This study also analyses the effect of tidal power plant contribution in the frequency regulation by inertia, primary and secondary frequency control.

Design and Analysis of Gate All Around Tunnel FET based Ring Oscillator Circuit

In this work, we have designed and simulated a Gate All Around TFET (GAATFET) based 3 stage ring oscillator circuit and compared its performance with the CMOS based counterpart. The results of SPICE simulations indicate that GAATFET based ring oscillator circuit consumes 3.5 times lower power consumption in active mode than CMOS based ring oscillator. However, 0.43 ns and 0.17 ns of propagation delay is observed for GAATFET based ring oscillator and CMOS based ring oscillator circuit respectively. The obtained output waveform frequency for CMOS based ring oscillator is 2.5 times higher than the GAAATFET based ring oscillator. Further, undershoot is also investigated and it is found that the amplitude of undershoot in case of GAATFET based oscillator is roughly 6.5 times more as compared to CMOS based counterpart. The undershoot and delay observed in case of GAATFET based ring oscillator can be over-shaded by the fact that it has lower active power consumption than the CMOS based ring oscillator. Simulation results signify that GAATFET based ring oscillator can be deployed in future low power VLSI circuits and systems.

Differentiating Sensitivity of Post-Stimulus Undershoot under Diffusion Weighting: Implication of Vascular and Neuronal Hierarchy

The widely used blood oxygenation level dependent (BOLD) signal during brain activation, as measured in typical fMRI methods, is composed of several distinct phases, the last of which, and perhaps the least understood, is the post-stimulus undershoot. Although this undershoot has been consistently observed, its hemodynamic and metabolic sources are still under debate, as evidences for sustained blood volume increases and metabolic activities have been presented. In order to help differentiate the origins of the undershoot from vascular and neuronal perspectives, we applied progressing diffusion weighting gradients to investigate the BOLD signals during visual stimulation. Three distinct regions were established and found to have fundamentally different properties in post-stimulus signal undershoot. The first region, with a small but focal spatial extent, shows a clear undershoot with decreasing magnitude under increasing diffusion weighting, which is inferred to represent intravascular signal from larger vessels with large apparent diffusion coefficients (ADC), or high mobility. The second region, with a large continuous spatial extent in which some surrounds the first region while some spreads beyond, also shows a clear undershoot but no change in undershoot amplitude with progressing diffusion weighting. This would indicate a source based on extravascular and small vessel signal with smaller ADC, or lower mobility. The third region shows no significant undershoot, and is largely confined to higher order visual areas. Given their intermediate ADC, it would likely include both large and small vessels. Thus the consistent observation of this third region would argue against a vascular origin but support a metabolic basis for the post-stimulus undershoot, and would appear to indicate a lack of sustained metabolic rate likely due to a lower oxygen metabolism in these higher visual areas. Our results are the first, to our knowledge, to suggest that the post-stimulus undershoots have a spatial dependence on the vascular and neuronal hierarchy, and that progressing flow-sensitized diffusion weighting can help delineate these dependences.

Activity-dependent extracellular K+ accumulation in rat optic nerve: the role of glial and axonal Na+ pumps.

1. We measured activity-dependent changes in [K+]o with K(+)-selective microelectrodes in adult rat optic nerve, a CNS white matter tract, to investigate the factors responsible for post-stimulus recovery of [K+]o. 2. Post-stimulus recovery of [K+]o followed a double-exponential time course with an initial, fast time constant, tau fast, of 0.9 +/- 0.2 s (mean +/- S.D.) and a later, slow time constant, tau slow, of 4.2 +/- 1 s following a 1 s, 100 Hz stimulus. tau fast, but not tau slow, decreased with increasing activity-dependent rises in [K+]o. tau slow, but not tau fast, increased with increasing stimulus duration. 3. Post-stimulus recovery of [K+]o was temperature sensitive. The apparent temperature coefficients (Q10, 27-37 degrees C) for the fast and slow components following a 1 s, 100 Hz stimulus were 1.7 and 2.6, respectively. 4. Post-stimulus recovery of [K+]o was sensitive to Na+ pump inhibition with 50 microM strophanthidin. Following a 1 s, 100 Hz stimulus, 50 microM strophanthidin increased tau fast and tau slow by 81 and 464%, respectively. Strophanthidin reduced the temperature sensitivity of post-stimulus recovery of [K+]o. 5. Post-stimulus recovery of [K+]o was minimally affected by the K+ channel blocker Ba2+ (0.2 mM). Following a 10 s, 100 Hz stimulus, 0.2 mM Ba2+ increased tau fast and tau slow by 24 and 18%, respectively. 6. Stimulated increases in [K+]o were followed by undershoots of [K+]o. Post-stimulus undershoot amplitude increased with stimulus duration but was independent of the peak preceding [K+]o increase. 7. These observations imply that two distinct processes contribute to post-stimulus recovery of [K+]o in central white matter. The results are compatible with a model of K+ removal that attributes the fast, initial phase of K+ removal to K+ uptake by glial Na+ pumps and the slower, sustained decline to K+ uptake via axonal Na+ pumps.

Extracellular K + concentration during electrical stimulation of rat isolated sympathetic ganglia, vagus and optic nerves

Recordings of extracellular potassium concentration ([K +] e) were made in rat isolated sympathetic ganglia, vagus and optic nerves using ion sensitive microelectrodes. Repetitive orthodromic stimulation of ganglia resulted in [K +] e increases of up to 7 mmol/1 above resting level (6 mmol/1), which were followed by post-stimulus undershoots. Activation of vagal A and B fibres did not significantly alter [K +] e but C-fibre activity induced rises of up to 5 mmol/1. Repetitive stimulation of the predominantly mylinated optic nerve resulted in [K +] e rises of up to 2.5 mmol/1. In the ganglion and vagus nerve, application of ouabain (30–1000 μmol/1) led to a raised baseline [K +] e concentration, an increase in the peak achieved during stimulation and a reduced undershoot amplitude. The amplitude of the undershoot in normal solution was shown to be dependent on the duration of the preceding stimulation period as well as the amplitude of the preceding [K +] e rise. In ganglia and vagus nerves, bath application of γ-aminobutyric acid (10–100μmol/1) and carbachol (10–1000 μmol/1) also elevated [K +] e. It is concluded that repetitive activity in rat peripheral and central nerve fibres leads to significant changes in extracellular K + ion-concentration and that the restoration of these levels is strongly dependent on the intact activity of the membrane Na +/K + pump.

Relation between extracellular potassium concentration and neuronal activities in cat thalamus (VPL) during projection of cortical epileptiform discharge

Neuronal and potassium activities (a k) were measured in the nucleus ventro-posterolateralis thalami (VPL) during propagated epileptiform activity from the somatosensory cortex of cats. Seizures were induced by repetitive electrical stimulation of the cortical surface or by topical application of penicillin. The recruitment of VPL into a seizure resulted in large increases of a k to levels of up to 11.6 mmoles/l, accompanied by increases in neuronal discharge rate to 300/sec. Sometimes the rise in a k preceded active participation of a given thalamo-cortical relay (TCR) neuron in the seizure. After reaching a peak level, a k and neuronal discharge rate slowly declined during an ictal episode. After cessation of seizures all TCR neurons were inhibited, while a k fell to subnormal levels. The duration of these postictal depressions increased with the amplitude of preceding increases and subsequent undershoots in a k and could last up to 120 sec. During decay and undershoot in a k, relay capability of TCR neurons was reduced. Also the probability that action potentials elicited in intracortical endings of TCR cells would antidromically invade their cell bodies was decreased. The duration of these periods varied with the amplitude of undershoot in a k. Seizure threshold was increased during undershoots. These observations are consistent with a long-lasting postical hyperpolarization of neuronal membranes. The hyperpolarization may be caused by the action of an electrogenic pump, which is probably involved in termination of seizure discharge.