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Recent Developments in the Theory of Ion Flow Across Membranes Under Imposed Electric Fields
Published in Andrew A. Marino, Modern Bioelectricity, 2020
The ion flow during an action potential has been analyzed using the voltage-clamp method, a technique that imposes a fixed polarization across the membrane and maintains this value by sensing any departure due to the flow of current through the membrane and passing an equal and opposite current to compensate. The voltage-clamp method therefore measures the membrane current with time, at a particular potential. Typical curves show an early inward current followed by an outward current. From ion substitution experiments, the early inward current was found to be related to the external Na+ ion concentration, and the later outward current was found to be associated with the internal K+ ion concentration. The Hodgkin-Huxley model of the action potential is based on the results of the voltage clamp technique, and it assumes that depolarization of an excitable cell membrane leads to an initial inwardly directed current due to sodium ions followed by a later outwardly directed current, due to potassium ions. The entire current is then given as the sum of the two ionic currents plus a small leak current and also a capacitance current that is related to the rapid charging processes associated with changes of polarization.
Electrophysiology
Published in Jay L. Nadeau, Introduction to Experimental Biophysics, 2017
Jay L. Nadeau, Christian A. Lindensmith, Thomas Knöpfel
Once the cell membrane and ion channel configuration have been prepared using one of the techniques above, the recording is done with specialized amplifiers that can drive and detect currents and voltages at levels appropriate for cells. In voltage-clamp mode, the amplifier is used to set the cell membrane at a particular voltage, and the resulting currents are measured. In current-clamp mode, the amplifier sets the current through the electrode, and the resulting voltage of the cell membrane is measured.
Model-guided concurrent data assimilation for calibrating cardiac ion-channel kinetics
Published in IISE Transactions on Healthcare Systems Engineering, 2023
Haedong Kim, Hui Yang, Andrew R. Ednie, Eric S. Bennett
We also perform a sensitivity analysis to identify a subset of the parameters that have significant impacts on the model output and only calibrate these sensitive parameters. Factorial designs are developed in which parameters vary at two levels contrasting their effect on the model output. As illustrated in Fig. 3, six markers are defined that capture characteristics of K+ current traces in voltage-clamp experiments. Each marker represents: (a) the current magnitude of 10 ms after applying a voltage step, which measures the activation rate; (b) 25% of the total recording time has elapsed, (c) 50%, and (d) 75%, which collectively estimate the inactivation rate over time; (e) the peak magnitude; and (f) the time when current has decayed ()% (almost 63%) from the peak. Marker f will be equal to the total recording time if current does not decline enough as in Fig. 3(c,d).
Modelling and analysis for processing energy consumption of mechanism and data integrated machine tool
Published in International Journal of Production Research, 2020
Lishu Lv, Zhaohui Deng, Can Yan, Tao Liu, Linlin Wan, Qianwei Gu
Grinding is a key process for machining parts, and has a direct impact on the accuracy, performance, and surface integrity of the workpiece (Deng and Xu 2019). To obtain the energy consumption data of each operating state during the grinding process, a MGK7120×6/F high-precision CNC plane grinder was selected to perform the grinding experiments. The size of the workpiece is 150 mm × 75.5 mm × 52 mm, and it is made of GCr15 bearing steel (chemical composition: C:0.95-1.05; Mn:0.25-0.45; Si:0.15-0.35; S:<=0.025; P:<=0.025; Cr:1.40-1.65; Mo:≤0.10; Ni:≤0.30; Cu:≤0.25; Ni+Cu≤0.50). The diameter of grinding wheel here is 200 mm, the thickness of grinding wheel is 26 mm, and its material is white corundum. An AWS2103 multi-function digital power metre (AC/DC current sensor, voltage clamp, and charge amplifier) was used for power data acquisition. The experimental apparatus and workpiece are shown in Figure 3.
A new nonisolated soft switched DC-DC bidirectional converter with high conversion ratio
Published in International Journal of Electronics, 2020
Mahmood Vesali, Majid Delshad, Ehsan Adib, Mohammad Reza Amini
Structure of the proposed converter is shown in Figure 1. The main elements in the proposed converter are S1, S2 with L1, which improve conversion ratio since they are coupled with L2. To create soft switching condition, an auxiliary switch with a capacitor is used and leakage inductance of the coupled inductors is also effective in creating this condition. The clamp capacitor used in the power transmission increases the conversion ratio of the proposed converter. Also, one voltage clamp circuit consists of D1, D2 and C2 is used to clamp and decrease voltage of S1. This clamp circuit also contributes to improvement of the voltage gain.