Current rise time

O2 consumption rate becomes smaller under 0.7 V, the O2 concentration at the reaction surface recovers, thus leading to an increase in the cell current density. The current rise time corresponds well with the characteristic time scale of gas phase transport as analyzed above. The rise in the cell current, however, experiences an overshoot because the polymer membrane still maintains a higher water content corresponding to 0.6 V. It then takes about 15 s for the membrane to adjust its water content at the steady state corresponding to 0.7 V. This numerical example clearly illustrates the profound impact of water management on transient dynamics of low humidity PEFC engines where the polymer membrane relies on reaction water for hydration or dehydration. 

Key. We—peak electron energy Ie—peak electron current tr—current rise time tv—voltage rise time %—pulselength rc—cathode radius W —peak ion energy N—ion number T]—ion acceleration efficiency. 

The switching device is a commercial Pseudospark, model FS 2000 (Alstom). The rated maximum anode voltage and current are 32 kV and 30 kA. In the present application, the anode voltage is 30 kV, but the peak anode current is only 4 kA. The switch operates at the transition between the hollow cathode and superemissive modes. The switch-current rise-time is 15 ns, limited by the current channel and connection inductances. 

The definition of the critical current of a multifilamentary composite or cable superconductor may lead to some difficulties when comparing the properties of different samples. Those difficulties can be solved by the adoption of standard definitions and measurement techniques [ ]. The maximum current that can be carried by a conductor cannot be specified by any criteria. This current is very dependent on the current-voltage characteristic of the conductor, the cooling conditions, and the operating conditions, which determine the losses during the current rise time. For the computation of hysteretic losses in a practical superconductor by means of the well-known formula, it is important to determine the actual values of the critical current density, which is very anisotropic. 

Generally, the fault must be cleared well within Zone I and for which the protective scheme must be chosen. As discussed in Section 25.4.2, protection of capacitor units with external fuses is not easy. It is not practical to contain a mild internal fault as isolation of the units is not possible on mild internal faults until the fault current rises to the level of the fuse s operating range (Figure 26.2 illustrates this). By then enough time will have elapsed to cause severe damage to the unit. 

Typical current pulses observed for x-cut quartz, z-cut lithium niobate, and y-cut lithium niobate are shown in Fig. 4.3. Following a sharp rise in current to an initial value (the initial rise time is due to tilt, misalignment of the impacting surfaces), the wave shapes show either modest increases in current during the wave transit time for quartz and z-cut lithium niobate... 

The rapid rise in computer speed over recent years has led to atom-based simulations of liquid crystals becoming an important new area of research. Molecular mechanics and Monte Carlo studies of isolated liquid crystal molecules are now routine. However, care must be taken to model properly the influence of a nematic mean field if information about molecular structure in a mesophase is required. The current state-of-the-art consists of studies of (in the order of) 100 molecules in the bulk, in contact with a surface, or in a bilayer in contact with a solvent. Current simulation times can extend to around 10 ns and are sufficient to observe the growth of mesophases from an isotropic liquid. The results from a number of studies look very promising, and a wealth of structural and dynamic data now exists for bulk phases, monolayers and bilayers. Continued development of force fields for liquid crystals will be particularly important in the next few years, and particular emphasis must be placed on the development of all-atom force fields that are able to reproduce liquid phase densities for small molecules. Without these it will be difficult to obtain accurate phase transition temperatures. It will also be necessary to extend atomistic models to several thousand molecules to remove major system size effects which are present in all current work. This will be greatly facilitated by modern parallel simulation methods that allow molecular dynamics simulations to be carried out in parallel on multi-processor systems [115]. 

Potentiostatic conditions are realized with electronic potentiostats. The potential of the working electrode is monitored continuously with the aid of a reference electrode. When the potential departs from a set value, the potentiostat will adjust the current flow in the cell automatically so as to restore the original value of potential. Important characteristics of potentiostats are their rise time and the maximum currents which they can deliver to the cell. Modem high-quality potentiostats have rise times of 10 to 10 s. 

Within the potential range where Ru(bpy)3 remains in the aqueous phase, photocurrent responses are clearly observed with a slow rising time of the order of 10 s as shown in Fig. 14(a). According to the convention employed by these authors, positive currents correspond to the transfer of a negative charge from water to DCE. No photoresponses were observed in the absence of either the dye in the aqueous phase or TCNQ in DCE. Further analysis of the interfacial behavior of the product TCNQ revealed that the ion transfer occurred outside of the polarizable window [cf. Fig. 14(d)], confirming that these photoresponses are not affected by coupled ion-transfer processes. An earlier report also showed photoeffects for the photoreduction of the viologen under similar conditions [131]. 

The effect is most prominent in free convection. Limiting-current curves recorded by Hickman (H3) at a horizontal cathode facing upward in free convection are shown in Fig. 6. The apparent limiting-current value is definitely dependent on the time necessary to reach the limiting current an 80% increase in this value is noted as the rate at which the current rises varies from 0.25 to 20 mA cm-2 min -. ... 

The double-layer charging current thus tends toward a plateau equal to Cdv with a rise time equal to RuCd (Figure 1.7). On the reverse scan,... 

Figure 6.2(b) shows a trace of current against time in response to the potential step. The trace shows a rapid rise in current, with this rise requiring perhaps as long as a few thousands of a second (i.e. milliseconds). The time between the potential step and the maximum is known as the rise time. The current trails off smoothly after the rise time until, eventually, it reaches zero. Such plots are often termed transients to emphasize their pronounced time dependence. 

The turn-on and turnoff measurements were performed at room temperature using a power supply voltage of 300V and a load resistance of approximately 20Q in common emitter mode. Typical turnoff and turn-on transients recorded at 25°C are shown in Figures 6.21 and 6.22. The device was turned off by simply removing the base current. A turn-on rise time of 160 ns and a turnoff fall time of 120 ns were observed at 25°C. In addition, a storage time of approximately 40 ns was observed. 

The furnace is heated by low voltage (usually 10 V) and high current (up to 500 A) from a well stabilized step-down transformer. For optimum precision, the voltage should be well stabilized, often by a feedback loop which may be temperature feed-back based (see Section 3.6.1). A rapid rise-time of the temperature is also preferable, because of theoretical considerations of peak shapes. This has implications for power supply design and furnace design, as will be shown below. Currently, furnaces are available that reach temperatures of up to 3000°C, and temperatures of 2500°C should be reached in less than 2 s in a well designed furnace. 

In the late 1980s, the system was reconsidered by Quadri Electronics who produced an improved supercapacitor under the trade name HYPERCAP . Very high rate and peak power capabilities - current pulses in excess of 10 A with rise times of the order of milliseconds, and 3 kW/kg, respectively - have been reported for these solid state devices. 

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