Resistance electrical analogue

The description of C02-diffusion in leaves by Fick s law in the form of Eq. (8b) is convenient because it allows the use of electrical analogue models. In this way the process of C02 diffusion can be described by a series of resistances. However, the external C02 is not the only C02 source for the C02 fixing enzyme system because within the plant cells C02 is produced by respiratory processes (see 6.4.). Thus one obtains the circuit analogue pattern for C02 fluxes depicted in Fig. 4. Then, the net C02 flux from environment into leaves is given by ... 

NEREM Realistically speaking, in terms of computer time, there is a limit to how many vessels you can have. Thus, one can only follow the network so far. At some point, you have to go to something that is either modelled in terms of an electric analogue as a resistance or to a porous media approach. 

Figure 7 Schematic presentation of a corrosion cell consisting of an anode and a cathode immersed in the same electrolyte and in electrical contact through an external resistance. Also shown is the electrical analogue of the corrosion cell including the voltage source oorr polarization resistances and the anode and the cathode, respectively, the internal resistance R due to the electrolyte, and the external resistance...

Fig. 16.2-2. Electrical analogues of two reactions affected by diffusion. These two cases correspond to those shown in Fig. 16.2-l(a) and 16.2-l(b), respectively. If the reactions are diffusion-controlled, then the resistances to chemical reaction will be relatively small.

Early models used a value for that remained constant throughout the day. However, measurements show that the deposition velocity increases during the day as surface heating increases atmospheric turbulence and hence diffusion, and plant stomatal activity increases (50—52). More recent models take this variation of into account. In one approach, the first step is to estimate the upper limit for in terms of the transport processes alone. This value is then modified to account for surface interaction, because the earth s surface is not a perfect sink for all pollutants. This method has led to what is referred to as the resistance model (52,53) that represents as the analogue of an electrical conductance... 

Photodiodes are the modem analogues to photocells. They increase their electrical resistance under light impact which, as part of an electric circuit, can be measured easily. Many current instruments display diode arrays instead of a single diode. Tens of photodiodes are arranged in a tight area. They are exposed to the sample bound spectrum where they respond to the color that corresponds to their positions in the diode array. A rapid, periodically performed electrical interrogation of all diodes (sequence periodicity in the order of milliseconds) reveals a quasi-stationary stable spectrogram. More sophisticated than photodiodes are phototransistors. They amplify internally the photoelectric effect, but the sensitivity of a photomultiplier cannot be achieved. 

Dry deposition processes are best understood by considering a resistance analogue. In direct analogy with electrical resistance theory, the major resistances to deposition are represented by three resistors in series. Considering the resistances in sequence, starting well above the ground, these are as follows ... 

Here, Ej is the effective value of the truncated rate constant of the stepwise transformation (1.34), while Rs is the total effective electric resistance of the electric circuit that is its analogue. 

Nernst applied the electrical bridge invented by Wheatstone to the measurement of the dielectric constants for aqueous electrolytes and different organic fluids. Nemst s approach was soon employed by others for measurement of dielectric properties and the resistance of galvanic cells. Finkelstein applied the technique to the analysis of the dielectric response of oxides. Warburg developed expressions for the impedance response associated with the laws of diffusion, developed almost 50 years earlier by Fick, and introduced the electrical circuit analogue for electrolytic systems in which the capacitance and resistance were functions of frequency. The concept of diffusion impedance was applied by Kruger to the capacitive response of mercury electrodes. ... 

As compared to mesoporous oxide nanofibers, much lesser attention has been paid to their mesoporous amorphous carbon analogues. However, mesoporous carbon exhibits superior resistance to acids and bases, excellent heat resistance, as well as high intrinsic electric conductivity. Potential applications for hybrid membranes consisting of mesoporous carbon within hard templates include size-selective electrosorption, electrosynthesis of nanostructures, catalysis, separation and storage. The first reported procedure for the synthesis of mesoporous carbon nanofibers involved the preparation of... 

The easiest electrical properties to measure accurately are voltage and resistance. Thus, the primary application tool of electrical measurement is the common volt-ohm meter (VOM), either as an analogue device or as its digital counterpart, the digital volt-ohm meter (DVOM). 

Since the technique was first employed in 1931 (Stahlane and Pyk, 1931) to measure the thermal conductivity of powders, there have been significant improvements in the practical realization of the technique. In modem instm-ments the wire sensor aets both as the heat source and as a thermometer. Rapid development of analogue and digital equipment as well as of eomputer-driven data-acquisition systems, have meant that precise measurements of transient electrical signals can be made quickly. Thus, it has become possible to measure the resistance change taking place in the hot wire as a consequence of its temperature rise with a... 

The current is analogous to permeation rate, the driving force or voltage is analogous to the concentration gradient or pressure differential, and the electrical resistance is then the analogue of resistance to permeate flow. The resistance to permeate flow can then be said to be Rf. 

To visualize the concept of the rate-determining step, electrical circuit analogues are useful. For a consecutive reaction, an electrical circuit with a series of two or more resistances and power can be used, and for a parallel reaction, parallel resistance and power as shown in Figure 5.10 can be used. For consecutive reactions with three reaction steps, the electric circuit has three resistors, Kj, Rj, and in series in addition, the power source (a fuel cell or a battery) has an internal resistance, R. The current (f) through the electrical circuit is given by the expression... 

A modified electrical, geometrical analogue for time-dependent heat generation problems that utilizes a mechanical device for creating a simulated exponential power use has been previously described. This mechanism is limited, however, to problems involving rather long periods due to inherent mechanical difficulties. Therefore, to eliminate this difficulty, an electronic device has been developed. This device consists of a d-c amplifier, a resistance-capacitance feed-back circuit, and a shorting switch as illustrated. 

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