Relaxation impedance

Impedance Spectra with Inductive Behavior at Low Frequencies Relaxation Impedance. Based on the concept of impedance elements, Gdhr [1986] described the Faradaic impedances as connections of impedance elanents each of which is associated with a single process. One of such an impedance element is the relaxation impedance, desalbing the surface relaxation of the interface and explaining the development of the pseudoinductive behavior in the low frequency range (frequency < 3 Hz) in the impedance spectra of the fuel cell. This behavior was first found by Muller et al. [1999] during poisoning the anode of a PEFC with... 

Figure 4.5.46. Equivalent circuit with relaxation impedance (Zt).

On the basis of this model and the equivalent circuit shown in Figure 4.5.67, the changes and differences, depending on the used anode in the fuel cell (Pt/C or PtRu/C) in the impedance spectra during the experiment, are dominated by the changes of the charge transfer resistance of the anode (Raj), the surface relaxation impedance (Rg, tg) and the finite diffusion impedance (Z ). 

Transient measnrements (relaxation measurements) are made before transitory processes have ended, hence the current in the system consists of faradaic and non-faradaic components. Such measurements are made to determine the kinetic parameters of fast electrochemical reactions (by measuring the kinetic currents under conditions when the contribution of concentration polarization still is small) and also to determine the properties of electrode surfaces, in particular the EDL capacitance (by measuring the nonfaradaic current). In 1940, A. N. Frumkin, B. V. Ershler, and P. I. Dolin were the first to use a relaxation method for the study of fast kinetics when they used impedance measurements to study the kinetics of the hydrogen discharge on a platinum electrode. 

Under potentiostatic conditions, the photocurrent dynamics is not only determined by faradaic elements, but also by double layer relaxation. A simplified equivalent circuit for the liquid-liquid junction under illumination at a constant DC potential is shown in Fig. 18. The difference between this case and the one shown in Fig. 7 arises from the type of perturbation introduced to the interface. For impedance measurements, a modulated potential is superimposed on the DC polarization, which induces periodic responses in connection with the ET reaction as well as transfer of the supporting electrolyte. In principle, periodic light intensity perturbations at constant potential do not affect the transfer behavior of the supporting electrolyte, therefore this element does not contribute to the frequency-dependent photocurrent. As further clarified later, the photoinduced ET... 

From a theoretical point of view, the equilibrium modulus very probably gives the best characterization of a cured rubber. This is due to the relationship between this macroscopic quantity and the molecular structure of the network. Therefore, the determination of the equilibrium modulus has been the subject of many investigations (e.g. 1-9). For just a few specific rubbers, the determination of the equilibrium modulus is relatively easy. The best example is provided by polydimethylsiloxane vulcanizates, which exhibit practically no prolonged relaxations (8, 9). However, the networks of most synthetic rubbers, including natural rubber, usually show very persistent relaxations which impede a close approach to the equilibrium condition (1-8). 

The appearance of capacitive or inductive impedance depends essentially on the value of the rate constants. Low frequency loops, in a general case, are all very sensitive to the pH of the electrolyte. The different time constants are attributed to the relaxation of surface coverage by a corresponding number of reaction Intermediates. 

Glaucoma Since drainage of aqueous humor is impeded during relaxation of the pupillary sphincter, intraocular pressure rises. 

Frequency dependent complex impedance measurements made over many decades of frequency provide a sensitive and convenient means for monitoring the cure process in thermosets and thermoplastics [1-4]. They are of particular importance for quality control monitoring of cure in complex resin systems because the measurement of dielectric relaxation is one of only a few instrumental techniques available for studying molecular properties in both the liquid and solid states. Furthermore, It is one of the few experimental techniques available for studying the poljfmerization process of going from a monomeric liquid of varying viscosity to a crosslinked. Insoluble, high temperature solid. 

At higher concentrations, nitroglycerin also relaxes arteriolar smooth muscle, which leads to a decrease in both peripheral vascular resistance and aortic impedance to left ventricular ejection (decreased afterload). The decreased resistance to ventricular ejection may also reduce myocardial wall tension and oxygen requirements. 

Clinically, these drugs have hypnotic and relaxant properties. The intoxication is characterized by impeded motor coordination, and the euphoria is not always obvious. To some extent, the attraction of use is more state dependent than in the case of opioids and central stimulants. Diazepam, for instance, is experienced as more rewarding in states of anxiety (negative reinforcement). It is also well known that expectancy factors have a significant role at low blood alcohol concentrations. The low-dose alcohol intake might be experienced as positive to a large extent by what one thinks will happen (Marlatt and Rohsenow 1980). 

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