Hysteresis Subject

Cyclic polarisation This type of measurement is similar to potentio-dynamic anodic polarisation with the difference that, following an anodic polarisation plot, the test specimen is subjected to a cathodic stimulus, i.e. a reverse scan. Any hysteresis, i.e. deviation from the anodic plot, can... 

In Part III heterogeneous equilibria involving clathrates are discussed from the experimental point of view. In particular a method is presented for the reversible investigation of the equilibrium between clathrate and gas, circumventing the hysteresis effects. The phase diagrams of a number of binary and ternary systems are considered in some detail, since controversial statements have appeared in the literature on this subject. 

Hysteresis effect The hysteresis effect is a retardation of the strain when a material is subjected to a force or load. Figure 2-12 are examples of different hysteresis recovery rates. 

Dielectric loss The dielectric loss factor represents energy that is lost to the insulator as a result of its being subjected to alternating current (AC) fields. The effect is caused by the rotation of dipoles in the plastic structure and by the displacement effects in the plastic chain caused by the electrical fields. The frictional effects cause energy absorption and the effect is analogous to the mechanical hysteresis effects except that the motion of the material is field induced instead of mechanically induced. 

The dynamical adhesion process described in this section is also referred to as adhesion hysteresis. We will come back to this subject in later sections when discussing the correlation between adhesion and friction. 

An HM-HEC monolayer at the air/aqueous interface was formed by adsorption from an aqueous solution of the polymer placed in the Langmuir trough overnight. In "stress-jump" experiments, HM-HEC monolayers were placed under rapid compression to a large degree and surface pressure was measured as a function of time after compression was stopped. (The compressional "jumps" required a minute or two to complete, and in some cases were on the order of the polymer monolayer relaxation times. See later section for discussion). In hysteresis experiments, the adsorbed monolayers were subjected to continuous compression-expansion cycles at a specific speed, while surface pressure was determined as a function of surface area. 

Furthermore, we employ the same assumptions to describe a different set of hysteresis experiments a monolayer with surface pressure it at equilibrium is subjected to expansion at a constant speed of v cm /sec. The theoretical curves of surface pressure are plotted against area for various q-values in Figure 4. The curves show that the reduction of surface pressure decreases when the expansion rate is decreased for a given mono-layer, i.e. as q becomes more negative. In Figure 5, curves are plotted for q = -2 with the two different modes initial compression and initial expansion. Because the theoretical curves of the second and subsequent cycles in both modes almost coincide, we can expect that the surface pressure vs. area curves will be independent of how the hysteresis experiment starts after about two initial cycles. 

Several important aspects of the SHG experiments are not described in a straight forward way by the model. These are the residual SHG prior to field perturbation and asymmetric response to fields of different polarity. These effects may be due to the fact that the dipoles within the stacks as formed are subjected to remnant fields from surrounding stacks. The asymmetry may be associated with structural asymmetry within the stacks or some higher ordering or arrangement which does not allow for a symmetric hysteresis about zero voltage. A distribution of nonidentical stacks is also possible. 

In the presence of bromide ions the electrode was subject to a drop in potential, (e.g., 1.5 to 5.7 mV at a Br iCl ratio of 2000 3) and to delayed response. A considerable hysteresis effect is also observed in concentrated solutions of chloride when the electrode is used in a 1M chloride solution and then dipped in one that is 0.02 M. Equilibrium is reached only after 10 min. The junction potential is minimised by diluting the test solution with the salt-bridge solution (10% aq. potassium nitrate). 

The precision and accuracy of the measurement also depend strongly on the reference electrode, which affects the results through fluctuations in its own potential and through the liquid-junction potential at the test solution-liquid bridge interface. This subject is extensively treated in [158]. Common electrodes of the second kind have sufficiently stable potentials at a constant temperature, but difficulties can be encountered due to temperature hysteresis. Silver chloride electrodes are preferable to calomel electrodes, because their temperature hysteresis is substantially smaller with a calomel electrode, potential stabilization after a change in the temperature may even take several hours. Negligible temperature hysteresis is exhibited by the thallamide reference electrode [26,... 

Genuine hysteresis is considered when contaminant release results only from desorption. Experimental data can be interpreted in terms of genuine desorption only when the system is at equilibrium and released molecules are those adsorbed onto the solid phase surface. Molecules brought back into the solution as result of dissolution, diffusion out of the solid matrix, or biotic/abiotic transformation cannot be considered desorbed molecules. In the subsurface, it is almost impossible to distinguish between desorbed molecules and molecules that were not subjected to adsorption and desorption. 

In many cases, a trace element retained on the subsurface soM phase may undergo chemical reactions that induce a hysteresis phenomenon during the release process. A relevant example of hysteresis due to precipitation of some of the initial contaminants is given by the behavior of Cr(VI), an industrial contaminant, which in the subsurface environment may be subject to reduction reactions. When an available source of electrons is present, such as organic matter, Cr(VI) is reduced to Cr(III) the rate of this reaction increases with decreases in pH (Ross et al. 1981). 

In 1919, Barkhausen performed an experiment by connecting a solenoid with a magnetic core to an amplifier and loudspeaker. When the magnet was subjected to full hysteresis (1, pp. 19-27), he heard a cracking noise in the speaker. When such a speaker is replaced by an oscilloscope, irregular voltage spikes may be observed. Those... 

Fig. 6. Counterclockwise hysteresis appearing between hearing threshold shift and quinine plasma concentration in a subject who received two identical oral doses (dotted and solid lines) and an infusion (dashed line) of quinine. (From Paintaud G, Alvan G, Beminger E et al. The concentration-effect relationship of quinine-induced hearing impairment. Clin Pharmacol Ther 1994 55 317-23, with permission from MOSBY Inc.)...

Cumulative volume curves generated by intruding mercury into porous samples are not followed as the pressure is lowered and mercury extrudes out of the pores. In all cases the depressurization curve lies above the pressurization curve and the hysteresis loop does not close even when the pressure is returned to zero, indicating that some mercury is entrapped in the pores. Usually after the sample has been subjected to a first pressurization-depressurization cycle, no additional entrapment occurs during subsequent cycles. In some cases, however, a third or even fourth cycle is required before entrapment ceases. 

The consequences of this type of activated physical adsorption is not only that the quantity adsorbed can lie off the isotherm but also that the measured quantity of adsorption is far less than the equilibrium value. No experiments have been conducted to illustrate whether or not the quantity adsorbed lies within the hysteresis loop. The occasional failure of the vacuum volumetric method to agree with the dynamic method, which is not subject to any pressure overshoot, may in part be attributed to this phenomenon. 

Figure 8.17 shows a hysteresis loop for an anelastic solid subjected to an oscillating stress. If the amplitude of the stress is a0, find the shape of the hysteresis loop ... 

HDI Heat buildup An abbreviation for hexamethylene diisocyanate. The temperature rise within an elastomer due to hysteresis. In many end-use applications, an elastomer can be subjected to repeated cycles of deformation-relaxation. As this occurs, friction between the elastomer molecules generates heat. As elastomers have relatively poor thermal conductivity, the heat generated builds up over time, progressively increasing the internal temperature of the elastomer. If the temperature increases above 70°C, the elastomer physical properties can begin to reduce. Design of the elastomer part can play an important role in minimizing the effects of heat buildup. 

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