Hysteresis phenomenon

The capillary pressure PC(S) exhibits a marked hysteresis phenomenon when the liquid is alternately withdrawn (drainage) and introduced (imbibition) into the particulate bed. Consequently, capillary pressure changes as a result of variations in saturation do not follow a unique functional relationship. In fact, the suction is always higher on the drainage side of the imbibition-drainage cycle (M8). In Fig. 7 the suction curve starts at zero when S = 1. 

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). 

The hysteresis phenomenon, i.e., static bifurcation as described earlier for the nonisother-mal CSTR that is associated with multiple steady states plays an important role in start-... 

To check if hysteresis was responsible for the beneficial effect of some salts at low relative humidities, experimental runs were made omitting this step. Table IV shows the results obtained at 54 and 17.4% relative humidity with and without prehumidification of the bed at 98% relative humidity. The additives used were NaCl, NaN03, and KC1. At 54% relative humidity even when some decrease of the Ca(0H)2 conversion was found without the prehumidification, the results are still far superior to the pure Ca(0H)2 case. Hysteresis then, can not explain all the beneficial effect observed at 54% relative humidity. At 17.4% relative humidity all the beneficial effect in the case of the NaCl appears to be due to the prehumidification of the bed, i.e., due to a hysteresis phenomenon. 

The relaxation phenomenon described herein is also called first-cycle effect, secondary break-in, waittime effect, memory effect, and hysteresis phenomenon which is in connection with the characteristic changes of the cyclic voltammograms obtained for -> polymer-modified electrodes [iii-vi]. 

The experiment began by charging the equilibrium cell with about 30 cm3 of either phenoPp-cresol or phenol-water solution mixture. The cell was then pressurized with either methane or carbon dioxide until the phenol clathrate formed under sufficient pressure. The systems were cooled to about 5 K below the anticipated clathrate-forming temperature. Clathrate nucleation was then induced by agitating the magnetic spin bar. After the clathrates formed, the cell temperature was slowly increased until the clathrate phase coexisted with the liquid and vapor phases. The nucleation and dissociation steps were repeated at least twice in order to diminish hysteresis phenomenon. The clathrates, however, exhibited minimal hysteresis and the excellent reproducibility of dissociation pressures was attained for all the temperatures and found to be within 0.1 K and 1.0 bar at each time. When a minute amount of phenol or p-cresol clathrate crystals remains and the system temperature was kept constant for at least 8 hours after attaining pressure stabilization, the pressure was considered as an equilibrium dissociation pressure at that specified temperature. 

Classical magnets were not well suited to fast scanning, which is necessary for GC coupling, for instance, because of the hysteresis phenomenon and the magnet heating up... 

Paul O, Bissonnette B. Effect of halothane on the cerebral circulation in young children a hysteresis phenomenon. Anaesthesia 2001 56(4) 360-5. 

Figure 9. Hysteresis phenomenon of I-V characteristic by the contaminated single probe...

In the closing section we will enlarge on the distinctive characteristics of adsorption hysteresis, which are typical for porous carbonaceous adsorbents. The peculiarities associated with adsorption on active carbon, in particular, with hysteresis phenomenon owe its origin to two major factors. The first one lies in the fact that porous carbon adsorbents, as a rule, are structurally labile, especially the carbon of steam-gas activation. Every adsorption-desorption cycle involving a thermal treatment leads to the irreversible changes of adsorbents, and only after several training cycles the adsorbent reaches a stable state. 

Figure 63.1a shows the equilibrium moisture content (dry basis) at the different a for the desorption experiments (obtained from samples dried by hot air) and also for the adsorption experiments (obtained from the freeze-dried samples). Both isotherms are very similar and no hysteresis phenomenon was observed. Hysteresis is justified by assuming that during... 

A hysteresis phenomenon was observed when the monolayer was expanded after 60 sec of compression. Increasing the rate of compression yields a set of tt vs. t curves similar to those in Figure 1 but with larger slopes dir/dT. The rate of compression had little or no effect on the... 

As already foreshadowed by the potentiometric titration and the hysteresis phenomenon observed on back-titration, the effect of pH and time on pepsinogen is more drastic. Inactivation occurs rapidly and is irreversible (Figure 11). All in all, one observes a process of aging. The protein molecule grows old rapidly and like all human beings, it loses its memory. 

As mentioned before, thermal denaturation of short parallel quadruplexes is often irreversible (illustrated in Figure 3(a)). One possibility to circumvent this problem is to record the denaturation profile after an extremely long equilibrium time at each temperature. However, this hysteresis phenomenon is sometimes extreme no renaturation is observed at low strand concentration or unacceptable incubation times are required. Even at a rate as slow as... 

The behavior of inorganic salts when RH is decreased is different from that discussed in Sections 10.2.2 and 10.2.3. For example, for (NH4)2S04, as RH decreases below 80% (the DRH of (NH4)2S04), the particle water evaporates, but not completely. The particle remains liquid until a RH of approximately 35%, where crystallization finally occurs (Figure 10.4). The RH at which the particle becomes dry is often called the efflorescence RH (ERH). This hysteresis phenomenon is characteristic of most salts. For such salts, knowledge of the RH alone is insufficient for determining the state of the aerosol in the RH between the efflorescence and deliquescence RH. One needs to know the RH history of the particle. 

An hysteresis phenomenon is observed when the plateau pressure determined for an absorption isotherm is higher than the plateau pressure measured at the same temperature for the desorption process. Hysteresis is caused by the large stresses associated with the metal to hydride transformation which give rise to internal defects such as dislocations and stacking faults. Hysteresis decreases with increasing temperature as thermally activated stress relaxation processes set in. It is in general important to eliminate or at least minimize hysteresis for most applications. 

The formation of a heavily twinned material on cooling can be reversed by an increase in temperature, which causes the material to transform to the untwinned pre-martensite state. The transformation starts at a temperature, usually called As, the austenite start temperature, and is complete at a temperature Af, the austenite finish temperature (Figure 8.16). (These terms are related to the fact that the best-known martensitic transformation is that of austenite to martensite, in steels.) For the alloy NiTi, As is 71 °C, and Af is 77 °C. It is seen that Ms and Mf differ from As and Af. This is a hysteresis phenomenon, commonly found in solid-state transformations. 

Food demonstrates a hysteresis phenomenon during adsorption and desorption processes. Irreversible physical and chemical changes are responsible for this behavior. Often the EMC of a food product in a given condition is varied by 2% points, depending on whether EMC is obtained by removing or adding moisture. 

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