Hysteresis-free

Both the cone-shaped and the wedge-like pore give rise to simple, hysteresis-free behaviour. The meniscus is nucleated at the apex of the cone (Fig. 3.14(a)) or at the intersection of the two planes of the wedge (Fig. 3.14(b)), giving a spherical meniscus in the first case and a cylindrical one in the second. In both systems the process of evaporation is the exact reverse of that of condensation, and hysteresis is therefore absent. 

Therefore, in most cases, pH values measured at high temperatures in dilute solution should be considered approximate values only. In cases where the investigators address this problem and are careful to select a suitable electrode (namely, one that manufacturers claim to have almost hysteresis-free pH measurement and a stable isopotential point over the temperature range), the error associated with electrode performance will be small, and differences in reported pH values will correspond to differences in actual pH. In cases where pH is measured in concentrated sucrose solutions, the reported pH value should be considered as a nominal value only, and the differences in nominal pH values might not correspond to actual differences in hydrogen ion activity. 

A square concentration pulse flow technique has been developed to study the kinetics of catalytic reactions over catalysts which change their stoichiometry in response to the reaction conditions. The technique makes it possible to obtain hysteresis-free kinetics data while greatly reducing the time during which the catalyst is exposed to the reaction mixture. 

In fig. 1.26 the effect of sample pretreatment is illustrated. The original sample is "Cab-0-Sir, a pyrogenic silica. It has a fairly low affinity for water. The isotherm type is between II and III (fig. 1.13). No hysteresis is observed. Stronger outgasslng (fig. (b)), further reduces the affinity for water the curve is now definitely of type II but also shows considerable hysteresis which was attributed to incomplete hydroxylation. In case (c) the surface is made hydro-phobic by methylatlon. The water adsorption isotherm (not shown) remains of type II but as Nj adsorption is not determined by hydrophilic groups, the corresponding Isotherm is of type III. Again, it is hysteresis-free. By application of the theories outlined before, information can be extracted from these isotherms in terms of available areas and enthalpies of adsorption. The authors extended this work with infrared studies. 

KjO, GeOj and AI2O3. Non-Inertness of silica is another problem. At high pH all of them dissolve to some extent, precipitated silica and glass more so than quartz. As the dissolved silicates also consume base, correction for this phenomenon Is mandatory to obtain hysteresis-free specific surface area. Several silicas are porous for protons, as judged by the absolute values of cf°, If based on the BET (Njl-area. The trend Is that these Increase virlth porosity, as illustrated by fig. 3.65, with for several samples a° exceeding full monolayer coverage. 

In this connection, it is not surprising that different investigators report different extents of hysteresis for one and the same system. Small changes in pretreatment or mechanical stability may make a leirge difference for instance vibration of the solid may reduce the difference between a(adv) and a(rec) ). The reason for this last phenomenon may be that the additional mechanical energy helps to move the system from one metastable state into the next. Systems that are fully hysteresis-free are rare. 

A water droplet placed on the contacted tube serves as the gating medium with a thin Ag/AgCl wire functioning as the gate electrode. Hysteresis-free field-... 

McGill, S. A., Rao, S. G., Manandhar, E, Xiong, P. and Hong, S. (2006), High-performance, hysteresis-free carbon nanotube field-effect transistors via directed assembly , Physics Letters, 89,163123.1-163123.3. 

Figure 9.28 illustrates the electro-optic responses observed at two 0 s 0° and 30°, where 0 is the angle between the layer normal and one of the crossed polarizer directions. As shown in Figure 9.28 [92], the electric field dependence of transmittance at 0 = 0° shows the typical thresholdless, hysteresis free, V-shaped switching. From the electro-optic measurements at every 5° of 0, the transmittance T versus 0 was obtained at given electric fields. Figure 9.29(a) shows three examples of T versus 0 curves at applied fields of 0, +6, and 6 V/pm [92]. The transmittance T is described by... 

In order to evaluate the sizes of the defects responsible of the wetting hysteresis, we considered a topographical defect consisting of a bump with lateral size a and a maximum slope Despite the fact that the value of tp is unknown, we estimated that the points reported on Fig. 9.13 correspond to defects sizes ranging from tens of nanometers down to 2 nm, which is compatible with electron microscopy observation of the nanoneedles." We also determined a minimal defect size necessary to obtain hysteresis, by comparing the dissipated energy on the defect to kT. This led to a value comparable with the size of liquid molecules, compatible with previous results, which explains why it is so challenging to obtain hysteresis-free surfaces. 

Hysteresis of contact angles is a practical complication all the above discussion ignored hysteresis. On very smooth, homogeneous, rigid solids, with slow movement of the liquid-vapor front, hysteresis is small. It is not yet known whether a truly hysteresis-free system of a liquid on a bulk polymer, with 0 > 0, exists. The lowest hysteresis observed by the author with a polymeric solid is of the order of 2 degrees. (A method of silicone treatment for glass, which yields a surface on which hysteresis is reported to be zero, has been described by Neumann et. al. and by Hertzberg et.al.. )... 

The variation in optieal transmittanee as a funetion of simultaneously measured resistivity in Lai-yYyH c alloy films is shown in fig. 94. For y < 0.30, the films were eompletely hysteresis free and have a sharp optieal transition, where as for 0.46 < y < 0.67, the optieal transition proeeeds more gradually and some hysteresis was present. The films with y 0.86, exhibit large hysteresis effeets. Exeept for the film with y = 0.67 (not shown in the figure), whieh was on the borderline of the fee-hex phase transition, for all other films the transmittanee versus resistivity eurves were observed to reaeh the final shape after the first absorption-desorption eyele. For the film with y = 0.67, the eyele was observed to beeome reprodueible from the third loading eyele onwards. 

The pressure-eomposition isotherm for a typieal Lui-yYyllx (Lao.55Yo.45H c) is shown in fig. 95. In agreement with the optieal and X-ray diffraetion measurements, the isotherms were observed to be hysteresis free and with out any plateau, indieating that these alloy films remains fee for all x > 2. Van Gogh et al. (2001), fitted the isotherms to the Laeher s equation (Laeher, 1938) and ealeulated the partial molar heat of solution AH. For example for Lao.54Yo.46H c alloy, the heat of solution AH was found to be —38.1 kJ/mole H. 

The isomorphous substitution of framework aliunimun in faujasite-type zeolites was evidenced by chemical analysis, XRD (unit cell contraction), mid-infra-red spectroscopy (shift of lattice vibrations) and adsorption measurements (hysteresis-free adsorption isotherms) [147] and later by Si MAS NMR spectroscopy [149,150,153] (see Fig. 5). 

With gate valves a controlled magnetic force F is brought into counterbalance with an elastic force, i.e., a dependent force. The input signal is allocated the appropriate cross-section for the valve with Xp and X.,. The decisive feature is hysteresis-free control in the area around the dydraulic middle position. Symmetrical or asymmetrical controlled cross-sections A can be controlled directly up to 700 mm. The Turcon CTo version with protection against over-speed rpm is available as a specially adapted gate valve. 

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