Excess property observed behavior

The thermodynamic treatment of systems in which at least one component is an electrolyte needs special comment. Such systems present the first case where we must choose between treating the system in terms of components or in terms of species. No decision can be based on thermodynamics alone. If we choose to work in terms of components, any effect of the presence of new species that are different from the components, would appear in the excess chemical potentials. No error would be involved, and the thermodynamic properties of the system expressed in terms of the excess chemical potentials and based on the components would be valid. It is only when we wish to explain the observed behavior of a system, to treat the system on the basis of some theoretical concept or, possibly, to obtain additional information concerning the molecular properties of the system, that we turn to the concept of species. For example, we can study the equilibrium between a dilute aqueous solution of sodium chloride and ice in terms of the components water and sodium chloride. However, we know that the observed effect of the lowering of the freezing point of water is approximately twice that expected for a nondissociable solute. This effect is explained in terms of the ionization. In any given case the choice of the species is dictated largely by our knowledge of the system obtained outside of the field of thermodynamics and, indeed, may be quite arbitrary. 

These observations are consistent with the prediction that sensitization induced by repeated drug exposure increases the basic responsiveness of DA neurons to stimuli (Robinson and Berridge, 1993). However, this conclusion, while consistent with the prediction of the theory, turns out to be deleterious for its validity as a model of human addiction. In fact, since sensitization increases the incentive properties of any appetitive stimulus, not only of drug-related ones, it can hardly account for a cardinal feature of drug addiction, namely that the excessive impact over behavior exerted by drug-conditioned stimuli is reciprocated by a reduced impact by stimuli conditioned to nondrug rewards. 

Feature 1 is a consequence of the definition of an excess property, Eq. (11.82) as any jc, approaches unity, both A/ and approach M,-, the correspondingproperty of pure species i. Features 2 and 3 are generalizations based on observation, and admit exceptions (note, e.g., the behavior of for the ethanoFwater system). 

The relations between excess properties and property changes of mixing (Sec. 12.3) facilitate discnssionof the molecular phenomena which give rise to observed excess-property behavior. An essential coimectionis provided by Eq. (12.33), which asserts the identity of and AH. Tims we focus on the mixing process (and hence on for explainingthe behavior of. ... 

This mode was subsequently used to predict excess properties (excess volume, excess enthalpy, AH ) of binary mixtures of -alkanes. For instance, the decrease of A// and the reversal of its sign with a change in the temperature, observed in several systems, are correctly predicted though the magnitude of the effect is underestimated. In addition, LCM behavior was predicted to occur in mixtures of poly(ethylene) and -alkanes, in agreement with experimental findings. Calculated LCST s, however, were only in qualitative agreement with the observed data, e.g., the location of the miscibility gap for ra-hexane/polyethylene was predicted to be about 60°C too low. 

Another property pecuHar to SMAs is the abiUty under certain conditions to exhibit superelastic behavior, also given the name linear superelasticity. This is distinguished from the pseudoelastic behavior, SIM. Many of the martensitic alloys, when deformed well beyond the point where the initial single coalesced martensite has formed, exhibit a stress-induced martensite-to-martensite transformation. In this mode of deformation, strain recovery occurs through the release of stress, not by a temperature-induced phase change, and recoverable strains in excess of 15% have been observed. This behavior has been exploited for medical devices. 

The semiconducting properties of the compounds of the SbSI type (see Table XXVIII) were predicted by Mooser and Pearson in 1958 228). They were first confirmed for SbSI, for which photoconductivity was found in 1960 243). The breakthrough was the observation of fer-roelectricity in this material 117) and other SbSI type compounds 244 see Table XXIX), in addition to phase transitions 184), nonlinear optical behavior 156), piezoelectric behavior 44), and electromechanical 183) and other properties. These photoconductors exhibit abnormally large temperature-coefficients for their band gaps they are strongly piezoelectric. Some are ferroelectric (see Table XXIX). They have anomalous electrooptic and optomechanical properties, namely, elongation or contraction under illumination. As already mentioned, these fields cannot be treated in any detail in this review for those interested in ferroelectricity, review articles 224, 352) are mentioned. The heat capacity of SbSI has been measured from - 180 to -l- 40°C and, from these data, the excess entropy of the ferro-paraelectric transition... 

Regarding the electrical properties of other dodecaborides, interestingly, Hamada et al. have reported that ScBi2 has p-type conduction (Hamada et al., 1993) in contrast to the n-type behavior observed for the other trivalent RB12 compounds and which is expected for these metals with excess electrons in the bonding as noted above. 

As described in the previous section, a powerful technique to probe most of the chemical or physical properties of molecular clusters is mass spectrometry after ionization of these clusters. Generally, an excess of energy is given by this ionization process and can lead to various dynamical behaviors from the simplest one—fragmentations of the clusters (evaporation)—to intracluster chemical reactions. This means that the observed distribution of the ionic clusters often does... 

The results In Table II help quantify the differences In cure behavior between 6K-60 and 6K-62. Previous experiments (2 ) using thermal analysis techniques have found that the Initiation period for BK-62 Is shorter than that for BK-60. The same trend Is seen In the mechanical properties data. Moreover, the rate at which the properties change once curing has begun Is approximately 50% greater for BK-62 than for BK-60. When these results are combined with the observation that a major problem with the performance of BK-62 on the press Is excessive drying on the plate, the Inescapable conclusion Is that the differences In curing behavior are a major source of the problems with BK-62. 

It Is easy to see how these differences In curing could lead to excessive drying on the plate. Even under conditions where excessive drying on the plate Is not observed, however, there will still be significant differences In the mechanical properties of the two Ink formulations due to the curing behavior. This would affect transfer on the feed rollers, wiping of the... 

One further phenomena observed In all 73 systems Is the decrease In opacity on curing at elevated temperatures. Above about 60 C the poly(tetramethylene glycol) and excess Isocyanate become miscible. This miscibility may be assisted by the fact that the MDI-BDO hard segments are above their glass transition temperature. To an extent which has not been quantified as yet, llquld-llquld phase separation of MDI and MDI terminated polyol In the prepolymer at low temperatures preslsts Into the final adhesive. The dynamic mechanical behavior of transparent or opaque adhesive, l.e., cured at 60-100 C compared to room temperature are virtually Identical. Similar Immlsclblllty has been observed In other prepolymers (20). This does not appear to adversely affect the adhesive properties of these Halthanes. 

Situations with an excess of ion exchanger occur if,. for example, a given ionic species has to be removed from the solution by a batch operation. An excess of particles with ion exchange properties is usually also present when the sorption of trace ions by soils or soil components (clay minerals, oxides, humic substances) is investigated. Especially in this latter case the particles will be invariably polydisperse. This anomalous kinetic behavior will, of course, only be observed experimentally if the concentration of ions A in the solution and in the various fractions of the ion-ex-changer particles in the mixture are measured continuously. 

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