Critical phenomena, history

The surfactant association structures have a long history of research ranging from the McBaln introduction of the aqueous micellar concept(1.) over the interpretation of mlcelllzatlon as a critical phenomenon — — to the analysis of the structure of lyotropic liquid crystals(A) and the comprehensive picture of the phase relations in water/surfactant/amphlphile systems.These studies have emphasized the relation between the association structures in isotropic liquid solutions and the liquid crystalline phases. Parallel extensive investigations in crystalline/ liquid crystalline lipid structureshave provided important insight in the mechanisms of the associations. 

Edmond Becquerel (1820-1891) was the nineteenth-century scientist who studied the phosphorescence phenomenon most intensely. Continuing Stokes s research, he determined the excitation and emission spectra of diverse phosphors, determined the influence of temperature and other parameters, and measured the time between excitation and emission of phosphorescence and the duration time of this same phenomenon. For this purpose he constructed in 1858 the first phosphoroscope, with which he was capable of measuring lifetimes as short as 10-4 s. It was known that lifetimes considerably varied from one compound to the other, and he demonstrated in this sense that the phosphorescence of Iceland spar stayed visible for some seconds after irradiation, while that of the potassium platinum cyanide ended after 3.10 4 s. In 1861 Becquerel established an exponential law for the decay of phosphorescence, and postulated two different types of decay kinetics, i.e., exponential and hyperbolic, attributing them to monomolecular or bimolecular decay mechanisms. Becquerel criticized the use of the term fluorescence, a term introduced by Stokes, instead of employing the term phosphorescence, already assigned for this use [17, 19, 20], His son, Henri Becquerel (1852-1908), is assigned a special position in history because of his accidental discovery of radioactivity in 1896, when studying the luminescence of some uranium salts [17]. 

This is the simultaneous existence, for the same given set of conditions, of two different stable stationary states. The selection of the state actually occupied at a given time is a consequence of the system past history. By appropriate variation of a parameter (or, possibly, by a sufficiently intense perturbation), the transition from one state to the other can be triggered. Since the value of the parameter for which this occurs depends on the direction of the applied variation, a classical hysteresis phenomenon occurs, which is of the same type as that observed in mechanics or magnetism. In addition, near the boundaries of the bistationary domain, the approach to the stationary state gets slower and slower the evolution is then subject to the so-called "critical slowing down". 

In principle, all of the parameters in this equation are measurable so it should be possible to determine the mobility from the voltage dependence of the current. However, the actual behaviour of cells of this type is critically dependent on the nature of the interface. The currents obtained can also depend on the history of the cell. One example of this and of another way that ppm levels of ionic impurities can cause problems is provided by the field anneal phenomenon [25, 26]. If the sample is heated into the isotropic phase and a DC current applied to the cell for a period of time ionic impurities become adsorbed on the electrode surface where they help to facilitate charge injection. Thereafter the I/V characteristics of the Col phase are found to be totally different and, in extreme cases, the measured conductivity can (apparently) be orders of magnitude higher Because of the extreme sensitivity of sandwich cell measurements to small difference in the electrode surface and, because experimentally the voltage dependence of the current often deviates quite markedly from the expected (V-Vc) behaviour, reliable determination of mobilities from the I/V curves is difficult and this approach is rarely used [27]. 

So, on the one hand, BASF faced seriously declining revenues due to the loss of its traditional markets, but, on the other hand, it had the capacity to convert its ammonia output into nitrates, the commodity in critical demand by the country s military. Here is clearly one of the origins of a phenomenon that marked so much of Germany s, and the world s, subsequent history the rise of a military-industrial complex.For BASF and the Second Reich this was a natural partnership the country s leading company looking for new markets, a state at war desperately needing... 

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