Unresolved problems

Despite numerous efforts using various techniques, precise knowledge of olefin content remains an unresolved problem. That is why it is worthwhile to mention two methods commonly employed which provide an answer to the problem. 

Does the concept of absolute electrode potential, defined in chapter 7, allow one to measure the absolute electrical potential difference, A(p, at a metal/electrolyte interface, one of the famous unresolved problems in electrochemistry ... 

It is well recognized that heavy atoms and heavy polar diatomic molecules are very promising candidates in the experimental search for permanent EDMs arising from the violation of P and T. The search for nonzero P,T-odd effects in these systems with the presently accessible level of experimental sensitivity would indicate the presence of new physics beyond the SM of electroweak and strong interactions [9], which is certainly of fundamental importance. Despite the well known drawbacks and unresolved problems of the SM, there are no experimental data available that would be in direct contradiction with this theory. In turn, some popular extensions of the SM, which allow one to overcome its disadvantages, are not yet confirmed experimentally [8, 10]. 

The purpose of this review is to solve these two unresolved problems by confirming the nucleation during the induction period of nucleation and the important role of the topological nature with experimental facts regarding the molecular weight (M)- or number density of the entanglement (independence of nucleation and growth rates. 

The former problem is a general problem not only for polymers but also for any other materials (atomic or low molecular weight systems). Although nucleation is a well-known concept, it has never been confirmed by direct observation due to the low number density of the nuclei to be detected with present experimental techniques, such as small angle X-ray scattering (SAXS). Therefore, one of the most important unresolved problems for basic science is to obtain direct evidence to solve the nucleation mechanism of any material. 

There are two typical definitions of the induction time (ti) in CNT given by Frisch [16] and by Andres and M. Boudart [17]. x is an increasing function of N, t,(N). In previous studies, the special case N = N was usually focused on. As any critical nucleus can not be directly observed, Tj(N ) has been estimated from r (N) of macroscopic nuclei by optical microscopy by correcting the time necessary for growth from N to N. Therefore, x (N ) is named r (OM) in this work. It should be noted that there is no guarantee that the estimated Xi(N ) = r (OM) is correct, that is also an important unresolved problem. 

The molecular weight (M) dependence of the steady (stationary) primary nucleation rate (I) of polymers has been an important unresolved problem. The purpose of this section is to present a power law of molecular weight of I of PE, I oc M-H, where H is a constant which depends on materials and phases [20,33,34]. It will be shown that the self-diffusion process of chain molecules controls the Mn dependence of I, while the critical nucleation process does not. It will be concluded that a topological process, such as chain sliding diffusion and entanglement, assumes the most important role in nucleation mechanisms of polymers, as was predicted in the chain sliding diffusion theory of Hikosaka [14,15]. 

The lateral growth rate (V) of crystals of linear chain polymers strongly depends on molecular weight (M) [37]. Although the M dependence of V of folded chain crystals (FCCs) of polymers has been rather well studied, it is still an important unresolved problem. Magill et al. presented an experimental formula, V ocM-0-5, for poly (tetramethyl-p-silpenyline siloxane), poly (ethylene terephthalate), etc [38]. 

Several important classes of polar monomers have so far eluded copolymerization by the Pd(II) system. Vinyl chloride insertion, for example, leads to catalyst deactivation following P-halide elimination to form inert chloride species such as 1.32, as shown by Jordan [90], Similarly, attempted vinyl acetate copolymerization results in deactivation by an analogous acetate elimination process, although the ester chelate intermediate that forms after insertion also effectively shuts down the reaction [90], Therefore, -elimination of polar groups represents a significant and unresolved problem for late transition metal polymerization systems unless access of the metal to it is restricted. 

Of course, even for the cyclic formals there are still unresolved problems, especially the mechanism by which metal halides initiate their polymerisation [16]. Once again it has become evident that attention to impurity effects and side-reactions is of paramount importance if the conclusions from chemical studies of catalytic reactions are to be valid. 

These selection and evaluation criteria were applied systematically to four technological fields, three of which contribute to new energy-efficient solutions. Passive houses, for example, with their major components of insulation solutions, window systems, ventilation and control techniques are close to market diffusion within the next ten years. Fuel cells for mobile uses in vehicles, however, are still a long way from market introduction, for instance, because of unresolved problems regarding the deactivation of the membrane electrode assembly (MEA) and the need for cost reductions by about one order of magnitude. Other types of fuel cells for stationary uses may be closer to market introduction, owing to less severe technical bottlenecks and better economic competitiveness. 

The differences between castoreum from different species and sources still need to be investigated. As suggested by Tang et al [69] it is quite likely that these differences could be diet related because the phenols are most likely derived from the diet of these animals. Indeed, already in 1949 Lederer [73] recognized this possibility and pointed out that 2, 3"-dihydroxydibenz-2-pyrone and 4,4 -dihydroxydiphenic acid dilactone 12 (Fig. 3) are closely related to ellagic acid, which is abundant in the bark of trees. A comprehensive chemical analysis of the polyphenols present in the preferred diet of the beavers and a comparison of these compounds with the phenols present in castoreum from animals fed exclusively on this diet could shed some light on this unresolved problem. 

Martin WP, Gast RG, Meyer GW (1976) Land application of waste materials unresolved problems and future outlook. Soil Conserv Soc Am 25 300... 

In any case, the use of these catalytic systems will depend on their stability. In fact, the still unresolved problem with the application of these catalysts to industrial processes is whether to prolong the life of the catalyst or to continuously regenerate the catalyst in an efficient way. 

Within the two groups of isomers formed, the alkyl perturbation favors the formation of ttc isomers whereas the introduction of nitrogen atoms favors the formation of ttt isomers. It is noteworthy that 1,2- dimethylenecyclohexane reacts with two butadiene molecules to form the ttc- and even the substituted ccc isomer (observed for the first time in a catalytic reaction - for unresolved problems see Sect. 2.5) rather than the tcc isomer. 

It would seem to be an unresolvable problem—to calculate the structure factors we need the atomic positions and to find the atomic positions we need both the amplitude and the phase of the resultant waves, and we only have the amplitude. Fortunately, many scientists over the years have worked at finding ways around this problem, and have been extremely successliil, to the extent that for many systems the solving of the structure has become a routine and fast procedure. 

The CIEEL mechanism, as initially proposed by Schuster20-22 41 114 115, has been applied to a wide variety of CL systems12-15 17-22-25-26-41 but this hypothesis has also been controversially discussed, mainly by Wilson25 130 and McCapra131 132. Here, we will but briefly point out the most important experimental evidence upon which the mechanistic proposal is based and indicate some as yet unresolved problems relating to the CIEEL mechanism. 

Although technically simple, the use of retroviruses and retroviral vectors has not found widespread application. This is mainly due to the size limitations for transfected DNA (about 10 kb), as well as to the unresolved problems of reproducibly expressing a virally transfected eukaryotic gene. However, the methods of pronuclear microinjection and the use of embryonic stem cells are being successfully applied by a growing number of research groups. 

At the end of this chapter we propose a number of unresolved problems related to the subjects discussed herein. 

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