Unsolved Problems Discussion

Gooden, and E. D. Owen for stimulating discussions regarding some of the unsolved problems that have been identified in this review. 

Naturally occurring isocyano compounds are no longer an oddity since their frequent isolation from members of the class of Demospongiae. Their biogenesis has intrigued chemists ever since the first terrestrial isocyano compound (an amino-acid derivative) was described from a micro-organism. All known marine isocyano compounds are terpenoid and their biosynthesis continues to pose an unsolved problem, which is discussed in Chapter 2. 

There were 29 one-hour talks and a total of seven half-hour talks, mostly by the students. In addition two round table discussions were organised to bring the important topics that still need careful consideration. One was devoted to questions and unsolved problems in Chaos, in particular Quantum Chaos. The other round table discussion considered the outstanding problems in Fundamental Interactions. There were extensive discussions during the two hours devoted to each area. Applications and development of new and diverse techniques was the real focus of these discussions. 

This paper may be regarded as a sequel to my second book on Cationic Polymerisation [1]. I have aimed here at providing a fairly detailed discussion of some theoretical aspects of the subject which is still (or perhaps now more than ever before) in Dainton s words rudis indigestaque moles (a crude and ill-digested, i.e., confused, mass) [2], I also intend to discuss specifically some of the problems raised by Mayo and Morton in their article Ionic Polymerization in the book Unsolved Problems in Polymer Science [3]. 

The pest control situation in California and Florida is reviewed, with particular attention to mechanical developments and the introduction of new fungicides and insecticides, such as the insoluble coppers and parathion, and the outstanding unsolved problems such as control for nematodes which will not injure the plant and the need for a systemic material which will control virus diseases. Emphasis is on needed lines of investigation. Pest control problems in Central America, the Caribbean Islands, and South America are discussed, with special reference to lack of suitable equipment and material because of dollar exchange problems. 

Polymeric materials are widely used to control the corrosion of metals, both to maintain appearance and to prevent loss of structural integrity. In this chapter, the fundamentals of metallic corrosion are briefly reviewed. Methods of studying corrosion, and of evaluating the performance of polymeric materials used in corrosion protection, are outlined. Factors that influence the corrosion protective perfoi iance of polymeric materials are discussed, and some of the research needs and important unsolved problems are highlighted. 

A beautiful month on Lake Qntario in a very friendly atmosphere. John Coleman, Bob Erdahl, Claude Garrod, Richard Hall, Hans Kummer, J. Lindenberg, R. McWeeny, Yngve Qhrn, David Peat, Mitja Rosina, Mary-Beth Ruskai, Darwin Smith, George Warsket, Antonio Ciampi, Ernest Davidson, and others discussed A-representability, the interpretation of RDMs, and other unsolved problems. 

At this type of meeting one becomes keenly aware of the controversial and unsolved problems that exist in the field under discussion. To put these problems in better perspective, I should like to spend some time discussing three points (1) areas of agreement which have been reached in the field of free radical oxidation (2) problems which are definitely unsettled at the moment, and about which there appears to be appreciable controversy (3) and finally, some of the unknown features of oxidations whose parameters are still not resolved. 

Giant axons from squid have a large diameter ranging from 300 to 700 ym. Because of this large size, we are able to insert metal electrodes directly into the axon and measure capacitance and conductance across the membrane. This is the most unequivocal method to measure transmembrane capacitance and is far better than the use of external electrodes as done previously by Cole and Curtis (11). In spite of the simplicity and ease of this technique, there are still a few unsolved problems which will be discussed later. Figure 3 shows one of the exemplary results of nerve membrane capacitance and conductance measurements. Comparison of this result with the one shown in Figure 2 readily demonstrates that there are considerable differences between these two sets of curves. 

The core of any CFD model is its Navier-Stokes solver. The numerical solution of these equations is considered by many to be a mature field, because it has been practiced for over 30 years, but the nature of turbulence is still one of the unsolved problems of physics. All current solvers are based on the approximations that have their effects on the applicability of the solver and the accuracy of the results—also in the fire simulations. The aspects of turbulence modeling are discussed in the next section. 

Some of the particular kinetic problems of hydrogen atom abstractions from O—H bonds have been discussed in the context of questions of general interest. The aim has been to make unsolved problems explicit rather than to give final solutions. It seems desirable to realize explicitly that many of our theories and treatments are entirely empirical (Guggenheim, 1938) strongly resembling the entirely empirical origin of the rate constant (Harcourt and Esson, 1866, 1867).4... 

Finding and characterizing the stationary states of systems with more than two DOFs is an unsolved problem. Isolated stationary points are the best known of these manifolds. In systems with two DOFs, in addition to isolated stationary points, it is also possible to find a closed loop of stationary points [77]. These are associated with parabolic resonances. More complicated manifolds wUl exist in systems having more than two DOFs. In the present discussion we wUl focus on the consequences of the existence of isolated points of stationary flow in phase space. 

The estrogenic activity of toxaphene and synergetic transactivation caused by other organochlorines according to Arnold et al. [249], have been discussed controversially [250-252]. The answer to this question is of central importance, since toxaphene itself is a multicomponent mixture If there is a synergetic potential, it is important to know which congeners have endocrine effects and whether or not there are synergetic effects between the compounds present in technical toxaphene. Because of these unsolved problems, a detailed discussion of this phenomenon is not possible at the moment. 

The development of molecular constitutive equations for commercial melts is still a challenging unsolved problem in polymer rheology. Nevertheless, it has been found that for many melts, especially those without long-chain branching, the rheological behavior can be described by empirical or semiempirical constitutive equations, such as the separable K-BKZ equation, Eq. (3-72), discussed in Section 3.7.4.4 (Larson 1988). To use the separable K-BKZ equation, the memory function m(t) and the strain-energy function U, or its strain derivatives dU/dli and W jdh, must be obtained empirically from rheological data. 

The general approach of this book is to familiarize you with the classes and types of reaction mechanisms that are known and to give you the tools to learn how to draw mechanisms for reactions that you have never seen before. The body of each chapter discusses the more common mechanistic pathways and suggests practical tips for drawing them. The discussion of each type of mechanism contains both worked and unworked problems. You are urged to work the unsolved problems yourself. Common error alerts are scattered throughout the text to warn you about common pitfalls and misconceptions that bedevil students. Pay attention to these alerts, as failure to observe their strictures has caused many, many exam points to be lost over the years. 

In the preceding chapters a number of unsolved problems were discussed. Almost all the theorems mentioned in this paper concern AHs, while NAHs are an open field for investigations by means of Graph Theory. The rules governing charge distributions in NAHs are rather interesting. 

The mechanisms of acid-catalyzed DME formation from methanol and aromatiza-tion of olefins were widely investigated in the years before the discovery of the methanol-to-gasoline reaction. There is a consensus that the intermediate in DME formation from methan.ol over solid acid catalysts is a protonated surface methoxyl, which is subject to nucleophilic attack by methanol [2]. Aroma-tization of olefins is believed to proceed along classical carbenium pathways, with concurrent hydrogen transfer [3]. The mechanism of the crucial step of initial C-C bond formation from MeOH/DME is an unsolved problem, however, and is the subject of ongoing controversy. At last tally, there were some two dozen mechanistic proposals in the literature. It is not possible here to present a comprehensive review of the entire field. However, a number of common themes can be identified. This commonality is discussed and the concepts currently in vogue are critically reviewed. Another issue, whether ethylene is the "first" olefin, has been widely debated [2], but is beyond the scope of this survey. 

This molecule is structurally more flexible than DNA. The database of resolved three-dimensional RNA structures is much smaller than that for proteins it contains only a few hundred molecules. Modeling three-dimensional structures of RNA is basically an unsolved problem, however, there are effective methods for modeling two-dimensional RNA structures. We do not discuss modeling RNA structures in this book and refer the reader to [6],... 

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