Outstanding problems

The principal objection to -PDA antiozonants is their staining characteristics. The lack of suitable alternative antiozonants for light-colored diene mbber articles is one of the outstanding problems in mbber technology. Pew chemical antiozonants outside the class of -PDAs have much commercial importance. One of the few exceptions to this rule is 6-ethoxy-l,2-dihydro-2,2,4-trimethylquinoline [91-53-2] one of the first commercial antiozonants. 

On a different note, after some 50 years of intensive research on high-pressure shock compression, there are still many outstanding problems that cannot be solved. For example, it is not possible to predict ab initio the time scales of the shock-transition process or the thermophysical and mechanical properties of condensed media under shock compression. For the most part, these properties must presently be evaluated experimentally for incorporation into semiempirical theories. To realize the potential of truly predictive capabilities, it will be necessary to develop first-principles theories that have robust predictive capability. This will require critical examination of the fundamental postulates and assumptions used to interpret shock-compression processes. For example, it is usually assumed that a steady state is achieved immediately after the shock-transition process. However, due to the fact that... 

The problem is this the third row of the periodic table contains 8, not 18, electrons. It turns out that while quantum numbers provide a satisfying deductive explanation of tbe total number of electrons that any shell can hold, the correspondence of tliese values with the number of elements that occur in any particular period is something of a coincidence. The familiar sequence In which the s, p, d, and f orbitals are filled (see diagram, left) has essentially been determined by empirical means. Indeed. Bohr s failure to derive the order for the filling of the orbitals has been described by some as one of the outstanding problems of quantum mechanics. 

The outstanding problem is to decide how much, if any, association exists between N02 and X" in the generally rate-determining step of the reaction. Kinetic studies tend to indicate the presence of different electrophiles under different conditions whereas the derived partial rate factors are closely similar and therefore indicate one electrophile common to most, if not all, nitrating agents. The more electron-attracting is X , the more easily is N02 displaced from it and hence a reactivity sequence should be... 

Polymer films that are sensitive to light, x-rays, or electrons— known as photoresists—are nsed extensively to transfer the pattern of an electronic circuit onto a semiconductor surface. Such films must adhere to the semiconductor surface, cross-link or decompose on exposure to radiation, and nndergo development in a solvent to achieve pattern definition. Virtually all aspects of photoresist processing involve surface and interfacial phenomena, and there are many outstanding problems where these phenomena mnst be controlled. For example, the fabrication of multilayer circuits requires that photoresist films of about 1-pm thickness be laid down over a semiconductor surface that has already been patterned in preceding steps. 

Some Outstanding Problems in the Mechanics of Rubbery Solids... 

The remarkable range of redox potentials in the iron sulfur proteins, already noted, illustrates the principle that nature, having discovered a ligand system, attempts to extract from it the maximum utility. Certainly the outstanding problem awaiting solution in these proteins is an explanation for the relationship between structure and redox potential. Thus... 

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. 

While short-term scheduling problems are important by themselves, they rarely arise in isolation, but they have to be considered as part of a production planning problem. Thus, the integration and simultaneous optimization of planning and scheduling so as to achieve consistency and optimality remains a major outstanding problem. 

At what temperature and density does the phase transition to quark matter occur To determine the phase diagram of thermodynamic QCD is an outstanding problem. The phases of matter are being mapped out by colliding heavy-ions and by observing compact stars. Since QCD has only one intrinsic scale, Aqcd> the phase transition of QCD matter should occur at that scale as matter is heated up or squeezed down. Indeed, recent lattice QCD calculations... 

The time-honored method of controlling insect-borne virus diseases is by breeding resistant varieties. This has been practical in annual crops, but is hopelessly slow in tree crops, where it may take 20 years or more to test a new variety. What is needed desperately is some sort of treatment which will control the virus, probably a systemic treatment, as the virus works within the plant cells. This is not a new idea and work has been done along this line by many workers. A sense of urgency is inevitable, however, when 500 to 600 acres of citrus can be wiped out completely in 3 to 5 years time, followed by an expensive replanting job and a wait of 5 to 6 years to get back into production. This is the outstanding problem at the present time and may need years to answer. 

Groves, D.I., Goldfarb, R.J., Robert, F., Hart, C.J.R. 2003. Gold deposits in metamorphic belts overview of current understanding, outstanding problems, future research, and exploration. Economic Geology, 98, 1-29. 

The bimolecular lipid membrane (BLM) produced in aqueous solution described in this paper is of considerable interest for two main reasons. First, the BLM is a new type of interfacial film of ultrathinness. The limiting thickness of BLM is 40-130 A. as estimated from various measurements. The values obtained by optical methods are probably most reliable, indicating that the thickness of the BLM is equal to about twice the length of the lipid molecules. The environment in which the BLM is formed and the molecular orientation at the biface lends itself as a promising tool in understanding some outstanding problems in colloid and interfacial chemistry such as Van der Waals attraction and... 

---