Problems Remaining Today

Abkowitz, M. A. (1979). In The Physics of Selenium and Tellurium (E. Gerlach and P. Grosse, eds.), p. 210. Springer-Verlag, Berlin and New York. 

Imamura, Y., Ataka, S., Takasaki, Y., Kusano, C., Hirai, T., and Maruyama, E. (1979). Appl. Phys. Lett. 35, 349. 

and Pfister, G. (1981). In Electronic Properties of Polymers (J. Mort and G. Pfister, eds.), Chapter 6. Wiley (Interscience), New York. 

Nakagawa, K., Komatsu, T., Hirai, H., Misumi, T., and Fukuda, T. (1981). Japanese Patent 56-1943. 

Silver, M., Madan, A., Adler, D., and Czubatyj, W. (1980). Conf Rec. IEEE Photovoltaic Spec. Conf. 14, 1062. 

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Sanitary issues were reduced by adding a bite valve cover. Prior to the cover, the hydration system bite valve danghng on the end of its tube could come into contact with a number of contaminants on the battlefield. The soldier would put it in his mouth to drink and become exposed to organisms that could lead to battlefield illness. The problem remains today in that some soldiers use their mouths to take the cover off the bite valve. 

The electron correlation problem remains a central research area for quantum chemists, as its solution would provide the exact energies for arbitrary systems. Today there exist many procedures for calculating the electron correlation energy (/), none of which, unfortunately, is both robust and computationally inexpensive. Configuration interaction (Cl) methods provide a conceptually simple route to correlation energies and a full Cl calculation will provide exact energies but only at prohibitive computational cost as it scales factorially with the number of basis functions, N. Truncated Cl methods such as CISD (A cost) are more computationally feasible but can still only be used for small systems and are neither size consistent nor size extensive. Coupled cluster... 

One of the most studied alloys is undoubtedly the Ni-Cu system. When the studies started, many problems remained open with regard to the phase and surface composition of these alloys and their electronic structure. Today, it seems that these problems have basically been solved admittedly not in all details, but to a sufficient extent to allow discussion of the results. 

Despite extraordinary achievement, many problems remained, and still remain. We do not have a single theory of the chemical bond that meets all our needs. The equations for the bonds in even the simplest molecules are difficult to solve, although Herzberg was triumphantly successful in his work on atomic and molecular spectra. But the quantum mechanical equations for complex molecules are still too difficult for us to solve in detail. An insightful comment in 1972, prompted by debates about rival theories for interpreting chemical bonding, remains valid even today ... 

Then along came Total Quality Leadership (TQL), a management improvement program developed by W. Edwards Deming. You will recall that Japanese automobile manufacturers used TQL principles to transform their inferior products into the worldwide leading products that remain today. TQL was unique because it used statistical analysis to study problem processes. As scientists, we found that approach appealing. 

YJ hile Wemer s classic paper 49) of 1891 can be regarded as the foundation of modern inorganic coordination chemistry, it has been only during the past 10 to 15 years that a rationalization of the many stereochemistries possible for a coordination complex has become possible— through the modern techniques of spectroscopy and magnetism. Even today, however, many problems remain to be solved, and it is the purpose of this review to outline some of these difficulties. 

Niacin is used as a feed and food additive. The presence of even small quantities of chromium, however beneficial this may be in practice (chromium is an essential trace metal in the human metabolism), is not likely to be accepted by either today s stringent legislation or by buyers who are geared to high-quality supplies. Removal of last traces of impurity is possible by recrystallization, but this increases the number of unit operations, is therefore expensive and energy consuming, and the problem remains as to what to do with the chromium-containing mother liquors. 

In the early 1960s, in addition to the early finding of stereoselectively reacting amine components, several new types of achiral amines were also found whose U-4CR products could be cleaved selectively according to 18 -> 28A [73]. However, even today, despite an ongoing search for optimal amine components, the simultaneous fulfillment of all conditions has not been accomplished. Indeed, it transpires that this problem remains one of the most difficult in preparative chemistry. 

Despite their promise, we are still a long way from seeing the commercial use of high-temperature superconductors. A number of technical problems remain, and so far scientists have not been able to make durable wires out of these materials in large quantities. Nevertheless, the payoff is so enormous that high-temperature superconductivity is one of the most actively researched areas in physics and chemistry today. 

Li-air batteries potentially can offer substantial increase in specific energy relative to today s most advanced Li-ion battery. At present, much remains to be learned about the fundamental chemistry behind Li-air batteries. Among these is the role of the electrolyte in the electrochemical formation and decomposition of lithium oxides. Compared to Li-ion batteries, the Li-airajj batteries are a relatively new concept and many problems remain to be solved. One of the key problems is the stability of the electrolytes on which this chapter is focused. The electrolyte stability is an issue... 

For closed tube-growth, numerous unsolved problems remain requiring further investigation. Quantitative experiments have shown that these tubes essentially conserve the volume of injected solutions within their expanding structures. In addition, semiquantitative models have been proposed by Thouvenel-Romans et al. [42] and Pantaleone et al. [38] to account for specific features of popping and budding tube growth, respectively. However, there are no quantitative models available today that address tube formation based on detailed reaction and transport processes. A major obstacle toward the study of such models relates to the involved free-boundary problems that affect fluid motion, transport, and possibly reaction rates in a nontrivial fashion. 

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