Key Unresolved Issues

The Atlantic basin, particularly the North Atlantic, is the most studied of the global oceans, yet there are several important processes and issues remaining to be addressed. Arguably, the most important issue is the paucity of data from the South Atlantic. There have been excellent expeditionary efforts there (i.e., the WOCE sections and the South Atlantic Ventilation Experiment), so the hydrographic system and the nutrient provinces can now be assessed in greater detail. However there has been little focus on processes of the nitrogen cycle in the basin. 

Second, nitrogen fixation remains a poorly quantified process We need to better understand the relationship of the excess nitrate signals in the thermocline to nitrogen sources and sinks, and the role of physical transport, in order to determine if those signals truly (and primarily) represent N2 fixation in the overlying waters. There are large differences in the published estimates of N2 fixation in the North Atlantic. 

temporal variability in nitrogen is poorly quantified. The time series stations are helpful but they are too few. Decadal re-occupation of most ocean sections (such as Alb) is too infrequent to resolve the processes forcing change. 

Finally, precise estimations of meridional transports provide powerful constraints of the basin scale nitrogen budgets. To provide better constraints, we require zonal sections including appropriately dense observations of the organic forms of dissolved nitrogen (measured at higher precision than now possible) to be used in quantification of the meridional transport of nitrogen. 

The authors gratefully acknowledge support from the U.S. National Science Foundation (OCE-0444316 to DAH OCE-0525974 to MJF) and the U.S. National Aeronautics and Space Administration. 

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As will be evident in the later parts of this section, the key unresolved issues about the platinum duplexes center on the 5 -G C base pair. In some studies, the 5 -G H(l) signal was not observed, whereas in others it is very weak. The absence of this signal could indicate that the 5 -G H(l) is... 

In light of the now well-recognized asymmetric chemi.stry of the carbon surface (.see Section II)—and despite the fact that many clues have been abundant in the literature, both explicitly and implicitly—the key heretofore unresolved issue has been the following Which surface sites are responsible for adsorption of inorganic species, and under which conditions Whether the entire adsorbent surface is available for adsorption depends basically on three factors ... 

In each section on the different ion channels, some unresolved issues and future directions will be addressed. In general, little is known about the precise molecular structures of the ion channels (e.g., K+ channels) in smooth muscle and our knowledge of endogenous agents as well as key signal transduction pathways that may modulate smooth muscle ion channels is far from complete. Further, as indicated previously, the modulation and expression of ion channels vary with the type of, and even within (e.g., large versus small arteries), smooth muscle. Studies on K+ channels in nonvascular types of smooth muscle will be discussed if similar material from arterial smooth muscle is limited. 

There are several reasons for investigating PDEs, such as simplicity of the device, ability to operate over a range of speeds from zero to hypersonic, and overall performance. As part of the U.S. Office of Naval Research (ONR) program, computational tools are being developed and applied to gain a better understanding of the operation and performance of PDEs. The basic technical issues to be addressed and the various computational tools needed have already been discussed in previous years reports [1]. Some of the key issues that remain unresolved are the ideal performance estimate of the PDE, rapid initiation of detonations with minimum oxygen, and operation with multiphase fuels. Here, the last accomplishments are presented, and their implications are discussed. 

Many aspects of the electron transfer reactions in P450 BM3 are now reasonably well understood, and the first mutagenesis experiments on the enzyme ruled out the involvement of a tryptophan residue adjacent to the heme in the flavin-to-heme electron transport process . However, even after two decades of study of this enzyme, several fundamental issues remain unresolved. Key among these are the reasons why the electron transfer reactions in the reductase domain of the enz5mie (and between FMN and heme) are so efficient by comparison with the eukaryotic P450 and CPR systems. Thus, further detailed rapid kinetic and structural studies are critical to gain a complete understanding of this efficient electron transfer system. 

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