Chemical methods spatial/temporal variability

As a first step in quantifying chemical loads to coastal waters, the amount of water flowing out of the subsurface must be determined. This is particularly challenging because groundwater flow is spatially and temporally variable. A number of qualitative and quantitative techniques have been developed to sample SGD, with each method sampling a particular spatial and temporal scale. Because of limitations with each sampling method, several techniques should be used at any particular site. 

Linear stability analysis provides one, rather abstract, approach to seeing where spatial patterns and waves come from. Another way to look at the problem has been suggested by Fife (1984), whose method is a bit less general but applies to a number of real systems. In Chapter 4, we used phase-plane analysis to examine a general two variable model, eqs. (4.1), from the point of view of temporal oscillations and excitability. Here, we consider the same system, augmented with diffusion terms a la Fife, as the basis for chemical wave generation ... 

Clearly, it would be more efficient to have a conceptual framework to guide development, or at least show where fundamental limits might lie. A complete theory of MALDI should quantitatively predict the observed mass spectrum as a function of variables such as matrix choice, analyte physical and chemical properties, concentrations, preparation method, laser characteristics (wavelength, spatial and temporal properties), local environment (such as ambient pressure or substrate temperature), and ion extraction method. Here we focus only on ionization mechanisms and do not address all factors affecting a MALDI experiment. Some of these are discussed in other contributions to this volume. Only mechanisms involving molecular matrices and laser excitation are included, methods that depend primarily on properties of the substrate, such as nanoparticles or stmctured surfaces (such as DIOS) are not Hybrid methods, such as laser ablation into electrosprays, are also out of our scope, but vacuum and higher-pressure (e.g., atmospheric pressure) MALDI are both considered to have the same underlying mechanisms discussed here. 

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