Proxy methods

Epistemic uncertainty —missing knowledge—is due to a lack of information that through R D you could buy directly or estimate through proxy methods, if you so chose. These are controllable risks, although in practice they may be unduly expensive to control relative to the risk exposure (threat x likelihood). 

In the sections that follow we will first develop and illustrate (Figures 1 and 2) the conceptual model and the proxy methods incorporated within this model—with additional details provided in the cited literature. The remainder of the chapter is devoted to demonstrating the utility of the model through a series of case studies ranging from the modem Black Sea to shales and argillites of the Precambrian. Based on these case studies, we conclude with a summary of similarities and differences in proxy application. 

Streamlined LCA methods are still too complicated for many applications. So proxy measures have been developed that use a single value to represent the environmental impact of a product or material. Examples include ... 

Bones and teeth, however, are primary archaeological materials and are common to many archaeological sites. Bones bearing cut marks from stone tools are a clear proxy for human occupation of a site, and in the study of human evolution, hominid remains provide the primary archive material. Hence, many attempts have been made to directly date bones and teeth using the U-series method. Unlike calcite, however, bones and teeth are open systems. Living bone, for example, contains a few parts per billion (ppb) of Uranium, but archaeological bone may contain 1-100 parts per million (ppm) of Uranium, taken up from the burial environment. Implicit in the calculation of a date from °Th/U or Pa/ U is a model for this Uranium uptake, and the reliability of a U-series date is dependent on the validity of this uptake model. 

COM interfaces are defined in an interface description language called IDL.6 These interfaces can be compiled to produce type libraries—the runtime representation of the structure of interfaces and methods—and to produce appropriate proxy, stub, and marshaling code for the case of remote object references. 

Many of the analytes of interest for solid phase chemical reference materials are the same as those in seawater, but the need for and the preparation of reference materials for suspended particulate matter and sediments is quite different. The low concentrations of many seawater species and the presence of the salt matrix create particular difficulties for seawater analyses. However while sediments frequently have higher component concentrations than seawater, they also have more complicated matrices that may require unique analytical methods. A number of particulate inorganic and organic materials are employed as paleoceano-graphic proxies, tracers of terrestrial and marine input to the sea, measures of carbon export from the surface waters to the deep sea, and tracers of food-web processes. Some of the most important analytes are discussed below as they relate to important oceanographic research questions. 

Subjects are to be informed about the aims, methods, risks, and benehts of the trial. The availabihty of alternatives should be explained to the subjects. Subjects should not be pressured into enrolUng in the trial, but rather should voluntarily join in and should be able to leave the trial at any time without duress or penalty. For young and incapacitated people who are not able to understand the requirements and implications of the trial, proxy decision from their representatives (parents or guardians) must be obtained. 

Potential interfering substances in a biological matrix include endogenous matrix components, metabolites, decomposition products, and in the actual study, concomitant medication. Whenever possible, the same biological matrix as the matrix in the intended samples should be used for validation purposes. For tissues of limited availability, such as bone marrow, physiologically appropriate proxy matrices can be substituted. Method selectivity should be evaluated during method development and method validation and can continue during the analysis of actual study samples. 

Several general approaches have been used to measure the activities of extracellular enzymes in aquatic systems. These methods typically measure a potential activity, inasmuch as a substrate added to a sample to measure enzyme activity is in competition with naturally occurring substrates (whose concentration is usually unknown) for enzyme active sites. The most commonly applied method involves a small substrate proxy, typically consisting of a monosaccharide or an amino acid covalently linked to a small fluorophore substrates frequently used include methyumbellifery- (MUF-) monosaccharides and 4-methyl-coumainylamide (MCA)- amino acids. Upon hydrolysis of the bond between the monomer and the fluorophore, the fluorophore becomes fluorescent, and hydrolysis is measured as an increase in fluorescence signal with time (Hoppe, 1983 Somville and Billen, 1983). 

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