Chemical ageing variations

The age variations highlighted above are undoubtedly coupled to differences in the chemical composition and reactivity of SPOM. Onstad et al. (2000) examined elemental, stable carbon isotope and lignin phenol characteristics of SPOM from rivers draining the south central US. Variations in values, ranging from... 

This information provides a more complete characterization of bone development, microstructure and aging because the chemical spatial variations contribute greatly to the structural integrity and ultimate biological function of bone. 

Due to the chemical structure, fimctionality and composition of their constituents, ordinary variations of the processing conditions as well as the quality of the raw materials have been observed to lead to changes of the fine structure which are often responsible of lower ageing resistence of the polymer. The data reported here correlate the morphology of some widely utilized epoxy matrices to the informations that can be obtained from the study of the sorption behaviours. 

The determination of an acceptable dose for humans involves the application of uncertainty factors to reflect the fact that, unlike the experimental animal, there is wide variability and susceptibility of response in the genetically diverse human population. Variations in gender, age, hormonal and disease status can affect the response to a chemical. In order to minimise any potential risks, uncertainty factors are applied to the NOAEL to arrive at a reduced exposure that is considered tolerable - namely the acceptable daily intake or ADI. These are usually tenfold for variations in susceptibility amongst the human population (the intra-species factor) and tenfold for the potential... 

The general experimental approach used in 2D correlation spectroscopy is based on the detection of dynamic variations of spectroscopic signals induced by an external perturbation (Figure 7.43). Various molecular-level excitations may be induced by electrical, thermal, magnetic, chemical, acoustic, or mechanical stimulations. The effect of perturbation-induced changes in the local molecular environment may be manifested by time-dependent fluctuations of various spectra representing the system. Such transient fluctuations of spectra are referred to as dynamic spectra of the system. Apart from time, other physical variables in a generalised 2D correlation analysis may be temperature, pressure, age, composition, or even concentration. 

Glaciochemical horizons are intervals of core with substantially higher or lower than average concentrations of certain chemical constituents. If a historical event of known age can be correlated with the event horizon in the core, the assigned age of that interval can be used to confirm the depth-age relationship which has been determined from seasonal variations or other dating methods. In addition, in deep ice where annual layers are too thin to count seasons reliably and dating is only possible by model calculations [15,30], these horizons provide check points for calculated ages. 

The addition of an aggressive chemical environment will greatly complicate the testing. All the problems of ageing tests apply, the uncertainty and variation in service conditions, the time scales involved, the validation of any accelerating process and the extrapolation to service conditions. Additional environmental effects will escalate the costs and the uncertainty of truly matching service rises steeply. 

Chemical weed control in the tropics is still in an experimental stage in most crops. With the exception of sugar cane, few applications have been made on a commercial scale. Even in the sugar cane, where 2,4-D is used almost universally, there is considerable variation in the techniques, the kind of 2,4-D employed, and the use of subsidiary chemicals. This is partly due to different environmental conditions in operation at various times and situations, including the types of weeds present, age of the weeds and crop, soil, and rainfall. Personal idiosyncracies are also an important factor. 

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