Exogenous noise

Our negative experience in this field suggests that it may be more effective to measure environmental toxins which, in contrast to PCBs, produce measurable metabolites in hair. Since exposure to environmental toxins involves the passive endogenous and exogenous deposition of chemicals in hair, and since the latter is the predominant process, the ratio of endogenous signal/exogenous noise will be maximized more effectively if metabolites rather than the parent toxins are measured. 

In view of this, a robust scheme based on the Hoo control theory [24] is developed in the present work. The algorithm guarantees both stability and performance for a family of perturbed plants with model uncertainties and exogenous inputs (i.e., chamber disturbances and sensor noises) over a wide range of operating conditions, an advantage especially desired for combustion dynamics problems. 

With a recorded waveform, we generally must assume that it represents the sum of nonsynchronized aperiodic signals, for example, from exogenic sources and endogenic activities such as respiration, peristaltic movements, heart beats, and nerve activities. In addition, there may be wideband noise and noise at discrete frequencies, for example, from the power line 50- or 60-Hz fundamentals. 

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