Noise intermittent/fluctuating

This phenomenon is often observed and is caused by the intermittent addition of small sample pulses into the illuminated region of the flow cell. As the sample concentration in the pulse tends to be different from the mean concentration inside the illuminated region, optical artefacts are formed along the radiation beam, which affects the measurements in a regular fashion. This leads to sinusoidal absorbance fluctuations superimposed on the main recorded signal (Fig. 4.13). As a constant frequency is involved, the related undulation can easily and efficiently be filtered out (see e.g., Ref. [4]). The signal-to-noise ratio, however, is adversely affected. 

Where equipment emits an intermittent or fluctuating noise (such as when it is being depressured or blown down) noise limits such as those shown below can be applied ... 

Unstable chaotic dynamics with properly tuned parameter intermittently switches between the stabilizing and destabilizing modes by exponentially amplifying microscopic fluctuations [15]. That is, fluctuations in the microscopic level such as the thermal noise, nonuniformity of chemical distributions, and the gel layer s uneven stiffness distribution (density distribution of crosslinked acto-myosins), are amplified to an extensive and sustained movements of the macroscopic level. Some form of positive feedback effect by the couphng of chemical, physiological, and hydrodynamic processes may be responsible for the amplification process. 

In a typical experiment, the test sample and a suitable reference material are contained in two separate, identical ampoules kept at constant temperature in separate, identically constructed wells of the calorimeter. Ideally, the reference material is identical or very similar to the test sample in mass, heat capacity and thermal conductivity, but, unlike the test sample, it is thermally inert (i.e. the reference material will not undergo changes that result in heat production or absorption under the conditions of the experiment). One example is a small quantity of ordinary glass beads in air at room temperature used as reference for the same amoimt of a hydrated ceramic material which is expected to lose water under the same conditions. Consequently, most of the noise arising from temperature fluctuations is removed when the reference data are subtracted. A feedback temperature control system between the wells (a) serves to ensure that the temperature difference between the weUs is zero and (b) provides an output that measures any difference in electric power requirement of one well relative to the other, needed to keep the temperature of both weUs the same. This power difference, as a function of time, is the output from the calorimeter, which is recorded continuously or intermittently over the duration of the test. 

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