Probe lag

The initial data with the fastest change in cL may not be correct because of possible probe lag effects. The degree of deviation depends on the response time of the probe and the magnitude of kLa (Philichi and Stenstrom, 1989). For commonly used laboratory oxygen probes (time constants < 10 s), truncation of the data below 20 % of cL is recommended (ASCE Standard, 1991). This problem can be taken into consideration in both linear and non-linear regression by choosing the appropriate start values for clo ta. 

Oxygen probe Immediate response to changes in cL Oxygen probe lag x Various models have been proposed to describe the oxygen probe lag (Dang et al., 1977 Linek et al., 1987) and can be used for ozone probes... 

Philichi T L, Stenstrom M K (1989) The effects of dissolved oxygen probe lag on oxygen transfer parameter estimation. Journal Water Pollution Control Federation 61 83-86. 

In Section V.A.4, we showed that optimal volume is proportional to t j and that there is a factor of about (1.5n ) " between the optimal volume with PI control (without uncertainty) and the volume required, assuming the performance bound is reached. The PI performance is governed by the effective delay it d — tJ4) rather than the actual pure delay. The maximum effective delay, assuming a mixing delay of 10 s, a probe lag of up to 30 s, and a CSTR with > td. , is 28.7 s. The measurement lag may therefore imply almost a threefold increase in the required volume, compared to that required with an instantaneous measurement response. 

The receptor-operated Cl -channels of the central nervous system (CNS) are gated by the respective agonists GABA and glycine. Most Cl -channels can be inhibited by disulphonate stilbenes. Muscle Cl -channels can be inhibited by anthracene-9-carboxylate (A9C) and probably by IAA-94. The ICOR Cl -channel is fairly sensitive to NPPB. It should be noted, however, that none of these probes, except for the GABA- and glycine-receptor Cl -channels, is of sufficient affinity and selectivity to permit the channel identification by its use. This dilemma is one of the reasons why the purification of epithelial Cl -channels lags behind that of the CNS Cl -channels. 

Another common perturbation of the circadian clock is the jet lag, which results from an abmpt shift in the phase of the LD cycle to which the rhythm is naturally entrained. The molecular bases of the jet lag are currently being investigated [124]. The model for the circadian clock is being used to probe the various ways by which the clock returns to the limit cycle trajectory after a sudden shift in the phase of the LD cycle. 

A later paper presented the results of a study of the mechanism of the sympathomimetic cardiovascular actions of I.H Cats and dogs anesthetized with allobarbital-urethane were used for measurements of pressure near the bifurcation of the descending aorta and of blood flow with electromagnetic probes. Intravenous Injection of I at 20 mg/kg was found to produce an immediate, sharp increase in blood pressure lasting for about 25 s and followed after a lag of about 6 s by an increase in blood flow. A slow drift downward of the peak systolic pressure followed. Repetition of the dose of I after an hour yielded responses similar to those after the first dose, but... 

If a system is disturbed by periodical variation of an external parameter such as temperature (92), pressure, concentration of a reactant (41,48,65), or the absolute configuration of a probe molecule (54,59), then all the species in the system that are affected by this parameter will also change periodically at the same frequency as the stimulation, or harmonics thereof (91). Figure 24 shows schematically the relationship between stimulation and response. A phase lag <)) between stimulation and response occurs if the time constant of the process giving rise to some signal is of the order of the time constant Inim of the excitation. The shape of the response may be different from the one of the stimulation if the system response is non-linear. At the beginning of the modulation, the system relaxes to a new quasi-stationary state, about which it oscillates at frequency cu, as depicted in Fig. 24. In this quasi-stationary state, the absorbance variations A(v, t) are followed by measuring spectra... 

The induction time is marked as 1 and includes the time taken for crystal nuclei to form which are not visible to macroscopic probes. The induction time is defined in practice as the time elapsed until the appearance of a detectable volume of hydrate phase or, equivalently, until the consumption of a detectable number of moles of hydrate former gas. The induction time is often also termed the hydrate nucleation or lag time (Section 3.1). (The induction or lag time is the time taken for hydrates to be detected macroscopically, after nucleation and onset of growth have occurred, whereas nucleation occurs on too small a size scale to be detected. Therefore, the term nucleation time will not be used in this context. Instead, the term induction time or induction period will be used. The induction time is most likely to be dominated by the nucleation period, but also includes growth up to the point at which hydrates are first detected.)... 

Possible reasons why transition state aromaticity is able to develop early while resonance development lags behind proton transfer at the transition state, and why anti-aromaticity lags behind proton transfer, will be discussed in the section on ab initio calculations. These calculations have provided important additional insights because they allow a direct probe of transition state aromaticity or anti-aromaticity. 

Temperature control is normally carried out using thermocouples in a stainless steel pocket. The type of thermocouple used is either a platinum resistance detector (RTD) or a thermocouple using two dissimilar metals that produce a voltage (EMF). The indicators for these thermocouples must match the probe type and grade. The positioning of the probes is very important as well as any lag (delay) in the system. The output from the probe is connected to the indicator and/or controllers. Most indicators have at least a set point with an on/off output. The more advanced units will allow anticipated switching, more than one set point, temperature ramping between temperatures, time, and hold facilities. Thermocouple break and over-temperature alarm outputs are also commonly provided features. 

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