Sampling time period

Researcher(s) Sample Time period Data source(s) Major assumptions Accounting rate of return Corrected rate of return Corrected ROR+ Accounting ROR... 

If the concentration of the analyte fluctuates with time, then the result of the sampling is a concentration averaged over the sampling time period. The shorter the sampling period, the greater will be the temporal resolution of the concentration variations of the analyte. 

Hyphenated analytical methods provide more complementary information in a shorter time period leading to faster and more reUable results, than data obtained from traditional instmmental methods. The types of analytical instmments that can be joined is very large depending only upon the nondestmction of samples after the initial analytical procedure and the ability of the manufacturer to interface the instmmental techniques. Combinations include separation—separation, separation—identification, and identification—identification techniques (see Analytical methods, survey). 

In Fig. 30-25, representation of the fault detection monitoring activity, there appears to be two distinct time periods of unit operation with a transition period between the two. The mean parameter value and corresponding sample standard deviation can be calculated for each time. These means can be tested by setting the null hypothesis that the means are the same and performing the appropriate t-test. Rejecting the null hypothesis indicates that there may have been a shift in operation of the unit. Diagnosis (troubleshooting) is the next step. 

Fig. 4-1. The same atmosphere measured by (a) a rapid-response irvstrument and by sampling and analytical procedures that integrate the concentration arriving at the receptor over a time period of (b) 15 min, (c) 1 hr, and (d) 6 hr.

The gravimetric method depends on the sampling of flowing, particulate-laden gas from different positions across the exhaust gas duct and the determination of the mass of the particulate material. The sample is collected over a certain time period from each point. The volumetric gas flow is measured. The result is obtained by the following steps ... 

Grab sample A sample of air collected over a short time period in the workspace. 

All of the above events would cause a pump failure over a period of time. Therefore, the events would qualify for inclusion in the failure rate. So, at one extreme there might be six catastrophic failures per sample time. However, a data analyst may decide that No. 2 is not a relevant failure since the cause was neither a function of the equipment nor the operational application, but was a mistake by an outside agent. The same might be said of No. 3. 

The final step in the process of standardizing our columns was to try and maintain the high quality of columns from batch to batch of gel from the manufacturer. This was done by following the basic procedures outlined earlier for the initial column evaluation with two exceptions. First, we did not continue to use the valley-to-peak ratios or the peak separation parameters. We decided that the D20 values told us enough information. The second modification that we made was to address the issue of discontinuities in the gel pore sizes (18,19). To do this, we selected six different polyethylenes made via five different production processes. These samples are run every time we do an evaluation to look for breaks or discontinuities that might indicate the presence of a gel mismatch. Because the resins were made by several different processes, the presence of a discontinuity in several of these samples would be a strong indication of a problem. Table 21.5 shows the results for several column evaluations that have been performed on different batches of gel over a 10-year period. Table 21.5 shows how the columns made by Polymer Laboratories have improved continuously over this time period. Figure 21.2 shows an example of a discontinuity that was identified in one particular evaluation. These were not accepted and the manufacturer quickly fixed the problem. 

The material s loss in weight or the change in optical transmission usually measures abrasion resistance and reflectance after a sample has been exposed to an abrasive surface. This is usually done under load, for a predetermined number of cycles or a time period specified by ASTM methods. 

In a chemical system, mass will flow until equilibrium is achieved. Consider, as an example, the approach to equilibrium between the liquid and gas phases of a substance. If a sample of liquid is introduced into an evacuated closed container, the liquid will begin to evaporate to form a gas phase. If one measures the pressure of this gas as a function of time, a graph similar to that shown in Figure 5.5 will be obtained.0 The pressure at first increases rapidly. After a short time period, however, it levels off at the value represented by p. ... 

Results of the leaching experiments at 25°C are more difficult to interpret. Basalt ground water is not the most effective leaching agent nor is shale the least effective. It appears that at the lower temperature fluoride plays a minor role and other, less obvious, factors predominate. Some of the differences could result from kinetic effects. This is a continuing study with further sampling scheduled at still longer time periods, so it is possible that later results will help clarify the 25°C data. 

Predict the amount of a radioactive sample that will remain after a given time period, given the decay constant or half-life of the sample (Example 17.3). 

NMR spectrometers have improved significantly, particularly in the present decade, with the development of very stable superconducting magnets and of minicomputers that allow measurements over long time periods under homogeneous field conditions. Repetitive scanning and signal accumulation allow H-NMR spectra to be obtained with very small sample quantities. 

Sampling time of 5 minutes, whereas the average concentrations reported in the table are related to the whole study period. 

OPPTS 860.1500, p. 16, indicates that 3-5 sampling points should be included in the decline trials. For applications close to the normal harvest time, the RAC may be harvested at selected intervals between the time of final application and a normal harvest or slightly delayed harvest. If the application is made long before the normal harvest, then representative plant tissues (including immature RAC) may need to be harvested in order to stretch the harvest period. A single composite sample is all that is required from each selected time point, but two or more samples may be harvested to reduce uncertainty about the actual amount of residue present at each sample time interval. These decline samples should be collected and treated the same as normal RAC samples. The samples should be frozen as soon as possible after collection. The instructions for decline sample collection and handling described in the protocol should be followed closely. 

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