Density: critical, 6 measurement

Measurement Requirements. Any analysis of measurement requirements must begin with consideration of the particular accuracy, repeatabihty, and range needed. Depending on the appHcation, other measurement considerations might be the speed of system response and the pressure drop across the flow meter. For control appHcations repeatabihty may be the principal criterion conversely for critical measurements, the total installed system accuracy should be considered. This latter includes the accuracy of the flow meter and associated readout devices as well as the effects of piping, temperature, pressure, and fluid density. The accuracy of the system may also relate to the required measurement range. 

Biosensors. Sensors are required to adequately monitor bioreactor performance. Ideally, one would like to have online sensors to minimize the number of samples to be taken from the bioreactor and to automate the bioreactor process. Most bioreactors have autoclavable pH and dissolved oxygen (D.O.) electrodes as online sensors, and use offline detectors to measure other critical parameters such as glucose and glutamine concentration, cell density, and carbon dioxide partial pressure (pC02). An online fiber-optic-based pC02 sensor is commercially available and appears to be robust.37 Probes are also commercially available that determine viable cell density by measuring the capacitance of a cell suspension. Data from perfusion and batch cultures indicate that these probes are reasonably accurate at cell concentrations greater than 0.5 X 106 cells/mL.38,39... 

Smoke Production. Smoke production can be a critical problem in fire-retardant formulations. The 25-ft tunnel test uses a photoelectric cell to measure the amount of smoke evolved. The smoke density is measured continuously and is assigned a value relative to the behavior of red oak. The effect of fire retardants on smoke production varies depending on the chemical. Figure 6 demonstrates this effect as measured in the 8-ft tunnel however, smoke values measured in various tunnel tests may not agree or correlate. 

To obtain a value for the viscosity of He" at the critical temperature for this analysis, the following procedure was followed. The constant-density viscosity measurements of Tjerkstra were extrapolated linearly to Tc as shown in Fig. 5. The 17 values at Tc, so obtained, w ere then plotted vs. density on semilog paper and extrapolated (shown in Fig. 6) to the critical density as reported by Edwards and Woodbury [ ] to determine rjc. The critical-point locus of Fig. 4 was constructed through the He and He critical-point viscosity values and those for the N2 and CO limits obtained by Thodos. The H2, N2, and He viscosity curves of Fig. 4 were then extrapolated by smoothed curves (broken lines) to their respective critical temperatures. Figure 7 was constructed in much the same fashion as already described for Fig. 3. Values of reduced viscosity at A = 1.00 and 1.22 were then taken from Fig. 7 to predict the respective viscosities of tritium and deuterium (broken lines of Fig, 4). The viscosity curves of Ne and CO closely parallel those of A and N2, respectively. 

Verification of general relations between critical currents and magnetic inductions given by Dew-Hughes [ Pinning force density curves measured at different temperatures should coincide after an appropriate reduction. 

The results of the PDQ and KENO verification calciila- tions are shown in Table I. PDQ and KENO agree well at the greater water density. The calculations indicate that the EPRl-CELL/PDQ model can be.used for sensitivity studies and that, for low water densities, EPRI-CELL/ PDQ Is conservative. Comparisons of KENO results and critical measurements are also presented in Table I excellent agreement is shown. 

Some groups criticize measurements in the pH regions relevant to site saturation in view of the errors introduced by the difference of two similar nmnbers (i.e., total and free-proton concentration become similar proton uptake is not an important percentage compared to the amount of protons added to the system). Because the site density... 

It is possible to identify particular spectral features in the modulated reflectivity spectra to band structure features. For example, in a direct band gap the joint density of states must resemble that of critical point. One of the first applications of the empirical pseudopotential method was to calculate reflectivity spectra for a given energy band. Differences between the calculated and measured reflectivity spectra could be assigned to errors in the energy band... 

Accuracy Square-edged orifices and venturi tubes have been so extensively studied and standardized that reproducibihties within 1 to 2 percent can be expected between standard meters when new and clean. This is therefore the order of reliabihty to be had, if one assumes (1) accurate measurement of meter differenfial, (2) selection of the coefficient of discharge from recommended published literature, (3) accurate knowledge of fluid density, (4) accurate measurement of critical meter dimensions, (5) smooth upstream face of orifice, and (6) proper location of the meter with respect to other flow-disturbing elements in the system. Care must also be taken to avoid even sh t corrosion or fouliug during use. 

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