Frequency of Measurements

The data obtained from ER probes, and those provided by test coupons, are similar in giving an integrated or average rate, but the former has the advantage that the data are obtained whilst the plant is operating. The time periods can be decided by the frequency of measurement, and periods of... 

A higher-MHz NMR spectrometer is always a better choice, since the sensitivity of the experiment is proportional to the frequency of measurement. Moreover, with highly concentrated solutions, the presence of some solid particles can cause an increase in T) (FID will be short) and line broadening of the NMR signals will result. Therefore, an optimum concentration (say, 25-50 millimolar solution) is recommended. Of course, H-NMR spectra can be readily measured at much lower concentrations, though higher concentrations are necessary for recording - C-NMR spectra. 

The peaks in s j dipolar (which are usually close to the peaks in e") can be used to determine the time or point in the cure process when the mean dipolar relaxation time has attained a specific value, i = 1/co, where to = 2nf is the frequency of measurement. The dipolar mobility as measured by the mean relaxation time t can be used as a molecular probe of the buildup in Tg. The time of occurrence of a given dipolar relaxation time as measured by a peak in a particular high frequency value of e"(co) can be quantitatively related to the attainment of a specific value of the resin s glass transition temperature. 

Dielectric Properfies Fluorine substitution often results in an overall decrease in the dielectric constant. However, it can also have the opposite effect, depending on the symmetry of substitution, frequency of measurement, and temperature 12,26,27,29,31-34,51-60 later. section). 

Fig. 19. Dependence of real s and imaginary s" permittivity component on acetone concentration a for two polyacrylamide networks (O, ) - nonionized network, ( ) - ionized network numbers denote frequency of measurement. From Liptak et al. [33]...

The densitometer uses a two beam comparator technique of measurement. A single lamp illuminates, through a variable neutral density filter, the emitter of an eleven stage photomultiplier tube. Because the frequency of measurement is five times the AC line frequency and the amplifiers are extremely high gain, the lamp must be operated from a regulated DC source, otherwise, 120 Hz brightness ripple of the lamp is recorded in the data. 

The methods of remote sounding of C02 fluxes are mainly based on NDVI measurements (Burgheimer et al., 2006 Myeong et al., 2006) using various satellite technologies as well as in situ measurements with SCIAMACHY carried by satellites of the ESA series. The surface resolution of SCIAMACHY constitutes 320 km, and the frequency of measurements is 36 hours. 

Here the parameters ge, /rB, coz, /, Mh and rr were the g-factor of the free electron, the Bohr magneton, the microwave frequency of measurement, the nuclear spin quantum number, its projection, and the molecular rotational correlation time in solution. The anisotropic parameters, A g, A a and eQVj 1(21 — 1) were estimated from line width coefficients, K, K2 and K4, respectively. Thus the analysis of the temperature dependences of coefficients K, K2 and K4 gave the anisotropic parameters, A g, A a and eQV/1(21 — 1) for all molecules. On the other hand,... 

Other interesting tests may be undertaken to decide whether the empirical distribution of the measurements obtained from samples follows a certain theoretical distribution, e.g. the normal distribution. In such cases it is quite common to perform the / test of goodness of fit or the KOLMOGOROV-SMIRNOV test. Both tests are based on the evaluation of the cumulative frequency of measured data and are described in detail in [MILLER and MILLER, 1993],... 

Fig. 5.1 Photographs of relief models showing the variation of relative permittivity and dielectric loss of poly(ethyleneterephthalate) with temperature and frequency of measurement. From Reddish (1950) with permission of the Royal Society of Chemistry.

T25 to 181 C were examined by the DSA technique. Figure 2 shows the composite loss tangent response as a function of the natural logarithm of time for a cure at 147 C at several frequencies. Two tan 6 peaks are observed. At fixed temperature both peaks become smaller, shift to longer times, and exhibit Improved resolution as the frequency Is decreased. Figure 3 displays the composite loss tangent as a function of the natural logarithm of time at a fixed frequency of 3.5 Hz for cures at several temperatures. At this, the lowest frequency of measurement, the two peaks are best resolved, smallest, and occur soonest In time as the temperature is Increased. 

The power-loss meter is the most common type of dielectric moisture meter. It senses the product of the dielectric constant and loss factor. Generally, the loss factor increases with wood moisture content but may exhibit variations from this behavior depending on the frequency of measurement (JO, 11, 14). An increase in temperature produces effects similar to increasing moisture content, with interaction between these two parameters. Therefore, temperature adjustments of meter readings are complex, sometimes increasing and sometimes decreasing the scale reading as temperature increases... 

Ignore the first frequency measured The impedance measured at the first frequency of measurement is often corrupted by a startup transient. The best option is to ignore the first measured frequency when regressing models to the data. 

Rate (frequency) of measurement. The most common two frequencies at which the electrical properties are reported in standard reference tables are one kilohertz (1 kHz = 1000 Hertz) and one megahertz (1 MHz = 1000000 Hertz). 

Polymers for which the frequency of measurement of tan 8 was not provided in the sources. 

Table 9.4. Measurement frequency v in Hertz, dielectric dissipation factor tan 8 and dielectric constant e observed at room temperature at the specified frequency of measurement, and the fitted value of tan 8 calculated as described in the text, for 206 data points covering a wide variety of polymers. Most measurements were made on commercial samples containing various plasticizers, fillers and other additives, so that the (exp) values listed for many polar polymers differ significantly from (i.e., exceed) the more "intrinsic" e(exp) values listed in Table 9.1. 

In answering the question what analytical technique should I use , it must be selective for the compound of interest over the required concentration range, it must exhibit acceptable accuracy, precision and levels of sensitivity, it should be reliable, robust and easy to use, the frequency of measurement and speed of analysis must be suitable and the cost per sample should not be prohibitive. Looking at the big picture, the outlay is normally large when investing in instrumentation but in terms of the saving of time due to less labour-intensive analytical steps, in the long run such equipment usually works out to be econom. 

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