Calibration indirect

Intensified metabolic control, especially in case of diabetes, demands minimal-invasive or non-invasive methods of analytical measurement. For this goal, a method has been developed to measure the blood glucose content in vivo, in direct contact with the skin, by means of diffuse reflection near infrared (NIR) spectroscopy on the basis of multivariate calibration and neural networks (Muller et al. [1997] Fischbacher et al. [1997] Danzer et al. [1998]). Because no patients with any standard blood glucose value are available in principle, a method of indirect calibration has... 

Fig. 6.14. Indirect calibration of NIR measurements vs BGA measurements for several test persons...

Direct calibration can be applied when the calibration coefficients are known, otherwise - in case of indirect calibration - the calibration coefficients are computed by means of experimentally estimated spectra-concentrations relations. 

The prediction of analytical values X according to the classical indirect calibration model follows Eq. (6.75) ... 

The classical direct or indirect calibration is carried out by OLS minimization according to Gauss. Error-free analytical values x are assumed or at... 

For the application of indirect calibration methods, one should have several samples available with known constitution. These samples should be of exactly the same type as the unknown sample. For example for the determination of the fat, water and protein content in wheat by near infrared reflectance spectrometry, one should have available a number of wheat flour samples of which the amount of fat, water and protein is known, or determined by a conventional method. 

The absolute velocity imparted to the drive shaft can be determined either directly or indirectly (30, 32, 87, 88). In the latter technique, the spectrum of a compound with well-established Mossbauer parameters is collected, and to the positions in the spectrum where resonances appear, specific absolute velocities can be assigned. The velocities at other positions in the spectrum are then inferred by interpolation between these known velocities. This indirect calibration is then used in the interpretation of other spectra obtained with the same drive unit. Unfortunately, compounds with well-established Mossbauer parameters may not be available for the Mossbauer isotope of interest. For 57Fe, however, this is not a problem, and metallic iron foils and sodium nitroprusside are often used for calibration purposes. Thus, the 57Fe resonance may be used to calibrate the drive unit, and this unit can then be used to study other Mossbauer isotopes if the drive unit is operated under identical conditions. 

In indirect calibration there is inevitably some loss of accuracy in using a separate bulb, but there is also the opportunity to use a glass bulb which can be properly cleaned. Any gas bubbles can be seen and withdrawn, and also there are no inaccessible regions in the vicinity of metal fittings and valves. 

Fig. 13. Pulse sequences for indirect pulse calibration (a) 90° pulses, (b) 180° pulses, (c) modified sequence for indirect calibration of 90° pulses on spin-1 nuclei."...

Figure 3.53. Indirect calibration of the proton pulse width with carbon observation using the sequence of Fig. 3.52. As the proton pulse width increases the carbon signal diminishes until it disappears at the H(90°) condition. Going beyond this causes the signal to reappear but with inverted phase (the same phase correction is used for all spectra). The sample is C-labelled methanoic acid in D2O.

The pulse calibration on the decoupler channel cannot be performed using the direct method since the pulse which is to be calibrated is transmitted on a different rf channel and resonance frequency to the observed nucleus. To calibrate the rf pulse on the decoupler channel it is necessary to determine the pulse length from the effect the pulse has on the nucleus observed on the transmitter/receiver channel. This indirect calibration is achieved by using a coupled IS spin system and transferring the detectable antiphase... 

Semiempirical (with some physical basis), based on isothermal heat treatments and indirect calibration via hardness measurement and able to predict hardness profiles across welds... 

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