Non-linear detector

ELSD Quasi-universal No dependence on eluent conditions Droplet size control Moderate sensitivity (low ng) Compound-dependent and non-linear detector response [31,51-53]... 

In the analysis of binary copolymers or polymer blends two different concentration detectors can be used. Typically, a combination of UV and RI detection is used, but other detector combinations have also been described. If the components of the copolymer have different UV-spectra, a diode-array detector will be the instrument of choice. One has, however, to keep in mind that non-linear detector response may also occur with UV detection. 

A non-linear detector response can be caused by direct transfer to the ground state (quenching) due to intermolecular collisions with co-eluting compounds or by phosphorescence. 

Although Equations 22 and 23 are written entirely in terms of physically real quantities, none of them are in fact directly observed experimentally. No matter what the details of the experimental apparatus used to observe the transient phenomena, all eventually observe the current generated by some sort of non-linear detector element. That current (in the square law regime) is proportional to the square of the total electric field incident on the detector, averaged over all times faster than the response time of the detector. It is therefore necessary to calculate the electric field produced at the end of the sample cell due to the polarization of the sample. 

One of the challenges in designing a wideband MIMO system is tremendous processing requirements at the receiver. MIMO symbol detection involves detecting symbol from a complex signal at the receiver. This detection process is considerably complex as compared to single antenna system. Several MIMO detection techniques have been proposed [8], These detection techniques can be broadly divided into linear and non-linear detection methods. Linear methods offer low complexity with degraded BER performance as compared to non-linear methods. This paper focuses on non-linear detectors and makes an effort to improve BER performance at the cost of complexity and vice versa. ML and V-BLAST detectors [9],[10] are well known non-linear MIMO detection methods. ML outperforms VBLAST in BER performance, while VBLAST is lesser complex than ML. In [11],[12] a performance complexity trade off between the two methods have been reported. 

The most connnonly used detector in EPR is a semiconducting silicon crystal in contact with a tungsten wire, which acts as an MW rectifier. At microwatt powers, crystal detectors are typically non-linear and render a... 

It is seen that, for a truly linear detector, the response index (a) will be unity and the experimentally determined value of (a) will be an accurate measure of the proximity of the response to strict linearity. It is also clear that (a) could be used to correct for any non-linearity that might occur in the detector and thus improve the accuracy of an analysis. 

It is seen that errors in the smaller component can be as great as 12.5% (1.25% absolute) when the response index is 0.94. Yet on examining the curve for a response index of 0.94 in figure 2 the non-linearity is scarcely apparent. When the response index is 1.05 the error is 9.5% (0.95% absolute) and again the poor linearity is not obvious in figure 2. As already stated, to obtain accurate results without employing a correction factor, the response index should lie between 0.98 and 1.02. Most LC detectors can be designed to meet this linearity criteria. 

The analogue system simply corrects for the non-linearity of the source and detector. The reflectance analogue system, given as 7.8.29. on the next page. 

In order to apply RBL or GRAFA successfully some attention has to be paid to the quality of the data. Like any other multivariate technique, the results obtained by RBL and GRAFA are affected by non-linearity of the data and heteroscedast-icity of the noise. By both phenomena the rank of the data matrix is higher than the number of species present in the sample. This has been demonstrated on the PCA results obtained for an anthracene standard solution eluted and detected by three different brands of diode array detectors [37]. In all three cases significant second eigenvalues were obtained and structure is seen in the second principal component. 

Faraday collector, simultaneously with U, U and U during the first sequence. This shortens the analysis routine, consuming less sample. Ion beam intensities are typically larger in MC-ICPMS than in TIMS due to the ease with which signal size can be increased by introducing a more concentrated solution. While this yields more precise data, non-linearity of the low-level detector response and uncertainties in its dead-time correction become more important for larger beam intensities, and must be carefully monitored (Cheng et al. 2000 Richter et al. 2001). 

The ELSD is not plagued with the problem of baseline shift and is significantly more sensitive however it presents other disadvantages, such as the strong non-linearity of the detector response and the possibility of interference from non-volatile compounds in the sample matrix [87]. The HPLC method using traditionally reversed-phase solvents and a hybrid column/pre-column has demonstrated the separation of ethoxylated homologues of broadly distributed linear AEOs... 

The simulated curve in Figure 5.6(a) shows the result of using these parameters in the simulation. The simulated data have been normalised to 150000 cps in the substrate peak, to allow for detector non-linearity. It is immediately clear that the layer peak is not in the correct position, and this arises... 

LA. Buryakov, Yu. N. Kolomiets and V.B. Louppou, Ion non-linear drift spectrometer (INLDS) — a selective detector for high-speed gas chromatography. International Journal for Ion Mobility Spectrometry 4(1) (2001) 13-15. 

Figure 4 shows calibration curves measured as the peak absorbance at 235 nm. This shows good linearity and high sensitivity for all substances. The detection limit is well below 10 ng for all substances and thus competes favourably with flame ionization detector - GC. The retention times were also measured at all concentrations since it was suspected, due to the apparent tailing, that the chromatography might be non-linear. This did not prove to be so. 

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