Adaptation, on-line

Bamberger, W. Hermann, R. Adaptive on-line steady-state optimization of slow dynamic processes. Automatica 1978, 14, 223-230. 

Ryhiner, G., Dunn, I.J., Heinzle, E., Rohani, S., 1992. Adaptive on-line optimal control of bioreactors apphcation to anaerobic degradation. Journal of Biotechnology 22, 89—106. 

Overall, use of learning systems has two main advantages. First, the construction cost may be lower, certainly if the system is not construeted from scratch but uses existing software tools and components. Second, a learning system is able to adapt to changing conditions, though not always on-line. 

A wide variety of particle size measurement methods have evolved to meet the almost endless variabiUty of iadustrial needs. For iastance, distinct technologies are requited if in situ analysis is requited, as opposed to sampling and performing the measurement at a later time and/or in a different location. In certain cases, it is necessary to perform the measurement in real time, such as in an on-line appHcation when size information is used for process control (qv), and in other cases, analysis following the completion of the finished product is satisfactory. Some methods rapidly count and measure particles individually other methods measure numerous particles simultaneously. Some methods have been developed or adapted to measure the size distribution of dry or airborne particles, or particles dispersed inhquids. 

Figure 15.1 Separation of pesticides from butter by using LC-GC-ECD. Peak identification is as follows 1, HCB 2, lindane 5, aldrin 7, o,p -DDE 10, endrin 11, o,p -DDT 13, p,p -DDT peaks 3, 4, 6, 8, 9, 12, 14, 15 and 16 were not identified. Adapted from Journal of High Resolution Chromatography, 13, R. Barcarolo, Coupled EC-GC a new method for the on-line analysis of organchlorine pesticide residues in fat , pp. 465-469, 1990, with permission from Wiley-VCH.

LC-GC, therefore, shows promise for forensic science applications, reducing sample handling and preparation steps by essentially using an on-line LC column in place of one or more extraction steps. This is followed by a traditional high resolution GC analysis. The methods described here for pesticides and hormones could be readily adapted to a variety of analyses, especially those involving fatty matrices. Such as tissues, food or blood. 

Figure 15.14 Separation of explosives exnacted from water by using SPE-SFE-GC at several SEE trapping temperatures, peak identification is as follows NG, nitroglycerin 2,6-DNT, 2,6-dinitrotoluene 2,4-DNT, 2,4-dinitrotoluene TNT, triniti otoluene IS, 1,3-tiichloroben-zene. Adapted Journal of High Resolution Chromatography, 16, G. C. Slack et al., Coupled solid phase extraction supercritical fluid extraction-on-line gas cliromatography of explosives from water , pp. 473-478, 1993, with permission from Wiley-VCH.

The space-frequency localization of wavelets has lead other researchers as well (Pati, 1992 Zhang and Benveniste, 1992) in considering their use in a NN scheme. In their schemes, however, the determination of the network involves the solution of complicated optimization problem where not only the coefficients but also the wavelet scales and positions in the input space are unknown. Such an approach evidently defies the on-line character of the learning problem and renders any structural adaptation procedure impractical. In that case, those networks suffer from all the deficiencies of NNs for which the network structure is a static decision. 

The simplest fluorescence measurement is that of intensity of emission, and most on-line detectors are restricted to this capability. Fluorescence, however, has been used to measure a number of molecular properties. Shifts in the fluorescence spectrum may indicate changes in the hydrophobicity of the fluorophore environment. The lifetime of a fluorescent state is often related to the mobility of the fluorophore. If a polarized light source is used, the emitted light may retain some degree of polarization. If the molecular rotation is far faster than the lifetime of the excited state, all polarization will be lost. If rotation is slow, however, some polarization may be retained. The polarization can be related to the rate of macromolecular tumbling, which, in turn, is related to the molecular size. Time-resolved and polarized fluorescence detectors require special excitation systems and highly sensitive detection systems and have not been commonly adapted for on-line use. 

The on-line viscosimeters currently available are adaptations of the classical dilute solution capillary viscosimeters. They work on the principle of measuring the pressure drop across a capillary with a differential pressure transducer. The pressure drop can be related to the reduced or inherent viscosity of the sample via Poiseuille s law.84 Intrinsic viscosity is determined using the equation ... 

Perhaps the most revolutionary development has been the application of on-line mass spectroscopic detection for compositional analysis. Polymer composition can be inferred from column retention time or from viscometric and other indirect detection methods, but mass spectroscopy has reduced much of the ambiguity associated with that process. Quantitation of end groups and of co-polymer composition can now be accomplished directly through mass spectroscopy. Mass spectroscopy is particularly well suited as an on-line GPC technique, since common GPC solvents interfere with other on-line detectors, including UV-VIS absorbance, nuclear magnetic resonance and infrared spectroscopic detectors. By contrast, common GPC solvents are readily adaptable to mass spectroscopic interfaces. No detection technique offers a combination of universality of analyte detection, specificity of information, and ease of use comparable to that of mass spectroscopy. 

We thank K. Eichhom for providing the source code of DIF4, Th. Kracht for help with the adaptation of the software to SPECTRA ON LINE, and H.-G. Krane for providing the cuprite sample. 

Image analysis is an important aspect of many areas of science and engineering, and imaging will play an important role in characterizing self-assembled structures as well as in on-line process control. Development of effective noise identification and suppression, contrast enhancements, visualization, pattern recognition, and correlation algorithms should be co-opted where possible and adapted to the analysis of self-assembled structures. 

Feedback provided by on-line monitoring of self-assembling processes will play an increasingly important role in controlling the microscopic and macroscopic architecture of molecular assemblies. Successful adaptation of char-... 

On-line Representativity Fouling Availability Good positioning of sensor Anti-fouling devices Adapted service Double sensing preferable... 

Neilen et al. [502] coupled an SFE system with a GC-ECD for on-line determination of PCBs which had been trapped onto solid adsorbents such as Tenax. Their application was primarily to determine organic compounds in the atmosphere, but such a system could be adapted to trap a cleaned-up extract from biological tissue prior to analysis by GC-ECD or MS. 

Adaptive control has been an active area of research for many years. The fullblown ideal adaptive controller continuously identifies (on-line) the parameters of the process as they change, and retunes the controller appropriately. Unfortunately, this on-line adaptation is fairly complex and has some pitfalls that can lead to poor performance. Also, it takes considerable time for the on-line identification to be achieved, which means that the plant may have already changed to a different condition. These are some of the reasons why on-line adaptive controllers are mot widely used in the chemical industry. 

However, the main reason for the lack of wide application of on-line adaptive control is the lack of economic incentive. On-line identification is rarely required because it is usually possible to predict with off-line tests how the controller must be retuned as conditions vary. The dynamics of the process are determined at different operating conditions, and appropriate controller settings are determined for all the different conditions. Then, when the process moves from one operating region to another, the controller settings are automatically changed. This is called openloop-adaptive control or atn scheduling. 

The one notable case where on-line adaptive control has been widely used is in pH control. The wide variations in titration curves as changes in buffering occur makes pH control ideal for on-line adaptive control methods. 

Several instrument vendors have developed commercial on-line adaptive controllers. Difficulties have been reported in two situations. First, when they are applied in a multivariable environment, the interaction among control loops can cause the adaptation to fail. Second, when few disturbances are occurring, the adaptive controller has little to work with and its performance may degrade drastically. 

G. Bastin and D. Dochain. On-Line Estimation and Adaptive Control of Bioreactors. Elsevier, Amsterdam, 1990. 

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