Real Time Considerations

A notorious underestimation of the dynamic properties of microbial and cellular populations results from matching the duration of the respective batch cultivations to the relevant time constant of the biosystem under investigation. However, metabolic regulation of enzyme activities and fluxes often takes place on a time scale of seconds rather than days although the latter may also be true. It is therefore in the scope of promoting biotechnological research to adopt and develop appropriate experimental concepts, methodologies and equipment [397]. 

What is fast What is slow What is relevant The relaxation time concept of Harder and Roels [148] (Fig. 28) maps typical time constants of microbial and cellular control on the level of modification of enzymes (activation, inhibition, dis/association of subunits, covalent modification or digestion) to the range of ms to s, on the level of regulation of gene expression (induction, repression or derepression of transcription) to min, on the level of population selection and evolution to days and larger units. The examples discussed below will clear up how bioengineering is facing the individual time constants. 

---

In designing a preconcentration scheme to operate in real time, consideration must be given to kinetic factors involved in the preconcentration step. In general, any preconcentration step will alter the trace metal s chemical equilibrium and will involve a time-dependent reaction or mass-transfer step. Of those species likely to be affected during preconcentration, the most thermodynamically and kinetically stable are typically the organically bound forms. Organically bound copper has been carefully studied and provides the best example. 

Dynamic behavior and live data. Many problems have a real-time aspect, including dynamic knowledge in differential equation form, such as equations of motion. Live data may be needed for the eventual deployment, and data access and real-time processing may be important. A framework which includes these real-time considerations in the expert system design is required. The framework allows simulation to provide real-time values for prototyping and development, to be supplanted by sensor-based data at installation. Data servers provide interfaces to other systems with a minimum of user work, so the prototype can become the actual application. 

The adliesion and fiision mechanisms between bilayers have also been studied with the SEA [M, 100]. Kuhl et al [17] found that solutions of short-chained polymers (PEG) could produce a short-range depletion attraction between lipid bilayers, which clearly depends on the polymer concentration (fignre Bl.20.1 It. This depletion attraction was found to mduce a membrane fusion widiin 10 minutes that was observed, in real-time, using PECO fringes. There has been considerable progress in the preparation of fluid membranes to mimic natural conditions in the SEA [ ], which promises even more exciting discoveries in biologically relevant areas. 

Data to demonstrate the stability characteristics of both the drug substance and the drug product must be collected. Studies using three different batches of both substance and product in their respective containers/packaging must be conducted. Real-time data should be collected under conditions of temperature and relative humidity in line with the recommended storage. Conditions in different world climatic zones must be taken into consideration for cases where normal environmental... 

Studies on the neutrophil also benefit from the fact that considerable work has already gone into defining fluorescent ligands (formyl peptide agonists and antagonists and C5a) and real-time methodology for analyzing the dynamics of LRG interactions (3). 

The refinement of other analytical methods, such as electrophoresis [34,36], the various techniques of optical spectroscopy [103-105], and nuclear magnetic resonance [201], is supplemented by the recent advances in real-time affinity measurements [152,202], contributing to the understanding of biomolecular reactivity. Taken together, the improvement of analytical methods will eventually allow a comprehensive characterization of the structure, topology, and properties of the nucleic acid-based supramolecular components under consideration for distinctive applications in nanobiotechnology. 

In petrochemical and bulk commodity chemical manufacture, real-time process control has been a fact of life for many years. There is considerable understanding of processes and control of process parameters is usually maintained within tight specifications to ensure statistical process control to within six sigma, or the occurrence of one defect in a million. This has been enabled through the use of real-time analytical capability that works with programmable logic circuits to make small changes to various process inputs and physical parameters as required. 

The problem with all such ideas is that they are only ideas. Before they can be tuned into real possibilities, considerable R. D. would have to be undertaken, perhaps lasting 10+ years. If successful, which of course cannot be guaranteed, commercially sized demonstration units would have to be built and operated satisfactorily before the generating industry would be Willing to take the risk of investing in these developments. All this implies that with the possible exception of the modular HTGR, it may be 20.years or more before the first commercial plants come into operation We may well have the time, but ways will have to be found to find the money. 

Despite the considerable amount of information that has been garnered from more traditional methods of study it is clearly desirable to be able to generate, spectroscopically characterize and follow the reaction kinetics of coordinatively unsaturated species in real time. Since desired timescales for reaction will typically be in the microsecond to sub-microsecond range, a system with a rapid time response will be required. Transient absorption systems employing a visible or UV probe which meet this criterion have been developed and have provided valuable information for metal carbonyl systems [14,15,27]. However, since metal carbonyls are extremely photolabile and their UV-visible absorption spectra are not very structure sensitive, the preferred choice for a spectroscopic probe is time resolved infrared spectroscopy. Unfortunately, infrared detectors are enormously less sensitive and significantly slower... 

Automatization of all stages of the analytical process is a trend that can be discerned in the development of modern analytical methods for chemical manufacture, to various extents depending on reliability and cost-benefit considerations. Among the elements of reliability one counts conformity of the accuracy and precision of the method to the specifications of the manufacturing process, stability of the analytical system and closeness to real-time analysis. The latter is a requirement for feedback into automatic process-control systems. Since the investment in equipment for automatic online analysis may be high, this is frequently replaced by monitoring a property that is easy and inexpensive to measure and correlating that property with the analyte of interest. Such compromise is usually accompanied by a collection of samples that are sent to the analytical laboratory for determination, possibly at a lower cost. 

In the real-time application of expert systems, a number of design considerations, beyond those usually considered in expert systems, become important. Execution efficiency is a prime consideration. 

As a process analytical solution, these extrinsic reactive approaches necessitate an extrinsic optode (see later discussion), an on-line sample conditioning system or an at-Une solution such as a flow injection analysis (FIA) system or other autonomous solutions. Reaction kinetics, post analysis cleanup such as rejuvenating a substrate (optode, immobilized based immunoassays, etc.) among other complexities are additional considerations for these types real-time analysis methods. ... 

For triggering behavior, the concentration at one point in time is more important than the average concentration. Therefore, in the real world, considerable deviation from time-averaging models is observed. In addition to timeaveraging models, peak concentrations of odors in turbulent systems have to be considered. Aylor (1976) estimated peak concentrations for air currents in forests. Average concentrations, as calculated by the Sutton formula, may be as low as only a few percent of maximmn (peak) concentrations. It is often the latter, however, that would trigger an animal s response. 

Internal reflection spectroscopy is widely applied for on-line process control. In this type of application, the chemical reactor is equipped with an internal reflection probe or an IRE. The goal of this type of application is the quantification of reactant and/or product concentrations to provide real-time information about the conversion within the reactor. In comparison with other analytical methods such as gas chromatography, high-pressure liquid chromatography, mass spectrometry, and NMR spectroscopy, ATR spectroscopy is considerably faster and does not require withdrawal of sample, which can be detrimental for monitoring of labile compounds and for some other applications. 

It must minimize the computer time needed to get the solutions to a given point in real time. This was purely an economic consideration. 

---