| 1. |
- Axelsson, Jan Peter, et al.
(författare)
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Substrate Control of Biotechnical Fedbatch Processes. Robustness and the Role of Adaptivity
- 1990
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Konferensbidrag (refereegranskat)abstract
- Results from experiments on laboratory scale fedbatch processes are presented as well as analysis and design of the control system. The main reason for control is to track the drastic growth in feed demand during a cultivation. Variations in the amount and quality of the inocculum makes precalculated dosage schemes of limited value to obtain reproducible cultivation conditions. Two processes have been studied on a laboratory scale, production of bakers' yeast, and production of the enzyme salicylate hydroxylase using a strain of bacteria. Direct measurement was used to monitor the feed demand. A regulator structure is proposed based on an observer for the exponentially growing feed demand. It can be viewed as a modified PID regulator around a dosage scheme, but it is less sensitive to errors in the dosage scheme than conventional PID control. The a priori knowledge of the feed profile is further relaxed by introduction of adaptation of the growth rate parameter. The obtained non-linear control system has a simple structure and stability is garanteed for a wide range of initial values using the technique of Liapunov function. The linearized system is analysed in the frequency domain and the adaptation is shown to have negligible influence on the loop phase margin. The adaptive regulator is tested in simulation against real feed profiles and shows good results.
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| 2. |
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| 3. |
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| 4. |
- Holst, Olle, et al.
(författare)
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Substrate Control in Fed-Batch Cultivations Using a Model-Based Modification of a PI-Controller
- 1992
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Ingår i: Proceedings of the 2nd IFAC Symposium on Modelling and Control of Biotechnical Processes.
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Konferensbidrag (refereegranskat)abstract
- A fedbatch process shows exponential growth under ideal conditions. To obtain good substrate concentration control it is necessary that the regulator can track an exponentially growing feed demand, and standard PI-control has to be supplemented with an estimated basic dosage to get reasonable control. However, an exponentially growing concentration error is impossible to avoid. An I-term could be interpreted as an observer of a constant demand, and we have proposed to replace it with a model-based observer for an exponentially growing demand. In the resulting controller the integrator is replaced by an unstable pole at s = μ, the specific growth rate, and the initial condition of this term is equivalent to the basic dosage part. The regulator can now track the exponentially growing feed demand without error. Pseudomonas cepacia was grown on salicylate as sole carbon and energy source. Salicylate is a toxic substrate, so it is important to have good substrate control. On-line measurement of salicylate concentration was carried out using a filtration system from which cell-free permeate was passed to a flow-through spectrophotometer. Introducing more instability into the controller requires attention to the anti-windup features. No such problems were found during the cultivations or in simulations of the effect of conceivable disturbances like pump-failure, air-bubbles in the spectrofotometer, and low oxygen concentration induced growth-rate reduction.
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| 5. |
- Bowman, Lawrence E., et al.
(författare)
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A single photon timing instrument that covers a broad temporal range in the reversed timing configuration
- 1993
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 64:2, s. 338-341
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Tidskriftsartikel (refereegranskat)abstract
- A versatile single-photon timing instrument based on the reversed timing configuration has been constructed. Unlike similar instruments, the apparatus described here is capable of recording a broad range of excited-state decay times owing to a switched fiber optic delay. This allows the user to readily collect time-resolved luminescence data over a variable time window in the reversed-timing configuration. With proper adjustment of the appropriate components, one can acquire a luminescence decay over a variable time range from less than 1 ns to nearly 1 μs. The full width at half-maximum of the instrument response function is 42 ps. The utility of a switched fiber optic delay is discussed and the device's construction is described.
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| 6. |
- Cerreta, M.K., et al.
(författare)
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Contact nuclei formation in aqueous dextrose solutions
- 1990
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 102:4, s. 869-876
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Tidskriftsartikel (refereegranskat)abstract
- A laser Raman microprobe was used in situ to observe the growth of alpha dextrose monohydrate on alpha anhydrous dextrose crystals. The Raman spectra indicate growth of the monohydrate below 28.1°C, but the presence of only the anhydrous form above 40.5°C. Contact nucleation experiments with parent anhydrous crystals yielded only monohydrate nuclei below 28.1°C, while contacts in solutions between 34.5 and 41.0°C produced both crystalline forms, and contacts in solutions above 43.5°C produced only anhydrous nuclei. The inability of the monohydrate to grow on anhydrous crystals in the same solution that forms the two crystalline phases with a single contact precludes a simple attrition mechanism of nuclei formation. For the same reason, the hypothetical mechanism involving parent crystal stabilization of pre-crystalline clusters, allowing the clusters to grow into nuclei, is also contradicted. A third, mechanism, which may be a combination of the two, is believed to apply.
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| 7. |
- Chakraborty, Reena, et al.
(författare)
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Steady state fluorescence spectroscopy of pyranine as a trace extrinsic probe to study structure in aqueous sugar solutions
- 1992
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 125:1-2, s. 81-96
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Tidskriftsartikel (refereegranskat)abstract
- The steady state fluorescence behavior of pyranine has been monitored in aqueous solutions of sucrose, glucose, fructose, and lactose. In each case it is possible to use the ratio of peak intensities at 440 and 511 nm (the PIR) as an indicator of the degree of supersaturation of the sugar solutions. We observed both bulk water and water of solvation in all solutions examined, regardless of degree of sapersaturation. In each case the amounts of bulk water and water of solvation per molecule of sugar appear to be nearly equal at saturation. We did not observe any evidence of solvent exclusive clusters in any of the systems we studied
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| 8. |
- Chakraborty, Reena, et al.
(författare)
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Use of pyranine as a trace fluorescent probe to study structure in aqueous sucrose solutions
- 1991
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Ingår i: Particle design via crystallization. - Washington, DC : American Institute of Chemical Engineers. - 0816905533 ; , s. 114-123
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Konferensbidrag (refereegranskat)abstract
- Emission spectroscopy using pyranine as a trace fluorescent probe was evaluated as a means of studying solution structure in aqueous sucrose solutions. Spectra of pyranine doped sucrose solutions of 0-70 wt% were obtained, indicating two microenvironments. The peak intensity ratio (defined as the ratio of peak intensities at 440 nm and 511 nm) was observed to be a very sensitive function of the water content in supersaturated solutions. The two microenvironments were designated as bulk water and that near the solvated sucrose molecules. Calculations yielded six water molecules of solvation per molecule of sucrose. This is in agreement with values in literature. The number of molecules of water per molecule of sucrose in the bulk water environment varies exponentially from 165 in a 10% solution to three for a 70% solution at 20 degrees C. These results indicate that this technique can be used successfully to measure water content in supersaturated solutions.
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| 9. |
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| 10. |
- Dunuwila, Dilum D., et al.
(författare)
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An investigation of the applicability of attenuated total reflection infrared spectroscopy for measurement of solubility and supersaturation of aqueous citric acid solutions
- 1994
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 137:3-4, s. 561-568
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Tidskriftsartikel (refereegranskat)abstract
- Currently applied methods for measurement of solubility and supersaturation based on viscometry, refractometry, interferometry and density require the separation of phases prior to measurement. ATR (attenuated total reflection) infrared spectroscopy provides a unique configuration in which the infrared spectrum of a liquid phase can be obtained in a slurry without phase separation. The applicability of the technique was investigated using a micro Circle® open boat cell equipped with a ZnSe (zinc selenide) ATR rod. Experiments conducted with aqueous citric acid proved that ATR infrared spectroscopy can be successfully employed to determine solubility and supersaturation.
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