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| 2. |
- Axelsson, Björn, et al.
(författare)
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Managing by International Travelling
- 1992
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Ingår i: Managing Networks in International Business. - : Gordon & Breach, Philadelphia. ; , s. 93-109
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 3. |
- Axelsson, Jan Peter, et al.
(författare)
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Control Design for a Bilinear System. Reachable Sets and Exact Linearization
- 1990
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Konferensbidrag (refereegranskat)abstract
- A bilinear system model of a continuous tank reactor from a biotechnology application (F. Mandenius et al., 1987) is studied. The concentrations of the substrate sugar and the product ethanol were measured on-line and utilized to control the flow-rate through the fermenter. The system can be integrated analytically making it possible to describe the reachable sets. Limited controllability is found on a line in the state space. These reachable set expressions are used to obtain a time-optimal controller that for large disturbances implies reversed control action as compared to linear control. Transformations used when applying exact linearization are described. The lack of controllability, also obtained using the Lie brackets of differential geometry, shows up as singularities in the transformations.
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| 4. |
- 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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| 5. |
- Axelsson, O., et al.
(författare)
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Reactive evaporation of potassium in CO2 and the formation of bulk intermediates
- 1994
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 12:1, s. 158-160
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Tidskriftsartikel (refereegranskat)abstract
- Potassium vapor condensed in CO2 has been studied by transmission infrared spectroscopy and by total pressure thermal desorption spectroscopy. The results are compared with surface spectroscopic data for CO2 adsorbed on alkali metal overlayers. Both systems show the formation of bulk coordinated oxalate species at cryogenic temperatures and the conversion to carbonate intermediates upon annealing.
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| 6. |
- Nilsson, Christer, et al.
(författare)
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Epithelial cells purified from choroid plexus have receptors for vasoactive intestinal polypeptide
- 1991
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Ingår i: Brain Research. - 1872-6240. ; 542:2, s. 241-247
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Tidskriftsartikel (refereegranskat)abstract
- Using the choroid plexus from pig a method has been developed to purify the epithelial cells from the underlying vascularized connective tissue stroma. An epithelial cell fraction was obtained that showed a purity of at least 95%, as determined by light microscopic analysis. The epithelial cells were investigated for the presence of binding sites for the neurotransmitter peptide, vasoactive intestinal polypeptide (VIP). Suspensions of epithelial cells were found to have high affinity binding sites for 125I-labelled VIP, with maximum binding obtained after 30 min incubation at 20 degrees C with a concentration of 50 micrograms cell protein per sample. Competition experiments with displacement of [125I]VIP binding by increasing concentrations of unlabeled VIP indicated the presence of a single class of binding sites with a Kd of 3 nM and a binding capacity of 970 pmol/g cell protein. Cross-linking of [125I]VIP to epithelial cells with disuccinimido dithiobis (propionate) (DSP), followed by SDS-polyacrylamide gel electrophoresis, demonstrated binding to a single 55 kD protein. The receptor was highly specific for VIP as binding was only inhibited in the presence of high concentrations of the related peptides helodermin, growth hormone-releasing factor, secretin, and peptide histidine isoleucine. This is the first demonstration of VIP-binding to choroid plexus epithelial cells.
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| 7. |
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| 8. |
- Shao, Y., et al.
(författare)
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Identification of intermediate states following carbon dioxide adsorption on alkali-metal surfaces
- 1993
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Ingår i: Journal of Physical Chemistry. - : American Chemical Society (ACS). - 0022-3654 .- 1541-5740. ; 97:29, s. 7652-7659
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Tidskriftsartikel (refereegranskat)abstract
- Bulk polycrystalline potassium was exposed to carbon dioxide, and intermediate states were identified by comparisons between spectroscopic information and calculated data. We utilize three routes for the identification of each intermediate: (i) vibrational spectra, (ii) ionization potentials, and (iii) theoretically determined total energies. Neutral C02 adsorbs at low temperatures with limited site specificity. C02 molecules also form oxalate ions, which penetrate into the potassium overlayer. These "mineral oxalates" decompose upon annealing to bulk unidentate carbonates. Our calculated data also provide references for the identification of CO2 derivatives on surfaces promoted by thin overlayers of alkali metals.
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