| 1. |
- Cedersund, G, 1978-
(författare)
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Elimination of the initial value parameters when identifying a system close to a Hopf bifurcation.
- 2006
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Ingår i: IEE Proceedings - Systems Biology. - : Institution of Engineering and Technology (IET). - 1741-2471 .- 1741-248X. ; 153:6, s. 448-456
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Tidskriftsartikel (refereegranskat)abstract
- One of the biggest problems when performing system identification of biological systems is that it is seldom possible to measure more than a small fraction of the total number of variables. If that is the case, the initial state, from where the simulation should start, has to be estimated along with the kinetic parameters appearing in the rate expressions. This is often done by introducing extra parameters, describing the initial state, and one way to eliminate them is by starting in a steady state. We report a generalisation of this approach to all systems starting on the centre manifold, close to a Hopf bifurcation. There exist biochemical systems where such data have already been collected, for example, of glycolysis in yeast. The initial value parameters are solved for in an optimisation sub-problem, for each step in the estimation of the other parameters. For systems starting in stationary oscillations, the sub-problem is solved in a straight-forward manner, without integration of the differential equations, and without the problem of local minima. This is possible because of a combination of a centre manifold and normal form reduction, which reveals the special structure of the Hopf bifurcation. The advantage of the method is demonstrated on the Brusselator.
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| 2. |
- Danø, Sune, et al.
(författare)
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Reduction of a biochemical model with preservation of its basic dynamic properties.
- 2006
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Ingår i: The FEBS Journal. - : Wiley. - 1742-464X .- 1742-4658. ; 273:21, s. 4862-4877
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Tidskriftsartikel (refereegranskat)abstract
- The complexity of full-scale metabolic models is a major obstacle for their effective use in computational systems biology. The aim of model reduction is to circumvent this problem by eliminating parts of a model that are unimportant for the properties of interest. The choice of reduction method is influenced both by the type of model complexity and by the objective of the reduction; therefore, no single method is superior in all cases. In this study we present a comparative study of two different methods applied to a 20D model of yeast glycolytic oscillations. Our objective is to obtain biochemically meaningful reduced models, which reproduce the dynamic properties of the 20D model. The first method uses lumping and subsequent constrained parameter optimization. The second method is a novel approach that eliminates variables not essential for the dynamics. The applications of the two methods result in models of eight (lumping), six (elimination) and three (lumping followed by elimination) dimensions. All models have similar dynamic properties and pin-point the same interactions as being crucial for generation of the oscillations. The advantage of the novel method is that it is algorithmic, and does not require input in the form of biochemical knowledge. The lumping approach, however, is better at preserving biochemical properties, as we show through extensive analyses of the models.
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| 3. |
- Shildrick, Margrit, 1949-, et al.
(författare)
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Troubling dimensions of heart transplantation
- 2009
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Ingår i: Medical Humanities. - : B M J Group. - 1468-215X .- 1473-4265. ; 35:1, s. 35-38
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Tidskriftsartikel (refereegranskat)abstract
- Heart transplantation is now the accepted therapy for end-stage heart failure that is resistant to medical treatment. Families of deceased donors routinely are urged to view the heart as a "gift of life" that will enable the donor to live on by extending and sustaining the life of a stranger. In contrast, heart recipients are encouraged to view the organ mechanistically--as a new pump that was rendered a spare, reusable part when a generous stranger died. Psychosocial and psychoanalytic research, anecdotal evidence and first-person accounts indicate that after transplant, many recipients experience unexpected changes or distress that cannot be understood adequately using biomedical explanatory models alone. In this paper it is argued that phenomenological philosophy offers a promising way to frame an ongoing empirical study that asks recipients to reflect on what it is like to incorporate the heart of another person. Merleau-Ponty and others have posited that any change to the body inevitably transforms the self. Hence, it is argued in this paper that replacing failing hearts with functioning hearts from deceased persons must be considered much more than a complex technical procedure. Acknowledging the disturbances to embodiment and personal identity associated with transplantation may explain adverse outcomes that heretofore have been inexplicable. Ultimately, a phenomenological understanding could lead to improvements in the consent process, preoperative teaching and follow-up care.
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| 4. |
- Yang, Geng, et al.
(författare)
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An ASIC Solution for Intelligent Electrodes and Active-cable Used in a Wearable ECG Monitoring System
- 2009
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Ingår i: BIODEVICES 2009 - Proceedings of the 2nd International Conference on Biomedical Electronics and Devices. - 9789898111647 ; , s. 209-213
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Konferensbidrag (refereegranskat)abstract
- This paper describes a digital CMOS Application Specific Integrated Circuit (ASIC) solution with the complete data acquisition and transmission for the use in a wearable electrocardiography (ECG) monitoring system. The main particularity of this system is related to the proposed reconfigurable microchip architecture for an intelligent electrode. The chip area is 2.3 mm(2) in a standard 0.18 mu m CMOS technology. The chip is operating at 24 MHz system clock with 3.3 V power supply for I/O cells and 1.8 V for the core circuit respectively. The estimated dynamic power dissipation is only 857 mu W. The post-layout simulation results show that the microchip embedded inside an intelligent electrode features ultra low power consumption and is quite feasible for a hand-held Personal Health Assistant (PHA) which uses a battery as energy source.
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