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- Gudmundson, Peter
(författare)
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On The Accuracy Of The Harmonic-Balance Method Concerning Vibrations Of Beams With Nonlinear Supports.
- 1989
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Ingår i: Archive of applied mechanics (1991). - 0939-1533 .- 1432-0681. ; 59:5, s. 333-344
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Tidskriftsartikel (refereegranskat)abstract
- A homogeneous beam supported by a nonlinear cubic rotational spring and excited by a prescribed harmonic translational motion was analysed by the harmonic balance method. Harmonic and subharmonicsolutions were determined as functions of frequency, excitation amplitude and material damping.The results were verified against numerical time integrations of the governing nonlinear differential equations.The numerical method was based on a component mode synthesis technique, using free normal modes and inertia relief attachment modes. It was found that the predictions by the harmonic balance method werein excellent agreement with the numerical solution in a frequency interval covering the three first cantileveredeigen frequencies of the beam. The only exceptions were two narrow frequency intervals in which the numerical solution showed quasi periodic oscillations.
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- Bendix, Tom, et al.
(författare)
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An evaluation of a tiltable office chair with respect to seat height, backrest position and task
- 1986
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Ingår i: European Journal of Applied Physiology and Occupational Physiology. - : Springer Science and Business Media LLC. - 0301-5548 .- 1432-1025 .- 1439-6327. ; 55:1, s. 30-36
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Tidskriftsartikel (refereegranskat)abstract
- The amount of spontaneous movement during seated office work was estimated by analysing the tilting movements of a tiltable office chair. Both movement frequency and amplitude range were considered. The seat inclinations and subjective acceptability were also recorded.The seat was moved more frequently and with a greater range when adjusted 6 cm above popliteal level compared to 1 cm below, or when the backrest was pushed anteriorly or posteriorly compared to a middle position. The greatest acceptability occurred with the highest seat adjustment and the backrest in the middle position. Typing or desk-work influenced movement to a similar extent.
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- Burström, Lage, et al.
(författare)
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Mechanical energy absorption in human hand-arm exposed to sinusoidal vibration
- 1988
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Ingår i: International Archives of Occupational and Environmental Health. - 0340-0131 .- 1432-1246. ; 61:3, s. 213-216
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Tidskriftsartikel (refereegranskat)abstract
- A possible basis for risk assessment of human exposure to vibration when using hand-held tools may be to determine the amount of mechanical energy that is absorbed by the hand-arm system. The aim of this investigation was to study the absorption of mechanical energy in the human hand-arm system during exposure to sinusoidal vibration within the frequency range of 20 to 1500 Hz. A handle, specially designed for this type of experiments, was used during the measurements. The influence of various experimental conditions, such as three different hand-arm postures, grip force (25–75 N) and vibration levels (27–53 mm/srms), were studied on eight subjects. The outcome clearly shows that the energy absorption properties of the human hand-arm system are more or less dependent on all of the experimental conditions studied, but mainly to the frequency of the vibration stimuli. Furthermore, the results indicate a non-linear relationship between the energy absorbed and all other variables studies.
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- Larsson, Karin M., et al.
(författare)
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Activity and stability of horse‐liver alcohol dehydrogenase in sodium dioctylsulfosuccinate/cyclohexane reverse micelles
- 1987
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Ingår i: European Journal of Biochemistry. - : Wiley. - 0014-2956 .- 1432-1033. ; 166:1, s. 157-161
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Tidskriftsartikel (refereegranskat)abstract
- Horse liver alcohol dehydrogenase (EC 1.1.1.1) solubilized in sodium dioctylsulfosuccinate (AOT)/cyclohexane reverse micelles was used for the oxidation of ethanol and reduction of cyclohexanone in a coupled substrate/coenzyme recycling system. The activity of the enzyme was studied as a function of pH and water content. The enzyme was optimally active in microemulsions prepared with buffer of pH around 8. An increase in enzymatic activity was observed as a function of increasing water content. The Km values for the substrates were calculated based on the total reaction volume. The apparent Km for ethanol in reverse micelles was about eight times lower as compared to that in buffer solution, whereas the Km for cyclohexanone was almost unaltered. Storage and operational stability were investigated. It was found that the specific activity of the alcohol dehydrogenase operating in reverse micellar solution was good for at least two weeks. The steroid eticholan‐3ß‐ol‐17‐one was also used as a substrate. In this case the reaction rate was approximately five times higher in a reverse micellar solution than in buffer.
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- Pettersson, Gösta, et al.
(författare)
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A rapid‐equilibrium model for the control of the Calvin photosynthesis cycle by cytosolic orthophosphate
- 1987
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Ingår i: European Journal of Biochemistry. - : Wiley. - 0014-2956 .- 1432-1033. ; 169:2, s. 423-429
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Tidskriftsartikel (refereegranskat)abstract
- A simple model based on rapid‐equilibrium assumptions is derived which relates the steady‐state activity of the Calvin cycle for photosynthetic carbohydrate formation in C3 plants to the kinetic properties of a single cycle enzyme (fructose bisphosphatase) and of the phosphate translocator which accounts for the export of photosynthate from the chloroplast. Depending on the kinetic interplay of these two catalysts, the model system may exhibit a single or two distinct modes of steady‐state operation, or may be unable to reach a steady state. The predictions of the model are analysed with regard to the effect of external orthophosphate on the steady‐state rate of photosynthesis in isolated chloroplasts under conditions of saturating light and CO2. Due to the possible existence of two distinct steady states, the model may account for the stimulatory as well as the inhibitory effects of external phosphate observed in experiments with intact chloroplasts. Stability arguments indicate, however, that only the steady‐state case corresponding to phosphate inhibition of the rate of photosynthesis could be of physiological interest. It is concluded that chloroplasts under physiological conditions most likely operate in a high‐velocity steady state characterized by a negative Calvin cycle flux control coefficient for the phosphate translocator. This means that any factor enhancing the export capacity of the phosphate translocator can be anticipated to decrease the actual steady‐state rate of photosynthate export due to a decreased steady‐state rate of cyelic photosynthate production.
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