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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Diabetologia 20 (1981), S. 213-216 
    ISSN: 1432-0428
    Schlagwort(e): Streptozotocin diabetes in rat ; fetal macrosomia ; rate of substrate influx ; leucine influx ; thymidine influx ; AIB influx
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Mild diabetes (blood glucose ranging from 130 to 200 mg/100 ml) was induced in female rats by streptozotocin administration prior to mating. Fetuses obtained from these diabetic mothers on 20.5, 19.5 and 18.5 days of gestation were compared with corresponding fetuses from control mothers. Macrosomia was defined as a fetus whose body weight exceeded the mean + 2.5 SD of fetal weight obtained from the control fetal population. Similarly, the rate of substrate influx was considered abnormally high when an individual value (cpm/g tissue of radioactive tracer) exceeded mean + 2.5 SD of control value. The frequencies of macrosomia in control groups and in diabetic groups were 1/98 and 15/110 respectively, on 20.5 day of gestation, 1/155 and 14/ 148 on 19.5 day, and 0/99 and 0/98 on 18.5 day. The rates of influx of thymidine, leucine, and alphaaminoisobutyric acid from maternal side to the macrosomic fetuses were increased as much as 20 times the corresponding rates in control fetuses. Despite the lack of macrosomia as defined here in the fetal population on 18.5 day of gestation, a significantly larger proportion of litters from diabetic mothers (5 litters/5 litters) contained one or more fetuses showing abnormally high rate of thymidine influx than the litters from control mothers (0 litter/5 litters). These results suggest that only a selected few fetuses in a litter from a diabetic mother become macrosomic and a marked stimulation in the rate of metabolite influx into fetuses precedes the manifestation of macrosomia.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Nonlinear dynamics 8 (1995), S. 385-413 
    ISSN: 1573-269X
    Schlagwort(e): Parametric excitation ; nonlinear random vibration ; bifurcation and stochastic stability ; experimental testing ; on-off intermittency ; moment closures ; Monte Carlo simulation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract The stochastic bifurcation and response statistics of nonlinear modal interaction under parametric random excitation are studied analytically, numerically and experimentally. Two basic definitions of stochastic bifurcation are first introduced. These are bifurcation in distribution and bifurcation in moments. bifurcation in moments is examined for the case of a coupled oscillator subjected to parametric filtered white noise. The center frequency of the excitation is selected to be close to either twice the first mode or second mode natural frequencies or the sum of the two. The stochastic bifurcation in moments is predicted using the Fokker-Planck equation together with gaussian and non-Gaussian closures and numerically using the Monte Carlo simulation. When one mode is parametrically excited it transfers energy to the other mode due to nonlinear modal interaction. The Gaussian closure solution gives close results to those predicted numerically only in regions well remote from bifurcation points. However, bifurcation points predicted by the non-Gaussian closure are in good agreement with those estimated by numerical simulation. Depending on the excitation level, the probability density of the excited mode is strongly non-Gaussian and exhibits multi-maxima as predicted by Monte Carlo simulation. Experimental tests are carried out at relatively low excitation levels. In the neighborhood of stochastic bifurcation in mean square the measured results exhibit different regimes of response characteristics including zero motion and occasional small random motion regimes. These two regimes are characterized by the phenomenon of on-off intermittency. Both regimes overlap and thus it is difficult to locate experimentally the bifurcation point.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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