A model with two masses is considered where the upper mass is self-excited due to the negative linear damping component and the lower mass represents the damped foundation subsystem. The passive means represents the positive linear damping of foundation subsystem and the active one the linear parametric excitation due to the periodic changing of the foundation mounts stiffness. In the case when only passive means are used the optimal tuning can be reached when stability limits for both vibration modes merge together. The condition for such tuning of the system in question is formulated. But when the stability condition is not met then this tuning of the system is not suitable for using in addition the active means in the form of parametric excitation. and Obsahuje seznam literatury
Abiotic and biotic factors determine success or failure of individual organisms, populations and species. The early life stages are often the most vulnerable to heavy mortality due to environmental conditions. The deer ked (Lipoptena cervi Linnaeus, 1758) is an invasive insect ectoparasite of cervids that spends an important period of the life cycle outside host as immobile pupa. During winter, dark-coloured pupae drop off the host onto the snow, where they are exposed to environmental temperature variation and predation as long as the new snowfall provides shelter against these mortality factors. The other possible option is to passively sink into the snow, which is aided by morphology of pupae. Here, we experimentally studied passive snow sinking capacity of pupae of L. cervi. We show that pupae have a notable passive snow sinking capacity, which is the most likely explained by pupal morphology enabling solar energy absorption and pupal weight. The present results can be used when planning future studies and when evaluating possible predation risk and overall survival of this invasive ectoparasite species in changing environmental conditions., Sirpa Kaunisto, Hannu Ylönen, Raine Kortet., and Obsahuje bibliografii
The aim of the present study was to examine the effect of prolonged passive smoking (lasting 3 weeks) on plasma catecholamine levels and reactivity of isolated rabbit arteries. Plasma noradrenaline, adrenaline and dopamine levels were determined radioenzymatically. Isolated rings of the thoracic aorta and carotid artery were suspended in organ chambers and connected to a force transducer for the recording of isometric tension. Plasma noradrenaline levels were found to be significantly elevated in rabbits subjected to passive smoking for 3 weeks. Plasma adrenaline and dopamine levels were not changed. Transmural nerve stimulation of arterial rings evoked frequency-dependent contractions. Prolonged passive smoking did not affect neurogenic contractions of the arteries tested. On the other hand, endothelium-dependent relaxations of phenylephrine-precontracted arteries were significantly impaired. Furthermore, hypertrophy of the left ventricle was observed. In conclusion, passive smoking impairs endothelium-dependent relaxations but not neurogenic contractions of systemic arteries. The impaired relaxations of arteries may be, at least in part, mediated through the degradation of released nitric oxide by superoxide anions derived from cigarette smoke., J. Török, A. Gvozdjáková, J. Kucharská, I. Balažovjech, S. Kyselá, F. Šimko, J. Gvozdják., and Obsahuje bibliografii
In this paper, the problem of passivity analysis for a class of uncertain stochastic neural networks with mixed delays and impulsive control is investigated. The mixed delays include constant delay in the leakage term, discrete and distributed delays. The discrete delays are assumed to be time-varying and belong to a given interval, which means that the lower and upper bounds of interval time-varying delays are available. By using Lyapunov stability theory, stochastic analysis, linear matrix inequality techniques and introducing some free-weighting matrices, several novel sufficient conditions are derived to guarantee the passivity of the suggested system in the sense of mean square under two cases: with known or unknown parameters. It is believed that these results are significant and useful for the design and applications of impulsive stochastic neural networks. Finally, two numerical examples are provided to show the effectiveness of the theoretical results.
A cascade scheme for passivity-based stabilization of a wide class of nonlinear systems is proposed in this paper. Starting from the definitions and basic concepts of passivity-based stabilization via feedback (which are applicable to minimum phase nonlinear systems expressed in their normal forms) a cascade stabilization scheme is proposed for minimum and non-minimum phase nonlinear systems where the constraint of stable zero dynamics imposed by previous stabilization approaches is abandoned. Simulation results of the proposed algorithm are presented to demonstrate its performance.