Using intense ns-laser pulses up to 2 x 10** photons per cm^ per pulse the intensity dependence of fluorescence yield (O) of different photosystem 2 (PS2) subunits in spinách on the intensity of excitation pulse (/) was measured. A sti ong drop of O was observed with increasing laser pulse I. Measurements of the light-harvesting complex of PS2, LHC2, were taken at excitation wavelengths of 645-700 nm. A shift of the í) vs. I curves to lower I with increasing absorption cross section was observed. Measurements of PS2 and thylakoid membrane ífagments taken at a fixed excitation wavelength of 645 nm showed the same O V5, I dependences as LHC2. This suggests that LHC2-pigment proteins dominate the exciton concentration in the photosynthetic apparatus. A smáli drop of O measured at CP29 and CC2 particles was possibly caused by smaller domains. Smaller drop of O measured at D1D2 particles was similar to that of free chlorophyll (Chl), indicating that bimolecular annihilation was absent. Experimental results could be described using a simple two-level model including exciton-exciton-annihilation and depletion of Chl ground States. Good fits of measured O-intensity ciu-ves were possible for LHC2 with all the ušed excitation wavelengths. Outputs of these approximations are statements about excited statě concentration and time dependence of their decay as a function of excitation irradiance.
This article describes a theoretical study of non-linear fracture behavior of the Double Cantilever Beam (DCB) configuration. The fracture is analyzed using the J-integral approach. A stress-strain curve with power-law hardening is used for describing the mechanical response of the DCB. It is assumed that the material has the same properties in tension and compression. A model based on Mechanics of materials is applied to find solutions of the J-integral at different levels of the external load. The effect of the exponent of the power law on the non-linear fracture behavior is evaluated. It is found that if higher values of the exponent of the power law are used, the J-integral value increases. The analytical approach developed here is very useful for parametric investigations, since it captures by relatively simple formulae the essential of the non-linear fracture. and Obsahuje seznam literatury
Non-native species are known to escape their parasites following introduction into a new range, but they also often acquire local parasites as a function of time since establishment. We compared the parasite faunas of five non-native Ponto-Caspian gobies (Gobiidae) and local fish species (Perca fluviatilis, Gymnocephalus cernua, Gobio gobio) in three European river systems; the Rivers Rhine, Vistula and Morava, where Ponto-Caspian gobies were introduced 4-13 years prior to the study. Overall parasite species richness was considerably lower in non-native gobies compared to local fish species, and the same result was found at the component and infra-community levels. Both parasite abundance and diversity greatly varied among the regions, with the highest values found in the River Vistula (Wloclawski Reservoir), compared to a relatively impoverished parasite fauna in the River Morava (Danube basin). While only half of parasite species found in local hosts were acquired by non-native gobies, most of the parasites found in gobies were shared with local fish species related either phylogenetically (percids) or ecologically (benthic gudgeon), including the co-introduced monogenean Gyrodactylus proterorhini. As a result, similarity in parasite communities strongly reflected regional affiliation, while phylogenetic distances between fish host species did not play a significant role in parasite community composition. In accordance with other studies, all parasites acquired by gobies in their new range were generalists, all of them infecting fish at the larval/subadult stage, indicating the possible importance of gobies in the life cycle of euryxenous parasites. The absence of adult generalists, particularly ectoparasites with low host specificity, in non-native fish may reflect their generally low abundance in the environment, while an absence of adult endoparasitic generalists was probably related to other factors.
In the paper, an attempt to interpret the PSInSAR data for the northern part of the Upper Silesian Coal Basin with the use o f kernel approximation is described. The PSI nSAR technique is characterised by the Permanent Scatterer points (so-called PS points, Permanent Scatterers), which usually correspond to the objects such as : buildings, industrial and transport infrastructure, and natural components of surface relief (Ferretti et. al., 2000, 2001). The PSInSAR technique allows to monitor ground movements. A non-uniform di stribution of the PS points makes the inte rpretation of PSInSAR data difficult, as well as the fact that one point can assume both positive an d negative values. The application of the kernel approximation for the interpretation of the PSInSAR data allowed of more unambiguous interpretation., Katarzyna Mirek and Janusz Mirek., and Obsahuje bibliografické odkazy
Paper is concerned with the flexural vibrations of imperfect bladed circular disk by analytical and numerical solutions. Dsk imperfection results from additional two groups of damping heads fixed on opposite ends of one diameter, which introduces point imperfections in mass, stiffness and nonlinear damping and non-proportional distribution of damping properties. The aim of this study is to investigate influence of friction damping among added bladed heads on decrease of resonance amplitudes. Examples based on application of equivalent linearized damping show the properties of such dampers. and Obsahuje seznam literatury
After anticholinesterase treatment in vivo, depolarization of the postsynaptic muscle fibre membrane by about 4 mV develops due to non-quantally released acetylcholine from the motor nerve terminal. This conclusion was supported by experiments with the curarization of diaphragm slices from anticholinesterase treated mice during intracellular microelectrode recordings.
There are two principal mechanisms of acetylcholine (ACh) release from the resting motor nerve terminal: quantal and non-quantal (NQR); the former being only a small fraction of the total, at least at rest. In the present article we summarize basic research about the NQR that is undoubtedly an important trophic factor during endplate development and in adult neuromuscular contacts. NQR helps to eliminate the polyneural innervation of developing muscle fibers, ensures higher excitability of the adult subsynaptic membrane by surplus polarization and protects the RMP from depolarization by regulating the NO cascade and chloride transport. It shortens the endplate potentials by promoting postsynaptic receptor desensitization when AChE is inhibited during anti-AChE poisoning. In adult synapses, it can also activate the electrogenic Na+/K+-pump, change the degree of synchronization of quanta released by the nerve stimulation and affects the contractility of skeletal muscles., F. Vyskočil, A. I. Malomouzh, E. E. Nikolsky., and Obsahuje seznam literatury
The review deals with thermal dissipation of absorbed excitation energy within pigment-protein complexes of thylakoid membranes in higher plants. We focus on the de-excitation regulatory processes within photosystem 2 (PS2) that can be monitored as non-photochemical quenching of chlorophyll (Chl) a fluorescence consisting of three components known as energy-dependent quenching (qE), state-transition quenching (qT), and photoinhibitory quenching (qI). We summarize the role of thylakoid lumen pH, xanthophylls, and PS2 proteins in qE mechanism. Further, both the similarity between qE and qI and specific features of qI are described. The other routes of thermal energy dissipation are also mentioned, that is dissipation within photosystem 1 and dissipation through the triplet Chl pathway. The significance of the individual de-excitation processes in protection against photo-oxidative damage to the photosynthetic apparatus under excess photon supply is stretched. and M. Štroch, V. Špunda, I. Kurasová.