Diurial variations in leaf conductance for water vapour (g^), and in rates of net photosynthesis (P^) transpiration (P) were investigated for individual Fagus crenata, Ginkgo biloba and Alnus firma trees during the growing season (May 12, June 3, August 19 and October 22, 1992), to defme the effects of main climatic factors limiting the photosynthetíc capacity of leaves. Measurements were undertaken at 1 h intervals in fully expanded leaves from 04.00 to 20.00 under sunny day and favourable water supply. Diumal patterns of gg and P^ in F. crenata were similar to G. biloba, showing strong dependence on irradiance in the early moraing and early evening, in May, June and August. The maximum values of P^, gg and water-use eíTiciency (WLIE) were recorded at 07.00 to 08.00 when photosynthetícally active radiation (PAR) and leaf temperature (Zj) were approximately 1200 pmol m'^ s"' and below 25 °C, respectively. P^, gg and WUE decreased from 08.00 to 13.00 contínuously, followed by a slight recovery at about 17.00 and a steep dechne until darkness. A. firma remained at maximum P^ from 07.00 to 14.00, and P^, gg and E were much higher than for the other two species. The peak of E in all three species always occurred at midday, coincident with maximum PAR and highest Ty But in October, P^ and E in all three species were highest around noon, also parallel to the maximum PAR and Ty
This paper concerns a study of the lubricant film formation and behavior of a point contact under non-steady state conditions. Transient Elastohydrodynamic (EHD) lubrication, where operating parameters such as speed and load vary over time,occurs in many machine elements including cams, gears and roller bearings. Therefore, an attention in last few years was focused on behavior and formation of a lubricant film in Elastohydrodynamic lubricated (EHL) contact under non-steady state conditions. The critical running sequences of EHL contacts include e.g. starting or halting of contact surfaces and also abrupt increases or decreases of surface speed and load. These cases can cause a rupture of a lubricant film and in consequence of this action also damage of contact surfaces. This study is devoted to the experimental research of the behavior of EHD films during reversal of entrainment in reciprocating motion. Moreover influence of surface tecturing on rolling contact fatigue life of rubbing surfaces was also studied. and Obsahuje seznam literatury
The iconic “twin paradox“ illustrates the specific nature of time in Einstein’s theory of relativity. Although there is no paradox, it is not easy for teachers at secondary schools to describe convincingly that the solution is consistent and unique. We summarize the usual approaches to this “paradox of time” based on special relativity and suggest an alternative, which considers uniformly accelerated observers. By applying the principle of equivalence, such a solution leads to identical results obtained in general relativity.
Electrochromic changes of the Qy absorption bands of chromophores (dimeric and monomeric bacteriochlorophylls and bacteriopheophytins) were measured in reaction centres from purple photosynthetic bacteria Rhodobacter sphaeroides. The observed electrochromic effects could be decomposed to changes dne to negative charge on the acceptor quinone complex and positive charge on the dimer. The coiďumed additivity (superposition) of the electrochromic effects indicated that the chromophores had fixed geometry in redox transitions. The Qy absorption band of the bacteriopheophytin proved to be a very sensitive indicator of the relaxational processes of electric charges (protons and/or cations) in the vicinity of the quinones: (7) the bandwidth was affected by pH around 10 which was close to the pK of protonation of the reduced primary quinone, (2) absorption changes at 748 nm were observed after flash excitation with time constant characteristic to that of light- induced proton binding in reaction centres.
Room temperature absorbance and 77 K fluorescence measurements were ušed in order to identity Pchlide and Chlide spectral forms involved in protochlorophyllide photoreductíon in greening leaves of barley. Pchlide55o (the subscript refers to the in vivo absorbance maximum of the pigment) is the main photoactíve Pchlide throughout the first 8 h of greening. Its photoreductíon triggers a succession of Chl(ide) spectral forms that are identícal to those normally found after photoreductíon in uitírradiated leaves. Afler an actinic radiation pulse, Chlide5g4 appears within 2 s from an intermediate at shorter wavelength and is transformed to Chlide572 in less than 2 min. The time-scale of the shifts is remarkably shorter than in unirradiated leaves, which is consistent with the acceleratíon of Chl accumulatíon during greening. Pchlide63o and Pchlide64o act as precursors of Pchlide65o during its regeneration, which exhibits a marked inhibition at temperatures above 30 °C.
Stať má dvě části: po typologickém úvodu autor v prvé části zkoumá úlohu životnosti při formovaní aktivní větné perspektivy v PrelE. V druhé části se zabýva frekvencí pádových forem. Autor si je vědom rozdílu mezi první systémově-strukturní a druhou kvantitativní částí stati. Konstatuje, že v dosavadním jazykovědném bádání bývají oba přístupy nedostatečně propojeny, což má mimo jiné příčinu v dosud značně oddělovaném myšlení o langue a o parole. Následkem toho pak systémové analýzy nejsou vždy doplňovány zcela paralelními výzkumy kvantitativními. Stať podle autora ukazuje, že kvantitativní analýzy mají zásadní význam pro porovnávání jazyků. Frekvence je jeden ze základních faktorů, které prostupují i typologii gramatických kategorií. Zanedbávání soustavného kvantitativního výzkumu neprospívá ani vývojovým, ani komparatistickým výzkumným programům.