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The relative importance of environmental factors and species pool in natural regeneration processes is still intensively disputed. Is environmental filtering especially important for species with higher requirements for temperature and soil fertility? Is the seed source limitation especially pronounced among tree species with lower dispersal abilities? Trees, seedlings and saplings measurements were conducted in 600 plots of 0.05 ha distributed in a regular grid in the Tatra Mountains (elevation range 817–1797 m a.s.l.). Boosted regression trees were used to analyse the relationships between the numbers of young trees, factors acting as environmental filters and the potential seed source availability. The most important factor affecting the distribution of young trees of most species was elevation; bedrock type was the second most important factor for Acer pseudoplatanus, while potential solar radiation was important for Sorbus aucuparia. The relationship between the presence of mature trees and abundance of young ones was strong in Fagus sylvatica, moderately strong in A. pseudoplatanus, and weak in Picea abies, Abies alba and S. aucuparia. The role of environmental factors in shaping the abundance of young trees varies strongly among species, while the seed source availability is very important for large-seeded trees.

The article concerns the possibility of precise picosecond lifetime measurements by the method of the time correlated single photon counting (TCSPC). The lifetimes (τ) of S2 fluorescence of xanthione measured in different solvents have shown that it is possible to obtain τ as short as a few picoseconds. The values of τ varying from ∼5 to ∼38 ps in solvents whose refraction indices range from 1.34 to 1.50 have been proposed as picosecond standards in lifetime measurements. However, in order to obtain reliable results some conditions must be met: the effect of the absorbing and emitting impurities must be eliminated, the instrument response function (IRF) must be very stable and correctly determined, and because of a much lower time resolution of the TCSPC method relative to that of the upconversion method, the procedure of measurements and numerical analysis of results proposed in our work should be applied. In the study reported the effect of impurities was eliminated by applying high performance liquid c...

Steady-state emission properties of gossypol in acetonitrile at room temperature have been studied using a HPLC system equipped with a specially improved highly sensitive fluorescence detector (ΦF⩾10−7). The fluorescence lifetimes (τ) have been determined using a time-correlated single photon counting system. At room temperature gossypol shows weak fluorescence with the overall quantum yield of ΦF=5×10−5. On the basis of a comparison of the excitation emission spectra with the absorption spectrum and the radiative properties of gossypol, the origin of gossypol fluorescence from two tautomeric forms: aldehyde in S 1 (n, π ∗ ) (τ=300 ps ) and S 2 ( π , π ∗ ) (τ=10 ps ) and lactol in S 1 (n, π ∗ ) (τ=18 ps ) state was suggested.

The Letter discusses the mechanism and dynamics of intra- and intermolecular electronic relaxation of the S 2 state of a xanthione molecule in acetonitrile, a quenching solvent, as well as the most important properties of the S 2 -exciplex formed upon the quenching process. Despite very efficient quenching of S 2 -XT and other thiones it has not been possible so far to observe the S 2 -exciplex. Therefore transient absorption system with 120 fs resolution was successfully applied for this purpose: the S 2 -exciplex was identified for the first time, its lifetime (∼30 ps) and transient absorption spectrum were determined as well as the mechanism of its formation and decay. Moreover, the authors observed the presence of a very fast intramolecular electronic relaxation process (S 2 v >0 →S 0 ) during S 2 -state deactivation which competes with intramolecular vibrational redistribution in the S 2 -state.

Systematic studies of the fluorescence picosecond lifetimes determination by laser-excited time-correlated single-photon-counting (TCSPC) have been undertaken. The results have been used to develop methods for determining lifetimes with much smaller error and much greater reproducibility than any hitherto reported. The error in the determination of the lifetimes (±three standard deviations) can be as low as that in simulations and amounts to 0.01 FWHM of the IRF. The lifetimes determined for the second excited singlet state of xanthione in toluene (5.1±0.3 ps ) and in benzene (8.1±0.3 ps ) can be treated as reliable standards of picosecond lifetimes.

The spinal overload syndrome develops as a result of the gradual wearing away of the structural elements of the spine due to loads exceeding their endurance strength in the setting of reduced adaptability. The aim of the investigation was to study the limitation of mobility in the cervical spine and determine the effect of the spinal overload syndrome on postural equilibrium.The study enrolled 27 patients with signs of overload of the cervical spine. Postural equilibrium was measured by stabilography. Range of motion in the cervical spine was also evaluated.The investigations of spinal mobility indicate a disturbance of muscular equilibrium. Most of the patients suffered from Lewit's upper crossed syndrome. The disturbance of postural equilibrium is of functional origin.

This paper describes a new type of spectrofluorimeter, composed of a high-performance liquid chromatography (HPLC) system directly connected to a fluorescence detector and an absorption photodiode array detector, designed for studying the emission of weakly emitting species. Procedures for measurements of emission spectra (ES), emission excitation spectra (EES), and quantum yields of emission (φE) for very weakly emitting systems (ΦE ≥ 10−7) have been proposed. The original methodical solution allows verification of whether the emission observed comes solely from the compound studied (and not from its impurities) or from some photochemical or thermal process taking place during measurements. Thanks to the use of this new type of spectrofluorimeter, it is possible to establish with a high probability that the dependence of the shape and position of the ES on the excitation wavelength and the differences between EES and absorptance spectra are due to photo-physical and/or photochemical properties of the compound studied and not due to the presence of emitting impurities. An especially interesting application of this method is to study the emission of species whose very weak emission is related to a very short lifetime as well as a low radiative rate constant. It is particularly suitable to the study of the emission properties of flexible molecules that can occur in a few conformers of different absorption and emission properties. The performance of the method is illustrated by the results of the emission studies carried out for Nα-acetyl-2-(uracil-5-yl)-L-tryptophan N-ethylamide.

Praca miala na celu zbadanie dymorfizmu plciowego i zmienności rozwojowej czaszki susla perelkowanego Citellus suslicus (Guldenstaedt, 1770) w populacji ze Slawecina pod Hrubieszowem. Material stanowily 194 czaszki w tym 91 samcow i i 103 samic. Wprowadzono podzial na 2 grupy wiekowe: mlode (niedojrzale plciowo) - 134 osobniki, oraz dorosle - 60 osobnikow.