Cathodoluminescent Properties of Single Crystal Materials for Electron Microscopy

The results of measurements of cathodoluminescence efficiencies, decay characteristics and emission spectra of YAG:Ce, YAP:Ce, P47 (Y2SiO5:Ce) and CaF2:Eu single crystals at excitation by electrons with an energy of 10 keV and a current density of the order of 10-8 A cm-2 are presented. Advantages and disadvantages of the individual single crystals intended for application in electron microscopes are dealt with. Attention is paid to the photomultiplier tube (PMT) matching, degradation and afterglow of the mentioned single crystals. For YAG:Ce, the effect of the activator concentration of crystals and the effect of the cleaning and annealing of crystal plates are included. The proposal for the application of YAG:Ce as a scintillator and as an image screen in electron microscopy is given. Sizes of electron interaction areas and absorbed energy distributions are simulated by using Monte Carlo method based on the plural large angle elastic scattering. Cathodoluminescence widths of YAG:Ce single crystals for an impact electron in the energy range 10-100 keV are estimated

Five centuries of Southern Moravian drought variations revealed from living and historic tree rings

Past, present, and projected fluctuations of the hydrological cycle, associated to anthropogenic climate change, describe a pending challenge for natural ecosystems and human civilizations. Here, we compile and analyze long meteorological records from Brno, Czech Republic and nearby tree-ring measurements of living and historic firs from Southern Moravia. This unique paleoclimatic compilation together with innovative reconstruction methods and error estimates allows regional-scale May-June drought variability to be estimated back to ad 1500. Driest and wettest conditions occurred in 1653 and 1713, respectively. The ten wettest decades are evenly distributed throughout time, whereas the driest episodes occurred in the seventeenth century and from the 1840s onward. Discussion emphasizes agreement between the new reconstruction and documentary evidence, and stresses possible sources of reconstruction uncertainty including station inhomogeneity, limited frequency preservation, reduced climate sensitivity, and large-scale constraint

Varijacije tijekom sezone u izokinetičkom vršnom momentu sile kod mladih nogometaša

The aim of the study was to investigate the seasonal variation in the strength of the knee flexors and extensors in highly trained youth soccer players. The players (n=16; age 16.7±0.7) were measured at the end of the competitive season, at the beginning of the off-season and during the sixth week of a new competitive season. Isokinetic concentric peak torque was measured at 60°•s-1, 180°•s-1, 360°•s-1 in a sitting position. The testing range of motion was set from 10–90° of knee flexion. Players performed a set of six maximal repetitions for both dominant and non-dominant limb. Average values of peak torque significantly changed during the observed periods. Significant differences (p<.05) between the three measurement sessions were noted with respect to the knee flexors at all angular velocities. A post-hoc test confirmed a significant increase between the first and the second measurement for flexion in both dominant (180°•s-1; p=.033) and non-dominant legs (360°•s-1; p=.004). A significant increase was also found between the first and the third session for both limbs during knee flexion at all angular velocities. The results indicate that peak torque values of knee flexors and extensors varied differently in trained youth soccer players depending on muscle group and movement velocity with statistically significant changes in knee flexors only.Cilj je ovog istraživanja bio utvrditi varijacije tijekom sezone u snazi pregibača i opružača potkoljenice vrhunskih treniranih mladih nogometaša. Igrači (n=16; dob 16,7±0,7) su testirani na kraju natjecateljske sezone, na početku prijelaznog perioda te tijekom šestog tjedna nove natjecateljske sezone. Izokinetički koncentrični vršni moment sile mjerio se pri brzinama od 60°/s, 180°/s i 360°/s u sjedećem položaju ispitanika. Opseg pokreta se tijekom testiranja kretao od 10 do 90° fleksije koljena. Igrači su izveli seriju od šest maksimalnih ponavljanja prvo dominantnom, a onda i nedominantnom nogom. Prosječne vrijednosti vršnog momenta sile značajno su se mijenjale tijekom promatranih perioda. Značajne razlike (p<0,05) u snazi pregibača potkoljenice zabilježene su između sva tri mjerenja pri sve tri brzine izveđonja. Post hoc test je također potvrdio značajno povećanje snage pregibača potkoljenice između prvoga i drugog mjerenja za dominantnu (180°/s; p=0,033) i nedominantnu (360°/s; p=0,004) nogu. Značajno povećanje vršnog momenta sile pregibača potkoljenice obje noge pri svim brzinama također je zabilježeno između drugoga i trećeg mjerenja. Rezultati pokazuju da vršni moment sile pregibača i opružača potkoljenice različito varira kod treniranih mladih nogometaša ovisno o mišićnoj grupi i brzini pokreta, sa statističkom značajnošću promjena samo za pregibače potkoljenice

Seasonal variation in isokinetic peak torque in youth soccer players

The aim of the study was to investigate the seasonal variation in the strength of the knee flexors and\ud extensors in highly trained youth soccer players. The players (n=16; age 16.7±0.7) were measured at the end\ud of the competitive season, at the beginning of the off-season and during the sixth week of a new competitive\ud season. Isokinetic concentric peak torque was measured at 60°·s-1, 180°·s-1, 360°·s-1 in a sitting position. The\ud testing range of motion was set from 10–90° of knee flexion. Players performed a set of six maximal repetitions\ud for both the dominant and non-dominant limb. Average values of peak torque significantly changed during\ud the observed periods. Significant differences (p<.05) between the three measurement sessions were noted\ud with respect to the knee flexors at all angular velocities. A post-hoc test confirmed a significant increase\ud between the first and the second measurement for flexion in both the dominant (180°·s-1; p=.033) and nondominant\ud legs (360°·s-1; p=.004). A significant increase was also found between the first and the third session\ud for both limbs during the knee flexion at all angular velocities. The results indicate that peak torque values\ud of knee flexors and extensors varied differently in trained youth soccer players depending on muscle group and movement velocity with statistically significant changes in knee flexors only