Vremenski razvoj intermetalnih difuznih spektara

LiZn and LiCd vapour mixtures prepared in the heat-pipe oven are irradiated with pulsed excimer laser emission at 308 nm. Temporal evolution of the fluorescence spectra is observed showing that different processes occur such as multiphoton excitation, collisional energy transfer, photochemical reaction, relaxation etc. Temporal change of the LiZn and LiCd blue-green diffuse bands spectral shape is observed and interpreted in terms of previous spectral simulations. The effective lifetimes of different spectral features are determined.Mješavine para Li-Zn i Li-Cd pripremili smo u toplovodnim pećima i obasjavali pulsnim excimerskim laserom na 308 nm. Opažanje vremenskog razvoja fluorescentnih spektara pokazalo je postojanje različitih procesa kao što je multifotonska pobuda, sudarni prijenos energije, fotokemijska reakcija, relaksacija itd. Opaženu vremensku promjenu spektralnog oblika plavo-zelenih difuznih vrpci LiZn i LiCd molekula objasnili smo pomoću ranijih svojstava spektralnih simulacija. Odredili smo efektivna vremena života različitih spektralnih pojava

Motivacija nastavnika zagrebačkih srednjih škola u primjeni e-učenja u nastavi

Cilj ovog rada jest utvrditi motivaciju nastavnika srednjih škola za primjenu e-učenja u nastavnom procesu. Pritom prvi dio rada donosi kratki teorijski pregled dva ključna pojma, a to su e-učenje i motivacija. Budući da su ti pojmovi već prilično iscrpno obrađeni - e-učenje u okviru informacijskih i komunikacijskih znanosti, a motivacija u okviru psihologije - naglasak se stavio na drugi dio rada, a to je istraživanje koje se provelo među nastavnicima srednjih škola u Zagrebu s ciljem utvrđivanja njihove osobne motivacije u primjeni e-učenja. Drugi dio rada tako donosi metodologiju istraživanja, kao i rezultate, odnosno odgovore na postavljena istraživačka pitanja. Naposljetku će se dati zaključak i uokviriti spoznaje do kojih se došlo istraživanjem

Wavelength calibration of the CI line at 94.5 nm for comparison with quasar data

With the use of an ultra-narrow-band extreme ultraviolet laser source, tunable near 94 nm, transition wavelengths are determined for lines connecting the 1s(2)2s(2)2p(2) P-3(0,1,2) ground-term levels to the 1s(2)2s2p(3) S-3(1) excited level in neutral carbon at an absolute accuracy of 4x10(-8). With the determination of the zero-velocity rest-frame wavelengths these lines can be included in an analysis of a possible temporal variation of the fine-structure constant alpha from a comparison with quasar data. A value for the C-12/C-13 transition isotope shift was also obtained yielding 0.5107(13) cm(-1), in average over the three fine-structure lines. The latter measurement will allow to study isotopic evolution in the universe and test models of nuclear processes in stars

Production and deceleration of a pulsed beam of metastable NH (a1Δa ^1\Delta) radicals

We report on the production of a pulsed molecular beam of metastable NH ($a ^1\Delta$) radicals and present first results on the Stark deceleration of the NH ($a ^1\Delta, J=2, M\Omega=-4$) radicals from 550 m/s to 330 m/s. The decelerated molecules are excited on the spin-forbidden $A ^3\Pi \leftarrow a ^1\Delta$ transition, and detected via their subsequent spontaneous fluorescence to the $X ^3\Sigma^{-}, v"=0$ ground-state. These experiments demonstrate the feasibility of our recently proposed scheme [Phys. Rev. A 64 (2001) 041401] to accumulate ground-state NH radicals in a magnetic trap.Comment: 11 pages, 4 figures, v2: fixed author name for web-abstract, no changes to manuscrip

Atomic transition frequencies, isotope shifts, and sensitivity to variation of the fine structure constant for studies of quasar absorption spectra

Theories unifying gravity with other interactions suggest spatial and temporal variation of fundamental "constants" in the Universe. A change in the fine structure constant, alpha, could be detected via shifts in the frequencies of atomic transitions in quasar absorption systems. Recent studies using 140 absorption systems from the Keck telescope and 153 from the Very Large Telescope, suggest that alpha varies spatially. That is, in one direction on the sky alpha seems to have been smaller at the time of absorption, while in the opposite direction it seems to have been larger. To continue this study we need accurate laboratory measurements of atomic transition frequencies. The aim of this paper is to provide a compilation of transitions of importance to the search for alpha variation. They are E1 transitions to the ground state in several different atoms and ions, with wavelengths ranging from around 900 - 6000 A, and require an accuracy of better than 10^{-4} A. We discuss isotope shift measurements that are needed in order to resolve systematic effects in the study. The coefficients of sensitivity to alpha-variation (q) are also presented.Comment: Includes updated version of the "alpha line" lis

VLT/UVES constraints on the carbon isotope ratio 12C/13C at z=1.15 toward the quasar HE 0515-4414

We analyzed the CI lines associated with the damped Ly-alpha system observed at zabs = 1.15 in the spectrum of HE 0515-4414 to derive the 12C/13C ratio. The spectrum was obtained by means of the UV-Visual Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT). The obtained lower limit 12C/13C > 80 (2sigma C.L.) shows for the first time that the abundance of 13C in the extragalactic intervening clouds is very low. This rules out a significant contribution from intermediate-mass stars to the chemical evolution of matter sampled by this line of sight. The estimated low amount of 13C is in agreement with low abundances of nitrogen observed in damped Ly-alpha systems - the element produced in the same nuclear cycles and from about the same stars as 13C.Comment: 4 pages, 3 figures, published in A&A, 447, L21-L24, 200

Extreme-ultraviolet laser metrology of OI transitions

Some 16 transitions in atomic oxygen originating from its P-3 ground state were measured using a tunable narrow-band extreme-ultraviolet laser source, with an unprecedented accuracy of Delta lambda/lambda= 8 x 10(-8). The results are relevant for comparisons with spectral absorption features observed in the line of sight of quasars, in order to test a possible variation of the fine-structure constant alpha on a cosmological time-scale