Motion of distant objects in the Universe

We give a brief survey of investigations of the structure of the Universe and of its expansion, for educational purposes. As we know it today, the size of the Universe is immense, enormous numbers of galaxies have been found in it, and in each galaxy enormous numbers of stars. The galaxies move from us at very high speeds, some of the more distant ones at speeds comparable to the velocity of light. Many theories have been developed to explain the vast amount of data that have been obtained by astronomical observations. We give a simplified theory of the cosmic expansion and present results of three models for the cosmic scale function R(t): the constant rate of expansion, the accelerated expansion and the constant Hubble parameter models

Motion of distant objects in the Universe

We give a brief survey of investigations of the structure of the Universe and of its expansion, for educational purposes. As we know it today, the size of the Universe is immense, enormous numbers of galaxies have been found in it, and in each galaxy enormous numbers of stars. The galaxies move from us at very high speeds, some of the more distant ones at speeds comparable to the velocity of light. Many theories have been developed to explain the vast amount of data that have been obtained by astronomical observations. We give a simplified theory of the cosmic expansion and present results of three models for the cosmic scale function R(t): the constant rate of expansion, the accelerated expansion and the constant Hubble parameter models

Rezonantni efekt u 3d → 1s dvofotonskom raspadu među unutarnjim atomskim ljuskama

Emission of photon pairs by the two-photon decay process from silver and hafnium atoms with a vacancy in the K shell was investigated. Radioactive decay of 109Cd and 179Ta was used to generate the K-shell vacancy states in silver and hafnium atoms, respectively. The measuring system consisted of a pair of planar high-purity germanium detectors, a fast-slow coincidence system, and a 128x512x512 channel pulse-height analyzer. Two-dimensional spectra of numbers of events as functions of amplitudes of coincident pulses from the two detectors were analyzed. The results on the 3d → 1s two-photon decay show the resonance behaviour, seen as a gradual increase of the differential transition probability as the partition of energy among the two photons of the pair deviates from equal-energy partition (E1=E2=E0/2). The effect was predicted by the second-order perturbation theory of two-photon decay in which summation over intermediate states is carried out over occupied and unoccupied bound states, and over unbound states.Istraživano je zračenje parova fotona procesom dvojnog fotonskog raspada u atomima srebra i hafnija s K supljinom. Radioaktivni raspad 109Cd i 179Ta služio je za tvorbu K šupljinskih stanja u atomima srebra odnosno hafnija. Mjerni uređaj sastojao se od para planarnih germanijskih detektora visoke čistoće, brzo-sporog sudesnog sustava, i 128 x 512 x 512 kanalnog amplitudnog analizatora. Analizirani su dvodimenzijski spektri brojeva događaja kao funkcije amplituda sudesnih impulsa iz dvaju detektora. Rezultati za 3d → 1s dvojni fotonski raspad pokazuju rezonantni efekt, koji se opaža kao postepen porast diferencijalne prijelazne vjerojatnosti kako razdjela energije među dvama fotonima para odstupa od jednake razdjele (E1 = E2 = E0/2). Taj je efekt predskazan u perturbacijskoj teoriji dvojnog fotonskog raspada drugog reda u kojoj se zbrajanje preko virtualnih međustanja provodi preko zauzetih i slobodnih vezanih stanja i preko nevezanih stanja elektrona

Single-point observation of rapidly moving objects

We study the kinematical problem of observation of motion of objects that move at velocities comparable to the velocity of signals which are used to determine the velocity and distance of the objects. The main purpose of this work is to demonstrate the importance of time delay between the emission of signals and their reception at the observation point. The simplest cases are considered, i.e., rectilinear motion and assuming the observational point at the path of the moving object. Sound and light signals are considered to transmit the information on the motion. The results relating to the motion at constant velocity and for the acceleration due to a constant force are presented

Hipersatelitski i satelitski prijelazi u atomima srebra

Previous measurements of the K X-rays emitted in the deexcitation of silver atoms with empty K-shells have been extended in order to obtain a better and more detailed quantitative description of the processes involved. The method of measurement has been improved and new data have been acquired. In addition, a more elaborate procedure for the analysis of data has been developed. In the analysis the complete set of peaks in the two-dimensional spectra originating from the hypersatellite-satellite cascades was treated in a self-consistent way. The Kα, Kβ1 ′ and Kβ2 ′ X-ray energy shifts caused by single K or L2,3 spectator vacancies have been determined along with the intensity ratios I(Kα2)/I(Kα1), I(Kβ1′ )/I(Kα1)and I(Kβ2 ′ )/I(Kα1) of the hypersatellite transitions (involving a K-shell spectator vacancy) and of the satellite transitions involving a single L2 or L3 spectator vacancy. The results are compared with the theoretical values.Ranija mjerenja K rendgentskog zračenja koje nastaje u raspadu atoma srebra s praznom K ljuskom nastavljena su radi postizanja boljeg i detaljnijeg opisa uključenih procesa. Poboljšana je metoda mjerenja i sakupljeni su novi podaci. Također je razvijena bolja metoda analize podataka u kojoj se cjelokupan skup vrhova u dvodimenzijskim spektrima, koji su posljedica kaskadnih raspada hipersatelit–satelit, obrađuje na samosaglasan način. Određeni su pomaci linija Kα, Kβ1 ′ i Kβ2 ′ zračenja uzrokovani pojedinačnim K ili L2,3 promatračkim šupljinama, te omjeri intenziteta hipersatelitskih linija (sa promatračkom šupljinom u K-ljusci) i satelitskih prijelaza sa šupljinom u L2 ili L3 podljusci. Rezultati su uspoređeni s teorijskim vrijednostima