In July 2015, the 46th International Physics Olympiad was held in Mumbai, the capital city of the Indian state, Maharashtra. Members of the Czech team obtained three silver medals and two bronze medals. In addition, the Slovak team won one silver and three bronze medals. In this article a theoretical task set during the competition is presented, which deals with calculations of a nuclear fission reactor. and Filip Studnička, Jan Kříž, Ľubomír Konrád, Bohumil Vybíral.
Activity of glycollate oxidase (GO) was inhibited by allantoin in spinách leaves after vacuum infiltration. The GO activity was inhibited by 60.1 % at 1.5 mM allantoin. The activity of catalase was inhibited by allantoin too, both in vitro and in vivo experiments, and accumulation of H2O2 inhibited the GO activity. Mercaptoethanol decreased the inhibitoiy effects induced by allantoin and protected the GO activity. As to the mechanism of the inhibitory elfect, it is possible tiiat allantoin inhibited GO indirectly through its inhibitory eťfect on catalase and subsequent H2O2 accumulation in spinách leaves. This, in tum, oxidized essential sulfhydryl group(s) on GO and inhibited its activity.
The effect of host variables such as size and density, on the transmission of cercariae of Diplostomum spathaceum (Rudolphi, 1819) into a second intermediate fish host, rainbow trout, Oncorhynchus mykiss (Walbaum), was studied quantitatively in laboratory experiments under varying exposure conditions. Differences in the number of established metacercariae were noted in differently sized fish exposed singly to the same number of cercariae and in water volumes related to the body surface area of the host. When exposed (1) singly in an equal water volume or, (2) simultaneously in the same tank, no differences in recovery of metacercariae per fish were found between “small” and “large" hosts. The latter observation is valid for three water volumes tested using the same number of cercariae per host. No significant difference in metacercarial infection was revealed in similar sized fish exposed at different host densities. It appears that transmission is more influenced by cercarial density (number of cercariae per water volume) and fish size than by fish density. These experimental findings support the view that cercarial infection offish occurs by chance, presumably mainly in the gill region. Accordingly, in the field, individual fish size and cercarial density rather than fish population density, prevail in parasite transmission from snail to fish. This is of interest in coastal areas heated by cooling water, where fish growth and fish population density are enhanced.
This paper ceals with a newly developed electronic system used in the INTERKOSMOS satellite tracking stations. The system consists
o microprocessor nbased single board microcomputer, laser clock board with 100ns accuracy and extermal synchronization logic, time gate board (full programable - delay 100ns to 1s, gate 100ns to 1ms. both with steps 100ns) with laser trigger logic and two communication boards. The system is very flexible by means of software. It may be used in the first generation laser radar (like in Vietnam station) or the second generation with reprate 10 Hz.
Sources of maser radio emission in the water vapour spectral line at 1.35 cm are considered, which are situated in star formation regions, in tho vicinity of young stellar objects. The H2O emission of many maser sources in subject to strong variability; maser activity is thereby of a cyclic character with a period of a few years. On the basis of observational data, it is aassumed that the region of maser generation is located in a rotating gas-dust disc around a young stellar object. The author auggests three models explaining the masers´ cyclic non-stationarity.
(1) The maser´s variability is connected with the variable luminosity of the central stellar object, due to non-stationary accretion onto it.
(2) In the central cavity of a large circumstellar disc containing the H2O maser, a smaller disc is located, with its axis tilted to that of the larger disc. The stellar wind jet collimated by the small disc and flowing out from its poles impacts connecutively onto different parts of the large disc´s internal surface. This results in the time- and space-variable maser pump.
(3) If the maser is unsaturated and amplifies the background continuum radiation, then strong maser flares may be connected with radio flares of the centra! object (due, e.g., to its magnetic activity) and the corresponding increase of the maser´s input intensity.
Oboervational tests for the suggested models are discussed.