Etching of moldavities under natural conditions

The hypothesis that a part of the lechatellierites which originated by etching from a basic moldavite mass became broken off after deposition of moldavite in the sedimentation layer is advanced. Those found close to the original moldavite were measured for statistical averaging of length. The average length of lechatelierite fibers per cubic mm of moldavite mass volume was determined by measurement under a microscope in toluene. The data were used to calculate the depth of the moldavite layer that had to be etched to produce the corresponding amount of lechatelierite fragments. The calculations from five "fields" of moldavite surface, where layers of fixed lechatelierite fragments were preserved, produced values of 2.0, 3.1, 3.5, 3.9 and 4.5. Due to inadvertent loss of some fragments the determined values are somewhat lower than those found in references. The difference may be explained by the fact that the depth of the layer is only that caused by etching after moldavite deposition

Characteristics and properties of structural steels

Import 22/07/2015Výroba oceli prošla složitým vývojem od období řemeslné malovýroby až k dnešní podobě průmyslové velkovýroby. Zdokonalováním a vývojem výrobních procesů bylo dosaženo vzniku širokého sortimentu a značek ocelí, proto byly značky rozděleny do tříd ocelí dle obsahu uhlíku a dále do skupin dle obsahu legujících prvků. Legující prvky jsou přidávány pro zlepšení vlastností ocelí a tím i rozšíření možností pro použití ocelí. Nejvíce používané značky ocelí jsou konstrukční oceli. Pro získání přehledu o chemickém složení, vlastnostech a možnostech použití byly vybrány k porovnání tři nejběžnější značky konstrukčních ocelí, tj. S235, S355 a C45. Konstrukční oceli jsou v současné době velmi žádaný materiál. Pro své vlastnosti a velké možnosti použití jsou konstrukční oceli základním materiálem pro stavební průmysl, strojírenství, automobilový průmysl, zemědělství a mnoho dalších odvětví průmyslu.Steel production passed complicated development from period of small-scale production as far as today´s form of industrial mass production. By perfection and development of industrial processes a rise of wide assortment and steel types were reached and therefore these types were divided to the grades of steel according to carbon content and further to the groups according to alloying elements. Alloying elements are added to steels for properties improvement and thereby for expanded posibilities of steel application. The most useal steel types are those of structual steels. To obtain knowledge about chemical composition properties and application, three the most common structural steel types, i.e. S235, S355 and C45 were chosen and compared mutually. At present, structual steels are very asked material. Thanks the properties and large application possibilities is the mentioned steel type a basic material for building industry, engineering, automotive industry, agriculture and other branches of industry.636 - Katedra materiálového inženýrstvívýborn

Appearance of innermost stable circular orbits of accretion discs around rotating neutron stars

The innermost stable cicular orbit (ISCO) of an accretion disc orbiting a neutron star (NS) is often assumed a unique prediction of general relativity. However, it has been argued that ISCO also appears around highly elliptic bodies described by Newtonian theory. In this sense, the behaviour of an ISCO around a rotating oblate neutron star is formed by the interplay between relativistic and Newtonian effects. Here we briefly explore the consequences of this interplay using a straightforward analytic approach as well as numerical models that involve modern NS equations of state. We examine the ratio K between the ISCO radius and the radius of the neutron star. We find that, with growing NS spin, the ratio K first decreases, but then starts to increase. This non-monotonic behaviour of K can give rise to a neutron star spin interval in which ISCO appears for two very different ranges of NS mass. This may strongly affect the distribution of neutron stars that have an ISCO (ISCO-NS). When (all) neutron stars are distributed around a high mass M0, the ISCO-NS spin distribution is roughly the same as the spin distribution corresponding to all neutron stars. In contrast, if M0 is low, the ISCO-NS distribution can only have a peak around a high value of spin. Finally, an intermediate value of M0 can imply an ISCO-NS distribution divided into two distinct groups of slow and fast rotators. Our findings have immediate astrophysical applications. They can be used for example to distinguish between different models of high-frequency quasiperiodic oscillations observed in low-mass NS X-ray binaries.Comment: 4 pages, 2 figures, accepted by A&A Letter

Neutrino trapping in braneworld extremely compact stars

Extremely Compact Stars (ECS) contain trapped null geodesics. When such objects enter the evolution period admitting geodetical motion of neutrinos, certain part of neutrinos produced in their interior will be trapped influencing their neutrino luminosity and thermal evolution. We study neutrino trapping in the braneworld ECS, assuming uniform distribution of neutrino emissivity and massless neutrinos. We give the efficiency of the neutrino trapping effects in the framework of the simple model of the internal spacetime with uniform distribution of energy density, and external spacetime described by the Reissner-Nordstr\"om geometry characterized by the braneworld "tidal" parameter $b$. For $b < 0$ the external spacetime is of the black-hole type, while for $b > 0$ the external spacetime can be of both black-hole and naked-singularity type. Then the ECS surface radius $R$ can be located also above the unstable (outer) photon circular orbit. Such basically new types of the spacetimes strongly alter the trapping phenomena as compared to the standard case of $b = 0$. It is shown that the neutrino trapping effects are slightly lowered by the presence of physically more plausible case of $b < 0$, as compared to the standard internal Schwarzschild spacetime, while they can be magnified by positive tidal charges if $b 1$. However, potential astrophysical relevance of the trapping phenomena is strongly enhanced for negative tidal charges enabling a significant enlargement of the ECS surface radius to values coherent with recent observations

Band-monitoring Payload for a CubeSat Satellite

During changing sun activity, the ionosphere is responding accordingly and therefore it is interesting to observe the propagation behavior of shortwave bands. For the above mentioned purpose we have designed a band-monitoring payload for an experimental CubeSat satellite. The payload consists of a receiver, which is able to receive SSB modulated narrowband signals in 28 MHz uplink band, and a transmitter with FM modulation in UHF downlink band. The receiver frequency is selected to be at the center of radio amateur activity with low data rate digital modulations

Data Processing in Multiport-Based Reflectometer System

The paper describes operations with DC output voltage of multiport based system. Proposed system is based on the same principle as common six ports systems, however the used coupler has more outputs. This allows extension of bandwidth and higher precision of the measurement. To process measured data standard six port system calculations are used. To get more accurate results than in the case of simple six port system additional statistical methods can be used. The higher number of outputs produces large amount of measurement and calibration data, however using described technique this amount of data were reduced