Mid-infrared region (2-8) μm is currently in the focus of laser physics, which is trying to develop new materials capable of generating coherent laser radiation in this region. This point of interest is connected to the so called infrared atmospheric window which offers new possibilities for solid-state lasers to be used as radars, LIDARs, tools for atmosphere diagnostics, etc. One of these new materials is the dysprosium doped lead-thiogallate (Dy:PbGa2 S4 ). In this article, we present brief characteristics of this laser active medium from the point of view of laser physics and we demonstrate the output radiation characteristics of three laser systems with dysprosium doped lead-thiogallate as their active media generating radiation at 2400 nm, 4300 nm a 5400 nm. The spatial structure, energy, impulse length and emission spectra of the output radiation were determined. and Stredná infračervená oblasť (2-8) μm je v súčasnosti terčom záujmu laserovej fyziky, ktorá sa snaží vyvinúť nové materiály, ktoré by mohli poskytovať koherentné laserové žiarenie v tejto oblasti. Tento záujem sa spája s existenciou tzv. infračerveného atmosférického okna, ktoré otvára nové možnosti aplikácií laserov generujúcich žiarenie v tejto oblasti ako sú radary, LIDARy, prostriedky pre diagnostiku atmosféry a podobne. Jedným z týchto nových materiálov majúcich takéto vlastnosti je dyspróziom dopovaný olovo-thiogalát (Dy:PbGa2 S4 ). V tomto článku prezentujeme stručnú charakteristiku tohto laserového aktívneho prostredia z pohľadu laserovej fyziky a demonštrujeme vlastnosti troch laserových systémov, obsahujúcich Dy:PbGa2 S4 ako aktívne médium, generujúcich žiarenie na vlnových dĺžkach 2400 nm, 4300 nm a 5400 nm. Výstupné žiarenie charakterizujeme z hľadiska priestorovej štruktúry, energie, dĺžky impulzu a emisného spektra.
According to the present author´s results a following system of the galactic dynamical constants is proposed: local escape velocity, u = (520+30) km s^-1, local circular velocity, u = (230+30) km s^-1, local angular velocity of rotation, ω = (25+5) km s^-1 kpc^-1, local circular frequency of planar oscillations, κp = (40+10) km s^-1, local circlar frequency of vertical oscillations, κz = (70120) km^-1 kpc^-1. The value of (9+1), kpc is assumed fpar the galactocentric distance of the Sun. The latter three values yield (0.09±0.03) pc^-3 for the local matter density, a value very close to the density obtained by use of statistical methods. On the basis of the proposed value it is concluded that the dark matter should to present in the form of a large, rerefied, massive, spherical corona.
The dynamical evolution of short-period comets, and in particular of those belonging to the so-called Jupiter family, is reviewed. Encounters with Jupiter play a dominant role in determining the
dynamical fate of these objects, although, in some peculiar cases, also interactions with other planets may be important. Frequent although temporary librations around resonances with Jupiter are displayed by more than one third of short-period comets. Integrations of motion of observed comets, over a time span comparable with their lifetime as active objects, are compared with previous numerical investigations, to get insight into the non observed phases of the dynamical evolution of these objects.
The dynamical evolution of star clusters is discussed. We investigate especially the possible disruption of globular clusters by massive black holes, which have been proposed as the major constituents of dark galactic coronae. As an example, we discuss here the globular clusters in the elliptical galaxy M87. The proposed massive black holes could be responsible for the observationally indicated depletion of the globular cluster system in the inner parts of M87 with respect to the stellar light distribution of this galaxy.
Position actuator with small DC motor, torque 1 Nm, range 210 grad, using dynamic superposition of vibrations for decreasing of friction effect and clearances in gear box. and Polohový servomechanismus s malým stejnosměrným motorkem, točivý moment 1 Nm, rozsah 210 grad, využívající dynamické superposice vibrací pro potlačení vlivu tření a vůlí v převodovce.
H. Weyl, jeden z prvních, kdo se zabýval rolí symetrie v kvantové mechanice, podal následující definici symetrie [1]: „Věc je symetrická, pokud se s ní dá něco udělat tak, že i po dokončení toho udělání vypadá stejně jako před tím.“ Tato věta se dá přeložit do poněkud exaktnějšího jazyka pomocí teorie grup - matematické disciplíny, která byla ještě na začátku 20. století považována za nepraktickou, spíše poněkud exotickou doménu ryze teoretického bádání. Především zásluhou fyziků se v následujících desetiletích z teorie grup stal jeden z nejdůležitějších nástrojů k uchopení reality. Fyzikální svět je plný symetrií!, Pavel Cejnar., and Obsahuje seznam literatury
In celestial mechanics interactions of radiation and small bodies in Solar system can be classified as scattering, absorption, radiation drag and thermal emission. The final one, in particular, induces important secular changes of orbits and rotation states of asteroids and meteoroids, as supported by a number of astronomical observations., Miroslav Brož., and Obsahuje seznam literatury
Protective coatings are widely used to improve the lifetime of some machine parts exposed to a repeated dynamical stress. An analysis technique called dynamical impact test is applied to determine a fatigue, wear resistance and possibility of protective coating optimisation as well. This technique and the unique dynamical impact tester employed at the Institute of Scientific Instruments of the Czech Academy of Sciences, v.v.i. are described. Some of the impact test results important to indicate the protective coatings behaviour under repeated dynamical load are noticed in the last part of this paper. and Ochranné vrstvy jsou často užívány ke zvýšení životnosti součástí přístrojů vystavených opakovanému dynamickému namáhání. Pro určení životnosti, otěruvzdornosti a následné optimalizaci ochranných vrstev je používána analýza pomocí tzv. dynamického impaktního testu. V textu je popsán princip této metody, přiblížen je i unikátní přístroj využívaný k impaktnímu testování na Ústavu přístrojové techniky AV ČR, v.v.i. V závěru jsou popsány některé výsledky testu důležité pro určení chování ochranných vrstev pod opakovanou dynamickou zátěží.
In this paper, a theory of the causes of condensations i the central parts of open star clusters is developed, which are in the state of approximate statistical equilibrium. A method is proposed of establishing the mean diameter of star clusters. Owing to galactic rtation, clusters of central densities smaller than 4.5 solar masses/parsec^3 show some elongation in the direction of the galactic plane. Clusters of central densities larger than 0.5 solar masses/parsec^3 may, as a whole, be regarded as stationary and their state as statistically in equilibrium. Assuming Maxwell´s velocity distribution, stars from the central parts of the star clusters will, on account of the shorter relaxation time, tend to escape quicker than these from the border. The star clusters will therefore contract quicker around the centre than at the border. After the state of the cluster has become stationary its central part has a larger kinetic energy than the border parts, in spite of the fact that the star energies of various cluster regions adjust themselves. The paper derives a method of determining initial residual star velocities in the cluster. Today´s value of the residual velocity, together with the initial velocity, allow us to estimate the age of the star cluster. The theoretical results were applied to moving cluster Hyades. The age was estimated as 1.1 x 10^9 years. The theoretical flatness of the cluster 0.69 agrees well with the observed value of 0.07, given by van Bueren [19].