In this paper, we consider self-mappings defined on a metric space endowed with a finite number of graphs. Under certain conditions imposed on the graphs, we establish a new fixed point theorem for such mappings. The obtained result extends, generalizes and improves many existing contributions in the literature including standard fixed point theorems, fixed point theorems on a metric space endowed with a partial order and fixed point theorems for cyclic mappings.
This paper investigates the fixed-time trajectory tracking control problem for a nonholonomic mobile robot. Firstly, the tracking error system is derived for the mobile robot by the aid of a global invertible transformation. Then, based on the unified error dynamics and by using the fixed-time control method, continuous fixed-time tracking controllers are developed for the mobile robot such that the robot can track the desired trajectory in a fixed time. Moreover, the settling time is independent of the system initial conditions and only determined by the controller parameters. Finally, numerical simulations are provided to demonstrate the effectiveness of the theoretical results.
The feasibility of using the new photoelectric magnetograph of the Ondřejov Observatory for measuring fast changes in the magnetic
and velocity fields of active regions is considered.
Large line-of-sight motions were found in growing and decaying
sunspots related with areas of magnetic field boundaries and
gradients.
For five flares we have considered magnetic fields, measured in the flaring region and underlying sunspots. Main results:
a) magnetic field in flare is longitudinal, buf it is mainly transversal in fhe sunspol which the flare is situated on;
b) magnetic field strengths measured by Zeeman splitting of Ihe emission lines ol Fel, D1, and D-2 Nal, D3 Hel and Hα reach 1000-3000G, offen exeeeds ones determined by absorption lines in underlying sunspols;
e) it appears fhat in flare the magnetic field changes slowly wifh heighf, so far as its vaues estimated by emission lines of helium, hydrogen and metal are approximately equal.
The present paper investigates the statistical behaviour of the solar flares through cycle 21 (1976-1986). The total number of solar flares and the number of flares of various importance are given. The year of maximum of all events was 1980 with 10132 flares. The subflares háve had their maximum values in 1979 (9278 events)
and in 1980 (9273 events) while, the other flares reached the maximum two - three years later. The asymmetry A for subflares and importance 1 flares favour the Southern hemisphere (A= -2.8 and -0.9) but thal of importance >2, the northem hemisphere (A=
+3.6). The maximum number of flares with importance >2 (Fmax) in solar cycle 21 took place two years later than the maximum number of solar spots (Rmax) but Fmax in cycle 20 appeared one year before Rmax and for cycle 19 in the same year of Rmax.
The study focuses on the phenomenon of barrel-organ playing in the context of Bohemian and Moravian streets and countryside from the beginning of its occurrence in our lands to date. The foreword describes the organologic nature of the instrument and its production. The major part of the work is a summary of available
sources about a barrel-organ player: his role in the life of people, whether during their daily encounters with an "itinerant" person, or his activity in the realm of customary tradition. The role of barrel-organ players has changed, in comparison to modern-day barrel-organ players - buskers as well as members of a
barrel-organ playing club who returned to the streets after 1989. Both lines of barrel-organ players are themes of particular chapters (Barrel-Organ and Busking; A Club of Friends of Mechanical Music and Barrel-Organs). The study ́s goal is to outline a unifying line between the historical and the contemporary practice in barrel-organ playing, as well as it explains when these trends
diverge.
Flat disk models for galaxies are studied on the basis of osscillations of distributed mass around equilibrium configuration. Convincing perspectives to existing galaxy types are available. Several kinds of galactic orbits are possible with peculiar rotation curves. Supersonic and very high velocities seem likely in the central region. Conventional rotation curve breaks into two, inner to the Solar circle and spiral arms. A new model for our galaxy is proposed.
In this paper, I discuss some moral dilemmas related to the COVID-19 crisis and their framing (mainly) in the public debate. The key assumption to engage with is this: that we need primarily to take into account the long-term economic consequences of the proposed safety measures of social distancing. I argue that the long-term economic concerns, though legitimate, cannot suspend the irreducibly moral nature of the demand placed on the decision-makers by those who are vulnerable, at risk, or in need of medical treatment. This is discussed in relation to two points: 1) The political endeavour and rhetoric of “flattening the curve” is not necessarily short-sighted but expresses the acknowledgment of a legitimate expectation placed on elected representatives. 2) Not being able to prevent harm (to those who are in real need, or otherwise vulnerable) may lead to genuine moral distress, even if it is not clear whether it was in one’s, or anybody’s, powers to prevent the situation, or even if the best possible outcome has been otherwise reached. The second point may be understood as a part of the broader context of the established criticisms of utilitarianism.