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1
Model systemu antenowego mikro-satelity do odbioru telekomend w paśmie S
Klonowski P., Kurek K.
Przegląd Telekomunikacyjny + Wiadomości Telekomunikacyjne
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2018
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nr 6
494--497, CD
PL
Artykuł opisuje propozycję systemu antenowego mikro-satelity dla łączności pomiędzy satelitą na orbicie a naziemną stacją kontrolną. System antenowy ma umożliwiać odbiór sygnału radiowego w paśmie S, wysyłanego do satelity z Ziemi (telekomendy sterujące pracą satelity) niezależnie od orientacji satelity względem Ziemi, W artykule zaproponowano wykorzystanie w tym celu systemu dwóch anten łatkowych umieszczonych na sąsiednich ściankach małego satelity. Przedstawiono wyniki symulacji i pomiarów opracowanego modelu takiego systemu.
EN
The paper describes a proposition of the antenna system of the micro-satellite, allowing to receive a radio signal from a ground control station (telecommands send to the satellite) in S band, regardless of the satellite orientation. The proposition of the use of two patch antennas placed on two satellite walls is described, and simulations and measurement results of realized model of such system is presented.
2
Content available An Impact of Technological Conditions on Surface Burning in Grinding of the Orbit
Stančeková Dana, Mrázik Jozef, Rybicka Iwona, Náprstková Nataša, Kraus Pavel
Advances in Science and Technology. Research Journal
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2018
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Vol. 12, no 4
19--27
EN
A process of quality development helps us reveal concrete deficiences, an analysis of their origin and realization of required modifications that are needed to solve a concrete problem. One of the aims of quality development of production in bearing industries is to find out an impact of tchnological conditions to form burning of surfaces in grinding of orbits of bearing rings. We try to describe an origin of the problem, to find reasons of burned surfaces in a process of grinding and to propose such technological conditions to avoid above-stated problems and to produce the least possible number of non-identical workpieces. To lower a number of burnings in grinding of the orbit to zero percentage is not real, however, we have to try to get a minimal number of parts with damaged surface.
3
Content available Cutting parameters and vibrations analysis of magnetic bearing spindle in milling process
Bouaziz A., Barkallah M., Bouaziz S., Choley J. Y., Haddar M.
Journal of Theoretical and Applied Mechanics
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2016
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Vol. 54 nr 3
691--703
EN
In modern production, milling is considered the widespread cutting process in the formatting field. It remains important to study this manufacturing process as it can be subject to some parasitic phenomena that can degrade surface roughness of the machined part, increase tool wear and reduce spindle life span. In fact, the best quality work piece is obtained with a suitable choice of parameters and cutting conditions. In another hand, the study of tool vibrations and the cutting force attitude is related to the study of bearings as they present an essential part in the spindle system. In this work, a modeling of a High Speed Milling (HSM) spindle supported by two pair of Active Magnetic Bearings (AMB) is presented. The spindle is modeled by Timoshenko beam finite elements where six degrees of freedom are taken into account. The rigid displacements are also introduced in the modeling. Gyroscopic and centrifugal terms are included in the general equation. The bearings reaction forces are modeled as linear functions of journal displacement and velocity in the bearing clearance. A cutting force model for peripheral milling is proposed to estimate the tool-tip dynamic responses as well as dynamic cutting forces which are also numerically investigated. The time history of response, orbit, FFT diagram at the tool-tip center and the bearings dynamic coefficients are plotted to analyze dynamic behavior of the spindle.
4
Content available remote Processing Transient Response of a Flexible Rotor-Bearing System with Unbalanced Disk
Attia Hili M., Bouaziz S., Maatar M., Fakhfakh T., Haddar M.
Machine Dynamics Research
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2010
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Vol. 34, No. 1
23-37
EN
Turbomachinery rotors are frequently supported on several oil lubricating bearings and so are statically indeterminate. In such cases, the bearings reaction forces and hence their stiffness and damping properties affect the relative location of the bearing centres, thereby significantly the vibration behaviour of the rotor bearing system. In this paper, the dynamic behaviour of symmetrical rotor bearing system with unbalanced disk is analyzed based on a continuum model. The finite difference method is employed with the successive over relaxation technique to solve the Reynolds equation. The finite element method with an iteration scheme is adopted in the analysis of the system state trajectories. Bearing's stiffness and damping are considered. The motions of journal and disk have been simulated with Newmark method. Linear transient simulation, with time integration procedure, and unbalanced responses are investigated. The present results provide a deeper understanding to predict undesirable behaviour of the rotor and bearings centres can be avoided.
5
Content available remote Geometry of pre quasi homogeneous polynomials of type (1/2, 1/4)
Kushner L., Saia M. J.
Demonstratio Mathematica
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2010
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Vol. 43, nr 2
461-471
EN
In this article we study the geometry of the orbits of the space V which consists of pre quasi homogeneous polynomials of type g(x, y) = a1x2 + a2xy2 + a3y4 + a4xy + a5y3 + a6x + a7y + a8y2 with ai ∈ R, for all i = 1, . . . , 8 under the action of the group G := {h(x, y) = (...), with (...) > 0}. To study these orbits we observe first that there are three subspaces of dimension 5, V1 := {g(x, y) = a1x2 + a2xy2 + a3y4 + a4xy + a5y3}, V2 := {g(x, y) = a1x2 + a2xy2 + a3y4 + a6x + a8y2} and V3 := {g(x, y) = a1x2 + a2xy2 + a3y4 + a7y + a8y2} of V which are also invariant under the action of this group. Then we describe the orbits which appear in these spaces and give the topological characterization of them by showing their stabilizers. We give a geometrical description of them inside R5. Moreover, we construct an appropriate map h : R6 - R5 and prove that the fibers given by the inverse image of the orbits by h are two dimensional surfaces diffeomorphic to R2 - (R × {0} ∪ {0} × R). We show that the points of these fibers which minimize the distance to the origin are indeed in the 3-torus (...)3 = S1 1/2 × S1 1/2 × S1 1/(...).
6
Content available remote Uniform parameterized theory of convection in medium sized icy satellites of Saturn
Czechowski L.
Acta Geophysica
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2009
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Vol. 57, no. 2
548-566
EN
We develop a parameterized theory of convection driven by radiogenic and tidal heating. The tidal heating depends on eccentricity e of a satellite's orbit. Using parameterized theory we determine the intensity of convection as a function of e and satellite's properties. The theory is used for 6 medium sized satellites of Saturn. We find that endogenic activity on Tethys and Dione is possible if e exceeds some critical values e[cr]. For Enceladus, e was probably close to the present value for billions of years. We cannot find constrains for e of Mimas and Iapetus. The theory successfully predicts the possibility of present endogenic activity in Dione and rules out such activity in Tethys. Both these facts were recently confirmed by Cassini mission.
7
Content available remote Common fixed point theorems for three expansive self-maps in D-metric spaces
Singh B., Jain S.
Demonstratio Mathematica
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2005
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Vol. 38, nr 3
703--713
EN
B. Singh and R. K. Sharma [Demonstratio Math. Vol. 36, No.l (2003), 215-220] have proved two common fixed point theorems for two self-maps satisfying an expansive condition in D- metric spaces. This note offers generalization for these theorems for three self-maps using weak- compatibility and reduces the domain of z to an orbit only. The last theorem proves that the continuity of none of two or three maps is required in the setting of D- metric space.
8
Content available remote On iterative roots of homeomorphisms of the circle
Zdun M.
Bulletin of the Polish Academy of Sciences. Mathematics
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2000
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Vol. 48, no 2
203-213
EN
In this paper we deal with the problem of existence and uniqueness of continuous iterative roots of homeomorphisms of the circle. Let F : [S^1 --> S^1] be a homeomorphism without periodic points. If the limit set of the orbit [F^k(z), k belongs to Z] equals [S^1], then F has exactly n iterative roots of n-th order. Otherwise F either has no iterative roots of n-th order or F has infinitely many iterative roots depending on an arbitrary function. In this case we determined all iterative roots of n-th order of F.
9
Content available remote Set-valued iterative square roots of bijections
Powierża T.
Bulletin of the Polish Academy of Sciences. Mathematics
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1999
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Vol. 47, no 4
377-383
EN
There are different ideas how to generalize the notion of an iterative root, especially when a function does not have a "real" root. We consider a multifunction as a substitute for this notion.
10
Content available remote Closed orbits for a class of Hamiltonian systems
Timouni M.
Demonstratio Mathematica
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1998
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Vol. 31, nr 1
1-10
EN
In this paper we prove the
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