494 research outputs found

### Orbital eccentricities as indicators of stellar populations: a kinematical analysis of the local disc from GAIA DR2 catalogue

Aims. Based on a local sample from Gaia DR2 catalogue composed of 74 339 stars, we are able to derive more accurate kinematic statistics defining the local stellar populations and classify the stars in terms of their planar and vertical orbital eccentricities. Methods. Firstly, we carried out a kinematical characterisation of stellar populations from a tested mixture model that fits the trivariate velocity cumulants up to the fourth order, maximises the entropy of the mixture probability, and minimises the ¿2 error. We then proposed several approaches to classifying the stars according to the population they are most likely to belong to. None of these approaches provided a definitive solution due to the overlapping of the partial distributions. Finally, by using the epicycle approximation, we transformed the three-dimensional velocity probability space into a two-dimensional diagram. In one direction, the information of the two planar velocity components is picked up by the planar eccentricity. In the other direction, the vertical eccentricity does the same with the vertical velocity component. However, in the vertical direction, the epicycle approximation is not valid and it is replaced by a biquadratic approximation. Results. In the eccentricity diagram, the region of maximum probability for a population is approximately delimited by straight line. We characterise three local kinematic populations: thin disc, thick disc (composed of two subpopulations: canonical thick disc and metal-weak thick disc), and kinematical halo (metal-rich thick-disc plus chemical halo). The Gaia DR2 sample allows us to estimate small mean radial differential motion of 5 ± 2 km s-1 between the thin and thick discs, and of 9 ± 3 km s-1 between both thick-disc subpopulations, as well as between the disc and the kinematical halo. All disc populations and subpopulations have significant vertex deviations. Conclusions. The classification of the stars from the eccentricity diagram resolves the problem of overlapping velocity distributions by producing a segregation that is more net, along with a more precise kinematical characterisation of populations.Peer ReviewedPostprint (author's final draft

### Orbital eccentricities as indicators of stellar populations. II. Vertical velocity distribution from the Gaia DR2 catalogue

Context. In previous work, we showed how the planar and vertical eccentricities of disc stars, e and e' , could be used as indicators of the stars’ kinematic populations. For a local stellar sample drawn from the Gaia DR2 catalogue, these populations were represented geometrically in the eccentricity diagram, e'² vs e² , approximately separated by straight lines.
Aims. In the current work, we propose a new relationship between the star’s perpendicular velocity and its vertical eccentricity, allowing for a reevaluation of the critical vertical eccentricity and maximum height, z_max, specific to each population component.
Methods. We approximated the local potential function to be consistent with the actual shape of the curve that relates the maximum vertical speed of a star and its maximum height. The curve corresponds to a non-linear restoring vertical force, where the stiffness decreases with an increase in the maximum height. The constants involved in this fitting, together with the population velocity dispersions, determine the specific region for each population in the eccentricity diagram.
Results. The new classification determines 88% of the sample is made up of thin disc stars and 9% of thick disc stars, whereby 3% of the stars have been relabelled, by providing thinner thin and thick discs. Nested thin disc subsamples allow us to estimate Strömberg’s asymmetric drift equation, leading to a heliocentric velocity of the circular orbit of V_c ˜ -12.9 km s -1 , an absolute rotation velocity of T_c ˜ 227 km s -1 , and a rotation component of the Galactocentric velocity of the Sun at T_¿ ˜ 240 km s -1 .
Conclusions. The thin disc stars of our local sample are characterised based on values 0 = e = 0.32, 0 = e' = 0.09, and z_max = 0.7 kpc. Disc stars satisfy 0 = e = 0.44, 0 = e' = 0.18, z_max = 1.5 kpc. The maximum vertical peculiar velocity for disc stars is found to be w_0 = 115 km s -1 . The assumed potential provides a stellar density of the disc vanishing at z_0 = 1.8 kpc. The approximate behaviour in the local disc is that a small decrease in the stiffness is associated with a relative decrease in the limiting velocity, which produces
a thinner disc and a loss of stars in the local cylinder, both in a similar proportion to the limiting velocity.Peer ReviewedPostprint (author's final draft

### The influence of pyrolysis type on shale oil generation and its composition (Upper layer of Aleksinac oil shale, Serbia)

The influence of pyrolysis type on shale oil generation and its composition was studied. Different methods such as Rock-Eval pyrolysis, thermogravimetric analysis (TGA) and pyrolysis in the open and closed systems were applied. Samples from the Upper layer of Aleksinac oil shale (Serbia) were used as a substrate and first time characterized in detail. The impact of kerogen content and type on the shale oil generation in different pyrolysis systems was also estimated. Majority of the analysed samples have total organic carbon content > 5 wt. % and contain oil prone kerogen types I and/or II. Therefore, they can be of particular interest for the pyrolytic processing. Thermal behavior of analysed samples obtained by TGA is in agreement with Rock-Eval parameters. Pyrolysis of oil shale in the open system gives higher yield of shale oil than pyrolysis in the closed system. The yield of hydrocarbons (HCs) in shale oil produced by open pyrolysis system corresponds to an excellent source rock potential, while HCs yield from the closed system indicates a very good source rock potential. The kerogen content has a greater impact on the shale oil generation than kerogen type in the open pyrolysis system, while kerogen type plays a more important role on generation of shale oil than the kerogen content in the closed system. The composition of obtained shale oil showed certain undesirable features, due to the relatively high contents of olefinic HCs (open system) and polar compounds (closed system), which may require further treatment to be used

### Real Time Control Of Rotary Inverted Pendulum

This paper proposes advanced control strategy for a rotary inverted pendulum (RIP). RIP is an underactuated mechanical system because it has only one control input and two degrees of freedom. Because of its complex nonlinear dynamics, RIP is usually used to test performance of different control algorithms. First, laboratory electromechanical system representing the full control system is described in short, followed by the mathematical model for the RIP. Control problem is divided and implemented in two different steps: swing-up and stabilization routines. Here, a partial
feedback linearization procedure and PID control are suggested for the control of RIP.
The effectiveness of the proposed control method is tested in Matlab Simulink
environment

### Sastav masnih kiselina šaranskih vrsta riba iz dva sistema gajenja

Cilj ovog rada je bio ispitivanje masnokiselinskog profila mišićnog tkiva šaranskih vrsta riba gajenih u polikulturi u dva ribnjaka sa poluintenzivnim uzgojem. Poređen je profil masnih kiselina mišićnog tkiva šarana, tolstolobika i amura u vidu ukupnih zasićenih (ZMK), mononezasićenih (MNMK) i polinezasićenih masnih kiselina (PNMK), kao i odnosi P/S i n-3/n-6. Odnos P/S u lipidima mišićnog tkiva šarana kretao se od 0,26 (amur) do 0,80 (šaran). Veći sadržaj n-3 PNMK uočen je u mišićnom tkivu amura. Odnos n-3/n-6 iznosio je kod amura 2.15, dok je kod tolstolobika i šarana bio 0.07. Dobijeni rezultati ukazuju da je glavna razlika između šaranskih vrsta bila u sadržaju ukupnih PNMK, posebno u sadržaju n-6 masnih kiselina. Sastav masnih kiselina amura iz dva ribnjaka nije se statistički značajno razlikovao. Šarani sa dva ribnjaka su se značajno razlikovali u ukupnom sadržaju MNMK i PNMK. Da bi se procenio kvalitet slatkovodne ribe sa domaćeg tržišta, dobijeni rezultati su, takođe, poređeni sa gajenim vijetnamskim somom (Pangasius hypophthalmus) koji je uzet sa našeg tržišta. S obzirom na masnokiselinski sastav, Pangasius se ne može smatrati nutritivno vrednom namirnicom. Dalja ispitivanja su neophodna da se oceni kvalitet slatkovodne ribe sa našeg tržišta

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