1,068 research outputs found
Eccentricity samples: implications on the potential and the velocity distribution
Planar and vertical epicycle frequencies and local angular velocity are related to the derivatives up to the second order of the local potential and can be used to test the shape of the potential from stellar disc samples. These samples show a more complex velocity distribution than halo stars and should provide a more realistic test. We assume an axisymmetric potential allowing a mixture of independent ellipsoidal velocity distributions, of separable or Staeckel form in cylindrical or spherical coordinates. We prove that values of local constants are not consistent with a potential separable in addition in cylindrical coordinates and with a spherically symmetric potential. The simplest potential that fits the local constants is used to show that the harmonical and non-harmonical terms of the potential are equally important. The same analysis is used to estimate the local constants. Two families of nested subsamples selected for decreasing planar and vertical eccentricities are used to borne out the relation between the mean squared planar and vertical eccentricities and the velocity dispersions of the subsamples. According to the first-order epicycle model, the radial and vertical velocity components provide accurate information on the planar and vertical epicycle frequencies. However, it is impossible to account for the asymmetric drift which introduces a systematic bias in estimation of the third constant. Under a more general model, when the asymmetric drift is taken into account, the rotation velocity dispersions together with their asymmetric drift provide the correct fit for the local angular velocity. The consistency of the results shows that this new method based on the distribution of eccentricities is worth using for kinematic stellar samples.Peer ReviewedPostprint (author's final draft
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
Cross reactive arrays of three-way junction sensors for steroid determination
This invention provides analyte sensitive oligonucleotide compositions for detecting and analyzing analytes in solution, including complex solutions using cross reactive arrays of analyte sensitive oligonucleotide compositions
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
Effect of Modified Atmosphere Pakaging on the Shelf-life of Common Carp (Cyprinus carpio) Steaks
AbstractThe effect of modified atmosphere packaging (MAP 1: 40%CO2+60%N2 and MAP 2: 100%CO2) on the shelf-life of carp steaks was studied. Carp steaks were stored at +3±0.5˚C and on days 1, 3, 6, 9, 13 and 15, microbiological, chemical and sensory testing was performed. Based primarily on odour scores it was observed that carp steaks packaged in MAP1 remained acceptable up to 13 days of storage, while carp steaks packaged in MAP2 remained unchanged until the end of the study. By using MAP, especially 100% CO2, products shelf-life can be significantly prolonged
Tachyon constant-roll inflation in Randall-Sundrum II cosmology
We study inflation in a model with constant second slow-roll parameter
. In this case, the Hubble expansion rate equation has analytical
solutions describing four possible, nontrivial inflation scenarios. The
evolution of the inflaton governed by a tachyon field is studied in the
framework of the standard and Randall-Sundrum II cosmology. The attractor
behavior of the solution is briefly demonstrated. Finally, the calculated
values of the parameters and are compared with observational
data
Phenolic Profile and Antioxidant Activity of Pulp and Peel from Peach and Nectarine Fruits
Peach (Prunus persica L.) is a fruit of high nutritional and economic value. Carbohydrates, dietary fibers, minerals and organic acids are among the major constituents of peach fruit, which contribute to the nutritional quality of both fresh fruits and juice. Polyphenolic compounds found in peach may play an important role in physiological functions related to human health. Different polyphenolics may have varied biological activities including antioxidant activity. In this study antioxidant characteristics between peel and pulp of different peach cultivars (‘RadmilovÄanka’, ‘June Gold’, ‘Blake’, ‘Hale’, ‘Vesna’, ‘Adria’) and one of nectarine (‘Fantasia’) were investigated. The peel and pulp extracts showed a huge amount of total phenolics (TP), total flavonoids (TF), total hydroxycinnamates (TH) and total flavonols (TFL), ranging from 42.7-211.4, 11.1-128.5 mg GAE/100 g fresh weight (f.w.) (TP), 21.9 -94.9, 5.0-58.9 mg CE/100 g f.w. (TF), 28.4-389.2, 8.5-165.8 mg kg-1 f.w. (TH) and 17.3-54 mg kg-1 f.w. (TFL). High contents of phenolic compounds were significantly correlated with high antioxidant capacities. Peach pulp and peel differ significantly in their phenolic profiles: the pulp contains mainly chlorogenic, neochlorogenic and p-coumaric acids, whereas the peel possesses chlorogenic, neochlorogenic and p-coumaric acids together with several flavonol glycosides in huge amounts. Our results indicate that cultivar and extraction solvent play important roles in phenolic compositions and antioxidant properties of peach and nectarine extracts, which was shown using statistical analysis (ANOVA). There are high correlations between extracted phenolic compounds and peach and nectarine cultivars, and used solvent and part of the fruit (peel and pulp)
A Wireless LC Sensor Coated with Ba0.9Bi0.066TiO3 for Measuring Temperature
This paper presents a passive LC wireless sensor for measuring temperature. The sensor is designed as a parallel connection of a spiral inductor and an interdigitated capacitor and it was fabricated in a conductive layer using LTCC (Low Temperature Co-fired Ceramic) technology. The inderdigitated capacitor electrodes were coated with a thin film of bismuth doped barium titanate (Ba0.9Bi0.066TiO3), whose permittivity changes with temperature, which directly induces changes in the capacitance of the interdigitated capacitor and consequently changes the resonant frequency of the sensor. The measurements of S-parameter of the sensor were performed using a Vector Network Analyzer (E5071B, Agilent Technologies, Santa Clara, CA, USA), whose port was connected to the antenna coil that was placed around the sensor in order to be able to wirelessly detect temperature, in the temperature range from 25 degrees C to 165 degrees C
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