ABSTRACT
Models of the Galaxy with analytical Ferrers bars can reproduce the residual velocities of OB associations in the Sagittarius, Perseus and Local System star-gas complexes located within ...3 kpc of the solar neighbourhood. Ferrers ellipsoids with a density distribution defined by power indices n = 1 and 2 are considered. The successful reproduction of velocity in the Local System is due to the large velocity dispersion, which weakens resonance effects by producing smaller systematic motions. Model galaxies form nuclear, inner and outer resonance rings R1 and R2. The outer rings R2 manage to catch twice as many particles as rings R1. The outer Lindblad resonance of the bar (OLR) is located 0.4 kpc beyond the solar circle, at ROLR = R0 + 0.4 kpc, corresponding to a bar angular velocity of Ωb = 50 km s−1 kpc−1. The solar position angle with respect to the bar, θb, that provides agreement between model and observed velocities is 40–52°. Unfortunately, the models considered cannot reproduce the residual velocities in the Carina and Cygnus star-gas complexes. A redistribution of the specific angular momentum, L, is found near the Lindblad resonances of the bar (inner Lindblad resonance (ILR) and OLR): the average value of L increases (decreases) at radii slightly smaller (larger) than those of the resonances, which could be connected with the existence of two types of periodic orbits elongated perpendicular to each other there.
ABSTRACT
We study the motions inside 28 OB associations with the use of Gaia DR2 proper motions. The average velocity dispersion calculated for 28 OB associations including more than 20 stars with ...Gaia DR2 proper motion is σv = 4.5 km s−1. The median virial and stellar masses of OB associations are Mvir = 8.9 × 105 and Mst = 8.1 × 103 M⊙, respectively. The median star-formation efficiency in parent giant molecular clouds appears to be ϵ = 1.2 per cent. Gaia DR2 proper motions confirm the expansion in the Per OB1, Car OB1, and Sgr OB1 associations found earlier with Gaia DR1 data. We also detect the expansion in Gem OB1, Ori OB1, and Sco OB1 associations, which became possible for the first time now when analysed with Gaia DR2 proper motions. The analysis of the distribution of OB stars in the Per OB1 association shows the presence of a shell-like structure with the radius of 40 pc. Probably, the expansion of the Per OB1 association started with the velocity greater than the present-day expansion velocity equal to 5.0 ± 1.7 km s−1.
On productivity of laser additive manufacturing Gusarov, Andrey V.; Grigoriev, Sergey N.; Volosova, Marina A. ...
Journal of materials processing technology,
November 2018, 2018-11-00, 20181101, Volume:
261
Journal Article
Peer reviewed
Display omitted
•The efficiency of laser additive manufacturing.•Influence of energy distribution in a laser beam.•Modulation of the laser beam with selective laser melting.•Optical diagnostics and ...production monitoring.•Modern tendencies for the development of 3D-printing from metal powder.
One of the most perspective methods of additive manufacturing is selective laser melting. It allows producing the parts directly from 3D-model to 3D-object from metallic powders and alloys. Nowadays the method has very low productivity, which limits its extensive use and possible application to solve a modern design problem by introducing direct and fast metal production. The solution of its productivity would allow receiving metallic 3D-objects with complex geometry in short production period.
The method was improved by the installation of laser beam profiling and online monitoring systems on the developed experimental setup. The profiler contributes to obtaining the alternative power density distributions of the laser beam. The CoCrMo powder was chosen because of its excellent melting qualities, and the initial powder was pre-treated with the purpose to get the diameter of the particles less than 20 μm. During the experiments, 3D-samples were obtained by the improved method of selective laser melting with parameters of two process windows for each of the laser beam spot. The 3D-samples were studied for the revelation of common material defects of the microstructure.
The chemicalanalyses of the samples were implemented by scanning electronic microscopy. The analyses showed that the samples of each laser beam spot had defects related to the formation of a solid solution. Application of Inverse Gaussian laser beam spot into the SLM-machine for production of 3D-objects allows producing the pieces with the values of the parameters exceeding the value for Gaussian laser beam spot in several times. The typically recommended parameters for production of the piece on the modern SLM-machine are less than 100 W for laser source power and less than 30 mm/s for scanning speed. The analytical data, presented in the article demonstrated the field of process parameters, which can give a possibility to obtain 3D-object with the parameters up to 1 kW for laser source power and up to 0.3 m/s for scanning speed. The analyses of microstructure give a possibility to conclude about no visible difference between the formation of the objects with different laser beam spots. The online video-monitoring shows that with the application of laser beam profiling system the negative effects of the selective laser melting reduces visibly.
Relevance. Statistical studies of water discharge in river systems conducted by various authors have shown that forms of distribution of river discharge probability density are polymodal. There are ...various hypotheses for the origin of this polymodal distribution. For example, in dynamic systems the formation of attractors is possible, or under conditions of perturbation of the initial data singular numbers can be transformed into a polymodal structure. However, the proposed hypotheses of formation of polymodal distribution of transformation intensity of elements of an open system are not always applicable to specific objects and are limited to certain conditions. Therefore, it is proposed to apply the universal theory of formation of polymodal distribution of transformation intensity of open systems to study water discharge distribution in river systems. Aim. To confirm the compliance of river flow modes with universal transformation principles in unifying the polymodal statistical probability distribution of water discharge in river systems. Object. Samples of water discharge intensity of hydrographic open systems of the Velikaya and Oka rivers in different seasonal period. Method. Determined on the basis of the derived universal equation of modes of unified polymodal probability density distributions for transformation of any open systems. Each mode in the unified polymodal distribution of river runoff corresponds to a certain universal principle of transformation of an open system under external influence. Its universality is based on the constants of the ratio of time parameters (internal time of transformation of system elements and external time of impact on the system) associated with the "golden" proportion. Soil evaporation and moistening reduce the flow rate and is an internal transforming process depending on atmospheric temperature, and precipitation is an external factor that increases river runoff. Results. Certain modes of polymodal distribution of water discharge fully correspond to universal states of transformation of open systems under external influence. For each seasonal period, the modes correspond to different, previously established principles of systems transformation. Conclusions. Based on a sample of water discharge in river systems, using the unification equation of polymodal distribution, it is possible to determine the state of the river system transformation in the present time and, knowing the parameters of external influence, to predict its future development.
ABSTRACT
We study the periodic enhancement of either trailing or leading segments of the resonance elliptical rings in the dynamical model of the Galaxy which reproduces distributions of observed ...velocities derived from Gaia DR3 (EDR3) data along the Galactocentric distance. The model disc forms a nuclear ring, an inner combined ring, and outer resonance rings R1 and R2. The backbone of the inner combined ring is banana-type orbits around the Lagrange equilibrium points L4 and L5. Orbits associated with the unstable equilibrium points L1 and L2 also support the inner ring. We have found the changes of the morphology of the inner ring with a period of P = 0.57 ± 0.02 Gyr, which is close to the period of revolution along the long-period orbits around the points L4 and L5. A possible explanation of these morphological changes is the formation of an overdensity which then begins circulating along the closed contour. In the region of the Outer Lindblad Resonance (OLR), we have found the changes of the morphology of the outer rings with a period of P = 2.0 ± 0.1 Gyr. Probably, the morphological changes of the outer rings are due to the orbits trapped by the OLR. These orbits exhibit librations of the direction of orbital elongation with respect to the minor axis of the bar as well as the long-term variations in the stellar angular momentum, energy, average radius of the orbit, and eccentricity. Among many librating orbits, we discovered orbits with the libration period of P = 1.91 ± 0.01 Gyr, which may cause the morphological changes of the outer rings.
We calculated the median parallaxes for 47 OB associations including at least 10 stars with known
Gaia
DR2 parallaxes. A comparison between trigonometric and photometric parallaxes of OB associations ...reveals a zero-point offset of
Δ
ϖ
=
−
0.11
±
0.04
mas indicating that
Gaia
DR2 parallaxes are, on average, underestimated and the distances derived from them are overestimated. The correction of
Δ
ϖ
=
−
0.11
mas is consistent with the estimate that Arenou et al. (
2018
) obtained for bright stars. An analysis of parallaxes of OB associations and high-luminosity field stars confirms our previous conclusion (Dambis et al.
2001
) that the distance scale for OB stars established by Blaha and Humphreys (
1989
) must be reduced by 10–20%. Spurious systematic motions of 10–20 km s
−1
at the distances of 2–3 kpc from the Sun are found to arise from the use of the uncorrected
Gaia
DR2 parallaxes.
This paper presents a preliminary analysis of the morphological, physiological, and biochemical parameters of somatic growth in the Black Sea scallop,
Flexopecten glaber
ponticus
Bucguoy, Dautzenberg ...et Dollfus 1889, from a coastal site near Sevastopol, Crimea. The species is one of the few marine Black Sea mollusks listed in the Red Book of Sevastopol and Crimea with the status “Diminishing in numbers.” The peculiarities of soft tissue somatic growth have been studied in three size groups differing in linear diameter: 13–17, 21–24, and 25–30 mm. An analysis of the total RNA in tissue homogenates has shown that the rate of protein synthesis in the first and second groups (under-yearlings) is 1.2–1.5 times higher compared to adults. The population reveals seven color morphs (phenotypes). Three phenotypes (beige, violet, and gray-and-brown) are characterized by high-level protein synthesis. Mollusks of a mixed “multi” phenotype have the lowest level of tissue biosynthesis, usually being 2.5 times lower than that for other morphs. The results obtained indicate that the growth processes are linked to the color of the mollusk shell. High direct correlations between the weights of the total wet mass and the tissue mass observed in all mollusk groups may be evidence of positive growth allometry.
We report the structural disorder effect on magnetic and electric transport properties of
Ni
50
Mn
35
In
15
Heusler alloy (HA) films. Two sets of samples were investigated: disordered (partially ...amorphous) and ordered (crystalline with
L2
1
structure) samples. Electric transport measurements vs. temperature shows that the process of structural ordering is accomplished with a two-stage drop in resistivity at 570 and 630 K which are ascribed to crystallization and
L2
1
-type structural ordering, respectively. Ordered films show a metallic and magnetization behavior typical for
Ni
50
Mn
35
In
15
HA. By contrast, disordered films show ten times lower saturation magnetization with comparable effective magnetization determined from ferromagnetic resonance. We explain this difference as the unusual effect of the inhomogeneous microstructure of the disordered films consisting of Ni clusters embedded in a nonmagnetic matrix.
Graphic abstract
The widespread nature of heat-resistant alloys is associated with the difficulties in their mechanical machining. It forces the use of the wire electrical discharge machining to be wider. The ...productivity, roughness, and dimensions of the modified layer of the machined surfaces are indicators of the machining quality. The search for new diagnostic parameters that can expand the information content of the operational monitoring/diagnostics of wire electrical discharge machining and accompany the currently used electrical parameters’ data is an urgent research task. The article presents the studies of the relationship between the parameters of acoustic emission signals accompanying wire electrical discharge machining of heat-resistant alloys, process quality indicators, and characteristics of discharge pulses. The results are presented as mathematical expressions and graphs demonstrating the experimentally obtained dependencies. The research focuses on the formed white layer during wire electrical discharge machining. Pictures of thin cross-sections of the machined surfaces with traces of the modified layer are provided. The issues of crack formation in the modified layer and base materials are considered.
ABSTRACT
A model of the Galaxy with the outer ring R1R2 can explain the observed distribution of the radial, VR, and azimuthal, VT, velocity components along the Galactocentric distance, R, derived ...from the Gaia EDR3 data. We selected stars from the Gaia EDR3 catalogue with reliable parallaxes, proper motions, and line-of-sight velocities lying near the Galactic plane, |z| < 200 pc, and in the sector of the Galactocentric angles |θ| < 15° and calculated the median velocities VR and VT in small bins along the distance R. The distribution of observed velocities appears to have some specific features: the radial velocity VR demonstrates a smooth fall from +5 km s−1 at the distance of R ≈ R0 − 1.5 kpc to −3 km s−1 at R ≈ R0 + 1.0 kpc while the azimuthal velocity VT shows a sharp drop by 7 km s−1 in the distance interval R0 < R < R0 + 1.0 kpc, where R0 is the solar Galactocentric distance. We build a model of the Galaxy including bulge, bar, disc, and halo components, which reproduces the observed specific features of the velocity distribution in the Galactocentric distance interval |R − R0| < 1.5 kpc. The best agreement corresponds to the time 1.8 ± 0.5 Gyr after the start of the simulation. A model of the Galaxy with the bar rotating at the angular velocity of Ωb = 55 ± 3 km s−1 kpc−1, which sets the OLR of the bar at the distance of R0 − 0.5 ± 0.4 kpc, provides the best agreement between the model and observed velocities. The position angle of the bar, θb, corresponding to the best agreement between the model and observed velocities is θb = 45 ± 15°.
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