Context.
As part of our international program aimed at obtaining accurate physical properties of trans-Neptunian objects (TNOs), we predicted a stellar occultation by the TNO (38628) Huya of the star
...Gaia
DR2 4352760586390566400 (
m
G
= 11.5 mag) on March 18, 2019. After an extensive observational campaign geared at obtaining the astrometric data, we updated the prediction and found it favorable to central Europe. Therefore, we mobilized half a hundred of professional and amateur astronomers in this region and the occultation was finally detected by 21 telescopes located at 18 sites in Europe and Asia. This places the Huya event among the best ever observed stellar occultation by a TNO in terms of the number of chords.
Aims.
The aim of our work is to determine an accurate size, shape, and geometric albedo for the TNO (38628) Huya by using the observations obtained from a multi-chord stellar occultation. We also aim to provide constraints on the density and other internal properties of this TNO.
Methods.
The 21 positive detections of the occultation by Huya allowed us to obtain well-separated chords which permitted us to fit an ellipse for the limb of the body at the moment of the occultation (i.e., the instantaneous limb) with kilometric accuracy.
Results.
The projected semi-major and minor axes of the best ellipse fit obtained using the occultation data are (
a
′
, b
′) = (217.6 ± 3.5 km, 194.1 ± 6.1 km) with a position angle for the minor axis of
P
′ = 55.2° ± 9.1. From this fit, the projected area-equivalent diameter is 411.0 ± 7.3 km. This diameter is compatible with the equivalent diameter for Huya obtained from radiometric techniques (
D
= 406 ± 16 km). From this instantaneous limb, we obtained the geometric albedo for Huya (
p
V
=
0.079 ± 0.004) and we explored possible three-dimensional shapes and constraints to the mass density for this TNO. We did not detect the satellite of Huya through this occultation, but the presence of rings or debris around Huya was constrained using the occultation data. We also derived an upper limit for a putative Pluto-like global atmosphere of about
p
surf
= 10 nbar.
The paper presents the results of viscous flow modeling using different turbulence models in the Ansys CFX program for the D. Eckardt and H. Krain stage. The impellers are with an outlet angle of 90 ...and 60 degrees. Isentropic efficiency and the total pressure ratio are compared with the experimental data. The evaluation of the static pressure contours structure at the impeller shroud is made. Recommendations for qualitative modeling of high-head stages are given.
RF magnetron-deposited Si\In2O3:Er films have the structure of the single-crystalline bixbyite bcc In2O3 nanowires bunched into the columns extended across the films. The obtained films have a ...typical In2O3 optical band gap of 3.55 eV and demonstrate the 1.54 m Er3+ room temperature photoluminescence. The current across the film flows inside the columns through the nanowires. The current through the MOS-structure with the intermediate low barrier In2O3:Er dielectric was investigated by the thermionic emission approach, with respect to the partial voltage drop in silicon. Schottky plots ln(I/T2) versus 1/kT of forward currents at small biases and backward currents in saturation give the electron forward n-Si\In2O3:Er barrier equal to 0.14 eV and the backward In\In2O3:Er barrier equal to 0.21 eV.
Abstract
The paper presents the results of modelling the flow of droplets in the flow of a non-Newtonian fluid. The task is solved in a nonstationary formulation. We determined the time of ...stabilization of the speed profile of the droplets and the length of the initial hydrodynamic sector. We compared the specified characteristics for the main flow of the non-Newtonian fluid and for the set of droplets in the flow. We show the coincidence of the lengths of the initial hydrodynamic sections determined by the stabilization of speeds for the droplets and the non-Newtonian medium.
The article is devoted to the study R134a refrigerating machine efficiency and consisting of a centrifugal compressor, a condenser, a temperature-regulating valve and an evaporator. The main purpose ...of the work is to analyze the centrifugal compressor gas dynamic characteristics effect on the refrigeration machine vapor-compression cycle efficiency. This goal is achieved through the study by actual working process numerical experiment in the refrigeration machine centrifugal compressor with an idealized process for other elements. The object of the study are the refrigeration machine characteristics, expressed by the theoretical refrigeration coefficient COPRt. Single-stage centrifugal compressors with the design conditional flow coefficient in the range from 0.035 to 0.12 are considered. The design of centrifugal compressors was carried out according to a new calculation method to the flow part efficiency increase. The method comprehensively combines the inviscid and viscous flow calculations with the use of the single-criteria and multiparametric optimization. Previously, the method was tested and compared with experimental data. The most important result is the results of the refrigeration cycle efficiency evaluating through the centrifugal compressors highly efficient flow parts design methodology application. An increase in COPRt was obtained taking into account the centrifugal compressor actual process in the range from 2.6% to 7.2%. The significance of the results obtained lies in the possibility of using high-efficiency centrifugal compressors gas dynamic characteristics for the chillers refrigeration cycles analysis and calculation. The level of the compressors isentropic efficiency ranges from 0.80 to 0.85, depending on the design conditional flow coefficient.
We describe acts over rectangular bands that have modular, distributive or linearly ordered congruence lattice. It turns out that such acts have at most 11 elements, and their congruence lattice has ...at most 300 elements. Furthermore, certain facts are established about the structure of acts with modular congruence lattice over an arbitrary semigroup and about the structure of the congruence lattice of an act over a rectangular band. The work is based on the description of acts over a completely (0-)simple semigroup obtained by Avdeev and Kozhukhov in 2000 and on the characterization of disconnected acts with modular or distributive congruence lattice by Ptakhov and Stepanova in 2013.
The method for the existing complex pneumatic systems efficiency increase has been developed, including the survey steps, mathematical technological process modeling, optimizing the pneumatic system ...configuration, its operation modes, selection of optimal compressor units and additional equipment. Practical application of the methodology is considered by the example of the existing pneumatic systems underground depot reconstruction. The first stage of the methodology is the survey of acting pneumatic system. The second stage of technique is multivariable mathematical modeling of the pneumatic system operation. The developed methodology is applicable to complex pneumatic systems.
Nowadays the optimization using computational fluid dynamics (CFD) plays an important role in the design process of turbomachines. However, for the successful and productive optimization it is ...necessary to define a simulation model correctly and rationally. The article deals with the choice of a grid and computational domain parameters for optimization of centrifugal compressor impellers using computational fluid dynamics. Searching and applying optimal parameters of the grid model, the computational domain and solver settings allows engineers to carry out a high-accuracy modelling and to use computational capability effectively. The presented research was conducted using Numeca Fine/Turbo package with Spalart-Allmaras and Shear Stress Transport turbulence models. Two radial impellers was investigated: the high-pressure at ψT=0.71 and the low-pressure at ψT=0.43. The following parameters of the computational model were considered: the location of inlet and outlet boundaries, type of mesh topology, size of mesh and mesh parameter y+. Results of the investigation demonstrate that the choice of optimal parameters leads to the significant reduction of the computational time. Optimal parameters in comparison with non-optimal but visually similar parameters can reduce the calculation time up to 4 times. Besides, it is established that some parameters have a major impact on the result of modelling.
The temperature range of SPICE models of bipolar and field-effect transistors is extended from the standard commercial level (<inline-formula> <tex-math notation="LaTeX">-60\,\,^\circ {\mathrm{ ...C}}\cdots +150\,\,^\circ \text{C} </tex-math></inline-formula>) to harsh conditions level (<inline-formula> <tex-math notation="LaTeX">-200\,\,^\circ {\mathrm{ C}}\cdots +300\,\,^\circ \text{C} </tex-math></inline-formula>) for low/high-temperature ICs design. This is done by including additional equations for temperature-dependent parameters, and by connecting additional elements to the device equivalent circuit to take into account the thermal effects. The universal automated methodology of model parameters extraction from the experimental data measured at low and high temperatures is proposed. The good agreement between simulated and measured device characteristics is achieved. The RMS error is not more than 10%-20%.
The study presents the results of multi-objective optimization for a high flow centrifugal compressor stage with impeller pressure ratio Π=1.3 and conditional flow rate coefficient Φ=0.108. The ...compressor stage includes an impeller with 3D backswept blades, a vane diffuser and an axial inlet. The goal of optimization is to increase polytropic efficiency and polytropic head ratio of the basic design. The CFD method is used to estimate compressor efficiency at rated duty. CAE optimization is applied based on the parametric optimization of impeller shroud contour and number of blades of the impeller and diffuser versus the original design. Parameterization of geometrics is also used to the width-ratio of vane diffuser in the range of b3 D2= 0.08-0.097. The study considers 52 cases of the optimization of impeller shroud contour and the number of blades in the search for the improved design. The optimization procedure uses the automatic generated computation grid and supplementary activation of solution to each design case. The numerical calculation for each case has been performed automatically by ANSYS CFX 14.5 soft application. The optimization allowed to obtain the improved design with total polytropic efficiency increase by 1.58% for the impeller and polytropic head coefficient increase by 0.58%. The polytropic efficiency and the polytropic head coefficient are calculated on the total parameters. The performance of the basic impeller has been exhaustibly validated by test records provided JSC "REPH ZAO". The resulted error range does not exceed 5% over the performance map, except near surge point.
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