Advances in Astronomy

The restricted concave kite five-body problem is a problem in which four positive masses, called the primaries, rotate in the concave kite configuration with a mass at the center of the triangle formed by three of the primaries. The fifth body has negligible mass and does not influence the motion of the four primaries. It is assumed that the fifth mass is in the same plane of the primaries and that the masses of the primaries are , , , and , respectively. Three different types of concave kite configurations are considered based on the masses of the primaries. In case I, one pair of primaries has equal masses; in case II, two pairs of primaries have equal masses; in case III, three of the primaries have equal masses. For all three cases, the regions of central configuration are obtained using both analytical and numerical techniques. The existence and uniqueness of equilibrium positions of the infinitesimal mass are investigated in the gravitational field of the four primaries. It is numerically confirmed that none of the equilibrium points are linearly stable. The Jacobian constant is used to investigate the regions of possible motion of the infinitesimal mass.

There are many factors that cause pointing errors in radio telescopes. As one of the motion positioning mechanisms of the radio telescope, the error caused by the elevation mechanism cannot be ignored. The source of error in the elevation mechanism comes mainly from the key transmission components and the support structure. Accurate measurement of the errors caused by them is the key to analyzing their law of change. Aiming at the main error factors in the antenna elevation mechanism, this study builds a scaled-down experimental platform for the elevation mechanism and proposes an error measurement method based on multiencoder information sources. The method compares the error law of change of the antenna elevation mechanism under different driving modes, different centerline deviations of the bearings, and different backlashes and designs error measurement experiments for the abovementioned operating conditions. The results show that the error measurement method based on multiencoder information sources can accurately measure the error of the antenna elevation mechanism under different driving modes. The method can also accurately reflect the law of change in transmission error when the backlash of the elevation mechanism and the centerline deviation of the bearings increase. The final experimental measurement shows that the driving mode of the dual-motor can eliminate about 70% of the mechanism error caused by the backlash. The average value of the error increases by a factor of 1.9 when the backlash increases from 0.1 mm to 1.26 mm. The average value of the error increases by a factor of 5 when the centerline deviation of the bearings increases from 0 to 1.5 mm. This has a good reference value to correct for the pointing error of a radio telescope.

Considering the stringent requirement of the pointing accuracy up to 2.5″ of the world’s largest full steerable radio telescope, this paper studies the welding experiment of the azimuth track of the antenna. First, the opposite deformation jig and welding process were designed for the QTT’s azimuth track. Then, the welding process was numerically simulated using a finite element model. The simulation results show that a better welding effect will be obtained by appropriately reducing the opposite force on the basis of the original. The three deformation processes of the track are regulated by the opposite deformation jig. The results show that the opposite deformation jig designed for QTT’s azimuth track can make the amount of deformation and flatness meet the design requirements. Finally, nondestructive testing was carried out to check the welding quality of the track surface and interior. The results show that there are no obvious defects in the welds of the azimuth track. The constraint jig and welding processes designed for QTT are effective and feasible.

The distribution of the spin directions of spiral galaxies in the Sloan Digital Sky Survey has been a topic of debate in the past two decades, with conflicting conclusions reported even in cases where the same data were used. Here, we follow one of the previous experiments by applying the SpArcFiRe algorithm to annotate the spin directions in an original dataset of Galaxy Zoo 1. The annotation of the galaxy spin directions is carried out after the first step of selecting the spiral galaxies in three different manners: manual analysis by Galaxy Zoo classifications, by a model-driven computer analysis, and with no selection of spiral galaxies. The results show that when spiral galaxies are selected by Galaxy Zoo volunteers, the distribution of their spin directions as determined by SpArcFiRe is not random, which agrees with previous reports. When selecting the spiral galaxies using a model-driven computer analysis or without selecting the spiral galaxies at all, the distribution is also not random. Simple binomial distribution analysis shows that the probability of the parity violation to occur by chance is lower than 0.01. Fitting the spin directions as observed from the Earth to cosine dependence exhibits a dipole axis with statistical strength of 2.33 to 3.97. These experiments show that regardless of the selection mechanism and the analysis method, all experiments show similar conclusions. These results are aligned with previous reports using other methods and telescopes, suggesting that the spin directions of spiral galaxies as observed from the Earth exhibit a dipole axis formed by their spin directions. Possible explanations can be related to the large-scale structure of the universe or to the internal structure of galaxies. The catalogs of annotated galaxies generated as part of this study are available.

In this article, we analyze Bianchi type–II, VIII, and IX spatially homogeneous and anisotropic space-times in the background of the Brans–Dicke theory of gravity within the framework of viscous holographic dark energy. To solve the field equations, we have used the relation between the metric potentials as and the relation between the scalar field and the scale factor as . Also, we have discussed some of the dynamical parameters of the obtained models, such as the deceleration parameter , the jerk parameter , the EoS parameter , the density parameter , Om-diagnostic, squared speed of sound , EoS plane , and statefinder plane through graphical representation, which are significant in the discussion of cosmology. Furthermore, all the models obtained and graphically presented shown an expanding and accelerating Universe, which is in better agreement with the latest experimental data. The viscous holographic dark energy models are compatible with explaining the present cosmic accelerated expansion.

The influence of the 15^th January 2010 annular solar eclipse on traveling ionospheric disturbances (TIDs) and equatorial plasma bubbles (EPBs) is studied using data from six global navigation and satellite system (GNSS) receivers spread across the path of annularity over the low latitude region of East Africa. The GNSS receivers are stationed at Nairobi (RCMN), Malindi (MAL2), and Eldoret (MOIU) in Kenya; Mbarara (MBAR) in Uganda; Kigali (NURK) in Rwanda; and Mtwara (MTWA) in Tanzania. The study period ranges from 12^th to 18^th January 2010, three days before and after the 15^th January 2010 annular solar eclipse. The year 2010 marked the beginning phase of solar cycle 24, evidently observed in low total electron content (TEC) values and the disturbed storm time index (Dst). The eclipse started at 7 : 06 LT and ended at 10 : 14 LT, with MOIU and RCMN experiencing eclipse magnitudes of 0.946 and 0.93, respectively. The maximum obscuration occurred between 8 : 21 LT and 8 : 34 LT across most of the stations. A detrending on vertical TEC (VTEC) derived from GNSS receivers across or close to the path of totality revealed a reduction of ∼2-3 TECU during the maximum phase of the eclipse. The level of reduction was highly close to the totality path and decreased smoothly away from the totality path. Using a background polynomial fitting technique on diurnal TEC, we analyzed TIDs along NURK-MBAR-MOIU and MOIU-RCMN-MAL2 GPS arrays. The results revealed a wavelike perturbation with a virtual horizontal velocity of 830m/s and ∼1 TECU amplitude propagating eastward along the MOIU-RCMN-MAL2 GPS array. The study reports a moderate scintillation activity of 0.5 ≤ ROTI ≤ 0.9 values, demonstrating the presence of few EPBs over the region. The results show a latitudinal variation in GPS-TEC scintillation activities and suggest a possible influence of the eclipse on the observed increase in average scintillation levels across East Africa.