Barrel Instability in Binary Asteroids

Most close-in planetary satellites are in synchronous rotation, which is usually the stable end-point of tidal despinning. Saturn’s moon Hyperion is a notable exception by having a chaotic rotation. Hyperion’s dynamical state is a consequence of its high eccentricity and its highly prolate shape. As many binary asteroids also have elongated secondaries, chaotic rotation is expected for moons in eccentric binaries, and a minority of asteroidal secondaries may be in that state. The question of secondary rotation is also important for the action of the binary Yarkovsky–O’Keefe–Radzievskii–Paddack (BYORP) effect, which can quickly evolve orbits of synchronous (but not nonsynchronous) secondaries. Here we report results of a large set of short numerical simulations which indicate that, apart from synchronous and classic chaotic rotation, close-in irregularly shaped asteroidal secondaries can occupy an additional, intermediate rotational state. In this “barrel instability” the secondary slowly rolls along its long axis, while the longest axis is staying largely aligned with the primary–secondary line. This behavior may be more difficult to detect through lightcurves than a fully chaotic rotation, but would likewise shut down BYORP. We show that the binary’s eccentricity, separation measured in secondary’s radii and the secondary’s shape are all important for determining whether the system settles in synchronous rotation, chaotic tumbling, or barrel instability. We compare our results for synthetic asteroids with known binary pairs to determine which of these behaviors may be present in the near-Earth asteroid binary population.

DEM Study on the Segregation of a Non-Spherical Intruder in a Vibrated Granular Bed

The segregation process of a single large intruder in a vibrated bed of small particles has been widely studied, but most previous studies focused on spherical intruders. In this work, the discrete element method was used to study the effects of vibration conditions and intruder shape on the dimensionless ascending velocity (va) of the intruder. The intruder was in a prolate shape with aspect ratio varied but its equivalent diameter fixed. Three equivalent diameters, namely volume-equivalent diameter, surface-area-equivalent diameter, and Sauter diameter, were used. It was found that va increases and then decreases with the rise of the dimensionless vibration amplitude (Ad) and the dimensionless vibration frequency (fd), and va increases with the decrease of the sphericity of the intruder (Φ). Moreover, the porosity variation in the vibrated bed and the granular temperature were analyzed, which can be linked to the change of va. It was further found that va can be uniformly correlated to Ad‧f 0.5 d, while the critical change of the response of va to Ad and fd occurs at Γ = 4.83, where Γ is the vibration intensity. Based on these findings, a piecewise equation was proposed to predict va as a function of Ad, fd, and Φ.

Karakterisasi Spesies Averrhoa yang Tumbuh di Kota Kediri Berdasarkan Pendekatan Palinologi

Averrhoa is a member of the Oxalidaceae family and has four types, namely Averrhoa carambola, Averrhoa bilimbi, Averrhoa leucopetala, Averrhoa dolichocarpa.. Among the four types of averhoa, the most commonly found growing and planted in Kediri's yards were Averrhoa carambola and Averrhoa bilimbi. Cultivation of this plant is usually done by vegetative and generative with seeds. Pollen has long been used as an indicator in plant taxonomy, because in pollen there are many secret characters. This study aims to determine characterization Averrhoa species that grow in Kediri City based on a palinological approach. The result of this research is Averrhoa pollen that grows in Kediri City has almost the same characteristics, namely very small size, spheroidal Prolate shape, trizonocolpate aperture and isopolar polarity. The similarity is so great because the environmental conditions in which these two types of plants grow are the same. The difference in the character of pollen that grows in Kediri City lies in its ornamentation. In Averrhoa carambola ornate Perforate-Foveolate and Averrhoa bilimbi with reticulate character. This difference in ornament is due to the fact that these two types of plants have different species.

Evolution of magnetic deformation in neutron star crust

In this study, we examine the magnetic field evolution occurring in a neutron star crust. Beyond the elastic limit, the lattice ions are assumed to act as a plastic flow. The Ohmic dissipation, Hall drift, and bulk fluid velocity driven by the Lorentz force are considered in our numerical simulation. A magnetically induced quadrupole deformation is observed in the crust during the evolution. Generally, the ellipticity decreases as the magnetic energy decreases. In a toroidal-field-dominated model, the sign of the ellipticity changes. Namely, the initial prolate shape tends to become oblate. This occurs because the toroidal component decays rapidly on a smaller timescale than the poloidal dipole component. We find that the magnetic dipole component does not change significantly on the Hall timescale of ∼1Myr for the considered simple initial models. Thus, a more complex initial model is required to study the fast decay of surface dipoles on the abovementioned timescale.

Constraining the orientation of the spin axes of extrasolar minor bodies 1I/2017 U1 (‘Oumuamua) and 2I/Borisov

Context. The orientation of the spin axis of a comet is defined by the values of its equatorial obliquity and its cometocentric longitude of the Sun at perihelion. These parameters can be computed from the components of the nongravitational force caused by outgassing if the cometary activity is well characterized. The trajectories of known interstellar bodies passing through the Solar System show nongravitational accelerations. Aims. The spin-axis orientation of 1I/2017 U1 (‘Oumuamua) remains to be determined; for 2I/Borisov, the already released results are mutually exclusive. In both cases, the values of the components of the nongravitational force are relatively well constrained. Here, we investigate – within the framework of the forced precession model of a nonspherical cometary nucleus – the orientation of the spin axes of ‘Oumuamua and 2I/Borisov using public orbit determinations that consider outgassing. Methods. We applied a Monte Carlo simulation using the covariance matrix method together with Monte Carlo random search techniques to compute the distributions of equatorial obliquities and cometocentric longitudes of the Sun at perihelion of ‘Oumuamua and 2I/Borisov from the values of the nongravitational parameters. Results. We find that the equatorial obliquity of ‘Oumuamua could be about 93°, if it has a very prolate (fusiform) shape, or close to 16°, if it is very oblate (disk-like). Different orbit determinations of 2I/Borisov gave obliquity values of 59° and 90°. The distributions of cometocentric longitudes were in general multimodal. Conclusions. Our calculations suggest that the most probable spin-axis direction of ‘Oumuamua in equatorial coordinates is (280°, +46°) if very prolate or (312°, −50°) if very oblate. Our analysis favors a prolate shape. For the orbit determinations of 2I/Borisov used here, we find most probable poles pointing near (275°, +65°) and (231°, +30°), respectively. Although our analysis favors an oblate shape for 2I/Borisov, a prolate one cannot be ruled out.

"Barrel Instability" for Elongated Secondaries in Binary Asteroids

<p>Most close-in planetary satellites are in synchronous rotation, which is usully the stable end-point of tidal despinning. Saturn's moon Hyperion is a notable exception by having a chaotic rotation. Hyperion's dynamical state is a consequence of its high eccentricity and its highly prolate shape (Wisdom et al. 1984). As many binary asteroids also have elongated secondaries, chaotic rotation is expected for moons in eccentric binaries (Cuk & Nesvorny 2010), and a minority of asteroidal secondaries may be in that state (Pravec et al. 2016). The question of the secondary's rotation is importrant for the action of the BYORP effect, which can quickly evolve orbits of synchrnous (but not non-synchronous) secondaries (Cuk & Burns 2005). Here we report preliminary numerical simulations which indicate that in binary systems with a large secondary and significant spin-orbit coupling a different kind of non-synchronous rotation may arise. In this "barrel instability" the secondary slowly rolls along its long axis, while the longest diameter is staying largelly aligned with the primary-secondary line. This behavior  may be more difficult to detect through lightcurves than a fully chaotic rotation, but would likewise shut down BYORP. Unlike fully chaotic rotation, barrel instability can happen even at low eccentricties. In our presentation we will discuss our theoretical results and their implications for the evolution of binary asteroids, such as the Didymos-Dimorphos pair.</p>

Total Routhian surface calculations to study the abrupt band termination phenomenon in 121,123I

The phenomenon of abrupt band termination in [Formula: see text]I has been revisited in the light of total Routhian surface (TRS) calculations. Both axial ([Formula: see text]) and nonaxial ([Formula: see text]) quadrupole deformation parameters have been estimated for the negative parity states. The calculation has also been extended for [Formula: see text]I and the theoretical result has been compared with the available experimental information. The calculated transition quadrupole moments ([Formula: see text]) are matching nicely upto [Formula: see text] MeV. The noncollective oblate shapes become yrast at higher angular frequency in [Formula: see text]I. At lower spin, all of these nuclei exhibit a collective prolate shape. This sudden change in shape at [Formula: see text] is indicative of the loss of collectivity at [Formula: see text]–[Formula: see text] MeV.

Peripheral Refraction in Myopic Children with and without Atropine Usage

Purpose. To compare the patterns of relative peripheral refractions of myopic children who were currently on atropine treatment for myopia control and myopic children who did not use atropine. Methods. Chinese children (n = 209) aged 7 to 12 years participated in the study, 106 used atropine and 103 did not. Participants were also classified into three groups: emmetropes (SE: +0.50 to −0.50 D), low myopes (SE: −0.50 to −3.00 D), and moderate myopes (SE: −3.00 to −6.00 D). The central and peripheral refractions along the horizontal meridians (for both nasal and temporal fields) were measured in 10-degree steps to 30 degrees. Results. There were no statistically significant differences in spherical equivalent and astigmatism of the three refractive groups in either the nasal or temporal retina. The atropine group showed a significant relative myopia in the temporal 30° field in spherical equivalent compared to the emmetropic group (t49 = 3.36, P=0.02). In eyes with low myopia, the atropine group had significant relative myopia in the nasal 30° and temporal 30° fields (t118 = 2.59, P=0.01; t118 = 2.06, P=0.04), and it is also observed at 20° and 30° of the nasal field for the moderate myopic group (t36 = 2.37, P=0.02; t2.84 = 2.84, P=0.01). Conclusion. Significant differences in relative peripheral refraction were found between the atropine group and its controls. The findings suggested that the eyes that received atropine may have a less prolate shape and thus explain why using atropine is effective in controlling myopia progression.

High spin states of Zr isotopes around A = 80 mass region — A study on cold and hot rotating nuclei

High spin structure of Zr isotopes, in particular, around [Formula: see text] has been studied in yrast and nonyrast regions. Spin dependence of shapes for the yrast levels are investigated by employing Cranked Hartree–Fock–Bogoliubov (CHFB) theory using a [Formula: see text] model interaction and the calculations are in good accord with the experimental data. The nonyrast states are treated by incorporating temperature degree of freedom using the statistical theory (ST). Highly deformed prolate shapes dominate the nonrotating proton rich region at low temperatures (T) with coexisting oblate and prolate shapes in [Formula: see text]Zr. Hot rotating nuclei show highest deformation around [Formula: see text] among all the other Zr isotopes even at high temperatures. [Formula: see text]Zr exhibits interesting structural transitions, hence studied in detail in yrast and non yrast regions. Triaxiality predominates in both yrast and nearly yrast (low temperature) regions at low spins with transition to elongated shapes at mid spin values 30–38[Formula: see text] to highly deformed oblate shapes at higher spins. CHFB predicts a strong backbending effect at 32[Formula: see text] and 40[Formula: see text]. A shape coexistence between the rare shape phase of noncollective prolate and oblate is reported in [Formula: see text]Zr at low temperature and [Formula: see text]. Prolate shape phase disappears with increasing temperature and spin but the nucleus remains highly deformed (with [Formula: see text] at spin [Formula: see text]40[Formula: see text]) even at high temperatures of the order of 3–3.5[Formula: see text]MeV, hence a very promising candidate for GDR probes of nuclear shapes.