Extremal bifurcations of rotating AdS4 black holes

The Weak Gravity Conjecture arises from the assertion that all extremal black holes, even those which are “classical” in the sense of being very massive, must decay by quantum-mechanical emission of particles or smaller black holes. This is interesting, because some observed astrophysical black holes are on the brink of being extremal — though this is due to rapid rotation rather than a large electric or magnetic charge. The possibility that rotating near-extremal black holes might, in addition to radiating spinning particles, also bifurcate by emitting smaller black holes, has attracted much attention of late. There is, however, a basic question to be answered here: can such a bifurcation be compatible with the second law of thermodynamics? This is by no means clear. Here we show that, if there is indeed such a mechanism for bifurcations of AdS4-Kerr-Newman black holes, then this process can in fact satisfy the second law.

Fragmenting Active Asteroid 331P/Gibbs

We describe active asteroid 331P/Gibbs (2012 F5) using archival Hubble Space Telescope (HST) data taken between 2015 and 2018. 331P is an outer main belt active asteroid with a long-lived debris trail that formed in 2011. Embedded in the debris trail we identify 19 fragments with radii between 0.04 and 0.11 km (albedo 0.05 assumed) containing about 1% of the mass of the primary nucleus. The largest shows a photometric range (∼1.5 mag), a V-shaped minimum, and a two-peaked lightcurve period near 9 hr, consistent with a symmetric contact binary. Less convincing explanations are that 331P-A is a monolithic, elongated splinter or that its surface shows hemispheric 4:1 albedo variations. The debris trail is composed of centimeter-sized and larger particles ejected with characteristic 10 cm s−1 speeds following a size distribution with index q = 3.7 ± 0.1 to 4.1 ± 0.2. The HST data show that earlier, ground-based measurements of the nucleus were contaminated by near-nucleus debris, which cleared by 2015. We find that the primary nucleus has effective radius 0.8 ± 0.1 km and is in rapid rotation (3.26 ± 0.01 hr), with a lightcurve range of 0.25 mag and a minimum density of 1600 kg m−3 if strengthless. The properties of 331P are consistent with (1) formation about 1.5 Myr ago by impact shattering of a precursor body, (2) spin-up by radiation torques to critical rotation, (3) ejection of about 1% of the nucleus mass in mid 2011 by rotational instability, and (4) subsequent evolution of the fragments and dispersal of the debris by radiation pressure.

An Intelligent System to Improve Athlete Depression and Eating Disorder using Artificial Intelligence and Big Data Analysis

The inspiration for the creation of this app stemmed from the deeply rooted history of eating disorders in sports, particularly in sports that emphasize appearance and muscularity which often includes gymnastics, figure skating, dance, and diving [1]. All three sports require rapid rotation in the air which automatically results in the necessity of a more stringent weight requirement. Eating disorders can also be aggravated by sports who focus on individual performances rather than team-oriented like basketball or soccer [5]. According to research, up to thirteen percent of all athletes have, or are currently suffering from a form of eating disorder such as anorexia [2] and bulimia [3]. In the National Collegiate Athletic Association, it is estimated that up to sixteen percent of male athletes and forty-five percent of female athletes have been diagnosed with an eating disorder.

A numerical scheme for the ground state of rotating spin-1 Bose–Einstein condensates

We study the existence of nontrivial solution branches of three-coupled Gross–Pitaevskii equations (CGPEs), which are used as the mathematical model for rotating spin-1 Bose–Einstein condensates (BEC). The Lyapunov–Schmidt reduction is exploited to test the branching of nontrivial solution curves from the trivial one in some neighborhoods of bifurcation points. A multilevel continuation method is proposed for computing the ground state solution of rotating spin-1 BEC. By properly choosing the constraint conditions associated with the components of the parameter variable, the proposed algorithm can effectively compute the ground states of spin-1 $$^{87}Rb$$ 87 R b and $$^{23}Na$$ 23 N a under rapid rotation. Extensive numerical results demonstrate the efficiency of the proposed algorithm. In particular, the affect of the magnetization on the CGPEs is investigated.

Thermonuclear X-ray bursts from 4U 1636 − 536 observed with AstroSat

ABSTRACT We report results obtained from the study of 12 thermonuclear X-ray bursts in six AstroSat observations of a neutron star X-ray binary and well-known X-ray burster, 4U 1636 − 536. Burst oscillations (BOs) at ∼ 581 Hz are observed with 4–5σ confidence in three of these X-ray bursts. The rising phase BOs show a decreasing trend of the fractional rms amplitude at 3σ confidence, by far the strongest evidence of thermonuclear flame spreading observed with AstroSat. During the initial 0.25 s of the rise a very high value ($34.0\pm 6.7{{{\ \rm per\ cent}}}$) is observed. The concave shape of the fractional amplitude profile provides a strong evidence of latitude-dependent flame speeds, possibly due to the effects of the Coriolis force. We observe decay phase oscillations with amplitudes comparable to that observed during the rising phase, plausibly due to the combined effect of both surface modes, as well as the cooling wake. The Doppler shifts due to the rapid rotation of the neutron star might cause hard pulses to precede the soft pulses, resulting in a soft lag. The distance to the source estimated using the photospheric radius expansion bursts is consistent with the known value of ∼6 kpc.

N2–O2 icing in single-crystal in-house X-ray diffraction experiments using an open-flow helium cryostat

This note reports a study of the coating of a crystal with `ice' at temperatures below 45 K during single-crystal in-house diffraction experiments when using an open-flow helium cryostat. The `ice' consists mainly of crystalline oxygen and nitrogen. This suggests completely different techniques for avoiding this type of icing compared with water icing. With appropriate choices of crystal mount, crystal position with respect to the nozzle and gas flow conditions, it is possible to avoid detectable condensation. However, sometimes this cannot be achieved in practice (poor diffraction from a smaller crystal, necessity of positioning the crystal in certain orientations to achieve desired data completeness, need to reduce helium consumption etc.). The problem of icing seems to be less common for powder experiments where the laminar gas flow is parallel to the capillary containing the sample, and for synchrotron experiments where the sample is comparatively small and almost continuously rotated, which facilitates the ice covering being removed by the gas flow. This last technique can in principle also be applied to single-crystal X-ray diffraction using laboratory diffractometers – periodic rapid rotation of the crystal can help to minimize any icing, but this technique will not work when the condensation rate is comparable to or faster than one frame of data collection. The coating around a sample crystal reduces the quality of the diffraction data, and the temperature at the sample below the coating may differ significantly from that at the cryostat nozzle reported by the instrument.

Features of remote work in a pandemic

This article examines the actual problem of organizing the workflow in a pandemic. The author identifies a number of trends that have a certain pattern, substantiated by a number of studies. The author highlighted the advantages of remote work, the difficulties associated with rapid rotation from the office to the external environment, managed to identify the factors of reducing and increasing the efficiency of remote work.

The most massive white dwarfs in the solar neighbourhood

ABSTRACT We present an analysis of the most massive white dwarf candidates in the Montreal White Dwarf Database 100 pc sample. We identify 25 objects that would be more massive than $1.3\, {\rm M}_{\odot }$ if they had pure H atmospheres and CO cores, including two outliers with unusually high photometric mass estimates near the Chandrasekhar limit. We provide follow-up spectroscopy of these two white dwarfs and show that they are indeed significantly below this limit. We expand our model calculations for CO core white dwarfs up to M = 1.334 M⊙, which corresponds to the high-density limit of our equation-of-state tables, ρ = 109 g cm−3. We find many objects close to this maximum mass of our CO core models. A significant fraction of ultramassive white dwarfs are predicted to form through binary mergers. Merger populations can reveal themselves through their kinematics, magnetism, or rapid rotation rates. We identify four outliers in transverse velocity, four likely magnetic white dwarfs (one of which is also an outlier in transverse velocity), and one with rapid rotation, indicating that at least 8 of the 25 ultramassive white dwarfs in our sample are likely merger products.

Research on Optimization Method of Tool Path in Five-Axis Process Singular Region

For the five-axis machine into the singular region in the process of parts processing, resulting in a discontinuous and rapid rotation of the axis of rotation of large angles. Based on the analysis of the cause of the obvious ripple on the machined surface and the influence on the machining precision, a mathematical model of the singular region is established, and an optimization method of the tool path in the singular region is proposed. The simulation and practical machining results show that the method can effectively overcome the problem of excessive movement of the rotating shaft in the Song singular region of 5-axis machine tool, and solve the surface corrugated defects caused by the problem, while improving the processing efficiency.

Ice giant magnetospheres

The ice giant planets provide some of the most interesting natural laboratories for studying the influence of large obliquities, rapid rotation, highly asymmetric magnetic fields and wide-ranging Alfvénic and sonic Mach numbers on magnetospheric processes. The geometries of the solar wind–magnetosphere interaction at the ice giants vary dramatically on diurnal timescales due to the large tilt of the magnetic axis relative to each planet's rotational axis and the apparent off-centred nature of the magnetic field. There is also a seasonal effect on this interaction geometry due to the large obliquity of each planet (especially Uranus). With in situ observations at Uranus and Neptune limited to a single encounter by the Voyager 2 spacecraft, a growing number of analytical and numerical models have been put forward to characterize these unique magnetospheres and test hypotheses related to the magnetic structures and the distribution of plasma observed. Yet many questions regarding magnetospheric structure and dynamics, magnetospheric coupling to the ionosphere and atmosphere, and potential interactions with orbiting satellites remain unanswered. Continuing to study and explore ice giant magnetospheres is important for comparative planetology as they represent critical benchmarks on a broad spectrum of planetary magnetospheric interactions, and provide insight beyond the scope of our own Solar System with implications for exoplanet magnetospheres and magnetic reversals. This article is part of a discussion meeting issue ‘Future exploration of ice giant systems'.