Orbital Radius Research Articles

ALMA 2D super-resolution imaging of Taurus–Auriga protoplanetary disks: Probing statistical properties of disk substructures

Abstract In the past decade, ALMA observations of protoplanetary disks revealed various substructures including gaps and rings. Their origin of substructures may be probed through statistical studies of their physical properties. We present the analyses of archival ALMA Band 6 continuum data of 43 disks (39 Class II and four Herbig Ae) in the Taurus–Auriga region. We employ a novel 2D super-resolution imaging technique based on sparse modeling to obtain images with high fidelity and spatial resolution. As a result, we have obtained images with spatial resolutions comparable to a few au (${0_{.}^{\prime\prime}02}$–${0_{.}^{\prime\prime}1}$), which is two to three times better than conventional CLEAN methods. All dust disks are spatially resolved, with the radii ranging from 8 to 238 au with a median radius of 45 au. Half of the disks harbor clear gap structures, the radial locations of which show a bimodal distribution with peaks at ≲20 au and ≳30 au. We also see structures indicating weak gaps at all the radii in the disk. We find that the widths of these gaps increase with their depths, which is consistent with the model of planet–disk interactions. The inferred planet mass–orbital radius distribution indicates that the planet distribution is analogous to our solar system. However, planets with Neptune mass or lower may exist in all the radii.

Kinematic Model Yields Two Geo-Synchronous Orbits of E-M System and M-P-D System Validated by Total Energy Analysis

In Black Holes (BH) studies , a well-tested method of total energy analysis is used by which the radius of Innermost Stable Circular Orbit (ISCO) around the central BH is analyzed and the dimensionless spin parameter of BH is extracted. The same total energy analysis is utilized in case of E-M and M-P planet-satellite pairs and their extremum points are obtained. The energy maxima happens to be the inner unstable co-rotational orbit (aG1) and the energy minima happens to be outer stable corotational orbit(aG2) in case of E-M and M-P systems and their values from KM correspond to those obtained from Energy Analysis. This vindicates KM of binary pairs

The most common habitable planets III – modelling temperature forcing and surface conditions on rocky exoplanets and exomoons

ABSTRACT Small rocky planets, as well as larger planets that suffered extensive volatile loss, tend to be drier and have thinner atmospheres as compared to Earth. Such planets probably outnumber worlds better endowed with volatiles, being the most common habitable planets. For the subgroup of fast rotators following eccentric orbits, atmospheres suffer radiative forcing and their heat capacity provides a method for gauging atmospheric thickness and surface conditions. We further explore the model presented in a previous paper and apply it to real and hypothetical exoplanets in the habitable zone of various classes of stars, simulating atmospheric and orbital characteristics. For planetary eccentricities e ∼ 0.3, the forcing-induced hypothetical temperature variation would reach ∼80 K for airless planets and ∼10 K for planets with substantial atmospheres. For Kepler-186 f and Kepler-442 b, assuming e ∼ 0.1, temperature variations can reach ∼24 K. We also consider habitable exomoons in circular orbits around gas giants within the habitable zone, which suffer radiative forcing due to their epicyclic motion. We study several combinations of parameters for the characterization of planets (mass, eccentricity, and semimajor axis) and exomoons (mass, orbital radius, albedo, and atmospheric characteristics) for different stellar types. For e ∼ 0.3, exomoon temperature varies up to ∼90 K, while for ∼0.6 variations can reach ∼200 K. Such exomoons may plausibly retain their volatiles by continued volcanic activity fuelled by tidal dissipation. Although currently undetectable, such effects might be within reach of future Extremely Large Telescope-class telescopes and space missions with mid-infrared and coronagraphic capabilities.

Out-of-plane dynamics: a study within the circular restricted eight-body framework

This manuscript thoroughly explores the dynamics of a test particle around out-of-plane equilibrium points within the circular restricted eight-body problem. This particular scenario features a central primary emitting radiation, and it is a specific case derived from Kalvouridis and Hadjifotinou's analysis of Maxwell's ring problem in 2011. Our investigation uncovers two symmetrical out-of-plane equilibrium points denoted as E1,2(0, 0, z0), where z0 is determined by the equation z0 = ±a tanυ; υ = arcsin[(‒q/6)1/3], with q falling within the range (‒6, 0). Here, a denotes the radius of the circular orbit of peripheral primaries around the radiating central primary, and q signifies the radiation factor due to the central primary. Significantly, for a critical radiation factor value, qc = ‒3/√2, the equilibrium points E1,2 precisely align along the z-axis on the sphere of radius a and centered at the central primary. Within the intervals of ‒6 < q < qc and qc < q < 0, equilibrium points E1 and E2 are situated outside and inside the mentioned sphere on the z-axis, respectively. Specifically, for q ≤ qc, | z0 | ≤ a, while for q > qc, | z0 | > a. The study further explores the linear stability of E1,2. By analyzing characteristic curves derived from the variational equations of motion for infinitesimal mass around these equilibrium points, particularly for q values of ‒3/4, ‒3/√2, and ‒9√3/4, we observe that these out-of-plane equilibria, E1,2, demonstrate linear instability. This insight provides a comprehensive understanding of the intricate dynamics in this specific multi-body problem. Finally, the research illustrates periodic orbits surrounding the out-of-plane equilibrium point for specific values of q.

The X-ray variability of active galactic nuclei: Power spectrum and variance analysis of the Swift/BAT light curves

Aims. We study the X-ray power spectrum of active galactic nuclei (AGN) in order to investigate whether Seyfert I and II power spectra are similar or not and whether AGN variability depends on the mass and accretion rate of black holes as well as to compare the power spectra of AGN with the power spectra of Galactic X-ray black hole binaries. Method. We used 14–195 keV band light curves from the 157-month Swift/BAT hard X-ray survey, and we computed the mean power spectrum and excess variance of AGN in narrow black hole mass and AGN luminosity bins. We fitted a power-law model to the AGN power spectra, and we investigated whether the power spectrum parameters and the excess variance depend on the black hole mass, luminosity, and accretion rate of AGN. Results. We found the Seyfert I and Seyfert II power spectra to be identical, in agreement with AGN unification models. The mean AGN X-ray power spectrum has the same power-law like shape, with a slope of −1 in all AGN irrespective of their luminosity and black hole mass. We did not detect any flattening to a slope of zero at frequencies as low as 10−9 Hz. We detected an anti-correlation between the power spectral density function (PSD) amplitude and the accretion rate, similar to what has been seen in the past in the 2–10 keV band. This implies that the variability amplitude in AGN decreases with an increasing accretion rate. The universal AGN power spectrum is consistent with the mean 2–9 keV band Cyg X-1 power spectrum in its soft state. We detected a small difference in amplitude, but this is probably due to the difference in energy. Conclusions. The mean low-frequency AGN X-ray power spectrum is consistent with the extension of the mean 0.01–25 Hz Cyg X-1 power spectrum in its soft state to lower frequencies. We cannot prove that the mean AGN PSD is analogous to the mean Cyg X-1 PSD in its soft state, as we do not know the location of the high-frequency break in the hard X-ray AGN PSDs. However, if this is the case, then the accretion disc in AGN probably extends to the radius of the innermost circular stable orbit (as is probably the case with the black hole binaries in their soft state). The X-ray corona will then be located on top, illuminating the disc and producing the X-ray reflection and disc reverberation phenomena commonly observed in these objects. Furthermore, the agreement between the PSD amplitude in AGN and the Cyg X-1 (either in the soft or the hard state) over many decades in frequency indicates that the X-ray variability process is probably the same in all accreting objects, irrespective of the mass of the compact object. We plan to investigate this issue further in the near future.

Fitting the light curves of Sagittarius A* with a hot-spot model

Context. Sagittarius A* (Sgr A*) exhibits frequent flaring activity across the electromagnetic spectrum. Signatures of an orbiting hot spot have been identified in the polarized millimeter wavelength light curves observed with ALMA in 2017 immediately after an X-ray flare. The nature of these hot spots remains uncertain. Aims. We expanded existing theoretical hot-spot models created to describe the Sgr A* polarized emission at millimeter wavelengths. We sampled the posterior space, identifying best-fitting parameters and characterizing uncertainties. Methods. Using the numerical radiative transfer code ipole, we defined a semi-analytical model describing a ball of plasma orbiting Sgr A*, threaded with a magnetic field and emitting synchrotron radiation. We then explored the posterior space in the Bayesian framework of dynesty. We fit the static background emission separately, using a radiatively inefficient accretion flow model. Results. We considered eight models with a varying level of complexity, distinguished by choices regarding dynamically important cooling, non-Keplerian motion, and magnetic field polarity. All models converge to realizations that fit the data, but one model without cooling, non-Keplerian motion, and magnetic field pointing toward us improved the fit significantly and also matched the observed circular polarization. Conclusions. Our models represent observational data well and allow testing various effects in a systematic manner. From our analysis, we have inferred an inclination of ∼155 − 160 deg, which corroborates previous estimates, a preferred period of ∼90 min, and an orbital radius of 9 − 12.0 gravitational radii. Our non-Keplerian models indicate a preference for an orbital velocity of 0.6–0.9 times the Keplerian value. Last, all our models agree on a high dimensionless spin value (a* &gt; 0.8), but the impact of spin on the corresponding light curves is subdominant with respect to other parameters.

Explaining QPOs data for black holes in the Starobinsky–Bel–Robinson gravity

In this work we explore the properties of the spacetime around the Schwarzschild-like black hole in the Starobinsky–Bel–Robinson gravity through a test particle motion and its quasi periodic oscillations (QPOs) in the circular orbits in the close vicinity of the black hole horizon. We show how the extra spacetime parameter β\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta $$\\end{document} affects the effective potential, energy, angular momentum, inner most circular orbit (ISCO) radius, and trajectory of a test particle. Next, we focus on the QPOs of particles and explore it in the relativistic precision model. Finally, we apply our analysis to explain the observational data obtained for several black hole candidates including GRO J1655-40, GRS 1915+105, XTE J1859+226, and XTE J1550-564 and get constraints on their spacetime parameters by employing the Markov Chain Monte Carlo analysis methodology.

Testing gravitational lensing effects by supermassive massive black holes with superstring theory metric: Astrophysical implications and EHT constraints

We investigate gravitational lensing, both strong and weak, induced by charged black holes within heterotic superstring theory – α′-corrected Reissner–Nordström (RN) black holes characterized by an additional parameter, denoted as α, in addition to mass M and charge Q. Our findings reveal that as the parameter α increases, various crucial parameters such as the unstable photon orbit radius rph, critical impact parameter uph, deflection angle αD(θ), and angular position θ∞ also increase. Concurrently, the angular separation s decreases, while the relative magnitude rmag increases with the growing value of α. Utilizing supermassive black holes (SMBH) Sgr A* and M87* as gravitational lenses, the deflection angle resulting from the α′-corrected RN black hole, in both strong and weak field limits, surpasses that of the RN black holes (α=0) and falls below that of Schwarzschild black holes (α=0, Q=0). For Sgr A*, the angular position θ∞ lies within (24.08, 26.38) μas, while for M87* it ranges from (18.23, 19.96) μas. Estimating the time delay between the first and second relativistic images using twenty supermassive galactic center black holes as lenses, we find, for instance, that the time delay for Sgr A* and M87*, with Q=0.5 and α=5, can reach approximately 9.81 min and 14835.6 min, respectively. Remarkably, the EHT results for Sgr A* impose more stringent limits on the parameter space of α′-corrected RN black holes compared to those established by the EHT results for M87*. Our analysis deduces that, within the 1σ region, a substantial portion of the parameter space for α′-corrected RN black holes aligns with the Event Horizon Telescope (EHT) results for M87* and Sgr A*, and that and one cannot rule out the possibility of that heterotic superstring theory’s α′-corrected RN black holes being strong candidates for astrophysical black holes.

Modelling Einstein cluster using Einasto profile

We demonstrate a general relativistic approach to model dark matter halos using the Einstein cluster, with the matter stress-energy generated by collisionless particles moving on circular geodesics in all possible angular directions and orbital radii. Such matter, as is known, allows an anisotropic pressure profile with non-zero tangential but zero radial pressure. We use the Einasto density profile for the Einstein cluster. Analytical studies on its properties (metric functions) and stability issues are investigated. Further, to establish this model (with the Einasto profile) as one for a dark matter halo,we use the SPARC galactic rotation curve data and estimate the best-fit values for the model parameters. General relativistic features (beyond the Keplerian velocities) such as the tangential pressure profile, are quantitatively explored. Thus, Einstein clusters with the Einasto profile, which tally well with observations, may be considered as a viable model for dark matter halos.

Validation of Advanced Kinematic Model of Earth-Moon System by Observed Length of Day Curve

NASA’s press release of ‘Moon having receded by 1 m from Earth in a quarter of century’ on the Silver Jubilee Anniversary (20 July 1994) of Man’s landing on Moon led to the development of the Kinematic Model(KM) of evolving Earth-Moon System. Best fit KM parameters are adopted for the analysis of evolving E-M system, The present length of day of Earth is assumed to be 24 hours, orbital period of Moon divided by spin period of Earth=LOM/LOD=27.322 and the age of Moon=4.467Gy. Using this best fit model parameters the velocity of recession of Moon is derived as 2.3cm/y as compared to 3.7cm/y by Lunar Laser Ranging experiment.KM is used to plot lengthening of day(LOD) curve from pre-cambrian period (2.5Gy ago) to the present time. This theoretical plot is superimposed on the observed lengthening of day curve. The observed plot is generated from the observed length of day in different geologic epochs by John West Wells, Charles P.Sonnet &amp; Chan and Kaula &amp; Harris by the study of coral fossils, ancient tidalites and marine creatures respectively. The superposition gives more than 25% mismatch in remote past around 2.5Gya. This KM did not consider the obliquity angle 23.44° of Earth and the inclination angle of 5.14° of Lunar Orbital Plane with respect to Ecliptic plane. The classical KM assumed monotonic spiral expansion of Moon from Earth as shown in Figure 1. A recent paper “Tidal evolution of Moon in high angular momentum, high obliquity Earth” has revolutionized the Earth-Moon modeling and paved the way for near-match between observated and theoretical LOD curve. In the new scenario Moon’s tidal evolution is anything but sedate and monotonic. It experienced a bumpy launch through gravitational sling shot at the first geo-synchronous orbit of 15,000Km. Moon was gravitationally catapulted and launched on an expanding spiral path but this expansion was turbulent, chaotic and got stalled at times due to huge lunar obliquity tides during Laplace Plane transition and due to Cassini state transition as shown in Figure 2. Only after Moon settles down in Cassini state II that it resumes its monotonic and sedate spiral expansion as envisaged in the classical picture but this spiral expansion was at accelerated pace so as to reach 3,84,499Km orbital radius in 4.5Gy. It transits in fits , in chaotic and turbulent phase, for 3.3Gy whereas it spends1.2Gy in bounded state therefore this new model is referred to as ‘Fits and Bound’ model of E-M system. On this time scale the modern time recession rate comes to be 3.7cm/y. If this accelerated time frame is adopted then we get near-exact match between theory and observed LOD curve with worst mis-match being -4%. In this accelerated time frame, all E-M system parameters are obtained and it is self consistent model with velocity of recession = 3.7cm/y, LOM/LOD = 27.322 and near match between theory and observed LOD curve and spending 3.3Gy in turbulent and stalled evolutionary phase and spending 1.2Gy in the present accelerated phase. This gives the final vindication to the advanced KM.

Dynamic analysis on an asymmetric spatial dumbbell-type model

The structural symmetric breaking of the spatial structure will enhance the coupling dynamic behaviors and bring new challenges for the dynamic analysis on the spatial structure inevitably. The main contribution of this paper is proposing a structure-preserving iteration method to investigate the effects of the dynamic symmetry-breaking factors on the dynamic behaviors of the rigid-flexible coupling systems. Firstly, the spatial flexible damping beam assembled with two particles on both ends is simplified as an asymmetric spatial dumbbell-type model. For this model, the coupling dynamic equations are presented based on the Hamiltonian variational principle. Then, connecting the symplectic precise integration method for the ordinary differential equations mainly controlling the plane motion of the model and the generalized multi-symplectic scheme for the partial differential equation mainly controlling the transverse vibration of the beam, a structure-preserving numerical iteration method is proposed, which provides a new way to analysis the dynamic behaviors of the coupling problems with the symmetric breaking. Finally, the effects of the absolute mass and the mass ratio of the additional particles on the orbit radius, the orbit true anomaly velocity, the attitude angle velocity of the model and the transverse vibration of the flexible beam are reproduced by using the structure-preserving numerical iteration method in the numerical simulations. Particularly, the effects of the additional particles on the attitude stability of the model and the vibration dissipation of the flexible damping beam are investigated, which gives some guidance for the attitude adjustment strategy and the vibration control method for the spatial flexible structure with the structural symmetric breaking.

Extreme mass-ratio inspiral as a probe of extra dimensions: The case of spinning massive object

Extreme mass-ratio inspiral (EMRI), as one of most important and promising gravitational wave (GW) sources, which is the ideal tool to test fundamental theories and nature of massive black hole (MBH). In this paper, we consider the EMRI system consisting of a rotating barneworld MBH with tidal charge Q and a stellar-mass compact object (CO), where a non-spinning CO inspirals on the equatorial and circular orbits around the MBH. Under the adiabatic approximate condition, we show the evolution of circular orbital radius by computing the EMRI fluxes and orbital phase modified by tidal charge. We find that the positive and negative values of tidal charges have the difference influences on the EMRI orbital dynamics. In particular, the inspiral motion of CO in the rotating barneworld MBH with a negative tidal charge would be end more earlier than the positive tidal charge case. Accordingly, the EMRI waveforms from the positive tidal charge cases can put more rigorous constraint results comparing with the negative tidal charge cases. Finally, we analyze the phase differences of two EMRI waveforms from Kerr BH and rotating braneworld BH with tidal charge by computing dephasing and mismatch. Our results indicate that LISA can distinguish the EMRI waveforms from rotating braneworld BH with the negative tidal charge as small as Qmin∼−10−6 under the suitable scenarios, which can sever as the unique discriminator of detecting the physics of extra dimensions.

The Uranus system from occultation observations (1977–2006): Rings, pole direction, gravity field, and masses of Cressida, Cordelia, and Ophelia

From an analysis of 31 Earth-based stellar occultations and three Voyager 2 occultations spanning 1977–2006 (French et al. 2023a), we determine the keplerian orbital elements of the centerlines of the nine main Uranian rings to high accuracy, with typical RMS residuals of 0.2–0.4 km and 1-σ formal errors in a,ae, and asini of order 0.1 km, registered on an absolute radius scale accurate to 0.2 km at the 2-σ level. The λ ring shows more substantial scatter, with few secure detections. We identify a host of free and forced normal modes in several of the ring centerlines and inner and outer edges. In addition to the previously-known free modes m=0 in the γ ring and m=2 in the δ ring, we find two additional outer Lindblad resonance (OLR) modes (m=−1 and −2) and a possible m=3 inner Lindblad resonance (ILR) mode in the γ ring. No normal modes are detected for rings 6, 5, 4, α, or β. Five separate normal modes are forced by small moonlets: the 3:2 inner ILR of Cressida with the η ring, the 6:5 ILR of Ophelia with the γ ring, the 23:22 ILR of Cordelia with the δ ring, the 14:13 ILR of Ophelia with the outer edge of the ϵ ring, and the counterpart 25:24 OLR of Cordelia with the ring’s inner edge. The phases of the modes and their pattern speeds are consistent with the mean longitudes and mean motions of the satellites, confirming their dynamical roles in the ring system. We find no evidence of normal modes excited by internal planetary oscillations. We determine the width–radius relations for nearly all of the detected modes, with positive width–radius slopes for ILR modes (including the m=1 elliptical orbits) and negative slopes for most of the detected OLR modes, supporting the standard self-gravity model for ring apse alignment. We find no convincing evidence for librations of any of the rings. The Uranus J2000 pole direction at epoch TDB 1986 Jan 19 12:00 is αP=77.311327±0.000141° and δP=15.172795±0.000618°. The slight pole precession predicted by Jacobson (2023) is not detectable in our orbit fits, and the absolute radius scale is not strongly correlated with the pole direction. From Monte Carlo fits to the measured apsidal precession and nodal regression rates of the eccentric and inclined rings, we determine the zonal gravitational coefficients J2=(3509.291±0.412)×10−6,J4=(−35.522±0.466)×10−6, and J6 fixed at 0.5×10−6, with a correlation coefficient ρ(J2,J4)=0.9861, for a reference radius R=25559 km. This result differs significantly from both earlier and more recent results (Jacobson 2014, 2023), owing to our inclusion of previously neglected systematic effects, such as the offset of semimajor axes of the geometric ring centerlines from their estimated dynamical centers of mass and the significant contributions of Cordelia and Ophelia to the precession rate of the ϵ ring. Although we cannot set useful independent limits on J6, we obtain strong joint constraints on combinations of J2,J4, and J6 that are consistent with our measurements. These can be used to limit the range of realistic models of the planet’s internal density distribution and wind profile with depth. The observed anomalous apsidal and nodal precession rates of the α and β rings are consistent with the presence of unseen moonlets with masses and orbital radii predicted by Chancia and Hedman (2016). The γ ring’s putative m=3 mode does not appear to be forced by a satellite, whose predicted size would be too large to have avoided prior detection. If this mode is excluded from the orbit fit, the solution for the γ ring has a very large anomalous apsidal precession rate of unknown origin. From the amplitudes and resonance radii of normal modes forced by moonlets, we determine the masses of Cressida, Cordelia, and Ophelia. Their estimated densities decrease systematically with increasing orbital radius and generally follow the radial trend of the Roche critical density for a shape parameter γ=1.6.

Orbital motion of gold heterodimer driven by optical force of circularly polarized light and reactive drag of medium

Abstract This theoretical study explores the two-dimensional orbital motion of an optically bound heterodimer consisting of two gold nanoparticles (NPs) of different sizes, driven by circularly polarized (CP) light. Although a CP light possesses only spin angular momentum without orbital angular momentum, it can still induce orbital revolution in the plasmonic heterodimer. This phenomenon arises from the interaction between the optical force and torque generated by the CP light and the reactive drag force and torque from the surrounding medium. We calculate the optical forces acting on each NP by analyzing the Maxwell stress tensor at their surfaces, and we account for the reactive drag force using Stokes’ law. These forces are used to simulate the trajectories of the NPs through dynamic equations of motion. Our results demonstrate that, regardless of the initial conditions of the two NPs, they will become optically bound together, exhibiting rigid-body translation and rotation. Notably, the center of mass of the heterodimer undergoes an orbital revolution around a fixed point eventually. The CP light-manipulated heterodimer behaves like a boomerang, acting as a spinning rotor on a circular path. The heterodimer's orbital radius and direction of revolution are influenced by the size disparity between the two NPs. Additionally, each NP experiences spin motion, with the spin direction determined by the handedness of the CP light. The optically bound gold heterodimer functions as a light-driven microrotor, with potential applications in microfluidic channels. These findings offer valuable insights into the optomechanical manipulation of non-monodisperse NP clusters using CP light.

Defected twisted ring topology for autonomous periodic flip-spin-orbit soft robot.

Periodic spin-orbit motion is ubiquitous in nature, observed from electrons orbiting nuclei to spinning planets orbiting the Sun. Achieving autonomous periodic orbiting motions, along circular and noncircular paths, in soft mobile robotics is crucial for adaptive and intelligent exploration of unknown environments-a grand challenge yet to be accomplished. Here, we report leveraging a closed-loop twisted ring topology with a defect for an autonomous soft robot capable of achieving periodic spin-orbiting motions with programmed circular and re-programmed irregular-shaped trajectories. Constructed by bonding a twisted liquid crystal elastomer ribbon into a closed-loop ring topology, the robot exhibits three coupled periodic self-motions in response to constant temperature or constant light sources: inside-out flipping, self-spinning around the ring center, and self-orbiting around a point outside the ring. The coupled spinning and orbiting motions share the same direction and period. The spinning or orbiting direction depends on the twisting chirality, while the orbital radius and period are determined by the twisted ring geometry and thermal actuation. The flip-spin and orbiting motions arise from the twisted ring topology and a bonding site defect that breaks the force symmetry, respectively. By utilizing the twisting-encoded autonomous flip-spin-orbit motions, we showcase the robot's potential for intelligently mapping the geometric boundaries of unknown confined spaces, including convex shapes like circles, squares, triangles, and pentagons and concaves shapes with multi-robots, as well as health monitoring of unknown confined spaces with boundary damages.

Irregularly Shaped Satellites-Phobos &amp; Deimos-Moons of Mars, and Their Evolutionary History

Phobos, a moon of Mars, is below the Clarke’s synchronous orbit and due to tidal interaction is losing altitude. With this altitude loss it is doomed to the fate of total destruction by direct collision with Mars. On the other hand Deimos, the second moon of Mars is in extrasynchronous orbit and almost stay put in the present orbit. The reported altitude loss of Phobos is 1.8 m per century by wikipedia and 60ft per century according to ozgate url . The reported time in which the destruction will take place is 50My and 40My respectively. The authors had proposed a planetary-satellite dynamics based on detailed study of Earth-Moon[personal communication: http://arXiv.org/abs/0805.0100 ]. Based on this planetary satellite dynamics, 2 m/century approach velocity leads to the age of Phobos to be 23 Gyrs which is physically untenable since our Solar System’s age is 4.567Gyrs. Hence the present altitude loss is assumed to be 20 m per century. This leads to the age of Phobos to be 2.3Gyrs and age of Deimos to be 2.26Gyrs which is an acceptable result and from this analysis it is predicted that the travel time from the present orbital radius of 9380 km to the Martian surface at 3397 km is 10.4Myrs. Hence doomsday of Phobos is at 10.4Myrs from now. Mars Express studies have confirmed that Phobos is indeed trapped in a death spiral.

Noncontact Haptic Rendering of Static Contact With Convex Surface Using Circular Movement of Ultrasound Focus on a Finger Pad.

A noncontact tactile stimulus can be presented by focusing airborne ultrasound on the human skin. Focused ultrasound has recently been reported to produce not only vibration but also static pressure sensation on the palm by modulating the sound pressure distribution at a low frequency. This finding expands the potential for tactile rendering in ultrasound haptics as static pressure sensation is perceived with a high spatial resolution. In this study, we verified that focused ultrasound can render a static pressure sensation associated with contact with a small convex surface on a finger pad. This static contact rendering enables noncontact tactile reproduction of a fine uneven surface using ultrasound. In the experiments, four ultrasound foci were simultaneously and circularly rotated on a finger pad at 5 Hz. When the orbit radius was 3 mm, vibration and focal movements were barely perceptible, and the stimulus was perceived as static pressure. Moreover, under the condition, the pressure sensation rendered a contact with a small convex surface with a radius of 2 mm. The perceived intensity of the static contact sensation was equivalent to a physical contact force of 0.24 N on average, 10.9 times the radiation force physically applied to the skin.

Influence factors of CO adsorption on C2N-supported dual-atom catalysts unveiled by machine learning and twofold feature engineering.

Dual-atom catalysts (DACs) have emerged as a compelling frontier in the realm of the electrochemical carbon dioxide reduction reaction (CO2RR). However, elucidating the intrinsic properties of dual-atom pairs and their direct correlation with catalytic activity poses significant challenges. Herein, we investigate CO adsorption on 248 kinds of C2N-supported DACs and analyze the underlying structure-activity relationships of dual transition metal (TM) atoms based on density functional theory (DFT) calculations and machine learning (ML) models. Compared to the direct input of atomic features in the decision tree model of ML, we confirm that extra feature engineering with the introduction of the arithmetic combination of atomic features can better reflect the correlation of dual TM atoms on C2N-based DACs. Further feature importance analysis reveals a strong relationship between the last one occupied orbital radius (rv), group number (G) for dual TM atoms and the CO binding strength, as well as a potential connection with the d band centre (εd). Our work provides deeper insights into the design of DACs and highlights the significance of twofold feature engineering for the synergistic effects between dual TM atoms.

A Pathway for Collisional Planetesimal Growth in the Ice-dominant Regions of Protoplanetary Disks

We present a semi-analytic model for the growth, drift, desorption, and fragmentation of millimeter- to meter-sized particles in protoplanetary disks. Fragmentation occurs where particle collision velocities exceed critical fragmentation velocities. Using this criterion, we produce fragmentation regions in disk orbital radius–particle size phase space for particles with a range of material properties, structures, and compositions (including SiO2, Mg2SiO4, H2O, CO2, and CO). For reasonable disk conditions, compact aggregate H2O, CO2, and CO ice particles do not reach destructive relative velocities and are thus not likely to undergo collisional fragmentation. Uncoated silicate particles are more susceptible to collisional destruction and are expected to fragment in the inner disk, consistent with previous work. We then calculate the growth, drift, and sublimation of small particles, initially located in the outer disk. We find that ice-coated particles can avoid fragmentation as they grow and drift inward under a substantial range of disk conditions, as long as the particles are aggregates composed of 0.1 μm-sized monomers. Such particles may undergo runaway growth in disk regions abundant in H2O or CO2 ice, depending on the assumed disk temperature structure. These results indicate that icy collisional growth to planetesimally relevant sizes may happen efficiently throughout a disk’s lifetime, and is particularly robust at early times when the disk’s dust-to-gas ratio is comparable to that of the interstellar medium.

New bearing model with flexible cage and study of dynamic behavior under variable-speed

Since rolling bearings frequently operate in variable speed conditions, the elastic deformation of the cage occurs intensely due to the enhanced excitation, which may lead to dynamic instability or even failure of the bearing. To this end, a flexible cage model based on the semi-flexible body element is developed in this paper. The force excitation from the ball and the guiding ring is considered to be applied to the cage. By coupling with the previous bearing model, a bearing dynamics model with flexible cage is presented. The results predicted by this model are closer to the experimental values than those of the rigid model. The differences between the two models in predicting the bearing dynamic performance under typical variable speed conditions are compared. The effect of preload on its dynamic behavior was further investigated with the flexible model. The results show that a slightly smaller radius of the cage orbit is predicted by the flexible model than that of the rigid model. Compared with the rigid model, more stability of cage motion is predicted by the flexible model. A similar phenomenon can be observed in the force excitation on the cage. There is not significant difference between these two models in predicting the velocity of the bearing assembly. The work in this paper provides a new idea for modeling flexible cages.