Non-axisymmetric Structures Research Articles

REBELS-25: discovery of a dynamically cold disc galaxy at z = 7.31

ABSTRACT We present high-resolution ($\sim 0.14$ arcsec = 710 pc) Atacama Large Millimetre/submillimetre Array [C ii] 158 $\mu$m and dust continuum follow-up observations of REBELS-25, a [C ii]-luminous ($L_{\mathrm{[CII]}}=(1.7\pm 0.2)\times 10^9\, \mathrm{L_{\odot }}$) galaxy at redshift $z=7.3065\pm 0.0001$. These high-resolution, high signal-to-noise observations allow us to study the sub-kpc morphology and kinematics of this massive ($M_* = 8^{+4}_{-2} \times 10^9 \mathrm{{\rm M}_{\odot }}$) star-forming (SFR$_{\mathrm{UV+IR}} = 199^{+101}_{-63} \mathrm{{\rm M}_{\odot }} \mathrm{yr}^{-1}$) galaxy in the Epoch of Reionization. By modelling the kinematics with $^{\mathrm{3D}}$BAROLO, we find it has a low-velocity dispersion ($\bar{\sigma } = 33^{+9}_{-7}$ km s$^{-1}$) and a high ratio of ordered-to-random motion ($V_{\mathrm{rot, ~max}}/\bar{\sigma } = 11 ^{+6}_{-5}$), indicating that REBELS-25 is a dynamically cold disc. Additionally, we find that the [C ii] distribution is well fit by a near-exponential disc model, with a Sérsic index, n, of $1.3 \pm 0.2$, and we see tentative evidence of more complex non-axisymmetric structures suggestive of a bar in the [C ii] and dust continuum emission. By comparing to other high spatial resolution cold gas kinematic studies, we find that dynamically cold discs seem to be more common in the high-redshift Universe than expected based on prevailing galaxy formation theories, which typically predict more turbulent and dispersion-dominated galaxies in the early Universe as an outcome of merger activity, gas accretion, and more intense feedback. This higher degree of rotational support seems instead to be consistent with recent cosmological simulations that have highlighted the contrast between cold and warm ionized gas tracers, particularly for massive galaxies. We therefore show that dynamically settled disc galaxies can form as early as 700 Myr after the big bang

Revealing asymmetry on mid-plane of protoplanetary disc through modelling of axisymmetric emission: methodology

ABSTRACT This study proposes an analytical framework for deriving the surface brightness profile and geometry of a geometrically thin axisymmetric disc from interferometric observation of continuum emission. Such precise modelling facilitates the exploration of faint non-axisymmetric structures, such as spirals and circumplanetary discs. As a demonstration, we simulate interferometric observations of geometrically thin axisymmetric discs. The proposed method can reasonably recover the injected axisymmetric structures, whereas Gaussian fitting of the same data yielded larger errors in disc orientation estimation. To further test the applicability of the method, it was applied to the mock data for $m=1,2$ spirals and a point source, which are embedded in a bright axisymmetric structure. The injected non-axisymmetric structures were reasonably recovered except for the innermost parts, and the disc geometric parameter estimations were better than Gasussian fitting. The method was then applied to the real data of Elias 20 and AS 209, and it adequately subtracted the axisymmetric component, notably in Elias 20, where substantial residuals remained without our method. We also applied our method to continuum data of PDS 70 to demonstrate the effectiveness of the method. We successfully recovered emission from PDS 70 c consistently with previous studies, and also tentatively discovered new substructures. The current formulation can be applied to any data for disc continuum emission, and aids in the search of spirals and circumplanetary discs, whose detection is still limited.

The AGORA High-resolution Galaxy Simulations Comparison Project. IV. Halo and Galaxy Mass Assembly in a Cosmological Zoom-in Simulation at z ≤ 2

In this fourth paper from the AGORA Collaboration, we study the evolution down to redshift z = 2 and below of a set of cosmological zoom-in simulations of a Milky Way mass galaxy by eight of the leading hydrodynamic simulation codes. We also compare this CosmoRun suite of simulations with dark matter-only simulations by the same eight codes. We analyze general properties of the halo and galaxy at z = 4 and 3, and before the last major merger, focusing on the formation of well-defined rotationally supported disks, the mass–metallicity relation, the specific star formation rate, the gas metallicity gradients, and the nonaxisymmetric structures in the stellar disks. Codes generally converge well to the stellar-to-halo mass ratios predicted by semianalytic models at z ∼ 2. We see that almost all the hydro codes develop rotationally supported structures at low redshifts. Most agree within 0.5 dex with the observed mass–metallicity relation at high and intermediate redshifts, and reproduce the gas metallicity gradients obtained from analytical models and low-redshift observations. We confirm that the intercode differences in the halo assembly history reported in the first paper of the collaboration also exist in CosmoRun, making the code-to-code comparison more difficult. We show that such differences are mainly due to variations in code-dependent parameters that control the time stepping strategy of the gravity solver. We find that variations in the early stellar feedback can also result in differences in the timing of the low-redshift mergers. All the simulation data down to z = 2 and the auxiliary data will be made publicly available.

Geometric deviation during incremental sheet forming process: Analytical modeling and experiment

Incremental sheet forming (ISF), a promising and flexible forming method, is generally restricted by the unsatisfied geometric deviation for industrial applications; therefore, effective control and accurate prediction of geometric deviation in ISF are essential for quality improvement. However, the geometric deviation in ISF is extremely sensitive to the geometric shape, toolpath, and process parameters, which is challenging to predict and control. In this study, the comprehensive geometric-related mechanisms in ISF were analyzed, including springback after local bending of the bent and contact zones, and the elastic deflection of the inclined wall, particularly the associated deformation in the weak-stiffness region. Through a creative equivalent mapping method for calculating the elastic deflection of complex structures and modeling the bending moment distribution in different zones, an analytical model was developed to accurately and universally predict the geometric deviations of parts by ISF. Based on the results of the experiments and comparative studies using a response surface model, the proposed model provided superior capability for predicting the geometric accuracies of parts made using ISF with different sheet materials, process parameters, and geometric shapes, even for complex parts with non-axisymmetric structures and stepped features. The geometric-related mechanisms, forming characteristics, and influences of crucial parameters in ISF are discussed by adopting an analytical model combined with numerical simulations, demonstrating that the elastic deflection on the inclined wall, particularly the associated deformation in the weak-stiffness region, plays a primary role in the geometric deviation of complex parts compared with other geometric-related mechanisms.

The rise and fall of bars in disc galaxies from z = 1 to z = 0

Context. Stellar bars are non-axisymmetric structures found in over 30 per cent of massive disc galaxies in the local Universe. The environment could play a significant role in determining whether or not a spiral galaxy is likely to develop a bar. Aims. We investigate the influence of the environment on the evolution of barred and unbarred disc galaxies with a mass of larger than 1010 M⊙ from z = 1 down to z = 0, employing the TNG50 magnetic-hydrodynamical simulation. Methods. We determined the fraction of barred galaxies that conserve their bar and the fraction of those that lost it by z = 0. We also estimate the fraction of unbarred galaxies at z = 1 that develop a bar at later times. We study the merger histories and the distance of close companions for each category to understand the role of the environment in the evolution of these galaxies. Results. We find that 49 per cent of z = 1 disc galaxies undergo a morphological transformation, transitioning into either a lenticular or spheroidal galaxy, while the other 51 per cent retain the large disc shape. The morphological alteration is mostly influenced by the environment. Lenticular and spheroidal galaxies tend to exist in denser environments and have more frequent mergers compared to disc galaxies. We find that bars are stable after they have formed, as over half of the barred galaxies (60.2 per cent) retain the bar structure and have experienced fewer mergers compared to those galaxies that lose their bars (5.6 per cent). These latter galaxies start with weaker and shorter bars at z = 1, are influenced by tidal interactions, and are frequently observed in more populated areas. Additionally, our study reveals that less than 20 per cent of unbarred galaxies will never develop a bar and exhibit the quietest merger history. Unbarred galaxies that undergo bar formation after z = 1 more frequently experience a merger event. Furthermore, tidal interactions with a close companion may account for bar formation in at least one-third of these instances. Conclusions. Our findings highlight that stable bars are prevalent in disc galaxies. Bar evolution may nonetheless be affected by the environment. Interactions with nearby companions or tidal forces caused by mergers have the capacity to disrupt the disc. This perturbance may materialise as the dissolution of the bar, the formation of a bar, or, in its most severe form, the complete destruction of the disc, resulting in morphological transformation. Bars that are weak and short at z = 1 and undergo major or minor mergers may eventually dissolve, whereas unbarred galaxies that enter crowded environments or experience a merger may develop a bar.

The smallest structures in Saturn’s rings from UVIS stellar occultations

On the largest scales Saturn’s rings are often thought of as axisymmetric annuli varying only radially in optical depth with exceptions of spiral waves and eccentric ringlets. But on scales smaller than a few tens of km yet still larger than the largest common ring particles, the assumption of azimuthal symmetry breaks down. Structures such as “straw” in the troughs of density waves, partial gaps around propeller moonlets, and ephemeral particle aggregates such as self-gravity wakes are responsible for the predominant variations in optical depth. During the 13 year Cassini mission, the Ultraviolet Imaging Spectrograph (UVIS) high speed photometer (HSP) measured 80 stellar chord occultations of Saturn’s main rings. In the vicinity of the minimum ring plane radius of each chord, the occultation line-of-sight slewed across the ring plane tangent to the Keplerian motion of the ring particles. These occultations measured ultraviolet light in the wavelength range 110–190 nm with 1- or 2-ms ms integration times, providing optical depth measurements with resolution comparable to the Fresnel scale of ∼10 m in the frame co-moving with the local Keplerian speed. These high-resolution chord occultations reach their minimum ring radii over a broad range of radial locations within Saturn’s main rings and resolve non-axisymmetric structures in a wide variety of ring regions. We measure the azimuthal length scales and optical depth profiles of “ghosts”, or azimuthally limited gaps with radial scales less than 30 m (Baillié et al., 2013), in the C ring plateaus. We measure the length scale of transparent gaps and self-gravity wakes in the peaks and troughs of spiral density waves. We present optical depth profiles which resolve axisymmetric waves in the A and B rings and constrain the azimuthal length scale over which the waves remain axisymmetric to ∼1000 km. We combine autocorrelation length scales from stellar occultations which cut across the minimum ring radius of a chord occultation with line-of-sight trajectories from other occultations which are not tangent to the rings to constrain the morphology of the azimuthally and temporally averaged mesoscale structures at that ring radius. 2D autocorrelation profiles from stellar occultations show self-gravity wakes and axisymmetric waves often coexisting.

Drop encapsulation and bubble bursting in surfactant-laden flows in capillary channels

We present a parametric study of the unsteady phenomena associated with the flow of elongated gas bubbles traveling through liquid-filled square capillaries under high Weber number conditions. These conditions induce the formation of an indentation at the back of the bubble that commonly gives way to a deep reentrant liquid jet penetrating the bubble. Subsequent steps include pinch-off events in the penetrating liquid to generate one or multiple encapsulated drops which may coalesce, in conjunction with the bursting of the bubble-liquid interface by either the liquid jet or the drops. Some of these interfacial instabilities have previously been reported experimentally and numerically for liquid-liquid flow in microchannels. We carry out three-dimensional direct numerical simulations based on a hybrid interface-tracking/level-set method capable of accounting for the presence and dynamic exchange of surfactants between the liquid bulk phase and the liquid-gas interface. Our results indicate that the delicate interplay among inertia, capillarity, viscosity, surfactant adsorption/desorption kinetics, and Marangoni stresses has a dramatic influence over the nonaxisymmetric morphological structures of the encapsulated drops-elongated bubble. This strong coupling also influences the pinch-off time, penetration depth of the liquid, and number, size, and velocity of the encapsulated drops across the bubble. The observed phenomena are summarized in three main morphological regimes based on surfactant-related parameters and dimensionless groups. A discussion of the flow regime maps is also provided. Published by the American Physical Society 2024

Unveiling the origins of galactic bars: insights from barred and unbarred galaxies

ABSTRACT A significant fraction of local galaxies exhibit stellar bars, non-axisymmetric structures composed of stars, gas, and dust. Identifying key differences between the properties of barred and unbarred galaxies can uncover clues about the conditions for triggering bar formation. We explore the early stages of bar formation in a small sample of disc barred galaxies extracted from the TNG50 cosmological simulation, and compare their properties to those of unbarred galaxies. According to our results, the most important difference between barred and unbarred galaxies is that the former have systematically higher fractions of stellar to dark matter mass in their inner regions, from very early stages and prior to the formation of the bars. They harbour high initial gas content, fostering increased star formation rates and leading to a central mass concentration that grows faster over time compared to unbarred galaxies. Examining the evolution of the halo spin within $10\, \mathrm{ckpc}$ reveals that barred galaxies have higher angular momentum transfer from the disc to the halo. Curiously, both barred and unbarred galaxies share similar initial low values of the halo spin, consistent with those proposed in the literature for bar formation. Furthermore, we evaluate existing stability criteria to capture the complexity of the process, and investigate the effects of mergers, flybys, and environment as possible drivers of bar formation. We find no clear link between mergers and disc instabilities resulting in the formation of bars, even though some of the simulated barred galaxies might have been influenced by these events.

Disc galaxies are still settling

When galactic discs settle and become massive enough, they are able to form stellar bars. These non-axisymmetric structures induce shocks in the gas, causing it to flow to the centre where nuclear structures, such as nuclear discs and rings, are formed. Previous theoretical and observational studies have hinted at the co-evolution of bars and nuclear discs, suggesting that nuclear discs grow ‘inside-out’ and thereby proposing that smaller discs reside in younger bars. Nevertheless, it remains unclear how the bar and the nuclear structures form and evolve over time. The smallest nuclear discs discovered to date tend to be larger than ∼200 pc, even though some theoretical studies have reported that when nuclear discs form, they can be much smaller. Using MUSE archival data, we report, for the first time, two extragalactic nuclear discs with radius measurements below 100 pc. Additionally, our estimations reveal the youngest bars found to date. We estimate that the bars in these galaxies formed 4.50−1.10+1.60(sys)−0.75+1.00(stat) and 0.7+2.60(sys)−0.05+0.05(stat) Gyr ago, for NGC 289 and NGC 1566, respectively. This suggests that at least some disc galaxies in the Local Universe may still be dynamically settling. By adding these results to previous findings in the literature, we are able to retrieve a stronger correlation between nuclear disc size and bar length. We also derive a tentative exponential growth scenario for nuclear discs.

Mode shape-dependent thermoacoustic interactions between a lean-premixed primary flame and an axially-staged transverse reacting jet

Axial fuel staging enables elevation of the turbine inlet temperature in advanced heavy-duty gas turbine combustors to ∼2000 K, ultimately to achieve more than 65% combined cycle efficiency, while limiting excessive nitrogen oxide production. While previous investigations have identified transverse jet-flow-dependent nitrogen oxides emission trends and the topological properties of reacting shear layers in vitiated crossflow environments, there exists a critical gap in the understanding of axial-fuel-staging-induced combustion instabilities. The present study therefore investigates the link between first- and second-stage flame dynamics in a lean-premixed combustor. We demonstrate that the second-stage jet-in-vitiated-crossflow flame is preferentially coupled to higher order acoustic modes than the upstream primary flame with the same characteristic nozzle dimension. The first- and second-stage-driven acoustic modes (two different timescales) are mutually incompatible, and the ensuing selective excitation is critically dependent on the position of the secondary injector relative to the mode shape. When the second-stage flame is located near a pressure node, or a velocity antinode, the transverse jet-stabilized flame is influenced by the primary flame-driven crossflow velocity oscillations, and exhibits conspicuous flapping motions in the crossflow direction accompanied by periodic partial extinction at the windward and leeward-side flame elements. If the second-stage flame is situated near a pressure antinode, on the other hand, the secondary jet flame's dynamics are governed by a combination of jet merging-induced flame surface destruction and the growth of non-axisymmetric coherent structures. In this case, high-intensity pressure oscillations are sustained by the local heat release fluctuations generated solely from the transverse reacting jets, whereas the upstream primary flame remains nearly unperturbed, or decoupled from the underlying feedback processes. This experimental observation is remarkable, and reflects previously unknown properties originating from the complex interactions between the two axially-staged lean-premixed flames.

Gaia Data Release 3

Context. With the most recent Gaia data release, the number of sources with complete 6D phase space information (position and velocity) has increased to well over 33 million stars, while stellar astrophysical parameters are provided for more than 470 million sources, and more than 11 million variable stars are identified. Aims. Using the astrophysical parameters and variability classifications provided in Gaia DR3, we selected various stellar populations to explore and identify non-axisymmetric features in the disc of the Milky Way in configuration and velocity space. Methods. Using more about 580 000 sources identified as hot OB stars, together with 988 known open clusters younger than 100 Myr, we mapped the spiral structure associated with star formation 4−5 kpc from the Sun. We selected over 2800 Classical Cepheids younger than 200 Myr that show spiral features extending as far as 10 kpc from the Sun in the outer disc. We also identified more than 8.7 million sources on the red giant branch (RGB), of which 5.7 million have line-of-sight velocities. This later sample allows the velocity field of the Milky Way to be mapped as far as 8 kpc from the Sun, including the inner disc. Results. The spiral structure revealed by the young populations is consistent with recent results using Gaia EDR3 astrometry and source lists based on near-infrared photometry, showing the Local (Orion) Arm to be at least 8 kpc long, and an outer arm consistent with what is seen in HI surveys, which seems to be a continuation of the Perseus arm into the third quadrant. The subset of RGB stars with velocities clearly reveals the large-scale kinematic signature of the bar in the inner disc, as well as evidence of streaming motions in the outer disc that might be associated with spiral arms or bar resonances. A local comparison of the velocity field of the OB stars reveals similarities and differences with the RGB sample. Conclusions. This cursory study of Gaia DR3 data shows there is a rich bounty of kinematic information to be explored more deeply, which will undoubtedly lead us to a clearer understanding of the dynamical nature of the non-axisymmetric structures of the Milky Way.

Theoretical and experimental studies of effects of non-axisymmetric inner structures on vibration signatures of axisymmetric submarine hulls

A unified hybrid analytical-numerical method is proposed for vibration analysis of stiffened hulls coupled with non-axisymmetric internal structures. The coupled system is firstly decomposed into the submarine hull and internal structures. Then, the stiffened hull is further divided into ring stiffeners, bulkheads and shell segments, including conical and cylindrical shell segments. The shell strips and axisymmetric reinforcements are uniformly described by the Flügge formula and power series method. For non-axisymmetric interior structures, finite element method is utilized to establish the motion equations owing to their irregular shapes. To synthesize the shell and non-axisymmetric internal structures, the receptance functions at coupling nodes are respectively deduced by condensing the global stiff matrices of the hull and interior substructures. A precise coupling method fully considering all 6 DOFs at coupling nodes, rather than just 3 or 4 DOFs in previous literature, is proposed to synthesize the receptance functions. To verify the validity of this approach, a stiffened conical-cylindrical-spherical shell coupled with two foundations is manufactured and the forced vibration characteristics of this coupled model subjected to multiple types of excitations are tested. Results obtained by semi-analytical method are simultaneously compared with the ones measured from this experiment and calculated through finite element method (FEM). Effects of the inner structures and different external excitations on forced vibrations are discussed by experiment. Furthermore, how non-axisymmetric internal structures modify wave propagation and conversion characteristics of axisymmetric hulls is investigated through the present method.

The EDGE-CALIFA survey: The role of spiral arms and bars in driving central molecular gas concentrations

Shocks and torques produced by non-axisymmetric structures such as spiral arms and bars may transport gas to galaxy central regions. We test this hypothesis by studying the dependence of the concentration of CO luminosity (CCO) and molecular gas (Cmol) and the star formation rate (CSFR) in the central ∼2 kpc on the strength of non-axisymmetric disk structure using a sample of 57 disk galaxies selected from the EDGE-CALIFA survey. The Cmol is calculated using a CO-to-H2 conversion factor that decreases with higher metallicity and higher stellar surface density. We find that Cmol is systematically 0.22 dex lower than CCO. We confirm that high Cmol and strong non-axisymmetric disk structure are more common in barred galaxies than in unbarred galaxies. However, we find that spiral arms also increase Cmol. We show that there is a good correlation between Cmol and the strength of non-axisymmetric structure (which can be due to a bar, spiral arms, or both). This suggests that the stronger the bars and spirals, the more efficient the galaxy is at transporting cold gas to its center. Despite the small subsample size, the Cmol of the four Seyferts are not significantly reduced compared to inactive galaxies of similar disk structure, implying that the active galactic nucleus feedback in Seyferts may not notably affect the molecular gas distribution in the central ∼2 kpc. We find that CSFR tightly correlates with Cmol in both unbarred and barred galaxies. Likewise, elevated CSFR is found in galaxies with strong disk structure. Our results suggest that the disk structure, either spirals or bars, can transport gas to the central regions, with higher inflow rates corresponding to stronger structure, and consequently boost central star formation. Both spirals and bars play, therefore, an essential role in the secular evolution of disk galaxies.

Warping Away Gravitational Instabilities in Protoplanetary Discs

Abstract We perform three-dimensional smoothed-particle hydrodynamics simulations of warped, non-coplanar gravitationally unstable discs to show that as the warp propagates through the self-gravitating disk, it heats up the disk rendering it gravitationally stable, thus losing their spiral structure and appearing completely axisymmetric. In their youth, protoplanetary discs are expected to be massive and self-gravitating, which results in nonaxisymmetric spiral structures. However recent observations of young protoplanetary discs with the Atacama Large Millimeter/submillimeter Array have revealed that discs with large-scale spiral structure are rarely observed in the midplane. Instead, axisymmetric discs, with some also having ring and gap structures, are more commonly observed. Our work invloving warps, non-coplanar disk structures that are expected to commonly occur in young discs, potentially resolves this discrepancy between observations and theoretical predictions. We demonstrate that they are able to suppress the large-scale spiral structure of self-gravitating protoplanetary discs.

Switch of Cell Manipulations using Vibration-Induced Flow around Non-axisymmetric Structures

Switch of Cell Manipulations using Vibration-Induced Flow around Non-axisymmetric Structures

Effects of non-axisymmetric internal structures on vibro-acoustic characteristics of a submerged cylindrical shell using wavenumber analysis

Non-axisymmetric structures (foundations, equipment etc.) have been extensively arranged in axisymmetric shells and proved to change the mechanism of vibration and sound radiation of the shell. To study the effect of non-axisymmetric internal structures, a hybrid analytic-numerical method is developed for vibro-acoustic characteristics analyses of a submerged cylindrical shell. The wave based method (WBM) and finite element method (FEM) are respectively employed to model the shell and internal structures. A precise coupling is carried out to assemble the shell and internal structures, which fully considers all six degree of freedoms (DOFs) at junctions between the two substructures. The acoustic pressure is described by the Helmholtz integral equation. According to the axisymmetric property of the shell, the surface integral is reduced into the curve integral. Subsequently, the final vibro-acoustic model is obtained by introducing the acoustic pressure into the dynamic equation of the coupled structure. The high accuracy of the present method is firstly demonstrated by FEM and boundary element method (BEM). Then by comparing vibro-acoustic responses of the shell with and without internal structures in wave domain, the effects of non-axisymmetric internal structures on vibro-acoustic characteristics of the shell are discussed.

The protoplanetary disc around HD 169142: circumstellar or circumbinary?

ABSTRACT Stellar binaries represent a substantial fraction of stellar systems, especially among young stellar objects. Accordingly, binaries play an important role in setting the architecture of a large number of protoplanetary discs. Binaries in coplanar and polar orientations with respect to the circumbinary disc are stable configurations and could induce non-axisymmetric structures in the dust and gas distributions. In this work, we suggest that the structures shown in the central region of the protoplanetary disc HD 169142 are produced by the presence of an inner stellar binary and a circumbinary (P-type) planet. We find that a companion with a mass ratio of 0.1, semimajor axis of 9.9 au, eccentricity of 0.2, and inclination of 90°, together with a 2 MJ coplanar planet on a circular orbit at 45 au reproduce the structures at the innermost ring observed at 1.3 mm and the shape of spiral features in scattered light observations. The model predicts changes in the disc’s dust structure, and star’s astrometric parameters, which would allow testing its veracity by monitoring this system over the next 20 yr.

Limits on Millimeter Continuum Emission from Circumplanetary Material in the DSHARP Disks

Abstract We present a detailed analysis for a subset of the high-resolution (∼35 mas, or 5 au) ALMA observations from the Disk Substructures at High Angular Resolution Project (DSHARP) to search for faint 1.3 mm continuum emission associated with dusty circumplanetary material located within the narrow annuli of depleted emission (gaps) in circumstellar disks. This search used the Jennings et al. frank modeling methodology to mitigate contamination from the local disk emission and then deployed a suite of injection–recovery experiments to statistically characterize point-like circumplanetary disks in residual images. While there are a few putative candidates in this sample, they have only marginal local signal-to-noise ratios and would require deeper measurements to confirm. Associating a 50% recovery fraction with an upper limit, we find that these data are sensitive to circumplanetary disks with flux densities ≳50–70 μJy in most cases. There are a few examples where those limits are inflated (≳110 μJy) owing to lingering nonaxisymmetric structures in their host circumstellar disks, most notably for a newly identified faint spiral in the HD 143006 disk. For standard assumptions, this analysis suggests that these data should be sensitive to circumplanetary disks with dust masses ≳ 0.001 – 0.2 M ⊕ . While those bounds are comparable to some theoretical expectations for young giant planets, we discuss how plausible system properties (e.g., relatively low host planet masses or the efficient radial drift of solids) could require much deeper observations to achieve robust detections.

Collision rates of planetesimals near mean-motion resonances

ABSTRACT In circumstellar discs, collisional grinding of planetesimals produces second-generation dust. While it remains unclear whether this ever becomes a major component of the total dust content, the presence of such dust, and potentially the substructure within it, can be used to explore a disc’s physical conditions. A perturbing planet produces non-axisymmetric structures and gaps in the dust, regardless of its origin. The dynamics of planetesimals, however, will be very different than that of small dust grains due to weaker gas interactions. Therefore, planetesimal collisions could create dusty disc structures that would not exist otherwise. In this work, we use N-body simulations to investigate the collision rate profile of planetesimals near mean-motion resonances. We find that a distinct bump or dip feature is produced in the collision profile, the presence of which depends on the libration width of the resonance and the separation between the peri- and apocentre distances of the edges of the resonance. The presence of one of these two features depends on the mass and eccentricity of the planet. Assuming that the radial dust emission traces the planetesimal collision profile, the presence of a bump or dip feature in the dust emission at the 2:1 mean-motion resonance can constrain the orbital properties of the perturbing planet. This assumption is valid, so long as radial drift does not play a significant role during the collisional cascade process. Under this assumption, these features in the dust emission should be marginally observable in nearby protoplanetary discs with ALMA.

Automated braiding of non-axisymmetric structures using an iterative inverse solution with angle control

Braiding reinforcing fibres into a shape using a mandrel is an efficient preforming method to produce composite products. Braiding consists of two yarn groups rotating and interlacing. Mechanical properties of the braided parts are related to the braiding angle, which is controlled by the take-off speed of the over-braided mandrel. This paper presents a novel approach to find the required speed profile to achieve the local targeted braiding angle. The proposed method computes the speed profile iteratively starting from an approximate model and correcting based on the results of the kinematic forward solution and feedback from actual angle measurements following actual braiding. Case studies have shown the validity of the approach for braiding on non-axisymmetric, curved, and variable cross-section mandrels. Implementation results have demonstrated that the proposed model lowers the error of the braid angle in every case, allowing the braid angle to be 1.0° off on average and even 0.7° off without outliers.