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We present TDS Simulator, a new software tool aimed at modelling thermal desorption spectroscopy (TDS) experiments. TDS is a widely used technique for quantifying key characteristics of hydrogen-material interactions, such as diffusivity and trapping. However, interpreting the output of TDS experiments is non-trivial and requires appropriate post-processing tools. This work introduces the first software tool capable of simulating TDS curves for arbitrary choices of material parameters and hydrogen trap characteristics, using the primary hydrogen diffusion and trapping models (Oriani, McNabb-Foster). Moreover, TDS Simulator contains a specific functionality for loading experimental TDS data and conducting the inverse calibration of a selected transport model, providing automatic estimates of the density and binding energy of each hydrogen trap type in the material. In its first version, TDS Simulator is provided as a MATLAB App, which is made freely available to the community and provides a simple graphical user interface (GUI) to make use of TDS Simulator straightforward. As reported in the present manuscript, the outputs of TDS Simulator have been extensively validated against literature data. Demonstrations of automatic determination of trap characteristics from experimental data through the optimisation tool are also provided. The present work enables an efficient and straightforward characterisation of hydrogen-material characteristics relevant to multiple applications, from nuclear fusion to the development of hydrogen-compatible materials for the hydrogen economy. TDS Simulator can be downloaded from https://mechmat.web.ox.ac.uk/codes.

Here we report the detection of dust depletion in a misaligned inner disk around UX Tau A using JWST MIRI spectra. Mid-infrared (MIR) continuum "seesaw" variability was detected in this disk by Spitzer and attributed to variable shadows cast on the outer disk by the inner disk. The JWST MIRI spectrum of UX Tau A also shows seesaw variability, but with a significant decrease of emission shortwards of 10 micron to nearly photospheric levels. We argue that UX Tau A's MIR continuum variability is due to depletion of dust in a misaligned inner disk. We speculate that this dust depletion occurs because the inner disk is misaligned from the outer disk, which can disrupt the replenishment of the inner disk from the outer disk. Using contemporaneous measurements of the mass accretion rate of UX Tau A and estimating the amount of dust necessary to produce the MIR excess in the Spitzer observations, we estimate a minimum dust depletion timescale of ~0.1 yr. These observations show that we can indirectly detect the signatures of misaligned inner disks through MIR continuum variability and that in some cases the inner disk may be significantly depleted of dust and become optically thin., Comment: accepted to ApJL

Observations of interstellar material infalling onto star- and planet-forming systems have become increasingly common thanks to recent advancements in radio interferometry. These structures replenish disks with fresh material, have the potential to significantly alter their dynamics, trigger the formation of substructures, induce shocks, and modify their physical and chemical properties. In this study, we combine new ALMA band 3 and archival band 6 observations to characterize the dust content and mass infall rate of a 4,000 au arc-like structure infalling onto M512, a class I young stellar object located in the Lynds 1641 region of the Orion A molecular cloud. We measure for the first time spectral index maps and derive a dust opacity index profile along a streamer, constraining grain properties and its dust mass. We measure a spectral index $\alpha \sim$ 3.2 across the entire structure, and a dust opacity index $\beta \sim$ 1.6. Given grain properties consistent with the measured $\beta$, the structure can host up to 245 M$_{\oplus}$ of dust, being comparable or even exceeding the mass of the inner, unresolved 600 au, which contains the protoplanetary disk of M512. Such a massive streamer can strongly affect the evolution of the star- and planet-forming inner system. Assuming typical ISM dust-to-gas ratio of 1%, free-fall timescales (50 kyr) imply total mass infall rates up to 1.5 $\cdot$ 10$^{-6}$ M$_{\odot}$/yr. M512 has been classified as an outbursting source with multi-epoch photometry, thus representing an interesting case study to explore the possible connection between infalling streamers and accretion outbursts., Comment: Accepted for publication in A&A, 13 pages, 5 figures, 3 tables

Understanding the formation of substructures in protoplanetary disks is vital for gaining insights into dust growth and the process of planet formation. Studying these substructures in highly embedded Class 0 objects using the Atacama Large Millimeter/submillimeter Array (ALMA), however, poses significant challenges. Nonetheless, it is imperative to do so to unravel the mechanisms and timing behind the formation of these substructures. In this study, we present high-resolution ALMA data at Bands 6 and 4 of the NGC1333 IRAS4A Class 0 protobinary system. This system consists of two components, A1 and A2, separated by 1.8" and located in the Perseus molecular cloud at $\sim$293 pc distance. To gain a comprehensive understanding of the dust properties and formation of substructures in the early stages, we conducted a multi-wavelength analysis of IRAS4A1. Additionally, we sought to address whether the lack of observed substructures in very young disks, could be attributed to factors such as high degrees of disk flaring and large scale heights. To explore this phenomenon, we employed radiative transfer models using RADMC-3D. Our multi-wavelength analysis of A1 discovered characteristics such as high dust surface density, substantial dust mass within the disk, and elevated dust temperatures. These findings suggest the presence of large dust grains compared to the ones in the interstellar medium (ISM), greater than 100 microns in size within the region. Furthermore, while there's no direct detection of any substructure, our models indicate that some, such as a small gap, must be present. In summary, this result implies that disk substructures may be masked or obscured by a large scale height in combination with a high degree of flaring in Class 0 disks. [Abridged], Comment: Accepted for publication in A&A, 13 pages, 7 figures

Early dust grain growth in protostellar envelopes infalling on young discs has been suggested in recent studies, supporting the hypothesis that dust particles start to agglomerate already during the Class 0/I phase of young stellar objects (YSOs). If this early evolution were confirmed, it would impact the usually assumed initial conditions of planet formation, where only particles with sizes $\lesssim 0.25 \mu$m are usually considered for protostellar envelopes. We aim to determine the maximum grain size of the dust population in the envelope of the Class 0/I protostar L1527 IRS, located in the Taurus star-forming region (140 pc). We use Atacama Large millimetre/sub-millimetre Array (ALMA) and Atacama Compact Array (ACA) archival data and present new observations, in an effort to both enhance the signal-to-noise ratio of the faint extended continuum emission and properly account for the compact emission from the inner disc. Using observations performed in four wavelength bands and extending the spatial range of previous studies, we aim to place tight constraints on the spectral ($\alpha$) and dust emissivity ($\beta$) indices in the envelope of L1527 IRS. We find a rather flat $\alpha \sim$ 3.0 profile in the range 50-2000 au. Accounting for the envelope temperature profile, we derive values for the dust emissivity index, 0.9 < $\beta$ < 1.6, and reveal a tentative, positive outward gradient. This could be interpreted as a distribution of mainly ISM-like grains at 2000 au, gradually progressing to (sub-)millimetre-sized dust grains in the inner envelope, where at R=300 au, $\beta$ = 1.1 +/- 0.1. Our study supports a variation of the dust properties in the envelope of L1527 IRS. We discuss how this can be the result of in-situ grain growth, dust differential collapse from the parent core, or upward transport of disc large grains., Comment: Accepted for publication in A&A. Contains 18 pages, 21 figures, 5 tables Replacement on Nov 22 to change title number of FAUST series from "X" to "IX."

We present ALMA multiwavelength observations of the protoplanetary disk around the nearby (d$\sim$100 pc) young solar analog MP Mus (PDS 66). These observations at 0.89 mm, 1.3 mm, and 2.2 mm have angular resolutions of $\sim$ 1", 0.05", and 0.25", respectively, and probe the dust and gas in the system with unprecedented detail and sensitivity. The disk appears smooth down to the 4 au resolution of the 1.3 mm observations, in contrast with most disks observed at comparable spatial scales. The dust disk has a radius of 60$\pm$5 au, a dust mass of $0.14_{-0.06}^{+0.11} M_{\rm Jup}$, and a mm spectral index $<2$ in the inner 30 au, suggesting optically thick emission from grains with high albedo in this region. Several molecular gas lines are also detected extending up to 130$\pm$15 au, similar to small grains traced by scattered light observations. Comparing the fluxes of different CO isotopologues with previous models yields a gas mass of $0.1-1 M_{\rm Jup}$, implying a gas to dust ratio of 1-10. We also measure a dynamical stellar mass of $M_{\rm dyn}$=1.30$\pm$0.08 $M_\odot$ and derive an age of 7-10 Myr for the system. The survival of large grains in an evolved disk without gaps/rings is surprising, and it is possible that existing substructures remain undetected due to optically thick emission at 1.3 mm. Alternatively, small structures may still remain unresolved with the current observations. Based on simple scaling relations for gap-opening planets and gap widths, this lack of substructures places upper limits to the masses of planets in the disk as low as 2 $M_\oplus$-0.06 $M_{\rm Jup}$ at $r > 40$ au. The lack of mm emission at radii $r > 60$ au also suggests that the gap in scattered light between 30-80 au is likely not a gap in the disk density, but a shadow cast by a puffed-up inner disk., Comment: 17 pages + 3 appendices. Accepted for publication in Astronomy & Astrophysics

We present a novel computational framework to simulate the electromechanical response of self-sensing carbon nanotube (CNT)-based composites experiencing fracture. The computational framework combines electrical-deformation-fracture finite element modelling with a mixed micromechanics formulation. The latter is used to estimate the constitutive properties of CNT-based composites, including the elastic tensor, fracture energy, electrical conductivity, and linear piezoresistive coefficients. These properties are inputted into a coupled electro-structural finite element model, which simulates the evolution of cracks based upon phase-field fracture. The coupled physical problem is solved in a monolithic manner, exploiting the robustness and efficiency of a quasi-Newton algorithm. 2D and 3D boundary value problems are simulated to illustrate the potential of the modelling framework in assessing the influence of defects on the electromechanical response of meso- and macro-scale smart structures. Case studies aim at shedding light into the interplay between fracture and the electromechanical material response and include parametric analyses, validation against experiments and the simulation of complex cracking conditions (multiple defects, crack merging). The presented numerical results showcase the efficiency and robustness of the computational framework, as well as its ability to model a large variety of structural configurations and damage patterns. The deformation-electrical-fracture finite element code developed is made freely available to download.

This paper presents a surrogate modelling technique based on domain partitioning for Bayesian parameter inference of highly nonlinear engineering models. In order to alleviate the computational burden typically involved in Bayesian inference applications, a multielement Polynomial Chaos Expansion based Kriging metamodel is proposed. The developed surrogate model combines in a piecewise function an array of local Polynomial Chaos based Kriging metamodels constructed on a finite set of non-overlapping subdomains of the stochastic input space. Therewith, the presence of non-smoothness in the response of the forward model (e.g.~ nonlinearities and sparseness) can be reproduced by the proposed metamodel with minimum computational costs owing to its local adaptation capabilities. The model parameter inference is conducted through a Markov chain Monte Carlo approach comprising adaptive exploration and delayed rejection. The efficiency and accuracy of the proposed approach are validated through two case studies, including an analytical benchmark and a numerical case study. The latter relates the partial differential equation governing the hydrogen diffusion phenomenon of metallic materials in Thermal Desorption Spectroscopy tests.

Accurate disk mass measurements are necessary to constrain disk evolution and the timescale of planet formation, but such measurements are difficult to make and are very dependent on assumptions. Here we look at the assumption that the disk is optically thin at radio wavelengths and the effect of this assumption on measurements of disk dust mass. We model the optical to radio spectral energy distributions (SEDs) of 41 protoplanetary disks located in the young (~1-3 Myr old) Lupus star-forming region, including 0.89 mm, 1.33 mm, and 3 mm flux densities when available. We measure disk dust masses that are ~1.5-6 times higher than when using the commonly adopted disk dust mass equation under the assumption of optically thin emission in the (sub-)millimeter. The cause of this discrepancy is that most disks are optically thick at millimeter wavelengths, even up to 3 mm, demonstrating that observations at longer wavelengths are needed to trace the fully optically thin emission of disks., Comment: accepted to ApJ

We present a novel micromechanics-based phase field approach to model crack initiation and propagation in carbon nanotube (CNT) based composites. The constitutive mechanical and fracture properties of the nanocomposites are first estimated by a mean-field homogenisation approach. Inhomogeneous dispersion of CNTs is accounted for by means of equivalent inclusions representing agglomerated CNTs. Detailed parametric analyses are presented to assess the effect of the main micromechanical properties upon the fracture behaviour of CNT-based composites. The second step of the proposed approach incorporates the previously estimated constitutive properties into a phase field fracture model to simulate crack initiation and growth in CNT-based composites. The modelling capabilities of the framework presented is demonstrated through three paradigmatic case studies involving mode I and mixed mode fracture conditions.

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, semi-major axis of 9.9 au, eccentricity of 0.2, and inclination of 90{\deg}, together with a 2 Jupiter Mass 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 years., Comment: 11 pages, 7 figures, accepted for publication in MNRAS

A multiwavelength observing campaign of the T Tauri star (TTS) GM Aur was undertaken in 2019 December that obtained Swift X-ray and NUV fluxes, HST NUV spectra, LCOGT ugri and TESS photometry, CHIRON Halpha spectra, ALMA 13CO and C18O line fluxes, and VLA 3 cm continuum fluxes taken contemporaneously over one month. The X-ray to optical observations were presented previously. Here we present the ALMA and VLA data and make comparisons to GM Aur's accretion and X-ray properties. We report no variability in the observed millimeter CO emission. Using disk chemistry models, we show that the magnitude of the changes seen in the FUV luminosity of GM Aur could lead to variation of up to ~6% in CO line emission and changes in the X-ray luminosity could lead to larger changes of ~25%. However, the FUV and X-ray luminosity increases must last at least 100 years in order to induce changes, which seems implausible in the TTS stage; also, these changes would be too small to be detectable by ALMA. We report no variability in the 3 cm emission observed by the VLA, showing that changes of less than a factor of ~3 in the accretion rates of TTSs do not lead to detectable changes in the mass-loss rate traced by the jet at centimeter wavelengths. We conclude that typically seen changes in the FUV and X-ray luminosities of TTSs do not lead to observable changes in millimeter CO line emission or jet centimeter continuum emission., Comment: accepted by ApJ

We model the spectral energy distributions (SEDs) of 23 protoplanetary disks in the Taurus-Auriga star-forming region using detailed disk models and a Bayesian approach. This is made possible by combining these models with artificial neural networks to drastically speed up their performance. Such a setup allows us to confront $\alpha$-disk models with observations while accounting for several uncertainties and degeneracies. Our results yield high viscosities and accretion rates for many sources, which is not consistent with recent measurements of low turbulence levels in disks. This inconsistency could imply that viscosity is not the main mechanism for angular momentum transport in disks, and that alternatives such as disk winds play an important role in this process. We also find that our SED-derived disk masses are systematically higher than those obtained solely from (sub)mm fluxes, suggesting that part of the disk emission could still be optically thick at (sub)mm wavelengths. This effect is particularly relevant for disk population studies and alleviates previous observational tensions between the masses of protoplanetary disks and exoplanetary systems., Comment: 24 pages (including appendices), 13 figures. Accepted for publication in Astronomy and Astrophysics

Recent high-angular resolution (40 mas) ALMA observations at 1.14 mm resolve a compact (R~200 au) flattened dust structure perpendicular to the HH 80-81 jet emanating from the GGD 27-MM1 high-mass protostar, making it a robust candidate for a true accretion disk. The jet/disk system (HH 80-81 / GGD 27-MM1) resemble those found in association with low- and intermediate-mass protostars. We present radiative transfer models that fit the 1.14 mm ALMA dust image of this disk which allow us to obtain its physical parameters and predict its density and temperature structure. Our results indicate that this accretion disk is compact (Rdisk~170 au) and massive (5Msun), about 20% of the stellar mass of 20 Msun. We estimate the total dynamical mass of the star-disk system from the molecular line emission finding a range between 21 and 30 Msun, which is consistent with our model. We fit the density and temperature structures found by our model with power law functions. These results suggest that accretion disks around massive stars are more massive and hotter than their low-mass siblings, but they still are quite stable. We also compare the temperature distribution in the GGD 27-MM1 disk with that found in low- and intermediate-mass stars and discuss possible implications on the water snow line. We have also carried about a study of the distance based on Gaia DR2 data and the population of young stellar objects (YSOs) in this region, and from the extinction maps. We conclude that the source distance is in within 1.2 and 1.4 kpc, closer than what was derived in previous studies (1.7 kpc)., Comment: 20 pages, 15 figures

Here we analyze the first simultaneous X-ray, ultraviolet, optical, infrared, and centimeter observations of a T Tauri star (TTS). We present three epochs of simultaneous Spitzer and VLA data of GM Aur separated by ~1 wk. These data are compared to previously published HST and Chandra observations from which mass accretion rates ($\dot M$) and X-ray luminosities, respectively, were measured. The mid-infrared emission increases along with $\dot M$, and we conclude that this is due to an increase in the mass in the inner disk. The cm emission, which probes the jet, also appears to increase as $\dot M$ increases, and the changes in the cm flux are consistent with the variability in $\dot M$ assuming the mass-loss rate is ~10% $\dot M$. The 3 cm emission morphology also appears changed compared with observations taken three years previously, suggesting that for the first time, we may be tracking changes in the jet morphology of a TTS. The X-ray luminosity is constant throughout the three epochs, ruling out variable high-energy stellar radiation as the cause for the increases in the mid-infrared or cm emission. Tying together the multiwavelength variability observed, we conclude that an increase in the surface density in the inner disk resulted in more mass loading onto the star and therefore a higher $\dot M$, which led to a higher mass-loss rate in the jet. These results stress the importance of coordinated multiwavelength work to better understand the star-disk-jet connection., Comment: accepted to ApJL

T Cha is a young star surrounded by a transitional disk with signatures of planet formation. We have obtained high-resolution and high-sensitivity ALMA observations of T Cha in the ${\rm CO}(3$--$2)$, ${\rm ^{13}CO}(3$--$2)$, and ${\rm CS}(7$--$6)$ emission lines to reveal the spatial distribution of the gaseous disk around the star. In order to study the dust within the disk we have also obtained continuum images at 850$\mu$m from the line-free channels. We have spatially resolved the outer disk around T Cha. Using the CO(3-2) emission we derive a radius of $\sim$230 AU. We also report the detection of the $^{13}$CO(3-2) and the CS(7-8) molecular emissions, which show smaller radii than the CO(3-2) detection. The continuum observations at 850$\mu$m allow the spatial resolution of the dusty disk, which shows two emission bumps separated by $\sim$40AU, consistent with the presence of a dust gap in the inner regions of the disk, and an outer radius of $\sim$80AU. Therefore, T Cha is surrounded by a compact dusty disk and a larger and more diffuse gaseous disk, as previously observed in other young stars. The continuum intensity profiles are different at both sides of the disk suggesting possible dust asymmetries. We derive an inclination of i(deg)=67$\pm$5, and a position angle of PA (deg)= 113$\pm$6, for both the gas and dust disks. The comparison of the ALMA data with radiative transfer models shows that the gas and dust components can only be simultaneously reproduced when we include a tapered edge prescription for the surface density profile. The best model suggests that most of the disk mass is placed within a radius of $R<$ 50AU. Finally, we derive a dynamical mass for the central object of $M_{*}$=1.5$\pm$0.2M$_{\odot}$, comparable to the one estimated with evolutionary models for an age of $\sim$10Myr., Comment: 5 pages, 5 figures, accepted for publication in A&A Letters