An Agent-Based Simulation API for Speculative PDES Runtime Environments

Agent-Based Modeling and Simulation (ABMS) is an effective paradigm to model systems exhibiting complex interactions, also with the goal of studying the emergent behavior of these systems. While ABMS has been effectively used in many disciplines, many successful models are still run only sequentially. Relying on simple and easy-to-use languages such as NetLogo limits the possibility to benefit from more effective runtime paradigms, such as speculative Parallel Discrete Event Simulation (PDES). In this paper, we discuss a semantically-rich API allowing to implement Agent-Based Models in a simple and effective way. We also describe the critical points which should be taken into account to implement this API in a speculative PDES environment, to scale up simulations on distributed massively-parallel clusters. We present an experimental assessment showing how our proposal allows to implement complicated interactions with a reduced complexity, while delivering a non-negligible performance increase

Effect of nitrogen in backing gas on duplex root weld properties of heavy-walled pipe

Duplex stainless steels are increasingly used for offshore subsea components as the technology allows for deeper recovery of oil and gas reserves. Alloy UNS S31803 (EN 1.4462/UNS S32205) combines high strength with good resistance to pitting and crevice corrosion. This grade is alloyed with nitrogen and has good weldability. For heavy-walled process piping intended for subsea sour service, the properties of the root pass are of high importance. For this reason, the effect of using nitrogen in the backing gas was investigated. Test pieces were manually welded with the gas tungsten arc welding (GTAW) process using an ER2209 filler wire. Tensile, bending and hardness testing was carried out and showed acceptable results across all specimens. Higher contents of nitrogen in the backing gas showed more austenite formation and a significant increase in pitting corrosion resistance when compared with pure argon. With Ar + 2 % N2, there was no pitting, but a small weight loss of 1.7 g/m2 was measured. 10 % N2 was required to pass both the corrosion tests ASTM G48 Method A (4 g/m2) and ASTM A923 (1 g/m2). The highest average impact toughness was achieved with pure nitrogen as the backing gas

The effects of subgrid models on the properties of giant molecular clouds in galaxy formation simulations

Recent cosmological hydrodynamical simulations are able to reproduce numerous statistical properties of galaxies that are consistent with observational data. Yet, the adopted subgrid models strongly affect the simulation outcomes, limiting the predictive power of these simulations. In this work, we perform a suite of isolated galactic disk simulations under the {\it SMUGGLE} framework and investigate how different subgrid models affect the properties of giant molecular clouds (GMCs). We employ {\sc astrodendro}, a hierarchical clump-finding algorithm, to identify GMCs in the simulations. We find that different choices of subgrid star formation efficiency, $\epsilon_{\rm ff}$, and stellar feedback channels, yield dramatically different mass and spatial distributions for the GMC populations. Without feedback, the mass function of GMCs has a shallower power-law slope and extends to higher mass ranges compared to runs with feedback. Moreover, higher $\epsilon_{\rm ff}$ results in faster molecular gas consumption and steeper mass function slopes. Feedback also suppresses power in the two-point correlation function (TPCF) of the spatial distribution of GMCs. Specifically, radiative feedback strongly reduces the TPCF on scales below 0.2~kpc, while supernova feedback reduces power on scales above 0.2~kpc. Finally, runs with higher $\epsilon_{\rm ff}$ exhibit a higher TPCF than runs with lower $\epsilon_{\rm ff}$, because the dense gas is depleted more efficiently thereby facilitating the formation of well-structured supernova bubbles. We argue that comparing simulated and observed GMC populations can help better constrain subgrid models in the next-generation of galaxy formation simulations.Comment: 12 pages, 8 figures, MNRAS in pres

"As long as they eat"? Therapist experiences, dilemmas and identity negotiations of Maudsley and family-based therapy for anorexia nervosa

Background: Maudsley Family Therapy and its manualised version Family-Based Therapy for Anorexia Nervosa (FBT-AN) have accrued the most significant research evidence-base for the treatment of adolescent Anorexia Nervosa (AN). A tradition of seeking augmentations for this treatment has also been established to enhance efficacy. There exists, however, a gap in the uptake of this form of manualised treatment into the “real world” of clinicians who work with adolescent AN. Aims: This research study investigated the key experiences and identity negotiations of a group of nine Australian clinicians who were interested in contributing to research into ways that Maudsley and FBT-AN might be improved. Methods: Nine clinicians, who at the time of the interview practised or had previously practised, FBT-AN participated in a semi-structured interview. A critical discursive analysis of interview transcripts generated a thematic map of these therapists’ experiences and identity negotiations in their practice of FBT-AN. Results: These therapists experienced the structure of FBT-AN as both a secure map for therapy, yet also constraining at times, in their work with adolescents and their families. Additionally, their professional identities were both invested and troubled by the identity position of themselves as evidence-based practitioners, particularly where evidence-based practice (EBP) meant strict fidelity to the manual and restrained them from tailoring a broader range of therapeutic interventions to an individual adolescent and their family. Within their narratives, these therapists refashioned alternative identity positions around what it meant to be an evidence-based practitioner through listening to and drawing on their clinical expertise of what works in therapeutic practice with an individual adolescent and their family. Conclusions: These therapists narratives highlight the power of the dominant discourse of EBP that works to privilege the research evidence over other forms of evidence that include clinician expertise and client preferences. The dilemmas faced by these therapists questioned not only the strict application of FBT-AN for adolescent AN across diverse therapeutic contexts, but also the effects of supervisory practices that paralleled this strict fidelity to the model. Further research is needed into therapeutic interventions and supervisory practices that give greater scope for clinicians to draw on their expertise in the flexible tailoring of treatments to the unique needs and preferences of the individual adolescent and their family

Simulating the interstellar medium and stellar feedback on a moving mesh: Implementation and isolated galaxies

We introduce the Stars and MUltiphase Gas in GaLaxiEs -- SMUGGLE model, an explicit and comprehensive stellar feedback model for the moving-mesh code arepo. This novel sub-resolution model resolves the multiphase gas structure of the interstellar medium and self-consistently generates gaseous outflows. The model implements crucial aspects of stellar feedback including photoionization, radiation pressure, energy and momentum injection from stellar winds and from supernovae. We explore this model in high-resolution isolated simulations of Milky Way-like disc galaxies. Stellar feedback regulates star formation to the observed level and naturally captures the establishment of a Kennicutt-Schmidt relation. This result is achieved independent of the numerical mass and spatial resolution of the simulations. Gaseous outflows are generated with average mass loading factors of the order of unity. Strong outflow activity is correlated with peaks in the star formation history of the galaxy with evidence that most of the ejected gas eventually rains down onto the disc in a galactic fountain flow that sustains late-time star formation. Finally, the interstellar gas in the galaxy shows a distinct multiphase distribution with a coexistence of cold, warm and hot phases.Comment: 29 pages, 15 figures, 3 tables, 1 appendix. Accepted for publication in MNRAS. Updated manuscript to match the published versio

Modeling Galactic Conformity with the Color-Halo Age Relation in the Illustris Simulation

Comparisons between observational surveys and galaxy formation models find that the mass of dark matter haloes can largely explain galaxies' stellar mass. However, it remains uncertain whether additional environmental variables, generally referred to as assembly bias, are necessary to explain other galaxy properties. We use the Illustris Simulation to investigate the role of assembly bias in producing galactic conformity by considering 18,000 galaxies with $M_{stellar}$ > $2 \times 10^9$ $M_{\odot}$. We find a significant signal of galactic conformity: out to distances of about 10 Mpc, the mean red fraction of galaxies around redder galaxies is higher than around bluer galaxies at fixed stellar mass. Dark matter haloes exhibit an analogous conformity signal, in which the fraction of haloes formed at earlier times (old haloes) is higher around old haloes than around younger ones at fixed halo mass. A plausible interpretation of galactic conformity can be given as a combination of the halo conformity signal with the galaxy color-halo age relation: at fixed stellar mass, particularly toward the low-mass end, Illustris' galaxy colors correlate with halo age, with the reddest galaxies (often satellites) being preferentially found in the oldest haloes. In fact, we can explain the galactic conformity effect with a simple semi-empirical model, by assigning stellar mass based on halo mass (abundance matching) and by assigning galaxy color based on halo age (age matching). We investigate other interpretations for the galactic conformity, particularly its dependence on the isolation criterion and on the central-satellite information. Regarding comparison to observations, we conclude that the adopted selection/isolation criteria, projection effects, and stacking techniques can have a significant impact on the measured amplitude of the conformity signal.Comment: 15 pages, 8 figures; accepted for publication in MNRAS (minor revisions to match accepted version

Synthetic Galaxy Images and Spectra from the Illustris Simulation

We present our methods for generating a catalog of 7,000 synthetic images and 40,000 integrated spectra of redshift z = 0 galaxies from the Illustris Simulation. The mock data products are produced by using stellar population synthesis models to assign spectral energy distributions (SED) to each star particle in the galaxies. The resulting synthetic images and integrated SEDs therefore properly reflect the spatial distribution, stellar metallicity distribution, and star formation history of the galaxies. From the synthetic data products it is possible to produce monochromatic or color-composite images, perform SED fitting, classify morphology, determine galaxy structural properties, and evaluate the impacts of galaxy viewing angle. The main contribution of this paper is to describe the production, format, and composition of the image catalog that makes up the Illustris Simulation Obsevatory. As a demonstration of this resource, we derive galactic stellar mass estimates by applying the SED fitting code FAST to the synthetic galaxy products, and compare the derived stellar masses against the true stellar masses from the simulation. We find from this idealized experiment that systematic biases exist in the photometrically derived stellar mass values that can be reduced by using a fixed metallicity in conjunction with a minimum galaxy age restriction.Comment: 21 pages, 17 figures, submitted to MNRAS. Comments welcom

Degeneracies Between Self-interacting Dark Matter and Supernova Feedback as cusp-core transformation mechanisms

We present a suite of 16 high-resolution hydrodynamic simulations of an isolated dwarf galaxy (gaseous and stellar disk plus a stellar bulge) within an initially cuspy dark matter (DM) halo, including self-interactions between the DM particles (SIDM); as well as stochastic star formation and subsequent supernova feedback (SNF), implemented using the stellar feedback model SMUGGLE. The simulations start from identical initial conditions and we regulate the strength of SIDM and SNF by systematically varying the SIDM momentum transfer cross section and the gas density threshold for star formation. The DM halo forms a constant density core of similar size and shape for several combinations of those two parameters. Haloes with cores that are formed due to SIDM (adiabatic cusp-core transformation) have velocity dispersion profiles which are closer to isothermal than those of haloes with cores that are formed due to SNF in simulations with bursty star formation (impulsive cusp-core transformation). Impulsive SNF can generate positive stellar age gradients and increase random motion in the gas at the centre of the galaxy. Simulated galaxies in haloes with cores that were formed adiabatically are spatially more extended, with stellar metallicity gradients that are shallower (at late times) than those of galaxies in other simulations. Such observable properties of the gas and the stars, which indicate either an adiabatic or an impulsive evolution of the gravitational potential, may be used to determine whether observed cores in DM haloes are formed through self-interactions between the DM particles or in response to impulsive SNF.Comment: accepted for publication in MNRAS, contains 3 appendices; main paper: 18 pages, 11 figures; appendices: 8 pages, 7 figures; for questions/comments contact [email protected] (Jan Burger