SearcharxivSearch

arXiv subjects

Mark Hancock

Publications and source records attributed to Mark Hancock.

12 recordsLinked to original sources

Embodied Explainability and Ontological Obstacles: Why We Struggle to Explain the Answers of Large Language Models (LLMs)

Explainability is often framed as a property of an AI model, with explanations extracted from its internals and shown to users. In this argument paper, we instead provide an embodied account of explainability based on Dourish and enactivist cognition: understanding is created in use as people act on affordances in shared practice. Using demonstrations and conceptual analysis, we reveal ontological obstacles when "looking inside" large language models: surrogates import external abstractions that can be mistaken for the model's, and focusing on internal reasoning misses that explainers participate in their own understanding. We discuss these obstacles in XAI practice, arguing that many explanations are misnamed, which skews their purpose and can increase overreliance. Finally, we highlight how embodied explanations reorganize sense-making by making what matters publicly available for action, and argue that explainability claims should be reserved for designs that provide affordances to probe, coordinate, and repair behaviour in situated practice.

cs.HC

Unraveling the Dilemma of AI Errors: Exploring the Effectiveness of Human and Machine Explanations for Large Language Models

The field of eXplainable artificial intelligence (XAI) has produced a plethora of methods (e.g., saliency-maps) to gain insight into artificial intelligence (AI) models, and has exploded with the rise of deep learning (DL). However, human-participant studies question the efficacy of these methods, particularly when the AI output is wrong. In this study, we collected and analyzed 156 human-generated text and saliency-based explanations collected in a question-answering task (N=40) and compared them empirically to state-of-the-art XAI explanations (integrated gradients, conservative LRP, and ChatGPT) in a human-participant study (N=136). Our findings show that participants found human saliency maps to be more helpful in explaining AI answers than machine saliency maps, but performance negatively correlated with trust in the AI model and explanations. This finding hints at the dilemma of AI errors in explanation, where helpful explanations can lead to lower task performance when they support wrong AI predictions.

cs.HC

The Effect of Resistivity on the Periodicity of Oscillatory Reconnection

The oscillatory reconnection mechanism is investigated for a parameter study of eight orders of magnitude of resistivity, with a particular interest in the evolution of the oscillating current density at the null point and its associated periodicity. The resistive, nonlinear MHD simulations are solved in 2.5D for different levels of resistivity. Three methods (wavelet analysis, Fourier transform and ANOVA) are used to investigate the effect of resistivity versus resultant period. It is found that there is an independence between the level of background resistivity and the period of the oscillatory reconnection mechanism. Conversely, it is found that resistivity has a significant effect on the maximum amplitude of the current density and the nature of its decay rate, as well as the magnitude of ohmic heating at the null.

astro-ph.SR

Organizing Family Support Services at ACM Conferences

This article reflects on our experiences providing family-support services to a large, interdisciplinary ACM conference (CHI2018) including, the policy decisions, the challenges, and the successes. The article incorporates empirical data collected from pre- and post-conference surveys, observed use of the services, and aspirational aims for future conferences. We are discussing best practices and recommendations to facilitate the implementation of child support services at other conferences. We believe our article will be of great interest to both practitioners and academics in expanding the inclusivity and family support provided by ACM conferences and beyond.

cs.CY

Spirals, Bridges, and Tails: A GALEX UV Atlas of Interacting Galaxies

We have used the GALEX ultraviolet telescope to study stellar populations and star formation morphology in a well-defined sample of 42 nearby optically-selected pre-merger interacting galaxy pairs. Galaxy interactions were likely far more common in the early Universe than in the present, thus our study provides a nearby well-resolved comparison sample for high redshift studies. We have combined the GALEX NUV and FUV images with broadband optical maps from the Sloan Digitized Sky Survey to investigate the ages and extinctions of the tidal features and the disks. The distributions of the UV/optical colors of the tidal features and the main disks of the galaxies are similar, however, the tidal features are bluer on average in NUV - g when compared with their own parent disks, thus tails and bridges are often more prominent relative to the disks in UV images compared to optical maps. This effect is likely due to enhanced star formation in the tidal features compared to the disks rather than reduced extinction, however, lower metallicities may also play a role. We have identified a few new candidate tidal dwarf galaxies in this sample. Other interesting morphologies such as accretion tails and `beads on a string' are also seen in these images. We also identify a possible `Taffy' galaxy in our sample, which may have been produced by a head-on collision between two galaxies. In only a few cases are strong tidal features seen in HI maps but not in GALEX.

astro-ph.CO

An Atlas of GALEX UV Images of Interacting Galaxies

We present GALEX ultraviolet images from a survey of strongly interacting galaxy pairs, and compare with images at other wavelengths. The tidal features are particularly striking in the UV images. Numerous knots of star formation are visible throughout the disks and the tails and bridges. We also identify a possible `Taffy' galaxy in our sample, which may have been produced by a head-on collision between two disk galaxies.

astro-ph.CO

Tidal Dwarf Galaxies, Accretion Tails, and `Beads on a String' in the `Spirals, Bridges, and Tails' Interacting Galaxy Survey

We have used the GALEX ultraviolet telescope to study stellar populations and star formation morphology in a well-defined sample of more than three dozen nearby optically-selected pre-merger interacting galaxy pairs. We have combined the GALEX NUV and FUV images with broadband optical maps from the Sloan Digitized Sky Survey to investigate the ages and extinctions of the tidal features and the disks. We have identified a few new candidate tidal dwarf galaxies in this sample, as well as other interesting morphologies such as accretion tails, `beads on a string', and `hinge clumps'. In only a few cases are strong tidal features seen in HI maps but not in GALEX.

astro-ph.CO

Star Cluster Dissolution in Arp 284

We present results from a study of proto-globular cluster candidates in the interacting galaxy system Arp 284 (NGC 7714/5). Studies of the Antennae and M51 have suggested that the majority of these star clusters dissolve within 20 Myr due to mass loss. We obtain cluster colors using archival \emph{HST} data, and estimate ages and extinctions for over 150 clusters using evolutionary synthesis models. We find that clusters in NGC 7714 are generally less than 20 Myr old, while the data in the bridge is too limited to allow good estimates for individual clusters. We also examine {H {\sc ii}} region complexes with lower-resolution \emph{GALEX} and ground-based H$α$ images. Several of these regions appear to be much older than the detected clusters within them, which may indicate the presence of an older, unresolved population of low mass or dispersed clusters.

astro-ph.CO

Star Clusters in the Interacting Galaxy System Arp 284

We present results from a study of proto-globular cluster candidates in the interacting galaxy system Arp 284 (NGC 7714/5) using data from the Hubble Space Telescope. Previous studies of the Antennae and M51 have suggested that the majority of young massive star clusters dissolve within 20 Myr due to mass loss. We use the evolutionary synthesis code Starburst99 to estimate ages and extinctions for approximately 175 clusters visible with HST. We also use lower-resolution GALEX and ground-based H-alpha data to estimate the ages of the giant HII regions in which these clusters are found, and compare the Spitzer colours of these HII regions to those of star forming regions in other interacting systems. The ages are also used to aid in the interpretation of Chandra X-ray data. Clusters in the tidal tails of NGC 7714 are generally found to have ages less than 20 Myr, though observational limits make the significance of this result uncertain. Older clusters, though not numerous, have nearly the same spatial distribution within the imaged portion of NGC 7714 as young clusters. The cluster population in the bridge connecting the two galaxies appears to be older, but the data in this part of the system is too limited to draw firm conclusions. The ages of the giant HII regions in NGC 7714 are generally older than those of their constituent clusters, possibly indicating that the young clusters we detect are surrounded by their dispersed predecessors.

astro-ph.CO

The Origin of the 4.5 micron Excess from Dwarf Galaxies

Dwarf galaxies tend to have redder [3.6 micron] - [4.5 micron] Spitzer broadband colors than spirals. To investigate this effect, for a large sample of dwarf galaxies we combine Spitzer fluxes with data at other wavelengths and compare to population synthesis models. Lower metallicity systems are found to have redder [3.6] - [4.5] colors on average, but with considerable scatter. The observed range in [3.6] - [4.5] color is too large to be accounted for solely by variations in stellar colors due to age or metallicity differences; interstellar effects must contribute as well. For the reddest systems, the 4.5 micron luminosity may not be a good tracer of stellar mass. We identify three factors that redden this color in dwarfs. First, in some systems, strong Br-alpha emission contributes significantly to the 4.5 micron emission. Second, in some cases high optical depths lead to strong reddening of the starlight in the Spitzer bands. Third, in some galaxies, the nebular continuum dominates the 4.5 micron flux, and in extreme cases, the 3.6 micron flux as well. The harder UV radiation fields in lower metallicity systems produce both more gaseous continuum in the infrared and more Br-alpha per star formation rate. The combination of these three factors can account for the 4.5 micron excess in our sample galaxies, thus it is not necessary to invoke a major contribution from hot dust to the 4.5 micron band. However, given the uncertainties, we are not able to completely rule out hot dust emission at 4.5 micron. More spectroscopic observations in the 3 - 5 micron range are needed to disentangle these effects.

astro-ph.CO

Candidate Tidal Dwarf Galaxies in Arp 305: Lessons on Dwarf Detachment and Globular Cluster Formation

To search for Tidal Dwarf Galaxies (TDGs) and to study star formation in tidal features, we are conducting a large UV imaging survey of interacting galaxies selected from the Arp (1996) Atlas using the GALEX telescope. As part of that study, we present a GALEX UV and SDSS and SARA optical study of the gas-rich interacting galaxy pair Arp 305 (NGC 4016/7). The GALEX UV data reveal much extended diffuse UV emission and star formation outside the disks. This includes a luminous star forming region between the two galaxies, and a number of such regions in tidal tails. We have identified 45 young star forming clumps in Arp 305, including several TDG candidates. By comparing the UV and optical colors to population synthesis models, we determined that the clumps are very young, with several having ages of about 6 Myr. We do not find many intermediate age clumps in spite of the fact that the last closest encounter was about 300 Myr ago. We have used a smooth particle hydrodynamics code to model the interaction and determine the fate of the star clusters and candidate TDGs.

astro-ph.GA

Large-scale Star Formation Triggering in the Low-mass Arp 82 System: A Nearby Example of Galaxy Downsizing Based on UV/Optical/Mid-IR Imaging

As part of our Spitzer Spirals, Bridges, and Tails project to help understand the effects of galaxy interactions on star formation, we analyze GALEX ultraviolet, SARA optical, and Spitzer infrared images of the interacting galaxy pair Arp 82 (NGC 2535/6) and compare to a numerical simulation of the interaction. We investigate the multiwavelength properties of several individual star forming complexes (clumps). Using optical and UV colors, EW(Halpha), and population synthesis models we constrain the ages of the clumps and find that the median clump age is about 12 Myr. The clumps have masses ranging from a few times 10^6 to 10^9 solar masses. In general, the clumps in the tidal features have similar ages to those in the spiral region, but are less massive. The 8 micron and 24 micron luminosities are used to estimate the far-infrared luminosities and the star formation rates of the clumps. The total clump star formation rate is 2.0+/-0.8 solar masses per year, while the entire Arp 82 system is forming stars at a rate of 4.9+/-2.0 solar masses per year. We find, for the first time, stars in the HI arc to the southeast of the NGC 2535 disk. Population synthesis models indicate that all of the observed populations have young to intermediate ages. We conclude that although the gas disks and some old stars may have formed early-on, the progenitors are late-type or low surface brightness and the evolution of these galaxies was halted until the recent encounter.

astro-ph