arXiv subjects

Stephen Todd

Publications and source records attributed to Stephen Todd.

8 recordsLinked to original sources

arXiv2026

METIS for ELT: optical alignment and testing of the IFU of the LM-band spectrometer

The METIS LMS (LM-band Spectrometer) is a high-resolution (R>100,000) mid-infrared integral field spectrometer for the ESO ELT. The instrument provides the capability to measure instantaneous spectra across a 0.577 x 0.897 arcsecond field-of-view with a spatial sampling of 8.2-9.1 mas using an image slicing IFU. This paper presents the optical testing and alignment performed for the IFU sub-system. This includes the detailed characterisation of the image slicing mirror array measured via: a re-imaging test in which the slicer is positioned to re-image a point source to form 28 images due to the different tilts of the 28 slicer mirrors; and precise interferometric measurements of each of the image slicer mirrors. The paper will also give an overview of the optical alignment strategy employed during the IFU AIT process in order to reach the tight alignment requirements.

astro-ph.IM↗

arXiv2026

Evolution & Foundation: AI Shares Creative Control

This paper investigates the creative process of automated design and artistic evaluation using an evolutionary system. We consider how a multimodal artificial intelligence (AI) model can communicate and guide a combined generative and evolutionary computational system. This creates a framework for the evolution of aesthetically pleasing complex 3D organic forms by integrating genetic algorithms with the visual reasoning capabilities of large-scale AI foundation models. The framework shifts the artist role from that of intensive direct selection to one of system design; transferring detailed step-by-step curation to an AI agent capable of multimodal aesthetic judgement. This framework enables the human artist/designer to rapidly traverse large areas of multi-dimensional evolutionary parameter space to find creative outcomes based on their semantic targets. Detailed audit trails of the AI's aesthetic reasoning are generated for each experiment. Interactive visualisation tools, together with AI-generated summaries and evolutionary narratives, enable deep exploration into each evolutionary experiment and providing a transparent insight into the AI-guided process.

cs.NE↗

arXiv2026

The Key to Unlocking Exoplanet Biosignatures: a UK-led IR Spectrograph for the Habitable Worlds Observatory Coronagraph

The detection of life on rocky exoplanets in the habitable zones of nearby stars would be a paradigm-shifting advance, and it is one of the greatest scientific challenges of our time. There is no single spectral feature that is an unambiguous sign of life on a given exoplanet. Instead, the current state-of-the-art approach involves detecting multiple molecular atmospheric features that should not exist together in equilibrium, e.g. simultaneous detection of O$_2$ and CH$_4$. Spectra across a wide wavelength (0.3-1.7 $\mu$m) range are necessary to cover multiple spectral features per molecule of interest and to contextualise the suite of molecular features detected. While the US will lead the optical arm of the Habitable Worlds Observatory (HWO) coronagraph, a UK-led contribution of a near-infrared Integral Field Spectrograph (IFS) for the infrared arm will ensure UK leadership in the flagship scientific goal of HWO - to search for signatures of life on potentially habitable exoplanets.

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arXiv2021

Active deployable primary mirrors on CubeSat

The volume available on small satellites restricts the size of optical apertures to a few centimetres, limiting the Ground-Sampling Distance (GSD) in the visible to typically 3 m at 500 km. We present in this paper the latest development of a laboratory demonstrator of a segmented deployable telescope that will triple the achievable ground resolution and improve photometric capability of CubeSat imagers. Each mirror segment is folded for launch and unfolds in space. We demonstrate through laboratory validation very high deployment repeatability of the mirrors <{\pm}5 {\mu}m. To enable diffraction-limited imaging, segments are controlled in piston, tip, and tilt. This is achieved by an initial coarse alignment of the mirrors followed by a fine phasing step. Finally, we investigate the impact of the thermal environment on high-order wavefront error and the conceptual design of a deployable secondary fitting inside 1U.

astro-ph.IM↗

arXiv2020

Predicting feature imputability in the absence of ground truth

Data imputation is the most popular method of dealing with missing values, but in most real life applications, large missing data can occur and it is difficult or impossible to evaluate whether data has been imputed accurately (lack of ground truth). This paper addresses these issues by proposing an effective and simple principal component based method for determining whether individual data features can be accurately imputed - feature imputability. In particular, we establish a strong linear relationship between principal component loadings and feature imputability, even in the presence of extreme missingness and lack of ground truth. This work will have important implications in practical data imputation strategies.

stat.ME↗

arXiv2018

Laboratory Demonstration of an Active Optics System for High-Resolution Deployable CubeSat

In this paper we present HighRes: a laboratory demonstration of a 3U CubeSat with a deployable primary mirror that has the potential of achieving high-resolution imaging for Earth Observation. The system is based on a Cassegrain telescope with a segmented primary mirror composed of 4 petals that form an effective aperture of 300 mm. The design provides diffraction limited performance over the entire field-of-view and allows for a panchromatic ground-sampling distance of less than 1 m at an altitude of 350 km. The alignment and co-phasing of the mirror segments is performed by focal plane sharpening and is validated through rigorous numerical simulations. The opto-mechanical design of the prototype and its laboratory demonstration are described and measurements from the on-board metrology sensors are presented. This data verifies that the performance of the mirror deployment and manipulation systems is sufficient for co-phasing. In addition, it is shown that the mirrors can be driven to any target position with an accuracy of 25 nm using closed-loop feedback between the mirror motors and the on-board metrology.

astro-ph.IM↗

arXiv2013

Hyper-Graph Based Database Partitioning for Transactional Workloads

A common approach to scaling transactional databases in practice is horizontal partitioning, which increases system scalability, high availability and self-manageability. Usu- ally it is very challenging to choose or design an optimal partitioning scheme for a given workload and database. In this technical report, we propose a fine-grained hyper-graph based database partitioning system for transactional work- loads. The partitioning system takes a database, a workload, a node cluster and partitioning constraints as input and out- puts a lookup-table encoding the final database partitioning decision. The database partitioning problem is modeled as a multi-constraints hyper-graph partitioning problem. By deriving a min-cut of the hyper-graph, our system can min- imize the total number of distributed transactions in the workload, balance the sizes and workload accesses of the partitions and satisfy all the partition constraints imposed. Our system is highly interactive as it allows users to im- pose partition constraints, watch visualized partitioning ef- fects, and provide feedback based on human expertise and indirect domain knowledge for generating better partition- ing schemes.

cs.DB↗

arXiv2006

A multi-object, multi-field spectrometer and imager for a European ELT

One of the highlights of the European ELT Science Case book is the study of resolved stellar populations, potentially out to the Virgo Cluster of galaxies. A European ELT would enable such studies in a wide range of unexplored distant environments, in terms of both galaxy morphology and metallicity. As part of a small study, a revised science case has been used to shape the conceptual design of a multi-object, multi-field spectrometer and imager (MOMSI). Here we present an overview of some key science drivers, and how to achieve these with elements such as multiplex, AO-correction, pick-off technology and spectral resolution.

astro-ph↗