Keith Butler
A central question regarding neutron star mergers is whether they are able to produce all the r-process elements, from first to third peak. The high abundances of first-peak elements (atomic number $Z \sim 31-40$) in the solar composition…
Machine learning interatomic potentials have revolutionized complex materials design by enabling rapid exploration of material configurational spaces via crystal structure prediction with ab initio accuracy. However, critical challenges…
Two-dimensional (2D) materials with large band gaps and strong and tunable second-harmonic generation (SHG) coefficients play an important role in the miniaturization of deep-ultraviolet (DUV) nonlinear optical (NLO) devices. Despite the…
Context. Late O-type stars at luminosities $\log L/L_\odot \lesssim 5.2$ show weak winds with mass-loss rates lower than 10$^{-8} M_\odot$ yr$^{-1}$. This implies that their photospheric layers are not strongly affected by the stellar wind.…
Classical force fields (FF) based on machine learning (ML) methods show great potential for large scale simulations of materials. MLFFs have hitherto largely been designed and fitted for specific systems and are not usually transferable to…
While the uptake of data-driven approaches for materials science and chemistry is at an exciting, early stage, to realise the true potential of machine learning models for successful scientific discovery, they must have qualities beyond…
An approach based on the Fisher information (FI) is developed to quantify the maximum information gain and optimal experimental design in neutron reflectometry experiments. In these experiments, the FI can be analytically calculated and…
This paper reviews some of the challenges posed by the huge growth of experimental data generated by the new generation of large-scale experiments at UK national facilities at the Rutherford Appleton Laboratory site at Harwell near Oxford.…
Many clinical workflows depend on interactive computer systems for highly technical, conceptual work products, such as diagnoses, treatment plans, care coordination, and case management. We describe an automatic logic reasoner to verify…
A precise quantitative spectral analysis - encompassing atmospheric parameter and chemical elemental abundance determination - is time consuming due to its iterative nature and the multi-parameter space to be explored, especially when done…
Extreme helium stars (EHe stars) are hydrogen-deficient supergiants of spectral type A and B. They are believed to result from mergers in double degenerate systems. In this paper we present a detailed quantitative non-LTE spectral analysis…
It is generally accepted that the atmospheres of cool/lukewarm stars of spectral types A and later are described well by LTE model atmospheres, while the O-type stars require a detailed treatment of NLTE effects. Here model atmosphere…
Hyper-velocity stars (HVSs) were first predicted by theory to be the result of the tidal disruption of a binary system by a super-massive black hole (SMBH) that accelerates one component to beyond the Galactic escape velocity (the Hills…
A representative sample of unevolved early B-type stars in nearby OB associations and the field is analysed to unprecedented precision using NLTE techniques. The resulting chemical composition is found to be more metal-rich and much more…
We evaluate the effect of variations in the electron-impact excitation cross sections on the non-LTE line formation for hydrogen in early-type stars. While the Balmer lines are basically unaffected by the choice of atomic data, the Brackett…
We investigate the synthesis of the Balmer and Paschen lines of the quiet Sun, using both classical semi-empirical and theoretical model atmospheres, modern line broadening theory and non-LTE line-formation. The computations alleviate…
We discuss aspects of non-LTE line formation for hydrogen in early-type stars. We evaluate the effect of variations in the electron-impact excitation cross sections in model atoms of differing complexity by comparison with observation.…
Elemental abundances of carbon, nitrogen, oxygen, magnesium, aluminum, and silicon are presented for a sample of twelve rapidly rotating OB star (v sin i > 60 km s^-1) members of the Cep OB2, Cyg OB3 and Cyg OB7 associations. The abundances…
We discuss results of an exploratory non-LTE analysis of two metal-rich A-type supergiants in M31. Using comprehensive model atoms we derive accurate atmospheric parameters from multiple indicators and show that non-LTE effects on the…
Accurate atomic data have become available in the recent past due to the demands of astrophysics and fusion research. We report on the impact of such data on non-LTE line-formation calculations for CNO in early-type stars. Considerable…