Tidal stripping as a mechanism for placing globular clusters on wide orbits: the case of MGC1 in M31

The globular clusters of large spiral galaxies can be divided into two populations: one which formed in-situ and one which comprises clusters tidally stripped away from other galaxies. In this paper we investigate the contribution to the outer globular cluster population in the M31 galaxy through donation of clusters from dwarf galaxies. We test this numerically by comparing the contribution of globular clusters from simulated encounters to the observed M31 globular cluster population. To constrain our simulations, we specifically investigate the outermost globular cluster in the M31 system, MGC1. The remote location of MGC1 favours the idea of it being captured, however, the cluster is devoid of features associated with tidal interactions. Hence we separate simulations where tidal features are present and where they are hidden. We find that our simulated encounters can place clusters on MGC1-like orbits. In addition, we find that tidal stripping of clusters from dwarf galaxies leaves them on orbits having a range of separations, broadly matching those observed in M31. We find that the specific energies of globular clusters captured by M31 closely matches those of the incoming host dwarf galaxies. Furthermore, in our simulations we find an equal number of accreted clusters on co-rotating and counter-rotating orbits within M31 and use this to infer the fraction of clusters that has been accreted. We find that even close in roughly 50% of the clusters are accreted, whilst this figure increases to over 80% further out.Comment: 17 pages, 12 figures. Accepted for publication in MNRA

The galactic scale impact of feedback from individual stars

Feedback from stars is essential for the formation and evolution of galaxies. It is an energy source that drives gas motions and chemically enriches the galaxy by supplying metals. Without this stellar feedback, numerical galaxy simulations result in galaxies with little resemblance to those observed in our Universe. Modern galaxy simulations frequently reach a mass resolution of a few tens of solar masses. Such high-resolution warrants models incorporating individual stars. These models enable a detailed treatment of when and where stars inject feedback. In this thesis, I present such a model and provide a series of papers exploring physical mechanisms unlocked by this model.In paper I, we investigate how runaway stars affect the galactic winds driven by stellar feedback in Milky Way-like galaxies. Massive runaway stars can venture to places where these short-lived stars are otherwise not found (e.g., between spiral arms). In these regions of diffuse gas, supernovae can efficiently incorporate energy into large volumes of gas, thereby boosting the gas outflow rate of the galaxy. Furthermore, the star formation rate is not significantly affected since parts of the feedback budget move away from star-forming gas. The result is a ten-fold boost in the mass loading factor.Paper II is a follow-up investigation of a surprising signal of star formation in spiral galaxies with runaway stars, found in Paper I. The signal is produced by the rapid migration of runaway stars to the galaxy's outskirts. Via direct comparison to observational data, we find that this explains faint far-ultraviolet radiation detected outside the optical radius of nearby spiral galaxies. This radiation manifests as a trend in the star formation relation with a slope similar to one produced by runaway stars escaping to these regions.In paper III, the star-by-star model is upgraded with a more advanced model for feedback and runaway stars. We showcase this model with a suit of simulations of isolated dwarf galaxies, testing a range of parameters for the natal velocity model of individual stars responsible for incorporating runaway stars. In stark contrast to the Milky Way-like galaxy, we find runaway stars play little to no role in determining outflows in dwarf galaxies. We discuss several possible reasons for the different effects in small and large galaxies

Probing the phase diagram of cuprates with YBa2_2Cu3_3O7−δ_{7-\delta} thin films and nanowires

We have grown and characterized 30 nm thick YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) films, deposited by pulsed laser deposition on both MgO (110) and SrTiO$_3$ (001) substrates, which induce opposite strain to the superconducting layer. By carefully tuning the in-situ post-annealing oxygen pressure, we achieved, in a reproducible way, films at different oxygen doping, spanning from the slightly overdoped down to the strongly underdoped region of the phase diagram. The transport properties of the films, investigated through resistance versus temperature measurements, are in perfect qualitative agreement with single crystals. Starting from these films, we have also successfully fabricated nanowires with widths down to 65 nm, at different oxygen doping. The nanostructures exhibit characteristic temperatures (as the critical temperature $T_{\mathrm{c}}$ and the pseudogap temperature $T^*$) similar to those of the as-grown films and carry critical current densities $J_{\mathrm{c}}$ close to the critical depairing value, limited by vortex entry. This implies that the superconducting and the normal state properties of underdoped YBCO are preserved in our films, and they can be studied as a function of the dimensionality of the system, down to the nanoscale.Comment: 11 pages, 9 figures, submitted to Phys. Rev. Material

True equivalent chip thickness for tools with a nose radius

A majority of the established systems for choice and optimization of cutting data are based on Woxén’s equivalent chip thickness, heW. In metal cutting theory and models, the equivalent chip thickness is of vital importance when the depth-of-cut ap is in the same order or smaller than the nose radius r. Woxén made considerable simplifications in his chip area model, that form the basis for calculations of the equivalent chip thickness. Basic mathematical solutions, e.g. describing the chip area on circular inserts, are lacking. This article describes the geometrical implications when machining with round inserts. The error in Woxén’s equivalent chip thickness is largest when the depth-of-cut is less than ¼ of the nose radius. The calculations of the equivalent chip thickness based on the Woxén model are up to 50 % wrong, for some combinations of cutting data in the finishing range. The presented results explain the difficulties in getting a good validity in the models used to calculate tool life in finishing machining. The error leads to an underrating of the tool load in many machining situations

Review article: the ethics of population policies

This is a review of contemporary philosophical discussions of population policies. The focus is on normative justification, and the main question is whether population policies can be ethically justified. Although few analytical philosophers have directly addressed this question - it has been discussed more in other academic fields - many arguments and considerations can be placed in the analytical philosophical discourse. This article offers a comprehensive review and analysis of ethically relevant aspects of population policies evaluated on the basis of the main ethical theories. This analysis is preceded by a brief historical contextualisation of when and how population policies became ethically contentious and how this relates to philosophical debates in environmental ethics, population ethics and political philosophy. The article also includes a conceptual analysis of population policies in which the empirical intricacies around individual fertility decisions are sorted out and the different ways in which they can be affected are categorised in a taxonomy which highlight the most relevant ethical aspects of population policies. The ethical analysis shows that while population policies can be justified on the basis of most ethical theories, it all depends on what prior assumptions are made about what is at stake

Runaway stars masquerading as star formation in galactic outskirts

In the outskirts of nearby spiral galaxies, star formation is observed in extremely low gas surface densities. Star formation in these regions, where the interstellar medium is dominated by diffuse atomic hydrogen, is difficult to explain with classic star formation theories. In this work, we introduce runaway stars as an explanation to this observation. Runaway stars, produced by collisional dynamics in young stellar clusters, can travel kilo-parsecs during their main sequence life time. Using galactic-scale hydrodynamic simulations including a treatment of individual stars, we demonstrate that this mechanism enables the ejection of young massive stars into environments where the gas is not dense enough to trigger star formation. This results in the appearance of star formation in regions where it ought to be impossible. We conclude that runaway stars are a contributing, if not dominant, factor to the observations of star formation in the outskirts of spiral galaxies.Comment: Submitted to MNRAS Letters, comments welcom

Manufacturing costs and Degree of Occupancy Based on the Principle of Characteristic Parts

In making capacity estimates and cost calculations in the manufacturing industry, many products and production systems are often involved, making the data in their totality difficult to grasp. Introducing the concept of the characteristic part, which is a fabricated part seen as representative of all parts produced in terms of demand, setup time, cycle time, average batch size and total number of batches involved, makes the calculations required much more manageable and much less time-consuming. The article takes up how the characteristic part is defined and how it can be used in calculating production capacity, system utilization and manufacturing costs