The ionization structure of planetary nebulae. Part 7: New observations in the ring nebula

New optical spectrophotometric observations of emission-line intensities have been made in eight positions in the Ring Nebula corresponding to those observed previously with the Ultraviolet Explorer satellite; the total coverage is therefore 1400 to 7200 A. The intensities are in generally good agreement with those found previously in corresponding positions. The 0(++) and Balmer continuum electron temperatures agree well on the average and, like the N(+) electron temperatures, decrease with increasing distance from the central star. As found previously for the Ring Nebula and for other planetaries in this series, the lambda 4267 C 2 line intensity near the central star implies a C(++) abundance that is higher than that determined from the lambda 1906, 1909 C 3 lines. The discrepancy again decreases with increasing distance from the central star and vanishes from the outermost positions, again suggesting that the excitation mechanism from the lambda 4267 line is not understood. Standard equations used to correct for the existence of elements in other than the optically observable ionization stages give results that are consistent and in appropriate agreement with abundances calculated using UV lines. The rather high abundances of O, N, and C, and, to some extent N, indicate that some mixing of CNO processed material into the nebular shell may have occurred in the Ring Nebula

Media philosophy

This article sets out my approach to media philosophy, focussing particularly on the concepts of the 'condition of userness' and 'multi-temporality'

Cultural techniques of play: a media philosophical approach to the study of time, history and memory in games

Taking Johan Huizinga's work on games and culture as a starting point—particularly his arguments about how play can be considered as primary to culture—this paper gives a new account of twenty-first-century play as Kulturtechniken (cultural technique). Using examples including the art games and indie games That Dragon, Cancer (Numinous Games, 2016), The Outlands (Haines and Hinterding, 2011), and Superhot (Superhot Team, 2016), the paper explores the way time is ordered in gaming and develops a media theoretical approach to explain the way play might "cultivate" a certain way of living in and thinking about the world, particularly through its time-critical operation. The three examples are chosen because in each of them we can see a different element of digital temporality, including the way time is ordered by computational systems; the way memories and histories are archived and made discoverable by digital systems; and the way interface design can facilitate experiences of being-in-time. By exploring gaming as a cultural technique, the paper enters into a field of debate in media and cultural studies that addresses the concepts of contemporaneity and digital temporality and offers a new way to approach these areas of study through a focus on games

The ionization structure of planetary nebulae. 9: NGC 1535

Spectrophotometric observations of emission-line intensities over the spectral range 1400 to 7200 A were made in five positions in the planetary nebula NGC 1535. There is some evidence for variation in the Balmer decrements between these positions. The O(++) electron temperature varies little from 11500 K across these positions; the Balmer continuum electron temperature averages a few hundred K higher than this, but this difference is insignificant when compared to the measurement errors. As found for most of the other planetaries in this series, the wavelength 4267 C II line intensity near the central star implies a C(++) abundance that is several times higher that that determined from the wavelength 1906, 1909 C III lines. The discrepancy again decreases with increasing distance from the central star, again suggesting that the excitation mechanism for the wavelength 4267 C II is not understood. Standard equations used to correct for the existence of elements in other than the optically observable ionization stages give consistent results for the different positions; there is no evidence for any abundance gradient in the nebula. The logarithmic abundances are He = 10.99, O = 8.51, N = 7.63, Ne = 7.89, C = 8.34, and Ar = 6.08. The abundances agree well with determinations by Aller and Czyzak and by Torres-Peimbert and Peimbert and are nearly identical to those found for NGC 6826. As for NGC 6826, the rather low abundances of He, N, and C suggest that there was little if any mixing of CNO-processed material into the nebular shell in the progenitor to NGC 1535. The O, Ne, Ar abundances appear to be somewhat low, suggesting that the progenitor to NGC 1535 may have formed out of somewhat metal-poor material

Impingement-Current-Erosion Characteristics of Accelerator Grids on Two-Grid Ion Thrusters

Accelerator grid sputter erosion resulting from charge-exchange-ion impingement is considered to be a primary cause of failure for electrostatic ion thrusters. An experimental method was developed and implemented to measure erosion characteristics of ion-thruster accel-grids for two-grid systems as a function of beam current, accel-grid potential, and facility background pressure. Intricate accelerator grid erosion patterns, that are typically produced in a short time (a few hours), are shown. Accelerator grid volumetric and depth-erosion rates are calculated from these erosion patterns and reported for each of the parameters investigated. A simple theoretical volumetric erosion model yields results that are compared to experimental findings. Results from the model and experiments agree to within 10%, thereby verifying the testing technique. In general, the local distribution of erosion is concentrated in pits between three adjacent holes and trenches that join pits. The shapes of the pits and trenches are shown to be dependent upon operating conditions. Increases in beam current and the accel-grid voltage magnitude lead to deeper pits and trenches. Competing effects cause complex changes in depth-erosion rates as background pressure is increased. Shape factors that describe pits and trenches (i.e. ratio of the average erosion width to the maximum possible width) are also affected in relatively complex ways by changes in beam current, ac tel-grid voltage magnitude, and background pressure. In all cases, however, gross volumetric erosion rates agree with theoretical predictions

The ionization structure of planetary nebulae 10: NGC 2392

Spectrophotometric observations of emission-line intensities over the spectral range 1400 to 7200 A were made in six positions in the planetary nebula NGC 2392. Standard equations used to correct for the existence of elements in other than the optically observable ionization stages give consistent results for the different positions that are in excellent agreement with abundances calculated using ultraviolet lines, and there is no evidence for any abundance gradient in the nebula. The logarithmic abundances agree well with determinations by Aller and Keyes

Michel Serres’ messengers

Although central to his philosophy of communication, the figure of the messenger in Michel Serres’ thought has so far received little attention in English speaking media and cultural theory. This essay explores the characters of messengers that Serres develops throughout his philosophical project, focusing on the way that they allow him to develop topics such as the ethics of exchange, interdisciplinarity, pedagogy, rituals of communication and what he sees as the violence of dialectics. The discussion of Serres’ work then leads to a discussion of the messenger figure in terms of the interruptions that they can introduce to systems of exchange, ending with an exploration of what Serres’ thought may offer as we try and grapple with a new culture of miscommunication

Collaborative learning with affective artificial study companions in a virtual learning environment

This research has been carried out in conjunction with Chapeltown and Harehills Assisted Learning Computer School (CHALCS) and local schools. CHALCS is an 'out-of-hours' school in a deprived inner-city community where unemployment is high and many children are failing to meet their educational potential. As the name implies CHALCS provides students with access to computers to support their learning. CHALCS relies on many volunteer tutors and specialist tutors are in short supply. This is especially true for subjects such as Advanced Level Physics with low numbers of students. This research aimed to investigate the feasibility of providing online study skills support to pupils at CHALCS and a local school. Research suggests that collaborative learning that prompts students to explain and justify their understanding can encourage deeper learning. As a potentially effective way of motivating deeper learning from hypertext course notes in a Virtual Learning Environment (VLE), this research investigates the feasibility of designing an artificial Agent capable of collaborating with the learner to jointly construct summary notes. Hypertext course notes covering a portion of the Advanced Level Physics curriculum were designed and uploaded into a WebCT based VLE. A specialist tutor validated the content of the course notes before the ease of use of the VLE was tested with target students. A study was then conducted to develop a model of the kinds of help students required in writing summary notes from the course-notes. Based on the derived process model of summarisation and an analysis of the content structure of the course notes, strategies for summarising the text were devised. An Animated Pedagogical Agent was designed incorporating these strategies. Two versions of the agent with opposing 'Affectations' (giving the appearance of different characters) were evaluated with users. It was therefore possible to test which artificial 'character' students preferred. From the evaluation study some conclusions are made concerning the effect of the two opposite characterisations on student perceptions of the agent and the degree to which it was helpful as a learning companion. Some recommendations for future work are then made

The transcendental and the agonistic: a media philosophy perspective

This critical response to Dominic Smith’s ‘Taking Exception: Philosophy of Technology as a Multidimensional Problem Space’ begins by outlining the key contributions of his essay, namely his insightful approach to the transcendental, on the one hand, and his introduction of the topological problem space as an image for thought, on the other. The response then suggests ways of furthering this approach by addressing potential reservations about determinism. The response concludes by suggesting a way out of these questions of determinism by thinking the transcendental in concert with the agonistic