Observations from Preliminary Experiments on Spatial and Temporal Pressure Measurements from Near-Field Free Air Explosions

It is self-evident that a crucial step in analysing the performance of protective structures is to be able to accurately quantify the blast load arising from a high explosive detonation. For structures located near to the source of a high explosive detonation, the resulting pressure is extremely high in magnitude and highly non-uniform over the face of the target. There exists very little direct measurement of blast parameters in the nearfield, mainly attributed to the lack of instrumentation sufficiently robust to survive extreme loading events yet sensitive enough to capture salient features of the blast. Instead literature guidance is informed largely by early numerical analyses and parametric studies. Furthermore, the lack of an accurate, reliable data set has prevented subsequent numerical analyses from being validated against experimental trials. This paper presents an experimental methodology that has been developed in part to enable such experimental data to be gathered. The experimental apparatus comprises an array of Hopkinson pressure bars, fitted through holes in a target, with the loaded faces of the bars flush with the target face. Thus, the bars are exposed to the normally or obliquely reflected shocks from the impingement of the blast wave with the target. Pressure-time recordings are presented along with associated Arbitary-Langrangian-Eulerian modelling using the LS-DYNA explicit numerical code. Experimental results are corrected for the effects of dispersion of the propagating waves in the pressure bars, enabling accurate characterisation of the peak pressures and impulses from these loadings. The combined results are used to make comments on the mechanism of the pressure load for very near-field blast events

Impact of the hypoxic microenvironment on spermatogonial stem cells in culture

The stem cell niche plays a crucial role in the decision to either self-renew or differentiate. Recent observations lead to the hypothesis that O2 supply by blood and local O2 tension could be key components of the testicular niche of spermatogonial stem cells (SSCs). In this study, we investigated the impact of different hypoxic conditions (3.5%, 1%, and 0.1% O2 tension) on murine and human SSCs in culture. We observed a deleterious effect of severe hypoxia (1% O2 and 0.1% O2) on the capacity of murine SSCs to form germ cell clusters when plated at low density. Severe effects on SSCs proliferation occur at an O2 tension ≤1% and hypoxia was shown to induce a slight differentiation bias under 1% and 0.1% O2 conditions. Exposure to hypoxia did not appear to change the mitochondrial mass and the potential of membrane of mitochondria in SSCs, but induced the generation of mitochondrial ROS at 3.5% and 1% O2. In 3.5% O2 conditions, the capacity of SSCs to form colonies was maintained at the level of 21% O2 at low cell density, but it was impossible to amplify and maintain stem cell number in high cell density culture. In addition, we observed that 3.5% hypoxia did not improve the maintenance and propagation of human SSCs. Finally, our data tend to show that the transcription factors HIF-1α and HIF-2α are not involved in the SSCs cell autonomous response to hypoxia

Becoming animate in education: immanent materiality and outdoor learning for sustainability

Outdoor environmental education has long postulated a link between experiences outdoors in ‘natural’ environments and environmental concern. This paper suggests a straightforward relationship is problematic due to its implicit assumption of a nature/culture divide. Critical outdoor education has sought to overcome this dualism by describing a relational understanding of the world emphasizing ecological systems and highlighting humanity’s ‘connection’ to the environment. This relational approach aims to tackle the ‘crisis of perception’, argued to be the root cause of anthropogenic planetary degradation. We draw from the philosophical work of Deleuze and Guattari to suggest that relational ontologies, as currently conceived, may reinforce a static conception of the world by emphasizing ‘points of being’ (subject and object). Deleuze and Guattari proffer immanent materiality, where points of being are dispelled by movement and ‘becoming’. We then describe ‘animism’ as a mode of living where the world is understood to be immanent and constantly becoming. The consequences of animism are explored with regards to conceptions of ‘nature’, ‘place’ and ‘outdoor’ learning for sustainability. Creative practices to tackle the ‘crisis of perception’ are suggested as approaches that circumvent static conceptions of the world implied by points in relations and prevailing conceptions of nature as ‘other’

On Schutz’s conception of science as one of multiple realities

This article examines Alfred Schutz’s concept of ‘multiple realities’, and in particular, his portrayal of science as one of these realities. It is noted that, while this concept has been widely cited, it has often been interpreted in ways that are at odds with key features of Schutz’s original formulation. A careful assessment is made of the main article he wrote dealing with this topic, focusing on the respects in which the ‘multiple realities’ he discusses are held to differ. Particular attention is given to the relationship between science and what Schutz calls ‘the paramount reality’, that of ‘daily life’. It is suggested that there are some serious problems with the distinctions he makes and that these relate to an ambiguity in his position: that he starts from within phenomenological psychology, drawing on the work of Husserl and James, but moves in a more naturalistic and sociological direction in his account of ‘the world of daily life’. This raises some fundamental questions about the nature of phenomenology and its relationship to social science

Besides affirmationism? On geography and negativity

This paper poses questions on the possibility of styles of working besides “affirmationism.” The paper begins by defining negativity as a force or status of disunification, and traces how it remains closely associated with dialectics within Geography. The paper goes on to explore how the renunciation of dialectics has meant that negativity more generally has been rendered outside thought, with a concomitant uptake of an affirmationist ethos. Despite the promise of such work, there remains disquiet. What is omitted or elided in the uptake of affirmationism? Critiques, largely from outside the discipline, highlight how affirmationism privileges the lively and Life, novelty and experimentation, and the generous and generative in conjunction with a suspicion of negativity. We home in on and reflect on three ostensible limits of affirmationism: affirmationist vitalism, affirmationist politics, and affirmationist critique. We argue that renouncing dialectics does not entail, necessarily so, a concomitant abandonment of negativity. Indeed, we need to embrace attempts to think and act that elude, or dispense with, the propensity to affirm, making space for affects that are far from hopeful, for those becomings-otherwise that do not increase capacities to act, or for modes of critique that refuse; in other words, for that which is besides affirmationism or simply “unaffirmable.” Crucially, however, we point towards the dangers of a simple (re)turn to negativity, preferring a steadfast refusal to settle these tensions