Experimental Procedure to Determine the Effectiveness Of Phase Change Materials to Cool a Railgun Armature

This Engineering Undergraduate Research Project (EURP) explores the possibility of using a railgun to assist in orbital launches of unmanned space vehicles. More specifically, the EURP focuses on the problem of heat management in the armature of a railgun. Phase Change Materials (PCM) are used to increase the latent heat of solids and are a potential candidate to cooling railgun armatures during the high energy pulse of the firing sequence. Electrical current pulses are applied to different metal samples using a capacitor bank. The Ohmic heating of these samples is compared to assess how much heat is absorbed by the different kind of PCMs. Control tests will be performed using samples without PCMs as well. The results of these preliminary experiments will be presented. This presentation will showcase the advantages of using PCMs to enhance latent heat cooling of railgun armatures. This presentation will also assess the relevance of this application of PCMs considering cost, mass management, and chemical hazards

Modeling of no radiative emission in non-equilibrium hypersonic flow

The thermochemistry of supersonic flows has been studies thoroughly in the context of military aircraft development. Similarly, High speed hypersonic flight has been studied by both defence and civilian entities in the context of re-entry vehicles and spaceflight more generally. Hypersonic flight in regimes which causes little to no ionisation, on the other hand, are still the subject of ongoing studies. The renewed interest by high-tech nations in hypersonic weapons and vehicles has highlighted the general lack of knowledge, as well as the challenge that complex hypersonic flow thermochemistry represents. Because of compressible flow effects, the chemical reactions and non equilibrium conditions found in the shock regions of hypersonic flows have to be measured using non-invasive optical diagnostic techniques. The creation of Nitric Oxide in hypersonic shocks can be measured both by radiative emission and absorption measurements. NO is an ideal optical diagnostic tool because it has a significant absorption cross section, and is a strong emitter in the IR and the UV. The ability to model radiative emission from NO is therefore crucial to the interpretation of optical diagnostics of hypersonic air flow. This work focuses on modeling NO radiation in the UV, as well as vibrationally and electronically excited populations of NO. The conditions used for the simulations are a shock tube and a cylinder in a Hypervelocity Expansion Tube (HET) experiment. The simulated HET conditions present a 2D flow field moving around the cylinder and presents several regions of interest including the bow shock and the expansion region. Overlay techniques are applied to DSMC flow solutions in order to compute radiative emission and transport. Self normalized integrated intensity profiles are computed using the NO gamma, beta, and delta bands in the 210 nm - 250 nm region for the HET conditions for the HET case. absolute spectra radiance measurement from a shock tube is simulated, using 1D solutions from several DSMC chemistry sets. Normalized spectra in the 210 nm - 250 nm region are used to extract nonequilibrium temperature by fitting the measurements with synthetic spectra. The number density of excited species in a flow are one of the challenging parameters to compute when modeling radiative emission. A Quasi Steady state (QSS) overlay method offers an alternative to a Boltzmann calculation for the population of electronically excited species. The prediction of these electronically excited populations are necessary for the modeling of UV radiative emission. The existing collisional-radiative model is expanded with a set of reactions which provide new population mechanisms for electronically excited states of NO and N2. Although not a contributor in terms of radiation in the spectral region of interest, N2 serves as an energy reservoir capable of re-excited quenched NO molecules. The resulting population calculations are compared with Boltzmann calculations for the HET at full density and in rarefied conditions. A collisional-radiative model for vibrationally excited population analogous to the QSS model is presented. This model uses experimentally determined quenching rates for the first three vibrationally excited states of NO and the first vibrationally excited state of N2 to compute the population of these states. The computation of these states is used for modeling IR radiative emission and inform absorption experiments. The vibrational collision model is applied as an overlay to the HET DSMC solution, similarly to the QSS computation. Time resolved vibrational calculations are performed at points in the wake region of the HET domain where the residence time of the flow allows for the collisional mechanisms to produce non-Boltzmann populations. Finally, this collisional-radiative model is added to a mass transport solver to determine the first three steady state vibrational populations of NO

Leverage points in the financial sector for seafood sustainability

Can finance contribute to seafood sustainability? This is an increasingly relevant question given the projected growth of seafood markets and the magnitude of social and environmental challenges associated with its seafood production. As more capital is injected into the seafood industry, it becomes crucial that such investments steer the sector towards improved sustainability, as opposed to fueling unsustainable working conditions and overexploitation of resources. Using a mixed-methods approach, we map where different financial mechanisms are most salient along a seafood firm’s development trajectory and identify three leverage points for sustainability that can redirect capital towards more sustainable practices: loan covenants, stock exchange listing rules and shareholder activism. Our results show that although they hold great promise for transformative capacity, this potential is currently unlikely to be realized due to limited social-ecological awareness within the finance industry. We argue that seafood sustainability requirements need to be integrated into traditional financial services and propose key research avenues for both the academic and the policy community. While our study focuses on the role of finance in seafood sustainability, the insights developed throughout are of high relevance to other extractive industries as well

Identifying multiple coral reef regimes and their drivers across the Hawaiian archipelago

Loss of coral reef resilience can lead to dramatic changes in benthic structure, often called regime shifts, which significantly alter ecosystem processes and functioning. In the face of global change and increasing direct human impacts, there is an urgent need to anticipate and prevent undesirable regime shifts and, conversely, to reverse shifts in already degraded reef systems. Such challenges require a better understanding of the human and natural drivers that support or undermine different reef regimes. The Hawaiian archipelago extends across a wide gradient of natural and anthropogenic conditions and provides us a unique opportunity to investigate the relationships between multiple reef regimes, their dynamics and potential drivers. We applied a combination of exploratory ordination methods and inferential statistics to one of the most comprehensive coral reef datasets available in order to detect, visualize and define potential multiple ecosystem regimes. This study demonstrates the existence of three distinct reef regimes dominated by hard corals, turf algae or macroalgae. Results from boosted regression trees show nonlinear patterns among predictors that help to explain the occurrence of these regimes, and highlight herbivore biomass as the key driver in addition to effluent, latitude and depth

Guiding coral reef futures in the Anthropocene

Anthropogenic changes to the Earth now rival those caused by the forces of nature and have shepherded us into a new planetary epoch – the Anthropocene. Such changes include profound and often unexpected alterations to coral reef ecosystems and the services they provide to human societies. Ensuring that reefs and their services endure during the Anthropocene will require that key drivers of coral reef change – fishing, water quality, and anthropogenic climate change – stay within acceptable levels or “safe operating spaces”. The capacity to remain within these safe boundaries hinges on understanding the local, but also the increasingly global and cross-scale, socioeconomic causes of these human drivers of change. Consequently, local and regional management efforts that are successful in the short term may ultimately fail if current decision making and institution-building around coral reef systems remains fragmented, poorly coordinated, and unable to keep pace with the escalating speed of social, technological, and ecological change

Local human impacts disrupt relationships between benthic reef assemblages and environmental predictors

Human activities are changing ecosystems at an unprecedented rate, yet large-scale studies into how local human impacts alter natural systems and interact with other aspects of global change are still lacking. Here we provide empirical evidence that local human impacts fundamentally alter relationships between ecological communities and environmental drivers. Using tropical coral reefs as a study system, we investigated the influence of contrasting levels of local human impact using a spatially extensive dataset spanning 62 outer reefs around inhabited Pacific islands. We tested how local human impacts (low versus high determined using a threshold of 25 people km−2 reef) affected benthic community (i) structure, and (ii) relationships with environmental predictors using pre-defined models and model selection tools. Data on reef depth, benthic assemblages, and herbivorous fish communities were collected from field surveys. Additional data on thermal stress, storm exposure, and market gravity (a function of human population size and reef accessibility) were extracted from public repositories. Findings revealed that reefs subject to high local human impact were characterised by relatively more turf algae (>10% higher mean absolute coverage) and lower live coral cover (9% less mean absolute coverage) than reefs subject to low local human impact, but had similar macroalgal cover and coral morphological composition. Models based on spatio-physical predictors were significantly more accurate in explaining the variation of benthic assemblages at sites with low (mean adjusted-R2 = 0.35) rather than high local human impact, where relationships became much weaker (mean adjusted-R2 = 0.10). Model selection procedures also identified a distinct shift in the relative importance of different herbivorous fish functional groups in explaining benthic communities depending on the local human impact level. These results demonstrate that local human impacts alter natural systems and indicate that projecting climate change impacts may be particularly challenging at reefs close to higher human populations, where dependency and pressure on ecosystem services are highest

Deciphering the nature and age of the protoliths and peak P−T conditions in retrogressed mafic eclogites from the Maures-Tannneron Massif (SE France) and implications for the southern European Variscides

We present new constraints on the age, nature, and tectonic setting of mafic eclogite protoliths from the Maures-Tanneron Massif, southern Variscan belt. Whole-rock major and trace element geochemistry was combined with zircon dating using 206Pb/238U by LA‒ICP‒MS to improve the understanding of this key-target of the European Southern Variscides. Geochemical data show that protoliths of the mafic eclogites are typical MORBs, while REE and HFSE patterns suggest an E-MORB affinity. However, the geochemical study shows several signs of crustal contamination that increases with the degree of retrogression. A comparison with Sardinian eclogites, which belong to the same Variscan microplate, namely, “MECS” (Maures-Estérel-Corsica-Sardinia), demonstrates that the eclogites are included in migmatites, which is the case for the studied samples, are the most contaminated. The Maures-Tanneron mafic eclogites represent the remnant of an oceanic basaltic crust. Zircon cores display homogeneous Th/U ratios (0.3–0.4), which are consistent with a magmatic origin, and define an age peak at 499.5 ± 2.9 Ma that is interpreted as the most likely emplacement age of the basaltic protolith. This age suggests that this protolith was part of an oceanic floor that was older than the Rheic Ocean and located to the north of the Gondwana active continental margin as predicted by recent unified full plate reconstruction models. Although the studied eclogites are retrogressed, the study of mineral inclusions trapped in garnets combined with thermodynamic modelling yields a P−T range of 17.2–18.5 kbar and 640–660 °C, which is consistent with the standard oceanic subduction palaeo-geotherm. These new data suggest that eclogites recognized in the “MECS” Variscan microplate represent the closure of oceanic domains of different ages (Cambrian or Ordovician)

Rethinking coral reef functional futures

Tropical coral reefs currently face an unprecedented restructuring since their extant form and function emerged ~24 million years ago in the early Neogene. They have entered the Anthropocene—an epoch where humans have become the dominant force of planetary change. Human impacts on and interactions with coral reefs are escalating across multiple trophic levels and scales, but we have a rudimentary understanding of what this means for their functional ecology. The overall goal of this special feature is to unpack what the Anthropocene means for the functional ecology of coral reefs, laying the foundations for new approaches and research directions in coral reef science. The collection describes the functional changes and novel dynamics that characterise Anthropocene reefs, from variations in their taxonomy and geology through to the resulting shifts in ecosystem services they provide to humanity. Common changes to coral reefs are occurring that are challenging their historical functional role. These include reductions in benthic calcifiers and declining carbonate production, and benthic assemblage shifts leading to a loss of structural complexity and flattening of reef seascapes. As reefs as we know them are lost from some locations, range extensions and the “tropicalisation” of temperate locations present novel ecosystem configurations that are challenging ecological paradigms and our historical approach to ecosystem management. Hindering our progress, however, is a “functionality crisis.” Coral reef functional ecology to date has lacked a clear and universal definition of the term “function,” and many assumed links between taxa and reef processes lack empirical evidence. Moving forward, we must establish causal links between functional traits, the species that possess them, and specific ecosystem processes if we are to successfully manage Anthropocene reefs. The functional space coral reefs occupy has arguably widened, presenting ethical challenges surrounding the increasingly interventionist management practices required to achieve particular functional endpoints. For us to steer coral reefs towards a desirable functional future will require a more mechanistic understanding between ecosystem attributes and the provision of services, acknowledging that such services are coproduced by the ecosystem and society. Ultimately, this era in coral reef ecology requires a new approach to coral reef science, one that addresses the complex socio-ecological nature of coral reefs. These works outline a path ahead for defining and studying the functional ecology of coral reefs, drive debate as to what we want their functional future to look like and call for ecosystem function to be at the heart of managing coral reef futures during this period of rapid transition. © 2019 The Authors. Functional Ecology © 2019 British Ecological Societ

Scale-dependent spatial patterns in benthic communities around a tropical island seascape

Understanding and predicting patterns of spatial organization across ecological communities is central to the field of landscape ecology, and a similar line of inquiry has begun to evolve sub-tidally among seascape ecologists. Much of our current understanding of the processes driving marine community patterns, particularly in the tropics, has come from small-scale, spatially-discrete data that are often not representative of the broader seascape. Here we expand the spatial extent of seascape ecology studies and combine spatially-expansive in situ digital imagery, oceanographic measurements, spatial statistics, and predictive modeling to test whether predictable patterns emerge between coral reef benthic competitors across scales in response to intra-island gradients in physical drivers. We do this around the entire circumference of a remote, uninhabited island in the central Pacific (Jarvis Island) that lacks the confounding effects of direct human impacts. We show, for the first time, that competing benthic groups demonstrate predictable scaling patterns of organization, with positive autocorrelation in the cover of each group at scales \u3c ~1 km. Moreover, we show how gradients in subsurface temperature and surface wave power drive spatially-abrupt transition points in group dominance, explaining 48–84% of the overall variation in benthic cover around the island. Along the western coast, we documented ten times more sub-surface cooling-hours than any other part of the coastline, with events typically resulting in a drop of 1–4°C over a period of \u3c 5 h. These high frequency temperature fluctuations are indicative of upwelling induced by internal waves and here result in localized nitrogen enrichment (NO 2 + NO 3 ) that promotes hard coral dominance around 44% of the island\u27s perimeter. Our findings show that, in the absence of confounding direct human impacts, the spatial organization of coral reef benthic competitors are predictable and somewhat bounded across the seascape by concurrent gradients in physical drivers

Accounting and accountability in the Anthropocene

This research received funding from the Walton Family Foundation (2017-693, 2018-1371), the David and Lucile Packard Foundation (2017-66205, 2019-68336), and the Gordon and Betty Moore Foundation (5668.01).Purpose: This paper aims to interrogate the nature and relevance of debates around the existence of, and ramifications arising from, the Anthropocene for accounting scholarship. Design/methodology/approach: The paper’s aim is achieved through an in-depth analysis of the Anthropocene, paying attention to cross disciplinary contributions, interpretations and contestations. Some points of connection between the Anthropocene and accounting scholarship are then proposed and illuminated through a case study drawn from the seafood sector. Findings: This paper develops findings in two areas. First, there are suggestions about how accounting scholarship might be further developed by the provocation that thinking about the Anthropocene provides. Second, we suggest new accounting research findings, through engagement with the case study, and propose that the concept of stewardship may re-emerge in discussions about accountability in the Anthropocene. Research limitations/implications: The paper argues that accounting scholarship focused on social, environmental and sustainability concerns may be further developed by engagement with Anthropocene debates. Practical implications: While accounting practice might have to change to deal with Anthropocene induces effects, this paper focuses on implications for accounting scholarship. Social implications: Human wellbeing is likely to be impacted should environmental impacts accelerate. In addition, an Anthropocene framing alters the understanding of nature-human interactions and how this affects accounting thought. Originality/value: This is the first paper in accounting to seek to establish connections between accounting, accountability and the Anthropocene.Publisher PDFPeer reviewe