195 research outputs found
Local Volume Effects in the Generalized Pseudopotential Theory
The generalized pseudopotential theory (GPT) is a powerful method for
deriving real-space transferable interatomic potentials. Using a coarse-grained
electronic structure, one can explicitly calculate the pair ion-ion and
multi-ion interactions in simple and transition metals. Whilst successful in
determining bulk properties, in central force metals the GPT fails to describe
crystal defects for which there is a significant local volume change. A
previous paper [PhysRevLett.66.3036 (1991)] found that by allowing the GPT
total energy to depend upon some spatially-averaged local electron density, the
energetics of vacancies and surfaces could be calculated within experimental
ranges. In this paper, we develop the formalism further by explicitly
calculating the forces and stress tensor associated with this total energy. We
call this scheme the adaptive GPT (aGPT) and it is capable of both molecular
dynamics and molecular statics. We apply the aGPT to vacancy formation and
divacancy binding in hcp Mg and also calculate the local electron density
corrections to the bulk elastic constants and phonon dispersion for which there
is refinement over the baseline GPT treatment.Comment: 11 pages, 6 figure
Wildlife Vaccination Strategies for Eliminating Bovine Tuberculosis in White-tailed Deer Populations
Migrations in our common home: Responding with care - Ireland's response to the Ukrainian crisis
Policy Brief produced by the Roundtable on Migrations in Our Common HomeIreland’s response to the Ukrainian migrants has been almost exemplary and this “human rights first” approach should be the blueprint for a reshaping of Ireland’s International Protection system. Beyond the immediate challenges faced by Ukrainian people forcibly displaced, the wider geopolitical impacts of the crisis – the dependency on Russian fossil fuel production and resultant risks, together with risks to food security – will be felt globally into the future, and disproportionately impact those who can least absorb them. Ireland needs to focus on the care, human rights and wellbeing of all. The legitimate expectations of people living in Ireland are not being met. This is most obvious in areas such as housing and homelessness, a two-tier healthcare system, the deepening rural-urban divide, and high levels of poverty and social exclusion, especially among children. These are all areas that must be grappled with in addition to our response to the Ukrainian crisis. This policy briefing takes a look at the key issues and makes a series of policy recommendations aimed at addressing immediate and future challenges
Cross-National Differences in Victimization : Disentangling the Impact of Composition and Context
Varying rates of criminal victimization across countries are assumed to be the outcome of countrylevel structural constraints that determine the supply ofmotivated o¡enders, as well as the differential composition within countries of suitable targets and capable guardianship. However, previous empirical tests of these ‘compositional’ and ‘contextual’ explanations of cross-national di¡erences
have been performed upon macro-level crime data due to the unavailability of comparable individual-level data across countries. This limitation has had two important consequences for cross-national crime research. First, micro-/meso-level mechanisms underlying cross-national differences cannot be truly inferred from macro-level data. Secondly, the e¡ects of contextual measures (e.g. income inequality) on crime are uncontrolled for compositional heterogeneity. In this
paper, these limitations are overcome by analysing individual-level victimization data across 18 countries from the International CrimeVictims Survey. Results from multi-level analyses on theft and violent victimization indicate that the national level of income inequality is positively related to risk, independent of compositional (i.e. micro- and meso-level) di¡erences. Furthermore, crossnational variation in victimization rates is not only shaped by di¡erences in national context, but
also by varying composition. More speci¢cally, countries had higher crime rates the more they consisted of urban residents and regions with lowaverage social cohesion.
Migrations in our common home: Planning for change - Climate change and migration
Policy briefing on Ireland's response to climate migration in the context of COP27Migration linked to climate change did not get the attention it deserves at COP27. The Global North must accept responsibility for its role in driving climate change and abide by their commitments made to schemes which address worsening conditions for those in the Global South – according to the Roundtable on Migration in Our Common Home. COP27 marks thirty years since the adoption of the United Nations Framework Convention on Climate Change. As the world grapples with the devastating consequences of intensifying climate change, this policy brief examines how climate change is impacting migration, displacement and food security. As COP27 draws to a close, this policy brief looks at the pledges made by Ireland, as well as Ireland’s obligations to Official Development Assistance (ODA) and Climate Finance and the compelling argument in favour of Loss and Damage funding made by the Global south for over three decades. As COP27 draws to a close, the Roundtable expresses its disappointment at the lack of ambition evident in Ireland’s response and the repackaging of previously announced, and inadequate, policies
AMI radio continuum observations of young stellar objects with known outflows
We present 16 GHz (1.9 cm) deep radio continuum observations made with the Arcminute Microkelvin Imager (AMI) of a sample of low-mass young stars driving jets. We combine these new data with archival information from an extensive literature search to examine spectral energy distributions (SEDs) for each source and calculate both the radio and sub-mm spectral indices in two different scenarios: (1) fixing the dust temperature (Td) according to evolutionary class; and (2) allowing Td to vary. We use the results of this analysis to place constraints on the physical mechanisms responsible for the radio emission. From AMI data alone, as well as from model fitting to the full SED in both scenarios, we find that 80 per cent of the objects in this sample have spectral indices consistent with freefree emission. We find an average spectral index in both Td scenarios, consistent with freefree emission. We examine correlations of the radio luminosity with bolometric luminosity, envelope mass and outflow force, and find that these data are consistent with the strong correlation with envelope mass seen in lower luminosity samples. We examine the errors associated with determining the radio luminosity and find that the dominant source of error is the uncertainty on the opacity index, beta. We examine the SEDs for variability in these young objects, and find evidence for possible radio flare events in the histories of L1551 IRS 5 and Serpens SMM 1
Acclimatization of the crustose coralline alga Porolithon onkodes to variable pCO2
Ocean acidification (OA) has important implications for the persistence of coral reef ecosystems, due to potentially negative effects on biomineralization. Many coral reefs are dynamic with respect to carbonate chemistry, and experience fluctuations in pCO2 that exceed OA projections for the near future. To understand the influence of dynamic pCO2 on an important reef calcifier, we tested the response of the crustose coralline alga Porolithon onkodes to oscillating pCO2. Individuals were exposed to ambient (400 ??atm), high (660 ??atm), or variable pCO2 (oscillating between 400/660 ??atm) treatments for 14 days. To explore the potential for coralline acclimatization, we collected individuals from low and high pCO2 variability sites (upstream and downstream respectively) on a back reef characterized by unidirectional water flow in Moorea, French Polynesia. We quantified the effects of treatment on algal calcification by measuring the change in buoyant weight, and on algal metabolism by conducting sealed incubations to measure rates of photosynthesis and respiration. Net photosynthesis was higher in the ambient treatment than the variable treatment, regardless of habitat origin, and there was no effect on respiration or gross photosynthesis. Exposure to high pCO2 decreased P. onkodes calcification by >70%, regardless of the original habitat. In the variable treatment, corallines from the high variability habitat calcified 42% more than corallines from the low variability habitat. The significance of the original habitat for the coralline calcification response to variable, high pCO2 indicates that individuals existing in dynamic pCO2 habitats may be acclimatized to OA within the scope of in situ variability. These results highlight the importance of accounting for natural pCO2 variability in OA manipulations, and provide insight into the potential for plasticity in habitat and species-specific responses to changing ocean chemistry.Funding was provided by grants from the National Science Foundation (OCE-0417412, OCE-10-26852, OCE-1041270) and gifts from the Gordon and Betty Moore Foundation. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript
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