The anisotropy of granular materials

The effect of the anisotropy on the elastoplastic response of two dimensional packed samples of polygons is investigated here, using molecular dynamics simulation. We show a correlation between fabric coefficients, characterizing the anisotropy of the granular skeleton, and the anisotropy of the elastic response. We also study the anisotropy induced by shearing on the subnetwork of the sliding contacts. This anisotropy provides an explanation to some features of the plastic deformation of granular media.Comment: Submitted to PR

Civil aviation, air pollution and human health

Air pollutant emissions from aircraft have been subjected to less rigorous control than road traffic emissions, and the rapid growth of global aviation is a matter of concern in relation to human exposures to pollutants, and consequent effects upon health. Yim et al (2015 Environ. Res. Lett. 3 034001) estimate exposures globally arising from aircraft engine emissions of primary particulate matter, and from secondary sulphates and ozone, and use concentration-response functions to calculate the impact upon mortality, which is monetised using the value of statistical life. This study makes a valuable contribution to estimating the magnitude of public health impact at various scales, ranging from local, near airport, regional and global. The results highlight the need to implement future mitigation actions to limit impacts of aviation upon air quality and public health. The approach adopted in Yim et al only accounts for the air pollutants emitted by aircraft engine exhausts. Whilst aircraft emissions are often considered as dominant near runways, there are a number of other sources and processes related to aviation that still need to be accounted for. This includes impacts of nitrate aerosol formed from NOx emissions, but probably more important, are the other airport-related emissions from ground service equipment and road traffic. By inclusion of these, and consideration of non-fatal impacts, future research will generate comprehensive estimates of impact related to aviation and airports

Slippery sliding on icy Iapetus

Enigmatically, some landslides flow farther than normal frictional resistance allows. Cassini images of Saturn’s icy moon Iapetus reveal a multitude of long-runout landslides that may have been enabled by flash heating along the sliding surface

Meteorological drivers and mortality associated with O3 and PM2.5 air pollution episodes in the UK in 2006

In this study we examine the meteorological drivers resulting in concurrent high levels of ozone (O3) and particulate matter smaller than 2.5 andmu;m in diameter (PM2.5) during two five-day air pollution episodes in 2006 (1st - 5th July and 18th andndash; 22nd July) using an air quality model (AQUM) at 12 km horizontal resolution to simulate air pollutant concentrations. The resultant UK health burden associated with short-term exposure to simulated maximum daily 8-h O3andnbsp;(MDA8 O3) and daily mean PM2.5andnbsp;is estimated at the national and regional level. Both episodes were found to be driven by anticyclonic conditions with light easterly and south easterly winds and high temperatures that aided pollution build up in the UK. The estimated total mortality burden associated with short-term exposure to MDA8 O3andnbsp;is similar during the chosen episodes with about 70 daily deaths brought forward (summed across the UK) during the first and second episode, respectively. The estimated health burden associated with short-term exposure to daily mean PM2.5andnbsp;concentrations differs between the first and second episode resulting in about 43 and 36 daily deaths brought forward, respectively. The corresponding percentage of all-cause mortality due to short-term exposure to MDA8 O3andnbsp;and daily mean PM2.5during these two episodes and across the UK regions, ranges from 3.4% to 5.2% and from 1.6% to 3.9%, respectively. The attributable percentage of all-cause mortality differs between the regions depending on the pollution levels in each episode, but the overall estimated health burdens are highest in regions with higher population totals. We estimate that during these episodes the short-term exposure to MDA8 O3and daily mean PM2.5andnbsp;is between 36-38% and 39andndash;56% higher, respectively, than if the pollution levels represented typical seasonal-mean concentrations. This highlights the potential of air pollution episodes to have substantial short-term impacts on public health.</p

Future air pollution related health burdens associated with RCP emission changes in the UK

Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathways (RCPs) are used to simulate future ozone (O3), nitrogen dioxide (NO2), and fine particulate matter (PM2.5) in the United Kingdom (UK) for the 2050s relative to the 2000s with an air quality model (AQUM) at a 12 km horizontal resolution. The present-day and future attributable fractions (AF) of mortality associated with long-term exposure to annual mean O3, NO2 and PM2.5 have accordingly been estimated for the first time for regions across England, Scotland and Wales. Across the three RCPs (RCP2.6, RCP6.0 and RCP8.5), simulated annual mean of the daily maximum 8-hr mean (MDA8) O3 concentrations increase compared to present-day, likely due to decreases in NOx (nitrogen oxides) emissions, leading to less titration of O3 by NO. Annual mean NO2 and PM2.5 concentrations decrease under all RCPs for the 2050s, mostly driven by decreases in NOx and sulphur dioxide (SO2) emissions, respectively. The AF of mortality associated with long-term exposure to annual mean MDA8 O3 is estimated to increase in the future across all the regions and for all RCPs. Reductions in NO2 and PM2.5 concentrations lead to reductions in the AF estimated for future periods under all RCPs, for both pollutants. Total mortality burdens are also highly sensitive to future population projections. Accounting for population projections exacerbates differences in total UK-wide MDA8 O3-health burdens between present-day and future by up to a factor of ~3 but diminishes differences in NO2-health burdens. For PM2.5, accounting for future population projections results in additional UK-wide deaths brought forward compared to present-day under RCP2.6 and RCP6.0, even though the simulated PM2.5 concentrations for the 2050s are estimated to decrease. Thus, these results highlight the sensitivity of future health burdens in the UK to future trends in atmospheric emissions over the UK as well as future population projections

Characterization of the material response in the granular ratcheting

The existence of a very special ratcheting regime has recently been reported in a granular packing subjected to cyclic loading \cite{alonso04}. In this state, the system accumulates a small permanent deformation after each cycle. After a short transient regime, the value of this permanent strain accumulation becomes independent on the number of cycles. We show that a characterization of the material response in this peculiar state is possible in terms of three simple macroscopic variables. They are defined that, they can be easily measured both in the experiments and in the simulations. We have carried out a thorough investigation of the micro- and macro-mechanical factors affecting these variables, by means of Molecular Dynamics simulations of a polydisperse disk packing, as a simple model system for granular material. Biaxial test boundary conditions with a periodically cycling load were implemented. The effect on the plastic response of the confining pressure, the deviatoric stress and the number of cycles has been investigated. The stiffness of the contacts and friction has been shown to play an important role in the overall response of the system. Specially elucidating is the influence of the particular hysteretical behavior in the stress-strain space on the accumulation of permanent strain and the energy dissipation.Comment: 13 pages, 20 figures. Submitted to PR

Phase coexistence in consolidating porous media

The appearence of the fluid-rich phase in saturated porous media under the effect of an external pressure is investigated. For this purpose we introduce a two field second gradient model allowing the complete description of the phenomenon. We study the coexistence profile between poor and rich fluid phases and we show that for a suitable choice of the parameters non-monotonic interfaces show-up at coexistence

Stress dependent thermal pressurization of a fluid-saturated rock

Temperature increase in saturated porous materials under undrained conditions leads to thermal pressurization of the pore fluid due to the discrepancy between the thermal expansion coefficients of the pore fluid and of the solid matrix. This increase in the pore fluid pressure induces a reduction of the effective mean stress and can lead to shear failure or hydraulic fracturing. The equations governing the phenomenon of thermal pressurization are presented and this phenomenon is studied experimentally for a saturated granular rock in an undrained heating test under constant isotropic stress. Careful analysis of the effect of mechanical and thermal deformation of the drainage and pressure measurement system is performed and a correction of the measured pore pressure is introduced. The test results are modelled using a non-linear thermo-poro-elastic constitutive model of the granular rock with emphasis on the stress-dependent character of the rock compressibility. The effects of stress and temperature on thermal pressurization observed in the tests are correctly reproduced by the model

Solastalgia mediates between bushfire impact and mental health outcomes: A study of Australia\u27s 2019–2020 bushfire season

In 2019–2020, Australia experienced an unprecedented bushfire season that caused widespread environmental destruction across the continent, and especially to its south-east corner. Over two studies, we examine mental health outcomes of individuals impacted by bushfire, drawing on the concept of solastalgia – the sense of distress arising from unwanted environmental change – as a potential explanation for the mental health consequences of bushfire. In Study 1, we surveyed 2084 residents from the Australian Capital Territory and surrounding regions directly after the bushfire season. Participants were asked about exposure to the 2019–2020 bushfires, and to a previous regional fire of significance, experience of solastalgia, and five mental health indicators. In Study 2, we broaden our focus to all of Australia, and administer our measures with a nationally representative sample six months after the conclusion of the bushfire season (N = 1477). In both studies, we find the severity of reported bushfire impact is significantly associated with mental health, such that greater impact predicts poorer outcomes. Moreover, we find the experience of solastalgia mediates the relationship between bushfire impact and mental health and wellbeing. Experiencing solastalgia is a partial, but important, mechanism for understanding the impact of bushfire exposure on mental health and wellbeing. Importantly, people not directly impacted by a bushfire event also experience solastalgia and subsequent poorer mental health outcomes following bushfires. We suggest that future measurements of the impact of abrupt environmental change events, including bushfires, consider the role of solastalgia and localised environmental contexts in shaping the mental health impacts to the population