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

Effect of rolling on dissipation in fault gouges

Sliding and rolling are two outstanding deformation modes in granular media. The first one induces frictional dissipation whereas the latter one involves deformation with negligible resistance. Using numerical simulations on two-dimensional shear cells, we investigate the effect of the grain rotation on the energy dissipation and the strength of granular materials under quasistatic shear deformation. Rolling and sliding are quantified in terms of the so-called Cosserat rotations. The observed spontaneous formation of vorticity cells and clusters of rotating bearings may provide an explanation for the long standing heat flow paradox of earthquake dynamics

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

A Correspondence between Two Approaches to Interprocedural Analysis in the Presence of Join

Many interprocedural static analyses perform a lossy join for reasons of termination or efficiency. We study the relationship between two predominant approaches to interprocedural analysis, the summary- based (or functional) approach and the call-strings (or k-CFA) approach, in the presence of a lossy join. Despite the use of radically different ways to distinguish procedure contexts by these two approaches, we prove that post-processing their results using a form of garbage collection ren- ders them equivalent. Our result extends the classic result by Sharir and Pnueli that showed the equivalence between these two approaches in the setting of distributive analysis, wherein the join is lossless. We also empirically compare these two approaches by applying them to a pointer analysis that performs a lossy join. Our experiments on ten Java programs of size 400K{900K bytecodes show that the summary-based approach outperforms an optimized implementation of the k-CFA approach: the k-CFA implementation does not scale beyond k=2, while the summary-based approach proves up to 46% more pointer analysis client queries than 2-CFA. The summary-based approach thus enables, via our equivalence result, to measure the precision of k-CFA with unbounded k, for the class of interprocedural analyses that perform a lossy join

Performance evaluation of a multiscale modelling system applied to particulate matter dispersion in a real traffic hot spot in Madrid (Spain)

Urban air pollution is one of the most important environmental problems nowadays. Understanding urban pollution is rather challenging due to different factors that produce a strongly heterogeneous pollutant distribution within streets. Observed concentrations depend on processes occurring at a wide range of spatial and temporal scales, complex wind flow and turbulence patterns induced by urban obstacles and irregular traffic emissions. The main objective of this paper is to model particulate matter dispersion at microscale while considering the effects of mesoscale processes. Computational Fluid Dynamic (CFD) PM10 simulations were performed taking into account high spatial resolution traffic emissions from a microscale traffic model and inlet vertical profiles of meteorological variables from Weather Research and Forecasting (WRF) model. This modelling system is evaluated by using meteorological and PM10 concentration data from intensive experimental campaigns carried out on 25th February and 6th July, 2015 in a real urban traffic hot-spot in Madrid. The effect of uncertainties in the inlet profiles from mesoscale input data on microscale results is assessed. Additionally, the importance of the sensible surface heat fluxes (SHF) provided by WRF and the selection of an appropriate turbulent Schmidt number in the dispersion equation are investigated. The main conclusion is that the modelling system accurately reproduces PM10 dispersion imposing appropriate inputs (meteorological variables and SHF) and a suitable turbulent Schmidt number. Better agreement is found for simulation with a low turbulent Schmidt number. This approach improves the standard microscale modelling alone because more realistic boundary conditions and mesoscale processes are considered

Coronavirus seasonality, respiratory infections and weather.

BACKGROUND: The survival of coronaviruses are influenced by weather conditions and seasonal coronaviruses are more common in winter months. We examine the seasonality of respiratory infections in England and Wales and the associations between weather parameters and seasonal coronavirus cases. METHODS: Respiratory virus disease data for England and Wales between 1989 and 2019 was extracted from the Second-Generation Surveillance System (SGSS) database used for routine surveillance. Seasonal coronaviruses from 2012 to 2019 were compared to daily average weather parameters for the period before the patient's specimen date with a range of lag periods. RESULTS: The seasonal distribution of 985,524 viral infections in England and Wales (1989-2019) showed coronavirus infections had a similar seasonal distribution to influenza A and bocavirus, with a winter peak between weeks 2 to 8. Ninety percent of infections occurred where the daily mean ambient temperatures were below 10 °C; where daily average global radiation exceeded 500 kJ/m2/h; where sunshine was less than 5 h per day; or where relative humidity was above 80%. Coronavirus infections were significantly more common where daily average global radiation was under 300 kJ/m2/h (OR 4.3; CI 3.9-4.6; p < 0.001); where average relative humidity was over 84% (OR 1.9; CI 3.9-4.6; p < 0.001); where average air temperature was below 10 °C (OR 6.7; CI 6.1-7.3; p < 0.001) or where sunshine was below 4 h (OR 2.4; CI 2.2-2.6; p < 0.001) when compared to the distribution of weather values for the same time period. Seasonal coronavirus infections in children under 3 years old were more frequent at the start of an annual epidemic than at the end, suggesting that the size of the susceptible child population may be important in the annual cycle. CONCLUSIONS: The dynamics of seasonal coronaviruses reflect immunological, weather, social and travel drivers of infection. Evidence from studies on different coronaviruses suggest that low temperature and low radiation/sunlight favour survival. This implies a seasonal increase in SARS-CoV-2 may occur in the UK and countries with a similar climate as a result of an increase in the R0 associated with reduced temperatures and solar radiation. Increased measures to reduce transmission will need to be introduced in winter months for COVID-19

In-street wind direction variability in the vicinity of a busy intersection in central London

We present results from fast-response wind measurements within and above a busy intersection between two street canyons (Marylebone Road and Gloucester Place) in Westminster, London taken as part of the DAPPLE (Dispersion of Air Pollution and Penetration into the Local Environment; www.dapple.org.uk) 2007 field campaign. The data reported here were collected using ultrasonic anemometers on the roof-top of a building adjacent to the intersection and at two heights on a pair of lamp-posts on opposite sides of the intersection. Site characteristics, data analysis and the variation of intersection flow with the above-roof wind direction (θref) are discussed. Evidence of both flow channelling and recirculation was identified within the canyon, only a few metres from the intersection for along-street and across-street roof-top winds respectively. Results also indicate that for oblique rooftop flows, the intersection flow is a complex combination of bifurcated channelled flows, recirculation and corner vortices. Asymmetries in local building geometry around the intersection and small changes in the background wind direction (changes in 15-min mean θref of 5–10 degrees) were also observed to have profound influences on the behaviour of intersection flow patterns. Consequently, short time-scale variability in the background flow direction can lead to highly scattered in-street mean flow angles masking the true multi-modal features of the flow and thus further complicating modelling challenges

Urban public health, a multidisciplinary approach

Urban environment is a highly complex interactive socio-physical system, with competing expectations and priorities. Public health interventions have always had a fundamental role in the control of diseases in cities. WHO considers urbanization as one of the key challenges for public health in the twenty-first century, since cities offer significant opportunities to improve public health if health-enhancing policies and actions are promoted. A multidisciplinary approach is required, but the basic differences existing between technical and health disciplines make the interaction difficult. The multidisciplinary collaboration is still at a very early stage of development, and needs to be further understood and planned. The author concludes stressing the need for a transversal training, but also for sharing knowledge, instruments and methods, involving all the actors in the planning process, to develop a real multidisciplinary approach

Advancing global health through environmental and public health tracking

Challenges such as climate change, resource depletion (with its huge implications for human health and wellbeing), and persistent social inequalities in health have been identified as global public health issues with implications for both communicable and noncommunicable diseases. This contributes to pressure on healthcare systems, as well as societal systems that affect health. A novel strategy to tackle these multiple, interacting and interdependent drivers of change is required to protect the population’s health. Public health professionals have found that building strong, enduring interdisciplinary partnerships across disciplines can address environment and health complexities, and that developing Environmental and Public Health Tracking (EPHT) systems has been an effective tool. EPHT aims to merge, integrate, analyse and interpret environmental hazards, exposure and health data. In this article, we explain that public health decision-makers can use EPHT insights to drive public health actions, reduce exposure and prevent the occurrence of disease more precisely in efficient and cost-effective ways. An international network exists for practitioners and researchers to monitor and use environmental health intelligence, and to support countries and local areas toward sustainable and healthy development. A global network of EPHT programs and professionals has the potential to advance global health by implementing and sharing experience, to magnify the impact of local efforts and to pursue data knowledge improvement strategies, aiming to recognise and support best practices. EPHT can help increase the understanding of environmental public health and global health, improve comparability of risks between different areas of the world including Low and Middle-Income Countries (LMICs), enable transparency and trust among citizens, institutions and the private sector, and inform preventive decision making consistent with sustainable and healthy development. This shows how EPHT advances global health efforts by sharing recent global EPHT activities and resources with those working in this field. Experiences from the US, Europe, Asia and Australasia are outlined for operating successful tracking systems to advance global health

Gravity-driven instabilities: interplay between state-and-velocity dependent frictional sliding and stress corrosion damage cracking

We model the progressive maturation of a heterogeneous mass towards a gravity-driven instability, characterized by the competition between frictional sliding and tension cracking, using array of slider blocks on an inclined basal surface, which interact via elastic-brittle springs. A realistic state- and rate-dependent friction law describes the block-surface interaction. The inner material damage occurs via stress corrosion. Three regimes, controlling the mass instability and its precursory behavior, are classified as a function of the ratio $T_c/T_f$ of two characteristic time scales associated with internal damage/creep and with frictional sliding. For $T_c/T_f \gg 1$, the whole mass undergoes a series of internal stick and slip events, associated with an initial slow average downward motion of the whole mass, and progressively accelerates until a global coherent runaway is observed. For $T_c/T_f \ll 1$, creep/damage occurs sufficiently fast compared with nucleation of sliding, causing bonds to break, and the bottom part of the mass undergoes a fragmentation process with the creation of a heterogeneous population of sliding blocks. For the intermediate regime $T_c/T_f \sim 1$, a macroscopic crack nucleates and propagates along the location of the largest curvature associated with the change of slope from the stable frictional state in the upper part to the unstable frictional sliding state in the lower part. The other important parameter is the Young modulus $Y$ which controls the correlation length of displacements in the system.Comment: 40 pages, 13 figure