Cosmological implications of the PSCz PDF and its moments

We compare the probability density function (PDF) and its low-order moments (variance and skewness) of the smoothed IRAS Point Source Catalogue Redshift Survey (PSC z ) galaxy density field and of the corresponding simulated PSC z look-alikes, generated from N -body simulations of six different dark matter models: four structure-normalized with     and     , one COBE -normalized, and the old standard cold dark matter model. The galaxy distributions are smoothed with a Gaussian window at three different smoothing scales,     , 10 and 15  h ⁻¹ Mpc. We find that the simulation PSC z look-alike PDFs are sensitive only to the normalization of the power spectrum, probably owing to the shape similarity of the simulated galaxy power spectrum on the relevant scales. We find that the only models that are consistent, at a high significance level, with the observed PSC z PDF are models with a relatively low power spectrum normalization     . From the phenomenologically derived σ ₈–moments relation, fitted from the simulation data, we find that the PSC z moments suggest     .     

Constraints on cosmological and biasing models using active galactic nucleus clustering

We attempt to put constraints on different cosmological and biasing models by combining the recent clustering results of X-ray sources in the local ( z ≤0.1) and distant Universe ( z ∼1) . To this end we compare the measured angular correlation function for bright (Akylas et al.) and faint (Vikhlinin & Forman) ROSAT X-ray sources respectively with those expected in three spatially flat cosmological models. Taking into account the different functional forms of the bias evolution, we find that there are two cosmological models which match the data well. In particular, low-Ω_○ cosmological models (Ω_Λ=1−Ω_○=0.7) that contain either (i) high σ ₈^mass=1.13 value with galaxy merging bias, b ( z )∝(1+ z )^1.8 or (ii) low σ ₈^mass=0.9 with non-bias, b ( z ) ≡ 1 best reproduce the AGN clustering results, while τ CDM models with different bias behaviour are ruled out at a high significance level.     

The Aspen–Amsterdam void finder comparison project

Despite a history that dates back at least a quarter of a century, studies of voids in the large-scale structure of the Universe are bedevilled by a major problem: there exist a large number of quite different void-finding algorithms, a fact that has so far got in the way of groups comparing their results without worrying about whether such a comparison in fact makes sense. Because of the recent increased interest in voids, both in very large galaxy surveys and in detailed simulations of cosmic structure formation, this situation is very unfortunate. We here present the first systematic comparison study of 13 different void finders constructed using particles, haloes, and semi-analytical model galaxies extracted from a subvolume of the Millennium simulation. This study includes many groups that have studied voids over the past decade. We show their results and discuss their differences and agreements. As it turns out, the basic results of the various methods agree very well with each other in that they all locate a major void near the centre of our volume. Voids have very underdense centres, reaching below 10 per cent of the mean cosmic density. In addition, those void finders that allow for void galaxies show that those galaxies follow similar trends. For example, the overdensity of void galaxies brighter than   m _B =−20  is found to be smaller than about −0.8 by all our void finding algorithms.     

ISORROPIA: A New Thermodynamic Equilibrium Model for Multiphase Multicomponent Inorganic Aerosols

A computationally efficient and rigorous thermodynamic model that predicts the physical state and composition of inorganic atmospheric aerosol is presented. One of the main features of the model is the implementation of mutual deliquescence of multicomponent salt particles, which lowers the deliquescence point of the aerosol phase.The model is used to examine the behavior of four types of tropospheric aerosol (marine, urban, remote continental and non-urban continental), and the results are compared with the predictions of two other models currently in use. The results of all three models were generally in good agreement. Differences were found primarily in the mutual deliquescence humidity regions, where the new model predicted the existence of water, and the other two did not. Differences in the behavior (speciation and water absorbing properties) between the aerosol types are pointed out. The new model also needed considerably less CPU time, and always shows stability and robust convergence.     

Hydro‐climatic impacts on the ice cover of the lower Peace River

Since the late 1960s, a paucity of ice‐jam flooding in the lower Peace River has resulted in prolonged dry periods and considerable reduction in the area covered by lakes and ponds that provide habitat for aquatic life in the Peace–Athabasca Delta (PAD) region. Though major ice jams occur at breakup, antecedent conditions play a significant role in their frequency and severity. These conditions are partly defined by the mode of freezeup and the maximum thickness that is attained during the winter, shortly before the onset of spring and development of positive net heat fluxes to the ice cover. Data from hydrometric gauge records and from field surveys are utilized herein to study these conditions. It is shown that freezeup flows are considerably larger at the present time than before regulation, and may be responsible for more frequent formation of porous accumulation covers. Despite a concomitant rise in winter temperatures, solid‐ice thickness has increased since the 1960s. Using a simple ice growth model, specifically developed for the study area, it is shown that porous accumulation covers enhance winter ice growth via accelerated freezing into the porous accumulation. Coupled with a reduction in winter snowfall, this effect can not only negate, but reverse, the effect of warmer winters on ice thickness, thus explaining present conditions. The present model is also shown to be a useful prediction tool, especially for extrapolating incomplete data to the end of the winter. Copyright © 2007 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.     

The COVID-19 pandemic and global environmental change: Emerging research needs

The outbreak of COVID-19 raised numerous questions on the interactions between the occurrence of new infections, the environment, climate and health. The European Union requested the H2020 HERA project which aims at setting priorities in research on environment, climate and health, to identify relevant research needs regarding Covid-19. The emergence and spread of SARS-CoV-2 appears to be related to urbanization, habitat destruction, live animal trade, intensive livestock farming and global travel. The contribution of climate and air pollution requires additional studies. Importantly, the severity of COVID-19 depends on the interactions between the viral infection, ageing and chronic diseases such as metabolic, respiratory and cardiovascular diseases and obesity which are themselves influenced by environmental stressors. The mechanisms of these interactions deserve additional scrutiny. Both the pandemic and the social response to the disease have elicited an array of behavioural and societal changes that may remain long after the pandemic and that may have long term health effects including on mental health. Recovery plans are currently being discussed or implemented and the environmental and health impacts of those plans are not clearly foreseen. Clearly, COVID-19 will have a long-lasting impact on the environmental health field and will open new research perspectives and policy needs.     

Catchment-wide estimate of single storm interrill soil erosion using an aggregate instability index: a model based on geographic information systems

The main objective of this paper is to estimate interrill erosion after rainfall in the basin of Mourganis river (442?km²; Kalabaka province, Trikala prefecture, Thessaly, Greece). For the estimation of the interrill erosion, the method of Valmis et al. (1988) was used, in combination with Nearing et al. (1989). Input data of the algorithm include the slope angle of the ground surface, the rainfall, the ground cover type, the height of canopy, and the instability of ground of the study area. The spatial data were processed by standard GIS software. Soil samples were collected in the field to calibrate the model. The results comprise soil erosion maps for two specific rainfall scenarios. The first rainfall scenario refers to the most extreme rainfall in this catchment that happened on the 7/21/1959 with 48?mm/h. The second scenario is closer to average as the intensity rainfall is 3.54?mm/h. The total mass of eroded material ranges from 0.048?t/ha (assuming mean rainfall intensity) up to 3.5?t/ha (for the extreme scenario). We note that the western part of the Mourgani basin exhibits higher erosion than the eastern part.     

Finite element analysis of buried steel pipelines under strike-slip fault displacements

The present paper investigates the mechanical behavior of buried steel pipelines, crossing an active strike-slip tectonic fault. The fault is normal to the pipeline direction and moves in the horizontal direction, causing stress and deformation in the pipeline. The interacting soil–pipeline system is modelled rigorously through finite elements, which account for large strains and displacements, nonlinear material behavior and special conditions of contact and friction on the soil–pipe interface. Considering steel pipelines of various diameter-to-thickness ratios, and typical steel material for pipeline applications (API 5L grades X65 and X80), the paper focuses on the effects of various soil and pipeline parameters on the structural response of the pipe, with particular emphasis on identifying pipeline failure (pipe wall wrinkling/local buckling or rupture). The effects of shear soil strength, soil stiffness, horizontal fault displacement, width of the fault slip zone are investigated. Furthermore, the influence of internal pressure on the structural response is examined. The results from the present investigation are aimed at determining the fault displacement at which the pipeline fails and can be used for pipeline design purposes. The results are presented in diagram form, which depicts the critical fault displacement, and the corresponding critical strain versus the pipe diameter-to-thickness ratio. A simplified analytical model is also developed to illustrate the counteracting effects of bending and axial stretching. The numerical results for the critical strain are also compared with the recent provisions of EN 1998-4 and ASCE MOP 119.     

Nonlinear FE analysis of precast RC pinned beam-to-column connections under monotonic and cyclic shear loading

In precast technology, mostly (but not exclusively), frame structures with pinned beam-to-column connections are preferred, especially in low-rise buildings due to the flexibility, lower cost and more favourable behaviour they provide, especially in the case of large spans and pretensioned interconnected members. However the available literature on the behaviour of pinned connections, especially under seismic loading, can be characterized as poor, even though their use in Europe and elsewhere is rather extended. In the terms of the present research a nonlinear 3D numerical model was developed and calibrated against available experimental data to be used as an effective tool for the analytical prediction of the behaviour of pinned connections, under monotonic and cyclic shear loading. The experimental data were derived from the European FP7 project SAFECAST, Grant Agreement Number 218417. The tests were performed at the Laboratory for Earthquake Engineering of the National Technical University of Athens, Greece. From the numerical results useful information was obtained on component level about: (a) the type of the observed failure mechanism; (b) the amount of dissipated energy; (c) the location of the developed plastic hinges along the steel dowel, and (d) the evolution of stresses and strains along the dowel(s) and in the mass of the surrounding grout. However the numerical model can be further utilized to investigate and quantify the effect of several parameters (that were not experimentally investigated in depth, or were not investigated at all) on the response of pinned connections.