Analysis of the Shaft Resistance of Nondisplacement Piles in Sand

The paper examines, using numerical modelling, the problem of the limit shaft resistance of non-displacement piles installed in sands. The modelling makes use of an advanced, two-surface-plasticity constitutive model. The constitutive model predicts the soil response in both the small- and the large-strain range, while taking into account the effects of the intermediate principal effective stress and of the inherent anisotropy of the sand. Finite element analyses of shearing along the pile shaft are performed in order to examine the development of limit unit shaft resistance and the changes in stress state around the shaft upon axial loading of the pile. Special focus is placed on the operative value of the lateral earth pressure coefficient when limit shaft resistance is reached. The analyses offer useful insights regarding the factors controlling the value of unit shaft resistance in sands. The simulations predict a significant build-up of horizontal effective stress for dense sands. Based on these simulations, we propose a relationship between the lateral earth pressure coefficient for use in the calculation of the limit shaft resistance of the pile and the initial density and stress state of the sand

Effect of Relative Density and Stress Level on the Bearing Capacity of Footings on Sand

The design of shallow foundations relies on bearing capacity values calculated using empirical procedures that are based in part on solutions obtained using the method of characteristics, which assumes a soil that is perfectly plastic following an associated flow rule. In this paper the problem of strip and circular footings resting on the surface of a sand layer is analysed using the finite-element method. Analyses are performed using a two-surface plasticity constitutive model that realistically captures the aspects of the mechanical response of sands that are relevant to the bearing capacity problem. In particular, the model accounts for non-associated flow, strain-softening, and both stress-induced and inherent anisotropy. Based on the results of the analyses, the paper examines the validity of the bearing capacity factors N γ and shape factors s γ used in practice. A relationship for determining appropriate values of friction angle for use in bearing capacity calculations is also proposed

Is diet partly responsible for differences in COVID-19 death rates between and within countries?

Correction: Volume: 10 Issue: 1 Article Number: 44 DOI: 10.1186/s13601-020-00351-w Published: OCT 26 2020Reported COVID-19 deaths in Germany are relatively low as compared to many European countries. Among the several explanations proposed, an early and large testing of the population was put forward. Most current debates on COVID-19 focus on the differences among countries, but little attention has been given to regional differences and diet. The low-death rate European countries (e.g. Austria, Baltic States, Czech Republic, Finland, Norway, Poland, Slovakia) have used different quarantine and/or confinement times and methods and none have performed as many early tests as Germany. Among other factors that may be significant are the dietary habits. It seems that some foods largely used in these countries may reduce angiotensin-converting enzyme activity or are anti-oxidants. Among the many possible areas of research, it might be important to understand diet and angiotensin-converting enzyme-2 (ACE2) levels in populations with different COVID-19 death rates since dietary interventions may be of great benefit.Peer reviewe

Cabbage and fermented vegetables : From death rate heterogeneity in countries to candidates for mitigation strategies of severe COVID-19

Large differences in COVID-19 death rates exist between countries and between regions of the same country. Some very low death rate countries such as Eastern Asia, Central Europe, or the Balkans have a common feature of eating large quantities of fermented foods. Although biases exist when examining ecological studies, fermented vegetables or cabbage have been associated with low death rates in European countries. SARS-CoV-2 binds to its receptor, the angiotensin-converting enzyme 2 (ACE2). As a result of SARS-CoV-2 binding, ACE2 downregulation enhances the angiotensin II receptor type 1 (AT(1)R) axis associated with oxidative stress. This leads to insulin resistance as well as lung and endothelial damage, two severe outcomes of COVID-19. The nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is the most potent antioxidant in humans and can block in particular the AT(1)R axis. Cabbage contains precursors of sulforaphane, the most active natural activator of Nrf2. Fermented vegetables contain many lactobacilli, which are also potent Nrf2 activators. Three examples are: kimchi in Korea, westernized foods, and the slum paradox. It is proposed that fermented cabbage is a proof-of-concept of dietary manipulations that may enhance Nrf2-associated antioxidant effects, helpful in mitigating COVID-19 severity.Peer reviewe

Nrf2-interacting nutrients and COVID-19 : time for research to develop adaptation strategies

There are large between- and within-country variations in COVID-19 death rates. Some very low death rate settings such as Eastern Asia, Central Europe, the Balkans and Africa have a common feature of eating large quantities of fermented foods whose intake is associated with the activation of the Nrf2 (Nuclear factor (erythroid-derived 2)-like 2) anti-oxidant transcription factor. There are many Nrf2-interacting nutrients (berberine, curcumin, epigallocatechin gallate, genistein, quercetin, resveratrol, sulforaphane) that all act similarly to reduce insulin resistance, endothelial damage, lung injury and cytokine storm. They also act on the same mechanisms (mTOR: Mammalian target of rapamycin, PPAR gamma:Peroxisome proliferator-activated receptor, NF kappa B: Nuclear factor kappa B, ERK: Extracellular signal-regulated kinases and eIF2 alpha:Elongation initiation factor 2 alpha). They may as a result be important in mitigating the severity of COVID-19, acting through the endoplasmic reticulum stress or ACE-Angiotensin-II-AT(1)R axis (AT(1)R) pathway. Many Nrf2-interacting nutrients are also interacting with TRPA1 and/or TRPV1. Interestingly, geographical areas with very low COVID-19 mortality are those with the lowest prevalence of obesity (Sub-Saharan Africa and Asia). It is tempting to propose that Nrf2-interacting foods and nutrients can re-balance insulin resistance and have a significant effect on COVID-19 severity. It is therefore possible that the intake of these foods may restore an optimal natural balance for the Nrf2 pathway and may be of interest in the mitigation of COVID-19 severity

Numerical modelling of large deformation problems in geotechnical engineering: A state-of-the-art review

Many problems in geotechnical engineering involve large movements or rotations, examples include natural processes such as landslides, and man-made processes such as earthmoving and pile penetration. While the use of numerical modelling, primarily the finite element method (FEM), is now routine in geotechnical design and analysis, the limitations of conventional FEMs soon become apparent when attempting to model large deformation problems. For this reason, the search for alternatives remains a key goal of many geotechnical researchers, both to find accurate methods but also to develop efficient ones. In this review paper, prompted by Technical Committee 103 of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE), we survey the current state-of-the-art in numerical modelling techniques aimed at large deformation problems in geotechnics. The review covers continuum and discontinuum methods and provides a clear picture of what is and is not currently possible, which will be of use to both practitioners seeking suitable methods and researchers developing existing or new methods

Analysis of fault rupture propagation through uniform soil cover

This paper presents results from numerical simulations of the propagation of an active dip-slip fault rupture through a uniform soil layer covering the rigid bedrock. Following verification of the numerical methodology against field evidence, a parametric study is performed for loose and dense sand, for normally consolidated and overconsolidated clay, as well as for different fault dip angles (normal and reverse faults) and for different thicknesses of the soil cover. The soil is modeled as an elasto-plastic, strain-softening material that obeys the Mohr-Coulomb failure criterion. The study aims at establishing criteria for the approximate depiction of the location and the width of the zone with significant ground surface distortion, where the differential ground displacements induced by the fault rupture may threaten the integrity of man-mad structures. (c) 2009 Elsevier Ltd. All rights reserved

The influence of matrix type on the proximal contact in class II resin composite restorations

Purpose: This in vitro study evaluated the efficiency of various types of matrices in reconstructing the proximal contact area in Class II resin composite restorations. Materials and Methods: Standardized MO cavities were prepared on artificial molars of a manikin model. Resin composite (Spectrum TPH-3) restorations were placed using the following matrices (n = 10): a) circumferential straight metal matrix with Tofflemire retainer-A, b) circumferential pre-contoured metal matrix system-B (Adapt SuperCap), c) circumferential pre-contoured transparent matrix system-C (Adapt SuperCap) and d) sectional precontoured metal matrix system-D (Palodent). After completion of each restoration, the manikin model was fixed on a tension-meter apparatus and an orthodontic wire was used to assess the contact tightness (CT), length of contact arc (LCA) and position of contact point relative to LCA% (PCP). The same measurements were performed on a group of intact molars (REF). The results were statistically analyzed with one-way ANOVA and the Tukey test, as well as the unpaired t-test (α = 0.05). Results: Matrix D provided the highest CT with the highest LCA, which presented a statistical difference relative to the intact tooth. Restorations with matrix B provided higher LCA than those with matrices A and C, which were found to be comparable to that of an intact tooth. The contact points (PCP) of the filled teeth were located more cervically in matrix D relative to the intact tooth (lower PCP), whereas matrices A, B and C showed more occlusal location (higher PCP). Conclusions: Differences were noted among all the matrices evaluated and none was proven sufficient to reconstruct the proximal contact characteristics of an intact tooth