Uniform Atomic Layer Deposition of Al2O3 on Graphene by Reversible Hydrogen Plasma Functionalization.

A novel method to form ultrathin, uniform Al2O3 layers on graphene using reversible hydrogen plasma functionalization followed by atomic layer deposition (ALD) is presented. ALD on pristine graphene is known to be a challenge due to the absence of dangling bonds, leading to nonuniform film coverage. We show that hydrogen plasma functionalization of graphene leads to uniform ALD of closed Al2O3 films down to 8 nm in thickness. Hall measurements and Raman spectroscopy reveal that the hydrogen plasma functionalization is reversible upon Al2O3 ALD and subsequent annealing at 400 °C and in this way does not deteriorate the graphene's charge carrier mobility. This is in contrast with oxygen plasma functionalization, which can lead to a uniform 5 nm thick closed film, but which is not reversible and leads to a reduction of the charge carrier mobility. Density functional theory (DFT) calculations attribute the uniform growth on both H2 and O2 plasma functionalized graphene to the enhanced adsorption of trimethylaluminum (TMA) on these surfaces. A DFT analysis of the possible reaction pathways for TMA precursor adsorption on hydrogenated graphene predicts a binding mechanism that cleans off the hydrogen functionalities from the surface, which explains the observed reversibility of the hydrogen plasma functionalization upon Al2O3 ALD

Association between stringency of lockdown measures and emergency department visits during the COVID-19 pandemic:A Dutch multicentre study

Introduction The COVID-19 outbreak disrupted regular health care, including the Emergency Department (ED), and resulted in insufficient ICU capacity. Lockdown measures were taken to prevent disease spread and hospital overcrowding. Little is known about the relationship of stringency of lockdown measures on ED utilization. Objective This study aimed to compare the frequency and characteristics of ED visits during the COVID-19 outbreak in 2020 to 2019, and their relation to stringency of lockdown measures. Material and methods A retrospective multicentre study among five Dutch hospitals was performed. The primary outcome was the absolute number of ED visits (year 2018 and 2019 compared to 2020). Secondary outcomes were age, sex, triage category, way of transportation, referral, disposition, and treating medical specialty. The relation between stringency of lockdown measures, measured with the Oxford Stringency Index (OSI) and number and characteristics of ED visits was analysed. Results The total number of ED visits in the five hospitals in 2019 was 165,894, whereas the total number of visits in 2020 was 135,762, which was a decrease of 18.2% (range per hospital: 10.5%-30.7%). The reduction in ED visits was greater during periods of high stringency lockdown measures, as indicated by OSI. Conclusion The number of ED visits in the Netherlands has significantly dropped during the first year of the COVID-19 pandemic, with a clear association between decreasing ED visits and increasing lockdown measures. The OSI could be used as an indicator in the management of ED visits during a future pandemic.</p

Association between stringency of lockdown measures and emergency department visits during the COVID-19 pandemic:A Dutch multicentre study

Introduction The COVID-19 outbreak disrupted regular health care, including the Emergency Department (ED), and resulted in insufficient ICU capacity. Lockdown measures were taken to prevent disease spread and hospital overcrowding. Little is known about the relationship of stringency of lockdown measures on ED utilization. Objective This study aimed to compare the frequency and characteristics of ED visits during the COVID-19 outbreak in 2020 to 2019, and their relation to stringency of lockdown measures. Material and methods A retrospective multicentre study among five Dutch hospitals was performed. The primary outcome was the absolute number of ED visits (year 2018 and 2019 compared to 2020). Secondary outcomes were age, sex, triage category, way of transportation, referral, disposition, and treating medical specialty. The relation between stringency of lockdown measures, measured with the Oxford Stringency Index (OSI) and number and characteristics of ED visits was analysed. Results The total number of ED visits in the five hospitals in 2019 was 165,894, whereas the total number of visits in 2020 was 135,762, which was a decrease of 18.2% (range per hospital: 10.5%-30.7%). The reduction in ED visits was greater during periods of high stringency lockdown measures, as indicated by OSI. Conclusion The number of ED visits in the Netherlands has significantly dropped during the first year of the COVID-19 pandemic, with a clear association between decreasing ED visits and increasing lockdown measures. The OSI could be used as an indicator in the management of ED visits during a future pandemic.</p

Numerical modeling of the tension stiffening in reinforced concrete members via discontinuum models

[prova tipográfica]This study presents a numerical investigation on the fracture mechanism of tension stiffening phenomenon in reinforced concrete members. A novel approach using the discrete element method (DEM) is proposed, where three-dimensional randomly generated distinct polyhedral blocks are used, representing concrete and one-dimensional truss elements are utilized, representing steel reinforcements. Thus, an explicit representation of reinforced concrete members is achieved, and the mechanical behavior of the system is solved by integrating the equations of motion for each block using the central difference algorithm. The inter-block interactions are taken into consideration at each contact point with springs and cohesive frictional elements. Once the applied modeling strategy is validated, based on previously published experimental findings, a sensitivity analysis is performed for bond stiffness, cohesion strength, and the number of truss elements. Hence, valuable inferences are made regarding discontinuum analysis of reinforced concrete members, including concrete-steel interaction and their macro behavior. The results demonstrate that the proposed phenomenological modeling strategy successfully captures the concrete-steel interaction and provides an accurate estimation of the macro behavior

FERTILISATION STRATEGIES ACROSS EUROPE: CURRENT SITUATION, POTENTIAL AND LIMITS FOR A HARMONISED APPROACH

Peer reviewe

A numerical analysis of pull-out anchor bolts

Anchor bolts are often used in concrete or steel structures. Nevertheless still empirical design procedures are used in order to determine the dimensions of the structure. Non linear fracture mechanics tries to describe fracture of heterogeneous materials like concrete. In the classical representation of concrete fracturing (figure 1.1), cohesive forces in the micro-crack-zone (ahead of the cracktip) contribute to the carrying capacity of the structure and cause softening of concrete. This concretesoftening can also be explained by discontinuous cracks that grow along aggregate particles and cause bridging of the cracks (crack-face bridging, see Van Mier (1991)). Insight in non linear fracture mechanics as well as increasing computer techniques finally gave the opportunity to investigate the behaviour of anchor bolts embedded in concrete in a proper way. The main goal of this study is to improve the knowledge about pull-out anchor bolts. Therefore several tests and numerical simulations have been performed in order to determine the maximum load, the deflection of the upper end of the anchor bolt and the load-deformation curve. In this report results of the numerical simulations of pull-out anchor bolts in a plane stress situation are presented.concrete structursDesign and ConstructionCivil Engineering and Geoscience

Ultimate limit state analysis of a segmented tunnel lining

Because of low hindrances during construction and lack of space in populated areas, shield driven tunnels are becoming more and more popular. Since 1997 these segmented tunnel linings are also constructed in the Netherlands but are difficult to accomplish in soft soils. Because of unexpected damages in the early constructed tunnels a full scale test set up has been build at the Delft University of Technology to obtain knowledge on the lining behaviour. The conducted tests were performed in the SLS in which it became clear that the joints in between the segments play an important role in the global lining behaviour. In order to asses the safety level of a concrete lining, and the ultimate load capacity, failure tests have been performed in the ULS. Generally a lining might fail due to concrete failure or by an ongoing rotation of the segment joints. With the aid of the collected test data a detailed description of the failure mechanisms is obtained. The influence of the segment joints and ring joints on the global lining behaviour is analysed especially at extreme loading conditions. Based on the measured segment joint rotations and lining deformations, interaction forces between adjoining rings are analysed. With the obtained knowledge on lining behaviour a FE model is developed in Diana for predicting internal forces and external deformations for loadings in the ULS. With the aid of this model different loading combinations can be analysed and eventually the influence of soil can be incorporated. Because the load capacity of the lining and its failure mechanisms is known, a probabilistic safety analysis may be performed for assessing the safety level of tunnel linings

Failure behavior of segmented tunnel linings: numerical modeling validated by full scale tests

In order to gain a better understanding of the complex structural lining behavior of bored tunnels in the specific Dutch soils, a test set-up has been developed in the Stevin Laboratory at Delft University of Technology. In this facility a full-scale model, consisting of three segmented rings of a tunnel lining, has been subjected to construction and serviceability loading conditions. The first test series five years ago have shown that higher stresses occur in the construction phase than under serviceability conditions. In view of recent test series the set-up has been adapted for performing tests at the ultimate limit state. Various tests have been performed in which the test specimen was loaded until failure of the rings. In the tests the axial prestressing force was varied and the interaction between the neighboring rings was studied. Simultaneously, simulations with the finite element program DIANA were conducted for studying the lining behavior in more detail. The test results have been used for validating the numerical model at the ultimate limit stat