Structural behaviour and design criteria of under-attack cable-supported foorbridges

Under-deck cable-supported footbridges are slender and effective structures comprising of cables located underneath the deck. They can be sorted into under-deck cable-stayed (UDCS), under-deck suspension (UDS) and stress-ribbon (SR) footbridges. All of them promote the axial behaviour and reduce the amount of required construction materials. In addition, to their high structural efficiency and sustainability they also possess aesthetic and construction advantages compared to conventional footbridges for covering medium spans. Nevertheless, they become more prone to vibrations that can be activated from the passage of pedestrians during service. In the present work, the dynamic response of UDCS, UDS, and SR footbridges under pedestrian loading in service was examined in detail. Due to the shortcomings of the current codes of practice to represent realistically human-induced vibrations, a stochastic pedestrian load model was implemented. This model simulates the actions induced by individuals, taking into account the inter-subject and intra-subject variability as well as the pedestrian-structure and pedestrian-pedestrian interaction. The pedestrian load model was applied to representative UDCS, UDS and SR benchmark footbridges in order to investigate their dynamic response. The effects of different sources of non-linearities were examined. As for all the benchmark footbridge configurations, when designed to fulfil only ultimate limit states, the acceleration response was found unsatisfactory, yielding to minimum comfort for their users, extensive parametric studies were carried out aiming to find critical design parameters able to improve their dynamic behaviour. Based on the investigation of the benchmark configurations and the parametric studies a set of comprehensive design criteria and recommendations for UDCS, UDS, and SR footbridges were proposed. For all those cases, decreasing the deck slenderness was found the most cost-effective way to improve the dynamic response and increase users’ comfort within appropriate design limits.Open Acces

Computational modelling of molecular nexopathies

Neurodegenerative diseases are an ever-increasing health problem, requiring substantial human and financial resources. They are caused by pathogenic proteins, which accumulate and spread in the brain's neural network, causing neuronal loss and brain atrophy. However, the mechanisms that govern pathogenic protein accumulation, spread, and toxic effects are still poorly understood, and many competing hypotheses regarding them have been presented by researchers. A better understanding of these mechanisms can help inform which hypotheses are more likely to be true, improve prognosis tools, and assist in drug development. Clinically, brain atrophy follows specific spatiotemporal patterns in each neurodegenerative disease, and each disease is linked to specific pathogenic proteins. This observation led to the `molecular nexopathies' hypothesis, which states that clinical phenotypes can be predicted if the specific pathogenic protein variant and the neural network characteristics are both known. However, little computational work has been done that links pathogenic protein mechanisms, the brain's neural network, and clinical phenotypes. In this thesis, I developed computational models for a variety of hypotheses regarding pathogenic protein mechanisms of accumulation, spread, and toxic effects on the brain, which occur at the neuronal scale, while linking them to neuroimaging data, which is acquired at the brain scale. After running simulations with the modelled mechanisms within a neural network, I compared simulation results over time against empirical data for Alzheimer's disease and three genetic variants of frontotemporal dementia. For each disease, the model that best fitted its atrophy progression was found, discovering differences among diseases with regards to what degree each mechanism played a role. I also analysed how each mechanism affected disease progression, discovered each disease's seed location, and found mechanisms that showed potential as candidate targets for therapies, in particular, increasing the firing frequency of neurons

Polarized Calabi-Yau threefolds in codimension 4

This work concerns the construction of Calabi-Yau threefolds in codimension 4. Based on a study of Hilbert series, we give a list of families of Calabi-Yau threefolds which may exist in codimension 3 and codimension 4. Using birational methods, we construct Calabi-Yau threefolds that realize several of the listed families. The main result is that the cases we consider in codimension 4 lie in two different deformation components

Polarized Calabi-Yau 3-folds in codimension 4.

We construct Calabi–Yau 3-fold orbifolds embedded in weighted projective space in codimension 4. Each Hilbert series we consider is realised by at least two deformation families of Calabi–Yau 3-folds, distinguished by their topology, echoing a similar phenomenon for Fano 3-folds in high codimension

Dynamic Dominators and Low-High Orders in DAGs

We consider practical algorithms for maintaining the dominator tree and a low-high order in directed acyclic graphs (DAGs) subject to dynamic operations. Let G be a directed graph with a distinguished start vertex s. The dominator tree D of G is a tree rooted at s, such that a vertex v is an ancestor of a vertex w if and only if all paths from s to w in G include v. The dominator tree is a central tool in program optimization and code generation, and has many applications in other diverse areas including constraint programming, circuit testing, biology, and in algorithms for graph connectivity problems. A low-high order of G is a preorder of D that certifies the correctness of D, and has further applications in connectivity and path-determination problems. We first provide a practical and carefully engineered version of a recent algorithm [ICALP 2017] for maintaining the dominator tree of a DAG through a sequence of edge deletions. The algorithm runs in O(mn) total time and O(m) space, where n is the number of vertices and m is the number of edges before any deletion. In addition, we present a new algorithm that maintains a low-high order of a DAG under edge deletions within the same bounds. Both results extend to the case of reducible graphs (a class that includes DAGs). Furthermore, we present a fully dynamic algorithm for maintaining the dominator tree of a DAG under an intermixed sequence of edge insertions and deletions. Although it does not maintain the O(mn) worst-case bound of the decremental algorithm, our experiments highlight that the fully dynamic algorithm performs very well in practice. Finally, we study the practical efficiency of all our algorithms by conducting an extensive experimental study on real-world and synthetic graphs

A displacement-based formulation for interaction problems between cracks and dislocation dipoles in couple-stress elasticity

Interaction problems of a finite-length crack with plane and antiplane dislocation dipoles in the context of couple-stress elasticity are presented in this study. The analysis is based on the distributed dislocation technique where infinitesimal dislocation dipoles are used as strain nuclei. The stress fields of these area defects are provided for the first time in the framework of couple-stress elasticity theory. In addition, a new rotational defect is introduced to satisfy the boundary conditions of the opening mode problem. This formulation leads to displacement-based hyper-singular integral equations that govern the crack problems, which are solved numerically. It is further shown that this method has several advantages over the slope formulation. Based on the obtained results, it is deduced that in all cases the cracked body behaves in a more rigid way when couple-stresses are considered. The effect of couple-stresses is highlighted in a small zone ahead of the crack-tip and around the dislocation dipole, where the stress level is significantly higher than the classical elasticity prediction. Further, the dependence of the energy release rate and the configurational force exerted on the defect on the characteristic material length and the distance between the defect and the crack-tip is discussed. In the plane problems, couple-stress theory predicts either strengthening or weakening effects while in the antiplane mode a strengthening effect is predicted

ACCURACY AND THROWING VELOCITY IN HANDBALL

INTRODUCTION: Accuracy and throwing velocity in handball are regarded as basic parameters of performance during competition. Several investigators have studied the relationship between the velocity of movement of the upper limbs and accuracy in hitting the target, which has led to interesting theories (Schmidt, 1982, Eliasz et al., 1990, Hore, 1996). The aim of the present study was the comparative analysis of accuracy, in combination with ball velocity, while performing shots in handball, using as subjects athletes of various levels and non-athletes. METHODS: In order to measure accuracy, an innovative electronic device was used which was placed on the inner side of a goal post and functioned as a ‘targetpointer’ (by means of a red light) and ‘hit-detector’. Another lab-made laser device was used for measuring ball velocity. Three groups of subjects took part in the experiments : one group of 15 handball athletes, the best of League A1 scorers (age 24.86 ± 2.91 yrs), another group of 12 handball athletes, the best of League A2 scorers (age 26.84 ± 5.67 yrs) and a random sample of 15 physical education students (21.72 ± 0.89 yrs). Accuracy and ball velocity were examined in three types of throws: (a) on the spot, (b) with a cross-over step and (c) with a vertical jump. The results were analyzed using one-way ANOVA. RESULTS: In all three types of throws examined, there was a significant difference in accuracy among groups, attributed to the higher deviation from the target observed in the student group (on the spot: Fratio= 16.422, p £ 0.001; with a crossover step: Fratio= 22.493, p £ 0.001; with an a vertical jump: Fratio= 6.825, p £ 0.003) (Table 1). Table 1 Mean values (± SD) of deviation from the target (in cm) and of ball velocity (in m/s), in the three types of throws for the three groups of subjects. on the spot with a cross-over step with a vertical jump [table] With regard to throwing velocity, a significant difference among groups was found in all types of throws examined (on the spot: Fratio= 54.585, p £ 0.001; with a crossover step: Fratio= 33.578, p £ 0.001; with an a vertical jump: Fratio= 20.795, p £ 0.001), which was attributable to the fact that all three groups differed significantly from each other. In the throw with a vertical jump the difference between the two groups of athletes was less than that observed in the other two types of throw. This was probably due to the advanced technical skill required for performing this type of throw. CONCLUSIONS: The throwing performance of the three groups of subjects was assessed both by the level of accuracy and the magnitude of ball velocity in their throws. The performance of the best scores in the League A1 group significantly exceeded that of the other groups for the variables studied in the three types of throwing examined by the present study. REFERENCES: Schmidt, R. (1982). Motor Control and Learning. A Behavioral Emphasis, 336-350. Eliasz, J., Janiak, J., Wit, A. (1990). Sport Wyczynowy 9/10, 17-23. Hore, J., Watt, S., Martin, J., Miller, B. (1995). Exp. Brain Res. 103, 277-286

Interaction problems between cracks and crystal defects in constrained Cosserat elasticity

In this work interaction problems between a finite-length crack with plane and antiplane crystal defects in the context of couple-stress elasticity are presented. Two alternative yet equivalent approaches for the formulation of crack problems are discussed based on the distributed dislocation technique. To this aim, the stress fields of climb and screw dislocation dipoles are derived within couple-stress theory and new ‘constrained’ rotational defects are introduced to satisfy the boundary conditions of the opening mode problem. Eventually, all interaction problems are described by single or systems of singular integral equations that are solved numerically using appropriate collocation techniques. The obtained results aim to highlight the deviation from classical elasticity solutions and underline the differences in interactions of cracks with single dislocations and dislocation dipoles. In general, it is concluded that the cracked body behaves in a more rigid way when couple-stresses are considered. Also, the stress level is significantly higher than the classical elasticity prediction. Moreover, the configurational forces acting on the defects are evaluated and their dependence on the characteristic material length of couple-stress theory and the distance between the defect and the crack-tip is discussed. This investigation reveals either a strengthening or a weakening effect in the opening mode problem while in the antiplane mode a strengthening effect is always obtained