Inverse modelling of an aneurysm’s stiffness using surrogate-based optimization and fluid-structure interaction simulations

Characterization of the mechanical properties of arterial tissues is highly relevant. In this work, we apply an inverse modelling approach to a model accounting for an aneurysm and the distal part of the circulation which can be modified using two independent stiffness parameters. For given values of these parameters, the position of the arterial wall as a function of time is calculated using a forward simulation which takes the fluid-structure interaction (FSI) into account. Using this forward simulation, the correct values of the stiffness parameters are obtained by minimizing a cost function, which is defined as the difference between the forward simulation and a measurement. The minimization is performed by means of surrogate-based optimization using a Kriging model combined with the expected improvement infill criterion. The results show that the stiffness parameters converge to the correct values, both for a zero-dimensional and for a three-dimensional model of the aneurysm.     

Dynamic Monte Carlo Simulations of Oscillatory Reactions

The dynamic Monte Carlo method has been used to simulate the 2 A + B₂ → 2 AB reaction catalyzed by a reconstructing substrate. Oscillatory behavior and spatio-temporal is studied as a function of grid size. Spatio-temporal pattern formation has been simulated in various forms: cellular patterns, target patterns, rotating spirals, and turbulent patterns. Cellular patterns are a manifestation of a local synchronization mechanism in which all reaction fronts periodically extinguish each other. This illustrates that dynamic Monte Carlo simulations form a promising technique and can be used to predict macroscopic kinetic phenomena on a molecular basis.     

Chaotic,fluid and unstable: an exploration of the complex housing trajectories of homeless people in Flanders,Belgium

This article analyses the housing and homeless pathways of (ex)homeless persons in the coastal city of Ostend. After a short review of the literature on the causes and meaning of the vulnerability of homeless persons, we describe how our case study with (former) homeless persons in Ostend was organised. We deal with some methodological issues and the analytic results, revealing a very complex housing trajectory. We focus on these dynamic and complex housing pathways and look at the role of relationships and relationship breakdown, work and unemployment, eviction after rent arrears and moving as an escape strategy. We also deal with the searching process for housing and the role of social networks. We end with some conclusions and interest points for policy.     

Inhibition of angiotensin I-converting enzyme by wheat gliadin hydrolysates

A tryptic gliadin hydrolysate was fractionated into peptide fractions, which were assigned to either the central domain (CD) or terminal domains (TD) of gliadins. The domains were expected to contain amino acid (AA) sequences which, when released from the parent protein, inhibit the angiotensin I-converting enzyme (ACE), which plays a key role in regulating blood pressure. A proline (Pro) poor TD related fraction, containing the smallest peptides, showed the highest ACE inhibitory activity (IC₅₀ = 0.33 mg/ml). Additional peptidases were selected based on their in silico predicted ability to release ACE inhibitory peptides. Further hydrolysis of the tryptic hydrolysate fractions with thermolysin, Clarex, Alcalase and Esperase increased ACE inhibitory activities. Immobilised Ni²⁺-ion affinity chromatography (IMAC) purification of a TD related peptide fraction obtained by sequential hydrolysis with trypsin and thermolysin yielded a fraction with an IC₅₀ value of 0.02 mg/ml. This IMAC fraction was enriched in histidine and hydrophobic AA (Pro, Val, Ile, Leu and Phe).     

Peaks Over Thresholds Modeling With Multivariate Generalized Pareto Distributions

When assessing the impact of extreme events, it is often not just a single component, but the combined behavior of several components which is important. Statistical modeling using multivariate generalized Pareto (GP) distributions constitutes the multivariate analogue of univariate peaks over thresholds modeling, which is widely used in finance and engineering. We develop general methods for construction of multivariate GP distributions and use them to create a variety of new statistical models. A censored likelihood procedure is proposed to make inference on these models, together with a threshold selection procedure, goodness-of-fit diagnostics, and a computationally tractable strategy for model selection. The models are fitted to returns of stock prices of four UK-based banks and to rainfall data in the context of landslide risk estimation. Supplementary materials and codes are available online.     

Assessment of distributed arterial network models

In drinking and drug surveys, peers are perceived as drinking more and using more drugs than the respondent. Particularly in youth studies, this majority fallacy is often interpreted as an indication of peer pressure toward drinking and drug use. However, exaggerating the alcohol and drug behaviours of significant others may be a way of reducing cognitive dissonance. The behaviour of most people deviates from their ideal norms. The ensuing dissonance can be alleviated by introducing the behaviour of others as a third element in the cognitive field. Data from three Scandinavian surveys support the following two predictions based on the theory of cognitive dissonance: (1) The tendency to report that other people drink more than oneself is more marked in restrictive than in permissive communities. (2) On each level of alcohol intake, the tendency to report that other people drink more than oneself is stronger among respondents having negative alcohol attitudes than among respondents with positive attitudes to alcohol. The need to alleviate the cognitive dissonance caused by a discrepancy between actual behaviour and normative standards is thus one of the mechanisms generating the majority fallacy: "I may not be perfect, but other people are still worse". Feeling better than others does not necessarily amount to a pressure to turn bad.