Tanja Van Hecke

The Influence of Random Element Displacement on DOA Estimates Obtained with (Khatri–Rao-)Root-MUSIC

Although a wide range of direction of arrival (DOA) estimation algorithms has been described for a diverse range of array configurations, no specific stochastic analysis framework has been established to assess the probability density function of the error on DOA estimates due to random errors in the array geometry. Therefore, we propose a stochastic collocation method that relies on a generalized polynomial chaos expansion to connect the statistical distribution of random position errors to the resulting distribution of the DOA estimates. We apply this technique to the conventional root-MUSIC and the Khatri-Rao-root-MUSIC methods. According to Monte-Carlo simulations, this novel approach yields a speedup by a factor of more than 100 in terms of CPU-time for a one-dimensional case and by a factor of 56 for a two-dimensional case.

Relationship between non-standard work arrangements and work-related accident absence in Belgium

The main objective of this study is to examine the relationship between indicators of nonstandard work arrangements, including precarious contract, long working hours, multiple jobs, shift work, and work‐related accident absence, using a representative Belgian sample and considering several sociodemographic and work characteristics.

Rent or Buy

Abstract When one looks around in everyday life, one sees mathematics everywhere: i.e., when making the right decisions whether to rent or buy a bicycle depending on the circumstances. Mathematics can determine (in case of renting a bicycle) the maximum rental cost to ensure that you will be able to pay the rental cost every month. The period you need the bicycle will also influence the rental cost you are prepared to pay. It is also possible to evaluate whether renting is better than buying, depending on the interest rate the bank is offering you for investing your saved money that you do not spend at once because you rent the bicycle.Abstract When one looks around in everyday life, one sees mathematics everywhere: i.e., when making the right decisions whether to rent or buy a bicycle depending on the circumstances. Mathematics can determine (in case of renting a bicycle) the maximum rental cost to ensure that you will be able to pay the rental cost every month. The period you need the bicycle will also influence the rental cost you are prepared to pay. It is also possible to evaluate whether renting is better than buying, depending on the interest rate the bank is offering you for investing your saved money that you do not spend at once because you rent the bicycle.

Stochastic Framework for Evaluating the Effect of Displaced Antenna Elements on DOA Estimation

We establish a statistical framework for investigating the influence of correlated random displacements of antenna elements in a uniform circular antenna array (UCA) on the distribution of direction-of-arrival (DOA) estimates. More specifically, we apply a stochastic collocation method for modeling the sparse UCA root-MUSIC-DOA estimates as polynomial expansions of the random displacements. Compared to Monte-Carlo simulations, this approach yields a speedup of about 40 for the case of a displacement of two antenna elements.

Improved Crank-Nicolson method for modelling diffusion of electromagnetic fields in hysteretic soft magnetic laminations

Abstract This paper studies the use of time stepping methods to integrate the equations which model the magnetodynamic fields in ferromagnetic laminations. A new high-order time stepping method is compared to well-known time stepping methods (Euler, Crank Nicolson, …) for a diffusion problem of electromagnetic fields in magnetic laminations with hysteresis. For validation purposes, firstly a theoretical problem with analytical solution is solved. Afterwards, more realistic problems are studied. As the presented method is A-stable, accurate numerical loops can be computed, even in the case of hysteresis effects.

Membrane permeability: characteristic times and lengths for oxygen, and a simulation-based test of the inhomogeneous solubility-diffusion model

The balance of normal and radial (lateral) diffusion of oxygen in phospholipid membranes is critical for biological function. Based on the Smoluchowski equation for the inhomogeneous solubility-diffusion model, Bayesian analysis (BA) can be applied to molecular dynamics trajectories of oxygen to extract the free energy and the normal and radial diffusion profiles. This paper derives a theoretical formalism to convert these profiles into characteristic times and lengths associated with entering, escaping, or completely crossing the membrane. The formalism computes mean first passage times and holds for any process described by rate equations between discrete states. BA of simulations of eight model membranes with varying lipid composition and temperature indicate that oxygen travels 3 to 5 times further in the radial than in the normal direction when crossing the membrane in a time of 15 to 32 ns, thereby confirming the anisotropy of passive oxygen transport in membranes. Moreover, the preceding times and distances estimated from the BA are compared to the aggregate of 280 membrane exits explicitly observed in the trajectories. BA predictions for the distances of oxygen radial diffusion within the membrane are statistically indistinguishable from the corresponding simulation values, yet BA oxygen exit times from the membrane interior are approximately 20% shorter than the simulation values, averaged over seven systems. The comparison supports the BA approach and, therefore, the applicability of the Smoluchowski equation to membrane diffusion. Given the shorter trajectories required for the BA, these results validate the BA as a computationally attractive alternative to direct observation of exits when estimating characteristic times and radial distances. The effect of collective membrane undulations on the BA is also discussed.

Shift Work and Occupational Accident Absence in Belgium: Findings from the Sixth European Working Condition Survey

(1) Background: Irregular and non-standard work arrangements have become a serious determinant to the health and safety of workers. The aim of this study is to investigate the relationship between shift work and occupational accident absence. A representative Belgian sample considering several sociodemographic and work characteristics is used. (2) Methods: This study is based on the data of the sixth European Working Condition Survey (EWCS). The sample is restricted to 2169 respondents from Belgium. By using multivariate logistic regression modeling techniques and adjusting several confounders, the associations between shift work and occupational accident absence are studied. (3) Results: It is found that about 11.1% of the workers undergo an occupational accident absence. A multivariate regression model demonstrates an increased occupational accident absence risk for workers who have shift work (odds ratio, or OR, 1.92, 95% CI 1.06–3.46). Also, gender and biomechanical exposure were significantly associated with occupational accident absence ((OR 2.07, 95% CI 1.16–3.69) and (OR 2.03, 95% CI 1.14–3.63), respectively). No significant interaction effects are found with gender and age variables. 4) Conclusion: This study confirms that doing shift work is significantly associated with occupational accidents. In order to reduce the significance of occupational accidents, shift work should be limited through national-level policies.

Effect of chain unsaturation and temperature on oxygen diffusion through lipid membranes from simulations

In order to maintain proper function, mammalian brain requires a significant fraction of the energy provided through whole body oxygen consumption and oxidative phosphorylation. This has been fairly well known for a long time. More recently there has been an increased appreciation that, while whole brain blood flow remains fairly constant, there are large regional changes in local blood flow to account for spatial and temporal heterogeneity of neuronal activity. This latter phenomenon requires an extensive regulatory system for local oxygen delivery that involves arteriolar and capillary control mechanisms. The ISOTT has been a major contributor to the study of oxygen supply and demand through studies of the mechanisms of vascular dilation and constriction in response to energy expenditure and availability of substrate and oxygen. Nevertheless, it has become clear in the past few decades that in addition to acute, physiological responses to energy demand and oxygen/substrate availability, there are regulatory mechanisms that are continuously operating to control the capillary distribution over a time course of weeks. This process of “ angioplasticity” results in the gradual acclimatization of the brain capillary bed to prolonged changes in oxygen/substrate availability and/or neuronal activity patterns. Angioplasticity is primarily regulated through the hypoxia inducible transcription factor, acting as a detector of the balance between oxygen delivery and energy demand at the level of the cell redox state, controlling vascular endothelial growth factor production which helps determine capillary density in consort with the cyclooxygenase-2/angiopoietin-2 pathway that controls endothelial cell junction mechanical stability. We can conclude that the structure-function of brain capillaries is regulated during prolonged challenges to energy supply-demand balance within the physiological range. We can conclude that over the physiological range of ambient oxygen, brain capillary density is proportional to fraction inspired oxygen. The primary mechanisms for regulation of brain capillary density are HIF-1/VEGF and COX-2/PGE2/ang-2 pathways of angiogenesis and angiolysis.

Work accident victims: a comparison between non-standard and standard workers in Belgium

SamenvattingOngezonde werkomstandigheden, bijvoorbeeld blootstelling aan lawaai, trillingen van handgereedschap of machines, hoge of lage temperaturen, het inademen van damp, rook of stofpartikels, de aanwezigheid van en het omgaan met chemische en gevaarlijke stoffen, blootstelling aan straling, lasten tillen, oncomfortabele posities, het hanteren van gevaarlijke werktuigen, valrisico en elektrocutiegevaar, kunnen leiden tot het optreden van beroepsziekten en arbeidsongevallen of werkgebonden blessures met verzuim of zelfs de dood tot gevolg. Ook het werken op uren met een negatieve impact op het sociaal leven (‘s nachts of op zondag werken, in ploegen werken) zijn risicofactoren voor arbeidsongevallen en werkgerelateerde gezondheidsproblemen. Het toepassen van nieuwe technologieën, de internationalisering en de globalisering resulteren in een verandering van de werkomstandigheden in België. Het reguliere arbeidscontract komt minder vaak voor in de arbeidsmarkt: de markt eist flexibiliteit. Het aantal ‘niet-standaard’ arbeidskrachten stijgt met rasse schreden. Hiermee bedoelen we tijdelijke krachten, zij die lange werkuren kloppen, zij die verschillende jobs combineren en zij die in ploegen werken.

Relationships between irregular work arrangements and occupational injuries in EU 27: findings from the fifth European working condition survey

The associations between several measures of low employment quality and some specific health and safety outcomes have become the subject of more recent investigation. The main objective of our study is to examine the relationships between irregular work arrangements indicators including contract type, long working hours, multiple jobs, shift work, and occupational injuries, taking into account several sociodemographic and work characteristics.