Chemical distribution in Belgium from 2007 to 2010:an empirical study

Chemical distribution is described from a product lifecycle perspective. The impact of the economic decline in 2009 on Belgian chemical distribution is given in figures. In 2010 the sector recovered sharply. Although the individual companies performed very differently, overall, 2010 was even better than 2008. Increasingly complex legislation on chemical products has initiated a consolidation trend in the sector which in turn has brought on trends in outsourcing and inventory management.<br

Computation of nucleation of a non-equilibrium first-order phase transition using a rare-event algorithm

We introduce a new Forward-Flux Sampling in Time (FFST) algorithm to efficiently measure transition times in rare-event processes in non-equilibrium systems, and apply it to study the first-order (discontinuous) kinetic transition in the Ziff-Gulari-Barshad model of catalytic surface reaction. The average time for the transition to take place, as well as both the spinodal and transition points, are clearly found by this method.Comment: 12 pages, 10 figure

Feather-like structures in positive streamers.

In experiments positive streamers can have a feather-like structure, with small hairs connected to the main streamer channel. These feathers were observed in pure nitrogen (with impurities of 1ppm oxygen or less) but not in air. Based on results of numerical simulations, we provide a theoretical explanation for the emergence of these hairs as well as why the hairs are visible in nitrogen, but not in air

Feather-like structures in positive streamers interpreted as electron avalanches

In experiments positive streamers can have a feather-like structure, with small hairs connected to the main streamer channel. These feathers were observed in pure nitrogen (with impurities of 1 ppm oxygen or less) but not in air. We hypothesize that these hairs are individual electron avalanches moving towards the streamer channel. Based on results of numerical simulations, we provide a theoretical explanation why these hairs are visible in nitrogen, but not in air

Dynamics and pattern formation in invasive tumor growth

In this work, we study the in-vitro dynamics of the most malignant form of the primary brain tumor: Glioblastoma Multiforme. Typically, the growing tumor consists of the inner dense proliferating zone and the outer less dense invasive region. Experiments with different types of cells show qualitatively different behavior. Wild-type cells invade a spherically symmetric manner, but mutant cells are organized in tenuous branches. We formulate a model for this sort of growth using two coupled reaction-diffusion equations for the cell and nutrient concentrations. When the ratio of the nutrient and cell diffusion coefficients exceeds some critical value, the plane propagating front becomes unstable with respect to transversal perturbations. The instability threshold and the full phase-plane diagram in the parameter space are determined. The results are in a good agreement with experimental findings for the two types of cells.Comment: 4 pages, 4 figure

Positive streamer propagation due to background or photo ionization: Experiments and theory

Positive streamers in air are generally believed to propagate against the electron drift direction due to the nonlocal photo-ionization reaction. Photo-ionization is the ionization of O2 molecules by UV radiation from excited N2 molecules; therefore this reaction depends on the ratio between oxygen and nitrogen. Another possible source of free electrons in front of a positive streamer is background ionization that can remain from previous discharges, or it can be created by cosmic rays or by radioactive species like radon. We study the effects of both photo- and background- ionization on propagation and morphology of positive streamers by changing the ratio between nitrogen and oxygen and by changing the repetition frequency. We also study streamers in pure nitrogen with a small addition of radioactive 85Kr to increase background ionization. While streamer velocities are amazingly insensitive to these changes, their overall morphology largely depends on gas composition, repetition rate and radioactive admixtures. Essential observations can are explained theoretically

Marriage in epilepsy: The impact of the question in knowledge, attitude, and practice surveys.

BACKGROUND: Knowledge, attitudes, and practice (KAP) questionnaire-based surveys have captured negative attitudes towards marriage involving people with epilepsy (PWE). The attitudes may vary according to the nature of the question posed, whether personal or generic, in addition to many other covariates. METHODS: We carried out meta-proportion and -regression analyses of epilepsy-related KAP surveys published between 1970 and 2016 in the medical literature analysis retrieval system online (MEDLINE) database. RESULTS: The pooled estimate of the proportion of those responding positively to the marriage question was 0.45 (95% confidence interval (95%CI): 0.35 to 0.54; I2res = 99.89%). The pooled proportion of positive responders to a personal question (0.40; 95%CI: 0.35 to 0.46) was significantly lower than those responding positively to a generic question (0.64; 95%CI: 0.57 to 0.70) (P = 0.001). When modeled individually in regression analyses, only the continent of origin of the survey (P = 0.001; tau2: 0.06; I2res: 99.8%; adjusted R2: 11.4%) and subject population type (P = 0.02; tau2: 0.07; I2res: 99.9%; adjusted R2: 4.2%) were associated with the pooled estimate of positive responders to the question on marriage. CONCLUSIONS: Personal questions probing the possibility of marriage of self or family members to someone with epilepsy bring about negative attitudes more often than generic questions inquiring the marriage-worthiness of PWE