29 research outputs found
Die Bybel in ons daaglikse lewenspraktyk
Omdat die konferensietema, sowel as hierdie spesifieke, onderwerp, in bepaalde terminologie uitgedruk word, is dit nodig dat 'n spreker self sĂȘ wat hy daaronder verstaan
Nonperturbative renormalization group approach to frustrated magnets
This article is devoted to the study of the critical properties of classical
XY and Heisenberg frustrated magnets in three dimensions. We first analyze the
experimental and numerical situations. We show that the unusual behaviors
encountered in these systems, typically nonuniversal scaling, are hardly
compatible with the hypothesis of a second order phase transition. We then
review the various perturbative and early nonperturbative approaches used to
investigate these systems. We argue that none of them provides a completely
satisfactory description of the three-dimensional critical behavior. We then
recall the principles of the nonperturbative approach - the effective average
action method - that we have used to investigate the physics of frustrated
magnets. First, we recall the treatment of the unfrustrated - O(N) - case with
this method. This allows to introduce its technical aspects. Then, we show how
this method unables to clarify most of the problems encountered in the previous
theoretical descriptions of frustrated magnets. Firstly, we get an explanation
of the long-standing mismatch between different perturbative approaches which
consists in a nonperturbative mechanism of annihilation of fixed points between
two and three dimensions. Secondly, we get a coherent picture of the physics of
frustrated magnets in qualitative and (semi-) quantitative agreement with the
numerical and experimental results. The central feature that emerges from our
approach is the existence of scaling behaviors without fixed or pseudo-fixed
point and that relies on a slowing-down of the renormalization group flow in a
whole region in the coupling constants space. This phenomenon allows to explain
the occurence of generic weak first order behaviors and to understand the
absence of universality in the critical behavior of frustrated magnets.Comment: 58 pages, 15 PS figure
Joint sequencing of human and pathogen genomes reveals the genetics of pneumococcal meningitis
Streptococcus pneumoniae is a common nasopharyngeal colonizer, but can also cause lifethreatening invasive diseases such as empyema, bacteremia and meningitis. Genetic variation
of host and pathogen is known to play a role in invasive pneumococcal disease, though to
what extent is unknown. In a genome-wide association study of human and pathogen we
show that human variation explains almost half of variation in susceptibility to pneumococcal
meningitis and one-third of variation in severity, identifying variants in CCDC33 associated
with susceptibility. Pneumococcal genetic variation explains a large amount of invasive
potential (70%), but has no effect on severity. Serotype alone is insufficient to explain
invasiveness, suggesting other pneumococcal factors are involved in progression to invasive
disease. We identify pneumococcal genes involved
Evaluating the Effects of SARS-CoV-2 Spike Mutation D614G on Transmissibility and Pathogenicity
Global dispersal and increasing frequency of the SARS-CoV-2 spike protein variant D614G are suggestive of a selective advantage but may also be due to a random founder effect. We investigate the hypothesis for positive selection of spike D614G in the United Kingdom using more than 25,000 whole genome SARS-CoV-2 sequences. Despite the availability of a large dataset, well represented by both spike 614 variants, not all approaches showed a conclusive signal of positive selection. Population genetic analysis indicates that 614G increases in frequency relative to 614D in a manner consistent with a selective advantage. We do not find any indication that patients infected with the spike 614G variant have higher COVID-19 mortality or clinical severity, but 614G is associated with higher viral load and younger age of patients. Significant differences in growth and size of 614G phylogenetic clusters indicate a need for continued study of this variant