Violent relaxation in two-dimensional flows with varying interaction range.

Understanding the relaxation of a system towards equilibrium is a long-standing problem in statistical mechanics. Here we address the role of long-range interactions in this process by considering a class of two-dimensional flows where the interaction between fluid particles varies with the distance as ∼r(α-2) for α>0. We find that changing α with a prescribed initial state leads to different flow patterns: for small α, a coarsening process leads to the formation of a sharp interface between two regions of homogenized α-vorticity; for large α, the flow is attracted to a stable dipolar structure through a filamentation process. Assuming that the energy E and the enstrophy Z are injected at a typical scale smaller than the domain scale L, we argue that convergence towards the equilibrium state is expected when the parameter (2π/L)(α)E/Z tends to one, while convergence towards a dipolar state occurs systematically when this parameter tends to zero. This suggests that weak long-range interacting systems are more prone to relax towards an equilibrium state than strong long-range interacting systems.

[Recurrent small-bowel intussusceptions revealing a disseminated BCG infection related to severe combined immunodeficiency]. / Invagination intestinale récidivante révélatrice d'une bécégite disséminée liée à un déficit immunitaire combiné sévère.

Infant small-bowel intussusceptions, most of the time idiopathic, may exceptionally reveal a severe digestive disease. We report the case of a 4-month-old infant who presented multiple and simultaneous ileal intussusceptions associated with severe acute gastroenteritis. Initially, the infant showed a protein-losing enteropathy with a clear alteration of the general state of health and undocumented fever, resistant to broad-spectrum antibiotic therapy. Skin and splenic nodules associated with hepatosplenomegaly and pancytopenia set in progressively. The etiologic evaluation led to the diagnosis of a Mycobacterium bovis BCG infection related to severe combined immune deficiency. The treatment consisted in anti-tuberculosis quadruple therapy in association with immunoglobin supplementation. Secondarily, the patient underwent gene therapy in a clinical trial. An early BCG vaccine in the first weeks of life, before the outbreak of infection revealing the immune deficiency, is a risk factor in triggering a disseminated BCG infection in immunodepressed infants. This clinical case is the first reported of severe combined immune deficiency revealed by small-bowel intussusceptions related to a disseminated BCG infection.

[Vogt-Koyanagi-Harada syndrome: a serious and rare emergency in children]. / Le syndrome de Vogt-Koyanagi-Harada: une urgence ophtalmologique grave et rare chez l'enfant.

Uveitis in children is a rare disease, often going undiagnosed. Vogt-Koyanagi-Harada syndrome, a uveomeningeal disease from an autoimmune process, rarely affects children, but an early diagnosis is essential in order to begin systemic corticosteroid therapy within the shortest delay possible for a better visual prognosis. We report a case of a 10-year-old boy, already treated with corticosteroids for the last 3 years for a nephrotic syndrome, referred for a sudden decrease in visual acuity affecting both eyes, associated with typical cutaneous manifestations of the disease.