Scroll waves in isotropic excitable media : linear instabilities, bifurcations and restabilized states

Scroll waves are three-dimensional analogs of spiral waves. The linear stability spectrum of untwisted and twisted scroll waves is computed for a two-variable reaction-diffusion model of an excitable medium. Different bands of modes are seen to be unstable in different regions of parameter space. The corresponding bifurcations and bifurcated states are characterized by performing direct numerical simulations. In addition, computations of the adjoint linear stability operator eigenmodes are also performed and serve to obtain a number of matrix elements characterizing the long-wavelength deformations of scroll waves.Comment: 30 pages 16 figures, submitted to Phys. Rev.

Prevalence of diffuse pancreatic beta islet cell disease with hyperinsulinism: Problems in recognition and management

Among 77 patients with endogenous hyperinsulinism seen in 2 medical centers, diffuse islet cell disease accounted for 17 (22%) patients. Since diffuse islet cell disease poses special problems in management, its prevalence is emphasized in this report. Among these patients with diffuse islet cell disease, there were 11 patients with adenomatosis, 4 with nesidioblastosis, and 2 with islet cell hyperplasia. Six of the 77 patients were found in multiple endocrine neoplasia, type I kindreds; diffuse islet cell disease was documented in 4 of these patients. We outline principles of management in patients with diffuse islet cell disease. Frozen section microscopy failed to identify nesidioblastosis or islet cell hyperplasia. Chez 77 malades, provenant de 2 centres médicaux, qui présentaient un hyperinsulinisme endogène, 17 cas de lésions diffuses des îlots de Langerhans ont été dénombrés. Ce fait est donc loin d'être exceptionnel et cette étude a pour but de le souligner. Parmi ces 17 malades, 11 présentaient des adénomes multiples (adénomatoses), 4 des nésidoblastomes (anomalies tissulaires multifocales), 2 des hyperplasies cellulaires insulaires. Chez ces 77 malades, 6 cas de MEN type I furent individualisés, 4 d'entre eux présentaient une maladie insulaire diffuse. Les auteurs, forts de cette expériences insistent sur les principes du traitement de ce type d'affection. Ils insistent sur le fait que l'étude histologique extemporanée ne permet pas d'identifier les nésidoblastomes et les hyperplasies cellulaires insulaires et que dans 70%–80% des cas les résections pancréatiques ne permettent pas d'obtenir la guérison. Un problema constante para el cirujano que opera pacientes con hiperinsulinismo endógeno es el de qué hacer cuando no se encuentre patología en el curso de la operación una vez realizada la exploración preliminar del páncreas. Los adenomas solitarios de células beta pueden pasar desapercibidos cuando no son palpables; la identificación de la enfermedad difusa de las células insulares plantea muchos problemas. Reconocemos tres alteraciones principales de tipo difuso: adenomatosis de células beta, nesidioblastosis e hiperplasia pancreática de células beta. Además, múltiples macroadenomas pueden coexistir o no con microadenomatosis o con hiperplasia en ciertos pacientes con hiperinsulinismo. Los desórdenes de células insulares de tipo multifocal son particularmente frecuentes en pacientes con Neoplasia Endocrina Multiple Tipo I.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41314/1/268_2005_Article_BF01654942.pd

Skilled for improvement? Learning communities and the skills needed to improve care: an evaluative service development

This report tells the story of the Learning Communities Initiative, in which an experienced research team used an action approach (combining action research and action learning) to study four improvement projects across two sites, while working with participants to facilitate the flow of knowledge and learning.The report provides a graphic and illuminating description of the difficulties and barriers which arise in improvement work