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At least 91 records · Page 5Linked to original sources
PubMed2000

Feedback-controlled forcing of meandering spiral waves in an open gel reactor

The control of spiral wave dynamics has attracted much interest recently. Besides external forcing at a fixed frequency, feedback-controlled forcing has been studied. One of the simplest feedback schemes is to measure the activity level at a particular point of the medium continuously and to apply a spatially uniform pulsatory modulation if a certain threshold is reached at the detector. We have realized this feedback loop using an open gel reactor for the light-sensitive Belousov-Zhabotinskii medium. This allows us to maintain stationary nonequilibrium conditions over several hundred rotation periods of the unperturbed spiral wave. By varying the distance between the detector and the spiral tip, we find different stable branches of the resonance attractor for the same medium. We confirm the constant spacing between neighboring stable branches as predicted by Zykov and Karma and measure the dependence of the resonance drift on the forcing amplitude.

Journal Article↗
PubMed2002

Spiral wave meandering induced by fluid convection in an excitable medium.

An isothermal reaction-diffusion system is considered in a two-dimensional fluid medium within a gravitational field. Inhomogeneities in the concentration field of the species give rise to a fluid flow due to buoyancy forces. A two-dimensional reaction-diffusion-convection model of an excitable medium is presented. The influence of hydrodynamics on spiral wave dynamics is systematically studied. A kinematic model is also introduced to better understand the mechanisms involved here.

Journal Article↗
PubMed2001

The meandering 45-year odyssey of a clinical immunologist.

My work on basic and clinical immunology has focused on the regulation of the human immune response and how its dysregulation can lead to immunodeficiency, autoimmune, and malignant disorders. The early focus in our laboratory was on pathogenic mechanisms underlying hypogammaglobulinemia. Our demonstration of active suppression by human suppressor T cells changed thinking about the pathogenesis of certain immunodeficiency disorders. Recently we have focused on the cytokines interleukin-2 (IL-2) and IL-15, which have competitive functions in adaptive immune responses. IL-2 is necessary to destroy self-reactive lymphocytes and thus favors peripheral tolerance to self-antigens, whereas IL-15 favors the persistence of lymphocytes involved in the memory and effector responses to invading pathogens but risks the development of inflammatory autoimmune diseases. Our murine anti-Tac monoclonal antibody exploits these differences, as does a humanized form (daclizumab) now approved for the prevention of renal allograft rejection. New forms of therapy directed at IL-2 and IL-15 receptors may be effective against certain neoplastic diseases and autoimmune disorders and in the prevention of allograft rejection.

Allergy and Immunology↗
PubMed2004

Serendipitous meanderings and adventures with molecular beams.

This is the story of a native-born American who came as a postdoc to the country of his parents, Germany. There, by good fortune, he could participate in the revival and the rebuilding of the physical sciences following the ravishments of the Second World War, becoming at the age of 38, the director of a Max-Planck-Institut in Gottingen. Working under nearly ideal conditions, he carried out basic research using molecular beams. Aided by many active, youthfully impulsive, yet perceptive and imaginative, students and experienced knowledgeable guest scientists from many countries, he enjoyed exciting adventures into unknown landscapes in the fields of molecular gas-phase interactions and solid-surface phenomena and, most recently, in the realms of quantum liquids and solids.

Journal Article↗