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Biomedical subjects

S Bohn

Publications and source records attributed to S Bohn.

13 recordsLinked to original sources
PubMed2005

Hierarchical crack pattern as formed by successive domain divisions. I. Temporal and geometrical hierarchy.

Crack patterns, as they can be observed in the glaze of ceramics or in desiccated mud layers, are formed by successive fractures and divide the two-dimensional plane into distinct domains. On the basis of experimental observation, we develop a description of the geometrical structure of these hierarchical networks. In particular, we show that the essential feature of such a structure can be represented by a genealogical tree of successive domain divisions. This approach allows for a detailed discussion of the relationship between the formation process and the geometric result. We show that--with some restraints--it is possible to reconstruct the history of the system from the geometry of the final pattern.

Journal Article↗
PubMed2005

Hierarchical crack pattern as formed by successive domain divisions. II. From disordered to deterministic behavior.

Hierarchical crack patterns, such as those formed in the glaze of ceramics or in desiccated layers of mud or gel, can be understood as a successive division of two-dimensional domains. We present an experimental study of the division of a single rectangular domain in drying starch and show that the dividing fracture essentially depends on the domain size, rescaled by the thickness of the cracking layer e. Utilizing basic assumptions regarding the conditions of crack nucleation, we show that the experimental results can be directly inferred from the equations of linear elasticity. Finally, we discuss the impact of these results on hierarchical crack patterns, and in particular the existence of a transition from disordered cracks at large scales--the first ones--to a deterministic behavior at small scales--the last cracks.

Journal Article↗
PubMed2005

Four sided domains in hierarchical space dividing patterns.

The cracks observed in the glaze of ceramics form networks, which divide the 2D plane into domains. It is shown that, on the average, the number of sides of these domains is four. This contrasts with the usual 2D space divisions observed in Voronoi tessellation or 2D soap froths. In the latter networks, the number of sides of a domain coincides with the number of its neighbors, which, according to Euler's theorem, has to be six on average. The four sided property observed in cracks is the result of a formation process which can be understood as the successive divisions of domains with no later reorganization. It is generic for all networks having such hierarchical construction rules. We introduce a "geometrical charge," analogous to Euler's topological charge, as the difference from four of the number of sides of a domain. It is preserved during the pattern formation of the crack pattern.

Journal Article↗
PubMed2003

Bubbles under stress.

We present an experimental and theoretical investigation of a system composed of two soap bubbles strained between two parallel solid surfaces. The two-bubble cluster can be found in several configurations. The existence and stability of each of these states is studied as a function of the distance between the two facing surfaces. The change of this distance can induce a transition from one configuration to another; we observe that most transitions are subcritical, showing that the system is often trapped in states where the minimum of free energy is only local. The hysteretic transitions are responsible for the dissipation of elastic energy. The existence of more than one stable states for given boundaries conditions combined with the absence of thermalization means that the history of the system has to be taken into account and that there is no unique stress-strain relation. In the present system, because of its simplicity, a complete quantitative analysis of these general processes is obtained. The presented results may contribute to a better understanding of the dynamics of more complex systems such as foams or granular materials where similar processes are at work.

Journal Article↗
PubMed2002

Constitutive property of the local organization of leaf venation networks.

The leaf venation of dicotyledons forms complex patterns. In spite of their large variety of morphologies these patterns have common features. They are formed of a hierarchy of structures, which are connected to form a reticulum. Excellent images of these patterns can be obtained from leaves from which the soft tissues have been removed. A numerical image processing has been developed, specially designed for a quantitative analysis of this type of network. It provides a precise characterization of its geometry. The resulting data reveals a surprising property of reticula's nodes: the angles between vein segments are very well defined and it is shown that they are directly related by the radii of the segments. The relation between radii and angles can be expressed very simply using a phenomenological analogy to mechanics. This local organization principle is universal; all leaf venation patterns studied show the same behavior. The results are compared with physical networks such as fracture arrays or soap froth in terms of hierarchy and reorganization.

Biophysical Phenomena↗
PubMed2000

Airborne contact dermatitis from methylchloroisothiazolinone in wall paint. Abolition of symptoms by chemical allergen inactivation.

Preservatives such as isothiazolinones in paints have been reported to cause airborne contact dermatitis. The patients whom we report experienced acute dermatitis on air-exposed skin and respiratory symptoms after staying in recently painted rooms. Kathon (methylchloroisothiazolinone/methylisothiazolinone) added as preservative to the wall paint was identified as causative agent. In one individual symptoms rapidly disappeared after treatment of the painted walls with inorganic sulfur salt, which leads to inactivation of the allergenic properties of methylchloroisothiazolinone/methylisothiazolinone. We describe the patients, the clinical course and review the literature pertinent to such cases. In addition we report on the chemical analyses of the decorating paints used, and on experiments on emission and air concentration of methylchloroisothiazolinone/methylisothiazolinone from a painted surface before and after inactivation by sodium bisulfite.

Adult↗
PubMed1997

[Erythema nodosum: 112 cases. Epidemiology, clinical aspects and histopathology].

In a retrospective study we analyzed the cases of 112 patients with erythema nodosum treated during the period 1983-1993 in the Department of Dermatology, University Hospital of Basel, Switzerland. The aim of the study was to investigate the epidemiology, incidence of different etiologies, relevance of laboratory investigations and the histopathologic features in our patients, 83% of whom were females. The peak incidence occurred between the ages of 18 and 34 years. The commonest cause of erythema nodosum was infection. Other etiologic factors were adverse drug reactions, sarcoidosis, Crohn's disease, non-Hodgkin lymphoma, pregnancy, discoid lupus erythematosus, Sharp syndrome and aspartame. Only 47% of patients showed the classic bilateral distribution of the nodes on the extensor surface of the lower extremities. 77% of infection-induced erythema nodosum healed after 7 weeks, the longest course being 18 weeks. In contrast, 30% of idiopathic erythema nodosum lasted more than 6 months. Patients in whom erythema nodosum was associated with non-Hodgkin lymphoma had an extremely protracted course. Erythema nodosum associated with non-Hodgkin lymphoma may precede the diagnosis of lymphoma by months. In 4 cases erythema nodosum was the initial sign of sarcoidosis. In 30% of biopsies we found single vessels with leukocytoclastic vasculitis. The histologic pattern failed to provide etiologic pointers.

Adolescent↗
PubMed1996

Trichorhinophalangeal syndrome type III.

Trichorhinophalangeal syndrome (TRPS) type III is a newly defined clinical entity. This symptom complex is inherited as an autosomal dominant trait and clinically characterized by growth retardation, craniofacial abnormalities, severe brachydactyly and sparse hair. In addition, absence of mental retardation and cartilaginous exostoses are required for the diagnosis of TRPS III. To further delineate this newly recognized entity, we report on a patient from a Turkish family segregating TRPS III in 7 family members. The patient had a very short stature (147 cm, < 3rd standard deviation), a thin upper lip and a prominent lower lip, a pear-shaped nose, stubby fingers and toes with cone-shaped epiphyses and sparse scalp hair. Scanning electron microscopy findings and results of energy-dispersive X-ray microanalysis are presented in such a patient for the first time.

Abnormalities, Multiple↗