Biomedical subjects

A Levermann

Publications and source records attributed to A Levermann.

4 recordsLinked to original sources

PubMed2003

Lymph node topography of the head and neck in New Zealand White rabbits.

Investigations of the lymphogenic metastatic spread of VX2 carcinomas in New Zealand White rabbits require an exact knowledge of the topography of cervical and facial lymph nodes. The topography of neck lymph nodes was evaluated from 16 rabbits macroscopically, histologically and by lymphographic investigations, and the possibility of their surgical removal (neck dissection) was examined. The upper aerodigestive tract and the ear of New Zealand White rabbits drain via four consistent groups of 12-18 lymph nodes. Except for the paratracheal lymph node, they are all easily accessible to surgery. The data presented in this study encourage the use of induced VX2 carcinomas in New Zealand White rabbits as an animal model to study the lymphogenic metastatic spread of squamous cell carcinomas of the head and neck. Such investigations could lead to an improvement of surgical and pharmaceutical treatment of this tumour entity.

Animals↗

PubMed2001

Thermodynamic formalism of the harmonic measure of diffusion limited aggregates: phase transition.

We study the nature of the phase transition in the multifractal formalism of the harmonic measure of diffusion limited aggregates. Contrary to previous work that relied on random walk simulations or ad hoc models to estimate the low probability events of deep fjord penetration, we employ the method of iterated conformal maps to obtain an accurate computation of the probability of the rarest events. We resolve probabilities as small as 10(-35). We show that the generalized dimensions D(q) are infinite for q<q*, where q* = -0.18+/-0.04. In the language of f(alpha) this means that alpha(max) is finite. We present a converged f(alpha) curve.

Journal Article↗

PubMed2001

Laplacian growth and diffusion limited aggregation: different universality classes.

It had been conjectured that diffusion limited aggregates and Laplacian growth patterns (with small surface tension) are in the same universality class. Using iterated conformal maps we construct a one-parameter family of fractal growth patterns with a continuously varying fractal dimension. This family can be used to bound the dimension of Laplacian growth patterns from below. The bound value is higher than the dimension of diffusion limited aggregates, showing that the two problems belong to two different universality classes.

Journal Article↗

PubMed2000

Convergent calculation of the asymptotic dimension of diffusion limited aggregates: scaling and renormalization of small clusters

Diffusion limited aggregation (DLA) is a model of fractal growth that had attained a paradigmatic status due to its simplicity and its underlying role for a variety of pattern forming processes. We present a convergent calculation of the fractal dimension D of DLA based on a renormalization scheme for the first Laurent coefficient of the conformal map from the unit circle to the expanding boundary of the fractal cluster. The theory is applicable from very small (2-3 particles) to asymptotically large (n-->infinity) clusters. The computed dimension is D=1.713+/-0.003.

Journal Article↗