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Biomedical subjects

T Pöschel

Publications and source records attributed to T Pöschel.

9 recordsLinked to original sources
PubMed2003

Correction algorithm for finite sample statistics.

Assume in a sample of size M one finds M(i) representatives of species i with i = 1..N*. The normalized frequency pi* triple bond Mi/M, based on the finite sample, may deviate considerably from the true probabilities p(i). We propose a method to infer rank-ordered true probabilities r(i) from measured frequencies M(i). We show that the rank-ordered probabilities provide important informations on the system, e.g., the true number of species, the Shannon- and the Renyi-entropies.

Algorithms↗
PubMed2001

Scaling properties of granular materials.

Given an assembly of viscoelastic spheres with certain material properties, we raise the question how the macroscopic properties of the assembly will change if all lengths of the system, i.e. radii, container size etc., are scaled by a constant. The result leads to a method to scale down experiments to lab size.

Journal Article↗
PubMed2001

Extremal collision sequences of particles on a line: optimal transmission of kinetic energy.

The transmission of kinetic energy through chains of inelastically colliding spheres is investigated for the case of constant coefficient of restitution epsilon=const and impact-velocity-dependent coefficient epsilon(v) for viscoelastic particles. We derive a theory for the optimal distribution of particle masses which maximize the energy transfer along the chain and check it numerically. We found that for epsilon=const, the mass distribution is a monotonous function which does not depend on the value of epsilon. In contrast, for epsilon(v) the mass distribution reveals a pronounced maximum, depending on the particle properties and on the chain length. The system investigated demonstrates that even for small and simple systems, the velocity dependence of the coefficient of restitution may lead to new effects with respect to the same systems under the simplifying approximation epsilon=const.

Journal Article↗
PubMed1999

Coefficient of restitution of colliding viscoelastic spheres.

We perform a dimension analysis for colliding viscoelastic spheres to show that the coefficient of normal restitution epsilon depends on the impact velocity g as epsilon=1-gamma(1)g(1/5)+gamma(2)g(2/5)-/+..., in accordance with recent findings. We develop a simple theory to find explicit expressions for coefficients gamma(1) and gamma(2). Using these and few next expansion coefficients for epsilon(g) we construct a Padé approximation for this function which may be used for a wide range of impact velocities where the concept of the viscoelastic collision is valid. The obtained expression reproduces quite accurately the existing experimental dependence epsilon(g) for ice particles.

Journal Article↗
PubMed1996

The hypercube structure of the genetic code explains conservative and non-conservative aminoacid substitutions in vivo and in vitro.

A representation of the genetic code as a six-dimensional Boolean hypercube is described. This structure is the result of the hierarchical order of the interaction energies of the bases in codon-anticodon recognition. In this paper it is applied to study molecular evolution in vivo and in vitro. In the first case we compared aligned positions in homologous protein sequences and found two different behaviors: (a) There are sites in which the different amino acids may be explained by one or two 'attractor nodes' (coding for the dominating amino acid(s)) and their one-bit neighbors in the codon hypercube; and (b) There are sites in which the amino acids correspond to codons located in closed paths in the hypercube. In the second case we studied the 'Sexual PCR'1 experiment described by Stemmer [Stemmer (1994)] and found that the success of this combination of usual PCR and recombination is in part due to the Gray code structure of the genetic code.

Amino Acids↗