1,721,142 research outputs found
An Automata Based Microscopic Model Inspired by the Clonal Expansion
No full textWe present a simple model based on microscopic automata to describe
the clonal expansion process. The model is based on a repertoire of antigens and T
lymphocytes interacting via the APC cells which present the antigens peptides. Each
cell is represented by an automaton moving randomly on a two dimensional lattice.
We use this simplified model in order to introduce local and spatial considerations
in the mathematical models of clonal expansion based on differential equations, and
at the same time to attempt an analytical interpretation of the results of computer
simulations. For this reason we derive also a mean field theory, whose results are in
good agreement with the solutions of the of microscopic model, at least for situations
that are not too far from equilibrium. This model may be used as the base of a more
realistic one that could follow the clone expansion process on a simplified version of
the lymphatic network
Sequence-dependent collective properties of DNA and their role in biological systems.
No full textInside the cell, DNA continuously interacts with the proteins involved in replication, transcription, repair, and regulation processes.
During these processes, the DNA transforms between
packed and unpacked architectures, like that of chromatin
or of other higher-order structures morphing into shapes
with structural spikes alternative to the canonical B-form in
connection with biological events. The base sequence
encodes the dynamics of these transformations from the
atomic to the nanometer scale length, and over higher
spatial scales. Therefore, an important part of the DNA
information content is not localized on the codon regions
but is related to collective features of relatively large tracts
of sequence. We proposed a model able to model the
effects of the sequence on the superstructural
properties of DNA by integrating over nano-scale the
theoretically evaluated slight structural and electronic
features of the different nucleotide steps along the
sequence. This model allows the prediction of the
thermodynamic constants of the sequence dependent
circularization reactions of DNA tracts and their writhing
transitions from relaxed to super-coiled circular forms as
well as the stability constants and positioning of nucleosomes along eukaryotic genomes in excellent agreement with the experiments
Critical behaviour of invariant curves in the standard map: a perturbative approach
No full textThe classical perturbation series is used to follow an invariant curve, of fixed winding number, up to its break-up point. The result obtained for the critical value of the perturbation and the corresponding behaviour of the invariant curve are in complete agreement with the results of Kadanoff and Shenker
Resonances and asymptotic behavior of Birkhoff series
No full textFor hamiltonian systems with two degrees of freedom a mechanism accounting for the divergence of perturbation series and the asymptotic relation between true and formal dynamics is proposed. In the special case of conservative quadratic maps numerical and analytical support is given for a piecewise geometric structure of the Birkhoff series, that is a sequence of pseudoconvergence radii is found which decreases to zero and is associated with the resonances approaching the rotation angle of the linear map
Euclid, Geometry and Nature
No full textA pedagogical treatment is given on how the euclidean geometry can be used to describe complex and fractal shapes found in nature
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Registrazione della pressione arteriosa in un pilota di forrmula 1ndurante le prove: probleemi tecnici e risultati.
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