1,184 research outputs found
Solitons in Yakushevich-like models of DNA dynamics with improved intrapair potential
The Yakushevich (Y) model provides a very simple pictures of DNA torsion
dynamics, yet yields remarkably correct predictions on certain physical
characteristics of the dynamics. In the standard Y model, the interaction
between bases of a pair is modelled by a harmonic potential, which becomes
anharmonic when described in terms of the rotation angles; here we substitute
to this different types of improved potentials, providing a more physical
description of the H-bond mediated interactions between the bases. We focus in
particular on soliton solutions; the Y model predicts the correct size of the
nonlinear excitations supposed to model the ``transcription bubbles'', and this
is essentially unchanged with the improved potential. Other features of soliton
dynamics, in particular curvature of soliton field configurations and the
Peierls-Nabarro barrier, are instead significantly changed
A New Anisotropic Four-Parameter Turbulence Model for Low Prandtl Number Fluids
Due to their interesting thermal properties, liquid metals are widely studied for heat transfer applications where large heat fluxes occur. In the framework of the Reynolds-Averaged Navier– Stokes (RANS) approach, the Simple Gradient Diffusion Hypothesis (SGDH) and the Reynolds Analogy are almost universally invoked for the closure of the turbulent heat flux. Even though these assumptions can represent a reasonable compromise in a wide range of applications, they are not reliable when considering low Prandtl number fluids and/or buoyant flows. More advanced closure models for the turbulent heat flux are required to improve the accuracy of the RANS models dealing with low Prandtl number fluids. In this work, we propose an anisotropic four-parameter turbulence model. The closure of the Reynolds stress tensor and turbulent heat flux is gained through nonlinear models. Particular attention is given to the modeling of dynamical and thermal time scales. Numerical simulations of low Prandtl number fluids have been performed over the plane channel and backward-facing step configurations
Clinicians need to be careful that they do not confuse mental health issues and long COVID in children and adolescents
No abstract available
How does the chromatin fiber deal with topological constraints?
In the nuclei of eukaryotic cells, DNA is packaged through several levels of
compaction in an orderly retrievable way that enables the correct regulation of
gene expression. The functional dynamics of this assembly involves the
unwinding of the so-called 30 nm chromatin fiber and accordingly imposes strong
topological constraints. We present a general method for computing both the
twist and the writhe of any winding pattern. An explicit derivation is
implemented for the chromatin fiber which provides the linking number of DNA in
eukaryotic chromosomes. We show that there exists one and only one unwinding
path which satisfies both topological and mechanical constraints that DNA has
to deal with during condensation/decondensation processes.Comment: Presented in Nature "News and views in brief" Vol. 429 (13 May 2004).
Movies available at
http://www.lptl.jussieu.fr/recherche/operationE_fichiers/Page_figurePRL.htm
Base sequence dependent sliding of proteins on DNA
The possibility that the sliding motion of proteins on DNA is influenced by
the base sequence through a base pair reading interaction, is considered.
Referring to the case of the T7 RNA-polymerase, we show that the protein should
follow a noise-influenced sequence-dependent motion which deviate from the
standard random walk usually assumed. The general validity and the implications
of the results are discussed.Comment: 12 pages, 3 figure
Experimental realization of a relativistic fluxon ratchet
We report the observation of the ratchet effect for a relativistic flux
quantum trapped in an annular Josephson junction embedded in an inhomogeneous
magnetic field. In such a solid state system mechanical quantities are
proportional to electrical quantities, so that the ratchet effect represents
the realization of a relativistic-flux-quantum-based diode. Mean static voltage
response, equivalent to directed fluxon motion, is experimentally demonstrated
in such a diode for deterministic current forcing both in the overdamped and in
the underdamped dynamical regime. In the underdamped regime, the recently
predicted phenomenon of current reversal is also recovered in our fluxon
ratchet.Comment: 4 pages, 6 figures. To appear in PHYSICA
- …