1,131 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
Pancreatic cystosis in cystic fibrosis. Sometimes a bike ride can help you decide
Pancreatic cystosis (PC) is an uncommon manifestation of pancreas involvement in cystic fibrosis (CF), characterized by the presence of multiple macrocysts partially or completely replacing pancreas. Only few reports are available from literature and management (surgery vs follow up) is commonly based on the presence of symptoms or complications due to local mass effect, although evidence-based recommendations are still not available. We here report the case of a young adult CF patient with PC, in which cardiopulmonary exercise testing (CPET) provided important information to be integrated to the radiological finding of inferior vena cava compression by the multicystic pancreas complex. Through the analysis of oxygen kinetic cardiodynamic phase pattern, CPET may be helpful to safely exclude significant mass effects on blood venous return and to improve the decision-making process on whether to consider surgery or not in patients with PC
Self-Focusing Dynamics of Coupled Optical Beams
We theoretically and experimentally investigate the mutual collapse dynamics
of two spatially separated optical beams in a Kerr medium. Depending on the
initial power, beam separation, and the relative phase, we observe repulsion or
attraction, which in the latter case reveals a sharp transition to a single
collapsing beam. This transition to fusion of the beams is accompanied by an
increase in the collapse distance, indicating the effect of the nonlinear
coupling on the individual collapse dynamics. Our results shed light on the
basic nonlinear interaction between self-focused beams and provide a mechanism
to control the collapse dynamics of such beams.Comment: 5 pages, 4 figure
High-Performance Silicon-Based Multiple Wavelength Source
We demonstrate a stable CMOS-compatible on-chip multiple-wavelength source by
filtering and modulating individual lines from a frequency comb generated by a
microring resonator optical parametric oscillator.. We show comb operation in a
low-noise state that is stable and usable for many hours. Bit-error rate
measurements demonstrate negligible power penalty from six independent
frequencies when compared to a tunable diode laser baseline. Open eye diagrams
confirm the fidelity of the 10 Gb/s data transmitted at the comb frequencies
and the suitability of this device for use as a fully integrated silicon-based
WDM source.Comment: 3 pages, 3 figure
Poincare' normal forms and simple compact Lie groups
We classify the possible behaviour of Poincar\'e-Dulac normal forms for
dynamical systems in with nonvanishing linear part and which are
equivariant under (the fundamental representation of) all the simple compact
Lie algebras and thus the corresponding simple compact Lie groups. The
``renormalized forms'' (in the sense of previous work by the author) of these
systems is also discussed; in this way we are able to simplify the
classification and moreover to analyze systems with zero linear part. We also
briefly discuss the convergence of the normalizing transformations.Comment: 17 pages; minor corrections in revised versio
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