34,311 research outputs found
Simple Non-Markovian Microscopic Models for the Depolarizing Channel of a Single Qubit
The archetypal one-qubit noisy channels ---depolarizing, phase-damping and
amplitude-damping channels--- describe both Markovian and non-Markovian
evolution. Simple microscopic models for the depolarizing channel, both
classical and quantum, are considered. Microscopic models which describe phase
damping and amplitude damping channels are briefly reviewed.Comment: 13 pages, 2 figures. Title corrected. Paper rewritten. Added
references. Some typos and errors corrected. Author adde
Quantum transport through single and multilayer icosahedral fullerenes
We use a tight-binding Hamiltonian and Green functions methods to calculate
the quantum transmission through single-wall fullerenes and bilayered and
trilayered onions of icosahedral symmetry attached to metallic leads. The
electronic structure of the onion-like fullerenes takes into account the
curvature and finite size of the fullerenes layers as well as the strength of
the intershell interactions depending on to the number of interacting atom
pairs belonging to adjacent shells. Misalignment of the symmetry axes of the
concentric icosahedral shells produces breaking of the level degeneracies of
the individual shells, giving rise some narrow quasi-continuum bands instead of
the localized discrete peaks of the individual fullerenes. As a result, the
transmission function for non symmetrical onions are rapidly varying functions
of the Fermi energy. Furthermore, we found that most of the features of the
transmission through the onions are due to the electronic structure of the
outer shell with additional Fano-like antiresonances arising from coupling with
or between the inner shells.Comment: 16 pages, 5 figur
Gamma-ray absorption in the microquasar SS433
We discuss the gamma-ray absorption in the inner region of the microquasar
SS433. Our investigation includes several contributions to the opacity of this
system. They result from the ambient fields generated by the primary star,
possibly an A-type supergiant, and a very extended disk around the black hole.
Besides the sharp and dramatic absorption effect that occurs every time the
star crosses the emission zone, we find in the UV photon field from the
extended disk an important source of absorption for very high energy
gamma-rays. This results in periodic gamma-ray observational signatures.Comment: 8 pages, 9 figures, to appear in Astropart.Phy
Modeling the thermal evolution of enzyme-created bubbles in DNA
The formation of bubbles in nucleic acids (NAs) are fundamental in many
biological processes such as DNA replication, recombination, telomeres
formation, nucleotide excision repair, as well as RNA transcription and
splicing. These precesses are carried out by assembled complexes with enzymes
that separate selected regions of NAs. Within the frame of a nonlinear dynamics
approach we model the structure of the DNA duplex by a nonlinear network of
coupled oscillators. We show that in fact from certain local structural
distortions there originate oscillating localized patterns, that is radial and
torsional breathers, which are associated with localized H-bond deformations,
being reminiscent of the replication bubble. We further study the temperature
dependence of these oscillating bubbles. To this aim the underlying nonlinear
oscillator network of the DNA duplex is brought in contact with a heat bath
using the Nos-Hoover-method. Special attention is paid to the
stability of the oscillating bubbles under the imposed thermal perturbations.
It is demonstrated that the radial and torsional breathers, sustain the impact
of thermal perturbations even at temperatures as high as room temperature.
Generally, for nonzero temperature the H-bond breathers move coherently along
the double chain whereas at T=0 standing radial and torsional breathers result.Comment: 19 pages, 7 figure
Renormalisation group determination of the order of the DNA denaturation transition
We report on the nature of the thermal denaturation transition of homogeneous
DNA as determined from a renormalisation group analysis of the
Peyrard-Bishop-Dauxois model. Our approach is based on an analogy with the
phenomenon of critical wetting that goes further than previous qualitative
comparisons, and shows that the transition is continuous for the average
base-pair separation. However, since the range of universal critical behaviour
appears to be very narrow, numerically observed denaturation transitions may
look first-order, as it has been reported in the literature.Comment: 6 pages; no figures; to appear in Europhysics Letter
The soft X-ray excess AGN RE J2248-511
We model the spectral energy distribution of the ultrasoft broad-line AGN RE
J2248-511 with Comptonised accretion disc models. These are able to reproduce
the steep optical and ultrasoft X-ray slopes, and the derived black hole mass
is consistent with independent mass estimates. This AGN displays properties of
both broad and narrow line Seyfert 1 galaxies, but we conclude that it is
intrinsically a `normal' Seyfert 1 viewed at high inclination angle.Comment: 4 pages, 1 figure. MG10 Proceeding
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