96,864 research outputs found
Disorder effects on the static scattering function of star branched polymers
We present an analysis of the impact of structural disorder on the static
scattering function of f-armed star branched polymers in d dimensions. To this
end, we consider the model of a star polymer immersed in a good solvent in the
presence of structural defects, correlated at large distances r according to a
power law \sim r^{-a}. In particular, we are interested in the ratio g(f) of
the radii of gyration of star and linear polymers of the same molecular weight,
which is a universal experimentally measurable quantity. We apply a direct
polymer renormalization approach and evaluate the results within the double
\varepsilon=4-d, \delta=4-a-expansion. We find an increase of g(f) with an
increasing \delta. Therefore, an increase of disorder correlations leads to an
increase of the size measure of a star relative to linear polymers of the same
molecular weight.Comment: 17 pages, 7 figure
Entanglement, fidelity, and quantum-classical correlations with an atom walking in a quantized cavity field
Stability and instability of quantum evolution are studied in the interaction
between a two-level atom with photon recoil and a quantized field mode in an
ideal cavity, the basic model of cavity quantum electrodynamics (QED). It is
shown that the Jaynes-Cummings dynamics can be unstable in the regime of
chaotic walking of the atomic center-of-mass in the quantized field of a
standing wave in the absence of any kind of interaction with environment. This
kind of quantum instability manifests itself in strong variations of reduced
quantum purity and entropy, correlating with the respective classical Lyapunov
exponent, and in exponential sensitivity of fidelity of quantum states to small
variations in the atom-field detuning. The connection between quantum
entanglement and fidelity and the center-of-mass motion is clarified
analytically and numerically for a few regimes of that motion. The results are
illustrated with two specific initial field states: the Fock and coherent ones.
Numerical experiments demonstrate various manifestations of the
quantum-classical correspondence, including dynamical chaos and fractals, which
can be, in principle, observed in real experiments with atoms and photons in
high finesse cavities
Nuclear reactions in hot stellar matter and nuclear surface deformation
Cross-sections for capture reactions of charged particles in hot stellar
matter turn out be increased by the quadrupole surface oscillations, if the
corresponding phonon energies are of the order of the star temperature. The
increase is studied in a model that combines barrier distribution induced by
surface oscillations and tunneling. The capture of charged particles by nuclei
with well-deformed ground-state is enhanced in stellar matter. It is found that
the influence of quadrupole surface deformation on the nuclear reactions in
stars grows, when mass and proton numbers in colliding nuclei increase.Comment: 12 pages, 10 figure
Scaling in public transport networks
We analyse the statistical properties of public transport networks. These
networks are defined by a set of public transport routes (bus lines) and the
stations serviced by these. For larger networks these appear to possess a
scale-free structure, as it is demonstrated e.g. by the Zipf law distribution
of the number of routes servicing a given station or for the distribution of
the number of stations which can be visited from the chosen one without
changing the means of transport. Moreover, a rather particular feature of the
public transport network is that many routes service common subsets of
stations. We discuss the possibility of new scaling laws that govern intrinsic
features of such subsets.Comment: 9 pages, 4 figure
Description of Double Giant Dipole Resonance within the Phonon Damping Model
In a recent Letter [1] an overall agreement with the experimental data for
the excitation of the single and double giant dipole resonances in relativistic
heavy ion collision in 136Xe and 208Pb nuclei has been reported. We point out
that this agreement is achieved by a wrong calculation of the DGDR excitation
mechanism. We also argue that the agreement with the data for the widths of
resonances is achieved by an unrealistically large value of a model parameter.
[1] Nguyen Dinh Dang, Vuong Kim Au, and Akito Arima, Phys. Rev. Lett. 85
(2000) 1827.Comment: Comment for Phys. Rev. Let
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