10,722 research outputs found
Interdependent networks with correlated degrees of mutually dependent nodes
We study a problem of failure of two interdependent networks in the case of
correlated degrees of mutually dependent nodes. We assume that both networks (A
and B) have the same number of nodes connected by the bidirectional
dependency links establishing a one-to-one correspondence between the nodes of
the two networks in a such a way that the mutually dependent nodes have the
same number of connectivity links, i.e. their degrees coincide. This implies
that both networks have the same degree distribution . We call such
networks correspondently coupled networks (CCN). We assume that the nodes in
each network are randomly connected. We define the mutually connected clusters
and the mutual giant component as in earlier works on randomly coupled
interdependent networks and assume that only the nodes which belong to the
mutual giant component remain functional. We assume that initially a
fraction of nodes are randomly removed due to an attack or failure and find
analytically, for an arbitrary , the fraction of nodes which
belong to the mutual giant component. We find that the system undergoes a
percolation transition at certain fraction which is always smaller than
the for randomly coupled networks with the same . We also find that
the system undergoes a first order transition at if has a finite
second moment. For the case of scale free networks with , the
transition becomes a second order transition. Moreover, if we find
as in percolation of a single network. For we find an exact
analytical expression for . Finally, we find that the robustness of CCN
increases with the broadness of their degree distribution.Comment: 18 pages, 3 figure
Electron-Ion Recombination Rate Coefficients and Photoionization Cross Sections for Astrophysically Abundant Elements. V. Relativistic calculations for Fe XXIV and Fe XXV for X-ray modeling
Photoionization and recombination cross sections and rate coefficients are
calculated for Li-like Fe XXIV and He-like Fe XXV using the Breit-Pauli
R-matrix (BPRM) method. A complete set of total and level-specific parameters
is obtained to enable X-ray photoionization and spectral modeling. The ab
initio calculations for the unified (e + ion) recombination rate coefficients
include both the non-resonant and the resonant recombination (radiative and
di-electronic recombination, RR and DR, respectively) for (e + Fe XXV) -> Fe
XXIV and (e + Fe XXVI) -> Fe XXV. The level specific rates are computed for all
fine structure levels up to n = 10, enabling accurate computation of
recombination-cascade matrices and effective rates for the X-ray lines. The
total recombination rate coefficients for both Fe XXIV and Fe XXV differ
considerably, by several factors, from the sum of RR and DR rates currently
used to compute ionization fractions in astrophysical models. As the
photoionization/recombination calculations are carried out using an identical
eigenfunction expansion, the cross sections for both processes are
theoretically self-consistent; the overall uncertainty is estimated to be about
10-20%. All data for Fe XXIV and Fe XXV (and also for H-like Fe XXVI, included
for completeness) are available electronically.Comment: 31 pages, 10fug
Variability of the X-ray P Cygni Line Profiles from Circinus X-1 Near Zero Phase
The luminous X-ray binary Circinus X-1 has been observed twice near zero
orbital phase using the High-Energy Transmission Grating Spectrometer (HETGS)
onboard Chandra. The source was in a high-flux state during a flare for the
first observation, and it was in a low-flux state during a dip for the second.
Spectra from both flux states show clear P Cygni lines, predominantly from
H-like and He-like ion species. These indicate the presence of a high-velocity
outflow from the Cir X-1 system which we interpret as an equatorial
accretion-disk wind, and from the blueshifted resonance absorption lines we
determine outflow velocities of 200 - 1900 km/s with no clear velocity
differences between the two flux states. The line strengths and profiles,
however, are strongly variable both between the two observations as well as
within the individual observations. We characterize this variability and
suggest that it is due to both changes in the amount of absorbing material
along the line of sight as well as changes in the ionization level of the wind.
We also refine constraints on the accretion-disk wind model using improved
plasma diagnostics such as the He-like Mg XI triplet, and we consider the
possibility that the X-ray absorption features seen from superluminal jet
sources can generally be explained via high-velocity outflows.Comment: 12 pages, 8 figures, accepted by ApJ (Main
Three-Dimensional FDTD Simulation of Biomaterial Exposure to Electromagnetic Nanopulses
Ultra-wideband (UWB) electromagnetic pulses of nanosecond duration, or
nanopulses, have been recently approved by the Federal Communications
Commission for a number of various applications. They are also being explored
for applications in biotechnology and medicine. The simulation of the
propagation of a nanopulse through biological matter, previously performed
using a two-dimensional finite difference-time domain method (FDTD), has been
extended here into a full three-dimensional computation. To account for the UWB
frequency range, a geometrical resolution of the exposed sample was ,
and the dielectric properties of biological matter were accurately described in
terms of the Debye model. The results obtained from three-dimensional
computation support the previously obtained results: the electromagnetic field
inside a biological tissue depends on the incident pulse rise time and width,
with increased importance of the rise time as the conductivity increases; no
thermal effects are possible for the low pulse repetition rates, supported by
recent experiments. New results show that the dielectric sample exposed to
nanopulses behaves as a dielectric resonator. For a sample in a cuvette, we
obtained the dominant resonant frequency and the -factor of the resonator.Comment: 15 pages, 8 figure
Local and Global Distinguishability in Quantum Interferometry
A statistical distinguishability based on relative entropy characterises the
fitness of quantum states for phase estimation. This criterion is employed in
the context of a Mach-Zehnder interferometer and used to interpolate between
two regimes, of local and global phase distinguishability. The scaling of
distinguishability in these regimes with photon number is explored for various
quantum states. It emerges that local distinguishability is dependent on a
discrepancy between quantum and classical rotational energy. Our analysis
demonstrates that the Heisenberg limit is the true upper limit for local phase
sensitivity. Only the `NOON' states share this bound, but other states exhibit
a better trade-off when comparing local and global phase regimes.Comment: 4 pages, in submission, minor revision
Effective action approach to strongly correlated fermion systems
We construct a new functional for the single particle Green's function, which
is a variant of the standard Baym Kadanoff functional.
The stability of the stationary solutions to the new functional is directly
related to aspects of the irreducible particle hole interaction through the
Bethe Salpeter equation.
A startling aspect of this functional is that it allows a simple and rigorous
derivation of both the standard and extended dynamical mean field (DMFT)
equations as stationary conditions. Though the DMFT equations were formerly
obtained only in the limit of infinite lattice coordination, the new functional
described in the work, presents a way of directly extending DMFT to finite
dimensional systems, both on a lattice and in a continuum. Instabilities of the
stationary solution at the bifurcation point of the functional, signal the
appearance of a zero mode at the Mott transition which then couples t o
physical quantities resulting in divergences at the transition.Comment: 9 page
High-resolution X-ray Spectra Of The Symbiotic Star SS73 17
SS73 17 was an innocuous Mira-type symbiotic star until Integral and Swift
discovered its bright hard X-ray emission, adding it to the small class of
"hard X-ray emitting symbiotics." Suzaku observations in 2006 then showed it
emits three bright iron lines as well, with little to no emission in the 0.3-2
keV bandpass. We present here followup observations with the Chandra HETG and
Suzaku that confirm the earlier detection of strong emission lines of Fe Kalpha
fluorescence, Fe XXV and Fe XXVI but also show significantly more soft X-ray
emission. The high resolution spectrum also shows emission lines of other
highly ionized ions as Si XIV and possibly S XVI. In addition, a reanalysis of
the 2006 Suzaku data using the latest calibration shows that the hard (15-50
keV) X-ray emission is brighter than previously thought and remains constant in
both the 2006 and 2008 data.
The G ratio calculated from the Fe XXV lines shows that these lines are
thermal, not photoionized, in origin. With the exception of the hard X-ray
emission, the spectra from both epochs can be fit using thermal radiation
assuming a differential emission measure based on a cooling flow model combined
with a full and partial absorber. We show that acceptable fits can be obtained
for all the data in the 1-10 keV band varying only the partial absorber. Based
on the temperature and accretion rate, the thermal emission appears to be
arising from the boundary layer between the accreting white dwarf and the
accretion disk.Comment: 7 pages, 5 figures. Accepted by the Astrophysical Journa
- …