10,863 research outputs found
Enhanced off-center stellar tidal disruptions by supermassive black holes in merging galaxies
Off-center stellar tidal disruption flares have been suggested to be a
powerful probe of recoiling supermassive black holes (SMBHs) out of galactic
centers due to anisotropic gravitational wave radiations. However, off-center
tidal flares can also be produced by SMBHs in merging galaxies. In this paper,
we computed the tidal flare rates by dual SMBHs in two merging galaxies before
the SMBHs become self-gravitationally bounded. We employ an analytical model to
calculate the tidal loss-cone feeding rates for both SMBHs, taking into account
two-body relaxation of stars, tidal perturbations by the companion galaxy, and
chaotic stellar orbits in triaxial gravitational potential. We show that for
typical SMBHs with mass 10^7 M_\sun, the loss-cone feeding rates are enhanced
by mergers up to \Gamma ~ 10^{-2} yr^{-1}, about two order of magnitude higher
than those by single SMBHs in isolated galaxies and about four orders of
magnitude higher than those by recoiling SMBHs. The enhancements are mainly due
to tidal perturbations by the companion galaxy. We suggest that off-center
tidal flares are overwhelmed by those from merging galaxies, making the
identification of recoiling SMBHs challenging. Based on the calculated rates,
we estimate the relative contributions of tidal flare events by single, binary,
and dual SMBH systems during cosmic time. Our calculations show that the
off-center tidal disruption flares by un-bound SMBHs in merging galaxies
contribute a fraction comparable to that by single SMBHs in isolated galaxies.
We conclude that off-center tidal disruptions are powerful tracers of the
merging history of galaxies and SMBHs.Comment: 17 pages, 8 figures; Typos are corrected to match the published
version in Ap
Low-complexity Noncoherent Iterative CPM Demodulator for FH Communication
In this paper, we investigate the noncoherent iterative demodulation of coded continuous phase modulation (CPM) in frequency hopped (FH) systems. In this field, one important problem is that the complexity of the optimal demodulator is prohibitive unless the number of symbols per hop duration is very small. To solve this problem, we propose a novel demodulator, which reduces the complexity by applying phase quantization and exploiting the phase rotational invariance property of CPM signals. As shown by computational complexity analysis and numerical results, the proposed demodulator approaches the performance of the optimal demodulator, and provides considerable performance improvement over the existing solutions with the same computational complexity
Holographic thermalization with a chemical potential in Gauss-Bonnet gravity
Holographic thermalization is studied in the framework of
Einstein-Maxwell-Gauss-Bonnet gravity. We use the two-point correlation
function and expectation value of Wilson loop, which are dual to the
renormalized geodesic length and minimal area surface in the bulk, to probe the
thermalization. The numeric result shows that larger the Gauss-Bonnet
coefficient is, shorter the thermalization time is, and larger the charge is,
longer the thermalization time is, which implies that the Gauss-Bonnet
coefficient can accelerate the thermalization while the charge has an opposite
effect. In addition, we obtain the functions with respect to the thermalization
time for both the thermalization probes at a fixed charge and Gauss-Bonnet
coefficient, and on the basis of these functions, we obtain the thermalization
velocity, which shows that the thermalization process is non-monotonic. At the
middle and later periods of the thermalization process, we find that there is a
phase transition point, which divides the thermalization into an acceleration
phase and a deceleration phase. We also study the effect of the charge and
Gauss-Bonnet coefficient on the phase transition point.Comment: 23 pages, many figures,footnote 4 is modified. arXiv admin note:
substantial text overlap with arXiv:1305.484
Holographic thermalization in noncommutative geometry
Gravitational collapse of a shell of dust in noncommutative geometry is
probed by the renormalized geodesic length, which is dual to probe the
thermalization by the two-point correlation function in the dual conformal
field theory. We find that larger the noncommutative parameter is, longer the
thermalization time is, which implies that the large noncommutative parameter
delays the thermalization process. We also investigate how the noncommutative
parameter affects the thermalization velocity and thermalization acceleration.Comment: some materials have been delete
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D-optimal designs formulti-response linear mixed models
Linear mixed models have become popular in many statistical applications duringrecent years. However design issues for multi-response linear mixed models are rarelydiscussed. Themain purpose of this paper is to investigate D-optimal designs formultiresponselinear mixed models. We provide two equivalence theorems to characterizethe optimal designs for the estimation of the fixed effects and the prediction of randomeffects, respectively. Two examples of the D-optimal designs formulti-response linearmixed models are given for illustration
Tidal stellar disruptions by massive black hole pairs: II. Decaying binaries
Tidal stellar disruptions have traditionally been discussed as a probe of the
single, massive black holes (MBHs) that are dormant in the nuclei of galaxies.
In Chen et al. (2009), we used numerical scattering experiments to show that
three-body interactions between bound stars in a stellar cusp and a
non-evolving "hard" MBH binary will also produce a burst of tidal disruptions,
caused by a combination of the secular "Kozai effect" and by close resonant
encounters with the secondary hole. Here we derive basic analytical scalings of
the stellar disruption rates with the system parameters, assess the relative
importance of the Kozai and resonant encounter mechanisms as a function of
time, discuss the impact of general relativistic (GR) and extended stellar cusp
effects, and develop a hybrid model to self-consistently follow the shrinking
of an MBH binary in a stellar background, including slingshot ejections and
tidal disruptions. In the case of a fiducial binary with primary hole mass
M_1=10^7\msun and mass ratio q=M_2/M_1=1/81, embedded in an isothermal cusp, we
derive a stellar disruption rate \dot{N_*} ~ 0.2/yr lasting ~ 3X10^5 yr. This
rate is 3 orders of magnitude larger than the corresponding value for a single
MBH fed by two-body relaxation, confirming our previous findings. For q<<0.01,
the Kozai/chaotic effect could be quenched due to GR/cusp effects by an order
of magnitude, but even in this case the stellar-disruption rate is still two
orders of magnitude larger than that given by standard relaxation processes
around a single MBH. Our results suggest that >~10% of the tidal-disruption
events may originate in MBH binaries.Comment: 16 pages, 20 figures, accepted for publication in the Astrophysical
Journa
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