6,423 research outputs found

### Gravitational wave detection from OJ 287 via a pulsar timing array

Blazar OJ 287 is a candidate nanoHertz (nHz) gravitational wave (GW) source.
In this article, we investigate the GWs generated by OJ 287 and their potential
detection through a pulsar timing array (PTA). First, we obtain the orbit and
the corresponding GW strain of OJ 287. During the time span of the next 10
years (2019 to 2029), the GW of OJ 287 will be active before 2021, with a peak
strain amplitude $8 \times 10^{-16}$, and then decay after that. When OJ 287 is
silent in the GW channel during 2021 to 2029, the timing residual signals of
the PTA will be dominated by the 'pulsar term' of the GW strain and this
provides an opportunity to observe this pulsar term. Furthermore, we choose 26
pulsars with white noise below 300 ns to detect the GW signal of OJ 287,
evaluating their timing residuals and signal-to-noise ratios (SNRs). The total
SNR (with a cadence of 2 weeks in the next 10 years) of the PTA ranges from 1.9
to 2.9, corresponding to a weak GW signal for the current sensitivity level.
Subsequently, we investigate the potential measurement of the parameters of OJ
287 using these pulsars. In particular, PSR J0437-4715, with a precisely
measured distance, has the potential to constrain the polarization angle with
an uncertainty below $8^{\deg}$ and this pulsar will play an important role in
future PTA observations.Comment: 12 pages, 8 figure

### Nuclear matter fourth-order symmetry energy in non-relativistic mean-field models

Based on systematic analyses of several popular non-relativistic energy
density functionals with mean-field approximation, we estimate the value of the
fourth-order symmetry energy $E_{\text{sym,4}}(\rho)$ at nuclear normal density
$\rho_0$ and its density dependence, and explore the correlation between
$E_{\text{sym,4}}(\rho_0)$ and other macroscopic quantities of nuclear matter
properties. We use the empirical values of some nuclear macroscopic quantities
to construct model parameter sets by Monte Carlo method for the conventional
Skyrme-Hartree-Fock (SHF) model, the extended Skyrme-Hartree-Fock (eSHF) model,
the Gogny-Hartree-Fock (GHF) model, and the momentum-dependent interaction
(MDI) model. The value of $E_{\text{sym,4}}(\rho_0)$ is estimated to be
$1.02\pm0.49$ MeV for the SHF model, $1.02\pm0.50$ MeV for the eSHF model,
$0.70\pm0.60$ MeV for the GHF model, and $0.74\pm0.63$ MeV for the MDI model.
Moreover, our results indicate that the density dependence of
$E_{\text{sym,4}}(\rho)$ is model dependent, especially at higher densities.
Furthermore, we find that the $E_{\text{sym},4}(\rho_0)$ has strong positive
(negative) correlation with isoscalar (isovector) nucleon effective mass
$m_{s,0}^*$ ($m_{v,0}^*$) at $\rho_0$. In particular, for the SHF and eSHF
models, the $E_{\text{sym,4}}(\rho)$ is completely determined by the isoscalar
and isovector nucleon effective masses $m_{s}^*(\rho)$ and $m_{v}^*(\rho)$, and
the analytical expression is given. In the mean-field models, the magnitude of
$E_{\text{sym,4}}(\rho_0)$ is generally less than $2$ MeV, and its density
dependence depends on models, especially at higher densities. $E_{\text{sym,4}}(\rho_0)$ is strongly correlated with $m_{s,0}^*$ and
$m_{v,0}^*$.Comment: 10 pages, 2 figures, 4 tables. Presentation improved and discussions
added. Accepted version to appear in PR

### SwipeCut: Interactive Segmentation with Diversified Seed Proposals

Interactive image segmentation algorithms rely on the user to provide
annotations as the guidance. When the task of interactive segmentation is
performed on a small touchscreen device, the requirement of providing precise
annotations could be cumbersome to the user. We design an efficient seed
proposal method that actively proposes annotation seeds for the user to label.
The user only needs to check which ones of the query seeds are inside the
region of interest (ROI). We enforce the sparsity and diversity criteria on the
selection of the query seeds. At each round of interaction the user is only
presented with a small number of informative query seeds that are far apart
from each other. As a result, we are able to derive a user friendly interaction
mechanism for annotation on small touchscreen devices. The user merely has to
swipe through on the ROI-relevant query seeds, which should be easy since those
gestures are commonly used on a touchscreen. The performance of our algorithm
is evaluated on six publicly available datasets. The evaluation results show
that our algorithm achieves high segmentation accuracy, with short response
time and less user feedback

### Vacuum and Gravitons of Relic Gravitational Waves, and Regularization of Spectrum and Energy-Momentum Tensor

The spectrum of relic gravitational wave (RGW) contains high-frequency
divergences, which should be removed. We present a systematic study of the
issue, based on the exact RGW solution that covers the five stages, from
inflation to the acceleration, each being a power law expansion. We show that
the present RGW consists of vacuum dominating at $f>10^{11}$Hz and graviton
dominating at $f<10^{11}$Hz, respectively. The gravitons are produced by the
four cosmic transitions, mostly by the inflation-reheating one. We perform
adiabatic regularization to remove vacuum divergences in three schemes: at
present, at the end of inflation, and at horizon-exit, to the 2-nd adiabatic
order for the spectrum, and the 4-th order for energy density and pressure. In
the first scheme a cutoff is needed to remove graviton divergences. We find
that all three schemes yield the spectra of a similar profile, and the
primordial spectrum defined far outside horizon during inflation is practically
unaffected. We also regularize the gauge-invariant perturbed inflaton and the
scalar curvature perturbation by the last two schemes, and find that the scalar
spectra, the tensor-to-scalar ratio, and the consistency relation remain
unchanged.Comment: 30 pages, 13 figures, accepted by Phys. Rev.

### Spatial chaos of Wang tiles with two symbols

This investigation completely classifies the spatial chaos problem in plane
edge coloring (Wang tiles) with two symbols. For a set of Wang tiles
$\mathcal{B}$, spatial chaos occurs when the spatial entropy $h(\mathcal{B})$
is positive. $\mathcal{B}$ is called a minimal cycle generator if
$\mathcal{P}(\mathcal{B})\neq\emptyset$ and
$\mathcal{P}(\mathcal{B}')=\emptyset$ whenever $\mathcal{B}'\subsetneqq
\mathcal{B}$, where $\mathcal{P}(\mathcal{B})$ is the set of all periodic
patterns on $\mathbb{Z}^{2}$ generated by $\mathcal{B}$. Given a set of Wang
tiles $\mathcal{B}$, write $\mathcal{B}=C_{1}\cup C_{2} \cup\cdots \cup C_{k}
\cup N$, where $C_{j}$, $1\leq j\leq k$, are minimal cycle generators and
$\mathcal{B}$ contains no minimal cycle generator except those contained in
$C_{1}\cup C_{2} \cup\cdots \cup C_{k}$. Then, the positivity of spatial
entropy $h(\mathcal{B})$ is completely determined by $C_{1}\cup C_{2}
\cup\cdots \cup C_{k}$.
Furthermore, there are 39 equivalent classes of marginal positive-entropy
(MPE) sets of Wang tiles and 18 equivalent classes of saturated zero-entropy
(SZE) sets of Wang tiles. For a set of Wang tiles $\mathcal{B}$,
$h(\mathcal{B})$ is positive if and only if $\mathcal{B}$ contains an MPE set,
and $h(\mathcal{B})$ is zero if and only if $\mathcal{B}$ is a subset of an SZE
set

### Transition between globule and stretch states of a self-attracting chain in the repulsive active particle bath

Folding and unfolding of biopolymers are often manipulated in experiment by
tuning pH, temperature, single-molecule force or shear field. Here we carry out
Brownian dynamics simulations to explore the behavior of a single
self-attracting chain in the suspension of self-propelling particles (SPPs). As
the propelling force increases, globule-stretch (G-S) transition of the chain
happens due to the enhanced disturbance from SPPs. Two distinct mechanisms of
the transition in the limits of low and high rotational diffusion rates of SPPs
have been observed: shear effect at low rate and collision-induced melting at
high rate. The G-S and S-G (stretch-globule) curves form hysteresis loop at low
rate, while they merge at high rate. Besides, we find two competing effects
result in the non-monotonic dependence of the G-S transition on the SPP density
at low rate. Our results suggest an alternative approach to manipulating the
folding and unfolding of (bio)polymers by utilizing active agents.Comment: 7pages, 4figure

### Improved Deterministic N-To-One Joint Remote Preparation of an Arbitrary Qubit via EPR Pairs

Recently, Bich et al. (Int. J. Theor. Phys. 51: 2272, 2012) proposed two
deterministic joint remote state preparation (JRSP) protocols of an arbitrary
single-qubit state: one is for two preparers to remotely prepare for a receiver
by using two Einstein-Podolsky-Rosen (ERP) pairs; the other is its generalized
form in the case of arbitrary N>2 preparers via N ERP pairs. In this paper,
Through reviewing and analyzing Bich et al.'s second protocols with N>2
preparers, we find that the success probability P_{suc}=1/4 < 1. In order to
solve the problem, we firstly constructed two sets of projective measurement
bases: the real-coefficient basis and the complex-coefficient one, and further
proposed an improved deterministic N-to-one JRSP protocol for an arbitrary
single-qubit state with unit success probability (i.e, P_{suc}=1). Morever, our
protocol is also flexible and convenient, and it can be used in a practical
network.Comment: 13 pages, 2 figures, two table

### Cryptanalysis and improvement of the quantum private comparison protocol based on Bell entangled states

Recently, Liu et al. [Commun. Theor. Phys. 57, 583, 2012] proposed a quantum
private comparison protocol based on entanglement swapping of Bell states,
which aims to securely compare the equality of two participants' information
with the help of a semi-honest third party (TP). However, this study points out
there is a fatal loophole in this protocol, i.e., TP can obtain all of the two
participants secret inputs without being detected through making a specific
Bell-basis measurement. To fix the problem, a simple solution, which uses
one-time eavesdropper checking with decoy photons instead of twice eavesdropper
checking with Bell states, is demonstrated. Compared with the original
protocol, it also reduces the Bell states consumption and simplifies the steps
in the protocol.Comment: 9 pages, 1 figur

### Primordial Magnetic Field from Gravitationally Coupled Electrodynamics in Bouncing Scenario

We in this paper study the generation of primordial magnetic field (PMF) in
the non-singular bouncing scenario, through the coupling of the electromagnetic
field to gravity. We adopt an electrodynamic model with a coupling coefficient
as a function of the scale factor $a$, i.e. $f=1+(a/a_\star)^{-n}$, with
$a_\star$ and $n>0$ being constants. The result implies that in this mechanism,
the power spectrum of PMF today is always blue tilted on large scales from $1$
Mpc to the Hubble length, and the observational constraints favor the
ekpyrotic-bounce scenario. Furthermore, the back reaction of the energy density
of PMF at the bouncing point yields theoretical constraints on the bouncing
model

### BCS-like critical fluctuations with limited overlap of Cooper pairs in FeSe

In conventional superconductors, very narrow superconducting fluctuation
regions are observed above $T_c$ because of the strong overlapping of Cooper
pairs in a coherence volume. In the bulk form of iron chalcogenide
superconductor FeSe, it is argued that the system may locate in the crossover
region of BCS to BEC, indicating a strong superconducting fluctuation. In this
respect, we have carried out measurements of magnetization, specific heat and
Nernst effect on FeSe single crystals in order to investigate the
superconducting fluctuation effect near $T_c$. The region of diamagnetization
induced by superconducting fluctuation seems very narrow above $T_c$. The
crossing point of temperature dependent magnetization curves measured at
different magnetic fields, which appears in many systems of cuprate
superconductors and is regarded as indication of strong critical fluctuation,
is however absent. The magnetization data can be scaled based on the
Ginzburg-Landau fluctuation theory for a quasi-two-dimensional system, but the
scaling result cannot be described by the theoretical function of the
fluctuation theory because of the limited fluctuation regions. The specific
heat jump near $T_c$ is rather sharp without the trace of strong
superconducting fluctuation. This is also supported by the Nernst effect
measurements which indicate a very limited region for vortex motion above
$T_c$. Associated with very small value of Ginzburg number and further
analyses, we conclude that the superconducting fluctuation is very weak above
$T_c$ in this material. Our results are strongly against the picture of
significant phase fluctuation in FeSe single crystals, although the system has
a very limited overlapping of Cooper pairs in the coherence volume. This
dichotomy provides new insights into the superconducting mechanism when the
system is with a dilute superfluid density.Comment: 11 pages, 6 figure

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