5,641 research outputs found
Exploring the deviation of cosmological constant by a generalized pressure dark energy model
We bring forward a generalized pressure dark energy (GPDE) model to explore
the evolution of the universe. This model has covered three common pressure
parameterization types and can be reconstructed as quintessence and phantom
scalar fields, respectively. We adopt the cosmic chronometer (CC) datasets to
constrain the parameters. The results show that the inferred late-universe
parameters of the GPDE model are (within ): The present value of
Hubble constant km s Mpc; Matter
density parameter , and the
universe bias towards quintessence. While when we combine CC data and the
data from Planck, the constraint implies that our model matches the
CDM model nicely. Then we perform dynamic analysis on the GPDE model
and find that there is an attractor or a saddle point in the system
corresponding to the different values of parameters. Finally, we discuss the
ultimate fate of the universe under the phantom scenario in the GPDE model. It
is demonstrated that three cases of pseudo rip, little rip, and big rip are all
possible.Comment: 11 pages, 5 figures, 5 table
Periodic Radio Variability in NRAO 530: Phase Dispersion Minimization Analysis
In this paper, a periodicity analysis of the radio light curves of the blazar
NRAO 530 at 14.5, 8.0, and 4.8 GHz is presented employing an improved Phase
Dispersion Minimization (PDM) technique. The result, which shows two persistent
periodic components of and years at all three frequencies,
is consistent with the results obtained with the Lomb-Scargle periodogram and
weighted wavelet Z-transform algorithms. The reliability of the derived
periodicities is confirmed by the Monte Carlo numerical simulations which show
a high statistical confidence. (Quasi-)Periodic fluctuations of the radio
luminosity of NRAO 530 might be associated with the oscillations of the
accretion disk triggered by hydrodynamic instabilities of the accreted flow.
\keywords{methods: statistical -- galaxies: active -- galaxies: quasar:
individual: NRAO 530}Comment: 8 pages, 5 figures, accepted by RA
MIMO Channel Information Feedback Using Deep Recurrent Network
In a multiple-input multiple-output (MIMO) system, the availability of
channel state information (CSI) at the transmitter is essential for performance
improvement. Recent convolutional neural network (NN) based techniques show
competitive ability in realizing CSI compression and feedback. By introducing a
new NN architecture, we enhance the accuracy of quantized CSI feedback in MIMO
communications. The proposed NN architecture invokes a module named long
short-term memory (LSTM) which admits the NN to benefit from exploiting
temporal and frequency correlations of wireless channels. Compromising
performance with complexity, we further modify the NN architecture with a
significantly reduced number of parameters to be trained. Finally, experiments
show that the proposed NN architectures achieve better performance in terms of
both CSI compression and recovery accuracy
Geometric deformation and redshift structure caused by plane gravitational waves
The curved spacetime induced by gravitational waves can give rise to visual
effects such as geometric distortions and redshift structures in the observed
image. By establishing a mapping from the object's surface coordinates to the
observer's screen coordinates, we study these effects in the context of plane
gravitational waves. The simulation reveals that the image of an object doesn't
merely seem compressed or stretched, but rather appears twisted and wobbled.
Furthermore, the redshift structure on the object's surface appears to rotate
as a whole. This outcome offers an intuitive depiction of the lensing effect in
plane gravitational wave spacetimes.Comment: 6 pages 2 columns, 3 figure
Image of Kerr-de Sitter black holes illuminated by equatorial thin accretion disks
To explore the influence of the cosmological constant on black hole images,
we have developed a comprehensive analytical method for simulating images of
Kerr-de Sitter black holes illuminated by equatorial thin accretion disks.
Through the application of explicit equations, we simulate images of Kerr-de
Sitter black holes illuminated by both prograde and retrograde accretion disks,
examining the impact of the cosmological constant on their characteristic
curves, relative sizes, and observed intensities. Our findings reveal that, in
comparison to Kerr black holes, the cosmological constant not only diminishes
the relative size of a black hole but also amplifies its luminosity. Moreover,
an observer's relative position in the universe () can influence both
the relative size and luminosity of a black hole, where is the distance
from the observer to the black hole, is the cosmological horizon
determined by the value of the cosmological constant .Comment: 17 pages, 10 figures, refs added, typos correcte
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