5,641 research outputs found

    Exploring the deviation of cosmological constant by a generalized pressure dark energy model

    Full text link
    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 1σ1\sigma): The present value of Hubble constant H0=(72.30−1.37+1.26)H_{0}=(72.30^{+1.26}_{-1.37})km s−1^{-1} Mpc−1^{-1}; Matter density parameter Ωm0=0.302−0.047+0.046\Omega_{\text{m0}}=0.302^{+0.046}_{-0.047}, and the universe bias towards quintessence. While when we combine CC data and the H0H_0 data from Planck, the constraint implies that our model matches the Λ\LambdaCDM 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

    Full text link
    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 ∼6 \sim 6 and ∼10 \sim 10 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

    Get PDF
    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

    Full text link
    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

    Full text link
    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 (r0/rCr_0/r_C) can influence both the relative size and luminosity of a black hole, where r0r_0 is the distance from the observer to the black hole, rCr_C is the cosmological horizon determined by the value of the cosmological constant Λ\Lambda.Comment: 17 pages, 10 figures, refs added, typos correcte
    • …
    corecore