Asymptotically Hyperbolic Metrics on Unit Ball Admitting Multiple Horizons

In this paper, we construct an asymptotically hyperbolic metric with scalar curvature -6 on unit ball $\mathbf{D}^3$, which contains multiple horizons.Comment: 11page

A Low-latency Collaborative HARQ Scheme for Control/User-plane Decoupled Railway Wireless Networks

ArticleThe recently proposed Control/User (C/U) plane decoupled railway wireless network is a promising new network architecture to meet the communication demands of both train control systems and onboard passengers by completely separating the C-plane and U-plane into different network nodes operating at different frequency bands. Although the system capacity of this network architecture can be highly increased, the forwarding latency of X3 interfaces to link the C-plane and U-plane becomes a serious concern, especially for hybrid automatic repeat request (HARQ) protocols which demand frequent interactions between the C-plane and U-plane. This concern becomes more pronounced for latency sensitive train control. To address this challenging problem, in this paper we propose a low-latency collaborative HARQ scheme. Through a newly designed collaborative transmission framework, the possible spare resources on lower frequency bands of macro cells by excluding those used by C-plane transmissions are utilized to help small cells relay erroneously received data. Compared to the conventional HARQ scheme, to reach the same transmission reliability, the proposed scheme requires fewer retransmissions on average, thereby mitigating the latency problem caused by HARQ retransmissions. Correspondingly, the channel mapping is also redesigned to conform to the proposed collaborative transmission framework. In the theoretical analysis, the expression of the average retransmission times related to the sum of independent Gamma variables is developed. Finally, simulation results show that a great decrease in the retransmission latency is gained by the proposed scheme, but at the sacrifice of few average system transmission rate

Revisiting the Gas Kinematics in SSA22 Lyman-α Blob 1 with Radiative Transfer Modeling in a Multiphase, Clumpy Medium

We present new observations of Lyman-α (Lyα) Blob 1 (LAB1) in the SSA22 protocluster region (z = 3.09) using the Keck Cosmic Web Imager (KCWI) and the Keck Multi-object Spectrometer for Infrared Exploration (MOSFIRE). By applying matched filtering to the KCWI datacube, we have created a narrow-band Lyα image and identified several prominent features. By comparing the spatial distributions and intensities of Lyα and Hβ, we find that recombination of photo-ionized HI gas followed by resonant scattering is sufficient to explain all the observed Lyα/Hβ ratios. We further decode the spatially-resolved Lyα profiles using both moment maps and Monte-Carlo radiative transfer (MCRT) modeling. By fitting a set of multiphase, 'clumpy' models to the observed Lyα profiles, we are able to reasonably constrain many parameters, namely the HI number density in the inter-clump medium (ICM), the cloud volume filling factor, the random velocity and outflow velocity of the clumps, the HI outflow velocity of the ICM and the local systemic redshift. Our model has successfully reproduced the diverse Lyα morphologies at different locations, and the main results are: (1) The observed Lyα spectra require relatively few clumps per line-of-sight as they have significant fluxes at the line center; (2) The velocity dispersion of the clumps yields a significant broadening of the spectra as observed; (3) The clump bulk outflow can also cause additional broadening if the HI in the ICM is optically thick; (4) The HI in the ICM is responsible for the absorption feature close to the Lyα line center