Modeling the IDV emissions of the BL Lac Objects with a Langevin type stochastic differential equation

In this paper, we introduce a simplified model for explaining the observations of the optical intraday variability (IDV) of the BL Lac Objects. We assume that the source of the IDV are the stochastic oscillations of an accretion disk around a supermassive black hole. The Stochastic Fluctuations on the vertical direction of the accretion disk are described by using a Langevin type equation with a damping term and a random, white noise type force. Furthermore, the preliminary numerical simulation results are presented, which are based on the numerical analysis of the Langevin stochastic differential equation.Comment: 4 pages, 4 figures, accepted for publication in J. Astrophys. Ast

Exploiting wireless interference in heterogeneous networks

In this work, the possibility of interference exploitation (IE) in heterogeneous networks is investigated. Based on the shared channel state information (CSI) and the transmitted data among the coordinated heterogeneous base stations (BS)s, we first formulate an IE-based coordinated multi-point (CoMP) scheme, which is able to utilize inter-cell interference as well as multiuser interference as constructive elements. Considering the effect of imperfect CSI at the BSs, we then minimize the transmission power consumption subject to users' statistical signal-to-interference-and-noise ratio (SINR) requirements. Simulation verifies that the proposed IE-based heterogeneous CoMP scheme significantly outperforms the benchmarks in terms of low power consumption. © 2021 SPIE

Drought events and their effects on vegetation productivity in China

Many parts of the world have experienced frequent and severe droughts during the last few decades. Most previous studies examined the effects of specific drought events on vegetation productivity. In this study, we characterized the drought events in China from 1982 to 2012 and assessed their effects on vegetation productivity inferred from satellite data. We first assessed the occurrence, spatial extent, frequency, and severity of drought using the Palmer Drought Severity Index (PDSI). We then examined the impacts of droughts on China\u27s terrestrial ecosystems using the Normalized Difference Vegetation Index (NDVI). During the period 1982–2012, China\u27s land area (%) experiencing drought showed an insignificant trend. However, the drought conditions had been more severe over most regions in northern parts of China since the end of the 1990s, indicating that droughts hit these regions more frequently due to the drier climate. The severe droughts substantially reduced annual and seasonal NDVI. The magnitude and direction of the detrended NDVI under drought stress varied with season and vegetation type. The inconsistency between the regional means of PDSI and detrended NDVI could be attributed to different responses of vegetation to drought and the timing, duration, severity, and lag effects of droughts. The negative effects of droughts on vegetation productivity were partly offset by the enhancement of plant growth resulting from factors such as lower cloudiness, warming climate, and human activities (e.g., afforestation, improved agricultural management practices)

Dynamical study of the possible molecular state X(3872) with the s-channel one gluon exchange interaction

The recently observed X(3872) resonance, which is difficult to be assigned a conventional $c\bar{c}$ charmonium state in the quark model, may be interpreted as a molecular state. Such a molecular state is a hidden flavor four quark state because of its charmonium-like quantum numbers. The s-channel one gluon exchange is an interaction which only acts in the hidden flavor multi-quark system. In this paper, we will study the X(3872) and other similiar hidden flavor molecular states in a quark model by taking into account of the s-channel one gluon exchange interaction

Secure Directional Modulation with Few-Bit Phase Shifters: Optimal and Iterative-Closed-Form Designs

In this paper, directional modulation (DM) is investigated to enhance physical layer security. Practical transmitter designs are exploited under imperfect channel state information (CSI) and hardware constraints, such as finite-resolution phase shifters (PSs) and per-antenna power budget. Tailored for the practical issues in realizing DM, a series of practical scenarios are investigated. Starting from the scenario where eavesdroppers (Eve)s’ information is completely unknown, corresponding designs are proposed to optimize legitimate users (LU)s’ receiving performance while randomizing the Eves’ received signal. When the Eves’ CSI is imperfectly known, in the second scenario, the Eves’ receiving performance is further deteriorated by imposing destructive interference to the Eves. For each scenario, three algorithms are proposed under hardware constraints and imperfect CSI, i.e. one direct-mapping algorithm suitable for high/moderate number of bits in PSs, one heuristic algorithm with improved receiving performance at the cost of complexity, and one iterative-closed-form algorithm with enhanced practicality of symbol-level based DM. Simulation demonstrates that the algorithms achieve lower symbol error rate (SER) at the LUs while significantly deteriorating the Eves’ SER, leading to an improved secrecy throughput over the benchmarks