arXiv subjects

Hao Xu

Publications and source records attributed to Hao Xu.

At least 433 records · Page 24Linked to original sources

arXiv2019

Interactions between two heavy mesons within heavy meson chiral effective field theory

We have studied the interactions between two heavy mesons ($D^{(*)}$-$D^{(*)}$, $\bar D^{(*)}$-$\bar D^{(*)}$, $B^{(*)}$-$B^{(*)}$, or $\bar B^{(*)}$-$\bar B^{(*)}$) within heavy meson chiral effective field theory and investigated possible molecular states. The effective potentials are obtained with Weinberg's scheme up to one-loop level. At the leading order, four body contact interactions and one pion exchange contributions are considered. In addition to two pion exchange diagrams, we include the one-loop chiral corrections to contact terms and one pion exchange diagrams at the next-to-leading order. The effective potentials both in momentum space and coordinate space are investigated and discussed extensively. The possible molecular states are also studied and the binding energies are provided by solving the Schrodinger equation. The results will be helpful for the experimental search for the doubly-heavy molecular states.

hep-ph↗

arXiv2019

D2D-LSTM based Prediction of the D2D Diffusion Path in Mobile Social Networks

Recently, how to expand data transmission to reduce cell data and repeated cell transmission has received more and more research attention. In mobile social networks, content popularity prediction has always been an important part of traffic offloading and expanding data dissemination. However, current mainstream content popularity prediction methods only use the number of downloads and shares or the distribution of user interests, which do not consider important time and geographic location information in mobile social networks, and all of data is from OSN which is not same as MSN. In this work, we propose D2D Long Short-Term Memory (D2D-LSTM), a deep neural network based on LSTM, which is designed to predict a complete D2D diffusion path. Our work is the first attempt in the world to use real data of MSN to predict diffusion path with deep neural networks which conforms to the D2D structure. Compared to linear sequence networks, only learn users' social features without time distribution or GPS distribution and files' content features, our model can predict the propagation path more accurately (up to 85.858\%) and can reach convergence faster (less than 100 steps) because of the neural network that conforms to the D2D structure and combines user social features and files features. Moreover, we can simulate generating a D2D propagation tree. After experiment and comparison, it is found to be very similar to the ground-truth trees. Finally, we define a user prototype refinement that can more accurately describe the propagation sharing habits of a prototype user (including content preferences, time preferences, and geographic location preferences), and experimentally validate the predictions when the user prototype is added to 1000 classes, it is almost identical to the 50 categories.

cs.SI↗

arXiv2019

EU H2020 Gauss project. Geo-Fencing Software System

The Geofencing system is the key to operate the Unmanned Aerial Vehicle (UAV) within the safe and appropriate zone to avoid public concerns and other privacy issues. The system is designed to keep the UAV away from geofenced obstacles using the onboard GNSS and IMU location. The Geofencing system is part of the H2020 GAUSS project and facilities other subsystems, for instance, to support the command and control link, which is the security measure to secure the UAV from hijacking and signal spoofing. The regulatory authorities expressed the concern of having UAVs flying in the no-fly zone and causing troubles from offending private privacy to hazards at airport airspace. Hence the geofence system shall provide guidance message, which enables the UAV to evacuate from no-fly-zone, based on real-time updated location. This thesis aims to first illustrate the generation of geofence and then apply the geofence system on UAV operation. This application enables UAV to fly in the designated area without human intervention. The project is built with JAVA using GIS-enabled Database Management System and Open Soured Map data powered by OpenStreetMap and OS map. This method has been tested by simulations which had results of high accuracy.

cs.OH↗

arXiv2019

Black hole evaporation in Lovelock gravity with diverse dimensions

We investigate the black hole evaporation process in Lovelock gravity with diverse dimensions. By selecting the appropriate coefficients, the space-time solutions can possess a unique AdS vacuum with a fixed cosmological constant $Λ=-\frac{(d-1)(d-2)}{2\ell^{2}}$. The black hole solutions can be divided into two cases: $d>2k+1$ and $d=2k+1$. In the case of $d>2k+1$, the black hole is in an analogy with the Schwarzschild AdS black hole, and the life time is bounded by a time of the order of $\ell^{d-2k+1}$, which reduces Page's result on the Einstein gravity in $k=1$. In the case of $d=2k+1$, the black hole resembles the three dimensional black hole. The black hole vacuum corresponds to $T=0$, so the black hole will take infinite time to evaporate away for any initial states, which obeys the third law of thermodynamics. In the asymptotically flat limit $\ell\rightarrow \infty$, the system reduces to the pure Lovelock gravity that only possesses the highest $k$-th order term. For a initial mass $M_0$, the life time of the black hole is in the order of $M_0^{\frac{d-2k+1}{d-2k-1}}$.

gr-qc↗

arXiv2019

Closed Loop Load Model Identification Using Small Disturbance Data

Load model identification using small disturbance data is studied. It is proved that the individual load to be identified and the rest of the system forms a closed-loop system. Then, the impacts of disturbances entering the feedforward channel (internal disturbance) and feedback channel (external disturbance) on relationship between load inputs and outputs are examined analytically. It is found out that relationship between load inputs and outputs is not determined by load itself (feedforward transfer function) only, but also related with equivalent network matrix (feedback transfer function). Thus, load identification is closed loop identification essentially and the impact of closed loop identification cannot be neglected when using small disturbance data to identify load parameters. Closed loop load model identification can be solved by prediction error method (PEM). Implementation of PEM based on a Kalman filtering formulation is detailed. Identification results using simulated data demonstrates the correctness and significance of theoretical analysis.

eess.SY↗

arXiv2019

Adaptive Intelligent Secondary Control of Microgrids Using a Biologically-Inspired Reinforcement Learning

In this paper, a biologically-inspired adaptive intelligent secondary controller is developed for microgrids to tackle system dynamics uncertainties, faults, and/or disturbances. The developed adaptive biologically-inspired controller adopts a novel computational model of emotional learning in mammalian limbic system. The learning capability of the proposed biologically-inspired intelligent controller makes it a promising approach to deal with the power system non-linear and volatile dynamics without increasing the controller complexity, and maintain the voltage and frequency stabilities by using an efficient reference tracking mechanism. The performance of the proposed intelligent secondary controller is validated in terms of the voltage and frequency absolute errors in the simulated microgrid. Simulation results highlight the efficiency and robustness of the proposed intelligent controller under the fault conditions and different system uncertainties compared to other benchmark controllers.

eess.SY↗

arXiv2019

A Neural-Network-Based Optimal Control of Ultra-Capacitors with System Uncertainties

In this paper, a neural-network (NN)-based online optimal control method (NN-OPT) is proposed for ultra-capacitors (UCs) energy storage system (ESS) in hybrid AC/DC microgrids involving multiple distributed generations (e.g., Photovoltaic (PV) system, battery storage, diesel generator). Conventional control strategies usually produce large disturbances to buses during charging and discharging (C&D) processes of UCs, which significantly degrades the power quality and system performance, especially under fast C&D modes. Therefore, the optimal control theory is adopted to optimize the C&D profile as well as to suppress the disturbances caused by UCs implementation. Specifically, an NN-based intelligent algorithm is developed to learn the optimal control policy for bidirectional-converter-interfaced UCs. The inaccuracies of system modeling are also considered in the control design. Since the designed NN-OPT method is decentralized that only requires the local measurements, plug & play of UCs can be easily realized with minimal communication efforts. In addition, the PV system is under the maximum power point tracking (MPPT) control to extract the maximum benefit. Both islanded and grid-tied modes are considered during the controller design. Extensive case studies have been conducted to evaluate the effectiveness of the proposed method.

math.OC↗

arXiv2019

Black hole evaporation in Conformal (Weyl) gravity

In this work, we explore all possible scenarios in the evaporation process of a spherical neutral AdS black hole in four-dimensional conformal gravity, where the equations of states are branched. In one branch, the final states correspond to the extremal black hole where the total decay time is divergent given any initial mass. In the other branch, the black holes always evaporate completely with in a finite time; the total decay time depends linearly on the AdS radius, when the mass is taken to be infinity.

gr-qc↗

arXiv2019

Singular solutions of linear problems with fractional Laplacian

In this paper, we study singular solutions of linear problems with fractional Laplacian. First, we establish Bôcher type theorems on a punctured ball via distributional approach. Then, we develop a few interesting maximum principles on a punctured ball. Our distributional approach only requires the basic local L-1 integrability. We also introduce several simple and useful lemmas, which enable us to unify the treatments for both Laplacian and fractional Laplacian. These theorems, lemmas and the methods introduced here can be adapted and applied in other situations.

math.AP↗

arXiv2019

Formation of massive black holes in rapidly growing pre-galactic gas clouds

The origin of supermassive black holes (SMBHs) that inhabit the centers of massive galaxies is largely unconstrained. Remnants from supermassive stars (SMSs) with masses around 10,000 solar masses provide the ideal seed candidates, known as direct collapse black holes. However, their very existence and formation environment in the early Universe are still under debate, with their supposed rarity further exacerbating the problem of modeling their ab-initio formation. SMS models have shown that rapid collapse, with an infall rate above a critical value, in metal-free haloes is a requirement for the formation of a proto-stellar core which will then form an SMS. Using a radiation hydrodynamics simulation of early galaxy formation, we show the natural emergence of metal-free haloes both massive enough, and with sufficiently high infall rates, to form an SMS. We find that haloes that are exposed to both a Lyman-Werner intensity of J_LW ~ 3 J_21 and that undergo at least one period of rapid growth early in their evolution are ideal cradles for SMS formation. This rapid growth induces substantial dynamical heating, amplifying the existing Lyman-Werner suppression originating from a group of young galaxies 20 kiloparsecs away. Our results strongly indicate that structure formation dynamics, rather than a critical Lyman-Werner (LW) flux, may be the main driver of massive black hole formation in the early Universe. We find that massive black hole seeds may be much more common in overdense regions of the early Universe than previously considered with a comoving number density up to 10^-3 Mpc^-3.

astro-ph.GA↗

arXiv2019

Productions of $f_{1}(1420)$ in pion and kaon induced reactions

The $f_{1}(1420)$ productions via pion and kaon induced reactions on a proton target are investigated in an effective Lagrangian approach. Two treatments of the $t$-channel Born term, the Feynman model and the Regge model, are introduced to calculate the total and differential cross sections of the $π^{-}p\rightarrow f_{1}(1420)n$ and $K^{-}p\rightarrow f_{1}(1420)Λ$ reactions. The numerical results indicate that the experimental data of the total cross section of the $π^{-}p\rightarrow f_{1}(1420)n$ reaction can be reproduced in both the Feynman and the Regge models. Based on the parameters determined in the pion induced reaction, the cross sections of the $K^{-}p\rightarrow f_{1}(1420)Λ$ reaction, about which there is little data found in the literature, are predicted in the same beam momentum range. It is found that the line shapes of the total cross section obtained in a kaon induced reaction with two treatments are quite different. The cross sections for both reactions are at an order of magnitude of $μ$b, or larger, at a beam momenta up to 10 GeV/c. The differential cross sections for both pion and kaon induced reactions are also present. It is found that in the Regge model, the $t$ channel provides a sharp increase at extreme forward angles. The results suggest that the experimental study of the $f_1(1420)$ in the kaon induced reaction on a proton target is as promising as in the pion induced reaction. Such an experimental measurement is also very helpful to clarify the production mechanism of the $f_1(1420)$.

hep-ph↗

arXiv2018

Fully Coupled Simulation of Cosmic Reionization. III. Stochastic Early Reionization by the Smallest Galaxies

Previously we identified a new class of early galaxy that we estimate contributes up to 30\% of the ionizing photons responsible for reionization. These are low mass halos in the range $M_h =10^{6.5}-10^{8} M_{\odot}$ that have been chemically enriched by supernova ejecta from prior Pop III star formation. Despite their low star formation rates, these Metal Cooling halos (MCs) are significant sources of ionizing radiation, especially at the onset of reionization, due to their high number density and ionizing escape fractions. Here we present a fully-coupled radiation hydrodynamic simulation of reionization that includes these MCs as well the more massive hydrogen atomic line cooling halos. Our method is novel: we perform halo finding inline with the radiation hydrodynamical simulation, and assign escaping ionizing fluxes to halos using a probability distribution function (PDF) measured from the galaxy-resolving Renaissance Simulations. The PDF captures the mass dependence of the ionizing escape fraction as well as the probability that a halo is actively forming stars. With MCs, reionization starts earlier than if only halos of $10^8 M_{\odot}$ and above are included, however the redshift when reionization completes is only marginally affected as this is driven by more massive galaxies. Because star formation is intermittent in MCs, the earliest phase of reionization exhibits a stochastic nature, with small H II regions forming and recombining. Only later, once halos of mass $\sim 10^9 M_{\odot}$ and above begin to dominate the ionizing emissivity, does reionization proceed smoothly in the usual manner deduced from previous studies. This occurs at $z\approx 10$ in our simulation.

astro-ph.CO↗

arXiv2018

Improving Wireless Physical Layer Security via D2D Communication

This paper investigates the physical layer security issue of a device-to-device (D2D) underlaid cellular system with a multi-antenna base station (BS) and a multi-antenna eavesdropper. To investigate the potential of D2D communication in improving network security, the conventional network without D2D users (DUs) is first considered. It is shown that the problem of maximizing the sum secrecy rate (SR) of cellular users (CUs) for this special case can be transformed to an assignment problem and optimally solved. Then, a D2D underlaid network is considered. Since the joint optimization of resource block (RB) allocation, CU-DU matching and power control is a mixed integer programming, the problem is difficult to handle. Hence, the RB assignment process is first conducted by ignoring D2D communication, and an iterative algorithm is then proposed to solve the remaining problem. Simulation results show that the sum SR of CUs can be greatly increased by D2D communication, and compared with the existing schemes, a better secrecy performance can be obtained by the proposed algorithms.

cs.IT↗

arXiv2018

On the thermodynamic phase structure of conformal gravity

The solutions of the Einstein equation are a subset of the solutions of conformal (Weyl) gravity, but the difference from the action means that the black hole thermodynamics of the two gravity theories would be different. In this paper we explore the thermodynamic phase structure for the conformal gravity in the four-dimensional AdS space-time. Special emphasis is put on the dependence on the parameter $c_1$ in the linear-$r$ term in the metric. The thermodynamic phase structure of the conformal gravity is very rich, including two branches of equations of states, negative thermodynamic volume, zeroth-order phase transition, and Hawking-Page like phase transition.

gr-qc↗

arXiv2018

National PM2.5 and NO2 Exposure Models for China Based on Land Use Regression, Satellite Measurements, and Universal Kriging

Outdoor air pollution is a major killer worldwide and the fourth largest contributor to the burden of disease in China. China is the most populous country in the world and also has the largest number of air pollution deaths per year, yet the spatial resolution of existing national air pollution estimates for China is generally relatively low. We address this knowledge gap by developing and evaluating national empirical models for China incorporating land-use regression (LUR), satellite measurements, and universal kriging (UK). We test the resulting models in several ways, including (1) comparing models developed using forward stepwise regression vs. partial least squares (PLS) regression, (2) comparing models developed with and without satellite measurements, and with and without UK, and (3) 10-fold cross-validation (CV), leave-one-province-out(LOPO) CV, and leave-one-city-out(LOCO) CV. Satellite data and kriging are complementary in making predictions more accurate: kriging improved the models in well-sampled areas; satellite data substantially improved performance at locations far away from monitors. Stepwise forward selection performs similarly to PLS in 10-fold CV, but better than PLS in LOPO-CV. Our best models employ forward selection and UK, with 10-fold CV R2 of 0.89 (for both 2014 and 2015) for PM2.5 and of 0.73 (year-2014) and 0.78 (year-2015) for NO2. Population-weighted concentrations during 2014-2015 decreased for PM2.5 (58.7 μg/m3 to 52.3 μg/m3) and NO2 (29.6 μg/m3 to 26.8 μg/m3). We produced the first high resolution national LUR models for annual-average concentrations in China. Models were applied on 1 km grid to support future research. In 2015, more than 80% of the Chinese population lived in areas that exceed the Chinese national PM2.5 standard, 35 μg/m3. Results here will be publicly available and may be useful for environmental health research.

stat.AP↗

arXiv2018

Performance Analysis of User-centric Virtual Cell Dense Networks over mmWave Channels

This paper analyzes the ergodic capacity of a user-centric virtual cell (VC) dense network, where multiple access points (APs) form a VC for each user equipment (UE) and transmit data cooperatively over millimeter wave (mmWave) channels. Different from traditional microwave radio communications, blockage phenomena have an important effect on mmWave transmissions. Accordingly, we adopt a distance-dependent line-of-sight (LOS) probability function and model the locations of the LOS and non-line-of-sight (NLOS) APs as two independent non-homogeneous Poisson point processes (PPP). Invoking this model in a VC dense network, new expressions are derived for the downlink ergodic capacity, accounting for: blockage, small-scale fading and AP cooperation. In particular, we compare the ergodic capacity for different types of fading distributions, including Rayleigh and Nakagami. Numerical results validate our analytical expressions and show that AP cooperation can provide notable capacity gain, especially in low-AP-density regions.

cs.IT↗

arXiv2018

Design and Evaluation of LAr Trigger Digitizer Board in the ATLAS Phase-I Upgrade

The LHC upgrade is planned to enhance the instantaneous luminosity during Run 3 from 2021 through 2023. The Phase-I upgrade of the trigger readout electronics for the ATLAS Liquid Argon (LAr) Calorimeters will be installed during the second long shutdown of LHC in 2019-2020. In this upgrade, the so-called super cells are introduced to provide higher granularity, higher resolution and longitudinal shower shape information from the LAr calorimeters to the level-1 trigger processors. A new LAr Trigger Digitizer Board (LTDB) will manipulate and digitize 320 channels of super cell signals, and transmit it via 40 fiber optical links to the back end where data are further processed and transmitted to the trigger processors. Five pairs of bidirectional GBT links are used for slow control from the Front-end LInks eXchange (FELIX) in the ATLAS TDAQ system. LTDB also outputs 64 summed analog signals to the current Tower Builder Board via the new baseplane. A test system is developed to test all functions of the LTDB and carry out the performance measurement. A back end PCIe card is designed which has the circuit to interface to the ATLAS trigger, time and control system. It can control the generation of injection signals to the LTDB for performance test. It also configures and calibrate all ASICs on the LTDB.

physics.ins-det↗

arXiv2018

Minimal surfaces in AdS C-metric

We shed some light on the field theory interpretation of C-metric by investigating the minimal surfaces which are homologous to the given boundary regions. The accelerating black holes change the asymptotic structure of the space-time. We focus on the geometry features of the minimal surface and study how deep it reaches into the bulk. The regularized area of the minimal surface is not well defined and we introduce a new quantity $D(m,θ_0)$, defined as the minimal surface divided by the area of the given boundary region, to study the system.

hep-th↗