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Xin Wu

Publications and source records attributed to Xin Wu.

At least 163 records · Page 9Linked to original sources
arXiv2018

The Wide Field Monitor onboard the eXTP mission

The eXTP (enhanced X-ray Timing and Polarimetry) mission is a major project of the Chinese Academy of Sciences (CAS) and China National Space Administration (CNSA) currently performing an extended phase A study and proposed for a launch by 2025 in a low-earth orbit. The eXTP scientific payload envisages a suite of instruments (Spectroscopy Focusing Array, Polarimetry Focusing Array, Large Area Detector and Wide Field Monitor) offering unprecedented simultaneous wide-band X-ray timing and polarimetry sensitivity. A large European consortium is contributing to the eXTP study and it is expected to provide key hardware elements, including a Wide Field Monitor (WFM). The WFM instrument for eXTP is based on the design originally proposed for the LOFT mission within the ESA context. The eXTP/WFM envisages a wide field X-ray monitor system in the 2-50 keV energy range, achieved through the technology of the large-area Silicon Drift Detectors. The WFM will consist of 3 pairs of coded mask cameras with a total combined Field of View (FoV) of 90x180 degrees at zero response and a source localization accuracy of ~1 arcmin. In this paper we provide an overview of the WFM instrument design, including new elements with respect to the earlier LOFT configuration, and anticipated performance.

astro-ph.IM↗
arXiv2018

In-flight energy calibration of the space-borne Compton polarimeter POLAR

POLAR is a compact wide-field space-borne detector for precise measurements of the linear polarisation of hard X-rays emitted by transient sources in the energy range from 50 keV to 500 keV. It consists of a 40$\times$40 array of plastic scintillator bars used as a detection material. The bars are grouped in 25 detector modules. The energy range sensitivity of POLAR is optimized to match with the prompt emission photons from the gamma-ray bursts (GRBs). Polarization measurements of the prompt emission would probe source geometries, emission mechanisms and magnetic structures in GRB jets. The instrument can also detect hard X-rays from solar flares and be used for precise measurement of their polarisation. POLAR was launched into a low Earth orbit on-board the Chinese space-lab TG-2 on September 15th, 2016. To achieve high accuracies in polarisation measurements it is essential to assure both before and during the flight a precise energy calibration. Such calibrations are performed with four low activity $^{22}$Na radioactive sources placed inside the instrument. Energy conversion factors are related to Compton edge positions from the collinear annihilation photons from the sources. This paper presents main principles of the in-flight calibration, describes studies of the method based on Monte Carlo simulations and its laboratory verification and finally provides some observation results based on the in-flight data analysis.

physics.ins-det↗
arXiv2018

In-Orbit Instrument Performance Study and Calibration for POLAR Polarization Measurements

POLAR is a compact space-borne detector designed to perform reliable measurements of the polarization for transient sources like Gamma-Ray Bursts in the energy range 50-500keV. The instrument works based on the Compton Scattering principle with the plastic scintillators as the main detection material along with the multi-anode photomultiplier tube. POLAR has been launched successfully onboard the Chinese space laboratory TG-2 on 15th September, 2016. In order to reliably reconstruct the polarization information a highly detailed understanding of the instrument is required for both data analysis and Monte Carlo studies. For this purpose a full study of the in-orbit performance was performed in order to obtain the instrument calibration parameters such as noise, pedestal, gain nonlinearity of the electronics, threshold, crosstalk and gain, as well as the effect of temperature on the above parameters. Furthermore the relationship between gain and high voltage of the multi-anode photomultiplier tube has been studied and the errors on all measurement values are presented. Finally the typical systematic error on polarization measurements of Gamma-Ray Bursts due to the measurement error of the calibration parameters are estimated using Monte Carlo simulations.

astro-ph.IM↗
arXiv2018

A note on spin rescalings in post-Newtonian theory

Usually, the reduced mass $μ$ is viewed as a dropped factor in $μl$ and $μh$, where $l$ and $h$ are dimensionless Lagrangian and Hamiltonian functions. However, it must be retained in post-Newtonian systems of spinning compact binaries under a set of scaling spin transformations $\mathbf{S}_i=\mathbf{s}_iGM^{2}$ because $l$ and $h$ do not keep the consistency of the orbital equations and the spin precession equations but $(μ/M) l$ and $(μ/M) h$ do. When another set of scaling spin transformations $\mathbf{S}_i=\mathbf{s}_iGμM$ are adopted, the consistency of the orbital and spin equations is kept in $l$ or $h$, and the factor $μ$ can be eliminated. In addition, there are some other interesting results as follows. The next-to-leading-order spin-orbit interaction is induced in the accelerations of the simple Lagrangian of spinning compact binaries with the Newtonian and leading-order spin-orbit contributions, and the next-to-leading-order spin-spin coupling is present in a post-Newtonian Hamiltonian that is exactly equivalent to the Lagrangian formalism. If any truncations occur in the Euler-Lagrangian equations or the Hamiltonian, then the Lagrangian and Hamiltonian formulations lose their equivalence. In fact, the Lagrangian including the accelerations with or without truncations can be chaotic for the two bodies spinning, whereas the Hamiltonian without the spin-spin term is integrable.

gr-qc↗
arXiv2018

Chaotic motion of neutral and charged particles in the magnetized Ernst-Schwarzschild spacetime

Neutral test particles around a Schwarzschild black hole immersed in an external uniform magnetic field have no interactions of electromagnetic forces, but their motions can be chaotic. This chaotic behavior is induced owing to the gravitational effect of the magnetic field leading to the nonintegrability of the magnetized Ernst-Schwarzschild spacetime geometry. In fact, chaos is strengthened typically with an increase of the energy or the magnetic field under appropriate circumstances. When these test particles have charges, the electromagnetic forces are included. As a result, the electromagnetic forces have an effect on strengthening or weakening the extent of chaos caused by the gravitational effect of the magnetic field.

gr-qc↗
arXiv2017

Offline software for the DAMPE experiment

A software system has been developed for the DArk Matter Particle Explorer (DAMPE) mission, a satellite-based experiment. The DAMPE software is mainly written in C++ and steered using Python script. This article presents an overview of the DAMPE offline software, including the major architecture design and specific implementation for simulation, calibration and reconstruction. The whole system has been successfully applied to DAMPE data analysis, based on which some results from simulation and beam test experiments are obtained and presented.

astro-ph.IM↗
arXiv2017

The e-ASTROGAM mission (exploring the extreme Universe with gamma rays in the MeV-GeV range)

e-ASTROGAM (`enhanced ASTROGAM') is a breakthrough Observatory mission dedicated to the study of the non-thermal Universe in the photon energy range from 0.3 MeV to 3 GeV. The mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with polarimetric capability. In the largely unexplored MeV-GeV domain, e-ASTROGAM will open a new window on the non-thermal Universe, making pioneering observations of the most powerful Galactic and extragalactic sources, elucidating the nature of their relativistic outflows and their effects on Galactic ecosystems. With a line sensitivity in the MeV energy range one to two orders of magnitude better than previous generation instruments, will determine the origin of key isotopes fundamental for the understanding of supernova explosion and the chemical evolution of our Galaxy. The mission will provide unique data of significant interest to a broad astronomical community, complementary to powerful observatories such as LIGO-Virgo-GEO600-KAGRA, SKA, ALMA, E-ELT, TMT, LSST, JWST, Athena, CTA, IceCube, KM3NeT, and the promise of eLISA. Keywords: High-energy gamma-ray astronomy, High-energy astrophysics, Nuclear Astrophysics, Compton and Pair creation telescope, Gamma-ray bursts, Active Galactic Nuclei, Jets, Outflows, Multiwavelength observations of the Universe, Counterparts of gravitational waves, Fermi, Dark Matter, Nucleosynthesis, Early Universe, Supernovae, Cosmic Rays, Cosmic antimatter.

astro-ph.HE↗
arXiv2017

Charge reconstruction study of the DAMPE Silicon-Tungsten Tracker with ion beams

The DArk Matter Particle Explorer (DAMPE) is one of the four satellites within Strategic Pioneer Research Program in Space Science of the Chinese Academy of Science (CAS). DAMPE can detect electrons, photons in a wide energy range (5 GeV to 10 TeV) and ions up to iron (100GeV to 100 TeV). Silicon-Tungsten Tracker (STK) is one of the four subdetectors in DAMPE, providing photon-electron conversion, track reconstruction and charge identification for ions. Ion beam test was carried out in CERN with 60GeV/u Lead primary beams. Charge reconstruction and charge resolution of STK detectors were investigated.

physics.ins-det↗
arXiv2016

Design of the readout electronics for the DAMPE Silicon Tracker detector

The Silicon Tracker (STK) is a detector of the DAMPE satellite to measure the incidence direction of high energy cosmic ray. It consists of 6 X-Y double layers of silicon micro-strip detectors with 73,728 readout channels. It's a great challenge to readout the channels and process the huge volume of data in the critical space environment. 1152 Application Specific Integrated Circuits (ASIC) and 384 ADCs are adopted to readout the detector channels. The 192 Tracker Front-end Hybrid (TFH) modules and 8 identical Tracker Readout Board (TRB) modules are designed to control and digitalize the front signals. In this paper, the design of the readout electronics for STK and its performance will be presented in detail.

physics.ins-det↗
arXiv2016

Second post-Newtonian Lagrangian dynamics of spinning compact binaries

The leading-order spin-orbit coupling is included in a post-Newtonian Lagrangian formulation of spinning compact binaries, which consists of the Newtonian term, first post-Newtonian (1PN) and 2PN non-spin terms and 2PN spin-spin coupling. This makes a 3PN spin-spin coupling occur in the derived Hamiltonian. The spin-spin couplings are mainly responsible for chaos in the Hamiltonians. However, the 3PN spin-spin Hamiltonian is small and has different signs, compared with the 2PN spin-spin Hamiltonian equivalent to the 2PN spin-spin Lagrangian. As a result, the probability of the occurrence of chaos in the Lagrangian formulation without the spin-orbit coupling is larger than that in the Lagrangian formulation with the spin-orbit coupling. Numerical evidences support the claim.

gr-qc↗
arXiv2015

A note on the equivalence of Lagrangian and Hamiltonian formulations at post-Newtonian approximations

It was claimed recently that a low order post-Newtonian (PN) Lagrangian formulation, which corresponds to the Euler-Lagrange equations up to an infinite PN order, can be identical to a PN Hamiltonian formulation at the infinite order from a theoretical point of view. This result is difficult to check because in most cases one does not know what both the Euler-Lagrange equations and the equivalent Hamiltonian are at the infinite order. However, no difficulty exists for a special 1PN Lagrangian formulation of relativistic circular restricted three-body problem, where both the Euler-Lagrange equations and the equivalent Hamiltonian not only are expanded to all PN orders but also have converged functions. Consequently, the analytical evidence supports this claim. As far as numerical evidences are concerned, the Hamiltonian equivalent to the Euler-Lagrange equations for the lower order Lagrangian requires that they both be only at higher enough finite orders.

physics.class-ph↗
arXiv2015

Modern middleware for the data acquisition of the Cherenkov Telescope Array

The data acquisition system (DAQ) of the future Cherenkov Telescope Array (CTA) must be ef- ficient, modular and robust to be able to cope with the very large data rate of up to 550 Gbps coming from many telescopes with different characteristics. The use of modern middleware, namely ZeroMQ and Protocol Buffers, can help to achieve these goals while keeping the development effort to a reasonable level. Protocol Buffers are used as an on-line data for- mat, while ZeroMQ is employed to communicate between processes. The DAQ will be controlled and monitored by the Alma Common Software (ACS). Protocol Buffers from Google are a way to define high-level data structures through an in- terface description language (IDL) and a meta-compiler. ZeroMQ is a middleware that augments the capabilities of TCP/IP sockets. It does not implement very high-level features like those found in CORBA for example, but makes use of sockets easier, more robust and almost as effective as raw TCP. The use of these two middlewares enabled us to rapidly develop a robust prototype of the DAQ including data persistence to compressed FITS files.

astro-ph.IM↗
arXiv2014

Software-Defined and Virtualized Future Mobile and Wireless Networks: A Survey

With the proliferation of mobile demands and increasingly multifarious services and applications, mobile Internet has been an irreversible trend. Unfortunately, the current mobile and wireless network (MWN) faces a series of pressing challenges caused by the inherent design. In this paper, we extend two latest and promising innovations of Internet, software-defined networking and network virtualization, to mobile and wireless scenarios. We first describe the challenges and expectations of MWN, and analyze the opportunities provided by the software-defined wireless network (SDWN) and wireless network virtualization (WNV). Then, this paper focuses on SDWN and WNV by presenting the main ideas, advantages, ongoing researches and key technologies, and open issues respectively. Moreover, we interpret that these two technologies highly complement each other, and further investigate efficient joint design between them. This paper confirms that SDWN and WNV may efficiently address the crucial challenges of MWN and significantly benefit the future mobile and wireless network.

cs.NI↗
arXiv2014

PANGU: A High Resolution Gamma-ray Space Telescope

We describe the instrument concept of a high angular resolution telescope dedicated to the sub-GeV (from $\gtrsim$10 MeV to $\gtrsim$1 GeV) gamma-ray photon detection. This mission, named PANGU (PAir-productioN Gamma-ray Unit), has been suggested as a candidate for the joint small mission between the European Space Agency (ESA) and the Chinese Academy of Science (CAS). A wide range of topics of both astronomy and fundamental physics can be attacked with PANGU, covering Galactic and extragalactic cosmic-ray physics, extreme physics of a variety of extended (e.g. supernova remnants, galaxies, galaxy clusters) and compact (e.g. black holes, pulsars, gamma-ray bursts) objects, solar and terrestrial gamma-ray phenomena, and searching for dark matter decay and/or annihilation signature etc. The unprecedented point spread function can be achieved with a pair-production telescope with a large number of thin active tracking layers to precisely reconstruct the pair-produced electron and positron tracks. Scintillating fibers or thin silicon micro-strip detectors are suitable technology for such a tracker. The energy measurement is achieved by measuring the momentum of the electrons and positrons through a magnetic field. The innovated spectrometer approach provides superior photon pointing resolution, and is particular suitable in the sub-GeV range. The level of tracking precision makes it possible to measure the polarization of gamma rays, which would open up a new frontier in gamma-ray astronomy. The frequent full-sky survey at sub-GeV with PANGU's large field of view and significantly improved point spread function would provide crucial information to GeV-TeV astrophysics for current/future missions including Fermi, DAMPE, HERD, and CTA, and other multi-wavelength telescopes.

astro-ph.IM↗
arXiv2014

Chaos in two black holes with next-to-leading order spin-spin interactions

We take into account the dynamics of a complete third post-Newtonian conservative Hamiltonian of two spinning black holes, where the orbital part arrives at the third post-Newtonian precision level and the spin-spin part with the spin-orbit part includes the leading-order and next-to-leading-order contributions. It is shown through numerical simulations that the next-to-leading order spin-spin couplings play an important role in chaos. A dynamical sensitivity to the variation of single parameter is also investigated. In particular, there are a number of \textit{observable} orbits whose initial radii are large enough and which become chaotic before coalescence.

gr-qc↗
arXiv2011

Optimal channel allocation with dynamic power control in cellular networks

Techniques for channel allocation in cellular networks have been an area of intense research interest for many years. An efficient channel allocation scheme can significantly reduce call-blocking and calldropping probabilities. Another important issue is to effectively manage the power requirements for communication. An efficient power control strategy leads to reduced power consumption and improved signal quality. In this paper, we present a novel integer linear program (ILP) formulation that jointly optimizes channel allocation and power control for incoming calls, based on the carrier-to-interference ratio (CIR). In our approach we use a hybrid channel assignment scheme, where an incoming call is admitted only if a suitable channel is found such that the CIR of all ongoing calls on that channel, as well as that of the new call, will be above a specified value. Our formulation also guarantees that the overall power requirement for the selected channel will be minimized as much as possible and that no ongoing calls will be dropped as a result of admitting the new call. We have run simulations on a benchmark 49 cell environment with 70 channels to investigate the effect of different parameters such as the desired CIR. The results indicate that our approach leads to significant improvements over existing techniques.

cs.NI↗
arXiv2010

Lyapunov indices with two nearby trajectories in a curved spacetime

We compare three methods for computing invariant Lyapunov exponents (LEs) in general relativity. They involve the geodesic deviation vector technique (M1), the two-nearby-orbits method with projection operations and with coordinate time as an independent variable (M2), and the two-nearby-orbits method without projection operations and with proper time as an independent variable (M3). An analysis indicates that M1 and M3 do not need any projection operation. In general, the values of LEs from the three methods are almost the same. As an advantage, M3 is simpler to use than M2. In addition, we propose to construct the invariant fast Lyapunov indictor (FLI) with two-nearby-trajectories and give its algorithm in order to quickly distinguish chaos from order. Taking a static axisymmetric spacetime as a physical model, we apply the invariant FLIs to explore the global dynamics of phase space of the system where regions of chaos and order are clearlyidentified.

gr-qc↗