arXiv subjects

Na Wang

Publications and source records attributed to Na Wang.

At least 163 records · Page 9Linked to original sources

arXiv2017

Dependence of pulsar death line on the equation of state

Pulsar death line can be defined in $P-\dot{P}$ diagram. Traditionally, radio-loud pulsars are supposed to locate above the death line where is the radio-loud region. With the development of observational equipment, the observational properties of the neutron star are remarkably diverse. In $P-\dot{P}$ diagram, some of the special sources are radio-quiet but lie above the death line. From the definition of the pulsar death line, different equation of states for neutron star or strange star results in different death lines. We discuss the influence of the equation of state on the pulsar death line and the possible link between different neutron star groups. The results show that central compact objects would be the small mass of self-bound strange stars, and rotating radio transients might be old pulsars on the verge of death. We suggest that PSR J2144-3933 is likely to be a large mass pulsar, which would be larger than $2.0\rm{M_{\odot}}$. Multiple observational facts would help us to reveal the nature of pulsars.

astro-ph.HE↗

arXiv2017

Charmless $B_{c} \to VV$ decays in the QCD factorization approach

In this paper, we studied the charmless $B_{c}\to VV$ ($V$ denotes the light ground $\rm SU(3)$ vector meson) decays within the framework of QCD factorization. In the evaluation, two different schemes for regulating the end-point divergence are adopted. One (scheme I) is to use parameterization model, which is usually employed in the QCD factorization approach; the other (scheme II) is based on the infrared finite gluon propagator of Cornwall prescription. It is found that, in the annihilation amplitudes, the end-point divergence appears only in the power-suppressed corrections related to the twist-3 distribution amplitudes of $V$-meson. The strength of annihilation amplitudes evaluated in scheme II is generally larger than the one in scheme I. Numerically, in the decay modes considered in this paper, the CKM-favored $B_{c} \to ρ^{-}ω, K^{*-}K^{*0} $ decays have the relatively large branching fractions, $\sim {\cal{O}}(10^{-7})$, and hence are likely to be the first observed by the future experiments. In addition, all of the decay modes are dominated by the longitudinal polarization state; numerically, $f_{L}(B_{c} \to VV) \gtrsim 99\%$.

hep-ph↗

arXiv2017

Satellite-Based Entanglement Distribution Over 1200 kilometers

Long-distance entanglement distribution is essential both for foundational tests of quantum physics and scalable quantum networks. Owing to channel loss, however, the previously achieved distance was limited to ~100 km. Here, we demonstrate satellite-based distribution of entangled photon pairs to two locations separated by 1203 km on the Earth, through satellite-to-ground two-downlink with a sum of length varies from 1600 km to 2400 km. We observe a survival of two-photon entanglement and a violation of Bell inequality by 2.37+/-0.09 under strict Einstein locality conditions. The obtained effective link efficiency at 1200 km in this work is over 12 orders of magnitude higher than the direct bidirectional transmission of the two photons through the best commercial telecommunication fibers with a loss of 0.16 dB/km.

quant-ph↗

arXiv2017

Possibility of searching for $B_{c}^{\ast}$ ${\to}$ $B_{u,d,s}V$, $B_{u,d,s}P$ decays

The $B_{c}^{\ast}$ ${\to}$ $B_{u,d,s}V$, $B_{u,d,s}P$ decays are investigated with the QCD factorization approach, where $V$ and $P$ denote the ground $SU(3)$ vector and pseudoscalar mesons, respectively. The $B_{c}^{\ast}$ ${\to}$ $B_{u,d,s}$ transition form factors are calculated with the Wirbel-Stech-Bauer model. It is found that branching ratios for the color-favored and Cabibbo-favored $B_{c}^{\ast}$ ${\to}$ $B_{s}ρ$, $B_{s}π$ decays can reach up to ${\cal O}(10^{-7})$, which might be measurable in the future LHC experiments.

hep-ph↗

arXiv2017

Quantum torus algebras and B(C) type Toda systems

In this paper, we construct a new even constrained B(C) type Toda hierarchy and derive its B(C) type Block type additional symmetry. Also we generalize the B(C) type Toda hierarchy to the $N$-component B(C) type Toda hierarchy which is proved to have symmetries of a coupled $\bigotimes^NQT_+ $ algebra ( $N$-folds direct product of the positive half of the quantum torus algebra $QT$).

nlin.SI↗

arXiv2017

Core Maintenance in Dynamic Graphs: A Parallel Approach based on Matching

The core number of a vertex is a basic index depicting cohesiveness of a graph, and has been widely used in large-scale graph analytics. In this paper, we study the update of core numbers of vertices in dynamic graphs with edge insertions/deletions, which is known as the core maintenance problem. Different from previous approaches that just focus on the case of single-edge insertion/deletion and sequentially handle the edges when multiple edges are inserted/deleted, we investigate the parallelism in the core maintenance procedure. Specifically, we show that if the inserted/deleted edges constitute a matching, the core number update with respect to each inserted/deleted edge can be handled in parallel. Based on this key observation, we propose parallel algorithms for core maintenance in both cases of edge insertions and deletions. We conduct extensive experiments to evaluate the efficiency, stability, parallelism and scalability of our algorithms on different types of real-world and synthetic graphs. Comparing with sequential approaches, our algorithms can improve the core maintenance efficiency significantly.

cs.DS↗

arXiv2017

Study on the $Υ(1S)$ ${\to}$ $B_{c}D_{s}$ decay

The branching ratio and direct $CP$ asymmetry of the $Υ(1S)$ ${\to}$ $B_{c}D_{s}$ weak decay are estimated with the perturbative QCD approach. It is found that (1) The direct $CP$-violating asymmetry is close to zero. (2) the branching ratio ${\cal B}r(Υ(1S){\to}B_{c}D_{s})$ ${\gtrsim}$ $10^{-10}$ might be measurable at the future experiments.

hep-ph↗

arXiv2017

Study of $B_{c}^{\ast}$ ${\to}$ $ψ(1S,2S)P$, $η_{c}(1S,2S)P$ weak decays

Motivated by the potential prospects of the $B_{c}^{\ast}$ meson samples at hadron colliders, the bottom-changing $B_{c}^{\ast}$ ${\to}$ $ψ(1S,2S)P$, $η_{c}(1S,2S)P$ weak decays are first studied with the perturbative QCD approach, where $P$ $=$ $π$ and $K$. It is found that branching ratio of the CKM-favored $B_{c}^{\ast}$ ${\to}$ $J/ψπ$ decay is about ${\sim}$ ${\cal O}(10^{-8})$, which might be measurable at the future LHC experiments.

hep-ph↗

arXiv2017

Deterministic Role of Concentration Surplus of Cation Vacancy over Anion Vacancy in Bipolar Memristive NiO

Migration of oxygen vacancies has been proposed to play an important role in the bipolar memristive behaviors since oxygen vacancies can directly determine the local conductivity in many systems. However, a recent theoretical work demonstrated that both migration of oxygen vacancies and coexistence of cation and anion vacancies are crucial to the occurrence of bipolar memristive switching, normally observed in the small-sized NiO. So far, experimental work addressing this issue is still lacking. In this work, with conductive atomic force microscope and combined scanning transmission electron microscopy & electron energy loss spectroscopy, we reveal that concentration surplus of Ni vacancy over O vacancy determines the bipolar memristive switching of NiO films. Our work supports the dual-defects-based model, which is of fundamental importance for understanding the memristor mechanisms beyond the well-established oxygen-vacancy-based model. Moreover, this work provides a methodology to investigate the effect of dual defects on memristive behaviors.

cond-mat.mtrl-sci↗

arXiv2016

Parallel Algorithms for Core Maintenance in Dynamic Graphs

This paper initiates the studies of parallel algorithms for core maintenance in dynamic graphs. The core number is a fundamental index reflecting the cohesiveness of a graph, which are widely used in large-scale graph analytics. The core maintenance problem requires to update the core numbers of vertices after a set of edges and vertices are inserted into or deleted from the graph. We investigate the parallelism in the core update process when multiple edges and vertices are inserted or deleted. Specifically, we discover a structure called superior edge set, the insertion or deletion of edges in which can be processed in parallel. Based on the structure of superior edge set, efficient parallel algorithms are then devised for incremental and decremental core maintenance respectively. To the best of our knowledge, the proposed algorithms are the first parallel ones for the fundamental core maintenance problem. The algorithms show a significant speedup in the processing time compared with previous results that sequentially handle edge and vertex insertions/deletions. Finally, extensive experiments are conducted on different types of real-world and synthetic datasets, and the results illustrate the efficiency, stability and scalability of the proposed algorithms.

cs.DS↗

arXiv2016

An improved solution to geometric distortion using an orthogonal method

The geometric distortion of CCD field of view has direct influence on the positional measurements of CCD observations. In order to obtain high precision astrometric results, the geometric distortion should be derived and corrected precisely. As presented in our previous work Peng et al. (2012), a convenient solution has been carried out and also been made with successful application to Phoebe's observations. In order to further improve the solution, an orthogonal method based on the Zernike polynomials is used in this work. Four nights of CCD observations including Himalia, the sixth satellite of Jupiter, and open clusters (NGC1664 or NGC2324) on each night have been processed to make an application. The observations were obtained from the 2.4 m telescope administered by Yunnan Observatories. The catalog UCAC4 was used to match reference stars in all of the CCD frames. The ephemeris of Himalia is retrieved from the (IMCCE). Our results show that the means of observed minus computed (O-C) positional residuals are -0.034 and -0.026 arcsec in right ascension and declination, respectively. The corresponding standard deviations are 0.031 and 0.028 arcsec. The measurement dispersion is significantly improved than that by using our previous solution.

astro-ph.IM↗

arXiv2016

A timing view of the heartbeat state of GRS 1915+105

We present a timing analysis of two Rossi X-ray Timing Explorer observations of the microquasar GRS 1915+105 during the heartbeat state. The phase-frequency-power maps show that the intermediate-frequency aperiodic X-ray variability weakens as the source softens in the slow rise phase, and when the quasi-periodic oscillation disappears in the rise phase of the pulse of the double-peaked class its sub-harmonic is still present with a hard phase lag. In the slow rise phase, the energy-frequency-power maps show that most of the aperiodic variability is produced in the corona, and may also induce the aperiodic variability observed at low energies from an accretion disk, which is further supported by the soft phase lag especially in the intermediate-frequency range (with a time delay up to 20 ms). In the rise phase of the pulse, the low-frequency aperiodic variability is enhanced significantly and there is a prominent hard lag (with a time delay up to 50 ms), indicating that the variability is induced by extension of the disk toward small radii as implied by the increase in flux and propagates into the corona. However, during the hard pulse of the double-peaked class, the variability shows no significant lag, which may be attributed to an optically thick corona. These timing results are generally consistent with the spectral results presented by Neilsen et al. (2011, 2012) which indicated that the slow rise phase corresponds to a local Eddington limit and the rise phase of the pulse corresponds to a radiation pressure instability in the disk.

astro-ph.HE↗

arXiv2016

Study on $Υ(nS)$ ${\to}$ $B_{c}M$ decays

With anticipation of abundant Upsilons data sample at high-luminosity heavy-flavor experiments in the future, we studied nonleptonic two-body weak decays of $Υ(nS)$ below the open-bottom threshold with $n$ $=$ $1$, $2$ and $3$. It is found that branching ratios for $Υ(1S,2S,3S)$ ${\to}$ $B_{c}ρ$ decays are relatively large among upsilons decay into $B_{c}M$ final states ($M$ $=$ $π$ $ρ$, $K$ and $K^{\ast}$) and can reach up to $10^{-10}$, which is promisingly detected by experiments at the running LHC and forthcoming SuperKEKB.

hep-ph↗

arXiv2016

Study on the $Υ(1S)$ ${\to}$ $B_{c}M$ weak decays

Motivated by the prospects of the potential $Υ(1S)$ particle at high-luminosity heavy-flavor experiments, we studied the $Υ(1S)$ ${\to}$ $B_{c}M$ weak decays, where $M$ $=$ $π$, $ρ$, $K^{(\ast)}$. The nonfactorizable contributions to hadronic matrix elements are taken into consideration with the QCDF approach. It is found that the CKM-favored $Υ(1S)$ ${\to}$ $B_{c}ρ$ decay has branching ratio of ${\cal O}(10^{-10})$, which might be measured promisingly by the future experiments.

hep-ph↗

arXiv2016

Electronic properties of SnTe-class topological crystalline insulator materials

The rise of topological insulators in recent years has broken new ground both in the conceptual cognition of condensed matter physics and the promising revolution of the electronic devices. It also stimulates the explorations of more topological states of matter. Topological crystalline insulator is a new topological phase, which combines the electronic topology and crystal symmetry together. In this article, we review the recent progress in the studies of SnTe-class topological crystalline insulator materials. Starting from the topological identifications in the aspects of the bulk topology, surface states calculations and experimental observations, we present the electronic properties of topological crystalline insulators under various perturbations, including native defect, chemical doping, strain, and thickness-dependent confinement effects, and then discuss their unique quantum transport properties, such as valley-selective filtering and helicity-resolved functionalities for Dirac fermions. The rich properties and high tunability make SnTe-class materials promising candidates for novel quantum devices.

cond-mat.mtrl-sci↗

arXiv2016

Numerically Fitting The Electron Fermi Energy and The Electron Fraction in A Neutron Star

Based on the basic definition of Fermi energy of degenerate and relativistic electrons, we obtain a special solution to electron Fermi energy, $E_{\rm F}(e)$, and express $E_{\rm F}(e)$ as a function of electron fraction, $Y_{e}$, and matter density, $ρ$. Several useful analytical formulae for $Y_{e}$ and $ρ$ within classical models and the work of Dutra et al. 2014 (Type-2) in relativistic mean field theory are obtained using numerically fitting. When describing the mean-field Lagrangian, density, we adopt the TMA parameter set, which is remarkably consistent with with the updated astrophysical observations of neutron stars. Due to the importance of the density dependence of the symmetry energy, $S$, in nuclear astrophysics, a brief discussion on the symmetry parameters $S_v$ and $L$ (the slope of $S$) is presented. Combining these fit formulae with boundary conditions for different density regions, we can evaluate the value of $E_{\rm F}(e)$ in any given matter density, and obtain a schematic diagram of $E_{\rm F}(e)$ as a continuous function of $ρ$. Compared with previous study on the electron Fermi energy in other models, our methods of calculating $E_{\rm F}(e)$ are more simple and convenient, and can be universally suitable for the relativistic electron regions in the circumstances of common neutron stars. We have deduced a general expression of $E_{\rm F}(e)$ and $n_{e}$, which could be used to indirectly test whether one EoS of a NS is correct in our future studies on neutron star matter properties. Since URCA reactions are expected in the center of a massive star due to high-value electron Fermi energy and electron fraction, this study could be useful in the future studies on the NS thermal evolution.

astro-ph.HE↗

arXiv2016

Charmless $B_{c}$ $\to$ $PP$, $PV$ decays in the QCD factorization approach

The charmless $B_{c}$ $\to$ $PP$, $PV$~(where $P$ and $V$ denote the light pseudoscalar and vector mesons, respectively) decays can occur only via the weak annihilation diagrams within the Standard Model and provide, therefore, an ideal place to probe the strength of annihilation contribution in hadronic $B_{u,d,s}$ decays. In this paper, we study these kinds of decays in the framework of QCD factorization, by adopting two different schemes: scheme I is similar to the method usually adopted in the QCD factorization approach, while scheme II is based on the infrared behavior of gluon propagator and running coupling. For comparison, in our calculation, we adopt three kinds of wave functions for $B_{c}$ meson. It is found that: (a) The predicted branching ratios in scheme I are, however, quite small and are almost impossible to be measured at the LHCb experiment. (b) In scheme II, by assigning a dynamical gluon mass to the gluon propagator, we can avoid enhancements of the contribution from soft endpoint region. The strength of annihilation contributions predicted in scheme II is enhanced compared to that obtained in scheme I. However, the predicted branching ratios are still smaller than the corresponding ones obtained in the perturbative QCD approach. The large discrepancies among these theoretical predictions indicate that more detailed studies of these decays are urgently needed and will be tested by the future measurements performed at the LHCb experiment.

hep-ph↗

arXiv2015

Electron emission of stripping foil and collimation system for CSNS/RCS

For the Rapid Cycling Synchrotron of the China Spallation Neutron Source (CSNS/RCS), the electron emission plays an important role in the accelerator limitation. The interactions between the proton beam and the stripping foil were studied, and the electron scattering processes were simulated by the ORBIT and FLUKA codes. Then, the electron energy distribution and the electron yielding rate can be given. Furthermore, the interactions between the proton beam and the collimation system were studied, and the electron scattering processes were simulated. Then, the energy distribution of the primary electron emission can be given and the yielding rate of the primary electron can be obtained.

physics.acc-ph↗