arXiv subjects

Gang Li

Publications and source records attributed to Gang Li.

At least 613 records · Page 34Linked to original sources

arXiv2017

Pulsations and Period Variations of the $δ$ Scuti Star AN Lyncis in a possible three-body system

Observations for the $δ$ Scuti star AN Lyn have been made between 2008 and 2016 with the 85-cm telescope at Xinglong station of National Astronomical Observatories of China, the 84-cm telescope at SPM Observatory of Mexico and the Nanshan One meter Wide field Telescope of Xinjiang Observatory of China. Data in $V$ in 50 nights and in $R$ in 34 nights are obtained in total. The bi-site observations from both Xinglong Station and SPM Observatory in 2014 are analyzed with Fourier Decomposition to detect pulsation frequencies. Two independent frequencies are resolved, including one non-radial mode. A number of stellar model tracks are constructed with the MESA code and the fit of frequencies leads to the best-fit model with the stellar mass of $M = 1.70 \pm 0.05~\mathrm{M_{\odot}}$ , the metallicity abundance of $Z = 0.020 \pm 0.001$, the age of $1.33 \pm 0.01$ billion years and the period change rate $1/P\cdot \mathrm{d}P/\mathrm{d}t =1.06 \times 10^{-9} ~\mathrm{yr^{-1}} $, locating the star at the evolutionary stage close to the terminal age main sequence (TAMS). The O-C diagram provides the period change rate of $1/P \cdot \mathrm{d}P /\mathrm{d}t =4.5(8)\times10^{-7}~\mathrm{yr^{-1}}$. However, the period change rate calculated from the models is smaller in two orders than the one derived from the O-C diagram. Together with the sinusoidal function signature, the period variations are regarded to be dominated by the light-travel time effect of the orbital motion of a three-body system with two low-luminosity components, rather than the stellar evolutionary effect.

astro-ph.SR↗

arXiv2017

Different production sources of light nuclei in relativistic heavy-ion collisions

We propose a new method, i.e., an exclusive quark combination model + an inclusive hadron recombination model, to study different production sources of light nuclei in relativistic heavy-ion collisions. We take deuterons and $^3$He produced in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV as examples to present contributions of different production sources by studying their rapidity densities $dN/dy$, yield ratios and transverse momentum ($p_T$) spectra just after the hadronization as well as at the final kinetic freeze-out. We find that: only very small fractions of $d$ and $^3$He are created just after the hadronization; nucleons from $Δ$ resonance decays make a much larger contribution to the regeneration of light nuclei at the hadronic phase stage, and this contribution takes about 79\% and 92\% for $d$ and $^3$He, respectively, observed at the final kinetic freeze-out. We also find that yield ratios $d/p$, $^3$He$/p$ and $^3$He$/d$ are good observables to probe contributions for light nuclei from different production sources, and provide a natural explanation for constant values of $d/p$ and $^3$He$/p$ as a function of the averaged charged multiplicity measured by the ALICE Collaboration.

hep-ph↗

arXiv2017

Insight-HXMT observations of the first binary neutron star merger GW170817

Finding the electromagnetic (EM) counterpart of binary compact star merger, especially the binary neutron star (BNS) merger, is critically important for gravitational wave (GW) astronomy, cosmology and fundamental physics. On Aug. 17, 2017, Advanced LIGO and \textit{Fermi}/GBM independently triggered the first BNS merger, GW170817, and its high energy EM counterpart, GRB 170817A, respectively, resulting in a global observation campaign covering gamma-ray, X-ray, UV, optical, IR, radio as well as neutrinos. The High Energy X-ray telescope (HE) onboard \textit{Insight}-HXMT (Hard X-ray Modulation Telescope) is the unique high-energy gamma-ray telescope that monitored the entire GW localization area and especially the optical counterpart (SSS17a/AT2017gfo) with very large collection area ($\sim$1000 cm$^2$) and microsecond time resolution in 0.2-5 MeV. In addition, \textit{Insight}-HXMT quickly implemented a Target of Opportunity (ToO) observation to scan the GW localization area for potential X-ray emission from the GW source. Although it did not detect any significant high energy (0.2-5 MeV) radiation from GW170817, its observation helped to confirm the unexpected weak and soft nature of GRB 170817A. Meanwhile, \textit{Insight}-HXMT/HE provides one of the most stringent constraints (~10$^{-7}$ to 10$^{-6}$ erg/cm$^2$/s) for both GRB170817A and any other possible precursor or extended emissions in 0.2-5 MeV, which help us to better understand the properties of EM radiation from this BNS merger. Therefore the observation of \textit{Insight}-HXMT constitutes an important chapter in the full context of multi-wavelength and multi-messenger observation of this historical GW event.

astro-ph.HE↗

arXiv2017

Long-wave magnons in a ferromagnetic film

An asymptotically exact theory of spectrum and transverse distribution of magnetization in long-wave magnons is presented. It is based on exact analytical solution of linearized Landau-Lifshitz equation in a film. The quantization of the transverse wave parameters and wave vectors is studied.

cond-mat.mes-hall↗

arXiv2017

Differentially Private Query Learning: from Data Publishing to Model Publishing

With the development of Big Data and cloud data sharing, privacy preserving data publishing becomes one of the most important topics in the past decade. As one of the most influential privacy definitions, differential privacy provides a rigorous and provable privacy guarantee for data publishing. Differentially private interactive publishing achieves good performance in many applications; however, the curator has to release a large number of queries in a batch or a synthetic dataset in the Big Data era. To provide accurate non-interactive publishing results in the constraint of differential privacy, two challenges need to be tackled: one is how to decrease the correlation between large sets of queries, while the other is how to predict on fresh queries. Neither is easy to solve by the traditional differential privacy mechanism. This paper transfers the data publishing problem to a machine learning problem, in which queries are considered as training samples and a prediction model will be released rather than query results or synthetic datasets. When the model is published, it can be used to answer current submitted queries and predict results for fresh queries from the public. Compared with the traditional method, the proposed prediction model enhances the accuracy of query results for non-interactive publishing. Experimental results show that the proposed solution outperforms traditional differential privacy in terms of Mean Absolute Value on a large group of queries. This also suggests the learning model can successfully retain the utility of published queries while preserving privacy.

cs.CR↗

arXiv2017

Tuning the diffusion of magnon in Y3Fe5O12 by light excitation

Deliberate control of magnon transportation will lead to an energy-efficient technology for information transmission and processing. Y3Fe5O12(YIG), exhibiting extremely large magnon diffusion length due to the low magnetic damping constant, has been intensively investigated for decades. While most of the previous works focused on the determination of magnon diffusion length by various techniques, herein we demonstrated how to tune magnon diffusion by light excitation. We found that the diffusion length of thermal magnons is strongly dependent on light wavelength when the magnon is generated by exposing YIG directly to laser beam. The diffusion length, determined by a nonlocal geometry at room temperature, is ~30 um for the magnons produced by visible light (400-650 nm), and ~136-156 um for the laser between 808 nm and 980 nm. The diffusion distance is much longer than the reported value. In addition to thermal gradient, we found that light illumination affected the electron configuration of the Fe3+ ion in YIG. Long wavelength laser triggers a high spin to low spin state transition of the Fe3+ ions in FeO6 octahedron. This in turn causes a substantial softening of the magnon thus a dramatic increase in diffusion distance. The present work paves the way towards an efficient tuning of magnon transport behavior which is crucially important for magnon spintronics.

cond-mat.mtrl-sci↗

arXiv2017

Triple point semimetal and topological phase transitions in NaCu$_{3}$Te$_{2}$

Quasiparticle excitations of free electrons in condensed-matter physics, characterized by the dimensionality of the band crossing, can find their elementary-particle analogs in high-energy physics, such as Majorana, Weyl, and Dirac fermions. While crystalline symmetry allows more quasiparticle excitations and exotic fermions to emerge. Using symmetry analysis and {\it ab-initio} calculations, we propose that the 3D honeycomb crystal NaCu$_3$Te$_2$ hosts triply degenerate nodal points (TDNPs) which are perfectly separated from the bulk states. We find a tunable phase transition between TDNPs and a weak TI triggered by a symmetry-allowed perturbation, and we further reveal the crucial role played by the spin-orbital coupling (SOC) for the emergence of the TDNPs in this system. Such topological non-trivial ternary compound not only serves as a perfect candidate for studying three-component fermions, but also provides a beautiful playground for understanding the topological phase transitions between TDNPs, TIs and trivial insulators, which distinguishes this system from other TDNP candidates.

cond-mat.mtrl-sci↗

arXiv2017

The {\it victory} project v1.0: an efficient parquet equations solver

{\it Victory}, i.e. \underline{vi}enna \underline{c}omputational \underline{to}ol deposito\underline{ry}, is a collection of numerical tools for solving the parquet equations for the Hubbard model and similar many body problems. The parquet formalism is a self-consistent theory at both the single- and two-particle levels, and can thus describe individual fermions as well as their collective behavior on equal footing. This is essential for the understanding of various emergent phases and their transitions in many-body systems, in particular for cases in which a single-particle description fails. Our implementation of {\it victory} is in modern Fortran and it fully respects the structure of various vertex functions in both momentum and Matsubara frequency space. We found the latter to be crucial for the convergence of the parquet equations, as well as for the correct determination of various physical observables. In this release, we thoroughly explain the program structure and the controlled approximations to efficiently solve the parquet equations, i.e. the two-level kernel approximation and the high-frequency regulation.

cond-mat.str-el↗

arXiv2017

Quantum Anomalous Hall State in Ferromagnetic SrRuO$_3$ (111) Bilayers

SrRuO$_3$ heterostructures grown in the (111) direction are a rare example of thin film ferromagnets. By means of density functional theory plus dynamical mean field theory we show that the half-metallic ferromagnetic state with an ordered magnetic moment of 2$μ_{B}$/Ru survives the ultimate dimensional confinement down to a bilayer, even at elevated temperatures of 500$\,$K. In the minority channel, the spin-orbit coupling opens a gap at the linear band crossing corresponding to $\frac34$ filling of the $t_{2g}$ shell. We demonstrate that the respective state is Haldane's quantum anomalous Hall state with Chern number $C$=1, without an external magnetic field or magnetic impurities.

cond-mat.str-el↗

arXiv2017

Modeling Transport of Energetic Particles in Corotating Interaction Region -- A case Study

We investigate energetic particle transport in Corotating Interaction Regions (CIRs) through a case study. The CIR event we study occurred on $2008$ February $08$ and was observed by both the Advanced Composition Explorer (ACE) and the twin Solar TErrestrial RElations Observatory (STEREO)-B spacecraft. An in-situ reverse shock was observed by STEREO-B ($1.0$ AU) but not ACE ($0.98$ AU). Using STEREO-B observations and assuming the CIR structure does not vary significantly in the corotating frame, we estimate the shock location at later times for both the STEREO-B and ACE observations. Further assuming the accelerated particle spectral shape at the shock does not vary with shock location, we calculate the particle differential intensities as observed by ACE and STEREO-B at two different times by solving the focused transport equation using a Monte-Carlo simulation. We assume that particles move along Parker's field and experience no cross-field diffusion. We find that the modulation of sub-MeV/nucleon particles is significant. To obtain reasonable comparisons between the simulations and the observations by both ACE and STEREO-B, one has to assume that the CIR shock can accelerate more particles at a larger heliocentric distance than at a smaller heliocentric distance.

physics.space-ph↗

arXiv2017

Simulation Experiment of BCI Based on Imagined Speech EEG Decoding

Brain Computer Interface (BCI) can help patients of neuromuscular diseases restore parts of the movement and communication abilities that they have lost. Most of BCIs rely on mapping brain activities to device instructions, but limited number of brain activities decides the limited abilities of BCIs. To deal with the problem of limited ablility of BCI, this paper verified the feasibility of constructing BCI based on decoding imagined speech electroencephalography (EEG). As sentences decoded from EEG can have rich meanings, BCIs based on EEG decoding can achieve numerous control instructions. By combining a modified EEG feature extraction mehtod with connectionist temporal classification (CTC), this paper simulated decoding imagined speech EEG using synthetic EEG data without help of speech signal. The performance of decoding model over synthetic data to a certain extent demonstrated the feasibility of constructing BCI based on imagined speech brain signal.

cs.HC↗

arXiv2017

PrivMin: Differentially Private MinHash for Jaccard Similarity Computation

In many industrial applications of big data, the Jaccard Similarity Computation has been widely used to measure the distance between two profiles or sets respectively owned by two users. Yet, one semi-honest user with unpredictable knowledge may also deduce the private or sensitive information (e.g., the existence of a single element in the original sets) of the other user via the shared similarity. In this paper, we aim at solving the privacy issues in Jaccard similarity computation with strict differential privacy guarantees. To achieve this, we first define the Conditional $ε$-DPSO, a relaxed differential privacy definition regarding set operations, and prove that the MinHash-based Jaccard Similarity Computation (MH-JSC) satisfies this definition. Then for achieving strict differential privacy in MH-JSC, we propose the PrivMin algorithm, which consists of two private operations: 1) the Private MinHash Value Generation that works by introducing the Exponential noise to the generation of MinHash signature. 2) the Randomized MinHashing Steps Selection that works by adopting Randomized Response technique to privately select several steps within the MinHashing phase that are deployed with the Exponential mechanism. Experiments on real datasets demonstrate that the proposed PrivMin algorithm can successfully retain the utility of the computed similarity while preserving privacy.

cs.DS↗

arXiv2017

Study on the radiative decays of $h_c$ via intermediate meson loops model

Recently, the BESIII Collaboration reported two new decay processes $h_c(1P)\to γη$ and $γη^\prime$. Inspired by this measurement, we propose to study the radiative decays of $h_c$ via intermediate charmed meson loops in an effective Lagrangian approach. With the acceptable cutoff parameter range, the calculated branching ratios of $h_c(1P)\to γη$ and $γη^\prime$ are orders of $10^{-4}\sim 10^{-3}$ and $10^{-3} \sim 10^{-2}$, respectively. The ratio $R_{h_c}= \mathcal{B}( h_c\to γη)/\mathcal{B}( h_c\to γη^\prime )$ can reproduce the experimental measurements with the commonly acceptable $α$ range. This ratio provide us some information on the $η-η^\prime$ mixing, which may be helpful for us to test SU(3)-flavor symmetries in QCD.

hep-ph↗

arXiv2017

Enhanced entanglement of two different mechanical resonators via coherent feedback

It was shown [New J. Phys. 17, 103037 (2015)] that large and robust entanglement between two different mechanical resonators could be achieved, either dynamically or in the steady state, in an optomechanical system in which the two mechanical resonators are coupled to a single cavity mode driven by a suitably chosen two-tone field. An important limitation of the scheme is that the cavity decay rate must be much smaller than the two mechanical frequencies and their difference. Here we show that the entanglement can be remarkably enhanced, and the validity of the scheme can be largely extended, by adding a coherent feedback loop that effectively reduces the cavity decay rate.

quant-ph↗

arXiv2017

Interchange reconnection associated with a confined filament eruption: Implications for the source of transient cold-dense plasma in solar winds

The cold-dense plasma is occasionally detected in the solar wind with in situ data, but the source of the cold-dense plasma remains illusive. Interchange reconnections (IRs) between closed fields and nearby open fields are well known to contribute to the formation of solar winds. We present a confined filament eruption associated with a puff-like coronal mass ejection (CME) on 2014 December 24. The filament underwent successive activations and finally erupted, due to continuous magnetic flux cancellations and emergences. The confined erupting filament showed a clear untwist motion, and most of the filament material fell back. During the eruption, some tiny blobs escaped from the confined filament body, along newly-formed open field lines rooted around the south end of the filament, and some bright plasma flowed from the north end of the filament to remote sites at nearby open fields. The newly-formed open field lines shifted southward with multiple branches. The puff-like CME also showed multiple bright fronts and a clear southward shift. All the results indicate an intermittent IR existed between closed fields of the confined erupting filament and nearby open fields, which released a portion of filament material (blobs) to form the puff-like CME. We suggest that the IR provides a possible source of cold-dense plasma in the solar wind.

astro-ph.SR↗

arXiv2017

Observation of topological states residing at step edges of WTe2

Topological states emerge at the boundary of solids as a consequence of the nontrivial topology of the bulk. Recently, theory predicts a topological edge state on single layer transition metal dichalcogenides with 1T' structure. However, its existence still lacks experimental proof. Here, we report the direct observations of the topological states at the step edge of WTe2 by spectroscopic-imaging scanning tunneling microscopy. A one-dimensional electronic state residing at the step edge of WTe2 is observed, which has a spatial extension of about 2.5 nm. First principles calculations rigorously verify the edge state has a topological origin, and its topological nature is unaffected by the presence of the substrate. Our study supports the existence of topological edge states in 1T'-WTe2, which may envision in-depth study of its topological physics and device applications.

cond-mat.mes-hall↗

arXiv2017

Testing CP-Violation in the Scalar Sector at Future $e^+e^-$ Colliders

We propose a {\em model-independent} method to test CP-violation in the scalar sector through measuring the inclusive cross sections of $e^+e^-\rightarrow Zh_1,Zh_2,h_1h_2$ processes with the recoil mass technique, where $h_1, h_2$ stand for the 125 GeV standard model (SM) like Higgs boson and a new lighter scalar respectively. This method effectively measures a quantity $K$ proportional to the product of the three couplings of $h_1ZZ,h_2ZZ,h_1h_2Z$ vertices. The value of $K$ encodes a part of information about CP-violation in the scalar sector. We simulate the signal and backgrounds for the processes mentioned above with $m_{2}=40\textrm{GeV}$ at the Circular Electron-Positron Collider (CEPC) with the integrated luminosity $5\textrm{ab}^{-1}$. We find that the discovery of both $Zh_2$ and $h_1h_2$ processes at $5σ$ level will indicate an $\mathcal{O}(10^{-2})$ $K$ value which can be measured to $16\%$ precision. The method is applied to the weakly-coupled Lee model in which CP-violation can be tested either before or after utilizing a "$p_T$ balance" cut (see \autoref{simu} for the definition). Lastly we point out that $K\neq 0$ is a sufficient but not a necessary condition for the existence of CP-violation in the scalar sector, namely $K = 0$ does not imply CP conservation in the scalar sector.

hep-ph↗

arXiv2017

On Uniqueness of Conformally Compact Einstein Metrics with Homogeneous Conformal Infinity

In this paper we show that for a Berger metric $\hat{g}$ on $S^3$, the non-positively curved conformally compact Einstein metric on the $4$-ball $B_1(0)$ with $(S^3, [\hat{g}])$ as its conformal infinity is unique up to isometries and it is the metric constructed by Pedersen \cite{Pedersen}. In particular, since in \cite{LiQingShi}, we proved that if the Yamabe constant of the conformal infinity $Y(S^3, [\hat{g}])$ is close to that of the round sphere then any conformally compact Einstein manifold filled in must be negatively curved and simply connected, therefore if $\hat{g}$ is a Berger metric on $S^3$ with $Y(S^3, [\hat{g}])$ close to that of the round metric, the conformally compact Einstein metric filled in is unique up to isometries.

math.DG↗