J. Y. Li

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (137)240.77 Total impact

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    ABSTRACT: Surface damage on 6H-SiC irradiated by highly-charged Xeq+ (q = 18, 26) ions to different fiuences in two geometries was studied by means of AFM, Raman scattering spectroscopy and FTIR spectrometry. The FTIR spectra analysis shows that for Xe26+ ions irradiation at normal incidence, a deep reflection dip appears at about 930 cm(-1). Moreover, the reflectance on top of reststrahlen band decreases as the ion fluence increases, and the reflectance at tilted incidence is larger than that at normal incidence. The Raman scattering spectra reveal that for Xe26+ ions at normal incidence, surface reconstruction occurs and amorphous stoichiometric SiC and Si-Si and C-C bonds are generated and original Si-C vibrational mode disappears. And the intensity of scattering peaks decreases with increasing dose. The AFM measurement shows that the surface swells after irradiation. With increasing ion fluence, the step height between the irradiated and the unirradiated region increases for Xe18+ ions irradiation; while for Xe-26+ ions irradiation, the step height first increases and then decreases with increasing ion fluence. Moreover, the step height at normal incidence is higher than that at tilted incidence by the irradiation with Xe18+ to the same ion fluence. A good agreement between the results from the three methods is found.
    Journal of Nuclear Materials 12/2014; 455(1-3):704-709. DOI:10.1016/j.jnucmat.2014.08.001 · 1.87 Impact Factor
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    ABSTRACT: Abstract:To prepare the upcoming laser cooling of relativistic C3+ ion beams at the experimental Cooler Storage Ring (CSRe), a novel experiment was performed using a reaction microscope to determine the ratio of C3+ ions in mixed ion beams of C3+ and O4+ that are produced by an Electron Cyclotron Resonance Ion Source (ECRIS). The mixed ion beams at an energy of 4 keV/u were directed to collide on a supersonic helium gas target. Using the single-electron capture channel and the coincidence technique, the fractions of C3+ and O4+ ions in the primary beam were obtained. Using different injection gases for ECRIS, including O2, CO, CO2, and CH4, at a fixed radio-frequency power of 300 W, the measured results showed that the fraction of C3+ ions was greater than 70% for the injection gases of CO and CO2. These measured results are very important and helpful for the upcoming laser cooling experiments.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 11/2014; 764:232-235. DOI:10.1016/j.nima.2014.06.067 · 1.22 Impact Factor
  • W Lu · J Y Li · L Kang · H P Liu · H Li · J D Li · L T Sun · X W Ma ·
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    ABSTRACT: The 320 kV platform for multi-discipline research with highly charged ions is a heavy ion beam acceleration instrument developed by Institute of Modern Physics, which is dedicated to basic scientific researches such as plasma, atom, material physics, and astrophysics, etc. The platform has delivered ion beams of 400 species for 36 000 h. The average operation time is around 5000 h/year. With the beams provided by the platform, lots of outstanding progresses were made in various research fields. The ion source of the platform is an all-permanent magnet electron cyclotron resonance ion source, LAPECR2 (Lanzhou All Permanent ECR ion source No. 2). The maximum axial magnetic fields are 1.28 T at injection and 1.07 T at extraction, and the radial magnetic field is up to 1.21 T at the inner wall of the plasma chamber. The ion source is capable to produce low, medium, and high charge state gaseous and metallic ion beams, such as H(+), (40)Ar(8+), (129)Xe(30+), (209)Bi(33+), etc. This paper will present the latest result of LAPECR2 and the routine operation status for the high voltage platform.
    The Review of scientific instruments 02/2014; 85(2):02A947. DOI:10.1063/1.4852215 · 1.61 Impact Factor
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    ABSTRACT: Epitaxial GaN layers grown by MOCVD on c-plane sapphire substrates were irradiated with 5.3 MeV Kr23+ and 2.3 MeV Ne8+ ions to various fluences. The pristine and the irradiated GaN samples were characterized using high resolution X-ray diffraction (HRXRD), UV–visible transmittance spectrum and Raman scattering spectrum analysis. The HRXRD results show an obvious increase in the FWHM and a decrease in the intensity of the GaN (0 0 0 2) peak with increasing ion fluences. Meanwhile the UV–visible transmittance spectra show a decrease in the band gap value after irradiation. The Raman scattering spectrum shows that new Raman bands around 300 and 670 cm−1 appear with increasing ion fluences. The new Raman bands can be ascribed to disorder-activated Raman scattering (DARS) from the highest acoustic-phonon branch and the optical-phonon branch at the brillouin zone boundaries, respectively.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 07/2013; 307:60–64. DOI:10.1016/j.nimb.2012.12.101 · 1.12 Impact Factor
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    ABSTRACT: We report the observation of a very high energy \gamma-ray source, whose position is coincident with HESS J1841-055. This source has been observed for 4.5 years by the ARGO-YBJ experiment from November 2007 to July 2012. Its emission is detected with a statistical significance of 5.3 standard deviations. Parameterizing the source shape with a two-dimensional Gaussian function we estimate an extension \sigma=(0.40(+0.32,-0.22}) degree, consistent with the HESS measurement. The observed energy spectrum is dN/dE =(9.0-+1.6) x 10^{-13}(E/5 TeV)^{-2.32-+0.23} photons cm^{-2} s^{-1} TeV^{-1}, in the energy range 0.9-50 TeV. The integral \gamma-ray flux above 1 TeV is 1.3-+0.4 Crab units, which is 3.2-+1.0 times the flux derived by HESS. The differences in the flux determination between HESS and ARGO-YBJ, and possible counterparts at other wavelengths are discussed.
    The Astrophysical Journal 03/2013; 767(2). DOI:10.1088/0004-637X/767/2/99 · 5.99 Impact Factor
  • L. Zhang · Y. Tan · F. M. Xu · J. Y. Li · H. Y. Wang · Z. Gu ·
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    ABSTRACT: The global shortage of solar grade silicon for production of solar cells has motivated a lot of research on the refining of metallurgical grade silicon. However, approaches to upgrade metallurgical grade silicon have been mainly handicapped by difficulties in reducing boron and phosphorus levels. In the present study, the possibility of refining metallurgical grade silicon to remove impurity boron using Na2O-CaO-SiO2 slags was investigated. Before slag melting, a process of mixing pulverized slags and silicon under an action of mechanical force was used to provide a higher probability of contact and reaction of slags and silicon. The melting time was reduced with an increase in contact area A S , resulting in improved efficiency of boron removal. The parameters, including the slag basicity, and the weight ratio of silicon to slag were discussed. The process of slag treatment was performed twice and directional solidification was conducted to promote the separation of slags from silicon. A maximum value of L B (5.81) was obtained when the basicity was 1.21, and the weight ratio of silicon to slag was 5.
    Separation Science and Technology 03/2013; 48(7). DOI:10.1080/01496395.2012.714438 · 1.17 Impact Factor
  • J.-Y. Li · C.-C. Li · Y.-Q. Li · Y. Tan ·
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    ABSTRACT: The electrochemical separation of aluminum-silicon alloy in the low temperature molten salt AlCl3-NaCl-KCl at constant current deposition was studied. Aluminum-silicon alloy for the anode electrode and stainless steel for the cathode electrode were used. The effects of temperature, current density and time on the current efficiency and the morphology of deposited aluminum were analyzed by the scanning electron microscope and X-ray diffraction. The results show that, when the current density is 50mA/cm2, the maximum current efficiency can reach 93.7% at 200°C for 60min using Si-50%Al(mass fraction) as anode electrode, and there is 90.4% silicon in the anode slime.
    Cailiao Gongcheng/Journal of Materials Engineering 01/2013; DOI:10.3969/j.issn.1001-4381.2013.11.001
  • J. Y. Li · Y. J. Liu · Y. Tan ·
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    ABSTRACT: The conversion efficiency of solar cells made from single crystalline Si is generally about 3-4% higher than those made from Si multicrystal by the casting method. In this paper, the single crystalline Si obtained by the Czochralski method using metallurgical grade silicon raw materials was characterised by minority carrier lifetime, optical microscopy, the concentration of impurities and the conversion efficiency. The influence of crystalline defects and impurity elements on the electrical property has been investigated. We can conclude that both defects and impurity elements play important roles in the deterioration of the minority carrier lifetime. The conversion efficiency of solar cell using the middle wafer can reach 11·39%.
    Material Research Innovations 11/2012; 16(6):425-428. DOI:10.1179/1433075X12Y.0000000018 · 0.83 Impact Factor
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    ABSTRACT: As one of the brightest active blazars in both X-ray and very high energy $\gamma$-ray bands, Mrk 501 is very useful for physics associated with jets from AGNs. The ARGO-YBJ experiment is monitoring it for $\gamma$-rays above 0.3 TeV since November 2007. Starting from October 2011 the largest flare since 2005 is observed, which lasts to about April 2012. In this paper, a detailed analysis is reported. During the brightest $\gamma$-rays flaring episodes from October 17 to November 22, 2011, an excess of the event rate over 6 $\sigma$ is detected by ARGO-YBJ in the direction of Mrk 501, corresponding to an increase of the $\gamma$-ray flux above 1 TeV by a factor of 6.6$\pm$2.2 from its steady emission. In particular, the $\gamma$-ray flux above 8 TeV is detected with a significance better than 4 $\sigma$. Based on time-dependent synchrotron self-Compton (SSC) processes, the broad-band energy spectrum is interpreted as the emission from an electron energy distribution parameterized with a single power-law function with an exponential cutoff at its high energy end. The average spectral energy distribution for the steady emission is well described by this simple one-zone SSC model. However, the detection of $\gamma$-rays above 8 TeV during the flare challenges this model due to the hardness of the spectra. Correlations between X-rays and $\gamma$-rays are also investigated.
    The Astrophysical Journal 09/2012; 758(1). DOI:10.1088/0004-637X/758/1/2 · 5.99 Impact Factor
  • J.J. Li · C.H. Zhang · C.L. Xu · X.J. Jia · Y. Song · J.Y. Li · Y.F. Jin ·
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    ABSTRACT: Specimens of 6H–SiC were implanted with Xe ions with multiple kinetic energies at room temperature to obtain nearly uniform Xe concentrations of 7.5, 30, 150 at. ppm, respectively, and were subsequently thermally annealed under high vacuum. The lattice damage and nanohardness of specimens were studied with high resolution X-ray diffraction spectrometry and nanoindentation measurements. In the low dose specimen (7.5 at. ppm), the occurrence of a plateau (with sub-peaks) at low angle side of the SiC (0 0 0 1 2) peak suggests a strain gradient in the direction normal to the specimen surface. Upon subsequent thermal annealing the strain relaxes gradually. The relaxation activation energy of the strain was estimated with Arrhenius law. For the specimens implanted to 30 and 150 at. ppm Xe, the disappearance of the plateau or peak indicates that the implanted region has been amorphized. However, a satellite peak near the main peak reappears after the thermal annealing. In addition, the main peak broadens toward high angle side after the annealing as the result of a shrinkage of crystal lattice. The nanohardness value of the specimen implanted to 7.5 at. ppm exceeds that of virgin SiC, whereas it is opposite for the case of 30 and 150 at. ppm implantation due to the formation of amorphous regions. Changes of nanohardness with thermal annealing temperature were studied. Underlying mechanisms were discussed.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 09/2012; 286:124–128. DOI:10.1016/j.nimb.2011.11.034 · 1.12 Impact Factor
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    ABSTRACT: Specimens of 6H–SiC single crystal were irradiated at room temperature with 2.3 MeV neon ions to three successively increasing fluences of 2 × 1014, 1.1 × 1015 and 3.8 × 1015 ions/cm2 and then annealed at room temperature, 500, 700 and 1000 °C, respectively. The strain in the specimens was investigated with a high resolution XRD spectrometer with an ω-2θ scanning. And the mechanical properties were investigated with the nano-indentation in the continuous stiffness measurement (CSM) mode with a diamond Berkovich indenter. The XRD curves of specimens after irradiation show the diffraction peaks arising at lower angles aside of the main Bragg peak ΘBragg, indicating that a positive strain is produced in the implanted layer. In the as-implanted specimens, the strain increases with the increase of the ion fluence or energy deposition. Recovery of the strain occurs on subsequent thermal annealing treatment and two stages of defects evolution process are displayed. An interpretation of defects migration, annihilation and evolution is given to explain the strain variations of the specimens after annealing. The nano-indentation measurements show that the hardness in as-implanted specimens first increases with the increase of the ion fluence, and a degradation of hardness occurs when the ion fluence exceeds a threshold. On the subsequent annealing, the hardness variations are regarded to be a combined effect of the covalent bonding and the pinning effect of defect clusters.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 09/2012; 286:129–133. DOI:10.1016/j.nimb.2012.01.009 · 1.12 Impact Factor
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    ABSTRACT: The ARGO-YBJ experiment detects extensive air showers in a wide energy range by means of a full-coverage detector which is in stable data taking in its full configuration since November 2007 at the YBJ International Cosmic Ray Observatory (4300 m a.s.l., Tibet, People’s Republic of China). In this paper the measurement of the light-component spectrum of primary cosmic rays in the energy region (5÷200) TeV is reported. The method exploited to analyze the experimental data is based on a Bayesian procedure. The measured intensities of the light component are consistent with the recent CREAM results and higher than that obtained adding the proton and helium spectra reported by the RUNJOB experiment.
    Physical Review D 05/2012; 85(9). DOI:10.1103/PhysRevD.85.092005 · 4.64 Impact Factor
  • H.Y. Wang · Y. Tan · J.Y. Li · Y.Q. Li · W. Dong ·
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    ABSTRACT: A novel method to separate silicon and silicon carbide from kerf loss slurry by Al–Si alloying process has been reported in this paper. The kerf loss slurry was washed and dried, and then aluminum was added on the top of these dry powders with silicon and silicon carbide. The Al–Si alloying process was performed in argon atmosphere using a vacuum carbon tube furnace at 1773 K. In this way, an Al–Si ingot was obtained, on the surface of which a lot of hexagonal crystals were observed. The Al–Si ingot was characterized by X-ray diffraction, scanning electron microscopy, X-ray fluorescence and electron probe micro-analyzer. The X-ray results indicated that the Al4C3 phase was obtained on the top of the cast. The scanning electron microscopy, X-ray diffraction and electron probe micro-analyzer results revealed that the Al–Si alloy without silicon carbide phase formed in the cast, which indicated that silicon and silicon carbide can be separated from slurry by this alloying process.
    Separation and Purification Technology 03/2012; 89:91–93. DOI:10.1016/j.seppur.2012.01.021 · 3.09 Impact Factor
  • Y Cao · W Lu · W H Zhang · S Sha · Y Yang · B H Ma · H Wang · Y H Zhu · J W Guo · X Fang · [...] · Y C Feng · J Y Li · H Y Zhao · H Y Ma · X Z Zhang · X H Guo · Q Wu · L T Sun · H W Zhao · D Z Xie ·
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    ABSTRACT: Ion beam transport from the Superconducting Electron Cyclotron Resonance ion source with Advanced design in Lanzhou (SECRAL) electron cyclotron resonance ion source was studied at the Institute of Modern Physics during 2010. Particle-in-cell simulations and experimental results have shown that both space charge and magnetic aberrations lead to a larger beam envelope and emittance growth. In the existing SECRAL extraction beam line, it has been shown that raising the solenoid lens magnetic field reduces aberrations in the subsequent dipole and results in lower emittance. Detailed beam emittance measurements are presented in this paper.
    The Review of scientific instruments 02/2012; 83(2):02B726. DOI:10.1063/1.3680545 · 1.61 Impact Factor
  • H W Zhao · W Lu · X Z Zhang · Y C Feng · J W Guo · Y Cao · J Y Li · X H Guo · S Sha · L T Sun · D Z Xie ·
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    ABSTRACT: SECRAL (superconducting ECR ion source with advanced design in Lanzhou) ion source has been in routine operation for Heavy Ion Research Facility in Lanzhou (HIRFL) accelerator complex since May 2007. To further enhance the SECRAL performance in order to satisfy the increasing demand for intensive highly charged ion beams, 3-5 kW high power 24 GHz single frequency and 24 GHz +18 GHz double frequency with an aluminum plasma chamber were tested, and some exciting results were produced with quite a few new record highly charged ion beam intensities, such as (129)Xe(35+) of 64 eμA, (129)Xe(42+) of 3 eμA, (209)Bi(41+) of 50 eμA, (209)Bi(50+) of 4.3 eμA and (209)Bi(54+) of 0.2 eμA. In most cases SECRAL is operated at 18 GHz to deliver highly charged heavy ion beams for the HIRFL accelerator, only for those very high charge states and very heavy ion beams such as (209)Bi(36+) and (209)Bi(41+), SECRAL has been operated at 24 GHz. The total operation beam time provided by SECRAL up to July 2011 has exceeded 7720 hours. In this paper, the latest performance, development, and operation status of SECRAL ion source are presented. The latest results and reliable long-term operation for the HIRFL accelerator have demonstrated that SECRAL performance for production of highly charged heavy ion beams remains improving at higher RF power with optimized tuning.
    The Review of scientific instruments 02/2012; 83(2):02A320. DOI:10.1063/1.3666913 · 1.61 Impact Factor
  • W Lu · D Z Xie · X Z Zhang · B Xiong · L Ruan · S Sha · W H Zhang · Y Cao · S H Lin · J W Guo · [...] · Q Wu · H Y Zhao · B H Ma · H Wang · Y H Zhu · Y C Feng · J Y Li · J Q Li · L T Sun · H W Zhao ·
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    ABSTRACT: A new room temperature electron cyclotron resonance (ECR) ion source, DRAGON, is under construction at IMP. DRAGON is designed to operate at microwaves of frequencies of 14.5-18 GHz. Its axial solenoid coils are cooled with evaporative medium to provide an axial magnetic mirror field of 2.5 T at the injection and 1.4 T at the extraction, respectively. In comparison to other conventional room temperature ECR ion sources, DRAGON has so far the largest bore plasma chamber of inner diameter of 126 mm with maximum radial fields of 1.4-1.5 T produced by a non-Halbach permanent sextupole magnet.
    The Review of scientific instruments 02/2012; 83(2):02A328. DOI:10.1063/1.3669800 · 1.61 Impact Factor
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    S Sha · H W Zhao · X H Guo · Z L Zhang · X Fang · J W Guo · W H Zhang · W Lu · Y Cao · H Y Ma · [...] · H Wang · Q Wu · J Y Li · Y C Feng · H Y Zhao · Y H Zhu · L T Sun · X Z Zhang · X M Chen · D Z Xie ·
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    ABSTRACT: A laser (Nd:YAG laser, 3 J, 1064 nm, 8-10 ns) ion source has been built and under development at IMP to provide pulsed high-charge-state heavy ion beams to a radio frequency quadrupole (RFQ) for upgrading the IMP accelerators with a new low-energy beam injector. The laser ion source currently operates in a direct plasma injection scheme to inject the high charge state ions produced from a solid target into the RFQ. The maximum power density on the target was about 8.4 × 10(12) W∕cm(2). The preliminary experimental results will be presented and discussed in this paper.
    The Review of scientific instruments 02/2012; 83(2):02B303. DOI:10.1063/1.3656391 · 1.61 Impact Factor
  • W H Zhang · H Y Ma · Y Yang · Q Wu · X Z Zhang · H Wang · B H Ma · Y C Feng · X Fang · J W Guo · [...] · S Sha · W Lu · S H Lin · X H Guo · H Y Zhao · L T Sun · D Z Xie · S X Peng · Z W Liu · H W Zhao ·
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    ABSTRACT: The structure and preliminary commissioning results of a new 2.45 GHz ECR proton ion source and a dual-lens low energy beam transport (LEBT) system are presented in this paper. The main magnetic field of the ion source is provided by a set of permanent magnets with two small electro-solenoid magnets at the injection and the extraction to fine tune the magnetic field for better microwave coupling. A 50 keV pulsed proton beam extracted by a three-electrode mechanism passes through the LEBT system of length of 1183 mm. This LEBT consists of a diagnosis chamber, two Glaser lenses, two steering magnets, and a final beam defining cone. A set of inner permanent magnetic rings is embedded in each of the two Glaser lenses to produce a flatter axial-field to reduce the lens aberrations.
    The Review of scientific instruments 02/2012; 83(2):02A329. DOI:10.1063/1.3669802 · 1.61 Impact Factor
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    ABSTRACT: Cosmic ray antiprotons provide an important probe to study the cosmic ray propagation in the interstellar space and to investigate the existence of dark matter. Acting the Earth-Moon system as a magnetic spectrometer, paths of primary antiprotons are deflected in the opposite sense with respect to those of the protons in their way to the Earth. This effect allows, in principle, the search for antiparticles in the direction opposite to the observed deficit of cosmic rays due to the Moon (the so-called “Moon shadow”). The ARGO-YBJ experiment, located at the Yangbajing Cosmic Ray Laboratory (Tibet, P.R. China, 4300 m a.s.l., 606 g/cm2), is particularly effective in measuring the cosmic ray antimatter content via the observation of the cosmic rays shadowing effect due to: (1) good angular resolution, pointing accuracy and long-term stability; (2) low energy threshold; (3) real sensitivity to the geomagnetic field. Based on all the data recorded during the period from July 2006 through November 2009 and on a full Monte Carlo simulation, we searched for the existence of the shadow cast by antiprotons in the TeV energy region. No evidence of the existence of antiprotons is found in this energy region. Upper limits to the p̅ /p flux ratio are set to 5% at a median energy of 1.4 TeV and 6% at 5 TeV with a confidence level of 90%. In the TeV energy range these limits are the lowest available.
    Physical Review D 01/2012; 85(2). DOI:10.1103/PhysRevD.85.022002 · 4.64 Impact Factor
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    ABSTRACT: We report the observation of TeV gamma-rays from the Cygnus region using the ARGO-YBJ data collected from 2007 November to 2011 August. Several TeV sources are located in this region including the two bright extended MGRO J2019+37 and MGRO J2031+41. According to the Milagro data set, at 20 TeV MGRO J2019+37 is the most significant source apart from the Crab Nebula. No signal from MGRO J2019+37 is detected by the ARGO-YBJ experiment, and the derived flux upper limits at 90% confidence level for all the events above 600 GeV with medium energy of 3 TeV are lower than the Milagro flux, implying that the source might be variable and hard to be identified as a pulsar wind nebula. The only statistically significant (6.4 standard deviations) gamma-ray signal is found from MGRO J2031+41, with a flux consistent with the measurement by Milagro.
    The Astrophysical Journal Letters 01/2012; 745(2). DOI:10.1088/2041-8205/745/2/L22 · 5.34 Impact Factor

Publication Stats

1k Citations
240.77 Total Impact Points


  • 2005-2014
    • Chinese Academy of Sciences
      • • Institute of Modern Physics
      • • Graduate School
      Peping, Beijing, China
  • 2008-2013
    • Dalian University of Technology
      • School of Materials Science and Engineering
      Lü-ta-shih, Liaoning, China
  • 1970-2013
    • Shandong University
      • Department of Physics
      Chi-nan-shih, Shandong Sheng, China
  • 2010
    • Southwest Jiaotong University
      Hua-yang, Sichuan, China
  • 2009-2010
    • Yunnan University
      • Department of Physics
      Yün-nan, Yunnan, China
  • 2000-2006
    • University of Jinan (Jinan, China)
      Chi-nan-shih, Shandong Sheng, China
  • 2003-2004
    • Hirosaki University
      Khirosaki, Aomori Prefecture, Japan