C. Ma

Qingdao University, Tsingtao, Shandong Sheng, China

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Publications (305)571.68 Total impact

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    ABSTRACT: This paper describes some experimental studies about the effect of interface wettability on hydrodynamic lubrication film thickness by a custom-made slider bearing tester. The lubricated contact pair consists of a fixed-incline slider and a transparent disc, and a thin lubrication film can be generated when the disc rotates. The film thickness was measured by interferometry. The wettability of different slider surfaces was evaluated by the contact angle of the lubricant on them. The relationship of film thickness versus disc speed was measured under different liquid–solid interfaces, and the results showed that slider surfaces with strong wettability to the lubricant could generate higher film thickness. Furthermore, case experiments were carried out to validate the hydrodynamic effect by tailored-slippage. By numerical simulations, the experimental findings were tentatively explained with the phenomenon of wall slippage.
    Tribology Letters 04/2014; 54(1). · 1.74 Impact Factor
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    ABSTRACT: The transition between different states in manganites can be driven by various external stimuli. Controlling these transitions with light opens the possibility to investigate the microscopic path through which they evolve. We performed femtosecond (fs) transmission electron microscopy on a bi-layered manganite to study its response to ultrafast photoexcitation. We show that a photoinduced temperature jump launches a pressure wave that provokes coherent oscillations of the lattice parameters, detected via ultrafast electron diffraction. Their impact on the electronic structure are monitored via ultrafast electron energy loss spectroscopy (EELS), revealing the dynamics of the different orbitals in response to specific structural distortions.
    01/2014;
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    ABSTRACT: The superconducting (SC) phase in the phase-separated (PS) K0.8Fe1.6+xSe2 (0<=x<=0.15) materials is found to crystallize on Archimedean solid-like frameworks, this structural feature originate from a spinodal phase separation (SPS) at around Ts~540K depending slightly on the Fe concentration. Two stable phases in K0.8Fe1.6+xSe2 are demonstrated to be the SC K0.5Fe2Se2 and antiferromagnetic (AFM) K0.8Fe1.6Se2. The spinodal waves go along the systematic [113] direction and result in notable lamellar structure as illustrated by using the strain-field theoretical simulation. The 3-dimentional SC framework is constructed by hollow truncated octahedra similar with what discussed for Archimedean solids. Based on this structural model, we can efficiently calculate the volume fraction of SC phase in this type of PS SC materials.
    01/2014;
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    ABSTRACT: The current filament phenomena in high gain gallium arsenide (GaAs) photoconductive semiconductor switches (PCSS) always draw a significant influence on the lifetime of the devices. This paper presents a study on the influence of the current filament over the material properties and output characteristics of the GaAs PCSS. The working principle of the current filaments has been analyzed and it is shown that the performance of GaAs PCSS degrades due to the heating effects of the current filaments. It is observed that the heating effect of current filament reduces the dark resistivity of the GaAs material; furthermore, it gradually damages electrode of PCSS, leading to the breakdown of PCSS. This paper presents the relationship between the turn-ON process and damage of the PCSS.
    IEEE Transactions on Electron Devices 01/2014; 61(7):2432-2436. · 2.06 Impact Factor
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    ABSTRACT: The structural features of the antiferromagnetic K0.8Fe1.6S2 have been studied in the temperature range from 300 K up to 700 K by means of in situ transmission electron microscopy (TEM). The superstructure with a wave vector originating from a Fe-vacancy order has been clearly observed; moreover, the structural analysis shows that K0.8Fe1.6S2 undergoes a transition from the Fe-vacancy order to disorder at about 585 K. The S substitution effect on the phase separation and superconductivity in the K0.8Fe1.75Se2−ySy materials has been systematically investigated by SEM and TEM structural analyses, as well as by electrical resistivity measurements. Our experimental results reveal that the S element adopts a homogeneous distribution in all investigated materials, and the essential phase-separation nature is very similar to what was observed in the K0.8Fe1.75Se2 superconductor. A phase-separated state formed by the coexistence of two Fe-vacancy orders with wave vectors and in K0.8Fe1.5+xS2 (0 < x < 0.1) has been briefly discussed.
    EPL (Europhysics Letters) 08/2013; 103(3):37010. · 2.26 Impact Factor
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    ABSTRACT: Two series of K0.8Fe1.75−xCuxSe2 () and K0.8Fe1.75Se2−yTey () single crystals of nominal composition have been prepared and their physical properties and microstructural features have been studied. Resistivity measurements demonstrate that the superconducting transition temperature decreases gradually with the increase of the substitution level and zero resistivity finally disappears in both systems. Systematic TEM, SEM and XRD structural analyses, in combination with the magnetic experimental data, reveal a rich variety of structural phenomena resulting from different types of substitution. Cu substitution gives rise to the volume of a new non-superconducting Cu-rich phase with modulation coexisting with the superconducting stripe domain. With the increase of the ratio of the new non-superconducting phase along with doping, the superconducting path is finally cut off, and results in the absence of zero resistivity. In contrast, the absence of superconductivity in Te-substituted materials is correlated with the complete disappearance of the q2 superconducting phase due to the suppression of phase separation.
    EPL (Europhysics Letters) 05/2013; 102(3):37010. · 2.26 Impact Factor
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    ABSTRACT: Multiferroic Bi1-xCaxFeO3-x/2 (0.10 ⩽ x ⩽ 0.50) materials have been synthesized via a high-temperature sintering method. The structural properties have been studied using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). The EELS measurements reveal that the oxidation state of Fe ions in these compounds is Fe+3, and oxygen vacancies are created as Ca substitutions for Bi. A series of superstructure modulations appear along the a-axis direction, and their wavelength can be written as L = na (n = 4, 5, 6 and 7) depending on the Ca contents. Based on our structural analysis, we interpret these superstructures in terms of oxygen-vacancy ordering associated with local structural distortions.
    EPL (Europhysics Letters) 04/2013; 102(2):27002-. · 2.26 Impact Factor
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    ABSTRACT: The interplay between magnetism and superconductivity is one of the dominant themes in the study of unconventional superconductors, such as high-Tc cuprates, iron pnictides and heavy fermions. In such systems, the same d- or f-electrons tend to form magnetically ordered states and participate in building up a high density of states at the Fermi level, which is responsible for the superconductivity. Charge-density-wave (CDW) is another fascinating collective quantum phenomenon in some low dimensional materials, like the prototypical transition-metal poly-chalcogenides, in which CDW instability is frequently found to accompany with superconducting transition at low temperatures. Remarkably, similar to the antiferromagnetic superconductors, superconductivity can also be achieved upon suppression of CDW order via chemical doping or applied pressure in 1T-TiSe2. However, in these CDW superconductors, the two ground states are believed to occur in different parts of Fermi surface (FS) sheets, derived mainly from chalcogen p-states and transition metal d-states, respectively. The origin of superconductivity and its interplay with CDW instability has not yet been unambiguously determined. Here we report on the discovery of bulk superconductivity in Pd-intercalated CDW RETen (RE=rare earth; n=2.5, 3) compounds, which belong to a large family of rare-earth poly-chalcogenides with CDW instability usually developing in the planar square nets of tellurium at remarkably high transition temperature and the electronic properties are also dominated by chalcogen p-orbitals. Our study demonstrates that the intercalation of palladium leads to the suppression of the CDW order and the emergence of the superconductivity. Our finding could provide an ideal model system for comprehensive studies of the interplay between CDW and superconductivity.
    01/2013;
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    ABSTRACT: A new inverse spinel ScMn2O4 has been synthesized and characterized by measurements of structural and physical properties. The crystal structure of ScMn2O4, similar with the spinel Mn3O4, is made up of Mn2+ located at tetrahedral site and Mn3+/Sc3+ ions randomly located at the octahedral site. Experimental results of magnetic susceptibility and heat capacity demonstrate that ScMn2O4 undergoes a ferrimagnetic phase transition at the temperature of about 58 K. Extensive analyses on the data obtained from structural refinement, electronic structural calculation and EELS spectra measurement suggests that substitution of Sc for Mn in MnO6 octahedron could greatly suppress Jahn–Teller distortions in comparison with what observed in Mn3O4.
    Solid State Communications 01/2013; 153(1):71–75. · 1.53 Impact Factor
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    ABSTRACT: Subbarrier fusion of the 7 Li+ 12 C reaction is studied using an antisymmetrized molecular dynamics model (AMD) with an after burner, GEMINI. In AMD, 7 Li shows an α + t structure at its ground state and it is significantly deformed. Simulations are made near the Coulomb barrier energies, i.e., Ecm = 3 − 8M eV . The total fusion cross section of the AMD + GEMINI calculations as a function of incident energy is compared to the experimental results and both are in good agreement at Ecm > 3M eV . The cross section for the different residue channels of the AMD + GEMINI at Ecm = 5M eV is also compared to the experimental results.
    01/2013; 420.
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    ABSTRACT: A series of oxygen deficient LuFe(2)O(4-δ) materials have been prepared under a controlled oxygen partial-pressure atmosphere. Measurements of magnetization reveal that the increase of oxygen deficiencies could evidently depress the ferrimagnetic phase transition temperature (T(N)). In additional to the well-known charge ordering within the ([Formula: see text]) crystal plane, a visible structural modulation with q = (0,1/4.2,7/8) commonly appears on the (100) plane in the oxygen deficient samples. An aberration-corrected transmission electron microscopy study on the oxygen deficient samples demonstrates the presence of oxygen vacancies and local structural distortion. The atomic structural features in correlation with the structural modulation, distortion of the FeO(5) polyhedron and the (001) twinning domains have been also examined.
    Journal of Physics Condensed Matter 10/2012; 24(43):435901. · 2.22 Impact Factor
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    ABSTRACT: Subbarrier fusion of the 7Li + 12C reaction is studied using an antisymmetrized molecular dynamics model (AMD) with an after burner, GEMINI. In AMD, 7Li shows an \alpha + t structure at its ground state and it is significantly deformed. Simulations are made near the Coulomb barrier energies, i.e., E_{cm} = 3 - 8 MeV. The total fusion cross section of the AMD + GEMINI calculations as a function of incident energy is compared to the experimental results and both are in good agreement at E_{cm} > 3 MeV. The cross section for the different residue channels of the AMD + GEMINI at E_{cm} = 5 MeV is also compared to the experimental results.
    Journal of Physics Conference Series 09/2012; 420(1).
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    ABSTRACT: Electronic structural features of the charge ordered (CO) state in Fe2OBO3 have been theoretically calculated by using the ab initio method and analyzed in comparison with the experimental results of electron energy-loss spectroscopy (EELS). Structural relaxations using GGA+U reveal that the CO structure has a supercell of 2a × b × c with the CO modulation along the a-axis direction. The theoretical investigations suggest that both lattice distortions and electrostatic repulsion are essentially important for understanding the properties of the CO state in the present system. This conclusion is also supported by the agreement between experimental and theoretical data for the O-K and Fe-L2,3 edges in the electron energy-loss spectra. Moreover, both bond-valence-sum and spectral analysis demonstrate that the CO state adopts a quasi-ionic nature in Fe2OBO3.
    Physical review. B, Condensed matter 07/2012; · 3.77 Impact Factor
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    ABSTRACT: Purpose: To analyze and report prostate intrafractional motion recorded online during external beam radiotherapy and to provide guidance for advanced prostate IMRT. Methods: Prostate intrafractional motion during IMRT and RapidARC treatments was tracked and recorded using a Calypso 4D-localization system. Data for 8600 treatment fractions of 230 prostate patients was analyzed. The percentage of treatment fractions, the fractional treatment time, and the fractional time of any individual minute were analyzed separately for prostate movements greater than the thresholds (2, 3, 5 and 7mm). Results: The percentages of fractions in which prostate shifted more than the thresholds for a duration >10 seconds are 66.2%, 34.9%, 8.9% and 2.6% (57.9%, 27.9%, 5.2% and 0.8% for >30 seconds duration), respectively. For 10 patients who exhibited the largest motion, the percentages are 95.2%, 76.0%, 43.2% and 14.7% (91.3%, 72.4%, 36.3% and 6.0% for >30 seconds duration). The fractional time for motion larger than the thresholds is 27.8%, 10.7%, 1.6% and 0.3% (56.2%, 33.7%, 11.2% and 2.1% for these patients). The posterior-direction motion is significantly higher than those in other directions. The fractional time of an individual minute with shift >3mm is higher at the 10th minute than at the 5th minute (20% vs. 10%) after the initial setup. For treatments completed within 5 minutes, the average fractional time with motion >3mm was lower than those within 10 minutes (4% vs. 12%). Irregular movements were observed most likely in the first minute after patient's setup, which were 12% and 7% among all fractions with movements >2mm and >3mm, respectively. Conclusions: The prostate intrafractional motion was within 3mm for most treatment fractions. However, larger movements were observed for some patients, who require real-time corrections or larger treatment margins. The results indicate that it is beneficial if the treatment can be completed within 5 minutes.
    Medical Physics 06/2012; 39(6):3617. · 2.91 Impact Factor
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    ABSTRACT: Purpose: To evaluate the 3D dose distributions using the PDP technique for VMAT H&N treatments. Methods: The novel PDP algorithm uses the patient structures, TPS dose calculation and plan as a base line, then applies the ARC delivery time dependent ArcCheck (Sun Nuclear, Inc.) measurement with the TPS phantom dose to derive patient dose. Five VMAT H&N plans were generated on a Rando phantom with PTV-to-skin distances of 0,1,2,3, and 5 mm, using the Eclipse TPS (Varian, Inc.). Treatments were then delivered on a Varian iX linear accelerator. We compared the measured to calculated data by using 3D gamma analysis, and examined the mean and maximum dose of the PTV DVH. Results: By using a recommended 2 mm(3) calculation voxel the 3D gamma analysis passed 99.6 to 99.9% for a 3% global dose difference and 3mm DTA with a 5% dose threshold. The PTV organ analysis hot-to-cold dose failing point ratio was about 33.8, 21.7 and 22.2, for the 5, 3, and 2 mm PTV-to-surface distance respectively. For the 1 mm distance case, the ratio was about 0.45 and for the 0 mm distance the ratio was found to be 0.37. With a PTV-to-surface distance decrease, the hot spot was found to increase, and the target coverage and homogeneity were degraded. Conclusions: For the recommended 5 mm PTV-to-surface distance the DVH analysis indicated a lower measured target coverage and homogeneity than the planned. This indication is more pronounced as the PTV-to-surface distance decreases. The failing points grew colder as the PTV moves closer to the skin, indicating a TPS over estimation of the surface dose, which agrees with TLD skin measurement published data.
    Medical Physics 06/2012; 39(6):3714. · 2.91 Impact Factor
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    ABSTRACT: Purpose: To examine and facilitate the feasibility of the ArcCheck cylindrical diode array system as a patient specific QA device for CyberKnife radiosurgery delivery. Methods: There is an obvious necessity for CyberKnife robotic radiosurgery patient QA procedures for hypofractionated treatment of larger planned treatment volumes (PTV), e.g. prostate. This need will increase when the future CyberKnife MLC is introduced. The small unflattened CyberKnife fields, along with the variation of beam-to-detector spatial angles, pose a significant detection challenge for dosimetric systems. The feasibility of the ArcCheck (Sun Nuclear Inc.) cylindrical diode array system for patient-specific QA on the CyberKnife is demonstrated using a beam-to-diode specific angular correction that was developed and has been applied. For localization and tracking, four gold seed fiducial markers were embedded in the system's central plug. We used a Monte Carlo 1% uncertainty for the dose calculation. Results: By disabling the Linac based corrections and applying the custom CyberKnife correction that we developed, the passing rate increased from 39.6% to 99.8% using a 3%3mm gamma criteria for a given lung case. An additional lung case passed 98.5%. In both cases, a 10% dose threshold was used. In addition, brain, trigeminal nerve and lung cases with synchrony tracking are being investigated. Conclusions: We demonstrated the ArcCheck feasibility for CyberKnife patient specific QA performance. The custom CK angular correction that we developed and applied showed a high passing rate for the lung cases. A verification of the polar angle response should be conducted, in addition to the azimuthal angle that was verified for Linacs. Any data that is being retrieved is additional data to the current chamber point measurement procedures.
    Medical Physics 06/2012; 39(6):3968. · 2.91 Impact Factor
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    ABSTRACT: Purpose: To evaluate the Volumetric Modulated Arc Therapy (VMAT, RapidArc) and IMRT plan quality for prostate deliveries conducted by two different treatment planning systems: Oncentra Masterplan (Nucletron inc.) and Eclipse (Varian inc.). Methods: We investigated ten prostate treatment delivery plans. For a given case studied we created a RapidArc plan (Eclipse), a VMAT and an IMRT plan (Oncentra) by using both treatment planning systems. The rotational therapy plans consisted of 2 to 3 arcs and the IMRT fields consisted of 7 to 9 fields. The prescription dose was 200 cGy X 40 fx using a Varian Trilogy with 10 MV beams. The treatment parameters were used to evaluate the plan quality: the minimal, mean and maximal doses to the target (PTV) and the volumes received 65Gy and 40 Gy, respectively, for the rectum and bladder, V65 and V40. In addition, we calculated the conformity index (CI) and the heterogeneity index (HI) for each delivery type. Results: No significant difference was found between RapidArc, VMAT and IMRT, regarding the minimal and average PTV dose value. The rectum and bladder constraints showed no significant variation as well. The PTV hot spot was significantly higher for the VMAT plan compared to the RapidArc plan (p=0.007). The target CI for VMAT (0.55±0.05) and IMRT (0.71±0.08) was found to be smaller than the RapidArc (0.82±0.04) and the difference is statistically significant (p=0). The HI, value was found to have no significant difference between RapidArc, VMAT and IMRT plan deliveries. Conclusions: Two TPS are capable of producing high-quality treatment plans for prostate cancer. The quality is associated with the degree of intensity modulation and the number of incident angles. Overall, the RapidArc plans with 2-3 arcs showed better dosimetric qualities than the VMAT and IMRT plans.
    Medical Physics 06/2012; 39(6):3842. · 2.91 Impact Factor
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    ABSTRACT: Purpose: The CyberKnife uses an online prediction model to track moving targets. The system works well if patients can breathe regularly. However, some patients cannot maintain a regular breathing pattern, which means a larger PTV margin is necessary for these patients to ensure sufficient CTV dose coverage. However, it is very difficult to predict a patient's breathing pattern in advance. The purpose of this study is to investigate a quick and easy way to adapt the treatment plan if extra margins are needed. Methods: Multiple algorithms have been developed to calculate the adjustment. Generally, if a larger target region requires coverage by the prescription dose, the size of the beams will be larger and they should move in a peripheral direction for a certain distance to avoid hot spots. Dose is recalculated and renormalized consistently after the adjustment. If the dose distribution of the new plan covers the new PTV with acceptable conformality and coverage, the plan will be used for treatment. Otherwise, more iterations of the adjustment are performed. Dose calculations are limited to a small region surrounding the target to reduce calculation time. Results: 5 clinical cases (3 lungs, 1 liver and 1 adrenal) have been tested in this study. The dose margin can be extended up to 10 mm without changing dose distributions around the target region dramatically. The average PTV coverage is 98.7% compared to 99.1% in the original plans and the average CI is 1.22, which is slightly less than the 1.24 in the original plans. Conclusions: Treatment margins can be sufficiently expanded resulting in satisfactory plan quality for patients with breathing irregularities.
    Medical Physics 06/2012; 39(6):3852-3853. · 2.91 Impact Factor
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    ABSTRACT: Purpose: This study aims to investigate the feasibility of using the images of the treatment fields acquired by an electronic portal imaging device (EPID) for real-time target localization. Methods: Forty one patients treated with IMRT and RapidArc were recruited in this study including 37 prostate patients and 4 lung patients. These patients were grouped as: prostate IMRT with lymph node (n=14), prostate IMRT without lymph node (n=17), prostate RapidArc (n=6), and lung IMRT (n=4). For each patient, two to four fiducial markers were implanted inside the tumor. The DRR, which projects the patient anatomy and the fiducial marker at the EPID location, was reconstructed for each field. The MLC aperture of each control point was overlay on its corresponding DRR to evaluate the fractional time when the fiducial marker was seen on the EPID image. The probability of seeing at least one, two, three, and four fiducial markers during the treatment was recorded. Results: For the prostate IMRT patients without lymph nodes included in the target volume, the average probability of seeing at least one, two, three, and four fiducial markers during the treatment was 50% (35%-59%), 39% (23%-51%), 24% (7%-38%), and 12% (4%-29%), respectively. For the prostate IMRT patients with lymph nodes, the probability was 41% (24%-51%), 29% (12%-42%), 15% (3%-24%), and 7% (4%-15%), respectively. For prostate RapidArc treatments using two arcs, the average probability of seeing at least one fiducial marker was 81% (58%-90%) for the full arc and 74% (53%-94%) for the partial arc. For the lung IMRT treatment, the average probability of seeing at least one fiducial marker was 34% (20%-52%). Conclusions: The continuous image acquisition from the EPID during the treatment provides sufficient target movement information for real-time target localization and intrafractional target motion correction for advanced radiotherapy treatments.
    Medical Physics 06/2012; 39(6):3684. · 2.91 Impact Factor
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    ABSTRACT: Purpose: There are two collimation systems associated with the CyberKnife system, the fixed cone collimator and the Iris collimator. The Iris collimator is used more frequently because of its superior flexibility. However, sometimes treatments have to be canceled or postponed due to Iris collimator mechanical failures. The purpose of this study is to investigate the feasibility of switching collimation systems without replanning. Methods: We first performed Monte Carlo simulations on 10 clinical cases using the Iris collimator and the fixed cone collimator. The conformality index (CI), target volume coverage and the maximum, minimum and mean doses to the critical structures from the iris and fixed plans were compared to determine the feasibility of switching between collimator types without replanning. Results: Our results showed that the two types of collimators deliver similar dose distributions. The average target doses for the fixed plans were 1% to 6% higher than those for the Iris plans. The average CI for the fixed plans was 1.36 compared to 1.28 for the Iris plans. Thus, we adjusted the Iris sizes with a scale factor of 1.024 to achieve a better dose match with the fixed collimators. Doses for the 10 cases were then recalculated. Once this correction was made, the difference between the average target doses for the two collimator plans was reduced to less than 2% and the CIs became almost identical. Conclusions: Small target dose differences were found between plans using different collimation systems, which may be compensated for by adjusting the Iris collimator sizes to ensure similar dose distributions. The differences in the doses to the critical structures between the collimation systems were insignificant. After adjusting the Iris collimator sizes and re-commissioning the planning system, patients can be safely switched from the Iris collimator to the fixed cone collimator without replanning.
    Medical Physics 06/2012; 39(6):3808. · 2.91 Impact Factor

Publication Stats

296 Citations
571.68 Total Impact Points

Institutions

  • 2014
    • Qingdao University
      Tsingtao, Shandong Sheng, China
  • 2013
    • Henan Normal University
      Henan’an, Guangdong, China
  • 2007–2013
    • Chinese Academy of Sciences
      • Institute of Physics
      Peping, Beijing, China
    • Beijing University of Chemical Technology
      Peping, Beijing, China
  • 2012
    • Qiqihar Medical University
      Zizikar, Heilongjiang Sheng, China
  • 2006–2011
    • Northeast Institute of Geography and Agroecology
      • Institute of Physics
      Beijing, Beijing Shi, China
    • Beijing University of Aeronautics and Astronautics (Beihang University)
      • School of Material Science and Engineering
      Beijing, Beijing Shi, China
  • 2010
    • Qingdao University of Science and Technology
      Tsingtao, Shandong Sheng, China
  • 2004–2010
    • Fox Chase Cancer Center
      • Department of Radiation Oncology
      Philadelphia, Pennsylvania, United States