Lei Zhao

Beijing University of Aeronautics and Astronautics (Beihang University), Beijing, Beijing Shi, China

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Publications (9)9.04 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: In the present paper, under optimum experimental condition, two middle-low alloy slab and homogeneous samples were analyzed under the condition of spatial resolution about 100 microm by scanning mode. Element 2D intensity distribution can be converted into 2D concentration distribution via establishing calibration curve. The results showed that there is a central segregation for C, Si, Mn, P, S and Cu for 86 # slab sample, and C, Si, P and Ti for 174 # slab sample, the width of segregation band was estimated, and it agrees well with metallographic analysis. Homogeneous sample was analyzed by scanning mode, the result showed that C, Si, Mn, P, S and so on are well distributed, and there is no segregation band existing. 2D distribution of element intensity or concentration can be used to indirectly reflect sample's homogeneity. Compared with traditional metallographic analysis, LIBS can not only show central segregation bands position and width, but also provide 2D concentration distribution for C, Si, Mn, P, S etc in detail. This method can be used to characterize segregation band position and its width rapidly, and provide theoretical guidance for improving metallurgical process.
    Guang pu xue yu guang pu fen xi = Guang pu 12/2013; 33(12):3383-7. · 0.29 Impact Factor
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    ABSTRACT: As a truly surface analytical tool, laser-induced breakdown spectroscopy (LIBS) was developed in recent ten years, and in this paper, fundamental theory, instrumentation and it's applications in material science are reviewed in detail. Application progress of elemental distribution and depth profile analysis are mainly discussed in the field of metallurgy, semiconductor and electronical materials at home and abroad. It is pointed out that the pulse energy, ambient gas and it's pressure, and energy distribution of laser beam strongly influence spatial and depth resolution, and meanwhile a approach to improving resolution considering analytical sensitivity is provided. Compared with traditional surface analytical methods, the advantage of LIBS is very large scanning area, high analytical speed, and that conducting materials or non-conducting materials both can be analyzed. It becomes a powerful complement of traditional surface analytical tool.
    Guang pu xue yu guang pu fen xi = Guang pu 06/2012; 32(6):1441-6. · 0.29 Impact Factor
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    ABSTRACT: It has been documented that mitosis orientation (MO) is guided by stress fibers (SFs), which are perpendicular to exogenous cyclic uniaxial stretch. However, the effect of mechanical forces on MO and the mechanism of stretch-induced SFs reorientation are not well elucidated to date. In the present study, we used murine 3T3 fibroblasts as a model, to investigate the effects of uniaxial stretch on SFO and MO utilizing custom-made stretch device. We found that cyclic uniaxial stretch induced both SFs and mitosis directions orienting perpendicularly to the stretch direction. The F-actin and myosin II blockages, which resulted in disoriented SFs and mitosis directions under uniaxial stretch, suggested a high correlation between SFO and MO. Y27632 (10 μM), ML7 (50 μM, or 75 μM), and blebbistatin (50 μM, or 75 μM) treatments resulted in SFO parallel to the principle stretch direction. Upon stimulating and inhibiting the phosphorylation of myosin light chain (p-MLC), we observed a monotonic proportion of SFO to the level of p-MLC. These results suggested that the level of cell contraction is crucial to the response of SFs, either perpendicular or parallel, to the external stretch. Showing the possible role of cell contractility in tuning SFO under external stretch, our experimental data are valuable to understand the predominant factor controlling SFO response to exogenous uniaxial stretch, and thus helpful for improving mechanical models.
    Journal of biomechanics 09/2011; 44(13):2388-94. · 2.66 Impact Factor
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    ABSTRACT: A photo-stimulated discharge (PSD) method is more effective than thermal methods to characterize the deep space charge traps in dielectric materials. In this paper, a new PSD measuring system was first built up based on the optical parametric oscillator laser. The laser can generate continuously tunable wavelengths whose range are 210-420 nm and with average output pulse energy 2.3 mJ. The system overcomes the shortcoming of weak output energy in past experiments, especially in the range of ultraviolet band. The PSD current spectra of PET were measured by this system. The results show that the energy level of charge traps in the PET film is mainly distributed in 4.08~5.18 eV, and the trap density maximum is at 4.22 eV. These data can provide the experimental basis for further research and improvement on electrical properties of materials.
    Modern Physics Letters B 01/2010; 24(18):1933-1941. · 0.48 Impact Factor
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    ABSTRACT: Understanding how hepatic precursor cells can generate differentiated bile ducts is crucial for studies on epithelial morphogenesis and for development of cell therapies for hepatobiliary diseases. Epimorphin (EPM) is a key morphogen for duct morphogenesis in various epithelial organs. The role of EPM in bile duct formation (DF) from hepatic precursor cells, however, is not known. To address this issue, we used WB-F344 rat epithelial stem-like cells as model for bile duct formation. A micropattern and a uniaxial static stretch device was used to investigate the effects of EPM and stress fiber bundles on the mitosis orientation (MO) of WB cells. Immunohistochemistry of liver tissue sections demonstrated high EPM expression around bile ducts in vivo. In vitro, recombinant EPM selectively induced DF through upregulation of CK19 expression and suppression of HNF3alpha and HNF6, with no effects on other hepatocytic genes investigated. Our data provide evidence that EPM guides MO of WB-F344 cells via effects on stress fiber bundles and focal adhesion assembly, as supported by blockade EPM, beta1 integrin, and F-actin assembly. These blockers can also inhibit EPM-induced DF. These results demonstrate a new biophysical action of EPM in bile duct formation, during which determination of MO plays a crucial role.
    PLoS ONE 01/2010; 5(3):e9732. · 3.73 Impact Factor
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    ABSTRACT: In this paper, the photo-stimulated discharge (PSD) current spectra of polyimide (PI) are obtained by the optical parametric oscillator (OPO) laser to characterize the deep space charge traps in the dielectric materials. The result shows that the energy level of charge traps in the PI film is distributed in 3.10~4.10eV, and the main part concentrates in 3.35~3.85eV. These data can provide experimental basis for the further research and improvement on electrical properties of materials.
    01/2010;
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    ABSTRACT: Photo-stimulated discharge (PSD) spectroscopy of polyester (PET), polypropylene (PP), polyimide (PI) of DuPont charged by either corona discharge or contact electrode were performed with self-made PSD measurement system in order to investigate the space charge traps of the polymers. The samples were irradiated with new type of continuously tunable wavelength laser based on the optical parametric oscillator (OPO) through the semi-transparent electrode. Experimental results indicate that the energy distribution of traps varies with different materials: there exists only one single trap energy level to be activated by OPO laser in PET, however, broad peaks spectrum in PI and PP. In the meanwhile some of deep trap are ascribed to factors like additives such as cross-linking agent. The effect of molecular motions on thermal erosion of the traps was also investigated.
    Properties and Applications of Dielectric Materials, 2009. ICPADM 2009. IEEE 9th International Conference on the; 08/2009
  • [show abstract] [hide abstract]
    ABSTRACT: Photo-stimulated discharge (PSD) is an effective method to characterize the deep traps in the dielectric materials. In this paper, a new PSD measuring system was firstly built up based on the optical parametric oscillator laser. The laser can generate continuously tunable wavelength output light of which wavelength range is 210-420 nm and average output pulse energy is 2.3 mJ. The system overcomes the shortcoming of weak output energy in the experiments before, especially in the range of ultraviolet band. Experiments proved that this PSD system can work well and can be widely used in the theoretical and practical research of the dielectric materials.
    01/2009;
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    ABSTRACT: Lens-to-sample distances, delay time, atmospheric condition, laser pulse energy, etc. had obvious effects on the analytical performance of laser-induced breakdown spectroscopy. In this paper, these parameters are investigated in greater detail and we will explain how they have influences on the analytical performance. The results show that the focal plane under the sample surface can improve precision and detection limit, and the delay time should be decided according to sensitivity and accuracy. Spectral line intensity is stronger in argon than helium, nitrogen and air gas environment. Pulse energy should exceed energy threshold (about 50 mJ) which can generate plasma, and the energy should not exceed about 300 mJ to avoid plasma shielding. Under optimum parameters, concentration relative standard deviation of C, Si, Mn, P, S, Ni, and Cr for low-alloyed steel (sample number 11278) which were measured 11 times is 2.37%, 2.18%, 2.23%, 7.8%, 9.34%, 1.92%, and 2.13%, respectively. And the detection limit of C, Si, Mn, P, S, Ni, and Cr for pure steel is 0.0045%, 0.0072%, 0.0069%, 0.0027%, 0.0024%, 0.0047%, and 0.0024%, respectively.
    Frontiers of Physics 7(6). · 1.59 Impact Factor

Publication Stats

12 Citations
277 Views
9.04 Total Impact Points

Institutions

  • 2010–2011
    • Beijing University of Aeronautics and Astronautics (Beihang University)
      • School of Biological and Medical Engineering
      Beijing, Beijing Shi, China