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Search Results: 1 - 10 of 157537 matches for " Q. Y. Zhang "
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Study on low-energy sputtering near the threshold energy by molecular dynamics simulations
C. Yan,Q. Y. Zhang
AIP Advances , 2012, DOI: 10.1063/1.4738951
Abstract: Using molecular dynamics simulation, we have studied the low-energy sputtering at the energies near the sputtering threshold. Different projectile-target combinations of noble metal atoms (Cu, Ag, Au, Ni, Pd, and Pt) are simulated in the range of incident energy from 0.1 to 200 eV. It is found that the threshold energies for sputtering are different for the cases of M1 < M2 and M1 ≥ M2, where M1 and M2 are atomic mass of projectile and target atoms, respectively. The sputtering yields are found to have a linear dependence on the reduced incident energy, but the dependence behaviors are different for the both cases. The two new formulas are suggested to describe the energy dependences of the both cases by fitting the simulation results with the determined threshold energies. With the study on the energy dependences of sticking probabilities and traces of the projectiles and recoils, we propose two different mechanisms to describe the sputtering behavior of low-energy atoms near the threshold energy for the cases of M1 < M2 and M1 ≥ M2, respectively.
Turbulent convection model in the overshooting region: II. Theoretical analysis
Q. S. Zhang,Y. Li
Physics , 2012, DOI: 10.1088/0004-637X/750/1/11
Abstract: Turbulent convection models are thought to be good tools to deal with the convective overshooting in the stellar interior. However, they are too complex to be applied in calculations of stellar structure and evolution. In order to understand the physical processes of the convective overshooting and to simplify the application of turbulent convection models, a semi-analytic solution is necessary. We obtain the approximate solution and asymptotic solution of the turbulent convection model in the overshooting region, and find some important properties of the convective overshooting: I. The overshooting region can be partitioned into three parts: a thin region just outside the convective boundary with high efficiency of turbulent heat transfer, a power law dissipation region of turbulent kinetic energy in the middle, and a thermal dissipation area with rapidly decreasing turbulent kinetic energy. The decaying indices of the turbulent correlations $k$, $\bar{u_{r}'T'}$, and $\bar{T'T'}$ are only determined by the parameters of the TCM, and there is an equilibrium value of the anisotropic degree $\omega$. II. The overshooting length of the turbulent heat flux $\bar{u_{r}'T'}$ is about $1H_k$($H_k=|\frac{dr}{dlnk}|$). III. The value of the turbulent kinetic energy at the convective boundary $k_C$ can be estimated by a method called \textsl{the maximum of diffusion}. Turbulent correlations in the overshooting region can be estimated by using $k_C$ and exponentially decreasing functions with the decaying indices.
Calibrating the updated overshoot mixing model on eclipsing binary stars: HY Vir, YZ Cas, X2 Hya & VV Crv
Y. Meng,Q. S. Zhang
Physics , 2014, DOI: 10.1088/0004-637X/787/2/127
Abstract: The detached eclipsing binary stars with convective cores provide a good tool to investigate the convective core overshoot. It has been performed on some binary stars to restrict the classical overshoot model which simply extends the boundary of fully mixed region. However, the classical overshoot model is physically unreasonable and inconsistent with the helioseismic investigation. An updated model of the overshoot mixing was established recently. There is a key parameter in the model. In this paper, we use the observations of four eclipsing binary stars, i.e., HY Vir, YZ Cas, $\rm{\chi^2}$ Hya and VV Crv, to investigate the suitable value for the parameter. It is found that the suggested value by the calibrations on eclipsing binary stars is same as the recommended value by other ways. And we have studied the effects of the updated overshoot model on the stellar structure. The diffusion coefficient of the convective/overshoot mixing is very high in the convection zone, then quickly decreases near the convective boundary, and exponentially decreases in the overshoot region. The low value of the diffusion coefficient in the overshoot region leads to weak mixing and the partially mixed overshoot region. The semi-convection, which appears in the standard stellar models of low-mass stars with convective core, is removed by the partial overshoot mixing.
Improvement of colchicine oral bioavailability by incorporating eugenol in the nanoemulsion as an oil excipient and enhancer
Shen Q, Wang Y, Zhang Y
International Journal of Nanomedicine , 2011, DOI: http://dx.doi.org/10.2147/IJN.S20903
Abstract: ovement of colchicine oral bioavailability by incorporating eugenol in the nanoemulsion as an oil excipient and enhancer Original Research (4154) Total Article Views Authors: Shen Q, Wang Y, Zhang Y Published Date June 2011 Volume 2011:6 Pages 1237 - 1243 DOI: http://dx.doi.org/10.2147/IJN.S20903 Qi Shen, Ying Wang, Yi Zhang School of Pharmacy, Shanghai Jiao Tong University, Dongchuan Road 800, Shanghai 200240, People’s Republic of China Abstract: The effect of eugenol on colchicine transport across an isolated rat intestinal membrane was studied using an in vitro diffusion chamber system. We found that eugenol increased the absorptive transport of the drug efficiently. The effect of eugenol on intestinal absorption of colchicine in an oral administrative nanoemulsion formulation was also demonstrated in vivo. The colchicine nanoemulsion was prepared with isopropyl myristate, eugenol, Tween80, ethanol and water, and eugenol was used as an oil phase in the formulation; an average particle size of this nanoemulsion was 41.2 ± 7.2 nm. The permeation of colchicine in the nanoemulsion across the intestinal membrane was significantly different from that of the control group (0.2 mM colchicine). Finally, co-administration of eugenol in colchicine nanoemulsion to enhance the colchicine bioavailability was investigated by an oral administration method. After oral administration of colchicine (8 mg/kg) in the form of either the nanoemulsion or in free colchicine solution, the relative bioavailability of nanoemulsion and eugenol–nanoemulsion were enhanced by about 1.6- and 2.1-fold, respectively, compared with free colchicine solution. The procedure indicated that the intestinal absorption of colchicine was enhanced significantly by eugenol in the tested nanoemulsion. All the results suggested that eugenol is an efficient component in an oral administrative formulation for improving the intestinal absorption of colchicine.
Improvement of colchicine oral bioavailability by incorporating eugenol in the nanoemulsion as an oil excipient and enhancer
Shen Q,Wang Y,Zhang Y
International Journal of Nanomedicine , 2011,
Abstract: Qi Shen, Ying Wang, Yi ZhangSchool of Pharmacy, Shanghai Jiao Tong University, Dongchuan Road 800, Shanghai 200240, People’s Republic of ChinaAbstract: The effect of eugenol on colchicine transport across an isolated rat intestinal membrane was studied using an in vitro diffusion chamber system. We found that eugenol increased the absorptive transport of the drug efficiently. The effect of eugenol on intestinal absorption of colchicine in an oral administrative nanoemulsion formulation was also demonstrated in vivo. The colchicine nanoemulsion was prepared with isopropyl myristate, eugenol, Tween80, ethanol and water, and eugenol was used as an oil phase in the formulation; an average particle size of this nanoemulsion was 41.2 ± 7.2 nm. The permeation of colchicine in the nanoemulsion across the intestinal membrane was significantly different from that of the control group (0.2 mM colchicine). Finally, co-administration of eugenol in colchicine nanoemulsion to enhance the colchicine bioavailability was investigated by an oral administration method. After oral administration of colchicine (8 mg/kg) in the form of either the nanoemulsion or in free colchicine solution, the relative bioavailability of nanoemulsion and eugenol–nanoemulsion were enhanced by about 1.6- and 2.1-fold, respectively, compared with free colchicine solution. The procedure indicated that the intestinal absorption of colchicine was enhanced significantly by eugenol in the tested nanoemulsion. All the results suggested that eugenol is an efficient component in an oral administrative formulation for improving the intestinal absorption of colchicine.Keywords: intestinal absorption, nanoemulsion, absorption enhancement, eugenol
Dynamic Monitoring of Plant Cover and Soil Erosion Using Remote Sensing, Mathematical Modeling, Computer Simulation and GIS Techniques  [PDF]
Z. Y. Zeng, J. Z. Cao, Z. J. Gu, Z. L. Zhang, W. Zheng, Y. Q. Cao, H. Y. Peng
American Journal of Plant Sciences (AJPS) , 2013, DOI: 10.4236/ajps.2013.47180
Abstract:

Dynamic monitoring of plant cover and soil erosion often uses remote sensing data, especially for estimating the plant cover rate (vegetation coverage) by vegetation index. However, the latter is influenced by atmospheric effects and methods for correcting them are still imperfect and disputed. This research supposed and practiced an indirect, fast, and operational method to conduct atmospheric correction of images for getting comparable vegetation index values in different times. It tries to find a variable free from atmospheric effects, e.g., the mean vegetation coverage value of the whole study area, as a basis to reduce atmospheric correction parameters by establishing mathematical models and conducting simulation calculations. Using these parameters, the images can be atmospherically corrected. And then, the vegetation index and corresponding vegetation coverage values for all pixels, the vegetation coverage maps and coverage grade maps for different years were calculated, i.e., the plant cover monitoring was realized. Using the vegetation coverage grade maps and the ground slope grade map from a DEM to generate soil erosion grade maps for different years, the soil erosion monitoring was also realized. The results show that in the study area the vegetation coverage was the lowest in 1976, much better in 1989, but a bit worse again in 2001. Towards the soil erosion, it had been mitigated continuously from 1976 to 1989 and then to 2001. It is interesting that a little decrease of vegetation coverage from 1989 to 2001 did not lead to increase of soil erosion. The reason is that the decrease of vegetation coverage was chiefly caused by urbanization and thus mainly occurred in very gentle terrains, where soil erosion was naturally slight. The results clearly indicate the details of plant cover and soil erosion change in 25 years and also offer a scientific foundation for plant and soil conservation.

Porous Bulk Metallic Glass Fabricated by Powder Consolidation  [PDF]
Z.Y. Suo, S.W. Liu, L. Zhang, H. L. Gao, H. Y. Zhang, K. Q. Qiu
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2008, DOI: 10.4236/jmmce.2008.72008
Abstract: A synthesis method for the production of porous bulk metallic glass (BMG) is introduced. This method utilizes the superplastic forming ability of amorphous powder in the supercooled liquid (SCL) state and intenerating salt mixture as a placeholder to produce BMG foam by using a hot die pressing method. Scanning electron microscope (SEM), x-ray diffraction (XRD) and differential scanning calorimetry (DSC) were employed to characterize the morphologies of foaming structure, the crystallization and percentage of amorphous phase of the as-produced porous BMG. The results suggest that the formation of porous structure by superplastic forming process is feasible. Good bonding effect was observed between amorphous powder particles. None of crystalline phases was formed during hot pressing, and less than 3.5% percent of residual salt was enclosed in the foam. In order to remove any residual salt particles, salt preform with three-dimensional network and good connectivity is necessary.
Chemiluminescence Behavior of Luminol-KIO4-Ag Nanoparticles System and Its Analytical Applications  [PDF]
S. F. Li, H. Y. Wang, X. Min, L. Zhang, J. Wang, J. Du, J. Q. Zhang, P. Wei, Z. Q. Wang, H. Zhang, X. W. Wu
Journal of Biomedical Science and Engineering (JBiSE) , 2014, DOI: 10.4236/jbise.2014.76033
Abstract: It was found that silver nanoparticles could strongly enhance the chemiluminescence (CL) of the luminol-KIO4 system in the presence of Co2+. The most intensive CL signals were obtained with silver nanoparticles in diameter of 22 nm. The studies of UV-visible spectra and CL spectra were carried out to explore the possible CL enhancement mechanism. Moreover, the influences of 17 amino acids and 25 organic compounds on the luminol-KIO4-Co2+-Ag NPs CL system were studied by a flow injection procedure, which led to an effective method to detect these compounds.
Influence of hydroxyurea on cell divisions and microtubular cytoskeleton in Allium cepa root meristem
H. Q. Zhang,Y. Q. Li,M. Kura?,J. Bednara
Acta Societatis Botanicorum Poloniae , 1996, DOI: 10.5586/asbp.1996.032
Abstract: In onion roots, hydroxyurea (HU) causes a gradual depression of mitotic activity which ceases after 24-36 hrs. The effect is reversible; divisions begin after several hours of recovery and after 12-14 hrs about 90% cells undergo mitosis. Mitotic activity commences in the distal region of the apical meristem, and as a wave it spreads towards the apex. In the roots treated with HU for a short time, the tubulin immunofluorescence method reveals normal arrays of microtubules (MTs). After 36 hrs of HU treatment there are only cortical and endocytoplasmatic MTs. In the recovering roots, preprophase bands (PB) mitotic spindles and phragmoplasts appear. Some PBs are split into two parallel rings. These abnormal PBs mostly occur in elongated cells. Apart from this, HU does not appear to have any significant influence on microtubular organization.
Joint effect of the western and eastern Pacific warm pools on ENSO cycle
Q. Qi,Y. Hou,Q. Zhang,T. Yan
Ocean Science Discussions (OSD) , 2008,
Abstract: The zonal displacement of the western Pacific warm pool (WPWP) and the meridional displacement of the eastern Pacific warm pool (EPWP) and their responses to wind anomalies over the tropical Pacific were investigated. Joint effect of the WPWP and EPWP on ENSO was examined based on a joint effect index, which is a combination of the standardized anomaly time series of the eastern edge of the WPWP and the southern edge of the EPWP. Results show that both WPWP and EPWP are major providers of warm water in the eastern equatorial Pacific. The anomalous eastward extension of the WPWP and abnormal southward extension of the EPWP can supply a large amount of warm water into Nino3 region of the north equator, result in dramatic local SST increase, and trigger El Ni o. To the contrary, as scope of the WPWP retreats westward and the EPWP retreats northward, a La Ni a will outburst. One cannot separate apart the roles played by the WPWP and EPWP on ENSO, and the joint effect of both warm pools must be considered. A joint index of 1.6 means a new El Ni o event is likely to happen.
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