Entity

Time filter

Source Type


Dong X.Q.,Taiyuan University of Technology | Dong X.Q.,Key Laboratory of Coal Science and Technology | Dong X.Q.,Seoul National University | Yang G.-H.,Taiyuan University of Technology | And 2 more authors.
Fresenius Environmental Bulletin | Year: 2012

The alternating current (AC) impedance characteristics of silty soil samples have been studied by measuring their AC impedance parameters within the frequency range of 50-10 6 Hz. The parameters include the real part Z′, imaginary part Z″, impedance module |Z|, and phase difference θ. The effects of the frequency f and the water content w on these parameters are analyzed. The electrical resistivity ρ s of silty soil is also calculated, and the relational expression between ρ s and w is fitted. Finally, a predication formula of soil w is developed using ρ s and f The results indicate that Z′, -Z″, and |Z| decrease with increasing logarithm of frequency, log f, and w. Also, θ increases with increasing log f, and 6 does not change with w, except at f= 50 and 10 2 Hz. Given the strong relation of Z′ with w, Z′ of silty soil is primarily determined by the polarizability of free water. In contrast, Z″ of silty soil mainly represents loss from conduction. |Z| is affected by the polarizability of free water and conduction loss. θ shows the capacitance of the silty soil. At every f an exponential function is used to simulate soil w increase with decreasing ρ s, which has a very high correlation coefficient. Calculated by the predication formula, w is very close to the true w, indicating the reliability of the formula. © by PSP Volume 21 - No 2a. 2012. Source


Dong X.,Taiyuan University of Technology | Dong X.,Key Laboratory of Coal Science and Technology | Dong X.,Seoul National University | Woo H.,Seoul National University | And 2 more authors.
Environmental Earth Sciences | Year: 2013

To verify the applicability of the time-continuous electrical conductivity (EC) measurement in analyzing the contaminant movement in the subsurface, a new column test device employing non-destructive four-electrode sensors was developed. Using the seawater to create a simple one-dimensional steady-flow condition, laboratory transport experiments were conducted and the EC breakthrough curves at different distances were obtained. Comparison between the EC breakthrough curves obtained from the EC sensors and those from the effluent solute chemical analysis showed that the estimated resident concentration from the EC breakthrough curves are useful in understanding solute transport in soils. The pore water velocity and longitudinal dispersion coefficient estimated using the computer code, CXTFIT, were found to be slightly underestimated, especially at sensors located at smaller distances from the outlet boundary. Results showed that the developed column test device employing the four-electrode sensors proposed in this study provides a non-destructive, convenient, and inexpensive means of evaluating the seawater transporting in soils. © 2013 Springer-Verlag Berlin Heidelberg. Source


Dong X.,Taiyuan University of Technology | Dong X.,Key Laboratory of Coal Science and Technology | Dong X.,Seoul National University | Liu X.,Taiyuan University of Technology | And 2 more authors.
Environmental Earth Sciences | Year: 2014

To obtain the breakthrough curves without efforts required in the sampling and chemical analysis, a new soil column test device was developed. The device can conduct time-continuous electrical conductivity (EC) measurements without disturbing the soil matrix at all stages of the test. This device is composed of soil column, channel selector, LCR meter, and data logger. The soil column employs three 4-electrode sensors installed at different positions. To verify its applicability, the electrical conductivity breakthrough curves at different distances have been obtained with the use of five different species influent solutions (KCl, NaCl, CaCl2, MgCl2, and seawater). Results showed that the EC breakthrough curves and the transport parameters (the pore-water velocity, the dispersion coefficient, and the dispersivity) are very reasonable, and understand the one-dimensional steady flow exactly. The developed soil column test device proposed in this study provides a nondestructive, convenient, and inexpensive means of obtaining EC breakthrough curves. © 2014, Springer-Verlag Berlin Heidelberg. Source


Dong X.-Q.,Taiyuan University of Technology | Dong X.-Q.,Key Laboratory of Coal Science and Technology | Dong X.-Q.,Seoul National University | Zhou Y.-T.,Tongji University | And 3 more authors.
Archive of Applied Mechanics | Year: 2014

An exact contact analysis of two collinear stamps over the surface of orthotropic materials is performed. Eigenvalue analyses related to the governing equations are conducted, and real fundamental solutions are obtained for each eigenvalue distribution. Using Fourier sine or cosine transforms, a singular integral equation of Cauchy type is obtained. In particular, the exact solution of the reduced singular integral equation is obtained in the case of two collinear flat or cylindrical stamps. Explicit expressions for various stresses are obtained in terms of elementary functions. Numerical results are presented, and interesting observations are found. For two collinear flat stamps, detailed calculations are provided to show influences of distance between two flat stamps on the contact stress and in-plane stress. For a cylindrical stamp, influences of distance between two cylindrical stamps, mechanical loading P, and the cylindrical stamp radius R on the surface normal stress and surface in-plane stress are detailed. © 2014 Springer-Verlag Berlin Heidelberg. Source


Zuo Z.-J.,Key Laboratory of Coal Science and Technology | Li J.,Key Laboratory of Coal Science and Technology | Han P.-D.,Taiyuan University of Technology | Huang W.,Key Laboratory of Coal Science and Technology
Journal of Physical Chemistry C | Year: 2014

To better understand the autoxidation mechanism of Cu-based catalysts, we studied the oxidation of Cu sheet exposed to ultrahigh vacuum and air at ambient temperature using X-ray photoelectron spectroscopy (XPS) and density functional theory. Six main stages of Cu autoxidation are revealed: (1) dissociative adsorption of O2, (2) coexistence of nondissociative and dissociative H2O adsorption, (3) diffusion of O and OH into Cu bulk, (4) formation of metastable Cu2O layer, (5) further oxidation and formation of metastable Cu(OH)2 and CuO layer, and (6) transformation phase of the metastable Cu(OH)2 to CuO. The formation of Cu(OH)2 depends on the relative humidity of air and the concentration of adsorbed OH of the Cu sheet. On the basis of these results, we propose that the preservation time of the Cu-based catalysts should be decreased or the catalysts should be preserved in a high vacuum and at low relative humidity. Considering the time of the sample preparation before ex situ XPS analysis and other surface characterizations, the Cu-based catalysts need to be etched by ∼10 s using an Ar ion gun. These findings serve as a guide for the preservation and preparation of Cu-based catalysts before actual measurement. © 2014 American Chemical Society. Source

Discover hidden collaborations