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Bai X.,Hohai University | Bai X.,Tsinghua University | Gu H.,Hohai University | Chen W.,Beijing Institutive of Technology | And 4 more authors.
Applied Biochemistry and Biotechnology

Poly(vinyl alcohol) (PVA) microspheres were prepared by inverse suspension crosslinked method, with glutaraldehyde as a crosslinking agent. PVA microspheres activated with aldehyde groups were employed for Trametes versicolor laccase immobilization. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize the activated PVA microspheres and PVA microspheres with immobilized laccase (Lac/PVA microspheres), which show that laccase was successfully immobilized on the PVA microspheres. The optimum pH and temperature coupling conditions for the immobilized laccase were determined to be 3.3 and 30°C, respectively. Residual activity was also investigated by soaking the immobilized laccase in organic solvents at different concentrations, proving it chemically stable. Immobilized laccase exhibited good storage stability at 4°C. The enzyme biosensor showed good performance in 2,2-azinobis(3-ethylthiazoline-6-sulfonate) and bisphenol A, with concentration ranges of 2 to 8 mM and 0.05 to 0.25 mM, respectively. Therefore, PVA microspheres may have high potential as support for enzyme thermistor applications. © 2014 Springer Science+Business Media. Source

Hua Z.,Hohai University | Yang B.,Hohai University | Chen W.,Beijing Institutive of Technology | Bai X.,Hohai University | And 2 more authors.
Applied Surface Science

We proposed a robust method for surface-functionalizing magnetic polyvinyl alcohol microspheres to detect heavy metal ions in aqueous solutions. The prepared chemosensor (PAR-MPVA) was characterized through scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectra (XPS). In neutral solutions, PAR-MPVA selectively recognized diatomic heavy metal ions, as indicated with a color change from earth yellow to red; in strong acidic solutions, the chemosensor only selectively detected Cu2+. PAR-MPVA microspheres had a detection limit as low as 0.5 μM by naked-eye and 0.16 μM by UV-vis spectrometer for Cu2+. Moreover, the sensor possessed magnetism for effective recovery, could easily be regenerated by a solution of EDTA, and also displayed perferable stability. The PAR-MPVA microspheres possessed preeminent properties of detecting copper (II) ions in aqueous solutions. © 2014 Elsevier B.V. All rights reserved. Source

Zhang H.,Southwest Jiaotong University | Zhu Z.,Southwest Jiaotong University | Zhu Z.,Chinese Academy of Sciences | Ning J.,Beijing Institutive of Technology | And 2 more authors.
Guti Lixue Xuebao/Acta Mechanica Solida Sinica

Investigation of dynamic behavior of frozen soil is of great importance to artificial ground freezing method in underground engineering, etc. In this article, split Hopkinson pressure bar (SHPB) was employed to investigate the dynamic behavior of artificial frozen soil under uni-axial stress condition. Tests were conducted at the temperature of -3, -8, -13, - 7, -23 and -28°C and strain rates from 300 to 1200 s-1. The stress-strain curves at different conditions were obtained. Result showed that: (1) the uni-axial stress-strain curves of frozen soil show brittle character; (2) the compressive strength of frozen soil shows positive strain-rate and negative temperature sensitivity, and the final strain of frozen soil shows positive strain-rate sensitivity over the range of strain rates and temperature considered; (3) the thermal effect of frozen soil is greater at higher loading strain rates, and the strain rates sensitivity of frozen soil is higher at lower temperature. The viscoelastic damage model mentioned in this article can describe the stress strain relation of frozen soil under dynamic loading. Source

Zhang Z.,Beijing Institutive of Technology | Zhang Z.,Taiyuan University of Science and Technology | Zhao H.,Beijing Institutive of Technology | Yu H.,Beijing Institutive of Technology
Gaoya Wuli Xuebao/Chinese Journal of High Pressure Physics

A light gas gun was used to conduct the dynamic mechanical properties experiments of plain concrete material under three different impact velocities, getting the time-stress curves. Then, numerical calculations were used to simulate concrete's light gas gun experiments, comparing the simulation results with experimental results. In this paper the propagation of wave in flyer and target was formulated. Further analysis shows that concrete material has obvious rate-related properties, lag effect and stress wave's attenuation features, and all of this is closely related to the evolution of internal damage in material. Concrete material finally forms macro fracture under the interaction of compression wave, side release effect and reflected tensile wave of left and right free surface. The size of target in the experiment is reasonable, avoiding the effect of side releasing on the test signals of manganin piezoresistive transducer. Source

Zhang Z.,Beijing Institutive of Technology | Zhang Z.,Taiyuan University of Science and Technology | Luan G.-B.,Beijing Institutive of Technology | Ning J.-G.,Beijing Institutive of Technology
Gaoya Wuli Xuebao/Chinese Journal of High Pressure Physics

The split Hopkinson pressure bar and light gas gun as the two common means of dynamic loading are widely used in dynamic mechanical characteristics of many materials, while it can not meet the experimental study requirements of the concrete and reinforced concrete because of the small loading samples dimensions. To solve this problem, a simple large-dimension explosive loading assembly, which directly drive the flyer devised cone shape to achieve a large-dimension loading, was presented. Numerical simulation was first used to complete the design optimization of experiment conception. The dynamic process which an explosion drove the flyer was simulated based on ALE and Lagrange coupling methods. Then target range experiments were performed and the flyer flatness was measured by using self-made concentric pins, pulse networks and two oscilloscopes. The improvement was proposed prepared for the finally dynamic experiments of the large-dimension concrete and reinforced concrete samples. Source

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