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1

Comparison of compressive strength and electrical resistivity of cementitious composites with different nano- and micro-fillers

Jiang S., Zhou D., Zhang L., Ouyang J., Yu X., Cui X., Han B.

Archives of Civil and Mechanical Engineering

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2018

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Vol. 18, no. 1

60--68

EN

Cementitious composites with 0–1.5 wt.% Nano-SiO2 (NS), nano-TiO2 (NT), carbon nanotubes (CNTs), carbon nanofibers (CNFs) and carbon microfibers (CFs) are fabricated and tested. The enhancing effects of different fillers on the compressive strength and electrical resistivity of composites are compared, and the underlying modification mechanisms of fillers to composites are investigated by analyzing the difference in the morphology of fillers and rheology of composites. The compressive strength of composites containing 0.1% NS, 0.5% NT, 0.1% CNTs and 0.5% CFs by weight of cement presents approximately 12.5%, 20.8%, 16.8% and 21.4% higher than that of control sample, respectively. It is revealed that CFs also have improving effect on the compressive strength of composites besides flexural strength. When the composites with nano-fillers cannot be processed to ideal state, the reinforcing effect of nano-fillers is no better but even worse than that of micro-fillers. Composites with CNTs, CNFs and CFs possess good electrical conductivity. Composites with CNFs and CFs have a percolation threshold of electrical resistivity below 0.5%, while the percolation threshold of electrical resistivity of composites with CNTs is about 1%. Although CNFs do not have significant effect on compressive strength of composites, they have the best improvement to electrical resistivity.

2

Target-guided isolation and purification of antioxidants from Elsholtzia densa benth. var. densa by DPPH antioxidant assay and dual-mode HSCCC

Zhou W. N., Ouyang J., Wang Z. H., Wang X. Y., Suo Y. R., Zhang Z., Wang H. L.

Acta Chromatographica

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2018

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Vol. 30, no. 3

180--185

EN

Elsholtzia densa Benth. var. densa (Lamiaceae) is a famous medicinal herb which has been widely used for treatment of colds, headaches, pharyngitis, fever, diarrhea, digestion disorder, rheumatic arthritis, nephritises, and nyctalopia in China. In this study, fraction of the ethyl alcohol extract of E. densa (aerial part) by different polarity solvents indicated that the ethyl acetate soluble fraction exhibited a potent 1,1-diphenyl-2-picryhydrazyl (DPPH) radical scavenging activity with the IC50 value of 148.2 μg/mL. Under the target guidance of DPPH experiment, isoquercitrin, trachelogenin, ethyl caffeate, and arctigenin were separated with purities 95.98%, 92.98%, 96.07%, and 88.83%, respectively, by a dual-mode high-speed counter-current chromatography (HSCCC) method using n-hexane–ethyl acetate–methanol–water (4.5:5:3:4, v/v/v/v) as the solvent system. In order to evaluate the scientific basis, antioxidant activity of four isolated compounds was assessed by the radical scavenging effect on DPPH radical; isoquercitrin and ethyl caffeate showed stronger antioxidant activities with IC50 values of 9.4 μg/mL and 9.2 μg/mL, respectively, while trachelogenin and arctigenin showed weak antioxidant activities with IC50 values of >500 μg/mL and 72.8 μg/mL, respectively. Results of the present study indicated that the combinative method using DPPH antioxidant assay and dual-mode HSCCC could be widely applied for rapid screening and isolating of antioxidants from complex traditional Chinese medicine extract.

3

Multifunctionality of cement based composite with electrostatic self-assembled CNT/NCB composite filler

Zhang L., Han B., Ouyang J., Yu X., Sun S., Ou J.

Archives of Civil and Mechanical Engineering

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2017

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Vol. 17, no. 2

354--364

EN

In this paper, electrostatic self-assembled carbon nanotube (CNT)/nanocarbon black (NCB) composite is employed as filler for developing multifunctional cement-based composites. The performances of the composites with different content of filler are investigated. The electrochemical impedance spectroscopy and equivalent circuit are used to explore the conductive and mechanical mechanisms of the composites. Experimental results indicate that the compressive strength and elasticity modulus of the composites sharply decrease when the filler content exceeds 0.77 vol.%. The percolation threshold zone of the electrical conductivity of the composites ranges from 0.39 vol.% to 1.52 vol.%. The piezoresistive properties of the composites with 2.40 vol.% filler are stable and sensitive, and the maximum fractional change of electrical resistivity is 25.4% when the stress amplitude is 10 MPa. The composites feature sensitive and linear thermal resistance effect when the filler content is 0.77 vol.%. Electromagnetic shielding effectiveness of the composites with 2.40 vol.% filler at 18 GHz is 5.0 dB, which is 2.2 times of that of the control samples. The composites exhibit high absorbing electromagnetic wave performances in the frequency range of 2–18 GHz, and the minimum reflectivity reaches −23.08 dB with 0.77 vol.% filler.

4

Load-bearing evaluation of spinal posterior column by measuring surface strain from lumbar pedicles. An in vitro study

Sun P., Zhao W., Bi Z., Wu Ch., Ouyang J.

Acta of Bioengineering and Biomechanics

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2012

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Vol. 14, no. 1

45-49

EN

An understanding of the load transfer within spinal posterior column of lumbar spine is necessary to determine the influence of mechanical factors on potential mechanisms of the motion-sparing implant such as artificial intervertebral disc and the dynamic spine stabilization systems. In this study, a new method has been developed for evaluating the load bearing of spinal posterior column by the surface strain of spinal pedicle response to the loading of spinal segment. Six cadaveric lumbar spine segments were biomechanically evaluated between levels L1 and L5 in intact condition and the strain gauges were pasted to an inferior surface of L2 pedicles. Multidirectional flexibility testing used the Panjabi testing protocol; pure moments for the intact condition with overall spinal motion and unconstrained intact moments of +-8 Nm were used for flexion-extension and lateral bending testing. High correlation coefficient (0.967-0.998) indicated a good agreement between the load of spinal segment and the surface strain of pedicle in all loading directions. Principal compressive strain could be observed in flexion direction and tensile strain in extension direction, respectively. In conclusion, the new method seems to be effective for evaluating posterior spinal column loads using pedicles' surface strain data collected during biomechanical testing of spine segments.

5

Towards a case-based computational model for the creative design of electromagnetic devices

Ouyang J., Lowther D.

Archives of Electrical Engineering

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2011

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Vol. 60, nr 4

485-496

EN

In order to explore creativity in design, a computational model based on Case-Based Reasoning (CBR) (an approach to employing old experiences to solve new problems) and other soft computing techniques from machine learning, is proposed in this paper. The new model is able to address the four challenging issues: generation of a design prototype from incomplete requirements, judgment and improvement of system performance given a sparse initial case base library, extraction of critical features from a given feature space, adaptation of retrieved previous solutions to similar problems for deriving a solution to a given design task. The core principle within this model is that different knowledge from various level cases can be explicitly explored and integrated into a practical design process. In order to demonstrate the practical significance of our presented computational model, a case-based design system for EM devices, which is capable of deriving a new design prototype from a real-world device case base with high dimensionality, has been developed.

6

A novel adaptation approach for electromagnetic device optimization

Ouyang J., Lowther D.

Archives of Electrical Engineering

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2011

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Vol. 60, nr 4

473-483

EN

The ability of case-based reasoning systems to solve new problems mainly depends on their case adaptation knowledge and adaptation strategies. In order to carry out a successful case adaptation in our case-based reasoning system for a low frequency electromagnetic device design, we make use of semantic networks to organize related domain knowledge, and then construct a rule-based inference system which is based on the network. Furthermore, based on the inference system, a novel adaptation algorithm is proposed to derive a new device case from a real-world induction motor case-base with high dimensionality.