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Yu Y.,Huazhong University of Science and Technology | Fan S.-S.,Huazhong University of Science and Technology | Dai H.-W.,Huazhong University of Science and Technology | Ma Z.-W.,Huazhong University of Science and Technology | And 3 more authors.
Applied Physics Letters | Year: 2014

The third-order optical nonlinearity and response time of Au nanobipyramids have been investigated by using optical Kerr effect technique. Large third-order nonlinear optical susceptibility (χ(3)) and ultrafast optical response time have been obtained at the longitudinal surface plasmon resonance (LSPR) wavelength. As the excitation laser wavelength varies from non-resonance wavelength of 780 nm to the LSPR wavelength of 825 nm, χ(3) increases from 7.4 × 10-14 to 3.9 × 10-13 esu, the fast component of the response time decreases from 141 ± 23 to 83 ± 8 fs and the ratio of the fast component remains around 48%, while the slow response time decreases from 3200 ± 200 to 2310 ± 158 fs. The large enhancement of χ(3) is due to the large local field enhancement caused by the surface plasmon resonance, and the shortening of the response times are induced by the increased probability of the electron-electron and electron-phonon scatterings in the nanosystem. This significant ultrafast optical property in Au nanobipyramids has great application in future ultrafast information processors. © 2014 AIP Publishing LLC. Source


Xie C.,Huazhong University of Science and Technology | Chen B.,Huazhong University of Science and Technology | Liu L.,Huazhong University of Science and Technology | Chen H.,Huazhong University of Science and Technology | Wu J.,Wenhua College
European Journal of Mechanics, B/Fluids | Year: 2016

Dielectrophoresis (DEP) for bio-particle manipulation has been drawing much attention in recent years. The equivalent dipole moment method (EDM) has widely been used to calculate DEP forces on single particle, but this method falls short to describe the interaction between neighboring particles. The Maxwell stress tensor method (MST) is theoretically rigorous for particle interaction, but its complicated numerical computation makes it difficult to implement in practice. In this paper, an iterative dipole moment method (IDM) is presented to investigate the interaction of multiple dielectrophoretic particles in a two-dimensional AC electric field. Without cumbersome numerical computation, the inter-particle forces, the particle trajectories and chain patterns calculated by the IDM method are found to be well consistent with those by the MST method for some published results and experimental observations. Furthermore, it is found that the final stable particle chain patterns strongly depend on the initial configuration of the particle distribution. An arbitrary small disturbance to the particle locations may lead to dramatically different motion trajectories and final particle chains. By tuning the frequency of AC field, the particles can be transformed between positive DEP particles and negative DEP particles, which results in different particle chains as well. © 2016 Elsevier Masson SAS. All rights reserved. Source


Zhu H.,Wenhua College | Hu L.,Huazhong University of Science and Technology
Measurement: Journal of the International Measurement Confederation | Year: 2016

In the displacement measurement using digital speckle correlation method, significant measuring error due to the multi-peak nature of the correlation coefficient function is a critical issue as sometimes the secondary peak can be wrongly determined as the maximum instead of the highest peak. In the multi-frequency harmonic wave correlation method (MHCM) as proposed in this work, for speckle patterns before and after the displacement, correlation calculations were performed on corresponding sets of data matrices assembled by amplitudes/intensities obtained from harmonic waves with different frequencies. The calculated maximum correlation coefficients were compared with each other to locate the maximum in order to measure the displacement. Both ultrasonic speckle MHCM and laser speckle MHCM were applied to the displacement measurement respectively. Measured results indicated that MHCM effectively helps to ensure the correct determination of the maximum correlation coefficient, to avoid random errors caused by other factors and improves the measurement accuracy in the meanwhile. © 2016 Elsevier Ltd. All rights reserved. Source


Zhu H.,Wenhua College | Wu Y.,Wuhan Institute of Technology
Applied Acoustics | Year: 2016

The digital ultrasonic speckle phase-shifting method (USPM), which is introduced in this paper, can be applied to the measurement of small displacement that is smaller than speckle size at the test point compared to traditional ultrasonic speckle correlation method (USCM). Using USPM, a digital ultrasonic reference signal is introduced to interfere with the ultrasonic speckle signal, which is picked up at the test point on an object surface and is referred to as the object signal. As the phase of the reference signal is shifted several times using the software and then they superimpose with the object signal respectively, the phase of the object signal can be calculated according to the intensities of the superimposed signals. If the object surface moves a small distance, the phase variation of the object speckle can be detected by the same process. As a result, the displacement of the object surface can be measured. Based on the feature of ultrasonic speckles, inner surface displacement of an object can be measured using this proposed method. In this case, the effect of outer surface roughness to the measurement accuracy of USPM is examined experimentally. The experimental results show that the measurement is successful when the displacement is smaller than half of the speckle size at the test point and the roughness parameter Ra of the outer surface of the specimen is less than about 5.47 μm. © 2015 Elsevier Ltd. All rights reserved. Source


Liu L.,Huazhong University of Science and Technology | Xie C.,Huazhong University of Science and Technology | Chen B.,Huazhong University of Science and Technology | Wu J.,Wenhua College
Journal of Chemical Technology and Biotechnology | Year: 2016

BACKGROUND: Dielectrophoresis (DEP) has widely been used to manipulate bio-particles in microfluidic system. The calculation of DEP interaction of a large number of dense particles has been a challenging issue. The Maxwell stress tensor (MST) method is strictly accurate in theory for DEP forces, but the complicated numerical computation is very difficult to implement. An iterative dipole moment method (IDM) is proposed in this paper to study the interaction forces and particle chains of a large number of dense particles in a uniform electrical field. RESULTS: The numerical example of ten particles interaction confirms that the IDM is able to calculate particle interaction forces in good agreement with the MST method. Particle chains of fifty randomly distributed dense particles in a uniform electrical field were simulated using the IDM method and were well consistent with experimental observations. Particle chains of different particle sizes are also investigated. CONCLUSION: The interaction forces of DEP particles calculated by the IDM method are found to be in good agreement with those obtained using the Maxwell stress tensor (MST) method and easy to implement. The simulated particle chains show essential characteristics well consistent with experimental observations. © 2015 Society of Chemical Industry © 2016 Society of Chemical Industry. Source

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