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February 15,2013
Volume 6,Issue 3
Pages -
Subject Area:Fluid Mechanics,Explosion Mechanics,Condensed Matter Physics,Acoustics

Title: Dynamic response and wave propagation of SHPB under impact of special shape striker

Authors: ZHOU Zilong, JIANG Yihui, ZOU Yang, LI Guonan
PP: 284-288
Abstract: Split Hopkinson pressure bar (SHPB) with the special shape striker has been widely accepted and used for its advantages of little oscillation, no dispersion effect, stress uniformity at cross-section, being able to get constant strain rates and good repeatability. In order to give more accurate information of this technique, it is necessary to understand its dynamic response and wave propagation characteristics in testing. Based on the analysis of dynamic response and wave propagation characteristics of SHPB with the special shape striker using finite element analyses, it was found that SHPB with the special shape striker gave a good half-sine incident wave, and had little wave dispersion in transmitting. The peak stress of incident wave had good linear relation with the impact velocities of the striker, but it was different with cylindrical striker. Oblique and off-axial impact analyses showed that the misalignment impacts usually triggered wave distortion and amplitude decrease, which could be used to identify the system abnormity.
Keywords: dynamics; special shape striker; split Hopkinson pressure bar; impact; dynamic response; wave propagation

Title: Visualization and measurement of vortex flow over conical forebody under high angles of attack

Authors: XU Changqun, LI Huaxing, MENG Xuanshi, LIU Feng, LUO Shijun
PP: 279-283
Abstract: In order to research the active control characteristics of plasma actuators on the asymmetric vortices over the conical forebody, particle image visualization and measurement experiment on the cone-cylinder combination were carried out in low speed wind tunnel. Under high angles of attack and various lay out of plasma actuators, the asymmetric vortices of conical forebody were investigated using particle image velocimetry (PIV) system. The test results clearly indicated that, when the attack angle was high, the vortices over the leeward side of the cone-cylinder combination was asymmetric and unstable, and the positions of the main vortices changed significantly. By the control of plasma actuators which were fixed on both left and right sides of conical forebody, the separation vortices could achieve steady state and the lateral force of conical forebody could be controlled well.
Keywords: fluid mechanics; stability of vortices; high angles of attack; slender conical forebody; asymmetrical vortices; active flow control

Title: Study on condensation in Prandtl-Meyer expansion wave

Authors: CAO Yun, LUO Xisheng
PP: 273-278
Abstract: In this paper, the effects of condensation on flow structure was studied in a case of backward-facing step flow using the flow visualization method. Experimental results showed that a diabatic shock wave due to the latent heat occurred in the expansion fan. The condensation shock was strengthening with the humidity of the oncoming flow increasing. When the saturation ratio reached to a certain value, a normal shock wave appeared upstream of the sharp edge, which in turn inhibited the condensation downstream. Meanwhile, numerical simulation was carried out for comparing with experiments. The numerical simulation results showed the same phenomena as that observed in experiments. Numerical simulation also showed that a self-excited oscillation of diabatic shock wave occurred under certain flow conditions.
Keywords: fluid mechanics; Prandtl-Meyer expansion wave; condensation; self-excited oscillation

Title: Numerical study on the influences of waving bottom on the fluid surface wave

Authors: WU Zhengren, MO Chongyuan, WANG Songling
PP: 268-272
Abstract: In the present paper, the fluid flowing over a linear waving bottom was studied and the effects of the linear simple harmonic wave on the fluid surface wave was analysed. When the basement linear wave was long wave and small amplitude, starting from the basic equations of potential flow theory and boundary conditions, the first-order approximate equation and second-order approximate equation were derived for fluid surface waves in the presence of waving bottom bed using the multiple scales perturbation method. Under the second-order approximation, the solution of first-order approximate equation was obtained, and then the solution of first-order approximate equation was numerically simulated by Matlab software. Simulation results showed that when the waving bottom was simple harmonic wave, the fluid surface wave was composed of two parts. One part was simple harmonic wave, whose frequency and phase were the same of the waving bottom function. The other part was a pair of the spread of KdV solitary waves, which propagated to the left and to the right respectively. With the development of time, this simple harmonic wave and the spread of KdV solitary waves were not affected each other, and they propagated independently. Therefore, it can be considered that the waveform of the fluid surface is concerned with the form of waving bottom bed.
Keywords: fluid mechanics; surface wave; multiple scales perturbation method; waving bottom; numerical simulation

Title: Dynamic response analysis of a simply supported beam under blast loading

Authors: HU Shigao, BU Rongli, DUAN Weidong
PP: 263-267
Abstract: Explosive dynamics and vibration mechanics theory were used to analyse the complex dynamic response of a simply supported beam under blast concentrated loading. The analysis showed that the reponse of a simply supported beam under blast concentrated loading had two stages, the first one was forced vibration under blast concentrated loading and the second one was free vibration. Then the relationship between deflection and stress was established to get the stress of one point at either stage that provided basis to judge whether the beam was damaged. At last, the relative errors of the maximum deflection were about 8% at the first stage and about 10% at the second stage by comparing theoretical results with numerical simulation results of a specific example.
Keywords: engineering mechanics; dynamic response; numerical simulation; theoretical calculation

Title: Investigation on the mechanical behavior of ice containing methane hydrate

Authors: ZHAO Honghua, LI Yanghui, LIU Weiguo, SONG Yongchen
PP: 256-262
Abstract: In order to study the influence of methane hydrate on the mechnical behavior of ice, the stress-strain relationship and strength of ice containing methane hydrate were studied using a high-pressure and low-temperature triaxial testing apparatus. The results showed that: 1) The strength increased with decrease of temperature; 2) The stress-strain relationship showed an elasto-plastic strain-hardening behavior. When the confining pressure was less than 10 MPa, the strength increased with confining pressure. While it decreased with further increase of confining pressure beyond 10 MPa. Based on the above experimental testing results, a bi-linear strength criteria was proposed.
Keywords: engineering mechanics; ice; methane hydrate; stress-strain relationship; strength; yield criteria

Title: Effects of the Dy addition on YBCO films

Authors: ZHANG Hong, WANG Wentao, ZHAO Yong
PP: 252-255
Abstract: For enhancing critical current density of YBa2Cu3O7-δ (YBCO) coating conductor, in this paper, YDyxBa2Cu3O7-δ films were prepared via a fluorine-free polymer-assisted metal organic deposition (PA-MOD) method. The microstructure and superconducting character of YBCO films were investigated. The results showed that there was no anticipative Dy2O3 in these films with the addition of Dy, and the critical current intensity was not increased efficiently. But the composition of YBCO occurred offseting, therefore the superconductivity capability of YBCO films degraded.
Keywords: superconductivity physics; YBa2Cu3O7-δ films; Dy addition; polymer-assisted metal organic deposition

Title: Electricity dipole lattice on CuO2 plane of high temperature superconductor

Authors: DONG Hang
PP: 246-251
Abstract: It is proved that, the ion lattice on CuO2 plane can be seen as a combination of regular lattice and dipole lattice. Regular lattice and carriers keep the balance of electron, while dipole lattice is from the violations of average electricity distribution. Considering that the character of cuprate superconductor is mainly dominated by the dipole lattice, the pairing mechanism, carrier concentration and the bell-shaped curbe, the d-wave symmetry and the linear temperature dependence of normal state resistivity are tersely interpreted.
Keywords: superconductivity physics; high temperature superconductor; electricity dipole; phase diagram; d-wave symmetry; normal state of super conductor

Title: Study on first principle for modification of graphene and BN films by an Ag atom

Authors: CHEN Xiaojie, WU Qisheng, CHEN Qian, WANG Jinlan
PP: 239-245
Abstract: First principle calculation was used to investigate the surface modification of two dimensional nano materials with an Ag atom. According to the results of calculation, we found that the properties of monolayer/bilayer graphene and BN film changed significantly after surface modification of monolayer or bilayer graphene and BN films by an Ag atom. After surface modification, the properties of monolayer or bilayer graphene changed from half-metallic to metallic of Ag atom, while for the case of monolayer or bilayer BN film, it changed from a wide band gap semiconductor to a narrow band gap semiconductor. This approach of tuning the magnetism and the band gap of materials by surface modification may play an important role in future spintronic devices and semiconductor optical decices.
Keywords: condensed matter physics; first principle; nano materials; surface modification; band gap

Title: Influences of SiO2 coating on water resistance of SrAl2O4:Eu2+,Dy3+

Authors: YANG Yun, HAO Huzai
PP: 234-238
Abstract: Luminescent powder SrAl2O4:Eu2+,Dy3+ was coated by SiO2 through liquid-phase method. Digital acidity meter, X-ray powder diffractometer patterns, fluorescent spectrophotometer and brightness meter with stopwatch were employed to characterize the water resistance, X-ray diffraction (XRD) spectra, photoluminescence spectra, and after-glow property of the uncoated and coated samples, respectively. The results indicated that the coated samples had better water resistance, the crystalline phase was not changed, and the peak location of emission and excitation spectra was also not changed, but the relative intensity decreased. Furthermore, both the initial intensity and after-glow time decreased slightly. Considering the requirement of water resistance property, spectra property, and after-glow property, the best amount of SiO2 coated on the surface was 15%.
Keywords: condensed matter physics；surface coated; liquid-phase method; green long after-glow material; water resisting

Title: Planar waveguides in magnesium-doped stoichiometric LiNbO3 formed by MeV oxygen ion implantations

Authors: WANG Lei, XIANG Bingxi
PP: 228-233
Abstract: The magnesium doped stiochiometric LiNbO3 is a man-made crystal with excellent nonlinear optical properties. The ion implantation is a powerful method to form guiding structure on lithium niobate crystal. The planar waveguides were formed in magnesium-doped stoichiometric LiNbO3 crystals by means of 4.5 MeV oxygen ion implantations with different doses. The dark mode spectra were measured using the prism coupling method. The Rutherford backscattering/channeling technique was used to investigate the damage on the near-surface region generated by the ion implantation. The annealing behaviors of the formed waveguides were characterized by a series of annealing treatments. The results showed that the ion implantation was an effective method to fabricate waveguide on magnesium-doped stoichiometric LiNbO3 crystal. The thickness of the formed waveguide was in microns, which was similar to the damage depth by stopping and range of ious in matter (SRIM) smulation. Therefore, the electronic energy depisition is found to be responsible for the formation of the waveguide.
Keywords: condensed matter physics; interactions between ions and solid materials; lithium niobate; ion implantation; waveguide

Title: Study on nonlinear impedance of stack in thermoacoustic refrigerator

Authors: GE Huan, FAN Li, ZHANG Shuyi, XIAO Shuyu, TAO Sha, QIU Meichen, ZHANG Hui
PP: 221-227
Abstract: In order to improve the acoustic coupling between each part of the thermoacoustic refrigerator system, and further improve the efficiency of the thermoacoustic refrigerator, this study designed an important part of thermoacoustic refrigerator, that is the nonlinear acoustic impedance of the stack. In this paper, three parameters such as the linear resisitance, nonlinear coefficient and effective mass of the stack are presented to describe the nonlinear impedance of the stack. It was found that the resistance of the stack exhibited obvious nonlinear effect with the increasing of the sound pressure, while the effective mass keeped constant. In addition, the three parameters decreased with the increasing of volume porosity of the stack, while the operating frequency hardly influenced them. Furthermore, the resistance of the stack also increased with the increasing of the stack length.
Keywords: acoustics; nonlinear; impedance measurement; thermoacoustic stack

Title: Performance research on conical gold/glass complex optical element of transmitting hard X-rays

Authors: LIN Xiaoyan, WANG Lili, LI Yude
PP: 215-220
Abstract: Based on the ray-tracing theory, a mathematics model for the hard X-ray transmission in a gold/glass complex optical element was built, and the theory simulation for the X-ray transmission in a gold/glass complex optical element was achieved using a Matlab program. Based on theory simulation, the transmission efficiency of conical gold/glass complex optical element with different energy X-rays was calculated and the intensity distribution of hard X-rays through transmission in a gold/glass complex optical element was obtained. The results showed that the gold/glass complex optical element could focus hard X-rays (E>40 keV) obviously and filter low energy X-rays (E<40 keV) well.
Keywords: nuclear physics; gold/glass complex optical element; hard X-rays; transmission efficiency; intensity distribution

Title: Field-free molecular alignment and orientation by chirped fs laser pusles

Authors: WU Jian
PP: 210-214
Abstract: In this paper, we investigated the effects of chirped fs laser pusles on field-free molecular alignment and orientation. Through analysis on molecular alignment and orientation induced by chirped fs laser pulses with different wavelengths and different chirped degree, we found that the molecular orientation was mainly determined by laser pulse parameters within transform limiting. However, due to the change of the asymmetry of pusles, the molecular orientaion degree decreased with the increase of the chirp in dual-color pusles.
Keywords: optics; ultrafast nonlinear optics; moelcular alignment and orientation; chirped fs laser pusle; two-color laser field

Title: A dual-mode cell imaging probe based on silica coated gold nanorods

Authors: ZONG Shenfei, WANG Zhuyuan, CHEN Hui, WANG Chunlei, XU Shuhong, CUI Yiping
PP: 203-209
Abstract: In this paper, a dual-mode surface enhanced Raman scattering (SERS) and fluorescence probe was proposed for cell imaging. In the fabrication process of the probe, SERS reporter molecules were first attached to the surfaces of the gold nanorods (GNRs) to generate SERS signals. Then, the surface of GNRs was coated with SiO2. Next, quantum dots (QDs) were adsorbed onto the SiO2 layer to generate fluorescence signals. Finally, the outmost surface of the nanoparticles were wrapped by polyelectrolytes (PEs) to improve the biocompatibility of the probes. After putting the probes into living cells, the dual-mode cell imaging of both SERS and fluorescence could be obtained through selecting different exciting wavelengths. This probe has a great potential application in cancer diagnosis and tumor targeting.
Keywords: optical engineering; surface enhanced Raman scattering; fluorescence; gold nanorods; quantum dots; cell imaging

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