2015年3期 (共 篇) 引用文章 全选
本平台内已出版文章查询 , REN YuXuan * 已出版文章查询
本平台内已出版文章查询 , LU RongDe * 已出版文章查询
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We have set up a novel system for shaping the Gaussian laser beams into super-Gaussian beams. The digital micro-mirror device (DMD) is able to modulate the laser light spatially through binary-amplitude modulation mechanism. With DMD, the irradiance of the laser beam can be redistributed flexibly and various beams with different intensity distribution can be produced. A super-Gaussian beam has been successfully shaped from the Gaussian beam with the use of DMD. This technique will be widely applied in lithography, quantum emulation and holographic optical tweezers which require precise control of beam profile.
本平台内已出版文章查询 , XU Ming 已出版文章查询
本平台内已出版文章查询 , WANG ChunDong * 已出版文章查询
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A finite-difference time-domain algorithm was applied to solve Maxwell's equations to obtain the redistribution of an electromagnetic plane wave in the vicinity of a trailing indent crack (TIC). The roles of five geometrical parameters playing in light intensification were calculated numerically under the irradiation of a 355-nm normal incidence laser. The results show that the light intensity enhancements between the nearest neighbor pits were remarkable, which may lead to damage. The calculated results reveal that the light intensity enhancement factor (LIEF) can be up to 11.2 when TIC is on the rear-surface. With the increase of the length as well as the depth of pits, LIEF increased. Conversely, with the increase of the axis of pits, LIEF gradually declined to a stable status. It was observed that there exists an optima width or gap, which enables LIEF to be increased dramatically and then decreased gently. By comparison, results suggest that the worst cases occur when the depth and the length are both very large, especially if the width equals to 2λ and the gap equals the width. This work provides a recommended theoretical criterion for defect inspection and classification.
Photovoltaic properties of ferroelectric solar cells based on polycrystalline BiFeO3 films sputtered on indium tin oxide substrates
本平台内已出版文章查询 , CHEN MengJiao 已出版文章查询
本平台内已出版文章查询 , QIU JianHua 已出版文章查询
本平台内已出版文章查询 , YUAN NingYi * 已出版文章查询
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To study the ferroelectric photovoltaic effect based on polycrystalline films, preparation of high-quality polycrystalline films with low leakage and high remnant polarization is essential. Polycrystalline BiFeO3 (BFO) thin films with extremely large remnant polarization (2Pr = 180 μC/cm2) were successfully deposited on glass substrates coated with indium tin oxide using a modified radio frequency magnetron sputtering method. Symmetric and asymmetric cells were constructed to investigate the ferroelectric photovoltaic effect in order to understand the relationship between polarization and photovoltaic response. All examined cells showed polarization-induced photovoltaic effect. Our findings also showed that the ferroelectric photovoltaic effect is highly dependent on the material used for the top electrode and the thickness of the polycrystalline film.
Structural topology optimization on sound radiation at resonance frequencies in thermal environments
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Thermal and acoustic environments pose severe challenges to the structural design of hypersonic vehicles. One of them is to find optimal design that exhibits ideal acoustic characteristics in a frequency band, which is discussed in this paper through topology optimization aiming at resonance sound radiation in thermal environments. The sound radiation at resonance frequencies is the main component of response, minimization on which is likely to provide a satisfactory design. A bi-material plate subjected to uniform temperature rise and excited by harmonic loading is studied here. Thermal stress is first evaluated and considered as prestress in the following dynamic analysis; radiated sound power is then calculated through Rayleigh integral. Sensitivity analysis is carried out through adjoint method considering the complicated relationship between stress-induced geometric stiffness and design variables. As the resonance frequency is constantly changing during the optimization, its sensitivity should be considered. It is also noticed that mode switching may occur, so mode tracking technique is employed in this work. Some numerical examples are finally discussed.
Simulation of residual stresses and their effects on thermal barrier coating systems using finite element method
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Thermal barrier coating (TBC) systems are widely used in industrial gas-turbine engines. However, premature failures have impaired the use of TBCs and cut down their lifetime, which requires a better understanding of their failure mechanisms. In the present study, experimental studies of isothermal cycling are firstly carried out with the observation and estimation of microstructures. According to the experimental results, a finite element model is established for the analysis of stress perpendicular to the TBC/BC interface. Detailed residual stress distributions in TBC are obtained to reflect the influence of mechanical properties, oxidation, and interfacial roughness. The calculated results show that the maximum tensile stress concentration appears at the peak of TBC and continues to increase with thermal cycles. Because of the microstructural characteristics of plasma-sprayed TBCs, cracks initialize in tensile stress concentration (TSC) regions at the peaks of TBC and propagate along the TBC/BC interface resulting in the spallation of TBC. Also, the inclusion of creep is crucial to failure prediction and is more important than the inclusion of sintering in the simulation.
本平台内已出版文章查询 , SONG RuiRong 已出版文章查询
本平台内已出版文章查询 , YUAN XiaoBo 已出版文章查询
本平台内已出版文章查询 , HU GuiChao 已出版文章查询
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A double T-shaped device model is constructed to investigate the spin polarized current injection and transportation properties in organic semiconductors. Based on the spin diffusion theory and Ohm's law and considering the different charge-spin relationship of the special carriers in organic semiconductors, the current spin polarization has been obtained. Effects of the branch current ratio and the polaron proportion on the spin polarized current injection efficiency are studied. From the calculation, it is found that the improvement of the spin polarized current injection efficiency can be obtained by adjusting the branch current ratio; moreover, high polaron proportion in organic semiconductors is beneficial for obtaining high current spin polarization.
本平台内已出版文章查询 , SONG ChengWei 已出版文章查询
本平台内已出版文章查询 , ZHANG JunJie * 已出版文章查询
本平台内已出版文章查询 , SUN Tao 已出版文章查询
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In the present work we elucidate the thermodynamic mechanisms of femtosecond (fs) laser ablation of amorphous polystyrene by means of molecular dynamics (MD) simulations. The effects of extrinsic parameter of laser pulse intensity and intrinsic parameter of molecular architecture on the laser ablation are further studied. Simulation results show that the laser ablation-induced polymeric material removal is achieved by evaporation from the surface and expansion within the bulk. Furthermore, inter-chain sliding and intra-chain change also play important roles in the microscopic deformation of the material. It is found that both the laser pulse intensity and the arrangement of phenyl groups have significant influence on the fs laser ablation of polystyrene.
Comparison between the time-integrated spectrum and the peak time spectrum of gamma-ray bursts and possible implications
本平台内已出版文章查询 , WANG YuanZhu 已出版文章查询
本平台内已出版文章查询 , LIANG YunFeng 已出版文章查询
本平台内已出版文章查询 , LIN TingTing 已出版文章查询
本平台内已出版文章查询 , HU YouDong 已出版文章查询
本平台内已出版文章查询 , LIANG EnWei * 已出版文章查询
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The mono-frequency peak luminosity and the corresponding photon energy of the time-integrated (Lps, Eps) and peak time (Lpt, Ept) vfv spectra were derived for a sample of 38 redshift-known Fermi GRBs by fitting the spectra with the Band function. It was found that Ept is generally consistent with Eps, and Lpt is averagely three times larger than Lps. The slope of the Lpt - Ept relation was consistent with that of the Lps - Eps relation. The photon indices in the peak time spectrum, particularly, the index of the low energy end was, were statistically larger than that in the time-integrated spectrum. These results indicate that Lps and Eps are dominated by Lpt and Ept, respectively. The difference of the spectral indices between the time-integrated and peak time spectra may be because of the overlap effect of a series of time-resolved spectra within a GRB. Our simulations, which were based on the observed spectral evolution and correlation between the energy flux and the peak energy within individual GRBs support our speculations. The Lpt-Ept relation may be less contaminated by the overlap effect, and it would may be an intrinsic feature of radiation physics.
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The formation of the present configuration of three hot super-Earths in the planet system HD 40307 is a challenge to dynamical astronomers. With the two successive period ratios both near and slightly larger than 2, the system may have evolved from pairwise 2:1 mean motion resonances (MMRs). In this paper, we investigate the evolutions of the period ratios of the three planets after the primordial gas disk was depleted. Three routines are found to probably result in the current configuration under tidal dissipation with the center star, they are: (i) through apsidal alignment only; (ii) out of pairwise 2:1MMRs, then through apsidal alignment; (iii) out of the 4:2:1 Laplace Resonance (LR), then through apsidal alignment. All the three scenarios require the initial eccentricities of planets ~0.15, which implies a planetary scattering history during and after the gas disk was depleted. All the three routines will go through the apsidal alignment phase, and enter a state with near-zero eccentricities finally. We also find some special characteristics for each routine. If the system went through pairwise 2:1 MMRs at the beginning, the MMR of the outer two planets would be broken first to reach the current state. As for routine (iii), the planets would be out of the LR at the place where some high-order resonances are located. At the high-order resonances 17:8 or 32:15 of the planets c and d, the system will possibly enter the current state as the final equilibrium.
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The magnetic damping rate was introduced in the evolution equations of r-modes, which shows that r-modes can generate strong toroidal magnetic fields in the core of accreting millisecond pulsars inducing by differential rotation. With consideration of the coupling evolution of r-modes, spin and thermal evolution, we investigated the influence of the magnetic damping on the differential rotation of nonlinear r-modes of accreting neutron stars. We derived the coupling evolution equations of the star involving the magnetic damping rate in the framework of second-order r-mode theory. The numerical results show that the magnetic damping suppressed the nonlinear evolution of r-modes since the saturation amplitude is reduced to a great extent. In particular, because of the presence of the generated toroidal magnetic field, the spin-down of the stars is terminated and the viscous heating effects are also weakened. Moreover, we could obtain a stronger generated toroidal magnetic field in the second-order r-mode theory. The gravitational radiation may be detected by the advanced laser interferometer detector LIGO if the amount of differential rotation is small when the r-mode instability becomes active and the accretion rate is not very high.
Two-post-Newtonian approximation of the scalar-tensor theory with an intermediate-range force for general matter
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Some future space missions measure distances of laser links and angles with unprecedented precision, allowing us to test theories of gravity up to the two-post-Newtonian (2PN) order. Besides, investigation of an intermediate-range force has been of considerable interests in gravitational experiments. Inspired by these ideas, within the framework of the scalar-tensor theory with an intermediaterange force, its 2PN approximation is obtained with Chandrasekhar's approach. It includes the 2PN metric and equations of motion for general matter without specific equation of state. The conserved quantities to the 2PN order are isolated with the aid of the energy-momentum complex. We also discuss the prospect of testing and distinguishing the intermediate-range force with the orbital motions of celestial bodies and spacecrafts.
Improved efficiency of ternary the blend polymer solar cells by doping a narrow band gap polymer material
本平台内已出版文章查询 , AN QiaoShi 已出版文章查询
本平台内已出版文章查询 , HUANG Hui * 已出版文章查询
本平台内已出版文章查询 , JIAO ChaoQun 已出版文章查询
本平台内已出版文章查询 , ZHANG FuJun * 已出版文章查询
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A series of P3HT:PC71BM polymer solar cells (PSCs) with different PIDTDTQx doping concentrations were fabricated to investigate the effect of the PIDTDTQx as a complementary electron donor on the performance of PSCs. The power conversion efficiency (PCE) of the optimized ternary blend PSCs (with 2 wt% PIDTDTQx) reached 3.87%, which is 28% higher than that of the PSCs based on P3HT:PC71BM (control cells). The short-circuit current density (Jsc) was increased to 10.20 mA/cm2 compared with the control cells. The PCE improvement could be attributed to more photon harvest and charge carrier transport by appropriate doping PIDTDTQx. The energy transfer from P3HT to PIDTDTQx was demonstrated from the 650 nm emission intensity decrease and the red-shifted emission peaks from 725 nm to 737 nm along with the increase of PIDTDTQx doping concentrations.
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We have compiled a list of all planet host star candidates reported in the literature, which are likely to be cluster members, and we checked their memberships by the spatial location, radial velocity, proper motion and photometric criteria. We found that only six stars, BD-13 2130, HD 28305, Kepler-66, Kepler-67, Pr0201 and Pr0211, are planet orbiting stars in open clusters to date. Two stars, HD 70573 and HD 89744, belong to moving groups and one star, TYC 8975-2606-1, may not be a planet host star, while three stars, HD 16175, HD 46375 and HD 108874 are not members of open clusters. We note that all these six planetary systems in the stellar cluster environment are younger than ~1 Gyr, which might indicate that the planetary system in open cluster can not survive for a long time, and we speculate that close stellar encounters between member stars in open cluster can potentially destroy, or at least strongly affect, the presence of planetary systems.
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Motivated by the recent LHCb collaboration measurements of charmless three-body decays of Bs0 meson, we calculate the branching fractions of Bs0 → K0π+π-, Bs0 → K0K+K-, Bs0 →K0π+K- and Bs0 → K0K+π- decay modes using the factorization approach. Both the resonant and nonresonant contributions are studied in detail. For the decays Bs0 → K0π+π- and Bs0 → K0K+K-, our results agree well with experimental data, and the former is dominated by the K*, while the latter one is dominated by the nonresonant contribution. Considering the flavor SU(3) symmetry violation, the sum of branching fractions of Bs0 → K0π+K- and Bs0 → K0K+π- could accommodate the data well too. It should be noted that both branching fractions are sensitive to the scalar density <Kπ|sq|0>. Furthermore, the resonant contributions are dominated by the scalar K0*(1430). We hope that these branching fractions could be measured individually in the experiments so as to test the factorization approach and the flavor SU(3) asymmetry. Moreover, the direct CP asymmetries of these decays are also investigated, which could be measured in the running LHCb experiment and Super-b factory in the future.
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The classical adiabatic approximation theory gives an adiabatic approximate solution to the Schrödinger equation (SE) by choosing a single eigenstate of the Hamiltonian as the initial state. The superposition principle of quantum states enables us to mathematically discuss the exact solution to the SE starting from a superposition of two different eigenstates of the time-dependent Hamiltonian H(0). Also, we can construct an approximate solution to the SE in terms of the corresponding instantaneous eigenstates of H(t). On the other hand, any physical experiment may bring errors so that the initial state (input state) may be a superposition of different eigenstates, not just at the desired eigenstate. In this paper, we consider the generalized adiabatic evolution of a quantum system starting from a superposition of two different eigenstates of the Hamiltonian at t = 0. A generalized adiabatic approximate solution (GAAS) is constructed and an upper bound for the generalized adiabatic approximation error is given. As an application, the fidelity of the exact solution and the GAAS is estimated.