Diode-pumped mode-locked femtosecond Tm:CLNGG disordered crystal laser

A diode-end-pumped passively mode-locked femtosecond Tm-doped calcium lithium niobium gallium garnet (Tm:CLNGG) disordered crystal laser was demonstrated for the first time to our knowledge. With a 790 nm laser diode pumping, stable CW mode-locking operation was obtained by using a semiconductor saturable absorber mirror. The disordered crystal laser generated mode-locked pulses as short as 479 fs, with an average output power of 288 mW, and repetition rate of 99 MHz in 2 μm spectral region.     

Synchronization between integer-order chaotic systems and a class of fractional-order chaotic systems via sliding mode control

In this paper, we focus on the synchronization between integer-order chaotic systems and a class of fractional-order chaotic system using the stability theory of fractional-order systems. A new sliding mode method is proposed to accomplish this end for different initial conditions and number of dimensions. More importantly, the vector controller is one-dimensional less than the system. Furthermore, three examples are presented to illustrate the effectiveness of the proposed scheme, which are the synchronization between a fractional-order Chen chaotic system and an integer-order T chaotic system, the synchronization between a fractional-order hyperchaotic system based on Chen's system and an integer-order hyperchaotic system, and the synchronization between a fractional-order hyperchaotic system based on Chen's system and an integer-order Lorenz chaotic system. Finally, numerical results are presented and are in agreement with theoretical analysis.     

Defects in room-temperature ferromagnetic Cu-doped ZnO films probed by x-ray absorption spectroscopy

We report a comprehensive study of the defects in room-temperature ferromagnetic (RTFM) Cu-doped ZnO thin films using x-ray absorption spectroscopy. The films are doped with 2 at.% Cu, and are prepared by reactive magnetron sputtering (RMS) and pulsed laser deposition (PLD), respectively. The results reveal unambiguously that atomic point defects exist in these RTFM thin films. The valence states of the Cu ions in both films are 2(+). In the film prepared by PLD, the oxygen vacancies (V(O)) form around both Zn ions and Cu ions in the hexagonal wurtzite structure. Upon annealing of the film in O(2), the V(O) population reduces and so does the RTFM. In the film prepared by RMS, the V(O)s around Cu ions are not detected, and the V(O) population around Zn ions is also smaller than in the PLD-prepared film. However, zinc vacancies (V(Zn)) are evidenced. Given the low doping level of spin-carrying Cu ions, these results provide strong support for defect-mediated ferromagnetism in Cu-doped ZnO thin films.     

Crystal growth and optical properties of Cr3+, Er3+, RE3+: Gd3Ga5O12 (RE=Tm,Ho, Eu) for mid-IR laser applications

In this paper we report on the optical properties of triply Cr³⁺, Er³⁺, and RE³⁺ (RE=Tm, Ho, Eu) doped Gd₃Ga₅O₁₂ crystals that were grown by the Czochralski method. Optical absorption, near-infrared (NIR), and mid-infrared (mid-IR) fluorescence spectra were characterized for the fabricated crystals and corresponding luminescence decay measurements under 654 nm excitation were also carried out. Based on the analysis of energy transfer process between Er and RE (RE=Tm, Ho, Eu) ions, the energy transfer efficiency (ETE) values were evaluated, correspondingly. From the spectral data of all the studied crystals, it is observed that the co-doped Cr³⁺ ion highly increases the absorption pump power and the three kinds of co-doped RE³⁺ ions depopulate the Er:⁴I_13/2 energy level effectively. The spectral analysis shows that titled rare earth doped crystals are promising materials for ～3.0 μm mid-IR laser applications and among them Cr,Er,Eu:GGG is relatively more suitable due to its excellent optical properties compared with others.     

DFT study on electronic structure and optical properties of N-doped,S-doped,and N/S co-doped SrTiO3

The electronic structures and optical properties of N-doped, S-doped and N/S co-doped SrTiO₃ have been investigated on the basis of density functional theory (DFT) calculations. Through band structure calculation, the top of the valence band is made up of the O 2p states for the pure SrTiO₃. When N and S atoms were introduced into SrTiO₃ lattice at O site, the electronic structure analysis shows that the doping of N and S atoms could substantially lower the band gap of SrTiO₃ by the presence of an impurity state of N 2p on the upper edge of the valence band and S 2p states hybrid with O 2p states, respectively. When the N/S co-doped, the energy gap has further narrowing compared with only N or S doped SrTiO₃. The calculations of optical properties also indicate a high photo response for visible light for N/S co-doped SrTiO₃. Besides, we find a new impurity state which separates from the O 2p states could improve the photocatalytic efficiency and we also propose a model for light electron-hole transportation which can explain the experiment results well. All these conclusions are in agreement with the recent experimental results.     

Non-uniform order mixed FEM approximation: Implementation,post-processing,computable error bound and adaptivity

The present work provides a straightforward and focused set of tools and corresponding theoretical support for the implementation of an adaptive high order finite element code with guaranteed error control for the approximation of elliptic problems in mixed form. The work contains: details of the discretisation using non-uniform order mixed finite elements of arbitrarily high order; a new local post-processing scheme for the primary variable; the use of the post-processing scheme in the derivation of new, fully computable bounds for the error in the flux variable; and, an hp-adaptive refinement strategy based on the a posteriori error estimator. Numerical examples are presented illustrating the results obtained when the procedure is applied to a challenging problem involving a ten-pole electric motor with singularities arising from both geometric features and discontinuities in material properties. The procedure is shown to be capable of producing high accuracy numerical approximations with relatively modest numbers of unknowns.     

覆盖度对S原子在Ir(001)表面吸附性质的影响

采用第一性原理方法模拟了覆盖度对S原子在Ir(001)表面吸附能和电子结构的影响。结果表明：在覆盖度0.50 ML以下,S原子吸附在Hollow空位最稳定,且吸附能几乎不随覆盖度变化;在覆盖度0.66 ML以上吸附能随覆盖度增加而减小。吸附体系金属表面d带电子结构随覆盖度变化与O/Pt(111)吸附体系相似。这些结果与Hammer-Nørskov模型吻合。     

The structural and magnetic properties of barium ferrite powders prepared by the solben gel method

In this paper, M-type hexagonal barium ferrite powders are synthesized using the sol-gel method. A dried precursor heated in air is analyzed in the temperature range from 50 to 1200 ℃ using thermo-gravimetric analysis and differential scanning calorimetry. The effects of the additives and the cacinating temperature on the magnetic properties are investigated, and the results show that single-phase barium ferrite powders can be formed. After heat-treating at 950 ℃ for 4h with 3 wt% additive, the coercivity and saturation magnetization are found to be 440 Oe and 57.9 emu/g, respectively.     

Initial guess by improved population-based intelligent algorithms for large inter-frame deformation measurement using digital image correlation

Digital image correlation (DIC) has received a widespread research and application in experimental mechanics. In DIC, the performance of subpixel registration algorithm (e.g., Newton-Raphson method, quasi-Newton method) relies heavily on the initial guess of deformation. In the case of small inter-frame deformation, the initial guess could be found by simple search scheme, the coarse-fine search for instance. While for large inter-frame deformation, it is difficult for simple search scheme to robustly estimate displacement parameters and deformation parameters simultaneously with low computational cost. In this paper, we proposed three improving strategies, i.e. Q-stage evolutionary strategy (T), parameter control strategy (C) and space expanding strategy (E), and then combined them into three population-based intelligent algorithms (PIAs), i.e. genetic algorithm (GA), differential evolution (DE) and particle swarm optimization (PSO), and finally derived eighteen different algorithms to calculate the initial guess for qN. The eighteen algorithms were compared in three sets of experiments including large rigid body translation, finite uniaxial strain and large rigid body rotation, and the results showed the effectiveness of proposed improving strategies. Among all compared algorithms, DE-TCE is the best which is robust, convenient and efficient for large inter-frame deformation measurement.     

Molecular dynamics simulations of displacement cascades in Fe-10%Cr systems

Molecular dynamics simulations of the displacement cascades in Fe-10%Cr systems are used to simulate the primary knocked-on atom events of the irradiation damage at temperatures 300,600,and 750 K with primary knockedon atom energies between 1 and 15 keV.The results indicate that the vacancies produced by the cascade are all in the central region of the displacement cascade.During the cascade,all recoil Fe and Cr atoms combine with each other to form Fe-Cr or Fe-Fe interstitial dumbbells as well as interstitial clusters.The number and the size of interstitial clusters increase with the energy of the primary knocked-on atom and the temperature.A few large clusters consist of a large number of Fe interstitials with a few Cr atoms,the rest are Fe-Cr clusters with small and medium sizes.The interstitial dumbbells of Fe-Fe and Fe-Cr are in the 111 and 110 series directions,respectively.