Dynamic crossover in [VIO~(2+)][Tf_2N~-]_2 ionic liquid

Ionic liquids usually behave as fragile liquids,and the temperature dependence of their dynamic properties obeys supper-Arrhenius law.In this work,a dynamic crossover is observed in([VIO²⁺][Tf₂N-]₂) ionic liquid at the temperature of 240-800 K.The diffusion coefficient does not obey a single Arrhenius law or a Vogel-Fulcher-Tammann(VFT) relation,but can be well fitted by three Arrhenius laws or a combination of a VFT relation and an Arrhenius law.The origin of the dynamic crossover is analyzed from correlation,structure,and thermodynamics.Ion gets a stronger backward correlation at a lower temperature,as shown by the fractal dimension of the random walk.The temperature dependence function of fractal dimension,heterogeneity order parameter,and thermodynamic data can be separated into three regions similar to that observed in the diffusion coefficient.The two crossover temperatures observed in the three types of data are almost the same as that in diffusion coefficient fitted by three Arrhenius laws.The results indicate that the dynamic crossover of[VIO2+][Tf2 N-]2 is attributed to the heterogeneous structure when it undergoes cooling.     

D形光纤Bragg光栅弯曲灵敏度的理论和实验研究

用材料力学理论分析了D形光纤Bragg光栅（D-shaped fiber Bragg grating,D-FBG）以及常规光纤Bragg光栅由弯曲引起的轴向应变,得到了光栅Bragg波长漂移的弯曲敏感特性.实验结果和理论计算结果基本相符.与常规FBG相比,该D-FBG的弯曲灵敏度要高近80倍.因此D-FBG可以直接应用于弯曲形变的测量,以及间接应用于压力、加速度等物理量的测量.理论分析和实验结果对采用该类型光纤光栅的器件和传感系统的设计具有参考意义.     

气相传输平衡法在(11-20)面蓝宝石上制备γ铝酸锂膜

为了寻找可能替代蓝宝石作为氮化镓外延的新型衬底,通过48 h的气相传输平衡,分别在1000℃、1030℃、1050℃、1070℃和1100℃制备了一层单相多晶的γ铝酸锂膜。X射线衍射和扫描电镜分别用于表征膜的物相、取向和表面形貌。结果显示,γ铝酸锂择优取向的好坏取决于气相平衡传输温度,在1050℃制备的γ铝酸锂具有高度的[100]择优取向;在γ铝酸锂(001)面上的双轴拉应力可能有助于[100]择优取向的形成;γ铝酸锂晶粒表面裂纹的方向一致性与其择优取向紧密相关。上述结果表明在合适的工艺条件下,气相传输平衡法制备的γ铝酸锂/蓝宝石可能成为一种很有前景且适合(1-100)面氮化镓生长的复合衬底。     

气相传输平衡技术制备LiGaO2薄膜

为获得与GaN薄膜晶格失配小的衬底材料,报道了利用气相传输平衡技术(VTE)在(100)-βGa2O3单晶衬底上制备高度[001]取向LiGaO2薄膜的方法。经过X射线衍射分析表明得到的薄膜是由单相LiGaO2组成。利用扫描电镜(SEM)观察表面形貌,发现经气相传输平衡技术处理得到的薄膜表面形貌主要受温度的影响,表面晶粒尺寸随温度上升而增大。而X射线衍射测试表明随着温度上升,所得到的薄膜也从多晶向单晶化转变。在经过退火处理后,通过观察吸收谱发现LiGaO2薄膜中产生色心,并且色心的种类与温度有关。表明可以通过气相传输平衡技术技术,在远低于LiGaO2熔点的温度制备外延GaN用(001)LiGaO2∥(100)β-Ga2O3复合衬底。     

Influence of Co–Zr substitution on coercivity in Ba ferrites

Polycrystalline BaCo_xZr_xFe_11.5−2xO_18.25 samples with 0?x?0.6$0?x?0.6$ ions per formula units were prepared by modified citrate precursor method with the initial ratio of Ba:Fe equal to 1:11.5. The cationic site preferences of Co²⁺ and Zr⁴⁺ in Co–Zr substituted Ba ferrite were investigated by magnetic measurements and X-ray diffractometer (XRD) analysis. The coercivity H_c was decreasing with increasing Co–Zr substitution. The datum showed that the max coercive force (H_c) was obtained when substitution of 0.2, while the best saturation magnetizations (M_s) was obtained when substitution of 0.4.     

光纤激光阵列目标在回路自适应光学系统的数值模拟

研究了光纤激光阵列目标在回路自适应光学系统在实际大气环境中的传输.从光纤激光阵列、激光在大气中的传输、目标和优化算法四个方面,建立了光纤激光阵列目标在回路自适应光学系统的理论模型.在不同强度大气湍流下,对系统补偿大气湍流影响的效果进行了研究,并对系统控制参数优化进行了简单探讨.结果表明,目标在回路闭环控制结构能够有效补...     

Design of periodic metal-insulator-metal waveguide back structures for the enhancement of light absorption in thin-film solar cells

To increase the absorption in a thin layer of absorbing material (amorphous silicon, a-Si), a light trapping design is presented. The designed structure incorporates periodic metal-insulator-metal waveguides to enhance the optical path length of light within the solar cells. The new design can result in broadband optical absorption enhancement not only for transverse magnetic (TM)-polarized light, but also for transverse electric (TE)-polarized light. No plasmonic modes can be excited in TE-polarization, but because of the coupling into the a-Si planar waveguide guiding modes and the diffraction of light by the bottom periodic structures into higher diffraction orders, the total absorption in the active region is also increased. The results from rigorous coupled wave analysis show that the overall optical absorption in the active layer can be greatly enhanced by up to 40%. The designed structures presented in this paper can be integrated with back contact technology to potentially produce high-efficiency thin-film solar cell devices.     

A low-threshold and high-power oxide-confined 850-nm AlInGaAs strained quantum-well vertical-cavity surface-emitting laser

A low-threshold and high-power oxide-confined 850-nm AlInGaAs strained quantum-well (QW) vertical-cavity surface-emitting laser (VCSEL) based on an intra-cavity contacted structure is fabricated. A threshold current of 1.5 mA for a 22 μm oxide aperture device is achieved, which corresponds to a threshold current density of 0.395 kA/cm². The peak output optical power reaches 17.5 mW at an injection current of 30 mA at room temperature under pulsed operation. While under continuous-wave (CW) operation, the maximum power attains 10.5 mW. Such a device demonstrates a high characteristic temperature of 327 K within a temperature range from -12℃ to 96℃ and good reliability under a lifetime test. There is almost no decrease of the optical power when the device operates at a current of 5 mA at room temperature under the CW injection current.     

扰动Nizhnik-Novikov-Veselov系统分形孤子渐近解

文章研究了一类扰动Nizhnik-Novikov-Veselov非线性系统, 利用特殊的渐近方法得到了相应系统分形孤子渐近解. 关键词： 孤子 渐近解 扰动