Experimental study of the time-resolved reflectivity of chromium film

The transient time-resolved reflectivity of chromium film is studied by femtosecond pump-probe technique with a 70-fs laser. Experimental results show that the reflectivity change increases with the power of the pump laser. The fast decrease of the reflectivity occurs between 0-200 fs which is mainly due to the electron-electron interaction. Subsequencely, the slower recovery of the reflectivity between 200-900 fs is mainly due to the electron-phonon coupling process. The reflectivity after 900 fs rises little to a near-constant value for the thermal equilibrium of the system. The experimental results can be explained properly with numerical simulation of the two-temperature model. It is helpful for understanding of the electron ultrafast dynamics in chromium film.     

有机半导体的物理掺杂理论

基于最低未被占据分子轨道（LUMO）和最高被占据分子轨道（HOMO）的高斯态密度分布与载流子在允许量子态中的费米-狄拉克（Fermi-Dirac）分布,提出有机半导体中物理掺杂的理论模型;研究了掺杂浓度、温度和禁带宽度对载流子浓度的影响,并与一些报道的实验结果做了比较.研究发现无论是否掺杂,温度升高时,有机半导体中的载流子浓度都会增大,并且随温度倒数的线性减小而指数增大;对于本征有机半导体,载流子浓度随禁带宽度的增大而指数下降,随高斯分布宽度的平方指数增加;对杂质和主体不同能级关系的掺杂情形下掺杂浓度对载 关键词： 有机半导体 掺杂 高斯态密度 载流子浓度     

A stable BaCeO3-based proton conductor for solid oxide fuel cells

In order to improve the chemical stability of BaCeO₃, Ti⁴⁺ was introduced into B site of BaCeO₃ to modify the chemical stability. XRD test demonstrates that \textBaC\texte_0.6\textT\texti_0.2\textY_0.2\textO_{3 - d} {\text{BaC}}{{\text{e}}_{0.6}}{\text{T}}{{\text{i}}_{0.2}}{{\text{Y}}_{0.2}}{{\text{O}}_{3 - \delta }} (BCTY) keeps its original pervoskite-type structure at a high doping level of 20%. After exposure in 94% N₂ + 3% CO₂ + 3% H₂O at 700 °C for 10 h, BCTY exhibited adequate chemical stability while decomposition was found in \textBaC\texte_0.8\textY_0.2\textO_{3 - d} {\text{BaC}}{{\text{e}}_{0.8}}{{\text{Y}}_{0.2}}{{\text{O}}_{3 - \delta }} (BCY). Accordingly, the conductivity of BCTY reaches 0.0072 S/cm at 700 °C in humidified hydrogen which is a little lower than BCY (0.0085). Besides, BCTY displayed better sintering characteristics than BCY at high temperatures and the relative density reaches 96.4% and 94.8%, respectively. The two samples also exhibited similar thermal expansion behavior from 30 to 1,000 °C. A fuel cell with BCTY as electrolyte exhibited 244 mW/cm² at 700 °C and the stable short-term performance further proved the stability of BCTY.     

Temperature-electric field hysteresis loop of multicaloric effects in PbZr0.8Ti0.2O3 thin films

The Multicaloric effect in the PbZr_0.8Ti_0.2O₃ thin films is investigated with the application of sine wave electric field, dc electric field and stress using a phase field method combined with the thermodynamic analysis. The simulation results show that the adiabatic temperature change-electric field curve presents a shape of butterfly in the presence of the sine wave electric field. In order to detect the effect of the sine wave electric field, the multicaloric effect and the domain structures under the direct electric field and the sine wave electric field are compared. It is found that the domain switching behaviors are quite different under the different applied electric fields. And the negative multicaloric effect in the PbZr_0.8Ti_0.2O₃ thin film is attribute to the domain switching under the external field.     

Exact Solutions to the Quantum Rabi-Stark Model Within Tunable Coherent States

The quantum Rabi-Stark model, where the linear dipole coupling and the nonlinear Stark-like coupling is present on an equal footing, is studied within the tunable extended coherent states. The eigenvalues and eigenstates are therefore obtained exactly. Surprisingly, the entanglement entropy in the ground-state is found to jump suddenly with the coupling strength. The first-order quantum phase transition can be detected by level crossing of the ground state and the first excited state, which is however lacking in the original linear quantum Rabi model. Performing the first-order approximation in the present theory, we can derive closed-form analytical results for the ground-state. Interestingly, it agrees well with the exact solutions up to the ultra-strong coupling regime in a wide range of model parameters. The spectral collapses when the absolute value of the nonlinear coupling strength approaches to twice the cavity frequency is observed with the help of new solutions in the limits.     

R717双蒸发温度回路三级混流制冷系统的研究设计

基于降低初投资、节约能源、与环境友好及符合国情的原则,从制冷剂选用和制冷系统构成两个方面,探究"超低温"冷库制冷系统的设计方案和适用技术路线,完成了以天然工质氨为制冷剂,双蒸发温度回路三级混流制冷系统的可行性研究及其关键设备的开发设计,并以此建造了具有-30℃和-60℃库温,库容分别为30吨和200吨双冷间的"超低温"实验冷库。试运行半年,完全达到设计要求,已通过山东省科技厅专家组技术鉴定。     

Study of electrochemical performances of multi-doped spinel Li1.1Mn1.85Co0.075Ni0.075O4 at 4.3 and 5 V

Li_1.1Mn_2???2x Co _x Ni _x O₄ (x?=?0, 0.075) spinel powders were successfully synthesized using a liquid stirred tank reactor method. The electrochemical performances of the undoped and doped spinels at 4.3 and 5 V were investigated by X-ray diffraction, field-emission scanning electron microscopy, and electrochemical impedance spectroscopy. The capacity of Li_1.1Mn_2???2x Co _x Ni _x O₄ could be divided into two parts, with 4.3 V as the dividing line in the 3–5 V charge–discharge range. Low capacity and good cyclic performance were obtained when cycled in the 3–4.3 V range for the multi-doped Li_1.1Mn_2???2x Co _x Ni _x O₄ spinel. In comparison with multi-doped spinel at 4.3 V, the results of the cyclic performance worsened at 5 V because the structure underwent further shrinkage, the charge transfer resistance rose and the electrolyte decomposed.     

真空传输线板-锥过渡结构的功率流分析

真空传输线板-锥转角过渡是多模块汇流的Z箍缩装置经常采用的结构,在不考虑磁绝缘失效、介质损耗的前提下,采用有限差分方法分析转角过渡对功率流传输的影响。初步的计算和分析表明:随着转角的变大,由阻抗不匹配引起的反射将使传输效率有所降低;前沿较陡的快脉冲在这种结构中发生严重畸变,而低频脉冲则几乎不受影响。在板-锥过渡设计中采用小转角结构,尽量减小脉冲传输方向的变化,对保证脉冲高效传输有利。     

托卡马克研究的现状及发展

核聚变能是未来理想的能源。经过半个多世纪的不懈努力,随着国际上一批托卡马克装置成功建设和运行,磁约束聚变研究取得了一系列重大成果,具备了建造和运行反应堆级托卡马克实验装置科学技术和工程建设条件。基于这一共识,世界上一些主要国家共同合作,启动并实施了国际热核聚变实验堆(ITER)计划,希望通过建设和运行ITER,验证和平利用核聚变能的科学技术和工程可行性。中国的托卡马克研究经过近40年的发展取得了很大的进展。未来5年,将建立近堆芯级稳态等离子体实验平台,开展高水平的科学实验;吸收消化、发展与储备聚变工程实验堆关键技术;完善聚变工程实验堆的设计和开展关键部件预研,为在2020年前后独立开展中国聚变工程堆奠定坚实的科学技术基础。     

Optimization of detection device geometry for NIR spectroscopy using a three-layered model of stone fruit

The influences of detection device geometry and fiber optic parameters on near infrared spectroscopy measurements were assessed using stone fruit models based on Monte Carlo simulation. The stone fruit was modeled as concentric spherical layered tissues including the skin, the flesh and the core. The choices of the detection angle, the diameter of the detection fiber, the numerical aperture, and the height of the probe were discussed. Receiving diffuse reflectance signals at detection angles in the range of 35°–50° and normalizing the detection signals by the collection area and the solid acceptance angle prior to use are suggested. Fiber probes with diameters D = 0.06 cm or 0.1 cm, NA = 0.20 or 0.30, and height h ≤ 0.8 cm are preferred. The probe deflection angle should be limited to within ±5° to guarantee measurement accuracy.