Generation of sub‐terahertz repetition rates from a monolithic self‐mode‐locked laser coupled with an external Fabry‐Perot cavity

A novel scheme to multiply the repetition rate of a monolithic self‐mode‐locked laser for generating sub‐terahertz pulse sources is successfully demonstrated. A coated Yb:KGW crystal is designed to achieve a self‐mode‐locked operation at a repetition rate of 24 GHz with an average output power exceeding 1.0 W at a pump power of 4.8 W. A partially reflective mirror is utilized to combine with the output surface of the gain medium to constitute an external Fabry‐Perot cavity. It is theoretically and experimentally verified that adjusting the external cavity length to satisfy the commensurate condition can lead to the frequency spacing to be various order harmonics of the mode spacing of the monolithic cavity. The maximum pulse repetition rate of the laser output can be up to 216 GHz and the pulse duration is as short as 330 fs. More importantly, the overall characteristics of the first‐order temporal autocorrelation traces obtained by sequentially scanning the external cavity.length display an intriguing phenomenon of temporally fractional revivals, similar to the feature of spatial Talbot revivals.

     

Redshift drift constraints on f(T) gravity

We explore the impact of the Sandage−Loeb (SL) test on the precision of cosmological constraints for f(T) gravity theories. The SL test is an important supplement to current cosmological observations because it measures the redshift drift in the Lyman-α forest in the spectra of distant quasars, covering the “redshift desert” of 2≲z≲5. To avoid data inconsistency, we use the best-fit models based on current combined observational data as fiducial models to simulate 30 mock SL test data. We quantify the impact of these SL test data on parameter estimation for f(T) gravity theories. Two typical f(T) models are considered, the power-law model f(T)_PL and the exponential-form model f(T)_EXP. The results show that the SL test can effectively break the existing strong degeneracy between the present-day matter density Ω_m and the Hubble constant H₀ in other cosmological observations. For the considered f(T) models, a 30-year observation of the SL test can improve the constraint precision of Ω_m and H₀ enormously but cannot effectively improve the constraint precision of the model parameters.     

基于网络的风机防喘振控制系统设计

针对某钢厂转炉煤气加压站大风机电机采用工频加变频的恒压闭环运行方式,变频风机极易发生喘振的现象,为了确保大风机稳定、安全的运行,在风机喘振的预防和控制方法上进行改进。采用两台风机同步变频调速与最小极值流量法的模糊PID控制相结合的防喘振控制方法,同步变频调速控制策略有效地预防喘振的发生,最小极值流量法的模糊PID控制策略最大限度的扩大了风机的运行区间,通过MATLAB软件仿真,证明模糊PID的动态响应速度和鲁棒性较常规PID有较大的改良。控制系统通过工业网络完成现场设备和远程的通讯,使控制系统达到高水平的智能自动化。     

航天通用测发控软件平台设计与应用

随着我国航天器频繁发射的常态化,对航天测发控软件技术的要求也逐渐提高,主要表现在提高软件通用性、自动化程度和数据处理能力三个方面。本文在分析测发控业务需求的基础上,提出了测发控信息全过程可配置、测试数据通用化处理、测试实时判读和试验数据快速后处理的方法,构建了航天通用测发控软件平台,实现了测发控软件的型号通用化,降低了软件研制成本,减少了现场测试人员和现场测试时间,提高了飞行器测发控效率。     

First principles study of structural,phonon, optical,elastic and electronic properties of Y3Al5O12

Structural, phonon, optical, elastic and electronic properties of Y₃Al₅O₁₂ have been investigated by means of the first principles method with the Cambridge Serial Total Energy Package (CASTEP) code based on the density functional theory. The calculated lattice parameters, valence charge density, bond length and single crystal elastic properties at zero pressure are in good agreement with the available experimental data. The close agreement with the experimental values provides a good confirmation of the reliability of the calculations. Optical, elastic and phonon properties of Y₃Al₅O₁₂ under pressures are performed. The results that are obtained show the changes of optical and elastic properties under the influence of applied pressure, and proving the dynamical stability of YAG are destructed when applied pressure up to 7 GPa. Moreover, polycrystalline elastic moduli are deduced according to the Reuss assumption. Those elastic constants provide important parameters that describe reliability of both physical model and engineering application at the atomistic level. The result of the density of states explains the nature of the electronic band structure.     

A study of fluorescence properties of citrinin in β-cyclodextrin aqueous solution and different solvents

Citrinin (CIT) is a nephrotoxic mycotoxin initially isolated from filamentous fungus Penicilliu citrinum. It was later isolated from several other species, such as Aspergillus and Monascus. It has a conjugated, planar structure that gives it a natural fluorescence ability, which can be used to develop sensitive methods for detecting CIT in food. In this paper, we used the spectro?uorescence technique to study the effects of pH value, β-cyclodextrin (β-CD) and organic solvents on the CIT fluorescence intensity. The results show that lower pH value, aceitc acid, β-CD and acetonitrile can induce a higher fluorescence intensity of CIT, but methanol or H₂O has a decreasing effect on the fluorescence intensity of CIT. Findings in this study provide a theoretical basis for development of a high sensitivity fluorescence-based trace analysis for CIT detection.     

An adaptive watermarking using fractal dimension based on random fractional Fourier transform

Based on random fractional Fourier transform (RFrFT), a novel adaptive watermarking algorithm using fractal dimension is proposed. Under fractal dimension, this algorithm is adaptive in the embedding position and the embedding intensity. The robustness and the imperceptibility of the watermarking algorithm are in good balance when block selection, high amplitude selection and amplitude shift keying are employed in this algorithm. Numerical simulation results have demonstrated the effectiveness of the proposed scheme and shown the robustness against attacks of noising, cropping and JPEG compression.     

非晶硅薄膜太阳能电池的紫外激光刻蚀工艺

为提高电池的光电转换效率,通过改善激光刻蚀工艺,采用355 nm紫外纳秒激光分别进行了ZnO：Al薄膜（AZO）刻蚀（P1）、非晶硅薄膜（-Si）刻蚀（P2）和背电极刻蚀（P3）研究。采用万用表测量P1隔离电阻,采用电子扫描显微镜（SEM）和三维激光扫描仪测量刻槽的微结构和三维成像,激光拉曼散射光谱检测非晶硅薄膜刻蚀边缘的晶化。实验结果表明,当刻蚀速度600 mm/s,重复频率40 kHz,功率1.74 W的紫外激光刻蚀ZnO：Al薄膜时,刻槽的隔离效果最佳,达20 M; 紫外激光刻蚀能够有效地减小激光热效应引起的热影响和刻槽边缘的晶化范围,提高非晶硅薄膜电池的性能。