Mode decoupling in solid state ring laser based on stimulated Raman effect in polar crystals

In this paper we study the gain saturation induced mode-coupling control in solid state ring laser devices based on the stimulated Raman effect of the polar crystals in order to realize solid state ring laser gyroscopes.We theoretically investigate the mode coupling induced by gain saturation between clockwise (CW) and counterclockwise (CCW) propagating laser modes.Because the CW and CCW running waves are pumped with counter-propagating lasers respectively,the independent coexistence can be ensured.     

Performance improvement of MEH-PPV:PCBM solar cells using bathocuproine and bathophenanthroline as the buffer layers

In this work, bathocuproine (BCP) and bathophenanthroline (Bphen), commonly used in small-molecule organic solar cells (OSCs), are adopted as the buffer layers to improve the performance of the polymer solar cells (PSCs) based on poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV): [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction. By inserting BCP or Bphen between the active layer and the top cathode, all the performance parameters are dramatically improved. The power conversion efficiency is increased by about 70% and 120% with 5-nm BCP and 12-nm Bphen layers, respectively, when compared with that of the devices without any buffer layer. The performance enhancement is attributed to BCP or Bphen (i) increasing the optical field, and hence the absorption in the active layer, (ii) effectively blocking the excitons generated in MEH-PPV from quenching at organic/aluminum (Al) interface due to the large band-gap of BCP or Bphen, which results in a significant reduction in series resistance (Rs), and (iii) preventing damage to the active layer during the metal deposition. Compared with the traditional device using LiF as the buffer layer, the BCP-based devices show a comparable efficiency, while the Bphen-based devices show a much larger efficiency. This is due to the higher electron mobility in Bphen than that in BCP, which facilitates the electron transport and extraction through the buffer layer to the cathode.     

Raman and mid-infrared spectroscopic study of geometrically frustrated hydroxyl cobalt halides at room temperature

Mid-infrared absorption and Raman spectra of the geometrically frustrated material series,hydroxyl cobalt halides β-Co 2 (OH) 3 Cl and β-Co 2 (OH) 3 Br,are first,to the best of our knowledge,measured at room temperature,to study the corresponding relationship between their vibrational spectral properties and crystal microstructures.Through the comparative analysis of the four spectra we have categorically assigned the OH-related vibration modes of hydroxyl groups in the trimeric hydrogen bond environment (Co 3 ≡OH) 3… Cl/Br,and tentatively suggested vibration modes of O-Co-O,Co-O and Cl/Br-Co-Cl/Br units.These results can also become the basis for analysing their low-temperature spectral properties,which can help to understand the underlying physics of their exotic geometric frustration phenomena around phase transition temperatures.     

Radiation characteristics and implosion dynamics of tungsten wire array Z-pinches on the YANG accelerator

We investigated the radiation characteristics and implosion dynamics of low-wire-number cylindrical tungsten wire array Z-pinches on the YANG accelerator with a peak current 0.8-1.1 MA and a rising time ～ 90 ns.The arrays are made up of(8-32)×5 μm wires 6/10 mm in diameter and 15 mm in height.The highest X-ray power obtained in the experiments was about 0.37 TW with the total radiation energy ～ 13 kJ and the energy conversion efficiency ～ 9%(24×5 μm wires,6 mm in diameter).Most of the X-ray emissions from tungsten Z-pinch plasmas were distributed in the spectral band of 100-600 eV,peaked at 250 and 375 eV.The dominant wavelengths of the wire ablation and the magneto-Rayleigh-Taylor instability were found and analyzed through measuring the time-gated self-emission and laser interferometric images.Through analyzing the implosion trajectories obtained by an optical streak camera,the run-in velocities of the Z-pinch plasmas at the end of the implosion phase were determined to be about(1.3-2.1)×10 7 cm/s.     

Dynamical analysis of axially moving plate by finite difference method

The complex natural frequencies for linear free vibrations and bifurcation and chaos for forced nonlinear vibration of axially moving viscoelastic plate are investigated in this paper. The governing partial differential equation of out-of-plane motion of the plate is derived by Newton’s second law. The finite difference method in spatial field is applied to the differential equation to study the instability due to flutter and divergence. The finite difference method in both spatial and temporal field is used in the analysis of a nonlinear partial differential equation to detect bifurcations and chaos of a nonlinear forced vibration of the system. Numerical results show that, with the increasing axially moving speed, the increasing excitation amplitude, and the decreasing viscosity coefficient, the equilibrium loses its stability and bifurcates into periodic motion, and then the periodic motion becomes chaotic motion by period-doubling bifurcation.     

Motion planning for redundant prismatic-jointed manipulators in the free-floating mode

This paper investigates the motion planning of redundant free-floating manipulators with seven prismatic joints. On the earth, prismatic-jointed manipulators could only position their end-effectors in a desired way. However, in space, the end-effectors of free-floating manipulators can achieve both the desired orientation and desired position due to the dynamical coupling between manipulator and satellite movement, which is formally expressed by linear and angular momentum conservation laws. In this study, a tractable algorithm particle swarm optimization combined with differential evolution (PSODE) is provided to deal with the motion planning of redundant free-floating prismatic-jointed manipulators, which could avoid the pseudo inverse of the Jacobian matrix. The polynomial functions, as argument in sine functions are used to specify the joint paths. The coefficients of the polynomials are optimized to achieve the desired end-effector orientation and position, and simultaneously minimize the unit-mass-kinetic energy using the redundancy. Relevant simulations prove that this method provides satisfactory smooth paths for redundant free-floating prismatic-jointed manipulators. This study could help to recognize the advantages of redundant prismatic-jointed space manipulators.     

激光诱导熔石英表面损伤修复中的气泡形成和控制研究

基于熔石英材料在CO_2激光作用下的温度分布和结构参数变化的计算结果,对熔石英损伤修复中的气泡形成和控制进行了研究.针对损伤尺寸介于150—250μm之间的损伤点,提出了一种能够有效控制气泡形成的长时间低温预热修复方法.基于低温下熔石英材料结构弛豫时间常数较长的特点,该方法在不引起熔石英材料结构发生显著变化的同时,能够解吸附表面和裂纹处所附着的气体和杂质,可有效降低裂纹闭合过程中气泡形成的概率.实验结果表明,长时间低温预热修复方法的成功修复概率可达到98%.     

微波辅助细菌纤维素酯的制备及对Pb(Ⅱ)的高效去除

以细菌纤维素(BC)为原料,通过微波辅助酯化改性的方法制得了两种改性细菌纤维素,细菌纤维素黄原酸酯(XMBC)和细菌纤维素硫酸酯(SMBC)。对所制备的样品进行X射线衍射(XRD)、扫描电镜-电子能谱(SEM-EDS)、傅里叶变换红外(FT-IR)光谱和BET比表面积分析,通过续批式实验考察其对Pb(Ⅱ)的去除效果。研究了pH值、反应时间、温度、污染物初始浓度、离子强度对其吸附能力的影响以及材料再生性能。结果表明,改性细菌纤维素的比表面积和孔容均有上升,其对Pb(Ⅱ)的吸附量随反应温度和离子强度的增加而降低,最优pH值为5.0。巯基的引入增强了细菌纤维素对Pb(Ⅱ)的吸附能力,改性后的吸附剂显示出比原始BC更优异的吸附性能,其中XMBC和SMBC的最大吸附量分别为144.93和126.58 mg·g^-1,该吸附过程符合准二级速率方程和Langmuir等温吸附模型。材料对Pb(Ⅱ)的吸附是自发的放热过程,且吸附剂易于再生和重复回收。因此, SMBC和XMBC作为从水中富集分离重金属的新型材料具有及大应用前景。     

Facile preparation of a three-coordinate copper(I) complex: Steric hindrance,supramolecular structure,optical property and TD-DFT study

The solution reaction of Cu(CH₃CN)₄(PF₆) with a NN ligand 2-(2′-quinolyl)benzimidazole and a sterically bulky P ligand tris(2-methylphenyl)phosphine facilely yielded the three-coordinate copper(I) complex [Cu(2-QBI)(o-Tol₃P)](PF₆) (1). The complex has been characterized by single-crystal X-ray diffraction, Fourier Transform infrared spectroscopy and elemental analysis, UV–Vis (ultraviolet–visible) and photoluminescent spectroscopy studies. Time-dependent density functional theory has been used for calculating the electronic origin of the low-lying excited states, which were unexpectedly assigned mainly as a ligand-to-ligand or an intra-ligand charge transfer state instead of the metal-to-ligand charge transfer transition. Interestingly, 1 exhibits a concentration-dependent absorption in solution. This absorption behavior is interpreted as some excimer's formation based on the study of supramolecular structure, spectroscopy and calculations.     

Quantum confinement and surface chemistry of 0.8–1.6 nm hydrosilylated silicon nanocrystals

In the framework of density functional theory(DFT), we have studied the electronic properties of alkene/alkynehydrosilylated silicon nanocrystals(Si NCs) in the size range from 0.8 nm to 1.6 nm. Among the alkenes with all kinds of functional groups considered in this work, only those containing –NH2and –C4H3S lead to significant hydrosilylationinduced changes in the gap between the highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO) of an Si NC at the ground state. The quantum confinement effect is dominant for all of the alkenehydrosilylated Si NCs at the ground state. At the excited state, the prevailing effect of surface chemistry only occurs at the smallest(0.8 nm) Si NCs hydrosilylated with alkenes containing –NH2and –C4H3S. Although the alkyne hydrosilylation gives rise to a more significant surface chemistry effect than alkene hydrosilylation, the quantum confinement effect remains dominant for alkyne-hydrosilylated Si NCs at the ground state. However, at the excited state, the effect of surface chemistry induced by the hydrosilylation with conjugated alkynes is strong enough to prevail over that of quantum confinement.