Phase-resolved laser Raman scattering and laser Doppler velocimetry applied to periodic instabilities in a gas turbine model combustor

The understanding of periodic flame instabilities belongs to the major challenges in modern combustion research and technology and is of special importance for lean premixed gas turbine combustion. This paper presents experimental investigations in a gas turbine model combustor using laser diagnostic techniques. A partially premixed CH₄/air flame operated at a thermal power of 10 kW at atmospheric pressure and an overall equivalence ratio of 0.75, which exhibited thermoacoustic oscillations at a frequency of 290 Hz, was investigated. Phase-locked laser Raman scattering was applied in order to determine the major species concentrations, temperature, and mixture fraction. In addition, laser Doppler velocimetry (LDV) was used separately for the measurement of the axial and radial velocity components. The measurements revealed pronounced phase-dependent variations of the velocity and the temperature, species, and mixture fraction distributions. The combined Raman and LDV results also enabled the determination of molecular species fluxes which showed that the fuel and air supply rates both varied during an oscillation cycle by ±33% but with a phase shift of 80 between them. The correlations between temperature and mixture fraction revealed strong deviations from equilibrium composition and temperature, and their phase-dependent changes reflected the transport and mixing processes near the nozzle. The emphasis of the paper lies on the demonstration of the potential of phase-locked laser Raman scattering for the study of phenomena of periodic flame instabilities. PACS 33.20; 39.30; 47.27; 47.70; 82.33; 82.40     

Chaotic biogeography-based optimization approach to target detection in UAV surveillance

This paper describes a novel chaotic biogeography-based optimization (CBBO) algorithm for target detection by means of template matching to meet the request of unmanned aerial vehicle (UAV) surveillance. Template matching has been widely applied in movement tracking and other fields and makes excellent performances in visual navigation. Biogeography-based optimization (BBO) algorithm emerges as a new kind of optimization method on the basis of biogeography concept. The idea of migration and mutation strategy of species in BBO contributes to solving optimization problems. Our work adds chaotic searching strategy into BBO and applies CBBO in template matching. By utilizing chaotic strategy, the population ergodicity and global searching ability are improved, thus avoiding local optimal solutions during evolution. Applying the algorithm to resolving template matching problem overcomes the defects of common image matching. Series of experimental results demonstrate the feasibility and effectiveness of our modified approach over other algorithms in solving template matching problems. Our modified BBO algorithm performs better in terms of convergence property and robustness when compared with basic BBO.     

非临界相位匹配RTP晶体1.6 μm光参量振荡器

采用非临界相位匹配切割,尺寸4 mm4 mm20 mm的磷酸钛氧铷（RTP）晶体作为非线性光学晶体,进行了半导体激光端面抽运Nd:YAG/RTP的内腔式光参量振荡获得人眼安全激光的实验研究。对比了不同声光调Q重复频率下的信号光输出特性。在10.5 W的抽运功率和15 kHz的重复频率下,获得了最高900 mW的1.62 m人眼安全激光输出,光光转换效率达8.6%。1.62 m信号光和对应的1.06 m基频光的脉冲宽度分别为4.6和8.2 ns。信号光中心波长在1618 nm,谱线宽度小于0.5 nm。     

Theoretical investigations of the local distortion and electron paramagnetic resonance parameter for CdCl2:V2+ and CsMgX3:V<sup>2+（X=Cl,Br） systems

This paper systematically investigates the local distortion and electron paramagnetic resonance (EPR) parameter for CdCl 2 :V 2+ and CsMgX 3 :V 2+ (X=Cl, Br) systems on the basis of the complete energy matrix, in which not only the contributions due to the spin–orbit coupling of the central ions but also that of the ligands are considered. To describe the difference of overlapping between d-orbits and p orbit, two spin–orbit coupling coefficients are introduced. By simulating the crystal field parameter and EPR parameter, the local distortion parameters are studied and the relationships between the EPR parameter and the spin–orbit coupling coefficients as well as divergent parameter are discussed. These results show that the local structures exhibit compression distortion for CdCl 2 :V 2+ and elongation distortions for CsMgX 3 :V 2+ (X=Cl, Br), respectively. It notes that the empirical formula R ≈ R H + (r i-r h )/2 is not suitable for CdCl 2 :V 2+ and CsMgX 3 :V 2+ (X=Cl, Br) systems. The contributions of ligand to spin–orbit coupling interaction cannot be neglected for strong covalent systems, especially for V 2+ doped in CsMgBr 3 :V 2+ .     

Eu3+-site occupation in CaTiO3 perovskite material at low temperature

In order to clarify the site occupancy of rare-earth ions in rare-earth doped perovskite materials, the un-doped pure CaTiO₃ and Eu³⁺-doped CaTiO₃ samples with a series of Ca/Ti ratio were synthesized via high-temperature solid-state reaction method. X-ray diffraction (XRD) powder patterns confirm that the crystal structure keeps invariant at various Ca/Ti ratios. Measurement results of unit-cell parameters and X-ray photoelectron spectroscopy (XPS) indicate that Eu³⁺ ions enter into the Ca²⁺ site. The high-resolution photoluminescence spectra of Eu³⁺ ions at 20 K in all samples did not witness a significant change under the excitation at different wavelength, implying that Eu³⁺ ions occupy only one type of site. Considering the small spectral splitting range of ⁵D₀ → ⁷F₂ transition and the large intensity ratio of ⁵D₀ → ⁷F₂/⁵D₀ → ⁷F₁, it can be concluded that Eu³⁺ occupies Ca²⁺ site with larger coordinate numbers rather than Ti⁴⁺ site.     

Photovoltaic effect of TiO2 thick films with an ultrathin BiFeO3 as buffer layer

The photovoltaic (PV) effect of a bilayer anatase TiO₂/BiFeO₃ (BFO) film has been studied. The 20-nm ultrathin BFO layers were deposited on the fluorine-doped tin oxide (FTO) glass substrates by the chemical solution deposition method. An anatase TiO₂ layer is deposited subsequently on the BFO surface via a screen-printing technique. It is found that the FTO/TiO₂/Au cell exhibits negligible PV effect under solar exposure, while the one after introducing an ultrathin BFO film between TiO₂ and FTO leads to a considerable PV effect with an open-circuit voltage of ?0.58 V and a photocurrent density of 18.27 µA/cm². The FTO/BiVO₄ (BVO)/TiO₂/Au cell was constructed to investigate the underlying mechanism for the observed effect. A negligible PV effect of the FTO/BVO/TiO₂/Au cell indicates that the PV effect of the FTO/BFO/TiO₂/Au cell arises mainly from a built-in electric field in the BFO film induced by the self-polarization. Our work opens up a new path to utilize TiO₂ and may influence the future design of solar cells.     

Stability in a general coupled laser array

For the first time we have presented a method to investigate the stability of quiescent state in a coupled laser array. By introducing tiny perturbation, stability of quiescent state can be known by investigating eigenvalues of coefficient matrix of the corresponding linear differential equations. Only when real parts of the eigenvalues were all negative or zero, the corresponding quiescent state is stable. Two tapes of coupled laser array with loop and linear topological structure were studied respectively. It was found that there were innumerable quiescent states and they could be divided into several types based on phase relation. Some types were stable and others were unstable. Topological structure affects the stability of quiescent state in a coupled laser array.     

基于动态溶胀法制备中空聚合物微球

以表面带正电荷的m级聚苯乙烯微球为种子,经过甲苯、二乙烯基苯溶胀,聚合与包覆等过程制备了直径约5 m的中空聚合物微球。研究了溶剂类型、溶剂用量对动态溶胀法制备的中空聚合物微球粒径、分布和结构的影响,讨论了中空聚合物微球的形成机理。结果表明:添加一定量甲苯、二甲苯等挥发性溶剂是动态溶胀法形成中空聚合物微球的前提;甲苯用量越多,溶胀后形成的中空结构越明显,孔径越大;选择低溶解性的二甲苯溶剂更有利于中空结构的形成。     

103 W in-band dual-end-pumped Ho:YAG laser

An efficient 2?μm in-band pumped Ho:YAG laser was demonstrated. The resonator involves two Ho:YAG crystals, each of which was dual-end-pumped by two orthogonally polarized diode-pumped Tm:YLF lasers. The maximum continuous wave output power of 103?W was achieved, corresponding to a slope efficiency of 67.8% with respect to the incident pump power and an optical-to-optical conversion efficiency of 63.5%. Under Q-switched mode, we obtained 101?W laser output at 30?kHz, corresponding to a slope efficiency of 66.2%. The beam quality or M² factor was found to be less than 2.     

Modulational instability of ion—acoustic waves in a warm plasma

Using the standard reductive perturbation technique,a nonlinear Schroedinger equation is derived to study the modulational instability of finite-amplitude ion-acoustic waves in a non-magnetized warm plasma.It is found that the inclusion of ion temperature in the equation modifies the nature of the ion-acoustic wave stability and the soliton stuctures.The effects of ion plasma temperature on the modulational stability and ion-acoustic wave properties are inestigated in detail.