基于Hamilton模型的永磁同步风力发电系统中混沌运动的H∞控制

针对永磁同步风力发电系统的混沌运动现象, 提出了基于系统Hamilton模型的H_∞控制方案, 使得系统脱离混沌, 运行稳定. 首先将永磁同步风力发电系统模型经过一系列状态变换, 转化为类Lorenz经典数学模型, 并验证了系统在一定参数区域内存在混沌现象. 随后基于Hamilton系统充分利用系统物理结构和无需补偿“无功力”的优点, 建立了混沌系统的Hamilton模型, 并考虑了系统存在外扰情况下的H_∞控制方法. 本文所设计的控制器不仅简单易实现而且反映了系统内部结构以及动态特性的信息. 仿真实验证明了控制器的有效性.     

时变不确定时滞连续系统的鲁棒H∞保成本控制

针对一类同时具有状态时滞和输入时滞的时变不确定连续系统,研究了H_∞保成本状态反馈控制器的设计,假定其中的时变不确定性项是范数有界的,但不需要满足匹配条件.通过构造广义Lyapunov函数和线性矩阵不等式(LMI)方法,给出了系统可H_∞鲁棒镇定同时满足保性能指标的一个充分条件,仅通过求解一个相应的线性矩阵不等式,就可得到鲁棒H_∞保性能控制器使得闭环系统的一个保成本函数对所有允许的不确定参数有上界,并经过迭代,通过求解凸优化问题得到最优鲁棒H_∞保性能控制器.最后用示例说明了该方法的有效性. 关键词： 连续系统 时滞 H_∞鲁棒控制')" href="#">H_∞鲁棒控制 保成本控制     

Conductivity and water uptake of Sr4(Sr2Nb2)O11·nH2O and Sr4(Sr2Ta2)O11·nH2O

The hydrated oxygen deficient complex perovskite-related materials Sr₄(Sr₂Nb₂)O₁₁·nH₂O and Sr₄(Sr₂Ta₂)O₁₁·nH₂O were studied at high water vapour pressures over a large temperature range by electrical conductivity measurements, thermogravimetry (TG), and X-ray powder diffraction (XRPD). In humid atmospheres both materials are known to exhibit protonic conductivity below dehydration temperatures, with peak-shaped maxima at about 500 °C. In this work we show that the peaks expand to plateaus of high conductivity from 500 to 700 °C at a water vapour pressure of 1 atm. However, in situ synchrotron XRPD of Sr₄(Sr₂Nb₂)O₁₁·nH₂O as a function of temperature shows that these observations are in fact coincident with melting and dehydration of a secondary phase Sr(OH)₂. The stability of Sr₄(Sr₂Nb₂)O₁₁·nH₂O and Sr₄(Sr₂Ta₂)O₁₁·nH₂O in humid atmospheres is thus insufficient, causing decomposition into perovskites with lower Sr content and SrO/Sr(OH)₂ secondary phases. This, in turn, rationalizes the observation of peaks and plateaus in the conductivity of these materials.     

Experimental and kinetic modeling study of C2H4 oxidation at high pressure

A detailed chemical kinetic model for oxidation of C₂H₄ in the intermediate temperature range and high pressure has been developed and validated experimentally. New ab initio calculations and RRKM analysis of the important C₂H₃ + O₂ reaction was used to obtain rate coefficients over a wide range of conditions (0.003-100 bar, 200-3000 K). The results indicate that at 60 bar and medium temperatures vinyl peroxide, rather than CH₂O and HCO, is the dominant product. The experiments, involving C₂H₄/O₂ mixtures diluted in N₂, were carried out in a high pressure flow reactor at 600-900 K and 60 bar, varying the reaction stoichiometry from very lean to fuel-rich conditions. Model predictions are generally satisfactory. The governing reaction mechanisms are outlined based on calculations with the kinetic model. Under the investigated conditions the oxidation pathways for C₂H₄ are more complex than those prevailing at higher temperatures and lower pressures. The major differences are the importance of the hydroxyethyl (CH₂CH₂OH) and 2-hydroperoxyethyl (CH₂CH₂OOH) radicals, formed from addition of OH and HO₂ to C₂H₄, and vinyl peroxide, formed from C₂H₃ + O₂. Hydroxyethyl is oxidized through the peroxide HOCH₂CH₂OO (lean conditions) or through ethenol (low O₂ concentration), while 2-hydroperoxyethyl is converted through oxirane.     

Luminescent properties of HTP AgGd1−xW2O8:Eux and AgGd1−x(W1−yMoy)2O8:Eux phosphor for white LED

Intense red phosphors, AgGd_1−xEu_x(W_1−yMo_y)₂O₈ (x=0.0-1.0, y=0.0-1.0), have been synthesized through traditional solid-state reaction and characterized by X-ray diffraction (XRD) and photoluminescence (PL). XRD results reveal that AgGd_1−xEu_xW₂O₈ synthesized at 1000 °C has a tetragonal crystal structure, which is named as high temperature phase (HTP) AgGdW₂O₈. All phosphors compositions with Eu³⁺ show red and green emission on excitation either in the charge-transfer or Eu³⁺ levels. Analysis of the emission spectra with different Eu³⁺ concentrations reveal that the optimum dopant concentration for Eu³⁺ is x=0.6 in the HTP AgGd_1−xEu_xW₂O₈ (x=0.0-1.0). Studies on the AgGd_0.4Eu_0.6(W_1−yMo_y)₂O₈ (y=0.0-1.0) and AgGd_1−xEu_x(W_0.7Mo_0.3)₂O₈ (x=0.0-1.0) show that the emission intensity is maximum for compositions with y=0.3 and x=0.5, respectively, and a decrease in emission intensity is observed for higher y or x values. The Mo⁶⁺ and Eu³⁺ co-doped AgGd(WO₄)₂ phosphors show higher emission intensity in comparison with the singly Eu³⁺-doped AgGd(WO₄)₂ in UV region. The intense emission of the tungstate/molybdate phosphors under 394 and 465 nm excitations, respectively, suggests that these materials are promising candidates as red-emitting phosphors for near-UV/blue GaN-based white LED for white light generation.     

XPS investigation of diffusion of two-layer ZrO2/SiO2 and SiO2/ZrO2 sol–gel films

Two-layer ZrO₂/SiO₂ and SiO₂/ZrO₂ films were deposited on K9 glass substrates by sol–gel dip coating method. X-ray photoelectron spectroscopy (XPS) technique was used to investigate the diffusion of ZrO₂/SiO₂ and SiO₂/ZrO₂ films. To explain the difference of diffusion between ZrO₂/SiO₂ and SiO₂/ZrO₂ films, porous ratio and surface morphology of monolayer SiO₂ and ZrO₂ films were analyzed by using ellipsometry and atomic force microscopy (AFM). We found that for the ZrO₂/SiO₂ films there was a diffusion layer with a certain thickness and the atomic concentrations of Si and Zr changed rapidly; for the SiO₂/ZrO₂ films, the atomic concentrations of Si and Zr changed relatively slowly, and the ZrO₂ layer had diffused through the entire SiO₂ layer. The difference of diffusion between ZrO₂/SiO₂ and SiO₂/ZrO₂ films was influenced by the microstructure of SiO₂ and ZrO₂.     

Effect of Y2O3 addition on the conductivity and elastic modulus of (CeO2)1 − x(YO1.5)x

The conductivity and elastic modulus of (CeO₂)_1 − x(YO_1.5)_x for x values of 0.10, 0.15, 0.20, 0.30, and 0.40 were investigated by experiments and molecular dynamics simulations. The calculated conductivity exhibited a maximum value at approximately 15 mol% Y₂O₃; this trend agreed with that of the experimental results. In order to clarify the reason for the occurrence of the maximum conductivity, the paths for the transfer of oxygen vacancies were counted. The numerical result revealed that as the content of Y₂O₃ dopant increases, the number of paths for the transfer of oxygen vacancies decreases, whereas the number of oxygen vacancies for conductivity increases. Thus, the trade-off between the increase in the number of vacancy sites and the decrease in the vacancy transfer was considered to be the reason for the maximum conductivity occurring at the Y₂O₃ dopant content of approximately 15 mol%. The calculated elastic modulus also exhibited a minimum value at approximately 20 mol% Y₂O₃, which also agreed with the experimental results. It was shown that the Y–O–Y bonding energy increased with the increasing content of Y₂O₃ dopant. Thus, the trade-off between the increase in the number of vacancy sites and that in the Y–O–Y bonding energy was considered to be the reason for the minimum elastic modulus occurring at the Y₂O₃ dopant content of approximately 20 mol%.     

一类非线性T-S模糊时滞系统的鲁棒观测器型H∞控制器设计

针对同时具有分布时滞和非线性项的T-S模糊时滞系统, 提出观测器型H_∞输出反馈控制器设计方法. 首先, 以非线性矩阵不等式形式给出时滞相关的满足H_∞性能指标的稳定性分析充分条件; 其次, 给出与所给稳定性条件等价的线性矩阵不等式条件. 在此基础上, 讨论带有非线性项的观测器型H_∞输出反馈控制的可解问题. 最后, 通过仿真算例说明控制器设计方法的可行性. 关键词： T-S模糊系统 分布时滞 观测器型输出反馈控制 H_∞控制')" href="#">H_∞控制     

Line shift and mixing in the ν4 and 2ν2 band of NH3 perturbed by H2 and Ar

Pressure induced line shift and line mixing parameters have been measured for 66 rovibrational lines in the ν₄ band and for 10 lines in the 2ν₂ band of NH₃ perturbed by H₂ and Ar at room temperature (T = 296 K). These lines with J values ranging from 2 to 10 are located in the spectral range 1450-1600 cm⁻¹. Experiments were made with a high-resolution Fourier transform spectrometer. The line shifts and line mixing parameters have been derived from the non-linear least-square multi-pressure fitting technique. The shift coefficients are compared with those calculated from the Robert-Bonamy formalism (RB). The results are generally in satisfactory agreement with the experimental data.     

三明治结构Tan(B3N3H6)n+1 团簇的磁性和量子输运性质

利用密度泛函理论和非平衡格林函数方法, 本文对小尺寸团簇Ta_n(B₃N₃H₆)_n+1 (n ≤ 4)的磁性和量子输运性质进行了系统的研究. 计算结果表明, 此类体系采用三明治结构作为其基态并且具有较高的稳定性. 体系的磁矩随团簇尺寸的增大而线性增大. 当把Ta_n(B₃N₃H₆)_n+1团簇耦合到Au电极上时, 形成的Au-Ta_n(B₃N₃H₆)_n+1-Au体系在有限偏压下展示出了较强的自旋过滤能力, 因而可以被看做是一类新型的低维自旋过滤器.     

The stability, frontier orbitals, bond character, and static linear polarizability of the fluorinated fullerene H20@C80F60

This paper uses the density functional theory under generalised gradient approximation to analyse the stability,frontier orbitals,bond character,and static linear polarizability of H20@C80F60,which has not been isolated,as well as those of the synthesised H 20 @C 80 H 60.The H20@C80F60 should be considerably stable by analysing its energy and aromaticity.The inside H and outside X will play different role in the chemical reaction involving H 20 @C 80 X 60(X=H and F).The covalence of C-H bond is in the order that the inside C-H bond of H20@C80F60 > the inside C-H bond of H 20 @C 80 H 60 > the outside C-H bond of H 20 @C 80 H 60,whereas the C-F bond of H20@C80F60 have both the covalent and ionic characters.The static linear polarizabilities of C 80 and H 20 @C 80 X 60(X=H and F) are all isotropic.     

Hydrostatic pressure study of the structural phase transitions and superconductivity in single crystals of (Ba1−xKx)Fe2As2 (x=0 and 0.45) and CaFe2As2

We studied the effect of hydrostatic pressure (P) on the structural phase transitions and superconductivity in the ternary and pseudo-ternary iron arsenides CaFe₂As₂, BaFe₂As₂, and (Ba_0.55K_0.45)Fe₂As₂, by means of measurements of electrical resistivity (ρ) in the 1.8-300 K temperature (T) range, pressures up to 20 kbar, and magnetic fields up to 9 T. CaFe₂As₂ and BaFe₂As₂ (lightly doped with Sn) display structural phase transitions near 170 and 85 K, respectively, and do not exhibit superconductivity in ambient pressure, while K-doped (Ba_0.55K_0.45)Fe₂As₂ is superconducting for T<30 K. The effect of pressure on BaFe₂As₂ is to shift the onset of the crystallographic transformation down in temperature at the rate of ~−1.04 K/kbar, while shifting the whole ρ(T) curves downward, whereas its effect on superconducting (Ba_0.55K_0.45)Fe₂As₂ is to shift the onset of superconductivity to lower temperatures at the rate of ~−0.21 K/kbar. The effect of pressure on CaFe₂As₂ is first to suppress the crystallographic transformation and induce superconductivity with onset near 12 K very rapidly, i.e., for P<5 kbar. However, higher pressures bring about another phase transformation characterized by reduced-resistivity, and the suppression of superconductivity, confining superconductivity to a narrow pressure dome centered near 5 kbar. Upper critical field (H_c2) data in (Ba_0.55K_0.45)Fe₂As₂ and CaFe₂As₂ are discussed.     

Homogeneous ignition of CH4/air and H2O and CO2-diluted CH4/O2 mixtures over Pt; an experimental and numerical investigation at pressures up to 16 bar

The homogeneous ignition of CH₄/air, CH₄/O₂/H₂O/N₂, and CH₄/O₂/CO₂/N₂ mixtures over platinum was investigated experimentally and numerically at pressures 4 bar p 16 bar, temperatures 1120 K T 1420 K, and fuel-to-oxygen equivalence ratios 0.30 0.40. Experiments have been performed in an optically accessible catalytic channel-flow reactor and included planar laser induced fluorescence (LIF) of the OH radical for the determination of homogeneous (gas-phase) ignition and one-dimensional Raman measurements of major species concentrations across the reactor boundary layer for the assessment of the heterogeneous (catalytic) processes preceding homogeneous ignition. Numerical predictions were carried out with a 2D elliptic CFD code that included elementary heterogeneous and homogeneous chemical reaction schemes and detailed transport. The employed heterogeneous reaction scheme accurately captured the catalytic methane conversion upstream of the gaseous combustion zone. Two well-known gas-phase reaction mechanisms were tested for their capacity to reproduce measured homogeneous ignition characteristics. There were substantial differences in the performance of the two schemes, which were ascribed to their ability to correctly capture the p–T– parameter range of the self-inhibited ignition behavior of methane. Comparisons between measured and predicted homogeneous ignition distances have led to the validation of a gaseous reaction scheme at 6 bar p 16 bar, a pressure range of particular interest to gas-turbine catalytically stabilized combustion (CST) applications. The presence of heterogeneously produced water chemically promoted the onset of homogeneous ignition. Experiments and predictions with CH₄/O₂/H₂O/N₂ mixtures containing 57% per volume H₂O have shown that the validated gaseous scheme was able to capture the chemical impact of water in the induction zone. Experiments with CO₂ addition (30% per volume) were in good agreement with the numerical simulations and have indicated that CO₂ had only a minor chemical impact on homogeneous ignition.     

Luminescence investigation of red phosphors Ca0.54Sr0.34−1.5xEu0.08Smx(MoO4)y (WO4)1−y for UV-white LED device

Ca_0.54Sr_0.34−1.5xEu_0.08Sm_x(MoO₄)_y (WO₄)_1−y red phosphors were prepared by solid-state reaction using Na⁺ as a charge compensator for light-emitting diodes (LED). The effects of Na⁺ concentration, synthesis temperature, reaction time and Eu³⁺ concentration were studied for the properties of luminescence and crystal structure of red phosphors. The results show that the optimum reaction condition is 6%, 900 °C, 2 h and 8%. The photoluminescence spectra show that red phosphors are effectively excited at 616 nm by 292, 395 and 465 nm. The wavelengths of 465 nm nicely match the widely applied emission wavelengths of blue LED chips.     

Luminescent properties of KGd1−x(WO4)2:Eux and KGd1−x(WO4)2−y(MoO4)y:Eux phosphors in UV-VUV regions

KGd_1−x(WO₄)_2−y(MoO₄)_y:Eu³⁺_x(0.1?x?0.75, y=0 and 0.2) phosphors are synthesized through traditional solid-state reaction and their luminescent properties in ultraviolet (UV) and vacuum ultraviolet (VUV) regions are investigated. Under 147 nm excitation, these phosphors show characteristic red emission with good color purity. In order to improve their emission intensity, the MoO₄²⁻ (20 wt%) is introduced into the anion of KGd_1−x(WO₄):Eu³⁺_x. The Mo⁶⁺ and Eu³⁺ co-doped KGd(WO₄)₂ phosphors show higher emission intensity in comparison with the singly Eu³⁺-doped KGd(WO₄)₂ in VUV region. The chromaticity coordination of KGd_0.45(WO₄):Eu³⁺_0.55 is (x=0.669, y=0.331), while that of KGd_0.45(WO₄)_1.8(MoO₄)_0.2:Eu³⁺_0.55 is (x=0.666, y=0.334) in VUV region.     

Transport properties and defect analysis of La1.9Sr0.1NiO4 + δ

The oxygen flux through La_1.9Sr_0.1NiO_4 + δ has been measured as a function of oxygen activity gradient and temperature (750–1000 °C). The oxygen nonstoichiometry was determined by thermogravimetry in the temperature range of 400–1000 °C and oxygen partial pressures of 0.0002–1 atm. The total conductivity was measured over a similar range of conditions. The oxide ion partial conductivity derived from the oxygen flux data is approximately 4 orders of magnitude lower than the total, mainly p-type electronic conductivity. The defect structure was derived based on the data. Combining the oxygen flux and oxygen nonstoichiometry, the self diffusion coefficient of oxygen interstitials was evaluated.     

Structure and magnetostriction of Tb0.2Pr0.8(Fe0.4Co0.6)1.93−xCx intermetallic compounds

The structure and magnetostriction of Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93−xC_x intermetallic compounds were studied by X-ray diffraction and magnetic measurements. Almost a single cubic Laves phase forms in the alloys for x ≤0.20, and a small amount of C can inhibit the formation of the 1:3 phase. The lattice parameter increases when 0≤x≤0.15, while the T_c and the spontaneous magnetization decreases with increasing x. The lattice parameter decreases slowly when 0.15≤x≤0.30, while the T_c decreases evidently with increasing x. The magnetostriction λ_a (=λ_∥-λ_⊥) is improved at low magnetic fields at room temperature for the compounds with 0.05≤x≤0.10, indicating that these C-containing compounds are promising magnetostrictive materials.     

Atomic-potential parameters for H2 and D2: quantum corrections in the calculation of second-virial coefficients

First-order quantum corrections were introduced into the computation of the second-virial coefficients of H₂ and D₂. The quantum effects, for the studied two light molecules, are considerable even at the room temperature and become prominent at low temperatures. Atomic potentials, incorporating the quadrupole interactions, were employed in the calculations. Optimum atomic-potential parameters ε_H, σ_H, ε_D and σ_D were obtained from the nonlinear least-squares fit of the experimental second-virial coefficients. The fitted virial coefficients cover the temperature ranges of 173-423 and 153- for H₂ and D₂, respectively.     

Reasons for the deactivation of Pt/TiO2 photocatalyst treated by inert gas N2

The effect of N₂ treatment on the photocatalytic activity of Pt⁰/TiO₂ was investigated. The results showed that after treatment at 500 °C in N₂, 70% of the photocatalytic activity of 1.0 wt.% Pt⁰/TiO₂ was lost by the evaluation of photocatalytic oxidation reaction of C₃H₆. Transmission electron microscopy (TEM) and Ar⁺ ion sputtering tests revealed that in the course of high-temperature N₂ treatment, the size of Pt⁰ particles on TiO₂ increases and a strong interaction between metal and support, i.e. Pt⁰ particles encapsulated by Ti_xO_y, happens, which are the reasons for the deactivation of Pt⁰/TiO₂ photocatalyst treated by high-temperature N₂.     

Theoretical investigation of EPR and optical spectra of Mo(V) in [Mo6O19][N(C4H9)4]3 salt

The electron paramagnetic resonance (EPR) spectral data (the g factors and hyperfine structure constants) and d–d transition spectra for the tetragonal Mo⁵⁺ centre in [Mo₆O₁₉][N(C₄H₉)₄]₃ salt are theoretically investigated from the complete diagonalization method (CDM) for a 4d¹ ion in tetragonally compressed octahedron. The theoretical results are in good agreement with the experimental data. The dependency of the g factors of the ground state on the R_∥(MoO bond length) has been studied. It is shown that the g factors varied with the R_∥ approximately in a linear way.