Theoretical investigation of hierarchical sub-wavelength photonic structures fabricated using high-order waveguide-mode interference lithograph

This paper presents the theoretical investigation of hierarchical sub-wavelength photonic structures with various periods and numbers of layers, which were fabricated using a high-order waveguide-mode interference field. A 442-nm laser was used to excite high-order waveguide modes in an asymmetric metal-cladding dielectric waveguide structure. The dispersion curve of the waveguide modes was theoretically analyzed, and the distribution of the interference field of high-order waveguide modes was numerically simulated using the finite-element method. The various dependences of the characteristics of hierarchical sub-wavelength photonic structures on the thickness and refractive index of the photoresist and the waveguide mode were investigated in detail. These hierarchical sub-wavelength photonic structures have various periods and numbers of layers and can be fabricated by a simple and low-cost method.

Coordinating optimization-based sliding mode variable structure control for electro-hydraulic servo system

A sliding mode variable structure control （SMVSC） based on a coordinating optimization algorithm has been developed. Steady state error and control switching frequency are used to constitute the system performance indexes in the coordinating optimization, while the tuning rate of boundary layer width （BLW） is employed as the optimization parameter. Based on the mathematical relationship between the BLW and steady-state error, an optimized BLW tuning rate is added to the nonlinear control term of SMVSC. Simulation experiment results applied to the positioning control of an electro-hydraulic servo system show the comprehensive superiority in dynamical and static state performance by using the proposed controller is better than that by using SMVSC without optimized BLW tuning rate. This succeeds in coordinately considering both chattering reduction and high-precision control realization in SMVSC.

LINEAR ACTIVE STRUCTURES AND MODES (Ⅱ) —DISCRETE SYSTEMS AND BEAMS

The basic concepts about the active structures and some attributes of the modes were presented in paper “Liner Active Structures and Modes]( I) ". The characteristics of the active discrete systems and active beams were discussed, especially, the stability of the active structures and the orthogonality of the eigenvectors. The notes about modes were portrayed by a model of a seven-storeyed building with sensors and actuators. The concept of the adjoint active structure was extended from the discrete systems to the beams that were the representations of the continuous structures. Two types of beams with different placements of the measuring and actuating systems were discussed in detail. One is the beam with the discrete sensors and actuators, and the other is the beam with distributed sensor and actuator function. The orthogonality conditions were derived with the modal shapes of the active beam and its adjoint active beam. An example shows that the variation of eigenvalues with feedback amplitude for the homo-configuration and non-homo-configuration active structures.

VARIABLE STRUCTURE CONTROL OF INDEFINITE-DIMENSIONAL SYSTEMS

In lhis paper, we study the variable structure control of indefinite-dimensionalcontrol systems with the functional analysis method. The reaching conditions, stabilityconditions and the approximating conditions of sliding mode, as well as the generalform of the variable structure control law are given. and the elementary frame of thevariable structure control of indefinite-dimensional systems is built.

Coordinated Control of Sliding Mode and Hamiltonian for PWM Rectifier

Aiming at the PWM rectifier control strategy of sliding mode control, steady state performance weak Hamiltonian control dynamic tracking performance is poor, the coordinated compound control is proposed, the feedback linearization controller and sliding mode controller Hamiltonian system is obtained, and the design of a coordinated control strategy. In order to verify the accuracy of this method, MATLAB/Simulink is used for simulation analysis. The simulation results show that the composite control can achieve the coordinated dynamic rapid tracking and constant DC output and unit power factor operation, and satisfy the control requirements of the rectifier, effectively reducing the disturbance effect on the system. Compared with Hamiltonian control, the proposed method combines the advantages of the two methods, which have the fast tracking performance and excellent steady-state characteristics, and the research prospect is broad.

First-principles simulation of Raman spectra and structural properties of quartz up to 5 GPa

The crystal structure and Raman spectra of quartz are calculated by using first-principles method in a pressure range from 0 to 5 GPa. The results show that the lattice constants（a, c, and V） decrease with increasing pressure and the a-axis is more compressible than the c axis. The Si–O bond distance decreases with increasing pressure, which is in contrast to experimental results reported by Hazen et al. [Hazen R M, Finger L W, Hemley R J and Mao H K 1989 Solid State Communications 725 507–511], and Glinnemann et al. [Glinnemann J, King H E Jr, Schulz H, Hahn T, La Placa S J and Dacol F 1992 Z. Kristallogr. 198 177–212]. The most striking changes are of inter-tetrahedral O–O distances and Si–O–Si angles. The volume of the SiO4^4- tetrahedron decreased by 0.9%（from 0 to 5 GPa）, which suggests that it is relatively rigid.Vibrational models of the quartz modes are identified by visualizing the associated atomic motions. Raman vibrations are mainly controlled by the deformation of the Si O4-4tetrahedron and the changes in the Si–O–Si bonds. Vibrational directions and intensities of atoms in all Raman modes just show little deviations when pressure increases from 0 to 5 GPa.The pressure derivatives（dνi/d P） of the 12 Raman frequencies are obtained at 0 GPa–5 GPa. The calculated results show that first-principles methods can well describe the high-pressure structural properties and Raman spectra of quartz. The combination of first-principles simulations of the Raman frequencies of minerals and Raman spectroscopy experiments is a useful tool for exploring the stress conditions within the Earth.

Optimized guided mode resonant structure as thermooptic sensor and liquid crystal tunable filter

Applicability of guided mode resonant structures to tunable optical filtering and sensing is demonstrated using nematic liquid crystals. As a sensor, a minimum refractive index detectivity of 10^-5 is demonstrated while as a tunable filter, tunability range of few tens of nanometers with 2-nm bandwidth is presented. The optimum design is achieved by maximizing the evanescent field region in the analyte which maximizes the overlap integral. The device can be operated in reflection or transmission modes at normal incidence. It can also be operated at a single wavelength by measuring the angular profile of the light beam.

Gap induced mode evolution under the asymmetric structure in a plasmonic resonator system

The modulation of resonance features in microcavities is important to applications in nanophotonics.Based on the asymmetric whispering-gallery modes(WGMs)in a plasmonic resonator,we theoretically studied the mode evolution in an asymmetric WGM plasmonic system.Exploiting the gap or nano-scatter in the plasmonic ring cavity,the symmetry of the system will be broken and the standing wave in the cavity will be tunable.Based on this asymmetric structure,the output coupling rate between the two cavity modes can also be tuned.Moreover,the proposed method could further be applied for sensing and detecting the position of defects in a WGM system.

Analysis of generation of cumulative second harmonics of Lamb modes in a layered planar structure

A technique for analyzing the nonlinear generation of the cumulative second har-monics of generalized Lamb modes in a layered planar structure is developed. A theoretical model for nonlinear generalized Lamb mode propagation in a layered planar structure has been established, based on a partial plane wave approach. The nonlinearity is treated as a second-order perturbation of the linear elastic response. This model reveals some interesting features of the physics of the cumulative second harmonic generation. Although Lamb mode propagation is dispersive in a layered structure, the results of this analysis show that the amplitudes of the second harmonics do accumulate with propagation distance under certain special conditions. On the basis of the boundary and initial conditions of excitation, the formal solution of the cumulative second harmonic has been derived. Using the formal solution, we have performed some numerical simulations and obtained the cumulative second harmonic field patterns, illus-trating the distortion effect along the propagation distance, as well as the dependence of the field patterns on the position of the excitation source.

Structural Probing on the Sn-C(C5 ring)Bond of the Sn(Ⅱ)Metallocenes in Both the Solid State and the Temperature-dependent Solution Relaxation State

Various bond modes of the M-C（C5 ring） exist in metallocene compounds of group 14 heavier elements,mostly due to an intricate interaction between the lone electron pairs at the M center and the 6 p-electrons of the C5 ring.The tin（Ⅱ） metallocene complexes LSn R（L = HC[CMe（N-2,6-iPr2C6H3）]2,R = cyclopentadienyl,C5H5（1）; indenyl,C9H7（2）; fluorenyl,C（13）H9（3）） stabilized by the β-diketiminato ligand were prepared and utilized in the study on their solid and solution state structures.X-ray single-crystal diffraction data revealed an η~1-mode of the Sn-C（C5 ring） bond in each 1~3.However,the room temperature ~1H NMR spectral studies disclosed such a fluxional bonding mode in solution.The 119 Sn NMR studies suggested a quadruple coordination nature of the Sn center in 1 while the triple coordination manner was for the Sn atom in both 2 and 3.Then the variable-temperature（25~–75 ℃） ~1H NMR spectral studies for each 1~3 were performed,which detected the relaxation state structures of 1~3 at lower temperature.All of these results indicate a stereochemical activity of the lone electron pairs at the tin（Ⅱ） atom that definitely has an electronic interaction with the 6 p-electrons of the C5 ring.The observed Sn-C（C5 ring） bond modes appear influenced by either the metallocene size or the compound state existed.

Research on Damage Localization of Plate-like Structure Using Mode Acoustic Emission and Matching Pursuit

Based on mode acoustic emission theory,the paper analyses the acoustic emission analog signal of thin steel plate using matching pursuit,then obtains the characteristics interpretation of the different frequency signal energy concentration degree; Combined with four-point arc positioning method,the papers researches the damage localization of the plate-like structure. Simulation experiment shows that this method can accurately detect and locate the damage. This can provide data support for further imaging research based on time reverse theory.

Electro-mechanical Modeling of Wind Turbine and Energy Storage Systems with Enhanced Inertial Response

In this paper,a coordinated control scheme for wind turbine generator(WTG)and supercapacitor energy storage system(ESS)is proposed for temporary frequency supports.Inertial control is designed by using generator torque limit considering the security of WTG system,while ESS releases its energy to compensate the sudden active power deficit during the recovery process of turbine rotor.WTG is modeled using the fatigue,aerodynamic,structure,turbulence(FAST)code,which identifies the mechanical loadings of the turbine and addresses electro-mechanical interactions in the wind energy system.A damping controller is augmented to the inertial control to suppress severe mechanical oscillations in the shaft and tower of the turbine during frequency supports.Furthermore,the result of small-signal stability analysis shows that the WTGESS tends to improve the stability of the whole multi-energy power grid.The major contributions of this paper will be validated by utilizing the proposed control method that combines the grid support capability and maintaining the integrity of structural design of the turbine for normal operations.

Researches on active structural acoustic control by radiation modes

Based on the radiation modes, an active control strategy is presented for sound radiation from elastic structures with an example of simply supported rectangular panel. The physical characteristics and mathematical meaning of the radiation modes are analyzed. The radiation efficiency of radiation mode falls off very rapidly with the increase of modes order at low frequency. A new control strategy is developed in which by canceling the adjoint coef- ficient of the first k radiation modes, the sound powers of the first k radiation modes is zero theoratically. The numerical calculation is made by using point force actuators as control forces.

黄土隧道新型组合结构支护效果分析及参数优化研究

黄土隧道在开挖过程中经常发生支护结构破坏或过度变形。依托某黄土隧道,提出一种新型组合结构支护体系(π形拱架),采用理论计算对比了π形拱架与传统工字钢提供的支护反力,结合现场监测和数值模拟分析了不同支护体系下围岩控制效果,优化新型组合结构的构造参数,同时基于正交试验探究了构造参数对围岩支承效果影响显著性大小。结果表明:π形拱架提供的支护反力是型钢钢架的3.14倍,具有强度大、承载力高的优势;建立对比分析模型,较传统支护体系相比,新型支护体系下的拱顶沉降降幅达到53.8%,等效塑性应变减少约64.4%,初期支护最大压应力和拉应力分别减少约35.3%、35.9%;进而建立参数优化模型,通过对围岩竖向位移和塑性区的综合评估,建议拱架壁厚取6 mm,灌浆强度选择C30,翼板长度以200 mm为宜;结合正交试验结果,各因素影响程度由小到大依次为因素B(灌浆强度)<因素A(钢管壁厚)<因素C(翼板长度)。本研究可进一步促进新型拱架在黄土隧道施工支护中的应用。

Impact of Dual-Volume Helmholtz Dampers on Longitudinal and Azimuthal Thermo-Acoustic Instabilities in an Annular Combustor

Dual-volume Helmholtz dampers with two resonant frequencies are proposed to simultaneously attenuate longitudinal and azimuthal thermo-acoustic instabilities in annular combustors. Thermo-acoustic instabilities in a swirled annular combustor equipped with dual-volume dampers are numerically investigated by the Helmholtz method, combined with a measured flame transfer function and the established damper impedance model. Furthermore, the influences of the damper number and circumferential configurations on oscillation attenuations and mode structures are explored. The established dual-volume damper model is well validated by the impedance tube tests. Numerical results indicate velocity fluctuation levels of the longitudinal and azimuthal modes decline after installing Helmholtz dampers, whereas those of the azimuthal modes further decrease by around 16% after using four retuned dual-volume dampers. The eigenfrequencies of the first longitudinal and azimuthal modes decrease and increase after installing dampers, respectively. After installing dual-volume dampers, the difference between the pressure fluctuation in the plenum and combustion chamber is reduced, and pressure waveforms of the azimuthal modes along the circumferential direction shifts. The pressure distribution of azimuthal modes becomes more uniform after using more dual-volume dampers. The specific absorption frequency band for azimuthal modes introduced by the dual-volume damper may lead to decreased oscillations and mode evolutions. The maximal absorbing ability can be approached by installing dampers with the same angle between adjacent dampers. When dampers are unevenly distributed, the symmetry between two azimuthal modes is broken and standing modes will emerge.

Evaluation of tensile properties of a compositemetal joint with a novel metal insert design by experimental and numerical methods

Composite-metal joints with a metal insert are one kind of connecting structure.In this paper,tensile experimental tests were carried out to investigate tensile properties of a compositemetal joint with a novel metal insert design.Finite element models of the joint were established,and strain distribution and tensile strength were analyzed.The numerical results are in good agreement with the experimental results.Results show that the joint failure is dominated by shear properties of the resin layer.Increasing the resin layer thickness in a certain range will improve the tensile strength of the joint,while increasing the radius of the fillet on the ending side of the metal insert will decrease the joint strength.Increasing the resin layer plasticity will improve the joint strength.The effect of the embedded depth of the metal insert can be ignored.

Mechanism of water savings and pollution reduction in paddy fields of three typical areas in southern China

Field irrigation and drainage regulation and fertilization application could affect water utilization and pollution transportation in a paddy field.In this study,representative rice-producing areas of Zhejiang Province in southern China were selected to study the effects of different field water level control(conventional irrigation and drainage W0,controlled irrigation and drainage W1 and W2)and different fertilization methods(2 times of fertilization F2 and three times of fertilization F3)on water irrigation quantity and consumption of rice,rice growth,water utilization,and pollution reduction.Results showed that field water level control had a great effect on irrigation quota in growing period rather than that in soaking period,and irrigation quota for W0 was 37.0%-71.7%higher than that for W1 and W2 in the whole growth period of rice.Although the upper limit of rain storage was greatly increased by W1 and W2,on the contrary,the yield under W1 and W2 was 0.4%-2.1%higher than that under W0.Water consumption,water leakage,and evapotranspiration were 16.63%-34.4%,39.97%-60.8%,and 9.40%-31.53%lower under W1 and W2 than those under W0,respectively,while it showed no significant changes under W1 and W2.Rainfall use rate and WUEI(water use efficiency of irrigation)under W1 and W2 had been significantly improved by 8.20%-129.58%and 31.58%-201.61%compared to W0.The contribution of nitrogen and phosphorus loss from surface water accounted for 90%and the total pollution load of total nitrogen(TN),NO_(3)^(-)-N,NH_(4)^(+)-N and chemical oxygen demand(COD)were 20.0%-63.4%,21.8%-66.3%,21.5%-63.8%,and 21.4%-46.5%lower for W1 and W2 than that for W0,respectively.Meanwhile,compared to F2,dispersed fertilization(F3)was beneficial to increase the yield and decrease pollutant load.Additionally,the path of IRA→NH_(4)^(+)-N→COD and IRA→WCA→WUE_(I) presented partial remediation effect,and the effect size was 23.6%and 38.1%,respectively,the path of IRA→WUE_(I)→WUE_(ET) presented a full remediation effect,and the path of IRA→WCA→WUE_(ET) presented suppression effect.

Fabrication of fiber-embedded multi-core photonic crystal fibers

A novel fabrication method of multi-core photonic crystal fibers is proposed on the basis of a fiber-embedded technique. A taper tower is used to modify the structures of the fiber preform, and four steps of fiber fabrication and different structures of fiber samples are given. The mode structures and beating characteristics of a photonic crystal fiber sample with two successive cores are investigated in detail with the help of a supercontinuum light source, a charge-coupled device （CCD） camera, and an optical spectrum analyzer. The test results show a clear beating phenomenon between two orthotropic polarization modes with a 2.8-nm peak interval in wavelength.