Mechanism of the excitation of single pure mode L（0, 2） and its interaction with the defect in a hollow cylinder

Guided elastic waves have a great potential in pipe inspection as an efficient and low-cost nondestructive evaluation （NDE） technique, among which the wave of mode L（0, 2） receives a lot of attention because this mode is the fastest mode in a weakly dispersive region of frequency to minimize dispersion effects over a long distance and sensitive to the defects distributed circumferentially. Though many experimental and numerical researches have already been carried out about the excitation of L（0, 2） and its interaction with the defect in a hollow cylinder, its excitation mechanism has not been clarified yet. In this paper based on the transient response solution of the hollow cylinder, derived by the method of eigenfunction expansion, the theory about the exciting mechanism of mode L（0, 2） is advanced and the effects of the spatial distribution, vibration frequency and direction of the external force on the excitation are discussed. And the pure mode L（0, 2） is excited successfully under the parameters obtained through theoretical analysis. Furthermore, its interactions with some kinds of defects in hollow cylinders are simulated with the method of finite element analysis （FEA） and the results agree well with those obtained by other researchers.

New periodic wave solutions, localized excitations and their interaction for (2+1)-dimensional Burgers equation

Based on the B/icklund method and the multilinear variable separation approach （MLVSA）, this paper finds a general solution including two arbitrary functions for the （2＋1）-dimensional Burgers equations. Then a class of new doubly periodic wave solutions for （2＋l）-dimensional Burgers equations is obtained by introducing appropriate Jacobi elliptic functions, Weierstrass elliptic functions and their combination in the general solutions （which contains two arbitrary functions）. Two types of limit cases are considered. Firstly, taking one of the moduli to be unity and the other zero, it obtains particular wave （called semi-localized） patterns, which is periodic in one direction, but localized in the other direction. Secondly, if both moduli are tending to 1 as a limit, it derives some novel localized excitations （two-dromion solution）.

Synthesis and Luminescence of SrZnO_2∶Eu^(3+), Li^+ Phosphor by Long Wavelength UV Excitation

SrZnO2 ： Eu^3 ＋ , Li^＋ phosphor powder by long wavelength UV excitation was synthesized by conventional solid-state reaction method. XRD and PL were employed to characterize their properties. The resuits show that Eu^3＋ ions preferentially occupy Sr^2＋ asymmetry cationic sites, thus emitting 612 nm red light originated from ^5D0 to ^7F2 transition. The luminescent intensity can be greatly enhanced with incorporation of Li^＋ ions. The excitation efficiency in range of 350 - 400 nm also increases greatly due to incorporating Li ^＋ ions. SrZnO2 ： Eu^3 ＋ , Li^＋ is a promising redemitting phosphor by long wavelength UV excitation.

One-photo excitation pathway in 2D in-plane heterostructures for effective visible-light-driven photocatalytic degradation

Broad-spectrum absorption and highly effective charge-carrier separation are two essential requirements to improve the photocatalytic performance of semiconductor-based photocatalysts.In this work,a fascinating one-photon system is reported by rationally fabricating 2D in-plane Bi_(2)O_(3)/BiOCl(i-Cl)heterostructures for efficient photocatalytic degradation of RhB and TC.Systematic investigations revealed that the matched band structure generated an internal electric field and a chemical bond connection between the Bi_(2)O_(3)and BiOCl in the Bi_(2)O_(3)/BiOCl composite that could effectively improve the utilization ratio of visible light and the separation effectivity of photo-generated carriers in space.The formed interactions at the 2D in-plane heterojunction interface induced the one-photon excitation pathway which has been confirmed by the experiment and DFT calculations.As a result,the i-Cl samples showed significantly enhanced photocatalytic efficiency towards the degradation of RhB and TC(RhB:0.106 min^(-1);TC:0.048 min^(-1))under visible light.The degradation activities of RhB and TC for i-Cl were 265.08 and 4.08times that of pure BiOCl,as well as 9.27 and 2.14 times that of mechanistically mixed Bi_(2)O_(3)/BiOCl samples,respectively.This work provides a logical strategy to construct other 2D in-plane heterojunctions with a one-photon excitation pathway with enhanced performance.

Study of the excitation properties of the Si_3 O_2 cluster under an external electric field

The structure of the Si3Ox （x =2, 3） cluster is investigated; we find that the geometry of Si3O2 is similar to that of Si3O3 except for the oxygen-deficient defect structure （Si-Si band） which exists only in the Si3O2 cluster. It is known that oxygen-deficient defects are used to explain visible luminescence （especially blue, purple and ultraviolet light） from silicon-based materials, which are directly bound up with the excited states of the molecules. Therefore the excitation properties of the two clusters are also studied. Our results show that the absorption spectrum of Si3O2 is concentrated in the visible light region. In contrast, the absorption spectrum of Si3O3 is mainly located in the ultraviolet light region. The calculations are perfectly consistent with experimental data and also support the theory of oxygen-deficient defects.

Folded Solitary Wave Excitations for(2+1)-Dimensional Nizhnik-Novikov-Veselov System

With the help of an improved mapping approach and a linear-variable-separation approach, a new family of exact solutions with arbitrary functions of the （2＋1）-dimensional Nizhnik-Novikov-Veselov system （NNV） is derived. Based on the derived solutions and using some multi-valued functions, we find a few new folded solitary wave excitations for the （2＋1）-dimensional NNV system.

Fractal Dromion,Fractal Lump,and Multiple peakon Excitations in a New （2＋1）—Dimensional Long Dispersive Wave SYstem

By means of variable separation approach, quite a general excitation of the new (2 + 1)-dimensional long dispersive wave system: is derived. Some types of the usual localized excitations such as dromions, lumps, rings, and oscillating soliton excitations can be easily constructed by selecting the arbitrary functions appropriately. Besides these usual localized structures, some new localized excitations like fractal-dromion, fractal-lump, and multi-peakon excitations of this new system are found by selecting appropriate functions.

Gapped Spin-1/2 Spinon Excitations in a New Kagome Quantum Spin Liquid Compound Cu_3Zn(OH)_6FBr

We report a new kagome quantum spin liquid candidate CuaZn（OH）6FBr, which does not experience any phase transition down to 50inK, more than three orders lower than the antiferromagnetic Curie-Weiss temperature （-200 K）. A clear gap opening at low temperature is observed in the uniform spin susceptibility obtained from 19F nuclear magnetic resonance measurements. We observe the characteristic magnetic field dependence of the gap as expected for fractionalized spin-1/2 spinon excitations. Our experimental results provide firm evidence for spin fractionalization in a topologically ordered spin system, resembling charge fraetionalization in the fractional quantum Hall state.

Photoluminescence of green nanophosphors Sr_(2)MgSi_(2)O_(7)doped with Tb^(3+)under 374-nm excitation

A series of Sr_(2)MgSi_(2)O_(7):Tb^(3+)nanophosphors is prepared using a high-temperature solid-state reaction.The x-ray diffraction patterns show that the crystal structure of the sample is not significantly affected by Tb^(3+)ions.However,the images of the scanning electron microscope illustrate that the average size of nanoparticles becomes larger with the increase of Tb^(3+)concentration.Unlike earlier investigations on down-conversion emission of Tb^(3+)ion excited by deep ultraviolet light,in this work,the photoluminescence characteristics of Sr_(2)MgSi_(2)O_(7)nanophosphors doped with different Tb^(3+)concentrations are analyzed under 374-nm excitations.The intense green emission at 545 nm is observed at an optimal doping concentration of 1.6 mol%.The main reason for the concentration quenching is due to the electric dipole-electric dipole interaction among Tb^(3+)ions.

Microscopic sdgIBM-2 description of low-lying excitation spectra of ^(48,52,56)Cr

Starting from the shell model configurations,valence nucleon effctive interactions and fermion E2 transition operator,a microscopic approach of sdgIBM-2 is used to calculate the energy spectra,E2 transitions,and binding energies for 48,52,56Cr.The results fit the experimental data quite well.

Discovery of Fractionalized Neutral Spin-1/2 Excitation of Topological Order

After the discovery of fraction quantum Hall states in the 1980s, it became more and more clear that Landau symmetry breaking theory does not describe all possible quantum phases of matter. The new quan- tum phases of matter were called topologically ordered phases（for gapped cases） or quantum ordered phases （for gapless cases）, which correspond to pat- terns of many-body entanglement. One may won- der： besides quantum Hall systems, are there other systems that realize the new topological/quantum order？

Dependence of Nonlinear Optical Response of Anatase TiO2 on Shape and Excitation Intensity

Nonlinear optical （NLO） properties of anatase TiO2 with nanostructures of nanopaxticle （NP）, nanowire （NW） and annealed nanowire （NWA） are studied by open-aperture and closed-aperture Z-scan techniques with a fem- tosecond pulsed laser at wavelengths of 532 nm and 780 nm simultaneously. At 532 nm, when increasing excitation intensity, NLO absorption of TiO2 NPs transforms from saturable absorption to reverse-saturable absorption. However, NWs and NWAs exhibit the opposite change. At 780nm, all samples show reverse-saturable absorption, but have different sensitivities to excitation intensity. Due to the larger surface-to-volume ratio of NPs and less defects of NWAs by annealing, nonlinear optical absorption coet^icients follow the order NPs≥ NWs≥ NWAs. The results also show that these shape and annealing effects axe dominant at low excitation intensity, but do not exhibit at the high excitation intensity. The NLO refractive index of NPs shows a positive linear relationship with the excitation intensity, whereas NW and NWAs exhibit a negative linear relationship. The results could provide some foundational guidance to applications of anatase TiO2 in optoelectronic devices or other aspects.

Two-photon excitation for C_2Vmolecules based on the full relativistic theory

The present work explores a new phenomenon that not all the transition probability of two photon processes is negligible at low irradiance. The irreducible representation 2B2 of C2v is unexpected, for there is no much deviation in oscillator strength for two-photon and single-photon process A1 to 2B2. This new phenomenon is only possible to be explored by the symmetrical consideration: the necessary and sufficient condition is molecular plane coincident with yz plane or the operation σ ’v(yz) for group C2v. It is only possible to be evaluated out by use of the full relativistic quantum mechanical theory.

Preparation of NaYF_4:Er^(3+)/TiO_2 composite and up-conversion luminescence properties under visible light excitation

The up-conversion luminescence composite NaYF4：Er3＋/TiO2 is prepared using the sol-gel method. The specimen has good crystallinity and two shapes, i.e., viereck and round, while the sizes of viereck and round particles are both micron-sized. The TiO2 has an anatase structure, while the NaYF4 has a hexagonal phase, which can be hardly obtained through the common sol-gel method. Due to the big particle size and the high crystallinity of pure NaYF4： Er3＋, the composite has a small specific surface area that is less than Degussa P25 TiO2. The NaYF4：Er3＋/TiO2 composite shows several emission peaks at 211, 237, and 251 nm under the excitation of 388 nm, at 395 nm and 411 nm under the excitation of 500 nm, and at 467, 481,492, and 508 nm under the excitation of 570 nm.

自激振荡脉冲SC-CO_(2)射流冲击频率调制

SC-CO_(2)射流钻完井技术能保证煤层气井稳定性、提高钻井速度和破岩效率,具有广泛的应用前景。但较高的破煤能耗和复杂的系统限制了其工程推广,自激振荡脉冲SC-CO_(2)射流冲击频率和煤岩体的固有频率相同或满足相位关系,能充分发挥谐振效应,达到更好的破煤效果。喷嘴结构是影响射流冲击频率的关键,现有的自振脉冲水射流频率调制方法并不适用于SC-CO_(2)射流。为实现对SC-CO_(2)射流冲击频率的调制,采用大涡模拟研究不同喷嘴结构对自激振荡脉冲SCCO_(2)射流冲击频率的影响规律,通过权重分析得到不同喷嘴结构参数对射流冲击频率的影响程度。采用射流冲击频率测定实验及破煤实验验证喷嘴结构对射流冲击频率的影响规律以及射流冲击频率调制方法的可靠性。结果表明:振荡腔直径、振荡腔长度、碰撞壁角度是影响射流冲击频率的关键因素,可通过调节振荡腔结构实现对射流冲击频率的大幅调制,从而达到谐振效应。调节振荡腔结构使射流冲击频率与煤的固有频率形成谐振时破煤效果显著提升,且谐振倍数越小,射流破煤效果越好,能够有效提高破煤效率。当煤的固有频率是25 Hz时,设置上游和下游喷嘴出口直径为2.5、3.0 mm,调节振荡腔直径、长度、角度分别为10 mm、3 mm、120°,射流冲击频率达到25051.83 Hz,是煤体固有频率的1002.0倍,与煤的固有频率形成谐振效应,有效提高了破煤效率。

Si_2O_2 molecule:structure of ground state and the excited properties under different external electric fields

Geometry and vibrational frequencies of the ground state of Si2O2 molecule are studied using density function theory （DFT） at the level of cc-pvtz and 6-311-k＋G^＊＊. It is found that the optimizing value by B31yp/cc-pvtz is closer to the experimental data. The excited properties under different external electric fields are also investigated by the time-dependent-DFT method. Transitions from the ground state of Si2O2 molecule to the first singlet state under different external electric fields can take place more easily. The corresponding absorption spectral line is about 360 nm in wavelength and the excitation energy is about 3.4 eV.

Tunable RF excited waveguide CO-2 laser with two unequal long channels

Presents a waveguide CO 2 laser with two unequal long channels excited by radio frequency (RF) which has more than 30 laser lines from a long channel of 400 mm with grating, and 3 laser lines from a short channel of 200 mm by PZT.

Four-Level Decay Model of^6P_(7/2) Excited State of Eu^(2+) Ion in KMgF_3

A four-level decay model of ~6P_(7/2) excited state of Eu^(2+_ ion in KMgF_3: Eu^(2+) has been proposed. The decay profiles of the ~6P_(7/2) excited state of Eu^(2+) are two exponential and the physical implication of each term in the fit equation responsible for the model is interpreted. The data obtained spectroscopically are in good agreement with the fit results.

用于激光照明的荧光粉@SiO_(2)气凝胶复合发光材料的制备与发光性能研究

通过溶胶-凝胶法成功制备了Tb_(3)Al_(5)O_(12)(TAG)荧光粉。热分析数据证实,增加H_(3)BO_(3)摩尔比会导致最终相的转变温度降低。同时,通过扫描电镜观察到,H_(3)BO_(3)摩尔比的提高会导致荧光粉颗粒尺寸增大。在激发波长为275 nm的条件下,发射光谱在480~650 nm范围内出现了由Tb^(3+)的5d→4f跃迁产生的多个发射峰。然后通过物理掺杂和超临界干燥工艺成功制备了荧光粉@SiO_(2)气凝胶复合发光材料。与荧光粉相比,荧光粉@SiO_(2)气凝胶复合发光材料的内量子产率显著增加,可达63.64%。采用波长为355 nm的激光源激发荧光粉@SiO_(2)气凝胶复合发光材料,可实现长距离无导线方式发光,并具有良好均匀性。以上结果证明了荧光粉@SiO_(2)气凝胶复合发光材料在激光应急照明领域具有潜在的应用前景。