单面柱局域共振声子晶体低频带隙特性分析及结构改进研究

基于有限元法对单面柱局域共振声子晶体进行带隙特性分析,研究了结构参数对该类型声子晶体的影响。结果表明:随着散射体高度的增加,单面柱声子晶体的第一完全带隙的起始频率逐渐降低,带宽逐渐增大;随着基板厚度的增大,单面柱声子晶体的起始频率逐渐升高,截止频率先增大后减小。并且在经典单面柱声子晶体的基础上,组合了两种新型的三组元单面柱声子晶体结构:嵌入式单面柱声子晶体(以下简称结构Ⅰ)和粘接式单面柱声子晶体(以下简称结构Ⅱ)。通过对其带隙特性的分析得出:这两种新结构与经典的单面柱声子晶体相比,都具有更低频的带隙,这对于低频减振降噪是非常有利的。本文的结果将对实际的工程应用提供一定的理论指导。     

基于声子晶体带隙特性的薄板减振设计

基于平面波展开法和薄板振动方程,计算了薄板型声子晶体的带隙和减振特性,通过与有限元软件的计算结果验证带隙计算的正确性,并进一步讨论了散射体几何形状及填充率、弹性模量比、密度比等对薄板型声子晶体带隙特性和减振的影响.结果表明正多边形散射体随边数的减小,第一带隙宽度逐渐增加,正方形散射体薄板减振效果明显.填充率对声子晶体带隙特性的影响不是线性的.随散射体基体弹性模量比数量级增大,第一带隙趋于低频,宽度降低.散射体基体弹性模量比较大时,密度比越大,第一带隙宽度越大,对应的薄板结构减振特性越好.     

局域共振型圆柱壳类声子晶体带隙特性研究

针对圆柱壳结构的减振问题,本文提出一种局域共振型圆柱壳类声子晶体结构,通过在圆柱壳圆周方向布置弹簧振子实现.该声子晶体的能带结构研究结果表明,该结构能够形成两条低频带隙,一条带隙的起始频率低至650 Hz,带宽为330 Hz,另一条带隙具有更低的频率范围,为0～371 Hz,带隙的形成是由于圆柱壳和弹簧振子振动的耦合.进一步分析了声子晶体的圆柱壳质量与弹簧振子的质量比、弹簧振子的刚度和元胞宽度对带隙的影响.对有限周期圆柱壳结构的传输特性分析,验证了局域共振型圆柱壳声子晶体在带隙范围内的抑制振动的能力.研究结果为圆柱壳结构的减振问题提供了理论参考.     

弯折臂格栅结构声子晶体带隙优化

通过对弯臂格栅结构声子晶体中密度、弹性模量以及模型几何参数等因素对第一带隙宽度的影响规律的研究,对弯臂格栅结构声子晶体设计参数进行了优化,优化后的结构较初始设计结构带隙宽度增加了近三倍,该优化方法有效地改善了声子晶体的带隙特性.选取与文献中相同的参数所得的计算结果与文献中的实验结果吻合良好,证明了计算模型的理论可行性,同时设计参数对带隙的影响规律与COMSOL进行了对比也验证了规律的正确性,在此基础上利用基于NSGA-II遗传算法的优化方法可以实现对声子晶体结构带隙的控制.     

双局域共振Helmholtz声子晶体带隙研究

设计了一种双局域共振原理的Helmholtz型声子晶体结构,该结构采用U字型嵌套设计,分为内外两个腔,摆脱了内腔空气对带隙上限的影响,使得低频带隙上限得以大大提高.在分析低频带隙形成机理和影响因素时,将弹性杆-弹簧模型引入理论计算,使得简化模型计算精度得以提高.研究表明:该结构具有良好的低频带隙特性,其最低带隙范围为86.9～445.9 Hz.结构低频带隙主要受晶格常数、壁厚、细管宽度和长度的影响.在保持其它参数不变的情况下,带隙上限随晶格常数、壁厚和细管长度的增加而降低,随细管宽度的增加而增加;带隙下限随晶格常数、细管长度的增加而降低,随细管宽度、壁厚的增大而增大.该研究为低频噪声控制提供了一定的理论支持,拓宽了声子晶体的设计思路.     

双迷宫型通道Helmholtz周期结构的低频带隙机理及隔声特性

为了解决飞机舱室中的低频噪声问题,本文设计了一种双迷宫型通道的Helmholtz周期结构。迷宫型开口通道的设计能够大大增加Helmholtz腔开口通道的长度,有效降低低频带隙下限,双通道的设计能够增加声子晶体局域共振的区域,可以增加低频带隙数目。本文采用有限元法(FEM)得到了该结构在0~500 Hz频率范围内的能带结构及隔声特性,经过深入研究发现,该Helmholtz 周期结构在0~500 Hz范围内存在多个低频带隙,且在低频范围内表现出较好的隔声特性。为了揭示其带隙产生机理,本文通过声-电类比方法建立了该结构的等效电路模型,并通过有限元法和等效电路模型,对低频带隙影响因素进行了详细分析。结果表明,增加开口通道的长度能够降低带隙起始频率,较小的晶格常数有利于拓宽带隙宽度。本文的研究进一步探索了声子晶体结构设计对带隙的影响,为解决飞机舱室的低频降噪问题提供了新方法。     

多重开孔式声子晶体隔声特性研究

设计了一种多重开孔式局域共振声子晶体结构,结合有限元方法计算结构的带隙和隔声特性,并进一步分析了影响隔声效果的因素.结果表明,该结构在41～1500 Hz范围内存在一个较宽的完全带隙和两个较宽的方向带隙.隔声峰出现的位置与带隙频率范围相对应.通过增加内部金芯体的半径,减小包覆层硅橡胶孔的尺寸,可以取得更好的隔声效果.通过在结构中新增一层复合层,可使整体结构的隔声性能进一步优化.     

基于磁流变弹性体的声子晶体带隙隔振研究

设计了一种基于磁流变弹性体的二维声子晶体隔振器,可用于中高频的机械设备隔振,并对其带隙特性进行分析.以圆柱形铅散射体按正方晶格排列在基体磁流变弹性体当中的二维声子晶体为模型,采用典型的平面波展开法和有限元法研究其能带结构和透射特性,分别计算了不同磁场和不同铁颗粒体积分数情况下声子晶体的带隙,并对禁带范围内的某一频率的位移场进行分析.结果表明:两种方法所计算的带隙结果吻合较好,最大误差为4.9;;铁颗粒体积分数保持不变,增大磁感应强度可以同时增加带隙的位置和宽度;一定的磁场环境下,增加铁颗粒体积分数,带隙位置上移,宽度基本不变;某一频率处,声子晶体的内部波场存在着共振现象.     

局域共振二维声子晶体的低频带隙特性研究

针对低频带隙难以打开的问题,本文提出一种局域共振二维声子晶体结构,采用有限元法计算其能带结构,分析其带隙的形成机理和影响因素,并在此基础上对结构进行优化设计.结果表明:该结构可在200 Hz以下的频率范围内打开宽度70.56 Hz的完全带隙,起始频率低至39.77 Hz.等效刚度k一定的情况下,带隙起始频率由芯体的密度决定,而截止频率主要由基体边框密度决定.优化后的结构能够打开更低更宽的带隙,且对振动波的衰减性能提升.该结构具有优越的低频带隙特性,在地铁减振隔振领域中具有潜在的应用前景.     

新型多重谐振结构声子晶体带隙特性研究

本文设计了一种新型的多重谐振声子晶体结构,建立了带隙上下界频率振动模态的等效模型,通过有限元方法分析了该结构的带隙产生机理以及影响带隙宽度的因素,并对模型的合理有效性进行了验证.结果表明:该结构属于局域共振型声子晶体,能够在中低频段内获得两个带隙,并且内层散射体质量决定第一带隙起始频率,外层散射体质量决定第二带隙的截止频率.通过对散射体质量,填充率,包覆层弹性模量的优化,可以对其带隙上下界频率进行调控.研究结果为声子晶体的结构设计提供了参考.     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Effect of alumina on enthalpy of mixing of mixed alkali silicate glasses

The enthalpy of mixing of mixed alkali (Na₂O and K₂O) silicate glasses containing various concentrations of alumina was determined using an ion-exchange equilibrium method. For glasses with a constant alkali concentration, the enthalpy of mixing was found to become less negative with alumina addition. Consistent with our previous results on the enthalpy of mixing of alumina-free mixed alkali silicate glasses, the magnitude of enthalpy of mixing exhibited a good correlation with the molar volume mismatch of the corresponding two single alkali glasses as well as with the extent of conductivity mixed alkali effect, e.g. excess activation energy of conductivity, ΔE. The reduction of the magnitude of the enthalpy of mixing with alumina addition can be attributed to the reduction of non-bridging oxygen and ionic field strength. Combining the present results with results obtained earlier, the magnitude of the enthalpy of mixing for all mixed alkali (Na₂O and K₂O) silicate glasses with and without alumina was expressed by a simple function of a modified Tobolsky parameter, which takes into account the alkali concentration and the difference in cation-to-effective anion distances. The enthalpy of mixing data of the mixed alkali glasses was then compared with reported experimental data on the conductivity of mixed alkali aluminosilicate glasses. What appears to be conflicting experimental data can be understood in terms of the magnitude of the enthalpy of mixing and we can conclude that the mixed alkali effect is closely correlated with the negative enthalpy of mixing.     

Mesomorphism Dependence on the Position of Substitution of a Pair of Esters

A novel homologous series of ethylene derivatives of thermotropic liquid crystals has been synthesized. The methoxy to octyloxy derivatives are nematogenic, the decyloxy to tetradecyloxy derivatives are smectogenic, in addition to nematogenic, and the hexadecyloxy homologue is smectogenic only. All the members of the series are enantiotropically mesogenic. Thermotropic behavior was determined by an optical polarizing microscope equipped with a heating stage and Differential Scanning Calorimetry (DSC) study. Analytical and spectral data confirm the molecular structures of homologues (infrared, nuclear magnetic resonance, mass spectra, X-ray, and DSC data). Textures of the nematic phase are threaded or Schlieren and that of smectic phase are focal conic fan-shaped of smectic A or C. Transition curves of the phase diagram behave in a normal manner except one or two deviations from the normal trend. The mesophase range (Sm+N) varies from 3°C to 44°C. The average thermal stability for smectic is 93°C and that for nematic 117.4°C. The LC behavior of the novel series is compared with a structurally similar known series.     

原位氮化法制备TiN纳米粉体

用溶胶凝胶法合成的纳米TiO2粉体作为原料,将该粉体在氨气中进行原位氮化制备了TiN纳米粉体.用XRD,TEM,化学分析等手段对合成的TiN纳米粉体的物相组成、形貌、成分进行了分析.实验分析表明:在1000℃和1100℃下分别氮化5h,可以制备粒径大约为40nm和80nm的TiN粉体,其TiN的含量分别为95.40;和98.37;;而在1000℃条件下氮化时间减少到2h时,TiN的含量仅为58.36;.氮化温度和氮化时间是合成纳米TiN的重要因素,提高合成温度和延长氮化时间均可形成纯度较高的TiN纳米粉体,但延长氮化时间更有利于获得粒径小的氮化钛粉体.     

立方晶系晶体本征铁弹相变序参量的选取

在本征铁弹相变的软模理论的基础上,依据弹性本构关系和居里原理,给出了立方晶系晶体所有可能的自发应变的种类,研究了立方晶系晶体本征铁弹相变序参量的选取问题.以Th群和Oh群为例,阐明了不同类的序参量导致晶体对称性变化相同的的原因,提出了该情况下序参量选取的“就少不就多”的原则.得到了发生本征铁弹相变时所有可能的序参量及晶体的对称性的变化.     

Features of transformations in REE-containing systems of nitrate precursors in preparatory processes of formation of multifunctional oxide materials

Abstract

The complex study provides a reliable idea of ??the trends in the joint behavior of structural components in the water-salt systems of nitrate precursors of REE, alkaline, alkaline earth metals in the preparatory stages of the processes of forming multicomponent oxide polyfunctional materials on their basis with thermal activation. Stages of such transformations are revealed; The regularities of complex and phase formation in systems and factors influencing them are determined; A number of physicochemical properties of the intermediate phases formed - coordination lanthanides nitrates: their composition, types of compounds, atomic-crystalline structure, regularities of transformations during heat treatment were studied.     

On the influence of structural features of DNA on the possibility of metabolic transfer of electrons

Abstract

A fragment of a DNA molecule is considered as one of the channels of metabolic electron transfer. The heterogeneity of the complementary chains is effectively taken into account. This made it possible to find the speed of the electron injected into the DNA conduction band and the current density that it creates. Estimates of electron mobility in nucleic acid chains are made. They were an order of magnitude smaller than that of typical semiconductors. For the specific conductivity of nucleic acid chains, estimates provide a conductivity of one to two orders of magnitude lower than in graphite.     

Growth and characterization of semicarbazone of cyclohexanone

A new organic single crystal of semicarbazone of cyclohexanone (SCCH) has been synthesized and grown as a bulk single crystal by low temperature solution growth technique for the first time in the literature. The grown crystal has been confirmed by X‐ray diffraction and proton nuclear magnetic resonance spectral analyses and also characterized by FT‐ir and FT‐Raman studies. Thermal properties of the grown crystals were studied by thermogravimetric and differential thermal analyses. Optical transmittance was studied by ultraviolet‐visible spectrum and the second harmonic generation property was tested by using Q switched Nd: YAG laser as a source. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of density of states on optical properties of GaSe thin film

A systematic investigation on the effect of substrate temperature on the structure, optical absorption and density of states of vacuum evaporated gallium monoselenide (GaSe) thin films is reported. The X‐ray diffraction analysis shows an occurrence of amorphous to polycrystalline transformation in the films deposited at higher‐temperature substrates (573K). The compositional analysis is made with Auger Electron Spectroscopy (AES). The thickness of the film (175nm) is measured by a multiple beam interferometery. Optical characteristics of the GaSe sample have been analyzed using spectrophotometer in the photon energy range of 1.0 ‐ 4 eV. The absorption mechanism has been recognized and the allowed indirect as well as forbidden direct transitions have been found. As‐deposited films show two indirect and allowed transitions due to spin‐orbit splitting of the valence band, as reported here for the first time. Low field conduction have enabled us to determine the density of states in amorphous and poly‐GaSe films. The amorphous and polycrystalline GaSe thin films have localized states density values of N (E_F) = 1.686 × 10¹⁷ cm^‐3 eV^‐1 and 1.257 × 10¹⁵ cm^‐3 eV^‐1 respectively. The experimental results are interpreted in terms of variations in the density of localized states due to progressive decrease of the unsaturated bonds during deposition. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

电子显微分析在表征纳米晶体化学组分中的应用

纳米材料的化学组分及含量影响其光、电、声、热、磁等物理性能,电子显微分析是表征纳米晶体化学组分的重要方法之一.本文综述了X-射线能谱(EDS)、X-射线波谱(WDS)、电子能量损失谱(EELS)和选区电子衍射(SAED)等现代电子显微分析技术在表征纳米晶体化学组分、形貌、尺寸和结构等方面的应用及其研究进展,并比较了这些分析方法存在的差异,提出了其应用中存在的不足及今后的研发方向.