Experimental and numerical investigations on acoustic damping of monoclinic crystalline wideband sound absorbing structures

In order to overcome the limitations of traditional microperforated plate with narrow sound absorption bandwidth and a single structure,two multi-cavity composite sound-absorbing materials were designed based on the shape of monoclinic crystals:uniaxial oblique structure(UOS)and biaxial oblique structure(BOS).Through finite element simulation and experimental research,the theoretical models of UOS and BOS were verified,and their sound absorption mechanisms were revealed.At the same time,the influence of multi-cavity composites on sound absorption performance was analyzed based on the theoretical model,and the influence of structural parameters on sound absorption performance was discussed.The research results show that,in the range of 100-2000 Hz,UOS has three sound absorption peaks and BOS has five sound absorption peaks.The frequency range of the half-absorption bandwidth(α>0.5)of UOS and BOS increases by 242% and 229%,respectively.Compared with traditional microperforated sound-absorbing structures,the series and parallel hybrid methods significantly increase the sound-absorbing bandwidth of the sound-absorbing structure.This research has guiding significance for noise control and has broad application prospects in the fields of transportation,construction,and mechanical design.

以二茂铁二羧酸为配体的锌配位聚合物[Zn(Py)_2L]_n的合成与晶体结构

The title compound [Zn(Py) 2L] n(L=1,2′-ferrocenedicarboxylate) was synthesized under mild conditions and its crystal structure was characterized. It crystallizes in a monoclinic system, space group C2/c with the cell parameters a=1.683 0(5) nm, b=1.380 4(3) nm, c=1.746 2(3) nm, β=108.78(2)°, V=3.840 8(15) nm 3, Z=8, M r=485.52, T=293(2) K, D c=3.359 Mg/m 3, μ= 4.073 mm -1, F(000)=3 872, R 1=0.040 1, wR 2=0.113 2. The compound exhibits an unusual one-dimensional chain consisting of two zigzag chains.

Synthesis and electrochemical properties of nanocrystalline Li[Li_(1/3)Ti_(5/3)O_4] by complex sol-gel method

Li[Li1/3Ti5/3O4] spinel-framework structure material is a kind of great interest for negative electrodes in energy storage cell. The synthesis of nanocrystalline Li[Li1/3Ti5/3O4] by sol-gel method using inorganic compounds and citric acid is developed, and single phase powder is obtained above 700 ℃. The electrochemical performances (of Li[Li1/3Ti5/3O4]) cathodes in lithium cell are studied. Special capacities are 131 mA·h·g-1 at 0.5C rate and 154 mA·h·g-1 at 0.1C in cycle test. No passivation layer is formed on Li[Li1/3Ti5/3O4] anode in lithium ion battery, and it is much safer than lithium metal and carbonaceous anodes. Faradic impedance in the charged cell is remarkably higher than that in discharged state, which is caused by distinct conductivities of Li[Li1/3Ti5/3O4] and (Li2[Li1/3Ti5/3O4].)

单轴压缩下微纳晶镍的孔洞演化模型

在含孔隙微纳晶材料受单轴压缩载荷下的大塑性变形中,由于孔洞与基体变形的不匹配,在孔洞周围将产生大量的几何必需位错,论文假设这些位错均匀地从孔洞表面向其内部发射,促使孔洞周围先产生局部非均匀变形,从而导致微纳晶镍试样内孔隙率的变化.基于这种假设论文首先建立了单轴压缩载荷下孔洞的演化发展模型,并用此模型预测了孔隙率的变化,将其与实验测定值进行了比较,结果表明孔洞演化发展模型具有一定合理性.在此基础上,讨论了固定孔隙率和演化发展的孔隙率对不同晶粒尺寸和不同应变速率下的微纳晶镍试样力学行为的影响.

Preface

With ever-increasing miniaturization and prominence of micro- and nano-scale materials and systems for engineering, func- tional and biological applications, understanding of the mechanical and thermal behavior of the nano- and micro-scale mate- rials/systems becomes critical to the development of technologies. Issues concerning mechanical and thermal response and reliability pervade a wide range of areas, from bulk materials to thin films, from crystalline materials to amorphous materials,

Hydrogen-bond organized 2D metal–organic microsheets:direct ultralong phosphorescence and color-tunable optical waveguides

Ultralong phosphorescent materials have numerous applications across biological imaging, lightemitting devices, X-ray detection and anti-counterfeiting. Triplet-state molecular phosphorescence typically accompanies the singlet-state fluorescence during photoluminescence, and it is still difficult to achieve direct triplet photoemission as ultralong room temperature phosphorescence(RTP). Here, we have designed Zn-IMDC(IMDC, 4,5-imidazoledicarboxylic acid) and Cd-IMDC, two-dimensional(2D)hydrogen-bond organized metal–organic crystalline microsheets that exhibit rarely direct ultralong RTP upon UV excitation, benefiting from the appropriate heavy-atom effect and multiple triplet energy levels. The excitation-dependent and thermally stimulated ultralong phosphorescence endow the metal–organic systems great opportunities for information safety application and temperature-gated afterglow emission. The well-defined 2D microsheets present color-tunable and anisotropic optical waveguides under different excitation and temperature conditions, providing an effective way to obtain intelligent RTP-based photonic systems at the micro-and nano-scales.

Te-seeded growth of few-quintuple layer Bi2Te3 nanoplates

We report on a Te-seeded epitaxial growth of ultrathin Bi2Te3 nanoplates （down to three quintuple layers （QL）） with large planar sizes （up to tens of micrometers） through vapor transport. Optical contrast has been systematically investigated for the as-grown Bi2Te3 nanoplates on the SiO2/Si substrates, experimentally and computationally. The high and distinct optical contrast provides a fast and convenient method for the thickness determination of few-QL Bi2Te3 nanoplates. By aberration-corrected scanning transmission electron microscopy, a hexagonal crystalline structure has been identified for the Te seeds, which form naturally during the growth process and initiate an epitaxial growth of the rhombohedral- structured Bi2Te3 nanoplates. The epitaxial relationship between Te and Bi2T% is identified to be perfect along both in-plane and out-of-plane directions of the layered nanoplate. Similar growth mechanism might be expected for other bismuth chalcogenide layered materials.

Luminescence enhancement from Si-based materials by introducing a photonic crystal double-heterostructure slot waveguide microcavity

We demonstrate a novel SOI-based photonic crystal（PC） double-heterostructure slot waveguide microcavity constructed by cascading three PC slot waveguides with different slot widths,and simulate the luminescence enhancement of sol-gel Er-doped SiO2 filled in the microcavity by finite-difference time-domain（FDTD） method.The calculated results indicate that a unique sharp resonant peak dominates in the spectrum at the expected telecommunication wavelength of 1.5509 mm,with very high normalized peak intensity of ~108.The electromagnetic field of the resonant mode exhibits the strongest in the microcavity,and decays rapidly to zero along both sides,which means that the resonant mode field is well confined in the microcavity.The simulation results fully verify the enhancement of luminescence by PC double-heterostructure slot waveguide microcavity theoretically,which is a promising way to realize the high-efficiency luminescence of Si-based materials.