Acoustic absorbers at low frequency based on split-tube metamaterials

The remarkable properties of acoustic metamaterials have attracted massive researches and applications, especially on low-frequency sound absorptions. Currently, most of the acoustic metamaterial absorbers employ resonances in plastic cavities, and their structural strengths are important in many circumstances, especially in harsh environment. However, studies of metamaterials including this point are very scarce. Here, we propose an acoustic metamaterial for low-frequency (<500 Hz) absorptions, composed of three nested square split tubes with inverted opening directions. The efficiency of the absorber is investigated both numerically and experimentally, and absorptions at the peeks are found to exceed 90% and the frequency can be effectively adjusted by tuning its geometric parameters. We further test its yield strength under compression and confirm its buckling behavior happens from the outmost layer. This tunable acoustic metamaterial with a fairly good mechanical strength may lead to broad applications in noise reduction.     

New Nitriminotetrazoles – Synthesis,Structures and Characterization

The reactions of 5‐nitriminotetrazole ( 4 ) with 1‐methyl‐5‐aminotetrazole ( 2 ) as well as 2‐methyl‐5‐aminotetrazole ( 3 ) were investigated. In the first reaction 2 was protonated yielding 1‐methyl‐5‐aminotetrazolium 5‐nitrimino‐1H‐tetrazolate monohydrate ( 7 ). In the latter case no protonation could be observed and a co‐crystallization of 5‐nitraminotetrazole and 2‐methyl‐5‐aminotetrazole was obtained. In this compound a new tautomer of 4 could be found. Both products were determined by low temperature single crystal X‐ray diffraction, IR, Raman and multinuclear (¹H, ¹³C, ¹⁵N) NMR spectroscopy, elemental analysis as well as differential scanning calorimetry. In addition the heats of formation were calculated using experimentally obtained heats of combustion. With these and the X‐ray densities several detonation parameter were computed using the EXPLO5 software. In addition the sensitivities towards impact, friction and electrostatic discharge were determined. Further, two crystal structures of the important starting materials in energetic research 5‐nitriminotetrazole monohydrate ( 4 ·H₂O) and 1‐methyl‐5‐nitriminotetrazolemonohydrate ( 5 ·H₂O) are presented and compared with the water‐free compounds. The heats of formation of 4 , 4 ·H₂O, 5 , 5 ·H₂O have been calculated by the atomization method using the CBS basis set. Inclusion of crystal water decrease heats of formation about 265 kJ mol^?1. Also the influence of crystal water on sensitivities (impact, friction, electrostatic discharge) but also performance is discussed.     

Self-organization in nonlinear dynamical systems and its relation to the materials science

This review paper presents briefly the main concepts of nonlinear dynamics and their exemplary manifestations in selected systems, including those important from the point of view of materials science. It is an extended version of the conference presentation. The conditions of instabilities leading to spontaneous formation of dissipative structures are given. Principles of nonlinear dynamics are illustrated with several examples from the homogeneous and heterogeneous and physical and chemical systems: pattern formation in the convective motion of fluids subject to various kinds of driving forces, periodic precipitation phenomena, oscillations, and pattern formation in the Belousov–Zhabotinski (BZ) reaction and the catalytic oxidation of thiocyanate ions with hydrogen peroxide, as well as bistability and tristability in the electrochemical reduction of azide complexes of nickel(II). The application of nonlinear dynamics in materials science is first exemplified by its role in polymerization reactions. Such processes can either exhibit internal couplings leading to oscillations or can be coupled with the chemical oscillatory process through, e.g., the covalent bonding of its catalyst to the polymer network. Other selected examples of the application of nonlinear dynamics in materials science, referring to electrochemical processes, were briefly reviewed. Nonlinear dynamics appears to be useful for designing new materials, including those at the nanoscale.

介孔碳材料对蛋白质的吸附行为

用紫外分光光度法,找出介孔碳材料对蛋白质的最佳吸附条件,并测定出该介孔碳材料对溶菌酶的最大吸附量。主要从3方面研究介孔碳材料对蛋白质吸附行为的影响。分别是介孔碳材料对蛋白质吸附行为随接触时间的变化产生的影响,pH值的改变对介孔碳材料吸附蛋白质行为的影响,以及介孔碳材料的量的改变对蛋白质吸附行为随接触时间的变化产生的影响。结果表明,当溶菌酶溶液的初始浓度为210μm ol/L,pH值为11.0,接触时间为96h时介孔碳材料对蛋白质即可达到吸附饱和。该介孔碳材料在最佳条件下对溶菌酶的最大吸附量为27.32μm ol/g,表现出优越的溶菌酶吸附性能。     

开放式柔性材料力学实验平台的建设与实践

提出建设以机器编号为标识,以计算机网络通信技术为支撑的柔性力学实验平台,在这个平台上,学生自主进行实验,而教师在后台监控学生实验,既提高了学生实验的积极性,也减轻了教师的工作量,使实验设备得到很好的保护和利用.     

天然高分子材料研究进展

综述了近年来天然高分子材料的研究进展。主要介绍纤维素、木质素、淀粉、甲壳素、壳聚糖、其它多糖、蛋白质以及天然橡胶等天然高分子通过化学、物理方法以及纳米技术改性制备具有各种功能及生物可降解性环境友好材料的研究状况,并对此类新材料的应用前景进行了展望。     

Surface composition of Fe-Al2O3 granular thin films by X-ray photoemission spectroscopy

X-ray photoemission Spectroscopy (XPS) results are presented which have given a direct insight into the surface composition of Fe-Al₂ O₃ “granular” thin films consisting of fine iron particles (φ ~ 40–150 Å) dispersed in an insulating alumina matrix. The data are mainly discussed in relation to: (i) the bulk iron content in the sample, (ii) the sample preparation procedure (e.g., by rotation of the sample target) and (iii) the mean iron particle size.At the surface, the iron is in a fully oxidized 3⁺ state within an alumina-rich partly hydrated region. Depth analysis, achieved by an Ar⁺ etching procedure, provides evidence of metallic iron and iron aluminate forms. In general, the metallic iron percentage increases with depth and with increasing iron bulk content.Good agreement is found between X-ray photoemission spectroscopy and Mössbauer Spectroscopy data. Fe²⁺ aluminate forms, which indicate an interaction between the metal particle and the alumina matrix, show increasing percentages with decreasing mean particle sizes.Particular attention is paid to evaluating the accuracy of XPS quantitative results, obtained by use of a first-principles model, and to assessing the importance of the artefacts associated with the Ar⁺ etching procedure.