MECHANISMS UNDERLYING TWO KINDS OF SURFACE EFFECTS ON ELASTIC CONSTANTS

Recently, people are confused with two opposite variations of elastic modulus with decreasing size of nano scale sample： elastic modulus either decreases or increases with decreasing sample size. In this paper, based on intermolecular potentials and a one dimensional model, we provide a unified understanding of the two opposite size effects. Firstly, we analyzed the microstructural variation near the surface of an fcc nanofilm based on the Lennard-Jones potential. It is found that the atomic lattice near the surface becomes looser in comparison with the bulk, indicating that atoms in the bulk are located at the balance of repulsive forces, and the elastic moduli decrease with the decreasing thickness of the film accordingly. In addition, the decrease in moduli should be attributed to both the looser surface layer and smaller coordination number of surface atoms. Furthermore, it is found that both looser and tighter lattice near the surface can appear for a general pair potential and the governing mechanism should be attributed to the surplus of the nearest force to all other long range interactions in the pair potential. Surprisingly, the surplus can be simply expressed by a sum of the long range interactions and the sum being positive or negative determines the looser or tighter lattice near surface respectively. To justify this concept, we examined ZnO in terms of Buckingham potential with long range Coulomb interactions. It is found that compared to its bulk lattice, the ZnO lattice near the surface becomes tighter, indicating the atoms in the bulk are located at the balance of attractive forces, owing to the long range Coulomb interaction. Correspondingly, the elastic modulus of one-dimensional ZnO chain increases with decreasing size. Finally, a kind of many-body potential for Cu was examined. In this case, the surface layer becomes tighter than the bulk and the modulus increases with deceasing size, owing to the long range repulsive pair interaction, as well as the cohesive many-body interaction caused by the electron redistribution.     

A 4-OTBS benzyl-based protective group for carboxylic acids

Reported herein is a novel 4-OTBS benzyl-based protective group for carboxylic acids. This protective group can be removed in the presence of TBAF or TFA with high efficiency, which makes it compatible with base-sensitive or acid-sensitive substrates. With this protective group, a near-infrared fluorogenic probe for the detection of γ-glutamyltranspeptidase activities was readily prepared.     

Low-loss plasmonic hybrid optical ridge waveguide on silicon-on-insulator substrate

To achieve low loss and complete confinement of light, we propose and study a plasmonic hybrid optical waveguide fabricated on an silicon-on-insulator substrate. Using controlled oxidation and etching processes, a deep submicrometer Si core is fabricated based on UV photolithography patterning. The as-fabricated waveguide demonstrates a very low propagation loss of 1.6 dB/mm at 1550 nm. The numerical study discloses the hybrid characteristics of the mode. It is shown that the optical power of the waveguiding mode distributes more in the high-index Si-core region, and the metal cover further confines the light beyond the diffraction limit. The hybrid waveguide may be applied in compact, high-density Si photonic integrated circuits.     

Strongly fluorescent cysteamine-coated copper nanoclusters as a fluorescent probe for determination of picric acid

Microchimica Acta - A fluorometric assay is described for doxycycline detection. It is based on the use of nitrogen-doped carbon quantum dots (NCQDs) coated with molecularly imprinted polymers...     

Unconventional temperature enhanced magnetism in Fe1.1Te

Our inelastic neutron scattering study of spin excitations in iron telluride reveals remarkable thermal evolution of the collective magnetism. In the temperature range relevant for the superconductivity in FeTe(1-x)Se(x) materials, where the local-moment behavior is dominated by liquidlike correlations of emergent spin plaquettes, we observe unusual, marked increase of magnetic fluctuations upon heating. The effective spin per Fe at T ≈ 10 K, in the phase with weak antiferromagnetic order, corresponds to S ≈ 1, consistent with the recent analyses that emphasize importance of Hund's coupling [K. Haule and G. Kotliar, New J. Phys. 11, 025021 (2009).]. However, it grows to S ≈ 3/2 in the high-T disordered phase, suggestive of the Kondo-type behavior, where local magnetic moments are entangled with the itinerant electrons.     

新型偶氮苯并冠醚衍生物在溶液和LB膜中的光致变色研究

本文合成了两种新型偶氮苯并冠醚衍生物１６ＡＢＣ－ＯＨ和１６ＡＢＣ－ＮＨ２,并对其在溶液中和Ｌａｎｇｍｕｉｒ－Ｂｌｏｄｇｅｔｔ膜中的光致变色现象进行了研究。结果表明：在溶液中１６ＡＢＣ－ＯＨ发生了反式－顺式异构化反应,且异构化反应为一组反应,而１６ＡＢＣ－ＮＨ２的顺反异构化反应较复杂,为非一组反应。在ＬＢ膜中,１６ＡＢＣ－ＯＨ无光组合记录且有一定程度的光致顺反异构反应,而１６ＡＢＣ－ＮＨ２自组合形成     

车致桥梁支座动反力频谱特性及影响因素研究

建立频域内的车辆-轨道-桥梁垂向耦合动力学模型,包括1/8车辆模型和CRTS-II型板式无砟轨道-桥梁-支座模型两部分,以快速求解100Hz以内的桥梁支座动反力。将CRTS-II型板式无砟轨道-桥梁-支座模型简化为4层叠合梁,采用Euler梁模拟钢轨、轨道板、底座板和箱梁,采用具有复刚度的弹簧模拟扣件、CA砂浆层、滑动层和桥梁支座。以32m简支桥梁为研究对象,分析了支座动反力的频谱特性,并讨论了轨道不平顺、扣件刚度和支座刚度对支座动反力的影响规律。结果表明:支座动反力在车轮-轨道系统的固有频率附近出现峰值;轨道不平顺幅值在很大程度上决定了支座动反力幅值,其峰值频率点在支座动反力曲线上得以体现;扣件刚度降低可一定程度上减小轮轨力及支座反力峰值、频段幅值及峰值频率;支座刚度降低可以减小支座反力幅值,同时降低峰值频率,其主要通过改变轨道-桥梁耦合系统的频响特性实现,而轮轨力基本不受其影响。