Effect of the Scanning Step on the Surface Quality of Microdevices in Femtosecond-Laser Micromachining and its Optimization

Direct writing technique is usually used in femtosecond-laser two-photon micromachining. The size of the scanning step has important influence on the surface quality and machining efficiency of microdevices. According to the mechanism of two-photon polymerization combining the distribution function of the light intensity and the free-radical-concentration theory, we establish the mathematical model of coverage of solidification unit and analyze the effect of coverage on the machining quality and efficiency of microdevices. Using the principle of exposure equivalence, we also obtain the analytic expression of the relationship between the surface-quality characteristic parameters of microdevices and the scanning step and carry out the numerical simulation and experiment. The results show that the scanning step has little influence on the surface quality of the line when it is much smaller than the size of the solidification unit. However, when the scanning step is gradually increasing, the smoothness of the line surface is reduced rapidly, and the surface quality becomes worse drastically. For stereo-device processing with different slopes, we propose a kind three-dimensional continuous-variable scanning method and provide the calculation expression of the scanning step. From the experimental example of fabricating a spherical structure, we show that, compared with the fixed-step scanning method, the continuous-variable scanning-step method should be used to improve the surface quality of microdevices.     

铜催化的α-氨基丙二腈的脱氰氧代反应：一种合成叔酰胺的新方法

新反应、新试剂的发展是有机合成化学的重要研究内容,基于前期在α-氨基丙二腈合成方法学方面的工作基础,我们发展了一例铜催化的α-氨基丙二腈的脱氰氧代反应.通过将甲酰胺转化为α-氨基丙二腈后,借助其亲核属性来合成α-氨基丙二腈底物,而后将底物重新转化为酰胺,从而实现形式上的氨基甲酰负离子的亲核加成（取代）反应.该工作首次完成了形式上的甲酰胺碳原子的极性反转,实现了将α-氨基丙二腈作为氨基甲酰负离子替代物的反应新模式,为叔酰胺化合物的合成提供了新的思路和方法,且具有反应条件简单,底物适用性广及适合克级规模制备等特点.     

水热沉淀法制备掺铁二氧化钛中空球及其光催化性能

 以碳球为模板剂, 采用水热沉淀法制备了不同配比掺 Fe 的 TiO2 (Fe-TiO2) 中空球, 并运用 X 射线粉末衍射、扫描电子显微镜、元素分析能谱、红外光谱和热重等方法对其进行了表征. 结果表明, 中空球为锐钛矿相, 大小为 0.5~3.20 ?m, 壳层厚度为 30~60 nm, 比表面积为 150~300 m2/g. 随着 Fe 掺杂量的增加, 中空球在可见光区的吸收强度逐渐增加. 光催化降解实验表明, 掺 Fe 后, TiO2 中空球的可见光催化活性升高, 其中 0.5% Fe-TiO2 在 80 min 内降解亚甲基蓝超过 75%. 同时还讨论了光催化机制.     

A Rapidly Self‐Healing Host–Guest Supramolecular Hydrogel with High Mechanical Strength and Excellent Biocompatibility

It is still a challenge to achieve both excellent mechanical strength and biocompatibility in hydrogels. In this study, we exploited two interactions to form a novel biocompatible, slicing‐resistant, and self‐healing hydrogel. The first was molecular host–guest recognition between a host (isocyanatoethyl acrylate modified β‐cyclodextrin) and a guest (2‐(2‐(2‐(2‐(adamantyl‐1‐oxy)ethoxy)ethoxy)ethoxy)ethanol acrylate) to form “three‐arm” host–guest supramolecules (HGSMs), and the second was covalent bonding between HGSMs (achieved by UV‐initiated polymerization) to form strong cross‐links in the hydrogel. The host–guest interaction enabled the hydrogel to rapidly self‐heal. When it was cut, fresh surfaces were formed with dangling host and guest molecules (due to the breaking of host–guest recognition), which rapidly recognized each other again to heal the hydrogel by recombination of the cut surfaces. The smart hydrogels hold promise for use as biomaterials for soft‐tissue repair.     

水液相环境下羟自由基诱导的苯丙氨酸分子损伤机理

在MP2/ SMD/6-311++g(3df, 2pd)//WB97X-D/SMD/6-311++G(d, p)理论水平上,研究了水液相环境下羟自由基诱导的苯丙氨酸分子的损伤机理。研究发现,羟自由基（水分子簇）抽取α-氢、β-氢、苯环-氢以及羟自由基与苯环加成均可致苯丙氨酸分子损伤。势能面计算表明,羟自由基（水分子簇）抽取α-氢和β-氢的最低能垒分别为68.4和89.3 kJ·mol^-1,羟自由基抽取苯环-氢的最低能垒为111.6 kJ·mol^-1,羟自由基加成到苯环不同位点碳的能垒大约在106.5~110.2 kJ·mol^-1,羟自由基（水分子簇）抽α-氢和β-氢是显著的放热反应。结果表明,羟自由基（水分子簇）抽取α-氢是苯丙氨酸分子损伤的主要途径。     

Tailoring MoS2 Ultrathin Sheets Anchored on Graphene Flexible Supports for Superstable Lithium‐Ion Battery Anodes

2D MoS₂ has a significant capacity decay due to the stack of layers during the charge/discharge process, which has seriously restricted its practical application in lithium‐ion batteries. Herein, a simple preform‐in situ process to fabricate vertically grown MoS₂ nanosheets with 8–12 layers anchored on reduced graphene oxide (rGO) flexible supports is presented. As an anode in MoS₂/rGO//Li half‐cell, the MoS₂/rGO electrode shows a high initial coulomb efficiency (84.1%) and excellent capacity retention (84.7% after 100 cycles) at a current density of 100 mA g^?1. Moreover, the MoS₂/rGO electrode keeps capacity as high as 786 mAh g^?1 after 1000 cycles with minimum degradation of 54 µAh g^?1 cycle^?1 after being further tested at a high current density of 1000 mA g^?1. When evaluated in a MoS₂/rGO//LiCoO₂ full‐cell, it delivers an initial charge capacity of 153 mAh g^?1 at a current density of 100 mA g^?1 and achieves an energy density of 208 Wh kg^?1 under the power density of 220 W kg^?1.     

Control of an ultrasonic transducer to realize low speed driven

This paper deals with the control of a transducer to realize low speed. A new PWM control is proposed to fit the transducer. By this control method, the transducer is directly excited by pulses whose width can be modulated. The noise induced by conventional PWM control is eliminated and the motor works more steadily and more quietly. Instead of the general method of decreasing vibrating amplitude of ultrasonic motor to realize low speed, in this paper, two fast contrary elliptical vibrations of the transducer's two Langevin vibrators are excited to restrain skip-slip influence on ultrasonic motor's low speed performance and the driven is realized by the difference of the two vibrators' vibrating amplitudes. Experiments had been carried out by driving an aerostatic guide and fuzzy control is applied. The controlled speed reached 0.1 mm/s.     

Rheology and crystallization behavior of asymmetric PLLA/PDLA blends based on linear PLLA and PDLA with different structures

In this study, several asymmetric poly(L‐lactide)/poly(D‐lactide) (PLLA/PDLA) blends were prepared by adding small amounts of PDLA with different structures into linear PLLA matrix. The effect of PDLA on rheological behavior, crystallization behavior, nucleation efficiency and spherulite growth of PLLA was investigated. Rheological results indicated that PLLA/PDLA blends showed solid‐like viscoelastic behavior at low temperature (<200°C), and the cross‐linking density of PLLA/PDLA melt at 180°C followed the order: PLLA/6PDLA > PLLA/L‐PDLA > PLLA/3PDLA > PLLA/4PDLA. No‐isotherm and isotherm crystallization results indicated that the crystallization capacity of PLLA/PDLA blends was strongly related to the PDLA structure, crystallization temperature and thermal treatment temperature. Furthermore, the dimension of crystal growth during isotherm crystallization presented the obvious dependent on the PDLA structure. The nucleation efficiency of sc‐crystallites in the blends and spherulite density during isothermal crystallization were also studied. Nucleation efficiency of sc‐crystallites in the PLLA/S‐PDLA blends showed the obvious dependent on thermal treatment temperature with respect to PLLA/L‐PDLA, and nucleation efficiency sc‐crystallites in the PLLA/S‐PDLA blends first decreased and then increased as the thermal treatment temperature increased. Spherulite density of PLLA/PDLA blends was also related to thermal treatment temperature and the PDLA structure. This study has discussed the temperature dependence of the stereocomplex networks between PLLA and PDLA with different structure, and then its consequential influence on rheology and crystallization capacity of PLLA, which would provide the theoretical direction for PLA processing. Copyright © 2016 John Wiley & Sons, Ltd.     

Monte-Carlo simulations of Al2O3 dosimetry in uniform MV photon beams: Influence of field and detector size

This work was to evaluate the absorbed dose to different sizes Al₂O₃ dosimeter in uniform MV photon beams using Monte Carlo simulation. The absorbed dose ratio factor f_md of Al₂O₃ dosimeters was calculated. The incident beams included 4 MV–24 MV X-rays using Mohan's spectra with different field sizes. Results show that the maximum variation of f_md due to different dosimeter sizes is 5%. As the field diameter increases from 1 cm to 3 cm, the difference of f_md can be up to 8%. The results of this work show that the effect of dosimeter size and the field size can't be neglected when using Al₂O₃ dosimeter.     

Tunable self-shifting Bloch modes in anisotropic hexagonal photonic lattices

We study controllable self-shifting Bloch modes in anisotropic hexagonal photonic lattices. The shifting results from a deformed band structure due to deformation of the index distribution in each unit cell. By reconfiguration of the index profile of the unit cell, the direction in which the Bloch modes move can be controlled. Our theoretical predictions are experimentally demonstrated in hexagonal lattices optically induced in an anisotropic nonlinear crystal.