镧对非晶／纳米晶Ni-Mo合金镀层结构及性能的影响

在碱性条件下获得了非晶/纳米晶Ni-Mo,Ni-Mo-La丑合金复合镀层,利用X射线衍射(XRD)、扫描电镜(SEM)和电化学分析研究了镧 (La)对获得镀层组织、表面形貌及化学活性的影响.结果表明,随着镧含量的增加,镀层中钼含量升高,形成的Ni-Mo合金的二次相出现α-NiMo,β-Ni4Mo,γ-Ni3Mo和δ-Ni8Mo,同时镀层表面团聚颗粒逐渐分散、细小且致密,镀层表面变得平整光滑.镀层的显微硬度随着La含量的增加先升高后降低.电化学性能实验表明,Ni-Mo-La合金具有良好的电催化性能与合金镀层中的稀土化合物有较高的化学活性有关,其在电解过程中为合金的催化作用提供了活性中心,降低了析氢过电位.     

Syntheses,Crystal Structures,and Properties of Two Novel CL‐20‐based Cocrystals

In recent years, cocrystallization has emerged as an effective way of tuning the properties of compounds and has been widely used in the field of energetic materials. In this study, we have prepared two novel cocrystals of CL‐20 and methylimidazole, including a 1:2 CL‐20 / 2‐mercapto‐1‐methylimidazole ( 1 ) and a 1:4 CL‐20 / 4‐methyl‐5‐nitroimidazole ( 2 ). Cocrystal 1 has good physical and detonation properties (ρ₁ = 1.652 g · cm^–3, D₁ = 7073 m · s^–1, P₁ = 21.6 GPa); however, cocrystal 2 shows higher properties (ρ₂ = 1.680 g · cm^–3, D₂ = 7945 m · s^–1, P₂ = 27.4 GPa). The performance of both cocrystals is better than those of TNT. Thermal performance suggests that both the cocrystals have moderate thermal stabilities. Cocrystal 1 decomposes at 164.9 °C and cocrystal 2 has an exothermic peak at 221 °C. Both cocrystals are insensitive energetic explosives (IS > 40 J, FS > 360 N). Methylimidazole compounds are rarely used as coformers to form cocrystals with CL‐20, which possess good properties for a range of potential applications. Herein, we provide new possible directions for enriching cocrystal speciation.     

A Q-switched Nd:YAlO3 laser emitting 1080 and 1342 nm

In this paper, the study of a switchable electro-optic Q-switched Nd:YAlO₃ laser emitting 1080 and 1342 nm wavelength was demonstrated. The two-wavelength lasers were eradiated by a Nd:YAlO₃ crystal pumped by a xenon lamp. Two KD*P Pockels cells were adopted as Q-switches. The output energy of 277.2 mJ at 1080 nm wavelength with a pulse width of 20 ns and that of 190.67 mJ at 1342 nm wavelength with a pulse width of 40 ns was obtained, respectively, in our experiment. By switching on or off the voltages applied to the Pockels cells, the operation of the two-wavelength lasers can be selected in free running mode or Q-switching mode.     

钢轨横向不均匀支撑刚度对钢轨波磨的影响

建立了钢轨波浪形磨损计算模型,模型中考虑车辆轨道垂向横向耦合动力学行为、轮轨三 维滚动接触力学行为和轮轨材料摩擦磨损的循环相互作用关系. 发展了相应的计算程序,并 用1: 1试验装置验证了理论模型. 详细分析了实际线路上由轨枕离散支撑导致的钢轨横向不均匀刚度和不同行车速度对曲线钢轨接触表面不均匀磨损的影响. 通过数值分析可知： (1)列车通过曲线钢轨时,轨枕离散支撑导致的钢轨横向不均匀刚度易引发曲线钢轨波磨的形 成和发展;(2)这类钢轨波磨具有与轨枕间距几乎相等的波长和28~35mm的短波长,这个短波长不均匀磨损主要是由轮轨高频接触振动引起;(3)同一个转向 架4个车轮作用下形成的钢轨波磨最大深度波谷的分布是不同的;(4) 改变过车速度不能有效地抑制轨枕离散支撑导致的钢轨波磨形成和发展速度.     

直接甲醇燃料电池质子膜研究进展

本文对直接甲醇燃料电池(DMFC)质子交换膜的要求及目前的研究状况作了简要的概述,特别是从基膜材料结构角度进行分类,较详细地介绍分析以Nafion膜为代表的全氟磺酸膜的各种改性研究及以PBI、PEEK、PSU等基膜材料为代表的聚芳环系列的DMFC质子交换膜的研究情况.总结了质子交换膜的一些研究方法,对直接甲醇燃料电池质子交换膜的发展前景进行了探讨。     

Stochastic analysis of a nonlinear energy harvester with fractional derivative damping

Nonlinear Dynamics - A fractionally damped vibration energy harvester excited by the wide-band random noise is investigated theoretically in this paper. Firstly, by introducing the generalized...     

Transparent and toughening epoxy thermosets modified by linear telechelic polymer containing rigid spiroacetal moieties: Uncovering the relationship between the heterogeneous crosslinked network and thermoset performances

Spiroacetal moieties containing linear telechelic polymers (LTPs) with two terminal epoxy groups were facilely synthesized via the successive thiol-ene and thiol-epoxy click additions. The LTPs were incorporated into epoxy matrix to fabricate the transparent and toughening thermosets. In term of the miscibility of epoxy with the adduct of ethanedithiol and 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]undecane (BTU), it is proposed that the size of the formed nanostructures was small enough to allow light penetrate. Therefore, the modified thermosets were transparent, which was further confirmed by small-angle X-ray scattering (SAXS) measurements. The LTPs with an alternating structure of rigid spiroacetal moiety and soft thioether could formed heterogeneous crosslinked networks (HCNs) and obviously toughen epoxy thermosets. Flexural strength increased from 1.06 GPa for neat epoxy to 2.09 GPa for toughening thermosets modified with 15 wt% LTPs. The stress field intensity (K_IC) value reached up to 3.93 by more than 125% compared with that of the control sample (1.75). This work uncovered the role of HCNs on performance and paved a way for technological advances toward transparent and toughening materials in epoxy thermosets.     

Atom‐Interferometry Measurement of the Fine Structure Constant

Using an atom interferometer to measure the quotient of the reduced Planck's constant and the mass of a cesium‐133 atom $?/m_{\mathrm{Cs}}$, the most accurate measurement of the fine structure constant $\alpha =1/137.035999046(27)$ is recorded, at an accuracy of 0.20 parts per billion (ppb). Using multiphoton interactions (Bragg diffraction and Bloch oscillations), the largest phase (12 million radians) of any Ramsey–Bordé interferometer and controlled systematic effects at a level of 0.12 ppb are demonstrated. Comparing the Penning trap measurements with the Standard Model prediction of the electron gyromagnetic anomaly $a_e$ based on the α measurement, a 2.5 $\sigma$ tension is observed, rejecting dark photons as the reason for the unexplained part of the muon's gyromagnetic moment discrepancy at a 99% confidence level according to frequentist statistics. Implications for dark‐sector candidates (e.g., scalar and pseudoscalar bosons, vector bosons, and axial‐vector bosons) may be a sign of physics beyond the Standard Model. A future upgrade of the cesium fountain atom interferometer is also proposed to increase the accuracy of $?/m_{\mathrm{Cs}}$ by 1 to 2 orders of magnitude, which would help resolve the tension.     

Oscillation results for fourth-order nonlinear dynamic equations

This work is concerned with the oscillation of a certain class of fourth-order nonlinear dynamic equations on time scales. A new oscillation result and an example are included.     

异伍兹烷衍生物的研究进展

六硝基六氮杂异伍兹烷(HNIW或CL-20)是当今世界上综合性能最好的单质炸药,在20余年的研究过程中,各国研究者合成出了百余种异伍兹烷衍生物.根据笼体上取代基的不同以及合成反应的类型,系统总结了各类衍生物的合成、用途及反应性.最后对异伍兹烷衍生物的发展方向进行了展望.