双基推进剂的高应变率力学特性及其含损伤ZWT本构

为了解双基推进剂在冲击载荷下的力学特性及本构行为,利用材料试验机和分离式霍普金森压杆（SHPB）对双基推进剂进行了单轴压缩实验,并对实验数据的有效性进行了检验。用二波法对实验数据进行处理,得到了双基推进剂的应力应变曲线。实验结果表明:双基推进剂具有明显的应变率相关性,动态下屈服应力与静态下相比明显提高,且屈服应力表现为应变率对数的双线性关系;双基推进剂屈服应变表现为延脆转换特性,在低应变率下表现为延展性,高应变率下表现为冲击脆化特性。利用含损伤朱王唐（ZWT）本构模型对实验结果进行了拟合,得到了模型中的本构参数,并对损伤因子项进行了分析。通过模型预测曲线与实验曲线的对比,发现含损伤ZWT本构能较好地描述双基推进剂在0～0.14应变范围内的力学特性。     

Domain structure and interphase dimensions in poly(urethaneurea) elastomers using DSC and SAXS

Small‐angle X‐ray scattering (SAXS) and differential scattering calorimetry (DSC) were used to demonstrate distinct differences in domain size, phase separation, and hydrogen bonding in a series of segmented urethaneurea elastomers prepared from isocyanate‐terminated prepolymers and aromatic diamine chain extenders. Two types of prepolymers were studied. The first contained a broadly polydisperse high molecular mass oligomer with relatively high levels of free isocyanate monomer. The second type of prepolymer contained low levels of high molecular mass oligomers with mass fractions greater than 90% of the two‐to‐one adduct of toluene diisocyanate (TDI) to polytetramethylene glycol (PTMEG). The mass fraction of the residual unreacted diisocyanate was less than 0.1% in the second type. Two chain extenders, 4,4′‐methylene bis‐(2‐chloroaniline)(Mboca) and 4,4′‐methylene bis‐(3‐chloro‐2,6‐diethylaniline) (MCDEA), were used to convert the prepolymers to poly(urethaneurea) elastomers. Materials prepared from the prepolymers with low oligomer polydispersity exhibited smaller hard segment domains with more ordered morphology, greater phase separation, and more hydrogen bonding than those prepared from prepolymers with high oligomer polydispersity. These tendencies were enhanced in those elastomers prepared by chain extension with MCDEA compared to those made with Mboca. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2586–2600, 1999     

Degradation and stabilization of polycyanoacrylates

Polycyanoacrylates were found to be inherently unstable. Even in the absence of a deliberately added strong base, their molecular weights decreased drastically on standing in solution in accord with observations by Ryan and McCann (Makromol Chem Rapid Commun 1996, 17, 217). The initial high molecular weight polymer disappeared over the course of a few hours in solution and was replaced by a much lower molecular weight material. For polymers made by anionic polymerization, the entire sample degraded, but for polymers made by free-radical polymerization, only a portion of the sample was affected. This behavior was consistent with the mechanism proposed by Ryan and McCann, in which the polymer chains are in dynamic equilibrium with their monomers and the polymer degrades from its chain terminus. Surprisingly, the degradation in molecular weight even occurred slowly in the solid state. The degradation was inhibited by acids and could be prevented by free-radical copolymerization with small amounts of more stable monomers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4570–4581, 1999     

Copper Oxide-Based Photocatalysts and Photocathodes: Fundamentals and Recent Advances

This work aims at reviewing the most impactful results obtained on the development of Cu-based photocathodes. The need of a sustainable exploitation of renewable energy sources and the parallel request of reducing pollutant emissions in airborne streams and in waters call for new technologies based on the use of efficient, abundant, low-toxicity and low-cost materials. Photoelectrochemical devices that adopts abundant element-based photoelectrodes might respond to these requests being an enabling technology for the direct use of sunlight to the production of energy fuels form water electrolysis (H₂) and CO₂ reduction (to alcohols, light hydrocarbons), as well as for the degradation of pollutants. This review analyses the physical chemical properties of Cu₂O (and CuO) and the possible strategies to tune them (doping, lattice strain). Combining Cu with other elements in multinary oxides or in composite photoelectrodes is also discussed in detail. Finally, a short overview on the possible applications of these materials is presented.     

激光刻蚀对镀金表面二次电子发射的有效抑制

使用红外激光刻蚀技术在镀金铝合金表面制备了多种形貌的微孔及交错沟槽阵列.表征了两类激光刻蚀微阵列结构的三维形貌和二维精细形貌,分析了样品表面非理想二级粗糙结构的形成机制.研究了微阵列结构二次电子发射特性对表面形貌的依赖规律.实验结果表明:激光刻蚀得到的微阵列结构能够有效抑制镀金表面二次电子产额(secondary electron yield,SEY),且抑制能力明显优于诸多其他表面处理技术;微阵列结构对SEY的抑制能力与其孔隙率及深宽比呈现正相关,且孔隙率对SEY的影响更为显著.使用蒙特卡罗模拟方法并结合二次电子发射唯象模型和电子轨迹追踪算法,仿真了各微结构表面二次电子发射特性,模拟结果从理论上验证了微阵列结构孔隙率及深宽比对表面SEY的影响规律.本文获得了能够剧烈降低镀金表面SEY的微阵列结构,理论分析了SEY对微结构特征参数的依赖规律,对开发空间微波系统中低SEY表面及提高镀金微波器件性能有重要意义.     

Ultrathin,Porous and Oxygen Vacancies‐Enriched Ag/WO3−x Heterostructures for Electrocatalytic Hydrogen Evolution

Exploring advanced electrocatalysts for electrocatalytic hydrogen evolution is highly desired but remains a challenge due to the lack of an efficient preparation method and reasonable structural design. Herein, we deliberately designed novel Ag/WO_3?x heterostructures through a supercritical CO₂‐assisted exfoliation‐oxidation route and the subsequent loading of Ag nanoparticles. The ultrathin and oxygen vacancies‐enriched WO_3?x nanosheets are ideal substrates for loading Ag nanoparticles, which can largely increase the active site density and improve electron transport. Besides, the resultant WO_3?x nanosheets with porous structure can form during the electrochemical cycling process induced by an electric field. As a result, the exquisite Ag/WO_3?x heterostructures show an enhanced hydrogen evolution reaction (HER) activity with a low onset overpotential of ≈30 mV, a small Tafel slope of ≈40 mV dec^?1 at 10 mA cm^?2, and as well as long‐term durability. This work sheds light on material design and preparation, and even opens up an avenue for the development of high‐efficiency electrocatalysts.     

Method for Finding the Exact Effective Hamiltonian of Time‐Driven Quantum Systems

Time‐driven quantum systems are important in many different fields of physics as cold atoms, solid state, optics, etc. Many of their properties are encoded in the time evolution operator or the effective Hamiltonian. Finding these operators usually requires very complex calculations that often involve some approximations. To perform this task, a systematic scheme that can be cast in the form of a symbolic computational algorithm is presented. It is suitable for periodic and non‐periodic potentials and, for convoluted systems, can also be adapted to yield numerical solutions. The method exploits the structure of the associated Lie group and a decomposition of the evolution operator on each group generator. To illustrate the use of the method, five examples are provided: harmonic oscillator with time‐dependent frequency (Paul trap), modulated optical lattice, time‐driven quantum oscillator, a step‐wise driving of a free particle, and the non‐periodic Caldirola‐Kanai Hamiltonian. To the extent of the authors' knowledge, whereas the exact form of Paul trap's evolution operator is well known, its effective Hamiltonian was until now unknown. The remaining four examples accurately reproduce previous results.     

Ultrathin Fe‐N‐C Nanosheets Coordinated Fe‐Doped CoNi Alloy Nanoparticles for Electrochemical Water Splitting

The development of highly active and cost‐effective catalyst materials toward electrochemical water splitting is of great importance for converting and storing the intermittent solar energy in the form of hydrogen. Herein, for the first time, an ultrathin Fe and N‐co‐doped carbon nanosheet encapsulated Fe‐doped CoNi alloy nanoparticle (FeCoNi@FeNC) composite is obtained and applied as a bifunctional catalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). This catalyst exhibits prominent catalytic performances for both HER and OER, which only requires overpotentials of 102 and 330 mV, respectively, to reach a current density of 10 mA cm^?2 in alkaline media. The high catalytic activity is intrinsically associated with the presence of Fe in both nanosheets and nanoparticles, which has triggered the occurrence of coordinative effects between Fe‐N‐C and FeCoNi that are beneficial for HER and OER, as revealed by electrochemical techniques. In an overall water splitting electrolyzer, FeCoNi@FeNC is employed as both the cathode and anode catalysts, achieving 12 mA cm^?2 at 1.63 V for a duration of more than 12 h.     

Microstructural evolution and phase transformation in the liquid-solid Al/Ni diffusion couple

The liquid-solid Al/Ni diffusion couple was successfully fabricated by annealing at 1373?K for 48?h followed by water-quenching. Cross-sectional scanning and transmission electron microscopic analyses show that the multilayered diffusion zones comprise the following sequence of layers: γ-Ni(Al) | γ′-Ni₃Al | β′-NiAl | Ni-rich β-NiAl | β-NiAl. The Ni-rich β-NiAl upon quenching undergoes a martensitic transformation from β (B2) to β′ (L1₀). The β′ martensite is found to be internally twinned on the {111}<112>system. The volume changes and strains due to martensitic phase transformation, the precipitation of γ′-Ni₃Al from γ-Ni(Al) and lattice mismatch between Ni-rich β-NiAl and β-NiAl in the Al/Ni diffusion couple are quantitatively determined. The cuboidal γ′ phase coherently precipitates cube-on-cube in γ-Ni(Al). Composition fluctuations existing in the supersaturated solid solution γ-Ni(Al), provide sufficient driving force for the precipitation and facilitate nucleation and growth of the γ′ phase under isothermal annealing.     

基于红外光谱聚类分析的纳滤膜污染动态发展行为研究

污水再生利用是解决水资源短缺问题的有效对策。纳滤技术由于能够生产高质量的再生水,成为污水深度处理、再生利用的有效方法之一。然而,在纳滤过程中存在复杂的、动态的膜污染现象,会导致产水通量、产水质量下降等问题。研究膜污染动态发展的行为,对于膜污染的分阶段针对性控制具有重要意义。有机物是污染层动态发展过程的重要指示性成分,红外光谱是表征污染层发展过程中表面有机物官能团变化情况的重要手段。但由于红外光谱中峰的数量多,系列样品之间峰强度的差别较小（尤其是当膜污染过程中的采样间隔较小时）,利用直观观察不易甄别不同样品间的谱图差异及其变化趋势,在此水平上难以对膜污染阶段进行准确识别、对各阶段特征进行有说服力的分类概括。为探索膜污染的动态发展过程,本研究将傅里叶变换红外光谱与统计学聚类分析相结合,对膜污染过程中不同时间点的膜样本进行红外光谱分析,再对红外光谱数据进行一系列预处理和系统聚类分析,从而客观解读膜污染动态发展过程中系列样品红外光谱分阶段变化规律。考虑到类别间距离度量方法、红外吸收峰强度标准化、峰之间自相关性、峰与样本之间交互作用等因素的影响,研究采用对应分析对红外数据进行预处理,提取各样本在主要维度上的得分,随后基于标准化欧式距离对各样本进行聚类。在为期一个月的城市污水深度处理纳滤试验过程中,由于污染物在膜表面累积,纳滤膜发生了较为严重的污染。通过对13个不同时间点的膜样本进行红外光谱聚类发现,膜污染可清晰划分为如下阶段：空白膜、阶段Ⅰ（3 h～8 d）、阶段Ⅱ（10～15 d）和阶段Ⅲ（20～30 d）。采用红外聚类,得到膜表面X射线光电子能谱（XPS）和三磷酸腺苷（ATP）含量分析等方法的交互验证。结果表明,随着膜污染的发展,膜表面有机物成分与共存微生物量发生协同变化,各阶段大致特征为：阶段Ⅰ各类有机污染物初步覆盖,微生物开始富集;阶段Ⅱ多糖类污染物比例上升,微生物的富集趋于稳定;阶段Ⅲ整体污染趋于成熟,有机污染物氢键特征更加明显。该研究通过对红外数据进行聚类分析,能够灵敏地探测各红外图谱之间的差别,有助于对红外光谱规律的深度挖掘,为膜污染阶段的识别和划分提供了一种客观、自动、可量化的辅助性方法,并且有助于归纳出不同阶段的污染层特征,可作为膜污染时序特征的侦查手段。此外,除了膜污染的研究,在材料、吸附等领域,只要有一系列变化的红外光谱,均可尝试采用红外光谱聚类分析方法,获取基于红外特征的定类信息或分阶段规律。