缺口裂纹起裂和扩展检测的直流电位法

本文从解析法、有限元分析和试验三方面探讨了直流电位法用于缺口问题的有效性。当缺口宽度与试样宽度之比较小时(如小于0.05),根据电位的改变量,解析法才能给出缺口裂纹扩展满意的推算.分析和试验说明,利用电位的改变反推缺口裂纹的扩展时,必须引入由于变形引起的缺口宽度变化对电位影响的修正.     

10kW峰值功率高脉冲能量全光纤结构2μm掺铥光纤激光器

基于增益开关技术在高掺杂浓度掺铥光纤中获得了稳定的2μm种子脉冲激光,输出激光中心波长为1 979.4nm,脉冲重复频率在1~100kHz之间可调,输出脉冲宽度变化范围为60~200ns。采用两级掺铥光纤放大器对该种子脉冲激光进行放大实验,当种子脉冲激光重复频率为20kHz时获得最大输出平均功率为17.2W,输出光谱没有观察到明显的放大自发辐射噪声。最大功率输出时,脉冲宽度为82ns,对应单脉冲能量为0.86mJ,脉冲峰值功率高于10kW。     

MDM2‐Associated Clusterization‐Triggered Emission and Apoptosis Induction Effectuated by a Theranostic Spiropolymer

Heteroatom‐containing spiropolymers were constructed in a facile manner by a catalyst‐free multicomponent spiropolymerization route. P1a2b as the most potent of these spiropolymers, demonstrates cluster‐triggered emission resulting from strong interactions with the MDM2 protein. By preventing the anti‐apoptotic p53/MDM2 interaction, P1a2b triggers apoptosis in cancerous cells, while demonstrating a good biocompatibility and non‐toxicity in non‐cancerous cells. The combined results from solution and cell‐based cluster‐triggered emission studies, docking, protein expression experiments and cytotoxicity data strongly support the MDM2‐binding hypothesis and indicate a potential application as a fluorescent cancer marker as well as therapeutic for this spiropolymer.     

An Energy Investigation into 1D/2D Oriented‐Attachment Assemblies of 1D Ag Nanocrystals

In the field of oriented‐attachment crystal growth, one‐dimensional nanocrystals are frequently employed as building blocks to synthesize two‐dimensional or large‐aspect‐ratio one‐dimensional nanocrystals. Despite recent extensive experimental advances, the underlying inter‐particle interaction in the synthesis still remains elusive. In this report, using Ag as a platform, we investigate the van der Waals interactions associated with the side‐by‐side and end‐to‐end assemblies of one‐dimensional nanorods. The size, aspect ratio, and inter‐particle separation of the Ag precursor nanorods are found to have dramatically different impacts on the van der Waals interactions in the two types of assemblies. Our work facilitates the fundamental understanding of the oriented‐attachment assembling mechanism based on one‐dimensional nanocrystals.     

Gaseous and Particle‐bound VOC Products of Combustion Extracted by Needle Trap Samplers

Gaseous benzene, toluene, ethylbenzene and o‐xylene (BTEX) were extracted by using the divinylbenzene (DVB) particles (mesh sizes 60–80, 80–100 and 100–120) as sorbents packed in passive needle trap samplers (NTS). This study performed feasibility tests of these self‐designed DVB‐NTS as diffusive time‐weighted average (TWA) samplers and compared extraction efficiency with that of 100 mm polydimethylsiloxane‐solid phase microextration (PDMS‐SPME) fiber for sampling gaseous and particle‐bound volatile organic compounds (VOCs) from burning mosquito coils. Experimental results indicated that extraction rate of NTS is a reliable index in extracting VOCs. Additionally, comparisons of the NTS in extracting BTEX mass showed the NTS packed with the smallest diameters of adsorbent particles (100–120 mesh DVB) were the most effective. The mass of gaseous BTEX extracted by 100 μm PDMS‐SPME fiber were substantially lower than that extracted by DVB‐NTS of all meshes for the 30‐min TWA sampling of burning mosquito coils, and NTS packed with 100–120 mesh DVB adsorbed BTEX 50–120 ng BTEX. Particles clogging inside the packed phase of NTS inhibited VOC extraction performance after 3–5 samplings of burning particles, especially NTS packed with small‐diameter adsorbents.     

Comparable study on the effect of diluted NH4Cl solution on the postdeposition surface texture of as-deposited aluminum-doped zinc oxide films by direct current pulse and direct current reactive magnetron sputtering

Effect of 5.0% diluted NH₄Cl aqueous solution was comparably investigated on the postdeposition surface texture of the as-deposited smooth aluminum-doped zinc oxide (AZO) films by direct current pulse reactive magnetron sputtering (DCP-sputtering) and direct current reactive magnetron sputtering (DC-sputtering). The as-deposited AZO films by DCP-sputtering showed an effective surface texture for light trapping upon the etching of 5.0% diluted NH₄Cl solution, while the as-deposited AZO films by DC-sputtering demonstrated an obscure surface texture upon the same etching treatment. The different result might be attributable to a big difference in film strain and film compactness. The formation of interstitial Zn, interstitial Al and grain boundary is the key to realize effective surface texture for the as-deposited AZO films.     

Formation of Pd/Au nanostructures from Pd nanowires via galvanic replacement reaction

Bimetallic nanostructures with non-random metal atoms distribution are very important for various applications. To synthesize such structures via benign wet chemistry approach remains challenging. This paper reports a synthesis of a Au/Pd alloy nanostructure through the galvanic replacement reaction between Pd ultrathin nanowires (2.4 +/- 0.2 nm in width, over 30 nm in length) and AuCl3 in toluene. Both morphological and structural changes were monitored during the reaction up to 10 h. Continuous changes of chemical composition and crystalline structure from Pd nanowires to Pd68Au32 and Pd45Au55 alloys, and to Au nanoparticles were observed. More interestingly, by using combined techniques such as high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDS), UV-vis absorption, and extended X-ray absorption fine structure (EXAFS) spectroscopy, we found the formation of Pd68Au32 non-random alloy with Au-rich core and Pd-rich shell, and random Pd45Au55 alloy with uniformly mixed Pd and Au atom inside the nanoparticles, respectively. Density functional theory (DFT) calculations indicated that alkylamine will strongly stabilize Pd to the surface, resulting in diffusion of Au atoms into the core region to form a non-random alloy. We believe such benign synthetic techniques can also enable the large scale preparation of various types of non-random alloys for several technically important catalysis applications.     

Reaction mechanisms of C2Cl3 + NO2 via nitro and nitrite adducts

The atmospherically and environmentally important reaction of chlorinated vinyl radical with nitrogen dioxide (C 2Cl 3 + NO 2) is investigated by step-scan time-resolved Fourier transform infrared emission spectroscopy and electronic structure calculations. Vibrationally excited products of CO, NO, Cl 2CO, and NO 2 are observed in the IR emission spectra. Geometries of the major intermediates and transition states along the potential energy surface are optimized at the B3LYP/6-311G(d) level, and their energies are refined at the CCSD(T)/6-311+G(d) level. The reaction mechanisms are characterized to be barrierless addition-elimination via nitro (C 2Cl 3-NO 2) and nitrite (C 2Cl 3-ONO) adducts. Four energetically accessible reaction routes are revealed, i.e., the decomposition of the nitrite adduct forming C 2Cl 3O + NO and its sequential dissociation to CO + NO + CCl 3, the elimination of ClNO from the nitrite adduct leading to ClNO + Cl 2CCO, the Cl-atom shift of the nitrite adduct followed by the decomposition to CCl 3CO + NO, and the O-atom shift of the nitro adduct followed by C-C bond cleavage forming ClCNO + Cl 2CO. In competition with these reactive fluxes, the back-decomposition of nitro or nitrite adducts leads to the prompt formation of vibrationally excited NO 2 and the long-lived reaction adducts facilitate the vibrational energy transfer. Moreover, the product channels and mechanisms of the C 2Cl 3 + NO 2 reaction are compared with the C 2H 3 + NO 2 reaction to explore the effect of chlorine substitution. It is found that the two reactions mainly differ in the initial addition preferentially by the N-attack forming nitro adducts (only N-attack is plausible for the C 2H 3 + NO 2 reaction) or the O-attack forming nitrite adducts (O-attack is slightly more favorable and N-attack is also plausible for the C 2Cl 3 + NO 2 reaction). The addition selectivity can be fundamentally correlated to the variation of the charge density of the end carbon atom of the double bond induced by chlorine substitution due to the electron-withdrawing effect of chlorine groups.     

Design and synthesis of C6-C8 bridged epothilone A

A conformationally restrained epothilone A analogue (3) with a short bridge between methyl groups at C6 and C8 was designed and synthesized. Preliminary biological evaluation indicates 3 to be only weakly active (IC50 = 8.5 microM) against the A2780 human ovarian cancer cell line.     

“One‐Step” Synthesis of Ionic Ferrocenyl Compounds of Ferrocenylmethyldimethylamine. Characterization,Migration, and Catalytic Properties During Combustion

Alkylferrocene‐based burning rate catalysts exhibit high migration tendency and volatility during prolonged storage and fabrication process of the solid propellants. To retard the migration problems, eight ionic compounds composed of ferrocenylmethyldimethylammonium cation paired with a common energetic anion, were synthesized by “one‐step” procedure. The compounds were characterized by FT‐IR, NMR, and UV/Vis spectroscopy as well as elementary analysis. Their crystal structures were confirmed by single‐crystal X‐ray diffraction. The TG and DSC analyses indicated that they exhibit high thermal stability. Cyclic voltammetry studies suggested that most of them show reversible or quasi‐reversible redox waves. The anti‐migration results revealed that 1 – 4 are low‐migratory compounds, but 5 exhibits high migration trends. The TG curves at 70 °C for 24 h showed that all of them have low volatility. They have from high to low impact sensitivity depending on the anions of the compounds. They all exhibit significant effect on the thermal decomposition of ammonium perchlorate (AP) and some of them accelerate the thermal degradation of 1,3,5‐trinitro‐1,3,5‐triazacyclohexane (RDX). Among them 4 is the best one. Unexpectedly, compound 5 , with 1H‐tetrazolate as anion, can decompose into its original reactants at the temperature just higher than its melting point and could show smart‐material functionality in solid propellants.