Growth,mechanical properties,and tribological performance of TiAlN/NbN and NbN/TiAlN bilayer coatings

Three different coatings, namely TiAlN, TiAlN (external)/NbN (internal) and NbN (external)/TiAlN (internal), were deposited on cemented carbides by arc ion plating. The comparative investigation conducted in this study elucidates the effect of the NbN layer and coating systems on the growth, mechanical properties, and tribological performance of the coatings. The results showed that the surface of the TiAlN and TiAlN/NbN coatings was smoother when TiAlN served as the external layer. The NbN/TiAlN coating, wherein NbN formed the external layer, had a much rougher but more symmetrical surface. With the introduction of the NbN layer, the increased micro stress induced a lower adhesion strength in the TiAlN/NbN and NbN/TiAlN coatings. The TiAlN/NbN and NbN/TiAlN coatings exhibited higher hardness and hardness/effective elastic modulus (H/E*). During the friction test, when the temperature was elevated to 700 °C, the tribological performance of the monolayer TiAlN coating was the lowest because of the TiO₂-induced breakage of the dense tribo-oxide film. The NbN layer participated in the formation of a NbO_x film at elevated temperatures, which was responsible for the high tribological performance of the two bilayer coatings. When the NbN layer was on the outermost layer and in direct contact with the elevated temperature atmosphere, the NbN/TiAlN coating generated a tribo-oxide film with high integrity, and its coefficient of friction decreased by 27% of that at room temperature. Therefore, the NbN/TiAlN coating exhibited the highest wear resistance at 700 °C.     

微量元素与早产婴幼儿生长发育的相关性

早产是新生儿和 5 岁以下儿童死亡的主要原因,同时作为一种常见的临床不良妊娠结局,不仅增加了母婴短期和长期并发症的风险,而且给个人、家庭和社会造成巨大负担,其发病原因及机制较为复杂,其中母体血液微量元素变化对胎儿发育有着非常重要的影响,微量元素的不平衡,可能导致不良妊娠结局。关于微量元素对早产婴幼儿的作用研究甚少,故本文结合近些年国内外关于微量元素应用的研究,综述了微量元素(铁、铜、锌、硒、锰5种)与早产婴幼儿生长发育的关系,以及微量元素影响早产发生的作用机制(炎症反应、氧化应激、内分泌调节机制),以期为微量元素在早产婴幼儿的生长发育研究中提供一定的理论指导依据。     

Status of Mysis diluviana in Lake Ontario in 2013: Lower abundance but higher fecundity than in the 1990s

Mysis diluviana is a major component of prey fish diets in the Great Lakes, so annual production of M. diluviana is important for understanding and modeling energy flow through Great Lakes food webs. However, only three lake-wide measurements of M. diluviana annual production in Lake Ontario are currently available (1971, 1990, 1995). During 2013, lake-wide coverage of Lake Ontario was achieved during four periods from April to November. Annual mean density and biomass of M. diluviana in 2013 were 99?#/m² (SE: 8) and 318?mg?dw/m² (SE: 28) – approximately half of values observed in 1990s. M. diluviana comprised 13–30% of offshore zooplankton biomass in each period. Reproduction peaked in fall, with mean brood size of 32 embryos (range: 11–49), at least 10% larger than in 1990s. Generation time was two years from embryo to initial reproduction. Growth rates were 0.052?mm/d for the age-0 cohort and 0.027?mm/d for the age-1 cohort. Age-0 growth rate was significantly higher than in 1980s–90s (0.035?mm/d). Annual production in 2013 was 0.85?g?dw/m²/yr (SE: 0.03) which was 30–40% of values observed in 1990 and 1995 (2.23 and 2.53?g/m²/yr). Annual production to biomass ratio (P/B) in 2013 was 2.65?/yr which was 80–85% of values observed in 1990 and 1995 (3.24 and 3.11?/yr), but this difference was not statistically significant. Our results suggest that changes in annual production over time can be estimated using changes in biomass over time and a mean P/B ratio.     

Growth mechanism of primary Ti5Si3 phases in special brasses and their effect on wear resistance

In the present work, in-situ Ti₅Si₃ reinforced special brasses were prepared by melt reaction method. The synthesized Ti₅Si₃ phase shows various morphologies in brasses with different Ti₅Si₃ content, and the3 D morphological evolution of primary Ti₅Si₃and its growth mechanism were investigated. The Ti₅Si₃ crystal, which bears D8₈ hexagonal crystal structure, grows along <0001> direction and is revealed by{1010} faces during growth. With the increase of Ti₅Si₃ content in the brasses, the morphology of primary Ti₅Si₃significantly changes from fibers to hexagonal prisms to short-rods with hollow. In addition,the influence of Ti₅Si₃ volume fraction and morphology on the wear behavior of special brass was also revealed. It was substantiated that the wear resistance increases with the increasing volume fraction of Ti₅Si₃, and the corresponding wear mechanism changes from delamination to slight adhesive wear and abrasive wear. However, the friction coefficient shows an abnormal increase when most of the Ti₅Si₃ containing hollows appears in the brass. That is mainly due to the fact that the Ti₅Si₃ is easier to break and fall off resulted by the hollow as a crack source, which makes it unable to resist the plastic deformation of the contact surface during the sliding.     

Chemistry of multifunctional polymers based on bis-MPA and their cutting-edge applications

Polymers play an important role in the advancement of materials for use in cutting-edge applications. A direct consequence of an increased demand for more sophisticated materials has been a drive toward developing polymers that exhibit a higher level of structural control, especially in terms of the number and type of functionalities provided within the polymer framework. A family of polymers that meets such a challenge is based on the readily available AB₂ monomer 2,2-bismethylolpropionic acid (bis-MPA) building block. Due to the ease with which the monomers can be synthesized, an array of multifunctional polymers have been produced including monodisperse dendrimers and dendrons and well-defined linear polymers as well as linear-dendritic hybridizations. This review outlines the evolution of the synthetic strategies for developing novel polymeric architectures based on bis-MPA and their assessment in both solution and substrate-based innovative applications.     

Prospects for polymer therapeutics in Parkinson's disease and other neurodegenerative disorders

Parkinson's disease (PD) is characterized by a progressive loss of dopaminergic neurons and represents a growing health burden to western societies. Like many neurodegenerative disorders the cause is unknown, however, as the pathogenesis becomes ever more elucidated, it is becoming clear that effective delivery is a key issue for new therapeutics. The versatility of today's polymerization techniques allows the synthesis of a wide range of polymer materials which hold great potential to aid in the delivery of small molecules, proteins, genetic material or cells. In this review, we capture the recent advances in polymer based therapeutics of the central nervous system (CNS). We place the advances in historical context and, furthermore, provide future prospects in line with newly discovered advancements in the understanding of PD and other neurodegenerative disorders. This review provides researchers in the field of polymer chemistry and materials science an up-to-date understanding of the requirements placed upon materials designed for use in the CNS aiding the focus of polymer therapeutic design.     

Influence of External Interface Normal Stress on the Growth of Cu-Sn IMC During Aging

A U-shape clamp was designed to apply stress perpendicular to the interface of Cu/Sn/Cu solder joints, and its influence on the growth behavior of Cu-Sn intermetallic compound (IMC) during thermal aging at 150 °C was investigated. The results show that compared with the sample at general stress-free state, the growth rate of IMC under compression is faster, while that under tension is slower. Moreover, the interface between IMC and Sn is smoother under compressive stress, and the corresponding IMC grains are smaller and more uniform than that under tensile stress. According to the growth kinetic analysis, the growth of IMC under general, compressive and tensile states is all controlled by the combination of grain boundary diffusion and volume diffusion with a similar growth exponent (n ≈ 0.4). However, external stress can affect the Ostwald ripening process of grain growth, causing a change of grain size and grain boundary density in the IMC layer. As a result, the IMC growth behavior at the interface of the solder joint will be affected by the applied external normal stress.     

严重事故下吸湿性气溶胶的自然去除研究

反应堆发生严重事故时，堆芯释放出的吸湿性气溶胶会在潮湿的安全壳内增大，从而影响其自然去除过程。本文理论推导了吸湿性气溶胶的增大模型并通过多种方法对其进行了验证。模型计算结果表明，气溶胶的增大过程由于受到溶解度的限制而存在临界湿度值，在该临界值以下时气溶胶不发生吸湿，但这未被其他严重事故分析程序所考虑。同时，基于某三代先进压水堆的特定严重事故工况，本文分析了干颗粒半径及湿度对气溶胶的平衡半径和自然去除系数的影响。结果表明:气溶胶的自然去除系数随干颗粒半径的增大将先减小后增加，并在1 μm时达到最小值；相同湿度下，干颗粒半径对气溶胶半径的最大增大比例的影响不大；湿度的增加对不同干颗粒半径气溶胶去除系数的影响不同。