Simplification and applicability studies of a hydrogen-air detailed reaction mechanism

The research of hydrogen fuel internal combustion engine (HICE) had great significance facing the challenges of energy and environmental problems. Based on the detailed hydrogen-air reaction mechanism, the pre-mix model of CHEMKIN-Pro software was selected to simplify the detailed mechanism GRI-3.0. The most important elements and reactions was chose to construct framework mechanism firstly based on the sensitivity coefficient for H₂O and NO formation, and additional elements and reactions were added to framework mechanism for complementing the oxidation path of N2 and H₂. A simplified mechanism including 24-step elementary reaction was obtained and the laminar burning velocity calculated by this simplified mechanism matches well with the detailed mechanism in a wide range. This simplified mechanism was also applied in a CFD model which predicted the cylinder instantaneous pressure and NOx emission accurately within a large range of fuel air equivalent ratio. Showing that this mechanism has good applicability.     

NiH/Hβ催化剂的制备及催化正己烷异构化性能

采用浸渍还原法制备了一种新型镍氢化物/分子筛（NiH/Hβ）烷烃异构化催化剂，考察了催化剂制备条件及反应条件对其催化正己烷异构化性能的影响。结果发现，当活性组分质量分数为0.5%，反应温度为300 ℃，反应压力为2.0 MPa，氢/油摩尔比为4.0及质量空速为1.0 h^-1时，NiH/Hβ催化剂催化正己烷异构化活性最优，正己烷的转化率为83.0%，异构烷烃的选择性与收率分别达到78.6%、65.2%。根据实验结果，提出了NiH/Hβ催化剂催化正己烷异构化反应机理，证明NiH金属活性中心具有良好的加氢/脱氢功能。     

Non-linear dissolution mechanisms of sodium calcium phosphate glasses as a function of pH in various aqueous media

Phosphate glasses for bioresorbable implants display dissolution rates that vary significantly with composition, however currently their mechanisms of dissolution are not well understood. Based on this systematic study we present new insights into these mechanisms. Two-stage dissolution was observed, with time dependence initially parabolic and later linear, and a two-stage model was developed to describe this behaviour. Dissolution was accelerated by lower Ca concentration in the glass, and lower pH in the dissolution medium. A new dissolution mechanism is proposed, involving an initial stage where diffusion-controlled formation of a conversion layer occurs. Once the conversion layer is stabilised, layer dissolution reactions become rate-limiting. Under this mechanism the transition time is sensitive to the nature of the conversion layer and solution conditions. These results reveal the dependence of P₂O₅–CaO–Na₂O glass dissolution on solution pH, and provide new insight into the dissolution mechanisms, particularly regarding the transition between the two dissolution stages.     

新型限力输出保护功能柔性夹钳的设计与参数评估

柔性夹钳因具有微/纳精密操作能力, 常应用于微操作系统中, 但因抓爪无法提供恒定输出力或恒力范围小, 容易造成操作对象的损伤或脱落。根据放大模块与常力模块串联的结构形式, 设计了一种具有常力特性的柔性夹钳。基于伪刚体法, 建立放大模块中桥式机构与杠杆机构的刚度和放大率数学模型, 通过对倾斜导向梁进行分析, 得到常力模块的力-位移关系式, 计算出恒定输出力为42.5 N, 输出范围为370 μm。最后, 结合不同柔顺梁的结构参数, 运用MATLAB仿真探究了各关键参数对常力特性的影响。研究结果可为常力柔性夹钳的构型设计和分析提供一定的理论支撑。     

A theoretically-based novel protocol for the analytic treatment of the glass failure stresses associated with coaxial double ring test method

With the aim of validating a new standardized Coaxial Double Ring testing procedure, without overpressure and with fixed geometry, an ad hoc theoretical approach has been proposed here to rearrange the laboratory outcomes accounting for the effects of the geometric non-linearities associated with such a testing configuration. By borrowing this idea, once the experimental values of the failure load have been determined, it has been possible to obtain an expression in closed form (fully defined by only two coefficients) of the maximum tensile stress (σ_max) in the core of the specimen. Following this, in order to make the laboratory outcomes comparable and homogeneous, the σ_max-values have been then re-scaled to a common reference condition (equibiaxial stress on a reference area, σ_eqbx), by means of the use of a correction coefficient (K) able to determine, under a condition of equal probability of failure, the effective area (A_eff) of the tested specimens. After being corrected to account for the effects of the stress corrosion cracking (static fatigue effect), all re-scaled data have been finally interpreted using a Weibull-type statistical distribution to determine the main fractile values of the glass strength. Doing so, despite some unavoidable approximations, this procedure furnished a highly effective means of determining the bending strength of float glass. Unlike the pure numerical approach proposed in codes and literature, which requires to correct the experimental data via FEM simulation, the rationale behind the proposed approach is in fact to elaborate the experimental data through an analytic treatment of the problem, which would greatly facilitate the interpretation of the data as well as the standardization of the testing procedure.     

New insight into subcritical rupture of SiC-based filaments at intermediate temperatures (400–900 °C) under air

The delayed failure of SiC fibrous reinforcement has continuously been investigated to warrant the long term performances of Ceramic Matrix Composite (CMC). Chiefly assessed on multifilament tow samples to alleviate some handling difficulties, subcritical crack growth (SCG) parameters are however ruled by structural artifacts which hinder the identification of intrinsic filament behavior. In this paper, we propose to estimate the true filament parameters for 5 fiber types from bundle behavior using a recently communicated Monte Carlo algorithm integrating flaw and stress distributions through a deterministic fracture mechanics law under Paris’ formulation. So computed tow lifetime are broadly dispersed, encompassing raw data, and show a structure-dependent scale effect, revealed by n_filament>n_tow where n is the stress exponent. The relationship between SCG coefficient and chemical composition of the substrate is discussed and highlights the major effect of doping elements (Ti or Zr), oxygen or hydrogen content.     

Microstructure and mechanical properties in the TLP joint of FeCoNiTiAl and Inconel 718 alloys using BNi2 filler

High entropy alloy(HEA) of Fe Co Ni Ti Al and Inconel 718 superalloy were firstly transient liquid phase(TLP) bonded by BNi2 filler due to the diffusion of Si and B in the filler to the base metals. The effects of bonding time on microstructure evolution and mechanical properties of the TLP joints were investigated.Owing to the complete isothermal solidification of the joints bonded for 30 min 120 min at 1100°C,no athermally solidified zones(ASZs) formed by eutectic phases were observed in the welded zone. Thus the TLP joints were only composed by the isothermally solidified zone(ISZ) and two diffusion affected zone(DAZ) adjacent to the dissimilar base metals and the negative effect of the ASZ on joint properties can be avoided. In addition, the increase of the bonding time can also make the Ti B2 borides precipitated in the DAZ near HEA and the brittle borides or carbides in the DAZ near IN718 alloy decrease and reduce the possibility of the stress concentration happened in the joints under loading. Therefore, the highest shear strength(632.1 MPa) of the TLP joints was obtained at 1100°C for 120 min, which was higher than that of the joint bonded for 30 min, 404.2 MPa. Furthermore, the extension of the bonding time made the fracture mechanism of the joint be transformed from the intergranular fracture to the transgranular fracture. However, as the brittle borides in the DAZ near IN718 can not be eliminated completely and refining of grains also happened in such region, all the TLP joints fractured inner the DAZ near IN718 alloy.     

Peptide-Mimicking Poly(2-oxazoline)s Displaying Potent Antimicrobial Properties

Poly(2-oxazoline)s have excellent biocompatibility and have been used as FDA-approved indirect food additives. The inert property of the hydrophilic poly(2-oxazoline)s suggests them as promising substitutes for poly(ethylene glycol) (PEG) in various applications such as anti-biofouling agents. It was recently reported that poly(2-oxazoline)s themselves have antimicrobial properties as synthetic mimics of host defense peptides. These studies revealed the bioactive properties of poly(2-oxazoline)s as a new class of functional peptide mimics, by mimicking host defense peptides to display potent and selective antimicrobial activities against methicillin-resistant Staphylococcus aureus both in vitro and in vivo, without concerns about antimicrobial resistance. The high structural diversity, facile synthesis, and potent and tunable antimicrobial properties underscore the great potential of poly(2-oxazoline)s as a class of novel antimicrobial agents in dealing with drug-resistant microbial infections and antimicrobial resistance.