Curing kinetics and mechanical properties of fast curing epoxy resins with isophorone diamine and N-(3-aminopropyl)-imidazole

Fast curing epoxy resins were prepared by the reactions of diglycidyl ether of bisphenol A with isophorone diamine (IPD) and N-(3-aminopropyl)-imidazole (API), and their curing kinetics and mechanical properties influenced by IPD content were also investigated. The analysis of curing kinetics was based on the nonisothermal differential scanning calorimetry (DSC) data with the typical Kissinger, Ozawa, and Flynn–Wall–Ozawa models, respectively. The glass-transition temperature was also measured by the same technique. Additionally, the mechanical properties including flexural, impact, and tensile performances were tested, and the curing time was estimated by isothermal DSC. The degree of cure (α) dependency of activation energy (E_a ) revealed the complexity of curing reaction. Detailed analysis of the curing kinetics at the molecular level indicated that the dependence of E_a on the α was a combined effect of addition reaction, autocatalytic reaction, viscosity, and steric hindrance. From the nonisothermal curves, the curing reaction mechanism could be proposed according to the increasingly obvious low temperature peaks generated by the addition reaction of epoxy group with the primary amines in API and IPD molecules. Using the preferred resin formulation, the resin system could be cured within 10 min at 120 °C with a relatively good mechanical performance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47950.     

Möbius变换下四次有理抛物-PH曲线的C2 Hermite插值

目的 曲线插值问题在机器人设计、机械工业、航天工业等诸多现代工业领域都有广泛的应用，而已知端点数据的Hermite插值是计算机辅助几何设计中一种常用的曲线构造方法，本文讨论了一种偶数次有理等距曲线，即四次抛物-PH曲线的C² Hermite插值问题。方法 基于M bius变换引入参数，利用复分析的方法构造了四次有理抛物-PH曲线的C² Hermite插值，给出了具体插值算法及相应的Bézier曲线表示和控制顶点的表达式。结果 通过给出"合理"的端点插值数据，以数值实例表明了该算法的有效性，所得12条插值曲线中，结合最小绝对旋转数和弹性弯曲能量最小化两种准则给出了判定满足插值条件最优曲线的选择方法，并以具体实例说明了与其他插值方法的对比分析结果。结论 本文构造了M bius变换下的四次有理抛物-PH曲线的C² Hermite插值，在保证曲线次数较低的情况下，达到了连续性更高的插值条件，计算更为简单，插值效果明显，较之传统奇数次PH曲线具有更加自然的几何形状，对偶数次PH曲线的相关研究具有一定意义。     

Influences of copolymers (Copovidone,Eudragit RL PO and Kollicoat MAE 30 DP) on stability and bioactivity of spray-dried and freeze-dried lysozyme

Protein stability is the most crucial factor in protein pharmaceutical preparations. Various techniques were applied for producing stable protein formulations such as spray-drying and freeze-drying. However, heating and freezing stresses are disadvantages for proteins using these methods, respectively. Accordingly, excipients have been used to preserve therapeutic effects of proteins during processing and for long period of time. Therefore, influences of Copovidone, Eudragit^® RL-PO and Kollicoat^® MAE-30 DP (as excipients) on stability and integrity of lysozyme (as a model protein) in spray-dried and freeze-dried forms were investigated. Protein formulations in both dried forms were prepared without and with the addition of mentioned excipients at different concentrations. Protein formulations were characterized for yield determination, morphology using scanning electron microscopic (SEM), thermal analysis by Differential Scanning Calorimetry (DSC), secondary structure stability using Fourier transform infrared (FT-IR) spectroscopy and biological activity. All protein formulations were subjected to a stability study as solid protein formulations for 3 weeks at 24?°C/76% relative humidity and aqueous protein samples were stored at 50?°C for 30?min in a water bath. Results showed that Copovidone successfully preserved integrity and biological activity of lysozyme before and after storage in both spray-dried and freeze-dried forms with more advantage for using higher concentration of the same excipient. Smooth spheres of spray-dried lysozyme formulations with Copovidone were smaller than spray-dried lysozyme without and with Kollicoat^® MAE-30 DP, which affected %yield produced. Copovidone has demonstrated valuable protection ability for lysozyme.     

Power grand composite curves shaping for adaptive energy management of hybrid microgrids

This work proposes a systematic approach for the adaptive identification and implementation of efficient power management strategies (PMS) in the course of operation of hybrid renewable energy microgrids. The approach is based on the temporal evolution of the system power grand composite curve (PGCC), which is adaptively shaped on-line and within short-term time intervals to form a sequence of decisions indicating the instant and duration of activation of different subsystems. It builds on from previous work where the potential for system performance enhancement could not be exploited through pre-specified PMS identified off-line. More specifically, it involves a stored energy targeting step that exploits the PGCC to identify the desired operational profile of an accumulator during a prediction horizon in order to satisfy the system operating goals. The identified energy targets are subsequently enforced through a sequence of control actions that enable the exact matching of the PGCC hence resulting in a new PMS. The method is elaborated graphically for multiple potential operating goals and is supported by a formal mathematical model that captures system structural and temporal characteristics. It is implemented on an actual hybrid microgrid considering multiple RES-based energy generation and storage options for expected and unexpected weather conditions.     

Effects of the biaxial orientation on the mechanical and optical properties and shrinkage of polyamide 6-66–montmorillonite–nanosilica nanocomposite films

Polyamide 6–66 (PA6-66)–montmorillonite (MMT)–nanosilica (NS) nanocomposite films were fabricated through a cast film process and then biaxially stretched on a laboratory stretcher. Uniaxial or biaxial stretching induced the elongated conformation of MMT and NS. The b axis of the α crystals and the amorphous phase were revealed to align along the machine direction (MD) after stretching, with the uniaxial orientation playing a more significant role. Furthermore, the crystallinity of PA6-66 stretching increased with the stretching ratio. Uniaxial stretching gave rise to a significantly enhanced tensile strength along the MD, whereas it slightly decreased the mechanical properties along the transverse direction (TD). In contrast, the films subjected to biaxial stretching exhibited more balanced mechanical properties. Uniaxial and biaxial stretching led to decreased transmittance and increased haze in the PA6-66–MMT–NS films; this could have been due to the elongated nanostructure of the two nanofillers, which inhibited the transmission and facilitated the scattering of visible light. The thermal shrinkage of the films increased with increasing stretching ratio, and the biaxially oriented films presented nearly equal shrinkage in the MD and TD. The addition of nanofillers decreased the shrinkage attributed to the mobility inhibition of the polymer chains during heating. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47504.     

Modified dynamic surface approach with bias torque for multi-motor servomechanism

This paper presents a modified neural dynamic surface control (DSC) with an adaptive bias torque for the multi-motor servomechanism (MMS) with backlash, friction and other disturbances. By introducing a continuous hybrid differentiator to replace the first-order filter in each step, a modified DSC is developed to improve the load tracking precision of MMS. However, when the MMS enters the backlash band, only DSC cannot guarantee the load tracking performance. Thus, an adaptive bias torque is firstly proposed based on the prescribed performance function technique to compensate the backlash nonlinearity and guarantee the load tracking performance of MMS. In addition, the unknown dynamics including the friction and other disturbances are approximated by using wavelet echo state networks where the weights are all updated online. By means of Lyapunov stability theory, the semi-globally uniformly ultimately bounded (SGUUB) property of all signals in the closed-loop system is proved. Finally, simulations and experimental results based on a four-motor servomechanism are presented to show the effectiveness of the proposed approach.     

A practical sampling method for profile measurement of complex blades

Blade is one of the most important parts in turbine machinery. The complex geometry of blades not only makes them difficult to fabricate, but also leads them difficult to inspect. Typically, the surface of blades is measured by using coordinate measuring machine (CMM). Since the measurement time and cost increase proportionally as the increase of measurement points, it is essential to sample measurement points which can represent entire blade with sufficient confidence and accuracy. In order to achieve a certain allowable deviation with a suitable set of points, a practical sampling method for surface measurement of blades was studied. Firstly, the leading edge curve and trailing edge curve were supposed to represent the twisted and bend information of blades. A sampling method based on maximum chordal deviation for leading edge curve and trailing edge curve was researched. Further, a fusion approach for sampling points on both edge curves, which determine the cross-sections, was proposed. Secondly, the inspection points sampling method for sectional curves were investigated. Finally, two simulation and one experimental examples were used to demonstrate the sampling methodology. The results indicated that the approach of this study can ensure the measurement precision at high curvature potion by measuring a small number of points.     

Palmitoleic Acid Enrichment of Seabuckthorn (Hippophaë rhamnoides L.) Pulp Oil by Crystallization Process

Abstract

Seabuckthorn pulp oil was fractionated using a crystallization process with acetone under controlled cooling rate of 0.25°C/min without agitation at different crystallization temperatures ranging from ? 15 to 15°C. The obtained liquid (LF) and solid (SF) fractions were analyzed for their fatty acid and triacylglycerol compositions and their melting profiles were characterized. Fractionation at ? 15°C yielded about 20% of LF where palmitoleic acid represented 53% of total lipids. The SF fraction was mainly rich in palmitic acid. LF were richer in triacylglycerol with acyl carbon numbers of 50 and 52 (C50 and C52) than SF, which contained a higher amount of C48. The melting curves of LF and SF showed multiple endothermic transitions.     

Stability of the passive state of Zr–Nb crystalline alloys

Stability of the passive state was assessed for pure Zr and four Zr–Nb alloys (2.5, 5.0, 10.0, 25.0 at.% Nb) after 24 h exposure to naturally aerated 3.5% NaCl solution (pH = 6). Open circuit potential values indicated that all the Zr–Nb alloys studied and the pure Zr undergo spontaneous passivation due to spontaneously formed oxide film passivating the metallic surface. It also indicated that the addition of increasing Nb contents to pure Zr seems to improve the protection characteristics of its spontaneous oxides. Potentiodynamic polarization curves showed an increase of the breakdown potential and the extent of the passive range following an increased niobium amount in the alloy. This leads to the conclusion that a progressive increase of niobium content positively affects the localized corrosion behaviour of the Zr–Nb alloys by enhancing the electrochemical stability of the passive film. Electrochemical impedance spectroscopy (EIS) studies showed high impedance values for all the samples, and its increase on increased niobium content in the alloy indicated an improvement in the corrosion resistance of the spontaneous oxide film. The fit obtained suggests a single passive film present on the metal surface, with resistance improving with the increase of niobium amount in the alloy. All these electrochemical results show the beneficial effect of increasing niobium contents on the passive state stability of the Zr–Nb alloys.     

Fatigue assessment of arc welded automotive components using local stress approaches: Application to a track control arm

The applicability of the structural and notch stress approach is examined on the basis of arc welded and dynamically loaded steel structures, taken from the automotive sector. In detail, this is a transverse control arm. Components and specimens with critical regions of failure are tested under cyclic loading with constant and variable amplitudes. With the help of strain gauges, the crack initiation is determined. The specimens are the basis for the application and evaluation of the different approaches for the assessment of fatigue life. The numerical determination of the nominal, structural and notch stresses is performed with finite-element models. Finally the experimental and computational results allow the derivation of structural and notch Woehler S-N curves.