响应面试验优化双酶酶解法制备鱼鳞抗菌肽工艺及其抑菌性能分析

采用双酶酶解法制备鱼鳞抗菌肽,进行酶筛选并通过响应面法优化酶解条件;通过葡聚糖凝胶G-25分离纯化酶解液,研究有效抑菌组分对不同菌的最小抑菌浓度（minimum inhibitory concentration,MIC）。结果表明,当采用碱性蛋白酶结合酸性蛋白酶分步酶解鱼鳞,底物质量浓度为30?g/100?mL时,最适酶解条件为碱性蛋白酶在pH?9.5时首次酶解,酶解时间62?min,酶解温度55?℃;酸性蛋白酶在pH?3.0时再次酶解,酶解时间3?h,酶解温度34.4?℃。此条件下制备的酶解液对副溶血性弧菌的抑菌圈直径为27.72?mm,与预测值基本相符。酶解液经层析后,其抑菌性G2组分对假单胞菌和希瓦氏菌的MIC为1.56?μg/mL,对金黄色葡萄球菌、枯草芽孢杆菌、大肠杆菌、沙门菌及副溶血性弧菌的MIC为6.25?μg/mL。可见,双酶酶解法制备的鱼鳞抗菌肽具有较强的抑菌性。     

Preparation and thermal stability of collagen from scales of grass carp (<Emphasis Type="Italic">Ctenopharyngodon idellus</Emphasis>)

Grass carp (Ctenopharyngodon idellus) scales (GCS) was swollen in water and treated with microwave for 2 min, followed by decalcifying with 8% aqueous citric acid solution. The collagen of GCS was then prepared by limited pepsin digestion with a yield of 25.64% on dry weight basis. SDS-PAGE, FT-IR and amino acid composition analysis indicated that the pepsin-solubilized collagen from GCS was typical type I collagen, consisting of three different α chains, α₁, α₂ and α₃. The thermal stability of pepsin-solubilized collagen from GCS was studied using viscometry, circular dichroism (CD) and Raman spectroscopies. The denaturation temperature (T _d) of collagen solution was 32 °C determined by viscometry. CD spectra analysis showed that the Td of GCS solution was between 35 °C and 40 °C, and further confirmed by Raman spectra. Thus, a large amount of collagen could be obtained from GCS and the preparation method is safe and time-economizing, and GCS will have potential as an important collagen source for use in various industries.     

基于多元L-P法的复合材料圆柱壳内共振分析

以不同材料构成的复合材料圆柱壳作为研究模型,考虑几何非线性,动态弹性模量等因素,根据Donnell’s简化壳理论及经典层合壳理论建立其非线性振动方程。采用Galerkin 方法对振动方程进行离散化,应用多元L-P法求解了系统包含两个相邻轴向模态的非线性振动响应,得到了反映复杂内共振的幅频特性曲线,表明能量在两个模态之间相互传递,彼此影响牵制,系统存在1:1 内共振现象。最后利用多尺度法与多元L-P 法所得结果进行比较,得到了相同的结论。     

桩基非线性轴向受迫振动稳态幅频响应分析

用多时间尺度法得到了一端固定、另一端自由的桩基非线性轴向受迫振动系统主共振时的稳态幅频响应曲线。研究表明:桩基非线性轴向受迫振动的幅频响应曲线不仅与派生线性振动系统的固有频率、土刚度和阻尼系数有关,而且也与振幅、相位和非线性特征量有关。幅频响应曲线中会出现一种典型的振幅跳跃的非线性现象,当激励频率接近线性系统固有频率时,系统产生共振从而响应幅值增大,而且同一激励频率可能会对应于振幅的多个不同值,运动状态具有不稳定性。随着非线性系数的增大,响应曲线峰值侧向弯曲;粘性阻尼会抑制响应振幅的增大;激励振幅增大会导致响应振幅增大。     

A study on hot corrosion behaviour of Ni–5Al coatings on Ni- and Fe-based superalloys in an aggressive environment at 900 °C

Ni–5Al coating was deposited on Ni- and Fe-based superalloys by high velocity oxy fuel (HVOF) process to enhance their high-temperature corrosion resistance. Hot corrosion studies were conducted on bare as well as HVOF-coated superalloy specimens after exposure to a molten salt environment at 900 °C under cyclic conditions. Each cycles consisted of 1 h heating in the silicon carbide tube furnace followed by 20 min cooling in air. Thermogravimetric technique was used to approximate the kinetics of corrosion. Techniques like X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDAX) were used to characterize the corrosion products. The coatings and the oxide scale formed on the exposed surface were found to be intact with the superalloys. Superfer 800 with Ni–5Al coating has provided a good protection to the superalloys in the given molten salt environment.     

Calculation of temperature transients in pulse electrochemical machining (PECM)

Pulse Electrochemical Machining (PECM) is a manufacturing process which provides an economical and effective method for machining hard materials into complex shapes. One important drawback of ECM is the lack of quantitative simulation software to predict the tool shape and machining parameters necessary to produce a given work-piece profile. Calculating temperature distributions in the system allows more accurate simulations, as well as the determination of the thermal limits of the system. In this paper temperature transients over multiple pulses are calculated. It is found that the way the system is modeled has a great impact on the temperature evolution in the thermal boundary layer. The presence of massive electrodes introduces extra time scales which may not be negligible. It is advantageous to identify the thermal time scales in the system, to see whether the heat produced during separate pulses will accumulate or not during the process. The occurring thermal time scales in the system are discussed in detail.     

The effect of an Al2O3 dispersion on the adhesion of Al2O3 scales on aluminized Co-10% Cr alloys

The beneficial effect of dispersions of reactive-metal oxide particles on the adhesion of Cr₂O₃ and Al₂O₃ scales formed on heat-resisting alloys is wellknown. It has been shown that an Al₂O₃ dispersion in an alloy can improve the adhesion of a Cr₂O₃ scale, and it is of particular interest in assessing the various theoretical proposals for the effect to determine whether such a dispersion can affect the adhesion of an Al₂O₃ scale. In this investigation, a Co–10% Cr–1 % Al alloy was first internally oxidized to form an Al₂O₃ dispersion. This alloy was then aluminized so that on subsequent oxidation an Al₂O₃ scale developed. It was shown that the dispersion did indeed improve the scale adhesion. The implications of this result are discussed.     

Comparison of analytical techniques for nonlinear vibrations of a parametrically excited cantilever

This paper is concerned with second-order approximations to the steady-state principal parametric resonance response of a vertically mounted flexible cantilever beam subjected to a vertical harmonic base motion. The unimodal form of the nonlinear equation describing the in-plane large amplitude parametric response of the beam, derived in Krishnamurthy (Ph.D. Thesis, Department of Mechanical Engineering, Washington State University, 1986) based on the previous analysis in Crespo da Silva and Glynn (Journal of Structural Mechanics 1978; 6:437–48), is analysed using the harmonic balance (HB) and the perturbation method of multiple time scales (MMS). Single term HB, two terms HB, and second-order MMS with reconstitution version I (Nayfeh and Sanchez, Journal of Sound and Vibration 1989; 24:483–97) and version II (Rahman and Burton, Journal of Sound and Vibration 1989; 133:369–79) approximations to the steady-sate frequency–amplitude curves of the principal parametric resonance for each of the first four natural modes of the cantilever beam are compared with each other and with those obtained by numerically integrating the unimodal equation of motion. The time transformation is used in obtaining these approximations; also detuning is used in obtaining the square of the forcing MMS approximations. The obtained results show that, for the problem under consideration, the MMS version II is, in comparison with MMS version I, simpler to apply and leads to qualitatively more accurate second-order results. These results, however, show that the MMS version II tends to produce appreciable over corrections to the first-order results and may breakdown at relatively low response amplitudes, whereas the two terms HB solutions tend to improve the first-order results and lead to fairly accurate results even for relatively large response amplitudes.     

Computer attitude scales: How relevant today?

Since the increase in the use of computers as learning tools, there have been many scales developed that can measure various aspects of ‘computer attitude’. The aim of this study is to examine the relevance of a number of these scales and determine whether they are still appropriate for use today. Four computer attitude scales, which are used widely, are assessed. It was found that the scales are reliable. However, the degree of predictive validity for each scale varied and the various underlying constructs appear to reflect different aspects of attitude. In addition, these constructs had changed since the original creation of the scales. This suggests that the traditional style of computer attitude scale is no longer as relevant as when first developed, and judicious selection and care need to be exercised over their use and the interpretation of findings.