n阶常系数非齐次线性微分方程特解的统一求法

对于n阶常系数非齐次线性微分方程,当f(x)分别为Pm(x),和时,给出了求特解的统一方法:"降阶法",有别于大多数《常微分方程》教材中的传统方法:"待定系数法"。     

浅析有效提升自媒体科学传播效果的路径

随着自媒体技术的普及和发展,中国的科学传播进入了新的时代。与此同时,自媒体科学传播也越来越需要系统性的规范和运营,为此应系统地研究提升自媒体时代科学传播的路径,实现其价值。     

Protective effects of bovine colostrum acid proteins on bone loss of ovariectomized rats and the ingredients identification

Scope: Milk basic proteins and bovine colostrum extracts have preventive effects on osteoporosis. However, the effects of bovine colostrum acidic proteins (BCAP) on properties of bone have not been reported. This study investigated the effect of BCAP on the prevention of bone loss in ovariectomized (OVX) rats. Methods and results: Forty‐eight 3‐month old female Sprague–Dawley rats were OVX and another 12 rats underwent a sham operation (Sham). The OVX rats were randomly separated into four groups, i.e. OVX control, OVX plus 2 mg/day BCAP, OVX plus 10 mg/day BCAP, and OVX plus 50 mg/day BCAP, and were gavaged once per day for 12 wk. The effects on bone mineral content, bone mineral density, microarchitecture and biomechanical properties were determined. The bioactive ingredients in BCAP were isolated and identified. Results showed that BCAP increased the bone mineral content and bone mineral density of the femur in a dose‐dependent manner. Scanning electron microscope observation and mechanical testing further confirmed the positive effects of BCAP. These positive effects attribute to the fact that osteopontin, lactoferrin, epidermal growth factor and insulin‐like growth factor‐2 are the dominant proteins in BCAP. Conclusions: BCAP (2–50 mg/day) could prevent osteoporosis caused by bone loss in OVX rats.     

Heterologous expression and purification of Zea mays transglutaminase in Pichia pastoris

Transglutaminases (TGases) are a family of enzymes that catalyze the cross-linking of proteins and are widely used in the food industry to improve the texture of dairy, meat, and bread products. Zea mays transglutaminase (TGZ) is a new type of TGase with a wide potential. TGZ was expressed in the yeast Pichia pastoris under an alcohol oxidase promoter. Maximal expression of recombinant TGZ was achieved by inducing recombinant GS115 (pPIC9K-tgz) in BMMY medium using 1.5% methanol for 96 h. Secreted TGZ was initially separated using Superdex 200 resin and further purified on cation exchange resin. The activity of TGZ following purification was 0.32 U/mg of protein. The polymerization effect of TGZ on casein catalyzed by recombinant TGZ was slightly lower than the effect of microbial transglutaminase (MTG). TGZ is a new potential additive for the food industry.     

乳酸菌Ⅱ类细菌素生物合成及其代谢调控策略

乳酸菌细菌素是乳酸菌经由核糖体合成的具有抑菌活性的多肽类物质,其中乳酸菌Ⅱ类细菌素具有很强的热稳定性和抑菌活性,但是产量较低尚不能实现商业化生产。因此,了解和掌握乳酸菌Ⅱ类细菌素合成及其代谢调控机制,对解决商业化生产过程的技术瓶颈具有重要的意义。该文综述了目前Ⅱ类细菌素生物合成和降解途径,并从代谢调控角度提出提高Ⅱ类细菌素产量的可行性策略,为提高Ⅱ类细菌素产量提供新的途径和思路,也为Ⅱ类细菌素工业化生产奠定基础。     

6082铝合金双轴肩FSW接头组织及腐蚀性能

利用光学显微镜及动电位极化曲线技术,研究了12mm厚6082一T6铝合金双轴肩搅拌摩擦焊接头组织形貌及其电化学性能．结果表明,主轴转速600r／min,焊接速度为300mm／min,搅拌头倾角为0°的焊缝组织出现了明显的变化,焊合区组织发生了动态再结晶,形成细小的等轴晶结构;母材的腐蚀形貌比较粗糙,表面有较深的点蚀坑,而接头焊核区表面腐蚀形貌均一,点蚀现象较轻;动电位极化测试表明双轴肩搅拌摩擦焊接头焊核区的腐蚀电压比母材高,耐腐蚀性能比母材好．     

铝合金薄板搅拌摩擦焊搭接界面缺陷与接头性能

针对2A12–T4铝合金薄板进行了搅拌摩擦焊搭接试验,研究了焊接参数对缺陷形态与接头性能的影响规律. 结果表明,勾状缺陷具有更大的高度和弯曲角度,最大缺陷高度为上板厚度的12.7%. 随焊接速度增大,缺陷高度减小.随转速提高,勾状缺陷高度先增加后减小,冷搭接缺陷高度呈“V”形变化. 在950 r/min,200 mm/min下接头强度最高,接头系数可达84%. 维氏显微硬度分布呈“W”形,上板出现接头软化,焊核区下部硬度高于上部硬度. 冷搭接缺陷是影响接头性能的主要因素,由于有效搭接宽度较小,接头断裂方式为沿搭接面的剪切断裂.     

Production of a transglutaminase from Zea mays in Escherichia coli and its impact on yoghurt properties

A gene from Zea mays coding a TGase was expressed in E. coli and identified by Western blotting. Under optimal expression conditions, the production and specific activity of refolded TGZ were 1.41 mg/L and 0.34 U/mg. The activated TGZ was employed to cross‐link milk proteins. The yoghurt treated with TGZ showed a lower syneresis, higher apparent viscosity and texture than untreated yoghurt. The properties of TGZ‐treated sample were better than those of MTG‐treated samples, so TGZ may have potential as an additive in yoghurt manufacture.     

Inhibitory Effects of Green Tea Polyphenols on the Retrogradation of Starches from Different Botanical Sources

This paper aims at investigating the effects of green tea polyphenols (GTPs) on the retrogradation of potato, rice, and maize starches. Starch/GTPs mixing ratios were 2/0, 2/0.1, 2/0.2, and 2/0.3 (w/w) that equated with starch containing 0%, 5%, 10%, and 15% GTPs (based on starch weight), respectively. The analytic samples had a water–starch/GTPs ratio of 2:1. The effects of GTPs on the retrogradation of these starches were analyzed by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The analysis of DSC indicates that the temperature and enthalpy of gelatinization of all the tested starches decreased as the GTPs level increased. After storage at 4 °C, retrogradation enthalpy (ΔH _ret) for potato starches with 5%, 10%, and 15% GTPs appeared after 10 days of storage, however ΔH _ret for rice and maize starches with 10% and 15% GTPs did not appear until storage of 20 days, and both the ΔH _ret and degree of retrogradation of the three starches significantly decreased with the increased level of GTPs. After 10 days of storage at 4 °C, the analysis of XRD shows that the intensity of X-ray diffraction peaks of potato starch gradually decreased with the concentration of GTPs increasing, and rice and maize starch gels with 10% and 15% GTPs had almost no recrystallization of the retrogradation. It is concluded that the addition of GTPs considerably inhibits the retrogradation of rice, maize, and potato starches.