Cut‐off Frequencies Induced by the Length of Strain Gauges Measuring Impact Events

Abstract: The finite length of strain gauges may induce filtering effects when measuring impact events. In this study, we are interested in quantifying these effects. Precisely, we determined the cut‐off frequencies of strain gauges cemented on visco‐elastic bars and measuring impact‐induced strain waves. This study shows that the cut‐off frequencies increase with the bar’s wave velocity and decrease with the bar’s diameter. The asymptotic value, corresponding to an infinite bar diameter, is reached rapidly (bar diameter ≈ 15 mm). Moreover, we showed that the mode cut‐off frequencies are more severe (lower) than the gauge length cut‐off frequencies for bar diameters greater than 8 mm.     

180m高钢筋混凝土烟囱三段单向控制爆破拆除

对复杂环境下180m高钢筋混凝土烟囱,采用三段单向分次控制爆破拆除。采用复式梯形爆破切口,确保烟囱倒塌方向;铺设黄土缓冲垫层和个体特殊防护措施,有效地控制烟囱倒塌触地振动;采用刚性和柔性复合式措施防控爆破飞石;采用高空吊篮法进行高空爆破切口施工。爆破后,烟囱倒塌方向准确,周边建筑物和设施安然无恙,取得了良好的爆破效果,达到了安全、精细和快速爆破拆除的目的,为以后类似爆破工程提供参考。     

Effects of rind removal on physicochemical quality characteristics of fresh‐cut watermelon [Citrullus lanatus (Thunb) Matsum & Nakai] during cold storage

The impact of removing the rind from fresh‐cut watermelon slices was assessed on the quality of the product during storage at 4 °C for 9 days. Flesh lycopene declined from 55.4 to 47.9 mg kg^?1 f.w. and colour lightness (L*) increased from 43.2 to 45.8 after 2 days of storage. Initial heart and placental flesh firmness increased from 7.3 and 9.8 N, respectively, to 9.5 and 12.8 N after 9 days, but were unaffected by rind processing. Electrolyte leakage from placental tissue was unaffected by storage and rind. Rind presence limited juice run‐off by 47.2% and maintained mean total soluble sugar concentration in the slices at 86.0 mg mL^?1 as opposed to 76.8 mg mL^?1 in rind‐less slices. Change in the quality was most pronounced between 0 and 2 day of storage. Removing the rind accelerated senescence and off‐flavour production, while the presence of rind improved the overall storage stability of fresh‐cut watermelon slices.     

不同预处理方式对西兰花等外品热风干燥粉体性质的影响

为明确西兰花等外品热风干燥制粉工艺适宜预处理方式,分别采用蒸汽蒸制、热水烫漂、切小丁的预处理方式制备西兰花等外品热风干燥粉体(the hot air drying powder of broccoli defective product,简称HBD粉),研究了不同预处理方式对HBD粉粉体性质的影响。结果表明:烫漂对HBD粉色泽保持效果最好,V_C保留量较高,但溶解性较差。烫漂10 s粉体流动性较差。烫漂30 s粉体较难吸湿,更利于压片成型和干燥保存;蒸汽蒸制粉体水溶性指数较大。蒸汽10 s粉体平均粒径最小,流动性较差,总糖、还原糖含量最高,吸湿能力最强,达22.8%。蒸汽30 s更利于压片成型;小丁粉体膨胀力、持水力较强。经烫漂10 s、蒸汽10 s预处理的HBD粉适宜作为功能配料添加到食品中或吸附于食品表面,经烫漂30 s、蒸汽30 s预处理的HBD粉体适宜片剂、胶囊等产品剂型加工。     

Edible coatings enriched with essential oils for extending the shelf‐life of ‘Bravo de Esmolfe’ fresh‐cut apples

Edible coatings based on sodium alginate (AL) and pectin (PE) at 1% and 2%(w/v) enriched with eugenol (Eug) and citral (Cit) at minimum inhibitory concentrations (MIC) (0.10% and 0.15%) and double MIC were used to preserve the quality of fresh‐cut apples ‘Bravo de Esmolfe’. Samples were taken, through 14 day at 4 °C, for analysis of colour CIE(L*h°C*), firmness, °Brix, weight loss, antioxidant activity (TEAC), microbial growth and taste panels. With those quality characteristics, three groups were formed by the principal component and hierarchical cluster analysis, for each coating base (AL or PE). Based on, for each quality parameter measured, the mean closest value to the one at harvest for colour, higher value for firmness, °Brix and TEAC, and lower value for weight loss and microbial spoilage, the best group was selected for AL and PE. From each group, two edible coatings with the highest scores in overall acceptability were selected for fresh‐cut apples: AL2% + Eug 0.1%, AL2% + Cit 0.15% + Eug 0.1%, PE 2% + Cit 0.15% and PE 2% + Eug 0.2%.     

韩家湾煤矿浅埋煤层综采面过切眼相似模拟实验研究

文章针对韩家湾煤矿浅埋煤层2403综采面回采时遇到如何过旧切眼的问题,进行了相似模拟实验,通过压力传感器实时监测和全站仪读取测点位移研究了综采面直接推过不同支护下的切眼的过程中支架载荷变化、支承压力变化及上覆岩层运动情况。研究结果表明:在对旧切眼适当支护后综采面直接推过该切眼是可行的。     

温度及防腐剂对切分包菜浸渍品质的影响

探讨了不同温度及防腐剂对4%食盐溶液浸渍切分包菜品质的影响。测定内容包括pH值、浊度、亚硝酸盐生成量、Vc、总糖和氨基酸含量。结果表明:低温对保持低盐、短期浸渍包菜的感官品质有较好的效果,有利于总糖成分的保存,但Vc主要以氧化型形式存在;添加山梨酸钾不能抑制乳酸菌的活动,对减少亚硝酸盐的生成无显著作用;低盐、短期浸渍包菜的亚硝酸盐生成量小于1mg/kg,远低于常规腌制菜。     

滚筒管板式烘丝机的蒸汽疏水系统改造

针对管板式烘丝机蒸汽加热滚筒和热风系统因设计、选型等,在应用中存在不能及时排除系统内的冷凝水、蒸汽含水、筒体温度波动大等问题,对管板式烘丝机疏水系统进行了改造:正确选型疏水阀;合理设计疏水系统管线.改造后,该烘丝机避免了管线内冷凝水聚积,消除了水锤,减小了温度控制波动范围;开机预热时间从改前的30min缩短到10 min,热风温度波动范围从改前的8℃减小到3℃,筒体温度波动范围从改前的5℃减小到1℃,在保证和提高工艺温湿度质量的同时,实现了对凝结水能量最大限度的回收,节约了热能.     

滚筒干燥过程中叶丝状态变化对其热物性的影响

为了分析烟草热湿加工处理中的传热过程,通过自行搭建的滚筒干燥过程中烟丝热物性在线测试平台,利用瞬态平面热源法测定了滚筒干燥过程中烟丝的热物性,考察分析了该过程中烟丝温度、含水率对烟丝导热系数、热扩散系数、体积热容的影响。结果表明:①当含水率相同时,烟丝导热系数、体积热容随着烟丝温度的升高而增大,热扩散系数随温度的升高而降低;②当烟丝温度相同时,烟丝导热系数、体积热容随含水率的降低而减小,热扩散系数随着含水率的降低而增大;③干燥过程中,烟丝含水率逐渐减小,烟丝温度逐渐升高,烟丝导热系数在温度与含水率的共同作用下整体有减小的趋势,表明烟丝含水率对导热系数的影响较温度显著。