Ultraviolet resistance and other physical properties of softwood polymer nanocomposites reinforced with ZnO nanoparticles and nanoclay

Wood polymer nanocomposites (WPNCs) based on nano-ZnO and nanoclay were prepared by impregnation of melamine formaldehyde–furfuryl alcohol copolymer, 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU), a cross-linking agent and a renewable polymer obtained as a gum from the plant Moringa oleifera under vacuum condition. Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometry (XRD) studies were employed for the characterization of modified ZnO and WPNCs. The change in crystallinity index (CrI) value of the cellulose in wood and the distribution of ZnO nanoparticles in composites were determined using FTIR and XRD. Scanning electron microscopy and Transmission electron microscopy showed the presence of nanoparticles and nanoclay in the cell lumen or cell wall of wood. An enhanced UV resistance property was shown by the treated wood samples as judged by lower weight loss, carbonyl index, lignin index, cellulose CrI values, and mechanical property loss compared to the untreated wood samples. Wood polymer composites treated with 3 phr each of nanoclay, ZnO, and the plant gum showed an improvement in mechanical properties, flame-retarding properties, thermal stability, and lower water uptake capacity.     

"80分"计分系统——对阵表

扑克牌作为休闲娱乐工具越来越受到人们的欢迎。本系统的研究和开发有利于集中管理参赛队员和比赛信息。本系统主要使用ADODB访问组件的Recordset对象和Connection对象操作基本数据库表,进行队员信息的管理、比赛对阵表的管理、比赛结果信息的管理。此处主要解决的问题是不同的轮次不能产生相同的对阵双方,采用的方法是二维数组存储变量区别比赛双方前面的轮次是否已进行了比赛。在选择队员的过程中,为减少程序的时间复杂度,每产生一个随机数将选中一个队伍。比赛轮次是不确定因素,存储对阵信息的数据表将动态生成。     

不同规模玉米种植技术效率差异分析——基于随机前沿生产函数与农户微观数据的研究

基于黑龙江、辽宁、河北和山东4个省的372组调研数据,运用倾向得分匹配法和随机前沿模型得到玉米种植农户生产效率模型,依据最大似然检测判断不同规模玉米种植户的生产效率模型,分别估算农户生产效率模型和生产效率水平。结果表明,匹配前的大规模农户效率高于小规模农户,匹配后结果相反。以研究结论为基础,本文为难以改变或不愿意改变玉米种植面积的农户提供效率水平提升的参考依据和建议。     

滞库片烟长期存放过程中主要化学成分的变化

以已醇化3年的福建南平C3F、云南曲靖C3F、贵州黔西南C3F和C4F片烟为材料，连续5年取样，测定片烟在滞库期间常规化学成分(总植物碱、总糖、还原糖、总氮)，高级脂肪酸(亚油酸、油酸、亚麻酸、十六酸、十八酸)和多酚化合物(绿原酸、隐绿原酸、莨菪亭、芸香苷)含量，并分析其变化。结果表明：片烟的总糖、还原糖、亚麻酸、绿原酸、隐绿原酸和芸香苷含量随着滞库时间的延长呈现逐渐降低的趋势；主成分分析表明，片烟的主成分综合得分在滞库期间逐年下降，且在滞库2～3年后片烟会出现明显的品质下降；比较黔西南C3F和C4F片烟，C3F片烟在滞库4年后的综合得分开始低于滞库前的C4F片烟综合得分，说明滞库时间过长会使得片烟发生品质降级现象；比较南平、曲靖、黔西南的C3F片烟，曲靖片烟较耐贮藏，南平片烟不耐贮藏。     

SiCW/Zn-22Al复合材料的组织与高温变形

对低压浸渗、挤压比为10：1的热挤压以及固溶处理制备的SiCw／Zn-22Al复合材料的组织与高温变形行为进行了研究。结果表明：SiCw的复合使材料中出现了熔点为655K的低熔点共晶组织。显著提高了变形抗力，降低了塑性，并使材料丧失了在共析温度区的超塑性；在出现适量液相的共晶温度区，复合材料具有超塑性。     

A quasi-experimental study on the impact of park accessibility on the mental health of undergraduate students

Public mental health issues have gained growing attention from academics and policymakers due to their increasing prevalence and multiple adverse and severe consequences. Although some studies have supported the benefits of parks on mental health, the causal relationship between park accessibility and mental health remains unclear. By converting a large cross-sectional sample of 22,060 undergraduates nationwide in China into a quasi-panel dataset, this study untangled the causal impact of park accessibility on mental health benefits. We employed a quasi-experimental research design and used a difference-in-difference (DID) model to estimate the causal effects of park accessibility on depression symptoms within varying buffer sizes (i.e., 0.5 km, 1 km, 1.5 km, and 2 km). Furthermore, propensity score matching (PSM) and the Heckman selection model were employed to mitigate the selection bias caused by the prior differences of the treatment group and the control group. The results revealed that park accessibility had a positive effect on mental health and that its influence decreased with increased buffer sizes. Regarding the gender and living-cost differences, park accessibility within the 0.5 km and 1 km buffers had a greater mental health impact on females than on males, and it had a greater impact on high-living cost undergraduates than on low-living cost undergraduates. To increase the mental health benefits of undergraduate students, this study suggests that the provision of parks within a 1 km radius buffer surrounding the campus should be a priority to improve the mental health of undergraduates.     

汽车复合材料内燃机缸体的分层精化机理

基于物理力学弹性半解析方法,对复合材料内燃机缸体进行了分层精化、本构控制理论研究和典型算例数值计算。采用缸体的动态实时测试,获得了缸体所受真实载荷下主要点的应变响应,并通过系统仿真方法对计算结果进行了验证,得出了汽车复合材料内燃机缸体分层精化方法的一些结论。     

饲养模式对黑水色湾藏猪肌肉氨基酸的影响

为了探究饲养方式差异对黑水色湾藏猪肌肉氨基酸的影响，以放牧、半舍饲、舍饲养殖出栏的黑水色湾藏猪五花肉为材料，测定氨基酸含量。结果表明：舍饲组TAA含量和EAA含量最高，分别为99.41%和36.36%；放牧组EAA/TAA和EAA/NEAA值高于其余两组，分别为39.56%和65.50%；半舍饲组SRC最高为73.77，为半舍饲组>放牧组>舍饲组；3 组藏猪肉赖氨酸RC值远大于1，赖氨酸含量丰富；苯丙氨酸RC值远小于1，为3种藏猪肉共同限制氨基酸。综上所述，3种模式出栏的藏猪肉含有丰富赖氨酸，但缺乏苯丙氨酸；舍饲出栏的猪肉EAA和TAA含量更高，放牧出栏的猪肉氨基酸组成则更优，而半舍饲出栏的藏猪肉蛋白质营养价值最高。     

多元化生态补偿背景下牲畜暖棚对畜牧业收入和草地质量的影响——基于PSM的准自然实验

在草原牲畜暖棚建设补贴的多元化生态补偿背景下，探究牲畜暖棚的经济和生态效益，对促进多元化草原生态补偿实践具有重要的理论与现实意义。本文基于隧穿环境库兹涅兹曲线(Environmental Kuznets curve, EKC)分析模型，设计了一组牲畜暖棚对牧户畜牧业收入和草地质量影响的准自然实验，并基于2020年若尔盖草原648个牧户的微观调查数据，同时运用倾向得分匹配(Propensity score matching, PSM)最邻近匹配、卡尺匹配、核匹配、局部线性回归匹配法，实证检验了牲畜暖棚对牧户畜牧业收入和草地质量的影响，并通过构造随机实验组的方式进行了安慰剂检验。研究结果表明：暖棚设施的使用，将为牧户带来畜牧业年均增收20 117.99元，同时牧户草地的生态质量提升约6.75%。因此，设施型的多元化生态补偿机制可以协同草地生态保护和牧户生计发展，支持现代化牲畜暖棚建设，将“造血”式赋能草原生态经济，促进牧区绿色发展。