Effects of sand-fixing and windbreak forests on wind flow: a synthesis of results from field experiments and numerical simulations

Sand-fixing and windbreak forests are widely used to protect or/and improve the ecological environments in arid and semi-arid regions. A full understanding of wind flow characteristics is essential to arranging the patterns of these protective forests for enhancing the effectiveness. In this study, the wind velocity over the underlying surface with sand-fixing forests and windbreak forests at the heights of 1–49 m was monitored from two 50-m high observation towers in an oasis of Minqin, Gansu Province of China. The wind velocities were simulated at different locations over these protective forests between those two towers by a two-dimensional Computational Fluid Dynamics(CFD) model. The results showed that at the heights of 1–49 m, the wind velocity profiles followed a classical logarithm law at the edge of the oasis and a multilayer structure inside the oasis. With increasing number of sand-fixing forest and windbreak forest arrays, the wind velocity at the heights of 1–49 m generally decreased along the downstream direction of the prevailing wind. Specifically, below the height of windbreak forests, the wind velocity decelerates as the airflow approaches to the windbreak forests and then accelerates as the airflow passes over the windbreak forests. In contrast, above the height of windbreak forests, the wind velocity accelerates as the airflow approaches to the windbreak forests and then generally decelerates as the airflow passes over the windbreak forests. Both the array number and array spacing of sand-fixing and windbreak forests could influence the wind velocity. The wind protection effects of sand-fixing forests were closely related to the array spacing of windbreak forests and increased with the addition of sand-fixing forests when the array of the forests was adequately spaced. However, if the array spacing of windbreak forests was smaller than seven times of the heights of windbreak forests, the effects were reduced or completely masked by the effects of windbreak forests. The results could offer theoretical guidelines on how to systematically arrange the patterns of sand-fixing and windbreak forests for preventing wind erosion in the most convenient and the cheapest ways.     

乙二醇二甲基丙烯酸酯原位聚合对杨木力学性能的改善1）

选用具有不饱和双端基的乙二醇二甲基丙烯酸酯（ EGDMA）作为改性剂,通过其在杨木多孔细胞腔结构中的原位聚合对木材的力学性能进行改良,以期赋予杨木高附加值用途。 SEM观察和FTIR分析表明,EGD-MA单体在木材细胞腔中原位聚合成聚合物,并均匀填充细胞腔;EGDMA聚合形成的聚合物冲击断面呈韧性断裂状态。 EGDMA聚合制得的木材—聚合物复合材料的冲击韧性、顺纹抗压强度、弹性模量、硬度分别较杨木未处理材提高了137％、60％、78％和147％。     

北方玉米产区玉米鞘腐病菌鉴定及其所产毒素测定

<正>玉米是我国重要的粮食作物，由不同种类镰孢菌Fusarium spp.引起的不同病害在玉米产区普遍发生。镰孢菌病害不仅直接造成玉米减产，而且其病原菌在寄主代谢过程中分泌毒素污染玉米籽粒从而带来安全隐患。2019年调查发现辽宁省玉米鞘腐病又有加重迹象，分离发现其病原菌与层出镰孢菌F. proliferatum不同，疑似禾谷镰孢菌复合种F. graminearum species complex（秦子惠等，2014）。     

实验红鲫线粒体DNA条形码特征分析及应用

为探索建立具有实验红鲫品系特异性的线粒体DNA条形码,对鲫属品种进行鉴定.本研究以实验红鲫和鲫属其他鱼类(洞庭湖鲫、日本白鲫、大眼鲫、兰氏鲫、金鱼、湘军金鱼和湘军花鲫)为测试群体,利用Sanger测序对所有个体的线粒体COⅠ、COⅢ、Cytb这3个基因和D-loop进行测序,同时构建3个基因的拼接序列,并分析它们的序列...