半轮属线虫3个新记录种的描述

从中国各地2773份植物根际土壤线虫标本中鉴定出半轮属线虫5个种 ,描述了其中的3个新记录种 :加利福尼亚半轮线虫(Hemicriconemoidescalifornianus)头部唇盘略突出 ,尾圆锥形 ,尾末端钝圆 ,尾端双层体鞘分离充分 ,口针较短 (72～78μm) ,V=90.2%～94.2% ;拟台湾半轮线虫(H.parataiwanensis)头部唇盘突出 ,头环2条后翻 ,尾圆锥形 ,尾端急剧缢缩 ,末端钝尖且环纹不清 ,口针较长 (76～80μm) ,V=89%～90.3% ;变环半轮线虫(H.varionodus)头部平截 ,唇区不突出 ,尾圆锥形、末端逐渐钝尖 ,双体鞘分离不充分 ,口针相对最长 (78～88μm) ,V=81.4%～91.5%。

半轮线虫属新种——拟中华半轮线虫 Hemicriconemoides parasinensissp.nov.的描述

拟中华半轮线虫新种 (Hemicriconemoidesparasinensissp .nov.)模式标本采集于辽宁省沈阳市沈阳农业大学校园的丁香 (Sy ringaoblata)根际土中 ,在河南省安阳市安阳公园的小叶女贞 (Ligustrumquihoui)根际土中也有分布。主要鉴别特征是虫体头区圆形 ,头环 2个 ,第 1头环略小于或等于第 2头环 ,排泄孔位于肠的前端 (Rex=2 9～ 33) ,体长中等 ,口针中等 (76～ 86 μm) ,体环数R值中等 (96～ 110 ) ,卵巢单生前伸 ,受精囊长圆形 ,尾部宽圆锥形、尾端半球形圆 ;幼虫具指状的棘片 ,约 12～ 16排 ,后翻 ;雄虫未见。该新种虫体形态特征与中国半轮线虫 (H .sinensisVovlas,1988) ,芒果半轮线虫 (H .mangiferaeSiddiqi,196 1)和微小半轮线虫(H .minutusEsser,196 0 )

Microstructure and mechanical properties of A356 aluminum alloy wheels prepared by thixo-forging combined with a low superheat casting process

The A356 aluminum alloy wheels were prepared by thixo-forging combined with a low superheat casting process. The as-cast microstructure, microstructure evolution during reheating and the mechanical properties of the thixo-forged A356 aluminum alloy wheels were investigated. The results show that the A356 aluminum alloy billet with fine, uniform and non-dendritic grains can be obtained when the melt is cast at 635 ℃. When the billet is reheated at 600 ℃ for 60 min, the non-dendritic grains are changed into spherical ones and the billet can be easily thixo-forged into wheels. The tensile strength and elongation of thixo-forged wheels with T6 heat treatment are 327.6 MPa and 7.8%, respectively, which are higher than those of a cast wheel. It is suggested that the thixo-forging combined with the low superheat casting process is an effective technique to produce aluminum alloy wheels with high mechanical properties.