铜-锰-锌-硅钎料的研制

研制成功的钎料适合用于钢件和硬质合金等材料的钎焊,文中阐述了钎料合金体系选择及各组元配比拟定的理论依据,以此钎料钎焊接头的强度远高于黄铜钎料钎焊接头的强度,具有特高的抗冲击性能,而合金的轧制性能亦良好;由于这种钎料的熔化温度较低(825.5℃～831.5℃),所以能降低钎焊温度,减少钎焊能耗。钎焊时工件钎焊应力和焊件变形降低,钎焊接头有较细的晶粒组织,提高了产品的质量;同时,钎料的熔化温度较低和含锌量较低,使钎焊时环境污染得到改善。     

Minority populations in the child welfare system: the visibility hypothesis reexamined

The high thrombogenicity of synthetic biomaterials has limited their use for reconstructive microsurgery. Prime factors in the thrombogenicity of synthetic materials in contact with blood include gas nuclei at the blood gas interface as well as the inherent thrombogenicity of the materials themselves. Expanded polytetrafluoroethylene (ePTFE) vascular prostheses were denucleated by placement in acetone and ethanol followed by degassed saline or by placement in degassed saline subjected to hydrostatic pressure. Heparinized grafts were prepared by coating with tridodecylmethylammonium chloride (TDMAC), followed by immersion in heparin. Grafts were installed to reconstruct the femoral artery (1 x 10 mm) or as renal-iliac bypasses (1 x 50 mm) in rats. In the femoral artery reconstruction model, control grafts thrombosed within 10 minutes of implantation. All acetone denucleated femoral grafts remained patent for 60 minutes but were occluded at day 1. All pressure denucleated femoral grafts remained patent for 60 minutes, whereas six were patent at 1 month. In contrast, 11 of 15 heparinized femoral grafts were patent at 1 month. In the renal iliac bypass model, all control grafts were thrombosed within 10 minutes, whereas all heparin bonded grafts remained patent at 1 month. This finding confirms that removal of air from small diameter ePTFE grafts decreases acute thrombogenicity and that heparin bonding further decreases thrombogenicity, suggesting that clinically useful lengths of microvascular prostheses may be possible.