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在工作流中应用访问控制,数据在工作流中流动,执行操作的用户在改变,用户的权限也在改变,这与数据处理的上下文环境相关。采用传统的访问控制技术,如DAC,MAC,则难以做到这一点,若采用RBAC,也需要频繁地更换角色,且不适合工作流程的运转。文章在契约式的安全业务流程设计的基础上,利用泳道,建立基于泳道的安全工作流的访问控制模型。 相似文献
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从力学性能、防护结构应用研究、吸能机理三个方面综述了聚脲弹性体在爆炸防护中的研究进展。聚脲弹性体的静/动态力学性能优异,断裂伸长率高、应变率效应强,在增强墙体、金属及复合材料等多种防护结构抗冲击性能方面的研究取得了重要进展,获得了一些规律性认识,包括聚脲弹性体在防护结构中的位置、质量比重等因素对抗爆性能的影响以及聚脲弹性体在墙体、金属、复合材料等不同结构中增强抗爆性能的机理。分析认为聚脲弹性体在爆炸防护中具有很大的应用潜力,指出未来需进一步研究聚脲弹性体的本构关系、影响聚脲弹性体抗爆性能的因素、防护结构尺寸效应与聚脲弹性体的微观吸能机理。 相似文献
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以废蚕茧为原料,通过Na2CO3脱胶、溶解、透析、冷冻干燥后得到丝素蛋白粉末。用蒸馏水溶解后,分别采用碱性蛋白酶(alcalase)、木瓜蛋白酶(papain)水解丝素蛋白,85℃将酶灭活,得到丝素肽溶液。采用反相高效液相色谱仪对10种丝素肽组分进行分析,并研究丝素肽对大肠杆菌(Escherichia coli)及金黄色葡萄球菌(Staphylococcus aureus)的抗菌效果,以及对人胚肾细胞(HEK293)的毒性。发现P1、A2、A4、A1丝素肽对大肠杆菌生长有抑制作用,P1、P2、P3丝素肽对金黄色葡萄球菌生长有抑制作用,具有抑菌作用的这6种丝素肽对HEK293细胞增殖没有毒性,且A1、A2、A4、P2丝素肽对HEK293细胞存活具有促进作用,为今后丝素肽的产品开发、生产及应用奠定一定的理论基础。 相似文献
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Acoustic-frequency induction melting together with rapid quenching was used to prepare Mg65Cu25Y10 bulk amorphous alloy containing primary crystalline phases. Transmission electron microscopy (TEM), X-ray diffractometry (XRD), environmental scanning electron microscopy (ESEM) and atomic force microscopy (AFM) were used to study the amorphization and morphology of the prepared alloy. Under micro condition, the sample alloy is composed of amorphous structure with cauliflorate shape, primary CuMg2 dendrite phase, mixed primary CuMg2 and Cu2Y crystalline phases, as well as Mg phase with small size. Further study under sub-micro condition shows that, the planar amorphous structure of cauliflorate shape is composed of the three-dimensional sub-micro morphology of "bulge-concavity" pattern, which extends into the space in terms of certain period. It is estimated that the major factors influencing the micro and sub-micro morphologies of amorphous alloy are its super-cooling liquid structure, rapid quenching transformation, as well as the melting conditions. 相似文献
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用喷射成形法制备了Fe73.5Cu1Nb3Si13.5B9(at%)的铁基非晶合金,目的在于研究非晶相的形成机理及其在高速冷却条件下生成特定的微观结构。喷射成形气流中,G/M为0.15,雾化气体为氮气。所得到的沉积体和过喷粉末的粒径在5μm左右,总重约2.2kg。借助X射线衍射(XRD)、光学显微镜(OM)以及透射电镜(TEM)等分析方法研究了沉积体的微观组织结构。发现随着厚度的改变,其成分、结构也有所变化,体现在中心区域厚度15mm和边缘区域厚度8mm的孔隙率分别为4%和9%。中心较厚区域为晶粒尺寸250nm左右的完全晶化相,而边缘较薄区域则有部分非晶相,其晶粒尺寸在40nm。由XRD谱线分析,过喷粉末为完全晶化相,用谢利方程(Scherrer formula)分析得到其晶粒在80nm左右。通过VSM分析,其软磁性能很差,饱和磁感只有0.3~0.6T,同时矫顽力上升得很快。 相似文献
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In order to study high-frequency soft magnetic properties of Finemet amorphous alloy, the microstructural change and nanocrystallization under different heat treatment conditions were investigated by XRD and TEM. The crystallite size of α-Fe was calculated from the XRD pattern using the Scherrer formula, while the high frequency magnetic properties were measured at room temperature by TPS-200SA exchange tester. The results of XRD and TEM indicate that the nanocrystallization occurs at 500 ℃. When the annealing temperature increases to 560 ℃, the amorphous alloy becomes totally nanocrystallized and the crystallites distribute homogeneously, thus an excellent combination of soft magnetic properties is obtained. 相似文献
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