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排序方式: 共有143条查询结果,搜索用时 890 毫秒
41.
以两种不同方法制备VPO催化剂,分别采用超临界流体干燥法(SCFD),常规见干燥法干燥。使用BET,XRD等测试手段,考察了催化剂在400℃下焙烧后的粒子比表面积的大小和晶相组成。实验结果表明:采用超临界流体法比采用常规干燥法所制得催化剂的比表面积明显增加,且对催化剂的晶相组成也有一定的影响。 相似文献
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Fuzzy concepts are introduced into structural optimization to solve fuzzy optimization problems with a crisp objective function and fuzzy constraints, also a non-membership function is used to convert fuzzy constrains into crisp constrains. Two models are discussed where the objective function considered is the volume of space frame and the fuzzy constrains are design limits by the axial strength, slenderness, deflection, thickness and diameter of space frame member. 相似文献
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阐述了双龙湖治理前水体富营养化污染状况及原因,介绍了双龙湖原位修复综合治理措施(如环湖截污、湖底生态清淤、复氧措施、边坡护理、湖滨带生态重建与景观恢复、后期监管等措施)。对原位修复综合治理措施实施后湖水净化效果进行了研究,结果表明:原位修复综合治理措施是治理双龙湖水体富营养化的有效措施,能够为国内外城市湖泊富营养化治理提供方法和技术借鉴。 相似文献
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Kaiser WJ Upton JW Long AB Livingston-Rosanoff D Daley-Bauer LP Hakem R Caspary T Mocarski ES 《Nature》2011,471(7338):368-372
Apoptosis and necroptosis are complementary pathways controlled by common signalling adaptors, kinases and proteases; among these, caspase-8 (Casp8) is critical for death receptor-induced apoptosis. This caspase has also been implicated in non-apoptotic pathways that regulate Fas-associated via death domain (FADD)-dependent signalling and other less defined biological processes as diverse as innate immune signalling and myeloid or lymphoid differentiation patterns. Casp8 suppresses RIP3-RIP1 (also known as RIPK3-RIPK1) kinase complex-dependent necroptosis that follows death receptor activation as well as a RIP3-dependent, RIP1-independent necrotic pathway that has emerged as a host defence mechanism against murine cytomegalovirus. Disruption of Casp8 expression leads to embryonic lethality in mice between embryonic days 10.5 and 11.5 (ref. 7). Thus, Casp8 may naturally hold alternative RIP3-dependent death pathways in check in addition to promoting apoptosis. We find that RIP3 is responsible for the mid-gestational death of Casp8-deficient embryos. Remarkably, Casp8(-/-)Rip3(-/-) double mutant mice are viable and mature into fertile adults with a full immune complement of myeloid and lymphoid cell types. These mice seem immunocompetent but develop lymphadenopathy by four months of age marked by accumulation of abnormal T cells in the periphery, a phenotype reminiscent of mice with Fas-deficiency (lpr/lpr; also known as Fas). Thus, Casp8 contributes to homeostatic control in the adult immune system; however, RIP3 and Casp8 are together completely dispensable for mammalian development. 相似文献
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Gram-negative bacteria, such as Escherichia coli, expel toxic chemicals through tripartite efflux pumps that span both the inner and outer membrane. The three parts are an inner membrane, substrate-binding transporter; a membrane fusion protein; and an outer-membrane-anchored channel. The fusion protein connects the transporter to the channel within the periplasmic space. A crystallographic model of this tripartite efflux complex has been unavailable because co-crystallization of the various components of the system has proven to be extremely difficult. We previously described the crystal structures of both the inner membrane transporter CusA and the membrane fusion protein CusB of the CusCBA efflux system of E. coli. Here we report the co-crystal structure of the CusBA efflux complex, showing that the transporter (or pump) CusA, which is present as a trimer, interacts with six CusB protomers and that the periplasmic domain of CusA is involved in these interactions. The six CusB molecules seem to form a continuous channel. The affinity of the CusA and CusB interaction was found to be in the micromolar range. Finally, we have predicted a three-dimensional structure for the trimeric CusC outer membrane channel and developed a model of the tripartite efflux assemblage. This CusC(3)-CusB(6)-CusA(3) model shows a 750-kilodalton efflux complex that spans the entire bacterial cell envelope and exports Cu I and Ag I ions. 相似文献
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Haixia Long Bing Liu Bing Hou Chao Wang Keith M. Kendrick Chunshui Yu Tianzi Jiang 《科学通报(英文版)》2014,59(13):1355-1361
The serotonin-transporter-linked polymorphic region (5-HTTLPR) is associated with mood disorders. This association is thought to be due to amygdala hyper- responsiveness to negative emotional stimuli as a result of reduced frontal cortical control. In Caucasians, the short form is associated with this effect, but in Han Chinese we recently found that the long form is involved. Serotonin receptors have rich expression in default mode network (DMN) regions and the recent studies have found an association between the short form of the 5-HTTLPR and DMN functional connectivity (FC) in Caucasians. The present study has investigated whether there may also be an ethnic difference in this influence of 5-HTTLPR on the DMN. We recruited 233 young Han Chinese subjects and calculated the resting-state default-network FC. Our study found that the L carriers had decreased FC in the bilateral medial prefrontal cortex, right parahippocampal gyrus, left middle temporal gyrus, and increased FC in left precuneus (Pcu) compared to SS. The PCC-Pcu FC in L carriers was significantly negatively correlated with the depression scores. Our findings, therefore, suggest that there is also a difference between Caucasian and Han Chinese subjects in the association between the different forms of the 5-HTTLPR and DMN functional connectivity. 相似文献