具有抗裂柱墙体的抗温度应力分析

在墙体中增设抗裂柱可以提高墙体的抗剪能力 ,并且抗裂柱应尽可能布置在房屋结构的两端部分的墙体内 .当墙段中有 2根以上抗裂柱 ,且抗裂柱间距较小时 ,在抗裂柱间距范围内 ,按照框架—砖墙协同工作考虑墙体的抗剪能力 .对典型墙体抗剪能力分析表明 ,抗裂柱间距减小 ,在抗裂柱范围内由抗裂柱承担的剪力比例增加 ;抗裂柱及圈梁截面面积增大 ,在抗裂柱范围内由抗裂柱承担的剪力比例增加 ;砖及砂浆的强度等级对抗裂柱范围内抗裂柱及墙体承担的剪力分配影响不大 .

Novel Stilbene Glycosides from Polygonum multiflorum

Two new stilbene glycosides (1 and 2), together with nine known compounds (3-11), were isolated from the water extract of Polygonum multiflorum Thunb. The structures of the new compounds were elucidated by their chemical properties and spectroscopic analyses, including extensive 2D NMR experiments. Compound 2 showed strong DNA cleavage activity, and compounds 1, 2 and 10 (2, 3, 4′, 5_tetrahydroxy_ trans _stilbene_2_O_β_ D _glucopyranoside) exhibited significant inhibition of lipid peroxidation.

Tumor suppressor protein C53 antagonizes checkpoint kinases to promote cyclin-dependent kinase 1 activation

Cyclin-dependent kinase 1 （Cdkl）/cyclin B1 complex is the driving force for mitotic entry, and its activation is tightly regulated by the G2/M checkpoint. We originally reported that a novel protein C53 （also known as Cdk5rap3 and LZAP） potentiates DNA damage-induced cell death by modulating the G2/M checkpoint. More recently, Wang et al. （2007） found that C53/LZAP may function as a tumor suppressor by way of inhibiting NF-kB signaling. We re- port here the identification of C53 protein as a novel regulator of Cdkl activation. We found that knockdown of C53 protein causes delayed Cdkl activation and mitotic entry. During DNA damage response, activation of checkpoint kinase 1 and 2 （Chkl and Chk2） is partially inhibited by C53 overexpression. Intriguingly, we found that C53 inter- acts with Chkl and antagonizes its function. Moreover, a portion of C53 protein is localized at the centrosome, and centrosome-targeting C53 potently promotes local Cdkl activation. Taken together, our results strongly suggest that C53 is a novel negative regulator of checkpoint response. By counteracting Chkl, C53 promotes Cdkl activation and mitotic entry in both unperturbed cell-cycle progression and DNA damage response.

Antioxidant activity of alcohol aqueous extracts of Crypthecodinium cohnii and Schizochytrium sp.

Crypthecodinium cohnii(dinoflagellate) and Schizochytrium sp.(thraustochytrid) are the main sources for docosahexaenoic acid(DHA). The present study aimed to evaluate the antioxidant activity of petroleum ether, ethyl acetate, n-butanol, and water fractions of alcohol aqueous extracts of these two microalgae and to provide a theoretical basis for comprehensive utilization. The antioxidant activity was determined by total antioxidant capacity(TAC) determination, 2,2-diphenyl-1-picrylhydrazyl(DPPH) radical scavenging assay, ferrous ion-chelating ability(FICA) assay, and reducing power(RP) assay. The total phenolic content(TPC) and total flavonoid content(TFC) were also measured by the Folin-Ciocalteu and spectrophotometry methods, respectively. The results indicated that the extracts from these two microalgae possessed good antioxidant capacity. Analysis showed that most antioxidant performance indicators(TAC, DPPH, and RP) were positively correlated with the TPC of the extracts, suggesting that the phenolics might be the major components in C. cohnii and Schizochytrium sp., contributing to their antioxidative function. Therefore, the polar fractions of C. cohnii and Schizochytrium sp. could be further examined and considered for application in health products or cosmetics.

Antioxidants in aqueous extract of Myristica fragrans(Houtt.) suppress mitosis and cyclophosphamide-induced chromosomal aberrations in Allium cepa L.cells

In this study, freeze-dried water extract from the leaves of Myristica fragrans （Houtt.） was tested for mutagenic and antimutagenic potentials using the Allium cepa assay. Freeze-dried water extract alone and its combination with cyclophosphamide （CP） （50 mg/kg） were separately dissolved in tap water at 500, 1000, 2000, and 4000 mg/kg. Onions （A. cepa） were suspended in the solutions and controls for 48 h in the dark. Root tips were prepared for microscopic evaluation. 2,2-Diphenyl-l-picrylhydrazyl （DPPH） free radicals＇ scavenging power of the extract was tested using butylated hydroxyanisole （BHA） and butylated hydroxytoluene （BHT） as standards. Water extract of Myristica fragrans scavenged free radicals better than BHA, but worse than BHT. The extract alone, as well as in combination with CP suppressed cell division, and induced chromosomal aberrations that were insignificantly different from the negative control （P≤0.05）. However, cytotoxic and mutagenic actions of CP were considerably suppressed. The observed effects on cell division and chromosomes of A. cepa may be principally connected to the antioxidant properties of the extract. The obtained results suggest mitodepressive and antimutagenic potentials of water extract of the leaves of M. fragrans as desirable properties of a promising anticancer agent.

Improving the thermal shock resistance of ceramics by crack arrest blocks

Ceramics used in the high temperature environment are inevitably subjected to sudden temperature change, which may lead to catastrophic thermal shock failure due to the intrinsic brittleness of ceramics. In this paper, an experimental platform is designed to realize the in-situ observation during the thermal shock experiments. Experimental results show that all the cracks initiate from one of the edge midpoints and propagate to another one for square specimens. Such experimental observation is consistent with the maximum tensile stress zone with the maximum temperature gradient given by the finite element method(FEM). The different crack modes resulting from different heating rates after thermal shock experiments are observed and analyzed. Comparison between different clamping methods is conducted to study the effects of boundary conditions on the thermal shock experiments. Furthermore, in order to improve the thermal shock performance of alumina ceramics, crack arrest blocks are added near the edge midpoint. The thickness, shape and arrangement of the blocks are systematically investigated to understand the mechanism of improvement of thermal shock resistance.