Comparative study of microstructural remodification to porous β-TCP and HA in rabbits

To assess the remolding ability of repaired bone in hydroxyapatite （HA） and β-calcium phosphate （β-TCP） scaffold, two 75% porosity bioceramics with the same three-dimensional geometry were implanted into femoral condyles of rabbits. Histological and micro-computed tomography （micro-CT） results demonstrated abundant new bone formation in the porous HA scaffold along with indistinctive scaffold degradation. Results also indicated that scaffold resorption in the β-TCP group, which was followed by a replacement with newly formed bone, was significantly higher than that in the HA group. The crosslinking trabeculae remodeled from the mixtures of the newly formed bone and β-TCP scaffold remnants might be helpful to promoting even loading and reducing stress. The bone remodeling pattern resulted from bone formation and scaffold resorption was significantly different for the two bioceramics. The results demonstrated that the 75% porous β-TCP was more suitable for new bone remodification than HA scaffold.     

不同生源地大学生的抗生素认知及使用行为调查

目的:为了解不同生源地大学生对抗生素相关知识了解程度及其使用行为差别,为今后更好地进行抗生素管理和预防抗生素的滥用情况提供参考.方法:采用分层、整群抽样相结合的方法随机对西北民族大学不同生源地的学生进行抗生素相关知识问卷调查.结果:在对抗生素的了解和认知方面,城市、城镇的大学生正确认识比例明显高于农村生源地的大学生(p<0.05),但在对抗生素的使用行为调查中,农村生源地大学生正确使用比例明显高于城市、城镇大学生(p<0.05).结论:不同生源地大学生在对抗生素的认知和使用行为两方面情况不同,总体说明大学生对抗生素相关知识的了解还比较匮乏,应针对各自特点加强相关知识宣传,正确干预,以促进大学生对抗生素的正确认识和使用.     

人误率预测技术方法的几个问题及应用时的建议

本文首先提出ＴＨＥＲＰ方法几个值得注意的问题：人误概率遵从对数正态分布假定的欠合理性、ＴＨＥＲＰ方法中设计出的条件人误概率不确定性边界的计算缺乏连贯性等．针对这些问题,提出了修正建议——假定人误概率Ｐ遵从贝塔分布,并阐述了这一建议的理由．但为了尽量保持ＴＨＥＲＰ方法定量分析的体系及便于计算,最终建议依实际分析的情况交替使用人误概率遵从贝塔分布和对数正态分布的假定并具体给出了实施方法     

Aluminium in Alzheimer’s disease: are we still at a crossroad?

Aluminium, an environmentally abundant non-redox trivalent cation has long been implicated in the pathogenesis of Alzheimers disease (AD). However, the definite mechanism of aluminium toxicity in AD is not known. Evidence suggests that trace metal homeostasis plays a crucial role in the normal functioning of the brain, and any disturbance in it can exacerbate events associated with AD. The present paper reviews the scientific literature linking aluminium with AD. The focus is on aluminium levels in brain, region-specific and subcellular distribution, its relation to neurofibrillary tangles, amyloid beta, and other metals. A detailed mechanism of the role of aluminium in oxidative stress and cell death is highlighted. The importance of complex speciation chemistry of aluminium in relation to biology has been emphasized. The debatable role of aluminium in AD and the cross-talk between aluminium and genetic susceptibility are also discussed. Finally, it is concluded based on extensive literature that the neurotoxic effects of aluminium are beyond any doubt, and aluminium as a factor in AD cannot be discarded. However, whether aluminium is a sole factor in AD and whether it is a factor in all AD cases still needs to be understood.Received 22 July 2004; received after revision 3 September 2004; accepted 16 September 2004     

Wnt signaling: multiple functions in neural development

Wnt signaling has proven to be essential for neural development at various stages and across species. Wnts are involved in morphogenesis and patterning, and their proliferation-promoting role is a key function in stem cell maintenance and the expansion of progenitor pools. Moreover, Wnt signaling is involved in differentiation processes and lineage decision events during both central and peripheral nervous system development. Additionally, several reports point to a role of Wnt signaling in axon guidance and neurite outgrowth. This article reviews and consolidates the existing evidence for the functions of Wnt signaling in neural development.Received 10 December 2004; received after revision 19 January 2005; accepted 21 January 2005     

Human and rodent type 1 11β-hydroxysteroid dehydrogenases are 7β-hydroxycholesterol dehydrogenases involved in oxysterol metabolism

Interconversion between cortisone and the glucocorticoid receptor ligand cortisol is carried out by 11-hydroxysteroid dehydrogenase (11-HSD)isozymes and constitutes a medically important example of pre-receptor control of steroid hormones. The enzyme 11-HSD type 1 (11-HSD1) catalyzes the conversion of cortisone to its active receptor-binding derivative cortisol, whereas 11-HSD type 2 performs the reverse reaction. Specific inhibitors against the type 1 enzyme lower intracellular levels of glucocorticoid hormone, with an important clinical application in insulin resistance and other metabolic disorders. We report here on the in vitro oxysterol-metabolizing properties of human and rodent 11-HSD1. The enzyme, either as full-length, membrane-attached, or as a transmembrane domain-deleted, soluble form, mediates exclusively conversion between 7-ketocholesterol and 7-hydroxycholesterol with similar k_cat values as observed with glucocorticoid hormones. Thus, human, rat, and mouse 11-HSD1 have dual enzyme activities like the recently described 7-hydroxysteroid dehydrogenase/11-hydroxysteroid dehydrogenase from hamster liver, but differ fundamentally from the latter in that 7-OH rather than 7-OH dehydrogenase constitutes the second activity. These results demonstrate an enzymatic origin of species differences in 7-oxysterol metabolism, establish the origin of endogenous 7-OH cholesterol in humans, and point to a possible involvement of 11-HSD1 in atherosclerosis.Received 30 December 2003; received after revision 16 February 2004; accepted 16 February 2004     

林肯链霉菌原生质体形成、再生和融合的研究

林肯链霉菌生长在0.5%甘氨酸的S培养基中,能较好地被溶菌酶破壁形成原生质体。原生质体能在RB培养基上再生,但不能在R_2培养基上再生,这和已报道过的其他链霉菌不同。78-11菌株的再生频率约为25.7%,S-3菌株的再生频率约为20.5%。PEG(聚乙二醇)1000对诱导融合的效果较好,重组频率最高可达10~(-2)。重组子和亲本在培养特性、孢子形态方面无特殊差异,但经C_O~(60)诱变后重组子的正变率超过亲本。     

Market timing using combined forecasts and machine learning

Successful market timing strategies depend on superior forecasting ability. We use a sentiment index model, a kitchen sink logistic regression model, and a machine learning model (least absolute shrinkage and selection operator, LASSO) to forecast 1‐month‐ahead S&P 500 Index returns. In order to determine how successful each strategy is at forecasting the market direction, a “beta optimization” strategy is implemented. We find that the LASSO model outperforms the other models with consistently higher annual returns and lower monthly drawdowns.     

碳纤维阴极电化学还原氯霉素的效能与机理

以CAP为对象,利用碳纤维阴极研究电化学还原氯霉素的效能与机制。重点探究电流密度、pH、CAP初始浓度、电解质浓度和种类对CAP降解效果、TOC去除率和脱氯效果等影响,研究表明电流密度和电解质种类对CAP的降解效果影响较大,阴极还原的最佳反应条件为：电流密度40 mA·cm^-2、CAP初始质量浓度10 mg·L^-1、Na₂SO₄浓度0.02 mol·L^-1。通过循环伏安法研究发现CAP在电极表面发生直接还原与间接还原,三维荧光测试结果表明反应后水中有机物含量仍较高。利用超高效液相-四极杆飞行时间质谱对中间产物进行检测并分析CAP在阴极降解的机理,还原后的产物主要为毒性较低的芳香胺物质。电化学处理CAP主要通过脱氯还原得到毒性较低的物质,从而降低了后续处理过程产生有毒物质的风险,研究结果为电化学还原去除水中抗生素的应用提供了相关探索和技术支撑。     

土壤放线菌分离及无抗菌活性株的激活

从广州的稻田土里分离出三支菌，其中一株（２０号）产生的抗生物质不仅可抑制多种细菌，而且也可抑制白色念珠菌，经初步鉴定为诺卡氏菌属放线菌；另外两支为天然无抗生活性的放线菌，属拟诺卡氏菌。对两株无活性的菌进行紫外照射，然后用四环素和盐酸羟胺复合诱变，经初筛后发现三支激活株，其中一支产生了较明显的抗真菌活力。最后对激活株和２０号菌所产生的抗生物质进行初步研究，证明可能是一种非多烯大环内酯类抗真菌抗生素。实验结果表明这几支天然无活性的供试菌中均含有可被激活的沉默基因，这些基因和抗生素合成有关。