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1.
As no single classification method outperforms other classification methods under all circumstances, decision-makers may solve a classification problem using several classification methods and examine their performance for classification purposes in the learning set. Based on this performance, better classification methods might be adopted and poor methods might be avoided. However, which single classification method is the best to predict the classification of new observations is still not clear, especially when some methods offer similar classification performance in the learning set. In this article we present various regression and classical methods, which combine several classification methods to predict the classification of new observations. The quality of the combined classifiers is examined on some real data. Nonparametric regression is the best method of combining classifiers.  相似文献   
2.
针对磷酸酯/Al3+ 交联的油基压裂液交联速度慢,交联剂溶解性慢、稳定性差和价格高等缺点,首次对磷酸酯/Fe3+ 交联的油基压裂液体系进行了研究。通过对铁交联剂体系的优化,筛选一种磷酸酯/Fe3+ 交联的新型交联剂体系,并对磷酸酯/Fe3+ 油基冻胶压裂液性能进行了评价。结果表明:采用30%Fe2(SO4)3+15% 二乙醇胺+55% 水制备的新型交联剂体系,直接与磷酸酯混合即可形成油基冻胶,其性能不受放置时间的影响,交联速度快,成胶性能好,10 min 就可达到最大黏度;压裂液的抗温抗剪切性能高,与常规铝交联剂体系比较,压裂液成胶速度提高了20 倍,压裂液的抗温能力由原来100 ℃提高到135 ℃,并且压裂液的破胶性和滤失性等性能均能达到压裂施工的要求。  相似文献   
3.

Background

Meconium stained amniotic fluid commonly occurs postdates (?>40 weeks gestation) indicating fetal maturity. Previous literature indicates that different ethnicities mature at different rates.

Aim

To compare the rate of meconium stained amniotic fluid of Australian-born and non-Australian born women.

Methods

A retrospective correlation study design was implemented, using data collected in the birth outcomes system at one tertiary hospital. Data was collected from all women who gave birth to a term (>/=37 weeks gestation), singleton, liveborn baby between January 1st to December 31st, 2014. Maternal country of birth was used for comparison. Categorical data was analyzed using Chi-Square test for Independence. Continuous variables were assessed for normality, and differences were compared using an Independent t-test or a Mann–Whitney U test. All tests were two-tailed and p < 0.05 was considered statistically significant.

Results

3,041 women were included; 1131 Australian-born and 1910 non-Australian born. Meconium stained amniotic fluid occurred more frequently in non-Australian born women compared to Australian-born women (23.5% vs. 19.8 p = 0.02). Their babies were significantly smaller (Mean = 3265 g, Standard Deviation 463.8 vs Mean = 3442 g, Standard Deviation 499.2, p < 0.001), with no difference in gestational length (Mean = 39.4, Standard Deviation 1.28 vs Mean = 39.5, Standard Deviation 1.18, p = 0.06). Increasing gestational age had the strongest association with meconium stained amniotic fluid;?>/=42 weeks gestation occurring 3.52 (95% Confidence Interval: 2.00, 6.22, p = <0.001) more than <40 weeks gestation.

Conclusion

Maternity health services should record ethnicity and region of birth to provide individualised care as women born overseas often have poorer perinatal outcomes when compared to Australian-born women.  相似文献   
4.
5.
Researchers have documented the consequences of relationship instability for parenting stress but have given little attention to within‐partner relationship instability. In this study, the authors used data from the Fragile Families and Child Wellbeing Study (N = 3,544) to estimate the association between within‐partner relationship instability (known as churning or on‐again/off‐again relationships) and parenting stress. First, they found that by the focal child's 5th birthday about 16% of biological parents experience churning. Second, compared to being stably together with or stably separated from the child's other parent, churning is associated with greater parenting stress for both mothers and fathers. Because parenting stress is the same or higher among churners compared to their counterparts who stably separate, this suggests that, more than a change in partner, relationship instability—whether within or across relationships—is tied to parenting stress.  相似文献   
6.
以一座三塔悬索桥为分析对象,采用SAP2000平台建立该桥空间动力有限元模型并进行非线性动力分析,研究了地震作用下,缆梁间设置中央扣、中塔与主梁间设置弹性索和二者组合使用对于该桥抗震性能的影响。分析结果表明,缆梁间设置中央扣可以显著减小主梁位移和中塔塔底剪力和弯矩,但会使各塔顶主索鞍座水平力和边塔内力增加;选用合理的弹性索刚度,可以有效控制主梁位移,同时使中塔与边塔的受力处于合理范围内;两者组合使用,能够进一步降低主梁位移和均衡中塔与边塔的受力,同时可以减小弹性索索力,更有利于中塔下横梁受力。  相似文献   
7.
评价泡沫钻井液性能最关键的参数是其稳定性,通常用泡沫半衰期来衡量。目前应用最为普遍的是常规量筒法测泡沫半衰期。该方法简便易操作,但由于人为原因存在较大误差,而且不能记录到泡沫衰变的中间过程。为克服这一局限,采用了一种评价泡沫稳定性的新方法,即采用近红外扫描分散稳定性扫描仪(MA-2000 TurbiScan)进行泡沫稳定性分析。该方法较先进和精确,完全由电脑控制仪器自动完成,分析结果为两条电脑输出的曲线,从曲线上可清楚地观测到泡沫衰变过程及读出泡沫半衰期。  相似文献   
8.
由于过度捕捞和环境污染,海洋渔业发展面临着资源衰竭、环境受损、生态失衡等一系列问题,海洋渔业生态系统承受着前所未有的压力,如若继续恶化,后果不言而喻。然而,现行的渔业生态保护与管理方式不是可持续发展的,甚至是背道而驰的。海洋渔业可持续发展需要创新的思维。弹性思维提供了理解周围世界和管理自然资源的一种不同方式,提倡用弹性的观念去看待事物的变化,是一种旨在增加系统可持续性的资源管理新方法。弹性思维及其所蕴含的弹性生态观既可以成为海洋渔业可持续发展的有效途径,又可以为海洋渔业生态补偿提供理论支持。  相似文献   
9.
Efforts to improve child survival in lower-income countries typically focus on fundamental factors such as economic resources and infrastructure provision, even though research from post-industrial countries confirms that family instability has important health consequences. We tested the association between maternal union instability and children’s mortality risk in Africa, Latin America and the Caribbean, and Asia using children’s actual experience of mortality (discrete-time probit hazard models) as well as their experience of untreated morbidity (probit regression). Children of divorced/separated mothers experience compromised survival chances, but children of mothers who have never been in a union generally do not. Among children of partnered women, those whose mothers have experienced prior union transitions have a higher mortality risk. Targeting children of mothers who have experienced union instability—regardless of current union status—may augment ongoing efforts to reduce childhood mortality, especially in Africa and Latin America where union transitions are common.  相似文献   
10.
社会领域也存在某种惯性趋势,即社会趋稳性。这一概念的提出旨在说明,一切不稳定的产生,必定是受到某种作用力的结果。而社会趋稳性与变动力量的结合,便会造成不同程度的反作用力。这种反弹行为在实践中很容易被界定为"不稳定因素"。由于维稳的主客体都是人,而"人是需求动物",所以,维稳的具体政策若不能够融入人的思考、理解及感情,将很难实现人际有效的沟通,进而妨碍动态稳定的实现。以组织平衡理论、需求层次理论、安全阀理论及组织学习理论为基础的双回路维稳模型的提出,旨在强调人类需求、基本秩序以及自然法则在维稳中的关键作用。  相似文献   
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