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991.
Guyll Max; Spoth Richard L.; Chao Wei; Wickrama K. A. S.; Russell Daniel 《Canadian Metallurgical Quarterly》2004,18(2):293
Four years of longitudinal data from 373 families participating in a randomized intervention-control clinical trial were used to examine whether intervention effects on adolescent alcohol and tobacco use trajectories were moderated by family risk, as defined by parental social emotional maladjustment. Consistent with earlier outcome evaluations based on analyses of covariance, analyses confirmed that both the Preparing for the Drug Free Years program and the Iowa Strengthening Families Program favorably influenced alcohol use index trajectories across the time frame of the study; only the latter program, however, evidenced positive effects on a tobacco use index. Concerning the primary research question, analyses provided no support for family risk moderation of any intervention effect. Findings indicate the feasibility of developing universal preventive interventions that offer comparable benefits to all families. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
992.
基于知识发现和决策规则的遥感图像城区土地覆盖/利用分类方法 总被引:5,自引:0,他引:5
李朝峰 《计算机工程与应用》2004,40(23):212-215
提出一种利用地类的色度信息、小波提取纹理特征、植被指数及形状知识等采用规则推理有效识别遥感土地类别的方法。采用知识发现和决策规则方法,可以充分吸收遥感专家的思想和工作经验,可以充分利用多种模糊性地学知识来提高遥感影像分类效果。最后通过实例证明了该方法的有效性。 相似文献
993.
一种P2P系统索引结构生成算法 总被引:2,自引:0,他引:2
论文分析了P2P系统的基本概念,研究了现有P2P系统由于缺乏分布式索引结构而产生不足的现状。从而提出了基于虚拟二叉键树的分布式索引模型及其构建算法。利用虚拟二叉键树可以把信息分散存放在各个节点上,并通过路由算法迅速有效地找到存放在其它节点上的信息。同时,建立索引的过程是节点间自发进行的,不需要中心服务器的支持。 相似文献
994.
舒栋才 《计算机工程与应用》2004,40(15):226-229
针对公司债券财务质量评级问题,采用投影寻踪聚类(PPC)模型,将多维数据指标转换到低维子空间,并利用免疫进化算法(IEA)优化其投影方向,根据投影函数值的大小评价出样本的优劣,从而做出决策。应用表明,该方法能利用一个综合反映多因素之间复杂关系的特征指标给出客观而直接的评价结果,且根据计算结果还可以分析各个指标对综合评价结果的影响程度,为公司债券财务质量评级提供了一种计算过程简单、直观的新方法。 相似文献
995.
Wavelet transform applied to EO-1 hyperspectral data for forest LAI and crown closure mapping 总被引:9,自引:0,他引:9
A comparison of the performance of three feature extraction methods was made for mapping forest crown closure (CC) and leaf area index (LAI) with EO-1 Hyperion data. The methods are band selection (SB), principal component analysis (PCA) and wavelet transform (WT). Hyperion data were acquired on October 9, 2001. A total of 38 field measurements of CC and LAI were collected on August 10-11, 2001, at Blodgett Forest Research Station, University of California at Berkeley, USA. The analysis method consists of (1) conducting atmospheric correction with High Accuracy Atmospheric Correction for Hyperspectral Data (HATCH) to retrieve surface reflectance, (2) extracting features with the three methods: SB, PCA and WT, (3) establishing multivariate regression prediction models, (4) predicting and mapping pixel-based CC and LAI values, and (5) validating the CC and LAI mapped results with photo-interpreted CC and LAI values. The experimental results indicate that the energy features extracted by the WT method are the most effective for mapping forest CC and LAI (mapped accuracy (MA) for CC=84.90%, LAI MA=75.39%), followed by the PCA method (CC MA=77.42%, LAI MA=52.36%). The SB method performed the worst (CC MA=57.77%, LAI MA=50.87%). 相似文献
996.
Sensitivity of spectral reflectance to variation in live fuel moisture content at leaf and canopy level 总被引:1,自引:0,他引:1
Wildland fires burn large areas of the earth's land surface annually, causing significant environmental damage and danger to human health. In order to mitigate the effects, and to better manage the incidence of such fires, fire behaviour models are used to predict, among other things, the likelihood of ignition, the rate of spread, and the intensity and duration of burning. A key input parameter to these models is the amount of water in the vegetation, described as the fuel moisture content (FMC). A number of studies have shown that vegetation indices (VI) calculated from red and NIR reflectances may be used to map spatial and temporal variation in FMC in a range of fire-prone environments, with varying degrees of success. Strong empirical relationships may be established between VI and FMC over grasslands, yet over shrublands and forests, the relationships are weaker. If FMC is to be estimated with greater accuracy and consistency than is currently achieved, it is necessary to fully understand the relative contribution that spatial and temporal variation in the various biophysical and geometrical variables make to reflectance variability at the leaf and canopy level.This paper uses a modelling approach to investigate the sensitivity of reflectance data at leaf and canopy level to variation in the biophysical variables that are used to compute FMC. At the leaf level, the results show that the sensitivity of reflectance to variation in leaf water and dry matter content, used to compute FMC, is greatest in the SWIR and NIR, respectively. Variation in FMC has no effect in the visible wavelengths. At the canopy level, the results show that the sensitivity of reflectance to variation in leaf water and dry matter content is heavily dependent upon the type of model used and the range of variation over which the variables are tested. In the longer wavelengths of the SWIR, the competing influence of variable leaf area index, fractional vegetation cover, and solar zenith angle is shown to be greater than that at the shorter wavelengths of the SWIR and NIR. Empirical relationships between the normalised difference water index (NDWI) and FMC are shown to be weaker than that with canopy water content. However, when the range of the variables under study is more limited, useful empirical relationships between FMC and remotely sensed VI may be established. 相似文献
997.
菜地选片规划应通过土壤详查和评价工作,选出最适地区,才能经济有效、持续发展。土壤评价中参评因素的选定与分级指标的划分是工作的核心。应选取对蔬菜的生长发育和生产力具有重大影响的、稳定性较高的限制因素,并以土壤属性为主,结合环境条件,因地制宜选定。参评因素的分级应尽量采用定量指标,为分等定级提出定量依据,其主要级差应尽量利用有生物学意义的临界指标。在目前全国无统一规定下,试图面向全国选定参评因素及划分为五等六级的分级指标。 相似文献
998.
999.
心电图时频域指标在驾驶疲劳评价中的有效性研究 总被引:12,自引:0,他引:12
驾驶疲劳是造成交通事故的重要原因,用心电图指标来评价驾驶疲劳对于驾驶疲劳的研究具有重要意义。这里采集了16名被测试者90分钟实验室模拟驾驶操作过程的心电信号,并对实验开始和结束时的15分钟时段心电信号的7项时频域指标进行分析。研究发现:有四项心电时频域指标与疲劳程度明显相关。驾驶疲劳实验后,心率变异性时域测量指标中的RR间期的标准差SD明显上升,心率变异性频域测量指标中的低频段功率值LF明显上升,高频段功率值HF明显下降,LF和HF的比值LF/HF明显上升。因而,采用此四项心电图时频域指标,可以对驾驶疲劳程度进行定量化的反映和评判。 相似文献
1000.
A range of functionalised polymethacrylate copolymers have been synthesised with different functionalities, polymer architecture
and molecular weight. It is shown that appropriately functionalised block copolymers give enhanced film thickness and greatly
reduced friction under low entrainment speed conditions, even with polymer concentration as low as 1% wt. This behaviour almost
certainly results from the formation of an adsorbed brush-like film of thickness ca 20 nm on each polar surface. These films provide a highly viscous inlet that promotes fluid entrainment and thus maintains
a separating film down to very low entrainment speed. The adsorbed polymer films are also able to maintain separation in stationary
contact conditions. Randomly distributed copolymers do not show this type of behaviour. The friction reduction observed is
more effective in unidirectional, mixed sliding–rolling than in reciprocating, sliding conditions. However, it is found that
functionalised polymers and conventional organic and molybdenum-based friction modifiers can be combined to provide effective
friction reduction over the whole range of rubbing conditions. 相似文献