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621.
为提高交通安全管理水平,促进交通的可持续发展。基于解释结构模型原理,综合考虑车、路和环境因素,构建了影响道路交通安全的影响因素结构模型。该模型不但能够弥补分析结构要素之间内在影响机制的不足,而且对于研究道路交通安全结构要素之间的层次性和复杂性有天然的优势。数据来源于由13位专家构成的ISM小组,其中7位为来自高校从事交通安全研究的教授,6位为来自北京市、上海市、广州市、武汉市等交通运输委员会的高层管理者,保证了数据的科学性和可靠性。采用解释结构图分析车、路和环境各影响因素之间的关系,结果表明,众多因素会对道路交通安全产生影响,车辆技术条件、定期检验合格率、车辆救援设备的完备状况、安全设施是制约道路交通安全的直接影响因素,道路限速、道路负荷度、大客(或货车)比例、交通量、交通监控是影响道路交通安全的间接因素,车辆超限(超载)状况、车流密度、道路路面类型、道路设施完备性、天气状况、单向车道数和地形特征是影响道路交通安全的最根本因素。为提高道路交通安全管理水平,首先,应进一步完善《道路交通安全法实施条例》,加强对车辆定期检验的监督;其次,健全道路信息公示制度,提升交通监控水平,引入相关路段道路限速、负荷度、交通量动态信息显示及预警机制;最后,加强车辆超限(超载)及车流密度的监控,健全道路设施的配套制度。 相似文献
622.
Molecular Weight Changes and Polymeric Matrix Changes Correlated with the Formation of Degradation Products in Biodegraded Polyethylene 总被引:3,自引:0,他引:3
Ann-Christine Albertsson Bengt Erlandsson Minna Hakkarainen Sigbritt Karlsson 《Journal of Polymers and the Environment》1998,6(4):187-195
The molecular weight changes in abiotically and biotically degraded LDPE and LDPE modified with starch and/or prooxidant were compared with the formation of degradation products. The samples were thermooxidized for 6 days at 100°C to initiate degradation and then either inoculated with Arthobacter paraffineus or kept sterile. After 3.5 years homologous series of mono- and dicarboxylic acids and ketoacids were identified by GC-MS in abiotic samples, while complete disappearance of these acids was observed in biotic environments. The molecular weights of the biotically aged samples were slightly higher than the molecular weights of the corresponding abiotically aged samples, which is exemplified by the increase in
from 5200 g/mol for a sterile sample with the highest amount of prooxidant to 6000 g/mol for the corresponding biodegraded sample. The higher molecular weight in the biotic environment is explained by the assimilation of carboxylic acids and low molecular weight polyethylene chains by microorganisms. Assimilation of the low molecular weight products is further confirmed by the absence of carboxylic acids in the biotic samples. Fewer carbonyls and more double bonds were seen by FTIR in the biodegraded samples, which is in agreement with the biodegradation mechanism of polyethylene. 相似文献
623.
The objectives of this study were to: (1) calculate revised estimates and projections of United States annual Down syndrome (DS) births for 1970–2002, and (2) estimate the effects of amniocentesis on these baseline DS birth projections. Three models of amniocentesis utilization among 30–34 and ≧ 35-year-old women were considered. The recently revised Census Bureau birth projections, and new single year maternal age DS risk rates estimated from a 1970–1983 Ohio data set, were used. Data from all three Census Bureau projection series were analysed; series II was considered in depth since it is consistent with recent fertility levels. Assuming no use of amniocentesis, total estimated DS births dropped from about 4770 in 1970 to 4120 in 1980 (a 14 per cent decline), but are projected to a plateau of about 5100 by the year 1990 (a 24 per cent increase). DS births to women ≧ 35 would increase dramatically from about 1050 in 1980 to 1900 in 2000 (an 81 per cent increase). Assuming 1983 Ohio prenatal diagnosis ratios for women aged 30–34 (1.7 per cent) and ≧ 35 (23.4 per cent) are used nationally, an annual reduction of about 7 per cent of DS births in 1986 and 9 per cent in 2002 would result. Fifty and 70 per cent utilization among women 30–34 and 235, respectively, would reduce DS births by about 33 per cent in 1986 and 38 per cent in 2002. Therefore, if the projected increase in DS births is to be averted, utilization of prenatal diagnosis by ≧ 30-year-old women must increase substantially. 相似文献
624.
Juriy W. Wladimiroff MD Ph.D. Wydia R. Bhaggoe Miranda Kristelijn Titia E. Cohen-Overbeek Nicolette S. Den Hollander Helen Brandenburg Frans J. Los 《黑龙江环境通报》1995,15(5):431-438
Structural pathology and outcome were studied in 170 chromosomally abnormal fetuses. Numerical chromosomal abnormalities were established in 158 (93 per cent) cases, of which 110 (71 per cent) represented trisomies, 30 (18 per cent) Turner syndrome, and 18 (11 per cent) triploidy. Structural chromosomal abnormalities were diagnosed in 12 (7 per cent) cases. Gestational age at referral was significantly shorter for pregnancies with Turner syndrome than for the other chromosomal abnormalities. Referral before 20 weeks of gestation was mainly based on fetal structural pathology alone (92 per cent); after 20 weeks, patients were referred because of structural pathology combined with small for gestational age, oligohydramnios, or polyhydramnios. Referral as a result of suspected multiple organ pathology occurred in 73.5 per cent of pregnancies. An abnormal amniotic fluid volume was present in 59/170 (34.5 per cent) chromosomally affected pregnancies, i.e., oligohydramnios in 31 and polyhydramnios in 28 cases. Birth weight was below the tenth percentile in over half of the chromosomally abnormal fetuses, except for Turnersyndrome. Fetal outcome was poor, with a survival rate at 1 month of 30 per cent for trisomies which was mainly determined by trisomy 21 (14/18=77.5 per cent). 相似文献
625.
苍洱地区居址环境的历史变迁 总被引:1,自引:0,他引:1
根据民族学和考古学资料进行的综合研究,可将苍洱地区居址环境划为4个历史变迁时期:4000多年前的先民们居住在沿海拔2500~2200米一线的一些向阳避风的苍山台地上。海拔2200~2000米一线的苍山脚下为汉晋时期先民们的聚居点。海拔2000米左右,沿滇藏公路一线的白族村落大致在唐宋南诏大理国时期形成。海拔1975米左右,今洱海边的白族村落大多数在元明清时期形成。其趋势是从高处往低处下移,随苍山上升,洱海水位下降,利用滩地形成新的居民群。其形成的间隔时间越来越短,加强洱海保护是迫切的任务。 相似文献
626.
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629.
Kenneth A. Baerenklau Bill Provencher 《Journal of Environmental Economics and Management》2005,50(3):617-636
This paper examines the consequences of using a static model of recreation trip-taking behavior when the underlying decision problem is dynamic. Specifically we examine the implications for trip forecasting and welfare estimation using a panel dataset of Lake Michigan salmon anglers for the 1996 and 1997 fishing seasons. We derive and estimate both a structural dynamic model using Bellman's equation, and a reduced-form static model with trip probability expressions mimicking those of the dynamic model. We illustrate an inherent identification problem in the reduced-form model that creates biased welfare estimates, and we discuss the general implications of this for the interpretation of preference parameters in static models. We then use both models to simulate trip taking behavior and show that although their in-sample trip forecasts are similar, their welfare estimates and out-of-sample forecasts are quite different. 相似文献
630.
Investigation of Pine (Pinus sylvestris L.)annual radial increment (width of annual tree rings) was carriedout in the surroundings of one of the largest pollution sources inLithuania – Jonava Nitrogen Fertilizers Plant. The main objectiveof investigation was to analyse different sides of anthropogenictransformations of tree-ring series in the polluted environment:changes in tree growth intensity; variance changes in tree-ringseries; changes in the relations with natural external factors.Three different periods of tree reaction to the environmentalpollution were singled out – fertilization period, depressionperiod and recovery period since annual emissions were essentiallyreduced. The variance of tree-ring series has increased severaltimes in the polluted environment. Reaction of trees to the impactof climatic factors (temperature, precipitation) has changedsignificantly in the polluted environment and their sensitivity hasalso increased. 相似文献