NitroGenius:氮决策支持系统--荷兰氮污染问题最佳解决方案的一个游戏模拟实验

利用计算机模拟的方法,我们为第二届国际氮会议研制开发了一个游戏形式的氮决策支持系统.研制这一系统的目的是:①使科学工作者和决策者们都能认识到荷兰氮污染问题的复杂性,因为荷兰是一个农业、工业和运输业活动密集的区域;②探索以最低的社会经济代价解决氮污染的最佳方案.NitroGenius由有关时空范围内的氮流动模型组成,其中包括氨和氮氧化合物的释放及其对地表水和地下水的污染.NitroGenius中还包括了一个经济模型,它描述了各个重要经济部门之间的关系,以及不同氮排放控制措施对国民生产总值(GDP)、失业率、能源消耗和环境的影响.在第二次国际氮会议期间,大约有50个研究组对NitroGenius进行了测试,结果表明,如果认真进行计划并选择适当的治理措施,就能够以适当的代价解决荷兰的氮污染问题.     

Prenatal diagnostic procedure for leukocyte adhesion deficiency

Leukocyte adhesion deficiency (LAD) is a rare autosomal recessive disorder which leads to recurrent severe infections due to impaired leukocyte functions. The disorder is caused by an absence or deficiency of leukocyte cell adhesion molecules (LeuCAMs) on the leukocyte membranes. The diagnosis is established with monoclonal antibodies against the LeuCAMs. We have carried out a prenatal diagnostic procedure by means of cordocentesis in a mother who was 20 weeks pregnant and had previously given birth to a child with LAD. This previous child had the severe form of LAD with undetectable mRNA for the β chain, the common subunit of the LeuCAMs. We found that the fetal granulocytes expressed the LeuCAMs normally. At birth, the baby was physically normal and showed no signs of impaired leukocyte functions.     

Floods and Other Possible Adverse Environmental Effects of Meadowland Area Decline in Former West Germany

6   ha, or 6% of the country's total area. The environmental implications of this large-scale conversion have so far received little attention; the present study examined some of these implications. A review of research on soil physical and chemical aspects of the conversion of permanent grassland into arable land reveals that such a large-scale conversion may have considerable effects upon the environment. For example, due to the mineralization of soil organic matter a release of NO₃ and CO₂ into the environment can be expected on the order of 10 t N and 100 t C per hectare. Environmentally equally severe, if not worse, is the increased amount of surface runoff that can be expected from converted grassland soils in arable land during winter because of surface sealing and soil compaction. This increased surface runoff, in combination with the runoff from other farmland, may be one of the reasons for the growing frequency of floods along major German rivers in recent years. In view of the lasting adverse environmental effects of permanent grassland conversion and the subsidized agricultural surpluses in Germany today, we conclude that a reconversion of arable land into permanent grassland may be beneficial both environmentally and economically.     

Fetal limb constriction: A possible complication of CVS

A case of fetal loss due to infection after first-trimester chorionic villus sampling is described. The fetus was born at 18 3/7 weeks and showed an annular constriction of one of the arms as seen in the amniotic band sequence. Induction of congenital defects might be one of the complications of chorionic villus sampling.     

First-trimester screening for fetal chromosomal abnormalities. Preliminary results

We have started a multicentre trial to study the possibilities of first-trimester maternal serum screening for fetal chromosomal abnormalities. Maternal blood samples were obtained before 13 weeks of gestation. We present the preliminary results of the first 950 patients on alpha-fetoprotein (AFP). Results on cancer antigen 125 (CA 125) in Down's syndrome and normal pregnancies are also presented. We conclude that the results on AFP are promising and that CA 125 might be predictive for fetal Down's syndrome.     

Nitrogen accumulation and plant species replacement in three salt marsh systems in the Wadden Sea

Salt marsh development on the coastal barrier island of Schiermonnikoog (The Netherlands) was compared with two other salt marsh systems in the Wadden Sea. Accretion rate, nitrogen accumulation and changes in plant species composition were investigated using chronosequences. The age of the marsh was estimated from aerial photographs and old maps. In 7230 plots, the elevation of the marsh surface, the thickness of the sediment layer (clay) and the presence of plant species was recorded. In addition, the nitrogen pool was measured at each successional stage. Accretion rates were similar in the three salt marshes. Higher accretion rates were found at younger marshes. A strong linear relationship between nitrogen pool size and thickness of the clay layer was found for the three marshes. The accumulation rate of nitrogen is therefore strongly related to the accretion rate. Thus, more nitrogen is present in the sediment of later successional stages where more clay has accumulated. On the high salt marsh (55 cm+MHT),Ameria maritima disappeared andArtemisia maritima, Juncus gerardi andElymus athericus established at sites with a thicker clay layer. On the low salt marsh (25 cm+MHT),Plantago maritima, Puccinellia maritima andLimonium vulgare disappeared andAtriplex (Halimione) portulacoides established. Apparently, with the accumulation of clay and therefore of nitrogen, tall growing species take over in salt marshes not grazed by livestock.     

Super-individuals a simple solution for modelling large populations on an individual basis

Modelling populations on an individual-by-individual basis has proven to be a fruitful approach. Many complex patterns that are observed on the population level have been shown to arise from simple interactions between individuals. However, a major problem with these models is that the typically large number of individuals needed requires impractically large computation times. The common solution, reduction of the number of individuals in the model, can lead to loss of variation, irregular dynamics, and large sensitivity to the value of random generator seeds. As a solution to these problems, we propose to add an extra variable feature to each model individual, namely the number of real individuals it actually represents. This approach allows zooming from a real individual-by-individual model to a cohort representation or ultimately an all-animals-are-equal view without changing the model formulation. Therefore, the super-individual concept offers easy possibilities to check whether the observed behaviour is an artifact of following a limited number of individuals or of lumping individuals, and also to verify whether individual variability is indeed an essential ingredient for the observed behaviour. In addition the approach offers arbitrarily large computational advantages. As an example the super-individual approach is applied to a generic model of the dynamics of a size-distributed consumer cohort as well as to an elaborate applied simulation model of the recruitment of striped bass.     

Sabaki River sediment load and coral stress: correlation between sediments and condition of the Malindi-Watamu reefs in Kenya (Indian Ocean)

Sediment discharges from rivers have a negative impact on coral reef ecosystems. Indicators of coral decline measured in the present study were: (1) injury to living stony corals; (2) soft coral cover; and (3) bare rocky substrate suitable for colonization by corals. The relationship between these indicators and the distribution of terrigenous sediment was studied for the Malindi-Watamu fringing reef complex along the Kenyan coast off East Africa during 1982 and 1983. Decline of this reef had been repeatedly noted during the preceding decade. The influence of terrigenous sediment from the Sabaki River appears to be strongest in the Watamu area in the south and in the northern-most part of the Malindi reef area. Correlations, between each of the above three coral stress response indicators, on the one hand, and quantitative indicators of sediment loading, on the other hand, were not clear. However, a combined coral stress indicator involving all three factors was shown to have a clear relationship with terrigenous sediment loading and provided a rapid means of field evaluation of the effects of sediment stress on stony corals. Values for the combined coral stress indicator were found to increase in proportion to increasing values of terrigenous sediment loads in both study areas. A higher coral stress indicator value means a high proportion of injured or algae infested corals, and/or a high soft coral cover, and/or a high proportion of rocky substrate suitable for, but unoccupied by, living corals.