Repeat maternal serum testing in multiple marker down's syndrome screening programmes

The effect of repeat testing in maternal serum multiple marker screening for Down's syndrome was estimated using samples stored in an antenatal serum bank. Human chorionic gonadotropin (hCG) and unconjugated oestriol (uE₃) levels were determined in 142 pairs of routinely collected samples which had already been tested for alpha-fetoprotein (AFP). For each marker, about two-thirds of the pairs of values were within 20 per cent of each other and most were within 40 per cent. A multivariate Gaussian model was used to estimate the detection and false-positive rates for different repeat testing policies. A policy of repeat testing those with a high risk of a Down's syndrome term pregnancy given age and marker levels would reduce the false-positive rate but there would also be a reduction in the detection rate. For example, using all three markers and a 1 in 250 cut-off risk, the estimated false-positive rate would fall from 5·3 to 3·8 per cent but the detection rate would decrease from 58 to 55 per cent. A policy of repeating those with either high or borderline risks would produce a modest improvement in screening efficiency. Repeating the 11 per cent with a risk exceeding 1 in 500 yields an estimated false-positive rate of 5·0 per cent and a detection rate of 60 per cent. A policy of selective repeat testing is not recommended as it would not substantially improve screening efficiency. Nonetheless, if a repeat test has been performed, the parameters given in this paper will enable an unbiased estimate of the Down's syndrome risk to be calculated for individual women.     

Optimizing the configuration of a clearwell by integrating pilot and full-scale tracer testing

In this paper, the main factors impacting the plug flow pattern of a clearwell were investigated by integrating pilot-scale, full-scale clearwell tracer testing and computational fluid dynamics (CFD) simulation. It was found that pilot tracer testing, full-scale tracer testing and CFD simulation all demonstrated that the correlation between the ratio of t ₁₀/T and L/W can be approximately expressed by: t ₁₀/T = 0.189 4ln(L/W)-0.049 4. This study confirmed that the installation of baffles within clearwells is an efficient way to optimize their configuration. In addition, the inlet velocity has a minimal contribution to the ratio of t ₁₀/T. However, the ratio of turning channel width to channel width (d/W) significantly contributes to the ratio of t ₁₀/T. The optimal ratio of d/W is 0.8–1.2 for maintaining better plug flow pattern. The number of turning channels is one of the main factors that impact the ratio of t ₁₀/T. When increasing the number of turning channels, a lower ratio of t ₁₀/T is obtained.     

Repeat maternal serum testing for down's syndrome screening using multiple markers with special reference to free α and free β-hCG

To determine the effect of routine repeat testing in serum screening for Down's syndrome, we compared estimates of the detection and false-positive rates. Five serum markers were measured-alpha-fetoprotein (AFP), unconjugated oestriol (uE₃), human chorionic gonadotrophin (hCG), and its two subunits, free α and free β-hCG. First and repeat test marker levels were available from 142 women whose samples had been routinely collected and stored in an antenatal serum bank. Different repeat testing policies were compared for various combinations of the markers. If all women had repeat tests using the four markers AFP, uE₃, and free α and free β-hCG, the detection rate for a 5 per cent false-positive rate was 69 per cent compared with 65 per cent if no women were repeated. Policies of repeating selected women gave similar results. The small gain in screening performance with repeat testing performed routinely is not worthwhile. If a woman does happen to have a repeat test, her risk estimate should, however, be based on both results, not just the second.     

多环芳烃对海洋贝类多生物水平毒性效应的研究进展

多环芳烃类化合物(PAHs)是海洋中常见的一类持久性有机污染物,对海洋生态安全及海洋生物健康造成严重威胁。海洋贝类作为海洋生态毒理学研究的模式生物,其滤食性、固着性等生理特点使其对PAHs具有较高的生物蓄积能力,可以在不同生物水平产生一系列的毒性效应。本文综述目前PAHs在海洋贝类多种生物水平所造成的生物毒性效应及其检测方法的研究进展,重点从个体生理特征、组织结构、细胞毒性和基因毒性4个层次展开讨论,为更有效地利用海洋贝类这一模型生物,深入开展PAHs对海洋生物的致毒效应与机制研究提供思路与检测方法参考。     

Effects of skin and hydraulic fractures on SVE wells

Soil vapor extraction (SVE) systems are intended to cause substantial volumes of air to flow through the subsurface with the purpose of removing volatile contaminants. The effectiveness of SVE can be influenced by any effect that changes the specific gas capacity (discharge as a function of vacuum) of a well. Skins of low permeability material enveloping a well bore are widely recognized to affect the performance of wells used to recover water, natural gas, or petroleum, and skin can also significantly diminish the performance of an SVE well. Skins a few mm thick consisting of material whose gas phase permeability is 0.01 of the formation can reduce the specific gas capacity of an SVE well by factors of 2 to 10 or more. Hydraulic fractures created in the vicinities of shallow wells commonly resemble sand-filled layers shaped like flat-lying disks or gently dipping saucers. The contrast between the gas-phase permeability of the sand in the fracture and that of the formation is particularly important, with significant effects requiring the ratio to be greater than approximately 50. Shallow hydraulic fractures filled with several tenths of m3 of sand in formations that are several orders of magnitude less permeable than that of the enveloping formation should increase specific gas capacity by factors of 10 or more. Field tests of the effects of hydraulic fractures on the performance of SVE were conducted by creating four wells intersecting fractures and a suite of control wells created using conventional methods in silty saprolite. Specific gas capacities ranged over more than an order of magnitude for 10 wells completed within a small area (2 m2) and at the same depth. Specific capacities correlate to the drilling method that was used to create the bore for the well: lowest values occurred in wells drilled with a machine auger, slightly better results were obtained using a Shelby tube, and the best results were obtained from conventional wells bored with a hand auger. Skin factors determined for wells created with a machine auger could be explained by a layer 1 cm thick that has 0.007 times the permeability of the enveloping material, which could readily have been created during the drilling procedure. Specific capacities of wells intersecting hydraulic fractures were 5 to 100 times more than those of conventional wells. The large difference in performance appears to be due in part to the beneficial effects of the fracture, and in part to the detrimental effects of well skin.     

Time course of isocyanate emission from curing polyurethane adhesives

The time course of isocyanate emission from curing polyurethane (PUR) resins and adhesives was studied in two different emission test chambers. The measured emissions were strongly dependent on the type of experiment. The adhesives under investigation contained different types of diisocyanates and are used for different applications, e.g. for fixing of textile floor coverings. The influence of the curing mechanism on emission was studied by comparing the emission curves of one-component adhesives (OCA) and two-component adhesives (TCA). For TCA, the decrease in isocyanate emission was found to follow a two-step process during curing. In the first step, the emission is dominated by surface evaporation, and the decay of emission is mainly caused by the decrease in monomer content due to reaction. In the second step, the release is limited by internal diffusion. The influence of monomer reactivity on the emission profile could be demonstrated for 2,4′- and 4,4′-MDI. The less-reactive 2,4′-MDI caused prolonged emission. A strong dependence of emission rates on temperature and adhesive viscosity was also obvious. The evaluation of emission rates of different commercially available PUR adhesives showed the highest emission from systems that are applied at high temperatures. The high reactivity of diisocyanates requires special techniques for sampling and analysis. Therefore, an analytical method using HPLC–MS/MS was developed that enables limits of quantitation of <5 ng/m³ with a sampling volume of 100 l.     

新疆核试验场周围地区主要食品中90Sr(锶)、137Cs(铯)水平及其所致居民剂量

本文报道了新疆核试验场周围地区9个调查区17种主要食品中⁹⁰Sr、¹³⁷Cs含量分别为1.1~72.3,0.3~40.7×10^-2Bq·Kg^-1;3个对照区分别为1.6~68.4,0.6~27.4×10^-2Bq·Kg^-1。两地区同类食品中⁹⁰Sr、¹³⁷Cs平均含量基本一致。调查区⁹⁰Sr、¹³⁷Cs所致成年居民有效剂量当量值分别为2μSV(集体剂量当量为30.0人· SV);0.3μSV(4.5人· SV)。对照区分别为2.2μSV(集体剂量当量为20.9人·SV);0.4μSV(3.0人·SV)。可见我国核试验产生的⁹⁰Sr、¹³⁷Cs对核试验场周围地区食品没有造成明显的局部污染,所致居民剂量当量负担仅为我国天然外照射所致年有效剂量当量(952μSV)的0.2%和0.03%。对该地区的广大居民健康不会产生有害的影响。     

活性污泥1号数学模型(ASMI)中的组分

活性污泥数学模型组分的鉴定对活性污泥1号数学模型的应用具有重要的意义。ASMI中的组分包括含碳组分、含氮组分、溶解氧和碱度。传统的组分可以直接用经典的测试方法获得。其余组分目前还没有统一的测定方法，试验测定方法分为生物方法和物理化学方法。     

民用飞机机载设备振动试验要求和应用分析（二）

阐述了民用飞机机载设备振动环境的特点和振动试验分类,归纳和汇总了DO 160 F/G中的各类民用飞机机载设备的振动试验要求,包括振动谱、振动量值和试验持续时间等,并进行了分析和说明,以便于查阅和使用。最后对民用飞机机载设备振动试验方法的应用进行了概括,介绍了民用固定翼飞机的机载设备振动试验要求,按设备在机上的区域不同进行分类,详细地对比说明各个位置上设备的振动试验要求;介绍了民用直升机的机载设备振动试验要求。     

飞机防火试验中的燃烧反应动力学模型研究

使用反应路径分析法对Jet-A型航空煤油燃烧的气相燃烧机理进行简化。选用POSF-4658机理作为Jet-A燃烧的详细反应机理,该机理包含1607种燃烧组分、6633个基元反应机理。将飞机防火试验条件作为简化过程的初始条件,得到78种组分,196个反应机理的Jet-A燃烧机理。通过对Jet-A的简化反应机理、详细反应机理和JetA实验数据的比较可以发现,简化反应机理可以较准确地反映Jet-A型航空煤油在防火试验条件下的燃烧特性。利用常用的Jet-A型航空煤油简化机理计算的绝热火焰温度、点火延迟时间及层流火焰速度与本文提出的简化的计算值进行比较。结果表明,提出的简化机理在防火试验条件下具有较高的精确度。得到的Jet-A简化反应机理可为飞机防火试验的仿真研究提供燃烧场的化学反应动力学模型。