First trimester PAPP-A in the detection of non-Down syndrome aneuploidy

Combined first trimester screening using pregnancy associated plasma protein-A (PAPP-A), free β-human chorionic gonadotrophin, and nuchal translucency (NT), is currently accepted as probably the best combination for the detection of Down syndrome (DS). Current first trimester algorithms provide computed risks only for DS. However, low PAPP-A is also associated with other chromosome anomalies such as trisomy 13, 18, and sex chromosome aneuploidy. Thus, using currently available algorithms, some chromosome anomalies may not be detected. The purpose of the present study was to establish a low-end cut-off value for PAPP-A that would increase the detection rates for non-DS chromosome anomalies. The study included 1408 patients who underwent combined first trimester screening. To determine a low-end cut-off value for PAPP-A, a Receiver–Operator Characteristic (ROC) curve analysis was performed. In the entire study group there were 18 cases of chromosome anomalies (trisomy 21, 13, 18, sex chromosome anomalies), 14 of which were among screen-positive patients, a detection rate of 77.7% for all chromosome anomalies (95% CI: 55.7–99.7%). ROC curve analysis detected a statistically significant cut-off for PAPP-A at 0.25 MoM. If the definition of screen-positive were to also include patients with PAPP-A<0.25 MoM, the detection rate would increase to 88.8% for all chromosome anomalies (95% CI: 71.6–106%). This low cut-off value may be used until specific algorithms are implemented for non-Down syndrome aneuploidy. Copyright © 2001 John Wiley & Sons, Ltd.     

污水处理厂除臭工艺及工程应用

根据国家标准对废气中H2S、NH3的最高排放浓度、臭气浓度的明确规定,结合广州市大坦沙污水处理厂除臭的工程实例,介绍了除臭系统的3种工艺:土壤法、生物滴滤法、等离子体法,分析了除臭过程中各种方法的优缺点.     

模拟酸雨对水稻叶片质膜H+-ATPase活性与胞内Ca2+浓度的影响

在水培条件下研究了模拟酸雨(pH=2.5～5.5)对水稻叶片胞内Ca2+浓度和质膜H+-ATPase活性的影响.结果表明:与对照组(CK)相比,酸雨处理5 d(胁迫期)后,pH=5.5和5.0处理组的水稻叶片胞内H+浓度、质膜H+-ATPase活性、胞内Ca2+浓度、质膜Ca2+-ATPase活性无显著变化;pH=4.0和3.5处理组各指标显著升高,且H+-ATPase活性随Ca2+浓度升高而上升;pH=3.0和2.5处理组各指标显著降低,此时胞内Ca2+缺失,对H+-ATPase活性的调节作用受到限制.经正常条件培养5 d(恢复期)后,pH=4.0和3.5处理组各指标均恢复至CK的处理水平,表明H+-ATPase活性受到Ca2+调控已恢复到正常;pH=3.0和2.5处理组的Ca2+浓度高于CK及胁迫期,H+-ATPase活性低于CK但高于胁迫期,表明H+-ATPase活性受Ca2+调控得到部分恢复.因此,酸雨胁迫下胞内Ca2+对质膜H+-ATPase活性有一定调节作用,且受酸雨强度的制约.     

Metallurgical and mechanical characterization of electron beam welded super-duplex stainless steel UNS 32750

This paper addresses the weldability of 6 mm thick plates of super-duplex stainless steel by electron beam welding (EBW) process. Microstructure investigations conducted using optical and SE microscopy showed the presence of large ferrite grains with intra- and inter-granular austenite. Ferrite content studies on the weld zone estimated that there is no significant element partitioning between austenite and ferrite phases. Hardness studies portrayed that the weld hardness is found to be greater than the parent metal which is acquainted due to the solid solution strengthening effect. Tensile results corroborated that the joints obtained by EB welding process have better strength than the base metal. A detailed structure–property relationships has also been carried out through point and line mapping EDAX analysis across the weldment to substantiate the discussions.     

Plasma arc welding: Process,sensing, control and modeling

This article introduces the basic principles of plasma arc welding (PAW) and provides a survey of the latest research and applications in the field. The PAW process is compared to gas tungsten arc welding, its process characteristics are listed, the classification is made, and two modes of operation in PAW, i.e., melt-in and keyhole, are explained. The keyhole mechanism and its influencing factors are introduced. The sensing and control methodologies of the PAW process are reviewed. The coupled behaviors of weld pool and keyhole, the heat transfer and fluid flow as well as three-dimensional modeling and simulation in PAW are discussed. Finally, a novel PAW process variant, the controlled pulse keyholing process and the corresponding experimental system are introduced.     

Influence of displacement constraints in thermomechanical analysis of laser micro-spot welding process

The evolution of mechanical components into smaller size generating a need for microwelding of these components using laser which offers better control as compared to arc and plasma processing. The present article describes the numerical simulation of laser micro-spot welding using finite element method. A two dimensional Gaussian distributed surface heat flux as a function of time is used to perform a sequentially coupled thermal and mechanical analysis. The model is used for simulating laser micro-spot welding of stainless steel sheet under different power conditions and configurations of mechanical constraints. The temperature dependent physical properties of SS304 have been considered for the simulation and an isotropic strain hardening model has been used. The simulated weld bead dimensions have been compared with experimental results and temperature profiles have been calculated. The maximum deformation of 0.02 mm is obtained with maximum laser power of 75 W. The thermal stress is more inducing factor to temperature induced residual stresses and plastic strain as compared to mechanical constraints. The plastic strain changes significantly by displacement constraints as compared to residual stress.     

Problems and issues in laser beam welding of aluminum–lithium alloys

Aluminum–lithium (Al–Li) alloys are very attractive for potential aerospace applications due to their lower density, higher specific strength and rigidity, better corrosion and fatigue crack growth resistance properties, compared to conventional aluminum alloys. Laser beam welding (LBW), being an advanced joining method, has already been approved for applications involving aluminum alloys. However, there are still a number of problems and issues to be answered and solved in LBW of Al–Li alloys. In this review, the properties of Al–Li alloys and the characteristics of LBW are introduced, the formation and prevention of the main weld defects such as porosity and hot cracking are discussed, and then the weld microstructure and the joint mechanical properties are described in highlight. At the end, an outlook on future trends is presented.     

A method for double-sided friction stir spot welding

A rotating anvil similar to a pinless friction stir welding (FSW) tool can be applied to friction stir spot welding (FSSW) of thin metal plates. FSSW is a solid-state joining process that is currently being used by automotive manufacturers as an alternative to rivets and traditional resistance spot welding. The principal detractor of this process is the keyhole left by pin extraction, which can be detrimental to the weld strength. A pinless tool can be used to eliminate the keyhole. However, this approach is limited to joining thin sheet (≤1 mm). Using a rotating anvil with the FSSW process permits the joining of thicker cross sections, improves the mechanical strength of the spot weld and reduces the reaction forces on the spot welding frame. A numerical model of the process, tensile shear tests and macrosection analysis are used to evaluate the spot welds.Macrosection and numerical analysis reveals that the material flow between the pinless tool and rotating anvil is complex and unique to this process. It has been found that the use of a rotating anvil for FSSW is a viable means to create quality spot welds in thicker weldments.     

脉冲电晕放电等离子体去除污染土壤热脱附尾气中的DDTs

为探索新型产业化应用热脱附尾气处理技术,采用脉冲电晕放电等离子体技术对含DDTs的热脱附尾气进行处理,考察了工艺参数如脉冲电压、脉冲频率、ρ（DDTs）和停留时间对DDTs处理效果的影响,分析了DDTs经低温等离子体处理后的分解产物.结果表明,DDTs的去除率随脉冲电压的升高、脉冲频率的增大和停留时间的延长而增加,随进气中ρ（DDTs）的升高而降低,但去除量随进气中ρ（DDTs）的升高而增大.进气中的ρ（DDTs）为30.0 mg/m3,停留时间为10 s,脉冲电压为30.0 kV,脉冲频率为50 Hz时,DDTs的去除率为82.5%.低温等离子体处理后,尾气中的ρ（p,p'-DDT）、ρ（o,p'-DDT）和ρ（p,p'-DDD）降低,ρ（p,p'-DDE）反而升高,另有微量的二苯甲烷、二苯甲醇、4,4'-二氯二苯甲烷、2,4'-二氯苯甲酮和1,1-双（对氯苯）-2-氯乙烯等分解产物被检出.研究显示,脉冲放电等离子体技术具有去除效率高等特点,可有效去除含DDTs的热脱附尾气.      

Oxidation of gaseous elemental mercury in a high voltage discharge reactor

Effects of the voltage waveform, discharge tooth wheel number and CO2/NO/SO2 concentration in the simulated flue gas on Hg0 oxidation were investigated using a link tooth wheel-cylinder reactor energized by di erent high voltage power supplies. Negative DC discharge induced more ozone production and a higher Hg0 oxidation e ciency than positive DC discharge and 12 kHz AC discharge. The discharge tooth wheel number had almost no e ect on the maximum Hg0 oxidation e ciency. The allowable supplied voltage decreased with the increase of discharge tooth wheel number. CO2 could stabilize the discharge process and increase the maximum voltage for a stable discharge. It has also been found that NO consumed O3 induced by high voltage discharge, thereby decreased Hg0 oxidation e ciency; while SO2 had a slight promoting e ect on Hg0 oxidation.