Prenatal screening and diagnosis of neural tube defects

This review article discusses prenatal screening and diagnosis of neural tube defects (NTD). High detection rates occur in countries operating ultrasound screening programmes because classical two-dimensional ultrasound cranial signs (lemon shaped head, banana cerebellum, ventriculomegaly) are important diagnostic clues to the presence of spina bifida. Careful evaluation of both the spine and a search for other abnormalities is warranted. Important prognostic information for spina bifida relates to the lesion level, with a “watershed” between L3 and L4 marking a very high chance of being wheelchair bound with the higher lesions. Three-dimensional ultrasound using multiplanar views can achieve diagnostic accuracy within one vertebral body in around 80% of patients. There are high rates of pregnancy termination for spina bifida in many European countries, but the use of new imagining techniques allow better prediction of outcome, and consequently a refinement of prenatal counselling. Copyright © 2009 John Wiley & Sons, Ltd.     

Disposal of hexachlorodisilane and its hydrolyzed deposits

Hexachlorodisilane (Si₂Cl₆, HCDS) is an important precursor used in semiconductor device manufacturing. It is a flammable as well as a water reactive liquid which hydrolyzes rapidly upon contact with water or moisture. The hydrolyzed deposits are also known to be shock-sensitive with explosion energy equivalent to trinitrotoluene (TNT). In this work, two phases of test program including disposal of HCDS and disposal of the shock sensitive HCDS hydrolyzed deposits were conducted. The first phase of the program was to find an agent that can completely dissolve/react the HCDS vapor without forming shock sensitive deposits. The second phase of the program attempted to find a suitable agent to suppress the Si–Si bonds, one of the essential roles of chemical functional groups in shock sensitivity of the HCDS hydrolyzed deposits to suppress the shock sensitivity. A variety of agents such as sulfuric acid solutions, aqueous sodium hydroxide (NaOH) solutions, aqueous potassium hydroxide (KOH) solutions, KOH/alcohol solutions were utilized as the suppressants in this work. Samples mixed with suppressants were not only tested for shock sensitivity by a Fall-hammer apparatus but also analyzed for chemical functional groups to identify the effect of each agent. Concentrated sulfuric acid was found to suppress the shock sensitivity of the liquid HCDS hydrolyzed deposits by acting as a medium that helps the hydrolyzed deposit to retain moisture. KOH/alcohol solutions can turn HCDS vapor into non-hazardous silica, so that, it provided a safe way to dispose HCDS. Finally, practical recommendations about handling and eliminating the risk of shock sensitivity are given for HCDS liquid spill, HCDS vapor vent and HCDS hydrolyzed deposits.     

Detonation transition criteria from the interaction of supersonic shock-flame complexes with different shaped obstacles

The present study is an experimental investigation of the last stages of the deflagration-to-detonation transition. A fast flame following a lead shock was generated by passing a detonation wave through a perforated plate. The shock flame complex then interacts with an obstacle of different shape. We study the influence of the obstacle shape on the transition mechanism to a detonation. The obstacles studied are a single round or square obstacle, a flat plate, a C-shaped and an H-shaped obstacle. The experiments were performed in a thin transparent channel permitting high speed schlieren visualization. Stoichiometric propane-oxygen was investigated at sub-atmospheric conditions. For each obstacle configuration, the initial pressure was changed to modify the flame burning velocity and the Mach number of the leading shock. The burning velocity prior to the interaction was measured experimentally from the displacement velocity of the flame in the videos. This required estimating the speed of the gas ahead of the flame. A linear correction to the speed immediately behind the lead shock was applied using the shock change equations and the measured pressure gradient behind the lead shock in order to account for the non-steadiness of the lead shock and viscous losses to the walls. Three main findings were that the obstacle shape had a minimal influence on the critical flame strength required for transition, although obstacles with a forward facing cavity were able to suppress the transition by isolating the re-initiation event inside the cavity. The main transition mechanism for all geometries was the enhancement of the flame burning velocity through the flame interaction with the shock reflected on the obstacle leading to Richtmyer-Meshkov instability. Finally, it was found that the flame burning velocity of the initial flame required for transition was closely approximated by the Chapman-Jouguet burning velocity. Consistent with the visual observations, this supports the view that transition is favored when the flame is in phase with the acoustic waves, and strong internal pressure waves can be amplified.     

The performance of solar powered desiccant dehumidifier in India: an experimental investigation

The regeneration and adsorption of desiccant wheel for producing the dry air was experimentally investigated. The air needed for regeneration was heated in an evacuated tube solar collector with surface area 4.44 m². The desiccant wheel is regenerated at the temperature in the range of 43.9–72.6°C. The regeneration and adsorption performances are affected by the regeneration temperature, wheel rotation, air flow rate (process and regeneration) and ambient conditions. By comparing the adsorption and regeneration performance at different air flow rate and constant rph, it was found that maximum adsorption and regeneration rates are obtained at air flow rate of 210.789 kg/h. Regeneration temperature directly affects the effectiveness of the desiccant wheel. Maximum desiccant wheel effectiveness of regeneration sector and adsorption sector is obtained at air flow rate of 105.394 kg/h. The regeneration performance of desiccant wheel with evacuated tube solar air collector is suitable for the Indian climate.     

管道烟气静压测量方法探讨

通过对三种常用管道烟气静压测定法进行理论和试验分析,推荐一种实用的静压间接测定法,并对该法进行理论分析和试验验证。     

Two- and three-dimensional ultrasound in malformations of the medullary canal: report of four cases

A comparison between two-dimensional (2D), and three-dimensional (3D) ultrasonography was made in four fetuses diagnosed with neural tube defect (NTD) in the first half of pregnancy. 3D ultrasonography (orthogonal and multiplanar systems) proved to be an excellent complement to 2D, particularly when using orthogonal planes. When using the 3D multiplanar surface imaging system, excellent images of the malformations can be rapidly obtained. Copyright © 2001 John Wiley & Sons, Ltd.