Passive air sampling using semipermeable membrane devices at different wind-speeds in situ calibrated by performance reference compounds

Semipermeable membrane devices (SPMDs) are passive samplers used to measure the vapor phase of organic pollutants in air. This study tested whether extremely high wind-speeds during a 21-day sampling increased the sampling rates of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), and whether the release of performance reference compounds (PRCs) was related to the uptakes at different wind-speeds. Five samplers were deployed in an indoor, unheated, and dark wind tunnel with different wind-speeds at each site (6-50 m s(-1)). In addition, one sampler was deployed outside the wind tunnel and one outside the building. To test whether a sampler, designed to reduce the wind-speeds, decreased the uptake and release rates, each sampler in the wind tunnel included two SPMDs positioned inside a protective device and one unprotected SPMD outside the device. The highest amounts of PAHs and PCBs were found in the SPMDs exposed to the assumed highest wind-speeds. Thus, the SPMD sampling rates increased with increasing wind-speeds, indicating that the uptake was largely controlled by the boundary layer at the membrane-air interface. The coefficient of variance (introduced by the 21-day sampling and the chemical analysis) for the air concentrations of three PAHs and three PCBs, calculated using the PRC data, was 28-46%. Thus, the PRCs had a high ability to predict site effects of wind and assess the actual sampling situation. Comparison between protected and unprotected SPMDs showed that the sampler design reduced the wind-speed inside the devices and thereby the uptake and release rates.     

Induced low temperature catalytic ignition by transient changes in the gas composition

The effect of gas composition changes on the low temperature activity for supported platinum model catalysts has been studied. By introducing well-controlled periodic O₂ pulses to a simple diluted gas mixture of CO and O₂, a substantial improvement of the low temperature oxidation activity was observed. The reason for low activity on noble metals at low temperatures is often attributed to self-poisoning by CO. The improved catalytic performance observed is proposed to origin from the transients causing a surface reactant composition that is favourable for the reaction rate, i.e. lower degree of self-poisoning. This was also confirmed by in situ Fourier transform infrared (FT-IR) spectroscopy in combination with mass spectrometry (MS) measurements, which gave evidence for the existence of a strong interplay between the gas phase concentration and the adsorbate composition for these catalysts.     

A simple health control for the elderly. Screening for vitamin B12 deficiency and thyroid disease

Screening for vitamin B12 deficiency and thyroid disease is cheap and enables early diagnosis to be made and treatment to be started while it is still simple and can prevent the development of such serious conditions as dementia, depression, or irreversible tissue damage. In 1995-6, 83% (126/151) of all 75-year-olds in H?rryda, a district (population 28,500) to the east of Gothenburg, agreed to undergo a health control designed to detect hypo- or hyper-thyroidism or vitamin B12 deficiency among elderly residents without symptoms (or with atypical symptoms not easily recognised). Of the 126 participants, four (3%) had low plasma cobalamin (vitamin B12) levels (a figure similar to or lower than those reported by others), and were treated with vitamin B12 after further examination; eight (6%) had serum thyroid stimulating hormone (TSH) levels below the lower normal limit, though further examination showed all eight to be euthyroid; and two (1.6%) were diagnosed as being hypothyroid (a lower prevalence than figures reported elsewhere), and were treated with laevothyroxine. The findings suggest that such screening might be useful in primary care. However, the clinical diagnosis of vitamin B12 deficiency, and of hypo- or hyperthyroidism, is often difficult, especially in the elderly; and although a low serum TSH level is also considered to be a reliable marker of hyperthyroidism, like others this study showed that it may occur even in the absence of disease. Thus, serum TSH and plasma B12 levels are useful screening variables, but need to be complemented by other tests before diagnosis is set.     

Experiences from experimental and numerical springback studies of a semi-industrial forming tool

The work reported in the present paper constitutes a part of a project on simulation of springback in sheet metal forming. Previous work in this project has been concentrated on material modeling and characterization with focus on springback applications. It has been demonstrated that, with proper considerations of all aspects of the material model and the material properties, excellent springback results can be obtained for simple problems. At the simulation of real, industrial parts, a number of additional problems are encountered. Many of these problems are associated with deviations from nominal geometries and other properties. These are examples of factors that influence the outcome of the forming process, but are unknown to the analyst, and can therefore not be considered in the simulation of the forming process. Other phenomena are known to exist, but due to their complexity, they are practically impossible to consider in industrial simulations. Examples of such phenomena are the true frictional behavior in contacts between the blank and the tools, and the flexibility of the press and the forming tool. The influence of these kinds of effects is discussed in the present paper. In the current study, a semi-industrial tool, specially designed to catch those springback problems that are encountered in the forming of real industrial, parts, is used. The tool includes several characteristics that can be found in typical forming tools, such as several draw radius steps and change-over in section geometries. Effects like flange/wall angle changes, sidewall curl and twist are obtained at springback. The sensitivity of the predicted springback is evaluated with respect to various numerical factors, such as the friction coefficient, the material model, and the mesh density. Finally, the quality of the predicted springback behavior for four different materials, commonly used in the automotive industry, is evaluated.     

Characterization of Particulate Matter from Direct Injected Gasoline Engines

The reactivity and reaction kinetics of particulate matter (PM) from direct injected gasoline (GDI) engines has been studied by O₂ and NO₂ based temperature programmed and isothermal step-response experiments, and the PM nano-structure has been characterized using HRTEM. The reactivity of the PM samples collected in filters during on-road driving was found to increase in the following order: Printex U < diesel < gasoline PI ≈ gasoline DI < ethanol for O₂ based combustion. The activation energies for O₂ and NO₂ based oxidation of PM collected from a GDI engine in an engine bench set-up was estimated to 146 and 71 kJ/mol respectively, which is comparable to corresponding values reported for diesel and model soot. Similar nano-structure features (crystallites plane dimensions, curvature and relative orientation) as observed for diesel soot were observed for gasoline PM.     

Multivariate analysis of a biologically activated carbon (BAC) system and its efficiency for removing PAHs and aliphatic hydrocarbons from wastewater polluted with petroleum products

The efficiency of a biologically activated carbon system for treating wastewater polluted with petroleum products was examined and the effects of process parameters on its efficacy were evaluated. In each experiment 17 alkylated and 19 non-alkylated polycyclic aromatic hydrocarbons (PAHs) and total petroleum hydrocarbons (TPHs, C₁₀–C₄₀) were extracted using semipermeable membrane devices from wastewater before and after treatment. The acquired data during experiments were analyzed using principal component analysis (PCA). The treatment system robustly removed dissolved PAHs across the studied ranges of the process parameters, providing overall removal efficiencies of 96.9–99.7% for the sum of 36 PAHs. However, the major contributor to their removal was sorption rather than biodegradation, and despite the general efficiency of the process there was up to a 9-fold range in the sums of quantified PAHs in the effluents between experiments. Combinations of long process contact time (24 h) with high temperature (24 °C) and moderate oxygen concentration (6–7 mg O₂ L⁻¹) resulted in good removal of bioavailable PAHs. The removal of TPHs was more dependent on biological activities during the wastewater treatment, and consequently more dependent on the process parameters. In addition, small but significant proportions of PAHs were volatilized and released during the wastewater treatment.     

An excavation method for large vertical cylindrical caverns

Construction of underground storage chambers in rock has traditionally adopted a construction-oriented approach; the cavern design and the method of excavation have been governed by the capabilities of the equipment available. One example is oil storage in unlined horizontal caverns. Today, however, equipment is no longer a limiting factor. The time has come to integrate the construction and operational aspects in the design process. This paper presents a construction concept developed for large vertical rock caverns with a circular or elliptical horizontal cross-section. The method of excavation, called PBM (Pillar Blasting Method), is condensed into a few main operations which are geometrically separated but overlapping in time. PBM is characterized by two main working sites per cavern, and by long-hole bench-drilling, massive blasting rounds, continuous loading and easy ventilation. Recent developments in drilling and blasting techniques are incorporated, such as the water-driven in-the-hole hammer and the electronic ignition system. PBM enables a high rate of excavation and provides a satisfactory working environment with respect to labour safety and human health (a limited exposure to large openings, no exposure to oil mist and to combustion and explosive fumes, etc). Considerable construction cost savings and time savings may thus be achieved compared to conventional methods of excavation for vertical and horizontal caverns of equal storage volume. A preliminary PCT patent (application No PCT/SE95/00324) has been granted. Examples of applications are fresh-water reservoirs, natural gas reservoirs, subsurface hydroelectric pump power plants, and similar objects which require a large underground storage space in preferably unlined rock caverns.