| 41. |
- Öberg, Tomas, 1956-
(författare)
-
Optimering är inget att vara rädd för
- 1998
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Ingår i: Tidningen Automation. - Solna : Automation. - 0345-1011. ; :8, s. 33-36
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 42. |
- Öberg, Tomas, 1956-
(författare)
-
Prediction of gas chromatographic separation for PBDE congeners from molecular descriptors
- 2004
-
Ingår i: The ESS Bulletin. - Kalmar : Environmental Science Section, Department of Biology and Environmental Science, University of Kalmar. - 1651-5382. ; 2:1, s. 74-90
-
Tidskriftsartikel (refereegranskat)abstract
- Polybrominated diphenyl ethers (PBDE) have been identified as environmental contaminants with a widespread distribution. The separation properties of PBDEs in high-resolution gas chromatography (HRGC) are important both for environmental analysis and for determining physical properties such as the vapour pressures. This study reports a quantitative structure-property relationship (QSPR), established between relative retention times on capillary HRGC and two constitutional structure descriptors that can perform equally well as more elaborate approaches. The simplified approach is recommended for explanatory models, while a more in-depth multivariate characterisation is suggested to assure similarity in applying prediction models.
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| 43. |
- Öberg, Tomas, 1956-, et al.
(författare)
-
Production of chlorinated aromatics in the post-combustion zone and boiler
- 1989
-
Ingår i: Chemosphere. - Oxford : Pergamon Press. - 0045-6535 .- 1879-1298. ; 19:1-6, s. 317-322
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Tidskriftsartikel (refereegranskat)abstract
- The production of halogenated aromatics has been investigated in the SAKAB hazardous waste incinerator, Norrtorp, Sweden. The measurement results show that there is a substantial net production of chlorinated aromatics in the boiler.
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| 44. |
- Öberg, Tomas, 1956-
(författare)
-
Replacement of PCBs (polychlorinated biphenyls) and HCB (hexachlorobenzene) : the Swedish experience
- 1996
-
Ingår i: Alternatives to persistent organic pollutants. - Solna : Kemikalieinspektionen. - 9923050106
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The total import to Sweden of PCB between 1957-1980 has been estimated to 8,000-10,000 metric tonnes. A substantial part of the import, probably more than 50% was re-exported in goods. The use of PCB in Sweden has been restricted since 1972, and in 1978 it was decided that no new permits to use PCB in new products should be issued. Remaining part in the power sector of the industry has also been removed. Transformers or capacitors containing PCB and with a higher rating than two kilovoltamperes (reactive) may not be used after the 31st of December 1994. PCB containing transformers were never manufactured in Sweden. The problem with PCB filled transformers and contaminated transformer oils has therefore been less severe, compared to many other industrialized countries. The main chemical alternative to PCB in transformers is mineral oil with different additives. PCB was used in the manufacture of capacitors in Sweden before 1978. The use for this purpose accounted for about 80% of the import of PCB. Chemical alternatives for PCB as capacitor fluid include a multitude of chemical compounds. The capacitor fluid most frequently used today in Sweden is a mixture of methyl(phenylmethyl)benzene and methylbis(phenylmethyl)benzene. PCB was used in different building materials as a plasticiser. Chemical alternatives include chlorinated paraffins and phthalates. Chlorinated paraffins are however replaced due to environ-mental concerns, and it has also been decided to phase out the phthalates. Substantial amounts of PCB, an estimated 190-650 metric tonnes, still remain in buildings. It is obvious that measures to deal with these problems may cost many times more than the replacement already accomplished. Destruction capability and capacity are keys to a successful and final solution to the PCB problem. The destruction cost is also the major cost factor in the replacement. 17,667 metric tonnes of PCB containing waste was received by SAKAB, the Swedish hazardous waste treatment plant, between 1987-1995. This gives an idea of how much PCB wastes that have to be handled. Minor amounts of HCB (hexachlorobenzene) has been used in some parts of the Swedish industry. HCB has not been manufactured in Sweden and previous use has been replaced. Estimates of the international production are contradictory. It therefore seems premature to neglect HCB as an organic micro-pollutant of environmental concern.
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| 45. |
- Öberg, Tomas, 1956-, et al.
(författare)
-
The correlation pattern of fly ash components : Chromium as a potential catalyst in the thermal formation of chlorinated aromatic compounds
- 2004
-
Ingår i: Environmental Chemistry. - 1448-2517 .- 1449-8979. ; 1:1, s. 18-21
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Tidskriftsartikel (refereegranskat)abstract
- Chlorinated aromatic compounds are unintentionally released from combustion sources into the environment. This thermal formation is catalyzed by fly ash components and much interest has been focussed on the role of copper. This study report results from a series of 16 full-scale trials with different fuel compositions. The correlation pattern of fly ash components seem to suggest that the catalytic effect may be due also to other metal oxychlorination catalysts. Chromium shows particularly strong and statistically significant correlations with many of the chlorinated phenols, benzenes, dibenzo-p-dioxins (PCDDs), and dibenzofurans (PCDFs).
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| 46. |
- Öberg, Tomas, 1956-
(författare)
-
Virtual screening for environmental pollutants : structure-activity relationships applied to a database of industrial chemicals
- 2006
-
Ingår i: Environmental Toxicology and Chemistry. - 0730-7268 .- 1552-8618. ; 25:4, s. 1178-1183
-
Tidskriftsartikel (refereegranskat)abstract
- The current risk paradigm calls for individual consideration and evaluation of each separate environmental pollutant, but this does not reflect accurately the cumulative impact of anthropogenic chemicals. In the present study, previously validated structure-activity relationships were used to estimate simultaneously the baseline toxicity and atmospheric persistence of approximately 50,000 compounds. The results from this virtual screening indicate fairly stable statistical distributions among small anthropogenic compounds. The baseline toxicity was not changed much by halogen substitution, but a distinct increase seemed to occur in the environmental persistence with increased halogenation. The ratio of the atmospheric half-lives to the median lethal concentrations provides a continuous scale with which to rank and summarize the incremental environmental impacts in a mixture-exposure situation. Halogenated compounds as a group obtained a high ranking in this data set, with well-known pollutants at the very top: DDT metabolites and derivatives, polychlorinated biphenyls, diphenyl ethers and dibenzofurans, chlorinated paraffins, chlorinated benzenes and derivatives, hydrochlorofluorocarbons, and dichlorononylphenol. Environmentally friendly chemicals that obtained the lowest rank are nearly all hydroxylated and water-soluble. Virtual screening can assist with "green chemistry" in designing safe and degradable products and enable assessment of the efficiency in chemicals risk management.
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| 47. |
- Cederqvist, Lars, et al.
(författare)
-
Reliability study of friction stir welded copper canisters containing Sweden's nuclear waste
- 2008
-
Ingår i: Reliability Engineering & System Safety. - : Elsevier. - 0951-8320 .- 1879-0836. ; 93:10, s. 1491-1499
-
Tidskriftsartikel (refereegranskat)abstract
- The plan for the final disposal of spent fuel from Swedish nuclear power plants is to place it in copper canisters that are sealed and stored in a deep repository. The canisters will be sealed by friction stir welding (FSW) and the reliability of this process has now been evaluated. The reliability study was performed in three steps: first an optimization experiment to identify optimal process settings and establish the process window; then a demonstration experiment with welding under production-like conditions; and finally a post-demonstration series to evaluate an adjustment in the welding equipment. A process window was defined around the optimal process setting, i.e., the limits within which the welding variables must lie in order for the process to produce the desired result. In the demonstration experiment, a series of 20 sealing welds was carried out under production-like conditions. The maximum discontinuity in each weld — detected by non-destructive testing — was fitted to a generalized extreme value distribution. The 95% confidence interval for the maximum discontinuity in a production series of 4500 canisters was estimated at 4.5–7.7 mm. The best estimate from the post-demonstration series suggests that the maximum size of a discontinuity will not exceed 2.3 mm. A main conclusion is that the FSW process produces reliable results, fulfilling the predetermined requirements for minimum copper thickness by a very good margin.
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| 48. |
- Filipsson, Monika, et al.
(författare)
-
Exponeringsfaktorer vid riskbedömning : Inventering av dataunderlag
- 2008
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Exponering definieras som kontakten mellan ett kemiskt, fysikaliskt eller biologiskt agens och den yttre avgränsningen för en organism. Människors exponering för kemiska ämnen i miljön styrs inte bara av förekomsten av en förorening, utan även av beteende, fysiologiska egenskaper och olika yttre faktorer. De mätbara variabler som används i exponeringsmodeller för att beskriva detta benämns exponeringsfaktorer. Den mest omfattande sammanställningen av data för olika exponeringsfaktorer härrör från USA, men det finns även ett par europeiska sammanställningar. Beteenden, fysiologiska egenskaper och yttre miljöfaktorer skiljer dock mellan olika länder. Det finns därför skäl att sammanställa sådana data även för svenskt vidkommande. En sammanställning kan även bidra till en viss standardisering av riskbedömningar. I föreliggande rapport redovisas exponeringsfaktorer för olika områden och i stora stycken överensstämmer urvalet med de tidigare nämnda internationella sammanställningarna. Redovisningen och dess omfattning påverkas även i hög grad av tillgången på data. Det innebär exempelvis att variabilitet (naturlig variation) och osäkerhet inte kan anges för alla faktorer. Dessa databrister är särskilt påtagliga vad gäller konsumtion av dricksvatten och hemodlade vegetabilier samt tidsanvändning. Dataunderlaget är däremot gott för fysiologiska parametrar som kroppsvikt och hudyta liksom den allmänna konsumtionen av livsmedel. För dessa exponeringsfaktorer redovisas statistiska parametrar som medelvärde, standardavvikelse, skevhet och kurtosis. Dessutom anges osäkerhetsintervall för dessa parametrar. Percentiler utgör ett användbart alternativ för presentera variabilitet (naturlig variation) och även sådana redovisas tillsammans med tillhörande osäkerhetsintervall. Ytterligare exponeringsfaktorer som behandlas i rapporten är åldersfördelning och flyttningsfrekvens, boende och byggnader, kontakt med mark och damm och markegenskaper. Förutom tabellerade värden återfinns även referenser till de primära datakällorna så att det är möjligt att själv gå vidare och fördjupa sig i underlaget. I rapporten jämförs även insamlade data med remissversionen av den svenska beräkningsmodellen för riktvärden för mark. Jämförelsen med denna modell visar att valda värden för exponeringsfaktorerna ibland motsvarar en bästa skattning (medelvärde/median), ofta en konservativ skattning och ibland en mycket konservativ skattning. Det går inte att utifrån dessa jämförelser dra några säkra slutsatser om dess inverkan på den slutliga riskbedömningen och beslut avseende åtgärder. Det är rapportförfattarnas förhoppning att föreliggande sammanställning ska underlätta och påskynda en övergång till riskbedömningsmetoder där variabilitet och osäkerhet kan uppskattas och redovisas kvantitativt.
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| 49. |
- Müller, Christina, et al.
(författare)
-
Strategy for verification and demonstration of the sealing process for canisters for spent fuel
- 2004
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Electron beam welding and friction stir welding are the two processes now being considered for sealing copper canisters with Sweden’s radioactive waste. This report outlines a strategy for verification and demonstration of the encapsulation process which here is considered to consist of the sealing of the canister by welding followed by quality control of the weld by non-destructive testing. Statistical methodology provides a firm basis for modern quality technology and design of experiments has been successful part of it. Factorial and fractional factorial designs can be used to evaluate main process factors and their interactions. Response surface methodology with multilevel designs enables further optimisation. Empirical polynomial models can through Taylor series expansions approximate the true underlying relationships sufficiently well. The fitting of response measurements is based on ordinary least squares regression or generalised linear methods. Unusual events, like failures in the lid welds, are best described with extreme value statistics and the extreme value paradigm give a rationale for extrapolation. Models based on block maxima (the generalised extreme value distribution) and peaks over threshold (the generalised Pareto distribution) are considered. Experiences from other fields of the materials sciences suggest that both of these approaches are useful. The initial verification experiments of the two welding technologies considered are suggested to proceed by experimental plans that can be accomplished with only four complete lid welds each. Similar experimental arrangements can be used to evaluate process "robustness" and optimisation of the process window. Two series of twenty demonstration trials each, mimicking assembly-line production, are suggested as a final evaluation before the selection of welding technology. This demonstration is also expected to provide a data base suitable for a baseline estimate of future performance. This estimate can then be used for the safety assessment. In order to provide data for the analysis of welds it is required to use well defined methods for the investigation of the weld integrity. As the total length of the welds produced during the verification and demonstration exceeds 140 m and these needs to be examined with a reasonable resolution non destructive methods (NDT) with high data acquisition rates are required. Destructive methods like metallographic sectioning and examination or tensile testing can be used only to provide complementary information as the acquisition of these data are labour-intensive and time consuming. As the analysis is relying on the reliability of the NDT it is required to have a strategy for the determination of this. Three different ways to investigate the reliability of NDT signals are described. The performance demonstration, the parameter approach and the Integral Approach: ROC – Receiver Operating Characteristic and its relation to POD (probability of detection). The first step of a performance demonstration is to define the essential technical parameters of the system. The ROC and POD methods are appropriate tools to provide a clear measure of integral performance of the system though it has to be paid by high effort in test series with realistic test samples. With POD the user can learn about the detection capability whereas the ROC gives more information about the system’s capability to distinguish between signal and noise. The modular approaches open the door to a promising technique – more efficient and with the capability also to optimize the system. The data evaluation methods chosen to be applied for this assessment is the quantitative POD (Probability of Detection) method according to MIL-STD 1823 /section B4/. The (1-POD) curve will provide the probability of missing a defect as function of defect size which can be used as input for probabilistic risk assessment. Finally, a hypothetical calculation example Appendix 2 is provided to illustrate the fitting of data and extrapolation using the extreme value models.
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| 50. |
- Öberg, Tomas, 1956-, et al.
(författare)
-
Metal catalyzed formation of chlorinated aromatic compounds : a study of the correlation pattern in incinerator fly ash.
- 2007
-
Ingår i: Chemosphere. - Oxford : Pergamon Press. - 0045-6535 .- 1879-1298. ; 67:9, s. S185-S190
-
Tidskriftsartikel (refereegranskat)abstract
- Chlorinated aromatics are unintentionally formed and released from combustion and other thermal processes involving organic matter and chlorine. The catalytic activity of incinerator fly ash in the low-temperature formation of chlorinated aromatics has been demonstrated in both laboratory experiments and full-scale trials. Copper has been shown to be an effective catalyst, but several other transition metals possess a similar activity. Here results are reported from a series of full-scale combustion trials with different fractions of household and industrial wastes, with waste from forestry as a reference fuel. The composition of elements and chlorinated aromatics in the fly ash was evaluated with principal component analysis and partial least squares regression. The observed correlation pattern indicates that metals other than copper are of equal importance for the catalytic activity. Chromium and nickel are two of these metals, which may contribute to the de novo formation of chlorinated benzenes, phenols, PCDD and PCDF.
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