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- Öberg, Tomas, 1956-
(författare)
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Importance of the first design matrix in experimental simplex optimization
- 1998
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Ingår i: Chemometrics and Intelligent Laboratory Systems. - Amsterdam : Elevier. - 0169-7439 .- 1873-3239. ; 44:1-2, s. 147-151
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Tidskriftsartikel (refereegranskat)abstract
- The basic and modified simplex methods are efficient optimization techniques applied in many fields of chemistry and engineering. Various first design matrices were evaluated on polynomial models with added noise. D-optimal linear design matrices performed better than regular or cornered first simplices in the normal experimental situation. These findings have been implemented in a new experimental design an optimization software, the MultiSimplex(R).
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| 2. |
- Öberg, Tomas, 1956-
(författare)
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Validering av prediktionsmodeller för NOx-mätning
- 1996
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Indirekt bestämning NOx-utsläpp med hjälp av prediktionsmodeller kan godtas för bestämning av miljöavgift. Kraven på tillförlitlighet förutsätts bli likartade som för mätutrustningar. Rapporten redovisar hur prediktionsmodeller bör utformas för att motsvara dessa krav. Ett stort antal anläggningar i USA använder redan nu prediktionsmodeller för att bestämma utsläppet av kväveoxider. De förslag till valideringskrav som har föreslagits är likartade som för mätutrustningar. Modellen skall upprättas utifrån mätdata från jämförande mätningar där olika driftsinställningar provas. Verifieringen genomförs likartat, med ett specificerat prestandakrav för precision och riktighet. I Sverige är detaljerade kvalitetskrav för prediktionsmodeller ännu inte fastställda. Följande punkter måste dock beaktas: - Ingångsdata för modelluppbyggnad. - Modellverifiering - rekalibrering. - Prestanda och definition av kalibreringsområde. - Kontroll av giltighet och signalvalidering. En genomgång av resultat från två genomförda projekt visar att indirekt bestämning av kväveoxider är tekniskt möjlig. Rapporten avslutas med ett förslag till "översättning" av Naturvårdsverkets nuvarande prestandakrav för mätinstrument. Det viktigaste prestandakraven för prediktionsmodellerna vid jämförande mätningar är att den systematiska skillnaden liksom standardavvikelsen högst får uppgå till 10% av kalibreringsområdet och högst 10 ppm tg.
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| 3. |
- Öberg, Tomas, 1956-
(författare)
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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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| 4. |
- Öberg, Tomas, 1956-
(författare)
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Replacement of PCBs (polychlorinated biphenyls) and HCB (hexachlorobenzene) : the Swedish experience
- 1996
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Ingår i: Alternatives to persistent organic pollutants. - Solna : Kemikalieinspektionen. - 9923050106
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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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| 5. |
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| 6. |
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| 7. |
- Fiedler, Heidelore, 1953-, et al.
(författare)
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Case study of a highly dioxin contaminated sports field : Environmental risk assessment and human exposure
- 1995
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Ingår i: Journal of Hazardous Materials. - : Elsevier. - 0304-3894 .- 1873-3336. ; 43:3, s. 217-227
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Tidskriftsartikel (refereegranskat)abstract
- Copper slag, containing high levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDF) was used as covering material of a community sports field. This led to a contamination up to 40 000 fold in comparison to background concentrations in soils. Levels and patterns of dioxins found in sediments of a nearby river proved a translocation of contaminated copper slag, while slightly elevated dioxin levels found in soil from nearby house gardens could not be attributed to the sports field as the source of dioxins.The annual flux of dioxins and furans to the environment was estimated using worst-case assumptions and the potential exposure of humans was deduced. Calculations of possible PCDD/PCDF-fluxes to the environment showed that only one major process - wind erosion - may have contributed to more than 90% of the total dioxin flux from the contaminated site to the surroundings, Based on PCDD/PCDF-exposure pathways for humans it was concluded that the PCDD/PCDF-content of the copper slag of the sports field did not pose a health hazard to athletes nor to the residents living in the neighbourhood.
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| 8. |
- Acke, Filip, et al.
(författare)
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Study of the reduction and reoxidation of a CaO surface
- 1997
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Ingår i: J Phys Chem B. - 1520-5207 .- 1520-6106. ; 101:33
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Tidskriftsartikel (refereegranskat)abstract
- The reduction of NO with CO and H2 is shown to comprise two basic reactions: a surface oxygen abstraction by the reducing agent and a reoxidation of the surface by NO. The former reaction step has been demonstrated by transient CO2 formation during CO exposure of oxidized CaO surfaces, while the latter was demonstrated by N2 and/or N2O transient formation during NO exposure of a prereduced CaO surface. It was shown that at low temperatures (between room temperature and 500 °C) both N2 and N2O were formed, but at temperatures above 500 °C only N2 was observed. The activation energies of the respective steps have been determined using temperature-programmed reaction experiments. The activation energy of the surface oxygen abstraction was determined to be 25 kcal/mol and is similar to the apparent activation energy of the overall reaction. The activation energy of the NO bond breakage was determined to be maximum 10 kcal/mol as measured by N2O formation. The importance of an N2O2- or N2O22- intermediate in the formation of N2O will be discussed, and the importance of N2O decomposition in forming N2 at temperatures above 500 °C will be compared with a N surface diffusion mechanism.
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| 9. |
- Fiedler, Heidelore, 1953-, et al.
(författare)
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Patterns and sources of polychlorinated dibenzo-p-dioxins and dibenzofurans found in soil and sediment samples in southern Mississippi
- 1996
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Ingår i: Chemosphere. - : Elsevier. - 0045-6535 .- 1879-1298. ; 32:3, s. 421-432
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Tidskriftsartikel (refereegranskat)abstract
- Using hierarchical cluster analysis and Principal Component Analysis (PCA), sediment and soil samples from the State of Mississippi were compared with the effluents of a pulp mill, a potential point source. Additionally, data of many known sources of PCDD/PCDF from the scientific literature were evaluated. Both methods were able to distinguish between different matrices with known PCDD/PCDF contamination (e.g. PCP, PCB, kraft pulp mill effluents). In some instances, a specific PCDD/PCDF source could be correlated to an environmental sample, e.g. the pattern of a U.S, brand of pentachlorophenate was found in sediment samples. None of the mathematical and statistical techniques could identify the pulp mill as the source of the PCDD/PCDF in the sediments and soils in the floodplain.
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| 10. |
- Fiedler, Heidelore, 1953-, et al.
(författare)
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PCDD, PCDF, and PCB in farm-raised catfish from southeast United States - Concentrations, sources, and CYP1A induction
- 1998
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Ingår i: Chemosphere. - : Elsevier. - 0045-6535 .- 1879-1298. ; 37:9-12, s. 1645-1656
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Tidskriftsartikel (refereegranskat)abstract
- Nine catfish fillets, three catfish nuggets, two feed samples, and one pond sediment were analyzed for PCDD, PCDF, and-PCB. Farm-raised catfish from Mississippi, Alabama, and Arkansas contained significant levels of 2,3,7,8-substituted PCDD and PCDF. In addition, a large number of non-2,3,7,8-substituted congeners were present in all samples. The catfish fillets and catfish nuggets also contained high concentrations of dioxin-like PCB, as well as a number of non-dioxin-like PCB. The TEQ based on PCDD and PCDF ranged from 9.5 to 43.0 pg/g lipid and the TEQ based on PCB ranged from 0.45 to 4.9 pg/g lipid for all catfish samples. The dioxin-like PCB contributed 4-16% to the total TEQ (PCDD/PCDF/PCB) for the catfish samples. The major source for the PCDD, PCDF, and PCB appears to be from feed and not from pond sediment. Immunoreactive CYP1A protein was elevated 2.5 fold in the pond-raised catfish compared to the aquarium-raised one. The results of this study suggest that the PCDD/PCDF are more important than the PCB in the CYP1A induction.
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