| 1. |
- Al-Najjar, Basim
(författare)
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Condition-Based Maintenance: Selection and Improvement of a Cost-Effective Vibration-Based Maintenance Policy for Rolling element Bearings
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modern machinery is expensive and therefore must run at high availability and effectiveness which cannot be achieved without an effective maintenance policy. Condition monitoring, (CM), techniques can be utilised to reduce or arrest the rate of deterioration of a component so increasing operating life. The main result reported in this thesis is that the rolling element bearing’s mean effective life could be extended appreciably if an existing vibration-based maintenance policy is used effectively. This result is achieved by a combination of data analysis and logical development. A new maintenance approach was developed to overcome some of the limitations of total productive maintenance, TPM, and reliability-centered maintenance, RCM, and is based upon the Deming managerial feedback cycle (Plan-Do-Check-Act). This method is called Total Quality Maintenance, (TQMain). It is a methodology to sustain and improve continuously the technical and economic effectiveness of the manufacturing process elements. It is shown logically that by using vibration-based monitoring, (VBM), program in the frame of a common database for a plant IT-system the causes behind quality deviations and failures can be identified and eliminated effectively at an early stage and the company’s economics would be improved. The condition-based maintenance effectiveness and accuracy are usually related to the ability of the CM system to detect failure causes and follow defect development. Criteria to select the most cost-effective VBM system and the most cost-effective vibration-based maintenance policy are developed. But, in most real cases, CM systems are not utilised effectively and companies are satisfied with the partial savings achieved in maintenance cost. It is shown, by two case studies, that improvements in vibration-based maintenance can be achieved by effective feedback of the results of failures, renewal condition and VBM history analysis. Unfortunately the data coverage and quality in these studies were not sufficient, among other reasons due to the low number of failures and long bearing lives, so the conclusions, although supported by the work results, remain strong qualitative indications, rather than statistical proof. Criteria to measure the effect of improvements to confirm whether it is economically beneficial and to identify the basic reasons why it is not, are developed. The contribution of this thesis is: The development of a sequential method for the selection and improvement of a cost-effective vibration-based maintenance policy. This methodology can be used to justify, on economic criteria, the use of VBM systems to indicate when rolling element bearings should be renewed. It is achieved through; Tools used in quality and maintenance technology and reliability analysis have either been modified or developed beyond their original concept such as; Maintenance cost equation, Total Time On Test-plots. Development of new tools to monitor maintenance effectiveness and accuracy, select the most informative CM parameter(s) and cost-effective vibration-based maintenance policy. A new maintenance approach, (TQMain), and a new envelope alarming method for VBM programs are also developed. Theoretical basis for improvements to the effectiveness of vibration-based maintenance of bearings in paper mill machines and two case studies which tend to confirm the theory.
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| 2. |
- Andersson, Håkan S
(författare)
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Towards the Rational Design of Molecularly Imprinted Polymers
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Molecular imprinting is a technique by which polymeric materials selective for a given target molecule can be created through a casting procedure. Functionalised monomers are added to a solution of molecular templates. Monomer-template complexes are formed and subsequently fixed through polymerisation, and following removal of the template species from the resultant molecularly imprinted polymer, MIP, a material containing binding sites able to specifically rebind the template is left. The objective of the present work has been to learn more about the mechanisms leading to the formation of selective binding sites in MIPs and the nature of these sites (1-3), with the goal to utilise this knowledge to develop better MIPs (4-7). 1) UV spectroscopic studies of the pre-polymerisation mixture were utilised to estimate the stabilities of monomer-template complexes under different conditions. It was observed that many templates are not fully complexed by monomers, possibly leading to different binding site populations. Such heterogeneity is indeed observed in MIPs. The method developed was found useful for rapid evaluation of different monomers or conditions for a given template. 2) Chromatographic studies were performed on polymers imprinted with various pyridyl templates. It was demonstrated that electrostatic interactions were those mainly responsible for binding in these systems. It was also demonstrated that free rotors in the template structure affected binding and selectivity negatively, and that the accessibilities of functional groups were essential for the utility of the template for molecular imprinting. 3) Load capacity studies of nicotine and 4,4´-bipyridyl MIPs revealed two different behaviours. The retention of 4,4´-bipyridyl decreased upon raising the sample load, but nicotine exhibited an increase. Two possible explanations to this unexpected effect were suggested: mobile phase related nicotine solvation effects or a type of cooperative binding. A maximum in resolution for the separation of (+/-)-nicotine at different sample loads indicated the presence of recognition sites for template-template complexes, implying the possible imprinting of template-template complexes. 4) A chiral tartaric acid based monomer was synthesised and employed for the imprinting of cinchona alkaloids. The chirality of the monomer was shown able to enhance selectivity for certain templates. Post-polymerisation debenzylation of the MIP enhanced both retention and selectivity due to a change from hydrogen bond interactions to ionic interactions. 5) Crown ethers were employed as co-templates in molecular imprinting to demonstrate a principle by which organic solvent non-solubles can be solubilised, and imprinted, in organic media. Rebinding studies in the absence of crown ether revealed imprinting related selectivity. 6) Imprinting in water was achieved through the introduction of a hydrophilic cross-linker, a highly acidic monomer, and a beta-cyclodextrin based monomer, able to interact by hydrophobic interactions with aromatic ring structures. By this approach, the enantiomers of phenylalanine were successfully imprinted. 7) A series of monomer combinations were evaluated to optimise the polymer system described in (6). Binding site hydrophobicities were examined by fluorescence spectroscopy. This thesis demonstrates that there is significant room for improving the performance of MIPs and points to some ways by which this can be achieved.
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| 3. |
- Andersson, Solbritt, et al.
(författare)
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Effects of lime (CaCO3) on ectomycorrhizal colonization of Picea abies (L.) Karst. - seedlings planted in a spruce forest
- 1995
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Ingår i: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 10:2, s. 149-154
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Tidskriftsartikel (refereegranskat)abstract
- In two consecutive years, seedlings of Norway spruce (Picea abies) were planted in a 50-yr-old Norway spruce forest in limed (3.8 tons CaCO3 ha-1) and control plots. After 6 months they were harvested and the mycorrhizal status of the roots was analysed. Six types of mycorrhiza were distinguished. Three decreased after liming, two increased and one was not affected consistently by the liming. The effects on the total mycorrhizal colonization of the roots were opposite for the two years, indicating that the effects of liming are influenced strongly by other environmental factors. Statistical analysis also revealed pronounced natural variation in space. An inventory of the sporocarp-producing fungi showed that the number of saprotrophic species producing sporocarps was significantly higher in the limed plots whereas the number of ectomycorrhizal species was lower in the limed plots, compared with the control plots. It is concluded that more information is needed concerning the effects of liming on different soil types before any general conclusions can be made about its effects on mycorrhizal colonization.
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| 4. |
- Andersson, Solbritt, et al.
(författare)
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Effects of liming on the uptake of organic and inorganic nitrogen by mycorrhizal (Paxillus involutus) and non-mycorrhizal Pinus sylvestris plants
- 1997
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Ingår i: New Phytologist. - : Wiley. - 1469-8137 .- 0028-646X. ; 135:4, s. 763-771
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Tidskriftsartikel (refereegranskat)abstract
- Seedlings of Pinus sylvestris L. were grown in Plexiglas(R) observation chambers in limed (CaCO3, pH 5.0 and 5.9) and untreated (pH 4.1) peat. The seedlings were either colonized by the mycorrhizal fungus Paxillus involutus (Batsch: Fr.) Fr. Or were non-mycorrhizal. After 18 wk in the observation chambers, N-15-labelled organic nitrogen, as lyophilized and ground mycelium of Suillus variegatus (Swartz: Fr.) O. Kuntze, or ammonium, was added to the peat. The plants were harvested after an uptake period of 14 d. Irrespective of the nitrogen form added, liming decreased both the content and concentration of N-15 in nonmycorrhizal plants, and, to a lesser extent, those in mycorrhizal plants. In mycorrhizal plants the uptake of N-15 was not correlated with area colonized by the mycorrhizal mycelium. The amount of KCl-extractable N-15 in peat without plants and mycorrhizal fungi decreased with liming. It is proposed that liming induced chemical or microbial immobilization of the added N-15. This is suggested to be the main reason for the decreased uptake of N-15 in lime treatments.
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| 5. |
- Andersson, Solbritt, et al.
(författare)
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Effects of mycorrhizal colonization by Paxillus involutus on uptake of Ca and P by Picea abies and Betula pendula grown in unlimed and limed peat
- 1996
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Ingår i: New Phytologist. - 1469-8137 .- 0028-646X. ; 133:4, s. 695-704
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Tidskriftsartikel (refereegranskat)abstract
- Uptake of P(P-32) and Ca(Ca-45) by seedlings of Picea abies (L.) Karst and Betula pendula Roth, non-mycorrhizal or mycorrhizal with Paxillus involutus (Batsch: Fr) Fr. was studied. Seedlings were grown in unamended peat (pH 4.0) or in peat limed (CaO) to pH 5.1 or 6.1. A double-labelled (P-32 and Ca-45) complete nutrient solution was added to the peat 7 wk after planting. An 8 d period was allowed for uptake of the isotopes before the seedlings were harvested. Mycorrhizal colonization clearly increased the uptake of P(P-32) in the unlimed substrate and in the substrate limed to a pH of 5.1. At the highest lime rate, the uptake of P(P-32) was greatly reduced in both mycorrhizal and non-mycorrhizal seedlings. The difference in P uptake between mycorrhizal and non-mycorrhizal seedlings was small at this lime rate. The mycorrhizal colonization of the roots was not affected by liming. However, it is possible that the mycelial growth into the substrate was inhibited. The reduction in uptake could thus be an effect of a lower availability of P in combination with a decreased fungal uptake surface at the highest lime rate. The mycorrhizal effect on uptake of Ca was much smaller than its effect on uptake of P. Mycorrhizal colonization increased the Ca(Ca-45) uptake in the unlimed treatment, where the Ca content in the substrate was very small. In the limed substrates the uptake of Ca was as high or higher in the non-mycorrhizal than in the mycorrhizal seedlings.
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| 6. |
- Björck, S., et al.
(författare)
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Synchronized terrestrial-atmospheric deglacial records around the North Atlantic.
- 1996
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 274:5290, s. 1155-1160
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Tidskriftsartikel (refereegranskat)abstract
- On the basis of synchronization of three carbon-14 (C-14)-dated lacustrine sequences from Sweden With tree ring and ice core records, the absolute age of the Younger Dryas-Preboreal climatic shift was determined to be 11,450 to 11,390 +/- 80 years before the present. A 150-year-long cooling in the early Preboreal, associated with rising Delta(14)C values, is evident in all records and indicates an ocean ventilation change. This cooling is similar to earlier deglacial coolings, and box-model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the North Atlantic heat conveyor, although the Younger Dryas may have begun as an anomalous meltwater event.
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| 7. |
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| 8. |
- Börjesson, Pål, et al.
(författare)
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Biomass Transportation
- 1996
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481. ; 9:1-4, s. 1033-1036, s. 1033-1036
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Tidskriftsartikel (refereegranskat)abstract
- Extensive utilisation of logging residues, straw, and energy crops will lead to short transportation distances and thus low transportation costs. The average distance of transportation of biomass to a large-scale conversion plant, suitable for electricity or methanol production using 300 000 dry tonne biomass yearly, will be about 30 km in Sweden, if the conversion plant is located at the centre of the biomass production area. The estimated Swedish biomass potential of 430 PJ/yr is based on production conditions around 2015, assuming that 30% of the available arable land is used for energy crop production. With present production conditions, resulting in a biomass potential of 220 PJ/yr, the transportation distance is about 42 km. The cost of transporting biomass 30-42 km will be equivalent to 20-25% of the total biomass cost. The total energy efficiency of biomass production and transportation will be 95-97%, where the energy losses from transportation are about 20%. Biomass transportation will contribute less than 10% to the total NOx, CO, and HC emissions from biomass production, transportation, and conversion.
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| 9. |
- Börjesson, Pål, et al.
(författare)
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Future Production and Utilisation of Biomass in Sweden: Potentials and CO2 Mitigation
- 1997
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Ingår i: Biomass & Bioenergy. - 1873-2909 .- 0961-9534. ; 13:6, s. 399-412
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Tidskriftsartikel (refereegranskat)abstract
- Swedish biomass production potential could be increased significantly if new production methods, such as optimised fertilisation, were to be used. Optimised fertilisation on 25% of Swedish forest land and the use of stem wood could almost double the biomass potential from forestry compared with no fertilisation, as both logging residues and large quantities of excess stem wood not needed for industrial purposes could be used for energy purposes. Together with energy crops and straw from agriculture, the total Swedish biomass potential would be about 230 TWh/yr or half the current Swedish energy supply if the demand for stem wood for building and industrial purposes were the same as today. The new production methods are assumed not to cause any significant negative impact on the local environment. The cost of utilising stem wood produced with optimised fertilisation for energy purposes has not been analysed and needs further investigation. Besides replacing fossil fuels and, thus, reducing current Swedish CO2 emissions by about 65%, this amount of biomass is enough to produce electricity equivalent to 20% of current power production. Biomass-based electricity is produced preferably through co-generation using district heating systems in densely populated regions, and pulp industries in forest regions. Alcohols for transportation and stand-alone power production are preferably produced in less densely populated regions with excess biomass. A high intensity in biomass production would reduce biomass transportation demands. There are uncertainties regarding the future demand for stem wood for building and industrial purposes, the amount of arable land available for energy crop production and future yields. These factors will influence Swedish biomass potential and earlier estimates of the potential vary from 15 to 125 TWh/yr.
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| 10. |
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