| 1. |
- Afzelius, Mikael, et al.
(författare)
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Dual-broadband rotational CARS modelling of nitrogen at pressures up to 9 MPa. I. Inter-branch interference effect
- 2002
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171. ; 75:6-7, s. 763-769
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Tidskriftsartikel (refereegranskat)abstract
- An improved model for pure rotational coherent anti-Stokes Raman scattering (CARS) has been developed or the dual-broadband approach. This model takes into account the fact that coherent anti-Stokes as well as Stokes radiation are generated simultaneously, and these two branches overlap and interact at high pressures giving rise to an inter-branch interference effect. In combustion studies, the anti-Stokes branch is used to determine temperature and concentrations of key species, of which nitrogen is the most widely used, and we have found that the interference effect on the anti-Stokes side is of such magnitude that it clearly needs to be taken into account at pressures of a few MPa. The necessary modifications to the total third-order susceptibility are presented and a derivation of the convolution integral for a finite-bandwidth pump source is given.
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| 2. |
- Afzelius, Mikael, et al.
(författare)
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Dual-broadband rotational CARS modelling of nitrogen at pressures up to 9 MPa. II. Rotational Raman line widths
- 2002
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171. ; 75:6-7, s. 771-778
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Tidskriftsartikel (refereegranskat)abstract
- Rotational coherent anti-Stokes Raman spectroscopy (CARS) is a well-established spectroscopic technique for thermometry at pre-combustion temperatures an atmospheric pressure. However, at pressures of several MPa, a previous investigation revealed large discrepancies between experimental data and the theoretical model. A re-evaluation has been made of these data (at room temperature and in the range 1.5-9 MPa) with two improvements to the spectral code. The first is the inclusion of an inter-branch interference effect, which is described in detail in Paper I. The second is the use of experimental S-1-branch Raman line widths measured at 295 K, with a temperature dependence extracted from semi-classical calculations following the Robert-Bonamy formalism. It is shown that these two modifications significantly improve the theoretical model, since both the spectral fits and the accuracy of the evaluated temperatures are considerably improved.
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| 3. |
- Afzelius, Mikael, et al.
(författare)
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Precision of single-shot dual-broadband rotational CARS thermometry with single-mode and multi-mode Nd : YAG lasers
- 2003
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 34:12, s. 940-945
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Konferensbidrag (refereegranskat)abstract
- The precision of single-shot coherent anti-Stokes Raman spectroscopy (CARS) thermometry is an important characteristic for the application of CARS in various combustion devices such as internal combustion engines. It is generally assumed that the precision of CARS is directly related to the spectral noise of the interacting laser fields, and previous studies have presented a theoretical model describing the behaviour of the noise as a function of various experimental parameters. In this work, the aim was to test the results predicted by the previously developed model for dual-broadband rotational CARS. We studied the precision of evaluated temperatures in pure nitrogen under different experimental conditions, namely the dependence of precision on the gas pressure and on the linewidth of the narrowband laser (the Nd: YAG laser). It was demonstrated that our experiments reproduce the main features of the model, and that a single-mode Nd: YAG laser leads to better precision than a multi-mode Nd: YAG laser for dual-broadband rotational CARS thermometry. Copyright (C) 2003 John Wiley Sons, Ltd.
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| 4. |
- Afzelius, Mikael, et al.
(författare)
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Pure rotational coherent anti-Stokes Raman spectroscopy in mixtures of CO and N-2
- 2004
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Ingår i: Applied Optics. - 2155-3165. ; 43:36, s. 6664-6672
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Tidskriftsartikel (refereegranskat)abstract
- We present a model for quantitative measurements in binary mixtures of nitrogen and carbon monoxide by the use of dual-broadband rotational coherent anti-Stokes Raman spectroscopy. The model has been compared with experimental rotational coherent anti-Stokes Raman scattering spectra recorded within the temperature range of 294-702 K. Temperatures and concentrations were evaluated by spectral fits using libraries of theoretically calculated spectra. The relative error of the temperature measurements was 1-2%, and the absolute error of the CO concentration measurements was <0.5% for temperatures less than or equal to600 K. For higher temperatures, the gas composition was not chemically stable, and we observed a conversion of CO to CO2. The influence of important spectroscopic parameters such as the anisotropic polarizability and Raman line-broadening coefficients are discussed in terms of concentration measurements. In particular, it is shown that the CO concentration measurement was more accurate if N-2-CO and CO-N-2 line-broadening coefficients were included in the calculation. The applicability of the model for quantitative flame measurements is demonstrated by measuring CO concentrations in ethylene/air flames. (C) 2004 Optical Society of America.
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| 5. |
- Afzelius, Mikael, et al.
(författare)
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Semiclassical calculations of collision line broadening in Raman spectra of N-2 and CO mixtures
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:18, s. 8616-8623
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed theoretical study of pressure-broadened Raman line shapes in binary mixtures of nitrogen and carbon monoxide. The semiclassical Robert-Bonamy theory was used to calculate self-broadened Q-branch linewidths of N-2 and CO, and Lennard-Jones (LJ) potential energy surface parameters were fixed by comparing our results with extensive experimental linewidth data. For the case of N-2, the ab initio PES8 potential energy surface was investigated, however, the anisotropic repulsive part had to be reduced to ensure a good agreement with experimental linewidths. The agreement between calculations and experiments was remarkably good, both for self-broadened N-2 and CO Q-branch linewidths. Yet, our calculations were not able to predict the experimentally observed difference between Q- and S-branch linewidths of self-broadened N-2. The central results of this work are the Q-branch linewidths of N-2-CO and CO-N-2, which have been calculated through an extrapolation of the parameters of the potential energy surfaces used for self-broadened linewidths by common combination rules. (C) 2004 American Institute of Physics.
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| 6. |
- Axelsson, Boman, et al.
(författare)
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Laser-induced incandescence for soot particle size and volume fraction measurements using on-line extinction calibration
- 2001
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 72:3, s. 367-372
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Tidskriftsartikel (refereegranskat)abstract
- A novel technique for two-dimensional measurements of soot volume fraction and particle size has been developed. It is based on a combined measurement of extinction and laser-induced incandescence using Nd:YAG laser wavelengths of 532 nm and 1064 nm. A low-energy laser pulse at 532 nm was used for extinction measurements and was followed by a more intense pulse at 1064 nm, delayed by 15 ns, for LII measurements. The 532-nm beam was split into a signal beam passing the flame and a reference beam, both of which were directed to a dye cell. The resulting fluorescence signals, from which the extinction was deduced, together with the LII signal, were registered on a single CCD detector. Thus the two-dimensional LII image could be converted to a soot volume fraction map through a calibration procedure during the same laser shot. The soot particle sizes were evaluated from the ratio of the temporal LII signals at two gate time positions. The uncertainty in the particle sizing arose mainly from the low signal for small particles at long gate times and the uncertainty in the flame temperature. The technique was applied to a well-characterized premixed flat flame, the soot properties of which had been previously thoroughly investigated.
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| 7. |
- Axelsson, Boman, et al.
(författare)
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Laser-Induced Incandescence for Soot Particle Size Measurements in Premixed Flat Flames
- 2000
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Ingår i: Applied Optics. - 2155-3165. ; 39:21, s. 3683-3690
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of soot properties by means of laser-induced incandescence (LII) and combined scattering–extinction were performed in well-characterized premixed ethylene–air flames. In particular, the possibility of using LII as a tool for quantitative particle sizing was investigated. Particle sizes were evaluated from the temporal decay of the LII signal combined with heat balance modeling of laser-heated particles, and these sizes were compared with the particle sizes deduced from scattering–extinction measurements based on isotropic sphere theory. The correspondence was good early in the soot-formation process but less good at later stages, possibly because aggregation to clusters began to occur. A critical analysis has been made of how uncertainties in different parameters, both experimental and in the model, affect the evaluated particle sizes for LII. A sensitivity analysis of the LII model identified the ambient-flame temperature as a major source of uncertainty in the evaluated particle size, a conclusion that was supported by an analysis based on temporal LII profiles.
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| 8. |
- Bengtsson, Bo, 1947-, et al.
(författare)
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Lokal kontroll och kollektivt handlande : En utvärdering av självförvaltning i Bostads AB Poseidon i Göteborg
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Local Control and Collective Action. An Evaluation of Self-Management in the Municipal Housing Company Poseidon in Gothenburg. This report presents an evaluation over three years of a programme on ’local democracy and self-management’ in the municipal housing company Poseidon in Gothenburg. The point of departure is the assumption that a programme of this type has to offer both local control and individual motives for collective action if it is to be sustainable. Tenants must be able to influence housing conditions together, as well as to have some individual motivation to take part in the activities. The evaluation is based mainly on three data sources: (1) a questionnaire distributed to a random sample of 1400 tenants; (2) a number of questionnaires distributed to all tenants who are active in the self-management, all chair-persons in local tenants associations (LTAs) in Poseidon’s housing stock, and all Poseidon’s ’area hosts’, who are responsible for the local management of the estates; (3) intensive studies of the processes of self-management in seven local housing estates. Use has also been made of official and company statistics, earlier surveys, programmes, agreements, minutes and other documents, as well as interviews with key informants, observations from meetings and inspections in the estates. The report includes a comprehensive evaluation in terms of tenants’ local control and collective action and a number of special studies on particular themes and perspectives.By Autumn 2002 self-management had been established in all Poseidon’s districts and in a considerable share of the housing stock. The number of active tenants was estimated at 800–1000. They are organised in about 80, mainly informal and rather loosely defined groups. The ambitious programme aiming at considerable local decision-making proved to be unrealistic, and activities today are based on informal collaboration between local staff and active tenants, in a few cases formalised in ’estate associations’. Initially both the area hosts and the representatives of the local tenants movement were rather sceptical of the self-management, but both groups have gradually acquired a more positive attitude.At the time of the tenant questionnaire (January 2001) no more than one fourth of all tenants knew about the project, but since the knowledge was clearly better in those districts where activities were most developed, the share today is probably considerably higher, perhaps nearly 40 per cent. Ordinary tenants consider that most physical aspects of the outdoor environment has been improved, in particular the care of plants and lawns. In contrast they see only minor positive effects on social relations. Active tenants, LTA chair-persons and area hosts all judge that the self-management has had clear positive effects on the outdoor environment and on tenants’ influence, as well as on the social ties and general well-being among residents. Tenants, and not only active tenants, feel an improved sense of control over their housing conditions.A majority of the active tenants are women. While women have been engaged in all types of activities, men have primarily taken on physically demanding tasks. Tenants with foreign background are somewhat fewer among the active than their share of the population, but still they are better represented than usual in local housing activities. This may be due to the informal organisation and the orientation towards practical work. The self-management also seems to have stimulated a higher growth in commitment and sense of responsibility among tenants with foreign background than among those with Swedish background.The active tenants are on average 55 years old; the active women on average nine years younger than the active men. The share of age pensioners is high, and a large number of the somewhat younger activists are also without gainful employment. The active tenants take part in organisational and political life somewhat more than the population in general. Their prime mover is a ’norm of local utility’, i.e. a norm that prescribes that they take part if it would mean a positive contribution to the common good of their neighbourhood. Economic incentives are less prominent, and the participation of one’s neighbours is rarely seen as a prerequisite of taking part oneself. The tenants’ most important resources are time in and knowledge of the estate, and the work carried out comprises an important contribution to the management of Poseidon’s housing stock.The intensive studies – in most cases in housing estates with a relatively high level of activity – confirm this picture. They also make clear that the self-management activities are dominated by informally organised practical work outdoors. The case studies also show that the mode of interplay between active tenants and local staff is formed to a large extent by local conditions and traditions. The decentralised organisation of Poseidon’s housing management has been of particular importance to the actual influence of the tenants. The decentralisation of decision-making has made it meaningful to keep up a continuous and goal-oriented dialogue about the different issues that have been raised locally.The self-management has improved the outdoor environment and strengthened the ties between the active tenants as well as their identification with the estate. However, the effect on ecological issues has been limited, and so have the direct economic effects on housing management. Conflicts have been few and the informal conflict management has been on the whole successful. The absence of formally democratic elections, decision-making and accountability has sometimes been a problem when controversial issues have come up on the local agenda. Still many active tenants in the case-study estates are sceptical of introducing more formal procedures. By now the self-management has reached a certain degree of institutionalisation within the company. In contrast the prospects of institutionalisation among tenants still seem uncertain. The absence of democratic forms of decision-making could make it difficult to deal with issues about rents, periodic maintenance and repair, local rules of conduct, etc. A crucial condition for Poseidon’s self-management to be sustainable is that the positive attitudes of the company and the local staff will continue, another that a workable division of responsibility between the tenants association and the self-management can be developed. The most plausible scenario is a development towards a higher degree of differentiation. This would mean some estates without local collective action, other estates remaining on the current level of informal work on the outdoor environment, and still other moving towards formal local democracy and influence.
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| 9. |
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| 10. |
- Bengtsson, Marcus, et al.
(författare)
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Technical Design of Condition Based Maintenance Systems - A Case Study Using Sound Analysis and Case-Based Reasoning
- 2004
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Konferensbidrag (refereegranskat)abstract
- Productivity is a key weapon for manufacturing companies to stay competitive in a continuous growing global market. Increased productivity can be achieved through increased availability. This has directed focus on different maintenance types and maintenance strategies. Increased availability through efficient maintenance can be achieved through less corrective maintenance actions and more accurate preventive maintenance intervals. Condition Based Maintenance (CBM) is a technology that strives to identify incipient faults before they become critical which enables more accurate planning of the preventive maintenance. CBM can be achieved by utilizing complex technical systems or by humans manually monitoring the condition by using their experience, normally a mixture of both is used. Although CBM holds a lot of benefits compared to other maintenance types it is not yet commonly utilized in industry. One reason for this might be that the maturity level in complex technical CBM system is too low. This paper will acknowledge this possible reason, although not trying to resolve it, but focusing on system technology with component strategy and an open approach to condition parameters as the objective is fulfilled. This paper will theoretically discuss the technical components of a complete CBM system approach and by a case study illustrate how a CBM system for industrial robot fault detection/diagnosis can be designed using the Artificial Intelligence method Case-Based Reasoning and sound analysis.
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