| 1. |
- Afzelius, Mikael, et al.
(author)
-
Development of multipoint vibrational coherent anti-Stokes Raman spectroscopy for flame applications
- 2006
-
In: Applied Optics. - 2155-3165. ; 45:6, s. 1177-1186
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Journal article (peer-reviewed)abstract
- A novel technique for coherent anti-Stokes Raman spectroscopy (CARS) measurements in multiple points is presented. In a multipass cavity the pump and Stokes laser beams are multiply reflected and refocused into a measurement volume with an adjustable number of separated points along a line. This optical arrangement was used in a vibrational CARS setup with planar BOXCARS phase-matching configuration. The CARS spectra from spatially separated points were recorded at different heights on a CCD camera. Measurements of temperature profiles were carried out in the burned gas zone of a premixed one-dimensional flame to demonstrate the applicability of this method for temperature measurements in high-temperature regions. The ability to measure in flames with strong density gradients was demonstrated by simultaneous measurements of Q-branch spectra of N-2 and CO in a Wolfhard-Parker burner flame. Interference phenomena found in multipoint spectra are discussed, and possible solutions are proposed. Merits and limitations of the technique are discussed. (c) 2006 Optical Society of America.
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| 2. |
- Bladh, Henrik, et al.
(author)
-
Experimental and theoretical comparison of spatially resolved laser-induced incandescence (LII) signals of soot in backward and right-angle configuration
- 2006
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 83:3, s. 423-433
-
Journal article (peer-reviewed)abstract
- In-situ measurements of soot volume fraction in the exhausts of jet engines can be carried out using the laser-induced incandescence (LII) technique in backward configuration, in which the signal is detected in the opposite direction of the laser beam propagation. In order to improve backward LII for quantitative measurements, we have in this work made a detailed experimental and theoretical investigation in which backward LII has been compared with the more commonly used right-angle LII technique. Both configurations were used in simultaneous visualization experiments at various pulse energies and gate timings in a stabilized methane diffusion flame. The spatial near-Gaussian laser energy distribution was monitored on-line as well as the time-resolved LII signal. A heat and mass transfer model for soot particles exposed to laser radiation was used to theoretically predict both the temporal and spatial LII signals. Comparison between experimental and theoretical LII signals indicates similar general behaviour, for example the broadening of the spatial LII distribution and the hole-burning effect at centre of the beam due to sublimation for increasing laser pulse energies. However, our comparison also indicates that the current heat and mass transfer model overpredicts signal intensities at higher fluence, and possible reasons for this behaviour are discussed.
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| 3. |
- Bladh, Henrik, et al.
(author)
-
Experimental and theoretical comparison of spatially resolved laser-induced incandescence signals in a sooting flame
- 2005
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In: Proceedings of the European Combustion Meeting.
-
Conference paper (other academic/artistic)abstract
- A detailed experimental and theoretical investigation has been made on the use of Laser-Induced Incandescence (LII) in two configurations; right-angle LII and backward LII. Both right-angle and backward LII imaging measurements were conducted in simultaneous experiments at various pulse energies. The theoretically calculated LII signals were based on a heat transfer model for soot particles exposed to laser radiation, and were compared with the experimental LII images. Both the experimental and theoretical results from this initial comparison showed similar general behaviour, for example the broadening of the spatial LII distribution and the hole-burning effect at centre for increasing laser pulse energies.
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| 4. |
- Bladh, Henrik, et al.
(author)
-
Flame propagation visualization in a spark-ignition engine using laser-induced fluorescence of cool-flame species
- 2005
-
In: Measurement Science & Technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 16:5, s. 1083-1091
-
Journal article (peer-reviewed)abstract
- The flame propagation in a spark-ignition engine has been studied using laser-induced fluorescence (LIF) of species formed during the first ignition stage of hydrocarbon combustion. The detected two-dimensional LIF images showed the distribution of unburned regions. For the excitation, two Nd:YAG lasers operating at 355 mn were used for two consecutive measurements within the same engine cycle with adjustable time separation between the pulses. Two ICCD cameras that were synchronized to each of the laser pulses recorded pairs of fluorescence images, i.e. the movement of the flame front could be tracked. It is well known that formaldehyde is excited using a wavelength of 355 nm and a spectral signature of this species was also identified in engine LIF spectra. Programme routines were developed and used for evaluation of the flame propagation velocity from the fluorescence images. This paper presents the potential and the characteristics of the experimental technique as well as the evaluation procedure. The measurements of cool-flame intermediates have also been compared with measurements of fuel-tracer as an indicator of unburned fuel-air mixture. A good agreement between position and shape of the signal areas was obtained at crank angles where both fluorescence signal from cool-flame species excited at 355 nm and added 3-pentanone excited at 266 nm could be detected.
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| 5. |
- Bladh, Henrik, et al.
(author)
-
Influence of spatial laser energy distribution on evaluated soot particle sizes using two-colour laser-induced incandescence in a flat premixed ethylene/air flame
- 2009
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 96:4, s. 645-656
-
Journal article (peer-reviewed)abstract
- Time-resolved laser-induced incandescence (LII) has been developed rapidly during the last decade as a useful non-intrusive technique for particle size determination. Still several parameters should be investigated in order to improve the accuracy of LII for particle sizing and the spatial distribution of the laser energy is one of these. Generally a top-hat profile is recommended, as this ensures a uniform heating of all particles in the measurement volume. As it is generally not straightforward to create a uniform beam profile, it is of interest to establish the influence of various profiles on the evaluated particle sizes. In this work we present both an experimental and a theoretical investigation of the influence of the spatial profile on evaluated sizes. All experiments were carried out using a newly developed setup for two-colour LII (2C-LII) which provides online monitoring of both the spatial and temporal profile as well as the laser pulse energy. The LII measurements were performed in a one-dimensional premixed sooting ethylene/air flame, and evaluated particle sizes from LII were compared with thermophoretically sampled soot particles analysed using transmission electron microscopy (TEM). The results show that although there is some influence of the spatial laser energy distribution on the evaluated particle sizes both in modelling and experiments, this effect is substantially smaller than the influence of the uncertainties in gas temperature and the thermal accommodation coefficient.
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| 6. |
- Bladh, Henrik, et al.
(author)
-
On the dependence of the laser-induced incandescence (LII) signal on soot volume fraction for variations in particle size
- 2008
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In: Applied Physics B: Lasers and Optics. - : Springer Science and Business Media LLC. ; 90:1, s. 109-125
-
Journal article (peer-reviewed)abstract
- “The laser-induced incandescence (LII) signal is proportional to soot volume fraction” is an often used statement in scientific papers, and it has – within experimental uncertainties – been validated in comparisons with other diagnostic techniques in several investigations. In 1984 it was shown theoretically in a paper by Melton that there is a deviation from this statement in that the presence of larger particles leads to some overestimation of soot volume fractions. In the present paper we present a detailed theoretical investigation of how the soot particle size influences the relationship between LII signal and soot volume fraction for different experimental conditions. Several parameters have been varied; detection wavelength, time and delay of detection gate, ambient gas temperature and pressure, laser fluence, level of aggregation and spatial profile. Based on these results we are able, firstly, to understand how experimental conditions should be chosen in order to minimize the errors introduced when assuming a linear dependence between the signal and volume fraction and secondly, to obtain knowledge on how to use this information to obtain more accurate soot volume fraction data if the particle size is known.
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| 7. |
- Bladh, Henrik, et al.
(author)
-
Quantitative soot measurements in an HSDI Diesel engine
- 2006
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Conference paper (peer-reviewed)abstract
- Quantitative in-cylinder measurements of soot volume fraction in a single-cylinder HSDI Diesel engine, based on a VOLVO D5, has been carried out using the laser-induced incandescence (LII) technique using laser excitation at 1064 nm and an ICCD camera with prompt gate detection. Quantitative data was obtained by relating the LII signal response from the engine to that from a calibration flame. The aim of this paper is twofold: to present quantitative data for relevant engine operating conditions and to discuss the issues related to quantification of the LII technique using the present approach. Two different operating condition schemes were investigated. In the first, the soot production for different amounts of EGR was investigated. The in-cylinder soot volume fraction levels were found to decrease with increasing EGR ratio in the tested EGR regime, which correlates well with engine-out soot emissions. In the second part of the investigation, the injection event was divided into one pilot injection and one main injection at a constant EGR ratio of 60%. The CAD position of the pilot injection was varied, while keeping the position of the main injection constant. Early pilot injection timings resulted in excessive fouling of the optical parts, thus limiting the accuracy of quantitative measurements. Still, the flow pattern of the soot within the cylinder is presented and discussed. The corrections needed to accurately estimate soot volume fractions in an optical engine by relating the integrated LII signal to that obtained in a calibration flame are discussed. Using a heat and mass transfer model for LII, the pressure and temperature effects on the absolute LII signals are investigated. Results show that the use of a short prompt gate (30 ns) is preferable in order to decrease systematic errors due to differences in the conditions between the engine and the calibration flame. Also the systematic errors introduced by potential particle aggregation are studied and discussed.
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| 8. |
- Bohlin, Alexis, et al.
(author)
-
Improvement of rotational CARS thermometry in fuel-rich hydrocarbon flames by inclusion of N-2-H-2 Raman line widths
- 2009
-
In: Journal Of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 40:7, s. 788-794
-
Conference paper (peer-reviewed)abstract
- In rotational coherent anti-Stokes Raman spectroscopy (CARS) thermometry applied to air-fed flames, the temperature sensitivity mainly depends on the intensity distribution of the nitrogen spectral lines. Temperatures are estimated by numerical fitting of theoretical spectra to experimental ones, and one uncertainty in the calculation of theoretical CARS spectra for specific flame conditions is the accuracy in utilized line-broadening coefficients. In a previous article, self-broadened N-2-N-2 line widths were considered in the spectral calculations as well as those of N-2-CO, N-2-CO2, N-2-H2O, and N-2-O-2- In the present article, we also include N-2-H-2 line widths calculated from a newly developed model, and it is shown that the evaluated temperature from flame spectra increases with increasing mole fractions of hydrogen. For example, in a very rich flame at Phi = 2.5, the use of available line-width data for all major species gives a temperature raise of 72 K at a temperature of similar to 1700 K, in comparison with using self-broadened N-2-N-2 line widths only. Half of this temperature raise is related to the inclusion of N-2-H-2 line widths. This article emphasizes the importance of using adequate line-broadening models for rotational CARS thermometry in flames. Copyright (C) 2009 John Wiley & Sons, Ltd.
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| 9. |
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| 10. |
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| 11. |
- Bondesson, Eva, et al.
(author)
-
Site of deposition and absorption of an inhaled hydrophilic solute
- 2007
-
In: British Journal of Clinical Pharmacology. - : Wiley. - 1365-2125 .- 0306-5251. ; 63:6, s. 722-731
-
Journal article (peer-reviewed)abstract
- Aims To characterize the absorption kinetics and bioavailability of an inhaled hydrophilic solute deposited at various sites within the airways. Methods Nine healthy nonsmokers received one intravenous, one oropharyngeal and two pulmonary doses of technetium-99 m-labelled diethylene triamine pentaacetic acid (Tc-99m-DTPA) in an open and crossover fashion. Pulmonary doses were administered as nebulized large and fine droplet-sized aerosols by Pari and UltraVent nebulizers at fairly rapid and slow inhalation flows, respectively. Plasma concentration-time profiles and 24 h urinary excretion of radioactivity were determined. One dose of Tc-99m-labelled Nanocoll, as a marker of mucociliary clearance (MCC), was also administered by Pari for similar lung deposition as the Tc-99m-DTPA and followed by repeated chest gamma-imaging. Results Intrapulmonary deposition patterns of Tc-99m-DTPA differed significantly (the mean ratio of penetration index (Pari : UltraVent) was 76% with 95% CI 63%, 91%). However, no differences in rate or extent of Tc-99m-DTPA absorption were detected. Mean absorption time was 1.8 h (mean difference (Pari-UltraVent): -0.1 h with 95% CI -0.6 h, 0.3 h) and the bioavailability was 70% (mean ratio (Pari : UltraVent): 101% with 95% CI 90%, 115%). The pulmonary elimination half-life of Tc-99m-Nanocoll (8 h and 45 min) was significantly longer than that of Tc-99m-DTPA (less than 2 h). The oral bioavailability of Tc-99m-DTPA was estimated to be 3.1%. Conclusions The main elimination pathway of the inhaled hydrophilic solute Tc-99m-DTPA from the lungs is trans-epithelial absorption. Despite different intrapulmonary radioaerosol deposition patterns, as verified by gamma scintigraphy, no differences in Tc-99m-DTPA absorption kinetics or bioavailability were detected.
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| 12. |
- Buldyreva, J, et al.
(author)
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Linewidth modelling of C2H2-N-2 mixtures tested by rotational CARS measurements
- 2006
-
In: Journal of Raman Spectroscopy. - : Wiley. - 1097-4555 .- 0377-0486. ; 37:6, s. 647-654
-
Journal article (peer-reviewed)abstract
- The acetylene-nitrogen system is investigated in a combined theoretical and experimental effort in view of its thermometry applications. Accurate values of the rotational Raman linewidths of acetylene are of crucial importance for the computation of spectra from rotational coherent anti-Stokes Raman scattering (CARS) used for temperature and concentration evaluations. Since the direct measurements of these linewidths are not available, they are rigorously calculated by a semi-classical Robert-Bonamy formalism employing exact trajectories. The computed linewidths are used as input parameters in the theoretical spectra simulation, which is also improved by the inclusion of an interbranch interference with coherent Stokes Raman scattering (CSRS). These theoretical spectra are used to evaluate the temperature from experimental CARS spectra of acetylene-nitrogen mixtures recorded in the pressure range 0.1-0.6 MPa. The new linewidths (NLWs) and the CSRS interference inclusion result in a clear improvement of spectral fitting as well as in reasonable values of evaluated temperatures. Copyright (c) 2006 John Wiley & Sons, Ltd.
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| 13. |
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| 14. |
- Faxén, Karl-Filip, et al.
(author)
-
Multicore computing--the state of the art
- 2009
-
Reports (other academic/artistic)abstract
- This document presents the current state of the art in multicore computing, in hardware and software, as well as ongoing activities, especially in Sweden. To a large extent, it draws on the presentations given at the Multicore Days 2008 organized by SICS, Swedish Multicore Initiative and Ericsson Software Research but the published literature and the experience of the authors has been equally important sources. It is clear that multicore processors will be with us for the foreseeable future; there seems to be no alternative way to provide substantial increases of microprocessor performance in the coming years. While processors with a few (2–8) cores are common today, this number is projected to grow as we enter the era of manycore computing. The road ahead for multicore and manycore hardware seems relatively clear, although some issues like the organization of the on-chip memory hierarchy remain to be settled. Multicore software is however much less mature, with fundamental questions of programming models, languages, tools and methodologies still outstanding.
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| 15. |
- Karlsson, Anders, et al.
(author)
-
Accurate method for predicting light scattering from soot aggregates with subparticles of arbitrary shape and structure
- 2009
-
In: Journal of the Optical Society of America A. - 1084-7529. ; 26:7, s. 1704-1713
-
Journal article (peer-reviewed)abstract
- Soot particles can be formed in hydrocarbon flames as a result of an inefficient combustion process. The particles are near-spherical, and at later stages in the soot growth process, they form chainlike sparse aggregates. When applying optical diagnostic methods, this aggregation influences the evaluation of soot properties based on assumptions of isolated particles. In this paper an efficient and accurate method for calculating scattering of light from these structures is presented. The method can handle aggregates with several hundred subparticles with no restrictions on shape, internal structure, or coagulation of the subparticles. The basic idea is that the induced dipole moments of the subparticles are determined from the solution of a quasi-static problem that can be solved with high accuracy by, e.g., the finite element method. (C) 2009 Optical Society of America
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| 16. |
- Kälvegren, Hanna, et al.
(author)
-
Correlation between rises in Chlamydia pneumoniae-specific antibodies, platelet activation and lipid peroxidation after percutaneous coronary intervention.
- 2008
-
In: European Journal of Clinical Microbiology and Infectious Diseases. - : Springer Science and Business Media LLC. - 0934-9723 .- 1435-4373. ; 27:7, s. 503-511
-
Journal article (peer-reviewed)abstract
- We recently showed that Chlamydia pneumoniae activates platelets in vitro, with an associated oxidation of low-density lipoproteins. The aim of this study was to investigate whether C. pneumoniae is released during percutaneous coronary intervention (PCI) and, thereby, causes platelet activation and lipid peroxidation. Seventy-three patients undergoing coronary angiography and following PCI or coronary artery bypass graft (CABG) and 57 controls were included in the study. C. pneumoniae antibodies, serotonin and lipid peroxidation were measured before and 24 h, 1 month and 6 months after angiography. The results show that serum C. pneumoniae IgA concentrations were significantly higher in patients than in the controls. Furthermore, in 38% of the C. pneumoniae IgG positive patients, the C. pneumoniae IgG concentration increased 1 month after PCI. The levels of C. pneumoniae IgG antibodies 1 month after PCI correlated with plasma-lipid peroxidation (r = 0.91, P < 0.0001) and platelet-derived serotonin (r = 0.62, P = 0.02). There was no elevation in the total serum IgG 1 month after PCI. In conclusion, the present results suggest that PCI treatment of coronary stenosis releases C. pneumoniae from the atherosclerotic lesions, which leads to platelet activation and lipid peroxidation.
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| 17. |
- Lindborg, Regina, et al.
(author)
-
A landscape perspective on conservation of semi-natural grasslands.
- 2008
-
In: Agriculture, Ecosystems and Environment. - : Elsevier BV. - 0167-8809. ; 125:1-4, s. 213-222
-
Journal article (peer-reviewed)abstract
- Current agri-environmental schemes and subsidies for conservation and restoration of semi-natural grasslands do not explicitly assess land use changes affecting whole landscapes, but have so far focused on single objects and small areas. In this paper, we discuss a landscape perspective versus a “single object” perspective when conserving semi-natural grassland in agricultural landscapes. The focus is on the values biodiversity, cultural heritage, a vital countryside, and effects on economy when land use changes. We conclude that when land use change in the landscape surrounding an object, important additional effects on the different values are found. For example, a countryside where animals graze former arable fields and where marginal habitats are managed will have a positive effect, not only on the biodiversity associated to semi-natural grasslands, but also for the image of a vital and dynamic landscape. An increased number of roads, on the other hand, may negatively affect cultural heritage and decrease biodiversity in grasslands, leading to negative effects on the value of common goods through isolation. Placing objects in a larger spatial context and combining several different aspects into a landscape perspective, will improve long-term preservation of values associated to semi-natural grasslands.
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| 18. |
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| 19. |
- Michelsen, H. A., et al.
(author)
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Modeling laser-induced incandescence of soot: a summary and comparison of LII models
- 2007
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 87:3, s. 503-521
-
Journal article (peer-reviewed)abstract
- We have performed a comparison of ten models that predict the temporal behavior of laser-induced incandescence (LII) of soot. In this paper we present a summary of the models and comparisons of calculated temperatures, diameters, signals, and energy-balance terms. The models were run assuming laser heating at 532 nm at fluences of 0.05 and 0.70 J/cm(2) with a laser temporal profile provided. Calculations were performed for a single primary particle with a diameter of 30 nm at an ambient temperature of 1800 K and a pressure of 1 bar. Preliminary calculations were performed with a fully constrained model. The comparison of unconstrained models demonstrates a wide spread in calculated LII signals. Many of the differences can be attributed to the values of a few important parameters, such as the refractive-index function E(m) and thermal and mass accommodation coefficients. Constraining these parameters brings most of the models into much better agreement with each other, particularly for the low-fluence case. Agreement among models is not as good for the high-fluence case, even when selected parameters are constrained. The reason for greater variability in model results at high fluence appears to be related to solution approaches to mass and heat loss by sublimation.
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| 20. |
- Ragnvaldsson, Daniel, 1976-
(author)
-
Hazard screening of contaminated sites : bioavailable fractions and biological in vitro tools
- 2007
-
Doctoral thesis (other academic/artistic)abstract
- The environmental bioavailability of contaminants, rather than their total concentrations in the soil compartment play a decisive role for the risks associated with contaminated sites. Various soil constituents and abiotic conditions have strong influence on bioavailability, which may vary substantially between different locations. It is therefore necessary to site-specifically use tools that reflect the fractions of contaminants that are available to biota and pose the highest potential environmental risks. Bioassays provide integrated toxic responses which include effects from unknown contaminants or combinatory toxic effects from mixtures of contaminants. Thus, biological effect data greatly contribute to establish more realistic exposure and risk-scenarios at contaminated sites. The work underlying this thesis presents possible techniques for high capacity screening for site-specific hazards at contaminated areas. By combining rapid water extractions and cell-based in vitro designs measures of the toxic potential in soils was obtained. Toxicologically bioavailable fractions of mixed metal pollution, including arsenic, were primarily investigated in this thesis. In two of the studies, environmental availability and toxicological bioavailability of arsenic was explored in CCA-contaminated soils. Application of cell-based in vitro screening techniques was also conducted at a metal contaminated industrial site to obtain spatial distribution of toxicity. Multivariate association techniques were employed in the interpretation of environmental exposure and cytotoxicity data. It was shown that cell-based in vitro systems for both basal cytotoxicity and specific end-points targeting arsenic could assess the toxic potential from extracts obtained by several water-based extraction techniques including Pressurised Liquid Extraction (PLE). The cell-based in vitro systems were found to add important information on the site-specific differences in arsenics genotoxic potential from CCA-contaminated soils. The results highlight the importance of taking speciation and toxicological bioavailability into account in the risk analysis, rather than to base risk estimates on total load of contaminants. The presented screening approach was successfully applied at a metal polluted industrial site where spatial distribution of toxicity was obtained. PLE extraction also provided means for combined toxicological and chemical screening of explosives in soils from live-fire training ranges. Multivariate association techniques highly facilitated the interpretation of complex environmental data. The PLE was found to be a rapid extraction technique that has sufficient environmental relevance to be used in environmental impact analyses. It was also concluded that other cell-based in vitro systems that target specific toxic effects have large potential for being used in screening for a variety of environmental chemicals. Keywords: Environmental availability, Environmental bioavailability, Toxicological bioavailability, mixture toxicity, hazard screening, contaminated soils, heavy metals, arsenic, CCA, explosives, soil extraction, water extracts, cell-based in vitro tests, cytotoxicity, genotoxicity, PLE, MVDA, PCA, PLS.
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| 21. |
- Vestin, Fredrik, et al.
(author)
-
Development of rotational CARS for combustion diagnostics using a polarization approach
- 2007
-
In: Proceedings of the Combustion Institute. - : Elsevier BV. - 1873-2704 .- 1540-7489. ; 31 I, s. 833-840
-
Conference paper (peer-reviewed)abstract
- Rotational Coherent anti-Stokes Raman spectroscopy (CARS) has the last decades been developed into a useful tool for thermometry and concentration measurements in combustion. In this paper, we present a novel polarization approach of the technique, which will enhance its potential and widen the range of conditions at which it can be utilized. The theory of the polarization approach is described in detail. It is shown that by specific arrangement of the polarizations of the laser beams, total suppression of the non-resonant background signal can be obtained, and thus by probing only the resonant CARS signal the diagnostic utility of the technique increases. The main benefit of the approach is in situations where the non-resonant background signal is relatively high in comparison with the resonant signal. The high potential of polarization rotational CARS for thermometry is demonstrated in some illustrative examples, for example, nitrogen thermometry on the fuel side of diffusion flames, and carbon monoxide thermometry in the product gas of ethylene/oxygen/argon-flames. © 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 22. |
- Vestin, Fredrik, et al.
(author)
-
Dual-broadband rotational CARS thermometry in the product gas of hydrocarbon flames
- 2005
-
In: Symposium (International) on Combustion. - : Elsevier BV. - 0082-0784. ; 30:1, s. 1673-1680
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Journal article (peer-reviewed)abstract
- Coherent anti-Stokes Raman spectroscopy (CARS) is an established technique for gas-phase thermometry in combustion. In this work, rotational CARS in the dual-broadband approach has been investigated for flame thermometry in the product gas of ethylene/air flames in a wide range of equivalence ratios (0.5 < phi < 2.5). The nitrogen lines dominated the rotational CARS spectra in the whole equivalence range, but for fuel-lean flames also oxygen lines gave significant spectral contributions. Therefore, the temperature evaluation was based on spectral fitting of both nitrogen and oxygen. Product gas species such as carbon dioxide, water, carbon monoxide, and hydrogen contribute to the non-resonant susceptibility of the gas and influence the nitrogen and oxygen linewidths through collisions. In this work, the main focus was on the influence of these collisions on the nitrogen and oxygen Raman linewidths and consequently the evaluated temperature in the product gas of flames. In the range of studied equivalence ratios with various amounts of different product gas species, the evaluated temperature was raised up to 45 K when including broadening from CO2, H2O, and CO on the measured nitrogen and oxygen lines. It was also concluded that H2O was the main contributor in all non-sooting flames. The influence of the non-resonant susceptibility in the spectral evaluation is discussed, and its coupling to the inclusion of the line broadening from product gas species as well. It has thus been shown that line-broadening effects from product gas species are highly important for quantitative rotational CARS thermometry in flames. (c) 2004 The Combustion Institute.
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| 23. |
- Vestin, Fredrik, et al.
(author)
-
Improved species concentration measurements using a species-specific weighting procedure on rotational CARS spectra
- 2005
-
In: Journal of Raman Spectroscopy. - : Wiley. - 1097-4555 .- 0377-0486. ; 36:2, s. 95-101
-
Journal article (peer-reviewed)abstract
- Rotational coherent anti-Stokes Raman spectroscopy (CARS) is used for measurements of temperatures and relative species concentrations. The evaluation of a rotational CARS spectrum is normally performed using a least-squares fitting algorithm to find the best-fit theoretical spectrum in a library of spectra calculated at different temperatures and relative concentrations. A general problem is that species with weak spectral features have a minor influence on the results in the standard evaluation procedure. A species-specific weighting (SSW) procedure enhancing the influence of weak spectral features in the spectral fitting algorithm has therefore been developed. The SSW procedure was tested on the evaluation of low concentrations Of 02 in mixtures with N-2, and it is shown that both the accuracy and precision of single-shot spectra concentration measurements are improved by use of the SSW evaluation procedure. Also, a comparison with previously used weighting procedures shows that this approach is superior. The application of the technique to oxygen concentration measurements in the product gas of a fuel-lean flame is demonstrated. In addition, a test was made using the developed weighting procedure for thermometry, by applying spectral weighting to the rotational spectrum originating from the first thermally excited vibrational state. The precision of the temperature measurements was then slightly improved.
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| 24. |
- Vestin, Fredrik, et al.
(author)
-
Improved temperature precision in rotational coherent anti-Stokes Raman spectroscopy with a modeless dye laser
- 2006
-
In: Applied Optics. - 2155-3165. ; 45:4, s. 744-747
-
Journal article (peer-reviewed)abstract
- Single-shot thermometry with dual-broadband rotational coherent anti-Stokes Raman spectroscopy that employs amplified spontaneous emission from a broadband modeless dye laser has been examined. Evaluation of single-shot spectra of air, N-2, and O-2 showed an improved temperature precision at room temperature compared with the precision obtained with a conventional dye laser. A comparison was also made between the use of single-mode and multimode Nd:YAG lasers as sources for narrowband radiation, and in all cases the single-mode Nd:YAG laser resulted in higher precision. The experimental results are compared with theoretical predictions. (c) 2006 Optical Society of America.
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| 25. |
- Vestin, Fredrik, et al.
(author)
-
Rotational CARS for simultaneous measurements of temperature and concentrations of N-2, O-2, CO, and CO2 demonstrated in a CO/air diffusion flame
- 2009
-
In: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 32, s. 847-854
-
Journal article (peer-reviewed)abstract
- Rotational coherent anti-Stokes Raman spectroscopy (CARS) has over the years demonstrated its strong potential to measure temperature and relative concentrations of major species in combustion. A recent work is the development and experimental validation of a CO2 model for thermometry, in addition to our previous rotational CARS models for other molecules. In the,present work, additional calibration measurements for relative CO2/N-2 concentrations have been made in the temperature range 294-1246 K in standardized CO2/N-2 mixtures. Following these calibration measurements, rotational CARS measurements were performed in a laminar CO/air diffusion flame stabilized on a Wolfhard-Parker burner. High-quality spectra were recorded from the fuel-rich region to the surrounding hot air in a lateral cross section of the flame. The spectra were evaluated to obtain simultaneous profiles of temperature and concentrations of all major species; N-2, O-2, CO, and CO2. The potential for rotational CARS as a multi-species detection technique is discussed in relation to corresponding strategies for vibrational CARS, (c) 2009 The Combustion institute. Published by Elsevier Inc. All rights reserved.
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| 26. |
- Vestin, Fredrik, et al.
(author)
-
Rotational CARS thermometry at high temperature (1800 K) and high pressure (0.1-1.55 MPa)
- 2007
-
In: Journal of Raman Spectroscopy. - : Wiley. - 1097-4555 .- 0377-0486. ; 38:8, s. 963-968
-
Journal article (peer-reviewed)abstract
- Dual-broadband rotational CARS (DB-RCARS) thermometry has been investigated at high temperature and high pressure. Single-shot measurements were performed at 1800 K, in air and nitrogen at pressures up to 1.55 MPa and in oxygen at pressures up to 0.5 MPa. For all conditions, the resonant signal contribution to the spectra clearly dominated over the non-resonant one, implying the high potential for DB-RCARS for temperature and concentration measurements also at the high temperatures and pressures used in the present investigation. The relative standard deviation was generally similar to 2% for single-shot data at pressures from 0.5 to 1.55 MPa. At the investigated temperature, 1800 K, rotational lines from thermally excited vibrational states could be observed in the highly resolved experimental spectra. Using a previously developed weighting procedure applied to these lines, it was demonstrated that the temperature standard deviation could be lowered with as much as 30%.
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| 27. |
- Vestin, Fredrik, et al.
(author)
-
Rotational coherent anti-Stokes Raman spectroscopy (CARS) applied to thermometry in high-pressure hydrocarbon flames
- 2008
-
In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 154:1-2, s. 143-152
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Journal article (peer-reviewed)abstract
- Dual-broadband rotational coherent anti-Stokes Raman spectroscopy (DB-RCARS) has been investigated for thermometry under high-pressure and high-temperature conditions, in the product gas of fuel-lean hydrocarbon flames up to 1 MPa. Initial calibration measurements made in nitrogen, oxygen, and air, at pressures up to 1.55 MPa and temperatures up to 1800 K, showed good agreement between experimental and theoretical spectra. In the high-pressure flames, high-quality single-shot spectra were recorded in which nitrogen lines dominated, and peaks from CO2 and O-2 were also visible. A spectral model including the species N-2, CO2, and O-2, as well as the best available Raman linewidth models for flame thermometry, were used to evaluate the experimental spectra. Experimental problems as well as considerations related to the spectral evaluation are discussed. This work demonstrates the significant potential of DB-RCARS thermometry for applications in high-pressure and high-temperature environments.
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| 28. |
- Vestin, Fredrik, et al.
(author)
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Validation of a rotational coherent anti-Stokes Raman spectroscopy model for carbon dioxide using high-resolution detection in the temperature range 294-1143 K
- 2008
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In: Applied Optics. - 2155-3165. ; 47:11, s. 1893-1901
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Journal article (peer-reviewed)abstract
- Experiments were performed in the temperature range of 294 - 1143 K in pure CO2 using high-resolution rotational coherent anti-Stokes Raman spectroscopy (CARS), in the dual-broadband approach. Experimental single-shot spectra were recorded with high spectral resolution using a single-mode Nd:YAG laser and a relay imaging lens system on the exit of a 1 m spectrometer. A theoretical rotational CARS model for CO, was developed for evaluation of the experimental spectra. The evaluated mean temperatures of the recorded single-shot dual-broadband rotational coherent anti-Stokes Raman spectroscopy (DB-RCARS) spectra using this model showed good agreement with thermocouple temperatures, and the relative standard deviation of evaluated single-shot temperatures was generally 2 - 3%. Simultaneous thermometry and relative CO2/N-2-concentration measurements were demonstrated in the product gas of premixed laminar CO/air flames at atmospheric pressure. Although the model proved to be accurate for thermometry up to 1143 K, limitations were observed at flame temperatures where temperatures were overestimated and relative CO2/N-2 concentrations were underestimated. Potential sources for these discrepancies are discussed.
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| 29. |
- Zhang, Quan, et al.
(author)
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R-type Ca2+-channel-evoked CICR regulates glucose-induced somatostatin secretion
- 2007
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In: Nature Cell Biology. - : Springer Science and Business Media LLC. - 1465-7392 .- 1476-4679. ; 9:4, s. 171-453
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Journal article (peer-reviewed)abstract
- Pancreatic islets have a central role in blood glucose homeostasis. In addition to insulin-producing beta-cells and glucagon-secreting alpha-cells, the islets contain somatostatin-releasing delta-cells(1). Somatostatin is a powerful inhibitor of insulin and glucagon secretion(2). It is normally secreted in response to glucose(3) and there is evidence suggesting its release becomes perturbed in diabetes(4). Little is known about the control of somatostatin release. Closure of ATP-regulated K+-channels (K-ATP-channels)(5) and a depolarization-evoked increase in cytoplasmic free Ca2+ concentration ([Ca2+](i))(6-8) have been proposed to be essential. Here, we report that somatostatin release evoked by high glucose (>= 10 mM) is unaffected by the K-ATP-channel activator diazoxide and proceeds normally in K-ATP-channel-deficient islets. Glucose-induced somatostatin secretion is instead primarily dependent on Ca2+-induced Ca2+-release (CICR). This constitutes a novel mechanism for K-ATP-channel-independent metabolic control of pancreatic hormone secretion.
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