| 1. |
- Afzelius, Mikael, et al.
(författare)
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Development of multipoint vibrational coherent anti-Stokes Raman spectroscopy for flame applications
- 2006
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Ingår i: Applied Optics. - 2155-3165. ; 45:6, s. 1177-1186
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Tidskriftsartikel (refereegranskat)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. |
- 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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| 3. |
- Alekseev, Vladimir A., et al.
(författare)
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Nitric oxide formation in flames of NH3/DME binary mixtures : Laser-induced fluorescence measurements and detailed kinetic analysis
- 2024
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Ingår i: Fuel. - 0016-2361. ; 371
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Tidskriftsartikel (refereegranskat)abstract
- Binary mixture of ammonia (NH3) and dimethyl ether (DME) has been considered in literature as a potential fuel for practical use. Nitric oxide (NO) is a major product of combustion of NH3-containing fuels, and its formation routes have to be comprehensively studied. In this work, concentration profiles of NO were experimentally measured in laminar axisymmetric flames using planar laser-induced fluorescence. The molar percentage of NH3 in the NH3/DME fuel mixture varied from 10% to 60%. Emission levels of NO have reached as much as around 1% for mixtures with around 50% NH3. NO formation was analyzed with numerical simulations of 1D laminar flames and several detailed kinetic mechanisms. Modeling was performed in Chemkin with the steady-state burner-stabilized and free-propagating planar laminar flame reactor models. It was observed that the most recent versions of the contemporary NH3/DME models are able to reproduce the experiments, and their predictions agree with each other due to similarities in the NH3 submechanisms. Kinetic analysis has revealed some disagreement was observed in terms of how much direct chemical coupling between carbon- and nitrogen-containing species affects NO formation.
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| 4. |
- Amdani, Rima Zuriah, et al.
(författare)
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Raman spectroscopy for characterizing porous carbon
- 2020
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Ingår i: Laser Applications to Chemical, Security and Environmental Analysis, LACSEA 2020. - 9781557528209
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Konferensbidrag (refereegranskat)abstract
- Raman spectroscopy is performed to disclose structural properties of porous carbon samples including lignocellulosic biomass. Analysis of spectral signatures of carbon, around 1350 cm-1 and 1580 cm-1, indicates higher porosity for the biomass sample.
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| 5. |
- Bengtsson, Anton, 1979, et al.
(författare)
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Effects of thermal processing on the in vitro bioaccessibility and microstructure of beta-carotene in orange-fleshed sweet potato
- 2010
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Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 58:20, s. 11090-11096
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Tidskriftsartikel (refereegranskat)abstract
- The effects of different preparation methods on the bioaccessibility of beta-carotene in orange-fleshed sweet potato (OFSP), an important food crop in sub-Saharan Africa, have been evaluated using an in vitro digestion procedure. The preparation methods included, on fresh roots, boiling followed by pureeing and oil addition (BOL) and homogenization followed by boiling and oil addition (HOM); on milled flour from freeze-dried fresh roots, cooking of porridge followed by oil addition (POA) and oil addition to flour followed by cooking of porridge (POB). The retention of all-trans-beta-carotene ranged from 58% (POB) to 72% (BOL). The presence of oil during heating resulted in a significantly higher formation of 13-cis-beta-carotene for the POB-treated samples than for the other samples. The efficiency of micellarization of all-trans-beta-carotene after in vitro digestion was 50% (HOM), 48% (POB), 31% (POA), and 16% (BOL). Brightfield microscopy of the cell structure after processing and in vitro digestion showed a high degree of cell-wall rupture for the HOM-treated samples, whereas cells appeared intact for the BOL samples. Also, coherent anti-Stokes Raman scattering (CARS) microscopy showed smaller beta-carotene bodies residing in the HOM samples than in the BOL samples after digestion. These results suggest that the in vitro bioaccessibility of beta-carotene in an OFSP meal can be improved by processing methods that promote cell-wall rupture.
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| 6. |
- Blomberg, Sara, et al.
(författare)
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Real-Time Gas-Phase Imaging over a Pd(110) Catalyst during CO Oxidation by Means of Planar Laser-Induced Fluorescence.
- 2015
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 5:4, s. 2028-2034
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Tidskriftsartikel (refereegranskat)abstract
- The gas composition surrounding a catalytic sample has direct impact on its surface structure, which is essential when in situ investigations of model catalysts are performed. Herein a study of the gas phase close to a Pd(110) surface during CO oxidation under semirealistic conditions is presented. Images of the gas phase, provided by planar laser-induced fluorescence, clearly visualize the formation of a boundary layer with a significantly lower CO partial pressure close to the catalytically active surface, in comparison to the overall concentration as detected by mass spectrometry. The CO partial pressure variation within the boundary layer will have a profound effect on the catalysts' surface structure and function and needs to be taken into consideration for in situ model catalysis studies.
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| 7. |
- Bood, Joakim, et al.
(författare)
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Multipoint temperature and oxygen-concentration measurements using rotational coherent anti-Stokes Raman spectroscopy
- 2000
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Ingår i: Optics Letters. - 0146-9592. ; 25:20, s. 1535-1537
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Tidskriftsartikel (refereegranskat)abstract
- A novel technique for coherent anti-Stokes Raman spectroscopy (CARS) measurements in multiple points is presented. With a system of cylindrical lenses, each laser beam is split into several focused beams, yielding separate planar boxcars configurations. Spectrally resolved CARS signals are detected at different heights on the CCD chip. With dual-broadband rotational CARS the setup is demonstrated for quantitative measurements of temperature- and oxygen-concentration profiles. The technique was demonstrated for three points only, but it can be extended to more points by use of special optics; this choice must be based on a sufficient signal-to-noise ratio in all points for the actual measurement condition.
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| 8. |
- Brackmann, Christian, 1973, et al.
(författare)
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CARS microscopy of lipid stores in yeast: the impact of nutritional state and genetic background
- 2009
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 40:7, s. 748-756
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a protocol for sub-micrometer resolved and chemically specific imaging of lipid storage in vivo employing coherent anti-Stokes Raman scattering (CARS) microscopy of one of the most important model organisms Saccharomyces cerevisiae - the yeast cell. By probing the carbon-hydrogen vibration using the nonlinear process of CARS, lipid droplets in the yeast cells clearly appear, as confirmed by comparative studies on relevant labeled organelles using two-photon fluorescence microscopy. From the images, unique quantitative data can be deduced with high three-dimensional resolution, such as the volume, shape, number, and intracellular location of the neutral lipid stores. We exemplify the strength and usability of the method for two cases: the impact on lipid storage of the nutritional condition (starvation and type of carbon source available) as well as of genetic modification of two fundamental metabolic regulation pathways involving carbohydrate and lipid storage (BCY1 and DGA1, LRO1, ARE1/2 deletions), respectively. While the impact of carbon source on the total cellular lipid volume was minimal, long-term starvation induces a significant accumulation of lipid droplets. We also confirm that the lipid-storage-deficient mutant is indeed unable to synthesize lipid droplets, and that the inability of the bcy1-mutant to store carbohydrates is compensated by a two-fold increase in stored neutral lipids. We note that there is a significant cell-to-cell variability in neutral lipid storage in general, i.e. that there is a correspondence to the noise found for gene expression also in lipidomics. Copyright (C) 2009 John Wiley & Sons, Ltd.
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| 9. |
- Brackmann, Christian, et al.
(författare)
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Characterization of ammonia two-photon laser-induced fluorescence for gas-phase diagnostics
- 2014
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 115:1, s. 25-33
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Tidskriftsartikel (refereegranskat)abstract
- Two-photon laser-induced fluorescence (LIF) of ammonia (NH3) with excitation of the C'-X transition at 304.8 nm and fluorescence detection in the 565 nm C'-A band has been investigated, targeting combustion diagnostics. The impact of laser irradiance, temperature, and pressure has been studied, and simulation of NH3-spectra, fitted to experimental data, facilitated interpretation of the results. The LIF-signal showed quadratic dependence on laser irradiance up to 2 GW/cm(2). Stimulated emission, resulting in loss of excited molecules, is induced above 10 GW/cm(2), i.e., above irradiances attainable for LIF imaging. Maximum LIF-signal was obtained for excitation at the 304.8 nm bandhead; however, lower temperature sensitivity over the range 400-700 K can be obtained probing lines around 304.9 nm. A decrease in fluorescence signal was observed with pressure up to 5 bar absolute and attributed to collisional quenching. A detection limit of 800 ppm, at signal-to-noise ratio 1.5, was identified for single-shot LIF imaging over an area of centimeter scale, whereas for single-point measurements, the technique shows potential for sub-ppm detection. Moreover, high-quality NH3-imaging has been achieved in laminar and turbulent premixed flames. Altogether, two-photon fluorescence provides a useful tool for imaging NH3-detection in combustion diagnostics.
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| 10. |
- Brackmann, Christian, 1973, et al.
(författare)
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Coherent anti-Stokes Raman scattering microscopy of human smooth muscle cells in bioengineered tissue scaffolds
- 2011
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Ingår i: Journal of Biomedical Optics. - : SPIE - International Society for Optical Engineering. - 1083-3668 .- 1560-2281. ; 16:2
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Tidskriftsartikel (refereegranskat)abstract
- The integration of living, human smooth muscle cells in biosynthesized cellulose scaffolds was monitored by nonlinear microscopy toward contractile artificial blood vessels. Combined coherent anti-Stokes Raman scattering (CARS) and second harmonic generation (SHG) microscopy was applied for studies of the cell interaction with the biopolymer network. CARS microscopy probing CH(2)-groups at 2845 cm(-1) permitted three-dimensional imaging of the cells with high contrast for lipid-rich intracellular structures. SHG microscopy visualized the fibers of the cellulose scaffold, together with a small signal obtained from the cytoplasmic myosin of the muscle cells. From the overlay images we conclude a close interaction between cells and cellulose fibers. We followed the cell migration into the three-dimensional structure, illustrating that while the cells submerge into the scaffold they extrude filopodia on top of the surface. A comparison between compact and porous scaffolds reveals a migration depth of <10 μm for the former, whereas the porous type shows cells further submerged into the cellulose. Thus, the scaffold architecture determines the degree of cell integration. We conclude that the unique ability of nonlinear microscopy to visualize the three-dimensional composition of living, soft matter makes it an ideal instrument within tissue engineering.
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