| 1. |
- Niklasson, Gunnar A., 1953-, et al.
(författare)
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Determination of scattering and absorption coefficients from experimental data : Application to sunscreen lotions
- 2013
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Ingår i: Optics & Photonics in Sweden 2013.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Materials with pronounced light scattering are of large interest in a variety of scientific and technical disciplines. Their optical properties can to a good approximation be described by two-flux (Kubelka-Munk) theory [1]. This theory considers one light beam propagating in the forward direction and one beam propagating in the backward direction in the material. The optical properties of the material are described by phenomenological scattering (S) and absorption (K) coefficients. Additional parameters are the internal reflection coefficients for diffuse light at the interfaces and the reflection coefficient for incident collimated light at the front interface. The large amount of parameters makes it difficult to invert experimental measurements of transmittance (T) and reflectance (R) in order to obtain the parameters S and K characterizing the material [2,3]. We propose a method to partially overcome this problem in special cases by invoking physically realistic approximations for the reflection coefficients. We consider viscous emulsions or polymeric materials positioned between two transparent substrates separated by a spacer. Many organic and polymeric materials have refractive indices sufficiently close to those of glass and quartz substrates so that reflections between the material and the glass can be neglected. The reflection coefficient of the substrate for collimated light is known from its refractive index. Measurements of R and T in a region of weak scattering and absorption allow us to put quite stringent limits on the internal reflection coefficients for diffuse light. In this way good approximative values for S and K can be obtained.We apply this method to spectrophotometric measurements on two commercial sunscreen lotions. A drop of lotion was applied on a quartz substrate and a second quartz plate was put on top. The quartz plates were separated by aluminium foil of thickness 11 mm, except in the area covered by the lotion. Measurements of total R and T were taken by a Perkin-Elmer lambda-900 spectrophotometer equipped with an integrating sphere, in the wavelength range 250-800 nm. The samples were completely diffuse scattering and measurements in a low scattering region indicated a preferential forward scattering. The absorption coefficient was found to be low in the visible region and increased very much in the ultraviolet (UV). The scattering coefficient increased towards shorter wavelengths in the visible but exhibited differing behaviours in the UV. A sunscreen containing TiO2 particles exhibited a very low UV scattering together with higher scattering in the visible range, see fig. 1. Fig. 1. Scattering (S) and absorption (K) coefficients for a sunscreen containing a mix of chemical pigments and TiO[1] P. Kubelka, J. Opt. Soc. Am. 38 (1948) 448.[2] R. Levinson, P. Berdahl and H. Akbari, Solar Energy Mater. Solar Cells, 89 (2005) 319.[3] D. Barrios, R. Vergaz, J.M. Sanchez-Pena, C.G. Granqvist and G.A. Niklasson, Solar Energy Mater. Solar Cells, 111 (2013) 115.
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| 2. |
- Niklasson, Gunnar A., 1953-, et al.
(författare)
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Non-Gaussian distributions of melodic intervals in music : The Lévy-stable approximation
- 2015
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Ingår i: Europhysics letters. - : EDP Sciences. - 0295-5075 .- 1286-4854. ; 112:4
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Tidskriftsartikel (refereegranskat)abstract
- The analysis of structural patterns in music is of interest in order to increase ourfundamental understanding of music, as well as for devising algorithms for computer-generatedmusic, so called algorithmic composition. Musical melodies can be analyzed in terms of a “music walk” between the pitches of successive tones in a notescript, in analogy with the “random walk”model commonly used in physics. We find that the distribution of melodic intervals between tones can be approximated with a L´evy-stable distribution. Since music also exibits self-affine scaling,we propose that the “music walk” should be modelled as a L´evy motion. We find that the L´evy motion model captures basic structural patterns in classical as well as in folk music.
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| 3. |
- Niklasson, Gunnar A., 1953-, et al.
(författare)
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Optics of sunscreen lotions : Preliminary results on scattering and absorption coefficients
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Sunscreen lotions are used to protect the skin from damage due to solar ultraviolet (UV) radiation. The active UV-blocking components can be organic molecules or inorganic particles, for example TiO2. While both in-vivo and in-vitro methods exist for assessing the protective capacity of sunscreens, their basic optical properties have received little attention. In this paper we take the first steps to address this issue by presenting a method to obtain spectra of absorption and scattering coefficients of a sunscreen by analysis of experimental transmittance and reflectance spectra. We model the optical properties of the sunscreen by two-flux theory, develop approximate expressions for interface reflection coefficients and obtain the remaining optical parameters by fitting the two-flux theory to measurements. We analyze spectrophotometric reflectance and transmittance spectra of experimental narrow band UV blocking materials based on mesoporous magnesium carbonate – TiO2 mixtures, as well as some commercial sunscreens. Our method is demonstrated in vitro using quartz substrates and is further used to model in vivo measurements on the upside of the hand of one of the authors. The obtained absorption and scattering coefficient spectra give information on the relative contributions of these processes to the UV-blocking effect as well as the scattering of visible light responsible for the whitening of the skin upon application of a sunscreen lotion. Our analysis method may be useful for computational optimization of novel sunscreen formulations as well as for the development of in-vivo test methods.
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| 4. |
- Niklasson, Gunnar, 1953-, et al.
(författare)
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Light Scattering Parameters by Inversion of Experimental Data: The Case of Sunscreen Lotions
- 2021
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Ingår i: Proceedings of the Bremen Zoom Workshop on Light Scattering 2021. - Bremen : Leibniz Institute for Materials Engineering IWT. ; , s. 16-19
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Konferensbidrag (refereegranskat)abstract
- We present a method to obtain absorption and backscattering coefficients of a light scattering material and apply it to the technologically important case of sunscreen lotions. While both in-vivo and in-vitro methods exist for assessing the ultraviolet (UV) protective capacity of sun-screens, their basic optical properties have previously received little attention. We model the light scattering properties by two-flux theory and invert spectrophotometric total transmittance and reflectance measurements to obtain backscattering and absorption coefficient spectra.
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| 5. |
- Niklasson, Maria, 1995-, et al.
(författare)
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The fractal dimension of music : melodic contours and time series of pitch
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We analyze the fractal dimension of melodic contours and pitch time series of classical music and folk music tunes. The fractal dimensions obtained from box counting and detrended fluctuation analysis show significant differences. They are ascribed to the low accuracy of box counting for dimensions close to two as well as to a possible bias because the pitches in the time series are connected by lines to obtain the melodic contour used in the box counting analysis. We observe a tendency that folk music exhibits lower fractal dimensions than classical music, but further studies are needed in order to assess cutoff effects in the comparatively short folk music tunes. We conclude that detrended fluctuation analysis is the preferable method for fractal analysis of music, and this verifies previous studies of analysis of short time series.
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| 6. |
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| 7. |
- Aijaz, Asim, et al.
(författare)
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Low-temperature synthesis of thermochromic vanadium dioxide thin films by reactive high power impulse magnetron sputtering
- 2016
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 149, s. 137-144
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Tidskriftsartikel (refereegranskat)abstract
- Thermochromic (TC) vanadium dioxide thin films provide means for controlling solar energy throughput and can be used for energy-saving applications such as smart windows. One of the factors limiting the deployment of VO2 films in TC devices is the growth temperature tau(s). At present, temperatures in excess of 450 degrees C are required, which clearly can be an impediment especially for temperature-sensitive substrates. Here we address the issue of high tau(s) by synthesizing VO2 thin films from highly ionized fluxes of depositing species generated in high power impulse magnetron sputtering (HiPIMS) discharges. The use of ions facilitates low-temperature film growth because the energy of the depositing species can be readily manipulated by substrate bias. For comparison, films were also synthesized by pulsed direct current magnetron sputtering. Structural and optical characterization of VO2 thin films on ITO-coated glass substrates confirms previous results that HiPIMS allows tau(s) to be reduced from 500 to 300 degrees C. Importantly, we demonstrated that HiPIMS permits the composition and TC response of the films to be tuned by altering the energy of the deposition flux via substrate bias. An optimum ion energy of 100 eV was identified, which points at a potential for further reduction of tau(s) thereby opening new possibilities for industrially-relevant applications of VO2-based TC thin films. Weak TC activity was observed even at tau(s) approximate to 200 degrees C in HiPIMS-produced films.
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| 8. |
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| 9. |
- Albers, E, et al.
(författare)
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Continuous estimation of product concentration with calorimetry and gas analysis during anaerobic fermentations of Saccharomyces cerevisiae
- 2002
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Ingår i: Thermochimica Acta. - 0040-6031. ; 394:1-2, s. 185-190
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Tidskriftsartikel (refereegranskat)abstract
- Product concentrations may be estimated from gas analysis or calorimetric measurements. These techniques of analysis are fast, simple, and provide a continuous output. To check the accuracy of these estimations, the anaerobic ethanol formation of an industrial strain of the yeast Saccharomyces cerevisiae was selected as a test system. Cultivations were carried out as batch cultures with different nitrogen sources (ammonium, glutamate and a mixture of amino acids) and 20 g/l of glucose as the carbon and energy source. The results showed that there was a good agreement between measured and calculated ethanol values. However, especially when using heat data the results are very sensitive to small changes in the stoichiometry of the catabolic reaction, i.e. ethanol is not the only product but there are also minor amounts of glycerol and acetate. The problems generated by these products when using heat data to calculate ethanol concentrations are discussed in detail. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 10. |
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