| 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. |
- Arvizu, Miguel A, et al.
(författare)
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Electrochemical pretreatment of electrochromic WO3 films gives greatly improved cycling durability
- 2018
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Ingår i: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 653, s. 1-3
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Tidskriftsartikel (refereegranskat)abstract
- Electrochromic WO3 thin films have important applications in devices such as smart windows for energy-efficient buildings. Long-term electrochemical cycling durability of these films is essential and challenging. Here we investigate reactively sputter-deposited WO3 films, backed by indium-tin oxide layers and immersed in electrolytes of LiClO4 in propylene carbonate, and demonstrate unprecedented electrochemical cycling durability after straight-forward electrochemical pretreatments by the application of a voltage of 6 V vs. Li/Li+ for several hours.
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| 7. |
- Arvizu, Miguel A., et al.
(författare)
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Electrochromic dc sputtered W1-x-y Moy Tix O3 thin films: : Optical properties and durability.
- 2016
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Konferensbidrag (refereegranskat)abstract
- The key component in an electrochromic (EC) device is its primary EC thin film. The outstanding intrinsic ECproperties of tungsten oxide (WO3) make this material the best option available for the cathodic layer in an ECdevice. Nevertheless much research remains in order to optimize WO3 with regard to optical properties, durability,etc. It is well known that addition of titanium (Ti) into the matrix of WO3 increases significantly the resistance of the film to electrochemical cycling both under norma loperation and during accelerated aging in extended voltage ranges [1]. On the other hand, using molybdenum (Mo) as an additive in small concentrations helps to improve the color rendering by shifting th eposition of the maximum of the coloration band to higher energies [2]. The present work reports our recent investigations on thin films of mixed oxides with a focus on ways to optimize tungsten oxide thin films regarding both their durability and color by the addition of Ti and Mo. The films were deposited by reactive DC cosputtering from Mo and W-Ti alloy targets. Cyclic voltammetry, in a three-electrode system consisting of the film and lithium foils, was performed in a solution 1 MLiClO4 in propylene carbonate (Li–PC) as electrolyte. Insitu and ex-situ optical characterization was done for the EC films, and the transmittance switching and coloration efficiency were determined. Durability was studied by analyzing how the charge density evolved and how rapidly the transmittance modulation deteriorated during cycling for the different concentrations of Mo and Ti .References[1] M.A. Arvizu, C.A. Triana, B.I. Stefanov, C.G.Granqvist , G.A. Niklasson, “Electrochromism in SputterdepositedW-Ti Oxide Films: Durability Enhancement dueto Ti”, Solar Energy Materials & Solar Cells 125 (2014)184-189 (and references therein).[2] M.A. Arvizu, C.G. Granqvist and G.A. Niklasson,“Electrochromism in sputter deposited W1–yMoyO3 thinfilms”, Journal of Physics: Conference Series 682 (2016)012005 (and references therein).
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| 8. |
- Arvizu, Miguel A, et al.
(författare)
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Electrochromic WO3 thin films attain unprecedented durability by potentiostatic pretreatment
- 2019
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Ingår i: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 7:6, s. 2908-2918
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Tidskriftsartikel (refereegranskat)abstract
- Electrochromic windows and glass facades are able to impart energy efficiency jointly with indoor comfort and convenience. Long-term durability is essential for practical implementation of this technology and has recently attracted broad interest. Here we show that a simple potentiostatic pretreatment of sputterdeposited thin films of amorphous WO3-the most widely studied electrochromic material-can yield unprecedented durability for charge exchange and optical modulation under harsh electrochemical cycling in a Li-ion-conducting electrolyte and effectively evades harmful trapping of Li. The pretreatment consisted of applying a voltage of 6.0 V vs. Li/Li+ for several hours to a film backed by a transparent conducting In2O3: Sn layer. Associated compositional and structural modifications were probed by several techniques, and improved durability was associated with elemental intermixing at the WO3/ITO and ITO/glass boundaries as well as with carbonaceous solid-electrolyte interfacial layers on the WO3 films. Our work provides important new insights into long-term durability of ion-exchange-based devices.
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| 9. |
- Arvizu, Miguel A., et al.
(författare)
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Electrochromism in DC sputtered W1-yMoyO3 thin films
- 2015
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Ingår i: INERA Conference 2015. - : Institute of Physics (IOP).
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Konferensbidrag (refereegranskat)abstract
- Electrochromic (EC) properties of tungsten–molybdenum oxide (W1–yMoyO3) thin films were investigated. The films were deposited on indium tin oxide covered glass by reactive DC sputtering from tungsten and molybdenum targets. Elemental compositions of the W1–yMoyO3 films were determined by Rutherford back scattering. Voltammetric cycling was performed in an electrolyte of 1 M LiClO4 in propylene carbonate. The increase in molybdenum content in the EC films caused both a shift towards higher energies and a quenching of the value of the maximum of the coloration band, as compared with WO3 EC films. Durability was also diminished for W1–yMoyO3 EC films.
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| 10. |
- Arvizu, Miguel A, et al.
(författare)
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Electrochromism in sputter-deposited W-Ti oxide films : Durability enhancement due to Ti
- 2014
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 125, s. 184-189
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of W-Ti oxide were prepared by reactive DC magnetron sputtering and were characterized by Rutherford bathcattering spectrometry, X-ray diffraction, scanning electron microscopy and atomic force microscopy. The electrochromic properties were studied by cyclic voltammetry in an electrolyte of lithium perchlorate in propylene carbonate and by optical transmittance measurements. The addition of Ti significantly promoted the amorphous nature of the films and stabilized their electrochemical cycling performance and dynamic range for electrochromism. (C) 2014 Elsevier B.V. All rights reserved.
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