| 1. |
- Gonzalez-Borrero, P. P., et al.
(författare)
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Optical band-gap determination of nanostructured WO3 film
- 2010
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 96:6
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Tidskriftsartikel (refereegranskat)abstract
- The optical band-gap energy of a nanostructured tungsten trioxide film is determined using the photoacoustic spectroscopy method under continuous light excitation. The mechanism of the photoacoustic signal generation is discussed. The band-gap energy is also computed by other methods. The absorption coefficient as well as the band-gap energy of three different crystal structures of tungsten trioxide is calculated by a first-principles Green's function approach using the projector augmented wave method. The theoretical study indicates that the cubic crystal structure shows good agreement with the experimental data.
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| 2. |
- 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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| 3. |
- Hellstrom, A., et al.
(författare)
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New insights into the development of retinopathy of prematurity - importance of early weight gain
- 2010
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Ingår i: Acta Pædiatrica. - : Wiley. - 1651-2227 .- 0803-5253. ; 99:4, s. 502-508
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Forskningsöversikt (refereegranskat)abstract
- Evidence is accumulating that one of the strongest predictors of retinopathy of prematurity (ROP), in addition to low gestational age, is poor weight gain during the first weeks of life. In infants born preterm, the retina is not fully vascularised. The more premature the child, the larger is the avascular area. In response to hypoxia, vascular endothelial growth factor (VEGF) is secreted. For appropriate VEGF-induced vessel growth, sufficient levels of insulin-like growth factor I (IGF-I) in serum are necessary. IGF-I is a peptide, related to nutrition supply, which is essential for both pre- and post-natal general growth as well as for growth of the retinal vasculature. In prematurely born infants, serum levels are closely related to gestational age and are lower in more prematurely born infants. At preterm birth the placental supply of nutrients is lost, growth factors are suddenly reduced and general as well as vascular growth slows down or ceases. In addition, the relative hyperoxia of the extra-uterine milieu, together with supplemental oxygen, causes a regression of already developed retinal vessels. Postnatal growth retardation is a major problem in very preterm infants. Both poor early weight gain and low serum levels of IGF-I during the first weeks/months of life have been found to be correlated with severity of ROP. Conclusion: This review will focus on the mechanisms leading to ROP by exploring factors responsible for poor early weight gain and abnormal vascularisation of the eye of the preterm infant.
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| 4. |
- Green, Sara, et al.
(författare)
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Structure and composition of sputter-deposited nickel-tungsten oxide films
- 2011
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 519:7, s. 2062-2066
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Tidskriftsartikel (refereegranskat)abstract
- Films of mixed nickel-tungsten oxide, denoted NixW1-x oxide, were prepared by reactive DC magnetron co-sputtering from metallic targets and were characterized by Rutherford backscattering spectrometry. X-ray photoelectron spectroscopy, X-ray diffractometry and Raman spectroscopy. A consistent picture of the structure and composition emerged, and at x<0.50 the films comprised a mixture of amorphous WO3 and nanosized NiWO4, at x = 0.50 the nanosized NiWO4 phase was dominating, and at x>0.50 the films contained nanosized NiO and NiWO4.
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| 5. |
- 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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| 6. |
- Purwandari, F. A., et al.
(författare)
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Pretreatment of oil palm empty fruit bunch (OPEFB) by N-methylmorpholine-N-oxide (NMMO) for biogas production: Structural changes and digestion improvement
- 2013
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Ingår i: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; 128, s. 461-466
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Tidskriftsartikel (refereegranskat)abstract
- Pretreatment of OPEFB (oil palm empty fruit bunch) by NMMO (N-methylmorpholine-N-oxide) on its subsequent digestions was investigated. The pretreatments were carried out at 90 and 120 degrees C for 1, 3, and 5 h in three different modes of dissolution (by 85% NMMO solution), ballooning (79% NMMO solution), and swelling (73% NMMO solution). The total solid recovery after the pretreatment was 89-94%. The pretreatment process did not have a major impact on the composition of OPEFB, other than a reduction of ash from 5.4% up to 1.3%. The best improvement in biogas production was achieved by a dissolution mode pretreatment of OPEFB, using conditions of 85% NMMO, 3 h, and 120 degrees C. It resulted in 0.408 Nm(3)/kg VS methane yield and 0.032 Nm(3) CH4/kg VS/day initial methane production rate, which correspond in improving by 48% and 167% compared to the untreated OPEFB, respectively.
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| 7. |
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| 8. |
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| 9. |
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| 10. |
- Barrios, David, et al.
(författare)
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Toward a quantitative model for suspended particle devices : Optical scattering and absorption coefficients
- 2013
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 111, s. 115-122
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Tidskriftsartikel (refereegranskat)abstract
- Suspended particle devices (SPDs) allow rapid voltage-controlled modulation of their optical transmittance and are of interest for solar-energy-related and other applications. We investigated the spectral total and diffuse transmittance of an SPD, including its angular dependence. The optical modulation was large for visible light but almost nil in the infrared, and the devices had noticeable haze. A theoretical two-flux model was formulated and provided a quantitative description of the absorption and scattering coefficients and thereby of the detailed optical performance. This analysis gives a benchmark for assessing improvements of the SPD technology as well as for comparing it with alternative technologies for optical modulation.
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