| 11. |
- Soltanmoradi, Reyhaneh, et al.
(författare)
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Multi-resonator structure based on continuous silver thin films for transparent conductors
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:6, s. 061110-
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Tidskriftsartikel (refereegranskat)abstract
- A type of metal-dielectric multilayered structures is investigated theoretically and experimentally for achieving optical transparency with a high electrical conductivity. The structure in our demonstrated case comprises of two coupled metal-dielectric-metal planar optical resonators with metal-layer thicknesses near to its skin depth. Simulations show that the maximum transmittance for visible light can easily reach 90% for silver-based structures. Experimentally, the sample fabricated exhibits a transmission window with a bandwidth of 150 nm and a maximum transmittance of 76% around 643 nm wavelength at normal incidence. Its sheet resistance is measured to be less than 10 Omega/square, much smaller than that of common indium-tin-oxide films. Transparent conductors functioning for blue light and even for the whole visible light are also shown to be theoretically possible. Owing to their simple fabrication procedure as well as design flexibility, such a layered structure can serve as a compelling alternative as transparent conductors for optoelectronic devices, especially for liquid-crystal displays and light-emitting diodes.
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| 12. |
- Yu, X., et al.
(författare)
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Coupling coefficient of two-core microstructured optical fiber
- 2006
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Ingår i: Optics Communications. - : Elsevier. - 0030-4018 .- 1873-0310. ; 260:1, s. 164-169
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, coupled-mode theory is applied to a two-core microstructured optical fiber for the first time to calculate the coupling coefficients for different fiber structures by employing a simple effective index model approach. The dependence of the mode coupling properties upon the geometrical parameters of the two-core structures (air-hole arrangement, hole size, and pitch size) and wavelength are evaluated systematically. The effective index coupled-mode theory is compared with the finite-element method based super-mode theory in details and the results show good agreement. The coupling characteristics are proven to be insensitive to the longitudinal strain by considering the photoelastic effects.
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| 13. |
- Andersson, Jennie, 1986, et al.
(författare)
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Ship-scale CFD benchmark study of a pre-swirl duct on KVLCC2
- 2022
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Ingår i: Applied Ocean Research. - : Elsevier Ltd. - 0141-1187 .- 1879-1549. ; 123
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Tidskriftsartikel (refereegranskat)abstract
- Installing an energy saving device such as a pre-swirl duct (PSD) is a major investment for a ship owner and prior to an order a reliable prediction of the energy savings is required. Currently there is no standard for how such a prediction is to be carried out, possible alternatives are both model-scale tests in towing tanks with associated scaling procedures, as well as methods based on computational fluid dynamics (CFD). This paper summarizes a CFD benchmark study comparing industrial state-of-the-art ship-scale CFD predictions of the power reduction through installation of a PSD, where the objective was to both obtain an indication on the reliability in this kind of prediction and to gain insight into how the computational procedure affects the results. It is a blind study, the KVLCC2, which the PSD is mounted on, has never been built and hence there is no ship-scale data available. The 10 participants conducted in total 22 different predictions of the power reduction with respect to a baseline case without PSD. The predicted power reductions are both positive and negative, on average 0.4%, with a standard deviation of 1.6%-units, when not considering two predictions based on model-scale CFD and two outliers associated with large uncertainties in the results. Among the variations present in computational procedure, two were found to significantly influence the predictions. First, a geometrically resolved propeller model applying sliding mesh interfaces is in average predicting a higher power reduction with the PSD compared to simplified propeller models. The second factor with notable influence on the power reduction prediction is the wake field prediction, which, besides numerical configuration, is affected by how hull roughness is considered. © 2022 The Authors
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| 14. |
- Barber, R. M., et al.
(författare)
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Healthcare Access and Quality Index based on mortality from causes amenable to personal health care in 195 countries and territories, 1990-2015: a novel analysis from the Global Burden of Disease Study 2015
- 2017
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Ingår i: Lancet. - : Elsevier BV. - 0140-6736. ; 390:10091, s. 231-266
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Tidskriftsartikel (refereegranskat)abstract
- Background National levels of personal health-care access and quality can be approximated by measuring mortality rates from causes that should not be fatal in the presence of effective medical care (ie, amenable mortality). Previous analyses of mortality amenable to health care only focused on high-income countries and faced several methodological challenges. In the present analysis, we use the highly standardised cause of death and risk factor estimates generated through the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) to improve and expand the quantification of personal health-care access and quality for 195 countries and territories from 1990 to 2015. Methods We mapped the most widely used list of causes amenable to personal health care developed by Nolte and McKee to 32 GBD causes. We accounted for variations in cause of death certification and misclassifications through the extensive data standardisation processes and redistribution algorithms developed for GBD. To isolate the effects of personal health-care access and quality, we risk-standardised cause-specific mortality rates for each geography-year by removing the joint effects of local environmental and behavioural risks, and adding back the global levels of risk exposure as estimated for GBD 2015. We employed principal component analysis to create a single, interpretable summary measure-the Healthcare Quality and Access (HAQ) Index-on a scale of 0 to 100. The HAQ Index showed strong convergence validity as compared with other health-system indicators, including health expenditure per capita (r= 0.88), an index of 11 universal health coverage interventions (r= 0.83), and human resources for health per 1000 (r= 0.77). We used free disposal hull analysis with bootstrapping to produce a frontier based on the relationship between the HAQ Index and the Socio-demographic Index (SDI), a measure of overall development consisting of income per capita, average years of education, and total fertility rates. This frontier allowed us to better quantify the maximum levels of personal health-care access and quality achieved across the development spectrum, and pinpoint geographies where gaps between observed and potential levels have narrowed or widened over time. Findings Between 1990 and 2015, nearly all countries and territories saw their HAQ Index values improve; nonetheless, the difference between the highest and lowest observed HAQ Index was larger in 2015 than in 1990, ranging from 28.6 to 94.6. Of 195 geographies, 167 had statistically significant increases in HAQ Index levels since 1990, with South Korea, Turkey, Peru, China, and the Maldives recording among the largest gains by 2015. Performance on the HAQ Index and individual causes showed distinct patterns by region and level of development, yet substantial heterogeneities emerged for several causes, including cancers in highest-SDI countries; chronic kidney disease, diabetes, diarrhoeal diseases, and lower respiratory infections among middle-SDI countries; and measles and tetanus among lowest-SDI countries. While the global HAQ Index average rose from 40.7 (95% uncertainty interval, 39.0-42.8) in 1990 to 53.7 (52.2-55.4) in 2015, far less progress occurred in narrowing the gap between observed HAQ Index values and maximum levels achieved; at the global level, the difference between the observed and frontier HAQ Index only decreased from 21.2 in 1990 to 20.1 in 2015. If every country and territory had achieved the highest observed HAQ Index by their corresponding level of SDI, the global average would have been 73.8 in 2015. Several countries, particularly in eastern and western sub-Saharan Africa, reached HAQ Index values similar to or beyond their development levels, whereas others, namely in southern sub-Saharan Africa, the Middle East, and south Asia, lagged behind what geographies of similar development attained between 1990 and 2015. Interpretation This novel extension of the GBD Study shows the untapped potential for personal health-care access and quality improvement across the development spectrum. Amid substantive advances in personal health care at the national level, heterogeneous patterns for individual causes in given countries or territories suggest that few places have consistently achieved optimal health-care access and quality across health-system functions and therapeutic areas. This is especially evident in middle-SDI countries, many of which have recently undergone or are currently experiencing epidemiological transitions. The HAQ Index, if paired with other measures of health-systemcharacteristics such as intervention coverage, could provide a robust avenue for tracking progress on universal health coverage and identifying local priorities for strengthening personal health-care quality and access throughout the world. Copyright (C) The Author(s). Published by Elsevier Ltd.
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| 15. |
- Chen, Hui
(författare)
-
Light Scattering Effects in Transparent Wood Biocomposites
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Transparent wood (TW) shows interesting optical properties and offers a sustainable alternative to petroleum-based polymer glasses. The influence of the TW internal structure (e.g. fiber alignment, volume fraction of cellulose, lignin content, defects from preparation process) on the optical properties is poorly understood, which limits its use in various applications. It is also true for transparent cellulose biocomposites in general. In this thesis, eco-friendly TW biocomposites are investigated. The work focuses on experimental characterization, structure-optical property relationships and possibilities to quantify such relationships. TWs made of delignified wood substrates with longitudinal direction of the tree parallel to the specimen surface are prepared. Relationships between anisotropic scattering and fiber alignment are studied by scattering angle measurement. Anisotropic photons distributions are compared between two fiber directions and various sample thicknesses. Next, attenuation coefficients (related to the anisotropic diffusion coefficients and absorption coefficient) for TWs are obtained by combining the photon diffusion equation with total transmittance measurements. The results indicate strong influence from the air gaps between wood substrate phase and polymer in the lumen pores on the scattering. Beside the airgaps between wood substrate and polymer, refractive index mismatch between polymer and wood substrate strongly influences the scattering. Thus, immersion liquid method (based on the total transmittance measurement) combined with a light transmission model (based on Fresnel reflection theory) is applied to estimate the refractive index of the delignified wood substrate. This facilitates TW design (i.e. the proper polymer selection for various applications) and modelling of the optical properties of delignified wood based transparent materials. Finally, extinction coefficients, Rayleigh scattering and absorption coefficients of TW are extracted from photon budget measurements combined with a light diffusion model developed. With higher volume fraction of cellulose, all these parameters are increased, although polymer-cellulose refractive index mismatch is the dominating factor controlling transmittance. The strong forward scattering in TW is analysed, and Rayleigh scattering has a strong effect on haze. The influence of lignin content on the absorption coefficient is also discussed.
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| 16. |
- Chen, Hui, et al.
(författare)
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Refractive index of delignified wood for transparent biocomposites
- 2020
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Ingår i: RSC Advances. - 2046-2069. ; 10, s. 40719-40724
-
Tidskriftsartikel (refereegranskat)abstract
- Refractive index (RI) determination for delignified wood templates is vital for transparent wood composite fabrication. Reported RIs in the literature are based on either single plant fibers or wood powder, measured by the immersion liquid method (ILM) combined with mathematical fitting. However, wood structure complexity and the physical background of the fitting were not considered. In this work, RIs of delignified wood templates were measured by the ILM combined with a light transmission model developed from the Fresnel reflection/refraction theory for composite materials. The RIs of delignified balsa wood are 1.536 ± 0.006 and 1.525 ± 0.008 at the wavelength of 589 nm for light propagating perpendicular and parallel to the wood fiber direction, respectively. For delignified birch wood, corresponding values are 1.537 ± 0.005 and 1.529 ± 0.006, respectively. The RI data for delignified wood scaffolds are important for tailoring optical properties of transparent wood biocomposites, and also vital in optical properties investigations by theoretical modelling of complex light propagation in transparent wood and related composites. The developed light transmission model in combination with the immersion liquid method can be used to determine the RI of complex porous or layered solid materials and composites.
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| 17. |
- Chen, Hui, et al.
(författare)
-
Refractive index of delignified wood for transparent biocomposites
- 2020
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Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 10:67, s. 40719-40724
-
Tidskriftsartikel (refereegranskat)abstract
- Refractive index (RI) determination for delignified wood templates is vital for transparent wood composite fabrication. Reported RIs in the literature are based on either single plant fibers or wood powder, measured by the immersion liquid method (ILM) combined with mathematical fitting. However, wood structure complexity and the physical background of the fitting were not considered. In this work, RIs of delignified wood templates were measured by the ILM combined with a light transmission model developed from the Fresnel reflection/refraction theory for composite materials. The RIs of delignified balsa wood are 1.536 ± 0.006 and 1.525 ± 0.008 at the wavelength of 589 nm for light propagating perpendicular and parallel to the wood fiber direction, respectively. For delignified birch wood, corresponding values are 1.537 ± 0.005 and 1.529 ± 0.006, respectively. The RI data for delignified wood scaffolds are important for tailoring optical properties of transparent wood biocomposites, and also vital in optical properties investigations by theoretical modelling of complex light propagation in transparent wood and related composites. The developed light transmission model in combination with the immersion liquid method can be used to determine the RI of complex porous or layered solid materials and composites.
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| 18. |
- Chen, Hui, et al.
(författare)
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Thickness Dependence of Optical Transmittance of Transparent Wood : Chemical Modification Effects
- 2019
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Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 11:38, s. 35451-35457
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Tidskriftsartikel (refereegranskat)abstract
- Transparent wood (TW) is an emerging optical material combining high optical transmittance and haze for structural applications. Unlike nonscattering absorbing media, the thickness dependence of light transmittance for TW is complicated because optical losses are also related to increased photon path length from multiple scattering. In the present study, starting from photon diffusion equation, it is found that the angle-integrated total light transmittance of TW has an exponentially decaying dependence on sample thickness. The expression reveals an attenuation coefficient which depends not only on the absorption coefficient but also on the diffusion coefficient. The total transmittance and thickness were measured for a range of TW samples, from both acetylated and nonacetylated balsa wood templates, and were fitted according to the derived relationship. The fitting gives a lower attenuation coefficient for the acetylated TW compared to the nonacetylated one. The lower attenuation coefficient for the acetylated TW is attributed to its lower scattering coefficient or correspondingly lower haze. The attenuation constant resulted from our model hence can serve as a singular material parameter that facilitates cross-comparison of different sample types, at even different thicknesses, when total optical transmittance is concerned. The model was verified with two other TWs (ash and birch) and is in general applicable to other scattering media.
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| 19. |
- Chuan Chen, Max, et al.
(författare)
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Low temperature activation of B implantation of Si subcell fabrication in III-V/Si tandem solar cells
- 2019
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Ingår i: Proceedings of the 36<sup>th</sup> EU PVSEC 2019. - : WIP. - 3936338604 ; , s. 764-768
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this work, we investigated the Si pre-amorphization implantation (PAI) assisted low temperatureannealing process to activate boron implantation in n-Si in a hydride vapor phase epitaxy (HVPE) reactor, which canbe used for the Si subcell fabrication in the III-V/Si tandem solar cells enabled by the corrugated epitaxial lateralovergrowth (CELOG). A uniform boron activation in Si and a low emitter sheet resistance of 77 /sq was obtained atannealing temperatures of 600-700°C. High-resolution x-ray diffraction was used to study the recrystallization ofamorphous silicon and the incorporation of boron dopants in Si. Hall measurements revealed p-type carrierconcentrations in the order of 1020 cm-3. The n-Si wafers with B implantation activated at 700°C by HVPE wereprocessed to solar cells and characterized by the standard light-current-voltage measurement under AM1.5 spectrumand external quantum efficiency measurements. The developed B implantation and low temperature activationprocesses are applied to the InP/Si seed template preparation for CELOG, on which CELOG GaInP over a Si subcellwith a direct heterojunction was demonstrated.
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| 20. |
- Dai, J., et al.
(författare)
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Enhanced near-field radiative heat transfer between corrugated metal plates : role of spoof surface plasmon polaritons
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 92:3
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate with the finite-difference time-domain method that radiative heat transfer between two parallel gold plates can be significantly enhanced by engraving periodic grooves with a subwavelength width on the plate surfaces. The enhancement increases with a decrease in the separation distance at near-field regime and it can be further efficiently improved by having a supercell with multiple grooves with different depths. We attribute this near-field enhancement to coupling of thermally excited spoof surface plasmon polaritons, a type of artificial surface wave inherent to structured metal surfaces [J. B. Pendry, L. Mart´ın-Moreno, and F. J. Garcia-Vidal, Science 305, 847 (2004)]. The frequency-dependent contribution to the heat transfer, or transmission-factor spectrum, is confirmed by calculating the dispersion relation of guided modes by the two parallel corrugated plates through a finite-element method. Especially, the photonic density of states derived from the dispersion relation is found to have excellent agreement to the transmission-factor spectrum.
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