Radial combustion experiments on Fe 2 O 3 /aluminum thermite thin circular samples were conducted. A stoichiometric (Fe 2 O 3 + 2Al) and four over aluminized mixtures were tested. The combustion products were characterized by X-ray diffraction and Mössbauer spectroscopy and the influence of Fe 2 O 3 /aluminum ratio on their composition was assessed. The main products were identified as alumina (␣-Al 2 O 3 ) and iron (Fe). A significant amount of hercynite (FeAl 2 O 4 ) was detected, decreasing with the aluminum excess in the reactants. Close to the sample/confinement interface, where reaction quenching occurs, a non-stoichiometric alumina (Al 2.667 O 4 ) was observed, being its XRD intensity correlated to the hercynite amount. Fe 3 Al intermetallic phase was found in the products of over aluminized mixtures. A reaction mechanism was proposed comprising: (i) Fe 2 O 3 reduction to Fe 3 O 4 and FeO; (ii) Al oxidation to Al 2 O 3 ; (iii) interaction of the remaining Al with Fe 3 O 4 and FeO with formation of iron-aluminates (hercynite) and iron; (iv) for the over aluminized mixtures, incorporation of Al into the iron-aluminates takes place with the formation of iron and alumina and, in parallel, Al reacts with iron to produce intermetallics.
The outset of realistic rendering is a desire to reproduce the appearance of the real world. Rendering techniques therefore operate at a scale corresponding to the size of objects that we observe with our naked eyes. At the same time, rendering techniques must be able to deal with objects of nearly arbitrary shapes and materials. These requirements lead to techniques that oftentimes leave the task of setting the optical properties of the materials to the user. Matching the appearance of real objects by manual adjustment of optical properties is however nearly impossible. We can render objects with a plausible appearance in this way but cannot compare the appearance of a manufactured item to that of its digital twin. This is especially true in the case of translucent objects, where we need more than a goniometric measurement of the optical properties. In this survey, we provide an overview of forward and inverse models for acquiring the optical properties of translucent materials. We map out the efforts in graphics research in this area and describe techniques available in related fields. Our objective is to provide a better understanding of the tools currently available for appearance specification when it comes to digital representations of real translucent objects.
Optical coherence tomography (OCT) scans were acquired from healthy controls and patients with diabetic macular edema (DME), a common complication of diabetes characterized by increased retinal thickness due to fluid accumulation. The collected OCT data was divided into three distinct groups: healthy subjects, DME patients with significantly increased outer nuclear layer (ONL) thickness and DME patients without visible changes in the ONL. For each group, the ONL was segmented and processed, yielding a representative A-scan. Using reference values for the physical and optical characteristics of the healthy human retina, we used a Monte Carlo method with a model for the ONL to simulate an A-scan for each group and compare it to the real OCT data. This allowed to identify which alterations in the cellular characteristics are responsible for the changes observed in the OCT scans of the diseased groups.
Quantum dots can be used in white LEDs for lighting applications to fill the spectral gaps in the combined emission spectrum of the blue pumping LED and a broad band phosphor, in order to improve the source color rendering properties. Because quantum dots are low scattering materials, their use can also reduce the amount of backscattered light which can increase the overall efficiency of the white LED. The absorption spectrum and narrow emission spectrum of quantum dots can be easily tuned by altering their synthesis parameters. Due to the re-absorption events between the different luminescent materials and the light interaction with the LED package, determining the optimal quantum dot properties is a highly non-trivial task. In this paper we propose a methodology to select the optimal quantum dot to be combined with a broad band phosphor in order to realize a white LED with optimal luminous efficacy and CRI. The methodology is based on accurate and efficient simulations using the extended adding-doubling approach that take into account all the optical interactions. The method is elaborated for the specific case of a hybrid, remote phosphor white LED with YAG:Ce phosphor in combination with InP/CdxZnSe type quantum dots. The absorption and emission spectrum of the quantum dots are generated in function of three synthesis parameters (core size, shell size and cadmium fraction) by a semi-empirical 'quantum dot model' to include the continuous tunability of these spectra. The sufficiently fast simulations allow to scan the full parameter space consisting of these synthesis parameters and luminescent material concentrations in terms of CRI and efficacy. A conclusive visualization of the final performance allows to make a well-considered trade-off between these performance parameters. For the hybrid white remote phosphor LED with YAG:Ce and InP/CdxZnSe quantum dots a CRI Ra = 90 (with R9>50) and an overall efficacy of 110 lm/W is found.
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