Representing three-dimensional cross fields using 4th order tensors

This paper presents a new way of describing cross fields based on fourth order tensors. We prove that the new formulation is forming a linear space in $\mathbb{R}^9$. The algebraic structure of the tensors and their projections on \mbox{SO}(3) are presented. The relationship of the new formulation with spherical harmonics is exposed. This paper is quite theoretical. Due to pages limitation, few practical aspects related to the computations of cross fields are exposed. Nevetheless, a global smoothing algorithm is briefly presented and computation of cross fields are finally depicted

Digital sculpture : conceptually motivated sculptural models through the application of three-dimensional computer-aided design and additive fabrication technologies

Thesis (D. Tech.) - Central University of Technology, Free State, 200

Review on Light Management by Nanostructures in Chalcopyrite Solar Cells

Light management has gained wide interest for various types of solar cells. This paper reviews the application of nanostructures for light management to chalcopyrite (CIGSe) type solar cells. Firstly, the relevance of light management for CIGSe solar cells will be introduced and applicable concepts of nanostructures for absorption enhancement discussed. The development of ultra- thin CIGSe solar cells and examples for nanoparticle fabrication techniques together with their chances and challenges for application to CIGSe will be presented. Particular attention will be paid to nanostructures that have been applied to CIGSe solar cells, revealing many theoretical and some experimental results. Metallic and dielectric nanostructures as well as intrinsic nanotextures will be covered. For the future, combined considerations of optical and electrical properties will gain in importance

High-order localized spoof surface plasmon resonances and experimental verifications

We theoretically demonstrated and experimentally verified high-order radial spoof localized surface plasmon resonances supported by textured metal particles. Through an effective medium theory and exact numerical simulations, we show the emergence of these geometrically-originated electromagnetic modes at microwave frequencies. The occurrence of high-order radial spoof plasmon resonances is experimentally verified in ultrathin disks. Their spectral and near-field properties are characterized experimentally, showing an excellent agreement with theoretical predictions. Our findings shed light into the nature of spoof localized surface plasmons, and open the way to the design of broadband plasmonic devices able to operate at very different frequency regimes.Comment: 29 pages, 10 figure

State of the Art in Example-based Texture Synthesis

International audienceRecent years have witnessed significant progress in example-based texture synthesis algorithms. Given an example texture, these methods produce a larger texture that is tailored to the user's needs. In this state-of-the-art report, we aim to achieve three goals: (1) provide a tutorial that is easy to follow for readers who are not already familiar with the subject, (2) make a comprehensive survey and comparisons of different methods, and (3) sketch a vision for future work that can help motivate and guide readers that are interested in texture synthesis research. We cover fundamental algorithms as well as extensions and applications of texture synthesis

Solar canvas:Nanoscale light management for ultra-thin, semi-transparent, and colourful solar cells

This thesis provides new solutions for integrable PV by exploiting nanophotonic principles in nanoscale architectures. It shows a high degree of control over the absorption/transmission spectrum by using optical waveguiding in either nanowires (NW) or thin films. In Chapter 2, we focus on understanding the optical properties of vertically standing semiconductor NWs as promising building blocks for next generation photonics and photovoltaics. In Chapter 3, we explore in detail the potential of semiconductor NW-based solar cells as a powerful and tunable-in-design approach for wavelength-selective semi-transparent solar cells for BIPV. Optical simulations and experimental demonstration of PMDS-embedded NW arrays confirm that by changing diameter and periodicity one can engineer the absorption and transmission spectra of the NW array to provide a broad range of bright colours, semi-transparency and high PV performance. Chapter 4 focuses on ultrathin, high efficiency and flexible Si solar cells as another photonic-based solution to minimize the compromise of high conversion efficiency for aesthetics in solar cells. Here we present a new family of surface texturing, based on correlated disordered hyperuniform patterns, capable of manipulating scattering spectrum of the incident light to be efficiently coupled into the silicon slab optical modes. We experimentally demonstrate 66.5% solar light absorption in free-standing 1um c-Si layers by using these nanotextures. Finally, in Chapter 5, we combine the unique light waveguiding and absorption in vertically standing NWs with k-space engineering given by their arrangement into arrays to increase absorption in an ultra-thin tandem cell beyond the bulk limits. The photonic and design concepts presented here combined with highly-performing PV materials make the intersection between high-efficiency, flexibility, colour-tunability and transparency closer to reality

Atmospheric pressure plasma jet for surface texturing of C/SiC

C/SiC composites are materials to be used in harsh environments overcoming the limits imposed by the intrinsic brittleness of their ceramic constituents while providing both high mechanical performances at high-temperature temperatures and low weight. In order to manufacture the final component, joining C/SiC, to itself or to other materials, is often necessary, and it is critical to maximize the strength of the joints (similar or dissimilar) in order to meet reliability criteria. In the present work, a pre-joining treatment based on an atmospheric pressure plasma jet (APPJ) was proposed to introduce a brush-like texture on the surface via the selective removal of carbon fibers. The investigation of treated surfaces via electron microscopy and confocal 3D-profilometry confirmed that the treatment was effective in introducing a brush-like texture and in increasing the available contact area. Wettability test and inspection of cross-section of CB4 wetted samples were then carried out. The latter confirmed the formation of anchoring points given by the brush-like texture. Finally, the effectiveness of the treatment in improving the joint strength was assessed by comparing the apparent shear strength of CB4 brazed composites, with and without the APPJ pre-treatment. The joints with plasma pre-treated C/SiC showed a shear strength of about 66 MPa, 44% more than the strength of joints produced with untreated C/SiC

Photon Management for Thin-Film Quantum Dot Solar Cells

L'abstract è presente nell'allegato / the abstract is in the attachmen