published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Contour laser transmission welding (LTW) is a technology that has potential for joining large and complicated thermoplastic parts. Thermal expansion is the primary driving force to bridge potential gaps at the weld. A comprehensive investigation into gap bridging was performed using experimental studies, finite element (FE) thermal-mechanical coupled modeling, and analytical analysis of the contour welding process for polycarbonate (PC), polyamide 6 (PA6) , and glass fibres reinforced polyamide 6 (PA6GF). The effects of material properties (carbon black level, glass fibres and crystallinity), process parameters (laser scan power, scan speed) and weld gap thickness on weld shear strength were assessed. The experimental study indicated that low concentration of laser absorbing pigment accompanied with high power laser scan improves gap bridging. Damage on the top surface of the laser-transparent part limited the allowable laser power that could be delivered onto the weld interface. Maximum gaps of 0.2, 0.4 and 0.25 mm were bridged in the experiment for the three types of polymers respectively. The thermal behavior of polymers in contour LTW was analyzed by the 3-D quasi-static thermal FE models. Thermal expansion into the gap was simulated by the simplified 2-D transient, thermal-mechanical coupled FE models. An analytical model describing laser beam transmission and absorption in light-scattering polymers was developed and applied in the FE simulation for PA6 and PA6GF. FE simulated results agree well with the experiment in contour welding with gap of PC and PA6. The optimum material and process parameters have been searched in the model to maximize gap bridging for PC. An analytical model has been developed to predict the temperature rise and the thermal expansion in high speed contour welding of amorphous polymers. The model indicates that the maximum temperature at weld increases linearly with the laser line energy and the laser absorption coefficient. Thermal expansion and hence gap bridging increases with laser line energy. Lower laser absorption coefficient allows higher laser scan energy to be delivered onto the weld interface so helps bridge larger gap. The predicted thermal expansions by the model agree well with the measured maximum gaps bridged for polycarbonate. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2009-09-24 22:24:11.734

Företag som kommunicerar sitt varumärke och eventuella tilläggsmärkningar utan medvetenhet om kundens uppfattning och förväntan riskerar att förlora sina kunder till konkurrenter. Därav syftar denna kandidatuppsats till att undersöka om det finns diskrepanser i ett företags kommunikation av en kvalitetsstämpel i förhållande till kundens uppfattning och förväntningar av denna kvalitetsstämpel. Vi kommer att beskriva diskrepanserna som gap och studien kommer att klargöra hur dessa gap kan ta sig uttryck samt utreda varför de uppstår. I vår studie undersöker vi AB Sporrong och deras kommunikation av kvalitetsstämpeln Kunglig Hovleverantör. Studien baseras på intervjuer med anställda på AB Sporrong samt kunder till företaget. Insamlad data har analyserats med hjälp av ett analysverktyg vi själva utvecklat med utgångspunkt ifrån Kapferers (2008) identitetsprisma samt teori inom ämnet varumärkeskommunikation. Likheter och diskrepanser återfinns i företagets kommunikation av det Kungliga Hovleverantörsskapet och kundens uppfattning och förväntan. De gap vi i studien har identifierat beror på bristande eller otydlig kommunikation och en undermålig medvetenhet kring kundens behov.

No description available.

A mixed hypergraph is a triple H = (X; C;D), where X is the vertex set, and each of C;D is a list of subsets of X. A strict t-coloring is a onto mapping from X to {1, 2,…,t} such that each c belongs to C contains two vertices have a common value and each d belongs to D has two vertices have distinct values. If H has a strict t-coloring, then t belongs to S(H), such S(H) is called the feasible set of H, and k is a gap if there are a value larger than k and a value less than k in the feasible set but k is not. We find the minimum and maximum gap of a mixed hypergraph with more than 5 vertices. Then we consider two special cases of the gap of mixed hypergraphs. First, if the mixed hypergraphs is spanned by a complete bipartite graph, then the gap is decided by the size of bipartition. Second, the (l,m)-uniform mixed hypergraphs has gaps if l > m/2 >2, and we prove that the minimum number of vertices of a (l,m)-uniform mixed hypergraph which has gaps is (m/2)( l -1) + m.

国立情報学研究所で電子化したコンテンツを使用している。

Heidelberg, Univ., Diss., 2008.

Mainz, Univ., Diss., 2001.

In this thesis we develop a new first-principles method for the calculation of optical absorption spectra and band structures in semiconductors and insulators at finite tem- peratures. The theoretical framework of our methodology originates back to 1950s in two pivotal research papers by F. Williams and M. Lax. Here, we expand the scope of the pioneering works by Williams and Lax, and we present a new theory of phonon- assisted optical absorption and temperature-dependent band structures. We demon- strate that our technique is highly efficient and simple to the point that a single calcu- lation is sufficient to capture temperature-dependent absorption coefficients including the effect of quantum zero-point motion. We report calculations of optical absorption spectra and of direct and indirect band gaps of Si, C, GaAs and MAPbI₃ . We obtain good agreement with experiment and with previous calculations. The approach pro- posed in this thesis is highly versatile, and can straightforwardly be combined with improved descriptions of the dielectric function by including electron-hole effects via the Bethe-Salpeter and GW equations. In this thesis we also investigate the underly- ing mechanisms leading to the "inverse Varshni effect" in materials that belong to the family of metal halide perovskites. We show, using the example of MAPbI 3 , that the vibrational modes with metal-halide-metal bending or rocking character are the major cause of the band gap opening with increasing temperature. To this aim we present an approach for elucidating the physics underpinning the changes of the band gap with vibrational motion. Our methodologies developed in this thesis are simple to imple- ment in any electronic structure package as a post-processing step, having the potential to find broad applications in the ab-initio community. We anticipate that our work will open the way to predictive calculations, as well as will contribute to the better under- standing of the optoelectronic properties of solids at finite temperatures.

No description available.