Electron-phonon interaction effects in semiconductor quantum dots: a non-perturbative approach

Multiphonon processes in a model quantum dot (QD) containing two electronic states and several optical phonon modes are considered by taking into account both intra- and nterlevel terms. The Hamiltonian is exactly diagonalized, including a finite number of multiphonon processes large enough to guarantee that the result can be considered exact in the physically important energy region. The physical properties are studied by calculating the electronic Green’s function and the QD dielectric function. When both the intra- and interlevel interactions are included, the calculated spectra allow several previously published experimental results obtained for spherical and self-assembled QD’s, such as enhanced two-LO-phonon replica in absorption spectra and up-converted photoluminescence to be explained. An explicit calculation of the spectral line shape due to intralevel interaction with a continuum of acoustic phonons is presented, where the multiphonon processes also are shown to be important. It is pointed out that such an interaction, under certain conditions, can lead to relaxation in the otherwise stationary polaron system.Fundação para a Ciência e a Tecnologia (FCT

A Blind Comparative Study of Focused Wave Interactions with a Fixed FPSO-like Structure (CCP-WSI Blind Test Series 1)

Results from Blind Test Series 1, part of the Collaborative ComputationalProject in Wave Structure Interaction (CCP-WSI), are presented. Partici-pants, with a range of numerical methods, simulate blindly the interactionbetween a fixed structure and focused waves ranging in steepness and di-rection. Numerical results are compared against corresponding physicaldata. The predictive capability of each method is assessed based on pres-sure and run-up measurements. In general, all methods perform well inthe cases considered, however, there is notable variation in the results(even between similar methods). Recommendations are made for appro-priate considerations and analysis in future comparative studies

The influence of the preparation of the radicular dentine surface on its adhesion to Herculite material

Celem pracy jest porównane wpływu EDTA i kwasu cytrynowego na adhezję pomiędzy zębiną korzeniową a materiałem kompozytowym Herculite. Właściwa adhezja pomiędzy materiałami wypełniającymi a strukturą zęba, stanowi odpowiednie zabezpieczenie przed mikroprzeciekiem, niezbędne do uzyskania zadawalających efektów w leczeniu stomatologicznym. Do badań użyto 40 korzeni ludzkich zębów trzonowych usuniętych ze względów stomatologicznych. Dwadzieścia losowo wybranych zębów przecinano prostopadle w stosunku do długiej osi korzenia zęba (grupa I), kolejne 20 równolegle (grupa II). Następnie poprzeczne (grupa I) i podłużne przekroje zębów (grupa II) podzielono losowo na dwie podgrupy: a i b po 10 zębów każda, aktywowano roztworami powszechnie stosowanymi w leczeniu endodontycznym i wytrawiono 37% kwasem ortofosforowym. Próbki zębów wszystkich grup pokryto systemem wiążącym Opti-Bond Solo Plus i spolimeryzowano. Na przygotowane w ten sposób powierzchnie, przy pomocy specjalnej formy o średnicy 3 mm, nanoszono materiał Herculite. Badania wykazały, że nie występują różnice istotne statystycznie w wytrzymałości na ścinanie pomiędzy połączeniem materiału Herculite z powierzchnią zębiny. Również ułożenie kanalików zębinowych w stosunku do powierzchni połączenia nie wpływa na ich wytrzymałość na ścinanie.The aim of this study is to compare the influence of EDTA and citric acid on adhesion between radicular dentine and composite material Herculite. Appropriate adhesion between filling material and tooth structure constitutes proper protection against coronal leak-age, indispensable to achieve a satisfactory effects in dentistry treatment. Forty human teeth molars roots, removed from dentistry indications were used in this study. Twenty randomly selected teeth were sliced perpendicularly to the long axis of dental radices (I group), following 20 parallely (group II). In the group I dentinal tubules were parallel to the analysed surface, whereas in group II perpendicular. Transversal and longitudinal teeth profiles were randomly divided into two subgroups of ten teeth each and activated by solutions which are commonly used in endodontic treatment and 37% ortophosphoric acid. Slices of all teeth were covered with a bonding system OptiBond Solo Plus and light cured. On the surfaces prepared in this way, Herculite composite material with using special form of 3 mm in diameter, was applied. The findings reveal that there are not statistical differences in shear strength between the dentine and Herculite material. Also the direction of the dentinal tubules does not influence the shear strength of the analysed samples

Application of a Riemann Solver Unstructured Finite Volume Method to Combustion Instabilities

Combustion instabilities are a common difficulty in the design of combustion systems for applications from power generation gas turbines to gas and liquid fuel rockets. Many low-order models have been developed for quick turnaround prediction of trends, while high-fidelity, large-eddy simulations are becoming a viable tool with the increasing availability of computing resources. In this paper, a three-dimensional linear thermoacoustic solver is developed to fill the void in design tools between the low-order modeling techniques and the expensive high-fidelity approach. The solver uses the finite volume method with a second-order Riemann solver flux calculation to solve the linearized Euler equations with unsteady heat release. The code is written for unstructured grids in order to easily accommodate the complex geometries ofindustrial combustors. Because the application requires the ability toresolve the effects of sharp gradients of mean density, a method for treating variable-coefficient hyperbolic systems is developed within the Riemann solver approach for unstructured grids. The code is tested with three verification cases with comparison toexact solution and three validation cases with comparisontoexperimental data. The codeisshown to predict the frequencies and limit-cycle amplitudes of the validation experiments well, comparing favorably to lower-order models. In the final validation case, the code predicts the frequency and limit-cycle amplitude within 5% for a realistic gas turbine combustor design. More important, the code predicts the subsequent stability of the mode after a change in the operating conditions