On the modelling of fire atmosphere/sprinkler spray interacting using an Euler-Lagrange framework

An Euler-Lagrange particle tracking model, developed for simulating fire atmosphere/sprinkler spray interactions, is described. Full details of the model along with the approximations made and restrictions applying are presented. Errors commonly found in previous formulations of the source terms used in this two-phase approach are described and corrected. In order to demonstrate the capabilities of the model it is applied to the simulation of a fire in a long corridor containing a sprinkler. The simulation presented is three-dimensional and transient and considers mass, momentum and energy transfer between the gaseous atmosphere and injected liquid droplets.

Absorption and luminescent excitation spectra of F and M centers in Kcl and NaF

Luminescent excitation spectra were measured for the F and M centers in KCl; in particular, for the F band, M band, and the M2 transition. In all 3 cases, the spectra were nearly double-Gaussian in shape, and the efficiency for luminescence was nearly independent of the wavelength of the exciting light. A comparison of the absorption spectrum with the excitation spectrum of the F-band region of crystals with M centers present and oriented provided further evidence for the existence of the M2 transition of van Doorn and Haven and of Okamoto, and against the energy transfer theory of Lambe and Compton. The efficiency for luminescence of the M center upon M-band excitation was equal to the efficiency for F centers in pulse-annealed crystals of low F-center concentrations. The ratio of the efficiencies of the Ml to M2 transitions was 1.2 ± .25. The oscillator strengths of 3 of the M-center transitions in KCl relative to the oscillator strength for the F center were found to be in better agreement with the results reported by Okamoto, than with the results reported by Delbecq. The polarization of luminescence of M centers in KCl was measured at right angles to the exciting light, and was found to agree with the predictions of the van Doorn-Haven model of the M center. In NaF crystals having no absorption bands to the red side of the M band, the absorption and excitation spectra of the M band were accurately double-Gaussian over a wide range of wavelengths; the efficiency of luminescence of the M center was independent of the wavelength of the exciting light in that range; and the polarization of luminescence upon M-band excitation agreed well with the calculations based on the van DoornHaven model of the M center, In crystals in which the F band was bleached sufficiently to make it smaller in absorption height than the M band, several new color centers appeared on the red side of the M band, in contrast to the results reported by Blum; in these crystals, the polarization of luminescence of the M center upon M-band excitation disagreed strongly with theory, even though the absorptions for the new color centers were small compared to the M-band absorption.

Síntese de sensores, funcionalização de nanopartículas e fibras óticas para reconhecimento de aniões

O trabalho descrito nesta dissertação envolve a síntese e caracterização de novos macrociclos tetrapirrólicos e afins com potencial aplicação como quimiossensores de aniões, tanto em solução como quando suportados em diferentes materiais. As porfirinas e ftalocianinas ocupam um lugar de destaque nesta dissertação, pelo que no primeiro capítulo, é feita uma revisão bibliográfica acerca das suas metodologias de síntese bem como das suas principais características e aplicações, nomeadamente como quimiossensores de aniões. No segundo capítulo é discutida a síntese e caracterização dos compostos porfirínicos e ftalocianinicos com grupos amina ou poliamina, posteriormente utilizados como hospedeiros de aniões. Descrevem-se, pormenorizadamente, os métodos de síntese, purificação e caracterização estrutural dos diversos compostos sintetizados. No terceiro capítulo realizaram-se os estudos de complexação com aniões em solução e determinaram-se as respetivas constantes de afinidade. Os compostos sintetizados apresentam capacidade de interagir com diferentes aniões. As porfirinas testadas apresentam elevadas constantes de afinidade para o anião di-hidrogenofosfato, mesmo em soluções aquosas quando testadas com cristais piezoelétricos. No caso das ftalocianinas verificou-se que estas interagem com vários aniões e apresentam propriedades cromogénicas, podendo mesmo distinguir aniões cianeto em soluções contendo água. No quarto capítulo estudou-se a imobilização dos quimiossensores, que demonstraram maior eficácia nos estudos de reconhecimento em solução, em diferentes materiais. Primeiro foi estudada a imobilização dos quimiossensores em nanopartículas de sílica (com e sem núcleo magnético) e testada a sua capacidade como sensor de aniões em solução. Numa segunda parte foi estudada a imobilização em fibras óticas. Estas, além das suas excecionais propriedades físico-químicas, têm a vantagem de poderem ser integradas em diferentes estruturas e/ou equipamentos de análise. Na ultima parte desta dissertação encontra-se a descrição da síntese e caracterização de novos conjugados porfirina-C60-OligoDNA com potencial aplicação em transferência eletrónica. Foram sintetizados e caracterizados novos compostos porfirina-OligoDNA e C60-OligoDNA. Esta parte do trabalho foi realizada no “Institute of Advanced Energy” na Universidade de Quioto, Japão.

Exploiting Collective Effects to Direct Light Absorption in Natural and Artificial Light-harvesters

Photosynthesis –the conversion of sunlight to chemical energy –is fundamental for supporting life on our planet. Despite its importance, the physical principles that underpin the primary steps of photosynthesis, from photon absorption to electronic charge separation, remain to be understood in full. Electronic coherence within tightly-packed light-harvesting (LH) units or within individual reaction centers (RCs) has been recognized as an important ingredient for a complete understanding of the excitation energy transfer (EET) dynamics. However, the electronic coherence across units –RC and LH or LH and LH –has been consistently neglected as it does not play a significant role during these relatively slow transfer processes. Here, we turn our attention to the absorption process, which, as we will show, has a much shorter built-in timescale. We demonstrate that the- often overlooked- spatially extended but short-lived excitonic delocalization plays a relevant role in general photosynthetic systems. Most strikingly, we find that absorption intensity is, quite generally, redistributed from LH units to the RC, increasing the number of excitations which can effect charge separation without further transfer steps. A biomemetic nano-system is proposed which is predicted to funnel excitation to the RC-analogue, and hence is the first step towards exploiting these new design principles for efficient artificial light-harvesting.

Ingestion of a bacterivorous ciliate by the oyster Crassostrea gigas: Protozoa as a trophic link between picoplankton and benthic suspension-feeders

The linked concepts of 'microbial loop' and 'protozoan trophic link' have been very well documented in filter-feeding microzooplankton such as copepods, but have not been applied to energy transfer to benthic suspension-feeding macrofauna, with the exception of the recent demonstration of heterotrophic flagellate assimilation by mussels. The oyster Crassostrea gigas obtains energy resources by filtering microalgae (similar to 5 to 100 mu m). However, in turbid estuaries, light-limited phytoplanktonic production cannot entirely account for oyster energy requirements. Conversely, picoplankters (<2 mu m), which are main effecters of coastal energy flow and matter cycling, are not efficiently retained by oyster filtration. Ciliate protozoal as both micro-sized cells (similar to 5 to 100 run) and bacteria grazers, may represent a major intermediary in trophic transfer between picoplankton and metazoa. The ciliate Uronema was intensely cultured and labelled, using the cyanobacteria Synechococcus as an auto-fluorescent biomarker. The labelled ciliates were offered as potential prey to oysters. We report here the first experimental evidence of a significant retention and ingestion of ciliates by oysters, supporting the role of protozoa as a realistic trophic link between picoplankters and filter-feeding bivalves and thus enhancing their potential importance in estuarine microbial food webs.

Sloshing and slamming oscillations in collapsible channel flow

We consider laminar high-Reynolds-number flow through a finite-length planar channel, where a portion of one wall is replaced by a thin massless elastic membrane that is held under longitudinal tension T and subject to an external pressure distribution. The flow is driven by a fixed pressure drop along the full length of the channel. We investigate the global stability of two-dimensional Poiseuille flow using a method of matched local eigenfunction expansions, which is compared to direct numerical simulations. We trace the neutral stability curve of the primary oscillatory instability of the system, illustrating a transition from high-frequency ‘sloshing’ oscillations at high T to vigorous ‘slamming’ motion at low T . Small-amplitude sloshing at high T can be captured using a low-order eigenmode truncation involving four surface-based modes in the compliant segment of the channel coupled to Womersley flow in the rigid segments. At lower tensions, we show that hydrodynamic modes contribute increasingly to the global instability and we demonstrate a change in the mechanism of energy transfer from the mean flow, with viscous effects being destabilising. Simulations of finite-amplitude oscillations at low T reveal a generic slamming motion, in which the the flexible membrane is drawn close to the opposite rigid wall before rapidly recovering. A simple model is used to demonstrate how fluid inertia in the downstream rigid channel segment, coupled to membrane curvature downstream of the moving constriction, together control slamming dynamics.

Effects of Drive Speed Modulation on Dynamics of Slender Rotating Structures

Slender rotating structures are used in many mechanical systems. These structures can suffer from undesired vibrations that can affect the components and safety of a system. Furthermore, since some these structures can operate in a harsh environment, installation and operation of sensors that are needed for closed-loop and collocated control schemes may not be feasible. Hence, the need for an open-loop non-collocated scheme for control of the dynamics of these structures. In this work, the effects of drive speed modulation on the dynamics of slender rotating structures are studied. Slender rotating structures are a type of mechanical rotating structures, whose length to diameter ratio is large. For these structures, the torsion mode natural frequencies can be low. In particular, for isotropic structures, the first few torsion mode frequencies can be of the same order as the first few bending mode frequencies. These situations can be conducive for energy transfer amongst bending and torsion modes. Scenarios with torsional vibrations experienced by rotating structures with continuous rotor-stator contact occur in many rotating mechanical systems. Drill strings used in the oil and gas industry are an example of rotating structures whose torsional vibrations can be deleterious to the components of the drilling system. As a novel approach to mitigate undesired vibrations, the effects of adding a sinusoidal excitation to the rotation speed of a drill string are studied. A portion of the drill string located within a borewell is considered and this rotating structure has been modeled as an extended Jeffcott rotor and a sinusoidal excitation has been added to the drive speed of the rotor. After constructing a three-degree-of-freedom model to capture lateral and torsional motions, the equations of motions are reduced to a single differential equation governing torsional vibrations during continuous stator contact. An approximate solution has been obtained by making use of the Method of Direct Partition of Motions with the governing torsional equation of motion. The results showed that for a rotor undergoing forward or backward whirling, the addition of sinusoidal excitation to the drive speed can cause an increase in the equivalent torsional stiffness, smooth the discontinuous friction force at contact, and reduce the regions of negative slope in the friction coefficient variation with respect to speed. Experiments with a scaled drill string apparatus have also been conducted and the experimental results show good agreement with the numerical results obtained from the developed models. These findings suggest that the extended Jeffcott rotordynamics model can be useful for studies of rotor dynamics in situations with continuous rotor-stator contact. Furthermore, the results obtained suggest that the drive speed modulation scheme can have value for attenuating drill-string vibrations.

Surface photochemistry of pesticides: an approach using diffuse reflectance and chromatography techniques

The photochemistry of pesticides triadimenol and triadimefon was studied on cellulose and beta-cyclodextrin (beta-CD) in controlled and natural conditions, using diffuse reflectance techniques and chromatographic analysis. The photochemistry of triadimenol occurs from the chlorophenoxyl moiety, while the photodegradation of triadimefon also involves the carbonyl group. The formation of 4-chlorophenoxyl radical is one of the major reaction pathways for both pesticides and leads to 4-chlorophenol. Triadimenol also undergoes photooxidation and dechlorination, leading to triadimefon and dechlorinated triadimenol, respectively. The other main reaction process of triadimefon involves alpha-cleavage from the carbonyl group, leading to decarbonylated compounds. Triadimenol undergoes photodegradation at 254 nm but was found to be stable at 313 nm, while triadimefon degradates in both conditions. Both pesticides undergo photochemical decomposition under solar radiation, being the initial degradation of rate per unit area of triadimefon 1 order of magnitude higher than the observed for triadimenol in both supports. The degradation rates of the pesticides were somewhat lower in beta-CD than on cellulose. Photoproduct distribution of triadimenol and triadimefon is similar for the different irradiation conditions, indicating an intramolecular energy transfer from the chlorophenoxyl moiety to the carbonyl group in the latter pesticide.