We investigate the influence of the built-in voltage on the performance of organic bulk heterojuction solar cells that are based on a p-i-n structure. Electrical doping in the hole and the electron transport layer allows to tune their work function and hence to adjust the built-in voltage: Changing the doping concentration from 0.5 to 32 wt% induces a shift of the work function towards the transport levels and increases the built-in voltage. To determine the built-in voltage, we use electroabsorption spectroscopy which is based on an evaluation of the spectra caused by a change in absorption due to an electric field (Stark effect). For a model system with a bulk heterojunction of BF-DPB and C60, we show that higher doping concentrations in both the electron and the hole transport layer increase the built-in voltage, leading to an enhanced short circuit current and solar cell performance.

Tesis por compendio / [ES] Generalmente, se utilizan tratamientos térmicos para la esterilización de emulsiones. Sin embargo, el calentamiento ha demostrado inducir la hidrólisis de lípidos y lecitina. En este sentido, las tecnologías no térmicas están surgiendo en la industria para alcanzar la estabilidad microbiana evitando la pérdida de calidad relacionada con el calor. El CO2 supercrítico (SC-CO2) y los campos eléctricos pulsados (PEF) son tecnologías no térmicas para la inactivación microbiana. Sin embargo, estas técnicas en ocasiones requieren altas intensidades o tiempos de tratamiento largos para garantizar la seguridad del producto. La literatura ha demostrado la capacidad de los ultrasonidos de alta potencia (HPU) para intensificar fenómenos de transferencia de masa y calor. Por lo tanto, su aplicación a tecnologías no térmicas podría ser un enfoque interesante para mejorar la efectividad de la inactivación microbiana. En este contexto, el objetivo fue evaluar el efecto de los tratamientos SC-CO2, PEF y HPU, aplicados de forma individual y combinada, sobre la inactivación de diferentes microorganismos en emulsiones. Para ello, por un lado, se estudió el efecto de la aplicación de HPU a los tratamientos SC-CO2 sobre diferentes tipos de microorganismos y sobre medios con diferente contenido en aceite. Por otro lado, se evaluó el efecto de los tratamientos PEF y HPU individuales y combinados sobre diferentes microorganismos Los resultados mostraron que, en general, la aplicación de HPU intensificó la capacidad de inactivación de SC-CO2. Los HPU probablemente facilitaron la solubilidad del CO2 en el medio y provocaron daños en las células. En este sentido, el análisis microscópico de las células inactivadas reveló importantes cambios morfológicos, incluyendo paredes celulares dañadas y pérdida del contenido citoplasmático. En cambio, los HPU no mejoraron la inactivación de SC-CO2 de las esporas de A. niger en emulsión. El aumento de la presión llevó a una mayor inactivación, a excepción de E. coli en agua, donde no se encontró efecto de la presión. Sin embargo, las presiones por encima de 350 bar no parecen ejercer ninguna inactivación adicional. El aumento de temperatura tuvo un efecto significativo para todos los tratamientos y microorganismos. En cuanto al efecto del medio, se sabe que la presencia de aceite protege a los microorganismos, como se observó en la inactivación de bacterias SC-CO2 en agua y en emulsiones con diferente contenido en aceite. Sin embargo, la aplicación de HPU enmascaró el efecto protector que ejerce el aceite en las emulsiones. En cambio, para las esporas de A. niger no se encontró efecto del medio sobre la efectividad de los tratamientos. En relación al efecto de los tratamientos de SC-CO2 + HPU sobre la calidad de las emulsiones, se encontró un efecto leve de las condiciones del proceso y mediante la selección de condiciones adecuadas de SC-CO2 + HPU, se pudieron obtener cambios mínimos en la calidad de las emulsiones y una inactivación satisfactoria de todos los microorganismos, excepto para las esporas de G. stearothermophilus. Con respecto a los tratamientos de PEF y HPU, no se logró la inactivación completa de las emulsiones con los tratamientos individuales. Sin embargo, cuando el PEF (152,3-176,3 kJ / kg) fue seguido de HPU (3 min), se obtuvieron niveles de inactivación de 8,2, 6,6 y 1,0 ciclos-log para E. coli, A. niger y B. pumilus. Además, la inactivación lograda por el tratamiento con PEF-HPU fue mayor que la de la suma de los tratamientos individuales para todos los microorganismos. Por el contrario, la inactivación lograda por el tratamiento HPU-PEF fue menor que la de la suma de los tratamientos individuales. Por lo tanto, la secuencia más eficaz fue aquella en la que el PEF fue seguido de los HPU. Se puede concluir que, la combinación de HPU con SC-CO2 o PEF generalmente mejoró la inactivación microbiana. En consecuencia, se podrían utili / [CA] Generalment, s'utilitzen tractaments tèrmics per a l'esterilització d'emulsions. No obstant això, el calfament ha demostrat induir la hidròlisi de lípids i lecitina. En aquest sentit, les tecnologies no tèrmiques estan sorgint en la indústria per a aconseguir l'estabilitat microbiana evitant la pèrdua de qualitat relacionada amb la calor. El CO¿ supercrític (SC-CO¿) i els camps elèctrics premuts (PEF) són tecnologies no tèrmiques per a la inactivació microbiana. No obstant això, aquestes tècniques a vegades requereixen altes intensitats o temps de tractament llargs per a garantir la seguretat del producte. La literatura ha demostrat la capacitat dels ultrasons d'alta potència (HPU) per a intensificar fenòmens de transferència de massa i calor. Per tant, la seua aplicació a tecnologies no tèrmiques podria ser un enfocament interessant per a millorar l'efectivitat de la inactivació microbiana. En aquest context, l'objectiu va ser avaluar l'efecte dels tractaments SC-CO¿, PEF i HPU, aplicats de manera individual i combinada, sobre la inactivació de diferents microorganismes en emulsions. Per a això, d'una banda, es va estudiar l'efecte de l'aplicació de HPU als tractaments SC-CO¿ sobre diferents tipus de microorganismes i sobre mitjans amb diferent contingut en oli. D'altra banda, es va avaluar l'efecte dels tractaments PEF i HPU individuals i combinats sobre diferents microorganismes Els resultats van mostrar que, en general, l'aplicació de HPU va intensificar la capacitat d'inactivació de SC-CO2. Els HPU probablement van facilitar la solubilitat del CO¿ en el mitjà i van provocar danys en les cèl·lules. En aquest sentit, l'anàlisi microscòpica de les cèl·lules inactivades va revelar importants canvis morfològics, incloent parets cel·lulars danyades i pèrdua del contingut citoplasmàtic. En canvi, els HPU no van millorar la inactivació de SC-CO2 de les espores de A. niger en emulsió. L'augment de la pressió va portar a una major inactivació, a excepció d'E. coli en aigua, on no es va trobar efecte de la pressió. No obstant això, les pressions per damunt de 350 bar no semblen exercir cap inactivació addicional. L'augment de temperatura va tindre un efecte significatiu per a tots els tractaments i microorganismes. Quant a l'efecte del medi, se sap que la presència d'oli protegeix els microorganismes, com es va observar en la inactivació de bacteris SC-CO¿ en aigua i en emulsions amb diferent contingut en oli. No obstant això, l'aplicació de HPU va emmascarar l'efecte protector que exerceix l'oli en les emulsions. En canvi, per a les espores de A. niger no es va trobar efecte del medi sobre l'efectivitat dels tractaments. En relació a aquest efecte dels tractaments de SC-CO2 + HPU sobre la qualitat de les emulsions, es va trobar un efecte lleu de les condicions del procés i mitjançant la selecció de condicions adequades de SC-CO2 + HPU, es van poder obtindre canvis mínims en la qualitat de les emulsions i una inactivació satisfactòria de tots els microorganismes, excepte per a les espores de G. stearothermophilus. Respecte als tractaments de PEF i HPU, no es va aconseguir la inactivació completa de les emulsions amb els tractaments individuals. No obstant això, quan el PEF (152,3-176,3 kJ / kg) va ser seguit de HPU (3 min), es van obtindre nivells d'inactivació de 8,2, 6,6 i 1,0 cicles- log per a E. coli, A. niger i B. pumilus. A més, la inactivació reeixida pel tractament amb PEF- HPU va ser major que la de la suma dels tractaments individuals per a tots els microorganismes. Per contra, la inactivació reeixida pel tractament HPU- PEF va ser menor que la de la suma dels tractaments individuals. Per tant, la seqüència més eficaç va ser aquella en la qual el PEF va ser seguit dels HPU. Es pot concloure que, la combinació de HPU amb SC-CO¿ o PEF generalment va millorar la inactivació microbiana. En conseqüència, es podrien utilitzar temps de / [EN] Thermal treatments are generally used for the sterilization of emulsions. However, heating has demonstrated its ability to induce the hydrolysis of lipids and lecithin. In this sense, non-thermal technologies are emerging in the industry with the aim of achieving microbial stability while avoiding the loss of quality related to heat. Supercritical carbon dioxide (SC-CO2) and pulsed electric fields (PEF) are non-thermal technologies for microbial inactivation. However, these techniques have demonstrated to require high treatment intensities or long treatment times to guarantee the product's safety. Therefore, there is still room for the improvement in the use of these technologies. Literature has illustrated the capacity of high power ultrasound (HPU) for the intensification of mass and/or heat transfer phenomena. Therefore, its application to non-thermal technologies could be an interesting approach to enhance the microbial inactivation effectiveness. In this context, the objective was to evaluate the effect of SC-CO2, PEF and HPU treatments, applied in individual and combined form, on the inactivation of different microorganisms in emulsions. In order to achieve this goal, on the one hand, the influence of the implementation of HPU to the SC-CO2 treatments was studied on different types of microorganisms and on media with different oil content. On the other hand, the effect of the individual and combined PEF and HPU treatments was assessed on different microorganisms. Results showed that, generally, the application of HPU intensified the inactivation capacity of SC-CO2. HPU probably enhanced the solubilization of CO2 into the medium and provoked damages in the cells. In this regard, the microscopy analysis of the inactivated cells revealed important morphological changes, including damaged cell walls and an important loss of the cytoplasmic content. Nevertheless, HPU did not improved the SC-CO2 inactivation of A. niger spores in emulsion. The increase of the pressure led to a higher inactivation, except for E. coli in water, where no effect of pressure was found. However, pressures above 350 bar did not seem to exert any additional inactivation. The increase of the temperature had a significant effect for all treatments and microorganisms. Regarding the effect of the medium, the presence of oil is known to protect microorganisms, as was observed in the SC-CO2 inactivation of bacteria in water and in emulsions with different oil content. However, the application of HPU masked the protective effect exerted by the oil in the emulsions. On the contrary, for A. niger spores no effect of the media was found on the effectiveness of the treatments In relation to the effect of the SC-CO2 + HPU treatments on the quality of the treated emulsions, only a mild effect of the process conditions was found and by the selection of suitable SC-CO2 + HPU conditions, minimal changes on the quality of the emulsions and a satisfactory inactivation for all the microorganisms, except for G. stearothermophilus spores, can be obtained. Regarding PEF and HPU treatments, the complete inactivation in the emulsions was not achieved with the individual treatments. However, when PEF (152.3-176.3 kJ/kg) was followed by HPU (3 min), inactivation levels of 8.2, 6.6 and 1.0 log-cycles were obtained for E. coli, A. niger and B. pumilus, respectively. Moreover, the inactivation achieved by the PEF-HPU treatment was higher than the sum of the individual treatments for all microorganisms. On the contrary, the inactivation achieved by HPU-PEF treatment was lower than that of the sum of the individual treatments. Thus, the most effective sequence for the combined treatment was the one in which PEF was followed by HPU. It can be concluded that, the combination of HPU with SC-CO2 or PEF generally improved the microbial inactivation. Consequently, reasonable processing times and mild process conditions could be used. / Gómez Gómez, Á. (2021). Pasteurization of Lipid Emulsions with Supercritical CO2 and High Power Ultrasound [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/175486 / TESIS / Compendio

The use of ferroelectric negative capacitance (NC) has been proposed as a promising way to reduce the power dissipation in nanoscale devices [1]. According to single-domain (SD) Landau theory, a hysteresis-free NC state in a ferroelectric might be stabilized in the presence of depolarization fields below a certain critical film thickness tF, SD. However, it is well-known that depolarization fields will cause the formation of domains in ferroelectrics to reduce the depolarization energy [2], which is rarely considered in the literature on NC [3]. The improvident use of SD Landau theory to model NC devices seems to be the main reason for the large discrepancy between experimental data and the current theory [4]. Here, we will show by simulation how anti-parallel domain formation can strongly limit the stability of the NC state in a metal-ferroelectric-insulator-metal (MFIM) structure, which is schematically shown in Fig. 1.

No description available.

Cette thèse examine une nouvelle méthode de diagnostic, appelée Polarimètrie de Mueller, pour l’étude des interactions plasma-surface. Cette technique d’imagerie permet la caractérisation optique résolue en temps des cibles exposées au plasma. Les matrices de Mueller mesurées sont analysées en utilisant la décomposition logarithmique donnant des informations polarimétriques sur la diattenuation, la dépolarisation et la biréfringence. Cette dernière est exploitée en examinant des matériaux optiquement actifs afin d’identifier des aspects spécifiques de l’interaction avec le plasma, tels que les champs électriques ou la température de surface.Ce travail se concentre sur les cibles électro-optiques, qui permettent principalement la détection de champs électriques induits par la charge de surface déposée lors de l’interaction. La biréfringence est couplée analytiquement au champ électrique, en rapportant le retard de phase du faisceau sonde de lumière polarisée, à l’ellipsoïde d’index perturbé suivant l’effet Pockels. Grâce à cette approche analytique, les matériaux ayant des propriétés électrooptiques spécifiques peuvent être choisis de telle manière que toutes les composantes individuelles de champ électrique (axiales et radiales) induites à l’intérieur de l’échantillon soient imagées séparément. Pour la première fois les composantes du champ électriques peuvent être découplées permettant de mieux comprendre la dynamique du plasma proche d’une surface diélectrique.Cette technique est utilisée pour étudier l’impact d’ondes d’ionisation sur des surfaces. Ces décharges, générées par un jet de plasma à pression atmosphérique dans la gamme kHz, sont des plasmas froids filamentaires généralement utilisés pour des applications diverses telles que la fonctionnalisation de surface de polymères ou des traitements biomédicaux, mais les méthodes de diagnostic disponibles pour étudier les effets induits sur les surfaces sont limités. L’imagerie de polarimètrie Mueller appliquée aux cibles électro-optiques permet d’examiner les champs axiaux et radiaux en termes d’amplitude (3-6 kV/cm), d’échelles spatiales (<1mm axiales and <1cm radiales) et d’échelles temporelles (< 1μs pulsée and < 10μs CA) pour divers paramètres de fonctionnement du jet, e.g. amplitude de tension et gaz environnant.Simultanément à la biréfringence transitoire induite par le champ électrique, un signal de fond constant est également observé. Il est induit par la contrainte résultante du gradient de température induit à l’intérieur du matériau ciblé. Une relation analytique est obtenue en utilisant l’effet photo-élastique, permettant de développer une procédure de fitting pour retrouver la distribution de température. Cette procédure est utilisée, après calibration, pour montrer que la température de l’échantillon peut varier jusqu’`a 25 degrés par rapport aux conditions ambiantes – tandis que les changements dans le champ électrique sont également mesurés – et dépend de la fréquence de la tension d’alimentation AC du jet de plasma. La détermination précise de la température induite dans les cibles est importante car la plupart des applications visent des échantillons thermosensibles.Enfin, ce travail montre comment des échantillons complexes (aussi bien en terme d’état de surface que de composition chimique) peuvent être examinés lors d’une interaction plasma-surface, en les combinant avec une cible électrooptique. En raison de l’ajout d’un échantillon complexe, une composante de dépolarisation est ajoutée due à la diffusion du faisceau lumineux polarisé. Les changements de dépolarisation sont liés à l’évolution de l’échantillon complexe au cours du traitement par plasma. Ceux-ci, couplés aux champs électriques mesurés simultanément, fournissent un outil de diagnostic unique pour examiner les interactions plasma-surface. Cela a été appliqué à un cas test où une seule couche de cellules d’oignon est exposée aux ondes d’ionisation générées par le jet de plasma froid. / In this thesis, a new diagnostic method called Mueller Polarimetry is examined for the investigation of plasma-surface interactions. This imaging technique allows the time-resolved optical characterization of targets under plasma exposure. The measured Mueller matrices are analyzed by using the logarithmic decomposition providing polarimetric data on diattenuation, depolarization, and birefringence. The latter is used by examining materials that possess optically active behavior to identify specific aspects of the plasma interaction, e.g. electric fields or temperature.This work focusses on electro-optic targets, which primarily enables the detection of electric fields induced by surface charge deposited during the interaction. The birefringence is coupled to the externally induced electric field by analytically relating the phase retardance for the probing polarized light beam to the perturbed index ellipsoid, according to the Pockels effect. Through this analytical approach, materials with specific electro-optic properties can be chosen in such a way – together with the orientation of the Mueller polarimeter itself – that all the individual electric field components (axial and radial) induced inside the sample are imaged separately. This has never been done before and allows to better understand the plasma dynamics in the vicinity of a dielectric surface.It is used to investigate the surface impact by guided ionization waves generated by a kHz-driven atmospheric pressure plasma jet. These non-thermal filamentary discharges are generally applied to various samples for e.g. surface functionalization of polymers or biomedical treatment of organic tissues. However, available diagnostic tools are limited to study these interactions. Imaging Mueller polarimetry applied to electro-optic targets examines the axial and radial field patterns in terms of amplitude (3-6 kV/cm), spatial scales (< 1mm axial and <1cm radial), and timescales (<1μs pulsed and <10μs AC) for various operating parameters of the jet, for example voltage amplitude and surrounding gas.Simultaneous with the transient birefringence induced by the electric field, a constant background pattern is also observed. This results from strain induced by temperature gradients inside the targeted material. An analytical relation is obtained following the photo-elastic effect, which allowed a fitting procedure to be designed to retrieve the temperature pattern. This procedure is used after calibration to show that the temperature of the sample can vary up to 25 degrees relative to room conditions – while changes in the electric field are seen as well – depending on the operating frequency of the AC driven plasma jet. The accurate determination of the temperature is important since most applications involve temperature sensitive samples.Lastly, this work shows how complex samples (in terms of surface geometry and/or chemical composition) can be examined during a plasma-surface interaction. This is done by combining them with the electro-optic targets. Due to the addition of a (thin) complex sample, depolarization is added to the system through scattering of the polarized light beam. In-situ observed changes of depolarization relate to the evolution of the complex sample during the plasma treatment. This, coupled with the simultaneously monitored electric field patterns, provides a unique diagnostic tool to examine the plasma-surface interactions. This has been applied for a test case where a single layer of onion cells is exposed to the ionization waves generated by the non-thermal plasma jet.

The inductively coupled plasma mass spectrometer (ICP-MS) has been used in laboratories for many years. The majority of the improvements to the instrument have been done empirically through trial and error. A few fluid models have been made, which have given a general description of the flow through the mass spectrometer interface. However, due to long mean free path effects and other factors, it is very difficult to simulate the flow details well enough to predict how changing the interface design will change the formation of the ion beam. Towards this end, Spencer et al. developed FENIX, a direct simulation Monte Carlo algorithm capable of modeling this transitional flow through the mass spectrometer interface, the transitional flow from disorganized plasma to focused ion beam. Their previous work describes how FENIX simulates the neutral ion flow. While understanding the argon flow is essential to understanding the ICP-MS, the true goal is to improve its analyte detection capabilities. In this work, we develop a model for adding analyte to FENIX and compare it to previously collected experimental data. We also calculate how much ambipolar fields, plasma sheaths, and electron-ion recombination affect the ion beam formation. We find that behind the sampling interface there is no evidence of turbulent mixing. The behavior of the analyte seems to be described simply by convection and diffusion. Also, ambipolar field effects are small and do not significantly affect ion beam formation between the sampler and skimmer cones. We also find that the plasma sheath that forms around the sampling cone does not significantly affect the analyte flow downstream from the skimmer. However, it does thermally insulate the electrons from the sampling cone, which reduces ion-electron recombination. We also develop a model for electron-ion recombination. By comparing it to experimental data, we find that significant amounts of electron-ion recombination occurs just downstream from the sampling interface.

<p>A short, 30cm, test section was used to study the effect of electrohydrodynamic (EHD) forces on flow redistribution in a horizontal, shell and tube heat exchanger subject to both boiling and condensation. The use of a short test section allows for a consistent flow pattern across the test section length which provides further insight into the true effect of EHD.</p> <p>It was found that the voltage polarity of the applied voltages influences the flow distribution. For the current geometry studied, it was found that positive polarity voltages tend to pull liquid away from heat transfer surface and that negative voltages tended to repel more liquid toward the heat transfer surface. Using this knowledge we were able to show that positive voltages were more effective for convective condensation heat transfer enhancement, whereas negative voltages were more effective for convective boiling heat transfer enhancement. A twofold enhancement of convective boiling heat transfer was achieved for positive voltages and a 4fold enhancement was achieved for negative voltages. Similar pressure drop penalties were seen for both cases, approximately twice that of the no EHD case.</p> <p>Furthermore, the effect of DC level, peak to peak voltage, frequency and duty cycle waveform parameters on convective boiling enhancement were studied to explore the range of controllability for the current set of flow parameters. It was found that these various waveform parameters can induce different flow patterns and consequently different heat transfer and pressure drop configurations. In general the heat transfer is enhanced by EHD, but different pressure drop penalties can be achieved for a given enhancement ratio using different waveforms. High heat transfer for relatively low pressure drop was achieved using either negative DC signals or 50%duty cycle pulse waveforms. In some cases the enhancement is quite little compared to the pressure drop, for example the zero DC level, varying peak to peak voltage data. It is suggested that in a system where the heat exchanger pressure drop due to EHD is more dominant than the system pressure drop, it may be possible to use EHD as a method of retarding the system rather than enhancing it thereby broadening the scope of controllability.</p> <p>Finally we showed the proof of concept of using DC EHD as a rapid control mechanism for the load conditions. Using -8kVDC the water side heat flux could be varied by approximately ±3.2 kW/m² within 5 seconds. As a comparison, the same experiment was repeated using the refrigerant flow rate to control the load. Response times were similar for both experiments and although the power required for the flow rate control was less, the minimal variability in flow parameters for the EHD control make it a more attractive method of load control.</p> / Master of Applied Science (MASc)

No description available.

L'utilisation de champs électriques pulsés (PEF) dans les secteurs de la médecine et de la biotechnologie est devenue de plus en plus courante au cours des dernières décennies. La recherche a montré qu'en ajustant la durée du PEF, nous pouvons prédire quels effets seront observés. Alors que les PEF dans la gamme micro - milliseconde ont été utilisés pour perméabiliser la membrane cellulaire et améliorer l'absorption de médicament ou de protéine, le PEF nanoseconde (nsPEF) a démontré des effets uniques sur les organites intracellulaires. Les deux PEF et nsPEF ont démontré un potentiel thérapeutique pour une variété de pathologies humaines, y compris le traitement du cancer. Utilisant l'imagerie des cellules vivantes, cette thèse a étudié in vitro les effets de champs pulsés d'une durée de 10 ns à 10 ms sur des lignées cancéreuses (U87 glioblastome multiforme) et non cancéreuses (neurones hippocampes de souris (HT22) et cellules ovariennes du hamster chinois (CHO)). Des résultats publiés antérieurement ont démontré que les cellules cancéreuses sont plus sensibles aux champs électriques que les cellules saines. Nos résultats sont en accord avec ces résultats, dans la mesure où les cellules U87 ont subi une dépolarisation significativement plus importante de leur potentiel transmembranaire après une seule impulsion électrique à toutes les durées. Dans un ensemble d'expériences parallèles, malgré des seuils de champ électrique similaires pour la perméabilisation membranaire, les cellules U87 ont démontré une absorption significativement améliorée de YO-PRO par rapport aux autres lignées cellulaires. Bien que les cellules U87 aient subi le plus grand changement dans la dépolarisation membranaire et la perméabilisation membranaire, elles ont également montré la constante de rescellement de la membrane la plus rapide, qui était environ 30 secondes plus rapide que les autres lignées cellulaires. Pour élucider certains des mécanismes sous-jacents par lesquels les cellules U87 répondent aux champs électriques, une série d'expériences a examiné le rôle des canaux ioniques transmembranaires. Plusieurs études récentes ont rapporté que les PEF peuvent agir directement sur les canaux ioniques voltage-dépendants. En utilisant divers modulateurs de canaux ioniques pharmacologiques spécifiques et à action large, nous avons démontré que nous pouvions presque entièrement inhiber la dépolarisation membranaire induite par le champ électrique dans les cellules U87 en bloquant certains canaux cationiques. Ces résultats étaient assez spécifiques, tels que le canal de potassium de grande conductance (BK), les canaux calciques de type L et T, et le canal cationique non spécifique, TRPM8, étaient capables d'inhiber la dépolarisation tandis que le blocage d'autres canaux ioniques ne produisait aucun changement significatif. . Les travaux de cette thèse ont montré que la lignée cellulaire maligne U87 présentait une plus grande sensibilité aux champs électriques allant de 10 ns à 10 ms par rapport aux lignées cellulaires non cancéreuses étudiées. Des améliorations potentielles aux protocoles de traitement actuels ont été proposées sur la base des résultats présentés ici. / The use of pulsed electric fields (PEF) in medical and biotechnology sectors has become increasingly prevalent over the last few decades. Research has shown that by adjusting the duration of the PEF we can predict what effects will be observed. Whereas PEF in the micro-to-millisecond range have been used to permeabilize the cell membrane and enhance drug or protein uptake, nanosecond PEF (nsPEF) have demonstrated unique effects on intracellular organelles. Both PEF and nsPEF have demonstrated therapeutic potential for a variety of human pathologies, including the treatment of cancer. Using live-cell imaging, this thesis investigated, in vitro, the effects of pulsed fields ranging in duration from 10 ns to 10 ms on cancerous (U87 glioblastoma multiforme) and non-cancerous cell lines (mouse hippocampal neurons (HT22) and Chinese hamster ovary (CHO) cells). Previously published results have demonstrated that cancerous cells have a greater sensitivity to applied electric fields than healthy cells do. Our results are in agreement with these findings, insofar as the U87 cells underwent a significantly greater depolarization of their transmembrane potential following a single electric pulse at all durations. In a parallel set of experiments, despite having similar electric field thresholds for membrane permeabilization, the U87 cells demonstrated significantly enhanced YO-PRO uptake compared to the other cells lines. Although U87 cells underwent the greatest change in both membrane depolarization and membrane permeabilization, they also showed the fastest membrane resealing constant, which was approximately 30 seconds faster than other cell lines. To elucidate some of the underlying mechanisms by which U87 cells respond to electric fields, a series of experiments looked at the role of transmembrane ion channels. Several recent studies have reported that PEFs can act directly on voltage-gated ion channels. Using a variety of specific and broad acting pharmacological ion channel modulators, we demonstrated that we could almost entirely inhibit the electric field-induced membrane depolarization in U87 cells by blocking certain cationic channels. These results were quite specific, such that the big conductance potassium (BK) channel, L- and T-type calcium channels, and the non-specific cationic channel, TRPM8, were able to inhibit depolarization while blocking other ion channels produced no significant change. The work in this thesis showed that the malignant U87 cell line showed a greater sensitivity to electric fields from ranging from 10 ns – 10 ms when compared to the non-cancerous cell lines that were investigated. Potential improvements to current treatment protocols have been proposed based on the findings presented herein.

<p>Modeling microbial inactivation has a great influence on the optimization, control and design of food processes. In the area of food safety, modeling is a valuable tool for characterizing survival curves and for supporting food safety decisions. The modeling of microbial behavior is based on the premise that the response of the microbial population to the environment factors is reproducible. And that from the past, it is possible to predict how these microorganisms would respond in other similar environments. Thus, the use of mathematical models has become an attractive and relevant tool in the food industry.</p> <p>This research provides tools to relate the inactivation of microorganisms of public health importance with processing conditions used in nonisothermal and non-thermal food processing technologies. Current models employ simple approaches that do not capture the realistic behavior of microbial inactivation. This oversight brings a number of fundamental and practical issues, such as excessive or insufficient processing, which can result in quality problems (when foods are over-processed) or safety problems (when foods are under-processed). Given these issues, there is an urgent need to develop reliable models that accurately describe the inactivation of dangerous microbial cells under more realistic processing conditions and that take into account the variability on microbial population, for instance their resistance to lethal agents. To address this urgency, this dissertation focused on mathematical models, combined mathematical tools with microbiological science to develop models that, by resembling realistic and practical processing conditions, can provide a better estimation of the efficacy of food processes. The objective of the approach is to relate the processing conditions to microbial inactivation. The development of the modeling approach went through all the phases of a modeling cycle from planning, data collection, formulation of the model approach according to the data analysis, and validation of the model under different conditions than those that the approach was developed.</p> <p>A non-linear ordinary differential equation was used to describe the inactivation curves with the hypothesis that the momentary inactivation rate is not constant and depends on the instantaneous processing conditions. The inactivation rate was related to key process parameters to describe the inactivation kinetics under more realistic processing conditions. From the solution of the non-linear ordinary differential equation and the optimization algorithm, safety inferences in the microbial response can be retrieved, such as the critical lethal variable that increases microbial inactivation. For example, for nonisothermal processes such as microwave heating, time-temperature profiles were modeled and incorporated into the inactivation rate equation. The critical temperature required to increase the microbial inactivation was obtained from the optimization analysis. For non-thermal processes, such as cold plasma, the time-varying concentration of reactive gas species was incorporated into the inactivation rate equation. The approach allowed the estimation of the critical gas concentration above which microbial inactivation becomes effective. For Pulsed Electric Fields (PEF), the energy density is the integral parameter that groups the wide range of parameters of the PEF process, such as the electric field strength, the treatment time and the electrical conductivity of the sample. The literature has shown that all of these parameters impact microbial inactivation. It has been hyphothesized that the inactivation rate is a function of the energy density and that above a threshold value significant microbial inactivation begins. </p> <p>The differential equation was solved numerically using the Runge-Kutta method (<i>ode45</i> in MATLAB ®). The<i> lsqcurvefit</i> function in MATLAB ® estimated the kinetic parameters. The approach to model microbial inactivation, whether when samples were subjected to nonisothermal or to non-thermal food processes, was validated using data published in the literature and/or in other samples and treatment conditions. The modeling approaches developed by this dissertation are expected to assist the food industry in the development and validation process to achieve the level of microbial reduction required by regulatory agencies. In addition, it is expected to assist the food industry in managing food safety systems through support food safety decision-making, such as the designation of the minimal critical parameter that may increase microbial inactivation. Finally, this dissertation will contribute in depth to the field of food safety and engineering, with the ultimate outcome of having a broad and highly positive impact on human health by ensuring the consumption of safe food products.</p>