Electroporation (EP) is a physical non-viral technique used to deliver therapeutic molecules across the cell membrane. During electroporation an external electric field is applied across a cell membrane and it causes pores to form. These pores then allow the surrounding media containing the therapeutics to diffuse across the membrane. This technique has been specifically studied as a promising gene and drug delivery system. Colloidal particles have also proven to be promising for a variety of biological applications including molecular delivery, imaging, and tumor ablation, due to their large surface area and tunable properties. In more recent years researchers have explored the use of both electroporation and particles simultaneously. In this research, the main objective was to investigate and determine the role of sub-micron particles in the electroporation process. Presented in this dissertation are results from the synthesis and characterization of colloidal particles of various sizes and different compositions. The use of these dielectric and metallic particles during in vitro electroporation were investigated along with various other electrical parameters associated with EP such as pulse length, number of pulses, and field strength. Computationally, aspects such as particle composition and particle concentration were explored in an attempt to predict experimental outcomes.

L’objectif de la thèse était d’analyser deux types de perturbations de l’ionosphère supérieure observées sur les mesures de plasma fournies par le satellite DEMETER.Les premières sont des Perturbations Ionosphériques Itinérantes de moyenne échelle engendrées par l’action sur le plasma des ondes de gravité atmosphériques qui se propagent jusqu’à haute altitude. Elles prennent la forme de variations quasi-périodiques de densité du plasma qui peuvent atteindre des amplitudes considérables et sont plus fréquentes dans l’hémisphère Sud avec un maximum au-dessus de l’Océan Pacifique. Elles peuvent modifier l’électrodynamique de l’ionosphère et amplifier le champ électrique d’origine dynamo.Les secondes sont observées dans l’ionosphère équatoriale comme des augmentations à grande échelle de la densité du plasma sous la forme de plateaux. En fonction des conditions d’activité magnétique, des dépressions de densité à moyenne échelle peuvent apparaitre sur les plateaux et conduire à la formation des bulles de plasma équatoriales. / This thesis aims at analyzing two kinds of ionospheric disturbances observed on plasma measurements on-board the DEMETER satellite.The first events are Mid-Scale Traveling Ionospheric Disturbances that develop through the interaction between atmospheric gravity waves and the ionospheric plasma. They are observed as quasi-periodic variations of the plasma density that may reach very large amplitudes and are more frequently observed in the Southern hemisphere with a maximum over the Pacific Ocean. These MSTID may strongly modify the electrodynamics of the mid latitude ionosphere and form structures where the dynamo electric field is significantly enhanced.The second events are detected in the equatorial ionosphere as large scale enhancements of the plasma density under the form of plateau. Depending on the level of magnetic activity these large scale structures may be modified by mid-scale density depletions that, eventually, get instable and led to the formation of depleted plasma bubbles.

Les verres du système BaO – TiO₂ – SiO₂ (BTS) présentent un intérêt majeur pour la synthèse de matériaux piézoélectriques par voie vitrocéramique. La fresnoite Ba₂TiSi₂O₈ possède en effet des propriétés piézoélectriques, ferroélectriques et d'optique non-linéaire. L'étude de la structure de verres BTS par spectroscopie Raman et EXAFS a permis d'expliquer l'évolution de leurs propriétés mécaniques à température ambiante et à Tg. Lorsque la teneur en TiO₂ est importante, ces verres présenteraient une séparation de phase menant à la formation de canaux de barium. Le verre 0,30BaO – 0,20TiO₂ – 0,50SiO₂ fut sélectionné comme matrice vitreuse pour la synthèse de vitrocéramiques texturées à base de fresnoite Ba₂TiSi₂O₈. L'étude de la cinétique de cristallisation a permis de contrôler précisément la cristallisation surfacique de cette phase piézoélectrique. L'utilisation d'un traitement par ultrasons précédent le traitement thermique a permis d'augmenter l'orientation de la croissance des cristaux surfaciques dans la direction de polarisation. Il fut ainsi possible de synthétiser des vitrocéramiques piézoélectriques texturées et transparentes présentant des propriétés mécaniques supérieures à celles de la matrice vitreuse. Les propriétés électriques de ces verres furent étudiées par spectroscopie d'impédance. Ceux-ci présentent à la fois une augmentation de leur conductivité et de leur constante diélectrique lors de l'augmentation de la teneur en TiO₂. Il fut suggéré que ces évolutions sont la conséquence de l'apparition des canaux de barium, facilitant la conduction ionique, et de groupements TiO₅, favorisant la polarisation. Finalement, l'effet d'un champ électrique sur la viscosité d'un verre fut investigué, et notamment le ramollissement du verre sous champ électrique intense. Il fut montré qu'il était possible de réduire grandement la viscosité du verre par application d'un champ AC ou DC. Si l'application d'un champ DC a des effets destructeurs sur le matériau, celui d'un champ AC est bien plus prometteur pour de potentielles applications dans la synthèse de matériau vitreux. / Glasses from the BaO – TiO₂ – SiO₂ (BTS) are of great interest for their use as glass-matrix to synthesise fresnoite glass-ceramics. These materials show numerous potential applications as piezoelectric and non-linear optic devices. It has been found that the addition of TiO2 in these glasses improves the cross-linking degree of the glass network as well as the volume density of energy and the glass temperature sensitivity. When the content of titanium is increasing, island-like Si\Ti rich units surrounded by barium-rich channels might form, leading to a similarity between the fresnoite crystal and the glass structure. Thanks to an ultrasonic and thermal heat-treatment it has been possible to control the growth of oriented fresnoite cristallites from the surface of 0,30BaO – 0,20TiO2 – 0,50SiO2 glass. The transparent glass-ceramic shows improved mechanical properties as well as evidence of piezoelectricity. The electrical properties of BTS glasses were investigated with the use of impedance spectroscopy. They show an increase in electric conductivity and dielectric constant as Ti is added to their composition. One explanation lies in the formation of these Ba-rich channels which may improve the ionic conduction. The formation of TiO5 groups would also be responsible for the overall increase in polarizability of the glass. Finally, the effect of an electric field on the glass viscosity was investigated. The glass showed great reduction of its viscosity under high electric field for both AC & DC. When AC field was applied, the material showed no deterioration which might be very interesting for the potential use of this effect for the synthesis of glassy materials.

The results of a solid-state 11B NMR study of a series of boronic acids, boronic esters, and boronic acid catechol cyclic esters with aromatic substituents are reported in this thesis. Boron-11 electric field gradient (EFG) and chemical shift (CS) tensors obtained from analyses of spectra acquired in magnetic fields of 9.4 T and 21.1 T are demonstrated to be useful for gaining insight into the molecular and electronic structure about the boron nucleus. It can be concluded that when adequate electronic variation is present in the compounds being studied, Ω is generally the most characteristic boron NMR parameter of the molecular and electronic environment for boronic acids and esters. Importantly, these data are only reliably accessible in ultrahigh magnetic fields. The experimental span values result from a delicate interplay of several competing factors, including hydrogen bonding, the value of the dihedral angle, and the type of aromatic ring system present.

Although the cost of investment in power lines insulators is 3-5% of the total cost of the installation, the impact of their performance on reliability, failure costs, maintenance routines, etc in power systems is tens of times higher. Composite insulators were introduced 50 years ago and have been used around the world with consistently good experience. Low weight, easy handling, good performance under high pollution, low maintenance costs, and resistance to vandalism are some of their advantages. Nevertheless, acid rain, salty dust deposition, corona discharges, ozone, UV radiation, and humidity among other factors, deteriorate the quality of the polymeric housing reducing their hydrophobicity. The synergistic action of ageing factors is extremely complex and the whole degradation process may change when any one variable is slightly modified. Many studies have been carried out to increase understanding of the physicochemical processes which control the electrical and mechanical stability of polymers during in-service ageing with the objective of predicting remaining life-times. Vital areas of knowledge about polymer insulators are still incomplete and lacking; three of them are: (1) early stages of degradation in service under different environmental conditions, (2) monitoring and diagnosis techniques suitable for distribution installations and (3) steps to establish an insulators management plan based on condition and risk of failure. In this research these three topics are covered. A full review of literature about management of electrical distribution assets is included, followed by a specific plan developed for monitoring, diagnosis and ranking of insulators mainly supported by visual inspections. Diagnosis of medium voltages EPDM insulators recovered from service aged under different conditions is done using both traditional techniques and, uniquely, dielectric impedance. The relationship between surface roughness and static contact angle is also used to characterize insulators' surfaces. Early stages of degradation are studied focusing the experimental work to evaluate the electrohydrodynamic processes which occur on new samples under different conditions, giving special attention to leakage current pulse analysis, electric field enhancement, and resistance/capacitive behaviour including phase of leakage current. Results from each specific topic offer additional understanding of polymer insulators degradation providing insight to monitoring, diagnosis and management. Additionally, results open new topics in which new investigations are proposed.

Dye sensitized solar cells (DSSCs) are an attractive way to convert light into electricity. Its development requires a detailed understanding and kinetic optimization of various electronic processes, especially those occurring at the mesoporous TiO2/dye/electrolyte interface. This dissertation work is focused on the exploration of the various electronic processes at the sensitized-electrode/electrolyte interface by using various electrochemical and photochemical methods. Firstly, an alternative redox couple—TEMPO/TEMPO·+ with a relatively high positive redox potential—is explored, aiming to reduce the energy loss during the dye regeneration process. Despite the fast dye regeneration, the charge recombination between the electrons in the conduction band of mesoporous TiO2 and the oxidized redox species is found to be the limiting factor of the device. Further, a more efficient tandem-electrolyte system is developed, leading to DSSCs with the power conversion efficiency of 10.5 % and 11.7 % at 1 sun and 0.5-sun illumination, respectively. An electron-transfer cascade process during dye regeneration by the redox mediators is discovered to be beneficial. Further stability studies on the device suggest the crucial role of TiO2/dye/electrolyte interfaces in the long-term stability of cobalt bipyridyl electrolyte-based DSSCs. On the fundamental level, the local electric field and Stark effects at the TiO2/dye/electrolyte interface are investigated in various aspects—including the charge compensation mechanism, the factors affecting the electric field strength, as well as its impact on charge transfer kinetics. These results give further insights about the TiO2/dye/electrolyte interface, and contribute to the further development and understanding of DSSCs.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-07-11T12:20:54Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Diego_Lopes_Dissertacao.pdf: 4018850 bytes, checksum: a5aa0e7bd17e5fbdc23ed085f38eca0c (MD5) / Made available in DSpace on 2017-07-11T12:20:54Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Diego_Lopes_Dissertacao.pdf: 4018850 bytes, checksum: a5aa0e7bd17e5fbdc23ed085f38eca0c (MD5) Previous issue date: 2016-07-19 / CAPES / A presente dissertação aplica um modelo computacional para mapeamento da distribuição de potencial e campo elétrico ao longo de dispositivos isolantes na presença de uma camada condutiva em sua superfície. Na natureza, a formação dessa camada se dá através da deposição de poluição juntamente com a umidade ambiental. A pesquisa teve como base outros estudos presentes na literatura que abordam a mesma temática. A avaliação do comportamento da distribuição de potencial e campo elétrico em peças isolantes é de fundamental importância na determinação de possíveis regiões, as quais esses dispositivos apresentem maior estresse elétrico, tais regiões podem levar a descargas parciais e possíveis desgastes dos acessórios levando assim à sua falha. O modelo aplicado foi implementado utilizando o MEF (Método dos Elementos Finitos) através da construção do ambiente nosoftwareCOMSOLMultiphysicse da representação gráfica do acessório noAutoCAD. O estudo foi realizado em isoladores de vidro e polimérico, bem como em espaçadores, sob diferentes níveis de poluição. Os resultados obtidos são coerentes e apresentam consonância com a teoria envolvida neste estudo. / This dissertation applies a computational model to map the voltage distribution and electric field along dielectric devices in presence of a thin conductive layer on its surface. In the nature this thin layer may appear due to pollution deposition with environmental humidity. The base of this research are another studies found in literature with the same theme. The behavior of voltage distribution and electric field in dielectric devices has significant importance helping to determine possible regions where this devices present higher stress levels, causing partial discharges and possible damage to the accessories leading them to a failure condition. The applied model was implemented using FEM (finite element method) building an environment in COMSOL Multiphysics software and graphically representing each accessory through using AutoCAD. The present study was done in insulators made of glass and polymer, as well as spacers, under several pollution levels. The obtained results are consistent and show consonance with the whole theory involved in this research.

O conceito de que estimulação elétrica promove o reparo de fraturas tem uma longa história, datada de 1812. O mecanismo pelo qual estimulação elétrica promove a osteogênese ainda é assunto de especulação científica, entretanto esse método não farmacológico, utilizado no presente trabalho, já mostrou efeitos positivos na promoção e estímulo da osteogênese. O presente trabalho objetivou analisar a influência da aplicação de campo elétrico pulsado nas características histológicas e propriedades mecânicas do tecido ósseo em osteotomias experimentais realizadas em tíbias de ratos. Foram utilizados 52 ratos com fraturas cirúrgicas unilaterais do terço médio da tíbia, sem lesão dos músculos e do periósteo. Os animais foram divididos em dois grupos: grupo controle, que não recebeu estimulação e grupo tratado com campo elétrico. Esses foram divididos em dois subgrupos: animais sacrificados no 19º pós-operatório e animais sacrificados no 27º pós-operatório. O membro fraturado foi tratado com campo elétrico pulsado com freqüência fundamental de 1,5 MHz e 200 \'mü\'s de largura de pulso, em sessões diárias de 20 minutos. Realizou-se radiografia desse membro no dia da cirurgia e do sacrifício. Após o tratamento sacrificaram-se os ratos e extraíram-se suas tíbias para a obtenção de material para a análise morfométrica e ensaio mecânico de flexão. Os ensaios biomecânicos revelaram que houve diferença significativa entre as médias dos grupos tratado 18 e 12 dias somente para a tensão, sendo esta maior para o grupo tratado 18 dias, para as demais propriedades mecânicas analisadas não houve diferença significativa. A análise morfométrica determinou que a relação entre os grupos controle 18 dias com tratado 18 dias bem como entre os grupos tratado 12 dias e tratado 18 dias das médias das áreas de osso formado apresentaram diferenças estatisticamente significantes. Esses resultados sugerem que existe um incremento na síntese de matriz orgânica no grupo tratado, não acompanhado linearmente pela síntese mineral. A diferença estatisticamente significativa nas tensões de ruptura, por outro lado, sugere que o aumento no grau de mineralização encontra-se em curso. / The concept that electrical stimulation promotes the repair of fractures has a long history, dated of 1812. The mechanism for which electrical stimulation promotes osteogenesis is still subject of scientific speculation, however that method non-pharmacological, used in the present work has already showed positive effects in the promotion and incentive of osteogenesis. The present work objectified to analyze the influence of the application of electric field pulsed in the histological characteristic and mechanical properties of the bone tissue in experimental osteotomy accomplished in tibias of rats. 52 rats were used with unilateral surgical fractures of the medium third of the tibia, without lesion of the muscles and of the periosteum. The animals were divided in two groups: group control, that didn\'t receive stimulation and treated group with electric field. These were divided in two subgroups: animals sacrificed in the 19th after operation and animals sacrificed in the 27th after operation. The fracture member was treated with electric field pulsed with fundamental frequency of 1,5 MHz and 200 \'mü\'s of pulse width, in daily sessions of 20 minutes. The x-ray of that member took place in the day of the surgery and of the sacrifice. After the treatment the rats were sacrificed and their tibias were extracted for the material obtaining for analysis morfometric and mechanical rehearsal of flexion. The mechanical rehearsals revealed that there was only significant difference among the averages of the treated groups 18 and 12 days for the tension, the treated group 18 days had a larger tension, for the other analyzed mechanical properties there was not significant difference. The averages of the moment of inertia and area went significantly larger for the treated group 18 days compared with the respective averages of the control group controls. The treated group 12 days presented averages significantly larger when compared to the properties: moment of inertia, neutral line and area with the control group 12 days. These results suggest that an increment exists in the synthesis of organic matrix in the treated group, not accompanied lineally by the mineral synthesis. The difference significant statistic in the rupture tensions, on the other hand, suggests that the increase in the mineralization degree meets in course.

There is a movement in the electronic industry toward building electronic devices with dimensions smaller than is currently possible. Atomically thin 2D material, such as graphene, bilayer graphene, hBN and MoS2 are great candidate for this goal and they have a potential set of novel electronic properties compare to their bulk counterparts due to the exhibition of quantum confinement effects. To this goal, we have investigated the electric field screening of multilayer 2D materials due to the presence of impurity charge in the interface and vertical electric fifield from back gate. Our result shows a dramatic difference of screening behavior in high and low charging limit, which depends on the number of layers as well. We also have an extensive study on quantum tunneling effect in graphene and bilayer graphene heterojunctions. The peculiar electronic properties of graphene lead to an unusual scattering effect of electron in graphene n-p junction. We implement the cohesive tunneling effect to explain the nonlinear electron transport in ultrashort channel graphene devices. This nonlinear behavior could make them tremendously useful for ultra-fast electronic applications.

abstract: Novel electric field-assisted microfluidic platforms were developed to exploit unique migration phenomena, particle manipulation, and enhanced droplet control. The platforms can facilitate various analytical challenges such as size-based separations, and delivery of protein crystals for structural discovery with both high selectivity and sensitivity. The vast complexity of biological analytes requires efficient transport and fractionation approaches to understand variations of biomolecular processes and signatures. Size heterogeneity is one characteristic that is especially important to understand for sub-micron organelles such as mitochondria and lipid droplets. It is crucial to resolve populations of sub-cellular or diagnostically relevant bioparticles when these often cannot be resolved with traditional methods. Herein, novel microfluidic tools were developed for the unique migration mechanism capable of separating sub-micron sized bioparticles by size. This based on a deterministic ratchet effect in a symmetrical post array with dielectrophoresis (DEP) for the fast migration allowing separation of polystyrene beads, mitochondria, and liposomes in tens of seconds. This mechanism was further demonstrated using high throughput DEP-based ratchet devices for versatile, continuous sub-micron size particle separation with large sample volumes. Serial femtosecond crystallography (SFX) with X-ray free-electron lasers (XFELs) revolutionized protein structure determination. In SFX experiments, a majority of the continuously injected liquid crystal suspension is wasted due to the unique X-ray pulse structure of XFELs, requiring a large amount (up to grams) of crystal sample to determine a protein structure. To reduce the sample consumption in such experiments, 3D printed droplet-based microfluidic platforms were developed for the generation of aqueous droplets in an oil phase. The implemented droplet-based sample delivery method showed 60% less sample volume consumption compared to the continuous injection at the European XFEL. For the enhanced control of aqueous droplet generation, the device allowed dynamic triggering of droplets for further improvement in synchronization between droplets and the X-ray pulses. This innovative technique of triggering droplets can play a crucial role in saving protein crystals in future SFX experiments. The electric field-assisted unique migration and separation phenomena in microfluidic platforms will be the key solution for revolutionizing the field of organelle separation and structural analysis of proteins. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2020