Nanosecond pulse electroporation of biological cells is gaining significant interest due to its ability to influence intracellular structures. In nanosecond pulse electroporation of biological cells nanosecond duration pulses with high frequency spectral content are applied to the cell. In this research we show that accurate modeling of the nanosecond pulse electroporation process requires considering the effect of the membrane dielectric relaxation on the electric potential across the membrane. We describe the dielectric relaxation of the membrane as dispersion in the time-domain and incorporate it into the nonlinear asymptotic model of electroporation. Our nonlinear dispersive model of a biological cell is solved using finite element method in 3-D space enabling arbitrary cell structures and internal organelles to be modeled. The simulation results demonstrate two essential differences between dispersive and non-dispersive membrane models: the process of electroporation occurs faster when the membrane dispersion is considered, and the minimum required electric field to electroporate the cell is significantly reduced for the dispersive model.

Nanosecond pulse electroporation of biological cells is gaining significant interest due to its ability to influence intracellular structures. In nanosecond pulse electroporation of biological cells nanosecond duration pulses with high frequency spectral content are applied to the cell. In this research we show that accurate modeling of the nanosecond pulse electroporation process requires considering the effect of the membrane dielectric relaxation on the electric potential across the membrane. We describe the dielectric relaxation of the membrane as dispersion in the time-domain and incorporate it into the nonlinear asymptotic model of electroporation. Our nonlinear dispersive model of a biological cell is solved using finite element method in 3-D space enabling arbitrary cell structures and internal organelles to be modeled. The simulation results demonstrate two essential differences between dispersive and non-dispersive membrane models: the process of electroporation occurs faster when the membrane dispersion is considered, and the minimum required electric field to electroporate the cell is significantly reduced for the dispersive model.

Computer simulation of electromagnetic behaviour of a device is a common practice in modern engineering. Maxwell's equations are solved on a computer with help of numerical methods. Contemporary devices constantly grow in size and complexity. Therefore, new numerical methods should be highly efficient. Many industrial and research applications of numerical methods need to account for the frequency dependent materials. The Finite-Difference Time-Domain (FDTD) method is one of the most widely adopted algorithms for the numerical solution of Maxwell's equations. A major drawback of the FDTD method is the interdependence of the spatial and temporal discretisation steps, known as the Courant-Friedrichs-Lewy (CFL) stability criterion. Due to the CFL condition the simulation of a large object with delicate geometry will require a high spatio-temporal resolution everywhere in the FDTD grid. Application of subgridding increases the efficiency of the FDTD method. Subgridding decomposes the simulation domain into several subdomains with different spatio-temporal resolutions. The research project described in this dissertation uses the Huygens Subgridding (HSG) method. The frequency dependence is included with the Auxiliary Differential Equation (ADE) approach based on the one-pole Debye relaxation model. The main contributions of this work are (i) extension of the one-dimensional (1D) frequency-dependent HSG method to three dimensions (3D), (ii) implementation of the frequency-dependent HSG method, termed the dispersive HSG, in Fortran 90, (iii) implementation of the radio environment setting from the PGM-files, (iv) simulation of the electromagnetic wave propagating from the defibrillator through the human torso and (v) analysis of the computational requirements of the dispersive HSG program.

Modulation instability (MI) is a general characteristic of wave propagation in nonlinear dispersive media and it has been intensively investigated in several branches of physics due to its fundamental nature as well as technological applications. This phenomenon corresponds to the exponential growth of weak harmonic perturbations in virtue of the interplay between dispersive and nonlinear effects. Hence, despite its important features, MI is also a main source of channel depletion and degradation in optical fiber communications. In this thesis, we investigate the modulational instability (MI) induced by cross-phase-modulation (XPM) of two incoherently coupled optical pulses co-propagating in a lossless fiber with a finite nonlinear response time. The non-instantaneous character of the nonlinear response is introduced through a Debye relaxation process. We analytically obtain the exact dispersion relation for weak harmonic perturbations over the stationary solution. We show that the instability spectrum, present in both normal and anomalous dispersive regimes in instantaneously responding Kerr media, develops a double peak structure whose relative strength and typical frequency range depend on the response time. Further, we reveal that there are two unstable modes in the entire frequency spectrum. We report the dependence of the maximum gain and central frequency within each unstable mode as a function of the group velocity mismatch and response time, showing the crossover between the regimes of fast and slow non-linear responses. / Fundação de Amparo a Pesquisa do Estado de Alagoas / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Instabilidade Modulacional (IM) é um fenômeno característico da propagação de ondas em meios dispersivos não-lineares e tem sido estudado em diversas áreas da Física devido a sua natureza fundamental bem como suas importantes plicações tecnológicas. Esse fenômeno corresponde ao enriquecimento exponencial de pequenas perturbações harmônicas devido a cooperação dos efeitos não-lineares e dispersivos. Portanto, não obstante sua aplicabilidade, IM é, de igual modo, uma fonte importante de degradação em sistemas de comunicação por fibras ópticas. Nesta tese investigamos a instabilidade modulacional (IM) induzida por Modulação de Fase Cruzada (MFC) de dois pulsos ópticos acoplados incoerentemente que se propagam em uma fibra sem perda com tempo de resposta não-linear finito. O caráter não-instantâneo da resposta não-linear é introduzido através de um processo de relaxação de Debye. Obtemos analiticamente, de modo exato, a relação de dispersão para fracas perturbações harmônicas da solução estacionária. Mostramos que o espectro de instabilidade, presente tanto no regime de dispersão normal quanto no anômalo em meios Kerr com resposta instantânea, desenvolve uma estrutura de pico duplo cuja a intensidade relativa e a frequência típica dependem do tempo de resposta considerado. Além do mais, revelamos que existem dois modos instáveis ao longo de todo o espectro de frequência. Apresentamos a dependência do ganho máximo e da frequência correspondente dentro de cada modo instável como função da diferença da velocidade de grupo e do tempo de resposta, mostrando o cruzamento entre os regimes de resposta não-linear rápida e lenta.

Segmental chain dynamics in polymer blends is a very important topic, not only from a fundamental point of view but also from technological applications. Because of the difficulties in the commercialization of new polymers, industries have turned increasingly towards blending of polymers to optimise their end use (mechanical, rheological) properties. The design of tailor-made materials would be enormously facilitated by the understanding of the blending phenomena at a molecular level. The key question to address is to understand the dynamics of each component of the blend modified by blending? The thesis has systematically studied the effect of multiwalled carbon nanotubes on the chain dynamics, demixing temperature, structural properties and evolution of morphology in a classical miscible polymer blend system (PVDF/PMMA). The thesis comprises of six chapters, Chapter 1 is an introductory chapter that outlines the fundamentals of polymer blends, crystallisation in polymer blends and the basics of dielectric spectroscopy. As one of the rationales of this work is to systematic study whether phase separated in these blends can be used as a tool to develop membrane for water purification. This chapter also gives an overview of the reported studies of ultrafiltration membrane fabrication, factors affecting membrane morphology and flux. In Chapter 2, the materials and methodology used to carry out experiments and the experimental procedures are discussed. Chapter 3 discusses the effect of concentration of PMMA and amine functionalized multiwalled carbon nanotubes (MWNTs) on the crystallisation induced phase separation using FTIR, XRD, POM and shear rheology. Electron microscopy and selective etching confirmed the localisation of MWNTs in the PVDF phase of the blends. Blends with MWNTs facilitated in heterogeneous nucleation manifesting in an increase in crystallisation temperature. The crystallisation induced phase separation in PVDF/PMMA blends was observed to influence the interconnected network of MWNTs in the blends. Chapter 4 discuss the effect of concentration of PMMA and MWNTs on the miscibility and the segmental relaxations was probed in situ by DSC and dielectric relaxation spectroscopy (DRS). The dynamic heterogeneity in the blends as manifested by the presence of an extra relaxation at a higher frequency at or below the crystallisation induced phase separation temperature was also discussed. We found that PVDF/PMMA blend (PVDF ≥ 80 wt%) exhibits three distinct relaxations; αc corresponding to crystalline PVDF, αβ segmental relaxation of PMMA and αm of amorphous miscibility whereas all relaxations overlap and constitute a single broad relaxation in PVDF/PMMA blend (PVDF ≤ 70 wt%). This confirms that there is a certain composition width in this blend wherein three distinct relaxations can be traced. This could due to many reasons like the width of crystal-amorphous interphase in the crystal lamellae, crystal size and morphology is strongly contingent on the concentration of PMMA. Relaxations are not very distinct in presence of MWNTs due to defective spherulites that shift the relaxations towards a higher frequency. Chapter 5 has attempted to tune the microporous morphology of PVDF membranes using crystallisation induced phase separation in PVDF/PMMA blends. As PVDF/PMMA is a melt-miscible blend, the samples were allowed to crystallise and the amorphous PMMA phase, which isolates in the interlamellar or inter-spherulitic regions in the blends, was etched out to generate microporous structures. The pore sizes can be tuned by varying the PMMA concentration in the blends. We observed that 60/40 PVDF/PMMA blends showed larger pores as compared to 90/10 PVDF/PMMA blends. We further modified PVDF membranes by sputtering silver on the surface. The bacterial cell viability was distinctly suppressed (99 %) in silver sputtered membranes. The ICP analysis suggests that slow Ag+ ions release from the sputtered membrane surface assisted in developing antibacterial surface. Our findings open new avenues in designing water filtration membranes and also help in understanding the crystallisation kinetics for tuning pore size in membranes. Chapter 6 summarises the important results of this work. MWNTs act as hetero nucleating agent and specifically interact with PVDF thereby influences the dynamics of PVDF chains. MWNTs can also restrict the amorphous segmental mobility and can influence the intermolecular cooperativity and coupling. The crystallisation induced phase separation in various blends can result in various crystalline morphologies depending on the PVDF concentration. By selectively etching PMMA from the phase-separated blends, microporous morphology can be generated

Dans le cadre de cette thèse, nous avons réalisé l’étude de systèmes amorphes moléculaires chiraux en évaluant leur vieillissement, leur mobilité ainsi que leur capacité à recristalliser en fonction de la composition énantiomérique du matériau. Pour limiter les facteurs additionnels à la chiralité, ce travail s’est concentré sur des systèmes modèles formant des conglomérats stables : N-acetyl-α-methylbenzylamine (Nac-MBA) et 5-ethyl-5-methylhydantoin (12H). De ces travaux il ressort que l’impact le plus spectaculaire de la chiralité est exprimé dans la propension à la cristallisation ou l’habilité à former un verre (qui augmente de façon inversement proportionnelle de l’excès enantiomérique (ee)). Les cinétiques de vieillissement sont implicitement impactées par l’ee : Celles-ci sont plus lentes pour les ee importants. Enfin, il semble que les processus de relaxation ainsi que les temps associés soient identiques quelle que soit l’ee, bien que le comportement à la cristallisation soit lui significativement impacté. A noter que la signature la plus manifeste de la chiralité dans l’état amorphe du Nac-MBA s’exprime dans l’intensité diélectrique des processus D et α. / In the framework of this thesis, we carried out the study of amorphous chiral molecular systems by evaluating their molecular mobility, the evolution of physical properties during aging and the recrystallization behavior as function of the initial enantiomeric excess (ee). In order to avoid factors additional to chirality itself, we focused on enantiomeric systems forming stable conglomerates (full chiral discrimination in the solid state) by choosing two model compounds: 5-ethy-5-methylhydantoin (12H) and N-acetyl-α-methylbenzylamine (Nac-MBA). From this thesis it was shown that the most spectacular effects of chirality in the amorphous state is expressed in the GFA or the crystallization propensity. The GFA increases as the ee decreases. The kinetics of physical aging is implicitly impacted by chirality. Glassy pure enantiomer requires more time to reach equilibrium than that of an intermediate composition. This situation is hypothetically due to constraints effects mostly resulting from a strong nucleation behavior in the glass state at high ee. Furthermore, the time scale of all the processes (D, α, βJG, γ) and the evolution of their temperature dependency are approximatively identical even though the crystallization behavior is highly impacted by ee. it seems that molecular mobility would not be a key parameter in the crystallization behavior of Nac-MBA. The main expression of chirality in amorphous Nac-MBA is evidenced in the signature of the dielectric strength of both D and α processes.