Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 41 for “"filamentation"”.
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Investigation of thermal filamentation instability over Gakona, Alaska
The thermal filamentation instability has been invoked to explain the formation of parallel plate waveguides in mid-latitude ionospheric plasmas during Arecibo, Puerto Rico heating experiments in 1997. The geometry of the kilometer-scale parallel plates predicted by thermal filamentation depends on …
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Investigating Bacterial Filamentation as a Survival Strategy for Infection
… immune cells like macrophages. Bacterial filamentation, as a strategy to avoid engulfment during infections, is a possible virulence pathway that has been highlighted in previous research but is yet to be fully explored. Investigations in this area could reveal novel insights into …
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Direct Observation of Laser Filamentation in High-Order Harmonic Generation
… direct evidence (to our knowledge) of laser filamentation under conditions ideal for high-order harmonic generation. The 30 fs, 4 mJ, laser pulses were observed to undergo double focusing within the gas cell, with about 4 cm separating the two foci. The region with best harmonic emission …
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On the Role of Linear Processes in the Development and Evolution of Filaments in Air
… undergo self-focusingleading to collapse and filamentation. During the initial stagesof propagation at low intensities the beamdynamics are dominated by diffraction and dispersion. During filamentation, self-focusing resulting from the nonlinear Kerr effect is balanced by higher order …
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Optical Filaments and Gas Dynamics in Air
… ultrashort laser pulses leading to optical filamentation in air has only been investigated in the frame of a dynamic balance between linear diffraction, Kerr self-focusing and plasma defocusing. This has led to the development of different theories surrounding the generation and persistence …
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Self-generated magnetic fields in intense laser-solid interactions relevant to relativistic plasma astrophysics
… resistivity on the onset of the resistive filamentation instability is investigated, both experimentally and numerically, in targets consisting of layers of ordered and disordered forms of carbon. It is demonstrated that the thickness of the disordered carbon layer influences the degree of …
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Polarization characterization of nonlinear laser propagation
… is maintained over long distances is known as "filamentation". Filaments created from a linearly polarized electric field have been studied by different research groups. However, it is interesting to know how the properties of the filament change with polarization and most importantly whether …
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Excitation of forced ion acoustic waves, large plasma sheets, and magnetic field fluctuations over Gakona, Alaska
… extension of my B.S. thesis research on thermal filamentation instability, which started in our summer Gakona experiments in 2005. Large plasma sheets (also known as sheet-like filaments) can be excited by HF O-mode and X-mode heater waves via thermal filamentation instability.
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The Effect of Anomalous Resistivity on the Electrothermal Instability
… In contrast, low-density ETI growth is mainly filamentation form, magnetically aligned modes, because the resistivity tends to decrease with temperature. Simulating ETI is challenging due to the coupling of magnetic field transport to equation of state over a large region of state space …
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Time Domain Spectroscopy of Graphene
… lattice. These pulses are created through filamentation based pulse compression. I studied how the filamentation process can be optimized through simple means to create the shortest possible pulse. I then examine the extent to which graphene can withstand irradiation from intense ultra-fast …
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High power pulse UV source development and its applications
… a high power UV source suitable for laser filamentation studies in air. The system was optimized to produce < 300 ps, ~ 0.3J pulses at 266 nm. This corresponds to a peak power of ~1 GW, which is well above the critical power required for filament generation. The system includes four …
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Molecular Analysis of Phenotypic Diversity in Human Fungal Pathogens
… was identified within Candida species. Notably, filamentation in the absence of inducing cues was observed in 28 Candida isolates from six patients, with most isolates harboring mutations in a transcriptional repressor of filamentation, NRG1. These mutants were resistant to the filament …
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The Mechanism of Oxygen and Nitric Oxide Toxicity in Escherichia Coli
… determine the mechanism of this synergism. The filamentation of the dead cells, and their protection by cell-permeable iron chelators, indicated that NO/H2O2 killed cells by damaging their DNA through the Fenton reaction. NO also blocked respiration, an event which previous studies have shown …
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DNA Binding Protein’s Structure, Mechanism, and Functional Relevance; From Filament Formation of SgrAI to Helicase Activity of B19V-NS1
… these two base pairs plays an important role in filamentation regulation. The mechanism by which this regulation occurs, however, is as yet unknown. In previous studies, the structure of SgrAI bound to the primary site and one type of secondary site was solved. Cryo-EM was also used to determine …
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Einfluss dynamischer Resonanzen auf die Wechselwirkung optischer Femtosekunden-Pulse mit transparenten Dielektrika
… phenomenological model of femtosecond filamentation in atomic gases can be extended by a quantum mechanically computed ionization rate.
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SPATIAL CHARACTERIZATION OF LASER FILAMENTS BY DETECTION OF SIGNATURES OF IONIZATION
Laser filamentation is a phenomenon currently being widely studied in which an ultrashort laser pulse self focuses as a result of the nonliner Kerr effect. Lim- ited data is available in terms of spatial characterization of the filament. We study the spatial distribution of molecular and atomic …
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Vortices in sinusoidal shear, with applications to Jupiter
… the drawback that the vortices lose enstrophy by filamentation and numerical dissipation, while continuing to deform and wobble. Adopting the local optimization technique of Hamiltonian Dirac Simulated Annealing overcomes this drawback and allows us to obtain steady/quasisteady vortices that have …
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Vortices in sinusoidal shear, with applications to Jupiter
… the drawback that the vortices lose enstrophy by filamentation and numerical dissipation, while continuing to deform and wobble. Adopting the local optimization technique of Hamiltonian Dirac Simulated Annealing overcomes this drawback and allows us to obtain steady/quasi-steady vortices that have …
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Optical Propagation of Self-sustaining Wavefronts and Nonlinear Dynamics in Parabolic Multimode Fibers
… cover the highly nonlinear process of optical filamentation. This chapter will almost entirely investigate the idea of the dressed filament, an entity which allows for substantial prolongation of this light string. I will then conclude by delving into the topic of supercontinuum generation in …
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On the Interaction of Jets with the Dense Medium of the Early Universe
… 10^4 globular clusters of 10^6 solar masses. Filamentation and fragmentation was confirmed at high resolution. Absorbers in far-off radio galaxies and globular cluster excesses in nearby CD galaxies can be explained that way. With literature parameters fo Cygnus~A, a 3D simulation, for the …
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