DNA condensates have attracted the attention of biophysicists, biochemists and polymer physicists for more than thirty years. In the biological community, the quest to understand DNA toroid formation has been motivated by its relevance to gene packing in certain viruses and by the potential use of DNA toroids in artificial gene delivery (e.g. gene therapy). In the physical sciences, DNA toroids are appreciated as a superb model system for studying particle formation by the collapse of a semiflexible, polyelectrolyte polymer. The thesis includes an analysis of the kinetic and thermodynamic factors governing DNA condensate morphology in solution, and discusses implications for future applications of DNA condensation in vitro as a model system for testing theories of polyelectrolyte collapse. In addition, DNA condensation by folded bovine protamine, a naturally occurring multivalent oligopeptide responsible for packing genomic DNA in bovine sperm cells, has been studied as well. The analysis of morphology, size, DNA strand packing density, and the stability of structural integrity of DNA condensates obtained with folded bovine protamines suggests that we have reconstituted native sperm cell chromatin. The results of this study were used to model the local structure of bovine sperm cell chromatin.

Satellite antenna design requirements are driving the satellite size to proportions that cannot be launched into space using current technology. In order to reduce the launch size and mass of satellites, inflatable structures, also known as gossamer structures, are being considered. Inflatable space-based structures are susceptible to vibration disturbance due to their low stiffness and damping. This thesis discusses the structural dynamics and vibration suppression via piezoelectric actuators, using active control of an inflatable torus. A commercial finite element package, ANSYS, is used to model the inflated torus. The effect of torus aspect ratio and inflation pressure on the vibratory response of the structure is investigated. The interaction with the torus of the surface-mounted piezoelectric patches, made of PVDF, is modeled using Euler-Bernoulli beam theory. A state space representation is created of the model in modal space and modal truncation is performed. Traditional control tools are used to suppress vibration in the structure. First observer-based full state feedback is used, then direct output velocity feedback is explored. The aspect ratio of the torus is found to significantly influence the mode shapes. Toroids of small aspect ratios, skinny toroids, act like rings, but the mode shapes of toroids with large aspect ratios are much more complicated. For toroids of small aspect ratios, increasing the inflation pressure simply results in stiffening the ring, thereby increasing the natural frequencies. Increasing the pressure in toroids with large aspect ratios changes both the mode shapes and natural frequencies. The passive effect of PVDF on the dynamics of the torus is small, the mode shapes do not change and the frequencies are only slightly reduced. Active control of toroids with small aspect ratios using piezoelectric devices is effective. It may be more difficult to control toroids with large aspect ratios because the mode shapes are much more complicated than the simple ring modes found in toroids with small aspect ratios. / Master of Science

Drop impact is a canonical problem in fluid mechanics, with numerous applications in industrial as well as natural phenomena. The extremely simple initial configuration of the experiment can produce a very large variety of fast and complex dynamics. Scientific progress was made in parallel with major improvements in imaging and computational technologies. Most recently, high-speed imaging video cameras have opened the exploration of new phenomena occurring at the micro-second scale, and parallel computing allowed realistic direct numerical simulations of drop impacts. We combine these tools to bring a new understanding of two fundamental aspects of drop impacts: splashing and air entrapment. The early dynamics of a drop impacting on a liquid pool at high velocity produces an ejecta sheet, emerging horizontally in the neck between the drop and the pool. We show how the interaction of this thin liquid sheet with the air, the drop or the pool, can produce micro-droplets and bubble rings. Then we detail how the breakup of the air film stretched between the drop and the pool for lower impact velocities can produce a myriad of micro-bubbles.

By using cryo-electron microscopy, we analyzed the morphology and structure of long double-stranded DNA chains condensed upon addition of varying amounts of the tetravalent polycation spermine (polyamine). Experiments have been performed i) with chains diluted in the bulk and ii) with individual chains confined in a virus capsid.Bulk experiments have been done with lambda DNA (48.5 kbp) at low concentration (0.03 mM Ph) and in low salt conditions (10 mM Tris HCl, 1 mM EDTA, pH 7.6). We explored a wide range of spermine concentration, from the onset of precipitation (0.05 mM sp) up to above the resolubilization limit (400 mM sp). Sixteen min after mixing spermine and DNA, samples have been trapped in thin films and vitrified in liquid ethane to keep ionic conditions unchanged, and imaged at low temperature with low doses of electrons (cryoTEM). DNA chains mostly form large aggregates of toroids in which DNA chains are hexagonally packed with interhelical spacings of 2.93, 2.88, and 2.95 nm at 0.05, 1 and 100 mM spermine, respectively, in agreement with previous X-ray data. At higher spermine concentration (200 mM), hexagonal toroids are replaced by cholesteric bundles with a larger interhelical spacing (3.32 nm). We conclude that the shape and the structure of the liquid crystalline sp-DNA condensates are linked to the DNA interhelix spacing and determined by the ionic conditions i.e. by the cohesive energy between DNA strands. Outside of the precipitation domain (400 mM spermine), DNA chains form a soluble network of thin fibers (4-6 nm in diameter) that let us reconsider the state of these DNA chains in excess of spermine. We also designed experiments to visualize condensates formed 6-60 sec after mixing Lambda DNA with 0.05 mM spermine, under identical buffer conditions. Among multiple original shapes (not found after 16 min), the presence of stretched and helical elongated fibers seen only 9sec after addition of spermine let us propose that DNA chains are immediately stretched upon addition of spermine, relax into helical structures and finally form small toroids (containing in some cases less than one Lambda chain) that further grow and aggregate. We also analyzed the dimensions and structural details of the complete collection of toroids, and reveal the existence of geometric constraints that remain to be clarified. Since it was only exceptionally possible to prevent the aggregation of DNA in dilute solution, we used another approach to observe the collapse of single DNA chains. We handled a population of T5 viruses containing a fraction of their initial genome (12-54 kbp long). The Na-DNA chain, initially confined in the small volume of the capsid (80nm in diameter) is collapsed by the addition of spermine. Compared to the first set of experiments, we explored a higher DNA concentration range (0.45 mM Phosphates in the whole sample) and the spermine concentration was varied from 0.05 to 0.5 mM (which corresponds to much lower +/- charge ratios). Experiments are thus performed close to the precipitation line, in the coexistence region, between the region where all chains are in a coil conformation, and the region where all chains are collapsed into toroids. We describe the existence of intermediate states between the coil and the toroidal globule that were not reported yet. In these "hairy toroids", part of the DNA chain is condensed in the toroid and the other part stays uncondensed outside of it. The interhelical spacing was also measured; it is larger in these partly-condensed toroids than in the fully organized toroids formed at higher spermine concentration.These two series of experiments show the interest of cryoEM to analyze the structural polymorphism and local structure of spermine-DNA aggregates. We also demonstrated how the confinement interferes with DNA condensation and the interest to investigate such effects that are important in the biological context.

Nous avons analysé par cryomicroscopie électronique la morphologie et la structure de longues chaines d’ADN condensées par un polycation tétravalent, la spermine (polyamine). Les expériences ont été réalisées i) avec des solutions de chaînes diluées et ii) avec des chaines isolées confinées dans la capside d’un virus.Les expériences ont été réalisées avec de l’ADN Lambda (48kbp) en solution diluée (0.03 mM Ph) et à faible concentration ionique (10 mM Tris HCl, 1 mM EDTA, pH 7.6). Nous avons exploré une large gamme de concentrations en spermine, allant du seuil de précipitation (0.05 mM sp) jusqu’à la limite de re-solubilization et au-delà (400 mM sp). Seize minutes après mélange de l’ADN et de la spermine, les échantillons sont piégés en film mince et vitrifiés à basse température pour garder intactes les conditions ioniques, puis imagés à basse température sous faibles doses d’électrons (cryoMET). La plupart des chaînes d’ADN forment des agrégats de tores de structure hexagonale avec des interdistances entre hélices de 2.93, 2.88, et 2.95 nm pour des concentrations en spermine respectivement égales à 0.05, 1 et 100 mM spermine, ce qui est en bon accord avec les données collectées précédemment par diffraction des rayons X. A concentration plus élevée en spermine (200mM), les tores hexagonaux sont remplacés par des faisceaux cholestériques de structure plus lâche (3.32 nm entre hélices). Nous en déduisons que la forme comme la structure des condensats cristallins liquides ADN-sp sont liées aux interdistances entre hélices et déterminés par les conditions ioniques i.e. par l’énergie cohésive entre chaînes d’ADN. En dehors du domaine de précipitation (400mM sp), les molécules d’ADN forment un réseau soluble de fines fibres (4-6nm de diamètre) qui nous amènent à reconsidérer l’état de ces chaiînes en présence de spermine. Nous avons également conçu des expériences pour visualiser les agrégats formés 6 à 60 sec après addition de la spermine dans les mêmes conditions de tampon. Parmi les nombreuses formes originales que nous avons observées (absentes après 16 min), la présence de fibres étirées ou en hélice, visibles seulement après 9sec, nous conduit à proposer que les chaines d’ADN soient immédiatement étirées après addition de spermine puis relaxent sous forme de fibres hélicoïdales qui donnent naissance à de petits toroids (comprenant quelquefois moins d’une chaine) qui grandissent et fusionnent. Nous avons également analysé les dimensions de l’ensemble des tores observés et montré l’existence de contraintes géométriques qui restent à élucider. Puisqu’il était généralement impossible de prévenir l’agrégation des chaines d’ADN, nous avons choisi une autre approche pour analyser le collapse de chaines d’ADN individuelles. Nous avons utilisé une population de virus T5 contenant une fraction de leur génome initial (12-54 kbp). La molécule d’ADN, initialement confinée dans le petit volume de la capside (de de 80nm diamètre) est collapsée par addition de spermine. Par comparaison avec le premier jeu de données, nous avons travaillé à concentration plus élevée en ADN (0.45 mM Phosphates dans l’ensemble de l’échantillon) et la concentration en spermine a été ajustée entre 0.05 et 0.5 mM (ce qui correspond à des rapports de charges +/- bien inférieurs). Ces expériences ont donc été réalisées au voisinage de la ligne de précipitation, dans la « région de coexistence », entre le domaine où les chaines sont en condition de pelote et le domaine ou les chaines sont toutes collapsées sous forme de tores. Nous avons montré l’existence de formes intermédiaires entre ces deux états que nous appelons « tores chevelus » dans lesquels une partie de la molécule est condensées dans le tore alors que l’autre partie reste non condensée. Les distances entre hélices ont également été mesurées. Elles sont plus grandes dans ces structures intermédiaires que dans les tores formés à plus forte concentration en spermine. Ces deux séries d’expériences montrent l’intérêt des méthodes de cryo-microscopie pour étudier la structure locale des phases condensées de l’ADN. Nous avons montré comment le confinement modifie le comportement de l’ADN en solution et l’intérêt d’étudier ces effets compte tenu de son importance dans le contexte biologique. / By using cryo-electron microscopy, we analyzed the morphology and structure of long double-stranded DNA chains condensed upon addition of varying amounts of the tetravalent polycation spermine (polyamine). Experiments have been performed i) with chains diluted in the bulk and ii) with individual chains confined in a virus capsid.Bulk experiments have been done with lambda DNA (48.5 kbp) at low concentration (0.03 mM Ph) and in low salt conditions (10 mM Tris HCl, 1 mM EDTA, pH 7.6). We explored a wide range of spermine concentration, from the onset of precipitation (0.05 mM sp) up to above the resolubilization limit (400 mM sp). Sixteen min after mixing spermine and DNA, samples have been trapped in thin films and vitrified in liquid ethane to keep ionic conditions unchanged, and imaged at low temperature with low doses of electrons (cryoTEM). DNA chains mostly form large aggregates of toroids in which DNA chains are hexagonally packed with interhelical spacings of 2.93, 2.88, and 2.95 nm at 0.05, 1 and 100 mM spermine, respectively, in agreement with previous X-ray data. At higher spermine concentration (200 mM), hexagonal toroids are replaced by cholesteric bundles with a larger interhelical spacing (3.32 nm). We conclude that the shape and the structure of the liquid crystalline sp-DNA condensates are linked to the DNA interhelix spacing and determined by the ionic conditions i.e. by the cohesive energy between DNA strands. Outside of the precipitation domain (400 mM spermine), DNA chains form a soluble network of thin fibers (4-6 nm in diameter) that let us reconsider the state of these DNA chains in excess of spermine. We also designed experiments to visualize condensates formed 6-60 sec after mixing Lambda DNA with 0.05 mM spermine, under identical buffer conditions. Among multiple original shapes (not found after 16 min), the presence of stretched and helical elongated fibers seen only 9sec after addition of spermine let us propose that DNA chains are immediately stretched upon addition of spermine, relax into helical structures and finally form small toroids (containing in some cases less than one Lambda chain) that further grow and aggregate. We also analyzed the dimensions and structural details of the complete collection of toroids, and reveal the existence of geometric constraints that remain to be clarified. Since it was only exceptionally possible to prevent the aggregation of DNA in dilute solution, we used another approach to observe the collapse of single DNA chains. We handled a population of T5 viruses containing a fraction of their initial genome (12-54 kbp long). The Na-DNA chain, initially confined in the small volume of the capsid (80nm in diameter) is collapsed by the addition of spermine. Compared to the first set of experiments, we explored a higher DNA concentration range (0.45 mM Phosphates in the whole sample) and the spermine concentration was varied from 0.05 to 0.5 mM (which corresponds to much lower +/- charge ratios). Experiments are thus performed close to the precipitation line, in the coexistence region, between the region where all chains are in a coil conformation, and the region where all chains are collapsed into toroids. We describe the existence of intermediate states between the coil and the toroidal globule that were not reported yet. In these “hairy toroids”, part of the DNA chain is condensed in the toroid and the other part stays uncondensed outside of it. The interhelical spacing was also measured; it is larger in these partly-condensed toroids than in the fully organized toroids formed at higher spermine concentration.These two series of experiments show the interest of cryoEM to analyze the structural polymorphism and local structure of spermine-DNA aggregates. We also demonstrated how the confinement interferes with DNA condensation and the interest to investigate such effects that are important in the biological context.

Ferrite phase shifters are key components of passive phased array antenna systems. In a modern radar system, microwave components in the transmit path should handle high microwave power levels. Also low loss operation in phase shifters is critical, since radar range depends on the microwave power transmitted from the antennas. In this respect, ferrite phase shifters provide required performance characteristics for phased array radar systems. In this thesis, Reggia-Spencer type and twin-toroid type ferrite phase shifters operating at X-Band are designed, simulated, fabricated and measured. Measurements of the fabricated ferrite phase shifters are compared with simulation results. Electromagnetic simulations are performed using CST.

Neste trabalho, foi realizado um estudo experimental detalhado sobre a fase de formação da configuração a campo reverso, no dispositivo denominado T.C.-I da UNICAMP, com a utilização de dignósticos ópticos passivos em plasmas de hélio e hidrogênio. Para cada tipo de gás, os valores do campo de polarização, pré-ionização com temporização do crowbar e pressão de trabalho foram variados para estudar os mecanismos de formação da configuração reversa de campo, através dos diagnósticos da emissão do plasma, complementados com sondas elétricas e magnéticas, externas e internas. Para a obtenção das condições ótimas de operação da máquina, a chave crowbar, construída no próprio Laboratório de Plasma da UNICAMP, demonstrou ser bastante confiável para essa finalidade, pois o tempo entre o final da pré-ionização e o início da descarga principal era um fator importante para uma boa dinâmica de implosão, sem a interferência das oscilações da pré-ionização sobre a fase principal. Nas operações com o plasma de hélio, a melhor pressão de operação do gás foi de 18 mTorr, obtida através das intensidades da linha de HeII (4686 Â), fotodiodos, copo de Faraday e diagnósticos de fluxo excluído. Os valores típicos da densidade e temperatura obtidos foram de 3.2 x 1015cm-3 e 77 eV respectivamente . O raio da separatriz foi de 2.5 cm, durante 1.5us, decaindo rapidamente após a formação da CCR. As medidas espectrais de HeII e OII(4699Â) no plasma de hélio levaram às temperaturas iônicas de 73 a 180 eV, para uma varredura de pressão de 3.8 a 18 mTorr . Em alguns casos, parece provável ter ocorrido efeitos Stark devido a aquecimentos turbulentos atribuídos a campos elétricos microscópicos de 58 kV/cm. Nas operações com hidrogênio , basicamente todos os processos usados para o plasma de hélio foram mantidos. As linhas espectrais analisadas foram Ha, OII, NII, NIII, CIII, CIV e SiIV, tendo sido obtido, a partir das linhas de impurezas, temperaturas iônicas no centro do plasma , mais altas que as do plasma de hélio . Além disso, as temperaturas fornecidas pelas linhas de potencial de ionização mais altos, como o CIII, CIV, SiIV foram maiores que as obtidas com NII ou NIII. Nesta fase, a temperatura e densidades obtidas para a pressão de 3.3 mTorr foram respectivamente 220 eV e 2.9 X1015cm-3. Semelhantemente ao caso do hélio, algumas descargas apresentaram fenômenos prováveis de efeito Stark, tendo sido estimado um campo elétrico microscópico de 21.8 kV/cm . Verificou-se que a influência de sondas magnéticas no interior do plasma é bastante crítica, produzindo uma queda de temperatura de 235 eV para 139 eV na presença da sonda, quando medido com a linha do NIII e de 532 eV para 253 eV quando obtidas com linhas de CIII e SilV. O raio de separatriz estimado para a pressão de operação de 3.3 mTorr foi de 2.2 em com tempo de vida de 3.0 us. Foi ainda observado um novo modo de operação, com a obtenção de modos rotacionais n=4, observados usualmente em pressões de operação mais altas, de 6 a 35 mTorr. / A detailed experimental study of the formation phase in field reversed configuration device T.C.-I at UNICAMP has been carried out for the first time, using passive optical diagnostics on helium and hidrogen gas plasmas. For each type of gas, the values of bias polarization field, pre-ionization with crowbar timing and gas fill pressure have been varied to study field reversed configuration formation mechanism by using plasma emission diagnostics supported by magnetic and electric external and internal multi array probes. For the machine operation condition results, the use of crowbar switch, built at UNICAMP Plasma Laboratory, has shown very reliable operation, where the interval timing between the end of pre-ionization and main discharge phase played important role on good implosion dynamics with no influence of the pre-ionization bank RLC oscillation into the main phase. In the helium plasma operation, the best fill pressure of 18mTorr was obtained using HeII ( 4686Â) spectrum line, photodiode Faraday cup, IMACON, excluded flux diagnostics. The typical density and temperature estimated were 3.2x1015cm-3 e 75 eV respectively. The separatrix radius of 2.5 cm was obtained for 1.5us, decaying soon after the FRC formation. The spectral measurements of HeII, 0II (4699Â) in helium plasma have shown ion temperatures from 73 eV to 180 eV when the pressure is varied from 3.8 to 35 mTorr. In some cases, probable Stark effects due to turbulent heating during implosion also were observed, attributed to 58 kV/cm microscopic electric field. In the hydrogen plasma operation, basically all the process used in helium plasma also were carried out. The spectral line analyzed were Ha\' OII,NII, NIII, eIII, eIV, SiIV, having been obtained temperatures higher than helium plasma in the center of the plasma, using the impurities line. Furthermore, the ion temperatures from higher ionization potential lines (eIII, eIV, SiIV) were higher than temperatures obtained by NII or NIII lines. The average temperature calculated from NII and NIII spectral line was 220 eV and the density for hydrogen plasma was 15 -3 of 2.9 x 10 cm. The influence of internal magnetic probes was very critical, dropping the ion temperature from 235 eV to 139 eV in the presence of probe, when the temperature is calculated through NIII line or from 532 to 253 eV for eIII and SiIV line calculation. Like the helium plasma, in this case also one has been observed a probable Stark effect, attributed to 21.8 kV/cm microscopic electric field. The separatrix radius estimated for fill pressure of 3.3 mTorr was 2.2 cm with the life time of 3.0us interrupted by decaying of external field. We also observed a new plasma mode operation of n=4, usually present at high fill pressure, from 6 mTorr to 35m Torr.

Neste trabalho, foi realizado um estudo experimental detalhado sobre a fase de formação da configuração a campo reverso, no dispositivo denominado T.C.-I da UNICAMP, com a utilização de dignósticos ópticos passivos em plasmas de hélio e hidrogênio. Para cada tipo de gás, os valores do campo de polarização, pré-ionização com temporização do crowbar e pressão de trabalho foram variados para estudar os mecanismos de formação da configuração reversa de campo, através dos diagnósticos da emissão do plasma, complementados com sondas elétricas e magnéticas, externas e internas. Para a obtenção das condições ótimas de operação da máquina, a chave crowbar, construída no próprio Laboratório de Plasma da UNICAMP, demonstrou ser bastante confiável para essa finalidade, pois o tempo entre o final da pré-ionização e o início da descarga principal era um fator importante para uma boa dinâmica de implosão, sem a interferência das oscilações da pré-ionização sobre a fase principal. Nas operações com o plasma de hélio, a melhor pressão de operação do gás foi de 18 mTorr, obtida através das intensidades da linha de HeII (4686 Â), fotodiodos, copo de Faraday e diagnósticos de fluxo excluído. Os valores típicos da densidade e temperatura obtidos foram de 3.2 x 1015cm-3 e 77 eV respectivamente . O raio da separatriz foi de 2.5 cm, durante 1.5us, decaindo rapidamente após a formação da CCR. As medidas espectrais de HeII e OII(4699Â) no plasma de hélio levaram às temperaturas iônicas de 73 a 180 eV, para uma varredura de pressão de 3.8 a 18 mTorr . Em alguns casos, parece provável ter ocorrido efeitos Stark devido a aquecimentos turbulentos atribuídos a campos elétricos microscópicos de 58 kV/cm. Nas operações com hidrogênio , basicamente todos os processos usados para o plasma de hélio foram mantidos. As linhas espectrais analisadas foram Ha, OII, NII, NIII, CIII, CIV e SiIV, tendo sido obtido, a partir das linhas de impurezas, temperaturas iônicas no centro do plasma , mais altas que as do plasma de hélio . Além disso, as temperaturas fornecidas pelas linhas de potencial de ionização mais altos, como o CIII, CIV, SiIV foram maiores que as obtidas com NII ou NIII. Nesta fase, a temperatura e densidades obtidas para a pressão de 3.3 mTorr foram respectivamente 220 eV e 2.9 X1015cm-3. Semelhantemente ao caso do hélio, algumas descargas apresentaram fenômenos prováveis de efeito Stark, tendo sido estimado um campo elétrico microscópico de 21.8 kV/cm . Verificou-se que a influência de sondas magnéticas no interior do plasma é bastante crítica, produzindo uma queda de temperatura de 235 eV para 139 eV na presença da sonda, quando medido com a linha do NIII e de 532 eV para 253 eV quando obtidas com linhas de CIII e SilV. O raio de separatriz estimado para a pressão de operação de 3.3 mTorr foi de 2.2 em com tempo de vida de 3.0 us. Foi ainda observado um novo modo de operação, com a obtenção de modos rotacionais n=4, observados usualmente em pressões de operação mais altas, de 6 a 35 mTorr. / A detailed experimental study of the formation phase in field reversed configuration device T.C.-I at UNICAMP has been carried out for the first time, using passive optical diagnostics on helium and hidrogen gas plasmas. For each type of gas, the values of bias polarization field, pre-ionization with crowbar timing and gas fill pressure have been varied to study field reversed configuration formation mechanism by using plasma emission diagnostics supported by magnetic and electric external and internal multi array probes. For the machine operation condition results, the use of crowbar switch, built at UNICAMP Plasma Laboratory, has shown very reliable operation, where the interval timing between the end of pre-ionization and main discharge phase played important role on good implosion dynamics with no influence of the pre-ionization bank RLC oscillation into the main phase. In the helium plasma operation, the best fill pressure of 18mTorr was obtained using HeII ( 4686Â) spectrum line, photodiode Faraday cup, IMACON, excluded flux diagnostics. The typical density and temperature estimated were 3.2x1015cm-3 e 75 eV respectively. The separatrix radius of 2.5 cm was obtained for 1.5us, decaying soon after the FRC formation. The spectral measurements of HeII, 0II (4699Â) in helium plasma have shown ion temperatures from 73 eV to 180 eV when the pressure is varied from 3.8 to 35 mTorr. In some cases, probable Stark effects due to turbulent heating during implosion also were observed, attributed to 58 kV/cm microscopic electric field. In the hydrogen plasma operation, basically all the process used in helium plasma also were carried out. The spectral line analyzed were Ha\' OII,NII, NIII, eIII, eIV, SiIV, having been obtained temperatures higher than helium plasma in the center of the plasma, using the impurities line. Furthermore, the ion temperatures from higher ionization potential lines (eIII, eIV, SiIV) were higher than temperatures obtained by NII or NIII lines. The average temperature calculated from NII and NIII spectral line was 220 eV and the density for hydrogen plasma was 15 -3 of 2.9 x 10 cm. The influence of internal magnetic probes was very critical, dropping the ion temperature from 235 eV to 139 eV in the presence of probe, when the temperature is calculated through NIII line or from 532 to 253 eV for eIII and SiIV line calculation. Like the helium plasma, in this case also one has been observed a probable Stark effect, attributed to 21.8 kV/cm microscopic electric field. The separatrix radius estimated for fill pressure of 3.3 mTorr was 2.2 cm with the life time of 3.0us interrupted by decaying of external field. We also observed a new plasma mode operation of n=4, usually present at high fill pressure, from 6 mTorr to 35m Torr.

The box corer is a relatively new tool used in the geotechnical community for collection of soft seabed sediments. Miniature full flow and model pipeline probes were developed as tools to characterize and obtain soil parameters of soft seabed sediments collected in the box core for design of offshore pipelines and analysis of shallow debris flows. Probes specifically developed for this study include the miniature t-bar, ball, motorized vane (MV), and toroid. The t-bar, ball, and MV were developed to measure intact and remolded undrained shear strengths (su and sur). The t-bar and ball can obtain continuous strength profiles and measure sur at discrete depths in the box corer while the MV measures su and sur at discrete depths. The toroid is a form of model pipeline testing which was developed to investigate pipe-soil interaction during axial pipeline movement. Vertical loading and displacement rates can be selected for the toroid to mimic axial pipeline displacement for a variety of pipe weights. A load frame for both miniature penetrometer and toroid testing was developed for testing directly on box core samples offshore. This research presents results from offshore and laboratory testing of the box core and recommended testing procedures for full flow and toroid probes on box core samples.

Turbulent wakes generated from an aircraft or submarine vehicles has been of main interest to researchers due to the broad band noise associated with such wakes. One such case is the noise generated by spiral vortices shed of from one blade interacting with another oncoming blade of helicopter rotor. Consequently, researchers have been trying to understand the basic physics and evolution of such wakes. Although there has been numerous studies done on plane wakes, there has been little research being done on laterally curved wakes. Single and two-point velocity measurements were taken on a plane and laterally curved turbulent wakes to understand the evolution and effect of lateral curvature into the far wake region. The analyses provide useful information in modeling curved or spiral wakes such as turbulence field surrounding tip vortices shed from a wing. In order to achieve our objectives, the Virginia Tech 3’ x 2’ subsonic wind tunnel was used to take velocity measurements of toroidal ring model and a straight cylinder as a control case. Velocity measurements were done using four sensor hot-wire anemometers, to obtain all mean velocity, Reynolds stress, triple product components of the turbulence field. Single point, spectra and two-point measurements of the wakes were performed throughout the development into the far wake region. The single point results reveal the universality of the mean axial velocity, however the Reynolds stresses and triple products were not universal illustrating that the turbulence field has its own length and velocity scales different from that of the mean flow. The effect of lateral curvature is mainly evidenced in the early development of the curved ring wake. The turbulent energy budget reveals similar trend for both wakes and plane wake achieves approximate equilibrium. The spectra result reveals for the plane wake that self-preservation is achieved for all scales of motion, while the ring wake does not achieve such a state. While the longitudinal correlations of both wakes are similar in form, in general difference in form and orientation prevailed over all indicating the difference in the turbulent structure of both wakes. Linear stochastic estimation reveals the presence of spanwise and double-roller eddy structures in the plane wake and only spanwise eddies were detected for the ring wake. / Master of Science