Understanding material behavior under extreme conditions is an important area of research in physics and material science. One method to study the behavior of materials under these conditions is to drive a strong shock wave through a material and watch its response. In many cases the material response is complicated by phase transitions such as lattice restructuring (Barker 1975; Mabire and Hereil 2000; Swift, Tierney et al. 2005) and melting (Asay 1975; Elias, Chapron et al. 1988; Werdiger, Eliezer et al. 1999; Mabire and Hereil 2000; Swift, Tierney et al. 2005). To study these dynamics we are using lasers in high time resolution pump-probe experiments to develop a real time diagnostic on the phase of a shocked material. This technique enables probing of the entire phase history of a material as it shock compresses and releases. In addition to linear reflectivity and ultra-fast 2D displacement interferometry, we developed a melting diagnostics based on the non-linear optical technique of third harmonic generation (THG) using a circularly polarized laser pulse. This diagnostic resolves the less than 300 fs melting transition of laser excited Si and GaAs, and it also detects a response in shock compressed silicon. Our results show that Si remains crystalline during compression of an elastic 100 kbar shock wave. Results from Si shocked to higher pressures (> 300 kbar) indicate a decrease in THG, suggesting some level of disordering or unexplained phase change. / text

This thesis was motivated by the promise that some physical aspects of astrophysical jets and collimation processes can be scaled to laboratory parameters through hydrodynamic scaling laws. The simulation of astrophysical jet phenomena with laser-produced plasmas was attractive because the laser-target interaction can inject energetic, repeatable plasma into an external environment. Novel laboratory simulations of astrophysical jets involved constructing and using the YOGA laser, giving a 1064 nm, 8 ns pulse laser with energies up to 3:7 - 0:2 J. Laser-produced plasmas were characterized using Schlieren, interferometry and ICCD photography for their use in simulating jet and magnetosphere physics. The evolution of the laser-produced plasma in various conditions was compared with self-similar solutions and HYADES computer simulations. Millimeter-scale magnetized collimated out-flows were produced by a centimeter scale cylindrically symmetric electrode conguration triggered by a laser-produced plasma. A cavity with a flared nozzle surrounded the center electrode and the electrode ablation created supersonic uncollimated flows. This flow became collimated when the center electrode changed from an anode to a cathode. The plasma jets were in axially directed permanent magnetic fields with strengths up to 5000 Gauss. The collimated magnetized jets were 0.1-0.3 cm wide, up to 2.0 cm long, and had velocities of ~ 4:0 x 10⁶ cm/s. The dynamics of the evolution of the jet were compared qualitatively and quantitatively with fluxtube simulations from Bellan's formulation [6] giving a calculated estimate of ~ 2:6 x 10⁶ cm=s for jet evolution velocity and evidence for jet rotation. The density measured with interferometry was 1.9 ± .2 x 10¹⁷ cm⁻³ compared with 2.1 x10¹⁶ cm⁻³ calculated with Bellan's pressure balance formulation [6]. Kinks in the jet column were produced consistent with the Kruskal-Shafranov condition which allowed stable and symmetric jets to form with the background magnetic fields. The Euler number for the laboratory jet was 9 compared with an estimate of 40 for young stellar object jets [135] which demonstrated adequate scaling between the two frames. A second experiment was performed concerning laboratory simulations of magnetospheres with plasma winds impinging on permanent magnetic dipoles. The ratio of the magnetopause measured with ICCD photography to the calculated magnetopause standoff distance was ~2. / text

No description available.

Thesis (M.S. in Applied Physics)--Naval Postgraduate School, June 2005. / Thesis Advisor(s): William B. Colson. Includes bibliographical references (p. 79-81). Also available online.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

O objetivo deste estudo foi analisar a influência da irradiação com lasers de alta intensidade antes da obturação de canais radiculares com cimentos endodônticos resinosos no selamento lateral. Dentes permanentes humanos (n=36) foram endodonticamente tratados e, então, divididos aleatoriamente em nove grupos experimentais (n=4), de acordo com o tratamento dentinário subsequente. Os grupos foram: G1(N-Rickert/sem laser) ; G2(Epiphany SE®/sem laser); G3(EndoREZ®/sem laser); G4(N-Rickert/laser Nd:YAG); G5(Epiphany SE®/laser Nd:YAG); G6 (EndoREZ®/ laser Nd:YAG); G7(N-Rickert/laser Er:YAG); G8(Epiphany SE®/laser Er:YAG)e G9 (EndoREZ®/ laser Er:YAG).Os parâmetros utilizados para o lasers foram: laser de Nd:YAG (1,5 W, 100 mJ, 15 Hz) e laser de Er:YAG (1 W, 100 mJ, 10 Hz). Todos os dentes foram obturados pelo mesmo operador, utilizando a técnica do cone único para os elementos obturados com os cimentos resinosos e cones múltiplos quando utilizado o cimento de N-Richert. Os cimentos estudados foram preparados conforme as instruções dos fabricantes. Após decorrido o tempo de espera de pressa total de todos os cimentos obturadores os espécimes tiveram sua superfície radicular impermeabilizada com Araldite, em toda a sua extensão. Tubos de microcentrífuga de 1,5 mililitros foram cortados em uma das extremidades e o dente foi inserido até que o ápice ficasse localizado externamente. O espaço existente entre a superfície radicular e o tubo de microcentrífuga foi selado com Araldite, esse selamento proporcionou o vedamento da porção inferior do tubo. Após isto os conjuntos foram submetidos processo de esterilização por óxido de etileno a uma temperatura de 56ºC por quatro horas. Os tubos foram imersos em vidros tipo penicilina que continham 5ml de BHI previamente estéreis. Colônias de Enterococcus faecalis foram semeadas dentro dos tubos, para observar ou não a percolação marginal dos cimentos estudados através da turvação do meio de cultura, por um período de 45 dias. Observou que os dentes dos G1, G3 e G8 0% de contaminação, G4, G5 e G6 50% de espécimes contaminadas, G2 e G9 75% de elementos contaminados e G7 100% dos espécimes contaminados após o período de avaliação. / The aim of this in vitro study was to analyze two high power lasers irradiation effects before the root canal filling procedure with resin endodontic cements on the lateral sealing. Thirty-six permanent human molars were endodontically treated and randomly assigned in nine experimental groups (n=4) according with the subsequent dentin treatment. The groups were as follows: G1 (N-Rickert); G2 (Epiphany SE®); G3 (Endo REZ®); G4 (N-Rickert / Nd:YAG laser irradiation); G5 (Epiphany SE® / Nd:YAG laser irradiation); G6 (EndoREZ® / Nd:YAG laser irradiation); G7 (N-Rickert / Er:YAG laser irradiation); G8 (Epiphany SE® / Er:YAG laser irradiation) and G9 (EndoREZ® / Er:YAG laser irradiation). The laser parameters used were: Nd:YAG laser (1064 nm) at 1.5W, 100 mJ, 15 Hz; and Er:YAG laser (2940 nm) at 1.0 W, 100 mJ, 10Hz. All the teeth were filled by the same operator using the single cone technique for the elements filled with resin cements and multiple cones when the NRickert cement was used. The analyzed cements were prepared following the manufacturers recommendations. After the waiting and total setting time of all the root canal filling materials all the samples were coated along their root surfaces with Araldite®. Micro centrifuge tubes of 1.5 ml were cut in one of the edges and the samples were introduced until their apexes were externally located. The space between the root surface and the micro centrifuge tubes was sealed with Araldite® in order to seal the inferior tube portion. Following this, all samples were sterilized by ethylene oxide at a temperature of 56oC for four hours. The tubes were immersed in penicillin glasses with 5 ml of BHI previously sterilized. Enterococcus faecalis colonies were sought inside the tubes in order to observe a possible marginal percolation of the studied cements through a culture media turbidity process for a period of 45 days. It was possible to observe after the evaluation period an absence of contamination (0%) on samples from G1, G3 and G8; 50% of contamination on samples from G5 and G6; 75% of contamination on samples from G2 and G9 and 100% of contamination on samples from G7.

Made available in DSpace on 2014-06-11T19:28:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2003Bitstream added on 2014-06-13T19:57:14Z : No. of bitstreams: 1 lopes_am_me_araca.pdf: 932429 bytes, checksum: 58f57b4ef355fad92340a3819101663b (MD5) / A atividade antimicrobiana do laser Er:YAG foi avaliada sobre biofilme bacteriano constituído por Escherichia coli ATCC 8739, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 6538 e 3 cepas de Fusobacterium nucleatum e sobre biofilme de microrganismos salivares. Os biofilmes foram submetidos à ação do laser a 1,2 W e 10 Hz por 5, 10, 15, 20, 30 e 60 s e fez-se a avaliação da microbiota residual em ágar sangue, em anaerobiose. O biofilme salivar se mostrou mais sensível nos primeiros tempos de irradiação. A redução microbiana em relação ao controle foi estatisticamente significativa entre todos os tempos testados. Avaliou-se também a ação do laser Er:YAG sobre 7 cepas de Fusobacterium nucleatum inoculadas sobre a superfície de corpos-de-prova (5mmX4mm) de dentes extraídos. Fez-se a aplicação do laser nos mesmos parâmetros físicos mencionados anteriormente, durante 15 s, levando à eliminação total do conteúdo séptico. O estudo avaliou também a irradiação do laser de Er:YAG durante tempos subinibitórios sobre a atividade hemolítica e susceptibilidade de 9 cepas de Fusobacterium nucleatum a amoxicilina, eritromicina, metronidazol e tetraciclina. Após a irradiação do laser, determinou-se a concentração inibitória mínima (CIM) para as drogas através do método de diluição em ágar. A ação do laser sobre a atividade hemolítica foi determinada em sangue humano. Verificou-se que o laser Er:YAG não afetou a atividade hemolítica de Fusobacterium nucleatum, que se mostrou α-hemolítica, tampouco a susceptibilidade a drogas dos isolados testados. / Antimicrobial activity of Er:YAG laser was evaluated on a bacterial biofilm constituted by Escherichia coli ATCC 8739, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 6538 and 3 strains of Fusobacterium nucleatum and on biofilm produced by salivary microorganisms. Biofilms were irradiated by Er:YAG laser, 1,2 W and 10 Hz, for 5, 10, 15, 20, 30, and 60 s and the evaluation of residual contamination was performed on blood agar, under anaerobiosis. It was verified that salivary biofilm showed to be more susceptibility to the Er:YAG laser in shorter periods of laser irradiation. Bacterial reduction was significative in all tested periods of irradiation. The activity of Er:YAG laser was also evaluated on 7 strains of Fusobacterium nucleatum inoculated on samples of human dentin (5mm X 4mm), obtained from extracted teeth. The laser was used following the same physical parameters, as previously described, for 15 s, leading to complete elimination of their septic content. The study also evaluated the effects of subinibitory irradiation of Er:YAG laser on bacterial susceptibility of 9 strains of Fusobacterium nucleatum to antimicrobial drugs (amoxicillin, erythromycin, metronidazole, tetracycline) and hemolysis. Thus, after laser irradiation, the minimal inhibitory concentration of antimicrobial drugs was determined by using an agar dilution method. The influence of laser on hemolysis was carried out on human blood. It was verified that Er:YAG laser did not produce any measurable effect on hemolytic activity and the microbial susceptibility to tested antimicrobial drugs.

O objetivo deste estudo foi analisar a influência da irradiação com lasers de alta intensidade antes da obturação de canais radiculares com cimentos endodônticos resinosos no selamento lateral. Dentes permanentes humanos (n=36) foram endodonticamente tratados e, então, divididos aleatoriamente em nove grupos experimentais (n=4), de acordo com o tratamento dentinário subsequente. Os grupos foram: G1(N-Rickert/sem laser) ; G2(Epiphany SE®/sem laser); G3(EndoREZ®/sem laser); G4(N-Rickert/laser Nd:YAG); G5(Epiphany SE®/laser Nd:YAG); G6 (EndoREZ®/ laser Nd:YAG); G7(N-Rickert/laser Er:YAG); G8(Epiphany SE®/laser Er:YAG)e G9 (EndoREZ®/ laser Er:YAG).Os parâmetros utilizados para o lasers foram: laser de Nd:YAG (1,5 W, 100 mJ, 15 Hz) e laser de Er:YAG (1 W, 100 mJ, 10 Hz). Todos os dentes foram obturados pelo mesmo operador, utilizando a técnica do cone único para os elementos obturados com os cimentos resinosos e cones múltiplos quando utilizado o cimento de N-Richert. Os cimentos estudados foram preparados conforme as instruções dos fabricantes. Após decorrido o tempo de espera de pressa total de todos os cimentos obturadores os espécimes tiveram sua superfície radicular impermeabilizada com Araldite, em toda a sua extensão. Tubos de microcentrífuga de 1,5 mililitros foram cortados em uma das extremidades e o dente foi inserido até que o ápice ficasse localizado externamente. O espaço existente entre a superfície radicular e o tubo de microcentrífuga foi selado com Araldite, esse selamento proporcionou o vedamento da porção inferior do tubo. Após isto os conjuntos foram submetidos processo de esterilização por óxido de etileno a uma temperatura de 56ºC por quatro horas. Os tubos foram imersos em vidros tipo penicilina que continham 5ml de BHI previamente estéreis. Colônias de Enterococcus faecalis foram semeadas dentro dos tubos, para observar ou não a percolação marginal dos cimentos estudados através da turvação do meio de cultura, por um período de 45 dias. Observou que os dentes dos G1, G3 e G8 0% de contaminação, G4, G5 e G6 50% de espécimes contaminadas, G2 e G9 75% de elementos contaminados e G7 100% dos espécimes contaminados após o período de avaliação. / The aim of this in vitro study was to analyze two high power lasers irradiation effects before the root canal filling procedure with resin endodontic cements on the lateral sealing. Thirty-six permanent human molars were endodontically treated and randomly assigned in nine experimental groups (n=4) according with the subsequent dentin treatment. The groups were as follows: G1 (N-Rickert); G2 (Epiphany SE®); G3 (Endo REZ®); G4 (N-Rickert / Nd:YAG laser irradiation); G5 (Epiphany SE® / Nd:YAG laser irradiation); G6 (EndoREZ® / Nd:YAG laser irradiation); G7 (N-Rickert / Er:YAG laser irradiation); G8 (Epiphany SE® / Er:YAG laser irradiation) and G9 (EndoREZ® / Er:YAG laser irradiation). The laser parameters used were: Nd:YAG laser (1064 nm) at 1.5W, 100 mJ, 15 Hz; and Er:YAG laser (2940 nm) at 1.0 W, 100 mJ, 10Hz. All the teeth were filled by the same operator using the single cone technique for the elements filled with resin cements and multiple cones when the NRickert cement was used. The analyzed cements were prepared following the manufacturers recommendations. After the waiting and total setting time of all the root canal filling materials all the samples were coated along their root surfaces with Araldite®. Micro centrifuge tubes of 1.5 ml were cut in one of the edges and the samples were introduced until their apexes were externally located. The space between the root surface and the micro centrifuge tubes was sealed with Araldite® in order to seal the inferior tube portion. Following this, all samples were sterilized by ethylene oxide at a temperature of 56oC for four hours. The tubes were immersed in penicillin glasses with 5 ml of BHI previously sterilized. Enterococcus faecalis colonies were sought inside the tubes in order to observe a possible marginal percolation of the studied cements through a culture media turbidity process for a period of 45 days. It was possible to observe after the evaluation period an absence of contamination (0%) on samples from G1, G3 and G8; 50% of contamination on samples from G5 and G6; 75% of contamination on samples from G2 and G9 and 100% of contamination on samples from G7.