Femtosecond laser ablation profile near an interface: analysis based on the correlation with superficial properties of individual materials

Femtosecond laser ablation of materials is turning to be an important tool for micromachining as well as\ud for selective removal of biological tissues. In a great number of applications, laser ablation has to process\ud through interfaces separating media of different properties. The investigation of the ablation behavior\ud within materials and passing through interfaces is the main aim of this study. Especially, the analysis of\ud the discontinuity in the ablation profile close to interfaces between distinct materials can reveal some of\ud the phenomena involved in the formation of an ablated microcavity geometry. We have used a method\ud that correlates the ablation cross sectional area with the local laser intensity. The effective intensity\ud ablation properties were obtained from surface ablation data of distinct materials. The application of\ud this method allows the prediction of the occurrence of a size discontinuity in the ablation geometry at\ud the interface of distinct media, a fact which becomes important when planning applications in different\ud media.FAPESPCNP

An analytical solution for the critical number of particles for stable bose-einstein condensation under the influence of an anisotropic potential

We have considered a Bose gas in an anisotropic potential. Applying the the Gross-Pitaevskii Equation (GPE) for a confined dilute atomic gas, we have used the methods of optimized perturbation theory and self-similar root approximants, to obtain an analytical formula for the critical number of particles as a function of the anisotropy parameter for the potential. The spectrum of the GPE is also discussed.CNPQCoordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES

Análise micromorfológica de esmalte e dentina expostos ao laser de Nd: YAG em regime de picossegundos

A eficiência da ablação com laser através de um regime de picossegundos minimiza a destruição do material adjacente devido à formação de plasma e ataque. Isso previne a geração excessiva de ondas de choque e promove uma considerável diminuição nos efeitos mecânicos. Nesse estudo foi utilizado um laser de Nd:YAG em picossegundo "Q-switched" e "mode-locked" (Antares 76-s, Coherent, Palo Alto, CA), três molares humanos recém-extraídos e foram realizados 15 microcavidades em esmalte e 9 em dentina. Os parâmetros para irradiar o esmalte seguiram uma freqüência fixa de 100 Hz e potência média de 1,3 W; enquanto que para a dentina, a freqüência foi fixa em 15 Hz enquanto que a potência média variou em 800, 700 e 600 mW. O esmalte demonstrou ser mais capaz de dissipar as ondas de choque do que a dentina, uma vez que as trincas originadas nas microcavidades foram mais freqüentes em tecido dentinário, diferentemente do esmalte. Em conclusão, parece que para manter os aspectos de definição de bordas é importante escolher tempos de irradiação mais curtos, quando as potências médias forem mantidas mais altas, ou seja, energia total entregue mais baixa e bem localizada.The efficiency of the ablation obtained with a picosecond-pulsed laser system minimizes material collateral damage because of the etching and plasma formation mechanism. It prevents the excessive generation of shock waves and promotes a considerable decrease of mechanical side effects. In this study, a Nd:YAG picosecond-pulsed Q-switched and mode-locked laser (Antares 76-s, Coherent, Palo Alto, CA) was used. Fifteen microcavities were prepared in the enamel, and nine microcavities were prepared in the dentin of three recently extracted human molars. The parameters for irradiating enamel followed a fixed frequency of 100 Hz and an average power level of 1.3 W; for dentin, the frequency was fixed in 15 Hz, and the average power level varied between 800, 700 and 600 mW. Enamel proved more capable to dissipate shock waves than dentin, since cracks originating from microcavities were more frequent in dentin. In conclusion, it seems that in order to keep defined edges, it is important to choose shorter irradiation periods when average power levels are kept high, which results in lower and best-localized total energy delivery

Compact Frequency Standard Based on an Intra-cavity Sample Cold Cesium Atoms

We have demonstrated the possibility for a compact frequency standard based on a sample of cold cesium atoms. In a cylindrical microwave cavity, the atoms are cooled and interrogated during a free expansion and then detected. The operation of this experiment is different from conventional atomic fountains, since all the steps are sequentially performed in the same position of space. In this paper we report the analysis of a Ramsey pattern observed to present a 47 Hz linewidth and a stability of 5x10^-13 for an integration time longer than 100s. Some of the main limitations of the standard are analyzed. This present report demonstrates considerable improvement of our previous work (S. T. Muller et al, J. Opt. Soc. Am. B, v.25, p.909, 2008) where the atoms were in a free space and not inside a microwave cavity.Comment: submitted to J. Opt. Soc. Am. B - 15 pages, 10 figure

Isoflurane as euthanasia method: mice mitochondrial bioenergetics impact: Isoflurano como método de eutanásia: impactos na bioenergética mitocondrial de camundongos

The mouse euthanasia method can impact some experiment types, which could add undesirable artifacts to the measurements. Hence the importance of investigating euthanasia methods that use anesthetics, which are generally used for this purpose as they imply minimal stress to the animal and to the researcher. This study proposes to investigate changes in mitochondrial bioenergetics that the use of isoflurane may imply in the euthanasia of female mice compared to the cervical displacement method that does not use drugs. To this end, a high-resolution respirometer, Oroboros®, was used in physiological conditions at 37 °C. Our results indicate that the use of isoflurane in high quantities and for a long time can significantly inhibit the phosphorylation state when complex I substrates are used, which can directly impact ATP production when compared to animals euthanized with cervical dislocation

Future of oncologic photodynamic therapy

Photodynamic therapy (PDT) is a tumor-ablative and function-sparing oncologic\ud intervention. The relative simplicity of photosensitizer application followed by light\ud activation resulting in the cytotoxic and vasculartoxic photodynamic reaction\ud has allowed PDT to reach a worldwide audience. With several commercially\ud available photosensitizing agents now on the market, numerous well designed\ud clinical trials have demonstrated the efficacy of PDT on various cutaneous and\ud deep tissue tumors. However, current photosensitizers and light sources still have\ud a number of limitations. Future PDT will build on those findings to allow development\ud and refinement of more optimal therapeutic agents and illumination devices.\ud This article reviews the current state of the art and limitations of PDT, and highlight\ud the progress being made towards the future of oncologic PDT