Analysis of nonlinear gain-induced effects on short-pulse amplification in doped fibers by use of an extended power equation

Optical pulse amplification in doped fibers is studied using an extended power transport equation for the coupled pulse spectral components. This equation includes the effects of gain saturation, gain dispersion, fiber dispersion, fiber nonlinearity, and amplified spontaneous emission. The new model is employed to study nonlinear gain-induced effects on the spectrotemporal characteristics of amplified subpicosecond pulses, in both the anomalous and the normal dispersion regimes.

Solder doped polycaprolactone scaffold enables reproducible laser tissue soldering

BACKGROUND AND OBJECTIVES: In this in vitro feasibility study we analyzed tissue fusion using bovine serum albumin (BSA) and Indocyanine green (ICG) doped polycaprolactone (PCL) scaffolds in combination with a diode laser as energy source while focusing on the influence of irradiation power and albumin concentration on the resulting tensile strength and induced tissue damage. MATERIALS AND METHODS: A porous PCL scaffold doped with either 25% or 40% (w/w) of BSA in combination with 0.1% (w/w) ICG was used to fuse rabbit aortas. Soldering energy was delivered through the vessel from the endoluminal side using a continuous wave diode laser at 808 nm via a 400 microm core fiber. Scaffold surface temperatures were analyzed with an infrared camera. Optimum parameters such as irradiation time, radiation power and temperature were determined in view of maximum tensile strength but simultaneously minimum thermally induced tissue damage. Differential scanning calorimetry (DSC) was performed to measure the influence of PCL on the denaturation temperature of BSA. RESULTS: Optimum parameter settings were found to be 60 seconds irradiation time and 1.5 W irradiation power resulting in tensile strengths of around 2,000 mN. Corresponding scaffold surface temperature was 117.4+/- 12 degrees C. Comparison of the two BSA concentration revealed that 40% BSA scaffold resulted in significant higher tensile strength compared to the 25%. At optimum parameter settings, thermal damage was restricted to the adventitia and its interface with the outermost layer of the tunica media. The DSC showed two endothermic peaks in BSA containing samples, both strongly depending on the water content and the presence of PCL and/or ICG. CONCLUSIONS: Diode laser soldering of vascular tissue using BSA-ICG-PCL-scaffolds leads to strong and reproducible tissue bonds, with vessel damage limited to the adventitia. Higher BSA content results in higher tensile strengths. The DSC-measurements showed that BSA denaturation temperature is lowered by addition of water and/or ICG-PCL.

Hydrogeochemical controls on uranium in aquifers of the Jacobsville Sandstone

The occurrence of elevated uranium (U) in sandstone aquifers was investigated in the Upper Peninsula of Michigan, focusing on aquifers of the Jacobsville Sandstone. The hydrogeochemical controls on groundwater U concentrations were characterized using a combination of water sampling and spectral gamma-ray logging of sandstone cliffs and residential water wells. 235U/238U isotope ratios were consistent with naturally occurring U. Approximately 25% of the 270 wells tested had U concentrations above the U.S. Environmental Protection Agency Maximum Contaminant Level (MCL) of 30 μg/L, with elevated U generally occurring in localized clusters. Water wells were logged to determine whether groundwater U anomalies could be explained by the heterogeneous distribution of U in the sandstone. Not all wells with relative U enrichment in the sandstone produced water with U above the MCL, indicating that the effect of U enrichment in the sandstone may be modified by other hydrogeochemical factors. Well water had high redox, indicating U is in its highly soluble (VI) valence. Equilibrium modeling indicated that aqueous U is complexed with carbonates. In general, wells with elevated U concentrations had low 235U/238U activity ratios. However, in some areas U concentrations and 235U/238U activity ratios were simultaneously high, possibly indicating differences in rock-water interactions. Limited groundwater age dating suggested that residence time may also help explain variations in well water U concentrations. Low levels of U enrichment (4 to 30 ppm) in the Jacobsville sandstone may make wells in its oxidized aquifers at risk for U concentrations above the MCL. On average, U concentrations were highest in heavy mineral and clay layers and rip up conglomerates. Uranium concentrations above 4 ppm also occurred in siltstones, sandstones and conglomerates. Uranium enrichment was likely controlled by deposition processes, sorption to clays, and groundwater flow, which was controlled by permeability variations in the sandstone. Low levels of U enrichment were found at deltaic, lacustrine and alluvial fan deposits and were not isolated to specific depositional environments.

Investigation into the impact of grain boundaries, film interface, and crystallographic orientation on the ionic conductivity of thin film gadolinium-doped ceria

The research reported in this dissertation investigates the impact of grain boundaries, film interface, and crystallographic orientation on the ionic conductivity of thin film Gd-doped CeO2 (GDC). Chapter 2 of this work addresses claims in the literature that submicron grain boundaries have the potential to dramatically increase the ionic conductivity of GDC films. Unambiguous testing of this claim requires directly comparing the ionic conductivity of single-crystal GDC films to films that are identical except for the presence of submicron grain boundaries. In this work techniques have been developed to grow GDC films by RF magnetron sputtering from a GDC target on single crystal r plane sapphire substrates. These techniques allow the growth of films that are single crystals or polycrystalline with 80 nm diameter grains. The ionic conductivities of these films have been measured and the data shows that the ionic conductivity of single crystal GDC is greater than that of the polycrystalline films by more than a factor of 4 over the 400-700°C temperature range. Chapter 3 of this work investigates the ionic conductivity of surface and interface regions of thin film Gd-doped CeO2. In this study, single crystal GDC films have been grown to thicknesses varying from 20 to 500 nm and their conductivities have been measured in the 500-700°C temperature range. Decreasing conductivity with decreasing film thickness was observed. Analysis of the conductivity data is consistent with the presence of an approximately 50 nm layer of less conductive material in every film. This study concludes that the surface and interface regions of thin film GDC are less conductive than the bulk single crystal regions, rather than being highly conductive paths. Chapter 4 of this work investigates the ionic conductivity of thin film Gd-doped CeO2 (GDC) as a function of crystallographic orientation. A theoretical expression has been developed for the ionic conductivity of the [100] and [110] directions in single crystal GDC. This relationship is compared to experimental data collected from a single crystal GDC film. The film was grown to a thickness of _300 nm and its conductivity measured along the [100] and [110] orientations in the 500-700°C temperature range. The experimental data shows no statistically significant difference in the conductivities of the [100] and [110] directions in single crystal GDC. This result agrees with the theoretical model which predicts no difference between the conductivities of the two directions.