Physico-chemical environment of Al impurity atoms in amorphous silica

The physico-chemical environment around the aluminum impurity atoms in commercial Herasil silica is studied by electron-induced X-ray emission spectroscopy. Despite the low concentration of aluminum and the charging effect occurring upon electron irradiation, we have been able to characterize the environment of the Al atoms. We show that the Al atoms are in an octahedral environment, i.e. surrounded by 6 oxygen atoms. The presence of Al clusters, whose metallic character would make them candidates to be ultraviolet absorption centers, is ruled out

Surface density enhancement of gold in silica film under laser irradiation at 355 nm

In order to understand the damage mechanisms inside the optics of the high power laser facilities, a model sample has been prepared by introducing gold nanoparticles into a silica film. The mean diameter of the gold clusters is 2.5 nm. Different parts of the sample were irradiated at wavelength 355 nm and fluences up to 1 J/cm2. By looking with x-ray photoelectron spectroscopy at the intensity of the Au 4f peak relative to that of the Si 2p peak, a surface Au density enrichment is observed. We interpret this as indicating that the gold atoms migrate toward the surface upon the laser irradiation

Electron kinetics and emission for metal nanoparticles exposed to intense laser pulses

A kinetic theory for the interaction of laser radiation with metal nanoparticles embedded in a wide-band-gap dielectric is presented. The formalism is based on the integration of the Boltzmann equation for electrons of an open system, adapted to the description of electron losses from the nanoparticle such as thermionic and photoelectric effects. Differential forms of the electron-electron and electron-phonon collision operators are introduced to perform kinetic calculations beyond the nanosecond time scale. This kinetic model, which also includes nanoparticle-matrix energy transfer, is used to calculate laser energy deposition, redistribution, and electron ejection for nanosecond or picosecond laser-pulse durations in a model system for laser damage investigation; gold nanoparticles embedded in SiO2 glass. Though electron-phonon relaxation times are small compared with laser-pulse duration, an important part of the electron population is found to be driven beyond a typical 10 eV energy. These results suggest that laser absorption by a metal nanoinclusion can create a plasma around the particle

Electron kinetics and emission for metal nanoparticles exposed to intense laser pulses

A kinetic theory for the interaction of laser radiation with metal nanoparticles embedded in a wide-band-gap dielectric is presented. The formalism is based on the integration of the Boltzmann equation for electrons of an open system, adapted to the description of electron losses from the nanoparticle such as thermionic and photoelectric effects. Differential forms of the electron-electron and electron-phonon collision operators are introduced to perform kinetic calculations beyond the nanosecond time scale. This kinetic model, which also includes nanoparticle-matrix energy transfer, is used to calculate laser energy deposition, redistribution, and electron ejection for nanosecond or picosecond laser-pulse durations in a model system for laser damage investigation; gold nanoparticles embedded in SiO2 glass. Though electron-phonon relaxation times are small compared with laser-pulse duration, an important part of the electron population is found to be driven beyond a typical 10 eV energy. These results suggest that laser absorption by a metal nanoinclusion can create a plasma around the particle

Hypolipidemic and Antioxidant Effects of <i>Guishe</i> Extract from <i>Agave lechuguilla,</i> a Mexican Plant with Biotechnological Potential, on Streptozotocin-Induced Diabetic Male Rats

In the present study, we used a by-product from Agave lechuguilla (guishe) to test its antidiabetic effect, hypolipidemic activity, and capacity to mitigate the oxidative stress in kidney mitochondria from streptozotocin-induced diabetic rats. Orally, a crude aqueous extract from lyophilized guishe was administered over 5 weeks at different doses. Blood glucose and body weight were monitored. Also, blood chemistry, bilirubin, and alanine aminotransferase were assayed. Furthermore, the activity of catalase, thiobarbituric acid reactive species, mitochondrial superoxide dismutase, glutathione and glutathione peroxidase were determined in isolated kidney mitochondria. Our results show that guishe extracts have no antidiabetic properties at any dose. Nevertheless, it was able to diminish serum triglyceride levels and regulate the oxidative stress observed in isolated kidney mitochondria. These observations indicate that the aqueous extract from guishe can be used to treat abnormalities in serum lipids, as a hypolipidemic, and mitigate the oxidative stress, as an antioxidant, occurring during diabetes

High Throughput Profiling of Flavonoid Abundance in Agave lechuguilla Residue-Valorizing under Explored Mexican Plant

Agave lechuguilla waste biomass (guishe) is an undervalued abundant plant material with natural active compounds such as flavonoids. Hence, the search and conservation of flavonoids through the different productive areas have to be studied to promote the use of this agro-residue for industrial purposes. In this work, we compared the proportion of total flavonoid content (TFC) among the total polyphenolics (TPC) and described the variation of specific flavonoid profiles (HPLC-UV-MS/MS) of guishe from three locations. Descriptive environmental analysis, using remote sensing, was used to understand the phytochemical variability among the productive regions. Furthermore, the effect of extractive solvent (ethanol and methanol) and storage conditions on specific flavonoid recovery were evaluated. The highest TPC (16.46 ± 1.09 GAE/g) was observed in the guishe from region 1, which also had a lower normalized difference water index (NDWI) and lower normalized difference vegetation index (NDVI). In contrast, the TFC was similar in the agro-residue from the three studied areas, suggesting that TFC is not affected by the studied environmental features. The highest TFC was found in the ethanolic extracts (6.32 ± 1.66 QE/g) compared to the methanolic extracts (3.81 ± 1.14 QE/g). Additionally, the highest diversity in flavonoids was found in the ethanolic extract of guishe from region 3, which presented an intermedia NDWI and a lower NDVI. Despite the geo-climatic induced variations of the phytochemical profiles, the results confirm that guishe is a valuable raw material in terms of its flavonoid-enriched bioactive extracts. Additionally, the bioactive flavonoids remain stable when the conditioned agro-residue was hermetically stored at room temperature in the dark for nine months. Finally, the results enabled the establishment of both agro-ecological and biotechnological implications