Oxidation kinetics of chromium and morphological phenomena

The oxidation kinetics of chromium at 900°C are independent of the oxygen partial pressure. Although this observation gives evidence for a defect mechanism where chromium interstitials account for the chromium transport in the oxide scale, the experimental phenomena do not support one single model. The occurrence of oxide whiskers and oxide ridges are explained by the energy of activation for the breakup of the oxidant molecule. Large oxide pegs are formed at metal multiple-grain junctions after scale breakdown.\u

The sulphidation properties of pre-oxidized yttrium-ion-implanted Incoloy 800H

On sulphidation of pre-oxidized yttrium-implanted Incoloy 800H an improvement in sulphidation resistance is obtained. Pre-oxidized krypton-implanted alloy and aluminium-implanted alloy have sulphidation rates which are about the same as that of non-implanted pre-oxidized Incoloy 800H. Scanning electron microscopy observations show that one of the effects of yttrium implantation is to decrease the corrosion rate at the alloy grain boundaries

Daily L-leucine supplementation in novice trainees during a 12-week weight training program.

PURPOSE: To investigate the effects of daily oral L-leucine ingestion on strength, bone mineral-free lean tissue mass (LTM) and fat mass (FM) of free living humans during a 12-wk resistance-training program. METHODS: Twenty-six initially untrained men (n = 13 per group) ingested either 4 g/d of L-leucine (leucine group: age 28.5 ± 8.2 y, body mass index 24.9 ± 4.2 kg/m2) or a corresponding amount of lactose (placebo group: age 28.2 ± 7.3 y, body mass index 24.9 ± 4.2 kg/m2). All participants trained under supervision twice per week following a prescribed resistance training program using eight standard exercise machines. Testing took place at baseline and at the end of the supplementation period. Strength on each exercise was assessed by five repetition maximum (5-RM), and body composition was assessed by dual energy X-ray absorptiometry (DXA). RESULTS: The leucine group demonstrated significantly higher gains in total 5-RM strength (sum of 5-RM in eight exercises) and 5-RM strength in five out of the eight exercises (P < .05). The percentage total 5-RM strength gains were 40.8% (± 7.8) and 31.0% (± 4.6) for the leucine and placebo groups respectively. Significant differences did not exist between groups in either total percentage LTM gains or total percentage FM losses (LTM: 2.9% ± 2.5 vs 2.0% ± 2.1, FM: 1.6% ± 15.6 vs 1.1% ± 7.6). CONCLUSION: These results suggest that 4 g/d of L-leucine supplementation may be used as a nutritional supplement to enhance strength performance during a 12-week resistance training program of initially untrained male participants

Purcell factor enhanced scattering efficiency in silicon nanocrystal doped micro-cavities

Scattering induced by nano-particles in a microcavity is investigated for the case of silicon nanocrystal doped microtoroids and a significant enhancement of scattering into the originally doubly-degenerate cavity eigenmodes is found, exceeding >99.42%

Ultralow-threshold erbium-implanted toroidal microlaser on silicon

We present an erbium-doped microlaser on silicon operating at a wavelength of 1.5 mum that operates at a launched pump threshold as low as 4.5 muW. The 40 mum diameter toroidal microresonator is made using a combination of erbium ion implantation, photolithography, wet and dry etching, and laser annealing, using a thermally grown SiO2 film on a Si substrate as a starting material. The microlaser, doped with an average Er concentration of 2x10^(19) cm(-3), is pumped at 1480 nm using an evanescently coupled tapered optical fiber. Cavity quality factors as high as 3.9x10^(7) are achieved, corresponding to a modal loss of 0.007 dB/cm, and single-mode lasing is observed

Purcell factor enhanced scattering efficiency in optical microcavities

Scattering processes in an optical microcavity are investigated for the case of silicon nanocrystals embedded in an ultra-high Q toroid microcavity. Using a novel measurement technique based on the observable mode-splitting, we demonstrate that light scattering is highly preferential: more than 99.8% of the scattered photon flux is scattered into the original doubly-degenerate cavity modes. The large capture efficiency is attributed to an increased scattering rate into the cavity mode, due to the enhancement of the optical density of states over the free space value and has the same origin as the Purcell effect in spontaneous emission. The experimentally determined Purcell factor amounts to 883

Demonstration of an erbium doped microdisk laser on a silicon chip

An erbium doped micro-laser is demonstrated utilizing $\mathrm{SiO_{2}}$ microdisk resonators on a silicon chip. Passive microdisk resonators exhibit whispering gallery type (WGM) modes with intrinsic optical quality factors of up to $6\times{10^{7}}$ and were doped with trivalent erbium ions (peak concentration $\mathrm{\sim3.8\times{10^{20}cm^{-3})}}$ using MeV ion implantation. Coupling to the fundamental WGM of the microdisk resonator was achieved by using a tapered optical fiber. Upon pumping of the $^{4}I_{15/2}\longrightarrow$ $^{4}I_{13/2}$ erbium transition at 1450 nm, a gradual transition from spontaneous to stimulated emission was observed in the 1550 nm band. Analysis of the pump-output power relation yielded a pump threshold of 43 $\mathrm{\mu}$W and allowed measuring the spontaneous emission coupling factor: $\beta\approx1\times10^{-3}$

Fabrication and characterization of erbium-doped toroidal microcavity lasers

Erbium-doped SiO2 toroidal microcavity lasers are fabricated on a Si substrate using a combination of optical lithography, etching, Er ion implantation, and CO2 laser reflow. Erbium is either preimplanted in the SiO2 base material or postimplanted into a fully fabricated microtoroid. Three-dimensional infrared confocal photoluminescence spectroscopy imaging is used to determine the spatial distribution of optically active Er ions in the two types of microtoroids, and distinct differences are found. Microprobe Rutherford backscattering spectrometry indicates that no macroscopic Er diffusion occurs during the laser reflow for preimplanted microtoroids. From the measured Er doping profiles and calculated optical mode distributions the overlap factor between the Er distribution and mode profile is calculated: Gamma=0.066 and Gamma=0.02 for postimplanted and preimplanted microtoroids, respectively. Single and multimode lasing around 1.5 µm is observed for both types of microtoroids, with the lowest lasing threshold (4.5 µW) observed for the preimplanted microtoroids, which possess the smallest mode volume. When excited in the proper geometry, a clear mode spectrum is observed superimposed on the Er spontaneous emission spectrum. This result indicates the coupling of Er ions to cavity modes

High-temperature corrosion and mechanical properties of protective scales on Incoloy 800H: The influence of preoxidation and ion implantation

Coatings, obtained by preoxidation of Incoloy 800H at low PO2 show good sulphidation resistance due to the higher chromia content in the oxide scale. Yttrium-ion implantation of Incoloy 800H has also a beneficial effect on sulphidation, if preoxidation is applied. The reason for this is presumably the segregation of yttrium to grain boundaries of the oxide. Furthermore, the oxidation kinetics of Incoloy 800H are independent of the partial pressure of the oxygen. Mechanical testing of the preformed oxide scale/substrate combinations in air at 600°C by means of constant-extension-rate experiments shows that preoxidation at low partial pressures of oxygen leads to earlier scalecracking

Tuning the emission wavelength of Si nanocrystals in SiO2 by oxidation

Si nanocrystals (diameter 2–5 nm) were formed by 35 keV Si + implantation at a fluence of 6 × 1016 Si/cm2 into a 100 nm thick thermally grown SiO2 film on Si (100), followed by thermal annealing at 1100 °C for 10 min. The nanocrystals show a broad photoluminescence spectrum, peaking at 880 nm, attributed to the recombination of quantum confined excitons. Rutherford backscattering spectrometry and transmission electron microscopy show that annealing these samples in flowing O2 at 1000 °C for times up to 30 min results in oxidation of the Si nanocrystals, first close to the SiO2 film surface and later at greater depths. Upon oxidation for 30 min the photoluminescence peak wavelength blueshifts by more than 200 nm. This blueshift is attributed to a quantum size effect in which a reduction of the average nanocrystal size leads to emission at shorter wavelengths. The room temperature luminescence lifetime measured at 700 nm increases from 12 µs for the unoxidized film to 43 µs for the film that was oxidized for 29 min