Quality factor of circular laser diode beam tailored by optical interference

The quality factor of a laser diode beam tailored by Lloyd’s mirror interference was investigated numerically and experimentally. The far and near-field patterns were analyzed by numerical calculations based on Huygens’ integral. An almost circular tailored beam was calculated to have a quality factor as low as 1.08. This beam-shaping technique was experimentally demonstrated using a commercial 640 nm laser diode and a mirror-polished GaAs substrate. The optical beam tailored by Lloyd’s mirror interference was nearly circular and its beam quality factor was measured to be 1.24. Although this measured beam quality factor is slightly higher than the numerically calculated one, it is acceptably low.     

Abiotic degradation of poly(dl-lactide), poly(ɛ-caprolactone) and their blends

An effective hydrolytic degradation of PDLLA, PCL and their blends in a phosphate-buffered solution of pH 4.0 at 37 °C for 18 weeks was achieved, observing a considerably faster degradation of PDLLA as compared to PCL due to the hydrophobic and semicrystalline nature of PCL matrix, able to partially prevent water diffusion into the bulk specimen.DSC and FTIR results indicated that PCL phase, in compositions rich in PCL, was very stable against hydrolysis, but the presence of PDLLA in the PDLLA/PCL blends seemed to catalyze the hydrolytic degradation of the PCL phase, probably associated to easier diffusion of water into the PCL domains by the presence of PDLLA amorphous regions. This last trend was proportional to the content of PDLLA in the blends, excepting for the composition 64%PDLLA/36%PCL. It was confirmed that PCL molecules partially delayed hydrolysis of PDLLA molecules, according to FTIR analysis, and the water diffusion prevention level was proportional to the content of PCL in the blends, except for the system 64%PDLLA/36%PCL, which presented a lower extent of degradation than neat PDLLA but higher than the blend 80%PDLLA/20%PCL. This indicated that PCL molecules did not significantly impede hydrolysis of PDLLA molecules in this blend, possibly due to the achievement of a particular structure of the PDLLA/PCL interphase in this blend. In general, hydrolysis of PDLLA/PCL blends was found to be a complex phenomenon depending not only on the content of both polymer phases, but also on the polymer phase crystallinity and morphology.     

Dependence of prefactor on the angle between an applied field and the easy axis for single-domain particles

The prefactor (attempt frequency) of particles with uniaxial anisotropy in an applied field at an oblique angle to the easy axis is studied systematically by calculating the smallest nonvanishing eigenvalue of the Fokker-Planck equation for several values of parameters under typical conditions in practical recording media. In the range of the damping constant 0.001-0.01, the prefactor increases with increasing the oblique angle from 0° to 30°, but for that angle of over 30° the prefactor increases very little. It is shown that the dependence of the prefactor on the energy barrier height is almost the same in the range of the oblique angle 5-60° of the applied field to the easy axis. It is confirmed that the prefactor under the conditions above takes from 10⁸ to 10¹⁰ per second.     

Evaluations of SGS Combustion,Scalar Flux and Stress Models in a Turbulent Jet Premixed Flame

A newly developed fractal dynamic SGS (FDSGS) combustion model and a scale self-recognition mixed (SSRM) SGS stress model are evaluated along with other SGS combustion, scalar flux and stress models in a priori and a posteriori manners using DNS data of a hydrogen-air turbulent plane jet premixed flame. A posteriori tests reveal that the LES using the FDSGS combustion model can predict the combustion field well in terms of mean temperature distributions and peak positions in the transverse distributions of filtered reaction progress variable fluctuations. A priori and a posteriori tests of the scalar flux models show that a model proposed by Clark et al. accurately predicts the counter-gradient transport as well as the gradient diffusion, and introduction of the model of Clark et al. into the LES yields slightly better predictions of the filtered progress variable fluctuations than that of a gradient diffusion model. Evaluations of the stress models reveal that the LES with the SSRM model predicts the velocity fluctuations well compared to that with the Smagorinsky model.     

Ruthenium-catalyzed hydration of 1-alkynes to give aldehydes: insight into anti-Markovnikov regiochemistry.

The mechanism of the selective conversion of 1-alkynes to aldehydes by hydration was investigated by isolating organic and organometallic byproducts, deuterium-labeling experiments, and DFT calculations. The D-labeled acetylenic hydrogen of 1-alkyne was found exclusively in the formyl group of the resulting aldehydes. After the reaction, the presence of metal-coordinated CO was confirmed. All of the experimental results strongly suggest the involvement of a metal-acyl intermediate with the original acetylenic hydrogen also bound to the metal center as a hydride, with the next step being release of aldehyde by reductive elimination. Theoretical analyses suggest that the first step of the catalytic cycle is not oxidative addition of acetylene C [bond] H or tautomerization of eta(2)-alkyne to a vinylidene complex, but rather protonation of the coordinated 1-alkyne at the substituted carbon to form a metal-vinyl intermediate. This cationic intermediate then isomerizes to Ru(IV)-hydride-vinylidene via alpha-hydride migration of the vinyl group to the metal center, followed by attack of the vinylidene alpha-carbon by OH(-) to give the metal-hydride-acyl intermediate.     

Hard X-ray generation using femtosecond irradiation of PbO glass

We have generated hard X-rays by front- and back-side femtosecond laser irradiation of PbO-rich glass. The actual Pb content of glasses was corroborated by Pb M-line emission intensities with an uncertainty of less than 20%. The elements K and As at concentrations of a few mol% were detected. X-ray generation by back-side irradiation helped to avoid an air breakdown; however, self-focusing and filamentation limited the achievable light intensity and effectiveness of X-ray generation. Characteristics and mechanisms of X-ray generation from the front- and back-side of glasses are discussed.     

Fragment distribution of thermal decomposition for lignin monomer by QMD calculations using the excited and charged model molecules

Simulations with a quantum molecular dynamics (QMD) method (MD with MO) were demonstrated on the thermal decomposition of lignin monomer at the ground state including excited and positive charged states. Geometry and energy optimized results of the lignin monomer at the singlet and triplet states in single excitation, and at (+2) positive charged state by semi-empirical AM1 MO calculations were used as the initial MD step of QMD calculations. In the QMD calculations, we controlled the total energy of the system using Nóse-Hoover thermostats in the total energy range of 0.69-0.95 eV, and the sampling position data with a time step of 0.5 fs were carried out up to 5000 steps at 50 different initial conditions. The calculated neutral, positive and negative charged fragment distributions of the monomer model with 0.82 eV energy control were obtained as 90.6, 3.5, and 5.9% to the total fragments, respectively. The ratios seem to correspond well with to the values observed experimentally in SIMS.