Extraction of Self-Diffraction Wave in Photorefractive Bi12SiO20 Crystals

When two waves are coupled in Bi₁₂SiO₂₀ crystals, the polarization states of the signal wave are affected by the self-diffraction. We have theoretically studied the influence of the self-diffraction on the polarization of the signal wave. The change of polarization states are strongly affected by the self-diffraction effect when the external field is applied. We present a new method that converts the change of polarization into an intensity signal.     

Absolute rate constants for reactions of free radicals in the high-temperature photolysis of formamide vapor. II. Amino radicals

The rotating-sector method has been applied to the photoinitiated radical-chain decomposition of formamide at 300°C to measure the rate constant for the bimolecular disappearance of NH₂ radicals. The decomposition is propagated by the reactions (1) (2) Conditions were chosen so that reaction (1) was rate controlling and NH₂ the terminating radical. A flow system was employed with C₂F₆ as a carrier gas at a pressure of 300 Tort, and the chain reaction was initiated by the photolysis of either formamide or NH₃. A value of 4.7(±2.0) × 10¹⁰ (M ·sec)^?1 was estimated for the termination reaction (3) and a value of 8.4 × 10⁶ (M ·sec)^?1 for reaction (1) in the same system, both at 300°C.     

Photoelectron spectra of styrenes

The photoelectron spectra of styrene and its methyl derivatives were measured and interpreted. The vinyl group twisted by the steric hindrance of the α- or orthomethyl group was found to play an important role in the interpretation of the photoelectron spectra of these compounds. The dependence of the higher occupied π orbital energies of styrene upon the twist angle of the vinyl group was estimated from the experimental data.     

Study on the single crystal growth of concentration gradient Ce:YAP rod and the dopant concentration dependence on the scintillation properties

Micro-pulling down (μ-PD) method allows to prepare single crystals quickly and relatively inexpensively. Since it is a melt growth and taking into account segregation phenomena, the μ-PD method allows also to obtain single crystals characterized by dopant concentration gradients. Especially, taking the advantage of the grown crystal high aspect ratio, it allows to prepare crystalline samples with variable and wide range concentrations of dopants. These samples can help in understanding the correlation between dopant concentration and luminescence properties.     

Polymer-nanoparticle complexes: from dilute solution to solid state

We report on the formation and the structural properties of "supermicellar" aggregates made from mineral nanoparticles and polyelectrolyte-neutral block copolymers in aqueous solutions. The mineral particles put under scrutiny are ultrafine and positively charged yttrium hydroxyacetate nanoparticles. Combining light, neutron, and X-ray scattering experiments, we have characterized the sizes and the aggregation numbers of the organic-inorganic complexes. We have found that the hybrid aggregates have typical sizes in the range of 100 nm and exhibit a remarkable colloidal stability with respect to ionic strength and concentration variations. Solid films with thicknesses up to several hundreds of micrometers were cast from solutions, resulting in a bulk polymer matrix in which nanoparticle clusters are dispersed and immobilized. It was found in addition that the structure of the complexes remains practically unchanged during film casting.     

Synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure study on oxidative etching of diamond-like carbon films by hyperthermal atomic oxygen

Surface structural changes of a hydrogenated diamond-like carbon (DLC) film exposed to a hyperthermal atomic oxygen beam were investigated by Rutherford backscattering spectroscopy (RBS), synchrotron radiation photoelectron spectroscopy (SR-PES), and near-edge X-ray absorption fine structure (NEXAFS). It was confirmed that the DLC surface was oxidized and etched by high-energy collisions of atomic oxygen. RBS and real-time mass-loss data showed a linear relationship between etching and atomic oxygen fluence. SR-PES data suggested that the oxide layer was restricted to the topmost surface of the DLC film. NEXAFS data were interpreted to mean that the sp² structure at the DLC surface was selectively etched by collisions with hyperthermal atomic oxygen, and an sp³-rich region remained at the topmost DLC surface. The formation of an sp³-rich layer at the DLC surface led to surface roughening and a reduced erosion yield relative to the pristine DLC surface.     

Finite-time blow-up for quasilinear degenerate Keller–Segel systems of parabolic–parabolic type

This paper deals with the quasilinear degenerate Keller–Segel systems of parabolic–parabolic type in a ball of ${\mathbb{R}}^N$ ($N\ge 2$). In the case of non-degenerate diffusion, Cie?lak–Stinner [3], [4] proved that if $q>m+\frac{2}{N}$, where m denotes the intensity of diffusion and q denotes the nonlinearity, then there exist initial data such that the corresponding solution blows up in finite time. As to the case of degenerate diffusion, it is known that a solution blows up if $q>m+\frac{2}{N}$ (see Ishida–Yokota [13]); however, whether the blow-up time is finite or infinite has been unknown. This paper gives an answer to the unsolved problem. Indeed, the finite-time blow-up of energy solutions is established when $q>m+\frac{2}{N}$.