Broadband nearly-zero ultra-flattened dispersion single mode index guiding holey fiber

This paper proposes and demonstrates a novel type of silica index guiding holey fibers (IGHFs) that has two cladding layers at the defective innermost structures. The proposed IGHFs exhibit remarkable chromatic dispersion properties such as nearly-zero and flattened dispersion over a wide spectral range and single mode guidance along with very low confinement loss. The numerical results indicate that 5 air-hole rings of nearly zero ultra-flattened dispersion single mode IGHFs can be designed with desire flattened dispersion of over a 340 nm bandwidth including the entire band of interest with low confinement loss of less than 10⁻⁶ dB/m.     

What Factors Determine Hierarchical Structure of Microbial Cellulose – Interplay among Physics,Chemistry and Biology –

A microbial cellulose film (pellicle), prepared by Acetorbactor xylinum, is a supramolecule system, absorbing a huge amount of water (99% by weight). To elucidate the affinity to water, we investigated the hierarchical structure in a pellicle by using ultra-small-angle and small-angle neutron scattering, observing a wide range of length scales from nm to µm. We successfully determined mass fractal dimensions for the amorphous structure, which hierarchically varies local concentration fluctuations, bundle and network, appeared as the length scale increases. On a basis of these findings, we discuss to address a question what factors determine the hierarchy in the microbial cellulose. This is a new topic of soft matter science, regarded as reaction-induced self-assembly in a non-equilibrium open system, therein soft matter physics, biochemistry and cell biology crucially interplay.     

A multiscale approach of nonlinear composites under finite deformation: Experimental characterization and numerical modeling

The present paper is devoted to the study of the mechanical behavior of an ethylene propylene diene monomer (EPDM) rubber reinforced by polypropylene (PP) particles, revealed as compressible. The hyperlastic behavior of this blend has been characterized under cyclic uni-axial tensile tests. The experimental results show a significant effect of the fraction of (PP) particles (5%, 10%, 25% and 30% by weight) on the macroscopic behavior of the composite. In order to model this behavior, we first develop and implement a micromechanically-based nonlinear model for hyperelastic composites. The approach is based on the second order homogenization method proposed by Ponte Castaneda and Tiberio (2000) and for which suitable energy densities are adopted for the matrix and the inclusions phases, both assumed as compressible. We then proceed to the model verification by comparison with Finite Element simulations on a unit cell. Finally, we propose an extension of the model in order to take into account damage due to voids growth phenomena. The comparison of the multiscale damage model predictions with the experimental data obtained on the EPDM/PP composite indicates a very good agreement.     

Carrier collection characteristics of microcrystalline silicon–germanium p–i–n junction solar cells

We report on the carrier collection characteristics of hydrogenated microcrystalline silicon–germanium (μc-Si_1?xGe_x:H) p–i–n junction solar cells fabricated by low-temperature (～200 °C) plasma-enhanced chemical vapor deposition. Spectral response measurements reveal that the Ge incorporation into absorber i-layer reduces the quantum efficiencies at short wavelengths. Furthermore, the illumination of the solar cells for x ? 0.35, particularly in the wavelength range of <650 nm, induces a strong injection-level-dependent p–i interface recombination and a weak collection enhancement in the bulk. These results indicate that space charges near the p–i interface are largely negative, which gives rise to an electric field distortion in the i-layer. We attribute the negative space charges to the presence of the acceptor-like states that are responsible for the strong p-type conduction observed in undoped μc-Si_1?xGe_x:H films for large Ge contents.     

Multiscaling dynamics of impurity transport in drift-wave turbulence

Intermittency effects and the associated multiscaling spectrum of exponents are investigated for impurities advection in tokamak edge plasmas. The two-dimensional Hasagawa-Wakatani model of resistive drift-wave turbulence is used as a paradigm to describe edge tokamak turbulence. Impurities are considered as a passive scalar advected by the plasma turbulent flow. The use of the extended self-similarity technique shows that the structure function relative scaling exponent of impurity density and vorticity follows the She-Leveque model. This confirms the intermittent character of the impurities advection in the turbulent plasma flow and suggests that impurities are advected by vorticity filaments.     

K-doping dependence of the Fermi surface of the iron-arsenic Ba1-xKxFe2As2 superconductor using angle-resolved photoemission spectroscopy

We use angle-resolved photoemission spectroscopy to investigate the electronic properties of the newly discovered iron-arsenic superconductor Ba_(1-x)K_(x)Fe_(2)As_(2) and nonsuperconducting BaFe_(2)As_(2). Our study indicates that the Fermi surface of the undoped, parent compound BaFe_(2)As_(2) consists of hole pocket(s) at Gamma (0,0) and larger electron pocket(s) at X (1,0), in general agreement with full-potential linearized plane wave calculations. Upon doping with potassium, the hole pocket expands and the electron pocket becomes smaller with its bottom approaching the chemical potential. Such an evolution of the Fermi surface is consistent with hole doping within a rigid-band shift model. Our results also indicate that the full-potential linearized plane wave calculation is a reasonable approach for modeling the electronic properties of both undoped and K-doped iron arsenites.     

Pressure effects on inter‐ and intramolecular vibrations in hydrogen‐bonded L‐ascorbic acid crystal

Pressure effects on the Raman spectra due to the inter‐ and intramolecular vibrations of the L ‐ascorbic acid crystal were studied. The intensity of the Raman bands due to the intermolecular vibrations varies in three different ways by application of pressure. The bands of the first group become stronger, those of the second one become weaker and the third group shows no prominent change in their intensity with increasing pressure. The bands due to the intermolecular vibrations show a blue shift, while the bands due to the intramolecular vibrations shift to the blue or red depending on the vibrational modes by application of pressure. The bands assigned to the O H stretching vibrations shift to the red, the bands assigned to the CO and CC stretching vibrations shift a little to the red and the bands assigned to the other vibrations shift to the blue under high pressure. The following conclusions were derived. (1) The hydrogen bonds forming helixes become stronger and the isolated hydrogen bond becomes weaker with increasing pressure. (2) The bands of the first group owing to the intermolecular vibrations are ascribed to the vibrations related to the helix hydrogen bonds and the second group bands to the isolated hydrogen bond. (3) The CO stretching vibration couples with the CC stretching vibration. (4) The phase transitions take place at 1.8 and 4 GPa in the crystal. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of optical feedback noise on tunable diode laser spectroscopy

The effect of optical feedback noise of a laser diode on the stability of gas-absorption spectra was investigated by monitoring the optical absorption of CO₂ gas. Lasing longitudinal mode instability greatly degraded the shape of the absorption spectra, and coherence collapse in the laser diode greatly broadened the spectra. The correlation between the optical feedback noise of the laser diode and the shape of the gas-absorption spectra was clarified on the basis of these spectral behaviors. PACS 42.62.Fi; 42.55.Px; 42.68.Ca