Exact Solution of a Test Particle in Presence of Thick Domain Walls

We have obtained the exact solution of the equations of motion of a test particle near a thick domain walls. From the solution it has been shown that the domain walls have repulsive gravitational fields.     

Planar nematic anchoring on SiO-coated substrates

Summary The nematic planar anchoring is usually explained by using simple elastic models: the surface easy axis corresponds to the surface direction that minimizes the excess of nematic elastic energy. When anisotropic rough substrates are used to align nematic liquid crystals, due to the complex surface morphology, usual elastic models are not directly applicable. This paper presents quantitative topographical data of rough substrates, obtained with oblique SiO evaporation under vacuum for nematic planar anchoring. Experimental data are obtained by means of Atomic Force Microscopy and they are used to demonstrate the self-affine nature of these substrates and to relate the nematic anchoring with the anisotropy of the local fractal properties of the substrate itself. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Large second-order optical nonlinearities of s-triazine derivatives: View from micro molecules to macro crystals

Organic nonlinear optics (NLO) is also called mo-lecular nonlinear optics. In recent years organic mate-rials have been intensively studied because of their large NLO coefficients and structural diversities[1―3]. Second harmonic generation (SHG) is a bas…     

Hydroxyapatite coating on porous silicon substrate obtained by precipitation process

Hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (HAP) is known as a bioactive and biocompatible material, HAP coatings were used to improve the biocompatible of substrate by many researcher, In this work, HAP thin films on porous silicon (PS) substrates have been prepared by aqueous precipitation method with rapid thermal annealing (RTA) processes. The HAP films had been prepared under the annealing temperature ranging from 300 to 1000 °C. By the measurement of X-ray diffraction (XRD), it was found that for the crystallinity optimization, the heat-treatment at 850–950 °C for 1 h would be favorable. Atomic force microscopy (AFM) and scanning electron microscope (SEM) measurements reveal a dense and smooth surface of the HAP film, and tightly adherence of the coating on porous silicon substrate after sintered. Thus, by this method, porous silicon could be increased its bioactivity and so that could be used in the biomedical area.     

MEASUREMENTS OF Fe AND Cu K-Shell IONIZATION CROSS SECTIONS BY SLOW ELECTRON IMPACT

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Surface effects in field-induced smectic transitions

We study the surface behavior of a semi-infinite smectogenic sample bounded by a solid wall, in the presence of an external electric field. Our analysis is performed in the framework of a Landau-de Gennes theory. For the sake of simplicity, we consider only the case in which, in the absence of field and surfaces, a direct isotropic to smectic-A transition occurs, while in the presence of the electric field a nonspontaneous nematic phase appears. Two new surface phases are identified, namely a parasmectic and a surface-induced smectic phase. The shifts in the transition temperatures and the critical behavior of the surface states are analyzed. Received: 25 August 1997 / Accepted: 23 January 1998     

Photorefractive shearing interferometer

A novel method of obtaining shearing interferogram by slightly moving the crystal in a photorefractive interferometer is proposed. This method can measure the phase of an object itself instead of its diffraction field, and it is easy to realize continuously changeable shearing distance in any lateral direction and introduce carrier fringes at the same time. Both the theoretical analysis and experimental verification are given.     

The effect of oxidation on physical properties of porous silicon layers for optical applications

In order to understand the optical loss mechanisms in porous silicon based waveguides, structural and optical studies have been performed. Scanning and transmission electron microscopic observations of porous silicon layers are obtained before and after an oxidation process at high temperature in wet O₂. Pore size and shape of heavily p-type doped Si wafers are estimated and correlated to the optical properties of the material before and after oxidation. The refractive index was measured and compared to that determined by the Bruggeman model.