Power limits for secondary devices operating on TV white spaces

The use of TV white spaces as an alternative to overcome spectrum scarcity is a huge opportunity for new telecommunication systems and services. While being attractive for its desirable propagation characteristics, this part of the spectrum imposes a major difficulty from design and regulatory perspectives: how to optimize the use of spectrum and to ensure the protection of primary users, TV systems for example, at the same time. This paper discusses strategies to be adopted by geo-location database operators to calculate adaptive maximum permitted power levels for secondary devices, according to permissible levels of interference into the digital terrestrial television primary system.     

Non-uniqueness and symmetry of optimal topology of a shell for minimum compliance

Uniqueness and symmetry of solution are investigated for topology optimization of a symmetric continuum structure subjected to symmetrically distributed loads. The structure is discretized into finite elements, and the compliance is minimized under constraint on the structural volume. The design variables are the densities of materials of elements, and intermediate densities are penalized to prevent convergence to a gray solution. A path of solution satisfying conditions for local optimality is traced using the continuation method with respect to the penalization parameter. It is shown that the rate form of the solution path can be formulated from the optimality conditions, and the uniqueness and bifurcation of the path are related to eigenvalues and eigenvectors of the Jacobian of the governing equations. This way, local uniqueness and symmetry breaking process of the solution are rigorously investigated through the bifurcation of a solution path.     

Adsorption properties of amphiphilic polyoxyalkylenated dimethylpolysiloxane derivatives on keratin

Adsorption properties of two types of dimethylpolysiloxane backbone derivatives, perfluoroalkyl polyoxyethylenated dimethylpolysiloxane (FPD) and polyoxyethylenated dimethylpolysiloxane (PD), onto keratin surfaces were investigated. Both polymers are amphiphilic, since they possess hydrophilic polyoxyethylene groups. FPD contains a perfluoroalkyl group that provides both water-and oil-repellent properties, whereas PD lacks these groups. Adsorption properties of these polymers onto keratin surfaces are considered a good index to evaluate these compounds as nonionics used in hair-coating agents, since keratin is a major component of hair. FPD was more likely to be adsorbed and less likely to be eliminated from the keratin surface than PD. Once FPD had been adsorbed onto the keratin surface, it was very slowly washed from the surface when it was immersed in stationary water, whereas PD polymers were quickly washed from the keratin surface. Even in running water, rapid elimination of FPD was not observed. The strong resistance to loss of FPD after washing with a large quantity of water may be due to the water-repellent nature of the perfluoroalkyl groups. As a comparison, FPD adsorption onto a glass surface was also investigated. The affinity to the glass surface was found to be less than to the keratin surface.     

One-Dimensional Phonon State of 4He Films Adsorbed in Straight Nanopores

We have studied heat capacities of ⁴He adsorbed in straight nanopores 1.8, 2.2, and 2.8 nm in diameter. Heat capacities of the ⁴He fluid film on the solid layer at 0.08–0.4 K show power laws close to T in 1.8 nm pores, close to T ² in 2.8 nm pores, and a crossover from T to T ² with increasing temperature in 2.2 nm pores. These heat capacities are explained by a model assuming a phonon dispersion with continuous one-dimensional (1D) states in the axial direction and discrete energy levels in the azimuthal direction. By fitting experimental data to the model, the phonon velocity along the pore axis and the energy gap for propagation in the cross section are derived. At temperatures sufficiently lower than the energy gap, where the thermal wave length of phonons is much longer than the effective pore diameter, the ⁴He fluid films show a T-linear heat capacity of 1D phonons propagating only along the pore axis. At higher temperatures, a 1D-2D crossover of phonons occurs.      

Effect of fluorine impurity on the oxidation of silicon oxynitride ceramics doped with gadolinium oxide

Impurities in raw Si₃N₄ powders remain in intergranular glassy phases in Si₃N₄ and Si₂N₂O ceramics and degrade their high-temperature properties. Fluorine is one of the typical impurities in the raw powders. The oxidation rate of Si₂N₂O ceramics doped with Gd₂O₃ greatly varied with a difference in impurity contents (especially F) of the raw Si₃N₄ powders used. When a high concentration of impurity existed in the intergranular glassy phase, the rate of oxidation was controlled by O^2– diffusion through the glassy phase in the partly oxidized scale and unoxidized body; outward diffusion of Gd³⁺ occurred concurrently. On the other hand, when the impurity contents in the intergranular glassy phase was very low, the diffusion rate of ions (Gd³⁺, O^2–, etc.) in the glassy phase became very low (substantially zero in the oxidation at 1300°C). Only cristobalite (SiO₂) was formed on the surface. The rate of oxidation was controlled by O₂ diffusion through the cristobalite layer, and was very low.     

TiO2 thin films using organic liquid materials prepared by Hot-Wire CVD method

TiO₂ thin films prepared by Hot-Wire CVD method have been studied as a protecting material of transparent conducting oxide (TCO) against atomic hydrogen exposures for the fabrications of Si thin film solar cells. It was found that electrical conductivity of the films at room temperature reached a value of 0.4 S/cm. This value is 2-3 orders of magnitude higher than that of TiO₂ films prepared by RF magnetron sputtering and electron-beam evaporation methods in our previous works. The conductivity improvement seems to be partly due to the enlargement of TiO₂ crystallites.     

Alternation on rolling contact properties of steel due to magnetic field

This paper describes the effects of magnetic field on rolling contact performance of steel/steel disc couple and presents an investigation into the mechanisms governing these effects by applying contact mechanics and magnetism theory.The tests were carried out in disc-on-disc contact configuration under 1.1 T [Tesla] of horizontal static magnetic fields created by permanent magnets in three different orientations.Wear amounts were decreased in the magnetic fields and there was difference in magnetic field orientation. For the characteristic of the surface, results of scanning electron microscope observations point out that finer wear particles and smoother worn surfaces are produced in the presence of magnetic field. The smoother surfaces are also confirmed by surface roughness measurements. For the generation of the finer wear particles, it is considered that subsurface crack initiation point is moved toward the surface due to magnetic field.The effect of magnetic field is considered by calculating the number of cycles required to generate wear particles and the cycle was reduced due to the presence of magnetic field.It is considered, from views of contact mechanics and magnetism theory, that domain walls near the contact region are caught by dislocations when the specimen is magnetised and part of the energy for magnetisation activates the dislocation movement resulting in crack initiation.     

Incorporation of a well-defined polyether side-chain into segmented poly(ether-urethane urea) and examination for blood-compatibility

A new method of introducing a hydrophilic polyether side chain into segmented polyurethane using a polypropylene oxide macromer with 1,3-diol at one chain-end, which behaves as chain extender, is described. In this procedure, a molecular-designed side-chain is incorporated quantitatively and directly into polyurethane biomedical elastomer. The design is also of interest to biomaterials in artificial organs.