Dynamic Bandwidth and Carrier Allocation for Video Broadcast/Multicast Over Multi-Cell Environments

Recently, broadcast/multicast over cellular networks has been actively discussed over commercial wireless mobile terminals. Compared to conventional terrestrial or satellite broadcasting systems, the quality-of-service (QoS) for edge users is an important issue due to inter-cell interference over multi-cell environments. In this paper, we introduce a dynamic bandwidth and carrier allocation (DBCA) technique by fully utilizing different visual importance of each layer in multi-layer video for broadcast/multicast services when the number of users is limited over macro/micro/femto cell environments. To ensure an acceptable video quality for edge users, the bandwidth and the loading ratio are dynamically controlled to enhance the utility through the radio resource control in accordance with the visual importance. The simulation results show that DBCA exhibits much better QoS by sending visually more important data with high priority in the cell border region.     

Resource Allocation with Partitioning Criterion for Macro-Femto Overlay Cellular Networks with Fractional Frequency Reuse

The interference mitigation technique based on fractional frequency reuse (FFR) provides improved cell-edge performance with similar overall cell capacity as that of systems with the frequency reuse factor of one. Furthermore, frequency sub-band allocation by FFR has the benefit of allowing flexibility for the deployment of femto-cells through frequency partitioning. Determination of a proper frequency partitioning criterion between the cell-center and the cell-edge, and between the cells with femto-cells is an important issue. In addition, time resource partitioning introduces another degree of freedom to the design of time-frequency resource allocation. In this paper, we propose a novel time-frequency resource allocation mechanism using FFR for a macro-femto overlay cellular network. Feasible frequency sub-band and time resource is allocated to the cell-center and the cell-edge region in a cell by the proposed partitioning criterion and the time partitioning ratio. We provide a guideline for how to determine the partitioning criterion for the regions and how to design the amount of time resource. We derive the average capacity of macro-cells and femto-cells, and introduce a new harmonic mean metric to maximize the average capacity of the regions while achieving the fairness among users in a cell.     

Crystallization and Photoactivity of Tio2 Films Formed on Soda Lime Glass by a Sol-Gel Dip-Coating Process

Transparent nanophase TiO₂ thin films on soda lime glass were prepared from titanium tetraisopropoxide (TTIP) by a sol-gel dip-coating method. The TiO₂ films had amorphous phase up to 400°C and anatase phase at 500°C. The amorphous TiO₂ films obtained at 300–400°C showed considerable photoactivity for the degradation of formic acid. The photoactivity of the TiO₂ films was enhanced with increasing calcination temperature from 300° to 500°C. The crystallinity of the anatase films at 500°C was improved with increasing calcination time up to 2 h and reduced with a further increase in calcination time to 4 h due to the significant formation of sodium titanate phase as a result of sodium diffusion. The four-time-dipping anatase films at 500°C exhibited the greatest photoactivity at the calcination time of 2 h. Sodium diffusion into TiO₂ films was retarded by a SiO₂ underlayer of 50 nm in thickness.     

A Unique Approach to Characterization of Sol‐Gel‐Derived Rare‐Earth‐Doped Oxyfluoride Glass‐Ceramics

Using the sol‐gel route Nd³⁺‐doped oxyfluoride glass‐ceramics were prepared. LiYF₄ and YF₃ crystals were deposited in the glass‐ceramics and their size, distribution, and amount ratio were varied by changing the compositions and heating temperatures. The incorporation of Nd³⁺ ions into both the fluoride crystals was confirmed by the high‐resolution elemental mapping of the glass‐ceramics. The incorporated Nd³⁺ ions showed up and down conversion photoluminescence whose properties were obviously different among the samples. The preliminary site analysis for Nd³⁺ ions was carried out using a unique approach associated with the Prony series approximation. Finally, the approach was found to be useful for the analysis of materials that are structurally complicating.     

Superhydrophilic Transparent Titania Films by Supersonic Aerosol Deposition

Photocatalytic and hydrophilic TiO₂ thin‐film applications include water purification, cancer therapy, solar energy conversion, self‐cleaning devices, and antifogging windows. We demonstrate superhydrophilicity of aerosol‐deposition (AD) TiO₂ films on a glass substrate without use of a carrier solvent, thereby removing the possibility of impurity contamination. AD films exhibit high visible light transmittance (greater than 80%) and superhydrophilicity (0° contact angle) with even minimal UV‐light irradiation exposure. This AD method represents a significant step toward the realization of economically viable, functional thin films for the aforementioned applications.     

The Application of a Gradient Method in the Finite Element Solution of Elastohydrodynamic Problems

A gradient method is described which can be used to solve problems in elastohydrodynamics. The method involves the minimization of an error function, and is compatible with such numerical schemes of solving continuum problems as the finite element or the finite difference method. A finite length slider bearing is used to illustrate the method, and numerical results for the elastohydrodynamic pressure distribution are presented.     

Design of thin plate-type speed reducers using balls for robots

A review of the recent trends of robots would show that robots are gradually being miniaturized. However, most commercially available speed reducers suffer from the limitations in terms of structure and vibration when applied to small robots. A new speed reducer mechanism was designed to check the reducer ratio and contact points between the balls and inclined planes. Contact force analysis between the gear curves and the balls and contact force analysis between the balls and inclined planes were conducted using a numerical method and FEM analysis. This virtual prototype simulation provided essential data and analysis foundation for the physical prototype’s manufacture and testing. Meanwhile, it also provided the important basis for optimizing the tooth profile and the performance. A speed reducer was manufactured to check the performance. This manufactured thin plate-type speed reducer imposed less compressive stress on the tooth profile and the balls, which greatly increased the facility of the robot.     

Effects of CO2 dilution on the interactions of a CH4–air nonpremixed jet flame with a single vortex

We carried out numerical simulations to understand how CO₂ dilution in either fuel or oxidizer stream changes the flame-vortex interactions in terms of hydrodynamic effects in CH₄–air nonpremixed jet flames. The simulation used a time-dependent, axisymmetric computational model and a low Mach number approximation. Reaction rates were calculated from a two-step global reaction mechanism that considered six species. Studies were conducted with fixed initial velocities for three different cases of CO₂ introduction: (1) without dilution, (2) dilution in a fuel stream, and (3) dilution in an oxidizer stream. A single vortex was generated by an axisymmetric jet driven of cold fuel, after a flame development was reached to quasi steady-state condition. The simulation shows that CO₂ dilution in a fuel stream leads to a slightly increased vortex radius and more entrainment of surrounding fluids compared to the other dilution methods tested. Thus, dilution of CO₂ in a fuel stream enhances the mixing inside a single vortex and increases the stretching of the flame surface. The vorticity transport equation budgets were examined to reveal the mechanisms of vortex formation in the presence of CO₂. In the stage of vortex formation, vortex production due to baroclinic torque and vortex destruction due to volumetric expansion were found to be greater in the case of CO₂ dilution in a fuel stream than in the other dilution cases. However, after vortex formation, there terms showed the opposite tendencies.     

Effect of Nafion gradient in dual catalyst layer on proton exchange membrane fuel cell performance

The role of Nafion^® binder in the electrodes was evaluated by changing its content for the membrane electrode assembly (MEA) fabrication. In the study, we prepared MEAs that have two different compositions of catalyst layers in electrodes. One layer which is close to the electrolyte membrane has the higher Nafion^® content. The other which is near the gas diffusion media (GDM) has the lower one. Also, we changed the thickness of two layers to find the ideal composition of the binder and Pt/C in the electrode. The dual catalyst layer coated MEA showed higher cell performance at high current density region than the pristine MEA.     

Indirect evaluation of the long-term oxidation properties of Al−21Ti−23Cr and Al−37Ti−12Cr coating materials for TiAl alloy

The most pertinent coating materials in the Al−Ti−Cr alloy system to improve the high temperature oxidation resistance of a TiAl alloy, with respect to oxidation properties, resistance to thermal stress, and chemical compatibility, are the two-phase alloys of Al−21Ti−23Cr (L1₂+Cr₂Al) and Al−37Ti−12Cr (γ+TiAlCr). In this study, cyclic oxidation tests at 1000 °C and 1200 °C were performed for the specimens coated with both materials of 10 im thickness. Furthermore, breakaway oxidation caused by the formation of a rutile TiO₂ scale was observed, though both bulk alloys showed very stable oxidation behavior. This phenomenon was resulted from the depleted Al content in the coating layer due to Al₂O₃ oxide growth and interdiffusion with the substrate. Considering the decrease of Al content due to oxide growth, the Al−21Ti−23Cr coating with the initial higher Al content was more effective for long-term oxidation protection of the TiAl alloy. On the other hand, when the Al content changes due to the interdiffusion with the substrate, the Al−37Ti−12Cr coating with a smaller compositional gradient with the TiAl substrate was more effective than the Al−21Ti−23Cr coating. Cyclic oxidation tests at 1000 °C and 1200 °C confirmed that for the longer lifetime of coating materials the initial Al content was more important than the smaller compositional gradient with the substrate. Consequently, the Al−21Ti−23Cr coating was considered as more effective one for the long-term oxidation resistance of TiAl alloys.