A 60-GHz-Band Analog Optical System-on-Package Transmitter for Fiber-Radio Communications

We developed an analog optical system-on-package (SoP) transmitter for a 60-GHz-band radio-over-fiber (RoF) link. The SoP transmitter consisted of an electroabsorption modulator, radio frequency amplifiers, and a bandpass filter. The 60-GHz RoF wireless link was prepared to measure the performance of the SoP transmitter. The transmission characteristics of 64-quadrature amplitude modulation (64-QAM) data of the 60-GHz RoF wireless link, including the SoP transmitter, were investigated by measuring the error vector magnitude (EVM) and signal-to-noise ratio (SNR) with a baseband frequency. The EVM of the 60-GHz RoF wireless link was between 2.25% and 2.80%, and the SNR was between 27.36 and 29.31 dB from 140 and 770 MHz, at input baseband power of -9 dBm. The noise figure had the minimum of 8.44 dB at 500 MHz. We successfully transmitted digital community antenna television (CATV) system signals through the 60-GHz RoF wireless link, including the SoP transmitter. Digital CATV signals of 86 channels could be transmitted through the 60-GHz RoF wireless link, and the total throughput was found to be 2.61 Gb/s.     

Monolithic integration of thin film μ-heater array with 4-channel WDM transmitter

We integrated a μ-heater array with a multi-wavelength laser array for accurate control of the channel spacing. A μ-heater array was formed on a 4-channel laser array with asymmetric sampled gratings. The lasers showed threshold current of 9-13 mA and slope efficiency of around 0.21 W/A. High side mode suppression ratio over 44 dB was observed as well. With the μ-heaters, all the laser wavelengths were precisely controlled simultaneously. The laser wavelength was red shifted with the μ-heater and the tuning efficiency was 3.3 nm/W. However, thermal crosstalk between neighboring channels was observed and it was measured to be 1.1 nm/W.     

In vitro and in vivo anti-inflammatory activities of mixed fruit and vegetable juice

Food Science and Biotechnology - In this study, we attempted to develop fruit-based functional juice with anti-inflammatory activity for consumers living under heavy air pollution. At first, four...     

1.55-/spl mu/m spot-size converter integrated laser diode with conventional buried-heterostructure laser process

A 1.55-/spl mu/m spot-size converter integrated laser diode is demonstrated with conventional buried-heterostructure laser process. For the spot-size converter, we employed a double-waveguide structure in which a ridge-based passive waveguide was incorporated. The passive waveguide was optically combined with a laterally tapered active waveguide to control mode size. The threshold current was measured to be 5 mA together with high slope efficiency of 0.45 W/A. The beam divergence angles in the horizontal and vertical directions were as small as 9.0/spl deg/ and 7.8/spl deg/, respectively.     

Optimization of charge and multiplication layers of 20-Gbps InGaAs/InAlAs avalanche photodiode

We calculated the correlation between the doping concentration of the charge layer and the multiplication layer for separate absorption, grading, charge, and multiplication InGaAs/InAlAs avalanche photodiodes (APDs). For this purpose, a predictable program was developed according to the concentration and thickness of the charge layer and the multiplication layer. We also optimized the design, fabrication, and characteristics of an APD for 20 Gbps application. The punch-through voltage and breakdown voltage of the fabricated device were 10 V and 33 V, respectively, and it was confirmed that these almost matched the designed values. The 3-dB bandwidth of the APD was 10.4 GHz, and the bit rate was approximately 20.8 Gbps.     

Making of tantalum powder using the hunter process

Tantalum powder was made from potassium heptafluorotantalate (K₂TaF₇) using sodium as a reductant based on the Hunter metallothermic reduction method. The apparatus for the experiment was designed and built specifically for the present study. The tantalum particle size greatly decreased as the reduction temperature decreased from 860 to 740°C. The particle size was fairly uniform, varying from 2–3 μm to submicron sizes depending on the reaction temperature. Holding the reactants for more than 10 minutes after the completion of a sodium feeding caused irregular particle growth, thereby affecting particle size uniformity. It was found to be possible to agglomerate the powder to tens of micrometers in size by a vacuum heat treatment at 1350°C. The formation of Ta₂C during the heat treatment shows that care must be taken to prevent contamination from the furnace environment.     

Analysis and prediction of indoor air pollutants in a subway station using a new key variable selection method

A new key variable selection and prediction model of IAQ that can select key variables governing indoor air quality (IAQ), such as PM₁₀, CO₂, CO, VOCs and formaldehyde, are suggested in this paper. The essential problem of the prediction model is the question of which of the original variables are the most important for predicting IAQ. The next issue is determining the number of key variables that should be ranked. A new index of discriminant importance in the projection (DIP) of Fisher??s linear discriminant (FLD) is suggested for selecting key variables of the prediction models with multiple linear regression (MLR) and partial least squares (PLS), as well as for ranking the importance of input measurement variables on IAQ prediction. The prediction models were applied to a real IAQ dataset from telemonitoring data (TMS) in a metro system. The prediction results of the model using all variables were compared with the results of the model using only key variables of DIP. It shows that the use of our new variable selection method cannot only reduce computational effort, but will also enhance the prediction performances of the models.     

Response of fetal rat calvarial cells to nanotubular titanium oxide surface

This study examined the cell response to a TiO2 nanotubular surface (Ti-NT) for future biomedical applications. The level of cell attachment and spreading at 20 min and 60 min was evaluated by SEM. IL-6 and PGE2 secretion was evaluated by ELISA. In SEM analysis, the Ti-NT surface had more fully spread cells compared to the machined titanium surface (Ti-S). ELISA revealed that the level of IL-6 and PGE2 production was higher on the Ti-NT than on the Ti-S. These results suggest that a surface treatment with a nanotubular TiO2 surface enhances the early osteoblast responses, such as cell spreading and cytokine release, which are important for subsequent cell functions and bone healing in vivo.     

A Study on Variation of Thermal Characteristics of Insulation Materials for Buildings According to Actual Long-Term Annual Aging Variation

Insulation materials used for buildings are broadly classified as organic insulation materials or inorganic insulation materials. Foam gas is used for producing organic insulation materials. The thermal conductivity of foam gas is generally lower than that of air. As a result, foam gas is discharged over time and replaced by outside air that has relatively less thermal resistance. The gas composition ratio in air bubbles inside the insulation materials changes rapidly, causing the performance degradation of insulation materials. Such performance degradation can be classified into different stages. Stage 1 appears to have a duration of 5 years, and Stage 2 takes a period of over 10 years. In this study, two insulation materials that are most frequently used in South Korea were analyzed, focusing on the changes thermal resistance for the period of over 5000 days. The measurement result indicated that the thermal resistance of expanded polystyrene fell below the KS performance standards after about 80–150 days from its production date. After about 5000 days, its thermal resistance decreased by 25.7 % to 42.7 % in comparison with the initial thermal resistance. In the case of rigid polyurethane, a pattern of rapid performance degradation appeared about 100 days post-production, and the thermal resistance fell below the KS performance standards after about 1000 days. The thermal resistance decreased by 22.5 % to 27.4 % in comparison with the initial thermal resistance after about 5000 days.