Evaluation of a Silver Nanoparticle Generator Using a Small Ceramic Heater for Inactivation of S. epidermidis Bioaerosols

Silver has been known to show antibacterial activity. Recently, silver nanoparticles have been become widely used in diverse applications. In a previous work by the authors, a small nanoparticle generator that uses a ceramic heater with a local heating area was developed. The performance of the device was evaluated in terms of the silver nanoparticles it generated. In the present article, a feasibility study regarding the inactivation of bacteria bioaerosols by the developed small silver nanoparticle generator is conducted to assess its possible use for the active control of indoor bioaerosols. To simulate the inactivation of bacteria on a surface exposed to air, an antibacterial test system consisting of an airborne silver nanoparticle generator, a bacteria bioaerosol generator, and two airborne bacteria samplers with membrane filters was utilized. Spherical polydisperse silver nanoparticles with mode diameters in the range of 10 ～ 27 nm were generated. Their size distribution was changed according the applied voltage and the airflow rate. S. epidermidis gram-positive bacteria having mode diameter of approximately 800 nm were aerosolized using a single-jet Collison nebulizer in an effort to verify the antibacterial activity of the silver nanoparticles in an air environment. With variables of 100 V and 6 L/min, the viability of S. epidermidis bacteria exposed to silver nanoparticles was lower than 5% for an exposure time ranging from 1 ～ 9 min. The viability curve was well represented in terms of the total surface area of the exposed silver nanoparticles. From the results, it was concluded that the developed small airborne silver nanoparticle generator has considerable potential as an active antimicrobial device for use in indoor air applications.     

Design and analysis of TX/RX dual microstrip antenna using FDTD at Ku-band

A TX/RX dual microstrip 8/spl times/4 array antenna for satellite communication is designed, fabricated and measured and its element characteristics are analysed using finite difference time domain (FDTD) method. TX/RX frequency ranges are 14.0-14.5 GHz, 11.7-12.75 GHz, respectively, and vertical and horizontal polarisations are used for TX and RX. This antenna uses microstrip direct feeding for RX and aperture coupled stripline feeding for TX and accommodates stacked elements for a high directivity and wide impedance bandwidth. FDTD gives more accurate results because of the consideration of finite structure and two imperfect ground planes. This element has a return loss below -8 and -14 dB over the TX and RX frequency ranges and a gain of 7.5 and 8.3 dBi at the centre frequency of TX and RX. Return loss below -10 and -14 dB and a gain of 21.4 and 20.0 dBi were achieved for the TX and RX array, respectively.     

Design of ultra-broadband on-glass antenna with a 250 /spl Omega/ system impedance for automobiles

The design of a very simple, ultra-broadband, on-glass antenna for automobiles is described. A 250 /spl Omega/ impedance system is proposed and a loop-based antenna structure with tuning arms is optimised by a genetic algorithm. The measured results on a prototype antenna show an average VSWR of 1.61 in the UHF and L bands.     

The effects of amine additives and flow rate on the performance of mixed-bed ion exchange at ultralow concentrations

Experimental data were obtained to evaluate the effects of amine additives for pH control of solution and the volumetric flow rate of feed solution on the performance of mixed-bed ion exchange for the removal of ionic impurities in solution. The experiments were performed under various temperatures and cation resin ratios by using a continuous column system with NaCl solution. The breakthrough curves of ions, plotted as the ratio of the effluent to influent concentration versus run time or treated solution volume, give detailed results about the effects of the existence of the pH controller, such as ammonia and morpholine, and the variable flow rate on the fate of each ion in the units. The experimental results show that the morpholine breakthrough occurs earlier than the ammonia breakthrough and that the effect of ammonia on both sodium and chloride exchange rates is more significant than that of morpholine. The addition of ammonia in solution results in the decrease of cation resin capacity for the sodium removal much more than the addition of morpholine. The step changes in the flow rate affect significantly the shapes of sodium and chloride breakthrough curves. The effluent concentrations of sodium and chloride change according to the flow rate. However, the effect increases with decreasing operation capacity of cation resin, while it becomes serious around the breakthrough time of chloride and negligible after the time.     

Fabrication of tin oxide film by sol–gel method for photovoltaic solar cell system

Transparent conducting tin(IV) oxide thin films have been developed with a sol–gel method, which is a low-cost process for the electrode materials of solar cell substrate. The precursor solution was made of tin isopropoxide dissolved in isopropyl alcohol. The hydrolysis rate was controlled by the addition of triethanolamine. Dipping and spin-coating technique were applied to coat tin oxide on borosilicate glass. The resistivity of the thin film was lower than 0.01 Ω-cm and the transmittance was higher than 90% in a visible range.     

Investigation of Sn Whisker Growth in Electroplated Sn and Sn-Ag as a Function of Plating Variables and Storage Conditions

Sn whiskers are becoming a serious reliability issue in Pb-free electronic packaging applications. Among the numerous Sn whisker mitigation strategies, minor alloying additions to Sn have been proven effective. In this study, several commercial Sn and Sn-Ag baths of low-whisker formulations are evaluated to develop optimum mitigation strategies for electroplated Sn and Sn-Ag. The effects of plating variables and storage conditions, including plating thickness and current density, on Sn whisker growth are investigated for matte Sn, matte Sn-Ag, and bright Sn-Ag electroplated on a Si substrate. Two different storage conditions are applied: an ambient condition (30°C, dry air) and a high-temperature/high-humidity condition (55°C, 85% relative humidity). Scanning electron microscopy is employed to record the Sn whisker growth history of each sample up to 4000 h. Transmission electron microscopy, x-ray diffraction, and focused ion beam techniques are used to understand the microstructure, the formation of intermetallic compounds (IMCs), oxidation, the Sn whisker growth mechanism, and other features. In this study, it is found that whiskers are observed only under ambient conditions for both thin and thick samples regardless of the current density variations for matte Sn. However, whiskers are not observed on Sn-Ag-plated surfaces due to the equiaxed grains and fine Ag₃Sn IMCs located at grain boundaries. In addition, Sn whiskers can be suppressed under the high-temperature/high-humidity conditions due to the random growth of IMCs and the formation of thick oxide layers.