Abstract: Unidirectional airflow cleanroom was designed to ideally control the flow in order to
overcome airborne contamination problems, and that design has not changed much over the past twenty years. However, in reality, it didn’t work as expected. Thus, airborne contamination problems in semiconductor and flat panel display industries still existed even if entire fabrication was processed in unidirectional cleanrooms. Eventually, flow-based re-evaluation of existing unidirectional cleanroom design became inevitable. In this study, we performed fluid dynamics simulations of
unidirectional cleanroom at various dimensions, and interpreted the results for further steps of cleanroom designs, such as, inlet/outlet ducts, perforated floors, and equipment arrangement. Furthermore, we developed the mathematical model that interprets the airflow inclination at various cleanroom dimensions into a unified representation to provide designers with concepts for flow-based integration of cleanroom layout. The predicted angle/location of the maximum flow inclination by our
mathematical model in terms of fundamental design parameters agreed well with the computational fluid dynamics simulation results and with the expected trends.
Abstract: Extracts of 33 samples of seaweed, shrimp, fish and shellfish, including two certified
reference materials, were investigated for their contents of arsenic compounds (arsenic speciation).An anion exchange high performance liquid chromatography procedure was optimized to separate six arsenic compounds present in the seafood samples with dynamic reaction gas cell by inductively coupled plasma mass spectrometry. The concentration of each species in the sample were: arsenobetaines - 0.019-1.04 mg/kg, arsenocholine - 0.033-69.0 mg/kg, arseniousacid - ND-1.25 mg/kg, dimethylarsinate - ND-3.75 mg/kg, monomethylarsonate - ND-8.33 mg/kg, arsenic acid - ND-0.55 mg/kg. Additionally, unknown arsenic species were present in most of samples. The intake of inorganic arsenic via ingestion of the seafood samples that were analyzed did not represent a
toxicological problem to humans. The limits of detection (LOD) were in the range of 0.5-2.5 µg/kg .
Abstract: In order to investigate the extent and degree of heavy metal contamination in soils and sediments influenced by past mining activities, and to estimate the effects of indigenous bacteria on Cd speciation and bioremoval efficiency in sediments according to the various environmental conditions, tailings, soils, waters and sediments were collected from the Hwacheon Au-Ag-Pb-Zn mine in Korea. Elevated levels of metals, i.e., 29 As mg/kg, 30 Cd mg/kg, 261 Cu mg/kg, 601 Pb mg/kg and 3128 Zn mg/kg were found in sediments. High concentrations of As and other heavy
metals in soils, waters and sediments were found near the tailings piles. From the results of sequential extraction analyses with tailings and soils, a high proportion of Cd is present as non-residual fractions. This indicates that Cd is more mobile and bioavailable than Cu, Pb and Zn. For seasonal variation, the concentrations of As and other heavy metals were much more elevated in soils collected before rainy
season than after rainy season. To estimate the bioremoval efficiency for Cd, bacteria which can adsorb Cd were isolated from sediments in this area. Microorganisms in sediments can alter the mobility of heavy metals and bacteria can leach heavy metals from sediments, adsorb them on their cell wall and accumulate them within an intracellular matrix. From the metal sorption tests with indigenous bacteria, the bioremoval efficiency of Cd in Cd single solution (10 ppm) was more than 90%. As well, the isolated bacterial strains exhibited a preferential metal sorption , i.e., Cd > Pb > Zn for single metal solutions and Pb > Cd > Zn for the mixed metal solutions. Therefore, the use of some microorganisms to remove heavy metals from contaminated sediments may represent an innovative purification process.
Abstract: The anodic degradation of aqueous phenol and 2-chlorophenol, which are model organic pollutants, has been studied using a flow-through electrochemical cell (FTEC) with carbon fibers as an anode material. For a controlled current electrolysis of an aqueous solution of 2-chlorophenol and phenol, experimental variables, including such as, the current input, the reaction time, and the flow rate of the solutions were considered. The degradation products of the oxidation reactions were identified with HPLC, GC/MS. Small aliphatic acids and CO2 were the main products. Depending on the values of the applied current and reaction time, a complete degradation or the partial oxidation of the compounds to other intermediates was obtained. At the flow rates of 2-6 mL/s were effective on the degradation efficiencies of the 2-chlorophenol and phenol.
Abstract: Biodegradable superabsorbents, hydrolyzed AN(acrylonitrile)-grafted-SA(sodium alginate) copolymers were prepared in this study by graft copolymerization of acrylonitrile on sodium alginate and the subsequent hydrolysis of the resulting grafted copolymer. The absorbency was found to significantly depend on the % add-on, graft copolymerization conditions and hydrolysis conditions. The optimum condition for graft copolymerization to obtain the maximum % add-on (64.5%) was 4g SA, 12g AN, and 8.42g H2O2 in 100ml water at 70 oC for 10hr., respectively. The optimum hydrolysis conditions for the graft copolymer (64.5 % add-on) to reach the maximum water absorbency (2518g/g), saline absorbency (1558g/g), and WRV (288g/g) is 1g graft copolymer in 10 ml aqueous NaOH (1.0N) at 110 oC for 1 hr. Furthermore, this hydrolyzed AN-graft-SA showed a
good biodegradability in enzymatic hydrolysis tests when compared with commercial superabsorbent materials.
Abstract: An anode-supported type solid oxide fuel cell (SOFC) is a promising structure resulting in a very high performance because it consists of a very thin electrolyte. In the preliminary stage, we have succeeded in the fabrication of Samaria-Doped Ceria (SDC) thin film on a porous Ni-Al substrate using a sol-gel coating technique. The thin electrolyte film binds the substrate well and a single cell made with the SDC thin-film electrolyte and porous LSM cathode exhibited a good performance in a mixed-gas condition, even at intermediate temperatures. The single cell, consisting of 20 µm thin SDC electrolytes, the porous Ni-Al anode substrate, and a LSM cathode,
exhibited an open circuit voltage of 0.82V and a maximum power density of 0.31 W.cm-2 at 700°C with humidified methane and air mixtures. This cell also generated an open circuit voltage of about 1.1V and a maximum power density of 0.34 W.cm-2 at 600°C with humidified hydrogen as the fuel and air as the oxidant.
Abstract: An advanced way of treating livestock wastewater made use of both Autothermal
Thermophilic Aerobic Digestion (ATAD), as a pre-step, and Expanded Granular Sludge Blanket (EGSB), as the post-step. As a result, the chemical oxygen demand (COD) concentration flowing out of the post step, including the EGSB, was 89mg/ℓ, while the suspended solid (SS) concentration was 28mg/ℓ, and the total nitrogen (TN) and total phosphorus (TP) concentrations were 62mg/ℓ and 5.7mg/ℓ, respectively. To maintain a high temperature in the ATAD reactor without external heating, the characteristics of influent were found to be very critical. The temperature of the ATAD reactor was significantly elevated only when the influent TSS was more 50,000mg/ℓ. The EGSB reactor was fed with increasingly higher livestock wastewater loading rates up to 6kg chemical oxygen demand (COD)/ m3/day and an average of 84.7% of the COD and 85.4% of the SS were
removed in EGSB. Biogas was generated on the 47th day of operation in the EGSB after startup and its production increased at a rapid rate. The methane percentage within the biogas was initially low but it also increased rapidly, up to 73%. When the HRTs were 0.5-3 days, the COD removal efficiency was over 80%, but did show a increase as the HRT increased to 3 days.
Abstract: A radioactivity analysis of OREOX and the sintering steps for the DUPIC fuel fabrication process has been conducted. This study utilized ORIGEN2 code to calculate and analyze the radioactivity of spent fuels for various burn-up and cooling times. The analysis results have shown that the activity reduction of spent fuels after DUPIC fuel fabrication process was 40∼51 % and higher with longer burn-up and cooling times. This study also shows that the distribution of gaseous waste generated from OREOX process is mainly attributed to Kr, Ru and H-3, regardless of burn-up and cooling times. On the other hand, in the off-gas of the sintering process, the radioactivity distribution of Cs is more than 98 %, regardless of burn-up and cooling times.
Abstract: We have chosen the GPR method for investigating the inner structure of a stone pagoda in a non-destructive way. The selection of a suitable source frequency of the GPR antenna is the key because the main frequency of its pulse controls the resolution and the depth of the investigation. Through theoretical consideration and numerical simulation, we found that 500 to 800 MHz is suitable for a field model with a foundation part of 3 to 4 m. To image the inner structure we selected 3-D Kirchhoff prestack depth migration technique used in seismic processing. We have used the
modified migration algorithm for the source and receiver configurations of common offset GPR data. To verify the scheme, we calculated the synthetic data using the 3-D FDTD algorithm and applied the migration technique to it. Through these experiments, we confirmed that the 3-D Kirchhoff prestack depth migration technique is a very powerful tool to image the inside of a stone pagoda with high resolution. We have also applied the technique to the field data of the foundation of a five-story stone pagoda at Jeongnim temple site in Buyeo City, Korea. Based on the 3-D migrated images, we inferred that the structure of the foundation of this pagoda seemed to be preserved quite well and the thickness of the outer wall was about 0.5 m.