• Journal of the Korean Institute of Gas
• /
• v.19 no.5
• /
• pp.20-28
• /
• 2015

This work investigated the size and shape effect of ${\gamma}$-alumina-supported metal oxides on the hydrocarbon selective catalytic reduction of nitrogen oxides. Several metal oxides including Ag, Cu and Ru were used as the catalysts, and n-heptane as the reducing agent. For the Ag/${\gamma}$-alumina catalyst, the $NO_x$ reduction efficiency in the range of $250{\sim}400^{\circ}C$ increased as the size of Ag decreased (20 nm>50 nm>80 nm). The shape effect of metal oxides on the $NO_x$ reduction was examined with spherical- and wire-shape nanoparticles. Under identical condition, higher catalytic activity for $NO_x$ reduction was observed with Ag and Cu wires than with the spheres, while spherical- and wire-shape Ru exhibited similar $NO_x$ reduction efficiency to each other. Among the metal oxides examined, the best catalytic activity for $NO_x$ reduction was obtained with Ag wire, showing almost complete $NO_x$ removal at a temperature of $300^{\circ}C$. For Cu and Ru catalysts, considerable amount of NO was oxidized to $NO_2$, rather than reduced to $N_2$, leading to lower $NO_x$ reduction efficiency.

• Journal of the Korean Institute of Telematics and Electronics C
• /
• v.34C no.12
• /
• pp.20-27
• /
• 1997

In this paper, a multiplying digital-to-analog converter (MDAC) circuit for low-power high-resolution CMOS algorithmic A/D converters (ADC's) is proposed. The proposed MDAC is designed to operte properly at a supply at a supply voltge between 3 V and 5 V and employs an analog0domain power reduction technique based on a bias switching circuit so that the total power consumption can be optimized. As metal-to-metal capacitors are implemented as frequency compensation capacitors, opamps' performance can be varied by imperfect process control. The MDAC minimizes the effects by the circuit performance variations with on-chip tuning circuits. The proposed low-power MDAC is implementd as a sub-block of a 10-bit 200kHz algorithmic ADC using a 0.6 um single-poly double-metal n-well CMOS technology. With the power-reduction technique enabled, the power consumption of the experimental ADC is reduced from 11mW to 7mW at a 3.3V supply voltage and the power reduction ratio of 36% is achieved.

• Journal of Ceramic Processing Research
• /
• v.19 no.6
• /
• pp.499-503
• /
• 2018

In this paper, cobalt embedded in nitrogen and sulfur co-doped carbon nanotubes (CoNSTs) were synthesized for oxygen reduction reaction (ORR) catalysts. The CoNSTs were prepared through a facile heat treatment method without any templates. Different amounts of the metal salt were employed to examine the physicochemical and electrochemical properties of the CoNSTs. The CoNSTs showed the bamboo-like tube morphology with the encased Co nanoparticles in the tubes. Through the x-ray photoelectron spectroscopy analysis, the catalysts exhibited different chemical states of the nitrogen and sulfur species. As a result, the CoNST performed high activity toward the ORR in an acidic condition with the onset potential of 0.863 V (vs. reversible hydrogen electrode). It was clearly demonstrated from the electrochemical characterizations that the quality of the nitrogen and sulfur species significantly influences the ORR activity rather than the total amount of the dopants.

• Journal of the Mineralogical Society of Korea
• /
• v.15 no.3
• /
• pp.231-240
• /
• 2002

Microbial metal reduction influences the biogeochemical cycles of carbon and metals as well as plays an important role in the bioremediation of metals, radionuclides, and organic contaminants. The use of bacteria to facilitate the production of magnetite nanoparticles and the formation of carbonate minerals may provide new biotechnological processes for material synthesis and carbon sequestration. Metal-reducing bacteria were isolated from a variety of extreme environments, such as deep terrestrial subsurface, deep marine sediments, water near Hydrothemal vents, and alkaline ponds. Metal-reducing bacteria isolated from diverse extreme environments were able to reduce Fe(III), Mn(IV), Cr(VI), Co(III), and U(VI) using short chain fatty acids and/or hydrogen as the electron donors. These bacteria exhibited diverse mineral precipitation capabilities including the formation of magnetite ($Fe_3$$O_4$), siderite ($FeCO_3$), calcite ($CaCO_3$), rhodochrosite ($MnCO_3$), vivianite [$Fe_3$($PO_4$)$_2$ .$8H_2$O], and uraninite ($UO_2$). Geochemical and environmental factors such as atmospheres, chemical milieu, and species of bacteria affected the extent of Fe(III)-reduction as well as the mineralogy and morphology of the crystalline iron mineral phases. Thermophilic bacteria use amorphous Fe(III)-oxyhydroxide plus metals (Co, Cr, Ni) as an electron acceptor and organic carbon as an electron donor to synthesize metal-substituted magnetite. Metal reducing bacteria were capable of $CO_2$conversion Into sparingly soluble carbonate minerals, such as siderite and calcite using amorphous Fe(III)-oxyhydroxide or metal-rich fly ash. These results indicate that microbial Fe(III)-reduction may not only play important roles in iron and carbon biogeochemistry in natural environments, but also be potentially useful f3r the synthesis of submicron-sized ferromagnetic materials.

• The Journal of Korean Society for Radiation Therapy
• /
• v.29 no.1
• /
• pp.49-56
• /
• 2017

Purpose: To evaluate the accuracy of the Iterative Metal Artifact Reduction (IMAR) algorithm in correcting CT (computed tomography) images distorted due to a metal artifact and to evaluate the usefulness when proton therapy plan was plan using the images on which IMAR algorithm was applied. Materials and Methods: We used a CT simulator to capture the images when metal was not inserted in the CIRS model 062 Phantom and when metal was inserted in it and Artifact occurred. We compared the differences in the CT numbers from the images without metal, with a metal artifact, and with IMAR algorithm by setting ROI 1 and ROI 2 at the same position in the phantom. In addition, CT numbers of the tissue equivalents located near the metal were compared. For the evaluation of Rando Phantom, CT was taken by inserting a titanium rod into the spinal region of the Rando phantom modelling a patient who underwent spinal implant surgery. In addition, the same proton therapy plan was established for each image, and the differences in Range at three sites were compared. Results: In the evaluation of CIRS Phantom, the CT numbers were -6.5 HU at ROI 1 and -10.5 HU at ROI 2 in the absence of metal. In the presence of metal, Fe, Ti, and W were -148.1, -45.1 and -151.7 HU at ROI 1, respectively, and when the IMAR algorithm was applied, it increased to -0.9, -2.0, -1.9 HU. In the presence of metal, they were 171.8, 63.9 and 177.0 HU at ROI 2 and after the application of IMAR algorithm they decreased to 10.0 6,7 and 8.1 HU. The CT numbers of the tissue equivalents were corrected close to the original CT numbers except those in the lung located farthest. In the evaluation of the Rando Phantom, the mean CT numbers were 9.9, -202.8, and 35.1 HU at ROI 1, and 9.0, 107.1, and 29 HU at ROI 2 in the absence, presence of metal, and in the application of IMAR algorithm. The difference between the absence of metal and the range of proton beam in the therapy was reduced on the average by 0.26 cm at point 1, 0.20 cm at point 2, and 0.12 cm at point 3 when the IMAR algorithm was applied. Conclusion: By applying the IMAR algorithm, the CT numbers were corrected close to the original ones obtained in the absence of metal. In the beam profile of the proton therapy, the difference in Range after applying the IMAR algorithm was reduced by 0.01 to 3.6 mm. There were slight differences as compared to the images absence of metal but it was thought that the application of the IMAR algorithm could result in less error compared with the conventional therapy.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.482-483
• /
• 2006

Synthesis of iron nanopowder by room-temperature electrochemical reduction process of ${\alpha}-Fe_2O_3$ nanopowder was investigated in terms of phase evolution and microstructure. As process variables, reduction time and applied voltage were changed in the range of $1{\sim}20$ h and $30{\sim}40$ V, respectively. From XRD analyses, it was found that volume of Fe phase increased with increasing reduction time and applied voltage, respectively. The crystallite size of Fe phase in all powder samples was less than 30 nm, implying that particle growth was inhibited by the reaction at room temperature. Based on the distinct equilibrium shape of crystalline particle, phase composition of nanoparticles was identified by TEM observation.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.19 no.2
• /
• pp.255-266
• /
• 2021

Solid-state mechanochemical reduction combined with subsequent melting consolidation was suggested as a technical option for the oxide reduction in pyroprocessing. Ni ingot was produced from NiO as a starting material through this technique while Li metal was used as a reducing agent. To determine the technical feasibility of this approach for pyroprocessing, which handles spent nuclear fuels, thermodynamic calculations of the phase stabilities of various metal oxides of U and other fission elements were made when several alkaline and alkali-earth metals were used as reducing agents. This technique is expected to be beneficial, not only for oxide reduction but also for other unit processes involved in pyroprocessing.

• Journal of Korea Technical Association of The Pulp and Paper Industry
• /
• v.45 no.6
• /
• pp.17-23
• /
• 2013

The reduction of metal ion from the cotton linter for the preparation of NMMO (N-methylmorpholine N-oxide)-based dissolving pulp was investigated. The NMMO-based dissolving pulp was usually used for the manufacture of high quality fabrics, and need to have high alpha cellulose content and high brightness. NMMO, which is environmentally friendly, and reusable after recovering process, is very sensitive to the metal ions such as Cu, Fe, Mg, and Cr. Electron beam, sulfuric acid, acetic acid, and ozone treatment before bleaching were used and the concentration changes of the metal ions were compared to that of EDTA, a chelating agent. It was found that both acid treatments (sulfuric and acetic acid) were very effective and comparable to EDTA treatment at the same dosage in metal ion reduction, but electron beam and ozone treatment were not. The sulfuric acid treatment turned out to be effective in metal ion reduction, and most inexpensive.

• Journal of the Korea Convergence Society
• /
• v.8 no.1
• /
• pp.43-49
• /
• 2017

In the analyzed cardiac CT algorithm applied when comparing the MAR self-made metal artifact reduction in pacemaker inserted phantom degree. Result of comparing the energy value by CT showed a decrease in the CT value in the case of BKG 40 KeV in WSA maximum decreased to 663.2% in the case of 140 KeV BHA were increased a maximum of 56.2%. In addition, the maximum was decreased by approximately 145% based on a 70 KeV artifacts in CT value comparison by type WSA, BHA was to increase up to approximately 46.38%. MAR Algorithm is believed to provide a more quality cardiac CT image if the energy changes, or have the effect that by type and irrespective of reduced metal artifacts occurrence of artifacts applied to the pacemaker when tracking a heart CT scan after inserting MAR algorithm.

• Transactions of the Korean hydrogen and new energy society
• /
• v.21 no.4
• /
• pp.301-306
• /
• 2010

The present work is performed to photocatalytically reduce Cr(VI) by means of metal deposited anodized $TiO_2$ tubes, which are prepared by anodization of Ti foil followed by metal deposition. Stably immobilized photo-reactive materials are favored in the field of detoxification in a conventional aqueous medium, preventing gradual loss of efficiency and process malfunction due to detachment of the materials. The prepared samples are characterized by SEM, TEM, EDAX, and photocurrent. The metal deposited-$TiO_2$ electrode shows higher efficiency for Cr(VI) reduction (ca. 20%) and higher ability for adsorption (4~5 times) than pure one.