17 results on '"Hansoo Kim"'
Search Results
2. Antibacterial and Anti-Inflammatory Potential of Mouthwash Composition Based on Natural Extracts
- Author
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Bongju Kim, Min-Sun Lee, Yu Jin Jung, Hansoo Kim, Won-Hyeon Kim, Kyung-Won Ju, Sung Ho Lee, and Jong-Ho Lee
- Subjects
0301 basic medicine ,Technology ,medicine.drug_class ,pathogenic oral bacteria ,QH301-705.5 ,QC1-999 ,Xylitol ,Cetylpyridinium chloride ,Anti-inflammatory ,03 medical and health sciences ,chemistry.chemical_compound ,0302 clinical medicine ,natural extract ,medicine ,General Materials Science ,Biology (General) ,Instrumentation ,QD1-999 ,Fluid Flow and Transfer Processes ,natural extract mixture ,biology ,Traditional medicine ,Benzethonium chloride ,Process Chemistry and Technology ,Physics ,Chlorhexidine ,General Engineering ,nonpathogenic oral bacteria ,030206 dentistry ,Propolis ,biology.organism_classification ,Engineering (General). Civil engineering (General) ,Computer Science Applications ,Triclosan ,Chemistry ,030104 developmental biology ,chemistry ,oral environment ,TA1-2040 ,Bacteria ,medicine.drug - Abstract
Mouthwash contains chlorhexidine, triclosan, cetylpyridinium chloride, benzethonium chloride, and fluoride. However, continuous use of these chemical substance affects both pathogenic and nonpathogenic oral bacteria and causes an imbalance in the oral environment, which is known to affect not only oral diseases but also systemic diseases. Therefore, in this study, we observed the possibility of replacing the composition of chemical compound mouthwash with a natural extract. Platycodon grandiflorum (PG), Chaenomeles sinensis Koehne (CSK), and Siraitia grosvenorii (SG) were used as natural extracts, and a mixture of enzyme salt, xylitol, mint, green tea, lemon, and propolis were used as the natural extract mixture series (M1–M5). The natural extracts and natural mixture series were evaluated for the antibacterial effect, anti-inflammatory effect, cell viability, and nitric oxide (NO) assay using eleven types of pathogenic oral bacteria, two types of nonpathogenic oral bacteria, and macrophages RAW 264.7 cells. Cell viability was measured as about 35.9–46.7% for the control group (GA and LIS), about 36.3–57.7% for the natural extract group (PG, CSK, SG), and about 95.8–97.9% for the natural extract mixture series group (M1–M5). In the NO assay tested with lipopolysaccharide (LPS)-stimulated inflammatory responses, the control group was measured at about 89%, the natural extracts group were measured at 84–88%, and the natural extract mixture series group at about 54–82%. It was observed that some natural extracts (PG, SG) and natural extract mixtures (M4, M5) inhibited LPS-induced NO production, which meant that natural extracts had anti-inflammation potential. In conclusion, it was observed that natural extracts mixed in proper proportions affect pathogenic oral bacteria and not nonpathogenic oral bacteria. It is considered that appropriately formulated natural extracts can maintain a healthy oral environment and further replace commercial mouthwash based on chemical compound mixtures.
- Published
- 2021
3. Strain hardening of novel high Al low-density steel consisting of austenite matrix and B2-ordered intermetallic second phase in the perspective of non-cell forming face-centered-cubic alloy with high stacking fault energy
- Author
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Hansoo Kim
- Subjects
010302 applied physics ,Austenite ,Materials science ,Mechanical Engineering ,Alloy ,Metals and Alloys ,Intermetallic ,02 engineering and technology ,engineering.material ,Strain hardening exponent ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Specific strength ,Mechanics of Materials ,Stacking-fault energy ,Phase (matter) ,0103 physical sciences ,engineering ,General Materials Science ,Composite material ,Deformation (engineering) ,0210 nano-technology - Abstract
It has recently been suggested that the extraordinary strain hardening rate in Fe-16Mn-10Al-0.86C-5Ni high specific strength steel [1] is due to the high back stresses arising from the strain incompatibility between austenite matrix and B2-ordered intermetallic second phase [2]. I argue here that the alloy matrix chemistry, particularly short-range ordering of constituent atoms, could be the intrinsic factor that affects the deformation and strain hardening, rather than the stress-strain partitioning caused by the microstructural heterogeneity.
- Published
- 2019
4. In Situ Measurement of Sound Attenuation by Fish Schools (Japanese Horse Mackerel, Trachurus japonicus) at Mid-Frequency Bands
- Author
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Hansoo Kim and Dong-Guk Paeng
- Subjects
01 natural sciences ,Sonar ,lcsh:Technology ,lcsh:Chemistry ,Mid-frequency ,0103 physical sciences ,General Materials Science ,mid-frequency ,010301 acoustics ,Instrumentation ,lcsh:QH301-705.5 ,in situ measurement ,010302 applied physics ,Fluid Flow and Transfer Processes ,fish schools ,biology ,Japanese horse mackerel ,lcsh:T ,Process Chemistry and Technology ,Attenuation ,General Engineering ,Acoustic wave ,biology.organism_classification ,Horse mackerel ,lcsh:QC1-999 ,Computer Science Applications ,Oceanography ,Sound attenuation ,lcsh:Biology (General) ,lcsh:QD1-999 ,lcsh:TA1-2040 ,Trachurus japonicus ,%22">Fish ,Environmental science ,lcsh:Engineering (General). Civil engineering (General) ,Acoustic attenuation ,lcsh:Physics - Abstract
Acoustic waves are attenuated by fish schools as they propagate through the ocean. The attenuation by fish schools is not currently considered in fishery acoustics and sonar applications, especially at mid-frequency bands. In this study, fish school attenuation experiments were conducted with a number of individual fish in situ in a net cage at mid-frequency bands (3–7 kHz). The target fish species was the Japanese horse mackerel (Trachurus japonicus), which typically forms fish schools in the coastal ocean of northeastern Asia. The attenuated acoustic waves were measured for the cases of non-net, only net (0), 100, 200, 300, 400, and 500 individual horse mackerels in the net cage. Results showed that the acoustic signal attenuation increased with the number of horse mackerels. The mean and maximum attenuation coefficients were approximately 6.0–15.4 dB/m and 6.5–21.8 dB/m for all frequencies, respectively. The measured attenuation coefficients were compared with the ones from previous studies to propose new regression models with normalized extinction cross-sections of weight and length of fish. This study confirmed that the fish school attenuation could not be ignored and compensated at mid-frequencies in the ocean. These results would be useful for fishery acoustics, especially in the development of scientific echo-sounder, and naval applications of sonar operations and analysis.
- Published
- 2021
- Full Text
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5. A Review on Thermophysical Property Assessment of Metal Oxide-Based Nanofluids: Industrial Perspectives
- Author
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Surendran V. Sujith, Hansoo Kim, and Joonho Lee
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pool boiling ,Physics::Fluid Dynamics ,Mining engineering. Metallurgy ,zetapotential ,viscosity ,TN1-997 ,Metals and Alloys ,wettability ,thermal conductivity ,General Materials Science ,specific heat - Abstract
Energy consumption in the industrial sector can be significantly reduced by improving heat transfer rates in heat exchanger circuits, pool boiling, metal cutting industries, etc. Numerous energy-related issues can be overcome to a large extent by improving heat flow properties by utilizing nanofluids. The present contribution reviews the improvement in thermophysical properties of metal oxide-based nanofluids. Key parameters affecting the thermophysical properties of nanofluids, such as particle volume fraction, temperature, particle size and various stabilizers, were reviewed. The importance of DLVO theory and zeta potential to control the electrostatic repulsion and pH values of nanofluids for stable nanofluid formulations were discussed. It has been observed that classical theories of thermal conductivity and viscosity cannot predict exact values for a wide range of variables. Therefore, various extensive correlations have been introduced to predict the thermophysical properties of nanofluids. In these correlations, individual dependent variables such as particle size, temperature, nanofluid layer thickness, and Brownian velocity of nanoparticles, etc. were considered for more accurate prediction. The heat transfer efficiencies of nanofluids to base fluids in the laminar and turbulent regimes have been discussed using various figures of merits. Finally, the scope of industrial applications of metal oxide-based nanofluids and future research opportunities have been discussed.
- Published
- 2022
6. A Study on the Properties of Recycled Aggregate Concrete and Its Production Facilities
- Author
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Chan-Soo Jeon, Hansoo Kim, Jungho Kim, Sae-Hyun Lee, and Jong-Hyun Sung
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0211 other engineering and technologies ,02 engineering and technology ,lcsh:Technology ,lcsh:Chemistry ,021105 building & construction ,construction waste ,Production (economics) ,General Materials Science ,021108 energy ,mechanical characteristics ,Instrumentation ,lcsh:QH301-705.5 ,Shrinkage ,Fluid Flow and Transfer Processes ,Aggregate (composite) ,Air volume ,Waste management ,lcsh:T ,Process Chemistry and Technology ,General Engineering ,Durability ,lcsh:QC1-999 ,Computer Science Applications ,Slump ,Compressive strength ,recycled aggregate ,lcsh:Biology (General) ,lcsh:QD1-999 ,lcsh:TA1-2040 ,Construction waste ,Environmental science ,concrete ,durable characteristics ,lcsh:Engineering (General). Civil engineering (General) ,lcsh:Physics - Abstract
In recent years, the amount of construction waste and recycled aggregate has been increasing every year in Korea. However, as the recycled aggregate is poor quality, it is not used for concrete, and the Korean government has strengthened the quality standards for recycled aggregate for concrete. In this study, research was conducted on the mechanical and durability characteristics of concrete using recycled aggregate, after developing equipment to improve the quality of recycled aggregate to increase the use of recycled aggregate for environmental improvements. The results illustrated improvements in the air volume, slump, compressive strength, freezing and thawing resistance, and drying shrinkage. Furthermore, this study is expected to contribute to the increased use of recycled aggregate in the future.
- Published
- 2019
7. Integration of a Three-Dimensional-Printed Titanium Implant in Human Tissues: Case Study
- Author
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Chae Ahn Song, Hyun Guy Kang, Jong Woong Park, Hansoo Kim, Kwun Mook Lim, and June Hyuk Kim
- Subjects
Titanium implant ,implant ,Tissue integration ,Adhesion (medicine) ,02 engineering and technology ,bone tumor ,lcsh:Technology ,Osseointegration ,lcsh:Chemistry ,03 medical and health sciences ,0302 clinical medicine ,medicine ,General Materials Science ,titanium ,human ,three-dimensional printing ,lcsh:QH301-705.5 ,Instrumentation ,Total Tissue ,Fluid Flow and Transfer Processes ,030222 orthopedics ,lcsh:T ,business.industry ,Process Chemistry and Technology ,Ulna ,General Engineering ,Soft tissue ,tissue integration ,021001 nanoscience & nanotechnology ,medicine.disease ,lcsh:QC1-999 ,Computer Science Applications ,medicine.anatomical_structure ,lcsh:Biology (General) ,lcsh:QD1-999 ,lcsh:TA1-2040 ,Implant ,lcsh:Engineering (General). Civil engineering (General) ,0210 nano-technology ,business ,lcsh:Physics ,Biomedical engineering - Abstract
A titanium alloy implant of appropriate pore size can potentially enhance osseointegration and soft tissue integration. However, the human clinical application of such implants has not been reported. Here, we present a case of limb salvage surgery for a bone tumor using customized three-dimensional (3D)-printed Ti6Al4V radius and ulna implants. The patient presented with local recurrence at the proximal junction of the ulna and underwent a re-wide excision. Single forearm bone surgery was performed using another 3D-printed implant after resection of the recurrent tumor with an ulnar implant. Host osseointegration and soft tissue integration of the retrieved implant were quantified through histological evaluation. The total tissue integration rates of the implant at the proximal and distal bone junctions were 45.96% and 15.03%, respectively. The mesh structure enhanced bone integration by up to 10.81% in the proximal and by up to 8.91% in the distal bone junction. Furthermore, the soft tissue adhesion rates of the implant shaft were 59.50% and 50.26% in the axial and longitudinal cuts, respectively. No area was left unoccupied throughout the shaft of the implant. Overall, these results indicate that the 3D-printed Ti6Al4V titanium alloy implant with a rough surface has considerable tissue integration ability.
- Published
- 2020
8. Acoustic Target Strength Measurements for Biomass Estimation of Aquaculture Fish, Redlip Mullet (Chelon haematocheilus)
- Author
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Hansoo Kim, Kiseon Kim, Sungho Cho, Mira Kim, Donhyug Kang, and Jisung Park
- Subjects
0106 biological sciences ,ex situ measurement ,Spatial distribution ,01 natural sciences ,lcsh:Technology ,Mullet ,Redlip mullet (Chelon haematocheilus) ,lcsh:Chemistry ,Aquaculture ,General Materials Science ,Target strength ,Underwater ,Instrumentation ,TS function ,lcsh:QH301-705.5 ,Fluid Flow and Transfer Processes ,Biomass (ecology) ,Target strength (TS) ,biology ,Chelon ,business.industry ,lcsh:T ,010604 marine biology & hydrobiology ,Process Chemistry and Technology ,General Engineering ,04 agricultural and veterinary sciences ,biology.organism_classification ,lcsh:QC1-999 ,Computer Science Applications ,Oceanography ,lcsh:Biology (General) ,lcsh:QD1-999 ,lcsh:TA1-2040 ,040102 fisheries ,0401 agriculture, forestry, and fisheries ,%22">Fish ,Environmental science ,business ,lcsh:Engineering (General). Civil engineering (General) ,lcsh:Physics - Abstract
Redlip mullet (Chelon haematocheilus) is distributed in coastal waters of the North-Western Pacific Ocean and is a cultured fish in Korea. A hydroacoustic technique constitutes a useful method to assess the biomass and spatial distribution of mullet in sea cages or in coastal waters, and acoustic target strength (TS) information of the target fish is an essential parameter in using this method. In this study, ex situ TS measurements of 16 live mullets were made in an aquaculture sea cage in Korea. The split-beam scientific echo-sounder used for measurements was comprised of 38, 120, 200, and 420 kHz frequencies. An underwater video camera was simultaneously used to observe the mullets&rsquo, behavior during the TS measurements. The mullet TS data was analyzed from a wide range of total fish length (FL: 14.3&ndash, 40.3 cm). As results for all frequencies, the frequency dependence of the mean TS values were relatively low, and the difference in mean TS was within 2.5 dB. When the slope of the least-squares regression line was forced to 20 into the TS equation, the resulting value for the constant term (b20) at each frequency was &minus, 67.0 dB, &minus, 68.3 dB, &minus, 66.3 dB, and &minus, 68.5 dB, respectively. The data tended to be frequency dependent. Additionally, the maximum TS appeared between tilt angles of 0°, and 10°, These results indicate that TS measurements can be applied to estimate the biomass of the mullet in sea cages or in coastal waters.
- Published
- 2018
9. Iron particles in carbon nanotubes
- Author
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Hansoo Kim and Wolfgang M. Sigmund
- Subjects
Nanotube ,Materials science ,Carbon nanofiber ,Astrophysics::High Energy Astrophysical Phenomena ,Nanotechnology ,Mechanical properties of carbon nanotubes ,General Chemistry ,Carbon nanotube ,law.invention ,Carbide ,Condensed Matter::Materials Science ,Chemical engineering ,law ,Phase (matter) ,Astrophysics::Solar and Stellar Astrophysics ,Particle ,General Materials Science ,Selected area diffraction - Abstract
Nanometer-size iron-rich particles in carbon nanotubes have been studied by transmission electron microscopy with and without in situ and ex situ heating. Several remarkable results were found; a high temperature phase (γ-Fe) of iron stable at low temperatures and preferential presence of iron and iron carbide in carbon nanotubes. Based upon these experimental results, thermodynamics of the Fe–C phase diagram and its kinetics were used to explain the non-uniform distribution of iron and iron carbide, which also yielded a deeper insight into the formation of carbon nanotubes. Some of the results also allowed describing the role of the graphitic structure in retaining the high temperature phase (γ-Fe) of iron at low temperatures. Furthermore, methods have been demonstrated with which γ-Fe can be produced in carbon nanotubes intentionally or in a large quantity. Selected area electron diffraction patterns of iron inside nanotubes demonstrated the crystallographic relationship of the iron to the nanotube axis along with phase changes of the iron. This paper summarizes the findings and draws further conclusions on the particle shape inside multiwalled carbon nanotubes.
- Published
- 2005
10. Phase transition of iron inside carbon nanotubes under electron irradiation
- Author
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Wolfgang M. Sigmund, Michael J. Kaufman, and Hansoo Kim
- Subjects
Nanotube ,Materials science ,Mechanical Engineering ,Inorganic nanotube ,Nanotechnology ,Carbon nanotube ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,law.invention ,Carbon nanotube quantum dot ,Optical properties of carbon nanotubes ,Condensed Matter::Materials Science ,Mechanics of Materials ,Transmission electron microscopy ,law ,Electron beam processing ,General Materials Science ,Carbon nanotube supported catalyst - Abstract
Selective encapsulation of different materials or phases of a material inside a carbon nanotube leads to controlling local properties of the nanotube. We report a method of synthesizing stable γ-Fe selectively inside a carbon nanotube by transforming α-Fe through electron irradiation in situ inside a transmission electron microscope. Therefore, this method enables a single nanotube to encase both high (γ-Fe) and low (α-Fe) temperature phases of iron simultaneously. γ-Fe produced by this method may be used as a novel catalyst, and its presence inside a carbon nanotube may affect the physical properties of the nanotube, which therefore can be used to modify the nanotube.
- Published
- 2004
11. Synthesis of hierarchical zinc oxide nanotubes
- Author
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Hansoo Kim and Wolfgang M. Sigmund
- Subjects
Materials science ,Opacity ,Mechanical Engineering ,chemistry.chemical_element ,Nanotechnology ,Zinc ,Condensed Matter Physics ,Catalysis ,chemistry ,Mechanics of Materials ,Transmission electron microscopy ,Transmittance ,General Materials Science ,Nanorod ,Layer (electronics) ,Wurtzite crystal structure - Abstract
In this paper, we report on the synthesis and structure of hierarchical zinc oxide nanotubes. Hierarchical nanotubes grown by physical vaporization of zinc in the presence of a catalyst were decorated with many secondary zinc oxide nanorods on the outer surface. The axis of these nanotubes with an average diameter of 65 nm was aligned along the c axis of wurtzite zinc oxide. The hierarchical zinc oxide nanotubes, many of which were single crystals, were transparent or opaque, depending on whether they had a zinc layer inside. The opaque nanotubes showed an abrupt change in electronic transmittance during investigation with transmission electron microscopy. The unique structure of the hierarchical ZnO nanotubes and the quantum effect resulting from the reduced dimension will modify the original properties of ZnO, leading to novel applications.
- Published
- 2003
12. Observation and formation mechanism of stable face-centered-cubic Fe nanorods in carbon nanotubes
- Author
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Michael J. Kaufman, David Jacques, Rodney Andrews, Hansoo Kim, and Wolfgang M. Sigmund
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Materials science ,Cementite ,Mechanical Engineering ,Nanoparticle ,Nanotechnology ,Mechanical properties of carbon nanotubes ,Crystal structure ,Carbon nanotube ,Cubic crystal system ,Condensed Matter Physics ,law.invention ,chemistry.chemical_compound ,Chemical engineering ,chemistry ,Mechanics of Materials ,law ,Phase (matter) ,General Materials Science ,Nanorod - Abstract
The crystallographic structure and orientation of iron nanoparticles present in carbon nanotubes (CNTs) was studied when iron was used as a catalyst. It was found that while most of the nanoparticles encapsulated inside the CNTs had the expected α–Fe (body-centered-cubic) phase, a significant number of them formed and retained the γ–Fe (face-centered-cubic) phase that is not the normal bulk phase at room temperature (nor even expected to form at the growth temperature used). It was also found iron particles at the tips of the nanotubes were either α–Fe or cementite (Fe3C). On the basis of these observations and thermodynamics, a mechanism for the formation of these particles and insights into CNT growth is proposed.
- Published
- 2003
13. Structural modifications of multiwalled carbon nanotubes and their effects on optical properties
- Author
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Younghyun Kim and Hansoo Kim
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3D optical data storage ,Photoluminescence ,Materials science ,Annealing (metallurgy) ,Bioengineering ,General Chemistry ,Carbon nanotube ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,law.invention ,Optical properties of carbon nanotubes ,Condensed Matter::Materials Science ,Crystallinity ,Chemical engineering ,law ,Modeling and Simulation ,General Materials Science ,Composite material ,Luminescence ,Electronic band structure - Abstract
Multiwalled carbon nanotubes (MWCNTs) with outermost diameters of ~5 to more than 100 nm are modified and investigated for structural and optical properties. MWCNTs are sonicated for a long time (100 min) to intentionally introduce defects and functional groups as well as annealed at a high temperature (2,000 °C) for further graphitization. They are examined for absorption and emission behavior and compared to the initial material. The MWCNTs are found to show plenty of highly-resolvable emission bands. Since they are observed from all the samples, the bands are considered to be intrinsic to MWCNTs. The mechanisms previously suggested for the emission of MWCNTs are compared using the structural features and the optical data. It was deduced that defects or functional groups are not involved in the luminescence. Rather, the emission bands imply interband transitions between van Hove singularities in the electronic band structure. These results not only help to understand inherent properties of MWCNTs but may also give insight into the luminescence phenomena of other carbon nanotube family such as double-walled carbon nanotubes and functionalized MWCNTs.
- Published
- 2013
14. Fe–Al–Mn–C lightweight structural alloys: a review on the microstructures and mechanical properties
- Author
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Dong-Woo Suh, Hansoo Kim, and Nack J. Kim
- Subjects
Materials science ,lcsh:Biotechnology ,Alloy ,TRIP steel ,lightweight steel ,chemistry.chemical_element ,engineering.material ,Corrosion ,Aluminium ,lcsh:TP248.13-248.65 ,lcsh:TA401-492 ,General Materials Science ,Ductility ,30.05 ,ordering ,30.04 ,Structural material ,Metallurgy ,Focus Articles ,Microstructure ,κ-carbide ,Deformation mechanism ,chemistry ,engineering ,lcsh:Materials of engineering and construction. Mechanics of materials ,TWIP steel ,planar glide - Abstract
Adding a large amount of light elements such as aluminum to steels is not a new concept recalling that several Fe–Al–Mn–C alloys were patented in 1950s for replacement of nickel or chromium in corrosion resistance steels. However, the so-called lightweight steels or low-density steels were revisited recently, which is driven by demands from the industry where steel has served as a major structural material. Strengthening without loss of ductility has been a triumph in steel research, but lowering the density of steel by mixing with light elements will be another prospect that may support the competitiveness against emerging alternatives such as magnesium alloys. In this paper, we review recent studies on lightweight steels, emphasizing the concept of alloy design for microstructures and mechanical properties. The influence of alloying elements on the phase constituents, mechanical properties and the change of density is critically reviewed. Deformation mechanisms of various lightweight steels are discussed as well. This paper provides a reason why the success of lightweight steels is strongly dependent on scientific achievements even though alloy development is closely related to industrial applications. Finally, we summarize some of the main directions for future investigations necessary for vitalizing this field of interest.
- Published
- 2013
15. ZnO nanocrystals synthesized by physical vapor deposition
- Author
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Hansoo Kim and Wolfgang M. Sigmund
- Subjects
Materials science ,Hot Temperature ,Manufactured Materials ,Surface Properties ,Biomedical Engineering ,Nanowire ,Molecular Conformation ,chemistry.chemical_element ,Bioengineering ,Zinc ,Catalysis ,Zno nanocrystals ,Vaporization ,Materials Testing ,Chemical Precipitation ,Nanotechnology ,General Materials Science ,Particle Size ,Wurtzite crystal structure ,Nanotubes ,Hybrid physical-chemical vapor deposition ,General Chemistry ,Condensed Matter Physics ,chemistry ,Chemical engineering ,Physical vapor deposition ,Gases ,Zinc Oxide ,Crystallization - Abstract
Various types of zinc oxide (ZnO) nanocrystais were synthesized by physical vaporization of zinc powders without the presence of catalysts and a subsequent exposure to air at a high temperature. These crystals were found to be composed of ZnO nanowires, sheets, and tetrapods. They were observed to crystallize as wurtzite ZnO single crystals. The nanowires are about 120 nm in diameter on average and up to a few dozens of micrometers in length, making aspect ratios higher than 10. The growth direction of the nanowires was identified to be the [001] direction of wurtzite ZnO structure. It was found from microscopic analyses that these ZnO nanowires can be highly flexible. The values for the thickness of ZnO sheets are scattered, averaging 100 nm. The tetrapods may have a different number of projections radiating from one central node.
- Published
- 2004
16. Non-quantum electronic responses of zinc oxide nanomaterials
- Author
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Younghyun Kim and Hansoo Kim
- Subjects
Materials science ,Condensed matter physics ,Oscillator strength ,Mechanical Engineering ,Exciton ,Nanowire ,Bioengineering ,Nanotechnology ,General Chemistry ,Dielectric ,Nanomaterials ,Condensed Matter::Materials Science ,Mechanics of Materials ,General Materials Science ,Electrical and Electronic Engineering ,Valence electron ,Plasmon ,Bohr radius - Abstract
The influence of the high surface-to-volume ratio of ZnO nanomaterials, whose sizes are large enough to exclude the quantum effect, on electronic properties was investigated by spatially resolved valence electron energy loss spectroscopy. ZnO nanowires, nanoplates, and nanotubes with different sizes were fabricated and characterized. Both the reduced volume and the increased surface area of the large ZnO nanomaterials were found to be able to modify electronic properties significantly. Hence, a nanoplate and a nanotube with very small volumes show unique energy loss functions and dielectric functions different from those of bulk ZnO at all the probe points. On the other hand, a nanowire with a relatively large diameter (70 nm) has electronic properties similar to those of bulk ZnO at the center. However, they are dissimilar at the edge of the nanowire due to the component of surface parallel to the electron path and the reduced interaction volume. Moreover, some interband transitions shift positions and bulk plasmons change oscillator strength depending upon the size of the volume and the geometry of the surface. These empirical results demonstrate that semiconducting nanomaterials larger than the exciton Bohr radius can still behave differently from bulk materials due to the high ratio between surface area and volume.
- Published
- 2013
17. Simple and fast annealing synthesis of titanium dioxide nanostructures and morphology transformation during annealing processes
- Author
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Yeontack Ryu, Jongbok Park, Hansoo Kim, and Choongho Yu
- Subjects
Hot Temperature ,Materials science ,Macromolecular Substances ,Surface Properties ,Annealing (metallurgy) ,Molecular Conformation ,Oxide ,chemistry.chemical_element ,Bioengineering ,Nanotechnology ,Catalysis ,chemistry.chemical_compound ,Hardness ,Materials Testing ,General Materials Science ,Particle Size ,Electrical and Electronic Engineering ,Eutectic system ,Titanium ,Mechanical Engineering ,General Chemistry ,Nanostructures ,chemistry ,Mechanics of Materials ,Rutile ,Titanium dioxide ,Melting point ,Crystallization - Abstract
Wire- and belt-like single-crystalline titanium dioxide nanostructures were synthesized by using a simple thermal annealing method, which has often been avoided for the synthesis of metal oxide nanostructures from high melting point metals such as Ti. The synthesis method requires neither high reaction temperature nor complicated reaction processes, and can be used for producing dense nanomaterials with relatively short reaction time at temperatures much lower than the melting point of titanium and titanium dioxide. Key synthesis factors including the choice of eutectic catalyst, growth temperature, and annealing time were systematically investigated. The synthesis reaction was promoted by a copper eutectic catalyst, producing long nanostructures with short reaction times. For example, it was observed that only 30 min of annealing time at 850 degrees C was enough to produce densely grown approximately 10 microm long nanowires with diameters of approximately 100 nm, and longer reaction time brought about morphology changes from wires to belts as well as producing longer nanostructures up to approximately 30 microm. The nanostructures have the crystalline rutile structure along the [Formula: see text] growth direction. Finally, our simple and effective method for the synthesis of TiO2 nanostructures could be utilized for growing other metal oxide nanowires from high melting temperature metals.
- Published
- 2009
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