• Clean Technology
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• v.29 no.3
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• pp.217-226
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• 2023

The amount of hydrogen adsorbed in arrays of single walled carbon nanotubes (SWNTs) was studied as a function of nanotube diameter and distance between the nearest-neighbor nanotubes on square arrangements using a grand canonical Monte Carlo simulation. The influence of the geometry of a triangle array with the same diameters and distances was also studied. Hydrogen-carbon and hydrogen-hydrogen interactions were modeled with Lennard-Jones potentials for short range interactions and electrostatic interactions were added for hydrogen-hydrogen pairs to consider quantum contributions at low temperatures. At 194.5 K, Type I isotherms for large-diameter SWNTs and Type IV isotherms without hysteresis between adsorption and desorption processes for wider tube separations were observed. At 200 bars, the gravimetric hydrogen storage capacity of the SWNTs was reached or exceeded the US Department of Energy (DOE) target, but the volumetric capacity was about 70% of the DOE target. At 77 K, a two-step adsorption was observed, corresponding to a monolayer formation step followed by a condensation step. Hydrogen was adsorbed first to the inner surface of the nanotubes, then to the outer surface, intratubular space and the interstitial channels between the nanotube bundles. The simulation indicated that SWNTs of various diameters and distances in a wide range of configurations exceeded the DOE gravimetric and volumetric targets at under 1 bar.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1B
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• pp.1-9
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• 2009

This study is focused on the analysis of loop characteristics of stage-discharge relation which is widely used for the production of discharge data and the simulation of loop stage-discharge relation using the numerical model. Analysis of consecutive stage and discharge data at 3 points revealed that loop of stage-discharge relationship is very strong. This means that the existing single stage-discharge relation may include large amount of error. Various flood events are simulated in mainstream of Han river with one-dimensional numerical model. The calculated stage data are compared with measured data. Especially continuous field-flow measurements concurrently collected with an Acoustic Doppler Velocity Meter (ADVM) on Hangang bridge in the case of 2007 flood event are used to verify the model applicability of estimating flows in open channels. This comparison shows that numerical model is an accurate and reliable alternative for making the real stage-discharge relation. Simulation of stage-discharge relation by a numerical model at Paldang and Hangang bridge showed good agreements with measured one, so it may be possible to generate real loop stage-discharge relation with properly calibrated and verified numerical model. It can be concluded that results of this study can contribute to error analysis of conventional single stage-discharge relation and development of loop stage-discharge relation with numerical model.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.6
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• pp.255-260
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• 2023

As demanding the detection of explosive molecules, it is required to develop rapidly and precisely responsive sensors with ultra-high sensitivity. Since two-dimensional semiconductors have an atomically thin body nature where mobile carriers accumulate, the abrupt modulation carrier in the thin body channel can be expected. To investigate the effectiveness of WSe₂ semiconductor materials as a detection material for TNT (Trinitrotoluene) explosives, WSe₂ was synthesized using thermal chemical vapor deposition, and afterward, WSe₂ FETs (Field Effect Transistors) were fabricated using standard photo-lithograph processes. Raman Spectrum and FT-IR (Fourier-transform infrared) spectroscopy reveal that the adsorption of TNT molecules induces the structural transition of WSe₂ crystalline. The electrical properties before and after adsorption of TNT molecules on the WSe₂ surface were compared; as -50 V was applied as the back gate bias, 0.02 μA was recorded in the bare state, and the drain current increased to 0.41 μA with a dropping 0.6% (w/v) TNT while maintaining the p-type behavior. Afterward, the electrical characteristics were additionally evaluated by comparing the carrier mobility, hysteresis, and on/off ratio. Consequently, the present report provides the milestone for developing ultra-sensitive sensors with rapid response and high precision.

• Industry Promotion Research
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• v.9 no.1
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• pp.31-38
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• 2024

In this study, evaluated the properties of layered silicate-based nanocomposite sensitive film. For the fabrication of nanocomposite materials, we selected organically modified layered silicate materials, specifically Cloisite^® and Bentone^®, which were treated with quaternary ammonium salts. The impedance of the humidity sensors containing organically modified montmorillonite/hectorite clay decreased with increasing relative humidity(RH%). In the case of the Cloisite^® humidity sensor exhibited slightly better impedance linearity and hysteresis compared to the Bentone^® 38 humidity sensor. Additionally the impedance of the sensor with Bentone^® 38 addition was the lowest when compared to the Cloisite^®-modified sensor. Comparing the Cloisite^®-modified sensors individually, we observed different moisture absorption characteristics based on the hydrophilic properties of the organic-treated materials. The response speed of Cloisite^® 93A tended to be slower due to differences in moisture evaporation rates influenced by the hydrophilic organic components. Based on these results, moisture barriers utilizing organically modified layered silicate materials may exhibit slightly lower moisture absorption properties compared to conventional polymer-based moisture barriers. However, their excellent stability, simple processing, and cost-effectiveness make them suitable for humidity sensor applications.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.1
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• pp.29-37
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• 1999

In this study, we have prepared PLT thin films having various La concentrations by using sol-gel method and studied on the effect of La concentration on the electrical properties of PLT thin films. As the La concentration increases from 5mol% to 28mol%, the dielectric constant at 10kHz increases from 428 to 761, while the loss tangent decreases from 0.063 to 0.024. Also, the leakage current density at 150kV/cm has a tendency to decrease from 6.96${\mu}A/cm^2$ to 0.79${\mu}A/cm^2$. In the result of hysteresis loops of PLT thin films, the remanent polariation and the coercive field decrease from 9.55${\mu}C/cm^2$ to 1.10${\mu}C/cm^2$ and from 46.4kV/cm to 13.7kV/cm, respectively. With the result of the fatigue test on the PLT thin films, we have found that the fatigue properties are improved remarkably as the La concentration increases from 5 mol% to 28mol%. In particular, the PLT28) has paraelectric phase and its charge storage clensity and leakage current density at 5V are 134fC/${\mu}cm^2$ and 1.01${\mu}A/cm^2$, respectively. The remanent polarization and coercive field of the PLT(10) film are 6.96${\mu}C/cm^2$ and 40.2kV/cm, respectively. After applying of $10^9$ square pulses with ${\pm}5V$, the remanent polarilzation of the PLT(10) film decreases about 20% from the initial state. In the results, we conclude that the 10mol% and the 28mol% La doped PLT thin films are very suitable for the capacitor dielectrics of new generation of DRAM and NVFRAM respecitively.

• Korean Journal of Heritage: History & Science
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• v.46 no.2
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• pp.186-205
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• 2013

${\ll}$Three Purities Album${\gg}$ in the Kansong Art Museum is an album of poems and pictures of apricot tree, orchids and bamboos drawn by Lee Jeong. Given that the poems and pictures in the album were drawn by Lee Jeong who has been recognized as a person who established the standards of ink bamboo drawings in the Joseon Dynasty, the album is highly valuable. Nevertheless, there are more values and meanings that Three Purities Album has. The production circumstances and transmission processes of Three Purities Album include the historical characteristics and meanings of the time so that it is also worthwhile as a historical material. During the Japanese Invasion of Korea in 1592, Lee Jeong was stabbed with a sword by Japanese invaders and got injured. After he suffered, he tried to make his masterpiece in his lifework and finally created Three Purities Album. For the work, Lee Jeong received memorial writings from Choi Rip, Cha Cheon-ro and Han Ho, and asked them writings. They were the best literary men in the poem and calligraphy fields at that time. Yu Geun, Lee An-nul, and Yu Mong-in made writings and poems to praise his work. Likewise, ${\ll}$Three Purities Album${\gg}$ is the 'treasure of the time' created through the participation of the best literary men at that time. Given the aspects, it is fair to say that ${\ll}$Three Purities Album${\gg}$ is not simply a personal artwork of Lee Jeong, but is a comprehensive artwork and also a cultural monument created through the skills and capabilities of the literary artists in the middle of the Joseon Dynasty. After the death of Lee Jeong, Three Purities Album was handed over to Hong Ju-won. But, during the second Manchu Invasion into Korea in 1636, the album was in danger of disappearance by fire. As of now, there are still signs of fire in it, which vividly shows the urgent situation at that time. After the second Manchu Invasion into Korea in 1636, Hong Ju-won recovered some damaged writings with the help of Yoon Shin-ji. Since then, the album had been handed down as a family treasure over the next 7 generations. It can be found in the writings by Song Si-yeol and Uh Yu-bong. Unlike the literary men who praised Three Purities Album in terms of its work when Lee Joeng was alive, they focused on the transmission courses of the album and involved persons. That seems to be because the stories and characters appearing in Three Purities Album impressed the later literary men and were meaningful to them rather than the album itself. It strongly reflected the positions of Hong Jung-gi and Hung Sang-han who asked for writings as the descendants of Hong Ju-won. That is because the traces of the persons involved in Three Purities Album are the causes for admiring their ancestors and enhancing their political legitimacy and family dignity. Therefore, in this aspect, it is possible to witness the fundamental causes of the unique artistic awareness by East Asian people who consider their historical meanings as well as the aesthetic value of artworks significant. Unfortunately, during the Japanese invasion at the end of the Joseon Dynasty, Three Purities Album was handed over to Japanese Tzuboikouso. But, fortunately, Jeon Hyeong-pil who made an effort to regain our cultural assets by investing his entire property during the Japanese Imperialism regained the album, which is now preserved in the Kansong Art Museum. ${\ll}$Three Purities Album${\gg}$ truly includes the whole processes to overcome national crises that Korean people experienced during the Japanese Invasion in 1592, the second Manchu Invasion of Korea in 1636, and the Japanese Imperialism, and it shows the sufferings of our cultural assets and the history of preservation. Also, the album shows that one artwork is able to accumulate its historical meanings in the process of transmission and thus enhances its meanings and values. ${\ll}$Three Purities Album${\gg}$ features accumulative and constant historical meanings and it is a typical case showing that an artwork is plenty of aesthetic and historical values. It is expected that this work will contribute to promoting more studies on finding historical meanings and hysteresis of artworks.