• Applied Chemistry for Engineering
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• v.29 no.5
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• pp.533-540
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• 2018

Graphene has been reported to be an excellent lubricant additive that reduces friction and wear when coated on the surface of various materials or when dispersed in lubricants as an atomic thin material with the low surface energy. In this study, alkyl functionalized graphene oxide (FGO) nanosheets for oil-based lubricant additives were prepared by using three types of alkyl chloride chemicals (butyl chloride, octyl chloride, and tetradecyl chloride). The chemical and structural properties of the synthesized FGOs were analyzed by Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), and transmission electron microscope (TEM). The synthesized FGOs were dispersed at 0.02 wt% in PAO-0W40 oil and its tribological characteristics were investigated using a high frequency friction/wear tester. The friction coefficient and the wear track width of poly alpha olefin (PAO) oil added with FGO-14 were tested by a ball-on-disk method, and the measured results were reduced by ~5.88 and ~3.8%, respectively compared with those of the conventional PAO oil. Thus, it was found that the wear resistance of PAO oil was improved. In this study, we demonstrated the successful functionalization of GO as well as the improvement of dispersion stability and tribological characteristics of FGOs based on various alkyl chain lengths.

• Economic and Environmental Geology
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• v.31 no.3
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• pp.215-222
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• 1998

The radon (Rn-222) potential of metropolitan subway stations and soils in Seoul city were delineated using alpha-track filter and EDA-200 radon detectors, respectively. The uranium (U) and thorium (Th) contents were also determined using a Multi Channel Analyzer to identify the sources of radon gas. The average U concentrations in Seoul varies according to basement rock types. For example, there is $9.40{\pm}10.11ppm$ in the Precambrian metasedimentary rock (PM), $9.08{\pm}2.85ppm$ in the Jurassic Kwanaksan granite (JK) and $4.94{\pm}1.43ppm$ in the Jurassic Seoul granite (JS). Uranium contents in soil samples are $10.30{\pm}4.74ppm$ in JK, $10.10{\pm}7.43ppm$ in PM and $6.69{\pm}3.95ppm$ in JS and these closely reflect the content of uraniferous minerals. The levels of soil radon are $604{\pm}273pCi/L$ in JK, $502{\pm}275$ in JS and $262{\pm}211pCi/L$ in PM. The soil radon concentrations are shown to reflect soil permeability and porosity rather than their U contents. The mean indoor radon contents in subway stations are $1.50{\pm}0.62pCi/L$ on the 4th line, $1.41{\pm}0.95pCi/L$ on the 3rd line, $0.84{\pm}0.13pCi/L$ on the 1st line and $0.80{\pm}0.25pCi/L$ on the 2nd line. The subway stations located in the JK have the highest average radon concentration with $2.04{\pm}0.65pCi/L$, where levels of $1.57{\pm}0.81pCi/L$ occur in the JS and $0.80{\pm}0.23pCi/L$ in the PM. The highest radon levels of 4.1 pCi/L occur mainly in Keongbokkung station on the 3rd line and these exceed 4 pCi/L of the US EPA action level.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.5-5
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• 2011

The research and development of hybrid electric vehicle (HEV), plug-in hybrid electric vehicle (PHEV) and electric vehicle (EV) are intensified due to the energy crisis and environmental concerns. In order to meet the challenging requirements of powering HEV, PHEV and EV, the current lithium battery technology needs to be significantly improved in terms of the cost, safety, power and energy density, as well as the calendar and cycle life. One new technology being developed is the utilization of composite cathode by mixing two different types of insertion compounds [e.g., spinel $LiMn_2O_4$ and layered $LiMO_2$ (M=Ni, Co, and Mn)]. Recently, some studies on mixing two different types of cathode materials to make a composite cathode have been reported, which were aimed at reducing cost and improving self-discharge. Numata et al. reported that when stored in a sealed can together with electrolyte at $80^{\circ}C$ for 10 days, the concentrations of both HF and $Mn^{2+}$ were lower in the can containing $LiMn_2O_4$ blended with $LiNi_{0.8}Co_{0.2}O_2$ than that containing $LiMn_2O_4$ only. That reports clearly showed that this blending technique can prevent the decline in capacity caused by cycling or storage at elevated temperatures. However, not much work has been reported on the charge-discharge characteristics and related structural phase transitions for these composite cathodes. In this presentation, we will report our in situ x-ray diffraction studies on this mixed composite cathode material during charge-discharge cycling. The mixed cathodes were incorporated into in situ XRD cells with a Li foil anode, a Celgard separator, and a 1M $LiPF_6$ electrolyte in a 1 : 1 EC : DMC solvent (LP 30 from EM Industries, Inc.). For in situ XRD cell, Mylar windows were used as has been described in detail elsewhere. All of these in situ XRD spectra were collected on beam line X18A at National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory using two different detectors. One is a conventional scintillation detector with data collection at 0.02 degree in two theta angle for each step. The other is a wide angle position sensitive detector (PSD). The wavelengths used were 1.1950 ${\AA}$ for the scintillation detector and 0.9999 A for the PSD. The newly installed PSD at beam line X18A of NSLS can collect XRD patterns as short as a few minutes covering $90^{\circ}$ of two theta angles simultaneously with good signal to noise ratio. It significantly reduced the data collection time for each scan, giving us a great advantage in studying the phase transition in real time. The two theta angles of all the XRD spectra presented in this paper have been recalculated and converted to corresponding angles for ${\lambda}=1.54\;{\AA}$, which is the wavelength of conventional x-ray tube source with Cu-$k{\alpha}$ radiation, for easy comparison with data in other literatures. The structural changes of the composite cathode made by mixing spinel $LiMn_2O_4$ and layered $Li-Ni_{1/3}Co_{1/3}Mn_{1/3}O_2$ in 1 : 1 wt% in both Li-half and Li-ion cells during charge/discharge are studied by in situ XRD. During the first charge up to ~5.2 V vs. $Li/Li^+$, the in situ XRD spectra for the composite cathode in the Li-half cell track the structural changes of each component. At the early stage of charge, the lithium extraction takes place in the $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component only. When the cell voltage reaches at ~4.0 V vs. $Li/Li^+$, lithium extraction from the spinel $LiMn_2O_4$ component starts and becomes the major contributor for the cell capacity due to the higher rate capability of $LiMn_2O_4$. When the voltage passed 4.3 V, the major structural changes are from the $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component, while the $LiMn_2O_4$ component is almost unchanged. In the Li-ion cell using a MCMB anode and a composite cathode cycled between 2.5 V and 4.2 V, the structural changes are dominated by the spinel $LiMn_2O_4$ component, with much less changes in the layered $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component, comparing with the Li-half cell results. These results give us valuable information about the structural changes relating to the contributions of each individual component to the cell capacity at certain charge/discharge state, which are helpful in designing and optimizing the composite cathode using spinel- and layered-type materials for Li-ion battery research. More detailed discussion will be presented at the meeting.

• Journal of Life Science
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• v.28 no.5
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• pp.621-626
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• 2018

We introduced the physiological responses of aging, active aging and also suggest the impact of physical exercise on body health status and elderly immunity. In this purpose, we searched the Pub Med data base for the articles (include our experimental papers) and review papers having the terms 'Aging', 'Active aging' and 'Physical activity and elderly' in the title, published from 1999 until 2018. The results were as follows: Exercise training has been extensively studied about the reduction of inflammation, oxidative stress, disease, and aging in syndrome X patients and elderly. Combined and aerobic or resistance exercise training could reduce obesity, insulin resistance, type 2 diabetes and hypertension. Exercise training has been extensively studied in cancer settings as part of prevention or treatment strategies. From this research, regular exercise has the potential to target tumor growth through regulation of inflammation and immune responses such as lactate clearance, NK cell activation (innate immunity), activation of cytotoxic immune cells, T cell activation (adaptive immunity), and immune surveillance. However, Endurance physical activity not only induces thermogenesis and diverse sports injuries but also elicits mobilization and functional enhancement of monocytes, neutrophils (which is caused by the cytokine changes such as TNF-alpha, IL-1) whereas it suppresses cell mediated immunity causing to increased susceptibility to inflammation and infections like cough and URTIs (upper respiratory track infections) in young and especially in elderly people. Therefore, Strategies to prevent physical fatigue, sports injuries include avoid overtraining, Adequate recovery and various type of rest during and after physical activity and assuring adequate nutrition supplementation such as glutamine, vitamin B, vitamin C, carbohydrate, ion or berry-contain sports beverages is helpful in physically active elderly.

• The Journal of Korean Academy of Prosthodontics
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• v.57 no.2
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• pp.110-117
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• 2019

Purpose: This study was to evaluate the wear resistance of 3D printed, milled, and conventionally cured provisional resin materials. Materials and methods: Four types of resin materials made with different methods were examined: Stereolithography apparatus (SLA) 3D printed resin (S3P), digital light processing (DLP) 3D printed resin (D3P), milled resin (MIL), conventionally self-cured resin (CON). In the 3D printed resin specimens, the build orientation and layer thickness were set to $0^{\circ}$ and $100{\mu}m$, respectively. The specimens were tested in a 2-axis chewing simulator with the steatite as the antagonist under thermocycling condition (5 kg, 30,000 cycles, 0.8 Hz, $5^{\circ}C/55^{\circ}C$). Wear losses of the specimens were calculated using CAD software and scanning electron microscope (SEM) was used to investigate wear surface of the specimens. Statistical significance was determined using One-way ANOVA and Dunnett T3 analysis (${\alpha}=.05$). Results: Wear losses of the S3P, D3P, and MIL groups significantly smaller than those of the CON group (P < .05). There was no significant difference among S3P, D3P, and MIL group (P > .05). In the SEM observations, in the S3P and D3P groups, vertical cracks were observed in the sliding direction of the antagonist. In the MIL group, there was an overall uniform wear surface, whereas in the CON group, a distinct wear track and numerous bubbles were observed. Conclusion: Within the limits of this study, provisional resin materials made with 3D printing show adequate wear resistance for applications in dentistry.