• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.174-174
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• 2014

Memristor devices are one of the most promising candidate approaches to next-generation memory technologies. Memristive switching phenomena usually rely on repeated electrical resistive switching between non-volatile resistance states in an active material under the application of an electrical stimulus, such as a voltage or current. Recent reports have explored the use of variety of external operating parameters, such as the modulation of an applied magnetic field, temperature, or illumination conditions to activate changes in the memristive switching behaviors. Among these possible choices of signal controlling factors of memristor, photon is particularly attractive because photonic signals are not only easier to reach directly over long distances than electrical signal, but they also efficiently manage the interactions between logic devices without any signal interference. Furthermore, due to the inherent wave characteristics of photons, the facile manipulation of the light ray enables incident light angle controlled memristive switching. So that, in the tautological sense, device orienting position with regard to a photon source determines the occurrence of memristive switching as well. To demonstrate this position controlled memory device functionality, we have fabricated a metal-semiconductor-metal memristive switching nanodevice using ZnO nanorods. Superhydrophobicity employed in this memristor gives rise to illumination direction selectivity as an extra controlling parameter which is important feature in emerging. When light irradiates from a point source in water to the surface treated device, refraction of light ray takes place at the water/air interface because of the optical density differences in two media (water/air). When incident light travels through a higher refractive index medium (water; n=1.33) to lower one (air; n=1), a total reflection occurs for incidence angles over the critical value. Thus, when we watch the submerged NW arrays at the view angles over the critical angle, a mirror-like surface is observed due to the presence of air pocket layer. From this processes, the reversible switching characteristics were verified by modulating the light incident angle between the resistor and memristor.

• 한국인터넷방송통신학회논문지
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• 제15권6호
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• pp.181-186
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• 2015

최근 통신 빛 반도체 기술의 급격한 발전과 함께 소규모 기기에도 컴퓨팅 기능을 탑재하는 사물인터넷 시장이 부상하고 있다. 사물인터넷을 위한 저장장치는 전력소모와 물리적 크기에 제한이 있어 기존 HDD나 SSD 대신 NVRAM 기반의 스토리지가 사용될 것으로 전망되고 있다. 그러나 현재 사물인터넷 플랫폼 기술은 기존의 전통적인 스토리지를 타겟으로 설계되어 NVRAM 스토리지에서는 다양한 비효율성을 초래할 수 있다. 본 논문은 현재의 다양한 운영체제의 I/O 기법들의 효용성과 성능을 NVRAM 스토리지 환경에서 평가하고 분석하여 향후 사물인터넷을 위한 스토리지 기술에 대해 방향성을 제시한다.

• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2002년도 생물공학의 동향 (X)
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• pp.257-260
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• 2002

Dissolved oxygen level of cell culture media has a critical effect on cellular metabolism, which governs specific productivity of recombinant proteins and mammalian cell growth However, in the cores of cell aggregates or cell-immobilized beads, oxygen level frequently goes below a critical level. Mammalian cells have a number of genes induced in the lower level of oxygen, and the genes contain a common cis-acting element (-RCGTG-), hypoxia response element (HRE). By binding of hypoxia inducible factor-l (HIF-I) to the HRE, promoters of hypoxia inducible genes are activated, which is a survival mechanism. In this work, to develop a CHO cell capable of producing recombinant proteins in immobilization and high density cell culture efficiently, mammalian expression vectors containing human tissue-type plasminogen activator (t-PA) gene controlled by HRE were constructed and stably transfected into the CHO cells. In $Ba^{2+}$ -alginate immobilization culture, CHO/pCl/dhfr/2HRE-t-PA cells produced 2 folds higher recombinant t-PA activity than CHO/pCl/dhfrlt-PA cells without $CoCl_2$ treatment. Furthermore, in repeated fed batch culture, productivity of t-PA in immobilized CHO/pCI/dhfr/2HRE-t-PA cells was 121 ng/ml/day, total production of 0.968 mg/day at 11 days culture while CHO/pCIIdhfrlt-PA cells was 22.8 ng/ml/day. All these results indicate that HRE is very useful for the enhancement of protein productivity in mammalian cell cultures.

• Nuclear Engineering and Technology
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• 제52권11호
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• pp.2471-2478
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• 2020

Pumps are essential machinery in the various industries. With the development of high-speed and large-scale pumps, especially high energy density, high requirements have been imposed on the vibration and noise performance of pumps, and cavitation is an important source of vibration and noise excitation in pumps, so it is necessary to improve pumps cavitation performance. The modern pump optimization design method mainly adopts parameterization and artificial intelligence coupling optimization, which requires direct correlation between geometric parameters and pump performance. The existing cavitation performance calculation method is difficult to be integrated into multi-objective automatic coupling optimization. Therefore, a fast prediction method for pump cavitation performance is urgently needed. This paper proposes a novel cavitation prediction method based on impeller pressure isosurface at single-phase media. When the cavitation occurs, the area of pressure isosurface S_iso increases linearly with the NPSH_a decrease. This demonstrates that with the development of cavitation, the variation law of the head with the NPSH_a and the variation law of the head with the area of pressure isosurface are consistent. Therefore, the area of pressure isosurface S_iso can be used to predict cavitation performance. For a certain impeller blade, since the area ratio R_s is proportional to the area of pressure isosurface S_iso, the cavitation performance can be predicted by the R_s. In this paper, a new cavitation performance prediction method is proposed, and the feasibility of this method is demonstrated in combination with experiments, which will greatly accelerate the pump hydraulic optimization design.

• 한국물환경학회지
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• 제33권5호
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• pp.538-545
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• 2017

The purpose of this study is to investigate growth response and toxigenicity under various temperature and nutritional conditions, in order to understand the physioecological characteristics of Aphanizomenon flos-aquae, which is a bloom-forming cyanobacterium in the Nakdong River. The strain was inoculated into media under combinations of four temperatures (4, 12, 21, $30^{\circ}C$) and three nutrients (modified CB medium, P-depleted CB medium, N-depleted CB medium) for 28 days. The algae-inhibition tests were performed to assess the potential allelopathic effects of the strains' filtrates on the growth of four algae strains (Microcystis aeruginosa, Aulacoseria ambigua f. spiralis, Aphanizomenon flos-aquae, Scenedesmus obliquus). Toxin production of a strain was measured by Enzyme-Linked ImmunoSolbent Assay (ELISA). The optimal growth temperature (Topt) of strains was $19.9^{\circ}C$ ($18.3-21.2^{\circ}C$), and the temperature range for growth was from $-0.3^{\circ}C$ to $34.3^{\circ}C$. Specific growth rate (${\mu}$) in modified CB medium varied from 0.10 to $0.16day^{-1}$, and the maximum growth rate (${\mu}_{max}$) was $0.17day^{-1}$. Although growth curves under N-existed and N-depleted conditions were almost the same, growth under N-depleted condition was relatively slowed (${\mu}=0.09$ to $0.14day^{-1}$), with a decreased maximum cell density. However, growth under the P-depleted condition was restricted for all temperatures, Two stains of Aphanizomenon flos-aquae were confirmed as not producing toxins, because saxitoxin and cylindrospermopsin were not detected by ELISA. The exudates or filtrates from the Aphanizomenon flos-aquae (DGUC003) resulted in significant inhibition of algal growth on the Aulacoseira ambigua f. spiralis (DGUD001) and Aphanizomenon flos-aquae (DGUC001) (p < 0.01).

• Journal of Microbiology and Biotechnology
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• 제18권11호
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• pp.1762-1767
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• 2008

Image contrast of whole bacteria was compared in Staphylococcus aureus and Escherichia coli depending on pre-stain suspension liquids by energy-filtering transmission electron microscopy. The two bacterial strains were suspended in three most commonly used liquids for negative staining (triple distilled water [DW], phosphate-buffered saline [PBS], and nutrient broth [NB]) and directly observed without staining or stained with neutralized potassium phosphotungstate (PTA), respectively. Even though in low contrast, unstained bacteria were observed owing to their inherent electron density and cell shape in zero-loss (elastic scattering) images. After being suspended in PBS, unstained bacteria appeared to have higher contrast and more refined periphery than DW-suspended ones, and extracellular appendage structures such as fimbriae and flagella could be discerned. The unstained bacteria appeared to be invariably surrounded with electron-lucent precipitates, possibly from PBS. As far as delineation of the structures, the combination of DW or PBS suspension with subsequent staining provided the most satisfactory results, as evidenced by the high contrast of bacterial morphology and appendage structures. However, after being suspended in NB and stained with PTA, bacteria often had too high contrast or poor staining, with electron-dense aggregates around the bacteria. These results suggest that suspension with concentrated organic aliquots including broth media before PTA staining could deteriorate image contrast, and should be used only in dilute form for visualizing bacterial morphology and appendage structures. Moreover the contrast enhancement of unstained bacteria by salt granules would be advantageous in demonstrating bacterial sorption of environmental particles like heavy metals, maintaining minimal contrast for cell imaging.

• Restorative Dentistry and Endodontics
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• 제43권3호
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• pp.24.1-24.12
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• 2018

Objectives: The aim of this in vitro study was to evaluate the biocompatibility of newly proposed root-end filling materials, Biodentine, Micro-Mega mineral trioxide aggregate (MM-MTA), polymethylmethacrylate (PMMA) bone cement, and Smart Dentin Replacement (SDR), in comparison with contemporary root-end filling materials, intermediate restorative material (IRM), Dyract compomer, ProRoot MTA (PMTA), and Vitrebond, using human periodontal ligament (hPDL) fibroblasts. Materials and Methods: Ten discs from each material were fabricated in sterile Teflon molds and 24-hour eluates were obtained from each root-end filling material in cell culture media after 1- or 3-day setting. hPDL fibroblasts were plated at a density of $5{\times}10^3/well$, and were incubated for 24 hours with 1:1, 1:2, 1:4, and 1:8 dilutions of eluates. Cell viability was evaluated by XTT assay. Data was statistically analysed. Apoptotic/necrotic activity of PDL cells exposed to material eluates was established by flow cytometry. Results: The Vitrebond and IRM were significantly more cytotoxic than the other root-end filling materials (p < 0.05). Those cells exposed to the Biodentine and Dyract compomer eluates showed the highest survival rates (p < 0.05), while the PMTA, MM-MTA, SDR, and PMMA groups exhibited similar cell viabilities. Three-day samples were more cytotoxic than 1-day samples (p < 0.05). Eluates from the cements at 1:1 dilution were significantly more cytotoxic (p < 0.05). Vitrebond induced cell necrosis as indicated by flow cytometry. Conclusions: This in vitro study demonstrated that Biodentine and Compomer were more biocompatible than the other root-end filling materials. Vitrebond eluate caused necrotic cell death.

• 한국초전도ㆍ저온공학회논문지
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• 제16권1호
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• pp.36-41
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• 2014

Since glass microsphere has high crush strength, low density and small particle size, it becomes alternative thermal insulation material for cryogenic systems, such as storage and transportation tank for cryogenic fluids. Although many experiments have been performed to verify the effective thermal conductivity of microsphere, prediction by calculation is still inaccurate due to the complicated geometries, including wide range of powder diameter distribution and different pore sizes. The accurate effective thermal conductivity model for microsphere is discussed in this paper. There are four mechanisms which contribute to the heat transfer of the evacuated powder: gaseous conduction ($k_g$), solid conduction ($k_s$), radiation ($k_r$) and thermal contact ($k_c$). Among these components, $k_g$ and $k_s$ were calculated by Zehner and Schlunder model (1970). Other component values for $k_c$ and $k_r$, which were obtained from experimental data under high vacuum conditions were added. In this research paper, the geometry of microsphere was simplified as a homogeneous solid sphere. The calculation results were compared with previous experimental data by R. Wawryk (1988), H. S. Kim (2010) and the experiment of this paper to show good agreement within error of 46%, 4.6% and 17 % for each result.

• 한국세라믹학회지
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• 제48권5호
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• pp.418-425
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• 2011

In this study, a high energy ball milling process was introduced in order to improve the densification of direct nitrided AlN powder. The sintering behavior and thermal conductivity of the AlN milled powder was investigated. The mixture of AlN powder and 5 wt% $Y_2O_3$ as a sintering additive was pulverized and dispersed by a bead mill with very small $ZrO_2$ bead media. The milled powders were sintered at $1700^{\circ}C-1800^{\circ}C$ for 4 h under $N_2$ atmosphere. The results showed that the sintered density was enhanced with increasing milling time due to the particle refinement as well as the increase in oxygen contents. Appropriate milling time was effective for the improvement of thermal conductivity, but the extensive millied powder formed more fractions of secondary phase during sintering, resulted in the decrease in thermal conductivity. The AlN powder milled for 10min after sintering at $1800^{\circ}C$ revealed the highest thermal conductivity, of 164W/$m{\cdot}K$ in tne densified AlN sintered at $1800^{\circ}C$.

• 운동영양학회지
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• 제23권4호
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• pp.14-22
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• 2019

[Purpose] Here, we aimed to determine the effect of Polygonum cuspidatum stem extract (PSE) on exorbital lacrimal gland-excised rat models and hyperosmotic stress-stimulated human conjunctival cells (HCCs). [Methods] Seven week old male Wistar rats were divided into six groups. Only the rats in the control group (NOR, n=5) did not undergo surgery. Three days after the surgery, the exorbital lacrimal gland-excised rats were randomly allocated to five groups: (1) vehicle-treated dry-eyed rats (DED, n=5); (2) PSE (10 mg/kg) treated DED rats (PSE-10, n=5); (3) PSE (100 mg/kg) treated DED rats (PSE-100, n=5); and (4) PSE (250 mg/kg) treated DED rats (PSE-250, n=5). In addition, the HCC line was co-treated with hyperosmolar media (528 mOsm) and PSE (1-100 μg/ml). [Results] PSE treatment restored the tear volume and goblet cell density by inhibiting severe corneal irregularities and damage. The treatment with PSE significantly attenuated the hyperosmolar stress-induced inflammation and cell death through the suppression of mRNA expression levels of Tumor necrosis factor-α (TNF-α), Interleukin-6 (IL-6), Interleukin-1β (IL-1β), and Interferon-γ (IFN-γ), and the expression of Bcl-2-associated X protein (Bax) as well as the activation of caspase-3 in vitro. [Conclusion] The inhibitory effects of PSE treatment on dry eye disease indicate the potential of nutritional intervention by PES against inflammatory diseases without adverse effects.