• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.02a
• /
• pp.196-196
• /
• 2012

Graphene, two-dimensional one-atom-thick planar sheet of carbon atoms densely packed in a honeycomb crystal lattice, has grabbled appreciable attention due to its extraordinary mechanical, thermal, electrical, and optical properties. Based on the graphene's high carrier mobility, high frequency graphene field effect transistors have been developed. Graphene is useful for photonic components as well as for the applications in electronic devices. Graphene's unique optical properties allowed us to develop ultra wide-bandwidth optical modulator, photo-detector, and broadband polarizer. Graphene can support SPP-like surface wave because it is considered as a two-dimensional metal-like systems. The SPPs are associated with the coupling between collective oscillation of free electrons in the metal and electromagnetic waves. The charged free carriers in the graphene contribute to support the surface waves at the graphene-dielectric interface by coupling to the electromagnetic wave. In addition, graphene can control the surface waves because its charge carrier density is tunable by means of a chemical doping method, varying the Fermi level by applying gate bias voltage, and/or applying magnetic field. As an extended application of graphene in photonics, we investigated the characteristics of the graphene-based plasmonic waveguide for optical signal transmission. The graphene strips embedded in a dielectric are served as a high-frequency optical signal guiding medium. The TM polarization wave is transmitted 6 mm-long graphene waveguide with the averaged extinction ratio of 19 dB at the telecom wavelength of $1.31{\mu}m$. 2.5 Gbps data transmission was successfully accomplished with the graphene waveguide. Based on these experimental results, we concluded that the graphene-based plasmonic waveguide can be exploited further for development of next-generation integrated photonic circuits on a chip.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.391-392
• /
• 2012

Graphene is a perfectly two-dimensional (2D) atomic crystal which consists of sp2 bonded carbon atoms like a honeycomb lattice. With its unique structure, graphene provides outstanding electrical, mechanical, and optical properties, thus enabling wide variety of applications including a strong potential to extend the technology beyond the conventional Si based electronic materials. Currently, the widespread application for electrostatically switchable devices is limited by its characteristic of zero-energy gap and complex process in its synthesis. Several groups have investigated nanoribbon, strained, or nanomeshed graphenes to induce a band gap. Among various techniques to synthesize graphene, chemical vapor deposition (CVD) is suited to make relatively large scale growth of graphene layers. Direct growth of graphene on hexagonal boron nitride (h-BN) using CVD has gained much attention as the atomically smooth surface, relatively small lattice mismatch (~1.7％) of h-BN provides good quality graphene with high mobility. In addition, induced band gap of graphene on h-BN has been demonstrated to a meaningful value about ~0.5 eV.[1] In this paper, we report the synthesis of grpahene / h-BN bilayer in a chemical vapor deposition (CVD) process by controlling the gas flux ratio and deposition rate with temperature. The h-BN (99.99％) substrate, pure Ar as carrier gas, and $CH_4$ are used to grow graphene. The number of graphene layer grown on the h-BN tends to be proportional to growth time and $CH_4$ gas flow rate. Epitaxially grown graphene on h-BN are characterized by scanning electron microscopy, atomic force microscopy, and Raman spectroscopy.

• The Journal of Internal Korean Medicine
• /
• v.26 no.3
• /
• pp.626-633
• /
• 2005

As age distributions of developed countries grow increasingly top-heavy with elderly, instances of bronchiectasis and pneumonia increase. An elderly patient was diagnosed with pneumonia by radiational examination, which showed pound glass opacity in the right middle lobe. Also, he was diagnosed with bronchiectasis in the honeycomb-like recticular area of the right lower lobe. He said that he was suffering from a cough, phlegm and general weakness. He was treated by oriental medicine treatment exclusively, through herbal medicine and acupuncture therapy. Yukmijihwabg-Tang(六味地黃湯), Gamijinhae-Tang(加味鎭咳湯), and Samchulbobi-Tang(參朮補脾湯) As a result, symptoms of cough phlegm and general weakness improved considerably. These results suggest that oriental medicine treatment is effective in improving quality of life fer chronic respiratory patients.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
• /
• v.10 no.4
• /
• pp.15-24
• /
• 2014

This study conducted a computational fluid dynamics(CFD) analysis to find an appropriate diameter or sectional area of air ducts and fluid pipes which have an electromagnetic pulse(EMP) shied to protect indoor electronic devices in special buildings like military fortifications. The result shows that the optimized outdoor air intake size can be defined with either the ratio of the maximum air velocity in the supply duct to the air intake size, or the shape ratio of indoor supply diffuser to the outdoor air intake. In the case of water channel, the fluid velocity at EMP shield with the identical size of the pipe, decreases by 25% in average due to the resistance of the shield. The enlargement of diameter at the shield, 2 step, improves the fluid flow. It illustrated that the diameter of downstream pipe size is 1step larger than the upstream for providing the design flow rate. The shield increases friction and resistance, in the case of oil pipe, so the average flow velocity at the middle of the shield increase by 50% in average. In consideration of the fluid viscosity, the oil pipe should be enlarged 4 or 5 step from the typical design configuration. Therefore, the fluid channel size for air, water, and oil, should be reconsidered by the engineering approach when EMP shield is placed in the middle of channel.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.630-630
• /
• 2013

Recently, atomically smooth hexagonal boron nitride(h-BN) known as a white graphene has drawn great attention since the discovery of graphene. h-BN is a III-V compound and has a honeycomb structure very similar to graphene with smaller lattice mismatch. Because of strong covalent sp2bonds like graphene, h-BN provides a high thermal conductivity and mechanical strength as well as chemical stability of h-BN superior to graphene. While graphene has a high electrical conductivity, h-BN has a highly dielectric property as an insulator with optical band gap up to 6eV. Similar to the graphene, h-BN can be applied to a variety of field, such as gate dielectric layers/substrate, ultraviolet emitter, transparent membrane, and protective coatings. However, up until recently, obtaining and controlling good quality monolayer h-BN layers have been too difficult and challenging. In this work, we investigate the controlled synthesis of h-BN layers according to the growth condition, time, temperature, and gas partial pressure. h-BN is obtained by using chemical vapor deposition on Cu foil with ammonia borane (BH3NH3) as a source for h-BN. Scanning Transmission Electron Microscopy (STEM, JEOL-JEM-ARM200F) is used for imaging and structural analysis of h-BN layer. Sample's surface morphology is characterized by Field emission scanning electron microscopy (SEM, JEOL JSM-7100F). h-BN is analyzed by Raman spectroscopy (HORIBA, ARAMIS) and its topographic variations by Atomic force microscopy (AFM, Park Systems XE-100).

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.08a
• /
• pp.285-285
• /
• 2013

Recently, hexagonal boron nitride (h-BN), which is III-V compound of boron and nitride by strong covalent sp2 bonds has gained great interests as a 2 dimensional insulating material since it has honeycomb structure with like graphene with very small lattice mismatch (1.7%). Unlike graphene that is semi-metallic, h-BN has large band gap up to 6 eV while providing outstanding properties such as high thermal conductivity, mechanical strength, and good chemical stability. Because of these excellent properties, hBN can potentially be used for variety of applications such as dielectric layer, deep UV optoelectronic device, and protective transparent substrate. Low pressure and atmospheric pressure chemical vapor deposition (LPCVD and APCVD) methods have been investigated to synthesize h-BN by using ammonia borane as a precursor. Ammonia borane decomposes to polyiminoborane (BHNH), hydrogen, and borazine. The produced borazine gas is a key material that is a used for the synthesis of h-BN, therefore controlling the condition of decomposed products from ammonia borane is very important. In this paper, we optimize the decomposition of ammonia borane by investigating temperature, amount of precursor, and other parameters to fabricate high quality monolayer h-BN. Synthesized h-BN is characterized by Raman spectroscopy and its absorbance is measured with UV spectrophotometer. Topological variations of the samples are analyzed by atomic force microscopy. Scanning electron microscopy and Scanning transmission Electron microscopy are used for imaging and analysis of structures and surface morphologies.

• Journal of Digital Convergence
• /
• v.17 no.6
• /
• pp.327-333
• /
• 2019

The purpose of this study is to suggest areas for improvement of KakaoTalk. KakaoTalk is used by everyone in Korea, and even elementary school students have been using it a lot recently. Therefore, to help parents feel safe about their children using KakaoTalk, and to ensure that children are not worried about their parents when using them, I would like to examine each user's experience to pinpoint the problem. As a method of study, a survey and interview was conducted on eight parents and eight children using KakaoTalk. Through this, the parents could not trust KakaoTalk in terms of reliability when they saw their children using KakaoTalk. Based on this research, we hope to improve KakaoTalk through further research so that parents and children can use Kakao Talk safely.

• Composites Research
• /
• v.33 no.6
• /
• pp.408-414
• /
• 2020

The present engineering sector focused on the sandwich composites and almost covered all engineering fields because of decent mechanical properties with a lightweight structure. It mainly consists of high strength fiber skin and porous structure core like corrugated, honeycomb, balsa wood, and foams which is playing a pivotal role in weight reduction. Recently researchers attention grabbed by Natural fiber sandwich composites due to biodegradability, renewable, low-cost, and environmentally friendly. However special focus is highly needed towards the flammability behavior of natural fibers used as reinforcement for composites. Herein, for the first time, the flame retardant natural fiber sandwich composite was fabricated by using flame retardant treated bamboo fabric and vinyl ester via the VARTM process. The impact of flame retardant treated bamboo fabric on mechanical and flame retardant properties were studied. The results concluded that the fabricated bamboo sandwich composites show structurally lightweight with significant mechanical strength and feasibility with respect to the flame.

• The Korean Journal of Cytopathology
• /
• v.4 no.2
• /
• pp.105-110
• /
• 1993

The major limitation of fine needle aspiration of the thyroid is in the evaluation of follicular tumors. it may be difficult or occasionally, impossible to distinguish on a cytologic basis, between hyperplastic nodular getter, follicular adenoma and well differentiated follicular carcinoma. We reviewed cytologic presentations of 15 histologically confirmed follicular neoplasms of the thyroid. Aspiration smears of 6 follicular adenomas were cell-rich with ball-like or syncytial aggregates of monotonous follicular cells, in contrast to honeycomb-like flat sheets of adenomatous goiter Mild nuclear pleomorphism and a small visible nucleolus were noted in 2 cases, respectively. Nine cases of follicular carcinoma showed very high cellularity, irregularly shaped cell clusters, and numerous isolated tumor cells. Nuclear pleomorphism and visible nucleoli were noted in 6 and 5 cases, respectively. Another characteristic finding, entrapped endothelial cells within the ceil clusters, was noted in 7 carcinomas and 1 adenoma. The background of the smears of all follicular neoplasms was hemorrhagic, with no or scanty colloid. We confirmed that the cytologic features of follicular adenoma and carcinoma were similar in general, with subtle differences in cell morphology, but the presence of isolated tumor cells and entrapped endothelial cells was suggestive of malignancy.

• Asian-Australasian Journal of Animal Sciences
• /
• v.20 no.6
• /
• pp.994-1001
• /
• 2007

Changes in shear force value, transverse sections, myofibrils and intramuscular connective tissue of bovine skeletal muscle exposed to the combination of high-pressure up to 400 MPa and heat (30 and $60^{\circ}C$) were studied. The shear force value decreased by pressure-heat treatment up to 200 MPa at 30 and $60^{\circ}C$, and then slightly increased over 200 MPa at $30^{\circ}C$. Shear force values of treated muscles were lower than those of untreated ones. Gaps between muscle fibers in the untreated muscle were a little clear, and then they became very clear in the treated muscles up to 200 MPa at 30 and $60^{\circ}C$. However, the gaps reduced significantly over 200 MPa at $30^{\circ}C$. The remarkable rupture of I-band and loss of M-line materials progressed in the myofibrils with increasing pressure applied. However, degradation and loss of the Z-line in myofibrils observed in the muscle treated at $60^{\circ}C$ was not apparent in the muscle treated at $30^{\circ}C$. The length of the sarcomere initially contracted by pressure-heat treatment of 100 MPa at $30^{\circ}C$ seemed to have recovered with increase of the pressure up to 400 MPa. In the muscle treated at $60^{\circ}C$, the length of sarcomere gradually decreased with increase of the pressure up to 400 MPa. In the treated muscles, changes in the honeycomb-like structure of endomysium were observed and accelerated with increase of the pressure. A wavy appearance clearly observed at the inside surface of endomysium in the untreated muscles gradually decreased in the treated muscles with increase of the pressure. Tearing of the membrane was observed in the muscles treated over 150 MPa at $30^{\circ}C$, as observed in the sample pressurized at 100 MPa at $60^{\circ}C$. The roughening, disruption and fraying of the membrane were observed over 200 MPa at $60^{\circ}C$. From the results obtained, the combination of high-pressure and heat treatments seems to be effective to tenderize tough meat. The shear force value may have some relationship with deformation of intramuscular connective tissue and myofibrils.