• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.10
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• pp.2247-2255
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• 2015

In very shallow water acoustic communication channel, underwater acoustic (UWA) communication signal is observed as frequency selective fading signal due to time-varying multipath. This induces a time and frequency dependent inter-symbol-interference (ISI) and degrades the UWA system performance. There is no study about how the performances of the error correction codes are related to a multipath fading statistics in very shallow water. In this study, the characteristics of very shallow water multipath fading channel is analyzed and the performances of two different forward error correction (FEC) codes are compared. The convolution code (CC) and Reed-Solomon (RS) code are adopted. Sea experimental results show that RS code is better choice than CC in frequency selective channel with fading.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.807-810
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• 2007

Recently, ultra-wideband (UWB) technology based on the transmission of short duration pulses has gained much interest for its application to wireless communications. UWB small scale channel modeling work, including statistical characterization and potential models, are discussed. The significance, in terms of performance, of the channel impulse response model chosen for the simulation of UWB communications systems is also evaluated. Three traditional models are found to be useful for modeling NLOS UWB channels, but not LOS channels. In this paper, a new model for LOS UWB channels is presented and shown to represent LOS channels much more accurately than the traditional models.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.12
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• pp.1681-1691
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• 2002

The heat transfer and pressure drop characteristics of heat exchangers with louver fins were experimentally investigated. The samples had small fin pitches (1.0 mm to 1.4 mm), and experiments were conducted up to a very low frontal air velocity (as low as 0.3 m/s). At a certain Reynolds number (critical Reynolds number), the flattening of the heat transfer coefficient curve was observed. The critical Reynolds number was insensitive to the louver angle, and decreased as the louver pitch to fin pitch ratio (L$_{p}$F$_{p}$) decreased. Existing correlations on the critical Reynolds number did not adequately predict the data. It is suggested that, for proper assessment of the heat transfer behavior, the louver pattern in addition to the flow characterization need to be considered. The heat transfer coefficient increased as the fin pitch decreased. At low Reynolds numbers, however, the trend was reversed. Possible explanation is provided considering the louver pattern between neighboring fins. Different from the heat transfer coefficient, the friction factor did not show the flattening characteristic. The reason may be attributed to the form drag by louvers, which offsets the decreased skin friction at a low Reynolds number. The friction factor increased as the fin pitch decreased and the louver angle increased. A new correlation predicted 92% of the heat transfer coefficient and 90% of the friction factor within $\pm$10%.10%.

• Korean Journal of Materials Research
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• v.20 no.12
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• pp.636-639
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• 2010

ZnO thin films were prepared on a glass substrate by radio frequency (RF) magnetron sputtering without intentional substrate heating and then surfaces of the ZnO films were irradiated with intense electrons in vacuum condition to investigate the effect of electron bombardment on crystallization, surface roughness, morphology and hydrogen gas sensitivity. In XRD pattern, as deposited ZnO films show a higher ZnO (002) peak intensity. However, the peak intensity for ZnO (002) is decreased with increase of electron bombarding energy. Atomic force microscope images show that surface morphology is also dependent on electron bombarding energy. The surface roughness increases due to intense electron bombardment as high as 2.7 nm. The observed optical transmittance means that the films irradiated with intense electron beams at 900 eV show lower transmittance than the others due to their rough surfaces. In addition, ZnO films irradiated by the electron beam at 900 eV show higher hydrogen gas sensitivity than the films that were electron beam irradiated at 450 eV. From XRD pattern and atomic force microscope observations, it is supposed that intense electron bombardment promotes a rough surface due to the intense bombardments and increased gas sensitivity of ZnO films for hydrogen gas. These results suggest that ZnO films irradiated with intense electron beams are promising for practical high performance hydrogen gas sensors.

• Korean Journal of Materials Research
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• v.28 no.1
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• pp.32-37
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• 2018

We report on the efficient detection of NO gas by an all-oxide semiconductor p-n heterojunction diode structure comprised of n-type zinc oxide (ZnO) nanorods embedded in p-type copper oxide (CuO) thin film. The CuO thin film/ZnO nanorod heterostructure was fabricated by directly sputtering CuO thin film onto a vertically aligned ZnO nanorod array synthesized via a hydrothemal method. The transport behavior and NO gas sensing properties of the fabricated CuO thin film/ZnO nanorod heterostructure were charcterized and revealed that the oxide semiconductor heterojunction exhibited a definite rectifying diode-like behavior at various temperatures ranging from room temperature to $250^{\circ}C$. The NO gas sensing experiment indicated that the CuO thin film/ZnO nanorod heterostructure had a good sensing performance for the efficient detection of NO gas in the range of 2-14 ppm under the conditions of an applied bias of 2 V and a comparatively low operating temperature of $150^{\circ}C$. The NO gas sensing process in the CuO/ZnO p-n heterostructure is discussed in terms of the electronic band structure.

• Membrane Journal
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• v.28 no.4
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• pp.271-278
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• 2018

In this study, the carbon electrodes using activated carbon fibers (ACFs) were prepared for the capacitive deionization process. The Polyvinylidene fluoride (PVDF) was used as the binder and the mixed ACFs with proper solvent was cast on the commercial graphite sheets to prepare the carbon electrodes. At this moment, the different particle sizes of ACFs were applied and the mixing ratio of solvent, PVDF and ACFs, 80 : 2 : 18 and 80 : 5 : 15, were used for the electrode preparation. Then their salt removal efficiencies were characterized under the various operating conditions, adsorption potential and time, desorption potential and time, concentration of feed NaCl solution and flow rate as well. Typically, the salt removal efficiency of 53.6% were obtained at the particle size below $32{\mu}m$, mixing ratio 80 : 2 : 18, adsorption 1.2 V and 3 min, desorption -0.1V and 1 min, and 15 mL/min flow rate of NaCl 100 mg/L.

• Journal of Korean Society of Rural Planning
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• v.15 no.4
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• pp.161-172
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• 2009

This study focuses on the application of landscape planning(i.e. including rural landscape character area designation and rural landscape planning etc.). That application of landscape planning provides the probably most operable and comprehensive version of what is generally accepted by the discipline. According to the planning discipline the schemes of planning are to; Firstly, we derived the improvement of landscape and the methods of landscape characterization subsequent to analyze the present condition and grasp the landscape resources in Yesan via reviewing the current study and field survey. Secondly, in order to achieve environmentally friendly rural landscape plan and characteristic rural landscape creation, we planed the draft landscape area such as woodland, hydrology area, urbanized area, rural communities, etc. which was classified by sphere of life moreover, we planed partly outdoor facilities, road and colour suchlike. Thirdly, we tried to seek the programme of conservation and utilization for scenic and characteristic rural landscape area via rural landscape character area designation. Lastly, it is proposed that rural landscape planning lead to inhabitant participation, system improvement, subject performance for carrying out efficient rural landscape planning.

• Journal of Sensor Science and Technology
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• v.23 no.3
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• pp.197-201
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• 2014

TEPC (Tissue Equivalent Proportional Counter) was usually used for high LET radiation dosimetry. We developed a prototype TEPC for micro-dosimetry in the range of $0.2{\sim}300 keV/{\mu}m$. And, the simulated site diameter of the TEPC is $2{\mu}m$, of similar size to a cell nucleus. For purposes of characterization the response for high LET radiation of the TEPC has been investigated under 135MeV/u Carbon ions in HIMAC (Heavy Ion Medical Accelerator). We determined the gas multiplication factor and measured the lineal energy spectrum [yd(y)] of 135 MeV/u Carbon ions. The value of the gas multiplication factor was 315 at 700 V bias voltage. As a result of the experiment, we could more understand the performance of the TEPC for high LET (Linear Energy Transfer) radiation. And the procedure of high LET radiation dosimetry using TEPC is established.

• Rapid Communication in Photoscience
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• v.3 no.1
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• pp.16-19
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• 2014

Anodic self-organized titania nanotube (TNT) arrays have a great potential as efficient electron-transport materials for dye-sensitized solar cells (DSSC). Herewith we report the photovoltaic and kinetic investigations for a series of heteroleptic ruthenium complexes (RD16-RD18) sensitized on TNT films for DSSC applications. We found that the RD16 device had an enhanced short-circuit current density ($J_{SC}/mAcm^{-2}=15.0$) and an efficiency of power conversion (${\eta}=7.2%$) greater than that of a N719 device (${\eta}=7.1%$) due to the increasing light-harvesting and the broadened spectral features with thiophene-based ligands. However, the device made of RD17 (adding one more hexyl chain) showed smaller $J_{SC}(14.1mAcm^{-2})$ and poorer ${\eta}(6.8%)$ compare to those of RD16 due to smaller amount of dye-loading and less efficient electron injection for the RD17 device than for the RD16 device. For the RD18 dye (adding one more thiophene unit and one more hexyl chain), we found that the device showed even lower $J_{SC}(13.2mAcm^{-2}) $ that led to a poorest device performance (${\eta}=6.2%$) for the RD18 device. These results are against to those obtained from the same dyes sensitized on $TiO_2$ nanoparticle films and they can be rationalized according to the electron transport kinetics measured using the methods of charge extraction and transient photovoltage decays.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.520-520
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• 2009

Organic by-products derived from cellulose and lignin during organosolv pretreatments of yellow poplar wood (Liriodendron tulipifera) in the presence of $H_2SO_4$ and NaOH as catalysts, respectively, were subjected to various analyses to elucidate their effects on further performance of biological ethanol fermentation and provide preliminary data for the structure and utilization of organosolv lignin. Monomeric sugars amounted to ca. 2.2-7.7% in the organosoluble fraction of the organosolv pretreatment with $H_2SO_4$, while significantly low amount of sugars (0.2-0.3%) were determined in that of the organosolv pretreatment with NaOH. In case of addition of $H_2SO_4$ during organosolv pretreatment of biomass, a fermentation of the organosoluble fraction could be considered as an essential process to increase an efficiency of biomass utilization as well as yield of bioethanol. Precipitates, insoluble by-products in the solvent mixture, were also cficiency oed by diverse analytical methods and revealed that these were typically composed of a lignin moiety regardless of catalyst. According to the results of nuclear magnetic resonance (NMR), Fourier Tcinsform Infrared Spectroscopy (FT-IR) and Gel permeation chromatograp r (GPC), the main components of precipitates seem to be lignin polymers. However, their structures could be slightly modified during pretreatment and mixed with some carbohydrates by chemical bonds and/or physical associations.