• Ocean Systems Engineering
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• v.14 no.2
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• pp.101-114
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• 2024

Seafloor sediment mapping is an essential research topic in shallow coastal waters, especially in port development, benthic habitat mapping, and underwater communications. The seafloor sediments can be interpreted by collecting sediment samples directly in the field using a grab sampler or corer. Another method is optical, especially using underwater cameras and videos. Both methods each have weaknesses in terms of area coverage (mechanic) and accurate positioning (optic). The latest technology used to overcome it is the acoustic method (echosounder) with Global Navigation Satellite System (GNSS) Real Time Kinematic (RTK) positioning. Therefore, in this study will propose the classification of seafloor sediments in coastal waters using acoustic method that is Multibeam Echosounder (MBES) multi-frequency with five frequency (200 kHz, 250 kHz, 300 kHz, 350 kHz, and 400 kHz). In this study, the deep neural network (DNN) used the bathymetric multi frequency, bathymetric difference inters frequencies, and bathymetric features from 5 (five) frequencies as input layer and 4 (four) sediment types in 74 (seventy-four) sample sediment as output layer to make a seafloor sediment map. Results of sediment mapping using the DNN method show an overall accuracy of 71.6% (significant) and a kappa coefficient of 0.59 (moderate). The distribution of seafloor sediment in the study area is mainly silt (41.6%), followed by clayey sand (36.6%), sandy silt (14.2%), and silty sand (7.5%).

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.1
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• pp.25-36
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• 2021

This paper presents a topology based on packet tracer and a five-step scenario model to make it easier for students to understand the network on which VLANs are applied. Virtual LAN (VLAN), developed as an alternative solution to the Routers that distribute broadcast traffic, is a virtual local area network that logically configured regardless of the physical network. The VLAN prevents the network performance degradation resulting from the broadcast traffic by dividing the broadcast domain so that the bandwidth can be used more efficiently. In addition, it enhances the security because on communication between the devices belonging to different VLANs is impossible. The five-step scenarios in this paper presented an efficient implementation case for students to understand and validate the various functions of VLANs through ping/telnet/tracert test and simulation, after setting up each step of programming switches and routers in the virtual network.

• Journal of Astronomy and Space Sciences
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• v.41 no.1
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• pp.25-33
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• 2024

This paper evaluates the influence of rainfall on propagated signal at different time exceedance percentages of an average year, over the climate zones of the country. Specifically, it demonstrates critical and non critical signal fade or signal outage time exceedance (0.001% to 1%) for Ku, K, and Ka-band systems in an average year. The study was carried out using meteorological data made available by the Nigerian Meteorological Agency (NiMet) over a period of 10 years (2009-2018). The four climate zones in the country were represented by five (5) locations; Maidugiri (warm desert climate), Sokoto (tropical dry climate), Port Harcourt (tropical monsoon climate), Abuja and Enugu (tropical savanna climate). The parameters were simulated into the International Telecommunications Union Recommended (ITU-R) models for rain attenuation over the tropics and results presented using MatLab and Origin Lab. Results of Ku band propagations showed that only locations in the tropical savanna and tropical monsoon climates experienced total signal outage for time percentage exceedance equal to or below 0.01% for both horizontal and vertical polarizations. At K band propagations, the five locations showed to have experienced signal outage at time exceedance equal to and below 0.01%, almost same was recorded for the Ka-band propagation. It was also observed that horizontal and vertical polarization of signal had slightly different rain attenuation values for the studied bands at the five locations, with horizontal polarization having higher values than vertical polarization.

• Journal of Forest and Environmental Science
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• v.34 no.4
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• pp.284-292
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• 2018

The study investigated the concentrations of Pb in soil, air and fruit of C. sinensis in selected landuse types in Port Harcourt Metropolis, Rivers State, Nigeria. Five fruits of C. sinensis were collected randomly in residential, commercial, industrial and natural forest (control). The weight, length and width of the C. sinensis fruits were measured. A total of three soil samples were collected around the C. sinensis trees where the fruits were collected into well labeled polythene bags and thereafter taken to laboratory for analysis. Pb concentrations in C. sinensis and soil samples were analysed using atomic absorption spectrophotometer (AAS). The concentration of Pb in the air was measured for 14 days using Aeroquel 500. The significant relationship between Pb concentration in the C. sinensis fruits, soil and air was determined using Spearman's rank correlation. Findings showed that the mean weight and width of C. sinensis fruits were highest in the residential landuse while the mean length of C. sinensis fruits was highest in the industrial landuse. However, the mean Pb concentration in the C. sinensis fruit was highest in the industrial landuse ($0.46{\pm}0.15mg\;kg^{-1}$), commercial landuse ($0.33{\pm}0.09mg\;kg^{-1}$) and the least was found in the natural forest ($0.25{\pm}0.06mg\;kg^{-1}$). The mean Pb concentration in the soil was highest in the industrial landuse ($0.177{\pm}0.16mg\;kg^{-1}$) and commercial landuse ($0.121{\pm}0.10mg\;kg^{-1}$). However, the mean Pb concentration in the air was highest in the industrial landuse ($0.85{\pm}0.09mg\;kg^{-1}$) and followed by commercial landuse ($0.30{\pm}0.17mg\;kg^{-1}$). The correlations between the Pb concentration in the C. sinensis fruit and soil (r=0.768, p<0.05) and air (r=0.642, p<0.05) were significant. The study concluded that the Pb concentration in the C. sinensis fruits was higher than the WHO standard; hence people should be discouraged to consume them, especially those from the industrial and commercial areas.

• Journal of Navigation and Port Research
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• v.41 no.6
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• pp.415-422
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• 2017

In a situation where there is excessive competition among logistics centers due to the low price of logistics centers for attracting freight volume, the conditions provided by the logistics centers are similar. Therefore, in order to determine the logistics center, we want to find out what kind of differentiated service the shippers desire, as well as what level of service they want in addition to al ow price. There are currently no studies about the service quality of logistics centers. The components of the service quality of the logistics center were extracted by applying them to the logistics center based on the existing service quality theory. Factor analysis revealed five dimensions of service quality: tangibility, reliability, empathy, assurance, and know-how. It was found that service quality had a statistically significant influence on customer satisfaction, from the investigation of the causal effect relationship. In addition, 'Know-How' among these factors has more influence on customer satisfaction, so it is important to accumulate differentiated 'Know-How' only in logistics centers.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.7
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• pp.1059-1066
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• 2021

In Korea, the importance of marine activities is great, and automatic weather observation facilities are operating on land to investigate abnormal weather phenomena caused by industrialization; however, the number of facilities at sea is insufficient. Marine survey ships are operated to establish marine safety information, but there are many places where marine survey ships are difficult to access and operating costs are high. Therefore, a small, unmanned vessel capable of marine surveys must be developed. The sail has a significant impact on the sailing performance, so much research has been conducted. In this study, the camber effect, which is a design variable of the twin curvy sail known to have higher aerodynamic performance than existing airfoil shapes, was investigated. Flow analysis results for five cases with different camber sizes show that the lift coefficient is highest when the camber size is 9%. Curvy twin sails had the highest lift coefficient at an angle of attack of 23° because of the interaction of the port and starboard sails. The port sail had the highest lift coef icient at an angle of attack of 20°, and the starboard sail had the lowest lift coef icient at an angle of attack of 15°. In addition, the curvy twin sail had a higher lift coefficient than NACA 0018 at all angles of attack.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.11
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• pp.538-543
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• 2006

A high-Power continuous-wave (CW) ten-vane double-strapped magnetron oscillator has been investigated using three-dimensional (3D) particle-in-cell (PIC) numerical simulation code, MAGIC3D. The resonant modes and their resonant frequencies of the ten-vane strapped magnetron resonator were obtained to show a large mode separation near the ${\pi}$-mode. An electron cloud formed in an anode-cathode gap, called an interaction space was confined well enough to result in no leakage current. Five spokes were clearly observed in the electron cloud, which definitely ensured the ${\pi}$-mode oscillation in the ten-vane magnetron. Numerical simulations predicted that the saturated microwave output power measured at the coaxial output port was 5.41 kW at the microwave frequency of 893 MHz, corresponding to a power conversion efficiency of 72.6% when the external axial magnetic field was 1150 gauss and the electron beam voltage and current were 6 kV and 1.25 A, respectively.

• Journal of ILASS-Korea
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• v.2 no.1
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• pp.46-51
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• 1997

In this study, spray characteristics of the pressure swirl atomizer have teen investigated. Four atomizers with the different orifice diameter and five tangential ports with the different inlet number were fabricated. For the purpose of the measurement of the mean drop sine, Malvern particle sizer was used. And also discharge coefficient was measured and spray cone angle was measured by using shadow graphy method. As a result when the injection pressure was increased, mean drop size was decreased. And the dominant factor which influence on the spray characteristics of pressure swirl atomizer was orifice diameter.

• 한국해양학회지
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• v.19 no.2
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• pp.210-216
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• 1984

Diurnal variations of coastal surface wind speed are analyzed with five years of hourly wind from Port Aransas, Texas. These data reveal the highest frequency of occurrence of the nighttime wind maximum near midnight, especially during those seasons when onshore flow prevails. Nighttime wind maxima with a southerly component occurred approximately three times more frequently than with a northerly component on the annual average. The neutral atmospheric stability prevails near the coast. Thus it allows downward transfer of momentum from the nocturnal low level jet under the onshore wind situation and strong wind shear between an elevated frontal and ground-based inversion for offshore wind, resulting in the nocturnal coastal surface wind maximum.

• Asian Pacific Journal of Cancer Prevention
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• v.13 no.10
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• pp.4849-4853
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• 2012

Relatively low numbers of malignant mesotheliomas have been reported from Eastern Asia. In order to explore the causes of this fact, the available data on mesothelioma incidence/mortality in five countries (Japan, South Korea, Taiwan, Hong Kong, and Singapore) were reviewed. Data on the industrial histories of the above countries were also examined. Mesothelioma incidence was low, despite a history of high shipbuilding and port activities, in which heavy exposure to asbestos generally has occurred. Underestimation of mesothelioma could partly explain the above discrepancy. Moreover, in some areas a sufficient latency period for mesothelioma development may have not yet elapsed, due to recent industrialization. However, other possibilities have to be considered. The cancer epidemiology in Eastern Asia differs deeply from that seen in Western countries, an indication of differences in etiologic factors of cancer as well as in co-factors. In addition, the oncogenic spectrum of asbestos is wide, and not completely defined. In a very different milieu from that of Western countries, asbestos could preferentially hit targets other than serosal membranes.