• Proceedings of the Korea Information Processing Society Conference
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• 2023.05a
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• pp.585-587
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• 2023

Long-tailed datasets have an imbalanced distribution because they consist of a different number of data samples for each class. However, there are problems of the performance degradation in tail-classes and class-accuracy imbalance for all classes. To address these problems, this paper suggests a learning method for training of long-tailed dataset. The proposed method uses and combines two methods; one is a resampling method to generate a uniform mini-batch to prevent the performance degradation in tail-classes, and the other is a reweighting method to address the accuracy imbalance problem. The purpose of our proposed method is to train the learning models to have uniform accuracy for each class in a long-tailed dataset.

• Ocean Systems Engineering
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• v.11 no.4
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• pp.373-392
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• 2021

The present paper purposes a numerical evaluation of the Thai Long-Tail Boat propeller (TLTBP) performance by without and with propeller boss cap fins (PBCF) in full-scale operating straight shaft condition in the first. Next, those are applied to inclined shaft conditions. The actual TLTBP has defined an inclined shaft propeller including the high rotational speed, therefore vortex from the propeller boss and boss cap (hub vortex) have been generated very much. The PBCF designs are considered to weaken of vortex behind the propeller boss which makes the saving energy for the propulsion systems. The blade sections of PBCF developed from the original TLTBP blade shape. The integrative for the TLTBP and the PBCF is analyzed to increase the performance using computational fluid dynamics (CFD). The computational results of propeller performance are thoroughly compared between without and with PBCF. Moreover, the effects of each PBCF component are computed to influence the TLTBP performance. The fluid flows around the propeller blades, propeller boss, boss cap, and vortex have been investigated in terms of pressure distribution and wake-fields to verify the increasing efficiency of propulsion systems.

• The Korean Journal of Applied Statistics
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• v.26 no.5
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• pp.759-766
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• 2013

The paper examines several classes of probability distributions with heavy tails. An (asymptotic) expression for tail probability needs to be known to understand which class a given probability distribution belongs to. It is usually not easy to get expressions for tail probabilities since most absolutely continuous probability distributions are specified by probability density functions and not by distribution functions. The paper proposes a method to obtain asymptotic expressions for tail probabilities using only probability density functions. Some examples are given to illustrate the proposed method.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.3
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• pp.123-129
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• 2000

To make high accuracy cutting of long materials and a piston for the engines it must be necessary to keep the thermal stability of spindle and tail stock in CNC lathe. If a object is clamped at the ends the thermal expansion and cutting process generate the deflection of cutting objects. Especially in the case of a piston ring piston ovality and piston profile the influences of deflection are very serious. In order to solve the problems most of piston cutting are worked under simply support. However the prob-lems exist yet. Therefore this paper proposes the new structure of tail stock which can compensates the deflection.

• Journal of Aerospace System Engineering
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• v.12 no.1
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• pp.35-41
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• 2018

Unmanned Aerial Vehicles (UAV) have been used for various purposes in multiple fields, such as observation, communication relaying, and information acquisition. Nowadays, UAVs must have high performance in order to acquire more precise information in larger amounts than is now possible while performing for long periods. At present, domestically, a high-altitude long-endurance UAV (HALE UAV) for long-term flight in the stratosphere has been developed in order to replace some functions of the satellite. In this study, as a part of structural soundness evaluation of the aircraft structure developed for the HALE UAV, the structural soundness of the fasteners of the fuselage and tail is evaluated by calculating the margin of safety(M.S). The result confirms the validity of the design of the fasteners in the aircraft structure of the UAV.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.12
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• pp.1715-1720
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• 2016

In the upcoming 5-generation mobile communication system, various techniques for improving the power efficiency and spectral efficiency have been proposed. 5G mobile communication system also have been studied a lot of multi-carrier-based modulation techniques like the 4G mobile communication system. In this paper, we analyzed the conventional system structure of the Zero-tail DFT-s-OFDM and UW (Unique Word) -DFT-s-OFDM system based on DFT-s-OFDM system in these techniques. UW and zero are added and used each system, and CP is removed. the result of quality of systems for simulation, OOB(Out of Band) power of Zero-tail DFT-s-OFDM and UW-DFT-s-OFDM use the less time resource as long as CP length, also both systems are reduced about 11dB than DFT-s-OFDM system. In these result, Zero-tail DFT-s-OFDM and UW-DFT-s-OFDM system are more effective than DFT-s-OFDM system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.8
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• pp.1756-1763
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• 2011

This paper was researched the straight cruise of fish robot according to biological mimic, and it was compared the proposed method which was considered up to 7th order components in fourier series of Liu's tail motion function with the approximate method which was used general sine function by simulation. If fish robot has a large number of links and if the length of tail link is long. The end rotary joint trajectory of tail motion function generally is different from sine function. Therefore The approximate method which expresses tail motion trajectories as fundamental component in fourier series has a problem. Through the computer simulation, the proposed method showed 10% excellent propulsion and velocity than the conventional method.

• Journal of Aquaculture
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• v.10 no.2
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• pp.189-197
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• 1997

A series of short (8 hours) and long term (96 hours) exposure studies was conducted on a laboratory scale to evaluation (1) the threshold concentrations of petroleum hydrocarbon in seawater which can lead to tainting problems in yellow tail (Seriola quinqueradiata) and (2) the time to recover (depuration period) once the tainting has occurred. The water-soluble fraction (WSF) of crude oil was prepared by stirring the oil with cold seawater. The main component of the WSF were low-boiling aromatics, although these were only al small proportion of the starting oil. From the sencory evaluation it was concluded that the threshold hydrocarbon levels in seawater which will impart a taint in yellow tail fillets within a 8-hour exposure period (short exposure period) are in the range of 0.4 to 1.0 ppm and within a 96-hour exposure period (long exposure period) are in the range of 0.2 to 0.5 ppm. Depuration trials were carried out with WSF from crude oil. The fish were exposed for 48 hours to concentration of 2.5 ppm hydrocarbons. After 48-hour exposure period, the fish were allowed to depurate in fresh, uncontaminated seawater. Depuration time for these fish was 10 days. The taste panelists were able to detect the contaminated fillets very easily while the depurated fish could not be distiguished from the control.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.817-820
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• 2006

The Tonpilz transducer is one of the essential elements in active sonar application. The characteristics of transducer depend on the piezoelectric ceramics and mechanical elements such as head mass, tail mass, pre-stress rod and so on. One of the important characteristics is electric and mechanical stability of transducer for long term high power transmitting operation. This parer presents the results about long term endurance tests of the underwater acoustic transducer.

• International Journal of Aeronautical and Space Sciences
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• v.10 no.2
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• pp.117-124
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• 2009

In the environment where various and complicated threat signals exist, RWR (Radar Warning Receiver), which can warn pilot of the existence of threats, has long been a necessary electronic warfare (EW) system to improve survivability of aircraft. The angle of arrival (AOA) information, the most reliable sorting parameter in the RWR, is measured by means of four-quadrant amplitude comparison direction finding (DF) technique. Each of four antennas (usually spiral antenna) of DF unit covers one of four quadrant zones, with 90 degrees apart with nearby antenna. According to the location of antenna installed in helicopter, RWR is subject to signal loss and interference by helicopter body and structures including tail bumper, rotor blade, and so on, causing a difficulty of detecting hostile emitters. In this paper, the performance degradation caused by signal interference by tail rotor blades has been estimated by measuring amplitude video signals into which RWR converts RF signals in case a part of antenna is screened by real tail rotor blade in anechoic chamber. The results show that corruption of pulse amplitude (PA) is main cause of DF error. We have proposed two algorithms for resolving the interference by tail rotor blades as below: First, expand the AOA group range for pulse grouping at the first signal analysis phase. Second, merge each of pulse trains with the other, that signal parameter except PRI and AOA is similar, after the first signal analysis phase. The presented method makes it possible to use RWR by reducing interference caused by blade screening in case antenna is screened by tail rotor blades.