• Journal of Korean Society of Industrial and Systems Engineering
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• v.43 no.4
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• pp.190-197
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• 2020

Recently there was an incident that military radars, coastal CCTVs and other surveillance equipment captured a small rubber boat smuggling a group of illegal immigrants into South Korea, but guards on duty failed to notice it until after they reached the shore and fled. After that, the detection of such vessels before it reach to the Korean shore has emerged as an important issue to be solved. In the fields of marine navigation, Automatic Identification System (AIS) is widely equipped in vessels, and the vessels incessantly transmits its position information. In this paper, we propose a method of automatically identifying abnormally behaving vessels with AIS using convolutional autoencoder (CAE). Vessel anomaly detection can be referred to as the process of detecting its trajectory that significantly deviated from the majority of the trajectories. In this method, the normal vessel trajectory is gridded as an image, and CAE are trained with images from historical normal vessel trajectories to reconstruct the input image. Features of normal trajectories are captured into weights in CAE. As a result, images of the trajectories of abnormal behaving vessels are poorly reconstructed and end up with large reconstruction errors. We show how correctly the model detects simulated abnormal trajectories shifted a few pixel from normal trajectories. Since the proposed model identifies abnormally behaving ships using actual AIS data, it is expected to contribute to the strengthening of security level when it is applied to various maritime surveillance systems.

• Advances in aircraft and spacecraft science
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• v.5 no.1
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• pp.73-105
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• 2018

A particular type of constant speed helical trajectory, with variable ascension rate, is proposed. Such trajectories are candidates of choice as motion primitives in automatic airplane trajectory planning; they can also be used by airplanes taking off or landing in limited space. The equations of motion for airplanes flying on such trajectories are exactly solvable. Their solution is presented, together with an analysis of the restrictions imposed on the geometrical parameters of the helical paths by the dynamical abilities of an airplane. The physical quantities taken into account are the airplane load factor, its lift coefficient, and the thrust its engines can produce. Formulas are provided for determining all the parameters of trajectories that would be flyable by a particular airplane, the final altitude reached, and the duration of the trajectory. It is shown how to construct speed interval tables, which would appreciably reduce the calculations to be done on board the airplane. Trajectories are characterized by their angle of inclination, their radius, and the rate of change of their inclination. Sample calculations are shown for the Cessna 182, a Silver Fox like unmanned aerial vehicle, and the F-16 Fighting Falcon.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.1
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• pp.10-20
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• 2017

This study presents the feasibility of CFD(computational fluid dynamic) analysis using the flow angularity wind tunnel test technique. The CFD analyzed data by the flow angularity technique has been constructed as the database to get store trajectories by 6-DOF simulation. The database has been checked out store aerodynamic coefficients by the analyses at each position under wing. After that process, the simulated trajectories by database have been compared with the store trajectories by CTS(Captive Trajectory Simulation) of CFD. The trajectories provided by the database of flow angularity have a good agreement with the store trajectories by CFD.

• Phonetics and Speech Sciences
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• v.1 no.4
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• pp.3-9
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• 2009

Acoustically English vowels are defined primarily by formant values. The measurements of the values have been usually made at a few time points of the vowel segment despite the fact that the majority of English vowel formants vary dynamically throughout the segment. This study attempts to collect acoustic data of the nine English vowels published by Hillenbrand et al. (1995) online and to examine the acoustic features of the English vowels for phoneticians and English teachers. The author used Praat to obtain the data systematically at six equidistant timepoints over the vowel segment. Obvious errors were corrected based on the spectrographic display of each vowel. Results show that the first two formant trajectories are important to separate the nine vowels within the front- or back-vowel groups. The third formant trajectories appear comparable except those of the high vowels. Second, the back vowels leave longer traces on the vowel space toward the locus of the following consonant /d/. Third, each vowel has inherent duration, pitch, and intensity patterns. The results match the findings of Yang (2009). From the results, the author concludes that dynamic spectral changes are important in specifying acoustic characteristics of English vowels. Further studies on the application of the vowel trajectories to English pronunciation lessons or on perceptual experiment of synthesized vowels are desirable.

• Korean Journal of Child Studies
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• v.37 no.6
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• pp.145-155
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• 2016

Objective: The purpose of this study was to investigate trajectories of child peer interaction and to compare the causal effects of their predictors, including child individual variables (i.e., gender, language ability, and cognitive ability) and teacher variables (i.e., teacher efficacy and teacher-child interaction). Methods: The participants of this study were 263 children and their teachers from the forth to sixth waves of longitudinal data from the Korean Children and Youth Panel Survey by the Korea Institute of Child Care and Education. The data was analyzed using Pearson's correlation and latent growth modeling. Results and Conclusion: The findings of this study are as follows: First, there was a linear decrease in child negative peer interaction over the course of 3 years, and significant individual differences were found in the trajectories (intercept and slope). Second, the predictors had significant casual effects on the trajectories of child negative peer interaction. The trajectories of child negative peer interaction involving girls, higher cognitive ability, and greater teacher-child interaction showed lower degree of intercept and a quicker decrease. Finally, the implications of findings are discussed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.10
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• pp.2140-2146
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• 2009

Since tags do not have location informations, the identifiers of tags which are symbolic data are used as the location informations. Therefore, it is difficult to define the proxmity between two trajectories of tags and inefficient to process the user queries for tags. In this paper, we define the perceptual space to model the location of a tag and propose the proximity of the perceptual spaces. The proximity of the perceptual spaces is composed of the static proximity and dynamic proximity. Using the proximity of the perceptual spaces, it is possible to measure the proximity between two trajectories of tags and build the efficient indexes for tag trajectories. We evaluated the performance of the proposed proximity function for tag trajectories on the IR-tree and the $R^*$-tree.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.12
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• pp.5782-5799
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• 2018

With the development of GPS and the popularity of mobile devices with positioning capability, collecting massive amounts of trajectory data is feasible and easy. The daily trajectories of moving objects convey a concise overview of their behaviors. Different social roles have different trajectory patterns. Therefore, we can identify users or groups based on similar trajectory patterns by mining implicit life patterns. However, most existing daily trajectories mining studies mainly focus on the spatial and temporal analysis of raw trajectory data but missing the essential semantic information or behaviors. In this paper, we propose a novel trajectory semantics calculation method to identify groups that have similar behaviors. In our model, we first propose a fast and efficient approach for stay regions extraction from daily trajectories, then generate semantic trajectories by enriching the stay regions with semantic labels. To measure the similarity between semantic trajectories, we design a semantic similarity measure model based on spatial and temporal similarity factor. Furthermore, a pruning strategy is proposed to lighten tedious calculations and comparisons. We have conducted extensive experiments on real trajectory dataset of Geolife project, and the experimental results show our proposed method is both effective and efficient.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.1181-1184
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• 1996

As usual systems, robot manipulators have also physical constraints for operating. It is a difficult problem that we operate manipulator in the minimal time under these constraints. In this paper, we solve this problem dividing it into two steps. In the first step, we find the minimal time trajectories by optimizing qubic polynomial joint trajectories using evolutionary algorithms. In the second step, we optimize controller for robot manipulator to track precisely trajectories optimized in the previous step.

• Journal of the Korean Statistical Society
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• v.35 no.3
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• pp.251-260
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• 2006

The proportional hazards model (PHM) can be associated with a non- homogeneous Markov chain (NHMC) in the sense that sample alignments in the PHM correspond to trajectories of the NHMC. As a result the partial likelihood widely used for the PHM is a probabilistic function of the trajectories of the NHMC. In this paper, we show that, as the total number of subjects involved increases, the trajectories of the NHMC, i.e. sample alignments in the PHM, converges to the solution of an ordinary differential equation which, subsequently, characterizes the almost sure limit of the partial likelihood.

• Asian Journal of Atmospheric Environment
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• v.7 no.2
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• pp.114-119
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• 2013

The characteristics of Asian dust (AD) in Korea between 1997 and 2005 were investigated, focusing on peak 1-hour $PM_{10}$ concentrations during AD events at seven cities over the Korean Peninsula. The frequency of AD events decreased from Seoul to Busan, indicating the major pathway of AD in Korea was from northwest to southeast. AD events were most frequent in 2001 while peak concentrations during AD events were much higher in 2002. Recent works show that the trajectories from northerly directions increased during the 2000s and later (Chun, 2009; Kim, 2008). In this work, the fraction of trajectories from the northwest was the largest on the whole, although trajectories from each direction varied by city and year. It is presumed that high concentrations of $PM_{10}$ during AD events are generally associated with trajectories from the northwest rather than from the source region.