• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 1999.10a
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• pp.273-280
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• 1999

Yard cranes are very useful equipments for handing of heavy containers, But rope-driven yard cranes must have a little of sway and skew motion because ropes are passive mechanical device. Therefore rope-driven yard cranes require skilled drivers to depress sway and skew motions. So many researches have been concentrated on anti-sway and anti-skew algorithm controlling trolley speed or rope tension. Although many efforts, the rope-driven method is not proper to an automated yard equipment because of sway and skew motion. This paper will propose a new concept yard crane which has a new structure, overcomes defects of rope-driven cranes and is proper to automation. And we will study its actuality

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.6
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• pp.607-613
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• 2009

In this paper, we made a simple paper feeding system which is one of MTS (media transport system) and controllers. The plant has a flexible paper and two driving rollers and two driven rollers. The control system has two conventional PID controllers. Skew angle and feeding speed of MTS deteriorate the quality of feeding system. In order to control a feeding speed and skew of feeding paper, we control rotational velocity of two driving rollers. Therefore, this controller has two inputs and two outputs as MIMO (multi-input and multi-output) system. The control inputs were the feeding speed and the skew displacement of the paper. The control outputs were the rotational velocity to each driving roller. To find appropriate PID gains of two controllers, we proposed an optimization technique. We assume the system variables and performance of a whole system as follows. PID gains of two controllers for skew and feeding speed are system variables. System performance is both skew and feeding speed. We simulates to making mathematical correlation using global Kriging interpolation. To find appropriate value of system variables, optimization method is simulation in sequence as following method. First, the optimization solver simulates with DOE (design of experiment) tables to find correlation equation of both system variable and performances. Then, the solver guesses the appropriate values and simulates if the system variables are appropriate or not. If the result of validation doesn't satisfy the convergence and iteration tolerance, the solver makes a new Kriging models and iterates this sequence until satisfy the tolerances.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.3
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• pp.123-130
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• 2006

This paper presents characteristics analysis of skewed Synchronous Reluctance Motor using equivalent magnetic circuit and compares with the result of Finite Element Method. Torque ripple must be reduced, because it is producing noise and vibration. There is many kinds of method to reduce torque ripple, but generally we apply skewing stator or rotor. The 2D Finite Element Method(FEM) or 3D FEM is used to analyze the motor, since skew influence the average torque in the motor. However, the FEM takes much time in spite of the advanced computer and numerical technique. This paper will analyze characteristics of skewed synchronous reluctance motor using equivalent magnetic circuit.

• Journal of Information Processing Systems
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• v.16 no.3
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• pp.541-556
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• 2020

Wireless networks have become integral to society as they provide mobility and scalability advantages. However, their disadvantage is that they cannot control the media, which makes them vulnerable to various types of attacks. One example of such attacks is the evil twin access point (AP) attack, in which an authorized AP is impersonated by mimicking its service set identifier (SSID) and media access control (MAC) address. Evil twin APs are a major source of deception in wireless networks, facilitating message forgery and eavesdropping. Hence, it is necessary to detect them rapidly. To this end, numerous methods using clock skew have been proposed for evil twin AP detection. However, clock skew is difficult to calculate precisely because wireless networks are vulnerable to noise. This paper proposes an evil twin AP detection method that uses a multiple-feature-based machine learning classification algorithm. The features used in the proposed method are clock skew, channel, received signal strength, and duration. The results of experiments conducted indicate that the proposed method has an evil twin AP detection accuracy of 100% using the random forest algorithm.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.3
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• pp.390-397
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• 2008

Permanent Magnet Linear Synchronous Motor (PMLSM) has high efficiency, high energy density, and high control-ability. But, the detent force always is produced by the structure of slot-teeth. There are the disadvantages such as noise and vibration of the apparatuses are induced and the control ability is curtailed because detent force acts as thrust ripple. Therefore, the detent force reduction is an essential requirement in PMLSM. Generally, the method, skewing permanent magnet or slot-teeth, is used to reduce the detent force. But the thrust is decreased at the same time. If permanent magnet is skewed, the lateral force which operates as the perpendicular direction of skew direction is generated in linear guide of PMLSM. So, V-skew model is proposed for the reduction of lateral force. The lateral force acts as braking force in linear motion guide, and it has bad influence to the characteristics of PMLSM. However, these problems will not be solved by 2-dimensional Finite Element Analysis (FEA). So, in this paper 3-dimensional FEA is applied to analyze the PMLSM where permanent magnet is skewed and has overhang. The detent force and thrust characteristics considering skew and overhang effects of permanent magnet are analyzed by 3-dimensional FEA and the results are compared with experimental values to verify the propriety of analysis.

• Composites Research
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• v.25 no.6
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• pp.217-223
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• 2012

This study investigates a geometrical nonlinear dynamic behaviors of laminated skew plates made of advanced composite materials (ACM). Based on the first-order shear deformation plate theory (FSDT), the Newmark method and Newton-Raphson iteration are used for the nonlinear dynamic solution. The effects of cutout sizes, skew angles and lay up sequences on the nonlinear dynamic response for various parameters are studied using a nonlinear dynamic finite element program developed for this study. The several numerical results were in good agreement with those reported by other investigators for square composite plates with or without central cutouts, and the new results reported in this paper show the significant interactions between the cutout, skew angles and layup sequence in the laminate. Key observation points are discussed and a brief design guideline of skew laminates is given.

• Journal of the Korean Statistical Society
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• v.34 no.3
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• pp.245-261
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• 2005

The marginal distribution of X is considered when (X, Y) has a truncated bivariate t-distribution. This paper mainly focuses on the marginal nontruncated distribution of X where Y is truncated below at its mean and its observations are not available. Several properties and applications of this distribution, including relationship with Azzalini's skew-normal distribution, are obtained. To circumvent inferential problem arises from adopting the frequentist's approach, a Bayesian method utilizing a data augmentation method is suggested. Illustrative examples demonstrate the performance of the method.

• International Journal of Aeronautical and Space Sciences
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• v.15 no.2
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• pp.173-182
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• 2014

The structured singular value (${\mu}$) analysis based method has many advantages for the robust stability analysis of missiles with uncertain parameters. Nevertheless, the present linear fractional transformation (LFT) modeling process, which is the basis of ${\mu}$ analysis, is complex, and not suitable for automatic implementation; on the other hand, ${\mu}$ analysis requires a large amount of computation, which is a burden for large-scale application. A constructive procedure, which is computationally more efficient, and which may lead to a lower order realization than existing algorithms, is proposed for LFT modeling. To reduce the calculation burden, an analysis method is developed, based on skew ${\mu}$. On this basis, calculation of the supremum of ${\mu}$ over a fixed frequency range converts into a single skew ${\mu}$ value calculation. Two algorithms are given, to calculate the upper and lower bounds of skew ${\mu}$, respectively. The validity of the proposed method is verified through robust stability analysis of a missile with real uncertain parameters.

• Journal of Korea Multimedia Society
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• v.10 no.2
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• pp.218-225
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• 2007

This paper presents a technique to detect a document skew that often occurs during document scanning. To correct a skewed document is essential for automatic processing system including character segmentation, character recognition and so on. The proposed algorithm can detect a skew angle exactly by searching characters baselines that have slant information of the document within a candidated area. To reduce processing time, we resized the image small and then established a ROI (region of interest) by morphology operations and connected components analysis. We compared our method with the existing method based on morphology operations and proved correctness and efficiency of the proposed algorithm through experiments and analysis with various kind of document images.

• Journal of KIISE:Databases
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• v.29 no.3
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• pp.180-192
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• 2002

We investigate the effect of the data skew of join attributes on the performance of a pipelined multi-way hash join method, and propose two new harsh join methods in the shared-nothing multiprocessor environment. The first proposed method allocates buckets statically by round-robin fashion, and the second one allocates buckets dynamically via a frequency distribution. Using harsh-based joins, multiple joins can be pipelined to that the early results from a join, before the whole join is completed, are sent to the next join processing without staying in disks. Shared nothing multiprocessor architecture is known to be more scalable to support very large databases. However, this hardware structure is very sensitive to the data skew. Unless the pipelining execution of multiple hash joins includes some dynamic load balancing mechanism, the skew effect can severely deteriorate the system performance. In this parer, we derive an execution model of the pipeline segment and a cost model, and develop a simulator for the study. As shown by our simulation with a wide range of parameters, join selectivities and sizes of relations deteriorate the system performance as the degree of data skew is larger. But the proposed method using a large number of buckets and a tuning technique can offer substantial robustness against a wide range of skew conditions.