• Journal of Digital Convergence
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• v.10 no.8
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• pp.159-172
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• 2012

In the recent, due to explosion of Digital Universe, the performance of computer and storage system is reducing. Therefore, the upgrade and capacity expansion needs is growing. Countermeasure for this problem is required fundamental and long-term solutions rather than piecemeal expansion. In this paper, we establish a data management policy for an enterprise through the operational status of storage system and the analysis of data value of it, and implement ILM-based tiered storage system on the basis of these. The results of this study shows the overall throughput was improved about 21% compared to the existing system, it is very effective to maintain continuous quality and reduce operating costs in the long term aspect.

• IEIE Transactions on Smart Processing and Computing
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• v.2 no.6
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• pp.357-366
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• 2013

Spectrum sensing, as a fundamental functionality of Cognitive Radio (CR), enables Secondary Users (SUs) to monitor the spectrum and detect spectrum holes that could be used. Recently, the security issues of Cognitive Radio Networks (CRNs) have attracted increasing research attention. As one of the attacks against CRNs, a Primary User Emulation (PUE) attack compromises the spectrum sensing of CR, where an attacker monopolizes the spectrum holes by impersonating the Primary User (PU) to prevent SUs from accessing the idle frequency bands. Energy detection is often used to sense the spectrum in CRNs, but the presence of PUE attack has not been considered. This study examined the effect of PUE attack on the performance of energy detection-based spectrum sensing technique. In the proposed protocol, the stationary helper nodes (HNs) are deployed in multiple stages and distributed over the coverage area of the PUs to deliver spectrum status information to the next stage of HNs and to SUs. On the other hand, the first stage of HNs is also responsible for inferring the existence of the PU based on the energy detection technique. In addition, this system provides the detection threshold under the constraints imposed on the probabilities of a miss detection and false alarm.

• Advances in aircraft and spacecraft science
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• v.7 no.5
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• pp.425-440
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• 2020

The work presented herein is a numerical investigation of the flow field inside a resonant igniter, with the aim of predicting the performances in terms of cavity temperature and noise spectrum. A resonance ignition system represens an attractive solution for the ignition of liquid rocket engines in space missions which require multiple engine re-ignitions, like for example debris removal. Furthermore, the current trend in avoiding toxic propellants leads to the adoption of green propellant which does not show hypergolic properties and so the presence of a reliable ignition system becomes fundamental. Resonant igniters are attractive for in-space thrusters due to the low weight and the absence of an electric power source. However, their performances are strongly influenced by several geometrical and environmental parameters. This motivates the study proposed in this work in which the flow field inside a resonant igniter is numerically investigated. The unsteady compressible Reynolds Averaged Navier-Stokes equations are solved by means of a finite volume scheme and the effects of several wall boundary conditions are investigated (adiabatic, isothermal, radiating). The results are compared with some available experimental data in terms of cavity temperature and noise spectrum.

• Smart Structures and Systems
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• v.18 no.6
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• pp.1111-1123
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• 2016

The present study aims at proposing an analytical method for semi-active structural control by using block pulse functions. The performance of the resulting controlled system and the requirements of the control devices are highly dependent on the control algorithm employed. In control problems, it is important to devise an accurate analytical method with less computational expenses. Block pulse functions (BPFs) set proved to be the most fundamental and it enjoyed immense popularity in different applications in the area of numerical analysis in systems science and control. This work focused on the application of BPFs in the control algorithm concerning decrease the computational expenses. Variable orifice dampers (VODs) are one of the common semi-active devices that can be used to control the response of civil Structures during seismic loads. To prove the efficiency of the proposed method, numerical simulations for a 10-story shear building frame equipped with VODs are presented. The controlled response of the frame was compared with results obtained by controlling the frame by the classical clipped-optimal control method based on linear quadratic regulator theory. The simulation results of this investigation indicated the proposed method had an acceptable accuracy with minor computational expenses and it can be advantageous in reducing seismic responses.

• Smart Structures and Systems
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• v.20 no.1
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• pp.99-114
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• 2017

In cognitive science, it is illustrated how the collective opinions of a group of individuals answers to questions involving quantity estimation. One example of this approach is introduced in this article as Star Graph (SG) algorithm. This graph describes the details of communication among individuals to share their information and make a new decision. A new labyrinthine network of neighbors is defined in the decision-making process of the algorithm. In order to prevent getting trapped in local optima, the neighboring networks are regenerated in each iteration of the algorithm. In this algorithm, the normal distribution is utilized for a group of agents with the best results (guidance group) to replace the existing infeasible solutions. Here, some new functions are introduced to provide a high convergence for the method. These functions not only increase the local and global search capabilities but also require less computational effort. Various benchmark functions and engineering problems are examined and the results are compared with those of some other algorithms to show the capability and performance of the presented method.

• Journal of the Ergonomics Society of Korea
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• v.20 no.1
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• pp.15-29
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• 2001

This study was conducted to develop a prototype of adjustable desk and chair for students from elementary to high school. The development process started with identifying the problems of existing adjustable desks and chairs that are currently available in the market. The following fundamental design criteria were established and then applied to develop the prototype. The criterion of minimization of production cost yielding lower the market selling price was the most critically considered in view of the school furniture buyers' price-consciousness. Other design criteria used in this development were designing for stable and solid structure, requiring few motions and no tools to adjust, requiring the use of only one hand to adjust, unrestricting the adjustable interval, providing extra space for foot and knee area, reducing weight to move easily, and requiring not to move around for cleaning up floor. To evaluate the performance of the prototype, the adjustability of prototype was specifically compared with both dimensions suggested by KS G 2010(Korean Standards for desks and chairs for students) and current anthropometric dimension in terms of the flexible range of accommodation. Results of this study illustrate that the prototype developed in this study could be accommodated for the both dimensions. As a concluding mark, appropriate adjustable range for various grades and age groups were presented.

• Journal of Korean Academy of Nursing
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• v.48 no.4
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• pp.419-431
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• 2018

Purpose: The purpose of this study was to develop and establish the psychometric properties of a clinical nursing competency evaluation tool to be utilized by clinical preceptors. Methods: The initial items were identified through in-depth literature review and field interviews based on a hybrid model. Content validation of the items was evaluated through three rounds of content validity testing. Participants were 34 clinical preceptors and 443 nursing students participating in clinical practice. Data were analyzed using exploratory and confirmatory factor analysis, convergence and discriminant validity, internal consistency and inter-rater reliability. Results: The final scale consisted of 23 items and four factors, fundamental nursing skills performance, critical thinking skills based on the nursing process, basic nursing knowledge, and professional attitude; these factor explained 69.7% of the total variance. The analysis with multi-trait/multi-item matrix correlation coefficients yielded 100.0% and 95.7 % convergence and discriminant validity, respectively. Cronbach's alpha for the total items was .95. The four subscale model tested by confirmatory factor analysis was satisfactory. Inter-rater reliability ranged from .912 to .967. Conclusion: This scale was found to be a reliable and valid instrument that clinical preceptors can apply for evaluating the clinical nursing competency of nursing students in clinical settings.

• Journal of the Optical Society of Korea
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• v.19 no.4
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• pp.363-370
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• 2015

The current waveform model of a laser altimeter is based on a Gaussian laser beam of fundamental mode, while the flattened Gaussian beam has many advantages such as nearly constant energy distribution on the center of the cross-section. Following the theory of the flattened Gaussian beam and the waveform theory of the laser altimeter, some of the primary parameters of the received waveform were derived, and a laser altimetry waveform simulator and waveform processing software were programmed and improved under the circumstance of a flattened Gaussian beam. The result showed that the bias between theoretical and simulated waveforms was less than 3% for every order mode, the waveform width and range error would increase as target slope or order number rose. Under higher order mode, the shapes of the received waveforms were no longer Gaussian, and could be fitted more precisely as a generalized Gaussian function with power bigger than 2. The flattened beam got much better performance for a multi-surface target, especially when the small surface is far from the center of the laser footprint. This article provides the waveform theoretical basis for the use of a flattened Gaussian beam in a laser altimeter.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.2 no.1
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• pp.11-15
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• 2009

In this study, we have developed the SMPS(Switched-mode power supply) power module for the medical kit. It is used the medical kit for improved supplying power better than the existing power module in performance, safety and reliability. The developed SMPS(Switched-mode power supply) is composed of the three fundamental electronic circuits, first one is for converting AC power to DC power, second one is for converting to high frequency, and the other is for absorbing noise frequency and preventing malfunction. It is possible for developed SMPS module to enlarge applications for PC, home appliances, switchboard as well as medical instruments.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.298-303
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• 2001

A fundamental study on the under water harvest-type ice storage system and its temperature characteristics in ice storage system was performed experimentally. The experiments were conducted by changing the inlet refrigerant temperature of an evaporator to analyzing the thermal fluid motion inside the ice storage tank. From the experimental results, the cold storage characteristics were investigated by measuring the axial and radial temperature variations inside the ice storage tank with respect to the inlet and outlet refrigerant temperatures of an evaporator. In case of the under water harvest-type ice storage system, thermal fluid. motion inside the ice storage tank was shown differently in comparison with that of other ice storage systems. During the cooling storage process, there was no supercooling phenomenon in the ice storage tank. These results show the characteristic of this system and the possibility of application to other fields.