• Journal of Biomedical Engineering Research
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• v.28 no.6
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• pp.756-767
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• 2007

For the combination of phosphor screens having various thicknesses and a photodiode array manufactured by complementary metal-oxide-semiconductor (CMOS) process, we report the observation of image-quality degradation under the irradiation of 45-kVp spectrum x rays. The image quality was assessed in terms of dark pixel signal, dynamic range, modulation-transfer function (MTF), noise-power spectrum (NPS), and detective quantum efficiency (DQE). For the accumulation of the absorbed dose, the radiation-induced increase both in dark signal and noise resulted in the gradual reduction in dynamic range. While the MTF was only slightly affected by the total ionizing dose, the noise power in the case of $Min-R^{TM}$ screen, which is the thinnest one among the considered screens in this study, became larger as the total dose was increased. This is caused by incomplete correction of the dark current fixed-pattern noise. In addition, the increase tendency in NPS was independent of the spatial frequency. For the cascaded model analysis, the additional noise source is from direct absorption of x-ray photons. The change in NPS with respect to the total dose degrades the DQE. However, with carefully updated and applied correction, we can overcome the detrimental effects of increased dark current on NPS and DQE. This study gives an initial motivation that the periodic monitoring of the image-quality degradation is an important issue for the long-term and healthy use of digital x-ray imaging detectors.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.9
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• pp.1078-1085
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• 2011

Prediction of a minimum crack size for growth, which is defined as a crack size that grows fast enough to keep ahead of its removal by contact wear and periodic grinding, is the most demanding work to prevent rail from fatigue failure and develop cost effective railway maintenance strategy In this study, we investigated the wheel load increment due to a rail defect during a train ran over it, and its effect on the minimum crack size for growth. For this purpose, we developed simulation software based on the Fletcher and Kapoor's "2.5D" model and measured wheel load increment during a train passed over a defect. A maximum contact pressure and contact patch size were calculated by 3D FEM and crack growth analyses were performed by varying two of dominant contact contributors; surface friction coefficient(0.1, 0.2, 0.3 and 0.4) and crack aspect ratio. The minimum crack sizes for growth were calculated from 0.29 to 1.44mm depending on the contact conditions. They were decreasing with increasing surface friction coefficient and decreasing with crack aspect ratio(a/b).

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.1
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• pp.45-57
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• 2005

In this paper, we extend the performance of bidirectional TCP connection over end-to-end network that uses transfer rate-based flow and congestion control. The sharing of a common buffer by TCP packets and acknowledgement has been known to result in an effect called ack compression, where acks of a connection arrive at the source bunched together, resulting in unfairness and degraded throughput. The degradation in throughput due to bidirectional traffic can be significant. Even in the simple case of symmetrical connections with adequate window size, the connection efficiency is improved about 20% for three levels of background traffic 2.5Mbps, 5.0Mbps and 7.5Mbps. Otherwise, the throughput of jitter is reduced about 50% because round trip delay time is smaller between source node and destination node. Also, we show that throughput curve is improved with connection rate algorithm which is proposed for TCP congetion avoidance as a function of aggressiveness threshold for three levels of background traffic 2.5Mbps, 5Mbps and 7.5Mbps. By analyzing the periodic bursty behavior of the source IP queue, we derive estimated for the maximum queue size and arrive at a simple predictor for the degraded throughput, applicable for relatively general situations.

• Korean Institute of Interior Design Journal
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• v.25 no.6
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• pp.127-138
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• 2016

As the dark side of society, Idle spaces, which occurred with the paradigm change due to rapid modernization and industralization, has been existing as a severed part in cities. But with the periodic change, interest in the existing place and regional regeneration, and the necessity of reconsidering about the idle spaces values of space, city environment, socio-culture, and economy was proposed. I estimated that the change of relational aesthetics aspect of modern arts resulted in the consideration of recognizing 'place' of art, through the study, it was revealed that the form of modern arts and change of enjoyment were related to space, and the fact that this had a relation with the rise of artistic regeneration of idle spaces. mutually communicative relationship formation and practical form of arts was deducted through the interpretation of relational aesthetics, Idle spaces and artistic regeneration space can be categorized into forms of experiential space, creative space, and cultural space, depending on the formation of relationship between author-art-audience. Through the comprehensive analysis, Artistic regeneration space by relationship formation is Vitalization of various forms of art and participation program eliminates the boundary between creation and enjoyment, and the space itself can be said to contain extensive, integral, and nonterritorialization meaning as a place of experiencing art. In other words, Artistic regeneration space of idle spaces forms a close relationship with the local society, and is placed within the context of daily domain as an open space, straying off from the existing separative and closed artistic space configuration. and artistic changeover of idle spaces is not only the appearance of space that simply fulfills function according to transfiguration of modern art, but signifies that art is coexisting with space as an indivisible relationship, and can be said to be the foothold of new relationship creation as the practical 'place' of art.

• Journal of Korea Multimedia Society
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• v.17 no.2
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• pp.132-142
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• 2014

Stereo camera is drawing attention as an essential sensor for future intelligence robot system since it has the advantage of acquiring not only distance but also other additive information for an object. However, it cannot match correlated point on target image for low textured region or periodic patterned region such as wall of building or room. In this paper, we propose a stereo matching technique that increase the matching performance by fusing belief propagation stereo matching algorithm and local distance measurements of 2D-laser range finder in order to overcome this kind of limitation. The proposed technique adds laser measurements by referring quad-tree based segment information on to the local-evidence of belief propagation stereo matching algorithm, and calculates compatibility function by reflecting over-segmented information. Experimental results of the proposed method using simulation and real test images show that the distance information for some low textured region can be acquired and the discontinuity of depth information is preserved by using segmentation information.

• Journal of the Korean Institute of Educational Facilities
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• v.19 no.6
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• pp.25-36
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• 2012

University campuses have been developed along with the historical development of mankind in association with the characteristics of urban changes. In particular, regarding the master plan reflecting periodic characteristics, now is the time to grope for crucial roles today that we are pursuing international growth of universities. Also, with the development of cities, in terms of the aspects of campus development, various borderline extension strategies are explored due to the physical limitation. And with the program methods through the exchange with the local community, we are concretizing this through the formation of new campuses. Seoul National University, the subject of this paper, is groping for ways of extension through the SNU-Valley Project with its Gwanak campus. Along with this, it is looking for ways of cubic borderline extension by forming Siheung international campus. The conclusion drawn through above contents is as written below: First, universities located in cites have relatively more limitations in the extension of campus space along with the development of urban space changes. To overcome this, various ways like political or physical space extension strategies are being explored. Second, along with the physical strategies visually shown in suggesting university campus master plans, we can recognize the importance of suggesting vision through specialization strategies. Third, it is about the importance of improving relationship with the local community. With the approaches based on human resources and reasonable connection of space, this also plays roles in enhancing the urbanity of the campus. Fourth, we can see the aspects of campus' urban function enhancing. It is needed to connect urban context that a region has with environment and grope for ways to enhance centrality, connection, and accessibility in it.

• Journal of Biomedical Engineering Research
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• v.31 no.5
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• pp.395-400
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• 2010

Hypertension is the chronic disease that the 16% of total population are suffering, and it needs to be studied to find alternative treatment because of the tolerance and side effect of medications that may bother some patients. in this paper, we verified practicality of implantable electrical stimulator that can readily change stimulus magnitude and frequency. And this device is possible to stimulate baroreflex or parasympathetic nerve. Therefore we performed in vitro tests and animal experiment for device's operating conditions. This device consist of implantable electrical stimulator and extracorporeal control/monitoring system. Stimulator was designed to make 1Hz~100Hz pulses and it can change continuous or periodic pulse train type. And this device can control stimulator's function and monitor stimulator's status and patients' blood pressure at exterior of body using ZigBee module as wireless telecommunication. We verified that stimulator have error rate under 5% at 50mm depth of organs and, stimulator makes high-efficiency energy with closer position of two electrodes. Also we can confirm the performance of device that decreasing blood pressure and heart rate of a rat by electrical stimulation.

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.11
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• pp.956-962
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• 2005

This paper presents an integrated analysis of production and financing decisions. We assume that a cash storage unit is installed to manage the cash flows related with production activities such as raw material procurement, process operating setup, Inventory holding cost and finished product sales. Temporarily financial investments are allowed for more profit. The production plant is modeled by the Batch-Storage Network with Recycle Streams in Yi and Reklaitis (2003). The objective function of the optimization is minimizing the opportunity costs of annualized capital investment and cash/material inventory while maximizing stockholder's benefit. No depletion of all the material and cash storage units is major constraints of the optimization. A novel production and inventory analysis formulation, the PSW(Periodic Square Wave) model, provides useful expressions for the upper/lower bounds and average level of the cash and material inventory holdups. The expressions for the Kuhn-Tucker conditions of the optimization problem can be reduced to two subproblems and analytical lot sizing equations under a mild assumption about the cash flow pattern of stockholder's dividend. The first subproblem is a separable concave minimization network flow problem whose solution yields the average material flow rates through the networks. The second subproblem determines the decisions about financial Investment. Finally, production and financial transaction lot sizes and startup times can be determined by analytical expressions as far as the average flow rates are calculated. The optimal production lot and storage sizes considering financial factors are smaller than those without such consideration. An illustrative example is presented to demonstrate the results obtainable using this approach.

• Journal of Institute of Control, Robotics and Systems
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• v.17 no.9
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• pp.932-940
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• 2011

This paper presents an integrated analysis of supply chain and financing decisions of multi-national corporation. We construct a model in which multiple currency storage units are installed to manage the currency flows associated with multi-national supply chain activities such as raw material procurement, process operation, inventory control, transportation and finished product sales. Core contribution of this study is to quantitatively investigate the influence of macroscopic economic factors such as exchange rates and taxes on operational decisions. The supply chain is modeled by the Process-Storage Network with recycle streams. The objective function of the optimization is minimizing the opportunity costs of annualized capital investments and currency/material inventories minus the benefit to stockholders interpreted by home currency. The major constraints of the optimization are that the material and currency storage units must not be depleted. A production and inventory analysis formulation, the periodic square wave (PSW) model, provides useful expressions for the upper/lower bounds and average levels of the currency and material inventory holdups. The expressions for the Kuhn-Tucker conditions of the optimization problem are reduced to a subproblem and analytical lot sizing equations. The procurement, production, transportation and financial transaction lot sizes can be determined by analytical expressions after the average flow rates are already known. We show that, when corporate income tax is taken into consideration, the optimal production lot and storage sizes are smaller than is the case when such factors are not considered typically by 20 %.

• Journal of the Korea Society of Computer and Information
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• v.19 no.7
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• pp.87-93
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• 2014

TIn analysis as the first step of S/W development, security requirements of identification and authentication, ID and password management, authentication process, authentication method, ete. should be defined. Identification is to uniquely identify certain users and applications running on a certain system. Authentication means the function to determine true or false users and applications in some cases. This paper is to suggest the security requirements for identification and authentication in analysis step. Firstly, individual ID should be uniquely identified. The second element is to apply the length limitations, combination and periodic changes of passwords. The third should require the more reinforced authentication methods besides ID and passwords and satisfy the defined security elements on authentication process. In this paper, the security requirements for the step of identification and authentication have been explained through several practical implementation methods.