• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2015년도 추계학술발표대회
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• pp.319-321
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• 2015

인지무선네트워크 (Cognitive Radio Networks) 환경에서 스펙트럼의 원소유주인 1차사용자가 전송을 개시하는 경우, 같은 채널을 사용하는 2차사용자의 TCP (Transmission Control Protocol) 는 전송 불능 상태가 되어 심각한 성능저하가 발생한다. 이러한 성능저하는 1차사용자의 등장으로 인해 채널이 사용 불가능 해지는 상태를 패킷 손실로 판단하여 재전송 타임아웃이 발생하기 때문에 발생된다. 우리는 이 문제를 링크 또는 물리 계층 (하위계층) 과 TCP간의 크로스레이어링을 통하여 해결하고자 한다. 하위 계층은 1차사용자의 전송이 감지되면, 이를 TCP에게 시그널링하고, TCP는 이를 통해 재전송 타이머와 혼잡 윈도우를 고정시키고, 패킷 전송을 중단하도록 한다. 또, 하위계층이 가용 채널을 감지하게 되면, 재차 TCP에게 시그널링을 함으로써, 전송이 신속하게 재개되도록 한다. 제안하는 방법은 실제 USRP(Universal Software Radio Peripheral)에 구현하여 성능의 향상을 검증한다.

• Journal of Smart Tourism
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• 제1권4호
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• pp.9-18
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• 2021

The impacts that AI and robotics systems can and will have on our everyday lives are already making themselves manifest. However, there is a lack of research on the ethical impacts and means for amelioration regarding AI and robotics within tourism and hospitality. Given the importance of designing technologies that cross national boundaries, and given that the tourism and hospitality industry is fundamentally predicated on multicultural interactions, this is an area of research and application that requires particular attention. Specifically, tourism and hospitality have a range of context-unique stakeholders that need to be accounted for in the salient design of AI systems is to be achieved. This paper adopts a stakeholder approach to develop the conceptual framework to centralize human values in designing and deploying AI and robotics systems in tourism and hospitality. The conceptual framework includes several layers - 'Human-human-AI' interaction level, direct and indirect stakeholders, and the macroenvironment. The ethical issues on each layer are outlined as well as some possible solutions to them. Additionally, the paper develops a research agenda on the topic.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.276-276
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• 2010

Localized surface plasmon resonance (LSPR) has been explored recently as a promising approach to increase energy conversion efficiency in photovoltaic devices, particularly for thin film hydrogenated amorphous silicon (a-Si:H) solar cells. The LSPR is frequently excited via an electromagnetic (EM) radiation in proximate metallic nanostructures and its primary con sequences are selective photon extinction and local EM enhancement which gives rise to improved photogeneration of electron-hole (e-h) pairs, and consequently increases photocurrent. In this work, high-dielectric-constant (k) $ZrO_2$ (refractive index n=2.22, dielectric constant $\varepsilon=4.93$ at the wavelength of 550 nm) is proposed as spacing layer to enhance the LSPR for application to the thin film silicon solar cells. Compared to excitation of the LSPR using $SiO_2$ (n=1.46, $\varepsilon=2.13$ at the wavelength of 546.1 nm) spacing layer with Au nanoparticles of the radius of 45nm, that using $ZrO_2$ dielectric shows the advantages of(i) ~2.5 times greater polarizability, (ii) ~3.5 times larger scattering cross-section and ~1.5 times larger absorption cross-section, (iii) 4.5% higher transmission coefficient of the same thickness and (iv) 7.8% greater transmitted electric filed intensity at the same depth. All those results are calculated by Mie theory and Fresnel equations, and simulated by finite-difference time-domain (FDTD) calculations with proper boundary conditions. Red-shifting of the LSPR wavelength using high-k $ZrO_2$ dielectric is also observed according to location of the peak and this is consistent with the other's report. Finally, our experimental results show that variation of short-circuit current density ($J_{sc}$) of the LSPR enhanced a-Si:H solar cell by using the $ZrO_2$ spacing layer is 45.4% higher than that using the $SiO_2$ spacing layer, supporting our calculation and theory.

• Steel and Composite Structures
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• 제51권4호
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• pp.441-456
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• 2024

This paper aims to develop Machine Learning (ML) algorithms to predict the buckling resistance of cold-formed steel (CFS) channels with restrained flanges, widely used in typical CFS sheathed wall panels, and provide practical design tools for engineers. The effects of cross-sectional restraints were first evaluated on the elastic buckling behaviour of CFS channels subjected to pure axial compressive load or bending moment. Feedforward multi-layer Artificial Neural Networks (ANNs) were then trained on different datasets comprising CFS channels with various dimensions and properties, plate thicknesses, and restraining conditions on one or two flanges, while the elastic distortional buckling resistance of the elements were determined according to the Finite Strip Method (FSM). To develop less biased networks and ensure that every observation from the original dataset has the chance of appearing in the training and test set, a K-fold cross-validation technique was implemented. In addition, the hyperparameters of the ANNs were tuned using a grid search technique to provide ANNs with optimum performances. The results demonstrated that the trained ANNs were able to predict the elastic distortional buckling resistance of CFS flange-restrained elements with an average accuracy of 99% in terms of coefficient of determination. The developed models were then used to propose a simple ANN-based design formula for the prediction of the elastic distortional buckling stress of CFS flange-restrained elements. Finally, the proposed formula was further evaluated on a separate set of unseen data to ensure its accuracy for practical applications.

• Steel and Composite Structures
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• 제25권5호
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• pp.557-569
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• 2017

Moment-thrust-curvatures ($M-P-{\Phi}$ curves) are fundamental quantities for detailed descriptions of basic properties such as stiffness and strength of a section under axial loads required for accurate computation of the deformations of reinforced concrete or composite columns. Currently, the finite-element-based methods adopting small fibers for analyzing a section are commonly used for generating the $M-P-{\Phi}$ curves and they require large amounts of computational time and effort. Further, the conventional numerical procedure using the force-control method might encounter divergence problems under high compression or tension. Therefore, this paper proposes a divergence-free approach, combining the use of the displacement-control and the Quasi-Newton scheme in the incremental-iterative procedure, for generating the $M-P-{\Phi}$ curves of arbitrary sections. An efficient method for computing the strength from concrete components is employed, where the stress integration is executed by layer-based algorithms. For easy modeling of residual stress, cross sections of structural steel components are meshed into fibers for strength resultants. The numerical procedure is elaborated in detail with flowcharts. Finally, extensive validating examples from previously published research are given for verifying the accuracy of the proposed method.

• 대한기계학회논문집B
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• 제26권3호
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• pp.474-481
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• 2002

Fouling deposits due to surface-coated particles have been calculated using CFD techniques. The sticking probabilities of the surface-coated particles are also evaluated on the basis of an energy balance. The sticking probabilities of the deposit surface are also included in the prediction of the deposition occurring through the multiple impaction of particles with the deposit surface. The sticking probability of an impacting particle is expressed in terms of such parameters as particle viscosity, surface tension, impact velocity, impact angle and the thickness of the sticky layer on a particle. Particulate behavior around a tube in cross flow was studied using the Lagrangian approach. Three important parameters i.e. impact velocity, impact angle, and particulate concentration, were used in the prediction of deposition rate. The computational predictions were found to be in good agreement with the experimental data.

• 대한전자공학회논문지TC
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• 제47권10호
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• pp.27-35
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• 2010

무선 패킷 망에서 무선 자원과 무선 단말의 전력을 얼마나 효율적으로 사용할 수 있는가 하는 것은 무선 패킷 망 보급을 위한 기본 해결 과제이다. 이에 단말의 전력 소모를 줄이면서 무선 망 용량 (capacity)을 증가시키는 기법으로 전송 파워 조절 기법이 주목받고 있다. 무선 패킷 망에 전송 파워 조절 기법을 적용할 때 전송 파워의 세기에 따라 공평한 전송성능을 보장하지 못하고 기아상태에 이르는 전송 불공평성 문제가 지금까지 깊이 연구되지 않고 있다. 이에 본 연구에서는 전송 파워의 세기에 따른 성능 불공평성을 경쟁자 수의 차이에 의한 불공평한 매체 접근 기회에 있음을 분석을 통해 보이고 불공평성을 해결하기 위한 간단한 물리-맥 (PHY-MAC) 계층 간 접근법을 제안한다.

• Journal of Communications and Networks
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• 제17권2호
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• pp.172-183
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• 2015

To provide an efficient link maintenance approach, we propose a cross layer medium access control (LM-MAC) protocol for multichannel cognitive radio ad hoc networks. Link establishment and reliable transmission are two key problems for a perfect link maintenance mechanism. Since the cognitive user (CU) pairs have to reestablish their links each frame, in the proposed MAC protocol, three different access modes are designed to guarantee transmission efficiency in continuous frames. To enhance the transmission reliability, each CU will create a father spectrum list (FSL) after joining in the network. FSL is divided into three groups of sub-channels with different functions to compensate the packet loss caused by the primary users' appearance and the deep fading. Meanwhile, since the transmitter and the receiver will share the same FSL, periodical cooperative sensing is adopted to further optimize the former problem. Finally, compared with the existing opportunistic multichannel (OMC)-MAC protocol, the proposed LM-MAC protocol achieves better system performance in terms of saturation throughput, continuity and access delay.

• 전기학회논문지
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• 제67권9호
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• pp.1224-1231
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• 2018

Automatic age estimation has been used in many social network applications, practical commercial applications, and human-computer interaction visual-surveillance biometrics. However, it has rarely been explored. In this paper, we propose an automatic age estimation system, which includes face detection and convolutional deep learning based on an inception module. The latter is a 22-layer-deep network that serves as the particular category of the inception design. To evaluate the proposed approach, we use 4,000 images of eight different age groups from the Adience age dataset. k-fold cross-validation (k = 5) is applied. A comparison of the performance of the proposed work and recent related methods is presented. The results show that the proposed method significantly outperforms existing methods in terms of the exact accuracy and off-by-one accuracy. The off-by-one accuracy is when the result is off by one adjacent age label to the above or below. For the exact accuracy, the age label of "60+" is classified with the highest accuracy of 76%.

• Advances in aircraft and spacecraft science
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• 제3권3호
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• pp.331-349
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• 2016

Stiff and light fibre reinforced composites as used in air- and space-craft applications tend to high sound emission. Therefore, the damping properties are essential for the entire structural and acoustic engineering. Viscous damping is an established and reasonably linear model of the dissipation behaviour. Commonly, it is assumed to be isotropic and constant over all modes. For anisotropic materials it depends on the fibre orientation as well as the elastic and thermal material properties. To portray the orthogonal anisotropic behaviour, a model for unidirectional fibre reinforced plastics (frp) has been developed based on the classical laminate theory by ADAMS and BACON starting in 1973. Their approach includes three damping coefficients - for longitudinal damping in fibre direction, damping transversal to the fibres and shear based dissipation. The damping of a laminate is then accumulated layer wise including the anisotropic stiffness. So far, the model has been applied mainly to thermoset matrix materials. In this study, an experimental parameter estimation for different thermoplastic frp with angle ply and cross ply layups was carried out by measuring free vibrations of cantilever beams. The results show potential and limits of the ADAMS/BACON damping criterion. In addition, a possibility of modelling the anisotropic damping is shown. The implementation in standard FEA software is used to study the influence of boundary conditions on the damping properties and numerically estimate the radiated sound power of thin-walled frp parts.