• International Journal of Control, Automation, and Systems
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• 제2권3호
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• pp.374-383
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• 2004

This paper presents a neural network adaptive controller for autonomous diving control of an autonomous underwater vehicle (AUV) using adaptive backstepping method. In general, the dynamics of underwater robotics vehicles (URVs) are highly nonlinear and the hydrodynamic coefficients of vehicles are difficult to be accurately determined a priori because of variations of these coefficients with different operating conditions. In this paper, the smooth unknown dynamics of a vehicle is approximated by a neural network, and the remaining unstructured uncertainties, such as disturbances and unmodeled dynamics, are assumed to be unbounded, although they still satisfy certain growth conditions characterized by 'bounding functions' composed of known functions multiplied by unknown constants. Under certain relaxed assumptions pertaining to the control gain functions, the proposed control scheme can guarantee that all the signals in the closed-loop system satisfy to be uniformly ultimately bounded (UUB). Simulation studies are included to illustrate the effectiveness of the proposed control scheme, and some practical features of the control laws are also discussed.

• 대한전자공학회논문지TC
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• 제48권11호
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• pp.22-27
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• 2011

스펙트럼 감지를 하기 위해 에너지 검파기는 수신 신호의 에너지를 미리 정해둔 임계값과 비교하여 1차 사용자가 면허 대역 내에서 활동을 하는 지 여부를 판단한다. 여기에서 임계값은 해당 주파수 대역에 존재하는 잡음의 전력 수준과 관련이 있다. 에너지 검파에 대한 과거의 연구 대부분은 잡음 전력을 미리 정확하게 알고 있다는 가정에 기초한 것이었다. 그러나 실제 환경에서는 잡음 전력에 대한 불확실성이 존재하기 때문에 이 가정은 현실적으로 유효하지 않다. 그러므로 잡음 전력의 불확실성이 에너지 검파기의 스펙트럼 감지 성능에 미치는 영향을 파악할 필요가 있다. 이에 이 논문에서는 유수 정리(residue theorem)에 기반을 둔 적분을 활용하여 그 영향을 수학적으로 분석하고 그 결과를 제시하고자 한다.

• 한국통신학회논문지
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• 제27권2A호
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• pp.165-172
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• 2002

MPEG-2 트랜스부호화기는 이미 부호화되어 있는 비트스트림의 비트율을 변경하는 것이다. 비트율제어를 위하여 기존의 제어 방식을 개선한 새로운 알고리듬을 제안하였으며 모의실험을 통해 임의의 비트율로 변경했을 때 우수한 성능을 보이는 것을 확인하였다. 비트율 제어에서는 비트스트립내의 정보를 이용하여 매크로블럭 단위의 비트율-양자화 파라미터 모델을 제안하였다. 이 모델은 DCT 계수를 사용하였기 때문에 화면의 종류에 관계없이 사용할 수 있었다. 비트율-양자화파라미터 모델의 정확도를 높이도록 매크로블럭의 활동도에 따른 구분도 하였다. 모의 실험결과, 특정 비트율을 가지는 비트스트림을 가지고 다른 비트율로 변환하였을 때 TM5로 재부호화 했을 때보다 제안한 방식이 더 높은 PSNR값과 제어 성능을 보였다. MPEG-2의 스케일러블 프로파일도 분석을 하였다. 그 결과 변환부호화기에는 적합하지 않다는 결과를 얻었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1801-1806
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• 2004

Stochastic nature of subgrid-scale stress causes the predictability problem in large eddy simulation (LES) by which the LES solution field decorrelates with field from filtered directnumerical simulation (DNS). In order to evaluate the predictability limit in a priori sense, the information on the interplay between resolved scale and subgrid-scale (SGS) is required. In this study, the analysis on the inter-scale interaction is performed by applying tophat and cutoff filters to DNS database of flow over a circular cylinder at Reynolds number of 3900. The effect of filter shape is investigated on the interpretation of correlation between scales. A critique is given on the use of tophat filter for SGS analysis using DNS database. It is shown that correlations between Karman vortex and SGS kinetic energy drastically decrease when the cutoff filter is used, which implies that the small scale universality holds even in the presence of the large scale coherent structure.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.168-177
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• 2020

Many coastal engineering designs utilize empirical formulas containing the Equivalent Deep-water Wave Height (EDWH), which is normally given a priori. However, no studies have explicitly discussed a method for determining the EDWH and the resulting design wave heights (DEWH) under irregular wave conditions. Unfortunately, it has been the case in many design practices that the EDWH is incorrectly estimated by dividing the Shallow-water Wave Height (SWH) at the structural position with its corresponding shoaling coefficient of regular wave. The present study reexamines the relationship between the Shallow-water Wave Height (SWH) at the structural position and its corresponding EDWH. Then, a new procedure is proposed to facilitate the correct estimation of EDWH. In this procedure, the EDWH and DEWH are determined differently according to the wave propagation model used to estimate the SWH. For this, Goda's original method for nonlinear irregular wave deformation is extended to produce values for linear shoaling. Finally, exemplary calculations are performed to assess the possible errors caused by a misuse of the wave height calculation procedure. The relative errors with respect to the correct values could exceed 20%, potentially leading to a significant under-design of coastal or harbor structures in some cases.

• Safety and Health at Work
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• 제11권4호
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• pp.385-396
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• 2020

Teachers are facing various job demands with psychosocial aspects being fundamental due to the nature of the occupation. Although teachers' work is associated with different psychosocial health risks, little is known on how to identify and tackle those. Thus, a systematic literature search as per the PRISMA statement was conducted via MEDLINE (PubMed), PSYNDEX (PubPsych), and ScienceDirect. Two reviewers independently screened 2261 titles and abstracts and 169 full-texts. According to the inclusion criteria established a priori, articles from peer-reviewed journals (English or German) on psychosocial risk management in teachers were incorporated. Despite a comprehensive and sensitive search, only four publications could be identified, outlining a process to implement risk management and different assessment tools. Taken together, data presented in the articles were scarce. Recommendations for process steps and the assessment of psychosocial risks can be derived from the findings. To implement effective psychosocial risk management in the teaching profession, further research is needed, though. Effective and practicable approaches, which are accepted by the target group, should be further developed and investigated. Relevant causes of occupational strain in the teaching profession must be identified and assessed reliably. Low-threshold interventions should be implemented, and the outcome must be evaluated afterward.

• 대한유전성대사질환학회지
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• 제23권2호
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• pp.1-7
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• 2023

유전성 대사질환은 생화학적 대사 이상에 의해 발생하는 질환 군으로, 매우 다양할 뿐만 아니라 임상 양상이 서로 겹칠 수 있어 진단에 어려움을 겪을 수 있다. 과거에는 유전성 대사질환의 원인이 될 수 있는 유전자를 선정한 후 한 개씩 분석하는 방식으로 유전자 검사를 시행했다. 하지만, 최근에는 차세대 염기서열분석 기술이 발전함에 따라 유전성 대사질환과 관련된 수백-수천개의 유전자를 한꺼번에 분석하거나, 인간의 모든 유전자를 포함하는 엑솜/게놈 분석을 시행한 후 원인 유전자를 찾는 방식으로 유전 진단의 패러다임이 바뀌고 있다. 본 종설에서는 차세대 염기서열분석을 이용한 유전성 대사질환의 유전 진단 방법과 진단율 및 주의점 등을 살펴보고자 한다.

• Journal of Ecology and Environment
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• 제32권2호
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• pp.103-107
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• 2009

We investigated colonization and extinction patterns in a meta population of the gold-spotted pond frog (Rana planeyi ehoseniea) near the Korea National University of Education, Chungbuk, Korea, by surveying the frogs in the nine occupied habitat patches in the study area four times per breeding season for three years (2006$\sim$2008) and recording whether the patches were occupied by frogs as well as how many frogs were calling in the patches. We then developed five a priori year-specific models using the Akaike Information Criterion (AIC). The models predicted that: 1) probabilities of colonization and local extinction of the frogs were better explained by year-dependent models than by constant models, 2) there are high local extinction and low colonization probabilities, 3) approximately 31% number of patches will be occupied at equilibrium, and 4) that considerable variation in occupation rate should occur over a 30-year period, due to demographic stochasticity (in our model, the occupation rate ranged from 0.222 to 0.889). Our results suggest that colonization is important in this metapopulation system, which is governed by mainly stochastic components, and that more constructive conservation effects are needed to increase local colonization rates.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.570-574
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• 2003

In most boundary estimation algorithms estimation in EIT (Electrical Impedance Tomography), anomaly boundaries can be expressed with Fourier series and the unknown coefficients are estimated with proper inverse algorithms. Furthermore, the number of anomalies is assumed to be available a priori. The prior knowledge on the number of anomalies may be unavailable in some cases, and we need to determine the number of anomalies with other methods. This paper presents an algorithm for the boundary estimation in EIT (Electrical Impedance Tomography) using the prior information from the conventional Newton-Raphson method. Although Newton-Raphson method generates so poor spatial resolution that the anomaly boundaries are hardly reconstructed, even after a few iterations it can give general feature of the object to be imaged such as the number of anomalies, their sizes and locations, as long as the anomalies are big enough. Some numerical experiments indicate that the Newton-Raphson method can be used as a good predictor of the unknown boundaries and the proposed boundary discrimination algorithm has a good performance.

• Journal of Communications and Networks
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• 제16권1호
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• pp.36-44
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• 2014

Exploiting the energy-delay tradeoff for energy saving is critical for developing green wireless communication systems. In this paper, we investigate the delay-constrained energy-efficient packet transmission. We aim to minimize the energy consumption of multiple randomly arrived packets in an additive white Gaussian noise channel subject to individual packet delay constraints, by taking into account the practical on-off circuit power consumption at the transmitter. First, we consider the offline case, by assuming that the full packet arrival information is known a priori at the transmitter, and formulate the energy minimization problem as a non-convex optimization problem. By exploiting the specific problem structure, we propose an efficient scheduling algorithm to obtain the globally optimal solution. It is shown that the optimal solution consists of two types of scheduling intervals, namely "selected-off" and "always-on" intervals, which correspond to bits-per-joule energy efficiency maximization and "lazy scheduling" rate allocation, respectively. Next, we consider the practical online case where only causal packet arrival information is available. Inspired by the optimal offline solution, we propose a new online scheme. It is shown by simulations that the proposed online scheme has a comparable performance with the optimal offline one and outperforms the design without considering on-off circuit power as well as the other heuristically designed online schemes.