• Journal of Advanced Marine Engineering and Technology
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• 제30권5호
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• pp.589-596
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• 2006

This study aims to propose a new model axial flow fan which attachs centrifugal blades, and to investigate the effect of centrifugal blades on the performance improvement of new model axial flow fan. A numerical simulation has been conducted using STAR-CD commercial code to solve the three dimensional incompressible Navier-Stokes equation for high Reynolds number $k-{\epsilon}$ turbulent model. Numerical simulation is carried out to investigate the detail phenomenon in the flow field and performance characteristics of new model and normal model fan. Calculation results are compared with normal model's results to investigate which centrifugal blades effect on velocity profile and pressure distribution at various flow field positions. and calculation results show that new model fan can improve the performance of total pressure.

• 천문학회지
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• 제47권4호
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• pp.123-135
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• 2014

A silicate carbon star is a carbon star which shows circumstellar silicate dust features. We collect a sample of 44 silicate carbon stars from the literature and investigate the validity of the classification. For some objects, it is uncertain whether the central star is a carbon star. We confirm that 29 objects are verified silicate carbon stars. We classify the confirmed objects into three subclasses based on the evolution phase of the central star. To investigate the effect of the chemical transition phase from O to C, we use the radiative transfer models for the detached silicate dust shells. The spectral energy distributions and the infrared two-color diagrams of the silicate carbon stars are compared with the theoretical model results. For the chemical transition model without considering the effect of a disk, we find that the life time of the silicate feature is about 50 to 400 years depending on the initial dust optical depth.

• 천문학논총
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• 제34권3호
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• pp.67-79
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• 2019

We present a semi-analytical method to calculate the global evolution of the ionized state of the intergalactic medium, on the basis of physically motivated star formation histories in the early universe. This method incorporates not only the conventional scenarios in which the star formation rate is proportional to the growth rate of the halo collapse fraction, but also the more sophisticated scenarios in which the star formation is self-regulated. We show that this variance in the star-formation model strongly impacts the resulting reionization history, which bears a prospect for observational discrimination of these models. We discuss how observations of the anisotropic polarization of the cosmic microwave background and the global 21cm signal from the high-redshift universe, most notably by Planck and EDGES, may probe the history of reionization.

• 한국통신학회논문지
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• 제12권4호
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• pp.357-364
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• 1987

본 논문에서는 다중프로세서 시스템을 구성하는 중요한 요소인 다단상호결합 네트웍의 성능을 고찰한다. Baseline 네트웍을 이용한 Star네트웍 시스템의 Hardware적인 구성을 고찰하며 Analytical Model로 Request가 받아들여질 확률과 Clustering 확률을 구한다. 그리고 Baseline네트웍 대신에 Delta네트웍을 이용하여 위에서 언급한 확률을 구한 다음 네트웍의 성능을 비교한다.

• 한국지구과학회지
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• 제35권5호
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• pp.362-374
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• 2014

This study investigated the initial mass function (IMF) and star formation history of high-mass stars in the Small Magellanic Cloud (SMC) using a population synthesis technique. We used the photometric survey catalog of Lee (2013) as the observable quantities and compare them with those of synthetic populations based on Bayesian inference. For the IMF slope (${\Gamma}$) range of -1.1 to -3.5 with steps of 0.1, five types of star formation models were tested: 1) continuous; 2) single burst at 10 Myr; 3) single burst at 60 Myr; 4) double bursts at those epochs; and 5) a complex hybrid model. In this study, a total of 125 models were tested. Based on the model calculations, it was found that the continuous model could simulate the high-mass stars of the SMC and that its IMF slope was -1.6 which is slightly steeper than Salpeter's IMF, i.e., ${\Gamma}=-1.35$.

• 한국항공우주학회지
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• 제34권2호
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• pp.96-100
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• 2006

본 논문은 위성의 자세정보를 획득하는 센서로서 과학기술위성2호에 장착하기 위해 개발 중인 이중 머리 별 추적기를 소개한다. 대부분의 별 센서는 위성의 한쪽 방향만 지향하기 때문에 태양 및 지구 영역으로 지향할 경우 별 인식이 불가능하다. 그래서 시스템은 두개의 카메라를 직각의 방향으로 지향하여 동시에 두개의 영상을 입력 받고 하나의 영상에서 별 인식을 실패할 경우 다른 영상에서 별 인식을 수행하여 별 인식률을 높이도록 구현하였다. 논문에서는 이중머리 별 추적기의 시험모델을 소개하고 별 인식 및 별 추적 알고리즘을 제안하였다.

• 천문학회지
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• 제43권1호
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• pp.1-8
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• 2010

JHK near-infrared photometry of star clusters in the dwarf irregular/dwarf starburst galaxy NGC 1569 are presented. After adopting several criteria to exclude other sources (foreground stars, background galaxies, etc.), 154 candidates of star clusters are identified in the near-infrared images of NGC 1569, which include very young star clusters. Especially, from analysis based on theoretical background, we found ten very young star clusters near the center of NGC 1569. The total reddening values toward these clusters are estimated to be $A_V$=1-9 mag from comparison with the theoretical estimates given by the Leitherer et al. (1999)'s star cluster model.

• 천문학회보
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• 제44권1호
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• pp.40.1-40.1
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• 2019

We utilize times since infall of cluster galaxies obtained from Yonsei Zoom-in Cluster Simulation (YZiCS), the cosmological hydrodynamic N-body simulations, and star formation rates from the SDSS data release 10 to study how quickly late-type galaxies are quenched in the cluster environments. In particular, we confirm that the distributions of both simulated and observed galaxies in phase-space diagrams are comparable and that each location of phase-space can provide the information of times since infall and star formation rates of cluster galaxies. Then, by limiting the location of phase-space of simulated and observed galaxies, we associate their star formation rates at z ~ 0.08 with times since infall using an abundance matching technique that employs the 10 quantiles of each probability distribution. Using a flexible quenching model covering different quenching scenarios, we find the star formation history of satellite galaxies that best reproduces the obtained relationship between time since infall and star formation rate at z ~ 0.08. Based on the derived star formation history, we constrain the quenching timescale (2 - 7 Gyr) with a clear stellar mass trend and confirm that the refined model is consistent with the "delayed-then-rapid" quenching scenario: the constant delayed phase as ~ 2.3 Gyr and the quenching efficiencies (i.e., e-folding timescale) outside and inside clusters as ~ 2 - 4 Gyr (${\propto}M_*^{-1}$) and 0.5 - 1.5 Gyr (${\propto}M_*^{-2}$), Finally, we suggest: (i) ram-pressure is the main driver of quenching of satellite galaxies for the local Universe, (ii) the quenching trend on stellar mass at z > 0.5 indicates other quenching mechanisms as the main driver.

• 한국정보시스템학회지:정보시스템연구
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• 제32권3호
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• pp.133-150
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• 2023

Purpose This study aims to develop classification models using a decision tree algorithm to identify core keywords and rules influencing online consumer review evaluations for the robot vacuum cleaner on Amazon.com. The difference from previous studies is that we analyze core keywords that affect the evaluation results by dividing the subjects that evaluate online consumer reviews into self-evaluation (star ratings) and peer evaluation (helpfulness votes). We investigate whether the core keywords influencing star ratings and helpfulness votes vary across different products and whether there is a similarity in the core keywords related to star ratings or helpfulness votes across all products. Design/methodology/approach We used random under-sampling to balance the dataset. We progressively removed independent variables based on decreasing importance through backwards elimination to evaluate the classification model's performance. As a result, we identified classification models that best predict star ratings and helpfulness votes for each product's online consumer reviews. Findings We have identified that the core keywords influencing self-evaluation and peer evaluation vary across different products, and even for the same model or features, the core keywords are not consistent. Therefore, companies' producers and marketing managers need to analyze the core keywords of each product to highlight the advantages and prepare customized strategies that compensate for the shortcomings.

• 정보처리학회논문지:소프트웨어 및 데이터공학
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• 제12권7호
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• pp.303-314
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• 2023

음성 변환(Voice Conversion)은 개인의 음성 데이터를 다른 사람의 음향적 특성(음조, 리듬, 성별 등)으로 재생성할 수 있는 기술로, 교육, 의사소통, 엔터테인먼트 등 다양한 분야에서 활용되고 있다. 본 논문은 StarGAN-VC 모델을 기반으로 한 접근 방식을 제안하여, 병렬 발화(Utterance) 없이도 현실적인 음성을 생성할 수 있다. 고정된 원본(source) 및 목표(target)화자 정보의 원핫 벡터(One-hot vector)를 이용하는 기존 StarGAN-VC 모델의 제약을 극복하기 위해, 본 논문에서는 사전 훈련된 Rawnet3를 사용하여 목표화자의 특징 벡터를 추출한다. 이를 통해 음성 변환은 직접적인 화자 간 매핑 없이 잠재 공간(latent space)에서 이루어져 many-to-many를 넘어서 any-to-any 구조가 가능하다. 기존 StarGAN-VC 모델에서 사용된 손실함수 외에도, Wasserstein-1 거리를 사용하여 생성된 음성 세그먼트가 목표 음성의 음향적 특성과 일치하도록 보장했다. 또한, 안정적인 훈련을 위해 Two Time-Scale Update Rule (TTUR)을 사용한다. 본 논문에서 제시한 평가 지표들을 적용한 실험 결과에 따르면, 제한된 목소리 변환만이 가능한 기존 StarGAN-VC 기법 대비, 본 논문의 제안 방법을 통해 다양한 발화자에 대한 성능이 개선된 음성 변환을 제공할 수 있음을 정량적으로 확인하였다.