• Title/Summary/Keyword: Acoustic Space

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Comparison of Discrete Noise with Broadband Noise from Small-scaled UH-1H Rotor (축소형 UH-1H 로터에서의 광역소음과 이산소음의 비교)

  • Ryu, Ki-Wahn
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.33 no.1
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    • pp.20-25
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    • 2005
  • The thickness, loading, and broadband noise generated from the trailing edge of the UH-1H main rotor are numerically compared each other. The Kocureck and Tangler's prescribed wake model is adopted to represent the wake geometry during the hovering motion. Three tip Mach numbers of $M_{T}$ = 0.2, 0.4, and 0.8, are selected to analyze the effects of different tip Mach numbers. At $M_{T}$ = 0.8, in considering the A-weighting and audible frequency band, the random noise is smaller than the tonal noises such as the thickness and the loading noise which have the low frequency characteristics. Especially most of the random noise frequency spread on the ultrasound region. On the other hand, below $M_{T}$ = 0.4, the band of random noise moves to the audible frequency region, and the random noise becomes larger than the tonal noise. It turns out that the random noise analysis of the rotor should be necessary at low speed operating condition.

Origin of Dark-Energy and Accelerating Universe

  • Keum, Yong-Yeon
    • Bulletin of the Korean Space Science Society
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    • 2009.10a
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    • pp.34.1-34.1
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    • 2009
  • After SNIa and WMAP observations during the last decade, the discovery of the accelerated expansion of the universe is a major challenge to particle physics and cosmology. There are currently three candidates for the dark energy which results in this accelerated expansion: $\cdot$ a non-zero cosmological constant, $\cdot$ a dynamical cosmological constant (quintessence scalar field), $\cdot$ modifications of Einstein's theory of gravity. The scalar field model like quintessence is a simple model with time-dependent w, which is generally larger than -w1. Because the different w lead to a different expansion history of the universe, the geometrical measurements of cosmic expansion through observations of SNIa, CMB and baryon acoustic oscillations (BAO) can give us tight constraints on w. One of the interesting ways to study the scalar field dark-energy models is to investigate the coupling between the dark energy and the other matter fields. In fact, a number of models which realize the interaction between dark energy and dark matter, or even visible matter, have been proposed so far. Observations of the effects of these interactions will offer an unique opportunity to detect a cosmological scalar field. In this talk, after briefly reviewing the main idea of the three possible candidates for dark energy and their cosmological phenomena, we discuss the interactinng dark-energy model, paying particular attention to the interacting mechanism between dark energy with a hot dark matter (neutrinos). In this so-called mass-varying neutrino (MVN) model, we calculate explicitly the cosmic microwave background (CMB) radiation and large-scale structure (LSS) within cosmological perturbation theory. The evolution of the mass of neutrinos is determined by the quintessence scalar field, which is responsible for the cosmic acceleration today.

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Dynamic Pressure Characteristics of Pulse Gun Device for Combustion Stability Rating of Liquid Rocket Engines (액체 로켓엔진 연소 안정성 평가를 위한 압력 교란 장치 특성 연구)

  • Seo,Seong-Hyeon;Go,Yeong-Seong;Lee,Gwang-Jin;Park,Seong-Jin;Lee,Su-Yong
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.7
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    • pp.94-99
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    • 2003
  • For the assessment of combustion stability of a liquid rocket engine, a device called "Pulse Gun" should be developed first, which can induce artificial perturbations that may lead to excitations of pressure oscillations in a combustion chamber. A model chamber has been used for identifying design parameters of a pulse gun that defines its characteristics. Dynamic pressure measurements showed that shock waves generated from pulse guns are axisymmetric around the axis of a pulse gun barrel. Pressure waves perturbed by a pulse gun induce resonant acoustic frequencies of a model chamber. This fact indicates that successful pressure field perturbations of the KSR-III combustion chamber can be performed by a newly developed pulse gun device. A maximum value of dynamic pressure peaks measured at the opposite point against a pulse gun outlet becomes stronger as charge mass of pulse gun powder increases.

A Semi-Active Control of the Combustion Instability in a Ducted Premixed Flame (덕트 형상 연소기의 연소불안정에 대한 Semi-Active Control)

  • Song, Jae-Cheon;Song, Jin-Kwan;Hwang, Jeong-Jae;Yoon, Young-Bin;Lee, Jong-Guen
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.11
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    • pp.1131-1139
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    • 2009
  • Combustion Instabilities are caused by a coupling between acoustic waves and unsteady heat release. They can be eliminated using passive controller such as a Helmholtz resonator. But, Helmholtz resonator is normally only effective over a narrow frequency range. In this work, Helmholtz resonator is applied for reducing the combustion oscillations and we vary the Helmholtz resonator volume using piston in oder to tune in the wide range of operating conditions. As the result, it is found that the dominant combustion oscillations can be largely reduced by optimizing the size of resonator volume. And, interesting relation for phase difference of dynamic pressure both combustor and the helmholtz resonator are presented in this paper. Also, we investigate semi-active control using Helmholtz equation and phase difference.

Development of shock wave induced microparticle acceleration system based on laser ablation and its application on drug delivery (충격파를 이용한 레이저 어블레이션 기반의 마이크로 입자 가속 시스템 개발 및 약물전달 응용)

  • Choi, Ji-Hee;Gojani, Ardian B.;Lee, Hyun-Hee;Yoh, Jai-Ick
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.36 no.6
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    • pp.587-593
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    • 2008
  • Transdermal and topical drug delivery with minimal tissue damage has been an area of vigorous research for years. Our research team has initiated the development of an effective method for delivering drug particles across the skin (transdermal) for systemic circulation, and to localized (topical) areas. The device consists of a laser ablation based micro-particle acceleration system that can be integrated with endoscopic surgical techniques. We have successfully delivered 3μm size cobalt particles into gelatin models that represent soft tissue with remarkable penetration depth.

The Phase Estimation Algorithm of Arrival Time Difference in MIMO Underwater Sensor Communication (MIMO 수중 통신에서 도착시간 차이에 따른 보상 알고리즘)

  • Baek, Chang-uk;Jung, Ji-won
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.19 no.7
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    • pp.1531-1538
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    • 2015
  • In this paper, we proposed receiver structure based on an iterative turbo equalization to cope with phase difference between two sensors in MIMO underwater communication channel. In a space-time coded system, it is often assumed that there are no phase errors among the multiple transmitter and receiver chains. In this paper, we have studied the effect of the phase errors between different transmit sensors and different propagation paths in the environment of MIMO underwater communication system, and have shown through BER performance by computer simulations that the bit-error-rate performance can be severely degraded. A decision-directed estimation and compensation algorithm has been proposed to minimize their effects on the system performance. In this paper, we investigate the phase differences and their effects on multiple-input and multiple-output systems, and propose a compensation algorithm for underwater channel model to minimize their effects.

Online anomaly detection algorithm based on deep support vector data description using incremental centroid update (점진적 중심 갱신을 이용한 deep support vector data description 기반의 온라인 비정상 탐지 알고리즘)

  • Lee, Kibae;Ko, Guhn Hyeok;Lee, Chong Hyun
    • The Journal of the Acoustical Society of Korea
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    • v.41 no.2
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    • pp.199-209
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    • 2022
  • Typical anomaly detection algorithms are trained by using prior data. Thus the batch learning based algorithms cause inevitable performance degradation when characteristics of newly incoming normal data change over time. We propose an online anomaly detection algorithm which can consider the gradual characteristic changes of incoming normal data. The proposed algorithm based on one-class classification model includes both offline and online learning procedures. In offline learning procedure, the algorithm learns the prior data to be close to centroid of the latent space and then updates the centroid of the latent space incrementally by new incoming data. In the online learning, the algorithm continues learning by using the updated centroid. Through experiments using public underwater acoustic data, the proposed online anomaly detection algorithm takes only approximately 2 % additional learning time for the incremental centroid update and learning. Nevertheless, the proposed algorithm shows 19.10 % improvement in Area Under the receiver operating characteristic Curve (AUC) performance compared to the offline learning model when new incoming normal data comes.

SAW Filter Made of ZnO/Nanocrystalline Diamond Thin Films (ZnO/나노결정다이아몬드 적층 박막 SAW 필터)

  • Jung, Doo-Young;Kang, Chan-Hyoung
    • Journal of the Korean institute of surface engineering
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    • v.42 no.5
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    • pp.216-219
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    • 2009
  • A surface acoustic wave (SAW) filter structure was fabricated employing $4{\mu}m$ thick nanocrystalline diamond (NCD) and $2.2{\mu}m$ thick ZnO films on Si wafer. The NCD film was deposited in an $Ar/CH_4$ gas mixture by microwave plasma chemical vapor deposition method. The ZnO film was formed over the NCD film in an RF magnetron sputter using ZnO target and $Ar/O_2$ gas. On the top of the two layers, copper film was deposited by the RF sputter and inter digital transducer (IDT) electrode pattern (line/space : $1.5/1.5{\mu}m$) was defined by the photolithography including a lift-off etching process. The fabricated SAW filter exhibited the center frequency of 1.66 GHz and the phase velocity of 9,960 m/s, which demonstrated that a giga Hertz SAW filter can be realized by utilizing the nanocrystalline diamond thin film.

Constraints on dark radiation from cosmological probes

  • Rossi, Graziano;Yeche, Christophe;Palanque-Delabrouille, Nathalie;Lesgourgues, Julien
    • The Bulletin of The Korean Astronomical Society
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    • v.40 no.1
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    • pp.44.1-44.1
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    • 2015
  • We present joint constraints on the number of effective neutrino species $N_{eff}$ and the sum of neutrino masses ${\Sigma}m_{\nu}$, based on a technique which exploits the full information contained in the one-dimensional Lyman-${\alpha}$ forest flux power spectrum, complemented by additional cosmological probes. In particular, we obtain $N_{eff}=2.91{\pm}0.22$ (95% CL) and ${\Sigma}m_{\nu}$ < 0.15 eV (95% CL) when we combine BOSS Lyman-${\alpha}$ forest data with CMB (Planck+ACT+SPT+WMAP polarization) measurements, and $N_{eff}=2.88{\pm}0.20$ (95% CL) and ${Sigma}m_{\nu}$ < 0.14 eV (95% CL) when we further add baryon acoustic oscillations. Our results tend to favor the normal hierarchy scenario for the masses of the active neutrino species, provide strong evidence for the Cosmic Neutrino Background from $N_{eff}{\approx}3$($N_{eff}=0$ is rejected at more than $14{\sigma}$), and rule out the possibility of a sterile neutrino thermalized with active neutrinos (i.e., $N_{eff}=4$) - or more generally any decoupled relativistic relic with $${\Delta}N_{eff}{\sim_=}1$$ - at a significance of over $5{\sigma}$, the strongest bound to date, implying that there is no need for exotic neutrino physics in the concordance ${\Lambda}CDM$ model.

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Applications of artificial neural networks;Detections of the location of a sound-source

  • Oobayashi, Koji;Yuan, Yan;Aoyama, Tomoo
    • 제어로봇시스템학회:학술대회논문집
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    • 2003.10a
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    • pp.1036-1041
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    • 2003
  • Non-destruction examinations are required in medical sciences and various engineering now. We wish to emulate the examinations in very simplified experiments. It is an educational program. We show a neural network analysis to predict the locations of a sound-source or a body irradiated by sound-waves in audio-region. The sound is an interest flux, and it enables to clear local-structures in a non-transparent space. However, the sound-propagation equations are not solved easily, therefore, we consider to adopt multi-layer neural-networks instead of the direct solutions. We used detected intensities and coordinates for input data and teaching data. A neural network learned them. The neural-network analysis decomposed the distance of 50cm. The resolution is rather rough; however, it is caused by the limitation of our equipments. Since there is no problem in the neural network processing, if we could revise experiments, then, progress of the resolution would be got. Thus, the proposed method functioned as an educational and simplified non-destruction examination.

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