18,473 research outputs found
Symmetry relations of two-dimensional photonic crystal cavity modes
No full textDegeneracy of resonant modes in two-dimensional (2-D) photonic crystal cavities are investigated using the symmetry relations. The 2-D photonic crystal cavity tends to have either a pair of doubly degenerate modes or nondegenerate modes. We derive simple relations between degenerate modes without using a rigorous group theory. These relations are useful for classifying the resonant modes into degenerate pairs and nondegenerate ones.One of the authors, S.-H. Kim, would like to thank G.-H. Kim
for his valuable assistance and discussions
Dataset for "Aerofoil trailing-edge noise prediction models for wind turbine applications"
No full textDataset supporting:
Lau, A. S. H., Kim, J. W., Hurault, J., Vronsky, T., & Joseph, P. (2017). Aerofoil trailing-edge noise prediction models for wind turbine applications. Wind Energy.</span
Intelligent broadcasting system and services for personalized semantic contents consumption
No full textCurrently, digital broadcasting tends to personalize the TV watching environment by offering services that can adapt to viewer preferences. In this paper, an intelligent broadcasting system for enhanced personalized-services, based on the semantics of broadcasting contents, is proposed. To implement the system, the MPEG-7 and TV-Anytime Forum (TVAF), as well as agent technology, are employed. For content-level services, real-time content filtering, personalized video skimming, and content-based retrieval using audio characteristic are implemented. To verify the usefulness of the proposed system, we demonstrate it with a test-bed on which content-level personalized services are implemented(1). (c) 2005 Elsevier Ltd. All rights reserved.We would like to thank Mr Sungtak Kim, Mr Jun Ho Cho,
and Mr Mun Jo Kim who participated in this project
Novel clay treatment and preparation of poly(ethylene terephthalate)/clay nanocomposite by in-situ polymerization
No full textNovel clay treatment was proposed for poly(ethylene terephthalate) (PET)/clay nanocomposite and the clay dispersed trimellitate ester oligomers were prepared by esterification with 1, 2, 4-Benzenetricarboxylic anhydride (TMA, trimellitic anhydride) and montmorillonite (MMT) dispersed ethylene glycol (EG). The structure, interlayer distance and thermal stability of the clay dispersed trimellitate ester oligomers were investigated by NMR, WAXD, SAXS and TGA techniques
Effects of the speed of moving noise sources on the sound visualization by means of moving frame acoustic holography
No full textThe moving frame acoustic holography (MFAH) method [H.-S. Kwon and Y.-H. Kim, J. Acoust. Sec. Am. 1.03, 1734-1742 (1998)] enables the visualization of noise generated by moving noise sources, e.g., moving vehicles, by using a line array of microphones affixed to the ground. However, the sound field of a moving noise source has a moving effect, which produces the wavefront distribution different from what would be generated by the source if it were not moving. The moving effect causes errors on the reconstructed hologram by means of MFAH. This paper studies this effect with regard to the speed of noise sources. A formula, which can show the effect, was derived. This enables the analysis of the effect not only on the hologram plane but also on a prediction plane. It was shown that the phase error is more undesirable than that of magnitude. The phase error, which is proportional to the speed of a noise source, shifts the position of noise sources and distorts radiation pattern. A theoretical investigation explicitly showed that the error is negligible for low Mach number (M < 0.1). Furthermore, the phase error can be reduced by introducing a correction factor. Several numerical examples illustrate the feasibility of the proposed correction method for low Mach number. (C) 2000 Acoustical Society of America. [S0001-4966(00)02412-7]
An improved moving frame acoustic holography for coherent bandlimited noise
No full textThe moving frame acoustic holography method, which can increase the aperture size and spatial resolution of a hologram was recently proposed [H. S. Kwon and Y.-H. Kim, J. Acoust. Sec. Am. 103, 1734-1742 (1998)]. This method continuously sweeps a stationary sound field by using a line array of microphones so that the hologram of a scanned plane can be obtained. This method enables us to visualize the noise generated by moving noise sources based on near-field acoustic holography. However, a drawback is that it can be applied only to sinusoidal components. This limits its practical application. In practice, bandlimited and transient noise, as well as a sinusoidal component, must be dealt with in order to effectively control the noise generated by the moving noise sources. This paper addresses a way to improve the moving frame acoustic holography method so that it can be applied not only to sinusoidal components, but also to a coherent bandlimited noise. The practical applicability of the improved method is also verified by experiments. (C) 1998 Acoustical Society ofAmerica. [S0001-4966(98)04111-3]
Physical layer DVB-SH performance prediction based on mutual information
No full textDigital Video Broadcasting-Satellite Handled (DVB-SH) is a hybrid satellite terrestrial broadcasting standard dedicated to provide video or audio services for handheld terminals. On the satellite part, this standard can make use of interleaving mechanisms to mitigate the effects of the Land Mobile Satellite channel. As a result, these mechanisms enable the in-time distribution of a codeword over a duration ranging from 100 ms to about 30 s, depending on their parameters. This mechanism significantly improves the error recovery performance of the code; however in the literature, a theoretical evaluation at system level of this improvement is missing. Moreover, carrying out Monte-Carlo simulations implementing real decoding processes on significant traveled distances is time prohibitive.
We propose hereafter a prediction method compatible with fast simulations to quantitatively evaluate the system performance in terms of Rate, Erroneous Second Ratio, and zapping time. This method is based on the computation of the mutual information between emitted and received symbols for QPSK modulation and turbo coding.
We demonstrate that our method reaches a prediction precision of the order of 0.1 dB, which is significantly better than two classical prediction methods. Moreover, our solution reduces the simulation time by a factor of 500 compared with Monte-Carlo. Beyond DVB-SH application, the presented approach can be applied in a large panel of satellite mobile systems and is completely new for the satellite community
Small, low-loss heterogeneous photonic bandedge laser
No full textWe have demonstrated the operation of a new type of heterogeneous photonic crystal laser, a five-lattice-constant large photonic bandedge laser assisted by a photonic bandgap, in a triangular lattice at room temperature. When the air hole radius of the surrounding photonic crystal ( PC) is slightly smaller than that of the bandedge mode region, most in-plane losses of the first K point bandedge mode in the central region are suppressed and the quality factor of the mode is greatly enhanced to 50000. We identified the photonic bandgap-bandedge (PBG-BE) lasing modes through the spectral position, near-field pattern, and the state of polarization, which correspond well with the results of the three-dimensional (3D) finite-difference time-domain (FDTD) method computation. The two-dimensional (2D) feedback mechanism of the first K bandedge was verified through the Fourier analysis. Low threshold incident peak pump power of similar to 0.24 mW is achieved owing to the low optical loss of the PBG-BE mode. (C) 2004 Optical Society of America.This work was supported by the National R&D Project for Nano Science and Technology of
KISTEP, Korea
Effects of total sleep-deprivation on waking human EEG: functional cluster analysis
No full textObjective: The purpose of the present study was to investigate the effects of total sleep deprivation (TSD) on brain functions with an identification procedure for strongly interactive brain regions, relying on functional cluster (FC) analysis in multichannel electroencephalogram (EEG) data. Methods: EEGs from 16 electrodes in 18 healthy, right-handed, young male volunteers were recorded before TSD (after normal sleep) and after 24 It of experimentally induced sleep deprivation. We estimated cluster index to characterize joint interactions among many brain regions in order to determine if a particular FC is present or not, and if so, its anatomy. Results: As a result, we confirmed the presence of FC and found different FC patterns in both before and after TSD. The C3 and F7 locations were outside the cluster under the TSD condition, but belonged to the cluster with C4 and F8 before the TSD condition, and the F3/F4, and O1 locations were new entries to the functional cluster during sustained wakefulness. Conclusions: These results indicate that the neuronal activities of the C3 and F7 location are functionally unrelated, whereas the F3/F4 locations are functionally involved with the C4, F8, and O1 locations after 24 It TSD. Our results suggest that FC changes with elapsed awake time and reflects the change of brain function due to TSD. Significance: This paper shows the existence of FC both before and after TSD, and the anatomy of each FC is different. So FC analysis would be a potential tool to investigate the simultaneous neuronal activity of human EEGs. (C) 2004 Published by Elsevier Ireland Ltd. on behalf of International Federation of Clinical Neurophysiology
EFFECTS OF ION-BEAM IRRADIATION ON THE PROPERTIES AND EPITAXIAL-GROWTH OF ALUMINUM NITRIDE FILM BY THE ION-BEAM-ASSISTED DEPOSITION PROCESS
No full textAluminium nitride thin films were grown on Si(111) substrates by ion beam assisted deposition. Epitaxial growth of the AlN films was obtained at the low temperature of 450 degrees C. Characterization of the AlN epitaxial layer was carried out by grazing-incidence diffraction (GID) and high resolution transmission electron microscopy (HRTEM). GID analysis showed two kinds of epitaxial orientation between AlN epitaxial layer and Si substrate. An amorphous layer was observed at the interface between AlN film and Si by cross-sectional HRTEM analysis. The amorphous layer could release the misfit strain between the AlN film and the Si substrate in an early stage of growth. The AlN epitaxial layer formed despite the large lattice mismatch. In addition, the optical properties of AlN films including transmittance, energy band gap, and refractive index were determined and discussed.X1112sciescopu
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