• Title/Summary/Keyword: local resonance

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A Study on Vibration Reduction of Local Structure of Medium-speed Diesel Engine (중속 디젤엔진 국부 구조물의 진동저감 연구)

  • Jung, Kun-Hwa;Lee, Jun-Ho;Son, Jung-Ho;Ryoo, Young-Seok
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2011.10a
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    • pp.257-261
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    • 2011
  • The failures of local structure of marine medium-speed diesel engine occurred in durability test. The vibration response of the whole engine was in an acceptance level, but the local structures were broken. ODS test and vibration measurement were carried out in order to investigate the root cause of durability problem. These tests revealed that the root cause of failures was excessive vibration by $4.5^{th}$ resonance between engine body and local structure. The best solution to reduce the vibration response is to change the type of mount. After a rigid mount was replaced by a flexible mount, maximum vibration level dropped to 72%.

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Babinet-principle-inspired Metasurfaces for Resonant Enhancement of Local Magnetic Fields

  • Seojoo, Lee;Ji-Hun, Kang
    • Current Optics and Photonics
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    • v.7 no.1
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    • pp.97-103
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    • 2023
  • In this paper, we propose Babinet-principle-inspired metasurfaces for strong resonant enhancement of local magnetic fields. The metasurfaces are designed as complementary structures of original metasurfaces supporting the local enhancement of electric fields. We show numerically that the complementary structures can support spoof magnetic surface plasmons that induce strong local magnetic fields without sacrificing the deep sub-wavelength-thick nature of the metasurface. By introducing a periodic array of metallic rods in the proximity of the metasurfaces, we demonstrate that a resonant enhancement of the local magnetic fields, more than 80 times the amplitude of an incident magnetic field, can emerge from a resonance of the spoof magnetic surface plasmons.

[ $^{11}B$ ] Nuclear Magnetic Resonance Study of Spin Structures in Terbium Tetraboride

  • Mean, B.J.;Kang, K.H.;Kim, J.H.;Hyun, I.N.;Lee, Moo-Hee;Cho, B.K.
    • Journal of the Korean Magnetic Resonance Society
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    • v.10 no.2
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    • pp.197-202
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    • 2006
  • [ $^{11}B$ ] nuclear magnetic resonance (NMR) measurements were performed on the single crystals of $TbB_4$ to investigate local electronic structure and 4f spin dynamics. $^{11}B$ NMR spectrum, Knight shift, spin-lattice and spin-spin relaxation rates were measured down to 4K at 8T. $^{11}B$ NMR shift and linewidth are huge and strongly temperature dependent due to the 4f moments. In addition, both are proportional to magnetic susceptibility, indicating that the hyperfine field at the boron site originates from the 4f spins of Tb. Below $T_N$, the single broad resonance peak of $^{11}B$ NMR splits into several peaks reflecting the local magnetic fields due to antiferromagnetic spin arrangements. The longitudinal and the transverse relaxation rates, $1/T_1\;and\;1/T_2$, independent of temperature above $T_N$, decreases tremendously confirming huge suppression of spin fluctuation below $T_N$.

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Noise Removal in Magnetic Resonance Images based on Non-Local Means and Guided Image Filtering (비 지역적 평균과 유도 영상 필터링에 기반한 자기 공명 영상의 잡음 제거)

  • Mahmood, Muhammad Tariq;Choi, Young Kyu
    • KIISE Transactions on Computing Practices
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    • v.20 no.11
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    • pp.573-578
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    • 2014
  • In this letter, we propose a noise reduction method for use in magnetic resonance images that is based on non-local mean and guided image filters. Our method consists of two phases. In the first phase, the guidance image is obtained from a noisy image by using an adaptive non-local mean filter. The spread of the kernel is adaptively by controlled by implementing the concept of edgeness. In the second phase, the noisy images and the guidance images are provided to the guided image filter as input in order to produce a noise-free image. The improved performance of the proposed method is investigated by conducting experiments on standard datasets that contain magnetic resonance images. The results show that the proposed scheme is superior over the existing approaches.

The Characteristic of Friction-Factor on Honeycomb Surfaces (Part II : Friction-Factor Jump Phenomenon) (허니콤 표면의 마찰계수 특성에 관한 연구 (Part 2 : 마찰계수 급상승현상에 관한 고찰))

  • 하태웅
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.6
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    • pp.1439-1447
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    • 1994
  • Test results of friction-factor for the flow of air in a narrow channel lined with various honeycomb geometries show that, generally, the friction-factor is nearly constant or slightly decreases as the Reynolds number(or Mach number) increases, a characteristic common to turbulent flow in pipes. However, in some test geometries this trend is remarkably different. The friction factor dramatically drops and then rises as the Mach number increases. This phenomenon can be characterized as a "friction-factor jump." Further investigations of the acoustic spectrum indicate that the "friction-factor jump" phenomenon is accompanied by an onset of a normal mode resonance excited coherent flow fluctuation structure, which occurs at Reynolds number of the order of $10^4$. New empirical friction-factor model for "friction-factor jump" cases is developed as a function of Mach number and local pressure.ach number and local pressure.

Characteristics of Local Vibration Modes of the Aluminium Extruded Panels for Rail Road Vehicles (철도 차량용 알미늄 압출재의 국부진동 모드특성)

  • 김석현;장호식;김정헌
    • Journal of the Korean Society for Railway
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    • v.4 no.3
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    • pp.87-93
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    • 2001
  • Characteristics of the local vibration modes of an aluminium extruded panel are investigated by the finite element analysis and modal testing. Practical methods to increase the damping of the local resonances are proposed. Effects by filling urethan foam in the core cavity and by coating tar on the panel surface are compared by experiments. Modified panel structures to shift the local resonance frequency band are proposed. The results of the study are utilized to predict the severe local resonances in the aluminium extruded panels and prevent their undesirable effect on the sound insulation.

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Assessment of Local Tumor Progression After Image-Guided Thermal Ablation for Renal Cell Carcinoma

  • Byung Kwan Park
    • Korean Journal of Radiology
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    • v.25 no.1
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    • pp.33-42
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    • 2024
  • Focal enhancement typically suggests local tumor progression (LTP) after renal cell carcinoma is percutaneously ablated. However, evaluating findings that are false positive or negative of LTP is less familiar to radiologists who have little experience with renal ablation. Various imaging features are encountered during and after thermal ablation. Ablation procedures and previous follow-up imaging should be reviewed before determining if there is LTP. Previous studies have focused on detecting the presence or absence of focal enhancement within the ablation zone. Therefore, various diagnostic pitfalls can be experienced using computed tomography or magnetic resonance imaging examinations. This review aimed to assess how to read images during or after ablation procedures, recognize imaging features of LTP and determine factors that influence LTP.

Quantum theory of multiwave mixing with a local field correction

  • An, Sung-Hyuck;Rhee, Bum-Ku
    • Journal of the Optical Society of Korea
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    • v.1 no.2
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    • pp.94-99
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    • 1997
  • In this paper, we calculate the four coefficients for the quantum theory of multiwave mixing including a local-field correction resulting from dipole-dipole interactions. We make contact with the semiclassical calculations of probe absorption and four-wave-mixing coupling coefficients, and illustrate the effects of local field corrections on resonance-fluorescence and coupled-mode-fluorescence spectra. The method uses the hybrid quantum-Langevin-equation master-equation approach of An and Sargent.

Evaluation of Elastic Properties for Nanoscale Coating Layers Using Ultrasonic Atomic Force Microscopy (초음파원자현미경을 이용한 나노스케일 박막 코팅층에 대한 탄성특성 평가)

  • Kwak, Dong Ryul;Cho, Seung Bum;Park, Ik Keun
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.24 no.5
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    • pp.475-480
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    • 2015
  • Ultrasonic atomic force microscopy (Ultrasonic-AFM) has been used to investigate the elastic property of the ultra-thin coating layer in a thin-film system. The modified Hertzian theory was applied to predict the contact resonance frequency through accurate theoretical analysis of the dynamic characteristics of the cantilever. We coat 200 nm thick Aluminum and Titanium thin films on the substrate using the DC Magnetron sputtering method. The amplitude and phase of the contact resonance frequency of a vibrating cantilever varies in response to the local stiffness constant. Ultrasonic-AFM images were obtained using the variations in the elastic property of the materials. The morphology of the surface was clearly observed in the Ultrasonic-AFM images, but was barely visible in the topography. This research demonstrates that Ultrasonic-AFM is a promising technique for visualizing the distribution of local stiffness in the nano-scale thin coatings.

Effects of Organic Thin Films on Local Resonance of Metamaterials under Photoexcitation

  • Song, Myeong-Seong;Hwang, In-Wook;Lee, Chang-Lyoul;Kang, Chul;Kee, Chul-Sik;Park, Sae June;Ahn, Yeong Hwan;Park, Doo Jae;Lee, Joong Wook
    • Current Optics and Photonics
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    • v.1 no.4
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    • pp.372-377
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    • 2017
  • We demonstrate that the local resonance of metamaterials can be tuned by the effects of organic thin films under photoexcitation. Tris (8-hydroxyquinolinato) aluminum ($Alq_3$) layers are deposited on metamaterial/silicon hybrid structures. By varying the thickness of the $Alq_3$ layer on the subwavelength scale, the resonant peak of the metamaterial becomes very adjustable, due to the effect of a thin dielectric substrate. In addition, under photoexcitation all the spectral peaks of the resonance shift to higher frequencies. This originates from the reduction of the capacitive response generated inside the gaps of split-ring resonators. The adjustability of the electromagnetic spectrum may be useful for developing optical systems requiring refractive-index engineering and active optical devices.