• Structural Engineering and Mechanics
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• 제40권4호
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• pp.563-581
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• 2011

Many novel materials, developed in recent years, have obvious properties with different modulus of elasticity in tension and compression. The ratio of their tensile modulus to compressive modulus is as high as five times. Nowadays, it has become a new trend to study the mechanical properties of these bimodular materials. At the present stage, there are extensive studies related to the strength analysis of bimodular structures, but the investigation of the buckling stability problem of bimodular rods seems to cover new ground. In this article, a semi-analytical method is proposed to acquire the buckling critical load of bimodular slender rod. By introducing non-dimensional parameters, the position of neutral axis of the bimodular rod in the critical state can be determined. Then by combining the phased integration method, the deflection differential equation of bimodular pin-ended slender rod is deduced. In addition, the buckling critical load is obtained by solving this equation. An example, which is conducted by comparing the calculation results between the three of the methods including the laboratory tests, numerical simulation method and the method we developed here, shows that the method proposed in the present work is reliable to use. Furthermore, the influence of bimodular characteristics on the stability is discussed and analyzed.

• 한국소음진동공학회논문집
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• 제20권3호
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• pp.215-222
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• 2010

Long and slender body, like a fuel rod, oscillating in axial flow can be unstabilized even by the small cross flow which can be activated by the flow mixer or turbulent generator. It is important to include these effects of flow disturbance in dynamic stability analysis of nuclear fuel rod. This work shows how eigen frequency of a multi-span fuel rod can be changed by the swirl flow, which is discretely generated by a flow mixer. By solving a state-space form of the eigenvalue equation for a multi-span fuel rod system, the critical velocity at which a fuel rod becomes unstable was calculated. Based on the simulation results, we evaluated how stability of a multi-spanned nuclear fuel rod with mixing vanes can be affected by the coolant flow in an operating reactor core.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.641-646
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• 2008

Long and slender body with or without flexible supports under severe operating condition can be unstabilized even by the small cross flow. Turbulent flow mixer, which actually increases thermal-hydraulic performance of the nuclear fuel by boosting turbulence, disturbs the flow field around the fuel rod and affects dynamic behavior of the nuclear fuel rods. Few studies on this problem can be found in the literature because these effects depend on the specific natures of the support and the design of the system. This work shows how the dynamics of a multi-span fuel rod can be affected by the turbulent flow, which is discretely activated by a flow mixer. By solving a state-space form of the eigenvalue equation for a multi-span fuel rod system, the critical velocity at which a fuel rod becomes unstable was established. Based on the simulation results, we evaluated how stability of a multi-spanned nuclear fuel rod with mixing vanes can be affected by the coolant flow in an operating reactor core.

• Nuclear Engineering and Technology
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• 제51권2호
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• pp.573-578
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• 2019

Anisotropic distribution of the turbulent kinetic energy and the near-field excitations are the main causes of the steady state Flow-Induced Vibration (FIV) which could lead to fretting wear damage in vertically arranged supported slender rods. In this article, a combined Computational Fluid Dynamics (CFD) and Computational Structural Mechanic (CSM) approach named two-way Fluid-Structure Interaction (FSI) is used to investigate the modal characteristics of a typical rod's vibration. Performance of an Unsteady Reynolds-Average Navier-Stokes (URANS) and Large Eddy Simulation (LES) turbulence models on asymmetric fluctuations of the flow field are investigated. Using the LES turbulence model, any large deformation damps into a weak oscillation which remains in the system. However, it is challenging to use LES in two-way FSI problems from fluid domain discretization point of view which is investigated in this article as the innovation. It is concluded that the near-wall meshes whiten the viscous sub-layer is of great importance to estimate the Root Mean Square (RMS) of FIV amplitude correctly as a significant fretting wear parameter otherwise it merely computes the frequency of FIV.

• Journal of the Optical Society of Korea
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• 제14권4호
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• pp.431-437
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• 2010

A stack of gradient-index (GRIN) rod lenses cannot be used for coherent anti-Stokes Raman scattering (CARS) microendoscopy for insertion to internal organs through a surgical keyhole with minimal invasiveness. That's because GRIN lens has large amount of inherent chromatic aberrations in spite of absolutely requiring a common focus for pump and Stokes beam with each frequency of ${\omega}_p$ and ${\omega}_S$. For this endoscopic purpose, we need to develop a long slender probe-type objective, namely probe-type microscope objective (PMO). In this paper, we introduce the structure, the working principle, and the design techniques of PMO which is composed of a probe-type lens module (PLM) and an adaptor lens module (ALM). PLM is first designed for a long slender type and ALM is successively designed by using several design parameters from PLM for eliminating optical discords between scanning unit and PLM. A combined module is optimized again to eliminate some coupling disparities between PLM and ALM for the best PMO. As a result, we can obtain a long slender PMO with perfectly diffraction-limited performance for pump beam of 817 nm and Stokes beam of 1064 nm.

• 환경생물
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• 제39권3호
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• pp.289-292
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• 2021

Henricia specimen was collected from the East Sea of Korea using fishing nets. The specimen was identified as Henricia hayashii (Djakonov 1961), belonging to the family Echinasteridae of the order Spinulosida. This species can be distinguished from other Henricia species by slender arms (R/r=7.4), constricted arm base, six to thirty-five slender spinelets, open-meshed, reticulated abactinal skeleton comprising semi-triangular, rod-like form, and small ossicles present inside the papular areas. This species superficially resembles H. reniossa in terms of its body size but differs in the shape and arrangement of the abactinal and actinal plates. To date, two genera of Echinasteridae, Aleutihenricia and Henricia, including a total of 14 species, have been reported in Korea. Herein, the morphological characteristics of H. hayashii are described, and photographs are provided.

• Applied Microscopy
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• 제35권4호
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• pp.42-54
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• 2005

본 연구는 무당개구리과 (Discoglossidae)의 무당개구리(Bombina orientalis) 정자의 형태적 특징을 광학현미경과 주사 및 투과 전자현미경으로 관찰하였다. 정자두부는 전 후방의 끝이 뾰족하고 다소 유연성을 갖는 초생달 혹은 버들 잎 모양의 특이한 구조를 취하고 있었다. 핵은 전 후방이 가늘고, 중앙 부분은 굵은 원뿔형이었다. 염색질은 완전하게 농축되어 있지 않고, 마치 널빤지를 겹쳐 놓은 듯한 지붕모양과 같은 형태로 불규칙하게 배열되어져 있었다. 핵 내에는 불규칙한 형태의 nuclear lacunae들이 흩어져 있었다. 정자경부와 중편부는 발달 되어 있지 않았다. 편모는 9+2 구조의 axoneme, axial rod 그리고 undulating membrane을 가지고 있었다. 미토콘드리아들은 핵의 상단부를 둘러싸고 있는 protoplasmic bead내에만 국한되어 존재하고 있었다. 특히, 본 연구에서 핵의 전방부에서 중앙 부위로 주행하는 nuclear rod는 섬유성 다발로 구성되었으며, 마치 사람의 속눈썹 모양과 같은 형태를 취하며, 핵의 2/3까지 뻗쳐져 있었다.

• 한국해양공학회지
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• 제8권2호
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• pp.151-156
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• 1994

The equations of motion of a submarine pipeline with the internal flowing fluid and subject to hydrodynamic loadings are derived by using Hamilton's principle. Coupling between the bending and the longitudinal extension due to axial load and thermal expansion are considered. Coupling between the twisting and extension are not considered. The equations of motion are well agreed with the results which are derived by the vector method.

• 미생물과산업
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• 제18권3호
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• pp.23-33
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• 1992

The general characteristics of campylobacters and related organisms (e.g., species of the genera Helicobacter and Wolinella, Bacteroides ureolyticus, and Bacteroides gracilis) are as follows: slender, non-sporeforming, gram-negative, vibroid bacteria (helical- or spiral- shpaed; except that B. ureolyticus and B. gracilis are straight-rod), 0.2-0.5 .mu.m in width and 0.5 .mu.m in length. (Smibert, 1984; Penner, 1988). The species of genus Campylobacter and related organisms are chemoorganotrophs; however, they neither oxidize nor ferment carbohydrates and instead obtain energy from amino acids, the salts of tricarboxylic acids (TCA) cycle intermediates, the salts of organic acids, or, in some species, H$\_$2/. With regard to their oxygen responses for growth, they all are microaeophilic i.e., they are capable of oxygen-dependent growth (respiring with oxygen as a terminal electron acceptor) but can not grow in the presence of a level of oxygen equivalent to that present in an air atmosphere (21% oxygen). This review will take interests in how these microorganisms response to oxygen for growth and what repiratory types they have.

• 한국어류학회지
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• 제17권1호
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• pp.36-42
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• 2005

한국의 메기과 (Siluridae) 어류의 수염을 조직학적으로 조사하였다. 메기, Silurus asotus의 상악 수염은 연골성 중축을 감싸는 진피와 표피로 구성 되었다. 표피층에는 점액세포, 과립형세포 및 미뢰가 있었다. 세포질이 약한 호염기성을 보이는 점액세포와 호염기성을 보이는 미뢰는 각각 표피의 표면과 표피 말단 부위에 위치 하였다. 표피와 진피는 기저막으로 구분되며 진피는 소성결합조직으로 구성 되었으며 신경세포와 혈관이 내재하고 있었다. 수염의 가장 내부에 연골성 중축이 존재 하였으며 근육층으로 둘러싸여 있었다. 미유기, S.microdorsalis의 상악 수염 구조는 메기의 상악 수염 구조와 비교시 별다른 차이는 보이지 않았으나, 상악 상부와 하부에서의 표피 % 두께 및 상악 상부와 중부에서의 미뢰 수에 있어 미유기는 메기에 비해 차이를 보였다. 본 연구결과 메기와 미유기의 상악 수염은 딱딱하고 굴절성형(stiff and flexible type)으로 파악 되었다.