• Advances in nano research
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• 제12권1호
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• pp.25-35
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• 2022

Within the framework of the density functional theory combined with the method of non-equilibrium Green's functions (DFT + NEGF), the features of electron transport in fullerene nanojunctions, which are «core-shell» nanoobjects made of a combination of fullerenes of different diameters C₂₀, C₈₀, C₁₈₀, placed between gold electrodes (in a nanogap), are studied. Their transmission spectra, the density of state, current-voltage characteristics and differential conductivity are determined. It was shown that in the energy range of -0.45-0.45 eV in the transmission spectrum of the "Au-C₁₈₀-Au" nanojunction appears a HOMO-LUMO gap with a width of 0.9 eV; when small-sized fullerenes C₂₀, C₈₀ are intercalation into the cavity C₁₈₀ the gap disappears, and a series of resonant structures are observed on their spectra. It has been established that distinct Coulomb steps appear on the current-voltage characteristics of the "Au-C₁₈₀-Au" nanojunction, but on the current-voltage characteristics "Au-C₈₀@C₁₈₀-Au", "Au-(C₂₀@C₈₀)@C₁₈₀-Au" these step structures are blurred due to a decrease in Coulomb energy. An increase in the number of Coulomb features on the dI/dV spectra of core-shell fullerene nanojunctions was revealed in comparison with nanojunctions based on fullerene C₆₀, which makes it possible to create high-speed single-electron devices on their basis. Models of single-electron transistors (SET) based on fullerene nanojunctions "Au-C₁₈₀-Au", "Au-C₈₀@C₁₈₀-Au" and "Au-(C₂₀@C₈₀)@C₁₈₀-Au" are considered. Their charge stability diagrams are analyzed and it is shown that SET based on C₈₀@C₁₈₀-, (C₂₀@C₈₀)@C₁₈₀- nanojunctions is output from the Coulomb blockade mode with the lowest drain-to-source voltage.

• 한국패류학회지
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• 제32권3호
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• pp.189-195
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• 2016

2000년 8월부터 2002년 7월까지 한반도 남서연안 곰소만 바지락 양식장에 서식하는 바지락의 성장에 대하여 조사하였다. 전조사기간동안 서식밀도는 평균 1,224 개체/$m^2$ 로서 2000년 11월에 최고 밀도를 보인 이후 지속적으로 감소하는 경향이 뚜렷하였다. 월별 각장 빈도분포는 단일 모드형으로 중앙값은 시간경과에 따른 각장 성장에 의해 오른쪽으로 이동하였다. 바지락의 각장 성장은 시간 경과에 따라 지속적으로 증가하는 양상을 보였으나 2001년 7월 이후부터 2002년 2월까지는 성장이 둔화하였고 2002년 3월 이후 다시 증가하였다. 무게 또한 시간이 갈수록 증가하는 양상을 보였으며 2002년 3월 이후 증가폭이 컸다. 각장과 각고와의 상관관계는 직선식으로 표시할 수 있었으며, 각장과 전중, 육질습중량, 건육중량 및 AFDW와의 관계식은 지수식으로 표시할 수 있었다. 비만도는 지속적으로 증가하는 양상을 보이다가 2001년 4월 이후에 감소하는 양상을 나타내었으며 2002년에도 동일한 양상을 보였다. 비만도 증감으로부터 2001년도 곰소만 양식장 바지락의 산란은 연 1회 5-10월 중으로 파악된다. 또한 곰소만 양식 바지락은 종패 살포이후 24개월 이후부터는 여름철 이전에 수확하는 것이 바람직할 것으로 판단된다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.835-841
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• 2013

Modern solid-state gyroscopes (HRG) with hemispherical resonators from high-purity quartz glass and special surface superfinishing and ultrathin gold coating become the best instruments for precise-grade inertial reference units (IRU) targeting long-term space missions. Designing of these sensors could be a notable contribution into development of Korea as a space nation. In participial, 40mm diameter thin-shell resonator from high-purity fused quartz, fabricated as a single-piece with its supporting stem has been designed, machined, etched, tuned, tested, and delivered by STM Co. (ATS of Ukraine) several years ago; an extremely-high Q-factor (upto 10~20 millions) has been shown. Understanding of the best way how to match such a unique sensor with inner glass assembly of the gyro means how to use the high potential in a maximal extent; and this has become the urgent task. Inner quartz glass assembly has a very thin indium (In) layer soldered the resonator and its silica base (case), but effects of internal resonances between operational modal pair of the shell-cup and its side (parasitic) modes can notable degrade the potential of the sensor as a whole, instead of so low level of resonator's intrinsic losses. Unfortunately, there are special combinations of dimensions of the parts (so-called, "resonant sizes"), when intensive losses of energy occurs. The authors proposed to use the length of stem's fixture as an additional design parameter to avoid such cases. So-called, a cyclic scheme of finite element method (FEM) and ANSYS software were employed to estimate different combinations of gyro assembly parameters. This variant has no mismatches of numerical origin due to FEM's discrete mesh. The optimum length and dangerous "resonant lengths" have been found. The special attention has been paid to analyses of 3D effects in a cup-stem transient zone, including determination of a difference between the positions of geometrical Pole of the resonant hemisphere and of its "dynamical Pole", i.e., its real zone of oscillation node. Boundary effects between the shell (cup) and 3D short "beams" (inner and outer stems) have been ranged. The results of the numerical experiments have been compared with the classic model of a quasi-hemispherical shell band with inextensional midsurface, and the solution using Rayleigh's functions of the $1^{st}$ and $2^{nd}$ kinds. To guarantee the truth of the recommended sizes to a designer of the real device, the analytical and FEM results have been compared with experimental data for a party of real resonators. The consistency of the results obtained by different means has been shown with errors less than 5%. The results notably differ from the data published earlier by different researchers.

• 한국전산구조공학회논문집
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• 제30권2호
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• pp.111-117
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• 2017

본 논문에서는 유한요소 자유진동해석을 수행하여 박판 보에서의 국소변형효과를 조사하였다. 자유진동해석은 단일셀 및 다중셀 박스보에 대해 수행하였으며, 풍력발전 블레이드를 가장 단순하게 모사할 수 있는 단일셀 박스보를 먼저 해석하였다. 쉘요소 해석결과를 보요소 해석결과와 비교하여 보았을 때 박스 보의 박판 두께가 정확도에 매우 중요한 역할을 함을 확인하였다. 두께가 얇은 경우에는 쉘의 국소변형(또는 쉘 모드)가 주요하게 나타난 반면에 두꺼울 경우에는 전단변형의 효과가 크게 나타남을 알 수 있었다. 목이 있는 단일셀 박스보에서의 국소변형은 목 주위에 집중되어 나타남을 확인하였다. 마지막으로 실제 블레이드와 유사한 다중셀 테이퍼 보의 주파수 및 모드형상을 분석하였다. 보 요소 해석결과는 쉘 요소 결과와 비교하여 약 5~7% 주파수 차이를 보였으며, 이는 보요소가 국소변형을 제대로 모사하지 못하기 때문이다. 특히 래그모드(lagwise mode)의 경우에는 단면의 분할 정도의 영향보다 국소변형의 효과가 매우 크다는 것을 알 수 있었다.

• 한국패류학회지
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• 제32권2호
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• pp.133-139
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• 2016

The incubation time required for hatching of O. ocellatus were investigated through the processes of egg and embryonic developments by the dissecting microscopic and visual observations. And differences in ecological characteristics of the plankton mode of life or the benthic mode of life according to total numbers of the suckers on each short arm of the hatched juvenile larvae of O. ocellatus were studied by comparisons with other octopodidae species. Compared with the recent a few results reported by other researchers associated with the incubation time required for hatching by female adult mother of O. minor (73-90 days after spawning at $20.9-21.5^{\circ}C$ ranges), in this study, the incubation time required for hatching by female adult mother of O. ocellatus was 56-57 days after spawning at $11.0-20.4^{\circ}C$. Therefore, the incubation time required for hatching by female adult mother varied with Octopodidae species. In this studies, each ovarian egg laid by a female was connected to an egg string attaching to the surface of the wall or bottom of vacunt shell of Rapana venosa. Egg and embryonic developments of this species were studied in the indoor aquaria, in the specific gravity ranging 1.024-1.025. the hatched juvenile of O. ocellatus is 10.3 mm in the mean total length and 4.5 mm in mantle length, and each of its short arms has 18-20 suckers. The just hatched juvenile larvae of O. ocellatus enter the benthic mode of life (benthic larval stage) after hatching. In particular, regarding differences in ecological characteristics of the mode of life according to total numbers of the suckers, O. vulgaris may not need to have many suckers because they enter the planktonic mode of life after hatching, however O. ocellatus may need to have many suckers, because they should adapt to the benthic mode of life. And also the just hatched juvenile larvae of O. minor (bearing many suckers more than O. ocellatus) enter the benthic mode of life (benthic larval stage) after hatching. Therefore, the total number of the suckers on each short arm of the hatched juvenile larvae can be used for determining whether an octopus species has planktonic larval stages or benthic larval stage (benthic mode of life). In particular, The intracohort cannibalism phenomena appeared at the hatched juvenile larval stage because the larval stage of O. ocellatus and O. minor enter into the benthic larval stage in the early stage, unlike entering into the plaktonic larval stage in other Octopus species such as O. vulgaris: at this time, the early hatched larvae fed the late hatched larvae (they are the same species and almost same ages). Therefore, the intracohort cannibalism pheneomena occur in the just hatched juvenile stage of only O. ocellatus and O. minor.

• Structural Engineering and Mechanics
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• 제64권5호
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• pp.621-640
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• 2017

This paper reports the numerical investigation conducted to study the influence of Local-Distortional (L-D) interaction mode buckling on post buckling strength erosion in fixed ended lipped channel cold formed steel columns. This investigation comprises of 81 column sections with various geometries and yield stresses that are carefully chosen to cover wide range of strength related parametric ratios like (i) distortional to local critical buckling stress ratio ($0.91{\leq}F_{CRD}/F_{CRL}{\leq}4.05$) (ii) non dimensional local slenderness ratio ($0.88{\leq}{\lambda}_L{\leq}3.54$) (iii) non-dimensional distortional slenderness ratio ($0.68{\leq}{\lambda}_D{\leq}3.23$) and (iv) yield to non-critical buckling stress ratio (0.45 to 10.4). The numerical investigation is carried out by conducting linear and non-linear shell finite element analysis (SFEA) using ABAQUS software. The non-linear SFEA includes both geometry and material non-linearity. The numerical results obtained are deeply analysed to understand the post buckling mechanics, failure modes and ultimate strength that are influenced by L-D interaction with respect to strength related parametric ratios. The ultimate strength data obtained from numerical analysis are compared with (i) the experimental tests data concerning L-D interaction mode buckling reported by other researchers (ii) column strength predicted by Direct Strength Method (DSM) column strength curves for local and distortional buckling specified in AISI S-100 (iii) strength predicted by available DSM based approaches that includes L-D interaction mode failure. The role of flange width to web depth ratio on post buckling strength erosion is reported. Then the paper concludes with merits and limitations of codified DSM and available DSM based approaches on accurate failure strength prediction.

• 비파괴검사학회지
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• 제19권3호
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• pp.189-199
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• 1999

산화막이 피복된 원전 연료봉의 원통형 쉘에 대한 공명산란 해석을 수행하고 원주파 전파 특성을 연구하였다. 피복 쉘에 대한 산란 음압의 정규 모우드 해를 구하였고 최근에 새롭게 제안된 고유 배경음압 계수를 이용하여 피복 쉘의 순수 공명 신호를 분리하였다. 12%의 상대 두께를 갖는 원통형 피복 쉘에 대하여 산화막 두께 증가에 따른 공명 원주파의 전파 특성을 해석하였다. 산화막의 존재와 그 두께가 증가할 때 정규 모우드의 차수에 따라 원주파의 전파 특성이 크게 변화한다. 제 1차 반대칭 ($A_1$) 원주파에서 특정 부분파의 위상속도는 산화막이 존재하고 그 두께가 증가함에도 불구하고 위상속도가 일정 한 특성을 보인다. 공명신호를 분리하고 공명 모우드를 확인하는 실험을 수행하여 $A_1$ 원주파의 전파 특성을 확인하였다. $A_1$ 원주파의 위상속도 일정 특성을 이용함으로써 산화막의 두께를 상대적으로 측정 할 수 있는 새로운 비파괴 평가방법을 제안하였다.

• 한국공간구조학회논문집
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• 제2권4호
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• pp.61-76
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• 2002

The structure system that is discreterized by continuous shells is usually used to make a large space structures and these structures show the collapse mechanisms that are captured at over the limit load, and snap-through and bifurcation are most well known of it. For the collapse mechanism, rise-span ratio, element stiffness and load mode are main factor, which it give an effect to unstable behavior. Moreover, resist force of structure can be reduced by initial condition and initial imperfection significantly. In order to investigate the instability of shell structures, the finite deformation theory can be applied and it becomes a nonlinear mathematics in which use equation of tangential stiffness incrementally. With an initial imperfection, using simple example and Flow Truss Dome, the buckling characteristics of space truss is main purpose of this paper, and unstable behavior is studied by proposed the numerical method. Also, by using MIDAS, this research work analyzes displacements and inner forces as the design load of model, and the ratio of buckling load of design load is investigated.

• 대한기계학회논문집A
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• 제21권8호
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• pp.1270-1275
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• 1997

This paper concerns with the finite element analysis of reactor internals with structural faults. For investigating the influence of hold-down spring faults on dynamic characteristics of CSB (core support barrel), reactor internals of Ulchin-1 nuclear power plant are modeled using finite element method and simulated with artificial defects on the hold-down springs. To prove the validity of the finite element models, the calculated natural frequencies of CSB in normal state are compared with those from the measurement results, which shows good agreement. According to results of finite element analysis, CSB beam mode natural frequency decreases by 4.5% in the case of 10% partial relaxation of hold-down springs, and decreases by 18.4% in the case of 20%. The range of shell mode natural frequency change is within 5.3%.

• 한국지진공학회논문집
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• 제22권7호
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• pp.401-409
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• 2018

Performance-based seismic evaluation is usually done by considering simplified models for the liquid storage tanks therefore, it is important to validate those simplified models before conducting such evaluation. The purpose of this study is to compare the seismic response results of the FSI (fluid-structure interaction) model and the simplified models for the cylindrical liquid storage tanks and to verify the applicability of the simplified models for estimating failure probability. Seismic analyses were carried out for two types of storage tanks with different aspect ratios (H/D) of 0.45 and 0.86. FSI model represents detailed 3D fluid-structure interaction model and simplified models are modeled as cantilever mass-spring model, frame type mass-spring model and shell type mass-spring model, considering impulsive and convective components. Seismic analyses were performed with modal analysis followed by time history analysis. Analysis results from all the models were verified by comparing with the results calculated by the code and literature. The results from simplified models show good agreement with the ones from detailed FSI model and calculated results from code and literature, confirming that all three types of simplified models are very valid for conducting failure probability analysis of the cylindrical liquid storage tanks.