• Steel and Composite Structures
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• 제16권6호
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• pp.703-718
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• 2014

The initial clamping forces of high strength bolts subjected to different faying surface conditions drop within 500 hours regardless of loading, any other external force or loosening of the nut. This study develops a mathematical model for relaxation confined to creep on a coated faying surface after initial clamping. The quantitative model for estimating relaxation was derived from a regression analysis for the relation between the creep strain of the coated surface and the elapsed time for 744 hours. This study establishes an expected model for estimating the relaxation of bolted joints with diverse coated surfaces. The candidate bolts are dacro-coated tension control bolts, ASTM A490 bolt, and plain tension control bolts. The test parameters were coating thickness, species of coating. As for 96, 128, 168, and $226{\mu}m$ thick inorganic zinc, when the coating thickness was increased, relaxation after the initial clamping rose to a much higher range from 10% to 18% due to creep of the coating. The amount of relaxation up to 7 days exceeded 85% of the entire relaxation. From this result, the equation for creep strain can be derived from a statistical regression analysis. Based on the acquired creep behavior, it is expected that the clamping force reflecting relaxation after the elapse of constant time can be calculated from the initial clamping force. The manufacturer's recommendation of inorganic zinc on faying surface as $75{\mu}m$, appears to be reasonable.

• 대한화학회지
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• 제56권1호
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• pp.20-27
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• 2012

Complex permittivity spectra of Allyl Chloride (AC), 2-Butanone (2-BU) and their binary mixtures over the entire range of concentration were obtained using the Time Domain Reflectometry (TDR) technique in microwave frequency range at various temperatures. Static dielectric constant and relaxation time are obtained from complex permittivity spectra. Density ($\rho$) and refractive index ($n_D$) are also measured. These parameters are used to determine excess dielectric constant, excess inverse relaxation time, excess molar volume, excess molar refraction, polarity, Bruggeman factor and thermodynamic parameters viz. enthalpy of activation and entropy of activation. The values of static dielectric constant and relaxation time increases while density and refractive index decreases with the percentage of 2-Butanone in Allyl Chloride increases. Excess parameters were fitted to a Redlich-Kister equation.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.278-278
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• 2016

Solution-processed metal-oxide semiconductors have been considered as the next generation semiconducting materials for transparent and flexible electronics due to their high electrical performance. Moreover, since the oxide semiconductors show high sensitivity to light illumination and possess persistent photoconductivity (PPC), these properties can be utilized in realizing optical memory devices, which can transport information much faster than the electrons. In previous works, metal-oxide semiconductors are utilized as a memory device by using the light (i.e. illumination does the "writing", no-gate bias recovery the "reading" operations) [1]. The key issues for realizing the optical memory devices is to have high photoconductivity and a long life time of free electrons in the oxide semiconductors. However, mono-layered indium-zinc-oxide (IZO) and mono-layered indium-gallium-zinc-oxide (IGZO) have limited photoconductivity and relaxation time of 570 nA, 122 sec, 190 nA and 53 sec, respectively. Here, we boosted up the photoconductivity and relaxation time using a double-layered IZO/IGZO active layer structure. Solution-processed IZO (top) and IGZO (bottom) layers are prepared on a Si/SiO2 wafer and we utilized the conventional thermal annealing method. To investigate the photoconductivity and relaxation time, we exposed 9 mW/cm2 intensity light for 30 sec and the decaying behaviors were evaluated. It was found that the double-layered IZO/IGZO showed high photoconductivity and relaxation time of 28 uA and 1048 sec.

• 한국지반신소재학회논문집
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• 제3권4호
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• pp.21-27
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• 2004

보호, 여과 및 배수, 차수기능을 가진 부직포 지오텍스타일과 지오멤브레인의 응력완화거동을 각각 분석하였다. '전이현상 평형이론'이 이들 토목합성재료의 응력완화거동 해석에 적용되었다. 응력완화거동의 초기 및 후기완화시간을 구성방정식으로 부터 구하였다. 초기완화거동은 부가변형률에 좌우되며, 온도에 따라 빨라짐을 알 수 있었다. 끝으로, 이들 토목합성재료의 초기 및 후기완화시간은 부가변형률 및 온도에 따라 짧아졌다.

• Steel and Composite Structures
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• 제46권6호
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• pp.805-821
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• 2023

This study developed an evaluation system to explore the effect of the environmental temperature on the stress redistribution produced by cable stress relaxation of structural members in a steel cable-stayed bridge. The generalized Maxwell model is used to estimate stress relaxation at different temperatures. The environmental temperature is represented using the thermal coefficients and temperature loads. The fmincon optimization function is used to determine the set of stress relaxation parameters at different temperatures for all cables. The ABAQUS software is employed to investigate the stress redistribution of the steel cable-stayed bridge caused by the cable stress relaxation and the environmental temperature. All of these steps are set up as an evaluation system to save time and ensure the accuracy of the study results. The developed evaluation system is then employed to investigate the effect of environmental temperature and cable type on stress redistribution. These studies' findings show that as environmental temperatures increased up to 40 ℃, the redistribution rate increased by up to 34.9% in some girders. The results also show that the cable type with low relaxation rates should be used in high environmental temperature areas to minimize the effect of cable stress relaxation.

• 한국전산유체공학회지
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• 제15권2호
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• pp.21-27
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• 2010

Immersed boundary lattice Boltzmann method (IBLBM) has been applied to simulate a turbulent flow over circular cylinder in a flow field effectively. Although IBLBM is very effective method to simulate the flow over a complex shape of obstacle in the flow field regardless of the constructed grids in the calculation domain, the results, however, become numerically unstable in high reynolds number flow. The most effective suggestion to archive the numerical stability in high Reynolds number flow is applying the multiple relaxation time (MRT) model instead of single relaxation time(SRT) model in the collision term of lattice Boltzmann equation. In the research MRT model for IBLBM was introduced and comparing the numerical results obtained by applying SRT and MRT. The hydraulic characteristic of cylinder in a flow field between two parallel plate at the range of $Re{\leqq}2000$represented and it is also compared the drag and lifting coefficients of the cylinder calculated by IBLBM with SRT and MRT model.

• 한국전기전자재료학회논문지
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• 제28권2호
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• pp.120-125
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• 2015

In this study, we have come to the following conclusions regarding to the electrification properties (electrostatic electrification voltage and electrification relaxation time) of electrostatics in the three type of specimen (size: $4cm{\times}4cm{\times}0.103cm$) of silicone rubber which is mixed with the ATH (Aluminium Trihydrate(Al($OH_3$)) of 30 phr, 60 phr, 120 phr as reinforcing filler. The electrification properties of electrostatics were measured for the different mixing ratio of ATH with the applied voltage of DC 10 kV at the temperature range of $10^{\circ}C{\sim}30^{\circ}C$ and humidity range of 60%~80%. When the temperature remained constant, the electrical resistance decreased as the humidity increasing in the range of 60%, 70%, 80%. In contrast, when the humidity remained constant, the electrical resistance increased as the temperature increasing in the range of $10^{\circ}C$, $20^{\circ}C$, $30^{\circ}C$. Regarding these results, may be it is because the absorption of O-H molecule appeared in the silicone specimen. It was confirmed that when the temperature remained constant, the electrification relaxation time decreased as the humidity increased. In contrast, when the humidity remained constant, the electrification relaxation time increased as the temperature increased.

• 한국세라믹학회지
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• 제36권9호
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• pp.923-929
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• 1999

The cause of optical nonlinearity induced in thermally poled silica glass is believed to be the space charge polarization. Since the second order optical nonlinearity (electro-optic effect) can be used in optical switches the optical nonlinearity in silica glass has drawn a large attention. Space charge polarization occurs when an ionic conducting material is subjected to dc electric field by the blocking electrode. Thermal poling performed to induce the optical nonlinearity in silica glass is basically identical to the process generating space charge polarization. As a first step to understand the mechanism of space charge polarization in silica glass hence the induced optical nonlinearity the absorption currents as functions of time were measured for various types of silica glasses and analyzed by the theory of space charge polarization. It was found that the electrical relaxation exhibited a step by the space charge polarization in the relatively long time range and dielectric loss peak showed a maximum at a specific temperature which is depending on type of silica glass. It was turned out that this relaxation might be a cause of nonlinearity in electrical conductivity of silica glass.

• Investigative Magnetic Resonance Imaging
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• 제7권1호
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• pp.39-46
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• 2003

목적 : 간(liver)과 림프절 특이성 등의 다기능성을 나타내는 미세 초상자성 산화철 입자(ultrasmall superparamagnetic iron oxide: USP IO)의 자기이완(magnetic relaxation)에 대한 이론적 모델을 제시하고 이러한 이론적 모델에 근거한 미세 초상자성 산화철 입자의 자기장의 세기에 따른 자기 이완시간의 변화를 컴퓨터 모의 실험을 통해 연구하였다. 대상 및 방법 : 초상자성 산화철 입자를 조영제로 사용하기 위해서는 생체적합성 고분자로 축약(encapsulation)시키게 되고 따라서 확산(diffusion) 및 전자스핀의 fluctuation 에 기인하여 발생하는 자유 물분자와 간접 상호작용인 "outsphere " 기전에 근거하여 자기이완모델을 개발하였다. 또한 초상자성체의 경우 자기 모멘트가 상자성 입자에 비해 최소 수백배에서 최대 수만배까지 더 크므로 일반적으로 상자성 조영제의 "out sphere" 기전에서 가정하는 저자장 근사치를 사용할 수 없고 따라서 본 연구에서는 Brillouin함수로 표현되는 총자화에 대한 표현을 적용하여 저자장뿐만 아니라 고자장의 경우까지를 모두 포함하는 "out sphere" 기전에 의한 T1 그리고 T2 이완율에 대한 모델을 개발하였다. 이렇게 개발된 자기이완모델을 사용하여 미세 초상자성 산화철 입자의 자기장의 세기에 따른 자기 이완시간의 변화를 symbolic computation tool 인 MathCad(MathCad, USA)를 사용한 컴퓨터 모의 실험을 통해 조사하였다. 결과 : 미세 초상자성 산화철 입자의 T1, T2 자기이완 특성은 먼저, 저자장 영역 (＜1.0 Mhz)에서는 이론적 모델의 spectral density function에 들어 있는 두 개의 correlation time중 $\tau$$_{s1}$ 중 (T2의 경우 ${\tau}_{S2}$)이 주된 역할을 하는 것을 알 수 있었고 이는 결과적으로 이러한 나노자성체 입자들이 낮은 자기장하에서는 열적으로 야기된 자기모멘트들의 재배열이 주된 역할을 하는 것으로 해석할 수 있다. 한편 고자장 영역에서는 correlation time 중 $\tau$가 주된 역할을 담당하는데는 $\tau$는 나노 입자의 크기와 연관되어 있으며 고자장에서 입자 크기에 따른 T1 이완율(R1)과 T2 이완율(R2)의 차이는 이러한 입자크기의 차이에 의해 발생하는 것으로 해석할 수 있다. 나노입자에 포함된 철 원자수를 변화시키는 경우 철 원자수가 증가 할 수록 R1과 R2가 증가하는 결과를 나타내었다. 한편 온도변화에 따른 T1, T2 자기이완시간의 변화는 정상체온 근처의 제한적인 온도범위내에서 저자장 영역에서의 아주 작은 변화를 제외하고는 큰 차이를 보이지 않았으나 T1에 비해 T2에서 이러한 변화가 상대적으로 더 작게 나타났다. 결론 : 임상적 다기능성을 나타낼 가능성이 많은 것으로 보고되고 있는 미세 초상자성 산화철 입자의 자기이완에 대한 이론적 모델을 초상자성 나노입자의 물리적 특성에 기초하여 제시하였고 이러한 이론적 모델에 근거한 미세 초상자성 산화철 입자의 자기장의 세기에 따른 자기 이완시간의 변화를 컴퓨터 모의 실험을 통해 조사하였다.다.

• 대한간호
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• 제31권2호
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• pp.70-85
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• 1992

Relaxation technique is an independent nursing intervention used in various stressful situations. The concept of relaxation must be explored for the meaning given by the people in their traditional thought and philosophy. Korean relaxation technique, wanting to become culturally acceptable and effective, is learning to recognize and develop Korean concepts, experiences, and musics of relaxation. This study was aimed at discovering Korean concepts, experiences and musics of relaxation and contributing the development of the relaxation technique for Korean people. The subjects were 59 mursing students, 39 hospitalized patients, 61 housewives, 21 rural residents and 16 researchers. Data were collected from September 4th to October 24th, 1991 by interviews or questionaires. The data analysis was done by qualitative research method, and validity assured by conformation of the concept and category by 2nursing scientists who had written a Master's thesis on the relaxation technique. The results of the study were summerized as follows; 1. The meaning of the relaxation concept; From 298 statements, 107 concepts were extracted and then 5 categories "Physical domain", "Psychological domain", "Complex domain", "Situation", and "environment" were organized. 'Don't have discomforts, 'don't have muscle tension', 'don't have energy(him in Korean)', 'don't have activities' subcategories were included in "Physical domain". 'Don't have anxiey', 'feel good', 'emotional stability', 'don't have wordly thoughts', 'feel one's brain muddled', 'loss of desire' subcategories were included in "physical domain" 'Comfort body and mind', 'don't have tension of body and mind', 'be sagged' 'liveliness of thoughts' subcategories were included in "Complex domain". 'Rest', 'sleep', 'others' subcategories were included in "Situation domain". And 'quite environment' & 'comfortable environment' subcategories were included in "Environmental domain". 2. The experiences of the relaxation; From 151 statements, 59 experiences were extracted. And then 9 categories-at rest after physical activities, after problem solving, fancy, bathing in the bed, situation, rest, particular time, others-were organized. 3. The musics of the relaxation; From 229 statements, 108 musics were extracted. and the 9 categories- Western classical music, semi classical music, Korean song, Korean popular classical music, song, western popular sonhg, hymn, characteristics of music, others - were organized. In conclusion, There are some differences between Korean concepts, experiences and musics of relasation and western concepts, experiences and musics of relaxation.