• 한국의류학회지
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• 제21권1호
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• pp.170-181
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• 1997

The purpose of this study was to determine the effect of knit structure and knit density (machine tightness factor) on the dimensional properties and K1-4 values of weft-knitted fabrics followed over eleven cycles of mechanical relaxation to provide the basic data for constructing weft-knitted fabrics for outwear with excellent dimensional stability The eighteenth weft-knitted fabrics were produced with different knit structure (1$\times$1 rib, half-cardigan rib, half-milano rib, interlock, single pique, crossmiss interlock) and machine tightness factor (loose, medium, tight) for this study. Dimensional properties such as width, lengh, area shrinkage and dimensional parameter (K) of eighteenth knitted fabrics including thickness and bulk property were measured. The results were as follows; 1. The dimensional behavior of the Ix1 rib and interlock in relaxation cycles was anisotropic, i.e., length shrinkage was usually associated with a width expansion, whereas the other weft-kntted fabrics which have tuck or miss loops in the knit structure behaved isotropically, i.e., length and width shrinkages were usually found. It was proposed that the difference in dimensional behavior between these structures was due to the dissimilar nonrelaxed geometrical shapes of the individual structural units forming these weft-knitted structures. The mechanical relaxation shrinkage of weft-knitted cotton fabrics was dependent on the tightness of construction. For a range of fabrics knitted on this study, an increase in fabric tightness caused a decrease in the length shrinkage of the fabric accompanied by an increase in its width shrinkage.

• Bulletin of the Korean Chemical Society
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• 제14권1호
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• pp.91-95
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• 1993

In this work we have studied the spin-lattice relaxation of $^{19}$F spins in benzotrifluoride in our quest for a reliable method of discriminating the contribution due to dipolar relaxation mechanism from that due to spin-rotational mechanism for nuclear spins located on methyl or substituted methyl group in organic molecules. Over the temperature range of 248-268 K the decay of normalized longitudinal magnetization was found to be well described by a two parameter equation of the form R(t) = exp(-st){$\frac{5}{6}$exp(-s$_1$)+$\frac{1}{6}$} which was derived under the assumption that interactions in the A3 spin system are modulated randomly and predominantly by internal rotational motions of -CF_3$ top, and it was shown that the separation of contribution due to dipolar interactions from that due to spin-rotation interaction could be successfully achieved by least-square fitting of observed data to this equation. The results indicate that the spin-rotational contribution is overwhelmingly larger than that of dipolar origin over the given temperature range and becomes more deminating at higher temperature.

• 한국초전도ㆍ저온공학회논문지
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• 제9권3호
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• pp.41-45
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• 2007

This paper presents transport current non-uniformity in a joint for superconducting multistage cable-in-conduit conductor (CICC) and relaxation in the CICC. The joint is considered to have a current loop linked to an external magnetic field so that it becomes an emf voltage source. It is numerically analyzed using an electrical transmission line model. The inductive current in a resistive joint is compared to that of a non-resistive joint when the ramping field is applied vertically to the joints. Regarding the parameter values of the model. a full scale $Nb_3Sn$ CICC and a strand-to-strand (STS) joint for the toroidal field magnet of the KSTAR (Korea Superconducting Tokamak Advanced Research) device are referenced to. It is found that the resistive joint prevents the current from rising too much and enhances decaying the current when the ramping stops. The 'flattop' current is found to be proportional to the ramp rate of the field (dB/dt). The relaxation length, which is defined as the length within which the maximum induced current falls by 1/e. is found to saturate within 0.27m.

• 전자공학회논문지
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• 제49권10호
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• pp.181-186
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• 2012

본 논문에서는 변수 불확실성과 필터이득 섭동을 가지는 시스템에 대한 견실비약성 $H_{\infty}$ 칼만형필터 설계기법을 제안한다. 필터가 존재할 충분조건과 견실비약성 $H_{\infty}$ 필터 설계기법을 선형행렬부등식 (LMI: Linear Matrix Inequality 접근법으로 제안하고 시스템과 필터의 불확실성을 매개변수화 선형행렬부등식(PLMI: Parameterized Linear Matrix Inequality)으로 구조화된 불확실성의 형태로 표현한 후 Lyapunov 함수를 통해 시스템의 불확실성과 더불어 필터이득섭동을 고려한 칼만형 $H_{\infty}$ 필터가 존재할 충분조건과 필터설계기법을 PLMI 형태로 보인다. PLMI는 무한개의 LMI의 형태로 나타나므로 완화기법(relaxation technique)을 적용하여 유한개의 LMI의 형태로 변환한 후 견실하고 최적화된 필터이득과 필터섭동범위를 계산하고, 예제와 모의실험을 통해 제시된 필터의 타당성을 검증한다.

• 한국세라믹학회지
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• 제53권3호
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• pp.273-281
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• 2016

This review examines computational simulations of thermoelectric properties, such as electrical conductivity, Seebeck coefficient, and thermal conductivity. With increasing computing power and the development of several efficient simulation codes for electronic structure and transport properties calculations, we can evaluate all the thermoelectric properties within the first-principles calculations with the relaxation time approximation. This review presents the basic principles of electrical and thermal transport equations and how they evaluate properties from the first-principles calculations. As a model case, this review presents results on $Bi_2Te_3$ and Si. Even though there is still an unsolved parameter such as the relaxation time, the effectiveness of the computational simulations on the transport properties will provide much help to experimental scientist researching novel thermoelectric materials.

• Steel and Composite Structures
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• 제24권3호
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• pp.297-307
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• 2017

A unified mathematical model of phase-lag Green-Naghdi magneto-thermoelasticty theories based on fractional derivative heat transfer for perfectly conducting media in the presence of a constant magnetic field is given. The GN theories as well as the theories of coupled and of generalized magneto-thermoelasticity with thermal relaxation follow as limit cases. The resulting nondimensional coupled equations together with the Laplace transforms techniques are applied to a half space, which is assumed to be traction free and subjected to a thermal shock that is a function of time. The inverse transforms are obtained by using a numerical method based on Fourier expansion techniques. The predictions of the theory are discussed and compared with those for the generalized theory of magneto-thermoelasticity with one relaxation time. The effects of Alfven velocity and the fractional order parameter on copper-like material are discussed in different types of GN theories.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1992년도 춘계학술대회
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• pp.64-67
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• 1992

To improve signal-to-noise ratio in sodium image, short echo time (2-3 ms) and long data acquisition (10-20 ms) protocols are used. Sodium in biological specimens demonstrates a bi-exponential decay of transverse magnetization and the fast decaying component of the sodium signal results in the reconstruction of images which are blurred significantly. The spatially-dependent nature of the blurs are due mainly to the presence of short local transverse relaxation values (0.7-3 ms) of sodium in tissue. We present an algorithm that corrects for object-dependent blurs due to fast-decaying T2 and improves the computational behavior of the algorithm by incorporating a relaxation parameter into the iterative process.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.186-189
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• 2004

Although magnesium has high potential for structural material due to the lightweight and high specific strength, the structural application has been limited by the low ductility at room temperature. The reason of the poor ductility is few activated slip systems of magnesium (HCP structure) during deformation. As temperature increases, however, additional non-basal slip systems are incorporated to exhibit higher ductility comparable to aluminum. In the present study, a series of tensile tests of Mg-Al alloy has been carried out to study deformation behavior with temperature variation. Analysis of load relaxation test results based on internal variable approach gave information about relationship between the micromechanical character and corresponding deformation behavior of magnesium. Especially, the material parameter, p representing dislocation permeability through barriers was altered from 0.1 to 0.15 as the non-basal slip systems were activated at high temperature.

• 소성∙가공
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• 제13권6호
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• pp.535-539
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• 2004

Although magnesium has high potential for structural material due to the lightweight and high specific strength, the structural application has been limited by the low ductility at room temperature. The reason of the poor ductility is few activated slip systems of magnesium (HCP structure) during deformation. As temperature increases, however, additional non-basal slip systems are incorporated to exhibit higher ductility comparable to aluminum. In the present study, a series of tensile tests of Mg-Al alloy has been carried out to study deformation behavior with temperature variation. Analysis of load relaxation test results based on internal variable approach gave information about relationship between the micromechanical character and corresponding deformation behavior of magnesium. Especially, the material parameter, p representing dislocation permeability through barriers was altered from 0.1 to 0.15 as the non-basal slip systems were activated at high temperature.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2000년도 제18회 학술발표회 논문개요집
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• pp.142-142
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• 2000

We performed a total energy calculation of clean alumunum surfaces of three low indices based on a density functional theory with a local density approximation, using the Ceperly-Alder exhange correlation parametrized by Perdew and Zunger. Pseudopotentials were generated for Al of which the plane wave cut-off was 15Ry. We used Gaussian broadening of a Fermi level to accelerate the convergence of our calculation with the Gaussian energy smearing parameter of 0.005Ry. First, we determine the lattice constant of the aluminum of an face-centered-cubic structure to be 3.96 which is comparable to the experimental data of 4.05 . The cohesive energy of 4.20eV/atom and the bulk modulus of 0.775$\times$1012dyne/cm2 are also comparable to the experimental values of 3.39eV/atom and 0.772$\times$1012dyne/cm2, respectively. Then we investigated the surface relaxation of (100), (110) and (111) surfaces using a 9-layer slab separated by 6-layer thick vacuum. The results are consistent with the existing experimental results.