• Journal of applied mathematics & informatics
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• 제15권1_2호
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• pp.147-158
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• 2004

Sufficient conditions are given under which a generalized class of kernel-type estimators allows asymptotic approximation on the modulus of continuity. This generalized class includes sample distribution function, kernel-type estimator of density function, and an estimator that may apply to the censored case. In addition, an application is given to asymptotic normality of recursive density estimators of density function at an unknown point.

• Journal of applied mathematics & informatics
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• 제37권1_2호
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• pp.37-52
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• 2019

In this paper we introduce a new concept for Riesz almost lacunary ${\chi}^3$ sequence spaces strong P - convergent to zero with respect to an Orlicz function and examine some properties of the resulting sequence spaces. We introduce and study statistical convergence of Riesz almost lacunary ${\chi}^3$ sequence spaces and some inclusion theorems are discussed.

• 한국도로학회논문집
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• 제10권4호
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• pp.31-40
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• 2008

아스팔트 콘크리트의 동탄성계수는 아스팔트 포장 해석 및 설계에 매우 중요하다. 동탄성계수의 메스터 곡선은 일반적으로 시그모이달 함수로 표현된다. Ramberg-Osgood 모델은 지반동역학분야에서 변형률 크기에 따른 정규화 탄성계수 감소 곡선에 대한 피팅모델로 널리 사용되고 있다. 동일한 동탄성계수 시험자료에 대하여 시그모이달 함수와 수정 Rambeyg-osgood 모델 모두를 사용하여 메스터 곡선을 획득하였으며, 두 피팅모델 모두 적용성이 우수함을 확인하였다. 시그모이달 함수의 계수들은 서로 연관되어 있어서 메스터 곡선의 절대값과 형상 특성을 서로 분리하는 것이 불가능하다. 그러나 Ramberg-Osgood 모델의 계수는 물리적 의미가 명확할 뿐 아니라 서로 분리되어 있어서 메스터 곡선에 대한 영향요소를 서로 분리하여 평가할 수 있음을 확인하였다.

• 비파괴검사학회지
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• 제26권6호
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• pp.390-402
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• 2006

The elastic properties and thickness of mullite environmental barrier coatings grown through chemical vapor deposition (CVD) on silicon carbide substrates were measured using frequency domain photoacoustic microscopy. In this technique, extremely narrow bandwidth surface acoustic waves are generated with an amplitude modulated laser source. A photorefractive crystal based interferometer is used to detect the resulting surface displacement. The complex displacement field is mapped as a function of source-to-receiver distance in order to extract the wavelength of the surface acoustic wave at a given excitation frequency, and the phase velocity is determined. The coatings tested exhibited spatial variations in thickness and mechanical properties. The measured surface wave dispersion curves were used to extract an effective value for the elastic modulus and the coating thickness. Nanoindentation was used to validate the measurements of the effective elastic modulus. The average elastic modulus measured through the coating thickness using nanoindentation is compared to the effective modulus found using the photoacoustic system. Optical microscopy is used to validate the thickness measurements. The results indicate that the photoacoustic microscopy technique can be used to estimate the effective elastic properties in coatings exhibiting spatial inhomogeneities, potentially providing valuable feedback for the optimization of the CVD growth process.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.796-801
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• 2007

The optical performance of the mirror for satellite camera is highly dependent on the adhesive properties between the mirror and its support. In order to design a mirror with high optical performance, the mechanical properties of adhesives should be well defined. In this research, the mechanical properties of three kinds of space adhesives are studied. In case of the materials which show nearly incompressible behavior such as space adhesives, it is important to measure shear modulus which governs deviatoric stress components. Shear moduli of the adhesives are determined by using single lap adhesively bonded joint. For the shear tests, several points have been selected from $-20^{\circ}C$ to $50^{\circ}C$ which is operating temperature range of the adhesive. The shear modulus of each adhesive is expressed as a function of temperature. Characteristics of the adhesives are discussed regarding their temperature sensitivity. The analysis results of RMS wavefront error w.r.t shear modulus are presented.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.852-858
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• 2007

The durability of carbon/epoxy composites under salt water environment was investigated through salt water spray tester. Salt water environment was obtained through salt spray and salt immersion. 5% NaCl solution was used for salt water as natural salt water. Mechanical test was performed to obtain tensile properties, flexural properties, and shear properties of carbon/epoxy composite over 12 months under salt water environment. Dynamic mechanical analyzer was used to investigate thermal analysis properties such storage modulus, loss modulus, and tan ${\delta}$. Also FT/IR test was conducted to investigate a change in chemical structure. According to the results, mechanical properties were found to be slowly degraded as a function of exposure times. Regarding to thermal analysis properties, storage modulus was insensitive to exposure times, but loss modulus was shown to be slightly decreased. Although the shape and location of peak in FT/IR were not much changed, the intensity of peak in FT/IR was affected on exposure times. We also found that salt water immersion was more severe to the durability of carbon/epoxy composite rather than salt water spray.

• 대한기계학회논문집A
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• 제33권5호
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• pp.489-495
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• 2009

A novel technique to measuret of viscoelastic properties of polymers is proposed to investigate complex Poisson's ratio as a function of frequency. The forced vibration responses for the samples under the normal and the shear deformation are to be measured with varying load masses. The measured data were used to obtain the viscoelastic properties of the material based on an accurate 2D numerical deformation model of the sample. The 2D model enabled us to exclude data correction by the empirical form factor used in 1D model. Comprehensive measurements of viscoelastic properties of two slightly varied silicone RTV rubber ($Silastic^{(R)}$ S2) compositions were performed. Standard composition (90% PDMS polymer + 10% catalyst) and modified composition (92.5% polymer + 7.5% catalyst) were tested in temperature range from $30^{\circ}C$ to $70^{\circ}C$. Shear modulus, modulus of elasticity, loss factor, and both the real and the imaginary parts of the Poisson's ratio were determined for frequencies from 50 to 400Hz in the linear deformation regime (at relative deformations $10^{-4}{\sim}10^{-3}$).

• 한국분말재료학회지
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• 제28권5호
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• pp.403-409
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• 2021

In this study, Ti-Mo-EB composites are prepared by ball milling and spark plasma sintering (SPS) to obtain a low elastic modulus and high strength and to evaluate the microstructure and mechanical properties as a function of the process conditions. As the milling time and sintering temperature increased, Mo, as a β-Ti stabilizing element, diffused, and the microstructure of β-Ti increased. In addition, the size of the observed phase was small, so the modulus and hardness of α-Ti and β-Ti were measured using nanoindentation equipment. In both phases, as the milling time and sintering temperature increased, the modulus of elasticity decreased, and the hardness increased. After 12 h of milling, the specimen sintered at 1000℃ showed the lowest values of modulus of elasticity of 117.52 and 101.46 GPa for α-Ti and β-Ti, respectively, confirming that the values are lower compared to the that in previously reported studies.

• 한국인터넷방송통신학회논문지
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• 제11권5호
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• pp.27-33
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• 2011

디지털 통신 시스템에서 채널에서 발생되는 ISI(Inter-Symbol Interference)를 줄이기 위해 사용되는 적응 등화기의 알고리즘으로 MCMA(Constant Modulus Algorithm)가 있다. MCMA는 비교적 간단한 연산량을 갖지만 어느 정도 적당한 수렴율과 정상 상태의 MSE(mean square error)를 가지므로 본 논문에서는 이를 개선키 위해 병렬 구조를 갖는 등화 방식을 제안하며, MCMA(Modified Constant Modulus Algorithm)과 MDD(Modified Decision Directed Algorithm)으로 구성이 되어있다. 제안 방식에서는 4-QAM 좌표와 16-QAM 좌표의 관계를 이용한, 새로운 비용 함수를 정의 하고, 만약 수신된 신호에 오프셋이 발생할 때, MCMA의 성능이 저하되므로 이를 극복하기 위해서 본 논문에서는 MDD(Modified Decision Direct) 알고리즘과 결합한 병렬형 구조를 적용하므로서 기존의 MCMA보다 빠른 수렴 속도와 낮은 MSE를 갖는 개선된 성능을 얻을 수 있음을 컴퓨터 시뮬레이션으로 확인하였다.

• 대한수학회논문집
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• 제36권4호
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• pp.743-757
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• 2021

We consider a different version of Schwarz Lemma for λ-spirallike function of complex order at the boundary of the unit disc D. We estimate the modulus of the angular derivative of the function $\frac{zf^{\prime}(z)}{f(z)}$ from below for λ-spirallike function f(z) of complex order at the boundary of the unit disc D by taking into account the zeros of the function f(z)-z which are different from zero. We also estimate the same function with the second derivatives of the function f at the points z = 0 and z = z₀ ≠ 0. We show the sharpness of these estimates and present examples.